8,675 research outputs found
Optimal Computation of Avoided Words
The deviation of the observed frequency of a word from its expected
frequency in a given sequence is used to determine whether or not the word
is avoided. This concept is particularly useful in DNA linguistic analysis. The
value of the standard deviation of , denoted by , effectively
characterises the extent of a word by its edge contrast in the context in which
it occurs. A word of length is a -avoided word in if
, for a given threshold . Notice that such a word
may be completely absent from . Hence computing all such words na\"{\i}vely
can be a very time-consuming procedure, in particular for large . In this
article, we propose an -time and -space algorithm to compute all
-avoided words of length in a given sequence of length over a
fixed-sized alphabet. We also present a time-optimal -time and
-space algorithm to compute all -avoided words (of any
length) in a sequence of length over an alphabet of size .
Furthermore, we provide a tight asymptotic upper bound for the number of
-avoided words and the expected length of the longest one. We make
available an open-source implementation of our algorithm. Experimental results,
using both real and synthetic data, show the efficiency of our implementation
Kinematic Effects of Tidal Interaction on Galaxy Rotation Curves
We use self-consistent N-body models, in conjunction with models of test
particles moving in galaxy potentials, to explore the initial effects of
interactions on the rotation curves of spiral galaxies. Using nearly
self-consistent disk/bulge/halo galaxy models (Kuijken & Dubinski 1995), we
simulate the first pass of galaxies on nearly parabolic orbits; we vary orbit
inclinations, galaxy halo masses and impact parameters. For each simulation, we
mimic observed rotation curves of the model galaxies. Transient
interaction-induced features of the curves include distinctly rising or falling
profiles at large radii and pronounced bumps in the central regions. Remarkably
similar features occur in our statistical sample of optical emission-line
rotation curves of spiral galaxies in tight pairs and n-tuples.Comment: 9 pages, 2 figures, accepted for publication in ApJ Letter
Non-linear electromagnetic interactions in thermal QED
We examine the behavior of the non-linear interactions between
electromagnetic fields at high temperature. It is shown that, in general, the
log(T) dependence on the temperature of the Green functions is simply related
to their UV behavior at zero-temperature. We argue that the effective action
describing the nonlinear thermal electromagnetic interactions has a finite
limit as T tends to infinity. This thermal action approaches, in the long
wavelength limit, the negative of the corresponding zero-temperature action.Comment: 7 pages, IFUSP/P-111
Hydrodynamic theory of an electron gas
The generalised hydrodynamic theory of an electron gas, which does not rely
on an assumption of a local equilibrium, is derived as the long-wave limit of a
kinetic equation. Apart from the common hydrodynamics variables the theory
includes the tensor fields of the higher moments of the distribution function.
In contrast to the Bloch hydrodynamics, the theory leads to the correct plasmon
dispersion and in the low frequency limit recovers the Navies-Stocks
hydrodynamics. The linear approximation to the generalised hydrodynamics is
closely related to the theory of highly viscous fluids.Comment: 4 pages, revte
The structure of the graviton self-energy at finite temperature
We study the graviton self-energy function in a general gauge, using a hard
thermal loop expansion which includes terms proportional to T^4, T^2 and
log(T). We verify explicitly the gauge independence of the leading T^4 term and
obtain a compact expression for the sub-leading T^2 contribution. It is shown
that the logarithmic term has the same structure as the ultraviolet pole part
of the T=0 self-energy function. We argue that the gauge-dependent part of the
T^2 contribution is effectively canceled in the dispersion relations of the
graviton plasma, and present the solutions of these equations.Comment: 27 pages, 6 figure
HLA-A and -B alleles and haplotypes in 240 index patients with common variable immunodeficiency and selective IgG subclass deficiency in central Alabama
BACKGROUND: We wanted to quantify HLA-A and -B phenotype and haplotype frequencies in Alabama index patients with common variable immunodeficiency (CVID) and selective IgG subclass deficiency (IgGSD), and in control subjects. METHODS: Phenotypes were detected using DNA-based typing (index cases) and microlymphocytotoxicity typing (controls). RESULTS: A and B phenotypes were determined in 240 index cases (114 CVID, 126 IgGSD) and 1,321 controls and haplotypes in 195 index cases and 751 controls. Phenotyping revealed that the "uncorrected" frequencies of A*24, B*14, B*15, B*35, B*40, B*49, and B*50 were significantly greater in index cases, and frequencies of B*35, B*58, B*62 were significantly lower in index cases. After Bonferroni corrections, the frequencies of phenotypes A*24, B*14, and B*40 were significantly greater in index cases, and the frequency of B*62 was significantly lower in index cases. The most common haplotypes in index cases were A*02-B*44 (frequency 0.1385), A*01-B*08 (frequency 0.1308), and A*03-B*07 (frequency 0.1000), and the frequency of each was significantly greater in index cases than in control subjects ("uncorrected" values of p < 0.0001, 0.0252, and 0.0011, respectively). After performing Bonferroni corrections, however, the frequency of A*02-B*44 alone was significantly increased in probands (p < 0.0085). Three other haplotypes were also significantly more frequent in index cases (A*03-B*14, A*31-B*40, and A*32-B*14). The combined frequencies of three latter haplotypes in index patients and control subjects were 0.0411 and 0.0126, respectively ("uncorrected" value of p < 0.0002; "corrected" value of p = 0.0166). Most phenotype and haplotype frequencies in CVID and IgGSD were similar. 