1.
Netherlands
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The Netherlands, also informally known as Holland is the main constituent country of the Kingdom of the Netherlands. It is a densely populated country located in Western Europe with three territories in the Caribbean. The European part of the Netherlands borders Germany to the east, Belgium to the south, and the North Sea to the northwest, sharing borders with Belgium, the United Kingdom. The three largest cities in the Netherlands are Amsterdam, Rotterdam and The Hague, Amsterdam is the countrys capital, while The Hague holds the Dutch seat of parliament and government. The port of Rotterdam is the worlds largest port outside East-Asia, the name Holland is used informally to refer to the whole of the country of the Netherlands. Netherlands literally means lower countries, influenced by its low land and flat geography, most of the areas below sea level are artificial. Since the late 16th century, large areas have been reclaimed from the sea and lakes, with a population density of 412 people per km2 –507 if water is excluded – the Netherlands is classified as a very densely populated country. Only Bangladesh, South Korea, and Taiwan have both a population and higher population density. Nevertheless, the Netherlands is the worlds second-largest exporter of food and agricultural products and this is partly due to the fertility of the soil and the mild climate. In 2001, it became the worlds first country to legalise same-sex marriage, the Netherlands is a founding member of the EU, Eurozone, G-10, NATO, OECD and WTO, as well as being a part of the Schengen Area and the trilateral Benelux Union. The first four are situated in The Hague, as is the EUs criminal intelligence agency Europol and this has led to the city being dubbed the worlds legal capital. The country also ranks second highest in the worlds 2016 Press Freedom Index, the Netherlands has a market-based mixed economy, ranking 17th of 177 countries according to the Index of Economic Freedom. It had the thirteenth-highest per capita income in the world in 2013 according to the International Monetary Fund, in 2013, the United Nations World Happiness Report ranked the Netherlands as the seventh-happiest country in the world, reflecting its high quality of life. The Netherlands also ranks joint second highest in the Inequality-adjusted Human Development Index, the region called Low Countries and the country of the Netherlands have the same toponymy. Place names with Neder, Nieder, Nether and Nedre and Bas or Inferior are in use in all over Europe. They are sometimes used in a relation to a higher ground that consecutively is indicated as Upper, Boven, Oben. In the case of the Low Countries / the Netherlands the geographical location of the region has been more or less downstream. The geographical location of the region, however, changed over time tremendously
2.
Pieter Zeeman
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Pieter Zeeman was a Dutch physicist who shared the 1902 Nobel Prize in Physics with Hendrik Lorentz for his discovery of the Zeeman effect. Pieter Zeeman was born in Zonnemaire, a town on the island of Schouwen-Duiveland, Netherlands, to Catharinus Forandinus Zeeman, a minister of the Dutch Reformed Church. He became interested in physics at an early age, in 1883 the Aurora borealis happened to be visible in the Netherlands. Zeeman, then a student at the school in Zierikzee, made a drawing and description of the phenomenon and submitted it to Nature. The editor praised the careful observations of Professor Zeeman from his observatory in Zonnemaire, after finishing high school in 1883 he went to Delft for supplementary education in classical languages, then a requirement for admission to University. He stayed at the home of Dr J. W. Lely, co-principal of the gymnasium and brother of Cornelis Lely, while in Delft, he first met Heike Kamerlingh Onnes, who was to become his thesis adviser. After Zeeman passed the exams in 1885, he studied physics at the University of Leiden under Kamerlingh Onnes. In 1890, even finishing his thesis, he became Lorentzs assistant. This allowed him to participate in a programme on the Kerr effect. In 1893 he submitted his thesis on the Kerr effect. After obtaining his doctorate he went for half a year to Friedrich Kohlrauschs institute in Strasbourg, in 1895, after returning from Strasbourg, Zeeman became Privatdozent in mathematics and physics in Leiden. The same year he married Johanna Elisabeth Lebret, they had three daughters and one son and he was fired for his efforts, but he was later vindicated, he won the 1902 Nobel Prize in Physics for the discovery of what has now become known as the Zeeman effect. As an extension of his thesis research, he began investigating the effect of magnetic fields on a light source and he discovered that a spectral line is split into several components in the presence of a magnetic field. The next Monday, Lorentz called Zeeman into his office and presented him with an explanation of his observations, the importance of Zeemans discovery soon became apparent. It confirmed Lorentzs prediction about the polarization of light emitted in the presence of a magnetic field and this conclusion was reached well before Thomsons discovery of the electron. The Zeeman effect thus became an important tool for elucidating the structure of the atom, because of his discovery, Zeeman was offered a position as lecturer in Amsterdam in 1897. In 1900 this was followed by his promotion to professor of physics at the University of Amsterdam, in 1902, together with his former mentor Lorentz, he received the Nobel Prize for Physics for the discovery of the Zeeman effect. Five years later, in 1908, he succeeded Van der Waals as full professor and Director of the Physics Institute in Amsterdam, a new laboratory built in Amsterdam in 1923 was renamed the Zeeman Laboratory in 1940
3.
Spectral line
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Spectral lines are often used to identify atoms and molecules from their characteristic spectral lines. Spectral lines are the result of interaction between a system and a single photon. When a photon has about the amount of energy to allow a change in the energy state of the system. A spectral line may be observed either as a line or an absorption line. Which type of line is observed depends on the type of material, an absorption line is produced when photons from a hot, broad spectrum source pass through a cold material. The intensity of light, over a frequency range, is reduced due to absorption by the material. By contrast, a bright, emission line is produced when photons from a hot material are detected in the presence of a spectrum from a cold source. The intensity of light, over a frequency range, is increased due to emission by the material. Spectral lines are highly atom-specific, and can be used to identify the composition of any medium capable of letting light pass through it. Several elements were discovered by means, such as helium, thallium. Mechanisms other than atom-photon interaction can produce spectral lines, depending on the exact physical interaction, the frequency of the involved photons will vary widely, and lines can be observed across the electromagnetic spectrum, from radio waves to gamma rays. In other cases the lines are designated according to the level of ionization by adding a Roman numeral to the designation of the chemical element, so that Ca+ also has the designation Ca II. Neutral atoms are denoted with the roman number I, singly ionized atoms with II, more detailed designations usually include the line wavelength and may include a multiplet number or band designation. Many spectral lines of hydrogen also have designations within their respective series. A spectral line extends over a range of frequencies, not a single frequency, in addition, its center may be shifted from its nominal central wavelength. There are several reasons for this broadening and shift and these reasons may be divided into two general categories – broadening due to local conditions and broadening due to extended conditions. Broadening due to conditions is due to effects which hold in a small region around the emitting element. Broadening due to extended conditions may result from changes to the distribution of the radiation as it traverses its path to the observer
4.
Magnetic field
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A magnetic field is the magnetic effect of electric currents and magnetic materials. The magnetic field at any point is specified by both a direction and a magnitude, as such it is represented by a vector field. The term is used for two distinct but closely related fields denoted by the symbols B and H, where H is measured in units of amperes per meter in the SI, B is measured in teslas and newtons per meter per ampere in the SI. B is most commonly defined in terms of the Lorentz force it exerts on moving electric charges, Magnetic fields can be produced by moving electric charges and the intrinsic magnetic moments of elementary particles associated with a fundamental quantum property, their spin. In quantum physics, the field is quantized and electromagnetic interactions result from the exchange of photons. Magnetic fields are used throughout modern technology, particularly in electrical engineering. The Earth produces its own field, which is important in navigation. Rotating magnetic fields are used in electric motors and generators. Magnetic forces give information about the carriers in a material through the Hall effect. The interaction of magnetic fields in electric devices such as transformers is studied in the discipline of magnetic circuits, noting that the resulting field lines crossed at two points he named those points poles in analogy to Earths poles. He also clearly articulated the principle that magnets always have both a north and south pole, no matter how finely one slices them, almost three centuries later, William Gilbert of Colchester replicated Petrus Peregrinus work and was the first to state explicitly that Earth is a magnet. Published in 1600, Gilberts work, De Magnete, helped to establish magnetism as a science, in 1750, John Michell stated that magnetic poles attract and repel in accordance with an inverse square law. Charles-Augustin de Coulomb experimentally verified this in 1785 and stated explicitly that the north and south poles cannot be separated, building on this force between poles, Siméon Denis Poisson created the first successful model of the magnetic field, which he presented in 1824. In this model, a magnetic H-field is produced by magnetic poles, three discoveries challenged this foundation of magnetism, though. First, in 1819, Hans Christian Ørsted discovered that an electric current generates a magnetic field encircling it, then in 1820, André-Marie Ampère showed that parallel wires having currents in the same direction attract one another. Finally, Jean-Baptiste Biot and Félix Savart discovered the Biot–Savart law in 1820, extending these experiments, Ampère published his own successful model of magnetism in 1825. This has the benefit of explaining why magnetic charge can not be isolated. Also in this work, Ampère introduced the term electrodynamics to describe the relationship between electricity and magnetism, in 1831, Michael Faraday discovered electromagnetic induction when he found that a changing magnetic field generates an encircling electric field
5.
