THE ENERGETIC STABILITY OF TORI AND SINGLE-WALL TUBES

Tessellated tori, generated here from square-like tiled lattices, are closely related to cylinders and capped tubes. This way of building them enables the orientation of their bonds, and so the geometric proportions of the torus, to be specified for molecular mechanics calculations and, along with their transformation into capped tubes this is illustrated and discussed in the light of their energetic stability.     

FEM modelling and experimental characterization of microbeams in presence of residual stress

Out-of-plane bending tests are here used to experimentally validate some numerical models of microbeams actuated by the electric field. Out-of-plane bending microcantilevers and clamped–clamped microbeams often suffer the presence of residual strain and stress, respectively, which affect their static and dynamic behaviour and pull-in voltage. In case of microcantilever an accurate modelling has to include the effect of an initial curvature due to microfabrication process, while in double clamped microbeams constraints may impose a pre-loading caused by a tensile stress. So-called geometrical nonlinearity sometimes occurs, when microcantilever exhibits large displacement, or because of the mechanical coupling between axial and flexural behaviours in double clamped microbeams. Modelling this kind of nonlinearity is an additional goal of this study. Experiments demonstrated a good agreement with results of FEM approaches proposed. In the case of microbridges numerical models are used to identify the residual stress. A reverse analysis is implemented, the axial pre-stress is calculated by means of the measured pull-in voltage.     

Quantum circuit’s reliability assessment with VHDL-based simulated fault injection

This paper presents a VHDL-based simulated fault injection (SFI) methodology for quantum circuits. The main objective is to attain a high error modeling capability at a technology independent level. For this purpose, gate level simulation models for quantum circuits have been developed using VHDL. The proposed methodology relies on specific techniques inspired from the simulated fault injection techniques developed for classical CMOS circuits: saboteurs and mutants. In order to perform the simulation campaigns, a library of quantum gates and simulated fault injection components has been developed. The simulation results show that a wide range of quantum faults and error models has been addressed. Furthermore, a comparison between the two SFI techniques is presented.     

Corrosion behaviour and biocompatibility of a new dental noble AuPdAgTi alloy

The aims of the study were to investigate the electrochemical response of a new dental Au‐20Pd‐10Ag‐5Ti alloy in artificial Carter‐Brugirard saliva and to assess its biocompatibility using gingival fibroblast culture. Electrochemical techniques of potentiodynamic and linear polarization were used. Also, the open circuit potentials and the corresponding open circuit potential gradients were monitored for 5000 exposure hours. The gingival fibroblast response to Au‐20Pd‐10Ag‐5Ti alloy was estimated by LDH‐cytotoxicity, MTT cell proliferation assays, the assessment of substrate‐dependent changes in extracellular fibronectin network, cell morphology and actin cytoskeleton organization. The cyclic potentiodynamic curves of Au‐20Pd‐10Ag‐5Ti alloy exhibited a passive behaviour with transpassive dissolution of silver, without pitting corrosion. Open circuit potentials were finally stable at noble values. Open circuit potential gradients have low values that could not generate galvanic or local corrosion. The new Au‐20Pd‐10Ag‐5Ti alloy did not promote cell damage and alterations in cell adhesion and morphological features, exhibiting a good biocompatibility.     

Synthesis and characterization of side-chain poly(methacrylate)s bearing new azo-moieties

New side-chain poly(methacrylate)s with azo moieties were prepared by free radical copolymerization, starting from methyl methacrylate (MMA) and some original azo-monomers. The chromophore content was evaluated from ¹H-NMR spectroscopy and elemental analyses; all structures exhibited a high content of azobenzene units. UV–Vis measurements have also supported this fact. Reactivity ratios for the methacrylate systems and their corresponding Q–e values were calculated based on several initial feed compositions (MMA and the newly synthesized azo-monomers) using an integral method with its appropriate software. The polymers were also characterized by FTIR, SEC and DSC-TGA techniques. The coloured poly(methacrylate)s exhibited glass transition temperatures between 141 and 168 °C and thermal stabilities up to 306 °C.     

Random walk method for the two‐ and three‐dimensional Laplace,Poisson and Helmholtz's equations

The random walk method (RWM) is developed here for solving the Laplace, Poisson, and Helmholtz equations in two and three dimensions. The RWM is a local method, i.e. the solution at an arbitrary point can be determined without having to obtain the complete field solution. The method is based on the properties of diffusion processes, the Itô formula, the Dynkin formula, the Feynman–Kac functional, and Monte Carlo simulation. Simplicity, stability, accuracy, and generality are the main features of the proposed method. The RWK is inherently parallel and this fact has been fully exploited in this paper. Extensive numerical results have been presented in order to understand the various parameters involved in the method. Copyright © 2001 John Wiley & Sons, Ltd.     

Magnetotransport study on as-grown and annealed n- and p-type modulation-doped GaInNAs/GaAs strained quantum well structures

We report the observation of thermal annealing- and nitrogen-induced effects on electronic transport properties of as-grown and annealed n- and p-type modulation-doped Ga_{1 - x}In_xN_yAs_{1 - y} (x = 0.32, y = 0, 0.009, and 0.012) strained quantum well (QW) structures using magnetotransport measurements. Strong and well-resolved Shubnikov de Haas (SdH) oscillations are observed at magnetic fields as low as 3 T and persist to temperatures as high as 20 K, which are used to determine effective mass, 2D carrier density, and Fermi energy. The analysis of temperature dependence of SdH oscillations revealed that the electron mass enhances with increasing nitrogen content. Furthermore, even the current theory of dilute nitrides does not predict a change in hole effective mass; nitrogen dependency of hole effective mass is found and attributed to both strain- and confinement-induced effects on the valence band. Both electron and hole effective masses are changed after thermal annealing process. Although all samples were doped with the same density, the presence of nitrogen in n-type material gives rise to an enhancement in the 2D electron density compared to the 2D hole density as a result of enhanced effective mass due to the effect of nitrogen on conduction band. Our results reveal that effective mass and 2D carrier density can be tailored by nitrogen composition and thermal annealing-induced effects.

PACS

72.00.00; 72.15.Gd; 72.80.Ey     

Photoluminenscence Blinking Dynamics of Colloidal Quantum Dots in the Presence of Controlled External Electron Traps

The effect of the external charge trap on the photoluminescence blinking dynamics of individual colloidal quantum dots is investigated with a series of colloidal quantum dot–bridge–fullerene dimers with varying bridge lengths, where the fullerene moiety acts as a well‐defined, well‐positioned external charge trap. It is found that charge transfer followed by charge recombination is an important mechanism in determining the blinking behavior of quantum dots when the external trap is properly coupled with the excited state of the quantum dot, leading to a quasi‐continuous distribution of ‘on' states and an early fall‐off from a power‐law distribution for both ‘on' and ‘off' times associated with quantum dot photoluminescence blinking.     

Copolymerization of a bisanthracene compound with bismaleimides by Diels–Alder cycloaddition

Four new polymers have been synthesized via succesive Diels–Alder cycloadditions of a bisdiene compound bearing two anthracene groups and four bisdienophiles, all containing bismaleimide functions. The polycondensation reaction was performed in N,N‐dimethylacetamide at 120 °C leading to polymers soluble in polar solvents having molecular weights lower than 6000 g mol^?1. © 2001 Society of Chemical Industry