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Results for “Equilibrium optimization”

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At least 343 records · Page 19Linked to original sources

PubMed1991

Human postural dynamics.

The study of posture dynamics is important not only to understand disorders of impaired equilibrium and protective reactions to unexpected displacements of the human body, but also to the design of prosthesis and functional neuromuscular stimulation as aids to patients with impaired postural stability and locomotion. Coordinated control of the body segments is a complex aspect of motor behavior, owing to the multiple degrees of freedom of the controlled system. Several interacting subsystems are involved in the dynamics of human posture and locomotion, including the skeletal, neuromuscular, and sensory systems. Human posture control is maintained by somatosensory, vestibular, and visual feedback, integrated within the locomotor and central nervous systems. Studies of posture dynamics and stability therefore entail the study of mechanical aspects of the human body, its sensory systems, and the principles governing coordination in motion control. In this paper is reviewed some of the research done in the field of human posture dynamics, including such topics as biomechanics, equilibrium, stability, motion coordination, neural feedback, neural control systems modeling, motion strategies, optimality of motion, and adaptation. We consider experimental approaches and theoretical models, as well as the gap between them. Principles for the experimental investigation of control systems are considered.

Animals↗

PubMed1988

Changes in phosphoproteins during commitment of HL60 cells to monocyte differentiation: evidence for multiple protein kinase involvement.

The human promyeloid cell line HL60 differentiates toward monocytes when treated with TPA. We have analyzed, by two-dimensional gel electrophoresis, the phosphoprotein patterns within HL60 cells, labeled to equilibrium with [32P]orthophosphate when cells were treated with suboptimal (1 nM), optimal (5 and 10 nM), and supraoptimal (40 and 100 nM) concentrations of 12-O-tetradecanylphorbol-13-acetate (TPA) as regards the induction of differentiation. No change was detected in the phosphoprotein pattern at 1 nM TPA, whereas four phosphoproteins showed increased levels of phosphorylation at 5 and 10 nM TPA. When cells were treated with 40 and 100 nM TPA, in total eight and ten proteins, respectively, were phosphorylated, including the above four proteins. Two proteins were dephosphorylated when cells were treated with 40 and 100 nM TPA. A 15-kd protein, phosphorylated when HL60 cells were treated with 5 nM TPA, was observed as an intense spot in autoradiographs of total cellular phosphoproteins of two variant HL60 cell lines that are unable to differentiate toward monocytes and prior to treatment with TPA. In the case of three variant cell lines, which like HL60 differentiate toward monocytes, the phosphoprotein spot was almost absent. Thus, paradoxically, the 15-kd phosphoprotein is affected by TPA although its constitutive level of expression or increased phosphorylation state is inversely related to the potential for monocyte differentiation. This observation, together with the TPA dose-response effects on protein phosphorylation, is discussed in relation to multiple protein kinase involvement.

Cell Differentiation↗

PubMed1984

Spectrophotometric assay of bisphosphoglycerate mutase: a reexamination of Rapoport-Luebering's method.

The saturation by substrates and cofactors, the effects of pH and the influence of salts and auxiliary enzymes have been studied. The linear NAD+ reduction observed before addition of haemolysate to the assay system was proportional to pH, being higher with phosphate than with Tris-HCl buffer. In the presence of bisphosphoglycerate mutase, an optimal pH (7.8-8.1) was obtained and the inhibition by sulfate ions could be confirmed. It can then be suggested that the absence of an equilibrium, the pH used by several authors and sulfate inhibition could be sources of error in the spectrophotometric assay of bisphosphoglycerate mutase activity. Once optimal conditions have been established, activities found in both human and rat erythrocytes are similar to those given by other accurate methods.

Animals↗

PubMed2001

Visuo-vestibular biofeedback in patients with peripheral vestibular disorders.

