Precise finite element modeling and analysis of dynamics of linear rolling guideway on supporting direction

The linear rolling guideway, in which exit a lot of rolling interfaces between the rolling balls and the grooves and exhibit complex mechanical behaviors under the static and dynamic loads on supporting direction, will directly affect the machining accuracy and efficiency of CNC machine tool. In the paper, the precise finite element modeling and analysis approach were studied for the dynamics on supporting direction of linear rolling guideway. Firstly, the contact characteristic between a single ball and grooves was analyzed, and the relative contact stiffness was determined under the different preload levels. Moreover, on the basis of considering the guideway structure and rolling ball distribution, the precise finite element model was created and the correctness of modeling method was verified by comparison with the analytic results. At last, the obtained precise modeling method of the linear rolling guideway was applied to the dynamics analysis of a working table of CNC machine tool and the rationality of analysis was explained by comparing with the experiment

Investigation of Durability and Performance of High Friction Surface Treatment

The Indiana Department of Transportation (INDOT) completed a total of 25 high friction surface treatment (HFST) projects across the state in 2018. This research study attempted to investigate the durability and performance of HFST in terms of its HFST-pavement system integrity and surface friction performance. Laboratory tests were conducted to determine the physical and mechanical properties of epoxy-bauxite mortar. Field inspections were carried out to identify site conditions and common early HFST distresses. Cyclic loading test and finite element method (FEM) analysis were performed to evaluate the bonding strength between HFST and existing pavement, in particular chip seal with different pretreatments such as vacuum sweeping, shotblasting, and scarification milling. Both surface friction and texture tests were undertaken periodically (generally once every 6 months) to evaluate the surface friction performance of HFST. Crash records over a 5-year period, i.e., 3 years before installation and 2 years after installation, were examined to determine the safety performance of HFST, crash modification factor (CMF) in particular. It was found that HFST epoxy-bauxite mortar has a coefficient of thermal expansion (CTE) significantly higher than those of hot mix asphalt (HMA) mixtures and Portland cement concrete (PCC), and good cracking resistance. The most common early HFST distresses in Indiana are reflective cracking, surface wrinkling, aggregate loss, and delamination. Vacuum sweeping is the optimal method for pretreating existing pavements, chip seal in particular. Chip seal in good condition is structurally capable of providing a sound base for HFST. On two-lane highway curves, HFST is capable of reducing the total vehicle crash by 30%, injury crash by 50%, and wet weather crash by 44%, and providing a CMF of 0.584 in Indiana. Great variability may arise in the results of friction tests on horizontal curves by the use of locked wheel skid tester (LWST) due both to the nature of vehicle dynamics and to the operation of test vehicle. Texture testing, however, is capable of providing continuous texture measurements that can be used to calculate a texture height parameter, i.e., mean profile depth (MPD), not only for evaluating friction performance but also implementing quality control (QC) and quality assurance (QA) plans for HFST

Pushing the resolution limit by correcting the Ewald sphere effect in single-particle Cryo-EM reconstructions

The Ewald sphere effect is generally neglected when using the Central Projection Theorem for cryo electron microscopy single-particle reconstructions. This can reduce the resolution of a reconstruction. Here we estimate the attainable resolution and report a “block-based” reconstruction method for extending the resolution limit. We find the Ewald sphere effect limits the resolution of large objects, especially large viruses. After processing two real datasets of large viruses, we show that our procedure can extend the resolution for both datasets and can accommodate the flexibility associated with large protein complexes

Assembly of complex viruses exemplified by a halophilic euryarchaeal virus

Many of the largest known viruses belong to the PRD1-adeno structural lineage characterised by conserved pseudo-hexameric capsomers composed of three copies of a single major capsid protein (MCP). Here, by high-resolution cryo-EM analysis, we show that a class of archaeal viruses possess hetero-hexameric MCPs which mimic the PRD1-adeno lineage trimer. These hetero-hexamers are built from heterodimers and utilise a jigsaw-puzzle system of pegs and holes, and underlying minor capsid proteins, to assemble the capsid laterally from the 5-fold vertices. At these vertices proteins engage inwards with the internal membrane vesicle whilst 2-fold symmetric horn-like structures protrude outwards. The horns are assembled from repeated globular domains attached to a central spine, presumably facilitating multimeric attachment to the cell receptor. Such viruses may represent precursors of the main PRD1-adeno lineage, similarly engaging cell-receptors via 5-fold spikes and using minor proteins to define particle size.Peer reviewe

Saturation evaluation of tight sandstone in the Dayi structure, West Sichuan Depression

