20,544 research outputs found
Development of data unfolding techniques for contoured semiconductor neutron spectrometer Final report
Data unfolding techniques for contoured semiconductor neutron spectromete
A study to determine the applicability of noise abatement approach procedures to McDonnell Douglas Aircraft
Analyses of McDonnell Douglas DC-8, DC-9, and DC-10 jet transports were conducted to investigate the applicability of two segment approach noise abatement procedures to these airplanes. All models had the required glide slope capability at the certified landing flap settings. The DC-8 models would probably be limited to an upper segment glide slope of 5.5 degrees and would probably not be suitable for the two segment procedure in icing conditions. The DC-8 would not be compatible with this procedure at a reduced landing flap setting. The feasibility of installing a two segment approach system in the Douglas-built fleet of commercial jet transports from a hardware viewpoint is discussed. The candidate system consists of a two segment computer plus the necessary peripheral equipment interfaced with the existing autopilot and associated avionics. The required modifications and additions to existing equipment are described and the attendant costs estimated. Potential problems which may be encountered are also discussed
The double life of electrons in magnetic iron pnictides, as revealed by NMR
We present a phenomenological, two-fluid approach to understanding the
magnetic excitations in Fe pnictides, in which a paramagnetic fluid with
gapless, incoherent particle-hole excitations coexists with an
antiferromagnetic fluid with gapped, coherent spin wave excitations. We show
that this two-fluid phenomenology provides an excellent quantitative
description of NMR data for magnetic "122" pnictides, and argue that it finds a
natural justification in LSDA and spin density wave calculations. We further
use this phenomenology to estimate the maximum renormalisation of the ordered
moment that can follow from low-energy spin fluctuations in Fe pnictides. We
find that this is too small to account for the discrepancy between ab intio
calculations and neutron scattering measurements.Comment: Accepted for publication in Europhys. Lett. 6 pages, 4 figure
The Minimum Description Length Principle and Model Selection in Spectropolarimetry
It is shown that the two-part Minimum Description Length Principle can be
used to discriminate among different models that can explain a given observed
dataset. The description length is chosen to be the sum of the lengths of the
message needed to encode the model plus the message needed to encode the data
when the model is applied to the dataset. It is verified that the proposed
principle can efficiently distinguish the model that correctly fits the
observations while avoiding over-fitting. The capabilities of this criterion
are shown in two simple problems for the analysis of observed
spectropolarimetric signals. The first is the de-noising of observations with
the aid of the PCA technique. The second is the selection of the optimal number
of parameters in LTE inversions. We propose this criterion as a quantitative
approach for distinguising the most plausible model among a set of proposed
models. This quantity is very easy to implement as an additional output on the
existing inversion codes.Comment: Accepted for publication in the Astrophysical Journa
Entropy exchange and entanglement in the Jaynes-Cummings model
The Jaynes-Cummings model is the simplest fully quantum model that describes
the interaction between light and matter. We extend a previous analysis by
Phoenix and Knight (S. J. D. Phoenix, P. L. Knight, Annals of Physics 186,
381). of the JCM by considering mixed states of both the light and matter. We
present examples of qualitatively different entropic correlations. In
particular, we explore the regime of entropy exchange between light and matter,
i.e. where the rate of change of the two are anti-correlated. This behavior
contrasts with the case of pure light-matter states in which the rate of change
of the two entropies are positively correlated and in fact identical. We give
an analytical derivation of the anti-correlation phenomenon and discuss the
regime of its validity. Finally, we show a strong correlation between the
region of the Bloch sphere characterized by entropy exchange and that
characterized by minimal entanglement as measured by the negative eigenvalues
of the partially transposed density matrix.Comment: 8 pages, 5 figure
Quantum data compression, quantum information generation, and the density-matrix renormalization group method
We have studied quantum data compression for finite quantum systems where the
site density matrices are not independent, i.e., the density matrix cannot be
given as direct product of site density matrices and the von Neumann entropy is
not equal to the sum of site entropies. Using the density-matrix
renormalization group (DMRG) method for the 1-d Hubbard model, we have shown
that a simple relationship exists between the entropy of the left or right
block and dimension of the Hilbert space of that block as well as of the
superblock for any fixed accuracy. The information loss during the RG procedure
has been investigated and a more rigorous control of the relative error has
been proposed based on Kholevo's theory. Our results are also supported by the
quantum chemistry version of DMRG applied to various molecules with system
lengths up to 60 lattice sites. A sum rule which relates site entropies and the
total information generated by the renormalization procedure has also been
given which serves as an alternative test of convergence of the DMRG method.Comment: 8 pages, 7 figure
Abstract composition rule for relativistic kinetic energy in the thermodynamical limit
We demonstrate by simple mathematical considerations that a power-law tailed
distribution in the kinetic energy of relativistic particles can be a limiting
distribution seen in relativistic heavy ion experiments. We prove that the
infinite repetition of an arbitrary composition rule on an infinitesimal amount
leads to a rule with a formal logarithm. As a consequence the stationary
distribution of energy in the thermodynamical limit follows the composed
function of the Boltzmann-Gibbs exponential with this formal logarithm. In
particular, interactions described as solely functions of the relative
four-momentum squared lead to kinetic energy distributions of the
Tsallis-Pareto (cut power-law) form in the high energy limit.Comment: Submitted to Europhysics Letters. LaTeX, 3 eps figure
Featured Piece
This year the General Editors decided to create a feature piece to show our appreciation for the History Department. We selected four professors from the faculty to answer a question about history: what figure/event/idea inspires your interest in history? Reading their responses helped give us insight into the thoughts of these brilliant minds and further help us understand their passion for the subject we all share a common love and interest in. We hope that you enjoy reading their responses as much as we did.
The four members of the faculty we spoke with are Dr. Timothy Shannon, Dr. Ian Isherwood, Dr. Jill Titus, and Dr. Scott Hancock
Classical Correlations and Entanglement in Quantum Measurements
We analyze a quantum measurement where the apparatus is initially in a mixed
state. We show that the amount of information gained in a measurement is not
equal to the amount of entanglement between the system and the apparatus, but
is instead equal to the degree of classical correlations between the two. As a
consequence, we derive an uncertainty-like expression relating the information
gain in the measurement and the initial mixedness of the apparatus. Final
entanglement between the environment and the apparatus is also shown to be
relevant for the efficiency of the measurement.Comment: to appear in Physical Review Letter
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