4,997 research outputs found
Bifurcation Boundary Conditions for Switching DC-DC Converters Under Constant On-Time Control
Sampled-data analysis and harmonic balance analysis are applied to analyze
switching DC-DC converters under constant on-time control. Design-oriented
boundary conditions for the period-doubling bifurcation and the saddle-node
bifurcation are derived. The required ramp slope to avoid the bifurcations and
the assigned pole locations associated with the ramp are also derived. The
derived boundary conditions are more general and accurate than those recently
obtained. Those recently obtained boundary conditions become special cases
under the general modeling approach presented in this paper. Different analyses
give different perspectives on the system dynamics and complement each other.
Under the sampled-data analysis, the boundary conditions are expressed in terms
of signal slopes and the ramp slope. Under the harmonic balance analysis, the
boundary conditions are expressed in terms of signal harmonics. The derived
boundary conditions are useful for a designer to design a converter to avoid
the occurrence of the period-doubling bifurcation and the saddle-node
bifurcation.Comment: Submitted to International Journal of Circuit Theory and Applications
on August 10, 2011; Manuscript ID: CTA-11-016
Angiopoietin-1 and keratinocyte growth factor restore the impaired alveolar fluid clearance induced by influenza H5N1 virus infection
Poster Session: Novel TherapeuticsBackground: Acute respiratory distress syndrome (ARDS) caused by high pathogenic avian influenza
(HPAI) H5N1 virus infection has resulted in severe illness and high mortality rates among patients.
Patients with ARDS are often characterized by impaired alveolar fluid clearance and alveolar edema.
An understanding of the mechanism responsible for human alveolar edema will lead to the
development of novel therapeutic treatments for ARDS patients. We hypothesized that the paracrine
soluble factors angiopoietin-1 (Ang-1) and keratinocyte growth factor (KGF) can resolve alveolar fluid
clearance by up-regulating the expression of major sodium and chloride transporters impaired by
HPAI H5N1 virus infection. Materials and Methods: Human alveolar epithelial cells grown on transwell
inserts were infected with HPAI H5N1 (A/HK/483/97) and low pathogenic avian influenza (LPAI) H1N1
(A/HK/54/98) viruses at MOI 0.1 or incubated with conditioned culture medium containing Ang-1
and/or KGF. At 24 and 48 h post-infection, the rate of alveolar fluid transport and protein permeability
across the alveolar epithelium was measured. Protein expression of sodium and chloride transporters
(Na-K-ATPase, CFTR, and epithelial sodium channel alpha subunit) was measured by qPCR, ELISA,
and Western blot. Results: HPAI H5N1 (A/HK/483/97) virus infection significantly reduced net alveolar
fluid transport and protein permeability when compared with H1N1 (A/HK/54/98) virus infection at 24 h
post-infection and further reduced it at 48 h post-infection. This reduction in alveolar fluid clearance
was associated with a substantial reduction in protein expression of Na-K-ATPase, CFTR, and
epithelial sodium channel alpha subunit. The influenza virus–infected cells treated with Ang-1 and
KGF restored the impaired alveolar edema fluid clearance and protein permeability after HPAI H5N1
virus infection. Furthermore, the paracrine soluble factors Ang-1 and KGF up-regulated the protein
expression of the major sodium and chloride transporters resulting from the HPAI influenza virus
infection. Conclusions: The paracrine soluble factors Ang-1 and KGF play an important role in
maintaining human alveolar fluid clearance by up-regulating the sodium and chloride transporting
systems in human alveolar epithelium. This study enriches the understanding of the development of
ARDS in human H5N1 disease and may aid in the development of possible therapeutic applications.published_or_final_versio
Measuring portfolio performance using a modified measure of risk
This paper reports the results of an investigation into the properties of a theoretical modification of beta proposed by Leland (1999) and based on earlier work of Rubinstein (1976). It is shown that when returns are elliptically symmetric, beta is the appropriate measure of risk and that there are other situations in which the modified beta will be similar to the traditional measure based on the capital asset pricing model. For the case where returns have a normal distribution, it is shown that the criterion either does not exist or reduces exactly to the conventional beta. It is therefore conjectured that the modified measure will only be useful for portfolios that have nonstandard return distributions which incorporate skewness. For such situations, it is shown how to estimate the measure using regression and how to compare the resulting statistic with a traditional estimated beta using Hotelling's test. An empirical study based on stocks from the FTSE350 does not find evidence to support the use of the new measure even in the presence of skewness.Journal of Asset Management (2007) 7, 388-403. doi:10.1057/palgrave.jam.225005
Agonist-Directed Desensitization of the β2-Adrenergic Receptor