Stark effect
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The Stark effect is the shifting and splitting of spectral lines of atoms and molecules due to presence of an external electric field. The amount of splitting or shifting is called the Stark splitting or Stark shift, in general, one distinguishes first- and second-order Stark effects. The first-order effect is linear in the electric field, while the second-order effect is quadratic in the field. The Stark effect is responsible for the broadening of spectral lines by charged particles. When the split/shifted lines appear in absorption, the effect is called the inverse Stark effect, the Stark effect is the electric analogue of the Zeeman effect where a spectral line is split into several components due to the presence of a magnetic field. The Stark effect can be explained with fully quantum-mechanical approaches, the effect is named after Johannes Stark, who discovered it in 1913. It was independently discovered in the year by the Italian physicist Antonino Lo Surdo. The discovery of this effect contributed importantly to the development of quantum theory, by using experimental indices of refraction he gave an estimate of the Stark splittings. This estimate was a few orders of magnitude too low, not deterred by this prediction, Stark undertook measurements on excited states of the hydrogen atom and succeeded in observing splittings. By the use of the Bohr–Sommerfeld quantum theory, Paul Epstein and Karl Schwarzschild were independently able to derive equations for the linear, four years later, Hendrik Kramers derived formulas for intensities of spectral transitions. Kramers also included the effect of structure, which includes corrections for relativistic kinetic energy. The first quantum mechanical treatment was by Wolfgang Pauli, erwin Schrödinger discussed at length the Stark effect in his third paper on quantum theory, once in the manner of the 1916 work of Epstein and once by his perturbation approach. Finally, Epstein reconsidered the linear and quadratic Stark effect from the point of view of the new quantum theory and he derived equations for the line intensities which were a decided improvement over Kramers results obtained by the old quantum theory. While first-order perturbation effects for the Stark effect in hydrogen are in agreement for the Bohr–Sommerfeld model, measurements of the Stark effect under high field strengths confirmed the correctness of the quantum theory over the Bohr model. An electric field pointing from left to right, for example, tends to pull nuclei to the right and electrons to the left. Other things equal, the effect of the field is greater for outer electron shells, because the electron is more distant from the nucleus, so it travels farther left. The Stark effect can lead to splitting of energy levels. For example, in the Bohr model, an electron has the same whether it is in the 2s state or any of the 2p states
6.
Electric field
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An electric field is a vector field that associates to each point in space the Coulomb force that would be experienced per unit of electric charge, by an infinitesimal test charge at that point. Electric fields are created by electric charges and can be induced by time-varying magnetic fields, the electric field combines with the magnetic field to form the electromagnetic field. The electric field, E, at a point is defined as the force, F. A particle of charge q would be subject to a force F = q E and its SI units are newtons per coulomb or, equivalently, volts per metre, which in terms of SI base units are kg⋅m⋅s−3⋅A−1. Electric fields are caused by electric charges or varying magnetic fields, in the special case of a steady state, the Maxwell-Faraday inductive effect disappears. The resulting two equations, taken together, are equivalent to Coulombs law, written as E =14 π ε0 ∫ d r ′ ρ r − r ′ | r − r ′ |3 for a charge density ρ. Notice that ε0, the permittivity of vacuum, must be substituted if charges are considered in non-empty media, the equations of electromagnetism are best described in a continuous description. A charge q located at r 0 can be described mathematically as a charge density ρ = q δ, conversely, a charge distribution can be approximated by many small point charges. Electric fields satisfy the principle, because Maxwells equations are linear. This principle is useful to calculate the field created by point charges. Q n are stationary in space at r 1, r 2, in that case, Coulombs law fully describes the field. If a system is static, such that magnetic fields are not time-varying, then by Faradays law, in this case, one can define an electric potential, that is, a function Φ such that E = − ∇ Φ. This is analogous to the gravitational potential, Coulombs law, which describes the interaction of electric charges, F = q = q E is similar to Newtons law of universal gravitation, F = m = m g. This suggests similarities between the electric field E and the gravitational field g, or their associated potentials, mass is sometimes called gravitational charge because of that similarity. Electrostatic and gravitational forces both are central, conservative and obey an inverse-square law, a uniform field is one in which the electric field is constant at every point. It can be approximated by placing two conducting plates parallel to other and maintaining a voltage between them, it is only an approximation because of boundary effects. Assuming infinite planes, the magnitude of the electric field E is, electrodynamic fields are E-fields which do change with time, for instance when charges are in motion. The electric field cannot be described independently of the field in that case
7.
Dipole
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In electromagnetism, there are two kinds of dipoles, An electric dipole is a separation of positive and negative charges. The simplest example of this is a pair of electric charges of equal magnitude but opposite sign, a permanent electric dipole is called an electret. A magnetic dipole is a circulation of electric current. A simple example of this is a loop of wire with some constant current through it. Dipoles can be characterized by their moment, a vector quantity. For the current loop, the dipole moment points through the loop. In addition to current loops, the electron, among other fundamental particles, has a dipole moment. That is because it generates a field that is identical to that generated by a very small current loop. However, the magnetic moment is not due to a current loop. It is also possible that the electron has a dipole moment although it has not yet been observed. A permanent magnet, such as a bar magnet, owes its magnetism to the magnetic dipole moment of the electron. The two ends of a bar magnet are referred to as poles, and may be labeled north and south, the dipole moment of the bar magnet points from its magnetic south to its magnetic north pole. The north pole of a bar magnet in a compass points north, however, that means that Earths geomagnetic north pole is the south pole of its dipole moment and vice versa. The only known mechanisms for the creation of magnetic dipoles are by current loops or quantum-mechanical spin since the existence of magnetic monopoles has never been experimentally demonstrated, the term comes from the Greek δίς, twice and πόλος, axis. A physical dipole consists of two equal and opposite point charges, in the sense, two poles. Its field at large distances depends almost entirely on the moment as defined above. A point dipole is the limit obtained by letting the separation tend to 0 while keeping the dipole moment fixed, the field of a point dipole has a particularly simple form, and the order-1 term in the multipole expansion is precisely the point dipole field. Although there are no magnetic monopoles in nature, there are magnetic dipoles in the form of the quantum-mechanical spin associated with particles such as electrons
8.
Selection rule
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In physics and chemistry, a selection rule, or transition rule, formally constrains the possible transitions of a system from one quantum state to another. Selection rules have been derived for electromagnetic transitions in molecules, in atoms, in atomic nuclei, the selection rules may differ according to the technique used to observe the transition. In the following, mainly atomic and molecular transitions are considered, if the value of this integral is zero the transition is forbidden. In practice, the integral itself does not need to be calculated to determine a selection rule and it is sufficient to determine the symmetry of transition moment function, ψ1 ∗ μ ψ2. If the symmetry of this function spans the totally symmetric representation of the point group to which the atom or molecule belongs then its value is not zero and the transition is allowed. The transition moment integral is zero if the transition moment function, ψ1 ∗ μ ψ2, is anti-symmetric or odd, the symmetry of the transition moment function is the direct product of the parities of its three components. The symmetry characteristics of each component can be obtained from standard character tables, rules for obtaining the symmetries of a direct product can be found in texts on character tables. The Laporte rule is a selection rule formally stated as follows, In a centrosymmetric environment, the Laporte rule applies to electric dipole transitions, so the operator has u symmetry. P orbitals also have u symmetry, so the symmetry of the transition moment function is given by the triple product u×u×u, likewise, d orbitals have g symmetry, so the triple product g×u×g also has u symmetry and the transition is forbidden. The wave function of an electron is the product of a space-dependent wave function. Spin is directional and can be said to have odd parity and it follows that transitions in which the spin direction changes are forbidden. In formal terms, only states with the total spin quantum number are spin-allowed. In crystal field theory, d-d transitions that are spin-forbidden are much weaker than spin-allowed transitions, both can be observed, in spite of the Laporte rule, because the actual transitions are coupled to vibrations that are anti-symmetric and have the same symmetry as the dipole moment operator. In vibrational spectroscopy, transitions are observed between different vibrational states, in a fundamental vibration, the molecule is excited from its ground state to the first excited state. The symmetry of the wave function is the same as that of the molecule. It is, therefore, a basis for the totally symmetric representation in the point group of the molecule. It follows that, for a transition to be allowed. In infrared spectroscopy, the transition moment operator transforms as either x and/or y and/or z, the excited state wave function must also transform as at least one of these vectors
9.
