Direct Simulation Monte Carlo Analysis on Thrust Vectoring of a Supersonic Micro Nozzle using Bypass Mass Injection

Converging diverging micro nozzle is fundamentally intended for flow acceleration through the generation of kinetic energy for the advanced micro-propulsion systems. Such supersonic micro nozzles have significant applications in the launching, propulsion and rapid directional control of the micro-satellites for a better maneuver. Micro scale analysis of such flow devices is extended to the rarefied flow regime. Present study has addressed thrust vectoring in a planar converging-diverging supersonic micro nozzle by the bypass mass injection technique. Direct Simulation Monte Carlo (DSMC) method has been used for numerical modelling. Primary focus is given on the thrust vectoring control of the micro nozzle with a throat height of 20 micro meter and an expansion ratio of 1.7. For the secondary injection, a rectangular channel of 5 different bypass widths (2 - 12 micro meter) is considered for two different outlet pressures (Pout = 10 kPa and 40 kPa) while keeping the inlet pressure (Pin) and temperature (Tin) fixed at 1 atm and 300 k respectively. The physical behavior of the micro nozzle is acknowledged through the analysis of Mach, pressure, temperature and density contours. Numerical results reveal that the secondary flow injection is adapted into the primary flow through the formation of a pressure bump in the diverging section. Moreover, the total mass flow rate, secondary flow percentage, thrust force, the thrust coefficient and specific impulse increase with the bypass channel width. A change in thrust direction is obtained which in turn produces a considerable vectoring effect in the supersonic micro nozzle. The vectoring angle for Pout of 40 kPa peaks at 6 micro meter bypass channel whereas a gradual increase of the vectoring angle with the bypass channel width is observed for Pout = 10 kPa.Comment: Journal paper and it's under revie

Equilibrium, Thermodynamic, and Kinetic Studies

Publisher Copyright: © 2022 Razia Sulthana et al.The economic viability of adsorbing crystal violet (CV) using pepper seed spent (PSS) as a biosorbent in an aqueous solution has been studied. A parametrical investigation was conducted considering parameters like initial concentration of dye, time of contact, pH value, and temperature variation. The analysis of experimental data obtained was carried out by evaluating with the isotherms of Freundlich, Sips, Tempkin, Jovanovic, Brouers-Sotolongo, Toth, Vieth-Sladek, Radke-Prausnitz, Langmuir, and Redlich-Peterson. The adsorption kinetics were studied by implementing the Dumwald-Wagner, Weber-Morris, pseudo-first-order, pseudo-second-order, film diffusion, and Avrami models. The experimental value of adsorption capacity (Qm=129.4 mg g-1) was observed to be quite close to the Jovanovic isotherm adsorption capacity (Qm=82.24 mg g-1) at (R2), coefficient of correlation of 0.945. The data validation was found to conform to that of pseudo-second-order and Avrami kinetic models. The adsorption process was specified as a spontaneous and endothermic process owing to the thermodynamic parametrical values of ΔG0, ΔH0, and ΔS0. The value of ΔH0 is an indicator of the process's physical nature. The adsorption of CV to the PSS was authenticated from infrared spectroscopy and scanning electron microscopy images. The interactions of the CV-PSS system have been discussed, and the observations noted suggest PSS as a feasible adsorbent to extract CV from an aqueous solution.publishersversionpublishe

Comparative studies of ultrasound and membrane emulsification for the production of stable Perfluorocarbon-in-water nanoemulsions

