Isfahan also rendered in English as Ispahan, Esfahan or Hispahan, is a city in Iran. It is located 406 kilometres south of Tehran, is the capital of Isfahan Province. Isfahan has a population of 2.0 million, making it the third largest city in Iran after Tehran and Mashhad, but was once one of the largest cities in the world. Isfahan is an important city as it is located at the intersection of the two principal north–south and east–west routes that traverse Iran. Isfahan flourished from 1050 to 1722 in the 16th and 17th centuries under the Safavid dynasty when it became the capital of Persia for the second time in its history under Shah Abbas the Great. Today the city retains much of its past glory, it is famous for its Perso–Islamic architecture, grand boulevards, covered bridges, tiled mosques, minarets. Isfahan has many historical buildings, monuments and artefacts; the fame of Isfahan led to the Persian pun and proverb "Esfahān nesf-e- jahān ast": Isfahan is half the world. The Naghsh-e Jahan Square in Isfahan is one of the largest city squares in the world.

UNESCO has designated it a World Heritage Site. "Isfahan" is derived from Middle Persian Spahān. Spahān is attested in various Middle Persian seals and inscriptions, including that of Zoroastrian Magi Kartir, is the Armenian name of the city; the present-day name is the Arabicized form of Ispahan. The region appears with the abbreviation GD on Sasanian numismatics. In Ptolemy's Geographia it appears as Aspadana, translating to "place of gathering for the army", it is believed. Human habitation of the Isfahan region can be traced back to the Palaeolithic period. Recent discoveries archaeologists have found artifacts dating back to the Palaeolithic, Neolithic and Iron ages. What was to become the city of Isfahan in historical periods emerged as a locality and settlement that developed over the course of the Elamite civilisation. Under Median rule, this commercial entrepôt began to show signs of a more sedentary urbanism growing into a noteworthy regional centre that benefited from the exceptionally fertile soil on the banks of the Zayandehrud River in a region called Aspandana or Ispandana.

Once Cyrus the Great had unified Persian and Median lands into the Achaemenid Empire, the religiously and ethnically diverse city of Isfahan became an early example of the king's fabled religious tolerance. It was Cyrus who, having just taken Babylon, made an edict in 538 BCE, declaring that the Jews in Babylon could return to Jerusalem. Now it seems that some of these freed Jews settled in Isfahan instead of returning to their homeland; the 10th-century Persian historian Ibn al-Faqih wrote:"When the Jews emigrated from Jerusalem, fleeing from Nebuchadnezzar, they carried with them a sample of the water and soil of Jerusalem. They did not settle down anywhere or in any city without examining the water and the soil of each place, they did all along. There they rested, found that both resembled Jerusalem. Thereupon they settled there, cultivated the soil, raised children and grandchildren, today the name of this settlement is Yahudia." The Parthians in the period 250–226 BCE continued the tradition of tolerance after the fall of the Achaemenids, fostering the Hellenistic dimension within Iranian culture and the political organisation introduced by Alexander the Great's invading armies.

Under the Parthians, Arsacid governors administered the provinces of the nation from Isfahan, the city's urban development accelerated to accommodate the needs of a capital city. The next empire to rule Persia, the Sassanids, presided over massive changes in their realm, instituting sweeping agricultural reform and reviving Iranian culture and the Zoroastrian religion. Both the city and region were called by the name Aspahan or Spahan; the city was governed by a group called the Espoohrans, who came from seven noble and important Iranian royal families. Extant foundations of some Sassanid-era bridges in Isfahan suggest that the Sasanian kings were fond of ambitious urban planning projects. While Isfahan's political importance declined during the period, many Sassanid princes would study statecraft in the city, its military role developed rapidly, its strategic location at the intersection of the ancient roads to Susa and Persepolis made it an ideal candidate to house a standing army, ready to march against Constantinople at any moment.

The words'Aspahan' and'Spahan' are derived from the Pahlavi or Middle Persian meaning'the place of the army'. Although many theories have been mentioned about the origin of Isfahan, in fact little is known of it before the rule of the Sasanian dynasty; the historical facts suggest that in the late 4th and early 5th centuries, Queen Shushandukht, the Jewish consort of Yazdegerd I settled a colony of Jews in Yahudiyyeh, a settlement 3 km northwest of the Zoroastrian city of Gabae (its Achaemid and Parthian name. The gradual population decrease of Gay and the simultaneous population increase of Yahudiyyeh and its suburbs after the Islamic conque

Dirac sea

The Dirac sea is a theoretical model of the vacuum as an infinite sea of particles with negative energy. It was first postulated by the British physicist Paul Dirac in 1930 to explain the anomalous negative-energy quantum states predicted by the Dirac equation for relativistic electrons; the positron, the antimatter counterpart of the electron, was conceived of as a hole in the Dirac sea, before its experimental discovery in 1932. In hole theory, the solutions with negative time evolution factors are reinterpreted as representing the positron, discovered by Carl Anderson; the interpretation of this result requires a Dirac sea, showing that the Dirac equation is not a combination of special relativity and quantum mechanics, but it implies that the number of particles cannot be conserved. Dirac sea theory has been displaced by quantum field theory, though they are mathematically compatible; the origins of the Dirac sea lie in the energy spectrum of the Dirac equation, an extension of the Schrödinger equation, consistent with special relativity, that Dirac had formulated in 1928.