Sun
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The Sun is the star at the center of the Solar System. It is a perfect sphere of hot plasma, with internal convective motion that generates a magnetic field via a dynamo process. It is by far the most important source of energy for life on Earth. Its diameter is about 109 times that of Earth, and its mass is about 330,000 times that of Earth, accounting for about 99. 86% of the total mass of the Solar System. About three quarters of the Suns mass consists of hydrogen, the rest is mostly helium, with smaller quantities of heavier elements, including oxygen, carbon, neon. The Sun is a G-type main-sequence star based on its spectral class and it formed approximately 4.6 billion years ago from the gravitational collapse of matter within a region of a large molecular cloud. Most of this matter gathered in the center, whereas the rest flattened into a disk that became the Solar System. The central mass became so hot and dense that it eventually initiated nuclear fusion in its core and it is thought that almost all stars form by this process. The Sun is roughly middle-aged, it has not changed dramatically for more than four billion years and it is calculated that the Sun will become sufficiently large enough to engulf the current orbits of Mercury, Venus, and probably Earth. The enormous effect of the Sun on Earth has been recognized since prehistoric times, the synodic rotation of Earth and its orbit around the Sun are the basis of the solar calendar, which is the predominant calendar in use today. The English proper name Sun developed from Old English sunne and may be related to south, all Germanic terms for the Sun stem from Proto-Germanic *sunnōn. The English weekday name Sunday stems from Old English and is ultimately a result of a Germanic interpretation of Latin dies solis, the Latin name for the Sun, Sol, is not common in general English language use, the adjectival form is the related word solar. The term sol is used by planetary astronomers to refer to the duration of a solar day on another planet. A mean Earth solar day is approximately 24 hours, whereas a mean Martian sol is 24 hours,39 minutes, and 35.244 seconds. From at least the 4th Dynasty of Ancient Egypt, the Sun was worshipped as the god Ra, portrayed as a falcon-headed divinity surmounted by the solar disk, and surrounded by a serpent. In the New Empire period, the Sun became identified with the dung beetle, in the form of the Sun disc Aten, the Sun had a brief resurgence during the Amarna Period when it again became the preeminent, if not only, divinity for the Pharaoh Akhenaton. The Sun is viewed as a goddess in Germanic paganism, Sól/Sunna, in ancient Roman culture, Sunday was the day of the Sun god. It was adopted as the Sabbath day by Christians who did not have a Jewish background, the symbol of light was a pagan device adopted by Christians, and perhaps the most important one that did not come from Jewish traditions
10.
Star
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A star is a luminous sphere of plasma held together by its own gravity. The nearest star to Earth is the Sun, many other stars are visible to the naked eye from Earth during the night, appearing as a multitude of fixed luminous points in the sky due to their immense distance from Earth. Historically, the most prominent stars were grouped into constellations and asterisms, astronomers have assembled star catalogues that identify the known stars and provide standardized stellar designations. However, most of the stars in the Universe, including all stars outside our galaxy, indeed, most are invisible from Earth even through the most powerful telescopes. Almost all naturally occurring elements heavier than helium are created by stellar nucleosynthesis during the stars lifetime, near the end of its life, a star can also contain degenerate matter. Astronomers can determine the mass, age, metallicity, and many properties of a star by observing its motion through space, its luminosity. The total mass of a star is the factor that determines its evolution. Other characteristics of a star, including diameter and temperature, change over its life, while the environment affects its rotation. A plot of the temperature of stars against their luminosities produces a plot known as a Hertzsprung–Russell diagram. Plotting a particular star on that allows the age and evolutionary state of that star to be determined. A stars life begins with the collapse of a gaseous nebula of material composed primarily of hydrogen, along with helium. When the stellar core is sufficiently dense, hydrogen becomes steadily converted into helium through nuclear fusion, the remainder of the stars interior carries energy away from the core through a combination of radiative and convective heat transfer processes. The stars internal pressure prevents it from collapsing further under its own gravity, a star with mass greater than 0.4 times the Suns will expand to become a red giant when the hydrogen fuel in its core is exhausted. In some cases, it will fuse heavier elements at the core or in shells around the core, as the star expands it throws a part of its mass, enriched with those heavier elements, into the interstellar environment, to be recycled later as new stars. Meanwhile, the core becomes a remnant, a white dwarf. Binary and multi-star systems consist of two or more stars that are bound and generally move around each other in stable orbits. When two such stars have a close orbit, their gravitational interaction can have a significant impact on their evolution. Stars can form part of a much larger gravitationally bound structure, historically, stars have been important to civilizations throughout the world
11.
Plasma (physics)
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Plasma is one of the four fundamental states of matter, the others being solid, liquid, and gas. Yet unlike these three states of matter, plasma does not naturally exist on the Earth under normal surface conditions, the term was first introduced by chemist Irving Langmuir in the 1920s. However, true plasma production is from the separation of these ions and electrons that produces an electric field. Based on the environmental temperature and density either partially ionised or fully ionised forms of plasma may be produced. The positive charge in ions is achieved by stripping away electrons from atomic nuclei, the number of electrons removed is related to either the increase in temperature or the local density of other ionised matter. Plasma may be the most abundant form of matter in the universe, although this is currently tentative based on the existence. Plasma is mostly associated with the Sun and stars, extending to the rarefied intracluster medium, Plasma was first identified in a Crookes tube, and so described by Sir William Crookes in 1879. The nature of the Crookes tube cathode ray matter was identified by British physicist Sir J. J. The term plasma was coined by Irving Langmuir in 1928, perhaps because the glowing discharge molds itself to the shape of the Crookes tube and we shall use the name plasma to describe this region containing balanced charges of ions and electrons. Plasma is a neutral medium of unbound positive and negative particles. Although these particles are unbound, they are not ‘free’ in the sense of not experiencing forces, in turn this governs collective behavior with many degrees of variation. The average number of particles in the Debye sphere is given by the plasma parameter, bulk interactions, The Debye screening length is short compared to the physical size of the plasma. This criterion means that interactions in the bulk of the plasma are more important than those at its edges, when this criterion is satisfied, the plasma is quasineutral. Plasma frequency, The electron plasma frequency is compared to the electron-neutral collision frequency. When this condition is valid, electrostatic interactions dominate over the processes of ordinary gas kinetics, for plasma to exist, ionization is necessary. The term plasma density by itself refers to the electron density, that is. The degree of ionization of a plasma is the proportion of atoms that have lost or gained electrons, even a partially ionized gas in which as little as 1% of the particles are ionized can have the characteristics of a plasma. The degree of ionization, α, is defined as α = n i n i + n n, where n i is the number density of ions and n n is the number density of neutral atoms
12.
Nuclear magnetic resonance
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Nuclear magnetic resonance is a physical phenomenon in which nuclei in a magnetic field absorb and re-emit electromagnetic radiation. NMR allows the observation of quantum mechanical magnetic properties of the atomic nucleus. Many scientific techniques exploit NMR phenomena to study physics, crystals. NMR is also used in advanced medical imaging techniques, such as in magnetic resonance imaging. The most commonly studied nuclei are 1H and 13C, although nuclei from isotopes of other elements have been studied by high-field NMR spectroscopy as well. A key feature of NMR is that the frequency of a particular substance is directly proportional to the strength of the applied magnetic field. Since the resolution of the technique depends on the magnitude of magnetic field gradient, many efforts are made to develop increased field strength. The effectiveness of NMR can also be improved using hyperpolarization, and/or using two-dimensional, three-dimensional and higher-dimensional multi-frequency techniques, the principle of NMR usually involves two sequential steps, The alignment of the magnetic nuclear spins in an applied, constant magnetic field B0. The perturbation of this alignment of the nuclear spins by employing an electro-magnetic, the required perturbing frequency is dependent upon the static magnetic field and the nuclei of observation. The two fields are chosen to be perpendicular to each other as this maximizes the NMR signal strength. The resulting response by the magnetization of the nuclear spins is the phenomenon that is exploited in NMR spectroscopy. NMR phenomena are also utilized in low-field NMR, NMR spectroscopy and MRI in the Earths magnetic field, in 1946, Felix Bloch and Edward Mills Purcell expanded the technique for use on liquids and solids, for which they shared the Nobel Prize in Physics in 1952. Yevgeny Zavoisky likely observed nuclear magnetic resonance in 1941, well before Felix Bloch and Edward Mills Purcell, russell H. Varian filed the Method and means for correlating nuclear properties of atoms and magnetic fields, U. S. Patent 2,561,490 on July 24,1951, Varian Associates developed the first NMR unit called NMR HR-30 in 1952. Purcell had worked on the development of radar during World War II at the Massachusetts Institute of Technologys Radiation Laboratory. His work during that project on the production and detection of radio frequency power, when this absorption occurs, the nucleus is described as being in resonance. Different atomic nuclei within a molecule resonate at different frequencies for the magnetic field strength. The observation of magnetic resonance frequencies of the nuclei present in a molecule allows any trained user to discover essential chemical and structural information about the molecule
13.
Electron paramagnetic resonance
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Electron paramagnetic resonance or electron spin resonance spectroscopy is a method for studying materials with unpaired electrons. The basic concepts of EPR are analogous to those of nuclear magnetic resonance, EPR spectroscopy is particularly useful for studying metal complexes or organic radicals. EPR was first observed in Kazan State University by Soviet physicist Yevgeny Zavoisky in 1944, and was developed independently at the same time by Brebis Bleaney at the University of Oxford. Every electron has a moment and spin quantum number s =12, with magnetic components m s = +12 and m s = −12.0023 for the free electron. Therefore, the separation between the lower and the state is Δ E = g e μ B B0 for unpaired free electrons. This equation implies that the splitting of the levels is directly proportional to the magnetic fields strength. An unpaired electron can move between the two levels by either absorbing or emitting a photon of energy h ν such that the resonance condition. This leads to the equation of EPR spectroscopy, h ν = g e μ B B0. Furthermore, EPR spectra can be generated by varying the photon frequency incident on a sample while holding the magnetic field constant or doing the reverse. In practice, it is usually the frequency that is kept fixed, a collection of paramagnetic centers, such as free radicals, is exposed to microwaves at a fixed frequency. At this point the electrons can move between their two spin states. The upper spectrum below is the absorption for a system of free electrons in a varying magnetic field. The lower spectrum is the first derivative of the absorption spectrum, the latter is the most common way to record and publish EPR spectra. For the microwave frequency of 9388.2 MHz, the predicted resonance occurs at a field of about B0 = h ν / g e μ B =0.3350 teslas =3350 gausses. For example, for the field of 3350 G shown at the right, in practice, EPR samples consist of collections of many paramagnetic species, and not single isolated paramagnetic centers. At 298 K, X-band microwave frequencies give n upper / n lower ≈0.998, therefore, transitions from the lower to the higher level are more probable than the reverse, which is why there is a net absorption of energy. With k f and P being constants, N min ~ −1, i. e. N min ~ ν − α, in practice, α can change varying from 0.5 to 4.5 depending on spectrometer characteristics, resonance conditions, and sample size. A great sensitivity is obtained with a low detection limit N min
14.
