PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “Equilibrium optimization”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 55 records · Page 3Linked to original sources

[Sample of high school students with a demonstration of intervening factors in school achievement and failure].

This research investigates the relationship and link between intellectual cathexis, school achievement and personality functioning in a representative sample of secondary school students aged 12 to 15 years. The level of structure of the personality plays a most significant role. Good school achievement does not necessarily depend on an optimal psychological equilibrium. In fact, the most determining factor seems to be the part played by the defense mechanisms--particularly those which aim at controlling libidinal drives--developed and elaborated during the period of latency. A certain intellectual potential, however, is a necessary but not sufficient condition for school achievement - indeed, an end of school certificate i.e. the Swiss "certificat de maturité" could be obtained by students of average intelligence. The capacity of maintaining an active intellectual investment seems to be an equally determining factor. This quality of functioning contains an oedipal component - particularly the ability of taking one's stand and of competing - as well as a pre-oedipal one - the narcissistic integrity, allowing one to preserve one's self-esteem facing difficulties. Contrary to our hypothesis, the quality of subject-environment interaction with family, peers, teachers, plays a relatively minor role. A more important aspect concerns the effects and results of relations established during childhood such as the interiorization of parental expectations, the quality of the superego, the degree of internal autonomy allowing compromise with external demands, etc. Underlying conflicts can intervene at several levels. One of these levels could result in the subject's incapacity to utilize his own resources and these imply consequences ranging from difficulties in basic school achievement to non-acquisition of cognitive mecanisms and under-development of symbolization. Psychological testing is a means of identifying the underlying difficulties and determining their nature. Remediating methods include psycho-pedagogical or psychotherapeutic intervention or, in some cases, both.

Achievement↗

On the optimal sex ratio.

The equilibrium structures for various multiallele sex-determining genetic models of panmictic populations with sex expression depending on the genotypes of either the zygote or a parent are described. Even-sex-ratio equilibrium surfaces can exist apart from equilibrium points having coincident male and female allelic frequency sets. The latter (symmetric) equilibrium states entail biased sex ratios. A stable symmetric equilibrium and an even-sex-ratio equilibrium segregating the same alleles cannot coexist. The tendency to evolve toward an even-sex ratio is embodied by the following optimality property: starting from an equilibrium having a biased sex ratio, mutant sex-determining alleles can accumulate only in the case in which in the augmented system all attainable equilibrium states have a sex ratio closer to one to one.

Alleles↗

A new potential toxaphene congener: synthesis, GC/EI-MS study, crystal structure, NMR analysis, and ab initio calculations of 3-endo,5-endo-dichloro-7,7-bis-chloromethyl-4-dichloromethyl-tricyclo[2.2.1.0(2,6)]heptane.

A new potential toxaphene congener 3-endo,5-endo-dichloro-7,7-bis-chloromethyl-4-dichloromethyl-tricyclo[2.2.1.0(2,6)]heptane 2 has been isolated from reaction mixture obtained by the chlorination of 2-exo, 10,10-trichlorobornane 1. The X-ray structural analysis of 2 revealed an unusual tricyclic structure, where the two chlorine atoms occupying endo-positions are in close spatial proximity with each other and near to the neighbouring CHCl2 group. Further, it revealed that the symmetry of the molecule is distorted. The 1H and 13C NMR spectra of 2 have been assigned by means of 1H, 1H double-quantum filtered correlation spectroscopy (DQF COSY), PFG 1H, 13C HMQC (pulsed field gradient heteronuclear multiple-quantum coherence), 1H, 13C heteronuclear multiple bond correlation (HMBC) experiments, and computer aided 1H NMR spectral analysis. The asymmetry of 2 is also discernible on the 1H NMR parameters. In addition, gas chromatographic (GC) properties and electron impact (EI) mass spectrum of 2 has been studied. Ab initio Hartree-Fock (HF) method with the basis set 6-31G(d) has been used for the optimization of the equilibrium geometry and calculation of total energy for 2. The optimized geometry is in good agreement with the crystal structure. According to the rotation energy profile calculated at the HF/6-31G(d) level, rotation of the chloromethyl and dichloromethyl groups are highly unlikely at the room temperature.

