39,603 research outputs found
The Effect of Radiative Cooling on the Sunyaev-Zel'dovich Cluster Counts and Angular Power Spectrum: Analytic Treatment
Recently, the entropy excess detected in the central cores of groups and
clusters has been successfully interpreted as being due to radiative cooling of
the hot intragroup/intracluster gas. In such a scenario, the entropy floors
in groups/clusters at any given redshift are completely
determined by the conservation of energy. In combination with the equation of
hydrostatic equilibrium and the universal density profile for dark matter, this
allows us to derive the remaining gas distribution of groups and clusters after
the cooled material is removed. Together with the Press-Schechter mass function
we are able to evaluate effectively how radiative cooling can modify the
predictions of SZ cluster counts and power spectrum. It appears that our
analytic results are in good agreement with those found by hydrodynamical
simulations. Namely, cooling leads to a moderate decrease of the predicted SZ
cluster counts and power spectrum as compared with standard scenario. However,
without taking into account energy feedback from star formation which may
greatly suppress cooling efficiency, it is still premature to claim that this
modification is significant for the cosmological applications of cluster SZ
effect.Comment: 16 pages, 3 figures, uses aastex.cls. ApJ accepte
Quasi-local mass in the covariant Newtonian space-time
In general relativity, quasi-local energy-momentum expressions have been
constructed from various formulae. However, Newtonian theory of gravity gives a
well known and an unique quasi-local mass expression (surface integration).
Since geometrical formulation of Newtonian gravity has been established in the
covariant Newtonian space-time, it provides a covariant approximation from
relativistic to Newtonian theories. By using this approximation, we calculate
Komar integral, Brown-York quasi-local energy and Dougan-Mason quasi-local mass
in the covariant Newtonian space-time. It turns out that Komar integral
naturally gives the Newtonian quasi-local mass expression, however, further
conditions (spherical symmetry) need to be made for Brown-York and Dougan-Mason
expressions.Comment: Submit to Class. Quantum Gra
Sensitivity analysis and calibration of a soil carbon model (SoilGen2) in two contrasting loess forest soils
To accurately estimate past terrestrial carbon pools is the key to understanding the global carbon cycle and its relationship with the climate system. SoilGen2 is a useful tool to obtain aspects of soil properties (including carbon content) by simulating soil formation processes; thus it offers an opportunity for both past soil carbon pool reconstruction and future carbon pool prediction. In order to apply it to various environmental conditions, parameters related to carbon cycle process in SoilGen2 are calibrated based on six soil pedons from two typical loess deposition regions (Belgium and China). Sensitivity analysis using the Morris method shows that decomposition rate of humus (<i>k</i><sub>HUM</sub>), fraction of incoming plant material as leaf litter (fr<sub>ecto</sub>) and decomposition rate of resistant plant material (<i>k</i><sub>RPM</sub>) are the three most sensitive parameters that would cause the greatest uncertainty in simulated change of soil organic carbon in both regions. According to the principle of minimizing the difference between simulated and measured organic carbon by comparing quality indices, the suited values of <i>k</i><sub>HUM</sub>, (fr<sub>ecto</sub> and <i>k</i><sub>RPM</sub> in the model are deduced step by step and validated for independent soil pedons. The difference of calibrated parameters between Belgium and China may be attributed to their different vegetation types and climate conditions. This calibrated model allows more accurate simulation of carbon change in the whole pedon and has potential for future modeling of carbon cycle over long timescales
G\"odel-type universes in f(T) gravity
The issue of causality in gravity is investigated by examining the
possibility of existence of the closed timelike curves in the G\"{o}del-type
metric. By assuming a perfect fluid as the matter source, we find that the
fluid must have an equation of state parameter greater than minus one in order
to allow the G\"{o}del solutions to exist, and furthermore the critical radius
, beyond which the causality is broken down, is finite and it depends on
both matter and gravity. Remarkably, for certain models, the perfect
fluid that allows the G\"{o}del-type solutions can even be normal matter, such
as pressureless matter or radiation. However, if the matter source is a special
scalar field rather than a perfect fluid, then and the
causality violation is thus avoided.Comment: 18 pages, introduction revised, reference adde
Live Poultry Exposure and Public Response to Influenza A(H7N9) in Urban and Rural China during Two Epidemic Waves in 2013-2014
Background
The novel influenza A(H7N9) virus has caused 2013 spring and 2013-2014 winter waves of human infections since its first emergence in China in March 2013. Exposure to live poultry is a risk factor for H7N9 infection. Public psychobehavioral responses often change during progression of an epidemic.
Methods
We conducted population-based surveys in southern China to examine human exposure to live poultry, and population psychological response and behavioral changes in the two waves. In Guangzhou, an urban area of Guangdong province, we collected data using telephone surveys with random digit dialing in May-June 2013 and again in December 2013 to January 2014. In Zijin county, a rural area of the same province, we used door-to-door surveys under a stratified sampling design in July 2013 and again in December 2013 to January 2014. All responses were weighted by age and sex to the respective adult populations.
Findings
Around half of the urban respondents (53.8%) reported having visited LPMs in the previous year in the first survey, around double that reported in the second survey (27.7%). In the rural surveys, around half of the participants reported raising backyard poultry in the past year in the first survey, increasing to 83.2% participants in the second survey. One third of urban subjects supported the permanent closure of LPMs in the first and second surveys, and factors associated with support for closure included female sex, higher level of worry towards H7N9, and worry induced by a hypothetical influenza-like illness.
Conclusions
Our study indicated high human exposure to live poultry and low support for permanent closure of markets in both urban and rural residents regardless of increased worry during the epidemic.published_or_final_versio
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