Process of faceting in nanoparticles of FCC metals: Results of simulation by the molecular-dynamics method

The process of formation of facets (faceting) in Ni, Al, and Au nanoparticles has been investigated by the molecular-dynamics method. It has been established that the surface of nanoparticles of fcc metals with attainment of a low-energy habit can be transformed via correlated displacements of atomic groups of the facet in the octahedral plane. It has been shown that such a process is similar to the surface diffusion of atomic n-mers with the activation energy depending on the facet size, and for particles with a diameter d < 3.0 nm the correlated displacement of atomic layers proves to be the dominant mechanism of faceting.     

Transformation of sputtered calcium copper titanate thin film into nanorods by sequential annealing

Rapid synthesis of long calcium copper titanate (CCTO) nanorods was carried out by sequential annealing. CCTO thin films have been deposited on p-Si substrate by RF sputtering technique and afterwards, the samples were thermally treated using a preheated furnace by varying the annealing temperature from 850 °C to 1100 °C. CCTO nanorods of 12 µm lengths and 400–600 nm diameters were synthesized at 1100 °C. Based on the FESEM observations, a plausible growth mechanism has been proposed to explain the formation of nanorods. The (220) XRD peak of the CCTO film became prominent for the annealing temperature of 950 °C. The presence of nanoscale crystals in amorphous matrix has been observed by HRTEM studies. The elemental mapping of CCTO nanorod has shown a spatial variation of elements throughout the nanorod. The oxide and interface charge density was found to be increased with the rise in annealing temperature.     

Partition coefficients of environmentally important phenols in a supercritical carbon dioxide-water system from cocurrent extraction without analysis of the compressible phase

Partition coefficients of phenol, salicylic acid, and several environmentally important chloro- and nitrophenols in a supercritical CO2-water system were measured using direct cocurrent extraction of aqueous solutions of the individual solutes with CO2. Partitioning data on the nitrophenols and salicylic acid were obtained for the first time. To bypass the troublesome and error-prone analysis of the CO2-rich phase, the present method employed only the solute concentrations in the aqueous phase before and after extraction to determine the partition coefficient. Unlike most previous engineering studies of phenol partitioning in a CO2-water system, the concentrations of phenolic solutes approached infinite dilution in both phases. This makes the results relevant to analytical-scale SFE of environmental water samples with CO2. Because of effective infinite dilution of the solutes, the partition coefficients provide a direct measure of relative CO2-philicity/hydrophilicity of the individual phenols. Compared to the octanol-water partition coefficients of substituted phenols, the CO2-water partition coefficients are more sensitive to substitution in the position neighboring the hydroxyl group.     

Nearest and reverse nearest neighbor queries for moving objects

With the continued proliferation of wireless communications and advances in positioning technologies, algorithms for efficiently answering queries about large populations of moving objects are gaining interest. This paper proposes algorithms for k nearest and reverse k nearest neighbor queries on the current and anticipated future positions of points moving continuously in the plane. The former type of query returns k objects nearest to a query object for each time point during a time interval, while the latter returns the objects that have a specified query object as one of their k closest neighbors, again for each time point during a time interval. In addition, algorithms for so-called persistent and continuous variants of these queries are provided. The algorithms are based on the indexing of object positions represented as linear functions of time. The results of empirical performance experiments are reported.     

Second generation waste package design and storage concept for the Yucca Mountain Repository

The reference waste package design and operating mode to be used in the Yucca Mountain Repository is reviewed. An alternate (second generation) operating concept and waste package design is proposed to reduce the risk of localized corrosion of waste packages and to reduce repository costs. The second generation waste package design and storage concept is proposed for implementation after the initial licensing and operation of the reference repository design. Implementation of the second generation concept at Yucca Mountain would follow regulatory processes analogous to those used successfully to extend the design life and uprate the power of commercial light water nuclear reactors in the United States. The second generation concept utilizes the benefits of hot dry storage to minimize the potential for localized corrosion of the waste package by liquid electrolytes. The second generation concept permits major reductions in repository costs by increasing the number of fuel assemblies stored in each waste package, by eliminating the need for titanium drip shields and by fabricating the outer container from corrosion resistant low alloy carbon steel.     

