441 research outputs found
Scale-free random branching tree in supercritical phase
We study the size and the lifetime distributions of scale-free random
branching tree in which branches are generated from a node at each time
step with probability . In particular, we focus on
finite-size trees in a supercritical phase, where the mean branching number
is larger than 1. The tree-size distribution exhibits a
crossover behavior when ; A characteristic tree size
exists such that for , and for , , where scales as . For , it follows the conventional
mean-field solution, with .
The lifetime distribution is also derived. It behaves as for , and for when branching step , and for all when . The analytic solutions are
corroborated by numerical results.Comment: 6 pages, 6 figure
Model for the hydration of non-polar compounds and polymers
We introduce an exactly solvable statistical-mechanical model of the
hydration of non-polar compounds, based on grouping water molecules in clusters
where hydrogen bonds and isotropic interactions occur; interactions between
clusters are neglected. Analytical results show that an effective strengthening
of hydrogen bonds in the presence of the solute, together with a geometric
reorganization of water molecules, are enough to yield hydrophobic behavior. We
extend our model to describe a non-polar homopolymer in aqueous solution,
obtaining a clear evidence of both ``cold'' and ``warm'' swelling transitions.
This suggests that our model could be relevant to describe some features of
protein folding.Comment: REVTeX, 6 pages, 3 figure
Extremal dynamics model on evolving networks
We investigate an extremal dynamics model of evolution with a variable number
of units. Due to addition and removal of the units, the topology of the network
evolves and the network splits into several clusters. The activity is mostly
concentrated in the largest cluster. The time dependence of the number of units
exhibits intermittent structure. The self-organized criticality is manifested
by a power-law distribution of forward avalanches, but two regimes with
distinct exponents tau = 1.98 +- 0.04 and tau^prime = 1.65 +- 0.05 are found.
The distribution of extinction sizes obeys a power law with exponent 2.32 +-
0.05.Comment: 4 pages, 5 figure
Dimorphic Fungal Coinfection as a Cause of Chronic Diarrhea and Pancolitis
Histoplasma capsulatum and Paracoccidioides brasiliensis are dimorphic fungi that cause systemic mycosis mostly in tropical South America and some areas of North America. Gastrointestinal involvement is not uncommon among these fungal diseases, but coinfection has not previously been reported. We report a patient with chronic diarrhea and pancolitis caused by paracoccidioidomycosis and histoplasmosis
Chronic Diarrhea and Pancolitis Caused by Paracoccidioidomycosis: A Case Report
South American blastomycosis is a systemic micosis caused by infection with Paracoccidioides brasiliensis. The most frequently affected sites are the lower lip buccal mucous membrane, palate, tongue, sublingual region, lymph glands, and lungs. However, colonic involvement is not a common expression of Paracoccidioidomycosis. We report a case of chronic diarrhea and pancolitis caused by Paracoccidioidomycosis with fatal outcome
Scale-Free networks from varying vertex intrinsic fitness
A new mechanism leading to scale-free networks is proposed in this Letter. It is shown that, in many cases of interest, the connectivity power-law behavior is neither related to dynamical properties nor to preferential attachment. Assigning a quenched fitness value xi to every vertex, and drawing links among vertices with a probability depending on the fitnesses of the two involved sites, gives rise to what we call a good-get-richer mechanism, in which sites with larger fitness are more likely to become hubs (i.e., to be highly connected)
Shortest paths and load scaling in scale-free trees
The average node-to-node distance of scale-free graphs depends
logarithmically on N, the number of nodes, while the probability distribution
function (pdf) of the distances may take various forms. Here we analyze these
by considering mean-field arguments and by mapping the m=1 case of the
Barabasi-Albert model into a tree with a depth-dependent branching ratio. This
shows the origins of the average distance scaling and allows a demonstration of
why the distribution approaches a Gaussian in the limit of N large. The load
(betweenness), the number of shortest distance paths passing through any node,
is discussed in the tree presentation.Comment: 8 pages, 8 figures; v2: load calculations extende
Gender and Time to Arrival among Ischemic Stroke Patients in the Greater Cincinnati/Northern Kentucky Stroke Study
Background
Some studies of stroke patients report longer pre-hospital delays in women, but others conflict; studies vary in their inclusion of factors including age and stroke severity. We aimed to investigate the relationship between gender and time to emergency department (ED) arrival and the influence of age and stroke severity on this relationship.
