528 research outputs found
Finding mesoscopic communities in sparse networks
We suggest a fast method to find possibly overlapping network communities of
a desired size and link density. Our method is a natural generalization of the
finite- superparamegnetic Potts clustering introduced by Blatt, Wiseman, and
Domany (Phys. Rev. Lett. v.76, 3251 (1996) and the recently suggested by
Reichard and Bornholdt (Phys. Rev. Lett. v.93, 21870 (2004)) annealing of Potts
model with global antiferromagnetic term. Similarly to both preceding works,
the proposed generalization is based on ordering of ferromagnetic Potts model;
the novelty of the proposed approach lies in the adjustable dependence of the
antiferromagnetic term on the population of each Potts state, which
interpolates between the two previously considered cases. This adjustability
allows to empirically tune the algorithm to detect the maximum number of
communities of the given size and link density. We illustrate the method by
detecting protein complexes in high-throughput protein binding networks.Comment: 8 pages, 2 figure, typos corrected, 1 figure adde
Cliques and duplication-divergence network growth
A population of complete subgraphs or cliques in a network evolving via
duplication-divergence is considered. We find that a number of cliques of each
size scales linearly with the size of the network. We also derive a clique
population distribution that is in perfect agreement with both the simulation
results and the clique statistic of the protein-protein binding network of the
fruit fly. In addition, we show that such features as fat-tail degree
distribution, various rates of average degree growth and non-averaging,
revealed recently for only the particular case of a completely asymmetric
divergence, are present in a general case of arbitrary divergence.Comment: 7 pages, 6 figure
Pigmented purpuric dermatosis: a review of the literature
The pigmented purpuric dermatoses (PPDs) are a group of benign, chronic diseases. The variants described to date represent different clinical presentations of the same entity, all having similar histopathologic characteristics. We provide an overview of the most common PPDs and describe their clinical, dermatopathologic, and epiluminescence features. PPDs are both rare and benign, and this, together with an as yet poor understanding of the pathogenic mechanisms involved, means that no standardized treatments exist. We review the treatments described to date. However, because most of the descriptions are based on isolated cases or small series, there is insufficient evidence to support the use of any of these treatments as first-line therapy
Brownian motion of a charged particle driven internally by correlated noise
We give an exact solution to the generalized Langevin equation of motion of a
charged Brownian particle in a uniform magnetic field that is driven internally
by an exponentially-correlated stochastic force. A strong dissipation regime is
described in which the ensemble-averaged fluctuations of the velocity exhibit
transient oscillations that arise from memory effects. Also, we calculate
generalized diffusion coefficients describing the transport of these particles
and briefly discuss how they are affected by the magnetic field strength and
correlation time. Our asymptotic results are extended to the general case of
internal driving by correlated Gaussian stochastic forces with finite
autocorrelation times.Comment: 10 pages, 4 figures with subfigures, RevTeX, v2: revise
Heat conductivity of DNA double helix
Thermal conductivity of isolated single molecule DNA fragments is of
importance for nanotechnology, but has not yet been measured experimentally.
