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A Multi-physics Methodology for Four States of Matter

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Communications on Applied Mathematics and Computation 2020年第3期2卷 487-514页

作者： Louisa Michael Stephen T.Millmore Nikolaos Nikiforakis laboratory for Scientifc Computing Cavendish LaboratoryDepartment of PhysicsUniversity of CambridgeCambridgeUK

We propose a numerical methodology for the simultaneous numerical simulation of four states of matter:gas,liquid,elastoplastic solids,and plasma.The distinct,interacting physical processes are described by a combination of compressible,inert,and reactive forms of the Euler equations,multi-phase equations,elastoplastic equations,and resistive MHD equations.Combinations of systems of equations are usually solved by coupling finite element for solid modelling and CFD models for fluid modelling or including material effects through boundary conditions rather than full material discretisation.Our simultaneous solution methodology lies on the recasting of all the equations in the same,hyperbolic form allowing their solution on the same grid with the same finite volume numerical schemes.We use a combination of sharp-and diffuse-interface methods to track or capture material interfaces,depending on the application.The communication between the distinct systems of equations(i.e.,materials separated by sharp interfaces)is facilitated by means of mixed-material Riemann solvers at the boundaries of the systems,which represent physical material boundaries.To this end,we derive approximate mixed-material Riemann solvers for each pair of the above models based on characteristic equations.To demonstrate the applicability of the new methodology,we consider a case study,where we investigate the possibility of ignition of a combustible gas that lies over a liquid in a metal container that is struck by a plasma arc akin to a lightning strike.We study the effect of the metal container material and its conductivity on the ignition of the combustible gas,as well as the effects of an additional dielectric coating,the sensitivity of the gas,and differences between scenarios with sealed and pre-damaged metal surfaces.

关键词： Plasma modelling Four states of matter Lightning Ignition Combustible gas Elastoplastic solids

Cluster Analysis of the Roma-BZCAT Blazars

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Research in Astronomy and Astrophysics 2024年第5期24卷 119-141页

作者： Dmitry O.Kudryavtsev Yulia V.Sotnikova Vladislav A.Stolyarov Timur V.Mufakharov Valery V.Vlasyuk Margarita L.Khabibullina Alexander G.Mikhailov Yulia V.Cherepkova Special Astrophysical Observatory of the Russian Academy of Sciences Astrophysics Group Cavendish Laboratory University of Cambridge Kazan Federal University

Based on the collected multiwavelength data, namely in the radio(NVSS, FIRST, RATAN-600), IR(WISE),optical(Pan-STARRS), UV(GALEX), and X-ray(ROSAT, Swift-XRT) ranges, we have performed a cluster analysis for the blazars of the Roma-BZCAT catalog. Using two machine learning methods, namely a combination of PCA with k-means clustering and Kohonen’s self-organizing maps(SOMs), we have constructed an independent classification of the blazars(five classes) and compared the classes with the known Roma-BZCAT classification(FSRQs, BL Lacs, galaxy-dominated BL Lacs, and blazars of an uncertain type) as well as with the high synchrotron peaked(HSP) blazars from the 3HSP catalog and blazars from the TeVCat catalog. The obtained groups demonstrate concordance with the BL Lac/FSRQ classification along with a continuous character of the change in the properties. The group of HSP blazars stands out against the overall distribution. We examine the characteristics of the five groups and demonstrate distinctions in their spectral energy distribution shapes. The effectiveness of the clustering technique for objective analysis of multiparametric arrays of experimental data is demonstrated.

关键词： (galaxies:) BL Lacertae objects: general galaxies: active methods: data analysis

A Many Worlds Interpretation of the Dark Universe

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Journal of High Energy Physics, Gravitation and Cosmology 2024年第2期10卷 828-835页

作者： Richard Douglas Bateson Cavendish Laboratory Cambridge UK

In this paper, we discuss a Many Worlds Interpretation (MWI) of Dark Energy and Dark Matter. The universe is viewed cosmologically as a fermionic fluid with a hydrostatic pressure from “Zitterbewegung”, the quantum “zig-zagging” of Dirac particles. At each point in space-time, the pressure from all possible velocity states existing in the Many Worlds sums to provide a dark energy. This provides a ratio of matter energy to pressure energy close to that observed experimentally. Visible matter is the matter observed or measured in a particular velocity state and dark matter is then considered as the unobserved fermion contributions from different orthogonal spatial directions.