Low-molecular weight perfluorocarbons (PFCs) are usually chemically and biologically inert, clear, colorless liquids, presenting a high affinity for many gases, namely for O2, NO and CO2, which turn them particularly suitable in various biomedical applications involving gas capture, transport and release. In fact, PFC-in-Water emulsions were one of the two major classes of systems proposed as blood substitutes and for O2/NO therapeutics. However there are still some important issues concerning this type of systems which have limited their efficiency, approval and commercial success, namely those related to emulsion stability, hydrodynamic size distribution and reduced shelf-lives. Stability issues can easily lead to PFC diffusion in water, to aggregation and to the consequent hydrodynamic size increase and emulsion degradation [1]. Nanoemulsions (typically within a range of hydrodynamic sizes of 10-100 nm) exhibit various advantages over typical microemulsions [2]. Hence, our aim is to produce monodisperse PFC nanoemulsions presenting larger surface-to-volume ratios, enhanced stabilities and more efficient gas capture/delivery properties. A first approach to achieve these goals is to prepare and to study a mixed surfactant system based on Tween 80 and on a perfluorinated surfactant (perfluorooctyl phosphocholine) at different relative compositions. PFC-in-Water nanoemulsions were produced by using the traditional ultrasound emulsification method (500W). The effects of co-surfactants relative compositions on CMC values, on the kinetics of emulsion formation and on the corresponding stabilities of prepared nanoemulsions were evaluated. Hydrodynamic sizes and Zeta-potentials were also assessed, being able to obtain stable nanoemulsions with hydrodynamic sizes between 150 and 200 nm. In a comparative study, PFC-in-Water nanoemulsions were also produced by membrane emulsification. This low energy-intensive technique has received increasing interest as it allows more flexible operating conditions. Regenerated cellulose membranes such as Nadir UC500 and Millipore Ultracel RC100, polyethersulphone membranes such as Nadir UP150 and Millipore PBHK04310, and a promising polycarbonate Whatman Track-ethched 30 nm Nuclepore membrane, were employed to produce nanoemulsions, and using the same mixed surfactant system and relative compositions. The energy inputs of these two methods were compared and discussed along with their efficiencies in terms of producing nanoemulsions presenting improved stabilities, smaller hydrodynamic sizes and narrower hydrodynamic size distributions. References [1] M.P. Krafft, A. Chittofrati, J.G. Riess, Curr Opin in Colloid Interface Sci., 8 (2003) 251–258 [2] E. Piacentini, E. Drioli, L. Giorno, J. of Membr. Sci., 468 (2014) 410–42

Secondary prevention of heart disease - knowledge among cardiologists and Omega-3 (Omega-3) fatty acid prescribing behaviors in Karachi, Pakistan

Background: The use of omega-3 fatty acids is a currently proven strategy for secondary prevention of heart disease. The prescription practices for this important nutraceutical is not currently known. It is imperative to assess the knowledge of cardiologists regarding the benefits of omega-3 fatty acids and to determine the frequency of its prescription. The aim of the study was to determine the practices and associations of dietary fish prescribing among cardiologists of Karachi and to assess their knowledge of fish oil supplementation and attitudes toward dietary practices. Methods: A cross sectional survey was conducted during the period of January to March, 2008. A self report questionnaire was employed. All practicing cardiologists of Karachi were included in the study. Multiple logistic regression analysis was performed to determine the independent factors associated with high fish prescribers. Results: The sample comprised of a total of 163 cardiologists practicing in Karachi, Pakistan. Most (73.6%) of the cardiologists fell in the age range of 28 - 45 years and were male (90.8%). High fish prescribers only comprised 36.2% of the respondents. After adjusting for age and gender, multivariate analysis revealed that only the variable of knowledge about fish oil\u27s role in reducing sudden cardiac death was independently associated with high fish prescribers OR = 6.38 [95% CI 2.58-15.78]. Conclusion: The level of knowledge about the benefits of omega-3 fatty acids is high and the cardiologists harbor a favorable attitude towards dispensing dietary fish advice. However, the prescription practices are less than optimal and not concordant with recommendations of organisations such as the American Heart Association and National Heart Foundation of Australia. The knowledge of prevention of sudden cardiac death in CVD Patients has been identified as an important predictor of high fish prescription. This particular life-saving property of omega-3 fatty acids should be the focus of any implemented educational strategy targeted to improve secondary CVD prevention via omega-3 fatty acid supplementation

