检索结果-南通市图书馆

维普期刊数据库

Pulsar Glitch Activities: The Spin Parameters Approach

在线全文

学校读者我要写书评

暂无评论

Research in astronomy and Astrophysics 2024年第6期24卷 336-359页

作者： Innocent Okwudili Eya Evaristus Uzochukwu Iyida physics/Electronics Technique—department of Science laboratory Technology University of Nigeria department of physics and astronomy University of Nigeria astronomy and Astrophysics Research lab University of Nigeria

Glitch activity refers to the mean increase in pulsar spin frequency per year due to rotational glitches. It is an important tool for studying super-nuclear matter using neutron star interiors as templates. Glitch events are typically observed in the spin frequency(ν) and frequency derivative( ν) of pulsars. The rate of glitch recurrence decreases as the pulsar ages, and the activity parameter is usually measured by linear regression of cumulative glitches over a given period. This method is effective for pulsars with multiple regular glitch events. however, due to the scarcity of glitch events and the difficulty of monitoring all known pulsars, only a few have multiple records of glitch events. This limits the use of the activity parameter in studying neutron star interiors with multiple pulsars.In this study, we examined the relationship between the activity parameters and pulsar spin parameters(spin frequency, frequency derivative, and pulsar characteristic age). We found that a quadratic function provides a better fit for the relationship between activity parameters and spin parameters than the commonly used linear functions.Using this information, we were able to estimate the activity parameters of other pulsars that do not have records of glitches. Our analysis shows that the relationship between the estimated activity parameters and pulsar spin parameters is consistent with that of the observed activity parameters in the ensemble of pulsars.

关键词： (stars:) pulsars: general methods: statistical stars: neutron

Recent progress in MnBi2nTe3n+1 intrinsic magnetic topological insulators: crystal growth, magnetism and chemical disorder

在线全文

同方期刊数据库

学校读者我要写书评

暂无评论

National Science Review 2024年第2期11卷 65-80页

作者： Chaowei hu Tiema Qian Ni Ni department of physics and astronomy and California Nano Systems Institute University of California-Los Angeles

The search for magnetic topological materials has been at the forefront of condensed matter research for their potential to host exotic states such as axion insulators, magnetic Weyl semimetals, Chern insulators,etc. To date, the MnBi2nTe3n+1family is the only group of materials showcasing van der Waals-layered structures, intrinsic magnetism and non-trivial band topology without trivial bands at the Fermi level. The interplay between magnetism and band topology in this family has led to the proposal of various topological phenomena, including the quantum anomalous hall effect, quantum spin hall effect and quantum magnetoelectric effect. Among these, the quantum anomalous hall effect has been experimentally observed at record-high temperatures, highlighting the unprecedented potential of this family of materials in fundamental science and technological innovation. In this paper, we provide a comprehensive review of the research progress in this intrinsic magnetic topological insulator family, with a focus on single-crystal growth, characterization of chemical disorder, manipulation of magnetism through chemical substitution and external pressure, and important questions that remain to be conclusively answered.

关键词： MnBi2Te4 magnetic topological insulator magnetism tuning antiferromagnetism ferromagnetism pressure chemical doping

Probing the Kinematic Signatures of Planet Formation in the Gas Disk of MWC 480

在线全文

同方期刊数据库

学校读者我要写书评

暂无评论

Research in astronomy and Astrophysics 2024年第6期24卷 112-120页

作者： Min Zhao haochuan Yu Zhengxiang li department of astronomy Beijing Normal University Sub-department of Astrophysics Department of Physics University of Oxford

The disk around MWC 480 has shown multiple substructures in both dust and gas observations, possibly suggesting ongoing planet formation in situ. In this paper, we explore the gas kinematics of the MWC 480 disk by analyzing the archival Atacama large Millimeter/submillimeter Array observations of12CO（J = 2-1）,13CO（J = 2-1）, and C18O（J = 2-1）. By modeling the line-of-sight velocities, inferred from the Doppler shifts of the emission lines, we are able to decompose the three-dimensional（3D） velocity field of the disk into rotational,radial, and vertical components. Further analysis reveals the presence of large-scale gas flows in the（r, z） plane.Notably, we identify potential meridional flows across various heights as traced by all three CO isotopologues in the 80–120 au region, possibly associated with ongoing planet formation activities in this region. Moreover, we find upward flows near 200 au for all three CO isotopologues, which may point to the presence of disk winds.

