2,023 research outputs found

    s-Process Nucleosynthesis in Advanced Burning Phases of Massive Stars

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    We present a detailed study of s-process nucleosynthesis in massive stars of solar-like initial composition and masses 15, 20,25, and 30 Msun. We update our previous results of s-process nucleosynthesis during the core He-burning of these stars and then focus on an analysis of the s-process under the physical conditions encountered during the shell-carbon burning. We show that the recent compilation of the Ne22(alpha,n)Mg25 rate leads to a remarkable reduction of the efficiency of the s-process during core He-burning. In particular, this rate leads to the lowest overproduction factor of Kr80 found to date during core He-burning in massive stars. The s-process yields resulting from shell carbon burning turn out to be very sensitive to the structural evolution of the carbon shell. This structure is influenced by the mass fraction of C12 attained at the end of core helium burning, which in turn is mainly determined by the C12(alpha,gamma)O16 reaction. The still present uncertainty in the rate for this reaction implies that the s-process in massive stars is also subject to this uncertainty. We identify some isotopes like Zn70 and Rb87 as the signatures of the s-process during shell carbon burning in massive stars. In determining the relative contribution of our s-only stellar yields to the solar abundances, we find it is important to take into account the neutron exposure of shell carbon burning. When we analyze our yields with a Salpeter Initial Mass Function, we find that massive stars contribute at least 40% to s-only nuclei with mass A 90, massive stars contribute on average ~7%, except for Gd152, Os187, and Hg198 which are ~14%, \~13%, and ~11%, respectively.Comment: 52 pages, 16 figures, accepted for publication in Ap

    Interaction of CO molecules with (Cu , Ag and Au) deposited on regular and defective MgO and BaO(001) surfaces: Density functional calculations

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    The adsorption properties and characteristics of CO on Cu, Ag and Au atoms deposited on various sites of the alkaline earth oxide MgO and BaO. The three members of morphological irregularities, terrace, edge, and oxygen terminated corner of MgO and BaO (001) surface have been studied by means of density functional calculations and embedded cluster model. The examined clusters were embedded in the simulated Coulomb fields that closely approximate the Madelung fields of the host surfaces. The  adsorption  properties  of  CO  have  been  analyzed  with reference  to  the  nature  of  the  oxide  support,  pairwise  and  non-pairwise  ..........Please read the full paper

    Evolution of Massive Stars Up to the End of Central Oxygen Burning

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    We present a detailed study of the evolution of massive stars of masses 15, 20, 25 and 30 \msun assuming solar-like initial chemical composition. The stellar sequences were evolved through the advanced burning phases up to the end of core oxygen burning. We present a careful analysis of the physical characteristics of the stellar models. In particular, we investigate the effect of the still unsettled reaction 12^{12}C(α\alpha,γ\gamma)16^{16}O on the advanced evolution by using recent compilations of this rate. We find that this rate has a significant impact on the evolution not only during the core helium burning phase, but also during the late burning phases, especially the shell carbon-burning. We have also considered the effect of different treatment of convective instability based on the Ledoux criterion in regions of varying molecular weight gradient during the hydrogen and helium burning phases. We compare our results with other investigations whenever available. Finally, our present study constitutes the basis of analyzing the nucleosynthesis processes in massive stars. In particular we will present a detail analysis of the {\it s}-process in a forthcoming paper.Comment: 46 pages, 15 figures. To be published in ApJ vol 611, August 10, 200

    Unmasking the interplay between mTOR and Nox4: novel insights into the mechanism connecting diabetes and cancer

