2,078 research outputs found

    Rubber friction: role of the flash temperature

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    When a rubber block is sliding on a hard rough substrate, the substrate asperities will exert time-dependent deformations of the rubber surface resulting in viscoelastic energy dissipation in the rubber, which gives a contribution to the sliding friction. Most surfaces of solids have roughness on many different length scales, and when calculating the friction force it is necessary to include the viscoelastic deformations on all length scales. The energy dissipation will result in local heating of the rubber. Since the viscoelastic properties of rubber-like materials are extremely strongly temperature dependent, it is necessary to include the local temperature increase in the analysis. At very low sliding velocity the temperature increase is negligible because of heat diffusion, but already for velocities of order 0.01 m/s the local heating may be very important. Here I study the influence of the local heating on the rubber friction, and I show that in a typical case the temperature increase results in a decrease in rubber friction with increasing sliding velocity for v > 0.01 m/s. This may result in stick-slip instabilities, and is of crucial importance in many practical applications, e.g., for the tire-road friction, and in particular for ABS-breaking systems.Comment: 22 pages, 27 figure

    Bildung einer Fiskalunion: Ein wirkungsvolles Instrument zur Stabilisierung der Eurozone?

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    Im Juni 2015 legten Jean-Claude Juncker, Donald Tusk, Jeroen Dijsselbloem, Mario Draghi und Martin Schulz Vorschläge zur »langfristigen Stärkung der Währungsunion« vor. Sie sehen unter anderem auch die Einsetzung eines beratenden Europäischen Fiskalausschusses vor, der die Arbeit der nationalen Räte für Finanzpolitik koordinieren soll. Kann das ein wirkungsvolles Instrument zur Stabilisierung der Eurozone sein? Nach Ansicht von Charles B. Blankart, Humboldt-Universität zu Berlin und Universität Luzern, hat sich die Europäische Union seit etwa 1992 grundlegend verändert. Während sie bis dahin dem zweiseitigen Handel, einem privaten Gut diente, stehe seither der Euro als ein öffentliches Gut im Vordergrund. Blankart sieht in den Zielen der Vorschläge die bekannten »Öffentlichen-Gut-Probleme« des Euro. Die Vorleistungen des einen bewirken nicht automatisch Gegenleistungen des anderen. Das Freifahrerverhalten wird nicht beseitigt. Katharina Gnath, Bertelsmann Stiftung, und Jörg Haas, Jacques Delors Institut – Berlin, argumentieren, dass eine Fiskalunion nur dann stabilisieren kann, wenn sie sowohl glaubwürdige Haushaltsregeln als auch Elemente der Teilung von Risiko umfasst. Sie sei ein wichtiges Mittel zur wirksamen Stärkung der Eurozone, dürfe aber nicht das einzige bleiben. Thiess Büttner, Universität Erlangen-Nürnberg, ist der Ansicht, dass der Vorschlag kaum geeignet sei, die Europäische Währungsunion durchgreifend zu stabilisieren. Je nach der Ausgestaltung könnte er sich sogar als kontraproduktiv erweisen. Frank Westermann, Universität Osnabrück, sieht Parallelen in der jüngsten Entwicklung der Europäischen Währungsunion zu derjenigen Ostdeutschlands nach der Wiedervereinigung. Die reale Lohnentwicklung eile der Produktivität voraus, und es entwickle sich ein Transfersystem, das einen Aufschub notwendiger Arbeitsmarktreformen ermögliche. Eine langfristig expansive Fiskalpolitik, die in einer Fiskalunion ins­titutionalisiert würde, könne nur kurzfristig die Nachf

    DC generation from peripheral blood mononuclear cells in patients with chronic myeloid leukemia: Influence of interferons on DC yield and functional properties

