An inexact Bregman proximal point method and its acceleration version for unbalanced optimal transport

The Unbalanced Optimal Transport (UOT) problem plays increasingly important roles in computational biology, computational imaging and deep learning. Scaling algorithm is widely used to solve UOT due to its convenience and good convergence properties. However, this algorithm has lower accuracy for large regularization parameters, and due to stability issues, small regularization parameters can easily lead to numerical overflow. We address this challenge by developing an inexact Bregman proximal point method for solving UOT. This algorithm approximates the proximal operator using the Scaling algorithm at each iteration. The algorithm (1) converges to the true solution of UOT, (2) has theoretical guarantees and robust regularization parameter selection, (3) mitigates numerical stability issues, and (4) can achieve comparable computational complexity to the Scaling algorithm in specific practice. Building upon this, we develop an accelerated version of inexact Bregman proximal point method for solving UOT by using acceleration techniques of Bregman proximal point method and provide theoretical guarantees and experimental validation of convergence and acceleration

Numerical simulation on the migration and permeable reaction barrier purification of groundwater contaminated by UCG

Underground coal gasification (UCG) is consistent with the development of low-carbon green transformation of energy in China. However, the groundwater pollution caused by it is the bottleneck preventing from the promotion and application of UCG. Permeable reaction barrier (PRB) is one of the research hotspots for in-situ groundwater remediation. In this paper, combined with the characteristics of UCG with shaft, the influence of PRB’s thickness and purification materials on the migration and dispersion of organic pollutants in groundwater, and purification and remediation were investigated by numerical simulation. On the foundation of the advection-diffusion equation (ADE), two hypotheses were introduced: ① The mass transfer involved in the adsorption and purification of pollutants in groundwater is related to: (i) the difference potential between the concentration of pollutants adsorbed in the liquid and solid phases, (ii) the difference potential between the current adsorption concentration of solid phase and the potential maximum adsorption concentration, and (iii) the process time; ② The strong adsorption ability of activated carbon may lead to the gradual accumulation of adsorption concentration in the solid phase and no longer easy desorption with the change of the external liquid phase concentration. Both the migration of pollutants and the adsorption and purification processes were simulated numerically and validated experimentally after that the finite element method and \begin{document}$\theta$\end{document}-format iteration were adapted and the corresponding program were coded in MATLAB. The results show that the remediation is enhanced with the increase of the thickness of PRB, but at a declining acceleration, and the marginal effect of the wall thickness increase on the purification shows the diminishing trend. The stronger the adsorption and purification rate of the wall material is, the better the purification of the PRB on pollutants will be, and the adsorption and purification rate also shows a diminishing trend of marginal effect on the purification. There is a synergistic influence between the thickness and the adsorption activity of the material, thus the thickness of PRB should be determined reasonably according to the adsorption and purification rate of the material when constructing PRB in order to obtain the best technical and economic consequence

High-Performance Non-enzymatic Glucose Sensors Based on CoNiCu Alloy Nanotubes Arrays Prepared by Electrodeposition

Transition metal alloys are good candidate electrodes for non-enzymatic glucose sensors due to their low cost and high performance. In this work, we reported the controllable electrodeposition of CoNiCu alloy nanotubes electrodes using anodic aluminum oxide (AAO) as template. Uniform CoNiCu alloy arrays of nanotubes about 2 μm in length and 280 nm in diameter were obtained by optimizing the electrodeposition parameters. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) measurements indicated that the as-prepared alloy nanotubes arrays are composed of 64.7 wt% Co-19.4 wt% Ni-15.9 wt% Cu. Non-enzymatic glucose sensing measurements indicated that the CoNiCu nanotubes arrays possessed a low detection limit of 0.5 μM, a high sensitivity of 791 μA mM−1 cm−2 from 50 to 1,551 μM and 322 μA mM−1 cm−2 from 1,551 to 4,050 μM. Besides, they showed high reliability with the capacity of anti-jamming. Tafel plots showed that alloying brought higher exchange current density and faster reaction speed. The high performance should be due to the synergistic effect of Co, Ni, and Cu metal elements and high surface area of nanotubes arrays

Effect of Two Graphene Coatings on the Friction and Wear of Sliding Electrical Contact Interface

Two kinds of graphene coatings are obtained by the graphene drop-coating drying method (DCDM) and the coating graphene conductive adhesive (CGCA). The effects of these two kinds of graphene coatings on the friction, wear, and voltage signals of the electrical contact interface are explored. The test results show that the presence of the graphene coating can effectively reduce the friction coefficient and friction force, and the graphene coating prepared by the DCDM possesses the best ability in reducing the friction coefficient. Although the presence of the graphene coating will lead to the increase in interface contact voltage at the initial stage, the voltage signal gradually becomes stable with the progress of friction and wear, suggesting that the graphene coating will not affect the stability of sliding electrical contact. Wear analysis results show that the graphene coating prepared by the DCDM has a good anti-wear effect, and the graphene particles in the abrasion area play the role of solid lubrication. Finite element analysis results show that the graphene coating will generate thermal expansion when electric current is applied, accordingly avoid the direct contact between the metal substrate, and, thus, reduce the interface friction and alleviate the wear degree of interface. However, the normal force fluctuation of the interface may increase

