14,783 research outputs found
Tractability of multivariate problems for standard and linear information in the worst case setting: part II
We study QPT (quasi-polynomial tractability) in the worst case setting for
linear tensor product problems defined over Hilbert spaces. We assume that the
domain space is a reproducing kernel Hilbert space so that function values are
well defined. We prove QPT for algorithms that use only function values under
the three assumptions:
1) the minimal errors for the univariate case decay polynomially fast to
zero,
2) the largest singular value for the univariate case is simple and
3) the eigenfunction corresponding to the largest singular value is a
multiple of the function value at some point.
The first two assumptions are necessary for QPT. The third assumption is
necessary for QPT for some Hilbert spaces
Optimal Summation and Integration by Deterministic, Randomized, and Quantum Algorithms
We survey old and new results about optimal algorithms for summation of
finite sequences and for integration of functions from Hoelder or Sobolev
spaces. First we discuss optimal deterministic and randomized algorithms. Then
we add a new aspect, which has not been covered before on conferences about
(quasi-) Monte Carlo methods: quantum computation. We give a short introduction
into this setting and present recent results of the authors on optimal quantum
algorithms for summation and integration. We discuss comparisons between the
three settings. The most interesting case for Monte Carlo and quantum
integration is that of moderate smoothness k and large dimension d which, in
fact, occurs in a number of important applied problems. In that case the
deterministic exponent is negligible, so the n^{-1/2} Monte Carlo and the
n^{-1} quantum speedup essentially constitute the entire convergence rate. We
observe that -- there is an exponential speed-up of quantum algorithms over
deterministic (classical) algorithms, if k/d tends to zero; -- there is a
(roughly) quadratic speed-up of quantum algorithms over randomized classical
algorithms, if k/d is small.Comment: 13 pages, contribution to the 4th International Conference on Monte
Carlo and Quasi-Monte Carlo Methods, Hong Kong 200
Pair Correlation Function of Wilson Loops
We give a path integral prescription for the pair correlation function of
Wilson loops lying in the worldvolume of Dbranes in the bosonic open and closed
string theory. The results can be applied both in ordinary flat spacetime in
the critical dimension d or in the presence of a generic background for the
Liouville field. We compute the potential between heavy nonrelativistic sources
in an abelian gauge theory in relative collinear motion with velocity v =
tanh(u), probing length scales down to r_min^2 = 2 \pi \alpha' u. We predict a
universal -(d-2)/r static interaction at short distances. We show that the
velocity dependent corrections to the short distance potential in the bosonic
string take the form of an infinite power series in the dimensionless variables
z = r_min^2/r^2, uz/\pi, and u^2.Comment: 16 pages, 1 figure, Revtex. Corrected factor of two in potential.
Some changes in discussio
The Retention of Chicago's Arts Students in Comparative Perspective
Highlights:* 58 percent of Chicago arts-school alumni took up residence in the city within 5 years of the date of their last attendance. Of the regions compared in this report, only New York City has a greater portion of its arts-school alumni taking up residence in the city within 5 years, at 66 percent.* 51 percent of Chicago arts-school alumni were out-of-state applicants who came to Chicago and were still living in the city within five years of their last date of attendance. This is the second highest portion of out-of-state applicants taking up residence in the city of their alma mater. New York City's rate was highest at 54 percent.* Of arts-school alumni who searched for work, 38 percent of those attending school in Chicago obtained work prior to leaving their institution; 85 percent obtained work within a year. Alumni from other regions had similar experiences.*50 percent of Chicago's alumni reported that their first job or work experience was "closely related" to their arts-school training. However, alumni from institutions in Los Angeles County, Cleveland/Columbus and New York City reported higher rates of their first work experience being closely related to their arts training
Public Funding for Art: Chicago Compared with 12 Peer Regions
