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PubMed1983

The amino acid requirements of growing turkeys. 1. Model construction and parameter estimation.

A model has been formulated to calculate the protein and amino acid requirements for growing turkeys. A requirement was taken as the sum of the needs for maintenance, for gain in carcass weight without feathers, and for the feathers. Parameters used in the model were obtained from a study of carcass composition along the growth period and from two balance trials with adult turkeys. The maintenance requirement was considered to be the sum of the needs for replacing skin and intestinal protein losses and for the obligatory creatinine excretion in the urine. Nitrogen retention was determined at 2.3 g/day in protein-fed adult (17 kg) male turkeys as an estimate for the replacement needs for skin protein loss. Creatinine excretion in these birds was 123 mg/day. When fed an N-free diet, 16.5 kg adult turkeys excreted a total of 3.5 g/day amino acids as a result of intestinal losses. The protein requirement for maintenance was estimated at 32 mg/day/g2/3 of body weight by summing up the different needs and dividing by .85, the coefficient of protein absorption. Protein and amino acid analyses of nude carcass and feathers and the growth curve were used to calculate the requirements for growth. These were then related to energy intake predicted by equations, which included previously determined coefficients for maintenance and growth (Hurwitz et al., 1980a), and the results of carcass lipid analysis. The calculated amino acid requirements were similar to those of the National Research Council (1977).

Amino Acids↗

PubMed1990

Mechanical impedance of the canine diaphragm. Part 2. Theoretical model and parameter estimation.

In the paper the equation of motion of the small amplitude transverse forced vibration of a radially prestressed and circularly clamped thin membrane has been developed. The material of the membrane is considered to be homogeneous, isotropic, incompressible and viscoelastic. From the analytical solution of this equation the incremental mechanical impedance of the membrane was derived as a function of frequency, geometrical parameters and incremental viscoelastic coefficients of the material. The parameters of the model were fitted to experimental impedance data using a global optimisation procedure to obtain the incremental viscoelastic moduli of the canine diaphragm. The estimated quasi-static behaviour of the model is shown to be consistent with the results of experimental quasi-static measurements. It is concluded that the incremental viscoelastic moduli of a soft tissue and the stress dependence of these material coefficients can be determined by fitting the parameters of the model to the impedance data of that particular tissue.

Animals↗

PubMed2006

Affine parameter estimation from the trace transform.

In this paper, we assume that we are given the images of two segmented objects, one of which may be an affinely distorted version of the other, and wish to recover the values of the parameters of the affine transformation between the two images. The images may also differ by the overall level of illumination. The multiplicative constant of such difference may also be recovered. We present a generic theoretical framework to solve this problem. In terms of this framework, other proposed methods may be interpreted. We show how, in this framework, one can recover the affine parameters in a way that is robust to various effects, such as occlusion and illumination variation. The proposed method is generic enough to be applicable also to matching two images that do not depict the same scene or object.

Algorithms↗

PubMed2003

Parameter estimation of sigmoid superpositions: dynamical system approach.

Superposition of sigmoid function over a finite time interval is shown to be equivalent to the linear combination of the solutions of a linearly parameterized system of logistic differential equations. Due to the linearity with respect to the parameters of the system, it is possible to design an effective procedure for parameter adjustment. Stability properties of this procedure are analyzed.

Computer Simulation↗

PubMed1991

Influence of method of model fitting and gender on estimated parameters for the relationship between starvation heat production and body size in the domestic fowl.

The relationship between starvation heat production (SHP) in kJ/d and body weight (W) in kg for domestic fowl was examined with compiled calorimetric data for 294 fowls (Johnson and Farrell, 1985). Linear regression analyses using ordinary least squares methods were performed before and after transformation of the data to a logarithmic scale (base = 10). Coefficients of determination (R2) were similar for untransformed and log-transformed data (R2's = .56 and .53, respectively). The slopes for untransformed data of males and females were different (P less than 0.033). When the model parameters for: SHP = b0 Wb1 were derived from log-transformed data, there were no significant differences in exponents for males vs. females (P greater than .95). However, when the coefficients were estimated using non-linear regression techniques, a difference was detected at the level of P = 0.072. It was determined that there is no advantage in describing the relationship of SHP as a non-linear function of W, nor is it appropriate to express physiological variables as a ratio of weight raised to some mass exponent without statistical justification. Using W or W2 as a covariable for the statistical analysis of physiological data would produce equally acceptable determinations of significance.

Animals↗

PubMed2006

Parameter estimation of a plant uptake model for cyanide: application to hydroponic data.

