IA Scholar Query: On Gauss quadrature and partial cross validation.
https://scholar.archive.org/
Internet Archive Scholar query results feedeninfo@archive.orgThu, 11 Aug 2022 00:00:00 GMTfatcat-scholarhttps://scholar.archive.org/help1440Burgers' equation in the complex plane
https://scholar.archive.org/work/h7e3ygwfczeong6ezbqgrrfkfi
Burgers' equation is a well-studied model in applied mathematics with connections to the Navier-Stokes equations in one spatial direction and traffic flow, for example. Following on from previous work, we analyse solutions to Burgers' equation in the complex plane, concentrating on the dynamics of the complex singularities and their relationship to the solution on the real line. For an initial condition with a simple pole in each of the upper- and lower-half planes, we apply formal asymptotics in the small- and large-time limits in order to characterise the initial and later motion of the singularities. The small-time limit highlights how infinitely many singularities are born at t=0 and how they orientate themselves to lie increasingly close to anti-Stokes lines in the far-field of the inner problem. This inner problem also reveals whether or not the closest singularity to the real axis moves toward the axis or away. For intermediate times, we use the exact solution, apply method of steepest descents, and implement the AAA approximation to track the complex singularities. Connections are made between the motion of the closest singularity to the real axis and the steepness of the solution on the real line. While Burgers' equation has an exact solution, we deliberately apply a mix of techniques in our analysis in an attempt to develop methodology that can be applied to other nonlinear partial differential equations that do not.Daniel J. VandenHeuvel, Christopher J. Lustri, John R. King, Ian W. Turner, Scott W. McCuework_h7e3ygwfczeong6ezbqgrrfkfiThu, 11 Aug 2022 00:00:00 GMTStrategies and performance of the CMS silicon tracker alignment during LHC Run 2
https://scholar.archive.org/work/hdegcjotcve5rf3iwfoxuxzg2m
The strategies for and the performance of the CMS silicon tracking system alignment during the 2015-2018 data-taking period of the LHC are described. The alignment procedures during and after data taking are explained. Alignment scenarios are also derived for use in the simulation of the detector response. Systematic effects, related to intrinsic symmetries of the alignment task or to external constraints, are discussed and illustrated for different scenarios.The CMS Collaboration, Armen R. Tumasyan, Konstantin Androsov, Malte Backhaus, Robert Becker, Pirmin Berger, Alessandro Calandri, Diogo Raphael Da Silva Di Calafiori, Annapaola de Cosa, Günther Dissertori, Michael Dittmar, Lubomir Djambazov, Mauro Donegà, Christian Dorfer, Florian Eble, Krunal Gedia, Franz Glessgen, Tirso Alejandro Gomez Espinosa, Christophorus Grab, Dmitry Alexandrovich Hits, Werner Lustermann, Anne-Mazarine Lyon, Riccardo A. Manzoni, Luigi Marchese, Cristina Martin Perez, Maren Tabea Meinhard, Francesca Nessi-Tedaldi, Jeremi Niedziela, Felicitas Pauss, Vladmir Perovic, Simone Pigazzini, Maria Giulia Ratti, Michael Reichmann, Christina Reissel, Thomas Reitenspiess, Branislav Ristic, Ulf Röser, Daniele Ruini, Diego Alejandro Sanz Becerra, Jan Sörensen, Vinzenz Stampf, Jan Steggemann, Rainer Wallny, D.H. Zhu, et al.work_hdegcjotcve5rf3iwfoxuxzg2mThu, 11 Aug 2022 00:00:00 GMTAn exactly curl-free staggered semi-implicit finite volume scheme for a first order hyperbolic model of viscous flow with surface tension
https://scholar.archive.org/work/mm3ypk7yzzcalduuxalv4d47ku
