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Periodic Signature Change in Spacetimes of Embedding Class One

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International Journal of Astronomy and Astrophysics 2022年第2期12卷 167-176页

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

The idea of an oscillating Universe has remained a topic of interest even after the discovery of dark energy. This paper confirms this idea by means of another well-established theory in general relativity, the embedding of curved spacetimes in higher-dimensional flat spacetimes: an n-dimensional Riemannian space is said to be of embedding class m if m +n is the lowest dimension of the flat space in which the given space can be embedded;here . So a four-dimensional Riemannian space is of class two and can therefore be embedded in a six-dimensional flat space. A line element of class two can be reduced to a line element of class one by a suitable coordinate transformation. The extra dimension can be either spacelike or timelike, leading to accelerating and decelerating expansions, respectively. Accordingly, it is proposed in this paper that the free parameter occurring in the transformation be a periodic function of time. The result is a mathematical model that can be interpreted as a periodic change in the signature of the embedding space. This signature change may be the best model for an oscillating Universe and complements various models proposed in the literature.

关键词： Signature Change Oscillating Universe Embedding Class One

Scalable Jet-Based fabrication of PEI-Hydrogel Particles for CO_(2) Capture

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Energy & Environmental Materials 2024年第6期7卷 351-358页

作者： Jieke Jiang Eline van Daatselaar Hylke Wijnja Tessa de Koning Gans Michel Schellevis Cornelis H.Venner Derk W.f.Brilman Claas Willem Visser Engineering fluid Dynamics Group Department of Thermal and Fluid EngineeringFaculty of Engineering TechnologyUniversity of Twente7500AEEnschedeThe Netherlands Sustainable Process Technology Faculty of Science and TechnologyUniversity of Twente7500AEEnschedeThe Netherlands

The capture,regeneration,and conversion of CO_(2) from ambient air and flue gas streams are critical aspects of mitigating global *** sorbents for CO_(2) absorption are very promising as they have high mass transfer areas without energy input and reduce emissions and minimize corrosion as compared to liquid ***,precisely tunable solid CO_(2) sorbents are difficult to ***,we demonstrate the high-throughput production of hydrogel-based CO_(2)-absorbing particles via liquid *** wrapping a liquid jet consisting of an aqueous solution of cross-linkable branched polyethylenimine(PEI)with a layer of suspension containing hydrophobic silica nanoparticles,monodisperse droplets with a silica nanoparticle coating layer was formed in the air.A stable Pickering emulsion containing PEI droplets was obtained after these ejected droplets were collected in a heated oil *** droplets turn into mm-sized particles after thermal curing in the *** diameter,PEI content,and silica content of the particles were systematically varied,and their CO_(2) absorption was measured as a function of *** regeneration of the particles enabled cyclic testing,revealing a CO_(2) absorption capacity of 6.5±0.5 mol kg^(−1)solid PEI in pure CO_(2) environments and 0.7±0.3 mol kg^(−1)solid PEI for direct air *** thousands of particles were produced per second at a rate of around 0.5 kg per hour,with a single *** process can be further scaled by *** complete toolbox for the design,fabrication,testing,and regeneration of functional hydrogel particles provides a powerful route toward novel solid sorbents for regenerative CO_(2) capture.

关键词： CO_(2) capture droplet hydrogel liquid jet particle steam regeneration

Assessment of Ballast flying in the National Railway Network of Ethiopia

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Engineering（科研） 2021年第7期13卷 420-429页

作者： fikadu Mengistu Henok f. Gebregziabher Awash-Kombolcha-Haragebeya Railway Project Ethiopian Railways Corporation Addis Ababa Ethiopia

One of the major problems in ballasted railroads is ballast flying, which is the projection of ballast particles from the at-rest position as the train passes over the track of a railway structure, mainly due to high speed. In this research, the possibility of railway ballast flying for the double track Addis-Adama section of the new Addis-Djibouti railway line is assessed by determining the major causes of ballast flying and applying Discrete Element Modeling (DEM) with the aid of Particle flow Code (PfC3D) software. The analysis comprised of an impact load and ballast material behavior which were used to determine the vibrational speed of individual ballast particles. The governing result from the series of discrete element analyses performed by considering fouled ballast gradation with grain-size diameter of 22.4 mm gives rise to a ballast maximum vibrational speed of 0.014 m/s. Since the ballast vibrational speed for Addis Ababa-Adama line is less than 0.02 m/s that is recommended by the literature, no ballast flight is expected under the present traffic and ballast conditions.

关键词： Railway Track Ballast flying Discrete Element Modeling Ballast Vibrational Speed Particle flow Code

维苏威和武尔卡诺火山碎屑物中磷灰石挥发组分的研究

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矿物学报 2011年第2期31卷 180-184页

作者：刘羽 Stoppa f. 福州大学紫金矿业学院 Dipartimento Scienze della Terra Università G.d'AnnunzioChieti66013Italy

磷灰石中挥发分的类质同象替换可以反映其结晶时岩浆体系的成分特点。采用扫描电镜、能谱、电子探针、X射线单晶晶胞参数测定和红外、拉曼光谱,对维苏威和武尔卡诺火山碎屑物中磷灰石进行了初步研究,发现其Ca、P位置上不出现替换,主要... 详细信息

磷灰石中挥发分的类质同象替换可以反映其结晶时岩浆体系的成分特点。采用扫描电镜、能谱、电子探针、X射线单晶晶胞参数测定和红外、拉曼光谱,对维苏威和武尔卡诺火山碎屑物中磷灰石进行了初步研究,发现其Ca、P位置上不出现替换,主要替换形成于通道位置上。武尔卡诺磷灰石低硫富Cl,晶胞参数c/a值很小,在低压高温下形成;而维苏威磷灰石含硫稍多,通道离子主要由OH-f组成,形成于压力较大、温度较低的环境,Cl趋向于在早期喷发物中富集,而f则趋向于在晚期喷发物中富集。

关键词：磷灰石挥发分结构通道替换

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

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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 σis 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

欧洲与北美制造的烧结青铜含油轴承性能的比较

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粉末冶金技术 2006年第4期24卷 304-309页

作者： Haward I.Sanderrow Leander f.Pease 韩凤麟 President Management & Engineering TechnologiesMET Group Inc. President Powder-Tech AssociatateInc.

