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PubMed2004

Thermal microdebridement does not affect the time zero biomechanical properties of human patellar tendons.

BACKGROUND: Thermal microdebridement for the treatment of chronic tendinopathy has recently been introduced. The effect of thermal microdebridement on the biomechanical properties of human tendons, however, remains unknown. HYPOTHESIS: Thermal microdebridement does not affect the biomechanical properties of human patellar tendons in a cadaveric model at the time of initial treatment. STUDY DESIGN: Controlled laboratory study. METHODS: The central 15 mm of 12 matched, human (mean age, 71 years; 8 male, 4 female), fresh-frozen patellar tendons was divided into 3 equal 5-mm specimens. The treatment group (n = 12) underwent thermal microdebridement with a radiofrequency probe. A sham treatment group (n = 12) underwent insertion of a deactivated probe. The control group (n = 12) underwent no treatment. After treatment, each specimen was tested to failure in a servo-hydraulic materials testing machine at an elongation rate of 3 mm/s. One-way repeated measures analysis of variance was used to determine differences between groups. RESULTS: No significant difference in ultimate stress at failure, elastic modulus, strain energy density, or strain at maximum load was found between the groups. The ultimate stress at failure for the treatment, sham, and control groups was 61.0, 66.7, and 63.0 MPa, respectively (P = .653), and the strain at maximum load was 0.12, 0.11, and 0.09, respectively (P = .279). CONCLUSIONS: Thermal microdebridement does not affect the biomechanical properties of cadaveric human patellar tendons at the time of initial treatment. CLINICAL RELEVANCE: It may be safe to proceed with aggressive rehabilitation after thermal microdebridement of the patellar tendon. However, the results in this cadaveric model should be interpreted with caution. Additional studies using an in vivo model will be required to completely assess the effects of thermal microdebridement on the biomechanical properties of human patellar tendons.

Aged↗
PubMed1993

A pharmaceutical care challenge: recruiting, training, and retaining pharmaceutical care practitioners.

We do not claim to have all the answers when it comes to implementing an ideal pharmaceutical care model. We are not even sure what all the characteristics of such a model should be. We have recognized, based on our interpretation of the model, that meeting the demands of pharmaceutical care will require changes and advanced skills in our staff. We continue to work in creating an environment where the concept of pharmaceutical care can flourish. Our department has focused on defining and then providing pharmaceutical care through individual practitioners and patient care teams. More employee empowerment with less management control was the key to facilitating initial phases in our pharmaceutical care model. A successful orientation process has further enhanced our abilities to hire new graduates and/or experienced practitioners for our open positions. We believe we have taken some significant first steps toward recruiting, training, and developing our staff to become competent and satisfied with their newly developing role as pharmaceutical care practitioners.

Clinical Competence↗
PubMed1987

Human hemoglobin cross-linked through the polyphosphate-binding site. Functional properties and evidence for conformers.

The properties of human hemoglobin reacted with 2-nor-2-formylpyridoxal 5'-phosphate, a bifunctional derivative of pyridoxal 5'-phosphate, have been investigated both from an equilibrium and kinetic point of view. The experimental data, interpreted in terms of the two-state allosteric model, indicate that a perturbed R state is characteristic of this modified low ligand affinity hemoglobin. In flash photolysis experiments, a quickly reacting component is always observed, in spite of the lack of dissociation into free dimers; this kinetic behavior is thought to reflect the presence of functionally independent alpha beta dimers, still connected by the flexible cross-link but forming an open hemoglobin tetramer. Two possible models for the interpretation of the kinetics of CO and/or haptoglobin binding are presented and discussed.

Hemoglobins↗
PubMed1997

An analysis of time-dependence for Chernobyl fallout in Italy.

We present here an analysis of the airborne radioactivity measured in Italy after the Chernobyl accident. We provide some quality assurance, isolate suspicious data, and devise a mathematical model to aid in interpreting time-dependent fallout data. The model consists of an interpolating function whose parameters can be related to 1) the arrival time of the radioactive cloud; 2) the time of the maximum radioactive concentration; and 3) the decay-rate of airborne radioactivity as the pollutant cloud passes. Multiple arrivals of the radioactive cloud in a given site can also be considered. The parametrization can be used to estimate concentrations of 137Cs using measurements of (131)I, 103Ru, or 132Te. The interpolating function is fitted to the data collected in several Italian Provinces. We feel this model is an useful tool for interpreting time-dependent fallout data.

