7,426 research outputs found
Turbulent Pair Diffusion
Kinematic Simulations of turbulent pair diffusion in planar turbulence with a
-5/3 energy spectrum reproduce the results of the laboratory measurements of
Jullien Phys. Rev. Lett. 82, 2872 (1999), in particular the stretched
exponential form of the PDF of pair separations and their correlation
functions. The root mean square separation is found to be strongly dependent on
initial conditions for very long stretches of times. This dependence is
consistent with the topological picture of turbulent pair diffusion where pairs
initially close enough travel together for long stretches of time and separate
violently when they meet straining regions around hyperbolic points. A new
argument based on the divergence of accelerations is given to support this
picture
Richardson's pair diffusion and the stagnation point structure of turbulence
DNS and laboratory experiments show that the spatial distribution of
straining stagnation points in homogeneous isotropic 3D turbulence has a
fractal structure with dimension D_s = 2. In Kinematic Simulations the time
exponent gamma in Richardson's law and the fractal dimension D_s are related by
gamma = 6/D_s. The Richardson constant is found to be an increasing function of
the number of straining stagnation points in agreement with pair duffusion
occuring in bursts when pairs meet such points in the flow.Comment: 4 pages; Submitted to Phys. Rev. Let
Investigating the role of dust in ice nucleation within clouds and further effects on the regional weather system over East Asia – Part 1: model development and validation
The GOCART–Thompson microphysics scheme coupling the GOCART
aerosol model and the aerosol-aware Thompson–Eidhammer microphysics scheme
has been implemented in the WRF-Chem to quantify and evaluate the effect of
dust on the ice nucleation process in the atmosphere by serving as ice
nuclei (IN). The performance of the GOCART–Thompson microphysics scheme in
simulating the effect of dust in atmospheric ice nucleation is then evaluated
over East Asia during spring, a typical dust-intensive season, in 2012. Based
upon the dust emission reasonably reproduced by WRF-Chem, the effect of dust
on atmospheric cloud ice water content is well reproduced. With abundant dust
particles serving as IN, the simulated ice water mixing ratio and ice crystal
number concentration increases by 15 and 7 % on average over the dust
source region and downwind areas during the investigated period. The
comparison with the ice water path from satellite observations demonstrated that
the simulation of the cloud ice profile is substantially improved by considering
the indirect effect of dust particles in the simulations. Additional
sensitivity experiments are carried out to optimize the parameters in the ice
nucleation parameterization in the GOCART–Thompson microphysics scheme.
Results suggest that lowering the threshold relative humidity with respect to
ice to 100 % for the ice nucleation parameterization leads to further
improvement in cloud ice simulation
Investigating the role of dust in ice nucleation within clouds and further effects on the regional weather system over East Asia – Part 2: modification of the weather system
An updated version of the Weather Research and Forecast model coupled with
Chemistry (WRF-Chem) was applied to quantify and investigate the full effects
of dust on the meteorological field over East Asia during March and April
2012. The performances of the model in simulating the shortwave and
longwave radiation, surface temperature, and precipitation over East Asia
are improved by incorporating the effects of dust in the simulations. The
radiative forcing induced by the direct radiative effect of dust is greater
than that by the dust-enhanced cloud radiative effect. The indirect effects
of dust result in a substantial increase in ice clouds at the middle to upper
troposphere and a reduction in liquid clouds at the low to mid-troposphere. The
radiative forcing combined with the redistribution of atmospheric water
vapor results in an overall decrease in near-surface temperature and an
increase in temperature at the middle to upper troposphere over East Asia,
leading to an inhibition of atmospheric instability over most land areas, but
an enhancement of atmospheric instability over south China. Upon considering
the effects of dust, convective precipitation exhibits an inhibition over
areas from central to east China and an enhancement over south China.
