Abstract
We present the second release of value-added catalogues of the LAMOST Spectroscopic Survey of the Galactic Anticentre (LSS-GAC DR2). The catalogues present values of radial velocity Vr, ...atmospheric parameters – effective temperature Teff, surface gravity log g, metallicity Fe/H, α-element to iron (metal) abundance ratio α/Fe (α/M), elemental abundances C/H and N/H and absolute magnitudes MV and $M_{K_{\rm s}}$ deduced from 1.8 million spectra of 1.4 million unique stars targeted by the LSS-GAC since 2011 September until 2014 June. The catalogues also give values of interstellar reddening, distance and orbital parameters determined with a variety of techniques, as well as proper motions and multiband photometry from the far-UV to the mid-IR collected from the literature and various surveys. Accuracies of radial velocities reach 5 km s−1 for the late-type stars, and those of distance estimates range between 10 and 30 per cent, depending on the spectral signal-to-noise ratios. Precisions of Fe/H, C/H and N/H estimates reach 0.1 dex, and those of α/Fe and α/M reach 0.05 dex. The large number of stars, the contiguous sky coverage, the simple yet non-trivial target selection function and the robust estimates of stellar radial velocities and atmospheric parameters, distances and elemental abundances make the catalogues a valuable data set to study the structure and evolution of the Galaxy, especially the solar-neighbourhood and the outer disc.
The plastic deformation behavior and the effects of the impact time on the LY2 aluminum (Al) alloy during multiple laser shock processing (LSP) impacts were investigated. The residual stress in the ...near-surface region was determined by X-ray diffraction. In addition, the micro-structural features of the hardening layer were characterized by scanning electron microscopy, optical microscopy and transmission electron microscopy. It was found that the micro-structure was obviously refined due to the ultra-high plastic strain induced by multiple LSP impacts. The minimum grain size in the top surface after multiple LSP impacts was about 100–200
nm. The grain refinement process after multiple LSP impacts can be described as follows: (i) the formation and development of dislocation lines in original grains; (ii) dislocation tangles (DTs) and the formation of dense dislocation walls (DDWs); (iii) transformation of DTs and DDWs into subgrain boundaries; and (iv) evolution of the continuous dynamic recrystallization in subgrain boundaries to refined grain boundaries.
Micro-structural evolution and grain refinement in ANSI 304 stainless steel subjected to multiple laser shock processing (LSP) impacts were investigated by means of cross-sectional optical microscopy ...and transmission electron microscopy observations. The plastic strain-induced grain refinement mechanism of the face-centered cubic (fcc) materials with very low stacking fault energy was identified. The micro-structure was obviously refined due to the ultra-high plastic strain induced by multiple LSP impacts. The minimum grain size in the top surface was about 50–200
nm. Multidirectional mechanical twin matrix (MT)–MT intersections led to grain subdivision at the top surface during multiple LSP impacts. Furthermore, a novel structure with submicron triangular blocks was found at the top surface subjected to three LSP impacts. The grain refinement process along the depth direction after multiple LSP impacts can be described as follows: (i) formation of planar dislocation arrays (PDAs) and stacking faults along multiple directions due to the pile up of dislocation lines; (ii) formation of submicron triangular blocks (or irregularly shaped blocks) by the intersection of MT–MT (or MT–PDA or PDA–PDA) along multiple directions; (iii) transformation of MTs into subgrain boundaries; (iv) evolution by continuous dynamic recrystallization of subgrain boundaries to refined grain boundaries. The experimental results and analyses indicate that a high strain with an ultra-high strain rate play a crucial role in the grain refinement process of fcc materials subjected to multiple LSP impacts.
By combining angle-resolved photoemission spectroscopy and quantum oscillation measurements, we performed a comprehensive investigation on the electronic structure of LaSb, which exhibits ...near-quadratic extremely large magnetoresistance (XMR) without any sign of saturation at magnetic fields as high as 40 T. We clearly resolve one spherical and one intersecting-ellipsoidal hole Fermi surfaces (FSs) at the Brillouin zone (BZ) center Γ and one ellipsoidal electron FS at the BZ boundary X. The hole and electron carriers calculated from the enclosed FS volumes are perfectly compensated, and the carrier compensation is unaffected by temperature. We further reveal that LaSb is topologically trivial but shares many similarities with the Weyl semimetal TaAs family in the bulk electronic structure. Based on these results, we have examined the mechanisms that have been proposed so far to explain the near-quadratic XMR in semimetals.
