SEARCH · PubMed Health

Results for “energy 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 703 records · Page 39Linked to original sources

PubMed1995

[A study of the simultaneous acquisition of dual energy SPECT with 99mTc and 123I: evaluation of optimal window setting with myocardial phantom].

To examine crosstalks (CRs) between 99mTc-methoxyisobutyl isonitrile (MIBI) and beta-methyl-p-(123I)iodophenyl-pentadecanoic acid (BMIPP), myocardial phantom studies of simultaneous acquisition were performed with three window widths and four energies where the window located. CRS in 99mTc window were less than 10.5% regardless of the window settings. CRs in 123I window were ranging from 17.0% to 8.6% depending on the window setting. There were significant correlations between the isotope concentration and counts of 99mTc and 123I, respectively (r = 0.98, p < 0.0001). We concluded that the optimal window setting of 99mTc-MIBI and 123I-BMIPP (10% width, 140 keV center 99mTc window and 10% width, 164 keV center 123I window) yields good quality images in dual isotope SPECT.

Aged↗

PubMed2003

Determination of proanthocyanidins in grape products by liquid chromatography/mass spectrometric detection under low collision energy.

A method has been established for the identification of proanthocyanidins and quantification of individual monoproanthocyanidins using liquid chromatography/electrospray ionization-mass spectrometric detection (LC/ESI-MSD) for raw grape products. The separated monoproanthocyanidins and oligoproanthocyanidins were individually analyzed and identified by their molecular ion peaks using LC/MS. Using HPLC/ESI-MSD, the proanthocyanidin monomers, (+)-catechin (C), (-)-epicatechin (EC), (-)-catechin gallate (CG), and (-)-epicatechin gallate (ECG) in grape products were successfully quantified by LC/MS/MS detection of protonated molecular ions and characteristic fragment ions for each component under the optimized low collision energy level of 20%. For the investigated concentration ranges of C (21.88-11,200 ng/mL), EC (21.10-10,800 ng/mL), CG (36.72-18,800 ng/mL), and ECG (39.84-20,400 ng/mL), good linearities (r2 > 0.99) for standard curves were obtained. Validation of this method showed an accuracy that was well below 15% and precision (RSD) within 8% for the four compounds. The method proposed here is simple, sensitive, and allows a direct sample preparation procedure. This is the first method that enables the determination of individual monoproanthocyanidins in grape products without any solid-phase extraction.

Anthocyanins↗

PubMed2006

Bounds on the overlap of the Hartree-Fock, optimized effective potential, and density functional approximations with the exact energy eigenstates.

In this paper, we examine the limits of accuracy of the single determinant approximations (Hartree-Fock, optimized effective potential, and density functional theory) to the exact energy eigenstates of many electron systems. We show that an approximate Slater determinant of S(z)=M gives maximum accuracy for states with S=M, provided that perturbation theory for the spin up minus spin down potential is applicable. The overlap with the exact energy eigenstates with S not equal M is much smaller. Therefore, for the case that the emphasis is on wave functions, one must use symmetry preserving theories, although this is at the expense of accuracy in energy.

Journal Article↗

PubMed2005

Pediatric obesity epidemic: treatment options.

The increasing prevalence of overweight youth in the United States and the associated increase in medical comorbidities has created a growing need for effective weight-management interventions. The recommended treatment for an overweight child to achieve a more healthful weight uses four primary behavioral strategies: (a) reduce energy intake while maintaining optimal nutrient intake to protect growth and development, (b) increase energy expenditure by promoting more physical movement and less sedentary activity, (c) actively engage parents and primary caretakers as agents of change, and (d) facilitate a supportive family environment. Although this approach has the most empirical support, the impact on the pediatric obesity epidemic has been limited, particularly for adolescents with more severe obesity and for African-American, Native-American, and Hispanic children. This has prompted efforts to adapt strategies that have been effective in adult weight management for use in pediatric behavioral intervention programs. These include using motivational interviewing to increase readiness for health behavior changes, modifying the carbohydrate content of children's diets, using culturally appropriate messages and materials, improving cultural competency of health care providers, and using computer-based strategies. Randomized, controlled clinical trials are needed to test the safety and efficacy of these approaches before they can be recommended for clinical practice. Pharmacotherapy and bariatric surgery are more aggressive and historically adult interventions with greater risk that are being considered for severely obese adolescents who have serious obesity-related medical complications and who have failed other more conventional methods.