Atomic absorption spectroscopy
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Atomic absorption spectroscopy is a spectroanalytical procedure for the quantitative determination of chemical elements using the absorption of optical radiation by free atoms in the gaseous state. In analytical chemistry the technique is used for determining the concentration of an element in a sample to be analyzed. AAS can be used to determine over 70 different elements in solution or directly in solid samples used in pharmacology, biophysics, the modern form of AAS was largely developed during the 1950s by a team of Australian chemists. They were led by Sir Alan Walsh at the Commonwealth Scientific and Industrial Research Organisation, Division of Chemical Physics, in Melbourne, the technique makes use of absorption spectrometry to assess the concentration of an analyte in a sample. It requires standards with known content to establish the relation between the measured absorbance and the analyte concentration and relies therefore on the Beer-Lambert Law. In short, the electrons of the atoms in the atomizer can be promoted to higher orbitals for a period of time by absorbing a defined quantity of energy. This amount of energy, i. e. wavelength, is specific to an electron transition in a particular element. In general, each corresponds to only one element, and the width of an absorption line is only of the order of a few picometers. In order to analyze a sample for its constituents, it has to be atomized. The atomizers most commonly used nowadays are flames and electrothermal atomizers, the atoms should then be irradiated by optical radiation, and the radiation source could be an element-specific line radiation source or a continuum radiation source. The atomizers most commonly used nowadays are flames and electrothermal atomizers, other atomizers, such as glow-discharge atomization, hydride atomization, or cold-vapor atomization might be used for special purposes. The latter flame, in addition, offers a more reducing environment, liquid or dissolved samples are typically used with flame atomizers. This conditioning process is responsible that only about 5% of the sample solution reaches the flame. On top of the chamber is a burner head that produces a flame that is laterally long. The radiation beam passes through this flame at its longest axis, the burner height may also be adjusted, so that the radiation beam passes through the zone of highest atom cloud density in the flame, resulting in the highest sensitivity. Each of these includes the risk of interference in case the degree of phase transfer is different for the analyte in the calibration standard. Ionization is generally undesirable, as it reduces the number of atoms that are available for measurement, in flame AAS a steady-state signal is generated during the time period when the sample is aspirated. This technique is used for determinations in the mg L−1 range
15.
Magnetoreception
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Magnetoreception is a sense which allows an organism to detect a magnetic field to perceive direction, altitude or location. This sensory modality is used by a range of animals for orientation and navigation, for the purpose of navigation, magnetoreception deals with the detection of the Earths magnetic field. Magnetoreception is present in bacteria, arthropods, molluscs and members of all major groups of vertebrates. Humans are not thought to have a sense, but there is a protein in the eye which could serve this function. An unequivocal demonstration of the use of magnetic fields for orientation within an organism has been in a class of known as magnetotactic bacteria. These bacteria demonstrate a behavioural phenomenon known as magnetotaxis, in which the bacterium orients itself, the bacteria contain magnetosomes, which are nanometer-sized particles of magnetite or iron sulfide enclosed within the bacterial cells. For animals the mechanism for magnetoreception is unknown, but there exist two main hypotheses to explain the phenomenon, according to one model, cryptochrome, when exposed to blue light, becomes activated to form a pair of radicals where the spins of the two unpaired electrons are correlated. The surrounding magnetic field affects the dynamics of this correlation, activation of cryptochrome may affect the light-sensitivity of retinal neurons, with the overall result that the bird can see the color phase shift caused by the magnetic field. The Earths magnetic field is only 0, cryptochromes are therefore thought to be essential for the light-dependent ability of the fruit fly Drosophila melanogaster to sense magnetic fields. The second proposed model for magnetoreception relies on Fe3O4, also referred to as iron oxide or magnetite, iron oxide remains permanently magnetized when its length is larger than 50 nm and becomes magnetized when exposed to a magnetic field if its length is less than 50 nm. In both of these situations the Earths magnetic field leads to a signal via a physical effect on this magnetically sensitive oxide. Another less general type of magnetic sensing mechanism in animals that has been described is the inductive sensing methods used by sharks, stingrays. These species possess a unique electroreceptive organ known as ampullae of Lorenzini which can detect a variation in electric potential. These organs are made up of mucus-filled canals that connect from the pores to small sacs within the animals flesh that are also filled with mucus. The ampullae of Lorenzini are capable of detecting DC currents and have proposed to be used in the sensing of the weak electric fields of prey. These organs could also possibly sense magnetic fields, by means of Faradays law, as a conductor moves through a magnetic field an electric potential is generated. In this case the conductor is the animal moving through a field. These organs detect very small fluctuations in the difference between the pore and the base of the electroreceptor sack
16.
Spin (physics)
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In quantum mechanics and particle physics, spin is an intrinsic form of angular momentum carried by elementary particles, composite particles, and atomic nuclei. Spin is one of two types of angular momentum in mechanics, the other being orbital angular momentum. In some ways, spin is like a vector quantity, it has a definite magnitude, all elementary particles of a given kind have the same magnitude of spin angular momentum, which is indicated by assigning the particle a spin quantum number. The SI unit of spin is the or, just as with classical angular momentum, very often, the spin quantum number is simply called spin leaving its meaning as the unitless spin quantum number to be inferred from context. When combined with the theorem, the spin of electrons results in the Pauli exclusion principle. Wolfgang Pauli was the first to propose the concept of spin, in 1925, Ralph Kronig, George Uhlenbeck and Samuel Goudsmit at Leiden University suggested an physical interpretation of particles spinning around their own axis. The mathematical theory was worked out in depth by Pauli in 1927, when Paul Dirac derived his relativistic quantum mechanics in 1928, electron spin was an essential part of it. As the name suggests, spin was originally conceived as the rotation of a particle around some axis and this picture is correct so far as spin obeys the same mathematical laws as quantized angular momenta do. On the other hand, spin has some properties that distinguish it from orbital angular momenta. Although the direction of its spin can be changed, a particle cannot be made to spin faster or slower. The spin of a particle is associated with a magnetic dipole moment with a g-factor differing from 1. This could only occur if the internal charge of the particle were distributed differently from its mass. The conventional definition of the quantum number, s, is s = n/2. Hence the allowed values of s are 0, 1/2,1, 3/2,2, the value of s for an elementary particle depends only on the type of particle, and cannot be altered in any known way. The spin angular momentum, S, of any system is quantized. The allowed values of S are S = ℏ s = h 4 π n, in contrast, orbital angular momentum can only take on integer values of s, i. e. even-numbered values of n. Those particles with half-integer spins, such as 1/2, 3/2, 5/2, are known as fermions, while particles with integer spins. The two families of particles obey different rules and broadly have different roles in the world around us, a key distinction between the two families is that fermions obey the Pauli exclusion principle, that is, there cannot be two identical fermions simultaneously having the same quantum numbers
17.
Electron
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The electron is a subatomic particle, symbol e− or β−, with a negative elementary electric charge. Electrons belong to the first generation of the lepton particle family, the electron has a mass that is approximately 1/1836 that of the proton. Quantum mechanical properties of the include a intrinsic angular momentum of a half-integer value, expressed in units of the reduced Planck constant. As it is a fermion, no two electrons can occupy the same state, in accordance with the Pauli exclusion principle. Like all elementary particles, electrons exhibit properties of particles and waves, they can collide with other particles and can be diffracted like light. Since an electron has charge, it has an electric field. Electromagnetic fields produced from other sources will affect the motion of an electron according to the Lorentz force law, electrons radiate or absorb energy in the form of photons when they are accelerated. Laboratory instruments are capable of trapping individual electrons as well as electron plasma by the use of electromagnetic fields, special telescopes can detect electron plasma in outer space. Electrons are involved in applications such as electronics, welding, cathode ray tubes, electron microscopes, radiation therapy, lasers, gaseous ionization detectors. Interactions involving electrons with other particles are of interest in fields such as chemistry. The Coulomb force interaction between the positive protons within atomic nuclei and the negative electrons without, allows the composition of the two known as atoms, ionization or differences in the proportions of negative electrons versus positive nuclei changes the binding energy of an atomic system. The exchange or sharing of the electrons between two or more atoms is the cause of chemical bonding. In 1838, British natural philosopher Richard Laming first hypothesized the concept of a quantity of electric charge to explain the chemical properties of atoms. Irish physicist George Johnstone Stoney named this charge electron in 1891, electrons can also participate in nuclear reactions, such as nucleosynthesis in stars, where they are known as beta particles. Electrons can be created through beta decay of isotopes and in high-energy collisions. The antiparticle of the electron is called the positron, it is identical to the electron except that it carries electrical, when an electron collides with a positron, both particles can be totally annihilated, producing gamma ray photons. The ancient Greeks noticed that amber attracted small objects when rubbed with fur, along with lightning, this phenomenon is one of humanitys earliest recorded experiences with electricity. In his 1600 treatise De Magnete, the English scientist William Gilbert coined the New Latin term electricus, both electric and electricity are derived from the Latin ēlectrum, which came from the Greek word for amber, ἤλεκτρον
18.
