Nontrivial rheological exponents in sheared yield stress fluids

In this work we discuss possible physical origins for non-trivial exponents in the athermal rheology of soft materials at low but finite driving rates. A key ingredient in our scenario is the presence of a self-consistent mechanical noise that stems from the spatial superposition of long-range elastic responses to localized plastically deforming regions. We study analytically a mean-field model, in which this mechanical noise is accounted for by a stress diffusion term coupled to the plastic activity. Within this description we show how a dependence of the shear modulus and/or the local relaxation time on the shear rate introduces corrections to the usual mean-field prediction, concerning the Herschel-Bulkley-type rheological response of exponent 1/2. This feature of the mean-field picture is then shown to be robust with respect to structural disorder and partial relaxation of the local stress. We test this prediction numerically on a mesoscopic lattice model that implements explicitly the long-range elastic response to localized shear transformations, and we conclude on how our scenario might be tested in rheological experiments

Out-of-equilibrium dynamical equations of infinite-dimensional particle systems. I. The isotropic case

We consider the Langevin dynamics of a many-body system of interacting particles in $d$ dimensions, in a very general setting suitable to model several out-of-equilibrium situations, such as liquid and glass rheology, active self-propelled particles, and glassy aging dynamics. The pair interaction potential is generic, and can be chosen to model colloids, atomic liquids, and granular materials. In the limit ${d\to\infty}$, we show that the dynamics can be exactly reduced to a single one-dimensional effective stochastic equation, with an effective thermal bath described by kernels that have to be determined self-consistently. We present two complementary derivations, via a dynamical cavity method and via a path-integral approach. From the effective stochastic equation, one can compute dynamical observables such as pressure, shear stress, particle mean-square displacement, and the associated response function. As an application of our results, we derive dynamically the `state-following' equations that describe the response of a glass to quasistatic perturbations, thus bypassing the use of replicas. The article is written in a modular way, that allows the reader to skip the details of the derivations and focus on the physical setting and the main results

Static fluctuations of a thick 1D interface in the 1+1 Directed Polymer formulation

Experimental realizations of a 1D interface always exhibit a finite microscopic width $\xi>0$; its influence is erased by thermal fluctuations at sufficiently high temperatures, but turns out to be a crucial ingredient for the description of the interface fluctuations below a characteristic temperature $T_c(\xi)$. Exploiting the exact mapping between the static 1D interface and a 1+1 Directed Polymer (DP) growing in a continuous space, we study analytically both the free-energy and geometrical fluctuations of a DP, at finite temperature $T$, with a short-range elasticity and submitted to a quenched random-bond Gaussian disorder of finite correlation length $\xi$. We derive the exact `time'-evolution equations of the disorder free-energy $\bar{F}(t,y)$, its derivative $\eta (t,y)$, and their respective two-point correlators $\bar{C}(t,y)$ and $\bar{R}(t,y)$. We compute the exact solution of its linearized evolution $\bar{R}^{lin}(t,y)$, and we combine its qualitative behavior and the asymptotic properties known for an uncorrelated disorder ($\xi=0$), to construct a `toymodel' leading to a simple description of the DP. This model is characterized by Brownian-like free-energy fluctuations, correlated at small $|y|<\xi$, of amplitude $\tilde{D}_{\infty}(T,\xi)$. We present an extended scaling analysis of the roughness predicting $\tilde{D}_{\infty} \sim 1/T$ at high-temperatures and $\tilde{D}_{\infty} \sim 1/T_c(\xi)$ at low-temperatures. We identify the connection between the temperature-induced crossover and the full replica-symmetry breaking in previous Gaussian Variational Method computations. Finally we discuss the consequences of the low-temperature regime for two experimental realizations of KPZ interfaces, namely the static and quasistatic behavior of magnetic domain walls and the high-velocity steady-state dynamics of interfaces in liquid crystals.Comment: 33 pages, 6 figures. The initial preprint arXiv:1209.0567v1 has been split into two parts upon refereeing process. The first part gathers the analytical results and is published (see reference below). It corresponds to the current version of arXiv:1209.0567. The second part gathers the numerical results and corresponds the other arXiv preprint arXiv:1305.236

On the relevance of disorder in athermal amorphous materials under shear

We show that, at least at a mean-field level, the effect of structural disorder in sheared amorphous media is very dissimilar depending on the thermal or athermal nature of their underlying dynamics. We first introduce a toy model, including explicitly two types of noise (thermal versus athermal). Within this interpretation framework, we argue that mean-field athermal dynamics can be accounted for by the so-called H{\'e}braud-Lequeux (HL) model, in which the mechanical noise stems explicitly from the plastic activity in the sheared medium. Then, we show that the inclusion of structural disorder, by means of a distribution of yield energy barriers, has no qualitative effect in the HL model, while such a disorder is known to be one of the key ingredients leading kinematically to a finite macroscopic yield stress in other mean-field descriptions, such as the Soft-Glassy-Rheology model. We conclude that the statistical mechanisms at play in the emergence of a macroscopic yield stress, and a complex stationary dynamics at low shear rate, are different in thermal and athermal amorphous systems

