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PubMed2006

Multivesicular release at developing Schaffer collateral-CA1 synapses: an analytic approach to describe experimental data.

We developed and analytically solved a simple and general stochastic model to distinguish the univesicular from the multivesicular mode of glutamate release. The model solution gives analytical mathematical expressions for average values of quantities that can be measured experimentally. Comparison of these quantities with the experimental measures allows one to discriminate the release mode and to determine the most probable values of model parameters. The model has been validated at glutamatergic CA3-CA1 synapses in the hippocampus from newborn (P1-P5 old) rats. Our results strongly support a multivesicular type of release process requiring a variable pool of immediately releasable vesicles. Moreover, computing quantities that are functions of the model parameters, the mean amplitude of the synaptic response to the release of a single vesicle (q) was estimated to be 5-10 pA, in very good agreement with experimental findings. In addition a multivesicular type of release was supported by the following experimental evidences: 1) a high variability of the amplitude of successes, with a coefficient of variation ranging from 0.12 to 0.73; 2) an average potency ratio a2/a1 between the second and first response to a pair of stimuli >1; and 3) changes in the potency of the synaptic response to the first stimulus when the release probability was modified by increasing or decreasing the extracellular calcium concentration. Our results indicate that at Schaffer collateral-CA1 synapses of the neonatal rat hippocampus a single action potential may induce the release of more than one vesicle from the same release site.

Action Potentials↗
PubMed2006

High-gain Brillouin amplification: an analytical approach.

We derive a closed-form approximate analytical formula for the gain of a Brillouin fiber amplifier operating in the depleted pump regime. We take into account the material loss of the medium, which is a strong effect in optical fibers. We validate obtained results numerically and experimentally. The presented analysis can be used to accurately predict the performance of high-gain Brillouin fiber amplifiers.

Journal Article↗
PubMed2003

Analytical approach for description of ion motion in quadrupole mass spectrometer.

Implementation of the analytical method of the solution of the Mathieu equation in conjunction with the algebraic presentation of Mathieu functions is discussed in this work. This approach is used for the analytical expression of fundamental properties of the quadrupole field such as ion trajectory stability and transmission. Extensive comparison with the matrix method is presented with demonstration of the fundamental advantages of the analytical method. However, contrary to the matrix method, the analytical method is limited to the cos trapping waveforms.

Energy Transfer↗
PubMed2001

A new approximate analytical approach for dispersion relation of the nonlinear Klein-Gordon equation.

A novel approach is presented for obtaining approximate analytical expressions for the dispersion relation of periodic wavetrains in the nonlinear Klein-Gordon equation with even potential function. By coupling linearization of the governing equation with the method of harmonic balance, we establish two general analytical approximate formulas for the dispersion relation, which depends on the amplitude of the periodic wavetrain. These formulas are valid for small as well as large amplitude of the wavetrain. They are also applicable to the large amplitude regime, which the conventional perturbation method fails to provide any solution, of the nonlinear system under study. Three examples are demonstrated to illustrate the excellent approximate solutions of the proposed formulas with respect to the exact solutions of the dispersion relation. (c) 2001 American Institute of Physics.

Journal Article↗
PubMed1981

Operability of nuclear instruments for medical use in developing countries. A decision-analytic approach.

Nuclear technology in diagnostic medicine has become a world-wide phenomenon. One of the problems encountered in implementing this technology in developing countries is predicting the operability of nuclear instruments under local conditions of maintenance and use. Our approach to this problem employs an analytic method often applied in medical decision making, and which can be incorporated into schemes for evaluating the total diagnostic process which utilizes nuclear technology. A recent survey of nine types of nuclear instruments in medical use in eight countries in Southeast Asia provided comprehensive information on the application and maintenance of these instruments, as well as a detailed record of actual operability and use of these instruments over a six-month period. A multivariate statistical analysis for predicting the operability of these instruments was carried out with some of the survey data. Responses to a set of 14 potentially important attributes of instrument use and maintenance obtained from the survey data were used to estimate the posterior probabilities of an instrument being inoperable for more than a given total number of hours in the six-month period during which operability was required. The posterior probabilities were determined by means of both Bayesian and discriminant analysis and summarized in the form of receiver operating characteristic (ROC) curves. Among a number of possible interpretations of the results, the analysis suggests that attributes generally involving installation, documentation, environment, and personnel training appear to be particularly important in predicting the operability of the instruments surveyed.

Decision Making↗
PubMed2005

Analytical approach to the MR signal.

In this work, an analytical evaluation of the MR signal is presented using the principle of reciprocity for any transmit and receive probe(s) with general geometrical structure(s). It is shown that the excitation of the spins cannot be explained using the principle of reciprocity in its standard form due to the asymmetry in the permeability tensor of the transverse magnetization. In the reception problem, the standard form of the principle of reciprocity is then utilized to calculate the NMR signal. As expected, the analysis shows that the strength of the NMR signal is a function of the receive coil's (fictitious) circularly polarized component of the field that poses an opposite sense of rotation to that corresponding with the excitation field, produced by the same coil, if it were to be used for excitation.