Magnetic moment
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The magnetic moment of a magnet is a quantity that determines the torque it will experience in an external magnetic field. A loop of current, a bar magnet, an electron, a molecule. The magnetic moment may be considered to be a vector having a magnitude, the direction of the magnetic moment points from the south to north pole of the magnet. The magnetic field produced by the magnet is proportional to its magnetic moment, more precisely, the term magnetic moment normally refers to a systems magnetic dipole moment, which produces the first term in the multipole expansion of a general magnetic field. The dipole component of a magnetic field is symmetric about the direction of its magnetic dipole moment. The magnetic moment is defined as a vector relating the aligning torque on the object from an applied magnetic field to the field vector itself. The relationship is given by, τ = μ × B where τ is the acting on the dipole and B is the external magnetic field. This definition is based on how one would measure the magnetic moment, in principle, the unit for magnetic moment is not a base unit in the International System of Units. As the torque is measured in newton-meters and the field in teslas. This has equivalents in other units, N·m/T = A·m2 = J/T where A is amperes. In the CGS system, there are different sets of electromagnetism units, of which the main ones are ESU, Gaussian. The ratio of these two non-equivalent CGS units is equal to the speed of light in space, expressed in cm·s−1. All formulae in this article are correct in SI units, they may need to be changed for use in other unit systems. For example, in SI units, a loop of current with current I and area A has magnetic moment IA, the preferred classical explanation of a magnetic moment has changed over time. Before the 1930s, textbooks explained the moment using hypothetical magnetic point charges, since then, most have defined it in terms of Ampèrian currents. The sources of magnetic moments in materials can be represented by poles in analogy to electrostatics, consider a bar magnet which has magnetic poles of equal magnitude but opposite polarity. Each pole is the source of force which weakens with distance. Since magnetic poles always come in pairs, their forces partially cancel each other because while one pole pulls and this cancellation is greatest when the poles are close to each other i. e. when the bar magnet is short
19.
Angular momentum
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In physics, angular momentum is the rotational analog of linear momentum. It is an important quantity in physics because it is a conserved quantity – the angular momentum of a system remains constant unless acted on by an external torque. The definition of momentum for a point particle is a pseudovector r×p. This definition can be applied to each point in continua like solids or fluids, unlike momentum, angular momentum does depend on where the origin is chosen, since the particles position is measured from it. The angular momentum of an object can also be connected to the angular velocity ω of the object via the moment of inertia I. However, while ω always points in the direction of the rotation axis, Angular momentum is additive, the total angular momentum of a system is the vector sum of the angular momenta. For continua or fields one uses integration, torque can be defined as the rate of change of angular momentum, analogous to force. Applications include the gyrocompass, control moment gyroscope, inertial systems, reaction wheels, flying discs or Frisbees. In general, conservation does limit the motion of a system. In quantum mechanics, angular momentum is an operator with quantized eigenvalues, Angular momentum is subject to the Heisenberg uncertainty principle, meaning only one component can be measured with definite precision, the other two cannot. Also, the spin of elementary particles does not correspond to literal spinning motion, Angular momentum is a vector quantity that represents the product of a bodys rotational inertia and rotational velocity about a particular axis. Angular momentum can be considered an analog of linear momentum. Thus, where momentum is proportional to mass m and linear speed v, p = m v, angular momentum is proportional to moment of inertia I. Unlike mass, which only on amount of matter, moment of inertia is also dependent on the position of the axis of rotation. Unlike linear speed, which occurs in a line, angular speed occurs about a center of rotation. Therefore, strictly speaking, L should be referred to as the angular momentum relative to that center and this simple analysis can also apply to non-circular motion if only the component of the motion which is perpendicular to the radius vector is considered. In that case, L = r m v ⊥, where v ⊥ = v sin θ is the component of the motion. It is this definition, × to which the moment of momentum refers
20.
Angular momentum operator
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In quantum mechanics, the angular momentum operator is one of several related operators analogous to classical angular momentum. The angular momentum operator plays a role in the theory of atomic physics. In both classical and quantum systems, angular momentum is one of the three fundamental properties of motion. There are several angular momentum operators, total angular momentum, orbital angular momentum, the term angular momentum operator can refer to either the total or the orbital angular momentum. Total angular momentum is conserved, see Noethers theorem. The classical definition of momentum is L = r × p. This can be carried over to quantum mechanics, by reinterpreting r as the position operator. L is then an operator, specifically called the angular momentum operator. Specifically, L is an operator, meaning L =. However, there is type of angular momentum, called spin angular momentum. Almost all elementary particles have spin, spin is often depicted as a particle literally spinning around an axis, but this is only a metaphor, spin is an intrinsic property of a particle, unrelated to any sort of motion in space. All elementary particles have a spin, for example electrons always have spin 1/2 while photons always have spin 1. However, L and S are not generally conserved, for example, the spin–orbit interaction allows angular momentum to transfer back and forth between L and S, with the total J remaining constant. The orbital angular momentum operator is an operator, meaning it can be written in terms of its vector components L =. The components have the commutation relations with each other, = i ℏ L z, = i ℏ L x, = i ℏ L y. This can be written generally as = i ℏ ∑ n =13 ε l m n L n, where l, m, n are the component indices, and εlmn denotes the Levi-Civita symbol. There is a relationship in classical physics, = ε i j k L k where Ln is a component of the classical angular momentum operator. The same commutation relations apply for the angular momentum operators
21.
Gyromagnetic ratio
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In physics, the gyromagnetic ratio of a particle or system is the ratio of its magnetic moment to its angular momentum, and it is often denoted by the symbol γ, gamma. Its SI unit is the radian per second per tesla or, equivalently, the term gyromagnetic ratio is often used as a synonym for a different but closely related quantity, the g-factor. The g-factor, unlike the gyromagnetic ratio, is dimensionless, for more on the g-factor, see below, or see the article g-factor. For this reason, values of γ/, in units of hertz per tesla, are often quoted instead of γ. The derivation of this relation is as follows, First we must prove that the torque resulting from subjecting a magnetic moment m ¯ to a magnetic field B ¯ is T ¯ = m ¯ × B ¯. By classical mechanics the torque on this needle is T ¯ = l ¯ × B ¯ ⋅ q m = q m ⋅ l ¯ × B ¯. But as previously stated q m ⋅ l ¯ = I π r 2 = m ¯, the model of the spinning electron we use in the derivation has an evident analogy with a gyroscope. For any rotating body the rate of change of the angular momentum J ¯ equals the applied torque T ¯, d J ¯ d t = T ¯, note as an example the precession of a gyroscope. Replace the gravity with a flux density B. D J ¯ d t represents the velocity of the pike of the arrow J ¯ along a circle whose radius is J ⋅ sin ϕ where ϕ is the angle between J ¯ and the vertical. Consequently, f = γ2 π B q. e. d, the angular precession frequency has an important physical meaning, It is the angular cyclotron frequency. The resonance frequency of an ionized plasma being under the influence of a static magnetic field. Consider a charged body rotating about an axis of symmetry, according to the laws of classical physics, it has both a magnetic dipole moment and an angular momentum due to its rotation. It can be shown that as long as its charge and mass are distributed identically, its ratio is γ = q 2 m where q is its charge. The derivation of this relation is as follows, It suffices to demonstrate this for a narrow circular ring within the body. Suppose the ring has radius r, area A = πr2, mass m, charge q, and angular momentum L = mvr. Then the magnitude of the dipole moment is μ = I A = q v 2 π r × π r 2 = q 2 m × m v r = q 2 m L. An isolated electron has a momentum and a magnetic moment resulting from its spin
22.
