SEARCH · PubMed Health

Results for “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 343 records · Page 19Linked to original sources

PubMed2004

Two-stage hybrid optimization of fiber Bragg gratings for design of linear phase filters.

We present a new hybrid optimization method for the synthesis of fiber Bragg gratings (FBGs) with complex characteristics. The hybrid optimization method is a two-tier search that employs a global optimization algorithm [i.e., the tabu search (TS) algorithm] and a local optimization method (i.e., the quasi-Netwon method). First the TS global optimization algorithm is used to find a "promising" FBG structure that has a spectral response as close as possible to the targeted spectral response. Then the quasi-Newton local optimization method is applied to further optimize the FBG structure obtained from the TS algorithm to arrive at a targeted spectral response. A dynamic mechanism for weighting of different requirements of the spectral response is employed to enhance the optimization efficiency. To demonstrate the effectiveness of the method, the synthesis of three linear-phase optical filters based on FBGs with different grating lengths is described.

Journal Article↗

PubMed2006

Building and testing optimized keyboards for specific text entry.

OBJECTIVE: We explore how to optimally design systems for information input. BACKGROUND: As computers are introduced into ever more devices with new methods of inputting information, there is a need for specialized systems that are optimally designed for their particular use. METHOD: The study demonstrates how to use a model of text entry times to build optimized keyboards for specific sets of text. The technique is demonstrated by using Fitts' law to model text entry times. Alphabet letters are assigned to keys in a way that minimizes predicted entry time for the specified set of text. The predicted entry times are validated by an experiment in which two keyboards are optimized for different sets of text. RESULTS: Text entry is faster for the keyboard optimized for that text compared with the keyboard optimized for the other text. Learning to use the keyboards is fairly quick, with significant learning being observed after only one half-hour session. CONCLUSION: There is a need and an ability to design specialized keyboards for some situations. The study demonstrates that optimization of keyboards can decrease text entry times. APPLICATION: This research shows how to design optimized keyboards for many different situations. The approach should be useful for aviation, medical, industrial, and other specialized situations in which normal keyboard designs cannot be used.

Electronic Data Processing↗

PubMed2005

Optimizing drug delivery systems using systematic "design of experiments." Part II: retrospect and prospects.

The first study on application of Design of Experiments (DoE) in optimizing drug formulation appeared in 1967. Since then the number of literature reports on the use of DoE optimization in development of drug delivery technologies has been piling up steadily. Such systematic techniques find their use in every type of conventional dosage form and modern drug delivery system. The drug delivery devices investigated for optimization using response surface methodology include controlled release compressed matrices, microparticulates, macroparticulates, vesicular systems, floating systems, bioadhesive systems, semisolids, transdermals, and inhalations. The optimized processes mainly include extrusion-spheronization, pelletization, microencapsulation, coating, granulation, and tableting. Part I of this article [Crit Rev Ther Drug Carrier Syst 2005; 22(1):27-106] dealt with the salient steps involved in the DoE optimization methodology using diverse experimental designs. Part II deals with various retrospective literature findings as well as the prospective application of such DoE procedures while optimizing varied drug delivery technologies. A vast account of various DoE reports on optimization of diverse drug delivery system and processes along with the critical graphical analysis of various designs, input, and response variables have been presented here in a categorical form. Such an explicit and updated review on drug delivery optimization has not been published anywhere else in the recent past.

Biological Availability↗

PubMed2006

Optimal movement strategies for social foragers in unpredictable environments.

Spatial movement models often base movement decision rules on traditional optimal foraging theories, including ideal free distribution (IFD) theory, more recently generalized as density-dependent habitat selection (DDHS) theory, and the marginal value theorem (MVT). Thus optimal patch departure times are predicted on the basis of the density-dependent resource level in the patch. Recently, alternatives to density as a habitat selection criterion, such as individual knowledge of the resource distribution, conspecific attraction, and site fidelity, have been recognized as important influences on movement behavior in environments with an uncertain resource distribution. For foraging processes incorporating these influences, it is not clear whether simple optimal foraging theories provide a reasonable approximation to animal behavior or whether they may be misleading. This study compares patch departure strategies predicted by DDHS theory and the MVT with evolutionarily optimal patch departure strategies for a wide range of foraging scenarios. The level of accuracy with which individuals can navigate toward local food sources is varied, and individual tendency for conspecific attraction or repulsion is optimized over a continuous spectrum. We find that DDHS theory and the MVT accurately predict the evolutionarily optimal patch departure strategy for foragers with high navigational accuracy for a wide range of resource distributions. As navigational accuracy is reduced, the patch departure strategy cannot be accurately predicted by these theories for environments with a heterogeneous resource distribution. In these situations, social forces improve foraging success and have a strong influence on optimal patch departure strategies, causing individuals to stay longer in patches than the optimal foraging theories predict.

