Magnetic properties of Mn-doped Ge46 and Ba8Ge46 clathrates

We present a detailed study of the magnetic properties of unique cluster assembled solids namely Mn doped Ge46 and Ba8Ge46 clathrates using density functional theory. We find that ferromagnetic (FM) ground states may be realized in both the compounds when doped with Mn. In Mn2Ge44, ferromagnetism is driven by hybridization induced negative exchange splitting, a generic mechanism operating in many diluted magnetic semiconductors. However, for Mn-doped Ba8Ge46 clathrates incorporation of conduction electrons via Ba encapsulation results in RKKY-like magnetic interactions between the Mn ions. We show that our results are consistent with the major experimental observations for this system.Comment: 6 pages, 4 figure

Methyl esters selectivity of transesterification reaction with homogenous alkaline catalyst to produce biodiesel in batch, plug flow, and continuous stirred tank reactors

Selectivity concept is essential in establishing the best operating conditions for attaining maximum production of the desired product. For complex reaction such as biodiesel fuel synthesis, kinetic studies of transesterification reaction have revealed the mechanism of the reaction and rate constants. The objectives of this research are to develop the kinetic parameters for determination of methyl esters and glycerol selectivity, evaluate the significance of the reverse reaction in transesterification reaction, and examine the influence of reaction characteristics (reaction temperature, methanol to oil molar ratio, and the amount of catalyst) on selectivity. For this study, published reaction rate constants of transesterification reaction were used to develop mathematical expressions for selectivities. In order to examine the base case and reversible transesterification, two calculation schemes (Case 1 and Case 2) were established. An enhanced selectivity was found in the base case of transesterification reaction. The selectivity was greatly improved at optimum reaction temperature (60 C), molar ratio (9 : 1), catalyst concentration (1.5 wt.%), and low free fatty acid feedstock. Further research might explore the application of selectivity for specifying reactor configurations

Methyl esters selectivity of transesterification reaction with homogenous alkaline catalyst to produce biodiesel in batch, plug flow, and continuous stirred tank reactors

Selectivity concept is essential in establishing the best operating conditions for attaining maximum production of the desired product. For complex reaction such as biodiesel fuel synthesis, kinetic studies of transesterification reaction have revealed the mechanism of the reaction and rate constants. The objectives of this research are to develop the kinetic parameters for determination of methyl esters and glycerol selectivity, evaluate the significance of the reverse reaction in transesterification reaction, and examine the influence of reaction characteristics (reaction temperature, methanol to oil molar ratio, and the amount of catalyst) on selectivity. For this study, published reaction rate constants of transesterification reaction were used to develop mathematical expressions for selectivities. In order to examine the base case and reversible transesterification, two calculation schemes (Case 1 and Case 2) were established. An enhanced selectivity was found in the base case of transesterification reaction. The selectivity was greatly improved at optimum reaction temperature (60 C), molar ratio (9 : 1), catalyst concentration (1.5 wt.%), and low free fatty acid feedstock. Further research might explore the application of selectivity for specifying reactor configurations

Incorporating the Delphi Technique to investigate renewable energy technology transfer in Saudi Arabia

Saudi Arabia is a major oil-producing nation facing a rapidly-growing population, high unemployment, climate change, and the depletion of its natural resources, potentially including its oil supply. Technology transfer is regarded as a means to diversify countries\u27 economies beyond their natural resources. This dissertation examined the opportunities and barriers to utilizing technology transfer successfully to build renewable energy resources in Saudi Arabia to diversify the economy beyond oil production. Examples of other developing countries that have successfully used technology transfer to transform their economies are explored, including Japan, Malayasia, and the United Arab Emirates. Brazil is presented as a detailed case study to illustrate its transition to an economy based to a much greater degree than before on renewable energy. Following a pilot study, the Delphi Method was used in this research to gather the opinions of a panel of technology transfer experts consisting of 10 heterogeneous members of different institutions in the Kingdom of Saudi Arabia, including aviation, telecommunication, oil industry, education, health systems, and military and governmental organizations. In three rounds of questioning, the experts identified Education, Dependence on Oil, and Manpower as the 3 most significant factors influencing the potential for success of renewable energy technology transfer for Saudi Arabia. Political factors were also rated toward the Very Important end of a Likert scale and were discussed as they impact Education, Oil Dependence, and Manpower. The experts\u27 opinions are presented and interpreted. They form the basis for recommended future research and discussion of how in light of its political system and its dependence on oil, Saudi Arabia can realistically move forward on renewable energy technology transfer and secure its economic future

Clinical Course of Acute Pancreatitis in Chronic Kidney Disease Patients in a Single Kidney Center (PGTi) in Karachi

Introduction: The aim of this study was to assess the clinical course, etiology and complications of acute pancreatitis among chronic kidney disease (CKD) patients in a tertiary care renal center in Karachi.Methods: We retrospectively evaluated the clinical course of CKD patients who presented to our emergency room with signs and symptoms of acute pancreatitis over a period of two years.Results: During the study period, 247 CKD patients presented to our emergency room with symptoms suggestive of acute pancreatitis. Only 43 patients (17.4%) had more than a threefold increase in serum amylase and/ or lipase levels fulfilling the diagnostic criteria of acute pancreatitis. They included 25 pre-dialysis CKD patients (58.13%) and 18 end stage renal failure patients (41.86%) on regular hemodialysis (HD). Among the 25 pre-dialysis CKD patients, 17 patients developed acute kidney injury(AKI), ten of whom required temporary HD. Twelve of those patients (70%) returned back to their baseline renal functions after 3-4 weeks. Gallstones were the cause of pancreatitis in seven patients (16.3%) while no cause was identified in 29 patients (67.4%). Nine patients (20.9%) developed multi-organ failure and 12 patients (27.9%) required admission to the intensive care unit (ICU). All patients survived except for one patient (2.3%) who died in the ICU. patients with less than threefold increasein serum amylase and lipase levels responded well to conservative management and had a favorable clinical course.Conclusion: In severe acute pancreatitis the mortality rate can be as high as 40-58% especially in association with comorbid conditions. In this series of CKD patients however, the overall mortality rate was 2.3%, probablydue to the predominance of milder forms of pancreatitis