Theoretical estimates based on simplified (1D) models predict anomalously high
thermal conductivity. To investigate thermal properties of single molecule DNA
we have developed a 3D coarse-grained (CG) model that retains the realism of
the full all-atom description, but is significantly more efficient. Within the
proposed model each nucleotide is represented by 6 particles or grains; the
grains interact via effective potentials inferred from classical molecular
dynamics (MD) trajectories based on a well-established all-atom potential
function. Comparisons of 10 ns long MD trajectories between the CG and the
corresponding all-atom model show similar root-mean-square deviations from the
canonical B-form DNA, and similar structural fluctuations. At the same time,
the CG model is 10 to 100 times faster depending on the length of the DNA
fragment in the simulation. Analysis of dispersion curves derived from the CG
model yields longitudinal sound velocity and torsional stiffness in close
agreement with existing experiments. The computational efficiency of the CG
model makes it possible to calculate thermal conductivity of a single DNA
molecule not yet available experimentally. For a uniform (polyG-polyC) DNA, the
estimated conductivity coefficient is 0.3 W/mK which is half the value of
thermal conductivity for water. This result is in stark contrast with estimates
of thermal conductivity for simplified, effectively 1D chains ("beads on a
spring") that predict anomalous (infinite) thermal conductivity. Thus, full 3D
character of DNA double-helix retained in the proposed model appears to be
essential for describing its thermal properties at a single molecule level.Comment: 16 pages, 12 figure
Equilibrium properties of a Josephson junction ladder with screening effects
In this paper we calculate the ground state phase diagram of a Josephson
Junction ladder when screening field effects are taken into account. We study
the ground state configuration as a function of the external field, the
penetration depth and the anisotropy of the ladder, using different
approximations to the calculation of the induced fields. A series of tongues,
characterized by the vortex density , is obtained. The vortex density
of the ground state, as a function of the external field, is a Devil's
staircase, with a plateau for every rational value of . The width of
each of these steps depends strongly on the approximation made when calculating
the inductance effect: if the self-inductance matrix is considered, the
phase tends to occupy all the diagram as the penetration depth
decreases. If, instead, the whole inductance matrix is considered, the width of
any step tends to a non-zero value in the limit of very low penetration depth.
We have also analyzed the stability of some simple metastable phases: screening
fields are shown to enlarge their stability range.Comment: 16 pp, RevTex. Figures available upon request at
[email protected] To be published in Physical Review B (01-Dec-96
Mesoscopic Model for Free Energy Landscape Analysis of DNA sequences
A mesoscopic model which allows us to identify and quantify the strength of
binding sites in DNA sequences is proposed. The model is based on the
Peyrard-Bishop-Dauxois model for the DNA chain coupled to a Brownian particle
which explores the sequence interacting more importantly with open base pairs
of the DNA chain. We apply the model to promoter sequences of different
organisms. The free energy landscape obtained for these promoters shows a
complex structure that is strongly connected to their biological behavior. The
analysis method used is able to quantify free energy differences of sites
within genome sequences.Comment: 7 pages, 5 figures, 1 tabl
Discrete breathers in nonlinear lattices: Experimental detection in a Josephson array
We present an experimental study of discrete breathers in an underdamped
Josephson-junction array. Breathers exist under a range of dc current biases
and temperatures, and are detected by measuring dc voltages. We find the
maximum allowable bias current for the breather is proportional to the array
depinning current while the minimum current seems to be related to a junction
retrapping mechanism. We have observed that this latter instability leads to
the formation of multi-site breather states in the array. We have also studied
the domain of existence of the breather at different values of the array
parameters by varying the temperature.Comment: 5 pages, 5 figures, submitted to Physical Revie
Chicken egg white — characteristics of its properties and the prospects for functional foods development
The overview presents the literature data and the results of our own research on prospects of using the chicken eggs as the basis of functional foods. The composition of chicken eggs and their components, characteristics of egg white proteins properties are presented thereto. The biologically active compounds included into egg composition are analyzed. The data on the biological value of egg white are given. The characteristic of egg white foaming ability is presented. It has been shown that the ability of proteins to form stable intermolecular structures, especially with partially denaturated proteins, allows them forming viscoelastic superficial films that ensure foam stability. The high foaming ability of chicken egg protein macromolecules is directly related to their interphase properties, i. e. the ability to form interphase layers at the “liquid — gas” interface. The foaming properties of the various egg proteins are not equal, and therefore they contribute to foaming properties at various extents. The model of egg white proteins gelation is considered and the factors influencing the gelation process are described. It has been shown that very important changes in proteins properties are caused by denaturation. The proteins lose their ability to hydrate; the protective aqueous shell around the globules disappears, the proteins stick together, grow larger and lose solubility. This process is called coagulation. The influence of denaturation and aggregation on variations of protein properties is described below. Data on protein fortification with functional ingredients (calcium, iodine, plant polyphenols) and creation of functional egg and meat foods are presented here
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