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Poisson image deblurring, which aims to restore the latent image from its blurred and noisy observation, has drawn significant attention in image processing. Due to its ill-posed nature, enhancing image quality often involves incorporating a well-defined prior to effectively regularize the ill-posed inverse problem. Building upon the framelet system, we propose a frame-based nonconvex regularization method for Poisson image deblurring. The method is formulated by combining a data-fitting term with the difference of two norms, namely ℓ 1 and ℓ 2 , on the latent image. We solve the optimization problem by combining the difference of convex functions algorithm (DCA) with the alternating direction method of multipliers (ADMM), establishing its convergence. We further employ a simulated annealing procedure and show that proposed algorithm almost certainly converges to a global minimum. Two different approaches are employed to handle the frame-based ℓ 1 norm within the ADMM framework. In particular, the frame-based nonconvex regularization method is also considered for the blind Poisson problem. An effective recovery model and its algorithm are presented. Experimental results demonstrate the effectiveness of our proposed models compared with other models in terms of quantitative metrics and visual quality. • Frame-based nonconvex regularization model is proposed to eliminate Poisson noise and blur from degraded image. • An efficient algorithm with convergence guarantees is proposed. • We study an accelerated algorithm and explore the blind Poisson problem. • Experimental results demonstrate the effectiveness of our proposed models compared with other models. [ABSTRACT FROM AUTHOR]

Tensor completion involves recovering the underlying tensor from partial observations, and in this paper we focus on the point that these observations obey the Poisson distribution. To contend with this problem, we adopt a popular method that minimizes the sum of the data-fitting term and the regularization term under a uniform sampling mechanism. Specifically, we consider the negative logarithmic maximum likelihood estimate of the Poisson distribution as the data-fitting term. To effectively characterize the intrinsic structure of the tensor data, we propose a parameter-free regularization term that can simultaneously capture the low rankness and local smoothness of the underlying tensor. Here, the transformed tensor nuclear norm is used to explore the low rankness under suitable unitary transformations. We present theoretical derivations to demonstrate the feasibility of the proposed model. Furthermore, we develop an algorithm based on the alternating direction multiplier method (ADMM) to efficiently solve the proposed optimization problem, with its overall convergence being established. A series of numerical experiments show that proposed model yields a pleasing accuracy over several state-of-the-art models. • We considers a tensor completion with Poisson observations, differing from common researches. • TCTV regularizer can simultaneously characterize global low rankness and local smoothness. • Transformed tensor nuclear norm is introduced to obtain lower transformed multi-rank. • ADMM-based optimization algorithm with global convergence guarantee is implemented. • Experiments show superior performance in recovering global structure and details. [ABSTRACT FROM AUTHOR]

MgB 2 /BN/MgB 2 trilayer films have been fabricated by using hybrid physical–chemical vapor deposition (HPCVD) method for the MgB 2 layers and chemical vapor deposition (CVD) method for the BN layers in the same reactor. The films are studied by X-ray photoelectron spectroscopy (XPS), transmission electron microscope (TEM), scanning electron microscope (SEM), X-ray diffraction (XRD) and magnetization measurements. These test outcomes indicate the trilayer films are grown without deteriorating the superconductivity of MgB 2 films. Our results show that it is feasible to grow MgB 2 /BN/MgB 2 trilayer films in the same reactor sequentially, which has the advantage of reducing contamination during the growth. This therefore opens the door for fabricating all-MgB 2 Josephson junctions by using the BN film as the insulating layer. [ABSTRACT FROM AUTHOR]

Studies the superconductivity of the compound MgB[sub2]. Discovery of the compound in January 2001 by the japanese scientist Akimitsu et al; Review of the electronic structure, high T[subc] mechanism and the superconducting parameters; Discussion on the issue of power transmission.

Demonstrates that high pressure chemical vapor deposition (HPCVD) is an effective and efficient approach to the synthesis of thick magnesium boride films over the stainless substrate. X-ray diffraction pattern of magnesium boride film grown on the stainless steel substrate; Deposition rate of the film; Tenacity and the bonding strength of the film to the substrate.

