522 research outputs found
Engineering a static verification tool for GPU kernels
We report on practical experiences over the last 2.5 years related to the engineering of GPUVerify, a static verification tool for OpenCL and CUDA GPU kernels, plotting the progress of GPUVerify from a prototype to a fully functional and relatively efficient analysis tool. Our hope is that this experience report will serve the verification community by helping to inform future tooling efforts. © 2014 Springer International Publishing
Classical Scattering for a driven inverted Gaussian potential in terms of the chaotic invariant set
We study the classical electron scattering from a driven inverted Gaussian
potential, an open system, in terms of its chaotic invariant set. This chaotic
invariant set is described by a ternary horseshoe construction on an
appropriate Poincare surface of section. We find the development parameters
that describe the hyperbolic component of the chaotic invariant set. In
addition, we show that the hierarchical structure of the fractal set of
singularities of the scattering functions is the same as the structure of the
chaotic invariant set. Finally, we construct a symbolic encoding of the
hierarchical structure of the set of singularities of the scattering functions
and use concepts from the thermodynamical formalism to obtain one of the
measures of chaos of the fractal set of singularities, the topological entropy.Comment: accepted in Phy. Rev.
An approximate empirical Bayesian method for large-scale linear-Gaussian inverse problems
We study Bayesian inference methods for solving linear inverse problems,
focusing on hierarchical formulations where the prior or the likelihood
function depend on unspecified hyperparameters. In practice, these
hyperparameters are often determined via an empirical Bayesian method that
maximizes the marginal likelihood function, i.e., the probability density of
the data conditional on the hyperparameters. Evaluating the marginal
likelihood, however, is computationally challenging for large-scale problems.
In this work, we present a method to approximately evaluate marginal likelihood
functions, based on a low-rank approximation of the update from the prior
covariance to the posterior covariance. We show that this approximation is
optimal in a minimax sense. Moreover, we provide an efficient algorithm to
implement the proposed method, based on a combination of the randomized SVD and
a spectral approximation method to compute square roots of the prior covariance
matrix. Several numerical examples demonstrate good performance of the proposed
method
Quantum phase retrieval of a Rydberg wave packet using a half-cycle pulse
A terahertz half-cycle pulse was used to retrieve information stored as
quantum phase in an -state Rydberg atom data register. The register was
prepared as a wave packet with one state phase-reversed from the others (the
"marked bit"). A half-cycle pulse then drove a significant portion of the
electron probability into the flipped state via multimode interference.Comment: accepted by PR
Hedgehog pathway dysregulation contributes to the pathogenesis of human gastrointestinal stromal tumors via GLI-mediated activation of KIT expression.
Gastrointestinal stromal tumors (GIST) arise within the interstitial cell of Cajal (ICC) lineage due to activating KIT/PDGFRA mutations. Both ICC and GIST possess primary cilia (PC), which coordinate PDGFRA and Hedgehog signaling, regulators of gastrointestinal mesenchymal development. Therefore, we hypothesized that Hedgehog signaling may be altered in human GIST and controls KIT expression. Quantitative RT-PCR, microarrays, and next generation sequencing were used to describe Hedgehog/PC-related genes in purified human ICC and GIST. Genetic and pharmacologic approaches were employed to investigate the effects of GLI manipulation on KIT expression and GIST cell viability. We report that Hedgehog pathway and PC components are expressed in ICC and GIST and subject to dysregulation during GIST oncogenesis, irrespective of KIT/PDGFRA mutation status. Using genomic profiling, 10.2% of 186 GIST studied had potentially deleterious genomic alterations in 5 Hedgehog-related genes analyzed, including in the PTCH1 tumor suppressor (1.6%). Expression of the predominantly repressive GLI isoform, GLI3, was inversely correlated with KIT mRNA levels in GIST cells and non-KIT/non-PDGFRA mutant GIST. Overexpression of the 83-kDa repressive form of GLI3 or small interfering RNA-mediated knockdown of the activating isoforms GLI1/2 reduced KIT mRNA. Treatment with GLI1/2 inhibitors, including arsenic trioxide, significantly increased GLI3 binding to the KIT promoter, decreased KIT expression, and reduced viability in imatinib-sensitive and imatinib-resistant GIST cells. These data offer new evidence that genes necessary for Hedgehog signaling and PC function in ICC are dysregulated in GIST. Hedgehog signaling activates KIT expression irrespective of mutation status, offering a novel approach to treat imatinib-resistant GIST
Optimally shaped terahertz pulses for phase retrieval in a Rydberg atom data register
We employ Optimal Control Theory to discover an efficient information
retrieval algorithm that can be performed on a Rydberg atom data register using
a shaped terahertz pulse. The register is a Rydberg wave packet with one
consituent orbital phase-reversed from the others (the ``marked bit''). The
terahertz pulse that performs the decoding algorithm does so by by driving
electron probability density into the marked orbital. Its shape is calculated
by modifying the target of an optimal control problem so that it represents the
direct product of all correct solutions to the algorithm.Comment: 6 pages, 3 figure
(Dis)Advantages of Student Subjects: What is Your Research Question?
