检索结果-南通市图书馆

Berry-Esseen bounds and moderate deviations for the norm, entries and spectral radius of products of positive random matrices

在线全文

学校读者我要写书评

暂无评论

Science China Mathematics 2024年第3期67卷 627-646页

作者： Hui Xiao Ion Grama Quansheng Liu institut fur mathematik und Angewandte Informatik Universitat HildesheimHildesheim 31141Germany Academy of Mathematics and Systems Science Chinese Academy of SciencesBeijing 100190China LMBA Universite Bretagne SudCNRS UMR 6205Vannes F-56000France

Let(g_(n))_(n≥1) be a sequence of independent and identically distributed positive random d×d matrices and consider the matrix product G_(n)=g_(n)…g_*** suitable conditions,we establish the Berry-Esseen bounds on the rate of convergence in the central limit theorem and Cramer-type moderate deviation expansions,for any matrix norm ‖G_(n)‖ of G_(n),its entries G_(n)^(i,j) and its spectral radius ρ(G_(n)).Extended versions of their joint law with the direction of the random walk G_(n)x are also established,where x is a starting point in the unit sphere of R~d.

关键词： Berry-Esseen bound Cramér-type moderate deviation product of random matrices operator norm entry spectral radius

Surviving covid-19:a multimodal discourse analysis of new media covid-19 vaccination-related pictorials

在线全文

学校读者我要写书评

暂无评论

Language and Semiotic Studies 2024年第2期10卷 290-315页

作者： Oluwayemisi Olusola Adebomi institut fur Anglistik und Amerikanistik Universität HamburgHamburgGermany General Studies Department Federal University of TechnologyAkureAkureNigeria

This paper explores the communicative acts deployed in covid-19 vaccination-related pictorials circulated on digital media *** internet images were purposively sampled with a view to exploring their communicative functions as well as their generic *** data,which were culled from the websites of the World Health Organisation,Centre for Disease Control,Pan American Health Organisation and Facebook,were subjected to qualitative *** study deployed van Leeuwen’s Multimodal Discourse Analysis and Yuen’s Generic Structure Potential as theoretical *** multimodal communicative acts are deployed for instructive,illustrative,informative,persuasive,inviting and advisory *** such as Lead,Emblem,Announcement and Enhancer are compulsory in the data while Display,Tag and Call-and-Visit Information are non-compulsory *** can be catalogued as:‘Lead^(Display)^Emblem^(Announcement)^(Enhancer)^(Tag)^(Call-and-Visit Information)’.The study contends that the various semiotic resources deployed in the internet-circulated covid-19 images are used not only for informative and other communicative purposes but also to evoke attitudinal change towards and encourage widespread acceptance of the covid-19 vaccines.

关键词： digital media covid-19 vaccination pictorials multimodal communicative acts generic structure potential

Ray tracing particle image velocimetry-Challenges in the application to a packed bed

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Particuology 2024年第1期84卷 194-208页

作者： Christin Velten Mirko Ebert Christian Lessig Katharina Zahringer Lehrstuhl für Strömungsmechanik und Strömungstechnik Otto-von-Guericke-Universität Magdeburg39106MagdeburgGermany institut für Simulation und Graphik Otto-von-Guericke-Universität Magdeburg39106MagdeburgGermany

Ray tracing Particle Image Velocimetry(RT-PIV)is an optical technique for high resolution velocity measurements in challenging optical systems,such as transparent packed beds,that uses ray tracing to correct for distortions introduced by transparent geometries in the light *** ray tracing based correction is a post processing step applied to the raw PIV particle images before classical PIV *** this study,RT-PIV is performed in the top layer of a body centred cubic(bcc)sphere packing with gaseous flow,where optical access is obtained by the use of transparent N-BK7 glass balls with a diameter of d=40 ***-PIV introduces new experimental and numerical challenges,for example a limited field of view,illumination difficulties,a very large required depth of field and high sensitivity to geometric parameters used in the ray tracing *** challenges and their implications are the main scope and discussed in the present ***,the validation of the ray tracing reconstruction step is presented and examples for the obtained corrected vector fields in a packed bed are *** results show the strength of the method in reconstructing velocity fields behind transparent spheres that would not have been accessible by optical measurement techniques without the ray tracing correction.

关键词： Ray tracing particle image velocimetry(RT-PIV) Transparent spherical particles Packed bed Distortion correction Gas flow

A Wavelet-Free Approach for Multiresolution-Based Grid Adaptation for Conservation Laws

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Communications on Applied Mathematics and Computation 2022年第1期4卷 108-142页

作者： Nils Gerhard Siegfried Müller Aleksey Sikstel institut für geometrie und praktische mathematik RWTH AachenTemplergraben 55Aachen 52056Germany

In recent years the concept of multiresolution-based adaptive discontinuous Galerkin(DG)schemes for hyperbolic conservation laws has been *** key idea is to perform a multiresolution analysis of the DG solution using multiwavelets defined on a hierarchy of nested *** this concept is applied to dyadic grid hierarchies where the explicit construction of the multiwavelets has to be performed only for one reference *** non-uniform grid hierarchies multiwavelets have to be constructed for each element and,thus,becomes extremely *** overcome this problem a multiresolution analysis is developed that avoids the explicit construction of multiwavelets.