Behavior Therapy↗

PubMed2001

Structural criteria for the rational design of selective ligands. 3. Quantitative structure-stability relationship for iron(III) complexation by tris-catecholamide siderophores.

We present an extended MM3 model for catecholamide ligands and their Fe(3+) complexes and the application of this model to understand how ligand architecture effects Fe(3+) binding affinity. Force field parameters were fit to geometries and energies from electronic structure calculations, and to crystal structure data. Optimized geometries are reported for phenol, acetamide, the phenol-phenol dimer, the acetamide-phenol dimer, and N-methylsalicylamide (HMSA) at the BLYP/DZVP2/A2 level of theory. Optimized geometries and relative energies are reported for the pseudo-octahedral ground state and the trigonal planar transition state of [Fe(CAT)(3)](3)(-) at the VWN/DZVP2/A1 level of theory. The MM3 model is validated by comparison of calculated structures with crystal structures containing 1,2-dihydroxybenzene (H(2)CAT) and 2,3-dihydroxy-N-methylbenzamide (H(2)MBA) fragments, crystal structures of [Fe(CAT)(3)](3)(-) and tris-catecholamide Fe(3+) complexes, and comparison of MM3 (6.8 kcal/mol) and VWN (5.9 kcal/mol) barriers for intramolecular octahedral inversion in [Fe(CAT)(3)](3)(-). The MM3 model also rationalizes the higher inversion barrier (14 to 18 kcal/mol) reported for [Ga(N,N-diisopropylterephthalamide)(3)](3)(-) ([Ga(DIPTA)(3)](3)(-)). Conformational searches were performed on enterobactin (H(6)ENT), 1,3,5-tris(2,3-dihydroxybenzamidomethyl)-2,4,6-triethylbenzene (H(6)EMECAM), 1,3,5-tris(2,3-dihydroxybenzamidomethyl)-2,4,6-trimethylbenzene (H(6)MMECAM), 1,3,5-tris(2,3-dihydroxybenzamidomethyl)benzene (H(6)MECAM), and 1,5,9-N,N',N' '-tris(2,3-dihydroxybenzoyl)cyclotriazatridecane (H(6)-3,3,4-CYCAM) and Fe(3+) complexes with each of these ligands. A conformational search also was done on the Fe(3+) complex with the 2,2',2' '-tris(2,3-dihydroxybenzamido)triethylammonium cation (H(7)TRENCAM(+)). The relationship between calculated steric energies and measured thermodynamic quantities is discussed, and linear correlations between formation constants and steric energy differences are reported. Extrapolation to zero strain predicts formation constants 8 +/- 5 orders of magnitude higher than that exhibited by ENT (10(49)) are possible. This prediction is supported by a formation constant of 10(63) estimated from the formation constant of [Fe(2,3-dihydroxy-N,N-dimethylbenzamide)(3)](3)(-) ([Fe(DMBA)(3)](3)(-)) by considering the entropic consequences of connecting three DMBA ligands to a rigid backbone. Structural criteria for the identification of improved tris-catecholate ligand architectures are presented.

Algorithms↗

PubMed2005

Physics-based protein-structure prediction using a hierarchical protocol based on the UNRES force field: assessment in two blind tests.

Recent improvements in the protein-structure prediction method developed in our laboratory, based on the thermodynamic hypothesis, are described. The conformational space is searched extensively at the united-residue level by using our physics-based UNRES energy function and the conformational space annealing method of global optimization. The lowest-energy coarse-grained structures are then converted to an all-atom representation and energy-minimized with the ECEPP/3 force field. The procedure was assessed in two recent blind tests of protein-structure prediction. During the first blind test, we predicted large fragments of alpha and alpha+beta proteins [60-70 residues with C(alpha) rms deviation (rmsd) <6 A]. However, for alpha+beta proteins, significant topological errors occurred despite low rmsd values. In the second exercise, we predicted whole structures of five proteins (two alpha and three alpha+beta, with sizes of 53-235 residues) with remarkably good accuracy. In particular, for the genomic target TM0487 (a 102-residue alpha+beta protein from Thermotoga maritima), we predicted the complete, topologically correct structure with 7.3-A C(alpha) rmsd. So far this protein is the largest alpha+beta protein predicted based solely on the amino acid sequence and a physics-based potential-energy function and search procedure. For target T0198, a phosphate transport system regulator PhoU from T. maritima (a 235-residue mainly alpha-helical protein), we predicted the topology of the whole six-helix bundle correctly within 8 A rmsd, except the 32 C-terminal residues, most of which form a beta-hairpin. These and other examples described in this work demonstrate significant progress in physics-based protein-structure prediction.

