排序方式： 共有43条查询结果，搜索用时 15 毫秒
21.
Armin Saeedi Vahdat 《Journal of The Franklin Institute》2011,348(4):622-639
This paper deals with effects of residual and axial stresses on thermoelastic damping (TED) in micro-beam resonators. Equations of coupled thermoelastic case for a capacitive micro-beam resonator have been governed using two dimensional non-Fourier heat conduction model based on continuum theory frame. A Galerkin based finite element formulation has been used to analyze TED for the first mode of vibration of the micro-beam resonator with both ends clamped and isothermal. Effect of axial stresses owing to stretching of the micro-beam on the TED ratio has been investigated. As results illustrate, this effect gets importance only when the resonator is vibrating about a large static deflection due to a bias DC voltage close to the pull-in voltage of the resonator, otherwise it can be neglected in calculations. Effect of compressive and tensile residual stresses has been also studied. The results show that compressive (tensile) residual stresses increase (decrease) the TED ratio considerably. The residual stresses effect has been also studied for various values of the micro-beam thicknesses. The results illustrate that the effect of residual stress on the TED ratio decreases by increasing the thickness of the micro-beam. The results show that, applying DC voltages near the pull-in voltage increases energy dissipation due to the TED considerably, therefore, there is a limitation for applied DC voltage for resonators, since residual stresses change the pull-in voltage of the resonator, hence, existing residual stresses can change the interval of the applied voltage limitation. 相似文献
22.
Hsieh Chen Jennifer I. Angerer Marina Napoleone Armin J. Reininger Stefan W. Schneider Achim Wixforth Matthias F. Schneider Alfredo Alexander-Katz 《Biomicrofluidics》2013,7(6)
Primary hemostasis and blood clotting is known to be influenced by the red blood cell volume fraction (hematocrit) in blood. Depressed or elevated levels of red blood cells can lead to vascular perfusion problems ranging from bleeding to thrombus formation. The early stage of hemostasis and thus blood clotting in all vessel sections from the arterial to the venous system involves the adhesion of platelets to von Willebrand factor. Here we present experimental and theoretical results showing that the adhesion probability of platelets to von Willebrand factor is strongly and nonlinearly dependent on hematocrit and flow rate. Interestingly, the actual binding forces are not markedly different, which suggest that the origin of such behavior is in the distribution of platelets. Using hydrodynamic simulations of a simple model, we explicitly show that the higher the hematocrit and the flow rate, the larger the amount of platelets residing close to the wall. Our simulation results, which are in excellent agreement with the experimental observations, explain why such phenomena occur. We believe that the nonhomogeneous red blood cell distribution as well as the shear dependent hydrodynamic interaction is key for the accumulation of platelets on the vessel wall. The work we present here is an important step forward from our earlier work on single molecules and extends into the collective cellular behavior of whole blood. It sheds new light on the correlation between hematocrit and the initial steps in hemostasis and thrombosis, and outlines advances for the treatment of vascular diseases associated with high levels of red blood cells. These results are not only highly relevant for the field of hemostasis and the physics of blood clotting but are also of powerful impact in applied science most obviously in drug delivery and colloidal science. 相似文献
23.
The aim of this study was to examine the importance of the change-over time in swimming relay races. Top-class international 4 x 100 m freestyle races were analysed across a 10-year period including three Olympic Games and five European and World Championships. A total of 220 swimmers (116 female, 104 male) were included in this study with an average participation of 1.7 ± 1.2 races. To consider such repeated measurements and other factors (e.g., ranking in the relay race, position in the relay team) linear mixed models for longitudinal data were used for the statistical evaluation. Our results showed significantly longer change-over times for male medallists (0.23 ± 0.08 s) than non-medallists (0.20 ± 0.09 s) which reflects a very likely effect (94.2%). Furthermore, there were significant differences in change-over times between female and male swimmers depending on the current race positions. In total, the influence of change-over time on the final performance in 4 x 100-m freestyle relay appears to be overrated in previous studies. 相似文献
24.
