30,593 research outputs found
Spacecraft Dynamics as Related to Laboratory Experiments in Space
Proceedings are presented of a conference sponsored by the Physics and Chemistry Experiments in Space Working Group to discuss the scientific and engineering aspects involved in the design and performance of reduced to zero gravity experiments affected by spacecraft environments and dynamics. The dynamics of drops, geophysical fluids, and superfluid helium are considered as well as two phase flow, combustion, and heat transfer. Interactions between spacecraft motions and the atmospheric cloud physics laboratory experiments are also examined
Long distance quantum teleportation in a quantum relay configuration
A long distance quantum teleportation experiment with a fiber-delayed Bell
State Measurement (BSM) is reported. The source creating the qubits to be
teleported and the source creating the necessary entangled state are connected
to the beam splitter realizing the BSM by two 2 km long optical fibers. In
addition, the teleported qubits are analyzed after 2,2 km of optical fiber, in
another lab separated by 55 m. Time bin qubits carried by photons at 1310 nm
are teleported onto photons at 1550 nm. The fidelity is of 77%, above the
maximal value obtainable without entanglement. This is the first realization of
an elementary quantum relay over significant distances, which will allow an
increase in the range of quantum communication and quantum key distribution.Comment: 4 pages, submitte
factorization of exclusive processes
We prove factorization theorem in perturbative QCD (PQCD) for exclusive
processes by considering and . The relevant form factors are expressed as the convolution of hard
amplitudes with two-parton meson wave functions in the impact parameter
space, being conjugate to the parton transverse momenta . The point is
that on-shell valence partons carry longitudinal momenta initially, and acquire
through collinear gluon exchanges. The -dependent two-parton wave
functions with an appropriate path for the Wilson links are gauge-invariant.
The hard amplitudes, defined as the difference between the parton-level
diagrams of on-shell external particles and their collinear approximation, are
also gauge-invariant. We compare the predictions for two-body nonleptonic
meson decays derived from factorization (the PQCD approach) and from
collinear factorization (the QCD factorization approach).Comment: 11 pages, REVTEX, 5 figure
Type II superlattices for infrared detectors and devices
Superlattices consisting of combinations of III-V semiconductors with type II band alignments are of interest for infrared applications because their energy gaps can be made smaller than those of any 'natural' III-V compounds. Specifically, it has been demonstrated that both InSb/InAsxSb1-x superlattices and Ga1-xInxSb/InAs superlattices can possess energy gaps in the 8-14 mu m range. The efforts have focused on the Ga1-xInxSb/InAs system because of its extreme broken gap band alignment, which results in narrow energy gaps for very short superlattice periods. The authors report the use of in situ chemical doping of Ga1-xInxSb/InAs superlattices to fabricate p-n photodiodes. These diodes display a clear photovoltaic response with a threshold near 12 mu m. They have also attained outstanding structural quality in Ga1-xInxSb/InAs superlattices grown on radiatively heated GaSb substrates. Cross-sectional transmission electron microscope images of these superlattices display no dislocations, while high resolution X-ray diffraction scans reveal sharp high-order superlattice satellites and strong Pendellosung fringes
Restoration of factorization for low hadron hadroproduction
We discuss the applicability of the factorization theorem to low-
hadron production in hadron-hadron collision in a simple toy model, which
involves only scalar particles and gluons. It has been shown that the
factorization for high- hadron hadroproduction is broken by soft gluons in
the Glauber region, which are exchanged among a transverse-momentum-dependent
(TMD) parton density and other subprocesses of the collision. We explain that
the contour of a loop momentum can be deformed away from the Glauber region at
low , so the above residual infrared divergence is factorized by means of
the standard eikonal approximation. The factorization is then restored in
the sense that a TMD parton density maintains its universality. Because the
resultant Glauber factor is independent of hadron flavors, experimental
constraints on its behavior are possible. The factorization can also be
restored for the transverse single-spin asymmetry in hadron-hadron collision at
low in a similar way, with the residual infrared divergence being
