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Register a new userSpeeches by V. F. Weisskopf, J. H. Van Vleck, I. I. Rabi, M. Hamermesh, B. T. Feld, R. P. Feynman, and D. Saxon, given in honor of Julian Schwinger at his 60th birthday
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Added by
Berthold-Georg Englert
Publication date
2019
fields
Physics
and research's language is
English
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In February 1978 Julian Schwingers 60th birthday was celebrated with a SchwingerFest at UCLA. This article consists of transcripts of historical talks given there.
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In the early 1980s, Schwinger made seminal contributions to the semiclassical theory of atoms. There had, of course, been earlier attempts at improving upon the Thomas--Fermi model of the 1920s. Yet, a consistent derivation of the leading and next-to-leading corrections to the formula for the total binding energy of neutral atoms, $$-frac{E}{e^2/a_0} = 0.768745Z^{7/3} - frac{1}{2}Z^2+0.269900Z^{5/3} + cdots,,$$ had not been accomplished before Schwinger got interested in the matter; here, $Z$ is the atomic number and $e^2/a_0$ is the Rydberg unit of energy. The corresponding improvements upon the Thomas--Fermi density were next on his agenda with, perhaps, less satisfactory results. Schwingers work not only triggered extensive investigations by mathematicians, who eventually convinced themselves that Schwinger got it right, but also laid the ground, in passing, for later refinements --- some of them very recent.
Boris R. Vainberg was born on March 17, 1938, in Moscow. His father was a Lead Engineer in an aviation design institute. His mother was a homemaker. From early age, Boris was attracted to mathematics and spent much of his time at home and in school working through collections of practice problems for the Moscow Mathematical Olympiad. His first mathematical library consisted of the books he received as one of the prize-winners of these olympiads.
Locally-rotationally-symmetric Bianchi type-I viscous and non -viscous cosmological models are explored in general relativity (GR) and in f(R,T) gravity. Solutions are obtained by assuming that the expansion scalar is proportional to the shear scalar which yields a constant value for the deceleration parameter (q=2). Constraints are obtained by requiring the physical viability of the solutions. A comparison is made between the viscous and non-viscous models, and between the models in GR and in f(R,T) gravity. The metric potentials remain the same in GR and in f(R,T) gravity. Consequently, the geometrical behavior of the $f(R,T)$ gravity models remains the same as the models in GR. It is found that f(R,T) gravity or bulk viscosity does not affect the behavior of effective matter which acts as a stiff fluid in all models. The individual fluids have very rich behavior. In one of the viscous models, the matter either follows a semi-realistic EoS or exhibits a transition from stiff matter to phantom, depending on the values of the parameter. In another model, the matter describes radiation, dust, quintessence, phantom, and the cosmological constant for different values of the parameter. In general, f(R,T) gravity diminishes the effect of bulk viscosity.
We show that the recent reinterpretation of oxygen isotope effects in cuprate superconductors by D. R. Harshman et al. is mathematically and physically incorrect violating the Anderson theorem and the Coulomb law.
An LRS Bianchi-I space-time model is studied with constant Hubble parameter in $f(R,T)=R+2lambda T$ gravity. Although a single (primary) matter source is considered, an additional matter appears due to the coupling between matter and $f(R,T)$ gravity. The constraints are obtained for a realistic cosmological scenario, i.e., one obeying the null and weak energy conditions. The solutions are also extended to the case of a scalar field (normal or phantom) model, and it is found that the model is consistent with a phantom scalar field only. The coupled matter also acts as phantom matter. The study shows that if one expects an accelerating universe from an anisotropic model, then the solutions become physically relevant only at late times when the universe enters into an accelerated phase. Placing some observational bounds on the present equation of state of dark energy, $omega_0$, the behavior of $omega(z)$ is depicted, which shows that the phantom field has started dominating very recently, somewhere between $0.2lesssim zlesssim0.5$.
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