Multifractal Analysis of Packed Swiss Cheese Cosmologies

The multifractal spectrum of various three-dimensional representations of Packed Swiss Cheese cosmologies in open, closed, and flat spaces are measured, and it is determined that the curvature of the space does not alter the associated fractal structure. These results are compared to observational data and simulated models of large scale galaxy clustering, to assess the viability of the PSC as a candidate for such structure formation. It is found that the PSC dimension spectra do not match those of observation, and possible solutions to this discrepancy are offered, including accounting for potential luminosity biasing effects. Various random and uniform sets are also analyzed to provide insight into the meaning of the multifractal spectrum as it relates to the observed scaling behaviors.Comment: 3 latex files, 18 ps figure

The Improvement of Efficiency in the Numerical Computation of Orbit Trajectories

An analysis, system design, programming, and evaluation of results are described for numerical computation of orbit trajectories. Evaluation of generalized methods, interaction of different formulations for satellite motion, transformation of equations of motion and integrator loads, and development of efficient integrators are also considered

Flame Instability and Transition to Detonation in Supersonic Reactive Flows

Multidimensional numerical simulations of a homogeneous, chemically reactive gas were used to study ignition, flame stability, and deflagration-to-detonation transition (DDT) in a supersonic combustor. The configuration studied was a rectangular channel with a supersonic inflow of stoichiometric ethylene-oxygen and a transimissive outflow boundary. The calculation is initialized with a velocity in the computational domain equal to that of the inflow, which is held constant for the duration of the calculation. The compressible reactive Navier-Stokes equations were solved by a high-order numerical algorithm on an adapting mesh. This paper describes two calculations, one with a Mach 3 inflow and one with Mach 5.25. In the Mach 3 case, the fuel-oxidizer mixture does not ignite and the flow reaches a steady-state oblique shock train structure. In the Mach 5.25 case, ignition occurs in the boundary layers and the flame front becomes unstable due to a Rayleigh-Taylor instability at the interface between the burned and unburned gas. Growth of the reaction front and expansion of the burned gas compress and preheat the unburned gas. DDT occurs in several locations, initiating both at the flame front and in the unburned gas, due to an energy-focusing mechanism. The growth of the flame instability that leads to DDT is analyzed using the Atwood number parameter

Character Sequence Models for ColorfulWords

We present a neural network architecture to predict a point in color space from the sequence of characters in the color's name. Using large scale color--name pairs obtained from an online color design forum, we evaluate our model on a "color Turing test" and find that, given a name, the colors predicted by our model are preferred by annotators to color names created by humans. Our datasets and demo system are available online at colorlab.us

Neutron detector simultaneously measures fluence and dose equivalent

Neutron detector acts as both an area monitoring instrument and a criticality dosimeter by simultaneously measuring dose equivalent and fluence. The fluence is determined by activation of six foils one inch below the surface of the moderator. Dose equivalent is determined from activation of three interlocked foils at the center of the moderator

Nano and Micro indentation studies of bulk zirconia and EB PVD TBCs

In order to model the erosion of a material it is necessary to know the material properties of both the impacting particles as well as the target. In the case of electron beam (EB) physical vapour deposited(PVD) thermal barrier coatings (TBCs) the properties of the columns as opposed to the coating as a whole are important. This is due to the fact that discrete erosion events are on a similar scale as the size of the individual columns. Thus nano* and micro* indentation were used to determine the hardness and the Young"s modulus of the columns. However, care had to be taken to ensure that it was the hardness of the columns that was being measured and not the coating as a whole. This paper discusses the differences in the results obtained when using the two different tests and relates them to the interactions between the indent and the columns of the EB PVD TBC microstructure. It was found that individual columns had a hardness of 14 GPa measured using nano indentation, while the hardness of the coating, using micro indentation decreased from 13 to 2.4 GPa as the indentation load increased from 0.1 to 3N. This decrease in hardness was attributed to the interaction between the indenter and a number of adjacent columns and the ability of the columns to move laterally under indentation

Phenotypic Plasticity May Facilitate Invasion by Aegilops triuncialis

One great obstacle to understanding the invasion of nonnative species into native ecosystems is the lack of information on the population biology of the invading species. In particular, morphological and physiological adaptations and potential for phenotypic plasticity will strongly influence a species’ ability to persist and spread in newly invaded ecosystems. Phenotypic plasticity can buffer populations from selection thereby allowing them to survive the establishment phase of the invasion. The annual grass Aegilops triuncialis (Poaceae, Triticeae) has become highly invasive in California (USA) and provides an opportunity to investigate the importance of phenotypic plasticity to persistence and spread in new habitats. This species produces dispersal units containing dimorphic caryopses (‘‘seeds’’) with different degrees of dormancy. Germination of the smaller seeds is suppressed by maternal tissues and by the larger sibling, but how this induced dormancy varies across populations is unknown. I used 12 populations from northern California to compare size relationships between seeds and to investigate variation in the strength of the maternal and sibling effects on germination. The larger seeds were never dormant while induced dormancy of the smaller seeds varied across populations and years. Thus, the factors governing induced dormancy were not genetically fixed, but appeared to be environmentally influenced. For A. triuncialis, reproductive strategies, such as seed-size dimorphism, may facilitate initial invasions into new environments, but variation in the strength of controls over germination may be important for facilitating post-invasion persistence and spread