1,721,784 research outputs found
Konzeption der Engergieversorgung und Antriebssteuerung für ein mobiles Roboter-Plattformsystem
No full textRoboter wurden in der Vergangenheit ausschließlich in der Industrie, wie beispielsweise in Fertigungsstraßen in der Automobilindustrie, oder zu Forschungszwecken eingesetzt. Dort werden die Arbeitsbereiche der Roboter streng von denen des Menschen abgetrennt. Seit wenigen Jahren gewinnt jedoch das Thema Service Robotik im menschlichen Umfeld zunehmend an Bedeutung. Bereits jetzt werden Menschen in vielen Bereichen von elektromechanischen Helfern unterstützt. Die Zahl der verschiedenen Roboerarten ist so groß wie die ihrer Einsatzgebiete. Sie werden häufig für Tätigkeiten herangezogen, die für den Menschen lästig, gefährlich oder so gar unmöglich sind. So gibt es inzwischen vollautomatische Rasenmäher und Staubsauger, Entschärfungsroboter für Sprengsätze, Aufklärungsdrohnen, autonome Reinigungsroboter für Abwasserrohre, Roboter für Unterwasserarbeiten und viele mehr.
Doch der Einzug der Roboter in das menschliche Umfeld hat gerade erst begonnen. Durch die fortschreitende Überalterung unserer Gesellschaft werden in Zukunft mehr und mehr Menschen auf die Hilfe von Dienstleistungsrobotern im Alltag angewiesen sein. Das Spektrum der verschiedenen Tätigkeiten, die ein Helfer im Alltag zu verrichten hat, umfasst dabei alles wozu auch ein gesunder Mensch imstande wäre. Es ist daher naheliegend Roboter zu entwickeln, die dem Menschen ähnlich sehen. Ein menschenähnlicher Roboter wäre nicht nur hervorragend an die menschliche Umgebung angepasst, der Mensch könnte dem Roboter auch sehr leicht etwas beibringen, ihn programmieren, indem er es ihm einfach vormacht.
Ein Ziel des Instituts für Robotik und Mechatronik ist daher, einen humanoiden Roboter zu entwickeln, der in seiner Größe und seinem kinematischen Aufbau dem Menschen ähnelt. Doch dabei stellt sich immer wieder heraus, dass eine Million Jahre menschliche Evolution einen in jeder Hinsicht höchst effizienten Bewegungsapparat hervorgebracht haben, der auch in nächster Zukunft nicht nachgebaut werden kann
Network science and e‑tourism
No full textNetwork science in tourism: a perspecive and a special issu
Simple fluid with broken time reversal invariance
Full text linkWe characterize a system of hard spheres with a simple collision rule that
breaks time reversal symmetry, but conserves energy. The collisions lead to an
a-chiral, isotropic, and homogeneous stationary state, whose properties are
determined in simulations and compared to an approximate theory originally
developed for elastic hard spheres. In the nonequilibrium fluid state,
velocities are correlated, a phenomenon known from other nonequilibrium
stationary states. The correlations are long-ranged decaying like in
dimensions. Such correlations are expected on general grounds far from
equilibrium and had previously been observed in driven or non-stationary
systems.Comment: 14 pages, 17 Figure
Evaluation of the probability current in the stochastic path integral formalism
No full textThe probability current is a vital quantity in the Fokker-Planck description of stochastic processes. It characterizes non-equilibrium stationary states and appears in linear response calculations. We recover and review the probability current in the Onsager-Machlup functional approach to Markov processes by deriving a self- contained expression in general non-equilibrium fluctuation-dissipation relations using field theoretical methods. The derived formulas hold for non-constant drift and diffusion tensors and are explicitly evaluated in an Ornstein-Uhlenbeck process with non-reciprocal interactions specified as a harmonically bound particle in shear flow. Our work clarifies the concept of the probability current — familiar from the Fokker-Planck equation — in the path integral approach.publishe
Emergence of Long-Ranged Stress Correlations at the Liquid to Glass Transition
No full textA theory for the nonlocal shear stress correlations in supercooled liquids is derived from first principles. It captures the crossover from viscous to elastic dynamics at an idealized liquid to glass transition and explains the emergence of long-ranged stress correlations in glass, as expected from classical continuum elasticity. The long-ranged stress correlations can be traced to the coupling of shear stress to transverse momentum, which is ignored in the classic Maxwell model. To rescue this widely used model, we suggest a generalization in terms of a single relaxation time τ for the fast degrees of freedom only. This generalized Maxwell model implies a divergent correlation length ξ∝τ as well as dynamic critical scaling and correctly accounts for the far-field stress correlations. It can be rephrased in terms of generalized hydrodynamic equations, which naturally couple stress and momentum and furthermore allow us to connect to fluidity and elastoplastic models.publishe
Stress auto-correlation tensor in glass-forming isothermal fluids: From viscous to elastic response
No full textWe develop a generalized hydrodynamic theory, which can account for the build-up of long-ranged and long-lived shear stress correlations in supercooled liquids as the glass transition is approached. Our theory is based on the decomposition of tensorial stress relaxation into fast microscopic processes and slow dynamics due to conservation laws. In the fluid, anisotropic shear stress correlations arise from the tensorial nature of stress. By approximating the fast microscopic processes by a single relaxation time in the spirit of Maxwell, we find viscoelastic precursors of the Eshelby-type correlations familiar in an elastic medium. The spatial extent of shear stress fluctuations is characterized by a correlation length ξ which grows like the viscosity η or time scale τ ∼ η, whose divergence signals the glass transition. In the solid, the correlation length is infinite and stress correlations decay algebraically as r−d in d dimensions.publishe
Brownian systems perturbed by mild shear: comparing response relations
No full textWe present a comprehensive study of the linear response of interacting underdamped Brownian particles to simple shear flow. We collect six different routes for computing the response, two of which are based on the symmetry of the considered system and observable with respect to the shear axes. We include the extension of the Green–Kubo relation to underdamped cases, which shows two unexpected additional terms. These six computational methods are applied to investigate the relaxation of the response towards the steady state for different observables, where interesting effects due to interactions and a finite particle mass are observed. Moreover, we compare the different response relations in terms of their statistical efficiency, identifying their relative demand on experimental measurement time or computational resources in computer simulations. Finally, several measures of breakdown of linear response theory for larger shear rates are discussed.publishe
Emergence of Goldstone excitations in stress correlations of glass-forming colloidal dispersions
No full textWe compute the dynamic correlations of the nonlocal shear stress at the liquid to glass transition in colloidal dispersions. Whereas Eshelby's elastic pattern is recovered independently of the dynamics, the Goldstone modes of the colloidal glass are diffusive, , because the transverse momentum is not conserved —excluding propagating transverse sound. Precursors of both, the Goldstone modes and the long-ranged, anisotropic stress correlations, can be observed in the colloidal fluid. The slow diffusive mode dominates the dynamics in the supercooled liquid for wave numbers with a correlation length which grows like the square root of the relaxation time τ. Time- and space-dependent stress correlations are anisotropic, decaying like . These results are derived within a hydrodynamic theory, generalising Maxwell‘s model to finite wave numbers, after the dynamics has been decomposed into potentially slow modes, associated with the order parameter, and fast microscopic degrees of freedom. Alternatively, hydrodynamic equations, closed by constitutive laws, can be used to predict the linear response of stress to an applied shear flow
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
- …
