Combination of Raman, Infrared, and X-Ray Energy-Dispersion Spectroscopies and X-Ray Diffraction to Study a Fossilization Process

X-ray diffraction was combined with X-ray energy-dispersion, Fourier-transform infrared, and Raman spectroscopies to study the fossilization of a Cretaceous specimen of the plant Brachyphyllum castilhoi, a fossil from the Ipubi Formation, in the Araripe Sedimentary Basin, Northeastern Brazil. Among the possible fossilization processes, which could involve pyrite, silicon oxide, calcium oxide, or other minerals, we were able to single out pyritization as the central mechanism producing the fossil, more than 100 million years ago. In addition to expanding the knowledge of the Ipubi Formation, this study shows that, when combined with other experimental techniques, Raman spectroscopy is a valuable tool at the paleontologist’s disposal.     

Statistical approaches for investigating silk properties

Amino acid repeats or motifs have engendered interest because of their significance for protein physical characteristics as well as folding properties. Spider dragline silk proteins are unique because they are composed of long repetitive sections and relatively short non-repetitive sections that are known to interact to generate the very peculiar mechanical and solubility properties of silk. Computational analysis compared with in vitro measurements suggest that the silks achieve their unique pattern of extreme solubility inside the spider glands/complete insolubility outside by correlating their repetitive hydrophobic regions through a type of stochastic resonance, generated by the addition of the non-repetitive sequences to a basically periodic hydrophobicity pattern. PACS 87.14.Ee; 87.15.Cc; 87.15.He; 02.50.Ey; 05.40.Ca     

Measurement of the p to s wave branching ratio of 187Re beta decay from beta environmental fine structure

The mixed occurrence of s-wave and p-wave contributions in a first forbidden unique Gamow-Teller beta decay has been investigated for the first time by measuring the beta environmental fine structure (BEFS) in a 187Re crystalline compound. The experiment has been carried out with an array of eight AgReO4 thermal detectors operating at a temperature of approximately 100 mK. A fit of the observed BEFS spectrum indicates the p-wave electron emission as the dominant channel. The complete understanding of the BEFS distortion of the 187Re beta decay spectrum is crucial for future experiments aiming at the precise calorimetric measurement of the antineutrino mass.     

Robust discretizations versus increase of the time step for the Lorenz system

When continuous systems are discretized, their solutions depend on the time step chosen a priori. Such solutions are not necessarily spurious in the sense that they can still correspond to a solution of the differential equations but with a displacement in the parameter space. Consequently, it is of great interest to obtain discrete equations which are robust even when the discretization time step is large. In this paper, different discretizations of the Lorenz system are discussed versus the values of the discretization time step. It is shown that the sets of difference equations proposed are more robust versus increases of the time step than conventional discretizations built with standard schemes such as the forward Euler, backward Euler, or centered finite difference schemes. The nonstandard schemes used here are Mickens' scheme and Monaco and Normand-Cyrot's scheme.     

The rectum of Oxaea flavescens (Andrenidae) has a specialized structure among bees

The rectum of the bee Oxaea flavescens contains six hollow rectal papillae, in contrast to rectal pads found in others Hymenoptera. The rectal epithelium is formed by cubical cells with structural specializations for fluid transport, such as apical plasma membrane invaginations, endocytic vesicles, scalariform junctions, wide extracellular space and double-membrane vesicles. Globular-shaped cells form the rectal papillae with surface plasma membrane invaginations that vary from small depressions to very large sinuses. The cell-cell contact is narrow, exhibiting extensive regions with scalariform junction, while cytoplasmic free ribosome-like material is prominent. These ultrastructural features are discussed in relation to their role in excretion in this bee.     

The algebra of differential operators on the circle and W KP (q)

Radul has recently introduced a map from the Lie algebra of differential operators on the circle of W _n . In this Letter, we extend this map to W _KP ^(q) , a recently introduced one-parameter deformation of W_KP - the second Hamiltonian structure of the KP hierarchy. We use this to give a short proof that W is the algebra of additional symmetries of the KP equation.     

Limited path percolation in complex networks

We study the stability of network communication after removal of a fraction q=1-p of links under the assumption that communication is effective only if the shortest path between nodes i and j after removal is shorter than al(ij)(a> or =1) where l(ij) is the shortest path before removal. For a large class of networks, we find analytically and numerically a new percolation transition at p(c)=(kappa(0)-1)((1-a)/a), where kappa(0) [triple bond] / and k is the node degree. Above p(c), order N nodes can communicate within the limited path length al(ij), while below p(c), N(delta) (delta<1) nodes can communicate. We expect our results to influence network design, routing algorithms, and immunization strategies, where short paths are most relevant.     

Evolution of the correlation between orthogonal polarization patterns in broad-area lasers

We measure polarization-resolved instantaneous patterns in a large-aspect ratio quasi-isotropic Nd:YAG laser. High correlation between the instantaneous orthogonal polarization patterns recorded at the earlier stages of the laser pulse has been found due to the strong cross saturation between both polarization modes.     

Quantum nonintegrability and the classical limit for usp(4) systems

We investigate the transition from integrability to chaos in a system built of usp(4) elements, both in the quantum case and in its classical limit, obtained using coherent states. This algebraic Hamiltonian consists in an integrable term plus a nonlinear perturbation, and we see that the level spacing distribution for the quantum system is well approximated by the Berry-Robnik-Brody distribution, and accordingly the classical limit displays mixed dynamics.