In this paper, we present a semi-implicit numerical solver for a first order hyperbolic formulation of two-phase flow with surface tension and viscosity. The numerical method addresses several complexities presented by the PDE system in consideration: (i) The presence of involution constraints of curl type in the governing equations requires explicit enforcement of the zero-curl property of certain vector fields (an interface field and a distortion field); the problem is eliminated entirely by adopting a set of compatible curl and gradient discrete differential operators on a staggered grid, allowing to preserve the Schwartz identity of cross-derivatives exactly. (ii) The evolution equations feature highly nonlinear stiff algebraic source terms which are used for the description of viscous interactions as emergent behaviour of an elasto-plastic solid in the stiff strain relaxation limit; such source terms are reliably integrated with an efficient semi-analytical technique. (iii) In the low-Mach number regime, standard explicit Godunov-type schemes lose efficiency and accuracy; the issue is addressed by means of a simple semi-implicit, pressure-based, split treatment of acoustic and non-acoustic waves, again using staggered grids that recover the implicit solution for a single scalar field (the pressure) through a sequence of symmetric-positive definite linear systems that can be efficiently solved via the conjugate gradient method.Simone Chiocchetti, Micheal Dumbserwork_mm3ypk7yzzcalduuxalv4d47kuThu, 11 Aug 2022 00:00:00 GMTEffect of a Micro-scale Dislocation Pileup on the Atomic-Scale Multi-variant Phase Transformation and Twinning
https://scholar.archive.org/work/p4f2spvqufdu3acnsvqnnnlhsu
In this paper, we perform concurrent atomistic-continuum (CAC) simulations to (i) characterize the internal stress induced by the microscale dislocation pileup at an atomically structured interface; (ii) decompose this stress into two parts, one of which is from the dislocations behind the pileup tip according to the Eshelby model and the other is from the dislocations at the pileup tip according to a super-dislocation model; and (iii) assess how such internal stresses contribute to the atomic-scale phase transformations (PTs), reverse PTs, and twinning. The main novelty of this work is to unify the atomistic description of the interface and the coarse-grained (CG) description of the lagging dislocations away from the interface within one single framework. Our major findings are: (a) the interface dynamically responds to a pileup by forming steps/ledges, the height of which is proportional to the number of dislocations arriving at the interface; (b) when the pre-sheared sample is compressed, a direct square-to-hexagonal PT occurs ahead of the pileup tip and eventually grows into a wedge shape; (c) upon a further increase of the loading, part of the newly formed hexagonal phase transforms back to the square phase. The square product phase resulting from this reverse PT forms a twin with respect to the initial square phase. All phase boundaries (PBs) and twin boundaries (TBs) are stationary and correspond to zero thermodynamic Eshelby driving forces; and (d) the stress intensity induced by a pileup consisting of 16 dislocations reduces the stress required for initiating a PT by a factor of 5.5, comparing with that in the sample containing no dislocations. This work is the first characterization of the behavior of PTs/twinning resulting from the reaction between a microscale dislocation slip and an atomically structured interface.Yipeng Peng, Rigelesaiyin Ji, Thanh Phan, Laurent Capolungo, Valery I. Levitas, Liming Xiongwork_p4f2spvqufdu3acnsvqnnnlhsuWed, 10 Aug 2022 00:00:00 GMTDevelopment of a three-dimensional grid refinement method for the application of the Lattice Boltzmann Method to high Reynolds flows
https://scholar.archive.org/work/pulike433ramljkzjvchs64vb4
The lattice Boltzmann method (LBM) models fluid dynamics based on kinetic theory. It discretises the continuous Boltzmann equation in velocity, space and time and solves a transport equation for particle populations. When solved on uniform Cartesian grids, this result in a highly scalable algorithm which can accurately and efficiently model unsteady and turbulent flows. However, the reliance on uniform grids makes the LBM prohibitively expensive for the simulation of high Reynolds number flows. To reduce computational costs, grid refinement is required. A hierarchical grid refinement method with regularised coupling is introduced in this thesis, and its implementation in the