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Recent results from LEPS

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Chinese physics C 2010年第9期34卷 1275-1280页

作者： K.Hicks department of physics and astronomy Ohio University

Photoproduction of baryons with strangeness,such as the Σ（1385）,Λ（1520） and possibly the Θ ＋,are described from measurements at the LEPS/SPring-8 facility in *** polarized photons in the energy range of 1.5–2.4 GeV,along with the forward-angle kinematics at LEPS,provide unique data to learn about these baryons,which are non-perturbative solutions of QCD.

关键词： photoproduction baryons mesons exotic pentaquark

Quark nova model for fast radio bursts

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Research in astronomy and Astrophysics 2016年第5期16卷 87-98页

作者： Zachary Shand Amir Ouyed Nico Koning Rachid Ouyed department of physics and astronomy University of Calgary

Fast radio bursts （FRBs） are puzzling, millisecond, energetic radio transients with no discernible source; observations show no counterparts in other frequency bands. The birth of a quark star from a parent neutron star experiencing a quark nova - previously thought undetectable when born in isolation - provides a natural explanation for the emission characteristics of FRBs. The generation of unstable r-process elements in the quark nova ejecta provides millisecond exponential injection of electrons into the surrounding strong magnetic field at the parent neutron star＇s light cylinder via β-decay. This radio synchrotron emission has a total duration of hundreds of milliseconds and matches the observed spectrum while reducing the inferred dispersion measure by approximately 200 cm-3 pc. The model allows indirect measurement of neutron star magnetic fields and periods in addition to providing astronomical measurements of β-decay chains of unstable neutron rich nuclei. Using this model, we can calculate expected FRB average energies （- 1041 erg） and spectral shapes, and provide a theoretical framework for determining distances.

关键词： stars: neutron -- nuclear reactions nucleosynthesis abundances -- radiation mechanisms:general -- radio continuum: general

A quark nova in the wake of a core-collapse supernova:a unifying model for long duration gamma-ray bursts and fast radio bursts

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Research in astronomy and Astrophysics 2020年第2期20卷 119-186页

作者： Rachid Ouyed Denis Leahy Nico Koning department of physics and astronomy University of Calgary

By appealing to a quark nova(QN;the explosive transition of a neutron star to a quark star) in the wake of a core-collapse supernova(CCSN) explosion of a massive star,we develop a unified model for long duration gamma-ray bursts(LGRBs) and fast radio bursts(FRBs).The time delay(years to decades)between the SN and the QN,and the fragmented nature(i.e.,millions of chunks) of the relativistic QN ejecta are key to yielding a robust LGRB *** our model,an LGRB light curve exhibits the interaction of the fragmented QN ejecta with turbulent(i.e.,filamentary and magnetically saturated) SN ejecta which is shaped by its interaction with an underlying pulsar wind nebula(PWN).The afterglow is due to the interaction of the QN chunks,exiting the SN ejecta,with the surrounding *** model can fit BAT/XRT prompt and afterglow light curves simultaneously with their spectra,thus yielding the observed properties of LGRBs(e.g.,the Band function and the X-ray flares).We find that the peak luminositypeak photon energy relationship(i.e.,the Yonetoku law),and the isotropic energy-peak photon energy relationship(i.e.,the Amati law) are not fundamental but ***-like emission in our model results from coherent synchrotron emission(CSE) when the QN chunks interact with non-turbulent weakly magnetized PWN-SN ejecta,where conditions are prone to the Weibel *** field amplification induced by the Weibel instability in the shocked chunk frame sets the bunching length for electrons and pairs to radiate *** resulting emission frequency,luminosity and duration in our model are consistent with FRB *** find a natural unification of high-energy burst phenomena from FRBs(i.e.,those connected to CCSNe) to LGRBs including X-ray flashes(XRFs) and X-ray rich GRBs(XRR-GRBs) as well as superluminous SNe(SLSNe).We find a possible connection between ultra-high energy cosmic rays and FRBs and propose that a QN following a binary neutron star merger can yiel

关键词： stars:neutron stars:quark pulsars:general supernovae:general gamma-ray burst:general fast radio burst:general

Nanoscale displacement of the image of an atomic source of radiation

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Chinese Optics Letters 2009年第2期7卷 149-151页

作者： Henk F. Arnoldus department of physics and astronomy Mississippi State University

Light emitted by an atomic source of radiation appears to travel along a straight line （ray） from the location of the source to the observer in the far field. However, when the energy flow pattern of the radiation is resolved with an accuracy better than an optical wavelength, it turns out that the field lines are usually curved. We consider electric dipole radiation, a prime example of which is the radiation emitted by an atom during an electronic transition, and we show that the field lines of energy flow are in general curves. Near the location of the dipole, the field lines exhibit a vortex structure, and in the far field they approach a straight line. The spatial extension of the vortex in the optical near field is of nanoscale dimension. Due to the rotation of the field lines near the source, the asymptotic limit of a field line is not exactly in the radially outward direction and as a consequence, the image in the far field is slightly shifted. This sub-wavelength displacement of the image of the source should be amenable to experimental observation with contemporary nanoscale-precision techniques.

