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Individual Events (individual + event)
Selected AbstractsA catchment scale evaluation of the SIBERIA and CAESAR landscape evolution modelsEARTH SURFACE PROCESSES AND LANDFORMS, Issue 8 2010GR Hancock Abstract Landscape evolution models provide a way to determine erosion rates and landscape stability over times scales from tens to thousands of years. The SIBERIA and CAESAR landscape evolution models both have the capability to simulate catchment,wide erosion and deposition over these time scales. They are both cellular, operate over a digital elevation model of the landscape, and represent fluvial and slope processes. However, they were initially developed to solve research questions at different time and space scales and subsequently the perspective, detail and process representation vary considerably between the models. Notably, CAESAR simulates individual events with a greater emphasis on fluvial processes whereas SIBERIA averages erosion rates across annual time scales. This paper describes how both models are applied to Tin Camp Creek, Northern Territory, Australia, where soil erosion rates have been closely monitored over the last 10 years. Results simulating 10,000 years of erosion are similar, yet also pick up subtle differences that indicate the relative strengths and weaknesses of the two models. The results from both the SIBERIA and CAESAR models compare well with independent field data determined for the site over different time scales. Representative hillslope cross-sections are very similar between the models. Geomorphologically there was little difference between the modelled catchments after 1000 years but significant differences were revealed at longer simulation times. Importantly, both models show that they are sensitive to input parameters and that hydrology and erosion parameter derivation has long-term implications for sediment transport prediction. Therefore selection of input parameters is critical. This study also provides a good example of how different models may be better suited to different applications or research questions. Copyright © 2010 John Wiley & Sons, Ltd and Commonwealth of Australia [source] Theoretical and conceptual issues in time,place discriminationEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 9 2009Jonathon D. Crystal Abstract The need to discover resources that are available under specific environmental constraints represents a fundamental environmental pressure on the evolution of behavior. Time,place discrimination refers to the ability to secure resources when they are available under specific temporal and spatial contingencies. This article reviews a number of examples of time,place discrimination. The review highlights theoretical and conceptual issues that are needed to behaviorally identify the mechanisms responsible for time,place performance. Next, limitations on time,place performance that may be imposed by a circadian system are described. Finally, a number of lines of research that broaden these limitations are discussed. These lines of research include studies that suggest that (i) a broad range of long intervals (outside the limited range of circadian entrainment) are timed, (ii) at least some long intervals (16,21 h) are timed with an endogenous self-sustaining oscillator, (iii) short intervals (in the range of 1,3 min) are timed with an endogenous self-sustaining oscillator, and (iv) memory for specific unique events (including when and where they occurred) is based on a circadian representation of time. It is concluded that a unified theory of timing that can retain the times of occurrence of individual events is needed. The time of occurrence of an event may be encoded not only with respect to a circadian oscillator but also with respect to other oscillators in the long-interval and short-interval ranges. [source] Whole ecosystem metabolic pulses following precipitation eventsFUNCTIONAL ECOLOGY, Issue 5 2008G. D. Jenerette Summary 1Ecosystem respiration varies substantially at short temporal intervals and identifying the role of coupled temperature- and precipitation-induced changes has been an ongoing challenge. To address this challenge we applied a metabolic ecological theory to identify pulses in ecosystem respiration following rain events. Using this metabolic framework, precipitation-induced pulses were described as a reduction in metabolic activation energy after individual precipitation events. 2We used this approach to estimate the responses of 237 individual events recorded over 2 years at four eddy-covariance sites in southern AZ, USA. The sites varied in both community type (woody and grass dominated) and landscape position (riparian and upland). We used a nonlinear inversion procedure to identify both the parameters for the pre-event temperature sensitivity and the predicted response of the temperature sensitivity to precipitation. By examining multiple events we evaluated the consistency of pulses between sites and discriminated between hypotheses regarding landscape position, event distributions, and pre-event ecosystem metabolism rates. 