Tag length [at least 200 articles]

Abstract

A Monte Carlo technique is employed to simulate the electron transport in SiO<SUB>2</SUB> at high electric fields (from 1.5×10<SUP>6</SUP> to 12×10<SUP>6</SUP> V/cm). Both the polar and the nonpolar electron-phonon scattering processes are considered. We show that the nonpolar interaction with the acoustic and band-edge phonons is a mechanism which must be included in order to explain the experimental evidence of a steady-state electron-transport regime at high average electron energy (~=3-4 eV) at these high fields. The LO phonons alone cannot prevent the electrons from running away at fields above 2×10<SUP>6</SUP> ...

Abstract

The absorption spectra, the pulse and current quantum yield spectra of electron emission and the energy distributions of emitted electrons for the XUV-induced electron emission of NaCl and KBr have been measured. The values of the mean electron escape depth, 43 nm for NaCl and 34 nm for KBr, have been established. In order to understand the role of various elementary processes, particularly of the electron-phonon scattering, an attempt is made to reproduce the main regularities of the experimental spectra by ...

Abstract

Collagen is most abundant in animal tissues as very long fibrils with a characteristic axial periodic structure. The fibrils provide the major biomechanical scaffold for cell attachment and anchorage of macromolecules, allowing the shape and form of tissues to be defined and maintained. How the fibrils are formed from their monomeric precursors is the primary concern of this review. Collagen fibril formation is basically a self-assembly process (i.e. one which is to a large extent determined by the intrinsic properties of ...

Abstract

The principle of parsimony also known as "Ockham's razor" has inspired many theories of model selection. Yet such theories, all making arguments in favor of parsimony, are based on very different premises and have developed distinct methodologies to derive algorithms. We have organized challenges and edited a special issue of JMLR and several conference proceedings around the theme of model selection. In this editorial, we revisit the problem of avoiding overfitting in light of the latest results. We note the remarkable ...

Abstract

BACKGROUND:It has been reported that potentiation of a skeletal muscle twitch response is proportional to muscle length with a negative slope during staircase, and a positive slope during posttetanic potentiation. This study was done to directly compare staircase and posttetanic responses with measurement of sarcomere length to compare their length-dependence.METHODS:Mouse extensor digitorum longus (EDL) muscles were dissected to small bundles of fibers, which permit measurement of sarcomere length (SL), by laser diffraction. In vitro fixed-end contractions of EDL fiber bundles were ...

Abstract

Laser-plasma wakefield-based electron accelerators are expected to deliver ultrashort electron bunches with unprecedented peak currents. However, their actual pulse duration has never been directly measured in a single-shot experiment. We present measurements of the ultrashort duration of such electron bunches by means of THz time-domain interferometry. With data obtained using a 0.5 J, 45 fs, 800 nm laser and a ZnTe-based electro-optical setup, we demonstrate the duration of laser-accelerated, quasimonoenergetic electron bunches [best fit of 32 fs (FWHM) with a 90% upper confidence level of ...

Abstract

An important function of microtubules is to move cellular structures such as chromosomes, mitotic spindles and other organelles around inside cells. This is achieved by attaching the ends of microtubules to cellular structures; as the microtubules grow and shrink, the structures are pushed or pulled around the cell. How do the ends of microtubules couple to cellular structures, and how does this coupling regulate the stability and distribution of the microtubules? It is now clear that there are at least three ...

Abstract

Gliding microtubules (MTs) on a surface coated with kinesin biomolecular motors have been suggested for the development of nanoscale transport systems. In order to establish a sorting function for gliding MTs, events for MTs approaching micro-scale grooves were investigated. MTs longer than the width of grooves fabricated on a Si substrate bridged the grooves (bridging) and many MTs shorter than the groove width almost began to bridge, but returned to the surface that they approached from (guiding). Occurrence probabilities for the ...

Abstract

PMID: 16218708 We report on a novel approach for the size-dependent fractionation of protein assemblies on polymeric surfaces. Using a simple temperature gradient method to generate one-dimensional gradients of grafted poly(ethylene glycol), we fabricated silicon-oxide chips with a gradually changing surface density of kinesin motor molecules. We demonstrate that such a bioactive surface can be used to sort gliding microtubules according to their length. To our knowledge, this is the first example of the self-organized sorting of protein assemblies on surfaces. ...

