2,279 research outputs found
Role of thermal friction in relaxation of turbulent Bose-Einstein condensates
In recent experiments, the relaxation dynamics of highly oblate, turbulent
Bose-Einstein condensates (BECs) was investigated by measuring the vortex decay
rates in various sample conditions [Phys. Rev. A , 063627 (2014)] and,
separately, the thermal friction coefficient for vortex motion was
measured from the long-time evolution of a corotating vortex pair in a BEC
[Phys. Rev. A , 051601(R) (2015)]. We present a comparative analysis of
the experimental results, and find that the vortex decay rate is
almost linearly proportional to . We perform numerical simulations of
the time evolution of a turbulent BEC using a point-vortex model equipped with
longitudinal friction and vortex-antivortex pair annihilation, and observe that
the linear dependence of on is quantitatively accounted for
in the dissipative point-vortex model. The numerical simulations reveal that
thermal friction in the experiment was too strong to allow for the emergence of
a vortex-clustered state out of decaying turbulence.Comment: 7 pages, 5 figure
Understanding the Latent Space of Diffusion Models through the Lens of Riemannian Geometry
Despite the success of diffusion models (DMs), we still lack a thorough
understanding of their latent space. To understand the latent space
, we analyze them from a geometrical perspective.
Specifically, we utilize the pullback metric to find the local latent basis in
and their corresponding local tangent basis in , the
intermediate feature maps of DMs. The discovered latent basis enables
unsupervised image editing capability through latent space traversal. We
investigate the discovered structure from two perspectives. First, we examine
how geometric structure evolves over diffusion timesteps. Through analysis, we
show that 1) the model focuses on low-frequency components early in the
generative process and attunes to high-frequency details later; 2) At early
timesteps, different samples share similar tangent spaces; and 3) The simpler
datasets that DMs trained on, the more consistent the tangent space for each
timestep. Second, we investigate how the geometric structure changes based on
text conditioning in Stable Diffusion. The results show that 1) similar prompts
yield comparable tangent spaces; and 2) the model depends less on text
conditions in later timesteps. To the best of our knowledge, this paper is the
first to present image editing through -space traversal and provide
thorough analyses of the latent structure of DMs
Exploration of Daily Rainfall Intensity Change in South Korea 1900–2010 Using Bias-Corrected ERA-20C
Bacterial community analysis of sediment seep in Kagoshima Bay, Japan
1902-1906Microorganisms in the deep-sea environments such as hydrothermal vent and cold-seep regions are primary energy producers and an important community in these ecosystems. We have used 454-Pyrosequencing and 16S rDNA clone library methods to determine the diversity of bacteria in the sediment of the seep regions around the vestimentiferan tubeworm habitat at Kagoshima Bay. Taxonomic composition from both libraries suggested that 454-Pyrosequencing methods can represent more diverse groups than the conventional clone library methods. Most abundant taxa with higher folds were Proteobacteria and Bacteroidetes found in both methods. Through the 454-Pyrosequencing method, we were able to detect underrepresented taxa as well as non-detectable taxa. This analyses and comparison provide bacterial taxonomic group detection efficiency of both library types and emphasize the different uses and utilities for exploring the unknown microbial domain
Optical properties of iron-based superconductor LiFeAs single crystal
We have measured the reflectivity spectra of the iron based superconductor
LiFeAs (Tc = 17.6 K) in the temperature range from 4 to 300 K. In the
superconducting state (T < Tc), the clear opening of the optical absorption gap
was observed below 25 cm-1, indicating an isotropic full gap formation. In the
normal state (T > Tc), the optical conductivity spectra display a typical
metallic behavior with the Drude type spectra at low frequencies, but we found
that the introduction of the two Drude components best fits the data,
indicating the multiband nature of this superconductor. A theoretical analysis
of the low temperature data (T=4K < Tc) also suggests that two superconducting
gaps best fit the data and their values were estimated as {\Delta}1 = 1.59 meV
and {\Delta}2 = 3.15 meV, respectively. Using the Ferrell-Glover-Tinkham (FGT)
sum rule and dielectric function {\epsilon}1({\omega}), the superconducting
plasma frequency ({\omega}ps) is consistently estimated to be 6,665 cm-1,
implying that about 59 % of the free carriers in the normal state condenses
into the SC condensate. To investigate the various interband transition
processes (for {\omega} > 200 cm-1), we have also performed the local-density
approximation (LDA) band calculation and calculated the optical spectra of the
interband transitions. The theoretical results provided a qualitative agreement
with the experimental data below 4000 cm-1Comment: 19 pages, 5 figures. This paper has been accepted for publication in
New Journal of Physic
Automatic Internal Stray Light Calibration of AMCW Coaxial Scanning LiDAR Using GMM and PSO
In this paper, an automatic calibration algorithm is proposed to reduce the
depth error caused by internal stray light in amplitude-modulated continuous
wave (AMCW) coaxial scanning light detection and ranging (LiDAR). Assuming that
the internal stray light generated in the process of emitting laser is static,
the amplitude and phase delay of internal stray light are estimated using the
Gaussian mixture model (GMM) and particle swarm optimization (PSO).