It is well known that diseases of the vestibular system can be compensated by increased spontaneous activity of other systems engaged in maintaining equilibrium, i.e. proprioceptive and visual systems. A complex approach using multisensory stimulation is the optimal way to achieve vestibular compensation. The aim of our study was to determine the effect of vestibular rehabilitation therapy as measured by posturography in a group of 72 patients suffering from vestibular disorders: Ménière's disease (n = 31), neuritis vestibularis (n = 21) and vertebrobasilar insufficiency (n = 20). Patients underwent the following examinations: electronystagmography; caloric, rotatory and optokinetic tests; computed posturography; craniocorpography; pure-tone audiometry; speech audiometry; and tinnitometry (tinnitus loudness, pitch). The instability in patients with Ménière's disease decreased 3 weeks after starting the therapy; nevertheless, the decrease in area (the surface formed by the movement of the patient's equilibrium point during a defined time) was transitory because of the increase in area values obtained between the 3rd and 6th weeks when measured with closed eyes. In the vestibular neuronitis patients, the measured values of area and the velocity of the patient's movement decreased continuously. The values measured in the patients suffering from vertebrobasilar insufficiency decreased continuously, the absolute values remaining pathological.

Adolescent↗

PubMed2002

Plant lipases: biocatalyst aqueous environment in relation to optimal catalytic activity in lipase-catalyzed synthesis reactions.

Adsorption and desorption isotherms of two commercial enzyme preparations of papain and bromelain were determined with a Dynamic Vapor System. The Guggenheim-Anderson-deBoer (GAB) modeling of the obtained sorption isotherms allowed the definition of different levels of hydration of those samples. Afterward, these enzyme preparations were used as biocatalysts in water and solvent-free esterification and alcoholysis reactions. The evolution of the obtained fatty acid ester level as a function of the initial hydration level of the biocatalyst, i.e., thermodynamic water activity (a(w)) and water content, was studied. The results show an important correlation between the initial hydration level of the biocatalyst and its catalytic activity during the lipase-catalyzed synthesis reactions. Thus, the Carica papaya lipase (crude papain preparation) catalytic activity is highly dependent on the biocatalyst hydration state. The optimized synthesis reaction yield is obtained when the a(w) value of the enzyme preparation is stabilized at 0.22, which corresponds to 2% water content. This optimal level of hydration occurs on the linear part of the biocatalyst's sorption isotherm, where the water molecules can form a mono- or multiple layer with the protein network. The synthesis reaction yield decreases when the a(w) of the preparation is higher than 0.22, because the excess water molecules modify the system equilibrium leading to the reverse and competitive reaction, i.e., hydrolysis. These results show also that an optimal storage condition for the highly hydrophilic crude papain preparation is a relative humidity strictly lower than 70% to avoid an irreversible structural transition leading to a useless biocatalyst. Concerning the bromelain preparation, no effect of the hydration level on the catalytic activity during esterification reactions was observed. This biocatalyst has too weak a catalytic activity which makes it difficult to observe any differences. Furthermore, the bromelain preparation is far more hydrophobic as it adsorbs only 18 g of water per 100 g of dry material at a(w) around 0.90. No deliquescence of this enzymatic preparation is observed at this a(w) value.

Alcohols↗

PubMed2002

Modelling the effects of trade-offs between long and short-term objectives in fisheries management.

Fisheries management is typically a complex problem, from both an environmental and political perspective. The main source of conflict occurs between the need for stock conservation and the need for fishing community well-being, which is typically measured by employment and income levels. For most fisheries, overexploitation of the stock requires a reduction in the level of fishing activity. While this may lead to long-term benefits (both conservation and economic), it also leads to a short-term reduction in employment and regional incomes. In regions which are heavily dependent on fisheries, short-term consequences of conservation efforts may be considerable. The relatively high degree of scientific uncertainty with respect to the status of the stocks and the relatively short lengths of political terms of office, generally give rise to the short-run view taking the highest priority when defining policy objectives. In this paper, a multi-objective model of the North Sea is developed that incorporates both long-term and short-term objectives. Optimal fleet sizes are estimated taking into consideration different preferences between the defined short-term and long-term objectives. The subsequent results from the model give the short-term and long-term equilibrium status of the fishery incorporating the effects of the short-term objectives. As would be expected, an optimal fleet from a short-term perspective is considerably larger than an optimal fleet from a long-run perspective. Conversely, stock sizes and sustainable yields are considerably lower in the long-term if a short-term perspective is used in setting management policies. The model results highlight what is essentially a principal-agent problem, with the objectives of the policy makers not necessarily reflecting the objectives of society as a whole.

Conservation of Natural Resources↗

PubMed1993

Regulation of inositol 1,4,5-trisphosphate receptors in rat basophilic leukemia cells. I. Multiple conformational states of the receptor in a microsomal preparation.

