Influence of the nucleon spectral function in photon and electron induced reactions on nuclei

We study the influence of the nucleon spectral function on eta photo- and electroproduction on nuclei. Besides kinematical effects due to groundstate correlations, also a modification of the S11(1535) decay width is taken into account, which is caused by the possible decay into nucleons with mass smaller than the pole mass in the medium. Hence, resonances with masses below the free N eta threshold can contribute to eta production.Comment: 13 pages, 8 figure

Investigation of continental drift, phase 1 effort Progress report, 1 Apr. - 30 Sep. 1968

Feasibility of using ultrashort pulse laser ranging and independent clock radio interferometry distance measurement methods to test for existence of continental drif

The procurement and evaluation of a prototype laser satellite-tracking system Final report, 1 Jan. 1967 - 30 Sep. 1968

Pulsed ruby laser satellite tracking syste

Photographic measurements of the energy distribution in the beam of a ruby laser

Photographic measurement of energy distribution in beam of Q-switched ruby lase

Measurements of satellite range with a ruby laser

Range measurements of GEOS-I and BE-C satellites with ruby lase

Use of a laser for satellite-range measurement

Optical laser satellite range measuring syste

The Chromium Impurity in ZnTe: Changes of the Charge State Detected by Optical and EPR Spectroscopy

In gasphase-grown p-type ZnTe crystals, the substitutional Cr impurity is detected in the neutral (Cr2+) and both ionized states Cr3+ and Cr+. While these three oxidation states are now identified by EPR, two of them emerge in the optical spectra as well. Optical irradiation of the samples at low temperatures influences the relative concentrations of these species. By monitoring the respective EPR or optical signals, thresholds for photoionization and photo-neutralization processes are derived. In addition to the strong 5E(D)→5T2(D) optical absorption of Cr2+(d4), the samples display a luminescence band near 4500 cm-1, structured by Jahn—Teller interaction. For the first time, a no-phonon line at 4989 cm-1 is resolved, accompanied by a TA(L) satellite and some local-mode structure. In EPR, the angular dependence of the ∆M = ±2 transition characteristic for Cr2+(d4) ions on lattice sites indicates the 5E(D) ground state subject to a static Jahn-Teller effect in the three (100) directions. Whereas an internal optical transition of Cr3+(d3) could not be identified, in EPR, an isotropie signal at g=3.3 discloses a strongly Jahn—Teller-disturbed 4T1(F) ground state. On irradiation with band-tail photons, the ionized acceptor state Cr+(d5) becomes detectable by EPR. Furthermore, an emission with an onset near 10,300 cm-1 is recorded for the first time. Its excitation and optical stimulation spectra are studied in wide spectral ranges; the exponential decay with ζ≅1 ms supports an assignment to a spin-forbidden transition. The acceptor ionization energy is determined as 10,500 cm-1 (1.3 eV)

Spectral Function of Quarks in Quark Matter

We investigate the spectral function of light quarks in infinite quark matter using a simple, albeit self-consistent model. The interactions between the quarks are described by the SU(2) Nambu--Jona-Lasinio model. Currently mean field effects are neglected and all calculations are performed in the chirally restored phase at zero temperature. Relations between correlation functions and collision rates are used to calculate the spectral function in an iterative process.Comment: final version, published in PRC; 15 pages, RevTeX

Delocalizing effect of the Hubbard repulsion for electrons on a two-dimensional disordered lattice

We study numerically the ground-state properties of the repulsive Hubbard model for spin-1/2 electrons on two-dimensional lattices with disordered on-site energies. The projector quantum Monte Carlo method is used to obtain very accurate values of the ground-state charge density distributions with $N_p$ and $N_p+1$ particles. The difference in these charge densities allows us to study the localization properties of an added particle. The results obtained at quarter-filling on finite clusters show that the Hubbard repulsion has a strong delocalizing effect on the electrons in disordered 2D lattices. However, numerical restrictions do not allow us to reach a definite conclusion about the existence of a metal-insulator transition in the thermodynamic limit in two-dimensions.Comment: revtex, 7 pages, 7 figure

Effect of applied field and rate of voltage rise on surface breakdown of oil-immersed polymers

In sub-systems of high-voltage, pulsed-power machines, the introduction of a solid into bulk liquid insulation located between two conductors is often necessary to provide mechanical support. Breakdown events on or around the surface of the solid can result in permanent damage to the insulation system. Described in the present paper are experimental results pertaining to surface breakdown of five different solid dielectrics held between plane-parallel electrodes immersed in mineral oil. The effect of varying level of peak applied field from 200 kV/cm (dV/dt 70 kV/µs) to 1 MV/cm (dV/dt 350 kV/µs) is investigated, and the breakdown voltages and times to breakdown are compared to those for an open oil gap. The time to breakdown is shown to be reduced by the introduction of a solid spacer into the gap. Rexolite and Torlon samples suffered significant mechanical damage, and consistently showed lower breakdown voltage than the other materials - average streamer propagation velocity up to 125 km/s was implied by the short times to breakdown. Although ultra-high molecular weight polyethylene yielded the longest times to breakdown of the five types of liquid-solid gap, breakdown events could be initiated at lower levels of applied field for spacers of this material than those with permittivity closely matched to that of the surrounding mineral oil. Polypropylene and low-density polyethylene are concluded to provide the most stable performance in mineral oil. Due to the similarity of the applied voltage wave-shape (1/6.5 µs) to short-tail lightning impulses, the results may also be of interest to high-voltage system designers in the power industry