Dynamic Response of Gradient Foams

The Voronoi-type density-gradient foams with three layers are numerically simulated, in order to study their dynamic response. The focus of the study is not only on the energy absorption and the distal stress of the gradient foam, but also the impact stress. The results obtained show that reduction of both the initial impact peak stress, and the early energy absorption of the gradient foam can be privided by reducing density of the first layer. The undesirable effect on the energy absorption can be alleviated by diminishing the thickness of the first layer. The difference between densities of the first two layers density should be limited to a certain range to avoid the peak stress appearing in the second layer. A weak distal layer can reduce the distal stress of the foam under high-velocity impact, while a high density gradient between the last two layers will result in the early increase of the distal stress under moderate-velocity impactС помощью численного метода исследованы динамические характеристики градиентных трехслойных пеноматериалов типа Вороного. Исследованы поглощение энергии, дистальные напряжения градиентного пеноматериала и напряжения при ударе. Установлено, что начальное максимальное напряжение при ударе и преждевременное поглощение энергии градиентного пеноматериала уменьшаются при низкой прочности первого слоя. Нежелательное влияние на поглощение энергии можно смягчить путем уменьшения толщины первого слоя. Различие между плотностью первых двух слоев необходимо контролировать в рамках предельного диапазона, чтобы избежать возникновения максимального напряжения во втором слое. Слабый дистальный слой может способствовать снижению дистального напряжения пеноматериала при высокой скорости удара, тогда как значительный градиент плотностей последних двух слоев приводит к преждевременному увеличению дистального напряжения при средней скорости удара.За допомогою числового методу досліджено динамічні характеристики градієнтних тришарових піноматеріалів типу Вороного. Досліджено поглинання енергії, дистальні напруження градієнтного піноматеріалу і напруження під час удару. Установлено,що початкове максимальне напруження під час удару і передчасне поглинання енергії градієнтного піноматеріалу зменшуються за низької міцності першого шару. Небажаний вплив на поглинання енергії можна зм’якшити шляхом зменшення товщини першого шару. Різницю між щільністю перших двох шарів необхідно контролювати у межах граничного діапазону, щоб запобігти виникненню максимального напруження у другому шарі. Слабкий дистальний шар може сприяти зниженню дистального напруження піноматеріалу за високої швидкості удару, в той час як значний градієнт щільностей останніх двох шарів призведе до передчасного збільшення дистального напруження при середній швидкості удару

Effect of alloying elements on magnesium alloy damping capacities at room temperature

Alloying is a good approach to increasing its strength but leads to a reduction of damping to pure magnesium. Classifying the alloying characteristics of various alloying elements in magnesium alloys and their combined effects on the damping and mechanical properties of magnesium alloys is important. In this paper, the properties of the Mg-0.6wt%X binary alloys were analyzed through strength measurements and dynamic mechanical analysis. The effects of foreign atoms on solid-solution strengthening and dislocation damping were studied comprehensively. The effect of solid solubility on damping capacity can be considered from two perspectives: the effect of single solid-solution atoms on the damping capacities of the alloy, and the effect of solubility on the damping capacities of the alloy. The results provide significant information that is useful in developing high-strength, high-damping magnesium alloys. This study will provide scientific guidance regarding the development of new types of damping magnesium alloys

Phylogenetic analysis and biochemical characterization of a thermostable dihydropyrimidinase from alkaliphilic Bacillus sp TS-23

