An investigation of the compressive strength of PRD-49-3/Epoxy composites

The development of unidirectional fiber composite materials is discussed. The mechanical and physical properties of the materials are described. Emphasis is placed in analyzing the compressive behavior of composite materials and developing methods for increasing compressive strength. The test program for evaluating the various procedures for improving compressive strength are reported

Emulating a flexible space structure: Modeling

Control Dynamics, in conjunction with Marshall Space Flight Center, has participated in the modeling and testing of Flexible Space Structures. Through the series of configurations tested and the many techniques used for collecting, analyzing, and modeling the data, many valuable insights have been gained and important lessons learned. This paper discusses the background of the Large Space Structure program, Control Dynamics' involvement in testing and modeling of the configurations (especially the Active Control Technique Evaluation for Spacecraft (ACES) configuration), the results from these two processes, and insights gained from this work

Disproportionation and electronic phase separation in parent manganite LaMnO_3

Nominally pure undoped parent manganite LaMnO_3 exhibits a puzzling behavior inconsistent with a simple picture of an A-type antiferromagnetic insulator (A-AFI) with a cooperative Jahn-Teller ordering. We do assign its anomalous properties to charge transfer instabilities and competition between insulating A-AFI phase and metallic-like dynamically disproportionated phase formally separated by a first-order phase transition at T_{disp}=T_{JT}\approx 750 K. The unconventional high-temperature phase is addressed to be a specific electron-hole Bose liquid (EHBL) rather than a simple "chemically" disproportionated R(Mn^{2+}Mn^{4+})O_3 phase. New phase does nucleate as a result of the charge transfer (CT) instability and evolves from the self-trapped CT excitons, or specific EH-dimers, which seem to be a precursor of both insulating and metallic-like ferromagnetic phases observed in manganites. We arrive at highly frustrated system of triplet (e_g^2)^3A_{2g} bosons moving in a lattice formed by hole Mn^{4+} centers. Starting with different experimental data we have reproduced a typical temperature dependence of the volume fraction of high-temperature mixed-valent EHBL phase. We argue that a slight nonisovalent substitution, photo-irradiation, external pressure or magnetic field gives rise to an electronic phase separation with a nucleation or an overgrowth of EH-droplets. Such a scenario provides a comprehensive explanation of numerous puzzling properties observed in parent and nonisovalently doped manganite LaMnO_3 including an intriguing manifestation of superconducting fluctuations.Comment: 20 pages, 8 figure

Random wave functions and percolation

Recently it was conjectured that nodal domains of random wave functions are adequately described by critical percolation theory. In this paper we strengthen this conjecture in two respects. First, we show that, though wave function correlations decay slowly, a careful use of Harris' criterion confirms that these correlations are unessential and nodal domains of random wave functions belong to the same universality class as non critical percolation. Second, we argue that level domains of random wave functions are described by the non-critical percolation model.Comment: 13 page

Oidiodendron: A survey of the named species and related anamorphs of Myxotrichum

AbstractSynoptic and dichotomous keys to 23 species of Oidiodendron and similar arthroconidial anamorphs of Myxotrichum were developed using morphological and physiological characters. Illustrations and brief descriptions based on living isolates and published descriptions are provided for all species treated. Included are the unnamed Oidiodendron states of Myxotrichum arcticum, M. cancellatum, M. emodense, M. setosum, and M. striatosporum, as well as the anamorphic species O. ambiguum, O. cerealis, O. chlamydosporicum (inclusive of O. scytaloides as a synonym), O. echinulatum, O. fimicola, O. flavum, O. fuscum, O. griseum, O. hughesii (inclusive of O. reticulatum as a synonym), O. maius (inclusive of O. maius var. citrinum and O. maius var. maius), O. muniellense, O. myxotrichoides, O. periconioides, O. pilicola, O. rhodogenum, O. setiferum (inclusive of O. ramosum as a synonym), O. tenuissimum, and O. truncatum. Oidiodendron fuscum, the original type species, is recognized as distinct. Oidiodendron robustum is excluded because of its large conidia and conidiophores and because the original drawings do not convincingly portray arthroconidia. Oidiodendron terrestre is excluded because its large, two-celled conidia, rapid growth, and hyaline conidiophores are inconsistent with the generic diagnosis and because the mode of its conidiogenesis is unclear from the original descriptions and illustrations.Taxonomic novelties: Oidiodendron maius var. citrinum (Barron) Rice & Currah stat. nov

The Statistics of the Points Where Nodal Lines Intersect a Reference Curve

We study the intersection points of a fixed planar curve $\Gamma$ with the nodal set of a translationally invariant and isotropic Gaussian random field \Psi(\bi{r}) and the zeros of its normal derivative across the curve. The intersection points form a discrete random process which is the object of this study. The field probability distribution function is completely specified by the correlation G(|\bi{r}-\bi{r}'|) = . Given an arbitrary G(|\bi{r}-\bi{r}'|), we compute the two point correlation function of the point process on the line, and derive other statistical measures (repulsion, rigidity) which characterize the short and long range correlations of the intersection points. We use these statistical measures to quantitatively characterize the complex patterns displayed by various kinds of nodal networks. We apply these statistics in particular to nodal patterns of random waves and of eigenfunctions of chaotic billiards. Of special interest is the observation that for monochromatic random waves, the number variance of the intersections with long straight segments grows like $L \ln L$, as opposed to the linear growth predicted by the percolation model, which was successfully used to predict other long range nodal properties of that field.Comment: 33 pages, 13 figures, 1 tabl

Dynamic interference of photoelectrons produced by high-frequency laser pulses

The ionization of an atom by a high-frequency intense laser pulse, where the energy of a single-photon is sufficient to ionize the system, is investigated from first principles. It is shown that as a consequence of an AC Stark effect in the continuum, the energy of the photoelectron follows the envelope of the laser pulse. This is demonstrated to result in strong dynamic interference of the photoelectrons of the same kinetic energy emitted at different times. Numerically exact computations on the hydrogen atom demonstrate that the dynamic interference spectacularly modifies the photoionization process and is prominently manifested in the photoelectron spectrum by the appearance of a distinct multi-peak pattern. The general theory is shown to be well approximated by explicit analytical expressions which allow for a transparent understanding of the discovered phenomena and for making predictions on the dependence of the measured spectrum on the properties of the pulse.Comment: 5 figure

Anisotropic superexchange of a 90 degree Cu-O-Cu bond

The magnetic anisotropy af a rectangular Cu-O-Cu bond is investigated in second order of the spin-orbit interaction. Such a bond is characteristic for cuprates having edge sharing CuO_2 chains, and exists also in the Cu_3O_4 plane or in ladder compounds. For a ferromagnetic coupling between the copper spins an easy axis is found perpendicular to the copper oxygen plaquettes in agreement with the experimental spin structure of Li_2CuO_2. In addition, a pseudo-dipolar interaction is derived. Its estimation in the case of the Cu_3O_4 plane (which is present for instance in Ba_2Cu_3O_4Cl_2 or Sr_2Cu_3O_4Cl_2) gives a value which is however two orders of magnitude smaller than the usual dipole-dipole interaction.Comment: 6 pages, 2 figures, improved referenc