5,473 research outputs found
Dental Dam Utilization by Dentists in an Intramural Faculty Practice
Objectives: From casual observation of our colleagues, only a few individuals use the dental dam for operative procedures in their faculty practice. The purpose of this study was to obtain faculty perceptions of the dental dam, quantify its utilization in their intramural faculty practice, and determine the factors that influence dental dam usage.Materials and Methods: A survey containing 11 questions was sent to 19 faculty members who teach full time and maintain an intramural dental practice involving operative dentistry. Thirty electronic dental health records of the 19 providers were reviewed to gather the following information from restorative procedures they completed: isolation methods, tooth location and involved surfaces, and dental restorative material.Results: Overall, dental dam was utilized for 30% of all restorative procedures and was used less than 20% of the time for placement of class II and class III composite resins. Dental dam utilization rate by general dentists was 37% and 17.6% for prosthodontists. Those general dentists with prior history of military dental practice had a utilization rate of 78.6% and nonmilitary dentists only 7.6%. Eight faculty members responded to the questionnaire for a 42% return rate. Those who practiced dentistry in the military strongly agreed that the dental dam is the standard of care, improves their quality of restorative work, and should be documented in the dental record.Conclusions: There were significantly different dental dam utilization rates between general dentists and prosthodontists and between dentists with prior military experience and those without
Distinct changes of genomic biases in nucleotide substitution at the time of mammalian radiation
Differences in the regional substitution patterns in the human genome created
patterns of large-scale variation of base composition known as genomic
isochores. To gain insight into the origin of the genomic isochores we develop
a maximum likelihood approach to determine the history of substitution patterns
in the human genome. This approach utilizes the vast amount of repetitive
sequence deposited in the human genome over the past ~250 MYR. Using this
approach we estimate the frequencies of seven types of substitutions: the four
transversions, two transitions, and the methyl-assisted transition of cytosine
in CpG. Comparing substitutional patterns in repetitive elements of various
ages, we reconstruct the history of the base-substitutional process in the
different isochores for the past 250 Myr. At around 90 Myr ago (around the time
of the mammalian radiation), we find an abrupt 4- to 8-fold increase of the
cytosine transition rate in CpG pairs compared to that of the reptilian
ancestor. Further analysis of nucleotide substitutions in regions with
different GC-content reveals concurrent changes in the substitutional patterns.
While the substitutional pattern was dependent on the regional GC-content in
such ways that it preserved the regional GC-content before the mammalian
radiation, it lost this dependence afterwards. The substitutional pattern
changed from an isochore-preserving to an isochore-degrading one. We conclude
that isochores have been established before the radiation of the eutherian
mammals and have been subject to the process of homogenization since then
Substantial regional variation in substitution rates in the human genome: importance of GC content, gene density and telomere-specific effects
This study presents the first global, 1 Mbp level analysis of patterns of
nucleotide substitutions along the human lineage. The study is based on the
analysis of a large amount of repetitive elements deposited into the human
genome since the mammalian radiation, yielding a number of results that would
have been difficult to obtain using the more conventional comparative method of
analysis. This analysis revealed substantial and consistent variability of
rates of substitution, with the variability ranging up to 2-fold among
different regions. The rates of substitutions of C or G nucleotides with A or T
nucleotides vary much more sharply than the reverse rates suggesting that much
of that variation is due to differences in mutation rates rather than in the
probabilities of fixation of C/G vs. A/T nucleotides across the genome. For all
types of substitution we observe substantially more hotspots than coldspots,
with hotspots showing substantial clustering over tens of Mbp's. Our analysis
revealed that GC-content of surrounding sequences is the best predictor of the
rates of substitution. The pattern of substitution appears very different near
telomeres compared to the rest of the genome and cannot be explained by the
genome-wide correlations of the substitution rates with GC content or exon
density. The telomere pattern of substitution is consistent with natural
selection or biased gene conversion acting to increase the GC-content of the
sequences that are within 10-15 Mbp away from the telomere.Comment: 35 pages, 6 figure
MIMO Channel Correlation in General Scattering Environments
This paper presents an analytical model for the fading channel correlation in
general scattering environments. In contrast to the existing correlation
models, our new approach treats the scattering environment as non-separable and
it is modeled using a bi-angular power distribution. The bi-angular power
distribution is parameterized by the mean departure and arrival angles, angular
spreads of the univariate angular power distributions at the transmitter and
receiver apertures, and a third parameter, the covariance between transmit and
receive angles which captures the statistical interdependency between angular
power distributions at the transmitter and receiver apertures. When this third
parameter is zero, this new model reduces to the well known "Kronecker" model.
Using the proposed model, we show that Kronecker model is a good approximation
to the actual channel when the scattering channel consists of a single
scattering cluster. In the presence of multiple remote scattering clusters we
show that Kronecker model over estimates the performance by artificially
increasing the number of multipaths in the channel.Comment: Australian Communication Theory Workshop Proceedings 2006, Perth
Western Australia. (accepted
On the valuation ofconstant barrier options under spectrally one-sided exponential L&evy models and Carr’s approximation for American puts.
This paper provides a general framework for pricing options with a constant barrier under spectrally one-sided exponential L&evy model, and uses it to implement ofCarr’s approximation for the value of the American put under this model. Simple analytic approximations for the exercise boundary and option value are obtained. c 2002 Elsevier Science B.V. All rights reservedAmerican options; Perpetual approximation; Spectrally negative exponential L&evy process;
Calibration of neural networks using genetic algorithms, with application to optimal path planning
Genetic algorithms (GA) are used to search the synaptic weight space of artificial neural systems (ANS) for weight vectors that optimize some network performance function. GAs do not suffer from some of the architectural constraints involved with other techniques and it is straightforward to incorporate terms into the performance function concerning the metastructure of the ANS. Hence GAs offer a remarkably general approach to calibrating ANS. GAs are applied to the problem of calibrating an ANS that finds optimal paths over a given surface. This problem involves training an ANS on a relatively small set of paths and then examining whether the calibrated ANS is able to find good paths between arbitrary start and end points on the surface
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