2,093 research outputs found
Shrinkage Confidence Procedures
The possibility of improving on the usual multivariate normal confidence was
first discussed in Stein (1962). Using the ideas of shrinkage, through Bayesian
and empirical Bayesian arguments, domination results, both analytic and
numerical, have been obtained. Here we trace some of the developments in
confidence set estimation.Comment: Published in at http://dx.doi.org/10.1214/10-STS319 the Statistical
Science (http://www.imstat.org/sts/) by the Institute of Mathematical
Statistics (http://www.imstat.org
Hot Carrier Transport and Photocurrent Response in Graphene
Strong electron-electron interactions in graphene are expected to result in
multiple-excitation generation by the absorption of a single photon. We show
that the impact of carrier multiplication on photocurrent response is enhanced
by very inefficient electron cooling, resulting in an abundance of hot
carriers. The hot-carrier-mediated energy transport dominates the photoresponse
and manifests itself in quantum efficiencies that can exceed unity, as well as
in a characteristic dependence of the photocurrent on gate voltages. The
pattern of multiple photocurrent sign changes as a function of gate voltage
provides a fingerprint of hot-carrier-dominated transport and carrier
multiplication.Comment: 4 pgs, 2 fg
Modulation of Nitric Oxide Release in Cultured Human Umbilical Vein Endothelial Cells by Myristoylated-PKC Epsilon Activator/Inhibitor Peptides
Protein kinase C epsilon (PKCε) is known to increase endothelial nitric oxide synthase (eNOS) activity and subsequent nitric oxide (NO) release via phosphorylation at serine 1177 of eNOS in previous in vitro and in vivo animal studies under normoxic conditions. However, the role of PKCε regulating eNOS activity and NO release is not well known in human endothelial cells. Moreover, understanding the role of PKCε in regulating eNOS activity would be essential in the clinical setting of myocardial infarction. Re-establishing blood flow after thrombus removal results in endothelial dysfunction and is characterized by decreased NO bioavailability and excess reactive oxygen species (ROS) generated by uncoupled eNOS during reperfusion. Therefore, determining NO release using selective cell permeable PKCε activator (Myr-PKCε+) and inhibitor peptides (Myr-PKCε- ) in cultured human umbilical vein endothelial cells (HUVECs) under normoxic conditions would provide a foundation to test these peptides under hypoxic-reoxygenation conditions when eNOS would be uncoupled and produce ROS instead of NO release. Single-donor HUVECs at passages 3-4 were grown to confluence in 6-well (106 cells/well) plates. NO release was measured in real time using a calibrated NO electrode following the administration of 10 μM Myr-PKCε+ or 10 μM Myr-PKCε- treatments in the absence or presence of 10 μM acetylcholine (Ach) stimulation of NO release. Basal NO release (83±12 pM) was determined by measuring the difference between wells with and without HUVECs (n=9, P\u3c0.05 compared to wells with no cells). In the absence of Ach stimulation, Myr-PKCε+ significantly enhanced NO release to 136±13 pM (n=6, p\u3c0.05) and Myr-PKCε- attenuated total NO release to 16±27 pM (n=7, p\u3c0.05) compared to basal levels. Similar to Myr-PKCε+, 10 μM Ach significantly enhanced NO release to 153±11 pM above basal levels (p\u3c0.05, n=20). Moreover, in the presence of 10 μM Ach, Myr-PKCε+ still significantly increased NO release (129±17 pM, p\u3c0.05, n=8) and Myr-PKCε- decreased NO release (34±12 pM, p\u3c0.05, n=7) compared to basal levels. In summary, these results suggest that in cultured HUVECs, Myr-PKCε+ presumably increase NO release via activation of eNOS; whereas Myr-PKCε- attenuates eNOS activity by inhibiting its phosphorylation. Therefore, the effects of Myr-PKCε+ and Myr-PKCε- are translational across species in regulating NO release
Manipulating infrared photons using plasmons in transparent graphene superlattices
Superlattices are artificial periodic nanostructures which can control the
flow of electrons. Their operation typically relies on the periodic modulation
of the electric potential in the direction of electron wave propagation. Here
we demonstrate transparent graphene superlattices which can manipulate infrared
photons utilizing the collective oscillations of carriers, i.e., plasmons of
the ensemble of multiple graphene layers. The superlattice is formed by
depositing alternating wafer-scale graphene sheets and thin insulating layers,
followed by patterning them all together into 3-dimensional
photonic-crystal-like structures. We demonstrate experimentally that the
collective oscillation of Dirac fermions in such graphene superlattices is
unambiguously nonclassical: compared to doping single layer graphene,
distributing carriers into multiple graphene layers strongly enhances the
plasmonic resonance frequency and magnitude, which is fundamentally different
from that in a conventional semiconductor superlattice. This property allows us
to construct widely tunable far-infrared notch filters with 8.2 dB rejection
ratio and terahertz linear polarizers with 9.5 dB extinction ratio, using a
superlattice with merely five graphene atomic layers. Moreover, an unpatterned
superlattice shields up to 97.5% of the electromagnetic radiations below 1.2
terahertz. This demonstration also opens an avenue for the realization of other
transparent mid- and far-infrared photonic devices such as detectors,
modulators, and 3-dimensional meta-material systems.Comment: under revie
Multi-Object Tracking by Iteratively Associating Detections with Uniform Appearance for Trawl-Based Fishing Bycatch Monitoring
The aim of in-trawl catch monitoring for use in fishing operations is to
detect, track and classify fish targets in real-time from video footage.
