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Little Sensitivity (little + sensitivity)

Distribution by Scientific Domains

Earth and Environmental Science	40%

Selected Abstracts

Trauma Team Activation Criteria as Predictors of Patient Disposition from the Emergency Department

ACADEMIC EMERGENCY MEDICINE, Issue 1 2004
Michael A. Kohn MD
Many trauma centers use mainly physiologic, first-tier criteria and mechanism-related, second-tier criteria to determine whether and at what level to activate a multidisciplinary trauma team in response to an out-of-hospital call. Some of these criteria result in a large number of unnecessary team activations while identifying only a few additional patients who require immediate operative intervention. Objectives: To separately evaluate the incremental predictive value of individual first-tier and second-tier trauma team activation criteria for severe injury as reflected by patient disposition from the emergency department (ED). Methods: This was a prospective cohort study in which activation criteria were collected prospectively on all adult patients for whom the trauma team was activated during a five-month period at an urban, Level 1 trauma center. Severe injury disposition ("appropriate" team activation) was defined as immediate operative intervention, admission to the intensive care unit (ICU), or death in the ED. Data analysis consisted of recursive partitioning and multiple logistic regression. Results: Of the 305 activations for the mainly physiologic first-tier criteria, 157 (51.5%) resulted in severe injury disposition. The first-tier criterion that caused the greatest increase in "inappropriate" activations for the lowest increase in "appropriate" activations was "age > 65." Of the 34 additional activations due to this criterion, seven (20.6%) resulted in severe injury disposition. Of the 700 activations for second-tier, mechanism-related criteria, 54 (7.7%) resulted in ICU or operating room admissions, and none resulted in ED death. The four least predictive second-tier criteria were "motorcycle crash with separation of rider,""pedestrian hit by motor vehicle,""motor vehicle crash with rollover," and "motor vehicle crash with death of occupant." Of the 452 activations for these four criteria, only 18 (4.0%) resulted in ICU or operating room admission. Conclusions: The four least predictive second-tier, mechanism-related criteria added little sensitivity to the trauma team activation rule at the cost of substantially decreased specificity, and they should be modified or eliminated. The first-tier, mainly physiologic criteria were all useful in predicting the need for an immediate multidisciplinary response. If increased specificity of the first-tier criteria is desired, the first criterion to eliminate is "age > 65." [source]

Biogeochemistry of microbial mats under Precambrian environmental conditions: a modelling study

GEOBIOLOGY, Issue 2 2005
E. K. HERMAN
ABSTRACT Microbial mats have arguably been the most important ecosystem on Earth over its 3.5 Gyr inhabitation. Mats have persisted as consortia for billions of years and occupy some of Earth's most hostile environments. With rare exceptions (e.g. microbial mats developed on geothermal springs at Yellowstone National Park, USA), today's mats do not exist under conditions analogous to Precambrian habitats with substantially lower oxygen and sulphate concentrations. This study uses a numerical model of a microbial mat to investigate how mat composition in the past might have differed from modern mats. We present a numerical model of mat biogeochemistry that simulates the growth of cyanobacteria (CYA), colourless sulphur bacteria (CSB), and purple sulphur bacteria (PSB), with sulphate-reducing bacteria (SRB) and heterotrophic bacteria represented by parameterized sulphate reduction rates and heterotrophic consumption rates, respectively. Variations in the availability of light, oxygen, sulphide, and sulphate at the upper boundary of the mat are the driving forces in the model. Mats with remarkably similar biomass and chemical profiles develop in models under oxygen boundary conditions ranging from 2.5 × 10,13 to 0.25 mm and sulphate boundary concentrations ranging from 0.29 to 29 mm, designed to simulate various environments from Archean to modern. The modelled mats show little sensitivity to oxygen boundary conditions because, independent of the overlying oxygen concentrations, cyanobacterial photosynthesis creates similar O2 concentrations of 0.45,0.65 mm in the upper reaches of the mat during the photoperiod. Varying sulphate boundary conditions have more effect on the biological composition of the mat. Sulphide generated from sulphate reduction controls the magnitude and distribution of the PSB population, and plays a part in the distribution of CSB. CSB are the most sensitive species to environmental change, varying with oxygen and sulphide. [source]

