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Approximate contact solutions for non-axisymmetric homogeneous and power-law graded elastic bodies:A practical tool for design engineers and tribologists

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Friction 2024年第2期12卷 340-355页

作者： Valentin L.POPOV Qiang LI Emanuel WILLERT Institute of Mechanics Technische Universität BerlinBerlin 10623Germany

In two recent papers,approximate solutions for compact non-axisymmetric contact problems of homogeneous and power-law graded elastic bodies have been suggested,which provide explicit analytical relations for the force–approach relation,the size and the shape of the contact area,as well as for the pressure distribution *** solutions were derived for profiles,which only slightly deviate from the axisymmetric *** the present paper,they undergo an extensive testing and validation by comparison of solutions with a great variety of profile shapes with numerical solutions obtained by the fast Fourier transform(FFT)-assisted boundary element method(BEM).Examples are given with quite significant deviations from axial symmetry and show surprisingly good agreement with numerical solutions.

关键词： normal contact non-axisymmetric indenter extremal principle generalized method of dimensionality reduction(MDR) functional elastic grading

Removing trace oxygen to obtain truly intrinsic transport in organic semiconductors

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Science China Materials 2024年第5期67卷 1668-1669页

作者： Hans Kleemann Dresden Integrated Center for Applied Physics and Photonic Materials Technische UniversitätDresdenGermany

Organic semiconductor is an emerging generation semiconductor material,which has a broad application prospect in the field of flexible and large-area *** now,tens of thousands of organic semiconductor molecules with diverse functions have been developed through elaborate molecular *** molecules are often classified into n-type and ptype,depending on whether the prevalent charge carriers are electrons or holes[1].

关键词： transport intrinsic moving

Dynamic convergent shock compression initiated by return current in high-intensity laser-solid interactions

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Matter and Radiation at Extremes 2024年第4期9卷 40-53页

作者： Long Yang Martin Rehwald Thomas Kluge Alejandro LasoGarcia Toma Toncian Karl Zeil Ulrich Schramm Thomas E.Cowan Lingen Huang Helmholtz-Zentrum Dresden-Rossendorf 01328 DresdenGermany technische universitat Dresden 01062 DresdenGermany

We investigate the dynamics of convergent shock compression in solid cylindrical targets irradiated by an ultrafast relativistic laser *** particle-in-cell simulations and coupled hydrodynamic simulations reveal that the compression process is initiated by both magnetic pressure and surface ablation associated with a strong transient surface return current with density of the order of 10^(17) A/m^(2) and lifetime of 100 *** results show that the dominant compression mechanism is governed by the plasma β,i.e.,the ratio of thermal pressure to magnetic *** targets with small radius and low atomic number Z,the magnetic pressure is the dominant shock compression *** to a scaling law,as the target radius and Z increase,the surface ablation pressure becomes the main mechanism generating convergent ***,an indirect experimental indication of shocked hydrogen compression is provided by optical shadowgraphy measurements of the evolution of the plasma expansion *** results presented here provide a novel basis for the generation of extremely high pressures exceeding Gbar(100 TPa)to enable the investigation of high-pressure physics using femtosecond J-level laser pulses,offering an alternative to nanosecond kJ-laser pulse-driven and pulsed power Z-pinch compression methods.

关键词： shock convergent return

Enhancing wood efficiency through comprehensive wood flow analysis:Methodology and strategic insights

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Forest Ecosystems 2024年第2期11卷 172-183页

作者： Ruisheng Wang Peer Haller Institute of Steel and Timber Construction Technische Universität Dresden01062DresdenGermany

