577 research outputs found
Fractal properties of relaxation clusters and phase transition in a stochastic sandpile automaton
We study numerically the spatial properties of relaxation clusters in a two
dimensional sandpile automaton with dynamic rules depending stochastically on a
parameter p, which models the effects of static friction. In the limiting cases
p=1 and p=0 the model reduces to the critical height model and critical slope
model, respectively. At p=p_c, a continuous phase transition occurs to the
state characterized by a nonzero average slope. Our analysis reveals that the
loss of finite average slope at the transition is accompanied by the loss of
fractal properties of the relaxation clusters.Comment: 11 page
Nuclear Structure in Nonmesonic Weak Decay of Hypernuclei
A general shell model formalism for the nonmesonic weak decay of the hypernuclei has been developed.It involves a partial wave expansion of the emitted nucleon waves,preserves naturally the antisymmetrization between the escaping particles and the residual core, and contains as a particular case the weak Lambda-core coupling formalism. The hypernuclei are grouped having in view their A-1 cores, that is in those with even-even, even-odd and odd-odd cores.It is shown that in all three cases the nuclear structure manifests itself basically through Pauli Principle, and very simple expressions are derived for the neutron and proton induced decays rates, which does not involve the spectroscopic factors
Towards pp -> VVjj at NLO QCD: Bosonic contributions to triple vector boson production plus jet
In this work, some of the NLO QCD corrections for pp -> VVjj + X are
presented. A program in Mathematica based on the structure of FeynCalc which
automatically simplifies a set of amplitudes up to the hexagon level of rank 5
has been created for this purpose. We focus on two different topologies. The
first involves all the virtual contributions needed for quadruple electroweak
vector boson production, i.e. pp -> VVVV + X. In the second, the remaining
"bosonic" corrections to electroweak triple vector boson production with an
additional jet (pp -> VVV j + X) are computed. We show the factorization
formula of the infrared divergences of the bosonic contributions for VVVV and
VVVj production with V=(W,Z,gamma). Stability issues associated with the
evaluation of the hexagons up to rank 5 are studied. The CPU time of the
FORTRAN subroutines rounds the 2 milliseconds and seems to be competitive with
other more sophisticated methods. Additionally, in Appendix A the master
equations to obtain the tensor coefficients up to the hexagon level in the
external momenta convention are presented including the ones needed for small
Gram determinants.Comment: 48 pages,16 figure
Hyperon Nonleptonic Weak Decays Revisited
We first review the current algebra - PCAC approach to nonleptonic octet
baryon 14 weak decay B (\to) (B^{\prime})(\pi) amplitudes. The needed four
parameters are independently determined by (\Omega \to \Xi \pi),(\Lambda K) and
(\Xi ^{-}\to \Sigma ^{-}\gamma) weak decays in dispersion theory tree order. We
also summarize the recent chiral perturbation theory (ChPT) version of the
eight independent B (\to) (B^{\prime}\pi) weak (\Delta I) = 1/2 amplitudes
containing considerably more than eight low-energy weak constants in one-loop
order.Comment: 10 pages, RevTe
Mirror matter admixtures and isospin breaking in the \Delta I=1/2 rule in \Omega^- two body non-leptonic decays
We discuss a description of \Omega^- two body non-leptonic decays based on
possible, albeit tiny, admixtures of mirror matter in ordinary hadrons. The
\Delta I=1/2 rule enhancement is obtained as a result of isospin symmetry and,
more importantly, the rather large observed deviations from this rule result
from small isospin breaking. This analysis lends support to the possibility
that the enhancement phenomenon observed in low energy weak interactions may be
systematically described by mirror matter admixtures in ordinary hadrons.Comment: Changed conten
Learning about knowledge: A complex network approach
This article describes an approach to modeling knowledge acquisition in terms
of walks along complex networks. Each subset of knowledge is represented as a
node, and relations between such knowledge are expressed as edges. Two types of
edges are considered, corresponding to free and conditional transitions. The
latter case implies that a node can only be reached after visiting previously a
set of nodes (the required conditions). The process of knowledge acquisition
can then be simulated by considering the number of nodes visited as a single
agent moves along the network, starting from its lowest layer. It is shown that
hierarchical networks, i.e. networks composed of successive interconnected
layers, arise naturally as a consequence of compositions of the prerequisite
relationships between the nodes. In order to avoid deadlocks, i.e. unreachable
nodes, the subnetwork in each layer is assumed to be a connected component.
Several configurations of such hierarchical knowledge networks are simulated
and the performance of the moving agent quantified in terms of the percentage
of visited nodes after each movement. The Barab\'asi-Albert and random models
are considered for the layer and interconnecting subnetworks. Although all
subnetworks in each realization have the same number of nodes, several
interconnectivities, defined by the average node degree of the interconnection
networks, have been considered. Two visiting strategies are investigated:
random choice among the existing edges and preferential choice to so far
untracked edges. A series of interesting results are obtained, including the
identification of a series of plateaux of knowledge stagnation in the case of
the preferential movements strategy in presence of conditional edges.Comment: 18 pages, 19 figure
Passive and catalytic antibodies and drug delivery
Antibodies are one of the most promising components of the biotechnology repertoire for the purpose of drug delivery. On the one hand, they are proven agents for cell-selective delivery of highly toxic agents in a small but expanding number of cases. This technology calls for the covalent attachment of the cytotoxin to a tumor-specific antibody by a linkage that is reversible under appropriate conditions (antibody conjugate therapy, ACT â"passive deliveryâ). On the other hand, the linker cleavage can be accomplished by a protein catalyst attached to the tumor-specific antibody ("catalytic deliveryâ). Where the catalyst is an enzyme, this approach is known as antibody-directed enzyme prodrug therapy (ADEPT). Where the transformation is brought about by a catalytic antibody, it has been termed antibody-directed abzyme prodrug therapy (ADAPT). These approaches will be illustrated with emphasis on how their demand for new biotechnology is being realized by structure-based protein engineerin
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