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PubMedDate not supplied

Equilibrium analysis for the forces in the human spinal column and its musculature.

The equations of equilibrium are set up for the thoracic and lumbar spine and involve body weight, external load, muscle forces, and intervertebral reactions. These equations are solved using a linear programming technique that minimizes the total force in the system. The solution gives numeric values for the muscle forces and intervertebral reactions. The results for a subject in progressive forward flexion and in lateral bend are presented. Also examined are the effects of three different orthotic devices on the muscle forces of a patient with a scoliotic spine.

Biomechanical Phenomena↗

PubMed1992

A weighting method for predicting protein structural class from amino acid composition.

A protein is generally classified into one of the following four structural classes: all alpha, all beta, alpha+beta and alpha/beta. In this paper, based on the weighting to the 20 constituent amino acids, a new method is proposed for predicting the structural class of a protein according to its amino acid composition. The 20 weighting parameters, which reflect the different properties of the 20 constituent amino acids, have been obtained from a training set of proteins through the linear-programming approach. The rate of correct prediction for a training set of proteins by means of the new method was 100%, whereas the highest rate of previous methods was 82.8%. Furthermore, the results showed that the more numerous training proteins, the more effective the new method.

Amino Acids↗

PubMedDate not supplied

Systmatic method of formulating liquid phantoms with a given elemental composition and density.

A general method of formulating tissue equivalent liquid mixtures of a given chemical composition and density using the technique of linear programming is described. It is used to generate mixtures with equivalent atomic composition as ICRP Standard Man and mammalian muscle (NBS Handbook 85) using eight compounds to cover the range of densities from 1.0 to 1.13. Use of the method to handle other parameters of a mixture is also described.

Body Burden↗

PubMedDate not supplied

Optimized dynamic rotation with wedges.

Dynamic rotation is a computer-controlled therapy technique utilizing an automated multileaf collimator in which the radiation beam shape changes dynamically as the treatment machine rotates about the patient so that at each instant the beam shape matches the projected shape of the target volume. In simple dynamic rotation, the dose rate remains constant during rotation. For optimized dynamic rotation, the dose rate is varied as a function of gantry angle. Optimum dose rate at each gantry angle is computed by linear programming. Wedges can be included in the optimized dynamic rotation therapy by using additional rotations. Simple and optimized dynamic rotation treatment plans, with and without wedges, for a pancreatic tumor have been compared using optimization cost function values, normal tissue complication probabilities, and positive difference statistic values. For planning purposes, a continuous rotation is approximated by static beams at a number of gantry angles equally spaced about the patient. In theory, the quality of optimized treatment planning solutions should improve as the number of static beams increases. The addition of wedges should further improve dose distributions. For the case studied, no significant improvements were seen for more than 36 beam angles. Open and wedged optimized dynamic rotations were better than simple dynamic rotation, but wedged optimized dynamic rotation showed no definitive improvement over open beam optimized dynamic rotation.

Humans↗

PubMed1979

Experience of the metabolisable energy system.

Advisory experience concerning the metabolisable energy standards for cattle and sheep introduced in 1976 is reviewed. The change appears to have proceeded smoothly, the new terminology and units being mastered and then used in discussions on dairy cow feeding. The system proposed has thrown new light on some old problems and also on established methods of feeding dairy cattle. "Feeding according to yield" and "lead feeding" need to be reinterpreted in the light of the probable dry matter intakes and live-weight changes of cows in early lactation. These parameters also affect the calculated levels of protein received in dairy compound feeds in early lactation. Group feeding of cows by stage of lactation, level of milk yield and live-weight change is readily accepted by managers of the larger dairy herds. Confidence in the accuracy of the dairy ME system has been built up, and its application to suckler cows has also proved successful. The variable net energy system for growing cattle enables ration formulation to be accomplished speedily and linear programming if desired. Published experiments have been used to confirm the accuracy of predicted live-weight gains when compared with observed gains. No sex effects are included in the system, although differences of +/- 10 per cent have been recorded in natural or hormone induced sex effect trials. The requirements for pregnant ewes have been shown to be too low and liable to reduce lamb birth-weights. In the case of growing lambs, a review of published experiments has shown that lambs grew faster than predicted, suggesting that the energy allowances are too high.

Animal Feed↗

PubMed1976

Shaping of isodose curves in intracavitary irradiation using the afterloading method. A feasibility study involving mathematical simulation.