Reading the footprints of strained islands

We report on recent advances in the understanding of surface processes occurring during growth and post-growth annealing of strained islands which may find application as self-assembled quantum dots. We investigate the model system SiGe/Si(0 0 1) by a new approach based on “reading the footprints” which islands leave on the substrate during their growth and evolution. Such footprints consist of trenches carved in the Si substrate. We distinguish between surface footprints and footprints buried below the islands. The former allow us to discriminate islands which are in the process of growing from those which are shrinking. Islands with steep morphologies grow at the expense of smaller and shallower islands, consistent with the kinetics of anomalous coarsening. While shrinking, islands change their shape according to thermodynamic predictions. Buried footprints are investigated by removing the SiGe epilayer by means of selective wet chemical etching. Their reading shows that: (i) during post-growth annealing islands move laterally because of surface-mediated Si–Ge intermixing; (ii) a tree-ring structure of trenches is created by dislocated islands during their “cyclic” growth. This allows us to distinguish coherent from dislocated islands and to establish whether the latter are the result of island coalescence.     

Variable-Gain Controllers for Nonlinear Systems Using the T–S Fuzzy Model

This correspondence proposes two novel control schemes with variable state-feedback gain to stabilize a Takagi-Sugeno (T-S) fuzzy system. The T-S fuzzy model is expressed as a linear plant with nonlinear disturbance terms in both schemes. In controller I, the T-S fuzzy model is expressed as a linear plant around a nominal plant arbitrarily selected from the set of linear subsystems that the T-S fuzzy model consists of. The variable gain then becomes a function of a gain parameter that is computed to neutralize the effect of disturbance term, which is, in essence, the deviation of the actual system dynamics from the nominal plant as the system traverses a specific trajectory. This controller is shown to stabilize the T-S fuzzy model. In controller II, individual linear subsystems are locally stabilized. Fuzzy blending of individual control actions is shown to make the T-S fuzzy system Lyapunov stable. Although applicability of both control schemes depends on the norm bound of unmatched state disturbance, this constraint is relaxed further in controller II. The efficacy of controllers I and II has been tested on two nonlinear systems     

Loading time history for tornado-generated missiles

Nuclear power plant structures in the USA are designed for impact by tornado-generated missiles. The design load for flexure and shear can be obtained from the deceleration of the missile on impact. The paper gives a simple method to determine the deceleration of the most critical pipe missile. Results, obtained by the simple method, are compared with full-scale test results. The comparisons between the predicted and actual deceleration time histories show excellent correlation.     

Temperature-dependent electrical properties of plasma-grown gate oxides on tensile-strained Si0.993 C0.007 layers

Ultra-thin (<10 nm) gate oxides have been grown directly on tensile-strained Si_0.993 C_0.007 layers at a low temperature using microwave O₂-plasma. The changes in gate voltage (V_g), flat-band voltage (V_FB), oxide charge density (Q_ox/q) an interface state density (D_it) have been studied using a metal-oxide-semiconductor structure over the temperature range of 77–450 K. Inversion capacitance increases with temperature above 400 K, leading to a transition from high-frequency to low-frequency characteristics. The dominant types of charges in the oxide are found to be strongly temperature dependent. It is found that charge-trapping properties under Fowler–Nordheim (F–N) constant-current stressing are significantly improved with increasing temperature.     

Galvanomagnetic effects in atomic-disordered HgSe<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>S<Subscript>x</Subscript> compounds

In HgSe and HgSe_1?xS_x single crystals irradiated with electrons of 5 MeV energy at 270 K, resistivity and the Hall effect have been studied in the temperature range 1.7–370 K in magnetic field up to 13.6 T. Changes in the carrier density and mobility upon generation of radiation-induced defects and subsequent isochronous annealings have been determined. The irradiation made it possible to reduce the electron density to a greater extent than do conventional methods, as well as to restore the initial value by annealing.