Head-on collision of viscous vortex rings

The head-on collision of two identical axisymmetric viscous vortex rings is studied through direct simulations of the incompressible Navier-Stokes equations. The initial vorticity distributions considered are those of Hill's spherical vortex and of rings with circular Gaussian cores, each at Reynolds numbers of about 350 and 1000. The Reynolds number is defined by Gamma/Nu, the ratio of circulation to viscosity. As the vortices approach each other by self-induction, the radii increase by mutual induction, and vorticy cancels through viscous cross-diffusion across the collision plane. Following contact, the vorticity distribution in the core forms a head-tail structure (for the cases considered). The characteristic time of vorticity annihilation is compared with that of a 3D collision experiment and 3D numerical simulations. It is found that the annihilation time is somewhat longer in the axisymmetric case than it is in the symmetry plane of the experiment and 3D numerical simulation. By comparing the annihilatiom time with a viscous timescale and a circulation timescale, it is deduced that both the strain rate due to local effects and to 3D vorticity realignment are important

A note on leapfrogging vortex rings

In this paper we provide examples, by numerical simulation using the Navier-Stokes equations for axisymmetric laminar flow, of the 'leapfrogging' motion of two, initially identical, vortex rings which share a common axis of symmetry. We show that the number of clear passes that each ring makes through the other increases with Reynolds number, and that as long as the configuration remains stable the two rings ultimately merge to form a single vortex ring

Nature and causes of land degradation and desertification in Libya: Need for sustainable land management

In this article, the characteristics of desertification, causative factors and efforts to combat desertification in Libya are presented. Also, the need to mainstream sustainable land management into land use planning is highlighted which could provide a firm basis for future policy decisions to combat desertification. Libya is characterized by a desert type environment and more than 95% of the country is desert or semi-desert. The processes of desertification have been aggravated by human activities coupled with climatic conditions. This intensification of desertification is believed to affect regional as well as global climate. Currently, desertification is one of the main environmental issues in Libya affecting environment and its resources. Among others, overexploitation of natural resources, inappropriate land use planning, insufficient water resources etc. are the main factors escalating the process of desertification and deteriorating environmental quality. Mainstreaming sustainable land management into land use planning has been considered a viable solution to moderate the effects of desertification and rampant usages of natural resources. However, this requires quantifying the severity of desertification by means of identified causative factor. Development of indicators of desertification process by means of using time-series satellite data coupled with ancillary data need to be attempted to establish a monitoring system to manage desertification in more sensitive areas. Moreover, environmental and livelihood implications of increasing desertification need to be addressed in order to promote regional economic sustainable development.Key words: Desertification, human impacts, Libya, natural resources, sustainable development, remote sensing, monitoring

Structural and Metamorphic History of the Moine and Dalradian Rocks, Glen Orchy, Argyllshire, Scotland

The geology of an area of about 27sq. km, lying within Glen Orchy is described. The area consists of rocks belonging to the upper part of the Grampian Division of the Moine succession and parts of the Appin and Argyll Groups of the Dalradian Supergroup. A lithostratigraphic sequence has been established using way-up evidence from cross-lamination and graded bedding. Moine psammite and semipelite occur at the base and pass up through a passage zone into Dalradian quartzite followed by pelite (with thin calcareous beds) and pebbly quartzite. A tectonic break, the Iltay Boundary Slide occurs between the pelite and the pebbly quartzite. Field and microscopic examination of the rocks in the area, have revealed the existence of a polyphase deformational history and has enabled four stages of folding (F1 to F4) to be recognised. The earliest deformation (D1) led to the formation of two major isoclinal recumbent folds, the Beinn Chuirn Anticline and Beinn Udlaidh Syncline. Both folds face to the south-east and plunge at a low to moderate angles to the south-west, and have curvilinear hinges. This interpretation of the Beinn Chuirn Anticline as a D1 structure disagrees with its current interpretation by other workers as a D2 synform. The Iltay Boundary Slide probably developed during D1 and was reactivated locally during the D2 deformation. No F2 major fold has been recognised in the area but F3 minor folding is associated with the development of a major late fold, the Glen Orchy Antiform. This antiform plunges to the SW-SSW or NE-NNE, and folds the Beinn Chuirn Anticline and Beinn Udlaidh Syncline. F4 folding is only locally developed and no major fold related to this phase of folding is seen. The rocks of the area lie within the garnet zone of the epidote amphibolite facies. No other higher grade index minerals were found. Periods of mineral growth have been related to the major deformational episodes on micro-textural evidence. The peak metamorphism of the area occurred during the D1 deformation, with the development of the garnet porphyroblasts. No MS2 garnet has been recognised in the area. Later retrogression resulted in the widespread alteration of biotite and garnet to chlorite

User perception of information credibility of news on Twitter

In this paper, we examine user perception of credibility for news-related tweets. We conduct a user study on a crowd-sourcing platform to judge the credibility of such tweets. By analysing user judgments and comments, we find that eight features, including some that can not be automatically identified from tweets, are perceived by users as important for judging information credibility. Moreover, distinct features like link in tweet, display name and user belief consistently lead users to judge tweets as credible. We also find that users can not consistently judge or even misjudge the credibility for some tweets on politics news

