Bistable nonlinear damper based on a buckled beam configuration

International audienceThis article addresses a particular realization of a compact bistable nonlinear absorber based on the concept of Nonlinear Energy Sink. The article presents both a detailed description of the absorber mechanics and an illustration of the targeted energy transfer between the absorber and a linear system. The experimental results are accompanied with the numerical simulations. Beside practical improvements linked to the features of absorber design, the obtained results stay in line with those found for simpler realizations of a bistable Nonlinear Energy Sinks

Nonlinear targeted energy transfer of two coupled cantilever beams coupled to a bistable light attachment

International audienceIn order to control the sound radiation by a structure, one aims to control vibration of radiating modes of vibration using " Energy Pumping " also named " Targeted Energy Transfer ". This principle is here applied to a simplified model of a double leaf panel. This model is made of two beams coupled by a spring. One of the beams is connected to a nonlinear absorber. This nonlinear absorber is made of a 3D-printed support on which is clamped a buckled thin small beam with a small mass fixed at its center having two equilibrium positions. The experiments showed that, once attached onto a vibrating system to be controlled, under forced excitation of the primary system, the light bistable oscillator allows a reduction of structural vibration up to 10 dB for significant amplitude and frequency range around the first two vibration modes of the system

Loss of correlation between HIV viral load and CD4+ T-cell counts in HIV/HTLV-1 co-infection in treatment naive Mozambican patients

Seven hundred and four HIV-1/2-positive, antiretroviral therapy (ART) naïve patients were screened for HTLV-1 infection. Antibodies to HTLV-1 were found in 32/704 (4.5%) of the patients. Each co-infected individual was matched with two HIV mono-infected patients according to World Health Organization clinical stage, age +/-5 years and gender. Key clinical and laboratory characteristics were compared between the two groups. Mono-infected and co-infected patients displayed similar clinical characteristics. However, co-infected patients had higher absolute CD4+ T-cell counts (P = 0.001), higher percentage CD4+ T-cell counts (P < 0.001) and higher CD4/CD8 ratios (P < 0.001). Although HIV plasma RNA viral loads were inversely correlated with CD4+ T-cell-counts in mono-infected patients (P < 0.0001), a correlation was not found in co-infected individuals (P = 0.11). Patients with untreated HIV and HTLV-1 co-infection show a dissociation between immunological and HIV virological markers. Current recommendations for initiating ART and chemoprophylaxis against opportunistic infections in resource-poor settings rely on more readily available CD4+ T-cell counts without viral load parameters. These guidelines are not appropriate for co-infected individuals in whom high CD4+ T-cell counts persist despite high HIV viral load states. Thus, for co-infected patients, even in resource-poor settings, HIV viral loads are likely to contribute information crucial for the appropriate timing of ART introduction

On the existence of compression-only discrete force networks that support assigned sets of nodal forces

We formulate a linear programming approach to the limit analysis of discrete element models of masonry structures. Numerical results show the ability of the given procedure to predict the limit value of the multiplier of variable horizontal forces, which are applied to masonry walls in association with a fixed vertical loading

Analyse expérimentale du sifflement d'un riser industriel

International audienceLe champ acoustique induit par un écoulement dans un tuyau corrugué est étudié depuis longtemps. Un regain d'intérêt s'est manifesté en lien avec le développement de l'exploitation de gisements de gaz en haute mer utilisant de grandes longueurs de riser pour le transport gazier. Sur de telles installations, le phénomène peut entraîner une défaillance de l'équipement adjacent aux risers. Dans ce cadre, un test a été effectué dans un tuyau flexible de 6 pouces de diamètre interne et de 18 mètres de longueur. Ce riser était équipé de manchettes en amont et en aval sur lesquelles étaient fixés des capteurs de vitesse par fil chaud, des capteurs de température, des capteurs de pression ainsi que des microphones. Une série d'essais a été conduite pour des pressions internes et des vitesses d'écoulements variées. Nous avons observé que les signaux mesurés en condition de sifflement présentaient des fluctuations significatives tant temporelles que fréquentielles. Nous avons pu montrer que ces dernières étaient liées à la géométrie du riser. En outre, ces analyses ont permis de montrer que le sifflement observé existait aux fréquences acoustiques transverses du riser tout en se propageant à la vitesse de convection de l'écoulement

