523 research outputs found
Understanding Pediatric Dentistsā Dental Caries Management Treatment Decisions: A Conjoint Experiment
When traditional ranking
and rating surveys are used to
assess dentistsā treatment decisions, the
patientās source of payment appears
to be of little importance. Therefore,
this study used the marketing research
tool conjoint analysis to investigate the
relative impact of source of payment
along with the childās age and cooperativeness
on pediatric dentistsā willingness
to use Atraumatic Restorative
Treatment (ART) to restore posterior
primary teeth. A conjoint survey was
completed by 707 pediatric dentists.
Three factors (age of the child, cooperativeness,
type of insurance) were varied
across 3 levels to create 9 patient
scenarios. The relative weights that
dentists placed on these factors in the
restorative treatment decision process
were determined by conjoint analysis.
āCooperativenessā (52%) was the most
important factor, āage of the childā
(26%) the second-most important factor,
followed by āinsurance status of
the childā (22%). For the third factor,
insurance, pediatric dentists were
least willing to use ART with publicly
insured children (ā0.082), and this
was significantly different from their
willingness to use ART with uninsured children (0.010) but not significantly
different than their willingness to use
ART for children with private insurance
(0.073). Unlike traditional ranking
and rating tools, conjoint analysis
found that the insurance status of
the patient appeared to be an important
factor in dentistsā decisions about
different restorative treatment options.
When pediatric dentists were forced
to make tradeoffs among different
patientsā factors, they were most willing
to use ART technique with young,
uncooperative patients when they had
no insurance.This project was funded by National
Institutes of Health / National Institute
of Dental and Craniofacial Research (T32
grant DEO 14678-06) and the Academic
Fellowship Program (Zamalah) for the
development of higher education. The
authors declare no potential conflicts of
interest with respect to the authorship
and/or publication of this article
Effect of Estrous Synchronization With Natural Service or Fixed-Timed Artificial Insemination Using Conventional or Gender-Kkewed Semen in Beef Females on Calving Distribution and Post Weaning Calf Performance
Study Description:
Within 10 herds, beef females (n = 1,620) were either: 1) not synchronized (NonSyn) and mated to bulls, 2) synchronized (7-d controlled internal drug release (CIDR)) and mated to bulls (SynNS) 3) synchronized (7-d CO-Synch plus CIDR) and artificially inseminated with conventional semen (SynAI), or 4) synchronized (7-d CO-Synch plus CIDR) and artificially inseminated with SEXED semen. Calving distributions (calves born from d 1 to 14, 1 to 21, 22 to 42, and 43 and greater) were determined by actual birthdates and calf gender was determined at birth. Over a two-year period, a subset of calves (n = 508) born to cows subjected to the previously discussed reproductive treatments in each of the 10 herds were fed to reach a target backfat (BF) of 0.50 inches, sent to harvest, and carcass data were collected. Calves were classified into calving groups as natural service born early (NS-Early, n = 189), natural service born late (NS-Late, n = 203), or AI sired born early (AI-Early, n = 116). Early was defined as the first 21 days of the calving season
Finite element simulation of plates under non-uniform blast loads using a point-load method: Blast wave clearing
There are two primary challenges associated with assessing the adequacy of a protective structure to resist explosive events: firstly the spatial variation of load acting on a target must be predicted to a sufficient level of accuracy; secondly, the response of the target to this load must also be quantified. If a target is embedded within a finite reflecting surface then the process of blast wave clearing will occur. Diffraction of the blast around the target edge causes a low pressure relief wave to propagate inwards towards the centre of the target, reducing the late-time development of pressure and resulting in high spatial non-uniformity of the blast load. This paper presents experimental measurements of the dynamic displacement-time histories of steel plates subjected to blast loads where the plate was situated within a finite reflecting surface to allow for clearing effects to take place. Associated finite element modelling is presented, where coupled blast-target interaction is modelled explicitly using the Arbitrary Lagrangian-Eulerian solver in LS-DYNA. An alternative method is presented, where the loading is applied as discrete load predictions at individual nodes. The results show that vast computational savings can be made when modelling the load in this manner, as well as better agreement with the experimental measurements owing to a more accurate representation of the applied load
Displacement timer pins: An experimental method for measuring the dynamic deformation of explosively loaded plates
The measurement of dynamic deformation of an explosively loaded plate is an extremely onerous task. Existing techniques such as digital image correlation are expensive and the equipment may be damaged by explosively driven debris/ejecta, particularly if it is necessary to locate such equipment close to loaded elements which are likely to fail. A new, inexpensive and robust measurement technique for use in full-scale blast testing is presented, which involves the placement of displacement timer pins (DTPs) at pre-defined distances from the rear surface of the centre of a plate. A strain gauge on the perimeter of each pin records the time at which the plate comes into contact with the end of each DTP and hence has deformed to that value of displacement, giving a direct measure of the time-varying deformation at a discrete point on the plate. An experimental proof-of-concept was conducted and the results are compared with numerical displacements determined using LS-DYNA. The numerical and experimental results were in very good agreement, which suggests that the proposed experimental method offers a valuable means for determining the full-scale response of structures subjected to blast loads in aggressive environments. Further improvements to the experimental procedure are outlined, along with applications where the DTPs are particularly suited. 2015 Elsevier Ltd. All rights reserved