Animals↗

PubMed1999

Geometric optimization of a tissue pattern for semilunar valve reconstruction.

BACKGROUND AND AIM OF THE STUDY: A novel geometric trefoil pattern has been suggested for semilunar valve reconstruction. Optimization of the geometry must rely on an appreciation of normal anatomy and knowledge of the mechanical properties of the tissue used for the reconstruction. METHODS: Computer-assisted design (CAD) was used to create an optimized leaflet geometry based on published dimensions for normal human aortic valves. The optimized leaflet geometry was subjected to finite element analysis (FEA) to study stress distribution with pressure loading of the leaflet. In vitro function of the optimized trefoil tissue pattern is being studied by static testing initially, with physiological saline. RESULTS: An optimized leaflet geometry has been developed by CAD, and further refined by FEA. Static testing of the optimized trefoil tissue pattern shows near-normal anatomy, with no prolapse or pin wheeling, and full valve competence to 90 mmHg pressure. CONCLUSIONS: An initial optimized geometry has been developed for a two-dimensional tissue pattern that can be used to reconstruct diseased semilunar heart valves with human pericardium. Optimization studies are based on the mechanical properties of the tissue, CAD to mimic normal anatomy, FEA to study stress distribution, and static load testing to confirm function.

Animals↗

PubMed2000

Optimizing replacement decisions for Finnish dairy herds.

The purposes of the study were to determine how "an optimal herd" would be structured with respect to its calving pattern, average herdlife and calving interval, and to evaluate how sensitive the optimal solution was to changes in input prices, which reflected the situation in Finland in 1998. The study used Finnish input values in an optimization model developed for dairy cow insemination and replacement decisions. The objective of the optimization model was to maximize the expected net present value from present and replacement cows over a given decision horizon. In the optimal solution, the average net revenues per cow were highest in December and lowest in July, due to seasonal milk pricing. Based on the expected net present value of a replacement heifer over the decision horizon, calving in September was optimal. In the optimal solution, an average calving interval was 363 days and average herdlife after first calving was 48.2 months (i.e., approximately 4 complete lactations). However, there was a marked seasonal variation in the length of a calving interval (it being longest in spring and early summer) that can be explained by the goal of having more cows calving in the fall. This, in turn, was due to seasonal milk pricing and higher production in the fall. In the optimal solution, total replacement percentage was 26, with the highest frequency of voluntary culling occurring at the end of the year. Seasonal patterns in calving and replacement frequencies by calendar month and variation in calving interval length or herdlife did not change meaningfully (< 1%-2% change in the output variables) with changes in calf, carcass or feed prices. When the price of a replacement heifer decreased, average herdlife was shorter and replacement percentage increased. When the price increased, the effect was the opposite.

Animal Feed↗

PubMed2002

Radiation dose and image quality in diagnostic radiology. Optimization of the dose-image quality relationship with clinical experience from scoliosis radiography, coronary intervention and a flat-panel digital detector.