Amino Acid Sequence↗

PubMed2004

Effect of replacement of pyruvate/lactate in culture medium with glucose on preimplantation development of porcine embryos in vitro.

The effect of glucose supplementation at different times in in vitro culture on the developmental competence of in vitro produced (IVP) porcine embryos was examined. In Experiment 1, when IVP embryos were cultured in modified NCSU-37 supplemented with pyruvate and lactate (IVC-pyr/lac) for 0 h, 24 h, 48 h, 72 h, 96 h, or 118 h and subsequently in modified NCSU-37 supplemented with glucose (IVC-glu) until Day 6 (Day 0=day of in vitro fertilization), the rates of blastocyst formation were significantly higher in embryos cultured in IVC-pyr/lac for 24 or 48 h (24.4% and 23.0%, respectively) than in embryos cultured in IVC-pyr/lac for the whole culture period (14.5%). However, there were no significant differences between embryos obtained after the energy source replacement and embryos cultured in IVC-glu for the whole culture period on the rates (15.2%-24.4%, and 16.8% respectively). Replacement of pyruvate/lactate with glucose at 58 h of culture in Experiment 2 significantly enhanced the rate (31.3%) compared to those after replacement at 48 h, 53 h and 63 h of culture (20.6%, 20.8%, and 21.1%, respectively). In conclusion, replacement of pyruvate/lactate with glucose as the energy substrate was optimal at 58 h of culture for the development of porcine embryos to the blastocyst stage.

Animals↗

PubMed1989

Compton spectroscopy in the diagnostic x-ray energy range. I. Spectrometer design.

The optimal design of a Compton spectrometer for measuring photon energy spectra from x-ray tubes in a clinical laboratory is analysed. The demands are: (i) coherent and multiple scattering distort the measurements and must be avoided; (ii) the measuring time should be as short as possible to avoid unnecessary wear on the x-ray tube; and (iii) the impairment in energy resolution due to the scattering geometry should be kept minimal. A scattering angle of 90 degrees is advocated. Scatterers (of low-atomic-number material) in the shape of long circular rods (0.5-4 mm diameter, 20-40 mm long) are preferable to scattering foils. Use of a short focus-scatterer distance (approximately 200 mm) is to be preferred compared to using a large detector area (greater than or equal to 4 mm diameter) in order to establish a sufficiently high count rate in the detector. Short focal distances and a 90 degrees scattering angle are advantages in measuring energy spectra in the gantry of CT machines where the available space is limited. To limit the geometrical energy broadening to less than 1 keV, the spread in scattering angles of registered photons must not exceed 1-2 degrees for incident photon energies of 100-150 keV.

Algorithms↗

PubMed2000

Design optimization of a breast imaging system based on silicon microstrip detectors.

A mammographic imaging set-up using silicon microstrip detectors in edge-on geometry was simulated using the GEANT package. Deposited energy in tissue of various thicknesses was evaluated and shown to agree to within 10% with reference calculations. Optimal energies as well as spectra for mammography with silicon detectors were determined by maximizing the figure of merit of a realistic imaging set-up. The scattered to primary radiation ratio was studied for various detector geometries. It was found that fan-shaped detectors are needed to maintain the image quality for divergent photon beams.

Computer Simulation↗

PubMed1985

Force, velocity and energy flow during the overarm throw in female handball players.

The overarm throw of 56 female handball players was analysed cinematographically. The time courses of the ball velocity, the force on the ball, the energy flow to the ball as well as the velocities of wrist, elbow and hip were calculated. The mean ball velocity at release was 17.2 m s-1. The major part (73%) of the work on the ball appeared to be done in the last 50 ms of the throw. It is shown that high maximal segmental velocities are important pre-requisites for an optimal flow of energy to the ball during that last phase of the throw. The consecutive actions of body segments from larger proximal segments to the relatively smaller distal segments seem to be connected to intrinsic muscle properties and to a flow of energy from proximal to distal segments.

Adult↗

PubMed1987

Optimal design of vertebrate and insect sarcomeres.

