5,073 research outputs found
Semi-analytical approach for the Vaidya metric in double-null coordinates
We reexamine here a problem considered in detail before by Waugh and Lake:
the solutions of spherically symmetric Einstein's equations with a radial flow
of unpolarized radiation (the Vaidya metric) in double-null coordinates. This
problem is known to be not analytically solvable, the only known explicit
solutions correspond to the constant mass case (Schwarzschild solution in
Kruskal-Szekeres form) and the linear and exponential mass functions originally
discovered by Waugh and Lake. We present here a semi-analytical approach that
can be used to discuss some qualitative and quantitative aspects of the Vaidya
metric in double-null coordinates for generic mass functions. We present also a
new analytical solution corresponding to -mass function.Comment: 5 pages, 6 figure
Linguistics
Contains reports on one research project.U. S. Air Force (Electronics Systems Division) under Contract AF 19(628)-2487Joint Services Electronics Programs (U. S. Army, U. S. Navy, and U. S. Air Force) under Contract DA 36-039-AMC-03200(E)National Science Foundation (Grant GK-835)National Institutes of Health (Grant 2 PO1 MH-04737-06)National Aeronautics and Space Administration (Grant NsG-496
Interspecific differences in the larval performance of Pieris butterflies (Lepidoptera: Pieridae) are associated with differences in the glucosinolate profiles of host plants
The tremendous diversity of plants and herbivores has arisen from a coevolutionary relationship characterized by plant defense and herbivore counter adaptation. Pierid butterfly species feed on Brassicales plants that produce glucosinolates as a chemical deterrent against herbivory. In turn, the larvae of pierids have nitrile specifier proteins (NSPs) that are expressed in their gut and disarm glucosinolates. Pierid butterflies are known to have diversified in response to glucosinolate diversification in Brassicales. Therefore, each pierid species is expected to have a spectrum of host plants characterized by specific glucosinolate profiles. In this study, we tested whether the larval performance of different Pieris species, a genus in Pieridae (Lepidoptera: Pieridae), was associated with plant defense traits of putative host plants. We conducted feeding assays using larvae of three Pieris species and 10 species of the Brassicaceae family possessing different leaf physical traits and glucosinolate profile measurements. The larvae of Pieris rapae responded differently in the feeding assays compared with the other two Pieris species. This difference was associated with differences in glucosinolate profiles but not with variations in physical traits of the host plants. This result suggests that individual Pieris species are adapted to a subset of glucosinolate profiles within the Brassicaceae. Our results support the idea that the host ranges of Pieris species depend on larval responses to glucosinolate diversification in the host species, supporting the hypothesis of coevolution between butterflies and host plants mediated by the chemical arms race
High field electro-thermal transport in metallic carbon nanotubes
We describe the electro-thermal transport in metallic carbon nanotubes
(m-CNTs) by a semi-classical approach that takes into account the high-field
dynamical interdependence between charge carrier and phonon populations. Our
model is based on the self-consistent solution of the Boltzmann transport
equation and the heat equation mediated by a phonon rate equation that accounts
for the onset of non-equilibrium (optical) phonons in the high-field regime.
Given the metallic nature of the nanostructures, a key ingredient of the model
is the assumption of local thermalization of charge carriers. Our theory
remarkably reproduces the room temperature electrical characteristics of m-CNTs
on substrate and free standing (suspended), shedding light on charge-heat
transport in these one dimensional nanostructures. In particular, the negative
differential resistance observed in suspended m-CNTs under electric stress is
attributed to inhomogeneous field profile induced by self-heating rather than
the presence of hot phonons.Comment: 10 pages, 10 figure
A mobile antineutrino detector with plastic scintillators
We propose a new type segmented antineutrino detector made of plastic
scintillators for the nuclear safeguard application. A small prototype was
built and tested to measure background events. A satisfactory unmanned field
operation of the detector system was demonstrated. Besides, a detailed Monte
Carlo simulation code was developed to estimate the antineutrino detection
efficiency of the detector.Comment: 23 pages, 11 figures; accepted for publication in Nuclear Instruments
and Methods in Physics Research
Optical observations of NEA 162173 (1999 JU3) during the 2011-2012 apparition
Near-Earth asteroid 162173 (1999 JU3) is a potential target of two asteroid
sample return missions, not only because of its accessibility but also because
of the first C-type asteroid for exploration missions. The lightcurve-related
physical properties of this object were investigated during the 2011-2012
apparition. We aim to confirm the physical parameters useful for JAXA's
Hayabusa 2 mission, such as rotational period, absolute magnitude, and phase
function. Our data complement previous studies that did not cover low phase
angles. With optical imagers and 1-2 m class telescopes, we acquired the
photometric data at different phase angles. We independently derived the
rotational lightcurve and the phase curve of the asteroid. We have analyzed the
lightcurve of 162173 (1999 JU3), and derived a synodic rotational period of
7.625 +/- 0.003 h, the axis ratio a/b = 1.12. The absolute magnitude H_R =
18.69 +/- 0.07 mag and the phase slope of G = -0.09 +/- 0.03 were also obtained
based on the observations made during the 2011-2012 apparition.Comment: 4 pages, 3 figure
Headless Relative Clauses in Modern Japanese and the Relevancy Condition
Proceedings of the 2nd Annual Meeting of the Berkeley Linguistics
Society (1976), pp. 269-27
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