88,059 research outputs found
Bose-Einstein Condensation of Helium and Hydrogen inside Bundles of Carbon Nanotubes
No full textHelium atoms or hydrogen molecules are believed to be strongly bound within the interstitial channels (between three carbon nanotubes) within a bundle of many nanotubes. The effects on adsorption of a nonuniform distribution of tubes are evaluated. The energy of a single-particle state is the sum of a discrete transverse energy E-t (that depends on the radii of neighboring tubes) and a quasicontinuous energy E-z of relatively free motion parallel to the axis of the tubes. At low temperature, the particles occupy the lowest-energy states, the focus of this study. The transverse energy attains a global minimum value (E-t=E-min) for radii near R-min=9.95 Angstrom for H-2 and 8.48 Angstrom for He-4. The density of states N(E) near the lowest energy is found to vary linearly above this threshold value, i.e., N(E) is proportional to (E-E-min). As a result, there occurs a Bose-Einstein condensation of the molecules into the channel with the lowest transverse energy. The transition is characterized approximately as that of a four-dimensional gas, neglecting the interactions between the adsorbed particles. The phenomenon is observable, in principle, from a singular heat capacity. The existence of this transition depends on the sample having a relatively broad distribution of radii values that include some near R-min
Capillary condensation for quantum fluids
No full textA simple model has been proposed and evaluated to predict the nature of capillary condensation in a slab geometry. We present a study of adsorption of fluids He-3 and He-4 that test this model. These calculations employ the density-functional method applicable at zero temperature. Overall, the simple model works well in comparison with microscopic calculations. [S0163-1829(99)01945-1]
Anomalous specific heat of He-3 in He-4-coated FSM-16 mesopores
No full textRecent experiments have found unusual behavior of the specific heat of He-3-He-4 mixtures within the regular porous material FSM-16. We analyze this problem with quantum. density functional calculations of He-4, followed by ideal gas calculations of He-3 in the resulting potential. The results are in semiquantitative agreement with the experimental data
From one to infinity: effective dimensionalities of fluids in nanoporous materials
No full textTheoretical arguments are presented concerning the low temperature (T) behavior of quantum gases inside or near nanoporous media. The density of states at low energy can be interpreted in terms of an effective dimensionality D, as can the low T heat capacity C(T). Depending on the circumstances, D is shown here to assume one of the values D=1,2,4,5 or infinity. Intriguing questions concerning this range of behavior are addressed
Intriguing examples of inhomogeneous broadening
No full textThree problems are considered in which inhomogeneous broadening can yield unusual consequences. One problem involves the energy levels of atoms moving within nanopores of nearly cylindrical cross section. A second involves atomic or molecular motion in a quasi-one-dimensional interstitial channel within a bundle of carbon nanotubes. The third problem involves motion within a groove between two nanotubes at the surface of such a bundle. In each case, the density of states at low energy is qualitatively different from that occurring in the perfectly homogeneous case
Dr. Glendon Swarthout
No full textHosted by Roger M. Busfield, MSU Assistant Professor of Speech and Theater, Meet the Author is designed to introduce a general audience to a contemporary author and their work through in-depth interviews. This episode features a conversation between Dr. Glendon Swarthout, prolific author and English professor at MSU, and assistant professors Sam S. Baskett and Theodore B. Strandness
Numerical analysis of a transmission problem with Signorini contact using mixed-FEM and BEM
No full text© EDP Sciences, SMAI 2011This paper is concerned with the dual formulation of the interface problem consisting of a linear partial differential equation with variable coefficients in some bounded Lipschitz domain Ω in
Rn (n ≥ 2) and the Laplace equation with some radiation condition in the unbounded exterior domain Ωc := Rn\￣Ω. The two problems are coupled by transmission and Signorini contact conditions on the interface Γ = ∂Ω. The exterior part of the interface problem is rewritten using a Neumann to Dirichlet mapping (NtD) given in terms of boundary integral operators. The resulting variational formulation becomes a variational inequality with a linear operator. Then we treat the corresponding numerical scheme and discuss an approximation of the NtD mapping with an appropriate discretization of the inverse Poincar´e-Steklov operator. In particular, assuming some abstract approximation properties and a discrete inf-sup condition, we show unique solvability of the discrete scheme and obtain the corresponding a-priori error estimate. Next, we prove that these assumptions are satisfied with Raviart- Thomas elements and piecewise constants in Ω, and continuous piecewise linear functions on Γ. We suggest a solver based on a modified Uzawa algorithm and show convergence. Finally we present some numerical results illustrating our theory
