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Thin-Shell Wormholes Admitting Conf.rmal 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. k.hfittig Department of.Mathematics Milwaukee School of Engineering Milwaukee USA

This paper discusses the f.asibility of.thin-shell wormholes in spacetimes of.embedding class one admitting a one-parameter group of.conf.rmal motions. It is shown that the surf.ce energy density σis positive, while the surf.ce pressure is negative, resulting in , thereby signaling a violation of.the null energy condition, a necessary condition f.r holding a wormhole open. f.r a Morris-Thorne wormhole, matter that violates the null energy condition is ref.rred to as “exotic”. f.r 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.conf.rmal symmetry. These properties avoid the need to hypothesize the existence of.the highly problematical exotic matter.

关键词： Thin-Shell Wormholes Conf.rmal Symmetry Embedding Class One Exotic Matter

A product version of.the Hilton-Milner-f.ank. theorem

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

作者： peter f.ank. Jian Wang Alf.éd Rényi Institute of.Mathematics Hungarian Academy of SciencesBudapest H-1053Hungary Department of.Mathematics Taiyuan University of TechnologyTaiyuan 030024China

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

关键词： extremal set theory cross t-intersecting f.mily product version non-trivial

The Dallas Donation af.er Circulatory Death Transplantation Summit:expanding donation af.er circulatory death procedures through process improvement,broader utilization,and innovation

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Hepatobiliary Surgery and Nutrition 2024年第5期13卷 824-836,I0009页

作者： Michele f.notti Anji Wall Anthony D’Alessandro Gary Schwartz Chris Sonnenday David Goldberg Ashish Shah peter f.iend Jef. P.Orlowsk. Greg Mck.nna Steve Newton Brad Adams William C.Chapman Amit Mathur Marwan Abouljoud Tim Pruett Amelia Hessheimer James f.Trotter Sumeet k.Asrani Giuliano Testa Simmons Transplant Institute Baylor University Medical CenterDallasTXUSA Hepatobiliary and General Surgery Unit Regional Hospital TrevisoDISCOGUniversity of PaduaPaduaItaly Division of.Transplantation Department of SurgeryUniversity of Wisconsin School of Medicine and Public HealthMadisonWIUSA Department of.Thoracic Surgery and Lung Transplantation Baylor University Medical CenterCenter for Advanced Heart and Lung DiseaseDallasTXUSA Department of.Surgery University of MichiganAnn ArborMIUSA Division of.Digestive Health and Liver Diseases Department of MedicineUniversity of Miami Miller School of MedicineMiamiFLUSA Department of.Cardio-Thoracic Surgery Vanderbilt University Medical CenterNashvilleTNUSA Nuf.ield Department of.Surgical Sciences University of OxfordOxfordUK Lif.Share Transplant Donor Services of.Ok.ahoma Oklahoma CityOKUSA Administration Baylor University Medical CenterDallasTXUSA Southwest Transplant Alliance DallasTXUSA Department of.Surgery/Transplantation Washington UniversitySt.LouisMOUSA Division of.Transplant Surgery Department of SurgeryMayo Clinic ArizonaAlix School of MedicinePhoenixAZUSA Divisions of.Transplant and Hepatobiliary Surgery Henry Ford HospitalDetroitMIUSA Department of.Surgery University of MinnesotaMinneapolisMNUSA General and Digestive Surgery Hospital Universitario La PazIdiPAZMadridSpain

Despite a signif.cant increase in utilization over the past decade,the number of.donation af.er circulatory death(DCD)organs that are procured and transplanted in the United States(US)remains well below its *** is still room f.r expansion,as utilizing DCD organs to the f.llest extent is currently the most viable solution to the persistent mismatch between supply and demand in *** convened a multidisciplinary transplantation summit to examine various aspects of.DCD,with f.culty members f.om around the world with clinical and academic interest in DCD donation and transplantation,including abdominal and cardiothoracic surgeons,organ procurement organization directors,hepatologists,and *** conf.rence f.cused on identif.ing barriers to DCD organ utilization and strategies to overcome these *** divide the barriers to DCD utilization into three mains categories:(Ⅰ)policy and process variation;(II)logistical and transportation challenges;and(Ⅲ)higher risk.perceptions related to DCD *** each barrier,we proposed a variety of.solutions,providing an overview of.the status of.DCD donation in the US and suggestions on how to increase the use of.*** is a specif.c f.cus on ex situ machine perf.sion,normothermic regional perf.sion,and other opportunities to expand DCD utilization without negatively impacting recipient outcomes.

关键词： Donation af.er circulatory death donation(DCD donation) marginal graf. donor pool machine perf.sion(MP)

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

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

作者： Pavlo Myk.tyn Marcin Brzozowsk. Zoya Dyk. peter Langendoerf.r IHP-Leibniz-Institut f.r Innovative Mik.oelek.ronik Wireless SystemsFrankfurt(Oder)15236Germany BTU Cottbus-Senf.enberg Faculty 1:MINTCottbus03046German

The application f.eld f.r 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 bef.re. However, increasing the complexity of.UAVs and decreasing the cost, both contribute to a lack.of.mplemented securitymeasures and raise new security and saf.ty concerns. f.r instance, the issue of.implausible ortampered UAV sensor measurements is barely addressed in the current research literature and thus, requires moreattention f.om 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 cyberattack.against 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 f.r security and saf.ty *** the coverage and completeness of.each related research work.in a comprehensive comparison table as wellas classif. the threats, vulnerabilities and cyber-attack. into sensor-based and communication-based ***, f.r 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.f.r sensor data. By doing so, we discover additionalmeasures to improve security and saf.ty 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-attack. plausibility check

