Acenaphthene is a polycyclic aromatic hydrocarbon consisting of naphthalene with an ethylene bridge connecting positions 1 and 8. It is a colourless solid. Coal tar consists of about 0.3% of this compound. Acenaphthene was prepared the first time from coal tar by Marcellin Berthelot. Berthelot and Bardy synthesized the compound by cyclization of α-ethylnaphthalene. Industrially, it is still obtained from coal tar together with its derivative acenaphthylene. Like other arenes, acenaphthene forms complexes with low valent metal centers. One example is Mn3]+, it is used on a large scale to prepare naphthalene dicarboxylic anhydride, a precursor to dyes and optical brighteners. Naphthalene dicarboxylic anhydride is the precursor to perylenetetracarboxylic dianhydride, precursor to several commercial pigments and dyes
A dye laser is a laser which uses an organic dye as the lasing medium as a liquid solution. Compared to gases and most solid state lasing media, a dye can be used for a much wider range of wavelengths spanning 50 to 100 nanometers or more; the wide bandwidth makes them suitable for tunable lasers and pulsed lasers. The dye rhodamine 6G, for example, can be tuned from 635 nm to 560 nm, produce pulses as short as 16 femtoseconds. Moreover, the dye can be replaced by another type in order to generate an broader range of wavelengths with the same laser, from the near-infrared to the near-ultraviolet, although this requires replacing other optical components in the laser as well, such as dielectric mirrors or pump lasers. Dye lasers were independently discovered by P. P. Sorokin and F. P. Schäfer in 1966. In addition to the usual liquid state, dye lasers are available as solid state dye lasers. SSDL use dye-doped organic matrices as gain medium. A dye laser uses a gain medium consisting of an organic dye, a carbon-based, soluble stain, fluorescent, such as the dye in a highlighter pen.
The dye is mixed with a compatible solvent, allowing the molecules to diffuse evenly throughout the liquid. The dye solution streamed through open air using a dye jet. A high energy source of light is needed to'pump' the liquid beyond its lasing threshold. A fast discharge flashtube or an external laser is used for this purpose. Mirrors are needed to oscillate the light produced by the dye’s fluorescence, amplified with each pass through the liquid; the output mirror is around 80% reflective, while all other mirrors are more than 99.9% reflective. The dye solution is circulated at high speeds, to help avoid triplet absorption and to decrease degradation of the dye. A prism or diffraction grating is mounted in the beam path, to allow tuning of the beam; because the liquid medium of a dye laser can fit any shape, there are a multitude of different configurations that can be used. A Fabry–Pérot laser cavity is used for flashtube pumped lasers, which consists of two mirrors, which may be flat or curved, mounted parallel to each other with the laser medium in between.
The dye cell is a thin tube equal in length to the flashtube, with both windows and an inlet/outlet for the liquid on each end. The dye cell is side-pumped, with one or more flashtubes running parallel to the dye cell in a reflector cavity; the reflector cavity is water cooled, to prevent thermal shock in the dye caused by the large amounts of near-infrared radiation which the flashtube produces. Axial pumped lasers have a hollow, annular-shaped flashtube that surrounds the dye cell, which has lower inductance for a shorter flash, improved transfer efficiency. Coaxial pumped lasers have an annular dye cell that surrounds the flashtube, for better transfer efficiency, but have a lower gain due to diffraction losses. Flash pumped. A ring laser design is chosen for continuous operation, although a Fabry–Pérot design is sometimes used. In a ring laser, the mirrors of the laser are positioned to allow the beam to travel in a circular path; the dye cell, or cuvette, is very small. Sometimes a dye jet is used to help avoid reflection losses.
The dye is pumped with an external laser, such as a nitrogen, excimer, or frequency doubled Nd:YAG laser. The liquid is circulated at high speeds, to prevent triplet absorption from cutting off the beam. Unlike Fabry–Pérot cavities, a ring laser does not generate standing waves which cause spatial hole burning, a phenomenon where energy becomes trapped in unused portions of the medium between the crests of the wave; this leads to a better gain from the lasing medium. The dyes used in these lasers contain rather organic molecules which fluoresce. Most dyes have a short time between the absorption and emission of light, referred to as the fluorescence lifetime, on the order of a few nanoseconds. Under standard laser-pumping conditions, the molecules emit their energy before a population inversion can properly build up, so dyes require rather specialized means of pumping. Liquid dyes have an high lasing threshold. In addition, the large molecules are subject to complex excited state transitions during which the spin can be "flipped" changing from the useful, fast-emitting "singlet" state to the slower "triplet" state.
