Collective oscillations of a Bose-Einstein condensate induced by a vortex ring

We study the collective oscillations of three-dimensional Bose-Einstein condensates (BECs) excited by a vortex ring. We identify independent, integrated, and stationary modes of the center-of-mass oscillation of the condensate with respect to the vortex ring movement. We show that the oscillation amplitude {of the center-of-mass of the condensate} depends strongly on the initial radius of the vortex ring, the inter-atomic interaction, and the aspect ration of the trap, while the oscillation frequency is fixed and equal to the frequency of the harmonic trap in the direction of the ring movement. However, when applying Kelvin wave perturbations on the vortex ring, the center-of-mass oscillation of the BEC is changed nontrivially with respect to the perturbation modes, the long-scale perturbation strength as well as the wave number of the perturbations. The parity of the wave number of the Kelvin perturbations plays important role on the mode of the center-of-mass oscillation of the condensate

Interference of Two-Dimensional Bose-Einstein Condensates in Micro-Gravity

We investigate the interference of two-dimensional Bose-Einstein condensates in micro-gravity, which influenced by the interaction strength, initial momentum, gravitational potential and phase difference. We demonstrate that the gravitational potential from the Earth can change the density distribution and phase distribution of the condensate's wave function. As time evolves, a portion of the gravitational potential energy of the microscopic particles can be converted into kinetic energy, which changes the motion of the microscopic particles, and leads to the varying of the density and phase distribution of the wave function. Nevertheless, the influences of the Earth's gravity on the wave function can be eliminated by the micro-gravity environment, which confirmed by many micro-gravity cold atom experiments. Our results present the influences of gravity and other parameters on interference of Bose-Einstein condensates, which help us to reveal the intrinsic natures of the related theoretical predictions and experimental phenomena. Furthermore, our work builds a bridge between the related physical phenomena and our physical intuition about the Bose-Einstein condensates in micro-gravity environment

Deep Lossy Plus Residual Coding for Lossless and Near-lossless Image Compression

Lossless and near-lossless image compression is of paramount importance to professional users in many technical fields, such as medicine, remote sensing, precision engineering and scientific research. But despite rapidly growing research interests in learning-based image compression, no published method offers both lossless and near-lossless modes. In this paper, we propose a unified and powerful deep lossy plus residual (DLPR) coding framework for both lossless and near-lossless image compression. In the lossless mode, the DLPR coding system first performs lossy compression and then lossless coding of residuals. We solve the joint lossy and residual compression problem in the approach of VAEs, and add autoregressive context modeling of the residuals to enhance lossless compression performance. In the near-lossless mode, we quantize the original residuals to satisfy a given $\ell_\infty$ error bound, and propose a scalable near-lossless compression scheme that works for variable $\ell_\infty$ bounds instead of training multiple networks. To expedite the DLPR coding, we increase the degree of algorithm parallelization by a novel design of coding context, and accelerate the entropy coding with adaptive residual interval. Experimental results demonstrate that the DLPR coding system achieves both the state-of-the-art lossless and near-lossless image compression performance with competitive coding speed.Comment: manuscript accepted by TPAMI, source code:https://github.com/BYchao100/Deep-Lossy-Plus-Residual-Codin

Three-dimensional Isotropic Droplets in Rydberg-dressed Bose Gases

We predict a scheme for the creation of isotropic three-dimensional droplets in Rydbeg-dressed Bose gases, which contain both repulsive contact interactions and attractive van der Waals interactions causing the quantum fluctuation effect non-negligible. We present detailed beyond mean-field calculations with Lee-Huang-Yang correction and demonstrate the existence of isotropic droplets under realistic experimental conditions. Stable droplets possess flat-top density distribution, and their chemical potentials decrease with the particle number expansion towarding a critical value. We distinguish droplets from bright solitons through peak density, width of condensate and quantum depletion calculations. We summarize a phase diagram of realizing droplets, and subsequently highlight the stability of droplets by real time evolution as well as collisions. Our work provides a novel platform for investigating excitation spectrum and superfluid nature of droplets

