2,499 research outputs found
Efficient Quantum Circuits for Schur and Clebsch-Gordan Transforms
The Schur basis on n d-dimensional quantum systems is a generalization of the
total angular momentum basis that is useful for exploiting symmetry under
permutations or collective unitary rotations. We present efficient (size
poly(n,d,log(1/\epsilon)) for accuracy \epsilon) quantum circuits for the Schur
transform, which is the change of basis between the computational and the Schur
bases. These circuits are based on efficient circuits for the Clebsch-Gordan
transformation. We also present an efficient circuit for a limited version of
the Schur transform in which one needs only to project onto different Schur
subspaces. This second circuit is based on a generalization of phase estimation
to any nonabelian finite group for which there exists a fast quantum Fourier
transform.Comment: 4 pages, 3 figure
On Nonzero Kronecker Coefficients and their Consequences for Spectra
A triple of spectra (r^A, r^B, r^{AB}) is said to be admissible if there is a
density operator rho^{AB} with (Spec rho^A, Spec rho^B, Spec rho^{AB})=(r^A,
r^B, r^{AB}). How can we characterise such triples? It turns out that the
admissible spectral triples correspond to Young diagrams (mu, nu, lambda) with
nonzero Kronecker coefficient [M. Christandl and G. Mitchison, to appear in
Comm. Math. Phys., quant-ph/0409016; A. Klyachko, quant-ph/0409113]. This means
that the irreducible representation V_lambda is contained in the tensor product
of V_mu and V_nu. Here, we show that such triples form a finitely generated
semigroup, thereby resolving a conjecture of Klyachko. As a consequence we are
able to obtain stronger results than in [M. Ch. and G. M. op. cit.] and give a
complete information-theoretic proof of the correspondence between triples of
spectra and representations. Finally, we show that spectral triples form a
convex polytope.Comment: 13 page
Wightman function and vacuum fluctuations in higher dimensional brane models
Wightman function and vacuum expectation value of the field square are
evaluated for a massive scalar field with general curvature coupling parameter
subject to Robin boundary conditions on two codimension one parallel branes
located on -dimensional background spacetime
with a warped internal space . The general case of different Robin
coefficients on separate branes is considered. The application of the
generalized Abel-Plana formula for the series over zeros of combinations of
cylinder functions allows us to extract manifestly the part due to the bulk
without boundaries. Unlike to the purely AdS bulk, the vacuum expectation value
of the field square induced by a single brane, in addition to the distance from
the brane, depends also on the position of the brane in the bulk. The brane
induced part in this expectation value vanishes when the brane position tends
to the AdS horizon or AdS boundary. The asymptotic behavior of the vacuum
densities near the branes and at large distances is investigated. The
contribution of Kaluza-Klein modes along is discussed in various
limiting cases. As an example the case is considered,
corresponding to the bulk with one compactified dimension. An
application to the higher dimensional generalization of the Randall-Sundrum
brane model with arbitrary mass terms on the branes is discussed.Comment: 25 pages, 2 figures, discussion added, accepted for publication in
Phys.Rev.
Wightman function and vacuum densities for a Z_2-symmetric thick brane in AdS spacetime
Positive frequency Wightman function, vacuum expectation values of the field
square and the energy-momentum tensor induced by a Z_{2}-symmetric brane with
finite thickness located on (D+1)- dimensional AdS background are evaluated for
a massive scalar field with general curvature coupling parameter. For the
general case of static plane symmetric interior structure the expectation
values in the region outside the brane are presented as the sum of free AdS and
brane induced parts. For a conformally coupled massless scalar the brane
induced part in the vacuum energy-momentum tensor vanishes. In the limit of
strong gravitational fields the brane induced parts are exponentially
suppressed for points not too close to the brane boundary. As an application of
general results a special model is considered in which the geometry inside the
brane is a slice of the Minkowski spacetime orbifolded along the direction
perpendicular to the brane. For this model the Wightman function, vacuum
expectation values of the field square and the energy-momentum tensor inside
the brane are evaluated as well and their behavior is discussed in various
asymptotic regions of the parameters. It is shown that for both minimally and
conformally coupled scalar fields the interior vacuum forces acting on the
brane boundaries tend to decrease the brane thickness.Comment: 25 pages, 6 figures, discussion adde
Flavor changing interactions mediated by scalars at the weak scale
The quark and lepton mass matrices possess approximate flavor symmetries.
