4,368 research outputs found
Next-to-Next-to-Leading Electroweak Logarithms for W-Pair Production at LHC
We derive the high energy asymptotic of one- and two-loop corrections in the
next-to-next-to-leading logarithmic approximation to the differential cross
section of -pair production at the LHC. For large invariant mass of the
W-pair the (negative) one-loop terms can reach more than 40%, which are
partially compensated by the (positive) two-loop terms of up to 10%.Comment: 23 pages, 9 figures, added explanations in section 3, corrected typos
and figures 7, 8,
Stable Equilibrium Based on L\'evy Statistics: Stochastic Collision Models Approach
We investigate equilibrium properties of two very different stochastic
collision models: (i) the Rayleigh particle and (ii) the driven Maxwell gas.
For both models the equilibrium velocity distribution is a L\'evy distribution,
the Maxwell distribution being a special case. We show how these models are
related to fractional kinetic equations. Our work demonstrates that a stable
power-law equilibrium, which is independent of details of the underlying
models, is a natural generalization of Maxwell's velocity distribution.Comment: PRE Rapid Communication (in press
Real sequence effects on the search dynamics of transcription factors on DNA
Recent experiments show that transcription factors (TFs) indeed use the
facilitated diffusion mechanism to locate their target sequences on DNA in
living bacteria cells: TFs alternate between sliding motion along DNA and
relocation events through the cytoplasm. From simulations and theoretical
analysis we study the TF-sliding motion for a large section of the DNA-sequence
of a common E. coli strain, based on the two-state TF-model with a fast-sliding
search state and a recognition state enabling target detection. For the
probability to detect the target before dissociating from DNA the TF-search
times self-consistently depend heavily on whether or not an auxiliary operator
(an accessible sequence similar to the main operator) is present in the genome
section. Importantly, within our model the extent to which the interconversion
rates between search and recognition states depend on the underlying nucleotide
sequence is varied. A moderate dependence maximises the capability to
distinguish between the main operator and similar sequences. Moreover, these
auxiliary operators serve as starting points for DNA looping with the main
operator, yielding a spectrum of target detection times spanning several orders
of magnitude. Auxiliary operators are shown to act as funnels facilitating
target detection by TFs.Comment: 26 pages, 7 figure
Random Time-Scale Invariant Diffusion and Transport Coefficients
Single particle tracking of mRNA molecules and lipid granules in living cells
shows that the time averaged mean squared displacement of
individual particles remains a random variable while indicating that the
particle motion is subdiffusive. We investigate this type of ergodicity
breaking within the continuous time random walk model and show that
differs from the corresponding ensemble average. In
particular we derive the distribution for the fluctuations of the random
variable . Similarly we quantify the response to a
constant external field, revealing a generalization of the Einstein relation.
Consequences for the interpretation of single molecule tracking data are
discussed.Comment: 4 pages, 4 figures.Article accompanied by a PRL Viewpoint in
Physics1, 8 (2008
Thermodynamics and Fractional Fokker-Planck Equations
The relaxation to equilibrium in many systems which show strange kinetics is
described by fractional Fokker-Planck equations (FFPEs). These can be
considered as phenomenological equations of linear nonequilibrium theory. We
show that the FFPEs describe the system whose noise in equilibrium funfills the
Nyquist theorem. Moreover, we show that for subdiffusive dynamics the solutions
of the corresponding FFPEs are probability densities for all cases where the
solutions of normal Fokker-Planck equation (with the same Fokker-Planck
operator and with the same initial and boundary conditions) exist. The
solutions of the FFPEs for superdiffusive dynamics are not always probability
densities. This fact means only that the corresponding kinetic coefficients are
incompatible with each other and with the initial conditions
A lattice Boltzmann model with random dynamical constraints
In this paper we introduce a modified lattice Boltzmann model (LBM) with the
capability of mimicking a fluid system with dynamic heterogeneities. The
physical system is modeled as a one-dimensional fluid, interacting with
finite-lifetime moving obstacles. Fluid motion is described by a lattice
Boltzmann equation and obstacles are randomly distributed semi-permeable
barriers which constrain the motion of the fluid particles. After a lifetime
delay, obstacles move to new random positions. It is found that the
non-linearly coupled dynamics of the fluid and obstacles produces heterogeneous
patterns in fluid density and non-exponential relaxation of two-time
autocorrelation function.Comment: 10 pages, 9 figures, to be published in Eur. Phys. J.
- …