检索结果-南通市图书馆

A product version of the Hilton-Milner-frankl theorem

在线全文

学校读者我要写书评

暂无评论

Science China Mathematics 2024年第2期67卷 455-474页

作者： peter frankl Jian Wang Alfréd Rényi Institute of Mathematics Hungarian Academy of SciencesBudapest H-1053Hungary Department of Mathematics Taiyuan University of TechnologyTaiyuan 030024China

Two families f and G of k-subsets of {1, 2,..., n} are called non-trivial cross t-intersecting if|f ∩ G|≥t for all f ∈ f, G ∈ G and | ∩ {f : f ∈ f}| < t, | ∩ {G : G ∈ G}| < t. In the present paper,we determine... 详细信息

Two families f and G of k-subsets of {1, 2,..., n} are called non-trivial cross t-intersecting if|f ∩ G|≥t for all f ∈ f, G ∈ G and | ∩ {f : f ∈ f}| f the sizes of two non-trivial cross t-intersecting families of k-subsets of{1, 2,..., n} for n≥4(t + 2)2k2, k≥5, which is a product version of the Hilton-Milner-frankl theorem.

关键词： extremal set theory cross t-intersecting family product version non-trivial

Macroscopic Traversable Wormholes: Minimum Requirements

在线全文

学校读者我要写书评

暂无评论

International Journal of Astronomy and Astrophysics 2024年第3期14卷 230-243页

作者： peter K. f. Kuhfittig Department of Mathematics Milwaukee School of Engineering Milwaukee USA

While wormholes are just as good a prediction of Einstein’s theory as black holes, they are subject to severe restrictions from quantum field theory. To allow for the possibility of interstellar travel, a macroscopic wormhole would need to maintain sufficiently low radial tidal forces. It is proposed in this paper that the assumption of zero tidal forces, i.e ., the limiting case, is sufficient for overcoming the restrictions from quantum field theory. The feasibility of this approach is subsequently discussed by 1) introducing the additional conditions needed to ensure that the radial tidal forces can indeed be sufficiently low and 2) by viewing traversable wormholes as emergent phenomena, thereby increasing the likelihood of their existence.

关键词： Morris-Thorne Wormholes Traversability Minimum Requirements Stability Compatibility with Quantum field Theory

Thin-Shell Wormholes Admitting Conformal Motions in Spacetimes of Embedding Class One

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

International Journal of Astronomy and Astrophysics 2024年第3期14卷 162-171页

作者： peter K. f. Kuhfittig Department of Mathematics Milwaukee School of Engineering Milwaukee USA

This paper discusses the feasibility of thin-shell wormholes in spacetimes of embedding class one admitting a one-parameter group of conformal motions. It is shown that the surface energy density σ is positive, while the surface pressure is negative, resulting in , thereby signaling a violation of the null energy condition, a necessary condition for holding a wormhole open. for a Morris-Thorne wormhole, matter that violates the null energy condition is referred to as “exotic”. for the thin-shell wormholes in this paper, however, the violation has a physical explanation since it is a direct consequence of the embedding theory in conjunction with the assumption of conformal symmetry. These properties avoid the need to hypothesize the existence of the highly problematical exotic matter.

关键词： Thin-Shell Wormholes Conformal Symmetry Embedding Class One Exotic Matter

Towards implementation of alloy-specific thermo-fluid modelling for laser powder-bed fusion of Mg alloys

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Journal of Magnesium and Alloys 2024年第6期12卷 2327-2344页

作者： Mohammad Hoseini-Athar Mikael Ersson peter Hedström Department of Material Science and Engineering KTH Royal Institute of TechnologyStockholmSE-10044 Sweden

Multi-physics thermo-fluid modeling has been extensively used as an approach to understand melt pool dynamics and defect formation as well as optimizing the process-related parameters of laser powder-bed fusion(L-PBf).However,its capabilities for being implemented as a reliable tool for material design,where minor changes in material-related parameters must be accurately captured,is still in *** the present research,first,a thermo-fluid computational fluid dynamics(CfD)model is developed and validated against experimental *** the predicted material properties of the pure Mg and commercial ZK60 and WE43 Mg alloys,parametric studies are done attempting to elucidate how the difference in some of the material properties,i.e.,saturated vapor pressure,viscosity,and solidification range,can influence the melt pool *** is found that a higher saturated vapor pressure,associated with the ZK60 alloy,leads to a deeper unstable keyhole,increasing the keyhole-induced porosity and evaporation mass *** viscosity and wider solidification range can increase the non-uniformity of temperature and velocity distribution on the keyhole walls,resulting in increased keyhole instability and formation of ***,the WE43 alloy showed the best behavior in terms of defect formation and evaporation mass loss,providing theoretical support to the extensive use of this alloy in *** summary,this study suggests an approach to investigate the effect of materials-related parameters on L-PBf melting and solidification,which can be extremely helpful for future design of new alloys suitable for L-PBf.

