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At least 271 records · Page 15Linked to original sources
PubMed1999

Theoretical analysis of simultaneous mixed irradiation with multiple types of radiation.

A survival model Eq.1 was presented for cells irradiated simultaneously with multiple types of radiation using the extended Zaider-Rossi model, which is model for mixed irradiation with two types of radiation. [equation : see text] Eq.1. Where q(t)=2t0/t-2(t0/t)2 ¿1-exp(-t0/t)¿ Eq.2. Eq.1 was proved by mathematical induction using the concept that mixed irradiation with n types of radiation is considered as mixed irradiation with two types of radiation regarding n-1 types as one type of radiation. The model is not limited by the dose rate of radiation, because its effect is corrected by reduction factor Eq.2. The problem of the model is that Eq.2 was led assuming repair function to be exponential given by Eq.3. tau(t)=exp(-t/t0) Eq.3. However, the repair function is usually expressed by biphasic Eq.4 rather than monophasic Eq.3. tau(t)=Aexp(-t/01)+(1-A)exp(-t/t02) Eq.4. It is, therefore, important to keep in mind that Eq. 4 should be used instead of Eq.3.

Cell Physiological Phenomena↗
PubMedDate not supplied

[Effectiveness of an educational intervention in improving the self concept of second to sixth grade students].

This study evaluated the effectiveness of an intervention in improving the general, academic, physical and social self-concepts of 2nd to 6th grade students. The activities were carried out by the teachers during the 1992-93 school year. A questionnaire was completed by 271 students of the experimental school and by 467 students of the control school, both before and after the intervention. The multiple regression analyses showed important adjusted gains for self-concepts related to physical appearance, mathematics and relationship with parents. In all three cases, students with the largest deficit benefitted most from the intervention. This study shows that it is possible to improve self-concept and to do so through an intervention carried out in the school environment. This double finding is important to the promotion of psycho-social adaptation since self-concept is an important determinant and since few interventions have reached similar objectives.

Body Image↗
PubMed2003

A light distribution model for an internally radiating photobioreactor.

Analysis of light energy distribution in culture is important for maximizing the growth efficiency of photosynthetic cells and the productivity of a photobioreactor. To characterize the irradiance conditions in a photobioreactor, we developed a light distribution model for a single-radiator system and then extended the model to multiple radiators using the concept of parallel translation. Mathematical expressions for the local light intensity and the average light intensity were derived for a cylindrical photobioreactor with multiple internal radiators. The proposed model was used to predict the irradiance levels inside an internally radiating photobioreactor using Synechococcus sp. PCC 6301 as a model photosynthetic microorganism. The effects of cell density and radiator number were interpreted through photographic and model simulation studies. The predicted light intensity values were found to be very close to those obtained experimentally, which suggests that the proposed model is capable of accurately interpreting the local light energy profiles inside the photobioreactor system. Due to the simplicity and flexibility of the proposed model, it was also possible to predict the light conditions in other complex photobioreactors, including optical-fiber and pond-type photobioreactors.

Bioreactors↗
PubMed2007

3D in silico modeling of the human respiratory system for inhaled drug delivery and imaging analysis.

The efficacies of inhaled pharmacologic drugs could be improved if drugs could be targeted to appropriate sites within the human respiratory system. The spatial deposition patterns of particles can now be detected with a high degree of resolution using advanced techniques of imaging (e.g., SPECT). However, the effectiveness of such laboratory regimens has been limited by the inability to clearly identify airway composition within images. Therefore, we have developed a theoretical protocol to map airways within human lungs that is designed to be used in a complementary manner with laboratory investigations. The in silico model has two components: a mathematical model based on concepts of topology; and, a computer algorithm which tracks the millions of constituent lung airways. The in silico model produces 3D lung structures that are anatomically correct and can be customized to each patient. We have applied the protocol to a SPECT study where the interiors of lungs were partitioned into a series of ten nested shells. Airway composition in the respective shells provides a heretofore unavailable quantification of scintigraphy images. The protocol can be employed in a practical manner in the medical arena to aid in the interpretation of SPECT images, and to provide a platform for the design of human subject tests.

Administration, Inhalation↗
PubMed2005

Simultaneous radiofrequency (RF) heating and magnetic resonance (MR) thermal mapping using an intravascular MR imaging/RF heating system.

