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At least 667 records · Page 37Linked to original sources
PubMed2003

The influence of working cast residual moisture and temperature on the fit of vacuum-forming athletic mouth guards.

STATEMENT OF PROBLEM: The comfort and effectiveness of athletic mouth guards are believed to depend on their degree of fit to oral tissues. Vacuum-forming machines are simpler and less expensive than pressure-forming machines. However, it is thought that vacuum-formed mouth guards often do not exhibit adequate adaptation. PURPOSE: The purpose of this study was to evaluate the effects of cast residual moisture and temperature on the fit of athletic mouth guards made with a vacuum-forming machine. MATERIAL AND METHODS: A metal master model simulating the cross section of the maxillary molar region was used to form 20 working plaster casts. The casts represented 4 (5 specimens each) conditions before the forming of the mouth guard specimens: storing in a wet environment at room temperature and storing in a dry environment at room temperature, 5 degrees C, and 40 degrees C. Mouth guard specimens were fabricated with ethylene vinyl acetate sheets (3.8-mm thick) with the use of a vacuum-forming machine. Test casts were created by pouring hand-mixed type III dental stone into each of the mouth guard specimens. The differences in the sagittal cross-sectional heights at the line angle area of the test casts and the working casts were compared. This was achieved by superimposing their 3-dimensional images scanned by a laser scanner. The air permeability was also measured for the hand-mixed stone casts under wet and dry conditions, the vacuum-mixed stone cast, and the high-strength stone specimen. This was achieved by measuring the volume of transmitted air passing through the specimen in the testing tube. One-way analysis of variance with the Scheffé post hoc test (P <.05) was applied to determine the conditions of the working cast required to achieve the best fit. RESULTS: With regard to the fit of the mouth guard specimens to the working cast, those with dry and heated working casts showed a significantly better fit than those with wet working casts (P<.05). A significantly larger volume of transmitted air was found in the dry stone specimen (P<.05) followed by the dry high-strength stone cast and then the wet stone cast. CONCLUSION: Within the limitations of this study, residual moisture in the working cast was the most critical factor in determining the fit of the mouth guard made by vacuum-forming machines. The best fit was achieved when the working cast was thoroughly dried and its surface temperature was elevated.

Air↗
PubMed1993

A comparison of controlled negative pressure and aerosol quantitative respirator fit test systems by using human subjects.

A quantitative respirator fit test system based on controlled negative pressure was evaluated by comparison testing with a computerized aerosol fit test system. Experiments ranged from multiple sequential tests of a single subject wearing a respirator equipped with a series of fixed leaks to sequential fit tests of 125 U.S. Air Force personnel using both systems. Throughout each test phase, measured negative pressure fit factors were consistently more conservative and less variable than aerosol fit factors. Comparison of subject and fixed leak fit factors indicated significant loss of aerosol during subject fit tests. Negative pressure system results did not show any effect from subject-related losses.

Aerosols↗
PubMed1995

Development of a new qualitative test for fit testing respirators.

A new qualitative fit test was developed using Bitrex (Macfarland Smith Limited) as the test agent. It was validated by running a series of paired qualitative and quantitative fit tests. Quantitative tests were conducted with a small corn oil aerosol, using a condensation nucleus counter as a detector. Qualitative fit tests were run with Bitrex and saccharin, following the established protocol for the saccharin fit test. Four models of National Institute for Occupational Safety and Health--approved replaceable filter respirators were used in the study. All were half mask models equipped with high efficiency filters. In some cases, respirators expected to be the correct size for test subjects were tested. In other cases, respirators expected to be too small or too large for the subjects were tested. Test results were analyzed using fit test method validation criteria recommended in the American National Standards Institute draft standard on fit testing (ANSIZ88.10). The Bitrex and saccharin tests were found to have virtually identical performance. Both met proposed American National Standards Institute requirements for a valid qualitative fit test.

Female↗
PubMed2003

Fitness components versus total demographic effects: evaluating herbivore impacts on a perennial herb.

