22,543 research outputs found
Absolute instruments and perfect imaging in geometrical optics
We investigate imaging by spherically symmetric absolute instruments that
provide perfect imaging in the sense of geometrical optics. We derive a number
of properties of such devices, present a general method for designing them and
use this method to propose several new absolute instruments, in particular a
lens providing a stigmatic image of an optically homogeneous region and having
a moderate refractive index range.Comment: 20 pages, 9 image
Levinson's Theorem for the Klein-Gordon Equation in Two Dimensions
The two-dimensional Levinson theorem for the Klein-Gordon equation with a
cylindrically symmetric potential is established. It is shown that
, where denotes
the difference between the number of bound states of the particle
and the ones of antiparticle with a fixed angular momentum , and
the is named phase shifts. The constants and
are introduced to symbol the critical cases where the half bound
states occur at .Comment: Revtex file 14 pages, submitted to Phys. Rev.
Minimally invasive presacral approach for revision of an Axial Lumbar Interbody Fusion rod due to fall-related lumbosacral instability: a case report
<p>Abstract</p> <p>Introduction</p> <p>The purpose of this study was to describe procedural details of a minimally invasive presacral approach for revision of an L5-S1 Axial Lumbar Interbody Fusion rod.</p> <p>Case presentation</p> <p>A 70-year-old Caucasian man presented to our facility with marked thoracolumbar scoliosis, osteoarthritic changes characterized by high-grade osteophytes, and significant intervertebral disc collapse and calcification. Our patient required crutches during ambulation and reported intractable axial and radicular pain. Multi-level reconstruction of L1-4 was accomplished with extreme lateral interbody fusion, although focal lumbosacral symptoms persisted due to disc space collapse at L5-S1.</p> <p>Lumbosacral interbody distraction and stabilization was achieved four weeks later with the Axial Lumbar Interbody Fusion System (TranS1 Inc., Wilmington, NC, USA) and rod implantation via an axial presacral approach.</p> <p>Despite symptom resolution following this procedure, our patient suffered a fall six weeks postoperatively with direct sacral impaction resulting in symptom recurrence and loss of L5-S1 distraction. Following seven months of unsuccessful conservative care, a revision of the Axial Lumbar Interbody Fusion rod was performed that utilized the same presacral approach and used a larger diameter implant. Minimal adhesions were encountered upon presacral re-entry. A precise operative trajectory to the base of the previously implanted rod was achieved using fluoroscopic guidance. Surgical removal of the implant was successful with minimal bone resection required. A larger diameter Axial Lumbar Interbody Fusion rod was then implanted and joint distraction was re-established. The radicular symptoms resolved following revision surgery and our patient was ambulating without assistance on post-operative day one. No adverse events were reported.</p> <p>Conclusions</p> <p>The Axial Lumbar Interbody Fusion distraction rod may be revised and replaced with a larger diameter rod using the same presacral approach.</p
Hadronic production and the Gottfried Sum Rule
The difference in production rate between and at hadron colliders
is very sensitive to the the difference between up- and down-quark
distributions in the proton. This sensitivity allows for a variety of useful
measurements. We consider the difference in the sea
distributions and the difference in the
polarized parton distribution functions. In both cases we construct an
asymmetry to reduce systematic uncertainties. Although we discuss measurements
at the Tevatron and future hadron colliders, we find that the Brookhaven
Relativistic Heavy Ion Collider (RHIC) is the most appropriate hadron collider
for these measurements.Comment: 19 pages (20 figures available from the authors), MAD/PH/74
Towards the critical behavior for the light nuclei by NIMROD detector
The critical behavior for the light nuclei with A has been
investigated experimentally by the NIMROD multi-detectors. The wide variety of
observables indicate the critical point has been reached in the disassembly of
hot nuclei at an excitation energy of 5.60.5 MeV/u.Comment: 4 pages, 2 figures; Proceeding of 18th Nuclear Physics Division
Conference of the Euro. Phys. Society (NPDC18) "Phase transitions in strongly
interacting matter", Prague, 23.8.-29.8. 2004. To be published in Nuclear
Physics
Quark Distributions of Octet Baryons from SU(3) Symmetry
SU(3) symmetry relations between the octet baryons are introduced in order to
connect both the unpolarized and polarized quark distributions of the octet
baryons with those of the nucleon. Two different parametrizations of the
nucleon quark distributions are used. A new scenario of quark flavor and spin
structure of the is found and compared with two other models: a
perturbative QCD based analysis and a quark diquark model. The and
quarks inside the are predicted to be positively polarized at large
Bjorken variable in the new scenario. By using an approximate relation
connecting the quark fragmentation functions with the quark distributions, the
hadron polarizations of the octet baryons in -annihilation, polarized
charged lepton deep inelastic scattering (DIS) processes, and neutrino
(antineutrino) DIS processes are predicted. The predictions for
polarizations in several processes are compatible with the available data at
large fragmentation momentum fraction , and support the prediction of
positively polarized and quarks inside the at large .