Spatial patterns of simulated transpiration response to climate variability in a snow dominated mountain ecosystem

HYDROLOGICAL PROCESSES, Issue 18 2008
Lindsey Christensen
Abstract Transpiration is an important component of soil water storage and stream-flow and is linked with ecosystem productivity, species distribution, and ecosystem health. In mountain environments, complex topography creates heterogeneity in key controls on transpiration as well as logistical challenges for collecting representative measurements. In these settings, ecosystem models can be used to account for variation in space and time of the dominant controls on transpiration and provide estimates of transpiration patterns and their sensitivity to climate variability and change. The Regional Hydro-Ecological Simulation System (RHESSys) model was used to assess elevational differences in sensitivity of transpiration rates to the spatiotemporal variability of climate variables across the Upper Merced River watershed, Yosemite Valley, California, USA. At the basin scale, predicted annual transpiration was lowest in driest and wettest years, and greatest in moderate precipitation years (R2 = 0·32 and 0·29, based on polynomial regression of maximum snow depth and annual precipitation, respectively). At finer spatial scales, responsiveness of transpiration rates to climate differed along an elevational gradient. Low elevations (1200,1800 m) showed little interannual variation in transpiration due to topographically controlled high soil moistures along the river corridor. Annual conifer stand transpiration at intermediate elevations (1800,2150 m) responded more strongly to precipitation, resulting in a unimodal relationship between transpiration and precipitation where highest transpiration occurred during moderate precipitation levels, regardless of annual air temperatures. Higher elevations (2150,2600 m) maintained this trend, but air temperature sensitivities were greater. At these elevations, snowfall provides enough moisture for growth, and increased temperatures influenced transpiration. Transpiration at the highest elevations (2600,4000 m) showed strong sensitivity to air temperature, little sensitivity to precipitation. Model results suggest elevational differences in vegetation water use and sensitivity to climate were significant and will likely play a key role in controlling responses and vulnerability of Sierra Nevada ecosystems to climate change. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Statistical prediction of global sea-surface temperature anomalies

INTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 14 2003
A. W. Colman
Abstract Sea-surface temperature (SST) is one of the principal factors that influence seasonal climate variability, and most seasonal prediction schemes make use of information regarding SST anomalies. In particular, dynamical atmospheric prediction models require global gridded SST data prescribed through the target season. The simplest way of providing those data is to persist the SST anomalies observed at the start of the forecast at each grid point, with some damping, and this strategy has proved to be quite effective in practice. In this paper we present a statistical scheme that aims to improve that basic strategy by combining three individual methods together: simple persistence, canonical correlation analysis (CCA), and nearest-neighbour regression. Several weighting schemes were tested: the best of these is one that uses equal weight in all areas except the east tropical Pacific, where CCA is preferred. The overall performance of the combined scheme is better than the individual schemes. The results show improvements in tropical ocean regions for lead times beyond 1 or 2 months, but the skill of simple persistence is difficult to beat in the extratropics at all lead times. Aspects such as averaging periods and grid size were also investigated: results showed little sensitivity to these factors. The combined statistical SST prediction scheme can also be used to improve statistical regional rainfall forecasts that use SST anomaly patterns as predictors. Copyright © Crown Copyright 2003. Published by John Wiley & Sons, Ltd. [source]

Splitting the S&P 500 futures

THE JOURNAL OF FUTURES MARKETS, Issue 12 2004
Jianli Chen
In this paper we investigate the consequences of the Chicago Mercantile Exchange's 1997 redesign of the S&P 500 futures contract. The focus is on two important measures of exchange efficacy: member proprietary income and outside customer volume. Floor traders did not appear to benefit in their proprietary trading from the redesign,revenue fell after the contract split and doubling of the minimum tick. On the other hand, looking at relative volumes, it appears that customer volume was relatively constant, showing little sensitivity to the increase in tick size, possibly due to an increased use of limit orders by customers, bypassing floor traders. Through this redesign the futures exchange was apparently interested in preserving customer volume in an increasingly competitive index trading environment, not enhancing member noncompetitive proprietary trading revenue. © 2004 Wiley Periodicals, Inc. Jrl Fut Mark 24:1147,1163, 2004 [source]