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Results for “Optimism”

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At least 73 records · Page 4Linked to original sources

PubMed1998

Optimal design of gradient coils in MR imaging: optimizing coil performance versus minimizing cost functions.

The "forward" method of an optimal gradient coil design provides a coil that has the minimal cost function value. It is shown in this study that the solution obtained by minimizing the cost function is directly dependent on the specified cost function and generally results in a deviation from the most desirable coil design. In this paper, a gradient coil design approach for obtaining the best achievable coil performance for pre-determined imaging applications is presented. Through this approach, all intermediate coil performance values calculated during an optimization process, using a simulated annealing algorithm, are stored and presented in a three-dimensional data set. Using this three-dimensional data set, a coil designer is able to make a balance between different coil performance parameters and to select a coil that is the most desirable for the pre-determined imaging applications.

Algorithms↗

PubMed2006

Birth weight and infant growth: optimal infant weight gain versus optimal infant weight.

OBJECTIVE: Infant growth assessment often focuses on "optimal" infant weights and lengths at specific ages, while de-emphasizing infant weight gain. Objective of this study was to examine infant growth patterns by measuring infant weight gain relative to birth weight. METHODS: We conducted this study based on data collected in a prospective cohort study including 3,302 births with follow up examinations of infants between the ages of 8 and 18 months. All infants were participants in the Louisiana State Women, Infant and Children Supplemental Food Program between 1999 and 2001. Growth was assessed by infant weight gain percentage (IWG%, defined as infant weight gain divided by birth weight) as well as by mean z-scores and percentiles for weight-for-age, length-for-age, and weight-for-length calculated based on growth charts published by the U.S. Centers for Disease Control (CDC). RESULTS: An inverse relationship was noted between birth weight category and IWG% (from 613.9% for infants with birth weights <1500 g to 151.3% for infants with birth weights of 4000 g or more). In contrast, low birth weight infants had lower weight-for-age, weight-for-length z-scores and percentiles compared to normal birth weight infants according to CDC growth charts. CONCLUSIONS: Although low birth weight infants had lower anthropometric measures compared to a national reference population, they had significant catch-up growth; High birth weight infants had significant slow-down growth. We suggest that growth assessments should compare infants' anthropometric data to their own previous growth measures as well as to a reference population. Further studies are needed to identify optimal ranges of infant weight gain.

Aid to Families with Dependent Children↗

PubMed1981

Toward the optimal lead system and optimal criteria for exercise electrocardiography.

To define the optimal lead system for exercise electrocardiography, data of the whole body surface potential distribution were analyzed in 25 normal subjects and in 25 patients with coronary artery disease at rest and during exercise. All patients had a normal electrocardiogram at rest. The sensitivity of the standard chest leads was 60 percent; it improved to 84 percent with the body surface map whereas both methods had a 100 percent specificity. On the basis of these data, and reports from other centers, it is concluded that a single bipolar lead from the right subclavian area to lead V5 is adequate in those laboratories that are restricted to testing subjects with a normal electrocardiogram at rest. In patients with a previous infarction or other abnormalities in the electrocardiogram at rest three (pseudo) orthogonal leads or several standard leads are necessary. Recommendations for optimal measurements from the exercise electrocardiogram are based on quantitative computer analysis of the selected leads in larger groups of patients. Best results were obtained with a combination of S-T amplitude, S-T slope and heart rate. The improvement in sensitivity from 50 percent with visual analysis to 85 percent with computer was similar to that obtained with body surface mapping. Changes of the P wave and QRS complex during exercise appeared to be of little diagnostic value. The pathophysiologic mechanisms that contribute to the changes of the electrocardiogram during exercise are discussed.

Adult↗

PubMed2005

Usefulness of D-optimal designs and multicriteria optimization in laborious analytical procedures. Application to the extraction of quinolones from eggs.

An analytical method has been developed to extract ciprofloxacin and enrofloxacin from eggs. The aim of this work is to determine the experimental conditions of extraction providing high recoveries with small standard deviations. An experimental design based on the D-optimality criterion and replicated three times was built to evaluate the effect of five factors related to the extraction which is the most inaccurate stage of the procedure. This non-classical design is needed because there are several practical constraints: (i) the extraction procedure is time-consuming, quinolones are not stable and the design must be performed in a single working session. (ii) The tube capacity of the centrifuge is 6, so the number of experiments will be 6 or a multiple of 6. In the optimal experimental conditions, the extraction is performed once with 5 ml of methanol. Then, fatty acids are removed with a mixture of hexane/ether. Analytes are finally separated and detected by HPLC-fluorescence without the additional step of purification by solid-phase extraction (SPE). Under these conditions, the mean recovery is 64% and 70% and the standard deviation 5% and 4% for ciprofloxacin and enrofloxacin, respectively. The capability of decision, CCalpha, is 3.1 and 2.8 microg kg(-1) of ciprofloxacin and enrofloxacin, respectively. The capability of detection, CCbeta, is 7.8 and 7.0 microg kg(-1) of ciprofloxacin and enrofloxacin, respectively. In both cases the probabilities of false positive, alpha, and of false negative, beta, were fixed at 0.05.

