Power exchanged between subsystems with non-diffuse fields in statistical energy analysis.

This article is a discussion on the necessity of the assumption of diffuse field in statistical energy analysis and the validity of the coupling power proportionality which states that the vibrational power exchanged between coupled subsystems is proportional to the difference of their modal energies. It is proposed to re-formulate the coupling power proportionality in terms of local energy density instead of modal energy. We show that this generalized form remains valid even if the vibrational field is not diffuse. Three causes of lack of diffuseness have been studied: coherence of rays in symmetrical geometries, nonergodic geometries, and the effect of high damping. Numerical simulations and experimental results conducted on flat plates in flexural vibration are provided to support these statements.

A versatile flexure-based six-axis force/torque sensor and its application to tribology.

Six-axis force/torque sensors are increasingly needed in mechanical engineering. Here, we introduce a flexure-based design for such sensors, which solves some of the drawbacks of the existing designs. In particular, it is backlash-free, it can be wirelessly monitored, it exactly enforces 90° angles between axes, and it enables visual inspection of the monitored system, thanks to its hollow structure. We first describe the generic design, implementation, and calibration procedure. We then demonstrate its capabilities through three illustration examples relevant to the field of tribology: low friction measurements under ultra-high vacuum, multi-directional friction measurements of elastomer contacts, and force/torque-based contact position monitoring.

Characteristics and outcome of varicella-zoster virus central nervous system infections in adults.

We conducted an observational retrospective study of all adults hospitalized for documented varicella-zoster virus (VZV) meningitis or encephalitis during years 2000-2015 in one referral centre. Thirty-six patients (21 males, 15 females) were included, with meningitis (n = 21), or meningoencephalitis (n = 15). Median age was 51 years [interquartile range, 35-76], and 6 patients (17%) were immunocompromised. Aciclovir was started in 32 patients (89%), with a median dose of 11 mg/kg/8 h [10-15]. No patient died, but 12 (33%) had neurological sequelae at discharge. Age was the only variable associated with adverse outcome (OR 1.98 [1.17-3.35] per 10-year increment, P = 0.011).

High-temporal-resolution quasideterministic dynamics of granular stick-slip.

We report high-temporal-resolution observations of the spontaneous instability of model granular materials under isotropic and triaxial compression in fully drained conditions during laboratory tests representative of earthquakes. Unlike in natural granular materials, in the model granular materials, during the first stage of the tests, i.e., isotropic compression, a series of local collapses of various amplitudes occurs under random triggering cell pressures. During the second stage, i.e., shearing under triaxial compression, the model granular samples exhibit very large quasiperiodic stick-slip motions at random deviatoric triggering stresses. These motions are responsible for very large stress drops that are described by power laws and are accurate over more than 3 decades in logarithmic space. Then, we identify the quasideterministic nature of these stick-slip events, assuming that they are fully controlled by the cell pressure and solid fraction. Finally, we discuss the potential mechanisms that could explain these intriguing behaviors and the possible links with natural earthquakes.

[Libman-Sacks endocarditis under apixaban in a patient with a high-risk profile venous antiphospholipid syndrome]. / Une endocardite de Libman-Sacks survenant sous apixaban chez une patiente atteinte de SAPL veineux de profil à haut risque.

INTRODUCTION: Libman-Sacks endocarditis is a rare complication of antiphospholipid syndrome. Anti-vitamin K therapy is the standard treatment, although valvular replacement surgery may be required in some severe cases. In the latest EULAR recommendations, it is advised not to use direct oral anticoagulants in the management of antiphospholipid syndrome, especially of high-risk profile. CASE REPORT: We present a case of a mitral Libman-Sacks endocarditis complicated with multiple strokes occurring in the setting of an antiphospholipid syndrome with triple positive antibody profile in a 63-year-old woman with multiple sclerosis. She was previously treated with apixaban for two years. Tinzaparin followed by prolonged warfarine treatment and two months of hydroxychloroquine resulted in valvular improvement. CONCLUSION: To our knowledge, this is the first case of Libman-Sacks endocarditis occurring during apixaban therapy in a patient with antiphospholipid syndrome. This severe case highlights the inefficiency of direct oral anticoagulants to prevent thrombotic events in the antiphospholipid syndrome.

Incidence and characteristics of nosocomial influenza in a country with low vaccine coverage.

