[en] The ZEUS experiment at HERA employs custom made analog pipeline memories, manufactured with a 2 μm CMOS process. These memories are used to store the signals from the high resolution uranium scintillator calorimeter during the latency of the first level trigger, and are mounted inside of the detector where they are exposed to background radiation. To improve the radiation hardness, thin oxide extension and guard bands were added to the layout of the NMOS transistors. Performance parameters of the pipeline and characteristics of discrete transistors and MOS capacitors were studied before and after irradiation with ionizing radiation from a Cs¹³⁷ source with doses up to 212 krad for the discrete components and 500 krad for the integrated circuit. The discrete devices were made with the same process as the integrated pipeline memory. The pipeline memories showed minor performance degradation after exposure of up to 500 krad. The dominant effects were the development of storage cell leakage current of the order of 1 pA, pedestal shifts of the output voltage Δp=25 mV, and a decrease of the speed of the readout amplifier, leading to an effective gain reduction by 1.5%. (orig.)

[en] We use a one-dimensional random walk on D-dimensional hyper-spheres to determine the critical behavior of statistical systems in hyper-spherical geometries. First, we demonstrate the properties of such walk by studying the phase diagram of a percolation problem. We find a line of second and first order phase transitions separated by a tricritical point. Then, we analyze the adsorption-desorption transition for a polymer growing near the attractive boundary of a cylindrical cell membrane. We find that the fraction of adsorbed monomers on the boundary vanishes exponentially when the adsorption energy decreases towards its critical value. We observe a crossover phenomenon to an area of linear growth at energies of the order of the inverse cell radius. ((orig.))

[en] A forward plug calorimeter (FPC) for the ZEUS detector at HERA has been built as a shashlik lead-scintillator calorimeter with wave length shifter fiber readout. Before installation it was tested and calibrated using the X5 test beam facility of the SPS accelerator at CERN. Electron, muon and pion beams in the momentum range of 10 to 100 GeV/c were used. Results of these measurements are presented as well as a calibration monitoring system based on a ⁶⁰Co source. (orig.)

[en] A new analytical method for extracting nonperturbative solutions to problems in physics is given. The procedure consists of expanding the solution as a perturbation series in powers of a nonperturbative parameter. The advantage of the procedure is that the zero-dimensional problem can be solved in closed form. 5 refs., 1 fig., 1 tab

[en] Temporal autocorrelation functions for avalanches in the Bak-Sneppen model display aging behavior similar to glassy systems. Numerical simulations show that they decay as power laws with two distinct regimes separated by a time scale which is the waiting time, or age, of the avalanche. Thus, time-translational invariance is dynamically broken. The critical exponent of the initial decay is that of the familiar stationary dynamics while a new critical exponent for the late-time behavior appears. This new exponent characterizes a nonstationary regime that has not been previously considered in the context of self-organized criticality. copyright 1997 The American Physical Society

[en] We use a one-dimensional random walk on D-dimensional hyperspheres to determine the critical behavior of statistical systems in hyperspherical geometries. First, we demonstrate the properties of such a walk by studying the phase diagram of a percolation problem. We find a line of second and first order phase transitions separated by a tricritical point. Then, we analyze the adsorption-desorption transition for a polymer growing near the attractive boundary of a cylindrical cell membrane. We find that the fraction of adsorbed monomers on the boundary vanishes exponentially when the adsorption energy decreases towards its critical value

[en] We introduce a self-organized critical model of punctuated equilibrium with many internal degrees of freedom (M) per site. We find exact solutions for M→∞ of cascade equations describing avalanche dynamics in the steady state. This proves the existence of simple power laws with critical exponents that verify general scaling relations for nonequilibrium phenomena. Punctuated equilibrium is described by a devil close-quote s staircase with a characteristic exponent τ_first=2-d/4 where d is the spatial dimension. copyright 1996 The American Physical Society

[en] A recently proposed technique, called dimensional expansion, uses the space-time dimension D as an expansion parameter to extract nonperturbative results in quantum field theory. Here we apply dimensional-expansion methods to examine the Ising limit of a self-interacting scalar field theory. We compute the first few coefficients in the dimensional expansion of γ_2n, the renormalized 2n-point Green's function at zero momentum, for n=2, 3, 4, and 5. Because the exact results for γ_2n are known at D=1 we can compare the predictions of the dimensional expansion at this value of D. We find typical accuracies of less than 5%. The radius of convergence of the dimensional expansion for γ_2n appears to be 2n/(n-1). As a function of the space-time dimension D, γ_2n appears to rise monotonically with increasing D and we conjecture that it becomes infinite at D=2n/(n-1). We presume that for values of D greater than this critical value γ_2n vanishes identically because the corresponding φ²ⁿ scalar quantum field theory is free for D>2n/(n-1)

[en] The condition of self-adjointness ensures that the eigenvalues of a Hamiltonian are real and bounded below. Replacing this condition by the weaker condition of PT symmetry, one obtains new infinite classes of complex Hamiltonians whose spectra are also real and positive. These PT symmetric theories may be viewed as analytic continuations of conventional theories from real to complex phase space. This paper describes the unusual classical and quantum properties of these theories. copyright 1998 The American Physical Society

[en] In a recent paper [S. Boettcher and M. Moshe, Phys. Rev. Lett. 74, 2410 (1995)], a simple method was proposed to generate solvable models that predict the critical properties of statistical systems in hyperspherical geometries. To that end, it was shown how to reduce a random walk in D dimensions to an anisotropic one-dimensional random walk on concentric hyperspheres. Here I construct such a random walk to model the adsorption-desorption transition of polymer chains growing near an attractive cylindrical boundary such as that of a cell membrane. I find that the fraction of adsorbed monomers on the boundary vanishes exponentially when the adsorption energy decreases towards its critical value. When the adsorption energy rises beyond a certain value above the critical point whose scale is set by the radius of the cell, the adsorption fraction exhibits a crossover to a linear increase characteristic of polymers growing near planar boundaries