Ordering in a fluid inert gas confined by flat surfaces     

Donnelly SE  Birtcher RC  Allen CW  Morrison I  Furuya K  Song M  Mitsuishi K  Dahmen U 《Science (New York, N.Y.)》2002,296(5567):507-510

High-resolution transmission electron microscopy images of room-temperature fluid xenon in small faceted cavities in aluminum reveal the presence of three well-defined layers within the fluid at each facet. Such interfacial layering of simple liquids has been theoretically predicted, but observational evidence has been ambiguous. Molecular dynamics simulations indicate that the density variation induced by the layering will cause xenon, confined to an approximately cubic cavity of volume approximately 8 cubic nanometers, to condense into the body-centered cubic phase, differing from the face-centered cubic phase of both bulk solid xenon and solid xenon confined in somewhat larger (>/=20 cubic nanometer) tetradecahedral cavities in face-centered cubic metals. Layering at the liquid-solid interface plays an important role in determining physical properties as diverse as the rheological behavior of two-dimensionally confined liquids and the dynamics of crystal growth.  相似文献   

Dynamic visualization of thrombopoiesis within bone marrow     

Junt T  Schulze H  Chen Z  Massberg S  Goerge T  Krueger A  Wagner DD  Graf T  Italiano JE  Shivdasani RA  von Andrian UH 《Science (New York, N.Y.)》2007,317(5845):1767-1770

Platelets are generated from megakaryocytes (MKs) in mammalian bone marrow (BM) by mechanisms that remain poorly understood. Here we describe the use of multiphoton intravital microscopy in intact BM to visualize platelet generation in mice. MKs were observed as sessile cells that extended dynamic proplatelet-like protrusions into microvessels. These intravascular extensions appeared to be sheared from their transendothelial stems by flowing blood, resulting in the appearance of proplatelets in peripheral blood. In vitro, proplatelet production from differentiating MKs was enhanced by fluid shear. These results confirm the concept of proplatelet formation in vivo and are consistent with the possibility that blood flow-induced hydrodynamic shear stress is a biophysical determinant of thrombopoiesis.  相似文献   

Arctic division meeting     

Weller GE 《Science (New York, N.Y.)》1982,218(4572):558-559

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Cytomegalovirus recruitment of cellular kinases to dissolve the nuclear lamina     

Muranyi W  Haas J  Wagner M  Krohne G  Koszinowski UH 《Science (New York, N.Y.)》2002,297(5582):854-857

The passage of large-sized herpesviral capsids through the nuclear lamina and the inner nuclear membrane to leave the nucleus requires a dissolution of the nuclear lamina. Here, we report on the functions of M50/p35, a beta-herpesviral protein of murine cytomegalovirus. M50/p35 inserts into the inner nuclear membrane and is aggregated by a second viral protein, M53/p38, to form the capsid docking site. M50/p35 recruits the cellular protein kinase C for phosphorylation and dissolution of the nuclear lamina, suggesting that herpesviruses target a critical element of nuclear architecture.  相似文献   

Materials science. How nanowires grow     

Schmidt V  Gösele U 《Science (New York, N.Y.)》2007,316(5825):698-699

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Identification of a DNA nonhomologous end-joining complex in bacteria     

Weller GR  Kysela B  Roy R  Tonkin LM  Scanlan E  Della M  Devine SK  Day JP  Wilkinson A  d'Adda di Fagagna F  Devine KM  Bowater RP  Jeggo PA  Jackson SP  Doherty AJ 《Science (New York, N.Y.)》2002,297(5587):1686-1689

In eukaryotic cells, double-strand breaks (DSBs) in DNA are generally repaired by the pathway of homologous recombination or by DNA nonhomologous end joining (NHEJ). Both pathways have been highly conserved throughout eukaryotic evolution, but no equivalent NHEJ system has been identified in prokaryotes. The NHEJ pathway requires a DNA end-binding component called Ku. We have identified bacterial Ku homologs and show that these proteins retain the biochemical characteristics of the eukaryotic Ku heterodimer. Furthermore, we show that bacterial Ku specifically recruits DNA ligase to DNA ends and stimulates DNA ligation. Loss of these proteins leads to hypersensitivity to ionizing radiation in Bacillus subtilis. These data provide evidence that many bacteria possess a DNA DSB repair apparatus that shares many features with the NHEJ system of eukarya and suggest that this DNA repair pathway arose before the prokaryotic and eukaryotic lineages diverged.  相似文献   

Multielemental fingerprinting as a tool for authentication of organic wheat, barley, faba bean, and potato     

Laursen KH  Schjoerring JK  Olesen JE  Askegaard M  Halekoh U  Husted S 《Journal of agricultural and food chemistry》2011,59(9):4385-4396

The multielemental composition of organic and conventional winter wheat, spring barley, faba bean, and potato was analyzed with inductively coupled plasma-optical emission spectrometry (ICP-OES) and -mass spectrometry (ICP-MS). The crops were cultivated in two years at three geographically different field locations, each accommodating one conventional and two organic cropping systems. The conventional system produced the highest harvest yields for all crops except the nitrogen-fixing faba bean, whereas the dry matter content of each crop was similar across systems. No systematic differences between organic and conventional crops were found in the content of essential plant nutrients when statistically analyzed individually. However, chemometric analysis of multielemental fingerprints comprising up to 14 elements allowed discrimination. The discrimination power was further enhanced by analysis of up to 25 elements derived from semiquantitative ICP-MS. It is concluded that multielemental fingerprinting with semiquantitative ICP-MS and chemometrics has the potential to enable authentication of organic crops.  相似文献   

