286 research outputs found
Adaptive Importance Sampling in General Mixture Classes
In this paper, we propose an adaptive algorithm that iteratively updates both
the weights and component parameters of a mixture importance sampling density
so as to optimise the importance sampling performances, as measured by an
entropy criterion. The method is shown to be applicable to a wide class of
importance sampling densities, which includes in particular mixtures of
multivariate Student t distributions. The performances of the proposed scheme
are studied on both artificial and real examples, highlighting in particular
the benefit of a novel Rao-Blackwellisation device which can be easily
incorporated in the updating scheme.Comment: Removed misleading comment in Section
Probing the Inner Disk Emission of the Herbig Ae Stars HD 163296 and HD 190073
The physical processes occurring within the inner few astronomical units of
proto-planetary disks surrounding Herbig Ae stars are crucial to setting the
environment in which the outer planet-forming disk evolves and put critical
constraints on the processes of accretion and planet migration. We present the
most complete published sample of high angular resolution H- and K-band
observations of the stars HD 163296 and HD 190073, including 30 previously
unpublished nights of observations of the former and 45 nights of the latter
with the CHARA long-baseline interferometer, in addition to archival VLTI data.
We confirm previous observations suggesting significant near-infrared emission
originates within the putative dust evaporation front of HD 163296 and show
this is the case for HD 190073 as well. The H- and K-band sizes are the same
within for HD 163296 and within for HD 190073. The
radial surface brightness profiles for both disks are remarkably Gaussian-like
with little or no sign of the sharp edge expected for a dust evaporation front.
Coupled with spectral energy distribution analysis, our direct measurements of
the stellar flux component at H and K bands suggest that HD 190073 is much
younger (<400 kyr) and more massive (~5.6 M) than previously thought,
mainly as a consequence of the new Gaia distance (891 pc).Comment: 19 pages, 6 figure
IL-15 trans-presentation promotes human NK cell development and differentiation in vivo
The in vivo requirements for human natural killer (NK) cell development and differentiation into cytotoxic effectors expressing inhibitory receptors for selfâmajor histocompatability complex class I (MHC-I; killer Ig-like receptors [KIRs]) remain undefined. Here, we dissect the role of interleukin (IL)-15 in human NK cell development using Rag2â/âÎłcâ/â mice transplanted with human hematopoietic stem cells. Human NK cell reconstitution was intrinsically low in this model because of the poor reactivity to mouse IL-15. Although exogenous human IL-15 (hIL-15) alone made little improvement, IL-15 coupled to IL-15 receptor α (IL-15Rα) significantly augmented human NK cells. IL-15âIL-15Rα complexes induced extensive NK cell proliferation and differentiation, resulting in accumulation of CD16+KIR+ NK cells, which was not uniquely dependent on enhanced survival or preferential responsiveness of this subset to IL-15. Human NK cell differentiation in vivo required hIL-15 and progressed in a linear fashion from CD56hiCD16âKIRâ to CD56loCD16+KIRâ, and finally to CD56loCD16+KIR+. These data provide the first evidence that IL-15 trans-presentation regulates human NK cell homeostasis. Use of hIL-15 receptor agonists generates a robust humanized immune system model to study human NK cells in vivo. IL-15 receptor agonists may provide therapeutic tools to improve NK cell reconstitution after bone marrow transplants, enhance graft versus leukemia effects, and increase the pool of IL-15âresponsive cells during immunotherapy strategies
From Expert Administration to Accountability Network: A New Paradigm for Comparative Administrative Law
Notwithstanding the radically changed landscape of contemporary administrative governance, the categories that guide comparative administrative law and that determine what will be compared remain similar to those used at the founding of the discipline in the late 1800s. These categories are rooted in confidence in an expert bureaucracy to accomplish public purposes and are mainly twofold - administrative organization and judicial review. This outdated model has limited the ability of comparative law to engage with contemporary debates on the administrative state, which instead display considerable skepticism of public administration and are premised on achieving the public good through a plural accountability network of public and private actors. This Article seeks to correct the anachronism by reframing comparative administrative law as an accountability network of rules and procedures designed to embed public administration and civil servants in their liberal democratic societies: accountability to elected officials, organized interests, the courts, and the general public. Based on this paradigm, the Article compares American and European administrative law in a global context. Among the many differences explored are parliamentary versus presidential political control, pluralist versus neo-corporatist forms of self-regulation and public-private collaboration, judicial review focused on fundamental rights versus policy rationality, and reliance on ombudsmen in lieu of courts. The Article concludes with a number of suggestions for how comparative law can speak to current debates on reforming administrative governance
