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At least 73 records · Page 4Linked to original sources
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↗
PubMed1990

Formulation, nutritive value and sensory evaluation of a new weaning food based on sweet corn (Nutrimaiz) dehydrated pulp.

The objective of the present work was to develop a formulation for complementary infant and child feeding employing linear programing as a mathematical model for optimization. High lysine/high tryptophan sweet corn pulp in the dehydrated form was used as the main ingredient. The restrictions imposed on the model were nutrient requirements, adequate protein/energy ratio and minimum cost. The formula derived by the computer (FC) matched the amino acid requirements, the protein/energy ratio (NDPCal%) and was rated high in laboratory tests in terms of sensory qualities. The cost determined for this formula was competitive in relation to commercial products used for the same purpose. Formula A, which contained 5% more sweet corn pulp and 10% less whole powdered milk, did not differ in nutritional, sensorial and functional properties from the formula FC and was chosen for the field acceptability trial because of its lower cost. Formula A had protein efficiency ratio and Biological Value similar to casein for the rat but protein digestibility and net protein utilization were statistically lower (p less than 0.05) for formula A than for casein. Acceptability tested on children who were 8-18 months of age ranged from 80-90%, average value 87%.

Amino Acids↗
PubMed1989

Indirect calorimetry evaluation of dietary protein and animal fat effects on energy utilization of laying hens.

A multichamber indirect calorimeter was constructed and used to measure energy utilization of laying hens. Four basic diets were formulated by a least cost linear program for use in this study. The first diet was formulated to meet the 1984 National Research Council (NRC) recommendations and contained by analysis 14.5% protein, .58% TSAA, and .68% lysine (designated NRC). The second diet (NRCAA) was formulated to the same amino acid specifications without a protein restriction and contained 12.9% protein, .57% TSAA, and .69% lysine. Another pair of diets was formulated with higher protein (HP) and amino acid restrictions. The HP diet contained 16% protein, .67% TSAA, and .85% lysine; whereas the HPAA diet had 14% protein, .68% TSAA, and .86% lysine. Four additional diets were formulated with the inclusion of 3% animal fat, using the same protein and amino acid restrictions as were used to formulate the first four diets. Animal fat supplementation significantly (P less than .05) improved energy balance (retention) of birds fed all formulations compared with the diets without added fat. Formulation of a diet based on amino acid restrictions significantly increased net energetic efficiency of birds fed amino acid levels higher than those recommended by the NRC (79.2 for HPAA vs. 62.1% for HP), but did not significantly affect net efficiency of birds fed the lower amino acid levels (NRC and NRCAA).

Animal Feed↗
PubMed1976

Adrenodoxin reductase-adrenodexin complex.

Adrenodoxin reductase and adrenodoxin have been shown (Chu, J.-W., and Kimura, T. (1973) J. Biol. Chem. 248, 5183-5187) to form a low dissociation constant, 1:1 complex when both proteins are in the oxidized form. We have found that when adrenodoxin: adrenodoxin reductase ratios are varied by increasing the adrenodoxin concentration, with adrenodoxin reductase held constant, an increasing rate of cytochrome c reduction, with NADPH as reductant, is seen up to a ratio of 1:1, indicating that cytochrome c reduction occurs via the protein-protein complex. Spectra observed during titration of this protein-protein complex with NADH were resolved into components by the linear programming method, using a computer program written in Fortran IV. Analysis of the data has shown that the flavoprotein is reduced prior to the iron sulfur protein, and that the midpoint oxidation-reduction potentials (pH 7.5) of the two proteins are -295 and -331 mV, respectively, when both are present in the complex. Complex formation does not alter the potential of adrenodoxin reductase, but changes that of adrenodoxin by -40 mV. Equilibrium constants derived from potential measurements show that the strength of the protein-protein interaction in the complex is unaltered by reduction of adrenodoxin reductase, but is decreased by about 1 kcal due to reduction of adrenodoxin. The low dissociation constants for both oxidized reduced forms of the adrenodoxin reductase-adrenodoxin complex indicate that the complex must remain associated throughout its catalytic cycle. Titration of the adrenodoxin reductase-adrenodoxin complex with the physiologic reductant, NADPH, was followed by EPR and visible spectra, and yielded an order of reduction of the components identical with that seen when NADH was used as reductant. Reduction of the protein-protein complex with NADPH yielded a ternary complex between NADP+, flavoprotein, and iron sulfur protein, with the two electrons located in a "charge transfer" complex between flavoprotein and pyridine nucleotide.

Adrenal Cortex↗
PubMed1990

[The optimization of the dosimetric plan in the intracavity radiotherapy of patients with cancer of the corpus uteri].

The potentialities of mathematical optimization were investigated with respect to dosimetric design of radiation therapy of endometrial cancer patients using AGAT-V and AGAT-VU [correction of Agat-B and Agat-Y] apparatus. The effectiveness of linear programming for creating in a pathological focus and in normal tissues of a dose distribution, meeting clinical requirements to the maximum, was shown.

