148 research outputs found
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Solution of the Forward Problem in Magnetic-Field Tomography (MFT) Based on Magnetoencephalography (MEG)
This paper presents the methodology and some of the results of accurate solution of the forward problem in magnetic-field tomography based on magnetoencephalography for brain imaging. The solution is based on modeling and computation of magnetic-field distribution in and around the head produced by distributed 2-D cortical and 3-D volume lead current sources. The 3-D finite-element model of the brain incorporates realistic geometry based on accurate magnetic resonance imaging data and inhomogeneous conductivity properties. The model allows arbitrary placement of line, surface, and volume current sources. This gives flexibility in the source current approximation in terms of size, orientation, placement, and spatial distribution
Large closed queueing networks in semi-Markov environment and its application
The paper studies closed queueing networks containing a server station and
client stations. The server station is an infinite server queueing system,
and client stations are single-server queueing systems with autonomous service,
i.e. every client station serves customers (units) only at random instants
generated by a strictly stationary and ergodic sequence of random variables.
The total number of units in the network is . The expected times between
departures in client stations are . After a service completion
in the server station, a unit is transmitted to the th client station with
probability , and being processed in the th client
station, the unit returns to the server station. The network is assumed to be
in a semi-Markov environment. A semi-Markov environment is defined by a finite
or countable infinite Markov chain and by sequences of independent and
identically distributed random variables. Then the routing probabilities
and transmission rates (which are expressed via
parameters of the network) depend on a Markov state of the environment. The
paper studies the queue-length processes in client stations of this network and
is aimed to the analysis of performance measures associated with this network.
The questions risen in this paper have immediate relation to quality control of
complex telecommunication networks, and the obtained results are expected to
lead to the solutions to many practical problems of this area of research.Comment: 35 pages, 1 figure, 12pt, accepted: Acta Appl. Mat
Spherical Model in a Random Field
We investigate the properties of the Gibbs states and thermodynamic
observables of the spherical model in a random field. We show that on the
low-temperature critical line the magnetization of the model is not a
self-averaging observable, but it self-averages conditionally. We also show
that an arbitrarily weak homogeneous boundary field dominates over fluctuations
of the random field once the model transits into a ferromagnetic phase. As a
result, a homogeneous boundary field restores the conventional self-averaging
of thermodynamic observables, like the magnetization and the susceptibility. We
also investigate the effective field created at the sites of the lattice by the
random field, and show that at the critical temperature of the spherical model
the effective field undergoes a transition into a phase with long-range
correlations .Comment: 29 page
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Investigation of optimal parameters for finite element solution of the forward problem in magnetic field tomography based on magnetoencephalography
This paper presents an investigation of optimal parameters for finite element (FE) solution of the forward problem in magnetic field tomography (MFT) brain imaging based on magnetoencephalography (MEG). It highlights detailed analyses of the main parameters involved and evaluates their optimal values for various cases of FE model solutions (e.g., steady-state, transient, etc.). In each case, a detail study of some of the main parameters and their effects on FE solution and its accuracy are carefully tested and evaluated. These parameters include: total number and size of 3D FE elements used, number and size of elements used in surface discretisation (of both white and grey matters of the brain), number and size of elements used for approximation of current sources, number of anisotropic properties used in steady-state and transient solutions, and the time steps used in transient analyses. The optimal values of these parameters in relation to solution accuracy and mesh convergence criteria have been found and presented
Nonlinear spectral calculus and super-expanders
Nonlinear spectral gaps with respect to uniformly convex normed spaces are
shown to satisfy a spectral calculus inequality that establishes their decay
along Cesaro averages. Nonlinear spectral gaps of graphs are also shown to
behave sub-multiplicatively under zigzag products. These results yield a
combinatorial construction of super-expanders, i.e., a sequence of 3-regular
graphs that does not admit a coarse embedding into any uniformly convex normed
space.Comment: Typos fixed based on referee comments. Some of the results of this
paper were announced in arXiv:0910.2041. The corresponding parts of
arXiv:0910.2041 are subsumed by the current pape
Исследование ортогональности сигналов с вращением вектора поляризации
