Effects of slight structural distortion on the luminescence performance in (Ca1-x Eux )WO4 luminescent materials.

(Ca1-x Eux )WO4 (x = 0-21 mol%) phosphors were prepared using the classical solid-state reaction method. The influence of Eu3+ ion doping on lattice structure was observed using powder X-ray diffraction and Fourier transform infrared spectroscopy. Furthermore, under this influence, the luminescence properties of all samples were analyzed. The results clearly illustrated that the element europium was successfully incorporated into the CaWO4 lattice with a scheelite structure in the form of a Eu3+ ion, which introduced a slight lattice distortion into the CaWO4 matrix. These lattice distortions had no effect on phase purity, but had regular effects on the intrinsic luminescence of the matrix and the f-f excitation transitions of Eu3+ activators. When the Eu3+ concentration was increased to 21 mol%, a local luminescence centre of [WO4 ]2- groups was detected in the matrix and manifested as the decay curves of [WO4 ]2- groups and luminescence changed from single exponential to double exponential fitting. Furthermore, the excitation transitions of Eu3+ between different energy levels (such as 7 F0 →5 L6 , 7 F0 →5 D2 ) also produced interesting changes. Based on analysis of photoluminescence spectra and the chromaticity coordinates in this study, it could be verified that the nonreversing energy transfer of [WO4 ]2- →Eu3+ was efficient and incomplete.

Molten salt synthesis and luminescence of Dy3+ -doped Y3 Al5 O12 phosphors.

Dy3+ -doped Y3 Al5 O12 phosphors were prepared at a relatively low temperature using molten salt synthesis. The phase of the prepared Dy3+ -doped Y3 Al5 O12 phosphors was confirmed using X-ray powder diffraction. Results indicated that Dy3+ doping did not change the Y3 Al5 O12 phase. Following excitation at 352 nm, emission spectra of the Dy3+ -doped Y3 Al5 O12 phosphors consisted of blue, yellow, and red emission bands. The influence of Dy3+ concentration and excitation wavelength on emission was investigated. The ratio of yellow light to blue light varied with change in Dy3+ doping concentration, due to changes in the structure around Dy3+ . Emission intensities also changed when the excitation wavelength was changed. This variation is luminescence generated a system for tunable white light for Dy3+ -doped Y3 Al5 O12 phosphors.

The EMT regulator ZEB2 is a novel dependency of human and murine acute myeloid leukemia.

Acute myeloid leukemia (AML) is a heterogeneous disease with complex molecular pathophysiology. To systematically characterize AML's genetic dependencies, we conducted genome-scale short hairpin RNA screens in 17 AML cell lines and analyzed dependencies relative to parallel screens in 199 cell lines of other cancer types. We identified 353 genes specifically required for AML cell proliferation. To validate the in vivo relevance of genetic dependencies observed in human cell lines, we performed a secondary screen in a syngeneic murine AML model driven by the MLL-AF9 oncogenic fusion protein. Integrating the results of these interference RNA screens and additional gene expression data, we identified the transcription factor ZEB2 as a novel AML dependency. ZEB2 depletion impaired the proliferation of both human and mouse AML cells and resulted in aberrant differentiation of human AML cells. Mechanistically, we showed that ZEB2 transcriptionally represses genes that regulate myeloid differentiation, including genes involved in cell adhesion and migration. In addition, we found that epigenetic silencing of the miR-200 family microRNAs affects ZEB2 expression. Our results extend the role of ZEB2 beyond regulating epithelial-mesenchymal transition (EMT) and establish ZEB2 as a novel regulator of AML proliferation and differentiation.

Theoretical Investigation on the Microscopic Mechanism of Lattice Thermal Conductivity of ZnXP2 (X = Si, Ge, and Sn).