3Over the 5-day post-event period across all sites the mean precipitation effect was attributed to 6·1 g CO2 m,2 of carbon release, which represented a 21% increase in respiration over the pre-event steady state trajectory of carbon loss. Differences in vegetation community were associated with differences in the integrated magnitude of pulse responses, while differences in topographic position were associated with the initial peak pulse rate. In conjunction with the differences between sites, the individual total pulse response was positively related to the drying time interval and metabolic rates prior to the event. The quantitative theory presented provides an approach for understanding ecosystem pulse dynamics and helps characterized the dependence of ecosystem metabolism on both temperature and precipitation. [source] Using cosmogenic beryllium,7 as a tracer in sediment budget investigationsGEOGRAFISKA ANNALER SERIES A: PHYSICAL GEOGRAPHY, Issue 2 2002W. H. Blake Recent advances in the use of the environmental radionuclides caesium,137 and unsupported lead,210 to quantify medium, and longer,term rates of erosion and sediment accumulation have proved of considerable value in catchment sediment budget investigations. However, there remains a need to explore the potential for using other shorter,lived radionuclides to provide evidence of sediment mobilisation, transport and storage over shorter timescales and particularly for individual events. This contribution reports the results of a study aimed at exploring the potential for using beryllium,7 (7Be, t½= 53.3 days) to meet this requirement. The study investigated the use of 7Be as a sediment tracer in three key components of the sediment budget, namely, soil erosion and sediment mobilisation from slopes, the transport, storage and remobilisation of fine sediment in river channels and overbank deposition on river floodplains. The results presented clearly demonstrate the potential for using 7Be to obtain information on short,term and event,based sediment redistribution rates for use in catchment sediment budget investigations. [source] Geomorphic and dendroecological impacts of slushflows in central Gaspé Peninsula (Québec, Canada)GEOGRAFISKA ANNALER SERIES A: PHYSICAL GEOGRAPHY, Issue 4 2001Sonya J. Larocque Slushflows are rare phenomena in southeastern Canada. Here we report for the first time the occurrence of slushflows in a subalpine environment in eastern Canada (Mt. Albert, Gaspé Peninsula, Québec). Because nothing is known of their frequency- magnitude in the area, we reconstructed the chronology of slushflow events over the past century using dendrogeomorphic techniques based on impact scars, reaction wood and traumatic resin ducts. Slushflows contributed to the formation of a tongue-shaped accumulation of 17900 m2 at the outlet of a firstorder drainage basin. The slushflow boulder tongue was composed of heterogeneous-sized, angular and unoriented clasts, which are markedly different from the sediments of an adjacent alluvial fan. Although movements were initiated above the subalpine forest limit, slushflows induced forest fragmentation along the treed slope. Three slushflow events were identified over the past century, in 1925, 1964 and 1988, respectively, which indicate exceptional initiation conditions and considerable geomorphic activity of individual events. [source] Upper mantle stratification by P and S receiver functionsGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 3 2000Véronique Farra Summary Seismic stratification of the upper mantle is investigated by applying two complementary techniques to the records of the Graefenberg array in southern Germany. The anisotropic P receiver function technique (Kosarev et al. 1984; Vinnik & Montagner 1996) is modified by using summary seismic events instead of individual events and different weighting functions instead of the same function for the harmonic angular analysis of the SV and T components of the Pds phases. The summary events provide better separation of the second azimuthal harmonic than the individual events. The parameters of the second harmonics of SV and T thus evaluated should be similar if they reflect the effects of azimuthal anisotropy. This can be used as a criterion to identify the anisotropy. To detect the Sdp phases and their azimuthal variations caused by azimuthal anisotropy we have developed a stacking technique, which can be termed the S receiver function technique It includes axis rotation to separate interfering