Abstract
The potential ability of an ensemble prediction system (EPS) to represent its own varying forecast error provides strong motivation to produce an EPS over a less expensive deterministic ...forecast. Traditionally, this ability has been assessed by correlating the realized forecast error with the ensemble's dispersion. This paper revisits the limitations of the skill–spread correlation, but uses aspects of the correlation to introduce two metrics to assess an EPS's capacity to provide a reliable likelihood of its own error. Using a perfect EPS, skill–spread correlation is shown to be limited by its dependence on how “skill” and “spread” are defined and, perhaps most fatally, by its inability to distill the skill–spread reliability from the stability properties of the physical system being modeled. Building from this, it is argued there are two aspects of an ensemble's dispersion that should be assessed. First, is there enough variability in the dispersion to justify the expense of the EPS? The factor that controls the theoretical upper limit of the spread–error correlation can be useful in diagnosing this. Second, does the variable dispersion of an ensemble relate to a variable expectation of the forecast error? Representing the spread–error correlation in relation to its theoretical limit can provide a simple diagnostic of this attribute. A context for these concepts is provided by assessing two operational ensembles: western U.S. temperature forecasts and Brahmaputra River flow before and after postprocessing. It is shown that “skill–spread” reliability can be improved by postprocessing to that of a perfect EPS, but at the cost of the potential information content of the EPS's variable dispersion.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
We present a community data set of daily forcing and hydrologic response data for 671 small- to medium-sized basins across the contiguous United States (median basin size of 336 km2) that spans a ...very wide range of hydroclimatic conditions. Area-averaged forcing data for the period 1980-2010 was generated for three basin spatial configurations - basin mean, hydrologic response units (HRUs) and elevation bands - by mapping daily, gridded meteorological data sets to the subbasin (Daymet) and basin polygons (Daymet, Maurer and NLDAS). Daily streamflow data was compiled from the United States Geological Survey National Water Information System. The focus of this paper is to (1) present the data set for community use and (2) provide a model performance benchmark using the coupled Snow-17 snow model and the Sacramento Soil Moisture Accounting Model, calibrated using the shuffled complex evolution global optimization routine. After optimization minimizing daily root mean squared error, 90% of the basins have Nash-Sutcliffe efficiency scores greater than or equal to 0.55 for the calibration period and 34% greater than or equal to 0.8. This benchmark provides a reference level of hydrologic model performance for a commonly used model and calibration system, and highlights some regional variations in model performance. For example, basins with a more pronounced seasonal cycle generally have a negative low flow bias, while basins with a smaller seasonal cycle have a positive low flow bias. Finally, we find that data points with extreme error (defined as individual days with a high fraction of total error) are more common in arid basins with limited snow and, for a given aridity, fewer extreme error days are present as the basin snow water equivalent increases.
Stochastic on-off conductivity switching observed in phenylene-ethynylene oligomers has been explained in terms of changes in ring conformations, or electron localization, or both. We report the ...observation of stochastic on-off switching in the simplest of wired molecules: octanedithiol, decanedithiol, and dodecanedithiol bonded on an Au(111) surface. Stochastic switching was observed even when a top gold contact was pressed on by a conducting atomic force microscope tip at constant force. The rate of switching increased substantially at 60°C, a temperature at which these films are commonly annealed. Because such switching in alkanethiols is unlikely to be caused by internal molecular electronic changes and cannot be fully accounted for by breaking of the top contact, we argue that the cause is the well-known mobility of molecules tethered to gold via a thiol linkage.
Wind power forecasting can enhance the value of wind energy by improving the reliability of integrating this variable resource and improving the economic feasibility. The National Center for ...Atmospheric Research (NCAR) has collaborated with Xcel Energy to develop a multifaceted wind power prediction system. Both the day-ahead forecast that is used in trading and the short-term forecast are critical to economic decision making. This wind power forecasting system includes high resolution and ensemble modeling capabilities, data assimilation, now-casting, and statistical postprocessing technologies. The system utilizes publicly available model data and observations as well as wind forecasts produced from an NCAR-developed deterministic mesoscale wind forecast model with real-time four-dimensional data assimilation and a 30-member model ensemble system, which is calibrated using an Analogue Ensemble Kalman Filter and Quantile Regression. The model forecast data are combined using NCAR's Dynamic Integrated Forecast System (DICast). This system has substantially improved Xcel's overall ability to incorporate wind energy into their power mix.
A molecular electronics toolbox Rawlett, Adam M; Hopson, Theresa J; Amlani, Islamshah ...
Nanotechnology,
03/2003, Letnik:
14, Številka:
3
Journal Article
Recenzirano
We are developing a 'toolbox' containing organic molecules, nanoparticles and carbon nanotubes (CNTs) that can be self-arranged into a very advanced information processing system. Before we can ...assemble these 'tools' in complex systems, it is imperative that we determine their physical, chemical and electrical properties. Here, we describe the development of three techniques to aid in evaluating the electrical properties of these 'tools'. Firstly, via a conducting atomic force microscope, we examine a method of measuring the electrical properties of a single (few) dithiolated electronic molecule(s) inserted into an 'insulating' self-assembled monolayer (SAM). Secondly, to expedite the transport measurements of electronic molecules, we present a hybrid assembly technique that consists of forming a SAM of the investigated molecule on pre-patterned electrodes and then bridging the electrodes with Au nanoparticles using an alternating electric field. Finally, to integrate single-wall carbon nanotubes into a circuit, we outline a single optical lithographic step approach to pattern catalyst islands on top of metal electrodes. Then, reduced pressure chemical vapor deposition is performed on the patterned substrates to form CNTs bridging neighboring electrodes and produce a circuit that is ready to test.
