An improved procedure for gene selection from microarray experiments using false discovery rate criterion

BACKGROUND: A large number of genes usually show differential expressions in a microarray experiment with two types of tissues, and the p-values of a proper statistical test are often used to quantify the significance of these differences. The genes with small p-values are then picked as the genes responsible for the differences in the tissue RNA expressions. One key question is what should be the threshold to consider the p-values small. There is always a trade off between this threshold and the rate of false claims. Recent statistical literature shows that the false discovery rate (FDR) criterion is a powerful and reasonable criterion to pick those genes with differential expression. Moreover, the power of detection can be increased by knowing the number of non-differential expression genes. While this number is unknown in practice, there are methods to estimate it from data. The purpose of this paper is to present a new method of estimating this number and use it for the FDR procedure construction. RESULTS: A combination of test functions is used to estimate the number of differentially expressed genes. Simulation study shows that the proposed method has a higher power to detect these genes than other existing methods, while still keeping the FDR under control. The improvement can be substantial if the proportion of true differentially expressed genes is large. This procedure has also been tested with good results using a real dataset. CONCLUSION: For a given expected FDR, the method proposed in this paper has better power to pick genes that show differentiation in their expression than two other well known methods

Implementation of CMRC on HBT power amplifier for WCDMA application

An InGaP/GaAs heterojunction bipolar transistor (HBT) is developed. By using this HBT, a power amplifier is designed for WCDMA user equipment, band-1 power class-2 application. The HBT power amplifier demonstrates a maximum output power (Pout) of 29.4dBm and a PAE of 48% at the frequency of 1.95GHz. When it operates in WCDMA standard, it achieves a Pout of 27dBm and a PAE of 32.4%. The Adjacent Channel Leakage power Ratio (ACLR) is -33dBc. To further improve the PAE, ACLR and IM3 performance, a CMRC circuit has been implemented on the HBT amplifier. The effect of CMRC on PAE and ACLR is investigated using a low power HBT amplifier. The results show that the ACLR can be improved by the CMRC. © 2004 IEEE.published_or_final_versio

A study of high-frequency-fed AC-DC converter with different DC-DC topologies

In this paper, the operation of high-frequency-fed AC-DC converters with different types of DC-DC topologies is presented. Based on the commonly used DC-DC converter topologies, the possibilities of new converter structure are investigated. Using buck and ZETA topologies as examples, the output voltage gain, output load range and switch stress of the converters are analytically studied. Both converter implementation examples will be given and experimentally demonstrated. © IEEE.published_or_final_versio

Energy loss of monoenergetic positrons passing through a thin carbon foil

In this paper, the measurements of energy loss and energy loss straggling for 1-10 keV monoenergetic positrons passing through thin carbon foils of different thicknesses ranging from 1.0 to 5.0 μg/cm 2 are presented. The stopping power dE/dx and positron transmission coefficient as a function of incident positron energy and foil thickness have also been investigated. Particularly, the experimental results obtained are compared with those from Monte Carlo simulation and theory with a view to providing a way to determine the actual thickness of a carbon foil. The ratio of the energy straggling to the foil thickness seems to have a linear relation with the beam energy. © 2011 Elsevier B.V. All rights reserved.postprin

Thickness dependence of positron induced secondary electron emission in forward geometry from thin carbon foils

Secondary electron (SE) emission from thin carbon foils induced by 1-20 keV positrons has been investigated over a range of nominal foil thicknesses from 1.0to5.0μg/cm 2. The measurement of SEs was carried out in forward geometry using a microchannel plate as a detector. The SE yield γ has been measured as a function of beam energy and compared with our Monte Carlo simulation results. We also present in this paper the material parameter Λ=γ/(dE/dx) and the emitted SE energy spectra. For incident positron energy of 5 keV or higher, the distribution is found to be characterized by the Sickafus form, AE- m and m is close to 1. For low energy incident positrons, however, another form, Bexp(-E/t), is proposed for describing the SE distribution. © 2011 Elsevier B.V. All rights reserved.postprin

iTag: Incentive-Based Tagging

In social tagging systems, such as Delicious1 and Flickr2, users are allowed to annotate resources (e.g., Web URLs and images) with textual descriptions called tags. Tags have proven to be invaluable building blocks in algorithms for searching, mining and recommending resources. In practice, however, not all resources receive the same attention from users, and as a result, most tags are added to the few highly-popular resources, while most of the resources receive few tags. Crucially, this incomplete tagging on resources can severely affect the effectiveness of all tagging applications. We present iTag, an incentive-based tagging system, which aims at improving tagging quality of resources, by incentivizing taggers under budget constraints. Our system is built upon traditional crowdsourcing systems such as Amazon Mechanical Turk (MTurk). In our demonstration, we will show how our system allows users to use simple but powerful strategies to significantly improve the tagging quality of resources.published_or_final_versio