Supported in part by Arts Alliance Illinois, and with the cooperation of several local arts agencies, including Chicago's Department of Cultural Affairs and Special events, and of the National Assembly of State Arts Agencies.This study compares the direct public dollars received by organizations and artists in Baltimore, Boston, Chicago, Cleveland, Columbus, Denver, Houston, Miami, Philadelphia, Phoenix, Portland (OR), San Diego, and San Francisco from 2002-2012.Often, studies of public funding for the arts look at appropriations made on the national and state levels and estimates of local expenditures, but this report delves more deeply using grant-level data to examine the dollars received by organizations and artists resident in each city or region.Key findings:In 2012, Chicago arts organizations received 1.2 million in grants, which is $0.44 per capita. Of the 13 local agencies analyzed, only Phoenix, Boston, and Baltimore spent less in total dollar or per capita terms in 2012.Over the past decade, DCASE annually awarded among the highest total number of grants compared with other regions' local agencies. In 2012, DCASE awarded 520 grants in total -- 305 to organizations and 215 to individuals. In 2012, it awarded competitive grants to approximately 31% of the arts and cultural organizations in the city.Aside from competitive grants, five of the 13 cities/metro regions included in this study provide support to select arts and cultural organizations through line-items, which serve as significant sources of general operating funds
Development of low modulus material for use in ceramic gas path seal applications
Three candidate materials were examined: Brunsbond (R) Pad; plasma sprayed porous NiCrAlY; and plasma sprayed low modulus microcracked zirconia. Evaluation consisted of mechanical, thermophysical, and oxidation resistance testing along with optical microscopy and a feasibility demonstration of attaching the material to a suitable substrate. The goals of the program were the following: feasibility of fastening or depositing the low modulus system onto a broad range of substrate alloys; feasibility of depositing or forming the low modulus system to a thickness of 0.19 cm to 0.38 cm; potential to attain a modulus of elasticity in the range of 3.4 to 6.9 GPa (0.5 to 1.0 MSI), and an ultimate strength of 17.2 MPa (2.5 ksi); suitable thermal conductivity; and static oxidation life of at least 1000 hours at 1311 K. The results of the program indicate that all three systems offer attractive properties as a strain isolator material
Association of inferior vena cava filter placement for venous thromboembolic disease and a contraindication to anticoagulation with 30-day mortality
Importance: Despite the absence of data from randomized clinical trials, professional societies recommend inferior vena cava (IVC) filters for patients with venous thromboembolic disease (VTE) and a contraindication to anticoagulation therapy. Prior observational studies of IVC filters have suggested a mortality benefit associated with IVC filter insertion but have often failed to adjust for immortal time bias, which is the time before IVC filter insertion, during which death can only occur in the control group.
Objective: To determine the association of IVC filter placement with 30-day mortality after adjustment for immortal time bias.
Design, Setting, and Participants: This comparative effectiveness, retrospective cohort study used a population-based sample of hospitalized patients with VTE and a contraindication to anticoagulation using the State Inpatient Database and the State Emergency Department Database, part of the Healthcare Cost and Utilization Project of the Agency for Healthcare Research and Quality, from hospitals in California (January 1, 2005, to December 31, 2011), Florida (January 1, 2005, to December 31, 2013), and New York (January 1, 2005, to December 31, 2012). Data analysis was conducted from September 15, 2015, to March 14, 2018.
Exposure: Inferior vena cava filter placement.
Main Outcomes and Measures: Multivariable Cox proportional hazard models were constructed with IVC filters as a time-dependent variable that adjusts for immortal time bias. The Cox model was further adjusted using the propensity score as an adjustment variable.
Results: Of 126 030 patients with VTE, 61 281 (48.6%) were male and the mean (SD) age was 66.9 (16.6) years. In this cohort, 45 771 (36.3%) were treated with an IVC filter, whereas 80 259 (63.7%) did not receive a filter. In the Cox model with IVC filter status analyzed as a time-dependent variable to account for immortal time bias, IVC filter placement was associated with a significantly increased hazard ratio of 30-day mortality (1.18; 95% CI, 1.13-1.22; P \u3c .001). When the propensity score was included in the Cox model, IVC filter placement remained associated with an increased hazard ratio of 30-day mortality (1.18; 95% CI, 1.13-1.22; P \u3c .001).
Conclusions and Relevance: After adjustment for immortal time bias, IVC filter placement was associated with increased 30-day mortality in patients with VTE and a contraindication to anticoagulation. Randomized clinical trials are needed to determine the efficacy of IVC filter placement in patients with VTE and a contraindication to anticoagulation
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