In this comment on Henrich et al. (2010) I argue that the right choice of subject pool is intimately linked to the research question. At least within economics, students are often the perfect subject pool for answering some fundamental research questions. Student subject pools can provide an invaluable benchmark for investigating generalizability across different social groups or cultures
Social preferences, accountability, and wage bargaining
We assess the extent of preferences for employment in a collective wage bargaining situation with heterogeneous workers. We vary the size of the union and introduce a treatment mechanism transforming the voting game into an individual allocation task. Our results show that highly productive workers do not take employment of low productive workers into account when making wage proposals, regardless of whether insiders determine the wage or all workers. The level of pro-social preferences is small in the voting game, while it increases as the game is transformed into an individual allocation task. We interpret this as an accountability effect
Auxiliary-level-assisted operations with charge qubits in semiconductors
We present a new scheme for rotations of a charge qubit associated with a
singly ionized pair of donor atoms in a semiconductor host. The logical states
of such a qubit proposed recently by Hollenberg et al. are defined by the
lowest two energy states of the remaining valence electron localized around one
or another donor. We show that an electron located initially at one donor site
can be transferred to another donor site via an auxiliary molecular level
formed upon the hybridization of the excited states of two donors. The electron
transfer is driven by a single resonant microwave pulse in the case that the
energies of the lowest donor states coincide or two resonant pulses in the case
that they differ from each other. Depending on the pulse parameters, various
one-qubit operations, including the phase gate, the NOT gate, and the Hadamard
gate, can be realized in short times. Decoherence of an electron due to the
interaction with acoustic phonons is analyzed and shown to be weak enough for
coherent qubit manipulation being possible, at least in the proof-of-principle
experiments on one-qubit devices.Comment: Extended version of cond-mat/0411605 with detailed discussion of
phonon-induced decoherence including dephasing and relaxation; to be
published in JET
Shape resonance for the anisotropic superconducting gaps near a Lifshitz transition: the effect of electron hopping between layers
The multigap superconductivity modulated by quantum confinement effects in a
superlattice of quantum wells is presented. Our theoretical BCS approach
captures the low-energy physics of a shape resonance in the superconducting
gaps when the chemical potential is tuned near a Lifshitz transition. We focus
on the case of weak Cooper-pairing coupling channels and strong pair exchange
interaction driven by repulsive Coulomb interaction that allows to use the BCS
theory in the weak-coupling regime neglecting retardation effects like in
quantum condensates of ultracold gases. The calculated matrix element effects
in the pairing interaction are shown to yield a complex physics near the
particular quantum critical points due to Lifshitz transitions in multigap
superconductivity. Strong deviations of the ratio from the
standard BCS value as a function of the position of the chemical potential
relative to the Lifshitz transition point measured by the Lifshitz parameter
are found. The response of the condensate phase to the tuning of the Lifshitz
parameter is compared with the response of ultracold gases in the BCS-BEC
crossover tuned by an external magnetic field. The results provide the
description of the condensates in this regime where matrix element effects play
a key role.Comment: 12 pages, 6 figure
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