8,626 research outputs found
Hadronic Freeze-Out in A+A Collisions meets the Lattice QCD Parton-Hadron Transition Line
We analyze hadrochemical freeze-out in central Pb+Pb collisions at CERN SPS
and LHC energies. Employing the UrQMD hybrid transport model we study the
effects of the final hadron/resonance expansion phase on the hadron
multiplicities established at hadronization. The bulk meson yields freeze out
directly at hadronization whereas the baryon-antibaryon sector is subject to
significant alterations, due to annihilation and regeneration processes. We
quantify the latter changes by survival factors for each species which are
applied to modify the statistical model predictions for the data. The modified
SM analysis recovers the hadronization points, which coincide with the recent
lattice QCD predictions of the parton-hadron transition line at finite
baryochemical potential.Comment: Proceedings of the 8th International Workshop on Critical Point and
Onset of Deconfinement, March 11 to 15, 2013 Napa, California, US
The rotation group in plate tectonics and the representation of uncertainties of plate reconstructions
The calculation of the uncertainty in an estimated rotation requires a parametrization of the rotation group; that is, a unique mapping of the rotation group to a point in 3-D Euclidean space, R^3. Numerous parametrizations of a rotation exist, including: (1) the latitude and longitude of the axis of rotation and the angle of rotation; (2) a representation as a Cartesian vector with length equal to the rotation angle and direction parallel to the rotation axis; (3) Euler angles; or (4) unit length quaternions (or, equivalently, Cayley-Klein parameters).
The uncertainty in a rotation is determined by the effect of nearby rotations on the rotated data. The uncertainty in a rotation is small, if rotations close to the best fitting rotation degrade the fit of the data by a large amount, and it is large, if only rotations differing by a large amount cause such a degradation. Ideally, we would like to parametrize the rotations in such a way so that their representation as points in R^3 would have the property that the distance between two points in R3 reflects the effects of the corresponding rotations on the fit of the data. It can be shown mathematically that this is impossible, but for rotations of small angle, it can be done to close approximation by using vectors in Cartesian coordinates. Thus, we are led to parametrizing the uncertainty separately from the parametrization of the best fitting rotation. This approach results in simpler, more efficient calculations than if uncertainties are described in terms of rotation parameters (i.e., latitude, longitude, and the angle). We illustrate this with the example of equations for determining the uncertainty in a composite rotation from the uncertainties of its constituents
Building validation tools for knowledge-based systems
The Expert Systems Validation Associate (EVA), a validation system under development at the Lockheed Artificial Intelligence Center for more than a year, provides a wide range of validation tools to check the correctness, consistency and completeness of a knowledge-based system. A declarative meta-language (higher-order language), is used to create a generic version of EVA to validate applications written in arbitrary expert system shells. The architecture and functionality of EVA are presented. The functionality includes Structure Check, Logic Check, Extended Structure Check (using semantic information), Extended Logic Check, Semantic Check, Omission Check, Rule Refinement, Control Check, Test Case Generation, Error Localization, and Behavior Verification
Excitations in the quantum paramagnetic phase of the quasi-one-dimensional Ising magnet CoNbO in a transverse field: Geometric frustration and quantum renormalization effects
The quasi-one-dimensional (1D) Ising ferromagnet CoNbO has recently
been driven via applied transverse magnetic fields through a continuous quantum
phase transition from spontaneous magnetic order to a quantum paramagnet, and
dramatic changes were observed in the spin dynamics, characteristic of weakly
perturbed 1D Ising quantum criticality. We report here extensive single-crystal
inelastic neutron scattering measurements of the magnetic excitations
throughout the three-dimensional (3D) Brillouin zone in the quantum
paramagnetic phase just above the critical field to characterize the effects of
the finite interchain couplings. In this phase, we observe that excitations
have a sharp, resolution-limited line shape at low energies and over most of
the dispersion bandwidth, as expected for spin-flip quasiparticles. We map the
full bandwidth along the strongly dispersive chain direction and resolve clear
modulations of the dispersions in the plane normal to the chains,
characteristic of frustrated interchain couplings in an antiferromagnetic
isosceles triangular lattice. The dispersions can be well parametrized using a
linear spin-wave model that includes interchain couplings and further neighbor
exchanges. The observed dispersion bandwidth along the chain direction is
smaller than that predicted by a linear spin-wave model using exchange values
determined at zero field, and this effect is attributed to quantum
renormalization of the dispersion beyond the spin-wave approximation in fields
slightly above the critical field, where quantum fluctuations are still
significant.Comment: 11 pages, 6 figures. Updated references. Minor changes to text and
figure
Characterizing upward lightning with and without a terrestrial gamma-ray flash
We compare two observations of gamma-rays before, during, and after lightning
flashes initiated by upward leaders from a tower during low-altitude winter
thunderstorms on the western coast of Honshu, Japan. While the two leaders
appear similar, one produced a terrestrial gamma-ray flash (TGF) so bright that
it paralyzed the gamma-ray detectors while it was occurring, and could be
observed only via the weaker flux of neutrons created in its wake, while the
other produced no detectable TGF gamma-rays at all. The ratio between the
indirectly derived gamma-ray fluence for the TGF and the 95% confidence
gamma-ray upper limit for the gamma-ray quiet flash is a factor of
. With the only two observations of this type providing such
dramatically different results -- a TGF probably as bright as those seen from
space and a powerful upper limit -- we recognize that weak, sub-luminous TGFs
in this situation are probably not common, and we quantify this conclusion.
