We use the eight year light curve database from the MACHO (MAssive Compact Halo Objects) project together with infrared colors and magnitudes from 2MASS (the Two Micron All Sky Survey) to identify a sample of 22,000 long period variables in the Large Magellanic Cloud (referred to hereafter as LMC LPVs). A period luminosity diagram of these stars reveals six well defined sequences, in substantial agreement with previous analyses of samples from OGLE (Optical Gravitational Lensing Experiment). In our analysis we identify analogues to galactic LPVs in the LMC LPV sample. We find that carbon dominated AGB stars populate only two of the sequences, one of which includes the Mira variables. The high luminosity end of the same two sequences are also the location of the only stars with J K{sub s} > 2, indicating that they are enshrouded in dust. The unknown mechanism that produces the variability of the last sequence--those stars with long secondary periods--produces different morphology in the period luminosity diagram than what is seen in the first four sequences, which are thought to be caused by pulsation. In particular, the last sequence extends to lower luminosity RGB stars and the luminosity function does not peak among the …

Unlike the common belief that crack propagation behavior can be predicted successfully by employing fracture criteria based on a constant crack tip opening displacement or angle (CTOD/CTOA), this paper shows that the initially non-constant portion of the CTOD/CTOA plays an essential role in predicting the fracture load for a growing crack. Three- and two-dimensional finite element analyses indicate that a severe underestimate of the experimental load vs. crack extension curve would occur if a constant CTOD/CTOA criterion is used. However, the use of a simplified, bilinear CTOD/CTOA criterion including its non-constant portion will closely duplicate the test data. Furthermore, as a result of using the experimental data from J-integral test with various crack length to specimen width ratios (a/W), it is demonstrated that the CTOD/CTOA is crack tip constraint dependent. The initially higher values of the CTOD/CTOA are in fact a natural consequence of crack growth process which is refl ected by the J-resistance curve and its slope (tearing modulus).

Ultra-wideband (UWB) technology has proven to be useful in short range, high data rate, robust, and low power communications. These features can make UWB systems ideal candidates for reliable data communications between nodes of a wireless sensor network (WSN). However, the low powered UWB pulses can be significantly degraded by channel noise, inter-node interference, and intentional jamming. In this paper we present a novel interference suppression technique for UWB based WSNs that promises self-organization in terms of power conservation, scalability, and channel estimation for the entire distributed network.

Raman spectroscopy has been used to study fluid water at approximately 1000 K and 2 to 60 GPa in a laser heated diamond anvil cell. First principles molecular dynamics (MD) simulations have also been employed to simulate water under similar conditions. The experimental Raman intensity of the O-H stretch mode was observed to decrease with pressure, and beyond 50 GPa this mode was no longer visible. At approximately the same pressure we inferred a change in the slope of the melting curve. Consistent with these experimental observations, the MD simulations show that water under these conditions forms a dynamically ionized liquid state, which is dominated by very short lived (<10 fs) H{sub 2}O, H{sub 3}O{sup +} and O{sup 2-} species.

Gas desorption and electron emission coefficients were measured for 1 MeV potassium ions incident on stainless steel at grazing angles (between 80 and 88 from normal incidence) using a new gas-electron source diagnostic (GESD). Issues addressed in design and commissioning of the GESD include effects from backscattering of ions at the surface, space-charge limited emission current, and reproducibility of desorption measurements. We find that electron emission coefficients {gamma}{sub e} scale as 1/cos({theta}) up to angles of 86, where {gamma}{sub e} = 90. Nearer grazing incidence, {gamma}{sub e} is reduced below the 1/cos({theta}) scaling by nuclear scattering of ions through large angles, reaching {gamma}{sub e} = 135 at 88. Electrons were emitted with a measured temperature of {approx}30 eV. Gas desorption coefficients {gamma}{sub sigma} were much larger, of order {gamma}{sub sigma} = 104. They also varied with angle, but much more slowly than 1/cos({theta}). From this we conclude that the desorption was not entirely from adsorbed layers of gas on the surface. Two mitigation techniques were investigated: rough surfaces reduced electron emission by a factor of ten and gas desorption by a factor of two; a mild bake to 230 had no effect on electron emission, but decreased gas desorption by …

The interaction of water with Si- and C- terminated {beta}-SiC(001) surfaces was investigated by means of ab initio molecular dynamics simulations. Irrespective of coverage, varied from 1/4 to 1 monolayer, we found that water dissociates on the Si-terminated surface, substantially modifying the clean surface reconstruction, while the C-terminated surface is nonreactive and hydrophobic. Based on our results, we propose that STM images and photoemission experiments may detect specific changes induced by water on both the structural and electronic properties of SiC(001) surfaces.