One-group Model Research Articles

Benchmark of interfacial area concentration approaches for the two-fluid model in gas-dispersed condensing flow

Accurate predictions of interfacial area concentration (IAC) are required for closure of the condensation phase change term. The interfacial area transport equation (IATE) can dynamically predict interfacial area concentration and is increasingly being used in the benchmarking of phase change flows over static based correlations which require a flow regime map. For higher flow regimes, the two-group two-fluid IATE model can separately model the transport of spherical bubbles and cap/slug bubbles. A modified formulation of the one-group and two-group two-fluid model with interfacial area transport equation was recently proposed for gas-dispersed condensing flows. Three datasets have been used for validation consisting of condensing two-phase flow data in the unheated section of a vertical annulus with conditions spanning a range of pressures, inlet subcoolings and mass fluxes for benchmarking the various IAC approaches. For bubbly flows, the coupled void transport - IATE simulation results in good agreement in the predictions of the void fraction and the interfacial area concentration under nearly all sixty conditions. Considering the proposed two-group two-fluid IATE model formulation, the group-2 Nusselt number correlation is investigated to account for the appropriate heat transfer length scale for group-2 bubbles. Validation of the proposed two-group two-fluid model against the new dataset shows good agreement with experimental data with significant improvement over the one-group IATE model for conditions with substantial group-2 void fraction throughout the simulation domain.

Modeling and control of xenon oscillations in thermal neutron reactors

We study axial core oscillations due to xenon poisoning in thermal neutron nuclear reactors with simple 1D models: a linear one-group model, a linear two-group model, and a non-linear model taking the Doppler effect into account. Even though nuclear reactor operators have some 3D computer codes to simulate such phenomena, we think that simple models are useful to identify the sensitive parameters, and study the efficiency of basic control laws. Our results are that, for the one-group model, if we denote the migration area by M 2 and by H the height of the core, the sensitive parameter is H/M. H being fixed, for the 2 groups model, there are still 2 sensitive parameters, the first one being replaced by M12+M22 where M12 denotes the migration area for fast neutrons and M22 the migration area for thermal neutrons. We show that the Doppler effect reduces the instability of xenon oscillations in a significant way. Finally, we show that some proportional/integral/derivative (PID) feedback control law can damp out xenon oscillations in a similar way to the well-known Shimazu control law [Y. Shimazu, Continuous guidance procedure for xenon oscillation control, J. Nucl. Sci. Technol. 32, 1159 (1995)]. The numerical models described in our paper have been applied to PWR.

CHANGE IN SENTIMENTS, ATTITUDES AND CONCERNS TOWARDS INCLUSIVE EDUCATION: A PERS

Inclusive education is a global movement that mediates the prevention of the exclusion of children with special needs in order to support their participation in the general education system. It is thought that the sentiments, attitudes, and concerns of the prospective preschool teachers towards inclusive education are related to their knowledge level about inclusive education. Therefore, in this study, the aim is to examine the change in the sentiments, attitudes, and concerns of the prospective preschool teachers towards inclusive education after they receive a training about inclusive education. The research adopted one-group pretest-posttest model as the experimental design. The study group was comprised of 138 prospective preschool teachers who attend Inclusive Education Program (IEP). IEP was developed by researchers with the purpose of increasing the level of knowledge, sentiments, and attitudes of prospective preschool teachers in terms of inclusive education and of decreasing their concern levels. IEP is a 10-week program prepared by researchers by examining the relevant literature and taking expert opinions. As data collection tools, “Personal Information Form” and “Sentiments, Attitudes, and Concerns Related to Inclusive Education Scale” were used. As a result of study, the sentiment, attitude, and concern levels of the prospective preschool teachers towards inclusive education were determined at a moderate level. In line with this conclusion, an intervention plan was made to increase the sentiment and attitude levels of the prospective preschool teachers and to decrease their concern levels. Following the implemented inclusive education training, it was observed that the sentiment and attitude levels of the prospective preschool teachers towards inclusive education increased and their concern levels decreased.

