de Bekker-Grob, Esther W.; Bergstra, Arnold D.; Bliemer, Michiel C. J.; Trijssenaar-Buhre, Inge J. M.; Burdorf, Alex
2015-01-01
Background To improve the information for and preparation of citizens at risk to hazardous material transport accidents, a first important step is to determine how different characteristics of hazardous material transport accidents will influence citizens’ protective behaviour. However, quantitative studies investigating citizens’ protective behaviour in case of hazardous material transport accidents are scarce. Methods A discrete choice experiment was conducted among subjects (19–64 years) living in the direct vicinity of a large waterway. Scenarios were described by three transport accident characteristics: odour perception, smoke/vapour perception, and the proportion of people in the environment that were leaving at their own discretion. Subjects were asked to consider each scenario as realistic and to choose the alternative that was most appealing to them: staying, seeking shelter, or escaping. A panel error component model was used to quantify how different transport accident characteristics influenced subjects’ protective behaviour. Results The response was 44% (881/1,994). The predicted probability that a subject would stay ranged from 1% in case of a severe looking accident till 62% in case of a mild looking accident. All three transport accident characteristics proved to influence protective behaviour. Particularly a perception of strong ammonia or mercaptan odours and visible smoke/vapour close to citizens had the strongest positive influence on escaping. In general, ‘escaping’ was more preferred than ‘seeking shelter’, although stated preference heterogeneity among subjects for these protective behaviour options was substantial. Males were less willing to seek shelter than females, whereas elderly people were more willing to escape than younger people. Conclusion Various characteristics of transport accident involving hazardous materials influence subjects’ protective behaviour. The preference heterogeneity shows that information needs
Choice-Based Conjoint Analysis: Classification vs. Discrete Choice Models
NASA Astrophysics Data System (ADS)
Giesen, Joachim; Mueller, Klaus; Taneva, Bilyana; Zolliker, Peter
Conjoint analysis is a family of techniques that originated in psychology and later became popular in market research. The main objective of conjoint analysis is to measure an individual's or a population's preferences on a class of options that can be described by parameters and their levels. We consider preference data obtained in choice-based conjoint analysis studies, where one observes test persons' choices on small subsets of the options. There are many ways to analyze choice-based conjoint analysis data. Here we discuss the intuition behind a classification based approach, and compare this approach to one based on statistical assumptions (discrete choice models) and to a regression approach. Our comparison on real and synthetic data indicates that the classification approach outperforms the discrete choice models.
Use of discrete choice experiments to elicit preferences
Ryan, M; Bate, A; Eastmond, C; Ludbrook, A
2001-01-01
This paper considers the application of discrete choice experiments for eliciting preferences in the delivery of health care. Drawing upon the results from a recently completed systematic review, the paper summarises the application of this technique in health care. It then presents a case study applying the technique to rheumatology outpatient clinics. 200 patients were questioned about the importance of six attributes: staff seen (junior doctor or specialist nurse); time in waiting area; continuity of contact with same staff; provision of a phone-in/advice service; length of consultation; and change in pain levels. The systematic review indicated that discrete choice experiments have been applied to a wide number of areas and a number of methodological issues have been addressed. Consistent with this literature, the case study found evidence of both rationality and theoretical validity of responses. The approach was used to establish the relative importance of different attributes, how individuals trade between these attributes, and overall benefit scores for different clinic configurations. The value of attributes was estimated in terms of time, and this was converted to a monetary measure using the value of waiting time for public transport. Discrete choice experiments represent a potentially useful instrument for eliciting preferences. Future methodological work should explore issues related to the experimental design of the study, methods of data collection and analysis, and satisfaction with the economic axioms of the instrument. Collaborative work with psychologists and qualitative researchers will prove useful in this research agenda. Key Words: discrete choice experiments; patient preference; decision making; patient-caregiver communication PMID:11533440
Distributed versus exclusive preference in discrete-trial choice.
Mazur, James E
2010-07-01
Two experiments on discrete-trial choice examined the conditions under which pigeons would exhibit exclusive preference for the better of two alternatives as opposed to distributed preference (making some choices for each alternative). In Experiment 1, pigeons chose between red and green response keys that delivered food after delays of different durations, and in Experiment 2 they chose between red and green keys that delivered food with different probabilities. Some conditions of Experiment 1 had fixed delays to food and other conditions had variable delays. In both experiments, exclusive or nearly exclusive preference for the better alternative was found in some conditions, but distributed preference was found in other conditions, especially in Experiment 2 when key location varied randomly over trials. The results were used to evaluate several different theories about discrete-trial choice. The results suggest that exclusive preference for one alternative is a frequent outcome in discrete-trial choice. When distributed preference does occur, it is not the result of inherent tendencies to sample alternatives or to match response percentages to the values of the alternatives. Rather, distributed preference may occur when two factors (such as reinforcer delay and position bias) compete for the control of choice, or when the consequences for the two alternatives are similar and difficult to discriminate.
Reconceptualising the external validity of discrete choice experiments.
Lancsar, Emily; Swait, Joffre
2014-10-01
External validity is a crucial but under-researched topic when considering using discrete choice experiment (DCE) results to inform decision making in clinical, commercial or policy contexts. We present the theory and tests traditionally used to explore external validity that focus on a comparison of final outcomes and review how this traditional definition has been empirically tested in health economics and other sectors (such as transport, environment and marketing) in which DCE methods are applied. While an important component, we argue that the investigation of external validity should be much broader than a comparison of final outcomes. In doing so, we introduce a new and more comprehensive conceptualisation of external validity, closely linked to process validity, that moves us from the simple characterisation of a model as being or not being externally valid on the basis of predictive performance, to the concept that external validity should be an objective pursued from the initial conceptualisation and design of any DCE. We discuss how such a broader definition of external validity can be fruitfully used and suggest innovative ways in which it can be explored in practice.
A deterministic discrete ordinates transport proxy application
2014-06-03
Kripke is a simple 3D deterministic discrete ordinates (Sn) particle transport code that maintains the computational load and communications pattern of a real transport code. It is intended to be a research tool to explore different data layouts, new programming paradigms and computer architectures.
Discrete elements method of neutral particle transport
Mathews, K.A.
1983-01-01
A new discrete elements (L/sub N/) transport method is derived and compared to the discrete ordinates S/sub N/ method, theoretically and by numerical experimentation. The discrete elements method is more accurate than discrete ordinates and strongly ameliorates ray effects for the practical problems studied. The discrete elements method is shown to be more cost effective, in terms of execution time with comparable storage to attain the same accuracy, for a one-dimensional test case using linear characteristic spatial quadrature. In a two-dimensional test case, a vacuum duct in a shield, L/sub N/ is more consistently convergent toward a Monte Carlo benchmark solution than S/sub N/, using step characteristic spatial quadrature. An analysis of the interaction of angular and spatial quadrature in xy-geometry indicates the desirability of using linear characteristic spatial quadrature with the L/sub N/ method.
Hybrid discrete choice models: Gained insights versus increasing effort.
Mariel, Petr; Meyerhoff, Jürgen
2016-10-15
Hybrid choice models expand the standard models in discrete choice modelling by incorporating psychological factors as latent variables. They could therefore provide further insights into choice processes and underlying taste heterogeneity but the costs of estimating these models often significantly increase. This paper aims at comparing the results from a hybrid choice model and a classical random parameter logit. Point of departure for this analysis is whether researchers and practitioners should add hybrid choice models to their suite of models routinely estimated. Our comparison reveals, in line with the few prior studies, that hybrid models gain in efficiency by the inclusion of additional information. The use of one of the two proposed approaches, however, depends on the objective of the analysis. If disentangling preference heterogeneity is most important, hybrid model seems to be preferable. If the focus is on predictive power, a standard random parameter logit model might be the better choice. Finally, we give recommendations for an adequate use of hybrid choice models based on known principles of elementary scientific inference. PMID:27310534
Hybrid discrete choice models: Gained insights versus increasing effort.
Mariel, Petr; Meyerhoff, Jürgen
2016-10-15
Hybrid choice models expand the standard models in discrete choice modelling by incorporating psychological factors as latent variables. They could therefore provide further insights into choice processes and underlying taste heterogeneity but the costs of estimating these models often significantly increase. This paper aims at comparing the results from a hybrid choice model and a classical random parameter logit. Point of departure for this analysis is whether researchers and practitioners should add hybrid choice models to their suite of models routinely estimated. Our comparison reveals, in line with the few prior studies, that hybrid models gain in efficiency by the inclusion of additional information. The use of one of the two proposed approaches, however, depends on the objective of the analysis. If disentangling preference heterogeneity is most important, hybrid model seems to be preferable. If the focus is on predictive power, a standard random parameter logit model might be the better choice. Finally, we give recommendations for an adequate use of hybrid choice models based on known principles of elementary scientific inference.
Air Cargo Transportation Route Choice Analysis
NASA Technical Reports Server (NTRS)
Obashi, Hiroshi; Kim, Tae-Seung; Oum, Tae Hoon
2003-01-01
Using a unique feature of air cargo transshipment data in the Northeast Asian region, this paper identifies the critical factors that determine the transshipment route choice. Taking advantage of the variations in the transport characteristics in each origin-destination airports pair, the paper uses a discrete choice model to describe the transshipping route choice decision made by an agent (i.e., freight forwarder, consolidator, and large shipper). The analysis incorporates two major factors, monetary cost (such as line-haul cost and landing fee) and time cost (i.e., aircraft turnaround time, including loading and unloading time, custom clearance time, and expected scheduled delay), along with other controls. The estimation method considers the presence of unobserved attributes, and corrects for resulting endogeneity by use of appropriate instrumental variables. Estimation results find that transshipment volumes are more sensitive to time cost, and that the reduction in aircraft turnaround time by 1 hour would be worth the increase in airport charges by more than $1000. Simulation exercises measures the impacts of alternative policy scenarios for a Korean airport, which has recently declared their intention to be a future regional hub in the Northeast Asian region. The results suggest that reducing aircraft turnaround time at the airport be an effective strategy, rather than subsidizing to reduce airport charges.
ECONOMICS NOBEL: Dealing With Biases and Discrete Choices.
Seife, C
2000-10-20
This year's Bank of Sweden Prize in Economic Sciences, given in honor of Alfred Nobel, goes to two researchers who gave the field of microeconomics--the study of individuals' economic behavior--new tools to help draw conclusions from imperfect data. James Heckman of the University of Chicago wins half of this year's prize for coming up with ways to deal with selection biases. Daniel McFadden of the University of California, Berkeley, tackled a different conundrum: how to quantify discrete choices rather than continuous ones. PMID:17844279
Lagarde, Mylene; Blaauw, Duane
2009-01-01
Although the factors influencing the shortage and maldistribution of health workers have been well-documented by cross-sectional surveys, there is less evidence on the relative determinants of health workers' job choices, or on the effects of policies designed to address these human resources problems. Recently, a few studies have adopted an innovative approach to studying the determinants of health workers' job preferences. In the absence of longitudinal datasets to analyse the decisions that health workers have actually made, authors have drawn on methods from marketing research and transport economics and used Discrete Choice Experiments to analyse stated preferences of health care providers for different job characteristics. We carried out a literature review of studies using discrete choice experiments to investigate human resources issues related to health workers, both in developed and developing countries. Several economic and health systems bibliographic databases were used, and contacts were made with practitioners in the field to identify published and grey literature. Ten studies were found that used discrete choice experiments to investigate the job preferences of health care providers. The use of discrete choice experiments techniques enabled researchers to determine the relative importance of different factors influencing health workers' choices. The studies showed that non-pecuniary incentives are significant determinants, sometimes more powerful than financial ones. The identified studies also emphasized the importance of investigating the preferences of different subgroups of health workers. Discrete choice experiments are a valuable tool for informing decision-makers on how to design strategies to address human resources problems. As they are relatively quick and cheap survey instruments, discrete choice experiments present various advantages for informing policies in developing countries, where longitudinal labour market data are seldom
Personal Traits Underlying Environmental Preferences: A Discrete Choice Experiment
Soliño, Mario; Farizo, Begoña A.
2014-01-01
Personality plays a role in human behavior, and thus can influence consumer decisions on environmental goods and services. This paper analyses the influence of the big five personality dimensions (extraversion, agreeableness, conscientiousness, neuroticism and openness) in a discrete choice experiment dealing with preferences for the development of an environmental program for forest management in Spain. For this purpose, a reduced version of the Big Five Inventory survey (the BFI-10) is implemented. Results show a positive effect of openness and extraversion and a negative effect of agreeableness and neuroticism in consumers' preferences for this environmental program. Moreover, results from a latent class model show that personal traits help to explain preference heterogeneity. PMID:24586905
Personal traits underlying environmental preferences: a discrete choice experiment.
Soliño, Mario; Farizo, Begoña A
2014-01-01
Personality plays a role in human behavior, and thus can influence consumer decisions on environmental goods and services. This paper analyses the influence of the big five personality dimensions (extraversion, agreeableness, conscientiousness, neuroticism and openness) in a discrete choice experiment dealing with preferences for the development of an environmental program for forest management in Spain. For this purpose, a reduced version of the Big Five Inventory survey (the BFI-10) is implemented. Results show a positive effect of openness and extraversion and a negative effect of agreeableness and neuroticism in consumers' preferences for this environmental program. Moreover, results from a latent class model show that personal traits help to explain preference heterogeneity. PMID:24586905
Energy-pointwise discrete ordinates transport methods
Williams, M.L.; Asgari, M.; Tashakorri, R.
1997-06-01
A very brief description is given of a one-dimensional code, CENTRM, which computes a detailed, space-dependent flux spectrum in a pointwise-energy representation within the resolved resonance range. The code will become a component in the SCALE system to improve computation of self-shielded cross sections, thereby enhancing the accuracy of codes such as KENO. CENTRM uses discrete-ordinates transport theory with an arbitrary angular quadrature order and a Legendre expansion of scattering anisotropy for moderator materials and heavy nuclides. The CENTRM program provides capability to deterministically compute full energy range, space-dependent angular flux spectra, rigorously accounting for resonance fine-structure and scattering anisotropy effects.
Segmenting patients and physicians using preferences from discrete choice experiments.
Deal, Ken
2014-01-01
People often form groups or segments that have similar interests and needs and seek similar benefits from health providers. Health organizations need to understand whether the same health treatments, prevention programs, services, and products should be applied to everyone in the relevant population or whether different treatments need to be provided to each of several segments that are relatively homogeneous internally but heterogeneous among segments. Our objective was to explain the purposes, benefits, and methods of segmentation for health organizations, and to illustrate the process of segmenting health populations based on preference coefficients from a discrete choice conjoint experiment (DCE) using an example study of prevention of cyberbullying among university students. We followed a two-level procedure for investigating segmentation incorporating several methods for forming segments in Level 1 using DCE preference coefficients and testing their quality, reproducibility, and usability by health decision makers. Covariates (demographic, behavioral, lifestyle, and health state variables) were included in Level 2 to further evaluate quality and to support the scoring of large databases and developing typing tools for assigning those in the relevant population, but not in the sample, to the segments. Several segmentation solution candidates were found during the Level 1 analysis, and the relationship of the preference coefficients to the segments was investigated using predictive methods. Those segmentations were tested for their quality and reproducibility and three were found to be very close in quality. While one seemed better than others in the Level 1 analysis, another was very similar in quality and proved ultimately better in predicting segment membership using covariates in Level 2. The two segments in the final solution were profiled for attributes that would support the development and acceptance of cyberbullying prevention programs among university
Discrete element modelling of bedload transport
NASA Astrophysics Data System (ADS)
Loyer, A.; Frey, P.
2011-12-01
Discrete element modelling (DEM) has been widely used in solid mechanics and in granular physics. In this type of modelling, each individual particle is taken into account and intergranular interactions are modelled with simple laws (e.g. Coulomb friction). Gravity and contact forces permit to solve the dynamical behaviour of the system. DEM is interesting to model configurations and access to parameters not directly available in laboratory experimentation, hence the term "numerical experimentations" sometimes used to describe DEM. DEM was used to model bedload transport experiments performed at the particle scale with spherical glass beads in a steep and narrow flume. Bedload is the larger material that is transported on the bed on stream channels. It has a great geomorphic impact. Physical processes ruling bedload transport and more generally coarse-particle/fluid systems are poorly known, arguably because granular interactions have been somewhat neglected. An existing DEM code (PFC3D) already computing granular interactions was used. We implemented basic hydrodynamic forces to model the fluid interactions (buoyancy, drag, lift). The idea was to use the minimum number of ingredients to match the experimental results. Experiments were performed with one-size and two-size mixtures of coarse spherical glass beads entrained by a shallow turbulent and supercritical water flow down a steep channel with a mobile bed. The particle diameters were 4 and 6mm, the channel width 6.5mm (about the same width as the coarser particles) and the channel inclination was typically 10%. The water flow rate and the particle rate were kept constant at the upstream entrance and adjusted to obtain bedload transport equilibrium. Flows were filmed from the side by a high-speed camera. Using image processing algorithms made it possible to determine the position, velocity and trajectory of both smaller and coarser particles. Modelled and experimental particle velocity and concentration depth
Abiiro, Gilbert Abotisem; Torbica, Aleksandra; Kwalamasa, Kassim; De Allegri, Manuela
2014-11-01
There is a limited understanding of preferences for micro health insurance (MHI) as a strategy for moving towards universal health coverage. Using a discrete choice experiment (DCE), we explored community preferences for the attributes and attribute-levels of a prospective MHI scheme, aimed at filling health coverage gaps in Malawi. Through a qualitative study informed by a literature review, we identified six MHI attributes (and attribute-levels): unit of enrollment, management structure, health service benefit package, copayment levels, transportation coverage, and monthly premium per person. Qualitative data was collected from 12 focus group discussions and 8 interviews in August-September, 2012. We constructed a D-efficient design of eighteen choice-sets, each comprising two MHI choice alternatives and an opt-out. Using pictorial images, trained interviewers administered the DCE in March-May, 2013, to 814 household heads and/or their spouse(s) in two rural districts. We estimated preferences for attribute-levels and relative importance of attributes using conditional and nested logit models. The results showed that all attribute-levels except management by external NGO significantly influenced respondents' choice behavior (P<0.05). These included: enrollment as core nuclear family (odds ratio (OR)=1.1574), extended family (OR=1.1132), compared to individual; management by community committee (OR=0.9494) compared to local micro finance institution; comprehensive health service package (OR=1.4621), medium service package (OR=1.2761), compared to basic service package; no copayment (OR=1.1347), 25% copayment (OR=1.1090), compared to 50% copayment; coverage of all transport (OR=1.5841), referral and emergency transport (OR=1.2610), compared to no transport; and premium (OR=0.9994). The relative importance of attributes is ordered as: transport, health services benefits, enrollment unit, premium, copayment, and management. To maximize consumer utility and encourage
ERIC Educational Resources Information Center
Cunningham, Charles E.; Vaillancourt, Tracy; Rimas, Heather; Deal, Ken; Cunningham, Lesley; Short, Kathy; Chen, Yvonne
2009-01-01
We used discrete choice conjoint analysis to model the bullying prevention program preferences of educators. Using themes from computerized decision support lab focus groups (n = 45 educators), we composed 20 three-level bullying prevention program design attributes. Each of 1,176 educators completed 25 choice tasks presenting experimentally…
Bech, Mickael; Kjaer, Trine; Lauridsen, Jørgen
2011-03-01
Optimising the design of discrete choice experiments (DCE) involves maximising not only the statistical efficiency, but also how the nature and complexity of the experiment itself affects model parameters and variance. The present paper contributes by investigating the impact of the number of DCE choice sets presented to each respondent on response rate, self-reported choice certainty, perceived choice difficulty, willingness-to-pay (WTP) estimates, and response variance. A sample of 1053 respondents was exposed to 5, 9 or 17 choice sets in a DCE eliciting preferences for dental services. Our results showed no differences in response rates and no systematic differences in the respondents' self-reported perception of the uncertainty of their DCE answers. There were some differences in WTP estimates suggesting that estimated preferences are to some extent context-dependent, but no differences in standard deviations for WTP estimates or goodness-of-fit statistics. Respondents exposed to 17 choice sets had somewhat higher response variance compared to those exposed to 5 choice sets, indicating that cognitive burden may increase with the number of choice sets beyond a certain threshold. Overall, our results suggest that respondents are capable of managing multiple choice sets - in this case 17 choice sets - without problems.
Multidimensional electron-photon transport with standard discrete ordinates codes
Drumm, C.R.
1995-12-31
A method is described for generating electron cross sections that are compatible with standard discrete ordinates codes without modification. There are many advantages of using an established discrete ordinates solver, e.g. immediately available adjoint capability. Coupled electron-photon transport capability is needed for many applications, including the modeling of the response of electronics components to space and man-made radiation environments. The cross sections have been successfully used in the DORT, TWODANT and TORT discrete ordinates codes. The cross sections are shown to provide accurate and efficient solutions to certain multidimensional electronphoton transport problems.
ERIC Educational Resources Information Center
Kennelly, Brendan; Flannery, Darragh; Considine, John; Doherty, Edel; Hynes, Stephen
2014-01-01
This paper outlines how a discrete choice experiment (DCE) can be used to learn more about how students are willing to trade off various features of assignments such as the nature and timing of feedback and the method used to submit assignments. A DCE identifies plausible levels of the key attributes of a good or service and then presents the…
Discrete elements method of neutral particle transport. Doctoral thesis
Mathews, K.A.
1983-10-01
A new 'discrete elements' (LN) transport method is derived and compared to the discrete ordinates SN method, theoretically and by numerical experimentation. The discrete elements method is more accurate than discrete ordinates and strongly ameliorates ray effects for the practical problems studied. The discrete elements method is shown to be more cost effective in terms of execution time with comparable storage to attain the same accuracy, for a one-dimensional test case using linear characteristic spatial quadrature. In a two-dimensional test case, a vacuum duct in a shield, LN is more consistently convergent toward a Monte Carlo benchmark solution than SN, using step characteristic spatial quadrature. An analysis of the interaction of angular and spatial quadrature in xy-geometry indicates the desirability of using linear characteristic spatial quadrature with the LN method. The discrete elements method is based on discretizing the Boltzmann equation over a set of elements of angle. The zeroth and first angular moments of the directional flux, over each element, are estimated by numerical quadrature and yield a flux-weighted average streaming direction for the element. (Data for this estimation are fluxes in fixed directions calculated as in SN.)
Eisenhauer, Philipp; Heckman, James J.; Mosso, Stefano
2015-01-01
We compare the performance of maximum likelihood (ML) and simulated method of moments (SMM) estimation for dynamic discrete choice models. We construct and estimate a simplified dynamic structural model of education that captures some basic features of educational choices in the United States in the 1980s and early 1990s. We use estimates from our model to simulate a synthetic dataset and assess the ability of ML and SMM to recover the model parameters on this sample. We investigate the performance of alternative tuning parameters for SMM. PMID:26494926
A discrete-continuous choice model of climate change impacts on energy
Morrison, W.N.; Mendelsohn, R.
1998-09-01
This paper estimates a discrete-continuous fuel choice model in order to explore climate impacts on the energy sector. The model is estimated on a national data set of firms and households. The results reveal that actors switch from oil in cold climates to electricity and natural gas in warm climates and that fuel-specific expenditures follow a U-shaped relationship with respect to temperature. The model implies that warming will increase American energy expenditures, reflecting a sizable welfare damage.
Benefit–risk assessment of HMG-CoA reductase inhibitors (statins): a discrete choice experiment
Sornlertlumvanich, Korn; Ngorsuraches, Surachat
2016-01-01
Objectives To conduct the benefit–risk assessment of 3-hydroxy-3-methyl-glutaryl (HMG) coenzyme A reductase inhibitors (statins) using a discrete choice experiment, based on 3 major stakeholders’ perspectives including patients, experts and policymakers in Thailand. Design A discrete choice experiment questionnaire survey in three stakeholders’ perspectives. Setting Public hospitals in Thailand. Participants A total of 353 policymakers, experts and patients. Outcomes Stakeholders’ preferences for assessment criteria (stroke reduction, myocardial infarction reduction, myalgia and hepatotoxicity). Statins’ ranking and maximum acceptable risk in all perspectives were also calculated. Results For any perspective, the most and least important criteria were the risk of hepatotoxicity and the benefit of myocardial infarction reduction, respectively. Patients and experts agreed on the order of importance for myalgia and stroke reduction, but policymakers had different order of importance in these criteria. Overall, results showed that the highest and lowest chances of being chosen were atorvastatin and rosuvastatin, respectively. Only patients’ ranking order was different from others. Maximum acceptable risk of hepatotoxicity was lower than that of myalgia, reflecting the greater concern of all perspectives to statin consequence on liver. Conclusions The results of benefit–risk assessment from every perspective were somewhat consistent. This study demonstrated the feasibility of applying a discrete choice experiment in the benefit–risk assessment of drugs and encouraged the engagement of multiple stakeholders in the decision-making process. PMID:26916689
Multidimensional electron-photon transport with standard discrete ordinates codes
Drumm, C.R.
1997-04-01
A method is described for generating electron cross sections that are comparable with standard discrete ordinates codes without modification. There are many advantages of using an established discrete ordinates solver, e.g. immediately available adjoint capability. Coupled electron-photon transport capability is needed for many applications, including the modeling of the response of electronics components to space and man-made radiation environments. The cross sections have been successfully used in the DORT, TWODANT and TORT discrete ordinates codes. The cross sections are shown to provide accurate and efficient solutions to certain multidimensional electron-photon transport problems. The key to the method is a simultaneous solution of the continuous-slowing-down (CSD) portion and elastic-scattering portion of the scattering source by the Goudsmit-Saunderson theory. The resulting multigroup-Legendre cross sections are much smaller than the true scattering cross sections that they represent. Under certain conditions, the cross sections are guaranteed positive and converge with a low-order Legendre expansion.
Multidimensional electron-photon transport with standard discrete ordinates codes
Drumm, C.R.
1997-09-01
A method is described for generating electron cross sections that are compatible with standard discrete ordinates codes without modification. There are many advantages to using an established discrete ordinates solver, e.g., immediately available adjoint capability. Coupled electron-photon transport capability is needed for many applications, including the modeling of the response of electronics components to space and synthetic radiation environments. The cross sections have been successfully used in the DORT, TWODANT, and TORT discrete ordinates codes. The cross sections are shown to provide accurate and efficient solutions to certain multidimensional electron-photon transport problems. The key to the method is a simultaneous solution of the continuous-slowing-down and elastic-scattering portions of the scattering source by the Goudsmit-Saunderson theory. The resulting multigroup-Legendre cross sections are much smaller than the true scattering cross sections that they represent. Under certain conditions, the cross sections are guaranteed positive and converge with a low-order Legendre expansion.
Urban transportation: Perspectives on mobility and choice
NASA Technical Reports Server (NTRS)
Sincoff, M. Z. (Editor); Dajani, J. S. (Editor); Arnold, G. R.; Bird, J. W.; Brooks, C. M. (Editor); Cobb, W. E.; Cross, J. E.; Darby, L. F.; Erb, N. H.; Ficht, J. C.
1974-01-01
A study of urban transportation systems are presented characterized by intensive scrutiny of many ideas, philosophies, and academic perspectives. This report is intended to communicate some dimensions of the urban transportation problem to the general public.
Exactly solvable potentials with finitely many discrete eigenvalues of arbitrary choice
NASA Astrophysics Data System (ADS)
Sasaki, Ryu
2014-06-01
We address the problem of possible deformations of exactly solvable potentials having finitely many discrete eigenvalues of arbitrary choice. As Kay and Moses showed in 1956, reflectionless potentials in one dimensional quantum mechanics are exactly solvable. With an additional time dependence these potentials are identified as the soliton solutions of the Korteweg de Vries (KdV) hierarchy. An N-soliton potential has the time t and 2N positive parameters, k1 < ⋯ < kN and {cj}, j = 1, …, N, corresponding to N discrete eigenvalues lbrace -k_j^2rbrace. The eigenfunctions are elementary functions expressed by the ratio of determinants. The Darboux-Crum-Krein-Adler transformations or the Abraham-Moses transformations based on eigenfunction deletions produce lower soliton number potentials with modified parameters lbrace c^' }_jrbrace. We explore various identities satisfied by the eigenfunctions of the soliton potentials, which reflect the uniqueness theorem of Gel'fand-Levitan-Marchenko equations for separable (degenerate) kernels.
Modelling discrete choice variables in assessment of teaching staff work satisfaction.
Mieilă, Mihai; Popescu, Constanţa; Tudorache, Ana-Maria; Toplicianu, Valerică
2015-01-01
Levels of self-reported job satisfaction and motivation were measured by survey in a sample of 286 teachers. Using the discrete choice framework, the paper tries to assess the relevance of the considered indicators (demographic, social, motivational) in overall teaching work satisfaction. The findings provide evidence that job satisfaction is correlated significantly with level of university degree held by the teacher, type of secondary school where the teacher is enrolled, revenues, and salary-tasks adequacy. This is important for the Romanian economy, since the education system is expected to provide future human resources with enhanced skills and abilities. PMID:25849295
Testing Ecological Theories of Offender Spatial Decision Making Using a Discrete Choice Model
Summers, Lucia
2015-01-01
Research demonstrates that crime is spatially concentrated. However, most research relies on information about where crimes occur, without reference to where offenders reside. This study examines how the characteristics of neighborhoods and their proximity to offender home locations affect offender spatial decision making. Using a discrete choice model and data for detected incidents of theft from vehicles (TFV), we test predictions from two theoretical perspectives—crime pattern and social disorganization theories. We demonstrate that offenders favor areas that are low in social cohesion and closer to their home, or other age-related activity nodes. For adult offenders, choices also appear to be influenced by how accessible a neighborhood is via the street network. The implications for criminological theory and crime prevention are discussed. PMID:25866412
Lancsar, Emily; Donaldson, Cam
2005-12-01
Bryan and Dolan have offered a critique of the use of discrete choice experiments in health economics. Their call for more open debate on "the relative strengths and limitations of the DCE method, particularly when applied in health settings" is warranted. However, their paper has only added to part of this debate in that it focuses on the application of choice experiments in the health sector but says little on the strengths and limitations of the DCE method in general. We argue that while the criticisms posed by Bryan and Dolan rightly challenge the manner in which DCEs have been applied in health economics, such criticism does not challenge the theoretical/methodological basis of DCEs per se.
A concurrent, multigroup, discrete ordinates model of neutron transport
Dorr, M.R.; Still, C.H.
1993-10-22
The authors present an algorithm for the concurrent solution of the linear system arising from a multigroup, discrete ordinates model of neutron transport. The target architectures consist of distributed memory computers ranging from workstation clusters to massively parallel computers. Based on an analysis of the memory requirement and floating point complexity of matrix-vector multiplication in the iterative solution of the linear system, the authors propose a data layout and communication strategy designed to achieve scalability with respect to all phase space variables. Numerical results are presented to demonstrate the performance of the algorithm on the nCUBE/2.
Transport and discrete particle noise in gyrokinetic simulations
NASA Astrophysics Data System (ADS)
Jenkins, Thomas; Lee, W. W.
2006-10-01
We present results from our recent investigations regarding the effects of discrete particle noise on the long-time behavior and transport properties of gyrokinetic particle-in-cell simulations. It is found that the amplitude of nonlinearly saturated drift waves is unaffected by discreteness-induced noise in plasmas whose behavior is dominated by a single mode in the saturated state. We further show that the scaling of this noise amplitude with particle count is correctly predicted by the fluctuation-dissipation theorem, even though the drift waves have driven the plasma from thermal equilibrium. As well, we find that the long-term behavior of the saturated system is unaffected by discreteness-induced noise even when multiple modes are included. Additional work utilizing a code with both total-f and δf capabilities is also presented, as part of our efforts to better understand the long- time balance between entropy production, collisional dissipation, and particle/heat flux in gyrokinetic plasmas.
ERIC Educational Resources Information Center
Cunningham, Charles E.; Deal, Ken; Rimas, Heather; Chen, Yvonne; Buchanan, Don H.; Sdao-Jarvie, Kathie
2009-01-01
We used discrete choice conjoint analysis to model the ways 645 children's mental health (CMH) professionals preferred to provide information to parents seeking CMH services. Participants completed 20 choice tasks presenting experimentally varied combinations of the study's 14 4-level CMH information transfer attributes. Latent class analysis…
ERIC Educational Resources Information Center
Waschbusch, Daniel A.; Cunningham, Charles E.; Pelham, William E., Jr.; Rimas, Heather L.; Greiner, Andrew R.; Gnagy, Elizabeth M.; Waxmonsky, James; Fabiano, Gregory A.; Robb, Jessica A.; Burrows-MacLean, Lisa; Scime, Mindy; Hoffman, Martin T.
2011-01-01
The current study examined treatment preferences of 183 parents of young (average age = 5.8 years, SD = 0.6), medication naive children with ADHD. Preferences were evaluated using a discrete choice experiment in which parents made choices between different combinations of treatment characteristics, outcomes, and costs. Latent class analysis…
Modeling improvements in booster seat use: a discrete choice conjoint experiment.
Cunningham, Charles E; Bruce, Beth S; Snowdon, Anne W; Chen, Yvonne; Kolga, Carol; Piotrowski, Caroline; Warda, Lynne; Correale, Heather; Clark, Erica; Barwick, Melanie
2011-11-01
Automobile crashes are the leading cause of death in children aged 1-14 years. Many children, however, are not properly restrained in safety seats that reduce serious injury and death. This study used a discrete choice conjoint experiment to study factors influencing the decision to use booster seats. Parents of 1714 children aged 4-9 years from nine Canadian provinces completed choice tasks presenting experimentally varied combinations of 15 4-level booster seat promotion attributes. Latent class analysis yielded three segments of parents. The choices of the Benefit Sensitive segment (50%) were most sensitive to the injury prevention benefits of booster seats. The choices of parents in the Context Sensitive segment (33.5%) were more likely to be influenced by installation complexity, oppositional behavior, and the prospect that their child may be teased for riding in booster seats. Parents in the High Risk segment (16.5%) were younger, less educated, and less knowledgeable about vehicle safety legislation. They anticipated fewer benefits, expected more barriers and were less likely to use booster seats. Simulations suggest that consistent enforcement coupled with advertising focusing on injury prevention and the use of booster seats by other parents would increase adoption.
Human group choice: discrete-trial and free-operant tests of the ideal free distribution.
Madden, Gregory J; Peden, Blaine F; Yamaguchi, Tetsuo
2002-07-01
Ideal free distribution theory predicts that foragers will form groups proportional in number to the resources available in alternative resource sites or patches, a phenomenon termed habitat matching. Three experiments tested this prediction with college students in discrete-trial simulations and a free-operant simulation. Sensitivity to differences in programmed reinforcement rates was quantified by using the sensitivity parameter of the generalized matching law (s). The first experiment, replicating prior published experiments, produced a greater degree of undermatching for the initial choice (s = 0.59) compared to final choices (s = 0.86). The second experiment, which extended prior findings by allowing only one choice per trial, produced comparable undermatching (s = 0.82). The third experiment used free-operant procedures more typical of laboratory studies of habitat matching with other species and produced the most undermatching (s = 0.71). The results of these experiments replicated previous results with human groups, supported predictions of the ideal free distribution, and suggested that undermatching represents a systematic deviation from the ideal free distribution. These results are consistent with a melioration account of individual behavior as the basis for group choice.
Modeling improvements in booster seat use: a discrete choice conjoint experiment.
Cunningham, Charles E; Bruce, Beth S; Snowdon, Anne W; Chen, Yvonne; Kolga, Carol; Piotrowski, Caroline; Warda, Lynne; Correale, Heather; Clark, Erica; Barwick, Melanie
2011-11-01
Automobile crashes are the leading cause of death in children aged 1-14 years. Many children, however, are not properly restrained in safety seats that reduce serious injury and death. This study used a discrete choice conjoint experiment to study factors influencing the decision to use booster seats. Parents of 1714 children aged 4-9 years from nine Canadian provinces completed choice tasks presenting experimentally varied combinations of 15 4-level booster seat promotion attributes. Latent class analysis yielded three segments of parents. The choices of the Benefit Sensitive segment (50%) were most sensitive to the injury prevention benefits of booster seats. The choices of parents in the Context Sensitive segment (33.5%) were more likely to be influenced by installation complexity, oppositional behavior, and the prospect that their child may be teased for riding in booster seats. Parents in the High Risk segment (16.5%) were younger, less educated, and less knowledgeable about vehicle safety legislation. They anticipated fewer benefits, expected more barriers and were less likely to use booster seats. Simulations suggest that consistent enforcement coupled with advertising focusing on injury prevention and the use of booster seats by other parents would increase adoption. PMID:21819828
Exploring foraging decisions in a social primate using discrete-choice models.
Marshall, Harry H; Carter, Alecia J; Coulson, Tim; Rowcliffe, J Marcus; Cowlishaw, Guy
2012-10-01
There is a growing appreciation of the multiple social and nonsocial factors influencing the foraging behavior of social animals but little understanding of how these factors depend on habitat characteristics or individual traits. This partly reflects the difficulties inherent in using conventional statistical techniques to analyze multifactor, multicontext foraging decisions. Discrete-choice models provide a way to do so, and we demonstrate this by using them to investigate patch preference in a wild population of social foragers (chacma baboons Papio ursinus). Data were collected from 29 adults across two social groups, encompassing 683 foraging decisions over a 6-month period and the results interpreted using an information-theoretic approach. Baboon foraging decisions were influenced by multiple nonsocial and social factors and were often contingent on the characteristics of the habitat or individual. Differences in decision making between habitats were consistent with changes in interference-competition costs but not with changes in social-foraging benefits. Individual differences in decision making were suggestive of a trade-off between dominance rank and social capital. Our findings emphasize that taking a multifactor, multicontext approach is important to fully understand animal decision making. We also demonstrate how discrete-choice models can be used to achieve this.
Discrete strategies to reduce intake of discretionary food choices: a scoping review.
Grieger, Jessica A; Wycherley, Thomas P; Johnson, Brittany J; Golley, Rebecca K
2016-01-01
On a population level, dietary improvement strategies have had limited success in preventing the surge in overweight and obesity or reducing risk factors for chronic disease. While numerous multi-component studies have examined whole-of-diet strategies, and single component (i.e. discrete) dietary intervention strategies have targeted an increase in core foods (e.g. fruits, vegetables, dairy), there is a paucity of evidence on the effectiveness of dietary intervention strategies targeting a decrease in discretionary choices. The aim of this review was to identify dietary intervention strategies that are potentially relevant to reducing intake of discretionary choices in 2-65 year olds. A scoping review was carried out to map the literature on key discrete dietary intervention strategies that are potentially applicable to reducing discretionary choices, and to identify the targeted health/nutrition effects (e.g. improve nutrient intake, decrease sugar intake, and reduce body weight) of these strategies. Studies conducted in participants aged 2-65 years and published in English by July 20, 2015, were located through electronic searches including the Cochrane Library, Medline, Embase, CINAHL, and Scopus. Three thousand two hundred and eighty three studies were identified from the search, of which 44 met the selection criteria. The dietary intervention strategies included reformulation (n = 13), substitution (n = 5), restriction/elimination (n = 9), supplementation (n = 13), and nutrition education/messages (n = 4). The key findings of the review were: restricting portion size was consistently beneficial for reducing energy intake in the acute setting; reformulating foods from higher fat to lower fat could be useful to reduce saturated fat intake; substituting discretionary choices for high fibre snacks, fruit, or low/no-calorie beverages may be an effective strategy for reducing energy intake; supplementing nutrient dense foods such as nuts and
The theory of planned behaviour and discrete food choices: a systematic review and meta-analysis.
McDermott, Máirtín S; Oliver, Madalyn; Svenson, Alexander; Simnadis, Thomas; Beck, Eleanor J; Coltman, Tim; Iverson, Don; Caputi, Peter; Sharma, Rajeev
2015-12-30
The combination of economic and social costs associated with non-communicable diseases provide a compelling argument for developing strategies that can influence modifiable risk factors, such as discrete food choices. Models of behaviour, such as the Theory of Planned Behaviour (TPB) provide conceptual order that allows program designers and policy makers to identify the substantive elements that drive behaviour and design effective interventions. The primary aim of the current review was to examine the association between TPB variables and discrete food choice behaviours. A systematic literature search was conducted to identify relevant studies. Calculation of the pooled mean effect size (r(+)) was conducted using inverse-variance weighted, random effects meta-analysis. Heterogeneity across studies was assessed using the Q- and I(2)-statistics. Meta-regression was used to test the impact of moderator variables: type of food choice behaviour; participants' age and gender. A total of 42 journal articles and four unpublished dissertations met the inclusion criteria. TPB variables were found to have medium to large associations with both intention and behaviour. Attitudes had the strongest association with intention (r(+) = 0.54) followed by perceived behavioural control (PBC, r(+) = 0.42) and subjective norm (SN, r(+) = 0.37). The association between intention and behaviour was r(+) = 0.45 and between PBC and behaviour was r(+) = 0.27. Moderator analyses revealed the complex nature of dietary behaviour and the factors that underpin individual food choices. Significantly higher PBC-behaviour associations were found for choosing health compromising compared to health promoting foods. Significantly higher intention-behaviour and PBC-behaviour associations were found for choosing health promoting foods compared to avoiding health compromising foods. Participant characteristics were also found to moderate associations within the model. Higher
The theory of planned behaviour and discrete food choices: a systematic review and meta-analysis.
McDermott, Máirtín S; Oliver, Madalyn; Svenson, Alexander; Simnadis, Thomas; Beck, Eleanor J; Coltman, Tim; Iverson, Don; Caputi, Peter; Sharma, Rajeev
2015-01-01
The combination of economic and social costs associated with non-communicable diseases provide a compelling argument for developing strategies that can influence modifiable risk factors, such as discrete food choices. Models of behaviour, such as the Theory of Planned Behaviour (TPB) provide conceptual order that allows program designers and policy makers to identify the substantive elements that drive behaviour and design effective interventions. The primary aim of the current review was to examine the association between TPB variables and discrete food choice behaviours. A systematic literature search was conducted to identify relevant studies. Calculation of the pooled mean effect size (r(+)) was conducted using inverse-variance weighted, random effects meta-analysis. Heterogeneity across studies was assessed using the Q- and I(2)-statistics. Meta-regression was used to test the impact of moderator variables: type of food choice behaviour; participants' age and gender. A total of 42 journal articles and four unpublished dissertations met the inclusion criteria. TPB variables were found to have medium to large associations with both intention and behaviour. Attitudes had the strongest association with intention (r(+) = 0.54) followed by perceived behavioural control (PBC, r(+) = 0.42) and subjective norm (SN, r(+) = 0.37). The association between intention and behaviour was r(+) = 0.45 and between PBC and behaviour was r(+) = 0.27. Moderator analyses revealed the complex nature of dietary behaviour and the factors that underpin individual food choices. Significantly higher PBC-behaviour associations were found for choosing health compromising compared to health promoting foods. Significantly higher intention-behaviour and PBC-behaviour associations were found for choosing health promoting foods compared to avoiding health compromising foods. Participant characteristics were also found to moderate associations within the model. Higher
Valuing health at the end of life: a stated preference discrete choice experiment.
Shah, Koonal K; Tsuchiya, Aki; Wailoo, Allan J
2015-01-01
A source of debate in the field of health care priority setting is whether health gains should be weighted differently for different groups of patients. The debate has recently focused on the relative value of life extensions for patients with short life expectancy. However, few studies have examined empirically whether society is prepared to fund life-extending end-of-life treatments that would not meet the reimbursement criteria used for other treatments. A web-based discrete choice experiment was conducted in 2012 using a sample of 3969 members of the general public in England and Wales. The study design was informed by the National Institute for Health and Care Excellence's supplementary policy for the appraisal of life-extending end-of-life treatments. The choice tasks involved asking respondents which of two hypothetical patients they would prefer to treat, assuming that the health service has enough funds to treat only one of them. Conditional logit regressions were used for modelling. Choices about which patient to treat were influenced more by the sizes of treatment gains than by patients' life expectancy without treatment. Some respondents appear to support a health-maximisation type objective throughout, whilst a small minority always seek to treat those who are worse off without treatment. The majority of respondents, however, seem to advocate a mixture of the two approaches. Overall, we find little evidence that members of the general public prefer to give higher priority to life-extending end-of-life treatments than to other types of treatment. When asked to make decisions about the treatment of hypothetical patients with relatively short life expectancies, most people's choices are driven by the size of the health gains offered by treatment.
Kaambwa, Billingsley; Lancsar, Emily; McCaffrey, Nicola; Chen, Gang; Gill, Liz; Cameron, Ian D; Crotty, Maria; Ratcliffe, Julie
2015-09-01
Consumer directed care (CDC) is currently being embraced internationally as a means to promote autonomy and choice for consumers (people aged 65 and over) receiving community aged care services (CACSs). CDC involves giving CACS clients (consumers and informal carers of consumers) control over how CACSs are administered. However, CDC models have largely developed in the absence of evidence on clients' views and preferences. We explored CACS clients' preferences for a variety of CDC attributes and identified factors that may influence these preferences and potentially inform improved design of future CDC models. Study participants were clients of CACSs delivered by five Australian providers. Using a discrete choice experiment (DCE) approach undertaken in a group setting between June and December 2013, we investigated the relative importance to CACS consumers and informal (family) carers of gradations relating to six salient features of CDC (choice of service provider(s), budget management, saving unused/unspent funds, choice of support/care worker(s), support-worker flexibility and level of contact with service coordinator). The DCE data were analysed using conditional, mixed and generalised logit regression models, accounting for preference and scale heterogeneity. Mean ages for 117 study participants were 80 years (87 consumers) and 74 years (30 informal carers). All participants preferred a CDC approach that allowed them to: save unused funds from a CACS package for future use; have support workers that were flexible in terms of changing activities within their CACS care plan and; choose the support workers that provide their day-to-day CACSs. The CDC attributes found to be important to both consumers and informal carers receiving CACSs will inform the design of future CDC models of service delivery. The DCE approach used in this study has the potential for wide applicability and facilitates the assessment of preferences for elements of potential future aged care
Kaambwa, Billingsley; Lancsar, Emily; McCaffrey, Nicola; Chen, Gang; Gill, Liz; Cameron, Ian D; Crotty, Maria; Ratcliffe, Julie
2015-09-01
Consumer directed care (CDC) is currently being embraced internationally as a means to promote autonomy and choice for consumers (people aged 65 and over) receiving community aged care services (CACSs). CDC involves giving CACS clients (consumers and informal carers of consumers) control over how CACSs are administered. However, CDC models have largely developed in the absence of evidence on clients' views and preferences. We explored CACS clients' preferences for a variety of CDC attributes and identified factors that may influence these preferences and potentially inform improved design of future CDC models. Study participants were clients of CACSs delivered by five Australian providers. Using a discrete choice experiment (DCE) approach undertaken in a group setting between June and December 2013, we investigated the relative importance to CACS consumers and informal (family) carers of gradations relating to six salient features of CDC (choice of service provider(s), budget management, saving unused/unspent funds, choice of support/care worker(s), support-worker flexibility and level of contact with service coordinator). The DCE data were analysed using conditional, mixed and generalised logit regression models, accounting for preference and scale heterogeneity. Mean ages for 117 study participants were 80 years (87 consumers) and 74 years (30 informal carers). All participants preferred a CDC approach that allowed them to: save unused funds from a CACS package for future use; have support workers that were flexible in terms of changing activities within their CACS care plan and; choose the support workers that provide their day-to-day CACSs. The CDC attributes found to be important to both consumers and informal carers receiving CACSs will inform the design of future CDC models of service delivery. The DCE approach used in this study has the potential for wide applicability and facilitates the assessment of preferences for elements of potential future aged care
Gu, Yuanyuan; Norman, Richard; Viney, Rosalie
2014-09-01
Using discrete choice experiments (DCEs) to estimate health state utility values has become an important alternative to the conventional methods of Time Trade-Off and Standard Gamble. Studies using DCEs have typically used the conditional logit to estimate the underlying utility function. The conditional logit is known for several limitations. In this paper, we propose two types of models based on the mixed logit: one using preference space and the other using quality-adjusted life year (QALY) space, a concept adapted from the willingness-to-pay literature. These methods are applied to a dataset collected using the EQ-5D. The results showcase the advantages of using QALY space and demonstrate that the preferred QALY space model provides lower estimates of the utility values than the conditional logit, with the divergence increasing with worsening health states.
Evaluating the welfare effects of improved wastewater treatment using a discrete choice experiment.
Ndunda, Ezekiel N; Mungatana, Eric D
2013-07-15
This paper employs the discrete choice experiment method to estimate the benefits of improved wastewater treatment programs to mitigate the impacts of water pollution in Nairobi, Kenya. Urban and peri-urban farmers who use wastewater for irrigation from Motoine to Ngong River in Nairobi were randomly selected for the study. A random parameter logit model was used to estimate the individual level willingness to pay for the wastewater treatment before reuse in irrigation. The results show that urban and peri-urban farmers are willing to pay significant monthly municipality taxes for treatment of wastewater. We find that the quality of treated wastewater, the quantity of treated wastewater and the riverine ecosystem restoration are significant factors of preference over alternative policy designs in reduction of water pollution. PMID:23583865
The use of alternative preference elicitation methods in complex discrete choice experiments.
Yoo, Hong Il; Doiron, Denise
2013-12-01
We analyse stated preference data over nursing jobs collected from two different discrete choice experiments: a multi-profile case best-worst scaling experiment (BWS) prompting selection of the best and worst among alternative jobs, and a profile case BWS wherein the respondents choose the best and worst job attributes. The latter allows identification of additional utility parameters and is believed to be cognitively easier. Results suggest that respondents place greater value on pecuniary over non-pecuniary gains in the multi-profile case. There is little evidence that this discrepancy is induced by the extra cognitive burden of processing several profiles at once in the multi-profile case. We offer thoughts on other likely mechanisms.
Poulos, Christine; Kinter, Elizabeth; Yang, Jui-Chen; Bridges, John F. P.; Posner, Joshua; Gleißner, Erika; Mühlbacher, Axel; Kieseier, Bernd
2016-01-01
Objectives: The aim of this study was to assess the relative importance of features of a hypothetical injectable disease-modifying treatment for patients with multiple sclerosis using a discrete-choice experiment. Methods: German residents at least 18 years of age with a self-reported physician diagnosis of multiple sclerosis completed a 25–30 minute online discrete-choice experiment. Patients were asked to choose one of two hypothetical injectable treatments for multiple sclerosis, defined by different levels of six attributes (disability progression, the number of relapses in the next 4 years, injection time, frequency of injections, presence of flu-like symptoms, and presence of injection-site reactions). The data were analyzed using a random-parameters logit model. Results: Of 202 adults who completed the survey, results from 189 were used in the analysis. Approximately 50% of all patients reported a diagnosis of relapsing–remitting multiple sclerosis, and 31% reported secondary progressive multiple sclerosis. Approximately 71% of patients had current or prior experience with injectable multiple sclerosis medication. Approximately 53% had experienced flu-like symptoms caused by their medication, and 47% had experienced mild injection-site reactions. At least one significant difference was seen between levels in all attributes, except injection time. The greatest change in relative importance between levels of an attribute was years until symptoms get worse from 1 to 4 years. The magnitude of this difference was about twice that of relapses in the next 4 years, frequency of injections, and flu-like symptoms. Conclusions: Most attributes examined in this experiment had an influence on patient preference. Patients placed a significant value on improvements in the frequency of dosing and disability progression. Results suggest that changes in injection frequency can be as important as changes in efficacy and safety attributes. Understanding which attributes of
Discrete and continuous-choice valuation of a hazardous-waste site's removal
Michaels, R.G.
1987-01-01
This study developed a methodology for valuing complete removal of a hazardous waste site or similar disamenity using location decisions in a metropolitan housing market. The objects were to integrate a description of household decisions in a model acknowledging existence of different market segments; to implement this mix in a case study; to evaluate the model as a depiction of the housing market; and to investigate the sensitivity of benefit measures to alternative assumptions about the housing-market equilibrium. The basis for benefit estimates is a model describing how consumers choose where to live and how hazardous-waste sites affect those decisions. The model combines discrete choice and hedonic approaches. The motivation is that each consumer is judged to perceive a discrete set of location alternatives, within which the optimal house is chosen. The alternatives are considered market segments, each having its own hedonic price function. Each segment conveys a fixed package of attributes, such as public services or the presence of hazardous waste sites. In choosing a segment the consumer chooses one such fixed package.
Women’s Preferences for Treatment of Perinatal Depression and Anxiety: A Discrete Choice Experiment
Ride, Jemimah; Lancsar, Emily
2016-01-01
Perinatal depression and anxiety (PNDA) are an international healthcare priority, associated with significant short- and long-term problems for women, their children and families. Effective treatment is available but uptake is suboptimal: some women go untreated whilst others choose treatments without strong evidence of efficacy. Better understanding of women’s preferences for treatment is needed to facilitate uptake of effective treatment. To address this issue, a discrete choice experiment (DCE) was administered to 217 pregnant or postnatal women in Australia, who were recruited through an online research company and had similar sociodemographic characteristics to Australian data for perinatal women. The DCE investigated preferences regarding cost, treatment type, availability of childcare, modality and efficacy. Data were analysed using logit-based models accounting for preference and scale heterogeneity. Predicted probability analysis was used to explore relative attribute importance and policy change scenarios, including how these differed by women’s sociodemographic characteristics. Cost and treatment type had the greatest impact on choice, such that a policy of subsidising effective treatments was predicted to double their uptake compared with the base case. There were differences in predicted uptake associated with certain sociodemographic characteristics: for example, women with higher educational attainment were more likely to choose effective treatment. The findings suggest policy directions for decision makers whose goal is to reduce the burden of PNDA on women, their children and families. PMID:27258096
Sadique, Md Z.; Devlin, Nancy; Edmunds, William J.; Parkin, David
2013-01-01
The demand for vaccination against infectious diseases involves a choice between vaccinating and not vaccinating, in which there is a trade-off between the benefits and costs of each option. The aim of this paper is to investigate these trade-offs and to estimate how the perceived prevalence and severity of both the disease against which the vaccine is given and any vaccine associated adverse events (VAAE) might affect demand. A Discrete Choice Experiment (DCE) was used to elicit stated preferences from a representative sample of 369 UK mothers of children below 5 years of age, for three hypothetical vaccines. Cost was included as an attribute, which enabled estimation of the willingness to pay for different vaccines having differing levels of the probability of occurrence and severity of both the infection and VAAE. The results suggest that the severity of the health effects associated with both the diseases and VAAEs exert an important influence on the demand for vaccination, whereas the probability of these events occurring was not a significant predictor. This has important implications for public health policy, which has tended to focus on the probability of these health effects as the main influence on decision making. Our results also suggest that anticipated regrets about the consequences of making the wrong decision also exert an influence on demand. PMID:23408936
Hall, Jane; Kenny, Patricia; King, Madeleine; Louviere, Jordan; Viney, Rosalie; Yeoh, Angela
2002-07-01
Applications of stated preference discrete choice modelling (SPDCM) in health economics have been used to estimate consumer willingness to pay and to broaden the range of consequences considered in economic evaluation. This paper demonstrates how SPDCM can be used to predict participation rates, using the case of varicella (chickenpox) vaccination. Varicella vaccination may be cost effective compared to other public health programs, but this conclusion is sensitive to the proportion of the target population immunised. A choice experiment was conducted on a sample of Australian parents to predict uptake across a range of hypothetical programs. Immunisation rates would be increased by providing immunisation at no cost, by requiring it for school entry, by increasing immunisation rates in the community and decreasing the incidence of mild and severe side effects. There were two significant interactions; price modified the effect of both support from authorities and severe side effects. Country of birth was the only significant demographic characteristic. Depending on aspects of the immunisation program, the immunisation rates of children with Australian-born parents varied from 9% to 99% while for the children with parents born outside Australia they varied from 40% to 99%. This demonstrates how SPDCM can be used to understand the levels of attributes that will induce a change in the decision to immunise, the modification of the effect of one attribute by another, and subgroups in the population. Such insights can contribute to the optimal design and targeting of health programs.
Preferences for pharmacist counselling in patients with breast cancer: a discrete choice experiment.
Kawaguchi, Takashi; Azuma, Kanako; Yamaguchi, Takuhiro; Iwase, Satoru; Matsunaga, Tadaharu; Yamada, Kimito; Miyamatsu, Hironobu; Takeuchi, Hironori; Kohno, Norio; Akashi, Takao; Unezaki, Sakae
2014-01-01
With the shift of a large proportion of cancer chemotherapy recipients to ambulatory care, the role of hospital pharmacists has changed, and their provision of information is essential care for cancer patients. There is little research on pharmacist-patient relations, particularly about pharmacist counselling, in Japan. To meet patients' needs, pharmacist counselling should be optimized. Here, breast cancer patients' preferences for pharmacist counselling were assessed using a discrete choice experiment. Bayesian nonlinear optimal methodology was employed to obtain six attributes (attitude of pharmacist, quality of information, explanation of side effects, frequency of pharmacist counselling before starting chemotherapy, cost of pharmacist counselling, and follow-up with the pharmacist after starting chemotherapy) of two to three levels each. The attributes and levels were used to create 12 hypothetical scenarios that were divided into two questionnaires of six choice sets each. Two hundred eighty participants were randomly assigned to complete one of these questionnaires (blocks). Attributes were analyzed by conditional logit model to determine significant predictors of patient preferences. The responses of 278 patients to 1667 scenarios were analyzed. Attitude of pharmacist, quality of information, cost of pharmacist counselling, and follow-up with the pharmacist after starting chemotherapy were significant predictors of patient preferences, with quality of information receiving the highest priority. Thus patients receiving pharmacist counselling before starting chemotherapy prefer to interact with a pharmacist with a friendly, interested attitude who provides individualized information. Further research is needed to elucidate the information that Japanese patients consider most important and to enhance pharmacist-patient communication.
Women's Preferences for Treatment of Perinatal Depression and Anxiety: A Discrete Choice Experiment.
Ride, Jemimah; Lancsar, Emily
2016-01-01
Perinatal depression and anxiety (PNDA) are an international healthcare priority, associated with significant short- and long-term problems for women, their children and families. Effective treatment is available but uptake is suboptimal: some women go untreated whilst others choose treatments without strong evidence of efficacy. Better understanding of women's preferences for treatment is needed to facilitate uptake of effective treatment. To address this issue, a discrete choice experiment (DCE) was administered to 217 pregnant or postnatal women in Australia, who were recruited through an online research company and had similar sociodemographic characteristics to Australian data for perinatal women. The DCE investigated preferences regarding cost, treatment type, availability of childcare, modality and efficacy. Data were analysed using logit-based models accounting for preference and scale heterogeneity. Predicted probability analysis was used to explore relative attribute importance and policy change scenarios, including how these differed by women's sociodemographic characteristics. Cost and treatment type had the greatest impact on choice, such that a policy of subsidising effective treatments was predicted to double their uptake compared with the base case. There were differences in predicted uptake associated with certain sociodemographic characteristics: for example, women with higher educational attainment were more likely to choose effective treatment. The findings suggest policy directions for decision makers whose goal is to reduce the burden of PNDA on women, their children and families.
Discrete choice experiments in health economics: a review of the literature.
de Bekker-Grob, Esther W; Ryan, Mandy; Gerard, Karen
2012-02-01
Discrete choice experiments (DCEs) have become a commonly used instrument in health economics. This paper updates a review of published papers between 1990 and 2000 for the years 2001-2008. Based on this previous review, and a number of other key review papers, focus is given to three issues: experimental design; estimation procedures; and validity of responses. Consideration is also given to how DCEs are applied and reported. We identified 114 DCEs, covering a wide range of policy questions. Applications took place in a broader range of health-care systems, and there has been a move to incorporating fewer attributes, more choices and interview-based surveys. There has also been a shift towards statistically more efficient designs and flexible econometric models. The reporting of monetary values continues to be popular, the use of utility scores has not gained popularity, and there has been an increasing use of odds ratios and probabilities. The latter are likely to be useful at the policy level to investigate take-up and acceptability of new interventions. Incorporation of interactions terms in the design and analysis of DCEs, explanations of risk, tests of external validity and incorporation of DCE results into a decision-making framework remain important areas for future research. PMID:22223558
Cunningham, Charles E; Vaillancourt, Tracy; Rimas, Heather; Deal, Ken; Cunningham, Lesley; Short, Kathy; Chen, Yvonne
2009-10-01
We used discrete choice conjoint analysis to model the bullying prevention program preferences of educators. Using themes from computerized decision support lab focus groups (n = 45 educators), we composed 20 three-level bullying prevention program design attributes. Each of 1,176 educators completed 25 choice tasks presenting experimentally varied combinations of the study's attribute levels. Latent class analysis yielded three segments with different preferences. Decision Sensitive educators (31%) preferred that individual schools select bullying prevention programs. In contrast, Support Sensitive educators (51%) preferred that local school boards chose bullying prevention programs. This segment preferred more logistical and social support at every stage of the adoption, training, implementation, and long term maintenance processes. Cost Sensitive educators (16%) showed a stronger preference for programs minimizing costs, training, and implementation time demands. They felt prevention programs were less effective and that the time and space in the curriculum for bullying prevention was less adequate. They were less likely to believe that bullying prevention was their responsibility and more likely to agree that prevention was the responsibility of parents. All segments preferred programs supported by the anecdotal reports of colleagues from other schools rather than those based on scientific evidence. To ensure that the bullying prevention options available reflect the complex combination of attributes influencing real world adoption decisions, program developers need to accommodate the differing views of the Decision, Support, and Cost Sensitive segments while maximizing the support of parents and students. PMID:19455413
Women's Preferences for Treatment of Perinatal Depression and Anxiety: A Discrete Choice Experiment.
