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PubMed1983

A preliminary model of double-minute-mediated gene amplification.

A mathematical model of double minute (dm) population dynamics has been developed based upon current concepts of the saltatory replication, random partitioning, nuclear exclusion and loss, and cellular growth inhibition of these extrachromosomal elements. A highly accurate approximate analytical solution has been obtained for the dm frequency distribution at steady state and preliminary analysis of transient states has been performed. The steady state solution has been fit to experimental frequency data of the SW527N carcinoma line, the excellent goodness of fit (X2 = 2.6, d.f. = 29) providing preliminary evidence for the consistency of this set of mechanisms. Two special cases are examined in which extrareplicative dms are produced on both the chromosome and existing dms at equal rates or on the chromosome alone. The model predicts that the population--average rate of extrareplicative dm production is 0.039 +/- S.E. 0.009 dms/hr/cell in the first case and is tenfold higher than when such replication occurs on the chromosome alone (0.0043 +/- S.E. 0.0004 dms/hr/cell). Allowable ranges of the extent of dm-related growth inhibition and dm loss are determined for the SW527N cell line. It is found that dm-related growth inhibition can be nearly as high as that observed for the S180 sarcoma lines (on the order of 0.5% per dm lengthening of the doubling time) or as low as zero.

Animals↗
PubMed1995

Comparative characterization of the fermentation pathway of Saccharomyces cerevisiae using biochemical systems theory and metabolic control analysis: steady-state analysis.

In the preceding paper in this issue, we have shown that metabolic control analysis and biochemical systems theory use the same experimental information to describe a metabolic system. In this paper, we analyze the steady-state properties of this pathway by applying both methods. Our results show the correspondence of the steady-state characterizations and illustrate the relationships between the different nomenclatures used. With both approaches, we identify metabolite pools that are strongly influenced by changes in enzyme concentration when cells are immobilized at pH 5.5. In the final paper of this series, which follows, we discuss the need to assess the quality of a model and the potential difficulties that may arise if the steady-state characterization is accepted without testing its quality. We then validate the different models using parameter sensitivity concepts.

Fermentation↗
PubMed1990

Elements of the dioptric power matrix and the concept of torsional power: a reinterpretation.

The elements of the dioptic power matrix have previously been interpreted in terms of power along particular meridians with the off-diagonal elements interpreted as a new form of dioptric power called torsional power. This paper shows that such new concepts are not necessary. Decomposition of the matrix provides an interpretation in terms that are quite familiar. The elements represent three component powers: the diagonal elements are two cylinders and the off-diagonal elements a crossed-cylinder with axes at 45 degrees and 135 degrees. The component crossed-cylinder obviates the need for the concept of torsional power. The concept of meridional power is avoided.

Mathematics↗
PubMed1977

Intermittent mandatory ventilation. A method to expand clinical applications.

The described modification of the Cameco URS-701 ventilator increases the frequency possibilities from zero to 40, without interfering with the ventilator pattern of each cycle and satisfies the required conditions for a classical IMV-system. Moreover it can provide longer periods of controlled ventilation alternating with periods of spontaneous respiration. This adaptation, mainly consisting of the introduction of a timer in the electrical circuit of the machine, provides us with a safe IMV system on our Engstrom 150 type ventilator and leads to a broader concept of IMV.

Humans↗
PubMed2003

Computer-assisted simulations in orthodontic diagnosis and the application of a new cone beam X-ray computed tomography.

Computational simulations which include three-dimensional (3-D) image processing and biomechanical calculations should provide useful information to our research and orthodontic clinic as a clinical tool defined as 'thinking'. In this review, 1) biomechanical simulations applied to predict the mandibular growth; 2) mathematical models of virtual bone cells and 3) 3-D images and solid model simulations for surgical planning are introduced. In biomechanical simulation, biting force, electromyographic (EMG) activity and cephalograms of 32 subjects were applied. Computational results of mathematical model were compared with actual bone growth in a rat. Three-dimensional image and solid model of 14 patients were utilized for their treatment planning. From the results, several concepts of our simulations were confirmed: 1) reaction forces generated by masticatory muscles at the condyle control the direction of mandibular growth; 2) some mathematical models have the possibility to describe the process of bone growth; 3) 3-D image processing software and solid models are necessary for diagnosis and planning of orthognathic surgery. We also believe that the orthodontists can more accurately predict the affects of surgical procedures and orthodontic tooth movement using the new cone beam X-ray computed tomography (CT) (CB MercuRay; Hitachi Medico Technology, Tokyo, Japan) and its advanced application software.

Animals↗
PubMed1992

Teaching statistics to health professionals: the legal analogy.

