Fabrication of binder-free ultrafine WC-6CO composites by coupled multi-physical fields activation technology

A novel sintering method, named as coupled multi-physical fields activation technology, has been introduced for the forming of various material powder systems. Compared with the conventional ones, this technique presents more advantages: lower sintering temperature, shorter forming time, and remarkable inhibition of the grains coarsening. In the study, the cylinders of Φ4.0mm×4.0mm had been formed with ultrafine WC-6Co powders. The relative properties of sintered WC-6Co cemented carbides, such as hardness and the microstructures, had been obtained. The study has shown that a relative density, 97.80%, of the formed samples, could been achieved when the case of temperature 850℃, heating rate 50℃/s, pressure 75MPa and Electro-heating loop 6 times, were used. More importantly, the circumscription for the growth of grain size of WC, attributed to the effect of electrical field, renders coupled multi-physical fields activation technology applicable for getting WC-6Co cemented carbides with fine grain size and good properties

Template effect in TiN/AlN multilayered coatings from first principles

Multilayered TiN/AlN coatings find many technological applications where superhardness is suspected to be affected by AlN structures and template effect. Here, we demonstrate, by first-principles calculations on alternative adsorptions of Al and N atoms on Ti- and N-terminated TiN surfaces, that the preferred stacking sequences (i.e., having the largest adsorption energy) transform from fcc- to hcp- mode in first a few AlN layers. Using several analytic methods, we identify that for the T-terminated surface, the third added N layer is critical to inducing the structural transition of AlN, weakening the interaction between the second added Al and first added N atoms. The findings provide insight to the complicated template effects in TiN/AlN multilayered coatings, which are practically relevant for further improving property of multilayered coatings at the atomic scale

Microstructure evolution and surface cleaning of Cu nanoparticles during micro-fields activated sintering technology

For the purpose of extensive utilization of powder metallurgy to micro/nano- fabrication of materials, the micro gear was prepared by a novel method, named as micro- forming fields activated sintering technology (Micro-FAST). Surface-cleaning of particles, especially during the initial stage of sintering, is a crucial issue for the densification mechanism. However, up to date, the mechanism of surface-cleaning is too complicated to be known. In this paper, the process of surface-cleaning of Micro-FAST was studied, employing the high resolution transmission electron microscopy (HRTEM) for observation of microstructure of micro-particles. According to the evolution of the microstructure, surface-cleaning is mainly ascribed to the effect of electro-thermal focusing. The process of surface-cleaning is achieved through rearrangement of grains, formation of vacancy, migration of vacancy and enhancement of electro-thermal focusing

A new densification mechanism of copper powder sintered under an electrical field

A new sintering mechanism is revealed for copper powder sintered under the influence of an electrical field and a force field during the formation of microcomponents. Analysis of the microstructure and grain boundary evolution of the sintered samples showed that the disappearance of the interface at contact areas between particles is a continuous process which involves new grain formation and grain refinement during this innovative microsintering process. The densification process is therefore different from what is known in a conventional powder sintering process

Effects of sintering temperature on the densification of WC-6Co cemented carbides sintered by coupled multi-physical-fields activated technology

Sample parts with WC-6Co cemented carbides were manufactured successfully with a novel method called coupled multi-physical-fields (electric field, temperature field and force field) activated sintering technology, using a Gleeble-1500D thermal simulation machine. Effects of sintering temperature on the densification, microstructures and hardness of samples were investigated. It was found that densification of the samples was enhanced with the increase of the sintering temperature and a relative density of as high as 98.76% achieved when a sintering temperature of 1200 °C was used. The particle size of the WC in sintered samples increased from 1.837 μm to 2.897 μm when the temperature was increased from 1000 °C to 1200 °C, resulting in the decrease of the hardness from HRC 63.5 to HRC 61.7. The presented work shows that, potentially, coupled multi-physical-fields activated technology is able to produce hard alloys to meet the engineering applications

Carbon materials : structures, properties, synthesis and applications

As one of the most versatile elements, carbon materials occupy the most plentiful allotropies composed of pure or mixed hybridization orbitals of sp1/sp2/sp3. The design and synthesis of new carbon materials may be stimulated based on a deeper understanding of underlying structures and related properties. In this review, the initial early discoveries of carbon materials are examined based on their hybridization of orbitals. According to the type of hybridization, the discovered carbon materials are firstly classified and introduced in detail based on their crystal structures. Secondly, its physical and chemical properties, mainly including mechanical properties, optical properties and electronic properties, are reviewed. Thirdly, the existing methods of predicting carbon structure and synthesizing carbon materials are classified and summarized, and some typical carbon materials predicted or prepared are discussed respectively. Then, the main applications of newly synthesized carbon materials in the last two decades are classified and summarized, and the microstructure is linked with the macro properties and specific applications. Finally, the future research opportunities for carbon materials and their potential applications are prospected from the aspects of the gap between theoretical prediction and preparation, the current research hotspot of carbon materials and the incomplete application of carbon materials. It is the authors' intention for this review paper to serve not only as a valuable reference for research into carbon materials and related composites, but also as a guidance for novel materials design at the atomic level