This paper offers a model for the normalized length-tension relation of a muscle fiber based upon sarcomere design. Comparison with measurements published by Gordon et al. ('66) shows an accurate fit as long as the inhomogeneity of sarcomere length in a single muscle fiber is taken into account. Sequential change of filament length and the length of the cross-bridge-free zone leads the model to suggest that most vertebrate sarcomeres tested match the condition of optimal construction for the output of mechanical energy over a full sarcomere contraction movement. Joint optimization of all three morphometric parameters suggests that a slightly better (0.3%) design is theoretically possible. However, this theoretical sarcomere, optimally designed for the conversion of energy, has a low normalized contraction velocity; it provides a poorer match to the combined functional demands of high energy output and high contraction velocity than the real sarcomeres of vertebrates. The sarcomeres in fish myotomes appear to be built suboptimally for isometric contraction, but built optimally for that shortening velocity generating maximum power. During swimming, these muscles do indeed contract concentrically only. The sarcomeres of insect asynchronous flight muscles contract only slightly. They are not built optimally for maximum output of energy across the full range of contraction encountered in vertebrate sarcomeres, but are built almost optimally for the contraction range that they do in fact employ.

Animals↗

PubMedDate not supplied

Many-body optimization using an ab initio monte carlo method.

Advances in computing power have made it possible to study solvated molecules using ab initio quantum chemistry. Inclusion of discrete solvent molecules is required to determine geometric information about solute/solvent clusters. Monte Carlo methods are well suited to finding minima in many-body systems, and ab initio methods are applicable to the widest range of systems. A first principles Monte Carlo (FPMC) method was developed to find minima in many-body systems, and emphasis was placed on implementing moves that increase the likelihood of finding minimum energy structures. Partial optimization and molecular interchange moves aid in finding minima and overcome the incomplete sampling that is unavoidable when using ab initio methods. FPMC was validated by studying the boron trifluoride-water system, and then the method was used to examine the methyl carbenium ion in water to demonstrate its application to solvation problems.

Journal Article↗

PubMed2006

Optimal beam quality selection in digital mammography.

An experimental method of determining the optimal beam quality for digital mammography systems was applied to two systems (Fuji Profect and GE Senographe 2000D). The mean glandular dose (MGD) and contrast-to-noise ratio (CNR) were measured using Perspex breast phantoms simulating breasts from 20 mm to 90 mm thick. For each thickness, four combinations of tube voltage and target/filter were tested. Optimal beam quality was defined as giving a target CNR for the lowest MGD and was similar for the two systems. For breasts with a thickness of 21 mm or 32 mm, a tube voltage of either 25 kV or 28 kV and a Mo/Mo target/filter combination was optimal. For breast thicknesses of 45 mm and greater, the combination that had the highest X-ray energy (34 kV Rh/Rh) was optimal. Optimization using the higher energy beam quality required greater detector dose to compensate for the lower contrast. Thus for a 75 mm thick breast the 34 kV Rh/Rh combination required about a 90% greater detector dose than 28 kV Mo/Mo to achieve the same CNR because of the 25% reduction in contrast. Nonetheless, the MGD was reduced by 32% by choosing the higher energy spectra and achieving the same CNR. Current automatic exposure control (AEC) designs that aim for a fixed detector dose are not optimal and greater use of higher energy spectra should be accompanied by higher detector doses at all breast thicknesses which are average or above. This may result in slightly higher doses, but better image quality for these breasts.

Breast↗

PubMed1986

On the role of optimization in the cardiovascular system.

This essay discusses in a very simple manner several aspects of the meaning of optimization in general and, particularly, the role of optimization in relation to the work and action of the heart. Starting out with historical considerations the role of the properties of the heart as a pump, its relation to the arterial system, the problem of pulsatility and blood pressure and the role of time intervals and coronary perfusion is discussed. Mathematical methods permit the calculation of the time course of the cardiac ejection which, under certain constraints, minimizes the energy consumption of the heart. The saving of energy by this optimization compared with a nonoptimal ejection pattern is rather small--in the order of a few percent. It is therefore interesting and important to discuss the physiological meaning of small variations of the cost-effect function. It seems that unexplained phenomena like synchronization of heart beat and respiration have something to do with an optimization process. The most important conclusion is that any optimization has to be seen as a process related to the functioning of the organism as a whole.

Animals↗

PubMed1990

Rates of energy processing by blowflies: the uses for a joule vary with food quality and quantity.

