867 research outputs found
The Calculus of M-estimation in R with geex
M-estimation, or estimating equation, methods are widely applicable for point
estimation and asymptotic inference. In this paper, we present an R package
that can find roots and compute the empirical sandwich variance estimator for
any set of user-specified, unbiased estimating equations. Examples from the
M-estimation primer by Stefanski and Boos (2002) demonstrate use of the
software. The package also includes a framework for finite sample variance
corrections and a website with an extensive collection of tutorials
Thick Slice Clarity for Localization of Novel Neuroactive Target Gene Products
This poster describes the Thick Slice CLARITY technique, an alternative to the whole tissue or whole body clarity technique. The CLARITY technique is a tissue clearing method allowing for both structural and molecular analysis of a tissue sample, but the method applied to whole tissue or body is very expensive and time consuming. Thick Slice CLARITY applies the same principles but to a 200 micrometer slice of brain tissue. This method, used in conjunction wit standard fluorescent staining methods and imaging via confocal microscopy, has allowed for the colocalization of GPR3 with neurons in the mouse striatum
A Study of the Shortest-Period Planets Found With Kepler
We present the results of a survey aimed at discovering and studying
transiting planets with orbital periods shorter than one day
(ultra--short-period, or USP, planets), using data from the {\em Kepler}
spacecraft. We computed Fourier transforms of the photometric time series for
all 200,000 target stars, and detected transit signals based on the presence of
regularly spaced sharp peaks in the Fourier spectrum. We present a list of 106
USP candidates, of which 18 have not previously been described in the
literature. In addition, among the objects we studied, there are 26 USP
candidates that had been previously reported in the literature which do not
pass our various tests. All 106 of our candidates have passed several standard
tests to rule out false positives due to eclipsing stellar systems. A low false
positive rate is also implied by the relatively high fraction of candidates for
which more than one transiting planet signal was detected. By assuming these
multi-transit candidates represent coplanar multi-planet systems, we are able
to infer that the USP planets are typically accompanied by other planets with
periods in the range 1-50 days, in contrast with hot Jupiters which very rarely
have companions in that same period range. Another clear pattern is that almost
all USP planets are smaller than 2 , possibly because gas giants in
very tight orbits would lose their atmospheres by photoevaporation when subject
to extremely strong stellar irradiation. Based on our survey statistics, USP
planets exist around approximately of G-dwarf stars, and
of K-dwarf stars.Comment: 20 pages, 10 figures. Submitted to ApJ. This version has been
reviewed by a refere
Gene Expression Changes in the Septum: Possible Implications for MicroRNAs in Sculpting the Maternal Brain
The transition from the non-maternal to the maternal state is characterized by a variety of CNS alterations that support the care of offspring. The septum (including lateral and medial portions) is a brain region previously linked to various emotional and motivational processes, including maternal care. In this study, we used microarrays (PLIER algorithm) to examine gene expression changes in the septum of postpartum mice and employed gene set enrichment analysis (GSEA) to identify possible regulators of altered gene expression. Genes of interest identified as differentially regulated with microarray analysis were validated with quantitative real-time PCR. We found that fatty acid binding protein 7 (Fabp7) and galanin (Gal) were downregulated, whereas insulin-like growth factor binding protein 3 (Igfbp3) was upregulated in postpartum mice compared to virgin females. These genes were previously found to be differentially regulated in other brain regions during lactation. We also identified altered expression of novel genes not previously linked to maternal behavior, but that could play a role in postpartum processes, including glutamate-ammonia ligase (Glul) and somatostatin receptor 1 (Sstr1) (both upregulated in postpartum). Genes implicated in metabolism, cell differentiation, or proliferation also exhibited altered expression. Unexpectedly, enrichment analysis revealed a high number of microRNAs, transcription factors, or conserved binding sites (177 with corrected P-value <0.05) that were significantly linked to maternal upregulated genes, while none were linked to downregulated genes. MicroRNAs have been linked to placenta and mammary gland development, but this is the first indication they may also play a key role in sculpting the maternal brain. Together, this study provides new insights into genes (along with possible mechanisms for their regulation) that are involved in septum-mediated adaptations during the postpartum period
Transits and Occultations of an Earth-Sized Planet in an 8.5-Hour Orbit
We report the discovery of an Earth-sized planet () in
an 8.5-hour orbit around a late G-type star (KIC 8435766, Kepler-78). The
object was identified in a search for short-period planets in the {\it Kepler}
database and confirmed to be a transiting planet (as opposed to an eclipsing
stellar system) through the absence of ellipsoidal light variations or
substantial radial-velocity variations. The unusually short orbital period and
the relative brightness of the host star ( = 11.5) enable robust
detections of the changing illumination of the visible hemisphere of the
planet, as well as the occultations of the planet by the star. We interpret
these signals as representing a combination of reflected and reprocessed light,
with the highest planet dayside temperature in the range of 2300 K to 3100 K.
Follow-up spectroscopy combined with finer sampling photometric observations
will further pin down the system parameters and may even yield the mass of the
planet.Comment: Accepted for publication, ApJ, 10 pages and 6 figure
Lattice study of ChPT beyond QCD
We describe initial results by the Lattice Strong Dynamics (LSD)
collaboration of a study into the variation of chiral properties of chiral
properties of SU(3) Yang-Mills gauge theory as the number of massless flavors
changes from to , with a focus on the use of chiral
perturbation theory.Comment: 9 pages, 3 figures. Presented at the 6th International Workshop on
Chiral Dynamics, University of Bern, Switzerland, July 6-10 200
Toward TeV Conformality
We study the chiral condensate for an SU(3) gauge theory
with massless Dirac fermions in the fundamental representation when
is increased from 2 to 6. For , our lattice simulations of , where is the Nambu-Goldstone-boson decay constant, agree with
the measured QCD value. For , this ratio shows significant
enhancement, presaging an even larger enhancement anticipated as
increases further, toward the critical value for transition from confinement to
infrared conformality.Comment: 4 pages, 4 figures. v2: revised version for PR
A Recipe for inferference: Start with Causal Inference. Add Interference. Mix Well with R.
In causal inference, interference occurs when the treatment of one subject affects the outcome of other subjects. Interference can distort research conclusions about causal effects when not accounted for properly. In the absence of interference, inverse probability weighted (IPW) estimators are commonly used to estimate causal effects from observational data. Recently, IPW estimators have been extended to handle interference. Tchetgen Tchetgen and VanderWeele (2012) proposed IPW methods to estimate direct and indirect (or spillover) effects that allow for interference between individuals within groups. In this paper, we present inferference, an R package that computes these IPW causal effect estimates when interference may be present within groups. We illustrate use of the package with examples from political science and infectious disease
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