Tailoring of nanoscale porosity in carbide-derived carbons for hydrogen storage

The poor performance of hydrogen storage materials continues to hinder development of fuel cell-powered automobiles. Nanoscale carbons, in particular (activated carbon, exfoliated graphite, fullerenes, nanotubes, nanofibers, and nanohorns), have not fulfilled their initial promise. Here we show that carbon materials can be rationally designed for H2 storage. Carbide-derived carbons (CDC), a largely unknown class of porous carbons, are produced by high-temperature chlorination of carbides. Metals and metalloids are removed as chlorides, leaving behind a collapsed noncrystalline carbon with up to 80% open pore volume. The detailed nature of the porosity-average size and size distribution, shape, and total specific surface area (SSA)-can be tuned with high sensitivity by selection of precursor carbide (composition, lattice type) and chlorination temperature. The optimum temperature is bounded from below by thermodynamics and kinetics of chlorination reactions and from above by graphitization, which decreases SSA and introduces H2-sorbing surfaces with binding energies too low to be useful. Intuitively, pores of different size and shape should not contribute equally to hydrogen storage. By correlating pore properties with 77 K H2 isotherms from a wide variety of CDCs, we experimentally confirm that gravimetric hydrogen storage capacity normalized to total pore volume is optimized in materials with primarily micropores ( approximately 1 nm) rather than mesopores. Thus, in agreement with theoretical predictions, a narrow size distribution of small pores is desirable for storing hydrogen, while large pores merely degrade the volumetric storage capacity.     

p-Hertz excitation spectroscopy of an optical antenna, optical transmitter-receiver mechanism

o-Xylene sensitized biacetyl fluorescence and phosphorescence have been investigated and photosensitized fluorescence and phosphorescence lifetimes of biacetyl in the vapor phase have been determined. Attempts to detect the triplet of biacetyl by its absorption spectrum were unsuccessful, primarily due to, it is believed, the low extinction coefficients of the triplet, and the low triplet concentrations produced by the optical pumping device at room temperature.     

Comparison of the radiopharmaceutical potentials of dithizone radiolabeled with 131I and with 99mTc

In this study, dithizone (diphenylthiocarbazone) has been separately radiolabeled with ¹³¹I and with ^99mTc for preliminarily testing their radiopharmaceutical potentials on male albino rabbits. ¹³¹I-dithizone and ^99mTc-dithizone were intravenously injected to rabbits via their ear veins after anesthetizing with a mixture of Alfazyne and Alfamine (Serva) to determine their dynamic and static statuses in the metabolism. Also, ^99mTc as pertechnetate and ¹³¹I as iodate were administered to rabbits as controls. Dynamic and static scintigrams were obtained using a gamma camera (Diacan Instruments). Dynamic scintigrams were obtained over the first half hour with frames of 1 minute following the administrations of the labeled compounds. Static images were obtained from posterior projection at different time intervals up to about 3 hours following the administration of the radiolabeled compounds. ^99mTc-dithizone was significantly uptaken by the pancreas in contrast to free ^99mTc. In the case of ¹³¹I-dithizone, the distribution of ¹³¹I activity in the metabolism was clearly different than the case of free ¹³¹I and the uptake of ¹³¹I-dithizone at the pancreas zone was also significant. These preliminary tests have clearly indicated that especially ^99mTc-dithizone has a significant potential to be used as a pancreatic radiopharmaceutical.     

Arylthio analogs of 5,8-quinolinedione: Synthesis,characterization, antibacterial,and antifungal evaluations

Abstract

A set of bis(arylthio) substituted 5,8-quinolinedione derivatives were synthesized and investigated for their in vitro antimicrobial effect. The antibacterial and antifungal activities of 6,7-bis(arylthio)-5,8-quinolinedione (4a–f) and 6,7-bis(arylthio)-2-methyl-5,8-quinolinedione (5a–f) were evaluated against four gram-negative bacteria, three gram-positive bacteria, and three fungi strains. The bis(methoxyarylthio) 5,8-quinolinedione analogs presented better activity against especially gram-positive bacteria compared to bis(halogenarylthio) 5,8-quinolinedione analogs. Bis(3-methoxyarylthio) 5,8-quinolinedione (4e) had the same activity of the reference drug against Staphylococcus aureus. Bis(2-methoxyarylthio) 5,8-quinolinedione (4f) showed two-and-a half-fold better activity with 89.69?μM against Enterococcus faecalis, and two-fold better activity with 11.20?μM against Staphylococcus epidermidis. Bis(2-methoxyarylthio)-2-methyl-5,8-quinolinedione 5f exhibited five-fold higher antibacterial activity with 43.44?μM against E. faecalis and also eight-fold activity of the reference drug with 2.71?μM against S. epidermidis.     

