7,894 research outputs found
Converting energy from fusion into useful forms
If fusion power reactors are to be feasible, it will still be necessary to
convert the energy of the nuclear reaction into usable form. The heat produced
will be removed from the reactor core by a primary coolant, which might be
water, helium, molten lithium-lead, molten lithium-containing salt, or CO2. The
heat could then be transferred to a conventional Rankine cycle or Brayton (gas
turbine) cycle. Alternatively it could be used for thermochemical processes
such as producing hydrogen or other transport fuels. Fusion presents new
problems because of the high energy neutrons released. These affect the
selection of materials and the operating temperature, ultimately determining
the choice of coolant and working cycle. The limited temperature ranges allowed
by present day irradiated structural materials, combined with the large
internal power demand of the plant, will limit the overall thermal efficiency.
The operating conditions of the fusion power source, the materials, coolant,
and energy conversion system will all need to be closely integrated.Comment: 22 pages, 4 figures, Proceedings of the Institution of Mechanical
Engineers, Part A: Journal of Power and Energy December 11, 201
Triple-Pomeron Matrix Model for Dispersive Corrections to Nucleon-Nucleus Total Cross Section
Dispersive corrections to the total cross section for high-energy scattering
from a heavy nucleus are calculated using a matrix model, based on the
triple-Pomeron behavior of diffractive scattering from a single nucleon, for
the cross section operator connecting different states of the projectile
nucleon . Energy-dependent effects due to the decrease in longitudinal momentum
transfers and the opening of more channels with increasing energy are included.
The three leading terms in an expansion in the number of inelastic transitions
are evaluated and compared to exact results for the model in the uniform
nuclear density approximation for the the scattering of nucleons from Pb^{208}
for laboratory momenta ranging from 50 to 200 GeV/c.Comment: 16 pages, 2 figures, RevTex
Calorons, instantons and constituent monopoles in SU(3) lattice gauge theory
We analyze the zero-modes of the Dirac operator in quenched SU(3) gauge
configurations at non-zero temperature and compare periodic and anti-periodic
temporal boundary conditions for the fermions. It is demonstrated that for the
different boundary conditions often the modes are localized at different
space-time points and have different sizes. Our observations are consistent
with patterns expected for Kraan - van Baal solutions of the classical
Yang-Mills equations. These solutions consist of constituent monopoles and the
zero-modes are localized on different constituents for different boundary
conditions. Our findings indicate that the excitations of the QCD vacuum are
more structured than simple instanton-like lumps.Comment: Remarks added. To appear in Phys. Rev.
Spectropolarimetry of the H-alpha line in Herbig Ae/Be stars
Using the HiVIS spectropolarimeter built for the Haleakala 3.7m AEOS
telescope, we have obtained a large number of high precision spectropolarimetrc
observations (284) of Herbig AeBe stars collected over 53 nights totaling more
than 300 hours of observing. Our sample of five HAeBe stars: AB Aurigae,
MWC480, MWC120, MWC158 and HD58647, all show systematic variations in the
linear polarization amplitude and direction as a function of time and
wavelength near the H-alpha line. In all our stars, the H-alpha line profiles
show evidence of an intervening disk or outflowing wind, evidenced by strong
emission with an absorptive component. The linear polarization varies by 0.2%
to 1.5% with the change typically centered in the absorptive part of the line
profile. These observations are inconsistent with a simple disk-scattering
model or a depolarization model which produce polarization changes centered on
the emmissive core. We speculate that polarized absorption via optical pumping
of the intervening gas may be the cause.Comment: Accepted for publication in ApJ Letter
Screening and Assessment of Cancer-Related Fatigue: A Clinical Practice Guideline for Health Care Providers
Cancer-related fatigue (CRF) is the most common side effect of cancer treatment. Regular surveillance is recommended, but few clinical practice guidelines transparently assess study bias, quality, and clinical utility in deriving recommendations of screening and assessment methods. The purpose of this clinical practice guideline (CPG) is to provide recommendations for the screening and assessment of CRF for health care professions treating individuals with cancer. Following best practices for development of a CPG using the Appraisal of Guidelines for Research and Evaluation (AGREE) Statement and Emergency Care Research Institute (ECRI) Guidelines Trust Scorecard, this CPG included a systematic search of the literature, quality assessment of included evidence, and stakeholder input from diverse health care fields to derive the final CPG. Ten screening and 15 assessment tools supported by 114 articles were reviewed. One screen (European Organisation for Research and Treatment of CancerâQuality of Life Questionnaireâ30 Core Questionnaire) and 3 assessments (Piper Fatigue ScaleâRevised, Functional Assessment of Chronic Illness TherapyâFatigue, and Patient Reported Outcome Measurement Information System [PROMIS] Fatigue-SF) received an A recommendation (âshould be used in clinical practiceâ), and 1 screen and 5 assessments received a B recommendation (âmay be used in clinical practiceâ). Health care providers have choice in determining appropriate screening and assessment tools to be used across the survivorship care continuum. The large number of tools available to screen for or assess CRF may result in a lack of comprehensive research evidence, leaving gaps in the body of evidence for measurement tools. More research into the responsiveness of these tools is needed in order to adopt their use as outcome measures.