The possibility of adjusting the irradiation scheme to shape the isodose curve around an intracavitary source arrangement was studied mathematically. The total number of millicurie hours of irradiation for each source position was derived by a linear programming approach, taking into account the shape of the tumor in three different cases. The practical isodose curves obtainable with the source arrangement chosen were compared with the shape desired.

Humans↗

PubMed1979

Information content of the multibreath nitrogen washout.

The distribution of ventilation per unit volume (Va/Vol) in the lung is often studied using the multibreath N2 washout test. Most approaches have focused on the determination of a single Va/Vol distribution (consisting of from two compartments to a continuum) compatible with the data, but because the potential number of lung units greatly exceeds the number of breaths measured, many distributions are usually compatible with a given set of washout data. Interpretation of single distributions therefore requires evaluation of the variability among all such compatible distributions. The technique of linear programing is well suited to evaluation of these compatible distributions and its application to the N2 washout is explained. Twelve examples of washout data are analyzed in this way. The results indicate that using the first 20 or so breaths of the washout, narrow distributions of Va/Vol are well specified. Distributions with up to four distinct modes are also well specified, but for broad distributions the shape cannot be adequately defined. Good resolution in the region of high Va/Vol is found to be critically dependent on measuring the first few breaths of the washout.

Computers↗

PubMed1983

A simple model of VA/Q distribution for analysis of inert gas elimination data.

A general procedure for fitting compartments models of alveolar ventilation-perfusion ratio (VA/Q) distribution to inert gas elimination data is described. The method can be applied to any model consisting of a number of compartments ventilated and perfused in parallel, each compartment of the model having a fixed predetermined VA/Q ratio. The number of compartments and their VA/Q ratios required for adequately fitting real data have been examined. A 13-compartment model consisting of a shunt, a dead space, and 11 compartments equally spaced on a logarithmic scale from VA/Q of 0.01 to 100 was found to be suitable. The fitting procedure and the 13-compartment model form the basis of a method of analysis of inert gas elimination data. Essentially the method consists of calculating a sample of 30 distributions compatible with the data analyzed taking into account experimental errors in the inert gas measurements. From this sample, the averages and standard deviations of the flows to 13 zones on the VA/Q scale are estimated. The averages are estimates of the true flows to these zones, and the standard deviations give an indication of the range of flows compatible with the data. The method has some advantages over both the enforced-smoothing approach and the Monte Carlo linear programming scheme of Evans and Wagner (J. Appl. Physiol.: Respirat. Environ. Exercise Physiol. 42: 889-898, 1977).

Computers↗

PubMed1984

Sensitivity and specificity of the computational model for maximal expiratory flow.

The computational model for forced expiratory flow from human lungs of Lambert and associates (J. Appl. Physiol.: Respirat. Environ. Exercise Physiol. 52: 44-56, 1982) was used to investigate the sensitivity of maximal expiratory flow to lung properties. It was found that maximal flow is very sensitive to recoil pressure and airway areas but not very sensitive to lung volume, airway compliance, and airway length. Linear programming was used to show that a given air flow-pressure curves was compatible with a fairly wide range of airway properties. Additional data for maximal flow with a He-O2 mixture narrowed the range somewhat. It was shown that the flow-pressure curve contains more information about central than peripheral airways and that information about the latter is obtainable only from flows at recoils less than 2 cmH2O. Parameter ranges compatible with individual flow-pressure curves showed differences that demonstrated that such curves give some indication of individual central airway properties.

Airway Resistance↗

PubMed1997

Heritability analysis of lipids and three gene loci in twins link the macrophage scavenger receptor to HDL cholesterol concentrations.

We studied 100 healthy monozygotic and 72 dizygotic twin pairs (mean age, 34 +/- 14 years) to test for genetic influences on blood lipids and to examine relevant gene loci. Total cholesterol (TC), LDL cholesterol (LDL-C), HDL cholesterol (HDL-C), and triglyceride (TG) levels were determined after a 12-hour fast. Zygosity was determined with the use of microsatellite markers. Heritability estimates were conducted by using the lisrel 8 program; a sib-pair analysis was conducted by using the sibpal program. Linear regression analyses were carried out between identical-by-descent status and squared within-pair differences of TC, LDL-C, HDL-C, and TG values. Heritability estimates of the lipid serum concentrations ranged from .58 to .66. A significant linkage relationship was found for HDL-C (P = .008) and TGs (P = .05) with D8S261 on chromosome 8p. However, no linkage was found between any of the lipid variables and the lipoprotein lipase gene locus (LPL GZ14/15 and D8S282). Because D8S261 is located approximately halfway between the LPL and macrophage scavenger receptor genes, we examined the nearby markers D8S549 and D8S1731. Linkage was found for HDL-C and D8S549 (P = .001) and for HDL-C and D8S1731 (P = .04). On the other hand, we found no linkage between the LDL receptor gene locus and LDL-C serum concentrations nor between the LPL gene locus and the various other lipid fractions. Our data suggest a significant influence of the macrophage scavenger receptor gene locus on HDL-C and weak influence on TG levels. We suggest that inherited variability in the macrophage scavenger receptor gene has an influence on serum lipid concentrations.

