1,051 research outputs found
Human rights violations in organ procurement practice in China
Over 90% of the organs transplanted in China before 2010 were procured from prisoners. Although Chinese officials announced in December 2014 that the country would completely cease using organs harvested from prisoners, no regulatory adjustments or changes in China’s organ donation laws followed. As a result, the use of prisoner organs remains legal in China if consent is obtained
Theory of periodic swarming of bacteria: application to Proteus mirabilis
The periodic swarming of bacteria is one of the simplest examples for pattern
formation produced by the self-organized collective behavior of a large number
of organisms. In the spectacular colonies of Proteus mirabilis (the most common
species exhibiting this type of growth) a series of concentric rings are
developed as the bacteria multiply and swarm following a scenario periodically
repeating itself. We have developed a theoretical description for this process
in order to get a deeper insight into some of the typical processes governing
the phenomena in systems of many interacting living units. All of our
theoretical results are in excellent quantitative agreement with the complete
set of available observations.Comment: 11 pages, 8 figure
Non-obviousness and Screening
The paper offers a novel justification for the non-obviousness patentability requirement. An innovation involves two stages: research results in a technology blueprint, which development transforms into a profitable activity. An innovator, who is either efficient or inefficient, must rely on outside finance for the development. Only patented technologies are developed. Strengthening the non-obviousness requirement alleviates adverse selection by discouraging inefficient innovators from doing research, but creates inefficiencies by excluding marginal innovations. We show that it is socially optimal to raise the non-obviousness requirement so as to exclude bad innovators; we also provide several robustness checks and discuss the policy implications
Maternal dietary intake during pregnancy and offspring body composition: The Healthy Start Study
Consistent evidence of an influence of maternal dietary intake during pregnancy on infant body size and composition in human populations is lacking, despite robust evidence in animal models
The Spin-Resolved Atomic Velocity Distribution and 21-cm Line Profile of Dark-Age Gas
The 21-cm hyperfine line of atomic hydrogen (HI) is a promising probe of the
cosmic dark ages. In past treatments of 21-cm radiation it was assumed the
hyperfine level populations of HI could be characterized by a
velocity-independent ``spin temperature'' T_s determined by a competition
between 21-cm radiative transitions, spin-changing collisions, and (at lower
redshifts) Lyman-alpha scattering. However we show here that, if the
collisional time is comparable to the radiative time, the spin temperature will
depend on atomic velocity, T_s=T_s(v), and one must replace the usual hyperfine
level rate equations with a Boltzmann equation describing the spin and velocity
dependence of the HI distribution function. We construct here the Boltzmann
equation relevant to the cosmic dark ages and solve it using a basis-function
method. Accounting for the actual spin-resolved atomic velocity distribution
results in up to a 2 per cent suppression of the 21-cm emissivity, and a
redshift and angular-projection dependent suppression or enhancement of the
linear power spectrum of 21-cm fluctuations of up to 5 per cent. The effect on
the 21-cm line profile is more dramatic -- its full-width at half maximum
(FWHM) can be enhanced by up to 60 per cent relative to the
velocity-independent calculation. We discuss the implications for 21-cm
tomography of the dark ages.Comment: 25 pages, 6 figures, submitted to Mon. Not. Roy. Astron. So
Simulating Cosmic Reionization at Large Scales II: the 21-cm Emission Features and Statistical Signals
We present detailed predictions for the redshifted 21cm signal from the epoch
of reionization. These predictions are obtained from radiative transfer
calculations on the results of large scale (100/h Mpc), high dynamic range,
cosmological simulations. We consider several scenarios for the reionization
history, of both early and extended reionization. From the simulations we
construct and analyze a range of observational characteristics, from the global
signal, via detailed images and spectra, to statistical representations of rms
fluctuations, angular power spectra, and probability distribution functions to
characterize the non-gaussianity of the 21cm signal. (abbreviated abstract)Comment: Revised version: brought in sync with MNRAS accepted version. 16
pages, 14 figure
Modelling Primordial Gas in Numerical Cosmology
We have reviewed the chemistry and cooling behaviour of low-density (n<10^4
cm^-3) primordial gas and devised a cooling model wich involves 19 collisional
and 9 radiative processes and is applicable for temperatures in the range (1 K
< T < 10^8 K). We derived new fits of rate coefficients for the
photo-attachment of neutral hydrogen, the formation of molecular hydrogen via
H-, charge exchange between H2 and H+, electron detachment of H- by neutral
hydrogen, dissociative recombination of H2 with slow electrons,
photodissociation of H2+, and photodissociation of H2. Further it was found
that the molecular hydrogen produced through the gas-phase processes, H2+ + H
-> H2 + H+, and H- + H -> H2 + e-, is likely to be converted into its para
configuration on a faster time scale than the formation time scale. We have
tested the model extensively and shown it to agree well with former studies. We
further studied the chemical kinetics in great detail and devised a minimal
model which is substantially simpler than the full reaction network but
predicts correct abundances. This minimal model shows convincingly that 12
collisional processes are sufficient to model the H, He, H+, H-, He+, He++, and
H2 abundances in low density primordial gas for applications with no radiation
fields.Comment: 26 pages of text, 4 tables, and 6 eps figures. The paper is also
available at http://zeus.ncsa.uiuc.edu:8080/~abel/PGas/bib.html Submitted to
New Astronomy. Note that some of the hyperlinks given in the paper are still
under constructio
Heating of the Intergalactic Medium by Primordial Miniquasars
A simple analytical model is used to calculate the X-ray heating of the IGM
for a range of black hole masses. This process is efficient enough to decouple
the spin temperature of the intergalactic medium from the cosmic microwave
background (CMB) temperature and produce a differential brightness temperature
of the order of out to distances as large as a few
co-moving Mpc, depending on the redshift, black hole mass and lifetime. We
explore the influence of two types of black holes, those with and without
ionising UV radiation. The results of the simple analytical model are compared
to those of a full spherically symmetric radiative transfer code. Two simple
scenarios are proposed for the formation and evolution of black hole mass
density in the Universe. The first considers an intermediate mass black hole
that form as an end-product of Population III stars, whereas the second
considers super-massive black holes that form directly through the collapse of
massive halos with low spin parameter. These scenarios are shown not to violate
any of the observational constraints, yet produce enough X-ray photons to
decouple the spin-temperature from that of the CMB. This is an important issue
for future high redshift 21 cm observations.Comment: Replaced with a revised version to match the MNRAS accepted versio
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