关键词： Atoms Electric dipole moments Flow patterns Nanotechnology Vortex flow

Anisotropy of rare-earth magnets

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Journal of Rare Earths 2009年第4期27卷 675-679页

作者： R.Skomski D.J.Sellmyer department of physics and astronomy NCMN University of Nebraska

Rare-earth intermetallics such as Nd2Fe14B and Sm-Co are widely used as high-performance permanent magnets, because they combine high magnetocrystalline anisotropy with reasonable magnetization and Curie temperature. The anisotropy is a combined effect of spin-orbit coupling and electrostatic crystal-field interactions. The main contribution comes from the rare-earth 4f electrons, which are well-screened from the crystalline environment but exhibit a strong spin-orbit coupling. In this limit, the magnetocrystalline anisotropy has a very transparent physical interpretation, the anisotropy energy essentially being equal to the energy of Hund＇s-rules 4f ion in the crystal field. The corresponding expression for the lowest-order uniaxial anisotropy constant K1 is used to discuss rare-earth substitutions, which have recently attracted renewed interest due to shifts in the rare-earth production and demand. Specific phenomena reviewed in this article are the enhancement of the anisotropy of Sm2Fe17 due to interstitial nitrogen, the use of Sm-Co magnets for high-temperature applications, and the comparison of rare-earth single-ion anisotropy with other single-ion and two-ion mechanisms.

关键词： magnetic anisotropy spin-orbit coupling crystal-field interaction interstitial modification permanent magnets rare earths

Seismic diagnostics of solar-like oscillating stars

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Research in astronomy and Astrophysics 2017年第5期17卷 51-64页

作者： Ya-Guang Li Ming-Hao Du Bo-Han Xie Zhi-Jia Tian Shao-Lan Bi Tan-Da Li Ya-Qian Wu Kang Liu department of astronomy Beijing Normal University department of astronomy Peking University Sydney Institute for astronomy (SIfA) School of Physics University of Sydney Stellar Astrophysics Centre Department of Physics and Astronomy Aarhus University

High precision and long-lasting Kepler data enabled us to estimate stellar properties with asteroseismology as an accurate tool. We performed asteroseismic analysis on six solar-like stars observed by the Kepler mission： KIC 6064910, KIC 6766513, KIC 7107778, KIC 10079226, KIC 10147635 and KIC 12069127. The extraction of seismic information includes two parts. First, we obtained two global asteroseismic parameters, mean large separation ？_ν and frequency of maximum power ν_（max）,with autocorrelation function and collapsed autocorrelation function. Second, we extracted individual oscillation modes ν_（nl） with low-l degree using a least-squares fit. Stellar grid models were built with Yale Rotating Stellar Evolution Code（YREC） to analyze stellar properties. They covered the range of M = 0.8 ~ 1.8 M_⊙with a step of 0.02 M_⊙ and [Fe/H] =-0.3 ~ 0.4 dex with a step of 0.1 *** used a Bayesian approach to estimate stellar fundamental parameters of the six stars, under the constraints of asteroseismic parameters（？_ν, ν_（max）） and non-asteroseismic parameters（Teff, [Fe/H]）. We discover that the six targets include five sub-giant stars with 1.2 ~1.5 M_⊙ and one main-sequence star with 1.08 M_⊙, and with ages in the range of 3 ~5 Gyr.