Body Dysmorphic Disorder: Gender differences and prevalence in a Pakistani medical student population

<p>Abstract</p> <p>Background</p> <p>Body dysmorphic disorder (BDD) is a psychiatric disorder characterized by a preoccupation with an imagined or slight defect which causes significant distress or impairment in functioning. Few studies have assessed gender differences in BDD in a non clinical population. Also no study assessed BDD in medical students. This study was designed to determine the point prevalence of BDD in Pakistani medical students and the gender differences in prevalence of BDD, body foci of concern and symptoms of BDD.</p> <p>Methods</p> <p>The medical students enrolled in a medical university in Karachi, Pakistan filled out a self-report questionnaire which assessed clinical features of BDD. BDD was diagnosed according to the DSM-IV criteria.</p> <p>Results</p> <p>Out of the 156 students, 57.1% were female. A total of 78.8% of the students reported dissatisfaction with some aspect of their appearance and 5.8% met the DSM-IV criteria for BDD. The male to female ratio for BDD was 1.7. Regarding gender differences in body foci of concern, the top three reported foci of concern in male students were head hair (34.3%), being fat (32.8%), skin (14.9%) and nose(14.9%), whereas in females they were being fat (40.4%), skin (24.7%) and teeth (18%). Females were significantly more concerned about being fat (p = 0.005). Male students were significantly more concerned about being thin (p = 0.01) and about head hair (p = 0.012).</p> <p>Conclusion</p> <p>BDD is fairly common in our medical student population, with a higher prevalence in males. Important gender differences in BDD symptomatology and reported body foci of concern were identified which reflected the influence of media on body image perception. The impact of cultural factors on the prevalence as well as gender differences in BDD symptomatology was also established.</p

Oxidation of olefins catalysed by (HEDTA) Ru<SUP>v</SUP>=O

The complex K[RuIII(HEDTA)Cl].H2O 1&#x0332; and [(HEDTA) Ruv=O] 2&#x0332; were prepared and characterised by elemental analysis, IR, UV-Vis spectroscopy, conductivity, magnetic susceptibility and electrochemical studies (HEDTA-hydroxyethyl-ethylenediaminetriacetate anion). The kinetics of oxygen atom transfer of [RuIII(HEDTA) (H2O)]1a&#x0332; to [(HEDTA) Ruv=O] 2&#x0332; with iodosoylbenzene was studied spectrophotometrically by using stopped-flow technique. The oxygen atom transfer from complex 2&#x0332; to cyclohexene, cyclooctene, styrene, cis andtrans-stilbene was studied by the disappearance of the characteristic oxo peak (&#955;max=391 nm) at constant pH (3.0) and ionic strength (&#956;=0.1 M NaClO4) and also product analysis by gas chromatography (GC). The activation parameters for both the oxygenation of complex1 to complex 2&#x0332;, and oxygen atom transfer from complex 2&#x0332; to the organic substrates studied were evaluated and suitable mechanisms proposed

Sustainable adsorption method for the remediation of malachite green dye using nutraceutical industrial fenugreek seed spent

Nutraceutical industrial fenugreek seed spent (NIFGS), a relatively low-cost material abundantly available with nearly negligible toxicity for the bioremediation of malachite green (MG) dye from aqueous media, is reported. Studies on the various parameters affecting the adsorption capacity of NIFGS were carried out to evaluate the kinetics and the equilibrium thermodynamics. All the experiments were designed at about pH 7. The adsorption isotherm model proposed by Langmuir fits better than the Freundlich isotherm model. Kinetic study data confirms the viability of pseudo-second-order model. Calculated thermodynamic factors suggest that the adsorption phenomenon is endothermic, almost instantaneous, and physical in nature

Geriatric patients' expectations of their physicians: findings from a tertiary care hospital in Pakistan

