Stochastic Properties of Static Friction

The onset of frictional motion is mediated by rupture-like slip fronts, which nucleate locally and propagate eventually along the entire interface causing global sliding. The static friction coefficient is a macroscopic measure of the applied force at this particular instant when the frictional interface loses stability. However, experimental studies are known to present important scatter in the measurement of static friction; the origin of which remains unexplained. Here, we study the nucleation of local slip at interfaces with slip-weakening friction of random strength and analyze the resulting variability in the measured global strength. Using numerical simulations that solve the elastodynamic equations, we observe that multiple slip patches nucleate simultaneously, many of which are stable and grow only slowly, but one reaches a critical length and starts propagating dynamically. We show that a theoretical criterion based on a static equilibrium solution predicts quantitatively well the onset of frictional sliding. We develop a Monte-Carlo model by adapting the theoretical criterion and pre-computing modal convolution terms, which enables us to run efficiently a large number of samples and to study variability in global strength distribution caused by the stochastic properties of local frictional strength. The results demonstrate that an increasing spatial correlation length on the interface, representing geometric imperfections and roughness, causes lower global static friction. Conversely, smaller correlation length increases the macroscopic strength while its variability decreases. We further show that randomness in local friction properties is insufficient for the existence of systematic precursory slip events. Random or systematic non-uniformity in the driving force, such as potential energy or stress drop, is required for arrested slip fronts. Our model and observations..

Characterizing the strength of wood truss joints

Probability density functions (normal, lognormal, and three-parameter Weibull) were used to characterize strength data for three different types of metal-plate-connected wood truss joints (web at the bottom chord, tension splice, and heel). Modulus of elasticity (MOE) of the lumber used to fabricate the joints was also characterized. A probability-plot technique, in conjunction with Kolmogorov-Smirnov and chi-square statistics, was used to determine which distribution best fit the data. Lumber MOE was best described by a lognormal distribution. No single distributional form fit the strength data for all three joint types with equal accuracy. Lumber MOE and joint strength were unrelated. Strength data for the web at the bottom chord and heel joints were best described by normal distributions; however, none of the distributions considered fit the data for the tension splice joints. The probability-plot technique provided a better visual inspection of fit than did a density function superimposed over a histogram. Fitted distributions are easy to work with and can be used in reliability analyses to simulate strength values of joints. The results presented here are for particular joint types and plates and should not be extrapolated to other truss joints

Statistics of non-linear stochastic dynamical systems under L\'evy noises by a convolution quadrature approach

This paper describes a novel numerical approach to find the statistics of the non-stationary response of scalar non-linear systems excited by L\'evy white noises. The proposed numerical procedure relies on the introduction of an integral transform of Wiener-Hopf type into the equation governing the characteristic function. Once this equation is rewritten as partial integro-differential equation, it is then solved by applying the method of convolution quadrature originally proposed by Lubich, here extended to deal with this particular integral transform. The proposed approach is relevant for two reasons: 1) Statistics of systems with several different drift terms can be handled in an efficient way, independently from the kind of white noise; 2) The particular form of Wiener-Hopf integral transform and its numerical evaluation, both introduced in this study, are generalizations of fractional integro-differential operators of potential type and Gr\"unwald-Letnikov fractional derivatives, respectively.Comment: 20 pages, 5 figure

Retrospective Study Minimally Invasive Management of Postoperative Lithiasis of the Common Bile Duct

Rezumat Studiu retrospectiv asupra managementului miniinvaziv al litiazei postoperatorii a cãii biliare principale Introducere: Litiaza postoperatorie a cãii biliare principale (CBP) ocupã un loc însemnat în patologia bilio-pancreaticã, atât prin frecvenåa mare, cât şi prin problemele de diagnostic şi tratament pe care le ridicã. Material aei metodã: Bazându-ne pe o experienåã, care s-a desfãşurat într-o perioadã de cinci ani (2008)(2009)(2010)(2011)(2012), evaluatã retrospectiv, totalizând 51 de pacienåi cu litiazã postoperatorie a CBP, am încercat sã formulãm câteva recomandãri în tratamentul acestei patologii. Acestea au fost ghidate de opåiunile terapeutice alternative existente şi de ideile vehiculate în literatura de specialitate, privind rezultatele înregistrate de fiecare manierã de tratament. Rezultate: Rata de clearence a CBP a fost de 93,6%, morbiditatea de 10,65% şi mortalitatea de 0%, acestea îndreptãåindu-ne sã apreciem eficienåa tratamentului miniinvaziv, ca fiind maximã în tratamentul acestei patologii. Concluzii: Tratamentul endoscopic al litiazei postoperatorii a CBP s-a dovedit a fi posibil, eficient şi credem cã este bine a se folosi de principiu, chirurgia deschisã rãmânând rezervatã doar eşecurilor sau contraindicaåiilor tratamentului miniinvaziv. Cuvinte cheie: litiazã coledocianã, ERCP, sfincterotomie endoscopicã Abstract Introduction: Postoperative common bile duct (CBD) lithiasis holdsa significant place in the bilio-pancreatic pathology, both due to its high frequency as well as to the diagnostic and treatment issues it triggers. Material and Methods: Based on a 5-year experience (2008)(2009)(2010)(2011)(2012), assessed retrospectively, totalling 51 patients with postoperative lithiasis of CBD, we tried to elaborate on several recommendations for the treatment of this pathology. The recommendations were guided by the existing alternative therapeutic options and by the ideas in the literature regarding the results achieved by every manner of treatment. Results: The rate of clearance of the CBD was of 93.6%, themorbidity rate was of 10.65% and the mortality rate was of 0%, which entitles us to deem the effectiveness of the minimally invasive treatment as maximum in the treatment of this pathology. Conclusions: The endoscopic treatment of postoperative lithiasis of the CBD proved to be possible, efficient and we believe it good to be used as a principle; open surgery should be the solution in case of failures or of contraindications to minimally invasive treatmen

