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Results for “Equilibrium optimization”

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PubMed2001

Phase diagram of a symmetric binary fluid in a porous matrix.

The phase behavior of a binary symmetric fluid in thermal equilibrium with a porous matrix has been studied with the optimized random phase approximation and grand canonical Monte Carlo simulations. Depending on the matrix properties and the matrix-fluid and fluid-fluid interactions we find three types of phase diagram characterized by a tricritical point, a tricritical point with a triple point, or a critical end point. Small changes in the properties of the matrix or in the interactions are demonstrated to lead to drastic modifications of the phase diagram of the fluid, in qualitative agreement with observations in experimental studies. We show, in particular, that the change between the different types of phase diagram is triggered not only by the fluid-fluid interactions (internal parameters) but also by the properties of the matrix and of the matrix-fluid potentials (external parameters).

Journal Article↗

PubMed1987

[The stability of hydrochlorothiazide and cyclopenthiazide in various dosage forms. 4. Stability of hydrochlorothiazide injection solutions II].

The hydrolytic decomposition of hydrochlorothiazide (1) in an optimized dispensing with polyethyleneglycol 400/ethanol as solvent led to an equilibrium in the isothermic short-term test as well as in the long-term stability test. Corresponding equilibrium concentrations were obtained for forward and back reaction. When comparing the precalculated equilibrium values with the long-term results the evaluation after Van't Hoff proved superior compared with an evaluation after the Arrhenius plot which is only applicable when the equilibrium concentrations are taken into consideration. By adding the decomposition product aminodisulfamide (2) the hydrolysis of 1 can be inhibited completely.

Cyclopenthiazide↗

PubMed1981

Protease mitogenic response of chick embryo fibroblasts and receptor binding/processing of human alpha-thrombin.

Quiescent cultures of chick embryo fibroblasts incubated with human alpha-thrombin (14-219 pM) incorporated [methyl-3H]thymidine proportional to concentration. Inactivated forms of this protease (e.g. active-site-conjugated alpha-thrombin or its hirudin complex) had no mitogenic activity and did not compete with 124I-alpha-thrombin for binding to specific plasma membrane receptors. The noncoagulant but esterolytic active forms, gamma- and nitro-alpha-thrombins, were weakly mitogenic and correspondingly competed weakly for binding. Trypsin competed equally as well as native thrombin for binding, whereas chymotrypsin, elastase, and human urokinase competed with 80-fold less affinity. Plasma, arginine-specific proteases associated with nerve or epidermal growth factors, insulin, and insulin-like growth factors did not compete for binding. These data demonstrate that (a) functional catalytic residues of the thrombin active site are necessary for mitogenic activity and for specific binding; (b) regions adjacent to the active site, i.e. the high affinity protein recognition site, appear to enhance binding; and (c) the receptor can discriminate between other proteases and binds those which are also mitogens for the avian cells. The characteristics of 125I-alpha-thrombin binding were determined, and it was found to be (i) proportional to cell number; (ii) optimal at pH 6.8; (iii) 70-90% specific; (iv) at equilibrium after 60 min of incubation at 22-24 degrees C or 180 min at 0-4 degrees C (the rate constants for association, i.e. ka, at 22 and 4 degrees C were 18 and 1.1 x 10(7) M-1 min-1, respectively); and (v) essentially nondissociable. Nondissociable thrombin that bound during incubation at 0-4 degrees C was distributed equally between trypsin-sensitive and insensitive compartments. Thrombin associated with the former was released into the media when the cells were incubated at 0-4 degrees C with hirudin or hydroxylamine, or transferred to the insensitive compartment when incubated at 22 degrees C. Finally, confluent cultures of fibroblasts bind 2-3 x 10(4) 125I-alpha-thrombin molecules/cell with an apparent binding constant, i.e. Kd, of 0.7 nM (a true Kd could not be determined because of the irreversible nature of thrombin binding). The binding capacity per cell and the apparent Kd value increased proportionally to an increase in culture density.

Animals↗

PubMedDate not supplied

[Selection and mutation from the theoretical information point of view--limits of the preservation of genetic information].

