Encapsulation of air‐filled poly(dimethylsiloxane) microballoons in polyimide as a polymeric low ε dielectric

Air‐filled microballoons of poly(dimethylsiloxane), ie PDMS, have been encapsulated in polyimide. The molecular assembly so formed has shown surface dominance by PDMS while analytical techniques, such as X‐ray photoelectron spectroscopy and infrared spectroscopy, have confirmed a similar distribution in the bulk. The electrical properties of the resultant polymer have been studied and the relative permittivity has been found to be very low while other beneficial attributes of the polyimide have been retained. Copyright © 2004 Society of Chemical Industry     

Nomadic Culture: Cultural Support for Working Anytime, Anywhere

This article argues that a nomadic culture is required to achieve the competitive benefits of a workforce using ubiquitous computing technologies. A nomadic culture is defined as a collection of artifacts, beliefs, and basic assumptions based on a prior published model of organizational culture in general, the term nomadic culture is defined in this article. the authors provide lists of questions for managers to conduct an internal cultural audit.     

PCB成像技术综述

前言 图象转移是PCB生产过程中的关键步骤。随着HDI板和微导通孔板的生产实践以及普通印制板生产技术的提高,传统的接触成像已不能满足高水平的技术要求,而且传统的曝光设备也已经不能满足生产中对照相底版、连接盘、导通孔、定位精确度、图形重合度的要求。基于上述需求,新型的以激光为基础的成像技术以及其他的成像技术已经开始逐步取代传统的接触成像技术。     

Improvement in thermomechanical properties of off‐grade natural magnesite by addition of Y2O3

Small amount of Y₂O₃ (0‐3 wt%) was added into off‐grade natural magnesite and its effects on the phase assemblage, microstructural evolution in correlation with mechanical and thermomechanical properties were investigated. Presence of Y₂O₃ facilitated the formation of calcium yttrium silicate and yttrialite phases, which prohibited the formation of detrimental‐phase monticellite, which was gradually reduced with the increase in Y₂O₃ content. Y₂O₃ promoted periclase grain growth and segregated the secondary phases at triple‐point junction of periclase grains. Also, high‐temperature (at 1200°C) flexural strength of the samples increased from 77.2 MPa (without Y₂O₃) to 137.45 MPa with the addition of 2 wt% Y₂O₃. Greater degree of direct bonding among periclase grains, compact microstructure, and uniform grain size distribution in addition to reduced amount of monticellite were responsible for the improvement in mechanical and thermomechanical properties.     

Hot Deformation Characteristics of 13Cr-4Ni Stainless Steel Using Constitutive Equation and Processing Map

Hot compression tests were performed to study the hot deformation characteristics of 13Cr-4Ni stainless steel. The tests were performed in the strain rate range of 0.001-10 s^?1 and temperature range of 900-1100 °C using Gleeble® 3800 simulator. A constitutive equation of Arrhenius type was established based on the experimental data to calculate the different material constants, and average value of apparent activation energy was found to be 444 kJ/mol. Zener-Hollomon parameter, Z, was estimated in order to characterize the flow stress behavior. Power dissipation and instability maps developed on the basis of dynamic materials model for true strain of 0.5 show optimum hot working conditions corresponding to peak efficiency range of about 28-32%. These lie in the temperature range of 950-1025 °C and corresponding strain rate range of 0.001-0.01 s^?1 and in the temperature range of 1050-1100 °C and corresponding strain rate range of 0.01-0.1 s^?1. The flow characteristics in these conditions show dynamic recrystallization behavior. The microstructures are correlated to the different stability domains indicated in the processing map.     

Synthesis,PASS-Predication and in Vitro Antimicrobial Activity of Benzyl 4-O-benzoyl-α-l-rhamnopyranoside Derivatives