Algorithms↗

PubMed2005

Optimization of glibenclamide tablet composition through the combined use of differential scanning calorimetry and D-optimal mixture experimental design.

A systematic analysis of the influence of different proportions of excipients on the stability of a solid dosage form was carried out. In particular, a d-optimal mixture experimental design was applied for the evaluation of glibenclamide compatibility in tablet formulations, consisting of four classic excipients (natrosol as binding agent, stearic acid as lubricant, sorbitol as diluent and cross-linked polyvinylpyrrolidone as disintegrant). The goal was to find the mixture component proportions which correspond to the optimal drug melting parameters, i.e. its maximum stability, using differential scanning calorimetry (DSC) to quickly obtain information about possible interactions among the formulation components. The absolute value of the difference between the melting peak temperature of pure drug endotherm and that in each analysed mixture and the absolute value of the difference between the enthalpy of the pure glibenclamide melting peak and that of its melting peak in the different analyzed mixtures, were chosen as indexes of the drug-excipient interaction degree.

Calorimetry, Differential Scanning↗

PubMed2003

Codon optimizer: a freeware tool for codon optimization.

Selection plays a major role in the determination of codon usage in all organisms studied so far. In highly expressed genes, a narrow set of codons is used and these codons correspond to the more abundant tRNA species. This minimizes the risk of tRNA depletion during translation. In fact, the codons in a gene may be true bottlenecks, especially in cases where foreign genes are expressed in a host in which the usage of codons in highly expressed genes does not resemble the usage of codons in the species from which the foreign gene originates. In such cases, it has been shown that substitution of rare codons in the introduced gene may increase the yield dramatically. In addition, replacement of rare codons might decrease the chance of misincorporation and protect the protein from premature turnover. Here, a piece of software is announced that calculates a codon-optimized sequence of any gene based on knowledge of highly expressed genes of a host. In addition, it calculates the codon adaptation index of the gene and identifies internal type II restriction sites of the optimized sequence. The program runs under Windows and is available as freeware for use in academia.

Animals↗

PubMed2001

Optimization and optimality of a short ribozyme ligase that joins non-Watson-Crick base pairings.

A small ribozyme ligase (L1) selected from a random sequence population appears to utilize non-Watson-Crick base pairs at its ligation junction. Mutational and selection analyses confirmed the presence of these base pairings. Randomization of the L1 core and selection of active ligases yielded highly active variants whose rates were on the order of 1 min(-1). Base-pairing covariations confirmed the general secondary structure of the ligase, and the most active ligases contained a novel pentuple sequence covariation. The optimized L1 ligases may be optimal within their sequence spaces, and minimal ligases that span less than 60 nt in length have been engineered based on these results.

Base Pairing↗

PubMedDate not supplied

Downstream process synthesis for biochemical production of butanol, ethanol, and acetone from grains: generation of optimal and near-optimal flowsheets with conventional operating units.

Manufacturing butanol, ethanol, and acetone through grain fermentation has been attracting increasing research interest. In the production of these chemicals from fermentation, the cost of product recovery constitutes the major portion of the total production cost. Developing cost-effective flowsheets for the downstream processing is, therefore, crucial to enhancing the economic viability of this manufacturing method. The present work is concerned with the synthesis of such a process that minimizes the cost of the downstream processing. At the outset, a wide variety of processing equipment and unit operations, i.e., operating units, is selected for possible inclusion in the process. Subsequently, the exactly defined superstructure with minimal complexity, termed maximal structure, is constructed from these operating units with the rigorous and highly efficient graph-theoretic method for process synthesis based on process graphs (P-graphs). Finally, the optimal and near-optimal flowsheets in terms of cost are identified.

Acetone↗

PubMedDate not supplied

Standardization protocols and optimized precursor sets for the efficient application of automated parallel synthesis to lead optimization: a Mitsunobu example.

