Non-steady States Research Articles

Modeling of cation diffusion in bifunctional polymers based on cis-tetraphenylcalix[4]resorcinarene

In this study, we report that interaction of the network functional polymers based on cis -tetraphenylcalix[4]resorcinarene with aqueous solutions of electrolytes is controlled by diffusion of ions in a polymeric phase. The nanoreactor effect consisting in sufficiently high rate increase of a cation diffusion flux in bifunctional polymers containing sulfonic acid and phenol ionogenic groups has been found. For steady and non-steady states the solutions of the fundamental differential equation of cation diffusion in bifunctional polymers by means of the spherical layer model are obtained for a variety of initial and boundary conditions with constant diffusion coefficient. The proposed mathematical model explains the nanoreactor effect in bifunctional polymers.

Individual-based modelling: an essential tool for microbiology.

Micro-organisms play a central role in every ecosystem and in the global biomass cycle. They are strongly involved in many fields of human interest, from medicine to the food industry and waste control. Nevertheless, most micro-organisms remain almost unknown, and nearly 99% of them have not yet been successfully cultured in vitro. Therefore, new approaches and new tools must be developed in order to understand the collective behaviour of microbial communities in any natural or artificial setting. In particular, theoretical and practical methodologies to deal with such systems at a mesoscopic level of description (covering the range from 100 to 10(8) cells) are required. Individual-based modelling (IBM) has become a widely used tool for describing complex systems made up of autonomous entities, such as ecosystems and social networks. Individual-based models (IBMs) provide some advantages over the traditional whole-population models: (a) they are bottom-up approaches, so they describe the behaviour of a system as a whole by establishing procedural rules for the individuals and for their interactions, and thus allow more realistic assumptions for the model of the individuals than population models do; (b) they permit the introduction of randomness and individual variability, so they can reproduce the diversity found in real systems; and (c) they can account for individual adaptive behaviour to their environmental conditions, so the evolution of the whole system arises from the dynamics that govern individuals in their pursuit of optimal fitness. However, they also present some drawbacks: they lack the clarity of continuous models and may easily become rambling, which makes them difficult to analyse and communicate. All in all, IBMs supply a holistic description of microbial systems and their emerging properties. They are specifically appropriate to deal with microbial communities in non-steady states, and spatially explicit IBMs are particularly appropriate to study laboratory and natural microbiological systems with spatial heterogeneity. In this paper, we review IBM methodology applied to microbiology. We also present some results obtained from the application of Individual Discrete Simulations, an IBM of ours, to the study of bacterial communities, yeast cultures and Plasmodium falciparum-infected erythrocytes in vitro cultures of Plasmodium falciparum-infected erythrocytes.

Metabolic Control Analysis of Complex Biological Systems

A systematic approach is proposed for the metabolic control analysis of various dynamic behaviors in biological systems. The complex kinetic models are reduced by identifying the conservation relations and the time scale analysis. Subsequently, the biological systems are categorized into the three groups: systems with the steady-states, sustained oscillations, or other non-steady states. The sensitivities are measured to calculate the corresponding control coefficients that are defined considering the characteristics of the dynamics of the systems. The proposed approach is illustrated with its application to the dynamic behaviors of a complex biological model.

Gradient-based similarity in the atmospheric boundary layer

The “flux-based” and “gradient-based” similarity in the stable boundary layer and also in the interfacial part of the convective boundary layer is discussed. The stable case is examined on the basis of data collected during the CASES-99 experiment. Its interfacial counterpart is considered in both the quasi-steady (mid-day) and non-steady states, utilizing the results of large-eddy simulations.

Divergence, Sensitivity, and Nonequilibrium in Ecosystems

Contemporary theoretical debate in ecology and biogeography is often focused on equilibrium vs. nonequilibrium behavior in ecosystems and on the nature and source of ecosystem dynamics. It is suggested that these debates be recast in terms of the way ecosystems develop and respond to disturbances, rather than in terms of concepts often imported from mathematics, physics, and other fields. Using nonlinear dynamical systems theory, it is shown that key theoretical implications can be cast in terms of geoecologically significant phenomenologies such as divergent evolution, sensitivity to initial conditions and small disturbances, historical contingency, and path dependence. Examples show these phenomena are widely observed in ecosystems. Ecological and biogeographical theory can be problematized from within geography and ecology rather than fuzzy, abstract concepts such as equilibrium, self‐organization, “balance of nature,” or chaos. Complexity, sensitivity, variability, nonsteady states, and other concepts often associated with nonequilibrium or complexity‐theory frameworks have manifestations that are evident in observable ecological phenomena, in addition to theory and models.

