摘要 :
Local test results for two enhanced condensing tubes (next-generation versions of the Wieland Gewa and Wolverine Turbo enhanced condensing tubes) are obtained for refrigerants R-134a and R-236fa on the center row of a three row-wi...
展开
Local test results for two enhanced condensing tubes (next-generation versions of the Wieland Gewa and Wolverine Turbo enhanced condensing tubes) are obtained for refrigerants R-134a and R-236fa on the center row of a three row-wide tube bundle. The "bundle effect" on the heat transfer performance of the test section is observed and described. New predictive methods for falling film condensation on bundles are proposed, based on a modification of the previous vertical single-row method with condensate slinging. The modifications performed to the experimental setup to allow for bundle tests are described. For two types of enhanced tubes and two refrigerants, the local heat flux is correlated as a function of condensation temperature difference, the film Reynolds number, the tube spacing, and liquid slinging effect.
收起
摘要 :
Computational tools are essential for most of our research. To use these tools, one needs to know how they work. Problems in application of computational methods to variation analysis can appear at several stages and affect, for e...
展开
Computational tools are essential for most of our research. To use these tools, one needs to know how they work. Problems in application of computational methods to variation analysis can appear at several stages and affect, for example, the interpretation of results. Such cases are discussed along with suggestions how to avoid them. The applications include incomplete reporting of methods, especially about the use of prediction tools; method selection on unscientific grounds and without consulting independent method performance assessments; extending application area of methods outside their intended purpose; use of the same data several times for obtaining majority vote; and filtering of datasets so that variants of interest are excluded. All these issues can be avoided by discontinuing the use software tools as black boxes.
收起
摘要 :
A newly introduced method called isotonic separation is evaluated in the prediction of firm bankruptcy. Feature reduction methods are first applied to reduce the ratios used in the prediction. Then, various classification methods,...
展开
A newly introduced method called isotonic separation is evaluated in the prediction of firm bankruptcy. Feature reduction methods are first applied to reduce the ratios used in the prediction. Then, various classification methods, including discriminant analysis, neural networks, decision tree induction, learning vector quantization, rough sets, and isotonic separation, are used with the reduced ratios. Experiments show that the isotonic separation method is a viable technique, performing generally better than other methods for short-term bankruptcy prediction.
收起
摘要 :
BackgroundVentricular premature contractions (VPCs) are common in the occult stage of cardiomyopathy in Doberman Pinschers. Although the gold standard for detecting arrhythmia is the 24-hour ambulatory electrocardiography (ECG) (H...
展开
BackgroundVentricular premature contractions (VPCs) are common in the occult stage of cardiomyopathy in Doberman Pinschers. Although the gold standard for detecting arrhythmia is the 24-hour ambulatory electrocardiography (ECG) (Holter), this method is more expensive, time-consuming and often not as readily available as common ECG.ObjectivesComparison of 5-minute ECGs with Holter examinations.AnimalsEight hundred and seventy-five 5-minute ECGs and Holter examinations of 431 Doberman Pinschers.MethodsEach examination included a 5-minute ECG and Holter examination. A cut-off value of > 100 VPCs/24 hours using Holter was considered diagnostic for the presence of cardiomyopathy. Statistical evaluation included calculation of sensitivity, specificity, positive predictive value, and negative predictive value.ResultsHolter examinations revealed > 100 VPCs/24 hours in 204/875 examinations. At least 1 VPC during a 5-minute ECG was detected in 131 (64.2%) of these 204 examinations. No VPCs were found in the 5-minute ECG in 73 (35.8%) examinations of affected Doberman Pinschers. A 5-minute ECG with at least 1 VPC as cut-off had a sensitivity of 64.2%, a specificity of 96.7%, a positive predictive value of 85.6% and a negative predictive value of 89.9% for the presence of > 100 VPCs/24 hours.Conclusions and Clinical ImportanceA 5-minute ECG is a rather insensitive method for detecting arrhythmias in Doberman Pinschers. However, the occurrence of at least 1 VPC in 5 minutes strongly warrants further examination of the dog, because specificity (96.7%) and positive predictive value (85.6%) are high and could suggest occult cardiomyopathy.
收起
摘要 :
Evapotranspiration (ET) flux constitutes a majorcomponent of both the water and energy balances at the landsurface. Among the many factors that control evapotranspiration,phenology poses a major source of uncertainty in attemptsto...
展开
Evapotranspiration (ET) flux constitutes a majorcomponent of both the water and energy balances at the landsurface. Among the many factors that control evapotranspiration,phenology poses a major source of uncertainty in attemptsto predict ET. Contemporary approaches to ET modelingand monitoring frequently summarize the complexityof the seasonal development of vegetation cover into staticphenological trajectories (or climatologies) that lack sensitivityto changing environmental conditions. The Event DrivenPhenology Model (EDPM) offers an alternative, interactiveapproach to representing phenology. This study presents theresults of an experiment designed to illustrate the differencesin ET arising from various techniques used to mimic phenologyin models of land surface processes. The experimentcompares and contrasts two realizations of static phenologiesderived from long-term satellite observations of the NormalizedDifference Vegetation Index (NDVI) against canopy trajectoriesproduced by the interactive EDPM trained on fluxtower observations. The assessment was carried out throughvalidation of predicted ET against records collected by fluxtower instruments. The VegET model (Senay, 2008) wasused as a framework to estimate daily actual evapotranspirationand supplied with seasonal canopy trajectories producedby the EDPM and traditional techniques. The interactive approachpresented the following advantages over phenologymodeled with static climatologies: (a) lower prediction biasin crops; (b) smaller root mean square error in daily ET –0.5mm per day on average; (c) stable level of errors throughoutthe season similar among different land cover types andlocations; and (d) better estimation of season duration andtotal seasonal ET.
