The temperature dependence of the response of 103a-0 and Tri-X at 4400 A

Temperature effects on 103a-0 and Tri-X photographic emulsion sensitivities at 4400

Precision determination of absolute neutron flux

A technique for establishing the total neutron rate of a highly-collimated monochromatic cold neutron beam was demonstrated using a method of an alpha-gamma counter. The method involves only the counting of measured rates and is independent of neutron cross sections, decay chain branching ratios, and neutron beam energy. For the measurement, a target of 10B-enriched boron carbide totally absorbed the neutrons in a monochromatic beam, and the rate of absorbed neutrons was determined by counting 478keV gamma rays from neutron capture on 10B with calibrated high-purity germanium detectors. A second measurement based on Bragg diffraction from a perfect silicon crystal was performed to determine the mean de Broglie wavelength of the beam to a precision of 0.024 %. With these measurements, the detection efficiency of a neutron monitor based on neutron absorption on 6Li was determined to an overall uncertainty of 0.058 %. We discuss the principle of the alpha-gamma method and present details of how the measurement was performed including the systematic effects. We also describe how this method may be used for applications in neutron dosimetry and metrology, fundamental neutron physics, and neutron cross section measurements.Comment: 44 page

Analysis of Factors Influencing Southeast Florida Coral Reef Community Composition

The southeast Florida reef system lies offshore a heavily populated and urbanized coast. These high latitude reefs are not only affected by their geography but also by anthropogenic factors that accompany an urban area such as dredging activities, ship groundings, waste water outfalls, runoff and beach erosion. Sedimentation has been shown to influence stony coral community composition including dominance, abundance, cover, diversity, and colony size. Using annual monitoring data collected since 2000, the southeastern Florida reef community is being analyzed to examine if and how sedimentation and other factors such as depth, distance from shore and distance from port channels might influence community composition. All data was collected by SCUBA divers conducting 30m2 belt transect surveys at 24 sites offshore Broward County (southeast), Florida within a depth range of 6 to 18 meters. Stony coral data included colony size, abundance, diversity, percent cover, and mortality. Sponge and octocoral density were collected to gather a more complete picture of community composition. Three sediment bottles at each annually monitored site were collected every 60 days. Weight and grain size of the contents were analyzed and used to determine sedimentation rates at each site. Additionally, the reefs off the southeast Florida coast can be categorized into unique habitat types. These habitat types are also being considered when studying reef community composition and its relationship to sedimentation and other factors

Global assessment of nitrogen deposition effects on terrestrial plant diversity : a synthesis

Atmospheric nitrogen (N) deposition is it recognized threat to plant diversity ill temperate and northern parts of Europe and North America. This paper assesses evidence from field experiments for N deposition effects and thresholds for terrestrial plant diversity protection across a latitudinal range of main categories of ecosystems. from arctic and boreal systems to tropical forests. Current thinking on the mechanisms of N deposition effects on plant diversity, the global distribution of G200 ecoregions, and current and future (2030) estimates of atmospheric N-deposition rates are then used to identify the risks to plant diversity in all major ecosystem types now and in the future. This synthesis paper clearly shows that N accumulation is the main driver of changes to species composition across the whole range of different ecosystem types by driving the competitive interactions that lead to composition change and/or making conditions unfavorable for some species. Other effects such its direct toxicity of nitrogen gases and aerosols long-term negative effects of increased ammonium and ammonia availability, soil-mediated effects of acidification, and secondary stress and disturbance are more ecosystem, and site-specific and often play a supporting role. N deposition effects in mediterranean ecosystems have now been identified, leading to a first estimate of an effect threshold. Importantly, ecosystems thought of as not N limited, such as tropical and subtropical systems, may be more vulnerable in the regeneration phase. in situations where heterogeneity in N availability is reduced by atmospheric N deposition, on sandy soils, or in montane areas. Critical loads are effect thresholds for N deposition. and the critical load concept has helped European governments make progress toward reducing N loads on sensitive ecosystems. More needs to be done in Europe and North America. especially for the more sensitive ecosystem types. including several ecosystems of high conservation importance. The results of this assessment Show that the Vulnerable regions outside Europe and North America which have not received enough attention are ecoregions in eastern and Southern Asia (China, India), an important part of the mediterranean ecoregion (California, southern Europe). and in the coming decades several subtropical and tropical parts of Latin America and Africa. Reductions in plant diversity by increased atmospheric N deposition may be more widespread than first thought, and more targeted Studies are required in low background areas, especially in the G200 ecoregions