Evaluation of Cultural Sensitivity in Healthcare Service among Nursing Students

<p style="text-align:justify">The aim of the study evaluates cultural sensitivity in healthcare services among senior nursing students to patients with different cultural backgrounds. The study had a one-group pre-posttest model descriptive study design. Thirty-four nursing students taking the courses Emergency Care and Diabetes were included into the study. Standardized patients were used as a simulation technique. The difference between intercultural sensitivity scores before the simulation and those after the simulation was not statistically significant (p>0.05). Even though there were no differences between intercultural sensitivity scores before the simulation and the scores after the simulation, simulation based education is an effective teaching method in enhancement of cultural sensitivity.</p>

The Effectiveness of Module and Compact Disc Poem Teaching Based on Local Wisdom

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P165 - Effect of Cooking Classes on Healthy Eating Behavior Among College Students

Background (Background, Rationale, Prior Research, and/or Theory): Many college students do not understand how to prepare healthy meals accounting for food safety, which can prompt students to consume convenient, often unhealthy foods. Objective: To determine if cooking classes tailored to college students would improve knowledge and behavior to eat healthfully and practice food safety. Study Design, Setting, Participants, Intervention: A one-group, pre- and post-test model was used. Three cooking-classes were developed with parameters of limited cooking skills, limited access to kitchen equipment, and shelf-stable ingredients that are readily available on campuses (i.e. convenience stores and salad bars). Participants (n = 38) were recruited using tabling, posters, email, and social media. Outcome Measures and Analysis: Pre- and post- surveys assessed nutrition knowledge, frequency of healthy eating, cooking confidence, cooking ability, cooking frequency, and food safety knowledge. Participants were also queried on their perception of the cooking classes and their dietary behaviors post-intervention. Results: Scores for nutrition knowledge (P = .000), cooking confidence (P = .026), ability to put together ready-made ingredients to make a complete meal (P = .016), and preparing dishes from basic ingredients (P = .006) increased. There were no changes in ability to cook convenience foods, cooking frequency, food safety knowledge, nor frequency of healthy food consumption. However, 83% of participants perceived that they were consuming healthier diets because of the cooking classes. Conclusions and Implications: Cooking classes tailored to college students with limited access to cooking facilities, equipment, and ingredients that can be purchased on campus were effective in improving nutrition knowledge, cooking confidence, the ability to put together ready-made ingredients to make a complete meal, and the ability to prepare dishes from basic ingredients. Despite participants' reports that their diets were healthier after the cooking classes; there was no significant change in the frequency of choosing healthier foods detected via survey assessments. Cooking classes tailored to the college student population can be used to educate about nutrition and food safety and improve confidence and cooking ability. Funding: USDA. The following is the supplementary data to this article: Download .pdf (.49 MB) Help with pdf files Poster

Code performance with improved two-group interfacial area concentration correlation for one-dimensional forced convective two-phase flow simulation

ABSTRACTIn gas–liquid two-phase flow simulation for reactor safety analysis, interfacial momentum transfer in two-fluid model plays an important role in predicting void fraction. Depending on flow conditions, a shape of the two-phase interface complicatedly evolves. One of the proposed approaches is to quantify the gas–liquid interface information using interfacial area transport equation. On the other hand, a more simplified and robust approach is to classify bubbles into two-groups based on their transport characteristics and utilize constitutive equations for interfacial area concentration for each group. In this paper, interfacial drag model based on the two-group interfacial area concentration correlations is implemented into system analysis code, and void fractions were calculated for the evaluation of numerical behaviors. The present analysis includes (1) comparison of one-group and two-group relative velocity models, (2) comparison with separate effect test database, (3) uncertainty evaluation of drag coefficient, (4) numerical stability assessment in flow regime transition, and (5) transient analysis for simulating the prototypic condition. Results showed that utilization of interfacial drag force term using constitutive equations of two-group interfacial area concentration yields satisfactory void fraction calculation results. The proposed solution technique is practical and advantageous in view of reducing the computational cost and simplifying the solution scheme.

On the Convergence of the Eigenvalue Response Matrix Method

A study of the convergence behavior of the eigenvalue response matrix method (ERMM) for nuclear reactor eigenvalue problems is presented. The eigenvalue response matrix equations are traditionally solved by a two-level iterative scheme in which an inner eigenproblem yields particle balance across node boundaries and an outer fixed-point iteration updates the global k-eigenvalue. Past work has shown the method converges rapidly, but the properties of its convergence have not been studied in detail. To perform a formal assessment of these properties, the one-dimensional, one-group diffusion approximation is used to derive the asymptotic error constant of the fixed-point iteration. Several problems are solved numerically, and the observed convergence behavior is compared to the analytic model based on buckling and nodal dimensions (in mean free paths). The results confirm the method converges quickly, with no degradation in the convergence rate for small nodes, which is an observation that suggests ERMM can be used for large-scale, parallel computations with no penalty from the decomposition of a domain into smaller nodes. In addition, results from multigroup problems show that convergence depends strongly on the heterogeneity and the energy representation of a model. In particular, the convergence for two-group and heterogeneous, one-group models is substantially slower than for the homogeneous, one-group model.

