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Results for “Equilibrium optimization”

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At least 433 records · Page 24Linked to original sources

PubMed2005

Headspace solid-phase microextraction-gas chromatography--mass spectrometry analysis of the volatile compounds of Evodia species fruits.

In this study the investigation of the aroma compounds of dried fruits of Evodia rutaecarpa (Juss.) Benth. and E. rutaecarpa (Juss.) Benth. var. officinalis (Dode) Huang (i.e. E. officinalis Dode) (Rutaceae family) was carried out to identify the odorous target components responsible for the characteristic aroma of these valuable natural products. To avoid the traditional and more time-consuming hydrodistillation, the analyses were carried out by means of headspace solid-phase microextraction (HS-SPME) coupled to gas chromatography-mass spectrometry (GC-MS). The SPME headspace volatiles were collected using a divinylbenzene-carboxen-polydimethylsiloxane (DVB-CAR-PDMS) fiber. The extraction conditions were optimized using a response surface experimental design to analyze the effect of three factors: extraction temperature, equilibrium time and extraction time. The best response was obtained when the extraction temperature was around 80 degrees C, equilibrium time near 25 min and extraction time close to 18 min. Analyses were performed by GC-MS with a 5% diphenyl-95% dimethyl polysiloxane (30 m x 0.25 mm I.D., film thickness 0.25 microm) capillary column using He as the carrier gas and a programmed temperature run. The main components of the HS-SPME samples of E. rutaecarpa (concentration >3.0%) were limonene (33.79%), beta-elemene (10.78%), linalool (8.15%), myrcene (5.83%), valencene (4.73%), beta-caryophyllene (4.62%), linalyl acetate (4.13%) and alpha-terpineol (3.99%). As for E. officinalis, the major compounds were myrcene (32.79%), limonene (18.36%), beta-caryophyllene (9.92%), trans-beta-ocimene (6.04%), linalool (5.88%), beta-elemene (7.85%) and valencene (4.62%).

Evodia↗

PubMedDate not supplied

Recovery of Acinetobacter radioresistens lipase by hydrophobic adsorption to n-hexadecane coated on nonwoven fabric.

A simple and clean adsorption/desorption process was proposed for recovering Acinetobacter radioresistens lipase from fermentation broth. The adsorbent used was n-hexadecane coated on a hydrophobic nonwoven fabric (NWF). n-Hexadecane has a melting point of 16-18 degrees C, and its affinity for lipase decreases markedly from liquid to solid state. Accordingly, performing the adsorption and desorption above and below, respectively, the melting point would need no extraneous materials for separation. The adsorption isotherms at various temperatures were found to follow the Langmuir model. Simulation of the batch adsorption/desorption process showed that there exists an optimal amount of adsorbent for both concentration factor and enzyme recovery; the process is restrained by equilibrium. The performance of column adsorption/desorption could also be simulated using the adsorption isotherm, and it was shown that the concentration factor was proportional to the amount of adsorbent used. The benefits of this process include easy preparation of adsorbent, low operational cost, no extraneous materials needed, negligible enzyme denaturation, high efficiency, and simple process simulation.

Acinetobacter↗

PubMed2005

Comparative investigation on non-IPR C68 and IPR C78 fullerenes encaging Sc3N molecules.

A computational study on the experimentally detected Sc(3)N@C(68) cluster is reported, involving quantum chemical analysis at the B3LYP/6-31G level. Extensive computations were carried out on the pure C(68) cage which does not conform with the isolated pentagon rule (IPR). The two maximally stable C(68) isomers were selected as initial Sc(3)N@C(68) cage structures. Full geometry optimization leads to a confirmation of an earlier assessment of the Sc(3)N@C(68) equilibrium geometry (Nature 2000, 408, 427), namely an eclipsed arrangement of Sc(3)N in the C(68) 6140 frame, where each Sc atom interacts with one pentagon pair. From a variety of theoretical procedures, a D(3h) structure is proposed for the free Sc(3)N molecule. Encapsulated into the C(68) enclosure, this unit is strongly stabilized with respect to rotation within the cage. The complexation energy of Sc(3)N@C(68) cage is found to be in the order of that determined for Sc(3)N@C(80) and exceeding the complexation energy of Sc(3)N@C(78). The cage-core interaction is investigated in terms of electron transfer from the encapsulated trimetallic cluster to the fullerene as well as hybridization between these two subsystems. The stabilization mechanism of Sc(3)N@C(68) is seen to be analogous to that operative in Sc(3)N@C(78). For both cages, C(68) and C(78), inclusion of Sc(3)N induces aromaticity of the cluster as a whole.