Kinematic Design, Analysis and Simulation of a Hybrid Robot with Terrain and Aerial Locomotion Capability

Having only one type of locomotion mechanism limits the stability and locomotion capability of a mobile robot on irregular terrain surfaces. One of the possible solution to this is combining more than one locomotion mechanisms in the robot. In this paper, robotic platform composed of a quadruped module for terrain locomotion and quadrotor module for aerial locomotion is introduced. This design is inspired by the way which birds are using their wings and legs for stability in slopped and uneven surfaces. The main idea is to combine the two systems in such a way that the strengths of both subsystems are used, and the weakness of the either systems are covered. The ability of the robot to reach the target position quickly and to avoid large terrestrial obstacles by flying expands its application in various areas of search and rescue. The same platform can be used for detailed 3D mapping and aerial mapping which are very helpful in rescue operations. In particular, this paper presents kinematic design, analysis and simulation of such a robotic system. Simulation and verification of results are done using MATLAB

Attention Where It Matters: Rethinking Visual Document Understanding with Selective Region Concentration

We propose a novel end-to-end document understanding model called SeRum (SElective Region Understanding Model) for extracting meaningful information from document images, including document analysis, retrieval, and office automation. Unlike state-of-the-art approaches that rely on multi-stage technical schemes and are computationally expensive, SeRum converts document image understanding and recognition tasks into a local decoding process of the visual tokens of interest, using a content-aware token merge module. This mechanism enables the model to pay more attention to regions of interest generated by the query decoder, improving the model's effectiveness and speeding up the decoding speed of the generative scheme. We also designed several pre-training tasks to enhance the understanding and local awareness of the model. Experimental results demonstrate that SeRum achieves state-of-the-art performance on document understanding tasks and competitive results on text spotting tasks. SeRum represents a substantial advancement towards enabling efficient and effective end-to-end document understanding.Comment: Accepted to ICCV 2023 main conferenc

Hepatic E4BP4 induction promotes lipid accumulation by suppressing AMPK signaling in response to chemical or diet- induced ER stress

Prolonged ER stress has been known to be one of the major drivers of impaired lipid homeostasis during the pathogenesis of non- alcoholic liver disease (NAFLD). However, the downstream mediators of ER stress pathway in promoting lipid accumulation remain poorly understood. Here, we present data showing the b- ZIP transcription factor E4BP4 in both the hepatocytes and the mouse liver is potently induced by the chemical ER stress inducer tunicamycin or by high- fat, low- methionine, and choline- deficient (HFLMCD) diet. We showed that such an induction is partially dependent on CHOP, a known mediator of ER stress and requires the E- box element of the E4bp4 promoter. Tunicamycin promotes the lipid droplet formation and alters lipid metabolic gene expression in primary mouse hepatocytes from E4bp4flox/flox but not E4bp4 liver- specific KO (E4bp4- LKO) mice. Compared with E4bp4flox/flox mice, E4bp4- LKO female mice exhibit reduced liver lipid accumulation and partially improved liver function after 10- week HFLMCD diet feeding. Mechanistically, we observed elevated AMPK activity and the AMPKβ1 abundance in the liver of E4bp4- LKO mice. We have evidence supporting that E4BP4 may suppress the AMPK activity via promoting the AMPKβ1 ubiquitination and degradation. Furthermore, acute depletion of the Ampkβ1 subunit restores lipid droplet formation in E4bp4- LKO primary mouse hepatocytes. Our study highlighted hepatic E4BP4 as a key factor linking ER stress and lipid accumulation in the liver. Targeting E4BP4 in the liver may be a novel therapeutic avenue for treating NAFLD.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/162728/3/fsb220918_am.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/162728/2/fsb220918-sup-0001-FigS1-S10.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/162728/1/fsb220918.pd

Hepatoprotective role of Sestrin2 against chronic ER stress

Upon prolonged endoplasmic reticulum (ER) stress, cells attenuate protein translation to prevent accumulation of unfolded proteins. Here we show that Sestrin2 is critical for this process. Sestrin2 expression is induced by an ER stress-activated transcription factor CCAATenhancer- binding protein beta (c/EBPβ). Once induced, Sestrin2 halts protein synthesis by inhibiting mammalian target of rapamycin complex 1 (mTORC1). As Sestrin2-deficient cells continue to translate a large amount of proteins during ER stress, they are highly susceptible to ER stress-associated cell death. Accordingly, dietary or genetically induced obesity, which does not lead to any pathological indication other than simple fat accumulation in the liver of wild-type (WT) mice, can provoke Sestrin2-deficient mice to develop severe ER stressassociated liver pathologies such as extensive liver damage, steatohepatitis and fibrosis. These pathologies are suppressed by liver-specific Sestrin2 reconstitution, mTORC1 inhibition or chemical chaperone administration. The Sestrin2-mediated unfolded protein response (UPR) may be a general protective mechanism against ER stress-associated diseases