1,478 research outputs found
Breathing oscillations of a trapped impurity in a Bose gas
Motivated by a recent experiment [J. Catani et al., arXiv:1106.0828v1
preprint, 2011], we study breathing oscillations in the width of a harmonically
trapped impurity interacting with a separately trapped Bose gas. We provide an
intuitive physical picture of such dynamics at zero temperature, using a
time-dependent variational approach. In the Gross-Pitaevskii regime we obtain
breathing oscillations whose amplitudes are suppressed by self trapping, due to
interactions with the Bose gas. Introducing phonons in the Bose gas leads to
the damping of breathing oscillations and non-Markovian dynamics of the width
of the impurity, the degree of which can be engineered through controllable
parameters. Our results reproduce the main features of the impurity dynamics
observed by Catani et al. despite experimental thermal effects, and are
supported by simulations of the system in the Gross-Pitaevskii regime.
Moreover, we predict novel effects at lower temperatures due to self-trapping
and the inhomogeneity of the trapped Bose gas.Comment: 7 pages, 3 figure
Compact tunable lowpass filter with sharp roll-off and low insertion loss
© 2017 Wiley Periodicals, Inc. A novel continuously tunable lowpass filter (LPF) with compact size, sharp roll-off and low insertion loss is presented in this paper. The filter employs two varactor diodes, a pair of open-ended coupled lines and a U-shape step impedance line (SIL) with an open-ended stub loaded at the center of the SIL to form a very compact layout. The odd- and even-mode analysis and equivalent circuit model are demonstrated for estimation of the transmission characteristics. Tuning the DC voltage applied on the varactor diodes, the varactor capacitance accordingly changes leading to a varying cutoff frequency fc. The measured results show that the achieved 3-dB fc tuning range is 60.6% (1.15–2.15 GHz). The measured insertion loss (IL) and roll-off rate are 0.2-0.4 dB and 50–73 dB/GHz, respectively. The overall size of the LPF is only 0.005λg2, which shows a competitive advantage comparing with the state-of-the-art work
Scaling Up 3D Kernels with Bayesian Frequency Re-parameterization for Medical Image Segmentation
With the inspiration of vision transformers, the concept of depth-wise
convolution revisits to provide a large Effective Receptive Field (ERF) using
Large Kernel (LK) sizes for medical image segmentation. However, the
segmentation performance might be saturated and even degraded as the kernel
sizes scaled up (e.g., ) in a Convolutional Neural
Network (CNN). We hypothesize that convolution with LK sizes is limited to
maintain an optimal convergence for locality learning. While Structural
Re-parameterization (SR) enhances the local convergence with small kernels in
parallel, optimal small kernel branches may hinder the computational efficiency
for training. In this work, we propose RepUX-Net, a pure CNN architecture with
a simple large kernel block design, which competes favorably with current
network state-of-the-art (SOTA) (e.g., 3D UX-Net, SwinUNETR) using 6
challenging public datasets. We derive an equivalency between kernel
re-parameterization and the branch-wise variation in kernel convergence.
Inspired by the spatial frequency in the human visual system, we extend to vary
the kernel convergence into element-wise setting and model the spatial
frequency as a Bayesian prior to re-parameterize convolutional weights during
training. Specifically, a reciprocal function is leveraged to estimate a
frequency-weighted value, which rescales the corresponding kernel element for
stochastic gradient descent. From the experimental results, RepUX-Net
consistently outperforms 3D SOTA benchmarks with internal validation (FLARE:
0.929 to 0.944), external validation (MSD: 0.901 to 0.932, KiTS: 0.815 to
0.847, LiTS: 0.933 to 0.949, TCIA: 0.736 to 0.779) and transfer learning (AMOS:
0.880 to 0.911) scenarios in Dice Score.Comment: Both codes and pretrained models are available at:
https://github.com/MASILab/RepUX-Ne
Effective electro-optical modulation with high extinction ratio by a graphene-silicon microring resonator
Graphene opens up for novel optoelectronic applications thanks to its high
carrier mobility, ultra-large absorption bandwidth, and extremely fast material
response. In particular, the opportunity to control optoelectronic properties
through tuning of Fermi level enables electro-optical modulation,
optical-optical switching, and other optoelectronics applications. However,
achieving a high modulation depth remains a challenge because of the modest
graphene-light interaction in the graphene-silicon devices, typically,
utilizing only a monolayer or few layers of graphene. Here, we comprehensively
study the interaction between graphene and a microring resonator, and its
influence on the optical modulation depth. We demonstrate graphene-silicon
microring devices showing a high modulation depth of 12.5 dB with a relatively
low bias voltage of 8.8 V. On-off electro-optical switching with an extinction
ratio of 3.8 dB is successfully demonstrated by applying a square-waveform with
a 4 V peak-to-peak voltage.Comment: 12 pages, including 7 figure
Weak Spin Fluctuation with Finite Wave Vector and Superconducting Gap Symmetry in KxFe2-ySe2: 77Se Nuclear Magnetic Resonance
We report Se-nuclear magnetic resonance (NMR) results down to
sufficiently low temperatures under magnetic fields parallel to both the
-plane and the c-axis in a paramagnetic/superconducting (PM/SC) phase of
