8,598 research outputs found
Two-particle dark state cooling of a nanomechanical resonator
The steady-state cooling of a nanomechanical resonator interacting with three
coupled quantum dots is studied. General conditions for the cooling to the
ground state with single and two-electron dark states are obtained. The results
show that in the case of the interaction of the resonator with a
single-electron dark state, no cooling of the resonator occurs unless the
quantum dots are not identical. The steady-state cooling is possible only if
the energy state of the quantum dot coupled to the drain electrode is detuned
from the energy states of the dots coupled to the electron source electrode.
The detuning has the effect of unequal shifting of the effective dressed states
of the system that the cooling and heating processes occur at different
frequencies. For the case of two electrons injected to the quantum dot system,
the creation of a two-particle dark state is established to be possible with
spin-antiparallel electrons. The results predict that with the two-particle
dark state, an effective cooling can be achieved even with identical quantum
dots subject of an asymmetry only in the charging potential energies coupling
the injected electrons. It is found that similar to the case of the
single-electron dark state, the asymmetries result in the cooling and heating
processes to occur at different frequencies. However, an important difference
between the single and two-particle dark state cases is that the cooling
process occurs at significantly different frequencies. This indicates that the
frequency at which the resonator could be cooled to its ground state can be
changed by switching from the one-electron to the two-electron Coulomb blockade
process.Comment: Published versio
Machine Learning Driven Sensitivity Analysis of E3SM Land Model Parameters for Wetland Methane Emissions
Methane (CH4) is the second most critical greenhouse gas after carbon
dioxide, contributing to 16-25% of the observed atmospheric warming. Wetlands
are the primary natural source of methane emissions globally. However, wetland
methane emission estimates from biogeochemistry models contain considerable
uncertainty. One of the main sources of this uncertainty arises from the
numerous uncertain model parameters within various physical, biological, and
chemical processes that influence methane production, oxidation, and transport.
Sensitivity Analysis (SA) can help identify critical parameters for methane
emission and achieve reduced biases and uncertainties in future projections.
This study performs SA for 19 selected parameters responsible for critical
biogeochemical processes in the methane module of the Energy Exascale Earth
System Model (E3SM) land model (ELM). The impact of these parameters on various
CH4 fluxes is examined at 14 FLUXNET- CH4 sites with diverse vegetation types.
Given the extensive number of model simulations needed for global
variance-based SA, we employ a machine learning (ML) algorithm to emulate the
complex behavior of ELM methane biogeochemistry. ML enables the computational
time to be shortened significantly from 6 CPU hours to 0.72 milliseconds,
achieving reduced computational costs. We found that parameters linked to CH4
production and diffusion generally present the highest sensitivities despite
apparent seasonal variation. Comparing simulated emissions from perturbed
parameter sets against FLUXNET-CH4 observations revealed that better
performances can be achieved at each site compared to the default parameter
values. This presents a scope for further improving simulated emissions using
parameter calibration with advanced optimization techniques like Bayesian
optimization.Comment: 24 pages, 9 figures and 2 table
Non-classical non-Gaussian state of a mechanical resonator via selectively incoherent damping in three-mode optomechanical systems
We theoretically propose a scheme for the generation of a non-classical
single-mode motional state of a mechanical resonator (MR) in the three-mode
optomechanical systems, in which two optical modes of the cavities are linearly
coupled to each other and one mechanical mode of the MR is optomechanically
coupled to the two optical modes with the same coupling strength
simultaneously. One cavity is driven by a coherent laser light. By properly
tuning the frequency of the weak driving field, we obtain engineered
Liouvillian superoperator via engineering the selective interaction Hamiltonian
confined to the Fock subspaces. In this case, the motional state of the MR can
be prepared into a non-Gaussian state, which possesses the sub-Poisson
statistics although its Wigner function is positive.Comment: 6 pages, 5 figure
Ambient Sound Helps: Audiovisual Crowd Counting in Extreme Conditions
Visual crowd counting has been recently studied as a way to enable people
counting in crowd scenes from images. Albeit successful, vision-based crowd
counting approaches could fail to capture informative features in extreme
conditions, e.g., imaging at night and occlusion. In this work, we introduce a
novel task of audiovisual crowd counting, in which visual and auditory
information are integrated for counting purposes. We collect a large-scale
benchmark, named auDiovISual Crowd cOunting (DISCO) dataset, consisting of
1,935 images and the corresponding audio clips, and 170,270 annotated
instances. In order to fuse the two modalities, we make use of a linear
feature-wise fusion module that carries out an affine transformation on visual
and auditory features. Finally, we conduct extensive experiments using the
proposed dataset and approach. Experimental results show that introducing
auditory information can benefit crowd counting under different illumination,
noise, and occlusion conditions. The dataset and code will be released. Code
and data have been made availabl
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