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Search Results: 1 - 10 of 578971 matches for " Rubel M. H. K. "
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New Superconductor (Na0.25K0.45) Ba3Bi4O12: A First-principles Study
Ali M. S.,Aftabuzzaman M.,Roknuzzaman M.,Rayhan M. A.,Parvin F.,Ali M. M.,Rubel M. H. K.,Islam A. K. M. A
Physics , 2014,
Abstract: A new superconductor (Na0.25K0.45)Ba3Bi4O12, having an A-site-ordered double perovskite structure, with a maximum Tc ~ 27 K has very recently been discovered through hydrothermal synthesis at 593 K. The structural, elastic, electronic, and thermal properties of the new synthesized compound have been investigated theoretically. Here we have employed the pseudo-potential plane-wave (PP-PW) approach based on the density functional (DFT) theory, within the generalized gradient approximation (GGA). The elastic constants (Cij), Pugh`s ratio, Cauchy`s pressure and other elastic parameters are derived and analyzed using energy strain method for the first time. We have discussed the bonding nature in the light of the electronic valence charge density. Both electron and hole-like Fermi surfaces are present in the compound under study which indicate the multiple-band nature of (Na0.25K0.45)Ba3Bi4O12. The compound is indicated to be a strongly coupled superconductor which is based on the estimated e-ph coupling constant. The thermodynamic properties such as bulk modulus, Debye temperature, heat capacities and volume thermal expansion coefficient at elevated temperature and pressure are calculated and analyzed for the first time by using quasi-harmonic model. Key words: double perovskite, superconductor, elastic properties, electronic properties, thermal properties
Influence of Porosity on Performance of Freeze-granulated Fe2O3/Al2O3 Oxygen Carriers Used for Chemical Looping Combustion
Yi Zhang,Aurora M. Rubel,Sameh Mehrez,James K. Neathery
Energy and Environment Research , 2012, DOI: 10.5539/eer.v2n1p217
Abstract: Chemical looping combustion (CLC) is a promising solution for the next coal-fired power generation technology with inherent CO2 separation capability. One of the critical aspects for the development of the CLC process is to develop suitable oxygen carrier (OC) particles to transfer oxygen to the fuel in the absence of air. Relevant studies have focused on active material screening, thermodynamic analysis and operational tests. This investigation was conducted on the microstructural property of OCs, to be specific, the particle porosity effect on the performance of iron-based OCs. Fe2O3, supported on Al2O3 was used as the oxygen carrier. The effect of water content of the spray slurry used to produce the OC was varied to determine the influence of OC porosity on reactivity, oxygen transfer capacity and mechanical durability. A preliminary test was done to establish the minimum and maximum water percentage needed to make slurry. A process that included freeze granulation (FG), freeze drying, and calcination was used to prepare four samples of iron oxide/alumina with various water-to-solid phase ratios. A scanning electron microscope (SEM) was used to characterize the porosity of FG Fe2O3/Al2O3 particles. A direct relationship was observed. A Shimpo FGE-10X force gauge was used to measure the crushing strength of selected samples. A thermogravimetric analyzer (TGA) coupled with a mass spectrometer (MS) was used to study the change in reaction rates through multiple reduction-oxidation cycles of the samples. Crystallinity of the OCs in reduced and oxidized forms were confirmed by XRD analysis.
Frictional Drag Between Coupled 2D Hole Gases in GaAs/AlGaAs Heterostructures
C. Joerger,S. J. Cheng,H. Rubel,W. Dietsche,R. Gerhardts,P. Specht,K. Eberl,K. von Klitzing
Physics , 1999, DOI: 10.1016/S1386-9477(99)00125-3
Abstract: We report on the first measurements of the drag effect between coupled 2D-hole gases. We investigate the coupling by changing the carrier densities in the quantum wells, the widths of the barriers between the gases and the perpendicular magnetic field. From the data we are able to attribute the frictional drag to phonon coupling, because the non-parabolicity allows to tune the Fermi wavevector and the Fermi velocity separately and, thereby, to distinguish between phonon- and plasmon-dominated coupling.