Brachytherapy↗
PubMed1992

Use of a spreadsheet program for Deming's linear regression analysis.

A spreadsheet program for Deming's linear regression analysis suitable for use with popular software packages such as Lotus 1-2-3 or Quattro is described. The program is controlled by an autoexecuting simple menu of operations allowing use by those with only limited experience of spreadsheet operation. Regression coefficients, identification of suspect outlying data values and confidence limits and graphical displays of fitted regression lines are provided.

Confidence Intervals↗
PubMed1976

A computer program suitable for fitting linear models when the dependent variable is dichotomous, polichotomous or censored survival and non-linear models when the dependent variable is quantitative.

Given a set of measurements of s explanatory variables corresponding to each experimental unit, a computer program, whose methodological background can be found in [2] has been written in FORTRAN IV language in order to perform regression analyses when the dependent variable is: (i) dichotomous; (ii) polichotomous; (iii) censored survival. In the two former the Cox's [6] linear logistic models are used while in the third one it has been resorted to the models suggested by Feigl and Zelen [8]. The statistical estimation procedure is maximum likelihood and among the different algorithms developed to reach this goal, the one published by Van der Voort and Dorpema [3], has been utilized. Furthermore, when the dependent variable is quantitative, the program is suitable to fit any function non-linear in the parameters; the pertinent function and its first and second derivatives must be provided by the user. In the present version, implemented on a Univac 1106 machine, the program fits directly the Gompertz function.

Computers↗
PubMed1988

A mechanistic and kinetic analysis of the interactions of the diastereoisomers of adenosine 3',5'-(cyclic)phosphorothioate with purified cyclic AMP-dependent protein kinase.

The binding affinities of the diastereoisomers of adenosine 3',5'-(cyclic)phosphorothioate, Sp-cAMP[S] and Rp-cAMP[S], for the cyclic AMP- (cAMP-)binding sites on purified and reconstituted pig heart type II cAMP-dependent protein kinase holoenzyme were determined by measuring the ability of these compounds to displace [3H]cAMP from this enzyme. Sp-cAMP[S], a cAMP agonist, displaced 50% of the [3H]cAMP bound to the holoenzyme at a concentration 10-fold higher than that of cAMP; Rp-cAMP[S], a cAMP antagonist, required a 100-fold higher concentration relative to cAMP. Activation of the isolated holoenzyme, determined as phosphotransferase activity, was measured in the presence of the agonist and in the absence and in the presence of increasing concentrations of the antagonist. The results of fitting the activation data to sigmoid curves with a non-linear-regression program and to Hill plots by using a linear-regression program showed that Rp-cAMP[S] had no effect on Vmax, increased the EC50 values for agonist activation and had no effect on the co-operativity of activation (h). A Ki value of 11 microM was determined for Rp-cAMP[S] inhibition of cAMP-induced activation of purified type II cAMP-dependent protein kinase. Electrophoresis of the holoenzyme on polyacrylamide gels under non-denaturing conditions in the presence of saturating concentrations of the diastereoisomers resulted in 100% dissociation of the subunits with Sp-cAMP[S] and 0% dissociation with Rp-cAMP[S]. Sp-cAMP[S], the isomer with an axial exocyclic sulphur atom, binds to the holoenzyme, releases the catalytic subunit and activates the phosphotransferase activity. Rp-cAMP[S], the isomer with an equatorial exocyclic sulphur atom, binds to the holoenzyme but does not result in dissociation, and thus acts as a competitive inhibitor of phosphotransferase activity.

Animals↗
PubMed1978

BANDSCAN--a computer program for on-line linear scanning of human banded chromosomes.

BANDSCAN, an interactive program for on-line linear scanning of human G-banded chromosomes quantitative analysis is described. This program was written for a Wang 720 C programmable desk calculator associated to the Zeiss scanning photometer MP01. The system can detect up to a maximum of 24 densitometric band peaks found along banded chromosome arms or chromatids, estimate the total arm length and localize bands in terms of their relative positions. The scanning stage under control is always returned to the pre-fixed scanning starting point (centromere) which allows a user to scan the specimen repeatedly at different sensitivities and thus to reject minor bands or suspected chromosome artifacts. This facilitates a better visualization of major bands and chromosome landmarks. A fully formated print-out on band localizations and their relative positions is obtained at the end of each scanning. The possibilities of the application of this program to band mapping of human chromosomes and to the study of small chromosome band aberrations is discussed.

Animals↗
PubMed1978

Program to estimate parameters of linear systems without numerical differentiation.