Effect of Two Graphene Coatings on the Friction and Wear of Sliding Electrical Contact Interface

Two kinds of graphene coatings are obtained by the graphene drop-coating drying method (DCDM) and the coating graphene conductive adhesive (CGCA). The effects of these two kinds of graphene coatings on the friction, wear, and voltage signals of the electrical contact interface are explored. The test results show that the presence of the graphene coating can effectively reduce the friction coefficient and friction force, and the graphene coating prepared by the DCDM possesses the best ability in reducing the friction coefficient. Although the presence of the graphene coating will lead to the increase in interface contact voltage at the initial stage, the voltage signal gradually becomes stable with the progress of friction and wear, suggesting that the graphene coating will not affect the stability of sliding electrical contact. Wear analysis results show that the graphene coating prepared by the DCDM has a good anti-wear effect, and the graphene particles in the abrasion area play the role of solid lubrication. Finite element analysis results show that the graphene coating will generate thermal expansion when electric current is applied, accordingly avoid the direct contact between the metal substrate, and, thus, reduce the interface friction and alleviate the wear degree of interface. However, the normal force fluctuation of the interface may increase

Release and Transformation of BTBPE During the Thermal Treatment of Flame Retardant ABS Plastics

Thermal scenarios inevitably occur during the lifecycle of engineering plastics laden with brominated flame retardants (BFRs). However, little information on the fate of embedded BFRs during the thermal processes is available. In this study, we measured the release and transformation of a typical BFR, 1,2-bis(2,4,6-tribromophenoxy)ethane (BTBPE), during the thermal treatment of acrylonitrile butadiene styrene (ABS) plastics. The possible thermal scenarios were simulated by varying the heating temperature and atmosphere. The maximum release rate of BTBPE was observed at 350 degrees C. A release kinetic model was developed to explore the mechanism of BTBPE release while heating ABS. Material phase diffusion was found to be the rate-determining step during release. According to the developed release model, it was estimated that 0.04-0.17% of embedded BTBPE could be released to air during the industrial processing of ABS plastics. When the heating temperature was >= 350 degrees C, approximately 15-56% of embedded BTBPE decomposed to bromophenols (BPs) and 1,3,5-tribromo-2-(vinyloxy) benzene (TBVOB), and the decomposition followed a first-order kinetics at 350 degrees C. Polybrominated dibenzo-p-dioxins and dibenzofurans (PBDD/Fs) were also significantly formed at >= 350 degrees C from BPs and TBVOB via a precursor mechanism. A higher temperature (>= 450 degrees C) was favorable for the formation of PBDFs

Dispersion of Short- and Medium-Chain Chlorinated Paraffins (CPs) from a CP Production Plant to the Surrounding Surface Soils and Coniferous Leaves

Chlorinated paraffin (CP) production is one important emission source for short- and medium-chain CPs (SCCPs and MCCPs) in the environment. In this study, 48 CP congener groups were measured in the surface soils and coniferous leaves collected from the inner and surrounding environment of a CP production plant that has been in operation for more than 30 years to investigate the dispersion and deposition behavior of SCCPs and MCCPs. The average concentrations of the sum of SCCPs and MCCPs in the in-plant coniferous leaves and surface soils were 4548.7 ng g^–1 dry weight (dw) and 3481.8 ng g^–1 dw, which were 2-fold and 10-fold higher than those in the surrounding environment, respectively. The Gaussian air pollution model explained the spatial distribution of CPs in the coniferous leaves, whereas the dispersion of CPs to the surrounding surface soils fits the Boltzmann equation well. Significant fractionation effect was observed for the atmospheric dispersion of CPs from the production plant. CP congener groups with higher octanol–air partitioning coefficients (<i>K</i>_OA) were more predominant in the in-plant environment, whereas the ones with lower <i>K</i>_OA values had the elevated proportion in the surrounding environment. A radius of approximately 4 km from the CP production plant was influenced by the atmospheric dispersion and deposition of CPs

Study of implosion dynamics of Z-pinch dynamic hohlraum on the Angara-5-1 facility

The Z-pinch dynamic hohlraum (ZPDH) is one of high-power X-ray sources that has been used in a variety of high energy-density experiments including inertial confinement fusion (ICF) studies. Dynamic hohlraums driven by a 12-mm and a 18-mm-diameter single tungsten wire arrays embedded with a C16H20O6 foam, respectively, exhibit no visible differences in radiation from the axial exit, although the radial radiation is a little higher in a large array. The analysis of the images suggests that the implosion of a large array is quasi-continuous and has a faster imploding velocity, indicating that the large array is matched to the embedded foam and, oppositely, the small array is mismatched. The analysis also shows that the Rayleigh-Taylor instability develops much harder in implosions of a large array, and this leads to a lower hohlraum temperature. The conclusion was drawn that, for the purpose of enhancing the hohlraum temperature, increasing the conversion efficiency of kinetic energy into thermal energy is more important than increasing the kinetic energy from wire plasma