KFeSe. The observation of anisotropy in the orbital part of the
Knight shift results in the anisotropy of its spin part increasing on
approaching the transition temperature. The anisotropy of the Korringa relation
suggests the presence of the weak spin fluctuations with a finite wave vector
, which induce the magnetic fluctuations along the ab-plane at the Se
site. Such fluctuations do not correspond to the stripe correlation
of the Fe moment observed in many Fe-based superconductors, and are not
contradictory to weak correlations. The nuclear spin-lattice
relaxation rate shows a field-independent behavior
at low temperatures for , which is attributed to the nonzero
density of states at the Fermi level and can be explained by the sign-changing
order parameter even for nodeless gaps. The temperature dependence of
is reproduced well by nodeless models with two isotropic gaps or a single
anisotropic gap. The obtained gap magnitude in the isotropic two-gap model is
comparable to those obtained in the angle-resolved photoemission spectroscopy
experiments.Comment: 6 pages, 6 figures, Accepted for the publication in J. Phys. Soc. Jp
Deep conditional generative models for longitudinal single-slice abdominal computed tomography harmonization
Two-dimensional single-slice abdominal computed tomography (CT) provides a
detailed tissue map with high resolution allowing quantitative characterization
of relationships between health conditions and aging. However, longitudinal
analysis of body composition changes using these scans is difficult due to
positional variation between slices acquired in different years, which leading
to different organs/tissues captured. To address this issue, we propose
C-SliceGen, which takes an arbitrary axial slice in the abdominal region as a
condition and generates a pre-defined vertebral level slice by estimating
structural changes in the latent space. Our experiments on 2608 volumetric CT
data from two in-house datasets and 50 subjects from the 2015 Multi-Atlas
Abdomen Labeling Challenge dataset (BTCV) Challenge demonstrate that our model
can generate high-quality images that are realistic and similar. We further
evaluate our method's capability to harmonize longitudinal positional variation
on 1033 subjects from the Baltimore Longitudinal Study of Aging (BLSA) dataset,
which contains longitudinal single abdominal slices, and confirmed that our
method can harmonize the slice positional variance in terms of visceral fat
area. This approach provides a promising direction for mapping slices from
different vertebral levels to a target slice and reducing positional variance
for single-slice longitudinal analysis. The source code is available at:
https://github.com/MASILab/C-SliceGen
Patterning graphene nanostripes in substrate-supported functionalized graphene: A promising route to integrated, robust, and superior transistors
It is promising to apply quantum-mechanically confined graphene systems in
field-effect transistors. High stability, superior performance, and large-scale
integration are the main challenges facing the practical application of
graphene transistors. Our understandings of the adatom-graphene interaction
combined with recent progress in the nanofabrication technology indicate that
very stable and high-quality graphene nanostripes could be integrated in
substrate-supported functionalized (hydrogenated or fluorinated) graphene using
electron-beam lithography. We also propose that parallelizing a couple of
graphene nanostripes in a transistor should be preferred for practical
application, which is also very useful for transistors based on graphene
nanoribbon.Comment: Frontiers of Physics (2012) to be publishe
Urban energy consumption and CO2 emissions in Beijing: current and future
This paper calculates the energy consumption and CO2 emissions of Beijing over 2005–2011 in light of the Beijing’s energy balance table and the carbon emission coefficients of IPCC. Furthermore, based on a series of energy conservation planning program issued in Beijing, the Long-range Energy Alternatives Planning System (LEAP)-BJ model is developed to study the energy consumption and CO2 emissions of Beijing’s six end-use sectors and the energy conversion sector over 2012–2030 under the BAU scenario and POL scenario. Some results are found in this research: (1) During 2005–2011, the energy consumption kept increasing, while the total CO2 emissions fluctuated obviously in 2008 and 2011. The energy structure and the industrial structure have been optimized to a certain extent. (2) If the policies are completely implemented, the POL scenario is projected to save 21.36 and 35.37 % of the total energy consumption and CO2 emissions than the BAU scenario during 2012 and 2030. (3) The POL scenario presents a more optimized energy structure compared with the BAU scenario, with the decrease of coal consumption and the increase of natural gas consumption. (4) The commerce and service sector and the energy conversion sector will become the largest contributor to energy consumption and CO2 emissions, respectively. The transport sector and the industrial sector are the two most potential sectors in energy savings and carbon reduction. In terms of subscenarios, the energy conservation in transport (TEC) is the most effective one. (5) The macroparameters, such as the GDP growth rate and the industrial structure, have great influence on the urban energy consumption and carbon emissions
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