Cycles of Myth Restoration One Approach to Understanding American Culture     

Jerome O. Steffen 《Journal of American culture (Malden, Mass. : 2003)》1993,16(1):25-33

  相似文献   

Der Entwurf strukturierter rollenbasierter Zugriffskontrollmodelle     

Steffen E. Seufert 《Informatik - Forschung und Entwicklung》2002,17(1):1-11

Zusammenfassung. In diesem Beitrag wird ein formaler Ansatz zur Ableitung von Zugriffsrechten auf der Basis eines formalen Organisationsmodells vorgestellt. Hierzu wird der Ansatz der rollenbasierten Zugriffskontrolle (engl. Role-Based Access Control, kurz RBAC) um die M?glichkeit erweitert, Aufbauorganisationen zu modellieren. Der Vorteil gegenüber rollenbasierten Ans?tzen mit einfachen Rollenhierarchien ist die klare Struktur, die einem Zugriffskontrollmodell durch die Organisationsform aufgepr?gt wird. Des Weiteren k?nnen organisatorische Regelungen, wie z.B. Urlaubsvertretung oder Weisungsbefugnis, direkt im Modell hinterlegt werden. Aufwendig zu pflegende und h?ufig inkonsistente Rollenkataloge werden obsolet. Sicherheitsstrategien mit unpr?zisen Vorgaben lassen sich mittels der vorgestellten Technik der sog. `Kompetenzerweiterung' umsetzen. Das zugrundeliegende Paradigma des vorgestellten Ansatzes unterscheidet sich stark von anderen Ans?tzen mit statischer Autorisation. Nutzer k?nnen sich Zugriffsrechte in fest definierten Grenzen selbstverantwortlich zuteilen, wobei jedoch eine nachtr?gliche Kontrolle stark vereinfacht und damit praktikabel wird. Eingegangen am 22. Februar 2001 / Angenommen am 22. Mai 2001  相似文献   

Unsteady flow phenomena in human undulatory swimming: a numerical approach     

Steffen Pacholak  Stefan Hochstein  Alexander Rudert  Christoph Brücker 《Sports biomechanics / International Society of Biomechanics in Sports》2014,13(2):176-194

The undulatory underwater sequence is one of the most important phases in competitive swimming. An understanding of the recurrent vortex dynamics around the human body and their generation could therefore be used to improve swimming techniques. In order to produce a dynamic model, we applied human joint kinematics to three-dimensional (3D) body scans of a female swimmer. The flow around this dynamic model was then calculated using computational fluid dynamics with the aid of moving 3D meshes. Evaluation of the numerical results delivered by the various motion cycles identified characteristic vortex structures for each of the cycles, which exhibited increasing intensity and drag influence. At maximum thrust, drag forces appear to be 12 times higher than those of a passive gliding swimmer. As far as we know, this is the first disclosure of vortex rings merging into vortex tubes in the wake after vortex recapturing. All unsteady structures were visualized using a modified Q-criterion also incorporated into our methods. At the very least, our approach is likely to be suited to further studies examining swimmers engaging in undulatory swimming during training or competition.  相似文献   

Mathematical and philosophical Newton     

Steffen Ducheyne 《Metascience》2011,20(3):467-476

  相似文献   

Transport and separation of micron sized particles at isotachophoretic transition zones     

Gabriele Goet  Tobias Baier    Steffen Hardt 《Biomicrofluidics》2011,5(1)

Conventionally, isotachophoresis (ITP) is used for separation of ionic samples according to their electrophoretic mobilities. We demonstrate that the scope of ITP applications may be extended toward particle concentration and separation. Owing to the distributions of electrolyte concentration and electric field inside a transition zone between two electrolytes, a number of different forces act on a small particle. As far as possible, we provide estimates for the order of magnitude of these forces and analyze their scaling with the particle size and the electric-field strength. Furthermore, we experimentally demonstrate that polymer beads of 5 μm diameter dispersed in a high mobility “leading” electrolyte are picked up and carried along by an ITP transition zone which is formed with a low mobility “trailing” electrolyte. By studying the particle positions and trajectories, we show that impurities in the electrolytes play a significant role in the experiments. Additionally, it is experimentally shown that different types of beads can be separated at an ITP transition zone. In particular, beads of 1 μm diameter are not carried along with the transition zone, in contrast to the 5 μm beads. The presented technique thus adds to the portfolio of electrokinetic transport, concentration, and separation methods in microfluidics.  相似文献   

