oalib

Publish in OALib Journal

ISSN: 2333-9721

APC: Only $99

Submit

Any time

2020 ( 1 )

2019 ( 117 )

2018 ( 839 )

2017 ( 825 )

Custom range...

Search Results: 1 - 10 of 52726 matches for " CAI Xu "
All listed articles are free for downloading (OA Articles)
Page 1 /52726
Display every page Item
Pulse-Width Pulse-Frequency Based Optimal Controller Design for Kinetic Kill Vehicle Attitude Tracking Control  [PDF]
Xingyuan Xu, Yuanli Cai
Applied Mathematics (AM) , 2011, DOI: 10.4236/am.2011.25075
Abstract: The attitude control problem of the kinetic kill vehicle is studied in this work. A new mathematical model of the kinetic kill vehicle is proposed, the linear quadratic regulator technique is used to design the optimal attitude controller, and the pulse-width pulse-frequency modulator is used to shape the continuous control command to pulse or on-off signals to meet the requirements of the reaction thrusters. The methods to select the appropriate parameters of pulse-width pulse-frequency are presented in detail. Numerical simulations show that the performance of the LQR/PWPF approach can achieve good control performance such as pseudo-linear operation, high accuracy, and fast enough tracking speed.
Spacelike hypersurfaces in de Sitter space with constant higher-order mean curvature
Kairen Cai,Huiqun Xu
International Journal of Mathematics and Mathematical Sciences , 2006, DOI: 10.1155/ijmms/2006/19545
Abstract: The authors apply the generalized Minkowski formula to set up a spherical theorem. It is shown that a compact connected hypersurface with positive constant higher-order mean curvature Hr for some fixed r , 1≤r≤n, immersed in the de Sitter space S1n
Stochastic Simulation of Delay-Induced Circadian Rhythms in Drosophila
Zhouyi Xu, Xiaodong Cai
EURASIP Journal on Bioinformatics and Systems Biology , 2009, DOI: 10.1155/2009/386853
Abstract: Almost all living organisms, including animals, plants, fungi, and cyanobacteria, exhibit daily periodic oscillations in their biochemical or physiological behavior, which are known as circadian rhythms [1–7]. The mechanism of circadian oscillation has been an extensive research topic in the last three decades. It has been found that circadian rhythms in fact are determined by oscillatory expression of certain genes [89]. Specifically, circadian clocks consist of a network of interlocked transcriptional-translational feedback loops formed by a number of genes [2]. In Drosophila, transcription of per and tim genes is activated by a heterodimer consisting of two transcriptional activators dCLOCK and CYCLE [10–13]. The PER protein in turn binds to the dCLOCK-CYCLE heterodimer, which inhibits the DNA binding activity of the dimer, thereby repressing the transcription of per and tim [11–14]. While this forms a negative feedback loop, there is also a positive feedback loop, in which PER and TIM activate dCLOCK synthesis by binding dCLOCK and relieving dCLOCK's repression of dclock transcription [1516].Several mathematical models have been proposed for circadian oscillation in Drosophila [121417–22]. The models of Smolen et al. [1214] introduce time delays in the expression of dclock and per genes, while other models do not have such delays. Numerical simulations using ordinary differential equations (ODE) show that all these models can produce circadian oscillations. In particular, times delays were found to be essential for simulation of circadian oscillations with the model of Smolen et al. [1214].Since there is significant stochasticity in gene expression arising from fluctuations in transcription and translation [23–25], it is desirable to simulate circadian oscillations in the presence of noise. Toward this end, several stochastic models were proposed [426–29], and Gillespie's stochastic simulation algorithm (SSA) [3031] was employed to simulate circadian oscillation
Weighted next reaction method and parameter selection for efficient simulation of rare events in biochemical reaction systems
Zhouyi Xu, Xiaodong Cai
EURASIP Journal on Bioinformatics and Systems Biology , 2011, DOI: 10.1186/1687-4153-2011-797251
