Cu-Zn-Al2O3 nanocomposites:study of microstructure,corrosion,and wear properties

Alumina nanoparticles were added to a Cu-Zn alloy to investigate their effect on the microstructural, tribological, and corrosion properties of the prepared alloys. Alloying was performed using a mixture of copper and zinc powders with 0vol% and 5vol% of α-Al nanopowder in a satellite ball mill. The results showed that the Cu-Zn solid solution formed after 18 h of mechanical alloying. The mechanically alloyed powder was compacted followed by sintering of the obtained green compacts at 750℃ for 30 min. Alumina nanoparticles were uniformly distributed in the matrix of the Cu-Zn alloy. The tribological properties were evaluated by pin-on-disk wear tests, which revealed that, upon the addition of alumina nanoparticles, the coefficient of friction and the wear rate were reduced to 20% and 40%, respectively. The corrosion properties of the samples exposed to a 3.5wt% NaCl solution were studied using the immersion and potentiodynamic polarization methods, which revealed that the addition of alumina nanoparticles reduced the corrosion current of the nanocomposite by 90%.     

Fabrication and densification enhancement of SiC-particulate-reinforced copper matrix composites prepared via the sinter-forging process

The fabrication of copper (Cu) and copper matrix silicon carbide (Cu/SiC_p) particulate composites via the sinter-forging process was investigated. Sintering and sinter-forging processes were performed under an inert Ar atmosphere. The influence of sinter-forging time, temperature, and compressive stress on the relative density and hardness of the prepared samples was systematically investigated and subsequently compared with that of the samples prepared by the conventional sintering process. The relative density and hardness of the composites were enhanced when they were prepared by the sinter-forging process. The relative density values of all Cu/SiC_p composite samples were observed to decrease with the increase in SiC content.     

Fabrication method and microstructural characteristics of coal-tar-pitch-based 2D carbon/carbon composites

The lignin-cellulosic texture of wood was used to produce two-dimensional (2D) carbon/carbon (C/C) composites using coal tar pitch. Ash content tests were conducted to select two samples among the different kinds of woods present in Iran, including walnut, white poplar, cherry, willow, buttonwood, apricots, berry, and blue wood. Walnut and white poplar with ash contents of 1.994wt% and 0.351wt%, respectively, were selected. The behavior of these woods during pyrolysis was investigated by differential thermal analysis (DTA) and thermo gravimetric (TG) analysis. The bulk density and open porosity were measured after carbonization and densification. The microstructural characteristics of samples were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier-transform infrared (FT-IR) spectroscopy. The results indicate that the density of both the walnut and white poplar is increased, and the open porosity is decreased with the increasing number of carbonization cycles. The XRD patterns of the wood charcoal change gradually with increasing pyrolysis temperature, possibly as a result of the ultra-structural changes in the charcoal or the presence of carbonized coal tar pitch in the composite's body.     

Evolution and biology of supernumerary B chromosomes

B chromosomes (Bs) are dispensable components of the genome exhibiting non-Mendelian inheritance and have been widely reported on over several thousand eukaryotes, but still remain an evolutionary mystery ever since their first discovery over a century ago [1]. Recent advances in genome analysis have significantly improved our knowledge on the origin and composition of Bs in the last few years. In contrast to the prevalent view that Bs do not harbor genes, recent analysis revealed that Bs of sequenced species are rich in gene-derived sequences. We summarize the latest findings on supernumerary chromosomes with a special focus on the origin, DNA composition, and the non-Mendelian accumulation mechanism of Bs.     

Warped time lens in temporal imaging for optical real-time data compression

We introduce for the first time the concept of anamorphic temporal imaging and its application to analog data compression in a time lens. Placed in front of a conventional spectrometer, this technique enhances the spectral resolution and the update rate. More importantly, it performs real-time optical data compression to reduce the volume of the generated digital data. Our technique introduces the concept of the warped time lens. We show that a specific class of warped time-to-frequency mapping operations combined with the nonlinear operation inherent in a photo-detector compresses the time-bandwidth product in a temporal imaging system. We employ our newly introduced Stretched Modulation Distribution to design the warp profile. Using this method, the narrow spectral features beyond the spectrometer resolution can be captured and at the same time the output bandwidth and hence the record length is minimized. The reduction in the record length results in higher update rate for the spectrometer without sacrificing the spectral resolution or bandwidth. Our method also benefits from amplitude and phase detection to recover the input complexfield spectrum. By compressing the time-bandwidth product, anamorphictemporal imaging addresses the Big Data problem in such highthroughput instruments.     

The common fragile site FRA16D gene product WWOX: roles in tumor suppression and genomic stability

The fragile WWOX gene, encompassing the chromosomal fragile site FRA16D, is frequently altered in human cancers. While vulnerable to DNA damage itself, recent evidence has shown that the WWOX protein is essential for proper DNA damage response (DDR). Furthermore, the gene product, WWOX, has been associated with multiple protein networks, highlighting its critical functions in normal cell homeostasis. Targeted deletion of Wwox in murine models suggests its in vivo requirement for proper growth, metabolism, and survival. Recent molecular and biochemical analyses of WWOX functions highlighted its role in modulating aerobic glycolysis and genomic stability. Cumulatively, we propose that the gene product of FRA16D, WWOX, is a functionally essential protein that is required for cell homeostasis and that its deletion has important consequences that contribute to the neoplastic process. This review discusses the essential role of WWOX in tumor suppression and genomic stability and how its alteration contributes to cancer transformation.     

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.     

DYNAMICS OF KNOWLEDGE ACCUMULATION IN TECHNOLOGY FOLLOWER COUNTRIES： A SYSTEM DYNAMICS APPROACH

In this paper the process of knowledge accumulation for a particular technology is studied. Two countries, say the technology follower and the technology frontier, are considered. The frontier’s knowledge growth is determined by its R&;D efforts on the technology. The level of knowledge stock for the follower country is augmented by its R&;D activities for the technology and absorbing some of the external knowledge through spillover from the frontier. The extent to which the follower is able to exploit the external knowledge depends on technological gap, absorptive capacity, absorption time and degree of spillover. New concepts such as natural and enhanced degree of spillover, background and innovative knowledge and absorption speed are introduced in the present work to deeply explore the process of knowledge spillover. The factors influencing the knowledge development in the long term are simultaneously studied in an integrated structure provided by the System Dynamics approach. This framework shows the responses to the changes and provides the basis for examining the interactions among the variables over time.     

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....