Cesium Radioisotopes↗
PubMed2006

Resonant scattering and multiple Bragg X-ray diffraction in LaMnO3; a classical view.

The mechanism for resonant scattering in LaMnO(3) has been the subject of some controversy between two models. Model (A) is based on orbital ordering, whereas model (B) invokes the Jahn-Teller distortion. From the structural point of view, the two models lead to different d-electron densities. The forbidden reflection 300 is turned on by resonance, leading to a well defined scheme for the lobes of the Mn d electrons [model (A)]. It turns out that the same experimental results could have been interpreted according to model (B). The only difference is that this alternative interpretation would have required a structure factor F(300) of opposite sign. This is a typical example of a phase problem. An experimental technique has been applied for phase determination based on multiple Bragg scattering. This shows that the multiple-beam results are in agreement with model (B), not with model (A), laying to rest a long overdue controversy.

Journal Article↗
PubMed2000

Theoretical and experimental studies for the interpretation of vibrational circular dichroism spectra in the CH-stretching overtone region

Two theoretical models for the interpretation of the existing data of CH-stretching overtones' vibrational circular dichroism data are presented. The first model is based on the quantum mechanical Van Vleck contact transformation theory and is applied to the full vibrational problem, the second is based on classical trajectories calculations, by which we treat a simplified three-degrees of freedom Hamiltonian. The latter allows one to derive a qualitative but efficacious picture of the behavior of coupled anharmonic oscillators. In this framework, we analyze the Poincare Surfaces of Section, and calculate the Fourier Cross Spectra of coupled CH-stretchings. Values for the harmonic frequencies and anharmonicities are derived from absorption spectra in the near infrared on partially deuterated compounds. The effect of large amplitude, low-frequency puckering or twisting modes on the ensemble of coupled CH-stretching is taken into account. Copyright 2000 Wiley-Liss, Inc.

Journal Article↗
PubMed2001

Dynamic random effects models for times between repeated events.

We consider recurrent event data when the duration or gap times between successive event occurrences are of intrinsic interest. Subject heterogeneity not attributed to observed covariates is usually handled by random effects which result in an exchangeable correlation structure for the gap times of a subject. Recently, efforts have been put into relaxing this restriction to allow non-exchangeable correlation. Here we consider dynamic models where random effects can vary stochastically over the gap times. We extend the traditional Gaussian variance components models and evaluate a previously proposed proportional hazards model through a simulation study and some examples. Besides, semiparametric estimation of the proportional hazards models is considered. Both models are easily used. The Gaussian models are easily interpreted in terms of the variance structure. On the other hand, the proportional hazards models would be more appropriate in the context of survival analysis, particularly in the interpretation of the regression parameters. They can be sensitive to the choice of model for random effects but not to the choice of the baseline hazard function.

Animals↗
PubMedDate not supplied

Comparison of MLR, PLS and GA-MLR in QSAR analysis.

The use of the internet has evolved in quantitative structure-activity relationship (QSAR) over the past decade with the development of web based activities like the availability of numerous public domain software tools for descriptor calculation and chemometric toolboxes. The importance of chemometrics in QSAR has accelerated in recent years for processing the enormous amount of information in form of predictive mathematical models for large datasets of molecules. With the availability of huge numbers of physicochemical and structural parameters, variable selection became crucial in deriving interpretable and predictive QSAR models. Among several approaches to address this problem, the principle component regression (PCR) and partial least squares (PLS) analyses provide highly predictive QSAR models but being more abstract, they are difficult to understand and interpret. Genetic algorithm (GA) is a stochastic method well suited to the problem of variable selection and to solve optimization problems. Consequently the hybrid approach (GA-MLR) combining GA with multiple linear regression (MLR) may be useful in derivation of highly predictive and interpretable QSAR models. In view of the above, a comparative study of stepwise-MLR, PLS and GA-MLR in deriving QSAR models for datasets of alpha1-adrenoreceptor antagonists and beta3-adrenoreceptor agonists has been carried out using the public domain software Dragon for computing descriptors and free Matlab codes for data modeling.

Adrenergic alpha-Agonists↗
PubMed1995

A unified model for cell-killing by heat: interpretation of continuous, step-down, step-up and split heating.