open-source LBM solver OpenLB is explained. The regularised coupling restricts the information exchange at the refinement interface to the leading order terms of the particle populations. This ensures that local viscous stresses are conserved across the interface and prevents numerical instabilities. The method is validated against two benchmarks: the vortex shedding flow around a circular cylinder and the lid-driven flow inside a cubic cavity. It is demonstrated that the grid-refined methodology accurately captures the flow features at different Reynolds numbers, including two instability modes during the cylinder wake transition. Refinement reduces the number of active cells by a factor of 28 for the cylinder at Reynolds number Re=300. For the lid-driven cavity case at Re=3200, the performance efficiency and continuity across the refinement interface are assessed. The regularised coupling diminishes the transmission of spurious waves and improves numerical stability. Finally, this method is applied with a Smagorinsky subgrid model to an open shallow cavity at Re=50,000. Good agreement between the LBM solution and reference experimental and numerical data in terms of time-average velocities and turbulence statistics exists. This successful application demonstrates that the newly implemented methods achieve accurate and stable LBM simulations [...]Zhishang Xu, Sina Stapelfeldt, Ricardo Puente Rico, China Scholarship Councilwork_pulike433ramljkzjvchs64vb4Wed, 10 Aug 2022 00:00:00 GMTAsymptotically consistent and computationally efficient modeling of short-ranged molecular interactions between curved slender fibers undergoing large 3D deformations
https://scholar.archive.org/work/aifqvcynijh7nmqdh2qqbvvxfq
This article proposes a novel computational modeling approach for short-ranged molecular interactions between curved slender fibers undergoing large 3D deformations, and gives a detailed overview how it fits into the framework of existing fiber or beam interaction models, either considering microscale molecular or macroscale contact effects. The direct evaluation of a molecular interaction potential between two general bodies in 3D space would require to integrate molecule densities over two 3D volumes, leading to a sixfold integral to be solved numerically. By exploiting the short-range nature of the considered class of interaction potentials as well as the fundamental kinematic assumption of undeformable fiber cross-sections, as typically applied in mechanical beam theories, a recently derived, closed-form analytical solution is applied for the interaction potential between a given section of the first fiber (slave beam) and the entire second fiber (master beam). This novel approach based on a pre-defined section-beam interaction potential (SBIP) requires only one single integration step along the slave beam length to be performed numerically. In terms of accuracy, the total beam-beam interaction potential resulting from this approach is shown to exhibit an asymptotically consistent angular and distance scaling behavior. In addition to elementary two-fiber systems, carefully chosen to verify accuracy and asymptotic consistence of the proposed SBIP approach, a potential practical application in form of adhesive nanofiber-grafted surfaces is studied. Involving a large number of helicoidal fibers undergoing large 3D deformations, arbitrary mutual fiber orientations as well as frequent local fiber pull-off and snap-into-contact events, this example demonstrates the robustness and computational efficiency of the new approach.Maximilian J. Grill, Wolfgang A. Wall, Christoph Meierwork_aifqvcynijh7nmqdh2qqbvvxfqWed, 10 Aug 2022 00:00:00 GMTPan-cancer integrative histology-genomic analysis via multimodal deep learning
https://scholar.archive.org/work/pggj3eouonffvm4wwl7ljwi66q