Double frictional receding contact problem for an orthotropic layer loaded by normal and tangential forces

With the increasing research in the field of contact mechanics, different types of contact models have been investigated by many researchers by employing various complex material models. To ascertain the orthotropy effect and modeling parameters on a receding contact model, the double frictional receding contact problem for an orthotropic bilayer loaded by a cylindrical punch is taken into account in this study. Assuming plane strain sliding conditions, the governing equations are found analytically using Fourier integral transformation technique. Then, the resulting singular integral equations are solved numerically using an iterative method. The weight function describing the asymptotic behavior of the stresses are investigated in detail and powers of the stress singularities are provided. To control the trustworthiness and correctness of the analytical formulation and to compare the resulting stress distributions and contact boundaries, a numerically efficient finite element method was employed using augmented Lagrange contact algorithm. The aim of this paper is to investigate the orthotropy effect, modeling parameters and coefficients of friction on the surface and interface stresses, surface and interface contact boundaries, powers of stress singularities, weight function and to provide highly parametric benchmark results for tribological community in designing wear resistant systems.

     

Optical absorption of a quantum well with an adjustable asymmetry

The effects of asymmetry and the electric field on the electronic subbands and the nonlinear intersubband optical absorption of GaAs quantum wells represented by a P?schl-Teller confining potential are studied. The potential itself can be made asymmetric through a correct choice of its parameter set and this adjustable asymmetry is important for optimizing the absorption. In that way optimal cases can be created. We calculate the modified wave functions and electronic subbands variationally. The linear and the nonlinear optical intersubband absorption coefficients are calculated. Numerical results for a typical GaAs quantum well are presented. The nonlinear part of the absorption coefficient is strongly modified by the asymmetry parameters while the electric field affects it at smaller values of the parameters. - 78.67.De Quantum wells     

Medialization Laryngoplasty With Gore-Tex: An Animal Study

Vocal cord paralysis is a disease that can cause voice disability and aspiration problems. Expanded polytetrafluoroethylene (ePTFE; Gore-Tex) has been widely used in cardiovascular and plastic surgery; however, its biocompatibility and safety have not been established precisely in the larynx. In this study, the biocompatibility and safety of ePTFE used in vocal cord medialization in the rabbit larynx were assessed. Type 1 thyroplasty with Gore-Tex was performed on one side of the larynx in eight rabbits. A sham procedure was applied on the contralateral side of their larynx. The rabbits were sacrificed after 6 months, and macroscopic and microscopic evaluations and comparisons were performed. No significant inflammatory response to Gore-Tex or displacement of the implant was seen. There was only a tiny fibrotic capsule surrounding the material in each specimen. Intense eosinophilic cell infiltration was seen surrounding one rabbit specimen. Gore-Tex seems to be a biocompatible, stable, and reversible material that can be safely used in laryngeal framework surgery.     

Unifying Optimal Partition Approach to Sensitivity Analysis in Conic Optimization

We study convex conic optimization problems in which the right-hand side and the cost vectors vary linearly as functions of a scalar parameter. We present a unifying geometric framework that subsumes the concept of the optimal partition in linear programming (LP) and semidefinite programming (SDP) and extends it to conic optimization. Similar to the optimal partition approach to sensitivity analysis in LP and SDP, the range of perturbations for which the optimal partition remains constant can be computed by solving two conic optimization problems. Under a weaker notion of nondegeneracy, this range is simply given by a minimum ratio test. We discuss briefly the properties of the optimal value function under such perturbations.     

On some closed sets in ideal minimal spaces

The purpose of this paper is to introduce ideal minimal spaces and to investigate the relationships between minimal spaces and ideal minimal spaces. We define some closed sets in these spaces to establish their relationships. Basic properties and characterizations related to these sets are given.