21,041 research outputs found
Diffractive Phenomena at Tevatron
Preliminary results from the D0 experiment on jet production with rapidity
gaps in collisions are presented. A class of dijet events with a
forward rapidity gap is observed at center-of-mass energies = 1800
GeV and 630 GeV. The number of events with rapidity gaps at both center-of-mass
energies is significantly greater than the expectation from multiplicity
fluctuations and is consistent with a hard single diffractive process. A class
of events with two forward gaps and central dijets are also observed at 1800
GeV. This topology is consistent with hard double pomeron exchange. We also
present proposed plans for extending these analysis into Run II through the use
of a forward proton detector.Comment: plain tex, 5 pages, 2 figure
Microscopic theory of vibronic dynamics in linear polyenes
We propose a novel approach to calculate dynamical processes at ultrafast
time scale in molecules in which vibrational and electronic motions are
strongly mixed. The relevant electronic orbitals and their interactions are
described by a Hubbard model, while electron-phonon interaction terms account
for the bond length dependence of the hopping and the change in ionic radii
with valence charge. The latter term plays a crucial role in the non-adiabatic
internal conversion process of the molecule. The time resolved photoelectron
spectra are in good qualitative agreement with experiments.Comment: 3 figures, other comment
Determination of convective diffusion heat/mass transfer rates to burner rig test targets comparable in size to cross-stream jet diameter
Two sets of experiments have been performed to be able to predict the convective diffusion heat/mass transfer rates to a cylindrical target whose height and diameter are comparable to, but less than, the diameter of the circular cross-stream jet, thereby simulating the same geometric configuration as a typical burner rig test specimen located in the cross-stream of the combustor exit nozzle. The first set exploits the naphthalene sublimation technique to determine the heat/mass transfer coefficient under isothermal conditions for various flow rates (Reynolds numbers). The second set, conducted at various combustion temperatures and Reynolds numbers, utilized the temperature variation along the surface of the above-mentioned target under steady-state conditions to estimate the effect of cooling (dilution) due to the entrainment of stagnant room temperature air. The experimental information obtained is used to predict high temperature, high velocity corrosive salt vapor deposition rates in burner rigs on collectors that are geometrically the same. The agreement with preliminary data obtained from Na2SO4 vapor deposition experiments is found to be excellent
Hot corrosion resistance of nickel-chromium-aluminum alloys
The hot corrosion resistance of nickel-chromium-aluminum alloy was examined by cyclically oxidizing sodium sulfate coated specimens in still air at 900, 1000 and 1100 C. The compositions tested were within the ternary region: Ni; Ni-50 at.% Cr; and Ni-50 at.% Al. At each temperature the corrosion data were statistically fitted to a third order regression equation as a function of chromium and aluminum contents. Corrosion isopleths were prepared from these equations. Compositional regions with the best hot corrosion resistance were identified
Minor salivary gland sialolithiasis: a clinical diagnostic challenge
Sialolithiasis is a non-neoplastic salivary gland disease that rarely affects the minor salivary glands. There are no guidelines in the literature which can suggest which is the best surgical approach to treat Minor Salivary Glands Sialolithiasis (MSGL). The present case was of a 48-year-old male patient complaining of painful swelling localized in the left back-commissural zone which was 0.5 mm in diameter, for which surgical enucleation approach was done and in that some small calcific masses ranging from 0.2 to 4 mm in diameter were found. They were surrounded by granulation tissue and associated with small pus oozing. Histopathological examination was carried out leading to a final diagnosis of MSGL
Experimental verification of corrosive vapor deposition rate theory in high velocity burner rigs
The ability to predict deposition rates is required to facilitate modelling of high temperature corrosion by fused salt condensates in turbine engines. A corrosive salt vapor deposition theory based on multicomponent chemically frozen boundary layers (CFBL) has been successfully verified by high velocity burner rig experiments. The experiments involved internally air-impingement cooled, both rotating full and stationary segmented cylindrical collectors located in the crossflow of sodium-seeded combustion gases. Excellent agreement is found between the CFBL theory an the experimental measurements for both the absolute amounts of Na2SO4 deposition rates and the behavior of deposition rate with respect to collector temperature, mass flowrate (velocity) and Na concentration
Distributed Approximation Algorithms for Weighted Shortest Paths
A distributed network is modeled by a graph having nodes (processors) and
diameter . We study the time complexity of approximating {\em weighted}
(undirected) shortest paths on distributed networks with a {\em
bandwidth restriction} on edges (the standard synchronous \congest model). The
question whether approximation algorithms help speed up the shortest paths
(more precisely distance computation) was raised since at least 2004 by Elkin
(SIGACT News 2004). The unweighted case of this problem is well-understood
while its weighted counterpart is fundamental problem in the area of
distributed approximation algorithms and remains widely open. We present new
algorithms for computing both single-source shortest paths (\sssp) and
all-pairs shortest paths (\apsp) in the weighted case.
Our main result is an algorithm for \sssp. Previous results are the classic
-time Bellman-Ford algorithm and an -time
-approximation algorithm, for any integer
, which follows from the result of Lenzen and Patt-Shamir (STOC 2013).
(Note that Lenzen and Patt-Shamir in fact solve a harder problem, and we use
to hide the O(\poly\log n) term.) We present an -time -approximation algorithm for \sssp. This
algorithm is {\em sublinear-time} as long as is sublinear, thus yielding a
sublinear-time algorithm with almost optimal solution. When is small, our
running time matches the lower bound of by Das Sarma
et al. (SICOMP 2012), which holds even when , up to a
\poly\log n factor.Comment: Full version of STOC 201
Faster annealing schedules for quantum annealing
New annealing schedules for quantum annealing are proposed based on the
adiabatic theorem. These schedules exhibit faster decrease of the excitation
probability than a linear schedule. To derive this conclusion, the asymptotic
form of the excitation probability for quantum annealing is explicitly obtained
in the limit of long annealing time. Its first-order term, which is inversely
proportional to the square of the annealing time, is shown to be determined
only by the information at the initial and final times. Our annealing schedules
make it possible to drop this term, thus leading to a higher order (smaller)
excitation probability. We verify these results by solving numerically the
time-dependent Schrodinger equation for small size systemsComment: 10 pages, 5 figures, minor correction
Lubricated friction between incommensurate substrates
This paper is part of a study of the frictional dynamics of a confined solid
lubricant film - modelled as a one-dimensional chain of interacting particles
confined between two ideally incommensurate substrates, one of which is driven
relative to the other through an attached spring moving at constant velocity.
This model system is characterized by three inherent length scales; depending
on the precise choice of incommensurability among them it displays a strikingly
different tribological behavior. Contrary to two length-scale systems such as
the standard Frenkel-Kontorova (FK) model, for large chain stiffness one finds
that here the most favorable (lowest friction) sliding regime is achieved by
chain-substrate incommensurabilities belonging to the class of non-quadratic
irrational numbers (e.g., the spiral mean). The well-known golden mean
(quadratic) incommensurability which slides best in the standard FK model shows
instead higher kinetic-friction values. The underlying reason lies in the
pinning properties of the lattice of solitons formed by the chain with the
substrate having the closest periodicity, with the other slider.Comment: 14 pagine latex - elsart, including 4 figures, submitted to Tribology
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