There is no doubt that evolution can only operate in accordance with the laws of thermodynamics. To transform this simple perception into a statement that can be quantified it is necessary to examine how the entropy (or the information content) changes by means of the two main factors of evolution: selection and mutation. In the present paper this aim was reached by using the methods of information theory. That evolution becomes possible the change of information by mutation and selection must not be negative in the long run. Consequently an upper limit for the information content of the genome must be assumed. If the evolution as a self-optimizing process gains this upper limit it reaches a dynamic equilibrium at which the increase of entropy by mutation balances the decrease of entropy by selection. In particular it was examined under which circumstances of dynamic equilibrium master-genotypes (genotypes that can preserve their specific sequence over a long time) can exist.

Biological Evolution↗

PubMed1993

Choice of optimality criteria for the design of crossbreeding experiments.

Crossbreeding experiments carried out over several generations and analyzed using genetic models including additive, dominance, and epistatic effects deserve careful planning. Designs should be optimized with respect to the specific aim of the experiment. Using an experiment with guinea pigs as an example, designs were optimized for three different criteria: D-optimality, where the determinant of the variance-covariance matrix of all parameters in the genetic model is minimized, DS-optimality, where a specific subset of parameters is of special interest and the respective determinant is minimized, and DA-optimality, where a linear function or a set of linear functions of the parameters in the model is of interest. The linear function used in this particular case relates to the comparison of a composite line of two breeds and a rotational crossbreeding system at equilibrium. The designs produced by a sequential design algorithm depend very much on the optimality criterion. Designs that are optimal for the comparison of composites and rotations are very inefficient for the estimation of the whole set of parameters in the model or the specific subset of special interest in this case. Assuming that the underlying genetic model is correct, composites and rotations at equilibrium may be compared extremely efficiently using only crosses arising in the first three generations of crossbreeding.

Algorithms↗

PubMed2006

Flexible simple point-charge water model with improved liquid-state properties.

In order to introduce flexibility into the simple point-charge (SPC) water model, the impact of the intramolecular degrees of freedom on liquid properties was systematically studied in this work as a function of many possible parameter sets. It was found that the diffusion constant is extremely sensitive to the equilibrium bond length and that this effect is mainly due to the strength of intermolecular hydrogen bonds. The static dielectric constant was found to be very sensitive to the equilibrium bond angle via the distribution of intermolecular angles in the liquid: A larger bond angle will increase the angle formed by two molecular dipoles, which is particularly significant for the first solvation shell. This result is in agreement with the work of Hochtl et al. [J. Chem. Phys. 109, 4927 (1998)]. A new flexible simple point-charge water model was derived by optimizing bulk diffusion and dielectric constants to the experimental values via the equilibrium bond length and angle. Due to the large sensitivities, the parametrization only slightly perturbs the molecular geometry of the base SPC model. Extensive comparisons of thermodynamic, structural, and kinetic properties indicate that the new model is much improved over the standard SPC model and its overall performance is comparable to or even better than the extended SPC model.

Algorithms↗

PubMed1996

Population genetic perspectives on the evolution of recombination.

Optimality arguments and modifier theory are reviewed as paradigms for the study of the evolution of recombination. Optimality criteria (such as maximization of mean fitness) may agree with results from models developed in terms of the evolution of recombination at modifier loci. Modifier models demonstrate, however, that equilibrium mean fitness can decrease during the evolution of recombination rates and is not always maximized. Therefore, optimality arguments do not successfully predict the conditions under which increased or decreased recombination will evolve. The results from modifier models indicate that decreased recombination rates are usually favored when the population is initially near a polymorphic equilibrium with linkage disequilibrium. When the population is subject to directional selection or to deleterious mutations, increased recombination may be favored under certain conditions, provided that there is negative epistasis among alleles.

Biological Evolution↗

PubMed2005

[High throughput screening of pharmacokinetics and metabolism in drug discovery (II)--investigation on in vitro and in vivo correlation in drug metabolism screening].