We have already proposed a model for the lethal effects of heat on cells. In the model, a three-step process for cellular inactivation was hypothesized: 1) heating produces sublethal damage; 2) the damage is repaired in a certain time period; 3) the cell is inactivated when it undergoes cumulative sublethal damage to the extent that it cannot be repaired. Using the previous model, we investigated the modifications of the survival curve in 1) continuous heating, 2) step-down heating, 3) step-up heating, and 4) recovery from the thermal injury by split heating. These four phenomena were explained well with the mathematical model.

Animals↗
PubMed1998

How can mental models theory account for content effects in conditional reasoning? A developmental perspective.

This article proposes a modification to Johnson-Laird's mental models theory applied to the interpretation of conditional statement of the form 'if ... then'. The model suggests that this interpretation is based on the construction of mental models supplied by establishing a correspondence between the semantic spaces associated with the antecedent and consequent of the statements. The construction of the models and the interpretation of the statements would depend on the nature of the semantic spaces involved, the interpretative context and the subject's knowledge and processing capacity. Three experiments show that the interpretation of conditional rules depends, for example, on whether or not the conditional rule possess binary terms (e.g. boy/girl). The developmental approach makes it possible to reveal phenomena which tend to remain hidden in studies of adult functioning. We show that the model accounts for a number of the reasoning biases described in the literature as well as for the interpretation of various conditional forms which do not have a truth-functional meaning.

Adolescent↗
PubMed2003

Aging dynamics in globular proteins: summary and analysis of experimental results and simulation by a modified trap model.

Recent results of spectral diffusion experiments by spectral hole-burning techniques carried out at cryogenic temperatures on various monomeric heme proteins unequivocally show interesting new features of conformational dynamics of globular proteins that were not emphasized in the literature until now. These new aspects of the protein dynamics are anomalous diffusion and the aging effect. Here, using the similarities between proteins and glassy systems, we present a model which can interpret the line broadening and-through this effect-the aging phenomenon as well. Leaving untouched the widely accepted energy landscape (EL) concept for the general description of protein dynamics, we concentrate on the bottom of the funnel-like EL, because this part corresponds to the native state(s) at low temperature. We suggest that the overall shape of the EL at the lowest energy range is rather smooth, but on a finer scale it consists of traps. The dynamics is defined by sequential jumps among these traps and the process is described by a Master equation, where the hopping rate only depends on the parameters of the starting state. This model was adapted to interpret the common results of spectral diffusion experiments. We tested our model in the simplest case by computer simulation, and it shows excellent agreement with the experimental data. To our knowledge this is the first work where a theoretical interpretation of the aging dynamics of proteins is directly and quantitatively related to the experimental observations. We also show that the model, after the generalization that the traps are hierarchically organized, is in accordance with the concept of other well-known EL models.

Biophysical Phenomena↗
PubMed2004

Statistical analyses of repeated measures in physiological research: a tutorial.

Experimental designs involving repeated measurements on experimental units are widely used in physiological research. Often, relatively many consecutive observations on each experimental unit are involved and the data may be quite nonlinear. Yet evidently, one of the most commonly used statistical methods for dealing with such data sets in physiological research is the repeated-measurements ANOVA model. The problem herewith is that it is not well suited for data sets with many consecutive measurements; it does not deal with nonlinear features of the data, and the interpretability of the model may be low. The use of inappropriate statistical models increases the likelihood of drawing wrong conclusions. The aim of this article is to illustrate, for a reasonably typical repeated-measurements data set, how fundamental assumptions of the repeated-measurements ANOVA model are inappropriate and how researchers may benefit from adopting different modeling approaches using a variety of different kinds of models. We emphasize intuitive ideas rather than mathematical rigor. We illustrate how such models represent alternatives that 1) can have much higher interpretability, 2) are more likely to meet underlying assumptions, 3) provide better fitted models, and 4) are readily implemented in widely distributed software products.

Animals↗
PubMed2004

Excitations of incoherent spin-waves due to spin-transfer torque.

The possibility of exciting microwave oscillations in a nanomagnet by a spin-polarized current, as predicted by Slonczewski and Berger, has recently been demonstrated. This observation opens important prospects of applications in radiofrequency components. However, some unresolved inconsistencies are found when interpreting the magnetization dynamics within the coherent spin-torque model. In some cases, the telegraph noise caused by spin-currents could not be quantitatively described by that model. This has led to controversy about the need for an effective magnetic temperature model. Here we interpret the experimental results of Kiselev et al. using micromagnetic simulations. We point out the key role played by incoherent spin-wave excitation due to spin-transfer torque. The incoherence is caused by spatial inhomogeneities in local fields generating distributions of local precession frequencies. We observe telegraph noise with gigahertz frequencies at zero temperature. This is a consequence of the chaotic dynamics and is associated with transitions between attraction wells in phase space.

