The spatial patterns through diffusion-driven instability in a predator-prey model

Studies on stability mechanism and bifurcation analysis of a system of interacting populations by the combined effect of self and cross-diffusion become an important issue in ecology. In the current investigation, we derive the conditions for existence and stability properties of a predator-prey model under the influence of self and cross-diffusion. Numerical simulations have been carried out in order to show the significant role of self and cross-diffusion coefficients and other important parameters of the system. Various contour pictures of spatial patterns through Turing instability are portrayed and analysed in order to substantiate the applicability of the present model. Finally, the paper ends with an extended discussion of biological implications of our findings.     

Stochastic dynamic lot-sizing problem using bi-level programming base on artificial intelligence techniques

Simulation is generally used to study non-deterministic problems in industry. When a simulation process finds the solution to an NP-hard problem, its efficiency is lowered, and computational costs increase. This paper proposes a stochastic dynamic lot-sizing problem with asymmetric deteriorating commodity, in which the optimal unit cost of material and unit holding cost would be determined. This problem covers a sub-problem of replenishment planning, which is NP-hard in the computational complexity theory. Therefore, this paper applies a decision system, based on an artificial neural network (ANN) and modified ant colony optimization (ACO) to solve this stochastic dynamic lot-sizing problem. In the methodology, ANN is used to learn the simulation results, followed by the application of a real-valued modified ACO algorithm to find the optimal decision variables. The test results show that the intelligent system is applicable to the proposed problem, and its performance is better than response surface methodology.     

新试剂2,7-双(5-羧基-1,3,4-三氮唑偶氮)-变色酸作为络合滴定铜指示剂的研究

研究了新试剂2,7-双(5-羧基-1,3,4-三氮唑偶氮)-变色酸(简称BCTZACA)作为络合滴定铜的指示剂的分析性能。在pH4.5-6.0范围内,加入8滴BCTZACA指示剂,用EDTA标准溶液进行络合滴定,终点由蓝色变为橙黄色,变色敏锐,准确度高,用于试剂样品和合金中铜的测定,结果与标准值相符,RSD(n=6)为0.11%-0.45%。     

Model-based design of a pilot-scale simulated moving bed for purification of citric acid from fermentation broth

One of the conventional processes used for the recovery of citric acid from its fermentation broth is environmentally harmful and cost intensive. In this work an innovative benign process, which comprises simulated moving bed (SMB) technology and use of a tailor-made tertiary poly(4-vinylpyridine) (PVP) resin as a stationary phase is proposed. This paper focuses on a model-based design of the operation conditions for an existing pilot-scale SMB plant. The SMB unit is modeled on the basis of experimentally determined hydrodynamics, thermodynamics and mass transfer characteristics in a single chromatographic column. Three mathematical models are applied and validated for the prediction of the experimentally attained breakthrough and elution profiles of citric acid and the main impurity component (glucose). The transport dispersive model was selected for the SMB simulation and design studies, since it gives a satisfactory prediction of the elution profiles within acceptable computational time. The equivalent true moving bed (TMB) and SMB models give a good prediction of the experimentally attained SMB separation performances, obtained with a real clarified and concentrated fermentation broth as a feed mixture. The SMB separation requirements are set to at least 99.8% citric acid purity and 90% citric acid recovery in the extract stream. The complete regeneration in sections 1 and 4 is unnecessary. Therefore the net flow rates in all four SMB sections have been considered in the unit design. The influences of the operating conditions (the flow rate in each section, switching time and unit configuration) on the SMB performances were investigated systematically. The resulting SMB design provides 99.8% citric acid purity and 97.2% citric acid recovery in the extract. In addition the citric acid concentration in the extract is a half of its concentration in the pretreated fermentation broth (feed).     

Practical sequential bounds for approximating two-terminal reliability

With increasing emphases on better and more reliable services, network systems have incorporated reliability analysis as an integral part in their planning, design and operation. This article first presents a simple exact decomposition algorithm for computing the NP-hard two-terminal reliability, which measures the probability of successful communication from specified source node to sink node in the network. Then a practical bounding algorithm, which is indispensable for large networks, is presented by modifying the exact algorithm for obtaining sequential lower and upper bounds on two-terminal reliability. Based on randomly generated large networks, computational experiments are conducted to compare the proposed algorithm to the well-known and widely used edge-packing approximation model and to explore the performance of the proposed bounding algorithm. Computational results reveal that the proposed bounding algorithm is superior to the edge-packing model, and the trade-off of accuracy for execution time ensures that an exact difference between upper and lower bounds on two-terminal reliability can be obtained within an acceptable time.     