Simulation of thermal plant optimization and hydraulic aspects of thermal distribution loops for large campuses
No full textFollowing an introduction, the author describes Texas A&M University and its utilities system. After that, the author presents how to construct simulation models for chilled water and heating hot water distribution systems. The simulation model was used in a $2.3 million Ross Street chilled water pipe replacement project at Texas A&M University. A second project conducted at the University of Texas at San Antonio was used as an example to demonstrate how to identify and design an optimal distribution system by using a simulation model. The author found that the minor losses of these closed loop thermal distribution systems are significantly higher than potable water distribution systems. In the second part of the report, the author presents the latest development of software called the Plant Optimization Program, which can simulate cogeneration plant operation, estimate its operation cost and provide optimized operation suggestions. The author also developed detailed simulation models for a gas turbine and heat recovery steam generator and identified significant potential savings. Finally, the author also used a steam turbine as an example to present a multi-regression method on constructing simulation models by using basic statistics and optimization algorithms. This report presents a survey of the author??s working experience at the Energy Systems Laboratory (ESL) at Texas A&M University during the period of January 2002 through March 2004. The purpose of the above work was to allow the author to become familiar with the practice of engineering. The result is that the author knows how to complete a project from start to finish and understands how both technical and nontechnical aspects of a project need to be considered in order to ensure a quality deliverable and bring a project to successful completion. This report concludes that the objectives of the internship were successfully accomplished and that the requirements for the degree of Degree of Engineering have been satisfied
Hydrogen scrambling over Rh/Ce0.68Zr0.32O2 and Rh/Al2O3 catalysts: Effects of support, metal precursor and redox aging
No full textThe effects of noble metal precursor, nature of the support and pre-treatment on hydrogen isotopic exchange were investigated over Rh/Al2O3 and Rh/Ce0.68Zr0.32O2 catalysts. It is observed that deuterium exchange occurs rather efficiently over both Rh-loaded Al2O3 and Ce0.68Zr0.32O2, mainly at sub-ambient temperatures in the case of Rh/Ce0.68Zr0.32O2, provided that no high temperature oxidation is employed as a pre-treatment. In fact, after this pre-treatment, H-2/D-2 scrambling is strongly hindered, the exchange being completed at temperatures which are higher by about 140-200degreesC. Interestingly, the unfavorable effect of high temperature oxidation appears related to kinetic aspects of the H-2/D-2 reaction since, irrespective of the pre-treatment, comparable amounts of H-2 spilt over the support were detected by static H-2 chemisorption. Using a chloride-containing Rh precursor, H-2/D-2 is partially blocked compared to using a nitrate-containing Rh precursor, suggesting effective blockage of hydrogen migration over the support by some retained Cl-species
C3H7NO2S effect on concrete steel-rebar corrosion in 0.5 M H2SO4 simulating industrial/microbial environment
No full textThis paper investigates C3H7NO2S (Cysteine) effect on the inhibition of reinforcing steel corrosion in concrete immersed in 0.5 M H2SO4, for simulating industrial/microbial environment. Different C3H7NO2S concentrations were admixed, in duplicates, in steel-reinforced concrete samples that were partially immersed in the acidic sulphate environment. Electrochemical monitoring techniques of open circuit potential, as per ASTM C876-91 R99, and corrosion rate, by linear polarization resistance, were then employed for studying anticorrosion effect in steel-reinforced concrete samples by the organic hydrocarbon admixture. Analyses of electrochemical test-data followed ASTM G16-95 R04 prescriptions including probability distribution modeling with significant testing by Kolmogorov-Smirnov and student's t-tests statistics. Results established that all datasets of corrosion potential distributed like the Normal, the Gumbel and the Weibull distributions but that only the Weibull model described all the corrosion rate datasets in the study, as per the Kolmogorov-Smirnov test-statistics. Results of the student's t-test showed that differences of corrosion test-data between duplicated samples with the same C3H7NO2S concentrations were not statistically significant. These results indicated that 0.06878 M C3H7NO2S exhibited optimal inhibition efficiency η = 90.52±1.29% on reinforcing steel corrosion in the concrete samples immersed in 0.5 M H2SO4, simulating industrial/microbial service-environment
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