Entropy and the Approach to the Thermodynamic Limit in Three-Dimensional Simplicial Gravity

We present numerical results supporting the existence of an exponential bound in the dynamical triangulation model of three-dimensional quantum gravity.Both the critical coupling and various other quantities show a slow power law approach to the infinite volume limit

Spectroscopy, Equation Of State And Monopole Percolation In Lattice QED With Two Flavors

Non-compact lattice QED with two flavors of light dynamical quarks is simulated on $16^4$ lattices, and the chiral condensate, monopole density and susceptibility and the meson masses are measured. Data from relatively high statistics runs at relatively small bare fermion masses of 0.005, 0.01, 0.02 and 0.03 (lattice units) are presented. Three independent methods of data analysis indicate that the critical point occurs at $\beta =0.225(5)$ and that the monopole condensation and chiral symmetry breaking transitions are coincident. The monopole condensation data satisfies finite size scaling hypotheses with critical indices compatible with four dimensional percolation. The best chiral equation of state fit produces critical exponents ($\delta=2.31$, $\beta_{mag}=0.763$) which deviate significantly from mean field expectations. Data for the ratio of the sigma to pion masses produces an estimate of the critical index $\delta$ in good agreement with chiral condensate measurements. In the strong coupling phase the ratio of the meson masses are $M_\sigma^2/M_\rho^2\approx 0.35$, $M_{A_1}^2/M_\rho^2\approx 1.4$ and $M_\pi^2/M_\rho^2\approx 0.0$, while on the weak coupling side of the transition $M_\pi^2/M_\rho^2\approx 1.0$, $M_{A_1}^2/M_\rho^2\approx 1.0$, indicating the restoration of chiral symmetry.\footnote{\,^{}}{August 1992}Comment: 21 pages, 24 figures (not included

Simplicial Gravity in Dimension Greater than Two

We consider two issues in the DT model of quantum gravity. First, it is shown that the triangulation space for D\u3e3 is dominated by triangulations containing a single singular (D-3)-simplex composed of vertices with divergent dual volumes. Second we study the ergodicity of current simulation algorithms. Results from runs conducted close to the phase transition of the four-dimensional theory are shown. We see no strong indications of ergodicity br eaking in the simulation and our data support recent claims that the transition is most probably first order. Furthermore, we show that the critical properties of the system are determined by the dynamics of remnant singular vertices

On the Absence of an Exponential Bound in Four Dimensional Simplicial Gravity

We have studied a model which has been proposed as a regularisation for four dimensional quantum gravity. The partition function is constructed by performing a weighted sum over all triangulations of the four sphere. Using numerical simulation we find that the number of such triangulations containing $V$ simplices grows faster than exponentially with $V$. This property ensures that the model has no thermodynamic limit.Comment: 8 pages, 2 figure

Investigation of the Reduction of Nitric Oxides by CO and H2 on Pt-Mo Catalysts under Oxidizing Conditions

The reduction of NO by CO on Pt has been extensively investigated in the past since it helps to eliminate NO of the exhaust gas of cars. However, the dissociation of NO in this reaction and the deactivation of the NO/CO reaction on Pt-supported catalysts still need to be discussed. In this work, the reduction of NO with CO is examined on a 0.5 % Pt-3.4 % MoO3/alpha-Al2O3 catalyst. The results of a kinetic modeling are presented and a new proposition concerning the mechanism of the observed deactivation is made. To the authors knowledge, this is the first study where the kinetics of the N2O formation on a Pt-catalyst is established

An Effective Model for Crumpling in Two Dimensions?

We investigate the crumpling transition for a dynamically triangulated random surface embedded in two dimensions using an effective model in which the disordering effect of the $X$ variables on the correlations of the normals is replaced by a long-range ``antiferromagnetic'' term. We compare the results from a Monte Carlo simulation with those obtained for the standard action which retains the $X$'s and discuss the nature of the phase transition.Comment: 5 page

NONDESTRUCTIVE TESTS OF COMPONENTS OF EBR-I, CORE IV

Eddy-current and ultrasonic tests on zirconium rod stock and wire, Zircaloy-2 tubing and rod stock, and stainless steel tubing for use in various core compoments are summarized. Eddy-current tests were also performed on the NaK annulus of assembled blanket elements. (D.C.W.

Microchannel reactors for fast periodic operation: the catalytic dehydrogenation of isopropanol

A microchannel reactor specially designed for periodic operation and a process to deposit a catalyst, g-alumina, inside the reactor channels were developed. The hydrodynamics of the reactor was characterised. Although the flow in the microchannels is laminar, a uniform radial concentration profile and consequently a narrow residence time distribution were obtained. Depending on the manufacturing method the Bodenstein number was found to be Bo=ud/Dm=~70. The catalytic coating had no influence on this distribution indicating a uniform deposition of the catalyst within the microchannels. As the inlet function was only slightly modified in the reactors, frequencies of up to 1 Hz could be imposed for periodic operation. The dehydration of isopropanol to propene was chosen as model reaction to study the dynamic behaviour of a microreactor under periodic concentration variations. The kinetics was firstly studied in a conventional fixed-bed reactor with the catalyst developed for the microreactor. Experimental results confirmed the theoretically predicted increase of the reactor performance under periodic operation exceeding the maximum obtainable performance under steady-state conditions

The nature of the continuum limit in the 2D RP2RP^2 gauge model

The RP(2) gauge model is studied in 2D. We use Monte-Carlo renormalization techniques for blocking the mean spin-spin interaction, , and the mean gauge field plaquette, . The presence of the O(3) renormalized trajectory is verified and is consistent with the known three-loop beta-function. The first-order `vorticity' transition observed by Solomon et al. is confirmed, and the location of the terminating critical point is established. New scaling flows in (,) are observed associated with a large exponent kappa in the range 4~5. The scaling flows give rise to a strong cross-over effect between regions of high and low vorticity and are likely to induce an apparent signal for scaling in the cross-over region which we propose explains the scaling observed for RP(2), RP(3) and SO(4)-matrix models. The signal for this `pseudo' scaling will occur for the RP(2) spin model in the cross-over region which is the region in which computer simulations are done. We find that the RP(2) spin model is in the same universality class as the O(3) spin model but that it is likely to require a very large correlation length before the true scaling of this class sets in. We conjecture that the scaling flows are due either to the influence of a nearby new renormalized trajectory or to the ghost of the Kosterlitz-Thouless trajectory in the associated XY model.Comment: 29 pages, LATEX2e, 10 figures, uses styles[epsfig,latexsym

Technicolor Theories with Negative S

We show that the pseudo Nambu--Goldstone boson contribution to the Peskin--Takeuchi electroweak parameter $S$ can be negative in a class of technicolor theories. This negative contribution can be large enough to cancel the positive techni-hadron contribution, showing that electroweak precision tests alone cannot be used to rule out technicolor as the mechanism of electroweak symmetry breaking.Comment: (LBL-32893, UCB-PTH 92/34, 10 pages; we added a discussion of uncertainties, fine-tuning, and SU(2) asymptotic freedom; the conclusions are unchanged.