110 research outputs found
An analysis of selected Indiana coals by the particle count method
Indiana Geological Survey Report of Progress 6The bituminous coals of Indiana show a characteristic bright and dull banding which is due to alternating bands of five distinct physical constituents, namely, vitrain, clarain, durain, fusain, and mineral matter. A petrographic analysis of Indiana Coals V, VI, and VII was made to determine whether any appreciable variation in the content of these ingredients occurred. The āparticle count methodā was used in analyzing the coals.
In order to establish a standard for comparing Coals V, VI, and VII, an index number was determined for each sample by dividing the combined clarain-durain content by the vitrain content. These index numbers are the most reliable and satisfactory basis for the comparison of coals, and they maybe used to some extent in coal correlation.
Because vitrain has the most desirable combustion properties, a coal that has a high vitrain content may be more desirable commercially. Coals VI and VII were found to have a distinctly higher vitrain content than Coal V. Localities of high-vitrain content within the various coal beds in Indiana are outlined in this report.
Suggestions for further use of the particle count method in coal analysis are made.Indiana Department of Conservatio
Target Space Entanglement Entropy
We define a notion of target space entanglement entropy. Rather than
partitioning the base space on which the theory is defined, we consider
partitions of the target space. This is the physical case of interest for
first-quantized theories, such as worldsheet string theory. We associate to
each subregion of the target space a suitably chosen sub-algebra of observables
. The entanglement entropy is calculated as the entropy of the
density matrix restricted to . As an example, we illustrate our
framework by computing spatial entanglement in first-quantized many-body
quantum mechanics. The algebra is chosen to reproduce the
entanglement entropy obtained by embedding the state in the fixed particle
sub-sector of the second-quantized Hilbert space. We then generalize our
construction to the quantum field-theoretical setting
A converse to Lieb-Robinson bounds in one dimension using index theory
Unitary dynamics with a strict causal cone (or "light cone") have been
studied extensively, under the name of quantum cellular automata (QCAs). In
particular, QCAs in one dimension have been completely classified by an index
theory. Physical systems often exhibit only approximate causal cones;
Hamiltonian evolutions on the lattice satisfy Lieb-Robinson bounds rather than
strict locality. This motivates us to study approximately locality preserving
unitaries (ALPUs). We show that the index theory is robust and completely
extends to one-dimensional ALPUs. As a consequence, we achieve a converse to
the Lieb-Robinson bounds: any ALPU of index zero can be exactly generated by
some time-dependent, quasi-local Hamiltonian in constant time. For the special
case of finite chains with open boundaries, any unitary satisfying the
Lieb-Robinson bound may be generated by such a Hamiltonian. We also discuss
some results on the stability of operator algebras which may be of independent
interest.Comment: 55 pages, 8 figure
The limit of open quantum systems with general Lindbladians: vanishing noise ensures classicality beyond the Ehrenfest time
Quantum and classical systems evolving under the same formal Hamiltonian
may exhibit dramatically different behavior after the Ehrenfest timescale , even as . Coupling the system to a
Markovian environment results in a Lindblad equation for the quantum evolution.
Its classical counterpart is given by the Fokker-Planck equation on phase
space, which describes Hamiltonian flow with friction and diffusive noise. The
quantum and classical evolutions may be compared via the Wigner-Weyl
representation. Due to decoherence, they are conjectured to match closely for
times far beyond the Ehrenfest timescale as . We prove a version
of this correspondence, bounding the error between the quantum and classical
evolutions for any sufficiently regular Hamiltonian and Lindblad
functions . The error is small when the strength of the diffusion
associated to the Lindblad functions satisfies , in
particular allowing vanishing noise in the classical limit. We use a
time-dependent semiclassical mixture of variably squeezed Gaussian states
evolving by a local harmonic approximation to the Lindblad dynamics. Both the
exact quantum trajectory and its classical counterpart can be expressed as
perturbations of this semiclassical mixture, with the errors bounded using
Duhamel's principle. We present heuristic arguments suggesting the
exponent is optimal and defines a boundary in the sense that asymptotically
weaker diffusion permits a breakdown of quantum-classical correspondence at the
Ehrenfest timescale. Our presentation aims to be comprehensive and accessible
to both mathematicians and physicists. In a shorter companion paper, we treat
the special case of Hamiltonians of the form and linear
Lindblad operators, with explicit bounds that can be applied directly to
physical systems.Comment: 53 pages + appendices, 2 figures. Companion to arXiv:2306.1371
The QAOA gets stuck starting from a good classical string
The Quantum Approximate Optimization Algorithm (QAOA) is designed to maximize
a cost function over bit strings. While the initial state is traditionally a
superposition over all strings, it is natural to try expediting the QAOA: first
use a classical algorithm to produce some good string, and then run the
ordinary QAOA starting in the computational basis state associated with that
string. Here we report numerical experiments that this method of initializing
the QAOA fails dramatically, exhibiting little to no improvement of the cost
function. We investigate criteria for the rare instances in which there is any
improvement at all, and we provide a statistical argument for the more typical
case of no improvement. The statistical argument holds for any string that
locally mimics the thermal ensemble at the appropriate temperature. Our
numerical experiments indicate this property holds for typical good strings. We
emphasize that our negative results only apply to our simple incarnation of the
warm-start QAOA and may not apply to other approaches in the literature. We
hope that our theoretical analysis will inform future algorithm design.Comment: 26 pages, 1 figure, 6 table
Beyond āpeer pressureā: rethinking drug use and āyouth cultureā
The study of drug use by young people in the West has been transformed over the last decade by the development of sociological approaches to drug use which take serious account of the cultural context in which young people encounter drugs. One consequence is that the notion of āpeer pressureā, as the primary articulation of the engagement between youth culture and drug use, has been displaced by that of ānormalisationā, which envisages ārecreationalā drug use as one expression of consumer-based youth cultural lifestyles. In stark contrast, academic discussion of drug use in Russia remains primarily concerned with the prevalence and health consequences of (intravenous) drug use while explanations of rising rates of drug use focus on structural factors related to the expansion of drugs supply and, to a lesser extent, post-Soviet social and economic dislocation. In this article, original empirical research in Russia is used to develop an understanding of young people's drug use that synthesises structural and cultural explanations of it. It does this by situating young people's narratives of their drugs choices in the context of local drugs markets and broader socio-economic processes. However, it attempts to go beyond seeing structural location as simply a āconstraintā on individual choice by adopting an understanding of āyouth cultureā as a range of youth cultural practices and formations that simultaneously embody, reproduce and negotiate the structural locations of their subjects
Omnivorousness in sport: The importance of social capital and networks
There has been for some time a significant and growing body of research around the relationship between sport and social capital. Similarly, within sociology there has been a corpus of work that has acknowledged the emergence of the omnivoreāunivore relationship. Surprisingly, relatively few studies examining sport and social capital have taken the omnivoreāunivore framework as a basis for understanding the relationship between sport and social capital. This gap in the sociology of sport literature and knowledge is rectified by this study that takes not Putnam, Coleman or Bourdieu, but Linās social network approach to social capital. The implications of this article are that researchers investigating sport and social capital need to understand more about how social networks and places for sport work to create social capital and, in particular, influence participating in sporting activities. The results indicate that social networks both facilitate and constrain sports participation; whilst family and friendship networks are central in active lifestyles, those who are less active have limited networks
- ā¦