1,710 research outputs found
Analysis of longitudinal bunching inan FEL driven two-beam accelerator
Recent experiments [1] have explored the use of a free-electron laser (FEL)
as a buncher for a microwave two-beam accelerator, and the subsequent driving
of a standing-wave rf output cavity. Here we present a deeper analysis of the
longitudinal dynamics of the electron bunches as they are transported from the
end of the FEL and through the output cavity. In particular, we examine the
effect of the transport region and cavity aperture to filter the bunched
portion of the beam.
[1] T. Lefevre, et. al., Phys. Rev. Lett. 84 (2000), 1188.Comment: 3 pages, 8 figures. Submitted to XX Int'l LINAC Conferenc
Transverse momentum dependence of the angular distribution of the Drell-Yan process
We calculate the transverse momentum Q_{\perp} dependence of the helicity
structure functions for the hadroproduction of a massive pair of leptons with
pair invariant mass Q. These structure functions determine the angular
distribution of the leptons in the pair rest frame. Unphysical behavior in the
region Q_{\perp} --> 0 is seen in the results of calculations done at
fixed-order in QCD perturbation theory. We use current conservation to
demonstrate that the unphysical inverse-power and \ln(Q/Q_{\perp}) logarithmic
divergences in three of the four independent helicity structure functions share
the same origin as the divergent terms in fixed-order calculations of the
angular-integrated cross section. We show that the resummation of these
divergences to all orders in the strong coupling strength \alpha_s can be
reduced to the solved problem of the resummation of the divergences in the
angular-integrated cross section, resulting in well-behaved predictions in the
small Q_{\perp} region. Among other results, we show the resummed part of the
helicity structure functions preserves the Lam-Tung relation between the
longitudinal and double spin-flip structure functions as a function of
Q_{\perp} to all orders in \alpha_s.Comment: 18 pages, 4 figures; typos corrected, references updated, a few
clarifications recommended by the referee. Paper accepted for publication in
Physical Review
Mott-Superfluid transition in bosonic ladders
We show that in a commensurate bosonic ladder, a quantum phase transition
occurs between a Mott insulator and a superfluid when interchain hopping
increases. We analyse the properties of such a transition as well as the
physical properties of the two phases. We discuss the physical consequences for
experimental systems such as Josephson Junction arrays.Comment: 4 pages, 2 figures, revtex
Effect of pressure on the Raman modes of antimony
The effect of pressure on the zone-center optical phonon modes of antimony in
the A7 structure has been investigated by Raman spectroscopy. The A_g and E_g
frequencies exhibit a pronounced softening with increasing pressure, the effect
being related to a gradual suppression of the Peierls-like distortion of the A7
phase relative to a cubic primitive lattice. Also, both Raman modes broaden
significantly under pressure. Spectra taken at low temperature indicate that
the broadening is at least partly caused by phonon-phonon interactions. We also
report results of ab initio frozen-phonon calculations of the A_g and E_g mode
frequencies. Presence of strong anharmonicity is clearly apparent in calculated
total energy versus atom displacement relations. Pronounced nonlinearities in
the force versus displacement relations are observed. Structural instabilities
of the Sb-A7 phase are briefly addressed in the Appendix.Comment: 10 pages, 8 figure
Mean Antarctic Circumpolar Current Transport Measured in Drake Passage
The Antarctic Circumpolar Current is an important component of the global climate system connecting the major ocean basins as it flows eastward around Antarctica, yet due to the paucity of data it remains unclear how much water is transported by the current. Between 2007 and 2011 flow through Drake Passage was continuously monitored with a line of moored instrumentation with unprecedented horizontal and temporal resolution. Annual mean near-bottom currents are remarkably stable from year to year. The mean depth-independent, or barotropic transport, determined from the near-bottom current meter records was 45.6 Sv with an uncertainty of 8.9 Sv. Summing the mean barotropic transport with the mean baroclinic transport relative to zero at the seafloor of 127.7 Sv gives a total transport through Drake Passage of 173.3 Sv. This new measurement is 30% larger than the canonical value often used as the benchmark for global circulation and climate models.Fil: Donohue, K. A.. University Of Rhode Island; Estados UnidosFil: Tracey, K. L.. University Of Rhode Island; Estados UnidosFil: Watts, D. R.. University Of Rhode Island; Estados UnidosFil: Chidichimo, María Paz. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Ministerio de Defensa. Armada Argentina. Servicio de Hidrografía Naval; Argentina. Universidad de Buenos Aires; ArgentinaFil: Chereskin, T. K.. University of California at San Diego. Scripps Institution of Oceanography; Estados Unido