Comparative evaluation of the impact of WRF/NMM and WRF/ARW meteorology on CMAQ simulations for PM_2.5 and its related precursors during the 2006 TexAQS/GoMACCS study

This study presents a comparative evaluation of the impact of WRF-NMM and WRF-ARW meteorology on CMAQ simulations of PM_2.5, its composition and related precursors over the eastern United States with the intensive observations obtained by aircraft (NOAA WP-3), ship and surface monitoring networks (AIRNow, IMPROVE, CASTNet and STN) during the 2006 TexAQS/GoMACCS study. The results at the AIRNow surface sites show that both ARW-CMAQ and NMM-CMAQ reproduced day-to-day variations of observed PM_2.5 and captured the majority of observed PM_2.5 within a factor of 2 with a NMB value of −0.4% for ARW-CMAQ and −18% for NMM-CMAQ. Both models performed much better at the urban sites than at the rural sites, with greater underpredictions at the rural sites. Both models consistently underestimated the observed PM_2.5 at the rural IMPROVE sites by −1% for the ARW-CMAQ and −19% for the NMM-CMAQ. The greater underestimations of SO₄²⁻, OC and EC by the NMM-CMAQ contributed to increased underestimation of PM_2.5 at the IMPROVE sites. The NMB values for PM_2.5 at the STN urban sites are 15% and −16% for the ARW-CMAQ and NMM-CMAQ, respectively. The underestimation of PM_2.5 at the STN sites by the NMM-CMAQ mainly results from the underestimations of the SO₄²⁻, NH₄⁺ and TCM components, whereas the overestimation of PM_2.5 at the STN sites by the ARW-CMAQ results from the overestimations of SO₄²⁻, NO₃⁻, and NH₄⁺. The Comparison with WP-3 aircraft measurements reveals that both ARW-CMAQ and NMM-CMAQ have very similar model performance for vertical profiles for PM_2.5 chemical components (SO₄²⁻, NH₄⁺) and related gaseous species (HNO₃, SO₂, NH₃, isoprene, toluene, terpenes) as both models used the same chemical mechanisms and emissions. The results of ship along the coast of southeastern Texas over the Gulf of Mexico show that both models captured the temporal variations and broad synoptic change seen in the observed HCHO and acetaldehyde with the means NMB <30% most of the time but they consistently underestimated terpenes, isoprene, toluene and SO₂

Fish and Coral Reef Communities of the Parque Nacional Sistema Arrecifal Veracruzano (Veracruz Coral Reef System National Park) Veracruz, Mexico: Preliminary Results

Effective resource management requires robust baseline datasets and efficient monitoring programs to identify and quantify temporal change. The Parque Nacional Sistema Arrecifal Veracruzano (Veracruz Coral Reef System National Park) encompasses a total of 52000ha including 23 coral reefs in two island groups separated by the mouth of the Jamapa River; one near the port of Veracruz, Mexico and one approximately 20km south near Punta Antón Lizardo. Both groups receive substantial fisheries pressure and other anthropogenic impacts. Using non-destructive, visual methods we surveyed fish and benthic assemblages at 18 sites, which included 10 individual coral reefs within the Park. For fishes, 221 point-count and 97 rover-diver surveys were conducted. In total, 92975 fish of 155 species were recorded. Using point-count data, fish abundance differed between Veracruz and Antón Lizardo sites (mean ± SEM: Veracruz = 535.52 ± 78.13; Antón Lizardo = 300.08 ± 30.68; p\u3c0.01, ANOVA). In contrast, there was no difference in fish species richness between these sites (Veracruz = 18.22 ± 0.36; Antón Lizardo = 18.75 ± 0.45); nor were there apparent differences in the MDS plot of Bray-Curtis similarity indices. A total of 27 stony coral species was identified on 170, 30-m point-intercept transects. Species richness ranged from 8 to 14 per site. Stony coral cover ranged from 4% to 38% with a mean of 22%. Other important functional groups included turf algae, macroalgae, and coralline algae. These groups generally contributed more to benthic cover than sponges or octocorals. Evidence of disease within the stony coral community was seen at all sites