59,981 research outputs found
Symmetric achromatic low-beta collider interaction region design concept
We present a new symmetry-based concept for an achromatic low-beta collider
interaction region design. A specially-designed symmetric Chromaticity
Compensation Block (CCB) induces an angle spread in the passing beam such that
it cancels the chromatic kick of the final focusing quadrupoles. Two such CCBs
placed symmetrically around an interaction point allow simultaneous
compensation of the 1st-order chromaticities and chromatic beam smear at the IP
without inducing significant 2nd-order aberrations to the particle trajectory.
We first develop an analytic description of this approach and explicitly
formulate 2nd-order aberration compensation conditions at the interaction
point. The concept is next applied to develop an interaction region design for
the ion collider ring of an electron-ion collider. We numerically evaluate
performance of the design in terms of momentum acceptance and dynamic aperture.
The advantages of the new concept are illustrated by comparing it to the
conventional distributed-sextupole chromaticity compensation scheme.Comment: 12 pages, 17 figures, to be submitted to Phys. Rev. ST Accel. Beam
Boson Core Compressibility
Strongly interacting atoms trapped in optical lattices can be used to explore
phase diagrams of Hubbard models. Spatial inhomogeneity due to trapping
typically obscures distinguishing observables. We propose that measures using
boson double occupancy avoid trapping effects to reveal key correlation
functions. We define a boson core compressibility and core superfluid stiffness
in terms of double occupancy. We use quantum Monte Carlo on the Bose-Hubbard
model to empirically show that these quantities intrinsically eliminate edge
effects to reveal correlations near the trap center. The boson core
compressibility offers a generally applicable tool that can be used to
experimentally map out phase transitions between compressible and
incompressible states.Comment: 11 pages, 11 figure
Statistics of nested spiral self-avoiding loops: exact results on the square and triangular lattices
The statistics of nested spiral self-avoiding loops, which is closely related
to the partition of integers into decreasing parts, is studied on the square
and triangular lattices.Comment: Old paper, for archiving. 7 pages, 2 figures, epsf, IOP macr
Strongly Localized Electrons in a Magnetic Field: Exact Results on Quantum Interference and Magnetoconductance
We study quantum interference effects on the transition strength for strongly
localized electrons hopping on 2D square and 3D cubic lattices in a magnetic
field B. In 2D, we obtain closed-form expressions for the tunneling probability
between two arbitrary sites by exactly summing the corresponding phase factors
of all directed paths connecting them. An analytic expression for the
magnetoconductance, as an explicit function of the magnetic flux, is derived.
In the experimentally important 3D case, we show how the interference patterns
and the small-B behavior of the magnetoconductance vary according to the
orientation of B.Comment: 4 pages, RevTe
Magnetic order in the pseudogap phase of high- superconductors
One of the leading issues in high- superconductors is the origin of the
pseudogap phase in underdoped cuprates. Using polarized elastic neutron
diffraction, we identify a novel magnetic order in the YBaCuO
system. The observed magnetic order preserves translational symmetry as
proposed for orbital moments in the circulating current theory of the pseudogap
state. To date, it is the first direct evidence of an hidden order parameter
characterizing the pseudogap phase in high- cuprates.Comment: 3 figure
Nucleon Spin in QCD: Old Crisis and New Resolution
We discuss the shortfalls of existing resolutions of the long-standing gauge
invariance problem of the canonical decomposition of the nucleon spin to the
spin and angular momentum of quarks and gluons. We provide two logically
flawless expressions of nucleon spin which have different physical meanings,
using the gauge independent Abelian decomposition. The first one is based on
the assumption that all gluons (binding and valence gluons) contribute to the
nucleon spin, but the second one is based on the assumption that only the
binding gluons (and the quarks) contribute to it. We propose the second
expression to be the physically correct one
Probing neutrino oscillations jointly in long and very long baseline experiments
We examine the prospects of making a joint analysis of neutrino oscillation
at two baselines with neutrino superbeams. Assuming narrow band superbeams and
a 100 kt water Cerenkov calorimeter, we calculate the event rates and
sensitivities to the matter effect, the signs of the neutrino mass differences,
the CP phase and the mixing angle \theta_{13}. Taking into account all possible
experimental errors under general consideration, we explored the optimum cases
of narrow band beam to measure the matter effect and the CP violation effect at
all baselines up to 3000 km. We then focus on two specific baselines, a long
baseline of 300 km and a very long baseline of 2100 km, and analyze their joint
capabilities. We found that the joint analysis can offer extra leverage to
resolve some of the ambiguities that are associated with the measurement at a
single baseline.Comment: 23 pages, 11 figure
Stronger prediction of motor recovery and outcome post-stroke by cortico-spinal tract integrity than functional connectivity
<div><p>Objectives</p><p>To examine longitudinal changes in structural and functional connectivity post-stroke in patients with motor impairment, and define their importance for recovery and outcome at 12 months.</p><p>Methods</p><p>First-time stroke patients (N = 31) were studied at 1â2 weeks, 3 months, and 12 months post-injury with a validated motor battery and resting-state fMRI to measure inter-hemispheric functional connectivity (FC). Fractional anisotropy (FA) of the cortico-spinal tract (CST) was derived from diffusion tensor imaging as a measure of white matter organization. ANOVAs were used to test for changes in FC, FA, and motor performance scores over time, and regression analysis related motor outcome to clinical and neuroimaging variables.</p><p>Results</p><p>FA of the ipsilesional CST improved significantly from 3 to 12 months and was strongly correlated with motor performance. FA improved even in the absence of direct damage to the CST. Inter-hemispheric FC also improved over time, but did not correlate with motor performance at 12 months. Clinical variables (early motor score, education level, and age) predicted 80.4% of the variation of motor outcome, and FA increased the predictability to 84.6%. FC did not contribute to the prediction of motor outcome.</p><p>Conclusions</p><p>Stroke causes changes to the CST microstructure that can account for behavioral variability even in the absence of demonstrable lesion. Ipsilesional CST undergoes remodeling post-stroke, even past the three-month window when most of the motor recovery happens. FA of the CST, but not inter-hemispheric FC, can improve to the prediction of motor outcome based on early motor scores.</p></div
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