The incoming light excites the dye molecules into the state of being ready to emit stimulated radiation. In this state, the molecules emit light via fluorescence, the dye is transparent to the lasing wavelength. Within a microsecond or less, the molecules will change to their triplet state. In the triplet state, light is emitted via phosphorescence, the molecules absorb the lasing wavelength, making the dye opaque. Flashlamp-pumped lasers need a flash with an short duration, to deliver the large amounts of energy necessary to bring the dye past threshold before triplet absorption overcomes singlet emission. Dye lasers with an external pump-laser can direct enough energy of the proper wavelength into the dye with a small amount of input energy, but the dye must be circulated at high speeds to keep the triplet molecules out of the beam path. Due to their high absorption, the pumping energy may be concentrated into a rather small volume of liquid. Since organic dyes tend to decompose under the influence of light, the d
Osaka University, or Handai, is a public research university located in Osaka Prefecture, Japan. Osaka University is one of Japan's National Seven Universities and is considered one of Japan's most prestigious institutions of higher learning, it is ranked among the top three public universities in Japan, along with the University of Tokyo and Kyoto University. It is ranked third overall among Japanese universities and 67th worldwide in the 2019 QS World University Rankings; the Japanese Ministry of Education, Sports and Technology has classified Osaka University as a leading university in the Top Global University Project. The ministry selected Osaka University as a Designated National University Corporation in 2018. Osaka University was the sixth modern university in Japan at its founding in 1931. However, the history of the institution includes much older predecessors in Osaka such as the Kaitokudō founded in 1724 and the Tekijuku founded in 1838. Numerous prominent scholars and scientists have attended or worked at Osaka University, such as Nobel Laureate in Physics Hideki Yukawa, manga artist Osamu Tezuka, Lasker Award winner Hidesaburō Hanafusa, author Ryōtarō Shiba, discoverer of regulatory T cells Shimon Sakaguchi.
The academic traditions of the university reach back to the Kaitokudō, an Edo-period school for local citizens founded in 1724, the Tekijuku, a school of Rangaku for samurai founded by Ogata Kōan in 1838. The spirit of the university's humanities programs is believed to be intimately rooted in the history of the Kaitokudō, whereas that of the natural and applied sciences is based upon the traditions of the Tekijuku. Osaka University traces its modern origins back the founding of Osaka Prefectural Medical School in downtown Osaka City in 1869; the school was designated the Osaka Prefectural Medical College with university status by the University Ordinance in 1919. The Medical College merged with the newly founded College of Science to form Osaka Imperial University in 1931. Osaka Imperial University was the sixth imperial university in Japan. Osaka Technical College was incorporated to form the School of Engineering two years later; the entire university was renamed Osaka University in 1947. After merging with Naniwa High School and Osaka High School as a result of the government's education system reform in 1949, Osaka University started its postwar era with five faculties: Science, Engineering and Law.
Since that time new faculties and research institutes have been established, including the first Japanese School of Engineering Science and the School of Human Sciences, which covers such cross-disciplinary research interests as broadly as psychology and education. Built on the then-existing faculties, ten graduate schools were set up as part of the government's education system reform program in 1953. Two more graduate faculties were added in 1994. In 1993, Osaka University Hospital was relocated from the Nakanoshima campus in downtown Osaka to the Suita campus, completing the implementation of the university's plan to integrate the scattered facilities into the Suita and Toyonaka campuses. In October 2007, a merger between Osaka University and the Osaka University of Foreign Studies in Minoh was completed; the merger made Osaka University one of two national universities in the country with a School of Foreign Studies, along with the Tokyo University of Foreign Studies. The merger made Osaka University the largest national university in Japan.
Suita and Minoh are the contemporary university's three campuses. Home to the university's headquarters, the Suita campus extends across Suita City and Ibaraki City in Osaka Prefecture; the Suita campus houses faculties of Human Sciences, Dentistry, Pharmaceutical Sciences, Engineering. It contains the Graduate School of Frontier Biosciences and a portion of the Graduate School of Information Science and Technology; the campus is home to the Osaka University Hospital and the Nationwide Joint Institute of Cybermedia Center and Research Center for Nuclear Physics. The Toyonaka campus is home to faculties of Letters, Economics and Engineering Science, it is the academic base for Graduate Schools of International Public Policy and Culture, a portion of Information Science, the Center for the Practice of Legal and Political Expertise. All undergraduates attend classes on the Toyonaka campus during their first year of enrollment. Sports activities are concentrated on the Toyonaka campus, with the exception of tennis, located in Suita.