Thermal conductivity is an important physical parameter for the application of nonlinear optical single crystal materials. The underlying science of thermal transport behavior is not well established both experimentally and theoretically. In the present work, we have studied the microscopic picture of lattice thermal conductivity of ZnXP2 (X = Si, Ge, Sn), chalcopyrite ABC2 type infrared optical crystals, by using a harmonic and anharmonic lattice dynamic method and phonon Boltzmann transport equation based on first-principle calculations. With the mass of atom X increased, the phonon frequencies and phonon group velocities of ZnXP2 (X = Si, Ge, Sn) are shown not surprisingly to be decreased. Nevertheless, the phonon lifetime of ZnXP2 is unexpectedly increased, which is the governing mechanism for the increased thermal conductivity as 12.5 W/(m·k), 31.6 W/(m·k), and 35.4 W/(m·k), for ZnSiP2, ZnGeP2, and ZnSnP2, respectively, at 300 K. The contributions of optical phonons (with the frequency below 150 cm-1) to the total thermal conductivity are remarkable, reaching 18%, 31%, and 34% for three compounds, due to the significantly increased phonon lifetime in the frequency range 50-150 cm-1. To explore the physical insights of phonon lifetime and phonon anharmonicity, three-phonon scattering phase space and electronic localization function analysis of the X-P bond are provided. The results show that the covalent nature of X-P bonds is enhanced with the increased mass of atom X = Si, Ge, Sn, which induces the reduction of three-phonon scattering phase space in the frequency range 50-150 cm-1, leading to the enhancement of the phonon lifetime and thermal conductivity of ZnXP2.

Crossover from metal to insulator in dense lithium-rich compound CLi4.

At room environment, all materials can be classified as insulators or metals or in-between semiconductors, by judging whether they are capable of conducting the flow of electrons. One can expect an insulator to convert into a metal and to remain in this state upon further compression, i.e., pressure-induced metallization. Some exceptions were reported recently in elementary metals such as all of the alkali metals and heavy alkaline earth metals (Ca, Sr, and Ba). Here we show that a compound of CLi4 becomes progressively less conductive and eventually insulating upon compression based on ab initio density-functional theory calculations. An unusual path with pressure is found for the phase transition from metal to semimetal, to semiconductor, and eventually to insulator. The Fermi surface filling parameter is used to describe such an antimetallization process.

Intrinsic sources of high thermal conductivity of CdSiP2 determined by first-principle anharmonic calculations.

CdSiP2 is an outstanding mid-infrared nonlinear optical crystal material with high thermal conductivity. However, the microscopic physics behind its thermal transport behavior is still unclear. In this study, we have investigated the source of the thermal conductivity of CdSiP2 based on anharmonicity lattice dynamics (ALD) and the first-principle calculation. The results are well accordance with the experimental measurement in a wide temperature range. Based on our results, the acoustic phonon lifetime of CdSiP2 is higher than that of the thermoelectric and semiconducting materials reported in previous studies, which is induced by the low lattice anharmonicity demonstrated by CdSiP2. The mode-dependent thermal conductivity is obtained with the contribution of optical phonons being significant (27%) above 300 K; this is mainly due to the high phonon group velocity and relatively long phonon lifetime of low-energy optical phonons (80-200 cm-1). A high lifetime of acoustic phonons and remarkable contribution of low-energy optical phonons can be responsible for the high thermal conductivity of CdSiP2.

Pressure-Stabilized Superconductive Ionic Tantalum Hydrides.

High-pressure structures of tantalum hydrides were investigated over a wide pressure range of 0-300 GPa by utilizing evolutionary structure searches. TaH and TaH2 were found to be thermodynamically stable over this entire pressure range, whereas TaH3, TaH4, and TaH6 become thermodynamically stable at pressures greater than 50 GPa. The dense Pnma (TaH2), R3̅m (TaH4), and Fdd2 (TaH6) compounds possess metallic character with a strong ionic feature. For the highly hydrogen-rich phase of Fdd2 (TaH6), a calculation of electron-phonon coupling reveals the potential high-Tc superconductivity with an estimated value of 124.2-135.8 K.