关键词： Mg alloys Laser powder-bed fusion(L-PBf) Melt pool dynamics Computational fluid dynamics fluid flow

地球演化历史中氧逸度变化对壳幔循环启动、风化和超大陆循环的指示

在线全文

学校读者我要写书评

暂无评论

Science Bulletin 2024年第1期69卷 97-102页

作者：王瑞邬绍宸 Roberto f.Weinberg William J.Collins peter A.Cawood State Key Laboratory of Geological Processes and Mineral Resources Institute of Earth SciencesChina University of GeosciencesBeijing 100083China frontiers Science Center for Deep-time Digital Earth China University of Geosciences(Beijing)Beijing 100083China School of Earth Atmosphere and EnvironmentMonash UniversityClayton VIC 3800Australia The Institute for Geoscience Research Curtin UniversityPerth WA 6102Australia

We apply a zircon redox index to a global compilation of detrital zircons to track the variation of oxidation state,expressed asΔfMQ,through Earth's *** from I-type rocks,which comprise mantle and crustal igneous protoliths,including tonalite–trondhjemite–granodiorites(TTGs),generally have a high oxidation state(ΔfMQ>0).In contrast,zircons from igneous rocks derived from supracrustal source rocks(S-type)are commonly reduced(ΔfMQfunction derived from the Gaussian-Kernel-Density-Estimation,we use the maximum likelihood estimation(MLE)to distinguish Stype from I-type zircons through Earth's history using zircon *** S-type magma production shows a ca.600 Ma cyclicity that is closely related to the supercontinent *** link a cyclic drop in redox values after 2.6 Ga to periodic S-type magma generation associated with burial and melting of metasedimentary rocks during supercontinent assembly and ***ΔfMQ of the detrital zircons rise at~3.5 Ga followed by a consistent averageΔfMQ>0 over the last 3 *** that the redox state of magmas is independent of crustal thickness and silica variation,and elevated values are likely more closely related to tectonic setting,we suggest that the consistent averageΔfMQ>0 from ca.3.5 Ga onwards relates to recycling of oceanic lithosphere back into the mantle in what eventually became established as subduction *** more reduced magmas associated with sedimentary sources,became established at 2.6 Ga,presumably in response to continental rocks rising above sealevel,and follow peaks of productivity associated with the supercontinent cycle.

关键词： Oxidation state Supercontinent Weathering Subduction Zircon Granite

A Survey on Sensor-and Communication-Based Issues of Autonomous UAVs

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Computer Modeling in Engineering & Sciences 2024年第2期138卷 1019-1050页

作者： Pavlo Mykytyn Marcin Brzozowski Zoya Dyka peter Langendoerfer IHP-Leibniz-Institut für Innovative Mikroelektronik Wireless SystemsFrankfurt(Oder)15236Germany BTU Cottbus-Senftenberg Faculty 1:MINTCottbus03046German

The application field for Unmanned Aerial Vehicle (UAV) technology and its adoption rate have been increasingsteadily in the past years. Decreasing cost of commercial drones has enabled their use at a scale broader thanever before. However, increasing the complexity of UAVs and decreasing the cost, both contribute to a lack ofimplemented securitymeasures and raise new security and safety concerns. for instance, the issue of implausible ortampered UAV sensor measurements is barely addressed in the current research literature and thus, requires moreattention from the research community. The goal of this survey is to extensively review state-of-the-art literatureregarding common sensor- and communication-based vulnerabilities, existing threats, and active or passive cyberattacksagainst UAVs, as well as shed light on the research gaps in the literature. In this work, we describe theUnmanned Aerial System (UAS) architecture to point out the origination sources for security and safety *** the coverage and completeness of each related research work in a comprehensive comparison table as wellas classify the threats, vulnerabilities and cyber-attacks into sensor-based and communication-based ***, for each individual cyber-attack, we describe existing countermeasures or detectionmechanisms andprovide a list of requirements to ensureUAV’s security and *** also address the problem of implausible sensormeasurements and introduce the idea of a plausibility check for sensor data. By doing so, we discover additionalmeasures to improve security and safety and report on a research niche that is not well represented in the currentresearch literature.

关键词： Unmanned aerial vehicle unmanned aerial system cyber security and privacy drone swarm security vulnerabilities cyber-threats cyber-attacks plausibility check

Investigation of WZ Sge-type Dwarf Nova ASASSN-19oc:Optical Spectroscopy and Multicolor Light Curve Analysis

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8期24卷 20-31页

作者： Viktoriia Krushevska Sergey Shugarov Paolo Ochner Yuliana Kuznyetsova Mykola Petrov peter Kroll Astronomical Institute of the Slovak Academy of Sciences Tatranska Lomnica05960 VysokéTatrySlovakia Main Astronomical Observatory of NAS of Ukraine 27 Akademika Zabolotnoho St.03143 KyivUkraine INAf—Osservatorio Astronomico di Padova Vicolo dell’Osservatorio 5I-35122 PadovaItaly Department of Physics and Astronomy University of PadovaVia F.Marzolo 8I-35131 PadovaItaly Max Planck Computing and Data facility(MPCDf) Gießenbachstrasse 2D-85748 GarchingGermany Sonneberg Observatory Sternwartestr.32D-96515 SonnebergGermany

