Les polygones polytaxiques

Habituellement, un protopavé est dit m-morphique si des copies congruentes du protopavé pavent le plan d’exactement m faqons non congruentes. I1 existe des protopavés r-morphiques connus pour r 5 10. Ici, un protopavé est défini comme étant t-taxique si des copies directement congruentes du protopavé pavent le plan d’exactement t façons non directement congruentes; un protopavé est appelé p-poïque si des copies directement congruentes du protopavé pavent le plan d’exactement p façons non congruentes. De nombreux exemples sont fournis, dont des polyominos 7-poïques et un polyomino 8-taxique.It is customary to say aprototile is 2m-morphic if congruent copies of the prototile tile the plane in exactly m noncongruent ways. There are known r-morphic prototiles for r ≤ 10. A prototile is defined here to be t-taxic if directly congruent copies of the prototile tile the plane in exactly t not directly congruent ways; a prototile is called p-poic if directly congruent copies of the prototile tile the plane in exactly p noncongruent ways. Numerous examples are given, including 7-poic polyominoes and one 8-taxic polyomino.Peer Reviewe

Symmetric Gobos in a finite projective plane

AbstractA gobo G in any incidence structure K is a (perhaps degenerate) tactical configuration having the property that no three points in G are collinear and no three lines in G are concurrent. General results are obtained where K is a finite projective plane of order n and G has k points and k lines such that each point (line) lies on r lines (points) of G. Particular attention is called to the contrast between the case r = 1 and the case r ≠ 1 when k = n

Application of distributed lag and autocorrelated error models to short-run demand analysis

The objective of the research reported here was to investigate the usefulness of distributed lag economic models and autocorrelated error statistical models for analysis of monthly and quarterly food demand. Distributed lags are a way of incorporating dynamic considerations into econometric models of consumer demand. In the distributed lag model used here, current consumption is the dependent variable, and lagged consumption is one explanatory variable. Testing the significance of the coefficient of lagged consumption tests the hypothesis of a lag in consumer adjustment to conditions affecting demand. The presence of autocorrelated errors can have serious effects on least squares (L.S.) estimates of coefficients. Autocorrelated errors may frequently occur in equations fitted to monthly and quarterly data. Therefore, equations were estimated by autoregressive least squares (A.L.S.) as well as by least squares. A.L.S.-1 assumes the errors ut to follow a first order autoregressive scheme, ut = β1ut-1 + et. It provides simultaneous estimates of β1 and of the coefficients in the demand equation. A.L.S.-2 assumes the errors to be generated by a second order autoregressive process, ut = β1ut-1 + β2ut-2 + et. It provides simultaneous estimates of β1, β2 and the coefficients in the demand equation

Relativistic Precessing Jets and Cosmological Gamma Ray Bursts

We discuss the possibility that gamma-ray bursts may result from cosmological relativistic blob emitting neutron star jets that precess past the line of sight. Beaming reduces the energy requirements, so that the jet emission can last longer than the observed burst duration. One precession mode maintains a short duration time scale, while a second keeps the beam from returning to the line of sight, consistent with the paucity of repeaters. The long life of these objects reduces the number required for production as compared to short lived jets. Blobs can account for the time structure of the bursts. Here we focus largely on kinematic and time scale considerations of beaming, precession, and blobs--issues which are reasonably independent of the acceleration and jet collimation mechanisms. We do suggest that large amplitude electro-magnetic waves could be a source of blob acceleration.Comment: 15 pages, plain TeX, accepted to ApJ

Quantum theory of electric polarization nonlinearity in metal nanofilms

We develop a quantum theory of electron confinement in metal nanofilms. The theory is used to compute the nonlinear response of the film to a static or low-frequency external electric field and to investigate the role of boundary conditions imposed on the metal surface. We find that the sign and magnitude of the nonlinear polarizability depends dramatically on the type of boundary condition used.Comment: Accepted to PRB in this for

Visualization of ribosomal RNA operon copy number distribution

<p>Abstract</p> <p>Background</p> <p>Results of microbial ecology studies using 16S rRNA sequence information can be deceiving due to differences in rRNA operon copy number and genome size of the detected organisms. It therefore will be useful for investigators to have a better understanding of how these two parameters differ in various organism types. In this study, the number of ribosomal operons and genome size were separately mapped onto a Bacterial phylogenetic tree.</p> <p>Results</p> <p>A representative Bacterial tree was constructed using 31 marker genes found in 578 bacterial genome sequences. Organism names are displayed on the trees using graduations of color such that similar colors indicate similar numbers of operons or genome size. The resulting images provide an intuitive understanding of how copy number and genome size vary in different Bacterial phyla.</p> <p>Conclusion</p> <p>Once the phylogenetic position of a novel organism is known the number of rRNA operons, and to a lesser extent the genome size, can be estimated by examination of the colored maps. Further detail can then be obtained for members of relevant taxa from the rrnDB database.</p

EXTENSION EDUCATORS' SUPPLY OF RISK MANAGEMENT TRAINING TO FARMERS

A univariate Tobit model of extension educators' provision of risk management educational training was conducted in Mississippi, Texas, Indiana, and Nebraska. A complementary relationship exists between percent of time devoted to agricultural responsibilities and the provision of risk management training courses. The results indicate that, as extension educators perceive farmers to be more knowledgeable of risk management tools, their provision of risk management education decreases. On the other hand, the provision of risk management courses increase as extension educators perceive themselves as being more knowledgeable on the use of risk management tools.Teaching/Communication/Extension/Profession,