The mat2,3-region of Schizosaccharomyces pombe is flanked by two inverted repeat elements, IRL and IRR, which define the boundaries of the silent domain resulting from heterochromatin assembly in the region. We employed a genetic screen to isolate factors whose mutations allowed spreading of heterochromatin across boundary elements. Surprisingly, this screen revealed that mutations in the genes required for deoxyribonucleotide biosynthesis, cdc22 (encoding the large subunit of ribonucleotide reductase) and tds1 (putative thymidylate synthase), cause silencing of marker genes inserted outside of the silent domain. Chromatin-immunoprecipitation analysis showed that histone H3 lysine 9 methylation modification, an epigenetic mark associated with gene silencing, is enriched by two- to three-fold in the cdc22 mutant as compared to the level found in the wild-type strain in regions outside the silent domain. The spreading of heterochromatin across barriers required functional Atf1/Pcr1, ATF-CREB family proteins, but not the RNA-interference Dcr1, Ago1, or Rdp1 factors, previously implicated in silencing. These results implicate the deoxyribonucleotide biosynthesis pathway in limiting epigenetic controls at barrier elements at the mating-type region, but the mechanism remains unknown. 相似文献
Catalysis Letters - Due to high surface area and low swelling property, Montmorillonite–K10 (MMT–K10) has been gaining widespread applications in heterogeneous catalysis as a material... 相似文献
Bioceramics have been widely utilized for orthopaedic applications in which the biocompatibility and mechanical properties of the materials are vital characteristics to be considered for their clinical use. Till date, extensive studies have been devoted to developing a range of scientific ways for tailoring the microstructure of bioceramics in order to attain the trade-off of mechanical properties and biocompatibility of the final product. Owing to low reactivity, earlier stabilization and longer functional life of bioceramic, the developed implants are capable of replicating the mechanical behaviour of original bone. As the safety of the patient and its ultimate functionality are the ultimate goal of the selected implant material hence, the present literature survey investigates and brings forth the important aspects associated to the mechanical, biological and microstructural characteristics of bioceramics employed in orthopaedic applications. The review paper majorly focuses on effective utilization of various materials as an additive in bioceramics and processing techniques used for enhancement of properties, enabling the use of material in orthopaedic applications. The influence of various additives on the microstructure, mechanical properties and biological performance of developed bioceramics orthopaedic implants has been elaborately discussed. Furthermore, future prospects are proposed to promote further innovations in bioceramics research. 相似文献
Making a relation between strains and stresses is an important subject in the rock engineering field. Shear behaviors of rock fractures have been extensively investigated by different researchers. Literature mostly consists of constitutive models in the form of empirical functions that represent experimental data using mathematical regression techniques. As an alternative, this study aims to present a new integrated intelligent computing paradigm to form a constitutive model applicable to rock fractures. To this end, an RBFNN-GWO model is presented, which integrates the radial basis function neural network (RBFNN) with grey wolf optimization (GWO). In the proposed model, the hyperparameters and weights of RBFNN were tuned using the GWO algorithm. The efficiency of the designed RBFNN-GWO was examined comparing it with the RBFNN-GA model (a combination of RBFNN and the Genetic Algorithm). The proposed models were trained based on the results of a systematic set of 84 direct shear tests gathered from the literature. The finding of the current study demonstrated the efficiency of both the RBFNN-GA and RBFNN-GWO models in predicting the dilation angle, peak shear displacement, and stress as the rock fracture properties. Among the two models proposed in this study, the statistical results revealed the superiority of RBFNN-GWO over RBFNN-GA in terms of prediction accuracy.
This paper reports the development of an artificial neural network based virtual linearizer for correcting nonlinearity associated with transducers connected to the data-acquisition system of a computer-based measurement system. In analog processing techniques, nonlinearity is considered to be a very serious problem that at one time was solved frequently by the piecewise linear segment approach modeled by linear electronic circuits. Since the cost of microcomputers has been reduced drastically, they are currently used in most applications of measurement, including data-acquisition subsystems. Therefore, the hardware-based analog techniques of linearization are often replaced by the software-based numerical ones. In this context, it has been found that a multilayer feed-forward back-propagation network trained with the Levenberg-Marquardt learning rule provides an optimal solution to implement an efficient soft compensator to correct transducer static-nonlinearity. 相似文献
This research work aims to investigate the inter-correlation between microstructure, thermal (thermal conductivity, thermo-gravimetric analysis), thermo-mechanical (dynamic mechanical analysis) and fracture characteristics of hybrid AA2024-SiC alloy composites fabricated via semi-automatic stir-casting process, as per standard industrial practice. Silicon Carbide (SiC) particulates of varying amount (0–6 wt%; @ step of 2%) were used to reinforce master batch of AA2024 wrought alloy, Silicon Nitride (Si3N4) and graphite particulates. The thermal conductivity and storage-modulus magnitudes of alloy composites have shown diminishing trend with hard SiC reinforcing phase, while material stability, viscous modulus, damping factor and fracture toughness have shown significant improvement. Uniform dispersion and better interfacial adhesion between matrix–reinforcement were observed from metallographic examination. The XRD analysis identified the different phases of the hybrid alloy composites. The trends in variations of physical, mechanical and tribological properties were supported by microstructure analysis, thermal analysis, thermo-mechanical analysis and fracture analysis. 相似文献