Previous studies have confirmed the possibility of using an intravascular MR imaging guidewire (MRIG) as a heating source to enhance vascular gene transfection/expression. This motivated us to develop a new intravascular system that can perform MR imaging, radiofrequncy (RF) heating, and MR temperature monitoring simultaneously in an MR scanner. To validate this concept, a series of mathematical simulations of RF power loss along a 0.032-inch MRIG and RF energy spatial distribution were performed to determine the optimum RF heating frequency. Then, an RF generator/amplifier and a filter box were built. The possibility for simultaneous RF heating and MR thermal mapping of the system was confirmed in vitro using a phantom, and the obtained thermal mapping profile was compared with the simulated RF power distribution. Subsequently, the feasibility of simultaneous RF heating and temperature monitoring was successfully validated in vivo in the aorta of living rabbits. This MR imaging/RF heating system offers a potential tool for intravascular MR-mediated, RF-enhanced vascular gene therapy.

Animals↗
PubMed2002

A mathematical analysis using fractals for binding interactions of nuclear estrogen receptors occurring on biosensor surfaces.

A mathematical approach using fractal concepts is presented for modeling the binding and dissociation interactions between analytes and nuclear estrogen receptors (ER) occurring on surface plasmon resonance biosensor chip surfaces. A kinetic knowledge of the binding interactions mediated by ER would help in better understanding the carcinogenicity of these steroidogenic compounds and assist in modulating these reactions. The fractal approach is applied to analyte-ER interaction data obtained from literature. Numerical values obtained for the binding and dissociation rate coefficients are linked to the degree of roughness or heterogeneity (fractal dimension, D(f)) present on the biosensor surface. For example, a single-fractal analysis is used to describe the binding and dissociation phases for the binding of estradiol and ERalpha in solution to clone 31 protein immobilized on a biosensor chip (C-S. Suen et al., 1998, J. Biol. Chem. 273(42), 27645-27653). The binding and the dissociation rate coefficients are 27.57 and 8.813, respectively, and the corresponding fractal dimensions are 1.986 and 2.268, respectively. In some examples dual-fractal models were employed to obtain a better fit of either the association or the dissociation phases or for both. Predictive relationships are developed for (a) the binding and the dissociation rate coefficients as a function of their respective fractal dimensions and (b) the ratio K(A) (= k/k(d)) as a function of the ratio of the fractal dimensions (D(f)/D(fd)). The analysis should provide further physical insights into the ER-mediated interactions occurring on biosensor and other surfaces.

Alitretinoin↗
PubMed2006

Grey parrot numerical competence: a review.

The extent to which humans and nonhumans share numerical competency is a matter of debate. Some researchers argue that nonhumans, lacking human language, possess only a simple understanding of small quantities, generally less than four. Animals that have, however, received some training in human communication systems might demonstrate abilities intermediate between those of untrained nonhumans and humans. Here I review data for a Grey parrot (Psittacus erithacus) that has been shown to quantify sets of up to and including six items (including heterogeneous subsets) using vocal English labels, to comprehend these labels fully, and to have a zero-like concept. Recent research demonstrates that he can also sum small quantities. His success shows that he understands number symbols as abstract representations of real-world collections, and that his sense of number compares favorably to that of chimpanzees and young human children.

Animals↗
PubMed2005

Monitoring of trophic chains.

In the paper simple trophic chains of the type resource-producer-primary consumer are considered. For an analysis of the dynamic state monitoring of this system, the concept of observability of mathematical systems theory is proposed. Using a linearization method of non-linear observation systems, biologically interpretable sufficient conditions are obtained to guarantee local observability. The latter means that based on the dynamic observation of a single component, the state of the whole system can be uniquely recovered, at least near a positive equilibrium.

Algorithms↗
PubMed1990

Verification of immune response optimality through cybernetic modeling.

An immune response cascade that is T cell independent begins with the stimulation of virgin lymphocytes by antigen to differentiate into large lymphocytes. These immune cells can either replicate themselves or differentiate into plasma cells or memory cells. Plasma cells produce antibody at a specific rate up to two orders of magnitude greater than large lymphocytes. However, plasma cells have short life-spans and cannot replicate. Memory cells produce only surface antibody, but in the event of a subsequent infection by the same antigen, memory cells revert rapidly to large lymphocytes. Immunologic memory is maintained throughout the organism's lifetime. Many immunologists believe that the optimal response strategy calls for large lymphocytes to replicate first, then differentiate into plasma cells and when the antigen has been nearly eliminated, they form memory cells. A mathematical model incorporating the concept of cybernetics has been developed to study the optimality of the immune response. Derived from the matching law of microeconomics, cybernetic variables control the allocation of large lymphocytes to maximize the instantaneous antibody production rate at any time during the response in order to most efficiently inactivate the antigen. A mouse is selected as the model organism and bacteria as the replicating antigen. In addition to verifying the optimal switching strategy, results showing how the immune response is affected by antigen growth rate, initial antigen concentration, and the number of antibodies required to eliminate an antigen are included.

