3,521 research outputs found
On the structure of non-full-rank perfect codes
The Krotov combining construction of perfect 1-error-correcting binary codes
from 2000 and a theorem of Heden saying that every non-full-rank perfect
1-error-correcting binary code can be constructed by this combining
construction is generalized to the -ary case. Simply, every non-full-rank
perfect code is the union of a well-defined family of -components
, where belongs to an "outer" perfect code , and these
components are at distance three from each other. Components from distinct
codes can thus freely be combined to obtain new perfect codes. The Phelps
general product construction of perfect binary code from 1984 is generalized to
obtain -components, and new lower bounds on the number of perfect
1-error-correcting -ary codes are presented.Comment: 8 page
Dirac fermions in a power-law-correlated random vector potential
We study localization properties of two-dimensional Dirac fermions subject to
a power-law-correlated random vector potential describing, e.g., the effect of
"ripples" in graphene. By using a variety of techniques (low-order perturbation
theory, self-consistent Born approximation, replicas, and supersymmetry) we
make a case for a possible complete localization of all the electronic states
and compute the density of states.Comment: Latex, 4+ page
A Computational Approach to Multistationarity of Power-Law Kinetic Systems
This paper presents a computational solution to determine if a chemical
reaction network endowed with power-law kinetics (PLK system) has the capacity
for multistationarity, i.e., whether there exist positive rate constants such
that the corresponding differential equations admit multiple positive steady
states within a stoichiometric class. The approach, which is called the
"Multistationarity Algorithm for PLK systems" (MSA), combines (i) the extension
of the "higher deficiency algorithm" of Ji and Feinberg for mass action to PLK
systems with reactant-determined interactions, and (ii) a method that
transforms any PLK system to a dynamically equivalent one with
reactant-determined interactions. Using this algorithm, we obtain two new
results: the monostationarity of a popular model of anaerobic yeast
fermentation pathway, and the multistationarity of a global carbon cycle model
with climate engineering, both in the generalized mass action format of
biochemical systems theory. We also provide examples of the broader scope of
our approach for deficiency one PLK systems in comparison to the extension of
Feinberg's "deficiency one algorithm" to such systems
Quartz Cherenkov Counters for Fast Timing: QUARTIC
We have developed particle detectors based on fused silica (quartz) Cherenkov
radiators read out with micro-channel plate photomultipliers (MCP-PMTs) or
silicon photomultipliers (SiPMs) for high precision timing (Sigma(t) about
10-15 ps). One application is to measure the times of small angle protons from
exclusive reactions, e.g. p + p - p + H + p, at the Large Hadron Collider, LHC.
They may also be used to measure directional particle fluxes close to external
or stored beams. The detectors have small areas (square cm), but need to be
active very close (a few mm) to the intense LHC beam, and so must be radiation
hard and nearly edgeless. We present results of tests of detectors with quartz
bars inclined at the Cherenkov angle, and with bars in the form of an "L" (with
a 90 degree corner). We also describe a possible design for a fast timing
hodoscope with elements of a few square mm.Comment: 24 pages, 14 figure
Statistical properties of contact vectors
We study the statistical properties of contact vectors, a construct to
characterize a protein's structure. The contact vector of an N-residue protein
is a list of N integers n_i, representing the number of residues in contact
with residue i. We study analytically (at mean-field level) and numerically the
amount of structural information contained in a contact vector. Analytical
calculations reveal that a large variance in the contact numbers reduces the
degeneracy of the mapping between contact vectors and structures. Exact
enumeration for lengths up to N=16 on the three dimensional cubic lattice
indicates that the growth rate of number of contact vectors as a function of N
is only 3% less than that for contact maps. In particular, for compact
structures we present numerical evidence that, practically, each contact vector
corresponds to only a handful of structures. We discuss how this information
can be used for better structure prediction.Comment: 20 pages, 6 figure
Extremal dynamics model on evolving networks
We investigate an extremal dynamics model of evolution with a variable number
of units. Due to addition and removal of the units, the topology of the network
evolves and the network splits into several clusters. The activity is mostly
concentrated in the largest cluster. The time dependence of the number of units
exhibits intermittent structure. The self-organized criticality is manifested
by a power-law distribution of forward avalanches, but two regimes with
distinct exponents tau = 1.98 +- 0.04 and tau^prime = 1.65 +- 0.05 are found.
The distribution of extinction sizes obeys a power law with exponent 2.32 +-
0.05.Comment: 4 pages, 5 figure
Shortest paths and load scaling in scale-free trees
The average node-to-node distance of scale-free graphs depends
logarithmically on N, the number of nodes, while the probability distribution
function (pdf) of the distances may take various forms. Here we analyze these
by considering mean-field arguments and by mapping the m=1 case of the
Barabasi-Albert model into a tree with a depth-dependent branching ratio. This
shows the origins of the average distance scaling and allows a demonstration of
why the distribution approaches a Gaussian in the limit of N large. The load
(betweenness), the number of shortest distance paths passing through any node,
is discussed in the tree presentation.Comment: 8 pages, 8 figures; v2: load calculations extende
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