Translation of a Motor Learning Walking Rehabilitation Program Into a Group-Based Exercise Program for Community-Dwelling Older Adults

BackgroundTraditional exercise programs for older adults, which focus on aerobic and strength training, have had only modest effects on walking. Recently, a motor learning exercise program was shown to have greater effects on walking compared with a traditional exercise program. Translating this novel motor learning exercise program into a group exercise program would allow it to be offered as an evidence-based, community-based program for older adults. ObjectiveTo translate a walking rehabilitation program based on motor learning theory from one-on-one to group delivery (On the Move) and evaluate multiple aspects of implementation in older adults with impaired mobility. DesignThe translation process involved multiple iterations, including meetings of experts in the field (Phase I), focus groups (Phase II), and implementation of the newly developed program (Phase III). Phase III was based on a one-group model of intervention development for feasibility, safety, potential effects, and acceptability. SettingCommunity sites, including 2 independent living facilities, an apartment building, and a community center. ParticipantsAdults 65 years of age or older who could ambulate independently and who were medically stable. Thirty-one adults, mean age 82.3 ± 5.6 years, were eligible to participate. MethodsThe group exercise program was held twice a week for 12 weeks. Main Outcome MeasurementsAcceptability of the program was determined by retention and adherence rates and a satisfaction survey. Risk was measured by adverse events and questions on perceived challenge and safety. Mobility was assessed pre- and postintervention by gait speed, Figure of 8 Walk Test, and 6-minute walk test. ResultsModifications to the program included adjustments to format/length, music, education, and group interaction. The 12-week program was completed by 24 of 31 entrants (77%). Adherence was high, with participants attending on average 83% of the classes. Safety was excellent, with only 1 subject experiencing a controlled, noninjurious fall. There was preliminary evidence for improved mobility after the intervention: gait speed improved from 0.76 ± 0.21 to 0.81 ± 0.22 m/s, P = .06; Figure of 8 Walk Test from 13.0 ± 3.9 to 12.0 ± 3.9 seconds, P = .07; and 6-minute walk test from 246 ± 75 to 281 ± 67 m, P = .02. ConclusionsThe group-based program was safe and acceptable to older adults with impaired mobility and resulted in potentially clinically meaningful improvements in mobility.

Goal-Oriented h-Adaptivity for the Multigroup SPN Equations

We investigate application of goal-oriented mesh adaptivity to the SPN multigroup equations. This technique utilizes knowledge of the computational goal and combines it with mesh adaptivity to accurately and rapidly compute quantities of interest. Specifically, the local error is weighted by the importance of a given cell toward the computational goal, resulting in appropriate goal-oriented error estimates. Even though this approach requires the solution of an adjoint (dual) problem, driven by a specific source term for a given quantity of interest, the work reported here clearly shows the benefits of such a method.We demonstrate the level of accuracy this method can achieve using two-dimensional and three-dimensional numerical test cases for one-group and two-group models and compare results with more traditional mesh refinement and uniformly refined meshes. The test cases consider situations in which the radiative flux of a source is shielded and are designed to prototypically explore the range of conditions under which our methods improve on other refinement algorithms. In particular, they model strong contrasts in material properties, a situation ubiquitous in nuclear engineering.

One-dimensional transport equation models for sound energy propagation in long spaces: Simulations and experiments

In this paper, the accuracy and efficiency of the previously discussed one-dimensional transport equation models [Y. Jing et al., J. Acoust. Soc. Am. 127, 2312-2322 (2010)] are examined both numerically and experimentally. The finite element method is employed to solve the equations. Artificial diffusion is applied in the numerical implementation to suppress oscillations of the solution. The transport equation models are then compared with the ray-tracing based method for different scenarios. In general, they are in good agreement, and the transport equation models are substantially less time consuming. In addition, the two-group model is found to yield more accurate results than the one-group model for the tested cases. Lastly, acoustic experimental results obtained from a 1:10 long room scale-model are used to verify the transport equation models. The results suggest that the transport equation models are able to accurately model the sound field in a long space.

Longitudinal Associations between Maternal Work Stress, Negative Work-Family Spillover, and Depressive Symptoms.

The current study examined associations over an 18-month period between maternal work stressors, negative work-family spillover, and depressive symptoms in a sample of 414 employed mothers with young children living in six predominantly nonmetropolitan counties in the Eastern United States. Results from a one-group mediation model revealed that a less flexible work environment and greater work pressure predicted higher levels of depressive symptoms, and further, that these associations were mediated by perceptions of negative work-family spillover. Additionally, results from a two-group mediation model suggested that work pressure predicted greater perceptions of spillover only for mothers employed full-time. Findings suggest the need for policies that reduce levels of work stress and help mothers manage their work and family responsibilities.

