16,879 research outputs found
A reading workbook of stories and exercises with first grade vocabulary and fourth grade interests
Thesis (Ed.M.)--Boston Universit
On Fusion Rules in Logarithmic Conformal Field Theories
We find the fusion rules for the c_{p,1} series of logarithmic conformal
field theories. This completes our attempts to generalize the concept of
rationality for conformal field theories to the logarithmic case. A novelty is
the appearance of negative fusion coefficients which can be understood in terms
of exceptional quantum group representations. The effective fusion rules (i.e.
without signs and multiplicities) resemble the BPZ fusion rules for the virtual
minimal models with conformal grid given via c = c_{3p,3}. This leads to the
conjecture that (almost) all minimal models with c = c_{p,q}, gcd(p,q) > 1,
belong to the class of rational logarithmic conformal field theories.Comment: 14 pages, LaTeX (or better LaTeX2e), no figures, also available at
http://www.sns.ias.edu/~flohr/, some corrections and clarification
Semimetallic features in quantum transport through a gate-defined point contact in bilayer graphene
We demonstrate that, at the onset of conduction, an electrostatically defined
quantum wire in bilayer graphene (BLG) with an interlayer asymmetry gap may act
as a 1D semimetal, due to the multiple minivalley dispersion of its lowest
subband. Formation of a non-monotonic subband coincides with a near-degeneracy
between the bottom edges of the lowest two subbands in the wire spectrum,
suggesting an step at the conduction threshold, and the semimetallic
behaviour of the lowest subband in the wire would be manifest as resonance
transmission peaks on an conductance plateau.Comment: 9 pages, 8 figures (including appendices
Twist-controlled Resonant Tunnelling between Monolayer and Bilayer Graphene
We investigate the current-voltage characteristics of a field-effect
tunnelling transistor comprised of both monolayer and bilayer graphene with
well-aligned crystallographic axes, separated by three layers of hexagonal
boron nitride. Using a self-consistent description of the device's
electrostatic configuration we relate the current to three distinct tunable
voltages across the system and hence produce a two-dimensional map of the I-V
characteristics in the low energy regime. We show that the use of gates either
side of the heterostructure offers a fine degree of control over the device's
rich array of characteristics, as does varying the twist between the graphene
electrodes.Comment: 5 pages including references and 3 figure
Database queries and constraints via lifting problems
Previous work has demonstrated that categories are useful and expressive
models for databases. In the present paper we build on that model, showing that
certain queries and constraints correspond to lifting problems, as found in
modern approaches to algebraic topology. In our formulation, each so-called
SPARQL graph pattern query corresponds to a category-theoretic lifting problem,
whereby the set of solutions to the query is precisely the set of lifts. We
interpret constraints within the same formalism and then investigate some basic
properties of queries and constraints. In particular, to any database we
can associate a certain derived database \Qry(\pi) of queries on . As an
application, we explain how giving users access to certain parts of
\Qry(\pi), rather than direct access to , improves ones ability to
manage the impact of schema evolution
Establishment Wage Differentials
Economists have long known that individual wages depend on a combination of employee and employer characteristics, as well as the interaction of the two. Although it is important to understand how employee and employer characteristics are related to wages, little is known about the magnitude and relation of these wage effects. This is primarily due to the lack of microdata which links individuals to the establishments where they work, but also due to technical difficulties associated with separating out employee and employer effects. This paper uses data from the Occupational Employment Statistics program at the Bureau of Labor Statistics that permit both of these issues to be addressed. Our results show that employer effects contribute substantially to earnings differences across individuals. We also find that establishments that pay well for one occupation also pay well for others. This paper contributes to the growing literature that analyzes firms’ compensation policies, and specifically the topic of employer effects on wages.Establishment Wage Differentials; Occupational Employment Statistics
EmBench: Quantifying Performance Variations of Deep Neural Networks across Modern Commodity Devices
In recent years, advances in deep learning have resulted in unprecedented
leaps in diverse tasks spanning from speech and object recognition to context
awareness and health monitoring. As a result, an increasing number of
AI-enabled applications are being developed targeting ubiquitous and mobile
