5,395 research outputs found
Optofluidic Distributed Feedback Dye Lasers
We review our recent work on poly(dimethylsiloxane) (PDMS)-based optofluidic dye lasers using a guided wave distributed feedback (DFB) cavity. We show experimental results of single-mode operation, an integrated laser array, multiple color dye lasing, mechanical and fluidic tuning, and monolithic integration with microfluidic circuits. Potential applications and future directions are discussed
Nature of well-defined conductance of amine anchored molecular junctions
Amine terminated molecules show well behaved conductance in the scanning
tunneling microscope break-junction experimental measurements. We performed
density functional theory based electron transport calculations to explain the
nature of this phenomenon. We find that amines can be adsorbed only on apex Au
atom, while thiolate group can be attached equally well to undercoordinated and
clean Au surfaces. Our calculations show that only one adsorption geo metry is
sterically and energetically possible for amine anchored junction whereas three
different adsorption geometries with very distinct transport pro perties are
almost equally probable for thiolate anchored junction. We calculated the
conductance as a function of the junction stretching when the molecules are
pulled by the scanning tunneling microscope tip from the Au electrode. Our
calculations show that the stretching of the thiolate anchored junction during
its formation is accompanied by significant electrode geometry distortio n. The
amine anchored junctions exhibit very different behavior -- the electrode
remains intact when the scan ning tunneling microscope tip stretches the
junction
Empirical Bayes estimation of posterior probabilities of enrichment
To interpret differentially expressed genes or other discovered features,
researchers conduct hypothesis tests to determine which biological categories
such as those of the Gene Ontology (GO) are enriched in the sense of having
differential representation among the discovered features. We study application
of better estimators of the local false discovery rate (LFDR), a probability
that the biological category has equivalent representation among the
preselected features.
We identified three promising estimators of the LFDR for detecting
differential representation: a semiparametric estimator (SPE), a normalized
maximum likelihood estimator (NMLE), and a maximum likelihood estimator (MLE).
We found that the MLE performs at least as well as the SPE for on the order of
100 of GO categories even when the ideal number of components in its underlying
mixture model is unknown. However, the MLE is unreliable when the number of GO
categories is small compared to the number of PMM components. Thus, if the
number of categories is on the order of 10, the SPE is a more reliable LFDR
estimator. The NMLE depends not only on the data but also on a specified value
of the prior probability of differential representation. It is therefore an
appropriate LFDR estimator only when the number of GO categories is too small
for application of the other methods.
For enrichment detection, we recommend estimating the LFDR by the MLE given
at least a medium number (~100) of GO categories, by the SPE given a small
number of GO categories (~10), and by the NMLE given a very small number (~1)
of GO categories.Comment: exhaustive revision of Zhenyu Yang and David R. Bickel, "Minimum
Description Length Measures of Evidence for Enrichment" (December 2010).
COBRA Preprint Series. Article 76. http://biostats.bepress.com/cobra/ps/art7
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