Integrated multi-sensor chip with photocured polymer membranes containing copolymerised plasticizer for direct pH, potassium, sodium and chloride ions determination in blood serum

An analytical system based on a sensor array with ion-selective field effect transistors (ISFETs) monolithically integrated in one chip covered with photocured polymer membranes containing copolymerised plasticizer and a sequential injection analysis (SIA) is shown to offer an automation of the analysis of blood serum components. For sequential injection system a custom made dual channel flow cell for the sensor array was developed. Optimisation of ion-sensitive membrane characteristics and calibration solution compositions were carried out. The system was used to analyze sodium, potassium, chloride ion contents in blood serum samples. The precision of the ion determination in samples was typical for potentiometic method with standard deviation of about 3-5%.     

Determination of bioavailable soluble arsenic and phosphates in mine tailings by spectrophotometric Sequential Injection Analysis

By using a simple Sequential Injection Analysis (SIA) manifold and in base to the kinetic reaction of the molybdenum with As(V) and P(V) was possible to determine As(III), As(V) and P(V) in simple, binary and ternary samples. The activation energies for the reaction between molybdenum and As(V) and P(V) were of 70.90 kJ mol⁻¹ and of 19.02 kJ mol⁻¹, respectively, therefore it was possible to determine both analytes in mixtures by using different reaction temperature. When the analyses were carried out at room temperature, only the P(V) supplied analytical signal; with increased temperature, the kinetics of reaction for As(V) also increased, and a signal was obtained, being 55 °C the optimum temperature. In order to determine As(III), it was oxidized into As(V) with KIO_3, and the reaction was carried out in the same way as for As(V). To resolve mixtures, an equations system from six calibration curves with different sequences of SIA at different temperature was performed. The lineal ranges were between 0.5 μg mL⁻¹ and 10 μg mL⁻¹ with a repeatability and reproducibility between 0.7% and 5.2% and detection limits between 0.36 μg mL⁻¹ and 0.58 μg mL⁻¹. In binary mixtures of P(V)/As(V) the recoveries were close to 100% for both analytes at ratios lesser than 10:1. For As(V)/As(III) ratios between 1:1 and 5:1 the recoveries were ranged between 85% and 95%. The method was applied in mine tailings and in arsenopyrite. The results showed that the soluble arsenic was found oxidized as As(V). These results were compared with those obtained by atomic absorption spectrometry and both proved to be very close.     

基于RTX的两种加速度模拟信号生成方法研究

针对某型箭载计算机所需加速度信号的实际需求,提出了两种在实时环境下生成信号的方法。重点研究了基于8254计数器和高速D/A方式实现加速度脉冲信号技术,分别采用PCI1751和PCI8238进行了软硬件实现,在RTX实时系统环境下进行了实时性设计,并基于两种方法实现了变加速度信号的生成。通过对比两种方式,分析其优缺点,选择了基于8254计数器的方式生成加速度模拟信号。     

Conformational stability of the tetrameric de novo designed hexcoil-Ala helical bundle

We have performed molecular dynamics method to investigate the conformational stability of the homotetramer form of HexCoil-Ala (PDB Code 3S0R). The previous experiments showed that the chains tend to form tetramer structures. The system was simulated in explicit water model at several temperatures by using isobaric-isothermal ensemble to better understand the behaviour of each monomer and its tetramer form. It was observed that central residues of each monomer have highly helical percentages in comparison with the termini residues. As the temperature increased, these percentages decreased, and bend-like configurations came into being due to the fact that the C-and N-terminals of the monomer were getting closer. When free energy landscapes of HexCoil-Ala were calculated by using the distance between Leu-Zipper and Ala-Coil interface, it was seen that the assemblies of monomers were very strong. What's more, the average values obtained from them were very close to the native case between 300?K and 350?K. It was also observed that the direct salt bridge forming between the residues E8 with R25 in the other chains plays a significant role for keeping tetramer structure. Consequently, our results are in better agreement with the results of experimental observations.