Instability of the symmetric Couette-flow in a granular gas: hydrodynamic field profiles and transport

We investigate the inelastic hard disk gas sheared by two parallel bumpy walls (Couette-flow). In our molecular dynamic simulations we found a sensitivity to the asymmetries of the initial condition of the particle places and velocities and an asymmetric stationary state, where the deviation from (anti)symmetric hydrodynamic fields is stronger as the normal restitution coefficient decreases. For the better understanding of this sensitivity we carried out a linear stability analysis of the former kinetic theoretical solution [Jenkins and Richman: J. Fluid. Mech. {\bf 171} (1986)] and found it to be unstable. The effect of this asymmetry on the self-diffusion coefficient is also discussed.Comment: 9 pages RevTeX, 14 postscript figures, sent to Phys. Rev.

Heat and Work Along Individual Trajectories of a Quantum Bit

We use a near quantum limited detector to experimentally track individual quantum state trajectories of a driven qubit formed by the hybridization of a waveguide cavity and a transmon circuit. For each measured quantum coherent trajectory, we separately identify energy changes of the qubit as heat and work, and verify the first law of thermodynamics for an open quantum system. We further establish the consistency of these results by comparison with the master equation approach and the two-projective-measurement scheme, both for open and closed dynamics, with the help of a quantum feedback loop that compensates for the exchanged heat and effectively isolates the qubit

Web-Based Educational Intervention for Patients With Uninvestigated Dyspepsia Referred for Upper Gastrointestinal Tract Endoscopy:A Randomized Clinical Trial

Item does not contain fulltextIMPORTANCE: Diagnostic yield of upper gastrointestinal (GI) tract endoscopy for uninvestigated dyspepsia is low, and its clinical implications are limited. There is an unmet need for better strategies to reduce the volume of upper GI tract endoscopic procedures for dyspepsia. OBJECTIVE: To study the effectiveness of a web-based educational intervention as a tool to reduce upper GI tract endoscopy in uninvestigated dyspepsia. DESIGN, SETTING, AND PARTICIPANTS: This open-label, multicenter, randomized clinical trial enrolled participants between November 1, 2017, and March 31, 2019, with follow-up 52 weeks after randomization, at 4 teaching hospitals in the Netherlands. Participants included patients with uninvestigated dyspeptic symptoms who were referred for upper GI tract endoscopy by their general health care clinician without prior consultation of a gastroenterologist. A total of 119 patients, aged 18 to 69 years, were included. Patients were excluded if any of the following red flag symptoms were present: (indirect) signs of upper GI tract hemorrhage (hematemesis, melena, hematochezia, or anemia), unintentional weight loss of 5% or higher of normal body weight during a period of 6 to 12 months, persistent vomiting, dysphagia, or jaundice. INTERVENTIONS: Patients were randomly assigned (1:1) to education (intervention) or upper GI tract endoscopy (control). Education consisted of a self-managed web-based educational intervention, containing information on gastric function, dyspepsia, and upper GI tract endoscopy. MAIN OUTCOMES AND MEASURES: Difference in the proportion of upper GI tract endoscopy procedures between those who received access to the web-based educational intervention and those who did not at 12 weeks and 52 weeks after randomization, analyzed in the intention-to-treat population. Secondary outcomes included quality of life (Nepean Dyspepsia Index) and symptom severity (Patient Assessment of Gastrointestinal Disorders Symptom Severity Index) measured at baseline and 12 weeks. RESULTS: Of 119 patients included (median age, 48 years [interquartile range, 37-56 years]; 48 men [40%]), 62 were randomized to web-based education (intervention) and 57 to upper GI tract endoscopy (control). Significantly fewer patients compared with controls underwent upper GI tract endoscopy after using the web-based educational intervention: 24 (39%) vs 47 (82%) (relative risk, 0.46; 95% CI, 0.33-0.64; P < .001). Symptom severity and quality of life improved equivalently in both groups. One additional patient in the intervention group required upper GI tract endoscopy during follow-up. CONCLUSIONS AND RELEVANCE: Findings of this study indicate that web-based patient education is an effective tool to decrease the need for upper GI tract endoscopy in uninvestigated dyspepsia. TRIAL REGISTRATION: ClinicalTrials.gov Identifier: NCT03205319

Electronic and thermal sequential transport in metallic and superconducting two-junction arrays

The description of transport phenomena in devices consisting of arrays of tunnel junctions, and the experimental confirmation of these predictions is one of the great successes of mesoscopic physics. The aim of this paper is to give a self-consistent review of sequential transport processes in such devices, based on the so-called "orthodox" model. We calculate numerically the current-voltage (I-V) curves, the conductance versus bias voltage (G-V) curves, and the associated thermal transport in symmetric and asymmetric two-junction arrays such as Coulomb-blockade thermometers (CBTs), superconducting-insulator-normal-insulator-superconducting (SINIS) structures, and superconducting single-electron transistors (SETs). We investigate the behavior of these systems at the singularity-matching bias points, the dependence of microrefrigeration effects on the charging energy of the island, and the effect of a finite superconducting gap on Coulomb-blockade thermometry.Comment: 23 pages, 12 figures; Berlin (ISBN: 978-3-642-12069-5

