Competition between finite-size effects and dipole-dipole interactions in few-atom systems

In this paper, we study the competition between finite-size effects (i.e. discernibility of particles) and dipole-dipole interactions in few-atom systems coupled to the electromagnetic field in vacuum. We consider two hallmarks of cooperative effects, superradiance and subradiance, and compute for each the rate of energy radiated by the atoms and the coherence of the atomic state during the time evolution. We adopt a statistical approach in order to extract the typical behavior of the atomic dynamics and average over random atomic distributions in spherical containers with prescribed $k_0R$ with $k_0$ the radiation wavenumber and $R$ the average interatomic distance. Our approach allows us to highlight the tradeoff between finite-size effects and dipole-dipole interactions in superradiance/subradiance. In particular, we show the existence of an optimal value of $k_0R$ for which the superradiant intensity and coherence pulses are the less affected by dephasing effects induced by dipole-dipole interactions and finite-size effects.Comment: 11 pages, 11 figure

Experimental Verification of the Number Relation at Room and Elevated Temperatures

The accuracy of the Neuber equation for predicting notch root stress-strain behavior at room temperature and at 650 C was experimentally investigated. Strains on notched specimens were measured with a non-contacting, interferometric technique and stresses were simulated with smooth specimens. Predictions of notch root stress-strain response were made from the Neuber Equation and smooth specimen behavior. Neuber predictions gave very accurate results at room temperature. However, the predicted interaction of creep and stress relaxation differed from experimentally measured behavior at 650 C

Experimental evaluation criteria for constitutive models of time dependent cyclic plasticity

Notched members were tested at temperatures far above those recorded till now. Simulation of the notch root stress response was accomplished to establish notch stress-strain behavior. Cyclic stress-strain profiles across the net-section were recorded and on-line direct notch strain control was accomplished. Data are compared to three analysis techniques with good results. The objective of the study is to generate experimental data that can be used to evaluate the accuracy of constitutive models of time dependent cyclic plasticity

A comparison of smooth specimen and analytical simulation techniques for notched members at elevated temperatures

Experimental strain measurements have been made at the highly strained regions on notched plate specimens that were made of Hastelloy X. Tests were performed at temperatures up to 1,600 F. Variable load patterns were chosen so as to produce plastic and creep strains. Were appropriate, notch root stresses were experimentally estimated by subjecting a smooth specimen to the measured notch root strains. The results of three analysis techniques are presented and compared to the experimental data. The most accurate results were obtained from an analysis procedure that used a smooth specimen and the Neuber relation to simulate the notch root stress-strain response. When a generalized constitutive relation was used with the Neuber relation, good results were also obtained, however, these results were not as accurate as those obtained when the smooth specimen was used directly. Finally, a general finite element program, ANYSIS, was used which resulted in acceptable solutions, but, these were the least accurate predictions

Summary results of the DOE flywheel development effort

The technology and applications evaluation task focuses on defining performance and cost requirements for flywheels in the various areas of application. To date the DOE program has focused on automotive applications. The composite materials effort entails the testing of new commercial composites to determine their engineering properties. The rotor and containment development work uses data from these program elements to design and fabricate flywheels. The flywheels are then tested at the Oak Ridge Flywheel Evaluation Laboratory and their performance is evaluated to indicate possible areas for improvement. Once a rotor has been fully developed it is transferred to the private sector

Instrumentation for nondestructive testing of composite honeycomb materials

Program develops instrumentation for nondestructive testing of adhesive-bond strength in honeycomb materials and air coupled inspection methods suitable for large tankage

Measuring the Higgs to Photon-Photon Branching Ratio at the Next Linear e+e−e^+e^- Collider

We examine the prospects for measuring the photon-photon branching ratio of a Standard-Model-like Higgs boson ($h$) at the Next Linear $e^+e^-$ Collider when the Higgs boson is produced via $W^+W^-$--fusion: $e^+e^-\to\nu_e \bar\nu_e h$. In particular, we study the accuracy of such a measurement and the statistical significance of the associated signal as a function of the electromagnetic calorimeter resolution and the Higgs boson mass. We compare results for the $W^+W^-$--fusion production/measurement mode with the results obtained for the $e^+e^-\rightarrow Z^*\rightarrow Z h$ production/measurement mode in a parallel earlier study.Comment: 5 pages, full postscript file also available via anonymous ftp at ftp://ucdhep.ucdavis.edu/gunion/htogamgam_sm96.ps To appear in ``Proceedings of the 1996 DPF/DPB Summer Study on New Directions for High Energy Physics'

On the Margulis constant for Kleinian groups, I curvature

The Margulis constant for Kleinian groups is the smallest constant $c$ such that for each discrete group $G$ and each point $x$ in the upper half space ${\bold H}^3$, the group generated by the elements in $G$ which move $x$ less than distance c is elementary. We take a first step towards determining this constant by proving that if $\langle f,g \rangle$ is nonelementary and discrete with $f$ parabolic or elliptic of order $n \geq 3$, then every point $x$ in ${\bold H}^3$ is moved at least distance $c$ by $f$ or $g$ where $c=.1829\ldots$. This bound is sharp