Three-dimensional Binary Superlattices of Oppositely-charged Colloids

We report the equilibrium self-assembly of binary crystals of oppositely-charged colloidal microspheres at high density. By varying the magnitude of the charge on near equal-sized spheres we show that the structure of the binary crystal may be switched between face-centered cubic, cesium chloride and sodium chloride. We interpret these transformations in terms of a competition between entropic and Coulombic forces

A New Determination of e/m from the Zeeman Effect

Values of e/m have been determined from the Zeeman separations of the Cd line 6439 and the Zn line 6362. For these lines the g-factors can be accurately determined from the theory. A magnetic field of 7300 gauss was produced by an air core solenoid in which the variation of field strength over a length of 6 cm at the center was less than 0.1 percent. The field to current ratio, K, of this solenoid was determined in terms of the calculated ratios of three single layer standard solenoids. The field strength during an exposure was then given by the product of this constant and the current flowing. Evaporation of Zn and Cd in the short (6 cm) positive column of a helium discharge tube gave the desired lines. The Zeeman patterns were photographed with a Fabry-Perot interferometer. The result is e/m = 1.7579 ± 0.0025 × 10^7 e.m.u. per gram

On the Validity of the Tomonaga Luttinger Liquid Relations for the One-dimensional Holstein Model

For the one-dimensional Holstein model, we show that the relations among the scaling exponents of various correlation functions of the Tomonaga Luttinger liquid (LL), while valid in the thermodynamic limit, are significantly modified by finite size corrections. We obtain analytical expressions for these corrections and find that they decrease very slowly with increasing system size. The interpretation of numerical data on finite size lattices in terms of LL theory must therefore take these corrections into account. As an important example, we re-examine the proposed metallic phase of the zero-temperature, half-filled one-dimensional Holstein model without employing the LL relations. In particular, using quantum Monte Carlo calculations, we study the competition between the singlet pairing and charge ordering. Our results do not support the existence of a dominant singlet pairing state.Comment: 7 page

Star Formation in the Field and Clusters of NGC 5253

We investigate the star formation history of both the bright star clusters and the diffuse `field star' population in the dwarf starburst galaxy NGC 5253 using STIS longslit ultraviolet spectroscopy. Our slit covers a physical area of 370 x 1.6 pc and includes 8 apparent clusters and several inter-cluster regions of diffuse light which we take to be the field. The diffuse light spectrum lacks the strong O-star wind features which are clearly visible in spectra of the brightest clusters. This discrepancy provides compelling evidence that the diffuse light is not reflected light from nearby clusters, but originates in a UV-bright field star population, and it raises the issue of whether the star formation process may be operating differently in the field than in clusters. We compare our spectra to STARBURST99 evolutionary synthesis models which incorporate a new low metallicity atlas of O-star spectra. We favor a scenario which accounts for the paucity of O-stars in the field without requiring the field to have a different IMF than the clusters: stellar clusters form continuously and then dissolve on ~10 Myr timescales and disperse their remaining stars into the field. We consider the probable contribution of an O-star deficient field population to the spatially unresolved spectra of high redshift galaxies. (Abridged)Comment: 26 pages, 10 figures, accepted for publication in Ap

On the Erasure and Regeneration of the Primordial Baryon Asymmetry by Sphalerons

We show that a cosmological baryon asymmetry generated at the GUT scale, which would be destroyed at lower temperatures by sphalerons and possible new B- or L-violating effects, can naturally be preserved by an asymmetry in the number of right-handed electrons. This results in a significant softening of previously derived baryogenesis-based constraints on the strength of exotic B- or L-violating interactions.Comment: 10 pp. LaTex (2 figures, included) UMN-TH-1201/9

An extreme paucity of second population AGB stars in the normal globular cluster M4

Galactic Globular clusters (GCs) are now known to harbour multiple stellar populations, which are chemically distinct in many light element abundances. It is becoming increasingly clear that asymptotic giant branch (AGB) stars in GCs show different abundance distributions in light elements compared to those in the red giant branch (RGB) and other phases, skewing toward more primordial, field-star-like abundances, which we refer to as subpopulation one (SP1). As part of a larger program targeting giants in GCs, we obtained high-resolution spectra for a sample of 106 RGB and 15 AGB stars in Messier 4 (NGC 6121) using the 2dF+HERMES facility on the Anglo-Australian Telescope. In this Letter we report an extreme paucity of AGB stars with [Na/O] > -0.17 in M4, which contrasts with the RGB that has abundances up to [Na/O] =0.55. The AGB abundance distribution is consistent with all AGB stars being from SP1. This result appears to imply that all subpopulation two stars (SP2; Na-rich, O-poor) avoid the AGB phase. This is an unexpected result given M4's horizontal branch morphology -- it does not have an extended blue horizontal branch. This is the first abundance study to be performed utilising the HERMES spectrograph.Comment: 5 pages, 2 figures, 4 tables (full Table 1 online). Accepted for publication in MNRAS Letter

Atomic Beams

Contains reports on two research projects.Lincoln Laboratory, Purchase Order DDL-B158Department of the ArmyDepartment of the NavyDepartment of the Air Force under Contract AF 19(122)-45

Functional decline and survival in dependent elderly people.

A survey of dependency levels was carried out in 1985 and 1989 in 41 residents of old peoples homes and 25 patients in geriatric continuing care wards. There was an increase in all levels of dependency for those in both types of care. In the hospital patients surveyed in 1985, mortality was greatest in the most dependent, particularly those with impaired mental function. There was a positive correlation between length of survival and mental function. The results of this study emphasise the important role of dementia in the health and survival of old people

Focused laser Doppler velocimeter

A system for remotely measuring velocities present in discrete volumes of air is described. A CO2 laser beam is focused by a telescope at such a volume, a focal volume, and within the focusable range, near field, of the telescope. The back scatter, or reflected light, principally from the focal volume, passes back through the telescope and is frequency compared with the original frequency of the laser, and the difference frequency or frequencies represent particle velocities in that focal volume