关键词： planet-disk interactions planet-star interactions protoplanetary disks

On the apparent line-of-sight alignment of the peak X-ray intensity of the magnetosheath and the tangent to the magnetopause,as viewed by SMIlE-SXI

在线全文

同方期刊数据库

学校读者我要写书评

暂无评论

Earth and Planetary physics 2024年第1期8卷 155-172页

作者： Andrew Read department of physics&astronomy University of LeicesterLeicesterLE17RHUK

The Soft X-ray Imager(SXI)on board the Solar wind Magnetosphere Ionosphere link Explorer(SMIlE)spacecraft will be able to view the Earth’s magnetosheath in soft X-rays.Simulated images of the X-ray emission visible from the position of SMIlE are created for a range of solar wind densities by using 3 years of the SMIlE mission orbit,together with models of the expected X-ray emissivity from the Earth’s magnetosheath.Results from global magnetohydrodynamic simulations and a simple model for exospheric neutral densities are used to compare the locations of the lines of sight along which integrated soft X-ray intensities peak with the lines of sight lying tangent to surfaces(defined here to be the magnetopause)along which local soft X-ray intensities peak or exhibit their strongest gradients,or both,for strongly southward interplanetary magnetic field conditions when no depletion or low-latitude boundary layers are expected.Where,in the parameter space of the various times and seasons,orbital phases,solar wind conditions,and magnetopause models,the alignment of the X-ray emission peak with the magnetopause tangent is good,or is not,is presented.The main results are as follows.The spacecraft needs to be positioned well outside the magnetopause;low-altitude times near perigee are not good.In addition,there are seasonal aspects:dayside-apogee orbits are generally very good because the spacecraft travels out sunward at high altitude,but nightside-apogee orbits,behind the Earth,are bad because the spacecraft only rarely leaves the magnetopause.Dusk-apogee and dawnapogee orbits are intermediate.Dayside-apogee orbits worsen slightly over the first three mission years,whereas nightside-apogee orbits improve slightly.Additionally,many more times of good agreement with the peak-to-tangent hypothesis occur when the solar wind is in a high-density state,as opposed to a low-density state.In a high-density state,the magnetopause is compressed,and the spacecraft is more often a good distance outside the magnetopause.

关键词： X-rays magnetosphere magnetosheath magnetopause Solar wind Magnetosphere Ionosphere link Explorer(SMIlE) Earth solar wind charge exchange

维普期刊数据库

What is the Role of Gravity, Turbulence and Magnetic Fields in high-mass Star Formation Clouds?

在线全文

学校读者我要写书评

暂无评论

Research in astronomy and Astrophysics 2024年第6期24卷 23-29页

作者： An-Xu luo hong-li liu Guang-Xing li Sirong Pan Dong-Ting Yang School of physics and astronomy Yunnan University South-Western Institute for astronomy Research Yunnan University

To explore the potential role of gravity,turbulence and magnetic fields in high-mass star formation in molecular clouds,this study revisits the velocity dispersion–size （σ–l） and density–size （ρ–l） scalings and the associated turbulent energy spectrum using an extensive data sample.The sample includes various hierarchical density structures in high-mass star formation clouds,across scales of 0.01–100 pc.We observe σ∝l0.26and ρ∝l-1.54scalings,converging toward a virial equilibrium state.A nearly flat virial parameter–mass (αvir-M) distribution is seen across all density scales,with αvirvalues centered around unity,suggesting a global equilibrium maintained by the interplay between gravity and turbulence across multiple scales.Our turbulent energy spectrum (E（k）)analysis,based on theσ–l andρ–l scalings,yields a characteristic E（k）∝k-1.52.These findings indicate the potential significance of gravity,turbulence,and possibly magnetic fields in regulating dynamics of molecular clouds and high-mass star formation therein.

关键词： ISM: clouds stars: formation stars: kinematics and dynamics

long Term X-Ray Spectral Variations of the Seyfert-1 Galaxy Mrk 279

在线全文

同方期刊数据库

学校读者我要写书评

暂无评论

Research in astronomy and Astrophysics 2024年第6期24卷 309-316页

作者： K.Akhila Ranjeev Misra Savithri h.Ezhikode K.Jeena department of physics Providence Women's College University of Calicut Inter-University Centre for astronomy and Astrophysics (IUCAA) department of physics and Electronics CHRIST (Deemed to be University)

We present the results from a long term X-ray analysis of Mrk 279 during the period 2018–2020. We use data from multiple missions–AstroSat, NuSTAR and XMM-Newton, for the purpose. The X-ray spectrum can be modeled as a double Comptonization along with the presence of neutral Fe Kα line emission, at all epochs. We determined the source’s X-ray flux and luminosity at these different epochs. We find significant variations in the source’s flux state. We also investigate the variations in the source’s spectral components during the observation period. We find that the photon index and hence the spectral shape follow the variations only over longer time periods. We probe the correlations between fluxes of different bands and their photon indices, and found no significant correlations between the parameters.

