80 research outputs found

    Dynamical effects of QCD in q2qˉ2q^2 \bar{q}^{2} systems

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    We study the coupling of a tetraquark system to an exchanged meson-meson channel, using a pure gluonic theory based four-quark potential {\em matrix} model which is known to fit well a large number of data points for lattice simulations of different geometries of a four-quark system. We find that if this minimal-area-based potential matrix replaces the earlier used simple Gaussian form for the gluon field overlap factor ff in its off-diagonal terms, the resulting TT-matrix and phase shifts develop an angle dependence whose partial wave analysis reveals DD wave and higher angular momentum components in it. In addition to the obvious implications of this result for the meson-meson scattering, this new feature indicates the possibility of orbital excitations influencing properties of meson-meson molecules through a polarization potential. We have used a formalism of the resonating group method, treated kinetic energy and overlap matrices on model of the potential matrix, but decoupled the resulting complicated integral equations through the Born approximation. In this exploratory study we have used a quadratic confinement and not included the spin-dependence; we also used the approximation of equal constituent quark masses.Comment: 18 pages, 9 figure

    Career goals of trainee physicians in internal medicine

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    OBJECTIVE: To survey Internal Medicine trainees\u27 future career choices and factors influencing their decision-making. DESIGN: Cross-sectional study. PLACE AND DURATION OF STUDY: The Aga Khan University Hospital, Karachi, from November 2006 to January 2007. SUBJECTS AND METHODS: A standard questionnaire was administered to the residents and Interns working in the Department of Internal Medicine of The Aga Khan University Hospital. The questionnaire covered demographic details, specialty choice, work-time distribution and factors influencing career choice. Descriptive statistics were applied. RESULTS: A total of 49 doctors participated with 57% females; and 43% males, having 33% interns and 67% residents. A minority (22%) opted for internal medicine, while 78% selected sub-specialties with cardiology (20%) being the most sought- after sub-specialty. Majority (69%) wanted to spend more time in clinical activities compared to administration (18%) or research (13%). Majority (92%) wanted to work in an academic setting. Availability of a structured training program (61%), ability to practice broad area of medicine (41%) and prestige of the specialty (41%) highly influenced their career choices. Forty one (82%) wanted to proceed abroad for further training and 80% wanted to eventually practice in Pakistan. CONCLUSION: Most of the interviewed under-training physicians wanted to pursue sub-specialty. Clinical work was more attractive compared to research. A structured training program was detrimental in affecting their choices. Majority wanted further training abroad but eventual settlement in Pakistan. The study results can help us create the basis for reforming the current training programs

    Energy-efficient indirect evaporative cooler design framework: An experimental and numerical study

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    A remarkable surge in cooling demand is observed in the last decades. Currently, the cooling market is dominated by mechanical vapor compression chillers which are energy intensive and use harmful chemical refrigerants. Therefore, the current focus of the current research in cooling is the development of unconventional, sustainable cooling systems. In this regard, indirect evaporative coolers have shown significant potential (particularly under hot-dry climates) with high energy efficiency, low cost, water-based sustainable operation, and benign emissions. However, these systems are in the development stage and have not yet been fully commercialized because of certain design challenges. An innovative indirect evaporative cooler is proposed, fabricated, and experimentally tested in this study. Particularly, the study is focused on the development of heat transfer coefficient correlation for the system for commercial-scale design and expansion. This is because the earlier available correlation is based on simple airflow between parallel plates assumption and does not incorporate the effect of the evaporative potential of the system resulting in under/over-estimation of the heat transfer characteristics. The results showed that the proposed system achieved a temperature drop of 20 °C, a cooling capacity of around 180 W, and an overall heat transfer coefficient of up to 30 W/m2K. Moreover, the study presents an experiment-regression-based heat transfer coefficient correlation that satisfactorily captures the effect of outdoor air temperature and airflow rate ratio which are critical in the design of evaporative coolers. The proposed correlation showed a high (±5%) with experimental data thus making it suitable for the future design of IEC systems over assorted operating scenarios

    Dˉ0D0\bar{D}^{0}D^{0*} (D0Dˉ0)(D^{0}\bar{D}^{0*}) System in QCD-Improved Many Body Potential