Two degenerate primers established from the alignment of highly conserved amino acid sequences of bacterial dihydropyrimidinases (DHPs) were used to amplify a 330-bp gene fragment from the genomic DNA of Bacillus sp. TS-23 and the amplified DNA was successfully used as a probe to clone a dhp gene from the strain. The open reading frame of the gene consisted of 1422 bp and was deduced to contain 472 amino acids with a molecular mass of 52 kDa. The deduced amino acid sequence exhibited greater than 45% identity with that of prokaryotic D-hydantoinases and eukaryotic DHPs. Phylogenetic analysis showed that Bacillus sp. TS-23 DHP is grouped together with Bacillus stearothermophilus D-hydantoinase and related to dihydroorotases and allantoinases from various organisms. His(6)-tagged DHP was over-expressed in Escherichia coli and purified by immobilized metal affinity chromatography to a specific activity of 3.46 U mg(-1) protein. The optimal pH and temperature for the purified enzyme were 8.0 and 60 degrees C, respectively. The half-life of His(6)-tagged DHP was 25 days at 50 degrees C. The enzyme activity was stimulated by Co2+ and Mn2+ ions. His(6)-tagged DHP was most active toward dihydrouracil followed by hydantoin derivatives. The catalytic efficiencies (k(cat)/K-m) of the enzyme for dihydrouracil and hydantoin were 2.58 and 0.61 s(-1) mM(-1), respectively

Detection of herb-symptom associations from traditional chinese medicine clinical data

YesTraditional Chinese medicine (TCM) is an individualized medicine by observing the symptoms and signs (symptoms in brief) of patients. We aim to extract the meaningful herb-symptom relationships from large scale TCM clinical data. To investigate the correlations between symptoms and herbs held for patients, we use four clinical data sets collected from TCM outpatient clinical settings and calculate the similarities between patient pairs in terms of the herb constituents of their prescriptions and their manifesting symptoms by cosine measure. To address the large-scale multiple testing problems for the detection of herb-symptom associations and the dependence between herbs involving similar efficacies, we propose a network-based correlation analysis (NetCorrA) method to detect the herb-symptom associations. The results show that there are strong positive correlations between symptom similarity and herb similarity, which indicates that herb-symptom correspondence is a clinical principle adhered to by most TCM physicians. Furthermore, the NetCorrA method obtains meaningful herb-symptom associations and performs better than the chi-square correlation method by filtering the false positive associations. Symptoms play significant roles for the prescriptions of herb treatment. The herb-symptom correspondence principle indicates that clinical phenotypic targets (i.e., symptoms) of herbs exist and would be valuable for further investigations

A thermostable leucine aminopeptidase from Bacillus kaustophilus CCRC 11223

Two degenerate primers established from the consensus sequences of bacterial leucine aminopeptidases (LAP) were used to amplify a 360-bp gene fragment from the chromosomal DNA of thermophilic Bacillus kaustophilus CCRC 11223 and the amplified fragment was successfully used as a probe to clone a leucine aminopeptidase (lap) gene from a genomic library of the strain. The gene consists of an open reading frame (ORF) of 1,494 bp and encodes a protein of 497 amino acid residues with a calculated molecular mass of 53.7 kDa. The complete amino acid sequence of the cloned enzyme showed greater than 30% identity with prokaryotic and eukaryotic LAPs. Phylogenetic analysis showed that B. kaustophilus LAP is closely related to the enzyme from Bacillus subtilis and is grouped with the M17 family. His(6)-tagged LAP was generated in Escherichia coli by cloning the coding region into pQE-30 and the recombinant enzyme was purified by nickel-chelate chromatography. The pH and temperature optima for the purified enzyme were 8 and 65degreesC, respectively, and 50% of its activity remained after incubation at 60degreesC for 32 min. The enzyme preferentially hydrolyzed L-leucine-p-nitroanilide (L-Leu-p-NA) followed by Cys derivative

Magnetotransport in Two-Dimensional Electron Systems with Spin-Orbit Interaction

We present magnetotransport calculations for homogeneous two-dimensional electron systems including the Rashba spin-orbit interaction, which mixes the spin-eigenstates and leads to a modified fan-chart with crossing Landau levels. The quantum mechanical Kubo formula is evaluated by taking into account spin-conserving scatterers in an extension of the self-consistent Born approximation that considers the spin degree of freedom. The calculated conductivity exhibits besides the well-known beating in the Shubnikov-de Haas (SdH) oscillations a modulation which is due to a suppression of scattering away from the crossing points of Landau levels and does not show up in the density of states. This modulation, surviving even at elevated temperatures when the SdH oscillations are damped out, could serve to identify spin-orbit coupling in magnetotransport experiments. Our magnetotransport calculations are extended also to lateral superlattices and predictions are made with respect to 1/B periodic oscillations in dependence on carrier density and strength of the spin-orbit coupling.Comment: 8 pages including 8 figures; submitted to PR

