Solvent‐Mediated Plasmon Tuning in a Gold‐Nanoparticle–Poly(Ionic Liquid) Composite

The design, synthesis, and characterization of a hierarchically ordered composite whose structure and optical properties can be reversibly switched by adjustment of solvent conditions are described. Solvent‐induced swelling and de‐swelling is shown to provide control over the internal packing arrangement and hence, optical properties of in situ synthesized metal nanoparticles. Specifically, a gold‐nanoparticle‐containing ionic‐liquid‐derived polymer is synthesized in a single step by UV irradiation of a metal‐ion‐precursor‐doped, self‐assembled ionic liquid gel, 1‐decyl‐3‐vinylimidazolium chloride. Small‐angle X‐ray scattering (SAXS) studies indicate that in the de‐swollen state, the freestanding polymer adopts a perforated lamellar structure. Optical spectroscopy of the dried composite reveals plasmon resonances positioned in the near‐IR. Strong particle–particle interactions arise from matrix‐promoted formation of aggregated 1D clusters or chains of gold nanoparticles. Upon swelling in alcohol, the composite undergoes a structural conversion to a disordered structure, which is accompanied by a color change from purple to pale pink and a shift in the surface plasmon resonance to 527 nm, consistent with isolated, non‐interacting particles. These results demonstrate the far‐field tuning of the plasmonic spectrum of gold nanoparticles by solvent‐mediated changes in its encapsulating matrix, offering a straightforward, low‐cost strategy for the fabrication of nanophotonic materials.     

Impedance studies of polycrystalline tin oxide

Polycrystalline SnO₂ samples prepared in the laboratory were irradiated with 2 MeV He ions having doses of 3.62 × 10¹⁵ ion/cm². The ac small-signal electrical data acquired for the polycrystalline SnO₂ in the frequency (f) range 100 Hz ≤ f ≤ 1 MHz and temperature (T) range 26°C ≤ T ≤ 100°C revealed one semicircular relaxation in the impedance plane for the He implanted sample. However, two semicircular relaxations were obtained in the same plane for the samples without He implantation. The He implantation indicated enhancement in the donor density in the polycrystalline SnO₂ as depicted via terminal conductance (or resistance). An erratum to this article can be found at     

A study of austenitization of SG iron

Austenitization process of three SG irons with varying compositions and as cast matrix microstructure has been studied at three austenitization temperatures of 850, 900 and 950C for different time periods. Microstructure, hardness and X-ray diffraction have been used to reveal the nature of dependence of the process on austenitization temperature, time and as cast structure. The optimum austenitization time is maximum for ferritic and minimum for pearlitic matrix.     

Adiabatic shear banding in a thick-walled steel tube

We analyze the initiation and propagation of adiabatic shear bands in a thick-walled 4340 steel tube with a V-notch in the middle. The material is modeled as strain hardening, strain-rate hardening and thermal softening. The deformations are assumed to be locally adiabatic and the effect of inertia forces is considered. Two different loadings, i.e., torsional, and combined torsional and axial pressure are considered. In each case, the load generally increases linearly from zero to the final value, is kept steady there for some time, then decreases to zero and is kept at zero; thus a finite amount of energy is input into the body. For the combined loading, the magnitude of the torsional loading pulse is kept fixed and the effect of varying the magnitude of the axial pressure preload is investigated. A shear band first initiates in the element adjoining the notch tip and propagates radially inwards. By recording the time when a shear band initiates at the centroids of different elements we determine its speed of propagation in the radial direction to vary from approximately 50 m/s at the instant of its initiation in an element abutting the notch tip, to nearly 90 m/s by the time it reaches the innermost surface of the tube; the speed also depends upon the overall loading rate, and whether or not the loading is multiaxial. The drop in the torque required to twist the tube at the initiation of a shear band is not as sharp as that in a thin-walled steel tube. We compute the distance through which a shear band propagates as a function of the energy input into the body and thus ascertain the energy required to drive a shear band through a unit distance. We also study torsional deformations of a thick-walled CR-300 steel tube, model its thermal softening by a relation proposed by Zhou et al. and use material properties derived from their data. In this case, the speed of a shear band initiating from an element abutting the notch tip is found to vary between 750 m/s and 1,000 m/s at different points on a radial line through the notch tip; this agrees with that observed by Zhou et al. in their experiments on single-notched plates.     

Growth and electrical characterization of the lead magnesium niobate-lead titanate (PMN-PT) single crystals for piezoelectric devices

The lead magnesium niobate-lead titanate is one of the new generations of piezoelectric materials with outstanding properties. Single crystals of 0.67Pb(Mg_1/3Nb_2/3)O₃-0.33PbTiO₃ (PMN-PT) show superior properties as compared to piezoelectric ceramics and piezoelectric films in device applications. Large size crystals are required for specific applications. Previously, transparent and high quality PMN-PT single crystals have been grown in our laboratory using the high temperature flux method. The size of the obtained crystals was small and varied from 2 to 8 mm³, mostly showing regular prismatic shape. In present attempt, PMN-PT crystals are grown from the vertical gradient freeze method with no flux using congruent melt. Processing conditions and growth parameters have been optimized to increase the size and yield of the perovskite crystals including cooling rate, soak time and soak temperature. The size of the grown crystals obtained by this method is very large relatively and varied from 5 to 30 mm³. The microstructure of the as grown single crystals is investigated by scanning electron microscopy. Piezoelectric properties of the grown crystals are also investigated. PMN-PT plates show excellent piezoelectric properties. Samples were poled under an applied electric field of 5 kV/cm. Dielectric properties at a frequency of 1 kHz are examined. Finally, the variation of pyroelectric coefficient with temperature is studied. The grown PMN-PT crystals show typical relaxor dielectric properties.     

Frequency response of thin film heads with longitudinal andtransverse anisotropy

A transmission surface model (TSM) that analyzes the conduction of flux by rotation and wall motion is reported. It has been used to quantitatively compare the predicted performance of thin-film heads with longitudinal and transverse magnetic anisotropy. The TSM analysis predicts that a transversely oriented type of thin-film head can be operated at much higher frequencies than a longitudinally oriented head. In addition, its group delay dispersion is much less. Finally, its susceptibility to wall pinning is an order of magnitude less. Therefore, it is concluded that the traditional aversion of head designers to the longitudinal orientation is justified for frequencies above several megahertz     

Class I alleles of the bovine major histocompatibility system and their association with economic traits

A total of 179 Holstein cows from the Agriculture Canada Research Branch herd at Ottawa and 271 progeny-tested Canadian Holstein bulls were typed for 37 lymphocyte antigens. Each antigen appears to be controlled by a distinct, codominant allele of the bovine lymphocyte antigen (BoLA)-A locus, which is a class I locus of the bovine major histocompatibility system. Only 10 and 16 alleles were present in Holstein cows and bulls, respectively. The association between bovine lymphocyte antigens and economically important traits was examined in gene substitution models. Separate models were used for the cow and bull data. The substitution of the W6.1 allele for the W10 allele was associated with increased protein yield in the milk in both analyses. The results were also consistent with a previous report that the presence of the W10 allele was associated with increased fat percentage compared with some, but not all, of the other alleles. However, more research is necessary to confirm these findings and to determine the biological mechanisms underlying these associations.