关键词： Discontinuous Galerkin Grid adaptivity Multiwavelets Multiresolution analysis Conservation laws

Photoelectrochemical Iron-Catalyzed C(sp^(3))-H Borylation of Alkanes in a Position-Selective Manner

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

CCS Chemistry 2024年第6期6卷 1430-1438页

作者： Wen Wei Bin Wang Simon L.Homölle Jinbin Zhu Yanjun Li Tristan von Münchow Isaac Maksso Lutz Ackermann institut für Organische und Biomolekulare Chemie Georg-August-Universität Göttingen37077 Göttingen

Catalytic C-H borylation is of prime topical importance,since easily available feedstock chemicals can thereby be transformed into valuable transient functional groups in the absence of directing ***,we disclose an iron-catalyzed C(sp^(3))-H borylation of simple,non-prefunctionalized alkanes,providing access to value-added products in a single step by means of *** power of merging photo-and electrochemistry was mirrored by ample scope and exceedingly mild reaction ***,an outstanding position-selectivity in favor of primary C(sp^(3))-H proved viable within the photoelectrochemical borylation through a chemo-selective anodic overoxidation *** ferro-photoelectrochemistry strategy avoids toxic precious transition metals,enabling C(sp^(3))-H borylations in a site-selective fashion.

关键词： photoelectrocatalysis C(sp^(3))-H borylation iron catalysis position-selectivity chlorine radical

A simulation study on spatial and time resolution for a cost-effective positron emission particle tracking system

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Particuology 2024年第5期88卷 312-322页

作者： Josephine Oppotsch Matthias Steinke Miriam Fritsch Fritz-Herbert Heinsius Thomas Held Nikoline Hilse Viktor Scherer Ulrich Wiedner Ruhr-Universität Bochum Institut für Experimentalphysik I44801 BochumGermany Ruhr-Universität Bochum Lehrstuhl für Energieanlagen und Energieprozesstechnik44801 BochumGermany

This work is the second part of a simulation study investigating the processing of densely packed and moving granular assemblies by positron emission particle tracking (PEPT).Since medical positron emission tomography (PET) scanners commonly used for PEPT are very expensive,a PET-like detector system based on cost-effective organic plastic scintillator bars is being developed and tested for its *** this context,the spatial resolution of a resting positron source,a source moving on a freely designed model path,and a particle motion given by a discrete element method (DEM) simulation is studied using Monte Carlo simulations and the software toolkit *** not only extended the simulation and reconstruction to a moving source but also significantly improved the spatial resolution compared to previous work by adding oversampling and iteration to the reconstruction ***,in the case of a source following a trajectory developed from DEM simulations,a very good resolution of about 1 mm in all three directions and an average 3D deviation between simulated and reconstructed events of 2.3 mm could be ***,the resolution for realistic particle motion within the generic grate system (which is the test rig for further experimental studies) is well below the smallest particle *** simulation of the dependence of the reconstruction accuracy on tracer particle location revealed a nearly constant efficiency within the entire detector system,which demonstrates that boundary effects can be neglected.

关键词： Positron emission particle tracking Monte Carlo method Time-of-flight Plastic scintillators Silicon photomultipliers(SiPMs)

A simulation study for a cost-effective PET-like detector system intended to track particles in granular assemblies

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Particuology 2024年第1期84卷 117-125页

作者： Josephine Oppotsch Antonios Athanassiadis Miriam Fritsch Fritz-Herbert Heinsius Thomas Held Nikoline Hilse Viktor Scherer Matthias Steinke Ulrich Wiedner Ruhr-Universität Bochum Institut für Experimentalphysik I44801 BochumGermany Ruhr-Universität Bochum Lehrstuhl für Energieanlagen und Energieprozesstechnik44801 BochumGermany

Since many industrial applications rely on the processing of densely packed and moving granular ma-terial,obtaining bulk internal information on the particle movement inside the reactors is of great *** information can be delivered by Positron Emission Particle Tracking(PEPT).By marking pellets with a positron-emitting radioisotope,the position of these tracer particles can be determined via the time-of-flight differences of the emitted gamma-ray *** current paper proposes a PET-like detector system based on cost-effective organic plastic scintillators instead of the more common but expensive inorganic *** system is currently under construction and was tested for its resolution and efficiency in this simulation *** Monte Carlo simulations and the software toolkit Geant4,three different geometries(an empty glass box,a generic grate system,and a cubic box of 1 m3 completely filled with pellets)were investigated,leading to a spatial resolution in the millimeter range and an efficiency,defined as the ratio of reconstructed decay locations to simulated decays,of 2.7%,1.4%,and 0.3%.