Fullerenes↗

PubMed1997

Interaction between antibodies and hapten-protein conjugates of different composition: theoretical predictions and experimental data.

Mathematical models of competitive ELISAs with labelled antibody and with labelled antigen taking into account bivalent interactions between antibodies and hapten-protein conjugates were developed and analyzed. It was shown that in the kinetic model of the immunochemical reaction the conjugate composition influenced the amplitude of detected signal but not ELISA sensitivity. In the equilibrium model decreased sensitivity correlated with bivalent complexes formation. The predictions were tested experimentally using 2,4-dichlorophenoxyacetic acid (2,4-D) and testosterone as haptens. It was confirmed that increasing of the hapten : protein ratio resulted in formation of bivalent complexes with antibodies. The equilibrium binding constants for these complexes were two orders of magnitude higher than for monovalent ones. Optimal conjugate compositions have been chosen for ELISA of these haptens.

Animals↗

PubMed2003

Influence of external information in the minority game.

The influence of a fixed number of agents with the same fixed behavior on the dynamics of the minority game is studied. Alternatively, the system studied can be considered the minority game with a change in the comfort threshold away from half filling. Agents in the frustrated, nonergodic phase tend to overreact to the information provided by the fixed agents, leading not only to large fluctuations, but to deviations of the average occupancies from their optimal values. Agents that discount their impact on the market, or that use individual strategies reach equilibrium states, which, unlike in the absence of the external information provided by the fixed agents, do not give the highest payoff to the collective.

Choice Behavior↗

PubMed2006

[Study of the pH sensitive polymer].

A pH sensitive polymer was prepared by copolymerization of methacrylic acid as monomer, diethylene glycol dimethacrylate as cross-linking reagent, heptane as porogen, and fluorescent dye eosin as indicator. The factors of influence on the preparation, and the character of the pH sensitive polymer for pH were studied. The maximal emission wavelength of eosin was red shifted in the polymer than in solution, the apparent Ka largened, and the dissociation equilibrium of indicator was shifted to acidity direction, because the polarity of polymer diminished. Under the optimal condition, the calibration curve of the pH sensitive polymer covered the range of pH 0-3.0 with good reproduction and reversibility.

Acrylates↗

PubMed1988

Tendon transfer for median nerve palsy.

A large number of tendon transfers have been described that restore opposition to the thumb and provide thumb and finger flexion. To provide optimal results following tendon transfers, one needs to follow the principles of tendon transfer: normal tissue equilibrium, movable joints, and a scar-free bed. Once these are present, we must look to available tables to determine an appropriate tendon transfer, matching up the lost muscle mass, fiber length, and cross-sectional area and then pick out muscle-tendon units of similar size, strength, and potential excursion. For low median nerve palsy (Table 4), we have found from our experimental and clinical studies that the FDS of the long and ring fingers or the wrist extensors (ECR or ECRL) best approximate the force and motion required for full thumb opposition and strength. These transfers are preferred in median nerve palsy or combined median ulnar nerve palsy when both strength and motion are required. In circumstances where only thumb mobility is desired, the EIP is an ideal transfer. Also, the extensor digitorum quinti (EDQ) and ADQ have sufficient mean fiber length (muscle excursion) to provide full thumb opposition. The palmaris longus transfer (Camitz transfer) is an abduction rather than an opposition transfer and should be reserved for selected cases of long-term carpal tunnel syndrome. For high median nerve palsy (Table 5), transfers of the brachioradialis or ECRL to restore lost thumb flexion (FPL) and side-to-side transfer of the FDP of the index finger are generally sufficient. A separate transfer to restore independent flexion of the index finger could be performed by utilizing the pronator teres or extensor carpi radialis ulnaris tendon muscle units. As they combine a proper direction of action, pulley location, and tendon insertion, tendon transfers for median nerve palsy are usually quite successful. In considering any of these elective procedures, however, it is important to remember that tendon transfers are muscle balance operations. The effect of transfer on restoring function must be carefully studied to assess the loss of function that such a transfer may endure.

Hand↗

PubMed1977

[Metabolic disorders and current treatment of the surgical patient with pancreatitis].

Very frequently in acute and chronic pancreatitis, the surgical treatment is indispensable. The disease itself is accompanied by metabolic disturbances, protein deficiency, hepatic lesion, by diabetes and malabsorption syndrome. Following the laboratory parameters we were able to perform partial or total hyperalimentation, correction of acid-base dis-equilibrium and to obtain the positive nitrogen balance, and in this way keep the patients in optimal conditions pre- and postoperatively.