收起
摘要 :
Based on the mathematically well defined Padé theory, a theoretically safe new procedure for the extraction of the pole mass and width of a resonance is proposed. In particular, thanks to the Montessus de Ballore theorem we are a...
展开
Based on the mathematically well defined Padé theory, a theoretically safe new procedure for the extraction of the pole mass and width of a resonance is proposed. In particular, thanks to the Montessus de Ballore theorem we are able to unfold the second Riemann sheet of an amplitude to search for the position of the resonance pole in the complex plane. The method is systematic and provides a model-independent treatment of the prediction and the corresponding errors of the approximation. Likewise, it can be used in combination with other well-established approaches to improve future determinations of resonance parameters.
收起
摘要 :
Computational fluid dynamics predictions based on machine learning methods have become an important area of turbulence and transition research. However, the otherwise efficient and low-cost transition models based on Reynolds-aver...
展开
Computational fluid dynamics predictions based on machine learning methods have become an important area of turbulence and transition research. However, the otherwise efficient and low-cost transition models based on Reynolds-averaged Navier-Stokes (RANS) methods have limited capability for dealing with hypersonic conditions, owing to the strong compressibility and multimodal features that are then present. This paper develops an augmented method for transition heat flux prediction. A deep neural network (DNN) is trained using flight test data from the China Aerodynamics Research and Development Center. The subject of the flight test is an inclined blunt cone on which temperature sensors are mounted. The training data consist of RANS solutions and flight test data, with the input being the mean strain/rotation rate tensor from RANS and the output the heat flux values from the flight test. The trained DNN model based on the RANS results can give heat flux values with similar accuracy to those from the flight test. For the blunt cone, the trained DNN model can accurately forecast the heat distribution caused by the Mack mode and the cross-flow transition under various inflow conditions, and the errors in the prediction results are all within 15%. Furthermore, the generalizability of the trained DNN model is also verified on an elliptic cone under different inflow conditions. This paper provides a new transition prediction approach with low computational cost and high accuracy. The proposed method solves the problem that the transition model fails in some working conditions and avoids re-modifying empirical criteria in the RANS model. It has both advantages of a transition model and flight tests and maintains the excellent potential for application.
收起
摘要 :
There are nearly two million subscribers to carsharing services worldwide. These services can provide large benefits both to users and the general public (e.g., through emissions reductions). There has not however previously exist...
展开
There are nearly two million subscribers to carsharing services worldwide. These services can provide large benefits both to users and the general public (e.g., through emissions reductions). There has not however previously existed a general framework for forecasting their market potential and impacts that is sensitive to the way that they re-structure the costs associated with personal car ownership. Techniques for predicting market scope and impacts ahead of field implementation are urgently required, both by entrepreneurs and the public sector, whose support, or at least acquiescence, is generally required.This paper draws on the Perceived Activity Set conceptual framework that was recently developed to address the methodological challenges posed by carsharing, and presents the first set of empirical findings from employing it to model carsharing. The empirical analysis makes uses of pooled data from the British National Travel Survey and a purpose-designed stated-choice survey. We investigate both the 'round-trip' and 'point-to-point' carsharing service models.The results suggest that the number of prospective subscribers to a point-to-point car-sharing service in London is between three and four times as large as the comparable number for round-trip carsharing. The greatest reduction in overall vehicle-miles of travel -including both carsharing cars and private cars - was found from introducing round-trip carsharing across all of London. Survey respondents indicated they would use point-to-point carsharing for commuting journeys much more frequently than round-trip carsharing. Finally, point-to-point carsharing was found to be a substitute for public transport, whilst round-trip carsharing was found to be a complement.
收起
摘要 :
The melting point of organic compounds was estimated using a simple group contribution method. The optimum parameters of this new method were obtained using particle swarm optimization in a multivariate linear regression. The melt...
展开
The melting point of organic compounds was estimated using a simple group contribution method. The optimum parameters of this new method were obtained using particle swarm optimization in a multivariate linear regression. The melting temperatures of 250 pure compounds were predicted, and the results were compared with experimental data and other models available in the literature. Compared to the currently used group contribution methods, the new method makes significant improvements in accuracy and applicability of this important property. The study shows that the proposed method presents an excellent alternative for the estimation of the melting temperature of organic compounds (AARD of 10%) from the knowledge of the molecular structure.
收起
摘要 :
Multireference correlation in diradical molecules can be captured by a single-reference 2-electron reduced-density-matrix (2-RDM) calculation with only single and double excitations in the 2-RDM parametrization. The 2-RDM parametr...
展开
Multireference correlation in diradical molecules can be captured by a single-reference 2-electron reduced-density-matrix (2-RDM) calculation with only single and double excitations in the 2-RDM parametrization. The 2-RDM parametrization is determined by N-representability conditions that are non-perturbative in their treatment of the electron correlation. Conventional single-reference wave function methods cannot describe the entanglement within diradical molecules without employing triple- and potentially even higher-order excitations of the mean-field determinant. In the isomerization of bicyclobutane to gauche-1,3-butadiene the parametric 2-RDM (p2-RDM) method predicts that the diradical disrotatory transition state is 58.9 kcal/mol above bicyclobutane. This barrier is in agreement with previous multireference calculations as well as recent Monte Carlo and higher-order coupled cluster calculations. The p2-RDM method predicts the Nth natural-orbital occupation number of the transition state to be 0.635, revealing its diradical character. The optimized geometry from the p2-RDM method differs in important details from the complete-active-space self-consistent-field geometry used in many previous studies including the Monte Carlo calculation.
收起
原文获取