Drag Reduction by Polymers in Wall Bounded Turbulence

We address the mechanism of drag reduction by polymers in turbulent wall bounded flows. On the basis of the equations of fluid mechanics we present a quantitative derivation of the "maximum drag reduction (MDR) asymptote" which is the maximum drag reduction attained by polymers. Based on Newtonian information only we prove the existence of drag reduction, and with one experimental parameter we reach a quantitative agreement with the experimental measurements.Comment: 4 pages, 1 fig., included, PRL, submitte

OPEC meetings, oil market volatility and herding behaviour in the Saudi Arabia stock market

We investigate the influence of oil market volatility and hand‐picked OPEC meetings data on herding tendency in the Saudi equity market. Our results show the presence of significant herding behaviour in the Saudi market; surprisingly this herding behaviour is independent of oil market volatility. Importantly, we find herding on and around the OPEC meeting days however this is only limited to a period of high global uncertainty that is, during the Global Financial Crisis period (GFC) of 2008–2010. However, when we filter out factor‐based herding in the Saudi equities, we also find persistent herding in the post GFC period. These results are consistent when we assess the impact of OPEC meetings using event windows of one to 5 days before and after the announcement. In consideration of the crucial role of OPEC in determining the oil prices, we explain our results of Saudi market herding on and around OPEC meeting days for the prior announcement ambiguity and corrections before, on and after the announcements on global supply. Our results show that this tendency has originated during the GFC, has persisted in the post‐GFC in the Saudi equities and surprisingly, is largely found absent in the periods when the Saudi equity market witnessed bullish market conditions. Our results are robust after accounting for common factor return variations in equity returns, the unconditional and conditional estimates of the volatility in oil prices and several event windows around OPEC meeting days

Factors influencing use of essential surgical services in North-East India: a cross-sectional study of obstetric and gynaecological surgery

Introduction There continues to be a large gap between need and actual use of surgery in low-resource settings. While policy frequently focuses on expanding the supply of services, demand-side factors are at least as important in determining under utilisation and over utilisation. The aim of this study is to understand how these factors influence the use of selected essential obstetric and gynaecological surgical procedures in the underserved and remote setting of North-East India. Methods The study combines and makes use of data from a variety of surveys and routine systems. Descriptive analysis of variations in caesarean section, hysterectomy and sterilisation and then multivariate logit analysis of demand-side and supply-side factors on access to these services is undertaken. Results Surgical rates vary substantially both across and within North-East India, correlated with service capacity and socioeconomic status. Travel times to surgical facilities are associated with rates of caesarean section and hysterectomy but not sterilisation where services are much more deconcentrated. Travel is less important for surgery in private facilities where capacity is much more dispersed but dominated by the non-poor. The presence of non-doctor medical staff is associated with lower levels of surgical activity. Conclusion In low resource, remote settings policy interventions to improve access to services must recognise that surgical rates in low-resource settings are heavily influenced by demand-side factors. As well as boosting services, mechanisms need to mitigate demand-side barriers particularly distance and influence practice to encourage surgical intervention only where clinically indicated

Optical injection and terahertz detection of the macroscopic Berry curvature

We propose an experimental scheme to probe the Berry curvature of solids. Our method is sensitive to arbitrary regions of the Brillouin zone, and employs only basic optical and terahertz techniques to yield a background free signal. Using semiconductor quantum wells as a prototypical system, we discuss how to inject Berry curvature macroscopically, and probe it in a way that provides information about the underlying microscopic Berry curvature.Comment: 4 pages, accepted in Physical Review Letter

Antibiofilm Potential of Metal Based Nanoparticles: Synthesis and Mode of Action

oai:ojs.pkp.sfu.ca:article/2Biofilm refers to a group of microbes colonizing together and often adhered to a surface. The adherence is attributed to secretion of polymeric substances comprising of extracellular DNA, proteins, and polysaccharides thereby limiting the access and inhibitory activity of existing antimicrobial agents. Biofilm are a major cause of acute infections and pose immense clinical threat especially in conditions employing the use of invasive devices thus being a major source of mortality and morbidity. Hence there is a dire need to develop alternative treatment against biofilm-related infections. Advances in nanotechnology has opened new horizons. Nanoparticles derived from various metal present promising candidates to ameliorate biofilms owing to their antioxidant potential

Additive Equivalence in Turbulent Drag Reduction by Flexible and Rodlike Polymers

We address the "Additive Equivalence" discovered by Virk and coworkers: drag reduction affected by flexible and rigid rodlike polymers added to turbulent wall-bounded flows is limited from above by a very similar Maximum Drag Reduction (MDR) asymptote. Considering the equations of motion of rodlike polymers in wall-bounded turbulent ensembles, we show that although the microscopic mechanism of attaining the MDR is very different, the macroscopic theory is isomorphic, rationalizing the interesting experimental observations.Comment: 8 pages, PRE, submitte

In vitro flowering in embryogenic cultures of Kinnow mandarin (Citrus nobilis Lour ´ C. deliciosa Tenora)

Embryogenic cultures of Kinnow mandarin (C. nobilis Lour × C. deliciosa Tenora) were raised from unfertilized ovules dissected from unopened flower buds of this plant inoculated on MS medium supplemented with 2 mg/L kinetin (KN). In vitro flowering was induced in these cultures by usingdifferent concentrations of KN and sucrose as well as subjecting these cultures to different photoperiods. Maximum percentage (31.94%) of cultures producing flowers and maximum number (5.58) of flowers per culture was observed on MS medium supplemented with KN (2 mg/L) and sucrose40 g/L at 12-h photoperiod