I examined the long-term effects of cryptic mollusk herbivory on seven fitness components in the perennial herb Lathyrus vernus and also calculated measures of total fitness effects. Natural correlations and experimental exclusion of mollusks showed that herbivory is associated with an increased probability of dying or staying dormant, poorer growth, and a lower probability of flowering. The average yearly reduction in population growth rate (lambda) caused by mollusks in the experiment was 0.14. The largest contribution to this decrease in total fitness occurred through a decreased survival of established plants. In contrast, seedling emergence and probability of flowering were the fitness components that were most affected in terms of relative change. The more important a life-cycle transition was for population growth rate in terms of its elasticity, the less it was affected by herbivore damage. These results suggest that simple analyses of the magnitudes of effects on individual components of plant performance are poor predictors of the magnitude of total fitness effects and tolerance to herbivory. This is because total fitness is differently sensitive to different phases of the life cycle and because plants strive to maintain the functions most important to fitness.

Animals↗
PubMed2005

Fitness correlates of song repertoire size in free-living song sparrows (Melospiza melodia).

Models of sexual selection propose that exaggerated secondary sexual ornaments indicate a male's own fitness and the fitness of his offspring. These hypotheses have rarely been thoroughly tested in free-living individuals because overall fitness, as opposed to fitness components, is difficult to measure. We used 20 years of data from song sparrows (Melospiza melodia) inhabiting Mandarte Island, British Columbia, Canada, to test whether a male's song repertoire size, a secondary sexual trait, predicted overall measures of male or offspring fitness. Males with larger song repertoires contributed more independent and recruited offspring, and independent and recruited grandoffspring, to Mandarte's population. This was because these males lived longer and reared a greater proportion of hatched chicks to independence from parental care, not because females mated to males with larger repertoires laid or hatched more eggs. Furthermore, independent offspring of males with larger repertoires were more likely to recruit and then to leave more grandoffspring than were offspring of males with small repertoires. Although we cannot distinguish whether observed fitness variation reflected genetic or environmental effects on males or their offspring, these data suggest that female song sparrows would gain immediate and intergenerational fitness benefits by pairing with males with large song repertoires.

Animals↗
PubMed2005

The use of the Levenberg-Marquardt curve-fitting algorithm in pharmacokinetic modelling of DCE-MRI data.

The use of curve-fitting and compartmental modelling for calculating physiological parameters from measured data has increased in popularity in recent years. Finding the 'best fit' of a model to data involves the minimization of a merit function. An example of a merit function is the sum of the squares of the differences between the data points and the model estimated points. This is facilitated by curve-fitting algorithms. Two curve-fitting methods, Levenberg-Marquardt and MINPACK-1, are investigated with respect to the search start points that they require and the accuracy of the returned fits. We have simulated one million dynamic contrast enhanced MRI curves using a range of parameters and investigated the use of single and multiple search starting points. We found that both algorithms, when used with a single starting point, return unreliable fits. When multiple start points are used, we found that both algorithms returned reliable parameters. However the MINPACK-1 method generally outperformed the Levenberg-Marquardt method. We conclude that the use of a single starting point when fitting compartmental modelling data such as this produces unsafe results and we recommend the use of multiple start points in order to find the global minima.

Algorithms↗
PubMed1983

Should individual fitness increase with heterozygosity?

Natural selection influences not only gamete frequencies in populations but also the multilocus fitness structures associated with segregating gametes. In particular, only certain patterns of multilocus fitnesses are consistent with the maintenance of stable multilocus polymorphisms. This paper offers support for the proposition that, at stable, viability-maintained, multilocus polymorphisms, the fitness of a genotype tends to increase with the number of heterozygous loci it contains. Average fitness always increases with heterozygosity at stable product equilibria (i.e., those without linkage disequilibrium) maintained by either additive or multiplicative fitness schemes. Simulations suggest that it "generally" increases for arbitrary fitness schemes. The empirical literature correlating allozyme heterozygosity with fitness-correlated traits is discussed in the light of these and other theoretical results.

Animals↗
PubMed1999

Unpredictable fitness transitions between haploid and diploid strains of the genetically loaded yeast Saccharomyces cerevisiae.