Ride, Jemimah; Lancsar, Emily
2016-01-01
Perinatal depression and anxiety (PNDA) are an international healthcare priority, associated with significant short- and long-term problems for women, their children and families. Effective treatment is available but uptake is suboptimal: some women go untreated whilst others choose treatments without strong evidence of efficacy. Better understanding of women's preferences for treatment is needed to facilitate uptake of effective treatment. To address this issue, a discrete choice experiment (DCE) was administered to 217 pregnant or postnatal women in Australia, who were recruited through an online research company and had similar sociodemographic characteristics to Australian data for perinatal women. The DCE investigated preferences regarding cost, treatment type, availability of childcare, modality and efficacy. Data were analysed using logit-based models accounting for preference and scale heterogeneity. Predicted probability analysis was used to explore relative attribute importance and policy change scenarios, including how these differed by women's sociodemographic characteristics. Cost and treatment type had the greatest impact on choice, such that a policy of subsidising effective treatments was predicted to double their uptake compared with the base case. There were differences in predicted uptake associated with certain sociodemographic characteristics: for example, women with higher educational attainment were more likely to choose effective treatment. The findings suggest policy directions for decision makers whose goal is to reduce the burden of PNDA on women, their children and families. PMID:27258096
Arbiol, Joseph; Yabe, Mitsuyasu; Nomura, Hisako; Borja, Maridel; Gloriani, Nina; Yoshida, Shin-ichi
2015-01-01
Leptospirosis is highly endemic in the Philippines and a serious concern to public health. Local research on candidate vaccine is moving through the development pipeline. The availability of vaccines alone does not guarantee acceptance because individuals' vaccination choice decision is influenced by several factors. This study assessed how vaccine attributes and socio-demographic factors affect the acceptability of leptospirosis vaccine; and estimated individuals' willingness to pay for leptospirosis vaccine. A discrete choice experiment was conducted among leptospirosis and non-leptospirosis case respondents (n = 342) living in Metro Manila. Random Parameters Logit model was used to estimate the relative importance of vaccine attributes and socio-demographic variables on respondents' leptospirosis vaccination choice decision. The estimated model coefficients were used to derive implicit prices and willingness to pay for leptospirosis vaccine. Both case respondents preferred leptospirosis vaccine with 70-100% efficacy, mild to moderate risk of side-effects, given in a single shot, and at a lower price. Non-leptospirosis case respondents preferred a vaccine with 7 to 10 y of protection, while leptospirosis case respondents preferred a vaccine with 10 y protection. The probability of leptospirosis vaccination acceptance was affected by respondents' age, education, family size and income, proximity of home to rivers and sewers, and leptospirosis awareness level. Respondents' willingness to pay for leptospirosis vaccine (US$ 31.14-US$ 65.89) was higher than the Japanese retail price (US$ 21.60-US$ 24.00). Our findings indicated significant potential for introducing leptospirosis vaccine in the Philippine vaccine market. Delivery strategies to ensure equitable access to future leptospirosis vaccine are recommended. PMID:25764105
Arbiol, Joseph; Yabe, Mitsuyasu; Nomura, Hisako; Borja, Maridel; Gloriani, Nina; Yoshida, Shin-ichi
2015-01-01
Leptospirosis is highly endemic in the Philippines and a serious concern to public health. Local research on candidate vaccine is moving through the development pipeline. The availability of vaccines alone does not guarantee acceptance because individuals’ vaccination choice decision is influenced by several factors. This study assessed how vaccine attributes and socio-demographic factors affect the acceptability of leptospirosis vaccine; and estimated individuals’ willingness to pay for leptospirosis vaccine. A discrete choice experiment was conducted among leptospirosis and non-leptospirosis case respondents (n = 342) living in Metro Manila. Random Parameters Logit model was used to estimate the relative importance of vaccine attributes and socio-demographic variables on respondents’ leptospirosis vaccination choice decision. The estimated model coefficients were used to derive implicit prices and willingness to pay for leptospirosis vaccine. Both case respondents preferred leptospirosis vaccine with 70–100% efficacy, mild to moderate risk of side-effects, given in a single shot, and at a lower price. Non-leptospirosis case respondents preferred a vaccine with 7 to 10 y of protection, while leptospirosis case respondents preferred a vaccine with 10 y protection. The probability of leptospirosis vaccination acceptance was affected by respondents’ age, education, family size and income, proximity of home to rivers and sewers, and leptospirosis awareness level. Respondents’ willingness to pay for leptospirosis vaccine (US$ 31.14–US$ 65.89) was higher than the Japanese retail price (US$ 21.60-US$ 24.00). Our findings indicated significant potential for introducing leptospirosis vaccine in the Philippine vaccine market. Delivery strategies to ensure equitable access to future leptospirosis vaccine are recommended. PMID:25764105
Salloum, Ramzi G; Maziak, Wasim; Hammond, David; Nakkash, Rima; Islam, Farahnaz; Cheng, Xi; Thrasher, James F
2015-01-01
Objectives Waterpipe smoking is highly prevalent among university students, and has been increasing in popularity despite mounting evidence showing it is harmful to health. The aim of this study was to measure preferences for waterpipe smoking and determine which product characteristics are most important to smokers. Setting A large university in the Southeastern USA. Participants Adult waterpipe smokers attending the university (N=367). Design Participants completed an Internet-based discrete choice experiment to reveal their preferences for, and trade-offs between, the attributes of hypothetical waterpipe smoking sessions. Participants were presented with waterpipe lounge menus, each with three fruit-flavoured options and one tobacco flavoured option, in addition to an opt out option. Nicotine content and price were provided for each choice. Participants were randomised to either receive menus with a text-only health-warning message or no message. Outcome measures Multinomial and nested logit models were used to estimate the impact on consumer choice of attributes and between-subject assignment of health warnings respectively. Results On average, participants preferred fruit-flavoured varieties to tobacco flavour. They were averse to options labelled with higher nicotine content. Females and non-smokers of cigarettes were more likely than their counterparts to prefer flavoured and nicotine-free varieties. Participants exposed to a health warning were more likely to opt out. Conclusions Fruit-flavoured tobacco and lower nicotine content labels, two strategies widely used by the industry, increase the demand for waterpipe smoking among young adults. Waterpipe-specific regulation should limit the availability of flavoured waterpipe tobacco and require accurate labelling of constituents. Waterpipe-specific tobacco control regulation, along with research to inform policy, is required to curb this emerging public health threat. PMID:26353876
Arbiol, Joseph; Yabe, Mitsuyasu; Nomura, Hisako; Borja, Maridel; Gloriani, Nina; Yoshida, Shin-ichi
2015-01-01
Leptospirosis is highly endemic in the Philippines and a serious concern to public health. Local research on candidate vaccine is moving through the development pipeline. The availability of vaccines alone does not guarantee acceptance because individuals' vaccination choice decision is influenced by several factors. This study assessed how vaccine attributes and socio-demographic factors affect the acceptability of leptospirosis vaccine; and estimated individuals' willingness to pay for leptospirosis vaccine. A discrete choice experiment was conducted among leptospirosis and non-leptospirosis case respondents (n = 342) living in Metro Manila. Random Parameters Logit model was used to estimate the relative importance of vaccine attributes and socio-demographic variables on respondents' leptospirosis vaccination choice decision. The estimated model coefficients were used to derive implicit prices and willingness to pay for leptospirosis vaccine. Both case respondents preferred leptospirosis vaccine with 70-100% efficacy, mild to moderate risk of side-effects, given in a single shot, and at a lower price. Non-leptospirosis case respondents preferred a vaccine with 7 to 10 y of protection, while leptospirosis case respondents preferred a vaccine with 10 y protection. The probability of leptospirosis vaccination acceptance was affected by respondents' age, education, family size and income, proximity of home to rivers and sewers, and leptospirosis awareness level. Respondents' willingness to pay for leptospirosis vaccine (US$ 31.14-US$ 65.89) was higher than the Japanese retail price (US$ 21.60-US$ 24.00). Our findings indicated significant potential for introducing leptospirosis vaccine in the Philippine vaccine market. Delivery strategies to ensure equitable access to future leptospirosis vaccine are recommended.
Conducting discrete choice experiments to inform healthcare decision making: a user's guide.
Lancsar, Emily; Louviere, Jordan
2008-01-01
Discrete choice experiments (DCEs) are regularly used in health economics to elicit preferences for healthcare products and programmes. There is growing recognition that DCEs can provide more than information on preferences and, in particular, they have the potential to contribute more directly to outcome measurement for use in economic evaluation. Almost uniquely, DCEs could potentially contribute to outcome measurement for use in both cost-benefit and cost-utility analysis. Within this expanding remit, our intention is to provide a resource for current practitioners as well as those considering undertaking a DCE, using DCE results in a policy/commercial context, or reviewing a DCE. We present the fundamental principles and theory underlying DCEs. To aid in undertaking and assessing the quality of DCEs, we discuss the process of carrying out a choice study and have developed a checklist covering conceptualizing the choice process, selecting attributes and levels, experimental design, questionnaire design, pilot testing, sampling and sample size, data collection, coding of data, econometric analysis, validity, interpretation and welfare and policy analysis. In this fast-moving area, a number of issues remain on the research frontier. We therefore outline potentially fruitful areas for future research associated both with DCEs in general, and with health applications specifically, paying attention to how the results of DCEs can be used in economic evaluation. We also discuss emerging research trends. We conclude that if appropriately designed, implemented, analysed and interpreted, DCEs offer several advantages in the health sector, the most important of which is that they provide rich data sources for economic evaluation and decision making, allowing investigation of many types of questions, some of which otherwise would be intractable analytically. Thus, they offer viable alternatives and complements to existing methods of valuation and preference elicitation.
Dahirel, Maxime; Vardakis, Michalis; Ansart, Armelle; Madec, Luc
2016-08-01
Dispersal movements, i.e. movements leading to gene flow, are key behaviours with important, but only partially understood, consequences for the dynamics and evolution of populations. In particular, density-dependent dispersal has been widely described, yet how it is determined by the interaction with individual traits, and whether density effects differ between the three steps of dispersal (departure, transience, and settlement), remains largely unknown. Using a semi-natural landscape, we studied dispersal choices of Cornu aspersum land snails, a species in which negative effects of crowding are well documented, and analysed them using dispersal discrete choice models, a new method allowing the analysis of dispersal decisions by explicitly considering the characteristics of all available alternatives and their interaction with individual traits. Subadults were more dispersive than adults, confirming existing results. In addition, departure and settlement were both density dependent: snails avoided crowded patches at both ends of the dispersal process, and subadults were more reluctant to settle into crowded patches than adults. Moreover, we found support for carry-over effects of release density on subsequent settlement decisions: snails from crowded contexts were more sensitive to density in their subsequent immigration choices. The fact that settlement decisions were informed indicates that costs of prospecting are not as important as previously thought in snails, and/or that snails use alternative ways to collect information, such as indirect social information (e.g. trail following). The observed density-dependent dispersal dynamics may play an important role in the ability of C. aspersum to successfully colonise frequently human-disturbed habitats around the world. PMID:27139427
Projected discrete ordinates methods for numerical transport problems
Larsen, E.W.
1985-01-01
A class of Projected Discrete-Ordinates (PDO) methods is described for obtaining iterative solutions of discrete-ordinates problems with convergence rates comparable to those observed using Diffusion Synthetic Acceleration (DSA). The spatially discretized PDO solutions are generally not equal to the DSA solutions, but unlike DSA, which requires great care in the use of spatial discretizations to preserve stability, the PDO solutions remain stable and rapidly convergent with essentially arbitrary spatial discretizations. Numerical results are presented which illustrate the rapid convergence and the accuracy of solutions obtained using PDO methods with commonplace differencing methods.
ERIC Educational Resources Information Center
Cunningham, Charles E.; Deal, Ken; Rimas, Heather; Buchanan, Don H.; Gold, Michelle; Sdao-Jarvie, Katherine; Boyle, Michael
2008-01-01
Although materials informing parents about children's mental health (CMH) problems can improve outcomes, we know relatively little about the design factors that might influence their utilization of available resources. We used a discrete choice conjoint experiment to model the information preferences of parents seeking mental health services for 6…
Uniform positive-weight quadratures for discrete ordinate transport calculations
Carew, J.F.; Zamonsky, G.
1999-02-01
Mechanical quadratures that allow systematic improvement and solution convergence are derived for application of the discrete ordinates method to the Boltzmann transport equation. the quadrature directions are arranged on n latitudinal levels, are uniformly distributed over the unit sphere, and have positive weights. Both a uniform and equal-weight quadrature set UE{sub n} and a uniform and Gauss-weight quadrature set UG{sub n} are derived. These quadratures have the advantage over the standard level-symmetric LQ{sub n} quadrature sets in that the weights are positive for all orders, and the solution may be systematically converged by increasing the order of the quadrature set. As the order of the quadrature is increased the points approach a uniform continuous distribution on the unit sphere and the quadrature is invariant with respect to spatial rotations. The numerical integrals converge for continuous functions as the order of the quadrature is increased. Numerical calculations were performed to evaluate the application of the UE{sub n} quadrature set. Comparisons of the exact moments and those calculated using the UE{sub n} quadrature set demonstrate that the moment integrals are performed accurately except for distributions that are very sharply peaked along the direction of the polar axis. A series of DORT transport calculations of the >1-Mev neutron flux for a typical reactor core/pressure vessel geometry were also carried out. These calculations employed the UE{sub n} (n = 6, 10, 12, 18, and 24) quadratures and indicate that the UE{sub n} solutions have converged to within {approximately}0.5%. The UE{sub 24} solutions were also found to be more accurate than the calculations performed with the S{sub 16} level-symmetric quadratures.
O’Hara, Nathan N.; Slobogean, Gerard P.; Mohammadi, Tima; Marra, Carlo A.; Vicente, Milena R.; Khakban, Amir; McKee, Michael D.
2016-01-01
Background Total shoulder arthroplasty (TSA) is a common treatment to decrease pain and improve shoulder function in patients with severe osteoarthritis (OA). In Canada, patients requiring this procedure often wait a year or more. Our objective was to determine patient preferences related to accessing TSA, specifically comparing out-of-pocket payments for treatment, travel time to hospital, the surgeon’s level of experience and wait times. Methods We administered a discrete choice experiment among patients with end-stage shoulder OA currently waiting for TSA. Respondents were presented with 14 different choice sets, each with 3 options, and they were asked to choose their preferred scenario. A conditional logit regression model was used to estimate the relative preference and willingness to pay for each attribute. Results Sixty-two respondents completed the questionnaire. Three of the 4 attributes significantly influenced treatment preferences. Respondents had a strong preference for an experienced surgeon (mean 0.89 ± standard error [SE] 0.11), while reductions in travel time (−0.07 ± 0.04) or wait time (−0.04 ± 0.01) were of less importance. Respondents were found to be strongly averse (−1.44 ± 0.18) to surgical treatment by a less experienced surgeon and to paying out-of-pocket for their surgical treatment (−0.56 ± 0.05). Conclusion Our results suggest that patients waiting for TSA to treat severe shoulder OA have minimal willingness to pay for a reduction in wait time or travel time for surgery, yet will pay higher amounts for treatment by an experienced surgeon. PMID:27007091
Rural practice preferences among medical students in Ghana: a discrete choice experiment
Johnson, Jennifer C; Gyakobo, Mawuli; Agyei-Baffour, Peter; Asabir, Kwesi; Kotha, S Rani; Kwansah, Janet; Nakua, Emmanuel; Snow, Rachel C; Dzodzomenyo, Mawuli
2010-01-01
Abstract Objective To determine how specific job attributes influenced fourth year medical students’ stated preference for hypothetical rural job postings in Ghana. Methods Based on discussions with medical student focus groups and physicians in practice and in the Ministry of Health, we created a discrete choice experiment (DCE) that assessed how students’ stated preference for certain rural postings was influenced by various job attributes: a higher salary, free superior housing, an educational allowance for children, improved equipment, supportive management, shorter contracts before study leave and a car. We conducted the DCE among all fourth year medical students in Ghana using a brief structured questionnaire and used mixed logit models to estimate the utility of each job attribute. Findings Complete data for DCE analysis were available for 302 of 310 (97%) students. All attribute parameter estimates differed significantly from zero and had the expected signs. In the main effects mixed logit model, improved equipment and supportive management were most strongly associated with job preference (β = 1.42; 95% confidence interval, CI: 1.17 to 1.66, and β = 1.17; 95% CI: 0.96 to 1.39, respectively), although shorter contracts and salary bonuses were also associated. Discontinuing the provision of basic housing had a large negative influence (β = −1.59; 95% CI: −1.88 to −1.31). In models including gender interaction terms, women’s preferences were more influenced by supportive management and men’s preferences by superior housing. Conclusion Better working conditions were strongly associated with the stated choice of hypothetical rural postings among fourth year Ghanaian medical students. Studies are needed to find out whether job attributes determine the actual uptake of rural jobs by graduating physicians. PMID:20458371
Mühlbacher, Axel; Bethge, Susanne
2013-01-01
Introduction Obesity is associated with increased risk of morbidity and mortality and also appears to have an adverse effect on health-related quality of life. Though advances in obesity therapy and rehabilitation can be observed, the long-lasting outcome is dissatisfying to most of the patients and, therefore, the whole health care system. Theory and methodology The study aims to identify key attributes of coordinated weight loss programmes and elicit patients’ preferences for overweight and obesity therapy in rehabilitation programmes. A self-administered survey measuring attitudes and preferences was conducted in Germany in 2009. Discrete-choice experiment scenarios were developed using a fractional factorial design and results analysed using a random effects logit model. Results N=110 patients completed the questionnaire, 51.82% of these were male, the mean age was 53.05 years and mean body mass index was 33.54 kg/m2 (SD 7.73). A total of 823 choices could be included in the final estimation. The most important aspects for the respondents’ selection were care coordination (coefficient 1.473; SE 0.185) and individual therapy (coefficient 1.446; SE 0.188). The aspect ‘infrastructure of care’ (coefficient 0.570; SE 0.175) was less relevant. All attributes led to significant coefficients. Conclusion Patients value coordination of care and individual therapy most highly. So weight reduction therapy should enable patients to receive a structured, coordinated and interpersonal therapy that is tailored to their personal needs, behaviour and circumstances. Patients are willing to forego infrastructure quality in favour of better coordination and structure in their therapy. PMID:24179457
Cunningham, Charles E; Hutchings, Tracy; Henderson, Jennifer; Rimas, Heather; Chen, Yvonne
2016-01-01
Background Patients and their families play an important role in efforts to improve health service safety. Objective The objective of this study is to understand the safety partnership preferences of patients and their families. Method We used a discrete choice conjoint experiment to model the safety partnership preferences of 1,084 patients or those such as parents acting on their behalf. Participants made choices between hypothetical safety partnerships composed by experimentally varying 15 four-level partnership design attributes. Results Participants preferred an approach to safety based on partnerships between patients and staff rather than a model delegating responsibility for safety to hospital staff. They valued the opportunity to participate in point of service safety partnerships, such as identity and medication double checks, that might afford an immediate risk reduction. Latent class analysis yielded two segments. Actively engaged participants (73.3%) comprised outpatients with higher education, who anticipated more benefits to safety partnerships, were more confident in their ability to contribute, and were more intent on participating. They were more likely to prefer a personal engagement strategy, valued scientific evidence, preferred a more active approach to safety education, and advocated disclosure of errors. The passively engaged segment (26.7%) anticipated fewer benefits, were less confident in their ability to contribute, and were less intent on participating. They were more likely to prefer an engagement strategy based on signage. They preferred that staff explain why they thought patients should help make care safer and decide whether errors were disclosed. Inpatients, those with immigrant backgrounds, and those with less education were more likely to be in this segment. Conclusion Health services need to communicate information regarding risks, ask about partnership preferences, create opportunities respecting individual differences, and
Benjamin, Laure; Cotté, François-Emery; Philippe, Caroline; Mercier, Florence; Bachelot, Thomas; Vidal-Trécan, Gwenaëlle
2012-04-01
Although efficacy and tolerability are classical criteria for treatment choice, patient adherence and tariff issues related to novel oral anticancer drugs may also influence therapeutic decisions. We estimated the relative influence of efficacy, tolerability, expected adherence and route of administration of a chemotherapy treatment on 203 French physicians' preferences who participated in a Discrete Choice Experiment (DCE), a quantitative method used to elicit preferences. From a questionnaire with six scenarii, respondents had to choose between two treatments which differed with respect to these four attributes. Scenarii were first presented in a curative setting then in a palliative setting. Efficacy, tolerability and expected adherence had two modalities (good versus moderate) and route of administration had three modalities (intravenous (€286-379/session), oral with the current tariff (€28/consultation), oral with a hypothetical tariff (€114)). Efficacy was the reference criterion in choosing a treatment whatever the therapeutic goal (β: 2.114, p<0.0001 in curative setting versus β: 1.063, p<0.0001 in palliative setting). The oral route of administration was important but only in a palliative setting (β: 0.612, p=0.035, and β: 0.506, p<0.0001 for the current and hypothetical tariff, respectively). Removing the efficacy attribute from logistic regression model, tolerability (β: 1.228, p=0.0001) and expected adherence (β: 1.223, p=0.0001) were influent in curative setting while the route of administration was still predominant in palliative setting (β: 0.431, p<0.0001). Results suggest that economic considerations as well as therapeutic efficacy play a significant role in choosing a treatment. Preference for oral chemotherapy with a hypothetical tariff for a patient support programme should be considered for the development of therapeutic education and healthcare coordination, currently not taken into account in the tariff of oral chemotherapy.
Fam, Justine; Westbrook, Fred; Arabzadeh, Ehsan
2015-03-22
We simulate two types of environments to investigate how closely rats approximate optimal foraging. Rats initiated a trial where they chose between two spouts for sucrose, which was delivered at distinct probabilities. The discrete trial procedure used allowed us to observe the relationship between choice proportions, response latencies and obtained rewards. Our results show that rats approximate the optimal strategy across a range of environments that differ in the average probability of reward as well as the dynamics of the depletion-renewal cycle. We found that the constituent components of a single choice differentially reflect environmental contingencies. Post-choice behaviour, measured as the duration of time rats spent licking at the spouts on unrewarded trials, was the most sensitive index of environmental variables, adjusting most rapidly to changes in the environment. These findings have implications for the role of confidence in choice outcomes for guiding future choices. PMID:25694623
Li, Zhelong; Zhang, Dongxiao; Li, Xiqing
2010-02-15
Advances in pore structure characterization and lattice-Boltzmann (LB) simulations of flow fields in pore spaces are making mechanistic simulations of colloid transport in real porous media a realistic goal. The primary challenge to reach this goal may be the computational demand of LB flow simulations in discretized porous medium domains at an assemblage scale. In this work, flow fields in simple cubic and dense packing systems were simulated at different discretization resolutions using the LB method. The simulated flow fields were incorporated into to a three-dimensional particle tracking model to simulate colloid transport in the two systems. The simulated colloid deposition tended to become asymptotic at a critical discretization resolution (voxel-grain size ratio = 0.01) at groundwater flow regimes for colloids down to submicrometer level under favorable conditions and down to around 1 microm under unfavorable conditions. The average simulated fluid velocities near grain surfaces were extracted to explain the sensitivities of simulated depositions to space discretization under both conditions. At the critical discretization resolution, current computation capacity would allow flow simulations and particle tracking in assemblage porous medium domains. In addition, particle tracking simulations revealed that colloids may be retained in flow vortices under conditions both favorable and unfavorable for deposition. Colloid retention in flow vortices has been proposed only very recently. Here we provide a mechanistic confirmation to this novel retention process. PMID:20088544
2014-01-01
Background Discrete choice experiments (DCEs) are attribute-driven experimental techniques used to elicit stakeholders’ preferences to support the design and implementation of policy interventions. The validity of a DCE, therefore, depends on the appropriate specification of the attributes and their levels. There have been recent calls for greater rigor in implementing and reporting on the processes of developing attributes and attribute-levels for discrete choice experiments (DCEs). This paper responds to such calls by carefully reporting a systematic process of developing micro health insurance attributes and attribute-levels for the design of a DCE in rural Malawi. Methods Conceptual attributes and attribute-levels were initially derived from a literature review which informed the design of qualitative data collection tools to identify context specific attributes and attribute-levels. Qualitative data was collected in August-September 2012 from 12 focus group discussions with community residents and 8 in-depth interviews with health workers. All participants were selected according to stratified purposive sampling. The material was tape-recorded, fully transcribed, and coded by three researchers to identify context-specific attributes and attribute-levels. Expert opinion was used to scale down the attributes and levels. A pilot study confirmed the appropriateness of the selected attributes and levels for a DCE. Results First, a consensus, emerging from an individual level analysis of the qualitative transcripts, identified 10 candidate attributes. Levels were assigned to all attributes based on data from transcripts and knowledge of the Malawian context, derived from literature. Second, through further discussions with experts, four attributes were discarded based on multiple criteria. The 6 remaining attributes were: premium level, unit of enrollment, management structure, health service benefit package, transportation coverage and copayment levels. A final
An Australian discrete choice experiment to value eq-5d health states.
Viney, Rosalie; Norman, Richard; Brazier, John; Cronin, Paula; King, Madeleine T; Ratcliffe, Julie; Street, Deborah
2014-06-01
Conventionally, generic quality-of-life health states, defined within multi-attribute utility instruments, have been valued using a Standard Gamble or a Time Trade-Off. Both are grounded in expected utility theory but impose strong assumptions about the form of the utility function. Preference elicitation tasks for both are complicated, limiting the number of health states that each respondent can value and, therefore, that can be valued overall. The usual approach has been to value a set of the possible health states and impute values for the remainder. Discrete Choice Experiments (DCEs) offer an attractive alternative, allowing investigation of more flexible specifications of the utility function and greater coverage of the response surface. We designed a DCE to obtain values for EQ-5D health states and implemented it in an Australia-representative online panel (n = 1,031). A range of specifications investigating non-linear preferences with respect to time and interactions between EQ-5D levels were estimated using a random-effects probit model. The results provide empirical support for a flexible utility function, including at least some two-factor interactions. We then constructed a preference index such that full health and death were valued at 1 and 0, respectively, to provide a DCE-based algorithm for Australian cost-utility analyses. PMID:23765787
Coast, Joanna; Al-Janabi, Hareth; Sutton, Eileen J; Horrocks, Susan A; Vosper, A Jane; Swancutt, Dawn R; Flynn, Terry N
2012-06-01
Attribute generation for discrete choice experiments (DCEs) is often poorly reported, and it is unclear whether this element of research is conducted rigorously. This paper explores issues associated with developing attributes for DCEs and contrasts different qualitative approaches. The paper draws on eight studies, four developed attributes for measures, and four developed attributes for more ad hoc policy questions. Issues that have become apparent through these studies include the following: the theoretical framework for random utility theory and the need for attributes that are neither too close to the latent construct nor too intrinsic to people's personality; the need to think about attribute development as a two-stage process involving conceptual development followed by refinement of language to convey the intended meaning; and the difficulty in resolving tensions inherent in the reductiveness of condensing complex and nuanced qualitative findings into precise terms. The comparison of alternative qualitative approaches suggests that the nature of data collection will depend both on the characteristics of the question (its sensitivity, for example) and the availability of existing qualitative information. An iterative, constant comparative approach to analysis is recommended. Finally, the paper provides a series of recommendations for improving the reporting of this element of DCE studies. PMID:21557381
Rafiei, Sima; Arab, Mohammad; Rashidian, Arash; Mahmoudi, Mahmood; Rahimi-Movaghar, Vafa
2015-01-01
Background: Health workforce shortages in rural and remote areas are a global challenge that almost every health system has to deal with. This study aimed to discover neurosurgeons’ job preferences and propose policy interventions that could possibly increase their retention in rural, remote, or underserved areas. Methods: A discrete choice experiment (DCE) was conducted in November 2014 with a sample of Iranian neurosurgeons selected from five contrary’s provinces representing the geographical diversity. Job attributes included income, dual practice opportunities, workload, proximity to family, clinical infrastructure, housing, educational facilities, and work location. Probit regression model was used to estimate the importance of different job attributes and examine the extent to which neurosurgeons were willing to tradeoff between monetary and nonmonetary attributes. Results: Findings indicated that increased salary, permission to undertake dual practice and access to adequate clinical infrastructure were the most important retention policies. Provision of subsidized housing and educational facilities also increased neurosurgeons’ attraction and retention in rural areas. Conclusion: A range of policy interventions focusing on both monetary and nonmonetary incentives are required to increase neurosurgeons’ retention in rural, remote, or underserved areas. PMID:26885340
Parameterising User Uptake in Economic Evaluations: The role of discrete choice experiments.
Terris-Prestholt, Fern; Quaife, Matthew; Vickerman, Peter
2016-02-01
Model-based economic evaluations of new interventions have shown that user behaviour (uptake) is a critical driver of overall impact achieved. However, early economic evaluations, prior to introduction, often rely on assumed levels of uptake based on expert opinion or uptake of similar interventions. In addition to the likely uncertainty surrounding these uptake assumptions, they also do not allow for uptake to be a function of product, intervention, or user characteristics. This letter proposes using uptake projections from discrete choice experiments (DCE) to better parameterize uptake and substitution in cost-effectiveness models. A simple impact model is developed and illustrated using an example from the HIV prevention field in South Africa. Comparison between the conventional approach and the DCE-based approach shows that, in our example, DCE-based impact predictions varied by up to 50% from conventional estimates and provided far more nuanced projections. In the absence of observed uptake data and to model the effect of variations in intervention characteristics, DCE-based uptake predictions are likely to greatly improve models parameterizing uptake solely based on expert opinion. This is particularly important for global and national level decision making around introducing new and probably more expensive interventions, particularly where resources are most constrained.
Discrete choice modeling of shovelnose sturgeon habitat selection in the Lower Missouri River
Bonnot, T.W.; Wildhaber, M.L.; Millspaugh, J.J.; DeLonay, A.J.; Jacobson, R.B.; Bryan, J.L.
2011-01-01
Substantive changes to physical habitat in the Lower Missouri River, resulting from intensive management, have been implicated in the decline of pallid (Scaphirhynchus albus) and shovelnose (S. platorynchus) sturgeon. To aid in habitat rehabilitation efforts, we evaluated habitat selection of gravid, female shovelnose sturgeon during the spawning season in two sections (lower and upper) of the Lower Missouri River in 2005 and in the upper section in 2007. We fit discrete choice models within an information theoretic framework to identify selection of means and variability in three components of physical habitat. Characterizing habitat within divisions around fish better explained selection than habitat values at the fish locations. In general, female shovelnose sturgeon were negatively associated with mean velocity between them and the bank and positively associated with variability in surrounding depths. For example, in the upper section in 2005, a 0.5ms-1 decrease in velocity within 10m in the bank direction increased the relative probability of selection 70%. In the upper section fish also selected sites with surrounding structure in depth (e.g., change in relief). Differences in models between sections and years, which are reinforced by validation rates, suggest that changes in habitat due to geomorphology, hydrology, and their interactions over time need to be addressed when evaluating habitat selection. Because of the importance of variability in surrounding depths, these results support an emphasis on restoring channel complexity as an objective of habitat restoration for shovelnose sturgeon in the Lower Missouri River. ?? 2011 Blackwell Verlag, Berlin.
Discrete choice modeling of shovelnose sturgeon habitat selection in the Lower Missouri River
Bonnot, T.W.; Wildhaber, M.L.; Millspaugh, J.J.; DeLonay, A.J.; Jacobson, R.B.; Bryan, J.L.
2011-01-01
Substantive changes to physical habitat in the Lower Missouri River, resulting from intensive management, have been implicated in the decline of pallid (Scaphirhynchus albus) and shovelnose (S. platorynchus) sturgeon. To aid in habitat rehabilitation efforts, we evaluated habitat selection of gravid, female shovelnose sturgeon during the spawning season in two sections (lower and upper) of the Lower Missouri River in 2005 and in the upper section in 2007. We fit discrete choice models within an information theoretic framework to identify selection of means and variability in three components of physical habitat. Characterizing habitat within divisions around fish better explained selection than habitat values at the fish locations. In general, female shovelnose sturgeon were negatively associated with mean velocity between them and the bank and positively associated with variability in surrounding depths. For example, in the upper section in 2005, a 0.5 m s-1 decrease in velocity within 10 m in the bank direction increased the relative probability of selection 70%. In the upper section fish also selected sites with surrounding structure in depth (e.g., change in relief). Differences in models between sections and years, which are reinforced by validation rates, suggest that changes in habitat due to geomorphology, hydrology, and their interactions over time need to be addressed when evaluating habitat selection. Because of the importance of variability in surrounding depths, these results support an emphasis on restoring channel complexity as an objective of habitat restoration for shovelnose sturgeon in the Lower Missouri River.
Abbyad, Christine W.; Kohler, Racquel E.; Kratka, Allison K.; Oh, Leighanne; Wood, Kathryn A.
2015-01-01
Introduction: Smoking prevalence rates in Lebanon are among the highest in the Eastern Mediterranean region. Few smoking cessation programs are offered in Lebanon and little is known about the preferences of Lebanese smokers for cessation treatment programs. Objective: To establish which attributes of smoking cessation programs are most important to Lebanese smokers. Methods: Smokers at the American University of Beirut were surveyed to elicit their preferences for, and tradeoffs between the attributes of a hypothetical university-based smoking cessation program. Preferences for medication type/mechanism, risk of benign side effects, availability of support, distance traveled to obtain medication, and price of complete treatment were assessed using the discrete choice experiment method. Results: The smokers’ responses (N = 191) to changes in attributes were statistically significant. Smokers were willing to make trade-offs between attributes. On average, smokers were willing to pay LBP 103,000 (USD 69) for cessation support. Respondents were willing to give up LBP 105,000 (USD 70) to avoid an additional 10% risk of minor side effects and LBP 18,000 (USD 12) to avoid an addition kilometer of travel to the nearest pharmacy. Heavy smokers were the least responsive group and had the lowest demand elasticities. Conclusions: Student smokers were willing to participate in a relatively complex exercise that weighs the advantages and disadvantages of a hypothetical smoking cessation program. Overall they were less interested in the pill form of smoking cessation treatment, but they were willing to make tradeoffs to be smoke-free. PMID:25239962
Carroll, Raymond J.; Delaigle, Aurore; Hall, Peter
2014-01-01
The data functions that are studied in the course of functional data analysis are assembled from discrete data, and the level of smoothing that is used is generally that which is appropriate for accurate approximation of the conceptually smooth functions that were not actually observed. Existing literature shows that this approach is effective, and even optimal, when using functional data methods for prediction or hypothesis testing. However, in the present paper we show that this approach is not effective in classification problems. There a useful rule of thumb is that undersmoothing is often desirable, but there are several surprising qualifications to that approach. First, the effect of smoothing the training data can be more significant than that of smoothing the new data set to be classified; second, undersmoothing is not always the right approach, and in fact in some cases using a relatively large bandwidth can be more effective; and third, these perverse results are the consequence of very unusual properties of error rates, expressed as functions of smoothing parameters. For example, the orders of magnitude of optimal smoothing parameter choices depend on the signs and sizes of terms in an expansion of error rate, and those signs and sizes can vary dramatically from one setting to another, even for the same classifier. PMID:25309640
Parameterising User Uptake in Economic Evaluations: The role of discrete choice experiments
Quaife, Matthew; Vickerman, Peter
2016-01-01
Abstract Model‐based economic evaluations of new interventions have shown that user behaviour (uptake) is a critical driver of overall impact achieved. However, early economic evaluations, prior to introduction, often rely on assumed levels of uptake based on expert opinion or uptake of similar interventions. In addition to the likely uncertainty surrounding these uptake assumptions, they also do not allow for uptake to be a function of product, intervention, or user characteristics. This letter proposes using uptake projections from discrete choice experiments (DCE) to better parameterize uptake and substitution in cost‐effectiveness models. A simple impact model is developed and illustrated using an example from the HIV prevention field in South Africa. Comparison between the conventional approach and the DCE‐based approach shows that, in our example, DCE‐based impact predictions varied by up to 50% from conventional estimates and provided far more nuanced projections. In the absence of observed uptake data and to model the effect of variations in intervention characteristics, DCE‐based uptake predictions are likely to greatly improve models parameterizing uptake solely based on expert opinion. This is particularly important for global and national level decision making around introducing new and probably more expensive interventions, particularly where resources are most constrained. PMID:26773825
Thomas, D.L.; Johnson, D.; Griffith, B.
2006-01-01
Bayesian hierarchical discrete-choice model for resource selection can provide managers with 2 components of population-level inference: average population selection and variability of selection. Both components are necessary to make sound management decisions based on animal selection.
Acceptability of Financial Incentives for Health Behaviours: A Discrete Choice Experiment
Giles, Emma L.; Becker, Frauke; Ternent, Laura; Sniehotta, Falko F.; McColl, Elaine
2016-01-01
Background Healthy behaviours are important determinants of health and disease, but many people find it difficult to perform these behaviours. Systematic reviews support the use of personal financial incentives to encourage healthy behaviours. There is concern that financial incentives may be unacceptable to the public, those delivering services and policymakers, but this has been poorly studied. Without widespread acceptability, financial incentives are unlikely to be widely implemented. We sought to answer two questions: what are the relative preferences of UK adults for attributes of financial incentives for healthy behaviours? Do preferences vary according to the respondents’ socio-demographic characteristics? Methods We conducted an online discrete choice experiment. Participants were adult members of a market research panel living in the UK selected using quota sampling. Preferences were examined for financial incentives for: smoking cessation, regular physical activity, attendance for vaccination, and attendance for screening. Attributes of interest (and their levels) were: type of incentive (none, cash, shopping vouchers or lottery tickets); value of incentive (a continuous variable); schedule of incentive (same value each week, or value increases as behaviour change is sustained); other information provided (none, written information, face-to-face discussion, or both); and recipients (all eligible individuals, people living in low-income households, or pregnant women). Results Cash or shopping voucher incentives were preferred as much as, or more than, no incentive in all cases. Lower value incentives and those offered to all eligible individuals were preferred. Preferences for additional information provided alongside incentives varied between behaviours. Younger participants and men were more likely to prefer incentives. There were no clear differences in preference according to educational attainment. Conclusions Cash or shopping voucher
2012-01-01
Background In 2004, a community-based health insurance scheme (CBI) was introduced in Nouna health district, Burkina Faso. Since its inception, coverage has remained low and dropout rates high. One important reason for low coverage and high dropout is that health workers do not support the CBI scheme because they are dissatisfied with the provider payment mechanism of the CBI. Methods A discrete choice experiment (DCE) was used to examine CBI provider payment attributes that influence health workers’ stated preferences for payment mechanisms. The DCE was conducted among 176 health workers employed at one of the 34 primary care facilities or the district hospital in Nouna health district. Conditional logit models with main effects and interactions terms were used for analysis. Results Reimbursement of service fees (adjusted odds ratio (aOR) 1.49, p < 0.001) and CBI contributions for medical supplies and equipment (aOR 1.47, p < 0.001) had the strongest effect on whether the health workers chose a given provider payment mechanism. The odds of selecting a payment mechanism decreased significantly if the mechanism included (i) results-based financing (RBF) payments made through the local health management team (instead of directly to the health workers (aOR 0.86, p < 0.001)) or (ii) RBF payments based on CBI coverage achieved in the health worker’s facility relative to the coverage achieved at other facilities (instead of payments based on the numbers of individuals or households enrolled at the health worker’s facility (aOR 0.86, p < 0.001)). Conclusions Provider payment mechanisms can crucially determine CBI performance. Based on the results from this DCE, revised CBI payment mechanisms were introduced in Nouna health district in January 2011, taking into consideration health worker preferences on how they are paid. PMID:22697498
Youssef, Elaney; Cooper, Vanessa; Miners, Alec; Llewellyn, Carrie; Pollard, Alex; Lagarde, Mylene; Sachikonye, Memory; Sabin, Caroline; Foreman, Claire; Perry, Nicky; Nixon, Eileen; Fisher, Martin
2016-01-01
Introduction While the care of HIV-positive patients, including the detection and management of comorbidities, has historically been provided in HIV specialist outpatient clinics, recent years have seen a greater involvement of non-HIV specialists and general practitioners (GPs). The aim of this study is to determine whether patients would prefer to see their GP or HIV physician given general symptoms, and to understand what aspects of care influence their preferences. Methods/analysis We have developed and piloted a discrete choice experiment (DCE) to better understand patients' preferences for care of non-HIV-related acute symptoms. The design of the DCE was informed by our exploratory research, including the findings of a systematic literature review and a qualitative study. Additional questionnaire items have been included to measure demographics, service use and experience of non-HIV illnesses and quality of life (EQ5D). We plan to recruit 1000 patients from 14 HIV clinics across South East England. Data will be analysed using random-effects logistic regression and latent class analysis. ORs and 95% CIs will be used to estimate the relative importance of each of the attribute levels. Latent class analysis will identify whether particular groups of people value the service attribute levels differently. Ethics/dissemination Ethical approval for this study was obtained from the Newcastle and North Tyneside Research Ethics Committee (reference number 14/NE/1193). The results will be disseminated at national and international conferences and peer-reviewed publications. A study report, written in plain English, will be made available to all participants. The Patient Advisory Group will develop a strategy for wider dissemination of the findings to patients and the public. PMID:27431895
2014-01-01
Background In many countries a high proportion of births begin as induced labours. Induction can be lengthy if cervical priming is required prior to induction. This usually occurs as an inpatient, however, an alternative is to allow women to go home after satisfactory fetal monitoring. The aim of this study was to assess the preferences of women for cervical priming for induction of labour in an outpatient or inpatient setting. Method A discrete choice experiment (DCE) was conducted alongside a randomised trial of inpatient and outpatient cervical priming (the OPRA trial) in two maternity hospitals in South Australia. 362 participants were included, and women’s preferences for cervical priming for induction of labour were assessed. Results Women were willing to accept an extra 1.4 trips to hospital (2.4 trips total) and a total travel time of 73.3 minutes to be able to return to their own home while waiting for the priming to work. For enhanced inpatient services, women were willing to accept a total travel time of 54.7 minutes to have a private room with private bathroom while waiting for the priming to work. The overall benefit score for outpatient priming was 3.63, 3.59 for enhanced inpatient care and 2.89 for basic inpatient care, suggesting slightly greater preferences for outpatient priming. Preferences for outpatient priming increased when women could return to their own home (compared to other offsite accommodation), and decreased with more trips to hospital and longer travel time. Conclusions Our results suggest that outpatient priming was slightly more preferred than either enhanced inpatient priming or basic care; these results should be confirmed in different clinical settings. There may be merit in providing women information about both options in the future, as preferences varied according to the characteristics of the services on offer and the sociodemographic background of the woman. PMID:25073486
34 CFR 200.48 - Funding for choice-related transportation and supplemental educational services.
Code of Federal Regulations, 2010 CFR
2010-07-01
... 34 Education 1 2010-07-01 2010-07-01 false Funding for choice-related transportation and... Agencies Lea and School Improvement § 200.48 Funding for choice-related transportation and supplemental educational services. (a) Amounts required. (1) To pay for choice-related transportation and...
Bailey, T S; Chang, J H; Warsa, J S; Adams, M L
2010-12-22
We present a new spatial discretization of the discrete-ordinates transport equation in two-dimensional Cartesian (X-Y) geometry for arbitrary polygonal meshes. The discretization is a discontinuous finite element method (DFEM) that utilizes piecewise bi-linear (PWBL) basis functions, which are formally introduced in this paper. We also present a series of numerical results on quadrilateral and polygonal grids and compare these results to a variety of other spatial discretizations that have been shown to be successful on these grid types. Finally, we note that the properties of the PWBL basis functions are such that the leading-order piecewise bi-linear discontinuous finite element (PWBLD) solution will satisfy a reasonably accurate diffusion discretization in the thick diffusion limit, making the PWBLD method a viable candidate for many different classes of transport problems.
Garcia-Dominguez, José Manuel; Muñoz, Delicias; Comellas, Marta; Gonzalbo, Irmina; Lizán, Luis; Polanco Sánchez, Carlos
2016-01-01
Objectives To assess disease-modifying therapy (DMT) preferences in a population of patients with multiple sclerosis (MS) and to estimate the association between sociodemographic and clinical factors and these preferences. Methods Preferences for DMTs attributes were measured using a discrete choice experiment. Analysis of preferences was assessed using mixed-logit hierarchical Bayes regression. A multilinear regression was used to evaluate the association between the preferences for each attribute and patients’ demographic and clinical characteristics. A Student’s t-test or Welch’s t-test was used for subgroup comparisons. Results A total of 125 patients were included in the final analysis (62.9% female, mean age 44.5 years, 71.5% with relapsing-remitting MS diagnosis). The most important factor for patients was the possibility of suffering from the side effects of the treatment (relative importance [RI] =50%), followed by a delay in disease progression (RI =19.4%), and route and frequency of administration (RI =14.3%). According to maximum acceptable risk, patients were willing to accept an increase of 3.8% in severity of side effects, for a delay of 1 year in disease progression. Treatment duration was the most prevalent factor affecting preferences, followed by the age of patients, type of MS, level of education, and the type of current treatment. Patients treated orally were significantly more concerned about the route and frequency of administration (P=0.026) than patients on injectable therapy. Naïve patients stated significantly less importance to prevention of relapses (P=0.021) and deterioration of the capacity for performing usual daily life activities (P=0.015). Finally, patients with >5 years since diagnosis were significantly less concerned about preventing disease progression (P=0.021), and more concerned about treatment side effects (P=0.052) than compared with patients with <5 years of MS history. Conclusion The most important attribute for
Robyn, Paul Jacob; Shroff, Zubin; Zang, Omer Ramses; Kingue, Samuel; Djienouassi, Sebastien; Kouontchou, Christian; Sorgho, Gaston
2015-01-01
Background: Nearly every nation in the world faces shortages of health workers in remote areas. Cameroon is no exception to this. The Ministry of Public Health (MoPH) is currently considering several rural retention strategies to motivate qualified health personnel to practice in remote rural areas. Methods: To better calibrate these mechanisms and to develop evidence-based retention strategies that are attractive and motivating to health workers, a Discrete Choice Experiment (DCE) was conducted to examine what job attributes are most attractive and important to health workers when considering postings in remote areas. The study was carried out between July and August 2012 among 351 medical students, nursing students and health workers in Cameroon. Mixed logit models were used to analyze the data. Results: Among medical and nursing students a rural retention bonus of 75% of base salary (aOR= 8.27, 95% CI: 5.28-12.96, P< 0.001) and improved health facility infrastructure (aOR= 3.54, 95% CI: 2.73-4.58) respectively were the attributes with the largest effect sizes. Among medical doctors and nurse aides, a rural retention bonus of 75% of base salary was the attribute with the largest effect size (medical doctors aOR= 5.60, 95% CI: 4.12-7.61, P< 0.001; nurse aides aOR= 4.29, 95% CI: 3.11-5.93, P< 0.001). On the other hand, improved health facility infrastructure (aOR= 3.56, 95% CI: 2.75-4.60, P< 0.001), was the attribute with the largest effect size among the state registered nurses surveyed. Willingness-to-Pay (WTP) estimates were generated for each health worker cadre for all the attributes. Preference impact measurements were also estimated to identify combination of incentives that health workers would find most attractive. Conclusion: Based on these findings, the study recommends the introduction of a system of substantial monetary bonuses for rural service along with ensuring adequate and functional equipment and uninterrupted supplies. By focusing on the
L/sub 2/-error estimates for the discrete ordinates method for three-dimensional neutron transport
Asadzadeh, M.
1988-02-01
We prove L/sub 2/-error estimates for the discrete ordinates method for the angular discretization of the three-dimensional neutron transport equation. The analysis is for monoenergetic three-dimensional transport of neutrons in a homogeneous uniform media and isotropic scattering is assumed. A special quadrature rule with relatively uniformly distributed discrete directions is considered.
34 CFR 200.48 - Funding for choice-related transportation and supplemental educational services.
Code of Federal Regulations, 2011 CFR
2011-07-01
... multiple complaints, supported by credible evidence, regarding implementation of the public school choice... 34 Education 1 2011-07-01 2011-07-01 false Funding for choice-related transportation and... Agencies Lea and School Improvement § 200.48 Funding for choice-related transportation and...
Dissolved and colloidal transport of cesium in natural discrete fractures.
Tang, Xiang-Yu; Weisbrod, Noam
2010-01-01
Transport of cesium (Cs) was investigated in a saturated natural chalk fracture with an average equivalent hydraulic aperture of 129 microm. The results show that Cs (inflow concentration of 0.22 mmol L(-1)) can be transported in its dissolved form and in association with montmorillonite. Humic acid (HA) did not sorb Cs but enhanced colloid-associated Cs transport by 12.5% in terms of breakthrough curve (BTC) recovery. The BTCs clearly showed desorption of Cs from the fracture walls during the artificial rainwater (ARW)-injection period. Cesium transport associated with montmorillonite colloids was significant, with a maximum colloid-associated Cs C/C(0) (outflow-to-inflow concentration ratio) value of 16.6 +/- 1.1% during the tracer (colloids and LiBr)-injection period. However, the relative contribution of colloid-associated Cs transport to total Cs transport was relatively low, amounting to 10.3 +/- 0.7% and 14.5 +/- 0.7% with montmorillonite (500 mg L(-1)) and the montmorillonite-HA (10 mg L(-1)) mixture, respectively. Readsorption of Cs onto the colloids occurred immediately on switching from the tracer suspension to the background solution of ARW. The significant colloid-associated Cs transport, the stripping effect of Cs from colloids, and the slow desorption of Cs from fracture walls reported in this study have important implications for risk assessments of Cs mobility in fractured carbonatic rocks. PMID:20400602
Hoyos, David; Mariel, Petr; Hess, Stephane
2015-02-01
Environmental economists are increasingly interested in better understanding how people cognitively organise their beliefs and attitudes towards environmental change in order to identify key motives and barriers that stimulate or prevent action. In this paper, we explore the utility of a commonly used psychometric scale, the awareness of consequences (AC) scale, in order to better understand stated choices. The main contribution of the paper is that it provides a novel approach to incorporate attitudinal information into discrete choice models for environmental valuation: firstly, environmental attitudes are incorporated using a reinterpretation of the classical AC scale recently proposed by Ryan and Spash (2012); and, secondly, attitudinal data is incorporated as latent variables under a hybrid choice modelling framework. This novel approach is applied to data from a survey conducted in the Basque Country (Spain) in 2008 aimed at valuing land-use policies in a Natura 2000 Network site. The results are relevant to policy-making because choice models that are able to accommodate underlying environmental attitudes may help in designing more effective environmental policies.
A Residual Monte Carlo Method for Spatially Discrete, Angularly Continuous Radiation Transport
Wollaeger, Ryan T.; Densmore, Jeffery D.
2012-06-19
Residual Monte Carlo provides exponential convergence of statistical error with respect to the number of particle histories. In the past, residual Monte Carlo has been applied to a variety of angularly discrete radiation-transport problems. Here, we apply residual Monte Carlo to spatially discrete, angularly continuous transport. By maintaining angular continuity, our method avoids the deficiencies of angular discretizations, such as ray effects. For planar geometry and step differencing, we use the corresponding integral transport equation to calculate an angularly independent residual from the scalar flux in each stage of residual Monte Carlo. We then demonstrate that the resulting residual Monte Carlo method does indeed converge exponentially to within machine precision of the exact step differenced solution.
Vanniyasingam, Thuva; Cunningham, Charles E; Foster, Gary; Thabane, Lehana
2016-01-01
Objectives Discrete choice experiments (DCEs) are routinely used to elicit patient preferences to improve health outcomes and healthcare services. While many fractional factorial designs can be created, some are more statistically optimal than others. The objective of this simulation study was to investigate how varying the number of (1) attributes, (2) levels within attributes, (3) alternatives and (4) choice tasks per survey will improve or compromise the statistical efficiency of an experimental design. Design and methods A total of 3204 DCE designs were created to assess how relative design efficiency (d-efficiency) is influenced by varying the number of choice tasks (2–20), alternatives (2–5), attributes (2–20) and attribute levels (2–5) of a design. Choice tasks were created by randomly allocating attribute and attribute level combinations into alternatives. Outcome Relative d-efficiency was used to measure the optimality of each DCE design. Results DCE design complexity influenced statistical efficiency. Across all designs, relative d-efficiency decreased as the number of attributes and attribute levels increased. It increased for designs with more alternatives. Lastly, relative d-efficiency converges as the number of choice tasks increases, where convergence may not be at 100% statistical optimality. Conclusions Achieving 100% d-efficiency is heavily dependent on the number of attributes, attribute levels, choice tasks and alternatives. Further exploration of overlaps and block sizes are needed. This study's results are widely applicable for researchers interested in creating optimal DCE designs to elicit individual preferences on health services, programmes, policies and products. PMID:27436671
Spatial and angular variation and discretization of the self-adjoint transport operator
Roberts, R.M.
1996-03-11
This mathematical treatise begins with a variational derivation of a second-order, self-adjoint form of the transport equation. Next, a space variational functional whose minimization solves the transport equation is derived. A one-dimensional example is given. Then, {ital S{sub N}} and {ital P{sub N}} discretized functionals are expressed. Next, the surface contributions to the functionals are discretized. Finally, the explicit forms of the {rvec D} and {rvec H} matrices are given for four different geometries: hexahedron, wedge, tetrahedron, and pyramid.
Spinks, Jean; Mortimer, Duncan
2015-01-01
It has been suggested that complementary medicines are currently 'under-regulated' in some countries due to their potential for harm as a direct result from side-effects or interactions; from delaying more effective care; or from the economic cost of purchasing an ineffective or inappropriate treatment. The requirement of additional labelling on complementary medicine products has been suggested in Australia and may provide additional information to consumers at the point of purchase. This paper details a unique way of testing the potential effects on consumer behaviour of including either a traffic light logo or regulatory statement on labels. Using a discrete choice experiment, data were collected in 2012 in a sample of 521 Australians with either type 2 diabetes or cardiovascular disease. We find that additional labelling can affect consumer behaviour, but in unpredictable ways. The results of this experiment are informative to further the dialogue concerning possible regulatory mechanisms. PMID:25483723
Spinks, Jean; Mortimer, Duncan
2015-01-01
It has been suggested that complementary medicines are currently 'under-regulated' in some countries due to their potential for harm as a direct result from side-effects or interactions; from delaying more effective care; or from the economic cost of purchasing an ineffective or inappropriate treatment. The requirement of additional labelling on complementary medicine products has been suggested in Australia and may provide additional information to consumers at the point of purchase. This paper details a unique way of testing the potential effects on consumer behaviour of including either a traffic light logo or regulatory statement on labels. Using a discrete choice experiment, data were collected in 2012 in a sample of 521 Australians with either type 2 diabetes or cardiovascular disease. We find that additional labelling can affect consumer behaviour, but in unpredictable ways. The results of this experiment are informative to further the dialogue concerning possible regulatory mechanisms.
Colloid facilitated transport of lanthanides through discrete fractures in chalk
NASA Astrophysics Data System (ADS)
Tran, Emily; Klein Ben-David, Ofra; Teutsch, Nadya; Weisbrod, Noam
2015-04-01
Geological disposal of high-level radioactive waste is the internationally agreed-upon, long term solution for the disposal of long lived radionuclides and spent fuel. Eventually, corrosion of the waste canisters may lead to leakage of their hazardous contents, and the radionuclides can ultimately make their way into groundwater and pose a threat to the biosphere. Engineered bentonite barriers placed around nuclear waste repositories are generally considered sufficient to impede the transport of radionuclides from their storage location to the groundwater. However, colloidal-sized mobile bentonite particles eroding from these barriers have come under investigation as a potential transport vector for radionuclides sorbed to them. In addition, the presence of organic matter in groundwater has been shown to additionally facilitate the uptake of radionuclides by the clay colloids. This study aims to evaluate the transport behaviors of radionuclides in colloid-facilitated transport through a fractured chalk matrix and under geochemical conditions representative of the Negev desert, Israel. Lanthanides are considered an acceptable substitute to actinides for research on radionuclide transportation due to their similar chemical behavior. In this study, the migration of Ce both with and without colloidal particles was explored and compared to the migration of a conservative tracer (bromide). Tracer solutions containing known concentrations of Ce, bentonite colloids, humic acid and bromide were prepared in a matrix solution containing salt concentrations representative of that of the average rain water found in the Negev. These solutions were then injected into a flow system constructed around a naturally fractured chalk core. Samples were analyzed for Ce and Br using ICP-MS, and colloid concentrations were determined using spectrophotographic analysis. Breakthrough curves comparing the rates of transportation of each tracer were obtained, allowing for comparison of
Colloid-facilitated transport of lead in natural discrete fractures.
Tang, Xiang-Yu; Weisbrod, Noam
2009-01-01
Colloid-facilitated transport of lead (Pb) was explored in a natural chalk fracture with an average equivalent hydraulic aperture of 139 microm. Tracer solution was prepared by adding montmorillonite (100 mg L(-1)) and/or humic acid (HA) (10 mg L(-1)) to modified artificial rainwater containing dissolved Pb (21.4 mg Pb L(-1)), naturally precipitated PbCO(3) particles (16.4 mg Pb L(-1)) and LiBr (39.0 mg L(-1)). We found that Pb is only mobile when associated with colloids. PbCO(3) particles were not mobile in the fracture. The addition of HA to the montmorillonite suspension increased the suspension's mobility and therefore promoted the colloid-facilitated transport of Pb. The increases in pH and sodium absorption ratio induced by the chalk-tracer solution interactions appeared to increase the dispersion and mobilization of colloids entering the fracture. The dominant colloid-facilitated transport of Pb reported in this study has significant implications for risk assessment of Pb mobility in fractured rocks. PMID:19395135
Whitty, Jennifer A.; Walker, Ruth; Golenko, Xanthe; Ratcliffe, Julie
2014-01-01
Objectives This study provides insights into the validity and acceptability of Discrete Choice Experiment (DCE) and profile-case Best Worst Scaling (BWS) methods for eliciting preferences for health care in a priority-setting context. Methods An adult sample (N = 24) undertook a traditional DCE and a BWS choice task as part of a wider survey on Health Technology Assessment decision criteria. A ‘think aloud’ protocol was applied, whereby participants verbalized their thinking while making choices. Internal validity and acceptability were assessed through a thematic analysis of the decision-making process emerging from the qualitative data and a repeated choice task. Results A thematic analysis of the decision-making process demonstrated clear evidence of ‘trading’ between multiple attribute/levels for the DCE, and to a lesser extent for the BWS task. Limited evidence consistent with a sequential decision-making model was observed for the BWS task. For the BWS task, some participants found choosing the worst attribute/level conceptually challenging. A desire to provide a complete ranking from best to worst was observed. The majority (18,75%) of participants indicated a preference for DCE, as they felt this enabled comparison of alternative full profiles. Those preferring BWS were averse to choosing an undesirable characteristic that was part of a ‘package’, or perceived BWS to be less ethically conflicting or burdensome. In a repeated choice task, more participants were consistent for the DCE (22,92%) than BWS (10,42%) (p = 0.002). Conclusions This study supports the validity and acceptability of the traditional DCE format. Findings relating to the application of BWS profile methods are less definitive. Research avenues to further clarify the comparative merits of these preference elicitation methods are identified. PMID:24759637
The Suppression of Energy Discretization Errors in Multigroup Transport Calculations
Larsen, Edward
2013-06-17
The Objective of this project is to develop, implement, and test new deterministric methods to solve, as efficiently as possible, multigroup neutron transport problems having an extremely large number of groups. Our approach was to (i) use the standard CMFD method to "coarsen" the space-angle grid, yielding a multigroup diffusion equation, and (ii) use a new multigrid-in-space-and-energy technique to efficiently solve the multigroup diffusion problem. The overall strategy of (i) how to coarsen the spatial an energy grids, and (ii) how to navigate through the various grids, has the goal of minimizing the overall computational effort. This approach yields not only the fine-grid solution, but also coarse-group flux-weighted cross sections that can be used for other related problems.
Greenberg, Jay
2008-09-01
Understanding how and why analysands make the choices they do is central to both the clinical and the theoretical projects of psychoanalysis. And yet we know very little about the process of choice or about the relationship between choices and motives. A striking parallel is to be found between the ways choice is narrated in ancient Greek texts and the experience of analysts as they observe patients making choices in everyday clinical work. Pursuing this convergence of classical and contemporary sensibilities will illuminate crucial elements of the various meanings of choice, and of the way that these meanings change over the course of psychoanalytic treatment.
Greenberg, Jay
2008-09-01
Understanding how and why analysands make the choices they do is central to both the clinical and the theoretical projects of psychoanalysis. And yet we know very little about the process of choice or about the relationship between choices and motives. A striking parallel is to be found between the ways choice is narrated in ancient Greek texts and the experience of analysts as they observe patients making choices in everyday clinical work. Pursuing this convergence of classical and contemporary sensibilities will illuminate crucial elements of the various meanings of choice, and of the way that these meanings change over the course of psychoanalytic treatment. PMID:18802123
A minimal coupled fluid-discrete element model for bedload transport
NASA Astrophysics Data System (ADS)
Maurin, R.; Chauchat, J.; Chareyre, B.; Frey, P.
