Thermophysical and transport properties of high temperature energy storage materials

Thermophysical and transport properties of high temperature energy storage material

Durability testing at one atmosphere of advanced catalysts and catalyst supports for automotive gas turbine engine combustors, part 1

The durability of catalysts and catalyst supports in a combustion environment was experimentally demonstrated. A test of 1000 hours duration was completed with two catalysts, using diesel fuel and operating at catalytically supported thermal combustion conditions. The performance of the catalysts was determined by monitoring emissions throughout the test, and by examining the physical condition of the catalyst core at the conclusion of the test. The test catalysts proved to be capable of low emissions operation after 1000 hours diesel aging, with no apparent physical degradation of the catalyst support

Computer aided design and analysis of gear tooth geometry

A simulation method for gear hobbing and shaping of straight and spiral bevel gears is presented. The method is based upon an enveloping theory for gear tooth profile generation. The procedure is applicable in the computer aided design of standard and nonstandard tooth forms. An inverse procedure for finding a conjugate gear tooth profile is presented for arbitrary cutter geometry. The kinematic relations for the tooth surfaces of straight and spiral bevel gears are proposed. The tooth surface equations for these gears are formulated in a manner suitable for their automated numerical development and solution

QCD Radiative Corrections to the Leptonic Decay Rate of the B_c Meson

The QCD radiative corrections to the leptonic decay rate of the $B_c$ meson are calculated using the formalism of nonrelativistic QCD (NRQCD) to separate short-distance and long-distance effects. The $B_c$ decay constant is factored into a sum of NRQCD matrix elements each multiplied by a short-distance coefficient. The short-distance coefficient for the leading matrix element is calculated to order $\alpha_s$ by matching a perturbative calculation in full QCD with the corresponding perturbative calculation in NRQCD. This short-distance correction decreases the leptonic decay rate by approximately $15\%$.Comment: Changed Eq. 2 to read 1/(8 \pi), put in a missing i M_{B_c} in Eq. 18, and put in a normalisation factor of 2 M_{B_c} in Eq. 19

Altering Enzymatic Activity: Recruitment of Carboxypeptidase Activity into an RTEM β-Lactamase/Penicillin-Binding Protein 5 Chimera

The D-Ala-D-Ala carboxypeptidases/transpeptidases (penicillin-binding proteins, PBPs) share considerable structural homology with class A β-lactamases (EC 3.5.2.6), although these β-lactamases have no observable D-Ala-D-Ala carboxypeptidase activity. With the objective of recruiting such activity into a β-lactamase background, we have prepared a chimeric protein by inserting a 28-amino acid segment of PBP-5 of Escherichia coli in place of the corresponding region of the RTEM-1 β-lactamase. The segment thus inserted encompasses two residues conserved in both families: Ser-70, which forms the acyl-enzyme intermediate during β-lactam hydrolysis, and Lys-73, whose presence has been shown to be necessary for catalysis. This chimera involves changes of 18 residues and gives a protein that differs at 7% of the residues from the parent. Whereas RTEM β-lactamase has no D-Ala-D-Ala carboxypeptidase activity, that of the chimera is significant and is, in fact, about 1% the activity of PBP-5 on diacetyl-L-Lys-D-Ala-D-Ala; in terms of free energy of activation, the chimera stabilizes the transition state for the reaction to within about 2.7 kcal/mol of the stabilization achieved by PBP-5. Furthermore, the chimera catalyzes hydrolysis exclusively at the carboxyl-terminal amide bond which is the site of cleavage by D-Ala-D-Ala carboxypeptidase. Though containing all those residues that are conserved throughout class A β-Lactamases and are thought to be essential for β-lactamase activity, the chimera has considerably reduced activity ({approx} 10^-5) on penams such as penicillins and ampicillins as substrates. As a catalyst, the chimera shows an induction period of {approx} 30 min, reflecting a slow conformational rearrangement from an inactive precursor to the active enzyme

Non-linear excitations in 1D correlated insulators

In this work we investigate charge transport in one-dimensional (1D) insulators via semi-classical and perturbative renormalization group (RG) methods. We consider the problem of electron-electron, electron-phonon and electron-two-level system interactions. We show that non-linear collective modes such as polarons and solitons are reponsible for transport. We find a new excitation in the Mott insulator: the polaronic soliton. We discuss the differences between band and Mott insulators in terms of their spin spectrum and obtain the charge and spin gaps in each one of these systems. We show that electron-electron interactions provide strong renormalizations of the energy scales in the problem.Comment: 29 page

Computer model of catalytic combustion/Stirling engine heater head

The basic Acurex HET code was modified to analyze specific problems for Stirling engine heater head applications. Specifically, the code can model: an adiabatic catalytic monolith reactor, an externally cooled catalytic cylindrical reactor/flat plate reactor, a coannular tube radiatively cooled reactor, and a monolithic reactor radiating to upstream and downstream heat exchangers

Estimating Form Factors of Bs→Ds(∗)B_s\rightarrow D_s^{(*)} and their Applications to Semi-leptonic and Non-leptonic Decays

$B_s^0\rightarrow D_s^{-}$ and $B_s^0\rightarrow D_s^{*-}$ weak transition form factors are estimated for the whole physical region with a method based on an instantaneous approximated Mandelstam formulation of transition matrix elements and the instantaneous Bethe-Salpeter equation. We apply the estimated form factors to branching ratios, CP asymmetries and polarization fractions of non-leptonic decays within the factorization approximation. And we study the non-factorizable effects and annihilation contributions with the perturbative QCD approach. The branching ratios of semi-leptonic $B_s^0\rightarrow D_s^{(*)-}l^+\nu_l$ decays are also evaluated. We show that the calculated decay rates agree well with the available experimental data. The longitudinal polarization fraction of $B_s\rightarrow D_s^*V(A)$ decays are $\sim0.8$ when $V(A)$ denotes a light meson, and are $\sim0.5$ when $V(A)$ denotes a $D_q$ ($q=d,s$) meson.Comment: Final version published in J Phys. G 39 (2012) 045002 (Title also changed