Characters, Commutators and Centers of Sylow Subgroups

The character table of a finite group G determines whether |P:P'|=p^2 and whether |P:Z(P)|=p^2, where P is a Sylow p-subgroup of G. To prove the latter, we give a detailed classification of those groups in terms of the generalized Fitting subgroup.Comment: 18 page

Retail globalization and household welfare:evidence from Mexico

The arrival of global retail chains in developing countries is causing a radical transformation in the way that households source their consumption. This paper draws on a new collection of Mexican microdata to estimate the effect of foreign supermarket entry on household welfare. The richness of the microdata allows us to estimate a general expression for the gains from retail FDI, and to decompose these gains into several distinct channels. We find that foreign retail entry causes large and significant welfare gains for the average household that are mainly driven by a reduction in the cost of living. About one quarter of this price index effect is due to pro-competitive effects on the prices charged by domestic stores, with the remaining three quarters due to the direct consumer gains from shopping at the new foreign stores. We find little evidence of significant changes in average municipality-level incomes or employment. We do, however, find evidence of store exit, adverse effects on domestic store profits and reductions in the incomes of traditional retail sector workers. Finally, we show that the gains from retail FDI are on average positive for all income groups but regressive, and quantify the opposing forces that underlie this finding

Fast and realistic large-scale structure from machine-learning-augmented random field simulations

Producing thousands of simulations of the dark matter distribution in the Universe with increasing precision is a challenging but critical task to facilitate the exploitation of current and forthcoming cosmological surveys. Many inexpensive substitutes to full N-body simulations have been proposed, even though they often fail to reproduce the statistics of the smaller non-linear scales. Among these alternatives, a common approximation is represented by the lognormal distribution, which comes with its own limitations as well, while being extremely fast to compute even for high-resolution density fields. In this work, we train a generative deep learning model, mainly made of convolutional layers, to transform projected lognormal dark matter density fields to more realistic dark matter maps, as obtained from full N-body simulations. We detail the procedure that we follow to generate highly correlated pairs of lognormal and simulated maps, which we use as our training data, exploiting the information of the Fourier phases. We demonstrate the performance of our model comparing various statistical tests with different field resolutions, redshifts, and cosmological parameters, proving its robustness and explaining its current limitations. When evaluated on 100 test maps, the augmented lognormal random fields reproduce the power spectrum up to wavenumbers of 1hMpc−1, and the bispectrum within 10 per cent, and always within the error bars, of the fiducial target simulations. Finally, we describe how we plan to integrate our proposed model with existing tools to yield more accurate spherical random fields for weak lensing analysis

Machine-learning cosmology from void properties

Cosmic voids are the largest and most underdense structures in the Universe. Their properties have been shown to encode precious information about the laws and constituents of the Universe. We show that machine learning techniques can unlock the information in void features for cosmological parameter inference. We rely on thousands of void catalogs from the GIGANTES dataset, where every catalog contains an average of 11,000 voids from a volume of $1~(h^{-1}{\rm Gpc})^3$. We focus on three properties of cosmic voids: ellipticity, density contrast, and radius. We train 1) fully connected neural networks on histograms from individual void properties and 2) deep sets from void catalogs, to perform likelihood-free inference on the value of cosmological parameters. We find that our best models are able to constrain the value of $\Omega_{\rm m}$, $\sigma_8$, and $n_s$ with mean relative errors of $10\%$, $4\%$, and $3\%$, respectively, without using any spatial information from the void catalogs. Our results provide an illustration for the use of machine learning to constrain cosmology with voids.Comment: 13 pages, 8 figures, 1 table, published on Ap

Design and Numerical Analysis of Flow Characteristics in a Scaled Volute and Vaned Nozzle of Radial Turbocharger Turbines

