29,728 research outputs found
Recommended from our members
Anharmonic multi-phonon nonradiative transition: An ab initio calculation approach
Nonradiative carrier recombinations at deep centers in semiconductors are of great importance for both fundamental physics and device engineering. In this article, we provide a revised analysis of Huang’s original nonradiative multi-phonon (NMP) theory with ab initio calculations. First, we confirmed at the first-principles level that Huang’s concise formula gives the same results as the matrix-based formula, and that Huang’s high-temperature formula provides an analytical expression for the coupling constant in Marcus theory. Secondly, we correct for anharmonic effects by taking into account local phonon-mode variations for different charge states of a defect. The corrected capture rates for defects in GaN and SiC agree well with experiments
Flat Dielectric Grating Reflectors with High Focusing Power
Sub-wavelength dielectric gratings (SWG) have emerged recently as a promising
alternative to distributed-Bragg-reflection (DBR) dielectric stacks for
broadband, high-reflectivity filtering applications. A SWG structure composed
of a single dielectric layer with the appropriate patterning can sometimes
perform as well as thirty or forty dielectric DBR layers, while providing new
functionalities such as polarization control and near-field amplification. In
this paper, we introduce a remarkable property of grating mirrors that cannot
be realized by their DBR counterpart: we show that a non-periodic patterning of
the grating surface can give full control over the phase front of reflected
light while maintaining a high reflectivity. This new feature of dielectric
gratings could have a substantial impact on a number of applications that
depend on low-cost, compact optical components, from laser cavities to CD/DVD
read/write heads.Comment: submitted to Nature Photonic
P2X receptors: epithelial ion channels and regulators of salt and water transport.
When the results from electrophysiological studies of renal epithelial cells are combined with data from in vivo tubule microperfusion experiments and immunohistochemical surveys of the nephron, the accumulated evidence suggests that ATP-gated ion channels, P2X receptors, play a specialized role in the regulation of ion and water movement across the renal tubule and are integral to electrolyte and fluid homeostasis. In this short review, we discuss the concept of P2X receptors as regulators of salt and water salvage pathways, as well as acknowledging their accepted role as ATP-gated ion channels
An integrated circuit to enable electrodeposition and amperometric readout of sensing electrodes
This paper presents the design of an integrated circuit (IC) for (i) electrochemical deposition of sensor layers on the on-chip pad openings to form sensing electrodes, and (ii) amperometric readout of electrochemical sensors. The IC consists of two main circuit blocks: a Beta-multiplier based current reference for galvanostatic electrodeposition, and a switch-capacitor based amperometric readout circuit. The circuits are designed and simulated in a 180-nm CMOS process. The reference circuit generates a stable current of 99 nA with a temperature coefficient of 141 ppm/°C at best and 170 ppm/°C on average (across corners) over a supply voltage range of 1.2-2.4 V, and a line regulation of 0.7 %/V. The readout circuit measures current within pm 2 mu mathrmA with 99.9% linearity and a minimum integrated input-referred noise of 0.88 pA
A knowledge-based weighting framework to boost the power of genome-wide association studies
Background: We are moving to second-wave analysis of genome-wide association studies (GWAS), characterized by comprehensive bioinformatical and statistical evaluation of genetic associations. Existing biological knowledge is very valuable for GWAS, which may help improve their detection power particularly for disease susceptibility loci of moderate effect size. However, a challenging question is how to utilize available resources that are very heterogeneous to quantitatively evaluate the statistic significances. Methodology/Principal Findings: We present a novel knowledge-based weighting framework to boost power of the GWAS and insightfully strengthen their explorative performance for follow-up replication and deep sequencing. Built upon diverse integrated biological knowledge, this framework directly models both the prior functional information and the association significances emerging from GWAS to optimally highlight single nucleotide polymorphisms (SNPs) for subsequent replication. In the theoretical calculation and computer simulation, it shows great potential to achieve extra over 15% power to identify an association signal of moderate strength or to use hundreds of whole-genome subjects fewer to approach similar power. In a case study on late-onset Alzheimer disease (LOAD) for a proof of principle, it highlighted some genes, which showed positive association with LOAD in previous independent studies, and two important LOAD related pathways. These genes and pathways could be originally ignored due to involved SNPs only having moderate association significance. Conclusions/Significance: With user-friendly implementation in an open-source Java package, this powerful framework will provide an important complementary solution to identify more true susceptibility loci with modest or even small effect size in current GWAS for complex diseases. © 2010 Li et al.published_or_final_versio
Alkylated-C-60 based soft materials: regulation of self-assembly and optoelectronic properties by chain branching
