Some new Wyman–Leibovitz–Adler type static relativistic charged anisotropic fluid spheres compatible to self-bound stellar modeling

This article was published in the The European Physical Journal C [© The Author(s) 2015. This article is published with open access at Springerlink.com] and the definite version is available at : http://10.1140/epjc/s10052-015-3737-6 The Journal's website is at: http://link.springer.com/article/10.1140/epjc/s10052-015-3737-6In this work some families of relativistic anisotropic charged fluid spheres have been obtained by solving the Einstein–Maxwell field equations with a preferred form of one of the metric potentials, and suitable forms of electric charge distribution and pressure anisotropy functions. The resulting equation of state (EOS) of the matter distribution has been obtained. Physical analysis shows that the relativistic stellar structure for the matter distribution considered in this work may reasonably model an electrically charged compact star whose energy density associated with the electric fields is on the same order of magnitude as the energy density of fluid matter itself (e.g., electrically charged bare strange stars). Furthermore these models permit a simple method of systematically fixing bounds on the maximum possible mass of cold compact electrically charged self-bound stars. It has been demonstrated, numerically, that the maximum compactness and mass increase in the presence of an electric field and anisotropic pressures. Based on the analytic models developed in this present work, the values of some relevant physical quantities have been calculated by assuming the estimated masses and radii of some well-known potential strange star candidates like PSR J1614-2230, PSR J1903+327, Vela X-1, and 4U 1820-30.Publishe

Simulation, Design and Optimization of Membrane Gas Separation, Chemical Absorption and Hybrid Processes for CO2 Capture

Coal-fired power plants are the largest anthropogenic point sources of CO2 emissions worldwide. About 40% of the world's electricity comes from coal. Approximately 49% of the US electricity in 2008 and 23% of the total electricity generation of Canada in 2000 came from coal-fired power plant (World Coal Association, and Statistic Canada). It is likely that in the near future there might be some form of CO2 regulation. Therefore, it is highly probable that CO2 capture will need to be implemented at many US and Canadian coal fired power plants at some point. Several technologies are available for CO2 capture from coal-fired power plants. One option is to separate CO2 from the combustion products using conventional approach such as chemical absorption/stripping with amine solvents, which is commercially available. Another potential alternative, membrane gas separation, involves no moving parts, is compact and modular with a small footprint, is gaining more and more attention. Both technologies can be retrofitted to existing power plants, but they demands significant energy requirement to capture, purify and compress the CO2 for transporting to the sequestration sites. This thesis is a techno-economical evaluation of the two approaches mentioned above along with another approach known as hybrid. This evaluation is based on the recent advancement in membrane materials and properties, and the adoption of systemic design procedures and optimization approach with the help of a commercial process simulator. Comparison of the process performance is developed in AspenPlus process simulation environment with a detailed multicomponent gas separation membrane model, and several rigorous rate-based absorption/stripping models. Fifteen various single and multi-stage membrane process configurations with or without recycle streams are examined through simulation and design study for industrial scale post-combustion CO2 capture. It is found that only two process configurations are capable to satisfy the process specifications i.e., 85% CO2 recovery and 98% CO2 purity for EOR. The power and membrane area requirement can be saved by up to 13% and 8% respectively by the optimizing the base design. A post-optimality sensitivity analysis reveals that any changes in any of the factors such as feed flow rate, feed concentration (CO2), permeate vacuum and compression condition have great impact on plant performance especially on power consumption and product recovery. Two different absorption/stripping process configurations (conventional and Fluor concept) with monoethanolamine (30 wt% MEA) solvent were simulated and designed using same design basis as above with tray columns. Both the rate-based and the equilibrium-stage based modeling approaches were adopted. Two kinetic models for modeling reactive absorption/stripping reactions of CO2 with aqueous MEA solution were evaluated. Depending on the options to account for mass transfer, the chemical reactions in the liquid film/phase, film resistance and film non-ideality, eight different absorber/stripper models were categorized and investigated. From a parametric design study, the optimum CO2 lean solvent loading was determined with respect to minimum reboiler energy requirement by varying the lean solvent flow rate in a closed-loop simulation environment for each model. It was realized that the success of modeling CO2 capture with MEA depends upon how the film discretization is carried out. It revealed that most of the CO2 was reacted in the film not in the bulk liquid. This insight could not be recognized with the traditional equilibrium-stage modeling. It was found that the optimum/or minimum lean solvent loading ranges from 0.29 to 0.40 and the reboiler energy ranges from 3.3 to 5.1 (GJ/ton captured CO2) depending on the model considered. Between the two process alternatives, the Fluor concept process performs well in terms of plant operating (i.e., 8.5% less energy) and capital cost (i.e., 50% less number of strippers). The potentiality of hybrid processes which combines membrane permeation and conventional gas absorption/stripping using MEA were also examined for post-combustion CO2 capture in AspenPlus®. It was found that the hybrid process may not be a promising alternative for post-combustion CO2 capture in terms of energy requirement for capture and compression. On the other hand, a stand-alone membrane gas separation process showed the lowest energy demand for CO2 capture and compression, and could save up to 15 to 35% energy compare to the MEA capture process depending on the absorption/stripping model used