<p>Abstract</p> <p>Background</p> <p>Geriatric health is a neglected and under-explored area internationally and in Pakistan. We aimed to ascertain the expectations of the geriatric patients from their physicians and the factors associated with patient satisfaction in this particular age bracket.</p> <p>Methods</p> <p>A cross-sectional survey was carried out at a tertiary care teaching hospital in Karachi, Pakistan. Data collection was carried out via face-to-face interviews based on structured, pre-tested questionnaires. All consenting individuals aged 65 years or above were recruited into the study. Convenience sampling was used to draw the sample. The data was analyzed using SPSS version 16. Geriatric patient's expectations from physicians were elicited using a set of 11 questions that were graded on a scale of 1-3 where 1 = not important, 2 = important, 3 = very important.</p> <p>Results</p> <p>Three hundred and eighty geriatric patients were interviewed. The response rate of this study was 89.8%. The mean age of the respondents was 73.4 ± 6.8 years. Two hundred and forty eight respondents (65.3%) were female. Diabetes mellitus (53.7%), hypertension (59.5%), arthritis (40.5%) and renal disease (32.1%) were common ailments among geriatric patients. More than 50% of the patients were visiting their physicians once every two to three months. Discussing treatment options and letting patients make the final decision (79.2%), prescribing minimum possible medications (84.5%), physician's holistic knowledge about the spectrum of care issues for geriatric patients (79.2%), being given a realistic but optimistic picture of future health by physicians (85.5%) were ranked as very important expectations by patients from their physicians. Cumulative household income (p = 0.005), most important health complaint (p = 0.01) and frequency of experiencing health complaint (p < 0.001) emerged as independent predictors of the satisfaction of geriatric patients from care provided by physicians.</p> <p>Conclusion</p> <p>We have documented the expectations of the geriatric patients from their physicians in a developing country. Physicians belonging to all disciplines should keep these expectations in mind during clinical encounters with geriatric patients.</p

Adherence to the European Society of Cardiology (ESC) guidelines for chronic heart failure - A national survey of the cardiologists in Pakistan

<p>Abstract</p> <p>Background</p> <p>The aims of this study were to evaluate the awareness of and attitudes towards the 2005 European Society of Cardiology (ESC) guidelines for Heart Failure (HF) of the cardiologists in Pakistan and assess barriers to adherence to guidelines.</p> <p>Methods</p> <p>A cross-sectional survey was conducted in person from March to July 2009 to all cardiologists practicing in 4 major cities in Pakistan (Karachi, Lahore, Quetta and Peshawar). A validated, semi-structured questionnaire assessing ESC 2005 Guidelines for HF was used to obtain information from cardiologists. It included questions about awareness and relevance of HF guidelines (See Additional File <supplr sid="S1">1</supplr>). Respondents' management choices were compared with those of an expert panel based on the guidelines for three fictitious patient cases. Cardiologists were also asked about major barriers to adherence to guidelines.</p> <suppl id="S1"> <title> <p>Additional file 1</p> </title> <text> <p><b>Questionnaire</b>. Description: Questionnaire that was administered to participants.</p> </text> <file name="1471-2261-11-68-S1.DOC"> <p>Click here for file</p> </file> </suppl> <p>Results</p> <p>A total of 372 cardiologists were approached; 305 consented to participate (overall response rate, 82.0%). The survey showed a very high awareness of CHF guidelines; 97.4% aware of any guideline. About 13.8% considered ESC guidelines as relevant or very relevant for guiding treatment decisions while 92.8% chose AHA guidelines in relevance. 87.2% of respondents perceived that they adhered to the HF guidelines. For the patient cases, the proportions of respondents who made recommendations that completely matched those of the guidelines were 7% (Scenario 1), 0% (Scenario 2) and 20% (Scenario 3). Respondents considered patient compliance (59%) and cost/health economics (50%) as major barriers to guideline implementation.</p> <p>Conclusion</p> <p>We found important self reported departures from recommended HF management guidelines among cardiologists of Pakistan.</p