2015-11-01
A minimal Lagrangian two-phase model to study turbulent bedload transport focusing on the granular phase is presented and validated with experiments. The model intends to describe bedload transport of massive particles in fully rough flows at relatively low Shields numbers, for which no suspension occurs. A discrete element method for the granular phase is coupled with a one dimensional volume-averaged two-phase momentum equation for the fluid phase. The coupling between the discrete granular phase and the continuous fluid phase is discussed, and a consistent averaging formulation adapted to bedload transport is introduced. An original simple discrete random walk model is proposed to account for the fluid velocity fluctuations. The model is compared with experiments considering both classical sediment transport rate as a function of the Shields number, and depth profiles of solid velocity, volume fraction, and transport rate density, from existing bedload transport experiments in inclined flume. The results successfully reproduce the classical 3/2 power law, and more importantly describe well the depth profiles of the granular phase, showing that the model is able to reproduce the particle scale mechanisms. From a sensitivity analysis, it is shown that the fluctuation model allows to reproduce a realistic critical Shields number, and that the influence of the granular parameters on the macroscopic results is weak. Nevertheless, the analysis of the corresponding depth profiles reveals an evolution of the depth structure of the granular phase with varying restitution and friction coefficients, which denotes the non-trivial underlying physical mechanisms.
Hyman, Jeffrey De'Haven; Painter, S. L.; Viswanathan, H.; Makedonska, N.; Karra, S.
2015-09-12
We investigate how the choice of injection mode impacts transport properties in kilometer-scale three-dimensional discrete fracture networks (DFN). The choice of injection mode, resident and flux-weighted, is designed to mimic different physical phenomena. It has been hypothesized that solute plumes injected under resident conditions evolve to behave similarly to solutes injected under flux-weighted conditions. Previously, computational limitations have prohibited the large-scale simulations required to investigate this hypothesis. We investigate this hypothesis by using a high-performance DFN suite, dfnWorks, to simulate flow in kilometer-scale three-dimensional DFNs based on fractured granite at the Forsmark site in Sweden, and adopt a Lagrangian approach to simulate transport therein. Results show that after traveling through a pre-equilibrium region, both injection methods exhibit linear scaling of the first moment of travel time and power law scaling of the breakthrough curve with similar exponents, slightly larger than 2. Lastly, the physical mechanisms behind this evolution appear to be the combination of in-network channeling of mass into larger fractures, which offer reduced resistance to flow, and in-fracture channeling, which results from the topology of the DFN.
Hyman, Jeffrey De'Haven; Painter, S. L.; Viswanathan, H.; Makedonska, N.; Karra, S.
2015-09-12
We investigate how the choice of injection mode impacts transport properties in kilometer-scale three-dimensional discrete fracture networks (DFN). The choice of injection mode, resident and flux-weighted, is designed to mimic different physical phenomena. It has been hypothesized that solute plumes injected under resident conditions evolve to behave similarly to solutes injected under flux-weighted conditions. Previously, computational limitations have prohibited the large-scale simulations required to investigate this hypothesis. We investigate this hypothesis by using a high-performance DFN suite, dfnWorks, to simulate flow in kilometer-scale three-dimensional DFNs based on fractured granite at the Forsmark site in Sweden, and adopt a Lagrangian approachmore » to simulate transport therein. Results show that after traveling through a pre-equilibrium region, both injection methods exhibit linear scaling of the first moment of travel time and power law scaling of the breakthrough curve with similar exponents, slightly larger than 2. Lastly, the physical mechanisms behind this evolution appear to be the combination of in-network channeling of mass into larger fractures, which offer reduced resistance to flow, and in-fracture channeling, which results from the topology of the DFN.« less
Byun, Ji-Hye; Kwon, Sun-Hong; Lee, Ji-Eun; Cheon, Ji-Eun; Jang, Eun-Jin; Lee, Eui-Kyung
2016-01-01
Purpose To elucidate and compare benefit–risk preferences among Korean patients and physicians concerning cyclooxygenase-2 (Cox-2) inhibitor treatments for arthritis. Materials and methods Subjects included 100 patients with arthritis and 60 board-certified orthopedic surgeon physicians in South Korea. Through a systematic review of the literature, beneficial attributes of using Cox-2 inhibitors were defined as a decrease in the Western Ontario and McMaster Universities Arthritis Index for pain score and improvement in physical function. Likewise, risk attributes included upper gastrointestinal (GI) complications and cardiovascular (CV) adverse events. Discrete choice experiments were used to determine preferences for these four attributes among Korean patients and physicians. Relative importance and maximum acceptable risk for improving beneficial attributes were assessed by analyzing the results of the discrete choice experiment by using a conditional logit model. Results Patients ranked the relative importance of benefit–risk attributes as follows: pain reduction (35.2%); physical function improvement (30.0%); fewer CV adverse events (21.5%); fewer GI complications (13.4%). The physicians’ ranking for the same attributes was as follows: fewer CV (33.5%); pain reduction (32.4%); fewer GI complications (18.1%); physical function improvement (16.0%). Patients were more willing than physicians to accept risks when pain improved from 20% or 45% to 55% and physical function improved from 15% or 35% to 45%. Conclusion We confirmed that patients and physicians had different benefit–risk preferences regarding Cox-2 inhibitors. Patients with arthritis prioritized the benefits of Cox-2 inhibitors over the risks; moreover, in comparison with the physicians, arthritis patients were more willing to accept the trade-off between benefits and risks to achieve the best treatment level. To reduce the preference gap and achieve treatment goals, physicians must better
Recommendations for a production discrete-ordinates coupled electron-photon transport capability
Morel, J.E.; Nelson, W.E.
1984-05-01
The purpose of this study was to determine if a production capability for discrete-ordinates coupled electron-photon transport calculations should be developed and, if so, to recommend how it should be done. It is concluded that such a capability should be developed. The purpose of this report is to detail reasons for making these conclusions, and further to make specific recommendations regarding the manner in which this dvelopment should be carried out. The discrete ordinates method is a deterministic method originally developed to solve the neutron transport equation. For this purpose, it has proven to be an accurate and efficient technique. In particular, it has proven to be much more efficient than Monte Carlo methods in one spatial dimension. All current production methods for coupled electron-photon transport calculations are based upon the condensed history method developed by Berger. This method is generally quite expensive for problems of interest to the weapons radiation effects community, even when the problems are limited to one spatial dimension. Thus, routine engineering design calculations involving coupled electron-photon transport must often be performed with rather crude and inaccurate methods due to cost constraints. The existence of this global deficiency is the main motivation for developing a discrete-ordinates coupled electron-photon transport capability. It has the potential of being as accurate as Monte Carlo yet efficient enough to be used in routine engineering design calculations.
Wang, Chi-Jen
2013-01-01
In this thesis, we analyze both the spatiotemporal behavior of: (A) non-linear “reaction” models utilizing (discrete) reaction-diffusion equations; and (B) spatial transport problems on surfaces and in nanopores utilizing the relevant (continuum) diffusion or Fokker-Planck equations. Thus, there are some common themes in these studies, as they all involve partial differential equations or their discrete analogues which incorporate a description of diffusion-type processes. However, there are also some qualitative differences, as shall be discussed below.
Cunningham, Charles E; Deal, Ken; Rimas, Heather; Chen, Yvonne; Buchanan, Don H; Sdao-Jarvie, Kathie
2009-11-01
We used discrete choice conjoint analysis to model the ways 645 children's mental health (CMH) professionals preferred to provide information to parents seeking CMH services. Participants completed 20 choice tasks presenting experimentally varied combinations of the study's 14 4-level CMH information transfer attributes. Latent class analysis revealed three segments. Open Access professionals (32.2%) preferred that intake workers automatically provide all parents with CMH information. They preferred information prepared by professional organizations and located at accessible settings such as public schools. They responded favorably to the internet as a source of information for parents. Controlled Access professionals (22.2%) preferred information that was approved and recommended by a child's therapist, prepared by an experienced clinician, and located at hospitals and CMH clinics. Process Sensitive professionals (45.6%) showed a stronger preference for active learning materials with parenting groups and therapist "coaching" calls supporting the knowledge transfer process. Simulations suggested that realizing the benefits of CMH information requires the development of knowledge transfer strategies that align the preferences of professionals with those of the families they serve.
Cunningham, Charles E; Deal, Ken; Rimas, Heather; Chen, Yvonne; Buchanan, Don H; Sdao-Jarvie, Kathie
2009-11-01
We used discrete choice conjoint analysis to model the ways 645 children's mental health (CMH) professionals preferred to provide information to parents seeking CMH services. Participants completed 20 choice tasks presenting experimentally varied combinations of the study's 14 4-level CMH information transfer attributes. Latent class analysis revealed three segments. Open Access professionals (32.2%) preferred that intake workers automatically provide all parents with CMH information. They preferred information prepared by professional organizations and located at accessible settings such as public schools. They responded favorably to the internet as a source of information for parents. Controlled Access professionals (22.2%) preferred information that was approved and recommended by a child's therapist, prepared by an experienced clinician, and located at hospitals and CMH clinics. Process Sensitive professionals (45.6%) showed a stronger preference for active learning materials with parenting groups and therapist "coaching" calls supporting the knowledge transfer process. Simulations suggested that realizing the benefits of CMH information requires the development of knowledge transfer strategies that align the preferences of professionals with those of the families they serve. PMID:19629676
Rakotonarivo, O Sarobidy; Schaafsma, Marije; Hockley, Neal
2016-12-01
While discrete choice experiments (DCEs) are increasingly used in the field of environmental valuation, they remain controversial because of their hypothetical nature and the contested reliability and validity of their results. We systematically reviewed evidence on the validity and reliability of environmental DCEs from the past thirteen years (Jan 2003-February 2016). 107 articles met our inclusion criteria. These studies provide limited and mixed evidence of the reliability and validity of DCE. Valuation results were susceptible to small changes in survey design in 45% of outcomes reporting reliability measures. DCE results were generally consistent with those of other stated preference techniques (convergent validity), but hypothetical bias was common. Evidence supporting theoretical validity (consistency with assumptions of rational choice theory) was limited. In content validity tests, 2-90% of respondents protested against a feature of the survey, and a considerable proportion found DCEs to be incomprehensible or inconsequential (17-40% and 10-62% respectively). DCE remains useful for non-market valuation, but its results should be used with caution. Given the sparse and inconclusive evidence base, we recommend that tests of reliability and validity are more routinely integrated into DCE studies and suggest how this might be achieved. PMID:27576151
Michaels-Igbokwe, Christine; Terris-Prestholt, Fern; Lagarde, Mylene; Chipeta, Effie; Cairns, John
2015-01-01
Objective To quantify the impact of service provider characteristics on young people’s choice of family planning (FP) service provider in rural Malawi in order to identify strategies for increasing access and uptake of FP among youth. Methods and Findings A discrete choice experiment was developed to assess the relative impact of service characteristics on preferences for FP service providers among young people (aged 15–24). Four alternative providers were included (government facility, private facility, outreach and community based distribution of FP) and described by six attributes (the distance between participants’ home and the service delivery point, frequency of service delivery, waiting time at the facility, service providers’ attitude, availability of FP commodities and price). A random parameters logit model was used to estimate preferences for service providers and the likely uptake of services following the expansion of outreach and community based distribution (CBDA) services. In the choice experiment young people were twice as likely to choose a friendly provider (government service odds ratio [OR] = 2.45, p<0.01; private service OR = 1.99, p<0.01; CBDA OR = 1.88, p<0.01) and more than two to three times more likely to choose a provider with an adequate supply of FP commodities (government service OR = 2.48, p<0.01; private service OR = 2.33, p<0.01; CBDA = 3.85, p<0.01). Uptake of community based services was greater than facility based services across a variety of simulated service scenarios indicating that such services may be an effective means of expanding access for youth in rural areas and an important tool for increasing service uptake among youth. Conclusions Ensuring that services are acceptable to young people may require additional training for service providers in order to ensure that all providers are friendly and non-judgemental when dealing with younger clients and to ensure that supplies are consistently available. PMID
Skedgel, Chris; Wailoo, Allan; Akehurst, Ron
2015-01-01
Economic theory suggests that resources should be allocated in a way that produces the greatest outputs, on the grounds that maximizing output allows for a redistribution that could benefit everyone. In health care, this is known as QALY (quality-adjusted life-year) maximization. This justification for QALY maximization may not hold, though, as it is difficult to reallocate health. Therefore, the allocation of health care should be seen as a matter of distributive justice as well as efficiency. A discrete choice experiment was undertaken to test consistency with the principles of QALY maximization and to quantify the willingness to trade life-year gains for distributive justice. An empirical ethics process was used to identify attributes that appeared relevant and ethically justified: patient age, severity (decomposed into initial quality and life expectancy), final health state, duration of benefit, and distributional concerns. Only 3% of respondents maximized QALYs with every choice, but scenarios with larger aggregate QALY gains were chosen more often and a majority of respondents maximized QALYs in a majority of their choices. However, respondents also appeared willing to prioritize smaller gains to preferred groups over larger gains to less preferred groups. Marginal analyses found a statistically significant preference for younger patients and a wider distribution of gains, as well as an aversion to patients with the shortest life expectancy or a poor final health state. These results support the existence of an equity-efficiency tradeoff and suggest that well-being could be enhanced by giving priority to programs that best satisfy societal preferences. Societal preferences could be incorporated through the use of explicit equity weights, although more research is required before such weights can be used in priority setting. PMID:25145575
Skedgel, Chris; Wailoo, Allan; Akehurst, Ron
2015-01-01
Economic theory suggests that resources should be allocated in a way that produces the greatest outputs, on the grounds that maximizing output allows for a redistribution that could benefit everyone. In health care, this is known as QALY (quality-adjusted life-year) maximization. This justification for QALY maximization may not hold, though, as it is difficult to reallocate health. Therefore, the allocation of health care should be seen as a matter of distributive justice as well as efficiency. A discrete choice experiment was undertaken to test consistency with the principles of QALY maximization and to quantify the willingness to trade life-year gains for distributive justice. An empirical ethics process was used to identify attributes that appeared relevant and ethically justified: patient age, severity (decomposed into initial quality and life expectancy), final health state, duration of benefit, and distributional concerns. Only 3% of respondents maximized QALYs with every choice, but scenarios with larger aggregate QALY gains were chosen more often and a majority of respondents maximized QALYs in a majority of their choices. However, respondents also appeared willing to prioritize smaller gains to preferred groups over larger gains to less preferred groups. Marginal analyses found a statistically significant preference for younger patients and a wider distribution of gains, as well as an aversion to patients with the shortest life expectancy or a poor final health state. These results support the existence of an equity-efficiency tradeoff and suggest that well-being could be enhanced by giving priority to programs that best satisfy societal preferences. Societal preferences could be incorporated through the use of explicit equity weights, although more research is required before such weights can be used in priority setting.
Berhane, Adugnaw; Enquselassie, Fikre
2015-01-01
Background Information from the patient’s point of view is essential in policy and clinical decisions. Prioritizing what patients value, need, and prefer in various aspects of a health program can be helpful in evaluating and designing hospital health care services. Objective To examine patients’ preference for attributes related to health care services and to ascertain the relative impact of attributes at hospitals in Amhara Region, northern Ethiopia. Methods A stated-preference discrete choice experiment survey was performed in multistage, stratified, and systematic sampling of patients who visited the hospitals. Attributes were selected based on a literature review of the most important characteristics of hospital health care service and reviewed and validated with inputs from patients and researchers in the field. Attributes included in the study were waiting time, physician communication, nursing communication, drug availability, continuity of care, and diagnostic facilities. A random-effects probit model was used to perform the analysis. Results One thousand and five respondents who received care in the outpatient and inpatient departments participated in the study. All attributes included in the study affected the choice of hospital. Patients were willing to wait up to 3.3 hours and 2.7 hours to get full drugs in the hospital and good nursing communication, respectively. The interaction terms indicate that preferences differ with the variables sex, occupation, and type of hospital. Patients expressed clear preferences in a decreasing order of all the significant attribute levels: a lot of diagnostic facilities, full drug availability, continuity of care, good nursing communication, partial drug availability, good physician communication, and shorter waiting time for the consultation. Conclusion Different hospital care attributes had a significant and different influence on patients’ choice of hospital. The study informs about patients’ preferences
Cunningham, Charles E; Walker, John R; Eastwood, John D; Westra, Henny; Rimas, Heather; Chen, Yvonne; Marcus, Madalyn; Swinson, Richard P; Bracken, Keyna; The Mobilizing Minds Research Group
2014-04-01
Although most young adults with mood and anxiety disorders do not seek treatment, those who are better informed about mental health problems are more likely to use services. The authors used conjoint analysis to model strategies for providing information about anxiety and depression to young adults. Participants (N = 1,035) completed 17 choice tasks presenting combinations of 15 four-level attributes of a mental health information strategy. Latent class analysis yielded 3 segments. The virtual segment (28.7%) preferred working independently on the Internet to obtain information recommended by young adults who had experienced anxiety or depression. Self-assessment options and links to service providers were more important to this segment. Conventional participants (30.1%) preferred books or pamphlets recommended by a doctor, endorsed by mental health professionals, and used with a doctor's support. They would devote more time to information acquisition but were less likely to use Internet social networking options. Brief sources of information were more important to the low interest segment (41.2%). All segments preferred information about alternative ways to reduce anxiety or depression rather than psychological approaches or medication. Maximizing the use of information requires active and passive approaches delivered through old-media (e.g., books) and new-media (e.g., Internet) channels. PMID:24266450
Cunningham, Charles E.; Walker, John R.; Eastwood, John D.; Westra, Henny; Rimas, Heather; Chen, Yvonne; Marcus, Madalyn; Swinson, Richard P.; Bracken, Keyna
2013-01-01
Although most young adults with mood and anxiety disorders do not seek treatment, those who are better informed about mental health problems are more likely to use services. The authors used conjoint analysis to model strategies for providing information about anxiety and depression to young adults. Participants (N = 1,035) completed 17 choice tasks presenting combinations of 15 four-level attributes of a mental health information strategy. Latent class analysis yielded 3 segments. The virtual segment (28.7%) preferred working independently on the Internet to obtain information recommended by young adults who had experienced anxiety or depression. Self-assessment options and links to service providers were more important to this segment. Conventional participants (30.1%) preferred books or pamphlets recommended by a doctor, endorsed by mental health professionals, and used with a doctor's support. They would devote more time to information acquisition but were less likely to use Internet social networking options. Brief sources of information were more important to the low interest segment (41.2%). All segments preferred information about alternative ways to reduce anxiety or depression rather than psychological approaches or medication. Maximizing the use of information requires active and passive approaches delivered through old-media (e.g. books) and new-media (e.g., Internet) channels. PMID:24266450
NASA Astrophysics Data System (ADS)
Kruppa, Lisa; König, Christoph M.; Becker, Martin; Seidel, Torsten
2016-04-01
Most hard rock aquifers, which are important for geothermal use, contain fractures of different type and scale. These fault systems are of major significance for heat flow in the groundwater. The hydrogeological characterization of fault systems must therefore be part of any site investigation in hard rock aquifers and hydraulically important fault systems need to be appropriately represented in associated numerical models. This contribution discusses different spatial discretization methods of fault systems in three-dimensional groundwater models and their impact on the simulated groundwater flow field as well as density and viscosity dependent heat transport. The analysis includes a comparison of the convergence behavior and numerical stability of the different discretization methods. To ensure defendable results, the utilized numerical model SPRING was first verified against data from the Hydrocoin Level 1 Case 2 project. After verification, the software was used to evaluate the impact of different discretization strategies on steady-state and transient groundwater flow and transport model results. The results show a significant influence of the spatial discretization strategy on predicted flow rates and subsequent mass fluxes as well as energy balances.
Walsh, J. A.; Palmer, T. S.; Urbatsch, T. J.
2013-07-01
A new method for generating discrete scattering cross sections to be used in charged particle transport calculations is investigated. The method of data generation is presented and compared to current methods for obtaining discrete cross sections. The new, more generalized approach allows greater flexibility in choosing a cross section model from which to derive discrete values. Cross section data generated with the new method is verified through a comparison with discrete data obtained with an existing method. Additionally, a charged particle transport capability is demonstrated in the time-dependent Implicit Monte Carlo radiative transfer code package, Milagro. The implementation of this capability is verified using test problems with analytic solutions as well as a comparison of electron dose-depth profiles calculated with Milagro and an already-established electron transport code. An initial investigation of a preliminary integration of the discrete cross section generation method with the new charged particle transport capability in Milagro is also presented. (authors)
The three-dimensional, discrete ordinates neutral particle transport code TORT: An overview
Azmy, Y.Y.
1996-12-31
The centerpiece of the Discrete Ordinates Oak Ridge System (DOORS), the three-dimensional neutral particle transport code TORT is reviewed. Its most prominent features pertaining to large applications, such as adjustable problem parameters, memory management, and coarse mesh methods, are described. Advanced, state-of-the-art capabilities including acceleration and multiprocessing are summarized here. Future enhancement of existing graphics and visualization tools is briefly presented.
Choices for Mobility Independence: Transportation Options for Older Adults
... In addition to the services described above, some communities have mobility managers who can guide you through the transportation resources and services that are available. Mobility managers know the community-wide transportation service network and understand how it ...
2012-01-01
Background In spite of the potential impact upon population health and expenditure, interventions promoting medication adherence have been found to be of moderate effectiveness and cost effectiveness. Understanding the relative influence of factors affecting patient medication adherence decisions and the characteristics of individuals associated with variation in adherence will lead to a better understanding of how future interventions should be designed and targeted. This study aims to explore medication-taking decisions that may underpin intentional medication non-adherence behaviour amongst a community sample and the relative importance of medication specific factors and patient background characteristics contributing to those decisions. Methods A discrete choice experiment conducted through a web-enabled online survey was used to estimate the relative importance of eight medication factors (immediate and long-term medication harms and benefits, cost, regimen, symptom severity, alcohol restrictions) on the preference to continue taking a medication. To reflect more closely what usually occurs in practice, non-disease specific medication and health terms were used to mimic decisions across multiple medications and conditions.161 general community participants, matching the national Australian census data (age, gender) were recruited through an online panel provider (participation rate: 10%) in 2010. Results Six of the eight factors (i.e. immediate and long-term medication harms and benefits, cost, and regimen) had a significant influence on medication choice. Patient background characteristics did not improve the model. Respondents with private health insurance appeared less sensitive to cost then those without private health insurance. In general, health outcomes, framed as a side-effect, were found to have a greater influence over adherence than outcomes framed as therapeutic benefits. Conclusions Medication-taking decisions are the subject of rational choices
ERIC Educational Resources Information Center
Abd-El-Hafez, Alaa Karem
2015-01-01
Teacher retention is a concern in all educational sectors in America. It is of special importance to Islamic schools, which tend to lack the resources necessary in recruiting and training new teachers. This dissertation addressed this problem in full-time Islamic schools in New York State by conducting a discrete choice experiment, which reflects…
Generalized discrete mapping treatment of nonresonant ripple transport in a tokamak
Albert, J.M.; Boozer, A.H.
1989-06-01
A discrete mapping is used to analyze nonresonant ripple transport in a tokamak. Pitch-angle scattering is manifested in two different terms, as in a previous treatment of resonant ripple transport. The mapping is a generalization of one which recovers the standard banana-drift regime. This is one limit of the more general mapping presented here; in the other, the quasilinear value for the diffusion coefficient emerges. When the quasilinear value applies, it can be either much greater or much less than the corresponding banana-drift value, depending on the parameter values of the mapping.
DeHart, M.D.
1992-12-01
A method for applying the discrete ordinates method for solution of the neutron transport equation in arbitary two-dimensional meshes has been developed. The finite difference approach normally used to approximate spatial derivatives in extrapolating angular fluxes across a cell is replaced by direct solution of the characteristic form of the transport equation for each discrete direction. Thus, computational cells are not restricted to the traditional shape of a mesh element within a given coordinate system. However, in terms of the treatment of energy and angular dependencies, this method resembles traditional discrete ordinates techniques. Using the method developed here, a general two-dimensional space can be approximated by an irregular mesh comprised of arbitrary polygons. The present work makes no assumptions about the orientations or the number of sides in a given cell, and computes all geometric relationships between each set of sides in each cell for each discrete direction. A set of non-reentrant polygons can therefore be used to represent any given two dimensional space. Results for a number of test problems have been compared to solutions obtained from traditional methods, with good agreement. Comparisons include benchmarks against analytical results for problems with simple geometry, as well numerical results obtained from traditional discrete ordinates methods by applying the ANISN and TWOTRAN computer programs. Numerical results were obtained for problems ranging from simple one-dimensional geometry to complicated multidimensional configurations. These results have demonstrated the ability of the developed method to closely approximate complex geometrical configurations and to obtain accurate results for problems that are extremely difficult to model using traditional methods.
Smith, Kyle C; Weaver, James C
2012-06-01
Electrically driven transport of molecules and ions within aqueous electrolytes is of long-standing interest, with direct relevance to applications that include the delivery/release of biologically active solutes to/from cells and tissues. Examples include iontophoretic and electroporation-mediated drug delivery. Here, we describe a robust method for characterizing electrodiffusive transport in physiologic aqueous media. Specifically, we treat the case of solute present in sufficiently low concentration as to negligibly contribute to the total ionic current within the system. In this limiting case, which applies to many systems of interest, the predominant electrical behavior due to small ions is decoupled from solute transport. Thus, electrical behavior may be characterized using existing methods and treated as known in characterizing electrodiffusive molecular transport. First, we present traditional continuum equations governing electrodiffusion of charged solutes within aqueous electrolytes and then adapt them to discretized systems. Second, we examine the time-dependent and steady-state interfacial concentration gradients that result from the combination of diffusion and electrical drift. Third, we show how interfacial concentration gradients are related to electric field strength and duration. Finally, we examine how discretization size affects the accuracy of these methods. Overall these methods are motivated by and well suited to addressing an outstanding goal: estimation of the net ionic and molecular transport facilitated by electroporation in biological systems.
Discrete ordinates transport methods for problems with highly forward-peaked scattering
Pautz, S.D.
1998-04-01
The author examines the solutions of the discrete ordinates (S{sub N}) method for problems with highly forward-peaked scattering kernels. He derives conditions necessary to obtain reasonable solutions in a certain forward-peaked limit, the Fokker-Planck (FP) limit. He also analyzes the acceleration of the iterative solution of such problems and offer improvements to it. He extends the analytic Fokker-Planck limit analysis to the S{sub N} equations. This analysis shows that in this asymptotic limit the S{sub N} solution satisfies a pseudospectral discretization of the FP equation, provided that the scattering term is handled in a certain way (which he describes) and that the analytic transport solution satisfies an analytic FP equation. Similar analyses of various spatially discretized S{sub N} equations reveal that they too produce solutions that satisfy discrete FP equations, given the same provisions. Numerical results agree with these theoretical predictions. He defines a multidimensional angular multigrid (ANMG) method to accelerate the iterative solution of highly forward-peaked problems. The analyses show that a straightforward application of this scheme is subject to high-frequency instabilities. However, by applying a diffusive filter to the ANMG corrections he is able to stabilize this method. Fourier analyses of model problems show that the resulting method is effective at accelerating the convergence rate when the scattering is forward-peaked. The numerical results demonstrate that these analyses are good predictors of the actual performance of the ANMG method.
Discrete ordinates transport methods for problems with highly forward-peaked scattering
NASA Astrophysics Data System (ADS)
Pautz, Shawn Daniel
1998-10-01
We examine the solutions of the discrete ordinates (SN) method for problems with highly forward- peaked scattering kernels. We derive conditions necessary to obtain reasonable solutions in a certain forward- peaked limit, the Fokker-Planck (FP) limit. We also analyze the acceleration of the iterative solution of such problems and offer improvements to it. We extend the analytic Fokker-Planck limit analysis to the SN equations. This analysis shows that in this asymptotic limit the SN solution satisfies a pseudospectral discretization of the FP equation, provided that the scattering term is handled in a certain way (which we describe) and that the analytic transport solution satisfies an analytic FP equation. Similar analyses of various spatially discretized SN equations reveal that they too produce solutions that satisfy discrete FP equations, given the same provisions. Numerical results agree with these theoretical predictions. We define a multidimensional angular multigrid (ANMG) method to accelerate the iterative solution of highly forward-peaked problems. Our analyses show that a straightforward application of this scheme is subject to high-frequency instabilities. However, by applying a diffusive filter to the ANMG corrections we are able to stabilize this method. Fourier analyses of model problems show that the resulting method is effective at accelerating the convergence rate when the scattering is forward-peaked. Our numerical results demonstrate that these analyses are good predictors of the actual performance of the ANMG method.
Thompson, K.G.
2000-11-01
In this work, we develop a new spatial discretization scheme that may be used to numerically solve the neutron transport equation. This new discretization extends the family of corner balance spatial discretizations to include spatial grids of arbitrary polyhedra. This scheme enforces balance on subcell volumes called corners. It produces a lower triangular matrix for sweeping, is algebraically linear, is non-negative in a source-free absorber, and produces a robust and accurate solution in thick diffusive regions. Using an asymptotic analysis, we design the scheme so that in thick diffusive regions it will attain the same solution as an accurate polyhedral diffusion discretization. We then refine the approximations in the scheme to reduce numerical diffusion in vacuums, and we attempt to capture a second order truncation error. After we develop this Upstream Corner Balance Linear (UCBL) discretization we analyze its characteristics in several limits. We complete a full diffusion limit analysis showing that we capture the desired diffusion discretization in optically thick and highly scattering media. We review the upstream and linear properties of our discretization and then demonstrate that our scheme captures strictly non-negative solutions in source-free purely absorbing media. We then demonstrate the minimization of numerical diffusion of a beam and then demonstrate that the scheme is, in general, first order accurate. We also note that for slab-like problems our method actually behaves like a second-order method over a range of cell thicknesses that are of practical interest. We also discuss why our scheme is first order accurate for truly 3D problems and suggest changes in the algorithm that should make it a second-order accurate scheme. Finally, we demonstrate 3D UCBL's performance on several very different test problems. We show good performance in diffusive and streaming problems. We analyze truncation error in a 3D problem and demonstrate robustness in a
Helter, Timea Mariann; Boehler, Christian Ernst Heinrich
2016-01-01
Abstract Discrete choice experiments (DCEs) become increasingly popular to value outcomes for health economic studies and gradually gain acceptance as an input into policy decisions. Developing attributes is a key aspect for the design of DCEs, as their results may misguide decision-makers if they are based on an inappropriate set of attributes. However, the area lacks guidance, and current health-related DCE studies vary considerably in their methods of attribute development, with the consequent danger of providing an unreliable input for policy decisions. The aim of this article is to inform the progress toward a more systematic approach to attribute development for DCE studies in health. A systematic review of the published health-related DCE literature was conducted to lay the foundations for a generic framework which was tested in a case study of alcohol misuse interventions. Four stages of a general attribute development process emerged: (i) raw data collection; (ii) data reduction; (iii) removing inappropriate attributes; and (iv) wording. The case study compared and contrasted a qualitative and mixed-methods approach for the development of attributes for DCEs in the area of alcohol misuse interventions. This article provides a reference point for the design of future DCE experiments in health. PMID:27695386
NASA Astrophysics Data System (ADS)
Ungureanu, Constantin; Rayavarapu, Raja Gopal; Manohar, Srirang; van Leeuwen, Ton G.
2009-05-01
Gold nanorods have interesting optical properties due to surface plasmon resonance effects. A variety of biomedical applications of these particles have been envisaged and feasibilities demonstrated in imaging, sensing, and therapy based on the interactions of light with these particles. In order to correctly interpret experimental data and tailor the nanorods and their environments for optimal use in these applications, simulations of the optical properties of the particles under various conditions are essential. Of various numerical methods available, the discrete dipole approximation (DDA) approach implemented in the publicly available DDSCAT code is a powerful method that had proved popular for studying gold nanorods. However, there is as yet no universal agreement on the shape used to represent the nanorods and on the dielectric function of gold required for the simulations. We systematically study the influence of these parameters on simulated results. We find large variations in the position of plasmon resonance peaks, their amplitudes, and shapes of the spectra depending on the choice of the parameters. We discuss these in the light of experimental optical extinction spectra of gold nanorods synthesized in our laboratory. We show that much care should be taken and prudence applied before DDA results be used to interpret experimental data and to help characterize nanoparticles synthesized.
Schreiner, J A; Latacz-Lohmann, U
2015-11-01
This paper investigates farmers' willingness to participate in a genetically modified organism (GMO)-free milk production scheme offered by some German dairy companies. The empirical analysis is based upon discrete choice experiments with 151 dairy farmers from 2 regions in Germany. A conditional logit estimation reveals a strong positive effect of the price premium on offer. Reliable feed monitoring and free technical support increase the likelihood of scheme adoption, the latter however only in farms that have been receiving technical support in other fields. By contrast, any interference with the entrepreneurial autonomy of farmers, through pre-arranged feed procurement or prescriptive advice on the part of the dairy company, lowers acceptance probabilities. Farmers' attitudes toward cultivation of genetically modified soy, their assessment of the market potential of GMO-free milk and future feed prices were found to be significant determinants of adoption, as are farmer age, educational status, and current feeding regimens. Respondents requested on average a mark-up of 0.80 eurocents per kilogram of milk to accept a contract. Comparison of the estimates for the 2 regions suggests that farmers in northern Germany are, on average, more likely to convert to genetically modified-free production; however, farmers in the south are, ceteris paribus, more responsive to an increase in the price premium offered. A latent class model reveals significant differences in the valuation of scheme attributes between 2 latent classes of adopters and nonadopters.
Schreiner, J A; Latacz-Lohmann, U
2015-11-01
This paper investigates farmers' willingness to participate in a genetically modified organism (GMO)-free milk production scheme offered by some German dairy companies. The empirical analysis is based upon discrete choice experiments with 151 dairy farmers from 2 regions in Germany. A conditional logit estimation reveals a strong positive effect of the price premium on offer. Reliable feed monitoring and free technical support increase the likelihood of scheme adoption, the latter however only in farms that have been receiving technical support in other fields. By contrast, any interference with the entrepreneurial autonomy of farmers, through pre-arranged feed procurement or prescriptive advice on the part of the dairy company, lowers acceptance probabilities. Farmers' attitudes toward cultivation of genetically modified soy, their assessment of the market potential of GMO-free milk and future feed prices were found to be significant determinants of adoption, as are farmer age, educational status, and current feeding regimens. Respondents requested on average a mark-up of 0.80 eurocents per kilogram of milk to accept a contract. Comparison of the estimates for the 2 regions suggests that farmers in northern Germany are, on average, more likely to convert to genetically modified-free production; however, farmers in the south are, ceteris paribus, more responsive to an increase in the price premium offered. A latent class model reveals significant differences in the valuation of scheme attributes between 2 latent classes of adopters and nonadopters. PMID:26342979
Bansback, Nick; Hole, Arne Risa; Mulhern, Brendan; Tsuchiya, Aki
2014-08-01
There is interest in the use of discrete choice experiments that include a duration attribute (DCETTO) to generate health utility values, but questions remain on its feasibility in large health state descriptive systems. This study examines the stability of DCETTO to estimate health utility values from the five-level EQ-5D, an instrument with depicts 3125 different health states. Between January and March 2011, we administered 120 DCETTO tasks based on the five-level EQ-5D to a total of 1799 respondents in the UK (each completed 15 DCETTO tasks on-line). We compared models across different sample sizes and different total numbers of observations. We found the DCETTO coefficients were generally consistent, with high agreement between individual ordinal preferences and aggregate cardinal values. Keeping the DCE design and the total number of observations fixed, subsamples consisting of 10 tasks per respondent with an intermediate sized sample, and 15 tasks with a smaller sample provide similar results in comparison to the whole sample model. In conclusion, we find that the DCETTO is a feasible method for developing values for larger descriptive systems such as EQ-5D-5L, and find evidence supporting important design features for future valuation studies that use the DCETTO.
Helter, Timea Mariann; Boehler, Christian Ernst Heinrich
2016-01-01
Abstract Discrete choice experiments (DCEs) become increasingly popular to value outcomes for health economic studies and gradually gain acceptance as an input into policy decisions. Developing attributes is a key aspect for the design of DCEs, as their results may misguide decision-makers if they are based on an inappropriate set of attributes. However, the area lacks guidance, and current health-related DCE studies vary considerably in their methods of attribute development, with the consequent danger of providing an unreliable input for policy decisions. The aim of this article is to inform the progress toward a more systematic approach to attribute development for DCE studies in health. A systematic review of the published health-related DCE literature was conducted to lay the foundations for a generic framework which was tested in a case study of alcohol misuse interventions. Four stages of a general attribute development process emerged: (i) raw data collection; (ii) data reduction; (iii) removing inappropriate attributes; and (iv) wording. The case study compared and contrasted a qualitative and mixed-methods approach for the development of attributes for DCEs in the area of alcohol misuse interventions. This article provides a reference point for the design of future DCE experiments in health.
Mortimer, Duncan; Segal, Leonie
2008-01-01
Background A number of recent findings imply that the value of a life saved, life-year (LY) saved or quality-adjusted life year (QALY) saved varies depending on the characteristics of the life, LY or QALY under consideration. Despite these findings, budget allocations continue to be made as if all healthy life-years are equivalent. This continued focus on simple health maximisation is partly attributable to gaps in the available evidence. The present study attempts to close some of these gaps. Methods Discrete choice experiment to estimate the marginal rate of substitution between cost, effectiveness and various non-health arguments. Odds of selecting profile B over profile A estimated via binary logistic regression. Marginal rates of substitution between attributes (including cost) then derived from estimated regression coefficients. Results Respondents were more likely to select less costly, more effective interventions with a strong evidence base where the beneficiary did not contribute to their illness. Results also suggest that respondents preferred prevention over cure. Interventions for young children were most preferred, followed by interventions for young adults, then interventions for working age adults and with interventions targeted at the elderly given lowest priority. Conclusion Results confirm that a trade-off exists between cost, effectiveness and non-health arguments when respondents prioritise health programs. That said, it is true that respondents were more likely to select less costly, more effective interventions – confirming that it is an adjustment to, rather than an outright rejection of, simple health maximisation that is required. PMID:18489787
Garcia, R.D.M.; Ono, S.
1999-09-01
An improved implementation of the discrete ordinates method for computing neutral particle transport in ducts is presented. The considered one-dimensional model makes use of two basic functions to represent the transverse and azimuthal dependencies of the particle angular flux in the duct. It is shown that if the problem is decomposed into uncollided and collided problems prior to using the discrete ordinates approximation, the number of ordinates necessary to achieve a desired degree of accuracy in the solution can be greatly reduced, especially for long ducts with significant wall absorption. Further savings in computer time can be attained by employing a composite quadrature based on a (nonstandard) half-range quadrature that can be generated in an effective and efficient way with one of the classical methods in the constructive theory of orthogonal polynomials.
Diallinas, George
2014-01-01
Transporters are ubiquitous proteins mediating the translocation of solutes across cell membranes, a biological process involved in nutrition, signaling, neurotransmission, cell communication and drug uptake or efflux. Similarly to enzymes, most transporters have a single substrate binding-site and thus their activity follows Michaelis-Menten kinetics. Substrate binding elicits a series of structural changes, which produce a transporter conformer open toward the side opposite to the one from where the substrate was originally bound. This mechanism, involving alternate outward- and inward-facing transporter conformers, has gained significant support from structural, genetic, biochemical and biophysical approaches. Most transporters are specific for a given substrate or a group of substrates with similar chemical structure, but substrate specificity and/or affinity can vary dramatically, even among members of a transporter family that show high overall amino acid sequence and structural similarity. The current view is that transporter substrate affinity or specificity is determined by a small number of interactions a given solute can make within a specific binding site. However, genetic, biochemical and in silico modeling studies with the purine transporter UapA of the filamentous ascomycete Aspergillus nidulans have challenged this dogma. This review highlights results leading to a novel concept, stating that substrate specificity, but also transport kinetics and transporter turnover, are determined by subtle intramolecular interactions between a major substrate binding site and independent outward- or cytoplasmically-facing gating domains, analogous to those present in channels. This concept is supported by recent structural evidence from several, phylogenetically and functionally distinct transporter families. The significance of this concept is discussed in relationship to the role and potential exploitation of transporters in drug action. PMID:25309439
Discrete Element Method simulations of the saturation of aeolian sand transport
NASA Astrophysics Data System (ADS)
Pähtz, Thomas; Omeradžić, Amir; Carneiro, Marcus V.; Araújo, Nuno A. M.; Herrmann, Hans J.
2015-03-01
The saturation length of aeolian sand transport (Ls), characterizing the distance needed by wind-blown sand to adapt to changes in the wind shear, is essential for accurate modeling of the morphodynamics of Earth's sandy landscapes and for explaining the formation and shape of sand dunes. In the last decade, it has become a widely accepted hypothesis that Ls is proportional to the characteristic distance needed by transported particles to reach the wind speed (the "drag length"). Here we challenge this hypothesis. From extensive numerical Discrete Element Method simulations, we find that, for medium and strong winds, Ls∝Vs2/g, where Vs is the saturated value of the average speed of sand particles traveling above the surface and g is the gravitational constant. We show that this proportionality is consistent with a recent analytical model, in which the drag length is just one of four similarly important length scales relevant for sand transport saturation.
GPU accelerated simulations of 3D deterministic particle transport using discrete ordinates method
Gong Chunye; Liu Jie; Chi Lihua; Huang Haowei; Fang Jingyue; Gong Zhenghu
2011-07-01
Graphics Processing Unit (GPU), originally developed for real-time, high-definition 3D graphics in computer games, now provides great faculty in solving scientific applications. The basis of particle transport simulation is the time-dependent, multi-group, inhomogeneous Boltzmann transport equation. The numerical solution to the Boltzmann equation involves the discrete ordinates (S{sub n}) method and the procedure of source iteration. In this paper, we present a GPU accelerated simulation of one energy group time-independent deterministic discrete ordinates particle transport in 3D Cartesian geometry (Sweep3D). The performance of the GPU simulations are reported with the simulations of vacuum boundary condition. The discussion of the relative advantages and disadvantages of the GPU implementation, the simulation on multi GPUs, the programming effort and code portability are also reported. The results show that the overall performance speedup of one NVIDIA Tesla M2050 GPU ranges from 2.56 compared with one Intel Xeon X5670 chip to 8.14 compared with one Intel Core Q6600 chip for no flux fixup. The simulation with flux fixup on one M2050 is 1.23 times faster than on one X5670.
Kjær, Trine; Bech, Mickael; Kronborg, Christian; Mørkbak, Morten Raun
2013-10-01
At present there are no nephrology facilities in Greenland. Greenlandic patients with renal failure needing dialysis thus have to travel to Denmark to obtain treatment. For patients in haemodialysis this necessitates a permanent residence in Denmark. Our study was aimed at examining Greenlanders' preferences for establishing nephrology facilities in Greenland at Queen Ingrid's Hospital in Nuuk, and to estimate the associated change in welfare. Preferences were elicited using a discrete choice experiment (DCE). A random sample of 500 individuals of the general population was sent a postal questionnaire in which they were asked to consider the trade-offs of establishing nephrology facilities in Greenland as opposed to the current situation. This involved trading off the benefits of having such facilities in their home country against the costs of the intervention. Besides including a payment attribute described in terms of incremental tax payment, the DCE included two interventions attributes related to (1) the organisation of labour, and (2) the physical settings of the patients. Respondents succeeded in answering the DCE despite cultural and linguistic disparity. We found that all the included attributes had a significant effect on respondents' choices, and that respondents' answers to the DCE were in keeping with their values as stated in the questionnaire. DCE data was analyzed using a random parameter logit model reparametrized in willingness-to-pay space. The results showed that establishing facilities in Greenland were preferred to the current treatment in Denmark. The welfare estimate from the DCE, at DKK 18.74 million, exceeds the estimated annual costs of establishing treatment facilities for patients with chronic renal failure. Given the estimated confidence interval this result seems robust. Establishing facilities in Greenland therefore would appear to be welfare-improving, deriving positive net benefits. Despite the relatively narrow policy focus, we
Ryan, Mandy; Bond, Christine; Watson, Margaret
2016-01-01
Background Demand for health services continues to rise. Greater use of community pharmacy services instead of medical services for minor ailments could help relieve pressure on healthcare providers in high-cost settings. Community pharmacies are recognised sources of treatment and advice for people wishing to manage these ailments. However, increasing the public’s use of pharmacy services may depend on attributes of pharmacies and their staff. This study aimed to determine the general public’s relative preferences for community pharmacy attributes using a discrete choice experiment (DCE). Method A UK-wide DCE survey of the general public was conducted using face-to-face computer-assisted personal interviews. Attributes and levels for the DCE were informed by a literature review and a cohort study of community pharmacy customers. The context for the experiment was a minor ailment scenario describing flu-like symptoms. The DCE choice sets described two hypothetical community pharmacy services; respondents were asked to choose which (if either) of the two pharmacies they would prefer to help them manage symptoms. Data from 1,049 interviews were analysed using an error components logit model. Willingness to pay (WTP), a monetary measure of benefit, was estimated for the different attribute levels. Results When seeking help or treatment for flu-like symptoms, respondents most valued a pharmacy service that would improve their understanding and management of symptoms (WTP = £6.28), provided by staff who are trained (WTP (pharmacist) = £2.63: WTP(trained assistant) = £3.22), friendly and approachable (WTP = £3.38). Waiting time, pharmacy location and availability of parking also contributed to respondents’ preferences. WTP for a service comprising the best possible combination of attributes and levels was calculated as £55.43. Conclusion Attributes of a community pharmacy and its staff may influence people’s decisions about which pharmacy they would visit to
Kjær, Trine; Bech, Mickael; Kronborg, Christian; Mørkbak, Morten Raun
2013-10-01
At present there are no nephrology facilities in Greenland. Greenlandic patients with renal failure needing dialysis thus have to travel to Denmark to obtain treatment. For patients in haemodialysis this necessitates a permanent residence in Denmark. Our study was aimed at examining Greenlanders' preferences for establishing nephrology facilities in Greenland at Queen Ingrid's Hospital in Nuuk, and to estimate the associated change in welfare. Preferences were elicited using a discrete choice experiment (DCE). A random sample of 500 individuals of the general population was sent a postal questionnaire in which they were asked to consider the trade-offs of establishing nephrology facilities in Greenland as opposed to the current situation. This involved trading off the benefits of having such facilities in their home country against the costs of the intervention. Besides including a payment attribute described in terms of incremental tax payment, the DCE included two interventions attributes related to (1) the organisation of labour, and (2) the physical settings of the patients. Respondents succeeded in answering the DCE despite cultural and linguistic disparity. We found that all the included attributes had a significant effect on respondents' choices, and that respondents' answers to the DCE were in keeping with their values as stated in the questionnaire. DCE data was analyzed using a random parameter logit model reparametrized in willingness-to-pay space. The results showed that establishing facilities in Greenland were preferred to the current treatment in Denmark. The welfare estimate from the DCE, at DKK 18.74 million, exceeds the estimated annual costs of establishing treatment facilities for patients with chronic renal failure. Given the estimated confidence interval this result seems robust. Establishing facilities in Greenland therefore would appear to be welfare-improving, deriving positive net benefits. Despite the relatively narrow policy focus, we
Advancements in generalized-geometry discrete ordinates transport for lattice physics calculations
DeHart, M. D.
2006-07-01
This paper describes the generalized-geometry capabilities of the two-dimensional NEWT transport solver, used within the TRITON depletion sequence of the SCALE code system for lattice physics calculation. With the release of SCALE 5.1 in 2006, NEWT will introduce a new automated grid generation procedure based on simple body specifications, using an input format based on the SCALE Generalized-Geometry Processor. The paper will contrast the discretization techniques against those used in other unstructured grid treatments; illustrate the ease of model development, features, capabilities; and demonstrate the unique adaptability of NEWT for a wide range of fuel configurations. (authors)
Spinks, Jean; Chaboyer, Wendy; Bucknall, Tracey; Tobiano, Georgia; Whitty, Jennifer A
2015-01-01
Introduction Nursing bedside handover in hospital has been identified as an opportunity to involve patients and promote patient-centred care. It is important to consider the preferences of both patients and nurses when implementing bedside handover to maximise the successful uptake of this policy. We outline a study which aims to (1) identify, compare and contrast the preferences for various aspects of handover common to nurses and patients while accounting for other factors, such as the time constraints of nurses that may influence these preferences.; (2) identify opportunities for nurses to better involve patients in bedside handover and (3) identify patient and nurse preferences that may challenge the full implementation of bedside handover in the acute medical setting. Methods and analysis We outline the protocol for a discrete choice experiment (DCE) which uses a survey design common to both patients and nurses. We describe the qualitative and pilot work undertaken to design the DCE. We use a D-efficient design which is informed by prior coefficients collected during the pilot phase. We also discuss the face-to-face administration of this survey in a population of acutely unwell, hospitalised patients and describe how data collection challenges have been informed by our pilot phase. Mixed multinomial logit regression analysis will be used to estimate the final results. Ethics and dissemination This study has been approved by a university ethics committee as well as two participating hospital ethics committees. Results will be used within a knowledge translation framework to inform any strategies that can be used by nursing staff to improve the uptake of bedside handover. Results will also be disseminated via peer-reviewed journal articles and will be presented at national and international conferences. PMID:26560060
Gong, Cynthia L; Hay, Joel W; Meeker, Daniella; Doctor, Jason N
2016-01-01
Objective To elicit prescribers' preferences for behavioural economics interventions designed to reduce inappropriate antibiotic prescribing, and compare these to actual behaviour. Design Discrete choice experiment (DCE). Setting 47 primary care centres in Boston and Los Angeles. Participants 234 primary care providers, with an average 20 years of practice. Main outcomes and measures Results of a behavioural economic intervention trial were compared to prescribers' stated preferences for the same interventions relative to monetary and time rewards for improved prescribing outcomes. In the randomised controlled trial (RCT) component, the 3 computerised prescription order entry-triggered interventions studied included: Suggested Alternatives (SA), an alert that populated non-antibiotic treatment options if an inappropriate antibiotic was prescribed; Accountable Justifications (JA), which prompted the prescriber to enter a justification for an inappropriately prescribed antibiotic that would then be documented in the patient's chart; and Peer Comparison (PC), an email periodically sent to each prescriber comparing his/her antibiotic prescribing rate with those who had the lowest rates of inappropriate antibiotic prescribing. A DCE study component was administered to determine whether prescribers felt SA, JA, PC, pay-for-performance or additional clinic time would most effectively reduce their inappropriate antibiotic prescribing. Willingness-to-pay (WTP) was calculated for each intervention. Results In the RCT, PC and JA were found to be the most effective interventions to reduce inappropriate antibiotic prescribing, whereas SA was not significantly different from controls. In the DCE however, regardless of treatment intervention received during the RCT, prescribers overwhelmingly preferred SA, followed by PC, then JA. WTP estimates indicated that each intervention would be significantly cheaper to implement than pay-for-performance incentives of $200/month
Boone, Darren; Mallett, Susan; Zhu, Shihua; Yao, Guiqing Lily; Bell, Nichola; Ghanouni, Alex; von Wagner, Christian; Taylor, Stuart A.; Altman, Douglas G.; Lilford, Richard; Halligan, Steve
2013-01-01
Purpose To establish the relative weighting given by patients and healthcare professionals to gains in diagnostic sensitivity versus loss of specificity when using CT colonography (CTC) for colorectal cancer screening. Materials and Methods Following ethical approval and informed consent, 75 patients and 50 healthcare professionals undertook a discrete choice experiment in which they chose between “standard” CTC and “enhanced” CTC that raised diagnostic sensitivity 10% for either cancer or polyps in exchange for varying levels of specificity. We established the relative increase in false-positive diagnoses participants traded for an increase in true-positive diagnoses. Results Data from 122 participants were analysed. There were 30 (25%) non-traders for the cancer scenario and 20 (16%) for the polyp scenario. For cancer, the 10% gain in sensitivity was traded up to a median 45% (IQR 25 to >85) drop in specificity, equating to 2250 (IQR 1250 to >4250) additional false-positives per additional true-positive cancer, at 0.2% prevalence. For polyps, the figure was 15% (IQR 7.5 to 55), equating to 6 (IQR 3 to 22) additional false-positives per additional true-positive polyp, at 25% prevalence. Tipping points were significantly higher for patients than professionals for both cancer (85 vs 25, p<0.001) and polyps (55 vs 15, p<0.001). Patients were willing to pay significantly more for increased sensitivity for cancer (p = 0.021). Conclusion When screening for colorectal cancer, patients and professionals believe gains in true-positive diagnoses are worth much more than the negative consequences of a corresponding rise in false-positives. Evaluation of screening tests should account for this. PMID:24349014
2014-01-01
Background An increased awareness of patients’ and parents’ care preferences regarding foot care is desirable from a clinical perspective as such information may be utilised to optimise care delivery. The aim of this study was to examine parents’ preferences for, and valuations of foot care and foot-related outcomes in juvenile idiopathic arthritis (JIA). Methods A discrete choice experiment (DCE) incorporating willingness-to-pay (WTP) questions was conducted by surveying 42 parents of children with JIA who were enrolled in a randomised-controlled trial of multidisciplinary foot care at a single UK paediatric rheumatology outpatients department. Attributes explored were: levels of pain; mobility; ability to perform activities of daily living (ADL); waiting time; referral route; and footwear. The DCE was administered at trial baseline. DCE data were analysed using a multinomial-logit-regression model to estimate preferences and relative importance of attributes of foot care. A stated-preference WTP question was presented to estimate parents’ monetary valuation of health and service improvements. Results Every attribute in the DCE was statistically significant (p < 0.01) except that of cost (p = 0.118), suggesting that all attributes, except cost, have an impact on parents’ preferences for foot care for their child. The magnitudes of the coefficients indicate that the strength of preference for each attribute was (in descending order): improved ability to perform ADL, reductions in foot pain, improved mobility, improved ability to wear desired footwear, multidisciplinary foot care route, and reduced waiting time. Parents’ estimated mean annual WTP for a multidisciplinary foot care service was £1,119.05. Conclusions In terms of foot care service provision for children with JIA, parents appear to prefer improvements in health outcomes over non-health outcomes and service process attributes. Cost was relatively less important than other attributes
Miranda, J. Jaime; Diez-Canseco, Francisco; Lema, Claudia; Lescano, Andrés G.; Lagarde, Mylene; Blaauw, Duane; Huicho, Luis
2012-01-01
Background Doctors’ scarcity in rural areas remains a serious problem in Latin America and Peru. Few studies have explored job preferences of doctors working in underserved areas. We aimed to investigate doctors’ stated preferences for rural jobs. Methods and Findings A labelled discrete choice experiment (DCE) was performed in Ayacucho, an underserved department of Peru. Preferences were assessed for three locations: rural community, Ayacucho city (Ayacucho’s capital) and other provincial capital city. Policy simulations were run to assess the effect of job attributes on uptake of a rural post. Multiple conditional logistic regressions were used to assess the relative importance of job attributes and of individual characteristics. A total of 102 doctors participated. They were five times more likely to choose a job post in Ayacucho city over a rural community (OR 4.97, 95%CI 1.2; 20.54). Salary increases and bonus points for specialization acted as incentives to choose a rural area, while increase in the number of years needed to get a permanent post acted as a disincentive. Being male and working in a hospital reduced considerably chances of choosing a rural job, while not living with a partner increased them. Policy simulations showed that a package of 75% salary increase, getting a permanent contract after two years in rural settings, and getting bonus points for further specialisation increased rural job uptake from 21% to 77%. A package of 50% salary increase plus bonus points for further specialisation would also increase the rural uptake from 21% to 52%. Conclusions Doctors are five times more likely to favour a job in urban areas over rural settings. This strong preference needs to be overcome by future policies aimed at improving the scarcity of rural doctors. Some incentives, alone or combined, seem feasible and sustainable, whilst others may pose a high fiscal burden. PMID:23272065
dfnWorks: A discrete fracture network framework for modeling subsurface flow and transport
Hyman, Jeffrey D.; Karra, Satish; Makedonska, Nataliia; Gable, Carl W.; Painter, Scott L.; Viswanathan, Hari S.
2015-11-01
DFNWORKS is a parallelized computational suite to generate three-dimensional discrete fracture networks (DFN) and simulate flow and transport. Developed at Los Alamos National Laboratory over the past five years, it has been used to study flow and transport in fractured media at scales ranging from millimeters to kilometers. The networks are created and meshed using DFNGEN, which combines FRAM (the feature rejection algorithm for meshing) methodology to stochastically generate three-dimensional DFNs with the LaGriT meshing toolbox to create a high-quality computational mesh representation. The representation produces a conforming Delaunay triangulation suitable for high performance computing finite volume solvers in an intrinsically parallel fashion. Flow through the network is simulated in dfnFlow, which utilizes the massively parallel subsurface flow and reactive transport finite volume code PFLOTRAN. A Lagrangian approach to simulating transport through the DFN is adopted within DFNTRANS to determine pathlines and solute transport through the DFN. Example applications of this suite in the areas of nuclear waste repository science, hydraulic fracturing and CO_{2} sequestration are also included.
dfnWorks: A discrete fracture network framework for modeling subsurface flow and transport
Hyman, Jeffrey D.; Karra, Satish; Makedonska, Nataliia; Gable, Carl W.; Painter, Scott L.; Viswanathan, Hari S.
2015-11-01
DFNWORKS is a parallelized computational suite to generate three-dimensional discrete fracture networks (DFN) and simulate flow and transport. Developed at Los Alamos National Laboratory over the past five years, it has been used to study flow and transport in fractured media at scales ranging from millimeters to kilometers. The networks are created and meshed using DFNGEN, which combines FRAM (the feature rejection algorithm for meshing) methodology to stochastically generate three-dimensional DFNs with the LaGriT meshing toolbox to create a high-quality computational mesh representation. The representation produces a conforming Delaunay triangulation suitable for high performance computing finite volume solvers in anmore » intrinsically parallel fashion. Flow through the network is simulated in dfnFlow, which utilizes the massively parallel subsurface flow and reactive transport finite volume code PFLOTRAN. A Lagrangian approach to simulating transport through the DFN is adopted within DFNTRANS to determine pathlines and solute transport through the DFN. Example applications of this suite in the areas of nuclear waste repository science, hydraulic fracturing and CO2 sequestration are also included.« less
NASA Astrophysics Data System (ADS)
Ezzedine, S. M.
2010-12-01
Fractures and fracture networks are the principle pathways for migration of water, heat and mass in enhanced geothermal systems, oil and gas reservoirs, CO2 leakage from saline aquifers, and radioactive and toxic industrial wastes from underground storage repositories. A major issue to overcome when characterizing a fractured reservoir is that of data limitation due to accessibility and affordability. Moreover, the ability to map discontinuities in the rock with available geological and geophysical tools tends to decrease particularly as the scale of the discontinuity goes down. Geological characterization data include measurements of fracture density, orientation, extent, and aperture, and are based on analysis of outcrops, borehole optical and acoustic televiewer logs, aerial photographs, and core samples among others. All of these measurements are taken at the field scale through a very sparse limited number of deep boreholes. These types of data are often reduced to probability distributions function for predictive modeling and simulation in a stochastic framework such as stochastic discrete fracture network. Stochastic discrete fracture network models enable, through Monte Carlo realizations and simulations, for probabilistic assessment of flow and transport phenomena that are not adequately captured using continuum models. Despite the fundamental uncertainties inherited within the probabilistic reduction of the sparse data collected, very little work has been conducted on quantifying uncertainty on the reduced probabilistic distribution functions. In the current study, using nested Monte Carlo simulations, we present the impact of parameter uncertainties of the distribution functions that characterize discrete fracture networks on the flow, heat and mass transport. Numerical results of first, second and third moments, normalized to a base case scenario, are presented and compared to theoretical results extended from percolation theory.
DOXCY - A discrete ordinates approximation of neutron transport in heterogeneous rod lattices
Martens, H.D.; Stegemann, D.
1987-08-01
For calculating the fine flux distribution in heterogeneous fuel rod lattices, an exact treatment of the geometry and the use of a high-order approximation of the transport theory is needed. For this purpose, a discrete ordinates solution of the neutron transport equation for mixed geometry has been developed. The discretization of the space is performed in separate one-dimensional cylindrical coordinate systems, imbedded in a two-dimensional rectangular mesh grid. The geometrical link between the cylindrical and the rectangular systems is achieved by approximating the outer circle of each cylindrical system by a polygon with side numbers greater than or equal to8. Thus, each cylindrical geometry is enclosed in a two-dimensional mesh grid consisting of rectangles, trapeziums, and triangles. Because of the different orientation of the angular segmentation in XY and R coordinates, transfer coefficients are derived to calculate the directional flux distribution on the boundary between both systems. A special set of equal-weighted quadrature coefficients (EQ/sub n/) is used to get transfer coefficients, providing a fast and accurate solution. The method is realized in a program called DOXCY, which runs within the nuclear program system RSYST. The program is verified on selected benchmark problems. The numerical results are given, showing the advantage and limits of the method.
