Collective excitations of a two-dimensional interacting Bose gas in anti-trap and linear external potentials

We present a method of finding approximate analytical solutions for the spectra and eigenvectors of collective modes in a two-dimensional system of interacting bosons subjected to a linear external potential or the potential of a special form $u(x,y)=\mu -u \cosh^2 x/l$, where $\mu$ is the chemical potential. The eigenvalue problem is solved analytically for an artificial model allowing the unbounded density of the particles. The spectra of collective modes are calculated numerically for the stripe, the rare density valley and the edge geometry and compared with the analytical results. It is shown that the energies of the modes localized at the rare density region and at the edge are well approximated by the analytical expressions. We discuss Bose-Einstein condensation (BEC) in the systems under investigations at $T\ne 0$ and find that in case of a finite number of the particles the regime of BEC can be realized, whereas the condensate disappears in the thermodynamic limit.Comment: 10 pages, 2 figures include

Generalized Bose-Einstein Condensation

Generalized Bose-Einstein condensation (GBEC) involves condensates appearing simultaneously in multiple states. We review examples of the three types in an ideal Bose gas with different geometries. In Type I there is a discrete number of quantum states each having macroscopic occupation; Type II has condensation into a continuous band of states, with each state having macroscopic occupation; in Type III each state is microscopically occupied while the entire condensate band is macroscopically occupied. We begin by discussing Type I or "normal" BEC into a single state for an isotropic harmonic oscillator potential. Other geometries and external potentials are then considered: the {}"channel" potential (harmonic in one dimension and hard-wall in the other), which displays Type II, the {}"cigar trap" (anisotropic harmonic potential), and the "Casimir prism" (an elongated box), the latter two having Type III condensations. General box geometries are considered in an appendix. We particularly focus on the cigar trap, which Van Druten and Ketterle first showed had a two-step condensation: a GBEC into a band of states at a temperature $T_{c}$ and another "one-dimensional" transition at a lower temperature $T_{1}$ into the ground state. In a thermodynamic limit in which the ratio of the dimensions of the anisotropic harmonic trap is kept fixed, $T_{1}$ merges with the upper transition, which then becomes a normal BEC. However, in the thermodynamic limit of Beau and Zagrebnov, in which the ratio of the boundary lengths increases exponentially, $T_{1}$ becomes fixed at the temperature of a true Type I phase transition. The effects of interactions on GBEC are discussed and we show that there is evidence that Type III condensation may have been observed in the cigar trap.Comment: 17 pages; 6 figures. Intended for American Journal of Physic

Characterization of radiological emergencies

Several severe radiological emergencies were reviewed to determine the likely range of conditions which must be coped with by a mobile teleoperator designed for emergencies. The events reviewed included accidents at TMI (1978), SL-1 (1961), Y-12 (1958), Bethesda (1982), Chalk River (1952 and 1958), Lucens (1969). The important conditions were: radiation fields over 10,000 R/h, severe contamination, possible critical excursion, possible inert atmosphere, temperatures from 50/sup 0/C to -20/sup 0/C, 100% relative humidity, 60-cm-high obstacles, stairs, airlocks, darkness, and lack of electric power

Decontamination of large horizontal concrete surfaces outdoors

A study is being conducted of the resources and planning that would be required to clean up an extensive contamination of the outdoor environment. As part of this study, an assessment of the fleet of machines needed for decontaminating large outdoor surfaces of horizontal concrete will be attempted. The operations required are described. The performance of applicable existing equipment is analyzed in terms of area cleaned per unit time, and the comprehensive cost of decontamination per unit area is derived. Shielded equipment for measuring directional radiation and continuously monitoring decontamination work are described. Shielding of drivers' cabs and remote control vehicles is addressed

Blast tests of expedient shelters

Oak Ridge National Laboratory field tests of expedient shelters during the past three years have resulted in the selection and development of six types of expedient shelters. These were demonstrated by construction exercises to be the most practical for average rural and small-town Americans to build in the principal environmental regions of the United States. Each type of shelter is designed to be built within 48 hours by average family groups of such Americans, using only widely available materials such as trees, to provide all members with high-protection-factor shelter. To evaluate the blast protection afforded by these six types of expedient shelters, they were blast tested as a part of Defense Nuclear Agency's Mixed bompany Event, in the blast area of a 500-ton TNT detonationequivalent in air blast effects to a 1.0 to 1.8 kiloton nuclear detonation. A total of twelve shelters, representing six expedient types, were subjected to blast effecta at surface overpressures ranging from 29 to 3 psi. All except the two Door-Covered Trench Shelters were tested as closed shelters. Only one shelter was damaged: the Door-Covered Trench Shelter that was tested as an open shelter at 5 psi. The six types of shelters. tested at the following measured surface overpressures, were: Two Small-Pole Shelters, at 29 psi; Three Wire-Catenary-Roofed Shelters, at 29 psi and 13 psi; One aboveground A-Frame Pole Shelter, at 17 psi; One Shored-Trench Stoop-in Shelter, at 13 psi; Two Log- Covered Trench Shelters, at 13 psi; and Two Door-Covered Trench Shelters, at 5 psi and 3 psi. Earth arching increased the strength of the shelters that had an adequate depth of earth cover relative to the roof span. A new design of quickly closable, expedient blast door was tested at 29, 17 and 13 psi surface overpressure ranges. Only the blast door at 17 psi was damaged, snd even it remained intact and securely closed. Also tested were two new designs of blast valves, both of which can protect against 100 psi overpressures and are closed in 1 to 2 milliseconds. One of these valves, the Overlapping-Flaps Blast Valve, requires only widely available materials and can be made in a few hours with common tools. (auth