Variational approximation for mixtures of linear mixed models

Mixtures of linear mixed models (MLMMs) are useful for clustering grouped data and can be estimated by likelihood maximization through the EM algorithm. The conventional approach to determining a suitable number of components is to compare different mixture models using penalized log-likelihood criteria such as BIC.We propose fitting MLMMs with variational methods which can perform parameter estimation and model selection simultaneously. A variational approximation is described where the variational lower bound and parameter updates are in closed form, allowing fast evaluation. A new variational greedy algorithm is developed for model selection and learning of the mixture components. This approach allows an automatic initialization of the algorithm and returns a plausible number of mixture components automatically. In cases of weak identifiability of certain model parameters, we use hierarchical centering to reparametrize the model and show empirically that there is a gain in efficiency by variational algorithms similar to that in MCMC algorithms. Related to this, we prove that the approximate rate of convergence of variational algorithms by Gaussian approximation is equal to that of the corresponding Gibbs sampler which suggests that reparametrizations can lead to improved convergence in variational algorithms as well.Comment: 36 pages, 5 figures, 2 tables, submitted to JCG

Adiabatic Elimination in Compound Quantum Systems with Feedback

Feedback in compound quantum systems is effected by using the output from one sub-system (``the system'') to control the evolution of a second sub-system (``the ancilla'') which is reversibly coupled to the system. In the limit where the ancilla responds to fluctuations on a much shorter time scale than does the system, we show that it can be adiabatically eliminated, yielding a master equation for the system alone. This is very significant as it decreases the necessary basis size for numerical simulation and allows the effect of the ancilla to be understood more easily. We consider two types of ancilla: a two-level ancilla (e.g. a two-level atom) and an infinite-level ancilla (e.g. an optical mode). For each, we consider two forms of feedback: coherent (for which a quantum mechanical description of the feedback loop is required) and incoherent (for which a classical description is sufficient). We test the master equations we obtain using numerical simulation of the full dynamics of the compound system. For the system (a parametric oscillator) and feedback (intensity-dependent detuning) we choose, good agreement is found in the limit of heavy damping of the ancilla. We discuss the relation of our work to previous work on feedback in compound quantum systems, and also to previous work on adiabatic elimination in general.Comment: 18 pages, 12 figures including two subplots as jpeg attachment

NMR Experiments on a Three-Dimensional Vibrofluidized Granular Medium

A three-dimensional granular system fluidized by vertical container vibrations was studied using pulsed field gradient (PFG) NMR coupled with one-dimensional magnetic resonance imaging (MRI). The system consisted of mustard seeds vibrated vertically at 50 Hz, and the number of layers N_ell <= 4 was sufficiently low to achieve a nearly time-independent granular fluid. Using NMR, the vertical profiles of density and granular temperature were directly measured, along with the distributions of vertical and horizontal grain velocities. The velocity distributions showed modest deviations from Maxwell-Boltzmann statistics, except for the vertical velocity distribution near the sample bottom which was highly skewed and non-Gaussian. Data taken for three values of N_ell and two dimensionless accelerations Gamma=15,18 were fit to a hydrodynamic theory, which successfully models the density and temperature profiles including a temperature inversion near the free upper surface.Comment: 14 pages, 15 figure

Circulating Cardiac Troponin T Exhibits a Diurnal Rhythm

ObjectivesThe goal of this study was to test the unverified assumption that chronically elevated cardiac troponin T (cTnT) levels fluctuate randomly around a homeostatic set point.BackgroundThe introduction of high-sensitivity cardiac troponin (cTn) assays has improved sensitivity for acute myocardial infarction (AMI). However, many patients with a single positive cTn test result do not have AMI. Therefore, the diagnosis of AMI relies strongly on serial testing and interpretation of cTn kinetics. Essential in this regard is a profound understanding of the biological variation of cTn.MethodsTwo studies were conducted to assess biological cTnT variation and to investigate the presence of a diurnal rhythm of cTnT. Study 1 comprised 23 male subjects with type 2 diabetes, with no acute cardiovascular disease. Serial venous blood samples were drawn over an 11-h period (8:30 am to 7:30 pm). In study 2, the presence of a diurnal cTnT rhythm was investigated by hourly sampling of 7 subjects from study 1 over 25 h.ResultsIn study 1, we observed a gradual decrease in cTnT concentrations during the day (24 ± 2%). This decrease was present in all participants and was most prominent in subjects with the highest baseline cTnT values (Pearson’s R 0.93). Diurnal variation of cTnT, as assessed in study 2, was characterized by peak concentrations during morning hours (8:30 am, 17.1 ± 2.9 ng/l), gradually decreasing values during daytime (8:30 pm, 11.9 ± 1.6 ng/l), and rising concentrations during nighttime (8:30 am the next day, 16.9 ± 2.8 ng/l).ConclusionsA diurnal cTnT rhythm substantiates the recommendation that all dynamic changes in cTnT should be interpreted in relation to the clinical presentation. Epidemiological studies and risk-stratification protocols with the use of cTnT may benefit from standardized sampling times. (Exercise and Glycemic Control in Type 2 Diabetes; NCT00945165