5,330 research outputs found
Importance sampling the union of rare events with an application to power systems analysis
Full text linkWe consider importance sampling to estimate the probability of a union
of rare events defined by a random variable . The
sampler we study has been used in spatial statistics, genomics and
combinatorics going back at least to Karp and Luby (1983). It works by sampling
one event at random, then sampling conditionally on that event
happening and it constructs an unbiased estimate of by multiplying an
inverse moment of the number of occuring events by the union bound. We prove
some variance bounds for this sampler. For a sample size of , it has a
variance no larger than where is the union
bound. It also has a coefficient of variation no larger than
regardless of the overlap pattern among the
events. Our motivating problem comes from power system reliability, where the
phase differences between connected nodes have a joint Gaussian distribution
and the rare events arise from unacceptably large phase differences. In the
grid reliability problems even some events defined by constraints in
dimensions, with probability below , are estimated with a
coefficient of variation of about with only sample
values
Optimal randomized multilevel algorithms for infinite-dimensional integration on function spaces with ANOVA-type decomposition
Full text linkIn this paper, we consider the infinite-dimensional integration problem on
weighted reproducing kernel Hilbert spaces with norms induced by an underlying
function space decomposition of ANOVA-type. The weights model the relative
importance of different groups of variables. We present new randomized
multilevel algorithms to tackle this integration problem and prove upper bounds
for their randomized error. Furthermore, we provide in this setting the first
non-trivial lower error bounds for general randomized algorithms, which, in
particular, may be adaptive or non-linear. These lower bounds show that our
multilevel algorithms are optimal. Our analysis refines and extends the
analysis provided in [F. J. Hickernell, T. M\"uller-Gronbach, B. Niu, K.
Ritter, J. Complexity 26 (2010), 229-254], and our error bounds improve
substantially on the error bounds presented there. As an illustrative example,
we discuss the unanchored Sobolev space and employ randomized quasi-Monte Carlo
multilevel algorithms based on scrambled polynomial lattice rules.Comment: 31 pages, 0 figure
Temporal discrimination: Mechanisms and relevance to adult-onset dystonia
Get PDFTemporal discrimination is the ability to determine that two sequential sensory stimuli are separated in time. For any individual, the temporal discrimination threshold (TDT) is the minimum interval at which paired sequential stimuli are perceived as being asynchronous; this can be assessed, with high test-retest and inter-rater reliability, using a simple psychophysical test. Temporal discrimination is disordered in a number of basal ganglia diseases including adult-onset dystonia, of which the two most common phenotypes are cervical dystonia and blepharospasm. The causes of adult-onset focal dystonia are unknown; genetic, epigenetic, and environmental factors are relevant. Abnormal TDTs in adult-onset dystonia are associated with structural and neurophysiological changes considered to reflect defective inhibitory interneuronal processing within a network which includes the superior colliculus, basal ganglia, and primary somatosensory cortex. It is hypothesized that abnormal temporal discrimination is a mediational endophenotype and, when present in unaffected relatives of patients with adult-onset dystonia, indicates non-manifesting gene carriage. Using the mediational endophenotype concept, etiological factors in adult-onset dystonia may be examined including (i) the role of environmental exposures in disease penetrance and expression; (ii) sexual dimorphism in sex ratios at age of onset; (iii) the pathogenesis of non-motor symptoms of adult-onset dystonia; and (iv) subcortical mechanisms in disease pathogenesis
Rescuing Economics From The Discipline: The Green Learning Community
Get PDFUndergraduate economics is poised for reform because of readily available data and multimedia content. However, we argue that deep reform is needed to teach complex contemporary problems. This requires including institutional and historical content and restructuring the classroom to facilitate interdisciplinary pedagogy. Using Colander’s (2006) analysis of reform as a starting point, we review the economics literature to identify alternative approaches and interdisciplinary pedagogy. The Green Learning Community is introduced as an intentional approach that links economics, humanities and environmental studies and provides first-year students adequate time to study, reflect upon, and internalize economic assumptions, models, values, and interdisciplinary insights
Computable error bounds for quasi-Monte Carlo using points with non-negative local discrepancy
Full text linkLet be a completely monotone integrand as defined by
Aistleitner and Dick (2015) and let points
have a non-negative
local discrepancy (NNLD) everywhere in . We show how to use these
properties to get a non-asymptotic and computable upper bound for the integral
of over . An analogous non-positive local discrepancy (NPLD)
property provides a computable lower bound. It has been known since Gabai
(1967) that the two dimensional Hammersley points in any base have
non-negative local discrepancy. Using the probabilistic notion of associated
random variables, we generalize Gabai's finding to digital nets in any base
and any dimension when the generator matrices are permutation
matrices. We show that permutation matrices cannot attain the best values of
the digital net quality parameter when . As a consequence the computable
absolutely sure bounds we provide come with less accurate estimates than the
usual digital net estimates do in high dimensions. We are also able to
construct high dimensional rank one lattice rules that are NNLD. We show that
those lattices do not have good discrepancy properties: any lattice rule with
the NNLD property in dimension either fails to be projection regular or
has all its points on the main diagonal
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ELMO1 has an essential role in the internalization of Salmonella Typhimurium into enteric macrophages that impacts disease outcome.
