219 research outputs found
Nuclear reactor control rod assembly with improved driving mechanism Patent
Nuclear reactor control rod assembly with improved driving mechanis
High torque bellows seal rotary drive
Bellows seal rotary drive device was developed which allows high torque transmission through sealed compartments. Bearing friction which would normally be carried by sealing bellows in comparable devices is absorbed by universal-gimbal joint. It can be used to transmit high torque, low speed, rotary motion through sealed barriers to prevent contamination or escape of fluids
MRI radiomic features are independently associated with overall survival in soft tissue sarcoma
Purpose: Soft tissue sarcomas (STS) represent a heterogeneous group of diseases, and selection of individualized treatments remains a challenge. The goal of this study was to determine whether radiomic features extracted from magnetic resonance (MR) images are independently associated with overall survival (OS) in STS.
Methods and Materials: This study analyzed 2 independent cohorts of adult patients with stage II-III STS treated at center 1 (N = 165) and center 2 (N = 61). Thirty radiomic features were extracted from pretreatment T1-weighted contrast-enhanced MR images. Prognostic models for OS were derived on the center 1 cohort and validated on the center 2 cohort. Clinical-only (C), radiomics-only (R), and clinical and radiomics (C+R) penalized Cox models were constructed. Model performance was assessed using Harrell\u27s concordance index.
Results: In the R model, tumor volume (hazard ratio [HR], 1.5) and 4 texture features (HR, 1.1-1.5) were selected. In the C+R model, both age (HR, 1.4) and grade (HR, 1.7) were selected along with 5 radiomic features. The adjusted c-indices of the 3 models ranged from 0.68 (C) to 0.74 (C+R) in the derivation cohort and 0.68 (R) to 0.78 (C+R) in the validation cohort. The radiomic features were independently associated with OS in the validation cohort after accounting for age and grade (HR, 2.4;
Conclusions: This study found that radiomic features extracted from MR images are independently associated with OS when accounting for age and tumor grade. The overall predictive performance of 3-year OS using a model based on clinical and radiomic features was replicated in an independent cohort. Optimal models using clinical and radiomic features could improve personalized selection of therapy in patients with STS
Analysis of the rotation period of asteroids (1865) Cerberus, (2100) Ra-Shalom, and (3103) Eger - search for the YORP effect
The spin state of small asteroids can change on a long timescale by the
Yarkovsky-O'Keefe-Radzievskii-Paddack (YORP) effect, the net torque that arises
from anisotropically scattered sunlight and proper thermal radiation from an
irregularly-shaped asteroid. The secular change in the rotation period caused
by the YORP effect can be detected by analysis of asteroid photometric
lightcurves. We analyzed photometric lightcurves of near-Earth asteroids (1865)
Cerberus, (2100) Ra-Shalom, and (3103) Eger with the aim to detect possible
deviations from the constant rotation caused by the YORP effect. We carried out
new photometric observations of the three asteroids, combined the new
lightcurves with archived data, and used the lightcurve inversion method to
model the asteroid shape, pole direction, and rotation rate. The YORP effect
was modeled as a linear change in the rotation rate in time d\omega /dt. Values
of d\omega/ dt derived from observations were compared with the values
predicted by theory. We derived physical models for all three asteroids. We had
to model Eger as a nonconvex body because the convex model failed to fit the
lightcurves observed at high phase angles. We probably detected the
acceleration of the rotation rate of Eger d\omega / dt = (1.4 +/- 0.6) x
10^{-8} rad/d (3\sigma error), which corresponds to a decrease in the rotation
period by 4.2 ms/yr. The photometry of Cerberus and Ra-Shalom was consistent
with a constant-period model, and no secular change in the spin rate was
detected. We could only constrain maximum values of |d\omega / dt| < 8 x
10^{-9} rad/d for Cerberus, and |d\omega / dt| < 3 x 10^{-8} rad/d for
Ra-Shalom
An Isothermal Model for Predicting Performance Loss in PEMFCs from BOP Leachates