Impact: Health care providers should screen for and assess CRF using one of the tools recommended by this CPG
Screening and Assessment of Cancer-Related Fatigue: An Executive Summary and Road Map for Clinical Implementation
Background: Cancer-related fatigue (CRF) prevalence is reported as high as 90%. Cancer-related fatigue is multidimensional and associated with lower health-related quality of life. Effective screening and assessment are dependent upon use of valid, reliable, and clinically feasible measures. This Executive Summary of the Screening and Assessment of Cancer-related Fatigue Clinical Practice Guideline provides recommendations for best measures to screen and assess for CRF based on the quality and level of evidence, psychometric strength of the tools, and clinical utility.
Methods: After a systematic review of the literature, studies evaluating CRF measurement tools were assessed for quality; data extraction included psychometrics and clinical utility. Measurement tools were categorized as either screens or assessments.
Results: Four screens are recommended: European Organization of Research and Treatment of Cancer Quality of Life Questionnaire, the MD Anderson Symptom Inventory, the Distress Thermometer, and the One-Item Fatigue Scale. Eight assessments are recommended: Functional Assessment of Chronic Illness TherapyâFatigue, Piper Fatigue ScaleâRevised, Brief Fatigue Inventory, Cancer Fatigue Scale, Fatigue Symptom Inventory, Patient-Reported Outcome Measurement Information System (PROMIS) Fatigue Short Form and CAT, and Multidimensional Fatigue Inventory-20.
Discussion: This Executive Summary is a synopsis of and road map for implementation of the Clinical Practice Guideline for Screening and Assessment of CRF. Review of the full Clinical Practice Guideline is recommended. Additional research focused on responsiveness of instruments is needed in order to consider them for use as outcome measures. Screening and assessing CRF will result in opportunities to improve the quality of life of individuals with cancer
Early events of B-cell receptor signaling are not essential for the proliferation and viability of AIDS-related lymphoma
Temperature dependence of instantons in QCD
We investigate the temperature dependence of the instanton contents of gluon
fields, using unquenched lattice QCD and the cooling method. The instanton size
parameter deduced from the correlation function decreases from 0.44fm below the
phase-transition temperature (MeV) to 0.33fm at 1.3 .
The instanton charge distribution is Poissonian above , but it deviates
from the convoluted Poisson at low temperature. The topological susceptibility
decreases rapidly below , showing the apparent restoration of the
symmetry already at .Comment: 8 pages TEX, 3 Postscript figures available at
http://www.krl.caltech.edu/preprints/MAP.htm
Four-Body Effects in Globular Cluster Black Hole Coalescence
In the high density cores of globular clusters, multibody interactions are
expected to be common, with the result that black holes in binaries are
hardened by interactions. It was shown by Sigurdsson & Hernquist (1993) and
others that 10 solar mass black holes interacting exclusively by three-body
encounters do not merge in the clusters themselves, because recoil kicks the
binaries out of the clusters before the binaries are tight enough to merge.
Here we consider a new mechanism, involving four-body encounters. Numerical
simulations by a number of authors suggest that roughly 20-50% of binary-binary
encounters will eject one star but leave behind a stable hierarchical triple.
If the orbital plane of the inner binary is strongly tilted with respect to the
orbital plane of the outer object, a secular Kozai resonance, first
investigated in the context of asteroids in the Solar System, can increase the
eccentricity of the inner body significantly. We show that in a substantial
fraction of cases the eccentricity is driven to a high enough value that the
inner binary will merge by gravitational radiation, without a strong
accompanying kick. Thus the merged object remains in the cluster; depending on
the binary fraction of black holes and the inclination distribution of
newly-formed hierarchical triples, this mechanism may allow massive black holes
to accumulate through successive mergers in the cores of globular clusters. It
may also increase the likelihood that stellar-mass black holes in globular
clusters will be detectable by their gravitational radiation.Comment: Submitted to ApJ Letters (includes emulateapj.sty
Nearby low-mass triple system GJ795
We report the results of our optical speckle-interferometric observations of
the nearby triple system GJ795 performed with the 6-m BTA telescope with
diffraction-limited angular resolution. The three components of the system were
optically resolved for the first time. Position measurements allowed us to
determine the elements of the inner orbit of the triple system. We use the
measured magnitude differences to estimate the absolute magnitudes and spectral
types of the components of the triple: =7.310.08,
=8.660.10, =8.420.10, K5,
K9, K8. The total mass of the system is
equal to =1.69. We show
GJ795 to be a hierarchical triple system which satisfies the empirical
stability criteria.Comment: 6 pages, 2 figures, published in Astrophysical Bulleti
- âŠ