The effect of grain size and strain rate on the

The substructural developments taking place in nickel 200 with grain diameters of 47, 108, 141, and 274 μm have been studied at four different strain rates of 0.01, 0.25, 2.5, and 5/min during tensile testing at room temperature. The percent strain necessary to develop well-defined cell boundaries increases with an increase in grain size at a given strain rate. The cell size refinement takes place throughout the entire range of percent strains (up to 30 pct) in tension for the nickel samples with grain diameters of 47, 108, and 141 μm at all four strain rates used in this article. However, nickel, with the largest grain diameter of 274 μm, shows refinement and then sat- uration for tensile strains greater than 25 pct. The cell size strengthening described by the mod- ified Hall-Petch (MHP) equation at the selected four strain rates of this article indicates that the flow stress is higher for smaller grain size samples at a given cell size. The effect of strain rate on the slope from the MHP plots is such that even though it does not change with an increase in strain rate up to 0.25/min for the four grain sizes, the actual value of the slope decreases with an increase in grain size at a given strain rate. Beyond this strain rate, even though an increase in the slope value as a function of strain rate has been observed for all four grain diameter samples, the influence of grain size on the slope of the MHP plots is so small that it can be assumed that they may become grain size independent at extremely high strain rates. JYOTHI G. RAO, formerly Graduate Student, JYOTHI G. RAO, formerly Graduate Student, JYOTHI G. RAO, formerly Graduate Student,     

Microstructural and electrical characteristics of rapidly annealed Ni/Mo Schottky rectifiers on cleaned n-type GaN (0001) surface

We have investigated the electrical and microstructural properties of Ni/Mo Schottky rectifiers to n-type GaN by current–voltage (I–V) and transmission electron microscopy (TEM) before and after annealing at 600 °C. The obtained barrier height for as-deposited Ni/Mo contact is 0.66 eV. It is observed that the barrier height increases with annealing temperature up to 500 °C, reaching a maximum value of 0.75 eV at this temperature. However, the Schottky barrier height of the Ni/Mo Schottky contact slightly decreased to 0.67 eV (I–V) when the contact was annealed at 600 °C. According to the HRTEM, STEM and EDX analysis, the formation of Ga-Ni interfacial layer at the interface results in the accumulation of gallium vacancies near the surface of the GaN layer. This could be the reason for increase in barrier heights upon annealing at elevated temperatures. The variation in the measured barrier height after annealing at 600 °C may be due to the formation of native oxide layer at the interface compared to the 500 °C annealed contact.     

Partially coherent phonon transport in two-dimensionally rough nanowires

Rough surface nanowires exhibit a severely reduced thermal conductivity compared to the bulk. Their thermal conductivities are much below the value predicted from the diffuse scattering model. Such low thermal conductivities are particularly promising for thermoelectric applications. We extend our previous work on understanding this phenomenon using a model of partially coherent phonon transport. Considering both azimuthal and longitudinal roughness, we show that it is the latter that dominates thermal conductivity reduction. Our work advanced fundamental phonon boundary scattering that is key in applications ranging from semiconductor devices to thermoelectric materials.     

Modeling of CMS-based nonuniform interconnects using FDTD technique

This paper presents the finite-difference time-domain model of nonuniform interconnects including skin effect losses based on the current mode signaling (CMS). For accurate analysis, the nonlinear CMOS inverter is used as a driver for coupled nonuniform interconnects. These effects are incorporated in the proposed model using the modified alpha power law model. Additionally, high-frequency losses are incorporated in the proposed model that further improves the accuracy. Using the proposed model, the performance of nonuniform interconnects is investigated using the CMS scheme. Time-domain analysis model is derived from CMS nonuniform interconnects using finite-difference time-domain technique. Both inductive and capacitive couplings have been considered to incorporate coupling effects in interconnects. The efficiency of CMS interconnects is evaluated by comparing with conventional voltage mode signaling interconnects. The propagation delays and dynamic and functional cross talk effects at the far end of the coupled nonuniform interconnect are analyzed at the 32-nm technology node. The proposed model results are validated using the standard HSPICE simulations.     

Optical,structural and morphological studies of nanostructures fabricated on silicon surface by femtosecond laser irradiation

Journal of Materials Science - We report here a detailed analysis of the ultrashort laser pulse irradiation effects on a single crystalline silicon surface. A systematic study has been performed to...     