Metabolic screening using liver microsomes of rats and humans is an indispensable tool to optimize a lead structure and to select compounds for in vivo study. Elucidating the relationship between in vitro intrinsic clearance (CL(int, app)) and in vivo clearance (CL(b)) is a prerequisite for screening. We investigated the relationship between CL(int, app) in rat liver microsomes and CL(b) after intravenous administration in rats in eight projects. No relationship between these two parameters was found across all of the projects examined. However, there was a certain relationship in the same core structure of six projects, but not in the other two projects. The poor correlation in the projects was improved by considering serum protein binding or microsomal binding in the estimation of in vitro clearances. Although the binding assay was labor intensive, unlike metabolic screening, the introduction of the equilibrium dialysis method using a 96-well format increased the throughput. Optimization of metabolic stability was conducted on the basis of the structure-metabolic stability relationship (SMR) in one of the projects, showing a good correlation without the binding factors. The replacement of the piperazine with a homopiperazine moiety improved metabolic stability in the rat and human liver microsomes. The compound also showed a desirable in vivo pharmacokinetic profile in rats, suggesting that the SMR study on the confirmed in vitro and in vivo correlation is essential to the optimization.

Animals↗

PubMed1986

Theoretical models for predicting the effect of bridging group recognition and conjugate substitution on hapten enzyme immunoassay dose-response curves.

Models for predicting the effect of immunological recognition of the bridge group on the dose-response curves obtained with heterogeneous hapten enzyme immunoassays are presented. Appropriate theoretical treatment shows that the greater affinity of antibodies toward the enzyme-labeled species than for the unlabeled hapten analyte results in assays with limited detection capabilities. This problem is compounded when enzyme conjugates possessing multiple haptens are used. In equilibrium type competitive arrangements, the concentrations of binder and labeled hapten may be optimized to some extent to improve assay performance. However, the results presented show that only when assays are performed in a sequential binding mode using carefully controlled timing of reagent incubations can the detection capabilities of the assays be fully maximized for analyte measurements. Unfortunately, it is also shown that such sequential binding approaches render the assays essentially nonselective. The effect of decreasing the affinity of the binder to the enzyme-labeled hapten relative to the unlabeled analyte by using heterologous conjugates in equilibrium arrangements is shown to improve detection capabilities but also at the expense of reduced selectivity. Suggestions for reagent concentrations and conjugate substitution (degree of conjugation), which provide optimized dose-response curves at a given ED50 value, are also presented as are proposals for using different binders which do not exhibit bridging group recognition.

Antibody Affinity↗

PubMed1997

Consequences of a small decrease of air temperature from thermal equilibrium on thermoregulation in sleeping neonates.

A new heating unit (servocontrolled skin temperature derivative system) has been designed to control the thermal environment in closed incubators. This type of control acts to attain and closely maintain a thermal equilibrium between a neonate's skin temperature and the environment. The present study aims to discover if thermal equilibrium is located within a thermoneutral range defined from oxygen consumption VO2 and body temperature, and whether it is more appropriate to define an optimal thermal environment. As regards VO2 and body temperature, results show that the air temperature reached at thermal equilibrium fulfils the definition of thermoneutrality. According to these criteria, a small decrease (1:5 degrees C) from thermal equilibrium also provides a near thermoneutral environment to the neonate but induces sleep disturbances and an increase in body movements. These two additional parameters delineate a narrower thermoneutral zone than does minimal metabolic rate because VO2 can stay constant even when air and body temperatures decrease. The results suggest that thermal equilibrium might be assimilated with a thermal comfort zone.

Automation↗

PubMed2006

Adsorption and recovery of lead(II) from aqueous solutions by immobilized Pseudomonas Aeruginosa PU21 beads.

In this study, immobilized Pseudomonas aeruginosa PU21 beads were used as an adsorbent for lead(II). Different weight percentages of chitosan were added to polyethylene glycol (PEG, 0.5 wt.% in aqueous solution) and alginate (18 wt.% in aqueous solution), and then blended or cross-linked using different concentrations of epichlorohydrin (ECH) to prepare beads of different sizes and increased mechanical strength. Before blending or cross-linking, different weight percentages of P. aeruginosa PU21 were added to increase lead(II) adsorption. Subsequently the optimized bead composition (concentration of ECH, percentages of chitosan and P. aeruginosa PU21) and the optimum adsorption conditions (agitation rate and pH in the aqueous solution) were ascertained. Finally, the optimized beads adsorbing lead(II) were regenerated by 0.1M aqueous HCl solutions and the most effective desorption agitation rate was ascertained. The results indicate that the reuse of immobilized P. aeruginosa PU21 beads was feasible. In addition, the equilibrium adsorption, kinetics, changes in the thermodynamic properties of adsorption of lead(II) on optimized beads were also investigated.

