Machining accuracy is the most critical indicator to evaluate the machining quality of parts in metal cutting industry. However, it is difficult to be identified before real cutting, because of a variety of error sources presented in a machining process system, such as assembly inaccuracy of machine tool, deformation caused by temperature variation and dynamic cutting force, tool wear, servo lag and so on. Consequently, it is difficult to determine whether a new machining process can satisfy accuracy requirements beforehand. Traditionally, a machining process is validated through the “trial and error” approach, which is time consuming and costly. If machining accuracy can be predicted to a large extent, a rational process can be planned to ensure the precision of parts and even to maximize resource utilization without trial cuts. For this purpose, this work focuses on machining accuracy prediction for five-axis peripheral milling based on the geometric errors. An error synthesis modeling method is proposed to integrate the geometric errors of the process system, including machine tool geometric error, workpiece locating error, cutting tool dimension error and setup error. From a multi-body system point of view, all these errors are synthesized to generate position error of the cutting contact point in the workpiece coordinate system. Then the machining error is obtained by projecting the position error to the workpiece normal vector, which can be measured by a coordinate measuring machine. The prediction model has been evaluated by a cutting test with our in-house-developed prototype software. The result shows that the proposed method is feasible and effective.

Surface layers (S-layers) are protective protein coats which form around all archaea and most bacterial cells. Clostridium difficile is a Gram-positive bacterium with an S-layer covering its peptidoglycan cell wall. The S-layer in C. difficile is constructed mainly of S-layer protein A (SlpA), which is a key virulence factor and an absolute requirement for disease. S-layer biogenesis is a complex multi-step process, disruption of which has severe consequences for the bacterium. We examined the subcellular localization of SlpA secretion and S-layer growth; observing formation of S-layer at specific sites that coincide with cell wall synthesis, while the secretion of SlpA from the cell is relatively delocalized. We conclude that this delocalized secretion of SlpA leads to a pool of precursor in the cell wall which is available to repair openings in the S-layer formed during cell growth or following damage. Clostridium difficile infection (CDI) is the major cause of antibiotic associated diarrhoea 1 and can lead to severe inflammatory complications 2. This Gram-positive bacterium has a cell wall encapsulating, proteinaceous surfacelayer (S-layer), a paracrystalline array that acts as a protective semipermeable shell and is essential for virulence 3. In C. difficile the S-layer largely consists of SlpA, the most abundant surface protein, with additional functionality added through the incorporation of up to 28 minor S-layer-associated cell wall proteins 4. SlpA is produced as a pre-protein (Fig. 1a) that is secreted and processed by the cell surface cysteine protease Cwp84 into low molecular weight (LMW) and high molecular weight (HMW) SLP subunits 5 (Fig. 1b). These two subunits form a heterodimeric complex that is then incorporated into the crystalline lattice of the S-layer, which is anchored to cell wall polysaccharide PS-II via three cell wall binding (CWB2) motifs within the HMW region 6,7 (Fig. 1a). The production and secretion of S-layer components are energetically expensive for the cell, suggesting that the process will display evolved efficiency. However, it is not yet clear how S-layer formation is spatially regulated and whether SlpA is targeted to areas of cellular growth before or after secretion (Fig. 1c). C. difficile express two homologs of the E. coli cytosolic protein export ATPase, SecA: SecA1 and SecA2 8. These two SecAs are thought to promote post-translational secretion through the general secretory (Sec) pathway. SecA2 is required for efficient SlpA secretion 8 and is encoded adjacent to slpA on the chromosome 9. It has been shown that some SecA2 systems secrete specific substrates (reviewed by 10) which may ease the burden on the general Sec system and allow spatial or temporal regulation of secretion. As an obligate anaerobe, C. difficile has been notoriously difficult to visualize using standard microscopy techniques with commonly used oxygen-dependent fluorescent proteins and this is further complicated by intrinsic autofluorescence in the green spectrum 11. To circumvent these problems, ...

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An effective and rapid procedure to synthesize hierarchical MOR (Hi-MOR) nanosheets by self-assembly between subnanocrystals and organic templates was reported. The hierarchical pore systems provided a large quantity of Brønsted acid sites. Compared with conventional mordenite, Hi-MOR showed higher activity, xylene selectivity and longer catalytic life in the reaction of toluene disproportionation, thanks to its excellent diffusion from hierarchical structure. Graphical Abstract Hierarchical morednite (Hi-MOR) nanosheets were synthesized by self-assembly between subnanocrystals and organic templates.