Indistinguishable Pairs Research Articles

Algorithms to compute bridging fault coverage ofIDDQtest sets

We present two algorithms, called list-based scheme and tree-based scheme, to compute bridging fault (BF) coverage ofIDDQtests. These algorithms use the novel ideal of “indistinguishable pairs,” which makes it more efficient and versatile than known fault simulation algorithms. Unlike known algorithms, the two algorithms can be used for combinational as well as sequential circuits and for arbitrary sets of BFs. Experiments show that the tree-based scheme is, in general, better than the list-based scheme. But the list-based scheme is better for some classes of faults.

The taxonomy and apparatus structure of the Silurian distomodontid conodont <i>Coryssognathus</i> Link & Druce, 1972

Abstract. Collections of discrete conodont elements from the Upper Whitcliffe Formation of the Welsh Borderland indicate a septimembrate plan for the feeding apparatus of Coryssognathus, comprising Pa, Pb, Pc, M, Sa/Sb, Sb and Sc elements. Each element is paired, and relative frequencies suggest that there was a total of 16 elements in the apparatus, including two indistinguishable pairs of Sc elements. Associated small coniform elements appear to represent discrete denticles of crown tissue that were sequentially incorporated into multidenticulate elements during ontogeny.

Comments on "Observability of discrete event dynamic systems" by C. M. Ozveren and A.S. Willsky

It is pointed out that the algorithm introduced in the above-titled work (see ibid., vol.35, no.7, p.797-806, July 1990) to compute the maximal set of indistinguishable state pairs is incorrect under the given definition of the automation O/sub p/. It is suggested that to remove the difficulty, either the definition of O/sub p/ or the algorithm itself should be modified.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Molecular mechanics of bridged ferrocene derivatives: Conformational energy surfaces of [3]‐, [4]‐ and [45] ferrocenophanes

AbstractA molecular mechanical model is presented which allows computational interpretation of stereodynamics in ferrocenophanes by using a simple form of bending potential for angles involving the central iron atom and extended to carbon atoms of different cyclopentadienyl rings. Potential energy surfaces of [3] ‐, [4] ‐ and [45] ferrocenophanes were studied in detail. For [3] ferrocenophane, the calculated energy barrier of the bridge reversal process agrees well with the experimental value. The previous interpretation of a rigid bridge in [4] ferrocenophane is questioned on the basis of the calculated low barriers. The predominance of experimentally indistinguishable enantiomeric pairs may be responsible for the misinterpretation. [45] Ferrocenophane is estimated to interconvert into D5‐symmetric global energy minima over barriers of 13–15 kcal mol−1 through one‐by‐one flipping of five tetramethylene bridges.

A theory of preattentive texture discrimination based on first-order statistics of textons.

The many indistinguishable texture pairs having identical second-, but different third- and higher-order statistics, led to the conjecture that globally the preattentive texture discrimination system cannot process statistical parameters of third- or higher-order. Thus in cases when iso-second-order textures yield discrimination this must be based on local conspicuous features called textons (Julesz, 1980). Here it is shown that globally even second-order statistical parameters, such as autocorrelation, cannot be processed by the textural system, and texture discrimination is solely the result of first-order statistics (density) of textons. It is also shown that the perceivable distance of statistical constraints (coherence distance) in densely packed stochastic textures is very short, four dots or less. As of now, only three texton classes were found: color, elongated blobs (line segments) of given width, orientation, and length, and the terminators (end-points) of these elongated blobs. The strength of these textons is demonstrated by several examples.

BARLEY CULTIVAR IDENTIFICATION BY SCANNING ELECTRON MICROSCOPIC ANALYSIS OF THE RACHILLA

Rachillae from 30 Canadian-grown barley cultivars were examined with a scanning electron microscope (SEM). Epicuticular wax crystal formations and cuticular ridges were prominent morphological features observed on the rachilla main stem. Distinct variations among cultivars, in the patterns of wax crystals and in the regularity, width and prominence of cuticular ridges were utilized alone or in combination to differentiate among cultivars. The ability to differentiate among cultivars was improved substantially by stereo SEM analysis of those morphological features. Twenty-six of the 30 cultivars studied could be identified by SEM analysis of the rachilla main stem. The remainder was divided into two indistinguishable pairs which could be distinguished from the other 26 cultivars. The effect of environment on the visual appearance of the epicuticular wax formations and cuticular ridges was studied. As a rule, environmental influence on these morphological features was not of sufficient significance to interfere with the identification of barley cultivars. SEM analysis of the rachilla would not be useful as a routine identification method and its use would be restricted to the laboratory. However, this technique would serve as a qualitative identification procedure which could be utilized to assist in the identification of barley cultivars which are impossible or difficult to distinguish by conventional means.

Do homologous chromosomes differ? Two statistical tests.

Two statistics are derived for testing whether measurements on otherwise indistinguishable chromosome pairs differ. The power of these tests is shown as well as a method for estimating the true homolog means. The tests and estimation procedures are simple to compute, and their use is illustrated on chromosome data. Results of applying the methods indicate that they are useful in discovering heretofore undetectable differences between homologous chromosomes.

Cytology and Phylogeny of Drosophila

The rediscovery of the polytene chromosomes in the salivary glands of the Diptera has allowed for a high order of accuracy in the identification of chromosomal rearrangements. The various types of chromosomal mutations are described and their relative importance in the evolution of the genus Drosophila is briefly discussed. Paracentric inversions are the most common changes observed; and these have been used in the construction of phylogenetic trees; the repleta group where the relationships among 46 species have been determined, is used as an example of such a study. Errors in the construction of the phyletic lines resulting from observational mistakes, cytological parallelism, cytological convergence and the segregation of independent inversions are discussed. Experimental work on naturally occurring paracentric inversions indicates that the selective values of these rearrangements appear not to be correlated with their actual breakage points, but are determined by the genetic material tied together by the action of the inversion as a suppressor of recombination. The genetic content of a rearrangement varies from locality to locality: each inversion, per se, therefore, has no definable adaptive value. Survival of a newly arisen inversion is dependent upon its fortuitous occurrence in a chromosomal region which is preadapted for a recombinant suppressor, that is, the region contains cooperating loci, among which recombination would be disadvantageous. Moreover, given the conditions for preadaptation, any one of a large number of distinguishable rearrangements could equally serve the purpose. In the repleta group, only about 144 inversions have survived during the history of the 46 species studied, indicating a very low incidence of such preadaptation in this species group. In view of the above, it is felt that the occurrence and survival of a pair of indistinguishable inversions in two phyletic lines, although possible, is highly unlikely. The probability of cytological parallel or convergent evolution involving two or more indistinguishable pairs of inversions in two phyletic lines can be considered zero. Phylogenies, therefore, based on inversional changes have an exceedingly high degree of accuracy. Phylogenetic relationships among the repleta group species are shown and their evolution is briefly discussed.