In this study,we present an investigation of the newly discovered dwarf nova ASASSN-19oc during its superoutburst on 2019 June *** carried out detailed UBVRcIc-photometric observations and also obtained a spectrum on day 7 of the outburst,which shows the presence of hydrogen absorption lines commonly found in dwarf nova *** of photometric data reveals the occurrence of early superhumps in the initial days of observations,followed by ordinary and late *** have accurately calculated the period of the ordinary superhumps as Pord=0.05681(10)days and determined the periods at different stages,as well as the rate of change of the superhump period(P_(dot)=(5)P/P=8.1×10^(-5)).Additionally,we have derived the mass ratio of the components(q=0.09),and estimated the color temperature during the outburst as~11,000 K,the distance to the system(d=560 pc)and absolute magnitude of the system in outburst(MV=5.3).We have shown that outbursts of this star are very rare:based on brightness measurements on 600 archival photographic plates,we found only one outburst that occurred in *** fact,as well as the properties listed above,convincingly shows that the variable ASASSN-19oc is a dwarf nova of WZ Sge type.

关键词： (stars)binaries(including multiple) close-(stars)novae-cataclysmic variables-stars dwarf novae

High-Performance and Large-Area Inverted Perovskite Solar Cells Based on NiOx films Enabled with A Novel Microstructure-Control Technology

在线全文

学校读者我要写书评

暂无评论

Energy & Environmental Materials 2024年第1期7卷 157-163页

作者： Guibin Shen Xin Li Yuqin Zou Hongye Dong Dongping Zhu Yanglin Jiang Xin Ren Ng fen Lin peter Müller-Buschbaum Cheng Mu Key Laboratory of Advanced Light Conversion Materials and Biophotonics Department of Chemistry Renmin University of China Solar Energy Research Institute of Singapore (SERIS) National University of Singapore Physik-Department Lehrstuhl für Funktionelle Materialien Technische Universit?t München Heinz Maier-Leibnitz Zentrum (MLZ) Technische Universit at München

The improvement in the efficiency of inverted perovskite solar cells（PSCs） is significantly limited by undesirable contact at the NiOx/perovskite *** this study,a novel microstructure-control technology is proposed for fabrication of porous NiOxfilms using Pluronic P123 as the structuredirecting agent and acetylacetone（AcAc） as the coordination agent.

关键词： interfacial contact inverted and large-area perovskite solar cells photovoltaic materials porous NiOX films renewable energy

地球演化历史中氧逸度变化对壳幔循环启动、风化和超大陆循环的指示（英文）

在线全文

同方期刊数据库

学校读者我要写书评

暂无评论

Science Bulletin 2024年第1期 97-102页

作者：王瑞邬绍宸 Roberto f.Weinberg William J.Collins peter A.Cawood State Key Laboratory of Geological Processes and Mineral Resources Institute of Earth Sciences China University of Geosciences frontiers Science Center for Deep-time Digital Earth China University of Geosciences (Beijing) School of Earth Atmosphere and Environment Monash University The Institute for Geoscience Research Curtin University

We apply a zircon redox index to a global compilation of detrital zircons to track the variation of oxidation state, expressed as ΔfMQ, through Earth’s history. Those from I-type rocks, which comprise mantle and crustal igneous protoliths, including tonalite–trondhjemite–granodiorites(TTGs), generally have a high oxidation state(ΔfMQ > 0). In contrast, zircons from igneous rocks derived from supracrustal source rocks(S-type) are commonly reduced(ΔfMQ function derived from the Gaussian-Kernel-Density-Estimation, we use the maximum likelihood estimation(MLE) to distinguish Stype from I-type zircons through Earth’s history using zircon redox. Voluminous S-type magma production shows a ca. 600 Ma cyclicity that is closely related to the supercontinent cycle. We link a cyclic drop in redox values after 2.6 Ga to periodic S-type magma generation associated with burial and melting of metasedimentary rocks during supercontinent assembly and amalgamation. The ΔfMQ of the detrital zircons rise at ～3.5 Ga followed by a consistent average ΔfMQ > 0 over the last 3 Ga. Given that the redox state of magmas is independent of crustal thickness and silica variation, and elevated values are likely more closely related to tectonic setting, we suggest that the consistent average ΔfMQ > 0 from ca.3.5 Ga onwards relates to recycling of oceanic lithosphere back into the mantle in what eventually became established as subduction zones. The more reduced magmas associated with sedimentary sources, became established at 2.6 Ga, presumably in response to continental rocks rising above sealevel, and follow peaks of productivity associated with the supercontinent cycle.

关键词：