Computational study of reservoir sand production mechanisms

A numerical model is developed to simulate fluid flow conditions around a wellbore and to evaluate mechanisms governing fluid flow, pressure gradients, rock failure and the ensuing sand production. The rock material behaviour matches sandstone described by the Drucker–Prager material failure model. Conditions for erosion are governed through two criteria: a material failure criterion described by the Drucker–Prager model and a sanding criterion expressed by an eroded solid mass generation model. The interplay between controlling operating and reservoir conditions is assessed. In addition, contributions of the following key factors to interstitial fluid velocity, plastic strain, pore pressure variation and sand production are appraised: drawdown, wellbore perforation depth, mud pressure and erosion criteria. Despite a decrease in pore fluid velocity at the vicinity of the wellbore at increasing depth, sand production increases with wellbore/perforation depth. Likewise, at constant drawdown, sand production is aggravated as wellbore/perforation depth increases. The rate of increase in the plastic zone following the onset of sand production is inconstant. Furthermore, mud pressure is demonstrated as an effective tool for attenuating sand production. An understanding of interactions between key parameters governing reservoir responses and the effect on sanding during oil/gas production is imperative if extraction operations are to be optimised.Published onlin

Infrared Studies of Molecular Shocks in the Supernova Remnant HB 21: II. Thermal Admixture of Shocked H2_2 Gas in the South

We present near- and mid-infrared observations on the shock-cloud interaction region in the southern part of the supernova remnant HB 21, performed with the InfraRed Camera (IRC) aboard AKARI satellite and the Wide InfraRed Camera (WIRC) at the Palomar 5 m telescope. The IRC 4 um (N4), 7 um (S7), and 11 um (S11) band images and the WIRC H2 v=1->0 S(1) 2.12 um image show similar diffuse features, around a shocked CO cloud. We analyzed the emission through comparison with the H2 line emission of several shock models. The IRC colors are well explained by the thermal admixture model of H2 gas--whose infinitesimal H2 column density has a power-law relation with the temperature $T$, $dN\sim T^{-b}dT$--with n(H2) $\sim3.9\times10^4$ cm^{-2}, $b\sim4.2$, and N(H2;T>100K) $\sim2.8\times10^{21}$ cm^{-2}. We interpreted these parameters with several different pictures of the shock-cloud interactions--multiple planar C-shocks, bow shocks, and shocked clumps--and discuss their weaknesses and strengths. The observed H2 v=1->0 S(1) intensity is four times greater than the prediction from the power-law admixture model, the same tendency as found in the northern part of HB 21 (Paper I). We also explored the limitation of the thermal admixture model with respect to the derived model parameters.Comment: 35 pages, 10 figures, Accepted in "Advances in Space Research", higher resolution @ http://astro.snu.ac.kr/~jhshinn/asr-20090921-submitted_arxiv.pdf ; rev.2 - deletion of section 6.4 and the related content

Dapsone induced cholangitis as a part of dapsone syndrome: a case report

BACKGROUND: Dapsone can rarely cause a hypersensitivity reaction called dapsone syndrome, consisting of fever, hepatitis, exfoliative dermatitis, lymphadenopathy and hemolytic anemia. Dapsone syndrome is a manifestation of the DRESS (drug rash with eosinophilia and systemic symptoms) syndrome which is a serious condition that has been reported in association with various drugs. Cholangitis in dapsone syndrome has not been reported so far in the world literature. CASE PRESENTATION: We report a patient who presented with fever, exfoliative dermatitis, jaundice and anemia within three weeks of starting of dapsone therapy. These features are typical of dapsone syndrome, which is due to dapsone hypersensitivity and is potentially fatal. Unlike previous reports of hepatitic or cholestatic injury in dapsone syndrome we report here a case that had cholangitic liver injury. It responded to corticosteroids. CONCLUSION: We conclude that cholangitis, though unusual, can also form a part of dapsone syndrome. Physicians should be aware of this unusual picture of potentially fatal dapsone syndrome

Substance use and its predictors among undergraduate medical students of Addis Ababa University in Ethiopia