The rapidly emerging field of computational pathology has demonstrated promise in developing objective prognostic models from histology images. However, most prognostic models are either based on histology or genomics alone and do not address how these data sources can be integrated to develop joint image-omic prognostic models. Additionally, identifying explainable morphological and molecular descriptors from these models that govern such prognosis is of interest. We use multimodal deep learning to jointly examine pathology whole-slide images and molecular profile data from 14 cancer types. Our weakly supervised, multimodal deep-learning algorithm is able to fuse these heterogeneous modalities to predict outcomes and discover prognostic features that correlate with poor and favorable outcomes. We present all analyses for morphological and molecular correlates of patient prognosis across the 14 cancer types at both a disease and a patient level in an interactive open-access database to allow for further exploration, biomarker discovery, and feature assessment.Richard J. Chen, Ming Y. Lu, Drew F.K. Williamson, Tiffany Y. Chen, Jana Lipkova, Zahra Noor, Muhammad Shaban, Maha Shady, Mane Williams, Bumjin Joo, Faisal Mahmoodwork_pggj3eouonffvm4wwl7ljwi66qMon, 08 Aug 2022 00:00:00 GMTThe hadronic running of the electromagnetic coupling and the electroweak mixing angle from lattice QCD
https://scholar.archive.org/work/6fkaj7u4mfcvhobeacdl2gamyy
We compute the hadronic running of the electromagnetic and weak couplings in lattice QCD with N_f=2+1 flavors of 𝒪(a) improved Wilson fermions. Using two different discretizations of the vector current, we compute the quark-connected and -disconnected contributions to the hadronic vacuum polarization (HVP) functions Π̅^γγ and Π̅^γ Z for Euclidean squared momenta Q^2≤ 7 GeV^2. Gauge field ensembles at four values of the lattice spacing and several values of the pion mass, including its physical value, are used to extrapolate the results to the physical point. The ability to perform an exact flavor decomposition allows us to present the most precise determination to date of the SU(3)-flavor-suppressed HVP function Π̅^08 that enters the running of sin^2θ_W. Our results for Π̅^γγ, Π̅^γ Z and Π̅^08 are presented in terms of rational functions for continuous values of Q^2 below 7 GeV^2. We observe a tension of up to 3.5 standard deviation between our lattice results for Δα^(5)_had(-Q^2) and estimates based on the R-ratio for space-like momenta in the range 3–7 GeV^2. The tension is, however, strongly diminished when translating our result to the Z pole, by employing the Euclidean split technique and perturbative QCD, which yields Δα^(5)_had(M_Z^2)=0.027 73(15) and agrees with results based on the R-ratio within the quoted uncertainties.Marco Cè, Antoine Gérardin, Georg von Hippel, Harvey B. Meyer, Kohtaroh Miura, Konstantin Ottnad, Andreas Risch, Teseo San José, Jonas Wilhelm, Hartmut Wittigwork_6fkaj7u4mfcvhobeacdl2gamyyMon, 08 Aug 2022 00:00:00 GMTAnalytical Study of Dynamic and Vibrational of Composite Shell with Piezoelectric Layer using GDQM Method
https://scholar.archive.org/work/ztx5jkykczgc7g5wpeanmztvyq
Piezoelectric materials, due to their electromechanical coupling properties, are widely used as actuators and sensors in intelligent structures to control vibrations and bends of multilayer sheets with piezoelectric layers. In this paper, the response of free vibrations of a multilayer composite shell with the new Generalized Differential Quadrature Method (GDQM) for different boundary conditions is investigated. The governing equations are obtained by assuming first-order shear theory and using Hamilton's principle. The generalized quadrature differential method is used to solve the obtained equations. To use this method, coding has been done in MATLAB software. Due to the same thickness of the layers, as the number of composite layers increases and the total thickness is constant, the thickness of each layer decreases, and consequently the thickness of the piezoelectric layer decreases. Comparing the results of this method with the work of other researchers shows that this method has good accuracy.Amin Moslemi Petrudi, Masoud Rahmani, Ionut Cristian Scurtuwork_ztx5jkykczgc7g5wpeanmztvyqSun, 07 Aug 2022 00:00:00 GMTCan the word superiority effect be modulated by serial position and prosodic structure?