Investigation of superconductivity in compressed vanadium hydrides.

Aiming at finding new superconducting materials, we performed systematical simulations on phase diagrams, crystal structures, and electronic properties of vanadium hydrides under high pressures. The VH, VH2, VH3, and VH5 species were found to be stable under high pressures; among these, VH2 had previously been investigated. Moreover, all three novel stoichiometries showed a strong ionic character as a result of the charge transfer from V to H. The electron-phonon coupling calculations revealed the potentially superconductive nature of these vanadium hydrides, with estimated superconducting critical temperature (Tc) values of 6.5-10.7 K for R3[combining overline]m (VH), 8.0-1.6 K for Fm3[combining overline]m (VH3), and 30.6-22.2 K for P6/mmm (VH5) within the pressure range from 150 GPa to 250 GPa.

Investigation of stable germane structures under high-pressure.

The evolutionary structure-searching method discovers that the energetically preferred compounds of germane can be synthesized at a pressure of 190 GPa. New structures with the space groups Ama2 and C2/c proposed here contain semimolecular H2 and V-type H3 units, respectively. Electronic structure analysis shows the metallic character and charge transfer from Ge to H. The conductivity of the two structures originates from the electrons around the hydrogen atoms. Further electron-phonon coupling calculations predict that the two phases are superconductors with a high Tc of 47-57 K for Ama2 at 250 GPa and 70-84 K for C2/c at 500 GPa from quasi-harmonic approximation calculations, which may be higher than under actual conditions.

Distinct roles for hu li tai shao and swallow in cytoskeletal organization during Drosophila oogenesis.

BACKGROUND: Cytoskeletal organization is essential for localization of developmentally significant molecules during Drosophila oogenesis. Swallow (Swa) and an isoform of Hu li tai shao (Ovhts-RC) have been implicated in the organization of actin filaments in developing oocytes but their precise roles have been obscured by the dependence of hts RNA localization on swa function. The functional significance of hts RNA localization in the oocyte has not been established. RESULTS: In this study we examine Ovhts-RC distribution and cytoskeletal organization under conditions in which Swa protein and/or hts RNA localization are perturbed. We find Swa is required for overall actin organization and for the maintenance of a distinct subset of microtubules in the oocyte. hts RNA localization modulates the distribution of Ovhts-RC in the oocyte and, in turn, local actin filament proliferation. CONCLUSIONS: Our results support separate contributions of Swa and hts RNA localization to actin organization during oogenesis. Swa is crucial for the organization of actin networks that lead to the formation of a specialized microtubule population, while Ovhts-RC acts to modulate spatially restricted actin filament growth at the oocyte cortex. This suggests RNA localization can lead to modifications of both the actin and microtubule cytoskeletons at specific subcellular locales.

Wide-Temperature Tunable Phonon Thermal Switch Based on Ferroelectric Domain Walls of Tetragonal KTN Single Crystal.

Ferroelectric domain walls (DWs) of perovskite oxide materials, which can be written and erased by an external electric field, offer the possibility to dynamically manipulate phonon scattering and thermal flux behavior. Different from previous ferroelectric materials, such as BaTiO3, PbTiO3, etc., with an immutable and low Curie temperature. The Curie temperature of perovskite oxide KTa1-xNbxO3 (KTN) crystal can be tuned by altering the Ta/Nb ratio. In this work, the ferroelectric KTa0.6Nb0.4O3 (KTN) single crystal is obtained by the Czochralski method. To understand the role of ferroelectric domains in thermal transport behavior, we perform a nonequilibrium molecular dynamics (NEMD) calculation on monodomain and 90° DWs of KTN at room temperature. The calculated thermal conductivity of monodomain KTN is 9.84 W/(m·k), consistent with experimental results of 8.96 W/(m·k), and distinctly decreased with the number of DWs indicating the outstanding performance of the thermal switch. We further evaluate the thermal boundary resistance (TBR) of KTN DWs. An interfacial thermal resistance value of 2.29 × 10-9 K·m2/W and a large thermal switch ratio of 4.76 was obtained for a single DW of KTN. Our study shows that the ferroelectric KTN can provide great potential for the application of thermal switch at room temperature and over a broad temperature range.