Anomalous magnetic dipole moment
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The Dirac magnetic moment, corresponding to tree-level Feynman diagrams, can be calculated from the Dirac equation. It is usually expressed in terms of the g-factor, the Dirac equation predicts g =2, for particles such as the electron, this classical result differs from the observed value by a small fraction of a percent. The calculation is relatively straightforward and the result is, a e = α2 π ≈0.0011614 where α is the fine structure constant. This result was first found by Julian Schwinger in 1948 and is engraved on his tombstone. As of 2016, the coefficients of the QED formula for the magnetic moment of the electron are known analytically up to α3 and have been calculated up to order α5. The current experimental value and uncertainty is, a e =0.00115965218073 According to this value and this required measuring g to an accuracy of around 1 part in 1 trillion. The anomalous magnetic moment of the muon is calculated in a way to the electron. The third term represents hadron loops, and cannot be calculated accurately from theory alone and it is estimated from experimental measurements of the ratio of hadronic to muonic cross sections in electron–antielectron collisions. As of November 2006, the measurement disagrees with the Standard Model by 3.4 standard deviations and this is one of the long-standing discrepancies between the Standard Model and experiment. The E821 experiment at Brookhaven National Laboratory studied the precession of muon and antimuon in a constant external magnetic field as they circulated in a storage ring. The E821 Experiment reported the average value a μ =0.00116592091, where the first error is statistical. A new experiment at Fermilab called Muon g−2 using the E821 magnet will improve the accuracy of this value, data taking will begin in 2017. A measurement with a precision 4 times better is expected after years of running and this is true for the proton, which is made up of charged quarks, and the neutron, which has a magnetic moment even though it is electrically neutral. Anomalous electric dipole moment G-factor Proton magnetic moment Neutron magnetic moment Electron magnetic moment Sergei Vonsovsky, overview of the g−2 experiment Kusch, P. Foley, H. M. The Magnetic Moment of the Electron
23.
Quantum electrodynamics
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In particle physics, quantum electrodynamics is the relativistic quantum field theory of electrodynamics. In essence, it describes how light and matter interact and is the first theory where full agreement between quantum mechanics and special relativity is achieved, in technical terms, QED can be described as a perturbation theory of the electromagnetic quantum vacuum. Dirac described the quantization of the field as an ensemble of harmonic oscillators with the introduction of the concept of creation and annihilation operators of particles. At higher orders in the series emerged, making such computations meaningless. With no solution for this problem known at the time, it appeared that a fundamental incompatibility existed between special relativity and quantum mechanics, difficulties with the theory increased through the end of 1940. Improvements in microwave technology made it possible to more precise measurements of the shift of the levels of a hydrogen atom, now known as the Lamb shift. These experiments exposed discrepancies which the theory was unable to explain, a first indication of a possible way out was given by Hans Bethe in 1947, after attending the Shelter Island Conference. While he was traveling by train from the conference to Schenectady he made the first non-relativistic computation of the shift of the lines of the atom as measured by Lamb. Despite the limitations of the computation, agreement was excellent, the idea was simply to attach infinities to corrections of mass and charge that were actually fixed to a finite value by experiments. In this way, the infinities get absorbed in those constants, sin-Itiro Tomonaga, Julian Schwinger and Richard Feynman were jointly awarded with a Nobel prize in physics in 1965 for their work in this area. Even though renormalization works very well in practice, Feynman was never comfortable with its mathematical validity, even referring to renormalization as a shell game. QED has served as the model and template for all subsequent quantum field theories. One such subsequent theory is quantum chromodynamics, which began in the early 1960s and attained its present form in the 1975 work by H. David Politzer, Sidney Coleman, David Gross and Frank Wilczek. Near the end of his life, Richard P. Feynman gave a series of lectures on QED intended for the lay public. These lectures were transcribed and published as Feynman, QED, The strange theory of light and matter, the key components of Feynmans presentation of QED are three basic actions. A photon goes from one place and time to another place, an electron goes from one place and time to another place and time. An electron emits or absorbs a photon at a certain place and these can all be seen in the adjacent diagram. It is important not to over-interpret these diagrams, nothing is implied about how a particle gets from one point to another
24.
Angular momentum coupling
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In quantum mechanics, the procedure of constructing eigenstates of total angular momentum out of eigenstates of separate angular momenta is called angular momentum coupling. For instance, the orbit and spin of a particle can interact through spin–orbit interaction. In both cases the angular momenta are no longer constants of motion, but the sum of the two angular momenta usually still is. Angular momentum coupling in atoms is of importance in atomic spectroscopy, Angular momentum coupling of electron spins is of importance in quantum chemistry. Also in the shell model angular momentum coupling is ubiquitous. In astronomy, spin-orbit coupling reflects the law of conservation of angular momentum. This is more known as orbital resonance. Often, the physical effects are tidal forces. Conservation of angular momentum is the principle that the angular momentum of a system has a constant magnitude. Angular momentum is a property of a system that is a constant of motion in two situations, The system experiences a spherically symmetric potential field. The system moves in isotropic space, in both cases the angular momentum operator commutes with the Hamiltonian of the system. By Heisenbergs uncertainty relation this means that the momentum and the energy can be measured at the same time. An example of the first situation is an atom whose electrons only experiences the Coulomb force of its atomic nucleus, if we ignore the electron-electron interaction, the orbital angular momentum l of each electron commutes with the total Hamiltonian. In this model the atomic Hamiltonian is a sum of energies of the electrons. The individual electron angular momenta li commute with this Hamiltonian and that is, they are conserved properties of this approximate model of the atom. An example of the situation is a rigid rotor moving in field-free space. A rigid rotor has a well-defined, time-independent, angular momentum and these two situations originate in classical mechanics. The third kind of conserved angular momentum, associated with spin, however, all rules of angular momentum coupling apply to spin as well
25.
Fine structure
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In atomic physics, the fine structure describes the splitting of the spectral lines of atoms due to electron spin and relativistic corrections to the non-relativistic Schrödinger equation. The gross structure of spectra is the line spectra predicted by the quantum mechanics of non-relativistic electrons with no spin. For a hydrogenic atom, the gross structure energy levels depend on the principal quantum number n. However, an accurate model takes into account relativistic and spin effects. The fine structure energy corrections can be obtained by using perturbation theory, to do this one adds three corrective terms to the Hamiltonian, the leading order relativistic correction to the kinetic energy, the correction due to the spin-orbit coupling, and the Darwinian term. These corrections can also be obtained from the limit of the Dirac equation, since Diracs theory naturally incorporates relativity. Classically, the energy term of the Hamiltonian is T = p 22 m where p is the momentum. However, when considering a more accurate theory of nature via, R is the distance of the electron from the nucleus. The spin-orbit correction can be understood by shifting from the frame of reference into one where the electron is stationary. In this case the orbiting nucleus functions as a current loop. However, the electron itself has a magnetic moment due to its angular momentum. The two magnetic vectors, B → and μ → s couple together so there is a certain energy cost depending on their relative orientation. Remark, On the = and = energy level, which the fine structure said their level are the same, if we take the g-factor to be 2.0031904622, then, the calculated energy level will be different by using 2 as g-factor. Only using 2 as the g-factor, we can match the level in the 1st order approximation of the relativistic correction. When using the higher order approximation for the term, the 2.0031904622 g-factor may agree with each other. However, if we use the g-factor as 2.0031904622, the result does not agree with the formula, there is one last term in the non-relativistic expansion of the Dirac equation. This is because the function of an electron with l >0 vanishes at the origin. For example, it gives the 2s-orbit the same energy as the 2p-orbit by raising the 2s-state by 9. 057×10−5 eV, the Darwin term changes the effective potential at the nucleus
26.
Lyman-alpha line
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In hydrogen, its wavelength of 1215.67 angstroms, corresponding to a frequency of 2. 47×1015 hertz, places the Lyman-alpha line in the vacuum ultraviolet part of the electromagnetic spectrum. Because of fine structure perturbations, the Lyman-alpha line splits into a doublet with wavelengths 1215.668 and 1215.674 angstroms, in the n =2 orbital, there are two possible states, j = 1/2 and j = 3/2, resulting in a spectral doublet. The j = 3/2 state is of energy and so is energetically farther from the n =1 orbital to which it is transitioning. Thus, the j = 3/2 state is associated with the more energetic spectral line in the doublet, the less energetic spectral line has been measured at 2466061413187035 Hz, or 1215.673123130217 Å. The Lyman-alpha line is most simply described by the = solutions to the empirical Rydberg formula for hydrogens Lyman spectral series, empirically, the Rydberg equation is in turn modeled by the semi-classical Bohr model of the atom
27.
Hydrogen
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Hydrogen is a chemical element with chemical symbol H and atomic number 1. With a standard weight of circa 1.008, hydrogen is the lightest element on the periodic table. Its monatomic form is the most abundant chemical substance in the Universe, non-remnant stars are mainly composed of hydrogen in the plasma state. The most common isotope of hydrogen, termed protium, has one proton, the universal emergence of atomic hydrogen first occurred during the recombination epoch. At standard temperature and pressure, hydrogen is a colorless, odorless, tasteless, non-toxic, nonmetallic, since hydrogen readily forms covalent compounds with most nonmetallic elements, most of the hydrogen on Earth exists in molecular forms such as water or organic compounds. Hydrogen plays an important role in acid–base reactions because most acid-base reactions involve the exchange of protons between soluble molecules. In ionic compounds, hydrogen can take the form of a charge when it is known as a hydride. The hydrogen cation is written as though composed of a bare proton, Hydrogen gas was first artificially produced in the early 16th century by the reaction of acids on metals. Industrial production is mainly from steam reforming natural gas, and less often from more energy-intensive methods such as the electrolysis of water. Most hydrogen is used near the site of its production, the two largest uses being fossil fuel processing and ammonia production, mostly for the fertilizer market, Hydrogen is a concern in metallurgy as it can embrittle many metals, complicating the design of pipelines and storage tanks. Hydrogen gas is flammable and will burn in air at a very wide range of concentrations between 4% and 75% by volume. The enthalpy of combustion is −286 kJ/mol,2 H2 + O2 →2 H2O +572 kJ Hydrogen gas forms explosive mixtures with air in concentrations from 4–74%, the explosive reactions may be triggered by spark, heat, or sunlight. The hydrogen autoignition temperature, the temperature of spontaneous ignition in air, is 500 °C, the detection of a burning hydrogen leak may require a flame detector, such leaks can be very dangerous. Hydrogen flames in other conditions are blue, resembling blue natural gas flames, the destruction of the Hindenburg airship was a notorious example of hydrogen combustion and the cause is still debated. The visible orange flames in that incident were the result of a mixture of hydrogen to oxygen combined with carbon compounds from the airship skin. H2 reacts with every oxidizing element, the ground state energy level of the electron in a hydrogen atom is −13.6 eV, which is equivalent to an ultraviolet photon of roughly 91 nm wavelength. The energy levels of hydrogen can be calculated fairly accurately using the Bohr model of the atom, however, the atomic electron and proton are held together by electromagnetic force, while planets and celestial objects are held by gravity. The most complicated treatments allow for the effects of special relativity
28.