Discrete particle model for bedload sediment transport in the surf zone
NASA Astrophysics Data System (ADS)
Calantoni, Joseph
2002-04-01
Predicting the evolution of nearshore bathymetry from the highest uprush of the swash offshore to the location of wave breaking is a difficult problem of significant importance, with economic, legal, engineering, scientific, and military implications for coastal environments. Despite the apparent accessibility of the phenomena of interest, namely, the motion of sand under the forcing of waves and currents, the predictive capability of existing models for nearshore evolution is poor. A detailed study of the forces exerted on individual sand grains is undertaken in an effort to elucidate sediment transport mechanisms in the surf zone. New results indicate that fluid acceleration is a particularly important feature of surf zone transport; likewise, the processes of particle size segregation and the role of particle shape are newly explored. The study methodology employs computer simulations that describe the collective and individual motions of discrete particles immersed in a Newtonian fluid having essentially arbitrary density and viscosity. In this study all particle properties are those of quartz sand, and the fluid properties correspond to saltwater at 20°C. Such discrete-particle models, having a basis in molecular dynamics studies, have a broad range of applications in addition to the sedimentological one of interest here; for example, similar methodologies have been applied to traffic flow, schooling fish, crowd control, and other problems in which the particulate nature of the phenomenon is of critical importance.
Richard Sanchez; Cristian Rabiti; Yaqi Wang
2013-11-01
Nonlinear acceleration of a continuous finite element (CFE) discretization of the transport equation requires a modification of the transport solution in order to achieve local conservation, a condition used in nonlinear acceleration to define the stopping criterion. In this work we implement a coarse-mesh finite difference acceleration for a CFE discretization of the second-order self-adjoint angular flux (SAAF) form of the transport equation and use a postprocessing to enforce local conservation. Numerical results are given for one-group source calculations of one-dimensional slabs. We also give a novel formal derivation of the boundary conditions for the SAAF.
Larson, Elysia; Vail, Daniel; Mbaruku, Godfrey M.; Kimweri, Angela; Freedman, Lynn P.; Kruk, Margaret E.
2015-01-01
Objective In order to develop patient-centered care we need to know what patients want and how changing socio-demographic factors shape their preferences. Methods We fielded a structured questionnaire that included a discrete choice experiment to investigate women’s preferences for place of delivery care in four rural districts of Pwani Region, Tanzania. The discrete choice experiment consisted of six attributes: kind treatment by the health worker, health worker medical knowledge, modern equipment and medicines, facility privacy, facility cleanliness, and cost of visit. Each woman received eight choice questions. The influence of potential supply- and demand- side factors on patient preferences was evaluated using mixed logit models. Results 3,003 women participated in the discrete choice experiment (93% response rate) completing 23,947 choice tasks. The greatest predictor of health facility preference was kind treatment by doctor (β = 1.13, p<0.001), followed by having a doctor with excellent medical knowledge (β = 0.89 p<0.001) and modern medical equipment and drugs (β = 0.66 p<0.001). Preferences for all attributes except kindness and cost were changed with changes to education, primiparity, media exposure and distance to nearest hospital. Conclusions Care quality, both technical and interpersonal, was more important than clinic inputs such as equipment and cleanliness. These results suggest that while basic clinic infrastructure is necessary, it is not sufficient for provision of high quality, patient-centered care. There is an urgent need to build an adequate, competent, and kind health workforce to raise facility delivery and promote patient-centered care. PMID:26262840
DFNWorks. A discrete fracture network framework for modeling subsurface flow and transport
Hyman, Jeffrey D.; Karra, Satish; Makedonska, Nataliia; Gable, Carl W.; Painter, Scott L.; Viswanathan, Hari S.
2015-08-10
DFNWorks is a parallalized computational suite to generate three-dimensional discrete fracture networks (DFN) and simulate flow and transport. Developed at Los Alamos National Laboratory over the past five years, it has been used to study flow and transport in fractured media at scales ranging from millimeters to kilometers. The networks are created and meshed using dfnGen, which combines fram (the feature rejection algorithm for meshing) methodology to stochastically generate three-dimensional DFNs on the basis of site specific data with the LaGriT meshing toolbox to create a high-quality computational mesh representation, specifically a conforming Delaunay triangulation suitable for high performance computing finite volume solvers, of the DFN in an intrinsically parallel fashion. Flow through the network is simulated in dfnFlow, which utilizes the massively parallel subsurface flow and reactive transport finite volume code pflotran. A Lagrangian approach to simulating transport through the DFN is adopted within dfnTrans, which is an extension of the walkabout particle tracking method to determine pathlines through the DFN. Example applications of this suite in the areas of nuclear waste repository science, hydraulic fracturing and CO2 sequestration are also included.
DFNWorks. A discrete fracture network framework for modeling subsurface flow and transport
Hyman, Jeffrey D.; Karra, Satish; Makedonska, Nataliia; Gable, Carl W.; Painter, Scott L.; Viswanathan, Hari S.
2015-08-10
DFNWorks is a parallalized computational suite to generate three-dimensional discrete fracture networks (DFN) and simulate flow and transport. Developed at Los Alamos National Laboratory over the past five years, it has been used to study flow and transport in fractured media at scales ranging from millimeters to kilometers. The networks are created and meshed using dfnGen, which combines fram (the feature rejection algorithm for meshing) methodology to stochastically generate three-dimensional DFNs on the basis of site specific data with the LaGriT meshing toolbox to create a high-quality computational mesh representation, specifically a conforming Delaunay triangulation suitable for high performance computingmore » finite volume solvers, of the DFN in an intrinsically parallel fashion. Flow through the network is simulated in dfnFlow, which utilizes the massively parallel subsurface flow and reactive transport finite volume code pflotran. A Lagrangian approach to simulating transport through the DFN is adopted within dfnTrans, which is an extension of the walkabout particle tracking method to determine pathlines through the DFN. Example applications of this suite in the areas of nuclear waste repository science, hydraulic fracturing and CO2 sequestration are also included.« less
Built environment influences on healthy transportation choices: bicycling versus driving.
Winters, Meghan; Brauer, Michael; Setton, Eleanor M; Teschke, Kay
2010-12-01
A growing body of evidence links the built environment to physical activity levels, health outcomes, and transportation behaviors. However, little of this research has focused on cycling, a sustainable transportation option with great potential for growth in North America. This study examines associations between decisions to bicycle (versus drive) and the built environment, with explicit consideration of three different spatial zones that may be relevant in travel behavior: trip origins, trip destinations, and along the route between. We analyzed 3,280 utilitarian bicycle and car trips in Metro Vancouver, Canada made by 1,902 adults, including both current and potential cyclists. Objective measures were developed for built environment characteristics related to the physical environment, land use patterns, the road network, and bicycle-specific facilities. Multilevel logistic regression was used to model the likelihood that a trip was made by bicycle, adjusting for trip distance and personal demographics. Separate models were constructed for each spatial zone, and a global model examined the relative influence of the three zones. In total, 31% (1,023 out of 3,280) of trips were made by bicycle. Increased odds of bicycling were associated with less hilliness; higher intersection density; less highways and arterials; presence of bicycle signage, traffic calming, and cyclist-activated traffic lights; more neighborhood commercial, educational, and industrial land uses; greater land use mix; and higher population density. Different factors were important within each spatial zone. Overall, the characteristics of routes were more influential than origin or destination characteristics. These findings indicate that the built environment has a significant influence on healthy travel decisions, and spatial context is important. Future research should explicitly consider relevant spatial zones when investigating the relationship between physical activity and urban form.
Chen, Li-Chia; Cheng, Li-Jen; Zhang, Yan; He, Xin; Knaggs, Roger D
2015-01-01
Acupuncture is a popular but controversial treatment option for low back pain. In China, it is practised as traditional Chinese medicine; other treatment strategies for low back pain are commonly practised as Western medicine. Research on patient preference for low back-pain treatment options has been mainly conducted in Western countries and is limited to a willingness-to-pay approach. A stated-preference, discrete choice experiment was conducted to determine Chinese patient preferences and trade-offs for acupuncture and low frequency infrared treatment in low back pain from September 2011 to August 2012 after approval from the Department of Scientific Research in the study settings. Eight-six adult outpatients who visited the 'traditional medicine department' at a traditional Chinese medicine hospital and the 'rehabilitation department' at a Western medicine hospital in Guangdong Province of China for chronic low back pain during study period participated in an interview survey. A questionnaire containing 10 scenarios (5 attributes in each scenario) was used to ask participants' preference for acupuncture, low frequency infrared treatment or neither option. Validated responses were analysed using a nested-logit model. The decision on whether to receive a therapy was not associated with the expected utility of receiving therapy, female gender and higher out-of-pocket payment significantly decreased chance to receive treatments. Of the utility of receiving either acupuncture or low frequency infrared treatment, the treatment sensation was the most important attribute as an indicator of treatment efficacy, followed by the maximum efficacy, maintenance duration and onset of efficacy, and the out-of-pocket payment. The willingness-to-pay for acupuncture and low frequency infrared treatment were about $618.6 and $592.4 USD per course respectively, demonstrated patients' demand of pain management. The treatment sensation was regarded as an indicator of treatment
Morillas, Carlos; Feliciano, Rosa; Catalina, Pablo Fernández; Ponte, Carla; Botella, Marta; Rodrigues, João; Esmatjes, Enric; Lafita, Javier; Lizán, Luis; Llorente, Ignacio; Morales, Cristóbal; Navarro-Pérez, Jorge; Orozco-Beltran, Domingo; Paz, Silvia; Ramirez de Arellano, Antonio; Cardoso, Cristina; Tribaldos Causadias, Maribel
2015-01-01
Objective To assess Spanish and Portuguese patients’ and physicians’ preferences regarding type 2 diabetes mellitus (T2DM) treatments and the monthly willingness to pay (WTP) to gain benefits or avoid side effects. Methods An observational, multicenter, exploratory study focused on routine clinical practice in Spain and Portugal. Physicians were recruited from multiple hospitals and outpatient clinics, while patients were recruited from eleven centers operating in the public health care system in different autonomous communities in Spain and Portugal. Preferences were measured via a discrete choice experiment by rating multiple T2DM medication attributes. Data were analyzed using the conditional logit model. Results Three-hundred and thirty (n=330) patients (49.7% female; mean age 62.4 [SD: 10.3] years, mean T2DM duration 13.9 [8.2] years, mean body mass index 32.5 [6.8] kg/m2, 41.8% received oral + injected medication, 40.3% received oral, and 17.6% injected treatments) and 221 physicians from Spain and Portugal (62% female; mean age 41.9 [SD: 10.5] years, 33.5% endocrinologists, 66.5% primary-care doctors) participated. Patients valued avoiding a gain in bodyweight of 3 kg/6 months (WTP: €68.14 [95% confidence interval: 54.55–85.08]) the most, followed by avoiding one hypoglycemic event/month (WTP: €54.80 [23.29–82.26]). Physicians valued avoiding one hypoglycemia/week (WTP: €287.18 [95% confidence interval: 160.31–1,387.21]) the most, followed by avoiding a 3 kg/6 months gain in bodyweight and decreasing cardiovascular risk (WTP: €166.87 [88.63–843.09] and €154.30 [98.13–434.19], respectively). Physicians and patients were willing to pay €125.92 (73.30–622.75) and €24.28 (18.41–30.31), respectively, to avoid a 1% increase in glycated hemoglobin, and €143.30 (73.39–543.62) and €42.74 (23.89–61.77) to avoid nausea. Conclusion Both patients and physicians in Spain and Portugal are willing to pay for the health benefits
NASA Astrophysics Data System (ADS)
Ezzedine, S. M.
2009-12-01
Fractures and fracture networks are the principal pathways for transport of water and contaminants in groundwater systems, enhanced geothermal system fluids, migration of oil and gas, carbon dioxide leakage from carbon sequestration sites, and of radioactive and toxic industrial wastes from underground storage repositories. A major issue to overcome when characterizing a fractured reservoir is that of data limitation due to accessibility and affordability. Moreover, the ability to map discontinuities in the rock with available geological and geophysical tools tends to decrease particularly as the scale of the discontinuity goes down. Geological characterization data include measurements of fracture density, orientation, extent, and aperture, and are based on analysis of outcrops, borehole optical and acoustic televiewer logs, aerial photographs, and core samples, among other techniques. All of these measurements are taken at the field scale through a very sparse limited number of deep boreholes. These types of data are often reduced to probability distribution functions for predictive modeling and simulation in a stochastic framework such as a stochastic discrete fracture network. Stochastic discrete fracture network models enable, through Monte Carlo realizations and simulations, probabilistic assessment of flow and transport phenomena that are not adequately captured using continuum models. Despite the fundamental uncertainties inherited within the probabilistic reduction of the sparse data collected, very little work has been conducted on quantifying uncertainty on the reduced probabilistic distribution functions. In the current study, using nested Monte Carlo simulations, we present the impact of parameter uncertainties of the distribution functions of fracture density, orientation, aperture and size on the flow and transport using topological measures such as fracture connectivity, physical characteristics such as effective hydraulic conductivity tensors, and
Bailey, T S; Adams, M L; Chang, J H
2008-10-01
We present a new spatial discretization of the discrete-ordinates transport equation in two-dimensional cylindrical (RZ) geometry for arbitrary polygonal meshes. This discretization is a discontinuous finite element method that utilizes the piecewise linear basis functions developed by Stone and Adams. We describe an asymptotic analysis that shows this method to be accurate for many problems in the thick diffusion limit on arbitrary polygons, allowing this method to be applied to radiative transfer problems with these types of meshes. We also present numerical results for multiple problems on quadrilateral grids and compare these results to the well-known bi-linear discontinuous finite element method.
Discrete-state, object-oriented simulation of coupled thermoelectric transport
NASA Astrophysics Data System (ADS)
Radkowski, Peter Paul Francis, III
The Discrete State Simulation (DSS) has been developed to model heat and charge transport on a micron-scale with nanometer-resolution. Written in object-oriented code, the DSS is a coupled cellular automata simulator that builds upon the objects and rules of quantum mechanics. The DSS represents global non-equilibrium processes as patterns that emerge through an ensemble of scattering events that are localized at vibronic nodes. By tracking the energy-momentum-position coordinates of the individual particles that define the vibronic state at a node, the DSS undercuts equilibrium concepts such as temperature. Consequently, the DSS can represent physical systems that are described by more than one temperature or that contain physical features that defy definitions of temperature. Using modified bootstrap sampling algorithms, the DSS depicted (1) shifts in distribution functions induced by external fields and temperature gradients, (2) field-dependent transitions from linear mobility to non-linear mobility, (3) saturation velocities, (4) non-exponential decay functions generated by multiple phonon scattering modes, and (5) charge separations and electric potentials generated by temperature gradients. Ensemble averages were sensitive to the structure of dispersion relations, to the energy of the system, and to quantum coupling strengths. Although the Discrete State Simulation requires more development before it becomes an engineering design tool, the reported research effort offers substantial justification for the development of object-oriented, discrete-state cellular automata. These computational machines would match the capabilities of conventional simulation techniques, and they would be able to address highly non-equilibrium situations by exercising dynamic rule construction---computational algorithms that evolve in response to the conditions that are being simulated.
NASA Astrophysics Data System (ADS)
Bai, Xiao-Dong; Malomed, Boris A.; Deng, Fu-Guo
2016-09-01
We consider the transfer of lattice wave packets through a tilted discrete breather (TDB) in opposite directions in the discrete nonlinear Schrödinger model with asymmetric defects, which may be realized as a Bose-Einstein condensate trapped in a deep optical lattice, or as optical beams in a waveguide array. A unidirectional transport mode is found, in which the incident wave packets, whose energy belongs to a certain interval between full reflection and full passage regions, pass the TDB only in one direction, while in the absence of the TDB, the same lattice admits bidirectional propagation. The operation of this mode is accurately explained by an analytical consideration of the respective energy barriers. The results suggest that the TDB may emulate the unidirectional propagation of atomic and optical beams in various settings. In the case of the passage of the incident wave packet, the scattering TDB typically shifts by one lattice unit in the direction from which the wave packet arrives, which is an example of the tractor-beam effect, provided by the same system, in addition to the rectification of incident waves.
NASA Astrophysics Data System (ADS)
Bürger, Raimund; Kumar, Sarvesh; Ruiz-Baier, Ricardo
2015-10-01
The sedimentation-consolidation and flow processes of a mixture of small particles dispersed in a viscous fluid at low Reynolds numbers can be described by a nonlinear transport equation for the solids concentration coupled with the Stokes problem written in terms of the mixture flow velocity and the pressure field. Here both the viscosity and the forcing term depend on the local solids concentration. A semi-discrete discontinuous finite volume element (DFVE) scheme is proposed for this model. The numerical method is constructed on a baseline finite element family of linear discontinuous elements for the approximation of velocity components and concentration field, whereas the pressure is approximated by piecewise constant elements. The unique solvability of both the nonlinear continuous problem and the semi-discrete DFVE scheme is discussed, and optimal convergence estimates in several spatial norms are derived. Properties of the model and the predicted space accuracy of the proposed formulation are illustrated by detailed numerical examples, including flows under gravity with changing direction, a secondary settling tank in an axisymmetric setting, and batch sedimentation in a tilted cylindrical vessel.
Finger-powered electrophoretic transport of discrete droplets for portable digital microfluidics.
Peng, Cheng; Wang, Yide; Sungtaek Ju, Y
2016-07-01
We report a finger-powered digital microfluidic device based on the electrophoretic transport of discrete droplets (EPD). An array of piezoelectric elements is connected in parallel to metal electrodes immersed in dielectric fluids. When deflected in a controlled sequence via human finger power, the piezoelectric elements charge and actuate droplets across each electrode pair through electrophoretic force. Successful droplet transportation requires the piezoelectric elements to provide both sufficient charge and voltage pulse duration. We quantify these requirements using numerical models to predict the electrical charges induced on the droplets and the corresponding electrophoretic forces. The models are experimentally validated by comparing the predicted and measured droplet translational velocities. We successfully demonstrated transport and merging of aqueous droplets over a range of droplet radii (0.6-0.9 mm). We further showed direct manipulation of body fluids, including droplets of saliva and urine, using our finger-powered EPD device. To facilitate practical implementation of multistep assays based on the approach, a hand/finger-rotated drum system with a programmable pattern of protrusions is designed to induce deflections of multiple piezoelectric elements and demonstrate programmable fluidic functions. An electrode-to-piezoelectric element connection scheme to minimize the number of piezoelectric elements necessary for a sequence of microfluidic functions is also explored. The present work establishes an engineering foundation to enable design and implementation of finger-powered portable EPD microfluidic devices. PMID:27292054
Nguyen, Jennifer; Hayakawa, Carole K; Mourant, Judith R; Venugopalan, Vasan; Spanier, Jerome
2016-05-01
We present a polarization-sensitive, transport-rigorous perturbation Monte Carlo (pMC) method to model the impact of optical property changes on reflectance measurements within a discrete particle scattering model. The model consists of three log-normally distributed populations of Mie scatterers that approximate biologically relevant cervical tissue properties. Our method provides reflectance estimates for perturbations across wavelength and/or scattering model parameters. We test our pMC model performance by perturbing across number densities and mean particle radii, and compare pMC reflectance estimates with those obtained from conventional Monte Carlo simulations. These tests allow us to explore different factors that control pMC performance and to evaluate the gains in computational efficiency that our pMC method provides. PMID:27231642
Nguyen, Jennifer; Hayakawa, Carole K.; Mourant, Judith R.; Venugopalan, Vasan; Spanier, Jerome
2016-01-01
We present a polarization-sensitive, transport-rigorous perturbation Monte Carlo (pMC) method to model the impact of optical property changes on reflectance measurements within a discrete particle scattering model. The model consists of three log-normally distributed populations of Mie scatterers that approximate biologically relevant cervical tissue properties. Our method provides reflectance estimates for perturbations across wavelength and/or scattering model parameters. We test our pMC model performance by perturbing across number densities and mean particle radii, and compare pMC reflectance estimates with those obtained from conventional Monte Carlo simulations. These tests allow us to explore different factors that control pMC performance and to evaluate the gains in computational efficiency that our pMC method provides. PMID:27231642
Analysis of Massively Parallel Discrete-Ordinates Transport Sweep Algorithms with Collisions
Bailey, T S; Falgout, R D
2008-10-14
We present theoretical scaling models for a variety of discrete-ordinates sweep algorithms. In these models, we pay particular attention to the way each algorithm handles collisions. A collision is defined as a processor having multiple angles with ready to be swept during one stage of the sweep. The models also take into account how subdomains are assigned to processors and how angles are grouped during the sweep. We describe a data driven algorithm that resolves collisions efficiently during the sweep as well as other algorithms that have been designed to avoid collisions completely. Our models are validated using the ARGES and AMTRAN transport codes. We then use the models to study and predict scaling trends in all of the sweep algorithms.
ERIC Educational Resources Information Center
National 4-H Council, Chevy Chase, MD.
This curriculum packet includes a teacher's introduction and five curriculum units that explore how transportation needs affect the environment, including the quality of air and water, habitat, and global climate. These materials encourage teens to apply wisdom, ingenuity, and sound science to the choices they make. Units are: (1)…
NASA Astrophysics Data System (ADS)
Makedonska, Nataliia; Hyman, Jeffrey D.; Karra, Satish; Painter, Scott L.; Gable, Carl W.; Viswanathan, Hari S.
2016-08-01
The apertures of natural fractures in fractured rock are highly heterogeneous. However, in-fracture aperture variability is often neglected in flow and transport modeling and individual fractures are assumed to have uniform aperture distribution. The relative importance of in-fracture variability in flow and transport modeling within kilometer-scale field-scale fracture networks has been under a matter of debate for a long time because the flow in each single fracture is controlled not only by in-fracture variability but also by boundary conditions. Computational limitations have previously prohibited researchers from investigating the relative importance of in-fracture variability in flow and transport modeling within large-scale fracture networks. We address this question by incorporating internal heterogeneity of individual fractures into flow simulations within kilometer scale three-dimensional fracture networks, where fracture intensity, P32 (ratio between total fracture area and domain volume) is between 0.027 and 0.031 [1/m]. A recently developed discrete fracture network (DFN) simulation capability, dfnWorks, is used to generate DFNs that include in-fracture aperture variability represented by a stationary log-normal stochastic field with various correlation lengths and variances. The Lagrangian transport parameters, non-reacting travel time and cumulative retention, are calculated along particles streamlines. It is observed that due to local flow channeling early particle travel times are more sensitive to in-fracture variability than the tails of travel time distributions, where no significant effect of the in-fracture transmissivity variations and spatial correlation length is observed.
Makedonska, Nataliia; Hyman, Jeffrey D.; Karra, Satish; Painter, Scott L.; Gable, Carl W.; Viswanathan, Hari S.
2016-06-17
The apertures of natural fractures in fractured rock are highly heterogeneous. However, in-fracture aperture variability is often neglected in flow and transport modeling and individual fractures are assumed to have uniform aperture distribution. The relative importance of in-fracture variability in flow and transport modeling within kilometer18 scale field–scale fracture networks has been under a matter of debate for a long time because the flow in each single fracture is controlled not only by in-fracture variability but also by boundary conditions. Computational limitations have previously prohibited researchers from investigating the relative importance of in-fracture variability in flow and transport modeling withinmore » large-scale fracture networks. We address this question by incorporating internal heterogeneity of individual fractures into 23 flow simulations within kilometer scale three-dimensional fracture networks, where fracture intensity, P32 (ratio between total fracture area and domain volume) is between 0.027 and 0.031 [1/m]. A recently developed discrete fracture network (DFN) simulation capability, dfnWorks, is used to generate DFNs that include in-fracture aperture variability represented by a stationary log-normal stochastic field with various correlation lengths and variances. The Lagrangian transport parameters, non-reacting travel time and cumulative retention, are calculated along particles streamlines. It is observed that due to local flow channeling early particle travel times are more sensitive to in-fracture variability than the tails of travel time distributions, where no significant effect of the in-fracture transmissivity variations and spatial correlation length is observed.« less
The TORT three-dimensional discrete ordinates neutron/photon transport code (TORT version 3)
Rhoades, W.A.; Simpson, D.B.
1997-10-01
TORT calculates the flux or fluence of neutrons and/or photons throughout three-dimensional systems due to particles incident upon the system`s external boundaries, due to fixed internal sources, or due to sources generated by interaction with the system materials. The transport process is represented by the Boltzman transport equation. The method of discrete ordinates is used to treat the directional variable, and a multigroup formulation treats the energy dependence. Anisotropic scattering is treated using a Legendre expansion. Various methods are used to treat spatial dependence, including nodal and characteristic procedures that have been especially adapted to resist numerical distortion. A method of body overlay assists in material zone specification, or the specification can be generated by an external code supplied by the user. Several special features are designed to concentrate machine resources where they are most needed. The directional quadrature and Legendre expansion can vary with energy group. A discontinuous mesh capability has been shown to reduce the size of large problems by a factor of roughly three in some cases. The emphasis in this code is a robust, adaptable application of time-tested methods, together with a few well-tested extensions.
C5 Benchmark Problem with Discrete Ordinate Radiation Transport Code DENOVO
Yesilyurt, Gokhan; Clarno, Kevin T; Evans, Thomas M; Davidson, Gregory G; Fox, Patricia B
2011-01-01
The C5 benchmark problem proposed by the Organisation for Economic Co-operation and Development/Nuclear Energy Agency was modeled to examine the capabilities of Denovo, a three-dimensional (3-D) parallel discrete ordinates (S{sub N}) radiation transport code, for problems with no spatial homogenization. Denovo uses state-of-the-art numerical methods to obtain accurate solutions to the Boltzmann transport equation. Problems were run in parallel on Jaguar, a high-performance supercomputer located at Oak Ridge National Laboratory. Both the two-dimensional (2-D) and 3-D configurations were analyzed, and the results were compared with the reference MCNP Monte Carlo calculations. For an additional comparison, SCALE/KENO-V.a Monte Carlo solutions were also included. In addition, a sensitivity analysis was performed for the optimal angular quadrature and mesh resolution for both the 2-D and 3-D infinite lattices of UO{sub 2} fuel pin cells. Denovo was verified with the C5 problem. The effective multiplication factors, pin powers, and assembly powers were found to be in good agreement with the reference MCNP and SCALE/KENO-V.a Monte Carlo calculations.
Hayakawa, Carole K.; Spanier, Jerome; Venugopalan, Vasan
2014-01-01
We examine the relative error of Monte Carlo simulations of radiative transport that employ two commonly used estimators that account for absorption differently, either discretely, at interaction points, or continuously, between interaction points. We provide a rigorous derivation of these discrete and continuous absorption weighting estimators within a stochastic model that we show to be equivalent to an analytic model, based on the radiative transport equation (RTE). We establish that both absorption weighting estimators are unbiased and, therefore, converge to the solution of the RTE. An analysis of spatially resolved reflectance predictions provided by these two estimators reveals no advantage to either in cases of highly scattering and highly anisotropic media. However, for moderate to highly absorbing media or isotropically scattering media, the discrete estimator provides smaller errors at proximal source locations while the continuous estimator provides smaller errors at distal locations. The origin of these differing variance characteristics can be understood through examination of the distribution of exiting photon weights. PMID:24562029
Waschbusch, Daniel A.; Cunningham, Charles E.; Pelham, William E.; Rimas, Heather L.; Greiner, Andrew R.; Gnagy, Elizabeth M.; Waxmonsky, James; Fabiano, Gregory A.; Robb, Jessica A.; Burrows-MacLean, Lisa; Scime, Mindy; Hoffman, Martin T.
2014-01-01
The current study examined treatment preferences of 183 parents of young (average age = 5.8 years; SD = 0.6), medication naïve children with ADHD. Preferences were evaluated using a discrete choice experiment in which parents made choices between different combinations of treatment characteristics, outcomes, and costs. Latent class analysis yielded two segments of parents: (1) Medication Avoidant parents constituted 70.5% of the sample whose treatment decisions were strongly influenced by a desire to avoid medication; (2) Outcome Oriented parents constituted 29.5% of the sample whose treatment decisions were most influenced by a desire for positive treatment outcomes. Parents in the Outcome Oriented segment were more stressed and depressed, had lower socioeconomic status and education, were more likely to be single parents, and had more disruptive and impaired children. Simulations predicted that parents would prefer treatments with behavior therapy over treatments with stimulant medication only. PMID:21722027
Byun, Ji-Hye; Kwon, Sun-Hong; Ha, Ji-Hye; Lee, Eui-Kyung
2016-01-01
Purpose The benefit–risk balance for drugs can alter post approval owing to additional data on efficacy or adverse events. This study developed a quantitative benefit–risk assessment (BRA) model for statins using multicriteria decision analysis with discrete choice experiments and compared a recent BRA with that at the time of approval. Patients and methods Following a systematic review of the literature, the benefit criteria within the statin BRA model were defined as a reduction in the plasma low-density lipoprotein cholesterol level and a reduction in myocardial infarction incidence; the risk criteria were hepatotoxicity (Liv) and fatal rhabdomyolysis (Rha). The scores for these criteria were estimated using mixed treatment comparison methods. Weighting was calculated from a discrete choice experiment involving 203 Korean patients. The scores and weights were integrated to produce an overall value representing the benefit–risk balance, and sensitivity analyses were conducted. Results In this BRA model, low-density lipoprotein (relative importance [RI]: 37.50%) was found to be a more important benefit criterion than myocardial infarction (RI: 35.43%), and Liv (RI: 16.28%) was a more important risk criterion than Rha (RI: 10.79%). Patients preferred atorvastatin, and the preference ranking of cerivastatin and simvastatin was switched post approval because of the emergence of additional risk information related to cerivastatin. Conclusion A quantitative statin BRA model confirmed that the preference ranking of statins changed post approval because of the identification of additional benefits or risks. PMID:27358567
Brazier, John; Rowen, Donna; Yang, Yaling; Tsuchiya, Aki
2012-10-01
Recent years have seen increasing interest in the use of ordinal methods to elicit health state utility values as an alternative to conventional methods such as standard gamble and time trade-off (TTO). However, in order to use these ordinal methods to produce health state values for use in cost-effectiveness analysis using cost per quality adjusted life year (QALY) analysis, these values must be anchored on the full health-dead scale. The paper reports on two feasibility studies that use two approaches to anchor health state utility values derived from discrete choice data on the full health-dead scale: normalising using (1) the TTO value of the worst state and (2) the coefficient on the 'dead' dummy variable. Health state utility values obtained using rank and discrete choice data are compared to more commonly used TTO utility values for two condition-specific preference-based measures; asthma and overactive bladder. Ordinal methods were found to offer a promising alternative to conventional cardinal methods of standard gamble and TTO. There remains a large and important research agenda to address. PMID:21959651
NASA Astrophysics Data System (ADS)
Zhong, Zhaopeng
In the past twenty 20 years considerable progress has been made in developing new methods for solving the multi-dimensional transport problem. However the effort devoted to the resonance self-shielding calculation has lagged, and much less progress has been made in enhancing resonance-shielding techniques for generating problem-dependent multi-group cross sections (XS) for the multi-dimensional transport calculations. In several applications, the error introduced by self-shielding methods exceeds that due to uncertainties in the basic nuclear data, and often they can be the limiting factor on the accuracy of the final results. This work is to improve the accuracy of the resonance self-shielding calculation by developing continuous energy multi-dimensional transport calculations for problem dependent self-shielding calculations. A new method has been developed, it can calculate the continuous-energy neutron fluxes for the whole two-dimensional domain, which can be utilized as weighting function to process the self-shielded multi-group cross sections for reactor analysis and criticality calculations, and during this process, the two-dimensional heterogeneous effect in the resonance self-shielding calculation can be fully included. A new code, GEMINEWTRN (Group and Energy-Pointwise Methodology Implemented in NEWT for Resonance Neutronics) has been developed in the developing version of SCALE [1], it combines the energy pointwise (PW) capability of the CENTRM [2] with the two-dimensional discrete ordinates transport capability of lattice physics code NEWT [14]. Considering the large number of energy points in the resonance region (typically more than 30,000), the computational burden and memory requirement for GEMINEWTRN is tremendously large, some efforts have been performed to improve the computational efficiency, parallel computation has been implemented into GEMINEWTRN, which can save the computation and memory requirement a lot; some energy points reducing
A verification regime for the spatial discretization of the SN transport equations
Schunert, S.; Azmy, Y.
2012-07-01
The order-of-accuracy test in conjunction with the method of manufactured solutions is the current state of the art in computer code verification. In this work we investigate the application of a verification procedure including the order-of-accuracy test on a generic SN transport solver that implements the AHOTN spatial discretization. Different types of semantic errors, e.g. removal of a line of code or changing a single character, are introduced randomly into the previously verified S{sub N} code and the proposed verification procedure is used to identify the coding mistakes (if possible) and classify them. Itemized by error type we record the stage of the verification procedure where the error is detected and report the frequency with which the errors are correctly identified at various stages of the verification. Errors that remain undetected by the verification procedure are further scrutinized to determine the reason why the introduced coding mistake eluded the verification procedure. The result of this work is that the verification procedure based on an order-of-accuracy test finds almost all detectable coding mistakes but rarely, 1.44% of the time, and under certain circumstances can fail. (authors)
Maginot, P. G.; Ragusa, J. C.; Morel, J. E.
2013-07-01
We examine several possible methods of mass matrix lumping for discontinuous finite element discrete ordinates transport using a Lagrange interpolatory polynomial trial space. Though positive outflow angular flux is guaranteed with traditional mass matrix lumping in a purely absorbing 1-D slab cell for the linear discontinuous approximation, we show that when used with higher degree interpolatory polynomial trial spaces, traditional lumping does yield strictly positive outflows and does not increase in accuracy with an increase in trial space polynomial degree. As an alternative, we examine methods which are 'self-lumping'. Self-lumping methods yield diagonal mass matrices by using numerical quadrature restricted to the Lagrange interpolatory points. Using equally-spaced interpolatory points, self-lumping is achieved through the use of closed Newton-Cotes formulas, resulting in strictly positive outflows in pure absorbers for odd power polynomials in 1-D slab geometry. By changing interpolatory points from the traditional equally-spaced points to the quadrature points of the Gauss-Legendre or Lobatto-Gauss-Legendre quadratures, it is possible to generate solution representations with a diagonal mass matrix and a strictly positive outflow for any degree polynomial solution representation in a pure absorber medium in 1-D slab geometry. Further, there is no inherent limit to local truncation error order of accuracy when using interpolatory points that correspond to the quadrature points of high order accuracy numerical quadrature schemes. (authors)
Anomalous transport in discrete arcs and simulation of double layers in a model auroral circuit
NASA Technical Reports Server (NTRS)
Smith, Robert A.
1987-01-01
The evolution and long-time stability of a double layer (DL) in a discrete auroral arc requires that the parallel current in the arc, which may be considered uniform at the source, be diverted within the arc to charge the flanks of the U-shaped double layer potential structure. A simple model is presented in which this current redistribution is effected by anomalous transport based on electrostatic lower hybrid waves driven by the flank structure itself. This process provides the limiting constraint on the double layer potential. The flank charging may be represented as that of a nonlinear transmission line. A simplified model circuit, in which the transmission line is represented by a nonlinear impedance in parallel with a variable resistor, is incorporated in a one-dimensional simulation model to give the current density at the DL boundaries. Results are presented for the scaling of the DL potential as a function of the width of the arc and the saturation efficiency of the lower hybrid instability mechanism.
Anomalous transport in discrete arcs and simulation of double layers in a model auroral circuit
NASA Technical Reports Server (NTRS)
Smith, Robert A.
1987-01-01
The evolution and long-time stability of a double layer in a discrete auroral arc requires that the parallel current in the arc, which may be considered uniform at the source, be diverted within the arc to charge the flanks of the U-shaped double-layer potential structure. A simple model is presented in which this current re-distribution is effected by anomalous transport based on electrostatic lower hybrid waves driven by the flank structure itself. This process provides the limiting constraint on the double-layer potential. The flank charging may be represented as that of a nonlinear transmission. A simplified model circuit, in which the transmission line is represented by a nonlinear impedance in parallel with a variable resistor, is incorporated in a 1-d simulation model to give the current density at the DL boundaries. Results are presented for the scaling of the DL potential as a function of the width of the arc and the saturation efficiency of the lower hybrid instability mechanism.
Mathews, K.; Sjoden, G.; Minor, B. )
1994-09-01
The exponential characteristic spatial quadrature for discrete ordinates neutral particle transport in slab geometry is derived and compared with current methods. It is similar to the linear characteristic (or, in slab geometry, the linear nodal) quadrature but differs by assuming an exponential distribution of the scattering source within each cell, S(x) = a exp(bx), whose parameters are root-solved to match the known (from the previous iteration) average and first moment of the source over the cell. Like the linear adaptive method, the exponential characteristic method is positive and nonlinear but more accurate and more readily extended to other cell shapes. The nonlinearity has not interfered with convergence. The authors introduce the exponential moment functions,'' a generalization of the functions used by Walters in the linear nodal method, and use them to avoid numerical ill-conditioning. The method exhibits O([Delta]x[sup 4]) truncation error on fine enough meshes; the error is insensitive to mesh size for coarse meshes. In a shielding problem, it is accurate to 10% using 16-mfp-thick cells; conventional methods err by 8 to 15 orders of magnitude. The exponential characteristic method is computationally more costly per cell than current methods but can be accurate with very thick cells, leading to increased computational efficiency on appropriate problems.
NASA Astrophysics Data System (ADS)
Zerr, Robert Joseph
2011-12-01
The integral transport matrix method (ITMM) has been used as the kernel of new parallel solution methods for the discrete ordinates approximation of the within-group neutron transport equation. The ITMM abandons the repetitive mesh sweeps of the traditional source iterations (SI) scheme in favor of constructing stored operators that account for the direct coupling factors among all the cells and between the cells and boundary surfaces. The main goals of this work were to develop the algorithms that construct these operators and employ them in the solution process, determine the most suitable way to parallelize the entire procedure, and evaluate the behavior and performance of the developed methods for increasing number of processes. This project compares the effectiveness of the ITMM with the SI scheme parallelized with the Koch-Baker-Alcouffe (KBA) method. The primary parallel solution method involves a decomposition of the domain into smaller spatial sub-domains, each with their own transport matrices, and coupled together via interface boundary angular fluxes. Each sub-domain has its own set of ITMM operators and represents an independent transport problem. Multiple iterative parallel solution methods have investigated, including parallel block Jacobi (PBJ), parallel red/black Gauss-Seidel (PGS), and parallel GMRES (PGMRES). The fastest observed parallel solution method, PGS, was used in a weak scaling comparison with the PARTISN code. Compared to the state-of-the-art SI-KBA with diffusion synthetic acceleration (DSA), this new method without acceleration/preconditioning is not competitive for any problem parameters considered. The best comparisons occur for problems that are difficult for SI DSA, namely highly scattering and optically thick. SI DSA execution time curves are generally steeper than the PGS ones. However, until further testing is performed it cannot be concluded that SI DSA does not outperform the ITMM with PGS even on several thousand or tens of
Minor, B.; Mathews, K.
1995-07-01
The exponential characteristic (EC) spatial quadrature for discrete ordinates neutral particle transport previously introduced in slab geometry is extended here to x-y geometry with rectangular cells. The method is derived and compared with current methods. It is similar to the linear characteristic (LC) quadrature (a linear-linear moments method) but differs by assuming an exponential distribution of the scattering source within each cell, S(x) = a exp(bx + cy), whose parameters are rootsolved to match the known (from the previous iteration) spatial average and first moments of the source over the cell. Similarly, EC assumes exponential distributions of flux along cell edges through which particles enter the cell, with parameters chosen to match the average and first moments of flux, as passed from the adjacent, upstream cells (or as determined by boundary conditions). Like the linear adaptive (LA) method, EC is positive and nonlinear. It is more accurate than LA and does not require subdivision of cells. The nonlinearity has not interfered with convergence. The exponential moment functions, which were introduced with the slab geometry method, are extended to arbitrary dimensions (numbers of arguments) and used to avoid numerical ill conditioning. As in slab geometry, the method approaches O({Delta}x{sup 4}) global truncation error on fine-enough meshes, while the error is insensitive to mesh size for coarse meshes. Performance of the method is compared with that of the step characteristic, LC, linear nodal, step adaptive, and LA schemes. The EC method is a strong performer with scattering ratios ranging from 0 to 0.9 (the range tested), particularly so for lower scattering ratios. As in slab geometry, EC is computationally more costly per cell than current methods but can be accurate with very thick cells, leading to increased computational efficiency on appropriate problems.
Kruk, Margaret E.; Riley, Patricia L.; Palma, Anton M.; Adhikari, Sweta; Ahoua, Laurence; Arnaldo, Carlos; Belo, Dercio F.; Brusamento, Serena; Cumba, Luisa I. G.; Dziuban, Eric J.; El-Sadr, Wafaa M.; Gutema, Yoseph; Habtamu, Zelalem; Heller, Thomas; Kidanu, Aklilu; Langa, Judite; Mahagaja, Epifanio; McCarthy, Carey F.; Melaku, Zenebe; Shodell, Daniel; Tsiouris, Fatima; Young, Paul R.; Rabkin, Miriam
2016-01-01
Introduction Option B+, an approach that involves provision of antiretroviral therapy (ART) to all HIV-infected pregnant women for life, is the preferred strategy for prevention of mother to child transmission of HIV. Lifelong retention in care is essential to its success. We conducted a discrete choice experiment in Ethiopia and Mozambique to identify health system characteristics preferred by HIV-infected women to promote continuity of care. Methods Women living with HIV and receiving care at hospitals in Oromia Region, Ethiopia and Zambézia Province, Mozambique were shown nine choice cards and asked to select one of two hypothetical health facilities, each with six varying characteristics related to the delivery of HIV services for long term treatment. Mixed logit models were used to estimate the influence of six health service attributes on choice of clinics. Results 2,033 women participated in the study (response rate 97.8% in Ethiopia and 94.7% in Mozambique). Among the various attributes of structure and content of lifelong ART services, the most important attributes identified in both countries were respectful provider attitude and ability to obtain non-HIV health services during HIV-related visits. Availability of counseling support services was also a driver of choice. Facility type, i.e., hospital versus health center, was substantially less important. Conclusions Efforts to enhance retention in HIV care and treatment for pregnant women should focus on promoting respectful care by providers and integrating access to non-HIV health services in the same visit, as well as continuing to strengthen counseling. PMID:27551785
Bell, Andrew Reid; Shah, M Azeem Ali; Ward, Patrick S
2014-01-01
It is widely argued that farmers are unwilling to pay adequate fees for surface water irrigation to recover the costs associated with maintenance and improvement of delivery systems. In this paper, we use a discrete choice experiment to study farmer preferences for irrigation characteristics along two branch canals in Punjab Province in eastern Pakistan. We find that farmers are generally willing to pay well in excess of current surface water irrigation costs for increased surface water reliability and that the amount that farmers are willing to pay is an increasing function of their existing surface water supply as well as location along the main canal branch. This explicit translation of implicit willingness-to-pay (WTP) for water (via expenditure on groundwater pumping) to WTP for reliable surface water demonstrates the potential for greatly enhanced cost recovery in the Indus Basin Irrigation System via appropriate setting of water user fees, driven by the higher WTP of those currently receiving reliable supplies. PMID:25552779
Meenakshi, J V; Banerji, A; Manyong, Victor; Tomlins, Keith; Mittal, Nitya; Hamukwala, Priscilla
2012-01-01
Using a discrete choice experiment, this paper estimates the willingness to pay for biofortified orange maize in rural Zambia. The study design has five treatment arms, which enable an analysis of the impact of nutrition information, comparing the use of simulated radio versus community leaders in transmitting the nutrition message, on willingness to pay, and to account for possible novelty effects in the magnitude of premiums or discounts. The estimation strategy also takes into account lexicographic preferences of a subset of our respondents. The results suggest that (a) orange maize is not confused with yellow maize, and has the potential to compete with white maize in the absence of a nutrition campaign, (b) there is a premium for orange maize with nutrition information, and (c) different modes of nutritional message dissemination have the same impact on consumer acceptance.
41 CFR 102-117.30 - What choices do I have when acquiring transportation or related services?
Code of Federal Regulations, 2010 CFR
2010-07-01
... 41 Public Contracts and Property Management 3 2010-07-01 2010-07-01 false What choices do I have...-117.30 What choices do I have when acquiring transportation or related services? When you acquire... Regulation (FAR) (48 CFR chapter 1); or (d) Negotiate a rate tender under a Federal...
Buttorff, Christine; Trujillo, Antonio J; Diez-Canseco, Francisco; Bernabe-Ortiz, Antonio; Miranda, J Jaime
2015-09-01
Many low-income individuals from around the world rely on local food vendors for daily sustenance. These small vendors quickly provide convenient, low-priced, tasty foods, however, they may be low in nutritional value. These vendors serve as an opportunity to use established delivery channels to explore the introduction of healthier products, e.g. fresh salad and fruits, to low-income populations. We sought to understand preferences for items prepared in Comedores Populares (CP), government-supported food vendors serving low-income Peruvians, to determine whether it would be feasible to introduce healthier items, specifically fruits and vegetables. We used a best-worst discrete choice experiment (DCE) that allowed participants to select their favorite and least favorite option from a series of three hypothetical menus. The characteristics were derived from a series of formative qualitative interviews conducted previously in the CPs. We examined preferences for six characteristics: price, salad, soup, sides, meat and fruit. A total of 432 individuals, from two districts in Lima, Peru responded to a discrete choice experiment and demographic survey in 2012. For the DCE, price contributed the most to individual's utility relative to the other attributes, with salad and soup following closely. Sides (e.g. rice and beans) were the least important. The willingness to pay for a meal with a large main course and salad was 2.6 Nuevos Soles, roughly a 1 Nuevo Sol increase from the average menu price, or USD $0.32 dollars. The willingness to pay for a meal with fruit was 1.6 Nuevo Soles. Overall, the perceived quality of service and food served in the CPs is high. The willingness to pay indicates that healthier additions to meals are feasible. Understanding consumer preferences can help policy makers design healthier meals in an organization with the potential to scale up to reach a considerable number of low-income families.
Buttorff, Christine; Trujillo, Antonio J; Diez-Canseco, Francisco; Bernabe-Ortiz, Antonio; Miranda, J Jaime
2015-09-01
Many low-income individuals from around the world rely on local food vendors for daily sustenance. These small vendors quickly provide convenient, low-priced, tasty foods, however, they may be low in nutritional value. These vendors serve as an opportunity to use established delivery channels to explore the introduction of healthier products, e.g. fresh salad and fruits, to low-income populations. We sought to understand preferences for items prepared in Comedores Populares (CP), government-supported food vendors serving low-income Peruvians, to determine whether it would be feasible to introduce healthier items, specifically fruits and vegetables. We used a best-worst discrete choice experiment (DCE) that allowed participants to select their favorite and least favorite option from a series of three hypothetical menus. The characteristics were derived from a series of formative qualitative interviews conducted previously in the CPs. We examined preferences for six characteristics: price, salad, soup, sides, meat and fruit. A total of 432 individuals, from two districts in Lima, Peru responded to a discrete choice experiment and demographic survey in 2012. For the DCE, price contributed the most to individual's utility relative to the other attributes, with salad and soup following closely. Sides (e.g. rice and beans) were the least important. The willingness to pay for a meal with a large main course and salad was 2.6 Nuevos Soles, roughly a 1 Nuevo Sol increase from the average menu price, or USD $0.32 dollars. The willingness to pay for a meal with fruit was 1.6 Nuevo Soles. Overall, the perceived quality of service and food served in the CPs is high. The willingness to pay indicates that healthier additions to meals are feasible. Understanding consumer preferences can help policy makers design healthier meals in an organization with the potential to scale up to reach a considerable number of low-income families. PMID:26184703
Perceived health status associated with transport choice for short distance trips
Scheepers, C.E.; Wendel-Vos, G.C.W.; van Wesemael, P.J.V.; den Hertog, F.R.J.; Stipdonk, H.L.; Int Panis, L.L.R.; van Kempen, E.E.M.M.; Schuit, A.J.
2015-01-01
Background This study examines the association between active transport and perceived general health, perceived psychological wellbeing and a healthy body weight in the Netherlands. Methods Data were collected by an online questionnaire (N = 3663) in the Netherlands. Data collection was conducted over a period of one calendar year starting July 2012. Logistic regression analyses were used to investigate the association between choice of transport mode (bicycling vs car use and walking vs car use) and perceived general health, perceived psychological wellbeing and having a healthy weight respectively. The presented OR's may be interpreted as the likelihood of an average person in our dataset to have a better perceived health or body weight when choosing active transport (either bicycling or walking) over using the car for trips up to 7.5 km. Results Cycling was found to be significantly associated with a better perceived general health (OR = 1.35, 95%CI:1.07–1.70) and having a healthy body weight (OR = 1.52, 95%CI:1.28–1.79), but not with a better perceived psychological wellbeing (OR = 1.12, 95%CI:0.93–1.34). Walking was found to be significantly associated with having a healthy body weight (OR = 1.35, 95%CI:1.09–1.69), but not with a better perceived general (OR = 1.12, 95%CI:0.84–1.51) or psychological wellbeing (OR = 0.85, 95%CI:0.67–1.08). Conclusion Our results suggest that active transport use has been associated with a better perceived general health and a healthy body weight. However, more research is needed to be able to elucidate which factors cause this better health. No associations were observed between transport choice and perceived psychological wellbeing. PMID:26844158
NASA Astrophysics Data System (ADS)
Schoenawa, Stefan; Hartmann, Ralf
2014-04-01
In this article we consider the development of Discontinuous Galerkin (DG) methods for the numerical approximation of the Reynolds-averaged Navier-Stokes (RANS) equations with the shear-stress transport (SST) model by Menter. This turbulence model is based on a blending of the Wilcox k-ω model used near the wall and the k-ɛ model used in the rest of the domain where the blending functions depend on the distance to the nearest wall. For the computation of the distance of each quadrature point in the domain to the nearest of the curved, piecewise polynomial wall boundaries, we propose a stabilized continuous finite element (FE) discretization of the eikonal equation. Furthermore, we propose a new wall boundary condition for the dissipation rate ω based on the projection of the analytic near-wall behavior of ω onto the discrete ansatz space of the DG discretization. Finally, we introduce an artificial viscosity to the discretization of the turbulence kinetic energy (k-)equation to suppress oscillations of k near the underresolved boundary layer edge. The wall distance computation based on the continuous FE discretization of the eikonal equation is demonstrated for an internal and three external/aerodynamic flow geometries including a three-element high-lift configuration. The DG discretization of the RANS equations with the SST model is demonstrated for turbulent flows past a flat plate and the RAE2822 airfoil (Cases 9 and 10). The results are compared to the underlying k-ω model and experimental data.
Hauber, A Brett; González, Juan Marcos; Groothuis-Oudshoorn, Catharina G M; Prior, Thomas; Marshall, Deborah A; Cunningham, Charles; IJzerman, Maarten J; Bridges, John F P
2016-06-01
Conjoint analysis is a stated-preference survey method that can be used to elicit responses that reveal preferences, priorities, and the relative importance of individual features associated with health care interventions or services. Conjoint analysis methods, particularly discrete choice experiments (DCEs), have been increasingly used to quantify preferences of patients, caregivers, physicians, and other stakeholders. Recent consensus-based guidance on good research practices, including two recent task force reports from the International Society for Pharmacoeconomics and Outcomes Research, has aided in improving the quality of conjoint analyses and DCEs in outcomes research. Nevertheless, uncertainty regarding good research practices for the statistical analysis of data from DCEs persists. There are multiple methods for analyzing DCE data. Understanding the characteristics and appropriate use of different analysis methods is critical to conducting a well-designed DCE study. This report will assist researchers in evaluating and selecting among alternative approaches to conducting statistical analysis of DCE data. We first present a simplistic DCE example and a simple method for using the resulting data. We then present a pedagogical example of a DCE and one of the most common approaches to analyzing data from such a question format-conditional logit. We then describe some common alternative methods for analyzing these data and the strengths and weaknesses of each alternative. We present the ESTIMATE checklist, which includes a list of questions to consider when justifying the choice of analysis method, describing the analysis, and interpreting the results.
Hauber, A Brett; González, Juan Marcos; Groothuis-Oudshoorn, Catharina G M; Prior, Thomas; Marshall, Deborah A; Cunningham, Charles; IJzerman, Maarten J; Bridges, John F P
2016-06-01
Conjoint analysis is a stated-preference survey method that can be used to elicit responses that reveal preferences, priorities, and the relative importance of individual features associated with health care interventions or services. Conjoint analysis methods, particularly discrete choice experiments (DCEs), have been increasingly used to quantify preferences of patients, caregivers, physicians, and other stakeholders. Recent consensus-based guidance on good research practices, including two recent task force reports from the International Society for Pharmacoeconomics and Outcomes Research, has aided in improving the quality of conjoint analyses and DCEs in outcomes research. Nevertheless, uncertainty regarding good research practices for the statistical analysis of data from DCEs persists. There are multiple methods for analyzing DCE data. Understanding the characteristics and appropriate use of different analysis methods is critical to conducting a well-designed DCE study. This report will assist researchers in evaluating and selecting among alternative approaches to conducting statistical analysis of DCE data. We first present a simplistic DCE example and a simple method for using the resulting data. We then present a pedagogical example of a DCE and one of the most common approaches to analyzing data from such a question format-conditional logit. We then describe some common alternative methods for analyzing these data and the strengths and weaknesses of each alternative. We present the ESTIMATE checklist, which includes a list of questions to consider when justifying the choice of analysis method, describing the analysis, and interpreting the results. PMID:27325321
Xie, Feng; Pullenayegum, Eleanor; Gaebel, Kathryn; Oppe, Mark; Krabbe, Paul F M
2014-04-01
Choice-based methods have been used widely in assessing healthcare programs. This study compared the binary discrete choice experiment (DCE) and the multiprofile case of best-worst scaling (BWS) in eliciting preferences for the EQ-5D-5L. Forty-eight EQ-5D-5L health states were selected using a Bayesian efficient design and grouped into 24 pairs for the DCE tasks and 8 sets for the BWS tasks (each set has three health states). A total of 100 participants completed 12 pairs and 8 sets in a random order. A probit regression model and ranked order logistic regression model were used to estimate the latent utilities from the DCE and BWS, respectively. Both tasks were well understood by the majority of participants. The DCE tasks were relatively easier and took a shorter time to complete. The intraclass correlation coefficient (ICC) of the DCE was higher than that of the BWS. The variances associated with the latent utilities estimated from the DCE were larger than those from the BWS. The DCE is more feasible and reliable than the BWS in valuing the EQ-5D-5L. Future studies could focus on comparing the consistency and accuracy of these techniques in predicting the health utilities of the EQ-5D-5L.
Terris-Prestholt, Fern; Hanson, Kara; MacPhail, Catherine; Vickerman, Peter; Rees, Helen; Watts, Charlotte
2013-01-01
Background For the first time in the history of HIV, new bio-medical interventions have been shown to be effective in preventing HIV transmission. For these new HIV prevention technologies (NPTs) to have an impact on the epidemic, they must be widely used. This study uses a discrete choice experiment (DCE) to: understand the relative strength of women’s preferences for product characteristics, understand the implications for substitution away from male condoms, and inform realistic modelling of their potential impact and cost-effectiveness. Methods A DCE was conducted among 1017 women in urban South Africa. Women were presented with choices between potential women’s NPTs (microbicides, diaphragm, female condom) and ‘what I did last time’ (use or not use a condom) with different HIV and pregnancy prevention effectiveness’ and prices. Choice probabilities are estimated using the nested logit model and used to predict uptake. Results In this high HIV prevalence setting, HIV prevention effectiveness is the main driver of uptake followed by pregnancy prevention effectiveness. For example a microbicide with poor effectiveness would have niche appeal at just 11% predicted uptake, while a highly effective microbicide (95% effective against HIV and pregnancy) would have far wider appeal (56% predicted uptake). Though women who reported not using condoms were more likely to choose the NPTs, at current very high rates of male condom use in South Africa (60%), about half of microbicide uptake is projected to be among those currently not using condoms. Conclusions Women are very interested in NPTs, especially if highly effective in preventing HIV and pregnancy. Women in greatest need were also most likely to switch to the new products. Where products are not yet available for distribution, proxy data, such as that generated by DCEs, can bring realism to overly optimistic uptake scenarios found in many current impact models. PMID:24386160
Marshall, Deborah A; Deal, Ken; Bombard, Yvonne; Leighl, Natasha; MacDonald, Karen V; Trudeau, Maureen
2016-01-01
Objectives Gene expression profiling (GEP) of tumours informs baseline risk prediction, potentially affecting adjuvant chemotherapy decisions for women with early-stage breast cancer. Since only 15% will experience a recurrence, concerns have been raised about potential harms from overtreatment and high GEP costs in publicly funded healthcare systems. We aimed to estimate preferences and personal utility of GEP testing information and benefit–risk trade-offs in chemotherapy treatment decisions. Design, setting and intervention Based on literature review and findings from our qualitative research (focus groups, interviews with patients with breast cancer and medical oncologists), we developed a discrete choice experiment (DCE) survey and administered it via an internet panel. The DCE included 12 choice tasks with 5 attributes and 3 alternatives considering orthogonality, D-efficiency and level balance. Participants The DCE survey was administered to 1004 Canadian women from the general population. Main outcome measures Preferences were analysed using conditional logit and hierarchical Bayes and evaluated for goodness of fit. We conducted simulation analyses for alternative scenarios. Results GEP test score indicating likely benefit from chemotherapy was the most important attribute. Doctor's clinical estimate of the risk of cancer returning, trust in your cancer doctor and side effects of chemotherapy (temporary and permanent) were relatively less important but showed significant differences among levels. In the scenario analyses, 78% were likely to choose chemotherapy in a high-risk scenario, 55% in a moderate-risk scenario and 33% in a low-risk scenario, with the other attributes held constant. A high GEP score was more important in influencing the choice of chemotherapy for those at intermediate clinical risk. Conclusions GEP testing information influences chemotherapy treatment decisions in early-stage breast cancer and varies depending on clinical risk
Vennedey, Vera; Danner, Marion; Evers, Silvia MAA; Fauser, Sascha; Stock, Stephanie; Dirksen, Carmen D; Hiligsmann, Mickaël
2016-01-01
Background Age-related macular degeneration (AMD) is the leading cause of visual impairment and blindness in industrialized countries. Currently, mainly three treatment options are available, which are all intravitreal injections, but differ with regard to the frequency of injections needed, their approval status, and cost. This study aims to estimate patients’ preferences for characteristics of treatment options for neovascular AMD. Methods An interviewer-assisted discrete choice experiment was conducted among patients suffering from AMD treated with intravitreal injections. A Bayesian efficient design was used for the development of 12 choice tasks. In each task patients indicated their preference for one out of two treatment scenarios described by the attributes: side effects, approval status, effect on visual function, injection and monitoring frequency. While answering the choice tasks, patients were asked to think aloud and explain the reasons for choosing or rejecting specific characteristics. Quantitative data were analyzed with a mixed multinomial logit model. Results Eighty-six patients completed the questionnaire. Patients significantly preferred treatments that improve visual function, are approved, are administered in a pro re nata regimen (as needed), and are accompanied by bimonthly monitoring. Patients significantly disliked less frequent monitoring visits (every 4 months) and explained this was due to fear of deterioration being left unnoticed, and in turn experiencing disease deterioration. Significant preference heterogeneity was found for all levels except for bimonthly monitoring visits and severe, rare eye-related side effects. Patients gave clear explanations of their individual preferences during the interviews. Conclusion Significant preference trends were discernible for the overall sample, despite the preference heterogeneity for most treatment characteristics. Patients like to be monitored and treated regularly, but not too frequently
Wang, Y.
2013-07-01
Nonlinear diffusion acceleration (NDA) can improve the performance of a neutron transport solver significantly especially for the multigroup eigenvalue problems. The high-order transport equation and the transport-corrected low-order diffusion equation form a nonlinear system in NDA, which can be solved via a Picard iteration. The consistency of the correction of the low-order equation is important to ensure the stabilization and effectiveness of the iteration. It also makes the low-order equation preserve the scalar flux of the high-order equation. In this paper, the consistent correction for a particular discretization scheme, self-adjoint angular flux (SAAF) formulation with discrete ordinates method (S{sub N}) and continuous finite element method (CFEM) is proposed for the multigroup neutron transport equation. Equations with the anisotropic scatterings and a void treatment are included. The Picard iteration with this scheme has been implemented and tested with RattleS{sub N}ake, a MOOSE-based application at INL. Convergence results are presented. (authors)
Role of serotonin transporter function in rat orbitofrontal cortex in impulsive choice
Darna, Mahesh; Chow, Jonathan J.; Yates, Justin R.; Charnigo, Richard J.; Beckmann, Joshua S.; Bardo, Michael T.; Dwoskin, Linda P.