The objects of this study were the properties of time-bound electromagnetic waves (wave packets) from rotating in space vectors of polarization with a constant angular velocity. It is shown that the formal condition of function orthogonality on some interval of their argument, which is an integrated energy characteristics of their mutual influence, can be extended to a system of time-wave packets with the specified polarization characteristics. It is designed an adjustable threshold criterion level, which defines the boundaries of signals orthogonality in a two-dimensional space of frequency-difference parameters. It has been demonstrated that with an increase in the duration of these packages there is a tendency to extend the set of frequency parameters that satisfy the criteria specified level of orthogonality.Объектами данного исследования являлись свойства ограниченных во времени электромагнитных колебаний (волновых пакетов) с вращающимися в пространстве с постоянной угловой скоростью векторами поляризации. Показано, что формальное условие ортогональности функций на некотором интервале их аргумента, которое представляет собой интегральную энергетическую характеристику их взаимного влияния, может быть распространено на систему ограниченных во времени волновых пакетов с указанными поляризационными характеристиками. Разработан пороговый критерий с регулируемым уровнем, определяющим границы ортогональности таких сигналов в двумерном пространстве их частотно-разностных параметров. Продемонстрировано, что с увеличением длительности указанных пакетов наблюдается тенденция расширения множества их частотных параметров, удовлетворяющих установ-енному уровню критерия ортогональности
Protective Antigens Against Glanders Identified by Expression Library Immunization
Burkholderia are highly evolved Gram-negative bacteria that primarily infect solipeds but are transmitted to humans by ingestion and cutaneous or aerosol exposures. Heightened concern over human infections of Burkholderia mallei and the very closely related species B. pseudomallei is due to the pathogens’ proven effectiveness as bioweapons, and to the increased potential for natural opportunistic infections in the growing diabetic and immuno-compromised populations. These Burkholderia species are nearly impervious to antibiotic treatments and no vaccine exists. In this study, the genome of the highly virulent B. mallei ATCC23344 strain was examined by expression library immunization for gene-encoded protective antigens. This protocol for genomic-scale functional screening was customized to accommodate the unusually large complexity of Burkholderia, and yielded 12 new putative vaccine candidates. Five of the candidates were individually tested as protein immunogens and three were found to confer significant partial protection against a lethal pulmonary infection in a murine model of disease. Determinations of peripheral blood cytokine and chemokine profiles following individual protein immunizations show that interleukin-2 (IL-2) and IL-4 are elicited by the three confirmed candidates, but unexpectedly interferon-γ and tumor necrosis factor-α are not. We suggest that these pathogen components, discovered using genetic immunization and confirmed in a conventional protein format, will be useful toward the development of a safe and effective glanders vaccine
High-quality gene assembly directly from unpurified mixtures of microarray-synthesized oligonucleotides
To meet the growing demand for synthetic genes more robust, scalable and inexpensive gene assembly technologies must be developed. Here, we present a protocol for high-quality gene assembly directly from low-cost marginal-quality microarray-synthesized oligonucleotides. Significantly, we eliminated the time- and money-consuming oligonucleotide purification steps through the use of hybridization-based selection embedded in the assembly process. The protocol was tested on mixtures of up to 2000 oligonucleotides eluted directly from microarrays obtained from three different chip manufacturers. These mixtures containing <5% perfect oligos, and were used directly for assembly of 27 test genes of different sizes. Gene quality was assessed by sequencing, and their activity was tested in coupled in vitro transcription/translation reactions. Genes assembled from the microarray-eluted material using the new protocol matched the quality of the genes assembled from >95% pure column-synthesized oligonucleotides by the standard protocol. Both averaged only 2.7 errors/kb, and genes assembled from microarray-eluted material without clonal selection produced only 30% less protein than sequence-confirmed clones. This report represents the first demonstration of cost-efficient gene assembly from microarray-synthesized oligonucleotides. The overall cost of assembly by this method approaches 5¢ per base, making gene synthesis more affordable than traditional cloning
Induction of vacuolar invertase inhibitor mRNA in potato tubers contributes to cold-induced sweetening resistance and includes spliced hybrid mRNA variants
Cold storage of tubers of potato (Solanum tuberosum L.) compromises tuber quality in many cultivars by the accumulation of hexose sugars in a process called cold-induced sweetening. This is caused by the breakdown of starch to sucrose, which is cleaved to glucose and fructose by vacuolar acid invertase. During processing of affected tubers, the high temperatures involved in baking and frying cause the Maillard reaction between reducing sugars and free amino acids, resulting in the accumulation of acrylamide. cDNA clones with deduced proteins homologous to known invertase inhibitors were isolated and the two most abundant forms, termed INH1 and INH2, were shown to possess apoplastic and vacuolar localization, respectively. The INH2 gene showed developmentally regulated alternative splicing, so, in addition to the INH2α transcript encoding the full-length protein, two hybrid mRNAs (INH2β*A and INH2β*B) that encoded deduced vacuolar invertase inhibitors with divergent C-termini were detected, the result of mRNA splicing of an upstream region of INH2 to a downstream region of INH1. Hybrid RNAs are common in animals, where they may add to the diversity of the proteome, but are rarely described in plants. During cold storage, INH2α and the hybrid INH2β mRNAs accumulated to higher abundance in cultivars resistant to cold-induced sweetening than in susceptible cultivars. Increased amounts of invertase inhibitor may contribute to the suppression of acid invertase activity and prevent cleavage of sucrose. Evidence for increased RNA splicing activity was detected in several resistant lines, a mechanism that in some circumstances may generate a range of proteins with additional functional capacity to aid adaptability
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