Abstract: The experiment for preparing MgB2 thin films by electron beam (e-beam) annealing of Mg–B multilayer is reported. The annealing process lasts less than 1s, which effectively suppresses the volatility of Mg as well as the reaction of Mg and oxygen. The influence of annealing parameters on the film quality including exposure time, accelerating voltage and beam current is investigated. It is found that e-beam with lower accelerating voltage can acquire MgB2 film with smaller annealing energy density. Also, double e-beam scan annealing process helps to obtain more uniform MgB2 thin films than the single scan. This rapid annealing method synthesizes MgB2 thin films with critical temperature Tc of 35K and critical current density Jc at 15K of 7.6×106 Acm−2. [Copyright &y& Elsevier]

Low-temperature sintering to fabricate MgB2 is considered a promising method because it reduces the formation of MgO and reduces the grain size, thereby increasing the critical current density. Chemical doping, ball milling of precursor and modifying the Mg source in precursor for low-temperature sintering have all been carefully investigated. However, the threshold of sintering temperature have been kept near 500 °C. A new in-situ method to low-temperature sintering using Mg(BH4)2 as a precursor is presented in this paper. Mg(BH4)2 decomposes into highly reactive nanoscale Mg and B in a molar ratio of 1:2 without impurities. In this method, only 2 h of sintering at 400 °C is required to completely react Mg with B to produce MgB2, and after 54 h sintering, the sample has comparable JC to the normal MgB2 from solid-state reaction method sintered at 800 °C. The sample sintered at 500 °C give better JC than normal MgB2 under both high and low magnetic field. [ABSTRACT FROM AUTHOR]

HT C SQUID has a great potential in ultra-weak magnetic signal detections due to its advantages of energy saving and volume reduction of the overall system, including the cryogenics. However, the application of HT C SQUID is limited because lack of proper magnetic shielding. Superconducting magnetic shielding is an efficient way for HT C SQUID. In this work, we fabricate MgB 2 thick film on a stainless steel cylinder using HPCVD to make a preliminary attempt for SMS with MgB 2 films. High quality MgB 2 film is deposited on the inner side of a hollowed cylinder. The transition temperature of the film is 37.5 K, and the critical current density is 7.6 × 10 6 A⋅cm −2 at 10 K and 4.6 × 10 6 A⋅cm −2 at 20 K, which is comparable with the planar films. The shielding effectiveness of the cylindrical MgB 2 film is numerical simulated. Height and thickness of the cylindrical magnetic shielding designed according to the simulation result was calculated and a corresponding shielding effectiveness of 65 dB is obtained. The numerical result shows the feasibility of using MgB 2 film as magnetic shielding. [ABSTRACT FROM AUTHOR]

MgB 2 has shown great potential in making medium strength superconducting magnet using electronic refrigeration without liquid helium. One of the major problem in building the MgB 2 superconducting magnet is the joints in the coils. An effective method of building a superconducting joint is crucial. In this work, we have demonstrated a novel process of building a superconducting joint utilizing sol-gel method. Two HPCVD MgB 2 thin film on SiC substrate is pasted face-to-face with Mg(BH 4 ) 2 •Et 2 O gel. After annealing in Mg vapor, Mg(BH 4 ) 2 •Et 2 O gel decomposed and turned to MgB 2 superconducting joint. The joint showed good connectivity between the two films and has a good T C of 34 K. Infield measurement of the joint showed that the joint work well at 20 K with the applied magnetic field up to 4 T. [ABSTRACT FROM AUTHOR]

MgB 2 superconducting films, whose thicknesses range from 10 nm to 8 µm, have been fabricated on SiC substrates by hybrid physical–chemical vapor deposition (HPCVD) method. It is the first time that the T c and the J c of MgB 2 films are studied on such a large scale. It is found that with the increasing of thickness, T c elevates first and then keeps roughly stable except for some slight fluctuations, while J c (5 K, 0 T) experiences a sharp increase followed by a relatively slow fall. The maximum J c (5 K, 0 T) = 2.3 × 10 8 A cm −2 is obtained for 100 nm films, which is the experimental evidence for preparing high-quality MgB 2 films by HPCVD method. Thus, this work may provide guidance on choosing the suitable thickness for applications. Meanwhile, the films prepared by us cover ultrathin films, thin films and thick films, so the study on them will bring a comprehensive understanding of MgB 2 films. [ABSTRACT FROM AUTHOR]

Magnesium diboride has shown potential as an alternative material for the application of superconducting RF cavities. However, if MgB 2 films are fabricated on niobium substrates with HPCVD method, hydrogen brittleness will cause cracks on MgB 2 film when it is bent. In this work, we have investigated the possibility of depositing MgB 2 film on niobium in other background gases rather than hydrogen to avoid hydrogen brittleness. Though MgB 2 films fabricated in nitrogen and argon have impurities and show poor superconducting properties, the MgB 2 film fabricated in helium has similar morphology and superconducting properties of that prepared in hydrogen and no cracks are observed after bending. The problem of hydrogen brittleness can be solved by using helium as the background gas when fabricating MgB 2 films on niobium substrates. [ABSTRACT FROM AUTHOR]