A detailed characterization of the inositol 1,4,5-trisphosphate (IP3) receptor in rat basophilic leukemia (RBL) cells, a neoplastic mast cell line, has been possible through the growth of solid RBL cell tumors which provide a rich source of IP3 receptor. Equilibrium binding studies show a 1.6 +/- 0.1 pmol/mg of protein maximal binding capacity for [3H]IP3 at optimal Ca2+ (10 microM). The specificity of the RBL cell IP3 receptor towards phosphoinositides, ATP and heparin parallels those previously described with excitable and nonexcitable tissues. [3H]IP3 binding is slightly enhanced from < 1 nM to 10 microM Ca2+ and inhibited by > 10 microM Ca2+. Kinetic and equilibrium studies provide evidence for at least two classes or conformational states of binding sites with pico- and nanomolar affinities. At nM concentrations of IP3, neither binding to the IP3 receptor nor IP3-induced Ca2+ efflux from permeabilized cells demonstrates cooperativity. In contrast, at pM concentrations, IP3 binding kinetics deviate from simple mass action suggesting a complex interaction among binding sites for IP3 on the receptor-channel oligomer. The mechanisms that regulate [3H]IP3 binding in RBL cells are unique when compared to what has been reported in other cells.

Animals↗

PubMed2003

Potentiometric, spectrophotometric and density functional study of the interaction of N-hydroxyacetamide with oxovanadium(IV): the influence of ligand to the V(IV)/V(V) oxi-reduction reaction.

The interaction of N-hydroxyacetamide (acetohydroxamic acid, HL) with V(IV) in aqueous solution has been investigated using potentiometric and spectrophotometric experiments. Density functional method (DFT) has been used aiming to understand the ligand chelation at a molecular level. Stability constants have been estimated for species with the metal/ligand ratios 1:1 and 1:2 from spectrophotometric and potentiometric measurements. The stability of these V(IV) species toward oxidation has been investigated. Experiments carried out in an oxygen atmosphere led to the displacement of the titration curves with respect to the one obtained under inert atmosphere. Spectrophotometric evidence of the V(IV)/V(V) oxidation in the presence of N-hydroxyacetamide is presented. It has been shown that V(IV)/V(V) oxidation in the presence of N-hydroxyacetamide by the oxygen can be simulated using the standard programs for simulating the equilibrium in a multiligand/multimetal system. In this approach, the oxygen is considered a ligand and the log beta estimated from the standard oxidation potential. The structure and respective tautomers of the species have been optimized from DFT calculations. Geometrical and thermodynamical properties have been estimated for the most stable complexes. The VOL-->VOL(2) equilibrium constant has been theoretically estimated with a less than 1.5 logarithmic unit of error with respect to the experimental estimate. The oxidation process has also been investigated and it is adequately described by the equation: 4[VOL(2)]+2H(2)O+O(2)-->4[VO(OH)L(2)]. The calculated value of DeltaG for this reaction is about -46.2 kcal mol(-1), in excellent agreement with the experimental estimates.

Hydroxamic Acids↗

PubMed2002

Guest-induced organization of an optimal receptor from a dynamic receptor library: spectroscopic screening.

Complexation of a cis-protected palladium ion and a family of exo-bidentate and -tridentate ligands results in the formation of an equilibrium mixture of numerous metal-linked receptors that are referred to as a dynamic receptor library. We found that a guest induced the selective formation of the optimal receptor of its own. Screening of the library by using difference NMR facilitates the search for new receptors because in difference NMR only receptors interacting with the guest can be observed. An unpredictable heterotopic receptor was discovered by this screening method. Interestingly, the new receptor thus found was assembled quantitatively only in the presence of its optimal guest.

Chemistry↗

PubMed2000

Glycosylations versus conformational preferences of cancer associated mucin core.

