17,428 research outputs found

### Diffractive Phenomena at Tevatron

Preliminary results from the D0 experiment on jet production with rapidity
gaps in $p\bar{p}$ collisions are presented. A class of dijet events with a
forward rapidity gap is observed at center-of-mass energies $\sqrt{s}$ = 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

### 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

### Distributed Approximation Algorithms for Weighted Shortest Paths

A distributed network is modeled by a graph having $n$ nodes (processors) and
diameter $D$. We study the time complexity of approximating {\em weighted}
(undirected) shortest paths on distributed networks with a $O(\log n)$ {\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
$O(n)$-time Bellman-Ford algorithm and an $\tilde O(n^{1/2+1/2k}+D)$-time
$(8k\lceil \log (k+1) \rceil -1)$-approximation algorithm, for any integer
$k\geq 1$, 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
$\tilde O(\cdot)$ to hide the O(\poly\log n) term.) We present an $\tilde
O(n^{1/2}D^{1/4}+D)$-time $(1+o(1))$-approximation algorithm for \sssp. This
algorithm is {\em sublinear-time} as long as $D$ is sublinear, thus yielding a
sublinear-time algorithm with almost optimal solution. When $D$ is small, our
running time matches the lower bound of $\tilde \Omega(n^{1/2}+D)$ by Das Sarma
et al. (SICOMP 2012), which holds even when $D=\Theta(\log n)$, 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
Internationa

### Isothermal and cyclic oxidation at 1000 and 1100 deg C of four nickel-base alloys: NASA-TRW VIA, B-1900, 713C, and 738X

The isothermal and cyclic oxidation resistance of four cast Ni-base gamma + gamma prime alloys, NASA-TRW Via, B-1900, 713C, and 738X, was determined in still air at 1000 and 1100 C. The oxidation process was evaluated by specific sample weight change with time, sample thickness change, X-ray diffraction of the scales, and sample metallography. The behavior is discussed in terms of the Cr, Al, and refractory metal contents of the alloys

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