Abstract: Biochemical reaction systems in living cells exhibit significant stochastic fluctuations due to a small number of molecules involved in processes such as the transcription and translation of genes [1]. A number of exact [2-7] or approximate simulation algorithms [8-19] have been developed for simulating the stochastic dynamics of such systems. Recent research shows that some rare events occurring in biochemical reaction system with an extremely small probability within a specified limited time can have profound and sometimes devastating effects [20,21]. Hence, it is important that computational simulation and analysis of systems with critical rare events can efficiently capture such rare events. However, the existing exact simulation methods such as Gillespie's exact SSA [2,3] often require prohibitive computation to estimate the probability of a rare events, while the approximate methods may not be able to estimate such probability accurately.The weighted stochastic simulation algorithm (wSSA) recently developed by Kuwahara and Mura [22] based on the importance sampling technique enables one to efficiently estimate the probability of a rare event. However, the wSSA does not provide any method for selecting optimal values for importance sampling parameters. More recently, Gillespie et al. [23] analyzed the accuracy of the results yielded from the wSSA and proposed a refined wSSA that employed a try-and-test method for selecting optimal values for importance sampling parameters. It was shown that the refined wSSA could further improve the performance of wSSA. However, the try-and-test method requires some initial guessing for the sets of values from which the parameters can take. If the guessed values do not include the optimal value, then one cannot get appropriate values for the parameters. Moreover, if the number of parameters is greater than one, a very large set of values need to be guessed and tested, which may increase the likelihood of missing the optimal val
Determination of iron and aluminum based on the catalytic effect on the reaction of xylene cyanol FF with hydrogen peroxide and potassium periodate
Cai, Longfei;Xu, Chunxiu;
Journal of the Brazilian Chemical Society , 2011, DOI: 10.1590/S0103-50532011001000021
Abstract: a simple, sensitive and selective method for the simultaneous determination of trace iron and aluminum by catalytic spectrophotometry is presented. this method is based on the catalytic effects of iron and aluminum on the reaction of xylene cyanol ff with hydrogen peroxide and potassium periodate. both iron and aluminum did not show catalytic effects on the oxidation reaction of xylene cyanol ff in the presence of either hydrogen peroxide or potassium periodate. however, significant catalytic effects of iron and aluminum were obtained when the two oxidants were simultaneously used. linear calibration graphs were obtained from 3.57 × 10-8 to 3.57 × 10-7 mol l-1 for fe and from 1.48 × 10-7 to 1.48 × 10-6 mol l-1 for al. the detection limits, based on the 3-fold standard deviation criterion, were 1.50 × 10-8 mol l-1 for fe and 6.10 × 10-8 mol l-1 for al. this method was applied to the simultaneous determination of trace iron and aluminum in tap water, lake water, river water and tea leaves without separation and preconcentration. contents of fe and al in tap water, lake water and river water were 3.13 × 10-7, 3.21 × 10-7, 2.74 × 10-7 mol l-1 for fe and 1.31 × 10-6, 9.83 ×10-7, 1.43× 10-6 mol l-1 for al, respectively. tea leaves contained 3.10 × 102 μg g-1 fe and 7.37 × 102 μg g-1 al. further research is required for understanding the catalytic mechanism of iron and aluminum on this novel oxidation reaction.
AN AUTOMATED METHOD FOR DETERMINATION OF ASCORBIC ACID IN URINE BY FLOW INJECTION CHEMILUMINESCENCE COUPLING WITH ON-LINE REMOVAL OF INTERFERENCE
CAI,LONGFEI; XU,CHUNXIU;
Journal of the Chilean Chemical Society , 2011, DOI: 10.4067/S0717-97072011000400025
Abstract: a simple and automated method for determination of ascorbic acid (aa) in complex samples by flow injection chemiluminescence (fi-cl) was presented. it is based on the inhibitory effect of ascorbic acid on the chemiluminescence reaction between luminol and hydrogen peroxide in the flow system. a home-made micro column of cation exchange resin was adapted to the fi manifold to achieve on-line removal of interference. this method was used to determine the aa content in urine samples with a detection limit of 6.03 x109 mol/l aa and recovery of 93.1-111.0%. this proposed method allows high - throughput determination of aa in urine samples without chromatographic separation, demonstrating that the fi-cl method has significant potential in determination of species in complex samples by adapting a micro column filled with various functionalized materials to the fi manifold.
Effect of spatial distance on search information correlation in complex systems
TingTing Zhao,Xu Cai
Chinese Science Bulletin , 2011, DOI: 10.1007/s11434-011-4795-2
