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71.
72.
This paper illustrates the implementation feasibility of an optimistic approach to concurrency control. After reviewing the approach and clarifying the underlying algorithms and assumptions, it is applied to the design of a multi-user version of an existing relational database management system. Two different system architectures for a UNIX 1 UNIX is a trademark of Bell Laboratories. -based environment are presented and prototype implementations have been constructed. We also provide some performance statistics on the optimistic approach to concurrency control and compare it with a traditional locking protocol. 相似文献
73.
Arjen P. De Vries Menzo Windhouwer Peter M. G. Apers Martin Kersten 《New Generation Computing》2000,18(4):323-339
With the increasing popularity of the WWW, the main challenge in computer science has become content-based retrieval of multimedia
objects. Access to multimedia objects in databases has long been limited to the information provided in manually assigned
keywords. Now, with the integration of feature-detection algorithms in database systems software, content-based retrieval
can be fully integrated with query processing. We describe our experimentation platform under development, making database
technology available to multimedia. Our approach is based on the new notion of feature databases. Its architecture fully integrates
traditional query processing and content-based retrieval techniques.
Arjen P. de Vries, Ph.D.: He received his Ph.D. in Computer Science from the University of Twente in 1999, on the integration of content management
in database systems. He is especially interested in the new requirements on the design of database systems to support content-based
retrieval in multimedia digital libraries. He has continued to work on multimedia database systems as a postdoc at the CWI
in Amsterdam as well as University of Twente.
Menzo Windhouwer: He received his MSc in Computer Science and Management from the University of Amsterdam in 1997. Currently he is working
in the CWI Database Research Group on his Ph.D., which is concerned with multimedia indexing and retrieval using feature grammars.
Peter M.G. Apers, Ph.D.: He is a full professor in the area of databases at the University of Twente, the Netherlands. He obtained his MSc and Ph.D.
at the Free University, Amsterdam, and has been a visiting researcher at the University of California, Santa Cruz and Stanford
University. His research interests are query optimization in parallel and distributed database systems to support new application
domains, such as multimedia applications and WWW. He has served on the program committees of major database conferences: VLDB,
SIGMOD, ICDE, EDBT. In 1996 he was the chairman of the EDBT PC. In 2001 he will, for the second time, be the chairman of the
European PC of the VLDB. Currently he is coordinating Editor-in-Chief of the VLDB Journal, editor of Data & Knowledge Engineering,
and editor of Distributed and Parallel Databases.
Martin Kersten, Ph.D.: He received his PhD in Computer Science from the Vrije Universiteit in 1985 on research in database security, whereafter
he moved to CWI to establish the Database Research Group. Since 1994 he is professor at the University of Amsterdam. Currently
he is heading a department involving 60 researchers in areas covering BDMS architectures, datamining, multimedia information
systems, and quantum computing. In 1995 he co-founded Data Distilleries, specialized in data mining technology, and became
a non-executive board member of the software company Consultdata Nederland. He has published ca. 130 scientific papers and
is member of the editorial board of VLDB journal and Parallel and Distributed Systems. He acts as a reviewer for ESPRIT projects
and is a trustee of the VLDB Endowment board. 相似文献
74.
Stefan Manegold Peter A. Boncz Martin L. Kersten 《The VLDB Journal The International Journal on Very Large Data Bases》2000,9(3):231-246
In the past decade, advances in the speed of commodity CPUs have far out-paced advances in memory latency. Main-memory access
is therefore increasingly a performance bottleneck for many computer applications, including database systems. In this article,
we use a simple scan test to show the severe impact of this bottleneck. The insights gained are translated into guidelines
for database architecture, in terms of both data structures and algorithms. We discuss how vertically fragmented data structures
optimize cache performance on sequential data access. We then focus on equi-join, typically a random-access operation, and
introduce radix algorithms for partitioned hash-join. The performance of these algorithms is quantified using a detailed analytical
model that incorporates memory access cost. Experiments that validate this model were performed on the Monet database system.
We obtained exact statistics on events such as TLB misses and L1 and L2 cache misses by using hardware performance counters
found in modern CPUs. Using our cost model, we show how the carefully tuned memory access pattern of our radix algorithms
makes them perform well, which is confirmed by experimental results.
Received April 20, 2000 / Accepted June 23, 2000 相似文献
75.