A particle swarm optimization based memetic algorithm for dynamic optimization problems

Copyright @ Springer Science + Business Media B.V. 2010.Recently, there has been an increasing concern from the evolutionary computation community on dynamic optimization problems since many real-world optimization problems are dynamic. This paper investigates a particle swarm optimization (PSO) based memetic algorithm that hybridizes PSO with a local search technique for dynamic optimization problems. Within the framework of the proposed algorithm, a local version of PSO with a ring-shape topology structure is used as the global search operator and a fuzzy cognition local search method is proposed as the local search technique. In addition, a self-organized random immigrants scheme is extended into our proposed algorithm in order to further enhance its exploration capacity for new peaks in the search space. Experimental study over the moving peaks benchmark problem shows that the proposed PSO-based memetic algorithm is robust and adaptable in dynamic environments.This work was supported by the National Nature Science Foundation of China (NSFC) under Grant No. 70431003 and Grant No. 70671020, the National Innovation Research Community Science Foundation of China under Grant No. 60521003, the National Support Plan of China under Grant No. 2006BAH02A09 and the Ministry of Education, science, and Technology in Korea through the Second-Phase of Brain Korea 21 Project in 2009, the Engineering and Physical Sciences Research Council (EPSRC) of UK under Grant EP/E060722/01 and the Hong Kong Polytechnic University Research Grants under Grant G-YH60

Post-growth annealing induced change of conductivity in As-doped ZnO grown by radio frequency magnetron sputtering

Arsenic-doped ZnO films were fabricated by radio frequency magnetron sputtering method at a relatively low substrate temperature of 200 C. Post-growth annealing in air was carried out up to a temperature of 1000 C. The samples were characterized by Hall measurement, positron annihilation spectroscopy (PAS), secondary ion mass spectroscopy (SIMS), and cathodoluminescence (CL). The as-grown sample was of n-type and it converted to p-type material after the 400 C annealing. The resulting hole concentration was found to increase with annealing temperature and reached a maximum of 6 10 17cm -3 at the annealing temperature of 600 C. The origin of the p-type conductivity was consistent with the As Zn(V Zn) 2 shallow acceptor model. Further increasing the annealing temperature would decrease the hole concentration of the samples finally converted the sample back to n-type. With evidence, it was suggested that the removal of the p-type conductivity was due to the dissociation of the As Zn(V Zn) 2 acceptor and the creation of the deep level defect giving rise to the green luminescence. © 2011 American Institute of Physics.published_or_final_versio

Suppression of hypoxia inducible factor-1α (HIF-1α) by YC-1 is dependent on murine double minute 2 (Mdm2)

Inhibition of HIF-1α activity provides an important strategy for the treatment of cancer. Recently, 3-(5′-hydroxymethyl-2′-furyl)-1-benzyl indazole (YC-1) has been identified as an anti-HIF-1α drug in cancer therapy with unclear molecular mechanism. In the present study, we aimed to investigate the effect and mechanism of YC-1 on HIF-1α in a hepatocellular carcinoma cell line under hypoxic condition, which was generated by incubating cells with 0.1% O2. The phenotypic and molecular changes of cells were determined by cell proliferation assay, apoptosis assay, luciferase promoter assay, and Western blot analysis. YC-1 arrested tumor cell growth in a dose-dependent manner, whereas it did not induce cell apoptosis. Hypoxia-induced upregulation of HIF-1α was suppressed by YC-1 administration. YC-1 inhibited HIF-1α protein synthesis under normoxia and affected protein stability under hypoxia. YC-1 suppressed the expression of total and phosphorylated forms of murine double minute 2 (Mdm2), whereas this inhibitory effect was blocked by overexpression of Mdm2. In conclusion, YC-1 suppressed both protein synthesis and stability of HIF-1α in HCC cells, and its inhibitory effects on HIF-1α were dependent on Mdm2. © 2006 Elsevier Inc. All rights reserved.postprin