5,657 research outputs found
Nonparametric Conditional Inference for Regression Coefficients with Application to Configural Polysampling
We consider inference procedures, conditional on an observed ancillary
statistic, for regression coefficients under a linear regression setup where
the unknown error distribution is specified nonparametrically. We establish
conditional asymptotic normality of the regression coefficient estimators under
regularity conditions, and formally justify the approach of plugging in
kernel-type density estimators in conditional inference procedures. Simulation
results show that the approach yields accurate conditional coverage
probabilities when used for constructing confidence intervals. The plug-in
approach can be applied in conjunction with configural polysampling to derive
robust conditional estimators adaptive to a confrontation of contrasting
scenarios. We demonstrate this by investigating the conditional mean squared
error of location estimators under various confrontations in a simulation
study, which successfully extends configural polysampling to a nonparametric
context
Does the BICEP2 Observation of Cosmological Tensor Modes Imply an Era of Nearly Planckian Energy Densities?
BICEP2 observations, interpreted most simply, suggest an era of inflation
with energy densities of order (, not far below the
Planck density. However, models of TeV gravity with large extra dimensions
might allow a very different interpretation involving much more modest energy
scales. We discuss the viability of inflation in such models, and conclude that
existing scenarios do not provide attractive alternatives to single field
inflation in four dimensions. Because the detection of tensor modes strengthens
our confidence that inflation occurred, it disfavors models of large extra
dimensions, at least for the moment.Comment: 4 pages, v3: version to appear in JHE
Determination of Nonlinear Genetic Architecture using Compressed Sensing
We introduce a statistical method that can reconstruct nonlinear genetic
models (i.e., including epistasis, or gene-gene interactions) from
phenotype-genotype (GWAS) data. The computational and data resource
requirements are similar to those necessary for reconstruction of linear
genetic models (or identification of gene-trait associations), assuming a
condition of generalized sparsity, which limits the total number of gene-gene
interactions. An example of a sparse nonlinear model is one in which a typical
locus interacts with several or even many others, but only a small subset of
all possible interactions exist. It seems plausible that most genetic
architectures fall in this category. Our method uses a generalization of
compressed sensing (L1-penalized regression) applied to nonlinear functions of
the sensing matrix. We give theoretical arguments suggesting that the method is
nearly optimal in performance, and demonstrate its effectiveness on broad
classes of nonlinear genetic models using both real and simulated human
genomes.Comment: 20 pages, 8 figures. arXiv admin note: text overlap with
arXiv:1408.342
Instability of Quantum de Sitter Spacetime
Quantized fields (e.g., the graviton itself) in de Sitter (dS) spacetime lead
to particle production: specifically, we consider a thermal spectrum resulting
from the dS (horizon) temperature. The energy required to excite these
particles reduces slightly the rate of expansion and eventually modifies the
semiclassical spacetime geometry. The resulting manifold no longer has constant
curvature nor time reversal invariance, and back-reaction renders the classical
dS background unstable to perturbations. In the case of AdS, there exists a
global static vacuum state; in this state there is no particle production and
the analogous instability does not arise.Comment: 3 pages, v2: version to appear in JHE
Iterated smoothed bootstrap confidence intervals for population quantiles
This paper investigates the effects of smoothed bootstrap iterations on
coverage probabilities of smoothed bootstrap and bootstrap-t confidence
intervals for population quantiles, and establishes the optimal kernel
bandwidths at various stages of the smoothing procedures. The conventional
smoothed bootstrap and bootstrap-t methods have been known to yield one-sided
coverage errors of orders O(n^{-1/2}) and o(n^{-2/3}), respectively, for
intervals based on the sample quantile of a random sample of size n. We sharpen
the latter result to O(n^{-5/6}) with proper choices of bandwidths at the
bootstrapping and Studentization steps. We show further that calibration of the
nominal coverage level by means of the iterated bootstrap succeeds in reducing
the coverage error of the smoothed bootstrap percentile interval to the order
O(n^{-2/3}) and that of the smoothed bootstrap-t interval to O(n^{-58/57}),
provided that bandwidths are selected of appropriate orders. Simulation results
confirm our asymptotic findings, suggesting that the iterated smoothed
bootstrap-t method yields the most accurate coverage. On the other hand, the
iterated smoothed bootstrap percentile method interval has the advantage of
being shorter and more stable than the bootstrap-t intervals.Comment: Published at http://dx.doi.org/10.1214/009053604000000878 in the
Annals of Statistics (http://www.imstat.org/aos/) by the Institute of
Mathematical Statistics (http://www.imstat.org
Diamond films from combustion of methyl acetylene and propadiene
To date diamond films grown with the combustion technique have used either acetylene or, rarely, ethylene as the fuel. However, there are barriers to large scale commercialization of the combustion technique using either fuel. For example, acetylene is relatively expensive and difficult to handle, while the use of ethylene gives relatively low growth rates. In this letter we propose replacing acetylene with MAPPTM gas, a commercial mixture of methyl acetylene and propadiene in liquefied petroleum gas (primarily propylene). MAPP gas is considerably cheaper, safer, and easier to handle than acetylene. Furthermore, the experiments described here suggest that MAPP gas flames are only slightly less efficient than acetylene flames at converting fuel carbon atoms into diamond
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