Despite the importance of statistical concepts to health professionals, the teaching of statistics to students from this field has generally been unrewarding. We feel that a few central concepts are crucial to all statistical thinking and that, for most health professionals, the communication of these is more important than learning about complex mathematical models. A device for demonstrating the parallels between a criminal legal trial and statistical hypothesis testing is presented. We feel that it can facilitate the learning of this central statistical concept.

Curriculum↗
PubMed1979

Induction/catastrophe theory: a behavioral ecological approach to cognition in human individuals.

Gibson's (1966) ecological formulation of perceptual processes as abstracted systems, the tenets and units of neobehaviorism as formulated within psychobiology and the experimental analysis of behavior, and the topological approaches of mathematical biology as formulated by Rashevsky (1951, 1960) and Thom (1975) are the elemental concepts that form the basis of the theory presented in this paper. A cognitive or decision process of individual human beings--living systems at the organism level--emerges as a one-step, match-contrast, serial pattern embedded as a triplet of Gibson frames in five-dimensional butterfly catastrophe. Some of the experimental, clinical and philosophical implications of a "catastrophic" formulation of induction are discussed.

Behaviorism↗
PubMed1990

Cognitive and hemispheric inversions when learning nonstandard arithmetic.

Understanding the proofs of compactness theorems regarding the consistency of the existence of infinite or infinitesimal numbers was found to be related to the dominance of the left cerebral hemisphere over the right one. This phenomenon is not weakened when learning, the compactness theorem is followed by learning about internal and external sets, which is also related to such a dominance. However, when the learning of the compactness theorem is followed by learning about monads and galaxies instead of internal and external sets, the understanding of the consistency of the existence of the infinite or infinitesimal numbers was found to be related to the dominance of the right cerebral hemisphere over the left one. A cognitive and neuropsychological model is given to explain these phenomena.

Adult↗
PubMed2002

The cognitive-behavioral model of bulimia nervosa: a direct evaluation.

OBJECTIVE: This study represented the first attempt to directly evaluate Fairburn et al's (1986) cognitive-behavioral model of bulimia nervosa--the model on which the most widely used treatment for bulimia nervosa is based. METHOD: The major predictions of the model were tested using structural equation modeling. Data were collected from the responses of 526 subjects to a number of self-report measures. RESULTS: The factors of self-esteem, overconcern with weight and shape, and dietary restraint accounted for a large proportion of the variance in binge eating and purging. The key pathway in the model was the link between overconcern with weight and shape and the adoption of purgative behaviors, which then fed into a vicious cycle of binge eating and purging. Contrary to Fairburn's hypothesis, high levels of dietary restraint did not predict increased binge eating. DISCUSSION: The results suggest that the components of Fairburn's model may operate to maintain the bulimic cycle in a slightly different way to that originally proposed.

Body Image↗
PubMed2000

On estimating the probability of aperiodic outbursts of microbial populations from their fluctuating counts.

The irregular sequence of counts of a microbial population, in the absence of observable corresponding environmental changes (e.g., temperature), can be regarded as reflecting the interplay of several unknown or random factors that favor or inhibit growth. Since these factors tend to balance one another, the fluctuations usually remain within bounds, and only by a coincidence--when all or most act in unison--does an 'outburst' occur. This situation can be represented mathematically as a sequence of independent random variables governed by a probability distribution. The concept was applied to reported microbial counts of ground meat and wastewater. It is found that the lognormal distribution could serve as a model, and that simulations from this model are indistinguishable from actual records. The parameters of the lognormal (or other) distribution can then be used to estimate the probability of a population outburst, i.e., an increase above a given threshold. Direct estimation of the outburst probability based on frequency of occurrence is also possible, but in some situations requires an impractically large number of observations. We compare the efficiency of these two methods of estimation. Such methods enable translation of irregular records of microbial counts into actual probabilities of an outburst of a given magnitude. Thus, if the environment remains 'stable' or in dynamic equilibrium, the fluctuations should not be regarded merely as noise, but as a source of information and an indicator of potential population outbursts even where obvious signs do not exist.

Animals↗
PubMed2001

Preservice Teachers' Self-Esteem and Mathematics Achievement.

The purpose of this article is to examine the relationship between preservice teachers' general self-esteem and mathematics achievement through the inclusion of variables that are supported by recent research in psychology and social cognitive theory. A structural equation model is used to examine the paths from mathematics achievement to general self-esteem and vice versa. To this end, the concepts of self-esteem and the relationships between self-esteem and academic achievement are first explained, followed by a description of the baseline model that was used for the analysis of the data. The methodology of the study, with emphasis on the description of the intervening variables, is then summarized. Last, the results of the study are discussed and conclusions are drawn from the main findings. Copyright 2001 Academic Press.

Journal Article↗
PubMed1995

Proof construction: adolescent development from inductive to deductive problem-solving strategies.