UNLABELLED: X-rays are known to cause malignancies, skin damage and other side effects and they are thus potentially dangerous. Therefore, it is essential and in fact mandatory to reduce the radiation dose in diagnostic radiology as far as possible. This is also known as the ALARA (as low as reasonably achievable) principle. However, the dose is linked to image quality and the image quality may not be lowered so far that it jeopardizes the diagnostic outcome of a radiographic procedure. The process of reaching this balance between dose and image quality is called optimization. The aim of this thesis was to propose and evaluate methods for optimizing the radiation dose-image quality relationship in diagnostic radiography with a focus on clinical usefulness. The work was performed in three main parts. OPTIMIZATION OF SCOLIOSIS RADIOGRAPHY: In the first part, two recently developed methods for digital scoliosis radiography (digital exposure and pulse fluoroscopy) were evaluated and compared to the standard screen-film method. Radiation dose was measured as kerma area-product (KAP), entrance surface dose (ESD) and effective dose; image quality was assessed with a contrast-detail phantom and through visual grading analysis. Accuracy in angle measurements was also evaluated. The radiation dose for digital exposure was nearly twice as high as the screen-film method at a comparable image quality while the dose for pulsed fluoroscopy was very low but with a considerably lower image quality. The variability in angle measurements was sufficiently low for all methods. Then, the digital exposure protocol was optimized to a considerably lower dose with a slightly lower image quality compared to the baseline. FLAT-PANEL DETECTOR: In the second part, an amorphous-silicon direct digital flat-panel detector was evaluated using a contrast-detail phantom, measuring dose as entrance dose. The flat-panel detector yielded a superior image quality at a lower dose than both storage phosphor plates and screen-film. Equivalent image quality compared to storage phosphor plates was reached at about one-third of the dose. OPTIMIZATION OF PERCUTANEOUS CORONARY INTERVENTION (PCI): In the third part, influence of various settings on radiation dose and image quality in coronary catheterisation and PCI was investigated. Based on these findings, the dose rate for fluoroscopy was reduced to one-third. The dose reduction was evaluated in a clinical series of 154 PCI procedures before and 138 after the optimization. Through this optimization, the total KAP was significantly reduced to two-thirds of the original value. IN SUMMARY: This thesis indicates the possibility of dose reduction in diagnostic radiology through optimization of the radiographic process.

Coronary Angiography↗

PubMed2004

[Patient dose evaluation and optimization of uropoietic multiphasic multislice CT examination].

PURPOSE: The aim of this study was to optimize acquisition data during multislice multiphasic CT examination of the renal excretory system in order to reduce patient effective dose without deterioration of the imaging quality. MATERIALS AND METHODS: With the aid of two dedicated software programmes we evaluated the patient effective dose during both multislice multiphasic CT examination of the renal excretory system and excretory urography. With the CT acquisition protocol, images of a test object (Helical CT phantom, CIRS) were examined by two expert radiologists to assess the number of visible inserted test images. Other scans of the test object were then obtained utilizing decreased tube current intensity; among these that with minor information loss was identified. Patient effective dose was measured utilizing correspondent acquisition data. RESULTS: Patient effective dose during multiphasic multislice CT examination before optimization (280 mA tube current intensity) was 22.9 mSv for males and 31.1 mSv for females; after optimization it was 19.6 mSv and 26.7 mSv, respectively, with a 14% decrease. Patient effective dose during CT direct phase before optimization was 8.9 mSv for males and 12.8 mSv for females, after optimization 7.6 mSv and 11 mSv with a 15% decrease. The absorbed dose for males is lower because the females gonads are completely included in the primary CT beam, whereas the testicles are hit by diffuse radiation only. DISCUSSION AND CONCLUSIONS: During CT direct phase the patient absorbed dose is 1.45 for males and 1.9 for females (1.2 and 1.6 respectively after optimization) higher than that absorbed during intravenous pyelography; the absorbed dose of a complete multiphasic CT examination is 3.7 for males and 4.6 for females (3.2 and 3.9 respectively after optimization) higher than that absorbed during intravenous pyelography. Such dosimetric data may be justified by diagnostic advantages in stone assessment, especially in males, and by the fact that multislice CT may unify different diagnostic tools such as intravenous pyelography, axial CT and angiography, thereby simplifying the entire diagnostic protocol. As far as exposure is concerned radiologists should follow the optimizing principle referred to each clinical query, bearing in mind that diagnostic accuracy is more important than the simple iconographic aspect.

Female↗

PubMed1993

Genetic algorithms-based design and optimization of statistical quality-control procedures.