关键词： Positron emission particle tracking Geant4 Monte Carlo method Time-of-flight Plastic scintillators Silicon photomultipliers(SiPMs)

Searching for the Highest Energy of Pulsation and Critical Luminosity of Swift J0243.6+6124 Observed by Insight-HXMT

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Research in Astronomy and Astrophysics 2024年第5期24卷 61-69页

作者： Qing-Xia Zhao Xian Hou Ming-Yu Ge Shuang-Nan Zhang Yun-Xiang Xiao You-Li Tuo Zi-Xu Yang Ling-Da Kong Jin-Lu Qu Shu Zhang Jian-Cheng Wang Yunnan Observatories Chinese Academy of SciencesKunming 650216China Key Laboratory of Particle Astrophysics Institute of High Energy PhysicsChinese Academy of SciencesBeijing 100049China University of Chinese Academy of Sciences ChineseAcademy of SciencesBeijing 100049China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of SciencesKunming 650216China institut fur Astronomic und Astrophysik Sand 1D-72076 TabingenGemany School of Physics and Optoelectronic Engineering Shandong University of TechnologyZibo 255000China

Owing to the broad energy coverage of Insight-HXMT in the hard X-ray band,we detected the highest energy of pulsation exceeding 200 keV around the 2017–2018 outburst peak of the first Galactic pulsating ultraluminous X-ray source (PULX) Swift J0243.6+6124,which is the highest energy detected from PULXs to *** also obtained the highest energy of pulsation of every exposure during the outburst in 2017–2018,and found the highest energy is roughly positively correlated with *** our newly developed method,we identified the critical luminosity being 4×10^(38)erg s^(-1) when the main peaks of the low and high energy pulse profiles became aligned,which separates the fan-beam dominated and pencil-beam dominated accretion *** the critical luminosity,the phase of the main peak shifted gradually from 0.5 to 0.8 until the outburst peak in al energy bands is reached,which is in agreement with the phase shift found previously at low *** result is consistent with what is derived from spectral analysis.

关键词： (stars:)pulsars-individual(Swift J0243.6+6124)-X-rays binaries–stars neutron

Impact of T_(i)/T_(e )ratio on ion transport based on EAST H-mode plasmas

在线全文

学校读者我要写书评

暂无评论

Plasma Science and Technology 2024年第4期26卷 68-78页

作者：刘建文臧庆梁云峰陈佳乐邬潇河 Alexander KNIEPS 扈嘉辉金仡飞张斌储宇奇刘海庆吕波段艳敏李妙辉陈颖杰龚先祖 the EAST Team institute of Plasma Physics Chinese Academy of SciencesHefei 230031People’s Republic of China University of Science and Technology of China Hefei 230026People’s Republic of China Forschungszentrum Jülich GmbH Institut für Energie-und Klimaforschung-PlasmaphysikPartner of the Trilateral Euregio Cluster(TEC)Jülich 52425Germany

At the EAST tokamak, the ion temperature(T_(i)) is observed to be clamped around 1.25 keV in electron cyclotron resonance(ECR)-heated plasmas, even at core electron temperatures up to 10 keV(depending on the ECR heating power and the plasma density). This clamping results from the lack of direct ion heating and high levels of turbulence-driven transport. Turbulent transport analysis shows that trapped electron mode and electron temperature gradient-driven modes are the most unstable modes in the core of ECR-heated H-mode plasmas. Nevertheless, recently it was found that the T_(i)/T_(e)ratio can increase further with the fraction of the neutral beam injection(NBI) power, which leads to a higher core ion temperature(Ti0). In NBI heating-dominant H-mode plasmas, the ion temperature gradient-driven modes become the most unstable ***, a strong and broad internal transport barrier(ITB) can form at the plasma core in high-power NBI-heated H-mode plasmas when the T_(i)/T_(e)ratio approaches ~1, which results in steep core Teand Tiprofiles, as well as a peaked neprofile. Power balance analysis shows a weaker Teprofile stiffness after the formation of ITBs in the core plasma region, where Ticlamping is broken,and the core Tican increase further above 2 keV, which is 80% higher than the value of Ticlamping in ECR-heated plasmas. This finding proposes a possible solution to the problem of Ticlamping on EAST and demonstrates an advanced operational regime with the formation of a strong and broad ITB for future fusion plasmas dominated by electron heating.

关键词： ion temperature clamping transport neutral beam injection stiffness internal transport barrier