► Effects of LSP on mechanical properties of stainless steel ANSI 304 are evaluated. ► LSP can clearly enhance the values of mechanical properties in the shocked region. ► Martensite transformation ...does not take place in the surface layer subjected to LSP. ► Enhancement mechanisms of LSP on mechanical property of stainless steel are revealed. ► The results can provide some insights on the surface modification of stainless steel.
The aim of this article is to address the effects of a single laser shock processing (LSP) impact on the nano-hardness, elastic modulus, residual stress and phase transformation of ANSI 304 austenitic stainless steel. Residual stress distribution of the LSP-shocked region is determined by X-ray diffraction (XRD) with sin
2
ψ method, and the micro-structural features in the near-surface layer are characterized by using cross-sectional optical microscopy (OM), X-ray diffraction (XRD) and transmission electron microscopy (TEM). By comparing with the untreated samples, LSP can clearly improve nano-hardness, elastic modulus, and residual stress in the LSP-shocked region. The underlying enhancement mechanisms of LSP on nano-hardness, elastic modulus and residual stress of stainless steel ANSI 304 are also revealed. These studies may provide some important insights into surface modification for metal materials.
Future Physics Programme of BESIII Ahmed, S.; Amoroso, A.; Bennett, J. V. ...
Chinese physics C,
04/2020, Letnik:
44, Številka:
4
Journal Article
Recenzirano
Odprti dostop
Abstract
There has recently been a dramatic renewal of interest in hadron spectroscopy and charm physics. This renaissance has been driven in part by the discovery of a plethora of charmonium-like
...XYZ
states at BESIII and
B
factories, and the observation of an intriguing proton-antiproton threshold enhancement and the possibly related
X
(1835) meson state at BESIII, as well as the threshold measurements of charm mesons and charm baryons.
We present a detailed survey of the important topics in tau-charm physics and hadron physics that can be further explored at BESIII during the remaining operation period of BEPCII. This survey will help in the optimization of the data-taking plan over the coming years, and provides physics motivation for the possible upgrade of BEPCII to higher luminosity.
► Weldments were done with laser shock processing impacts after cavitation erosion. ► Laser shock processing enhanced the erosion and corrosion resistance of weldments. ► Tensile residual stress and ...surface roughness decreased by laser shock processing. ► Microstructure was observed to explain the improvement by laser shock processing. ► Obvious passivation areas occurred with laser shock processing impacts.
Effects of laser shock processing (LSP) on electrochemical corrosion resistance of weldments after cavitation erosion were investigated by X-ray diffraction (XRD) technology, scanning electron microscope (SEM), roughness tester and optical microscope (OM). Some main factors to influence erosion and corrosion of weldments, residual stresses, surface roughness, grain refinements and slip, were discussed in detail. Results show that LSP impacts can induce compressive residual stresses, decrease surface roughness, refine grains and generate the slip. Thus, the erosion and corrosion resistance with LSP impacts is improved.
The cross section of the process e+e−→K+K− is measured at a number of center-of-mass energies s from 2.00 to 3.08 GeV with the BESIII detector at the Beijing Electron Positron Collider (BEPCII). The ...results provide the best precision achieved so far. A resonant structure around 2.2 GeV is observed in the cross section line shape. A Breit-Wigner fit yields a mass of M=2239.2±7.1±11.3 MeV/c2 and a width of Γ=139.8±12.3±20.6 MeV, where the first uncertainties are statistical and the second ones are systematic. In addition, the timelike electromagnetic form factor of the kaon is determined at the individual center-of-mass energy points.
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► LSP can generate high-level compressive residual stresses and refine original grains. ► Massive LSP impacts can effectively prevent the SCC initiation of the U-bend sample. ► ...Mechanism of massive LSP impacts on SCC was also entirely revealed.
The effects of massive laser peening (LP) impacts on surface residual stress, micro-structure, and stress corrosion cracking (SCC) behaviour of U-bend samples were investigated by X-ray diffraction (XRD) technology, optical microscope (OM) and transmission electron microscope (TEM) observations. Two important factors to influence SCC initiation, residual stress and grain refinement, were discussed in detail by using different types of treatment processes. Results showed massive LP impacts can induce both deep compressive residual stress and refined grains in the surface layer of ANSI 304 stainless steel, and the corrosion mechanism of massive LP impacts on SCC was also analysed and revealed.
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