20,780 research outputs found
The structure of the graviton self-energy at finite temperature
We study the graviton self-energy function in a general gauge, using a hard
thermal loop expansion which includes terms proportional to T^4, T^2 and
log(T). We verify explicitly the gauge independence of the leading T^4 term and
obtain a compact expression for the sub-leading T^2 contribution. It is shown
that the logarithmic term has the same structure as the ultraviolet pole part
of the T=0 self-energy function. We argue that the gauge-dependent part of the
T^2 contribution is effectively canceled in the dispersion relations of the
graviton plasma, and present the solutions of these equations.Comment: 27 pages, 6 figure
Etching of High Purity Zinc
A method of etching high purity zinc to reveal various etch figures on {101¯0} planes is presented in this
paper. Etch figures are formed by polishing in a dichromic acid solution after the introduction of mercury
to the crystal surface. No measurable aging time is required to form etch figures at newly formed dislocation
sites when mercury is on the surface prior to deformation. The mercury concentrates at the sites
where etch figures form and may be removed by vacuum distillation and chemical polishing before it appreciably
affects the purity of the bulk of the crystal
Dislocations and etch figures in high purity zinc
A method of etching high purity zinc single crystals to reveal various etch figures on {1010} planes is presented in the preceding paper. The procedure involves the introduction of mercury to the crystal surface prior to a chemical polish with dichromic acid. The mercury was found to be concentrated at the etch figures. This paper presents the results of several experiments which support the conclusion that there exists a one-to-one correspondence between etch figures and dislocations. Some observations of slip on (0001) basal planes and {1212} pyramidal planes, and of twinning in zinc are also presented
Thermal one- and two-graviton Green's functions in the temporal gauge
The thermal one- and two-graviton Green's function are computed using a
temporal gauge. In order to handle the extra poles which are present in the
propagator, we employ an ambiguity-free technique in the imaginary-time
formalism. For temperatures T high compared with the external momentum, we
obtain the leading T^4 as well as the subleading T^2 and log(T) contributions
to the graviton self-energy. The gauge fixing independence of the leading T^4
terms as well as the Ward identity relating the self-energy with the one-point
function are explicitly verified. We also verify the 't Hooft identities for
the subleading T^2 terms and show that the logarithmic part has the same
structure as the residue of the ultraviolet pole of the zero temperature
graviton self-energy. We explicitly compute the extra terms generated by the
prescription poles and verify that they do not change the behavior of the
leading and sub-leading contributions from the hard thermal loop region. We
discuss the modification of the solutions of the dispersion relations in the
graviton plasma induced by the subleading T^2 contributions.Comment: 17 pages, 5 figures. Revised version to be published in Phys. Rev.
Analytic Solution for the Critical State in Superconducting Elliptic Films
A thin superconductor platelet with elliptic shape in a perpendicular
magnetic field is considered. Using a method originally applied to circular
disks, we obtain an approximate analytic solution for the two-dimensional
critical state of this ellipse. In the limits of the circular disk and the long
strip this solution is exact, i.e. the current density is constant in the
region penetrated by flux. For ellipses with arbitrary axis ratio the obtained
current density is constant to typically 0.001, and the magnetic moment
deviates by less than 0.001 from the exact value. This analytic solution is
thus very accurate. In increasing applied magnetic field, the penetrating flux
fronts are approximately concentric ellipses whose axis ratio b/a < 1 decreases
and shrinks to zero when the flux front reaches the center, the long axis
staying finite in the fully penetrated state. Analytic expressions for these
axes, the sheet current, the magnetic moment, and the perpendicular magnetic
field are presented and discussed. This solution applies also to
superconductors with anisotropic critical current if the anisotropy has a
particular, rather realistic form.Comment: Revtex file and 13 postscript figures, gives 10 pages of text with
figures built i
Déjà vu and the entorhinal cortex: dissociating recollective from familiarity disruptions in a single case patient
Past research has demonstrated a relationship between déjà vu and the entorhinal cortex in patients with wider medial temporal lobe damage. The aim of the present research was to investigate this crucial link in a patient (MR) with a selective lesion to the left lateral entorhinal cortex to provide a more direct exploration of this relationship. Two experiments investigated the experiences of déjà vécu (using the IDEA questionnaire) and déjà vu (using an adapted DRM paradigm) in MR and a set of matched controls. The results demonstrated that MR had quantitatively more and qualitatively richer recollective experiences of déjà vécu. In addition, under laboratory-based déjà vu conditions designed to elicit both false recollection (critical lures) and false familiarity (weakly-associated lures), MR only revealed greater memory impairments for the latter. The present results are therefore the first to demonstrate a direct relationship between the entorhinal cortex and the experience of both déjà vu and déjà vécu. They furthermore suggest that the entorhinal cortex is involved in both weakly-associative false memory as well as strongly-associative memory under conditions that promote familiarity-based processing
Non-linear electromagnetic interactions in thermal QED
We examine the behavior of the non-linear interactions between
electromagnetic fields at high temperature. It is shown that, in general, the
log(T) dependence on the temperature of the Green functions is simply related
to their UV behavior at zero-temperature. We argue that the effective action
describing the nonlinear thermal electromagnetic interactions has a finite
limit as T tends to infinity. This thermal action approaches, in the long
wavelength limit, the negative of the corresponding zero-temperature action.Comment: 7 pages, IFUSP/P-111
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