Tight sandstone reservoirs are characterized by poor physical properties, strong heterogeneity, and complex pore structures, resulting in low reservoir saturation calculation accuracy, and the log interpretations do not match the gas test results. In response to the aforementioned problems, the tight sandstone reservoir of the third member of the Xujiahe Formation of the Dayi structure in the Western Sichuan Depression was investigated through a series of experiments on petrophysical properties, casting thin-section identification, rock resistivity, nuclear magnetic resonance, and high-pressure mercury intrusion. Then, after a systematic analysis of the influence of different factors, including physical properties, mineral composition, and pore structure, on the rock-electric parameters, the parameters of the Archie model were appropriately corrected. The results showed that, for tight sandstone reservoirs, the cementation exponent was mainly affected by the physical properties and clay content, and the saturation exponent was controlled by the proportion of relatively large pore components in the total pore system. Therefore, the non-linear least squares method was used to construct the variable cementation index model; the pseudo-capillary pressure curve was constructed, and a new parameter “the large-pore proportion,” which is used to optimize the saturation exponent, was proposed in combination with the fractal theory. Finally, an Archie model with variable parameters was used to process the actual logging data in the study area. The results show that this method can obtain more accurate gas saturation, providing a new idea and method for fine sandstone saturation logging evaluation

Thingking and utilization technology of coalbed methane in soft and low permeability coal seams in Huainan Mining Area

In order to solve the problems that restrict the efficient development of coalbed methane resources under the conditions of soft and low permeability outburst coal seams in Huainan Mining Area, such as complex coal seam structure, multi-source gas emission, rapid decline of drainage flow, high rock roadway and drilling costs, and low (ultra-low) concentration coalbed methane utilization rate, six key technologies suitable for the coordinated development mode of coal and coalbed methane under the condition of coal seam group mining in Huainan mining area are put forward, namely: coalbed methane extraction technology of ground level staged fracturing wells, shield rapid construction technology of coalbed methane extraction roadways, enhanced extraction technology of underground soft coalbed methane, coalbed methane extraction technology of pressure relief in ground mining area, the construction technology of "replacing roadways with holes", and cascade utilization technology of low concentration coalbed methane. The application of supporting key technologies shows that staged fracturing technology and refined drainage and production technology of roof horizontal wells in broken and soft coal seam have effectively improved the pre pumping production of coalbed methane; The full face hard rock roadheader in deep coal mine roadway greatly improves the roadway excavation efficiency, realizing the automation and less humanization of hard rock excavation; Sand adding of hydraulic fracturing and ultra-high hydraulic slotting have realized pressure relief and permeability enhancement in large areas underground coal mine; Type III and IV surface mining area wells can replace the roof high drainage roadway in the treatment of pressure relief gas in coal seam group mining, and reduce the coalbed methane drainage intensity of other measures; The technology of "replacing roadways with holes" has significantly improved the quality of successful directional drilling at middle and high levels in complex roof; Cascade utilization technology of low concentration coalbed methane has greatly reduced the emission of coalbed methane. The six key technologies have guaranteed the safe production in Huainan mining area, and comprehensively improved the output of coal and coalbed methane and the utilization level of coalbed methane. Six key technologies ensure the safe production in Huainan mining area, and comprehensively improved the output of coal and coalbed methane and the utilization level of coalbed methane. Finally, in view of the problems such as high operation cost, low production, small scope of hydraulic fracturing coal reservoir reconstruction technology for surface horizontal wells, and the risk of breakage of mining wells, and small scale of cascade utilization of ultra-low concentration coalbed methane, the development direction of deep CBM precise geological guidance, super large scale efficient reservoir volume transformation, pumping effect evaluation technology, stable and continuous pumping technology of surface wells in mining areas, underground large area intelligent hydraulic enhanced permeability technology, "one well with multiple uses" collaborative pumping CBM technology, and full concentration CBM comprehensive utilization technology are proposed

Towards the Rational Design of Stable Electrocatalysts for Green Hydrogen Production

Now, it is time to set up reliable water electrolysis stacks with active and robust electrocatalysts to produce green hydrogen. Compared with catalytic kinetics, much less attention has been paid to catalyst stability, and the weak understanding of the catalyst deactivation mechanism restricts the design of robust electrocatalysts. Herein, we discuss the issues of catalysts’ stability evaluation and characterization, and the degradation mechanism. The systematic understanding of the degradation mechanism would help us to formulate principles for the design of stable catalysts. Particularly, we found that the dissolution rate for different 3d transition metals differed greatly: Fe dissolves 114 and 84 times faster than Co and Ni. Based on this trend, we designed Fe@Ni and FeNi@Ni core-shell structures to achieve excellent stability in a 1 A cm−2 current density, as well as good catalytic activity at the same time