230,630 research outputs found
Effect of Plasma Irradiation on films
The effect of plasma irradiation is studied systematically on a 4H polytype
(002) oriented stoichiometric film having compressive residual
stress. Plasma irradiation was found to change the orientation to (110) of the
film at certain moderate irradiation distances. A linear decrease in grain size
and residual stress was observed with decreasing irradiation distance (or
increasing ion energy) consistent with both structural and morphological
observations. The direct optical energy gap was found to increase
linearly at the rate with the compressive stress. The
combined data of present compressive stress and from earlier reported tensile
stress show a consistent trend of change with stress. The
iodine-iodine distance in the unit cell could be responsible for the observed
change in with stress.Comment: 13 pages and 10 fi
Phononic Rogue Waves
We present a theoretical study of extreme events occurring in phononic
lattices. In particular, we focus on the formation of rogue or freak waves,
which are characterized by their localization in both spatial and temporal
domains. We consider two examples. The first one is the prototypical nonlinear
mass-spring system in the form of a homogeneous Fermi-Pasta-Ulam-Tsingou (FPUT)
lattice with a polynomial potential. By deriving an approximation based on the
nonlinear Schroedinger (NLS) equation, we are able to initialize the FPUT model
using a suitably transformed Peregrine soliton solution of the NLS, obtaining
dynamics that resembles a rogue wave on the FPUT lattice. We also show that
Gaussian initial data can lead to dynamics featuring rogue wave for
sufficiently wide Gaussians. The second example is a diatomic granular crystal
exhibiting rogue wave like dynamics, which we also obtain through an NLS
reduction and numerical simulations. The granular crystal (a chain of particles
that interact elastically) is a widely studied system that lends itself to
experimental studies. This study serves to illustrate the potential of such
dynamical lattices towards the experimental observation of acoustic rogue
waves.Comment: 9 pages, 4 figure
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Life in polar impact-shocked rocks — an analog for micro-habitats at the Martian poles
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Simple devices for concentration of microbial life: Experiments in Haughton impact structure
Simple devices that create environments with high levels of light and moisture could attract extant microbial life on a planetary surface and hence enhance the detection of it. Experience in the Haughton crater shows that this can occur readily
Structure and chemistry of Orion S
We present interferometric observations of the SiO J = 2-1, H^(13)CO^+ J = 1-0, HC_3N J = 11-10, CH_3OH J_K = 2_0-1_0, and SO_2 J(K_pK_0) = 8_(17)-8_(08) transitions along with the λ = 3.1 mm continuum toward the young stellar object Orion S. The HC_3N and H^(13)CO^+ emission trace similar spatial and velocity distributions which are extended and follow the Orion molecular ridge. The SiO emission is more spatially confined, peaking to the west of the λ = 3.1 mm continuum source, while the CH_3OH emission peaks to the southwest. Weak SO_2 emission was detected southeast of the continuum source position. Column densities and fractional abundances are derived for each species at different positions in the region. In general, the molecular abundances near the continuum source are similar to those in the quiescent material near IRc 2, but the abundances decrease toward the continuum source position indicating localized depletions of at least a factor of three. The presence of strong SiO emission with much weaker SO_2 emission is interpreted as resulting from high-velocity shock interactions between the outflow from Orion S and the surrounding cloud. The apparent molecular depletions directly toward Orion S, and the similarity of
abundances between the Orion S region and quiescent ridge material, suggest that Orion S is at an early stage
of chemical evolution, prior to when substantial chemical differentiation occurs
Critical behavior of the three- and ten-state short-range Potts glass: A Monte Carlo study
We study the critical behavior of the short-range p-state Potts spin glass in
three and four dimensions using Monte Carlo simulations. In three dimensions,
for p = 3, a finite-size scaling analysis of the correlation length shows clear
evidence of a transition to a spin-glass phase at T_c = 0.273(5) for a Gaussian
distribution of interactions and T_c = 0.377(5) for a bimodal distribution.
These results indicate that the lower critical dimension of the 3-state Potts
glass is below three. By contrast, the correlation length of the ten-state (p =
10) Potts glass in three dimensions remains small even at very low temperatures
and thus shows no sign of a transition. In four dimensions we find that the p =
3 Potts glass with Gaussian interactions has a spin-glass transition at T_c
=0.536(3).Comment: 11 pages, 13 figures, 6 table
Computational structures for robotic computations
The computational problem of inverse kinematics and inverse dynamics of robot manipulators by taking advantage of parallelism and pipelining architectures is discussed. For the computation of inverse kinematic position solution, a maximum pipelined CORDIC architecture has been designed based on a functional decomposition of the closed-form joint equations. For the inverse dynamics computation, an efficient p-fold parallel algorithm to overcome the recurrence problem of the Newton-Euler equations of motion to achieve the time lower bound of O(log sub 2 n) has also been developed
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Microbial preservation in sulfates in the Haughton impact structure suggests target in search for life on Mars
Microbes occur within transparent gypsum crystals in the Haughton crater. The crystals transmit light for photosynthesis, but protect from dehydration and wind. Sulfates on the Martian surface should be a priority target in the search for life
Bose-Einstein Condensation Temperature of a Homogeneous Weakly Interacting Bose Gas : PIMC study
Using a finite-temperature Path Integral Monte Carlo simulation (PIMC) method
and finite-size scaling, we have investigated the interaction-induced shift of
the phase transition temperature for Bose-Einstein condensation of homogeneous
weakly interacting Bose gases in three dimensions, which is given by a proposed
analytical expression , where
is the critical temperature for an ideal gas, is the s-wave
scattering length, and is the number density. We have used smaller number
densities and more time slices than in the previous PIMC simulations [Gruter
{\it et al.}, Phys. Rev. Lett. {\bf 79}, 3549 (1997)] in order to understand
the difference in the value of the coefficient between their results
and the (apparently) other reliable results in the literature. Our results show
that depends strongly on the
interaction strength while the previous PIMC results are
considerably flatter and smaller than our results. We obtain = 1.32
0.14, in agreement with results from recent Monte Carlo methods of
three-dimensional O(2) scalar field theory and variational
perturbation theory
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