1,832 research outputs found
On the universality of the scaling of fluctuations in traffic on complex networks
We study the scaling of fluctuations with the mean of traffic in complex
networks using a model where the arrival and departure of "packets" follow
exponential distributions, and the processing capability of nodes is either
unlimited or finite. The model presents a wide variety of exponents between 1/2
and 1 for this scaling, revealing their dependence on the few parameters
considered, and questioning the existence of universality classes. We also
report the experimental scaling of the fluctuations in the Internet for the
Abilene backbone network. We found scaling exponents between 0.71 and 0.86 that
do not fit with the exponent 1/2 reported in the literature.Comment: 4 pages, 4 figure
A Family of Tunable Spherically-Symmetric Potentials that Span the Range from Hard Spheres to Water-like Behavior
We investigate the equation of state, diffusion coefficient, and structural
order of a family of spherically-symmetric potentials consisting of a hard core
and a linear repulsive ramp. This generic potential has two characteristic
length scales: the hard and soft core diameters. The family of potentials is
generated by varying their ratio, . We find negative thermal expansion
(thermodynamic anomaly) and an increase of the diffusion coefficient upon
isothermal compression (dynamic anomaly) for . As in water,
the regions where these anomalies occur are nested domes in the () or
() planes, with the thermodynamic anomaly dome contained entirely within
the dynamic anomaly dome. We calculate translational and orientational order
parameters ( and ), and project equilibrium state points onto the () plane, or order map. The order map evolves from water-like behavior to
hard-sphere-like behavior upon varying between 4/7 and 6/7. Thus, we
traverse the range of liquid behavior encompassed by hard spheres ()
and water-like () with a family of tunable
spherically-symmetric potentials by simply varying the ratio of hard to
soft-core diameters. Although dynamic and thermodynamic anomalies occur almost
across the entire range , water-like structural anomalies
(i.e., decrease in both and upon compression and strictly correlated
and in the anomalous region) occur only around .
Water-like anomalies in structure, dynamics and thermodynamics arise solely due
to the existence of two length scales, orientation-dependent interactions being
absent by design.Comment: total 21 pages, 6 figure
Thermodynamics, Structure, and Dynamics of Water Confined between Hydrophobic Plates
We perform molecular dynamics simulations of 512 water-like molecules that
interact via the TIP5P potential and are confined between two smooth
hydrophobic plates that are separated by 1.10 nm. We find that the anomalous
thermodynamic properties of water are shifted to lower temperatures relative to
the bulk by K. The dynamics and structure of the confined water
resemble bulk water at higher temperatures, consistent with the shift of
thermodynamic anomalies to lower temperature. Due to this shift, our
confined water simulations (down to K) do not reach sufficiently low
temperature to observe a liquid-liquid phase transition found for bulk water at
K using the TIP5P potential. We find that the different
crystalline structures that can form for two different separations of the
plates, 0.7 nm and 1.10 nm, have no counterparts in the bulk system, and
discuss the relevance to experiments on confined water.Comment: 31 pages, 14 figure
Cartilage-selective genes identified in genome-scale analysis of non-cartilage and cartilage gene expression
<p>Abstract</p> <p>Background</p> <p>Cartilage plays a fundamental role in the development of the human skeleton. Early in embryogenesis, mesenchymal cells condense and differentiate into chondrocytes to shape the early skeleton. Subsequently, the cartilage anlagen differentiate to form the growth plates, which are responsible for linear bone growth, and the articular chondrocytes, which facilitate joint function. However, despite the multiplicity of roles of cartilage during human fetal life, surprisingly little is known about its transcriptome. To address this, a whole genome microarray expression profile was generated using RNA isolated from 18–22 week human distal femur fetal cartilage and compared with a database of control normal human tissues aggregated at UCLA, termed Celsius.</p> <p>Results</p> <p>161 cartilage-selective genes were identified, defined as genes significantly expressed in cartilage with low expression and little variation across a panel of 34 non-cartilage tissues. Among these 161 genes were cartilage-specific genes such as cartilage collagen genes and 25 genes which have been associated with skeletal phenotypes in humans and/or mice. Many of the other cartilage-selective genes do not have established roles in cartilage or are novel, unannotated genes. Quantitative RT-PCR confirmed the unique pattern of gene expression observed by microarray analysis.</p> <p>Conclusion</p> <p>Defining the gene expression pattern for cartilage has identified new genes that may contribute to human skeletogenesis as well as provided further candidate genes for skeletal dysplasias. The data suggest that fetal cartilage is a complex and transcriptionally active tissue and demonstrate that the set of genes selectively expressed in the tissue has been greatly underestimated.</p
Quantum Field Effects on Cosmological Phase Transition in Anisotropic Spacetimes
The one-loop renormalized effective potentials for the massive
theory on the spatially homogeneous models of Bianchi type I and
Kantowski-Sachs type are evaluated. It is used to see how the quantum field
affects the cosmological phase transition in the anisotropic spacetimes. For
reasons of the mathematical technique it is assumed that the spacetimes are
slowly varying or have specially metric forms. We obtain the analytic results
and present detailed discussions about the quantum field corrections to the
symmetry breaking or symmetry restoration in the model spacetimes.Comment: Latex 17 page
Prevention effects on trajectories of African American adolescents\u27 exposure to interparental conflict and depressive symptoms.