A plant uptake model is applied to describe free cyanide and ferrocyanide transport and fate in willow (Salix eriocephala var. Michaux) grown in hydroponics. The model is applied to experimental data to determine best-fit parameter values, their associated uncertainty, and their relative importance to field-scale phytoremediation applications. The fitted model results, using least-squares optimization of the observed log concentrations, indicate that free cyanide volatilization from leaf tissue and free cyanide cell wall adsorption were negligible. The free cyanide maximum uptake rate and assimilate (noncyanide 15N) first-order leaf loss rate were the only coefficients that significantly affected the model goodness of fit and were concurrently sensitive to data uncertainty in the parameter optimization. Saturation kinetics may be applicable for free cyanide uptake into plants, but not for ferrocyanide uptake, which may occur via preferential protein-mediated or inefficient transpiration stream uptake. Within the free cyanide system, the relative magnitudes of the saturation uptake parameters and the demonstration of an active role for plants in uptake relative to transpiration suggest the potential importance of preferential diffusion through the cell membranes as reported in the literature, rather than protein-mediated uptake. The fitted 13-parameter model matched the observed data well except for the predicted stem and leaf tissue assimilate concentrations, which were significantly underestimated, particularly in the free cyanide system. These low predicted values, combined with the slightly underestimated solution free cyanide removal, suggest that noncyanide 15N redistribution in phloem should be considered.

Biodegradation, Environmental↗

PubMedDate not supplied

A simple steady state kinetic model for alcohol dehydrogenase. Use of reaction progress curves for parameters estimation at pH 7.4.

A simple rate equation for alcohol dehydrogenase was obtained by assuming independent binding sites for ethanol and NAD+ and fully competitive inhibition by the products of the reaction, acetaldehyde and NADH. A random binding order was also assumed. The rate equation is described by six parameters: four association constants (two for the substrates and two for the products of the reaction), Vf for the forward direction, and the equilibrium constant of the reaction. The six parameters were determined at pH 7.4 by numerical analysis of progress curves of reactions started with different concentrations of ethanol and NAD+. The parameters for alcohol dehydrogenase partially purified from rat liver were: Km for ethanol = 0.746 mM, Km for NAD+ = 0.0563 mM, Km for acetaldehyde = 7.07 microM, Km for NADH = 4.77 microM and Keq = 2.36 X 10(-4). The computed values allowed a very good simulation of the experimental progress curves and little variation was observed in the kinetic parameters when the reactions were started in the presence of either NADH or acetaldehyde.

Alcohol Dehydrogenase↗

PubMed1992

Confidence limits for the parameter estimation in the dipole localization method on the basis of spatial correlation of background EEG.

A new residual function in the inverse problem of equivalent dipole localization methods is proposed which is based on the spatial correlation of the background EEG. This residual has the advantage that it allows the calculation of confidence limits for dipole model parameters. The method was applied to VEP data, and it was studied how the localization precision depends on the recording time of the EEG. It was found that the tangential position of an equivalent dipole can be located at 99% confidence in a region of the order 7 x 7mm for a head radius of 10cm, while the 99% confidence interval of the depth estimate is approximately 1cm, with a recording time of 20 minutes. It was also observed that an EEG recording time of more than 10-15 minutes is needed to obtain stable localization precision estimates.

Brain↗

PubMed1984

Analytical approximations of sensitivities of steady state predictions to errors in parameter estimation: II. Michaelis-Menten kinetics.

Linear sensitivity theory is used to estimate the reliability of predictions of the minimum and maximum concentrations at steady state in the Michaelis-Menten model with i.v. bolus. The dependence of the relative errors in the predictions on the errors in the pharmacokinetic parameters is derived in an analytical form. It is shown that the quality of the predictions is not equally sensitive to all errors in parameters, and that the sensitivity factors vary with the degree of saturation of the system. An example of application for a drug, such as phenytoin, is discussed. It is suggested that sensitivity analysis may be useful in design of pharmacokinetic experiments aimed at the control of steady state levels for drugs with Michaelis-Menten kinetics.

Kinetics↗

PubMed1999

The evolution of codon preferences in Drosophila: a maximum-likelihood approach to parameter estimation and hypothesis testing.