Benzyl α-l-rhamnopyranoside 4, obtained by both conventional and microwave assisted glycosidation techniques, was subjected to 2,3-O-isopropylidene protection to yield compound 5 which on benzoylation and subsequent deprotection of isopropylidene group gave the desired 4-O-benzoylrhamnopyranoside 7 in reasonable yield. Di-O-acetyl derivative of benzoate 7 was prepared to get newer rhamnopyranoside. The structure activity relationship (SAR) of the designed compounds was performed along with the prediction of activity spectra for substances (PASS) training set. Experimental studies based on antimicrobial activities verified the predictions obtained by the PASS software. Protected rhamnopyranosides 5 and 6 exhibited slight distortion from regular ¹C₄ conformation, probably due to the fusion of pyranose and isopropylidene ring. Synthesized rhamnopyranosides 4–8 were employed as test chemicals for in vitro antimicrobial evaluation against eight human pathogenic bacteria and two fungi. Antimicrobial and SAR study showed that the rhamnopyranosides were prone against fungal organisms as compared to that of the bacterial pathogens. Interestingly, PASS prediction of the rhamnopyranoside derivatives 4–8 were 0.49 < P_a < 0.60 (where P_a is probability ‘to be active’) as antibacterial and 0.65 < P_a < 0.73 as antifungal activities, which showed significant agreement with experimental data, suggesting rhamnopyranoside derivatives 4–8 were more active against pathogenic fungi as compared to human pathogenic bacteria thus, there is a more than 50% chance that the rhamnopyranoside derivative structures 4–8 have not been reported with antimicrobial activity, making it a possible valuable lead compound.     

Synergistic Effect of Halloysite Nanotubes and MA-g-PE on Thermo-Mechanical Properties of Polycarbonate-Cyclic Olefin Copolymer Based Nanocomposite

This article explores the synergistic effect of halloysite nanotubes along with maleic anhydride grafted polyethylene on the physical, mechanical, and thermo-mechanical properties of polycarbonate/cyclic olefin copolymer polymer blend system. Halloysite nanotubes filled polycarbonate/cyclic olefin copolymer blend nanocomposites were prepared in the presence and absence of polymeric compatibilizer by melt blending. Besides the constructive outcome of nanotubular fillers, the maleic anhydride grafted polyethylene played a complementary role in improving the properties of the nanocomposites. Structural changes of blend matrix, nanofiller distributions, nanofiller-polymer matrix interaction, nucleating effect, storage modulus, and thermal stability were widely investigated with various sophisticated instruments.     

Studies on Enhancement of Silt Erosion Resistance of 13/4 Martensitic Stainless Steel by Low-Temperature Salt Bath Nitriding

Low-temperature salt bath nitriding of heat treated and tempered 13/4 Martensitic stainless steel (13/4HTT) was carried at 450 °C (N450) and 500 °C (N500) for 10 h each. The nitrided samples were characterized by using x-ray diffractometer, field emission scanning electron microscope and optical microscope. The nanohardness and elastic modulus of the cross section of nitrided specimen were measured by nanoindentation test using Hysitron TI950 triboindenter. The nitrided 13/4HTT (N450 and N500) and 13/4HTT specimens were subjected to slurry erosion test in a slurry pot tester. The test was conducted for 48 h, and weight loss was measured after every 6 h. The relative speed of slurry with respect to specimen was 4.55 m/s. It was found that the weight loss due to erosion of the N450 is 83% less than that of 13/4HTT and that of N500 was 92% more than that of 13/4HTT. The erosion mechanism is correlated to the phases present in the specimens. The improvement in the slurry erosion resistance of N450 is due to presence of expanded martensite (\(\alpha_{N}\)-Fe). Increasing the temperature of nitriding to 500 °C led to the decrease in the slurry erosion resistance of N500 due to the formation of brittle CrN phase.     

Leaf-Like-Dendritic Cesium Nitrate:Poly (Ethylene Oxide) Composite Films and Their Thermal and Ferroelectric Properties

Leaf-like-dendritic structures of cesium nitrate: poly (ethylene oxide) (CsNO₃:PEO) composite films have been fabricated by a simple solvent-cast method. The field emission scanning electron microscopy image analysis revealed that the dendritic structures were composed of multilevel generations with a long main trunk and many well-aligned side branches. The diameters of the trunks, branches, and sub-branches were controlled with variation of wt.% of CsNO₃ in the composition. The curly PEO chains conceivably play a key role in growth of leaf-like-dendritic structures. The crystallite size in the composite films was found to be large as compared to pure CsNO₃ film, and maximum for 40–60 wt.% CsNO₃ in composite films. The ferroelectric phase transition peak was observed in the differential scanning calorimetry scan. The optimization of the ferroelectric properties of the composite films as a function of composition gave 50 wt.% to be the optimum value.