Several results follow if the interactions of new scalars possess these
approximate symmetries. Present experimental bounds allow these exotic scalars
to have a weak scale mass. The Glashow-Weinberg criterion is rendered
unnecessary. Finally, rare leptonic B meson decays provide powerful probes of
these scalars, especially if they are leptoquarks.Comment: 13 pages, report LBL-3234
Statistical Mechanics of Semi-Supervised Clustering in Sparse Graphs
We theoretically study semi-supervised clustering in sparse graphs in the
presence of pairwise constraints on the cluster assignments of nodes. We focus
on bi-cluster graphs, and study the impact of semi-supervision for varying
constraint density and overlap between the clusters. Recent results for
unsupervised clustering in sparse graphs indicate that there is a critical
ratio of within-cluster and between-cluster connectivities below which clusters
cannot be recovered with better than random accuracy. The goal of this paper is
to examine the impact of pairwise constraints on the clustering accuracy. Our
results suggests that the addition of constraints does not provide automatic
improvement over the unsupervised case. When the density of the constraints is
sufficiently small, their only impact is to shift the detection threshold while
preserving the criticality. Conversely, if the density of (hard) constraints is
above the percolation threshold, the criticality is suppressed and the
detection threshold disappears.Comment: 8 pages, 4 figure
Generalized statistical models of voids and hierarchical structure in cosmology
Generalized statistical models of voids and hierarchical structure in
cosmology are developed. The often quoted negative binomial model and
frequently used thermodynamic model are shown to be special cases of a more
general distribution which contains a parameter "a". The parameter is related
to the Levy index alpha and the Fisher critical exponent tau, the latter
describing the power law fall off of clumps of matter around a phase
transition. The parameter"a", exponent tau, or index alpha can be obtained from
properties of a void scaling function. A stochastic probability variable "p" is
introduced into a statistical model which represent the adhesive growth of
galaxy structure. For p<1/2, the galaxy count distribution decays exponential
fast with size. For p>1/2, an adhesive growth can go on indefinitely thereby
forming an infinite supercluster. At p=1/2 a scale free power law distribution
for the galaxy count distribution is present. The stochastic description also
leads to consequences that have some parallels with cosmic string results,
percolation theory and phase transitions.Comment: 25 page
Efficacy of Thermotherapy to Treat Cutaneous Leishmaniasis Caused by Leishmania tropica in Kabul, Afghanistan: A Randomized, Controlled Trial
BACKGROUND: Pentavalent antimony is the agent recommended for treatment of cutaneous leishmaniasis (CL). Its use is problematic, because it is expensive and because of the potential for drug-associated adverse effects during a lengthy and painful treatment course.
METHODS: We tested the efficacy of thermotherapy for the treatment of CL due to Leishmania tropica in a randomized, controlled trial in Kabul, Afghanistan. We enrolled 401 patients with a single CL lesion and administered thermotherapy using radio-frequency waves (1 treatment of ≥1 consecutive application at 50°C for 30 s) or sodium stibogluconate (SSG), administered either intralesionally (a total of 5 injections of 25 mL every 57 days, depending on lesion size) or intramuscularly (20 mg/kg daily for 21 days).
RESULTS: Cure, defined as complete reepithelialization at 100 days after treatment initiation, was observed in 75 (69.4%) of 108 patients who received thermotherapy, 70 (75.3%) of 93 patients who received intralesional SSG, and 26 (44.8%) of 58 patients who received intramuscular SSG. The OR for cure with thermotherapy was 2.80 (95% confidence interval [CI], 1.455.41), compared with intramuscular SSG treatment (P = .002). No statistically significant difference was observed in the odds of cure in comparison of intralesional SSG and thermotherapy treatments. The OR for cure with intralesional SSG treatment was 3.75 (95% CI, 1.867.54), compared with intramuscular SSG treatment (P 100 days, respectively; P = .003).
CONCLUSIONS: Thermotherapy is an effective, comparatively well-tolerated, and rapid treatment for CL, and it should be considered as an alternative to antimony treatment
Provider Stakeholders’ Perceived Benefit from a Nascent Health Information Exchange: A Qualitative Analysis
We sought to better understand the perceived costs and benefits of joining a nascent health information exchange (HIE) from the perspective of potential provider organization participants. We therefore conducted semi-structured interviews with organizational representatives. Interview transcriptions were thematically coded, and coded text was subsequently aggregated to summarize the breadth and depth of responses. Although no respondents expected HIE to result in net financial benefit to their organization, all respondents recognized some potential benefits, and some respondents expected HIE to result in overall organizational benefit. Disproportionate benefit was expected for the poorest, sickest patients. Many respondents had concerns about HIE increasing the risk of data security breaches, and these concerns were most pronounced at larger organizations. We found little evidence of organizational concern regarding loss of patients to other organizations or publication of unfavorable quality data. If HIE’s greatest benefactors are indeed the poorest, sickest patients, our current health care financing environment will make it difficult to align HIE costs with benefits. To sustain HIE, state and federal governments may need to consider ongoing subsidies. Furthermore, these governments will need to ensure that policies regulating data exchange have sufficient nationwide coordination and liability limitations that the perceived organizational risks of joining HIEs do not outweigh perceived benefits. HIE founders can address organizational concerns by attempting to coordinate HIE policies with those of their largest founding organizations, particularly for data security policies. Early HIE development and promotional efforts should not only focus on potential benefits, but should also address organizational concerns
Adaptive Boolean Networks and Minority Games with Time--Dependent Capacities
In this paper we consider a network of boolean agents that compete for a
limited resource. The agents play the so called Generalized Minority Game where
the capacity level is allowed to vary externally. We study the properties of
such a system for different values of the mean connectivity of the network,
and show that the system with K=2 shows a high degree of coordination for
relatively large variations of the capacity level.Comment: 4 pages, 4 figure
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