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Search Results: 1 - 10 of 337248 matches for " J. Xu "
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A Survey of Synchronous Collaboration Tools
J. Xu,J. Zhang
Information Technology Journal , 2008,
Abstract: This study investigates the features of synchronous collaboration tools, the meanings of the features and identifies common and key characteristics of synchronous collaboration tools. We organize features by the six stages of meeting process: starting meeting, communication, presentation, interaction, administration and ending meeting. We test nine collaboration tools that are today`s market leaders. Data collected in this study come from our experiments and online documents. This study will help professionals gain knowledge of what current online meeting market has to offer and aid them make right decisions in selecting tools based on their meeting needs.
An NP-hardness Result on the Monoid Frobenius Problem
Zhi Xu,J. Shallit
Computer Science , 2008,
Abstract: The following problem is NP-hard: given a regular expression $E$, decide if $E^*$ is not co-finite.
Estimation of Longest Stability Interval for a Kind of Explicit Linear Multistep Methods
Y. Xu,J. J. Zhao
Discrete Dynamics in Nature and Society , 2010, DOI: 10.1155/2010/912691
Abstract: The new explicit linear three-order four-step methods with longest interval of absolute stability are proposed. Some numerical experiments are made for comparing different kinds of linear multistep methods. It is shown that the stability intervals of proposed methods can be longer than that of known explicit linear multistep methods. 1. Introduction For the initial value problem of the ordinary differential equation (ODE) where and with , there are a lot of numerical methods to be proposed for the numerical integration. Among them, linear multistep methods (LMMs) are a class of the most prominent and most widely used methods, see [1, 2] and the references therein. Adams methods are among the oldest of LMMs, dating back to the nineteenth century. Nevertheless, they continue to play a key role in efficient modern algorithms. The first to use such a method was Adams in solving a problem of Bashforth in connection with capillary action, see [3]. In contrast to one-step methods, where the numerical solution is obtained solely from the differential equation and the initial value , a linear multistep ( -step) method requires ( ) starting values and a multistep ( -step) formula to obtain an approximation to the exact solution, see [4]. So far as we know, explicit linear multistep methods (ELMMs) have some advantages such as simple calculation formulae, and small error constants. However, due to the famous Dahlquist barrier in [5], an explicit linear multistep method cannot be A-stable. Therefore, we try to find the new explicit linear multistep methods with the longest interval of stability region in this paper. And some numerical experiments are given to compare the proposed methods with existing methods such as Adams-Bashforth method, Adams-Moulton methods, and BDF methods. Practical calculations have shown that these proposed methods are adaptive. 2. Linear Multistep Methods Applying the linear multistep ( -step) methods to the initial value problem (1.1), we obtain the recurrence relation where denotes an approximation to the solution , , for , the constant steplength , and starting conditions are required. Here, and are constants subject to the condition . If , then the corresponding methods (2.1) are explicit, and implicit otherwise. Then, we define the first and second generating polynomials by where is a dummy variable. Consider the scalar test equation where and . Its characteristic polynomial can be written as where . Here, we quote some important definitions (see Sections , , and in the reference [2]). Definition 2.1. The set is called the region of
Redshift evolution of extragalactic rotation measures
J. Xu,J. L. Han
Physics , 2014, DOI: 10.1093/mnras/stu1018
Abstract: We obtained rotation measures of 2642 quasars by cross-identification of the most updated quasar catalog and rotation measure catalog. After discounting the foreground Galactic Faraday rotation of the Milky Way, we get the residual rotation measure (RRM) of these quasars. We carefully discarded the effects from measurement and systematical uncertainties of RRMs as well as large RRMs from outliers, and get marginal evidence for the redshift evolution of real dispersion of RRMs which steady increases to 10 rad m$^{-2}$ from $z=0$ to $z\sim1$ and is saturated around the value at higher redshifts. The ionized clouds in the form of galaxy, galaxy clusters or cosmological filaments could produce the observed RRM evolutions with different dispersion width. However current data sets can not constrain the contributions from galaxy halos and cosmic webs. Future RM measurements for a large sample of quasars with high precision are desired to disentangle these different contributions.
A compiled catalog of rotation measures of radio point sources
J. Xu,J. L. Han
Physics , 2014, DOI: 10.1088/1674-4527/14/8/005
Abstract: We compiled a catalog of Faraday rotation measures (RMs) for 4553 extragalactic radio point sources ublished in literature. These RMs were derived from multi-frequency polarization observations. The RM data are compared to those in the NRAO VLA Sky Survey (NVSS) RM catalog. We reveal a systematic uncertainty of about $10.0 \pm 1.5$\,rad~m$^{-2}$ in the NVSS RM catalog. The Galactic foreground RM is calculated through a weighted averaging method by using the compiled RM catalog together with the NVSS RM catalog, with careful consideration of uncertainties in the RM data. The data from the catalog and the interface for the Galactic foreground RM calculations are publicly available on the webpage: http://zmtt.bao.ac.cn/RM/.