In the past, studies and book recommendations on relay starts in swimming have been predominantly focused on the change-over time (COT) as a performance criterion. Aside from the circular backswing start with parallel foot placement, few studies have analysed differences in the take-off movement including step approaches as well. Although trends could be identified, the results remained still somewhat inconclusive. In contrast, no study has examined as has examined whether a reduction of COT in between wall contact of the income swimmer and the take-off of the outgoing swimmer is an optimal relay start strategy, as advocated by various swimming experts. Therefore, the purpose of this study was to compare two different relay start strategies: offensive strategy minimizing COT and conservative strategy to maximize horizontal peak force (HPF). In this regard, a learning intervention with 24 elite-level swimmers (12 females, 12 male) was conducted to compare both strategies regarding relay start time, HPF and COT. Subjects were randomly assigned to two feedback groups: COT versus HPF at take-off. The results of this study showed a clear advantage for HPF feedback for relay start performance measured by wall contact of the incoming swimmer and head passage at 7.5?m of the outgoing swimmer. In addition, similar reductions in COTs were found in both training groups. In conclusion, swimmers should focus on force production rather than minimizing COT. For the latter, deteriorating consequences for force production must be considered. 相似文献
25.
Dirk Siebert Patrick Neumann Armin Schulz Gabriele Faulkner Thomas Tolxdorff 《Informatik - Forschung und Entwicklung》2001,4(3):93-102
Für ein vollst?ndig computergestütztes Planungssystem zum Zwecke der kieferchirurgischen Operationsplanung ist die Bereitstellung von virtuellen Werkzeugen für den Chirurgen eine grundlegende Voraussetzung. Ausgehend von den Volumendaten mit Sch?del- und Kieferknochen des Patienten erm?glicht ein einfaches Interface unter Verwendung einer geeigneten Visualisierung und haptischer Eingabeger?te die interaktive Definition und Manipulation einzelner virtueller Knochensegmente. Wir haben moderne kraftrückgekoppelte Ger?te aus dem Niedrigpreisbereich eingebunden und auf ihre F?higkeit untersucht, das dreidimensionale Verst?ndnis im Planungsproze?durch Anlehnung an die Vorg?nge bei der chirurgischen Prozedur zu erh?hen. Durch diese Eingabeger?te ist es m?glich, die Knochensegmentierung für eine Osteotomie des Unterkiefers intuitiver und schneller durchzuführen. Die definierten Teilvolumina ergeben zusammen mit ihrer r?umlichen Neuanordnung auf Grundlage einer kephalometrischen Analyse einen Operationsplan. Nach erfolgter Planung werden die Planungsergebnisse in den Operationssaal übertragen. Die intraoperativen Techniken beinhalten die Visualisierung der Planungsergebnisse, die Steuerung der Anwendung über Sprache und die Bestimmung der Patientenposition mittels eines elektromagnetischen 3D-Trackingsystems. 相似文献
26.
Martin Wimmer Pia Ehrnlechner Armin Fischer Alfons Kemper 《Informatik - Forschung und Entwicklung》2005,92(3):167-181
Die plattformunabh?ngige und organisationsübergreifende Web Services-Interoperabilit?t setzt ein leistungsf?higes und flexibles
Autorisierungssystem voraus. In diesem Beitrag wird ein Zugriffskontrollsystem vorgestellt, welches sich durch das Zusammenspiel
lokaler und verteilter Autorisierung auszeichnet. Im Zusammenhang mit lokaler Zugriffskontrolle, bei der Rechte innerhalb
einer Organisation ausgewertet werden, stellt sich insbesondere die Herausforderung, Autorisierungsregeln zu konsolidieren:
Da die Funktionalit?t von Web Services h?ufig auf weitere Anwendungen und Betriebsmittel wie Datenbanksystemen aufsetzt, ergeben
sich Abh?ngigkeiten bezüglich der Autorisierung, die überprüft und eingehalten werden müssen. über eine verteilte Zugriffskontrolle
wird der Aufbau von Kollaborationsnetzwerken erm?glicht. Der Augenmerk liegt im Folgenden auf schwach gekoppelten Zusammenschlüssen,
die die Autonomie der beteiligten Organisationen beibeh?lt. Skalierbarkeit und Effizenz werden durch den Einsatz von rollenbasierter
Zugriffskontrolle einerseits und dem Caching ?hnlicher, wiederkehrender Autorisierungen andererseits erreicht. 相似文献
27.