Wood,an essential natural resource in human civilization,remains widely used despite advances in technology and material *** surge in greenhouse gas emissions and environmental concerns accentuates the need for optimizing wood *** flow analysis is a powerful tool for tracking material flows and stocks,aiding resource management and environmental ***,the full extent of its methodological dimensions,particularly within the context of the wood supply chain,remains relatively *** this study,we delve into the existing literature on wood flow analysis,discussing its primary objectives,materials involved,temporal and spatial scales,data sources,units,and conversion ***,data uncertainty,data reconciliation and crucial assumptions in material flow analysis are highlighted in this *** findings reveal the significance of wood cascading and substitution effects by replacing non-wood materials,where they can reduce greenhouse gas emissions more than the natural carbon sink of forests and wood *** immediate impact of short-term wood cascading might not be as robust as the substitution effect,with energy substitution showcasing better results than material ***,it's crucial to note that these conclusions could experience significant reversal from a long-term and global *** for improving wood efficiency involve maximizing material use,advancing construction technologies,extending product lifespans,promoting cascade use,and optimizing energy recovery *** study underscores the need for standardized approaches in wood flow analysis and emphasizes the potential of wood efficiency strategies in addressing environmental challenges.

关键词： Material flow analysis Wood Methodology Cascade use Substitution effects

Controlling the reaction network of Ni/silica derived conversion of bio-oil surrogate guaiacol

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Carbon Resources Conversion 2024年第1期7卷 39-60页

作者： Nils Kretzschmar Oliver Busse Markus Seifert technische universität Dresden Faculty of Chemistry and Food Chemistry01062 DresdenGermany

Replacing fossil carbon sources with green bio-oils is a promising route to switch to a sustainable chemical industry,although their high oxygen contents are *** hydrodeoxygenation is a favored route to upgrade bio-oils to renewable fuels and basic *** this work,we investigated Ni/SiO2 catalysts with differing metal dispersity in continuous mode conversion of guaiacol with a statistical experimental design for 250℃to 400℃,2 h up to 5 h time on stream(ToS)and subsequently different residence time besides other *** low temperature(250℃)promotes cyclohexanol formation from guaiacol,high temperature(400℃)inhibits hydrogenation,leading to phenol and *** medium temperature(340℃),the selectivity for cyclohexanone *** and cyclohexanone(KA-oil)are the industrial basis for polyamide ***,we clarified the role of 2-methoxycyclohexanol(2MC)in the reaction network towards KA-oil for continuous-mode *** analysis was used to predict and optimize product selectivity and yield,leading to the best yield of cyclohexanone/-ol at 327.5℃,low ToS,medium residence time,high particle dispersity,and medium hydrogen pressure(15 bar(g)).

关键词： Hydrodeoxygenation Design of experiments Bio-oil Nickel silica catalyst Continuous mode flow reactor KA-oil Cyclohexanol Cyclohexanone

APPROXIMATING THE STATIONARY BELLMAN EQUATION BY HIERARCHICAL TENSOR PRODUCTS

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Journal of Computational Mathematics 2024年第3期42卷 638-661页

作者： Mathias Oster Leon Sallandt Reinhold Schneider technische universität Berlin Strasse des 17.Juni 13510623 BerlinGermany

We treat infinite horizon optimal control problems by solving the associated stationary Bellman equation numerically to compute the value function and an optimal feedback *** dynamical systems under consideration are spatial discretizations of non linear parabolic partial differential equations(PDE),which means that the Bellman equation suffers from the curse of *** non linearity is handled by the Policy Iteration algorithm,where the problem is reduced to a sequence of linear equations,which remain the computational bottleneck due to their high *** reformulate the linearized Bellman equations via the Koopman operator into an operator equation,that is solved using a minimal residual *** the Koopman operator we identify a preconditioner for operator equation,which deems essential in our numerical *** overcome computational infeasability we use low rank hierarchical tensor product approximation/tree-based tensor formats,in particular tensor trains(TT tensors)and multi-polynomials,together with high-dimensional quadrature,*** controlling a destabilized version of viscous Burgers and a diffusion equation with unstable reaction term numerical evidence is given.

