Shearing of loose granular materials: A statistical mesoscopic model

A two-dimensional lattice model for the formation and evolution of shear bands in granular media is proposed. Each lattice site is assigned a random variable which reflects the local density. At every time step, the strain is localized along a single shear-band which is a spanning path on the lattice chosen through an extremum condition. The dynamics consists of randomly changing the `density' of the sites only along the shear band, and then repeating the procedure of locating the extremal path and changing it. Starting from an initially uncorrelated density field, it is found that this dynamics leads to a slow compaction along with a non-trivial patterning of the system, with high density regions forming which shelter long-lived low-density valleys. Further, as a result of these large density fluctuations, the shear band which was initially equally likely to be found anywhere on the lattice, gets progressively trapped for longer and longer periods of time. This state is however meta-stable, and the system continues to evolve slowly in a manner reminiscent of glassy dynamics. Several quantities have been studied numerically which support this picture and elucidate the unusual system-size effects at play.Comment: 11 pages, 15 figures revtex, submitted to PRE, See also: cond-mat/020921

Dynamics of Highly Supercooled Liquids:Heterogeneity, Rheology, and Diffusion

Highly supercooled liquids with soft-core potentials are studied via molecular dynamics simulations in two and three dimensions in quiescent and sheared conditions.We may define bonds between neighboring particle pairs unambiguously owing to the sharpness of the first peak of the pair correlation functions. Upon structural rearrangements, they break collectively in the form of clusters whose sizes grow with lowering the temperature $T$. The bond life time $\tau_b$, which depends on $T$ and the shear rate \gdot, is on the order of the usual structural or $\alpha$ relaxation time $\tau_{\alpha}$ in weak shear \gdot \tau_{\alpha} \ll 1, while it decreases as 1/\gdot in strong shear \gdot\tau_{\alpha} \gg 1 due to shear-induced cage breakage. Accumulated broken bonds in a time interval ($\sim 0.05\tau_b$) closely resemble the critical fluctuations of Ising spin systems. For example, their structure factor is well fitted to the Ornstein-Zernike form, which yields the correlation length $\xi$ representing the maximum size of the clusters composed of broken bonds. We also find a dynamical scaling relation, $\tau_b \sim \xi^{z}$, valid for any $T$ and \gdot with $z=4$ in two dimensions and $z=2$ in three dimensions. The viscosity is of order $\tau_b$ for any $T$ and \gdot, so marked shear-thinning behavior emerges. The shear stress is close to a limiting stress in a wide shear region. We also examine motion of tagged particles in shear in three dimensions. The diffusion constant is found to be of order $\tau_b^{-\nu}$ with $\nu=0.75 \sim 0.8$ for any $T$ and \gdot, so it is much enhanced in strong shear compared with its value at zero shear. This indicates breakdown of the Einstein-Stokes relation in accord with experiments. Some possible experiments are also proposed.Comment: 20pages (including figures

Condomless sex in HIV-diagnosed men who have sex with men in the UK: prevalence, correlates, and implications for HIV transmission

OBJECTIVE: HIV transmission is ongoing among men who have sex with men (MSM) in the UK. Sex without a condom (condomless sex, CLS) is the main risk factor. We investigated the prevalence of and factors associated with types of CLS. METHODS: Cross-sectional questionnaire study in UK HIV clinics in 2011/2012 (ASTRA). MSM diagnosed with HIV for ≥3 months reported on anal and vaginal sex, CLS with HIV-serodifferent partners (CLS-D) and CLS with HIV-seroconcordant (CLS-C) partners in the previous 3 months. Mutually exclusive sexual behaviours were as follows: (1) Higher HIV risk CLS-D (not on antiretroviral therapy (ART) or clinic-recorded viral load(VL) >50 c/mL), (2) Other CLS-D, (3) CLS-C without CLS-D, (4) Condom-protected sex only and (5) No anal or vaginal sex. Associations were examined of sociodemographic, HIV-related, lifestyle, and other sexual measures with the five categories of sexual behaviour. We examined the prevalence of higher HIV risk CLS-D incorporating (in addition to ART and VL) time on ART, ART non-adherence, and recent sexually transmitted infections (STIs). RESULTS: Among 2189 HIV-diagnosed MSM (87% on ART), prevalence of any CLS in the past 3 months was 38.2% (95% CI 36.2% to 40.4%) and that of any CLS-D was 16.3% (14.8%–17.9%). The five-category classification was as follows: (1) Higher HIV risk CLS-D: 4.2% (3.5% to 5.2%), (2) Other CLS-D: 12.1% (10.8% to 13.5%), (3) CLS-C without CLS-D: 21.9% (20.2% to 23.7%), (4) Condom-protected sex only: 25.4% (23.6% to 27.3%) and (5) No anal or vaginal sex: 36.4% (34.3% to 38.4%). Compared with men who reported condom-protected sex only, MSM who reported any CLS in the past 3 months had higher prevalence of STIs, chemsex-associated drug use, group sex, higher partner numbers, and lifetime hepatitis C. Prevalence of higher HIV risk CLS-D ranged from 4.2% to 7.5% according to criteria included. CONCLUSION: CLS was prevalent among HIV-diagnosed MSM, but CLS-D with higher HIV transmission risk was overall low. CLS-D is no longer the most appropriate measure of HIV transmission risk behaviour among people with diagnosed HIV; accounting for VL is important