Abstract

The microtubule cytoskeleton and the mitotic spindle are highly dynamic structures1, yet their sizes are remarkably constant, thus indicating that the growth and shrinkage of their constituent microtubules are finely balanced2, 3. This balance is achieved, in part, through kinesin-8 proteins (such as Kip3p in budding yeast and KLP67A in Drosophila) that destabilize microtubules3, 4, 5, 6, 7, 8. Here, we directly demonstrate that Kip3p destabilizes microtubules by depolymerizing them — accounting for the effects of kinesin-8 perturbations on microtubule and ...

Abstract

Pseudogenes arise from the decay of gene copies following either RNA-mediated duplication (processed pseudogenes) or DNA-mediated duplication (nonprocessed pseudogenes). Here, we show that long protein-coding genes tend to produce more nonprocessed pseudogenes than short genes, whereas the opposite is true for processed pseudogenes. Protein-coding genes longer than 3000 bp are 6 times more likely to produce nonprocessed pseudogenes than processed ones.REVIEWERS:This article was reviewed by Dr. Dan Graur and Dr. Craig Nelson (nominated by Dr. J Peter Gogarten). ...

Abstract

Increased interest in semisolid metal processing during the recent years has created the need for accurate evaluation of the effects of processing parameters on the microstructure of primary features formed in semisolid metal slurries. This paper reports the effects of initial solid fraction and stirring speed on the microstructure of a rheo-centrifuged cast Al–7.1 wt%Si alloy. Results showed that size of the primary features increased by increasing the solid fraction or decreasing the stirring speed. Moreover roundness of primary granules increased with ...

Abstract

Lower fluidity of semisolid metallic slurries considerably limits their mold filling ability in rheocasting processes. In this paper, rheo-centrifuged casting (RCC) process was introduced and its performance was evaluated in terms of casting fluidity. Slurries were continuously cooled and stirred until reaching the desired fraction liquids up on which they were poured into a rotating sand mold. It was found that fluidity of Al–7.1 wt% Si semisolid slurry increased approximately linearly with the square of the initial fraction liquid. Casting fluidity also ...

Abstract

Quenching of the fluorescence of Trp residues in a membrane protein by lipids with bromine-containing fatty acyl chains provides a powerful technique for measuring lipid-protein binding constants. Single Trp residues have been placed on the periplasmic and cytoplasmic sides of the mechanosensitive channel of large conductance MscL from Mycobacterium tuberculosis to measure, separately, lipid binding constants on the two faces of MscL. The chain-length dependence of lipid binding was found to be different on the two sides of MscL, the chain-length ...

Abstract

We report a theoretical calculation of the elasticity of the peptidoglycan network, the only stress-bearing part of rod-shaped Gram-negative eubacteria. The peptidoglycan network consists of elastic peptides and inextensible glycan strands, and it has been proposed that the latter form zigzag filaments along the circumference of the cylindrical bacterial shell. The zigzag geometry of the glycan strands gives rise to nonlinear elastic behavior. The four elastic moduli of the peptidoglycan network depend on its stressed state. For a bacterium under physiological ...

Abstract

Gram-negative micro-organisms possess only a very thin murein sacculus to resist the stress caused by the internal hydrostatic pressure. The sacculus consists of at most one molecular layer of peptidoglycan in an extended conformation. It must grow by the insertion and cross-linking of new murein to the old before the selective cleavages of the stress-bearing murein are made which allow wall enlargement. Since insertion of new murein occurs all over the surface of Escherichia coli (even in completed poles), the internal ...

Abstract

The introduction of disulfide bonds into proteins creates additional mechanical barriers and limits the unfolded contour length (i.e., the maximal extension) measured by single-molecule force spectroscopy. Here, we engineer single disulfide bonds into four different locations of the human cardiac titin module (I27) to control the contour length while keeping the distance to the transition state unchanged. This enables the study of several biologically important parameters. First, we are able to precisely determine the end-to-end length of the transition state before ...