Adsorption↗

PubMed2005

Optimizing experimental parameters in isothermal titration calorimetry.

In isothermal titration calorimetry, the statistical precisions with which the equilibrium constant (K) and reaction enthalpy (DeltaH degrees ) can be estimated from data for 1:1 binding depend on a number of quantities, key among them being the products c identical with K[M](0) and h identical with DeltaH degrees [M](0), the stoichiometry range (R(m)(), ratio of total titrant X to total titrate M after the last injection), and the number of injections of titrant. A study of the statistical errors as functions of these quantities leads to the following prescription for optimizing throughput and precision: (1) Make 10 injections of titrant. (2) Set the concentrations in accord with the empirical equation R(m)() = 6.4/c(0.2) + 13/c (but no smaller than 1.1). (3) Make the starting concentration [M](0) as large as possible within the large-signal limits of the instrumentation but limited to c < 10(3) for estimating K. With this procedure, both K and [M](0) are predicted to have relative standard errors <1% over large ranges of K. Systematic errors in the concentrations, [X](0) and [M](0), are fully compensated by the "site number" or stoichiometry parameter (n). On the other hand, altering and freezing any of the fit parameters leads to a deterioration of the fit quality and to predictable changes in the other parameters. Fit divergence at very small c is avoidable through a simple redefinition of the fit parameters; however, unless n can be fixed from other information, DeltaH degrees may be statistically ill-defined in this region.

Journal Article↗

PubMed1985

Competition and medical groups. A survivor analysis.

This paper extends the survivor analysis of medical practice provided by Frech and Ginsburg (1974). Changes in the distribution of medical practice sizes are examined for the periods 1965-69, 1969-75, and 1975-80. Through 1975, we find that, almost uniformly, all sizes of medical groups were found to be optimal. In particular, the optimality of large (100 or more physicians) multi-specialty groups was strongly confirmed. Later data, however, suggest that the equilibrium size distribution may have shifted. For the 1975-80 period only large multi-specialty groups continue to be in the optimal size range. In addition, we find some evidence that suggests that solo practices may be optimal in some geographic regions.

Catchment Area, Health↗

PubMed2004

Microarray results improve significantly as hybridization approaches equilibrium.

Dual-channel long oligonucleotide microarrays are in widespread use. Although much attention has been given to proper experimental design and analysis regarding long oligonucleotide microarrays, relatively little information is available concerning the optimization of protocols. We carried out a series of microarray experiments designed to investigate the effects of different levels of target concentration and hybridization times using a long oligonucleotide library. Based on principles developed from nucleic acid renaturation kinetics studies, we show that increasing the time of hybridization from 18 h to 42 h and 66 h, especially when lower than optimal concentrations of target were used, significantly improved the quality of the microarray results. Longer hybridization times significantly increased the number of spots detected, signal-to-noise ratios, and the number of differentially expressed genes and correlations among replicate arrays. We conclude that at 18 h of incubation, target-to-probe hybridization has not reached equilibrium and that a relatively high proportion of nonspecific hybridization occurs. This result is striking, given that most, if not all, published microarray protocols stipulate 8-24 h for hybridization. Using shorter than optimal hybridization times (i.e., not allowing hybridization to reach equilibrium) has the consequence of underestimating the fold change of differentially expressed genes and of missing less represented sequences.

Algorithms↗

PubMed1999

Enhancement of both reaction yield and rate of synthesis of structured triacylglycerol containing eicosapentaenoic acid under vacuum with water activity control.