BACKGROUND: Influenza vaccination coverage is low in France, in at-risk patients and in healthcare workers. AIM: We aimed to estimate the incidence of nosocomial influenza, its characteristics and outcome. METHODS: During one influenza season, we retrospectively evaluated all cases of documented influenza. Inpatients with symptoms onset ≥48 h after admission were enrolled. Data were collected on a standardized questionnaire. RESULTS: From November 2017 to April 2018, 860 patients tested positive for influenza by polymerase chain reaction analysis on a respiratory sample. Among them, 204 (23.7%) were diagnosed ≥48 h after admission, of whom 57 (6.6% of all influenza cases) fulfilled inclusion criteria for nosocomial influenza: 26 women and 31 men, median age 82 years (interquartile range, 72.2-86.9). Twenty patients (38.6%) had recently (<6 months) received the seasonal influenza vaccine. Median time between admission and symptoms onset, and between symptoms onset and diagnosis were, respectively, 11 days (7-19.5) and 29 h (15.5-48). Influenza was mostly acquired in a double-bedded room (N = 39, 68.4%), with documented exposure in 14 cases. Influenza B virus was more common in nosocomial (46/57, 80.7%), than in community-acquired cases (359/803, 44.6%), P<0.001. Mortality rate at three months was 15.8% (N = 9). Incidence of nosocomial influenza was estimated at 0.22 per 1000 hospital-days during the study period. CONCLUSION: Nosocomial influenza is not rare in elderly inpatients, and may have severe consequences. Influenza B virus was over-represented, which suggests higher transmissibility and/or transmission clusters.

Analytical solution for bending vibration of a thin-walled cylinder rolling on a time-varying force.

This paper presents the analytical solution of radial vibration of a rolling cylinder submitted to a time-varying point force. In the simplest situation of simply supported edges and zero in-plane vibration, the cylinder is equivalent to an orthotropic pre-stressed plate resting on a visco-elastic foundation. We give the closed-form solution of vibration as a series of normal modes whose coefficients are explicitly calculated. Cases of both deterministic and random forces are examined. We analyse the effect of rolling speed on merging of vibrational energy induced by Doppler's effect for the example of rolling tyre.

[Non-infective endocarditis]. / Les endocardites non infectieuses.

Non-infective endocarditis, also referred to as non-bacterial thrombotic endocarditis, represent a wide range of rare pathologies, often severe. This review gathered the data available in the literature, to decipher the major information collected on the pathophysiology, the diagnosis and the treatment of these heterogeneous diseases, often misdiagnosed. Characteristics of non-infective endocarditis are similar to infective endocarditis in terms of valvular lesions (mostly left-sided, with regurgitations and vegetations), and their complications (embolism). The diagnosis of non-infective endocarditis is usually considered in patients with blood culture-negative endocarditis. Beyond the usual suspects - marastic endocarditis and systemic lupus erythematosus - which represent more than 75% of the cases, Behçet disease and hypereosinophilic syndrome are the main causes of non-infective endocarditis. More seldomly, rheumatoid arthritis, adult-onset Still disease, allergy to pork in patients with valvular procine bioprosthesis, systemic scleroderma, Cogan or Sneddon syndrome should be suspected. Diagnostic approach is based on history and physical examination, with a special focus on extra-cardiac manifestations, as well as echocardiography, and computed tomography. Treatment relies on intensive management of the underlying disease. Curative anticoagulation is often necessary. Although indications for cardiac surgery are poorly defined, as compared to infective endocarditis, data currently available suggest that an optimal control of the underlying disease before cardiac surgery is of utmost importance, as it dramatically reduces the risk of postoperative complications.

Coupling strength assumption in statistical energy analysis.

This paper is a discussion of the hypothesis of weak coupling in statistical energy analysis (SEA). The examples of coupled oscillators and statistical ensembles of coupled plates excited by broadband random forces are discussed. In each case, a reference calculation is compared with the SEA calculation. First, it is shown that the main SEA relation, the coupling power proportionality, is always valid for two oscillators irrespective of the coupling strength. But the case of three subsystems, consisting of oscillators or ensembles of plates, indicates that the coupling power proportionality fails when the coupling is strong. Strong coupling leads to non-zero indirect coupling loss factors and, sometimes, even to a reversal of the energy flow direction from low to high vibrational temperature.

Entropy in sound and vibration: towards a new paradigm.

This paper describes a discussion on the method and the status of a statistical theory of sound and vibration, called statistical energy analysis (SEA). SEA is a simple theory of sound and vibration in elastic structures that applies when the vibrational energy is diffusely distributed. We show that SEA is a thermodynamical theory of sound and vibration, based on a law of exchange of energy analogous to the Clausius principle. We further investigate the notion of entropy in this context and discuss its meaning. We show that entropy is a measure of information lost in the passage from the classical theory of sound and vibration and SEA, its thermodynamical counterpart.

Efficacy of intraoperative dexmedetomidine compared with placebo for surgery in adults: a meta-analysis of published studies.