Abstract

In this study Year 1 students in a new, primary care-oriented undergraduate course were offered a practice multiple-choice question (MCQ) examination with two question item formats - with and without brief primary care-based clinical scenarios - with the same correct answers. Data collected included: completion time; number correct; and responses to a questionnaire seeking student perception on the time required, clarity, ease of choice, and curriculum relevance.The mean scores for both groups of students were no different, although about 20% more ...

Abstract

Motor proteins in the kinesin-8 family depolymerize microtubules in a length-dependent manner that may be crucial for controlling the length of organelles such as the mitotic spindle. We used single-molecule microscopy to understand the mechanism of length-dependent depolymerization by the budding yeast kinesin-8, Kip3p. We found that after binding at a random position on a microtubule and walking to the plus end, an individual Kip3p molecule pauses there until an incoming Kip3p molecule bumps it off. Kip3p dissociation is accompanied by removal ...

Abstract

This paper describes a new hybrid term extraction technique for technical corpora. Our main goal is to reduce the amount of noise in the list of candidate terms by restricting the lexical items that can appear inside candidate terms. In order to do so, we base our term extraction process on lexical items selected by a statistical test that targets items that are highly specific to the technical corpus being analyzed. ...

Abstract

INTRODUCTION: Class III growth in white subjects is poorly characterized because of the low prevalence of the disharmony and the clinical tendency to treat this condition early. The purpose of this study was to investigate craniofacial growth changes by using longitudinal cephalometric records of white subjects with untreated Class III malocclusions to provide comparison data for studies of Class III treatment outcomes. METHODS: Longitudinal records of 103 subjects were analyzed. Annual incremental growth changes in craniofacial variables from early childhood to ...

Abstract

It is known that ceramides can influence the lateral organization in biological membranes. In particular ceramides have been shown to alter the composition of cholesterol and sphingolipid enriched nanoscopic domains, by displacing cholesterol, and forming gel phase domains with sphingomyelin. Here we have investigated how the bilayer content of ceramides and their chain length influence sterol partitioning into the membranes. The effect of ceramides with saturated chains ranging from 4 to 24 carbons in length was investigated. In addition, unsaturated 18:1- ...

Abstract

We analyse query length, and fit power-law and Poisson distributions to four different query sets. We provide a practical model for query length, based on the truncation of a Poisson distribution for short queries and a power-law distribution for longer queries, that better fits real query length distributions than earlier proposals. ...

Abstract

10.1101/gr.2450504 We propose a method for estimating the evolutionary distance between DNA sequences in terms of insertions and deletions (indels), defined as the per site number of indels accumulated in the course of divergence of the two sequences. We derive a maximal likelihood estimate of this distance from differences between lengths of orthologous introns or other segments of sequences delimited by conservative markers. When indels accumulate, lengths of orthologous introns diverge only slightly slower than linearly, because long indels occur with ...

Abstract

10.1073/pnas.0508489102 The exon/intron architecture of genes determines whether components of the spliceosome recognize splice sites across the intron or across the exon. Using splicing assays, we demonstrate that splice-site recognition across introns ceases when intron size is between 200 and 250 nucleotides. Beyond this threshold, splice sites are recognized across the exon. Splice-site recognition across the intron is significantly more efficient than splice-site recognition across the exon, resulting in enhanced inclusion of exons with weak splice sites. Thus, intron size ...

Abstract

10.1261/rna.1024908 Recent studies report that alternatively spliced exons tend to occur in longer introns, which is attributed to the length constraints for splice site pairing for the two major splicing mechanisms, intron definition versus exon definition. Using genome-wide studies of EST and microarray data from human and mouse, we have analyzed the distribution of various subsets of alternatively spliced exons, based on their inclusion level and evolutionary history, versus increasing intron length. Alternative exons may be included in either a major ...

Abstract

Abstract  Enhanced backward-acceleration of ions is experimentally observed when ultra-short, high-intensity and ultra-high-contrast laser pulses interact with thin foils having thicknesses in the order of the penetration depth of the laser light. Below the experimentally observed optimum foil thickness for the maximum ion energy versus thickness, there arises a second peak. 1D simulations on foils with an initial plasma density gradient show a similar trend as the experiment. It appears that in this regime of extremely thin foils it is important to ...