Although the equation was successful in describing electron dynamics, it possesses a rather peculiar feature: for each quantum state possessing a positive energy E, there is a corresponding state with energy -E. This is not a big difficulty when an isolated electron is considered, because its energy is conserved and negative-energy electrons may be left out. However, difficulties arise when effects of the electromagnetic field are considered, because a positive-energy electron would be able to shed energy by continuously emitting photons, a process that could continue without limit as the electron descends into lower and lower energy states. Real electrons do not behave in this way. Dirac's solution to this was to turn to the Pauli exclusion principle. Electrons are fermions, obey the exclusion principle, which means that no two electrons can share a single energy state within an atom. Dirac hypothesized that what we think of as the "vacuum" is the state in which all the negative-energy states are filled, none of the positive-energy states.

Therefore, if we want to introduce a single electron we would have to put it in a positive-energy state, as all the negative-energy states are occupied. Furthermore if the electron loses energy by emitting photons it would be forbidden from dropping below zero energy. Dirac pointed out that a situation might exist in which all the negative-energy states are occupied except one; this "hole" in the sea of negative-energy electrons would respond to electric fields as though it were a positively charged particle. Dirac identified this hole as a proton. However, Robert Oppenheimer pointed out that an electron and its hole would be able to annihilate each other, releasing energy on the order of the electron's rest energy in the form of energetic photons. Hermann Weyl noted that a hole should act as though it has the same mass as an electron, whereas the proton is about two thousand times heavier; the issue was resolved in 1932 when the positron was discovered by Carl Anderson, with all the physical properties predicted for the Dirac hole.

Despite its success, the idea of the Dirac sea tends not to strike people as elegant. The existence of the sea implies an infinite negative electric charge filling all of space. In order to make any sense out of this, one must assume that the "bare vacuum" must have an infinite positive charge density, cancelled by the Dirac sea. Since the absolute energy density is unobservable—the cosmological constant aside—the infinite energy density of the vacuum does not represent a problem. Only changes in the energy density are observable. Geoffrey Landis notes that Pauli exclusion does not definitively mean that a filled Dirac sea cannot accept more electrons, since, as Hilbert elucidated, a sea of infinite extent can accept new particles if it is filled; this happens when we have a gauge instanton. The development of quantum field theory in the 1930s made it possible to reformulate the Dirac equation in a way that treats the positron as a "real" particle rather than the absence of a particle, makes the vacuum the state in which no particles exist instead of an infinite sea of particles.

This picture is much more convincing since it recaptures all the valid predictions of the Dirac sea, such as electron-positron annihilation. On the other hand, the field formulation does not eliminate all the difficulties raised by the Dirac sea. Upon solving the free Dirac equation, i ℏ ∂ Ψ ∂ t = Ψ, one finds Ψ p λ = N exp

Teddington Park

Teddington Park is a neighbourhood in Toronto, Canada. It is bordered by Yonge Street to the west and Bayview Avenue to the east, from Snowden Road in the south to north of Glen Echo Road and Rosedale Golf Club. Development occurred in and around the 1930s, was farmland before that time; the neighbourhood is residential with only a small stretch of retail businesses along Yonge Street, in addition to the Rosedale Golf Club. Via Yonge Street Teddington Park is connected to Highway 401 within a five- to ten-minute drive. Glen Echo Drive is the main local street in the area. Mount Pleasant Road and Yonge Streets are the major roads in the area. Glen Echo Road was the terminus of the North Yonge Railways radial line until 1947. From 1892 to 1930 it was served by the Metropolitan line; the terminus hosted a large terminal structure, car barn and freight shed were located northwest of Glen Echo Road. After the end of the radial line, the site became Toronto Transportation Commission's Glen Echo Loop serving North Yonge buses replaced with the 59 North Yonge and the current 97 Yonge bus.

The bus loop was no longer in use in the late 1970s and the car barn became a dealership and North York Township Market. The Yonge-University-Spadina line runs on the western boundary of Teddington Park. There are no subway stations within the neighbourhood, though both York Mills Station and Lawrence Station are nearby. William McDougall was born and owned land in the area of Lawrence and Yonge to the north of farm land of Peter Lawrence Jacob Lawrence. City of Toronto - Bridle Path-Sunnybrook-York Mills neighbourhood profile City of Toronto - Lawrence Park North neighbourhood profile