https://scholar.archive.org/work/piwk5p55gfdhrdgphvxhxwmuga
In this study, we examined the word superiority effect in Arabic and English, two languages with significantly different morphological and writing systems. Thirty-two Arabic–English bilingual speakers performed a post-cued letter-in-string identification task in words, pseudo-words, and non-words. The results established the presence of the word superiority effect in Arabic and a robust effect of context in both languages. However, they revealed that, compared to the non-word context, word and pseudo-word contexts facilitated letter identification more in Arabic than in English. In addition, the difference between word and pseudo-word contexts was smaller in Arabic compared to English. Finally, there was a consistent first-letter advantage in English regardless of the context, while this was more consistent only in the word and pseudo-word contexts in Arabic. We discuss these results in light of previous findings and argue that the differences between the patterns reported for Arabic and English are due to the qualitative difference between word morphophonological representations in the two languages.Yousri Marzouki, Sara Abdulaziz Al-Otaibi, Muneera Tariq Al-Tamimi, Ali Idrissiwork_piwk5p55gfdhrdgphvxhxwmugaFri, 05 Aug 2022 00:00:00 GMTModel Reduction for Nonlinear Systems by Balanced Truncation of State and Gradient Covariance
https://scholar.archive.org/work/ymc72qvltvfapconr53l6bhdd4
Data-driven reduced-order models often fail to make accurate forecasts of high-dimensional nonlinear systems that are sensitive along coordinates with low-variance because such coordinates are often truncated, e.g., by proper orthogonal decomposition, kernel principal component analysis, and autoencoders. Such systems are encountered frequently in shear-dominated fluid flows where non-normality plays a significant role in the growth of disturbances. In order to address these issues, we employ ideas from active subspaces to find low-dimensional systems of coordinates for model reduction that balance adjoint-based information about the system's sensitivity with the variance of states along trajectories. The resulting method, which we refer to as covariance balancing reduction using adjoint snapshots (CoBRAS), is analogous to balanced truncation with state and adjoint-based gradient covariance matrices replacing the system Gramians and obeying the same key transformation laws. Here, the extracted coordinates are associated with an oblique projection that can be used to construct Petrov-Galerkin reduced-order models. We provide an efficient snapshot-based computational method analogous to balanced proper orthogonal decomposition. This also leads to the observation that the reduced coordinates can be computed relying on inner products of state and gradient samples alone, allowing us to find rich nonlinear coordinates by replacing the inner product with a kernel function. In these coordinates, reduced-order models can be learned using regression. We demonstrate these techniques and compare to a variety of other methods on a simple, yet challenging three-dimensional system and an axisymmetric jet flow simulation with 10^5 state variables.Samuel E. Otto, Alberto Padovan, Clarence W. Rowleywork_ymc72qvltvfapconr53l6bhdd4Wed, 03 Aug 2022 00:00:00 GMTDynamic deformables
https://scholar.archive.org/work/ail7xnlyuzeblargndqwropb3e
Simulating dynamic deformation has been an integral component of Pixar's storytelling since Boo's shirt in Monsters, Inc. (2001). Recently, several key transformations have been applied to Pixar's core simulator Fizt that improve its speed, robustness, and generality. Starting with Coco (2017), improved collision detection and response were incorporated into the cloth solver, then with Cars 3 (2017) 3D solids were introduced, and in Onward (2020) clothing is allowed to interact with a character's body with two-way coupling. The 3D solids are based on a fast, compact, and powerful new formulation that we have published over the last few years at SIGGRAPH. Under this formulation, the construction and eigendecomposition of the force gradient, long considered the most onerous part of the implementation, becomes fast and simple. We provide a detailed, self-contained, and unified treatment here that is not available in the technical papers. We also provide, for the first time, open-source C++ implementations of many of the described algorithms. This new formulation is only a starting point for creating a simulator that is up challenges of a production environment. One challenge is performance: we discuss our current best practices for accelerating system assembly and solver performance. Another challenge that requires considerable attention is robust collision detection and response. Much has been written about collision detection approaches such as proximity-queries, continuous collisions and global intersection analysis. We discuss our strategies for using these techniques, which provides us with valuable information that is needed to handle challenging scenarios.Theodore Kim, David Eberlework_ail7xnlyuzeblargndqwropb3eTue, 02 Aug 2022 00:00:00 GMTCode Comparison for Fast Flavor Instability Simulation