Acute Disease↗

PubMed1996

Tissue impedance as a function of temperature and time.

Tissue impedance dependence on temperature has been measured for six tissue types. The information was gathered using an automated laboratory under computer control. This information is needed to be able to input these values into a computer model that predicts temperature distribution produced by delivery of radio frequency energy. Due to the thermal dose of time and temperature, tissue properties change and no published data are available that document this. Since there are no theoretical predictions, empirical data were measured to supply this information. Using an aluminum cylindrical cavity of volume 1.69 cm3, muscle, liver, brain, and fat tissue impedance were measured at 500 kHz over a range of temperatures. All tests began at room temperature where baseline measurements were made. The cylinder was then placed in a constant temperature water bath at between 30 and 90 degrees C. The tests were run for a period of 10 to 30 minutes. Temperature homogeneity was carefully studied throughout the volume of the cylinder. It was found that thermal equilibrium occurred within four minutes. Special care was taken with the tissue sample in regard to optimize moisture and freshness, and minimize fat content. Grain orientation was also taken into consideration depending on the test. For all tissue types, resistivity decreased initially as the sample temperature equilibrated with the bath temperature. For temperatures less than 75 degrees C, resistivity values remained approximately constant over time.

Adipose Tissue↗

PubMed2006

Bone morphogenetic protein-2 binds as multilayers to a collagen delivery matrix: an equilibrium thermodynamic analysis.

Recombinant human bone morphogenetic protein-2 (rhBMP-2) promotes bone growth but must be retained at the delivery site for optimal efficacy in vivo. rhBMP-2 release from a collagen-based matrix has shown favorable pharmacokinetics. The present study assessed binding affinity and binding saturation of rhBMP-2 to a collagen matrix as a function of solution and rhBMP-2 isoform variables. Results indicate that rhBMP-2 binds to the collagen matrix with affinities on the order of 10(3) to 10(4) M(-1). Maximum binding, nu, was primarily a function of pH for heterogeneous rhBMP-2 and the extended (T(266)/T(266)) isoform. However, binding saturation of the <Q(283)/<Q(283) isoform was unaffected by pH. Overall, binding saturation was higher than the calculated saturation of a rhBMP-2 monolayer, suggesting both hydrophobic and ionic interactions in a multilayer formation. The contributions of pH and ionic strength to the linkage free energy of interaction was on the order of 1.3 kcal mol(-1) and approximately 0.3 kcal mol(-1), respectively. This thermodynamic approach can serve to optimize interactions between therapeutic proteins and delivery systems.

Bone Morphogenetic Protein 2↗

PubMed2006

The eternal quest for optimal balance between maximizing pleasure and minimizing harm: the compensatory health beliefs model.

Particularly in the health domain, humans thrive to reach an equilibrium between maximizing pleasure and minimizing harm. We propose that a cognitive strategy people employ to reach this equilibrium is the activation of Compensatory Health Beliefs (CHBs). CHBs are beliefs that the negative effects of an unhealthy behaviour can be compensated for, or "neutralized," by engaging in another, healthy behaviour. "I can eat this piece of cake now because I will exercise this evening" is an example of such beliefs. Our theoretical framework aims at explaining why people create CHBs and how they employ CHBs to regulate their health behaviours. The model extends current health behaviour models by explicitly integrating the motivational conflict that emerges from the interplay between affective states (i.e., cravings or desires) and motivation (i.e., health goals). As predicted by the model, previous research has shown that holding CHBs hinder an individual's success at positive health behaviour change, and may explain why many people fail to adhere to behaviour change programs such as dieting or exercising. Moreover, future research using the model and implications for possible interventions are discussed.

Attitude to Health↗

PubMed1977

Steady state kinetics and binding of eukaryotic cytochromes c with yeast cytochrome c peroxidase.