Abstract

A common representation used in text categorization is the bag of words model (aka. unigram model). Learning with this particular representation involves typically some preprocessing, e.g. stopwords-removal, stemming. This results in one explicit tokenization of the corpus. In this work, we introduce a logistic regression approach where learning involves automatic tokenization. This allows us to weaken the a-priori required knowledge about the corpus and results in a tokenization with variable-length (word or character) n-grams as basic tokens. We accomplish ...

Abstract

Automatic authorship identification offers a valuable tool for supporting crime investigation and security. It can be seen as a multi-class, single-label text categorization task. Character n-grams are a very successful approach to represent text for stylistic purposes since they are able to capture nuances in lexical, syntactical, and structural level. So far, character n-grams of fixed length have been used for authorship identification. In this paper, we propose a variable-length n-gram approach inspired by previous work for selecting variable-length word sequences. ...

Abstract

The presence of an axial magnetic field in a laser beat wave accelerator enhances the oscillatory velocity of electrons due to cyclotron resonance effect leading to higher amplitude of the ponderomotive force driven plasma wave, and higher energy of accelerating electrons. The axial magnetic field inhibits the transverse escape of electrons and thus causes a growth of the interaction length. The surfatron acceleration of electrons also shows a similar enhancement. A surfatron transverse magnetic field deflects the electrons parallel to the ...

Abstract

10.1073/pnas.0603931103 Microtubules are hollow cylindrical structures that constitute one of the three major classes of cytoskeletal filaments. On the mesoscopic length scale of a cell, their material properties are characterized by a single stiffness parameter, the persistence length ℓ. Its value, in general, depends on the microscopic interactions between the constituent tubulin dimers and the architecture of the microtubule. Here, we use single-particle tracking methods combined with a fluctuation analysis to systematically study the dependence of ℓ on the total filament ...

Abstract

A templated catalytic etching process has been developed to fabricate large-area arrays of silicon nanowires with controlled diameter, length, and density. The figure shows an example of an array constructed by this technique. Etched polystyrene spheres are used as templates to define the lateral dimensions of the array, whereas the length of the nanowires is defined by the duration of the etching process. ...

Abstract

1. The calcium-sensitive photoprotein aequorin was micro-injected into cells of rat and cat ventricular muscles. The resulting light emission is a function of intracellular free calcium concentration ([Ca2+]i). The transient increases in [Ca2+]i that accompany contraction were monitored. 2. After an increase in muscle length, the developed tension increased immediately and then showed a slow increase over a period of minutes. The peak [Ca2+]i in each contraction was initially unchanged after an increase in muscle length but then showed a slow ...

Abstract

Compact tuneable sources of ultrashort hard x-ray pulses can be realized by Thomson scattering, taking advantage of the comparatively short wavelength of a scattered laser pulse with respect to the period length of conventional undulators. Here, we present a detailed analysis and optimization of the efficiency of linear and non-linear Thomson scattering when the process is driven with relativistic laser pulses and when the conventional accelerator is replaced by a laser-plasma wakefield accelerator. ...

Abstract

Cellular motility is mediated by protein motors such as myosin; dynein; and kinesin. We propose a simple but substantial extension of the statistical dynamical model by A. F. Huxley; in which we incorporate the spatial nonlocality of the cytoskeletal filaments translocated by protein motors. This model reveals the existence of the filament-length dependent temporal correlation in the translocation process; and is also in close agreement with recent in vitro experiments by K. Tawada; Y. Imafuku; and Y. Y. Toyoshima ...

Abstract

10.1073/pnas.0704169105 The mechanics of microtubules, cylindrical protein filaments that constitute the cytoskeleton, have been well characterized on long length scales. Here, we investigate the persistence length of short (≈0.1 μm) ends of microtubules by measuring the trajectories of kinesin-propelled microtubules under perpendicular electric forces. We relate the measured trajectory curvatures to the biased thermal fluctuations of the leading microtubule end, and upon including all electrohydrodynamic forces, we find that the persistence length of the microtubule ends is only 0.08 ± 0.02 ...

