A Sub-cellular Localization of the Gene Product of the DNase-1 Locus in Drosophila melanogaster

A study was undertaken to determine the subcellular location of DNase-I, a major acid deoxyribonuclease in Drosophila melanogaster. Embryonic tissue used in these experiments was derived from a wild type strain and from a strain homozygous at the DNase-l locus (3-61.8) for the null activity allele, DNase-lnl24. The majority of total acid DNase and DNase-l activity is found in the small particulate fraction of tissue homogenates fractionated by differential centrifugation. The activity exhibits latency in these extracts indicating that it is membrane delimited. DNase-I activity also co-equilibrates in sucrose density gradients with acid phosphatase activity which, in D. melanogaster, is known to be lysosomal. These results suggest that DNase-l is localized largely within the Iysosomes of embryonic tissue. Functional implications of a lysosomal location for DNase-l are discussed

A Generic Surface Sampler for Monte Carlo Simulations

We present an implementation of a Monte Carlo algorithm that generates points randomly and uniformly on a set of arbitrary surfaces. The algorithm is completely general and only requires the geometry modeling software to provide the intersection points of an arbitrary line with the surface being sampled. We demonstrate the algorithm using the Geant4 Monte Carlo simulation toolkit. The efficiency of the sampling algorithm is discussed, along with various options in the implementation and example applications

Validation of spallation neutron production and propagation within Geant4

Using simulations to understand backgrounds from muon-induced neutrons is important in designing next-generation low-background underground experiments. Validation of relevant physics within the Geant4 simulation package has been completed by comparing to data from two recent experiments. Verification focused on the production and propagation of neutrons at energies important to underground experiments. Discrepancies were observed between experimental data and the simulation. Techniques were explored to correct for these discrepancies.Comment: 12 pages, 6 figures, 5 tables, submitted to NIM A. 6 Aug 200

Predicting dissolution patterns in variable aperture fractures: 1. Development and evaluation of an enhanced depth-averaged computational model

Water-rock interactions within variable-aperture fractures can lead to dissolution of fracture surfaces and local alteration of fracture apertures, potentially transforming the transport properties of the fracture over time. Because fractures often provide dominant pathways for subsurface flow and transport, developing models that effectively quantify the role of dissolution on changing transport properties over a range of scales is critical to understanding potential impacts of natural and anthropogenic processes. Dissolution of fracture surfaces is controlled by surface-reaction kinetics and transport of reactants and products to and from the fracture surfaces. We present development and evaluation of a depth-averaged model of fracture flow and reactive transport that explicitly calculates local dissolution-induced alterations in fracture apertures. The model incorporates an effective mass transfer relationship that implicitly represents the transition from reaction-limited dissolution to transport-limited dissolution. We evaluate the model through direct comparison to previously reported physical experiments in transparent analog fractures fabricated by mating an inert, transparent rough surface with a smooth single crystal of potassium dihydrogen phosphate (KDP), which allowed direct measurement of fracture aperture during dissolution experiments using well-established light transmission techniques [Detwiler, et al., 2003]. Comparison of experiments and simulations at different flow rates demonstrate the relative impact of the dimensionless Peclet and Damkohler numbers on fracture dissolution and the ability of the computational model to simulate dissolution. Despite some discrepancies in the small-scale details of dissolution patterns, the simulations predict the evolution of large-scale features quite well for the different experimental conditions. This suggests that our depth-averaged approach to simulating fracture dissolution provides a useful approach for extending laboratory results that are often limited in scale to scales that are more representative of geologic processes of interest

Influence of the disorder on tracer dispersion in a flow channel

Tracer dispersion is studied experimentally in periodic or disordered arrays of beads in a capillary tube. Dispersion is measured from light absorption variations near the outlet following a steplike injection of dye at the inlet. Visualizations using dye and pure glycerol are also performed in similar geometries. Taylor dispersion is dominant both in an empty tube and for a periodic array of beads: the dispersivity $l\_d$ increases with the P\'eclet number $Pe$ respectively as $Pe$ and $Pe^{0.82}$ and is larger by a factor of 8 in the second case. In a disordered packing of smaller beads (1/3 of the tube diameter) geometrical dispersion associated to the disorder of the flow field is dominant with a constant value of $l\_d$ reached at high P\'eclet numbers. The minimum dispersivity is slightly higher than in homogeneous nonconsolidated packings of small grains, likely due heterogeneities resulting from wall effects. In a disordered packing with the same beads as in the periodic configuration, $l\_d$ is up to 20 times lower than in the latter and varies as $Pe^\alpha$ with $\alpha = 0.5$ or $= 0.69$ (depending on the fluid viscosity). A simple model accounting for this latter result is suggested.Comment: available online at http://www.edpsciences.org/journal/index.cfm?edpsname=epjap&niv1=contents&niv2=archive

The Paluxy River Footprints Revisited

Field research by the authors at various times between 1982 and 1989 helped expose some of the elongate impressions imbedded in alleged 108 million year old Cretaceous ledges along the Paluxy River near Glen Rose, Texas. These human-like footprints were exposed in the same horizon with theropod dinosaur ichnites, as have prints in river itself over the decades, as reported by the local residents (I, 2). In order to thoroughly document such significant discoveries, several excavations were initiated since the 1986 ICC proceedings in the search for pristine ichnites. The results of these excavations plus the observable results of many previous excavations and the aspect ratio studies of many of the footprints strongly support the hypothesis that humans and dinosaurs coexisted. Furthermore, when radiocarbon dating results are combined with the paleoanthropological studies, the most logical conclusions are that: dinosaur extinction 65 million years ago is a myth; the long ages for sedimentary rock strata formation are non-existent; dinosaur extinction could have been caused by a major worldwide catastrophe happening perhaps only thousands of years ago