This paper describes a computer program for estimating the parameters of a linear differential equation systen with constant coefficients by use of a nonlinear least-squares method. For minimization the sum of squares of an existing standard program, the Gauss-Newton gradient procedure, is employed. The differential equation system is solved by the Taylor expansion method. The advantage of this approach is that the derivatives with respect to the parameters are available without numerical differentiation. Therefore the inaccuracy inherent in numerical differentiation and the problem of choosing the modification of the parameters are eliminated. The given procedure is applicable for all the first order gradient methods. The presented method was tested with generated data from a four-compartmental model.

Computers↗
PubMed1991

Comparison of power and exponential field programming in field-flow fractionation.

Field programming in field-flow fractionation has the purpose of expanding the molecular weight or particle diameter range subject to a single analytical run. The two most widely used field programs are those in which the field strength decays with time according to an exponential function and a power function, respectively. The performances of these two programming functions are compared by obtaining limiting equations showing how retention time tr, standard deviation in retention sigma t, and fractionating power Fd vary with particle diameter d. It is shown that uniform fractionating power (Fd independent of d) can be obtained with power programming but that in exponential programming Fd is always non-uniform, varying as d-1/2. In exponential programming a linear relationship arises between tr and log d. This particular relationship is impossible to realize in power programming but an alternative linear relationship can be obtained by plotting tr versus dt/3. These results are made more concrete by plotting and comparing field strength, relative field strength, Fd and tr for specific programming cases.

Chemical Fractionation↗
PubMed1989

The use of a non-linear regression approach for the analysis of the ouabain-K+ interaction with (Na+ + K+)-ATPase from guinea pig and rat hearts.

1. The interaction between ouabain and K+ and their effects on (Na+ + K+)-ATPase activity were studied using microsomes from guinea pig and rat heart. 2. Microsomes were incubated in the presence of various concentrations of K+ and ouabain and ATPase activity was estimated by measuring the inorganic phosphate liberated. The experimental data were analyzed statistically by micro-computer, using a non-linear regression program based on the steepest descent technique. 3. The experimental data were best fitted by a model which assumes that ouabain acts like a mixed inhibitor with respect to the apparently cooperative K+ activation of (Na+ + K+)-ATPase. This quantitative approach provided estimates (with approximate standard deviations) of all the parameters involved in the model. 4. The inhibition constant for the uncompetitive term of the effect was 7- to 9-fold higher than the inhibition constant for the competitive term for both the guinea pig and rat heart preparations. 5. The present results indicate that graphical analyses are helpful for illustrative purposes but suggest that a computerized, non-linear regression program simultaneously analyzing all the non-linearized data should be used to quantify the complex kinetic parameters and to discriminate objectively among possible models.

Animals↗
PubMed1990

The influence of dose constraint point placement on optimized radiation therapy treatment planning.

To efficiently use linear and quadratic programming for treatment planning optimization on a routine basis, automated methods are needed for placing dose constraint points. We have investigated, for linear programming optimization, the minimum number of constraint points needed to achieve an acceptable approximation to the desired (ideal) solution. Seven different constraint point placement algorithms were evaluated for a given objective function. One of these algorithms was chosen for routine clinical use at our institution. This algorithm places constraint points on the perimeter of the target volume and on the perimeter and in the interior of each normal structure. Additional points are placed on the perimeter of a constant thickness buffer region surrounding the target volume. Excellent optimization results are obtained with 40-70 constraint points per treatment planning slice.

Computer Simulation↗
PubMed1991

Gas chromatographic system for the identification of halogenated pesticides by retention indices using n-alkanes as standards.

A gas chromatographic system for the evaluation of linear temperature-programmed retention indices allowing n-alkanes to be adopted as the reference retention markers for any type of analyte, irrespective of the atoms present in their molecules, is described. It is based on the simultaneous use of two different detectors (a flame ionization detector and a specific detector suitable for the sample components), both connected (in parallel) to the same column outlet. The performance of this system has been tested by measuring the retention indices of fifteen chlorinated pesticides under conditions of linear programming temperature, by adopting an electron-capture detector as the specific detector. The reliability of the retention indices thus determined has been proven by verifying that they can be reproduced under different chromatographic conditions.

Alkanes↗
PubMed1989

BOOMER, a simulation and modeling program for pharmacokinetic and pharmacodynamic data analysis.

BOOMER is an improved version of an earlier non-linear regression program, MULTI-FORTE. Rather than the user writing a FORTRAN subroutine, models are defined by means of the parameters which make up the model. Models based on differential equations are specified by means of zero-order, first-order, or Michaelis-Menten-type rate constants. Doses (in units of mass) are translated into the usually observed concentration units by a reciprocal volume parameter. Integrated equation models are specified in terms of baseline terms, exponential terms, or the emax function with slope term as described by the Hill equation. Time points can be specified as parameters to specify dose times, infusion start/stop times, or lag times. With careful selection of parameters quite complex models can be specified. The user has a choice of differential equation solvers and fitting algorithms.

Computer Simulation↗