Multiwalled Nanotubes: Their Formation by Irradiating Graphite with High Doses of Electrons

We report the production of carbon nanotubes by high dose of electron irradiation. The irradiation was performed with a 2 MeV Van de Graaff accelerator, while the irradiation conditions were the following: voltage 1.3 MeV, current 5 µA, dose rate 25 kGy/min, and total dosage 1000 kGy. The samples were analyzed in a high-resolution transmission electron microscope. The main features observed on the samples, were huge nanotubes of several nanometer long and few nanometer wide, which are capped at one end. It is good to point out, that at this level of irradiation, we were not able to find either onion-like or particle structures throughout the material, as it is usual in similar hexagonal structures. This behavior could be attributed to the level of irradiation used to create the nanotubes under investigation.     

Microwave-Assisted Fabrication of Superamphiphobic Surfaces on Aluminum Substrates

The field of superamphiphobic surface fabrication has evolved rapidly in the last decade; however, research on important issues such as sustainability and green chemistry procedures is still scarce. Herein, a simple method of microwave irradiation (MW) to minimize energy consumption during the preparation of superamphiphobic aluminum (Al) surfaces is reported. Al substrates are first etched in diluted HCl solutions to generate a microstructure and then irradiated in a commercial microwave unit for several time intervals, temperatures, and pressures. The surfaces are then coated with different compounds, and the wettability is tested with high and very-low surface tension liquids. Optical profilometry and scanning electron microscopy images show that the density of hierarchical micro-nanostructures increases with MW time, temperature, and pressure. At 170 °C and 7.9 bar, the surfaces present a high density of structures and re-entrant topographies. The obtained coatings display excellent repellence to liquids with surface tensions as low as 27.5 mN m⁻¹. X-ray photoelectron spectroscopy data show the importance of efficient surface functionalization for the production of superamphiphobicity in Al substrates. The results show that MW irradiation of Al substrates can be a green and efficient method for fabricating superamphiphobic surfaces.     

Possibility of the application of the computational intelligence in the production of superhard materials. Report 2

A new system to control a 630-ton and a 2500-ton presses has been developed. By using this system it has been made possible to define new parameters related to pressure and temperature and the influence of certain factors on them. Furthermore, the new system has been shown to indicate that other parameters, such as height of the gasket formed (h _c ), electrical resistance of the reaction cell, and the frequency of activation of the pump or multiplier, can serve as important indicators of the improvement of superhard material production technologies, implementing the Computational Intelligence (CI).     

Use of HF Doppler radars for the investigation of the wind-current relationship

The theoretical behaviour of the near-surface wind-driven currents is strongly dependent upon the models used to describe the mixed surface layer (especially the kinematic viscosity profile). This paper investigates measurements of ocean currents by HF Doppler radars in order to shed some light on this problem. It is found that the relative directions of the wind and current velocities and the variation of the current speed with respect to radar frequency (i.e. with respect to depth) are the most sensitive parameters to analyse for discriminating among the various models. The results of a preliminary experiment which was conducted in the western Mediterranean during the autumn of 1981 are presented. In this experiment the current was measured on 8 consecutive days at two radar frequencies corresponding to integration depths of 1 and 2 m, respectively. A special study shows that the near-surface current is only weakly influenced by the proximity of the coast (the measurements were obtained between 10 and 34km offshore). Because of the shortness of the experiment analysis of the wind-current relation does not provide the required accuracy whereas analysis of the current shear, which can process simultaneously the data obtained in nine different sea cells, gives a significant result supporting models with small shears (like Ekman's model with a constant kinematic viscosity profile). Some future improvements are briefly discussed.     

A dynamic two phase flow model for a pilot scale sodium borohydride hydrogen generation reactor

A two-dimensional, non-isothermal and dynamic model was developed to describe a sodium borohydride/hydrogen reactor for stationary use. All relevant transport phenomena were treated in detail and the kinetic model developed previously by the authors was introduced into the algorithm. In this paper the reactive solution was modelled as a two phase flow; with this approach the impact of the hydrogen production on the solution stirring could be observed and quantified.     

High surface area LaNiO<Subscript>3</Subscript> electrodes for oxygen electrocatalysis in alkaline media

LaNiO₃ coatings on nickel-foam supports were prepared by brush painting. The electrochemical properties were investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Comparative studies were performed with LaNiO₃-pelleted electrodes. The roughness factors were determined by CV and found to be 5,208 ± 350 and 4,037 ± 250 for the pelleted and coated electrodes, respectively. EIS measurements confirm the results obtained by CV. Values lower than 0.3 were calculated for the morphology factors for both electrodes, indicating low electrochemical porosity. The experimental method used in this work to synthesise the oxide coupled with the use of Ni foam as support has proved to be very effective in producing oxide electrodes with surface areas higher than those referred to in relevant literature.     

SIMULATION OF METAL DROPLET DEPOSITION WITH SOLIDIFICATION INCLUDING UNDERCOOLING AND CONTACT RESISTANCE EFFECTS

A numerical procedure for the deformation and solidification of a metal droplet impinging on a flat surface is developed and a sample calculation is presented. A previously derived second-order ordinary differential equation (ODE) that approximates the splat as a cylinder and describes the droplet size evolution based on the mechanical energy equation in conjunction with kinematic and geometrical compatibility is used. The thermal energy equations for the liquid and solid regions of the splat and the substrate are separately solved coupled by boundary conditions such as contact resistance and undercooling in a regularized calculation domain produced by algebraic grid generation. The solidified layer thickness is calculated by solving a hyperbolic partial differential equation (PDE) resulting from the interface energy equation at the phase change boundary. Physical processes such as convective heat loss, substrate heat loss, viscous dissipation, and surface tension are modeled through appropriate nondimensional parameters.     

Route duration modeling for mobile ad-hoc networks

In this paper, we present a model that estimates the time duration of routes formed by several intermediate nodes in mobile multi-hop ad-hoc networks. First, we analyze a 3-node route, where only the intermediate node is in movement while source and destination nodes remain static. From this case, we show how route duration is affected by the initial position of the intermediate node and the size of the region where it is located. We also consider a second case where all nodes of 3-node routes are mobile. Based on extensive analysis of these routes, we determine the PDF of route duration under two different mobility models. This PDF can be determined by either analytical or statistical methods. The main contribution of this paper is that the time duration of a route formed by N intermediate nodes can be accurately computed by considering the minimum route duration of a set of N routes of 3 nodes each. Simulation work was conducted using the NS-2 network simulator to verify the accuracy of the proposed model and to compare it with other proposals found in the literature. We show that our model is in better agreement with simulation results as compared with other models. Results from this work can be used to compute overhead signaling during route-maintenance of unicast and multicast routing protocols for mobile ad-hoc networks. Similarly, because route duration decreases with route length, this study can be used to scale the network size up/down.