Magnetic Resonance Imaging↗
PubMed2005

Analytical approaches to expanding the use of capillary electrophoresis in routine food analysis.

Capillary Electrophoresis (CE) is becoming an ever more powerful analytical technique for the separation, identification, and quantification of a wide variety of compounds of interest in many application fields. Particularly in food analysis this technique can offer interesting advantages over chromatographic techniques because of its greater simplicity and efficiency. Nevertheless, CE needs to advance with regard to compatibility with sample matrices, sensitivity, and robustness of the methodologies in order to gain even wider acceptance in food analysis laboratories, specially for routine work. This article presents various approaches to expanding the analytical usefulness of CE in food analysis, discussing their advantages over conventional CE. These approaches focus on sample screening, automated sample preparation with on-line CE arrangements, and the automatic integration of calibration in routine analytical work with CE.

Automation↗
PubMed1999

Analytical approach to time lag in binary nucleation.

We present an analytical formula for the time required to establish steady state in a nucleating binary system. To test our solution, we evaluate the time lag for a range of activities of both components at the vapor-liquid transition, and show that our result is in much better agreement with a purely numerical simulation than other available analytical formulas, which overestimate the time lag by factors of from 2 to 200.

Journal Article↗
PubMed2005

Cost-efficacy of imatinib versus allogeneic bone marrow transplantation with a matched unrelated donor in the treatment of chronic myelogenous leukemia: a decision-analytic approach.

STUDY OBJECTIVE: To develop and populate a decision-analytic model for comparing the 2-year cost and efficacy of imatinib versus allogeneic bone marrow transplantation (BMT) with a matched unrelated donor in the treatment of a 35-year-old man with newly diagnosed, Philadelphia chromosome-positive (Ph[+]) chronic myelogenous leukemia (CML) in the chronic phase. DESIGN: Markov cohort analysis and first-order Monte Carlo microsimulation. MEASUREMENTS AND MAIN RESULTS: Direct medical costs were measured from the perspective of a third-party payer. Efficacy data and probabilities were obtained from survivability findings, most of which were derived from randomized controlled trials. We employed a 2-year time horizon with 3-month treatment cycles. The comparator was BMT with a matched unrelated donor, and the base case was defined as a 35-year-old, Ph(+) man with newly diagnosed CML. The Monte Carlo microsimulation indicated that the incremental cost:efficacy ratio was -$5000 for imatinib (95% confidence interval -$70,000-84,000). Analysis of the cost-efficacy plane revealed that imatinib was dominant over BMT in 84.69% of cases, whereas BMT dominated imatinib in 0.76% of cases. Trade-offs were warranted in the remaining cases. Sensitivity analyses of costs and discount rates found these results to be generally robust. CONCLUSION: In most cases, imatinib was both less costly and more efficacious than BMT in the 2-year treatment of CML. Results of this investigation should be viewed in the context of emerging long-term clinical data. These data are necessary to assess cost-efficacy beyond the short-term time horizon of this study.

Adult↗
PubMed2004

Analytical approach to localized structures in a simple reaction-diffusion system.

We study from an analytical point of view a simple reaction-diffusion model, which admits stable oscillating localized structures as a consequence of the coexistence between a stable limit cycle and a stable fixed point. Using a generalized matching approach we are able to find approximate analytical expressions for localized oscillating structures in this reaction-diffusion model capturing all the essential ingredients of these breathing particlelike solutions.

Diffusion↗
PubMed1984

An analytic approach to resolving problems in medical ethics.

Education in ethics among practising professionals should provide a systematic procedure for resolving moral problems. A method for such decision-making is outlined using the two classical orientations in moral philosophy, teleology and deontology. Teleological views such as utilitarianism resolve moral dilemmas by calculating the excess of good over harm expected to be produced by each feasible alternative for action. The deontological view focuses on rights, duties, and principles of justice. Both methods are used to resolve the 1971 Johns Hopkins case of a baby born with Down's syndrome and duodenal atresia.

Decision Making↗
PubMed1994

[Integration of geographic and analytical approach in environmental epidemiology].

Some developments of research in environmental epidemiology are reviewed, with special emphasis on the limitations of currently adopted methods. At the light of causal criteria commonly used in the evaluation of epidemiologic studies, an approach based on the integration of geographic and analytic studies is suggested, in order to obtain results relevant in terms of public health.

Environmental Health↗
PubMed2006

Analytic approach to the evolutionary effects of genetic exchange.