关键词： Feedback control Dynamic programming Hamilton-Jacobi-Bellman Tensor product approximation Variational Monte-Carlo

Single-atom catalysts for neutral zinc-air batteries

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Science China Materials 2024年第5期67卷 1674-1675页

作者： Jiaxu Zhang Minghao Yu Faculty of Chemistry and Food Chemistry&Center for Advancing Electronics Dresden(CfAED) Technische Universität DresdenDresden01062Germany

The escalating global energy demand underscores the urgency of developing sustainable battery ***-air batteries(ZABs)have emerged as promising candidates due to their costeffectiveness,safety,and high energy density[1-4].Conventional ZABs typically rely on a four-electron(4e-)oxygen reduction reaction(ORR)in strongly alkaline electrolytes.

关键词： battery neutral typically

Performance characteristics of the airlift pump under vertical solid-water-gas flow conditions for conveying centimetric-sized coal particles

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International Journal of Coal Science & Technology 2024年第2期11卷 53-66页

作者： Parviz Enany Carsten Drebenshtedt Faculty of Mining and Special Civil Engineering Technische Universitat BergakademieGustav-Zeuner StraBe 1A09599FreibergGermany

In this study,the installation of an airlift pump with inner diameter of 102 mm and length of 5.64 m was utilized to consider the conveying process of non-spherical coal particles with density of 1340 kg/m3 and graining 25-44.5 *** test results revealed that the magnitude of increase in the solid transport rate due to the changes in the three tested parameters between compressed air velocity,submergence ratio,and feeding coal possibility was not the same,which are stand in range of 20%,75%,and 40%,***,creating the optimal airlift pump performance is highly dependent on submergence *** importantly,we measured the solid volume fraction using the method of one-way valves in order to minimize the disadvantages of conventional devices,such as fast speed camera and conductivity ring *** results confirmed that the volume fraction of the solid phase in the transfer process was always less than 12%.To validate present experimental data,the existing empirical correlations together with the theoretical equations related to the multiphase flow was *** overall agreement between the theory and experimental solid delivery results was particularly good instead of the first stage of conveying *** drawback can be corrected by omitting the role of friction and shear stress at low air income *** was also found that the model developed by Kalenik failed to predict the performance of our airlift operation in terms of the mass flow rate of the coal particles.

关键词： Vertical velocity Non-spherical particle Submergence ratio Three-phase flow Churn flow Superficial velocity

Distortions in focusing laser pulses due to spatio-temporal couplings:an analytic description

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High Power Laser Science and Engineering 2024年第3期12卷 20-40页

作者： Klaus Steiniger Fabia Dietrich Daniel Albach Michael Bussmann Arie Irman Markus Loeser Richard Pausch Thomas Püschel Roland Sauerbrey Susanne Schöbel Ulrich Schramm Mathias Siebold Karl Zeil Alexander Debus Helmholtz-Zentrum Dresden-Rossendorf DresdenGermany CASUS-Center for Advanced Systems Understanding GörlitzGermany technische universität Dresden DresdenGermany

In ultra-short laser pulses,small changes in dispersion properties before the final focusing mirror can lead to severe pulse distortions around the focus and therefore to very different pulse properties at the point of laser±matter interaction,yielding unexpected interaction *** mapping between far-and near-field laser properties intricately depends on the spatial and angular dispersion properties as well as the focal *** a focused Gaussian laser pulse under the influence of angular,spatial and group-delay dispersion,we derive analytical expressions for its pulse-front tilt,duration and width from a fully analytic expression for its electric field in the time±space domain obtained with scalar diffraction *** expression is not only valid in and near the focus but also along the entire propagation distance from the focusing mirror to the *** relating angular,spatial and group-delay dispersion before focusing at an off-axis parabola,where they are well measurable,to the respective values in the pulse’s focus are obtained by a ray tracing ***,these formulas are used to show in example setups that the pulse-front tilts of lasers with small initial dispersion can become several tens of degrees larger in the vicinity of the focus while being small directly in the *** formulas derived here provide the analytical foundation for observations previously made in numerical *** numerically simulating Gaussian pulse propagation and measuring properties of the pulse at distances several Rayleigh lengths off the focus,we verify the analytic expressions.

关键词： group-delay dispersion pulse-front tilt spatio-temporal couplings third-order dispersion ultra-short laser pulses