P and S arrivals, determination of the principal (M) component of the S -wave motion, deconvolution of the P components of many recordings by their respective M components and stacking of the deconvolved P components with weights depending on the level of noise and the angle between the M direction and the backazimuth of the event. Both techniques yield consistent results for the Graefenberg array. As indicated by the P receiver functions, the upper layer of the mantle between the Moho and 80 km depth is anisotropic with dVs/Vs around 0.03 and the fast direction close to 20° clockwise from north. The fast direction of anisotropy below this layer is around 110°, The boundary between the upper and the lower anisotropic layers is manifested by the detectable Pds and Sdp converted phases. Shear wave splitting in SKS is strongly dominated by azimuthal anisotropy in the lower layer (asthenosphere). [source] Suspended sediment transport regime in a debris-flow gully on Vancouver Island, British ColumbiaHYDROLOGICAL PROCESSES, Issue 4 2005Craig J. Nistor Abstract In debris-flow-prone channels, normal fluvial sediment transport occurs (nearly exclusively in suspended mode) between episodic debris-flow events. Observations of suspended sediment transport through a winter season in a steepland gully in logged terrain revealed two event types. When flows exceeded a threshold of 270 l s,1, events yielded significant quantities of sediment and suspended sediment concentration increased with flow. Smaller events were strongly ,supply limited'; sediment concentration decreased as flow increased. Overall, there is no consistent correlation between runoff and sediment yield. Within the season, three subseasons were identified (demarcated by periods of freezing weather) within which a pattern of fine sediment replenishment and evacuation occurred. Finally, a signature of fine sediment mobilization and exhaustion was observed within individual events. Fine sediment transport occurred in discrete pulses within storm periods, most of the yield occurring within 5 to 15% of storm runoff duration, so that it is unlikely that scheduled sampling programs would identify significant transport. Significant events are, however, generally forecastable on the basis of regional heavy rainfall warnings, providing a basis for targeted observations. Radiative snowmelt events and rain-on-snow remain difficult to forecast, since the projection of temperatures from the nearest regular weather station yields variable results. Copyright © 2004 John Wiley & Sons, Ltd. [source] Olanzapine versus placebo in the treatment of psychosis with or without associated behavioral disturbances in patients with Alzheimer's diseaseINTERNATIONAL JOURNAL OF GERIATRIC PSYCHIATRY, Issue 2 2004Peter Paul De Deyn Abstract Objectives Psychotic symptoms and behavioral disturbances are a concern in the care of elderly patients with Alzheimer's dementia (AD). This study was conducted to compare the efficacy of olanzapine versus placebo in patients with psychotic symptoms associated with AD in long-term or continuing-care settings. Methods Patients (n,=,652) with AD and delusions or hallucinations were randomly assigned to 10 weeks of double-blind treatment with placebo or fixed-dose olanzapine (1.0, 2.5, 5.0, 7.5,mg/day). Results Mean age was 76.6±10.4 years. Repeated-measures analysis showed significant improvement from baseline in NPI/NH Psychosis Total scores (sum of Delusions, Hallucinations items,primary efficacy measure) in all five treatment groups (p<0.001), but no pairwise treatment differences were seen at the 10-week endpoint. However, under LOCF analysis, improvement in the 7.5,mg olanzapine group (,6.2,±,4.9) was significantly greater than with placebo (,5.0,±,6.1, p,=,0.008), while endpoint CGI-C scores showed the greatest improvement in the Olz,2.5 olanzapine group (2.8,±,1.4, p,=,0.030) relative to placebo (3.2,±,1.4). There were significant overall treatment-group differences in increased weight, anorexia, and urinary incontinence, with olanzapine showing numerically higher incidences. However, neither the incidence of any other individual events, including extrapyramidal symptoms, nor of total adverse events occurred with significantly higher frequency in any olanzapine group relative to placebo. No clinically relevant significant changes were seen across groups in cognition or any other vital sign or laboratory measure, including glucose, triglyceride, and cholesterol. Conclusions While 1.0,mg olanzapine did not show significant differences from placebo, the 2.5,mg dose was a reasonable starting dose. Olanzapine at 7.5,mg/day significantly decreased psychosis and overall behavioral disturbances (NPI/NH, BPRS) and was well tolerated. Copyright © 2004 John Wiley & Sons, Ltd. [source] SUPRACENTER: Locating fireball