12,029 research outputs found
Convergence to equilibrium for the discrete coagulation-fragmentation equations with detailed balance
Under the condition of detailed balance and some additional restrictions on
the size of the coefficients, we identify the equilibrium distribution to which
solutions of the discrete coagulation-fragmentation system of equations
converge for large times, thus showing that there is a critical mass which
marks a change in the behavior of the solutions. This was previously known only
for particular cases as the generalized Becker-D\"oring equations. Our proof is
based on an inequality between the entropy and the entropy production which
also gives some information on the rate of convergence to equilibrium for
solutions under the critical mass.Comment: 28 page
On almost randomizing channels with a short Kraus decomposition
For large d, we study quantum channels on C^d obtained by selecting randomly
N independent Kraus operators according to a probability measure mu on the
unitary group U(d). When mu is the Haar measure, we show that for
N>d/epsilon^2. For d=2^k (k qubits), this includes Kraus operators
obtained by tensoring k random Pauli matrices. The proof uses recent results on
empirical processes in Banach spaces.Comment: We added some background on geometry of Banach space
Brief review on semileptonic B decays
We concisely review semileptonic B decays, focussing on recent progress on
both theoretical and experimental sides.Comment: 18 pages, 2 figures; version to be published in Mod. Phys. Lett.
coupling constant in light cone QCD sum rules
We employ the light cone QCD sum rules to calculate coupling
constant by studying the two point correlation function between the vacuum and
the pion state. Our result is consistent with the traditional QCD sum rules
calculations and it is in agreement with the experimental value.Comment: 8 pages, latex, 2 figure
Heavy-to-Light Form Factors in the Final Hadron Large Energy Limit of QCD
We argue that the Large Energy Effective Theory (LEET), originally proposed
by Dugan and Grinstein, is applicable to exclusive semileptonic, radiative and
rare heavy-to-light transitions in the region where the energy release E is
large compared to the strong interaction scale and to the mass of the final
hadron, i.e. for q^2 not close to the zero-recoil point. We derive the
Effective Lagrangian from the QCD one, and show that in the limit of heavy mass
M for the initial hadron and large energy E for the final one, the heavy and
light quark fields behave as two-component spinors. Neglecting QCD
short-distance corrections, this implies that there are only three form factors
describing all the pseudoscalar to pseudoscalar or vector weak current matrix
elements. We argue that the dependence of these form factors with respect to M
and E should be factorizable, the M-dependence (sqrt(M)) being derived from the
usual heavy quark expansion while the E-dependence is controlled by the
behaviour of the light-cone distribution amplitude near the end-point u=1. The
usual expectation of the (1-u) behaviour leads to a 1/E^2 scaling law, that is
a dipole form in q^2. We also show explicitly that in the appropriate limit,
the Light-Cone Sum Rule method satisfies our general relations as well as the
scaling laws in M and E of the form factors, and obtain very compact and simple
expressions for the latter. Finally we note that this formalism gives
theoretical support to the quark model-inspired methods existing in the
literature.Comment: Latex2e, 25 pages, no figure. Slight changes in the title and the
phrasing. Misprint in Eq. (25) corrected. To appear in Phys. Rev.
Toolbox for analyzing finite two-state trajectories
In many experiments, the aim is to deduce an underlying multi-substate on-off
kinetic scheme (KS) from the statistical properties of a two-state trajectory.
However, the mapping of a KS into a two-state trajectory leads to the loss of
information about the KS, and so, in many cases, more than one KS can be
associated with the data. We recently showed that the optimal way to solve this
problem is to use canonical forms of reduced dimensions (RD). RD forms are
on-off networks with connections only between substates of different states,
where the connections can have non-exponential waiting time probability density
functions (WT-PDFs). In theory, only a single RD form can be associated with
the data. To utilize RD forms in the analysis of the data, a RD form should be
associated with the data. Here, we give a toolbox for building a RD form from a
finite two-state trajectory. The methods in the toolbox are based on known
statistical methods in data analysis, combined with statistical methods and
numerical algorithms designed specifically for the current problem. Our toolbox
is self-contained - it builds a mechanism based only on the information it
extracts from the data, and its implementation on the data is fast (analyzing a
10^6 cycle trajectory from a thirty-parameter mechanism takes a couple of hours
on a PC with a 2.66 GHz processor). The toolbox is automated and is freely
available for academic research upon electronic request
Predictions on , and from QCD Light-Cone Sum Rules
The form factors of the , and transitions
are calculated from QCD light-cone sum rules (LCSR) and used to predict the
widths and differential distributions of the exclusive semileptonic decays
, and ,
where . The current theoretical uncertainties are estimated. The LCSR
results are found to agree with the results of lattice QCD calculations and
with experimental data on exclusive semileptonic D decays. Comparison of the
LCSR prediction on with the CLEO measurement yields a
value of |V_{ub}| in agreement with other determinations.Comment: 24 pages, 12 figures, Latex, epsfig, some additional remarks on the
two-pole parameterization, prediction on the form factor added,
version to appear in Phys. Rev.
Phenomenological Bounds on B to Light Semileptonic Form Factors
The form factors for the weak currents between B and light mesons are studied
by relating them to the corresponding D form factors at q^2_{max} according to
HQET, by evaluating them at q^2=0 by QCD sum rules, and by assuming a polar q^2
dependence. The results found are consistent with the information obtained from
exclusive non-leptonic two-body decays and, with the only exception of A_1,
with lattice calculations.Comment: 8 LaTeX pages + 2 figures. Will appear in Mod. Phys. Lett.
Heterotrimeric G protein subunits are located on rat liver endosomes
BACKGROUND: Rat liver endosomes contain activated insulin receptors and downstream signal transduction molecules. We undertook these studies to determine whether endosomes also contain heterotrimeric G proteins that may be involved in signal transduction from G protein-coupled receptors. RESULTS: By Western blotting G(sα), G(iα1,2), G(iα3 )and G(ÎČ )were enriched in both canalicular (CM) and basolateral (BLM) membranes but also readily detectable on three types of purified rat liver endosomes in the order recycling receptor compartment (RRC) > compartment for uncoupling of receptor and ligand (CURL) > multivesicular bodies (MVB) >> purified secondary lysosomes. Western blotting with antibodies to Na, K-ATPase and to other proteins associated with plasma membranes and intracellular organelles indicated this was not due to contamination of endosome preparations by CM or BLM. Adenylate cyclase (AC) was also identified on purified CM, BLM, RRC, CURL and MVB. Percoll gradient fractionation of liver postnuclear supernatants demonstrated co-occurrence of endosomes and heterotrimeric G protein subunits in fractions with little plasma membrane markers. By confocal microscopy, punctate staining for G(sα), G(iα3 )and G(ÎČ )corresponded to punctate areas of endocytosed Texas red-dextran in hepatocytes from control and cholera toxin-treated livers. CONCLUSION: We conclude that heterotrimeric G protein subunits as well as AC likely traffic into hepatocytes on endosome membranes, possibly generating downstream signals spatially separate from signalling generated at the plasma membrane, analogous to the role(s) of internalized insulin receptors
Constraints on the IR behaviour of gluon and ghost propagator from Ward-Slavnov-Taylor identities
We consider the constraints of the Slavnov-Taylor identity of the IR
behaviour of gluon and ghost propagators and their compatibility with solutions
of the ghost Dyson-Schwinger equation and with the lattice picture.Comment: 5 pages, 2 figure
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