A strategy has been developed for the efficient application of automated parallel synthesis to specific aspects of the lead optimization processes employed in drug discovery. The method involves the synthesis of collections of compounds using sets of precursors designed to encompass established medicinal chemistry principles and that have been concurrently optimized with respect to a specific chemical transformation. The strategy is illustrated using an automated Mitsunobu protocol employing sets of aliphatic alcohols and phenols as precursors. The former has been formatted to perform simple alkyl homologation exercises, with the latter being designed for use in diversity-based studies.

Journal Article↗

PubMedDate not supplied

Optimized block-wise variable combination by particle swarm optimization for partial least squares modeling in quantitative structure-activity relationship studies.

The use of numerous descriptors that are indicative of molecular structure is becoming common in quantitative structure-activity relationship (QSAR) studies. As all of the descriptors might carry more or less molecular information, it seems more advisable to investigate the possible variable combination rather than variable selection. In this paper, an optimized block-wise variable combination (OBVC) by particle swarm optimization based on partial least squares modeling has been proposed for variable combination. An F statistic is also introduced to determine the dimensionality of the PLS model. The performance is assessed using two QSAR data sets. Experimental results have shown the good performance of this technique compared to those obtained by stepwise regression.

Amines↗

PubMed2005

Simplex optimization of generalized topological index (GTI-simplex): a unified approach to optimize QSPR models.

GTI-simplex is a new methodology that combines the generalized topological indices and the down hill simplex optimization procedure to search for optimized quantitative structure-property relationship models (Chem. Phys. Lett. 2005, 410, 343). In this study, the fundamental role of the graph topological distance inducing a local shell structure on vertexes and a detailed derivation of the GTI-decomposition in terms of the so-called "geodesic-brackets", i.e., functions that mix the local shell structure for different vertexes are presented. Applications of the GTI-simplex to a set of physicochemical properties covering those depending on intramolecular and/or intermolecular interactions are included. GTI-simplex has showed to be a very effective methodology for the description of different properties from a unified point of view. No ad hoc definition for topological index is required to each property as in the traditional use of topological indices or other molecular descriptors to QSAR/QSPR studies.

Journal Article↗

PubMed2004

Optimal control theory for a target state distributed in time: optimizing the probe-pulse signal of a pump-probe-scheme.

Optimal control theory (OCT) is formulated for the case of a two-color pump-probe experiment. The approach allows to calculate the pump-pulse shape in such a way that the probe-pulse absorption signal is maximized. Since the latter quantity is given by the time-averaged expectation value of a time dependent operator (the probe-pulse field-strength times the dipole operator) a version of OCT has to be used where the target state is distributed in time. The method is applied to a molecular three-level system with the pump-pulse driving the transition from the electronic ground state into the first-excited electronic state and the probe-pulse connecting the first-excited state with a higher lying electronic state. Depending on the probe-pulse duration, the vibrational wave packet becomes localized or at least highly concentrated in the Franck-Condon window for the transition into the higher-excited state. The dependence on the probe-pulse duration and on the delay time between the optimized pump-pulse and the probe-pulse is discussed in detail. The whole study demonstrates the feasibility of laser pulse induced temporal wave packet localization and the use of spectroscopic quantities as target states in experiments on femtosecond laser pulse control.

Journal Article↗

PubMed2003

Delayed selfing as an optimal mating strategy in preferentially outcrossing species: theoretical analysis of the optimal age at first reproduction in relation to mate availability.

The evolution of mating systems and that of life history have usually been modeled separately. However, they may be to some extent coupled in natural situations because they rely on the same phenotypic traits. Here, we focus on one of these traits, the age at first reproduction, in a species able to self- and cross-fertilize. When inbreeding depression is strong, self-fertile species preferentially cross-fertilize. However, outcrossing is not always possible when the availability of sexual partners is limited. The optimal reproductive strategy in this case would be to wait for a sexual partner for a certain period of time (the waiting time) and then switch to selfing if no mates have been encountered (reproductive assurance strategy). We predict the evolution of an optimal waiting time depending on the efficiency of resource reallocation to late fecundity, on the inbreeding depression, and on the instantaneous probability of encountering a partner versus dying. As a consequence of reduced mate availability, intermediate selfing rates can be generated in preferentially outcrossing populations, but they are lowered by the existence of a waiting time. Our model may thus explain low selfing rates observed in natural populations of many self-fertile, preferentially outcrossing plants or animal species.

Age Factors↗

PubMedDate not supplied

Engineering an improved acellular nerve graft via optimized chemical processing.

