3,037 research outputs found
Electromagnetically controlled multiferroic thermal diode
We propose an electromagnetically tunable thermal diode based on a two phase
multiferroics composite. Analytical and full numerical calculations for
prototypical heterojunction composed of Iron on Barium titanate in the
tetragonal phase demonstrate a strong heat rectification effect that can be
controlled externally by a moderate electric field. This finding is of an
importance for thermally based information processing and sensing and can also
be integrated in (spin)electronic circuits for heat management and recycling.Comment: Accepted in Phys. Rev.
Quantum phase transition in easy-axis antiferromagnetic Heisenberg spin-1 chain
The fidelity and entropy in an easy-axis antiferromagnetic Heisenberg spin-1
chain are studied numerically. By using the method of density-matrix
renormalization group, the effects of anisotropy on fidelity and entanglement
entropy are investigated. Their relations with quantum phase transition are
analyzed. It is found that the quantum phase transition from the Haldane spin
liquid to N\'eel spin solid can be well characterized by the fidelity. The
phase transition can be hardly detected by the entropy but it can be
successfully detected by the first deviation of the entropy.Comment: 3 figure
How to project a bipartite network?
The one-mode projecting is extensively used to compress the bipartite
networks. Since the one-mode projection is always less informative than the
bipartite representation, a proper weighting method is required to better
retain the original information. In this article, inspired by the network-based
resource-allocation dynamics, we raise a weighting method, which can be
directly applied in extracting the hidden information of networks, with
remarkably better performance than the widely used global ranking method as
well as collaborative filtering. This work not only provides a creditable
method in compressing bipartite networks, but also highlights a possible way
for the better solution of a long-standing challenge in modern information
science: How to do personal recommendation?Comment: 7 pages, 4 figure
Quasi-2D Optomechanical Crystal Cavity for Quantum Optomechanics
We present the design and characterization of a quasi-two-dimensional optomechanical crystal cavity. At a refrigerated temperature of 10 mK, an intrinsic mechanical quality factor of 1.2 billion is observed and an effective quantum cooperativity greater than unity is realized under steady-state optical pumping
Phononics: Manipulating heat flow with electronic analogs and beyond
The form of energy termed heat that typically derives from lattice
vibrations, i.e. the phonons, is usually considered as waste energy and,
moreover, deleterious to information processing. However, with this colloquium,
we attempt to rebut this common view: By use of tailored models we demonstrate
that phonons can be manipulated like electrons and photons can, thus enabling
controlled heat transport. Moreover, we explain that phonons can be put to
beneficial use to carry and process information. In a first part we present
ways to control heat transport and how to process information for physical
systems which are driven by a temperature bias. Particularly, we put forward
the toolkit of familiar electronic analogs for exercising phononics; i.e.
phononic devices which act as thermal diodes, thermal transistors, thermal
logic gates and thermal memories, etc.. These concepts are then put to work to
transport, control and rectify heat in physical realistic nanosystems by
devising practical designs of hybrid nanostructures that permit the operation
of functional phononic devices and, as well, report first experimental
realizations. Next, we discuss yet richer possibilities to manipulate heat flow
by use of time varying thermal bath temperatures or various other external
fields. These give rise to a plenty of intriguing phononic nonequilibrium
phenomena as for example the directed shuttling of heat, a geometrical phase
induced heat pumping, or the phonon Hall effect, that all may find its way into
operation with electronic analogs.Comment: 24 pages, 16 figures, modified title and revised, accepted for
publication in Rev. Mod. Phy
Controlling complex networks: How much energy is needed?
The outstanding problem of controlling complex networks is relevant to many
areas of science and engineering, and has the potential to generate
technological breakthroughs as well. We address the physically important issue
of the energy required for achieving control by deriving and validating scaling
laws for the lower and upper energy bounds. These bounds represent a reasonable
estimate of the energy cost associated with control, and provide a step forward
from the current research on controllability toward ultimate control of complex
networked dynamical systems.Comment: 4 pages paper + 5 pages supplement. accepted for publication in
Physical Review Letters;
http://link.aps.org/doi/10.1103/PhysRevLett.108.21870
Duality and fluctuation relations for statistics of currents on cyclic graphs
We consider stochastic motion of a particle on a cyclic graph with
arbitrarily periodic time dependent kinetic rates. We demonstrate duality
relations for statistics of currents in this model and in its continuous
version of a diffusion in one dimension. Our duality relations are valid beyond
detailed balance constraints and lead to exact expressions that relate
statistics of currents induced by dual driving protocols. We also show that
previously known no-pumping theorems and some of the fluctuation relations,
when they are applied to cyclic graphs or to one dimensional diffusion, are
special consequences of our duality.Comment: 2 figure, 6 pages (In twocolumn). Accepted by JSTA
Out-of-Distribution Detection and Selective Generation for Conditional Language Models
Machine learning algorithms typically assume independent and identically
distributed samples in training and at test time. Much work has shown that
high-performing ML classifiers can degrade significantly and provide
overly-confident, wrong classification predictions, particularly for
out-of-distribution (OOD) inputs. Conditional language models (CLMs) are
predominantly trained to classify the next token in an output sequence, and may
suffer even worse degradation on OOD inputs as the prediction is done
auto-regressively over many steps. Furthermore, the space of potential
low-quality outputs is larger as arbitrary text can be generated and it is
important to know when to trust the generated output. We present a highly
accurate and lightweight OOD detection method for CLMs, and demonstrate its
effectiveness on abstractive summarization and translation. We also show how
our method can be used under the common and realistic setting of distribution
shift for selective generation (analogous to selective prediction for
classification) of high-quality outputs, while automatically abstaining from
low-quality ones, enabling safer deployment of generative language models
Equation of State for Neutralino Star as a Form of Cold Dark Matter
In order to study the structure of neutralino star and dark galaxy, we
consider dynamical interactions due to boson-exchange in the neutralino matter.
Taking into account interactions of neutralinos with bosons, we derive the
equation of state (EOS) of neutralino stars in terms of the relativistic mean
field approach. Then we apply the resulting EOS to investigate properties of
the neutralino star such as its density profile and mass limit. For example, if
the neutralino mass is around 1 TeV, the Oppenheimer mass limit of the
neutralino star is obtained as , and the
corresponding radius is about 7.8 mm. Actually, due to an increasing
annihilation rate as indicated by our calculation, this dense state can never
be realized in practice. Our results also show that the low density neutralino
star may be a possible aggregation of the cold dark matter.Comment: 5 pages, 5 figures; v2: matches published versio
Friedmann cosmology with a generalized equation of state and bulk viscosity
The universe media is considered as a non-perfect fluid with bulk viscosity
and described by a more general equation of state. We assume the bulk viscosity
is a linear combination of the two terms: one is constant, and the other is
proportional to the scalar expansion . The equation of state
is described as , where is a parameter. This model
can be used to explain the dark energy dominated universe. Different choices of
the parameters may lead to three kinds of fates of the cosmological evolution:
no future singularity, big rip, or Type III singularity of Ref. [S. Nojiri,
S.D. Odintsov, and S. Tsujikawa, Phys. Rev. D \textbf{71}, 063004 (2005)].Comment: 5 pages and 4 fig
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