Positivity-preserving entropy filtering for the ideal magnetohydrodynamics equations

In this work, we present a positivity-preserving adaptive filtering approach for discontinuous spectral element approximations of the ideal magnetohydrodynamics equations. This approach combines the entropy filtering method (Dzanic and Witherden, J. Comput. Phys., 468, 2022) for shock capturing in gas dynamics along with the eight-wave method for enforcing a divergence-free magnetic field. Due to the inclusion of non-conservative source terms, an operator-splitting approach is introduced to ensure that the positivity and entropy constraints remain satisfied by the discrete solution. Furthermore, a computationally efficient algorithm for solving the optimization process for this nonlinear filtering approach is presented. The resulting scheme can robustly resolve strong discontinuities on general unstructured grids without tunable parameters while recovering high-order accuracy for smooth solutions. The efficacy of the scheme is shown in numerical experiments on various problems including extremely magnetized blast waves and three-dimensional magnetohydrodynamic instabilities.Comment: 24 pages, 17 figure

Influence of Flood Pulse on Termite Diversity (INSECTA: ISOPTERA) in the Pantanal

This research aimed to associate termite diversity to flood pulse by Paraguay River, and with savannas and pasture areas. The study was conducted nearby the town of Cáceres, in Pantanal - Mato Grosso, on six livestock farms subject to Paraguay River flood pulse. Types of land use sampled were native savanna and cultivated pasture. Flooded and dry plots were selected, both the savanna and the pasture in each sampling area. Termite richness and abundance was analysed based on the  environments as an explanatory variable (FP – flooded pasture, DP – dry pasture, FS – flooded savanna, DS – dry savanna) through GLM; Tukey’s test was subsequently performed to determine whether land use and/or flood pulse can significantly affect the termite community. There were 37 termite species and 19 genera. Richness and abundance of termite species cannot be explain by flooding pulse, but were explained only by land use (pasture and savanna). The similarity analysis also identified that species composition was quite affected by flood in grazing areas, but this disturbance does not affect the savanna areas. In conclusion, flood pulse is not a determining factor for savannas or pasture termite richness, but change the composition of the termite fauna in the environment

Validation of wall boundary conditions for simulating complex fluid flows via the Boltzmann equation: Momentum transport and skin friction

The influence and validity of wall boundary conditions for non-equilibrium fluid flows described by the Boltzmann equation remains an open problem. The substantial computational cost of directly solving the Boltzmann equation has limited the extent of numerical validation studies to simple, often two-dimensional, flow problems. Recent algorithmic advancements for the Boltzmann--BGK equation introduced by the authors, consisting of a high-order spatial discretization augmented with a discretely-conservative velocity model, have made it feasible to accurately simulate unsteady three-dimensional flow problems across both the rarefied and continuum regimes. This work presents a comprehensive evaluation and validation of wall boundary conditions across a variety of flow regimes, primarily for the purpose of exploring their effects on momentum transfer in the low Mach limit. Results are presented for a range of steady and unsteady wall-bounded flow problems across both the rarefied and continuum regimes, from canonical two-dimensional laminar flows to unsteady three-dimensional transitional and turbulent flows, the latter of which are the first instances of wall-bounded turbulent flows computed by directly solving the Boltzmann equation. We show that approximations of the molecular gas dynamics equations can accurately predict both non-equilibrium phenomena and complex hydrodynamic flow instabilities and show how spatial and velocity domain resolution affect the accuracy. The results indicate that an accurate approximation of particle transport (i.e. high spatial resolution) is significantly more important than particle collision (i.e. high velocity domain resolution) for predicting flow instabilities and momentum transfer consistent with that predicted by the hydrodynamic equations and that these effects can be computed accurately even with very few degrees of freedom in the velocity domain.Comment: 34 pages, 36 figure

A positivity-preserving and conservative high-order flux reconstruction method for the polyatomic Boltzmann--BGK equation

In this work, we present a positivity-preserving high-order flux reconstruction method for the polyatomic Boltzmann--BGK equation augmented with a discrete velocity model that ensures the scheme is discretely conservative. Through modeling the internal degrees of freedom, the approach is further extended to polyatomic molecules and can encompass arbitrary constitutive laws. The approach is validated on a series of large-scale complex numerical experiments, ranging from shock-dominated flows computed on unstructured grids to direct numerical simulation of three-dimensional compressible turbulent flows, the latter of which is the first instance of such a flow computed by directly solving the Boltzmann equation. The results show the ability of the scheme to directly resolve shock structures without any ad hoc numerical shock capturing method and correctly approximate turbulent flow phenomena in a consistent manner with the hydrodynamic equations.Comment: 31 pages, 20 figure