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    In Chronic Myeloid Leukemia (CML), standard treatment consists of modern tyrosine-kinase inhibitors (TKI). Nevertheless, there is evidence that immune responses against leukemia-associated antigens (LAA) may play an important role in disease control. Dendritic cell (DC)- based immunotherapy is able to induce T cell responses against LAA and might therefore pose an interesting therapeutic option in CML, especially in the setting of minimal residual disease (MRD). GMP production of DC for clinical vaccination remains a time- and cost- intensive procedure and standardized DC generation is warranted. We asked whether maturation-induction with IFN-{gamma} and IFN-{alpha} has an influence on functional properties of DC derived from peripheral blood mononuclear cells (PBMC) in CML patients. Monocyte-derived DC from healthy donors and from patients with CML were analyzed after maturation-induction with our TNF-{alpha}-containing standard cytokine cocktail with or without addition of IFN-{alpha} and/or IFN-{gamma}. Our results confirm that the addition of IFN-{gamma} leads to enhanced IL-12 secretion in healthy donors. In contrast, in CML patients, IFN-{gamma} was not able to increase IL-12 secretion, possibly due to a higher degree of cell adherence and lower cell yield during the cell culture. Our data suggest, that- in contrast to healthy donors-, additional interferons are not beneficial for maturation induction during large-scale DC production in patients with CML

    Immunological Memory Transferred with CD4 T Cells Specific for Tuberculosis Antigens Ag85B-TB10.4: Persisting Antigen Enhances Protection

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    BACKGROUND:High levels of death and morbidity worldwide caused by tuberculosis has stimulated efforts to develop a new vaccine to replace BCG. A number of Mycobacterium tuberculosis (Mtb)-specific antigens have been synthesised as recombinant subunit vaccines for clinical evaluation. Recently a fusion protein of TB antigen Ag85B combined with a second immunodominant TB antigen TB10.4 was emulsified with a novel non-phospholipid-based liposomal adjuvant to produce a new subunit vaccine, investigated here. Currently, there is no consensus as to whether or not long-term T cell memory depends on a source of persisting antigen. To explore this and questions regarding lifespan, phenotype and cytokine patterns of CD4 memory T cells, we developed an animal model in which vaccine-induced CD4 memory T cells could transfer immunity to irradiated recipients. METHODOLOGY/PRINCIPAL FINDINGS:The transfer of protective immunity using Ag85B-TB10.4-specific, CD45RB(low) CD62L(low) CD4 T cells was assessed in sub-lethally irradiated recipients following challenge with live BCG, used here as a surrogate for virulent Mtb. Donor T cells also carried an allotype marker allowing us to monitor numbers of antigen-specific, cytokine-producing CD4 T cells in recipients. The results showed that both Ag85B-TB10.4 and BCG vaccination induced immunity that could be transferred with a single injection of 3x10(6) CD4 T cells. Ten times fewer numbers of CD4 T cells (0.3x10(6)) from donors immunised with Ag85B-TB10.4 vaccine alone, transferred equivalent protection. CD4 T cells from donors primed by BCG and boosted with the vaccine similarly transferred protective immunity. When BCG challenge was delayed for 1 or 2 months after transfer (a test of memory T cell survival) recipients remained protected. Importantly, recipients that contained persisting antigen, either live BCG or inert vaccine, showed significantly higher levels of protection (p<0.01). Overall the numbers of IFN-gamma-producing CD4 T cells were poorly correlated with levels of protection. CONCLUSIONS/SIGNIFICANCE:The Ag85B-TB10.4 vaccine, with or without BCG-priming, generated TB-specific CD4 T cells that transferred protective immunity in mice challenged with BCG. The level of protection was enhanced in recipients containing a residual source of specific antigen that could be either viable or inert

    Investigating the association between children’s screen media exposure and vocabulary size in the UK

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    Children are growing up in a digital age with increasing exposure to television and touchscreen devices. We tested whether exposure to screen media is associated with children’s early language development. One hundred and thirty-one highly educated caregivers of UK children aged 6–36 months completed a media exposure questionnaire and vocabulary measure. 99% of children were read to daily, 82% watched television, and 49% used mobile touchscreen devices daily. Regression analyses revealed that time spent reading positively predicted vocabulary comprehension and production scores at 6–18 months, but time spent engaging with television or mobile touchscreen devices was not associated with vocabulary scores. Critically, correlations revealed that time spent reading or engaging with other non-screen activities was not offset by time spent engaging with television or mobile touchscreen devices. Thus, there was no evidence to suggest that screen media exposure adversely influenced vocabulary size in our sample of highly educated families with moderate media use
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