<p>Abstract</p> <p>Background</p> <p>Substance use remains high among Ethiopian youth and young adolescents particularly in high schools and colleges. The use of alcohol, <it>khat </it>and tobacco by college and university students can be harmful; leading to decreased academic performance, increased risk of contracting HIV and other sexually transmitted diseases. However, the magnitude of substance use and the factors associated with it has not been investigated among medical students in the country. This study was conducted to determine the prevalence of substance use and identify factors that influenced the behavior among undergraduate medical students of Addis Ababa University in Ethiopia.</p> <p>Methods</p> <p>A cross-sectional study using a pre-tested structured self-administered quantitative questionnaire was conducted in June 2009 among 622 medical students (Year I to Internship program) at the School of Medicine. The data were entered into Epi Info version 6.04d and analyzed using SPSS version 15 software program. Descriptive statistics were used for data summarization and presentation. Differences in proportions were compared for significance using Chi Square test, with significance level set at p < 0.05. Multivariate logistic regression analyses were used to assess the magnitude of associations between substance use and socio-demographic and behavioral correlates.</p> <p>Results</p> <p>In the last 12 months, alcohol was consumed by 22% (25% males vs. 14% females, p = 0.002) and <it>khat </it>use was reported by 7% (9% males vs. 1.5% females, p < 0.001) of the students. About 9% of the respondents (10.6% males vs. 4.6% females, p = 0.014) reported ever use of cigarette smoking, and 1.8% were found to be current smokers. Using multiple logistic regression models, being male was strongly associated with alcohol use in the last 12 months (adjusted OR = 2.14, 95% CI = 1.22-3.76). Students whose friends currently consume alcohol were more likely to consume alcohol (adjusted OR = 2.47, 95% CI = 1.50-4.08) and whose friends' use tobacco more likely to smoke (adjusted OR = 3.89, 95% CI = 1.83-8.30). <it>Khat </it>use within the past 12 months was strongly and positively associated with alcohol consumption (adjusted OR = 15.11, 95% CI = 4.24-53.91). Similarly, ever use of cigarette was also significantly associated with alcohol consumption (adjusted OR = 8.65, 95% CI = 3.48-21.50).</p> <p>Conclusions</p> <p>Concordant use of alcohol, <it>khat </it>and tobacco is observed and exposure to friends' use of substances is often implicated. Alcohol consumption or <it>khat </it>use has been significantly associated with tobacco use. While the findings of this study suggest that substance use among the medical students was not alarming, but its trend increased among students from Year I to Internship program. The university must be vigilant in monitoring and educating the students about the consequences of substance use.</p

Mesenchymal Stem Cell-Mediated Functional Tooth Regeneration in Swine

Mesenchymal stem cell-mediated tissue regeneration is a promising approach for regenerative medicine for a wide range of applications. Here we report a new population of stem cells isolated from the root apical papilla of human teeth (SCAP, stem cells from apical papilla). Using a minipig model, we transplanted both human SCAP and periodontal ligament stem cells (PDLSCs) to generate a root/periodontal complex capable of supporting a porcelain crown, resulting in normal tooth function. This work integrates a stem cell-mediated tissue regeneration strategy, engineered materials for structure, and current dental crown technologies. This hybridized tissue engineering approach led to recovery of tooth strength and appearance

Genome-Wide Meta-Analyses of Smoking Behaviors in African Americans

The identification and exploration of genetic loci that influence smoking behaviors have been conducted primarily in populations of the European ancestry. Here we report results of the first genome-wide association study meta-analysis of smoking behavior in African Americans in the Study of Tobacco in Minority Populations Genetics Consortium (n=32 389). We identified one non-coding single-nucleotide polymorphism (SNP; rs2036527[A]) on chromosome 15q25.1 associated with smoking quantity (cigarettes per day), which exceeded genome-wide significance ($\beta$=0.040, s.e.=0.007, P=1.84 × 10$^{−8}$). This variant is present in the 5′-distal enhancer region of the CHRNA5 gene and defines the primary index signal reported in studies of the European ancestry. No other SNP reached genome-wide significance for smoking initiation (SI, ever vs never smoking), age of SI, or smoking cessation (SC, former vs current smoking). Informative associations that approached genome-wide significance included three modestly correlated variants, at 15q25.1 within PSMA4, CHRNA5 and CHRNA3 for smoking quantity, which are associated with a second signal previously reported in studies in European ancestry populations, and a signal represented by three SNPs in the SPOCK2 gene on chr10q22.1. The association at 15q25.1 confirms this region as an important susceptibility locus for smoking quantity in men and women of African ancestry. Larger studies will be needed to validate the suggestive loci that did not reach genome-wide significance and further elucidate the contribution of genetic variation to disparities in cigarette consumption, SC and smoking-attributable disease between African Americans and European Americans

Association between XPF Polymorphisms and Cancer Risk: A Meta-Analysis

Background: Xeroderma pigmentosum complementation group F (XPF or ERCC4) plays a key role in DNA repair that protects against genetic instability and carcinogenesis. A series of epidemiological studies have examined associations between XPF polymorphisms and cancer risk, but the findings remain inconclusive. Methodology/Principal Findings: In this meta-analysis of 47,639 cancer cases and 51,915 controls, by searching three electronic databases (i.e., MEDLINE, EMBASE and CNKI), we summarized 43 case-control studies from 29 publications on four commonly studied polymorphisms of XPF (i.e., rs1800067, rs1799801, rs2020955 and rs744154), and we did not find statistical evidence of any significant association with overall cancer risk. However, in stratification analyses, we found a significant association of XPF-rs1799801 with a reduced cancer risk in Caucasian populations (4,845 cases and 5,556 controls; recessive model: OR = 0.87, 95% CI = 0.76–1.00, P = 0.049, P = 0.723 for heterogeneity test, I2 = 0). Further genotype-phenotype correlation analysis showed that the homozygous variant CC genotype carriers had higher XPF expression levels than that of the TT genotype carriers (Student’s t test for a recessive model: P = 0.046). No publication bias was found by using the funnel plot and Egger’s test. Conclusion: This meta-analysis suggests a lack of statistical evidence for the association between the four XPF SNPs and overall risk of cancers. However, XPF-rs1799801 may be associated with cancer risk in Caucasian populations, which needs to be further validated in single large, well-designed prospective studies