Mutator strains of yeast were used to accumulate random point mutations. Most of the observed changes in fitness were negative and relatively small, although major decreases and increases were also present. The average fitness of haploid strains was lowered by approximately 25% due to the accumulated genetic load. The impact of the load remained basically unchanged when a homozygous diploid was compared with the haploid from which it was derived. In other experiments a heterozygous diploid was compared with the two different loaded haploids from which it was obtained. The fitness of such a loaded diploid was much less reduced and did not correlate with the average fitness of the two haploids. There was a fitness correlation, however, when genetically related heterozygous diploids were compared, indicating that the fitness effects of the new alleles were not entirely lost in the heterozygotes. It is argued here that to explain the observed pattern of fitness transitions it is necessary to invoke nonadditive genetic interactions that go beyond the uniform masking effect of wild-type alleles. Thus, the results gathered with haploids and homozygotes should be extrapolated to heterozygotes with caution when multiple loci contribute to the genetic load.

Adaptation, Biological↗
PubMed2001

Estimates of the rate and distribution of fitness effects of spontaneous mutation in Saccharomyces cerevisiae.

The per-genome, per-generation rate of spontaneous mutation affecting fitness (U) and the mean fitness cost per mutation (s) are important parameters in evolutionary genetics, but have been estimated for few species. We estimated U and sh (the heterozygous effect of mutations) for two diploid yeast strains differing only in the DNA mismatch-repair deficiency used to elevate the mutation rate in one (mutator) strain. Mutations were allowed to accumulate in 50 replicate lines of each strain, during 36 transfers of randomly chosen single colonies (approximately 600 generations). Among wild-type lines, fitnesses were bimodal, with one mode showing no change in mean fitness. The other mode showed a mean 29.6% fitness decline and the petite phenotype, usually caused by partial deletion of the mitochondrial genome. Excluding petites, maximum-likelihood estimates adjusted for the effect of selection were U = 9.5 x 10(-5) and sh = 0.217 for the wild type. Among the mutator lines, the best fit was obtained with 0.005 < or = U < or = 0.94 and 0.049 > or = sh > or = 0.0003. Like other recently tested model organisms, wild-type yeast have low mutation rates, with high mean fitness costs per mutation. Inactivation of mismatch repair increases the frequency of slightly deleterious mutations by approximately two orders of magnitude.

Base Pair Mismatch↗
PubMedDate not supplied

Age-specific fitness components in hybrid females of Drosophila pseudoobscura and D. persimilis.

Most models of hybridization assume that hybrids are less fit than their parental taxa. In contrast, some researchers have explored the possibility that hybrid individuals may actually have higher fitness and so play an important role in the generation of new species or adaptations. By estimating age-specific fitness components, we can determine not only how hybrid fitness differs from parental taxa, but also whether the fitness of hybrids relative to parental taxa changes with age. Here we describe an analysis of age-specific fitness traits in two species of Drosophila, D. pseudoobscura and D. persimilis, and their F1 hybrids. At early ages, hybrid females lay as many eggs as parental individuals, on average, but produce far fewer offspring. By late ages, in contrast, parental taxa show a steep decline in production not seen in hybrids, such that hybrids produce more offspring, on average, than parental taxa. Furthermore, egg-adult survival in hybrids is negatively correlated with egg density, whereas these traits are only weakly correlated in parental taxa. The results are limited somewhat by the fact that we analyze only two strains, and that these may be partially inbred. Nonetheless, the results are certainly illustrative, pointing out not only that at least some hybrid individuals may be as fit or fitter than parental taxa, but also that the difference between hybrids and parental taxa varies with age.

Age Factors↗
PubMed1997

Changes in speech intelligibility as a function of time and signal processing strategy for an Ineraid patient fitted with continuous interleaved sampling (CIS) processors.

OBJECTIVE: To assess changes in speech intelligibility as a function of signal processing strategy and as a function of time for one of the first two Ineraid patients in the United States fitted with a continuous interleaved sampling (CIS) signal processor. DESIGN: In Experiment 1, the patient was fitted with a CIS processor and measures of speech intelligibility were taken over a period of 4 mo. These data were compared with data collected with the Ineraid. In Experiment 2, three new signal processing strategies were tested. Measures of speech intelligibility were taken at fitting and after a week's use of the processor. In Experiment 3, the number of channels in the processor was reduced to 5, 4, and 3. Each processor was tested at fitting and after a week's use of the processor. RESULTS: In Experiment 1, immediately on fitting, the CIS processor produced better speech intelligibility for consonants, vowels, and the CID sentences than did the Ineraid. Performance improved over periods ranging from 1 to 4 mo depending on the test material. In Experiment 2, two processors produced significantly better speech intelligibility than did other processors. Most generally, performance dropped slightly when a new processor was fitted and then improved over the course of week. All of the processors produced better speech intelligibility than did the Ineraid. In Experiment 3, five channels allowed similar levels of performance as did six channels. The effect of four and three channels varied as a function of test material. Four CIS channels allowed better performance than did the four analogue channels of the Ineraid. CONCLUSIONS: We conclude 1) that CIS processors can provide much better speech intelligibility than can the analogue processor of the Ineraid; 2) that many CIS strategies, not just one, will produce better speech intelligibility than will the Ineraid; 3) that for this patient, five channels can allow as high a level of word intelligibility as can six channels; 4) that when the number of CIS and analogue channels are equated (at four), the CIS strategy provides better speech intelligibility than does the Ineraid; and 5) that speech intelligibility with CIS processors improves over periods as short as a week and as long as several months after fitting of the processor.