Effect of Water on Mechanical Properties and Fracture Evolution of Fissured Sandstone under Uniaxial Compression: Insights from Experimental Investigation

AbstractPreexisting discontinuities and the water affect the fracture evolution process as well as the rock stability the most extensively. To ensure operational safety, the effects of water on the mechanical properties of fissured rock masses must be understood well. In this study, a series of uniaxial compressive tests is conducted on both dry and saturated fissured specimens with varying fissure angles. Real-time acoustic emission and digital image correlation are applied to monitor the fracture evolution process. The failure mode is investigated by identifying the types of cracks present in the ultimate failure forms of the fissured specimens. The results indicate that (1) the saturated and dry specimens exhibit significantly different strengths and stiffnesses, wherein the saturated specimens exhibit weaker strength by 25.64%–32.59% and a lower elastic modulus by 20.30%–29.22%. (2) The fissure angle and water jointly control the failure mode of fissured sandstone. (3) The observed fracture evolution processes can be classified into six distinct stages to facilitate the understanding of rock failure mechanisms. (4) The presence of water accelerates the nucleation of microcracks at the tips of the prefabricated fissures, enlarges the range of microcrack coalescence, and facilitates the emergence of unstable cracks owing to an increase in pore water pressure and a decrease in the friction resistance of crack surfaces

Decreased Connection Between Reward Systems and Paralimbic Cortex in Depressive Patients

Despite decades of research on depression, the underlying pathophysiology of depression remains incompletely understood. Emerging evidence from task-based studies suggests that the abnormal reward-related processing contribute to the development of depression. It is unclear about the function pattern of reward-related circuit during resting state in depressive patients. In present study, seed-based functional connectivity was used to evaluate the functional pattern of reward-related circuit during resting state. Selected seeds were two key nodes in reward processing, medial orbitofrontal cortex (mOFC) and nucleus accumbens (NAcc). Fifty depressive patients and 57 healthy participants were included in present study. Clinical severity of participants was assessed with Hamilton depression scale and Hamilton anxiety scale. We found that compared with healthy participants, depressive patients showed decreased connectivity of right mOFC with left temporal pole (TP_L), right insula extending to superior temporal gyrus (INS_R/STG) and increased connectivity of right mOFC with left precuneus. Similarly, decreased connectivity of left mOFC with TP_L and increased connectivity with cuneus were found in depressive patients. There is also decreased connectivity of right NAcc with bilateral temporal pole, as well as decreased connectivity of left NAcc with INS_R/STG. In addition, the functional connectivity of right nucleus accumbens with right temporal pole (TP_R) was negatively correlated with clinical severity. Our results emphasize the role of communication deficits between reward systems and paralimbic cortex in the pathophysiology of depression

Experimental study on pool boiling in a porous artery structure

In this work, a porous artery structure is proposed to enhance the critical heat flux (CHF) of pool boiling based on the concept of “phase separation and modulation” and extensive experimental studies have been carried out for validation. In the experiment, multiple rectangular arteries were machined directly into the top surface of a copper rod to provide individual flow paths for vapor escaping. The arteries were covered by a microporous copper plate where capillary forces can be developed at the liquid/vapor interface to prevent the vapor from penetrating the porous structure and realize strong liquid suction simultaneously. The pool wall was made of transparent quartz glass to enable a visualization study where the liquid/vapor distribution and movement can be observed directly. Favorable results have been reached as expected, and a maximum heat flux up to 805 W/cm2 was achieved with no indication of any dry-out, which successfully validated this new concept. In addition, the effects of the diameter and thickness of the porous copper plate, and the connection method between the porous copper plate and copper fin on the pool boiling heat transfer in the porous artery structure were investigated, and the inherent physical mechanisms were analyzed and discussed