The Jiao Tong University Spectroscopic Telescope Project

The Jiao Tong University Spectroscopic Telescope(JUST)is a 4.4-meter f/6.0 segmented-mirror telescope dedicated to spectroscopic observations.The JUST primary mirror is composed of 18 hexagonal segments,each with a diameter of 1.1 m.JUST provides two Nasmyth platforms for placing science instruments.One Nasmyth focus fits a field of view of 10′and the other has an extended field of view of 1.2°with correction optics.A tertiary mirror is used to switch between the two Nasmyth foci.JUST will be installed at a site at Lenghu in Qinghai Province,China,and will conduct spectroscopic observations with three types of instruments to explore the dark universe,trace the dynamic universe,and search for exoplanets:(1)a multi-fiber(2000 fibers)medium-resolution spectrometer(R=4000-5000)to spectroscopically map galaxies and large-scale structure;(2)an integral field unit(IFU)array of 500 optical fibers and/or a long-slit spectrograph dedicated to fast follow-ups of transient sources for multi-messenger astronomy;(3)a high-resolution spectrometer(R~100000)designed to identify Jupiter analogs and Earth-like planets,with the capability to characterize the atmospheres of hot exoplanets.

Piezoelectric bimorph MEMS speakers

One of the key requirements for MEMS speakers is to increase the sound pressure level(SPL)while keeping the size as small as possible.In this paper we present a MEMS speaker based on piezoelectric bimorph cantilevers that produces a higher SPL than conventional unimorph cantilever speakers.The active diaphragm size is 1.4×1.4 mm^(2).The bimorph cantilevers are connected in parallel to make full use of the actuation voltage.At 1 kHz,the measured SPL reached 73 dB and the peak SPL reached 102 dB at the resonance frequency of 10 kHz in a 711 ear simulator under a driving voltage of 10 V_(rms).The total harmonic distortion of the MEMS speaker was less than 3%in the range from 100 Hz to 20 kHz.Although the absolute SPL was not the highest,this work provides a better SPL for all piezoelectric MEMS speakers.

Establishing HI mass vs. stellar mass and halo mass scaling relations using an abundance matching method

We combined data from the Sloan Digital Sky Survey(SDSS) and the Arecibo Legacy Fast ALFA Survey(ALFALFA) to establish the HI mass vs. stellar mass and halo mass scaling relations using an abundance matching method that is free of the Malmquist bias. To enable abundance matching, a cross-match between the SDSS DR7 galaxy group sample and the ALFALFA HI sources provides a catalog of 16520 HI-galaxy pairs within 14270 galaxy groups(halos). By applying the observational completeness reductions for both optical and HI observations, we used the remaining 8180 ALFALFA matched sources to construct the model constraints. Taking into account the dependence of HI mass on both the galaxy and group properties, we establish two sets of scaling relations: one with a combination of stellar mass,(g-r) color and halo mass, and the other with stellar mass,specific star-formation rate(sSFR), and halo mass. We demonstrate that our models can reproduce the HI mass component as both stellar mass and halo mass. Additional tests showed that the conditional HI mass distributions as a function of the cosmic web type and the satellite fractions were well recovered.

TC11钛合金中α″相和α′相的组织演变和显微硬度

研究了TC11钛合金中α"相和α'相的显微组织转变和显微硬度。金相显微组织观察和X射线衍射分析的结果表明:随着固溶温度的提高α"相逐渐向α'相的晶体结构转变,α相、α"相和α'相的显微组织演变规律为:α+α",α+α"+α',α+α',α'。显微硬度测试的结果表明:在935~995℃固溶后显微硬度随着温度的提高先增大后减少,在985℃固溶后显微硬度达到峰值。综合分析显微组织影响合金显微硬度的机理:在935~985℃固溶后α'片层的厚度和间距变化的幅度小,β转变组织长大缓慢,在β转变组织中先后析出α"和α'相,随着固溶温度的提高α'片层的含量随之提高产生了相变强度效果,使其显微硬度提高;在985~995℃固溶后α'片层的厚度和间距明显增大,β转变组织变粗大,α"相消失,α'相的含量降低,相变强化的效果减弱,使β转变组织的显微硬度降低。