The Minoh campus was incorporated following the merger with the Osaka University of Foreign Studies in October 2007. The Minoh campus is home to the School of Foreign Studies, the Research Institute for World Languages, the Center for Japanese Language and Culture. In addition to these three campuses, the former Nakanoshima campus, the university's earliest campus located in downtown Osaka, served as the hub for the faculty of medicine until the transfer to the Suita campus was completed in 1993. In April 2004, the Nakanoshima campus became the university's Nakanoshima Center, serving as a venue for information exchange, adult education classes, activities involving academic as well as non-academic communities. Osaka University is organized into 11 faculties for 16 graduate schools; the undergraduate programs are the School of Letters, School of Human Sciences, School of Foreign Studies, School of Law, School of Economics, School of Science, Faculty of Medicine, Faculty of Dentistry, School of Pharmaceutical Science, School of Engineering, School of Engineering Science.
The graduate programs are in the Graduate School of
Polycyclic aromatic hydrocarbon
Polycyclic aromatic hydrocarbons are hydrocarbons—organic compounds containing only carbon and hydrogen—that are composed of multiple aromatic rings. The simplest such chemicals are naphthalene, having two aromatic rings, the three-ring compounds anthracene and phenanthrene. PAHs are uncharged, non-polar molecules found in tar deposits, they are produced by the thermal decomposition of organic matter. PAHs are abundant in the universe, have been found to have formed as early as the first couple of billion years after the Big Bang, in association with formation of new stars and exoplanets; some studies suggest. Polycyclic aromatic hydrocarbons are discussed as possible starting materials for abiotic syntheses of materials required by the earliest forms of life. By definition, polycyclic aromatic hydrocarbons have multiple cycles, precluding benzene from being considered a PAH. Naphthalene is considered the simplest polycyclic aromatic hydrocarbon by the US EPA and US CDC for policy contexts. Other authors consider PAHs to start with the tricyclic species anthracene.
PAHs are not considered to contain heteroatoms or carry substituents. PAHs with five or six-membered rings are most common; those composed only of six-membered rings are called alternant PAHs. The following are examples of PAHs that vary in the number and arrangement of their rings: Principal PAH Compounds PAHs are nonpolar and lipophilic. Larger PAHs are insoluble in water, although some smaller PAHs are soluble and known contaminants in drinking water; the larger members are poorly soluble in organic solvents and in lipids. They are colorless; the aromaticity varies for PAHs. According to Clar's rule, the resonance structure of a PAH that has the largest number of disjoint aromatic pi sextets—i.e. Benzene-like moieties—is the most important for the characterization of the properties of that PAH. Benzene-substructure resonance analysis for Clar's rule For example, in phenanthrene one Clar structure has two sextets—the first and third rings—while the other resonance structure has just one central sextet.
In contrast, in anthracene the resonance structures have one sextet each, which can be at any of the three rings, the aromaticity spreads out more evenly across the whole molecule. This difference in number of sextets is reflected in the differing ultraviolet–visible spectra of these two isomers, as higher Clar pi-sextets are associated with larger HOMO-LUMO gaps. Three Clar structures with two sextets each are present in the four-ring chrysene structure: one having sextets in the first and third rings, one in the second and fourth rings, one in the first and fourth rings. Superposition of these structures reveals that the aromaticity in the outer rings is greater compared to the inner rings. Polycyclic aromatic compounds characteristically reduce to the radical anions; the redox potential correlates with the size of the PAH. Polycyclic aromatic hydrocarbons are found in natural sources such as creosote, they can result from the incomplete combustion of organic matter. PAHs can be produced geologically when organic sediments are chemically transformed into fossil fuels such as oil and coal.
PAHs are considered ubiquitous in the environment and can be formed from either natural or manmade combustion sources. The dominant sources of PAHs in the environment are thus from human activity: wood-burning and combustion of other biofuels such as dung or crop residues contribute more than half of annual global PAH emissions due to biofuel use in India and China; as of 2004, industrial processes and the extraction and use of fossil fuels made up more than one quarter of global PAH emissions, dominating outputs in industrial countries such as the United States. Wildfires are another notable source. Higher outdoor air and water concentrations of PAHs have been measured in Asia and Latin America than in Europe, the U. S. and Canada. PAHs are found as complex mixtures. Lower-temperature combustion, such as tobacco smoking or wood-burning, tends to generate low molecular weight PAHs, whereas high-temperature industrial processes generate PAHs with higher molecular weights. Most PAHs are insoluble in water, which limits their mobility in the environment, although PAHs sorb to fine-grained organic-rich sediments.
