In the present study, Ni-modified α-Al2O3 with Ni/Al ratios of 0.3 and 0.5 were prepared by sol–gel and solvothermal method and then were impregnated with 0.3 wt.% Pd. Due to different crystallization mechanism of the two preparation methods used, addition of nickel during preparation of α-Al2O3 resulted in various species such as NiAl2O4, mixed phases between NiAl2O4 and α-Al2O3, and mixed phases between NiAl2O4 and NiO. As revealed by NH3-temperature programmed desorption, formation of NiAl2O4 drastically reduced acidity of alumina, hence lower amounts of coke deposited during acetylene hydrogenation was found for the Ni-modified α-Al2O3 supported catalysts. For any given method, ethylene selectivity was improved in the order of Pd/Ni–Al2O3-0.5 > Pd/Ni–Al2O3-0.3 > Pd/Ni–Al2O3-0 Pd/α–Al2O3-commercial. When comparing the samples prepared by different techniques, the sol–gel-made samples showed better performances than the solvothermal-derived ones. 相似文献
This paper reports on the photoluminescence results of Dy3+ or Tb3+ ions in Ca3Ln(Y,Gd)(VO4)3 powder phosphors. Emission spectra of Dy3+:Ca3Ln(Y,Gd)(VO4)3 powder phosphors have shown blue emissions (4F9/2 → 6H15/2) at 481 nm, yellow emissions (4F9/2 → 6H13/2) at 572 nm and a weak red emissions (4F9/2 → 6H11/2) at 661 nm upon excitation with λexci = 310 nm (6H15/2 → 4L19/2). Similarly photoluminescence spectra of Tb3+:Ca3Ln(Y,Gd)(VO4)3 have shown green emissions (5D4 → 7F5) at 545 nm with λexci = 312 nm. For these phosphors XRD, FTIR, SEM and EDAX measurements have also been carried out. 相似文献
Emission properties of Ho3+ at 2.0 μm and the energy transfer mechanism between Yb3+, Er3+ and Ho3+ ions in fluorophosphate glasses are investigated. The measured emission spectra show that the 5I7 → 5I8 transition of Ho3+ upon 980 nm laser diode excitation is strong. Judd–Ofelt intensity parameters (Ωλ, λ = 2, 4, 6), spontaneous transition probability (Arad), radiative lifetime (τr), absorption cross section (σa), stimulated emission cross section (σe) and FWHM × for the transition of Ho3+: 5I7 → 5I8 are calculated and discussed. The obtained results show that the present Yb3+/Er3+/Ho3+ triply-doped fluorophosphate glass can be identified to be a promising material at 2.0 μm emission. 相似文献
Application of reaction-produced γ-rays to diagnostics of energetic particles in burning plasmas is analyzed. Particularly, we focus on 0.981 MeV γ-rays emitted in the nuclear reaction solely governed in the plasmas by energetic tritons. It is shown that these γ quanta can serve as a promising tool to diagnose α knock-on tritons and α-particles confined in burning DT plasmas. Key parameters of the α knock-on triton population and the α-particle confinement property can be obtained by comparing the experimental γ-ray yield and spectrum with theoretical slowing-down calculations. Even if the γ-ray spectral shape cannot be acquired, one can monitor densities of these tritons and α-particles at energies of 0.6–1.8 MeV and 2.0–3.5 MeV, respectively, in a nearly steady-state plasma. The 0.981-MeV photons also would help to display time evolution of the α-particle population in experiments of deuterium plasmas with pulsed tritium beam shots. 相似文献
The effect of β-iron intermetallics and porosity on the tensile properties in cast Al–Si–Cu and Al–Si–Mg alloys were investigated for this research study, using experimental and industrial 319.2 alloys, and industrial A356.2 alloys. The results showed that the alloy ductility and ultimate tensile strength (UTS) were subject to deterioration as a result of an increase in the size of β-iron intermetallics, most noticeable up to β-iron intermetallic lengths of 100 μm in 319.2 alloys, or 70 μm in A356.2 alloys. An increase in the size of the porosity was also deleterious to alloy ductility and UTS. Although tensile properties are interpreted by means of UTS vs. log elongation plots in the present study, the properties for all sample conditions were best interpreted by means of log UTS vs. log elongation plots, where the properties increased linearly between conditions of low cooling rate–high Fe and high cooling rate–low Fe. The results are explained in terms of the β-Al5FeSi platelet size and porosity values obtained. 相似文献