1. The steady state kinetics for the oxidation of ferrocytochrome c by yeast cytochrome c peroxidase are biphasic under most conditions. The same biphasic kinetics were observed for yeast iso-1, yeast iso-2, horse, tuna, and cicada cytochromes c. On changing ionic strength, buffer anions, and pH, the apparent Km values for the initial phase (Km1) varied relatively little while the corresponding apparent maximal velocities varied over a much larger range. 2. The highest apparent Vmax1 for horse cytochrome c is attained at relatively low pH (congruent to 6.0) and low ionic strength (congruent to 0.05), while maximal activity for the yeast protein is at higher pH (congruent to 7.0) and higher ionic strength (congruent to 0.2), with some variations depending on the nature of the buffering ions. 3. Direct binding studies showed that cytochrome c binds to two sites on the peroxidase, under conditions that give biphasic kinetics. Under those ionic conditions that yield monophasic kinetics, binding occurred at only one site. At the optimal buffer concentrations for both yeast and horse cytochromes c, the KD1 and KD2 values approximate the Km1 and Km2 values. At ionic strengths below optimal, binding becomes too strong and above optimal, too weak. 4. Under ionic conditions that are optimal and give monophasic kinetics with horse cytochrome c but are suboptimal for the yeast protein, yeast cytochrome c strongly inhibits the reaction of horse cytochrome c with peroxidase, uncompetitively at one site and competitively at a second site. The appearance of the second site under monophasic conditions is interpreted as an allosteric effect of the inhibitor binding to the first site. 5. The simplest model accounting for these observations postulates two kinetically active sites on each molecule of peroxidase, a high affinity and a low affinity site, that may correspond to the free radical and the heme iron (IV) of the oxidized enzyme, respectively. Both oxidizing equivalents may be discharged at either site. Furthermore, the enzyme appears to exist as an equilibrium mixture of a high ionic strength form, EH and a low ionic strength form, EL, the former reacting optimally with yeast cytochrome c, and the latter with horse cytochrome c.

Animals↗

PubMedDate not supplied

Factors affecting multiresidue determination of priority herbicides when using solid-phase microextraction.

A solid-phase microextraction (SPME) procedure was developed for the determination of 10 selected organonitrogen herbicides (s-ethyl dibropylthiocarbamate [EPTC], molinate, propachlor, trifluralin, simazine, atrazine, propazine, terbuthylazine, alachlor, and prometryn) and was tested with various natural waters. Gas chromatography coupled with flame thermionic and mass spectrometric detection was used for quantitation. For this purpose, polydimethylsiloxane and polyacrylate fibers were used and the factors affecting the SPME process such as pH, ionic strength, methanol content, memory effect, stirring rate, and adsorption-time profile were investigated and optimized. By using spiked liquid chromatography water, optimal factors were determined to be 25% salt, <0.5% methanol, stirring rate of 960 rpm, pH 4, and an equilibrium time of 30 min. These conditions were used in further studies of the fibers and in analysis of natural water samples. The method was applied to spiked natural waters such as ground water, sea water, lake water, and river water at a concentration range of 0.5-10 microg/L. Limits of detection ranged from 5 to 90 ng/L, and precision ranged from 5 to 15% (as relative standard deviation), depending on the pesticide, fiber, and detector used. The recoveries of herbicides were 70.2-118.4%, and the average r2 values of the calibration curves were >0.99 for all analytes. The results demonstrate the suitability of the SPME method to determine these organonitrogen herbicides in various natural waters. River water samples originating from the Epirus region (Northwestern Greece) were analyzed to verify the performance of the optimized method by comparing the results obtained by SPME with those obtained by using conventional solid-phase extraction of the selected herbicides.

Calibration↗

PubMedDate not supplied

[The role of the oxygen-binding properties of the blood in maintaining pro-oxidant-antioxidant equilibrium in the body].

Tissue pro-oxidant generation under standard conditions is equilibrated with the activity of intra- and extracellular antioxidants; thus some optimal level of pro-oxidant-antioxidant balance is created. Oxygen-dependent nature of lipid peroxidation processes implicates its complex multilevel regulatory system, where systemic mechanisms may dominate upon the intracellular ones. This suggests a necessity in the investigation of body oxygen transport not only in terms of the requirements of energetic metabolism in electron acceptor but also as a physiological mechanism for antioxidant defense and, in general, as the mechanism involved in a maintenance of pro-oxidant-antioxidant balance. The hemoglobin-oxygen affinity has a special place in a complex antioxidant system hierarchy, because it determines the condition of oxygen diffusion to tissues and ultimately the value of tissue pO2. The blood oxygen-binding properties under different hyperthermic states with or without a correction of hemoglobin-oxygen affinity and L-arginine-NO pathway were shown to be involved into a complex integration with elements of different functional systems and to play an important role in complex physiologic mechanisms for the maintenance of pro-oxidant-antioxidant balance. The oxyhemoglobin dissociation curve shift leftwards may have an adaptive effect under conditions of low oxygen utilization because of limitation of oxygen fraction spent on a free radical generation and the following initiation of lipid peroxidation processes.

