Structure and Stacking Faults in Sr₂Be₂B₂O7 Crystal

X. Y. Meng,X. H. Wen,G. L. Liu 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.52 No.4

Inspired by the successful study on the structure instability of Na₂Al₂B₂O7 (NABO), we extend our interest to a theoretical study, by using density functional theory, on the crystal structures of Sr₂Be₂B₂O7 (SBBO), which possess pretty much the same [M₂B₂O7]∞ (M = Be, Al) double layers as those of the NABO crystal. The energy differences of the SBBO structural variants are found to be so slight that stacking faults could readily occur in the crystal. We propose that different phases may coexist in the same SBBO crystallite, forming domain structure similar to those of NABO which were found by using single-crystal X-ray diffraction. The structural stability of SBBO is closely related to the cohesion forces between [Be₂B₂O7 ∞ layers. A similar structure analysis can be extended to the SBBO isomorphism. Inspired by the successful study on the structure instability of Na₂Al₂B₂O7 (NABO), we extend our interest to a theoretical study, by using density functional theory, on the crystal structures of Sr₂Be₂B₂O7 (SBBO), which possess pretty much the same [M₂B₂O7]∞ (M = Be, Al) double layers as those of the NABO crystal. The energy differences of the SBBO structural variants are found to be so slight that stacking faults could readily occur in the crystal. We propose that different phases may coexist in the same SBBO crystallite, forming domain structure similar to those of NABO which were found by using single-crystal X-ray diffraction. The structural stability of SBBO is closely related to the cohesion forces between [Be₂B₂O7 ∞ layers. A similar structure analysis can be extended to the SBBO isomorphism.

Annealing Dependence of Solution-Processed Ultra-Thin ZrOx Films for Gate Dielectric Applications.

Liu, G X,Liu, A,Meng, Y,Shan, F K,Shin, B C,Lee, W J,Cho, C R American Scientific Publishers 2015 Journal of Nanoscience and Nanotechnology Vol.15 No.3

<P>Ultra-thin ZrOx thin films on Si substrates were prepared by sol-gel technique and processed with different methods (baked on hot plate at 150 °C, annealed at 500 °C in furnace, and photo-annealed under UV light). The decomposition of the organic groups and the formation of Zr-O bonding in the ZrOx thin films were confirmed by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. It is found that the ZrOx thin film annealed under UV light shows decent characteristics, including an ultra-small surface roughness, a low leakage current density of 10(-9) A/cm2 at 1 MV/cm, a large breakdown electric field of 9.5 MV/cm, and a large areal capacitance of 775 nF/cm2.</P>

Multi-pass laser welding of thick plate with filler wire by using a narrow gap joint configuration

Y. C. Yu,S. L. Yang,Y. Yin,C. M. Wang,X. Y. Hu,X. X. Meng,S. F. Yu 대한기계학회 2013 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.27 No.7

A 17 mm low-carbon steel plate is welded by a fiber laser with a narrow gap joint configuration and multi-pass technique. A highspeed camera is used to real-time monitor the welding process, and the effects of groove size and the side shielding gas on the weld quality are studied. Experimental results showed that a concave shape in the bottom of weld can be formed when use a general shielding gas nozzle with the 8.0 mm external diameter. Through a special design of the shielding gas nozzle with the 2.0 mm external diameter which can deep into the interior of groove, the pressure from shielding gas can balance the surface tension from the liquid in the top of groove,so the shielding effect can be dramatically improved and the concave shape in the bottom of weld can be eliminated. When the filler wire and laser beam can smoothly enter the groove, using a relatively small groove size not only reduce the consumption of filler wire but also reduce the deflection of filler wire in the gap that can improve the fusion of groove.