Separation of indium using nanofiltration membranes:A non-steady-state study

In this work, the performances of a nanofiltration membrane NTR7450 separating a multivalent cation (In 3+ ) under non-steady and steady states were compared. The effect of both pH and concentration of the feed solution was studied. The ability of indium to form complexes even under acidic conditions could be theoretically determined using the solubility constants for various end products. Turbidity studies were carried out to determine the non-steady and steady phases of indium chloride solutions at room temperature. Two hypotheses were formulated from the turbidity studies and subsequently verified by the results of nanofiltration experiments. While InCl 3 solution aged under the non-steady state, the rejection rate of indium by nanofiltration gradually increased from 64 to 88%. Under the steady state, indium rejection rate of NTR7450 was found constant and independent of the feed concentration. The results demonstrated the significant impact of indium complexation on the performance of nanofiltration. Based on the basic principles of electrochemistry, a semi-empirical model was proposed to link the change of solution structures with nanofiltration performance. The steady state of indium chloride solutions could be also reached by pH adjustment using NaOH. At increased pH, a non-steady state was not observed during nanofiltration.

Separation of indium using nanofiltration membranes:: A non-steady-state study

In this work, the performances of a nanofiltration membrane NTR7450 separating a multivalent cation (In 3+) under non-steady and steady states were compared. The effect of both pH and concentration of the feed solution was studied. The ability of indium to form complexes even under acidic conditions could be theoretically determined using the solubility constants for various end products. Turbidity studies were carried out to determine the non-steady and steady phases of indium chloride solutions at room temperature. Two hypotheses were formulated from the turbidity studies and subsequently verified by the results of nanofiltration experiments. While InCl 3 solution aged under the non-steady state, the rejection rate of indium by nanofiltration gradually increased from 64 to 88%. Under the steady state, indium rejection rate of NTR7450 was found constant and independent of the feed concentration. The results demonstrated the significant impact of indium complexation on the performance of nanofiltration. Based on the basic principles of electrochemistry, a semi-empirical model was proposed to link the change of solution structures with nanofiltration performance. The steady state of indium chloride solutions could be also reached by pH adjustment using NaOH. At increased pH, a non-steady state was not observed during nanofiltration.

Biokinetic evaluation and modeling of continuous thiocyanate biodegradation by Klebsiella sp.

Biokinetics for autotrophic degradation of thiocyanate using batch culture of Klebsiella sp. were evaluated both analytically and numerically. A sequential approach with an analytical method followed by a numerical approximation was used to evaluate and to ensure the accuracy of the parameter estimation. The nonlinear least-squares method with a 95% confidence interval was employed. The growth conditions were maintained at pH 7 and 38 degrees C for all experiments. With an automated incubation and turbidity reader, a total of 16 different initial thiocyanate concentrations, ranging from 10 to 300 mg L(-1), were used to develop a kinetic expression of specific growth rate as a function of substrate concentration. The biodegradation of thiocyanate with Klebsiella sp. followed a substrate inhibition pattern. Three identical automated bioreactors with working volumes of 1.5 L, equipped with sterilizable sampling ports, were also used for the numerical approximation of the biokinetic parameters in batch mode. A fourth order Runge-Kutta method was used to approximate the substrate inhibition kinetics of the Klebsiella sp. utilizing thiocyanate. Although the kinetic coefficients estimated by analytical and numerical methods were not statistically different at a 0.05 alpha level, model responses of numerical approximation generated a better prediction of changes in thiocyanate and cell mass concentrations. The hypothetical maximum growth rate, micro m, half saturation coefficient, Ks, microbial yield coefficient, Y, cell mass decay rate coefficient, kd, and substrate inhibition coefficient, Ksi, were evaluated as being 0.62 +/- 0.05 d(-1), 85 +/- 8 mg SCN- L(-1), 0.076 +/- 0.011 mg cell mass (mg SCN)(-1), 0.03 +/- 0.002 d(-1), and 131 +/- 22 mg SCN- L(-1), respectively. The calculated maximal substrate concentration, Sm, and apparent maximum specific growth rate, micro'm, were 105.5 +/- 8.7 mg SCN- L(-1) and 0.24 +/- 0.01 d(-1), respectively. Using these estimated parameters, the theoretical performance of the continuous operation was also illustrated, which depicts the residual thiocyanate and Klebsiella sp. concentrations in the non-steady and steady states at different hydraulic retention times (HRTs). Assuming the influent concentration of 250 mg SCN- L(-1), the expected treatment efficiency ranged from 94.9% to 69.4% between 20 and 5 days HRT, respectively. Klebsiella sp. was expected to be washed out at 4.8 days HRT, thus resulting in no treatment of thiocyanate.

