32,568 research outputs found
Metal drilling with portable hand drills
Study of metal drilling solves problems of excessive burring, oversized holes, and out-of-round holes. Recommendations deal with using the proper chemical coolants, applying the coolants effectively, employing cutting oils, and dissipating the heat caused by drilling
SNAP-8 refractory boiler development. Topical report 3 - Evaluation of SNAP-8, SN-1 boiler
Performance tests of SNAP-8 boile
Compatibility of columbium base alloys with lithium fluoride
Thermal cycling tests of lithium fluoride compatibility with columbium base alloy
Study of Chromium-Frit-Type Coatings for High-Temperature Protection of Molybdenum
The achievement of more compact and efficient power plants for aircraft is dependent, among other factors, on the perfection of heat-resisting materials that are superior to those in current use. Molybdenum is one of the high-melting metals (melting point, 4750 F). It is fairly abundant and also can be worked into many of the shapes required in modern power plants. To permit its widespread use at elevated temperatures, however, some means must first be found to prevent its rapid oxidation. The application of a protective coating is one method that might be used to achieve this goal. In the present work, a number of chromium-frit-type coatings were studied. These were bonded to molybdenum specimens by firing in controlled atmospheres to temperatures in the range of 2400 to 2700 F
Quantum interference in deformed carbon nanotube waveguides
Quantum interference (QI) in two types of deformed carbon nanotubes (CNTs),
i.e., axially stretched and AFM tip-deformed CNTs, has been investigated by the
pi-electron only and four-orbital tight-binding (TB) method. It is found that
the rapid conductance oscillation (RCO) period is very sensitive to the applied
strains, and decreases in an inverse proportion to the deformation degree,
which could be used as a powerful experimental tool to detect precisely the
deformation degree of the deformed CNTs. Also, the sigma-pi coupling effect is
found to be negligible under axially stretched strain, while it works on the
transport properties of the tip-deformed CNTs.Comment: 14 pages and 5 figure
Absence of Hybridization Gap in Heavy Electron Systems and Analysis of YbAl3 in terms of Nearly Free Electron Conduction Band
In the analysis of the heavy electron systems, theoretical models with c-f
hybridization gap are often used. We point out that such a gap does not exist
and the simple picture with the hybridization gap is misleading in the metallic
systems, and present a correct picture by explicitly constructing an effective
band model of YbAl_3. Hamiltonian consists of a nearly free electron model for
conduction bands which hybridize with localized f-electrons, and includes only
a few parameters. Density of states, Sommerfeld coefficient, f-electron number
and optical conductivity are calculated and compared with the band calculations
and the experiments.Comment: 9 pages, 9 figures, submitted to J. Phys. Soc. Jp
Modeling of gas adsorption on graphene nanoribbons
We present a theory to study gas molecules adsorption on armchair graphene
nanoribbons (AGNRs) by applying the results of \emph{ab} \emph{initio}
calculations to the single-band tight-binding approximation. In addition, the
effect of edge states on the electronic properties of AGNR is included in the
calculations. Under the assumption that the gas molecules adsorb on the ribbon
sites with uniform probability distribution, the applicability of the method is
examined for finite concentrations of adsorption of several simple gas
molecules (CO, NO, CO, NH) on 10-AGNR. We show that the states
contributed by the adsorbed CO and NO molecules are quite localized near the
center of original band gap and suggest that the charge transport in such
systems cannot be enhanced considerably, while CO and NH molecules
adsorption acts as acceptor and donor, respectively. The results of this theory
at low gas concentration are in good agreement with those obtained by
density-functional theory calculations.Comment: 7 pages, 6 figure
Testing Lorentz invariance by use of vacuum and matter filled cavity resonators
We consider tests of Lorentz invariance for the photon and fermion sector
that use vacuum and matter-filled cavities. Assumptions on the wave-function of
the electrons in crystals are eliminated from the underlying theory and
accurate sensitivity coefficients (including some exceptionally large ones) are
calculated for various materials. We derive the Lorentz-violating shift in the
index of refraction n, which leads to additional sensitivity for matter-filled
cavities ; and to birefringence in initially isotropic media. Using published
experimental data, we obtain improved bounds on Lorentz violation for photons
and electrons at levels of 10^-15 and below. We discuss implications for future
experiments and propose a new Michelson-Morley type experiment based on
birefringence in matter.Comment: 15 pages, 8 table
Polaron Induced Deformations in Carbon Nanotubes
We compute for the first time full elastic deformations, as well as length,
of self-trapped electronic states in carbon nanotubes of general radius and
chirality, within the unifying framework of a recently introduced two field
model for electromechanics of carbon nano-structures. We find that deformations
are highly non monotonic in the chiral angle, whereas the length of the polaron
is not. Applications include nano-mechanical devices as electrically or
optically driven nano-actuators.Comment: 4 Pages, 1 Figure Phys Rev B Brief Repor
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