Animals↗
PubMed2000

Modelling the production of nitric oxide within the human airways.

The measurement of exhaled nitric oxide (NO) is well established for monitoring of airway inflammation in bronchial asthma. It is known that the concentration of NO determined as steady state (plateau) value at a constant expiratory flow rate depends on the flow rate chosen. This suggests that the exhaled NO is released within the conducting airways, whereas alveolar NO levels are negligible. The processes involved can be described through a lung model comprising an alveolar compartment and an airway compartment thought of as a pipe. This concept has been formulated mathematically and the models proposed in the literature are essentially equivalent. NO plateau levels obtained at different flow rates allow the estimation of 1) an effective airway wall NO concentration that represents the driving force for NO release, 2) an airway diffusing capacity for NO which depends on factors impeding or facilitating NO transport, including an increase in NO-producing surface area. Clinical studies will have to assess whether the knowledge of these or related parameters offers a significant advantage over the determination of exhaled NO at a single flow rate.

Biological Transport↗
PubMed1989

Numerical competence in a chimpanzee (Pan troglodytes).

A chimpanzee (Pan troglodytes), trained to count foods and objects by using Arabic numbers, demonstrated the ability to sum arrays of 0-4 food items placed in 2 of 3 possible sites. To address representational use of numbers, we next baited sites with Arabic numbers as stimuli. In both cases performance was significantly above chance from the first sessions, which suggests that without explicit training in combining arrays, the animal was able to select the correct arithmetic sum for arrays of foods or Arabic numbers under novel test conditions. These findings demonstrate that counting strategies and the representational use of numbers lie within the cognitive domain of the chimpanzee and compare favorably with the spontaneous use of addition algorithms demonstrated in preschool children.

Animals↗
PubMed1999

Chaos, but in voting and apportionments?

Mathematical chaos and related concepts are used to explain and resolve issues ranging from voting paradoxes to the apportioning of congressional seats.

Journal Article↗
PubMed1997

CT measurement of anteversion in the femoral neck. The influence of femur positioning.

PURPOSE: To evaluate CT methods of measuring anteversion in the femoral neck with respect to measurement accuracy and with respect to the influence exerted by different femoral shaft positions; and to describe a new CT measurement concept that introduces a mathematical adjustment for different femoral shaft positions. The new technique facilitates the taking of measurements in patients who cannot be correctly positioned in traditional methods. MATERIAL AND METHODS: CT examinations of previously measured anteversions in the femoral neck were reviewed in retrospect in 30 patients with fractures of the femoral neck. The position of the femoral shaft was assessed. A reference angle was compared with direct traditional measurements and with measurements adjusted for the actual position of the femoral shaft by means of a 3D mathematical reconstruction. Reproducibility and inter- and intraobserver variability were assessed in 10 cases. RESULTS: All femurs varied in position within the gantry. The mean difference between the direct CT measurement and the adjusted CT measurement compared to the reference angle were -8.8 degrees (range -35.0-16.3 degrees) and -0.1 degrees (range -1.4-1.4 degrees), respectively. For the adjusted CT method, reproducibility and inter- and intraobserver variability were 1.4 degrees, 1.6 degrees and 1.4 degrees (SD of difference), respectively. CONCLUSION: CT measurement of femoral anteversion in clinical practice can only be accurate when corrected for variation in the position of the femoral shaft.

Aged↗
PubMed2005

An integrated addition and interaction model for assessing toxicity of chemical mixtures.

