Correction of some formulas of Agarwal's fast Fourier transform least-squares algorithm

Copyright © International Union of CrystallographyCorrection of formulas (34), (37) and (38) of Agarwal's fast Fourier transform least-squares algorithm [Acta Cryst. (1978), A34, 791-809]

On the choice of the model cell and the integration volume in the use of the rotation function

Copyright © International Union of CrystallographyIn the general case where there is only one molecule in the asymmetric unit, and in the absence of non-crystallographic symmetry, molecular-replacement (MR) techniques can be used to solve an unknown crystal structure from a closely related known molecular model. The procedure comprises two stages in order to find (i) the orientation of the model in the crystal, and (ii) the position of the well oriented model relative to the crystallographic symmetry elements. The most widely used rotation function R(θ) [Rossmann & Blow (1962). Acta Cryst. 15, 24—31], for stage (i), correlates the rotated central portion U of the Patterson function of the observed crystal with the calculated Patterson function of the proposed model. The calculation of the Patterson function of the model is performed in an arbitrary celi of sufficient size to prevent the overlap of intramolecular vectors from adjacent origins. Tollin & Rossmann [Acta Cryst. (1966), 21, 872—876] have proposed a criterion for the choice of the cell; this criterion is in fact sufficient but not necessary: after a discussion on the shape and the size of U, it is shown in this paper that the volume of the cell can be generally halved for the very same resulting map and, as a consequence, the computing time is also halved. Moreover, the size of the cell, even over-reduced, has a relatively weak influence on the ultimate conclusion ofthe MR calculation

Visualisation de photographies sur une imprimante rapide d'ordinateur. Application à la simulation de topographies en pose fixe par la méthode de Lang

Copyright © International Union of CrystallographyIn the simulation of X-ray section topographs by the means of a computer some problems occur concerning the representation of the photographic image. The grey scales used in the case of electron microscopy may not be applied to the case of X-ray topographs. We have studied a new grey scale and we have adapted the levels of intensity to the specific case of X-rays. Experimental and theoretical results are in good agreement but it is shown that quantitative measurements on photographic plates may be quite delicate

Fast Lexically Constrained Viterbi Algorithm (FLCVA): Simultaneous Optimization of Speed and Memory

Lexical constraints on the input of speech and on-line handwriting systems improve the performance of such systems. A significant gain in speed can be achieved by integrating in a digraph structure the different Hidden Markov Models (HMM) corresponding to the words of the relevant lexicon. This integration avoids redundant computations by sharing intermediate results between HMM's corresponding to different words of the lexicon. In this paper, we introduce a token passing method to perform simultaneously the computation of the a posteriori probabilities of all the words of the lexicon. The coding scheme that we introduce for the tokens is optimal in the information theory sense. The tokens use the minimum possible number of bits. Overall, we optimize simultaneously the execution speed and the memory requirement of the recognition systems.Comment: 5 pages, 2 figures, 4 table

O sal na Capitania de São Paulo no século XVIII

(Primeiro Parágrafo do Artigo)O abastecimento de sal da Captiania de São Paulo, para o Sustento da vida, para o aumento das crianças, e subsistencia das tropas, que vem do Sul, constituiu um problema enfentado por toda a população, no período colonial.