Predictions for Drell-Yan processes from and beams on an
isoscalar target are also given and discussed.Comment: 29 latex pages, 16 figures, to appear in PR
Phenomenological Tests of Supersymmetric A_4 Family Symmetry Model of Neutrino Mass
Recently Babu, Ma and Valle proposed a model of quark and lepton mixing based
on symmetry. Within this model the lepton and slepton mixings are
intimately related. We perform a numerical study in order to derive the slepton
masses and mixings in agreement with present data from neutrino physics. We
show that, starting from three-fold degeneracy of the neutrino masses at a high
energy scale, a viable low energy neutrino mass matrix can indeed be obtained
in agreement with constraints on lepton flavour violating
and decays. The resulting slepton spectrum must necessarily
include at least one mass below 200 GeV which can be produced at the LHC. The
predictions for the absolute Majorana neutrino mass scale eV
ensure that the model will be tested by future cosmological tests and
searches.
Rates for lepton flavour violating processes
in the range of sensitivity of current
experiments are typical in the model, with BR(\mu \to e \gamma) \gsim
10^{-15} and the lower bound BR. To first
approximation, the model leads to maximal leptonic CP violation in neutrino
oscillations.Comment: 23 pages, 7 figure
Renormalization group and nonequilibrium action in stochastic field theory
We investigate the renormalization group approach to nonequilibrium field
theory. We show that it is possible to derive nontrivial renormalization group
flow from iterative coarse graining of a closed-time-path action. This
renormalization group is different from the usual in quantum field theory
textbooks, in that it describes nontrivial noise and dissipation. We work out a
specific example where the variation of the closed-time-path action leads to
the so-called Kardar-Parisi-Zhang equation, and show that the renormalization
group obtained by coarse graining this action, agrees with the dynamical
renormalization group derived by directly coarse graining the equations of
motion.Comment: 33 pages, 3 figures included in the text. Revised; one reference
adde
Evidence of Critical Behavior in the Disassembly of Nuclei with A ~ 36
A wide variety of observables indicate that maximal fluctuations in the
disassembly of hot nuclei with A ~ 36 occur at an excitation energy of 5.6 +-
0.5 MeV/u and temperature of 8.3 +- 0.5 MeV. Associated with this point of
maximal fluctuations are a number of quantitative indicators of apparent
critical behavior. The associated caloric curve does not appear to show a
flattening such as that seen for heavier systems. This suggests that, in
contrast to similar signals seen for liquid-gas transitions in heavier nuclei,
the observed behavior in these very light nuclei is associated with a
transition much closer to the critical point.Comment: v2: Major changes, new model calculations, new figure
Critical Behavior in Light Nuclear Systems: Experimental Aspects
An extensive experimental survey of the features of the disassembly of a
small quasi-projectile system with 36, produced in the reactions of 47
MeV/nucleon Ar + Al, Ti and Ni, has been carried
out. Nuclei in the excitation energy range of 1-9 MeV/u have been investigated
employing a new method to reconstruct the quasi-projectile source. At an
excitation energy 5.6 MeV/nucleon many observables indicate the presence
of maximal fluctuations in the de-excitation processes. The fragment
topological structure shows that the rank sorted fragments obey Zipf's law at
the point of largest fluctuations providing another indication of a liquid gas
phase transition. The caloric curve for this system shows a monotonic increase
of temperature with excitation energy and no apparent plateau. The temperature
at the point of maximal fluctuations is MeV. Taking this
temperature as the critical temperature and employing the caloric curve
information we have extracted the critical exponents , and
from the data. Their values are also consistent with the values of the
universality class of the liquid gas phase transition. Taken together, this
body of evidence strongly suggests a phase change in an equilibrated mesoscopic
system at, or extremely close to, the critical point.Comment: Physical Review C, in press; some discussions about the validity of
excitation energy in peripheral collisions have been added; 24 pages and 32
figures; longer abstract in the preprin
- âŠ