Investigation of energy transfer and concentration quenching of Dy³⁺ luminescence in Gd(BO₂)₃ by means of fluorescence dynamics

Zhang, X.,Meng, F.,Li, W.,Kim, S.I.,Yu, Y.M.,Seo, H.J. Elsevier Sequoia 2013 Journal of alloys and compounds Vol.578 No.-

In this paper, the photoluminescence (PL) properties of Dy<SUP>3+</SUP> activated Gd(BO<SUB>2</SUB>)<SUB>3</SUB> phosphors are presented by means of fluorescence dynamics excited by pulsed laser light (λ=266nm). Energy transfer from Gd<SUP>3+</SUP> to Dy<SUP>3+</SUP> and concentration quenching of the Dy<SUP>3+</SUP> luminescence are studied. From the PL spectra and decay curves the energy transfer from Gd<SUP>3+</SUP> to Dy<SUP>3+</SUP> is confirmed. The decay curves of Dy<SUP>3+4</SUP>F<SUB>9/2</SUB>→<SUP>6</SUP>H<SUB>13/2</SUB> transition exhibiting build-up and decay process confirm the energy transfer between Gd<SUP>3+</SUP> to Dy<SUP>3+</SUP>. The rise time becomes shorter as the Dy<SUP>3+</SUP> concentration increases. The theoretical luminescence decay curves of (Gd<SUB>1-x</SUB>Dy<SUB>x</SUB>)(BO<SUB>2</SUB>)<SUB>3</SUB> samples agree well with the experimental observations. The concentration quenching of the Dy<SUP>3+</SUP> ion emission can be ascribed to resonant cross-relaxation. The interaction between the Dy<SUP>3+</SUP> ions is probably of the electric dipole-dipole type through fitting the data with Inokuti-Hirayama (I-H) model. The energy transfer parameters and critical distance for the transfer processes are given.

Extending the nuclear chart by continuum: From oxygen to titanium

Qu, X.,Chen, Y.,Zhang, S.,Zhao, P.,Shin, I. J.,Lim, Y.,Kim, Y.,Meng, J. Springer Science + Business Media 2013 Science China. Physics, mechanics & astronomy Vol.56 No.11

Luminescence properties of Eu³⁺ in gadolinium molybdate β'-Gd₂Mo₃O₁₂ phosphors

Meng, F.,Zhang, X.,Kim, S.I.,Yu, Y.M.,Seo, H.J. Wissenschaftliche Verlagsgesellschaft m. b. H 2014 OPTIK -STUTTGART- Vol.125 No.14

In this paper, we report the synthesis and photoluminescence (PL) properties of β'-Gd<SUB>2</SUB>Mo<SUB>3</SUB>O<SUB>12</SUB> doped with Eu<SUP>3+</SUP> ions. The relationship between Eu<SUP>3+</SUP> luminescence versus concentration and temperature is discussed. In order to investigate the mechanism of concentration quenching, luminescence decay curves are measured and the Inokuti-Hirayama model is used to analyze them. The activation energy for the thermal quenching is estimated by the Arrhenius fitting. The emission spectrum of β'-Gd<SUB>2</SUB>Mo<SUB>3</SUB>O<SUB>12</SUB> exhibits the strongest emission peak at 614.5nm due to electric-dipole transition. The excitation spectrum shows several sets of lines in the range of 350-425nm which are associated with the typical intra-configurational 4f<SUP>6</SUP> transitions of Eu<SUP>3+</SUP>. The spectral positions of these lines match well with the emission spectra of near-UV LEDs, which makes the phosphor find a potential application for white light-emitting-diodes.

SIMPLER AXIOMATIC SYSTEMS OF LATTICE TOPOLOGIES

Meng, J.,Jun, Y.B.,Xin, X.L. The Youngnam Mathematical Society Korea 1993 East Asian mathematical journal Vol.9 No.2

Concentrations of Progesterone and Estradiol in Peripheral Plasma during the Estrous Cycle and after Ovariectomy in Huanghuai Goats of High or Poor Prolificacy

Pang, X.S.,Wang, Z.Y.,Zhu, T.G.,Yin, D.Z.,Zhang, Y.L.,Meng, L.,Wang, F. Asian Australasian Association of Animal Productio 2010 Animal Bioscience Vol.23 No.2