Abstract: Spatial distance has a remarkable effect on the attended mode of a network embedded in a certain space. First, we investigate how spatial restriction leads to information-information correlation that is strong, linear and positive in real networks. We then construct a two-dimensional space, define the action radius R for nodes of networks, and propose a class of models that depend on spatial distance. Information correlation of the models is consistent with that of real networks. The spatial distance plays a leading role in generating assortative mixing by degree, while the generation of disassortative mixing relies on both the degree of preferential attachment and spatial restriction.
Stochastic Simulation of Delay-Induced Circadian Rhythms in Drosophila
Xu Zhouyi,Cai Xiaodong
EURASIP Journal on Bioinformatics and Systems Biology , 2009,
Abstract: Circadian rhythms are ubiquitous in all eukaryotes and some prokaryotes. Several computational models with or without time delays have been developed for circadian rhythms. Exact stochastic simulations have been carried out for several models without time delays, but no exact stochastic simulation has been done for models with delays. In this paper, we proposed a detailed and a reduced stochastic model with delays for circadian rhythms in Drosophila based on two deterministic models of Smolen et al. and employed exact stochastic simulation to simulate circadian oscillations. Our simulations showed that both models can produce sustained oscillations and that the oscillation is robust to noise in the sense that there is very little variability in oscillation period although there are significant random fluctuations in oscillation peeks. Moreover, although average time delays are essential to simulation of oscillation, random changes in time delays within certain range around fixed average time delay cause little variability in the oscillation period. Our simulation results also showed that both models are robust to parameter variations and that oscillation can be entrained by light/dark circles. Our simulations further demonstrated that within a reasonable range around the experimental result, the rates that dclock and per promoters switch back and forth between activated and repressed sites have little impact on oscillation period.
Weighted next reaction method and parameter selection for efficient simulation of rare events in biochemical reaction systems
Xu Zhouyi,Cai Xiaodong
EURASIP Journal on Bioinformatics and Systems Biology , 2011,
Abstract: The weighted stochastic simulation algorithm (wSSA) recently developed by Kuwahara and Mura and the refined wSSA proposed by Gillespie et al. based on the importance sampling technique open the door for efficient estimation of the probability of rare events in biochemical reaction systems. In this paper, we first apply the importance sampling technique to the next reaction method (NRM) of the stochastic simulation algorithm and develop a weighted NRM (wNRM). We then develop a systematic method for selecting the values of importance sampling parameters, which can be applied to both the wSSA and the wNRM. Numerical results demonstrate that our parameter selection method can substantially improve the performance of the wSSA and the wNRM in terms of simulation efficiency and accuracy.
AN AUTOMATED METHOD FOR DETERMINATION OF ASCORBIC ACID IN URINE BY FLOW INJECTION CHEMILUMINESCENCE COUPLING WITH ON-LINE REMOVAL OF INTERFERENCE
LONGFEI CAI,CHUNXIU XU
Journal of the Chilean Chemical Society , 2011,
Abstract: A simple and automated method for determination of ascorbic acid (AA) in complex samples by flow injection chemiluminescence (FI-CL) was presented. It is based on the inhibitory effect of ascorbic acid on the chemiluminescence reaction between luminol and hydrogen peroxide in the flow system. A home-made micro column of cation exchange resin was adapted to the FI manifold to achieve on-line removal of interference. This method was used to determine the AA content in urine samples with a detection limit of 6.03 x10(9) mol/L AA and recovery of 93.1-111.0%. This proposed method allows high - throughput determination of AA in urine samples without chromatographic separation, demonstrating that the FI-CL method has significant potential in determination of species in complex samples by adapting a micro column filled with various functionalized materials to the FI manifold.
Page 1 /52726
Display every page Item


Home
Copyright © 2008-2017 Open Access Library. All rights reserved.