Origin of crystallization-induced refractive index changes in photo-thermo-refractive glass

Photo-thermo-refractive (PTR) glass is a multi-component silicate that undergoes localized refractive index decrease after UV-exposure and thermal treatment for partial crystallization. Based on this refractive index change, high efficiency volume Bragg gratings have been developed in PTR glass and have been successfully used for laser beam control. However, despite the fact that this type of glass has been widely studied and used over the last 20 years, the origin of the refractive index change upon crystallization is poorly understood. In this paper, we introduce three possible mechanisms (the precipitation of nano-sized NaF crystals and the associated local chemical changes of the glass matrix, the volumetric changes due to relaxation, and the local residual stresses) for the refractive index decrement in PTR glass and estimate the partial refractive index change due to each mechanism. Refractive index measurements are compared with high temperature XRD experiments and a general approach for the simulation of the refractive index change in PTR glass is proposed. We show that among the studied variables the residual stresses surrounding the crystals are the main responsible for the local refractive index decrement in this glass.     

The degradation of novolak containing metal nitrates and the formation of YBCO

Polymers that form a complex with metal ions from nitrate salts can be used to prepare precursors for the production of high temperature superconductor (HTSC) ceramics that can be processed using advantageous polymer processing techniques and then pyrolyzed. This paper describes the production of HTSC from a precursor based on m-cresol formaldehyde novolak resin (mCFNR) that contains yttrium, barium and copper nitrate salts in the proportions needed for the formation of YBa₂Cu₃O_7−x (YBCO). The degradation of the precursor and the effects of the pyrolysis process (temperature, time, environment, substrate) were studied in detail. The mechanisms of degradation for mCFNR and for the HTSC precursors were significantly different with the precursor degradation beginning at significantly lower temperatures. The optimal pyrolysis begins in an inert atmosphere to hinder BaCO₃ formation and then continues in oxygen to 950 °C. A dense orthorhombic YBCO film with preferential [001] orientation results from topotaxial growth on SrTiO₃.     

CARBON ADSORBENTS FROM SHALE PHENOLS

ABSTRACT

The article describes the preparation of adsorbents from shale phenols, their properties and applications. Highly effective microporous adsorbents have been produced, with high sorption indices. New adsorbents can be useful for the purposed of air purification, maintaining the required temperatures in food storage facilities, as well as treating gaseous and liquid wastes from nuclear plant     

ITO-free flexible organic solar cells with printed current collecting grids

The presence of a transparent conductive electrode such as indium tin oxide (ITO) limits the reliability and cost price of organic photovoltaic devices as it is brittle and expensive. Moreover, the relative high sheet resistance of an ITO electrode on flexible substrates limits the maximum width of a single cell. We have developed an alternative ITO-free transparent anode, based on solution processed high conductive PEDOT:PSS in combination with a printed current collecting grid. The screen printed silver grid demonstrates a typical sheet resistance of 1 Ω/□ with 6.4-8% surface coverage. The efficiency of a flexible device with an active area of 4 cm² with such a grid is much higher than a similar device based on ITO. Furthermore, as this composite anode is solution-processed, it is a step forward towards low-cost large area processing.     

Martensitic Transformations and Mechanical and Corrosion Properties of Fe-Mn-Si Alloys for Biodegradable Medical Implants

Metallurgical and Materials Transactions A - The Fe-Mn-Si alloys are promising materials for biodegradable metallic implants for temporary healing process in the human body. In this study, three...     

The “space of physics journals”: topological structure and the Journal Impact Factor

An empirical distribution function of citations to journal articles (EDF for short) can become fundamental tool for analyzing the scientific journals. Endeavors at making bibliometric analysis independent of the intuition conveyed by average citation levels have led us to the study of qualitative properties of physics journals in the functional space of EDFs. We show that the structure of this space establishes the connections and relationships that determine the essential features of physics journals. The research provides an analysis of 240 physics journals indexed in Journal Citation Reports 2015. The relevance of EDFs clustering is discussed. Our findings reveal four-cluster space of physics journals. The space brings to light the essential distinctions between physics journals and shows different level of influence of scientific publishers belonging to different types (professional physics societies, transnational and local publishers). The study of EDFs grouped by publishers reveals two binary oppositions that structure relations between them: “global–local” publishers and “high cited–low cited” publishers.     

Selection of the composition of roller-compacted concretes

Translated from Gidrotekhnicheskoe Stroitel'stvo, No. 1, pp. 18–21, January, 1990.     

纳米流体驱提高原油采收率的三维孔隙尺度模拟

基于不同渗透率岩心的三维微观模型,采用流体体积法对纳米流体驱油进行数值模拟;利用实验测得的含SiO2纳米颗粒的悬浮液界面张力、接触角和黏度,针对质量分数为0～1％、具有不同粒径的SiO2纳米颗粒的水基悬浮液,研究了纳米颗粒质量分数和粒径、驱替液流速、原油黏度和岩心渗透率对纳米流体驱油效率的影响.研究表明:采收率随着颗粒...     

DNA nanotechnology for nucleic acid analysis: DX motif-based sensor

A light on the tiles: A sensor that fluoresces in the presence of specific nucleic acids was designed and characterized. The sensor uses a molecular beacon probe and three adaptor strands to form a five-stranded assembly, a DX-tile, with a specific analyte. This sensor is a highly selective and affordable tool for the real-time analysis of DNA and RNA.