High performance carbon-supported catalysts for fuel cells via phosphonation

Carbon-supported catalysts were phosphonated using 2-aminoethylphosphonic acid, and the resulting catalysts with largely enhanced proton conductivity performed substantially better than the untreated counterparts in proton-exchange membrane fuel cells.     

Analysis of Nonionic Surfactants by High Performance Liquid Chromatography

Abstract

This review discusses the principles of immobilized metal ion affinity chromatography (IMAC) and its applications to protein separations. IMAC functions by binding the accessible electron-donating pendant groups of a protein - such as histidine, cysteine, and tryptophan - to a metal ion which is held by a chelating group covalently attached on a stationary support. A common chelating group is iminodiacetate. The ions commonly used are of borderline or soft metals, such as Cu²⁺, Ni²⁺, Co²⁺, and Zn²⁺. Protein retention in IMAC depends on the number and type of pendant groups which can interact with the metal. The interaction is affected by a variety of independent variables such as pH, temperature, solvent type, salt type, salt concentration, nature of immobilized metal and chelate, ligand density, and protein size. Proteins are usually eluted by a decreasing pH gradient or by an increasing gradient of a competitive agent, such as imidazole, in a buffer. There are still several unresolved issues in IMAC. The exact structures of protein-immobilized metal complexes need to be known so that retention behavior of proteins can be fully understood and sorbent structures can be optimized. Engineering parameters, such as adsorption/desorption rate constants, sorbent capacities, and intraparticle diffusivities, need to be developed for most protein systems. Engineering analysis and quantitative understanding are also needed so that IMAC can be used efficiently for large scale protein separations.     

An ab initio method for approximation of the frozen molecular fragment

An ab initio method for calculation on many-electron molecular systems with the approximation of the inactive part of a molecule by frozen molecular fragment is presented. In the following method the SCF calculations are performed in two series. First the molecular orbitals resulting from the first SCF calculation (modest basis set) are localized. In the second SCF run, the basis set is extended for the active part of the molecule, while molecular orbitals of the inactive part, selected from the localized set, are kept frozen. The results are in good agreement with the extended basis set calculation.     

Ab initio MRD-CI calculations for breaking a chemical bond in a molecule in a crystal or other solid environment. III. Me2N?NO2 decomposition of dimethylnitramine in a large crystalline environment

Recently we extended our strategy for MRD-CI (multireference double excitation-configuration interaction) calculations, based on localized/local orbitals and an “effective” CI Hamiltonian, for molecular decompositions of large molecules to breaking a chemical bond in a molecule in a crystalline or other solid environment. Our technique begins with an explicit quantum chemical SCF calculation for a reference molecule surrounded by a number of other molecules in the multipole environment of more distant neighbors. The resulting canonical molecular orbitals are then localized, and the localized occupied and virtual orbitals in the region of interest are included explicitly in the MRD-CI with the remainder of the occupied localized orbitals being folded into an “effective” CI Hamiltonian. The MRD-CI calculations are then carried out for breaking a bond in the reference molecule. This method is completely general in that the space treated explicitly, as well as the surrounding space, may contain voids, defects, deformations, dislocations, impurities, dopants, edges and surfaces, boundaries, etc. Dimethylnitramine is the smallest prototype of the energetic R₂N—NO₂ nitramines, such as the 6-member ring RDX or the 8-member ring HMX. Decomposition of energetic compounds is initiated in the solid by a breaking of the target bond. Thus, it is crucial to know the difference in energy between breaking a bond in an isolated energetic molecule versus in the molecule in a solid. In the present study, we have carried out MRD-CI calculations for the Me₂N—NO₂ dissociation of dimethylnitramine in a dimethylnitramine crystal. The cases we investigated were one dimethylnitramine molecule (surrounded by 53 and 685 neighboring dimethylnitramine molecules represented by multipoles), three dimethylnitramine molecules, and three dimethylnitramine molecules (surrounded by 683 neighbors). All multipoles were cumulative atomic multipoles up through quadrupoles. The MRD-CI calculations on dimethylnitramine required large numbers of reference configurations from which were allowed all single and double excitations.     

A biological process for the reclamation of flue gas desulfurization gypsum using mixed sulfate-reducing bacteria with inexpensive carbon sources

A combined chemical and biological process for the recycling of flue gas desulfurization (FGD) gypsum into calcium carbonate and elemental sulfur is demonstrated. In this process, a mixed culture of sulfate-reducing bacteria (SRB) utilizes inexpensive carbon sources, such as sewage digest or synthesis gas, to reduce FGD gypsum to hydrogen sulfide. The sulfide is then oxidized to elemental sulfur via reaction with ferric sulfate, and accumulating calcium ions are precipitated as calcium carbonate using carbon dioxide. Employing anaerobically digested municipal sewage sludge (AD-MSS) medium as a carbon source, SRBs in serum bottles demonstrated an FGD gypsum reduction rate of 8 mg/L/h (10⁹ cells)^-1. A chemostat with continuous addition of both AD-MSS media and gypsum exhibited sulfate reduction rates as high as 1.3 kg FGD gypsum/m³d. The increased biocatalyst density afforded by cell immobilization in a columnar reactor allowed a productivity of 152 mg SO₄ ^-2/Lh or 6.6 kg FGD gypsum/m³d. Both reactors demonstrated 100% conversion of sulfate, with 75–100% recovery of elemental sulfur and chemical oxygen demand utilization as high as 70%. Calcium carbonate was recovered from the reactor effluent on precipitation using carbon dioxide. It was demonstrated that SRBs may also use synthesis gas (CO, H₂, and CO₂ in the reduction of gypsum, further decreasing process costs. The formation of two marketable products—elemental sulfur and calcium carbonate—from FGD gypsum sludge, combined with the use of a low-cost carbon source and further improvements in reactor design, promises to offer an attractive alternative to the landfilling of FGD gypsum.

     

A note on tilde algebras

A closed setE is constructed so thatA∼(E) is an inseparable Banach space but its maximal ideal space isE. Supported in part by the National Science Foundation.     

Multimaterial preform coextrusion for robust chalcogenide optical fibers and tapers

The development of robust infrared fibers is crucial for harnessing the capabilities of new mid-infrared lasers. We present a novel approach to the fabrication of chalcogenide glass fiber preforms: one-step multimaterial extrusion. The preform consists of a glass core and cladding surrounded by a built-in, thermally compatible, polymer jacket for mechanical support. Using this approach we extrude several preform structures and draw them into robust composite fibers. Furthermore, the polymer cladding allows us to produce robust tapers with submicrometer core diameter.     

An ODE-based approach to nonlinearly constrained minimax problems

We consider the following problem: Choosex ₁, ...,x _n to wherem ₁,m ₂,m ₃ are integers with 0m ₁m ₂m ₃, thef _i are given real numbers, and theg _i are given smooth functions. Constraints of the formg _i (x ₁, ...,x _n )=0 can also be handled without problem. Each iteration of our algorithm involves approximately solving a certain non-linear system of first-order ordinary differential equations to get a search direction for a line search and using a Newton-like approach to correct back into the feasible region when necessary. The algorithm and our Fortran implementation of it will be discussed along with some examples. Our experience to date has been that the program is more robust than any of the library routines we have tried, although it generally requires more computer time. We have found this program to be an extremely useful tool in diverse areas, including polymer rheology, computer vision, and computation of convexity-preserving rational splines.