A dynamical model for the dusty ring in the Coalsack

Lada et al. recently presented a detailed near-infrared extinction map of Globule G2 in the Coalsack molecular cloud complex, showing that this starless core has a well-defined central extinction minimum. We propose a model for G2 in which a rapid increase in external pressure is driving an approximately symmetric compression wave into the core. The rapid increase in external pressure could arise because the core has recently been assimilated by the Coalsack cloud complex, or because the Coalsack has recently been created by two large-scale converging flows. The resulting compression wave has not yet converged on the centre of the core, so there is a central rarefaction. The compression wave has increased the density in the swept-up gas by about a factor of ten, and accelerated it inwards to speeds of order $0.4 {\rm km} {\rm s}^{-1}$. It is shown that even small levels of initial turbulence destroy the ring seen in projection almost completely. In the scenario of strong external compression that we are proposing this implies that the initial turbulent energy in this globule is such that $E_{{\rm turb}} / E_{{\rm grav}} \le 2$. Protostar formation should occur in about $40,000 {\rm years}$.Comment: Accepted for publication in A&

Why is CDMA the solution for mobile satellite communication

It is demonstrated that spread spectrum Code Division Multiple Access (CDMA) systems provide an economically superior solution to satellite mobile communications by increasing the system maximum capacity with respect to single channel per carrier Frequency Division Multiple Access (FDMA) systems. Following the comparative analysis of CDMA and FDMA systems, the design of a model that was developed to test the feasibility of the approach and the performance of a spread spectrum system in a mobile environment. Results of extensive computer simulations as well as laboratory and field tests results are presented

Nonlinear Effects in Squeeze Film Gas Damping on Microbeams

We consider squeeze film gas damping during microbeam motion away and toward a substrate as occurs during opening and closing of RF switches and other MEMS devices. The numerical solution of the gas damping problem in two-dimensional geometries is obtained based on the Boltzmann-ESBGK equation. The difference in damping force between downward and upward moving beams is shown to vary from as little from as 5% for low beam velocities of 0.1m/s to more than 200% at 2.4m/s. For a constant velocity magnitude of 0.8m/s, this difference increases from 60% to almost 90% when the pressure is reduced by an order of magnitude. The numerical simulations are consistent with earlier observations of a significantly higher damping force during the closing of a capacitive RF MEMS switch reported by Steeneken et al. (JMM, 15, 176-184, 2005). The physical mechanism leading to this non-linear dependence of the damping force on velocity has been attributed to the differences in the flow rarefaction regime for the gas in the microgap

New Horizons: Long-Range Kuiper Belt Targets Observed by the Hubble Space Telescope

We report on Hubble Space Telescope (HST) observations of three Kuiper Belt Objects (KBOs), discovered in our dedicated ground-based search campaign, that are candidates for long-range observations from the New Horizons spacecraft: 2011 JY31, 2011 HZ102, and 2013 LU35. Astrometry with HST enables both current and future critical accuracy improvements for orbit precision, required for possible New Horizons observations, beyond what can be obtained from the ground. Photometric colors of all three objects are red, typical of the Cold Classical dynamical population within which they reside; they are also the faintest KBOs to have had their colors measured. None are observed to be binary with HST above separations of ~0.02 arcsec (~700 km at 44 AU) and {\Delta}m less than or equal to 0.5.Comment: Pages: 11, Figures: 2, Tables: 3, Icarus, available online May 2014 (http://dx.doi.org/10.1016/j.icarus.2014.04.014