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Unveiling the inner structure of electron pulses generated from a laser-wakefield accelerator

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Light(Science & Applications) 2023年第10期12卷 1992-1994页

作者： malte C.Kaluza Institute of Optics and Quantum Electronics Max-Wien-Platz 107743JenaGermany Helmholtz-Institute Jena Fröbelstieg 307743JenaGermany

A novel diagnostic method has been used to gain deeper insight into the transverse structure and its evolution of electron pulses generated from a laser-wakefield accelerator.

关键词： structure field laser

LOCAL PRESSURE CORRECTION FOR THE STOKES SYSTEM

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Journal of Computational Mathematics 2020年第1期38卷 125-141页

作者： malte Braack Utku Kaya Mathematical Seminar University of KielGermany

Pressure correction methods constitute the most widely used solvers for the timedependent Navier-Stokes *** are several different pressure correction methods,where each time step usually consists in a predictor step for a non-divergence-free velocity,followed by a Poisson problem for the pressure(or pressure update),and a final velocity correction to obtain a divergence-free vector *** some situations,the equations for the velocities are solved explicitly,so that the numerical most expensive step is the elliptic pressure *** here propose to solve this Poisson problem by a domain decomposition method which does not need any communication between the ***,this system is perfectly adapted for parallel *** show under certain assumptions that this new scheme has the same order of convergence as the original pressure correction scheme(with global projection).Numerical examples for the Stokes system show the effectivity of this new pressure correction *** convergence order O(k^2)for resulting velocity fields can be observed in the norm l^2(0,T;L^2(Ω)).

关键词： Stokes system Navier-Stokes Pressure correction Finite elements

Evaluating the morphology of the degradation layer of pure magnesium via 3D imaging at resolutions below 40 nm

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Bioactive Materials 2021年第12期6卷 4368-4376页

作者： Berit Zeller-Plumhoff Daniel Laipple Hanna Slominska Kamila Iskhakova Elena Longo Alexander Hermann Silja Flenner Imke Greving malte.storm Regine Willumeit-Romer Helmholtz-Zentrum hereon GmbH Institute of Metallic BiomaterialsMax-Planck-Straße 121502GeesthachtGermany Helmholtz-Zentrum hereon GmbH Research ReactorMax-Planck-Straße 121502GeesthachtGermany Helmholtz-Zentrum hereon GmbH Institute of Materials PhysicsMax-Planck-Straße 121502GeesthachtGermany Helmholtz-Zentrum hereon GmbH Institute of Materials Systems ModellingMax-Planck-Straße 121502GeesthachtGermany Diamond Light Source Ltd. Diamond HouseHarwell Science and Innovation CampusDidcotOX110DEUnited Kingdom

Magnesium is attractive for the application as a temporary bone implant due to its inherent biodegradability,non-toxicity and suitable mechanical *** degradation process of magnesium in physiological environments is complex and is thought to be a diffusion-limited transport *** use a multi-scale imaging approach using micro computed tomography and transmission X-ray microscopy(TXM)at resolutions below 40 ***,we are able to evaluate the nanoporosity of the degradation layer and infer its impact on the degradation process of pure magnesium in two physiological *** samples were degraded in simulated body fluid(SBF)or Dulbecco’s modified Eagle’s medium(DMEM)with 10%fetal bovine serum(FBS)for one to four *** reveals the three-dimensional interconnected pore network within the degradation layer for both *** pore network morphology and degradation layer composition are similar for all *** contrast,the degradation layer thickness in samples degraded in SBF was significantly higher and more inhomogeneous than in DMEM+10%*** features could be observed within the degradation layer of samples degraded in SBF,suggesting the formation of microgalvanic cells,which are not present in samples degraded in DMEM+10%*** results suggest that the nanoporosity of the degradation layer and the resulting ion diffusion processes therein have a limited influence on the overall degradation *** indicates that the influence of organic components on the dampening of the degradation rate by the suppression of microgalvanic degradation is much greater in the present study.