Environmental Pollutants↗

A coupled-enzyme equilibrium method for measuring urea in serum: optimization and evaluation of the AACC study group on urea candidate reference method.

We describe a coupled-enzyme equilibrium method for measuring urea in serum, which is performed on supernates prepared by treating each specimen with Ba(OH)2 and ZnSO4 (Somogyi reagent). Analytical recovery of [14C]urea added to a variety of matrices was essentially complete (mean, 100.6%) for the supernates after precipitation. Nine variables were univariately examined in arriving at the reaction conditions for the method: glutamate dehydrogenase, urease, 2-oxoglutarate, ADP, Tris . HCI, NADH, EDTA, pH, and temperature. The reagent is stable for at least 48 days at--20 degrees C and for 23 days at 4 degrees C. Mean analytical recovery of urea (14 mmol/L) added to seven different specimens (three different matrices) was 100.8%. The analytical linear range of the method extends to 30 mmol of urea per liter. Of 22 potential interferents, only bilirubin at 1 mmol/L (580 mg/L), hemoglobin at 10 g/L, and hydroxyurea at 6 mmol/L showed more than 2% interference. We discuss precision and effects of specimen dilution, and compare results for 100 human serum specimens with those measured for the same specimens with four other urea methods. We examined the effects of measuring a blank, consisting of sample and reagent without urease, with each specimen.

Animals↗

Full length synthetic surfactant proteins, SP-B and SP-C, reduce surfactant inactivation by serum.

The failure of some infants with respiratory distress syndrome to respond to therapy with surfactant may be explained in part by inactivation of surfactant caused by leakage of plasma constituents into air spaces. Surfactant-associated proteins (SP-A, SP-B and SP-C) reduce the susceptibility of surfactants to inactivation in vitro. To study this phenomenon further, we used full length synthetic proteins, SP-B [1-78] and SP-C [1-31], mixed with surfactant lipids in different ratios and different concentrations. Equilibrium and minimum surface tensions of these mixtures, with or without serum and calcium, were measured using a pulsating surfactometer. Mixtures containing both SP-B and SP-C had optimal minimum and equilibrium surface tensions of < 5 and < 28 mN/m, respectively. Mixtures with SP-B had optimal minimum surface tensions, but equilibrium surface tensions averaged 35 mN/m. Mixtures with SP-C had high minimal (19 mN/m) and high equilibrium surface tensions (35 mN/m). When serum was added to these mixtures, the least inactivation was found with mixtures containing 3% protein at 1:1 ratio of SP-B/SP-C with 2 mM calcium chloride. These data indicate that SP-B and SP-C, particularly in the presence of calcium, reduce surfactant inactivation that may be caused by plasma constituents. The results lead to the hypothesis that charge interactions among ions, lipids, surfactant proteins, and serum inactivators are a major element in pathophysiological surfactant inactivation.

Adult↗

[Hemodynamic impact of positive end expiratory pressure (PEEP) during severe respiratory failure: present view].

Bedside evaluation of pulmonary mechanics and thoracic computed axial tomography have changed the ventilatory management of patients suffering an acute respiratory failure caused by adult respiratory distress syndrome (ARDS). Mortality has been reduced limiting tidal volumes, which avoids alveolar overdistention and by the use of positive end expiratory pressure (PEEP), that reduces the damage caused by cyclical alveolar collapse-reopening. Nowadays, it is well known that inappropriate mechanical ventilation enhances lung damage caused by the underlying disease. However, the optimal adjustment of PEEP is not yet established. Usually, it is not easy to achieve an equilibrium between an optimal lung recruitment without producing alveolar overdistention and hemodynamic adverse effects such as hypotension and reduction of cardiac output. This paper reviews the interactions between heart and lung.

Adult↗

A simple method for estimating equilibrium constants for serum testosterone binding resulting in an optimal free testosterone index for use in elderly men.