The objective of this study was to characterize the litter sizes in Huanghuai goats with high prolificacy (HP, five or more kids born per litter on at least one occasion), and to compare their peripheral blood concentrations of progesterone and estradiol with those of goats with poor prolificacy (PP, up to three kids born per litter on any occasion). The circulating concentrations of progesterone and estradiol were measured by radioimmunoassay from daily blood samples taken during natural estrus cycles and at 1-5 days after ovariectomy. Estrus was synchronized using two doses of a prostaglandin analog. Litter size for the HP goats increased up to a parity of five and decreased thereafter. The percentage of goats with litter sizes of $\geq$4 from parities 3 to 6 ranged from 44.5% to 58.3%. Although small differences in litter size were obtained for goats of parities three, four and six relative to five, parity five does had the highest mean litter size. Progesterone concentrations began to rise earlier and were higher in the HP than in the PP goats on most days of the luteal phase, but not during the follicular phase of the cycle or after ovariectomy. There was a significant difference between the two groups (p<0.05) in the magnitude of the progesterone plateau. Mean estradiol concentrations in the HP group remained significantly higher than in the PP group (p<0.05) during the estrus cycle. There were two estradiol peaks in the HP goats during the early luteal phase, but only one in the PP group. Measurements of individual corpora lutea (CL) in vitro showed that there was a greater prevalence of small CL (<6 mm in diameter) in the HP group than in the PP group (p<0.05). After ovariectomy, the estradiol level on day 1 was significantly higher than at the nadir during the estrus cycle in both the HP (p<0.01) and PP (p<0.05) goats, while levels decreased by 12.3% and 26.2% respectively compared with the mid-luteal period in HP and PP goats (p<0.05). The overall mean estradiol concentrations in HP goats were lower than in the PP group, but no significant differences were found between groups at 1-5 days after ovariectomy.

Hollow and yolk-shell structured off-stoichiometric tungsten trioxide via selective leaching and hydrogenation for enhanced lithium storage properties

Wang, W.,Meng, X.,Zhang, K.,Li, P.,Choi, D.,Park, J.H.,Son, Y. Pergamon Press 2016 ELECTROCHIMICA ACTA Vol.215 No.-

Highly porous off-stoichiometric tungsten trioxide (WO<SUB>3-σ</SUB>) with hollow and yolk-shell structures have been successfully synthesized via a selective leaching strategy, following hydrogenation using PbWO<SUB>4</SUB> spheres as the starting material. It was found that the yolk-shell WO<SUB>3-σ</SUB> could be obtained from hollow WO<SUB>3-σ</SUB> by dividing the continuous leaching process into two intervallic processes. The unique structural features and high conductivity facilitate both ion and electron transport, greatly enhancing reversible lithium storage capacity. In comparisons of the hollow WO<SUB>3-σ</SUB> and yolk-shell WO<SUB>3-σ</SUB>, the yolk-shell structure exhibited more long-term stability due to extra spatial elasticity.

Experimental Observations of Boiling and Flow Evolution in a Coiled Tube

P. Ye,X. F. Peng,H. L. Wu,M. Meng,Y. Eric Gong 대한설비공학회 2008 International Journal Of Air-Conditioning and Refr Vol.16 No.1

A sequence of visually experimental observations was conducted to investigate the flow boiling and two-phase flow in a coiled tube. Different boiling modes and bubble dynamical evolutions were identified for better recognizing the phenomena and understanding the two-phase flow evolution and heat transfer mechanisms. The dissolved gases and remained vapor would serve as foreign nucleation sites, and together with the effect of buoyancy, centrifugal force and liquid flow, these also induce very different flow boiling nucleation, boiling modes, bubble dynamical behavior, and further the boiling heat transfer performance. Bubbly flow, plug flow, slug flow, stratified/wavy flow and annular flow were observed during the boiling process in the coiled tube. Particularly the effects of flow reconstructing and thermal non-equilibrium release in the bends were noted and discussed with the physical understanding. Coupled with the effects of the buoyancy, centrifugal force and inertia or momentum ratio of the two fluids, the flow reconstructing and thermal non-equilibrium release effects have critical importance for flow pattern in the bends and flow evolution in next straight sections.