200 nm Ni film is coated on 25 μm thick Mo foil, and graphene is grown on the Ni–Mo system by CVD method. After the annealing process of CVD, the Ni/Mo bilayer transforms into Ni–Mo alloy, then we have successfully fabricated MgB 2 films on graphene/Ni–Mo alloy system via the hybrid physical–chemical vapor deposition (HPCVD) technique. The transition temperature T c onset is 38.25 K with a corresponding transition width of 0.75 K. The average thickness of MgB 2 films is 200 nm (25% concentration B 2 H 6 ). The critical current density derives from the magnetization measurement at 5 K is, j c (5 K, 0 T) = 9.6 × 10 6 A/cm 2 . We can easily deposite MgB 2 on graphene/Ni–Mo alloy system with a lower B 2 H 6 concentration and less gas flow, which lays a good foundation for depositing MgB 2 thick films. The graphene in this system is multilayer and with defects, it may act like an intermediary film for the growth of MgB 2 , or a carbon-doping source. [ABSTRACT FROM AUTHOR]

l A sol-gel method for superconducting joints of high-performance MgB 2 films. l Two types of MgB 2 joints a two-piece-face-to-face joint, and a three-piece-bridging joints. l The joint showed a high T C of 40 K, a high I C of 340 mA at 0 T. Large-area high-quality MgB 2 thin films were needed in many superconducting applications such as superconducting radio frequency (RF) cavities. However, fabricating large films with high quality can be difficult. Thus, a jointing method between MgB 2 films can be crucial in a lot of superconducting electronic applications. In this article, we successfully fabricated superconducting joints for MgB 2 films. The sol-gel of Mg(BH 4) 2 ·Et 2 O was used as the glue. Two types of MgB 2 joints were shown in this work, a two-piece face-to-face joint, and a three-piece bridging joint. The sol-gel derived MgB 2 joints have shown very good superconducting performance, with a high superconducting critical temperature (T C) of 40 K, a high critical current (I C) of 340 mA at 0 T, and very nice current capacity in magnetic fields up to 4 T. [ABSTRACT FROM AUTHOR]

Abstract: MgB2 thin films were prepared by ex-situ annealing of Mg/B multilayers. Different precursor, substrate and annealing condition were investigated. After annealed in a flow of Mg vapor with reducing hydrogen ambient for 1–4min, high quality 20nm-thick c-oriented MgB2 thin films with and critical current density J C =2×106 Acm−2 at 30K were obtained. The mean roughness of the 20nm-thick film was 2.68nm. [Copyright &y& Elsevier]

The article presents a study which demonstrates the magnesium diboride (MgB2) superconducting whiskers synthesized by hybrid physical-chemical vapor deposition (HPCVD). The HPCVD setups that were employed in this experiment were quartz chamber with induction heating and stainless steel chamber with resistivity heating. A scanning electron microscope was used to analyze the morphologies of the whiskers. It has observed an onset temperature of 39 K.

Superconducting MgB2 wires were prepared by exposing boron fiber to magnesium powder in high temperature. Pulse current method has been used to study the V–I characteristics systematically in a large current range. Using a scaling function, all the R–T curves in different field converge into a single universal curve. From the V–I curves, we find a much sharp N–S transition and in high field a reasonable large Jc is found. [Copyright &y& Elsevier]

Graphene is a well-known material with various potential applications. Here we report the manufacture of high-quality and large-scale monolayer graphene pasters via polyvinyl butyral (PVB). These pasters have good self-supporting properties and overcome the drawback of weak mechanical strength of PMMA. Manual manipulations to monolayer graphene become realizable via graphene pasters. Graphene pasters can be quickly diverted onto any substrate with sufficient contact and greatly minimize the challenges in graphene transfer, measurements, and other applications. The improved transfer process via graphene pasters protects the integrity of monolayer graphene and introduces few cracks or tears into graphene. Large-scale monolayer graphene films diverted onto SiO2/Si by using graphene pasters maintain low resistivity and low Dirac point, while also exhibiting a higher magnetoresistance than traditional results. High magnetoresistance up to 600% and signs of saturation at high magnetic fields can be seen. Obvious negative magnetoresistance at low magnetic fields due to weak localization also can be observed. Graphene pasters can be used in many different domains and will promote future studies and applications of graphene. [ABSTRACT FROM AUTHOR]

High quality single-crystal magnesium diboride (MgB2) nanowires with lengths exceeding 10 μm were successfully synthesized by hybrid physical chemical vapor deposition. The magnetization and electrical transport properties of single-crystal MgB2 nanowires (NWs) were measured. The superconducting transition temperature of the NWs was 37 K, as confirmed by magnetization measurements. The disordered behavior of the nanowires was observed by four-terminal current–voltage characteristic measurements of an individual NW from T = 10 to 300 K. The temperature-dependent resistivity curves for seven NWs collapsed into a universal curve described by the variable range hopping model, showing intrinsic nonmetallic transport properties. This implies that the granular superconducting defect states are critical to the superconductivity of the individual MgB2 NWs. [ABSTRACT FROM AUTHOR]