Production of carbon clusters C3\text{C}_3 to C12\text{C}_{12} with a cryogenic buffer-gas beam source

Cryogenic buffer-gas beam sources are capable of producing intense beams of a wide variety of molecules, and have a number of advantages over traditional supersonic expansion sources. In this work, we report on a neon matrix isolation study of carbon clusters produced with a cryogenic buffer-gas beam source. Carbon clusters created by laser ablation of graphite are trapped in a neon matrix and detected with a Fourier transform infrared spectrometer in the spectral range $4000-1000~\text{cm}^{-1}$. Through a study of carbon cluster production as a function of various system parameters, we characterize the behavior of the buffer-gas beam source and find that approximately $10^{11}-10^{12}$ of each cluster is produced with each pulse of the ablation laser. These measurements demonstrate the usefulness of cryogenic buffer-gas beam sources for producing molecular beams of clusters.Comment: 7 pages, 4 figure

Economic, Neurobiological and Behavioral Perspectives on Building America's Future Workforce

A growing proportion of the U.S. workforce will have been raised in disadvantaged environments that are associated with relatively high proportions of individuals with diminished cognitive and social skills. A cross-disciplinary examination of research in economics, developmental psychology, and neurobiology reveals a striking convergence on a set of common principles that account for the potent effects of early environment on the capacity for human skill development. Central to these principles are the findings that early experiences have a uniquely powerful influence on the development of cognitive and social skills, as well as on brain architecture and neurochemistry; that both skill development and brain maturation are hierarchical processes in which higher level functions depend on, and build on, lower level functions; and that the capacity for change in the foundations of human skill development and neural circuitry is highest earlier in life and decreases over time. These findings lead to the conclusion that the most efficient strategy for strengthening the future workforce, both economically and neurobiologically, and for improving its quality of life is to invest in the environments of disadvantaged children during the early childhood years.

Doppler-beaming in the Kepler light curve of LHS 6343 A

Context. Kepler observations revealed a brown dwarf eclipsing the M-type star LHS 6343 A with a period of 12.71 days. In addition, an out-of-eclipse light modulation with the same period and a relative semi-amplitude of 2 x 10^-4 was observed showing an almost constant phase lag to the eclipses produced by the brown dwarf. In a previous work, we concluded that this was due to the light modulation induced by photospheric active regions in LHS 6343 A. Aims. In the present work, we prove that most of the out-of-eclipse light modulation is caused by the Doppler-beaming induced by the orbital motion of the primary star. Methods. We introduce a model of the Doppler-beaming for an eccentric orbit and also considered the ellipsoidal effect. The data were fitted using a Bayesian approach implemented through a Monte Carlo Markov chain method. Model residuals were analysed by searching for periodicities using a Lomb-Scargle periodogram. Results. For the first seven quarters of Kepler observations and the orbit previously derived from the radial velocity measurements, we show that the light modulation of the system outside eclipses is dominated by the Doppler-beaming effect. A period search performed on the residuals shows a significant periodicity of 42.5 +- 3.2 days with a false-alarm probability of 5 x 10^-4, probably associated with the rotational modulation of the primary component.Comment: 6 pages, 7 figure

Magnetic Structure of Rapidly Rotating FK Comae-Type Coronae

We present a three-dimensional simulation of the corona of an FK Com-type rapidly rotating G giant using a magnetohydrodynamic model that was originally developed for the solar corona in order to capture the more realistic, non-potential coronal structure. We drive the simulation with surface maps for the radial magnetic field obtained from a stellar dynamo model of the FK Com system. This enables us to obtain the coronal structure for different field topologies representing different periods of time. We find that the corona of such an FK Com-like star, including the large scale coronal loops, is dominated by a strong toroidal component of the magnetic field. This is a result of part of the field being dragged by the radial outflow, while the other part remains attached to the rapidly rotating stellar surface. This tangling of the magnetic field,in addition to a reduction in the radial flow component, leads to a flattening of the gas density profile with distance in the inner part of the corona. The three-dimensional simulation provides a global view of the coronal structure. Some aspects of the results, such as the toroidal wrapping of the magnetic field, should also be applicable to coronae on fast rotators in general, which our study shows can be considerably different from the well-studied and well-observed solar corona. Studying the global structure of such coronae should also lead to a better understanding of their related stellar processes, such as flares and coronal mass ejections, and in particular, should lead to an improved understanding of mass and angular momentum loss from such systems.Comment: Accepted to ApJ, 10 pages, 6 figure

