2,248 research outputs found
Alkaline battery separator characterization studies Quarterly report, 28 Jun. - 28 Sep. 1969
Membrane and absorber screening tests for alkaline battery separator
Abrupt transition in quasiparticle dynamics at optimal doping in a cuprate superconductor system
We report time-resolved measurements of the photoinduced change in
reflectivity, Delta R, in the Bi2Sr2Ca(1-y)Dy(y)Cu2O(8+delta) (BSCCO) system of
cuprate superconductors as a function of hole concentration. We find that the
kinetics of quasiparticle decay and the sign of Delta R both change abruptly
where the superconducting transition temperature Tc is maximal. These
coincident changes suggest that a sharp transition in quasiparticle dynamics
takes place precisely at optimal doping in the BSCCO system.Comment: 10 pages, 4 figure
Zero temperature optical conductivity of ultra-clean Fermi liquids and superconductors
We calculate the low-frequency optical conductivity sigma(w) of clean metals
and superconductors at zero temperature neglecting the effects of impurities
and phonons. In general, the frequency and temperature dependences of sigma
have very little in common. For small Fermi surfaces in three dimensions (but
not in 2D) we find for example that Re sigma(w>0)=const. for low w which
corresponds to a scattering rate Gamma proportional to w^2 even in the absence
of Umklapp scattering when there is no T^2 contribution to Gamma. In the main
part of the paper we discuss in detail the optical conductivity of d-wave
superconductors in 2D where Re sigma(w>0) \propto w^4 for the smallest
frequencies and the Umklapp processes typically set in smoothly above a finite
threshold w_0 smaller than twice the maximal gap Delta. In cases where the
nodes are located at (pi/2, pi/2), such that direct Umklapp scattering among
them is possible, one obtains Re sigma(w) \propto w^2.Comment: 7 pages, 3 figure
Human immunodeficiency virus infection of the human thymus and disruption of the thymic microenvironment in the SCID-hu mouse.
Infection with the human immunodeficiency virus (HIV) results in immunosuppression and depletion of circulating CD4+ T cells. Since the thymus is the primary organ in which T cells mature it is of interest to examine the effects of HIV infection in this tissue. HIV infection has been demonstrated in the thymuses of infected individuals and thymocytes have been previously demonstrated to be susceptible to HIV infection both in vivo, using the SCID-hu mouse, and in vitro. The present study sought to determine which subsets of thymocytes were infected in the SCID-hu mouse model and to evaluate HIV-related alterations in the thymic microenvironment. Using two different primary HIV isolates, infection was found in CD4+/CD8+ double positive thymocytes as well as in both the CD4+ and CD8+ single positive subsets of thymocytes. The kinetics of infection and resulting viral burden differed among the three thymocyte subsets and depended on which HIV isolate was used for infection. Thymic epithelial (TE) cells were also shown to endocytose virus and to often contain copious amounts of viral RNA in the cytoplasm by in situ hybridization, although productive infection of these cells could not be definitively shown. Furthermore, degenerating TE cells were observed even without detection of HIV in the degenerating cells. Two striking morphologic patterns of infection were seen, involving either predominantly thymocyte infection and depletion, or TE cell involvement with detectable cytoplasmic viral RNA and/or TE cell toxicity. Thus, a variety of cells in the human thymus is susceptible to HIV infection, and infection with HIV results in a marked disruption of the thymic microenvironment leading to depletion of thymocytes and degeneration of TE cells
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