On the anti-aliasing properties of entropy filtering for discontinuous spectral element approximations of under-resolved turbulent flows

For large Reynolds number flows, it is typically necessary to perform simulations that are under-resolved with respect to the underlying flow physics. For nodal discontinuous spectral element approximations of these under-resolved flows, the collocation projection of the nonlinear flux can introduce aliasing errors which can result in numerical instabilities. In Dzanic and Witherden (J. Comput. Phys., 468, 2022), an entropy-based adaptive filtering approach was introduced as a robust, parameter-free shock-capturing method for discontinuous spectral element methods. This work explores the ability of entropy filtering for mitigating aliasing-driven instabilities in the simulation of under-resolved turbulent flows through high-order implicit large eddy simulations of a NACA0021 airfoil in deep stall at a Reynolds number of 270,000. It was observed that entropy filtering can adequately mitigate aliasing-driven instabilities without degrading the accuracy of the underlying high-order scheme on par with standard anti-aliasing methods such as over-integration, albeit with marginally worse performance at higher approximation orders.Comment: 13 pages, 8 figure

Boston Hospitality Review: Winter 2017

Table of contents: Family, Team or Something Else? by John Murtha -- Kitchen Organization in Full-Service Restaurants: Reducing Heat and Stress by Peter Szende and Justin Cipriano -- Rules of Engagement: Building Brand Relationships by Alex Friedman -- Corporate Social Responsibility in the Hospitality Sector by Manisha Singal and Yinyoung Rhou -- “Hold on, I have to post this on Instagram”: Trends, Talk, and Transactions of the Experiential Consumer by Steve Kent -- C-corporation Hotels vs. Hotel-REITs: A Theoretical and Practical Comparison by Tarik Dogru -- Sisters in Restaurant Success: A History of The Maramor by Jan WhitakerFamily, Team or Something Else? by John Murtha -- Kitchen Organization in Full-Service Restaurants: Reducing Heat and Stress by Peter Szende and Justin Cipriano -- Rules of Engagement: Building Brand Relationships by Alex Friedman -- Corporate Social Responsibility in the Hospitality Sector by Manisha Singal and Yinyoung Rhou -- “Hold on, I have to post this on Instagram”: Trends, Talk, and Transactions of the Experiential Consumer by Steve Kent -- C-corporation Hotels vs. Hotel-REITs: A Theoretical and Practical Comparison by Tarik Dogru -- Sisters in Restaurant Success: A History of The Maramor by Jan Whitake

The health benefits of reducing micro-heat islands: A 22-year analysis of the impact of urban temperature reduction on heat-related illnesses in California's major cities

This study investigates the relationship between temporal changes in temperatures characterizing local urban heat islands (UHIs) and heat-related illnesses (HRIs) in seven major cities of California. UHIs, which are a phenomenon that arises in the presence of impervious surfaces or the lack of green spaces exacerbate the effects of extreme heat events, can be measured longitudinally using satellite products. The two objectives of this study were: (1) to identify temperature trends in local temperatures to characterize UHIs across zip code tabulation areas (ZCTAs) in the seven observed cities over a 22-year period and (2) to use propensity score and inverse probability weighting to achieve exchangeability between different types of ZCTAs and assess the difference in hospital admissions recorded as HRIs attributable to temporal changes in UHIs. We use monthly land surface temperature data derived from MODIS Terra imagery from the summer months (June-September) from 2000 to 2022. We categorized ZCTAs (into three groups) based on their monthly land surface temperature trends. Of the 216 ZCTAs included in this study, the summertime land surface temperature trends of 43 decreased, while 161 remained unchanged, and 12 increased. Los Angeles had the greatest number of decreased ZCTAs, San Diego and San Jose had the highest number of increased ZCTAs. To analyze the number of monthly HRI attributable to changes in UHI, we used inverse probability of treatment weighting to analyze the difference in HRI between the years of 2006 and 2017 which were two major extreme heat events over the entire State. We observed an average reduction of 3.2 (95 % CI: 0.5; 5.9) HRIs per month and per ZCTAs in decreased neighborhoods as compared to unchanged. This study emphasizes the importance of urban climate adaptation strategies to mitigate the intensity and prevalence of UHIs to reduce health risks related to heat