Absolute cross-section normalization of magnetic neutron scattering data
Guangyong Xu,Zhijun Xu,J. M. Tranquada
Physics , 2013, DOI: 10.1063/1.4818323
Abstract: We discuss various methods to obtain the resolution volume for neutron scattering experiments, in order to perform absolute normalization on inelastic magnetic neutron scattering data. Examples from previous experiments are given. We also try to provide clear definitions of a number of physical quantities which are commonly used to describe neutron magnetic scattering results, including the dynamic spin correlation function and the imaginary part of the dynamic susceptibility. Formulas that can be used for general purposes are provided and the advantages of the different normalization processes are discussed.
Recovery of Metals from Aluminum Dross and Saltcake  [PDF]
J.Y. Hwang, X. Huang, Z. Xu
Journal of Minerals and Materials Characterization and Engineering (JMMCE) , 2006, DOI: 10.4236/jmmce.2006.51003
Abstract: Various aluminum-smelting by-products from three production sources were received and characterized. The waste materials were tested for compound identification and environmental acceptance. A coarse metallic aluminum recovery test using an Eddy Current separator (ECS) was performed using two different Circuit configurations. White dross performed equally well with either Circuit, while black dross processing shows significant difference on the separation results. It was found that ECS technology was effective for particle sizes down to 6-10 mesh.
Evaluation of the Management of Hyperlipidemia and Hypertension in an Outpatient Cardiac Transplant Clinic  [PDF]
Jane J. Xu, Ilene Burton, Wayne J. Tymchak, Glen J. Pearson
Pharmacology & Pharmacy (PP) , 2016, DOI: 10.4236/pp.2016.71010
Abstract: Background: Allograft coronary artery disease (ACAD) is a common cause of morbidity and mortality post-orthotopic heart transplantation (OHT). ACAD progression may be reduced by modifying cardiovascular risk factors, such as hyperlipidemia and hypertension. We sought to evaluate the management of hyperlipidemia and hypertension among OHT recipients followed in an outpatient cardiac transplant clinic. Objective: The primary objective was to assess the proportion of OHT patients achieving both the recommended LDL target of <2.0 mmol/L and BP targets of <140/90 mmHg (or <130/80 mmHg for diabetics) in an outpatient cardiac transplant clinic. Methods: A cross-sectional retrospective analysis of the medical records of all adult OHT recipients actively followed in our outpatient cardiac transplant between January-March 2009. Results: Of the 193 patients included, both the low-density lipoprotein (LDL) cholesterol and blood pressure (BP) targets were achieved in 111 (57.5%) patients. The LDL target alone was achieved by 140 (72.5%) patients and the BP target alone by 153 (79.3%) patients. Statins were prescribed in 183 (94.8%) patients with a mean LDL of 1.81 mmol/L (±0.55). Angiotensin converting enzyme-inhibitors [ACE-I] (or angiotensin receptor blockers [ARB]) were prescribed in 154 (79.8%) patients, diltiazem in 101 (52.3%) patients, and both in 85 (44.0%) patients, with a mean BP of 124.2/77.8 mmHg (±13.6/8.2). Adverse reactions related to statins, ACE-inhibitors or diltiazem were uncommon and rarely resulted in drug discontinuation. Conclusions: Guideline recommended that LDL and BP targets are achievable in a significant proportion of OHT recipients. The high utilization rates of statins for dyslipidemia and ACE-I (or ARB) and diltiazem for BP were consistent with guideline recommendations for the prevention of ACAD. Despite concerns regarding the potential for pharmacokinetic drug interactions in OHT patients, the reported rates of any drug intolerance to these medications were low in our population.
A Further Study of Relative longitude shift of Pulsar Beams
R. X. Xu,J. W. Xu,G. J. Qiao
Physics , 2001,
Abstract: It is of great important to study pulsar beam shapes if we are concerned with emission theories and pulsar birth rate. Both observations and/or the inverse Compton scattering model show that different emission components are emitted from different heights. The relative longitude phase shifts due to different heights of emission components and to the toroidal velocity of electron are considered in this paper. Several possible observational features arising from the phase shift effects are presented. The emission beams may not have circular cross sections although the emission regions may be symmetric with respect to the magnetic axes.
Double Hopf Bifurcation with Strong Resonances in Delayed Systems with Nonlinerities
J. Xu,K. W. Chung
Mathematical Problems in Engineering , 2009, DOI: 10.1155/2009/759363
Abstract: An efficient method is proposed to study delay-induced strong resonant double Hopf bifurcation for nonlinear systems with time delay. As an illustration, the proposed method is employed to investigate the 1 : 2 double Hopf bifurcation in the van der Pol system with time delay. Dynamics arising from the bifurcation are classified qualitatively and expressed approximately in a closed form for either square or cubic nonlinearity. The results show that 1 : 2 resonance can lead to codimension-three and codimension-two bifurcations. The validity of analytical predictions is shown by their consistency with numerical simulations.
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