573 research outputs found
Scoring schemes of palindrome clusters for more sensitive prediction of replication origins in herpesviruses
Many empirical studies show that there are unusual clusters of palindromes, closely spaced direct and inverted repeats around the replication origins of herpesviruses. In this paper, we introduce two new scoring schemes to quantify the spatial abundance of palindromes in a genomic sequence. Based on these scoring schemes, a computational method to predict the locations of replication origins is developed. When our predictions are compared with 39 known or annotated replication origins in 19 herpesviruses, close to 80% of the replication origins are located within 2% of the genome length. A list of predicted locations of replication origins in all the known herpesviruses with complete genome sequences is reported
Long-range interactions and non-extensivity in ferromagnetic spin models
The Ising model with ferromagnetic interactions that decay as is
analyzed in the non-extensive regime , where the
thermodynamic limit is not defined. In order to study the asymptotic properties
of the model in the limit ( being the number of spins)
we propose a generalization of the Curie-Weiss model, for which the
limit is well defined for all . We
conjecture that mean field theory is {\it exact} in the last model for all
. This conjecture is supported by Monte Carlo heat bath
simulations in the case. Moreover, we confirm a recently conjectured
scaling (Tsallis\cite{Tsallis}) which allows for a unification of extensive
() and non-extensive () regimes.Comment: RevTex, 12 pages, 1 eps figur
Perturbation and Variational Methods in Nonextensive Tsallis Statistics
A unified presentation of the perturbation and variational methods for the
generalized statistical mechanics based on Tsallis entropy is given here. In
the case of the variational method, the Bogoliubov inequality is generalized in
a very natural way following the Feynman proof for the usual statistical
mechanics. The inequality turns out to be form-invariant with respect to the
entropic index . The method is illustrated with a simple example in
classical mechanics. The formalisms developed here are expected to be useful in
the discussion of nonextensive systems.Comment: revte
The field theoretic derivation of the contact value theorem in planar geometries and its modification by the Casimir effect
The contact value theorem for Coulomb gases in planar or film-like geometries
is derived using a Hamiltonian field theoretic representation of the system.
The case where the film is enclosed by a material of different dielectric
constant to that of the film is shown to contain an additional Casimir-like
term which is generated by fluctuations of the electric potential about its
mean-field value.Comment: Link between Sine-Gordon and Coulomb gas pressures via subtraction of
self interaction terms included. Discussion of results within Debye-Huckel
approximation included. Added reference
Average Entropy of a Subsystem from its Average Tsallis Entropy
In the nonextensive Tsallis scenario, Page's conjecture for the average
entropy of a subsystem[Phys. Rev. Lett. {\bf 71}, 1291(1993)] as well as its
demonstration are generalized, i.e., when a pure quantum system, whose Hilbert
space dimension is , is considered, the average Tsallis entropy of an
-dimensional subsystem is obtained. This demonstration is expected to be
useful to study systems where the usual entropy does not give satisfactory
results.Comment: Revtex, 6 pages, 2 figures. To appear in Phys. Rev.
Data Mining and Machine Learning in Astronomy
We review the current state of data mining and machine learning in astronomy.