Data on the variation of crop volumes with time for blowflies (Phormia regina Meigen) fed various volumes and concentrations of fructose or sucrose (from Gelperin, 1966, and Edgecomb et al. 1987) were used to characterize energy processing rates to test the assumption of food energy addivity of optimal foraging theories. Six regression models (linear, square root, cube root, hyperbolic, inverse cube root and exponential) were compared for data from Edgecomb et al. (1987) with measurements of crop volumes from 10 min to 5 h after blowflies were fed 9.7 or 14.5 microliters of 0.25 moll-1 sucrose. Only the hyperbolic regression could be discriminated as statistically different, and the linear model was selected as most parsimonious for examining rates of energy processing. About the same volume bypassed the crop for flies fed 9.7 or 14.5 microliters. Volume rates of crop emptying (from Gelperin, 1966) did not change at intermediate concentrations but decreased from lowest and to highest concentrations. Energy processing patterns indicate that long-term storage rates increase with meal size and at intermediate concentrations and decrease (3.0 moll-1 fructose) or remain constant (2.0 moll-1 sucrose) at high concentrations, so the uses for a unit of energy are not additive across concentrations and meal sizes. Animals that process energy in this way should attempt to maximize meal size and include high-energy foods in their diet out of proportion to the amount of energy gained for the time spent foraging.

Animals↗

PubMed2006

Approaches for biological and biomimetic energy conversion.

This article highlights areas of research at the interface of nanotechnology, the physical sciences, and biology that are related to energy conversion: specifically, those related to photovoltaic applications. Although much ongoing work is seeking to understand basic processes of photosynthesis and chemical conversion, such as light harvesting, electron transfer, and ion transport, application of this knowledge to the development of fully synthetic and/or hybrid devices is still in its infancy. To develop systems that produce energy in an efficient manner, it is important both to understand the biological mechanisms of energy flow for optimization of primary structure and to appreciate the roles of architecture and assembly. Whether devices are completely synthetic and mimic biological processes or devices use natural biomolecules, much of the research for future power systems will happen at the intersection of disciplines.

Biology↗

PubMed1999

Why Are Copper(II) Amino Acid Complexes Not Planar in Their Crystal Structures? An ab Initio and Molecular Mechanics Study.

This paper presents geometries of copper(II) chelates with L-alanine, L-leucine, and L-N,N-dimethylvaline optimized by the hybrid density functional method B3LYP. According to the molecular quantum mechanics results, a square-planar copper(II) coordination geometry is electronically favored in vacuo. Deviations from the planar configuration observed in the crystal state should be attributed to sterical intramolecular and/or intermolecular effects. This paper proposes a new molecular mechanics model for tetracoordinated copper(II) amino acidates to investigate these effects in detail. The empirical parameter set for the selected potential energy functions was optimized both with respect to the X-ray crystal structures (internal coordinates and unit cell constants) and with respect to the quantum mechanically derived valence angles around copper. To test this newly developed force field (FF), the equilibrium geometries of 10 molecules are predicted in vacuo and in approximate crystalline surrounding. The results were compared with their ab initio and experimental crystal structures, respectively. The unit cell volumes were reproduced in a range from -7.0% to 2.1%. The total root-mean-square deviations between the experimental and FF in crystal internal coordinates were 0.017 Å in the bond lengths, 2.2 degrees in the valence angles, and 3.6 degrees in the torsion angles. The force field is capable of reproducing the changes in the chelate rings' torsion angles caused by the crystal packing forces and successfully explains the nonplanarity of Cu(II) amino acid complexes in their crystal structures.

Journal Article↗

PubMed1999

Thermodynamic framework for discrete optimal control in multiphase flow systems.

Bellman's method of dynamic programming is used to synthesize diverse optimization approaches to active (work producing) and inactive (entropy generating) multiphase flow systems. Thermal machines, optimally controlled unit operations, nonlinear heat conduction, spontaneous relaxation processes, and self-propagating wave fronts are all shown to satisfy a discrete Hamilton-Jacobi-Bellman equation and a corresponding discrete optimization algorithm of Pontryagin's type, with the maximum principle for a Hamiltonian. The extremal structures are always canonical. A common unifying criterion is set for all considered systems, which is the criterion of a minimum generated entropy. It is shown that constraints can modify the entropy functionals in a different way for each group of the processes considered; thus the resulting structures of these functionals may differ significantly. Practical conclusions are formulated regarding the energy savings and energy policy in optimally controlled systems.

Journal Article↗