[EN] Over the past few decades, the aerodynamic improvements of turbocharger turbines contributed significantly to the overall efficiency augmentation and the advancements in downsizing of internal combustion engines. Due to the compact size of automotive turbochargers, the experimental measurement of the complex internal aerodynamics has been insufficiently studied. Hence, turbine designs mostly rely on the results of numerical simulations and the validation of zero-dimensional parameters as efficiency and reduced mass flow. To push the aerodynamic development even further, a precise validation of three-dimensional flow patterns predicted by applied computational fluid dynamics (CFD) methods is in need. This paper presents the design of an up-scaled volute-stator model, which allows optical experimental measurement techniques. In a preliminary step, numerical results indicate that the enlarged geometry will be representative of the flow patterns and characteristic non-dimensional numbers at defined flow sections of the real size turbine. Limitations due to rotor-stator interactions are highlighted. Measurement sections of interest for available measurement techniques are predefined.The authors disclose receipt of the following financial support for the research, authorship, and/or publication of this article: This work was partly sponsored by the program "Ayuda a Primeros Proyectos de Investigacion (PAID-06-18), Vicerrectorado de Investigacion, Innovacion y Transferencia de la Universitat Politecnica de Valencia (UPV), Spain". The support given to Ms. N.H.G. by Universitat Politecnica de Valencia through the "FPI-Subprograma 2" (No.FPI-2018-S2-1368) grant within the "Programa de Apoyo para la Investigacion y Desarrollo (PAID-01-18)" is gratefully acknowledgedTiseira, A.; Navarro, R.; Inhestern, LB.; Hervás-Gómez, N. (2020). Design and Numerical Analysis of Flow Characteristics in a Scaled Volute and Vaned Nozzle of Radial Turbocharger Turbines. Energies. 13(11):1-19. https://doi.org/10.3390/en13112930S1191311Praveena, V., & Martin, M. L. J. (2018). A review on various after treatment techniques to reduce NOx emissions in a CI engine. Journal of the Energy Institute, 91(5), 704-720. doi:10.1016/j.joei.2017.05.010Sindhu, R., Amba Prasad Rao, G., & Madhu Murthy, K. (2018). Effective reduction of NOx emissions from diesel engine using split injections. Alexandria Engineering Journal, 57(3), 1379-1392. doi:10.1016/j.aej.2017.06.009Gil, A., Tiseira, A. O., García-Cuevas, L. M., Usaquén, T. R., & Mijotte, G. (2018). Fast three-dimensional heat transfer model for computing internal temperatures in the bearing housing of automotive turbochargers. International Journal of Engine Research, 21(8), 1286-1297. doi:10.1177/1468087418804949Suhrmann, J. F., Peitsch, D., Gugau, M., & Heuer, T. (2012). On the Effect of Volute Tongue Design on Radial Turbine Performance. Volume 8: Turbomachinery, Parts A, B, and C. doi:10.1115/gt2012-69525Roumeas, M., & Cros, S. (2012). Aerodynamic Investigation of a Nozzle Clearance Effect on Radial Turbine Performance. Volume 8: Turbomachinery, Parts A, B, and C. doi:10.1115/gt2012-68835Liu, Y., Yang, C., Qi, M., Zhang, H., & Zhao, B. (2014). Shock, Leakage Flow and Wake Interactions in a Radial Turbine With Variable Guide Vanes. Volume 2D: Turbomachinery. doi:10.1115/gt2014-25888Cornolti, L., Onorati, A., Cerri, T., Montenegro, G., & Piscaglia, F. (2013). 1D simulation of a turbocharged Diesel engine with comparison of short and long EGR route solutions. Applied Energy, 111, 1-15. doi:10.1016/j.apenergy.2013.04.016Bohbot, J., Chryssakis, C., & Miche, M. (2006). Simulation of a 4-Cylinder Turbocharged Gasoline Direct Injection Engine Using a Direct Temporal Coupling Between a 1D Simulation Software and a 3D Combustion Code. SAE Technical Paper Series. doi:10.4271/2006-01-3263Inhestern, L. B. (s. f.). Measurement, Simulation, and 1D-Modeling of Turbocharger Radial Turbines at Design and Extreme Off-Design Conditions. doi:10.4995/thesis/10251/119989Tamaki, H., & Unno, M. (2008). Study on Flow Fields in Variable Area Nozzles for Radial Turbines. International Journal of Fluid