'Data Mining' can have a somewhat mixed connotation from the point of view of a
researcher in this field. If used correctly, it can be a powerful approach,
holding the potential to fully exploit the exponentially increasing amount of
available data, promising great scientific advance. However, if misused, it can
be little more than the black-box application of complex computing algorithms
that may give little physical insight, and provide questionable results. Here,
we give an overview of the entire data mining process, from data collection
through to the interpretation of results. We cover common machine learning
algorithms, such as artificial neural networks and support vector machines,
applications from a broad range of astronomy, emphasizing those where data
mining techniques directly resulted in improved science, and important current
and future directions, including probability density functions, parallel
algorithms, petascale computing, and the time domain. We conclude that, so long
as one carefully selects an appropriate algorithm, and is guided by the
astronomical problem at hand, data mining can be very much the powerful tool,
and not the questionable black box.Comment: Published in IJMPD. 61 pages, uses ws-ijmpd.cls. Several extra
figures, some minor additions to the tex
Self-gravitating Brownian particles in two dimensions: the case of N=2 particles
We study the motion of N=2 overdamped Brownian particles in gravitational
interaction in a space of dimension d=2. This is equivalent to the simplified
motion of two biological entities interacting via chemotaxis when time delay
and degradation of the chemical are ignored. This problem also bears some
similarities with the stochastic motion of two point vortices in viscous
hydrodynamics [Agullo & Verga, Phys. Rev. E, 63, 056304 (2001)]. We
analytically obtain the density probability of finding the particles at a
distance r from each other at time t. We also determine the probability that
the particles have coalesced and formed a Dirac peak at time t (i.e. the
probability that the reduced particle has reached r=0 at time t). Finally, we
investigate the variance of the distribution and discuss the proper form
of the virial theorem for this system. The reduced particle has a normal
diffusion behaviour for small times with a gravity-modified diffusion
coefficient =r_0^2+(4k_B/\xi\mu)(T-T_*)t, where k_BT_{*}=Gm_1m_2/2 is a
critical temperature, and an anomalous diffusion for large times
~t^(1-T_*/T). As a by-product, our solution also describes the growth of
the Dirac peak (condensate) that forms in the post-collapse regime of the
Smoluchowski-Poisson system (or Keller-Segel model) for T<T_c=GMm/(4k_B). We
find that the saturation of the mass of the condensate to the total mass is
algebraic in an infinite domain and exponential in a bounded domain.Comment: Revised version (20/5/2010) accepted for publication in EPJ
HAMAP: a database of completely sequenced microbial proteome sets and manually curated microbial protein families in UniProtKB/Swiss-Prot
The growth in the number of completely sequenced microbial genomes (bacterial and archaeal) has generated a need for a procedure that provides UniProtKB/Swiss-Prot-quality annotation to as many protein sequences as possible. We have devised a semi-automated system, HAMAP (High-quality Automated and Manual Annotation of microbial Proteomes), that uses manually built annotation templates for protein families to propagate annotation to all members of manually defined protein families, using very strict criteria. The HAMAP system is composed of two databases, the proteome database and the family database, and of an automatic annotation pipeline. The proteome database comprises biological and sequence information for each completely sequenced microbial proteome, and it offers several tools for CDS searches, BLAST options and retrieval of specific sets of proteins. The family database currently comprises more than 1500 manually curated protein families and their annotation templates that are used to annotate proteins that belong to one of the HAMAP families. On the HAMAP website, individual sequences as well as whole genomes can be scanned against all HAMAP families. The system provides warnings for the absence of conserved amino acid residues, unusual sequence length, etc. Thanks to the implementation of HAMAP, more than 200 000 microbial proteins have been fully annotated in UniProtKB/Swiss-Prot (HAMAP website: http://www.expasy.org/sprot/hamap)
Ventrolateral Origin of Each Cycle of Rhythmic Activity Generated by the Spinal Cord of the Chick Embryo
BACKGROUND: The mechanisms responsible for generating rhythmic motor activity in the developing spinal cord of the chick embryo are poorly understood. Here we investigate whether the activity of motoneurons occurs before other neuronal populations at the beginning of each cycle of rhythmic discharge. METHODOLOGY/PRINCIPAL FINDINGS: The spatiotemporal organization of neural activity in transverse slices of the lumbosacral cord of the chick embryo (E8-E11) was investigated using intrinsic and voltage-sensitive dye (VSD) imaging. VSD signals accompanying episodes of activity comprised a rhythmic decrease in light transmission that corresponded to each cycle of electrical activity recorded from the ipsilateral ventral root. The rhythmic signals were widely synchronized across the cord face, and the largest signal amplitude was in the ventrolateral region where motoneurons are located. In unstained slices we recorded two classes of intrinsic signal. In the first, an episode of rhythmic activity was accompanied by a slow decrease in light transmission that peaked in the dorsal horn and decayed dorsoventrally. Superimposed on this signal was a much smaller rhythmic increase in transmission that was coincident with each cycle of discharge and whose amplitude and spatial distribution was similar to that of the VSD signals. At the onset of a spontaneously occurring episode and each subsequent cycle, both the intrinsic and VSD signals originated within the lateral motor column and spread medially and then dorsally. By contrast, following a dorsal root stimulus, the optical signals originated within the dorsal horn and traveled ventrally to reach the lateral motor column. CONCLUSIONS/SIGNIFICANCE: These findings suggest that motoneuron activity contributes to the initiation of each cycle of rhythmic activity, and that motoneuron and/or R-interneuron synapses are a plausible site for the activity-dependent synaptic depression that modeling studies have identified as a critical mechanism for cycling within an episode
- …