The influence of microtexture on the formation mechanism of nodules in Zircaloy-4 alloy tube

Corrosion re sistance of Zircaloy-4 alloy tube in superheated steam at 673 K/10.3 MPa is anisotropic.A part of the surface undergoes uniform corrosion while the other suffers nodular corrosion.Narrow and wide nodules are observed after an exposure period of 3 and 30 days,respectively.A new matrix transformation method is established in order to study the formation mechanism of nodules in the cross-section(CS) of Zircaloy-4 alloy tube using the EBSD technique,while the CS perpendicular to axial direction(AD).The results reveal that the microtexture is a key factor behind the two types of corrosion.Furthermore,the oxide layers grow anisotropically over the corroded surface.A thick oxide layer forms over the nodular corrosion region on the grains with c-axis oriented in the range of 40° around tangential direction(TD),whereas a thin oxide layer over the uniform corrosion region is detected on the grains with c-axis oriented in the range of 68° around TD.In short,the anisotropic growth of oxide layer was caused by the change of microtexture of the Zr-4 alloy tube,and this anisotropic growth of oxide layer contributed to the nodules formation.

Deformation twinning in octahe dron-base d face-centere d cubic metallic structures:Localized shear-force dipoles drive atomic displacements

Twinning is found to impart favorable mechanical,physical and chemical properties to nanostructured materials.Deformation twinning prevails in face-centered cubic(FCC)nanocrystalline materials upon loading.In FCC structures,the<112>{111}deformation twinning is traditionally believed to nucleate and grow through layer-by-layer emission of 1/6<112>Shockley partial dislocations on consecutive{111}planes.We report that deformation twinning is able to occur in crystalline(Fe,Nb)_(23)Zr_(6)nanoparticles(NPs)that have a large Mn 23 Th 6-type FCC structure with a Zr-octahedron as a motif.Based on direct atomic-scale observations,we discover a new zero-net-strain path for the<112>{111}deformation twin-ning in FCC structures.To form a[¯1¯12]/(111)twin,for example,short(¯1¯11)planes within two adjacent(111)plane layers in the repeated three-layer sequence of(111)planes are shear deformed continuously by a shear-force dipole along the[11¯2]direction like a domino effect,whereas the other(111)plane in the repeated sequence remains intact.In addition,a loading criterion for deformation twinning of a FCC NP under uniaxial compression is proposed based on our observations.Our work here not only extends the fundamental understanding on deformation twinning in FCC structures,but also opens up studies of deformation behaviors in a class of Mn 23 Th 6-type FCC materials.

Intermediate state of hexagonal close-packed structure to face-centered cubic structure transformation: Direct evidence for basal-type face-centered cubic phase via partial dislocation in zirconium

1.Introduction Zirconium(Zr)and its alloys show great applications in nuclear and chemical industry thanks to their appropriate mechanical properties,low thermal neutron absorption cross-section and excellent corrosion resistance[1–3].Zr displays three different crystal structures on the temperature-pressure phase diagram:the hexagonal close-packed structure(HCP,α-Zr),the body centered cubic structure(BCC,β-Zr)and the simple hexagonal structure(ω-Zr).

A new type face-centered cubic zirconium phase in pure zirconium

So far,only two orientation relationships(OR)between hexagonal close-packed(HCP)(αphase)and facecentered cubic(FCC)structures in zirconium and titanium alloys have been reported.Here a new type FCC phase(named γ phase)with OR:<11■0>_(α)‖<100>_(γ) and{0001}_(α)‖{002}_(γ) was observed for the first time in annealed pure zirconium by means of transmission electron microscopy(TEM)technique.The α→γ phase transformation can be accomplished via expansion along[1■00]direction and slip of Shockley partial dislocation with 1/3[1■00]on(0001)basal planes.