Synthetic oligosaccharide vaccines based on core STn (sialyl alpha2-6 GalNAc) carbohydrate epitopes are being evaluated by a number of biopharmaceutical firms as potential immunotherapeutics in the treatment of mucin-expressing adenocarcinomas. The STn carbohydrate epitopes exist as discontinuous clusters, O-linked to proximal serine and threonine residues within the mucin sequence. In an effort to probe the structure and dynamics of STn carbohydrate clusters as they may exist on the cancer-associated mucin, we have used NMR spectroscopy and MD simulations to study the effect of O-glycosylation of adjacent serine residues in a repeating (Ser)n sequence. Three model peptides/glyco-peptides were studied: a serine trimer containing no carbohydrate groups ((Ser)3 trimer); a serine trimer containing three Tn (GalNAc) carbohydrates alpha-linked to the hydroxyls of adjacent serine sidechains ((Ser.Tn)3 trimer); and a serine trimer containing three STn carbohydrates alpha-linked to the hydroxyls of adjacent serine sidechains ((Ser.STn)3 trimer). Our results demonstrate that clustering of carbohydrates shifts the conformational equilibrium of the underlying peptide backbone into a more extended and rigid state, an arrangement that could function to optimally present the clustered carbohydrate antigen to the immune system. Steric effects appear to drive these changes since an increase in the size of the attached carbohydrate (STn versus Tn) is accompanied by a stronger shift in the equilibrium toward the extended state. In addition, NMR evidence points to the formation of hydrogen bonds between the peptide backbone NH protons and the proximal GalNAc groups in the (Ser.Tn)3 and (Ser.STn)3 trimers. The putative peptide-sugar hydrogen bonds may also play a role in influencing the conformation of the underlying peptide backbone, as well as the orientation of the O-linked carbohydrate. The significance of these results will be discussed within the framework of developing clustered STn-based vaccines, capable of targeting the clustered STn epitopes on the cancer-associated mucin.

Adenocarcinoma↗

PubMed2003

N-PtIV-H/N-H...PtII intramolecular redox equilibrium in a product of H-C(sp2) cleavage and unusual alkane/arene C-H bond selectivity of ([2.1.1]pyridinophane)PtII(CH3)+.

T-shaped 14 valence electron (eta2-L)PtMe+ (based on DFT geometry optimization, L = [2.1.1]-2,6-pyridinophane) reacts with benzene to give (eta3-L) PtIV(Ph)2H+ and methane; the latter cation is in thermal equilibrium with the N-protonated PtII tautomer (eta2-L-H)Pt(Ph)2+, and these complexes react with ethane or cyclopentane to produce benzene and (L)PtH(olefin)+.

Journal Article↗

PubMed2000

An optimization approach to design of generalized BSB neural associative memories.

This article is concerned with the synthesis of the optimally performing GBSB (generalized brain-state-in-a-box) neural associative memory given a set of desired binary patterns to be stored as asymptotically stable equilibrium points. Based on some known qualitative properties and newly observed fundamental properties of the GBSB model, the synthesis problem is formulated as a constrained optimization problem. Next, we convert this problem into a quasi-convex optimization problem called GEVP (generalized eigenvalue problem). This conversion is particularly useful in practice, because GEVPs can be efficiently solved by recently developed interior point methods. Design examples are given to illustrate the proposed approach and to compare with existing synthesis methods.

Association Learning↗

PubMed2001

A novel approach for solving constrained nonlinear optimization problems using neurofuzzy systems.

A neural network model for solving constrained nonlinear optimization problems with bounded variables is presented in this paper. More specifically, a modified Hopfield network is developed and its internal parameters are computed using the valid-subspace technique. These parameters guarantee the convergence of the network to the equilibrium points. The network is shown to be completely stable and globally convergent to the solutions of constrained nonlinear optimization problems. A fuzzy logic controller is incorporated in the network to minimize convergence time. Simulation results are presented to validate the proposed approach.

Fuzzy Logic↗

PubMed2006

The equilibrium structure of ferrocene.

The molecular structures of ferrocene in the eclipsed (equilibrium) and staggered (saddle-point) conformations have been determined by full geometry optimizations at the levels of second-order Møller-Plesset (MP2) theory, coupled-cluster singles-and-doubles (CCSD) theory, and CCSD theory with a perturbative triples correction [CCSD(T)] in a TZV2P+f basis set. Existing experimental results are reviewed. The agreement between the CCSD(T) results and experiment is in all cases excellent; the calculated structure parameters and the barrier to internal rotation of the ligand rings differ from the most accurate experimental values by less than two estimated standard deviations. The CCSD(T) calculations for single-configuration-dominated transition metal complexes such as ferrocene thus appear to have an accuracy comparable to that observed for molecules containing only first- and second-row atoms, and to be of a quality similar to that obtained experimentally. A comparison with previous DFT results indicates that the B3LYP model gives overall the best DFT results, with a deviation of around 2 pm for the metal-carbon distance and smaller errors for the cyclopentadienyl rings.