Experimental Study on the Salt Freezing Durability of Multi-Walled Carbon Nanotube Ultra-High-Performance Concrete.

Ultra-high-performance concrete (UHPC) is a new type of high-performance cement-based composite. It is widely used in important buildings, bridges, national defense construction, etc. because of its excellent mechanical properties and durability. Freeze thaw and salt erosion damage are one of the main causes of concrete structure failure. The use of UHPC prepared with multi-walled carbon nanotubes (MWCNTs) is an effective method to enhance the durability of concrete structures in complex environments. In this work, the optimal mix proportion based on mechanical properties was obtained by changing the content of MWCNTs and water binder ratio to prepare MWCNTs UHPC. Then, based on the changes in the compressive strength, mass loss rate, and relative dynamic modulus of elasticity (RDME), the damage degree of concrete under different salt erosion during 1500 freeze-thaw (FT) cycles was analyzed. The changes in the micro pore structure were characterized by scanning electron microscope (SEM) and nuclear magnetic resonance (NMR). The test results showed that the optimum mix proportion at the water binder ratio was 0.19 and 0.1% MWCNTs. At this time, the compressive strength was 34.1% higher and the flexural strength was 13.6% higher than when the MWCNTs content was 0. After 1500 salt freezing cycles, the appearance and mass loss of MWCNTs-UHPC prepared according to the best ratio changed little, and the maximum mass loss was 3.18%. The higher the mass fraction of the erosion solution is, the lower the compressive strength and RDME of concrete after FT cycles. The SEM test showed that cracks appeared in the internal structure and gradually increased due to salt freezing damage. However, the microstructure of the concrete was still relatively dense after 1500 salt freezing cycles. The NMR test showed that the salt freezing cycle has a significant influence on the change in the small pores, and the larger the mass fraction of the erosion solution, the smaller the change in the proportion of pores. After 1500 salt freezing cycles, the samples did not fail, which shows that MWCNTs UHPC with a design service life of 150 years has good salt freezing resistance under the coupling effect of salt corrosion and the FT cycle.

Luminescence of Tb3Al5O12 phosphors co-doped with Ce3+/Gd3+ for white light-emitting diodes.

Tb2.96- x Ce0.04GdxAl5O12 phosphors were synthesized through solid-state reactions. The influence of Gd3+ on the luminescence was investigated. Under the excitation at 460 nm, Tb2.96Ce0.04Al5O12 shows the characteristic emission band of Ce3+ with a peak wavelength at about 554 nm. After co-doping Gd3+ into Tb2.96Ce0.04Al5O12, the peak wavelength of the Ce3+ emission band shifts to longer wavelengths, which is induced by the increasing crystal field splitting. However, the Ce3+ emission intensity also decreases because the substitution of Tb3+ with Gd3+ causes lattice deformation and generates numerous structural and chemical defects. By comparing the light parameters of white light-emitting diodes (WLEDs) containing Y2.96Ce0.04Al5O12, Tb2.96Ce0.04Al5O12 and Tb2.81Ce0.04Gd0.15Al5O12 phosphors, we can find that the WLED containing the Tb2.81Ce0.04Gd0.15Al5O12 phosphor generates warmer light than the WLEDs containing Y2.96Ce0.04Al5O12 and Tb2.96Ce0.04Al5O12 phosphors. Moreover, the WLEDs fabricated by integrating a blue LED chip and Ce3+/Gd3+-co-doped Tb3Al5O12 phosphors show outstanding colour stability when driven under different currents.

Ab initio structure determination of n-diamond.