방열판 직접압출공정의 성형성 향상에 관한 연구

At present, the design of extrusion dies and operation in extrusion companies are primarily based on trial and error. The experience of the die designer, the press operator and the die corrector determine the performance of the extrusion die and the efficiency of the process. In order to produce defect-free products of desirable quality in terms of strength, surface quality and geometrical dimensions, it is important to obtain more knowledge of the processes that occur during extrusion. Recently, to reduce the costs of designing and manufacturing of extrusion dies, and to ensure the quality of the extruded products, numerical simulation for extrusion processes such as FEM (finite element method) is applied increasingly and becomes a very important tool for the design and development of new products. However, most of the studies about FE simulation have been accomplished for simple geometry and low extrusion ratio in the filed of steady metal flow conditions. The extruded products of AI alloy in industrial practice involve complicated sectional geometry. This study was designed to reduce the time of die design and manufacturing in the extrusion process using FEM simulation. FEM simulations of extrusion process were performed in non-steady states conditions by changing weld plate included in extrusion die set. Product which was employed in this study is heat sink that has been used in the parts of heat exchanger of electric circuits. It is generally applied for aluminum or its alloys due to heat efficiency and easy production of complicated shapes, and manufactured by extrusion process. The simulated results showed that weld plate shape in extrusion dies influences meta] flow and dimensional accuracy of products.

Divergence, Sensitivity, and Nonequilibrium in Ecosystems

Contemporary theoretical debate in ecology and biogeography is often focused on equilibrium vs. nonequilibrium behavior in ecosystems and on the nature and source of ecosystem dynamics. It is suggested that these debates be recast in terms of the way ecosystems develop and respond to disturbances, rather than in terms of concepts often imported from mathematics, physics, and other fields. Using nonlinear dynamical systems theory, it is shown that key theoretical implications can be cast in terms of geoecologically significant phenomenologies such as divergent evolution, sensitivity to initial conditions and small disturbances, historical contingency, and path dependence. Examples show these phenomena are widely observed in ecosystems. Ecological and biogeographical theory can be problematized from within geography and ecology rather than fuzzy, abstract concepts such as equilibrium, self-organization, “balance of nature,” or chaos. Complexity, sensitivity, variability, nonsteady states, and other concepts often associated with nonequilibrium or complexity-theory frameworks have manifestations that are evident in observable ecological phenomena, in addition to theory and models.

Rates of Production of Acetate, Propionate, and Butyrate in the Rumen of Lactating Dairy Cows Given Normal and Low-Roughage Diets

Five lactating dairy cows with a permanent cannula in the rumen were given (kg DM/d) a normal diet (7.8 concentrates, 5.1 hay) or a low-roughage (LR) diet (11.5 concentrates, 1.2 hay) in two meals daily in a two-period crossover design. Milk fat (g/kg) was severely reduced on diet LR. To measure rates of production of individual volatile fatty acids (VFA) in the rumen, 0.5mCi 1-14C-acetic acid, 2-14C-propionic acid, or 1-14C-n-butyric acid were infused into the rumen for 22h at intervals of 2 to 6 d; rumen samples were taken over the last 12h. To measure rumen volume, we infused Cr-EDTA into the rumen continuously, and polyethylene glycol was injected 2h before the morning feed. Results were very variable, so volumes measured by rumen emptying were used instead. Net production of propionic acid more than doubled on LR, but acetate and butyrate production was only numerically lower. Net production rates pooled across both diets were significantly related to concentrations for each VFA. Molar proportions of net production were only slightly higher than molar proportions of concentrations for acetate and propionate but were lower for butyrate. The net energy value (MJ/d) of production of the three VFA increased from 89.5 on normal to 109.1 on LR, equivalent to 55 and 64% of digestible energy, respectively. Fully interchanging, three-pool models of VFA C fluxes are presented. It is concluded that net production rates of VFA can be measured in non-steady states without the need to measure rumen volumes.