Theory of the Relativistic Brownian Motion. The (1+1)-Dimensional Case

We construct a theory for the 1+1-dimensional Brownian motion in a viscous medium, which is (i) consistent with Einstein's theory of special relativity, and (ii) reduces to the standard Brownian motion in the Newtonian limit case. In the first part of this work the classical Langevin equations of motion, governing the nonrelativistic dynamics of a free Brownian particle in the presence of a heat bath (white noise), are generalized in the framework of special relativity. Subsequently, the corresponding relativistic Langevin equations are discussed in the context of the generalized Ito (pre-point discretization rule) vs. the Stratonovich (mid-point discretization rule) dilemma: It is found that the relativistic Langevin equation in the Haenggi-Klimontovich interpretation (with the post-point discretization rule) is the only one that yields agreement with the relativistic Maxwell distribution. Numerical results for the relativistic Langevin equation of a free Brownian particle are presented.Comment: see cond-mat/0607082 for an improved theor

Continuous professional development: elevating thoracic oncology education in Europe

The @EuroRespSoc launches a new thoracic oncology continuous professional development programme http://bit.ly/31ShuTp

The DIAMORFOSIS (DIAgnosis and Management Of lung canceR and FibrOSIS) survey: international survey and call for consensus.

Background Currently there is major lack of agreement on the diagnostic and therapeutic management of patients with idiopathic pulmonary fibrosis (IPF) and lung cancer. Our aim was to identify variations in diagnostic and management strategies across different institutions and provide rationale for a consensus statement on this issue. Methods This was a joint-survey by European Respiratory Society (ERS) Assemblies 8, 11 and 12. The survey consisted of 25 questions. Results Four hundred and ninety-four (n=494) physicians from 68 different countries and five continents responded to the survey. Ninety-four per cent of participants were pulmonologists, 1.8% thoracic surgeons and 1.9% oncologists; 97.7% were involved in multidisciplinary team approaches on diagnosis and management. Regular low-dose high-resolution computed tomography (HRCT) scan was used by 49.5% of the respondents to screen for lung cancer in IPF. Positron emission tomography (PET) scan and endobronchial ultrasound (EBUS) is performed by 60% and 88% to diagnose nodular lesions with mediastinal lymphadenopathy in patients with advanced and mild IPF, respectively. Eighty-three per cent of respondents continue anti-fibrotics following lung cancer diagnosis; safety precautions during surgical interventions including low tidal volume are applied by 67%. Stereotactic radiotherapy is used to treat patients with advanced IPF (diffusing capacity of the lung for carbon monoxide (DLCO) <35%) and otherwise operable nonsmall cell lung cancer (NSCLC) by 54% of respondents and doublet platinum regimens and immunotherapy for metastatic disease by 25% and 31.9%, respectively. Almost all participants (93%) replied that a consensus statement for the management of these patients is highly warranted. Conclusion The diagnosis and management of IPF-lung cancer (LC) is heterogeneous with most respondents calling for a consensus statement

Disseminated tuberculosis presenting with polymorphonuclear effusion and septic shock in an HIV-seropositive patient: a case report

<p>Abstract</p> <p>Introduction</p> <p>Because a substantial number of patients present with few or atypical symptoms, the recognition of tuberculosis remains challenging. Disseminated tuberculosis presenting with septic shock has already been described in some case reports, but, to the best of our knowledge, it has never been associated with polymorphonuclear effusion.</p> <p>Case presentation</p> <p>We describe the case of a 27-year-old man from western Africa who was seropositive for human immunodeficiency virus. He presented with pleural and abdominal polymorphonuclear effusions and quickly developed septic shock due to disseminated <it>Mycobacterium tuberculosis </it>infection leading to multiple organ failure and death.</p> <p>Conclusion</p> <p>In high-risk patients, <it>Mycobacterium tuberculosis </it>infection should be considered even in exceptional clinical presentations, such as septic shock and polymorphonuclear effusions.</p

Non-linear dynamic response of a cable system with a tuned mass damper to stochastic base excitation via equivalent linearization technique

Abstract: Non-linear dynamic model of a cable–mass system with a transverse tuned mass damper is considered. The system is moving in a vertical host structure therefore the cable length varies slowly over time. Under the time-dependent external loads the sway of host structure with low frequencies and high amplitudes can be observed. That yields the base excitation which in turn results in the excitation of a cable system. The original model is governed by a system of non-linear partial differential equations with corresponding boundary conditions defined in a slowly time-variant space domain. To discretise the continuous model the Galerkin method is used. The assumption of the analysis is that the lateral displacements of the cable are coupled with its longitudinal elastic stretching. This brings the quadratic couplings between the longitudinal and transverse modes and cubic nonlinear terms due to the couplings between the transverse modes. To mitigate the dynamic response of the cable in the resonance region the tuned mass damper is applied. The stochastic base excitation, assumed as a narrow-band process mean-square equivalent to the harmonic process, is idealized with the aid of two linear filters: one second-order and one first-order. To determine the stochastic response the equivalent linearization technique is used. Mean values and variances of particular random state variable have been calculated numerically under various operational conditions. The stochastic results have been compared with the deterministic response to a harmonic process base excitation