A systematic computational study on the crystal structure of n-diamond has been performed using first-principle methods. A novel carbon allotrope with hexagonal symmetry R32 space group has been predicted. We name it as HR-carbon. HR-carbon composed of lonsdaleite layers and unique C3 isosceles triangle rings, is stable over graphite phase above 14.2 GPa. The simulated x-ray diffraction pattern, Raman, and energy-loss near-edge spectrum can match the experimental results very well, indicating that HR-carbon is a likely candidate structure for n-diamond. HR-carbon has an incompressible atomic arrangement because of unique C3 isosceles triangle rings. The hardness and bulk modulus of HR-carbon are calculated to be 80 GPa and 427 GPa, respectively, which are comparable to those of diamond. C3 isosceles triangle rings are very important for the stability and hardness of HR-carbon.

Structural, mechanical, and electronic properties of Rh2B and RhB2: first-principles calculations.

The crystal structures of Rh2B and RhB2 at ambient pressure were explored by using the evolutionary methodology. A monoclinic P21/m structure of Rh2B was predicted and donated as Rh2B-I, which is energetically much superior to the previously experimentally proposed Pnma structure. At the pressure of about 39 GPa, the P21/m phase of Rh2B transforms to the C2/m phases. For RhB2, a new monoclinic P21/m phase was predicted, named as RhB2-II, it has the same structure type with Rh2B. Rh2B-I and RhB2-II are both mechanically and dynamically stable. They are potential low compressible materials. The analysis of electronic density of states and chemical bonding indicates that the formation of strong and directional covalent B-B and Rh-B bonds in these compounds contribute greatly to their stabilities and high incompressibility.

First-principles study on the structural and electronic properties of metallic HfH2 under pressure.

The crystal structures and properties of hafnium hydride under pressure are explored using the first-principles calculations based on density function theory. The material undergoes pressure-induced structural phase transition I4/mmm → Cmma → P21/m at 180 and 250 GPa, respectively, and all of these structures are metallic. The superconducting critical temperature Tc values of I4/mmm, Cmma, and P21/m are 47-193 mK, 5.99-8.16 K and 10.62-12.8 K at 1 atm, 180 and 260 GPa, respectively. Furthermore, the bonding nature of HfH2 is investigated with the help of the electron localization function, the difference charge density and Bader charge analyses, which show that HfH2 is classified as a ionic crystal with the charges transferring from Hf atom to H.

High-temperature superconductivity in compressed solid silane.

Crystal structures of silane have been extensively investigated using ab initio evolutionary simulation methods at high pressures. Two metallic structures with P21/c and C2/m symmetries are found stable above 383 GPa. The superconductivities of metallic phases are fully explored under BCS theory, including the reported C2/c one. Perturbative linear-response calculations for C2/m silane at 610 GPa reveal a high superconducting critical temperature that beyond the order of 10(2) K.

Crystal structure prediction and hydrogen-bond symmetrization of solid hydrazine under high pressure: a first-principles study.

In this article, the crystal structure of solid hydrazine under pressure has been extensively investigated using ab initio evolutionary simulation methods. Calculations indicate that hydrazine remains both insulating and stable up to at least 300 GPa at low temperatures. A structure with P21 symmetry is found for the first time through theoretical prediction in the pressure range 0-99 GPa and it is consistent with previous experimental results. Two novel structures are also proposed, in the space groups Cc and C2/c, postulated to be stable in the range 99-235 GPa and above 235 GPa, respectively. Below 3.5 GPa, C2 symmetry is found originally, but it becomes unstable after adding the van der Waals interactions. The P21→Cc transition is first order, with a volume discontinuity of 2.4%, while the Cc→C2/c transition is second order with a continuous volume change. Pressure-induced hydrogen-bond symmetrization occurs at 235 GPa during the Cc→C2/c transition. The underlying mechanism of hydrogen-bond symmetrization has also been investigated by analysis of electron localization functions and vibrational Raman/IR spectra.