29,769 research outputs found
Single transverse-spin asymmetry in Drell-Yan lepton angular distribution
We calculate a single transverse-spin asymmetry for the Drell-Yan
lepton-pair's angular distribution in perturbative QCD. At leading order in the
strong coupling constant, the asymmetry is expressed in terms of a twist-3
quark-gluon correlation function T_F^{(V)}(x_1,x_2). In our calculation, the
same result was obtained in both light-cone and covariant gauge in QCD, while
keeping explicit electromagnetic current conservation for the virtual photon
that decays into the lepton pair. We also present a numerical estimate of the
asymmetry and compare the result to an existing other prediction.Comment: 15 pages, Revtex, 5 Postscript figures, uses aps.sty, epsfig.st
Surface-mode microcavity
Optical microcavities based on zero-group-velocity surface modes in photonic
crystal slabs are studied. It is shown that high quality factors can be easily
obtained for such microcavities in photonic crystal slabs. With increasing of
the cavity length, the quality factor is gradually enhanced and the resonant
frequency converges to that of the zero-group-velocity surface mode in the
photonic crystal. The number of the resonant modes with high quality factors is
mainly determined by the number of surface modes with zero-group velocity.Comment: 11 pages, 4 figure
Two-tape finite automata with quantum and classical states
{\it Two-way finite automata with quantum and classical states} (2QCFA) were
introduced by Ambainis and Watrous, and {\it two-way two-tape deterministic
finite automata} (2TFA) were introduced by Rabin and Scott. In this paper we
study 2TFA and propose a new computing model called {\it two-way two-tape
finite automata with quantum and classical states} (2TQCFA). First, we give
efficient 2TFA algorithms for recognizing languages which can be recognized by
2QCFA. Second, we give efficient 2TQCFA algorithms to recognize several
languages whose status vis-a-vis 2QCFA have been posed as open questions, such
as . Third, we show that
can be recognized by {\it -tape
deterministic finite automata} (TFA). Finally, we introduce {\it
-tape automata with quantum and classical states} (TQCFA) and prove that
can be recognized by TQCFA.Comment: 25 page
Ion-beam-enhanced adhesion in the electronic stopping region
The use of ion beams in the electronic stopping region to improve the adhesion of insulators to other materials is described. In particular, the bonding of Au films to Teflon, ferrite, and SiO2 was improved by bombarding them with He and Cl, respectively. Improvements in bonding were also observed for Au on glass, Au and Cu on sapphire, and Si3N4 on Si. The mechanism is apparently associated with sputtering and track forming processes occurring in the electronic stopping region. Some applications are discussed
IRIS Observations of the Mg II h & k Lines During a Solar Flare
The bulk of the radiative output of a solar flare is emitted from the
chromosphere, which produces enhancements in the optical and UV continuum, and
in many lines, both optically thick and thin. We have, until very recently,
lacked observations of two of the strongest of these lines: the Mg II h & k
resonance lines. We present a detailed study of the response of these lines to
a solar flare. The spatial and temporal behaviour of the integrated
intensities, k/h line ratios, line of sight velocities, line widths and line
asymmetries were investigated during an M class flare (SOL2014-02-13T01:40).
Very intense, spatially localised energy input at the outer edge of the ribbon
is observed, resulting in redshifts equivalent to velocities of ~15-26km/s,
line broadenings, and a blue asymmetry in the most intense sources. The
characteristic central reversal feature that is ubiquitous in quiet Sun
observations is absent in flaring profiles, indicating that the source function
increases with height during the flare. Despite the absence of the central
reversal feature, the k/h line ratio indicates that the lines remain optically
thick during the flare. Subordinate lines in the Mg II passband are observed to
be in emission in flaring sources, brightening and cooling with similar
timescales to the resonance lines. This work represents a first analysis of
potential diagnostic information of the flaring atmosphere using these lines,
and provides observations to which synthetic spectra from advanced radiative
transfer codes can be compared.Comment: 12 pages, 14 figures, Accepted for publication in Astronomy and
Astrophysic
Mode mixing in asymmetric double trench photonic crystal waveguides
e investigate both experimentally and theoretically the waveguiding
properties of a novel double trench waveguide where a conventional single-mode
strip waveguide is embedded in a two dimensional photonic crystal (PhC) slab
formed in silicon on insulator (SOI) wafers. We demonstrate that the bandwidth
for relatively low-loss (50dB/cm) waveguiding is significantly expanded to
250nm covering almost all the photonic band gap owing to nearly linear
dispersion of the TE-like waveguiding mode. The flat transmission spectrum
however is interrupted by numerous narrow stop bands. We found that these stop
bands can be attributed to anti-crossing between TE-like (positive parity) and
TM-like (negative parity) modes. This effect is a direct result of the strong
asymmetry of the waveguides that have an upper cladding of air and lower
cladding of oxide. To our knowledge this is the first demonstration of the
effects of cladding asymmetry on the transmission characteristics of the PhC
slab waveguides.Comment: 7 pages, 6 figure
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