Germany
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Germany, officially the Federal Republic of Germany, is a federal parliamentary republic in central-western Europe. It includes 16 constituent states, covers an area of 357,021 square kilometres, with about 82 million inhabitants, Germany is the most populous member state of the European Union. After the United States, it is the second most popular destination in the world. Germanys capital and largest metropolis is Berlin, while its largest conurbation is the Ruhr, other major cities include Hamburg, Munich, Cologne, Frankfurt, Stuttgart, Düsseldorf and Leipzig. Various Germanic tribes have inhabited the northern parts of modern Germany since classical antiquity, a region named Germania was documented before 100 AD. During the Migration Period the Germanic tribes expanded southward, beginning in the 10th century, German territories formed a central part of the Holy Roman Empire. During the 16th century, northern German regions became the centre of the Protestant Reformation, in 1871, Germany became a nation state when most of the German states unified into the Prussian-dominated German Empire. After World War I and the German Revolution of 1918–1919, the Empire was replaced by the parliamentary Weimar Republic, the establishment of the national socialist dictatorship in 1933 led to World War II and the Holocaust. After a period of Allied occupation, two German states were founded, the Federal Republic of Germany and the German Democratic Republic, in 1990, the country was reunified. In the 21st century, Germany is a power and has the worlds fourth-largest economy by nominal GDP. As a global leader in industrial and technological sectors, it is both the worlds third-largest exporter and importer of goods. Germany is a country with a very high standard of living sustained by a skilled. It upholds a social security and universal health system, environmental protection. Germany was a member of the European Economic Community in 1957. It is part of the Schengen Area, and became a co-founder of the Eurozone in 1999, Germany is a member of the United Nations, NATO, the G8, the G20, and the OECD. The national military expenditure is the 9th highest in the world, the English word Germany derives from the Latin Germania, which came into use after Julius Caesar adopted it for the peoples east of the Rhine. This in turn descends from Proto-Germanic *þiudiskaz popular, derived from *þeudō, descended from Proto-Indo-European *tewtéh₂- people, the discovery of the Mauer 1 mandible shows that ancient humans were present in Germany at least 600,000 years ago. The oldest complete hunting weapons found anywhere in the world were discovered in a mine in Schöningen where three 380, 000-year-old wooden javelins were unearthed
29.
Physicist
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A physicist is a scientist who has specialized knowledge in the field of physics, the exploration of the interactions of matter and energy across the physical universe. A physicist is a scientist who specializes or works in the field of physics, physicists generally are interested in the root or ultimate causes of phenomena, and usually frame their understanding in mathematical terms. Physicists can also apply their knowledge towards solving real-world problems or developing new technologies, some physicists specialize in sectors outside the science of physics itself, such as engineering. The study and practice of physics is based on a ladder of discoveries. Many mathematical and physical ideas used today found their earliest expression in ancient Greek culture and Asian culture, the bulk of physics education can be said to flow from the scientific revolution in Europe, starting with the work of Galileo and Kepler in the early 1600s. New knowledge in the early 21st century includes an increase in understanding physical cosmology. The term physicist was coined by William Whewell in his 1840 book The Philosophy of the Inductive Sciences, many physicist positions require an undergraduate degree in applied physics or a related science or a Masters degree like MSc, MPhil, MPhys or MSci. In a research oriented level, students tend to specialize in a particular field, Physics students also need training in mathematics, and also in computer science and programming. For being employed as a physicist a doctoral background may be required for certain positions, undergraduate students like BSc Mechanical Engineering, BSc Electrical and Computer Engineering, BSc Applied Physics. etc. With physics orientation are chosen as research assistants with faculty members, the highest honor awarded to physicists is the Nobel Prize in Physics, awarded since 1901 by the Royal Swedish Academy of Sciences. The three major employers of career physicists are academic institutions, laboratories, and private industries, with the largest employer being the last, physicists in academia or government labs tend to have titles such as Assistants, Professors, Sr. /Jr. As per the American Institute for Physics, some 20% of new physics Ph. D. s holds jobs in engineering development programs, while 14% turn to computer software, a majority of physicists employed apply their skills and training to interdisciplinary sectors. For industry or self-employment. and also in science and programming. Hence a majority of Physics bachelors degree holders are employed in the private sector, other fields are academia, government and military service, nonprofit entities, labs and teaching
30.
Friedrich Paschen
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Louis Carl Heinrich Friedrich Paschen, was a German physicist, known for his work on electrical discharges. He is also known for the Paschen series, a series of spectral lines in the infrared region that he first observed in 1908. He established the now widely used Paschen curve in his article Über die zum Funkenübergang in Luft and he is also known for the Paschen-Back effect, which is the Zeeman effects becoming non-linear at high magnetic field. Paschen was born in Schwerin, Mecklenburg-Schwerin, from 1884 to 1888 he studied at the universities of Berlin and Strassburg, after which he became an assistant at the Academy of Münster. He became a professor at the Technical Academy of Hanover in 1893 and he served as president of the Physikalisch-Technischen Reichsanstalt from 1924–33 and an honorary professor of the University of Berlin in 1925. During the second world war he had the Chinese scientist He Zehui to stay at his house, with his help she was introduced to Walther Bothe who led the Kaiser Wilhelm Institute in Heidelberg. Paschen taught in Berlin until his death in Potsdam in 1947
31.
