Mixed-Alkali Effect in Li2O–Na2O–K2O–B2O3 Glasses: Infrared and Optical Absorption Studies

The mixed-alkali effect (MAE) has been investigated in the glass system (40 ? x)Li₂O–xNa₂O–10K₂O–50B₂O₃ (0 mol% ≤ x ≤ 40 mol%) through density, modulated differential scanning calorimetry (DSC), and optical absorption studies. From the absorption studies, the values of the optical band gap (E _opt) for direct transition and Urbach energy (ΔE) have been evaluated. The values of E _opt and ΔE show nonlinear behavior with the compositional parameter. The density and glass-transition temperature of the present glasses also show nonlinear variation, supporting the existence of MAE. The infrared (IR) spectra of the glasses reveal the presence of three- and four-coordinated boron atoms. The specific vibrations of Li–O, Na–O, and K–O bonds were observed in the present IR study.     

Effect of the lateral substituent on the mesomorphic behavior of side-chain liquid-crystalline polymers containing a Schiff base ester

New polymerizable macromers containing a Schiff base ester linkage have been synthesized. These macromers were used to synthesize side-chain liquid-crystalline polymers (SCLCPs) by radical polymerization. The chemical structures of the macromers and polymers were characterized by spectroscopic techniques (FTIR, ¹H NMR, and ¹³C NMR). The mesomorphic properties of the macromers as well as the polymers were studied by polarized optical microscopy (POM) and differential scanning calorimetry (DSC) and confirmed by powder X-ray diffraction (PXRD). POM and DSC studies revealed that all of the macromers and polymers showed liquid crystal behavior, with their nematic phases occurring in different mesophase ranges. The macromer without a lateral unit in the mesogen (M1) showed a thermal transition at a relatively high temperature (181.4 °C), whereas the macromer with a lateral unit in the mesogen (M2) showed a thermal transition at a relatively low temperature (101.8 °C). The SCLCP from macromer M1 (HPM1) also showed a comparatively high-temperature thermal transition compared to that of the polymer from macromer M2 (HPM2). The thermal properties of the polymers were studied by thermogravimetric analysis (TGA). The polymer from the macromer with a lateral unit in the mesogen (M2) showed higher thermal stability than the polymer from the macromer without a lateral unit (M1).     

Poly(methylmethacrylate)-block-poly(N-hydroxyethylacrylamide) diblock copolymers: direct ATRP synthesis and characterization

Diblock copolymers consisting of methylmethacrylate (MMA) and N-hydroxyethylacrylamide (HEAAm) polymer were successfully synthesized via direct two steps atom transfer radical polymerization (ATRP). At first, poly(methylmethacrylate) (PMMA) macroinitiators were prepared using methyl 4-(bromo-methyl) benzoate initiator and were used for synthesizing PMMA-b-PHEAAm block copolymers. PMMA homopolymers were synthesized in N,N′-dimethylformamide (DMF) using CuBr/2, 2′bipyridine catalyst system at 110 °C temperature in nitrogen atmosphere. Block copolymers were synthesized in mixture of DMF/water (8/2 v/v%) and in pure DMF in the presence of CuBr/1,1,4,7,10,10-hexamethyltriethylenetetramine (HMTETA) catalyst system at 85 and 100 °C, respectively, while argon was used for deoxygenation and inert environment. Purification of block copolymers was conducted through dialysis against deionized water using a dialysis tubing (MWCO 3,500, cellulose membrane). Molecular weights of PMMA polymers (M _n  = 4,400, 6,200 and 8,400 Da) were determined by size exclusion chromatography using tetrahydrofuran (THF) as eluent. The chemical structure and actual copolymer compositions were determined using elemental analysis (EA), attenuated total reflectance infrared (ATR-IR) and proton nuclear magnetic resonance (¹H NMR) spectroscopic analysis. Phase separation of diblock copolymers resulting in two glass transition temperatures as detected by differential scanning calorimeter (DSC) proves their amphiphilic behavior. Thermogravimetric analysis (TGA) also showed that diblock copolymer, with two-step decomposition has higher thermal stability than PMMA.     

