4,426 research outputs found
Etaprime and Eta Mesons with Connection to Anomalous Glue
We review the present understanding of etaprime and eta meson physics and
these mesons as a probe of gluon dynamics in low-energy QCD. Recent highlights
include the production mechanism of eta and etaprime mesons in proton-nucleon
collisions from threshold to high-energy, the etaprime effective mass shift in
the nuclear medium, searches for possible eta and etaprime bound states in
nuclei as well as precision measurements of eta decays as a probe of
light-quark masses. We discuss recent experimental data, theoretical
interpretation of the different measurements and the open questions and
challenges for future investigation.Comment: Review, 25 pages, 11 figures, to appear in Reviews of Modern Physic
Hamiltonian quantum simulation with bounded-strength controls
We propose dynamical control schemes for Hamiltonian simulation in many-body
quantum systems that avoid instantaneous control operations and rely solely on
realistic bounded-strength control Hamiltonians. Each simulation protocol
consists of periodic repetitions of a basic control block, constructed as a
suitable modification of an "Eulerian decoupling cycle," that would otherwise
implement a trivial (zero) target Hamiltonian. For an open quantum system
coupled to an uncontrollable environment, our approach may be employed to
engineer an effective evolution that simulates a target Hamiltonian on the
system, while suppressing unwanted decoherence to the leading order. We present
illustrative applications to both closed- and open-system simulation settings,
with emphasis on simulation of non-local (two-body) Hamiltonians using only
local (one-body) controls. In particular, we provide simulation schemes
applicable to Heisenberg-coupled spin chains exposed to general linear
decoherence, and show how to simulate Kitaev's honeycomb lattice Hamiltonian
starting from Ising-coupled qubits, as potentially relevant to the dynamical
generation of a topologically protected quantum memory. Additional implications
for quantum information processing are discussed.Comment: 24 pages, 5 color figure
Testing quantum expanders is co-QMA-complete
A quantum expander is a unital quantum channel that is rapidly mixing, has
only a few Kraus operators, and can be implemented efficiently on a quantum
computer. We consider the problem of estimating the mixing time (i.e., the
spectral gap) of a quantum expander. We show that this problem is
co-QMA-complete. This has applications to testing randomized constructions of
quantum expanders, and studying thermalization of open quantum systems
Testing quantum expanders is co-QMA-complete
A quantum expander is a unital quantum channel that is rapidly mixing, has
only a few Kraus operators, and can be implemented efficiently on a quantum
computer. We consider the problem of estimating the mixing time (i.e., the
spectral gap) of a quantum expander. We show that this problem is
co-QMA-complete. This has applications to testing randomized constructions of
quantum expanders, and studying thermalization of open quantum systems
Toward positive psychosocial practice in psychosis: In pursuit of subjective wellbeing in severe mental ill-health
This article summarises and reflects on the scarce literature on the subject of positive psychosocial practice in the clinical specialism of complex and enduring mental health needs, such as psychosis. An attempt is made to demonstrate that such practice is not only achievable among individuals with severe psychological difficulties but, indeed, has already begun to develop, although it seems still in its infancy. The literature reviewed in this paper appears to indicate that a person with psychosis is as capable of experiencing subjective wellbeing as any other person in the general population. However, in order to promote wellbeing and sustained recovery among such individuals, a specialist psychosocial input needs to be delivered in a positive – that is integrative, person-based, collaborative, socially inclusive, and flow-inducing – manner. Furthermore, the article endeavours to demonstrate that in order to effect a fundamental shift in the perception of severe mental ill-health from a deficit-based and psychopathology-oriented stance toward a person-based and socially inclusive one, the principles of positive practice need to inform a wide range of clinical and social activities, including assessment, intervention, interpersonal reengagement and public policy development. It is nevertheless acknowledged that positive psychosocial approaches to psychosis are still in their infancy and relevant research studies remain considerably underrepresented, and in many aspects virtually non-existent. Hence, it is suggested that future research in positive clinical psychology within the specialty of complex, severe and enduring mental ill-health is actively encouraged and pursued by both clinicians and academics