关键词： diagnostics stars stellar Bayesian constraints lasting oscillation oscillating giant smoothed

Geoelectrical Investigation of Groundwater Potentials of Northern Paiko,Niger State,North Central Nigeria

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Journal of Earth Science 2017年第1期28卷 103-112页

作者： Usman D.Alhassan Daniel Nnaemeka Obiora Francisca Nneka Okeke department of physics Federal University of Technology department of physics and astronomy University of Nigeria

Vertical electrical sounding（VES） was carried out in northern part of Paiko, North Central Nigeria, using Abem terrameter model SAS 4000 to determine the subsurface layer parameters（resistivities, depths and thickness） employed in delineating the groundwater potential of the area. A total of six transverses with ten VES stations along each traverse, at intervals of 50 m were investigated. It has a maximum current electrode separation（AB/2） of 100 m. Three to four distinct geoelectric layers were observed, namely, the top layer, the weathered layer, the fractured/fresh layer, and the fresh basement layer. The observed frequencies in curve types include 21% of H, 4.2% of HA, 2.4% of K, 4.2% of A, 1.67% of KH and 3% of HK. Eight VES stations were delineated as ground water potentials of the area, with third and fourth layer resistivities ranging from 191 to 398 ？·m. Depths range from 13.60 to 36.60 m and thickness varies from 9.23 to 30.51 m. A correlation of the borehole log with the VES lithology is in agreement. Viable boreholes for good portable water should be sited at VES stations J8 and J10 having a fine aquifer at a depth of 36.60 and 17.80 m respectively with thickness of 30.51 and 15.07 m, respectively.

关键词： vertical electrical sounding groundwater potential northern Paiko resistivity aquifer,geoelectric layer Abem terrameter.

Thickness modulation effect of CeO_2 layer for YBCO films grown by pulsed laser deposition

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Rare Metals 2018年第3期37卷 225-231页

作者： Xiang Wu Lin-Fei Liu Yan-Jie Yao Meng-Lin Wang Bin-Bin Wang Yi-Jie Li department of physics and astronomy Shanghai Jiao Tong University

CeO2 film plays an essential role in nucleation and growth of YBa2 Cu3 O（7-x）（YBCO） films. In this work,the dependence of superconducting properties of YBCO on CeO2 films with different thicknesses was investigated,in order to achieve fabrication of high-performance YBCO coated conductors in industrial scale. The crystalline structure and morphology of CeO2 films with thickness ranging from 21 to 563 nm were systematically characterized by means of X-ray diffraction（XRD）, atomic force microscope（AFM） and reflection high-energy electron diffraction（RHEED）. Additional focus was addressed on evolution of the surface quality of CeO2 films with thickness increasing. The results show that at the optimal thickness of 221 nm, CeO2 film exhibits sharp in-plane and out-of-plane texture with full width of half maximum（FWHM） values of 5.9° and 1.8°, respectively, and smooth surface with a mean root-mean-square（RMS） roughness value as low as 0.6 nm. Combing RHEED and transmission electron microscope（TEM） cross-sectional analysis, it is found that nucleation and growth of CeO2 films at early stage remain in island growth mode with rougher surface,while further increasing the thickness beyond the optimal thickness leads to weak surface quality, consequently resulting in degradation of superconductor layers deposited subsequently. Eventually, a critical current density（Jc） as high as 4.6×10-6 A·cm-（-2）（77 K, self-field） is achieved on a YBCO film on a thickness-modulated CeO2/MgO/Y2 O3/Al2 O3/C276 architecture, demonstrating the advantages of CeO2 films as buffer layer in high-throughput manufacture of coated conductors.

关键词： CeO2 films Thickness modulation Pulsed laser deposition Surface quality

PeV neutrinos from wind breakouts of type Ⅱ supernovae

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Science China(physics,Mechanics & astronomy) 2019年第5期62卷 114-120页

作者： Zhuo Li department of astronomy School of Physics Peking University Kavli Institute for astronomy and Astrophysics Peking University

Recently,rapid multiwavelength photometry and flash spectra of supernova(SN)2013fs imply that the progenitor stars of regular type Ⅱ supernovae(SNe Ⅱ)may be commonly surrounded by a confined,dense stellar wind ejected from the progenitor star at a large mass loss rate over few years before the *** on the assumption that the pre-SN progenitor stars of SNe Ⅱ emit wind similar to SN 2013fs,with a mass loss rate■,we investigated neutrino emissions during the wind breakouts of SN *** find that a typical SNe Ⅱ can convert～10^(-3)of their bulk kinetic energy into neutrino emissions,contributing a significant fraction of the IceCube-detected neutrino flux at ■300 ***,■200 TeV IceCube neutrinos can be accounted for by the cosmic rays produced by shocks of all SN remnants,losing energy in their host galaxies,i.e.,the starburst *** future follow-up observations of high energy neutrinos and gamma-rays from nearby individual SNe Ⅱ,days to weeks after the explosions,will test this model.

关键词： neutrinos gamma rays supernovae