Experimental studies of the effect of rapid afterburn on shock development of near-field explosions
Many conventional high explosives do not contain sufficient internal oxygen to fully combust the gaseous products
which result from detonation of the explosive material. Because of this, under-oxygenated explosives continue
to burn after detonation. This process, called afterburn, is known to influence the late-time pressure and energy
released by the explosive, which has particular significance for confined explosives. Recent experimental work
at the University of Sheffield, along with a small number of previous studies, has shown that some afterburn
occurs at timescales commensurate with the development of the shock wave. This article presents the results
from a series of tests measuring the reflected pressure acting on a rigid target following the detonation of small
explosive charges. High-speed video is used to capture the emerging structure of the detonation products and
air shock, while the spatial and temporal distributions of the reflected pressure are recorded using an array of 17
Hopkinson pressure bars set flush with an effectively rigid target. Tests are conducted in inert atmospheres and
oxygen-rich atmospheres in order to assess the contribution of rapid afterburn on the development of the shock
front and interaction with a rigid target situated close to the explosive charge. The results show that early-stage
afterburn has a significant influence on the reflected shock parameters in the near-field
Localised variations in reflected pressure from explosives buried in uniform and well-graded soils
Recent experiments into characterisation of the loading resulting from detonation of a shallow buried explosive have
highlighted the complex underlying physical mechanisms present at the face of a target situated above the soil
surface. This paper presents the results from such experiments, where the localised blast pressure and impulse is
measured using an array of Hopkinson pressure bars at specific points on the target surface. Two different soil types
are tested; a relatively uniform sand, and well-graded sandy-gravel. It is observed that the variability in localised
loading is intrinsically linked to the particle size distribution of the soil medium; the uniform soil produces repeatable
data with little variation whereas the well-graded soil demonstrates considerable spread. The cause of this spread is
quantified and discussed with reference to the distinct loading mechanisms acting on the target as seen in the
experimental data
Reflected pressures from explosives buried in idealised cohesive soils
Recent work has concentrated on the characterisation of the temporal and spatial impulse distribution of blast form
buried charges. A new soil container preparation methodology has been created to allow for the generation of highly
repeatable, tightly controlled clay beds which will allow clays of different undrained strengths to be generated. Tests
using these well controlled beds has allowed for an improved understanding into which geotechnical parameters
govern the impulse delivered by a buried charge. Namely in the current programme of work this is an investigation
into the āundrained strengthā of a cohesive material as an indicator of potential impulse output.
Initial results are compared against previously published work on cohesionless soils (sands) to try to establish the full
range of loading which can be generated by a buried charge
Predicting the role of geotechnical parameters on the output from shallow buried explosives
Experiments have been conducted to quantify the effect the geotechnical conditions surrounding a buried charge have on the resulting output. From the results obtained the critical importance of moisture content in governing the magnitude of impulse delivered is highlighted. This has led to the development of a first-order predictive model for the impulse delivered from a buried charge, based on bulk density and moisture content, allowing rapid assessment of the effect of varying the geotechnical conditions. The work utilised a half-scale impulse measurement apparatus which incorporated a deformable target plate. Impulse, peak and residual target deflections were recorded for each test. No variations the charge geometry, mass of explosive, burial depth or stand-off were considered, with the focus solely being on the effect of the geotechnical conditions on the magnitude of loading and structural response. Five different types or grades of soils were used in the work, with both cohesive and cohesionless soils represented. The effect of air voids on the impulse generated was also investigated which showed that while strongly correlated, air voids alone is a poorer predictor of impulse than moisture content
Influence of particle size distribution on the blast pressure profile from explosives buried in saturated soils
The spatial and temporal distribution of pressure
and impulse from explosives buried in saturated
cohesive and cohesionless soils has been measured experimentally
for the first time. Ten experiments have
been conducted at quarter-scale, where localised pressure
loading was measured using an array of 17 Hopkinson
pressure bars. The blast pressure measurements
are used in conjunction with high-speed video filmed
at 100,000 fps to investigate in detail the physical processes
occurring at the loaded face. Two coarse cohesionless
soils and one fine cohesive soil were tested: a relatively
uniform sand, a well-graded sandy-gravel, and
a fine-grained clay. The results show that there is a
single fundamental loading mechanism when explosives
are detonated in saturated soil, invariant of particle size
and soil cohesion. It is also shown that variability in localised
loading is intrinsically linked to the particle size
distribution of the surrounding soil
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