The Local Role in Homeland Security
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/73848/1/j.1540-5893.2005.00236.x.pd
Glass transition in systems without static correlations: a microscopic theory
We present a first step toward a microscopic theory for the glass transition
in systems with trivial static correlations. As an example we have chosen N
infinitely thin hard rods with length L, fixed with their centers on a periodic
lattice with lattice constant a. Starting from the N-rod Smoluchowski equation
we derive a coupled set of equations for fluctuations of reduced k-rod
densities. We approximate the influence of the surrounding rods onto the
dynamics of a pair of rods by introduction of an effective rotational diffusion
tensor D and in this way we obtain a self-consistent equation for D. This
equation exhibits a feedback mechanism leading to a slowing down of the
relaxation. It involves as an input the Laplace transform v_0(l/r) at z=0,
l=L/a, of a torque-torque correlator of an isolated pair of rods with distance
R=ar. Our equation predicts the existence of a continuous ergodicity-breaking
transition at a critical length l_c=L_c/a. To estimate the critical length we
perform an approximate analytical calculation of v_0(l/r) based on a
variational approach and obtain l_c^{var}=5.68, 4.84 and 3.96 for an sc, bcc
and fcc lattice. We also evaluate v_0(l/r) numerically exactly from a two-rod
simulation. The latter calculation leads to l_c^{num}=3.45, 2.78 and 2.20 for
the corresponding lattices. Close to l_c the rotational diffusion constant
decreases as D(l) ~ (l_c - l)^\gamma with \gamma=1 and a diverging time scale
t_\epsilon ~ |l_c - l|^{-\delta}, \delta=2, appears. On this time scale the t-
and l-dependence of the 1-rod density is determined by a master function
depending only on t/t_\epsilon. In contrast to present microscopic theories our
approach predicts a glass transition despite the absence of any static
correlations.Comment: 22 pages, 7 figures (minor revisions in the text, corrected figures
Reliability of clinical tests to evaluate nerve function and mechanosensitivity of the upper limb peripheral nervous system
BACKGROUND: Clinical tests to assess peripheral nerve disorders can be classified into two categories: tests for afferent/efferent nerve function such as nerve conduction (bedside neurological examination) and tests for increased mechanosensitivity (e.g. upper limb neurodynamic tests (ULNTs) and nerve palpation). Reliability reports of nerve palpation and the interpretation of neurodynamic tests are scarce. This study therefore investigated the intertester reliability of nerve palpation and ULNTs. ULNTs were interpreted based on symptom reproduction and structural differentiation. To put the reliability of these tests in perspective, a comparison with the reliability of clinical tests for nerve function was made.
METHODS: Two experienced clinicians examined 31 patients with unilateral arm and/or neck pain. The examination included clinical tests for nerve function (sensory testing, reflexes and manual muscle testing (MMT)) and mechanosensitivity (ULNTs and palpation of the median, radial and ulnar nerve). Kappa statistics were calculated to evaluate intertester reliability. A meta-analysis determined an overall kappa for the domains with multiple kappa values (MMT, ULNT, palpation). We then compared the difference in reliability between the tests of mechanosensitivity and nerve function using a one-sample t-test.
RESULTS: We observed moderate to substantial reliability for the tests for afferent/efferent nerve function (sensory testing: kappa = 0.53; MMT: kappa = 0.68; no kappa was calculated for reflexes due to a lack of variation). Tests to investigate mechanosensitivity demonstrated moderate reliability (ULNT: kappa = 0.45; palpation: kappa = 0.59). When compared statistically, there was no difference in reliability for tests for nerve function and mechanosensitivity (p = 0.06).
CONCLUSION: This study demonstrates that clinical tests which evaluate increased nerve mechanosensitivity and afferent/efferent nerve function have comparable moderate to substantial reliability. To further investigate the clinometric properties of these tests, more studies are needed to evaluate their validity
Homogenization via formal multiscale asymptotics and volume averaging: How do the two techniques compare?
A wide variety of techniques have been developed to homogenize transport equations in multiscale and multiphase systems. This has yielded a rich and diverse field, but has also resulted in the emergence of isolated scientific communities and disconnected bodies of literature. Here, our goal is to bridge the gap between formal multiscale asymptotics and the volume averaging theory. We illustrate the methodologies via a simple example application describing a parabolic transport problem and, in so doing, compare their respective advantages/disadvantages from a practical point of view. This paper is also intended as a pedagogical guide and may be viewed as a tutorial for graduate students as we provide historical context, detail subtle points with great care, and reference many fundamental works
Evaluation of accuracy and efficiency of some simulation and sampling methods in structural reliability analysis
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