Circular Counterpart Research Articles

Isolating Apparently Pure Libraries of Replication Origins from Complex Genomes

Because of the complexity of higher eukaryotic genomes and the lack of a reliable autonomously replicating sequence (ARS) assay for isolating potential replicators, the identification of origins has proven to be extremely challenging and time consuming. We have developed a new origin-trapping method based on the partially circular nature of restriction fragments containing replication bubbles and have prepared a library of approximately 1,000 clones from early S phase CHO cells. When 15 randomly selected clones were analyzed by a stringent two-dimensional (2D) gel replicon mapping method, all were shown to correspond to active, early firing origins. Furthermore, most of these appear to derive from broad zones of potential sites, and the five that were analyzed in a time-course study are all inefficient. This bubble-trapping scheme will allow the construction of comprehensive origin libraries from any complex genome so that their natures and distributions vis-a-vis other chromosomal markers can be established.

Gas avalanche pixel detectors with amorphous silicon carbide (a-Si:C:H) overcoating

The performance of gas avalanche pixel detectors of square and circular geometry, with and without semiconducting surface coating, was characterized in terms of gas gain and active region. Although the electric field profile of the square geometry cannot be radially uniform, a 200 /spl mu/m pitch detector of this type exhibited a maximum gain of /spl sim/12000 which is comparable to that of the circular counterpart. Due to the existence of the anode bus lines passing under the cathodes, there is a defocusing effect of the drift field lines converging to the anodes, resulting in inactive regions where electrons produced from gas ionization are not collected at the anodes. Variation of the count rate with the drift field was measured to probe these defocusing effects. The p-type a-Si:C:H surface coating was effective in reducing these inactive regions.

Coupled Planar Helices

Properties of a system of coupled planar helices are investigated. A set of transmission line equations are derived for the coupled system. From these transmission line equations, a dispersion relation is obtained. The computed results for the planar helix couplers indicate that its performance is comparable with that of its circular helix counterpart and hence it can be used to couple in and out of a planar helix slow wake structure.

Study of planar-helix slow-Wave structure for application to travelling-wave tubes

A planar helix, constituted of a pair of unidirectionally conducting screens conducting in different directions, is suggested as a slow-wave structure for application in a travelling-wave tube (TWT). Circuit parameters, such as interaction impedance and space-charge parameter, are derived for the suggested planar-helix TWT. Computed results for the planar helix indicate a performance comparable with that of its circular helix counterpart. Also, the change in interaction impedance and the dispersion characteristics of the planar helix, are considered in the presence of dielectric substrates and a metal shield. Results are obtained for a few different possible configurations of the planar helix on dielectric substrates with or without a metal shield. The phase velocity and interaction impedance reduce, both as the substrate thickness increases and as the metal shields are brought closer to the planar helix. However, the resulting degradation in the characteristics of the structure with commonly used substrate materials, for example alumina and beryllia, is less severe than in the case of the circular helix.

An Approximate Distribution of a Noncircular Serial Correlation Coefficient

The paper applies a smoothing technique to obtain an approximate sampling distribution of a noncircular serial correlation coefficient. This technique is similar to the one employed by Koopmans and Dixon for finding the circular counterpart and thus provides an immediate comparison with that of the circularly denned coefficient. In fact, it is shown that the latter is a special case of the present result which is obtained in a generalized Leipnik's form with a correction factor to account for noncircularity. Also, the equivalence of this method of smoothing with the saddle point technique adopted by Daniels is demonstrated.

An approximate distribution of a noncircular serial correlation coefficient

SUMMARY The paper applies a smoothing technique to obtain an approximate sampling distribution of a noncircular serial correlation coefficient. This technique is similar to the one employed by Koopmans and Dixon for finding the circular counterpart and thus provides an immediate comparison with that of the circularly defined coefficient. In fact, it is shown that the latter is a special case of the present result which is obtained in a generalized Leipnik's form with a correction factor to account for noncircularity. Also, the equivalence of this method of smoothing with the saddle point technique adopted by Daniels is demonstrated. The need for an inquiry into the sampling distribution of a serial correlation coefficient, r, requires no special emphasis; for example, econometric applications of time series data make the need immediate and obvious. Tractability for these distributions is achieved by a number of ingenious devices. One is to assume a circular definition for r. Other equally elegant manipulations are described by Durbin & Watson (1950, 1951). While the circular definition helps to provide an exact distribution, it suffers from the possibility of becoming too distant from reality when, for instance, the length of the sample series is as small as often happens with economic variables or has to be kept so for the risk of running into incomparability due to changes in the underlying structure. At the same time, as Koopmans (1942) has shown, the exact distribution of a noncircular r involves hyperelliptic integrals. The method of Koopmans and those of others for the noncircular serial correlation coefficient are briefly surveyed for the null case in a recent paper by Durbin & Watson (1971, Appendix 1). The practical computation of the exact probabilities of the distribution of a noncircular r to any desired degree of accuracy has become possible by the methods of Imhof (1961) and Pan Jie-Jian (1968) coupled with the present day electronic computer facilities. Given the distribution function F(ro) = pr (r < ro),