Production of structured triacylglycerols (sTAG) containing eicosapentaenoic acid (EPA) at the sn-1 (or 3) position using Lipozyme in a solvent-free system was studied. Optimal water activity (a(w)) for the synthesis of the sTAG was investigated. Vacuum was applied to shift reaction equilibrium toward the synthesis reaction by removing by-products. During vacuum application, the water level of the reaction system was controlled at the optimal level by addition of a suitable amount of water at a predetermined interval. Intermittent periodic addition of a suitable amount of water into the reaction mixture made the reaction rate faster than that without adding water. A molar yield of 89.7% of the targeted sTAG was obtained after 16 h reaction with a(w) control during the vacuum application as compared with the yield of 87.0% after 24 h of reaction without a(w) control during the vacuum application.

Adsorption↗

PubMed1992

Base-pair probability profiles of RNA secondary structures.

Dynamic programming algorithms are able to predict optimal and suboptimal secondary structures of RNA. These suboptimal or alternative secondary structures are important for the biological function of RNA. The distribution of secondary structures present in solution is governed by the thermodynamic equilibrium between the different structures. An algorithm is presented which approximates the total partition function by a Boltzmann-weighted summation of optimal and suboptimal secondary structures at several temperatures. A clear representation of the equilibrium distribution of secondary structures is derived from a two-dimensional bonding matrix with base-pairing probability as the third dimension. The temperature dependence of the equilibrium distribution gives the denaturation behavior of the nucleic acid, which may be compared to experimental optical denaturation curves after correction for the hypochromicities of the different base-pairs. Similarly, temperature-induced mobility changes detected in temperature-gradient gel electrophoresis of nucleic acids may be interpreted on the basis of the temperature dependence of the equilibrium distribution. Results are illustrated for natural circular and synthetic linear potato spindle tuber viroid RNA respectively, and are compared to experimental data.

Algorithms↗

PubMed1998

Pre-evaluation and system optimization of the Elecsys thyroid electrochemiluminescence immunoassays.

We present the results of a pre-evaluation of the thyroid function test free thyroxine, free triiodothyronine and third generation TSH using the Elecsys electrochemiluminescence immunoassay system. A collaborative field study between the development center of the manufacturer and a clinical chemistry laboratory addressed the reliability and comparability of the new Elecsys assays to established methods under clinical laboratory conditions using samples from routine in vitro thyroid testing. Preliminary (reference) formulations of the reagents and several electrochemiluminescent pilot models were used for assay measurements, either in the company's research center or in the clinical setting. The new thyroid assays were compared with the respective Enzymun-Test assays, performed on the ES300 automated immunoassay analyzer. A WHO standard was used for standardization of TSH, whereas an equilibrium dialysis method was applied for free triiodothyronine. The free thyroxine assay was standardized against the Enzymun-Test free thyroxine assay, which had previously been calibrated against equilibrium dialysis. The aim of this field study was to support the optimization of the technology used for Elecsys in an early stage of development and thereby prepare the ground for the adaptation of the immunoassays to the final Elecsys 2010 random access analyzer. A subsequent multicenter evaluation demonstrated that the requirements of routine thyroid testing in terms of reliability were fulfilled by the system.

Electrochemistry↗

PubMed1974

Further analysis of a simple prototypal muscle model near to and far from equilibrium.

The same prototypal model used in a previous paper to illustrate proper construction of a muscle model is modified here with the much more realistic choice e(Deltap) = 10(8) rather than e(Deltap) = 100, where e(Deltap) is the ratio of physiological ATP activity to equilibrium ATP activity. For steady isotonic contractions, the range 1 </= e(Delta) </= 10(4) can be approximated quite well by use of linear terms only in expansions of F (force) and J (ATP flux) in powers of e(Delta) - 1 and v (velocity). This will presumably also be true in most cases of much more complicated models. However, this region is of theoretical interest only (irreversible thermodynamics, etc.) because F and J are very small. In addition, numerical calculations of F and J were made in the region 10(4) </= e(Delta) </= 10(8). The optimal efficiency eta(*) is larger under physiological conditions (about 1%) than at equilibrium by a factor of 2.1 x 10(4). The rate of entropy production is discussed in this connection.

Adenosine Triphosphate↗