https://scholar.archive.org/work/hkqsxumblvc5lhxbkybo6v365y
The fast flavor instability (FFI) is expected to be ubiquitous in core-collapse supernovae and neutron star mergers. It rapidly shuffles neutrino flavor in a way that could impact the explosion mechanism, neutrino signals, mass outflows, and nucleosynthesis. The variety of initial conditions and simulation methods employed in simulations of the FFI prevent an apples-to-apples comparison of the results. We simulate a standardized test problem using five independent codes and verify that they are all faithfully simulating the underlying quantum kinetic equations under the assumptions of axial symmetry and homogeneity in two directions. We quantify the amount of numerical error in each method and demonstrate that each method is superior in at least one metric of this error. We make the results publicly available to serve as a benchmark.Sherwood Richers, Huaiyu Duan, Meng-Ru Wu, Soumya Bhattacharyya, Masamichi Zaizen, Manu George, Chun-Yu Lin, Zewei Xiongwork_hkqsxumblvc5lhxbkybo6v365yMon, 01 Aug 2022 00:00:00 GMTStudy on Sensitivity of Observation Error Statistics of Doppler Radars to the Radar forward Operator in Convective-Scale Data Assimilation
https://scholar.archive.org/work/e5bhntjojzc3zd3pjvtx6rihsu
In the present work, we investigate the impacts on the observation error (OE) statistics due to different types of errors in the forward operator (FE) for both radar reflectivity and radial wind data, in the context of convective-scale data assimilation in the summertime. A series of sensitivity experiments were conducted with the Efficient Modular VOlume RADar Operator (EMVORADO), using the operational data assimilation system of the Deutscher Wetterdienst (DWD, German Weather Service). The investigated FEs are versatile, including errors caused by neglecting the terminal fall speed of hydrometeor, the reflectivity weighting, and the beam broadening and attenuation effects, as well as errors caused by different scattering schemes and formulations for melting particles. For reflectivity, it is found that accounting for the beam broadening effect evidently reduces the standard deviations, especially at higher altitudes. However, it does not shorten the horizontal or along-beam correlation length scales. In comparison between the Rayleigh and the Mie schemes (with specific configurations), the former one results in much smaller standard deviations for heights up to 4 km, and aloft, slightly larger standard deviations. Imposing the attenuation to the Mie scheme slightly reduces the standard deviations at lower altitudes; however, it largely increases the standard deviations at higher altitudes and it also leads to longer correlation length scales. For radial wind, positive impacts of considering the beam broadening effect on standard deviations and neutral impacts on correlations are observed. For both reflectivity and radial wind, taking the terminal fall speed of hydrometeor and the reflectivity weighting into account does not make remarkable differences in the estimated OE statistics.Yuefei Zeng, Hong Li, Yuxuan Feng, Ulrich Blahak, Alberto de Lozar, Jingyao Luo, Jinzhong Minwork_e5bhntjojzc3zd3pjvtx6rihsuMon, 01 Aug 2022 00:00:00 GMTSPEX X-ray spectral fitting package
https://scholar.archive.org/work/ecrbc5ln6zcaneop73hspeh2nm