Journal Article↗

PubMed2004

Differential susceptibility epidemic models.

We formulate compartmental differential susceptibility (DS) susceptible-infective-removed (SIR) models by dividing the susceptible population into multiple subgroups according to the susceptibility of individuals in each group. We analyze the impact of disease-induced mortality in the situations where the number of contacts per individual is either constant or proportional to the total population. We derive an explicit formula for the reproductive number of infection for each model by investigating the local stability of the infection-free equilibrium. We further prove that the infection-free equilibrium of each model is globally asymptotically stable by qualitative analysis of the dynamics of the model system and by utilizing an appropriately chosen Liapunov function. We show that if the reproductive number is greater than one, then there exists a unique endemic equilibrium for all of the DS models studied in this paper. We prove that the endemic equilibrium is locally asymptotically stable for the models with no disease-induced mortality and the models with contact numbers proportional to the total population. We also provide sufficient conditions for the stability of the endemic equilibrium for other situations. We briefly discuss applications of the DS models to optimal vaccine strategies and the connections between the DS models and predator-prey models with multiple prey populations or host-parasitic interaction models with multiple hosts are also given.

Communicable Diseases↗

PubMed1996

Characterization of topoisomerase II-DNA interaction and identification of a DNA-binding domain by ultraviolet laser crosslinking.

We have used ultraviolet laser crosslinking to characterize the DNA-binding properties of highly purified yeast topoisomerase II in the absence of ATP. A single 5 ns, 20 mJ pulse of 266 nm light produced optimal crosslinking to a short DNA duplex, with an efficiency of 0.25%. An equilibrium binding constant (Keq) of 1.2 +/- 0.5 x 10(8) M(-1) was determined from kinetic analysis. Topoisomerase II showed highest affinity for supercoiled DNA. Limited proteolysis of crosslinked topoisomerase II-DNA complexes showed a site of crosslinking to be within a 29-kDa fragment with Leu-681 at its amino-terminal end. This region contains the active Tyr-783 and is homologous to the amino-terminal region of the DNA-binding bacterial gyrase GyrA subunit, suggesting a conserved DNA-binding mechanism.

Base Sequence↗

PubMed1988

Angiotensin II receptors in the fowl aorta.

In the domestic fowl, angiotensin II (ANG II) causes an in vivo depressor response and in vitro relaxation of aortic rings which appear to be a direct action of ANG II on the blood vessels. Thus, we determined whether binding sites specific to ANG II exist in the membrane fraction of the fowl aorta. The particulate fraction of aortas from adult female fowl, Gallus gallus, exhibits high specific binding to ANG II ligand. 125I-[Ile5]ANG II (0.5 nM) binding to the above fraction (30 micrograms protein) in 50 mM Tris (pH 7.2), 10 mM MgCl2, and 0.2% bovine serum albumin at 12 degrees (1) is rapid, saturable, and reversible; (2) increases as a function of ligand or membrane concentration, time, and temperature; and (3) optimally fits to a two-site (high and low affinity) model. The equilibrium dissociation constant (0.15 +/- 0.03 nM) and binding site concentration (28.7 +/- 8.1 fmol/mg protein) of the high affinity site as well as association (0.055 nM-1.min-1) and dissociation (0.0122 min-1) rate constants are similar to those of mammalian vascular ANG II receptors. Both 125I-[Ile5]ANG II and 125I-[Val5]ANG II are competitively displaced by unlabeled ANG II. These results suggest that specific ANG II receptors exist in the fowl aorta.

Angiotensin II↗

PubMed1982

The manpower situation in pathology: implications for the future.

With the exception of academic pathology and specific subspecialty areas, manpower in pathology is currently in a state of apparent equilibrium between supply and demand. Exogenous influences, and especially an influx of Americans who have attended foreign-chartered medical schools, could disturb this apparent equilibrium. Other key manpower issues with respect to pathology include mechanisms to determine optimal numbers of pathologists, the future productivity of pathologists, current and prospective needs in academic pathology and subspecialty areas, and the role of the federal government in the area of medical manpower. Recommendations to deal with these and related issues are presented.

Foreign Medical Graduates↗