An algorithm was developed to evaluate equilibrium constants for testosterone (Te) and sex hormone-binding globulin (SHBG) or albumin from serum free testosterone (FTe) measurements performed in a panel of 30 healthy elderly men by means of a near-reference method, i.e., symmetric dialysis (affinity constants: SHBG-Te, 1.13 x 10(9) L/mol; albumin-Te, 4.4 x 10(4) L/mol). Using these estimates, a free testosterone index (FTeI) was calculated from total Te and SHBG concentrations in a further 35 elderly men. This FTeI perfectly matches with actually measured free testosterone concentrations by symmetric dialysis in this second group, with a mean ratio index/measurement of 0.998+/-0.016 (SEM). The efficacy of the algorithm, which represents a simple alternative to previous cumbersome methods for estimation of equilibrium constants, is thereby demonstrated.

Aged↗

Harvesting under density-dependent mortality and fecundity.

The problem of optimal harvesting in equilibrium is considered in a Leslie matrix model in which both mortality and fecundity in all age-classes may be density-dependent. The conclusion is that the optimal strategy is of the two-age-class type, in common with results obtained previously for simpler models.

Fertility↗

Carbon dioxide fixation by reversible pyrrole-2-carboxylate decarboxylase from Bacillus megaterium PYR2910.

Pyrrole-2-carboxylate decarboxylase from Bacillus megaterium PYR2910 attains a balanced reaction equilibrium with an equilibrium constant of 0.3-0.4 M. Therefore, the enzyme catalyzes the reverse carboxylation of pyrrole after addition of bicarbonate. For the synthesis of pyrrole-2-carboxylate, the reverse reaction was optimized and the equilibrium was shifted towards the carboxylate. The product yield was 230 mM (25.5 g/l) pyrrole-2-carboxylate from 300 mM pyrrole in a batch reaction and 325 mM (36.1 g/l) from 400 mM pyrrole in a fed-batch reaction, using both whole cells and the purified enzyme in a pH 8.0 reaction mixture with bicarbonate saturation of 1.9 M. Kinetic studies indicated, that bicarbonate is the reactive species used by this carbon dioxide-fixation enzyme.

Bacillus megaterium↗

[Optimization of methods of immobilization of anti-immunoglobulins. Equilibrium parameters of the interaction of immobilized antibodies with an antigen].

Methods for immobilization of anti-immunoglobulins on insoluble supports were optimized, and the interaction of immunoadsorbents obtained with [125I]-labeled rabbit IgG was investigated. It was shown that this interaction can be adequately described by a rather simple equilibrium model which reflects the interaction of a monovalent antigen with two independent types of binding sites. Within the framework of this model the association constants as well as the concentrations of high affinity binding sites which influence the capacity and efficiency of the separation system were determined. Optimization of the immobilization methods implicated a study on the role of certain functional groups of the antibody involved in the formation of covalent bonds, on the effect of the spacer arm length on the properties of immobilized antibody as well as on the role of the degree of immobilization. It was found that immunoadsorbents obtained after antibody immobilization via lysine or tyrosine residues on matrices with a specific spacer group are the optimal ones.

Animals↗

Protein-binding of secretin in human plasma.

Protein-binding of endogenous plasma secretin and of 125I-labelled secretin incubated with charcoal-treated plasma examined by gel filtration on a Sephacryl S-200 Superfine column (16 X 980 mm) showed that secretin in plasma appears both to be bound to at least two different plasma proteins where albumin appears to be the major binding protein, and also to occur as a free molecular form. In addition, protein-binding studied by incubating 125I-labelled secretin with charcoal-treated plasma under various conditions followed by charcoal separation of bound from free label indicated the presence of more specific secretin-binding sites on the plasma proteins with an avidity comparable to that otherwise reported for albumin as a binding protein. The protein-binding of 125I-labelled secretin was optimal or reached equilibrium after 2 days incubation at 20 degrees C and first after 8 days incubation at 4 degrees C. Also, the protein-binding of 125I-labelled secretin was higher at an incubation temperature of 20 than of 4 degrees C; was optimal at pH 7.4; increased with increasing amounts of charcoal-treated plasma up to an amount of 800 microliters in our assay system before levelling off; and increased in a constant and predictable manner with increasing amounts of 125I-labelled secretin at least with the amounts of labelled secretin examined here.