SPEX is a software package for fitting astrophysical X-ray spectra. It has been developed since the 1970s at SRON Netherlands Institute for Space Research. SPEX is an interactive command-line program for the computation of emergent spectra of optically thin plasmas such as stellar coronal loop structures, supernova remnants (also including transient ionization effects), photo-ionized plasmas, and optically thick plasmas. These model spectra can be fitted to measured X-ray spectra from various X-ray observatories, like XMM-Newton and Chandra. SPEX has been optimized for high-resolution X-ray spectroscopy, which makes it especially suitable for analyzing grating and micro-calorimeter spectra.J. S. Kaastra, A. J. J. Raassen, J. de Plaa, Liyi Gu, Frans Alkemade, Gert-Jan Bartelds, Ehud Behar, Alex Blustin, Elisa Costantini, Max Duysens, Jacobo Ebrero, Irma Eggenkamp, Andrzej Fludra, Yan Grange, Ed Gronenschild, Theo Gunsing, Jorgen Hansen, Wouter Hartmann, Kurt van der Heyden, Fred Jansen, Lucien Kuiper, Jim Lemen, Duane Liedahl, Junjie Mao, Pasquale Mazzotta, Missagh Mehdipour, Rolf Mewe, Hans Nieuwenhuijzen, Bert van den Oord, Ken Phillips, Ciro Pinto, Remco van der Rijst, Daniele Rogantini, Makoto Sawada, Hans Schrijver, Karel Schrijver, Tiemen Schut, Katrien Steenbrugge, Janusz Sylwester, Rob Smeets, Jeroen Stil, Igone Urdampilleta, Dima Verner, Jacco Vink, Frank van der Wolf, Sascha Zeegers, Piotr Zyckiwork_ecrbc5ln6zcaneop73hspeh2nmMon, 01 Aug 2022 00:00:00 GMTAI-Enabled Intelligent Visible Light Communications: Challenges, Progress, and Future
https://scholar.archive.org/work/rtlc2ay2brbldmbznhn7hxcz2u
Visible light communication (VLC) is a highly promising complement to conventional wireless communication for local-area networking in future 6G. However, the extra electro-optical and photoelectric conversions in VLC systems usually introduce exceeding complexity to communication channels, in particular severe nonlinearities. Artificial intelligence (AI) techniques are investigated to overcome the unique challenges in VLC, whereas considerable obstacles are found in practical VLC systems applied with intelligent learning approaches. In this paper, we present a comprehensive study of the intelligent physical and network layer technologies for AI-empowered intelligent VLC (IVLC). We first depict a full model of the visible light channel and discuss its main challenges. The advantages and disadvantages of machine learning in VLC are discussed and analyzed by simulation. We then present a detailed overview of advances in intelligent physical layers, including optimal coding, channel emulator, MIMO, channel equalization, and optimal decision. Finally, we envision the prospects of IVLC in both the intelligent physical and network layers. This article lays out a roadmap for developing machine learning-based intelligent visible light communication in 6G.Jianyang Shi, Wenqing Niu, Yinaer Ha, Zengyi Xu, Ziwei Li, Shaohua Yu, Nan Chiwork_rtlc2ay2brbldmbznhn7hxcz2uFri, 29 Jul 2022 00:00:00 GMTProbing Physics Beyond the Standard Model: Limits from BBN and the CMB Independently and Combined
https://scholar.archive.org/work/qazhucuz4ne2bcuyux7jmqewvu
We present new Big Bang Nucleosynthesis (BBN) limits on the cosmic expansion rate or relativistic energy density, quantified via the number N_ν of equivalent neutrino species. We use the latest light element observations, neutron mean lifetime, and update our evaluation for the nuclear rates d+d → He3 + n and d+d → H3 + p. Combining this result with the independent constraints from the cosmic microwave background (CMB) yields tight limits on new physics that perturbs N_ν and η prior to cosmic nucleosynthesis: a joint BBN+CMB analysis gives N_ν = 2.898 ± 0.141, resulting in N_ν < 3.180 at 2σ. We apply these limits to a wide variety of new physics scenarios including right-handed neutrinos, dark radiation, and a stochastic gravitational wave background. We also search for limits on potential changes in N_ν and/or the baryon-to-photon ratio η between the two epochs. The present data place strong constraints on the allowed changes in N_ν between BBN and CMB decoupling; for example, we find -0.708 < N_ν^ CMB-N_ν^ BBN < 0.328 in the case where η and the primordial helium mass fraction Y_p are unchanged between the two epochs; we also give limits on the allowed variations in η or in (η,N_ν) jointly. Looking to the future, we forecast the tightened precision for N_ν arising from both CMB Stage 4 measurements as well as improvements in astronomical 4 measurements. We find that CMB-S4 combined with present BBN and light element observation precision can give σ(N_ν) ≃ 0.03. Such future precision would reveal the expected effect of neutrino heating (N_ eff-3=0.044) of the CMB during BBN, and would be near the level to reveal any particle species ever in thermal equilibrium with the standard model.Tsung-Han Yeh, Jessie Shelton, Keith A. Olive, Brian D. Fieldswork_qazhucuz4ne2bcuyux7jmqewvuTue, 26 Jul 2022 00:00:00 GMTOn thermalization of radiation in hydrostatic atmospheres
https://scholar.archive.org/work/bldqfhvslzbw7lbhjpajg7tewi
