Geomorphology, sediment analysis and restoration plan for an incised urban creek : Don Dahvee Creek, Monterey, California

The progression of urbanization throughout the state of California has had overwhelming and long-term effects on the state\u27s waterways. Don Dahvee Creek appears to be physically declining because of active channel erosion due to urbanization. This erosion has affected the amount of sediment being conveyed into Lake El Estero and the Monterey Bay. For this assessment the geometry of Don Dahvee Creek, adjacent to Whole Foods Market in Monterey, CA, was examined to determine rates of erosion. Suspended sediment concentration samples (SSC) were taken in an attempt to determine if the creek is a source of water pollution due to bank erosion, creating excess sediment downstream. Using a regression model of SSC it was found that there is no significant difference between the amount of sediment in the water entering and leaving the stream reach, during low-flow conditions. The P-values from the regression of SSC against distance downstream are much greater than .01; therefore, we fail to reject the null hypothesis at 99% confidence, leading to our conclusion that the stream banks are not generating sediment during low-flow conditions. A budget analysis used for discharge determined that there is a loss of 1/3 the water between the upper and lower culvert during low-flow conditions, possibly due to infiltration. Using cross sectional data it has been determined that the best restoration plan for Don Dahvee Creek involves dressing back and stabilizing both the bed and banks with a combination of vegetation and rock, increasing the width/depth and entrenchment ratio

Monte Carlo Calculations of the Extraction of Scintillation Light from Cryogenic N-type GaAs

The high scintillation luminosity of n-type GaAs at 10K is surprising because (1) with a refractive index of about 3.5, escape is inhibited by total internal reflection and (2) narrow-beam experiments at 90K report infrared absorption coefficients of several per cm. This paper presents Monte Carlo calculations showing that the high luminosity at 10K can be explained if (1) narrow-beam absorption is almost all optical scattering and (2) the absolute absorption coefficient is below 0.1 per cm. Sixteen surface reflector configurations are simulated for a range of internal scattering and absolute absorption coefficients, and these can guide the design of cryogenic scintillating GaAs targets for the direct detection of dark matter. The discussion section presents a possible infrared scattering mechanism based on the metallic nature of n-type GaAs. Appendix A describes the Monte Carlo program steps in detail. Appendix B shows how narrow-beam and integrating sphere experiments can measure the cryogenic optical scattering and absolute absorption coefficients.Comment: 12 pages, 7 tables, 2 Appendices. Submitted to Nuclear Instruments and Methods

Stem Cell Tourism: The Challenge and Promise of International Regulation of Embryonic Stem Cell-Based Therapies

Note of the Yea

Direct Detection of sub-GeV Dark Matter with Scintillating Targets

We describe a novel search for MeV-to-GeV-mass dark matter, in which the dark matter scatters off electrons in a scintillating target. The excitation and subsequent de-excitation of the electron produces one or more photons, which could be detected with an array of cryogenic low-noise photodetectors, such as transition edge sensors (TES) or microwave kinetic inductance devices (MKID). Scintillators may have distinct advantages over other experiments searching for a low ionization signal from sub-GeV DM. First, the detection of one or a few photons may be technologically easier. Second, since no electric field is required to detect the photons, there may be far fewer dark counts mimicking a DM signal. We discuss various target choices, but focus on calculating the expected dark matter-electron scattering rates in three scintillating crystals, sodium iodide (NaI), cesium iodide (CsI), and gallium arsenide (GaAs). Among these, GaAs has the lowest band gap (1.52 eV) compared to NaI (5.9 eV) or CsI (6.4 eV), allowing it to probe dark matter masses possibly as low as ~0.5 MeV, compared to ~1.5 MeV with NaI or CsI. We compare these scattering rates with those expected in silicon (Si) and germanium (Ge). The proposed experimental concept presents an important complementary path to existing efforts, and its potential advantages may make it the most sensitive direct-detection probe of DM down to MeV masses.Comment: 5 pages + 8 pages of supplementary materials & references, 5 figures, 3 table