A class of proportional-integral sliding mode control with application to active suspension system

The purpose of this paper is to present a new robust strategy in controlling the active suspension system. The strategy utilized the proportional-integral sliding mode control scheme. A quarter-car model is used in the study and the performance of the controller is compared to the linear quadratic regulator and with the existing passive suspension system. A simulation study is performed to prove the effectiveness and robustness of the control approach.     

Performance investigation of flat plate,v-corrugated and finned air collectors

In this study, flat plate, finned and v-corrugated air heaters were investigated both experimentally and theoretically in an effort to improve the performance of conventional air heaters. Collectors were also tested in double pass mode to investigate the extent of improvement in efficiency that could be achieved without increasing the collector size or cost. A series of experiments were conducted, based on the ASHRAE standard, under climatic conditions of Singapore. The performance of all three collectors was examined over a wide range of operating and design conditions. The v-corrugated collector was found to be the most efficient collector and the flat plate collector to be the least efficient. Results showed that the v-corrugated collector is 10–15 and 5–11% more efficient in single pass and double pass modes, respectively, compared to flat plate collectors. The double pass operation of the collector improved the efficiency of all three collectors. The improvement in efficiency for double pass mode was most significant in the flat plate collector and least in the v-groove collectors.     

Development of new magnesium based alloys and their nanocomposites

In the present study, 1 and 2 wt.% of aluminum were successfully incorporated into magnesium based AZ31 alloy to develop new AZ41 and AZ51 alloys using the technique of disintegrated melt deposition. AZ41-Al₂O₃ and AZ51-Al₂O₃ nanocomposites were also successfully synthesized through the simultaneous addition of aluminum (1 and 2 wt.%, respectively) and 1.5 vol.% nano-sized alumina into AZ31 magnesium following same route. Alloy and composite samples were then subsequently hot extruded at 400 °C and characterized. Microstructural characterization studies revealed equiaxed grain structure, reasonably uniform distribution of particulate and intermetallics in the matrix and minimal porosity. Physical properties characterization revealed that addition of both aluminum and nano-sized alumina reduced the coefficient of thermal expansion of monolithic AZ31. The presence of both Al and nano-sized Al₂O₃ particles also assisted in improving overall mechanical properties including microhardness, engineering and specific tensile strengths, ductility and work of fracture. The results suggest that these alloys and nanocomposites have significant potential in diverse engineering applications when compared to magnesium AZ31 alloy.     

Enhanced trace phosphate removal from water by zirconium(IV) loaded fibrous adsorbent

This study was investigated for the trace phosphate removal at high feed flow rate by ligand exchange fibrous adsorbent. The zirconium(IV) loaded bifunctional fibers containing both phosphonate and sulfonate were used as a highly selective ligand exchange adsorbent for trace phosphate removal from water. The precursory fiber of the bifunctional fibers was co-grafted by polymerization of chloromethylstyrene and styrene onto polyethylene coated polypropylene fiber and then bifunctional fibers were prepared by Arbusov reaction followed by phosphorylation and sulfonation. Phosphate adsorption experimental work was carried out in column approach. Phosphate adsorption increased with decreasing the pH of feed solutions. An increase in the feeds flow rate brings a decrease in both breakthrough capacity and total adsorption. The effect of competing anions on phosphate adsorption systems was investigated. The experimental findings reveal that the phosphate adsorption was not affected in the presence of competing anions such as chloride and sulfate despite the enhancement of the breakthrough points and total adsorption. Due to high selectivity to phosphate species, low concentration level of phosphate (0.22 mg/L) was removed at high feed flow rate of 450 h⁻¹ in space velocity. The adsorbed phosphate on the Zr(IV) loaded fibrous column was quantitatively eluted with 0.1 M NaOH solution and then the column was regenerated by 0.5 M H₂SO₄ for the next adsorption operation. During many adsorption-elution-regeneration cycles, no measurable Zr(IV) was found in the column effluents. Therefore, the Zr(IV) loaded bifunctional fibrous adsorbent is to be an effective means to treat wastewater to prevent eutrophication in the receiving water bodies for long time without any deterioration.     