Specifically, the pixel positions in a raw signal amplitude map of calibration
checkboard are segmented by GMM with two clusters considering the dark and
bright image pattern. The loss function is then defined as L1-norm of
difference between mean depths of two amplitude-segmented clusters. To avoid
overfitting at a specific distance in PSO process, the calibration check board
is actually measured at multiple distances and the average of corresponding L1
loss functions is chosen as the actual loss. Such loss is minimized by PSO to
find the two optimal target parameters: the amplitude and phase delay of
internal stray light. According to the validation of the proposed algorithm,
the original loss is reduced from tens of centimeters to 3.2 mm when the
measured distances of the calibration checkboard are between 1 m and 4 m. This
accurate calibration performance is also maintained in geometrically complex
measured scene. The proposed internal stray light calibration algorithm in this
paper can be used for any type of AMCW coaxial scanning LiDAR regardless of its
optical characteristics
Highly precise AMCW time-of-flight scanning sensor based on digital-parallel demodulation
In this paper, a novel amplitude-modulated continuous wave (AMCW)
time-of-flight (ToF) scanning sensor based on digital-parallel demodulation is
proposed and demonstrated in the aspect of distance measurement precision.
Since digital-parallel demodulation utilizes a high-amplitude demodulation
signal with zero-offset, the proposed sensor platform can maintain extremely
high demodulation contrast. Meanwhile, as all cross correlated samples are
calculated in parallel and in extremely short integration time, the proposed
sensor platform can utilize a 2D laser scanning structure with a single photo
detector, maintaining a moderate frame rate. This optical structure can
increase the received optical SNR and remove the crosstalk of image pixel
array. Based on these measurement properties, the proposed AMCW ToF scanning
sensor shows highly precise 3D depth measurement performance. In this study,
this precise measurement performance is explained in detail. Additionally, the
actual measurement performance of the proposed sensor platform is
experimentally validated under various conditions
Characteristics of the aberrant pyramidal tract in comparison with the pyramidal tract in the human brain
<p>Abstract</p> <p>Background</p> <p>The aberrant pyramidal tract (APT) refers to the collateral pathway of the pyramidal tract (PT) through the medial lemniscus in the midbrain and pons. Using diffusion tensor tractography (DTT), we investigated the characteristics of the APT in comparison with the PT in the normal human brain.</p> <p>Results</p> <p>In thirty-four (18.3%, right hemisphere: 20, left hemisphere: 14) of the 186 hemispheres, the APTs separated from the PT at the upper midbrain level, descended through the medial lemniscus from the midbrain to the pons, and then rejoined with the PT at the upper medulla. Nine (26.5%) of the 34 APTs were found to originate from the primary somatosensory cortex without a primary motor cortex origin. Values of fractional anisotropy (FA) and tract volume of the APT were lower than those of the PT (<it>P </it>< 0.05); however, no difference in mean diffusivity (MD) value was observed (<it>P ></it>0.05).</p> <p>Conclusion</p> <p>We found that the APT has different characteristics, including less directionality, fewer neural fibers, and less origin from the primary motor cortex than the PT.</p
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