2016-01-01
Impulsivity is a multi-faceted personality construct that plays a prominent role in drug abuse vulnerability. Dysregulation of 5-hydroxytryptamine (serotonin, 5-HT) systems in subregions of the prefrontal cortex has been implicated in impulsivity. Extracellular 5-HT concentrations are regulated by 5-HT transporters (SERTs), indicating that these transporters may be important molecular targets underlying individual differences in impulsivity and drug abuse vulnerability. The present study evaluated the role of SERT in mediating individual differences in impulsivity. Rats were tested for both impulsive action using the cued go/no-go task and for impulsive choice using a delay discounting task in a counterbalanced design. Following behavioral evaluation, Km and Vmax were obtained from kinetic analysis of [3H]5-HT uptake by SERT using synaptosomes prepared from both orbitofrontal cortex (OFC) and medial prefrontal cortex (mPFC) obtained from each individual rat. Vmax for SERT in OFC, but not mPFC, was negatively correlated with mean adjusted delay scores in the delay discounting task. In contrast, Vmax for SERT in OFC and mPFC was not correlated with performance in the cued go/no-go task. To further evaluate the relationship between SERT function and impulsive choice, a selective SERT inhibitor, fluoxetine (0, 15, 50 and 150 pmol/side) was microinjected bilaterally into OFC and effects on the delay discounting task determined. Following stabilization of behavior, fluoxetine increased mean adjusted delay scores (decreased impulsivity) in high impulsive rats compared to saline microinjection, but had no effect in low impulsive rats. These ex vivo and in vivo results suggest that enhanced SERT function in OFC underlies high impulsive choice behavior. PMID:26183652
41 CFR 102-117.30 - What choices do I have when acquiring transportation or related services?
Code of Federal Regulations, 2011 CFR
2011-01-01
... Regulation (FAR) (48 CFR chapter 1); or (d) Negotiate a rate tender under a Federal transportation... 41 Public Contracts and Property Management 3 2011-01-01 2011-01-01 false What choices do I have when acquiring transportation or related services? 102-117.30 Section 102-117.30 Public Contracts...
Minor, B.M.
1993-09-01
The exponential characteristic spatial quadrature for discrete ordinates neutral particle transport with rectangular cells is developed. Numerical problems arising in the derivation required the development of exponential moment functions. These functions are used to remove indeterminant forms which can cause catastrophic cancellations. The EC method is positive and nonlinear. It conserves particles and satisfies first moment balance. Comparisons of the EC method's performance to other methods in optically thin and thick spatial cells were performed. For optically thin cells, the EC method was shown to converge to the correct answer, with third order truncation error in the thin cell limit. In deep penetration problems, the EC method attained its highest computational efficiencies compared to the other methods. For all the deep penetration problems examined, the number of spatial cells required by the EC method to attain a desired accuracy was less than the other methods.... Mathematics functions, Nuclear radiation, Nuclear engineering, Radiation attenuation, Radiation shielding, Transport theory, Radiation transport.
NASA Astrophysics Data System (ADS)
Homma, Yuto; Moriwaki, Hiroyuki; Ohki, Shigeo; Ikeda, Kazumi
2014-06-01
This paper deals with verification of three dimensional triangular prismatic discrete ordinates transport calculation code ENSEMBLE-TRIZ by comparison with multi-group Monte Carlo calculation code GMVP in a large fast breeder reactor. The reactor is a 750 MWe electric power sodium cooled reactor. Nuclear characteristics are calculated at beginning of cycle of an initial core and at beginning and end of cycle of equilibrium core. According to the calculations, the differences between the two methodologies are smaller than 0.0002 Δk in the multi-plication factor, relatively about 1% in the control rod reactivity, and 1% in the sodium void reactivity.
Filho, J. F. P.
2013-07-01
In this work, an analytical discrete ordinates method is used to solve a nodal formulation of a neutron transport problem in x, y-geometry. The proposed approach leads to an important reduction in the order of the associated eigenvalue systems, when combined with the classical level symmetric quadrature scheme. Auxiliary equations are proposed, as usually required for nodal methods, to express the unknown fluxes at the boundary introduced as additional unknowns in the integrated equations. Numerical results, for the problem defined by a two-dimensional region with a spatially constant and isotropically emitting source, are presented and compared with those available in the literature. (authors)
Makedonska, Nataliia; Painter, Scott L.; Bui, Quan M.; Gable, Carl W.; Karra, Satish
2015-09-16
The discrete fracture network (DFN) model is a method to mimic discrete pathways for fluid flow through a fractured low-permeable rock mass, and may be combined with particle tracking simulations to address solute transport. However, experience has shown that it is challenging to obtain accurate transport results in three-dimensional DFNs because of the high computational burden and difficulty in constructing a high-quality unstructured computational mesh on simulated fractures. We present a new particle tracking capability, which is adapted to control volume (Voronoi polygons) flow solutions on unstructured grids (Delaunay triangulations) on three-dimensional DFNs. The locally mass-conserving finite-volume approach eliminates mass balance-related problems during particle tracking. The scalar fluxes calculated for each control volume face by the flow solver are used to reconstruct a Darcy velocity at each control volume centroid. The groundwater velocities can then be continuously interpolated to any point in the domain of interest. The control volumes at fracture intersections are split into four pieces, and the velocity is reconstructed independently on each piece, which results in multiple groundwater velocities at the intersection, one for each fracture on each side of the intersection line. This technique enables detailed particle transport representation through a complex DFN structure. Verified for small DFNs, the new simulation capability enables numerical experiments on advective transport in large DFNs to be performed. As a result, we demonstrate this particle transport approach on a DFN model using parameters similar to those of crystalline rock at a proposed geologic repository for spent nuclear fuel in Forsmark, Sweden.
Makedonska, Nataliia; Painter, Scott L.; Bui, Quan M.; Gable, Carl W.; Karra, Satish
2015-09-16
The discrete fracture network (DFN) model is a method to mimic discrete pathways for fluid flow through a fractured low-permeable rock mass, and may be combined with particle tracking simulations to address solute transport. However, experience has shown that it is challenging to obtain accurate transport results in three-dimensional DFNs because of the high computational burden and difficulty in constructing a high-quality unstructured computational mesh on simulated fractures. We present a new particle tracking capability, which is adapted to control volume (Voronoi polygons) flow solutions on unstructured grids (Delaunay triangulations) on three-dimensional DFNs. The locally mass-conserving finite-volume approach eliminates massmore » balance-related problems during particle tracking. The scalar fluxes calculated for each control volume face by the flow solver are used to reconstruct a Darcy velocity at each control volume centroid. The groundwater velocities can then be continuously interpolated to any point in the domain of interest. The control volumes at fracture intersections are split into four pieces, and the velocity is reconstructed independently on each piece, which results in multiple groundwater velocities at the intersection, one for each fracture on each side of the intersection line. This technique enables detailed particle transport representation through a complex DFN structure. Verified for small DFNs, the new simulation capability enables numerical experiments on advective transport in large DFNs to be performed. As a result, we demonstrate this particle transport approach on a DFN model using parameters similar to those of crystalline rock at a proposed geologic repository for spent nuclear fuel in Forsmark, Sweden.« less
Chen, Gang; Cheng, Allen C; Richards, Michael; Graves, Nicholas; Ratcliffe, Julie; Hall, Lisa
2016-01-01
Objective To identify key stakeholder preferences and priorities when considering a national healthcare-associated infection (HAI) surveillance programme through the use of a discrete choice experiment (DCE). Setting Australia does not have a national HAI surveillance programme. An online web-based DCE was developed and made available to participants in Australia. Participants A sample of 184 purposively selected healthcare workers based on their senior leadership role in infection prevention in Australia. Primary and secondary outcomes A DCE requiring respondents to select 1 HAI surveillance programme over another based on 5 different characteristics (or attributes) in repeated hypothetical scenarios. Data were analysed using a mixed logit model to evaluate preferences and identify the relative importance of each attribute. Results A total of 122 participants completed the survey (response rate 66%) over a 5-week period. Excluding 22 who mismatched a duplicate choice scenario, analysis was conducted on 100 responses. The key findings included: 72% of stakeholders exhibited a preference for a surveillance programme with continuous mandatory core components (mean coefficient 0.640 (p<0.01)), 65% for a standard surveillance protocol where patient-level data are collected on infected and non-infected patients (mean coefficient 0.641 (p<0.01)), and 92% for hospital-level data that are publicly reported on a website and not associated with financial penalties (mean coefficient 1.663 (p<0.01)). Conclusions The use of the DCE has provided a unique insight to key stakeholder priorities when considering a national HAI surveillance programme. The application of a DCE offers a meaningful method to explore and quantify preferences in this setting. PMID:27147392
de Vries, Sieta T.; de Vries, Folgerdiena M.; Dekker, Thijs; Haaijer-Ruskamp, Flora M.; de Zeeuw, Dick; Ranchor, Adelita V.; Denig, Petra
2015-01-01
Objectives To assess whether patients’ willingness to add a blood pressure-lowering drug and the importance they attach to specific treatment characteristics differ among age groups in patients with type 2 diabetes. Materials and Methods Patients being prescribed at least an oral glucose-lowering and a blood pressure-lowering drug completed a questionnaire including a discrete choice experiment. This experiment contained choice sets with hypothetical blood pressure-lowering drugs and a no additional drug alternative, which differed in their characteristics (i.e. effects and intake moments). Differences in willingness to add a drug were compared between patients <75 years (non-aged) and ≥75 years (aged) using Pearson χ2-tests. Multinomial logit models were used to assess and compare the importance attached to the characteristics. Results Of the 161 patients who completed the questionnaire, 151 (72%) could be included in the analyses (mean age 68 years; 42% female). Aged patients were less willing to add a drug than non-aged patients (67% versus 84% respectively; P = 0.017). In both age groups, the effect on blood pressure was most important for choosing a drug, followed by the risk of adverse drug events and the risk of death. The effect on limitations due to stroke was only significant in the non-aged group. The effect on blood pressure was slightly more important in the non-aged than the aged group (P = 0.043). Conclusions Aged patients appear less willing to add a preventive drug than non-aged patients. The importance attached to various treatment characteristics does not seem to differ much among age groups. PMID:26445349
Multi-choice stochastic transportation problem involving general form of distributions.
Quddoos, Abdul; Ull Hasan, Md Gulzar; Khalid, Mohammad Masood
2014-01-01
Many authors have presented studies of multi-choice stochastic transportation problem (MCSTP) where availability and demand parameters follow a particular probability distribution (such as exponential, weibull, cauchy or extreme value). In this paper an MCSTP is considered where availability and demand parameters follow general form of distribution and a generalized equivalent deterministic model (GMCSTP) of MCSTP is obtained. It is also shown that all previous models obtained by different authors can be deduced with the help of GMCSTP. MCSTP with pareto, power function or burr-XII distributions are also considered and equivalent deterministic models are obtained. To illustrate the proposed model two numerical examples are presented and solved using LINGO 13.0 software package. PMID:25332865
Zheng, Zhongquan C.; Wei, Zhenglun A.; Bennett, James S.; Yang, Xiaofan
2012-12-11
In simulating fluid/solid-particle multiphase -flows, various methods are available. One approach is the combined Euler-Lagrange method, which simulates the fluid phase flow in the Eulerian framework and the discrete phase (particle) motion in the Lagrangian framework simultaneously. The Lagrangian approach, where particle motion is determined by the current state of the fluid phase flow, is also called the discrete phase model (DPM), in the context of numerical flow simulation. In this method, the influence of the particle motions on the fluid flow can be included (two-way interactions) but are more commonly excluded (one-way interactions, when the discrete phase concentration is dilute. The other approach is to treat the particle number concentration as a continuous species, a necessarily passive quantity determined by the fluid flow, with no influences from the particles on the fluid flow (one-way interactions only), except to the extent the discrete phase “continuum” alters the overall fluid properties, such as density. In this paper, we compare these two methods with experimental data for an indoor environmental chamber. The effects of injection particle numbers and the related boundary conditions are investigated. In the Euler-Lagrange interaction or DPM model for incompressible flow, the Eulerian continuous phase is governed by the Reynolds-averaged N-S (RANS) equations. The motions of particles are governed by Newton’s second law. The effects of particle motions are communicated to the continuous phase through a force term in the RANS equations. The second formulation is a pure Eulerian type, where only the particle-number concentration is addressed, rather than the motion of each individual particle. The fluid flow is governed by the same RANS equations without the particle force term. The particle-number concentration is simulated by a species transport equation. Comparisons among the models and with experimental and literature data are presented
Lefebvre, P; Brouillette, L; Felteau, C
1994-12-01
"We suppose that women (couples), who are less than 40 years old, are faced with three types of sequential decisions: the fertility decision, the decision relative to the number of children to have and the decision concerning labour force participation.... We use a nested polychotomous discrete choice model to estimate the responsiveness of the behaviour of 'married' women in Quebec to variations in the expected flow of revenue resulting from changes in the parameters of the personal income tax and in the level of public monetary transfers conditional on the number of children. The model is estimated with micro-data from 9 repeated cross-sections for the years 1975 to 1987 with a full information maximum likelihood method.... This empirical setting is used to simulate the effects of changes made to the fiscal and transfer policies in favor of families with dependent children on fertility, [women's] labor force participation and the importance of spending costs for the two levels of government." (SUMMARY IN ENG) PMID:12291903
Aggarwal, S.; Ryland, S.; Peck, R.
1980-06-19
This report outlines a methodology to study the effects of disruptive events on nuclear waste material in stable geologic sites. The methodology is based upon developing a discrete events model that can be simulated on the computer. This methodology allows a natural development of simulation models that use computer resources in an efficient manner. Accurate modeling in this area depends in large part upon accurate modeling of ion transport behavior in the storage media. Unfortunately, developments in this area are not at a stage where there is any consensus on proper models for such transport. Consequently, our work is directed primarily towards showing how disruptive events can be properly incorporated in such a model, rather than as a predictive tool at this stage. When and if proper geologic parameters can be determined, then it would be possible to use this as a predictive model. Assumptions and their bases are discussed, and the mathematical and computer model are described.
A discrete mathematical model of the dynamic evolution of a transportation network
NASA Astrophysics Data System (ADS)
Malinetskii, G. G.; Stepantsov, M. E.
2009-09-01
A dynamic model of the evolution of a transportation network is proposed. The main feature of this model is that the evolution of the transportation network is not a process of centralized transportation optimization. Rather, its dynamic behavior is a result of the system self-organization that occurs in the course of the satisfaction of needs in goods transportation and the evolution of the infrastructure of the network nodes. Nonetheless, the possibility of soft control of the network evolution direction is taken into account.
Daskalov, G.M.; Baker, R.S.; Little, R.C.; Rogers, D.W.O.; Williamson, J.F.
2000-02-01
The DANTSYS discrete ordinates computer code system is applied to quantitative estimation of water kerma rate distributions in the vicinity of discrete photon sources with energies in the 20- to 800-keV range in two-dimensional cylindrical r-z geometry. Unencapsulated sources immersed in cylindrical water phantoms of 40-cm diameter and 40-cm height are modeled in either homogeneous phantoms or shielded by Ti, Fe, and Pb filters with thicknesses of 1 and 2 mean free paths. The obtained dose results are compared with corresponding photon Monte Carlo simulations. A 210-group photon cross-section library for applications in this energy range is developed and applied, together with a general-purpose 42-group library developed at Los Alamos National Laboratory, for DANTSYS calculations. The accuracy of DANTSYS with the 42-group library relative to Monte Carlo exhibits large pointwise fluctuations from {minus}42 to +84%. The major cause for the observed discrepancies is determined to be the inadequacy of the weighting function used for the 42-group library derivation. DANTSYS simulations with a finer 210-group library show excellent accuracy on and off the source transverse plane relative to Monte Carlo kerma calculations, varying from {minus}4.9 to 3.7%. The P{sub 3} Legendre polynomial expansion of the angular scattering function is shown to be sufficient for accurate calculations. The results demonstrate that DANTSYS is capable of calculating photon doses in very good agreement with Monte Carlo and that the multigroup cross-section library and efficient techniques for mitigation of ray effects are critical for accurate discrete ordinates implementation.
NASA Astrophysics Data System (ADS)
Hamon, F. P.; Mallison, B.; Tchelepi, H.
2015-12-01
The systems of algebraic equations arising from implicit (backward-Euler) finite-volume discretization of the conservation laws governing multiphase flow in porous media are quite challenging for nonlinear solvers. In the presence of counter-current flow due to buoyancy, the coupling between flow (pressure) and transport (saturations) is often the cause of nonlinear problems when single-point Phase-Potential Upwinding (PPU) is used. To overcome such convergence problems in practice, the time step is reduced and Newton's method is restarted from the solution at the previous converged time step. Here, we generalize the work of Lee, Efendiev and Tchelepi [Advances in Water Resources, 2015] to propose an Implicit Hybrid Upwinding (IHU) scheme for coupled flow and transport. In the pure transport problem, we show that the numerical flux obtained with IHU is differentiable, monotone and consistent for two and three-phase flow. For coupled flow and transport, we prove saturation physical bounds as well as the existence of a solution to our scheme. Challenging two- and three-phase heterogeneous multi-dimensional numerical tests confirm that the new scheme is non-oscillatory and convergent, and illustrate the superior convergence rate of our IHU-based Newton solver for large time steps.
Transport dynamics in quantum lattice models and the discrete truncated Wigner approximation
NASA Astrophysics Data System (ADS)
Schachenmayer, Johannes; Pupillo, Guido; Tignone, Edoardo; Genes, Claudiu; Pikovski, Alexander; Rey, Ana Maria
2015-05-01
Transport of physical quantities such as energy, charge, or information plays a crucial role in a vast variety of scientific fields ranging from materials science/solid-state physics, to photonics/quantum information, to biological systems. The robustness of quantum coherences in the presence of de-coherent sources, and how those affect transport efficiency are important open questions. Addressing them can not only impact our fundamental understanding of quantum science but at the same time can lead to important technological applications. Here, we present a scheme of how to dramatically enhance the energy transport efficiency of a material by coupling it to a cavity mode, an idea with profound implications for organic semi-conductor materials. In addition we report on progress of how to numerically tackle the problem of quantum transport dynamics with a newly developed method, the dTWA, which allows to simulate quantum-dynamics even in large systems and high dimensions.
Chang, B
2004-03-22
This paper contains three analytical solutions of transport problems which can be used to test ray-effect errors in the numerical solutions of the Boltzmann Transport Equation (BTE). We derived the first two solutions and the third was shown to us by M. Prasad. Since this paper is intended to be an internal LLNL report, no attempt was made to find the original derivations of the solutions in the literature in order to cite the authors for their work.
NASA Astrophysics Data System (ADS)
Mendes, B. S.; Draper, D.
2008-12-01
The issue of model uncertainty and model choice is central in any groundwater modeling effort [Neuman and Wierenga, 2003]; among the several approaches to the problem we favour using Bayesian statistics because it is a method that integrates in a natural way uncertainties (arising from any source) and experimental data. In this work, we experiment with several Bayesian approaches to model choice, focusing primarily on demonstrating the usefulness of the Reversible Jump Markov Chain Monte Carlo (RJMCMC) simulation method [Green, 1995]; this is an extension of the now- common MCMC methods. Standard MCMC techniques approximate posterior distributions for quantities of interest, often by creating a random walk in parameter space; RJMCMC allows the random walk to take place between parameter spaces with different dimensionalities. This fact allows us to explore state spaces that are associated with different deterministic models for experimental data. Our work is exploratory in nature; we restrict our study to comparing two simple transport models applied to a data set gathered to estimate the breakthrough curve for a tracer compound in groundwater. One model has a mean surface based on a simple advection dispersion differential equation; the second model's mean surface is also governed by a differential equation but in two dimensions. We focus on artificial data sets (in which truth is known) to see if model identification is done correctly, but we also address the issues of over and under-paramerization, and we compare RJMCMC's performance with other traditional methods for model selection and propagation of model uncertainty, including Bayesian model averaging, BIC and DIC.References Neuman and Wierenga (2003). A Comprehensive Strategy of Hydrogeologic Modeling and Uncertainty Analysis for Nuclear Facilities and Sites. NUREG/CR-6805, Division of Systems Analysis and Regulatory Effectiveness Office of Nuclear Regulatory Research, U. S. Nuclear Regulatory Commission
NASA Astrophysics Data System (ADS)
Cvetkovic, V.; Frampton, A.; Painter, S.; Selroos, J.
2008-12-01
An important challenge in subsurface hydrology is predictive modeling of tracer transport in sparsely fractured rock. A particular issue relevant for applications is how to accurately account for retention processes that are due to exchange (diffusion-sorption) of tracers between mobile fluid in fractures and immobile fluid in the rock matrix. Typically, tracers are subject to decay processes which may involve chains and in-growth (e.g., for radionuclides and some classes of hydrocarbons). Recently, a comprehensive particle-based methodology for upscaling transport with emphasis on tracer retention has been presented and applied to stochastic 2D discrete fracture networks (Frampton and Cvetkovic 2007, WRR, 43, W10429). Furthermore, a time domain random walk method has also recently been presented that effectively accounts for different exchange mechanisms and in-growth (Painter et al. 2008, WRR, 44, W01406). Now we present further advances in coupling these novel methodologies for solving radionuclide transport, and apply them to realistic 3D fracture networks, based on comprehensive data sets obtained from site characterization of the Laxemar area in south-east Sweden. Site measurements have revealed at least five fracture sets based on statistically significant orientation data, exhibiting power-law behaviour for fracture size and inferred transmissivity distributions. A few equally probable DFN realizations are generated based on these interpretations of the field data, in which advective fluid flow is solved using boundary conditions that mimic natural conditions. Thereafter, many particles are injected and tracked through the system, providing first- passage distributions of particle residence time and of the transport resistance parameter (quantifying the hydrodynamic control of retention). These distributions are then used as a basis for implementing the particle time-domain random walk model for radionuclide transport with retention and in-growth. Also, an
Reed Johnson, F; Lancsar, Emily; Marshall, Deborah; Kilambi, Vikram; Mühlbacher, Axel; Regier, Dean A; Bresnahan, Brian W; Kanninen, Barbara; Bridges, John F P
2013-01-01
Stated-preference methods are a class of evaluation techniques for studying the preferences of patients and other stakeholders. While these methods span a variety of techniques, conjoint-analysis methods-and particularly discrete-choice experiments (DCEs)-have become the most frequently applied approach in health care in recent years. Experimental design is an important stage in the development of such methods, but establishing a consensus on standards is hampered by lack of understanding of available techniques and software. This report builds on the previous ISPOR Conjoint Analysis Task Force Report: Conjoint Analysis Applications in Health-A Checklist: A Report of the ISPOR Good Research Practices for Conjoint Analysis Task Force. This report aims to assist researchers specifically in evaluating alternative approaches to experimental design, a difficult and important element of successful DCEs. While this report does not endorse any specific approach, it does provide a guide for choosing an approach that is appropriate for a particular study. In particular, it provides an overview of the role of experimental designs for the successful implementation of the DCE approach in health care studies, and it provides researchers with an introduction to constructing experimental designs on the basis of study objectives and the statistical model researchers have selected for the study. The report outlines the theoretical requirements for designs that identify choice-model preference parameters and summarizes and compares a number of available approaches for constructing experimental designs. The task-force leadership group met via bimonthly teleconferences and in person at ISPOR meetings in the United States and Europe. An international group of experimental-design experts was consulted during this process to discuss existing approaches for experimental design and to review the task force's draft reports. In addition, ISPOR members contributed to developing a consensus
Reed Johnson, F; Lancsar, Emily; Marshall, Deborah; Kilambi, Vikram; Mühlbacher, Axel; Regier, Dean A; Bresnahan, Brian W; Kanninen, Barbara; Bridges, John F P
2013-01-01
Stated-preference methods are a class of evaluation techniques for studying the preferences of patients and other stakeholders. While these methods span a variety of techniques, conjoint-analysis methods-and particularly discrete-choice experiments (DCEs)-have become the most frequently applied approach in health care in recent years. Experimental design is an important stage in the development of such methods, but establishing a consensus on standards is hampered by lack of understanding of available techniques and software. This report builds on the previous ISPOR Conjoint Analysis Task Force Report: Conjoint Analysis Applications in Health-A Checklist: A Report of the ISPOR Good Research Practices for Conjoint Analysis Task Force. This report aims to assist researchers specifically in evaluating alternative approaches to experimental design, a difficult and important element of successful DCEs. While this report does not endorse any specific approach, it does provide a guide for choosing an approach that is appropriate for a particular study. In particular, it provides an overview of the role of experimental designs for the successful implementation of the DCE approach in health care studies, and it provides researchers with an introduction to constructing experimental designs on the basis of study objectives and the statistical model researchers have selected for the study. The report outlines the theoretical requirements for designs that identify choice-model preference parameters and summarizes and compares a number of available approaches for constructing experimental designs. The task-force leadership group met via bimonthly teleconferences and in person at ISPOR meetings in the United States and Europe. An international group of experimental-design experts was consulted during this process to discuss existing approaches for experimental design and to review the task force's draft reports. In addition, ISPOR members contributed to developing a consensus
Carlsten, B.E.
1997-02-01
The author analyzes the emittance growth mechanisms for a continuous, intense electron beam in a focusing transport channel, over distances short enough that the beam does not reach equilibrium. The emittance grows from the effect of nonlinear forces arising from (1) current density nonuniformities, (2) energy variations leading to nonlinearities in the space-charge force even if the current density is uniform, (3) axial variations in the radial vector potential, (4) an axial velocity shear along the beam, and (5) an energy redistribution of the beam as the beam compresses or expands. The emittance growth is studied analytically and numerically for the cases of balanced flow, tight focusing, and slight beam scalloping, and is additionally studied numerically for an existing 6-MeV induction linear accelerator. Rules for minimizing the emittance along a beamline are established. Some emittance growth will always occur, both from current density nonuniformities that arise along the transport and from beam radius changes along the transport.
Least-squares finite element discretizations of neutron transport equations in 3 dimensions
Manteuffel, T.A; Ressel, K.J.; Starkes, G.
1996-12-31
The least-squares finite element framework to the neutron transport equation introduced in is based on the minimization of a least-squares functional applied to the properly scaled neutron transport equation. Here we report on some practical aspects of this approach for neutron transport calculations in three space dimensions. The systems of partial differential equations resulting from a P{sub 1} and P{sub 2} approximation of the angular dependence are derived. In the diffusive limit, the system is essentially a Poisson equation for zeroth moment and has a divergence structure for the set of moments of order 1. One of the key features of the least-squares approach is that it produces a posteriori error bounds. We report on the numerical results obtained for the minimum of the least-squares functional augmented by an additional boundary term using trilinear finite elements on a uniform tesselation into cubes.
Sjoden, G.E.
1992-03-01
A new discrete ordinates spatial quadrature scheme is presented for solving neutral particle transport problems. This new scheme, called the exponential characteristic method, is developed here in slab geometry with isotropic scattering. This method uses a characteristic integration of the Boltzmann transport equation with an exponential function as the assumed from of the source distribution, continuous across each spatial cell. The exponential source function is constructed to globally conserve zeroth and first spatial source moments and is non-negative. Characteristic integration ensures non-negative fluxes and flux moments. Numerical testing indicates that convergence of the exponential characteristic scheme is fourth order in the limit of vanishingly thin cells. Highly accurate solutions to optically thick problems can result using this scheme with very coarse meshes. Comparing accuracy and computational cost with existing spatial quadrature schemes (diamond difference, linear discontinuous, linear characteristic, linear adaptive, etc.), the exponential characteristic scheme typically performed best. This scheme is expected to be expandable to two dimensions in a straight forward manner. Due to the high accuracies achievable using coarse meshes, this scheme may allow researchers to obtain solutions to transport problems once thought too large or too difficult to be adequately solved conventional computer systems.
Huang, Lei; Zuo, Chao; Idir, Mourad; Qu, Weijuan; Asundi, Anand
2015-04-21
A novel transport-of-intensity equation (TIE) based phase retrieval method is proposed with putting an arbitrarily-shaped aperture into the optical wavefield. In this arbitrarily-shaped aperture, the TIE can be solved under non-uniform illuminations and even non-homogeneous boundary conditions by iterative discrete cosine transforms with a phase compensation mechanism. Simulation with arbitrary phase, arbitrary aperture shape, and non-uniform intensity distribution verifies the effective compensation and high accuracy of the proposed method. Experiment is also carried out to check the feasibility of the proposed method in real measurement. Comparing to the existing methods, the proposed method is applicable for any types of phasemore » distribution under non-uniform illumination and non-homogeneous boundary conditions within an arbitrarily-shaped aperture, which enables the technique of TIE with hard aperture become a more flexible phase retrieval tool in practical measurements.« less
Masiello, E.; Rossi, T.
2013-07-01
In this paper we discuss the latest upgrades of the Boundary Projection Acceleration (BPA) applied to the XYZ transport solver of APOLLO3, namely IDT. The acceleration method is a well-known effective technique for the speed-up of the source iterations of the discrete-ordinates method. The BPA in IDT has been improved in three aspects: the taking into account of the residue on boundary conditions as a boundary source for the acceleration problem, the extension of the method to higher order angular moments in the case of anisotropic scattering and, finally, the application of the method to the multigroup iterations for the acceleration of the fission source and k-effective. The spectrum of the method has been Fourier-analyzed to explore the effectiveness. The 3D mock-up geometry of the ZPPR is presented as final study to test the performances of the acceleration on a realistic whole-core 3D calculation. (authors)
Huang, Lei; Zuo, Chao; Idir, Mourad; Qu, Weijuan; Asundi, Anand
2015-04-21
A novel transport-of-intensity equation (TIE) based phase retrieval method is proposed with putting an arbitrarily-shaped aperture into the optical wavefield. In this arbitrarily-shaped aperture, the TIE can be solved under non-uniform illuminations and even non-homogeneous boundary conditions by iterative discrete cosine transforms with a phase compensation mechanism. Simulation with arbitrary phase, arbitrary aperture shape, and non-uniform intensity distribution verifies the effective compensation and high accuracy of the proposed method. Experiment is also carried out to check the feasibility of the proposed method in real measurement. Comparing to the existing methods, the proposed method is applicable for any types of phase distribution under non-uniform illumination and non-homogeneous boundary conditions within an arbitrarily-shaped aperture, which enables the technique of TIE with hard aperture become a more flexible phase retrieval tool in practical measurements.
NASA Astrophysics Data System (ADS)
Weisbrod, N.; Tran, E. L.; Klein-BenDavid, O.; Teutsch, N.
2015-12-01
Geological disposal of high-level radioactive waste is the long term solution for the disposal of long lived radionuclides and spent fuel. However, some radionuclides might be released from these repositories into the subsurface as a result of leakage, which ultimately make their way into groundwater. Engineered bentonite barriers around nuclear waste repositories are generally considered sufficient to impede the transport of radionuclides from their source to the groundwater. However, colloidal-sized mobile bentonite particles ("carrier" colloids) originating from these barriers have come under investigation as a potential transport vector for radionuclides sorbed to them. As lanthanides are generally accepted to have the same chemical behaviors as their more toxic actinide counterparts, lanthanides are considered an acceptable substitute for research on radionuclide transportation. This study aims to evaluate the transport behaviors of lanthanides in colloid-facilitated transport through a fractured chalk matrix and under geochemical conditions representative the Negev desert, Israel. The migration of Ce both with and without colloidal particles was explored and compared to the migration of a conservative tracer (bromide) using a flow system constructed around a naturally fractured chalk core. Results suggest that mobility of Ce as a solute is negligible. In experiments conducted without bentonite colloids, the 1% of the Ce that was recovered migrated as "intrinsic" colloids in the form of carbonate precipitates. However, the total recovery of the Ce increased to 9% when it was injected into the core in the presence of bentonite colloids and 13% when both bentonite and precipitate colloids were injected. This indicates that lanthanides are essentially immobile in chalk as a solute but may be mobile as carbonate precipitates. Bentonite colloids, however, markedly increase the mobility of lanthanides through fractured chalk matrices.
Stephan, W; Kleutsch, B; Frehland, E
1983-11-21
In studying the single file model in its discrete as well as in its continuum form the relationship between the phenomenological continuum theory of diffusion and the rate theory approach is analyzed. The single file model in its original form is discrete and represents the most general rate theory model for ion transport through rigid pores in biological membranes. In neglecting the interionic interactions which the single file model takes into account, the Nernst-Planck equation of macroscopic free diffusion can be derived from single file by means of the procedure n leads to infinity (where n is the number of binding sites within a pore) and the classical diffusion theory can thereby be integrated into the more general concept of single filing transport. Moreover, the single file model has been transformed in the limit n leads to infinity into the corresponding continuum form involving interionic interactions. The essential differences between the two derived continuum forms are: In the macroscopic diffusion model, the interionic interactions are regarded in the form of a "mean field". Thus we only get one equation of motion (Nernst-Planck equation) for the ionic concentration c(x, t) within the membrane. In the continuum version of the single file model, however, we obtain a hierarchy of Fokker-Planck equations for the probability density functions Pm(x1, . . . , xm, t) (where m is the number of ions within a pore). The interactions of the single file system are incorporated in detail into the Fokker-Planck equation as well as into the corresponding boundary conditions. As a consequence, the boundary conditions are highly complex in comparison with periodic conditions or Dirichlet conditions often used for the Nernst-Planck equation in electrophysiology. Two types of boundary conditions have been found which are principally different: The first one is to regulate the entry and exit of the ions at the pore mouth by a negative feedback mechanism, the second one
Ryman, J.C.; Eckerman, K.F.; Shultis, J.K.; Faw, R.E.; Dillman, L.T.
1996-04-01
Federal Guidance Report No. 12 tabulates dose coefficients for external exposure to photons and electrons emitted by radionuclides distributed in air, water, and soil. Although the dose coefficients of this report are based on previously developed dosimetric methodologies, they are derived from new, detailed calculations of energy and angular distributions of the radiations incident on the body and the transport of these radiations within the body. Effort was devoted to expanding the information available for assessment of radiation dose from radionuclides distributed on or below the surface of the ground. A companion paper (External Exposure to Radionuclides in Air, Water, and Soil) discusses the significance of the new tabulations of coefficients and provides detiled comparisons to previously published values. This paper discusses details of the photon transport calculations.
Brooks III, E D; Szoke, A; Peterson, J L
2005-11-15
We describe a Monte Carlo solution for time dependent photon transport, in the difference formulation with the material in local thermodynamic equilibrium (LTE), that is piecewise linear in its treatment of the material state variable. Our method employs a Galerkin solution for the material energy equation while using Symbolic Implicit Monte Carlo (SIMC) to solve the transport equation. In constructing the scheme, one has the freedom to choose between expanding the material temperature, or the equivalent black body radiation energy density at the material temperature, in terms of finite element basis functions. The former provides a linear treatment of the material energy while the latter provides a linear treatment of the radiative coupling between zones. Subject to the conditional use of a lumped material energy in the vicinity of strong gradients, possible with a linear treatment of the material energy, our approach provides a robust solution for time dependent transport of thermally emitted radiation that can address a wide range of problems. It produces accurate results in the diffusion limit.
Prinja, A.K.
1995-08-01
We have developed and successfully implemented a two-dimensional bilinear discontinuous in space and time, used in conjunction with the S{sub N} angular approximation, to numerically solve the time dependent, one-dimensional, one-speed, slab geometry, (ion) transport equation. Numerical results and comparison with analytical solutions have shown that the bilinear-discontinuous (BLD) scheme is third-order accurate in the space ad time dimensions independently. Comparison of the BLD results with diamond-difference methods indicate that the BLD method is both quantitavely and qualitatively superior to the DD scheme. We note that the form of the transport operator is such that these conclusions carry over to energy dependent problems that include the constant-slowing-down-approximation term, and to multiple space dimensions or combinations thereof. An optimized marching or inversion scheme or a parallel algorithm should be investigated to determine if the increased accuracy can compensate for the extra overhead required for a BLD solution, and then could be compared to other discretization methods such as nodal or characteristic schemes.
Zonal Variations of Eddy Diffusivities in an ACC-like Channel: Discrete Transport Corridors.
NASA Astrophysics Data System (ADS)
Lazar, A.; Thompson, A. F.
2014-12-01
The meridional overturning circulation in a wind-driven re-entrant channel arises from a balance between an Eulerian mean overturning and an eddy overturning. These cancel to leading order in the Southern Ocean's Antarctic Circumpolar Current (ACC). An ACC-like flow, with realistic stratification, zonal transport and distributions of eddy kinetic energy, develops even when these two overturning components cancel completely. Many studies have noted that an enhancement of the Eulerian overturning circulation, which tends to steepen isopycnals, is balanced in part by an enhancement of the eddy circulation that relaxes isopycnal tilt. Thus the domain-averaged isopycnal slope and zonal transport are relatively insensitive to changes in wind forcing. However, the response of the system's mesoscale variability and eddy fluxes is not uniform throughout the domain. We present a process study of an idealized eddy-resolving ACC-like channel with negligible residual overturning to explore how the along-stream distribution of eddy characteristics establishes a balance between wind and eddy overturning circulations. For each simulation, we decompose the overturning circulation into mean, standing and transient components. As the surface wind stress increases, the standing component balances a larger portion of the mean overturning. This in turn leads to an increasing departure from zonally-symmetric eddy characteristics. A zonal-mean, or net, eddy diffusivity Κnet is defined as the eddy diffusivity required to exactly balance the mean overturning based on the zonal-mean isopycnal slope, s. This gives Κnet=τ/ρ0fs, where τ is the wind stress, ρ0 is a reference density and f is the Coriolis parameter. Κnet is compared to local eddy diffusivities, Κlocal, diagnosed directly from the divergent component of the eddy buoyancy flux divided by the local isopycnal slope. We find that with a simple topographic ridge and moderate wind forcing, along-stream averages of
Filippone, W.L.; Baker, R.S.
1990-12-31
The neutron transport equation is solved by a hybrid method that iteratively couples regions where deterministic (S{sub N}) and stochastic (Monte Carlo) methods are applied. Unlike previous hybrid methods, the Monte Carlo and S{sub N} regions are fully coupled in the sense that no assumption is made about geometrical separation or decoupling. The hybrid method provides a new means of solving problems involving both optically thick and optically thin regions that neither Monte Carlo nor S{sub N} is well suited for by themselves. The fully coupled Monte Carlo/S{sub N} technique consists of defining spatial and/or energy regions of a problem in which either a Monte Carlo calculation or an S{sub N} calculation is to be performed. The Monte Carlo region may comprise the entire spatial region for selected energy groups, or may consist of a rectangular area that is either completely or partially embedded in an arbitrary S{sub N} region. The Monte Carlo and S{sub N} regions are then connected through the common angular boundary fluxes, which are determined iteratively using the response matrix technique, and volumetric sources. The hybrid method has been implemented in the S{sub N} code TWODANT by adding special-purpose Monte Carlo subroutines to calculate the response matrices and volumetric sources, and linkage subrountines to carry out the interface flux iterations. The common angular boundary fluxes are included in the S{sub N} code as interior boundary sources, leaving the logic for the solution of the transport flux unchanged, while, with minor modifications, the diffusion synthetic accelerator remains effective in accelerating S{sub N} calculations. The special-purpose Monte Carlo routines used are essentially analog, with few variance reduction techniques employed. However, the routines have been successfully vectorized, with approximately a factor of five increase in speed over the non-vectorized version.
NASA Astrophysics Data System (ADS)
Gable, C. W.; Hyman, J.; Karra, S.; Makedonska, N.; Painter, S. L.; Viswanathan, H. S.
2015-12-01
dfnWorks generates discrete fracture networks (DFN) of planar polygons, creates a high quality conforming Delaunay triangulation of the intersecting DFN polygons, assigns properties (aperture, permeability) using geostatistics, sets boundary and initial conditions, solves pressure/flow in single or multi-phase fluids (water, air, CO2) using the parallel PFLOTRAN or serial FEHM, and solves for transport using Lagrangian particle tracking. We outline the dfnWorks workflow and present applications from a range of fractured rock systems. dfnWorks (http://www.lanl.gov/expertise/teams/view/dfnworks) is composed of three main components, all of which are freely available. dfnGen generates a distribution of fracture polygons from site characterization data (statistics or deterministic fractures) and utilizes the FRAM (Feature Rejection Algorithm for Meshing) to guarantee the mesh generation package LaGriT (lagrit.lanl.gov) will generate a high quality conforming Delaunay triangular mesh. dfnWorks links the mesh to either PFLOTRAN (pflotran.org) or FEHM (fehm.lanl.gov) for solving flow and transport. The various physics options available in FEHM and PFLOTRAN such as single and multi-phase flow and reactive transport are all available with appropriate initial and boundary conditions and material property models. dfnTrans utilizes explicit Lagrangian particle tracking on the DFN using a velocity field reconstructed from the steady state pressure/flow field solution obtained in PFLOTRAN or FEHM. Applications are demonstrated for nuclear waste repository in fractured granite, CO2 sequestration and extraction of unconventional hydrocarbon resources.
Oder, J.M.
1997-12-01
Several new quadrature sets for use in the discrete ordinates method of solving the Boltzmann neutral particle transport equation are derived. These symmetric quadratures extend the traditional symmetric quadratures by allowing ordinates perpendicular to one or two of the coordinate axes. Comparable accuracy with fewer required ordinates is obtained. Quadratures up to seventh order are presented. The validity and efficiency of the quadratures is then tested and compared with the Sn level symmetric quadratures relative to a Monte Carlo benchmark solution. The criteria for comparison include current through the surface, scalar flux at the surface, volume average scalar flux, and time required for convergence. Appreciable computational cost was saved when used in an unstructured tetrahedral cell code using highly accurate characteristic methods. However, no appreciable savings in computation time was found using the new quadratures compared with traditional Sn methods on a regular Cartesian mesh using the standard diamond difference method. These quadratures are recommended for use in three-dimensional calculations on an unstructured mesh.
Zuo, Chao; Chen, Qian; Asundi, Anand
2014-04-21
The transport of intensity equation (TIE) is a two-dimensional second order elliptic partial differential equation that must be solved under appropriate boundary conditions. However, the boundary conditions are difficult to obtain in practice. The fast Fourier transform (FFT) based TIE solutions are widely adopted for its speed and simplicity. However, it implies periodic boundary conditions, which lead to significant boundary artifacts when the imposed assumption is violated. In this work, TIE phase retrieval is considered as an inhomogeneous Neumann boundary value problem with the boundary values experimentally measurable around a hard-edged aperture, without any assumption or prior knowledge about the test object and the setup. The analytic integral solution via Green's function is given, as well as a fast numerical implementation for a rectangular region using the discrete cosine transform. This approach is applicable for the case of non-uniform intensity distribution with no extra effort to extract the boundary values from the intensity derivative signals. Its efficiency and robustness have been verified by several numerical simulations even when the objects are complex and the intensity measurements are noisy. This method promises to be an effective fast TIE solver for quantitative phase imaging applications. PMID:24787811
NASA Astrophysics Data System (ADS)
Mahajan, B. M.
1982-01-01
The transport of discrete solids with surge flows in a partially filled slightly pitched horizontal pipe was investigated. The experimental apparatus, instrumentation, and procedures are described. The experiments were conducted using a cylindrical solid in a 10.0 cm (4 in) diameter pipe. The water surge flows were obtained by discharging different volumes of water into the pipe from a falling head open container which simulated a water closet. Flow induced solid velocities and stream depth histories at various locations along the length of the pipe were measured. The effects of water volume used, pipe slope, and size of the solid on the solid velocities were examined. Solid velocities were compared with the maximum water velocities estimated from the stream depth histories. Also, the distance traversed by the solids in the pipe were measured for those cases in which the solids did not clear the pipe. The solid velocity increased with an increase in water volume used, a decrease in the size of the solid, and an increase in the pipe slope. The solid velocity in the initial reach of the pipe was less than the maximum water velocity; and the solid velocity approaches the maximum water velocity as the solid traveled downstream, except for some experiments with small water volumes.
Adams, Jean; Bateman, Belinda; Becker, Frauke; Cresswell, Tricia; Flynn, Darren; McNaughton, Rebekah; Oluboyede, Yemi; Robalino, Shannon; Ternent, Laura; Sood, Benjamin Gardner; Michie, Susan; Shucksmith, Janet; Sniehotta, Falko F; Wigham, Sarah
2015-01-01
BACKGROUND Uptake of preschool vaccinations is less than optimal. Financial incentives and quasi-mandatory policies (restricting access to child care or educational settings to fully vaccinated children) have been used to increase uptake internationally, but not in the UK. OBJECTIVE To provide evidence on the effectiveness, acceptability and economic costs and consequences of parental financial incentives and quasi-mandatory schemes for increasing the uptake of preschool vaccinations. DESIGN Systematic review, qualitative study and discrete choice experiment (DCE) with questionnaire. SETTING Community, health and education settings in England. PARTICIPANTS Qualitative study - parents and carers of preschool children, health and educational professionals. DCE - parents and carers of preschool children identified as 'at high risk' and 'not at high risk' of incompletely vaccinating their children. DATA SOURCES Qualitative study - focus groups and individual interviews. DCE - online questionnaire. REVIEW METHODS The review included studies exploring the effectiveness, acceptability or economic costs and consequences of interventions that offered contingent rewards or penalties with real material value for preschool vaccinations, or quasi-mandatory schemes that restricted access to 'universal' services, compared with usual care or no intervention. Electronic database, reference and citation searches were conducted. RESULTS Systematic review - there was insufficient evidence to conclude that the interventions considered are effective. There was some evidence that the quasi-mandatory interventions were acceptable. There was insufficient evidence to draw conclusions on economic costs and consequences. Qualitative study - there was little appetite for parental financial incentives. Quasi-mandatory schemes were more acceptable. Optimising current services was consistently preferred to the interventions proposed. DCE and questionnaire - universal parental financial incentives
NASA Astrophysics Data System (ADS)
Steefel, C. I.; Lichtner, P. C.
1998-08-01
A numerical multicomponent reactive transport model described fully in Steefel and Lichtner (1998)[Steefel, C.I., Lichtner, P.C., 1998. Multicomponent reactive transport in discrete fractures, I. Controls on reaction front geometry. J. Hydrol. (in press)] is used to simulate the infiltration of hyperalkaline groundwater along discrete fractures at Maqarin, Jordan, a site considered as a natural analogue to cement-bearing nuclear waste repositories. In the Eastern Springs area at Maqarin, two prominent sets of sub-parallel fractures trending NW-SE are approximately perpendicular to the local water table contours, with the slope of the water table indicating north-westward flow. Extensive mineralogic investigations [Alexander W.R. (Ed.), 1992. A natural analogue study of cement-buffered, hyperalkaline groundwaters and their interaction with a sedimentary host rock. NAgrA Technical Report (NTB 91-10), Wettingen, Switzerland; Milodowski, A.E., Hyslop, E.K., Pearce, J.M., Wetton, P.D., Kemp, S.J., Longworth, G., Hodginson, E., and Hughes, C.R., 1998. Mineralogy and geochemistry of the western springs area. In: Smellie, J.A.T. (ed.), 1998: Maqarin Natural Analogue Study: Phase III. SKB Technical Report TR98-04, Stockholm, Sweden] indicate that the width of intense rock alteration zone bordering the fractures changes from about 4 mm at one locality (the M1 sampling site) to approximately 1 mm 100 m to the north-west in the flow direction (the M2 site), suggesting a lessening of alteration intensity in that direction. Using this information, the dimensionless parameter δ v/φ D' (φ=porosity, D'=effective diffusion coefficient in rock matrix, δ=fracture aperture, and v=fluid velocity in the fracture) and measurements of the local hydraulic head gradient and effective diffusion coefficient in the rock matrix, a mean fracture aperture of 0.194 mm is calculated assuming the cubic law applies. This information, in combination with measured groundwater compositions at the
Mode choice between private and public transport in Klang Valley, Malaysia.
Chiu Chuen, Onn; Karim, Mohamed Rehan; Yusoff, Sumiani
2014-01-01
In 2010, Klang Valley has only 17% trips each day were completed using public transport, with the rest of the 83% trips were made through private transport. The inclination towards private car usage will only get worse if the transport policy continues to be inefficient and ineffective. Under the National Key Economic Area, the priority aimed to stimulate the increase of modal share of public transport in the Klang Valley to 50% by 2020. In the 10th Malaysia Plan, the Klang Valley Mass Rapid Transit was proposed, equipped with 141 km of MRT system, and will integrate with the existing rail networks. Nevertheless, adding kilometers into the rail system will not help, if people do not make the shift from private into public transport. This research would like to assess the possible mode shift of travellers in the Klang Valley towards using public transport, based on the utility function of available transport modes. It intends to identify the criteria that will trigger their willingness to make changes in favour of public transport as targeted by the NKEA.
Mode Choice between Private and Public Transport in Klang Valley, Malaysia
Karim, Mohamed Rehan; Yusoff, Sumiani
2014-01-01
In 2010, Klang Valley has only 17% trips each day were completed using public transport, with the rest of the 83% trips were made through private transport. The inclination towards private car usage will only get worse if the transport policy continues to be inefficient and ineffective. Under the National Key Economic Area, the priority aimed to stimulate the increase of modal share of public transport in the Klang Valley to 50% by 2020. In the 10th Malaysia Plan, the Klang Valley Mass Rapid Transit was proposed, equipped with 141 km of MRT system, and will integrate with the existing rail networks. Nevertheless, adding kilometers into the rail system will not help, if people do not make the shift from private into public transport. This research would like to assess the possible mode shift of travellers in the Klang Valley towards using public transport, based on the utility function of available transport modes. It intends to identify the criteria that will trigger their willingness to make changes in favour of public transport as targeted by the NKEA. PMID:24701165
Policy Choice for Urban Low-carbon transportation in Beijing: Scenario Analysis Based on LEAP model
NASA Astrophysics Data System (ADS)
Zhang, Yu
2016-04-01
Beijing is a fast developing megacity with serious traffic problems, such as high energy consumption, high CO2 emission and traffic congestion. The coming 13th Five-Year Plan for Beijing economic and social development will focus on the low-carbon transportation policy to achieve the urban traffic sustainable development. In order to improve the feasibility of urban low-carbon transportation policies, this paper analyzes the future trends of CO2 emissions from transportation of Beijing. Firstly, five policies scenarios are developed according to the coming Beijing 13th Five-Year Plan, including the "Business As Usual (BAU)", the "Public Transportation Priority(PTP)", the "New Energy Vehicle(NEV)", the "Active Transportation(AT)", the "Private Car Regulation(PCR)" and the "Hybrid Policy(HP)". Then the Long-range Energy Alternatives Planning System(LEAP model) framework is adopted to estimate CO2 emission under given policies scenarios up to year 2020 and analyze the implications. The results demonstrate that the low-carbon transportation policies can reduce CO2 emission effectively. Specifically, the "Hybrid Policy(HP)" has the best performance. In terms of single policy effect, the "Private Car Regulation(PCR)" comes first followed by the "Public Transportation Priority(PTP)".
ERIC Educational Resources Information Center
Mid-Hudson Migrant Education Center, New Paltz, NY.
Written in Spanish, this guide for the grade 2 career education unit for migrant children focuses on the fields of recreation and transportation. Like the English version, the guide covers 11 jobs--travel agent, tour guide, camp counselor, coach, usher, school bus driver, airplane pilot, trucker, mover, railroad conductor, and astronaut. Student…
NASA Astrophysics Data System (ADS)
Mercure, J.-F.; Lam, A.
2015-06-01
The effectiveness of fiscal policy to influence vehicle purchases for emissions reductions in private passenger road transport depends on its ability to incentivise consumers to make choices oriented towards lower emissions vehicles. However, car purchase choices are known to be strongly socially determined, and this sector is highly diverse due to significant socio-economic differences between consumer groups. Here, we present a comprehensive dataset and analysis of the structure of the 2012 private passenger vehicle fleet-years in six major economies across the World (UK, USA, China, India, Japan and Brazil) in terms of price, engine size and emissions distributions. We argue that choices and aggregate elasticities of substitution can be predicted using this data, enabling us to evaluate the effectiveness of potential fiscal and technological change policies on fleet-year emissions reductions. We provide tools to do so based on the distributive structure of prices and emissions in segments of a diverse market, both for conventional as well as unconventional engine technologies. We find that markets differ significantly between nations, and that correlations between engine sizes, emissions and prices exist strongly in some markets and not strongly in others. We furthermore find that markets for unconventional engine technologies have patchy coverages of varying levels. These findings are interpreted in terms of policy strategy.
Steinbach, Rebecca; Green, Judith; Datta, Jessica; Edwards, Phil
2011-04-01
As a form of 'active transport', cycling has been encouraged as a route to improving population health. However, in many high-income countries, despite being widely seen as a 'healthy' choice, few people do cycle for transport. Further, where cycling is rare, it is not a choice made equally across the population. In London, for instance, cycling is disproportionately an activity of affluent, White, men. This paper takes London as a case study to explore why the meanings of cycling might resonate differently across urban, gendered, ethnic and class identities. Drawing on qualitative interview data with 78 individuals, we suggest first that the relative visibility of cycling when few do it means that it is publicly gendered in a way that more normalised modes of transport are not; conversely, the very invisibility of Black and Asian cyclists reduces their opportunities to see cycling as a candidate mode of transport. Second, following Bourdieu, we argue that the affinities different population groups have for cycling may reflect the locally constituted 'accomplishments' contained in cycling. In London, cycling represents the archetypal efficient mode for autonomous individuals to travel in ways that maximise their future-health gain, and minimise wasted time and dependence on others. However, it relies on the cultivation of a particular 'assertive' style to defend against the risks of road danger and aggression. While the identities of some professional (largely White) men and women could be bolstered by cycling, the aesthetic and symbolic goals of cycling were less appealing to those with other class, gendered and ethnic identities. PMID:21396761
An expected consequence approach to route choice in the maritime transportation of crude oil.
Siddiqui, Atiq; Verma, Manish
2013-11-01
Maritime transportation is the major conduit of international trade, and the primary link for global crude oil movement. Given the volume of oil transported on international maritime links, it is not surprising that oil spills of both minor and major types result, although most of the risk-related work has been confined to the local settings. We propose an expected consequence approach for assessing oil-spill risk from intercontinental transportation of crude oil that not only adheres to the safety guidelines specified by the International Maritime Organization but also outlines a novel technique that makes use of coarse global data to estimate accident probabilities. The proposed estimation technique, together with four of the most popular cost-of-spill models from the literature, were applied to study and analyze a realistic size problem instance. Numerical analyses showed that: a shorter route may not necessarily be less risky; an understanding of the inherent oil-spill risk of different routes could potentially facilitate tanker routing decisions; and the associated negotiations over insurance premium between the transport company and the not-for-profit prevention and indemnity clubs. Finally, we note that only the linear model should be used with one of the three nonlinear cost-of-spill models for evaluating tanker routes.
Recreation/Transportation. B3. CHOICE: Challenging Options in Career Education.
ERIC Educational Resources Information Center
Putnam and Northern Westchester Counties Board of Cooperative Educational Services, Yorktown Heights, NY.
The documents aggregated here comprise the second grade unit of a career education curriculum for migrant children. The unit for grade 2 foucses on the fields of recreation and transportation. Travel agent, tour guide, camp counselor, coach, usher, school bus driver, airplane pilot, trucker, mover, railroad engineer, and astronaut are the 11 jobs…
Enhanced Neuronal Glucose Transporter Expression Reveals Metabolic Choice in a HD Drosophila Model
Besson, Marie Thérèse; Alegría, Karin; Garrido-Gerter, Pamela; Barros, Luis Felipe; Liévens, Jean-Charles
2015-01-01
Huntington’s disease is a neurodegenerative disorder caused by toxic insertions of polyglutamine residues in the Huntingtin protein and characterized by progressive deterioration of cognitive and motor functions. Altered brain glucose metabolism has long been suggested and a possible link has been proposed in HD. However, the precise function of glucose transporters was not yet determined. Here, we report the effects of the specifically-neuronal human glucose transporter expression in neurons of a Drosophila model carrying the exon 1 of the human huntingtin gene with 93 glutamine repeats (HQ93). We demonstrated that overexpression of the human glucose transporter in neurons ameliorated significantly the status of HD flies by increasing their lifespan, reducing their locomotor deficits and rescuing eye neurodegeneration. Then, we investigated whether increasing the major pathways of glucose catabolism, glycolysis and pentose-phosphate pathway (PPP) impacts HD. To mimic increased glycolytic flux, we overexpressed phosphofructokinase (PFK) which catalyzes an irreversible step in glycolysis. Overexpression of PFK did not affect HQ93 fly survival, but protected from photoreceptor loss. Overexpression of glucose-6-phosphate dehydrogenase (G6PD), the key enzyme of the PPP, extended significantly the lifespan of HD flies and rescued eye neurodegeneration. Since G6PD is able to synthesize NADPH involved in cell survival by maintenance of the redox state, we showed that tolerance to experimental oxidative stress was enhanced in flies co-expressing HQ93 and G6PD. Additionally overexpressions of hGluT3, G6PD or PFK were able to circumvent mitochondrial deficits induced by specific silencing of genes necessary for mitochondrial homeostasis. Our study confirms the involvement of bioenergetic deficits in HD course; they can be rescued by specific expression of a glucose transporter in neurons. Finally, the PPP and, to a lesser extent, the glycolysis seem to mediate the hGluT3
Enhanced neuronal glucose transporter expression reveals metabolic choice in a HD Drosophila model.
Besson, Marie Thérèse; Alegría, Karin; Garrido-Gerter, Pamela; Barros, Luis Felipe; Liévens, Jean-Charles
2015-01-01
Huntington's disease is a neurodegenerative disorder caused by toxic insertions of polyglutamine residues in the Huntingtin protein and characterized by progressive deterioration of cognitive and motor functions. Altered brain glucose metabolism has long been suggested and a possible link has been proposed in HD. However, the precise function of glucose transporters was not yet determined. Here, we report the effects of the specifically-neuronal human glucose transporter expression in neurons of a Drosophila model carrying the exon 1 of the human huntingtin gene with 93 glutamine repeats (HQ93). We demonstrated that overexpression of the human glucose transporter in neurons ameliorated significantly the status of HD flies by increasing their lifespan, reducing their locomotor deficits and rescuing eye neurodegeneration. Then, we investigated whether increasing the major pathways of glucose catabolism, glycolysis and pentose-phosphate pathway (PPP) impacts HD. To mimic increased glycolytic flux, we overexpressed phosphofructokinase (PFK) which catalyzes an irreversible step in glycolysis. Overexpression of PFK did not affect HQ93 fly survival, but protected from photoreceptor loss. Overexpression of glucose-6-phosphate dehydrogenase (G6PD), the key enzyme of the PPP, extended significantly the lifespan of HD flies and rescued eye neurodegeneration. Since G6PD is able to synthesize NADPH involved in cell survival by maintenance of the redox state, we showed that tolerance to experimental oxidative stress was enhanced in flies co-expressing HQ93 and G6PD. Additionally overexpressions of hGluT3, G6PD or PFK were able to circumvent mitochondrial deficits induced by specific silencing of genes necessary for mitochondrial homeostasis. Our study confirms the involvement of bioenergetic deficits in HD course; they can be rescued by specific expression of a glucose transporter in neurons. Finally, the PPP and, to a lesser extent, the glycolysis seem to mediate the hGluT3
Route choices of transport bicyclists: a comparison of actually used and shortest routes
2014-01-01
Background Despite evidence that environmental features are related to physical activity, the association between the built environment and bicycling for transportation remains a poorly investigated subject. The aim of the study was to improve our understanding of the environmental determinants of bicycling as a means of transportation in urban European settings by comparing the spatial differences between the routes actually used by bicyclists and the shortest possible routes. Methods In the present study we examined differences in the currently used and the shortest possible bicycling routes, with respect to distance, type of street, and environmental characteristics, in the city of Graz, Austria. The objective measurement methods of a Global Positioning System (GPS) and a Geographic Information System (GIS) were used. Results Bicycling routes actually used were significantly longer than the shortest possible routes. Furthermore, the following attributes were also significantly different between the used route compared to the shortest possible route: Bicyclists often used bicycle lanes and pathways, flat and green areas, and they rarely used main roads and crossings. Conclusion The results of the study support our hypothesis that bicyclists prefer bicycle pathways and lanes instead of the shortest possible routes. This underlines the importance of a well-developed bicycling infrastructure in urban communities. PMID:24597725
Duncan, Dustin T.; Méline, Julie; Kestens, Yan; Day, Kristen; Elbel, Brian; Trasande, Leonardo; Chaix, Basile
2016-01-01
Background: Few studies have used GPS data to analyze the relationship between Walk Score, transportation choice and walking. Additionally, the influence of Walk Score is understudied using trips rather than individuals as statistical units. The purpose of this study is to examine associations at the trip level between Walk Score, transportation mode choice, and walking among Paris adults who were tracked with GPS receivers and accelerometers in the RECORD GPS Study. Methods: In the RECORD GPS Study, 227 participants were tracked during seven days with GPS receivers and accelerometers. Participants were also surveyed with a GPS-based web mapping application on their activities and transportation modes for all trips (6969 trips). Walk Score, which calculates neighborhood walkability, was assessed for each origin and destination of every trip. Multilevel logistic and linear regression analyses were conducted to estimate associations between Walk Score and walking in the trip or accelerometry-assessed number of steps for each trip, after adjustment for individual/neighborhood characteristics. Results: The mean overall Walk Scores for trip origins were 87.1 (SD = 14.4) and for trip destinations 87.1 (SD = 14.5). In adjusted trip-level associations between Walk Score and walking only in the trip, we found that a walkable neighborhood in the trip origin and trip destination was associated with increased odds of walking in the trip assessed in the survey. The odds of only walking in the trip were 3.48 (95% CI: 2.73 to 4.44) times higher when the Walk Score for the trip origin was “Walker’s Paradise” compared to less walkable neighborhoods (Very/Car-Dependent or Somewhat Walkable), with an identical independent effect of trip destination Walk Score on walking. The number of steps per 10 min (as assessed with accelerometry) was cumulatively higher for trips both originating and ending in walkable neighborhoods (i.e., “Very Walkable”). Conclusions: Walkable
NASA Astrophysics Data System (ADS)
Suriano, Mark Allen
2001-07-01
Accurate, reliable, and robust discrete neutral particle radiation transport codes are needed in order to perform realistic 3D engineering calculations. Current neutron transport codes use low order spatial quadratures that are inaccurate unless a highly refined spatial mesh is used. In this work various higher order characteristic spatial quadratures are derived, implemented, and tested. Regular meshes of rectangular (2D) and of rectangular parallelepiped (boxoid) cells are supported. Short characteristic (linear characteristic [LC] and exponential characteristic [EC]) methods are compared with the corresponding independent characteristic (ILC and IEC) methods. The latter readily provide for plane parallel implementation. All transport results were benchmarked against Monte Carlo calculations. The diamond difference (DD) method was also tested and compared to the characteristic spatial quadratures. IEC and EC were found to be robust, reliable, and accurate for thin, intermediate, and optically thick cells. LC was robust, reliable, and accurate for cells of thin to intermediate (approximately 2 mean free paths) optical thickness. ILC was not pursued in 3D due to its anticipated excessive computational cost. DD was unreliable (as expected) over the range of test problems. We conclude that IEC and EC are apt methods for a wide range of problems, and provide the ability to perform realistic engineering calculations on coarse cells given nonnegative group-to-group, ordinate-to-ordinate cross section data.