Aged↗
PubMed1999

The variance in inbreeding depression and the recovery of fitness in bottlenecked populations.

Theoretical analyses of inbreeding suggest that following an increased degree of inbreeding there may be a temporary recovery of fitness, because of selection either within or among inbred lineages. This is possible because selection can act more efficiently to remove deleterious alleles given the greater homozygosity of such populations. If common, recovery of fitness following inbreeding may be important for understanding some evolutionary processes and for management strategies of remnant populations, yet empirical evidence for such recovery in animals is scant. Here we describe the effects of single-pair population bottlenecks on a measure of fitness in Drosophila melanogaster. We compared a large number of families from each of 52 inbred lines with many families from the outbred population from which the inbred lineages were derived. Measures were made at the third and the 20th generations after the bottleneck. In both generations there was, on average, substantial inbreeding depression together with a highly significant variance among the inbred lines in the amount of fitness reduction. The average fitness of inbred lines was correlated across generations. Our data provide evidence for the possibility of recovery of fitness at two levels, because (i) the average fitness reduction in the F20 generation was significantly less than in the F3 generation, which implies that selection within lines has occurred, and (ii) the large variance in inbreeding depression among inbred lines implies that selection among them is possible. The high variance in inbreeding depression among replicate lines implies that modes of evolution which require a low level of inbreeding depression can function at least in a fraction of inbred populations within a species and that results from studies with low levels of replication should be treated with caution.

Animals↗
PubMed2000

Body mass and individual fitness in female ungulates: bigger is not always better.

In female vertebrates, differences in fitness often correspond to differences in phenotypic quality, suggesting that larger females have greater fitness. Variation in individual fitness can result from variation in life span and/or variation in yearly reproductive success, but no study has yet assessed the relationships between the components of fitness and phenotypic quality while controlling for life span. We tried to fill this gap using data from long-term monitoring (23 years) of marked roe deer and bighorn sheep, two ungulates with very different life histories. In both species, we found a strong positive relationship between an adult female's mass and her probability of reaching old age: over the long term, bigger is indeed better for ungulate females. On the other hand, we found no evidence in either species that heavier females had higher fitness when differences in life span were accounted for: over the short term, bigger is not necessarily better. Our results indicate that, while broad differences in phenotypic quality affect individual fitness, when differences in life span are accounted for phenotypic quality has no residual effect on fitness. Therefore, within a given range of phenotypic quality, bigger is not always better, for reasons which may differ between species.

Animals↗
PubMed2002

The X chromosome is a hot spot for sexually antagonistic fitness variation.

Sexually antagonistic alleles are selected discordantly between the sexes. Experimental evidence indicates that sexually antagonistic fitness variation is abundant in the genome of Drosophila melanogaster. Theory predicts that the X chromosome will be enriched with this type of variation. To test this prediction in D. melanogaster, we sampled, and cytogenetically cloned, 20 X chromosomes and compared their fitness variation to genome-wide levels. At the juvenile stage, in which gender roles are most similar, the X chromosome made no detectable contribution to genome-wide fitness variation. At the adult stage, in which gender roles diverge, the X chromosome was estimated to harbour 45% of the genome-wide fitness variation and 97% of the genome-wide sexually antagonistic variation. This genomic structure has important implications for the process of sexual selection because X-linked sexually antagonistic variation contributes to negative intersexual heritability for fitness, i.e. high-fitness males (females) produce, on average, low-fitness daughters (sons).