Growth Parameters of Agaricus brasiliensis Mycelium on Wheat Grains in Solid-state Fermentation
H.S. Dalla-Santa,R. Rubel,F.M.D. Vitola,J.A. Rodriguez-Leon
Biotechnology , 2012,
Abstract: Agaricus brasiliensis mycelium is rich in antitumoral molecules such proteoglycans and ergosterol and this is the first study to report production of mycelium and ergosterol by A. brasiliensis in solid-state fermentation. The aim of this research was to study the biomass content and several growth parameters of A. brasiliensis mycelium on grounded wheat grain as the substrate in solid-state fermentation with ergosterol as the main growth indicator. The growth parameters were determined by the respirometric activity in the columns of a bioreactor with forced aeration and the outlet air composition was determined by gas chromatography. Ergosterol was extracted, measured by liquid chromatography and used for calculating biomass production. Then, the respirometric activity and ergosterol production data were used to estimate biomass production with the program Fersol (F). The growth parameters resulted in an achieved specific growth velocity of 0.016 h-1 at 18 h and biomass yield (YX/O) = 0.160 g of biomass g-1 of consumed O2 at 302 h of fermentation. The analysis resulted in ergosterol values of 6.71 mg g-1 of fungi biomass (Dry Weight: DW) from submerged fermentation and 1.95 mg g-1 of solid-state-fermented wheat grains. The correlation with biomass production allowed us to estimate a value of 0.29 g g-1 of fungi biomass per gram of the solid-state-fermented wheat grains. The importance of this study is allow calculation of the fungi biomass percentage in solid-state-fermented wheat grains and determination of the growth parameters of the main mycelium A. brasiliensis in this substrate, which can be milled to obtain a bio-flour to produce nutraceutical foods with beneficial effects due the presence of ergosterol which has recognized antitumor activity.
Study on Periodic MHD Flow with Temperature Dependent Viscosity and Thermal Conductivity past an Isothermal Oscillating Cylinder  [PDF]
Rubel Ahmed, Reaz Uddin, B. M. Jewel Rana, Rafrafin Selim, Sarder Firoz Ahmmed
World Journal of Mechanics (WJM) , 2016, DOI: 10.4236/wjm.2016.611030
Abstract: Temperature dependent viscosity and thermal conducting heat and mass transfer flow with chemical reaction and periodic magnetic field past an isothermal oscillating cylinder have been considered. The partial dimensionless equations governing the flow have been solved numerically by applying explicit finite difference method with the help Compaq visual 6.6a. The obtained outcome of this inquisition has been discussed for different values of well-known flow parameters with different time steps and oscillation angle. The effect of chemical reaction and periodic MHD parameters on the velocity field, temperature field and concentration field, skin-friction, Nusselt number and Sherwood number have been studied and results are presented by graphically. The novelty of the present problem is to study the streamlines by taking into account periodic magnetic field.
The environment effect on operation of in-vessel mirrors for plasma diagnostics in fusion devices
V. S. Voitsenya,Ch. Gil,V. G. Konovalov,A. Litnovsky,M. Lipa,M. Rubel,A. Sagara,A. Sakasai,B. Schunke,T. Sugie,G. De Temmerman,K. Yu Vukolov,S. N. Zvonkov,P. Wienhold
Physics , 2004,
Abstract: First mirrors will be the plasma facing components of optical diagnostic systems in ITER. Mirror surfaces will undergo modification caused by erosion and re-deposition processes [1,2]. As a consequence, the mirror performance may be changed and may deteriorate [3,4]. In the divertor region it may also be obscured by deposition [5-7]. The limited access to in-vessel components of ITER calls for testing the mirror materials in present day devices in order to gather information on the material damage and degradation of the mirror performance, i.e. reflectivity. A dedicated experimental programme, First Mirror Test (FMT), has been initiated at the JET tokamak within the framework Tritium Retention Studies (TRS).