Aqueous solubility of PAHs decreases logarithmically as molecular mass increases. Two-ringed PAHs, to a lesser extent three-ringed PAHs, dissolve in water, making them more available for biological uptake and degradation. Further, two- to four-ringed PAHs volatilize sufficiently to appear in the atmosphere predominantly in gaseous form, although the physical state of four-ring PAHs can depend on temperature. In contrast, compounds with five or more rings have low solubility in water and low volatility. In solid state, these compounds are less accessible for biological uptake or degradation, increasing their persistence in the environment. Spiral galaxy NGC 5529 has been
The melting point of a substance is the temperature at which it changes state from solid to liquid. At the melting point the solid and liquid phase exist in equilibrium; the melting point of a substance depends on pressure and is specified at a standard pressure such as 1 atmosphere or 100 kPa. When considered as the temperature of the reverse change from liquid to solid, it is referred to as the freezing point or crystallization point; because of the ability of some substances to supercool, the freezing point is not considered as a characteristic property of a substance. When the "characteristic freezing point" of a substance is determined, in fact the actual methodology is always "the principle of observing the disappearance rather than the formation of ice", that is, the melting point. For most substances and freezing points are equal. For example, the melting point and freezing point of mercury is 234.32 kelvins. However, certain substances possess differing solid-liquid transition temperatures.
For example, agar melts at 85 °C and solidifies from 31 °C. The melting point of ice at 1 atmosphere of pressure is close to 0 °C. In the presence of nucleating substances, the freezing point of water is not always the same as the melting point. In the absence of nucleators water can exist as a supercooled liquid down to −48.3 °C before freezing. The chemical element with the highest melting point is tungsten, at 3,414 °C; the often-cited carbon does not melt at ambient pressure but sublimes at about 3,726.85 °C. Tantalum hafnium carbide is a refractory compound with a high melting point of 4215 K. At the other end of the scale, helium does not freeze at all at normal pressure at temperatures arbitrarily close to absolute zero. Many laboratory techniques exist for the determination of melting points. A Kofler bench is a metal strip with a temperature gradient. Any substance can be placed on a section of the strip, revealing its thermal behaviour at the temperature at that point. Differential scanning calorimetry gives information on melting point together with its enthalpy of fusion.
A basic melting point apparatus for the analysis of crystalline solids consists of an oil bath with a transparent window and a simple magnifier. The several grains of a solid are placed in a thin glass tube and immersed in the oil bath; the oil bath is heated and with the aid of the magnifier melting of the individual crystals at a certain temperature can be observed. In large/small devices, the sample is placed in a heating block, optical detection is automated; the measurement can be made continuously with an operating process. For instance, oil refineries measure the freeze point of diesel fuel online, meaning that the sample is taken from the process and measured automatically; this allows for more frequent measurements as the sample does not have to be manually collected and taken to a remote laboratory. For refractory materials the high melting point may be determined by heating the material in a black body furnace and measuring the black-body temperature with an optical pyrometer. For the highest melting materials, this may require extrapolation by several hundred degrees.
The spectral radiance from an incandescent body is known to be a function of its temperature. An optical pyrometer matches the radiance of a body under study to the radiance of a source, calibrated as a function of temperature. In this way, the measurement of the absolute magnitude of the intensity of radiation is unnecessary. However, known temperatures must be used to determine the calibration of the pyrometer. For temperatures above the calibration range of the source, an extrapolation technique must be employed; this extrapolation is accomplished by using Planck's law of radiation. The constants in this equation are not known with sufficient accuracy, causing errors in the extrapolation to become larger at higher temperatures. However, standard techniques have been developed to perform this extrapolation. Consider the case of using gold as the source. In this technique, the current through the filament of the pyrometer is adjusted until the light intensity of the filament matches that of a black-body at the melting point of gold.
This establishes the primary calibration temperature and can be expressed in terms of current through the pyrometer lamp. With the same current setting, the pyrometer is sighted on another black-body at a higher temperature. An absorbing medium of known transmission is inserted between this black-body; the temperature of the black-body is adjusted until a match exists between its intensity and that of the pyrometer filament. The true higher temperature of the black-body is determined from Planck's Law; the absorbing medium is removed and the current through the filament is adjusted to match the filament intensity to that of the black-body. This establishes a second calibration point for the pyrometer; this step is repeated to carry the calibration to hi
The Jmol applet, among other abilities, offers an alternative to the Chime plug-in, no longer under active development. While Jmol has many features that Chime lacks, it does not claim to reproduce all Chime functions, most notably, the Sculpt mode. Chime requires plug-in installation and Internet Explorer 6.0 or Firefox 2.0 on Microsoft Windows, or Netscape Communicator 4.8 on Mac OS 9. Jmol operates on a wide variety of platforms. For example, Jmol is functional in Mozilla Firefox, Internet Explorer, Google Chrome, Safari. Chemistry Development Kit Comparison of software for molecular mechanics modeling Jmol extension for MediaWiki List of molecular graphics systems Molecular graphics Molecule editor Proteopedia PyMOL SAMSON Official website Wiki with listings of websites and moodles Willighagen, Egon. "Fast and Scriptable Molecular Graphics in Web Browsers without Java3D". Doi:10.1038/npre.2007.50.1