A new method of ultrasound color flow mapping

Conventional ultrasound color flow mapping systems estimate and visualize only the axial velocity component. To obtain the transverse velocity component a modification of a multiple-beam method is proposed. The new two-dimensional color flow mapping system has a small size and consists of three transducers. The central transducer is an appodized and focused phased array. The other transducers are unfocused probes. Three transducers act as receivers and the central transducer operates as a transmitter. All receivers acquire rf scan lines that are then processed to estimate three axial velocity components using an autocorrelation method. These estimates are then combined to estimate the transverse velocity component, taking into account the geometric relationships among three transducers. Two algorithms for transverse velocity estimation are proposed. The first uses the Doppler angle estimate for calculation of the transverse velocity component. The other algorithm calculates the transverse velocity component directly from the axial components. The accuracy of the flow velocity estimators is estimated by simulations. Analysis of accuracy allows choosing the more effective algorithm for two-dimensional velocity estimation, which is insensitive to variations of the Doppler angle.     

Relative Chebyshev centers in normed linear spaces, part II

Let E be a normed linear space, A a bounded set in E, and G an arbitrary set in E. The relative Chebyshev center of A in G is the set of points in G best approximating A. We have obtained elsewhere general results characterizing the spaces in which the center reduces to a singleton in terms of structural properties related to uniform and strict convexity. In this paper, an analysis of the Chebyshev norm case, which falls outside the scope of the previous analysis, is presented.     

Groups withS 2′-subgroups andS 3′-subgroups

In this paper we formulate criteria for the solvability of groups of typeE _2′ andE _3′     

The maximum amplitude cost functional in linear systems

The maximum amplitude cost of a control function u(t) taken to be ess sup g(t, u(t)), where g(t, u) is a given function. (A particular example is g(t, u) = the norm of u.) We consider linear systems with this cost functional. The existence of optimal control is proved, and it is shown that the ess sup is uniformly essential with respect to the optimal controls. Properties of the extended attainable set are discussed and compared with the case of an integral cost. Finally, we show in what sense a cost functional of the form $\text{(∝ g(t, u(t))}{}^{\mathrm{q}}\text{)}{}^{\mathrm{<mtext>1</mtext><mtext>q</mtext>}}$ approximates the ess sup cost functional.     

On symmetric basic sequences in Lorentz sequence spaces

We examine the symmetric basic sequences in some classes of Banach spaces with symmetric bases. We show that the Lorentz sequence spaced(a,p) has a unique symmetric basis and every infinite dimensional subspace ofd(a,p) contains a subspace isomorphic tol ^p. The symmetric basic sequences ind(a,p) are identified and a necessary and sufficient condition for a Lorents sequence space with exactly two nonequivalent symmetric basic sequences in given. We conclude by exhibiting an example of a Lorentz sequence space having a subspace with symmetric basis which is not isomorphic either to a Lorentz sequence space or to anl ^p-space. This is part of the first author's Ph. D. thesis, prepared at the Hebrew University of Jerusalem under the supervision of Dr. L. Tzafriri.     

Bounds on the Optimal Location to the Weber Problem under Conditions of Uncertainty

Optimal and Heuristic bounds are given for the optimal location to the Weber problem when the locations of demand points are not deterministic but may be within given circles. Rectilinear, Euclidean and square Euclidean types of distance measure are discussed. The exact shape of all possible optimal points is given in the rectilinear and square Euclidean cases. A heuristic method for the computation of the region of possible optimal points is developed in the case of Euclidean distance problem. The maximal distance between a possible optimal point and the deterministic solution is also computed heuristically.     

Financial Applications of a Tabu Search Variable Selection Model

We illustrate how a comparatively new technique, a Tabu search variable selection model [Drezner, Marcoulides and Salhi (1999)], can be applied efficiently within finance when the researcher must select a subset of variables from among the whole set of explanatory variables under consideration. Several types of problems in finance, including corporate and personal bankruptcy prediction, mortgage and credit scoring, and the selection of variables for the Arbitrage Pricing Model, require the researcher to select a subset of variables from a larger set. In order to demonstrate the usefulness of the Tabu search variable selection model, we: (1) illustrate its efficiency in comparison to the main alternative search procedures, such as stepwise regression and the Maximum R 2 procedure, and (2) show how a version of the Tabu search procedure may be implemented when attempting to predict corporate bankruptcy. We accomplish (2) by indicating that a Tabu Search procedure increases the predictability of corporate bankruptcy by up to 10 percentage points in comparison to Altman's (1968) Z-Score model.