Geotextile bag revetments for large rivers in Bangladesh

Since the late 1990s, riverbank revetments constructed of sand-filled geotextile bags (geotextile bags) have been developed in Bangladesh in response to the lack of traditional erosion-protection materials, particularly rock. After independence in 1971 and the related loss of access to quarries, rock was replaced by concrete cubes, but those are expensive and slow to manufacture. Geotextile bags on the other hand, first used as emergency measures during the second half of the 1990s, can be filled with local sand and therefore provide the opportunity to respond quickly to dynamic river changes.Geotextile bags also provide the potential for substantial cost reduction, due to the use of locally available resources. The use of the abundant local sand reduces transport distance and cost, while local labor is used for filling, transporting, and dumping of the 75-250 kg bags. Driven by the need for longer protection, the idea of using geotextile bags for permanent riverbank protection emerged in 2001. Eight years of experience have enabled systematic placement of geotextile bag protection along about 12 km of major riverbanks at a unit cost of around USD 2 M per km. By comparison, concrete-block revetments cost around USD 5 M per km. In addition, there are strong indications that geotextile bags perform better than concrete blocks as underwater protection, largely due to their inherent filter properties and better launching behavior when the toe of the protected underwater slope is under-scoured.This article reports the outcome of the last eight years of development work under the ADB-supported Jamuna-Meghna River Erosion Mitigation Project (ADB, 2002), implemented by the Bangladesh Water Development Board. Besides substituting geotextile bags for concrete blocks as protective elements, the project involved development of a comprehensive planning system to improve the overall reliability and sustainability of riverbank protection works.     

受压轻型钢-加气混凝土-钢组合墙体的结构性能

由试验结果和分析结果介绍了一种由2层薄壁钢板中夹轻质加气混凝土(LFC)组成的墙体结构在轴向压力作用下的结构性能。试验中的试件尺寸为400mm×400mm×100mm,共制作了2组共12个试件。这些试件有6个不同的参数:不同钢板厚(0.4mm和0.8mm),三种边界条件。LFC的密度为1000kg/m3。试验结果包括破坏模式、最大荷载和沿垂直于力作用方向的应变反应。在分析中,假定钢板与LFC不产生相对滑移,并且LFC能有效阻止钢板的向内屈曲。对钢板运用了屈曲后有效宽度的方法计算试件的承载能力并与试验结果进行了对比。研究发现结合Uy和Bradford的板局部屈曲系数与Liang和Uy的有效宽度方程的计算结果与试验结果能良好地吻合。最后,对这种新型组合墙体在低层建筑中的适用性和局限性作了可行性研究。     

Direct production of D-arabinose from D-xylose by a coupling reaction using D-xylose isomerase, D-tagatose 3-epimerase and D-arabinose isomerase

Klebsiella pneumoniae 40bXX, a mutant strain that constitutively produces D-arabinose isomerase (D-AI), was isolated through a series of repeated subcultures from the parent strain on a mineral salt medium supplemented with L-Xylose as the sole carbon source. D-AI could be efficiently immobilized on chitopearl beads. The optimum temperature for the activity of the immobilized enzyme was 40 degrees C and the enzyme was stable up to 50 degrees C. The D-Al was active at pH 10.0 and was stable in the range of pH 6.0-11.0. The enzyme required manganese ions for maximum activity. Three immobilized enzymes, D-xylose isomerase (D-XI), D-tagatose 3-epimerase (D-TE and D-AI were used for the preparation of D-arabinose from D-xylose in a coupling reaction. After completion of the reaction, degradation of D-xylulose was carried out by Saccharomyces cerevisiae. The reaction mixture containing D-Xylose, D-ribulose and the product was then separated by ion exchange column chromatography. After crystallization, the product was checked by HPLC, IR spectroscopy, NMR spectroscopy and optical rotation measurements. Finally, 2.0 g of D-arabinose could be obtained from 5 g of the substrate.