The present study investigates the trajectory of children\u27s exposure to interparental conflict during adolescence, its effects on adolescents\u27 psychological adjustment, as well as the ability of a family-centered prevention program to alter this trajectory. A total of 331 African American couples with an adolescent or preadolescent child participated in a randomized control trial of the Promoting Strong African American Families program, a newly developed program targeting couple and cocaregiving processes. Using a multi-informant, latent growth curve approach, child exposure to interparental conflict during adolescence was found to be stable over a period of 2 years among families in the control group, but significantly declined among families in the treatment condition. Rates of change were significantly different between intervention and control groups based on parents\u27 report of youth exposure to interparental conflict, but not for child\u27s report. Structural equation models found trajectory parameters of interparental conflict predicted changes in adolescent depressive symptoms, with increasing rates of changes in conflict associated with increases in adolescent internalizing symptoms over the 2-year duration of the study. Finally, a significant indirect effect was identified linking treatment, changes in parents\u27 reports of child exposure to interparental conflict, and adolescent depressive symptoms. The implications for research and intervention are discussed
Impact of previous hepatitis B infection on the clinical outcomes from chronic hepatitis C? A population-level analysis
Chronic coinfection with hepatitis C virus (HCV) and hepatitis B virus (HBV) is associated with adverse liver outcomes. The clinical impact of previous HBV infection on liver disease in HCV infection is unknown. We aimed at determining any association of previous HBV infection with liver outcomes using antibodies to the hepatitis B core antigen (HBcAb) positivity as a marker of exposure. The Scottish Hepatitis C Clinical Database containing data for all patients attending HCV clinics in participating health boards was linked to the HBV diagnostic registry and mortality data from Information Services Division, Scotland. Survival analyses with competing risks were constructed for time from the first appointment to decompensated cirrhosis, hepatocellular carcinoma (HCC) and liver‐related mortality. Records of 8513 chronic HCV patients were included in the analyses (87 HBcAb positive and HBV surface antigen [HBsAg] positive, 1577 HBcAb positive and HBsAg negative, and 6849 HBcAb negative). Multivariate cause‐specific proportional hazards models showed previous HBV infection (HBcAb positive and HBsAg negative) significantly increased the risks of decompensated cirrhosis (hazard ratio [HR]: 1.29, 95% CI: 1.01‐1.65) and HCC (HR: 1.64, 95% CI: 1.09‐2.49), but not liver‐related death (HR: 1.02, 95% CI: 0.80‐1.30). This is the largest study to date showing an association between previous HBV infection and certain adverse liver outcomes in HCV infection. Our analyses add significantly to evidence which suggests that HBV infection adversely affects liver health despite apparent clearance. This has important implications for HBV vaccination policy and indications for prioritization of HCV therapy
Dispersity-Driven Melting Transition in Two Dimensional Solids
We perform extensive simulations of Lennard-Jones particles to study
the effect of particle size dispersity on the thermodynamic stability of
two-dimensional solids. We find a novel phase diagram in the dispersity-density
parameter space. We observe that for large values of the density there is a
threshold value of the size dispersity above which the solid melts to a liquid
along a line of first order phase transitions. For smaller values of density,
our results are consistent with the presence of an intermediate hexatic phase.
Further, these findings support the possibility of a multicritical point in the
dispersity-density parameter space.Comment: In revtex format, 4 pages, 6 postscript figures. Submitted to PR
Dimensional Crossover in the Large N Limit
We consider dimensional crossover for an Landau-Ginzburg-Wilson model
on a -dimensional film geometry of thickness in the large -limit. We
calculate the full universal crossover scaling forms for the free energy and
the equation of state. We compare the results obtained using ``environmentally
friendly'' renormalization with those found using a direct, non-renormalization
group approach. A set of effective critical exponents are calculated and
scaling laws for these exponents are shown to hold exactly, thereby yielding
non-trivial relations between the various thermodynamic scaling functions.Comment: 25 pages of PlainTe
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