Copy number variants (CNVs) are pieces of genomic DNA of 1000 base pairs or longer which occur in a given genome at a different frequency than in a reference genome. Their importance as a source for phenotypic variability has been recognized only in the last couple of years. Chromosomal deletions can be seen as a special case of CNVs where stretches of DNA are missing in certain lines when compared to the reference genome of the mouse line C57BL/6, for example. Based upon more than 8 million single nucleotide polymorphisms (SNPs) in the fifteen inbred mouse lines which were determined in a whole genome chip based resequencing project by Perlegen Sciences, we detected 20166 such long chromosomal deletions. They cover altogether between 4.4 million and 8.8 million base pairs, depending on the mouse line. Thus, their extent is comparable to that of SNPs. The chromosomal deletions were found by searching for clusters of missing values in the genotyping data by applying bioinformatics and biostatistical methods. In contrast to isolated missing values, clusters are likely the consequence of missing DNA probe rather than of a failed hybridization or deficient oligos. We analyzed these deletion sites in various ways. Twenty-two percent of these deletion sites overlap with exons; they could therefore affect a gene's functioning. The corresponding genes seem to exist in alternative forms, a phenomenon that reminds of the alternative forms of mRNA generated during gene splicing. We furthermore detected statistically significant association between hundreds of deletion sites and fat weight at the age of eight weeks. 相似文献
28.
While much is understood about the role of the family context and educational experiences for moral development, less attention has been devoted to the occupational context. In this research, we used Kohlberg’s approach of moral education as a framework and investigated the relationship between structurally anchored organizational democracy and employees’ moral development. Employees (N = 285) of five conventional (i.e., traditionally owned and hierarchically managed) and five democratic (i.e., collectively owned and democratically managed) enterprises participated in our study. Consistently with our theoretically derived hypotheses, the results provide initial support for the theoretical model in that employees from democratic firms scored higher on moral development than employees from conventional firms. In turn, contrary to our expectations, the socio-moral climate within organizations failed to explain variance in moral development. Theoretical implications of our findings as well as suggestions for future research are discussed. 相似文献
29.
Sebastian Fischer Armin Kibele 《Sports biomechanics / International Society of Biomechanics in Sports》2016,15(4):397-408
The aim of this study was to analyse the significance of various biomechanical parameters in swim start performance for the grab and track start techniques. To do so, structural equation models were analysed, incorporating measurements for the take-off phase, flight phase and entry phase. Forty-six elite German swimmers (18 female and 28 male; age: 20.1 ± 4.2 yrs; PB (100 m Freestyle): 53.6 ± 2.9 s) participated in the study. Their swim start performance was examined within a 25-m sprint test. Structural equation modelling was conducted in separate models for the block time, flight time and water time and in a combined model for swim start time. Our main finding was that swim start time is predominantly related to water time and determined to a lesser extent by block time and flight time. We conclude that more emphasis should be given to the water immersion behaviour and the gliding phase when analysing swim start performance. Furthermore, significant differences were found between the grab start and track techniques as regards the biomechanical parameters representing the take-off phase and water phase. 相似文献
30.
Fourth graders’ dyadic learning on multi-touch interfaces—versatile effects of verbalization prompts
Schmitt Lara Johanna Weinberger Armin 《Educational technology research and development : ETR & D》2019,67(3):519-539
Educational technology research and development - Multi-touch interfaces allow for direct and simultaneous input by several co-present learners and afford hands-on learning experiences. Additional... 相似文献