Meanwhile, the locations of non-convective precipitation are shifted due to
the perturbation of cloud water path. The total amount of precipitation over
East Asia remains unchanged; however, the precipitation locations are
shifted. The precipitation can be enhanced or inhibited by up to 20 % at
particular areas.</p
Efficiency of feedback process in cavity quantum electrodynamics
Utilizing the continuous frequency mode quantization scheme, we study from
first principle the efficiency of a feedback scheme that can generate maximally
entangled states of two atoms in an optical cavity through their interactions
with a single input photon. The spectral function of the photon emitted from
the cavity, which will be used as the input of the next round in the feedback
process, is obtained analytically. We find that the spectral function of the
photon is modified in each round and deviates from the original one. The
efficiency of the feedback scheme consequently deteriorates gradually after
several rounds of operation.Comment: 11 pages, 5 figures, accepted for publication in Journal of Physics
A physical modeling approach for identification of source regions of primary and secondary air pollutants
International audienceThis paper describes a simple but practical methodology to identify the contribution of primary and secondary air pollutants from the local/regional emission sources to Hong Kong, a highly urbanized city with complex terrain and coastlines. The meteorological model MM5 coupled with a three-dimensional, mutli-particle trajectory model is used to identify salient aspects of regional air pollutant transport characteristics during some typical meteorological conditions over the Pearl River Delta (PRD) region. Several weighting factors are determined for calculating the air mass/pollutant trajectory and are used to evaluate the local and regional contribution of primary pollutants over the PRD to Hong Kong pollution. The relationships between emission inventories, physical paths and chemical transformation rates of the pollutants, and observational measurements are formulated. The local and regional contributions of secondary pollutants are obtained by this conceptual module under different weather scenarios. Our results demonstrate that major pollution sources over Hong Kong come from regional transport. In calm-weather situations, 78% of the respirable suspended particulates (RSP) totals in Hong Kong are contributed by regional transport, and 49% are contributed by the power plants within the PRD. In normal-day situations, 71% of the RSP are contributed by regional transport, and 45% are contributed by the power plants
Rejection of human intestinal allografts: Alone or in combination with the liver
The current results of the present series demonstrate that intestinal allografts are more vulnerable to rejection and continue to be at a significantly higher risk long after transplantation compared with isolated liver allograft recipients. Unexpectedly, a combined liver allograft does not protect small bowel from rejection. The necessarily continuous heavy immunosuppression for these unique recipients is potentially self-defeating. This is clearly demonstrated by their high susceptibility to early and late infectious complications after transplantation as reported in this issue. With the minimal graft-versus-host disease threat in this clinical trial, our revised protocol for future intestinal transplantation is to maximize the passenger leukocyte traffic with supplementary bone marrow from the same intestinal donor in an attempt to augment the development of systemic chimerism and the gradual induction of donor-specific nonreactivity
Hepatitis C virus genotypes in liver transplant recipients: Impact on posttransplant recurrence, infections, response to interferon-α therapy and outcome
Background. End-stage liver disease due to hepatitis C virus (HCV) is the most common indication for liver transplantation in U.S. veterans. We investigated the influence of HCV genotypes on the incidence and timing of recurrent HCV hepatitis, survival, infectious morbidity, and response to interferon-α therapy in this unique patient population. Methods. HCV genotype was determined by direct sequencing of the NS5 region of HCV with type-specific primers. Results. Genotype 1a (66%, 32/47) was the predominant genotype. Type 1b was found in 25% (12/47) of patients and type 2b was found in 9% (4/47). His topathologically recurrent HCV hepatitis developed in 53% (25/47) of the patients after transplantation. This group included 45% (14/31) of the patients with type 1a, 67% (8/12) of the patients with type 1b, and 25% (1/4) of the patients with type 2b (P>0.5). The time to recurrence and the severity of HCV recurrence as defined by aminotransferase levels or Knodell scores were not different among the three genotypes. There was a trend toward a higher incidence of major infections in patients with type 1b (75%) versus type 1a (48%) and type 2b (50%) (P=0.11). The response to interferon-α therapy did not differ significantly among the genotypes. Mortality at 5 years was 16% (5/31) in patients with genotype 1a, 42% (5/12) in patients with genotype 1b, and 50% (2/4) in patients with genotype 2b (P=0.06). Conclusions. The incidence, time to recurrence, and response to interferon-α therapy did not differ be tween the various genotypes in our liver transplant recipients. However, there was a trend toward higher infectious morbidity and overall mortality in patients with genotype 1b after transplantation
- …