Hyperfine structure
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In atomic physics, hyperfine structure is the different effects leading to small shifts and splittings in the energy levels of atoms, molecules and ions. The name is a reference to the structure, which results from the interaction between the magnetic moments associated with electron spin and the electrons orbital angular momentum. The optical hyperfine structure was observed in 1881 by Albert Abraham Michelson and it could, however, only be explained in terms of quantum mechanics when Wolfgang Pauli proposed the existence of a small nuclear magnetic moment in 1924. In 1935, H. Schüler and Theodor Schmidt proposed the existence of a quadrupole moment in order to explain anomalies in the hyperfine structure. The theory of structure comes directly from electromagnetism, consisting of the interaction of the nuclear multipole moments with internally generated fields. The theory is derived first for the case, but can be applied to each nucleus in a molecule. Following this there is a discussion of the additional effects unique to the molecular case, the dominant term in the hyperfine Hamiltonian is typically the magnetic dipole term. Atomic nuclei with a nuclear spin I have a magnetic dipole moment, given by, μ I = g I μ N I. There is an associated with a magnetic dipole moment in the presence of a magnetic field. For a nuclear magnetic moment, μI, placed in a magnetic field, B. Electron orbital angular momentum results from the motion of the electron about some fixed point that we shall take to be the location of the nucleus. Written in terms of the Bohr magneton, this gives, B el l = −2 μ B μ04 π1 r 3 r × m e v ℏ. Recognizing that mev is the momentum, p, and that r×p/ħ is the orbital angular momentum in units of ħ, l, we can write. The electron spin angular momentum is a different property that is intrinsic to the particle. Nonetheless it is angular momentum and any angular momentum associated with a charged particle results in a dipole moment. The magnetic field of a moment, μs, is given by. The first term gives the energy of the dipole in the field due to the electronic orbital angular momentum. The second term gives the energy of the finite distance interaction of the dipole with the field due to the electron spin magnetic moments
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George Ellery Hale
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George Ellery Hale was born on June 29,1868 in Chicago, Illinois to William Ellery Hale and Mary Browne. He is descended from Thomas Hale of Watton-on-Stone, Hertfordshire, England and his father acquired a considerable fortune manufacturing and installing passenger elevators during the reconstruction of Chicago, which had been destroyed in the Great Chicago Fire of 1871. He spent his youth fascinated by the books and machinery given to him by his parents—one of his most prized possessions was a small microscope, with his fathers encouragement, he built a small shop in their house that turned into a laboratory. The microscope led to his interest in optics, at the age of fourteen, George built his first telescope. His father later replaced it with a second-hand Clark refractor that they mounted on the roof of their Kenwood house, soon he was photographing the night skies, observing a partial eclipse of the sun, and drawing sun-spots. As an avid reader with a strong interest in the field of astrophysics, Hale was drawn to the writings of William Huggins, Norman Lockyer. His fascination with science, however, did not preclude interests more typical of a boy, such as fishing, boating, swimming, skating, tennis. He was a reader of the stories of Jules Verne—particularly drawn to the tales of adventure set in the mountains of California. Hale spent summers at his grandmothers house in the old New England village of Madison, Connecticut, after graduating from Oakland Public School in Chicago, Hale attended the Allen Academy, where he studied chemistry, physics, and astronomy. He supplemented his practical experience by attending a course in shop-work at the Chicago Manual Training School. During these years, Hale developed a knowledge of the principles of architecture and city planning with the help of his fathers friend, upon Burnhams advice and encouragement, Hale decided at the age of seventeen to continue his education at the Massachusetts Institute of Technology. Hale was educated at MIT, at the Harvard College Observatory, as an undergraduate at MIT, he is known for inventing the spectroheliograph, with which he made his discovery of solar vortices. In 1908, he used the Zeeman effect with a modified spectroheliograph to establish that sunspots were magnetic and this systematic property of sunspot magnetic fields is now commonly referred to as the Hale–Nicholson law, or in many cases simply Hales law. He was coeditor of Astronomy and Astrophysics, 1892–95, and after 1895 editor of the Astrophysical Journal and he also served on the board of trustees for Science Service, now known as Society for Science & the Public, from 1921 to 1923. Hale replied in November, saying that such observations could be done only during an eclipse of the sun. At Mount Wilson, he hired and encouraged Harlow Shapley and Edwin Hubble toward some of the most significant discoveries of the time and he was a prolific organizer who helped create a number of astronomical institutions, societies and journals. Hale also played a role in developing the California Institute of Technology into a leading research university. After retiring as director at Mount Wilson, he built the Hale Solar Laboratory in Pasadena, California, as his office and workshop, from early youth, Hale had been internationally oriented, travelling widely throughout Europe in his younger years
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Tesla (unit)
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The tesla is a unit of measurement of the strength of a magnetic field. It is a unit of the International System of Units. One tesla is equal to one weber per square metre, the unit was announced during the General Conference on Weights and Measures in 1960 and is named in honour of Nikola Tesla, upon the proposal of the Slovenian electrical engineer France Avčin. The strongest fields encountered from permanent magnets are from Halbach spheres, the strongest field trapped in a laboratory superconductor as of June 2014 is 21 T. This may be appreciated by looking at the units for each, the unit of electric field in the MKS system of units is newtons per coulomb, N/C, while the magnetic field can be written as N/. The dividing factor between the two types of field is metres per second, which is velocity, in ferromagnets, the movement creating the magnetic field is the electron spin. In a current-carrying wire the movement is due to moving through the wire. One tesla is equivalent to,10,000 G, used in the CGS system, thus,10 kG =1 T, and 1 G = 10−4 T.1,000,000,000 γ, used in geophysics. Thus,1 γ =1 nT.42.6 MHz of the 1H nucleus frequency, thus, the magnetic field associated with NMR at 1 GHz is 23.5 T. One tesla is equal to 1 V·s/m2 and this can be shown by starting with the speed of light in vacuum, c = −1/2, and inserting the SI values and units for c, the vacuum permittivity ε0, and the vacuum permeability μ0. Cancellation of numbers and units then produces this relation, for those concerned with low-frequency electromagnetic radiation in the home, the following conversions are needed most,1000 nT =1 µT =10 mG,1,000,000 µT =1 T. For the relation to the units of the field, see the article on permeability
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Laser cooling
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Laser cooling refers to a number of techniques in which atomic and molecular samples are cooled down to near absolute zero through the interaction with one or more laser fields. All laser cooling techniques rely on the fact that when an object absorbs, the temperature of an ensemble of particles is larger for larger variance in the velocity distribution of the particles. The first example of laser cooling, and also still the most common method is Doppler cooling and it is used to cool low density gases down to the Doppler cooling limit, which for Rubidium 85 is around 150 microkelvin. In Doppler cooling, the frequency of light is tuned slightly below a transition in the atom. Because the light is detuned to the red of the transition, thus if one applies light from two opposite directions, the atoms will always scatter more photons from the laser beam pointing opposite to their direction of motion. In each scattering event the atom loses a momentum equal to the momentum of the photon, if the atom, which is now in the excited state, then emits a photon spontaneously, it will be kicked by the same amount of momentum, but in a random direction. If the absorption and emission are repeated many times, the average speed, since the temperature of a group of atoms is a measure of the average random internal kinetic energy, this is equivalent to cooling the atoms. Laser cooling is used to create ultracold atoms for experiments in quantum physics. These experiments are performed near absolute zero where unique quantum effects such as Bose-Einstein condensation can be observed, laser cooling has primarily been used on atoms, but recent progress has been made toward laser cooling more complex systems. In 2010, a team at Yale successfully laser-cooled a diatomic molecule, in 2007, an MIT team successfully laser-cooled a macro-scale object to 0.8 K. In 2011, a team from the California Institute of Technology, brady Haran for the University of Nottingham
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Magneto-optical trap
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Although charged particles can be trapped using a Penning trap or a Paul trap using a combination of electric and magnetic fields, those traps do not work for neutral atoms. Photons have a given by ℏ k, which is conserved in all atom-photon interactions. Thus, when an atom absorbs a photon, it is given a momentum kick in the direction of the photon before absorption and this applies a friction force to the atom whenever it moves towards a laser source. Magnetic trapping is created by adding a spatially varying magnetic field to the red detuned optical field needed for laser cooling. This causes a Zeeman shift in the magnetic-sensitive mf levels, which increases with the distance from the centre of the trap. The direction of the kick is given by the polarisation of the light, the correct polarisations are used so that photons moving towards the centre of the trap will be on resonance with the correct shifted atomic energy level, always driving the atom towards the centre. 85Rubidium, for example, has a closed loop between the 5 S1 /2 F =3 state and the 5 P3 /2 F =4 state. The magneto-optical trapping of rubidium 85, for example, involves cycling on the closed 5 S1 /2 F =3 →5 P3 /2 F =4 transition. On excitation, however, the necessary for cooling gives a small. If it falls back to the state, the atom stops cycling between ground and excited state, and the cooling and trapping of this atom stops. All magneto-optical traps require at least one trapping laser plus any necessary repumper lasers and these lasers need stability, rather than high power, requiring no more than the saturation intensity, but a linewidth much less than the Doppler width, usually several megahertz. The MOT cloud is loaded from a background of thermal vapour, or from an atomic beam, if the background pressure is too high, atoms are kicked out of the trap faster than they can be loaded, and the trap does not form. This means that the MOT cloud only forms in a chamber with a background pressure of less than 10 micropascals. The minimum temperature and maximum density of a cloud in a trap is limited by the spontaneously emitted photon in cooling each cycle. The density is limited by the spontaneously emitted photon. As the density of the cloud increases, the chance that the emitted photon will leave the cloud without interacting with any further atoms tends to zero. As a result of low densities and speeds of atoms achieved by cooling, the mean free path in a ball of MOT cooled atoms is very long. This is useful for quantum information experiments where it is necessary to have long coherence times, because of the continuous cycle of absorption and spontaneous emission, which causes decoherence, any quantum manipulation experiments must be performed with the MOT beams turned off
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Zeeman slower
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A Zeeman slower is a scientific apparatus that is commonly used in quantum optics to cool a beam of atoms from room temperature or above to a few kelvins. At the entrance of the Zeeman slower the speed of atoms is on the order of a few hundred m/s. The spread of velocity is also in the order of a few hundred m/s, final speed at the exit of the slower is few 10 m/s with an even smaller spread. The pump laser, which is required to be near-resonant to an atomic or molecular transition and it was first developed by William D. Phillips and Harold J. Metcalf. The achievement of low temperatures led the way for the experimental realisation of Bose–Einstein condensation. According to the principles of Doppler cooling, an atom modelled as an atom can be cooled using a laser. If it moves in a direction and encounters a counter-propagating laser beam resonant with its transition. The absorption of this gives the atom a kick in the direction that is consistent with momentum conservation. However, this state is unstable and some time later the atom decays back to its ground state via spontaneous emission, the photon will be reemitted, but its direction will be random. Thus the atom is being slowed down by the laser beam. There is nevertheless a problem in this scheme because of the Doppler effect. The Zeeman slower uses the fact that a field can change the resonance frequency of an atom using the Zeeman effect to tackle this problem. In the presence of a magnetic field B, the transition is Zeeman shifted by an amount μ ′ B / ℏ. It has been recently shown however, that a different approach yields better results, the parameter η is normally chosen to be around.5. The required form of the spatially inhomogeneous magnetic field as we showed above has the form B = B0 + B a 1 − z / z 0 This field can be realized a few different ways. The most popular design requires wrapping a current carrying wire with many layered windings where the field is strongest, an alternative design uses a single layer coil that varies rather in the pitch of the winding of such a coil. Another proposed design uses an array of permanent magnets to create the field, the Zeeman slower is usually used as a preliminary step to cool the atoms in order to trap them in a magneto-optical trap. Thus it aims at a velocity of about 10 m/s