6,039 research outputs found
Automated method for study of drug metabolism
Commercially available equipment can be modified to provide automated system for assaying drug metabolism by continuous flow-through. System includes steps and devices for mixing drug with enzyme and cofactor in the presence of pure oxygen, dialyzing resulting metabolite against buffer, and determining amount of metabolite by colorimetric method
Convergence of continuous-time quantum walks on the line
The position density of a "particle" performing a continuous-time quantum
walk on the integer lattice, viewed on length scales inversely proportional to
the time t, converges (as t tends to infinity) to a probability distribution
that depends on the initial state of the particle. This convergence behavior
has recently been demonstrated for the simplest continuous-time random walk
[see quant-ph/0408140]. In this brief report, we use a different technique to
establish the same convergence for a very large class of continuous-time
quantum walks, and we identify the limit distribution in the general case.Comment: Version to appear in Phys. Rev.
Conversion of acetate to lipids and co2 by liver of rats exposed to acceleration stress
Acetate conversion to lipids and carbon dioxide by exposure of rat liver to acceleration stres
Computer system for monitoring radiorepirometry data
System monitors expired breath patterns simultaneously from four small animals after they have been injected with carbon-14 substrates. It has revealed significant quantitative differences in oxidation patterns of glucose following such mild treatments of rats as a change in diet or environment
Singular solutions of the diffusion equation of population genetics
The forward diffusion equation for gene frequency dynamics is solved subject to the condition that the total probability is conserved at all times. This can lead to solutions developing singular spikes (Dirac delta functions) at the gene frequencies 0 and 1. When such spikes appear in solutions they signal gene loss or gene fixation, with the "weight" associated with the spikes corresponding to the probability of loss or fixation. The forward diffusion equation is thus solved for all gene frequencies, namely the absorbing frequencies of 0 and 1 along with the continuous range of gene frequencies on the interval (0; 1) that excludes the frequencies 0 and 1. Previously, the probabilities if the absorbing frequencies 0 and 1 were found by appeal to the backward diffusion equation, while those in the continuous range (0; 1) were found from the forward diffusion equation. Our uni fied approach does not require two separate equations for a complete dynamical treatment of all gene frequencies within a diffusion approximation framework. For cases involving mutation, migration and selection, it is shown that a property of the deterministic part of gene frequency dynamics determines when fixation and loss can occur. It is also shown how solution of the forward equation, at long times, leads to the standard result for the fixation probability
Conditioning an additive functional of a markov chain to stay non-negative. I, Survival for a long time
Let (X-t)(t >= 0) be a continuous-time irreducible Markov chain on a finite state space E, let v be a map v: E -> R \ {0}, and let (phi(t))(t >= 0) be an additive functional defined by phi(t) = integral(0)(t)(X-s) ds. We consider the case in which the process (phi(t))(t >= 0) is oscillating and that in which (phi(t))(t >= 0) has a negative drift. In each of these cases, we condition the process (X-t, phi(t))(t >= 0) on the event that (phi(t))(t >= 0) is nonnegative until time T and prove weak convergence of the conditioned process as T -> infinity
Deuxième contribution é l'étude de Formica bruni Kutter (Hymenoptera, Formicidae)
Formica bruni décrite en 1966 par Kutter appartient au sous-genre Coptoformica Müll. connue de Forel sous le nom de Formica pressilabris "un peu exsecta ". La biologie de cette espèce est demeurée inconnue jusqu'à nous jours. La découverte d'une nouvelle station au Bois de Chênes, près de Nyon (Vaud, Suisse), nous a poussé à entreprendre une série de travaux afin de savoir dans quelle mesure cette espèce diffère des autres espèces de Coptoformica. La zone étudiée comportait 61 nids en 1978, 18 nids habités par 7 sociétés en 1983 et 2 nids occupés par deux sociétés en juillet 1984. F. bruni est une espèce vraisemblablement polygyne et facultativement polycalique; aucune agressivité n'a été observée entre les sociétés qui, d'autre part, exploitent en commun un même territoire trophique. Les sociétés sont de petites tailles et leur territoire exploité ainsi que leur taux d'activité dépendent principalement de la quantité de nourriture à disposition. Différents facteurs susceptibles de la quasi extinction de cette espèce dans cette station sont discutés (fauchage, pâturage, etc...)
Comparison of prediction methods and studies of relaxation in hypersonic turbulent nozzle-wall boundary layers
Turbulent boundary layer measurements on axisymmetric hypersonic nozzle wall
The delayed uncoupled continuous-time random walks do not provide a model for the telegraph equation
It has been alleged in several papers that the so called delayed
continuous-time random walks (DCTRWs) provide a model for the one-dimensional
telegraph equation at microscopic level. This conclusion, being widespread now,
is strange, since the telegraph equation describes phenomena with finite
propagation speed, while the velocity of the motion of particles in the DCTRWs
is infinite. In this paper we investigate how accurate are the approximations
to the DCTRWs provided by the telegraph equation. We show that the diffusion
equation, being the correct limit of the DCTRWs, gives better approximations in
norm to the DCTRWs than the telegraph equation. We conclude therefore
that, first, the DCTRWs do not provide any correct microscopic interpretation
of the one-dimensional telegraph equation, and second, the kinetic (exact)
model of the telegraph equation is different from the model based on the
DCTRWs.Comment: 12 pages, 9 figure
Geometric origin of scaling in large traffic networks
Large scale traffic networks are an indispensable part of contemporary human
mobility and international trade. Networks of airport travel or cargo ships
movements are invaluable for the understanding of human mobility
patterns\cite{Guimera2005}, epidemic spreading\cite{Colizza2006}, global
trade\cite{Imo2006} and spread of invasive species\cite{Ruiz2000}. Universal
features of such networks are necessary ingredients of their description and
can point to important mechanisms of their formation. Different
studies\cite{Barthelemy2010} point to the universal character of some of the
exponents measured in such networks. Here we show that exponents which relate
i) the strength of nodes to their degree and ii) weights of links to degrees of
nodes that they connect have a geometric origin. We present a simple robust
model which exhibits the observed power laws and relates exponents to the
dimensionality of 2D space in which traffic networks are embedded. The model is
studied both analytically and in simulations and the conditions which result
with previously reported exponents are clearly explained. We show that the
relation between weight strength and degree is , the relation
between distance strength and degree is and the relation
between weight of link and degrees of linked nodes is
on the plane 2D surface. We further analyse the
influence of spherical geometry, relevant for the whole planet, on exact values
of these exponents. Our model predicts that these exponents should be found in
future studies of port networks and impose constraints on more refined models
of port networks.Comment: 17 pages, 5 figures, 1 tabl
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