Effect of parasympathetic stimulation on brain activity during appraisal of fearful expressions

Autonomic nervous system activity is an important component of human emotion. Mental processes influence bodily physiology, which in turn feeds back to influence thoughts and feelings. Afferent cardiovascular signals from arterial baroreceptors in the carotid sinuses are processed within the brain and contribute to this two-way communication with the body. These carotid baroreceptors can be stimulated non-invasively by externally applying focal negative pressure bilaterally to the neck. In an experiment combining functional neuroimaging (fMRI) with carotid stimulation in healthy participants, we tested the hypothesis that manipulating afferent cardiovascular signals alters the central processing of emotional information (fearful and neutral facial expressions). Carotid stimulation, compared with sham stimulation, broadly attenuated activity across cortical and brainstem regions. Modulation of emotional processing was apparent as a significant expression-by-stimulation interaction within left amygdala, where responses during appraisal of fearful faces were selectively reduced by carotid stimulation. Moreover, activity reductions within insula, amygdala, and hippocampus correlated with the degree of stimulation-evoked change in the explicit emotional ratings of fearful faces. Across participants, individual differences in autonomic state (heart rate variability, a proxy measure of autonomic balance toward parasympathetic activity) predicted the extent to which carotid stimulation influenced neural (amygdala) responses during appraisal and subjective rating of fearful faces. Together our results provide mechanistic insight into the visceral component of emotion by identifying the neural substrates mediating cardiovascular influences on the processing of fear signals, potentially implicating central baroreflex mechanisms for anxiolytic treatment targets

Secular Evolution in Mira Variable Pulsations

Stellar evolution theory predicts that asymptotic giant branch stars undergo a series of short thermal pulses that significantly change their luminosity and mass on timescales of hundreds to thousands of years. Secular changes in these stars resulting from thermal pulses can be detected as measurable changes in period if the star is undergoing Mira pulsations. The American Association of Variable Star Observers (AAVSO) International Database currently contains visual data for over 1500 Mira variables. Light curves for these stars span nearly a century in some cases, making it possible to study the secular evolution of the pulsation behavior on these timescales. In this paper, we present the results of our study of period change in 547 Mira variables using data from the AAVSO. We find non-zero rates of period change, dlnP/dt, at the 2-sigma significance level in 57 of the 547 stars, at the 3-sigma level in 21 stars, and at the level of 6-sigma or greater in eight of the 547. The latter eight stars have been previously noted in the literature, and our derived rates of period changes largely agree with published values. The largest and most statistically significant dlnP/dt are consistent with the rates of period change expected during thermal pulses on the AGB. A number of other stars exhibit non-monotonic period changes on decades-long timescales, the cause of which is not yet known.Comment: 37 pages, with 9 figures and 1 table. The complete electronic version of Table 1 is available from the authors upon request. Accepted for publication in The Astronomical Journa

Trichphyton violaceum and T. soudanese: re-emerging pathogens in Italy, 2005-2013

Dermatomycoses due to Trichophyton violaceum are described in Mediterranean Countries, North Africa and in the Horn of Africa where T. soudanense is present too, but it was rare until few years ago in Italy. Aim of the present study was to evaluate an Italian multicenter 9 year (2005-2013) experience concerning these re-emerging pathogens. Fifty three fungal strains were sent from clinical laboratories to the Medical Mycology Committee (CoSM) - Italian Association of Clinical Microbiology (AMCLI) for mycological confirmation. Strains were identified as T. violaceum (23) and T. soudanense (30) by phenotypic and genotypic methods. These dermatophytes present epidemiological (high rate of inter-human transmission, high risk among adopted children coming from countries of either the Horn of Africa or Sub-Saharan Africa also in outbreaks of tinea capitis) and clinical peculiarities (reduced alopecia, presence of exudative lesions) confirming the originality of these \u201cimported\u201d dermatophyte infection