4,746 research outputs found
Improved linings for integrating spheres
Sphere surface is covered with plain weave of glass fibers coated with polytetrafluoroethylene and one or two layers of magnesium oxide vapor. The resultant lining is suitable for measurement of radiation in the ultraviolet, visible, and near-infrared wavelengths, is not damage prone, and is easily cleaned
1/f noise in the Two-Body Random Ensemble
We show that the spectral fluctuations of the Two-Body Random Ensemble (TBRE)
exhibit 1/f noise. This result supports a recent conjecture stating that
chaotic quantum systems are characterized by 1/f noise in their energy level
fluctuations. After suitable individual averaging, we also study the
distribution of the exponent \alpha in the 1/f^{\alpha} noise for the
individual members of the ensemble. Almost all the exponents lie inside a
narrow interval around \alpha=1 suggesting that also individual members exhibit
1/f noise, provided they are individually unfoldedComment: 4 pages, 3 figures, Accepted for publication in Phys. Rev.
Duality Between the Weak and Strong Interaction Limits for Randomly Interacting Fermions
We establish the existence of a duality transformation for generic models of
interacting fermions with two-body interactions. The eigenstates at weak and
strong interaction U possess similar statistical properties when expressed in
the U=0 and U=infinity eigenstates bases respectively. This implies the
existence of a duality point U_d where the eigenstates have the same spreading
in both bases. U_d is surrounded by an interval of finite width which is
characterized by a non Lorentzian spreading of the strength function in both
bases. Scaling arguments predict the survival of this intermediate regime as
the number of particles is increased.Comment: RevTex4, 4 pages, 4 figures. Accepted for publication at Phys. Rev.
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Loschmidt echoes in two-body random matrix ensembles
Fidelity decay is studied for quantum many-body systems with a dominant
independent particle Hamiltonian resulting e.g. from a mean field theory with a
weak two-body interaction. The diagonal terms of the interaction are included
in the unperturbed Hamiltonian, while the off-diagonal terms constitute the
perturbation that distorts the echo. We give the linear response solution for
this problem in a random matrix framework. While the ensemble average shows no
surprising behavior, we find that the typical ensemble member as represented by
the median displays a very slow fidelity decay known as ``freeze''. Numerical
calculations confirm this result and show, that the ground state even on
average displays the freeze. This may contribute to explanation of the
``unreasonable'' success of mean field theories.Comment: 9 pages, 5 figures (6 eps files), RevTex; v2: slight modifications
following referees' suggestion
Eigenlevel statistics of the quantum adiabatic algorithm
We study the eigenlevel spectrum of quantum adiabatic algorithm for
3-satisfiability problem, focusing on single-solution instances. The properties
of the ground state and the associated gap, crucial for determining the running
time of the algorithm, are found to be far from the predictions of random
matrix theory. The distribution of gaps between the ground and the first
excited state shows an abundance of small gaps. Eigenstates from the central
part of the spectrum are, on the other hand, well described by random matrix
theory.Comment: 8 pages, 10 ps figure
Interactions and Disorder in Quantum Dots: Instabilities and Phase Transitions
Using a fermionic renormalization group approach we analyse a model where the
electrons diffusing on a quantum dot interact via Fermi-liquid interactions.
Describing the single-particle states by Random Matrix Theory, we find that
interactions can induce phase transitions (or crossovers for finite systems) to
regimes where fluctuations and collective effects dominate at low energies.
Implications for experiments and numerical work on quantum dots are discussed.Comment: 4 pages, 1 figure; version to appear in Phys Rev Letter
Clinical features of low back pain in people with hip osteoarthritis: A cross sectional study.
BACKGROUND: Low back pain (LBP) is commonly reported in people with hip osteoarthritis (OA) and is a poor prognostic indicator of outcome in OA. This study aimed to identify the clinical features associated with LBP in people with hip OA attending orthopaedic and rheumatology clinics.
METHODS: A cross-sectional study was undertaken. Twenty-four people with radiographically confirmed OA were recruited and completed self-report questionnaires for hip and LBP severity (Visual Analogue Scale), hip-related disability (Western Ontario and McMaster Universities Osteoarthritis Index) and back-related disability (Roland Morris Disability Questionnaire). Physical examination comprised spinal palpation, pelvic girdle pain provocation tests and hip and spinal range of motion tests. Between-group (presence/absence of LBP) differences in self-report and physical examination items were compared using Mann-Whitney U and Chi-squared tests.
RESULTS: A total of 16/24 (66.7%) patients reported LBP. Those with LBP were younger, reported more pain locations and had higher self-report pain and disability. On physical examination, people with LBP and OA hip had reduced hip flexion, greater pain provocation with hip abduction, hip lateral rotation, spinal palpation and a greater number of painful pelvic girdle tests and spinal level palpation.
CONCLUSIONS: Assessment of patients with hip OA should incorporate examination of the lumbar spine and pelvic regions. It appears from our study that LBP is a common co-morbidity in those with OA of the hip and may indicate greater severity of hip disease, although the small sample size limits interpretation of results. Further research should investigate the exact relationships between presence of LBP and hip OA
Statistical Theory of Parity Nonconservation in Compound Nuclei
We present the first application of statistical spectroscopy to study the
root-mean-square value of the parity nonconserving (PNC) interaction matrix
element M determined experimentally by scattering longitudinally polarized
neutrons from compound nuclei. Our effective PNC interaction consists of a
standard two-body meson-exchange piece and a doorway term to account for
spin-flip excitations. Strength functions are calculated using realistic
single-particle energies and a residual strong interaction adjusted to fit the
experimental density of states for the targets, ^{238} U for A\sim 230 and
^{104,105,106,108} Pd for A\sim 100. Using the standard Desplanques, Donoghue,
and Holstein estimates of the weak PNC meson-nucleon coupling constants, we
find that M is about a factor of 3 smaller than the experimental value for
^{238} U and about a factor of 1.7 smaller for Pd. The significance of this
result for refining the empirical determination of the weak coupling constants
is discussed.Comment: Latex file, no Fig
Random matrix analysis of complex networks
We study complex networks under random matrix theory (RMT) framework. Using
nearest-neighbor and next-nearest-neighbor spacing distributions we analyze the
eigenvalues of adjacency matrix of various model networks, namely, random,
scale-free and small-world networks. These distributions follow Gaussian
orthogonal ensemble statistic of RMT. To probe long-range correlations in the
eigenvalues we study spectral rigidity via statistic of RMT as well.
It follows RMT prediction of linear behavior in semi-logarithmic scale with
slope being . Random and scale-free networks follow RMT
prediction for very large scale. Small-world network follows it for
sufficiently large scale, but much less than the random and scale-free
networks.Comment: accepted in Phys. Rev. E (replaced with the final version
Spectral statistics of the k-body random-interaction model
We reconsider the question of the spectral statistics of the k-body
random-interaction model, investigated recently by Benet, Rupp, and
Weidenmueller, who concluded that the spectral statistics are Poissonian. The
binary-correlation method that these authors used involves formal manipulations
of divergent series. We argue that Borel summation does not suffice to define
these divergent series without further (arbitrary) regularization, and that
this constitutes a significant gap in the demonstration of Poissonian
statistics. Our conclusion is that the spectral statistics of the k-body
random-interaction model remains an open question.Comment: 17 pages, no figure
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