Clinico-epidemiological study of stasis eczema

Background: This study was done to determine the epidemiological aspects of stasis eczema and the association of various risk factors of the disease in the local population.Methods: This cross-sectional study was done at a tertiary hospital in southern India over a period of 1 year. Epidemiological and clinical data of stasis dermatitis patients above 20 years of age were recorded. Data was tabulated and analyzed using Microsoft excel software.Results: Of the study population of 120 prevalence is found to be highest in the age group of 50 to 60 years (42.5%) and males are more commonly affected. Occupation involving prolonged standing or sitting and lack of exercise activity is found to be a significant risk factor. The commonest skin finding in present study is eczema (80%). The most common complication was ulcer which was seen in 12.5% of our patients. Reticular veins are the most common dilated veins seen in our patients. About 70% of patients in present study fall under C4a stage of CEAP classification. About one half of symptomatic patients in present study (53.3%) had no radiological evidence of incompetent veins. Among patients with valvular incompetence, perforator veins were most commonly found to be incompetent (62.5%) followed by involvement of the saphenous venous system (23.2%).Conclusions: The study confirms the importance of environmental factors in the development of stasis eczema. There is a ten-fold higher prevalence of the disease in men in our population compared to previous studies which invariably reports a female preponderance

A study on antimicrobial sensitivity pattern in Neisseria gonorrhoeae in a tertiary care hospital

Background: Sexually transmitted diseases are prevalent throughout the world. Sexually transmitted diseases (STD) play a major role in the transmission of HIV infection. The risk of acquiring HIV infection in non-ulcerative STD is 3 to 5 times more than that in persons without any sexually transmitted infections. One of the main non-ulcerative STD is gonorrhoea. The relative incidence of gonococcal infections is about 10 to 13% of total sexually transmitted infections in STD clinics. Aims and objectives was to identify gonococcal infection in patients attending the STD clinic and associated sexually transmitted infections and to study the antimicrobial susceptibility of gonococcus and to modify the disease intervention strategies.Methods: A retrospective study was conducted in our institute of venereology, government general hospital and madras medical college, Chennai-03, Tamil Nadu, India. 43 patients with gram stained smear or culture positive for gonococcus who attended the institute from February 2013 to September 2014 were taken into the study. All the details were collected from the case records of the patients. The antibiotic sensitivity testing in N. gonorrhoeae had been done by Kirby-Bauer disc diffusion method. Screening for other sexually transmitted diseases had been done and were treated according to the institute guidelines.Results: Specimens from 43 patients (40 male, 3 females) had been collected. 40 specimens were found to be culture positive. Antibiotic sensitivity tests were carried out on those 40 isolates of Neisseria gonorrhoeae obtained in pure culture. 70% of isolates were resistant to penicillin and 30% were less sensitive to it. 52.5% of the isolates were PPNG. 57.5% of isolates were resistant to ciprofloxacin and 42.5% were less sensitive to it. 7.5% were resistant to ceftriaxone, 12.5% were resistant to cefixime and 15% were resistant to spectinomycin. All the isolates were sensitive to Azithromycin. Three male patients had HIV (6.9%), three had syphilis and one had genital wart. One female patient had trichomoniasis.Conclusions: The results of the study indicate that multidrug resistant Neisseria gonorrhoeae is prevalent in this region. Associated STDs must be investigated to prevent the transmission of HIV and further complications. The need for establishing a national surveillance programme for antibiotic resistance becomes clear with this study

PROTON PUMP INHIBITORS AND THE RISK OF CHRONIC KIDNEY DISEASES: A CRITICAL REVIEW

Proton pump inhibitors (PPIs) are most widely used medications for acid related gastrointestinal disorders. Accessible evidence based studies suggest that the increased use of PPI is linked to a greater risk of developing kidney diseases. This review aims to determine the association of kidney disease with the use of proton pump inhibitor with various study designs. PubMed, Scopus and Google Scholar databases as well as a reference list of relevant articles were systematically searched for studies by using the following search terms; ‘proton pump inhibitors’, ‘acute kidney injury’, ‘chronic kidney disease’ and ‘end stage renal disease’. Both observational and randomized controlled trials (RCTs) exploring the association of PPI use with kidney disease were eligible for inclusion. A total of 8 articles, including 9 studies (n = 794,349 participants) were identified and included in the review. Majority of the studies showed a higher risk of kidney outcomes in patients taking PPIs, with effect higher of acute kidney injury (4-to 6-fold) compared with chronic kidney disease and end stage renal disease (1.5-to 2.5-fold). However, the studies suggest that the strength of evidence is weak and could not prove causation. The risk increased considerably with the use of high dose of PPIs and prolonged duration of exposure necessitates the monitoring of renal function. Exercising vigilance in PPI use and cessation of proton pump inhibitor when there is no clear indication may be a reasonable approach to reduce the population burden of kidney diseases

Correlation analysis of reader's demographics and tweet credibility perception

When searching on Twitter, readers have to determine the credibility level of tweets on their own. Previous work has mostly studied how the text content of tweets in uences credibility perception. In this paper, we study reader demographics and information credibility perception on Twitter. We nd reader's educational background and geolocation have signi cant correlation with credibility perception. Further investigation reveals that combinations of demographic attributes correlating with credibility perception are insigni cant. Despite di erences in demographics, readers nd features regarding topic keyword and the writing style of a tweet to be independently helpful in perceiving tweets' credibility. While previous studies reported the use of features independently, our result shows that readers use combination of features to help in making credibility perception of tweets