Alleles↗
PubMed2004

Fitness and evolutionary stability in game theoretic models of finite populations.

We investigate two methods of measuring fitness in evolutionary games played among members of a finite population. Classical notions of stability account for the action of selection only, and use immediate reproductive gains as a measure of fitness. This classical interpretation of fitness is what we call reproductive fitness (RF), and is found in the early studies of evolutionary stability in finite populations. More recent work has incorporated the influence of random genetic drift by applying fixation probability (FP) as a measure of fitness. When defined in this way, fitness represents a measure of ultimate evolutionary success. Our main result describes an equivalence between candidate evolutionarily stable strategies under both the RF and FP interpretations of fitness. We apply this result to matrix games in which the use of mixed strategies is permitted, and find here an equivalence between the RF and FP conditions for evolutionary stability.

Biological Evolution↗
PubMed2004

Solvable biological evolution models with general fitness functions and multiple mutations in parallel mutation-selection scheme.

In a recent paper [Phys. Rev. E 69, 046121 (2004)]], we used the Suzuki-Trottere formalism to study a quasispecies biological evolution model in a parallel mutation-selection scheme with a single-peak fitness function and a point mutation. In the present paper, we extend such a study to evolution models with more general fitness functions or multiple mutations in the parallel mutation-selection scheme. We give some analytical equations to define the error thresholds for some general cases of mean-field-like or symmetric mutation schemes and fitness functions. We derive some equations for the dynamics in the case of a point mutation and polynomial fitness functions. We derive exact dynamics for two-point mutations, asymmetric mutations, and the four-value spin model with a single-peak fitness function. The same method is applied for the model with a royal road fitness function. We derive the steady-state distribution for the single-peak fitness function.

Biological Evolution↗
PubMed2001

A new software routine that automates the fitting of protein X-ray crystallographic electron-density maps.

The classical approach to building the amino-acid residues into the initial electron-density map requires days to weeks of a skilled investigator's time. Automating this procedure should not only save time, but has the potential to provide a more accurate starting model for input to refinement programs. The new software routine MAID builds the protein structure into the electron-density map in a series of sequential steps. The first step is the fitting of the secondary alpha-helix and beta-sheet structures. These 'fits' are then used to determine the local amino-acid sequence assignment. These assigned fits are then extended through the loop regions and fused with the neighboring sheet or helix. The program was tested on the unaveraged 2.5 A selenomethionine multiple-wavelength anomalous dispersion (SMAD) electron-density map that was originally used to solve the structure of the 291-residue protein human heart short-chain L-3-hydroxyacyl-CoA dehydrogenase (SHAD). Inputting just the map density and the amino-acid sequence, MAID fitted 80% of the residues with an r.m.s.d. error of 0.43 A for the main-chain atoms and 1.0 A for all atoms without any user intervention. When tested on a higher quality 1.9 A SMAD map, MAID correctly fitted 100% (418) of the residues. A major advantage of the MAID fitting procedure is that it maintains ideal bond lengths and angles and constrains phi/psi angles to the appropriate Ramachandran regions. Recycling the output of this new routine through a partial structure-refinement program may have the potential to completely automate the fitting of electron-density maps.

Crystallography, X-Ray↗
PubMed2004

Stable fitting of 2D curves and 3D surfaces by implicit polynomials.

This work deals with fitting 2D and 3D implicit polynomials (IPs) to 2D curves and 3D surfaces, respectively. The zero-set of the polynomial is determined by the IP coefficients and describes the data. The polynomial fitting algorithms proposed in this paper aim at reducing the sensitivity of the polynomial to coefficient errors. Errors in coefficient values may be the result of numerical calculations, when solving the fitting problem or due to coefficient quantization. It is demonstrated that the effect of reducing this sensitivity also improves the fitting tightness and stability of the proposed two algorithms in fitting noisy data, as compared to existing algorithms like the well-known 3L and gradient-one algorithms. The development of the proposed algorithms is based on an analysis of the sensitivity of the zero-set to small coefficient changes and on minimizing a bound on the maximal error for one algorithm and minimizing the error variance for the second. Simulation results show that the proposed algorithms provide a significant reduction in fitting errors, particularly when fitting noisy data of complex shapes with high order polynomials, as compared to the performance obtained by the abovementioned existing algorithms.

Algorithms↗