Analysis of the effect of temperature changes combined with different alkaline pH on the β-lactoglobulin trypsin hydrolysis pattern using MALDI-TOF-MS/MS     

Chelulei Cheison S  Brand J  Leeb E  Kulozik U 《Journal of agricultural and food chemistry》2011,59(5):1572-1581

Temperature and pH influence the conformation of the whey protein β-lactoglobulin (β-Lg) monomer, dimer, and octamer formation, its denaturation, and solubility. Most hydrolyses have been reported at trypsin (EC 3.4.21.4) optimum conditions (pH 7.8 and 37 °C), while the hydrolysate mass spectrometry was largely limited to peptides with <4 kDa. There are few reports on trypsin peptide release patterns away from optimum. This work investigated the influence of alkaline (8.65 and 9.5) and optimum (7.8) pH at different temperatures (25, 37.5, and 50 °C) on β-Lg (7.5%, w/v) hydrolysis. Sample aliquots were drawn out before the addition of trypsin (blank sample) and at various time intervals (15 s to 10 min) thereafter. Matrix-assisted laser desorption/ionization time-of-flight tandem mass spectrometry (MALDI-TOF-MS/MS) was used to monitor peptide evolution over time with the use of two matrixes: α-cyano-4-hydroxycinnamic acid (HCCA) and 2.5-dihydroxyacetophenone (DHAP). Mass analysis showed that the N- and C-terminals (Lys(8)-Gly(9), Lys(100)-Lys(101), Arg(124)-Thr(125), Lys(141)-Ala(142), and Arg(148)-Leu(149)) of β-Lg were cleaved early (15 s) implying the ease of trypsinolysis at the exposed terminals. Hydrolyses at 25 °C and pH 7.8 as well as at 50 °C and pH 9.5 were slowed down and ordered. Nonspecific chymotrypsin-like behavior occurred more at higher temperatures (50 °C) than at lower ones (25 and 37.5 °C). In addition to our earlier work in the acid pH region, it can be concluded that there is potential for controlled hydrolysis outside the trypsin optimum, where different target peptides with predictable biofunctionalities could be produced.  相似文献   

Kinetics of jump landing in agility dogs     

Pfau T  Garland de Rivaz A  Brighton S  Weller R 《Veterinary journal (London, England : 1997)》2011,190(2):278-283

A recent survey reported an increased risk of injury in dogs participating in agility, a competitive canine sport involving different jumping activities. The aim of this study was to quantify the kinetic parameters during jump landing for commonly used obstacle types. It was hypothesised that with increasing obstacle height, the vertical force and vertical and accelerative horizontal impulse will increase as a result of a lengthened aerial phase, a more acute landing angle and the need to convert potential into forwards kinetic energy. Simultaneous kinetic and kinematic data were recorded from 11 competition agility dogs jumping over obstacle combinations of different height and inter-obstacle distance. Speed and landing angle of the second of the two consecutive jumps were successfully controlled by obstacle height and distance between obstacles. Statistical analysis showed differences between obstacles for peak vertical force, vertical impulse and accelerative horizontal impulse (increasing values with more acute landing angles). Extremely high peak vertical force was observed in the forelimbs (4.5 times bodyweight) when landing from a hurdle jump at high speed. Further detailed studies into the consequences for internal limb structures are warranted in order to clarify how this might be related to injury.  相似文献   

Genetic variability of six indigenous goat breeds using major histocompatibility complex-associated microsatellite markers     

Patricy de Andrade Salles  Silvana C. Santos  Davide Rondina  Mathias Weller 《Journal of veterinary science (Suw?n-si, Korea)》2011,12(2):127-132

The present study aimed at analyzing the genetic variability of indigenous goat breeds (Capra hircus) using the MHC-associated microsatellite markers BF1, BM1818, BM1258, DYMS1, and SMHCC1. The following breeds were included: Chinese Xuhuai, Indian Changthangi and Pashmina, Kenyan Small East African (SEA) and Galla, and Albanian Vendi. To examine genetic variability, the levels of heterozigosity, degrees of inbreeding, and genetic differences among the breeds were analyzed. The mean number of alleles ranged from nine in the Galla to 14.5 in the Vendi breed. The mean observed heterozygosity and mean expected heterozygosity varied from 0.483 in the Vendi to 0.577 in the Galla breed, and from 0.767 in the SEA to 0.879 in the Vendi breed, respectively. Significant loss of heterozygosity (p < 0.01) indicated that these loci were not in Hardy-Weinberg equilibrium. The mean F_IS values ranged from 0.3299 in the SEA to 0.4605 in the Vendi breed with a mean value of 0.3623 in all breeds (p < 0.001). Analysis of molecular variance indicated that 7.14% and 4.74% genetic variation existed among the different breeds and geographic groups, whereas 92.86% and 95.26% existed in the breeds and the geographic groups, respectively (p < 0.001). The microsatellite marker analysis disclosed a high degree of genetic polymorphism. Loss of heterozygosity could be due to genetic drift and endogamy. The genetic variation among populations and geographic groups does not indicate a correlation of genetic differences with geographic distance.  相似文献