terminal bursts in the atmosphere using seismic arrivalsMETEORITICS & PLANETARY SCIENCE, Issue 9 2004W. N. EDWARDS A computer program, SUPRACENTER, calculates travel times by ray tracing through realistic atmospheres (that include winds) and locates source positions by minimization of travel time residuals. This is analogous to earthquake hypocenter location in the solid Earth but is done through a variably moving medium. Inclusion of realistic atmospheric ray tracing has removed the need for the simplifying assumption of an isotropic atmosphere or an approximation to account for "wind drift." This "drift" is on the order of several km when strong, unidirectional winds are present in the atmosphere at the time of a fireball's occurrence. SUPRACENTER-derived locations of three seismically recorded fireballs: 1) the October 9, 1997 El Paso superbolide; 2) the January 25, 1989 Mt. Adams fireball; and 3) the May 6, 2000 Morávka fireball (with its associated meteorite fall), are consistent with (and, probably, an improvement upon) the locations derived from eyewitness, photographic, and video observations from the respective individual events. If direct acoustic seismic arrivals can be quickly identified for a fireball event, terminal burst locations (and, potentially, trajectory geometry and velocity information) can be quickly derived, aiding any meteorite recovery efforts during the early days after the fall. Potentially, seismic records may yield enough trajectory information to assist in the derivation of orbits for entering projectiles. [source] Retention of Inorganic Nitrogen by Epiphytic Bryophytes in a Tropical Montane Forest,BIOTROPICA, Issue 3 2005Kenneth L. Clark ABSTRACT We developed and evaluated a model of the canopy of a tropical montane forest at Monteverde, Costa Rica, to estimate inorganic nitrogen (N) retention by epiphytes from atmospheric deposition. We first estimated net retention of inorganic N by samples of epiphytic bryophytes, epiphyte assemblages, vascular epiphyte foliage, and host tree foliage that we exposed to cloud water and precipitation solutions. Results were then scaled up to the ecosystem level using a multilayered model of the canopy derived from measurements of forest structure and epiphyte mass. The model was driven with hourly meteorological and event-based atmospheric deposition data, and model predictions were evaluated against measurements of throughfall collected at the site. Model predictions were similar to field measurements for both event-based and annual hydrologic and inorganic N fluxes in throughfall. Simulation of individual events indicated that epiphytic bryophytes and epiphyte assemblages retained 33,67 percent of the inorganic N deposited in cloud water and precipitation. On an annual basis, the model predicted that epiphytic components retained 3.4 kg N ha/yr, equivalent to 50 percent of the inorganic N in atmospheric deposition (6.8 kg N ha/yr). Our results indicate that epiphytic bryophytes play a major role in N retention and cycling in this canopy by transforming highly mobile inorganic N (ca. 50% of atmospheric deposition is NO,3) to less mobile (exchangeable NH+4) and recalcitrant forms in biomass and remaining litter and humus. RESUMEN En este estudio se desarrollo y se evaluo un modelo para estimar la retención de nitrogeno (N) inorganico atmospherico en el dosel de un bosque tropical montano en Monteverde, Costa Rica. Primeramente, estimamos la retención de N inorganico en muestras de briófitas, grupos de epífitas, hojas de epífitas, y hojas de árboles que fueron expuestas a agua de neblina y de lluvia. Basandose en medidas de estructure del bosque y la biomasa de epífitas se derivo un modelo multi nivel de dosel, estos resultados fueron aumentados a la escala de ecosystema. El modelo fue guiado por datos meteorológicos tomados a cada hora y datos de deposición atmosféricos y las predicciónes del modelo fueron evaluadas con medidas de la lluvia indirecta (throughfall) del sitio. Las predicciónes del modelo fueron similares a los datos de campo para eventos individuales, el ciclo hidrológico anual y las fluctuaciones de N en la lluvia indirecta. La simulación de eventos individuales indicaron que las briófitas y grupos de epífitas retuvieron 33,67 por ciento de N inorganico en agua de nubes y de lluvia. Predicciónes anuales del modelo indican que los grupos de epífitas retienen 3.4 kg N ha/año, equivalente al 50 por ciento del N inorganico en la deposición atmosférica (6.8 kg N ha/año). Nuestros resultados indican que las briófitas en el dosel desempeñan un papel muy importante en la retención y ciclaje de N inorganico, porque transforman el N con alta mobilidad en N de baja mobilidad y a formas mas recalcitrantes en la biomasa, la hojarasca y el humus. 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