Superstring motivated gauge models based on a rank six subgroup ofE 6

We discuss gauge models based on a superstring motivated rank six subgroup ofE ₆. Lepton number is an accidental unbroken symmetry of the models which leads to an essentially stable proton. One of the neutral gauge bosons couples toB-L and may have mass below a TeV.     

Weak type (1, 1) inequalities of maximal convolution operators

In this paper we study the behavior of the constants which appear in the weak type (1, 1) inequalities for maximal convolution operators by means of discrete methods. One of the first applications of these techniques will give us a very simple proof of the ergodic theorem. We also present partial results in order to investigate the best constant in the weak type (1, 1) inequality for the Hardy-Littlewood centered maximal operator in dimension one. In dimension bigger than one we also obtain some lower bounds for that constant.     

Existence for nonoscillatory solutions of higher-order nonlinear neutral difference equations

In this paper, we consider the following forced higher-order nonlinear neutral difference equation

     

Experimental study of enhanced emission of the laser-ablated plume in backing gas

The effects of background gases on the optical emission of the excimer-laser-ablated plume from a brass target have been studied experimentally. It is found that the plume emission can be enhanced significantly in a proper gas ambient. In hydrogen, the highest peak intensity is detected, and in argon, there is a distinctive difference in the pressure-dependent emission between in He and in the other three gases, Ar, N₂ and H₂. Moreover, the monitored line peak intensity remains unchanged in Ar and N₂ and increases in H₂ within a distance above the target surface; but in He, the observed peak intensity decreases with distance like in vacuum. Furthermore, the emissions of several more atomic lines of Cu and Zn atoms from the plume are also found to be enhanced in the same manner in gas ambient. Some physical processes involved in the plume expansion and the possible mechanisms for the enhanced emission of the plume in backing gas are discussed.     

Variational estimates of chiral order parameter in 1+1 dimensional lattice QCD

We discuss analytically the vacuum structure and chiral-symmetry breaking in 1+1 dimensional lattice QCD with naive and Wilson fermions, using a unitary transformation and the variational method developed recently. As an example, the chiral order parameter is evaluated systematically for any coupling constant and fermion mass by including the multilink-terms in the transformation. The expected scaling behavior is observed. Our results are consistent with the continuum predictions.     

Near optimality of stochastic control in systems with unknown parameter processes

Stochastic control for systems with an unknown parameter is considered in this paper. The underlying problem is to minimize a functional subject to a system described by a singularly perturbed differential equation with an unknown parameter process driven by fast fluctuating random disturbances. This problem arises in the context of stochastic adaptive control, adaptive signal processing, and failure-prone manufacturing systems. Due to the nature of the wide-bandwidth noise processes, identifying the parameter process for eacht is very hard since the driving noise changes very rapidly. An alternative approach is used, and an auxiliary control problem is introduced to overcome the difficulties. By means of weak convergence methods and comparison control techniques, nearly optimal controls are obtained.This research was supported in part by the National Science Foundation under Grant DMS-9022139 and DMS-9224372.     

Accurate singular values and differential qd algorithms

Summary. We have discovered a new implementation of the qd algorithm that has a far wider domain of stability than Rutishauser's version. Our algorithm was developed from an examination of the {Cholesky~LR} transformation and can be adapted to parallel computation in stark contrast to traditional qd. Our algorithm also yields useful a posteriori upper and lower bounds on the smallest singular value of a bidiagonal matrix. The zero-shift bidiagonal QR of Demmel and Kahan computes the smallest singular values to maximal relative accuracy and the others to maximal absolute accuracy with little or no degradation in efficiency when compared with the LINPACK code. Our algorithm obtains maximal relative accuracy for all the singular values and runs at least four times faster than the LINPACK code. Received August 8, 1993/Revised version received May 26, 1993     

Frozen strain moiré used in the analysis of impact loading

This paper presents a solution to the problem of the displacement fields and strains in a semi-infinite plate with two half-circular holes during the propagation of a stress wave. The solution was realized experimentally by means of the method of the frozen strain moiré using a double-pulse ruby laser. The load of impact was applied by a pendulum hammer. Two suitable external-trigger mechanisms were used to fire the ruby laser at predetermined intervals. The moiré fringe patterns of the U and V displacement fields were recorded on a holographic film adhered to the specimen at different time delays after impact.     

Extrapolation of astrophysical <Emphasis Type="Italic">S</Emphasis> factors for the reaction <Superscript>14</Superscript>N((<Emphasis Type="Italic">p, γ</Emphasis>) <Superscript>15</Superscript>O to near-zero energies

The astrophysical S factors for the radiative-capture reaction ¹⁴N(p, γ)¹⁵O in the region of ultralow energies were calculated on the basis of the R-matrix approach. The values of the radiative and protonic widths were fitted to new experimental data. The contribution of direct radiative capture to bound states of the ¹⁵O nucleus was determined with the aid of asymptotic normalization coefficients, whose values were refined in the present study on the basis of the results obtained from an analysis of the reaction ¹⁴N(³He, d)¹⁵O at three different energies of incident helium ions. A value of S(0) = 1.79 ± 0.31 keV b was obtained for the total astrophysical S factor, and the reaction rate was determined for the process ¹⁴N(p, γ)¹⁵O.     

Cryopreservation of in vitro grown shoot tips of Diospyros kaki thunb. using different methods

The objective of this study was to compare the potential of different cryopreservation strategies for in vitro shoot tips of Diospyros kaki Thunb. The treatments consisted of three different cryopreservation methods: vitrification, droplet-vitrification and modified droplet-vitrification. The following variables were assessed: cold acclimation, sucrose concentration in the preculture medium and PVS2 treatment time. A higher average survival level was obtained using the modified droplet-vitrification method compared to the other two methods.