Hyman, Jeffrey De'Haven; Aldrich, Garrett Allen; Viswanathan, Hari S.; Makedonska, Nataliia; Karra, Satish
2016-08-25
We characterize how different fracture size-transmissivity relationships influence flow and transport simulations through sparse three-dimensional discrete fracture networks. Although it is generally accepted that there is a positive correlation between a fracture's size and its transmissivity/aperture, the functional form of that relationship remains a matter of debate. Relationships that assume perfect correlation, semicorrelation, and noncorrelation between the two have been proposed. To study the impact that adopting one of these relationships has on transport properties, we generate multiple sparse fracture networks composed of circular fractures whose radii follow a truncated power law distribution. The distribution of transmissivities are selected somore » that the mean transmissivity of the fracture networks are the same and the distributions of aperture and transmissivity in models that include a stochastic term are also the same. We observe that adopting a correlation between a fracture size and its transmissivity leads to earlier breakthrough times and higher effective permeability when compared to networks where no correlation is used. While fracture network geometry plays the principal role in determining where transport occurs within the network, the relationship between size and transmissivity controls the flow speed. Lastly, these observations indicate DFN modelers should be aware that breakthrough times and effective permeabilities can be strongly influenced by such a relationship in addition to fracture and network statistics.« less
NASA Technical Reports Server (NTRS)
Ghorai, S. K.
1983-01-01
The purpose of this project was to use a one-dimensional discrete coordinates transport code called ANISN in order to determine the energy-angle-spatial distribution of neutrons in a 6-feet cube rock box which houses a D-T neutron generator at its center. The project was two-fold. The first phase of the project involved adaptation of the ANISN code written for an IBM 360/75/91 computer to the UNIVAC system at JSC. The second phase of the project was to use the code with proper geometry, source function and rock material composition in order to determine the neutron flux distribution around the rock box when a 14.1 MeV neutron generator placed at its center is activated.
Hirsch, Jana A; Diez Roux, Ana V; Rodriguez, Daniel A; Brines, Shannon J; Moore, Kari A
2013-11-01
This study examines associations of disaggregate land uses with self-reported walking for transportation among participants of the Multi-Ethnic Study of Atherosclerosis (MESA) in Forsyth County, NC and New York, NY. Network distance to each use (in miles), intensity (number of uses per 1/2-mile network buffer) of each use and diversity (number of different uses per 1/2-mile network buffer) of uses were calculated using Geographic Information Systems (GIS). Associations with odds of meeting recommended physical activity levels (150min/week) were examined after controlling for individual- and census-tract-level covariates. Greater distance to and lower intensity of pedestrian-oriented uses, specifically those for social interactions, were associated with lower odds of meeting recommendations in NY. Results suggest that land uses linked to social interactions may be useful for encouraging increased transportation walking.
Ranganathan, Kamalakannan; Shanmugam, Ilango; Kamruddin, Mohammed; Tyagi, Ashok K
2016-01-01
CVD grown, few walled carbon nanotubes (FWCNTs) were quasi decorated with SnO₂nanoparticles (FWCNTs-SnO₂) and its gas sensing properties were analyzed with ammonia and ethanol. At room temperature FWCNTs-SnO₂show enhanced 'p type' gas sensing response than FWCNTs. Activation of SnO₂at high temperatures led to systematic changes in the sensing behavior towards 'n type' response. Temperature dependent transport behavior was found to be a one dimensional variable range hopping mechanism (1 D-VRH) for the FWCNTs and a 3D-VRH mechanism for the FWCNTs-SnO2. These temperature dependent gas transport and sensing properties elucidate the hybrid nature of the nanocomposite with novel characteristics. This also implies its importance as a potential gas sensor material. PMID:27398589
Discrete breathers in crystals
NASA Astrophysics Data System (ADS)
Dmitriev, S. V.; Korznikova, E. A.; Baimova, Yu A.; Velarde, M. G.
2016-05-01
It is well known that periodic discrete defect-containing systems, in addition to traveling waves, support vibrational defect-localized modes. It turned out that if a periodic discrete system is nonlinear, it can support spatially localized vibrational modes as exact solutions even in the absence of defects. Since the nodes of the system are all on equal footing, it is only through the special choice of initial conditions that a group of nodes can be found on which such a mode, called a discrete breather (DB), will be excited. The DB frequency must be outside the frequency range of the small-amplitude traveling waves. Not resonating with and expending no energy on the excitation of traveling waves, a DB can theoretically conserve its vibrational energy forever provided no thermal vibrations or other perturbations are present. Crystals are nonlinear discrete systems, and the discovery in them of DBs was only a matter of time. It is well known that periodic discrete defect-containing systems support both traveling waves and vibrational defect-localized modes. It turns out that if a periodic discrete system is nonlinear, it can support spatially localized vibrational modes as exact solutions even in the absence of defects. Because the nodes of the system are all on equal footing, only a special choice of the initial conditions allows selecting a group of nodes on which such a mode, called a discrete breather (DB), can be excited. The DB frequency must be outside the frequency range of small-amplitude traveling waves. Not resonating with and expending no energy on the excitation of traveling waves, a DB can theoretically preserve its vibrational energy forever if no thermal vibrations or other perturbations are present. Crystals are nonlinear discrete systems, and the discovery of DBs in them was only a matter of time. Experimental studies of DBs encounter major technical difficulties, leaving atomistic computer simulations as the primary investigation tool. Despite
Eakle, Robyn; Cabrera, Maria; Vickerman, Peter; Tsepe, Motlalepule; Cianci, Fiona; Delany-Moretlwe, Sinead; Terris-Prestholt, Fern
2016-01-01
Introduction For the past few decades, condoms have been the main method of HIV prevention. Recent advances in antiretroviral (ARV)-based prevention products have substantially changed the prevention landscape, yet little is known about how popular these products will be among potential users, or whether new methods might be used in conjunction with, or instead of, condoms. This study will use a discrete choice experiment (DCE) to (1) explore potential users' preferences regarding HIV prevention products, (2) quantify the importance of product attributes and (3) predict the uptake of products to inform estimates of their potential impact on the HIV epidemic in South Africa. We consider preferences for oral pre-exposure prophylaxis; a vaginal microbicide gel; a long-acting vaginal ring; a SILCS diaphragm used in concert with gel; and a long-acting ARV-based injectable. Methods and analysis This study will gather data from 4 populations: 200 women, 200 men, 200 adolescent girls (aged 16–17 years) and 200 female sex workers. The DCE attributes and design will be developed through a literature review, supplemented by a thematic analysis of qualitative focus group discussions. Extensive piloting will be carried out in each population through semistructured interviews. The final survey will be conducted using computer tablets via a household sample (for women, men and adolescents) and respondent-driven sampling (for female sex workers), and DCE data analysed using a range of multinomial logit models. Ethics and dissemination This study has been approved by the University of the Witwatersrand Human Research Ethics Committee and the Research Ethics Committee at the London School of Hygiene and Tropical Medicine. Findings will be presented to international conferences and peer-reviewed journals. Meetings will be held with opinion leaders in South Africa, while results will be disseminated to participants in Ekurhuleni through a public meeting or newsletter. PMID:27354071
NASA Astrophysics Data System (ADS)
Owens, A. R.; Welch, J. A.; Kópházi, J.; Eaton, M. D.
2016-06-01
In this paper two discontinuous Galerkin isogeometric analysis methods are developed and applied to the first-order form of the neutron transport equation with a discrete ordinate (SN) angular discretisation. The discontinuous Galerkin projection approach was taken on both an element level and the patch level for a given Non-Uniform Rational B-Spline (NURBS) patch. This paper describes the detailed dispersion analysis that has been used to analyse the numerical stability of both of these schemes. The convergence of the schemes for both smooth and non-smooth solutions was also investigated using the method of manufactured solutions (MMS) for multidimensional problems and a 1D semi-analytical benchmark whose solution contains a strongly discontinuous first derivative. This paper also investigates the challenges posed by strongly curved boundaries at both the NURBS element and patch level with several algorithms developed to deal with such cases. Finally numerical results are presented both for a simple pincell test problem as well as the C5G7 quarter core MOX/UOX small Light Water Reactor (LWR) benchmark problem. These numerical results produced by the isogeometric analysis (IGA) methods are compared and contrasted against linear and quadratic discontinuous Galerkin finite element (DGFEM) SN based methods.
Dorda, Antonius Schürrer, Ferdinand
2015-03-01
We present a novel numerical scheme for the deterministic solution of the Wigner transport equation, especially suited to deal with situations in which strong quantum effects are present. The unique feature of the algorithm is the expansion of the Wigner function in local basis functions, similar to finite element or finite volume methods. This procedure yields a discretization of the pseudo-differential operator that conserves the particle density on arbitrarily chosen grids. The high flexibility in refining the grid spacing together with the weighted essentially non-oscillatory (WENO) scheme for the advection term allows for an accurate and well-resolved simulation of the phase space dynamics. A resonant tunneling diode is considered as test case and a detailed convergence study is given by comparing the results to a non-equilibrium Green's functions calculation. The impact of the considered domain size and of the grid spacing is analyzed. The obtained convergence of the results towards a quasi-exact agreement of the steady state Wigner and Green's functions computations demonstrates the accuracy of the scheme, as well as the high flexibility to adjust to different physical situations.
Dorda, Antonius; Schürrer, Ferdinand
2015-01-01
We present a novel numerical scheme for the deterministic solution of the Wigner transport equation, especially suited to deal with situations in which strong quantum effects are present. The unique feature of the algorithm is the expansion of the Wigner function in local basis functions, similar to finite element or finite volume methods. This procedure yields a discretization of the pseudo-differential operator that conserves the particle density on arbitrarily chosen grids. The high flexibility in refining the grid spacing together with the weighted essentially non-oscillatory (WENO) scheme for the advection term allows for an accurate and well-resolved simulation of the phase space dynamics. A resonant tunneling diode is considered as test case and a detailed convergence study is given by comparing the results to a non-equilibrium Green's functions calculation. The impact of the considered domain size and of the grid spacing is analyzed. The obtained convergence of the results towards a quasi-exact agreement of the steady state Wigner and Green's functions computations demonstrates the accuracy of the scheme, as well as the high flexibility to adjust to different physical situations. PMID:25892748
School Choice in Less Populated Areas.
ERIC Educational Resources Information Center
Hammond, Tom; Dennison, Bill
1995-01-01
Discusses a parental choice case involving a rural (British) school with a 13+ transfer age to determine parents' use of the open enrollment system, effects of transport policy on exercising parental choice, quality of information provided, and factors influencing choice. Transportation was problematic. Four choice factors stood out: teacher…
Hong, X; Gao, H
2014-06-15
Purpose: The Linear Boltzmann Transport Equation (LBTE) solved through statistical Monte Carlo (MC) method provides the accurate dose calculation in radiotherapy. This work is to investigate the alternative way for accurately solving LBTE using deterministic numerical method due to its possible advantage in computational speed from MC. Methods: Instead of using traditional spherical harmonics to approximate angular scattering kernel, our deterministic numerical method directly computes angular scattering weights, based on a new angular discretization method that utilizes linear finite element method on the local triangulation of unit angular sphere. As a Result, our angular discretization method has the unique advantage in positivity, i.e., to maintain all scattering weights nonnegative all the time, which is physically correct. Moreover, our method is local in angular space, and therefore handles the anisotropic scattering well, such as the forward-peaking scattering. To be compatible with image-guided radiotherapy, the spatial variables are discretized on the structured grid with the standard diamond scheme. After discretization, the improved sourceiteration method is utilized for solving the linear system without saving the linear system to memory. The accuracy of our 3D solver is validated using analytic solutions and benchmarked with Geant4, a popular MC solver. Results: The differences between Geant4 solutions and our solutions were less than 1.5% for various testing cases that mimic the practical cases. More details are available in the supporting document. Conclusion: We have developed a 3D LBTE solver based on a new angular discretization method that guarantees the positivity of scattering weights for physical correctness, and it has been benchmarked with Geant4 for photon dose calculation.
5 CFR 572.102 - Agency discretion.
Code of Federal Regulations, 2010 CFR
2010-01-01
... 5 Administrative Personnel 1 2010-01-01 2010-01-01 false Agency discretion. 572.102 Section 572.102 Administrative Personnel OFFICE OF PERSONNEL MANAGEMENT CIVIL SERVICE REGULATIONS TRAVEL AND TRANSPORTATION EXPENSES; NEW APPOINTEES AND INTERVIEWS § 572.102 Agency discretion. Payment of travel...
Colorado's clean energy choices
Strawn, N.; Jones, J.
2000-04-15
The daily choices made as consumers affect the environment and the economy. Based on the state of today's technology and economics, Colorado consumers can include energy efficiency and renewable energy into many aspects of their lives. These choices include where they obtain electricity, how they use energy at home, and how they transport themselves from one place to another. In addition to outlining how they can use clean energy, Colorado's Clean Energy Choices gives consumers contacts and links to Web sites for where to get more information.
Reduced discretization error in HZETRN
NASA Astrophysics Data System (ADS)
Slaba, Tony C.; Blattnig, Steve R.; Tweed, John
2013-02-01
The deterministic particle transport code HZETRN is an efficient analysis tool for studying the effects of space radiation on humans, electronics, and shielding materials. In a previous work, numerical methods in the code were reviewed, and new methods were developed that further improved efficiency and reduced overall discretization error. It was also shown that the remaining discretization error could be attributed to low energy light ions (A < 4) with residual ranges smaller than the physical step-size taken by the code. Accurately resolving the spectrum of low energy light particles is important in assessing risk associated with astronaut radiation exposure. In this work, modifications to the light particle transport formalism are presented that accurately resolve the spectrum of low energy light ion target fragments. The modified formalism is shown to significantly reduce overall discretization error and allows a physical approximation to be removed. For typical step-sizes and energy grids used in HZETRN, discretization errors for the revised light particle transport algorithms are shown to be less than 4% for aluminum and water shielding thicknesses as large as 100 g/cm2 exposed to both solar particle event and galactic cosmic ray environments.
Reduced discretization error in HZETRN
Slaba, Tony C.; Blattnig, Steve R.; Tweed, John
2013-02-01
The deterministic particle transport code HZETRN is an efficient analysis tool for studying the effects of space radiation on humans, electronics, and shielding materials. In a previous work, numerical methods in the code were reviewed, and new methods were developed that further improved efficiency and reduced overall discretization error. It was also shown that the remaining discretization error could be attributed to low energy light ions (A < 4) with residual ranges smaller than the physical step-size taken by the code. Accurately resolving the spectrum of low energy light particles is important in assessing risk associated with astronaut radiation exposure. In this work, modifications to the light particle transport formalism are presented that accurately resolve the spectrum of low energy light ion target fragments. The modified formalism is shown to significantly reduce overall discretization error and allows a physical approximation to be removed. For typical step-sizes and energy grids used in HZETRN, discretization errors for the revised light particle transport algorithms are shown to be less than 4% for aluminum and water shielding thicknesses as large as 100 g/cm{sup 2} exposed to both solar particle event and galactic cosmic ray environments.
Household Mobility, School Choices, and School Outcomes.
ERIC Educational Resources Information Center
Bayer, Patrick J.
This paper summarizes work from a dissertation, the main contribution of which was to develop and estimate a new empirical framework for analyzing the equilibrium outcomes of families' choices for choosing a particular residence. The principal component of the framework is a random-coefficients discrete-choice model of the residential location…
NASA Astrophysics Data System (ADS)
Hansen, Scott K.; Kueper, Bernard H.
2014-01-01
This paper concerns a new modeling approach to multicomponent NAPL dissolution and transport, based on analytic solutions and Laguerre series. This approach allows virtually any of the numerous existing 1-D analytic transport solutions in the literature to be coupled with arbitrary boundary conditions stemming from nonlinear NAPL dissolution, as dictated by Raoult's Law. A computer implementation of this approach to coupled dissolution and transport in parallel fractures—which no other screening tool known to the authors covers—is presented. This is verified against an existing analytic transport solution that assumes a constant boundary condition. Subsequently, the model is demonstrated via a study of separation of PAH and phenolic plumes generated by dissolution of creosote, using the new computer implementation. The PAH and phenolic constituents of creosote strongly differ in both their dissolution and their transport behavior, and this is shown to necessitate the use of a tool that can account for both processes, such as the one developed here. We also find the possibility of PAH and phenolic plumes becoming entirely disjoint.
ERIC Educational Resources Information Center
Heleen, Owen
1992-01-01
Choice plans include private schools (voucher plans, tax credits and deductions, and contract services and charter plans) and public schools (intradistrict choice, interdistrict choice, and statewide choice). Issues spanning both areas are those of curricular choice and residential choice. (SLD)
Schoellhamer, David H.
1994-01-01
Sediments are an important component of the San Francisco Bay estuarine system. Potentially toxic substances, such as metals and pesticides, adsorb to sediment particles. The sediments on the bottom of the Bay provide the habitat for benthic communities which can ingest these substances and introduce them into the food web. The bottom sediments are also a reservoir of nutrients. The transport and fate of suspended sediment is an important factor in determining the transport and fate of the constituents adsorbed on the sediment. Suspended sediments also limit light availability in the bay, which limits photosynthesis and primary production, and deposit in ports and shipping channels, which require dredging. Dredged materials are disposed in Central San Francisco Bay.
Principles of Discrete Time Mechanics
NASA Astrophysics Data System (ADS)
Jaroszkiewicz, George
2014-04-01
1. Introduction; 2. The physics of discreteness; 3. The road to calculus; 4. Temporal discretization; 5. Discrete time dynamics architecture; 6. Some models; 7. Classical cellular automata; 8. The action sum; 9. Worked examples; 10. Lee's approach to discrete time mechanics; 11. Elliptic billiards; 12. The construction of system functions; 13. The classical discrete time oscillator; 14. Type 2 temporal discretization; 15. Intermission; 16. Discrete time quantum mechanics; 17. The quantized discrete time oscillator; 18. Path integrals; 19. Quantum encoding; 20. Discrete time classical field equations; 21. The discrete time Schrodinger equation; 22. The discrete time Klein-Gordon equation; 23. The discrete time Dirac equation; 24. Discrete time Maxwell's equations; 25. The discrete time Skyrme model; 26. Discrete time quantum field theory; 27. Interacting discrete time scalar fields; 28. Space, time and gravitation; 29. Causality and observation; 30. Concluding remarks; Appendix A. Coherent states; Appendix B. The time-dependent oscillator; Appendix C. Quaternions; Appendix D. Quantum registers; References; Index.
ERIC Educational Resources Information Center
Hicks, Darcy
2001-01-01
Describes how the author allows the children to make choices about their art and writing, enabling them to make connections between their own lives and work. Suggests that educators need to provide doorways to the things that give students ideas: books, music, objects, pictures, smells, sounds, and textures. (SG)
Schoellhamer, David H.
1996-01-01
Sediments are an important component of the San Francisco Bay estuarine system. Potentially toxic substances, such as metals and pesticides, adsorb to sediment particles (Kuwabara and others, 1989; Domagalski and Kuivila, 1993). Sediments on the bottom of the bay provide the habitat for benthic communities that can ingest these substances and introduce them into the food web (Luoma and others, 1985). Nutrients, metals, and other substances are stored in bottom sediments and pore water in which chemical reactions occur and which provide an important source and/or sink to the water column (Hammond and others, 1985; Flegal and others, 1991). The transport and fate of suspended sediment is an important factor in determining the transport and fate of the constituents adsorbed on the sediment. Seasonal changes in sediment erosion and deposition patterns contribute to seasonal changes in the abundance of benthic macroinvertebrates (Nichols and Thompson, 1985). Tidal marshes are an ecologically important habitat that were created and are maintained by sedimentation processes (Atwater and others, 1979). In Suisun Bay, the maximum suspended-sediment concentration marks the position of the turbidity maximum, which is a crucial ecological region in which suspended sediment, nutrients, phytoplankton, zooplankton, larvae, and juvenile fish accumulate (Peterson and others, 1975; Arthur and Ball, 1979; Kimmerer, 1992; Jassby and Powell, 1994). Suspended sediments confine the photic zone to the upper part of the water column, and this limitation on light availability is a major control on phytoplankton production in San Francisco Bay (Cloern, 1987; Cole and Cloern, 1987). Suspended sediments also deposit in ports and shipping channels, which must be dredged to maintain navigation (U.S. Environmental Protection Agency, 1992).
ERIC Educational Resources Information Center
Crank, Ron
This instructional unit is one of 10 developed by students on various energy-related areas that deals specifically with transportation and energy use. Its objective is for the student to be able to discuss the implication of energy usage as it applies to the area of transportation. Some topics covered are efficiencies of various transportation…
Seleson, Pablo; Du, Qiang; Parks, Michael L.
2016-08-16
The peridynamic theory of solid mechanics is a nonlocal reformulation of the classical continuum mechanics theory. At the continuum level, it has been demonstrated that classical (local) elasticity is a special case of peridynamics. Such a connection between these theories has not been extensively explored at the discrete level. This paper investigates the consistency between nearest-neighbor discretizations of linear elastic peridynamic models and finite difference discretizations of the Navier–Cauchy equation of classical elasticity. While nearest-neighbor discretizations in peridynamics have been numerically observed to present grid-dependent crack paths or spurious microcracks, this paper focuses on a different, analytical aspect of suchmore » discretizations. We demonstrate that, even in the absence of cracks, such discretizations may be problematic unless a proper selection of weights is used. Specifically, we demonstrate that using the standard meshfree approach in peridynamics, nearest-neighbor discretizations do not reduce, in general, to discretizations of corresponding classical models. We study nodal-based quadratures for the discretization of peridynamic models, and we derive quadrature weights that result in consistency between nearest-neighbor discretizations of peridynamic models and discretized classical models. The quadrature weights that lead to such consistency are, however, model-/discretization-dependent. We motivate the choice of those quadrature weights through a quadratic approximation of displacement fields. The stability of nearest-neighbor peridynamic schemes is demonstrated through a Fourier mode analysis. Finally, an approach based on a normalization of peridynamic constitutive constants at the discrete level is explored. This approach results in the desired consistency for one-dimensional models, but does not work in higher dimensions. The results of the work presented in this paper suggest that even though nearest
Discrete Mathematics Re "Tooled."
ERIC Educational Resources Information Center
Grassl, Richard M.; Mingus, Tabitha T. Y.
1999-01-01
Indicates the importance of teaching discrete mathematics. Describes how the use of technology can enhance the teaching and learning of discrete mathematics. Explorations using Excel, Derive, and the TI-92 proved how preservice and inservice teachers experienced a new dimension in problem solving and discovery. (ASK)
On the definition of discrete hydrodynamic variables.
Español, Pep; Zúñiga, Ignacio
2009-10-28
The Green-Kubo formula for discrete hydrodynamic variables involves information about not only the fluid transport coefficients but also about discrete versions of the differential operators that govern the evolution of the discrete variables. This gives an intimate connection between discretization procedures in fluid dynamics and coarse-graining procedures used to obtain hydrodynamic behavior of molecular fluids. We observed that a natural definition of discrete hydrodynamic variables in terms of Voronoi cells leads to a Green-Kubo formula which is divergent, rendering the full coarse-graining strategy useless. In order to understand this subtle issue, in the present paper we consider the coarse graining of noninteracting Brownian particles. The discrete hydrodynamic variable for this problem is the number of particles within Voronoi cells. Thanks to the simplicity of the model we spot the origin of the singular behavior of the correlation functions. We offer an alternative definition, based on the concept of a Delaunay cell that behaves properly, suggesting the use of the Delaunay construction for the coarse graining of molecular fluids at the discrete hydrodynamic level.
Morris, J; Johnson, S
2007-12-03
The Distinct Element Method (also frequently referred to as the Discrete Element Method) (DEM) is a Lagrangian numerical technique where the computational domain consists of discrete solid elements which interact via compliant contacts. This can be contrasted with Finite Element Methods where the computational domain is assumed to represent a continuum (although many modern implementations of the FEM can accommodate some Distinct Element capabilities). Often the terms Discrete Element Method and Distinct Element Method are used interchangeably in the literature, although Cundall and Hart (1992) suggested that Discrete Element Methods should be a more inclusive term covering Distinct Element Methods, Displacement Discontinuity Analysis and Modal Methods. In this work, DEM specifically refers to the Distinct Element Method, where the discrete elements interact via compliant contacts, in contrast with Displacement Discontinuity Analysis where the contacts are rigid and all compliance is taken up by the adjacent intact material.
Synchronous Discrete Harmonic Oscillator
Antippa, Adel F.; Dubois, Daniel M.
2008-10-17
We introduce the synchronous discrete harmonic oscillator, and present an analytical, numerical and graphical study of its characteristics. The oscillator is synchronous when the time T for one revolution covering an angle of 2{pi} in phase space, is an integral multiple N of the discrete time step {delta}t. It is fully synchronous when N is even. It is pseudo-synchronous when T/{delta}t is rational. In the energy conserving hyperincursive representation, the phase space trajectories are perfectly stable at all time scales, and in both synchronous and pseudo-synchronous modes they cycle through a finite number of phase space points. Consequently, both the synchronous and the pseudo-synchronous hyperincursive modes of time-discretization provide a physically realistic and mathematically coherent, procedure for dynamic, background independent, discretization of spacetime. The procedure is applicable to any stable periodic dynamical system, and provokes an intrinsic correlation between space and time, whereby space-discretization is a direct consequence of background-independent time-discretization. Hence, synchronous discretization moves the formalism of classical mechanics towards that of special relativity. The frequency of the hyperincursive discrete harmonic oscillator is ''blue shifted'' relative to its continuum counterpart. The frequency shift has the precise value needed to make the speed of the system point in phase space independent of the discretizing time interval {delta}t. That is the speed of the system point is the same on the polygonal (in the discrete case) and the circular (in the continuum case) phase space trajectories.
Discrete ordinates methods in xy geometry with spatially varying angular discretization
Bal, G.; Warin, X.
1997-10-01
The efficiency of a new quadrature rule adapted to the numerical resolution of a neutron transport problem in xy geometry is presented based on the use of the discrete ordinates method for the angular variable. The purpose of introducing this quadrature rule is to couple two different angular discretizations used on two nonoverlapping subdomains, which is useful for performing local refinement. This coupling and some numerical results of source problems are presented.
Carlsten, B.E.; Haynes, W.B.
1996-08-01
The authors theoretically and numerically investigate the operation and behavior of the discrete monotron oscillator, a novel high-power microwave source. The discrete monotron differs from conventional monotrons and transit time oscillators by shielding the electron beam from the monotron cavity`s RF fields except at two distinct locations. This makes the discrete monotron act more like a klystron than a distributed traveling wave device. As a result, the oscillator has higher efficiency and can operate with higher beam powers than other single cavity oscillators and has more stable operation without requiring a seed input signal than mildly relativistic, intense-beam klystron oscillators.
Constraint analysis for variational discrete systems
Dittrich, Bianca; Höhn, Philipp A.
2013-09-15
A canonical formalism and constraint analysis for discrete systems subject to a variational action principle are devised. The formalism is equivalent to the covariant formulation, encompasses global and local discrete time evolution moves and naturally incorporates both constant and evolving phase spaces, the latter of which is necessary for a time varying discretization. The different roles of constraints in the discrete and the conditions under which they are first or second class and/or symmetry generators are clarified. The (non-) preservation of constraints and the symplectic structure is discussed; on evolving phase spaces the number of constraints at a fixed time step depends on the initial and final time step of evolution. Moreover, the definition of observables and a reduced phase space is provided; again, on evolving phase spaces the notion of an observable as a propagating degree of freedom requires specification of an initial and final step and crucially depends on this choice, in contrast to the continuum. However, upon restriction to translation invariant systems, one regains the usual time step independence of canonical concepts. This analysis applies, e.g., to discrete mechanics, lattice field theory, quantum gravity models, and numerical analysis.
Discrete choice modeling of environmental security. Research report
Carson, K.S.
1998-10-01
The presence of overpopulation or unsustainable population growth may place pressure on the food and water supplies of countries in sensitive areas of the world. Severe air or water pollution may place additional pressure on these resources. These pressures may generate both internal and international conflict in these areas as nations struggle to provide for their citizens. Such conflicts may result in United States intervention, either unilaterally, or through the United Nations. Therefore, it is in the interests of the United States to identify potential areas of conflict in order to properly train and allocate forces. The purpose of this research is to forecast the probability of conflict in a nation as a function of it s environmental conditions. Probit, logit and ordered probit models are employed to forecast the probability of a given level of conflict. Data from 95 countries are used to estimate the models. Probability forecasts are generated for these 95 nations. Out-of sample forecasts are generated for an additional 22 nations. These probabilities are then used to rank nations from highest probability of conflict to lowest. The results indicate that the dependence of a nation`s economy on agriculture, the rate of deforestation, and the population density are important variables in forecasting the probability and level of conflict. These results indicate that environmental variables do play a role in generating or exacerbating conflict. It is unclear that the United States military has any direct role in mitigating the environmental conditions that may generate conflict. A more important role for the military is to aid in data gathering to generate better forecasts so that the troops are adequntely prepared when conflicts arises.
ERIC Educational Resources Information Center
Peters, James V.
2004-01-01
Using the methods of finite difference equations the discrete analogue of the parabolic and catenary cable are analysed. The fibonacci numbers and the golden ratio arise in the treatment of the catenary.
Depression: discrete or continuous?
Bowins, Brad
2015-01-01
Elucidating the true structure of depression is necessary if we are to advance our understanding and treatment options. Central to the issue of structure is whether depression represents discrete types or occurs on a continuum. Nature almost universally operates on the basis of continuums, whereas human perception favors discrete categories. This reality might be formalized into a 'continuum principle': natural phenomena tend to occur on a continuum, and any instance of hypothesized discreteness requires unassailable proof. Research evidence for discrete types falls far short of this standard, with most evidence supporting a continuum. However, quantitative variation can yield qualitative differences as an emergent property, fostering the appearance of discreteness. Depression as a continuum is best characterized by duration and severity dimensions, with the latter understood in terms of depressive inhibition. In the absence of some degree of cognitive, emotional, social, and physical inhibition, depression should not be diagnosed. Combining the dimensions of duration and severity provides an optimal way to characterize the quantitative and related qualitative aspects of depression and to describe the overall degree of dysfunction. The presence of other symptom types occurs when anxiety, hypomanic/manic, psychotic, and personality continuums interface with the depression continuum. PMID:25531962
NASA Astrophysics Data System (ADS)
Arzano, Michele; Kowalski-Glikman, Jerzy
2016-09-01
We construct discrete symmetry transformations for deformed relativistic kinematics based on group valued momenta. We focus on the specific example of κ-deformations of the Poincaré algebra with associated momenta living on (a sub-manifold of) de Sitter space. Our approach relies on the description of quantum states constructed from deformed kinematics and the observable charges associated with them. The results we present provide the first step towards the analysis of experimental bounds on the deformation parameter κ to be derived via precision measurements of discrete symmetries and CPT.
ERIC Educational Resources Information Center
Sharp, Karen Tobey
This paper cites information received from a number of sources, e.g., mathematics teachers in two-year colleges, publishers, and convention speakers, about the nature of discrete mathematics and about what topics a course in this subject should contain. Note is taken of the book edited by Ralston and Young which discusses the future of college…
Peschel, U; Egorov, O; Lederer, F
2004-08-15
We derive evolution equations describing light propagation in an array of coupled-waveguide resonators and predict the existence of discrete cavity solitons. We identify stable, unstable, and oscillating solitons by varying the coupling strength between the anticontinuous and the continuous limit. PMID:15357356
Analysis hierarchical model for discrete event systems
NASA Astrophysics Data System (ADS)
Ciortea, E. M.
2015-11-01
The This paper presents the hierarchical model based on discrete event network for robotic systems. Based on the hierarchical approach, Petri network is analysed as a network of the highest conceptual level and the lowest level of local control. For modelling and control of complex robotic systems using extended Petri nets. Such a system is structured, controlled and analysed in this paper by using Visual Object Net ++ package that is relatively simple and easy to use, and the results are shown as representations easy to interpret. The hierarchical structure of the robotic system is implemented on computers analysed using specialized programs. Implementation of hierarchical model discrete event systems, as a real-time operating system on a computer network connected via a serial bus is possible, where each computer is dedicated to local and Petri model of a subsystem global robotic system. Since Petri models are simplified to apply general computers, analysis, modelling, complex manufacturing systems control can be achieved using Petri nets. Discrete event systems is a pragmatic tool for modelling industrial systems. For system modelling using Petri nets because we have our system where discrete event. To highlight the auxiliary time Petri model using transport stream divided into hierarchical levels and sections are analysed successively. Proposed robotic system simulation using timed Petri, offers the opportunity to view the robotic time. Application of goods or robotic and transmission times obtained by measuring spot is obtained graphics showing the average time for transport activity, using the parameters sets of finished products. individually.
Discreteness induced extinction
NASA Astrophysics Data System (ADS)
dos Santos, Renato Vieira; da Silva, Linaena Méricy
2015-11-01
Two simple models based on ecological problems are discussed from the point of view of non-equilibrium statistical mechanics. It is shown how discrepant may be the results of the models that include spatial distribution with discrete interactions when compared with the continuous analogous models. In the continuous case we have, under certain circumstances, the population explosion. When we take into account the finiteness of the population, we get the opposite result, extinction. We will analyze how these results depend on the dimension d of the space and describe the phenomenon of the "Discreteness Inducing Extinction" (DIE). The results are interpreted in the context of the "paradox of sex", an old problem of evolutionary biology.
A paradigm for discrete physics
Noyes, H.P.; McGoveran, D.; Etter, T.; Manthey, M.J.; Gefwert, C.
1987-01-01
An example is outlined for constructing a discrete physics using as a starting point the insight from quantum physics that events are discrete, indivisible and non-local. Initial postulates are finiteness, discreteness, finite computability, absolute nonuniqueness (i.e., homogeneity in the absence of specific cause) and additivity.
ERIC Educational Resources Information Center
Young, Timothy W.; Clinchy, Evans
There has been much recent debate in both educational and political circles about the utility of choice as a means of improving the educational system. This book argues that any discussion of choice must address choice in public schools. The book is organized into seven chapters. Chapter 1 provides an overview of choice in public education,…
On the discrete-ordinates method via Case`s solution
Ganguly, K.; Allen, E.J.; Coskun, E.; Nielsen, S.
1993-07-01
In this paper, we have used Case`s analysis of the neutron transport equation to obtain a new set of quadrature coefficients for the discrete-ordinates method. We perform the transport calculations by this set of quadratures, dependent on the medium. We also use the orthogonality relations in the discrete case to derive the full-range formulation of the half-range problem. This solution can, be profitably used in the new discrete-ordinates method.
Dynamical properties of Discrete Reaction Networks.
Paulevé, Loïc; Craciun, Gheorghe; Koeppl, Heinz
2014-07-01
Reaction networks are commonly used to model the dynamics of populations subject to transformations that follow an imposed stoichiometry. This paper focuses on the efficient characterisation of dynamical properties of Discrete Reaction Networks (DRNs). DRNs can be seen as modeling the underlying discrete nondeterministic transitions of stochastic models of reaction networks. In that sense, a proof of non-reachability in a given DRN has immediate implications for any concrete stochastic model based on that DRN, independent of the choice of kinetic laws and constants. Moreover, if we assume that stochastic kinetic rates are given by the mass-action law (or any other kinetic law that gives non-vanishing probability to each reaction if the required number of interacting substrates is present), then reachability properties are equivalent in the two settings. The analysis of two types of global dynamical properties of DRNs is addressed: irreducibility, i.e., the ability to reach any discrete state from any other state; and recurrence, i.e., the ability to return to any initial state. Our results consider both the verification of such properties when species are present in a large copy number, and in the general case. The necessary and sufficient conditions obtained involve algebraic conditions on the network reactions which in most cases can be verified using linear programming. Finally, the relationship of DRN irreducibility and recurrence with dynamical properties of stochastic and continuous models of reaction networks is discussed.
NASA Astrophysics Data System (ADS)
Wuensche, Andrew
DDLab is interactive graphics software for creating, visualizing, and analyzing many aspects of Cellular Automata, Random Boolean Networks, and Discrete Dynamical Networks in general and studying their behavior, both from the time-series perspective — space-time patterns, and from the state-space perspective — attractor basins. DDLab is relevant to research, applications, and education in the fields of complexity, self-organization, emergent phenomena, chaos, collision-based computing, neural networks, content addressable memory, genetic regulatory networks, dynamical encryption, generative art and music, and the study of the abstract mathematical/physical/dynamical phenomena in their own right.
NASA Astrophysics Data System (ADS)
Calogero, Francesco
2011-08-01
The original continuous-time ''goldfish'' dynamical system is characterized by two neat formulas, the first of which provides the N Newtonian equations of motion of this dynamical system, while the second provides the solution of the corresponding initial-value problem. Several other, more general, solvable dynamical systems ''of goldfish type'' have been identified over time, featuring, in the right-hand (''forces'') side of their Newtonian equations of motion, in addition to other contributions, a velocity-dependent term such as that appearing in the right-hand side of the first formula mentioned above. The solvable character of these models allows detailed analyses of their behavior, which in some cases is quite remarkable (for instance isochronous or asymptotically isochronous). In this paper we introduce and discuss various discrete-time dynamical systems, which are as well solvable, which also display interesting behaviors (including isochrony and asymptotic isochrony) and which reduce to dynamical systems of goldfish type in the limit when the discrete-time independent variable l=0,1,2,... becomes the standard continuous-time independent variable t, 0≤t<∞.
Discrete modelling of drapery systems
NASA Astrophysics Data System (ADS)
Thoeni, Klaus; Giacomini, Anna
2016-04-01
.L., editors. Rockfall: Characterization and Control. Washington, DC: Transportation Research Board, 554-576. Giacomini, A., Thoeni, K., Lambert, C., Booth, S., Sloan, S.W. (2012) Experimental study on rockfall drapery systems for open pit highwalls. International Journal of Rock Mechanics and Mining Sciences 56, 171-181. Šmilauer, V., Catalano, E., Chareyre, B., Dorofenko, S., Duriez, J., Gladky, A., Kozicki, J., Modenese, C., Scholtès, L., Sibille, L., Stránskỳ, J., Thoeni, K. (2010) Yade Documentation. The Yade Project, 1st ed., http://yade-dem.org/doc/. Thoeni, K., Giacomini, A., Lambert, C., Sloan, S.W., Carter, J.P. (2014) A 3D discrete element modelling approach for rockfall analysis with drapery systems. International Journal of Rock Mechanics and Mining Sciences 68, 107-119. Thoeni, K., Lambert, C., Giacomini, A., Sloan, S.W. (2013) Discrete modelling of hexagonal wire meshes with a stochastically distorted contact model. Computers and Geotechnics, 49, 158-69.
DelGrande, J. Mark; Mathews, Kirk A.
2001-09-15
Conventional discrete ordinates transport calculations often produce negative fluxes due to unphysical negative scattering cross sections and/or as artifacts of spatial differencing schemes such as diamond difference. Inherently nonnegative spatial methods, such as the nonlinear, exponential characteristic spatial quadrature, eliminate negative fluxes while providing excellent accuracy, presuming the group-to-group, ordinate-to-ordinate cross sections are all nonnegative. A hybrid approach is introduced in which the flow from spatial cell to spatial cell uses discrete ordinates spatial quadratures, while anisotropic scattering of flux from one energy-angle bin (energy group and discrete element of solid angle) to another such bin is modeled using a Monte Carlo simulation to evaluate the bin-to-bin cross sections. The directional elements tile the sphere of directions; the ordinates for the spatial quadrature are at the centroids of the elements. The method is developed and contrasted with previous schemes for positive cross sections. An algorithm for evaluating the Monte Carlo (MC)-discrete elements (MC-DE) cross sections is described, and some test cases are presented. Transport calculations using MC-DE cross sections are compared with calculations using conventional cross sections and with MCNP calculations. In this testing, the new method is about as accurate as the conventional approach, and often is more accurate. The exponential characteristic spatial quadrature, using the MC-DE cross sections, is shown to provide useful results where linear characteristic and spherical harmonics provide negative scalar fluxes in every cell in a region.
Integrable discrete PT symmetric model.
Ablowitz, Mark J; Musslimani, Ziad H
2014-09-01
An exactly solvable discrete PT invariant nonlinear Schrödinger-like model is introduced. It is an integrable Hamiltonian system that exhibits a nontrivial nonlinear PT symmetry. A discrete one-soliton solution is constructed using a left-right Riemann-Hilbert formulation. It is shown that this pure soliton exhibits unique features such as power oscillations and singularity formation. The proposed model can be viewed as a discretization of a recently obtained integrable nonlocal nonlinear Schrödinger equation.
Nonintegrable Schrodinger discrete breathers.
Gómez-Gardeñes, J; Floría, L M; Peyrard, M; Bishop, A R
2004-12-01
In an extensive numerical investigation of nonintegrable translational motion of discrete breathers in nonlinear Schrödinger lattices, we have used a regularized Newton algorithm to continue these solutions from the limit of the integrable Ablowitz-Ladik lattice. These solutions are shown to be a superposition of a localized moving core and an excited extended state (background) to which the localized moving pulse is spatially asymptotic. The background is a linear combination of small amplitude nonlinear resonant plane waves and it plays an essential role in the energy balance governing the translational motion of the localized core. Perturbative collective variable theory predictions are critically analyzed in the light of the numerical results.
Discrete bisoliton fiber laser
Liu, X. M.; Han, X. X.; Yao, X. K.
2016-01-01
Dissipative solitons, which result from the intricate balance between dispersion and nonlinearity as well as gain and loss, are of the fundamental scientific interest and numerous important applications. Here, we report a fiber laser that generates bisoliton – two consecutive dissipative solitons that preserve a fixed separation between them. Deviations from this separation result in its restoration. It is also found that these bisolitons have multiple discrete equilibrium distances with the quantized separations, as is confirmed by the theoretical analysis and the experimental observations. The main feature of our laser is the anomalous dispersion that is increased by an order of magnitude in comparison to previous studies. Then the spectral filtering effect plays a significant role in pulse-shaping. The proposed laser has the potential applications in optical communications and high-resolution optics for coding and transmission of information in higher-level modulation formats. PMID:27767075
Discrete Minimal Surface Algebras
NASA Astrophysics Data System (ADS)
Arnlind, Joakim; Hoppe, Jens
2010-05-01
We consider discrete minimal surface algebras (DMSA) as generalized noncommutative analogues of minimal surfaces in higher dimensional spheres. These algebras appear naturally in membrane theory, where sequences of their representations are used as a regularization. After showing that the defining relations of the algebra are consistent, and that one can compute a basis of the enveloping algebra, we give several explicit examples of DMSAs in terms of subsets of sln (any semi-simple Lie algebra providing a trivial example by itself). A special class of DMSAs are Yang-Mills algebras. The representation graph is introduced to study representations of DMSAs of dimension d ≤ 4, and properties of representations are related to properties of graphs. The representation graph of a tensor product is (generically) the Cartesian product of the corresponding graphs. We provide explicit examples of irreducible representations and, for coinciding eigenvalues, classify all the unitary representations of the corresponding algebras.
Discrete Pearson distributions
Bowman, K.O. ); Shenton, L.R. ); Kastenbaum, M.A. , Basye, VA )
1991-11-01
These distributions are generated by a first order recursive scheme which equates the ratio of successive probabilities to the ratio of two corresponding quadratics. The use of a linearized form of this model will produce equations in the unknowns matched by an appropriate set of moments (assumed to exist). Given the moments we may find valid solutions. These are two cases; (1) distributions defined on the non-negative integers (finite or infinite) and (2) distributions defined on negative integers as well. For (1), given the first four moments, it is possible to set this up as equations of finite or infinite degree in the probability of a zero occurrence, the sth component being a product of s ratios of linear forms in this probability in general. For (2) the equation for the zero probability is purely linear but may involve slowly converging series; here a particular case is the discrete normal. Regions of validity are being studied. 11 refs.
Noyes, H.P. ); Starson, S. )
1991-03-01
Discrete physics, because it replaces time evolution generated by the energy operator with a global bit-string generator (program universe) and replaces fields'' with the relativistic Wheeler-Feynman action at a distance,'' allows the consistent formulation of the concept of signed gravitational charge for massive particles. The resulting prediction made by this version of the theory is that free anti-particles near the surface of the earth will fall'' up with the same acceleration that the corresponding particles fall down. So far as we can see, no current experimental information is in conflict with this prediction of our theory. The experiment crusis will be one of the anti-proton or anti-hydrogen experiments at CERN. Our prediction should be much easier to test than the small effects which those experiments are currently designed to detect or bound. 23 refs.
ERIC Educational Resources Information Center
Pearson, Judith
This book presents concerns and raises questions about the choice programs being proposed and implemented around the United States. It argues that poorly conceived, hastily enacted choice programs may do more harm than good. The demand for educational choice may result in lost opportunities for students (some groups more than others), weakened…
Privatization and Educational Choice.
ERIC Educational Resources Information Center
Lieberman, Myron
This book describes how and why educational choice movements will affect public education. It uses a public-choice approach to argue that both the supporters and opponents of private and school choice have failed to address several critical issues. Following an introductory chapter, chapter 2 is devoted to the rationale for contracting out…
Some unsolved problems in discrete mathematics and mathematical cybernetics
NASA Astrophysics Data System (ADS)
Korshunov, Aleksei D.
2009-10-01
There are many unsolved problems in discrete mathematics and mathematical cybernetics. Writing a comprehensive survey of such problems involves great difficulties. First, such problems are rather numerous and varied. Second, they greatly differ from each other in degree of completeness of their solution. Therefore, even a comprehensive survey should not attempt to cover the whole variety of such problems; only the most important and significant problems should be reviewed. An impersonal choice of problems to include is quite hard. This paper includes 13 unsolved problems related to combinatorial mathematics and computational complexity theory. The problems selected give an indication of the author's studies for 50 years; for this reason, the choice of the problems reviewed here is, to some extent, subjective. At the same time, these problems are very difficult and quite important for discrete mathematics and mathematical cybernetics. Bibliography: 74 items.
Optical tomography with discretized path integral
Yuan, Bingzhi; Tamaki, Toru; Kushida, Takahiro; Mukaigawa, Yasuhiro; Kubo, Hiroyuki; Raytchev, Bisser; Kaneda, Kazufumi
2015-01-01
Abstract. We present a framework for optical tomography based on a path integral. Instead of directly solving the radiative transport equations, which have been widely used in optical tomography, we use a path integral that has been developed for rendering participating media based on the volume rendering equation in computer graphics. For a discretized two-dimensional layered grid, we develop an algorithm to estimate the extinction coefficients of each voxel with an interior point method. Numerical simulation results are shown to demonstrate that the proposed method works well. PMID:26839903
Discrete Mathematics and Its Applications
ERIC Educational Resources Information Center
Oxley, Alan
2010-01-01
The article gives ideas that lecturers of undergraduate Discrete Mathematics courses can use in order to make the subject more interesting for students and encourage them to undertake further studies in the subject. It is possible to teach Discrete Mathematics with little or no reference to computing. However, students are more likely to be…
Khan, M M; Varma, M P; Cleland, J; O'Kane, H O; Webb, S W; Mulholland, H C; Adgey, A A
1981-01-01
Data concerning 17 consecutive patients with discrete subaortic stenosis are recorded. Twelve patients underwent operative resection of the obstructing lesion. Of these all except one were symptomatic and all had electrocardiographic evidence of left ventricular hypertrophy or left ventricular hypertrophy with strain. They had a peak resting systolic left ventricular outflow tract gradient of greater than 50 mmHg as predicted from the combined cuff measurement of systolic blood pressure and the echocardiographically estimated left ventricular systolic pressure and/or as determined by cardiac catheterisation. The outflow tract gradient as predicted from M-mode echocardiography and peak systolic pressure showed close correlation with that measured at cardiac catheterisation or operation. During the postoperative follow-up from one month to 11 years, of 11 patients, one patient required a further operation for recurrence of the obstruction four years after the initial operation. All patients are now asymptomatic. Five patients have not had an operation. The left ventricular outflow tract gradient as assessed at the time of cardiac catheterisation was greater than 50 mmHg. One patient has been lost to follow-up. The remaining four have been followed from four to eight years and have remained asymptomatic and the electrocardiograms have remained unchanged. Careful follow-up of all patients is essential with continuing clinical assessment, electrocardiograms, M-mode and two-dimensional echocardiograms, and if necessary cardiac catheterisation. Prophylaxis against bacterial endocarditis is also essential. Images PMID:6457617
Discreteness inducing coexistence
NASA Astrophysics Data System (ADS)
dos Santos, Renato Vieira
2013-12-01
Consider two species that diffuse through space. Consider further that they differ only in initial densities and, possibly, in diffusion constants. Otherwise they are identical. What happens if they compete with each other in the same environment? What is the influence of the discrete nature of the interactions on the final destination? And what are the influence of diffusion and additive fluctuations corresponding to random migration and immigration of individuals? This paper aims to answer these questions for a particular competition model that incorporates intra and interspecific competition between the species. Based on mean field theory, the model has a stationary state dependent on the initial density conditions. We investigate how this initial density dependence is affected by the presence of demographic multiplicative noise and additive noise in space and time. There are three main conclusions: (1) Additive noise favors denser populations at the expense of the less dense, ratifying the competitive exclusion principle. (2) Demographic noise, on the other hand, favors less dense populations at the expense of the denser ones, inducing equal densities at the quasi-stationary state, violating the aforementioned principle. (3) The slower species always suffers the more deleterious effects of statistical fluctuations in a homogeneous medium.
Discrete Darboux transformation for discrete polynomials of hypergeometric type
NASA Astrophysics Data System (ADS)
Bangerezako, Gaspard
1998-03-01
The Darboux transformation, well known in second-order differential operator theory, is applied to the difference equations satisfied by the discrete hypergeometric polynomials (Charlier, Meixner-Kravchuk, Hahn).
Discrete Dirac Structures and Implicit Discrete Lagrangian and Hamiltonian Systems
NASA Astrophysics Data System (ADS)
Leok, Melvin; Ohsawa, Tomoki
2010-07-01
We present discrete analogues of Dirac structures and the Tulczyjew's triple by considering the geometry of symplectic maps and their associated generating functions. We demonstrate that this framework provides a means of deriving discrete analogues of implicit Lagrangian and Hamiltonian systems. In particular, this yields implicit nonholonomic Lagrangian and Hamiltonian integrators. We also introduce discrete Lagrange-d'Alembert-Pontryagin and Hamilton-d'Alembert variational principles, which provide an alternative derivation of the same set of integration algorithms. In addition to providing a unified treatment of discrete Lagrangian and Hamiltonian mechanics in the more general setting of Dirac mechanics, it provides a generalization of symplectic and Poisson integrators to the broader category of Dirac integrators.
Automatic Mesh Coarsening for Discrete Ordinates Codes
Turner, Scott A.
1999-03-11
This paper describes the use of a ''mesh potential'' function for automatic coarsening of meshes in discrete ordinates neutral particle transport codes. For many transport calculations, a user may find it helpful to have the code determine a ''good'' neutronics mesh. The complexity of a problem involving millions of mesh cells, dozens of materials, and many energy groups makes it difficult to determine an adequate level of mesh refinement with a minimum number of cells. A method has been implemented in PARTISN (Parallel Time-dependent SN) to calculate a ''mesh potential'' in each original cell of a problem, and use this information to determine the maximum coarseness allowed in the mesh while maintaining accuracy in the solution. Results are presented for a simple x-y-z fuel/control/reflector problem.
Novel approach to data discretization
NASA Astrophysics Data System (ADS)
Borowik, Grzegorz; Kowalski, Karol; Jankowski, Cezary
2015-09-01
Discretization is an important preprocessing step in data mining. The data discretization method involves determining the ranges of values for numeric attributes, which ultimately represent discrete intervals for new attributes. The ranges for the proposed set of cuts are analyzed, in order to obtain a minimal set of ranges while retaining the possibility of classification. For this purpose, a special discernibility function can be constructed as a conjunction of alternative cuts set for each pair of different objects of different decisions- cuts discern these objects. However, the data mining methods based on discernibility matrix are insufficient for large databases. The purpose of this paper is the idea of implementation of a new data discretization algorithm that is based on statistics of attribute values and that avoids building the discernibility matrix explicitly. Evaluation of time complexity has shown that the proposed method is much more efficient than currently available solutions for large data sets.
40 CFR 152.111 - Choice of standards for review of applications.
Code of Federal Regulations, 2010 CFR
2010-07-01
... 40 Protection of Environment 23 2010-07-01 2010-07-01 false Choice of standards for review of applications. 152.111 Section 152.111 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED....111 Choice of standards for review of applications. The Agency has discretion to review...
Concurrency and discrete event control
NASA Technical Reports Server (NTRS)
Heymann, Michael
1990-01-01
Much of discrete event control theory has been developed within the framework of automata and formal languages. An alternative approach inspired by the theories of process-algebra as developed in the computer science literature is presented. The framework, which rests on a new formalism of concurrency, can adequately handle nondeterminism and can be used for analysis of a wide range of discrete event phenomena.
Discrete photonics in waveguide arrays.
Moison, J M; Belabas, N; Minot, C; Levenson, J A
2009-08-15
In homogeneous arrays of coupled waveguides, Floquet-Bloch waves are known to travel freely across the waveguides. We introduce a systematic discussion of the built-in patterning of the coupling constant between neighboring waveguides. Key patterns provide functions such as redirecting, guiding, and focusing these waves, up to nonlinear all-optical routing. This opens the way to light control in a functionalized discrete space, i.e., discrete photonics.
MEDICAL EXPENDITURE RISK AND HOUSEHOLD PORTFOLIO CHOICE
Goldman, Dana
2013-01-01
Medical expenses are an increasingly important contributor to household financial risk. We examine the effect of medical expenditure risk on the willingness of Medicare beneficiaries to hold risky assets. Using a discrete factor maximum likelihood method to address the endogeneity of insurance choices, we find that having a moderately protective Medigap or employer supplemental policy increases risky asset holding by 7.1 percentage points relative to those without supplemental coverage, while participation in a highly protective Medicare HMO increases risky asset holding by 13.0 percentage points. Our results highlight an important link between the availability of health insurance and financial behavior. PMID:23997424
ERIC Educational Resources Information Center
DeArmond, Michael; Jochim, Ashley; Lake, Robin
2014-01-01
School choice is increasingly the new normal in urban education. But in cities with multiple public school options, how can civic leaders create a choice system that works for all families, whether they choose a charter or district public school? To answer this question, the Center on Reinventing Public Education (CRPE) researchers surveyed 4,000…
ERIC Educational Resources Information Center
Dills, Angela K.; Hernandez-Julian, Rey
2011-01-01
Previous research debates whether public school choice improves students' academic outcomes, but there is little examination of its effects on their nonacademic outcomes. We use data from a nationally representative sample of high school students, a previously developed Tiebout choice measure, and metropolitan-level data on teenage arrest rates to…
ERIC Educational Resources Information Center
Gastic, Billie; Coronado, Diana Salas
2011-01-01
The authors describe how Latino students are underrepresented in public schools of choice. They provide evidence to refute the claim that Latino students who choose to leave assigned public schools enroll in religious schools instead. Charter schools stand out as the type of public schools of choice where Latino students are well represented.…
ERIC Educational Resources Information Center
Chitty, Clyde
2004-01-01
Both New Labour and the Conservatives are keen to emphasise choice and diversity in crucial areas of public provision--and particularly with regard to education and health. In this article, "FORUM" co-Editor Clyde Chitty concentrates on recent proposals by the two main parties for promoting greater choice in secondary schooling in England. This…
Table of Contents Your Genes, Your Choices describes the Human Genome Project, the science behind it, and the ethical, legal, and social issues that are ... Nothing could be further from the truth. Your Genes, Your Choices points out how the progress of ...
ERIC Educational Resources Information Center
Butcher, Jonathan
2013-01-01
One year ago, the "Wall Street Journal" dubbed 2011 "the year of school choice," opining that "this year is shaping up as the best for reformers in a very long time." School-choice laws took great strides in 2011, both in the number of programs that succeeded across states and also in the size and scope of the adopted programs. Yet education…
Choice: The Historical Perspective.
ERIC Educational Resources Information Center
Wagoner, Jennings L., Jr.
The issue of choice in U.S. education is traced historically. Consideration is given to the purposes of publicly supported education and reasons underlying the historic distinction between public and private education. It is suggested that the issue of choice concerns the rights and obligations of the individual and the state. The relationship…
Discrete Diffusion Monte Carlo for grey Implicit Monte Carlo simulations.
Densmore, J. D.; Urbatsch, T. J.; Evans, T. M.; Buksas, M. W.
2005-01-01
Discrete Diffusion Monte Carlo (DDMC) is a hybrid transport-diffusion method for Monte Carlo simulations in diffusive media. In DDMC, particles take discrete steps between spatial cells according to a discretized diffusion equation. Thus, DDMC produces accurate solutions while increasing the efficiency of the Monte Carlo calculation. In this paper, we extend previously developed DDMC techniques in several ways that improve the accuracy and utility of DDMC for grey Implicit Monte Carlo calculations. First, we employ a diffusion equation that is discretized in space but is continuous time. Not only is this methodology theoretically more accurate than temporally discretized DDMC techniques, but it also has the benefit that a particle's time is always known. Thus, there is no ambiguity regarding what time to assign a particle that leaves an optically thick region (where DDMC is used) and begins transporting by standard Monte Carlo in an optically thin region. In addition, we treat particles incident on an optically thick region using the asymptotic diffusion-limit boundary condition. This interface technique can produce accurate solutions even if the incident particles are distributed anisotropically in angle. Finally, we develop a method for estimating radiation momentum deposition during the DDMC simulation. With a set of numerical examples, we demonstrate the accuracy and efficiency of our improved DDMC method.
Steenfeldt-Kristensen, Catherine; Thornton, Ian M.
2013-01-01
Choice blindness is the failure to notice a mismatch between intention and outcome when making decisions. It is unknown whether choice blindness occurs when participants have extended interaction with real objects. Here, we examined the case when objects could be touched but not seen. Participants examined pairs of common, everyday objects inside a specially constructed box where a silent turntable was used to switch objects between initial choice and later justification. For similar pairs of objects, we found detection rates of around 22%, consistent with previous studies of choice blindness. For pairs consisting of more distinctive exemplars, the detection rate rose to 70%. Our results indicate that choice blindness does occur after haptic interaction with real objects, but is strongly modulated by similarity. PMID:23799197
Design and analysis of simple choice surveys for natural resource management
Fieberg, John; Cornicelli, Louis; Fulton, David C.; Grund, Marrett D.
2010-01-01
We used a simple yet powerful method for judging public support for management actions from randomized surveys. We asked respondents to rank choices (representing management regulations under consideration) according to their preference, and we then used discrete choice models to estimate probability of choosing among options (conditional on the set of options presented to respondents). Because choices may share similar unmodeled characteristics, the multinomial logit model, commonly applied to discrete choice data, may not be appropriate. We introduced the nested logit model, which offers a simple approach for incorporating correlation among choices. This forced choice survey approach provides a useful method of gathering public input; it is relatively easy to apply in practice, and the data are likely to be more informative than asking constituents to rate attractiveness of each option separately.
Using Decision Trees for Estimating Mode Choice of Trips in Buca-Izmir
NASA Astrophysics Data System (ADS)
Oral, L. O.; Tecim, V.
2013-05-01
Decision makers develop transportation plans and models for providing sustainable transport systems in urban areas. Mode Choice is one of the stages in transportation modelling. Data mining techniques can discover factors affecting the mode choice. These techniques can be applied with knowledge process approach. In this study a data mining process model is applied to determine the factors affecting the mode choice with decision trees techniques by considering individual trip behaviours from household survey data collected within Izmir Transportation Master Plan. From this perspective transport mode choice problem is solved on a case in district of Buca-Izmir, Turkey with CRISP-DM knowledge process model.
