1,996 research outputs found
Biocomplexity: A pluralist research strategy is necessary for a mechanistic explanation of the "live" state
The biological sciences study (bio) complex living systems. Research directed at the mechanistic explanation of the "live" state truly requires a pluralist research program, i.e. BioComplexity research. The program should apply multiple intra-level and inter-level theories and methodologies. We substantiate this thesis with analysis of BioComplexity: metabolic and modular control analysis of metabolic pathways, emergence of osculations, and the analysis of the functioning of glycolysis
Langevin dynamics with dichotomous noise; direct simulation and applications
We consider the motion of a Brownian particle moving in a potential field and
driven by dichotomous noise with exponential correlation. Traditionally, the
analytic as well as the numerical treatments of the problem, in general, rely
on Fokker-Planck description. We present a method for direct numerical
simulation of dichotomous noise to solve the Langevin equation. The method is
applied to calculate nonequilibrium fluctuation induced current in a symmetric
periodic potential using asymmetric dichotomous noise and compared to
Fokker-Planck-Master equation based algorithm for a range of parameter values.
Our second application concerns the study of resonant activation over a
fluctuating barrier.Comment: Accepted in Journal of Statistical Mechanics: Theory and Experimen
Generalized Smoluchowski equation with correlation between clusters
In this paper we compute new reaction rates of the Smoluchowski equation
which takes into account correlations. The new rate K = KMF + KC is the sum of
two terms. The first term is the known Smoluchowski rate with the mean-field
approximation. The second takes into account a correlation between clusters.
For this purpose we introduce the average path of a cluster. We relate the
length of this path to the reaction rate of the Smoluchowski equation. We solve
the implicit dependence between the average path and the density of clusters.
We show that this correlation length is the same for all clusters. Our result
depends strongly on the spatial dimension d. The mean-field term KMFi,j = (Di +
Dj)(rj + ri)d-2, which vanishes for d = 1 and is valid up to logarithmic
correction for d = 2, is the usual rate found with the Smoluchowski model
without correlation (where ri is the radius and Di is the diffusion constant of
the cluster). We compute a new rate: the correlation rate K_{i,j}^{C}
(D_i+D_j)(r_j+r_i)^{d-1}M{\big(\frac{d-1}{d_f}}\big) is valid for d \leq
1(where M(\alpha) = \sum+\infty i=1i\alphaNi is the moment of the density of
clusters and df is the fractal dimension of the cluster). The result is valid
for a large class of diffusion processes and mass radius relations. This
approach confirms some analytical solutions in d 1 found with other methods. We
also show Monte Carlo simulations which illustrate some exact new solvable
models
Stochastic Physics, Complex Systems and Biology
In complex systems, the interplay between nonlinear and stochastic dynamics,
e.g., J. Monod's necessity and chance, gives rise to an evolutionary process in
Darwinian sense, in terms of discrete jumps among attractors, with punctuated
equilibrium, spontaneous random "mutations" and "adaptations". On an
evlutionary time scale it produces sustainable diversity among individuals in a
homogeneous population rather than convergence as usually predicted by a
deterministic dynamics. The emergent discrete states in such a system, i.e.,
attractors, have natural robustness against both internal and external
perturbations. Phenotypic states of a biological cell, a mesoscopic nonlinear
stochastic open biochemical system, could be understood through such a
perspective.Comment: 10 page
A Survey of the Northern Sky for TeV Point Sources
A search for steady TeV point sources anywhere in the northern sky has been
made with data from the Milagrito air-shower-particle detector. Over 3 x 10**9
events collected from 1997 February to 1998 May have been used in this study.
No statistically significant excess above the background from the isotropic
flux of cosmic rays was found for any direction of the sky with declination
between -5 degrees and 71.7 degrees. Upper limits are derived for the photon
flux above 1 TeV from any steady point source in the northern sky.Comment: 2 Figure
DEVELOPMENT OF A FIELD EXPERIMENT OF CO 2 STORAGE IN COAL SEAMS IN THE UPPER SILESIAN BASIN OF POLAND (RECOPOL)
ABSTRACT In 2001 the RECOPOL project, which aims at the development of the first European field demonstration of CO 2 sequestration in subsurface coal seams, started. The required research, design and operation of the pilot field test is executed by an international consortium of research institutes, universities and industrial partners. A site was selected in the Silesian Basin in Poland where two CBM-wells are present at short distance from each other. One injection well will be drilled in between; drilling is scheduled in spring 2003. Injection is planned to start in the summer of 2003 and will continue until the end of 2004. Reservoir modelling shows that the distance between the injection well and the updip production well should be less than 200 m to increase the chance of breakthrough of CO 2 within the test period. Breakthrough is important for a thorough understanding of the process. After and during the injection period monitoring will be performed by direct measurements of CO 2 -concentration and by time lapse seismic monitoring
Very high energy particle acceleration powered by the jets of the microquasar SS 433
SS 433 is a binary system containing a supergiant star that is overflowing
its Roche lobe with matter accreting onto a compact object (either a black hole
or neutron star). Two jets of ionized matter with a bulk velocity of
extend from the binary, perpendicular to the line of sight, and
terminate inside W50, a supernova remnant that is being distorted by the jets.
SS 433 differs from other microquasars in that the accretion is believed to be
super-Eddington, and the luminosity of the system is erg
s. The lobes of W50 in which the jets terminate, about 40 pc from the
central source, are expected to accelerate charged particles, and indeed radio
and X-ray emission consistent with electron synchrotron emission in a magnetic
field have been observed. At higher energies (>100 GeV), the particle fluxes of
rays from X-ray hotspots around SS 433 have been reported as flux
upper limits. In this energy regime, it has been unclear whether the emission
is dominated by electrons that are interacting with photons from the cosmic
microwave background through inverse-Compton scattering or by protons
interacting with the ambient gas. Here we report TeV -ray observations
of the SS 433/W50 system where the lobes are spatially resolved. The TeV
emission is localized to structures in the lobes, far from the center of the
system where the jets are formed. We have measured photon energies of at least
25 TeV, and these are certainly not Doppler boosted, because of the viewing
geometry. We conclude that the emission from radio to TeV energies is
consistent with a single population of electrons with energies extending to at
least hundreds of TeV in a magnetic field of ~micro-Gauss.Comment: Preprint version of Nature paper. Contacts: S. BenZvi, B. Dingus, K.
Fang, C.D. Rho , H. Zhang, H. Zho
- …