Bildung,Ausbildung und soziale Ungleichheiten im Lebenslauf     

Steffen Hillmert 《Zeitschrift für Erziehungswissenschaft》2014,17(2):73-94

This paper describes mutual links between educational attainment and social inequality from a life course perspective. Analytically we distinguish between aspects of inequality with regard to access to education, consequences of education, and social reproduction through education. A special emphasis is put on the role institutions play in these processes. The paper presents selected empirical findings, discusses theoretical mechanisms, and draws some conclusions for the conceptualisation of education systems.  相似文献   

CONFU-digital image discussion group Educational fair use guidelines for digital images,discussion draft of july 1,1996     

Jens Basanow  Pascal Neis  Steffen Neubauer  Arne Schilling  Alexander Zipf 《Archives and Museum Informatics》1996,10(2):173-184

  相似文献   

Controlled electroporation of the plasma membrane in microfluidic devices for single cell analysis   总被引：1，自引：0，他引：1  

Shah D  Steffen M  Lilge L 《Biomicrofluidics》2012,6(1):14111-1411110

Chemical cytometry on a single cell level is of interest to various biological fields ranging from cancer to stem cell research. The impact chemical cytometry can exert in these fields depends on the dimensionality of the retrievable analytes content. To this point, the number of different analytes identifiable and additionally their subcellular localization is of interest. To address this, we present an electroporation based approach for selective lysis of only the plasma membrane, which permits analysis of the dissolved cytoplasm, while reducing contributions from the nucleus and membrane bound fractions of the cell analytes. The use of 100 μs long pulse and a well defined DC electric field gradient of ∼4.5 kV·cm⁻¹ generated by 3D electrodes initiates release of a cytoplasm marker in ≪1 s, while retaining nuclear fluorescence markers.  相似文献   

Leg amputation side determines performance in curve sprinting: a case study on a Paralympic medalist     

Johannes Funken  Kai Heinrich  Steffen Willwacher  Ralf Müller  Jonas Böcker  Hiroaki Hobara 《Sports biomechanics / International Society of Biomechanics in Sports》2019,18(1):75-87

The lower limb kinetics of curve sprinting in amputees are not well described in the literature, particularly with respect to the effect of the side of amputation. This is an issue due to the importance of the knowledge for prosthetic design and classification of athletes. Thus, the aim of this study was to investigate the influence of side of amputation on curve sprinting performance in athletes with a unilateral leg amputation. A three-dimensional motion analysis system (Vicon), four force plates (Kistler) and a modified mathematical human model (ALASKA) were used to compare clockwise and counter clockwise curve sprinting lower limb kinematics and kinetics of a Paralympic medalist with a left-sided knee exarticular amputation. Results reveal that vertical ground reaction force application and total vertical impulse were lower when the affected limb was at the inside of the curve. The unaffected limb showed joint mechanics different to those established for non-amputee athletes and might contribute better to propulsion when being the inside limb. Curve sprinting biomechanics and the ability to attain high radial velocities are directly dependent on the side of amputation relative to the curve direction in a unilateral amputee athlete of highest performance level.  相似文献   

Enhancing Scientific Communication Skills: a Real-World Simulation in a Tertiary-Level Life Science Class Using E-Learning Technology in Biomedical Literature Perception,Reflective Review Writing on a Clinical Issue,and Self and Peer Assessments     

Eppler  Elisabeth  Meyer  Jan  Serowy  Steffen  Link  Karl  Pauk  Barbara  Filgueira  Luis 《Research in Science Education》2021,51(2):277-299

Research in Science Education - This educational study aimed to explore the feasibility and acceptance of a literacy exercise adopted from the realworld of scientific publishing in a cell and...  相似文献