Methods
Ischemic stroke patients ≥ 20 years old who presented to 15 hospitals within a 5-county region of Greater Cincinnati/Northern Kentucky during 2010 were included. Time from symptom onset to ED arrival and covariates were abstracted by study nurses and reviewed by study physicians. Data were analyzed using logistic regression with time to arrival dichotomized at ≤ 3 hours, in the overall sample and then stratified by NIHSS and age.
Results
1991 strokes (55% women) were included. Time to arrival was slightly longer in women (geometric mean 337 minutes [95%CI 307–369] vs. 297 [95%CI 268–329], p =0.05), and 24% of women vs. 27% of men arrived within 3 hours (p=0.15). After adjusting for age, race, NIHSS, living situation, and other covariates, gender was not associated with delayed time to arrival (OR=1.00, 95%CI 0.78–1.28). This did not change across age or NIHSS categories.
Conclusions
After adjusting for factors including age, NIHSS, and living alone, women and men with ischemic stroke had similar times to arrival. Arrival time is not likely a major contributor to differences in outcome between men and women
Sex-specific stroke incidence over time in the Greater Cincinnati/Northern Kentucky Stroke Study
OBJECTIVE:
Recent data suggest stroke incidence is decreasing over time, but it is unknown whether incidence is decreasing in women and men to the same extent.
METHODS:
Within our population of 1.3 million, all incident strokes among residents ≥20 years old were ascertained at all hospitals during July 1993-June 1994 and calendar years 1999, 2005, and 2010. A sampling scheme was used to ascertain out-of-hospital cases. Sex-specific incidence rates per 100,000 among black and white participants, age- and race-adjusted, were standardized to the 2000 US Census population. Trends over time by sex were compared; a Bonferroni correction was applied for multiple comparisons.
RESULTS:
Over the 4 study periods, there were 7,710 incident strokes; 57.2% (n = 4,412) were women. Women were older than men (mean ± SE 72.4 ± 0.34 vs 68.2 ± 0.32, p < 0.001). Incidence of all strokes decreased over time in men (263 [confidence interval 246-281] to 192 [179-205], p < 0.001) but not in women (217 [205-230] to 198 [187-210], p = 0.15). Similar sex differences were seen for ischemic stroke (men, 238 [223-257] to 165 [153-177], p < 0.01; women, 193 [181-205] to 173 [162-184], p = 0.09). Incidence of all strokes and of ischemic strokes was similar between women and men in 2010. Incidence of intracerebral hemorrhage and subarachnoid hemorrhage were stable over time in both sexes.
CONCLUSIONS:
Decreases in stroke incidence over time are driven by a decrease in ischemic stroke in men. Contrary to previous study periods, stroke incidence rates were similar by sex in 2010. Future research is needed to understand why the decrease in ischemic stroke incidence is more pronounced in men
Statistical properties of contact vectors
We study the statistical properties of contact vectors, a construct to
characterize a protein's structure. The contact vector of an N-residue protein
is a list of N integers n_i, representing the number of residues in contact
with residue i. We study analytically (at mean-field level) and numerically the
amount of structural information contained in a contact vector. Analytical
calculations reveal that a large variance in the contact numbers reduces the
degeneracy of the mapping between contact vectors and structures. Exact
enumeration for lengths up to N=16 on the three dimensional cubic lattice
indicates that the growth rate of number of contact vectors as a function of N
is only 3% less than that for contact maps. In particular, for compact
structures we present numerical evidence that, practically, each contact vector
corresponds to only a handful of structures. We discuss how this information
can be used for better structure prediction.Comment: 20 pages, 6 figure
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