26.7% of index patients were HLA-haploidentical with one or more other index patients. We diagnosed CVID or IgGSD in first-degree or other relatives of 26 of 195 index patients for whom HLA-A and -B haplotypes had been ascertained; A*01-B*08, A*02-B*44, and A*29-B*44 were most frequently associated with CVID or IgGSD in these families. We conservatively estimated the combined population frequency of CVID and IgGSD to be 0.0092 in adults, based on the occurrence of CVID and IgGSD in spouses of the index cases. CONCLUSIONS: CVID and IgGSD in adults are significantly associated with several HLA haplotypes, many of which are also common in the Alabama Caucasian population. Immunoglobulin phenotype variability demonstrated in index cases and family studies herein suggests that there are multiple gene(s) on Ch6p or other chromosomes that modify immunoglobulin phenotypes of CVID and IgGSD. The estimated prevalence of CVID and IgGSD in central Alabama could be reasonably attributed to the fact that many HLA haplotypes significantly associated with these disorders are also common in the general population
Equation of motion and subsonic-transonic transitions of rectilinear edge dislocations: A collective-variable approach
A theoretical framework is proposed to derive a dynamic equation motion for
rectilinear dislocations within isotropic continuum elastodynamics. The theory
relies on a recent dynamic extension of the Peierls-Nabarro equation, so as to
account for core-width generalized stacking-fault energy effects. The degrees
of freedom of the solution of the latter equation are reduced by means of the
collective-variable method, well known in soliton theory, which we reformulate
in a way suitable to the problem at hand. Through these means, two coupled
governing equations for the dislocation position and core width are obtained,
which are combined into one single complex-valued equation of motion, of
compact form. The latter equation embodies the history dependence of
dislocation inertia. It is employed to investigate the motion of an edge
dislocation under uniform time-dependent loading, with focus on the
subsonic/transonic transition. Except in the steady-state supersonic range of
velocities---which the equation does not address---our results are in good
agreement with atomistic simulations on tungsten. In particular, we provide an
explanation for the transition, showing that it is governed by a
loading-dependent dynamic critical stress. The transition has the character of
a delayed bifurcation. Moreover, various quantitative predictions are made,
that could be tested in atomistic simulations. Overall, this work demonstrates
the crucial role played by core-width variations in dynamic dislocation motion.Comment: v1: 11 pages, 4 figures. v2: title changed, extensive rewriting, and
new material added; 19 pages, 12 figures (content as published
Improvements to the Method of Dispersion Relations for B Nonleptonic Decays
We bring some clarifications and improvements to the method of dispersion
relations in the external masses variables, that we proposed recently for
investigating the final state interactions in the B nonleptonic decays. We
first present arguments for the existence of an additional term in the
dispersion representation, which arises from an equal-time commutator in the
LSZ formalism and can be approximated by the conventional factorized amplitude.
The reality properties of the spectral function and the Goldberger-Treiman
procedure to perform the hadronic unitarity sum are analyzed in more detail. We
also improve the treatment of the strong interaction part by including the
contributions of both t and u-channel trajectories in the Regge amplitudes.
Applications to the and decays are
presented.Comment: 16 pages, 4 new figures. modifications of the dispersion
representatio
Generalized forward scattering amplitudes in QCD at high temperature
We extend to a general class of covariant gauges an approach which relates
the thermal Green functions to forward scattering amplitudes of thermal
particles. A brief discussion of the non-transversality of the thermal gluon
polarization tensor is given in this context. This method is then applied to
the calculation of the ln(T) contributions associated with general
configurations of 2 and 3-point gluon functions. The results are Lorentz
covariant and have the same structure as the ultraviolet divergent
contributions which occur at zero temperature.Comment: 10 pages, 3 figure
TarO : a target optimisation system for structural biology
This work was funded by the UK Biotechnology and Biological Sciences Research Council (BBSRC) Structural Proteomics of Rational Targets (SPoRT) initiative, (Grant BBS/B/14434). Funding to pay the Open Access publication charges for this article was provided by BBSRC.TarO (http://www.compbio.dundee.ac.uk/taro) offers a single point of reference for key bioinformatics analyses relevant to selecting proteins or domains for study by structural biology techniques. The protein sequence is analysed by 17 algorithms and compared to 8 databases. TarO gathers putative homologues, including orthologues, and then obtains predictions of properties for these sequences including crystallisation propensity, protein disorder and post-translational modifications. Analyses are run on a high-performance computing cluster, the results integrated, stored in a database and accessed through a web-based user interface. Output is in tabulated format and in the form of an annotated multiple sequence alignment (MSA) that may be edited interactively in the program Jalview. TarO also simplifies the gathering of additional annotations via the Distributed Annotation System, both from the MSA in Jalview and through links to Dasty2. Routes to other information gateways are included, for example to relevant pages from UniProt, COG and the Conserved Domains Database. Open access to TarO is available from a guest account with private accounts for academic use available on request. Future development of TarO will include further analysis steps and integration with the Protein Information Management System (PIMS), a sister project in the BBSRC Structural Proteomics of Rational Targets initiative.Publisher PDFPeer reviewe
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