Blood Proteins↗

Optimal screening of surface-displayed polypeptide libraries.

Cell surface display of polypeptide libraries combined with flow cytometric cell sorting presents remarkable potential for enhancement of protein-ligand recognition properties. To maximize the utility of this approach, screening and purification conditions must be optimized to take full advantage of the quantitative feature of this technique. In particular, discrimination of improved library mutants from an excess of wild-type polypeptides is dependent upon an effective screening methodology. Fluorescence discrimination profiles for improved library mutants were derived from a mathematical model of expected cell fluorescence intensities for polypeptide libraries screened with fluorescent ligand. Profiles for surface-displayed libraries under equilibrium or kinetic screening conditions demonstrate distinct discrimination optima from which optimal equilibrium and kinetic screening parameters were derived. In addition, a statistical model of low cytometrically analyzed cell populations indicates the importance of low-stringency sorting followed by amplification through regrowth and resorting at increased stringency. This analysis further yields quantitative recommendations for cell-sorting stringency.

Cells↗

Evidence of conformational equilibrium of 1-ethyl-3-methylimidazolium in its ionic liquid salts: Raman spectroscopic study and quantum chemical calculations.

Raman spectra of liquid 1-ethyl-3-methylimidazolium (EMI+) salts, EMI(+)BF4-, EMI(+)PF6-, EMI(+)CF3SO3-, and EMI(+)N(CF3SO2)2-, were measured over the frequency range 200-1600 cm(-1). In the range 200-500 cm(-1), we found five bands originating from the EMI+ ion at 241, 297, 387, 430, and 448 cm(-1). However, the 448 cm(-1) band could hardly be reproduced by theoretical calculations in terms of a given EMI+ conformer, implying that the band originates from another conformer. This is expected because the EMI+ involves an ethyl group bound to the N atom of the imidazolium ring, and the ethyl group can rotate along the C-N bond to yield conformers. The torsion energy for the rotation was then theoretically calculated. Two local minima with an energy difference of ca. 2 kJ mol(-1) were found, suggesting that two conformers are present in equilibrium. Full geometry optimizations followed by normal frequency analyses indicate that the two conformers are those with planar and nonplanar ethyl groups against the imidazolium ring plane, and the nonplanar conformer is favorable. It elucidates that bands at 241, 297, 387, and 430 cm(-1) mainly originate from the nonplanar conformer, whereas the 448 cm(-1) band does originate from the planar conformer. Indeed, the enthalpy for conformational change from nonplanar to planar EMI+ experimentally obtained by analyzing band intensities of the conformers at varying temperatures is practically the same as that evaluated by theoretical calculations. We thus conclude that the EMI+ ion exists as either a nonplanar or planar conformer in equilibrium in its liquid salts.

Journal Article↗

Optimal body size and energy expenditure during winter: why are voles smaller in declining populations?

Winter is energetically challenging for small herbivores because of greater energy requirements for thermogenesis at a time when little energy is available. We formulated a model predicting optimal wintering body size, accounting for the scaling of both energy expenditure and assimilation to body size, and the trade-off between survival benefits of a large size and avoiding survival costs of foraging. The model predicts that if the energy cost of maintaining a given body mass differs between environments, animals should be smaller in the more demanding environments, and there should be a negative correlation between body mass and daily energy expenditure (DEE) across environments. In contrast, if animals adjust their energy intake according to variation in survival costs of foraging, there should be a positive correlation between body mass and DEE. Decreasing temperature always increases equilibrium DEE, but optimal body mass may either increase or decrease in colder climates depending on the exact effects of temperature on mass-specific survival and energy demands. Measuring DEE with doubly labeled water on wintering Microtus agrestis at four field sites, we found that DEE was highest at the sites where voles were smallest despite a positive correlation between DEE and body mass within sites. This suggests that variation in wintering body mass between sites was due to variation in food quality/availability and not adjustments in foraging activity to varying risks of predation.