In general, one cannot use algebraic or enumerative methods to optimize a quality-control (QC) procedure for detecting the total allowable analytical error with a stated probability with the minimum probability for false rejection. Genetic algorithms (GAs) offer an alternative, as they do not require knowledge of the objective function to be optimized and can search through large parameter spaces quickly. To explore the application of GAs in statistical QC, I developed two interactive computer programs based on the deterministic crowding genetic algorithm. Given an analytical process, the program "Optimize" optimizes a user-defined QC procedure, whereas the program "Design" designs a novel optimized QC procedure. The programs search through the parameter space and find the optimal or near-optimal solution. The possible solutions of the optimization problem are evaluated with computer simulation.

Algorithms↗

PubMed1997

[The role of the atrium and optimal values of AV intervals in sequentially paced patients].

In 1995, 2249 dual chamber pacemakers were implanted in the Czech Republic. These pacemakers make it possible to set an optimal AV delay between the atrial and ventricular impulse. Although the optimization of the AV interval has its well defined physiologic advantages, it does not seem to be necessary in otherwise healthy individuals with a good atrial and ventricular function. In these patients the default value, usually about 170 ms, is acceptable. However, AV interval optimization--i.e. finding the interval at which the atrial contribution to ventricular filling is maximal--should be done in all patients with left ventricular dysfunction, indicated for pacing because of bradyarrhthmia. In this subset of patients, even a small improvement in ventricular filling is believed to be clinically useful. Moreover, it has been documented, that in some types of ventricular dysfunction the so-called "primary optimization" (i.e. optimization of the AV interval in patients, in whom the pacemaker is not indicated for bradyarrhthmia but for ventricular dysfunction that might be improved by AV interval optimization) may be clinically useful. It is the case in patients with hypertrophic obstructive cardiomyopathy, dilated cardiomyopathy with presystolic regurgitation and AV interval prolongation, and perhaps even in some patients with impairment of ventricular systolic function and substantial prolongation of the AV interval. Despite all that, optimization of the AV interval is not routinely performed because even the best available optimization procedures (stroke volume measurements at different AV intervals by aortic Doppler echography) is observer dependent, time-consuming and costly.

Arrhythmias, Cardiac↗

PubMed2004

Dispositional optimism and all-cause and cardiovascular mortality in a prospective cohort of elderly dutch men and women.

BACKGROUND: Major depression is known to be related to higher cardiovascular mortality. However, epidemiological data regarding dispositional optimism in relation to mortality are scanty. OBJECTIVE: To test whether subjects who are optimistic live longer than those who are pessimistic. DESIGN: Our analysis formed part of a prospective population-based cohort study in the Netherlands (Arnhem Elderly Study). SETTING: General community. PARTICIPANTS: Elderly subjects aged 65 to 85 years (999 men and women) completed the 30-item validated Dutch Scale of Subjective Well-being for Older Persons, with 5 subscales: health, self-respect, morale, optimism, and contacts. A total of 941 subjects (466 men and 475 women) had complete dispositional optimism data, and these subjects were divided into quartiles. MAIN OUTCOME MEASURE: Number of deaths during the follow-up period. RESULTS: During the follow-up period of 9.1 years (1991-2001), there were 397 deaths. Compared with subjects with a high level of pessimism, those reporting a high level of optimism had an age- and sex-adjusted hazard ratio of 0.55 (95% confidence interval, 0.42-0.74; upper vs lower quartile) for all-cause mortality. For cardiovascular mortality, the hazard ratio was 0.23 (95% confidence interval, 0.10-0.55) when adjusted for age, sex, chronic disease, education, smoking, alcohol consumption, history of cardiovascular disease or hypertension, body mass index, and total cholesterol level. Protective trend relationships were observed between the level of optimism and all-cause and cardiovascular mortality (P<.001 and P = .001 for trend, respectively). Interaction with sex (P = .04) supported a stronger protective effect of optimism in men than women for all-cause mortality but not for cardiovascular mortality. CONCLUSIONS: Our results provide support for a graded and independent protective relationship between dispositional optimism and all-cause mortality in old age. Prevention of cardiovascular mortality accounted for much of the effect.

Age Factors↗

PubMed1998

Optimism, coping and long-term recovery from coronary artery surgery in women.