NASA Astrophysics Data System (ADS)
Karimi-Fard, M.; Durlofsky, L. J.
2016-10-01
A comprehensive framework for modeling flow in porous media containing thin, discrete features, which could be high-permeability fractures or low-permeability deformation bands, is presented. The key steps of the methodology are mesh generation, fine-grid discretization, upscaling, and coarse-grid discretization. Our specialized gridding technique combines a set of intersecting triangulated surfaces by constructing approximate intersections using existing edges. This procedure creates a conforming mesh of all surfaces, which defines the internal boundaries for the volumetric mesh. The flow equations are discretized on this conforming fine mesh using an optimized two-point flux finite-volume approximation. The resulting discrete model is represented by a list of control-volumes with associated positions and pore-volumes, and a list of cell-to-cell connections with associated transmissibilities. Coarse models are then constructed by the aggregation of fine-grid cells, and the transmissibilities between adjacent coarse cells are obtained using flow-based upscaling procedures. Through appropriate computation of fracture-matrix transmissibilities, a dual-continuum representation is obtained on the coarse scale in regions with connected fracture networks. The fine and coarse discrete models generated within the framework are compatible with any connectivity-based simulator. The applicability of the methodology is illustrated for several two- and three-dimensional examples. In particular, we consider gas production from naturally fractured low-permeability formations, and transport through complex fracture networks. In all cases, highly accurate solutions are obtained with significant model reduction.
Distributed Relaxation for Conservative Discretizations
NASA Technical Reports Server (NTRS)
Diskin, Boris; Thomas, James L.
2001-01-01
A multigrid method is defined as having textbook multigrid efficiency (TME) if the solutions to the governing system of equations are attained in a computational work that is a small (less than 10) multiple of the operation count in one target-grid residual evaluation. The way to achieve this efficiency is the distributed relaxation approach. TME solvers employing distributed relaxation have already been demonstrated for nonconservative formulations of high-Reynolds-number viscous incompressible and subsonic compressible flow regimes. The purpose of this paper is to provide foundations for applications of distributed relaxation to conservative discretizations. A direct correspondence between the primitive variable interpolations for calculating fluxes in conservative finite-volume discretizations and stencils of the discretized derivatives in the nonconservative formulation has been established. Based on this correspondence, one can arrive at a conservative discretization which is very efficiently solved with a nonconservative relaxation scheme and this is demonstrated for conservative discretization of the quasi one-dimensional Euler equations. Formulations for both staggered and collocated grid arrangements are considered and extensions of the general procedure to multiple dimensions are discussed.
Discrete event simulation of continuous systems
Nutaro, James J
2007-01-01
Computer simulation of a system described by differential equations requires that some element of the system be approximated by discrete quantities. There are two system aspects that can be made discrete; time and state. When time is discrete, the differential equation is approximated by a difference equation (i.e., a discrete time system), and the solution is calculated at fixed points in time. When the state is discrete, the differential equation is approximated by a discrete event system. Events correspond to jumps through the discrete state space of the approximation.
Educational Choice: Practical Policy Questions. Occasional Paper Series No. 7.
ERIC Educational Resources Information Center
First, Patricia F.
The consideration of school choice plans raises policy questions for school administrators. This paper addresses pragmatic concerns about definitions and policy questions related to educational finance. Interdistrict choice, emphasizing families' right to choose among existing public schools, raises questions regarding transportation and…
PEER REVIEW FOR THE CONSUMER VEHICLE CHOICE MODEL
The U.S. Environmental Protection Agency’s (EPA) Office of Transportation and Air Quality (OTAQ) has recently sponsored the development of a Consumer Vehicle Choice Model (CVCM) by the Oak Ridge National Laboratory (ORNL). The specification by OTAQ to ORNL for consumer choice mod...
Geometry of discrete quantum computing
NASA Astrophysics Data System (ADS)
Hanson, Andrew J.; Ortiz, Gerardo; Sabry, Amr; Tai, Yu-Tsung
2013-05-01
Conventional quantum computing entails a geometry based on the description of an n-qubit state using 2n infinite precision complex numbers denoting a vector in a Hilbert space. Such numbers are in general uncomputable using any real-world resources, and, if we have the idea of physical law as some kind of computational algorithm of the universe, we would be compelled to alter our descriptions of physics to be consistent with computable numbers. Our purpose here is to examine the geometric implications of using finite fields Fp and finite complexified fields \\mathbf {F}_{p^2} (based on primes p congruent to 3 (mod4)) as the basis for computations in a theory of discrete quantum computing, which would therefore become a computable theory. Because the states of a discrete n-qubit system are in principle enumerable, we are able to determine the proportions of entangled and unentangled states. In particular, we extend the Hopf fibration that defines the irreducible state space of conventional continuous n-qubit theories (which is the complex projective space \\mathbf {CP}^{2^{n}-1}) to an analogous discrete geometry in which the Hopf circle for any n is found to be a discrete set of p + 1 points. The tally of unit-length n-qubit states is given, and reduced via the generalized Hopf fibration to \\mathbf {DCP}^{2^{n}-1}, the discrete analogue of the complex projective space, which has p^{2^{n}-1} (p-1)\\,\\prod _{k=1}^{n-1} ( p^{2^{k}}+1) irreducible states. Using a measure of entanglement, the purity, we explore the entanglement features of discrete quantum states and find that the n-qubit states based on the complexified field \\mathbf {F}_{p^2} have pn(p - 1)n unentangled states (the product of the tally for a single qubit) with purity 1, and they have pn + 1(p - 1)(p + 1)n - 1 maximally entangled states with purity zero.
Discrete Element Modelling of Floating Debris
NASA Astrophysics Data System (ADS)
Mahaffey, Samantha; Liang, Qiuhua; Parkin, Geoff; Large, Andy; Rouainia, Mohamed
2016-04-01
Flash flooding is characterised by high velocity flows which impact vulnerable catchments with little warning time and as such, result in complex flow dynamics which are difficult to replicate through modelling. The impacts of flash flooding can be made yet more severe by the transport of both natural and anthropogenic debris, ranging from tree trunks to vehicles, wheelie bins and even storage containers, the effects of which have been clearly evident during recent UK flooding. This cargo of debris can have wide reaching effects and result in actual flood impacts which diverge from those predicted. A build-up of debris may lead to partial channel blockage and potential flow rerouting through urban centres. Build-up at bridges and river structures also leads to increased hydraulic loading which may result in damage and possible structural failure. Predicting the impacts of debris transport; however, is difficult as conventional hydrodynamic modelling schemes do not intrinsically include floating debris within their calculations. Subsequently a new tool has been developed using an emerging approach, which incorporates debris transport through the coupling of two existing modelling techniques. A 1D hydrodynamic modelling scheme has here been coupled with a 2D discrete element scheme to form a new modelling tool which predicts the motion and flow-interaction of floating debris. Hydraulic forces arising from flow around the object are applied to instigate its motion. Likewise, an equivalent opposing force is applied to fluid cells, enabling backwater effects to be simulated. Shock capturing capabilities make the tool applicable to predicting the complex flow dynamics associated with flash flooding. The modelling scheme has been applied to experimental case studies where cylindrical wooden dowels are transported by a dam-break wave. These case studies enable validation of the tool's shock capturing capabilities and the coupling technique applied between the two numerical
Intertemporal choice in lemurs.
Stevens, Jeffrey R; Mühlhoff, Nelly
2012-02-01
Different species vary in their ability to wait for delayed rewards in intertemporal choice tasks. Models of rate maximization account for part of this variation, but other factors such as social structure and feeding ecology seem to underly some species differences. Though studies have evaluated intertemporal choice in several primate species, including Old World monkeys, New World monkeys, and apes, prosimians have not been tested. This study investigated intertemporal choices in three species of lemur (black-and-white ruffed lemurs, Varecia variegata, red ruffed lemurs, Varecia rubra, and black lemurs, Eulemur macaco) to assess how they compare to other primate species and whether their choices are consistent with rate maximization. We offered lemurs a choice between two food items available immediately and six food items available after a delay. We found that by adjusting the delay to the larger reward, the lemurs were indifferent between the two options at a mean delay of 17 s, ranging from 9 to 25 s. These data are comparable to data collected from common marmosets (Callithrix jacchus). The lemur data were not consistent with models of rate maximization. The addition of lemurs to the list of species tested in these tasks will help uncover the role of life history and socio-ecological factors influencing intertemporal choices. PMID:22024661
Discrete cloud structure on Neptune
NASA Astrophysics Data System (ADS)
Hammel, H. B.
1989-07-01
Recent CCD imaging data for the discrete cloud structure of Neptune shows that while cloud features at CH4-band wavelengths are manifest in the southern hemisphere, they have not been encountered in the northern hemisphere since 1986. A literature search has shown the reflected CH4-band light from the planet to have come from a single discrete feature at least twice in the last 10 years. Disk-integrated photometry derived from the imaging has demonstrated that a bright cloud feature was responsible for the observed 8900 A diurnal variation in 1986 and 1987.
Stochastic discrete model of karstic networks
NASA Astrophysics Data System (ADS)
Jaquet, O.; Siegel, P.; Klubertanz, G.; Benabderrhamane, H.
Karst aquifers are characterised by an extreme spatial heterogeneity that strongly influences their hydraulic behaviour and the transport of pollutants. These aquifers are particularly vulnerable to contamination because of their highly permeable networks of conduits. A stochastic model is proposed for the simulation of the geometry of karstic networks at a regional scale. The model integrates the relevant physical processes governing the formation of karstic networks. The discrete simulation of karstic networks is performed with a modified lattice-gas cellular automaton for a representative description of the karstic aquifer geometry. Consequently, more reliable modelling results can be obtained for the management and the protection of karst aquifers. The stochastic model was applied jointly with groundwater modelling techniques to a regional karst aquifer in France for the purpose of resolving surface pollution issues.
Hyperbolic value addition and general models of animal choice.
Mazur, J E
2001-01-01
Three mathematical models of choice--the contextual-choice model (R. Grace, 1994), delay-reduction theory (N. Squires & E. Fantino, 1971), and a new model called the hyperbolic value-added model--were compared in their ability to predict the results from a wide variety of experiments with animal subjects. When supplied with 2 or 3 free parameters, all 3 models made fairly accurate predictions for a large set of experiments that used concurrent-chain procedures. One advantage of the hyperbolic value-added model is that it is derived from a simpler model that makes accurate predictions for many experiments using discrete-trial adjusting-delay procedures. Some results favor the hyperbolic value-added model and delay-reduction theory over the contextual-choice model, but more data are needed from choice situations for which the models make distinctly different predictions.
Some discrete multiple orthogonal polynomials
NASA Astrophysics Data System (ADS)
Arvesú, J.; Coussement, J.; van Assche, W.
2003-04-01
In this paper, we extend the theory of discrete orthogonal polynomials (on a linear lattice) to polynomials satisfying orthogonality conditions with respect to r positive discrete measures. First we recall the known results of the classical orthogonal polynomials of Charlier, Meixner, Kravchuk and Hahn (T.S. Chihara, An Introduction to Orthogonal Polynomials, Gordon and Breach, New York, 1978; R. Koekoek and R.F. Swarttouw, Reports of the Faculty of Technical Mathematics and Informatics No. 98-17, Delft, 1998; A.F. Nikiforov et al., Classical Orthogonal Polynomials of a Discrete Variable, Springer, Berlin, 1991). These polynomials have a lowering and raising operator, which give rise to a Rodrigues formula, a second order difference equation, and an explicit expression from which the coefficients of the three-term recurrence relation can be obtained. Then we consider r positive discrete measures and define two types of multiple orthogonal polynomials. The continuous case (Jacobi, Laguerre, Hermite, etc.) was studied by Van Assche and Coussement (J. Comput. Appl. Math. 127 (2001) 317-347) and Aptekarev et al. (Multiple orthogonal polynomials for classical weights, manuscript). The families of multiple orthogonal polynomials (of type II) that we will study have a raising operator and hence a Rodrigues formula. This will give us an explicit formula for the polynomials. Finally, there also exists a recurrence relation of order r+1 for these multiple orthogonal polynomials of type II. We compute the coefficients of the recurrence relation explicitly when r=2.
Arons, Alexander M M; Krabbe, Paul F M
2013-02-01
Interest is rising in measuring subjective health outcomes, such as treatment outcomes that are not directly quantifiable (functional disability, symptoms, complaints, side effects and health-related quality of life). Health economists in particular have applied probabilistic choice models in the area of health evaluation. They increasingly use discrete choice models based on random utility theory to derive values for healthcare goods or services. Recent attempts have been made to use discrete choice models as an alternative method to derive values for health states. In this article, various probabilistic choice models are described according to their underlying theory. A historical overview traces their development and applications in diverse fields. The discussion highlights some theoretical and technical aspects of the choice models and their similarity and dissimilarity. The objective of the article is to elucidate the position of each model and their applications for health-state valuation.
Choice and conditioned reinforcement.
Fantino, E; Freed, D; Preston, R A; Williams, W A
1991-03-01
A potential weakness of one formulation of delay-reduction theory is its failure to include a term for rate of conditioned reinforcement, that is, the rate at which the terminal-link stimuli occur in concurrent-chains schedules. The present studies assessed whether or not rate of conditioned reinforcement has an independent effect upon choice. Pigeons responded on either modified concurrent-chains schedules or on comparable concurrent-tandem schedules. The initial link was shortened on only one of two concurrent-chains schedules and on only one of two corresponding concurrent-tandem schedules. This manipulation increased rate of conditioned reinforcement sharply in the chain but not in the tandem schedule. According to a formulation of delay-reduction theory, when the outcomes chosen (the terminal links) are equal, as in Experiment 1, choice should depend only on rate of primary reinforcement; thus, choice should be equivalent for the tandem and chain schedules despite a large difference in rate of conditioned reinforcement. When the outcomes chosen are unequal, however, as in Experiment 2, choice should depend upon both rate of primary reinforcement and relative signaled delay reduction; thus, larger preferences should occur in the chain than in the tandem schedules. These predictions were confirmed, suggesting that increasing the rate of conditioned reinforcement on concurrent-chains schedules may have no independent effect on choice.
ERIC Educational Resources Information Center
Thomson, Kendra; Martin, Garry L.; Arnal, Lindsay; Fazzio, Daniela; Yu, C. T.
2009-01-01
Early intensive behavioral intervention (EIBI) has been identified as the treatment of choice for children with autism spectrum disorders. A common strategy for conducting EIBI is discrete-trials teaching (DTT). There is a demand for research-based, economical, rapid training techniques to teach tutors and parents of children with autism to…
Molar and molecular views of choice.
Baum, William M
2004-06-30
The molar and molecular views of behavior are not different theories or levels of analysis; they are different paradigms. The molecular paradigm views behavior as composed of discrete units (responses) occurring at moments in time and strung together in chains to make up complex performances. The discrete pieces are held together as a result of association by contiguity. The molecular view has a long history both in early thought about reflexes and in associationism, and, although it was helpful to getting a science of behavior started, it has outlived its usefulness. The molar view stems from a conviction that behavior is continuous, as argued by John Dewey, Gestalt psychologists, Karl Lashley, and others. The molar paradigm views behavior as inherently extended in time and composed of activities that have integrated parts. In the molar paradigm, activities vary in their scale of organization--i.e., as to whether they are local or extended--and behavior may be controlled sometimes by short-term relations and sometimes by long-term relations. Applied to choice, the molar paradigm rests on two simple principles: (a) all behavior constitutes choice; and (b) all activities take time. Equivalence between choice and behavior occurs because every situation contains more than one alternative activity. The principle that behavior takes time refers not simply to any notion of response duration, but to the necessity that identifying one action or another requires a sample extended in time. The molecular paradigm's momentary responses are inferred from extended samples in retrospect. In this sense, momentary responses constitute abstractions, whereas extended activities constitute concrete particulars. Explanations conceived within the molecular paradigm invariably involve hypothetical constructs, because they require causes to be contiguous with responses. Explanations conceived within the molar paradigm retain direct contact with observable variables.
Distributed mean curvature on a discrete manifold for Regge calculus
NASA Astrophysics Data System (ADS)
Conboye, Rory; Miller, Warner A.; Ray, Shannon
2015-09-01
The integrated mean curvature of a simplicial manifold is well understood in both Regge Calculus and Discrete Differential Geometry. However, a well motivated pointwise definition of curvature requires a careful choice of the volume over which to uniformly distribute the local integrated curvature. We show that hybrid cells formed using both the simplicial lattice and its circumcentric dual emerge as a remarkably natural structure for the distribution of this local integrated curvature. These hybrid cells form a complete tessellation of the simplicial manifold, contain a geometric orthonormal basis, and are also shown to give a pointwise mean curvature with a natural interpretation as the fractional rate of change of the normal vector.
Measuring improved patient choice.
Holmes-Rovner, M; Rovner, D R
2000-08-01
Patient decision support (PDS) tools or decision aids have been developed as adjuncts to the clinical encounter. Their aim is to support evidence-based patient choice. Clinical trials of PDS tools have used an array of outcome measures to determine efficacy, including knowledge, satisfaction, health status and consistency between patient choice and values. This paper proposes that the correlation between 'subjective expected utility' (SEU) and decision may be the best primary endpoint for trials. SEU is a measure usually used in behavioural decision theory. The paper first describes how decision support tools may use decision analysis to structure the presentation of evidence and guide patient decision-making. Uses of expected utility (EU) are suggested for evaluating PDS tools when improving population health status is the objective. SEU is the theoretically better measure when internal consistency of patient choices is the objective. PMID:11083037
Naqvi, Hassan R; Mathur, Shawn; Covarrubias, David; Curcio, Josephine A; Schmidt, Christian
2008-01-01
Convictions are a driving force for actions. Considering that every individual has a different set of convictions and larger groups act once a consensus decision is reached, one can see that debate is an inherent exercise in decision-making. This requires a sustainably generated surplus to allow time for intellectual exchange, gathering of information and dissemination of findings. It is essential that the full spectrum of options remain treated equally. At the end of this process, a choice has to be made. Looking back at a later time point, a retrospective analysis sometimes reveals that the choice was neither completely free nor a truly conscious one. Leaving the issue of consequences of a once made decision aside, we wish to contribute to the debate of the problem of choice. PMID:19025607
Choosing health, constrained choices.
Chee Khoon Chan
2009-12-01
In parallel with the neo-liberal retrenchment of the welfarist state, an increasing emphasis on the responsibility of individuals in managing their own affairs and their well-being has been evident. In the health arena for instance, this was a major theme permeating the UK government's White Paper Choosing Health: Making Healthy Choices Easier (2004), which appealed to an ethos of autonomy and self-actualization through activity and consumption which merited esteem. As a counterpoint to this growing trend of informed responsibilization, constrained choices (constrained agency) provides a useful framework for a judicious balance and sense of proportion between an individual behavioural focus and a focus on societal, systemic, and structural determinants of health and well-being. Constrained choices is also a conceptual bridge between responsibilization and population health which could be further developed within an integrative biosocial perspective one might refer to as the social ecology of health and disease.
Sebastian Schunert; Yousry Y. Azmy; Damien Fournier
2011-05-01
We present a comprehensive error estimation of four spatial discretization schemes of the two-dimensional Discrete Ordinates (SN) equations on Cartesian grids utilizing a Method of Manufactured Solution (MMS) benchmark suite based on variants of Larsen’s benchmark featuring different orders of smoothness of the underlying exact solution. The considered spatial discretization schemes include the arbitrarily high order transport methods of the nodal (AHOTN) and characteristic (AHOTC) types, the discontinuous Galerkin Finite Element method (DGFEM) and the recently proposed higher order diamond difference method (HODD) of spatial expansion orders 0 through 3. While AHOTN and AHOTC rely on approximate analytical solutions of the transport equation within a mesh cell, DGFEM and HODD utilize a polynomial expansion to mimick the angular flux profile across each mesh cell. Intuitively, due to the higher degree of analyticity, we expect AHOTN and AHOTC to feature superior accuracy compared with DGFEM and HODD, but at the price of potentially longer grind times and numerical instabilities. The latter disadvantages can result from the presence of exponential terms evaluated at the cell optical thickness that arise from the semianalytical solution process. This work quantifies the order of accuracy and the magnitude of the error of all four discretization methods for different optical thicknesses, scattering ratios and degrees of smoothness of the underlying exact solutions in order to verify or contradict the aforementioned intuitive expectation.
Serotonergic Genotypes, Neuroticism, and Financial Choices
Kuhnen, Camelia M.; Samanez-Larkin, Gregory R.; Knutson, Brian
2013-01-01
Life financial outcomes carry a significant heritable component, but the mechanisms by which genes influence financial choices remain unclear. Focusing on a polymorphism in the promoter region of the serotonin transporter gene (5-HTTLPR), we found that individuals possessing the short allele of this gene invested less in equities, were less engaged in actively making investment decisions, and had fewer credit lines. Short allele carriers also showed higher levels of the personality trait neuroticism, despite not differing from others with respect to cognitive skills, education, or wealth. Mediation analysis suggested that the presence of the 5-HTTLPR short allele decreased real life measures of financial risk taking through its influence on neuroticism. These findings show that 5-HTTLPR short allele carriers avoid risky and complex financial choices due to negative emotional reactions, and have implications for understanding and managing individual differences in financial choice. PMID:23382929
Discrete analysis of stochastic NMR.II
NASA Astrophysics Data System (ADS)
Wong, S. T. S.; Rods, M. S.; Newmark, R. D.; Budinger, T. F.
Stochastic NMR is an efficient technique for high-field in vivo imaging and spectroscopic studies where the peak RF power required may be prohibitively high for conventional pulsed NMR techniques. A stochastic NMR experiment excites the spin system with a sequence of RF pulses where the flip angles or the phases of the pulses are samples of a discrete stochastic process. In a previous paper the stochastic experiment was analyzed and analytic expressions for the input-output cross-correlations, average signal power, and signal spectral density were obtained for a general stochastic RF excitation. In this paper specific cases of excitation with random phase, fixed flip angle, and excitation with two random components in quadrature are analyzed. The input-output cross-correlation for these two types of excitations is shown to be Lorentzian. Line broadening is the only spectral distortion as the RF excitation power is increased. The systematic noise power is inversely proportional to the number of data points N used in the spectral reconstruction. The use of a complete maximum length sequence (MLS) may improve the signal-to-systematic-noise ratio by 20 dB relative to random binary excitation, but peculiar features in the higher-order autocorrelations of MLS cause noise-like distortion in the reconstructed spectra when the excitation power is high. The amount of noise-like distortion depends on the choice of the MLS generator.
Discrete gauge symmetries in discrete MSSM-like orientifolds
NASA Astrophysics Data System (ADS)
Ibáñez, L. E.; Schellekens, A. N.; Uranga, A. M.
2012-12-01
Motivated by the necessity of discrete ZN symmetries in the MSSM to insure baryon stability, we study the origin of discrete gauge symmetries from open string sector U(1)'s in orientifolds based on rational conformal field theory. By means of an explicit construction, we find an integral basis for the couplings of axions and U(1) factors for all simple current MIPFs and orientifolds of all 168 Gepner models, a total of 32 990 distinct cases. We discuss how the presence of discrete symmetries surviving as a subgroup of broken U(1)'s can be derived using this basis. We apply this procedure to models with MSSM chiral spectrum, concretely to all known U(3)×U(2)×U(1)×U(1) and U(3)×Sp(2)×U(1)×U(1) configurations with chiral bi-fundamentals, but no chiral tensors, as well as some SU(5) GUT models. We find examples of models with Z2 (R-parity) and Z3 symmetries that forbid certain B and/or L violating MSSM couplings. Their presence is however relatively rare, at the level of a few percent of all cases.
Special Issue Topic: School Choice.
ERIC Educational Resources Information Center
Brogan, Bernard R.; And Others
1991-01-01
Includes "The Choice Movement" (Brogan); "Choice in American Education" (Witte); "Role of Parents in Education" (Mawdsley); "As Arrows in the Hand" (Coons); "Vouchers in Wisconsin" (Underwood); "Milwaukee Parental Choice Program (MPCP)" (Grover); "Civil Liberties and the MPCP" (Bolick); "Comments on School Choice" (Jauch); "Two Classes of…
Phase computations and phase models for discrete molecular oscillators
2012-01-01
Background Biochemical oscillators perform crucial functions in cells, e.g., they set up circadian clocks. The dynamical behavior of oscillators is best described and analyzed in terms of the scalar quantity, phase. A rigorous and useful definition for phase is based on the so-called isochrons of oscillators. Phase computation techniques for continuous oscillators that are based on isochrons have been used for characterizing the behavior of various types of oscillators under the influence of perturbations such as noise. Results In this article, we extend the applicability of these phase computation methods to biochemical oscillators as discrete molecular systems, upon the information obtained from a continuous-state approximation of such oscillators. In particular, we describe techniques for computing the instantaneous phase of discrete, molecular oscillators for stochastic simulation algorithm generated sample paths. We comment on the accuracies and derive certain measures for assessing the feasibilities of the proposed phase computation methods. Phase computation experiments on the sample paths of well-known biological oscillators validate our analyses. Conclusions The impact of noise that arises from the discrete and random nature of the mechanisms that make up molecular oscillators can be characterized based on the phase computation techniques proposed in this article. The concept of isochrons is the natural choice upon which the phase notion of oscillators can be founded. The isochron-theoretic phase computation methods that we propose can be applied to discrete molecular oscillators of any dimension, provided that the oscillatory behavior observed in discrete-state does not vanish in a continuous-state approximation. Analysis of the full versatility of phase noise phenomena in molecular oscillators will be possible if a proper phase model theory is developed, without resorting to such approximations. PMID:22687330
Dark Energy from Discrete Spacetime
Trout, Aaron D.
2013-01-01
Dark energy accounts for most of the matter-energy content of our universe, yet current theories of its origin rely on radical physical assumptions such as the holographic principle or controversial anthropic arguments. We give a better motivated explanation for dark energy, claiming that it arises from a small negative scalar-curvature present even in empty spacetime. The vacuum has this curvature because spacetime is fundamentally discrete and there are more ways for a discrete geometry to have negative curvature than positive. We explicitly compute this effect using a variant of the well known dynamical-triangulations (DT) model for quantum gravity. Our model predicts a time-varying non-zero cosmological constant with a current value, in natural units, in agreement with observation. This calculation is made possible by a novel characterization of the possible DT action values combined with numerical evidence concerning their degeneracies. PMID:24312502
Dark energy from discrete spacetime.
Trout, Aaron D
2013-01-01
Dark energy accounts for most of the matter-energy content of our universe, yet current theories of its origin rely on radical physical assumptions such as the holographic principle or controversial anthropic arguments. We give a better motivated explanation for dark energy, claiming that it arises from a small negative scalar-curvature present even in empty spacetime. The vacuum has this curvature because spacetime is fundamentally discrete and there are more ways for a discrete geometry to have negative curvature than positive. We explicitly compute this effect using a variant of the well known dynamical-triangulations (DT) model for quantum gravity. Our model predicts a time-varying non-zero cosmological constant with a current value, [Formula: see text] in natural units, in agreement with observation. This calculation is made possible by a novel characterization of the possible DT action values combined with numerical evidence concerning their degeneracies.
ERIC Educational Resources Information Center
Peterson, Paul E., Ed.; Hassel, Bryan C., Ed.
This volume contains revised versions of 16 essays presented at a conference, "Rethinking School Governance," hosted by Harvard's Program on Education Policy and Governance in June 1997. Part 1, "Introduction," contains two chapters: (1) "School Choice: A Report Card" (Paul E. Peterson); and (2) "The Case for Charter Schools" (Bryan C. Hassel).…
ERIC Educational Resources Information Center
Penning, Nick
1992-01-01
Name of Bush Administration's choice game is publicly financed vouchers allowing those already sending their children to private and parochial schools to avoid tuition fees at taxpayer expense. Although private schools administer entrance exams, public schools accept every child regardless of academic record, status, or race. U.S. Senate recently…
Jeffs, E.
1994-01-01
In Finland, a decision on a fifth nuclear power plant is stalled for at least two years. This leaves the country with a difficult choice for meeting anticipated electricity demand in the years ahead. This article examines the various energy alternatives of Finland and the political aspects of their energy development.
Choices, Frameworks and Refinement
NASA Technical Reports Server (NTRS)
Campbell, Roy H.; Islam, Nayeem; Johnson, Ralph; Kougiouris, Panos; Madany, Peter
1991-01-01
In this paper we present a method for designing operating systems using object-oriented frameworks. A framework can be refined into subframeworks. Constraints specify the interactions between the subframeworks. We describe how we used object-oriented frameworks to design Choices, an object-oriented operating system.
ERIC Educational Resources Information Center
Bennett, Scott
2006-01-01
We are building conventional library space without making the paradigm shift our digital environment requires. The chief obstacles to change lie in our conception of readers as information consumers, in our allegiance to library operations as the drivers of library design, and in the choice made between foundational and non-foundational views of…
Deterministic Walks with Choice
Beeler, Katy E.; Berenhaut, Kenneth S.; Cooper, Joshua N.; Hunter, Meagan N.; Barr, Peter S.
2014-01-10
This paper studies deterministic movement over toroidal grids, integrating local information, bounded memory and choice at individual nodes. The research is motivated by recent work on deterministic random walks, and applications in multi-agent systems. Several results regarding passing tokens through toroidal grids are discussed, as well as some open questions.
ERIC Educational Resources Information Center
Geis, George L.
"By 'student choice' we mean a situation in which the behavior (of 'choosing') is not overly determined by the instructional system. That is, the student is presented with a situation in which individual variables...are major determinants of the response emitted..." This definition, found in the first of three sections of this paper, forms the…
Variation, Repetition, and Choice
ERIC Educational Resources Information Center
Abreu-Rodrigues, Josele; Lattal, Kennon A.; dos Santos, Cristiano V.; Matos, Ricardo A.
2005-01-01
Experiment 1 investigated the controlling properties of variability contingencies on choice between repeated and variable responding. Pigeons were exposed to concurrent-chains schedules with two alternatives. In the REPEAT alternative, reinforcers in the terminal link depended on a single sequence of four responses. In the VARY alternative, a…
ERIC Educational Resources Information Center
Molnar, Alex
1992-01-01
Nonpublic school educational choice proposals are largely derived from monetarist economic and social theory and exemplify right-wing privatization goals. The U.S. health care system has plenty of competition among insurers, hospitals, and doctors; but it is the most expensive, least equitable system in the industrial world. The mystical belief…
A FORTRAN Program for Discrete Discriminant Analysis
ERIC Educational Resources Information Center
Boone, James O.; Brewer, James K.
1976-01-01
A Fortran program is presented for discriminant analysis of discrete variables. The program assumes discrete, nominal data with no distributional, variance-covariance assumptions. The program handles a maximum of fifty predictor variables and twelve outcome groups. (Author/JKS)
Practice effects on the preprogramming of discrete movements in Parkinson's disease.
Worringham, C J; Stelmach, G E
1990-01-01
The effects of practice on the simple and choice reaction times (RTs) of Parkinson's disease (PD) and control subjects in a discrete aiming task were analysed. For controls, practice led to a selective decrease in choice RTs, as has been reported previously. An opposite effect was seen in the PD group, with little change in choice RTs and substantial reduction in simple RTs. The results suggest that PD subjects can use advance information to initiate discrete movements more rapidly, but that this ability to "preprogramme" movements requires practice. Reconciliation of these results with studies reporting an inability to preprogramme in PD are made in a discussion of task characteristics which may allow or preclude preprogramming. PMID:2213049
Anomalies and Discrete Chiral Symmetries
Creutz, M.
2009-09-07
The quantum anomaly that breaks the U(1) axial symmetry of massless multi-flavored QCD leaves behind a discrete flavor-singlet chiral invariance. With massive quarks, this residual symmetry has a close connection with the strong CP-violating parameter theta. One result is that if the lightest quarks are degenerate, then a first order transition will occur when theta passes through pi. The resulting framework helps clarify when the rooting prescription for extrapolating in the number of flavors is valid.
Multiphase multi-velocity discrete population balance model of fragmenting particulate flows
NASA Astrophysics Data System (ADS)
Panchagnula, Mahesh; Rayapati, Prasad; Peddieson, John
2008-11-01
Fragmenting particulate flows are studied using discrete population balance modeling. The range of particle sizes is divided into N classes with each size class being allowed to behave as an individual fluid-like phase. The particulate phases are embedded in a continuous phase with which they share a pressure field and are coupled through drag forces. The particulate material is therefore modeled as a mixture of N+1 inter-penetrating continua. The fragmentation process is modeled using the population balance approach which allows for parent size-class particles to break up into any of the smaller daughter size-classes following a pre-defined breakage phenomenology. The accompanying mass and momentum exchange between the size-classes is modeled as source terms in the conservation equations. The model is applied to a micro-centrifuge flow field. We show here that the larger particles, while being encouraged to break up are also preferentially transported towards the walls of the centrifuge, owing to the swirl induced radial pressure gradient. By experimenting with various breakage phenomenologies, we show that the classical log-normal particle size distribution can be recovered in the long time limit for all breakage phenomenologies but the short time evolution of the particle size distribution is sensitive to that choice.
Observability of discretized partial differential equations
NASA Technical Reports Server (NTRS)
Cohn, Stephen E.; Dee, Dick P.
1988-01-01
It is shown that complete observability of the discrete model used to assimilate data from a linear partial differential equation (PDE) system is necessary and sufficient for asymptotic stability of the data assimilation process. The observability theory for discrete systems is reviewed and applied to obtain simple observability tests for discretized constant-coefficient PDEs. Examples are used to show how numerical dispersion can result in discrete dynamics with multiple eigenvalues, thereby detracting from observability.
Alternative fuels and vehicles choice model
Greene, D.L.
1994-10-01
This report describes the theory and implementation of a model of alternative fuel and vehicle choice (AFVC), designed for use with the US Department of Energy`s Alternative Fuels Trade Model (AFTM). The AFTM is a static equilibrium model of the world supply and demand for liquid fuels, encompassing resource production, conversion processes, transportation, and consumption. The AFTM also includes fuel-switching behavior by incorporating multinomial logit-type equations for choice of alternative fuel vehicles and alternative fuels. This allows the model to solve for market shares of vehicles and fuels, as well as for fuel prices and quantities. The AFVC model includes fuel-flexible, bi-fuel, and dedicated fuel vehicles. For multi-fuel vehicles, the choice of fuel is subsumed within the vehicle choice framework, resulting in a nested multinomial logit design. The nesting is shown to be required by the different price elasticities of fuel and vehicle choice. A unique feature of the AFVC is that its parameters are derived directly from the characteristics of alternative fuels and vehicle technologies, together with a few key assumptions about consumer behavior. This not only establishes a direct link between assumptions and model predictions, but facilitates sensitivity testing, as well. The implementation of the AFVC model as a spreadsheet is also described.
Fam, Justine; Westbrook, Fred; Arabzadeh, Ehsan
2015-01-01
One characteristic of natural environments is that outcomes vary across time. Animals need to adapt to these environmental changes and adjust their choices accordingly. In this experiment, we investigated the sensitivity with which rats could detect, and adapt to, multiple changes in the environment. Rats chose between two spouts which delivered 5% sucrose rewards with distinct probabilities. Across three phases, reward probabilities changed in size (large or small) and direction (increase or decrease). A discrete trial-structure was used, which allowed the choice process to be decomposed into three distinct response latency measures (choice execution latency, spout sampling duration, and trial-initiation latency). We found that a large decrease in reward probabilities rapidly produced the greatest change in choice proportions. The time taken to execute a choice reflected the differences in reward probabilities across the two spouts in some cases, but also reflected training history. By contrast, the amount of time rats spent responding at reward spouts in anticipation of reward consistently reflected the relative likelihood of reward across the two spouts and not the absolute probability of reward. The latency to initiate the subsequent trial reflected choice evaluation. These three response latencies thus indexed key behavioral correlates of the choice process as it unfolds in time. We discuss how this paradigm can be used to assess the corresponding neural correlates of decision-making. PMID:26483649
49 CFR 40.369 - What is the discretion of an initiating official in starting a PIE proceeding?
Code of Federal Regulations, 2010 CFR
2010-10-01
... Exclusions § 40.369 What is the discretion of an initiating official in starting a PIE proceeding? (a) Initiating officials have broad discretion in deciding whether to start a PIE proceeding. (b) In exercising... in starting a PIE proceeding? 40.369 Section 40.369 Transportation Office of the Secretary...
49 CFR 40.369 - What is the discretion of an initiating official in starting a PIE proceeding?
Code of Federal Regulations, 2011 CFR
2011-10-01
... Exclusions § 40.369 What is the discretion of an initiating official in starting a PIE proceeding? (a) Initiating officials have broad discretion in deciding whether to start a PIE proceeding. (b) In exercising... in starting a PIE proceeding? 40.369 Section 40.369 Transportation Office of the Secretary...
49 CFR 40.369 - What is the discretion of an initiating official in starting a PIE proceeding?
Code of Federal Regulations, 2014 CFR
2014-10-01
... Exclusions § 40.369 What is the discretion of an initiating official in starting a PIE proceeding? (a) Initiating officials have broad discretion in deciding whether to start a PIE proceeding. (b) In exercising... in starting a PIE proceeding? 40.369 Section 40.369 Transportation Office of the Secretary...
49 CFR 40.369 - What is the discretion of an initiating official in starting a PIE proceeding?
Code of Federal Regulations, 2013 CFR
2013-10-01
... Exclusions § 40.369 What is the discretion of an initiating official in starting a PIE proceeding? (a) Initiating officials have broad discretion in deciding whether to start a PIE proceeding. (b) In exercising... in starting a PIE proceeding? 40.369 Section 40.369 Transportation Office of the Secretary...
49 CFR 40.369 - What is the discretion of an initiating official in starting a PIE proceeding?
Code of Federal Regulations, 2012 CFR
2012-10-01
... Exclusions § 40.369 What is the discretion of an initiating official in starting a PIE proceeding? (a) Initiating officials have broad discretion in deciding whether to start a PIE proceeding. (b) In exercising... in starting a PIE proceeding? 40.369 Section 40.369 Transportation Office of the Secretary...
Jozefowiez, Jeremie; Cerutti, Daniel T.; Staddon, John E. R.
2005-01-01
In Experiment 1, pigeons chose between variable- and fixed-interval schedules. The timer for 1 schedule was reset by a reinforcement on that schedule or on either schedule. In both cases, the pigeons timed reinforcement on each schedule from trial onset. The data further suggest that their behavior reflects 2 independent processes: 1 deciding when a response should be emitted and responsible for the timing of the overall activity, and the other determining what this response should be and responsible for the allocation of behavior between the 2 response keys. Results from Experiment 2, which studied choice between 2 fixed-interval schedules, support those 2 conclusions. These results have implications for the study of operant choice in general. PMID:15839777
Application of the discrete ordinates method to compute radiant heat loss in a diesel engine
Abraham, J.; Magi, V.
1997-05-09
A three-dimensional model for computing flows, sprays, and combustion in internal combustion engines is modified to include radiant heat loss. Radiant heat loss is computed by solving the radiative transport equation using a discrete ordinates approximation method. Such a method solves the radiative transport equation for a set of discrete directions spanning the range of 4{pi} solid angle. Angular integrals of intensity are discretized by numerical quadrature. The resulting discrete ordinates equations are numerically solved by using a finite volume approach in contravariant formulation. Computations are made with and without radiant heat loss in a diesel engine, and the effects of the radiant heat loss on the computed temperature and NO and soot concentrations are discussed. Inclusion of radiant heat loss reduces the peak temperature by about 10%. As a result, the predicted frozen NO concentrations are found to be lowered. However, the soot concentrations are not significantly altered.
Balmford, A
1991-03-01
In lek-breeding animals, males defend tiny territories clustered into arenas, where females come to mate. Typically, most lek males secure relatively few copulations while a small number are highly successful. Recent studies suggest that the skewed distribution of matings seen at leks may be the result of females using a variety of criteria to select particular mating partners. Nevertheless, the possible benefits to females of mate choice at leks, where males offer neither resources nor paternal care, remain obscure.
O'Dell, R.D.; Alcouffe, R.E.
1987-09-01
This report is for the serious user of discrete ordinates transport computer codes for performing nuclear analysis calculations. The first section after the introduction provides a reasonably thorough mathematical description of the analytic Boltzmann transport equation. Next is a section on the numerical discretization of the energy, angle, and space variables in the transport equation, along with an introduction to the source iteration method. The fourth section provides numerical details and features pertinent to discrete ordinates codes. That section details angular quadrature, spatial discretization methods, iteration acceleration methods, and search capabilities. The fifth section presents considerations in choosing a discrete ordinates code for use, and this is followed by a section on typical discrete ordinates codes available throughout the world. The report ends with some guidance for the user. 73 refs., 18 figs., 13 tabs.
Discrete threshold versus continuous strength models of perceptual recognition.
Paap, K R; Chun, E; Vonnahme, P
1999-12-01
Two experiments were designed to test discrete-threshold models of letter and word recognition against models that assume that decision criteria are applied to measures of continuous strength. Although our goal is to adjudicate this matter with respect to broad classes of models, some of the specific predictions for discrete-threshold are generated from Grainger and Jacobs' (1994) Dual-Readout Model (DROM) and some of the predictions for continuous strength are generated from a revised version of the Activation-Verification Model (Paap, Newsome, McDonald, & Schvaneveldt, 1982). Experiment 1 uses a two-alternative forced-choice task that is followed by an assessment of confidence and then a whole report if a word is recognized. Factors are manipulated to assess the presence or magnitude of a neighbourhood-frequency effect, a lexical-bias effect, a word-superiority effect, and a pseudoword advantage. Several discrepancies between DROM's predictions and the obtained data are noted. Both types of models were also used to predict the distribution of responses across the levels of confidence for each individual participant. The predictions based on continuous strength were superior. Experiment 2 used a same-different task and confidence ratings to enable the generation of receiver operating characteristics (ROCs). The shapes of the ROCs are more consistent with the continuous strength assumption than with a discrete threshold. PMID:10646200
Abarca, N; Fantino, E
1982-09-01
In Experiment 1, six naive pigeons were trained on a foraging schedule characterized by different states beginning with a search state in which completion of a fixed-interval on a white key led to a choice state. In the choice state the subject could, by appropriate responding on a fixed ratio of three, either accept or reject the schedule of reinforcement that was offered (either a variable-interval five-second or a variable-interval 20-second). If the subject accepted the schedule, it entered a "handling state" in which the appropriate variable-interval schedule was presented. Completion of the variable-interval schedule produced food. The independent variable was the fixed-interval value in the search state, and the dependent variable was the rate of acceptance of the long variable-interval in the choice state. Experiment 2 was identical except that the search state required completion of a variable-interval, instead of a fixed-interval, schedule. The rate of acceptance of the long variable-interval schedule in both experiments was a direct function of the length of the search state, in accordance with both optimality theory and the delay-reduction hypothesis.
Miller, G F; Todd, P M
1998-05-01
Evolutionary psychology has revolutionized research on human mate choice and sexual attraction in recent years, combining a rigorous Darwinian framework based on sexual selection theory with a loosely cognitivist orientation to task analysis and mechanism modelling. This hard Darwinian, soft computational approach has been most successful at revealing the adaptive logic behind physical beauty, demonstrating that many sexual cues computed from face and body shape are not arbitrary, but function as reliable indicators of phenotypic and genetic quality. The same approach could be extended from physical to psychological cues if evolutionary psychology built stronger ties with personality psychology, psychometrics and behavioral genetics. A major challenge for mate choice research is to develop more explicit computational models at three levels, specifying: (1) the perceptual adaptations that register sexual cues given sensory input, (2) the judgment adaptations that integrate multiple cues into assessments of overall attractiveness, and (3) the search strategies that people follow in trying to form mutually attracted pairs. We describe both recent efforts and possible extensions in these directions. The resulting confluence between evolutionary principles, cognitive models and game-theoretic insights can put mate choice research at the vanguard of an emerging `evolutionary cognitive science' more concerned with domain-specific mental adaptations than with domain-general intelligence. PMID:21227154
An adaptive mesh refinement algorithm for the discrete ordinates method
Jessee, J.P.; Fiveland, W.A.; Howell, L.H.; Colella, P.; Pember, R.B.
1996-03-01
The discrete ordinates form of the radiative transport equation (RTE) is spatially discretized and solved using an adaptive mesh refinement (AMR) algorithm. This technique permits the local grid refinement to minimize spatial discretization error of the RTE. An error estimator is applied to define regions for local grid refinement; overlapping refined grids are recursively placed in these regions; and the RTE is then solved over the entire domain. The procedure continues until the spatial discretization error has been reduced to a sufficient level. The following aspects of the algorithm are discussed: error estimation, grid generation, communication between refined levels, and solution sequencing. This initial formulation employs the step scheme, and is valid for absorbing and isotopically scattering media in two-dimensional enclosures. The utility of the algorithm is tested by comparing the convergence characteristics and accuracy to those of the standard single-grid algorithm for several benchmark cases. The AMR algorithm provides a reduction in memory requirements and maintains the convergence characteristics of the standard single-grid algorithm; however, the cases illustrate that efficiency gains of the AMR algorithm will not be fully realized until three-dimensional geometries are considered.
Occupational Choice and Student Values
ERIC Educational Resources Information Center
McSweeney, R. V.
1973-01-01
Article attempts to set out a way of measuring determination, the element capable of making students' occupational choice' a reality not just an ideal, by exploration of the part played by the value system in relation to occupational choice. (Author)
Study of Ray Effects in Discrete Ordinates Calculations.
NASA Astrophysics Data System (ADS)
Gomes, Luisa Maria Torres
Ray effects, an inherent problem in the formulation of the discrete ordinates approximation to the transport equation, is studied in this research. In particular, the effectiveness of using Monte Carlo procedures to generate a first collision source or a second collision source is investigated. Monte Carlo procedures provide a general methodology that can be applied to the discrete ordinates solution of complex problems in either two- or three-dimensional geometries, for which ray effects are likely to occur. The Monte Carlo method, which is intrinsically free from ray effects, performs the transport of the source particle to the first collision site. The Monte Carlo estimated uncollided fluxes or first collided fluxes are used to compute the scattering sources in a format suitable for input into the DORT two-dimensional and the TORT three -dimensional discrete ordinates codes. The computational time and precision requirements of the Monte Carlo calculation are analyzed. Also, three procedures for estimating the second collision source with the modified version of MORSE are investigated. The results show that significant improvements are achieved in the solution of the test problems when using the first collision source and that virtual elimination of ray effects is realized when using the second collision source.
A unified framework for modeling landscape evolution by discrete flows
NASA Astrophysics Data System (ADS)
Shelef, Eitan; Hilley, George E.
2016-05-01
Topographic features such as branched valley networks and undissected convex-up hillslopes are observed in disparate physical environments. In some cases, these features are formed by sediment transport processes that occur discretely in space and time, while in others, by transport processes that are uniformly distributed across the landscape. This paper presents an analytical framework that reconciles the basic attributes of such sediment transport processes with the topographic features that they form and casts those in terms that are likely common to different physical environments. In this framework, temporal changes in surface elevation reflect the frequency with which the landscape is traversed by geophysical flows generated discretely in time and space. This frequency depends on the distance to which flows travel downslope, which depends on the dynamics of individual flows, the lithologic and topographic properties of the underlying substrate, and the coevolution of topography, erosion, and the routing of flows over the topographic surface. To explore this framework, we postulate simple formulations for sediment transport and flow runout distance and demonstrate that the conditions for hillslope and channel network formation can be cast in terms of fundamental parameters such as distance from drainage divide and a friction-like coefficient that describes a flow's resistance to motion. The framework we propose is intentionally general, but the postulated formulas can be substituted with those that aim to describe a specific process and to capture variations in the size distribution of such flow events.
Discreteness effects in population dynamics
NASA Astrophysics Data System (ADS)
Guevara Hidalgo, Esteban; Lecomte, Vivien
2016-05-01
We analyse numerically the effects of small population size in the initial transient regime of a simple example population dynamics. These effects play an important role for the numerical determination of large deviation functions of additive observables for stochastic processes. A method commonly used in order to determine such functions is the so-called cloning algorithm which in its non-constant population version essentially reduces to the determination of the growth rate of a population, averaged over many realizations of the dynamics. However, the averaging of populations is highly dependent not only on the number of realizations of the population dynamics, and on the initial population size but also on the cut-off time (or population) considered to stop their numerical evolution. This may result in an over-influence of discreteness effects at initial times, caused by small population size. We overcome these effects by introducing a (realization-dependent) time delay in the evolution of populations, additional to the discarding of the initial transient regime of the population growth where these discreteness effects are strong. We show that the improvement in the estimation of the large deviation function comes precisely from these two main contributions.
Discrete auroras and magnetotail processes.
NASA Astrophysics Data System (ADS)
Lyons, L. R.
Important information about magnetospheric phenomena associated with auroras and substorms can be inferred from low-altitude auroral observations. Satellite observations have shown that discrete auroral arcs lie within a boundary plasma sheet (BPS) region that is outside the central plasma sheet (CPS). The observations imply that arcs are generated along BPS field lines by magnetospheric processes that form large, perpendicular electric field structures. The BPS and the arc generation processes apparently lie along field lines that are in the vicinity of the boundary between open and closed field lines and cross the tail (or magnetopause) current sheet. Ground-based observations show that the first indication of a substorm onset is the brightening of a quiet, discrete arc. This suggests that substorms are initiated along the BPS field lines associated with arc generation, and not within the CPS. Finally, auroral observations have shown that the area of open, polar-cap field lines varies considerably during periods of geomagnetic activity. Expansion of the polar cap has the potential for releasing trapped plasma sheet particles along freshly open field lines. The resulting evacuation of field lines has the potential for being an important loss process for the plasma sheet and for being a source of tailward flows and energetic particle bursts in the tail.
NASA Astrophysics Data System (ADS)
Sonis, M.
Socio-ecological dynamics emerged from the field of Mathematical SocialSciences and opened up avenues for re-examination of classical problems of collective behavior in Social and Spatial sciences. The ``engine" of this collective behavior is the subjective mental evaluation of level of utilities in the future, presenting sets of composite socio-economic-temporal-locational advantages. These dynamics present new laws of collective multi-population behavior which are the meso-level counterparts of the utility optimization individual behavior. The central core of the socio-ecological choice dynamics includes the following first principle of the collective choice behavior of ``Homo Socialis" based on the existence of ``collective consciousness": the choice behavior of ``Homo Socialis" is a collective meso-level choice behavior such that the relative changes in choice frequencies depend on the distribution of innovation alternatives between adopters of innovations. The mathematical basis of the Socio-Ecological Dynamics includes two complementary analytical approaches both based on the use of computer modeling as a theoretical and simulation tool. First approach is the ``continuous approach" --- the systems of ordinary and partial differential equations reflecting the continuous time Volterra ecological formalism in a form of antagonistic and/or cooperative collective hyper-games between different sub-sets of choice alternatives. Second approach is the ``discrete approach" --- systems of difference equations presenting a new branch of the non-linear discrete dynamics --- the Discrete Relative m-population/n-innovations Socio-Spatial Dynamics (Dendrinos and Sonis, 1990). The generalization of the Volterra formalism leads further to the meso-level variational principle of collective choice behavior determining the balance between the resulting cumulative social spatio-temporal interactions among the population of adopters susceptible to the choice alternatives and the
School Choice. Trends and Issues.
ERIC Educational Resources Information Center
Hadderman, Margaret, Comp.
This document examines many of the issues surrounding school choice. It summarizes the prevalence of school choice and touches on elements of the debate, such as the dilemma in finding the right balance between individual/family freedom and the interests of the community. In looking at school-choice options, the paper divides them into…
Student Curriculum Choice and Change.
ERIC Educational Resources Information Center
Miner, Norris
This study investigated changes in student curriculum choice at Seminole Junior College (Florida) A code system was developed for 72 curriculum choices (23 in terminal degree areas), grouped into 19 broad clusters. A computerized Student Flow Matrix was then constructed to display the first and second term curriculum choices of 1,391 students who…
Dynamics of Choice: A Tutorial
ERIC Educational Resources Information Center
Baum, William M.
2010-01-01
Choice may be defined as the allocation of behavior among activities. Since all activities take up time, choice is conveniently thought of as the allocation of time among activities, even if activities like pecking are most easily measured by counting. Since dynamics refers to change through time, the dynamics of choice refers to change of…
How choice modifies preference: neural correlates of choice justification.
Qin, Jungang; Kimel, Sasha; Kitayama, Shinobu; Wang, Xiaoying; Yang, Xuedong; Han, Shihui
2011-03-01
When making a difficult choice, people often justify the choice by increasing their liking for the chosen object and decreasing their liking for the rejected object. To uncover the neural signatures of choice justification, we used functional magnetic resonance imaging to monitor neural activity when subjects rated their preference for chosen and rejected musical CDs before and after they made their choices. We observed that the trial-by-trial attitude change (i.e., increase of preference for chosen items and decrease of preference for rejected items) was predicted by post-choice activity in the ventral medial prefrontal cortex (MPFC), right temporal-parietal junction, anterior insula, and bilateral cerebellum. Furthermore, individual difference in choice justification (i.e., increased preference for chosen items minus decreased preference for rejected items) was predicted by post-choice neural activity in the dorsal MPFC, left lateral prefrontal cortex, and right precentral cortex positively. In addition, interdependent self-construal was correlated with decreased activity in the ventral MPFC in the post-choice than pre-choice sessions. These findings suggest that both negative arousal/regulation and self-reflection are associated with choice justification. This provides evidence for the self-threat theory of choice justification.
The neural predictors of choice preference in intertemporal choice.
Liu, Lei; Feng, Tingyong
2012-02-01
Intertemporal choice may involve two processing stages: a valuation stage and a choice stage. Decision makers must integrate the various dimensions of an option (e.g., money, time) into a single measure of its subjective value (the valuation stage) and then choose the option that is the most valuable (the choice stage). Although previous studies have implicated that subjective values are represented by a diverse set of brain regions (e.g., vmPFC, VStr, and PCC) in intertemporal choice, it is not yet known which of these regions contain information that directly predicts subsequent choice. To address this question, we measured brain activity using functional MRI while participants performed a simple intertemporal choice task. The results found that participants' decision could be encoded by three specific brain areas (vmPFC, ACC, and PCC) even before they were required to make a choice, while the left posterior insula showed positively active in the choice stage when individuals selected the delayed rewards compared to the immediate rewards. These findings suggest that activation patterns in the vmPFC, ACC, and PCC were able to predict the subsequent choice preference; however, left posterior insula may play an important role for choice preference in the choice stage.
Overconfidence and Career Choice.
Schulz, Jonathan F; Thöni, Christian
2016-01-01
People self-assess their relative ability when making career choices. Thus, confidence in their own abilities is likely an important factor for selection into various career paths. In a sample of 711 first-year students we examine whether there are systematic differences in confidence levels across fields of study. We find that our experimental confidence measures significantly vary between fields of study: While students in business related academic disciplines (Political Science, Law, Economics, and Business Administration) exhibit the highest confidence levels, students of Humanities range at the other end of the scale. This may have important implications for subsequent earnings and professions students select themselves in.
Overconfidence and Career Choice.
Schulz, Jonathan F; Thöni, Christian
2016-01-01
People self-assess their relative ability when making career choices. Thus, confidence in their own abilities is likely an important factor for selection into various career paths. In a sample of 711 first-year students we examine whether there are systematic differences in confidence levels across fields of study. We find that our experimental confidence measures significantly vary between fields of study: While students in business related academic disciplines (Political Science, Law, Economics, and Business Administration) exhibit the highest confidence levels, students of Humanities range at the other end of the scale. This may have important implications for subsequent earnings and professions students select themselves in. PMID:26808273
Overconfidence and Career Choice
Schulz, Jonathan F.; Thöni, Christian
2016-01-01
People self-assess their relative ability when making career choices. Thus, confidence in their own abilities is likely an important factor for selection into various career paths. In a sample of 711 first-year students we examine whether there are systematic differences in confidence levels across fields of study. We find that our experimental confidence measures significantly vary between fields of study: While students in business related academic disciplines (Political Science, Law, Economics, and Business Administration) exhibit the highest confidence levels, students of Humanities range at the other end of the scale. This may have important implications for subsequent earnings and professions students select themselves in. PMID:26808273
Discrete Ordinates Solutions for Highly Forward Peaked Scattering
Sanchez, Richard; McCormick, Norman J.
2004-07-15
The limitations of asymptotic methods for numerically solving highly forward peaked scattering (HFPS) problems are reviewed before resorting to a discrete ordinates solution for such problems based on biased angular quadrature formulas to increase the precision of the angular representation and on source evaluation from cell-averaged angular fluxes to reduce memory requirements. Also, a twice-collided source is introduced to avoid numerical representation of singularities in the solution. As an example the propagation and spreading of a collimated particle beam in an HFPS medium has been calculated with a discrete ordinates diamond-differenced numerical solution of the transport equation in two-dimensional curvilinear cylindrical coordinates. The calculation was carried out for a strongly forward peaked Henyey-Greenstein scattering law for which Fokker-Planck asymptotic models are not valid. The results show promise for numerically calculated reference solutions based on accurate spatial representations for checking the accuracy of standard asymptotic models for these types of problems.
He, Lin; Wang, Mingxian; Chen, Wei; Conzelmann, Guenter
2014-10-01
While discrete choice analysis is prevalent in capturing consumer preferences and describing their choice behaviors in product design, the traditional choice modeling approach assumes that each individual makes independent decisions, without considering the social impact. However, empirical studies show that choice is social - influenced by many factors beyond engineering performance of a product and consumer attributes. To alleviate this limitation, we propose a new choice modeling framework to capture the dynamic influence from social networks on consumer adoption of new products. By introducing social influence attributes into a choice utility function, social network simulation is integrated with the traditional discrete choice analysis in a three-stage process. Our study shows the need for considering social impact in forecasting new product adoption. Using hybrid electric vehicles as an example, our work illustrates the procedure of social network construction, social influence evaluation, and choice model estimation based on data from the National Household Travel Survey. Our study also demonstrates several interesting findings on the dynamic nature of new technology adoption and how social networks may influence hybrid electric vehicle adoption. (C) 2014 Elsevier Ltd. All rights reserved
Discrete network models of interacting nephrons
NASA Astrophysics Data System (ADS)
Moss, Rob; Kazmierczak, Ed; Kirley, Michael; Harris, Peter
2009-11-01
The kidney is one of the major organs involved in whole-body homeostasis, and exhibits many of the properties of a complex system. The functional unit of the kidney is the nephron, a complex, segmented tube into which blood plasma is filtered and its composition adjusted. Although the behaviour of individual nephrons can fluctuate widely and even chaotically, the behaviour of the kidney remains stable. In this paper, we investigate how the filtration rate of a multi-nephron system is affected by interactions between nephrons. We introduce a discrete-time multi-nephron network model. The tubular mechanisms that have the greatest effect on filtration rate are the transport of sodium and water, consequently our model attempts to capture these mechanisms. Multi-nephron systems also incorporate two competing coupling mechanisms-vascular and hemodynamic-that enforce in-phase and anti-phase synchronisations respectively. Using a two-nephron model, we demonstrate how changing the strength of the hemodynamic coupling mechanism and changing the arterial blood pressure have equivalent effects on the system. The same two-nephron system is then used to demonstrate the interactions that arise between the two coupling mechanisms. We conclude by arguing that our approach is scalable to large numbers of nephrons, based on the performance characteristics of the model.
Goldshmidt, J N; Lattal, K M; Fantino, E
1998-11-01
Four pigeons responded on a concurrent-chains schedule in four experiments that examined whether the effectiveness of a stimulus as a conditioned reinforcer is best described by a global approach, as measured by the average interreinforcement interval, or by a local contextual approach, as measured by the onset of the stimulus preceding the conditioned reinforcer. The interreinforcement interval was manipulated by the inclusion of an intertrial interval, which increased the overall time to reinforcement but did not change the local contingencies on a given trial A global analysis predicted choice for the richer alternative to decrease with the inclusion of an intertrial interval, whereas a local analysis predicted no change in preference. Experiment 1 examined sensitivity to intertrial intervals when each was signaled by the same houselight that operated throughout the session. In Experiment 2, the intertrial interval always was signaled by the stimulus correlated with the richer terminal link. In Experiment 3, the intertrial interval was signaled by the keylights correlated with the initial links and two novel houselights. Experiment 4 provided free food pseudorandomly during the intertrial interval. In all experiments, subjects' preferences were consistent with a local analysis of choice in concurrent chains. These results are discussed in terms of delay-reduction theory, which traditionally has failed to distinguish global and local contexts.
Goldshmidt, J N; Lattal, K M; Fantino, E
1998-01-01
Four pigeons responded on a concurrent-chains schedule in four experiments that examined whether the effectiveness of a stimulus as a conditioned reinforcer is best described by a global approach, as measured by the average interreinforcement interval, or by a local contextual approach, as measured by the onset of the stimulus preceding the conditioned reinforcer. The interreinforcement interval was manipulated by the inclusion of an intertrial interval, which increased the overall time to reinforcement but did not change the local contingencies on a given trial A global analysis predicted choice for the richer alternative to decrease with the inclusion of an intertrial interval, whereas a local analysis predicted no change in preference. Experiment 1 examined sensitivity to intertrial intervals when each was signaled by the same houselight that operated throughout the session. In Experiment 2, the intertrial interval always was signaled by the stimulus correlated with the richer terminal link. In Experiment 3, the intertrial interval was signaled by the keylights correlated with the initial links and two novel houselights. Experiment 4 provided free food pseudorandomly during the intertrial interval. In all experiments, subjects' preferences were consistent with a local analysis of choice in concurrent chains. These results are discussed in terms of delay-reduction theory, which traditionally has failed to distinguish global and local contexts. PMID:9821681
Observers for discrete-time nonlinear systems
NASA Astrophysics Data System (ADS)
Grossman, Walter D.