Information gathered could be used to release unwanted bycatch in real-time.
However, traditional multi-object tracking (MOT) methods have limitations, as
they are developed for tracking vehicles or pedestrians with linear motions and
diverse appearances, which are different from the scenarios such as livestock
monitoring. Therefore, we propose a novel MOT method, built upon an existing
observation-centric tracking algorithm, by adopting a new iterative association
step to significantly boost the performance of tracking targets with a uniform
appearance. The iterative association module is designed as an extendable
component that can be merged into most existing tracking methods. Our method
offers improved performance in tracking targets with uniform appearance and
outperforms state-of-the-art techniques on our underwater fish datasets as well
as the MOT17 dataset, without increasing latency nor sacrificing accuracy as
measured by HOTA, MOTA, and IDF1 performance metrics
Competing Ultrafast Energy Relaxation Pathways in Photoexcited Graphene
For most optoelectronic applications of graphene a thorough understanding of
the processes that govern energy relaxation of photoexcited carriers is
essential. The ultrafast energy relaxation in graphene occurs through two
competing pathways: carrier-carrier scattering -- creating an elevated carrier
temperature -- and optical phonon emission. At present, it is not clear what
determines the dominating relaxation pathway. Here we reach a unifying picture
of the ultrafast energy relaxation by investigating the terahertz
photoconductivity, while varying the Fermi energy, photon energy, and fluence
over a wide range. We find that sufficiently low fluence ( 4
J/cm) in conjunction with sufficiently high Fermi energy (
0.1 eV) gives rise to energy relaxation that is dominated by carrier-carrier
scattering, which leads to efficient carrier heating. Upon increasing the
fluence or decreasing the Fermi energy, the carrier heating efficiency
decreases, presumably due to energy relaxation that becomes increasingly
dominated by phonon emission. Carrier heating through carrier-carrier
scattering accounts for the negative photoconductivity for doped graphene
observed at terahertz frequencies. We present a simple model that reproduces
the data for a wide range of Fermi levels and excitation energies, and allows
us to qualitatively assess how the branching ratio between the two distinct
relaxation pathways depends on excitation fluence and Fermi energy.Comment: Nano Letters 201
Loss Functions for Set Estimations
23 pages, 1 article*Loss Functions for Set Estimations* (Casella, George; Hwang, J. T.-Gene; Robert, Christian P.) 23 page
PCB Exposure and in Vivo CYP1A2 Activity among Native Americans
Cytochrome P-450 1A2 (CYP1A2) is an enzyme involved in the metabolic activation of some carcinogens and is believed to be induced by xenobiotics. Very few studies, however, have investigated the association between environmental exposures and in vivo CYP1A2 activity in humans. To address this issue, a study was conducted of CYP1A2 activity among Native Americans exposed to polychlorinated biphenyls (PCBs) from the consumption of fish from the St. Lawrence River. At the Mohawk Nation at Akwesasne (in New York and in Ontario and Quebec, Canada), 103 adults were interviewed, and they donated blood for serum PCB analysis and underwent the caffeine breath test (CBT), a safe and noninvasive procedure that uses caffeine as a probe for CYP1A2 activity in vivo. The results supported the findings of other studies that CBT values are higher among smokers and men and lower among women who use oral contraceptives. Despite a relatively low average total PCB body burden in this population, the sum of serum levels for nine mono- or di-ortho-substituted PCB congeners showed positive associations with CBT values (p = 0.052 wet weight and p = 0.029 lipid adjusted), as did toxic equivalent quantities (TEQs; p = 0.091 for wet weight and 0.048 for lipid adjusted). Regarding individual congeners, serum levels of PCB-153, PCB-170, and PCB-180 were significantly correlated with CBT values. The results support the notion that CYP1A2 activity may be a marker of an early biological effect of exposure to PCBs in humans and that the CBT may be a useful tool to monitor such effects
The X-ray spectra and spectral variability of intermediate type Seyfert galaxies: ASCA observations of NGC 4388 and ESO 103-G35
The X-ray spectra of two intermediate type Seyfert galaxies are investigated
using ASCA observations separated by more than a year. Both NGC 4388 and ESO
103-G35 exhibit strong, narrow Fe K alpha line emission and absorption by cold
neutral gas with a column density ~ 10^23 cm^-2, characteristic of the X-ray
spectra of type 2 Seyfert galaxies. The power law continuum flux has changed by
a factor of 2 over a time-scale of ~ 2 years for both objects, declining in the
case of NGC 4388 and rising in ESO 103-G35. No variation was observed in the
equivalent width of the Fe K alpha line in the spectra of NGC 4388, implying
that the line flux declined with the continuum. We find that the strength of
the line cannot be accounted for by fluorescence in line-of-sight material with
the measured column density unless a `leaky-absorber' model of the type favored
for IRAS 04575-7537 is employed. The equivalent width of the Fe K alpha
emission line is seen to decrease between the observations of ESO 103-G35 while
the continuum flux increased. The 1996 observation of ESO 103-G35 can also be
fitted with an absorption edge at 7.4 0.2 keV due to partially ionized
iron, and when an ionized absorber model is fitted to the data it is found that
the equivalent column of neutral hydrogen rises to 3.5 x 10^23 cm^-2. The Fe K
alpha line flux can be accounted by fluorescence in this material alone and
this model is also a good representation of the 1988 and 1991 Ginga
observations. There is then no requirement for a reflection component in the
ASCA spectra of ESO 103-G35 or NGC 4388.Comment: 45 pages, 5 tables, 11 figures. Accepted for publication in the
Astrophysical Journa
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