Sabrina Gallus Dr. Theo Peschke Dr. Malte Paulsen Dr. Teresa Burgahn Prof. Christof M. Niemeyer Dr. Kersten S. Rabe 《Chembiochem : a European journal of chemical biology》2020,21(15):2126-2131
The display of complex proteins on the surface of cells is of great importance for protein engineering and other fields of biotechnology. Herein, we describe a modular approach, in which the membrane anchor protein Lpp-OmpA and a protein of interest (passenger) are expressed independently as genetically fused SpyCatcher and SpyTag units and assembled in situ by post-translational coupling. Using fluorescent proteins, we first demonstrate that this strategy allows the construct to be installed on the surface of E. coli cells. The scope of our approach was then demonstrated by using three different functional enzymes, the stereoselective ketoreductase Gre2p, the homotetrameric glucose 1-dehydrogenase GDH, and the bulky heme- and diflavin-containing cytochrome P450 BM3 (BM3). In all cases, the SpyCatcher-SpyTag method enabled the generation of functional whole-cell biocatalysts, even for the bulky BM3, which could not be displayed by conventional fusion with Lpp-OmpA. Furthermore, by using a GDH variant carrying an internal SpyTag, the system could be used to display an enzyme with unmodified N- and C-termini. 相似文献
76.
Fenske D Gnida M Schneider K Meyer-Klaucke W Schemberg J Henschel V Meyer AK Knöchel A Müller A 《Chembiochem : a European journal of chemical biology》2005,6(2):405-413
Azotobacter vinelandii is a diazotrophic bacterium characterized by the outstanding capability of storing Mo in a special storage protein, which guarantees Mo-dependent nitrogen fixation even under growth conditions of extreme Mo starvation. The Mo storage protein is constitutively synthesized with respect to the nitrogen source and is regulated by molybdenum at an extremely low concentration level (0-50 nM). This protein was isolated as an alpha4beta4 octamer with a total molecular mass of about 240 kg mol(-1) and its shape was determined by small-angle X-ray scattering. The genes of the alpha and beta subunits were unequivocally identified; the amino acid sequences thereby determined reveal that the Mo storage protein is not related to any other known molybdoprotein. Each protein molecule can store at least 90 Mo atoms. Extended X-ray absorption fine-structure spectroscopy identified a metal-oxygen cluster bound to the Mo storage protein. The binding of Mo (biosynthesis and incorporation of the cluster) is dependent on adenosine triphosphate (ATP); Mo release is ATP-independent but pH-regulated, occurring only above pH 7.1. This Mo storage protein is the only known noniron metal storage system in the biosphere containing a metal-oxygen cluster. 相似文献
77.
Ladisa JF Olson LE Ropella KM Molthen RC Haworth ST Kersten JR Warltier DC Pagel PS 《Computer methods and programs in biomedicine》2005,79(2):121-134
Restenosis caused by neointimal hyperplasia (NH) remains an important clinical problem after stent implantation. Restenosis varies with stent geometry, and idealized computational fluid dynamics (CFD) models have indicated that geometric properties of the implanted stent may differentially influence NH. However, 3D studies capturing the in vivo flow domain within stented vessels have not been conducted at a resolution sufficient to detect subtle alterations in vascular geometry caused by the stent and the subsequent temporal development of NH. We present the details and limitations of a series of post-processing operations used in conjunction with microfocal X-ray CT imaging and reconstruction to generate geometrically accurate flow domains within the localized region of a stent several weeks after implantation. Microfocal X-ray CT reconstruction volumes were subjected to an automated program to perform arterial thresholding, spatial orientation, and surface smoothing of stented and unstented rabbit iliac arteries several weeks after antegrade implantation. A transfer function was obtained for the current post-processing methodology containing reconstructed 16 mm stents implanted into rabbit iliac arteries for up to 21 days after implantation and resolved at circumferential and axial resolutions of 32 and 50 microm, respectively. The results indicate that the techniques presented are sufficient to resolve distributions of WSS with 80% accuracy in segments containing 16 surface perturbations over a 16 mm stented region. These methods will be used to test the hypothesis that reductions in normalized wall shear stress (WSS) and increases in the spatial disparity of WSS immediately after stent implantation may spatially correlate with the temporal development of NH within the stented region. 相似文献
78.