While the gamma-ray quiet flash appeared to have a faster leader and more
powerful initial continuous current pulse than the flash that produced a TGF,
the TGF-producing flash occurred during a weak gamma-ray "glow", while the
gamma-ray quiet flash did not, implying a higher electric field aloft when the
TGF was produced. We suggest that the field in the high-field region approached
by a leader may be more important for whether a TGF is produced than the
characteristics of the leader itself.Comment: 21 pages, 6 figures, accepted for publication by the Journal of
Geophysical Research - Atmosphere
Measurement of Both Gas and Particle Velocity in Turbulent Two-Phase Flow
A laser-Doppler anemometer was used to measure the velocity of both the gas and particles in a turbulent two-phase flow for conditions when the distribution of the velocities of the two phases overlaps. The velocities from the two phases are separated by comparing the Doppler amplitude to the pedestal amplitude. Results of the measure of the gas-particle flow downstream of a nozzle mounted in a circular pipe are presented
Ancient origins of low lean mass among South Asians and implications for modern type 2 diabetes susceptibility
Living South Asians have low lean tissue mass relative to height, which contributes to their elevated type 2 diabetes susceptibility, particularly when accompanied by obesity. While ongoing lifestyle transitions account for rising obesity, the origins of low lean mass remain unclear. We analysed proxies for lean mass and stature among South Asian skeletons spanning the last 11,000 years (n = 197) to investigate the origins of South Asian low lean mass. Compared with a worldwide sample (n = 2,003), South Asian skeletons indicate low lean mass. Stature-adjusted lean mass increased significantly over time in South Asia, but to a very minor extent (0.04 z-score units per 1,000 years, adjusted R2 = 0.01). In contrast stature decreased sharply when agriculture was adopted. Our results indicate that low lean mass has characterised South Asians since at least the early Holocene and may represent long-term climatic adaptation or neutral variation. This phenotype is therefore unlikely to change extensively in the short term, so other strategies to address increasing non-communicable disease rates must be pursued. © 2019, The Author(s)
The quantum metrology triangle and the re-definition of the SI ampere and kilogram; Analysis of a reduced set of observational equations
We have developed a set of seven observational equations that include all of
the physics necessary to relate the most important of the fundamental constants
to the definitions of the SI kilogram and ampere. We have used these to
determine the influence of alternative definitions being considered for the SI
kilogram and ampere on the uncertainty of three of the fundamental constants
(h, e and mu). We have also reviewed the experimental evidence for the
exactness of the quantum metrology triangle resulting from experiments
combining the quantum Hall effect, the Josephson effects and single-electron
tunnelling.Comment: 16 pages, 3 figures & 5 table
Simulation and Flight Test Capability for Testing Prototype Sense and Avoid System Elements
NASA Langley Research Center (LaRC) and The MITRE Corporation (MITRE) have developed, and successfully demonstrated, an integrated simulation-to-flight capability for evaluating sense and avoid (SAA) system elements. This integrated capability consists of a MITRE developed fast-time computer simulation for evaluating SAA algorithms, and a NASA LaRC surrogate unmanned aircraft system (UAS) equipped to support hardware and software in-the-loop evaluation of SAA system elements (e.g., algorithms, sensors, architecture, communications, autonomous systems), concepts, and procedures. The fast-time computer simulation subjects algorithms to simulated flight encounters/ conditions and generates a fitness report that records strengths, weaknesses, and overall performance. Reviewed algorithms (and their fitness report) are then transferred to NASA LaRC where additional (joint) airworthiness evaluations are performed on the candidate SAA system-element configurations, concepts, and/or procedures of interest; software and hardware components are integrated into the Surrogate UAS research systems; and flight safety and mission planning activities are completed. Onboard the Surrogate UAS, candidate SAA system element configurations, concepts, and/or procedures are subjected to flight evaluations and in-flight performance is monitored. The Surrogate UAS, which can be controlled remotely via generic Ground Station uplink or automatically via onboard systems, operates with a NASA Safety Pilot/Pilot in Command onboard to permit safe operations in mixed airspace with manned aircraft. An end-to-end demonstration of a typical application of the capability was performed in non-exclusionary airspace in October 2011; additional research, development, flight testing, and evaluation efforts using this integrated capability are planned throughout fiscal year 2012 and 2013
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