Optimism, coping strategies, and psychological and functional outcomes were measured in 55 women undergoing coronary artery surgery. Data were collected in-hospital and at 1, 6, and 12 months after surgery. Optimism was related to positive moods and life satisfaction, and inversely related to negative moods. Few relationships were found between optimism and functional ability. Cognitive coping strategies accounted for a mediating effect between optimism and negative mood. Optimists were more likely to accept their situation, and less likely to use escapism. In turn, these coping strategies were inversely related to negative mood and mediated the relationship between optimism and this outcome. Optimism was not related to problem-focused coping strategies; this, these coping strategies cannot explain the relationship between optimism and outcomes.

Adaptation, Psychological↗

PubMed2000

Optimal cryogen spray cooling parameters for pulsed laser treatment of port wine stains.

BACKGROUND AND OBJECTIVE: In dermatologic laser therapy, cryogen spray cooling (CSC) is a means to protect the epidermis while leaving dermal structures susceptible to thermal damage. The purpose of this study was to determine optimal spurt duration, tau(s), and optimal delay, tau(d), between the cryogen spurt and laser pulse when using CSC in treatment of port wine stain birthmarks. STUDY DESIGN/MATERIALS AND METHODS: A finite difference method is used to compute temperature distributions in human skin in response to CSC. Optimal tau(s) and tau(d) are determined by maximizing the temperature difference between a modeled basal layer and an imaginary target chromophore. RESULTS: The model predicts an optimal tau(s) of 170-300 msec and approximately 400 msec for shallow (150 microm) and deeper (400 microm) targets, respectively. Spraying for longer than the optimal tau(s) does not critically impair cooling selectivity. For a spurt duration of 100 msec, optimal delays are 5-10 msec and 25-70 msec for a shallow and deep basal layer, respectively. CONCLUSION: In the absence of knowledge about the lesion anatomy, using a tau(s) of 100-200 msec and no delay is a good compromise. A delay is justified only when basal layer and target chromophore are relatively deep and the optimal spurt duration cannot be applied, e.g., to avoid frostbite.

Cryotherapy↗

PubMed2000

Framework for online optimization of recombinant protein expression in high-cell-density Escherichia coli cultures using GFP-fusion monitoring.

A framework for the online optimization of protein induction using green fluorescent protein (GFP)-monitoring technology was developed for high-cell-density cultivation of Escherichia coli. A simple and unstructured mathematical model was developed that described well the dynamics of cloned chloramphenicol acetyltransferase (CAT) production in E. coli JM105 was developed. A sequential quadratic programming (SQP) optimization algorithm was used to estimate model parameter values and to solve optimal open-loop control problems for piecewise control of inducer feed rates that maximize productivity. The optimal inducer feeding profile for an arabinose induction system was different from that of an isopropyl-beta-D-thiogalactopyranoside (IPTG) induction system. Also, model-based online parameter estimation and online optimization algorithms were developed to determine optimal inducer feeding rates for eventual use of a feedback signal from a GFP fluorescence probe (direct product monitoring with 95-minute time delay). Because the numerical algorithms required minimal processing time, the potential for product-based and model-based online optimal control methodology can be realized.

Algorithms↗

PubMed2002

Optimal temperature policy for immobilized enzyme packed bed reactor performing reversible Michaelis-Menten kinetics using the disjoint policy.

The optimal temperature policy that maximizes the time-averaged productivity of a continuous immobilized enzyme packed bed reactor is determined. This optimization study takes into consideration the enzyme thermal deactivation with substrate protection during the reactor operation. The general case of reversible Michaelis-Menten kinetics under constant reactor feed flow rate is assumed. The corresponding nonlinear optimization problem is solved using the calculus of variations by applying the disjoint policy. This policy reduces the optimization problem into a differential-algebraic system, DAE. This DAE system defines completely the optimal temperature-time profiles. These profiles depend on the kinetic parameters, feed substrate concentration, operating period, and the residence time and are characterized by increasing form with time. Also, general analytical expressions for the slopes of the temperature and residual enzyme activity profiles are derived. An efficient solution algorithm is developed to solve the DAE system, which results into a one-dimensional optimization problem with simple bounds on the initial feed temperature. The enzymatic isomerization of glucose into fructose is selected as a case study. The computed productivities are very close to that obtained by numerical nonlinear optimization with simpler problem to solve. Moreover, the computed conversion profiles are almost constant over 90% of the operating periods, thus producing a homogeneous product.

