11 research outputs found
Log-Poisson Non-Gaussianity of Ly Transmitted Flux Fluctuations at High Redshift
We investigate the non-Gaussian features of the IGM at redshift
using Ly transmitted flux of quasar absorption spectra and cosmological
hydrodynamic simulation of the concordance CDM universe. We show that
the neutral hydrogen mass density field and Ly transmitted flux
fluctuations possess all the non-Gaussian features predicted by the log-Poisson
hierarchy, which depends only on two dimensionless parameters and
, describing, respectively, the intermittence and singularity of the
random fields. We find that the non-Gaussianity of the Ly transmitted
flux of quasars from to can be well reconstructed by the
hydrodynamical simulation samples. Although the Gunn-Peterson optical depth and
its variance underwent a significant evolution in the redshift range of , the intermittency measured by is almost redshift-independent in
this range. More interesting, the intermittency of quasar's absorption spectra
on physical scales hMpc in redshift are found to be
about the same as that on physical scales hMpc at redshifts . Considering the Jeans length is less than 0.1 hMpc at , and
hMpc at , these results imply that the nonlinear evolution
in high and low redshifts will lead the cosmic baryon fluid to a state similar
to fully developed turbulence. The log-Poisson high order behavior of current
high redshift data of quasar's spectrum can be explained by uniform UV
background in the redshift range considered. We also studied the log-Poisson
non-Gaussianity by considering inhomogeneous background. With several
simplified models of inhomogeneous background, we found the effect of the
inhomogeneous background on the log-Poisson non-Gaussianity is not larger than
1-sigma.Comment: 12 pages 10 figures, accepted by MNRA
Combined Effect of Glycine and Sea Salt on Aerosol Cloud Droplet Activation Predicted by Molecular Dynamics Simulations
The
present study illustrates the combined effect of organic and
inorganic compounds on cloud droplet nucleation and activation processes
representative for the marine environment. Amino acids and sea salt
are common marine cloud condensation nuclei (CCN) which act as a prerequisite
for growth of cloud droplets. The chemical and physical properties
of these CCN play a key role for interfacial properties such as surface
tension, which is important for the optical properties of clouds and
for heterogeneous reactions. However, there is a lack of detailed
information and in situ measurements of surface tension of such nanosized
droplets. Here we present a study of the combined effect of zwitterionic
glycine (ZGLY) and sea salt in nanosized water droplets using molecular
dynamics simulations, where particular emphasis is placed on the surface
tension for the nanosized droplets. The critical supersaturation is
estimated by the Köhler equation. It is found that dissolved
sea salt interacts with ZGLY through a water bridge and weakens the
hydrogen bonds among ZGLYs, which has a significant effect on both
surface tension and water vapor supersaturation. Clusters of glycine
mixed with sea salt deliquesce more efficiently and have higher growth
factors
An Alternative to Vermiculite: Composting on Tropical Islands Using Coral Sand to Enhance Nitrogen Retention during Ventilation
Reducing nitrogen loss during composting with forced ventilation was comprehensively investigated in this study. Coral sand was tailored in the co-composting in the co-composting of sludge and litters. The physicochemical results revealed that forced ventilation prolonged the thermophilic phase and accelerated the substrate decomposition. With the addition of 10% native coral sand, the amount of nitrogen loss decreased by 9.2% compared with the original group. The microbial community evaluation revealed that the effect of forced ventilation on colony abundance was significantly greater than that of adding coral sand. This study demonstrated that when composting on a tropical island, adding coral sand under forced ventilation was a viable solution for realizing sustainable development
Cross-Linked Polysaccharide Assemblies in Marine Gels: An Atomistic Simulation
Marine
polymeric gels or colloidal nano- and microgels have been
shown to contribute significantly to the primary marine aerosol and
cloud condensation nuclei over remote marine areas. A microscopic
understanding of such biologically derived matter at the sea–air
interface is important for future development of global climate models,
but unfortunately cannot be obtained from modern characterization
techniques. In this contribution, we employ molecular dynamics simulations
to reveal the atomistic details of marine polymeric gels represented
by anionic polysaccharide assemblies. The ionic bonds formed between
polysaccharides and metal ions in seawater as well as the hydrophobic
contribution to surface area are investigated in detail, and destabilization
of the assemblies upon removal of Ca<sup>2+</sup> or acidification
is explained. These results provide insight into physicochemical properties
of polysaccharide–Ca<sup>2+</sup> structures and enable future
studies of their roles of in the wetting process of cloud droplet
activation
The Role of Protein Dynamics in Thymidylate Synthase Catalysis: Variants of Conserved 2‘-Deoxyuridine 5‘-Monophosphate (dUMP)-Binding Tyr-261 â€
A wide star–black-hole binary system from radial-velocity measurements
All stellar mass black holes have hitherto been identified by X-rays emitted
by gas that is accreting onto the black hole from a companion star. These
systems are all binaries with black holes below 30 M. Theory
predicts, however, that X-ray emitting systems form a minority of the total
population of star-black hole binaries. When the black hole is not
accreting gas, it can be found through radial velocity measurements of the
motion of the companion star. Here we report radial velocity measurements of a
Galactic star, LB-1, which is a B-type star, taken over two years. We find that
the motion of the B-star and an accompanying H emission line require
the presence of a dark companion with a mass of M,
which can only be a black hole. The long orbital period of 78.9 days shows that
this is a wide binary system. The gravitational wave experiments have detected
similarly massive black holes, but forming such massive ones in a
high-metallicity environment would be extremely challenging to current stellar
evolution theories.Comment: Published in Nature on Nov 28, 201