Synonymous codon usage in related species may differ as a result of variation in mutation biases, differences in the overall strength and efficiency of selection, and shifts in codon preference-the selective hierarchy of codons within and between amino acids. We have developed a maximum-likelihood method to employ explicit population genetic models to analyze the evolution of parameters determining codon usage. The method is applied to twofold degenerate amino acids in 50 orthologous genes from D. melanogaster and D. virilis. We find that D. virilis has significantly reduced selection on codon usage for all amino acids, but the data are incompatible with a simple model in which there is a single difference in the long-term Ne, or overall strength of selection, between the two species, indicating shifts in codon preference. The strength of selection acting on codon usage in D. melanogaster is estimated to be |Nes| approximately 0.4 for most CT-ending twofold degenerate amino acids, but 1.7 times greater for cysteine and 1.4 times greater for AG-ending codons. In D. virilis, the strength of selection acting on codon usage for most amino acids is only half that acting in D. melanogaster but is considerably greater than half for cysteine, perhaps indicating the dual selection pressures of translational efficiency and accuracy. Selection coefficients in orthologues are highly correlated (rho = 0.46), but a number of genes deviate significantly from this relationship.

Amino Acids↗

PubMed1990

Determination of a constitutive relation for passive myocardium: II. Parameter estimation.

In the first paper of this series, we proposed a new transversely isotropic pseudostrain-energy function W for describing the biomechanical behavior of excised noncontracting myocardium. The specific functional form of W was inferred directly from biaxial data to be a polynomial function of two coordinate invariant measures of the finite deformation and five material parameters. In this paper, best-fit values of the material parameters are determined from biaxial data using a nonlinear least-squares regression. These values of the parameters are shown to be well-determined, and the final constitutive relation is shown to have good predictive capabilities. Since the proposed constitutive relation describes much broader classes of in-vitro biaxial data than previously proposed relations, it may be better applicable to analyses of stress in the passive heart.

Animals↗

PubMed1998

Tests of a linear model of visual-vestibular interaction using the technique of parameter estimation.

The goal of this study was to test whether a superposition model of smooth-pursuit and vestibuloocular reflex (VOR) eye movements could account for the stability of gaze that subjects show as they view a stationary target, during head rotations at frequencies that correspond to natural movements. Horizontal smooth-pursuit and the VOR were tested using sinusoidal stimuli with frequencies in the range 1.0-3.5 Hz. During head rotation, subjects viewed a stationary target either directly or through an optical device that required eye movements to be approximately twice the amplitude of head movements in order to maintain foveal vision of the target. The gain of compensatory eye movements during viewing through the optical device was generally greater than during direct viewing or during attempted fixation of the remembered target location in darkness. This suggests that visual factors influence the response, even at high frequencies of head rotation. During viewing through the optical device, the gain of compensatory eye movements declined as a function of the frequency of head rotation (P < 0.001) but, at any particular frequency, there was no correlation with peak head velocity 9P > 0.23), peak head acceleration (P > 0.22) or retinal slip speed (P > 0.22). The optimal values of parameters of smooth-pursuit and VOR components of a simple superposition model were estimated in the frequency domain, using the measured responses during head rotation, as each subject viewed the stationary target through the optical device. We then compared the model's prediction of smooth-pursuit gain and phase, at each frequency, with values obtained experimentally. Each subject's pursuit showed lower gain and greater phase lag than the model predicted. Smooth-pursuit performance did not improve significantly if the moving target was a 10 deg x 10 deg Amsler grid, or if sinusoidal oscillation of the target was superimposed on ramp motion. Further, subjects were still able to modulate the gain of compensatory eye movements during pseudo-random head perturbations, making improved predictor performance during visual-vestibular interactions unlikely. We conclude that the increase in gain of eye movements that compensate for head rotations when subjects view, rather than imagine, a stationary target cannot be adequately explained by superposition of VOR and smooth-pursuit signals. Instead, vision may affect VOR performance by determining the context of the behavior.

Adult↗

PubMed1985

Discrimination of the isozymes of human placental hexosaminidase by kinetic parameter estimation.

Human placental beta-N-acetylhexosaminidase (EC 3.2.1.52) (HEX) is a lysosomal glycosyl hydrolase with an acidic pH optimum. Four isozymes (HEX B, HEX I1, HEX I2, and HEX A) have been isolated from human placenta. HEX BA derived from the subunit rearrangement of HEX A was also prepared. To determine if the isozymes of hexosaminidase differ in their kinetic parameters, the conditions for 4-methylumbelliferyl-beta-D-N-acetylglucosaminide hydrolysis were optimized for each isozyme. The Km values were essentially similar and varied from 0.64 +/- 0.06 for HEX BA to 0.85 +/- 0.13 for HEX I1. The Vmax values were similar only for HEX I1 (3.90 +/- 0.28 kat kg-1) and HEX I2 (4.40 +/- 0.17). Vmax values varied significantly between HEX A (9.68 +/- 0.52), HEX B (8.00 +/- 0.75), HEX BA (4.81 +/- 0.17), and the HEX I values.