Dexmedetomidine (Dex) demonstrates sedative and analgesic effects. We investigated the intraoperative and postoperative effects of intraoperative Dex administration during surgery in adult patients. A search for randomized placebo-controlled trials was conducted in Pubmed and Embase databases to identify randomized controlled clinical trials using intraoperative Dex for surgery in adult population. Outcome assessed were: intraoperative and postoperative opioid consumption, time of recovery from anesthesia, postoperative pain, and postoperative nausea or vomiting (PONV) in the first 24 hours. Data from each trial were combined to calculate pooled odds ratios (OR), mean difference (MD) or standardized mean difference (SMD) and 95% confidence interval (95 % CI). Heterogeneity was measured using I² statistics. Eighteen randomized controlled trials were analyzed. Dex was administered to 815 patients and 410 received placebo. Overall, Dex significantly decreased intraoperative opioid consumption (SMD=-1.58 [-2.98, -0.19], I²=95 %, P<0.00001), but did not decrease time of recovery from anesthesia (SMD=-0.13 [-1.60, 1.34] minutes, I²=95 %, P<0.00001). Dex significantly reduced postoperative opioid consumption (SMD=-1.58 [-2.98, -0.19], I²=95 %, P<0.00001), postoperative pain intensity (SMD=-0.73 [-1.19, -0.27], I²=62 %, P=0.03), and the prevalence of PONV (OR=0.43 [0.27, 0.69], I²=0 %, P=0.46). This meta-analysis shows that intraoperative Dex administration in adult patients reduces intra and postoperative opioid consumption, postoperative pain and PONV. Time of recovery is not affected.

Dynamic indentation on human skin in vivo: ageing effects.

BACKGROUND/PURPOSE: Knowledge of the mechanical properties of the human skin is very important for cosmetic and clinical research. Objective and quantitative measurements are essential to compare studies performed by different experimenters in different centres. The aim of this paper is to present a method to measure the viscoelastic properties of human skin in vivo using dynamic indentation. METHODS: A complete device to assess the stiffness and damping of skin has been developed. The frequency and strain amplitude range from 10 to 60 Hz and from 1 to 10 mum. Tests on pure elastic inert materials have been performed to validate the device. An in vivo study including dynamic indentation, suction test, hydration measurement and topographic analysis has been performed on 46 subjects aged from 18 to 70 years, divided into three groups. RESULTS: Results on inert materials show the validity of the device developed. The mechanical behaviour of the skin can be described by a Kelvin-Voight model under dynamic indentation. A comparison with a suction test, hydration and topographic measurements shows that the stiffness and the damping measured by dynamic indentation correspond mainly to the natural tense state of the skin on the body due to the dermis. A weak correlation has been found between dynamic indentation and suction parameters. The complex modulus measured by dynamic indentation at 10 Hz frequency stress ranges from 7.2 +/- 2.1 kPa for the oldest group to 10.7 +/- 2.6 kPa for the youngest group. CONCLUSION: The device presented gives convincing results. The measurement of stiffness and damping complements the viscoelastic phenomenological parameters of the suction test.

In vivo characterization of viscoelastic properties of human skin using dynamic micro-indentation.

The human skin, the interface between the body and the outside environment, has a very complex mechanical behaviour. Knowledge of its in vivo mechanical characteristics is essential to characterize the effects of medical or cosmetic products. The aim of this work is to present a non-invasive device using dynamic indentation to quantify the viscoelastic properties of human skin in vivo. The frequency and strain amplitude are in the range of 10 to 60 Hz and 1 to 10 microm. The results on 4 subjects show that a Kelvin Voigt model describes the mechanical behaviour of in vivo human skin with dynamic indentation well. The frequency average values of stiffness and damping have also been used to compare skin properties. We found a stiffness value of 47.3 to 128.3 N/m, and damping of 0.08 to 0.121 N.s/m, corresponding to a complex modulus of 13.2 to 33.4 kPa. These results show the ability of this device to characterize viscoelastic properties of human skin.

A functional equation for the specular reflection of rays.

This paper aims to generalize the "radiosity method" when applied to specular reflection. Within the field of thermics, the radiosity method is also called the "standard procedure." The integral equation for incident energy, which is usually derived for diffuse reflection, is replaced by a more appropriate functional equation. The latter is used to solve some specific problems and it is shown that all the classical features of specular reflection, for example, the existence of image sources, are embodied within this equation. This equation can be solved with the ray-tracing technique, despite the implemented mathematics being quite different. Several interesting features of the energy field are presented.

Comparison of an integral equation on energy and the ray-tracing technique in room acoustics.

This paper deals with a comparison of two room acoustic models. The first one is an integral formulation stemming from power balance and the second is the ray-tracing technique with a perfectly diffuse reflection law. The common assumptions to both models are the uncorrelated wave hypothesis and the perfectly diffuse reflection law. The latter allows the use of these methods for nondiffuse fields beyond the validity domain of Sabine's formula. Comparisons of numerical simulations performed with the softwares RAYON and CeReS point out that these results are close to each other and finally, a formal proof is proposed showing that both methods are actually equivalent.