关键词： Magnesium degradation Porosity Transmission X-ray microscopy 3D imaging

REVIEW ARTICLE FINITE ELEMENTS WITH LOCAL PROJECTION STABILIZATION FOR INCOMPRESSIBLE FLOW PROBLEMS

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Journal of Computational Mathematics 2009年第2期27卷 116-147页

作者： malte Braack Gerr Lube Mathematisches Seminar Christian-Albrechts-Universitt zu KielLudewig-Meyn-Str.4D-24098 KielGermany Institut für Numerische und Angewandte Mathematik Georg-August Universitt GttingenLotzestrasse 16-18 D-37083 GttingenGermany

In this paper we review recent developments in the analysis of finite element methods for incompressible flow problems with local projection stabilization （LPS）. These methods preserve the favourable stability and approximation properties of classical residual-based stabilization （RBS） techniques but avoid the strong coupling of velocity and pressure in the stabilization terms. LPS-methods belong to the class of symmetric stabilization techniques and may be characterized as variational multiscale methods. In this work we summarize the most important a priori estimates of this class of stabilization schemes developed in the past 6 years. We consider the Stokes equations, the Oseen linearization and the NavierStokes equations. Furthermore, we apply it to optimal control problems with linear（ized） flow problems, since the symmetry of the stabilization leads to the nice feature that the operations ＂discretize＂ and ＂optimize＂ commute.

关键词： Finite element method Stabilization Computational fluid dynamics Errorestimates Navier-Stokes Stokes

DIRECTIONAL DO-NOTHING CONDITION FOR THE NAVIER-STOKES EQUATIONS

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Journal of Computational Mathematics 2014年第5期32卷 507-521页

作者： malte Braack Piotr Boguslaw Mucha Mathematisches Seminar Christian-Albrechts-Universitat zu Kiel Ludewig-Meyn-Str. 4 D-24098 Kiel Germany Institute of Applied Mathematics and Mechanics University of Warsaw ul Banacha 2 02-097 Warszawa Poland

The numerical solution of flow problems usually requires bounded domains although the physical problem may take place in an unbounded or substantially larger domain. In this case, artificial boundaries are necessary. A well established artificial boundary condition for the Navier-Stokes equations diseretized by finite elements is the “do-nothing” condition. The reason for this is the fact that this condition appears automatically in the variational formulation after partial integration of the viscous term and the pressure gradient. This condition is one of the most established outflow conditions for Navier-Stokes but there are very few analytical insight into this boundary condition. We address the question of existence and stability of weak solutions for the Navier-Stokes equations with a “directional do-nothing” condition. In contrast to the usual “do-nothing” condition this boundary condition has enhanced stability properties. In the case of pure outflow, the condition is equivalent to the original one, whereas in the case of inflow a dissipative effect appears. We show existence of weak solutions and illustrate the effect of this boundary condition by computation of steady and non-steady flows.

关键词： Boundary conditions Navier-Stokes Outflow condition Existence.

New opportunities and challenges in surveying underground cavities using photogrammetric methods

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International Journal of Mining Science and Technology 2021年第1期31卷 9-13页

作者： malte J.M.Gurgel Axel Preusse Institute for Mine Surveying Mining Subsidence Engineering and Geophysics in MiningRWTH Aachen UniversityAachen 52062Germany

The exploitation of the underground is currently undergoing a major transformation *** mining,alternative ways of utilization are playing an increasingly important *** alternative utilizations include the storage of gases,the disposal of radioactive wastes,and the implementation of geothermal storage *** addition,more and more mining operations are being shut down,like the German hard coal mining industry in *** the integrity of closed mines must be ensured in the post-mining *** order to capture such large and complex structures efficiently and reliably,new surveying techniques are required.A promising approach is the use of photogrammetric methods to generate three-dimensional models of the *** is currently known mainly from aerial *** is conceivable to use such methods for underground *** recent years,significant progress has been made in the algorithm-based orientation of unstructured image *** powerful computer systems and the growing range of unmanned aerial vehicles could enable partially automated ***,a number of problems have to be solved for underground imaging *** exposure conditions complicate image ***,the models must be integrated into existing surveying systems with a sufficiently high degree of *** order to consider the numerous technical aspects,the development of an integrated capture and evaluation approach is *** could make an important contribution to the monitoring of critical cavities of different *** an approach would also fit into the current digitization trend in the mining industry and provide new opportunities for ground control in particular.