关键词： galaxies: individual (Mrk 335) galaxies: Seyfert X-rays: galaxies

Tuning structural,electrical,dielectric and magnetic properties of Mg-Cu-Co ferrites via dysprosium(Dy^(3+))doping

在线全文

同方期刊数据库

学校读者我要写书评

暂无评论

Journal of Rare Earths 2024年第1期42卷 137-146,I0005页

作者： Maria Akhtar M.S.hasan Nasir Amin N.A.Morley Muhammad Imran Arshad department of physics Government College UniversityFaisalabad38000Pakistan department of physics The University of Lahore53700Pakistan department of Materials Science and Engineering The University of SheffieldS13JDUK department of physics&astronomy University College LondonUK

In current research work,Dy3+substituted Mg0.5Cu0.25Co0.25Fe2-xDyxO4(0.0≤x≤0.04 with the step interval of 0.01)soft ferrites were synthesized by the sol-gel auto combustion method.The prepared samples were characterized by the techniques using X-ray diffraction(XRD),scanning electron microscopy(SEM),energy dispersive X-ray spectroscopy(EDS),Fourier transform infrared(FTIR)spectroscopy,curre nt-voltage(Ⅰ-Ⅴ)measurement,lCR meter,vibrating sample magnetometer(VSM)and Raman.XRD data reveal that the average crystallite size is 49.71 nm and the lattice constant is 0.83703 nm for sample x=0.03.The non-uniform grain growth was demonstrated by micrographs and impurity-free elemental composition was observed from EDX analysis.The DC resistivity has an increasing and decreasing trend in ferromagnetic and paramagnetic regions with an increase in temperature.Moreover,the high resistivity is observed with the order of 1010Ω·cm,and the activation energy is 0.944 eV for samples x=0.03.The dielectric parameters including dielectric constant,dielectric losses,and impedance gradually decrease with the increase in frequency from 8 hz to 8 Mhz.The minimum dielectric loss at high frequency is found for sample x=0.03.The coercivity(hc)and saturation magnetization(Ms)are found in the ranges of 520.82-544.02 Oe and 20.5841-21.1473 emu/g,respectively.These observations confirm that dysprosium(x=0.03)doped MCC-soft ferrites may be applicable in transformer cores,microwave absorbance,and telecommunication devices.

关键词： Soft ferrites DC resistivity Dielectric loss Impedance Coercivity Rare earths

维普期刊数据库

Beyond the lab:a nanoimprint metalens arraybased augmented reality

在线全文

学校读者我要写书评

暂无评论

light(Science & Applications) 2024年第5期13卷 801-802页

作者： Chi lio haoran Ren School of physics and astronomy Monash UniversityMelbourneVICAustralia

A see-through augmented reality prototype has been developed based on an ultrathin nanoimprint metalens array,opening up a full-colour,video-rate,and low-cost 3D near-eye display.

关键词： cost ens imprint

Nonlinear Rydberg exciton-polaritons in Cu2O microcavities

维普期刊数据库评论

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

light(Science & Applications) 2024年第4期13卷 619-627页

作者： Maxim Makhonin Anthonin Delphan Kok Wee Song Paul Walker Tommi Isoniemi Peter Claronino Konstantinos Orfanakis Sai Kiran Rajendran hamid Ohadi Julian heckötter Marc Assmann Manfred Bayer Alexander Tartakovskii Maurice Skolnick Oleksandr Kyriienko Dmitry Krizhanovskii department of physics and astronomy University of SheffieldSheffield S37RHUK. department of physics and astronomy University of ExeterStocker RoadExeter EX44PYUK. SUPA School of Physics and AstronomyUniversity of St AndrewsSt Andrews KY169SSUK. Fakultät Physik TU DortmundAugust-Schmidt-Straße 444227 DortmundGermany

Rydberg excitons(analogues of Rydberg atoms in condensed matter systems)are highly excited bound electron-hole states with large Bohr radii.The interaction between them as well as exciton coupling to light may lead to strong optical nonlinearity,with applications in sensing and quantum information processing.here,we achieve strong effective photon–photon interactions(Kerr-like optical nonlinearity)via the Rydberg blockade phenomenon and the hybridisation of excitons and photons forming polaritons in a Cu2O-filled microresonator.Under pulsed resonant excitation polariton resonance frequencies are renormalised due to the reduction of the photon-exciton coupling with increasing exciton density.Theoretical analysis shows that the Rydberg blockade plays a major role in the experimentally observed scaling of the polariton nonlinearity coefficient as∝n4.4±1.8 for principal quantum numbers up to n=7.Such high principal quantum numbers studied in a polariton system for the first time are essential for realisation of high Rydberg optical nonlinearities,which paves the way towards quantum optical applications and fundamental studies of strongly correlated photonic(polaritonic)states in a solid state system.

关键词： density. Rydberg polar