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    Cancer was recently annexed to diabetic complications. Furthermore, recent studies suggest that cancer can increase the risk of diabetes. Consequently, diabetes and cancer share many risk factors, but the cellular and molecular pathways correlating diabetes and colon and rectal cancer (CRC) remain far from understood. In this study, we assess the effect of hyperglycemia on cancer cell aggressiveness in human colon epithelial adenocarcinoma cells in vitro and in an experimental animal model of CRC. Our results show that Nox (NADPH oxidase enzyme) 4-induced reactive oxygen species (ROS) production is deregulated in both diabetes and CRC. This is paralleled by inactivation of the AMPK and activation of the mammalian target of rapamycin (mTOR) C1 signaling pathways, resulting in 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG) accumulation, induction of DNA damage, and exacerbation of cancer cell aggressiveness, thus contributing to the genomic instability and predisposition to increased tumorigenesis in the diabetic milieu. Pharmacologic activation of AMPK, inhibition of mTORC1, or blockade of Nox4 reduce ROS production, restore the homeostatic signaling of 8-oxoguanine DNA glycosylase/8-oxodG, and lessen the progression of CRC malignancy in a diabetic milieu. Taken together, our results identify the AMPK/mTORC1/Nox4 signaling axis as a molecular switch correlating diabetes and CRC. Modulating this pathway may be a strategic target of therapeutic potential aimed at reversing or slowing the progression of CRC in patients with or without diabetes.-Mroueh, F. M., Noureldein, M., Zeidan, Y. H., Boutary, S., Irani, S. A. M., Eid, S., Haddad, M., Barakat, R., Harb, F., Costantine, J., Kanj, R., Sauleau, E.-A., Ouhtit, A., Azar, S. T., Eid, A. H., Eid, A. A. Unmasking the interplay between mTOR and Nox4: novel insights into the mechanism connecting diabetes and cancer.Scopu

    Anti-hypertensive Herbs and their Mechanisms of Action: Part I

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    The use of herbal therapies for treatment and management of cardiovascular diseases (CVDs) is increasing. Plants contain a bounty of phytochemicals that have proven to be protective by reducing the risk of various ailments and diseases. Indeed, accumulating literature provides the scientific evidence and hence reason d'etre for the application of herbal therapy in relation to CVDs. Slowly, but absolutely, herbal remedies are being entrenched into evidence-based medical practice. This is partly due to the supporting clinical trials and epidemiological studies. The rationale for this expanding interest and use of plant based treatments being that a significant proportion of hypertensive patients do not respond to Modern therapeutic medication. Other elements to this equation are the cost of medication, side-effects, accessibility, and availability of drugs. Therefore, we believe it is pertinent to review the literature on the beneficial effects of herbs and their isolated compounds as medication for treatment of hypertension, a prevalent risk factor for CVDs. Our search utilized the PubMed and ScienceDirect databases, and the criterion for inclusion was based on the following keywords and phrases: hypertension, high blood pressure, herbal medicine, complementary and alternative medicine (CAM), nitric oxide, vascular smooth muscle cell (VSMC) proliferation, hydrogen sulfide, nuclear factor kappa-B, oxidative stress, and epigenetics/epigenomics. Each of the aforementioned keywords was co-joined with herb in question, and where possible with its constituent molecule(s). In this first of a two-part review, we provide a brief introduction of hypertension, followed by a discussion of the molecular and cellular mechanisms. We then present and discuss the plants that are most commonly used in the treatment and management of hypertension.NPRP# 4-571-3-171 from the Qatar National Research Fund (a member of Qatar Foundation)

    Radiation effect on viscous flow of a nanofluid and heat transfer over a nonlinearly stretching sheet

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    In this work, we study the flow and heat transfer characteristics of a viscous nanofluid over a nonlinearly stretching sheet in the presence of thermal radiation, included in the energy equation, and variable wall temperature. A similarity transformation was used to transform the governing partial differential equations to a system of nonlinear ordinary differential equations. An efficient numerical shooting technique with a fourth-order Runge-Kutta scheme was used to obtain the solution of the boundary value problem. The variations of dimensionless surface temperature, as well as flow and heat-transfer characteristics with the governing dimensionless parameters of the problem, which include the nanoparticle volume fraction ϕ, the nonlinearly stretching sheet parameter n, the thermal radiation parameter NR, and the viscous dissipation parameter Ec, were graphed and tabulated. Excellent validation of the present numerical results has been achieved with the earlier nonlinearly stretching sheet problem of Cortell for local Nusselt number without taking the effect of nanoparticles

    Intra-articular dexmedetomidine with bupivacaine versus bupivacaine alone for postoperative analgesia after knee arthroscopy