Measurements of the observed cross sections for exclusive light hadron production in e^+e^- annihilation at \sqrt{s}= 3.773 and 3.650 GeV

By analyzing the data sets of 17.3 pb$^{-1}$ taken at $\sqrt{s}=3.773$ GeV and 6.5 pb$^{-1}$ taken at $\sqrt{s}=3.650$ GeV with the BESII detector at the BEPC collider, we have measured the observed cross sections for 12 exclusive light hadron final states produced in $e^+e^-$ annihilation at the two energy points. We have also set the upper limits on the observed cross sections and the branching fractions for $\psi(3770)$ decay to these final states at 90% C.L.Comment: 8 pages, 5 figur

A fault identification and classification scheme for an automobile door assembly process

A process fault identification and classification scheme for an automobile door assembly process is presented based on multivariate in-line dimensional measurements and principal component factor analysis. First, the door assembly process and the dimensional measurement system are briefly introduced. Second, the technique of principal component factor analysis is presented for process fault identification. Process faults are summarized based on off-line identified case studies. Finally a machine classification scheme based on principal components and principal factors is presented and evaluated, using the pattern knowledge obtained off-line. This scheme is shown to be effective in classifying process faults using production data.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/45569/1/10696_2005_Article_BF01324797.pd

Measurements of psi(2S) decays to octet baryon-antibaryon pairs

With a sample of 14 million psi(2S) events collected by the BESII detector at the Beijing Electron Positron Collider (BEPC), the decay channels psi(2S)->p p-bar, Lambda Lambda-bar, Sigma0 Sigma0-bar, Xi Xi-bar are measured, and their branching ratios are determined to be (3.36+-0.09+-0.24)*10E-4, (3.39+-0.20+-0.32)*10E-4, (2.35+-0.36+-0.32)*10E-4, (3.03+-0.40+-0.32)*10E-4, respectively. In the decay psi(2S)->p p-bar, the angular distribution parameter alpha is determined to be 0.82+-0.17+-0.04.Comment: 8 pages, 8 figure

Running coupling: Does the coupling between dark energy and dark matter change sign during the cosmological evolution?

In this paper we put forward a running coupling scenario for describing the interaction between dark energy and dark matter. The dark sector interaction in our scenario is free of the assumption that the interaction term $Q$ is proportional to the Hubble expansion rate and the energy densities of dark sectors. We only use a time-variable coupling $b(a)$ (with $a$ the scale factor of the universe) to characterize the interaction $Q$. We propose a parametrization form for the running coupling $b(a)=b_0a+b_e(1-a)$ in which the early-time coupling is given by a constant $b_e$, while today the coupling is given by another constant, $b_0$. For investigating the feature of the running coupling, we employ three dark energy models, namely, the cosmological constant model ($w=-1$), the constant $w$ model ($w=w_0$), and the time-dependent $w$ model ($w(a)=w_0+w_1(1-a)$). We constrain the models with the current observational data, including the type Ia supernova, the baryon acoustic oscillation, the cosmic microwave background, the Hubble expansion rate, and the X-ray gas mass fraction data. The fitting results indicate that a time-varying vacuum scenario is favored, in which the coupling $b(z)$ crosses the noninteracting line ($b=0$) during the cosmological evolution and the sign changes from negative to positive. The crossing of the noninteracting line happens at around $z=0.2-0.3$, and the crossing behavior is favored at about 1$\sigma$ confidence level. Our work implies that we should pay more attention to the time-varying vacuum model and seriously consider the phenomenological construction of a sign-changeable or oscillatory interaction between dark sectors.Comment: 8 pages, 5 figures; refs added; to appear in EPJ