Algorithms↗

PubMed1975

Application of modified Rosenbrock's method for optimization of nutrient media used in microorganism culturing.

The Rosenbrock's procedure has been modified for optimization of nutrient medium composition and has been found to be less tedious than the Box-Wilson method, especially for larger numbers of optimized parameters. Its merits are particularly obvious with multiparameter optimization where the gradient method, so far the only one employed in microbiology from a variety of optimization methods (e.g., refs, 9 and 10), becomes impractical because of the excessive number of experiments required. The method suggested is also more stable during optimization than the gradient methods which are very sensitive to the selection of steps in the direction of the gradient and may thus easily shoot out of the optimized region. It is also anticipated that other direct search methods, particularly simplex design, may be easily adapted for optimization of medium composition. It is obvious that direct search methods may find an application in process improvement in antibiotic and related industries.

Culture Media↗

PubMed2003

Randomized clinical trial of multimodal optimization and standard perioperative surgical care.

BACKGROUND: Multimodal optimization of surgical care has been associated with reduced hospital stay and improved physical function. The aim of this randomized trial was to compare multimodal optimization with standard care in patients undergoing colonic resection. METHODS: Twenty-five patients requiring elective right or left hemicolectomy were randomized to receive a ten-point optimization programme (14 patients) or conventional care (11). The groups were similar in terms of age (64 versus 68 years), male : female sex ratio (6 : 8 versus 5 : 6) and Physiological and Operative Severity Score for the enUmeration of Mortality and morbidity (POSSUM) score (both 26). Outcome measures were recorded before operation and on postoperative days 1, 7 and 30. They included hand grip strength, lung spirometry, and pain and fatigue scores. Further outcome measures included time to achieve a predetermined mobilization target, time to resumption of normal diet, and length of stay. RESULTS: Optimization was associated with maintained grip strength, earlier mobilization (46 versus 69 h; P = 0.043), and significantly lower pain and fatigue scores. Patients in the optimization group tolerated a regular hospital diet significantly earlier than controls (48 versus 76 h; P < 0.001). Optimization significantly reduced the median length of hospital stay (3 versus 7 days; P = 0.002). CONCLUSION: Optimization of surgical care significantly improved patients' physical and psychological function in the early postoperative period and facilitated early hospital discharge.

Aged↗

PubMed2006

Estimating the optimal radiotherapy utilization for carcinoma of the central nervous system, thyroid carcinoma, and carcinoma of unknown primary origin from evidence-based clinical guidelines.

BACKGROUND: In this one in a series of articles, the objective was to estimate the ideal proportion of patients with cancer who should receive radiotherapy at least once during the course of their illness based on the best available evidence. This estimate should be useful in planning for future radiotherapy facilities. Optimal rates of radiotherapy for patients with central nervous system (CNS) carcinoma, thyroid carcinoma, or carcinoma of unknown primary site (CUP) have not been studied previously. METHODS: A systematic review of evidence-based treatment guidelines for the treatment of CNS carcinoma, CUP, and thyroid carcinoma was undertaken. An optimal radiotherapy utilization tree was constructed for each of these malignancies depicting the indications for radiotherapy at various stages of disease. The proportion of patients who had clinical attributes that indicated a possible benefit from radiotherapy was calculated by adding epidemiological data to the radiotherapy utilization tree. The optimal proportion of patients who should receive radiotherapy was then calculated using specialized decision-analysis software. Sensitivity analyses using univariate analysis and Monte Carlo simulations were performed. RESULTS: The optimal rates of radiotherapy utilization for carcinoma of the CNS, thyroid carcinoma, and CUP were 92%, 10%, and 61%, respectively. Comparison with actual rates of utilization in South Australia, Sweden, and the U.S. suggested an under-utilization of radiotherapy for CNS carcinoma and CUP. However, the actual rates of radiotherapy for thyroid carcinoma exceeded the optimal rate for some jurisdictions, although some data may have included radioactive iodine, which was not included in the current project. CONCLUSIONS: It was possible to estimate optimal radiotherapy utilization rates based on evidence. This methodology allowed a comparison of optimal rates with actual rates to identify areas in which improvements in the evidence-based use of radiotherapy can be made, and it may provide valuable data for future radiotherapy service planning.

Aged↗