Wolf Haberer Thomas Schmitt Peter Schreier Anne-Katrin Eggert Josef K. Müller 《Journal of chemical ecology》2017,43(10):971-977
In burying beetles, Nicrophorus spp. (Coleoptera: Silphidae: Nicrophorinae) mate finding is mediated by male produced volatile compounds. To date, pheromone components of only two species have been identified. In an attempt to better understand the evolution of male pheromone signaling in burying beetles, we investigated the male released volatiles of ten Nicrophorus species and one closely related nicrophorine species, Ptomascopus mori. Volatiles emitted by calling males were collected in the laboratory by means of solid phase micro extraction and analyzed using gas chromatography coupled with mass spectrometry. Identified volatiles included short chain esters of 4-methylcarboxylic acids, terpenoids, and some other aliphatic compounds. The long-range volatile signals of the burying beetle species included in this study are blends of two to seven components. We found that methyl or ethyl esters of 4-methylheptanoic acid and 4-methyloctanoic acid are produced by eight of the ten investigated Nicrophorus species. These esters may play a key role in chemical communication. Their widespread occurrence suggests that these compounds did not evolve recently, but appeared relatively early in the phylogeny of the genus. Although Ptomascopus is considered the sister genus of Nicrophorus, P. morio males do not produce any of the Nicrophorus compounds, but release 3-methylalkan-2-ones, which are absent in Nicrophorus. A better understanding of the evolution of burying beetle pheromones, however, will only be possible once more species have been studied. 相似文献
79.
JR Kersten AP Brayer PS Pagel JP Tessmer DC Warltier 《Canadian Metallurgical Quarterly》1994,81(4):995-1004
BACKGROUND: Sevoflurane produces direct vasodilation of coronary arteries in vitro and decreases coronary vascular resistance in vivo, pharmacologic properties that may contribute to the development of "coronary steal." This investigation examined the effects of sevoflurane on the distribution of regional myocardial perfusion in chronically instrumented dogs with steal-prone coronary artery anatomy. METHODS: Dogs were chronically instrumented for measurement of aortic and left ventricular pressure, diastolic coronary blood flow velocity and subendocardial segment length. After recovery from surgery, dogs underwent repetitive, brief, left anterior descending coronary artery (LAD) occlusions via an implanted hydraulic vascular occluder to enhance collateral development. A progressive left circumflex coronary artery (LCCA) stenosis was also obtained using an ameroid constrictor. After development of LCCA stenosis, the LAD was totally occluded to produce a model of multivessel coronary artery disease. Systemic hemodynamics, regional contractile function and myocardial perfusion measured with radioactive microspheres were assessed in the conscious state and during sevoflurane anesthesia at 1.0 and 1.5 MAC with and without restoration of arterial blood pressure and heart rate to conscious levels. RESULTS: Total LAD occlusion with simultaneous LCCA stenosis increased heart rate, mean arterial pressure, left ventricular systolic and end-diastolic pressures, end-diastolic segment length, and rate-pressure product in conscious dogs. Subsequent administration of sevoflurane caused dose-related decreases in arterial pressure, left ventricular systolic pressure, double product, and peak rate of increase of left ventricular pressure at 50 mmHg. Perfusion of normal myocardium was unchanged during sevoflurane anesthesia. In contrast, sevoflurane caused dose-dependent decreases in blood flow to myocardium supplied by the stenotic LCCA, which returned to control levels after restoration of heart rate and arterial pressure. No reduction in collaterally derived blood flow to the occluded region was produced by 1.0 or 1.5 MAC sevoflurane. No redistribution of blood flow away from the occluded LAD region to normal or stenotic myocardium occurred during sevoflurane anesthesia. In fact, increases in the ratio of blood flow between occluded and normal zones or occluded and stenotic zones were observed in the subepicardium during 1.5 MAC sevoflurane with maintenance of the heart rate and arterial pressure at conscious levels. CONCLUSIONS: The results demonstrate that sevoflurane does not reduce or abnormally redistribute myocardial blood flow derived from coronary collateral vessels in a chronically instrumented canine model of multivessel coronary artery obstruction. 相似文献
80.
Four-bar mechanisms and their variations yield two positions for which the output angle β or the coupler angle γ is identical. These positions are called “conjugate positions” and their significance is discussed. The kinematic inversions of mechanisms in certain conjugate positions leads to new mechanisms with special coupler curves. Coupler points which trace a path with two cusps are easily determined. A similar treatment of the non-turnable double rocker yields coupler curves with three cusps. Requirements for symmetrical coupler curves with two or three cusps can be satisfied. 相似文献