The problem of thermalization of radiation within a self-emitting hydrogen isothermal atmosphere is considered for the case of a hydrostatic profile of the plasma density. The probabilistic approach to define the thermalization depth for the photon of a given frequency is used. Quantitative conclusions are made on the value of the optical depth at which the radiation can be viewed as thermalized up to a given frequency. The analytical and numerical solutions of the radiative transfer equation confirm these results. The frequency dependencies of the single-interaction free-free absorption probability in a cold nonmagnetized and magnetized plasma are calculated.M. I. Gornostaevwork_bldqfhvslzbw7lbhjpajg7tewiTue, 26 Jul 2022 00:00:00 GMTLarge-scale globally propagating coronal waves
https://scholar.archive.org/work/ayslear5w5b55ea6753bo7t3g4
Large-scale, globally propagating wave-like disturbances have been observed in the solar chromosphere and by inference in the corona since the 1960s. However, detailed analysis of these phenomena has only been conducted since the late 1990s. This was prompted by the availability of high-cadence coronal imaging data from numerous spaced-based instruments, which routinely show spectacular globally propagating bright fronts. Coronal waves, as these perturbations are usually referred to, have now been observed in a wide range of spectral channels, yielding a wealth of information. Many findings have supported the "classical" interpretation of the disturbances: fast-mode MHD waves or shocks that are propagating in the solar corona. However, observations that seemed inconsistent with this picture have stimulated the development of alternative models in which "pseudo waves" are generated by magnetic reconfiguration in the framework of an expanding coronal mass ejection. This has resulted in a vigorous debate on the physical nature of these disturbances. This review focuses on demonstrating how the numerous observational findings of the last one and a half decades can be used to constrain our models of large-scale coronal waves, and how a coherent physical understanding of these disturbances is finally emerging.Alexander Warmuth, Technische Informationsbibliothek (TIB)work_ayslear5w5b55ea6753bo7t3g4Fri, 22 Jul 2022 00:00:00 GMTAlgebraically constrained finite element methods for hyperbolic problems with applications in geophysics and gas dynamics
https://scholar.archive.org/work/fqeijfrpzrannlpdhhcrf6ws7e
The research conducted in this thesis is focused on property-preserving discretizations of hyperbolic partial differential equations. Computational methods for solving such problems need to be carefully designed to produce physically meaningful numerical solutions. In particular, approximations to some quantities of interest should satisfy local and global discrete maximum principles. Moreover, numerical methods need to obey certain conservation relations, and convergence of approximations to the physically relevant exact solution should be ensured if multiple solutions may exist. Many algorithms based on the aforementioned design principles fall into the category of algebraic flux correction (AFC) schemes. Modern AFC discretizations of nonlinear hyperbolic systems express approximate solutions as convex combinations of intermediate states and constrain these states to be admissible. The main focus of our work is on monolithic convex limiting (MCL) strategies that modify spatial semi-discretizations in this way. Contrary to limiting approaches of predictor-corrector type, their monolithic counterparts are well suited for transient and steady problems alike. Further benefits of the MCL framework presented in this thesis include the possibility of enforcing entropy stability conditions in addition to discrete maximum principles. Using the AFC methodology, we transform finite element discretizations into property-preserving low order methods and perform flux correction to recover higher orders of accuracy without losing any desirable properties. The presented methods produce physics-compatible approximations, which exhibit excellent shock capturing capabilities. One novelty of this work is the tailor-made extension of monolithic convex limiting to the shallow water equations with a nonconservative topography term. Our generalized MCL schemes are entropy stable, positivity preserving, and well balanced in the sense that lake at rest equilibria are preserved. Another desirable property of numerical methods for the sha [...]Hennes Hajduk, Technische Universität Dortmundwork_fqeijfrpzrannlpdhhcrf6ws7eThu, 21 Jul 2022 00:00:00 GMT