1,456 research outputs found
Interferometry based on quantum Kibble-Zurek mechanism
We propose an interferometry within quantum Kibble-Zurek mechanism, which is
exemplified by two prototypical quench schemes, namely the round-trip and
quarter-turn ones, in the transverse Ising and quantum chains. Each scheme
contains two linear quenches that drive the system across the quantum critical
point twice. The two linear quenches arouse two respective critical dynamics
that are well described by the quantum Kibble-Zurek mechanism. However, in
combination, the two critical dynamics can interfere with each other deeply. As
an effect of the interference, the dynamical phase is exposed in the final
excitation probability, which leads to a quantum coherent many-body oscillation
in the density of defects with predictable characteristic period. Thus such an
interference is available for direct experimental observations. In the quantum
model, we show that an interference can also arise from the interplay
between two different critical dynamics derived from a critical point and a
tricritical point. Furthermore, we demonstrate that the interference influences
the dephasing of the excited quasiparticle modes intricately by disclosing a
remarkable phenomenon of multiple length scales, diagonal and off-diagonal
ones, in the defect-defect correlators. It turns out that the dephased result
relies on how the diagonal and off-diagonal lengths are modulated by the
controllable parameter in a quench scheme.Comment: 19 pages, 12 figures, with table of content
Varying quench dynamics: the Kibble-Zurek, saturated, and pre-saturated regimes
According to the Kibble-Zurek mechanism, there is a universal power-law
relationship between the defect density and the quench rate during a slow
linear quench through a critical point. It is generally accepted that a fast
quench results in a deviation from the Kibble-Zurek scaling law and leads to
the formation of a saturated plateau in the defect density. Our focus is on the
transitions of quench dynamics as quench rates vary from slow to very fast
limits. We identify a pre-saturated regime that lies between the saturated and
Kibble-Zurek regimes. This conclusion is elucidated through the
adiabatic-impulse approximation and verified by a rigorous analysis on the
transverse Ising chain. As we approach the transition point from the saturated
to pre-saturated regimes, we notice a change in scaling laws and, with an
increase in the initial transverse field, a shrinking of the saturated regime
until it disappears. During another transition from the Kibble-Zurek to
pre-saturated regimes, we observe an attenuation of the dephasing effect and a
change in the behavior of the kink-kink correlation function from a Gaussian
decay to an exponential decay. Finally, the coherent many-body oscillation
after quench is investigated, which shows different behaviors in the three
regimes and demonstrates a significant transition of scaling behavior between
the S and PS regimes.Comment: 11 pages, 7 figure
A multi-wavelength observation and investigation of six infrared dark clouds
Context. Infrared dark clouds (IRDCs) are ubiquitous in the Milky Way, yet
they play a crucial role in breeding newly-formed stars.
Aims. With the aim of further understanding the dynamics, chemistry, and
evolution of IRDCs, we carried out multi-wavelength observations on a small
sample.
Methods. We performed new observations with the IRAM 30 m and CSO 10.4 m
telescopes, with tracers , HCN, , ,
DCO, SiO, and DCN toward six IRDCs G031.97+00.07, G033.69-00.01,
G034.43+00.24, G035.39-00.33, G038.95-00.47, and G053.11+00.05.
Results. We investigated 44 cores including 37 cores reported in previous
work and seven newly-identified cores. Toward the dense cores, we detected 6
DCO, and 5 DCN lines. Using pixel-by-pixel spectral energy distribution
(SED) fits of the 70 to 500 m, we obtained dust
temperature and column density distributions of the IRDCs. We found that emission has a strong correlation with the dust temperature and column
density distributions, while showed the weakest correlation. It
is suggested that is indeed a good tracer in very dense
conditions, but is an unreliable one, as it has a relatively
low critical density and is vulnerable to freezing-out onto the surface of cold
dust grains. The dynamics within IRDCs are active, with infall, outflow, and
collapse; the spectra are abundant especially in deuterium species.
Conclusions. We observe many blueshifted and redshifted profiles,
respectively, with and toward the same core. This
case can be well explained by model "envelope expansion with core collapse
(EECC)".Comment: 24 pages, 11 figures, 4 tables. To be published in A&A. The
resolutions of the pictures are cut dow
Online Job Scheduling in Distributed Machine Learning Clusters
Nowadays large-scale distributed machine learning systems have been deployed
to support various analytics and intelligence services in IT firms. To train a
large dataset and derive the prediction/inference model, e.g., a deep neural
network, multiple workers are run in parallel to train partitions of the input
dataset, and update shared model parameters. In a shared cluster handling
multiple training jobs, a fundamental issue is how to efficiently schedule jobs
and set the number of concurrent workers to run for each job, such that server
resources are maximally utilized and model training can be completed in time.
Targeting a distributed machine learning system using the parameter server
framework, we design an online algorithm for scheduling the arriving jobs and
deciding the adjusted numbers of concurrent workers and parameter servers for
each job over its course, to maximize overall utility of all jobs, contingent
on their completion times. Our online algorithm design utilizes a primal-dual
framework coupled with efficient dual subroutines, achieving good long-term
performance guarantees with polynomial time complexity. Practical effectiveness
of the online algorithm is evaluated using trace-driven simulation and testbed
experiments, which demonstrate its outperformance as compared to commonly
adopted scheduling algorithms in today's cloud systems
Composite Differential Evolution for Constrained Evolutionary Optimization
When solving constrained optimization problems (COPs) by evolutionary algorithms, the search algorithm plays a crucial role. In general, we expect that the search algorithm has the capability to balance not only diversity and convergence but also constraints and objective function during the evolution. For this purpose, this paper proposes a composite differential evolution (DE) for constrained optimization, which includes three different trial vector generation strategies with distinct advantages. In order to strike a balance between diversity and convergence, one of these three trial vector generation strategies is able to increase diversity, and the other two exhibit the property of convergence. In addition, to accomplish the tradeoff between constraints and objective function, one of the two trial vector generation strategies for convergence is guided by the individual with the least degree of constraint violation in the population, and the other is guided by the individual with the best objective function value in the population. After producing offspring by the proposed composite DE, the feasibility rule and the ϵ constrained method are combined elaborately for selection in this paper. Moreover, a restart scheme is proposed to help the population jump out of a local optimum in the infeasible region for some extremely complicated COPs. By assembling the above techniques together, a constrained composite DE is proposed. The experiments on two sets of benchmark test functions with various features, i.e., 24 test functions from IEEE CEC2006 and 18 test functions with 10 dimensions and 30 dimensions from IEEE CEC2010, have demonstrated that the proposed method shows better or at least competitive performance against other state-of-the-art methods
- …