Derivatization of fullerene (C60) with branched aliphatic chains softens C60-based materials and enables the formation of thermotropic liquid crystals and room temperature nonvolatile liquids. This work demonstrates that by carefully tuning parameters such as type, number and substituent position of the branched chains, liquid crystalline C60 materials with mesophase temperatures suited for photovoltaic cell fabrication and room temperature nonvolatile liquid fullerenes with tunable viscosity can be obtained. In particular, compound 1, with branched chains, exhibits a smectic liquid crystalline phase extending from 84 °C to room temperature. Analysis of bulk heterojunction (BHJ) organic solar cells with a ca. 100 nm active layer of compound 1 and poly(3-hexylthiophene) (P3HT) as an electron acceptor and an electron donor, respectively, reveals an improved performance (power conversion efficiency, PCE: 1.6 ± 0.1%) in comparison with another compound, 10 (PCE: 0.5 ± 0.1%). The latter, in contrast to 1, carries linear aliphatic chains and thus forms a highly ordered solid lamellar phase at room temperature. The solar cell performance of 1 blended with P3HT approaches that of PCBM/P3HT for the same active layer thickness. This indicates that C60 derivatives bearing branched tails are a promising class of electron acceptors in soft (flexible) photovoltaic devices
Subtle biological responses to increased CO2 concentrations by Phaeocystis globosa Scherffel, a harmful algal bloom species
Recent investigations into the role of carbon dioxide on phytoplankton growth and composition have clearly shown differential effects among species and assemblages, suggesting that increases in oceanic CO2 may play a critical role in structuring lower trophic levels of marine systems in the future. Furthermore, alarming increases in the occurrence of harmful algal blooms (HABs) in coastal waters have been observed, and while not uniform among systems, appear in some manner to be linked to human impacts (eutrophication) on coastal systems. Models of HABs are in their infancy and do not at present include sophisticated biological effects or their environmental controls. Here we show that subtle biological responses occur in the HAB species Phaeocystis globosa Scherffel as a result of CO2 enrichment induced by gentle bubbling. The alga, which has a polymorphic life history involving the formation of both colonies and solitary cells, exhibited altered growth rates of colonial and solitary forms at [CO2] of 750 ppm, as well as increased colony formation. In addition, substantial modifications of elemental and photosynthetic constituents of the cells (C cell(-1), N cell(-1), potential quantum yield, chl a cell(-1)) occurred under elevated CO2 concentrations compared to those found at present CO2 levels. In contrast, other individual and population variables (e. g., colony diameter, total chlorophyll concentration, carbon/nitrogen ratio) were unaffected by increased CO2. Our results suggest that predictions of the future impacts of Phaeocystis blooms on coastal ecosystems and local biogeochemistry need to carefully examine the subtle biological responses of this alga in addition to community and ecosystem effects. Citation: Wang, Y., W. O. Smith Jr., X. Wang, and S. Li (2010), Subtle biological responses to increased CO2 concentrations by Phaeocystis globosa Scherffel, a harmful algal bloom species, Geophys. Res. Lett., 37, L09604, doi: 10.1029/2010GL042666
Drive-By Blind Modal Identification with Singular Spectrum Analysis
© 2019 American Society of Civil Engineers. Drive-by bridge parameter identification has been an active research area in recent years. An instrumented vehicle passing over a bridge deck captures dynamic information of the bridge structure without bridge closure and on-site instrumentation. The vehicle dynamic response includes components associated with the bridge surface roughness and the vehicle and bridge vibration. It is a challenge to separate these components and extract the bridge modal parameters from the vehicle response. A novel drive-by blind modal identification with singular spectrum analysis is proposed to extract the bridge modal frequencies from the vehicle dynamic response. The single-channel measured vehicular response is decomposed into a multichannel data set using singular spectrum analysis, and the bridge frequencies are then extracted via the blind modal identification. Numerical results showed that the proposed method is effective and robust to extract the bridge frequencies from the vehicle response measurement even with Class B road surface roughness. The effects of the moving speed and the vehicle parameters on the identification were studied. A vehicle-bridge interaction model in the laboratory was studied to further verify the proposed method using one- and two-axle vehicles
Holographic non-relativistic fermionic fixed point by the charged dilatonic black hole
Driven by the landscape of garden-variety condensed matter systems, we have
investigated how the dual spectral function behaves at the non-relativistic as
well as relativistic fermionic fixed point by considering the probe Dirac
fermion in an extremal charged dilatonic black hole with zero entropy. Although
the pattern for both of the appearance of flat band and emergence of Fermi
surface is qualitatively similar to that given by the probe fermion in the
extremal Reissner-Nordstrom AdS black hole, we find a distinctly different low
energy behavior around the Fermi surface, which can be traced back to the
different near horizon geometry. In particular, with the peculiar near horizon
geometry of our extremal charged dilatonic black hole, the low energy behavior
exhibits the universal linear dispersion relation and scaling property, where
the former indicates that the dual liquid is a Fermi one while the latter
implies that the dual liquid is not exactly of Landau Fermi type
Recommended from our members
New emissive mononuclear copper (I) complex: Structural and photophysical characterization focusing on solvatochromism, rigidochromism and oxygen sensing in mesoporous solid matrix
- …