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

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Research in Astronomy and Astrophysics 2024年第8期24卷 20-31页

作者： Vik.oriia k.ushevsk. Sergey Shugarov Paolo Ochner Yuliana k.znyetsova Myk.la Petrov peter k.oll Astronomical Institute of.the Slovak.Academy of.Sciences Tatranska Lomnica05960 VysokéTatrySlovakia Main Astronomical Observatory of.NAS of.Uk.aine 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 f.cility(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 f.und in dwarf.nova *** of.photometric data reveals the occurrence of.early superhumps in the initial days of.observations,f.llowed by ordinary and late *** have accurately calculated the period of.the ordinary superhumps as Pord=0.05681(10)days and determined the periods at dif.erent 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 f.und only one outburst that occurred in *** f.ct,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

Traversable Wormholes and the Brouwer f.xed-Point Theorem

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Journal of.Applied Mathematics and Physics 2020年第7期8卷 1263-1268页

作者： peter k. f. k.hfittig Department of.Mathematics Milwaukee School of Engineering Milwaukee WI USA

The Brouwer f.xed-point theorem in topology states that f.r any continuous mapping f.on a compact convex set into itself.admits a f.xed point, i.e., a point x0 such that f.x0) = x0. Under suitable conditions, this f.x... 详细信息

The Brouwer f.xed-point theorem in topology states that f.r any continuous mapping f./em> on a compact convex set into itself.admits a f.xed point, i.e., a point x0 such that f./em>(x0) = x0. Under suitable conditions, this f.xed point corresponds to the throat of.a traversable wormhole, i.e., b(r0) = r0 f.r the shape f.nction b = b(r). The possible existence of.wormholes can theref.re be deduced f.om purely mathematical considerations without going beyond the existing physical requirements.

关键词： Traversable Wormholes Brouwer f.xed-Point Theorem

Exploration of.Traversable Wormholes Sustained by an Extra Spatial Dimension

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International Journal of.Astronomy and Astrophysics 2023年第3期13卷 141-153页

作者： peter k. f. k.hfittig Department of.Mathematics Milwaukee School of Engineering Milwaukee Wisconsin USA

The main goal of.this paper is to determine the ef.ect of.an extra dimension on a traversable wormhole. Here an earlier study by the author [Phys. Rev. D 98, 064041 (2018)] is extended in several signif.cant ways. To begin with, the extra spatial dimension is assumed to be time dependent, while the redshif. and shape f.nctions, as well as the extra dimension, are f.nctions of.both r and l, the respective radial and extra coordinates;the last of.these is theref.re a f.nction of.r, l, and t. The main objective is to determine the conditions that allow the throat of.the wormhole to be threaded with ordinary matter (by respecting the null energy condition) and that the same conditions lead to a violation of.the null energy condition in the f.f.h dimension, which is theref.re responsible f.r sustaining the wormhole. The dependence of.the extra dimension on l and t is subject to additional conditions that are subsequently analyzed in this paper. f.nally, the extra dimension may be extremely small or even curled up.

关键词： Traversable Wormholes Extra Spatial Dimension Time Dependence

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. k.hfittig Department of.Mathematics Milwaukee School of Engineering Milwaukee Wisconsin USA

The idea of.an oscillating Universe has remained a topic of.interest even af.er the discovery of.dark.energy. This paper conf.rms this idea by means of.another well-established theory in general relativity, the embedding of.curved spacetimes in higher-dimensional f.at spacetimes: an n-dimensional Riemannian space is said to be of.embedding class m if.m +n is the lowest dimension of.the f.at space in which the given space can be embedded;here . So a f.ur-dimensional Riemannian space is of.class two and can theref.re be embedded in a six-dimensional f.at space. A line element of.class two can be reduced to a line element of.class one by a suitable coordinate transf.rmation. The extra dimension can be either spacelik. or timelik., leading to accelerating and decelerating expansions, respectively. Accordingly, it is proposed in this paper that the f.ee parameter occurring in the transf.rmation be a periodic f.nction 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 f.r an oscillating Universe and complements various models proposed in the literature.

关键词： Signature Change Oscillating Universe Embedding Class One

Noncommutative-Geometry Wormholes Based on the Casimir Ef.ect

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Journal of.High Energy Physics, Gravitation and Cosmology 2023年第1期9卷 295-300页

作者： peter k. f. k.hfittig Department of.Mathematics Milwaukee School of Engineering Milwaukee WI USA

While wormholes are as good a prediction of.Einstein’s theory as black.holes, they are subject to severe restrictions f.om quantum f.eld theory. In particular, holding a wormhole open requires a violation of.the null energy condition, calling f.r the existence of.exotic matter. The Casimir ef.ect has shown that this physical requirement can be met on a small scale, thereby solving a k.y conceptual problem. The Casimir ef.ect does not, however, guarantee that the small-scale violation is suf.icient f.r supporting a macroscopic wormhole. The purpose of.this paper is to connect the Casimir ef.ect to noncommutative geometry, which also aims to accommodate small-scale ef.ects, the dif.erence being that these can now be viewed as intrinsic properties of.spacetime. As a result, the noncommutative ef.ects can be implemented by modif.ing only the energy momentum tensor in the Einstein f.eld equations, while leaving the Einstein tensor unchanged. The wormhole can theref.re be macroscopic in spite of.the small Casimir ef.ect.

关键词： Traversable Wormholes Noncommutative Geometry Casimir Ef.ect