Animals↗

Thermal rearrangements of 2-vinylcyclopropylidene to cyclopentadiene and vinylallene: a theoretical investigation.

In an attempt to clarify the favored rearrangement reaction of vinylcyclopropylidenes, the prototype thermal rearrangements of singlet 2-vinylcyclopropylidene (1) leading to 1,3cyclopentadiene (2) and 1,2,4-pentatriene (vinylallene) (3) were investigated by means of ab initio quantum-mechanical electronic-structure calculations. The B3LYP functional with the 6-31G(d) basis set was employed for geometry optimization of the equilibrium and transition-state structures relevant to the two reaction pathways and for computing their harmonic vibrational frequencies. Final energies were evaluated by single-point calculations at the CCSD(T) level of theory with the 6-311 + G(3df,2p) basis set. The rearrangement of s-cis 1 to 2 is found to occur by a three-step pathway. The first step involves the formation of a nonclassical carbene (5), which is an internal pi complex between the pi molecular orbital of the double bond and the empty p atomic orbital of the carbene carbon. In the second step, the nonplanar five-membered ring geometry of 5 flattens to reach the planar structure of 3-cyclopentenylidene (4). The last step is the 1,2-migration of a alpha-hydrogen atom to the carbene center in 4. The rate-determining step for the rearrangement of s-cis 1 to 2 is the formation of 5, with a predicted global deltaG++(220 K) of only 0.6 kcalmol(-1). The rearrangement of s-trans 1 to 2 requires an initial conversion of s-trans 1 to the s-cis conformer, with a predicted deltaG++(220 K) of 1.8 kcalmol(-1). The transition structure for the ring-opening of s-trans 1 into s-trans 3 (deltaG++(220 K)=4.7 kcalmol(-1)) is more energetic than that for the ring-opening of s-cis 1 into s-cis 3 (deltaG++(220 K)=2.5 kcalmol(-2)) due to larger repulsive nonbonded H...H interactions in the former transition structure. On the basis of these results, it is suggested that if the reaction of 1,1-dibromo-2-vinylcyclopropane with methyllithium at -78 degrees C leads to the initial formation of carbene 1, then the reaction should yield 2 as the main product together with small amounts of 3. This theoretical prediction nicely agrees with experimental findings.

Journal Article↗

New generation of monomer-stabilized very small superparamagnetic iron oxide particles (VSOP) as contrast medium for MR angiography: preclinical results in rats and rabbits.

The purpose of this study was to evaluate the signal enhancement characteristics of very small superparamagnetic iron oxide particles (VSOP)-C63, a new monomer-coated, iron oxide-based magnetic resonance (MR) blood pool contrast medium with a very small particle size and optimized physical properties. Equilibrium MR angiography (MRA) of rats (thoracic and abdominal vessels) was performed at 1.5 T with a three-dimensional gradient-recalled echo (3D GRE) technique (TR/TE 6.6/2.3 msec, flip angle 25 degrees ) before and after (every 3-5 minutes up to 50 minutes) i.v. injection of VSOP-C63 [dosages: 15, 30, 45, 60, 75, and 90 micromol Fe/kg; diameter: 8 nm; relaxivities at 0.47 T: R1 = 30 l/(mmol * s); R2 = 39 l/(mmol * s)]. First-pass MRA images (3D-GRE, TR/TE 4.5/1.7 msec, flip angle 25 degrees ) were obtained with 45 micromol Fe/kg VSOP-C63 in comparison with 0.2 mmol Gd/kg of gadolinium diethylene triamine pentaacetic acid (Gd DTPA; before and every 5 seconds p.i.). MRA (3D GRE, TR/TE 4.5/1.7 msec, flip angle 25 degrees) of coronary vessels in rabbits was performed after i.v. injection of 45 micromol Fe/kg of VSOP-C63. In rats maximal S/N ratio in thoracic and abdominal arteries directly after i.v. injection of VSOP-C63 was 25 +/- 1, 43 +/- 2, 49 +/- 4, 57 +/- 3, 64 +/- 3, and 63 +/- 3 for the different dosages. Blood half-life was dose dependent (15 +/- 2, 20 +/- 3, 29 +/- 6, 37 +/- 5, 61 +/- 16, and 86 +/- 21 minutes). At a dose of 30 micromol Fe/kg even small intrarenal arteries were sharply delineated. First-pass MRA showed no significant difference in the S/N ratio between Gd-DTPA (71.5 +/- 11.5) and VSOP-C63 (65.1 +/- 18. 3). The proximal segments of the coronary arteries in rabbits were clearly depicted at a dose of 45 micromol Fe/kg. The monomer-coated, iron oxide-based contrast medium VSOP-C63 exhibits favorable properties as a blood pool agent for both equilibrium and first-pass MRA. J. Magn. Reson. Imaging 2000;12:905-911.