Animals↗

PubMed2006

Optimization and evaluation of a coarse-grained model of protein motion using x-ray crystal data.

Simple coarse-grained models, such as the Gaussian network model, have been shown to capture some of the features of equilibrium protein dynamics. We extend this model by using atomic contacts to define residue interactions and introducing more than one interaction parameter between residues. We use B-factors from 98 ultra-high resolution (<or=1.0 A) x-ray crystal structures to optimize the interaction parameters. The average correlation between Gaussian network-model fluctuation predictions and the B-factors is 0.64 for the data set, consistent with a previous large-scale study. By separating residue interactions into covalent and noncovalent, we achieve an average correlation of 0.74, and addition of ligands and cofactors further improves the correlation to 0.75. However, further separating the noncovalent interactions into nonpolar, polar, and mixed yields no significant improvement. The addition of simple chemical information results in better prediction quality without increasing the size of the coarse-grained model.

Calmodulin↗

PubMed2002

Multistage electrophoresis II: treatment of a kinetic separation as a pseudoequilibrium process.

An electrophoresis device is described which separates cells, particles, proteins and other separands by collecting samples having decreasing electrophoretic mobility in a train of inverted cavities while an electric field is applied between the inverted cavities and a sample cuvette containing a mixture of cells, particles, proteins or other separands. A circular plate is provided for the inverted cavities, and this circular plate is rotated to collect fractions. The system utilizes an innovative purification method that combines free electrophoresis and multistage extraction in an instrument capable of separating living cells, particles, and proteins in useful quantities at high concentrations. Most multistage processes are based on equilibrium separations, but electrophoresis is a kinetic separation; therefore, a pseudoequilibrium paradigm was developed for use in optimizing separation parameters including number of stages and electrophoresis time per stage. This paradigm allows the application of McCabe-Thiele type analysis, and it was calculated, for example, that two separands differing by 20% in electrophoretic mobility can be purified to 95% purity with acceptable yield in about seven stages. Laboratory experiments demonstrated a 95% purification in four stages of a separand originally present at 4% when electrophoretic mobilities differed by 80%.

Anions↗

PubMed2003

Sex ratio evolution through group selection using diffusion approximation.

We consider a haploid, hermaphrodite population subdivided into an infinite number of demes of finite size N. Assuming recurrent mutation, random union of gametes, partial dispersal, genetic drift, and incorporating group competition, a diffusion approximation is used to describe the evolution of sex ratio, corresponding to sex allocation to male versus female functions. The stationary distribution is deduced. In presence of group selection, a female-biased sex ratio in the whole population is found to be optimal in the sense that an allele coding for this sex ratio is always more frequent at equilibrium when segregating with another allele coding for a different sex ratio than for the same sex ratio. Numerical studies are presented to check the validity and accuracy of this prediction.

Algorithms↗

PubMed1984

Comparison of equilibrium and disequilibrium assay conditions for ergocalciferol, cholecalciferol and their major metabolites.

The comparison of equilibrium and disequilibrium assay conditions for ergocalciferol, cholecalciferol and their major metabolites were investigated to evaluate: (1) optimization of sensitivity (2) crossreactivity of these compounds in their respective assays and (3) side chain steric requirements of the vitamin D molecule for optimum binding to the calciferol binding protein or bovine thymus receptor. Disequilibrium assay conditions improved assay sensitivity 30-fold for the calciferol assay and approx 3-fold for metabolites in the 25-hydroxycalciferol and 1,25-dihydroxycalciferol assays. Ergocalciferol compounds were uniformly less efficient in their association with the proteins tested than were their cholecalciferol counterparts, with one exception. In the calciferol assay, cholecalciferol had greater affinity for the the calciferol binding protein than did ergocalciferol. In the 25-hydroxycalciferol assay affinity for the calciferol binding protein was 25-hydroxycholecalciferol = 24,25-dihydroxycholecalciferol greater than 25-hydroxyergocalciferol greater than 25S,26-dihydroxycholecalciferol greater than 24,25-dihydroxyergocalciferol greater than 25,26-dihydroxyergocalciferol. In the assay for 1,25-dihydroxycalciferol, bovine thymus receptor recognized 1,25-dihydroxyergocalciferol and 1,25-dihydroxycholecalciferol equally. From the forthcoming data it appears that hydroxyl and/or methyl groups on the calciferol side chain alter the ability of these physiological compounds to associate with the calciferol binding protein.

Binding, Competitive↗