651 research outputs found
Precision Measurement Of The Neutron's Beta Asymmetry Using Ultra-Cold Neutrons
A measurement of A_β, the correlation between the electron momentum and neutron (n) spin (the beta asymmetry) in n beta-decay, together with the n lifetime, provides a method for extracting fundamental parameters for the charged-current weak interaction of the nucleon. In particular when combined with decay measurements, one can extract the V_(ud) element of the CKM matrix, a critical element in CKM unitarity tests. By using a new SD_2 super-thermal source at LANSCE, large fluxes of UCN (ultra-cold neutrons) are expected for the UCNA project. These UCN will be 100% polarized using a 7 T magnetic field, and directed into the β spectrometer. This approach, together with an expected large reduction in backgrounds, will result in an order of magnitude reduction in the critical systematic corrections associated with current n β-asymmetry measurements. This paper will give an overview of the UCNA Aβ measurement as well as an update on the status of the experiment
Spatially resolved spectral determination of polysaccharides in hydrothermally carbonized biomass
Reliable information on the decomposition of polysaccharides is important to evaluate the evolution and properties of hydrothermally carbonized chars. Hyperspectral imaging offers a quick and robust alternative to expensive and time-consuming laboratory methods to determine the polysaccharide contents of biomass and biomass-derived chars. Here, we show that the decomposition of hemicellulose and cellulose were visible in the acquired hyperspectral images even without image calibration. Image regression based on sample holocellulose, glucan and the sum of xylan, galactan, arabinan and mannan provided good calibration models and enabled visualizing the decomposition of polysaccharides based on carbonization temperature. Hyperspectral imaging thus provides a non-destructive alternative to traditional polysaccharide analyses of hydrochars for laboratory and potential future industrial applications.Peer reviewe
Microcanonical statistics of black holes and bootstrap condition
The microcanonical statistics of the Schwarzschild black holes as well as the
Reissner-Nordstrm black holes are analyzed. In both cases we set
up the inequalities in the microcanonical density of states.
These are then used to show that the most probable configuration in the gases
of black holes is that one black hole acquires all of the mass and all of the
charge at high energy limit. Thus the black holes obey the statistical
bootstrap condition and, in contrast to the other investigation, we see that
U(1) charge does not break the bootstrap property.Comment: 16 pages. late
Hyperglycemia and lower diet quality in pregnant overweight women and increased infant size at birth and at 13 months of age - STEPS study
Conclusions: Maternal prepregnancy overweight increases risk of hyperglycemia in late-pregnancy and increased infant size at birth and 13 months possibly predisposing the infant to health risks later in life. (C) 2013 Elsevier Ireland Ltd. All rights reserved.</p
Building blocks of a black hole
What is the nature of the energy spectrum of a black hole ? The algebraic
approach to black hole quantization requires the horizon area eigenvalues to be
equally spaced. As stressed long ago by by Mukhanov, such eigenvalues must be
exponentially degenerate with respect to the area quantum number if one is to
understand black hole entropy as reflecting degeneracy of the observable
states. Here we construct the black hole states by means of a pair of "creation
operators" subject to a particular simple algebra, a slight generalization of
that for the harmonic oscillator. We then prove rigorously that the n-th area
eigenvalue is exactly 2 raised to the n-fold degenerate. Thus black hole
entropy qua logarithm of the number of states for fixed horizon area comes out
proportional to that area.Comment: PhysRevTeX, 14 page
The spectrum of quantum black holes and quasinormal modes
The spectrum of multiple level transitions of the quantum black hole is
considered, and the line widths calculated. Initial evidence is found for these
higher order transitions in the spectrum of quasinormal modes for Schwarzschild
and Kerr black holes, further bolstering the idea that there exists a
correspondence principle between quantum transitions and classical ``ringing
modes''. Several puzzles are noted, including a fine-tuning problem between the
line width and the level degeneracy. A more general explanation is provided for
why setting the Immirzi parameter of loop quantum gravity from the black hole
spectrum necessarily gives the correct value for the black hole entropy.Comment: 5 pages, 5 figures, version to appear in Phys. Rev.
Population-Based Rates of Revision of Primary Total Hip Arthroplasty: A Systematic Review
Background: Most research on failure leading to revision total hip arthroplasty (THA) is reported from single centers. We searched PubMed between January 2000 and August 2010 to identify population- or community-based studies evaluating ten-year revision risks. We report ten-year revision risk using the Kaplan-Meier method, stratifying by age and fixation technique. Results: Thirteen papers met the inclusion criteria. Cemented prostheses had Kaplan-Meier estimates of revision-free implant survival of ten years ranging from 88 % to 95%; uncemented prostheses had Kaplan-Meier estimates from 80 % to 85%. Estimates ranged from 72 % to 86 % in patients less than 60 years old and from 90 to 96 % in older patients. Conclusion: Data reported from national registries suggest revision risks of 5 to 20 % ten years following primary THA. Revision risks are lower in older THA recipients. Uncemented implants may have higher ten-year rates of revision, regardless of age
Effects of the midnight temperature maximum observed in the thermosphere–ionosphere over the northeast of Brazil
Search for the Neutron Decay n X+ where X is a dark matter particle
In a recent paper submitted to Physical Review Letters, Fornal and Grinstein
have suggested that the discrepancy between two different methods of neutron
lifetime measurements, the beam and bottle methods can be explained by a
previously unobserved dark matter decay mode, n X+ where X
is a dark matter particle. We have performed a search for this decay mode over
the allowed range of energies of the monoenergetic gamma ray for X to be a dark
matter particle. We exclude the possibility of a sufficiently strong branch to
explain the lifetime discrepancy with greater than 4 sigma confidence.Comment: 6 pages 3 figure
Area Spectrum of Kerr and extremal Kerr Black Holes from Quasinormal Modes
Motivated by the recent interest in quantization of black hole area spectrum,
we consider the area spectrum of Kerr and extremal Kerr black holes. Based on
the proposal by Bekenstein and others that the black hole area spectrum is
discrete and equally spaced, we implement Kunstatter's method to derive the
area spectrum for the Kerr and extremal Kerr black holes. The real part of the
quasinormal frequencies of Kerr black hole used for this computation is of the
form where is the angular velocity of the black hole
horizon. The resulting spectrum is discrete but not as expected uniformly
spaced. Thus, we infer that the function describing the real part of
quasinormal frequencies of Kerr black hole is not the correct one. This
conclusion is in agreement with the numerical results for the highly damped
quasinormal modes of Kerr black hole recently presented by Berti, Cardoso and
Yoshida. On the contrary, extremal Kerr black hole is shown to have a discrete
area spectrum which in addition is evenly spaced. The area spacing derived in
our analysis for the extremal Kerr black hole area spectrum is not proportional
to . Therefore, it does not give support to Hod's statement that the
area spectrum should be valid for a generic
Kerr-Newman black hole.Comment: 10 pages, no figure, LaTeX; v2: 12 pages, clarifying comments and an
Appendix are added, version to appear in Mod. Phys. Lett.
- …