Tensile properties of natural fabric Hildegardia populifolia/polycarbonate toughened epoxy composites

The environmentally friendly composites of natural fabric Hildegardia populifolia/polycarbonate toughened epoxy were prepared. The effect of fabric content and the orientation of the fibers in the fabric on the tensile properties of the composites was studied. The effect of alkali treatment of the fabric and a silane coupling agent on the tensile properties was also studied. The tensile properties improved with alkali treated fabric content when a coupling agent was used. Polym. Compos. 25:563–568, 2004. © 2004 Society of Plastics Engineers.     

Grafting of polymeric side chains to gelatin

Kinetics of grafting of poly(butyl acrylate) onto gelatin was studied with H₂O₂—ascorbic acid redox systm. Percent grafting, grafting efficiency, R_g, and R_h were determined as a function of time, temperature, initiator, monomer, and backbone concentration. It was found that R_g depends on first power of monomer concentration and 0.5 power to the initiator concentrations. A detailed kinetic scheme is proposed to explain these results.     

Enhancement of test data compression with multistage encoding

In this paper, we present two multistage compression techniques to reduce the test data volume in scan test applications. We have proposed two encoding schemes namely alternating frequency-directed equal-run-length (AFDER) coding and run-length based Huffman coding (RLHC). These encoding schemes together with the nine-coded compression technique enhance the test data compression ratio. In the first stage, the pre-generated test cubes with unspecified bits are encoded using the nine-coded compression scheme. Later, the proposed encoding schemes exploit the properties of compressed data to enhance the test data compression. This multistage compression is effective especially when the percentage of do not cares in a test set is very high. We also present the simple decoder architecture to decode the original data. The experimental results obtained from ISCAS'89 benchmark circuits confirm the average compression ratio of 74.2% and 77.5% with the proposed 9C-AFDER and 9C-RLHC schemes respectively.     

正交频分复用水声通信子载波干扰抑制

在引入正交频分复用调制技术的水声通信中,发送端与接收端采样频率偏差及多普勒频移会引起子载波间的干扰,为了抑制信号产生幅度衰落和相位畸变并降低系统误码率,根据多载波水声通信的特点提出了一种抑制载波间干扰的方法.利用导频序列拟合出采样频偏,通过重采样滤波器进行补偿,对多普勒因子粗补后,利用各象限解调数据方差的极小值确定解调数据长度,通过高分辨率傅里叶变换实现多普勒干扰抑制.3次实验结果证明该方法有效可行,能够较好地抑制子载波干扰,可显著提高多载波水声通信的系统性能.     

Structure–property relationship of blocked diisocyanates: synthesis of polyimides using imidazole‐blocked isocyanates

Imidazole, 2‐methylimidazole and benzimidazole‐blocked aromatic and aliphatic diisocyanates have been prepared and polymerized with pyromellitic dianhydride in the presence of a basic catalyst. The polymers are characterized with FTIR, ¹H NMR and ¹³C NMR spectroscopy and GPC, DSC and TGA. The structure–property relationship of blocked diisocyanates are discussed in terms of molecular weight of the polyimides obtained. Considering the blocking agent, GPC results show that the benzimidazole blocked adduct yields higher molecular weight polymer than the 2‐methylimidazole‐blocked adduct which, in turn, yields higher molecular weight polymer than the imidazole‐blocked adduct. Considering the structure of the isocyanate, the molecular weight of polymer increases from isophorone diisocyanate to hexamethylene diisocyanate and to toluene diisocyanate (TDI). DSC traces of the polymers derived from TDI show glass transitions (T_g) in the temperature range 152–180 °C and the values increase from the polymer based on imidazole‐blocked TDI to 2‐methylimidazole‐blocked TDI and to benzimidazole‐blocked TDI. © 2000 Society of Chemical Industry     

Practical aspects of polymerization of D,L-Lactide initiated with tetraphenyltin

Melt polymerization conditions for D ,L -Lactide initiated with tetraphenyltin were studied with regard to polymer molecular weight. The combined effect of time and temperature on polymer molecular weight and degree of conversion of D ,L -Lactide is described. Polymerization at constant initiator concentrations resulted in a narrow scattering of reproducible molecular weight values. The presence of air/moisture and other impurities during the melt polymerization most likely have a deterimental effect on molecular weight. After a short induction period the rather slow polymerization of D ,L -Lactide resulted in a maximal molecular weight followed by an almost constant value of molecular weight. © 1995 John Wiley & Sons, Inc.     

Chain-extended polyurethanes—Synthesis and characterization

Thermoset polyurethane (PU) elastomers were prepared using hydroxyl-terminated polybutadiene (HTPB), toluene diisocyanate (TDI) and hexamethylene diisocyanate (HMDI). The effects of various diamines and diols on the mechanical and thermal properties of polyurethanes are discussed. The average molecular weight between crosslinks (M?/_c) was determined by swelling studies. The properties imparted by the extenders are explained on the basis of the groups present in the diamines and the number of methylene carbons in the diols.     

Investigation of Raman Modes and Born‐Effective Charges in AgNb1/2Ta1/2O3: A Density‐Functional and Raman Scattering Study

Using ab initio density‐functional theory, the Born‐effective charge tensors and zone‐center phonon mode frequencies are computed for AgNb_1/2Ta_1/2O₃ in monoclinic P2/m and orthorombic Pbcm symmetries. The experimental mode frequencies are obtained from deconvolution of Raman spectrum of prepared AgNb_1/2Ta_1/2O₃ samples and are compared with computed mode frequencies. The Raman modes with high (>350 cm^?1) and low frequencies (<90 cm^?1) correspond to Ag and O vibrations, respectively. The modes in intermediate frequency band (120–350 cm^?1) are dominated by Nb(Ta)–O vibrations. The computed effective charge tensors of cations at A (Ag) and B (Nb, Ta) sites are found to be diagonal. The off‐diagonal components of charge tensor are found sizeable only for O ions in orthorhombic AgNb_1/2Ta_1/2O₃ with Pbcm symmetry. Further, charge tensor structure of O ions is found to depend on site symmetry in the unit cell. Charge tensor components for Nb, Ta, and O ions differ significantly from their nominal ionic values suggesting (1) large local dipole moments induced by off‐centering of Nb(Ta) ions and tilting(rotations) of Nb(Ta)O₆ octahedra, (2) hybridization between d‐orbitals of Nb(Ta) and p‐orbitals of O atoms. Furthermore, the electronic structure, directional dependence of effective charges and performance of LDA (GGA) exchange‐correlation functionals with regard to computed values are also discussed.     

Studies on Ethylene Propylene Diene Rubber and Thermoplastic Polyurethane Blends: The Effect of Maleation

Blends of maleated ethylene propylene diene rubber (EPDM) and thermoplastic polyurethane (TPU) have been studied to understand the effect of the maleation level of EPDM on the compatibility and morphology of the blends. Blends with different maleation levels on EPDM (0.25, 0.50, and 0.75 wt%) were compared for mechanical, thermal, and other properties. The appearance of single T _g for 0.5% and 0.75% confirms that a maleation level of more than 0.5 wt% is required for EPDM blends with TPU. However, best mechanical properties are obtained for 0.5% maleated EPDM and TPU blends. Aging, filler reinforcement, and weather resistance measurements were also studied for the blends of varying maleation levels.