A novel CMOS triode transconductor based on current division

A compact transconductor based on transistors operating in the triode region is presented. A novel V–I conversion stage made up of current dividers is proposed. The circuit allows tunability by adjusting a dc current and the transconductance is independent of transconductance parameter of the triode transistors. Besides, the circuit is simple because feedback structures to fix source-drain voltages of triode transistors are not needed, saving area and featuring low power consumption. Measurement and simulation results are presented and analyzed for validating the proposed technique.     

The Fractal Pattern of the French Gothic Cathedrals

The classic patterns of Euclidean Geometry were used in the construction of the Gothic cathedrals to provide them with proportion and beauty. Still, there is also another complex concept related to them: the un-evenness of their structures, which determines their space-filling ability, that is, their level of roughness. In this paper we use the techniques of Fractal Geometry to generate parameters which provide a measure of roughness. In this way we show that the French Gothic cathedrals do not only follow Euclidean geometric patterns, but also have a general non-random fractal pattern.     

Automatic CPU/GPU Generation of Multi-versioned OpenCL Kernels for C++ Scientific Applications

Parallelism has become one of the most extended paradigms used to improve performance. However, it forces software developers to adapt applications and coding mechanisms to exploit the available computing devices. Legacy source code needs to be re-written to take advantage of multi- core and many-core computing devices. Writing parallel applications in a traditional way is hard, expensive, and time consuming. Furthermore, there is often more than one possible transformation or optimization that can be applied to a single piece of legacy code. Therefore many parallel versions of the same original sequential code need to be considered. In this paper, we describe an automatic parallel source code generation workflow (REWORK) for parallel heterogeneous platforms. REWORK automatically identifies promising kernels on legacy C++ source code and generates multiple specific versions of kernels for improving C++ applications, selecting the most adequate version based on both static source code and target platform characteristics.     

Effects of balanced and unbalanced voltage sags on DC adjustable-speed drives

This paper analyzes the sensitivity of DC adjustable-speed drives to balanced and unbalanced voltage sags. The influence of sag type, depth, duration and phase-angle jump on DC drives is studied. The control of the DC drive has been taken into account to understand drive behavior in the presence of voltage sags. Two working modes of the DC motor are considered in the study: as a consumer load and as a regenerative load. When the DC motor works as a consumer load, the study shows that sag type and depth have a significant influence on drive behavior. However, the voltage sag can be ridden through if the rectifier firing angle is set correctly by the control. When the DC motor works as a regenerative load, the study shows the consequences of the three-phase rectifier commutation failure due to the voltage sag.     

Robust Indoor Positioning Provided by Real-Time RSSI Values in Unmodified WLAN Networks

The positioning methods based on received signal strength (RSS) measurements, link the RSS values to the position of the mobile station(MS) to be located. Their accuracy depends on the suitability of the propagation models used for the actual propagation conditions. In indoor wireless networks, these propagation conditions are very difficult to predict due to the unwieldy and dynamic nature of the RSS. In this paper, we present a novel method which dynamically estimates the propagation models that best fit the propagation environments, by using only RSS measurements obtained in real time. This method is based on maximizing compatibility of the MS to access points (AP) distance estimates. Once the propagation models are estimated in real time, it is possible to accurately determine the distance between the MS and each AP. By means of these distance estimates, the location of the MS can be obtained by trilateration. The method proposed coupled with simulations and measurements in a real indoor environment, demonstrates its feasibility and suitability, since it outperforms conventional RSS-based indoor location methods without using any radio map information nor a calibration stage.     

Dynamic Routing and Wavelength Assignment in Optical Networks by Means of Genetic Algorithms

We propose a novel genetic algorithm for solving the dynamic routing and wavelength assignment (DRWA) problem in wavelength-routed optical networks. The algorithm not only obtains low call blocking probability, but it also employs a very short computation time. Moreover, it is capable of providing fairness among connections, that is, to offer approximately the same quality of service (in terms of blocking probability) for all source-destination node pairs. Since requirements on optical network availability are highly severe, we also propose an extension of the algorithm to provide fault-tolerance capability at the optical layer. It is achieved by means of protection, where each optical connection request is provided with a pair of lightpaths (a primary and a backup lightpath). Again, the genetic algorithm proves to be highly efficient, in this case, at performing routing and wavelength assignment of pairs of lightpaths.     

The Sluggish Diffusion of Cations in CeO2 Probed through Molecular Dynamics and Metadynamics Simulations

Cation diffusion in fluorite-structured CeO₂, though far slower than anion diffusion, is an important, high-temperature process because it governs diverse fabrication and degradation phenomena. Herein, cation diffusion is studied by means of classical molecular dynamics and metadynamics simulations. Three different mechanisms are examined: migration involving an isolated cerium vacancy, migration involving a cerium vacancy in a defect associate with an oxygen vacancy, and migration involving a cation divacancy. For each mechanism, defect diffusion coefficients are calculated as a function of temperature, from which the respective activation enthalpy of defect migration is obtained. Through comparisons with experimental cation diffusion data (specifically, of the absolute magnitude of the cation diffusivity as well as its activation enthalpy), it is concluded that cation diffusion takes place predominantly neither by isolated vacancies nor by cation vacancy–oxygen vacancy associates but by cation divacancies.     

Investigation on the structural,elastic, electronic,and magnetic properties of half-metallic $$\hbox {Co}_{2}\hbox {MnSi}$$ and CoMnIrSi via first-principles calculations

We investigated the structural, elastic, electronic, and magnetic properties of \(\hbox {Co}_{2}\hbox {MnSi}\) and CoMnIrSi full-Heusler compounds by means of density functional theory based on the full-potential linearized augmented plane wave (FP-LAPW) approach. The generalized gradient approximation as proposed by Wu and Cohen (GGA-WC) was employed to treat the exchange-correlation effect. The results show that both alloys are structurally and mechanically stable. \(\hbox {Co}_{2}\hbox {MnSi}\) is almost elastically isotropic, while CoMnIrSi is anisotropic, and both alloys are ductile. The studied compounds have perfect spin polarization of 100 %, with down-spin bandgap of 0.796 eV and 0.728 eV, respectively. The calculated magnetic properties indicate that the Slater–Pauling rule is satisfied in both cases. Finally, the effect of strain on the half-metallic properties of \(\hbox {Co}_{2}\hbox {MnSi}\) and CoMnIrSi was also investigated by varying the lattice constant over a wide range.     

Computation of Multi-facility Location Nash Equilibria on a Network Under Quantity Competition

We deal with the location-quantity problem for competing firms when they locate multiple facilities and offer the same type of product. Competition is performed under delivered quantities that are sent from the facilities to the customers. This problem is reduced to a location game when the competing firms deliver the Cournot equilibrium quantities. While existence conditions for a Nash equilibrium of the location game have been discussed in many contributions in the literature, computing an equilibrium on a network when multiple facilities are to be located by each firm is a problem not previously addressed. We propose an integer linear programming formulation to fill this gap. The formulation solves the profit maximization problem for a firm, assuming that the other firms have fixed their facility locations. This allows us to compute location Nash equilibria by the best response procedure. A study with data of Spanish municipalities under different scenarios is presented and conclusions are drawn from a sensitivity analysis.