Predatory Insects and Spiders From Suburban Lawns in Lexington, Kentucky

Predatory arthropods were caught in pitfall traps in suburban lawns in Lexington, Kentucky. The relative abundance of species of Lycosidae, Carabidae, and Staphylinidae was compared in Kentucky bluegrass and tall fescue turf. Nine species of Lycosidae were collected from both the bluegrass and tall fescue lawns. More species or phena of Carabidae were collected from bluegrass than from tall fescue turf. More than 40 species or phena of staphylinids were collected from each grass habitat. Both Kentucky bluegrass and tall fescue are inhabited by an abundant and diverse array of predatory arthropods

Large antenna apertures and arrays for deep space communications

Effect of frequency on communications capability, single antennas and arrays, and economic balance between ground station and spacecraft developmen

Femtosecond probing of bimolecular reactions: The collision complex

Progress has been made in probing the femtosecond dynamics of transition states of chemical reactions.(1) The "half-collision" case of unimolecular reactions has been experimentally investigated for a number of systems and much theoretical work has already been developed.(2) For bimolecular reactions, the case of full collision, the zero of time is a problem which makes the femtosecond temporal resolution of the dynamics a difficult task

Femtosecond real-time probing of reactions. VIII. The bimolecular reaction Br+I2

In this paper, we discuss the experimental technique for real-time measurement of the lifetimes of the collision complex of bimolecular reactions. An application to the atom–molecule Br+I_2 reaction at two collision energies is made. Building on our earlier Communication [J. Chem. Phys. 95, 7763 (1991)], we report on the observed transients and lifetimes for the collision complex, the nature of the transition state, and the dynamics near threshold. Classical trajectory calculations provide a framework for deriving the global nature of the reactive potential energy surface, and for discussing the real-time, scattering, and asymptotic (product-state distribution) aspects of the dynamics. These experimental and theoretical results are compared with the extensive array of kinetic, crossed beam, and theoretical studies found in the literature for halogen radical–halogen molecule exchange reactions

Toward an accurate mass function for precision cosmology

Cosmological surveys aim to use the evolution of the abundance of galaxy clusters to accurately constrain the cosmological model. In the context of LCDM, we show that it is possible to achieve the required percent level accuracy in the halo mass function with gravity-only cosmological simulations, and we provide simulation start and run parameter guidelines for doing so. Some previous works have had sufficient statistical precision, but lacked robust verification of absolute accuracy. Convergence tests of the mass function with, for example, simulation start redshift can exhibit false convergence of the mass function due to counteracting errors, potentially misleading one to infer overly optimistic estimations of simulation accuracy. Percent level accuracy is possible if initial condition particle mapping uses second order Lagrangian Perturbation Theory, and if the start epoch is between 10 and 50 expansion factors before the epoch of halo formation of interest. The mass function for halos with fewer than ~1000 particles is highly sensitive to simulation parameters and start redshift, implying a practical minimum mass resolution limit due to mass discreteness. The narrow range in converged start redshift suggests that it is not presently possible for a single simulation to capture accurately the cluster mass function while also starting early enough to model accurately the numbers of reionisation era galaxies, whose baryon feedback processes may affect later cluster properties. Ultimately, to fully exploit current and future cosmological surveys will require accurate modeling of baryon physics and observable properties, a formidable challenge for which accurate gravity-only simulations are just an initial step.Comment: revised in response to referee suggestions, MNRAS accepte

Testing Theoretical Evolutionary Models with AB Dor C and the Initial Mass Function

We assess the constraints on the evolutionary models of young low-mass objects that are provided by the measurements of the companion AB Dor C by Close and coworkers and by a new comparison of model-derived IMFs of star-forming regions to the well-calibrated IMF of the solar neighborhood. After performing an independent analysis of Close's imaging and spectroscopic data for AB Dor C, we find that AB Dor C is not detected at a significant level (SN 1.2) in the SDI images when one narrow-band image is subtracted from another, but that it does appear in the individual SDI frames as well as the images at JHK. Using the age of 75-150 Myr for AB Dor from Luhman, Stauffer, & Mamajek, the luminosity predicted by the models of Chabrier & Baraffe is consistent with the value that we estimate. We measure a spectral type of M6+/-1 from the K-band spectrum of AB Dor C, which is earlier than the value of M8+/-1 from Close and is consistent with the model predictions when a dwarf temperature scale is adopted. In a test of these models at much younger ages, we show that the low-mass IMFs that they produce for star-forming regions are similar to the IMF of the solar neighborhood. If the masses of the low-mass stars and brown dwarfs in these IMFs of star-forming regions were underestimated by a factor of two as suggested by Close, then the IMF characterizing the current generation of Galactic star formation would have to be radically different from the IMF of the solar neighborhood.Comment: 15 pages, accepted to the Astrophysical Journa