An application of radon inversion to diffraction tomography

Basic equations of linear computer tomography are considered; a connection of the mathermatical formulation of problems of computer tomography with problems of integral geometry is indicated; the properties of the Radon transform for even- and odd-dimensional spaces are analyzed, and applications of Radon inversion to problems of diffraction tomography are presented. Bibliography: 5 titles. Translated fromZapiski Nauchnykh Seminarov POMI, Vol. 230, 1995, pp. 264–277. Translated by V. N. Troyan.     

A highly selective solid phase extraction sorbent for pre-concentration of sameridine made by molecular imprinting

Summary A novel approach to solid phase extraction, based on the use of a highly selective molecularly imprinted polymer, is presented. The versatility of this type of sorbent for solid phase extraction was demonstrated in a model batch-wise pre-concentration of sameridine prior to gas chromatography. Problems associated with leakage of remaining imprint molecules during the desorption phase could be eliminated by the use of a close structural analogue of sameridine as the imprint species. It was found that a major benefit of the imprinted polymer was its specificity, which lead to distinctly cleaner chromatographic traces and ability to improve sensitivity by extracting sameridine from larger sample volumes.     

Laser systems specialized for laser spectroscopy at storage rings

Laser spectroscopy at storage rings often suffers from a limited resolution due to Doppler-broadened resonances. Broadening is caused by the velocity spread of the ions stored in the beam. In the following, the present status of our work on laser systems specialized on the specific needs of laser spectroscopy at storage rings is reported. Two pulsed laser systems were developed. One is a dye laser whose spectral bandwidth can be switched by inserting different Littrow-prisms into the resonator. An increase in bandwidth up to a factor of 45 was achieved. This laser was used for fast qualitative scans and high resolution measurements. The other laser system is a Nd : YAG laser pumped optical parametric oscillator. It is a tunable laser system covering the spectral range from 410 to 4000 nm. Furthermore, a continuous wave laser with a frequency shifted feedback cavity is described. It shows broadband emission with an adjustable bandwidth of up to 4.5 GHz. This laser can be advantageous for laser cooling of ion beams. This revised version was published online in August 2006 with corrections to the Cover Date.     

Success and survival of operational research groups—A review

Operational Research groups were established in private and public sector organizations following on from their success supporting the military in the Second World War. In the early years their numbers grew rapidly but by the mid-1970s evidence started to accumulate that they were being viewed less favourably. Many organizations chose not to set up OR groups. Established groups were closed down or dispersed to operating units in organizations, particularly during the recessionary periods. In 1993 following on the closures of some major OR groups in the UK, the Operational Research Society decided to fund research to examine those factors influencing a group's success and survival. This review, which forms part of the research, first examines the history of OR groups in the UK and North America, arguing that in practice they were one of a number of internal organizational consultancies. As such they were judged by their competitive performance. Despite the intent of the founding fathers of OR many groups found their scope was limited to mainly tactical problems using analytical model based approaches although there were exceptions that were successful in making major contributions at the strategic level also. Within their chosen fields of activity however many groups flourished whilst some failed. This review presents a comprehensive list of influences on success and survival. They include changes in the external environment, together with shifts in managerial style and culture, organizational factors, and the OR group itself. The review concludes that, while OR groups can do much to protect themselves from closure, organizational changes within a hostile managerial culture demand a creative response that acknowledges new requirements. Areas where an OR group has greatest influence over its effectiveness include its leadership and personnel, project balance and management. In addition, to be successful OR groups need to positively develop and market their services in an increasingly competitive managerial climate.     

Global Optimization of a Quadratic Functional with Quadratic Equality Constraints, Part 2

In this paper, we investigate a constrained optimization problem with a quadratic cost functional and two quadratic equality constraints. It is assumed that the cost functional is positive definite and that the constraints are both feasible and regular (but otherwise they are unrestricted quadratic functions). Thus, the existence of a global constrained minimum is assured. We develop a necessary and sufficient condition that completely characterizes the global minimum cost. Such a condition is of essential importance in iterative numerical methods for solving the constrained minimization problem, because it readily distinguishes between local minima and global minima and thus provides a stopping criterion for the computation. The result is similar to one obtained previously by the authors. In the previous result, we gave a characterization of the global minimum of a constrained quadratic minimization problem in which the cost functional was an arbitrary quadratic functional (as opposed to positive-definite here) and the constraints were at least positive-semidefinite quadratic functions (as opposed to essentially unrestricted here).     

A compact shock-assisted free-piston driver for impulse facilities

A free-piston driver that employs entropy-raising shock processes with diaphragm rupture has been constructed, which promises significant theoretical advantages over isentropic compression. Results from a range of conditions with helium and argon driver gases are reported. Significant performance gains were achieved in some test cases. Heat losses are shown to have a strong effect on driver processes. Measurements compare well with predictions from a quasi-one-dimensional numerical code. Received 7 September 1996 / Accepted 5 October 1996     

Critical fields and currents in a weakly nonlinear medium near the percolation threshold

For fields above a critical value the expansion of the conductivity in powers of the field ceases to be valid and the weak-nonlinearity approximation no longer works. The density behavior of the critical fields in strongly inhomogeneous media near the percolation threshold is found on the basis of two criteria—an average criterion and a local criterion. The parameter values of the medium for which crossover—a change of the critical behavior—occurs are determined. Similar calculations are performed for the critical currents. Zh. Tekh. Fiz. 68, 5–8 (June 1998)     

Transfer theorems and the algebra of modal operators

A set theory ZFI′ which does not employ the Law of the Excluded Middle φ ∀ ⊥ φ, for all φ, retians the stock of expressive capacities of the classical set theory ZF, on the one hand, and has many of the features of an effective theory on the other. In the article, a broad class of formulas σ is constructed for which ZF ⊥ σ implies ZFI′ ⊥ σ. This result provides a generalization of Friedman's theorem on AE-arithmetic formulas. Besides, we prove transfer theorems of classical logic for the case of rings; in particular, Hilbert's theorem on zeros and Artin's theorem on ordered fields are extended to the case of regular f-rings, and we bring in appropriate upper bounds for them. Supported by RFFR grant No. 93-012-1027. Translated fromAlgebra i Logika, Vol. 36, No. 3, pp. 282–303, May–June, 1997.