Electrophoresis, Polyacrylamide Gel↗

PubMed2005

Estimating parameters in the Rasch model in the presence of null categories.

A category with a frequency of zero is called a null category. When null categories are present in polytomous responses, then in the Rasch model for such responses, the thresholds that define the categories are inestimable with the commonly used joint maximum likelihood, marginal maximum likelihood, or standard conditional maximum likelihood estimation algorithms. The reason for this situation is that in principle, these estimation algorithms involve frequencies of each category. Andrich and Luo (2003) describe an algorithm in which the thresholds are reparameterized into their principal components and in which the estimate of any threshold is based on a function of the frequencies of all categories of the item rather than the frequency of a particular category. This algorithm works in the presence of null categories. However, in situations where the null categories are at the extremes of a set of categories, the estimates themselves can become too extreme. This paper describes a procedure in which the solution algorithm described by Andrich and Luo is further adapted in the presence of null categories by using their expected frequencies. The procedure is demonstrated with simulated and real data.

Algorithms↗

PubMed1979

Dynamic evaluation of human vestibulo-ocular function using white noise rotation stimulus and linear system parameter estimation techniques.

White noise acceleration inputs were used to determine the human VOR transfer function both for normal subjects and for patients falling into two pilot categories: unilateral labyrinthectomy and reduced bilateral responses. The systematic patterns shown in the transfer function of the pilot abnormal categories as compared to the normal data suggests one method of classifying test results (table I). Frequency domain linear systems parameter fits were also made using the same data. The changes in these fit parameters, when pilot abnormal data is compared to normal data, suggests the use of the parameter fits themselves as a second classification scheme (fig. 1). The second scheme is not appropriate in cases where the response is unrelated to the stimulus.

Eye Movements↗

PubMed1990

Two methods for parameter estimation using multiple-trait models and beef cattle field data.

Two methods are presented for estimating variances and covariances from beef cattle field data using multiple-trait sire models. Both methods require that the first trait have no missing records and that the contemporary groups for the second trait be subsets of the contemporary groups for the first trait; however, the second trait may have missing records. One method uses pseudo expectations involving quadratics composed of the solutions and the right-hand sides of the mixed model equations. The other method is an extension of Henderson's Simple Method to the multiple trait case. Neither of these methods requires any inversions of large matrices in the computation of the parameters; therefore, both methods can handle very large sets of data. Four simulated data sets were generated to evaluate the methods. In general, both methods estimated genetic correlations and heritabilities that were close to the Restricted Maximum Likelihood estimates and the true data set values, even when selection within contemporary groups was practiced. The estimates of residual correlations by both methods, however, were biased by selection. These two methods can be useful in estimating variances and covariances from multiple-trait models in large populations that have undergone a minimal amount of selection within contemporary groups.

Analysis of Variance↗

PubMed2006

Estimating the parameters of a model for protein-protein interaction graphs.

We find accurate approximations for the expected number of three-cycles and unchorded four-cycles under a stochastic distribution for graphs that has been proposed for modelling yeast two-hybrid protein-protein interaction networks. We show that unchorded four-cycles are characteristic motifs under this model and that the count of unchorded four-cycles in the graph is a reliable statistic on which to base parameter estimation. Finally, we test our model against a range of experimental data, obtain parameter estimates from these data and investigate possible improvements in the model. Characterization of this model lays the foundation for its use as a prior distribution in a Bayesian analysis of yeast two-hybrid networks that can potentially aid in identifying false-positive and false-negative results.

Algorithms↗

PubMed1989

Preventive distinction of patients with primary or secondary hypertension by discriminant analysis of chronobiologic parameters estimated on 24-hour blood pressure patterns.

This investigation deals with a statistical probatory that patients with primary (PH) or secondary (SH) hypertension may be correctly diagnosed by a discriminant analysis of the chronobiologic characteristics computed on the 24-hour blood pressure (BP) patterns. The methodology concerning non-invasive 24-h BP monitoring, chronobiologic analysis and the discrimination process is detailed. Substantial dissimilarities were found in the statistical distribution for systolic and diastolic BP rhythmometric parameters (mesor, amplitude and acrophase) by a retrospective assessment of two groups, consisting of 54 patients with PH and 16 patients with SH. The group-related distribution for rhythmometric parameters was found to be significantly different to generate a statistically significant intergroup discriminatory boundary. The discriminant analysis correctly diagnosed patients with PH and SH in a percentage of about 91% and 63%, respectively. The high incidence of success is convincing that the combination of 24-h BP monitoring/chronobiologic analysis/discrimination process cna be a practical tool for confidently selecting patients with a presumable PH or SH.

Adolescent↗