Computer Simulation↗
PubMed1990

The epidemiology of schistosome infections of snails: taking the theory into the field.

Most field studies of the epidemiology of schistosome infections of snails have been essentially descriptive in nature. Although much use has been made of epidemiological models in the interpretation of experimental studies of schistosome-snail interactions, the models have had restricted application outside the laboratory. Here, Mark Woolhouse and Steve Chandiwana make use of a theoretical framework in discussing current understanding of schistisome-snail epidemiological patterns in the field, and then consider the implications of the analysis for the control of schistosomiasis.

Journal Article↗
PubMedDate not supplied

Multimodel ranking and inference in ground water modeling.

Uncertainty of hydrogeologic conditions makes it important to consider alternative plausible models in an effort to evaluate the character of a ground water system, maintain parsimony, and make predictions with reasonable definition of their uncertainty. When multiple models are considered, data collection and analysis focus on evaluation of which model(s) is(are) most supported by the data. Generally, more than one model provides a similar acceptable fit to the observations; thus, inference should be made from multiple models. Kullback-Leibler (K-L) information provides a rigorous foundation for model inference that is simple to compute, is easy to interpret, selects parsimonious models, and provides a more realistic measure of precision than evaluation of any one model or evaluation based on other commonly referenced model selection criteria. These alternative criteria strive to identify the true (or quasi-true) model, assume it is represented by one of the models in the set, and given their preference for parsimony regardless of the available number of observations the selected model may be underfit. This is in sharp contrast to the K-L information approach, where models are considered to be approximations to reality, and it is expected that more details of the system will be revealed when more data are available. We provide a simple, computer-generated example to illustrate the procedure for multimodel inference based on K-L information and present arguments, based on statistical underpinnings that have been overlooked with time, that its theoretical basis renders it preferable to other approaches.

Evaluation Studies as Topic↗
PubMed1991

A compartmental model to analyze ruminal digestion.

In contrast to digestion models that include a discrete lag phase, a compartmental digestion model was proposed. It assumed the existence of a lag compartment and a digestion compartment. Substrate present in the digestion compartment was subject to first-order kinetics digestion. Flow of substrate from the lag compartment to the digestion compartment was proposed to be a first-order process and likely was affected by hydration of substrate, bacterial attachment, and colonization. The proposed model was compared with models that assumed the existence of a discrete lag phase. Parameter estimates for these models were obtained either through logarithmic transformation of data or nonlinear regression. Statistically, there was no difference between the compartmental model and the nonlinear model with a discrete lag phase. Differences in parameter estimates between these two models were small. Residual mean squares were higher for the logarithmically transformed models. Differences in parameter estimates between these models and the compartmental model depended on the structure of the experimental data. In a number of cases, the nonlinear parameters of the compartmental model converged to the same value, resulting in a different interpretation of the model. Residual mean squares for predicting rate of disappearance were lowest for the compartmental model.

Animals↗
PubMed2003

A probabilistic approach to interpreting verbal autopsies: methodology and preliminary validation in Vietnam.

AIMS: Verbal autopsy (VA) has become an important tool in the past 20 years for determining cause of death in communities where there is no routine registration. In many cases, expert physicians have been used to interpret the VA findings and so assign individual causes of death. However, this is time consuming and not always repeatable. Other approaches such as algorithms and neural networks have been developed in some settings. This paper aims to develop a method that is simple, reliable and consistent, which could represent an advance in VA interpretation. METHODS: This paper describes the development of a Bayesian probability model for VA interpretation as an attempt to find a better approach. This methodology and a preliminary implementation are described, with an evaluation based on VA material from rural Vietnam. RESULTS: The new model was tested against a series of 189 VA interviews from a rural community in Vietnam. Using this very basic model, over 70% of individual causes of death corresponded with those determined by two physicians increasing to over 80% if those cases ascribed to old age or as being indeterminate by the physicians were excluded. DISCUSSION: Although there is a clear need to improve the preliminary model and to test more extensively with larger and more varied datasets, these preliminary results suggest that there may be good potential in this probabilistic approach.

Autopsy↗