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[en] A novel differential capacitive accelerometer with a frame-mass structure is presented in the paper. The equivalent circuit model of the accelerometer is simulated with the software SPICE. The accelerometer with the frame-mass can increase the effectual static capacitance. The micro-accelerometer, with the size of 2800x3000x60μm, the static capacitance of 3.618pf, and the inertial mass of 0.14mg, can be implemented in closed-loop system efficiently, and endure overload of 5000g or above. Through the systematic simulation, the accelerometer with the sensitivity of 75mv/g, the full-scale range of 0∼±50g and the system bandwidth of 10 KHz, is supplied with the voltage of 18V
[en] We report the discovery of two methane dwarfs in the dark cloud L 1688 of the ρ Oph star-forming region. The two objects were among the T dwarf candidates with possible methane absorption and cool atmospheres, as diagnosed by infrared colors using deep Wide-field InfraRed Camera/Canada–France–Hawaii Telescope HK plus CH4ON images, and IRAC/Spitzer c2d data. Follow-up spectroscopic observations with the FLAMINGOS-2/Gemini South confirmed the methane absorption at 1.6 μm. Compared with spectral templates of known T dwarfs in the field, i.e., of the old populations, Oph J162738−245240 (Oph-T3) is a T0/T1 type, whereas Oph J162645−241949 (Oph-T17) is consistent with a T3/T4 type in the H band but an L8/T1 in the K band. Compared with the BT-Settl model, both Oph-T3 and Oph-T17 are consistent with being cool, ∼1000 K and ∼900 K, respectively, and of low surface gravity, With an age no more than a couple Myr, these two methane dwarfs thereby represent the youngest T dwarfs ever confirmed. A young late L dwarf, Oph J162651−242110, was found serendipitously in our spectroscopic observations.
[en] A census of classical T Tauri stars and Herbig Ae/Be stars has been performed around the Orion-Eridanus Superbubble that is ionized and created by the Ori OB1 association. This sample is used to study the spatial distribution of newborn stars, hence the recent star formation sequence, in the region that includes two giant molecular clouds (Orions A and B) and additional smaller clouds (NGC 2149, GN 05.51.4, VdB 64, the Crossbones, the Northern Filament, LDN 1551, LDN 1558, and LDN 1563). Most of the molecular clouds are located on the border of the Superbubble, and associated with Hα filaments and star formation activity, except the Northern Filament which is probably located outside the Superbubble. This suggests that while star formation progresses from the oldest Ori OB1a subgroup to 1b, 1c, and 1d, the Superbubble compresses and initiates starbirth in clouds such as NGC 2149, GN 05.51.4, VdB 64, and the Crossbones, which are located more than 100 pc away from the center of the Superbubble, and even in clouds some 200 pc away, i.e., in LDN 1551, LDN 1558, and LDN 1563. A superbubble appears to have potentially a long-range influence in triggering next-generation star formation in an OB association.
[en] Our star-count analysis of the Two Micron All Sky Survey point sources resulted in an identification of the star cluster G144.9+0.4. The cluster was found, but not characterized, by Glushkova et al. We show that the cluster is physically associated with the Cam OB1 association at a distance of about 1 kpc and with an age of 1-2 Myr. Pre-main sequence stars are identified on the basis of photometric and proper motion data. A total of 91 additional OB star candidates was found in subgroups 1A and 1B, a significant increase from the currently known 43 OB stars. The OB members show an age spread that indicates a sustained star formation for at least the last 10-15 Myr. The young cluster G144.9+0.4 represents the latest episode of sequential star formation in this cloud complex
[en] The shapes and sizes of 116 Galactic globular clusters (GCs) are presented, based on the analysis of the spatial distribution of 2MASS point sources. In general, Galactic GCs are slightly flattened in shape, with a median axial ratio of 0.87. The GCs close to the Galactic bulge have various degrees of flattening, and those exhibiting obvious flattening tend to have their elongation pointing toward the Galactic center, manifesting the tidal effect from the bulge. In comparison, GCs away from the Galactic center tend to be spherical. A few GCs in the halo are also found to have elongated shape. Three notable cases of highly flattened clusters were previously known to be associated with stellar streams or particular dynamical history: NGC 5897 is known to have a stellar tidal tail extending to its equatorial north and south; NGC 6838 had a recent encounter with the Galactic plane; and IC 4499 is spatially close to, and collimated with, the 'Magellanic Stream'. We also found 31 GCs associated with possible clumpy structures in stellar distributions, as diagnosed by possible cluster members selected by colors and magnitudes. Four such cases of stellar debris are presented: NGC 6366 is experiencing heavy tidal stripping and NGC 2808 has been known to have multiple main-sequence branches. NGC 3201 and NGC 6397, like the flattened cluster, NGC 6838, also have their recent passage through the Galactic plane. Our sample is derived from the most inclusive analysis of the morphology of Galactic GCs, and should provide a valuable database to probe the mass distribution, or merging history of the Milky Way galaxy.