We present an approximate analytic study of our previously introduced model of evolution including the effects of genetic exchange. This model is motivated by the process of bacterial transformation. We solve for the velocity, the rate of increase of fitness, as a function of the fixed population size, N. We find the velocity increases with ln N, eventually saturating at an N which depends on the strength of the recombination process. The analytical treatment is seen to agree well with direct numerical simulations of our model equations.

Journal Article↗
PubMed1998

A decision analytic approach to commissioning ambulance cardiac services.

The paper discusses how a decision analytic framework has been used by an English health authority in relation to the commissioning of ambulance cardiac services. Strategies for the management by ambulance personnel of victims of cardiac arrest and persons with acute chest pain of cardiac origin were modelled in a decision-event tree, and a bibliographic database established. The international research literature prior to 1997 was searched in order to derive probability values for the tree. However, after checking whether the subgroupings of results in the papers were in accordance with the variables in the tree, the number of useful papers on acute chest pain was found to be only two. In the almost complete absence of information--even from small observational studies--on the management of the great majority of patients with cardiac symptoms transported by ambulance, the local ambulance service and the main providers of hospital services in the district are now collaborating in field studies of cardiac care in order to improve the inputs into the model.

Algorithms↗
PubMedDate not supplied

Decision analytic approach to the management of gonorrhea contacts.

We used a combination of decision analytic and modeling techniques in constructing a model for study of the management of an asymptomatic woman presenting to a sexually transmitted disease clinic as a contact of a man with gonorrhea. Total cost (physical, emotional, and economic) is expressed in units of dysutility. Initially the probabilities and "costs" of anogenital gonorrhea, incubating syphilis, carriage of the agents of nongonococcal urethritis, and coincident pharyngeal gonorrhea are considered; complications and sequelae are then accounted for. The best strategy is to culture for Neisseria gonorrhoeae, treat immediately with tetracycline, and follow up sexual partners if the culture is positive. Dysutility values calculated for the strategies of just treating with standard regimens of tetracycline, procaine penicillin, or amoxicillin are 288, 310, and 560, respectively. Sensitivity analyses show that the most important factors in determining optimal strategy are the probabilities and costs associated with the patient's carriage of the agents of nongonococcal urethritis. In order for this decision to change, the dysutility value for nongonococcal urethritis would have to decrease to 17% of our best estimate, or the overall prevalence of nongonococcal urethritis would have to be reduced to 16% of our best estimate.

Costs and Cost Analysis↗
PubMed2002

Analytical approach to viscous fingering in a cylindrical Hele-Shaw cell.

We report analytical results for the development of the viscous fingering instability in a cylindrical Hele-Shaw cell of radius a and thickness b. We derive a generalized version of Darcy's law in such cylindrical background, and find it recovers the usual Darcy's law for flow in flat, rectangular cells, with corrections of higher order in b/a. We focus our interest on the influence of the cell's radius of curvature on the instability characteristics. Linear and slightly nonlinear flow regimes are studied through a mode-coupling analysis. Our analytical results reveal that linear growth rates and finger competition are inhibited for an increasingly larger radius of curvature. The absence of tip-splitting events in cylindrical cells is also discussed.

Journal Article↗
PubMed2003

Phenomenology of hallucinations: a factor analytic approach.

The present study was carried out with the aim of obtaining a factor analytic solution of parameters of hallucinations in schizophrenia. Seventy-five chronic hallucinating schizophrenic patients were assessed on the Phenomenology of Hallucinations Scale and Brief Psychiatric Rating Scale. A factor analytic solution was obtained by principal component analysis using varimax rotation. Two factors, 'reality of hallucinatory perception' and 'immersion in hallucination', were obtained. Findings are discussed in relation to existing literature.

Adult↗
PubMed2005

Analytical approach to noncircular section birdcage coil design: verification with a Cassinian oval coil.

A general analytical framework is presented for the design of birdcage radiofrequency resonators on cylindrical formers having arbitrary cross-sectional shape. The primary objective of such shapes would be to improve the sensitivity of the NMR experiment to noncircular regions of the human anatomy while maintaining field homogeneity and quadrature polarization comparable to those of standard circular birdcage coils. The shape of the corresponding radiofrequency screen, which is required to decouple the coil from the rest of the NMR system and which is key to the performance, is also provided by this methodology. The theory was tested by constructing a 3-T, quadrature, proton coil on a shape conforming to the anthropomorphic mean of the human head, namely, the oval of Cassini. Both bench tests (Q) and in vivo spectral and imaging comparisons of the Cassinian coil with an equivalently dimensioned and constructed circular birdcage coil, respectively, predicted and demonstrated in vivo an improvement in SNR of approximately 24% over the circular section coil. The experimental RF field homogeneity and quadrature performance were comparable for both coil geometries, with the circular coil being marginally superior.

Equipment Design↗