Relationship of Emotional Characteristics and Depression with Intelligence Quotient in Children with Attention Deficit Hyperactivity Disorder

Abstract: Introduction: Attention Deficit Hyeperactivity Disorder (ADHD) is a relatively prevalent disorder in children and is associated with some other disorders including depression. This problem also affects the emotional characteristics and intelligence quotient. The aim of this study was to examine the relationship of Emotional Characteristics (EC) and depression with Intelligence Quotient (IQ) in children with ADHD. Method: Fifty six children with ADHD and fifty six normal children matched for age and sex were selected. To determine EC, depression and IQ, the Bender – Gestalt test, Children Depression Scale, and the Raven Progressive Matrices were administered respectively. Results: There was a positive significant correlation between EC and IQ (P<0.01), depression and IQ (P<0.01). According to 2-variable regression analysis the regression for IQ on EC and depression was significant (P<0.01).The R2 quotient showed that nearly 41% of the IQ score was accounted for by two other independent variables of which the role of EC was 32%. Also, the results of the regression analysis indicated that the addition of a depression variable to the regression equation only increases the prediction power by 9% and among the mentioned variables, EC was the best predicators of IQ in ADHD children. Finally a t test showed a significant difference between the studied variables in ADHD and normal groups (P<0.01). Conclusion: Considering the high correlation between EC and IQ as well as the significant difference between the children with ADHD and normal children, monitoring of EC has an important role in increasing the affected children's IQ. Keywords: Emotional characteristics, Depression, Intelligent Quotient (IQ), Attention Deficit Hyperactivity Disorder (ADHD

256-slice computed tomography in the diagnosis of coronary artery disease in patients presenting with aortic dissection between 2011 and 2014 and the influence of concomitant coronary artery disease on in-hospital mortality

Background: In recent years, noninvasive methods have replaced angiography in the diagnosis of aortic dissection and concomitant coronary artery disease (CAD). Computed tomography (CT) angiography allows the assessment of CAD in this setting. Methods: In this retrospective study, we investigated the incidence of CAD in patients presenting with type A or B aortic dissection between 2011 and 2014 as assessed by CT angiography and the influence of concomitant CAD and coronary artery bypass grafting (CABG) on the in-hospital outcomes of these patients. Results: Ninety-one patients (67 male) were included in this study. Thirty-five (38.5) patients had concomitant CAD on their CT angiography, and coronary artery ectasia was observed in 17 (18.7) patients. Sixty-seven (73.6) patients underwent surgery for their aortic dissection. Concurrent CABG was performed in 22 (62.8) patients, who had significant coronary stenosis on coronary CT angiography. Mortality was significantly higher in the patients who had concomitant CAD. (Sixty-seven percent of the patients with CAD died; P<0.001.) The total in-hospital mortality rate was 29.7 (n =27). Mortality was higher in the patients with more severe CAD in terms of 2- and 3-vessel diseases, and CABG was significantly associated with higher mortality. Conclusions: Nowadays, invasive coronary angiography is infrequently performed in acute type A aortic dissection due to delay in surgery and increase in the risk of rupture. Multi-slice coronary CT angiography is a good alternative modality for the diagnosis of aortic dissection and CAD simultaneously with acceptable accuracy. � 2016, Iranian Heart Association. All rights reserved