Psychological Therapies in Patients with Irritable Bowel Syndrome: A Systematic Review and Meta-Analysis of Randomized Controlled Trials

Background. Irritable bowel syndrome (IBS) is a poorly understood disease with few effective treatments. Psychosocial factors are believed to contribute to the pathogenesis of IBS. Objective. To evaluate the evidence for psychological therapies in IBS treatment. Methods. We searched six medical databases through February 6, 2014, for randomized controlled trials (RCTs) of psychological therapies for the treatment of IBS. Two independent reviewers identified the RCTs, extracted the data, and assessed trial quality. We used the random-effect model to pool standardized mean difference (SMD) and 95% confidence interval (CI) across trials. Results. 15 RCTs that mostly evaluated cognitive behavioral therapy were included. Psychological therapies were associated with improvement in IBS symptoms severity scales (SMD −0.618; 95% CI: −0.853 to −0.383), IBS-Quality of Life (SMD 0.604; 95% CI: 0.440 to 0.768), and abdominal pain (SMD −0.282; 95% CI: −0.562 to −0.001). No statistically significant effect was observed on diarrhea or constipation. Limitations. The trials were at increased risk of bias and the overall sample size was small leading to imprecision. Conclusion. Psychological therapies may improve the quality of life and symptom severity in IBS. The effect size noted is moderate to large and is clinically meaningful

Association between industry affiliation and position on cardiovascular risk with rosiglitazone: cross sectional systematic review

Objective To explore a possible link between authors’ financial conflicts of interest and their position on the association of rosiglitazone with increased risk of myocardial infarction in patients with diabetes

A systematic review and meta-analysis of randomized trials of carotid endarterectomy vs stenting

ObjectiveThe purpose of this systematic review and meta-analysis was to synthesize the available evidence derived from randomized controlled trials (RCTs) regarding the relative efficacy and safety of endarterectomy vs stenting in patients with carotid artery disease.MethodsWe searched MEDLINE, EMBASE, Current Contents, and Cochrane CENTRAL through July 2010 to update previous systematic reviews. Two reviewers determined trial eligibility and extracted descriptive, methodologic, and outcome data (death, nonfatal stroke, and nonfatal myocardial infarction). Random-effects meta-analysis was used to pool relative risks and the I2 statistic was used to assess heterogeneity.ResultsThirteen RCTs proved eligible enrolling 7484 patients, of which 80% had symptomatic disease. Methodological quality was moderate to high, with better quality among RCTs published after 2008. Compared with carotid endarterectomy, stenting was associated with increased risk of any stroke (relative risk [RR], 1.45; 95% confidence interval [CI], 1.06-1.99; I2 = 40%), decreased risk of periprocedural myocardial infarction (MI; RR, 0.43; 95% CI, 0.26- 0.71; I2 = 0%), and nonsignificant increase in mortality (RR, 1.40; 95% CI, 0.85-2.33; I2 = 5%). When analysis was restricted to the two most recent trials with the better methodology and more contemporary technique, we found stenting to be associated with a significant increase in the risk of any stroke (RR, 1.82; 95% CI, 1.35-2.45) and mortality (RR, 2.53; 95% CI, 1.27-5.08) and a nonsignificant reduction of the risk of MI (RR, 0.39; 95% CI, 0.12-1.23). For every 1000 patients opting for stenting rather than endarterectomy, 19 more patients would have strokes and 10 fewer would have MIs. Outcome data in asymptomatic patients were sparse and imprecise; hence, these conclusions apply primarily to symptomatic patients.ConclusionCompared with endarterectomy, carotid artery stenting (CAS) significantly increases the risk of any stroke and decreases the risk of MI