Inductive and deductive approaches to the construction of problem-solving proofs were examined using a task that requires the discovery of a geometrical figure hidden behind a series of covers. It was proposed that during adolescence, with the acquisition of a formal reasoning competence (as measured by Overton's [1990] version of Wason's selection task), there would be a transition from inductive to deductive proof construction strategies. One hundred adolescents were assessed on both the problem-solving proof task and the reasoning competence is associated with taking a deductive approach to proof construction. Formal reasoners tend to construct a proof based on the use of a falsification strategy as demonstrated by their search for disconfirming instances. A nonformal level of competence on the other hand is associated with inductive approaches. In this situation nonformal subjects tend to employ a verification strategy as demonstrated by the generation of redundant information. Results support the hypothesis that there is a cognitive developmental progression from an inductive approach to the construction of proofs to a deductive approach.

Adolescent↗
PubMed1999

Calculations of multipulse sequence in NQR of spins 32.

The general formalism of the interaction representation with respect to an operator which is its own inverse is developed and applied to pure NQR of spins I = 32. Under the assumption of no relaxation and no dipolar coupling, it is shown that the calculation of the response to pure NQR multipulse sequences can be performed with the same concepts used in high field NMR, such as coherence pathways. All the tools and mathematical expressions to predict the time evolution of the signal created by a pure NQR multipulse sequence are presented explicitly. It takes into account the off-resonance irradiation as well as the angular dependence of the excitation and detection for every value of the electric field gradient asymmetry parameter. Particular attention is devoted to the powder average, which is performed via a probability function derived analytically for the first time, leading to a drastic reduction of simulation times. The theory is illustrated by the study of the optimization and excitation bandwidths of one- to three-pulse sequences and compared to experimental results on Chloranil. We show that the three-pulse "stimulated echo" sequence gives a more uniform excitation profile than the traditional two-pulse echo sequence for powder samples. Thus, the "stimulated echo" sequence could be useful to cover a large spectrum when the experiment duration, or the signal to noise ratio, are not critical parameters. Analytical expressions for the nutation spectra obtained by one or two-pulse sequences are also derived for the first time.

Chloranil↗
PubMed1990

Effect of alcohol on perceived exertion in relation to heart rate and blood lactate.

The purpose of the study was to determine whether the perception of exertion is affected by alcohol during physical performance and whether altered self-rating of exertion is the result of an altered perception per se or of an altered physical capacity to perform work. Ten healthy men participated. Each subject was his own control and received an alcohol dose corresponding to 1 g.kg-1 body mass in 40% solution in the experimental session. The exercise test was performed on a cycle ergometer with an initial intensity of 50 W which was increased stepwise by 50 W at 4-min intervals up to near-maximal. The rating of perceived exertion (RPE) did not differ between alcohol and control sessions. Alcohol induced a significant increase in heart rate during exercise at 50 W (delta x = 8 beats.min-1) and at 100 W (delta x = 10 beats.min-1), while the change at higher intensities was insignificant. The systolic blood pressure and the blood lactate concentration were not significantly changed by alcohol. It is concluded that a moderate dose of alcohol does not alter RPE during physical exercise either per se or secondarily to an altered physical capacity to perform work.

Adult↗
PubMed1986

The concept of visual field indices.

Statistical methods for the evaluation of quantitative visual fields are presented in addition to a mathematical description of the calculation of different visual field indices. The "mean defect" is important for diffuse damage as well as for follow-up in advanced stages. "Short-term fluctuation" provides information about the reliability of the results as well as about possible early damage. "Corrected loss variance" quantifies local defects in an early stage; it also separates real local defects from increased scatter. "Skewness" is a test for very early local defects, and "spatial correlation" provides a measurement of the clustering of any local defects that may be present.

Humans↗
PubMed1988

Developmental functions for speeds of cognitive processes.

In Experiment 1, 8- to 21-year-olds were tested on a visual search task in which they determined whether a target digit was present in a set of one to five digits and a memory search task in which they determined whether a target digit was a member of a previously presented set of one to five digits. Increases with age in speeds of visual and memory search were both described well by exponential functions, and the rate of developmental change was similar for the two processes. In Experiment 2, 8- to 22-year-olds were tested on a memory search task, a mental rotation task in which they judged whether a stimulus presented in various orientations was a letter or a mirror image of a letter, an analogical reasoning task in which they judged whether sets of pictures were related to one another according to the same rule, and a mental addition task in which they judged the accuracy of problems such as 2 + 3 = 6. Here, too, for three of the four tasks developmental change was described well by exponential functions with a common rate of change. Results are interpreted in terms of a central mechanism that limits speeded performance and that changes with age.

Adolescent↗