Self Enhancement, Inc., is a grassroots, community-service organization working in the most disadvantaged high-risk community in Portland, Oregon. Its violence-prevention program targets ...middle-school and high-school students by providing classroom and community activities to these young people. These activities are designed to enhance protective factors and build resilience in youths to enable them to attain healthy and productive lives and to resist the threats of gangs, violence, and drugs. RMC Research Corporation works in partnership with Self Enhancement, Inc., to conduct research and evaluation on the effectiveness of its programs. The Self Enhancement, Inc., program works primarily at the individual student and interpersonal relationship levels. Resilience Theory and its culturally specific Relationship Model drive the formulation of specific strategies and activities. Program staff mentor each student through his or her preadolescent and adolescent years, promoting positive, prosocial norms and expectations for behavior through their peer group activities. The Self Enhancement, Inc., program consists of three major components: classroom, exposure, and proactive education. Classroom education focuses on anger management, conflict resolution, and problem solving. Exposure education consists of quarterly field trips to agencies and organizations in the Portland area that deal with the causes and consequences of violence in the community. Proactive education includes newsletters, student-run assemblies and conferences, and radio/ television public service announcements that communicate antiviolence messages. The evaluation plan is a longitudinal, matched comparison group designed to assess the outcomes of the violence-prevention program. Key outcomes are protective factors, health-risk behaviors, and academic measures. Standardized assessment instruments (the Individual Protective Factors Index and the Youth Risk Behavior Survey) were administered to all students during winter 1994. The instruments will be readministered during the same period in the following two years of the project. School records were extracted to assess students’ attendance and progress through their academic programs. Of the 326 seventh-, eighth-, and ninth-grade students participating in this study, 95% are African Americans and 51% are boys. The prevalence of fighting (56%) during the past 12 months is higher than that among African-American high-school students nationally, but weapon carrying (27%), alcohol use (30%), and marijuana use (18%) are the same or lower than national averages for this group. All baseline indicators are equivalent between the program and comparison groups with the exception of weapon carrying. Program students report carrying weapons more than do their comparison group counterparts. Baseline indicators of violence-related behaviors clearly indicate the need for intervention in this highly disadvantaged, African-American community. Through its historical presence and recent program development efforts, Self Enhancement, Inc., is well positioned to make a difference in the lives of these young people. The equivalence of program and comparison group students on baseline indicators of violence bodes well for an unequivocal assessment of program effectiveness over time.
Understanding and acting on the link between weather and meningitis in the Sahel could help improve vaccine distribution and save lives. People living there know that meningitis epidemics occur in ...the dry season and end after the start of the rainy season. Integrating and analyzing newly available epidemiological and meteorological data quantified this relationship, showing that that the risk of meningitis epidemics climbed from a background level of 2% to a maximum risk of 25% during the dry season. These data also suggested that, of all meteorological variables, relative humidity has the strongest correlation to cases of meningitis.
Weather acts alongside a complex set of environmental, social, and economic drivers, and a complementary investigation of local and regional knowledge, attitudes, and practices suggested several additional interventions to manage meningitis. These include improved awareness of early meningitis symptoms and vaccinations for farmworkers who migrate seasonally. An economic survey showed that the cost of a single case of meningitis is 3 times the average annual household income, underscoring the need for improved vaccination strategy.
Using these insights, meteorologists and public health workers developed a tool to guide vaccination decisions. Iterative development allowed a multinational team of public health officials to use the tool while guiding its refinement and directed research toward maximum practical use. That meant focusing on predicting areas where high humidity would naturally end epidemics so vaccines could be moved elsewhere. Using this tool and this approach could have prevented an estimated 24,000 cases of meningitis over a 3-yr period.
Celotno besedilo
Dostopno za:
BFBNIB, DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
This researcher aimed to determine how data collected from computer-based assessment programs, specifically EasyCBM and AIMSweb, was used in data-driven instruction and used to identify risk levels ...in math and reading areas proficiency. Data from intervention programs were collected from six participating high schools. The data collection included math and reading universal screening scores and levels of risk indicators from Tier 2 and Tier 3 levels of their response to intervention (RTI) programs. Section A included math data within a baseline score and a risk indicator level. Section B had reading scores with a baseline score and a risk indicator level.A descriptive quantitative study was conducted to determine if significant differences in EasyCBM and AIMSweb exist in student universal screener scores over an academic calendar year. Independent variables included: math and reading universal screener scores, tier level identifiers, and level of risk indicators. Factors that influenced the rates of effectiveness included: interventionist utilization of data, student entry tier levels, and time spent in intervention from the fall to winter benchmarking period.The study's findings indicated a significant difference in universal screener scores between EasyCBM and AIMSweb when analyzed over the same period from school to school. Additional analysis was utilized to reveal substantial differences between Tier 2 in reading and math risk indicators and Tier 3 in reading and math risk indicators. Student participation in the program did indicate a significant difference when applied longer than one-half a calendar year. Results showed that students displayed higher improvement rates through continued application of both programs throughout the fall and winter.
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