Quantum Hall Ferrimagnetism in lateral quantum dot molecules
We demonstrate the existance of ferrimagnetic and ferromagnetic phases in a
spin phase diagram of coupled lateral quantum dot molecules in the quantum Hall
regime. The spin phase diagram is determined from Hartree-Fock Configuration
Interaction method as a function of electron numbers N, magnetic field B,
Zeeman energy, and tunneling barrier height. The quantum Hall ferrimagnetic
phase corresponds to spatially imbalanced spin droplets resulting from strong
inter-dot coupling of identical dots. The quantum Hall ferromagnetic phases
correspond to ferromagnetic coupling of spin polarization at filling factors
between and .Comment: 4 pages, 4 figure
Atomistic theory of electronic and optical properties of InAs/InP self-assembled quantum dots on patterned substrates
We report on a atomistic theory of electronic structure and optical
properties of a single InAs quantum dot grown on InP patterned substrate. The
spatial positioning of individual dots using InP nano-templates results in a
quantum dot embedded in InP pyramid. The strain distribution of a quantum dot
in InP pyramid is calculated using the continuum elasticity theory. The
electron and valence hole single-particle states are calculated using atomistic
effective-bond-orbital model with second nearest-neighbor interactions, coupled
to strain via Bir-Pikus Hamiltonian. The optical properties are determined by
solving many-exciton Hamiltonian for interacting electron and hole complexes
using the configuration-interaction method. The effect of positioning of
quantum dots using nanotemplate on their optical spectra is determined by a
comparison with dots on unpatterned substrates, and with experimental results.
The possibility of tuning the quantum dot properties with varying the
nano-template is explored.Comment: 9 pages, 12 figure
Are There Topological Black Hole Solitons in String Theory?
We point out that the celebrated Hawking effect of quantum instability of
black holes seems to be related to a nonperturbative effect in string theory.
Studying quantum dynamics of strings in the gravitational background of black
holes we find classical instability due to emission of massless string
excitations. The topology of a black hole seems to play a fundamental role in
developing the string theory classical instability due to the effect of sigma
model instantons. We argue that string theory allows for a qualitative
description of black holes with very small masses and it predicts topological
solitons with quantized spectrum of masses. These solitons would not decay into
string massless excitations but could be pair created and may annihilate also.
Semiclassical mass quantization of topological solitons in string theory is
based on the argument showing existence of nontrivial zeros of beta function of
the renormalization group.Comment: 12 pages, TeX, requires phyzzx.tex, published in Gen. Rel. Grav. 19
(1987) 1173; comment added on December 18, 199
Characterizing Deep-Learning I/O Workloads in TensorFlow
The performance of Deep-Learning (DL) computing frameworks rely on the
performance of data ingestion and checkpointing. In fact, during the training,
a considerable high number of relatively small files are first loaded and
pre-processed on CPUs and then moved to accelerator for computation. In
addition, checkpointing and restart operations are carried out to allow DL
computing frameworks to restart quickly from a checkpoint. Because of this, I/O
affects the performance of DL applications. In this work, we characterize the
I/O performance and scaling of TensorFlow, an open-source programming framework
developed by Google and specifically designed for solving DL problems. To
measure TensorFlow I/O performance, we first design a micro-benchmark to
measure TensorFlow reads, and then use a TensorFlow mini-application based on
AlexNet to measure the performance cost of I/O and checkpointing in TensorFlow.
To improve the checkpointing performance, we design and implement a burst
buffer. We find that increasing the number of threads increases TensorFlow
bandwidth by a maximum of 2.3x and 7.8x on our benchmark environments. The use
of the tensorFlow prefetcher results in a complete overlap of computation on
accelerator and input pipeline on CPU eliminating the effective cost of I/O on
the overall performance. The use of a burst buffer to checkpoint to a fast
small capacity storage and copy asynchronously the checkpoints to a slower
large capacity storage resulted in a performance improvement of 2.6x with
respect to checkpointing directly to slower storage on our benchmark
environment.Comment: Accepted for publication at pdsw-DISCS 201
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