987 research outputs found
Fatigue Investigation of Full-scale Transport-airplane Wings : Summary of Constant-amplitude Tests Through 1953
Anti-HIV and anti-HBV activity and resistance profile of 2',3'-dideoxy-3'-thiacytidine (3TC) and its arylphosphoramidate derivative CF 1109
Evaporation of a two-dimensional charged black hole
We construct a dilatonic two-dimensional model of a charged black hole. The
classical solution is a static charged black hole, characterized by two
parameters, and , representing the black hole's mass and charge. Then we
study the semiclassical effects, and calculate the evaporation rate of both
and , as a function of these two quantities. Analyzing this dynamical
system, we find two qualitatively different regimes, depending on the
electromagnetic coupling constant . If the latter is greater than a
certain critical value, the charge-to-mass ratio decays to zero upon
evaporation. On the other hand, for smaller than the critical value,
the charge-to-mass ratio approaches a non-zero constant that depends on
but not on the initial values of and .Comment: Latex, 30 pages, accepted for publication in Phys. Rev.
Influence of solute doping on the high-temperature deformation behavior of GaAs
The role of isovalent dopants in the highâtemperature deformation of GaAs has been studied in the temperature range 500â1150â°C. Additions of In, Sb, and B increase the critical resolved shear stress for deformation at a given strain rate and result in lowering the dislocation density of asâgrown liquidâencapsulated Czochralski GaAs crystals. Phosphorus, because of its minor influence on the lattice strain, shows little enhancement of the yield stress. These results are consistent with a solute hardening model, in which the solute atom surrounded tetrahedrally by four Ga or As atoms comprise the hardening cluster. Codoping with In and Si hardens GaAs, but codoping with Si is less effective than the isovalent solutes In, Sb, and B, and produces softening at high temperatures. The effect of solutes on both dislocation nucleation and multiplication are reviewed here
Comparison of p53 and DNA content abnormalities in adenocarcinoma of the oesophagus and gastric cardia.
This study examined the association between 17p allelic loss, p53 gene mutation, p53 protein expression and DNA aneuploidy in a series of adenocarcinomas arising in the oesophagus and gastric cardia. 17p allelic loss was detected in 79% (15 of 19) of oesophageal and in 83% (29 of 35) of gastric adenocarcinomas. p53 mutations were detected in 70% (14 of 20) and 63% (26 of 41) of oesophageal and of gastric adenocarcinomas respectively. Both tumour types were associated with a predominance of base transitions at CpG dinucleotides. In five cases of oesophageal adenocarcinoma, the same mutation was detected both in tumour and in adjacent dysplastic Barrett's epithelium. Diffuse p53 protein expression was detected in 65% (13 of 20) and 59% (24 of 41) of oesophageal and of gastric tumours, respectively, and was associated with the presence of p53 missense mutation (Chi-squared, P < 0.0001). DNA aneuploidy was detected in 80% (16 of 20) of oesophageal and in 70% (28 of 40) of gastric tumours. No association was found between p53 or DNA content abnormalities and tumour stage or histological subtype. In conclusion, this study detected a similar pattern of p53 alterations in adenocarcinoma of the oesophagus and gastric cardia--molecular data consistent with the observation that these tumours demonstrate similar clinical and epidemiological features
Flat World of Dilatonic Domain Walls
We study dilatonic domain walls specific to superstring theory.
Along with the matter fields and metric the dilaton also changes its value in
the wall background. We found supersymmetric (extreme) solutions which in
general interpolate between isolated superstring vacua with non-equal value of
the matter potential; they correspond to the static, planar domain walls with
{\it flat} metric in the string (sigma model) frame.
We point out similarities between the space-time of dilatonic walls and that
of charged dilatonic black holes. We also comment on non-extreme solutions
corresponding to expanding bubbles.Comment: 11 pgs (+2 figures available upon request), UPR-560-
Dimensional reduction of 4d heterotic string black holes
We perform the spherical symmetric dimensional reduction of
heterotic string theory. We find a class of two-dimensional (2d) dilaton
gravity models that gives a general description of the near-horizon,
near-extremal behavior of four-dimensional (4d) heterotic string black holes.
We show that the duality group of the 4d theory is realized in two dimensions
in terms of Weyl transformations of the metric. We use the 2d dilaton gravity
theory to compute the statistical entropy of the near-extremal 4d,
, black hole.Comment: 12 pages, LaTex fil
Exact Models of Extremal Dyonic 4D Black Hole Solutions of Heterotic String Theory
Families of exact supersymmetric conformal field theories of
magnetically and electrically charged extremal 4D black hole solutions of
heterotic string theory are presented. They are constructed using a
supersymmetric WZW model where anomalously embedded
subgroups are gauged. Crucial cancelations of the
anomalies coming from the supersymmetric fermions, the current algebra fermions
and the gauging ensure that there is a consistency of these models at the
quantum level. Various 2D models, which may be considered as building blocks
for extremal 4D constructions, are presented. They generalise the class of 2D
models which might be obtained from gauging and coincide with known
heterotic string backgrounds. The exact conformal field theory presented by
Giddings, Polchinski and Strominger describing the angular sector of the
extremal magnetically charged black hole is a special case of this
construction. An example where the radial and angular theories are mixed
non--trivially is studied in detail, resulting in an extremal dilatonic
Taub--NUT--like dyon.Comment: 42 pages (Plain TEX), IASSNS-HEP-94/20 (Revised version has minor
corrections, references and a note added and is now identical to published
version in Phys Rev D.
Selective and Contagious Prosocial Resource Donation in Capuchin Monkeys, Chimpanzees and Humans
Prosocial acts benefitting others are widespread amongst humans. By contrast, chimpanzees have failed to demonstrate such a disposition in several studies, leading some authors to conclude that the forms of prosociality studied evolved in humans since our common ancestry. However, similar prosocial behavior has since been documented in other primates, such as capuchin monkeys. Here, applying the same methodology to humans, chimpanzees, and capuchins, we provide evidence that all three species will display prosocial behavior, but only in certain conditions. Fundamental forms of prosociality were age-dependent in children, conditional on self-beneficial resource distributions even at age seven, and conditional on social or resource configurations in chimpanzees and capuchins. We provide the first evidence that experience of conspecific companionsâ prosocial behavior facilitates prosocial behavior in children and chimpanzees. Prosocial actions were manifested in all three species following rules of contingency that may reflect strategically adaptive responses
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