Yield of products from catalytic cracking of vacuum gasoils

In catalytic cracking of vacuum gasoils, the yields of products are correlated with their hydrogen content. A correlation that allows predicting the yields of products of this process was elaborated based on the results of cracking of 11 gasoils of different origin and data on their density, refractive index, and 50% distillation temperature. However, it is not possible to predict the octane number of the naphtha obtained in cracking with the group hydrocarbon composition of the feedstock. __________ Translated from Khimiya i Tekhnologiya Topliv i Masel, No. 4, pp. 31–34, July–August, 2007.     

Impact of Preferential P-Diffusion Along the Grain Boundaries on Fine-Grained Polysilicon Solar Cells

Thin-film polysilicon solar cells are a promising low-cost alternative for bulk silicon solar cells due to their reduced material thickness. Recently, we showed that the use of an amorphous silicon/polycrystalline silicon heterojunction emitter instead of a diffused homojunction emitter led to a boost in the open-circuit voltage by 90 mV. Now, we present a full evidence that shows that this improvement is related to the absence of dopant smearing along the grain boundaries. By using scanning spreading resistance microscopy, we found an enlargement of the junction area by a factor of five in case of a homojunction. The tips of the dopant spikes represent lowly doped areas with an enhanced recombination.     

Direct Instantaneous Torque Control in Direct Drive Permanent Magnet Synchronous Motors—a New Approach

In this paper, a novel direct instantaneous torque control scheme for a direct drive (DD) permanent magnet synchronous motor (PMSM) is presented. A hybrid control structure combining the internal model principle and the variable structure control (VSC) approach is proposed. First, a variable structure torque controller is adopted to regulate the torque angle increment according to the torque feedback error. Second, the appropriate control voltage vector is determined using the reference stator flux vector and the estimated dynamic back electromotive force (EMF) vector, as an internal model, in a deadbeat control manner. Subsequently, better disturbance rejection can be obtained with the proposed cascaded control structure. To robustly obtain the instantaneous torque and flux information, a robust adaptive motor model is proposed. The Lyapunov stability theory is used to analyze the stability of the augmented robust adaptive motor model and to give a guideline for tuning model parameters. Experimental results are presented to demonstrate the validity and effectiveness of the proposed instantaneous torque control scheme.     

A Chamber for X-Ray Diffractometry of Gas Hydrates Samples for Pressures of Up to 700 atm

A chamber for X-ray diffractometry of gas-hydrate samples designed for operation at pressures of up to 700 atm and low temperatures is described. The leakproof character of the chamber at temperatures down to ?150°C is ensured by an Amaga-type seal with a fluoroplastic gasket pressed by disk springs. The chamber was used to study double hydrates using a synchrotron radiation source and a pressure generator based on a thermal multiplier.     

Analysis of dinosaur samples by nuclear microscopy

Several dinosaur bone and eggshell fossil samples unearthed at different sites in China were analyzed by means of nuclear microscopy. Concentrations and distributions of elements such as Na, Mg, Al, P, S, Ca, Cr, Mn, Fe, Cu, Zn, As, Br, Sr, Y, Ce, Pb and U, etc. were obtained for each sample. The results of quantitative PIXE and RBS analyses show unusually high concentrations of U and Ce in several samples obtained from a period near the K-T boundary (between Cretaceous and Tertiary periods, 65 million years ago), suggesting that some form of environmental pollution could be the cause of dinosaur extinction.     

Optimal control of nonlinear systems to given orbits

Using optimal control techniques we derive and demonstrate the use of an explicit single-step control method for directing a nonlinear system to a target orbit and keeping it there. We require that control values remain near the uncontrolled settings. The full nonlinearity of the problem in state space variables is retained. The “one-step” of the control is typically a composition of known or learned maps over (a) the time required to learn the state, (b) the time to compute the control and (c) the time to apply the control. No special targeting is required, yet the time to control is quite rapid. Working with the dynamics of a well-studied nonlinear electrical circuit, we show how this method works efficiently and accurately in two situations: when the known circuit equations are used, and when control is performed only on a Poincaré section of the reconstructed phase space. In each case, because the control rule is known analytically, the control strategy is computationally efficient while retaining high accuracy. The target locations on the selected target trajectory at each control stage are determined dynamically by the initial conditions and the system dynamics, and the target trajectory is an approximation to an unstable periodic orbit of the uncontrolled system. A linear stability analysis shows that dissipation in the dynamical system is essential for reaching a controllable state.     

CXFTV2: A Fortran subroutine for the discrete least squares convex approximation

A Fortan subroutine calculates the least squares approximation to n data values containing random errors subject to non-negative second divided differences (convexity). The method employs a dual active set quadratic programming technique that allows several concavities of an iterate to be corrected simultaneously, which is a distinctive feature of this calculation. A B-spline representation of the iterates reduces each active set calculation to an unconstrained minimization with fewer variables that requires only O(n) computer operations. Details in these techniques including the data structure that establishes the implementation of the method are specified. Numerical testing on a variety of data sets indicates that the subroutine is particularly efficient, terminating after a small number of active set changes, the subroutine being suitable for large numbers of data. A numerical example and its output is provided to help the use of the software.