在亚稳奥氏体不锈钢中进行温度跳跃拉伸试验以诱导最佳TRIP/TWIP效应

本文通过将AISI 304L奥氏体不锈钢的变形温度控制在0~200oC范围内,初步调整了其塑性变形机制以优化强塑性协同效应。研究表明,孪生诱发塑性效应（TWIP）/相变诱导塑性效应（TRIP）的协同效应和通过调节变形温度将TRIP效应的应变范围扩大到更高的应变范围,是提高亚稳不锈钢强塑性协同性的有效策略。在这方面,考虑到观察到的塑性变形的温度依赖性,通过预先设计的温度跳跃拉伸试验,实现TWIP和TRIP效应的受控序列,以实现良好的强度–延性权衡。因此,在应变的后期,通过利用100oC下的TWIP效应和25oC时的TRIP效应的优势,这种方法获得了846 MJ/m3的拉伸韧性和133%的总伸长率。此外,基于加工硬化分析,发现变形诱发的α′-马氏体屈服是制约塑性和强化性能进一步提高的主要原因。     

Prox1 function is crucial for mouse lens-fibre elongation

Although insights have emerged regarding genes controlling the early stages of eye formation, little is known about lens-fibre differentiation and elongation. The expression pattern of the Prox1 homeobox gene suggests it has a role in a variety of embryonic tissues, including lens. To analyse the requirement for Prox1 during mammalian development, we inactivated the locus in mice. Homozygous Prox1-null mice die at mid-gestation from multiple developmental defects; here we describe the specific effect on lens development. Prox1 inactivation causes abnormal cellular proliferation, downregulated expression of the cell-cycle inhibitors Cdkn1b (also known as p27KIP1) and Cdkn1c (also known as p57KIP2), misexpression of E-cadherin and inappropriate apoptosis. Consequently, mutant lens cells fail to polarize and elongate properly, resulting in a hollow lens. Our data provide evidence that the progression of terminal fibre differentiation and elongation is dependent on Prox1 activity during lens development.     

A Systemic Framework for Business Model Design and Development -Part B: Practical Perspective

Systemic Practice and Action Research - Profit-making requires innovation in the design of a successful business model that brings about sustainable competitive advantage for the organization....     

Effect of sulfated and non-sulfated gastrin and octapeptide-cholecystokinin on cat gall bladder in vitro

Summary This study demonstrates that for the isolated cat gall bladder a smaller molar dose of the sulfated form of OP-CCK and gastrin is required to produce contraction as compared to the respective non-sulfated forms. For OP the D₅₀ for the sulfated form versus the non-sulfated form was 1.94. For gastrin it was 1.10.This study was supported in part from NIH grant No. HL 15422 from the National Heart and Lung Institute.     

Robust Control of Robotic Manipulators in the Task-Space Using an Adaptive Observer Based on Chebyshev Polynomials

In this paper, an adaptive observer for robust control of robotic manipulators is proposed.The lumped uncertainty is estimated using Chebyshev polynomials. Usually, the uncertainty upper bound is required in designing observer-controller structures. However, obtaining this bound is a challenging task. To solve this problem, many uncertainty estimation techniques have been proposed in the literature based on neuro-fuzzy systems. As an alternative, in this paper, Chebyshev polynomials have been applied to uncertainty estimation due to their simpler structure and less computational load.Based on strictly-positive-real(SPR) Lyapunov theory, the stability of the closed-loop system can be verified. The Chebyshev coefficients are tuned based on the adaptation rules obtained in the stability analysis. Also, to compensate the truncation error of the Chebyshev polynomials, a continuous robust control term is designed while in previous related works, usually a discontinuous term is used. An SCARA manipulator actuated by permanent magnet DC motors is used for computer simulations.Simulation results reveal the superiority of the designed method.     