关键词： Photogrammetry Surveying Subsurface spatial planning

Endoscopic ultrasound-guided techniques for diagnosing pancreatic mass lesions: Can we do better?

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World Journal of Gastroenterology 2016年第39期22卷 8658-8669页

作者： Andrew C storm Linda S Lee Division of Gastroenterology Hepatology and Endoscopy Brigham and Women’s Hospital Harvard Medical School

The diagnostic approach to a possible pancreatic mass lesion relies first upon various non-invasive imaging modalities, including computed tomography, ultrasound, and magnetic resonance imaging techniques. Once a suspect lesion has been identified, tissue acquisition for characterization of the lesion is often paramount in developing an individualized therapeutic approach. Given the high prevalence and mortality associated with pancreatic cancer, an ideal approach to diagnosing pancreatic mass lesions would be safe, highly sensitive, and reproducible across various practice settings. Tools, in addition to radiologic imaging, currently employed in the initial evaluation of a patient with a pancreatic mass lesion include serum tumor markers, endoscopic retrograde cholangiopancreatography, and endoscopic ultrasound-guided fine needle aspiration(EUS-FNA). EUS-FNA has grown to become the gold standard in tissue diagnosis of pancreatic lesions.

关键词： Endoscopic ultrasound Fine needle aspiration Pancreatic cancer Pancreatic mass Endoscopy

Influence of humidity on conduction processes in gas-insulated devices

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High Voltage 2020年第2期5卷 143-150页

作者： malte Tschentscher David Graber Christian M.Franck High Voltage Laboratory ETH Zurich8092 ZurichSwitzerland

Humidity has been considered as one of the main influencing factors that determine the conduction processes and electric strength of gas-insulated *** in the past,various studies focused on the change in the partial discharge inception voltages,breakdown strength of homogeneous and inhomogeneous field arrangements,and insulator flashover voltage,recent studies have investigated the changes in ion currents measured through different gas *** the framework of this contribution,a highly precise humidity control circuit has been developed to analyse the significance of humidity in the range from−25 to−5°C frost-point,which is fully applicable to operating gas-insulated *** sulphur hexafluoride(SF6)as the insulation gas at 0.45 MPa,Al2O3-filled epoxy resin insulators,and technically rough electrodes,the humidity was found to significantly influence the intensity of microdischarges at *** generation from microdischarges at the interfaces substantially increased with increasing *** an electric field of 5 kV/mm that were applicable to the dimensioning of gas-insulated devices,humidity strongly influences the charge provision from technically rough interfaces and potentially contributes to the surface-charge accumulation at insulator *** the other hand,for low-field conduction phenomena,no increase in the ion currents from natural ionisation or electrophoretic conduction was *** the investigated range of parameters,humidity is expected to be highly relevant for the design of gas-insulated devices.

关键词： conduction humidity sulphur

Dielectric tunability of magnetic properties in orthorhombic ferromagnetic monolayer CrSBr

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npj Computational Materials 2023年第1期9卷 1514-1523页

作者： Alexander N.Rudenko malte Rösner Mikhail I.Katsnelson Radboud University Institute for Molecules and MaterialsHeijendaalseweg 1356525AJ NijmegenThe Netherlands

Monolayer CrSBr is a recently discovered semiconducting spin-3/2 ferromagnet with a Curie temperature of around 146 *** contrast to many other known 2D magnets,the orthorhombic lattice of CrSBr gives rise to spatial anisotropy of magnetic excitations within the 2D *** magnetic anisotropy and considerable magnetic dipolar interactions in CrSBr challenge its theoretical description in terms of spin ***,we employ a Green’s function formalism combined with first-principles calculations to study the magnetic properties of monolayer CrSBr in different regimes of surrounding dielectric *** the free-standing limit,the system is close to an easy-plane magnet,whose long-range ordering is partially *** the contrary,in the regime of large external screening,monolayer CrSBr behaves like an easy-axis ferromagnet with more stable magnetic *** findings suggest that anisotropic layered magnets form a potentially promising platform for studying the effects of substrate screening on magnetic ordering in 2D.

关键词： monolayer orthorhombic anisotropy