[en] NiMnGaSi alloys were prepared by diffusion-reduction reacting which is a new and simple method. The effect of small mount of Si addition on the martensitic transformation temperature (Tm) and strain was investigated. It was found that the addition of Si caused a stronger magnetic exchange interaction leading to higher Curie temperature and giant magnetic field-induced strain. The typical Ni43.03Mn32.07Ga18.48Si6.43 alloy shows high martensitic transformation temperature (Tm) of 300K and a 0.56% giant strain measure at a magnetic field of 0.7 T.
[en] This paper presents the design and geometry optimization of a conductivity probe with a vertical multiple electrode array (VMEA), which can be used to measure the volume fraction and axial velocity of two-phase flow. The designed VMEA electrodes are axially flush mounted on the inside wall of an insulating duct. On the basis of a finite element analysis method, some new sensor optimization concepts of the electric field such as uniform degree, spatial sensitivity and effective information content are proposed. The designed VMEA measurement system has been tested through the multiphase flow loop and shows that the optimized VMEA can be used to measure cross-correlation velocity and predict volume fraction in vertical upward gas–water two-phase flow with satisfactory accuracy. The proposed optimization method of VMEA can also be useful in investigating other types of conductivity probes
[en] We present the analysis of the morphological shape of Berkeley 17, the oldest known open cluster (∼10 Gyr), using the probabilistic star counting of Pan-STARRS point sources, and confirm its core-tail shape, plus an antitail, previously detected with the 2MASS data. The stellar population, as diagnosed by the color–magnitude diagram and theoretical isochrones, shows many massive members in the clusters core, whereas there is a paucity of such members in both of the tails. This manifests mass segregation in this aged star cluster with the low-mass members being stripped away from the system. It has been claimed that Berkeley 17 is associated with an excessive number of blue straggler candidates. A comparison of nearby reference fields indicates that about half of these may be field contamination.
[en] Perovskite barium zirconate titanate nanoparticles (25-20 nm in diameter) were synthesized at low temperatures and under ambient pressure using titanium alkoxide, zirconium alkoxide and barium hydroxide as the starting materials. Microstructural analyses by X-ray diffraction and transmission electron microscopy indicated that the powders were nano-scaled, well crystallized, and had a perovskite phase. It is proposed that an acid-base neutralization reaction is the key mechanism behind the formation of such nanoparticles
[en] We present Be star candidates in the open cluster NGC 663, identified by Hα imaging photometry with the Palomar Transient Factory Survey, as a pilot program to investigate how the Be star phenomena, the emission spectra, extended circumstellar envelopes, and fast rotation, correlate with massive stellar evolution. Stellar membership of the candidates was verified by 2MASS magnitudes and colors and by proper motions (PMs). We discover four new Be stars and exclude one known Be star from being a member due to its inconsistent PMs. The fraction of Be stars to member stars [N(Be)/N(members)] in NGC 663 is 3.5%. The spectral type of the 34 Be stars in NGC 663 shows bimodal peaks at B0–B2 and B5–B7, which is consistent with the statistics in most star clusters. Additionally, we also discover 23 emission-line stars of different types, including non-member Be stars, dwarfs, and giants.