Validation of Volumetric Contact Dynamics Models

A volumetric contact dynamics model has been proposed by Gonthier et al. [1, 2, 3] for the purpose of rapidly generating reliable simulations of space-based manipulator contact dynamics. By assuming materials behave as a Winkler elastic foundation model, forces and moments between two bodies in contact can be expressed in terms of the volume of interference between the undeformed geometries of the bodies. Friction between bodies is modelled by a dwell-time dependent bristle model for both tangential friction, and spinning friction torque. This volumetric model has a number of advantages. Unlike point-contact models, it allows for the modelling of contact between complex geometries and scenarios where the contact surface is relatively large, while being less computationally expensive than finite element methods. Rolling resistance is included in the model through damping effects across the volume of interference. The friction model accounts for dwell-time dependent slip-stick effects, spinning friction torque, and the Contensou effect. In this thesis, an experimental validation of the volumetric contact model is presented for the first time. Models for simple geometries in contact (e.g. cylinder-on-plane, sphere-on-plane) have been developed for stationary contact and for contact with motion normal and tangential to the contact surface. Tangential motion is modelled with pure translation, pure rotation about the normal axis, and combined motion, in order to separately consider friction forces, spinning friction torque, and the Contensou effect, respectively. An apparatus has been developed to experimentally validate these models for metal-on-metal contact. The apparatus has two configurations, one for validating the normal contact models and the other for the friction models. Experimental measurements of forces and displacements are used to identify model parameters (e.g. volumetric stiffness, friction coefficients, etc.). For normal force experiments, modelling the contact forces as proportional to volume of interference was found to be a reasonable approximation. A Hertzian model was compared with the volumetric model for spherical payloads loaded quasi-statically. Using stiffnesses estimated from spherical experiments, small misalignments of the cylindrical payloads were estimated that corresponded well with measured results. Dynamic experiments suggest an inverse relationship between impact velocity and the hysteretic damping coefficient. The high normal forces applied in the friction experiments were found to create significant wear on the contact surfaces. Coefficients of friction between titanium and aluminum were found to be consistent translationally and rotationally. Friction forces from combined translation and rotation demonstrate that the Contensou effect is accurately described by the volumetric contact model

Attitudes towards people with dementia in Germany

People with dementia belong to long-life societies. As dementia affects all areas of a person's life, those affected and their relatives require support from very different areas of society. Against this background, it is important to investigate attitudes among the general population towards people with dementia. Of particular interest is how familiar the general population is with the topic of dementia, as well as perceptions of the possible support for people with dementia. Equally relevant is the extent to which people avoid contact with people with dementia in everyday life or even encounter them with fear. The study is based on data of 4.175 persons of the age of 45 to 90 years from the German Ageing Survey. Core statements: Many people are unfamiliar with dementia, while few are afraid of people with dementia. There are no significant differences in attitudes between age groups or between men and women. People with a higher educational level show a higher familiarity with dementia. A higher household income is associated with less fear and more perceived support opportunities in relation to people with dementia. However, household income is not related to willingness to provide care. Willingness to care for people with dementia is strongly related to familiarity with dementia

The process gg -> WW as a background to the Higgs signal at the LHC

The production of W pairs from the one-loop gluon fusion process is studied. Formulas are presented for the helicity amplitudes keeping the top mass finite, but all other quark masses zero. The correlations among the leptons coming from the W bosons are kept. The contribution of this background to the Higgs boson search in the WW decay mode at the LHC is estimated by applying the cuts foreseen in experimental searches using the PYTHIA Monte Carlo program. Kinematic distributions for the final state leptons are compared to those of the Higgs boson signal and of the q qbar -> WW background. After applying final cuts, the gg background is found to be large, at the level of 35% of the q qbar background.The characteristics of the gg background are very similar to those of the signal. Therefore, an experimental normalization of this background component appears to be very difficult and the uncertainty must largely be determined by theory. As a result, the significance of a Higgs signal in the gg -> H -> WW mode at the LHC is reduced.Comment: 24 pages, 4 figure

Semileptonic decays of polarised top quarks: V + A admixture and QCD corrections

The semileptonic decays of polarised top quarks are analysed for a general chirality-conserving tbW vertex. We calculate double differential distributions for the charged lepton and the neutrino to order \alpha_s in the QCD coupling. We present these QCD corrections in terms of compact parameterisations that should be useful for the future investigation of the structure of the top decay vertex on the basis of large data samples.Comment: 7 pages, 2 figures, Late

String correlation functions of the spin-1/2 Heisenberg XXZ chain

We calculate certain string correlation functions, originally introduced as order parameters in integer spin chains, for the spin-1/2 XXZ Heisenberg chain at zero temperature and in the thermodynamic limit. For small distances, we obtain exact results from Bethe Ansatz and exact diagonalization, whereas in the large-distance limit, field-theoretical arguments yield an asymptotic algebraic decay. We also make contact with two-point spin-correlation functions in the asymptotic limit.Comment: 23 pages, 4 figures. An incomplete discussion on the limit to the spin-spin correlation function is corrected on page 1

An immunohistochemical study of the tissue bridging adult spondylolytic defects—the presence and significance of fibrocartilaginous entheses

