Mechanical properties of nanocomposites from sorbitol plasticized starch and tunicin whiskers

Nanocomposite materials were obtained using sorbitol plasticized waxy maize starch as matrix and tunicin whiskers as the reinforcement. The effect of filler load (0–25 wt % whiskers) and the relative humidity levels (0–98%) on the mechanical behavior of the films are discussed for linear and nonlinear deformation. The performance of the films is explained, based on the morphology and structural behavior of the composite materials (Mathew and Dufresne, Biomacromolecules 2002, 3, 609). The nanocomposites exhibit good mechanical strength due to the strong interaction between tunicin whiskers, matrix, plasticizer (sorbitol), and water, and due to the ability of the cellulose filler to form a rigid three‐dimensional network. The evolution of T_g as a function of relative humidity level and filler load is studied in detail. A decrease in crystallinity of the amylopectin phase is observed at high filler loads, due to the resistance to chain rearrangement imposed by the whiskers. The mechanical strength increased proportionally with filler loads, showing an effective stress transfer from the matrix to the whiskers. An even distribution of whiskers (as determined by SEM) and plasticizer in the matrix contributes to the mechanical performance. The mechanical properties of the nanocomposites showed a strong dependence on relative humidity conditions. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Thermal creep properties of alloy D9 stainless steel and 316 stainless steel fuel clad tubes

Uniaxial thermal creep rupture properties of 20% cold worked alloy D9 stainless steel (alloy D9 SS) fuel clad tubes for fast breeder reactors have been evaluated at 973 K in the stress range 125–250 MPa. The rupture lives were in the range 90–8100 h. The results are compared with the properties of 20% cold worked type 316 stainless steel (316 SS) clad tubes. Alloy D9 SS were found to have higher creep rupture strengths, lower creep rates and lower rupture ductility than 316 SS. The deformation and damage processes were related through Monkman Grant relationship and modified Monkman Grant relationship. The creep damage tolerance parameter indicates that creep fracture takes place by intergranular cavitation. Precipitation of titanium carbides in the matrix and chromium carbides on the grain boundaries, dislocation substructure and twins were observed in transmission electron microscopic investigations of alloy D9 SS. The improvement in strength is attributed to the precipitation of fine titanium carbides in the matrix which prevents the recovery and recrystallisation of the cold worked microstructure.     

Selection of filler wire for and effect of auto tempering on the mechanical properties of dissimilar metal joint between 403 and 304L(N) stainless steels

Weldability of the dissimilar weld joint between austenitic 304L(N) stainless steel (SS) and martensitic 403 SS made by gas tungsten arc welding process using ERNiCr-3 filler metal has been studied. For this study, 12 mm thick plates of these two materials were joined using a K-type weld groove joint, with the straight edge on the 403 SS side buttered using ERNiCr-3 filler wire. Two types of weld joints were prepared—one using as-buttered 403 SS and the other one with buttered and post-weld heat-treated 403 SS plate. The joint made with the as-buttered 403 SS plate exhibits good bend ductility and toughness on the heat-affected zone (HAZ) of the 403 SS side and it is comparable with that of the buttered and post-weld heat-treated 403SS weld joint properties. Thus, buttering of the 403 SS plate enabled dissimilar welding with the 304L(N) SS plate without any post-weld heat treatment because of auto tempering of the martensite present in the 403 SS HAZ formed due to weld thermal cycle.     

Threshold Voltage Adjustment in Nanoscale DG FinFETs Via Limited Source/Drain Dopants in the Channel

Nanoscale double-gate (DG) FinFETs with undoped fin bodies are shown to have threshold voltages (Vt) that can be adjusted for independent I _ON and I _OFF control by allowing limited source/drain (S/D) dopants in the channel. S/D engineering of the lateral doping profile in the extension is proposed as a viable means for effecting such channel doping [as well as gate-S/D (G-S/D) underlap] and, thus, adjusting Vt for optimal I _ON/I _OFF in low-power and high-performance applications of nanoscale-FinFET CMOS. Physics-based device simulations, numerical simulations, and measured current-voltage characteristics are used to demonstrate and support the proposed Vt design approach.     

Effect of the nature of crosslinking agent on the unusual metal ion specificity and selectivity of N,N‐bis(2‐aminoethyl)polyacrylamide

Metal ion desorbed crosslinked N,N‐bis(2‐aminoethyl)polyacrylamides showed enhanced specificity for the desorbed metal ion, and these polymers selectively rebind the desorbed metal ion from a mixture of metal ions. For this, polyacrylamide with 8 mol % divinylbenzene (DVB) and N,N′‐methylene‐bisacrylamide (NNMBA) crosslinking were prepared by solution polymerization. Diethylenetriamino functions were incorporated into the polymers by polymer analogous reactions. The complexing ability of the amino polymers were investigated toward various transition metal ions like Co(II), Ni(II), Cu(II), and Zn(II). Polymeric ligand and metal complexes were characterized by various spectral methods. The removal of the metal ion from the polymer matrix resulted in a memory for the desorbed metal ion. On rebinding, these polymers specifically rebind the desorbed metal ion and from a mixture of metal ions, it showed selectivity to the desorbed metal ion. Thus, the Cu(II) desorbed polymer specifically and selectively rebind Cu(II) ion from a mixture of Cu(II) and other metal ion. This selectivity is higher in the rigid DVB‐crosslinked system, resulting from the high rigidity of the crosslinked matrix compared to the semirigid NNMBA‐crosslinked system. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Structures of Biological Minerals in Dental Research

Structural features of some calcium phosphates of biological interest are described. Structure of hydroxyapatite (OHAp), considered as the prototype for the inorganic component of bones and teeth is discussed with respect to the kinds and locations of ionic substitutions. Octacalcium phosphate (OCP), is a probable precursor in biological mineralization. OCP has a layer type structure, with one layer quite similar to that of OHAp and the other, a hydrated layer consisting of more widely spaced Ca, and PO₄ ions and the water molecules. The closeness of fit in the apatitic layers of OCP and OHAp accounts for the epitaxial, interlayered mixtures formed by these compounds and the in situ conversion of OCP to OHAp. Possible roles of OCP in biological mineralization are discussed.     

SRAM新架构提高网络应用存储器带宽

在高性能系统中，SRAM（静态随机存取存储器）一直是关键性器件。SRAM广泛用做计算机中的二级（L2）缓存、存储常用变量和数据的高速暂存存储器，以及网络系统中的查找表等。做为关键的系统支持元件，SRAM应该永远能满足系统性能。但不幸的是，情况并非总是这样。部分原因是由于可供选择的SRAM架构很有限。一种专门满足大带宽网络应用需求的突破性SRAM新架构应运而生。