671 research outputs found
Quantification and Characterization of Aluminum Distributions in Commercial Beta and Mordenite Zeolites by Cobalt Exchange
The aluminum distribution throughout the zeolite framework determines the structural, ion-exchange and catalytic properties of the zeolite. Several methods have been proposed to control the Al distribution, but in order to accurately assess these methods a procedure is needed to quantify Al distribution in various zeolite frameworks. Co2+ ions exchange onto the zeolite framework at Al pairs, and atomic absorbance spectroscopy (AAS) can be used to quantify the number of exchanged Co2+ ions and, in turn, the overall number of Al pairs. Each framework exhibits differences in pore size and channel configuration which affect the equilibrium conditions needed for saturation of all paired Al sites with Co2+ ions. In order to achieve saturation of the Co2+ ions, a reproducible exchange procedure must be developed for each framework of interest. Commercial beta (BEA) and mordenite (MOR) zeolites were subjected to liquid-phase cobalt ion exchange with varying exchange solution molarity, temperature, number of repetitions and time of exchange. The zeolites were then washed and treated in an oxidizing environment at high temperatures before undergoing AAS analysis to determine Co2+ concentration and diffuse reflectance UV-Vis spectroscopy (DRUV-VIS) to ensure only bare Co2+ ions were present. The BEA framework was found to achieve saturation at the following conditions: 0.50 M Co(NO3)2 exchange solution, ambient temperature, 1 repetition and 12 hour exchange time. The exchange procedure for MOR zeolites requires a 0.05 M Co(NO3)2 solution, ambient temperature, 24 hour exchange time and 1 repetition. These procedures will aid in the creation of an accurate catalog of the Al distribution in various commercially available BEA and MOR zeolites, as well as aiding in further synthesis studies to control the Al distribution in BEA and MOR zeolites
Two dimensional lattice Gross--Neveu model with domain-wall fermions
We investigate the two dimensional lattice Gross--Neveu model in large flavor
number limit using the domain-wall fermion formulation, as a toy model of
lattice QCD. We study nonperturbative behaviorn of the restoration of chiral
symmetry of the domain-wall fermions as the extent of the extra dimension
is increased to infinity. We find the the parity broken phase (Aoki
phase) for finite , and study the phase diagram, which is related to the
mechanism of the chiral restoration in limit. The continuum
limit is taken and scaling violation of observables vanishes in
limit. We also examine the systematic dependencies of
observables to the parameters.Comment: 36 pages (26 figures), Latex (epsf style-file needed
Probing the Region of Massless Quarks in Quenched Lattice QCD using Wilson Fermions
We study the spectrum of with being the
Wilson-Dirac operator on the lattice with bare mass equal to . The
background gauge fields are generated using the SU(3) Wilson action at
on an lattice. We find evidence that the spectrum of
is gapless for , implying that the physical quark is
massless in this whole region.Comment: 22 pages, LaTeX file, uses elsart.sty, includes 11 figures A
typographical error in one reference has been fixe
IMECE2002-32157 GPS-BASED REAL-TIME IDENTIFICATION OF TIRE-ROAD FRICTION COEFFICIENT
ABSTRACT Vehicle control systems such as collision avoidance, adaptive cruise control and automated lane-keeping systems as well as ABS and stability control systems can benefit significantly from being made "road-adaptive". The estimation of tire-road friction coefficient at the wheels allows the control algorithm in such systems to adapt to external driving conditions. This paper develops a new tire-road friction coefficient estimation algorithm based on measurements related to the lateral dynamics of the vehicle. A lateral tire force model parameterized as a function of slip angle, friction coefficient, normal force and cornering stiffness is used. A real-time parameter identification algorithm that utilizes measurements from a differential GPS system and a gyroscope is used to identify the tire-road friction coefficient and cornering stiffness parameters of the tire. The advantage of the developed algorithm is that it does not require large longitudinal slip in order to provide reliable friction estimates. Simulation studies indicate that a parameter convergence rate of one second can be obtained. Experiments conducted on both dry and slippery road indicate that the algorithm can work very effectively in identifying a slippery road. Two other new approaches to realtime tire road friction identification system are also discussed in the paper
Chemistry-induced Intrinsic Stress Variations During the Chemical Vapor Deposition of Polycrystalline Diamond
Intrinsic tensile stresses in polycrystalline films are often attributed to the coalescence of neighboring grains during the early stages of film growth, where the energy decrease associated with converting two free surfaces into a grain boundary provides the driving force for creating tensile stress. Several recent models have analyzed this energy trade off to establish relationships between the stress and the surfaceâinterfacial energy driving force, the elastic properties of the film, and the grain size. To investigate these predictions, experiments were conducted with diamond films produced by chemical vapor deposition. A multistep processing procedure was used to produce films with significant variations in the tensile stress, but with essentially identical grain sizes. The experimental results demonstrate that modest changes in the deposition chemistry can lead to significant changes in the resultant tensile stresses. Two general approaches were considered to reconcile this data with existing models of stress evolution. Geometric effects associated with the shape of the growing crystal were evaluated with a finite element model of stress evolution, and variations in the surfaceâinterfacial energy driving force were assessed in terms of both chemical changes in the deposition atmosphere and differences in the crystal growth morphology. These attempts to explain the experimental results were only partially successful, which suggests that other factors probably affect intrinsic tensile stress evolution due to grain boundary formation
Static Safety for an Actor Dedicated Process Calculus by Abstract Interpretation
The actor model eases the definition of concurrent programs with non uniform
behaviors. Static analysis of such a model was previously done in a data-flow
oriented way, with type systems. This approach was based on constraint set
resolution and was not able to deal with precise properties for communications
of behaviors. We present here a new approach, control-flow oriented, based on
the abstract interpretation framework, able to deal with communication of
behaviors. Within our new analyses, we are able to verify most of the previous
properties we observed as well as new ones, principally based on occurrence
counting
Potential for modulation of the hydrophobic effect inside chaperonins
Despite the spontaneity of some in vitro protein folding reactions, native
folding in vivo often requires the participation of barrel-shaped multimeric
complexes known as chaperonins. Although it has long been known that chaperonin
substrates fold upon sequestration inside the chaperonin barrel, the precise
mechanism by which confinement within this space facilitates folding remains
unknown. In this study, we examine the possibility that the chaperonin mediates
a favorable reorganization of the solvent for the folding reaction. We begin by
discussing the effect of electrostatic charge on solvent-mediated hydrophobic
forces in an aqueous environment. Based on these initial physical arguments, we
construct a simple, phenomenological theory for the thermodynamics of density
and hydrogen bond order fluctuations in liquid water. Within the framework of
this model, we investigate the effect of confinement within a chaperonin-like
cavity on the configurational free energy of water by calculating solvent free
energies for cavities corresponding to the different conformational states in
the ATP- driven catalytic cycle of the prokaryotic chaperonin GroEL. Our
findings suggest that one function of chaperonins may be to trap unfolded
proteins and subsequently expose them to a micro-environment in which the
hydrophobic effect, a crucial thermodynamic driving force for folding, is
enhanced
Chiral Fermions on the Lattice
An expression for the lattice effective action induced by chiral fermions in
any even dimensions in terms of an overlap of two states is shown to have
promising properties in two dimensions: The correct abelian anomaly is
reproduced and instantons are suppressed.Comment: 9p, Postscript file, RU--93--3
- âŠ