Abstract

PMID: 17887718 We present a simple method to determine the persistence length of short submicrometer microtubule ends from their stochastic trajectories on kinesin-coated surfaces. The tangent angle of a microtubule trajectory is similar to a random walk, which is solely determined by the stiffness of the leading tip and the velocity of the microtubule. We demonstrate that even a single-microtubule trajectory suffices to obtain a reliable value of the persistence length. We do this by calculating the variance in the tangent ...

Abstract

BACKGROUND:Several recent studies have demonstrated the effectiveness of deep sequencing for transcriptome analysis (RNA-seq) in mammals. As RNA-seq becomes more affordable, whole genome transcriptional profiling is likely to become the platform of choice for species with good genomic sequences. As yet, a rigorous analysis methodology has not been developed and we are still in the stages of exploring the features of the data.RESULTS:We investigated the effect of transcript length bias in RNA-seq data using three different published data sets. For standard ...

Abstract

Alkyl betaines and alkyl dimethylamine oxides have been shown to have pronounced antimicrobial activity when used individually or in combination. Although several studies have been conducted with these compounds in combinations, only equimolar concentrations of the C(12)/C(12) and C(16)/C(14) chain lengths for the betaine and the amine oxide, respectively, have been investigated. This study investigates the antimicrobial activity of a wide range of chain lengths (C(8) to C(18)) for both the betaine and amine oxide and attempts to correlate their micelle-forming ...

Abstract

We investigate tag and query logs to see if the terms people use to annotate websites are similar to the ones they use to query for them. Over a set of URLs, we compare the distribution of tags used to annotate each URL with the distribution of query terms for clicks on the same URL. Understanding the relationship between the distributions is important to determine how useful tag data may be for improving search results and conversely, query data for improving ...

Abstract

In this paper we study the lengths of the routes in ad hoc networks. We propose a simplified theoretical model having as objective to estimate the path length for the routing protocols that are using flooding during their path discovery phase. We show how to evaluate the average gain in the hop number that one can obtain by using a simple reduction strategy. We prove the gain to be linear under very general conditions and show how it can be computed ...

Abstract

Experimental results are reported from two measurement techniques (semiconductor switching and electro-optic sampling) that allow temporal characterization of electron bunches produced by a laser-driven plasma-based accelerator. As femtosecond electron bunches exit the plasma-vacuum interface, coherent transition radiation (at THz frequencies) is emitted. Measuring the properties of this radiation allows characterization of the electron bunches. Theoretical work on the emission mechanism is presented, including a model that calculates the THz wave form from a given bunch profile. It is found that the ...

Abstract

Recently, the genus Salmonella has been studied by multilocus enzyme electrophoresis (MLEE) and three collections of strains defined by this method, SARA, SARB and SARC, have been assembled to represent the genetic diversity of Salmonella choleraesuis (commonly known as Salmonella enterica) subspecies I and of the genus as a whole. The novel technique fluorescent amplified-fragment length polymorphism (FAFLP) analysis was applied to these collections to determine the genetic diversity of Salmonella. FAFLP broadly confirmed the MLEE findings but added precision to ...

Abstract

Meralgia paresthetica consists of pain and dysthesia in the lateral thigh caused by entrapment of the lateral femoral cutaneous nerve (L2-L3) underneath the inguinal ligament. Abdominal distension, tight clothing, and hip hyperextension are all described causes of this condition. To our knowledge this has never been attributed to a limb length discrepancy. We present a 51-year-old man with a long-standing history of right sided meralgia paresthetica. History and physical and radiological examination were unrewarding except that his left leg was shorter ...

Abstract

The trinucleotide repeats that expand to cause human disease form hairpin structures in vitro that are proposed to be the major source of their genetic instability in vivo. If a replication fork is a train speeding along a track of double-stranded DNA, the trinucleotide repeats are a hairpin curve in the track. Experiments have demonstrated that the train can become derailed at the hairpin curve, resulting in significant damage to the track. Repair of the track often results in contractions and ...

Abstract

Eukaryotic genomes are mostly composed of noncoding DNA whose role is still poorly understood. Studies in several organisms have shown correlations between the length of the intergenic and genic sequences of a gene and the expression of its corresponding mRNA transcript. Some studies have found a positive relationship between intergenic sequence length and expression diversity between tissues, and concluded that genes under greater regulatory control require more regulatory information in their intergenic sequences. Other reports found a negative relationship between expression ...