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1.
Comput Biol Med ; 82: 3-11, 2017 03 01.
Article in English | MEDLINE | ID: mdl-28119191

ABSTRACT

We examine both maximum likelihood and Bayesian approaches for estimating probabilistic decompression sickness model parameters. Maximum likelihood estimation treats parameters as fixed values and determines the best estimate through repeated trials, whereas the Bayesian approach treats parameters as random variables and determines the parameter probability distributions. We would ultimately like to know the probability that a parameter lies in a certain range rather than simply make statements about the repeatability of our estimator. Although both represent powerful methods of inference, for models with complex or multi-peaked likelihoods, maximum likelihood parameter estimates can prove more difficult to interpret than the estimates of the parameter distributions provided by the Bayesian approach. For models of decompression sickness, we show that while these two estimation methods are complementary, the credible intervals generated by the Bayesian approach are more naturally suited to quantifying uncertainty in the model parameters.


Subject(s)
Decompression Sickness/epidemiology , Decompression Sickness/physiopathology , Diving/statistics & numerical data , Models, Biological , Models, Statistical , Nitrogen/blood , Oxygen/blood , Bayes Theorem , Computer Simulation , Humans , Likelihood Functions , Prevalence , Prognosis , Proportional Hazards Models , Reproducibility of Results , Risk Assessment/methods , Risk Factors , Sensitivity and Specificity
2.
Bioinspir Biomim ; 4(4): 046001, 2009 Dec.
Article in English | MEDLINE | ID: mdl-19834251

ABSTRACT

When a phenomenon in nature is mimicked for practical applications, it is often done so in an idealized fashion, such as representing the shape found in nature with convenient, piece-wise smooth mathematical functions. The aim of idealization is to capture the advantageous features of the natural phenomenon without having to exactly replicate it, and it is often assumed that the idealization process does in fact capture the relevant geometry. We explored the consequences of the idealization process by creating exact scale models of cetacean flippers using CT scans, creating corresponding idealized versions and then determining the hydrodynamic characteristics of the models via water tunnel testing. We found that the majority of the idealized models did not exhibit fluid dynamic properties that were drastically different from those of the real models, although multiple consequences resulting from the idealization process were evident. Drag performance was significantly improved by idealization. Overall, idealization is an excellent way to capture the relevant effects of a phenomenon found in nature, which spares the researcher from having to painstakingly create exact models, although we have found that there are situations where idealization may have unintended consequences such as one model that exhibited a decrease in lift performance.


Subject(s)
Biomimetic Materials , Cetacea/physiology , Extremities/physiology , Models, Biological , Rheology/instrumentation , Swimming/physiology , Animals , Computer Simulation , Equipment Design , Equipment Failure Analysis , Rheology/methods
3.
Int J Hyperthermia ; 15(6): 509-18, 1999.
Article in English | MEDLINE | ID: mdl-10598948

ABSTRACT

Tissue equivalent radio frequency (RF) phantoms provide a means for measuring the power deposition of various hyperthermia therapy applicators. Temperature measurements made in phantoms are used to verify the accuracy of various numerical approaches for computing the power and/or temperature distributions. For the numerical simulations to be accurate, the electrical and thermal properties of the materials that form the phantom should be accurately characterized. This paper reports on the experimentally measured thermal properties of two commonly used phantom materials, i.e. a rigid material with the electrical properties of human fat, and a low concentration polymer gel with the electrical properties of human muscle. Particularities of the two samples required the design of alternative measuring techniques for the specific heat and thermal conductivity. For the specific heat, a calorimeter method is used. For the thermal diffusivity, a method derived from the standard guarded comparative-longitudinal heat flow technique was used for both materials. For the 'muscle'-like material, the thermal conductivity, density and specific heat at constant pressure were measured as: k = 0.31 +/- 0.001 W(mK)(-1), p = 1026 +/- 7 kgm(-3), and c(p) = 4584 +/- 107 J(kgK)(-1). For the 'fat'-like material, the literature reports on the density and specific heat such that only the thermal conductivity was measured as k = 0.55 W(mK)(-1).


Subject(s)
Models, Biological , Evaluation Studies as Topic , Humans
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