Epidemic Models with Heterogeneous Mixing and Treatment

We consider a two-group epidemic model with treatment and establish a final size relation that gives the extent of the epidemic. This relation can be established with arbitrary mixing between the groups even though it may not be feasible to determine the reproduction number for the model. If the mixing of the two groups is proportionate, there is an explicit expression for the reproductive number and the final size relation is expressible in terms of the components of the reproduction number. We also extend the results to a two-group influenza model with proportionate mixing. Some numerical simulations suggest that (i) the assumption of no disease deaths is a good approximation if the disease death rate is small and (ii) a one-group model is a close approximation to a two-group model but a two-group model is necessary for comparing targeted treatment strategies.

Relational and Physical Aggression, Prosocial Behavior, and Peer Relations

In this 3-year prospective study (N = 458) spanning a transition to middle school, bidirectional associations between children’s relations with schoolmates (social preference andimpact)and behaviors (physical and relational aggression, prosocial behavior) were examined using structural equation modeling. Gender moderation of all estimated paths was examined. There was no gender difference in relational aggression in Grade 3; girls were more relationally aggressive than boys in Grade 6. Males were more physically aggressive than females; females were more prosocial and preferred by peers. Longitudinal and bidirectional associations between relations with peers and behaviors were found. Compared to one-group models of social preference and impact, gender moderation models improved model fit significantly. With regard to social preference and children’s behaviors, gender moderated concurrent, but not longitudinal, associations. With regards to social impact and children’s behaviors, gender moderated both concurrent and longitudinal associations. There was moderate stability of behaviors, including relational aggression.

Ecosystem changes after the SEEDS iron fertilization in the western North Pacific simulated by a one-dimensional ecosystem model

We have developed a one-dimensional ecosystem model considering explicitly two groups of diatoms: centric and pennate. The model was applied to the iron-enrichment experiment, SEEDS (Subarctic Pacific Iron Experiment for Ecosystem Dynamics Study) in the western North Pacific (48.5°N, 165°E). We assumed that the pennate diatoms are not stressed by the iron limitation, but that the centric diatoms are significantly stressed and their photosynthetic rate is high when released from iron limitation. The iron-enrichment experiment was conducted by changing the physiological parameters for diatoms (the initial slope of the photosynthetic rate and the potential maximum photosynthetic rate). The model successfully reproduced the time-series of CO 2 fugacity and the vertical distributions of chlorophyll- a and nutrients observed in SEEDS. The simulated results in the two-group model, especially the starting time of the diatom bloom, are better than those in the one-group model. We find that it is the transition of dominance, from pennate to centric diatoms, rather than a physiological response of each group that causes the lag between iron-enrichment and the diatom bloom. In the simulations, the added iron’s effect on the ecosystem continues for about 40 days. The model results suggest that the export flux during the observation period is only about 20% of the total export flux generated by iron-enrichment. For SEEDS, our simulated uptake of atmospheric CO 2 and the export of particulate organic carbon at 100 m depth are 0.57 and 1.29 mol C m −2, respectively, which are converted to 1720 and 3880 tC by assuming the patch’s area to be 250 km 2, and to 4.90 and 11.1 tC kg −1 Fe with the addition of 350 kg of iron.

A 3-D neutronics model for the calibration of the control rod of the syrian MNSR

An accurate 3-D model using the core calculation code CITATION for the calibration of the control rod in MNSR was developed. The model can easily be extended to other research reactors having more complicated geometries. Using the 3-D model, calibration of the control rod at positions which would be difficult experimentally was made possible. Good agreement between calculated and measured control rod worths was obtained. Comparison between theoretically established one-group and two-group models for the calculation of control rod worth against 3-D model results was made.

Peach Bottom 2 Turbine Trip Simulation Using TRAC-BF1/COS3D, a Best-Estimate Coupled 3-D Core and Thermal-Hydraulic Code System