The high propensity for simultaneous exposure to multiple environmental chemicals necessitates the development and use of models that provide insight into the toxicity of chemical mixtures. In this study, we developed a mathematical model that combines concepts of concentration addition, response addition, and toxicokinetic chemical interaction to assess toxicity of chemical mixtures. A ternary mixture of acetylcholinesterase inhibiting organophosphates (malathion and parathion) and the P450 inhibitor piperonyl butoxide was used to model toxicity. Concentration-response curves were generated for individual chemicals as well as for mixtures of the chemicals using acute toxicity tests with Daphnia magna. The toxicity of binary combinations of malathion and parathion adhered to the principles of concentration addition. The contribution of piperonyl butoxide to mixture toxicity was integrated using a model for response addition. Piperonyl butoxide also modified the toxicity of the organophosphates by inhibiting their metabolic activation. The antagonistic effects of piperonyl butoxide towards the organophosphates were quantified as coefficients of interactions (K-functions) and incorporated into the mixture model. Finally, toxicity of the ternary mixture was modeled at 30 different mixture formulations using three additive models that assumed no interaction (concentration addition, response addition, and integrated addition) and using the integrated addition and interaction (IAI) model. Toxicity of the 30 mixtures was then experimentally determined and compared to model results. Only the IAI model accurately predicted the toxicity of the mixtures. The IAI model holds promise as a means for assessing hazard of complex chemical mixtures.

Acetylcholinesterase↗
PubMed1985

Radon entry into houses having a crawl space.

The transport of 222Rn from soil, through a vented crawl space, and into the living space of single-family residences was studied. Two houses were monitored in detail for periods of 5 and 7 weeks. With crawl space vents open, the average indoor 222Rn concentrations were 1.2 and 0.6 pCi 1.-1 (44 and 22 Bq m-3); with the vents sealed the averages rose to 2.2 and 1.0 pCi 1.-1 (81 and 37 Bq m-3). The data suggest that, of the Rn released into the crawl space from the soil beneath the house, a significant fraction, perhaps 50% or more, enters the living space. The effect of 3 meteorological parameters--wind speed, indoor-outdoor temperature difference, and rate of barometric pressure change--on Rn concentration and entry rate were examined. In 1 of the houses a higher temperature difference corresponded to a higher indoor concentration, suggesting that the increased infiltration rate is more than compensated by an increase in the Rn entry rate. On the other hand, a high wind speed tended to reduce the indoor concentration, presumably by increasing both cross-ventilation of the crawl space and the infiltration rate of the living space. Results suggest that Rn transport into the crawl space of at least 1 of the houses occurred by pressure-driven flow, rather than solely by molecular diffusion. The diffusion coefficient of 222Rn through polyethylene sheeting, such as was present on the ground beneath this house, was measured in the laboratory and found to range from 0.65 X 10(-7) cm2 s-1 at 11 degrees C to 1.6 X 10(-7) cm2 s-1 at 25 degrees C, implying that the maximum diffusive flux through the sheet was many times smaller than that necessary to account for the rate of Rn entry into the house. A third house was studied using a tracer gas injected into the crawl space at a controlled rate. The fraction of air leaving the crawl space that entered the living space ranged from 0.3 to 0.65, in good agreement with results for Rn transmission in the other 2 houses, assuming that the 222Rn flux into the crawl space was comparable to that which would have resulted from molecular diffusion from soil having a 222Rn diffusion length of 1.0 m. By sealing leaks in the floor of this house, the average infiltration rate was reduced by 25%, but the indoor concentration of the tracer gas remained constant.

Air Pollutants↗
PubMed1985

The limitations of atmospheric dispersion data and their contribution to uncertainties in dose assessment.

The calculation of atmospheric dispersion patterns is often an important component of radiation dose estimates. These dispersion calculations are a possible source of error and such errors or uncertainties need to be quantified. An important source of uncertainty is the meteorological data used in the calculations. Such data may be less than ideal because of constraints imposed by both availability and by the variances associated with population from which the data are obtained. We have studied a simple and much used model of atmospheric dispersion--the Gaussian plume. We discuss the uncertainties on the meteorological data which are input to the model and how these uncertainties could be used to estimate uncertainties for the modeling results. In doing this we have addressed both the uncertainty associated with a recorded climatology and the added uncertainty arising from the year-to-year variability at any given location.

Air Pollution, Radioactive↗
PubMed1988

The inhalation hazard of radioactive fallout.

The inhalation hazard of fallout particles from a nuclear ground burst has been evaluated with the ICRP Task Group Lung Model and the DELFIC fallout model for the 0.5-kt to 10-Mt yield range. It was found that for the conditions considered in this work, the inhalation of fallout particles does not present a significant radiological hazard.

Environmental Exposure↗