2,163 research outputs found
Current Japanese attitudes toward the Jews and their implications for U.S.-Japan relations
Arms Control & Domestic and International Security (ACDIS
Boyle's law and gravitational instability
We have re-examined the classical problem of the macroscopic equation of
state for a hydrostatic isothermal self-gravitating gas cloud bounded by an
external medium at constant pressure. We have obtained analytical conditions
for its equilibrium and stability without imposing any specific shape and
symmetry to the cloud density distribution. The equilibrium condition can be
stated in the form of an upper limit to the cloud mass; this is found to be
inversely proportional to the power 3/2 of a form factor \mu characterizing the
shape of the cloud. In this respect, the spherical solution, associated with
the maximum value of the form factor, \mu = 1, turns out to correspond to the
shape that is most difficult to realize. Surprisingly, the condition that
defines the onset of the Bonnor instability (or gravothermal catastrophe) can
be cast in the form of an upper limit to the density contrast within the cloud
that is independent of the cloud shape. We have then carried out a similar
analysis in the two-dimensional case of infinite cylinders, without assuming
axisymmetry. The results obtained in this paper generalize well-known results
available for spherical or axisymmetric cylindrical isothermal clouds that have
had wide astrophysical applications, especially in the study of the
interstellar medium.Comment: 9 pages, 2 figures, to appear in A&
Australia’s Response to the China Threat: The Case for Engagement
The dominance of the China Threat discourse in Australia’s public affairs suggests poor prospects for any continued Australia-China relations, let alone positive interactions of mutual benefit. An exploration of alternative ways to approach Australia’s relationship with China may though prove not only more constructive but also better future-proofed. The first step is to recognize that while China certainly poses challenges to Australia the perception of threat is more relevant to the USA. The second is the recognition of differences and the development of ways to mediate those differences. And the third is to build on the complementarities for the benefit of both Australia and China, not just through economic but also through social interactions. As Europe discovered in the 1950s, the development of mutual understanding of other peoples, their cultures, and their social and economic systems is a precursor not simply to respect and the avoidance of unwarranted prejudice, but to cooperation for a wider public good
Blue horizontal branch stars in the Sloan Digital Sky Survey: II. Kinematics of the Galactic halo
We carry out a maximum-likelihood kinematic analysis of a sample of 1170 blue
horizontal branch (BHB) stars from the Sloan Digital Sky Survey presented in
Sirko et al. (2003) (Paper I). Monte Carlo simulations and resampling show that
the results are robust to distance and velocity errors at least as large as the
estimated errors from Paper I. The best-fit velocities of the Sun (circular)
and halo (rotational) are 245.9 +/- 13.5 km/s and 23.8 +/- 20.1 km/s but are
strongly covariant, so that v_0 - v_halo = 222.1 +/- 7.7 km/s. If one adopts
standard values for the local standard of rest and solar motion, then the halo
scarcely rotates. The velocity ellipsoid inferred for our sample is much more
isotropic [(sigma_r,sigma_theta,sigma_phi) = (101.4 +/- 2.8, 97.7 +/- 16.4,
107.4 +/- 16.6) km/s] than that of halo stars in the solar neighborhood, in
agreement with a recent study of the distant halo by Sommer-Larsen et al.
(1997). The line-of-sight velocity distribution of the entire sample, corrected
for the Sun's motion, is accurately gaussian with a dispersion of 101.6 +/- 3.0
km/s.Comment: 23 pages including 4 figures, 1 color; submitted to A
PCR and Mosquito dissection as tools to monitor filarial infection levels following mass treatment
BACKGROUND: Entomological methods may provide important tools for monitoring the progress of lymphatic filariasis elimination programs. In this study, we compared dissection of the vector, Culex quinquefasciatus, with the polymerase chain reaction (PCR) to assess filarial infection levels in mosquitoes in the context of a lymphatic filariasis elimination program in Leogane, Haiti. METHODS: Mosquitoes were collected using gravid traps located in 4 sentinel communities with Wuchereria bancrofti microfilaria prevalence that ranged from 0.8% to 15.9%. Captured mosquitoes were divided between dissection, to enumerate W. bancrofti larvae (L1, L2, L3) and desiccation for later analysis by PCR. PCR was conducted on DNA extracts from pooled mosquitoes (1–15 pooled females) utilizing a competitive PCR system with primers specific for the Ssp I repeat. PCR products were analyzed with a hybridization ELISA using probes specific for a control sequence and the Ssp I repeat. RESULTS: The prevalence of mosquito infection with W. bancrofti ranged from 0%–3.66% by dissection (L1–L3) and point estimates of infection prevalence, as assayed by PCR, ranged from 0.25% – 9.16%. Following mass treatment, W. bancrofti infection prevalence dropped significantly as determined by PCR and dissection in 2 of the 4 sentinel sites (Leogane and Barrier Jeudi, P = 0.04 and P = 0.005, respectively). Although transmission declined in the other two sites, larval recoveries were low and these changes were not statistically significant. DISCUSSION: Our results suggest that a single round of mass treatment can have an impact on transmission of lymphatic filariasis. The use of entomologic methods as a tool to monitor filariasis programs and the statistical limitations of mosquito trapping are discussed
BIGRE: a low cross-talk integral field unit tailored for extrasolar planets imaging spectroscopy
Integral field spectroscopy (IFS) represents a powerful technique for the
detection and characterization of extrasolar planets through high contrast
imaging, since it allows to obtain simultaneously a large number of
monochromatic images. These can be used to calibrate and then to reduce the
impact of speckles, once their chromatic dependence is taken into account. The
main concern in designing integral field spectrographs for high contrast
imaging is the impact of the diffraction effects and the non-common path
aberrations together with an efficient use of the detector pixels. We focus our
attention on integral field spectrographs based on lenslet-arrays, discussing
the main features of these designs: the conditions of appropriate spatial and
spectral sampling of the resulting spectrograph's slit functions and their
related cross-talk terms when the system works at the diffraction limit. We
present a new scheme for the integral field unit (IFU) based on a dual-lenslet
device (BIGRE), that solves some of the problems related to the classical TIGER
design when used for such applications. We show that BIGRE provides much lower
cross-talk signals than TIGER, allowing a more efficient use of the detector
pixels and a considerable saving of the overall cost of a lenslet-based
integral field spectrograph.Comment: 17 pages, 18 figures, accepted for publication in Ap
Stereoselective Synthesis of 1-Hydroxymethyl-4-phenylsulfonylbutadienes
Reactividad de sulfonas para la obtención de sistemas dienicos.[ES]Reactividad de sulfonas para la obtención de sistemas dienicos.CICYT, Junta Castilla y
Leon (SA 44-96) y Ministerio de Educación y Cienci
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