Adult↗

PubMed1991

Changes in rates of unscheduled hospital readmissions and changes in efficiency following the introduction of the Medicare prospective payment system. An analysis using risk-adjusted data.

The purpose of this study was to analyze changes in rates of unscheduled readmissions and changes in technical efficiency following the introduction of the Medicare Prospective Payment System (PPS). We developed the Risk-Adjusted Readmissions Index (RARI), which allowed us to make comparisons in rates of unanticipated readmissions across hospitals and over time. Data envelopment analysis (DEA), a linear programming technique, was used to measure changes in technical efficiency by comparing the inputs used and the outputs produced across a cohort of hospitals, while adjusting for changes over time in case mix and case complexity. Rates of unscheduled readmissions and efficiency scores were computed for a sample of 245 hospitals for each year. Although both readmission rates and efficiency scores increased for most hospitals, there was no evidence that those hospitals that experienced the greatest increases in efficiency had the largest increases in their rates of unscheduled readmissions.

Abstracting and Indexing↗

PubMed1990

Managing physician efficiency and effectiveness in providing hospital services.

Physicians control more than 80 percent of the decisions affecting health costs. Consequently, managing physician practice patterns is an important avenue to reducing health care costs. One approach to identifying inefficient practice patterns is demonstrated in this pilot study of physicians treating heart shock patients. Physicians are evaluated using data envelopment analysis (DEA), a relatively new linear-program-based efficiency evaluation tool. This approach (1) locates physicians using excess resources in treating patients, (2) estimates the amount of excess resources used, and (3) explicitly considers the quality of patient care in the overall assessment of the physician's practice patterns. Findings of physician inefficiency that are stable over time could be used to alter practice patterns and subsequently to assist in cost containment.

Data Collection↗

PubMed1993

Optimal design of a six-bar linkage with one degree of freedom for an anthropomorphic three-jointed finger mechanism.

This research concerns the design of a three-jointed, anthropomorphic, finger mechanism for use as a prosthesis or robotic end-effector. Based on a study of finger configurations for the human hand, a six-bar linkage with one degree of freedom is proposed. A model of the fingertip displacement of the mechanism is derived by a vector analysis approach. The effects of joint friction on the transmission efficiency are analysed. By measuring the joint positions of a human finger, a mathematical model of the pinching and holding configurations are developed. Optimal parameters for the finger mechanism are obtained by non-linear programming based on an objective functional involving motion posture and locus, transmission efficiency and weight subject to geometric and bionic constraints. Simulation results indicate that the mechanism is useful for a variety of prosthetic and robotic applications.

Biomechanical Phenomena↗

PubMed1998

[Nutritional analysis and complementation of a food basket derived from consumption].

INTRODUCTION: The DISEASE & PROCON Basket (DPB) is a list of basic foodstuffs, drawn up on the basis of a Standard of Living and Work Research project in S. Paulo city, Brazil. Seeing that it has been used as a standard for price variations, it is desirable that such an economic instrument as this, should also represent a truly healthy standard of nutrition. Thus, this study seeks to verify the adequacy of the food products in the DPB in relation to the nutritional needs of a typical reference family in S. Paulo city. It also proposes some techniques for dietary complementation. METHODOLOGY: A demographic census, undertaken in 1991 has been used to establish the reference family, as well as 2/3rds of RDA as corresponding to its nutritional needs, and the food composition tables of McCance & Widdowson to analyse the nutrient content of the DPB. Dietary complementation were undertaken by three different methods: Ad Hoc (direct suggestions), Linear Programming (computer software was utilized to minimize costs), and Hybrid (a combination of the first two). RESULTS: Food items in the DPB showed insufficient values for vitamins A, C, B2 and B6, and for minerals Ca, Mg, Fe, Zn, I and Se; besides, a relatively high fat content was found. The Hybrid Method of food complementation seems to present the best results, associating low cost and local dietary habits. DISCUSSION: A relation between the dietary deficiencies of the DPB and the nutritional transition in the developing countries may be infered. The epidemiological risks associated with these changes in eating patterns should not be incorporated into a reliable economic instrument.