The long-term goal of our research is to engineer an acellular nerve graft for clinical nerve repair and for use as a model system with which to study nerve-extracellular matrix interactions during nerve regeneration. To develop this model acellular nerve graft we (1) examined the effects of detergents on peripheral nerve tissue, and (2) used that knowledge to create a nerve graft devoid of cells with a well-preserved extracellular matrix. Using histochemistry and Western analysis, the impact of each detergent on cellular and extracellular tissue components was determined. An optimized protocol was created with the detergents Triton X-200, sulfobetaine-16, and sulfobetaine-10. This study represents the most comprehensive examination to date of the effects of detergents on peripheral nerve tissue morphology and protein composition. Also presented is an improved chemical decellularization protocol that preserves the internal structure of native nerve more than the predominant current protocol.

Animals↗

PubMed1999

Inhibition of apoptosis and clonogenic survival of cells expressing crmA variants: optimal caspase substrates are not necessarily optimal inhibitors.

To study the role of various caspases during apoptosis, we have designed a series of caspase inhibitors based on the cowpox virus cytokine response modifier A (crmA) protein. Wild-type crmA inhibits caspases 1 and 8 and thereby protects cells from apoptosis triggered by ligation of CD95 or tumour necrosis factor (TNF) receptors, but it does not protect against death mediated by other caspases. By replacing the tetrapeptide pseudosubstrate region of crmA (LVAD) with tetrapeptides that are optimal substrates for the different families of caspases, or with the four residues from the cleavage site of the baculovirus protein p35 (DQMD), we have generated a family of caspase inhibitors that show altered ability to protect against cell death. Although DEVD is the optimal substrate for caspase 3, crmA DEVD was degraded rapidly and was a weaker inhibitor than crmA DQMD, which was not degraded. Unlike wild-type crmA and crmA DEVD, crmA DQMD was able to inhibit apoptosis caused by direct activation of caspase 3 and protected lymphoid cells from death induced by radiation and dexamethasone. Significantly, the protected cells were capable of sustained growth.

Amino Acid Sequence↗

PubMed2004

Optimization of probe length and the number of probes per gene for optimal microarray analysis of gene expression.

Gene-specific oligonucleotide probes are currently used in microarrays to avoid cross-hybridization of highly similar sequences. We developed an approach to determine the optimal number and length of gene-specific probes for accurate transcriptional profiling studies. The study surveyed probe lengths from 25 to 1000 nt. Long probes yield better signal intensity than short probes. The signal intensity of short probes can be improved by addition of spacers or using higher probe concentration for spotting. We also found that accurate gene expression measurement can be achieved with multiple probes per gene and fewer probes are needed if longer probes rather than shorter probes are used. Based on theoretical considerations that were confirmed experimentally, our results showed that 150mer is the optimal probe length for expression measurement. Gene-specific probes can be identified using a computational approach for 150mer probes and they can be treated like long cDNA probes in terms of the hybridization reaction for high sensitivity detection. Our experimental data also show that probes which do not generate good signal intensity give erroneous expression ratio measurement results. To use microarray probes without experimental validation, gene-specific probes approximately 150mer in length are necessary. However, shorter oligonucleotide probes also work well in gene expression analysis if the probes are validated by experimental selection or if multiple probes per gene are used for expression measurement.

Escherichia coli↗

PubMed1999

Optimization algorithm performance in determining optimal controls in human movement analyses.

The objective of this study was to evaluate the performance of different multivariate optimization algorithms by solving a "tracking" problem using a forward dynamic model of pedaling. The tracking problem was defined as solving for the muscle controls (muscle stimulation onset, offset, and magnitude) that minimized the error between experimentally collected kinetic and kinematic data and the simulation results of pedaling at 90 rpm and 250 W. Three different algorithms were evaluated: a downhill simplex method, a gradient-based sequential quadratic programming algorithm, and a simulated annealing global optimization routine. The results showed that the simulated annealing algorithm performed for superior to the conventional routines by converging more rapidly and avoiding local minima.

Algorithms↗

PubMed2004

Optimism, pessimism, and gambling: the downside of optimism.

Three studies examined the relation between dispositional optimism and gambling. In Study 1, optimists were more likely than pessimists to have positive gambling expectations and report maintaining these expectations following losses. They also were more likely to indicate that winning money was a primary motivation for their gambling. Study 2 demonstrated that pessimists but not optimists reduce their betting and expectations after poor gaming performance. Study 3 replicated this effect using a more controlled experiment and showed that after losing, optimists report remembering more near wins than do pessimists. Thus, all three studies suggest that optimists, more than pessimists, maintain positive expectations and continue gambling after experiencing negative gaming outcomes. The authors suggest that despite optimism's many benefits, there are common situations in which the pessimistic tendency to disengage is beneficial.

Adult↗