13,601 research outputs found
Development of nonflammable adhesives Final technical report, 17 Sep. 1968 - 20 Jan. 1970
Development of nonflammable fluorinated polyurethane adhesives for spacecraft system
Theory and Simulation of the diffusion of kinks on dislocations in bcc metals
Isolated kinks on thermally fluctuating (1/2) screw, edge and
(1/2) edge dislocations in bcc iron are simulated under zero stress
conditions using molecular dynamics (MD). Kinks are seen to perform stochastic
motion in a potential landscape that depends on the dislocation character and
geometry, and their motion provides fresh insight into the coupling of
dislocations to a heat bath. The kink formation energy, migration barrier and
friction parameter are deduced from the simulations. A discrete
Frenkel-Kontorova-Langevin (FKL) model is able to reproduce the coarse grained
data from MD at a fraction of the computational cost, without assuming an a
priori temperature dependence beyond the fluctuation-dissipation theorem.
Analytic results reveal that discreteness effects play an essential r\^ole in
thermally activated dislocation glide, revealing the existence of a crucial
intermediate length scale between molecular and dislocation dynamics. The model
is used to investigate dislocation motion under the vanishingly small stress
levels found in the evolution of dislocation microstructures in irradiated
materials
Poly/vinyl ethers/ synthesis for fundamental study of viscoelastic state Final report
Large scale synthesis of amorphous poly/vinyl ethers/ for viscoelastic state stud
A Ring of Warm Dust in the HD 32297 Debris Disk
We report the detection of a ring of warm dust in the edge-on disk
surrounding HD 32297 with the Gemini-N/MICHELLE mid-infrared imager. Our
N'-band image shows elongated structure consistent with the orientation of the
scattered-light disk. The Fnu(11.2 um) = 49.9+/-2.1 mJy flux is significantly
above the 28.2+/-0.6 mJy photosphere. Subtraction of the stellar point spread
function reveals a bilobed structure with peaks 0.5"-0.6" from the star. An
analysis of the stellar component of the SED suggests a spectral type later
than A0, in contrast to commonly cited literature values. We fit
three-dimensional, single-size grain models of an optically thin dust ring to
our image and the SED using a Markov chain Monte Carlo algorithm in a Bayesian
framework. The best-fit effective grain sizes are submicron, suggesting the
same dust population is responsible for the bulk of the scattered light. The
inner boundary of the warm dust is located 0.5"-0.7" (~65 AU) from the star,
which is approximately cospatial with the outer boundary of the scattered-light
asymmetry inward of 0.5". The addition of a separate component of larger,
cooler grains that provide a portion of the 60 um flux improves both the
fidelity of the model fit and consistency with the slopes of the
scattered-light brightness profiles. Previous indirect estimates of the stellar
age (~30 Myr) indicate the dust is composed of debris. The peak vertical
optical depths in our models (~0.3-1 x 1e-2) imply that grain-grain collisions
likely play a significant role in dust dynamics and evolution. Submicron grains
can survive radiation pressure blow-out if they are icy and porous. Similarly,
the inferred warm temperatures (130-200 K) suggest that ice sublimation may
play a role in truncating the inner disk.Comment: ApJ accepted, 8 pages, 4 figure
Laser Fabrication by Using Photonic Crystal
This paper involves the calculation for composition of different layer used in laser structure and the simulation of cavity, formed by creating air columns in the InGaAsP medium, for square lattice. The aim of this project is to fabricate approximately zero threshold current lasers. This project involves FDTD simulation for optimizing dimension of the device, fabrication of laser structure and finally characterization of the device structure.Singapore-MIT Alliance (SMA
Ferromagnetism in substituted zinc oxide
Room-temperature ferromagnetism is observed in (110) oriented ZnO films
containing 5 at % of Sc, Ti, V, Fe, Co or Ni, but not Cr, Mn or Cu ions. There
are large moments, 1.9 and 0.5 muB/atom for Co- and Ti-substituted oxides,
respectively. Sc-substituted ZnO shows also a moment of 0.3 muB/Sc.
Magnetization is very anisotropic, with variations of up to a factor three
depending on the orientation of the applied field relative to the R-cut
sapphire substrates. Results are interpreted in terms of a spin-split donor
impurity band model, which can account for ferromagnetism in insulating or
conducting high-k oxides with concentrations of magnetic ions that lie far
below the percolation threshold. The variation of the ferromagnetism with
oxygen pressure used during film growth is evidence of a link between
ferromagnetism and defect concentration.Comment: 15 pages, 4 figure
Conceptualisations of children’s wellbeing at school: the contribution of recognition theory
A large study in Australian schools aimed to elucidate understandings of ‘wellbeing’ and of factors in school life that contribute to it. Students and teachers understood wellbeing primarily, and holistically, in terms of interpersonal relationships, in contrast to policy documents which mainly focused on ‘problem areas’ such as mental health. The study also drew on recognition theory as developed by the social philosopher Axel Honneth. Results indicate that recognition theory may be useful in understanding wellbeing in schools, and that empirical research in schools may give rise to further questions regarding theory
Doubly Special Relativity with a minimum speed and the Uncertainty Principle
The present work aims to search for an implementation of a new symmetry in
the space-time by introducing the idea of an invariant minimum speed scale
(). Such a lowest limit , being unattainable by the particles, represents
a fundamental and preferred reference frame connected to a universal background
field (a vacuum energy) that breaks Lorentz symmetry. So there emerges a new
principle of symmetry in the space-time at the subatomic level for very low
energies close to the background frame (), providing a fundamental
understanding for the uncertainty principle, i.e., the uncertainty relations
should emerge from the space-time with an invariant minimum speed.Comment: 10 pages, 8 figures, Correlated paper in:
http://www.worldscientific.com/worldscinet/ijmpd?journalTabs=read. arXiv
admin note: substantial text overlap with arXiv:physics/0702095,
arXiv:0705.4315, arXiv:0709.1727, arXiv:0805.120
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