关键词： Dark Energy Dark Matter Many Worlds

An Evaluation Method for Automotive Technical and Comprehensive Performance

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Automotive Innovation 2023年第2期6卷 231-243页

作者： Mengfei Liu Xinyu Ouyang Ruikai Lu Zijun Hao Raphael Blumenfeld Xin Tang Gang Lei Hongwu Ouyang School of Mechanical and Electrical Engineering Central South UniversityChangsha 410083China State Key laboratory of High‑Performance Complex Manufacturing Central South UniversityChangsha 410083China University of Sheffield Sheffield S102TNUK Cavendish Laboratory University of CambridgeCambridge CB21TNUK

An objective evaluation scheme for automotive technical and comprehensive performance could provide critical and instructive insights for academic research,engineering practice,and commercial marketing of vehicles.In this paper,the technical performance index A=S∕T_(1)⋅T_(2)(m∕(s^(2)⋅L))and comprehensive performance index F=M⋅S∕T_(1)⋅T_(2),(kN⋅L^(−1),where M is the vehicle mass)are formulated by incorporating the vehicle 0–100 km⋅h^(−1) acceleration duration T_(1),100–0 km⋅h^(−1) braking duration T_(2),and fuel economy S(mileage per liter fuel at constant speed)to assess the vehicle’s longitudinal dynamic performance.A and F offer a clear physical implication of a vehicle’s acceleration capability and traction efficiency acquired per unit of fuel consumption,respectively.These indexes are used for wide case studies of popular market sedans and SUVs of joint ventures(JVs)and domestic brands in China over the last 17 years.The findings prove that this approach could be effectively and reliably utilized for the objective evaluation and analysis of the technical and comprehensive performance of automotive models.

关键词： Automobile Technical performance evaluation Comprehensive performance evaluation Sedan SUV

Versatile multiplexed super-resolution imaging of nanostructures by Quencher-Exchange-PAINT

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Nano Research 2018年第12期11卷 6141-6154页

作者： Tobias Lutz Alexander H.Clowsley Ruisheng Lin Stefano Pagliara Lorenzo Di Michele Christian Soeller Living Systems Institute & Biomedical Physics University of ExeterExeter EX44QDUK Cavendish Laboratory University of CambridgeCambridge CB30HEUK

The optical super-resolution technique DNA-PAINT (Point Accumulation Imaging in Nanoscale Topography) provides a flexible way to achieve imaging of nanoscale structures at ∼10-nanometer resolution. In DNA-PAINT, fluorescently labeled DNA “imager” strands bind transiently and with high specificity to complementary target “docking” strands anchored to the structure of interest. The localization of single binding events enables the assembly of a super-resolution image, and this approach effectively circumvents photobleaching. The solution exchange of imager strands is the basis of Exchange-PAINT, which enables multiplexed imaging that avoids chromatic aberrations. Fluid exchange during imaging typically requires specialized chambers or washes, which can disturb the sample. Additionally, diffusional washout of imager strands is slow in thick samples such as biological tissue slices. Here, we introduce Quencher-Exchange-PAINT—a new approach to Exchange-PAINT in regular open-top imaging chambers—which overcomes the comparatively slow imager strand switching via diffusional imager washout. Quencher-Exchange-PAINT uses “quencher” strands, i.e., oligonucleotides that prevent the imager from binding to the targets, to rapidly reduce unwanted single-stranded imager concentrations to negligible levels, decoupled from the absolute imager concentration. The quencher strands contain an effective dye quencher that reduces the fluorescence of quenched imager strands to negligible levels. We characterized Quencher-Exchange-PAINT when applied to synthetic, cellular, and thick tissue samples. Quencher-Exchange-PAINT opens the way for efficient multiplexed imaging of complex nanostructures, e.g., in thick tissues, without the need for washing steps.

关键词： super-resolution microscopy fluorescence imaging DNA nanotechnology DNA-PAINT fluorescence quencher

Mid-infrared-perturbed molecular vibrational signatures in plasmonic nanocavities

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Light(Science & Applications) 2022年第1期11卷 127-135页

作者： Rohit Chikkaraddy Angelos Xomalis Lukas A.Jakob Jeremy J.Baumberg NanoPhotonics Centre Cavendish LaboratoryDepartment of PhysicsJJ Thompson AvenueUniversity of CambridgeCambridge CB30HEUK Empa Swiss Federal Laboratories for Materials Science and TechnologyLaboratory for Mechanics of Materials and NanostructuresThunSwitzerland

Recent developments in surface-enhanced Raman scattering(SERS)enable observation of single-bond vibrations in real time at room temperature.By contrast,mid-infrared(MIR)vibrational spectroscopy is limited to inefficient slow detection.Here we develop a new method for MIR sensing using SERS.This method utilizes nanoparticle-on-foil(NPoF)nanocavities supporting both visible and MIR plasmonic hotspots in the same nanogap formed by a monolayer of molecules.Molecular SERS signals from individual NPoF nanocavities are modulated in the presence of MIR photons.The strength of this modulation depends on the MIR wavelength,and is maximized at the 6–12μm absorption bands of SiO_(2) or polystyrene placed under the foil.Using a single-photon lock-in detection scheme we time-resolve the rise and decay of the signal in a few 100 ns.Our observations reveal that the phonon resonances of SiO_(2) can trap intense MIR surface plasmons within the Reststrahlen band,tuning the visible-wavelength localized plasmons by reversibly perturbing the localized few-nm-thick water shell trapped in the nanostructure crevices.This suggests new ways to couple nanoscale bond vibrations for optomechanics,with potential to push detection limits down to single-photon and single-molecule regimes.