Relations between bacterial biomass and carbon cycle in marine sediments: an early diagenetic model.

A new model for early diagenetic processes has been developed through a new formula explicitly accounting for microbial population dynamics. Following a mechanistic approach based on enzymatic reactions, a new model has been proposed for oxic mineralisation and denitrification. It incorporates the dynamics of bacterial metabolism. We find a general formula for inhibition processes of which some other mathematical expressions are particular cases. Moreover a fast numerical algorithm has been developed. It allows us to perform simulations of different diagenetic models in non-steady states. We use this algorithm to compare our model to a classical one (Soetaert et al., 1996). Dynamical evolutions of a perturbation of particulate organic carbon (POC) input are studied for both models. The results are very similar for stationary cases. But with variable inputs, the bacterial biomass dynamics brings about noticeable differences, and these are discussed.

Rate-correction technique for QT interval in long-term telemetry ECG recording in beagle dogs.

The establishment of a new rate-correction method for the QT interval is presented for long-term telemetry ECG recording in free-moving beagle dogs. First, in order to define the QT-RR relation to derive the correction formula, the diurnal variations of the QT and RR intervals and the influencing factors were analyzed, and the QT-RR regression coefficient beta was estimated under various conditions: steady and non-steady states of animal, light and dark periods, and over 24 h. In the results, the diurnal rhythm of the QT interval was synchronized with the RR interval reflecting the physical and emotional states of the animal. The coefficient beta had considerable variation during the day: beta; 0.276 +/- 0.052 (maximum to minimum: 0.495 to 0.153). Thus, it was considered that the ideal rate-correction technique for telemetry ECG requires the selection of a flexible coefficient beta adjusted to the condition of the measurement. Therefore, rate-correction utilizing analysis of covariance estimating the coefficient beta for each dog, was compared with previously proposed formulas which fix the rate-correction coefficient, based on the capacity to dissociate the effects of heart rate on the QT interval. This was then tested by the levels of discrimination apparent in the QT prolongation caused by a class III antiarrhythmic drug, which ranked the formulas on the levels of correction achieved as follows: covariance adjustment > Matsunaga > Van de Water > Bazett. Thus, the rate-correction method utilizing analysis of covariance is proven adequate for data from telemetry ECG recordings.

A Decentralized Market with Common Values Uncertainty: Non-Steady States

We analyse a market where (i) trade proceeds by random and anonymous pairwise meetings with bargaining; (ii) agents are asymmetrically informed about the value of the traded good; and (iii) no new entrants are allowed once the market is open. We show that information revelation and efficiency never obtain in equilibrium, even as discounting is removed. This holds whether the asymmetry is two-sided or one-sided. In some cases there exist equilibria where a substantial amount goes untraded. This contrasts with the earlier literature, which was based on the steadystate equilibria of a model where agents enter the market every period.

Formation and sustainment of electrostatically driven spheromaks in the resistive magnetohydrodynamic model

The nonlinear time-dependent equations of resistive magnetohydrodynamics are solved in simply connected domains to investigate spheromak formation and sustainment with electrostatic current drive. Spheromak magnetic fields are generated in three-dimensional computations as the nonlinear state resulting from an unstable pinch. Perturbations convert continuously supplied toroidal magnetic flux into poloidal magnetic flux, leading to “flux amplification” of field embedded in the electrodes. Relaxation of the axisymmetric component of the parallel current profile can be substantial, and the final nonlinear state is steady over a wide range of parameters. However, for sufficiently large values of Lundquist number or sufficiently large applied potential, nonsteady final states are observed with periodic relaxation events in some cases. Under most conditions, the saturated configuration exhibits chaotic scattering of the magnetic field lines. Conditions just above the marginal point of pinch instability sustain large closed flux surfaces in steady state; a weakly kinked pinch current threads the toroidal region of closed flux surfaces and imposes stellarator-like helical transform. Closed flux surfaces also form during decay, due to reduced fluctuation levels and average toroidal current driven directly by inductive electric field.