Adolescent↗

PubMed1990

Feed intake, weaning weight and net returns comparisons for four breeding systems.

Feed intake, weaning weight and direct and maternal contributions to weaning weight were estimated for four breeding systems using data collected between 1979 and 1986 from 773 cow-calf pairs at the Elora Beef Research Centre. Breeding systems included purebred Hereford (HE), small rotational dual purpose (SR) (a four-way rotational crossing system utilizing Tarentaise, Angus, Gelbvieh and Pinzgauer breeds), large rotational beef (LR) (composed of Maine-Anjou, Simmental and Charolais) and Angus-sired large rotational beef (AL) utilizing Angus as the sire breed and LR as the maternal breed. Large rotational dams had the highest feed intakes for both dry (8.9 kg DM/d) and lactation (11.5 kg DM/d) periods. Conversely, HE calves consumed the greatest amounts of creep feed (309 kg DM), followed by AL, SR and LR. The large rotational system had the highest weaning weights (265 kg) and direct (12.3 kg greater than average of observations) and maternal (9.6 kg greater than average of observations) contributions to weaning weight, followed by AL, SR and HE for all three traits. An equation was derived for net returns that included parameters for feed intake and direct and maternal weaning weight. A linear programming model was designed to incorporate this equation as the objective function and determine the breeding system(s) that maximized net returns under various production conditions. In general, LR produced the greatest net returns, followed by SR and either AL or HE, depending on specific resource constraints (limited feed supply or herd size) included in the model.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1990

Influence of variations in biological and economical parameters on beef production net returns.

Net returns were defined as a function of the monetary returns (revenue) generated by the outputs less the monetary costs generated by the variable inputs. Outputs included total weaning weights of steers and heifers, weight of cull cows and weight of open heifers. Inputs included both feed and nonfeed costs. The net returns equation was incorporated as the objective function in a linear programming model. By maximizing the objective function, the breeding system that generated the highest net returns could be identified considering certain resource constraints. Breeding systems included purebred Herefords; small rotational dual purpose (SR), utilizing the breeds Angus, Pinzgauer, Gelbvieh and Tarentaise; large rotational (LR), a three-way rotational cross with the breeds Charolais, Simmental and Maine-Anjou; and Angus-sired terminal (AL) utilizing Angus as the sire breed and LR heifers as the maternal breed. Large rotational generally produced the greatest net returns, followed by SR and either AL or HE, depending on specific resource constraints (limited feed supply or herd size), calving rates, management systems, environment, beef to feed price ratios and purchased or farm-produced (inexpensive) feed utilized. Only under the conditions of a herd size constraint and farm-produced feed did AL exceed SR in net returns. Hereford had larger net returns than LR only when the two breeding systems were evaluated in an environment assumed to be reproductively stressful to LR. Ranking of breeding systems were dependent on specific conditions and indicated that one must consider each resource constraint and environment in which cattle are expected to produce before making breeding system recommendations.

Animal Feed↗

PubMed1991

A Markovian decision model for beef cattle replacement that considers spring and fall calving.

In certain production environments, beef cows are mated during a breeding season that starts in early summer. Cows found not to be pregnant at the end of the breeding season could either be culled or retained and remated the following summer. Alternatively, nonpregnant cows could be mated in the winter. This option would result in having both a spring and a fall calving herd. The purpose of our study was to determine the optimal replacement policy (maximizing long-run average net returns) for a specific production environment by determining for each age of cow, reproductive status (nonpregnant or pregnant), and season of pregnancy checking (spring or fall) whether the cow should be retained to the next breeding season (summer or winter) or be replaced by a pregnant heifer. The problem was formulated as a Markovian decision process and the optimal policy was found by linear programming. The optimal policy was one in which nonpregnant cows were always culled and replaced by heifers in the summer breeding herd, resulting in spring calving only.

Animals↗

PubMed1975

Rumen modeling: rumen input-output balance models.

Two models of rumen fermentative relationships expressed as systems of simultaneous linear equations and based on requirements for maintenance of balances of elementary imput and output and metabolic pathways are presented in matrix format consistent with solution by linear programs. Matrix entries defining the two models were verified carefully based upon a survey of the literature, and conceptual bases of the models were validated by comparisons of model outputs with experimental data not used in model construction. The models then were used to evaluate interactions among feed composition, volatile fatty acid yields and patterns, microbial growth yields and efficiencies, and microbial metabolic pathways.

Amino Acids↗