Nano-refinement of the face-centered cubic Zr(Fe,Cr)_(2)secondary phase particles in Zircaloy-4 alloy via localized-shearing/bending-driven fracture under high-temperature compression

Nanoparticles are extensively introduced to improve the mechanical,physical,and chemical properties of alloys.In the present study,the underlying nano-refinement mechanisms of face-centered cubic Zr(Fe,Cr)_(2)secondary phase particles(SPPs)that precipitated in Zircaloy-4 alloy under high-temperature compression were investigated in detail by utilizing high-resolution transmission electron microscopy(HRTEM)and conventional TEM techniques.The frequently observed Zr(Fe,Cr)_(2)SPPs were incoherent with the matrix and exhibited brittle fracture behaviors without measurable plasticity.HRTEM observations revealed two mechanisms underlying the nano-refinement of incoherent micro-sized SPPs via localized shear fracture on{11¯2}SPP and nanoprecipitate-assisted bending fracture,respectively.The latter was,for the first time,found to occur when the movements of large SPPs were blocked by nanometer-sized SPP during alloy deformation.Accordingly,two force models were proposed to visualize their potential nano-refinement processes.The knowledge attained from this study sheds new light on the deformation behaviors of Zr(Fe,Cr)_(2)SPPs and their associated size refinement mechanisms under high-temperature compression,and is expected to greatly benefit the process optimization of zirconium alloys to achieve precipitate nano-refinement.

Formation of Face‑Centered Cubic Phase in Ti35 Alloy Under In Situ Heating Transmission Electron Microscopy

A thermally induced hexagonal close-packed(HCP)to face-centered cubic(FCC)phase transition was investigated in anα-type Ti35 alloy with twinned structure by in situ heating transmission electron microscopy(TEM)and ab initio calculations.TEM observations indicated that the HCP to FCC phase transition occurred both within matrix/twin and at the twin boundaries in the thinner region of the TEM film,and the FCC-Ti precipitated as plates within the matrix/twin,while as equiaxed cells at twin boundaries.The crystallographic orientation relationship between HCP-Ti and FCC-Ti can be described as:{111}FCC//{0002}HCP and<110>FCC//<1210>HCP.The HCP to FCC phase transition was accomplished by forming an intermediate state with a BB stacking sequence through the slip of partial dislocations.The formation of such FCC-Ti may be related to the thermal stress and temperature.Ab initio calculations showed that the formation of FCC-Ti may also be related to the contamination of interstitial atoms such as oxygen.

A giant central red disk galaxy at redshift z=0.76:Challenge to theories of galaxy formation

We report a giant red central disk galaxy in the XMM-LSS north region. The region is covered with a rich variety of multi-band photometric and spectroscopic observations. Using the photometric data of the Canada-France-Hawaii Telescope Legacy Survey(CFHTLS) and spectroscopic observation of the baryon oscillation spectroscopic survey(BOSS), we find that the galaxy has a stellar mass of ~1011.6 M⊙. The galaxy has a red color and has an old stellar population, and thus its star formation has stopped.With the photometric image data of the Hyper Suprime-Cam(HSC) Subaru Strategic Program, we demonstrate that its luminosity profile is perfectly described by a Sérsic form with n=1.22 consistent with that of a disk. We also analyze its environment based on the VIMOS Public Extragalactic Redshift Survey(VIPERS) photometric catalog, and find that its close neighbors are all less massive, indicating that our observed galaxy is sitting at the center of its dark matter host halo. Existence of such a giant red central disk galaxy seriously challenges the current standard paradigm of galaxy formation, as there is no known physical mechanism to explain the quenching of its star formation. This conclusion is supported by state-of-the-art hydrodynamical simulations of galaxy formation.