In the development of proton exchange membrane fuel cells (PEMFCs), the cost of balance of plant (BOP) materials and their effect on PEMFC durability can retard commercialization. 1 One opportunity to decrease these costs would be to use off-the-shelf materials rather than custommade materials if leachates from the less expensive materials do not affect performance and lifetime. To understand contamination mechanisms and their impacts on PEMFCs, experimental studies conducted and found the sensitivity of performance to the low levels of contamination. 2-9 A model for contamination of a PEMFC which includes adsorption on the Pt catalyst, absorption into the membrane, and ion-exchange with ionomeric components is presented. The model predictions for three sources of voltage (i.e., performance) loss account for two-dimensional timedependent contamination along the channel and into the membrane as shown in 9 For typical parameters, the predicted voltage loss in the electrode by an ion-exchange mechanism shows slower reaction rates but greater performance losses than other mechanisms. More broadly, the model also provides a tolerance limits for contamination
Number-phase-squeezed few-photon state generated from squeezed atoms
This paper develops a method of manipulating the squeezed atom state to
generate a few-photon state whose phase or photon-number fluctuations are
prescribed at our disposal. The squeezed atom state is a collective atomic
state whose quantum fluctuations in population difference or collective dipole
are smaller than those of the coherent atom state. It is shown that the
squeezed atom state can be generated by the interaction of atoms with a
coherent state of the electromagnetic field, and that it can be used as a
tunable source of squeezed radiation. A variety of squeezed states, including
the photon-number squeezed state and the phase squeezed state, can be produced
by manipulating the atomic state. This is owing to the fact that
quantum-statistical information of the atomic state is faithfully transferred
to that of the photon state. Possible experimental situations to implement our
theory are discussed.Comment: 17 pages, RevTex, 14 figures, using epsf.sty, title is changed,
discussion about dissipation is added, accepted for publication in Physical
Review
Formation of asteroid pairs by rotational fission
Asteroid pairs sharing similar heliocentric orbits were found recently.
Backward integrations of their orbits indicated that they separated gently with
low relative velocities, but did not provide additional insight into their
formation mechanism. A previously hypothesized rotational fission process4 may
explain their formation - critical predictions are that the mass ratios are
less than about 0.2 and, as the mass ratio approaches this upper limit, the
spin period of the larger body becomes long. Here we report photometric
observations of a sample of asteroid pairs revealing that primaries of pairs
with mass ratios much less than 0.2 rotate rapidly, near their critical fission
frequency. As the mass ratio approaches 0.2, the primary period grows long.
This occurs as the total energy of the system approaches zero requiring the
asteroid pair to extract an increasing fraction of energy from the primary's
spin in order to escape. We do not find asteroid pairs with mass ratios larger
than 0.2. Rotationally fissioned systems beyond this limit have insufficient
energy to disrupt. We conclude that asteroid pairs are formed by the rotational
fission of a parent asteroid into a proto-binary system which subsequently
disrupts under its own internal system dynamics soon after formation.Comment: 12 pages, 2 figures, 1 table + Supplementary Informatio
IMPROVED DISTANCES TO TYPE Ia SUPERNOVAE WITH TWO SPECTROSCOPIC SUBCLASSES
We study the observables of 158 relatively normal Type Ia supernovae (SNe Ia)
by dividing them into two groups in terms of the expansion velocity inferred
from the absorption minimum of the Si II 6355 line in their spectra near B-band
maximum brightness. One group ("Normal") consists of normal SNe Ia populating a
narrow strip in the Si II velocity distribution, with an average expansion
velocity v=10,600+/-400 km/s near B maximum; the other group ("HV") consists of
objects with higher velocities, v > 11,800 km/s. Compared with the Normal
group, the HV one shows a narrower distribution in both the peak luminosity and
the luminosity decline rate dm_{15}. In particular, their B-V colors at maximum
brightness are found to be on average redder by ~0.1, suggesting that they
either are associated with dusty environments or have intrinsically red B-V
colors. The HV SNe Ia are also found to prefer a lower extinction ratio Rv~1.6
(versus ~2.4 for the Normal ones). Applying such an absorption-correction
dichotomy to SNe Ia of these two groups remarkably reduces the dispersion in
their peak luminosity from 0.178 mag to only 0.125 mag.Comment: Accepted for publication in ApJ Letters, 8 pages, 4 figures, 1 tabl
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