关键词： visible signature utilize

Spatial coherence of electrically pumped random terahertz lasers

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Photonics Research 2022年第2期10卷 524-534页

作者： Eva A.A.Pogna Alessandra Di Gaspare Kimberly Reichel Chiara Liberatore Harvey E.Beere David A.Ritchie Miriam S.Vitiello NEST CNR-Istituto Nanoscienze-Scuola Normale Superiore56127 PisaItaly Cavendish Laboratory University of CambridgeCambridge CB3 OHEUK

Light sources with high radiance and tailored coherence properties are highly desirable for imaging applications in the mid-infrared and terahertz(THz) spectral regions, which host a large variety of molecular absorptions and distinctive fingerprints to be exploited for sensing and tomography. Here, we characterize the spatial coherence of random multimode THz quantum cascade lasers(QCLs) emitting > m W optical power per mode and showing low divergence(10°–30°), performing a modified Young’s double-slit experiment. Partial spatial coherence values ranging between 0.16 and 0.34 are retrieved, depending on the specific degree of disorder. These values are significantly lower than those(0.82) of conventional Fabry–Perot THz QCLs exploiting an identical active region quantum design. We then incorporate the devised low spatial coherence random lasers into a confocal imaging system with micrometer spatial resolution and demonstrate notable imaging performances, at THz frequencies,against spatial cross talk and speckles.

关键词： pumped random quantum

High-yield fabrication of perpendicularly magnetised synthetic antiferromagnetic nanodiscs

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Nano Research 2021年第11期14卷 3873-3878页

作者： Emma N.Welbourne Tarun Vemulkar Russell P.Cowburn Department of Physics Cavendish LaboratoryUniversity of CambridgeJ.J.Thomson AvenueCambridgeCB30HEUK

Synthetic antiferromagnetic (SAF) particles with perpendicular anisotropy display a number of desirable characteristics for applications in biological and other fluid environments. We present an efficient and effective method for the patterning of ultrathin Ruderman-Kittel-Kasuya-Yoshida coupled, perpendicularly magnetised SAFs using a combination of nanosphere lithography and ion milling. A Ge sacrificial layer is utilised, which provides a clean and simple lift-off process, as well as maintaining the key magnetic properties that are beneficial to target applications. We demonstrate that the method is capable of producing a particularly high yield of well-defined, thin film based nanoparticles.

关键词： nanodiscs synthetic antiferromagnets perpendicular anisotropy sacrificial layers nanofabrication

Coexistence of plastic and partially diffusive phases in a helium-methane compound

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National Science Review 2020年第10期7卷 1540-1547页

作者： Hao Gao Cong Liu Andreas Hermann Richard J.Needs Chris J.Pickard Hui-Tian Wang Dingyu Xing Jian Sun National laboratory of Solid State Microstructures School of Physics and Collaborative Innovation Center of Advanced MicrostructuresNanjing University Centre for Science at Extreme Conditions and The School of Physics and Astronomy The University of Edinburgh Theory of Condensed Matter Group Cavendish Laboratory Department of Materials Science & Metallurgy University of Cambridge Advanced Institute for Materials Research Tohoku University

Helium and methane are major components of giant icy planets and are abundant in the universe. However,helium is the most inert element in the periodic table and methane is one of the most hydrophobic molecules, thus whether they can react with each other is of fundamental importance. Here, our crystal structure searches and first-principles calculations predict that a He;CH;compound is stable over a wide range of pressures from 55 to 155 GPa and a HeCH;compound becomes stable around 105 GPa. As nice examples of pure van der Waals crystals, the insertion of helium atoms changes the original packing of pure methane molecules and also largely hinders the polymerization of methane at higher pressures. After analyzing the diffusive properties during the melting of He;CH;at high pressure and high temperature, in addition to a plastic methane phase, we have discovered an unusual phase which exhibits coexistence of diffusive helium and plastic methane. In addition, the range of the diffusive behavior within the helium-methane phase diagram is found to be much narrower compared to that of previously predicted helium-water compounds. This may be due to the weaker van der Waals interactions between methane molecules compared to those in helium-water compounds, and that the helium-methane compound melts more easily.

关键词： crystal structure prediction ab initio molecular dynamics ab initio calculations high pressure and high temperature melting and phase transition collective motion