35,519 research outputs found

    Two new charismatic Pristimantis species (Anura: Craugastoridae) from the tepuis of “The Lost World” (Pantepui region, South America)

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    Two new colourful species of direct-developing frogs of the genus Pristimantis are described from the summit of two isolated tepuis (sandstone table mountains) in the Eastern Pantepui District of the Guiana Shield highlands. Pristimantis jamescameroni sp. nov. is described from the summit of Aprada-tepui from 2557-2571 m elevation, and P. imthurni sp. nov. is described from the summit of Ptaritepui at 2471 m elevation. Both species share the absence of a differentiated tympanic membrane and external tympanic annulus (but presence of tiny pharyngeal ostia), the presence of nuptial pads in males, and the presence of lateral fringes on fingers and toes, a combination of characters that immediately distinguishes them from all other known Pantepui congeners. The two new species are morphologically similar to each other and are phylogenetically closely related, but they can be distinguished based on colour pattern and morphological characters such as head proportions, dorsal skin texture, and condition of the supratympanic fold. The IUCN conservation status of the new species is considered as Endangered (EN) owing to their apparent very restricted ranges. The number of described Pristimantis species occurring exclusively on tepui (and faunistically related granitic mountains) summits and upper slopes now reaches eleven

    Proof of a Conjectured Three-Valued Family of Weil Sums of Binomials

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    We consider Weil sums of binomials of the form WF,d(a)=xFψ(xdax)W_{F,d}(a)=\sum_{x \in F} \psi(x^d-a x), where FF is a finite field, ψ ⁣:FC\psi\colon F\to {\mathbb C} is the canonical additive character, gcd(d,F×)=1\gcd(d,|F^\times|)=1, and aF×a \in F^\times. If we fix FF and dd and examine the values of WF,d(a)W_{F,d}(a) as aa runs through F×F^\times, we always obtain at least three distinct values unless dd is degenerate (a power of the characteristic of FF modulo F×|F^\times|). Choices of FF and dd for which we obtain only three values are quite rare and desirable in a wide variety of applications. We show that if FF is a field of order 3n3^n with nn odd, and d=3r+2d=3^r+2 with 4r1(modn)4 r \equiv 1 \pmod{n}, then WF,d(a)W_{F,d}(a) assumes only the three values 00 and ±3(n+1)/2\pm 3^{(n+1)/2}. This proves the 2001 conjecture of Dobbertin, Helleseth, Kumar, and Martinsen. The proof employs diverse methods involving trilinear forms, counting points on curves via multiplicative character sums, divisibility properties of Gauss sums, and graph theory.Comment: 19 page

    The Control of Dynamical Systems - Recovering Order from Chaos -

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    Following a brief historical introduction of the notions of chaos in dynamical systems, we will present recent developments that attempt to profit from the rich structure and complexity of the chaotic dynamics. In particular, we will demonstrate the ability to control chaos in realistic complex environments. Several applications will serve to illustrate the theory and to highlight its advantages and weaknesses. The presentation will end with a survey of possible generalizations and extensions of the basic formalism as well as a discussion of applications outside the field of the physical sciences. Future research avenues in this rapidly growing field will also be addressed.Comment: 18 pages, 9 figures. Invited Talk at the XXIth International Conference on the Physics of Electronic and Atomic Collisions (ICPEAC), July 22-27, 1999 (Sendai, Japan

    Heavy-Quarkonium Production in High Energy Proton-Proton Collisions at RHIC

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    We update the study of the total Psi and Upsilon production cross section in proton-proton collisions at RHIC energies using the QCD-based Color-Singlet (CS) Model, including next-to-leading order partonic matrix elements. We also include charm-quark initiated processes which appear at leading order in alpha_s, but which have so far been overlooked in such studies. Contrary to earlier claims, we show that the CS yield is consistent with measurements over a broad range of J/Psi rapidities. We also find that charm-quark initiated processes, including both intrinsic and sea-like charm components, typically contribute at least 20% of the direct J/Psi yield, improving the agreement with data both for the integrated cross section and its rapidity dependence. The key signature for such processes is the observation of a charm-quark jet opposite in azimuthal angle phi to the detected J/Psi. Our results have impact on the proper interpretation of heavy-quarkonium production in heavy-ion collisions and its use as a probe for the quark-gluon plasma.Comment: 5 pages, 11 figures, LaTeX, version to appear as a Rapid Communication in Phys. Rev.

    Analysis of video sequences: table of content and index creation

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    This paper deals with the representation of video sequences useful for tasks such as long-term analysis, indexing or browsing. A Table Of Content and index creation algorithm is presented, as well as additional tools involved in their creation. The proposed method does not assume any a priori knowledge about the content or the structure of the video. It is therefore a generic technique. Some examples are presented in order to assess the performance of the algorithmPeer ReviewedPostprint (published version

    Nano-structures at martensite macrotwin interfaces in Ni65Al35Ni_{65}Al_{35}

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    The atomic configurations at macrotwin interfaces between microtwinned martensite plates in Ni65Al35Ni_{65}Al_{35} material are investigated using transmission electron microscopy. The observed structures are interpreted in view of possible formation mechanisms for these interfaces. A distinction is made between cases in which the microtwins, originating from mutually perpendicular \{110\} austenite planes, enclose a final angle larger or smaller than 9090^{\circ}. Two different configurations, a crossing and a step type are described. Depending on the actual case, tapering, bending and tip splitting of the smaller microtwin variants are observed. The most reproducible deformations occur in a region of approximately 5-10nm width around the interface while a variety of structural defects are observed further away from the interface. These structures and deformations are interpreted in terms of the coalescence of two separately nucleated microtwinned martensite plates and the need to accommodate remaining stresses