Cost-effective flow injection analysis systems for acetic acid

We propose cost-effective flow injection analysis systems for acetic acid. The flow systems can be assembled with different types of components, including a clinical saline bag and laboratory-made detectors, resulting in various degrees of automation, varying from very simple ones to fully computerized control. The flow injection titrations are based on neutralization and are monitored by either spectrophotometry or conductometry. The flow injection procedures can be performed under conditions at non-steady or steady states. The proposed procedures are demonstrated for the application of analysis of vinegar samples for acidity. © 2000 John Wiley & Sons, Inc. Lab Robotics and Automation 12:129–132, 2000

Analysis of Voltage and Temperature Distribution for Polycrystalline Diamond Synthesis.

A computational model to analyse the synthesis process of carbonado type synthetic polycrystalline diamond was performed through numerical simulation. In this model it is possible to analyse the voltage, the electrical power and the temperature distribution for different construction designs in both steady and nonsteady states. The simulation results allowed an understanding of the influence of the design on the temperature profile as well as the effect of increasing voltage in the temperature distribution during the process.

Numerical simulation of fluid flow in porous filters for a particulate removal facility

In order to simulate the fluid flow in a porous filter in a dust removal facility, gas velocity and pressure distributions in the filter element at T = 673 K and P c = 20 atm were calculated numerically for both steady and non-steady states. The effects of the diameter and length of the filter element on those distributions were also studied. The size of a porous filter had influence on the baseline pressure loss and the distribution of flow in the filter during filtration and cleaning. Filter size was, however, restricted by cleaning performance because a large amount of cleaning gas had to be flushed into the internal filter. As the length of the filter increases and the diameter decreases, total pressure and the inlet velocity of the cleaning gas increases rapidly. It can produce an insufficient cleaning effect, forming cleaning velocity distributions within filter. In an analysis of the transient region from filtration to cleaning, the flow in the filter approached steady state in 50 ms after injecting pulse jets. Initially after injecting pulse jets, the pressure was relatively high at the inlet regime of filter.

The deconvolution of nucleation and growth rates from electrochemical current–time transients

Two new algorithms have been developed for the deconvolution of nucleation and growth rates from electrochemical current–time transients. The first is called Bootstrap, and is based on the method of successive approximations. The second is called Simplefit, and utilizes a curve-fitting procedure based on the simplex method. Both are able to provide numerical estimates of the number of crystals as a function of time, to better than 2% accuracy, in the presence of significant noise. The advantage of the algorithms is that they produce accurate output under conditions where standard methods fail. In particular, the number of crystals versus time can be determined even when crystal growth switches from interfacial control to diffusion control on the timescale of measurements. The efficacy of the algorithms is demonstrated on two real systems, namely the nucleation of zinc on carbon, and the nucleation of lead on carbon. In both cases non-steady states of nucleation are readily observed in the presence of time-varying crystal growth rates. In addition, a new phenomenon is seen for which the name ''nucleation persistence'' is suggested. This is the transient continuation of a high rate of nucleation after a rapid decrease in overpotential. The phenomenon is attributed to the slow readjustment of the size distribution of microscopic nuclei on the electrode surface. Interestingly, the existence of nucleation persistence invalidates the double potential step technique, which has previously been regarded as the standard method for observing electrochemical nucleation and growth. Finally, the mathematical theory of nucleation persistence is briefly sketched.

On resistive nonlocal Josephson electrodynamics

New solutions of one-dimensional nonlocal Josephson electrodynamics are proposed that describe the steady and nonsteady Abrikosov-Josephson vortex states of the resistive model; these solutions are based on the superposition principle of the vortex structures whose properties are determined by the nonlinear interaction of the vortices. The stability of the current-voltage characteristic (1.13) is shown and the relaxation-oscillation mode of establishing the corresponding state is investigated. The laws governing the annihilation and dispersal of the interacting Abrikosov-Josephson vortices are examined.