92 research outputs found
Magnetocaloric Studies of the Peak Effect in Nb
We report a magnetocaloric study of the peak effect and Bragg glass
transition in a Nb single crystal. The thermomagnetic effects due to vortex
flow into and out of the sample are measured. The magnetocaloric signature of
the peak effect anomaly is identified. It is found that the peak effect
disappears in magnetocaloric measurements at fields significantly higher than
those reported in previous ac-susceptometry measurements. Investigation of the
superconducting to normal transition reveals that the disappearance of the bulk
peak effect is related to inhomogeneity broadening of the superconducting
transition. The emerging picture also explains the concurrent disappearance of
the peak effect and surface superconductivity, which was reported previously in
the sample under investigation. Based on our findings we discuss the
possibilities of multicriticality associated with the disappearance of the peak
effect.Comment: 30 pages, 10 figure
Polymer Crystallization in 25 nm Spheres
Crystallization within the discrete spheres of a block copolymer mesophase
was studied by time-resolved x-ray scattering. The cubic packing of
microdomains, established by self-assembly in the melt, is preserved throughout
crystallization by strong interblock segregation even though the amorphous
matrix block is well above its glass transition temperature. Homogeneous
nucleation within each sphere yields isothermal crystallizations which follow
first-order kinetics, contrasting with the sigmoidal kinetics normally
exhibited in the quiescent crystallization of bulk polymers.Comment: accepted for publication in Physical Review Letters, 2/28/2000;
scheduled for 5/1/2000 issu
A "hair-raising" history of alopecia areata
YesA 3500âyearâold papyrus from ancient Egypt provides a list of treatments for many diseases including âbite hair loss,â most likely alopecia areata (AA). The treatment of AA remained largely unchanged for over 1500 years. In 30 CE, Celsus described AA presenting as scalp alopecia in spots or the âwindings of a snakeâ and suggested treatment with caustic compounds and scarification. The first âmodernâ description of AA came in 1813, though treatment still largely employed caustic agents. From the midâ19th century onwards, various hypotheses of AA development were put forward including infectious microbes (1843), nerve defects (1858), physical trauma and psychological stress (1881), focal inflammation (1891), diseased teeth (1902), toxins (1912) and endocrine disorders (1913). The 1950s brought new treatment developments with the first use of corticosteroid compounds (1952), and the first suggestion that AA was an autoimmune disease (1958). Research progressively shifted towards identifying hair follicleâspecific autoantibodies (1995). The potential role of lymphocytes in AA was made implicit with immunohistological studies (1980s). However, studies confirming their functional role were not published until the development of rodent models (1990s). Genetic studies, particularly genomeâwide association studies, have now come to the forefront and open up a new era of AA investigation (2000s). Today, AA research is actively focused on genetics, the microbiome, dietary modulators, the role of atopy, immune cell types in AA pathogenesis, primary antigenic targets, mechanisms by which immune cells influence hair growth, and of course the development of new treatments based on these discoveries.Alopecia UK
Problems of Evaluation in a âBlindâ Study of Triamcinolone Acetonide and Hydrocortisone Creams**From the Dermatology Service, Veterans Administration Hospital, Kecoughtan, Virginia.
THE BLOOD VESSELS OF THE SCALP IN PATIENTS WTTH ALOPECIA AREATA BEFORE AND AFTER CORTICOSTEHOID THERAPY
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