Introduction Spondylolytic spondylolisthesis is an osseous discontinuity of the vertebral arch that predominantly affects the fifth lumbar vertebra. Biomechanical factors are closely related to the condition. An immunohistochemical investigation of lysis-zone tissue obtained from patients with isthmic spondylolisthesis was performed to determine the molecular composition of the lysis-zone tissue and enable interpretation of the mechanical demands to which the tissue is subject. Methods: During surgery, the tissue filling the spondylytic defects was removed from 13 patients. Twelve spondylolistheses were at the L5/S1 level with slippage being less than Meyerding grade II. Samples were methanol fixed, decalcified and cryosectioned. Sections were labelled with a panel of monoclonal antibodies directed against collagens, glycosaminoglycans and proteoglycans. Results: The lysis-zone tissue had an ordered collagenous structure with distinct fibrocartilaginous entheses at both ends. Typically, these had zones of calcified and uncalcified fibrocartilage labelling strongly for type II collagen and aggrecan. Labelling was also detected around bony spurs that extended from the enthesis into the lysis-zone. The entheses also labelled for types I, III and VI collagens, chondroitin four and six sulfate, keratan and dermatan sulfate, link protein, versican and tenascin. Conclusions: Although the gap filled by the lysis tissue is a pathological feature, the tissue itself has hallmarks of a normal ligament—i.e. fibrocartilaginous entheses at either end of an ordered collagenous fibre structure. The fibrocartilage is believed to dissipate stress concentration at the hard/soft tissue boundary. The widespread occurrence of molecules typical of cartilage in the attachment of the lysis tissue, suggests that compressive and shear forces are present to which the enthesis is adapted, in addition to the expected tensile forces across the spondylolysis. Such a combination of tensile, shear and compressive forces must operate whenever there is any opening or closing of the spondylolytic ga

Einstellungen zu Menschen mit Demenz in Deutschland

Menschen mit Demenz gehören zu Gesellschaften des langen Lebens. Weil eine Demenz alle Lebensbereiche eines Menschen betrifft, benötigen Betroffene und ihre Angehörigen Unterstützung aus ganz unterschiedlichen Bereichen der Gesellschaft. Von besonderem Interesse ist hierbei, wie stark die Bevölkerung mit dem Thema Demenz vertraut ist und inwieweit Unterstützungsmöglichkeiten für die Lebenssituation von Menschen mit Demenz gesehen werden. Ebenso relevant ist die Frage, inwieweit Menschen im Alltag den Kontakt zu Menschen mit Demenz scheuen oder ihnen gar mit Angst begegnen. Dem geht die vorliegende Untersuchung mit Daten des Deutschen Alterssurvey nach. Die Befunde beruhen auf den Angaben von 4.175 Personen im Alter von 45 bis 90 Jahren. Viele Menschen sind nicht mit Demenz vertraut, gleichzeitig haben nur wenige Angst vor Menschen mit Demenz. Zwischen Altersgruppen sowie zwischen Männern und Frauen gibt es keine bedeutsamen Einstellungsunterschiede. Menschen mit höherer Bildung zeigen eine höhere Vertrautheit mit Demenz. Ein höheres Haushaltseinkommen geht mit weniger Angst und mehr wahrgenommenen Unterstützungsmöglichkeiten in Bezug auf Menschen mit Demenz einher - mit der Bereitschaft zur Übernahme von Betreuung und Pflege hängt das Haushaltseinkommen allerdings nicht zusammen. Die Bereitschaft zur Betreuung von Menschen mit Demenz hängt stark mit der Vertrautheit mit Demenz zusammen

Gluon-induced W-boson pair production at the LHC

Pair production of W bosons constitutes an important background to Higgs boson and new physics searches at the Large Hadron Collider LHC. We have calculated the loop-induced gluon-fusion process gg -> W*W* -> leptons, including intermediate light and heavy quarks and allowing for arbitrary invariant masses of the W bosons. While formally of next-to-next-to-leading order, the gg -> W*W* -> leptons process is enhanced by the large gluon flux at the LHC and by experimental Higgs search cuts, and increases the next-to-leading order WW background estimate for Higgs searches by about 30%. We have extended our previous calculation to include the contribution from the intermediate top-bottom massive quark loop and the Higgs signal process. We provide updated results for cross sections and differential distributions and study the interference between the different gluon scattering contributions. We describe important analytical and numerical aspects of our calculation and present the public GG2WW event generator.Comment: 20 pages, 4 figure

A genesis index for monsoon disturbances

Synoptic-scale monsoon disturbances produce the majority of continental rainfall in the monsoon regions of South Asia and Australia, yet there is little understanding of the conditions that foster development of these low pressure systems. Here a genesis index is used to associate monsoon disturbance genesis in a global domain with monthly mean, climatological environmental variables. This monsoon disturbance genesis index (MDGI) is based on four objectively selected variables: total column water vapor, low-level absolute vorticity, an approximate measure of convective available potential energy, and midtropospheric relative humidity. A Poisson regression is used to estimate the index coefficients. Unlike existing tropical cyclone genesis indices, the MDGI is defined over both land and ocean, consistent with the fact that monsoon disturbance genesis can occur over land. The index coefficients change little from their global values when estimated separately for the Asian–Australian monsoon region or the Indian monsoon region, suggesting that the conditions favorable for monsoon disturbance genesis, and perhaps the dynamics of genesis itself, are common across multiple monsoon regions. Vertical wind shear is found to be a useful predictor in some regional subdomains; although previous studies suggested that baroclinicity may foster monsoon disturbance genesis, here genesis frequency is shown to be reduced in regions of strong climatological vertical shear. The coefficients of the MDGI suggest that monsoon disturbance genesis is fostered by humid, convectively unstable environments that are rich in vorticity. Similarities with indices used to describe the distribution of tropical cyclone genesis are discussed

A local limit theorem for sums of dependent random variables

A local version of the central limit theorem is established for normalized sums of dependent random variables when a global theorem is known and conditional distributions are sufficiently smooth. The proof uses ideas from Statistics, by representing the density as the integral of a score function for a translation family of distributions.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/28703/1/0000523.pd