Fragmentation of Cast Iron Blocks by a Confined Explosive Charge: A new performance evaluation test for commercial explosives

This paper describes a new method to assess the performance of small diameter explosives under laboratory conditions. While conventional strength tests often do not correctly reflect the performance characteristics of such explosives, model tests using rocks are not convenient due to constraints imposed by the size of the test block. Cast iron being a brittle material, fractures like rock and also its mechanical properties make it a suitable material for simulating rock under laboratory conditions. Tests have been carried out with different explosives in a cylindrical block of cast iron having a 27-mm diameter central hole of a certain depth. Mean fragment size (X50) has been used as the criterion to rank different explosives with respect to their strength. Using fracture surface energy of cast iron and detonation properties of the explosives tested, the maximum fragment size could be predicted on the basis of an energy balance model. The predicted maximum fragment sizes are in fair agreement with the experimentally obtained ones. While the limitations of the proposed test are pointed out, it appears that cast iron block fragmentation could serve as an useful technique for evaluating the strength of commercial explosives.     

Achiral Dihydroxylation of Olefins by Osmate (OsO42−) Stabilised on Nanocrystalline Magnesium Oxide

A recoverable and reusable new heterogeneous AP‐Mg‐OsO₄ catalyst was designed and developed for the first time via a counterionic stabilisation of OsO₄²⁻ with Mg²⁺ present on the corner or edge of nanocrystalline MgO. AP‐Mg‐OsO₄ catalysed the dihydroxylation of olefins to afford diols with excellent yields in the presence of N‐methylmorpholine N‐oxide for the first time. The absence of osmium and no progress of the dihydroxylation reaction with the filtrate samples withdrawn periodically during the reaction rule out the leaching of osmium unambiguously and provide evidence for the heterogeneity of the reaction. Identification of surface intermediate species by XPS and TGA‐DTA‐mass thermography gives an insight into the mechanism of the dihydroxylation reaction.     

Effect of pre-soaking treatments on the nutritional profile and browning index of sweet potato and yam flours

The use of sweet potato and yams for product development is hindered by the discoloration from enzymatic and non-enzymatic browning. The effect of pre-soaking treatments on the nutritional changes and browning index (BI) of sweet potato and yam (greater yam and white yam) flours was investigated. Ascorbic acid (AsA), citric acid (CA), acetic acid (AA) and sodium metabisulfite (SMS) were used for soaking at three concentrations (0.25%, 0.50% and 1.00%) and two durations (1 h and 2 h). AsA and SMS removed more starch during soaking of sweet potato, while CA and AA removed more starch from greater yam and CA removed more starch from white yam. Highest removal of reducing sugars was observed in sweet potato in AA, while CA removed maximum reducing sugars from both the yams. Phenol and total free amino acid (TFA) levels were more in SMS treatment than the control sweet potato flour, and least in AA (2 h). Whilst AsA raised the phenols and TFA in greater yam, it removed phenols to the maximum in white yam. Maximum BI was in AsA treatment for the three crops, and least for flour from CA (0.25%) treated yams and AA (1.00%) treated sweet potato.Industrial RelevanceBrowning resulting from enzymatic and non-enzymatic reactions is a major drawback in the processing of sweet potato and yams for product development. The study showed that this could be successfully tackled through soaking the slices in low cost chemicals like acetic acid or citric acid and sodium metabisulfite at low concentrations. The treated slices yielded flour with very low browning indices compared to the respective native flours, which could enhance the potential of such flours in the development of food products.     

Response Surface Methodology for the Optimization and Characterization of Cassava Starch‐graft‐Poly(acrylamide)

Response surface methodology (RSM) was employed for the synthesis of cassava starch‐graft‐poly(acrylamide) using ceric ammonium nitrate as free radical initiator. Concentration of acrylamide, concentration of ceric ammonium nitrate, reaction temperature and duration of reaction were optimized using a 4‐factor 3‐level Box‐Behnken design. The dependent variables were percentage grafting (%G) and grafting efficiency (GE). Second order polynomial relationships were obtained for %G and GE, which explained the main, quadratic and interaction effects of factors. The highest%G and GE obtained were 174.8% and 90.7%, respectively. The optimum values of parameters predicted through RSM were 20 g acrylamide/10 g dry starch, 3.3 g/L ceric ammonium nitrate, 180 min reaction duration and 45ºC temperature with a %G of 190.0. For GE, the predicted levels of factors for the optimum value of 90.8% were 17.5 g acrylamide/10 g dry starch, 4.1 g/L ceric ammonium nitrate, 180 min reaction duration and 55ºC temperature. The graft reaction was confirmed by FTIR analysis, where the absorption bands corresponding to the C=O stretching and N‐H bending of the –CONH₂ group were observed. Scanning electron microscopic studies on grafted starches revealed that the granular structure of the starch was affected by the reaction. X‐ray diffraction analysis showed that the crystallinity of starch was decreased as a result of grafting and the reduction was higher for the grafted starches with higher percentage grafting.