factorized into the same Glauber factor.Comment: 12 pages, 2 figures, version to appear in EPJ
Elective Modernism and the Politics of (Bio) Ethical Expertise
In this essay I consider whether the political perspective of third wave science studies – ‘elective modernism’ – offers a suitable framework for understanding the policy-making contributions that (bio)ethical experts might make. The question arises as a consequence of the fact that I have taken inspiration from the third wave in order to develop an account of (bio)ethical expertise. I offer a précis of this work and a brief summary of elective modernism before considering their relation. The view I set out suggests that elective modernism is a political philosophy and that although its use in relation to the use of scientific expertise in political and policy-making process has implications for the role of (bio)ethical expertise it does not, in the final analysis, provide an account that is appropriate for this latter form of specialist expertise. Nevertheless, it is an informative perspective, and one that can help us make sense of the political uses of (bio)ethical expertise
Resummed Cross Section for Jet Production at Hadron Colliders
We study the resummation of large logarithmic perturbative corrections to the
single-inclusive jet cross section at hadron colliders. The corrections we
address arise near the threshold for the partonic reaction, when the incoming
partons have just enough energy to produce the high-transverse-momentum final
state. The structure of the resulting logarithmic corrections is known to
depend crucially on the treatment of the invariant mass of the produced jet at
threshold. We allow the jet to have a non-vanishing mass at threshold, which
most closely corresponds to the situation in experiment. Matching our results
to available semi-analytical next-to-leading-order calculations, we derive
resummed results valid to next-to-leading logarithmic accuracy. We present
numerical results for the resummation effects at Tevatron and RHIC energies.Comment: 10 figures include
Relative distributions of W's and Z's at low transverse momenta
Despite large uncertainties in the and transverse momentum
() distributions for q_T\lsim 10 GeV, the ratio of the distributions
varys little. The uncertainty in the ratio of to distributions is
on the order of a few percent, independent of the details of the
nonperturbative parameterization.Comment: 13 pages in revtex, 5 postscript figures available upon request,
UIOWA-94-0
Dilepton production near partonic threshold in transversely polarized proton-antiproton collisions
It has recently been suggested that collisions of transversely polarized
protons and antiprotons at the GSI could be used to determine the nucleon's
transversity densities from measurements of the double-spin asymmetry for the
Drell-Yan process. We analyze the role of higher-order perturbative QCD
corrections in this kinematic regime, in terms of the available fixed-order
contributions as well as of all-order soft-gluon resummations. We find that the
combined perturbative corrections to the individual unpolarized and
transversely polarized cross sections are large. We trace these large
enhancements to soft gluon emission near partonic threshold, and we suggest
that with a physically-motivated cut-off enhancements beyond lowest order are
moderated relative to resummed perturbation theory, but still significant. The
unpolarized dilepton cross section for the GSI kinematics may therefore provide
information on the relation of perturbative and nonperturbative dynamics in
hadronic scattering. The spin asymmetry turns out to be rather robust,
relatively insensitive to higher orders, resummation, and the cut-offs.Comment: 23 pages, 19 figures as eps. Some discussion and references added.
Final version to appear in Phys. Rev.
Dihadron fragmentation functions and high Pt hadron-hadron correlations
We propose the formulation of a dihadron fragmentation function in terms of
parton matrix elements. Under the collinear factorization approximation and
facilitated by the cut-vertex technique, the two hadron inclusive cross section
at leading order (LO) in e+ e- annihilation is shown to factorize into a short
distance parton cross section and the long distance dihadron fragmentation
function. We also derive the DGLAP evolution equation of this function at
leading log. The evolution equation for the non-singlet quark fragmentation
function is solved numerically with a simple ansatz for the initial condition
and results are presented for cases of physical interest.Comment: Latex, 4 pages, 4 figures, talk given at Quark Matter 2004, To appear
in J. Phys.
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