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    Background: Optimal relief of pain after knee arthroscopy is essential for early rehabilitation and mobilisation and to minimise postoperative morbidity. This study’s aim was to assess dexmedetomidine as an additive to intra-articular (IA) bupivacaine in terms of analgesic duration and postoperative rescue analgesic consumption following arthroscopic knee surgery.Methods: A total of 70 patients, ASA physical status I and II, undergoing knee arthroscopy under general anaesthesia were enrolled in this double-blinded randomised controlled study, after Pan African Clinical Trial Registry (PACTR201507001048242) approval was obtained. Patients were randomly assigned into two groups; the bupivacaine group (B) received IA 19 ml bupivacaine 0.5% + 1 ml normal saline, bupivacaine dexmedetomidine group (BD) received IA injection of 19 ml bupivacaine 0.5% + dexmedetomidine 100 μg (1 ml). Postoperative visual analogue pain score (VAS), duration of analgesia and postoperative analgesic requirement were assessed.Results: VAS scores at rest and on mobilisation were significantly lower in the BD group at 4 h, 6 h and 8 h postoperatively in comparison with group B (p < 0.05). VAS scores were comparable between studied groups during the first 2 h, and at 12 h and 24 h postoperatively. Duration of analgesia was significantly longer in group BD (458.9 ± 93.5 min) than in the B group (229.1 ± 83.7 min) (p < 0.05). Postoperative analgesic consumption was lowered in the BD group compared with the B group (p < 0.05).Conclusions: Adding dexmedetomidine to IA bupivacaine after knee arthroscopy prolongs analgesic duration and decreases postoperative analgesic requirement.Keywords: arthroscopy, dexmedetomidine, intra-articular, postoperative pai

    Evolution of low-mass metal-free stars including effects of diffusion and external pollution

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    We investigate the evolution of low-mass metal-free Population III stars. Emphasis is laid upon the question of internal and external sources for CNO-elements, which - if present in sufficient amounts in the hydrogen-burning regions - lead to a strong modification of the stars' evolutionary behavior. For the production of carbon due to nuclear processes inside the stars, we use an extended nuclear network, demonstrating that hot pp-chains do not suffice to produce enough carbon or are less effective than the triple3-alpha-process. As an external source of CNO-elements we test the efficiency of pollution by a nearby massive star combined with particle diffusion. For all cases investigated, the additional metals fail to reach nuclear burning regions before deep convection on the Red Giant Branch obliterates the previous evolution. The surface abundance history of the polluted Pop III stars is presented. The possibilities to discriminate between a Pop II and a polluted Pop III field star are also discussed.Comment: Accepted for publication in Ap

    Effect of physical therapy rehabilitation program (exercise-therapy) on Irritable Bowel Syndrome

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    To evaluate the effect of physical therapy rehabilitation program consisted of moderate intensity aerobic exercise training (60% MHR) (Maximum Heart Rate) treadmill training on irritable bowel syndrome (IBS) symptom and quality of Life in post cholecystectomy patients. Thirty post cholecystectomy patients complaining from irritable bowel syndrome were recruited for this study; age ranged from 25 to 40 years, Patients were divided randomly into two equal groups, Group (A): received 4 weeks moderate intensity aerobic training program (60% MHR treadmill training (3 sessions per week) plus routine medical treatment protocol, Group (B): received routine medical care only. Patients assessed by Irritable Bowel Syndrome Symptom Severity Score (IBS-SSS) and Irritable Bowel Syndrome Quality of Life (IBS-QOL), Assessment was carried out before treatment and 4 weeks after treatment in both groups. Results showed that there was a significant decrease in post treatment values of IBS-SSS and IBS-QOL in comparison to pre-treatment values at both groups with (p-value < .001). Comparison between both groups post treatment showed significant difference in IBS-SSS and IBS-QOL variables, in group (A) more than group (B). Moderate intensity aerobic exercise training (60% MHR) for 4 weeks is effective in treatment of IBS post cholecystectomy through reducing IBS symptoms and improving Quality of Life
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