Machinery and Systems, 1(1), 47-56. doi:10.5293/ijfms.2008.1.1.047Eroglu, H., & Tabakoff, W. (1991). LDV Measurements and Investigation of Flow Field Through Radial Turbine Guide Vanes. Journal of Fluids Engineering, 113(4), 660-667. doi:10.1115/1.2926531Karamanis, N., Martinez-Botas, R. F., & Su, C. C. (2000). Mixed Flow Turbines: Inlet and Exit Flow Under Steady and Pulsating Conditions. Volume 1: Aircraft Engine; Marine; Turbomachinery; Microturbines and Small Turbomachinery. doi:10.1115/2000-gt-0470Galindo, J., Tiseira Izaguirre, A. O., García-Cuevas, L. M., & Hervás Gómez, N. (2020). Experimental approach for the analysis of the flow behaviour in the stator of a real centripetal turbine. International Journal of Engine Research, 22(6), 2010-2020. doi:10.1177/1468087420916281Dufour, G., Carbonneau, X., Cazalbou, J.-B., & Chassaing, P. (2006). Practical Use of Similarity and Scaling Laws for Centrifugal Compressor Design. Volume 6: Turbomachinery, Parts A and B. doi:10.1115/gt2006-91227Tancrez, M., Galindo, J., Guardiola, C., Fajardo, P., & Varnier, O. (2011). Turbine adapted maps for turbocharger engine matching. Experimental Thermal and Fluid Science, 35(1), 146-153. doi:10.1016/j.expthermflusci.2010.07.018Menter, F. R. (1994). Two-equation eddy-viscosity turbulence models for engineering applications. AIAA Journal, 32(8), 1598-1605. doi:10.2514/3.12149Broatch, A., Galindo, J., Navarro, R., & García-Tíscar, J. (2014). Methodology for experimental validation of a CFD model for predicting noise generation in centrifugal compressors. International Journal of Heat and Fluid Flow, 50, 134-144. doi:10.1016/j.ijheatfluidflow.2014.06.006Smirnov, P. E., Hansen, T., & Menter, F. R. (2007). Numerical Simulation of Turbulent Flows in Centrifugal Compressor Stages With Different Radial Gaps. Volume 6: Turbo Expo 2007, Parts A and B. doi:10.1115/gt2007-27376Serrano, J. R., Olmeda, P., Arnau, F. J., Dombrovsky, A., & Smith, L. (2014). Analysis and Methodology to Characterize Heat Transfer Phenomena in Automotive Turbochargers. Journal of Engineering for Gas Turbines and Power, 137(2). doi:10.1115/1.4028261Serrano, J. R., Olmeda, P., Arnau, F. J., Dombrovsky, A., & Smith, L. (2015). Turbocharger heat transfer and mechanical losses influence in predicting engines performance by using one-dimensional simulation codes. Energy, 86, 204-218. doi:10.1016/j.energy.2015.03.130Serrano, J. R., Tiseira, A., García-Cuevas, L. M., Inhestern, L. B., & Tartoussi, H. (2017). Radial turbine performance measurement under extreme off-design conditions. Energy, 125, 72-84. doi:10.1016/j.energy.2017.02.118Serrano, J. R., Gil, A., Navarro, R., & Inhestern, L. B. (2017). Extremely Low Mass Flow at High Blade to Jet Speed Ratio in Variable Geometry Radial Turbines and its Influence on the Flow Pattern: A CFD Analysis. Volume 8: Microturbines, Turbochargers and Small Turbomachines; Steam Turbines. doi:10.1115/gt2017-63368Serrano, J. R., Navarro, R., García-Cuevas, L. M., & Inhestern, L. B. (2019). Contribution to tip leakage loss modeling in radial turbines based on 3D flow analysis and 1D characterization. International Journal of Heat and Fluid Flow, 78, 108423. doi:10.1016/j.ijheatfluidflow.2019.108423Choi, M., Baek, J. H., Chung, H. T., Oh, S. H., & Ko, H. Y. (2008). Effects of the low Reynolds number on the loss characteristics in an axial compressor. Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy, 222(2), 209-218. doi:10.1243/09576509jpe520Klausner, E., & Gampe, U. (2014). Evaluation and Enhancement of a One-Dimensional Performance Analysis Method for Centrifugal Compressors. Volume 2D: Turbomachinery. doi:10.1115/gt2014-25141Tiainen, J., Jaatinen-Värri, A., Grönman, A., Turunen-Saaresti, T., & Backman, J. (2018). Effect of FreeStream Velocity Definition on Boundary Layer Thickness and Losses in Centrifugal Compressors. Journal of Turbomachinery, 140(5). doi:10.1115/1.4038872Vinuesa, R., Hosseini, S. M., Hanifi, A., Henningson, D. S., & Schlatter, P. (2017). Pressure-Gradient Turbulent Boundary Layers Developing Around a Wing Section. Flow, Turbulence and Combustion, 99(3-4), 613-641. doi:10.1007/s10494-017-9840-