Co-movements of Oil, Gold, the U.S. Dollar, and Stocks  [PDF]
Subarna K. Samanta, Ali H. M. Zadeh
Modern Economy (ME) , 2012, DOI: 10.4236/me.2012.31015
Abstract: This paper examines the comovements of several macro-variables in the world economy over a period of more than twenty years. Long-term co movements are examined by tracking the cointegration, common trend factor and the spiller index over these variables (gold price, stock price, real exchange rate for dollar and the oil price of crude oil). Preminary examination suggests the possibility of cointegration among these variables indicating comovements, although the spillover indices are found to be very small.
Asymptotic Boundary Forms for Tight Gabor Frames and Lattice Localization Domains  [PDF]
H. G. Feichtinger, K. Nowak, M. Pap
Journal of Applied Mathematics and Physics (JAMP) , 2015, DOI: 10.4236/jamp.2015.310160
Abstract: We consider Gabor localization operators \"\"?defined by two parameters, the generating function \"\"?of a tight Gabor frame \"\", indexed by a lattice \"\", and a domain \"\"?whose boundary consists of line segments connecting certain points of . We provide an explicit formula for the boundary form \"\", the normalized limit of the projection functional \"\", where \"\"?are the eigenvalues of the localization operators \"\"?applied to dilated domains \"\", R is an integer and is\"\" the area of the fundamental domain. The boundary form expresses quantitatively the asymptotic interactions between the generating function \"\"?and the oriented boundary \"\"?from the point of view of the projection functional, which measures to what degree a given trace class operator fails to be an orthogonal projection. Keeping the area of the localization domain \"\"?bounded above corresponds to controlling the relative dimensionality of the localization problem.
Estimation and Forecasting Survival of Diabetic CABG Patients (Kalman Filter Smoothing Approach)  [PDF]
M. Saleem, K. H. Khan, Nusrat Yasmin
American Journal of Computational Mathematics (AJCM) , 2015, DOI: 10.4236/ajcm.2015.54035

In this paper, we present a new approach (Kalman Filter Smoothing) to estimate and forecast survival of Diabetic and Non Diabetic Coronary Artery Bypass Graft Surgery (CABG) patients. Survival proportions of the patients are obtained from a lifetime representing parametric model (Weibull distribution with Kalman Filter approach). Moreover, an approach of complete population (CP) from its incomplete population (IP) of the patients with 12 years observations/follow-up is used for their survival analysis [1]. The survival proportions of the CP obtained from Kaplan Meier method are used as observed values yt?at time t (input) for Kalman Filter Smoothing process to update time varying parameters. In case of CP, the term representing censored observations may be dropped from likelihood function of the distribution. Maximum likelihood method, in-conjunction with Davidon-Fletcher-Powell (DFP) optimization method [2] and Cubic Interpolation method is used in estimation of the survivor’s proportions. The estimated and forecasted survival proportions of CP of the Diabetic and Non Diabetic CABG patients from the Kalman Filter Smoothing approach are presented in terms of statistics, survival curves, discussion and conclusion.

Analytical Study of Mechanism of Concrete Cracking and Its Propagation Due to Corrosion of Reinforcement in RCC  [PDF]
A. M. Jadhav, H. K. Munot
Open Journal of Civil Engineering (OJCE) , 2016, DOI: 10.4236/ojce.2016.62024
Abstract: The experimental results which were carried out by different researchers on corrosion of RCC beam were validated in ABAQUS. A finite element (FE) model similar to experimental condition was generated in ABAQUS. The model with different percentages of corrosion and with varying load conditions was also generated. The deflections of RCC beam for different corrosion percentages and for varying load conditions were then validated. The model is then used to explore the effects of bar radial expansion, due to formation of corrosion products, on the cracking of cover concrete. The predictions are compared with tests results from reinforced concrete accelerated corrosion specimens. The aim of the analytical investigation was to reveal the mechanism for the development of concrete cracking due to corrosion of reinforcement. Further the finite element model will be used to explain qualitatively the experimentally determined relationship between amount of corrosion for concrete cracking and ratio of concrete cover to bar diameter, as well as that between reinforcement bond strength and amount of corrosion.
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