Doctors and Patients' Susceptibility to Framing Bias: A Randomized Trial

ABSTRACT: BACKGROUND: Framing of risk influences the perceptions of treatment benefit. OBJECTIVE: To determine which risk framing format corresponds best to comprehensive multi-faceted information, and to compare framing bias in doctors and in patients. DESIGN: Randomized mail surveys. PARTICIPANTS: One thousand four hundred and thirty-one doctors (56% response rate) and 1121 recently hospitalized patients (65% response rate). INTERVENTION: Respondents were asked to interpret the results of a hypothetical clinical trial comparing an old and a new drug. They were randomly assigned to the following framing formats: absolute survival (new drug: 96% versus old drug: 94%), absolute mortality (4% versus 6%), relative mortality reduction (reduction by a third) or all three (fully informed condition). The new drug was reported to cause more side-effects. MAIN MEASURE: Rating of the new drug as more effective than the old drug. RESULTS: The proportions of doctors who rated the new drug as more effective varied by risk presentation format (abolute survival 51.8%, absolute mortality 68.3%, relative mortality reduction 93.8%, and fully informed condition 69.8%, p  0.1). In comparison to the fully informed condition, the odds ratio of greater perceived effectiveness was 0.45 for absolute survival (p < 0.001), 0.89 for absolute mortality (p = 0.29), and 4.40 for relative mortality reduction (p < 0.001). CONCLUSIONS: Framing bias affects doctors and patients similarly. Describing clinical trial results as absolute risks is the least biased format, for both doctors and patients. Presenting several risk formats (on both absolute and relative scales) should be encourage

Patient-reported conformity of informed consent procedures and participation in clinical research

Background: There is growing evidence that the quality of informed consent in clinical research is often sub-optimal. Aims: To explore the conformity of patient recruitment with recommended informed consent procedures among patients who were invited to participate in a clinical study at a general teaching hospital, and to examine the association between consent procedures and the patients' decision to participate. Design and Methods: All inpatients discharged during a 1-month period were invited to complete a mailed survey in which they reported whether they were invited to participate in a study and whether 13 recommended elements of informed consent actually occurred. Results: Among 1303 respondents, 265 (20.3%) reported that they had been invited to participate in a study, and 191 (72.1%) accepted. While the majority of potential participants were fully informed about practical issues related to the study (e.g. what their participation would consist in), <50% were informed of possible risks or benefits, and only 20% about the origin of the study funds. Only 60% reported satisfactory answers to items assessing the overall information process (e.g. explanations were easy to understand). Older and sicker patients reported lower levels of conformity with informed consent procedures, as did patients who refused to participate in a study. Conclusions: Our results confirm that informed consent procedures fail to meet standards for many patients. In particular, consent information should be adapted to the needs of older and sicker patients. Improving the quality of informed consent may increase patients' participation in clinical researc

Out-of-equilibrium dynamical equations of infinite-dimensional particle systems. II. The anisotropic case under shear strain

As an extension of the isotropic setting presented in the companion paper [J. Phys. A 52, 144002 (2019)], we consider the Langevin dynamics of a many-body system of pairwise interacting particles in $d$ dimensions, submitted to an external shear strain. We show that the anisotropy introduced by the shear strain can be simply addressed by moving into the co-shearing frame, leading to simple dynamical mean field equations in the limit ${d\to\infty}$. The dynamics is then controlled by a single one-dimensional effective stochastic process which depends on three distinct strain-dependent kernels - self-consistently determined by the process itself - encoding the effective restoring force, friction and noise terms due to the particle interactions. From there one can compute dynamical observables such as particle mean-square displacements and shear stress fluctuations, and eventually aim at providing an exact ${d \to \infty}$ benchmark for liquid and glass rheology. As an application of our results, we derive dynamically the 'state-following' equations that describe the static response of a glass to a finite shear strain until it yields.Comment: Typo corrected in Eq. (47

Patient reports of undesirable events during hospitalization

BACKGROUND: Thus far, incident reporting in health care has relied on health professionals. However, patients too may be able to signal the occurrence of undesirable events. OBJECTIVE: To estimate the frequency of undesirable events reported by recently discharged patients, and to identify correlates of undesirable events. DESIGN: Mailed patient survey. SETTING: Swiss public teaching hospital. PARTICIPANTS: Adult patients (N=1,518) discharged from hospital. MEASUREMENTS: Self-reports of 27 undesirable events during hospitalization, including 9 medical complications, 9 interpersonal problems, and 9 incidents related to the health care process. RESULTS: Most survey respondents (1,433, 94.4%) completed the section about undesirable events, and 725 (50.6%) reported at least 1 event. The most frequent events were phlebitis (11.0%), unavailable medical record (9.5%), failure to respect confidentiality (8.4%), and hospital-acquired infection (8.2%). The odds of an unfavorable rating increased with each additional interpersonal problem (odds ratio [OR] 1.6, 95% confidence interval [CI] 1.3 to 1.8), each additional process-related problem (OR 1.5, 95% CI 1.3 to 1.9), but not with each additional medical complication (OR 1.0, 95% CI 0.9 to 1.2). Longer duration of stay, poor health, and depressed mood were all related to a greater reported frequency of undesirable events. CONCLUSION: Patients are able to report undesirable events that occur during hospital care. Such events occur in about a half of the hospitalizations, and have a negative impact on satisfaction with car