Locking Solar Tracking Bushing

The contents of this final design review (FDR) outline the progress made by a team of four mechanical engineering students at California Polytechnic State University, San Luis Obispo to solve the problem of torsional galloping in solar tracker panels since the preliminary design review. The project proposed by the sponsor, Christian Friedrich, on behalf of ARaymond is a design for a friction based braking system integrated into a redesigned bushing. The CDR contains details about the system design, the design justification, the manufacturing plan, and design verification plan. In the system design section, the four manufacturing subsystems (bushing mount, actuation, power screw, and braking system) will be analyzed. This analysis will be expanded upon in the manufacturing plan where the current manufacturing plan for the project deliverable will be explained. The CDR will also detail any changes that have been made since the preliminary design review (PDR). Since the PDR, the frictional force that is needed to dampen the system has been adjusted to emulate the system more accurately. The project objectives are to dampen oscillation through frictional means, withstand gravitational and wind static loads of 7.5 metric tons, and endure wearing for 30 years. The overall structure of the bushing has been altered in a variety of different ways. First, the outer journal has been completely separated into two parts to increase the available contact area for the band brake which permits multiple different band orientations to test. As a result, the inner journal has increased in axial length in accordance with the outer journal separation. The lever arm system has also been altered to allow the power screw to interface with the lever arm system. The lever arm system also straddles the I-beam support for ease of rotation and proper power screw engagement. In order to accommodate the separation between the outer journals, an additional mounting plate has been incorporated to mount both halves of the outer journal. Finally, the power screw has been re-oriented to be perpendicular with the I-beam to increase support and adjustability

Contribution to Tip Leakage Loss Modeling in Radial Turbines Based on 3D Flow Analysis and 1D Characterization

[EN] The characterization of tip leakage flow plays an important role for one-dimesional loss modeling and design in radial turbine research. Tip leakage losses can be expressed as function of fluid momentum and mass flow passing through the tip gap. Friction-driven flow and contrariwise oriented pressure gradient-driven flow are highly coupled. However, these numbers are mostly unknown and dependent on tip gap geometry and turbine running condition. Based on a commonly used definition of a non-dimensional tip leakage momentum ratio, a novel correlation has been derived. This allows a consistent characterization for variable tip gap sizes over a wide range of operating conditions. The correlation has been validated by means of CFD data with high variety in reduced speed tip gap geometry and expansion ratios. Results of the novel number show significant improvements of quantitative and qualitative results over a wide range of running conditions in comparison to existing correlations. Furthermore, correlations for tip leakage velocities, that can easily be used in one-dimensional models, have been derived. Finally, it has been demonstrated, that the influence of inlet flow momentum on the tip leakage flow can be analyzed with presented correlations.The work has been partially supported by FEDER and the Spanish Ministry of Economy and Competitiveness through grant number TRA2016-79185-R. The authors would also like to acknowledge the Research and Development Aid Program PAID-01-16 of the Universitat Politecnica de Valencia, Spain.Serrano, J.; Navarro, R.; García-Cuevas González, LM.; Inhestern, LB. (2019). Contribution to Tip Leakage Loss Modeling in Radial Turbines Based on 3D Flow Analysis and 1D Characterization. International Journal of Heat and Fluid Flow. 78. https://doi.org/10.1016/j.ijheatfluidflow.2019.108423S7