Get PDFBackgrounds and aims4-6 million people die of enteric infections each year. After invading intestinal epithelial cells, enteric bacteria encounter phagocytes. However, little is known about how phagocytes internalize the bacteria to generate host responses. Previously, we have shown that BAI1 (Brain Angiogenesis Inhibitor 1) binds and internalizes Gram-negative bacteria through an ELMO1 (Engulfment and cell Motility protein 1)/Rac1-dependent mechanism. Here we delineate the role of ELMO1 in host inflammatory responses following enteric infection.MethodsELMO1-depleted murine macrophage cell lines, intestinal macrophages and ELMO1 deficient mice (total or myeloid-cell specific) was infected with Salmonella enterica serovar Typhimurium. The bacterial load, inflammatory cytokines and histopathology was evaluated in the ileum, cecum and spleen. The ELMO1 dependent host cytokines were detected by a cytokine array. ELMO1 mediated Rac1 activity was measured by pulldown assay.ResultsThe cytokine array showed reduced release of pro-inflammatory cytokines, including TNF-α and MCP-1, by ELMO1-depleted macrophages. Inhibition of ELMO1 expression in macrophages decreased Rac1 activation (~6 fold) and reduced internalization of Salmonella. ELMO1-dependent internalization was indispensable for TNF-α and MCP-1. Simultaneous inhibition of ELMO1 and Rac function virtually abrogated TNF-α responses to infection. Further, activation of NF-κB, ERK1/2 and p38 MAP kinases were impaired in ELMO1-depleted cells. Strikingly, bacterial internalization by intestinal macrophages was completely dependent on ELMO1. Salmonella infection of ELMO1-deficient mice resulted in a 90% reduction in bacterial burden and attenuated inflammatory responses in the ileum, spleen and cecum.ConclusionThese findings suggest a novel role for ELMO1 in facilitating intracellular bacterial sensing and the induction of inflammatory responses following infection with Salmonella
A 2D Microphysical Analysis of Aerosol Nucleation in the Polar Winter Stratosphere: Implications for H2SO4 Photolysis and Nucleation Mechanisms
Get PDFEach spring a layer of small particles forms between 20 and 30 km in the polar regions. Results are presented from a 2D microphysical model of sulfate aerosol, which provide the first self-consistent explanation of the observed "CN layer." Photochemical conversion of sulfuric acid to SO2 in the upper stratosphere and mesosphere is necessary for this layer to form. Recent laboratory measurements of H2SO4 and SO3 photolysis rates are consistent with such conversion, though an additional source of SO2 may be required. Nucleation throughout the polar winter extends the top of the aerosol layer to higher altitudes, despite strong downward transport of ambient air. This finding may be important to heterogeneous chemistry at the top of the aerosol layer in polar winter and spring
United States Regulation of Stem Cell Research: Recasting Government\u27s Role and Questions to Be Resolved
Get PDFThis article directly addresses the stem cell controversy, but also the broader history and norms regarding the roles of federal and state government in U.S. science research funding
Interventional Radiology and the Care of the Oncology Patient
Get PDFInterventional Radiology (IR) is occupying an increasingly prominent role in the care of patients with cancer, with involvement from initial diagnosis, right through to minimally invasive treatment of the malignancy and its complications. Adequate diagnostic samples can be obtained under image guidance by percutaneous biopsy and needle aspiration in an accurate and minimally invasive manner. IR techniques may be used to place central venous access devices with well-established safety and efficacy. Therapeutic applications of IR in the oncology patient include local tumour treatments such as transarterial chemo-embolisation and radiofrequency ablation, as well as management of complications of malignancy such as pain, organ obstruction, and venous thrombosis
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