The best-estimate coupled three-dimensional (3-D) core and thermal-hydraulic code system TRAC-BF1/COS3D has been developed. COS3D, based on a modified one-group neutronic model, is a 3-D core simulator used for licensing analyses and core management of commercial boiling water reactor (BWR) plants in Japan. TRAC-BF1 is a plant simulator based on a two-fluid model. TRAC-BF1/COS3D is a coupled system of both codes, which are connected using a parallel computing tool. This code system was applied to the OECD/NRC BWR Turbine Trip Benchmark. Since the two-group cross-section tables are provided by the benchmark team, COS3D was modified to apply to this specification. Three best-estimate scenarios and four hypothetical scenarios were calculated using this code system. In the best-estimate scenario, the predicted core power with TRAC-BF1/COS3D is slightly underestimated compared with the measured data. The reason seems to be a slight difference in the core boundary conditions, that is, pressure changes and the core inlet flow distribution, because the peak in this analysis is sensitive to them. However, the results of this benchmark analysis show that TRAC-BF1/COS3D gives good precision for the prediction of the actual BWR transient behavior on the whole. Furthermore, the results with the modified one-group model and the two-group model were compared to verify the application of the modified one-group model to this benchmark. This comparison shows that the results of the modified one-group model are appropriate and sufficiently precise.

Minimum critical mass and flat flux in a 2-group model

Solutions for a flat thermal flux in a two-group diffusion model are found for a range of assumptions, since this is a requisite for both a minimum and a maximum fuel loading in the model. It is shown that a maximum fuel loading then arises when such a region, at unity infinite multiplication factor, is complemented by an outer core to bring the finite reactor critical. Correspondingly, when a core with a flat flux is surrounded by a reflector, the core fuel may be so distributed as to flatten the flux using the ‘flux-trap’ phenomenon and provide a minimum loading. Critical conditions and necessary fuel density are derived in finite and infinitely thick reflectors. A curiosity is the possibility of observing ‘negative’ reflector savings. Fuel savings are estimated for a range of models for the minimum loading compared to a correspondingly critical uniform core loading. In some circumstances a saving of up to 70% is indicated with economic and safety implications. It is shown how the reduction of the minimum loading solution from a two- to a one-group model retains the flat flux in the core but fails to satisfy the thermal boundary condition unless a reflector, with the flux-trap, is used so that without it, the two-group minimum fuel loading solution cannot fully transform to a minimum loading in one group. The full solution for a two-group model flat flux core with finite thickness reflector is given. It is shown that as the reflector is reduced it becomes necessary to increase the fuel density at the centre to a point where this exceeds the capability of the chosen fuel, thus providing a secondary criticality equation. The increasing steepness (negative slope) of the flux distribution is required to make the flux trap phenomenon possible in the reducing reflector region. The range in which there may be two reflector thicknesses leading to the same size core, but different fuel distributions observed by Williams, is determined. Constrained solutions that limit either the size of core or the maximum fuel density are considered, generalising the original work of Goertzel to a practicable core design.

PLUTON: A Three-Group Model for the Radial Distribution of Plutonium, Burnup, and Power Profiles in Highly Irradiated LWR Fuel Rods

A three-group model (PLUTON) is described, which predicts the power density distribution, plutonium buildup, and burnup profiles across the fuel pellet radius as a function of in-pile time and parameters characterizing the type of reactor system with respect to fuel temperature and changes of density during the irradiation period. The PLUTON model is a part of two fuel performance codes (ASFAD and FEMAXI-V), which provide all necessary input for this model, mainly local temperatures and fuel matrix density across the radius. Comparisons between measurements and predictions of the PLUTON model are made on fuels with enrichments in the range 2.9 to 8.25% and with burnup between 21 000 and 64 000 MWd/t. It is shown that the PLUTON predictions are in good agreement with measurements as well as with predictions of the well-known TUBRNP model. The proposed model is flexibly applicable for all types of light water reactor (LWR) fuels, including mixed oxide, and for fuel tested in the Organization for Economic Corporation and Development’s Halden heavy water reactor. The PLUTON three-group model is based on analytical (theoretical) consideration of neutron absorption in a resonant region of the fuel in its apparent form. It makes the model more flexible in comparison with the semi-empirical TUBRNP one-group model and allows the physically based model analysis of commercial LWR-type fuels at high burnup as well as analysis of experimental fuel rods tested in the Halden heavy water reactor, which is one of the main test reactors in the world. The differences in fuel behavior in the Halden reactor in terms of burnup distribution and plutonium buildup can be more clearly understood with the PLUTON model.

Pulsed turbulence of the neutron field in nuclear reactors

It is shown on the basis of a one-group diffusion model with delayed neutrons that if the pulsed feedback function is negative and nonmonotonic and the gain of the feedback is large, an autooscillatory regime of spatiotemporal chaos, called the regime of pulsed turbulence of the neutron field, arises in small reactors. It consists in the fact that neutron bursts with random intensity arise at random times in local regions of the reactor, whose size, shape, and arrangement in the core vary irregularly with time. It is indicated that this regime is possible and could be desirable in reactors with a gaseous core.