devices. While deep neural networks (DNNs) are getting bigger and more complex,
they also impose a heavy computational and energy burden on the host devices,
which has led to the integration of various specialized processors in commodity
devices. Given the broad range of competing DNN architectures and the
heterogeneity of the target hardware, there is an emerging need to understand
the compatibility between DNN-platform pairs and the expected performance
benefits on each platform. This work attempts to demystify this landscape by
systematically evaluating a collection of state-of-the-art DNNs on a wide
variety of commodity devices. In this respect, we identify potential
bottlenecks in each architecture and provide important guidelines that can
assist the community in the co-design of more efficient DNNs and accelerators.Comment: Accepted at MobiSys 2019: 3rd International Workshop on Embedded and
Mobile Deep Learning (EMDL), 201
Entropic Origin of Pseudogap Physics and a Mott-Slater Transition in Cuprates
We propose a new approach to understand the origin of the pseudogap in the
cuprates, in terms of bosonic entropy. The near-simultaneous softening of a
large number of different -bosons yields an extended range of short-range
order, wherein the growth of magnetic correlations with decreasing temperature
is anomalously slow. These entropic effects cause the spectral weight
associated with the Van Hove singularity (VHS) to shift rapidly and nearly
linearly toward half filling at higher , consistent with a picture of the
VHS driving the pseudogap transition at a temperature . As a
byproduct, we develop an order-parameter classification scheme that predicts
supertransitions between families of order parameters. As one example, we find
that by tuning the hopping parameters, it is possible to drive the cuprates
across a {\it transition between Mott and Slater physics}, where a
spin-frustrated state emerges at the crossover.Comment: 24 pgs, 15 figs + Supp. Material [6pgs, 3 figs]. Major revision of
arXiv:1505.0477
Characterization of Thin Film Materials using SCAN meta-GGA, an Accurate Nonempirical Density Functional
We discuss self-consistently obtained ground-state electronic properties of
monolayers of graphene and a number of beyond graphene compounds, including
films of transition-metal dichalcogenides (TMDs), using the recently proposed
strongly constrained and appropriately normed (SCAN) meta-generalized gradient
approximation (meta-GGA) to the density functional theory. The SCAN meta-GGA
results are compared with those based on the local density approximation (LDA)
as well as the generalized gradient approximation (GGA). As expected, the GGA
yields expanded lattices and softened bonds in relation to the LDA, but the
SCAN meta-GGA systematically improves the agreement with experiment. Our study
suggests the efficacy of the SCAN functional for accurate modeling of
electronic structures of layered materials in high-throughput calculations more
generally
Ultracold, radiative charge transfer in hybrid Yb ion - Rb atom traps
Ultracold hybrid ion-atom traps offer the possibility of microscopic
manipulation of quantum coherences in the gas using the ion as a probe.
However, inelastic processes, particularly charge transfer can be a significant
process of ion loss and has been measured experimentally for the Yb ion
immersed in a Rb vapour. We use first-principles quantum chemistry codes to
obtain the potential energy curves and dipole moments for the lowest-lying
energy states of this complex. Calculations for the radiative decay processes
cross sections and rate coefficients are presented for the total decay
processes. Comparing the semi-classical Langevin approximation with the quantum
approach, we find it provides a very good estimate of the background at higher
energies. The results demonstrate that radiative decay mechanisms are important
over the energy and temperature region considered. In fact, the Langevin
process of ion-atom collisions dominates cold ion-atom collisions. For spin
dependent processes \cite{kohl13} the anisotropic magnetic dipole-dipole
interaction and the second-order spin-orbit coupling can play important roles,
inducing couplingbetween the spin and the orbital motion. They measured the
spin-relaxing collision rate to be approximately 5 orders of magnitude higher
than the charge-exchange collision rate \cite{kohl13}. Regarding the measured
radiative charge transfer collision rate, we find that our calculation is in
very good agreement with experiment and with previous calculations.
Nonetheless, we find no broad resonances features that might underly a strong
isotope effect. In conclusion, we find, in agreement with previous theory that
the isotope anomaly observed in experiment remains an open question.Comment: 7 figures, 1 table accepted for publication in J. Phys. B: At. Mol.
Opt. Phys. arXiv admin note: text overlap with arXiv:1107.114
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