The Angular Momentum Evolution of Very Low Mass Stars

We present theoretical models of the angular momentum evolution of very low mass stars (0.1 - 0.5 M_sun) and solar analogues (0.6 - 1.1 M_sun). We investigate the effect of rotation on the effective temperature and luminosity of these stars. We find that the decrease in T_eff and L can be significant at the higher end of our mass range, but becomes negligible below 0.4 M_sun. Formulae for relating T_eff to mass and v_rot are presented. We compare our models to rotational data from young open clusters of different ages to infer the rotational history of low mass stars, and the dependence of initial conditions and rotational evolution on mass. We find that the qualitative conclusions for stars below 0.6 M_sun do not depend on the assumptions about internal angular momentum transport, which makes these low mass stars ideal candidates for the study of the angular momentum loss law and distribution of initial conditions. We find that neither models with solid body nor differential rotation can simultaneously reproduce the observed stellar spin down in the 0.6 to 1.1 M_sun mass range and for stars between 0.1 and 0.6 M_sun. The most likely explanation is that the saturation threshold drops more steeply at low masses than would be predicted with a simple Rossby scaling. In young clusters there is a systematic increase in the mean rotation rate with decreased temperature below 3500 K (0.4 M_sun). This suggests either inefficient angular momentum loss or mass-dependent initial conditions for stars near the fully convective boundary. (abridged)Comment: To appear in the May 10, 2000 Ap

Fusion energy from the Moon for the twenty-first century

It is shown in this paper that the D-He-3 fusion fuel cycle is not only credible from a physics standpoint, but that its breakeven and ignition characteristics could be developed on roughly the same time schedule as the DT cycle. It was also shown that the extremely low fraction of power in neutrons, the lack of significant radioactivity in the reactants, and the potential for very high conversion efficiencies, can result in definite advantages for the D-He-3 cycle with respect to DT fusion and fission reactors in the twenty-first century. More specifically, the D-He-3 cycle can accomplish the following: (1) eliminate the need for deep geologic waste burial facilities and the wastes can qualify for Class A, near-surface land burial; (2) allow 'inherently safe' reactors to be built that, under the worst conceivable accident, cannot cause a civilian fatality or result in a significant (greater than 100 mrem) exposure to a member of the public; (3) reduce the radiation damage levels to a point where no scheduled replacement of reactor structural components is required, i.e., full reactor lifetimes (approximately 30 FPY) can be credibly claimed; (4) increase the reliability and availability of fusion reactors compared to DT systems because of the greatly reduced radioactivity, the low neutron damage, and the elimination of T breeding; and (5) greatly reduce the capital costs of fusion power plants (compared to DT systems) by as much as 50 percent and present the potential for a significant reduction on the COE. The concepts presented in this paper tie together two of the most ambitious high-technology endeavors of the twentieth century: the development of controlled thermonuclear fusion for civilian power applications and the utilization of outer space for the benefit of mankind on Earth

Use of Topographic Data on Land-Use Land-Cover Delineation by ERTS Imagery

The use of ERTS imagery for estimating land-use land-cover is of particular importance for the Canadian Department of the Environment for many reasons, one of which is the fact that this Department is using a lands-wide data bank of river basins characteristics for interpolation of hydrologic information in which land-use land-cover is an important one. Initially data on land-use land-cover were obtained by abstracting them by hand from 1/200,000 topographic maps, and were limited to the following elements: forested area, lake covered areas, swamp covered areas, and urbanized areas. The roughness of the information thus obtained, together with the fact that the data obtained could not be updated, resulted in significant difficulties in using the data in the interpolation of hydrologic information. This is particularly true when the technique of interpolation was a spatially distributed hydrologic model, recently developed and applied with success where detailed information on land-use and land-cover was available

Force-Free Models of Magnetically Linked Star-Disk Systems

Disk accretion onto a magnetized star occurs in a variety of astrophysical contexts, from young stars to X-ray pulsars. The magnetohydrodynamic interaction between the stellar field and the accreting matter can have a strong effect on the disk structure, the transfer of mass and angular momentum between the disk and the star, and the production of bipolar outflows, e.g., plasma jets. We study a key element of this interaction - the time evolution of the magnetic field configuration brought about by the relative rotation between the disk and the star - using simplified, largely semianalytic, models. We first discuss the rapid inflation and opening up of the magnetic field lines in the corona above the accretion disk, which is caused by the differential rotation twisting. Then we consider additional physical effects that tend to limit this expansion, such as the effect of plasma inertia and the possibility of reconnection in the disk's corona, the latter possibly leading to repeated cycles in the evolution. We also derive the condition for the existence of a steady state for a resistive disk and conclude that a steady state configuration is not realistically possible. Finally, we generalize our analysis of the opening of magnetic field lines by using a non-self-similar numerical model that applies to an arbitrarily rotating (e.g. keplerian) disk.Comment: 75 pages, 22 figures, 2 tables. Submitted to Astrophysical Journa