Animals↗

Acid-catalyzed ethanolysis of temazepam in anhydrous and aqueous ethanol solutions.

The benzodiazepines are a family of anxiolytic and hypnotic drugs. When taken concurrently with ethanol, a pharmacological interaction may occur, potentiating the central nervous system depression produced by either drug. In addition to this pharmacological interaction, this report describes a novel chemical reaction between temazepam (a 3-hydroxy-1,4-benzodiazepine) and ethanol under acidic conditions similar to those found in vivo, resulting in a 3-ethoxylated product. Optimal conditions, kinetics, equilibrium, and the mechanism of this acid-catalyzed ethanolysis are reported. The results raise the possibility that the ethanolysis reaction may occur in the stomach of people who consume alcohol and 3-hydroxy-1,4-benzodiazepine on a regular basis. The acid-catalyzed ethanol-drug reaction is a relatively unexplored area and may alter the pharmacological action of some drugs.

Anti-Anxiety Agents↗

A radiolabeled peptide ligand of the hERG channel, [125I]-BeKm-1.

The wild-type scorpion toxin BeKm-1, which selectively blocks human ether-a-go-go related (hERG) channels, was radiolabeled with iodine at tyrosine 11. Both the mono- and di-iodinated derivatives were found to be biologically active. In electrophysiological patch-clamp recordings mono-[127I]-BeKm-1 had a concentration of half-maximal inhibition (IC50 value) of 27 nM, while wild-type BeKm-1 inhibited hERG channels with an IC50 value of 7 nM. Mono-[125I]-BeKm-1 was found to bind in a concentration-dependent manner and with picomolar affinity to hERG channel protein in purified membrane vesicles from transfected human embryonic kidney cells (HEK-293). Under optimized conditions the equilibrium dissociation constant ( Kd) values from saturation and kinetic binding analysis were 13 and 14 pM, respectively. Both the association and dissociation of [(125)I]-BeKm-1 were fast (association rate constant, k(on)=3.6 x 10(7) M(-1)s(-1); dissociation rate constant, k(off)=0.005 s(-1)). Wild-type BeKm-1 displaced binding of [125I]-BeKm-1 with half-maximal inhibitory concentrations of 44 pM. In contrast, competition experiments with a BeKm-1 mutant BeKm-1-K18A, in which the toxin interaction site is disrupted, resulted in a drop in affinity by more than 300-fold as compared to the wild-type toxin. Iberiotoxin and apamin, peptide inhibitors of Ca2+-activated K+-channels, had no effect on [125I]-BeKm-1 binding. Adding the classical rapid delayed rectifier current (IKr) blocker E-4031 reduced binding of [125I]-BeKm-1 to the hERG channel to an IC50 of 7 nM. In autoradiographic studies on rat hearts, binding of [125I]-BeKm-1 was dose-dependent and could partially be displaced by the addition of excess amounts of non-radioactive BeKm-1. The density of the radioactive signal was equally distributed in the myocardium of both the ventricle and atria indicating a homogenous expression of hERG channels throughout the heart.

Animals↗