Structural basis for the selectivity of the external thioesterase of the surfactin synthetase

Non-ribosomal peptide synthetases (NRPS) and polyketide synthases (PKS) found in bacteria, fungi and plants use two different types of thioesterases for the production of highly active biological compounds. Type I thioesterases (TEI) catalyse the release step from the assembly line of the final product where it is transported from one reaction centre to the next as a thioester linked to a 4'-phosphopantetheine (4'-PP) cofactor that is covalently attached to thiolation (T) domains. The second enzyme involved in the synthesis of these secondary metabolites, the type II thioesterase (TEII), is a crucial repair enzyme for the regeneration of functional 4'-PP cofactors of holo-T domains of NRPS and PKS systems. Mispriming of 4'-PP cofactors by acetyl- and short-chain acyl-residues interrupts the biosynthetic system. This repair reaction is very important, because roughly 80% of CoA, the precursor of the 4'-PP cofactor, is acetylated in bacteria. Here we report the three-dimensional structure of a type II thioesterase from Bacillus subtilis free and in complex with a T domain. Comparison with structures of TEI enzymes shows the basis for substrate selectivity and the different modes of interaction of TEII and TEI enzymes with T domains. Furthermore, we show that the TEII enzyme exists in several conformations of which only one is selected on interaction with its native substrate, a modified holo-T domain.     

Large-scale traveling ionospheric disturbances observed by GPS receivers in Antarctica

The paper examines the propagation direction and velocity of largescale traveling ionospheric disturbances (LSTIDs) during extreme geomagnetic storms in the 23rd solar cycle (e.g., October 2003 and No-vember 2003 storms) using GPS observations. In the analysis, the time delay between the vertical total electron content (VTEC) structures at Scott Base, McMurdo, Davis and Casey GPS stations and the distance between these stations were the main parameters in the determination of LSTIDs propagation speed and di...     

Gut hormone PYY(3-36) physiologically inhibits food intake

Food intake is regulated by the hypothalamus, including the melanocortin and neuropeptide Y (NPY) systems in the arcuate nucleus. The NPY Y2 receptor (Y2R), a putative inhibitory presynaptic receptor, is highly expressed on NPY neurons in the arcuate nucleus, which is accessible to peripheral hormones. Peptide YY(3-36) (PYY(3-36)), a Y2R agonist, is released from the gastrointestinal tract postprandially in proportion to the calorie content of a meal. Here we show that peripheral injection of PYY(3-36) in rats inhibits food intake and reduces weight gain. PYY(3-36) also inhibits food intake in mice but not in Y2r-null mice, which suggests that the anorectic effect requires the Y2R. Peripheral administration of PYY(3-36) increases c-Fos immunoreactivity in the arcuate nucleus and decreases hypothalamic Npy messenger RNA. Intra-arcuate injection of PYY(3-36) inhibits food intake. PYY(3-36) also inhibits electrical activity of NPY nerve terminals, thus activating adjacent pro-opiomelanocortin (POMC) neurons. In humans, infusion of normal postprandial concentrations of PYY(3-36) significantly decreases appetite and reduces food intake by 33% over 24 h. Thus, postprandial elevation of PYY(3-36) may act through the arcuate nucleus Y2R to inhibit feeding in a gut-hypothalamic pathway.     

Premature ageing in mice expressing defective mitochondrial DNA polymerase

Point mutations and deletions of mitochondrial DNA (mtDNA) accumulate in a variety of tissues during ageing in humans, monkeys and rodents. These mutations are unevenly distributed and can accumulate clonally in certain cells, causing a mosaic pattern of respiratory chain deficiency in tissues such as heart, skeletal muscle and brain. In terms of the ageing process, their possible causative effects have been intensely debated because of their low abundance and purely correlative connection with ageing. We have now addressed this question experimentally by creating homozygous knock-in mice that express a proof-reading-deficient version of PolgA, the nucleus-encoded catalytic subunit of mtDNA polymerase. Here we show that the knock-in mice develop an mtDNA mutator phenotype with a threefold to fivefold increase in the levels of point mutations, as well as increased amounts of deleted mtDNA. This increase in somatic mtDNA mutations is associated with reduced lifespan and premature onset of ageing-related phenotypes such as weight loss, reduced subcutaneous fat, alopecia (hair loss), kyphosis (curvature of the spine), osteoporosis, anaemia, reduced fertility and heart enlargement. Our results thus provide a causative link between mtDNA mutations and ageing phenotypes in mammals.