The β2-adrenergic receptor (β2AR) agonists with reduced tachyphylaxis may offer new therapeutic agents with improved tolerance profile. However, receptor desensitization assays are often inferred at the single signaling molecule level, thus ligand-directed desensitization is poorly understood. Here we report a label-free biosensor whole cell assay with microfluidics to determine ligand-directed desensitization of the β2AR. Together with mechanistic deconvolution using small molecule inhibitors, the receptor desensitization and resensitization patterns under the short-term agonist exposure manifested the long-acting agonism of salmeterol, and differentiated the mechanisms of agonist-directed desensitization between a full agonist epinephrine and a partial agonist pindolol. This study reveals the cellular mechanisms of agonist-selective β2AR desensitization at the whole cell level
A momentum-dependent perspective on quasiparticle interference in Bi_{2}Sr_{2}CaCu_{2}O_{8+\delta}
Angle Resolved Photoemission Spectroscopy (ARPES) probes the momentum-space
electronic structure of materials, and provides invaluable information about
the high-temperature superconducting cuprates. Likewise, the cuprate
real-space, inhomogeneous electronic structure is elucidated by Scanning
Tunneling Spectroscopy (STS). Recently, STS has exploited quasiparticle
interference (QPI) - wave-like electrons scattering off impurities to produce
periodic interference patterns - to infer properties of the QP in
momentum-space. Surprisingly, some interference peaks in
Bi_{2}Sr_{2}CaCu_{2}O_{8+\delta} (Bi-2212) are absent beyond the
antiferromagnetic (AF) zone boundary, implying the dominance of particular
scattering process. Here, we show that ARPES sees no evidence of quasiparticle
(QP) extinction: QP-like peaks are measured everywhere on the Fermi surface,
evolving smoothly across the AF zone boundary. This apparent contradiction
stems from different natures of single-particle (ARPES) and two-particle (STS)
processes underlying these probes. Using a simple model, we demonstrate
extinction of QPI without implying the loss of QP beyond the AF zone boundary
Stability of Mine Car Motion in Curves of Invariable and Variable Radii
We discuss our experiences adapting three recent algorithms for maximum common (connected) subgraph problems to exploit multi-core parallelism. These algorithms do not easily lend themselves to parallel search, as the search trees are extremely irregular, making balanced work distribution hard, and runtimes are very sensitive to value-ordering heuristic behaviour. Nonetheless, our results show that each algorithm can be parallelised successfully, with the threaded algorithms we create being clearly better than the sequential ones. We then look in more detail at the results, and discuss how speedups should be measured for this kind of algorithm. Because of the difficulty in quantifying an average speedup when so-called anomalous speedups (superlinear and sublinear) are common, we propose a new measure called aggregate speedup
Response of Laser-Induced Thermal Lens Effect at Solid Surface
Recently Kuo et al. [1,2] and Satio et al.[3] presented the surface-thermal lens (STL) technique, this novel photothermal deformation technique has attracted great attention because it is a highly sensitive, noncontact and nondestructive measurement[4–6]. In this technique, a modulated pump beam is focused on the sample surface to produce the surface deformation and a cw probe beam is incident at the deformation region. Differing from the conventional photothermal deformation techniques, the spot size of the probe beam at the sample surface is much larger than the pump beam one. Then the probe beam reflected from the surface produces a diffraction pattern at the detection plane. More recently, STL technique has been successfully applied to study the temperature dependence of the thermal conductivity of semiconductor materials[5], weak absorption of optical thin films[6] and characterization of the solid materials[7,8]. However, the mechanism of STL phenomena has not been completely understood. Most theoretical models took no account of the influence of the air-thermal lens (ATL), although some experiment showed that the air significantly affected the detected diffraction pattern[2]. In addition, it is necessary to characterize frequency responses of signals because the response is used to determine the thermal property of the solid materials[5]
A gene signature for post-infectious chronic fatigue syndrome
Background: At present, there are no clinically reliable disease markers for chronic fatigue syndrome. DNA chip microarray technology provides a method for examining the differential expression of mRNA from a large number of genes. Our hypothesis was that a gene expression signature, generated by microarray assays, could help identify genes which are dysregulated in patients with post-infectious CFS and so help identify biomarkers for the condition. Methods: Human genome-wide Affymetrix GeneChip arrays (39,000 transcripts derived from 33,000 gene sequences) were used to compare the levels of gene expression in the peripheral blood mononuclear cells of male patients with post-infectious chronic fatigue (n = 8) and male healthy control subjects (n = 7). Results: Patients and healthy subjects differed significantly in the level of expression of 366 genes. Analysis of the differentially expressed genes indicated functional implications in immune modulation, oxidative stress and apoptosis. Prototype biomarkers were identified on the basis of differential levels of gene expression and possible biological significance Conclusion: Differential expression of key genes identified in this study offer an insight into the possible mechanism of chronic fatigue following infection. The representative biomarkers identified in this research appear promising as potential biomarkers for diagnosis and treatment
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