多孔性青铜含油轴承是全世界都在生产的,最早与最无处不用的现代粉末冶金产品。然而,各地区产品之间仍存在着明显差异。近期发布的粉末冶金材料的全球标准ISO5755,其中有2个描述轴承材料性能的数据表。其中列举的几项关键性轴承特性和M... 详细信息

多孔性青铜含油轴承是全世界都在生产的,最早与最无处不用的现代粉末冶金产品。然而,各地区产品之间仍存在着明显差异。近期发布的粉末冶金材料的全球标准ISO5755,其中有2个描述轴承材料性能的数据表。其中列举的几项关键性轴承特性和MPIf标准35或相应的ASTM标准中列出的轴承性能有所不同。因此,MPIf标准委员会进行一项小型试验,对标准90%(质量分数)Cu-10%(质量分数)Sn轴承的关键特性进行了对比。这项研究的样品零件来自欧洲与北美的大批量生产厂家。数据证实孔隙度与径向压溃强度不同,这种差异是原料粉与制造工艺的微妙差异所致。最终用户应该了解这些差异,和确认ISO5755中列举的特性能满足他们对轴承的要求。

关键词：粉末冶金轴承性能青铜含油轴承

Comparison between Pt/TiO_2/Pt and Pt/TaO_X/TaO_Y/Pt based bipolar resistive switching devices

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Journal of Semiconductors 2016年第6期37卷 39-51页

作者： Patrick W.C.Ho firas Odai Hatem Haider Abbas f.Almurib T.Nandha Kumar Department of Electrical and Electronic Engineering University of Nottingham Malaysia Campus

Nonvolatile memories have emerged in recent years and have become a leading candidate towards replacing dynamic and static random-access memory *** this article,the performances of T1O_2 and TaO_2nonvolatile memristive devices were compared and the factors that make TaO_2 memristive devices better than T1O_2 memristive devices were ***_2 memristive devices have shown better endurance performances（10~8times more switching cycles） and faster switching speed（5 times） than TiO_2 memristive *** of TaO_2 memristive devices requires ~ 4.5 times less energy than TiO_2 memristive devices of a similar *** retention period of TaO_2 memristive devices is expected to exceed 10 years with sufficient experimental *** addition to comparing device performances,this article also explains the differences in physical device structure,switching mechanism,and resistance switching performances of TiO_2 and TaO_2 memristive *** article summarizes the reasons that give TaO_2 memristive devices the advantage over TiO_2 memristive devices,in terms of electroformation,switching speed,and endurance.

关键词： resistive switching devices TiO2 devices TaO2 devices non-volatile memory devices

Depth determination of the Moho interface beneath the Tibetan plateau and other areas of China

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Earthquake Science 2012年第5期25卷 415-431页

作者： Youshun Sun Diming Yu M Nafi Toksz f Dale Morgan Xiyu Wang Jinrong Su Jun Liu State Key Laboratory of Geodesy and Earth's Dynamics Institute of Geodesy and GeophysicsChinese Academy of Sciences Department of Earth Atmospheric and Planetary SciencesMassachusetts Institute of Technology Earthquake Administration of Sichuan Province School of Civil Engineering and Architecture Wuhan University of Technology

We apply the adaptive moving window method of Sun et al. to the most recent catalog data and the data recorded by portable stations to construct the velocity structure of the crust and upper mantle, and to determine the depth of the Moho interface beneath the Tibetan plateau and other areas of China. We first select 2 600 locations in the study region with 1° intervals, then at each location invert for a five-layer 1-D P-wave velocity model from the surface down to the uppermost mantle by performing a Monte Carlo random search. The Moho depth at each location is then determined, and the Moho interface beneath the study region is obtained through proper interpolation with certain smoothing. Compared to depths obtained by previous studies, our results show more accurate Moho depths in the Tibetan plateau, Tianshan region and other areas of the study region.

关键词： Moho depth Moho interface Tibetan plateau

OBSERVING THE HEAT EQUATION ON A TORUS ALONG A DENSE GEODESIC

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Systems Science and Mathematical Sciences 1991年第2期4卷 186-192页

作者： Lance D.Drager Robert L.foote Clyde f.Martin Department of Mathematics Texas Tech.University.LubbockTX 79409USA Department of Mathematics Wabash CollegeCrawfordsvilleIN 47933USA Department of Mathematics Texas Tech.UniversityLubbockTX 79409USA

Several authors have considered observability problems for the heat equation and relatedpartial differential equations.A basic problem is to determine what kinds of sampling providesufficient information to uniquely determine the initial heat *** address the case wherethe temperature is measured while travelling along a *** consider the special case where the space is a flat torus(of arbitrary dimension)and thecurve is a *** is shown that,in this case,the observed temperature is sufficient informationto uniquely determine the initial heat distribution if and only if the geodesic is dense in the *** the case of a torus,fourier analysis techniques can be used to write down the solution of theheat *** allows us to derive an explicit representation of the observed temperature interms of the initial *** use this representation and some ideas from the theory ofalmost periodic functions to show that the fourier coefficients of the initial distribution can berecovered from the observation.

关键词： Observability heat equation inverse problems