Observer synthesis for discrete-time nonlinear systems with special applications to parameter estimation is analyzed. Two new types of observers are developed. The first new observer is an adaptation of the Friedland continuous-time parameter estimator to discrete-time systems. The second observer is an adaptation of the continuous-time Gauthier observer to discrete-time systems. By adapting these observers to discrete-time continuous-time parameter estimation problems which were formerly intractable become tractable. In addition to the two newly developed observers, two observers already described in the literature are analyzed and deficiencies with respect to noise rejection are demonstrated. Improved versions of these observers are proposed and their performance demonstrated. The issues of discrete-time observability, discrete-time system inversion, and optimal probing are also addressed.
Ideal shrinking and expansion of discrete sequences
NASA Technical Reports Server (NTRS)
Watson, Andrew B.
1986-01-01
Ideal methods are described for shrinking or expanding a discrete sequence, image, or image sequence. The methods are ideal in the sense that they preserve the frequency spectrum of the input up to the Nyquist limit of the input or output, whichever is smaller. Fast implementations that make use of the discrete Fourier transform or the discrete Hartley transform are described. The techniques lead to a new multiresolution image pyramid.
Determinant Expressions for Discrete Integrable Maps
NASA Astrophysics Data System (ADS)
Sogo, Kiyoshi
2006-08-01
Explicit formulas for several discrete integrable maps with periodic boundary condition are obtained, which give the sequential time developments in a form of the quotient of successive determinants of tri-diagonal matrices. We can expect that such formulas make the corresponding numerical simulations simple and stable. The cases of discrete Lotka-Volterra and discrete KdV equations are demonstrated by using the common algorithm computing determinants of tri-diagonal matrices.
Discretizing gravity in warped spacetime
Schwartz, Matthew; Randall, Lisa; Schwartz, Matthew D.; Thambyahpillai, Shiyamala
2005-07-11
We investigate the discretized version of the compact Randall-Sundrum model. By studying the mass eigenstates of the lattice theory, we demonstrate that for warped space, unlike for flat space, the strong coupling scale does not depend on the IR scale and lattice size. However, strong coupling does prevent us from taking the continuum limit of the lattice theory. Nonetheless, the lattice theory works in the manifestly holographic regime and successfully reproduces the most significant features of the warped theory. It is even in some respects better than the KK theory, which must be carefully regulated to obtain the correct physical results. Because it is easier to construct lattice theories than to find exact solutions to GR, we expect lattice gravity to be a useful tool for exploring field theory in curved space.
Lepton mixing and discrete symmetries
NASA Astrophysics Data System (ADS)
Hernandez, D.; Smirnov, A. Yu.
2012-09-01
The pattern of lepton mixing can emerge from breaking a flavor symmetry in different ways in the neutrino and charged lepton Yukawa sectors. In this framework, we derive the model-independent conditions imposed on the mixing matrix by the structure of discrete groups of the von Dyck type which include A4, S4, and A5. We show that, in general, these conditions lead to at least two equations for the mixing parameters (angles and CP phase δ). These constraints, which correspond to unbroken residual symmetries, are consistent with nonzero 13 mixing and deviations from maximal 2-3 mixing. For the simplest case, which leads to an S4 model and reproduces the allowed values of the mixing angles, we predict δ=(90°-120°).
Scalar discrete nonlinear multipoint boundary value problems
NASA Astrophysics Data System (ADS)
Rodriguez, Jesus; Taylor, Padraic
2007-06-01
In this paper we provide sufficient conditions for the existence of solutions to scalar discrete nonlinear multipoint boundary value problems. By allowing more general boundary conditions and by imposing less restrictions on the nonlinearities, we obtain results that extend previous work in the area of discrete boundary value problems [Debra L. Etheridge, Jesus Rodriguez, Periodic solutions of nonlinear discrete-time systems, Appl. Anal. 62 (1996) 119-137; Debra L. Etheridge, Jesus Rodriguez, Scalar discrete nonlinear two-point boundary value problems, J. Difference Equ. Appl. 4 (1998) 127-144].
A discrete event method for wave simulation
Nutaro, James J
2006-01-01
This article describes a discrete event interpretation of the finite difference time domain (FDTD) and digital wave guide network (DWN) wave simulation schemes. The discrete event method is formalized using the discrete event system specification (DEVS). The scheme is shown to have errors that are proportional to the resolution of the spatial grid. A numerical example demonstrates the relative efficiency of the scheme with respect to FDTD and DWN schemes. The potential for the discrete event scheme to reduce numerical dispersion and attenuation errors is discussed.
Genetic Algorithms for Multiple-Choice Problems
NASA Astrophysics Data System (ADS)
Aickelin, Uwe
2010-04-01
This thesis investigates the use of problem-specific knowledge to enhance a genetic algorithm approach to multiple-choice optimisation problems.It shows that such information can significantly enhance performance, but that the choice of information and the way it is included are important factors for success.Two multiple-choice problems are considered.The first is constructing a feasible nurse roster that considers as many requests as possible.In the second problem, shops are allocated to locations in a mall subject to constraints and maximising the overall income.Genetic algorithms are chosen for their well-known robustness and ability to solve large and complex discrete optimisation problems.However, a survey of the literature reveals room for further research into generic ways to include constraints into a genetic algorithm framework.Hence, the main theme of this work is to balance feasibility and cost of solutions.In particular, co-operative co-evolution with hierarchical sub-populations, problem structure exploiting repair schemes and indirect genetic algorithms with self-adjusting decoder functions are identified as promising approaches.The research starts by applying standard genetic algorithms to the problems and explaining the failure of such approaches due to epistasis.To overcome this, problem-specific information is added in a variety of ways, some of which are designed to increase the number of feasible solutions found whilst others are intended to improve the quality of such solutions.As well as a theoretical discussion as to the underlying reasons for using each operator,extensive computational experiments are carried out on a variety of data.These show that the indirect approach relies less on problem structure and hence is easier to implement and superior in solution quality.
Mcfadden, P
1994-06-01
The choice of motherhood for women and women's rights have been forbidden in law by men, in religious doctrines by men, and within the medical system by men. Women in poverty have little say in determining whether to have children or not. When choice is exercised for abortion, poor women have unsafe and illegal abortions, which can be life-threatening. Rich women have safer options. Women historically have allowed their rights to be eroded by gender inequality and patriarchal manipulation. The religious right and the Roman Catholic church have been allowed to speak and decide for women. Abortion rights are not about western influences, but about maternal mortality. The right to make choices about one's life is the fundamental premise of the universal rights of all human beings. African governments have signed the UN Convention on elimination of all forms of discrimination against women, but the practice of human rights has not been implemented at the local and family level. Motherhood needs to be demystified. Motherhood is linked with the absence of personhood and bodily integrity. The rhetoric of moral obligations and the rights of the unborn child take precedence over the rights of women. The right of an African woman not to have children is not recognized in most Africa societies. The issue of AIDS creates an even more difficult milieu for women. The interests of the family and the interests of men overwhelm the interests of women to protect themselves. Motherhood is essential to validating one's heterosexuality and gaining stature, and females without a child are marginalized and unrecognized. Women whose babies do not survive are marginalized further than barren women. Men derive power from women's birthing. The terminology of male power is replete with expressions such as "pregnant with promise" and "miscarriage of justice's", no one says "uterus envy." Male psychologists only recognize "penis envy." Men need children for purposes of property, lineage, and
NASA Astrophysics Data System (ADS)
Bhat, Chandra R.; Sener, Ipek N.
2009-09-01
This study focuses on accommodating spatial dependency in data indexed by geographic location. In particular, the emphasis is on accommodating spatial error correlation across observational units in binary discrete choice models. We propose a copula-based approach to spatial dependence modeling based on a spatial logit structure rather than a spatial probit structure. In this approach, the dependence between the logistic error terms of different observational units is directly accommodated using a multivariate logistic distribution based on the Farlie-Gumbel-Morgenstein (FGM) copula. The approach represents a simple and powerful technique that results in a closed-form analytic expression for the joint probability of choice across observational units, and is straightforward to apply using a standard and direct maximum likelihood inference procedure. There is no simulation machinery involved, leading to substantial computation gains relative to current methods to address spatial correlation. The approach is applied to teenagers’ physical activity participation levels, a subject of considerable interest in the public health, transportation, sociology, and adolescence development fields. The results indicate that failing to accommodate heteroscedasticity and spatial correlation can lead to inconsistent and inefficient parameter estimates, as well as incorrect conclusions regarding the elasticity effects of exogenous variables.
Discretization vs. Rounding Error in Euler's Method
ERIC Educational Resources Information Center
Borges, Carlos F.
2011-01-01
Euler's method for solving initial value problems is an excellent vehicle for observing the relationship between discretization error and rounding error in numerical computation. Reductions in stepsize, in order to decrease discretization error, necessarily increase the number of steps and so introduce additional rounding error. The problem is…
Current Density and Continuity in Discretized Models
ERIC Educational Resources Information Center
Boykin, Timothy B.; Luisier, Mathieu; Klimeck, Gerhard
2010-01-01
Discrete approaches have long been used in numerical modelling of physical systems in both research and teaching. Discrete versions of the Schrodinger equation employing either one or several basis functions per mesh point are often used by senior undergraduates and beginning graduate students in computational physics projects. In studying…
Covariance control of discrete stochastic bilinear systems
NASA Technical Reports Server (NTRS)
Skelton, R. E.; Kherat, S. M.; Yaz, E.
1991-01-01
The covariances that certain bilinear stochastic discrete time systems may possess are characterized. An explicit parameterization of all controllers that assign such covariances is given. The state feedback assignability and robustness of the system are discussed from a deterministic point of view. This work extends the theory of covariance control for continuous time bilinear systems to a discrete time setting.
Discrete/PWM Ballast-Resistor Controller
NASA Technical Reports Server (NTRS)
King, Roger J.
1994-01-01
Circuit offers low switching loss and automatic compensation for failure of ballast resistor. Discrete/PWM ballast-resistor controller improved shunt voltage-regulator circuit designed to supply power from high-resistance source to low-impedance bus. Provides both coarse discrete voltage levels (by switching of ballast resistors) and continuous fine control of voltage via pulse-width modulation.
Discreteness and Gradience in Intonational Contrasts.
ERIC Educational Resources Information Center
Gussenhoven, Carlos
1999-01-01
Three experimental techniques that can be used to investigate the gradient of discrete nature of intonational differences, the semantic task, the imitation task, and the pitch range task are discussed and evaluated. It is pointed out that categorical perception is a sufficient but not a necessary, property of phonological discreteness. (Author/VWL)
A Bell-Curved Based Algorithm for Mixed Continuous and Discrete Structural Optimization
NASA Technical Reports Server (NTRS)
Kincaid, Rex K.; Weber, Michael; Sobieszczanski-Sobieski, Jaroslaw
2001-01-01
An evolutionary based strategy utilizing two normal distributions to generate children is developed to solve mixed integer nonlinear programming problems. This Bell-Curve Based (BCB) evolutionary algorithm is similar in spirit to (mu + mu) evolutionary strategies and evolutionary programs but with fewer parameters to adjust and no mechanism for self adaptation. First, a new version of BCB to solve purely discrete optimization problems is described and its performance tested against a tabu search code for an actuator placement problem. Next, the performance of a combined version of discrete and continuous BCB is tested on 2-dimensional shape problems and on a minimum weight hub design problem. In the latter case the discrete portion is the choice of the underlying beam shape (I, triangular, circular, rectangular, or U).
Active control of turbomachine discrete tones
NASA Astrophysics Data System (ADS)
Fleeter, Sanford
This paper was directed at active control of discrete frequency noise generated by subsonic blade rows through cancellation of the blade row interaction generated propagating acoustic waves. First discrete frequency noise generated by a rotor and stator in a duct was analyzed to determine the propagating acoustic pressure waves. Then a mathematical model was developed to analyze and predict the active control of discrete frequency noise generated by subsonic blade rows through cancellation of the propagating acoustic waves, accomplished by utilizing oscillating airfoil surfaces to generate additional control propagating pressure waves. These control waves interact with the propagating acoustic waves, thereby, in principle, canceling the acoustic waves and thus, the far field discrete frequency tones. This model was then applied to a fan exit guide vane to investigate active airfoil surface techniques for control of the propagating acoustic waves, and thus the far field discrete frequency tones, generated by blade row interactions.
Generalized exponential function and discrete growth models
NASA Astrophysics Data System (ADS)
Souto Martinez, Alexandre; Silva González, Rodrigo; Lauri Espíndola, Aquino
2009-07-01
Here we show that a particular one-parameter generalization of the exponential function is suitable to unify most of the popular one-species discrete population dynamic models into a simple formula. A physical interpretation is given to this new introduced parameter in the context of the continuous Richards model, which remains valid for the discrete case. From the discretization of the continuous Richards’ model (generalization of the Gompertz and Verhulst models), one obtains a generalized logistic map and we briefly study its properties. Notice, however that the physical interpretation for the introduced parameter persists valid for the discrete case. Next, we generalize the (scramble competition) θ-Ricker discrete model and analytically calculate the fixed points as well as their stabilities. In contrast to previous generalizations, from the generalized θ-Ricker model one is able to retrieve either scramble or contest models.
Clutter from non-discrete seabed structures.
Holland, Charles W; Ellis, Dale D
2012-06-01
Clutter, or discrete target-like returns, is the most significant problem in the employment of active sonar. It is well understood that discrete objects, which are of the same spatial scale as the target and which possess a significant impedance contrast to the surrounding ocean, can lead to clutter. Here a somewhat counter-intuitive result is shown: that discrete target-like returns can occur from slowly varying seabed structures. The range dependence of the seabed can be weak and smooth-due to changes in layer thicknesses, sound speed, or both. Thus, this clutter mechanism may be a viable hypothesis for areas in which seabed clutter has been observed, but no discrete features, buried or proud, could be found. By using a broadband source, the time-frequency evolution of this clutter could be a useful way to discriminate against other kinds of clutter; e.g., that due to discrete objects.
Connecting cognition and consumer choice.
Bartels, Daniel M; Johnson, Eric J
2015-02-01
We describe what can be gained from connecting cognition and consumer choice by discussing two contexts ripe for interaction between the two fields. The first-context effects on choice-has already been addressed by cognitive science yielding insights about cognitive process but there is promise for more interaction. The second is learning and representation in choice where relevant theories in cognitive science could be informed by consumer choice, and in return, could pose and answer new questions. We conclude by discussing how these two fields of research stand to benefit from more interaction, citing examples of how interfaces of cognitive science with other fields have been illuminating for theories of cognition.
MULTISCALE DISCRETIZATION OF SHAPE CONTOURS
Prasad, L.; Rao, R.
2000-09-01
We present an efficient multi-scale scheme to adaptively approximate the continuous (or densely sampled) contour of a planar shape at varying resolutions. The notion of shape is intimately related to the notion of contour, and the efficient representation of the contour of a shape is vital to a computational understanding of the shape. Any polygonal approximation of a planar smooth curve is equivalent to a piecewise constant approximation of the parameterized X and Y coordinate functions of a discrete point set obtained by densely sampling the curve. Using the Haar wavelet transform for the piecewise approximation yields a hierarchical scheme in which the size of the approximating point set is traded off against the morphological accuracy of the approximation. Our algorithm compresses the representation of the initial shape contour to a sparse sequence of points in the plane defining the vertices of the shape's polygonal approximation. Furthermore, it is possible to control the overall resolution of the approximation by a single, scale-independent parameter.
Medical futility and physician discretion
Wreen, M
2004-01-01
Some patients have no chance of surviving if not treated, but very little chance if treated. A number of medical ethicists and physicians have argued that treatment in such cases is medically futile and a matter of physician discretion. This paper critically examines that position. According to Howard Brody and others, a judgment of medical futility is a purely technical matter, which physicians are uniquely qualified to make. Although Brody later retracted these claims, he held to the view that physicians need not consult the patient or his family to determine their values before deciding not to treat. This is because professional integrity dictates that treatment should not be undertaken. The argument for this claim is that medicine is a profession and a social practice, and thus capable of breaches of professional integrity. Underlying professional integrity are two moral principles, one concerning harm, the other fraud. According to Brody both point to the fact that when the odds of survival are very low treatment is a violation of professional integrity. The details of this skeletal argument are exposed and explained, and the full argument is criticised. On a number of counts, it is found wanting. If anything, professional integrity points to the opposite conclusion. PMID:15173362
Tuned oscillatory behavior in discrete quantum walks on star clusters
NASA Astrophysics Data System (ADS)
Andrade, R. F. S.; Souza, A. M. C.
2015-10-01
A discrete time quantum walk on the star network is considered, on which the walker has a waiting probability at any time step and for any of the N nodes. This contrasts with a previous continuous time analysis, in which the walker in any of the N -1 leaf nodes is forced to jump back to the central hub. The model amounts to considering two coin operators, one for the hub (with N possible states) and another one for all leaf nodes (with two possible states). The solution depends on N and θ , an angle gauging the action of the coin operator on the leaf nodes. Periodic solutions are identified, which can be represented as superposition of large-period branches, sharing a relative small number of shapes and displaced by a regular interval. It is shown that the large period is very sensitive to the choice of N and θ . The possibility of experimental applications of this property is briefly mentioned.
Parental Voucher Enrollment Decisions: Choice within Choice in New Orleans
ERIC Educational Resources Information Center
Beabout, Brian R.; Cambre, Belinda M.
2013-01-01
Set in the context of a choice-saturated public school system, this study examines the school choice process of low-income parents who participated in Louisiana's 2008 voucher program. Based on semistructured interviews with 16 parents at 1 Catholic school, we report that spirituality, small class and school size, character/values,…
(Discrete kinetic theory, lattice gas dynamics and foundations of hydrodynamics)
Protopopescu, V.
1988-10-07
The traveler participated successively in the Workshop of Discrete Kinetic Theory, Lattice Gas Dynamics and Foundations of Hydrodynamics, Villa Gualino-Torino, Italy, and in the Third International Workshop on Mathematical Aspects of Fluid and Plasma Dynamics, Salice Terme-Pavia, Italy, as a guest of the Italian CNR (National Council for Research, Mathematical Physics Group). At the first Workshop, there were approximately 65 participants among whom 35 were speakers. The topics discussed were discrete kinetic theory, cellular automata, and the relationship between microscopic/mesoscopic and macroscopic evolution equations. Cellular automata and lattice gas dynamics emerged as main areas of promising research and future applications. At the second Workshop, there were approximately 80 attendants, 20 contributed papers, and 15 invited papers. The main subjects of the papers were general methods to study nonlinear equations, advances in plasma theory, numerical methods, efficient computational schemes, and nonlinear transport problems. The Italian scientists expressed interest in strengthening the collaboration with ORNL in the areas of nonlinear partial differential equations, and discrete dynamics with applications to competitive systems.
Smith, Leon E.; Gesh, Christopher J.; Pagh, Richard T.; Miller, Erin A.; Shaver, Mark W.; Ashbaker, Eric D.; Batdorf, Michael T.; Ellis, J. E.; Kaye, William R.; McConn, Ronald J.; Meriwether, George H.; Ressler, Jennifer J.; Valsan, Andrei B.; Wareing, Todd A.
2008-10-31
Radiation transport modeling methods used in the radiation detection community fall into one of two broad categories: stochastic (Monte Carlo) and deterministic. Monte Carlo methods are typically the tool of choice for simulating gamma-ray spectrometers operating in homeland and national security settings (e.g. portal monitoring of vehicles or isotope identification using handheld devices), but deterministic codes that discretize the linear Boltzmann transport equation in space, angle, and energy offer potential advantages in computational efficiency for many complex radiation detection problems. This paper describes the development of a scenario simulation framework based on deterministic algorithms. Key challenges include: formulating methods to automatically define an energy group structure that can support modeling of gamma-ray spectrometers ranging from low to high resolution; combining deterministic transport algorithms (e.g. ray-tracing and discrete ordinates) to mitigate ray effects for a wide range of problem types; and developing efficient and accurate methods to calculate gamma-ray spectrometer response functions from the deterministic angular flux solutions. The software framework aimed at addressing these challenges is described and results from test problems that compare coupled deterministic-Monte Carlo methods and purely Monte Carlo approaches are provided.
Smoking in young adolescents: an approach with multilevel discrete choice models
Pinilla, J; Gonzalez, B; Barber, P; Santana, Y
2002-01-01
Design: Cross sectional analysis performed by multilevel logistic regression with pupils at the first level and schools at the second level. The data came from a stratified sample of students surveyed on their own, their families' and their friends' smoking habits, their schools, and their awareness of cigarette prices and advertising. Setting: The study was performed in the Island of Gran Canaria, Spain. Participants: 1877 students from 30 secondary schools in spring of 2000 (model's effective sample sizes 1697 and 1738) . Main results: 14.2% of the young teenagers surveyed use tobacco, almost half of them (6.3% of the total surveyed) on a daily basis. According to the ordered logistic regression model, to have a smoker as the best friend increases significantly the probability of smoking (odds ratio: 6.96, 95% confidence intervals (CI) (4.93 to 9.84), and the same stands for one smoker living at home compared with a smoking free home (odds ratio: 2.03, 95% CI 1.22 to 3.36). Girls smoke more (odds ratio: 1.85, 95% CI 1.33 to 2.59). Experience with alcohol, and lack of interest in studies are also significant factors affecting smoking. Multilevel models of logistic regression showed that factors related to the school affect the smoking behaviour of young teenagers. More specifically, whether a school complies with antismoking rules or not is the main factor to predict smoking prevalence in schools. The remainder of the differences can be attributed to individual and family characteristics, tobacco consumption by parents or other close relatives, and peer group. Conclusions: A great deal of the individual differences in smoking are explained by factors at the school level, therefore the context is very relevant in this case. The most relevant predictors for smoking in young adolescents include some factors related to the schools they attend. One variable stood out in accounting for the school to school differences: how well they enforced the no smoking rule. Therefore we can prevent or delay tobacco smoking in adolescents not only by publicising health risks, but also by better enforcing no smoking rules in schools. PMID:11854347
Evidence based contraceptive choices.
Scott, Alison; Glasier, Anna
2006-10-01
People who attend for contraceptive advice have usually formulated an idea of the type of contraceptive that will suit them best. They may wish to use a method that is long, short or medium acting. These are defined as follows: Long-acting method requires renewal no more frequently than every 3 months (e.g. injectable or intrauterine). Short-acting method used daily or with every act of intercourse (e.g. pills, condoms) Medium-acting method requires renewal weekly or monthly (e.g. ring, patch). For men the choice is limited to condoms or vasectomy. Some women do not wish to use hormonal preparations or have an intrauterine device (IUD) or implant inserted. There may also be cultural influences making certain methods of contraception unacceptable. Each of these factors influences the final decision of which method of contraception is decided upon. In addition to taking a full medical and sexual history to identify any risks to the individual's health, which might be increased by a particular contraceptive, time must be spent discussing the options available. It is important to ensure that there is a full understanding of the advantages and disadvantages of each method. The most successful contraceptive method is likely to be the one that the woman (or man) chooses, rather than the one the clinician chooses for them. Access for women to contraception can be improved by having convenient clinic times and service developments such as nurse prescribing and Patient Group Directions.
Addiction: Choice or Compulsion?
Henden, Edmund; Melberg, Hans Olav; Røgeberg, Ole Jørgen
2013-01-01
Normative thinking about addiction has traditionally been divided between, on the one hand, a medical model which sees addiction as a disease characterized by compulsive and relapsing drug use over which the addict has little or no control and, on the other, a moral model which sees addiction as a choice characterized by voluntary behavior under the control of the addict. Proponents of the former appeal to evidence showing that regular consumption of drugs causes persistent changes in the brain structures and functions known to be involved in the motivation of behavior. On this evidence, it is often concluded that becoming addicted involves a transition from voluntary, chosen drug use to non-voluntary compulsive drug use. Against this view, proponents of the moral model provide ample evidence that addictive drug use involves voluntary chosen behavior. In this article we argue that although they are right about something, both views are mistaken. We present a third model that neither rules out the view of addictive drug use as compulsive, nor that it involves voluntary chosen behavior. PMID:23966955
Sparrow, Margaret June
2004-04-01
Abortion is now the most common gynaecological operation in New Zealand and Australia. Early legal abortion is a safe procedure whether carried out surgically or medically. In contrast, the traditional use of abortifacients has been mostly unscientific, illegal and shrouded in secrecy. Mifepristone as an option for induced abortion has only recently become available in New Zealand and is not yet available in Australia. The reasons for the delay in introducing a significant new abortion technique are political, professional, legal, socioeconomic and commercial. Istar, a not-for-profit company, was formed in New Zealand in 1999 to import mifepristone. The drug was approved for use in New Zealand on 30 August 2001. It was first used in October 2001 in Wellington for mid-trimester abortions and in April 2002 for early medical abortions. Legal ambiguities were clarified in a High Court Judgment on 10 April 2003. The experience with mifepristone raises concerns about the introduction of new drugs for reproductive health care, given the commercial risks associated with their development. The Royal Australian and New Zealand College of Obstetricians and Gynaecologists has a role to play in ensuring that safe abortion services are available for women. Advocates of women's rights in reproductive health care have made a significant impact in the last three decades and the conclusion that abortion must be the woman's choice is strongly supported.
Pemberton, Bradley E.; May, Christopher P.; Rossabi, Joseph; Riha, Brian D.; Nichols, Ralph L.
1999-01-01
A sampling port is provided which has threaded ends for incorporating the port into a length of subsurface pipe. The port defines an internal receptacle which is in communication with subsurface fluids through a series of fine filtering slits. The receptacle is in further communication through a bore with a fitting carrying a length of tubing there which samples are transported to the surface. Each port further defines an additional bore through which tubing, cables, or similar components of adjacent ports may pass.
Pemberton, Bradley E.; May, Christopher P.; Rossabi, Joseph; Riha, Brian D.; Nichols, Ralph L.
1998-07-07
A sampling port is provided which has threaded ends for incorporating the port into a length of subsurface pipe. The port defines an internal receptacle which is in communication with subsurface fluids through a series of fine filtering slits. The receptacle is in further communication through a bore with a fitting carrying a length of tubing there which samples are transported to the surface. Each port further defines an additional bore through which tubing, cables, or similar components of adjacent ports may pass.
Compatible Spatial Discretizations for Partial Differential Equations
Arnold, Douglas, N, ed.
2004-11-25
From May 11--15, 2004, the Institute for Mathematics and its Applications held a hot topics workshop on Compatible Spatial Discretizations for Partial Differential Equations. The numerical solution of partial differential equations (PDE) is a fundamental task in science and engineering. The goal of the workshop was to bring together a spectrum of scientists at the forefront of the research in the numerical solution of PDEs to discuss compatible spatial discretizations. We define compatible spatial discretizations as those that inherit or mimic fundamental properties of the PDE such as topology, conservation, symmetries, and positivity structures and maximum principles. A wide variety of discretization methods applied across a wide range of scientific and engineering applications have been designed to or found to inherit or mimic intrinsic spatial structure and reproduce fundamental properties of the solution of the continuous PDE model at the finite dimensional level. A profusion of such methods and concepts relevant to understanding them have been developed and explored: mixed finite element methods, mimetic finite differences, support operator methods, control volume methods, discrete differential forms, Whitney forms, conservative differencing, discrete Hodge operators, discrete Helmholtz decomposition, finite integration techniques, staggered grid and dual grid methods, etc. This workshop seeks to foster communication among the diverse groups of researchers designing, applying, and studying such methods as well as researchers involved in practical solution of large scale problems that may benefit from advancements in such discretizations; to help elucidate the relations between the different methods and concepts; and to generally advance our understanding in the area of compatible spatial discretization methods for PDE. Particular points of emphasis included: + Identification of intrinsic properties of PDE models that are critical for the fidelity of numerical
Discrete Element Modeling of Triboelectrically Charged Particles
NASA Technical Reports Server (NTRS)
Hogue, Michael D.; Calle, Carlos I.; Weitzman, Peter S.; Curry, David R.
2008-01-01
Tribocharging of particles is common in many processes including fine powder handling and mixing, printer toner transport and dust extraction. In a lunar environment with its high vacuum and lack of water, electrostatic forces are an important factor to consider when designing and operating equipment. Dust mitigation and management is critical to safe and predictable performance of people and equipment. The extreme nature of lunar conditions makes it difficult and costly to carry out experiments on earth which are necessary to better understand how particles gather and transfer charge between each other and with equipment surfaces. DEM (Discrete Element Modeling) provides an excellent virtual laboratory for studying tribocharging of particles as well as for design of devices for dust mitigation and for other purposes related to handling and processing of lunar regolith. Theoretical and experimental work has been performed pursuant to incorporating screened Coulombic electrostatic forces into EDEM, a commercial DEM software package. The DEM software is used to model the trajectories of large numbers of particles for industrial particulate handling and processing applications and can be coupled with other solvers and numerical models to calculate particle interaction with surrounding media and force fields. While simple Coulombic force between two particles is well understood, its operation in an ensemble of particles is more complex. When the tribocharging of particles and surfaces due to frictional contact is also considered, it is necessary to consider longer range of interaction of particles in response to electrostatic charging. The standard DEM algorithm accounts for particle mechanical properties and inertia as a function of particle shape and mass. If fluid drag is neglected, then particle dynamics are governed by contact between particles, between particles and equipment surfaces and gravity forces. Consideration of particle charge and any tribocharging and
Cooperative transport in nanochannels.
Bauer, Wolfgang R; Nadler, Walter
2013-07-01
Channel transport of different species of particles is viewed usually only in terms of competition and selectivity. In this paper we show that transport of one species may be promoted by the presence of another and that both may even mutually cooperate. We investigate a discretized Markovian model of nanochannel transport via in-channel sites, allowing for the simultaneous transport of several different species of particles; interaction between transported particles is included via the condition of single occupancy on a channel site. By numerically solving the model exactly, particularly an analysis of situations of crowding in the channel is possible and we observe three situations: mutual cooperation, promotion of one species at the cost of the other, and mutual competition. The physical situation has a strong nonequilibrium character as Onsager's relations on coupled flows do not hold.
Method for coupling two-dimensional to three-dimensional discrete ordinates calculations
Thompson, J.L.; Emmett, M.B.; Rhoades, W.A.; Dodds, H.L. Jr.
1985-01-01
A three-dimensional (3-D) discrete ordinates transport code, TORT, has been developed at the Oak Ridge National Laboratory for radiation penetration studies. It is not feasible to solve some 3-D penetration problems with TORT, such as a building located a large distance from a point source, because (1) the discretized 3-D problem is simply too big to fit on the computer or (2) the computing time (and corresponding cost) is prohibitive. Fortunately, such problems can be solved with a hybrid approach by coupling a two-dimensional (2-D) description of the point source, which is assumed to be azimuthally symmetric, to a 3-D description of the building, the region of interest. The purpose of this paper is to describe this hybrid methodology along with its implementation and evaluation in the DOTTOR (Discrete Ordinates to Three-dimensional Oak Ridge Transport) code.
Moment-Preserving SN Discretizations for the One-Dimensional Fokker-Planck Equation
Warsa, James S.; Prinja, Anil K.
2012-06-14
The Fokker-Planck equation: (1) Describes the transport and interactions of charged particles, (2) Many small-angle scattering collisions, (3) Asymptotic limit of the Boltzmann equation (Pomraning, 1992), and (4) The Boltzmann collision operator becomes the angular Laplacian. SN angular discretization: (1) Angular flux is collocated at the SN quadrature points, (2) The second-order derivatives in the Laplacian term must be discretized, and (3) Weighted finite-difference method preserves zeroth and first moments (Morel, 1985). Moment-preserving methods: (1) Collocate the Fokker-Planck operator at the SN quadrature points, (2) Develop several related and/or equivalent methods, and (3) Motivated by discretizations for the angular derivative appearing in the transport equation in one-dimensional spherical coordinates.
Religious Education and Religious Choice
ERIC Educational Resources Information Center
Hand, Michael
2015-01-01
According to the "religious choice case" for compulsory religious education, pupils have a right to be made aware of the religious and irreligious paths open to them and equipped with the wherewithal to choose between them. A familiar objection to this argument is that the idea of religious choice reduces religion to a matter of taste. I…
School Choice: Examining the Evidence.
ERIC Educational Resources Information Center
Rasell, Edith, Ed.; Rothstein, Richard, Ed.
This book presents a summary of school-choice issues, and is organized around a 1992 seminar entitled "Choice: What Role in American Education?" Each part presents a set of conference papers, followed by discussants' remarks and excerpts from audience discussion. The introduction summarizes the papers' positions and conclusions. Participants…
College Choice in the Philippines
ERIC Educational Resources Information Center
Tan, Christine Joy
2009-01-01
This descriptive and correlational study examined the applicability of major U.S. college choice factors to Philippine high school seniors. A sample of 226 students from a private school in Manila completed the College Choice Survey for High School Seniors. Cronbach's alpha for the survey composite index was 0.933. The purposes of this…
PATERNAL INFLUENCE ON CAREER CHOICE.
ERIC Educational Resources Information Center
WERTS, CHARLES E.
FATHER'S OCCUPATION WAS COMPARED WITH SON'S CAREER CHOICE FOR A SAMPLE OF 76,015 MALE, COLLEGE FRESHMEN. RESULTS INDICATED THAT CERTAIN TYPES OF FATHERS' OCCUPATIONS WERE ASSOCIATED WITH SIMILAR TYPES OF CAREER CHOICES BY SONS. BOYS WHOSE FATHERS WERE IN SCIENTIFIC OCCUPATIONS (ENGINEERS, MILITARY OFFICERS, ARCHITECTS, BIOLOGISTS, CHEMISTS, AND…
ERIC Educational Resources Information Center
Organisation for Economic Cooperation and Development, Paris (France). Centre for Educational Research and Innovation.
Measures to improve parent and student choice of school have recently become an important issue for educational reform in a number of Organisation for Economic Co-operation and Development (OECD) countries. This book summarizes the school-choice experiences of selected OECD countries. The data, collected by the OECD/Centre for Educational Research…
Educational Choice. A Background Paper.
ERIC Educational Resources Information Center
Quality Education for Minorities Network, Washington, DC.
This paper addresses school choice, one proposal to address parental involvement concerns, focusing on historical background, definitions, rationale for advocating choice, implementation strategies, and implications for minorities and low-income families. In the past, transfer payment programs such as tuition tax credits and vouchers were…
School Choice with Chinese Characteristics
ERIC Educational Resources Information Center
Wu, Xiaoxin
2012-01-01
This paper explores the major characteristics of school choice in the Chinese context. It highlights the involvement of cultural and economic capital, such as choice fees, donations, prize-winning certificates and awards in gaining school admission, as well as the use of social capital in the form of "guanxi". The requirement for these resources…
Hermens, Frouke; Matthews, William J.
2015-01-01
Abstract We asked participants to make simple risky choices while we recorded their eye movements. We built a complete statistical model of the eye movements and found very little systematic variation in eye movements over the time course of a choice or across the different choices. The only exceptions were finding more (of the same) eye movements when choice options were similar, and an emerging gaze bias in which people looked more at the gamble they ultimately chose. These findings are inconsistent with prospect theory, the priority heuristic, or decision field theory. However, the eye movements made during a choice have a large relationship with the final choice, and this is mostly independent from the contribution of the actual attribute values in the choice options. That is, eye movements tell us not just about the processing of attribute values but also are independently associated with choice. The pattern is simple—people choose the gamble they look at more often, independently of the actual numbers they see—and this pattern is simpler than predicted by decision field theory, decision by sampling, and the parallel constraint satisfaction model. © 2015 The Authors. Journal of Behavioral Decision Making published by John Wiley & Sons Ltd. PMID:27522985
Preference Reversal in Multiattribute Choice
ERIC Educational Resources Information Center
Tsetsos, Konstantinos; Usher, Marius; Chater, Nick
2010-01-01
A central puzzle for theories of choice is that people's preferences between options can be reversed by the presence of decoy options (that are not chosen) or by the presence of other irrelevant options added to the choice set. Three types of reversal effect reported in the decision-making literature, the attraction, compromise, and similarity…
Marriage Enrichment through Choice Awareness.
ERIC Educational Resources Information Center
Nelson, Richard C.; Friest, Wendell P.
1980-01-01
Choice Awareness is a cognitive-affective-behavioral system that goes beyond both communication training and behavioral bartering approaches to marriage enrichment. Couples explore thoughts, feelings, and actions in their relationships and develop personal power in making choices and in taking responsibility for their own lives. (Author)
ERIC Educational Resources Information Center
Maile, Simeon
2004-01-01
In this article, the author investigates the basic elements of choice and markets theory. In recent years, children were moving from rural and township schools to suburban White schools. This trend emerged in the late 1980s and simmered after the demise of apartheid. At face value, school choice appears to be happening merely for the reason of…
ERIC Educational Resources Information Center
Wagner, Tony
1996-01-01
Debunks two fantasies: the feasibility of a free-market educational system and the idea that greater choice automatically means better schools. Public education is too labor-intensive and undercapitalized to be profitable. Communities need "skunk works" schools of choice to do research and development and smaller, collaboratively managed schools…
The Globalisation of School Choice?
ERIC Educational Resources Information Center
Forsey, Martin, Ed.; Davies, Scott, Ed.; Walford, Geoffrey, Ed.
2008-01-01
"Which school should I choose for my child?" For many parents, this question is one of the most important of their lives. "School choice" is a slogan being voiced around the globe, conjuring images of a marketplace with an abundance of educational options. Those promoting educational choice also promise equality, social advantage, autonomy, and…
Effects of using a continuum representation of discrete fracture networks
Hull, L.C.; Clemo, T.M.
1987-01-01
The substitution of matrix or continuum permeability for discrete fracture permeability in the simulation of complex fracture systems requires a radically different treatment of transport in the matrix. The spatial distribution of pressure is reasonably well described by inclusion of only the major fractures. Transport of tracer and heat, however, depends on a detailed knowledge of fluid velocities. Two factors are involved. First, the velocities are dependent on the active porosity of the system. Because fractures channel flow, the active porosity may be much smaller than the total porosity of the system. Secondly, the distribution of velocities is generally not normally distributed precluding the use of a Gaussian dispersion model. Characterization of the active porosity and velocity distribution are necessary to quantify tracer and heat movement.
State Regulators Promote Consumer Choice in Retail Gas Markets
1996-01-01
Restructuring of interstate pipeline companies has created new choices and challenges for local distribution companies (LDCs), their regulators, and their customers. The process of separating interstate pipeline gas sales from transportation service has been completed and has resulted in greater gas procurement options for LDCs.
Open Enrollment/Educational Choice: A National Review.
ERIC Educational Resources Information Center
Sheane, Kim; Bierlein, Louann
Descriptive information on open enrollment/choice programs in a variety of states is provided in this report. Following an introduction, key program components are discussed, which include transportation, information, and funding issues; state guidelines for student acceptance; and athletic recruiting. Private school issues are examined in the…
Discrete symmetries and de Sitter spacetime
Cotăescu, Ion I. Pascu, Gabriel
2014-11-24
Aspects of the ambiguity in defining quantum modes on de Sitter spacetime using a commuting system composed only of differential operators are discussed. Discrete symmetries and their actions on the wavefunction in commonly used coordinate charts are reviewed. It is argued that the system of commuting operators can be supplemented by requiring the invariance of the wavefunction to combined discrete symmetries- a criterion which selects a single state out of the α-vacuum family. Two such members of this family are singled out by particular combined discrete symmetries- states between which exists a well-known thermality relation.
Multigravity from a discrete extra dimension
NASA Astrophysics Data System (ADS)
Deffayet, C.; Mourad, J.
2004-06-01
Multigravity theories are constructed from the discretization of the extra dimension of five-dimensional gravity. Using an ADM decomposition, the discretization is performed while maintaining the four-dimensional diffeomorphism invariance on each site. We relate the Goldstone bosons used to realize nonlinearly general covariance in discretized gravity to the shift fields of the higher-dimensional metric. We investigate the scalar excitations of the resulting theory and show the absence of ghosts and massive modes; this is due to a local symmetry inherited from the reparametrization invariance along the fifth dimension.
High-accuracy discrete positioning device
NASA Technical Reports Server (NTRS)
Brooks, John J. (Inventor)
1994-01-01
An article (30) is controllably and precisely positioned at one of three discrete locations defined by a linkage. The positioning apparatus includes two independently driven cranks (34, 42), with a link (50) pivotably connected between the two cranks (34, 42). Another connector (44) is pivotably connected between one of the cranks (34 or 42) and the article (30) to be positioned. The cranks (34, 42) are rotationally adjusted so that the pivot points (52, 54) of the link (50) are collinear with the axes of rotation of the cranks (40, 48), thereby defining one of the three discrete locations. Additional cranks and links can be provided to define additional discrete locations.
Discrete flavour symmetries from the Heisenberg group
NASA Astrophysics Data System (ADS)
Floratos, E. G.; Leontaris, G. K.
2016-04-01
Non-abelian discrete symmetries are of particular importance in model building. They are mainly invoked to explain the various fermion mass hierarchies and forbid dangerous superpotential terms. In string models they are usually associated to the geometry of the compactification manifold and more particularly to the magnetised branes in toroidal compactifications. Motivated by these facts, in this note we propose a unified framework to construct representations of finite discrete family groups based on the automorphisms of the discrete and finite Heisenberg group. We focus in particular, on the PSL2 (p) groups which contain the phenomenologically interesting cases.
Advanced Algorithms and Automation Tools for Discrete Ordinates Methods in Parallel Environments
Alireza Haghighat
2003-05-07
This final report discusses major accomplishments of a 3-year project under the DOE's NEER Program. The project has developed innovative and automated algorithms, codes, and tools for solving the discrete ordinates particle transport method efficiently in parallel environments. Using a number of benchmark and real-life problems, the performance and accuracy of the new algorithms have been measured and analyzed.
FUNGIBILITY AND CONSUMER CHOICE: EVIDENCE FROM COMMODITY PRICE SHOCKS*
Hastings, Justine S.; Shapiro, Jesse M.
2015-01-01
We formulate a test of the fungibility of money based on parallel shifts in the prices of different quality grades of a commodity. We embed the test in a discrete-choice model of product quality choice and estimate the model using panel microdata on gasoline purchases. We find that when gasoline prices rise consumers substitute to lower octane gasoline, to an extent that cannot be explained by income effects. Across a wide range of specifications, we consistently reject the null hypothesis that households treat “gas money” as fungible with other income. We compare the empirical fit of three psychological models of decision-making. A simple model of category budgeting fits the data well, with models of loss aversion and salience both capturing important features of the time series. PMID:26937053
Expanded Access to Non-VA Care Through the Veterans Choice Program. Interim final rule.
2015-12-01
The Department of Veterans Affairs (VA) revises its medical regulations that implement section 101 of the Veterans Access, Choice, and Accountability Act of 2014 (hereafter referred to as "the Choice Act"), which requires VA to establish a program to furnish hospital care and medical services through eligible non-VA health care providers to eligible veterans who either cannot be seen within the wait-time goals of the Veterans Health Administration (VHA) or who qualify based on their place of residence (hereafter referred to as the "Veterans Choice Program" or the "Program"). These regulatory revisions are required by the most recent amendments to the Choice Act made by the Construction Authorization and Choice Improvement Act of 2014, and by the Surface Transportation and Veterans Health Care Choice Improvement Act of 2015. The Construction Authorization and Choice Improvement Act of 2014 amended the Choice Act to define additional criteria that VA may use to determine that a veteran's travel to a VA medical facility is an "unusual or excessive burden," and the Surface Transportation and Veterans Health Care Choice Improvement Act of 2015 amended the Choice Act to cover all veterans enrolled in the VA health care system, remove the 60-day limit on an episode of care, modify the wait-time and 40-mile distance eligibility criteria, and expand provider eligibility based on criteria as determined by VA. This interim final rule revises VA regulations consistent with the changes made to the Choice Act as described above.
Discrete-element modeling of particulate aerosol flows
Marshall, J.S.
2009-03-20
A multiple-time step computational approach is presented for efficient discrete-element modeling of aerosol flows containing adhesive solid particles. Adhesive aerosol particulates are found in numerous dust and smoke contamination problems, including smoke particle transport in the lungs, particle clogging of heat exchangers in construction vehicles, industrial nanoparticle transport and filtration systems, and dust fouling of electronic systems and MEMS components. Dust fouling of equipment is of particular concern for potential human occupation on dusty planets, such as Mars. The discrete-element method presented in this paper can be used for prediction of aggregate structure and breakup, for prediction of the effect of aggregate formation on the bulk fluid flow, and for prediction of the effects of small-scale flow features (e.g., due to surface roughness or MEMS patterning) on the aggregate formation. After presentation of the overall computational structure, the forces and torques acting on the particles resulting from fluid motion, particle-particle collision, and adhesion under van der Waals forces are reviewed. The effect of various parameters of normal collision and adhesion of two particles are examined in detail. The method is then used to examine aggregate formation and particle clogging in pipe and channel flow.
Displacement in the parameter space versus spurious solution of discretization with large time step
NASA Astrophysics Data System (ADS)
Mendes, Eduardo; Letellier, Christophe
2004-01-01
In order to investigate a possible correspondence between differential and difference equations, it is important to possess discretization of ordinary differential equations. It is well known that when differential equations are discretized, the solution thus obtained depends on the time step used. In the majority of cases, such a solution is considered spurious when it does not resemble the expected solution of the differential equation. This often happens when the time step taken into consideration is too large. In this work, we show that, even for quite large time steps, some solutions which do not correspond to the expected ones are still topologically equivalent to solutions of the original continuous system if a displacement in the parameter space is considered. To reduce such a displacement, a judicious choice of the discretization scheme should be made. To this end, a recent discretization scheme, based on the Lie expansion of the original differential equations, proposed by Monaco and Normand-Cyrot will be analysed. Such a scheme will be shown to be sufficient for providing an adequate discretization for quite large time steps compared to the pseudo-period of the underlying dynamics.
Multilevel methods for transport equations in diffusive regimes
NASA Technical Reports Server (NTRS)
Manteuffel, Thomas A.; Ressel, Klaus
1993-01-01
We consider the numerical solution of the single-group, steady state, isotropic transport equation. An analysis by means of the moment equations shows that a discrete ordinate S(sub N) discretization in direction (angle) with a least squares finite element discretization in space does not behave properly in the diffusion limit. A scaling of the S(sub N) equations is introduced so that the least squares discretization has the correct diffusion limit. For the resulting discrete system a full multigrid algorithm was developed.
Kópházi, József Lathouwers, Danny
2015-09-15
In this paper a new method for the discretization of the radiation transport equation is presented, based on a discontinuous Galerkin method in space and angle that allows for local refinement in angle where any spatial element can support its own angular discretization. To cope with the discontinuous spatial nature of the solution, a generalized Riemann procedure is required to distinguish between incoming and outgoing contributions of the numerical fluxes. A new consistent framework is introduced that is based on the solution of a generalized eigenvalue problem. The resulting numerical fluxes for the various possible cases where neighboring elements have an equal, higher or lower level of refinement in angle are derived based on tensor algebra and the resulting expressions have a very clear physical interpretation. The choice of discontinuous trial functions not only has the advantage of easing local refinement, it also facilitates the use of efficient sweep-based solvers due to decoupling of unknowns on a large scale thereby approaching the efficiency of discrete ordinates methods with local angular resolution. The approach is illustrated by a series of numerical experiments. Results show high orders of convergence for the scalar flux on angular refinement. The generalized Riemann upwinding procedure leads to stable and consistent solutions. Further the sweep-based solver performs well when used as a preconditioner for a Krylov method.
Eye Movements in Strategic Choice
Gächter, Simon; Noguchi, Takao; Mullett, Timothy L.
2015-01-01
Abstract In risky and other multiattribute choices, the process of choosing is well described by random walk or drift diffusion models in which evidence is accumulated over time to threshold. In strategic choices, level‐k and cognitive hierarchy models have been offered as accounts of the choice process, in which people simulate the choice processes of their opponents or partners. We recorded the eye movements in 2 × 2 symmetric games including dominance‐solvable games like prisoner's dilemma and asymmetric coordination games like stag hunt and hawk–dove. The evidence was most consistent with the accumulation of payoff differences over time: we found longer duration choices with more fixations when payoffs differences were more finely balanced, an emerging bias to gaze more at the payoffs for the action ultimately chosen, and that a simple count of transitions between payoffs—whether or not the comparison is strategically informative—was strongly associated with the final choice. The accumulator models do account for these strategic choice process measures, but the level‐k and cognitive hierarchy models do not. © 2015 The Authors. Journal of Behavioral Decision Making published by John Wiley & Sons Ltd. PMID:27513881
Local discrete symmetries from superstring derived models
NASA Astrophysics Data System (ADS)
Faraggi, Alon E.
1997-02-01
Discrete and global symmetries play an essential role in many extensions of the Standard Model, for example, to preserve the proton lifetime, to prevent flavor changing neutral currents, etc. An important question is how can such symmetries survive in a theory of quantum gravity, like superstring theory. In a specific string model I illustrate how local discrete symmetries may arise in string models and play an important role in preventing fast proton decay and flavor changing neutral currents. The local discrete symmetry arises due to the breaking of the non-Abelian gauge symmetries by Wilson lines in the superstring models and forbids, for example dimension five operators which mediate rapid proton decay, to all orders of nonrenormalizable terms. In the context of models of unification of the gauge and gravitational interactions, it is precisely this type of local discrete symmetries that must be found in order to insure that a given model is not in conflict with experimental observations.
Geometric phases in discrete dynamical systems
NASA Astrophysics Data System (ADS)
Cartwright, Julyan H. E.; Piro, Nicolas; Piro, Oreste; Tuval, Idan
2016-10-01
In order to study the behaviour of discrete dynamical systems under adiabatic cyclic variations of their parameters, we consider discrete versions of adiabatically-rotated rotators. Parallelling the studies in continuous systems, we generalize the concept of geometric phase to discrete dynamics and investigate its presence in these rotators. For the rotated sine circle map, we demonstrate an analytical relationship between the geometric phase and the rotation number of the system. For the discrete version of the rotated rotator considered by Berry, the rotated standard map, we further explore this connection as well as the role of the geometric phase at the onset of chaos. Further into the chaotic regime, we show that the geometric phase is also related to the diffusive behaviour of the dynamical variables and the Lyapunov exponent.
Dynamic discretization method for solving Kepler's equation
NASA Astrophysics Data System (ADS)
Feinstein, Scott A.; McLaughlin, Craig A.
2006-09-01
Kepler’s equation needs to be solved many times for a variety of problems in Celestial Mechanics. Therefore, computing the solution to Kepler’s equation in an efficient manner is of great importance to that community. There are some historical and many modern methods that address this problem. Of the methods known to the authors, Fukushima’s discretization technique performs the best. By taking more of a system approach and combining the use of discretization with the standard computer science technique known as dynamic programming, we were able to achieve even better performance than Fukushima. We begin by defining Kepler’s equation for the elliptical case and describe existing solution methods. We then present our dynamic discretization method and show the results of a comparative analysis. This analysis will demonstrate that, for the conditions of our tests, dynamic discretization performs the best.
A discrete control model of PLANT
NASA Technical Reports Server (NTRS)
Mitchell, C. M.
1985-01-01
A model of the PLANT system using the discrete control modeling techniques developed by Miller is described. Discrete control models attempt to represent in a mathematical form how a human operator might decompose a complex system into simpler parts and how the control actions and system configuration are coordinated so that acceptable overall system performance is achieved. Basic questions include knowledge representation, information flow, and decision making in complex systems. The structure of the model is a general hierarchical/heterarchical scheme which structurally accounts for coordination and dynamic focus of attention. Mathematically, the discrete control model is defined in terms of a network of finite state systems. Specifically, the discrete control model accounts for how specific control actions are selected from information about the controlled system, the environment, and the context of the situation. The objective is to provide a plausible and empirically testable accounting and, if possible, explanation of control behavior.
Motion of Discrete Interfaces Through Mushy Layers
NASA Astrophysics Data System (ADS)
Braides, Andrea; Solci, Margherita
2016-08-01
We study the geometric motion of sets in the plane derived from the homogenization of discrete ferromagnetic energies with weak inclusions. We show that the discrete sets are composed by a `bulky' part and an external `mushy region' composed only of weak inclusions. The relevant motion is that of the bulky part, which asymptotically obeys to a motion by crystalline mean curvature with a forcing term, due to the energetic contribution of the mushy layers, and pinning effects, due to discreteness. From an analytical standpoint, it is interesting to note that the presence of the mushy layers implies only a weak and not strong convergence of the discrete motions, so that the convergence of the energies does not commute with the evolution. From a mechanical standpoint it is interesting to note the geometrical similarity of some phenomena in the cooling of binary melts.
Running Parallel Discrete Event Simulators on Sierra
Barnes, P. D.; Jefferson, D. R.
2015-12-03
In this proposal we consider porting the ROSS/Charm++ simulator and the discrete event models that run under its control so that they run on the Sierra architecture and make efficient use of the Volta GPUs.
Comparing the Discrete and Continuous Logistic Models
ERIC Educational Resources Information Center
Gordon, Sheldon P.
2008-01-01
The solutions of the discrete logistic growth model based on a difference equation and the continuous logistic growth model based on a differential equation are compared and contrasted. The investigation is conducted using a dynamic interactive spreadsheet. (Contains 5 figures.)
A Few Continuous and Discrete Dynamical Systems
NASA Astrophysics Data System (ADS)
Zhang, Yufeng; Rui, Wenjuan
2016-08-01
Starting from a 2-unimodular group, we construct its new Lie algebras for which the positive-order Lax pairs and the negative-order Lax pairs are introduced, respectively. With the help of the resulting structure equation of the group we generate some partial differential equations including the well-known MKdV equation, the sine-Gordon equation, the hyperbolic sine-Gordon equation and other new nonlinear evolution equations. With the aid of the Tu scheme combined with the given Lax pairs, we obtain the isospectral and nonisospectral hierarchies of evolution equations, from which we generate two sets of symmetries of a generalized nonlinear Schrödinger (gNLS) equation. Finally, we discretize the Lax pairs to obtain a set of coupled semi-discrete equations. As their reduction, we produce the semi-discrete MKdV equation and semi-discrete NLS equation.
Discrete Tchebycheff orthonormal polynomials and applications
NASA Technical Reports Server (NTRS)
Lear, W. M.
1980-01-01
Discrete Tchebycheff orthonormal polynomials offer a convenient way to make least squares polynomial fits of uniformly spaced discrete data. Computer programs to do so are simple and fast, and appear to be less affected by computer roundoff error, for the higher order fits, than conventional least squares programs. They are useful for any application of polynomial least squares fits: approximation of mathematical functions, noise analysis of radar data, and real time smoothing of noisy data, to name a few.
Development of discrete components. Final report
Brown, R.J.
1995-11-01
Allied-Signal Inc, Kansas City Division, was provided with funding to maintain the capability to procure discrete components for various applications. A development project was undertaken to procure transistor die from one supplier for assembly into finished components by a different supplier. These components would be SA-equivalent with appropriate preconditioning, testing, and certification, The methodologies developed herein go far to ensure the future availability of discrete components.
Reaction-Transport Fronts Propagating into Unstable States
NASA Astrophysics Data System (ADS)
Méndez, Vicenç; Fedotov, Sergei; Horsthemke, Werner
In this chapter we consider the problem of propagating fronts traveling into an unstable state of a reaction-transport system. The purpose is to present the general formalism for the asymptotic analysis of traveling fronts. The method relies on the hyperbolic scaling procedure, the theory of large deviations, and the Hamilton-Jacobi technique. A generic model that describes phenomena of this type is the RD equation (2.3) with appropriate kinetics, such as the FKPP equation (4.1). The propagation velocity of fronts of this equation has been studied in Chap.4. The RD equation involves implicitly a long-time large-scale parabolic scaling, while as far as propagating fronts are concerned, the appropriate scaling must be a hyperbolic one. The macroscopic transport process arises from the overall effect of many particles performing complex random movements. Classical diffusion is simply an approximation for this transport in the long-time large-scale parabolic limit. In general, this approximation is not appropriate for problems involving propagating fronts. The basic idea is that the kinetic term in the RD equation with KPP kinetics is very sensitive to the tails of a density profile. These tails are typically "non-universal," "non-diffusional," and dependent on the microscopic details of the underlying random walk. The purpose of this chapter is to demonstrate that the macroscopic dynamics of the front for a reaction-transport system are dependent on the choice of the underlying random walk model for the transport process. To illustrate the idea of an alternative description of front propagation into an unstable state of reaction-transport system, we consider several models including discrete-in-time or continuous-in-time Markov models with long-distance dispersal kernels, non-Markovian models with memory effects, etc., instead of the RD equation. Let us give a few examples of such models.
NASA Astrophysics Data System (ADS)
Mohamed, Mamdouh S.; Hirani, Anil N.; Samtaney, Ravi
2016-05-01
A conservative discretization of incompressible Navier-Stokes equations is developed based on discrete exterior calculus (DEC). A distinguishing feature of our method is the use of an algebraic discretization of the interior product operator and a combinatorial discretization of the wedge product. The governing equations are first rewritten using the exterior calculus notation, replacing vector calculus differential operators by the exterior derivative, Hodge star and wedge product operators. The discretization is then carried out by substituting with the corresponding discrete operators based on the DEC framework. Numerical experiments for flows over surfaces reveal a second order accuracy for the developed scheme when using structured-triangular meshes, and first order accuracy for otherwise unstructured meshes. By construction, the method is conservative in that both mass and vorticity are conserved up to machine precision. The relative error in kinetic energy for inviscid flow test cases converges in a second order fashion with both the mesh size and the time step.
Discrete differential geometry: the nonplanar quadrilateral mesh.
Twining, Carole J; Marsland, Stephen
2012-06-01
We consider the problem of constructing a discrete differential geometry defined on nonplanar quadrilateral meshes. Physical models on discrete nonflat spaces are of inherent interest, as well as being used in applications such as computation for electromagnetism, fluid mechanics, and image analysis. However, the majority of analysis has focused on triangulated meshes. We consider two approaches: discretizing the tensor calculus, and a discrete mesh version of differential forms. While these two approaches are equivalent in the continuum, we show that this is not true in the discrete case. Nevertheless, we show that it is possible to construct mesh versions of the Levi-Civita connection (and hence the tensorial covariant derivative and the associated covariant exterior derivative), the torsion, and the curvature. We show how discrete analogs of the usual vector integral theorems are constructed in such a way that the appropriate conservation laws hold exactly on the mesh, rather than only as approximations to the continuum limit. We demonstrate the success of our method by constructing a mesh version of classical electromagnetism and discuss how our formalism could be used to deal with other physical models, such as fluids.
Coupling of Monte Carlo adjoint leakages with three-dimensional discrete ordinates forward fluences
Slater, C.O.; Lillie, R.A.; Johnson, J.O.; Simpson, D.B.
1998-04-01
A computer code, DRC3, has been developed for coupling Monte Carlo adjoint leakages with three-dimensional discrete ordinates forward fluences in order to solve a special category of geometrically-complex deep penetration shielding problems. The code extends the capabilities of earlier methods that coupled Monte Carlo adjoint leakages with two-dimensional discrete ordinates forward fluences. The problems involve the calculation of fluences and responses in a perturbation to an otherwise simple two- or three-dimensional radiation field. In general, the perturbation complicates the geometry such that it cannot be modeled exactly using any of the discrete ordinates geometry options and thus a direct discrete ordinates solution is not possible. Also, the calculation of radiation transport from the source to the perturbation involves deep penetration. One approach to solving such problems is to perform the calculations in three steps: (1) a forward discrete ordinates calculation, (2) a localized adjoint Monte Carlo calculation, and (3) a coupling of forward fluences from the first calculation with adjoint leakages from the second calculation to obtain the response of interest (fluence, dose, etc.). A description of this approach is presented along with results from test problems used to verify the method. The test problems that were selected could also be solved directly by the discrete ordinates method. The good agreement between the DRC3 results and the direct-solution results verify the correctness of DRC3.
41 CFR 102-117.220 - What choices do I have to ship HHG?
Code of Federal Regulations, 2010 CFR
2010-07-01
... 41 Public Contracts and Property Management 3 2010-07-01 2010-07-01 false What choices do I have to ship HHG? 102-117.220 Section 102-117.220 Public Contracts and Property Management Federal...-TRANSPORTATION MANAGEMENT Shipping Household Goods § 102-117.220 What choices do I have to ship HHG? (a) You...
41 CFR 102-117.220 - What choices do I have to ship HHG?
Code of Federal Regulations, 2011 CFR
2011-01-01
... 41 Public Contracts and Property Management 3 2011-01-01 2011-01-01 false What choices do I have to ship HHG? 102-117.220 Section 102-117.220 Public Contracts and Property Management Federal...-TRANSPORTATION MANAGEMENT Shipping Household Goods § 102-117.220 What choices do I have to ship HHG? (a) You...