7,718 research outputs found
Can skills assessment on a virtual reality trainer predict a surgical trainee's talent in laparoscopic surgery?
Background: A number of studies have investigated several aspects of feasibility and validity of performance assessments with virtual reality surgical simulators. However, the validity of performance assessments is limited by the reliability of such measurements, and some issues of reliability still need to be addressed. This study aimed to evaluate the hypothesis that test subjects show logarithmic performance curves on repetitive trials for a component task of laparoscopic cholecystectomy on a virtual reality simulator, and that interindividual differences in performance after considerable training are significant. According to kinesiologic theory, logarithmic performance curves are expected and an individual's learning capacity for a specific task can be extrapolated, allowing quantification of a person's innate ability to develop task-specific skills. Methods: In this study, 20 medical students at the University of Basel Medical School performed five trials of a standardized task on the LS 500 virtual reality simulator for laparoscopic surgery. Task completion time, number of errors, economy of instrument movements, and maximum speed of instrument movements were measured. Results: The hypothesis was confirmed by the fact that the performance curves for some of the simulator measurements were very close to logarithmic curves, and there were significant interindividual differences in performance at the end of the repetitive trials. Conclusions: Assessment of perceptual motor skills and the innate ability of an individual with no prior experience in laparoscopic surgery to develop such skills using the LS 500 VR surgical simulator is feasible and reliabl
A Flattened Protostellar Envelope in Absorption around L1157
Deep Spitzer IRAC images of L1157 reveal many of the details of the outflow
and the circumstellar environment of this Class 0 protostar. In IRAC band 4, 8
microns, there is a flattened structure seen in absorption against the
background emission. The structure is perpendicular to the outflow and is
extended to a diameter of 2 arcminutes. This structure is the first clear
detection of a flattened circumstellar envelope or pseudo-disk around a Class 0
protostar. Such a flattened morphology is an expected outcome for many collapse
theories that include magnetic fields or rotation. We construct an extinction
model for a power-law density profile, but we do not constrain the density
power-law index.Comment: ApJL accepte
Simulation of individual leaf areas in grain sorghum
Most crop simulation models that incorporate environmental conditions estimate leaf area development. The grain sorghum growth simulation model, SORKAM, calculates individual leaf area based on leaf number and maturity class. The objective of this study was to generalize present leaf growth routines in SORKAM to be independent of maturity since there are no generally accepted maturing classes. Modified relationships between leaf number and leaf growth parameters were developed from existing studies and were tested against independent detailed leaf growth data sets. The revised relationships improved the r2 between simulated and actual individual leaf areas from 0.80 to 0.88, reduced the bias from 32 cm2 to 9 cm2, and the RMSE from 80 cm2 to 52 cm2. With the improved simulation, estimated leaf area index through the season was also improved from the original SORKAM estimate (RMSE decreased from 0.77 to 0.63; RMSE: root mean square error). Although simulation of individual leaf areas was improved, total leaf area produced over the season was not
Symbolic vector/dyadic multibody formalism for tree-topology systems
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76159/1/AIAA-20780-671.pd
Multifluid, Magnetohydrodynamic Shock Waves with Grain Dynamics II. Dust and the Critical Speed for C Shocks
This is the second in a series of papers on the effects of dust on
multifluid, MHD shock waves in weakly ionized molecular gas. We investigate the
influence of dust on the critical shock speed, v_crit, above which C shocks
cease to exist. Chernoff showed that v_crit cannot exceed the grain
magnetosound speed, v_gms, if dust grains are dynamically well coupled to the
magnetic field. We present numerical simulations of steady shocks where the
grains may be well- or poorly coupled to the field. We use a time-dependent,
multifluid MHD code that models the plasma as a system of interacting fluids:
neutral particles, ions, electrons, and various ``dust fluids'' comprised of
grains with different sizes and charges. Our simulations include grain inertia
and grain charge fluctuations but to highlight the essential physics we assume
adiabatic flow, single-size grains, and neglect the effects of chemistry. We
show that the existence of a phase speed v_phi does not necessarily mean that C
shocks will form for all shock speeds v_s less than v_phi. When the grains are
weakly coupled to the field, steady, adiabatic shocks resemble shocks with no
dust: the transition to J type flow occurs at v_crit = 2.76 v_nA, where v_nA is
the neutral Alfven speed, and steady shocks with v_s > 2.76 v_nA are J shocks
with magnetic precursors in the ion-electron fluid. When the grains are
strongly coupled to the field, v_crit = min(2.76 v_nA, v_gms). Shocks with
v_crit < v_s < v_gms have magnetic precursors in the ion-electron-dust fluid.
Shocks with v_s > v_gms have no magnetic precursor in any fluid. We present
time-dependent calculations to study the formation of steady multifluid shocks.
The dynamics differ qualitatively depending on whether or not the grains and
field are well coupled.Comment: 43 pages with 17 figures, aastex, accepted by The Astrophysical
Journa
Stellar Model Analysis of the Oscillation Spectrum of eta Bootis Obtained from MOST
Eight consecutive low-frequency radial p-modes are identified in the G0 IV
star eta Bootis based on 27 days of ultraprecise rapid photometry obtained by
the MOST (Microvariability & Oscillations of Stars) satellite. The MOST data
extend smoothly to lower overtones the sequence of radial p-modes reported in
earlier groundbased spectroscopy by other groups. The lower-overtone modes from
the MOST data constrain the interior structure of the model of eta Boo. With
the interior fit anchored by the lower-overtone modes seen by MOST, standard
models are not able to fit the higher-overtone modes with the same level of
accuracy. The discrepancy is similar to the discrepancy that exists between the
Sun's observed p-mode frequencies and the p-mode frequencies of the standard
solar model. This discrepancy promises to be a powerful constraint on models of
3D convection.Comment: 30 pages with 14 figures. Accepted for publication in Ap
Using Markov chain Monte Carlo methods for estimating parameters with gravitational radiation data
We present a Bayesian approach to the problem of determining parameters for
coalescing binary systems observed with laser interferometric detectors. By
applying a Markov Chain Monte Carlo (MCMC) algorithm, specifically the Gibbs
sampler, we demonstrate the potential that MCMC techniques may hold for the
computation of posterior distributions of parameters of the binary system that
created the gravity radiation signal. We describe the use of the Gibbs sampler
method, and present examples whereby signals are detected and analyzed from
within noisy data.Comment: 21 pages, 10 figure
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