Intrinsic transverse momentum and the polarized Drell-Yan process
In this paper we study the cross section at leading order in for
polarized Drell-Yan scattering at measured lepton-pair transverse momentum
. We find that for a hadron with spin the quark content at leading
order is described by six distribution functions for each flavor, which depend
on both the lightcone momentum fraction , and the quark transverse momentum
\bbox{k}_T^2. These functions are illustrated for a free-quark ensemble. The
cross sections for both longitudinal and transverse polarizations are expressed
in terms of convolution integrals over the distribution functions.Comment: 25 pages, REVTEX 3.0 (3 figures included in separate LATEX file using
feynman.tex), NIKHEF-94-P1 (Revised version
Impact testing to determine the mechanical properties of articular cartilage in isolation and on bone
The original publication is available at www.springerlink.comNon peer reviewedPostprin
Structure functions in the polarized Drell-Yan processes with spin-1/2 and spin-1 hadrons: II. parton model
We analyze the polarized Drell-Yan processes with spin-1/2 and spin-1 hadrons
in a parton model. Quark and antiquark correlation functions are expressed in
terms of possible combinations of Lorentz vectors and pseudovectors with the
constrains of Hermiticity, parity conservation, and time-reversal invariance.
Then, we find tensor polarized distributions for a spin-1 hadron. The naive
parton model predicts that there exist 19 structure functions. However, there
are only four or five non-vanishing structure functions, depending on whether
the cross section is integrated over the virtual-photon transverse momentum
\vec Q_T or the limit Q_T->0 is taken. One of the finite structure functions is
related to the tensor polarized distribution b_1, and it does not exist in the
proton-proton reactions. The vanishing structure functions should be associated
with higher-twist physics. The tensor distributions can be measured by the
quadrupole polarization measurements. The Drell-Yan process has an advantage
over the lepton reaction in the sense that the antiquark tensor polarization
could be extracted rather easily.Comment: 27 pages, REVTeX, amsmath.sty, epsfig.sty, revtex.cls, 2 eps figures.
Phys. Rev. D in press. Complete postscript file is available at
http://www2.cc.saga-u.ac.jp/saga-u/riko/physics/quantum1/structure.html
Email: [email protected], [email protected]
Boron in copper: a perfect misfit in the bulk and cohesion enhancer at a grain boundary
Our ab initio study suggests that boron segregation to the Sigma 5(310)[001]
grain boundary should strengthen the boundary up to 1.5 ML coverage (15.24
at/nm^2). The maximal effect is observed at 0.5 ML and corresponds to boron
atoms filling exclusively grain boundary interstices. In copper bulk, B causes
significant distortion both in interstitial and regular lattice sites for which
boron atoms are either too big or too small. The distortion is compensated to
large extent when the interstitial and substitutional boron combine together to
form a strongly bound dumbell. Our prediction is that bound boron impurities
should appear in sizable proportion if not dominate in most experimental
conditions. A large discrepancy between calculated heats of solution and
experimental terminal solubility of B in Cu is found, indicating either a sound
failure of the local density approximation or, more likely, strongly
overestimated solubility limits in the existing B-Cu phase diagram.Comment: 16 pages, 9 figure
Temperature-dependent Raman spectroscopy in BaRuO systems
We investigated the temperature-dependence of the Raman spectra of a
nine-layer BaRuO single crystal and a four-layer BaRuO epitaxial film,
which show pseudogap formations in their metallic states. From the polarized
and depolarized spectra, the observed phonon modes are assigned properly
according to the predictions of group theory analysis. In both compounds, with
decreasing temperature, while modes show a strong hardening, (or
) modes experience a softening or no significant shift. Their different
temperature-dependent behaviors could be related to a direct Ru metal-bonding
through the face-sharing of RuO. It is also observed that another
mode of the oxygen participating in the face-sharing becomes split at low
temperatures in the four layer BaRuO. And, the temperature-dependence of
the Raman continua between 250 600 cm is strongly correlated to
the square of the plasma frequency. Our observations imply that there should be
a structural instability in the face-shared structure, which could be closely
related to the pseudogap formation of BaRuO systems.Comment: 8 pages, 6 figures. to be published in Phys. Rev.
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