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    For a system of current interest (composed of charm, anticharm quarks and a pair of light ones), we show trends in phenomenological implications of QCD-based improvements to a simple quark model treatment. We employ resonating group method to render this difficult four-body problem manageable. We use a quadratic confinement so as to be able to improve beyond the Born approximation. We report the position of the pole corresponding to Dˉ0D0\bar{D}^{0}D^{0*} molecule for the best fit of a model parameter to the relevant QCD simulations. We point out the interesting possibility that the pole can be shifted to 38723872 MeV by introducing another parameter I0I_{0} that changes the strength of the interaction in this one component of X(3872)X(3872). The revised value of this second parameter can guide future trends in modeling of the full exotic meson X(3872)X(3872). We also report the changes with I0I_{0} in the SS-wave spin averaged cross sections for Dˉ0D0ωJ/ψ\bar{D}^{0}D^{0*}\longrightarrow\omega J/\psi and Dˉ0D0ρJ/ψ\bar{D}^{0}D^{0*}\longrightarrow\rho J/\psi. These cross sections are important regarding the study of QGP (quark gluon plasma).Comment: It is to be published in Chinese Physics

    Waste Animal Bones as Catalysts for Biodiesel Production; A Mini Review

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    Slaughterhouse waste is considered to be an emerging issue because of its disposal cost. As an alternative, it would be a great prospect for the bioeconomy society to explore new usages of these leftover materials. As per food safety rules mentioned by EU legislation, all bone waste generated by slaughterhouses ought to be disposed of by rendering. The huge quantity of worldwide bone waste generation (130 billion kilograms per annum) is an environmental burden if not properly managed. The waste animal bones can be efficiently employed as a heterogeneous catalyst to produce biodiesel. This mini review summarized the recent literature reported for biodiesel generation using waste animal bones derived heterogeneous catalyst. It discusses the sources of bone waste, catalyst preparation methods, particularly calcination and its effects, and important characteristics of bones derived catalyst. It suggests that catalysts extracted from waste animal bones have suitable catalytic activity in transesterification of different oil sources to generate a good quality biodiesel

    Syncope: experience at a tertiary care hospital in Karachi, Pakistan

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    Introduction:Our aim was to determine the characteristics of Patients presenting with syncope at a tertiary care hospital in Karachi, Pakistan.Methods: A review of medical records was conducted retrospectively at the Department of Medicine, Aga Khan University Hospital, Karachi. Patients aged 16 and above, admitted from January 2000 to December 2005 with the diagnosis of syncope made by the attending physician were included.Results:A total of 269 Patients were included (75% males, mean age: 57.4 years). Neurogenic (vasovagal) syncope was the most common cause (47%), followed by cardiogenic syncope (18%) and orthostatic syncope (9%). A total of 24% were discharged undiagnosed. Twenty Patients (7.4%) did not have any prodrome. Common prodromal symptoms included dizziness (61%), sweating (25%), palpitations (19%), nausea/vomiting (19%) and visual symptoms (17%). The distribution of symptoms according to cause of syncope revealed only breathlessness to be significantly associated with cardiogenic syncope (p = 0.002). Most Patients with cardiogenic syncope were aged above 40 (98%, p \u3c 0.001), had coronary artery disease (72%, p \u3c 0.001) and abnormal electrocardiogram at presentation (92%, p \u3c 0.001).Conclusion:Despite differences in burden of diseases, our findings were similar to those of published syncope literature. Further studies are needed to develop a protocol to expedite the evaluation and limit the work-up and admission in low-risk Patients

    Revamping of Chronic Respiratory Diseases in Low- and Middle-Income Countries

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    Low- and middle-income countries (LMICs) endure an asymmetrically high burden of worldwide disease and death caused by chronic respiratory diseases (CRDs), i.e., asthma, emphysema, bronchiectasis, and post-tuberculosis lung disease (PTLD). CRDs are firmly related with indigence, infectious diseases, and other non-communicable diseases (NCDs) and add to complex multi-disease with great impact on the lives and livelihood of those affected. The pertinence of CRDs to health and demographic wellbeing is relied upon to increment in the long time ahead, as expectations of life rise and the contending dangers of right on time youth mortality and irresistible infections level. The WHO has distinguished the counteraction and control of NCDs as an earnest improvement issue and crucial for the sustainable development goals (SDSs) by 2030. In this review, we center on CRDs in LMICs. We examine the early life roots of CRDs, challenges in their avoidance, identification and administration in LMICs, and the pathways to resolve for accomplish valid widespread wellbeing inclusion
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