By means of electron gun evaporation Ge1 − xSix:N thin films, in the entire range 0 ≤ x ≤ 1, were prepared on Si (100) and glass substrates. The initial vacuum reached was 6.6 × 10− 4 Pa, then a pressure of 2.7 × 10− 2 Pa of high purity N2 was introduced into the chamber. The deposition time was 4 min. Crucible-substrate distance was 18 cm. X-ray diffraction patterns indicate that all the films were amorphous (a-Ge1 − xSix:N). The nitrogen concentration was of the order of 1 at% for all the films. From optical absorption spectra data and by using the Tauc method the energy band gap (Eg) was calculated. The Raman spectra only reveal the presence of SiSi, GeGe, and SiGe bonds. Nevertheless, infrared spectra demonstrate the existence of SiN and GeN bonds. The forbidden energy band gap (Eg) as a function of x in the entire range 0 ≤ x ≤ 1 shows two well defined regions: 0 ≤ x ≤ 0.67 and 0.67 ≤ x ≤ 1, due to two different behaviors of the band gap, where for x > 0.67 exists an abruptly change of Eg(x). In this case Eg(x) versus x is different to the variation of Eg in a-Ge1 − xSix and a-Ge1 − xSix:H. This fact can be related to the formation of Ge3N4 and GeSi2N4 when x ≤ 0.67, and to the formation of Si3N4 and GeSi2N4 for 0.67 ≤ x. 相似文献
The dielectric properties at microwave frequencies and the microstructures of nano (α + θ)-Al2O3 ceramics were investigated. Using the high-purity nano (α + θ)-Al2O3 powders can effectively increase the value of the quality factor and lower the sintering temperature of the ceramic samples. Grain growth can be limited with θ-phase Al2O3 addition and high-density alumina ceramics can be obtained with smaller grain size comparing to pure α-Al2O3. Relative density of sintered samples can be as high as 99.49% at 1400 °C for 8 h. The unloaded quality factors Q × f are strongly dependent on the sintering time. Further improvement of the Q × f value can be achieved by extending the sintering time to 8 h. A dielectric constant (r) of 10, a high Q × f value of 634,000 GHz (measured at 14 GHz) and a temperature coefficient of resonant frequency (τf) of −39.88 ppm/°C were obtained for specimen sintered at 1400 °C for 8 h. Sintered ceramic samples were also characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). 相似文献
The Zn2+ stored in the secretory vesicles of glutamatergic neurons is coreleased with glutamate upon stimulation, resulting in the elevation of extracellular Zn2+ concentration (). This elevation of regulates the neurotransmission and facilitates the fibrilization of amyloid‐β (Aβ). However, the exact surrounding neurons under (patho)physiological conditions is not clear and the connection between and the Aβ fibrilization remains obscure. Here, a silicon nanowire field‐effect transistor (SiNW‐FET) with the Zn2+‐sensitive fluorophore, FluoZin‐3 (FZ‐3), to quantify the in real time is modified. This FZ‐3/SiNW‐FET device has a dissociation constant of ≈12 × 10?9m against Zn2+. By placing a coverslip seeded with cultured embryonic cortical neurons atop an FZ‐3/SiNW‐FET, the elevated to ≈110 × 10?9m upon stimulation with α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazolepropionic acid (AMPA). Blockers against the AMPA receptor or exocytosis greatly suppress this elevation, indicating that the Zn2+ stored in the synaptic vesicles is the major source responsible for this elevation of . In addition, a SiNW‐FET modified with Aβ could bind Zn2+ with a dissociation constant of ≈633 × 10?9m and respond to the Zn2+ released from AMPA‐stimulated neurons. Therefore, the can reach a level high enough to bind Aβ and the Zn2+ homeostasis can be a therapeutic strategy to prevent neurodegeneration. 相似文献
The four-point bending creep properties of a hot-pressed β-sialon with Sm–melilite solid solution (denoted as M′) as intergranular phase have been studied in the temperature range 1250–1350°C in air. Creep rates plotted against stresses gave stress exponents of 1.45, 1.51 and 1.72 at 1250, 1300 and 1350°C, respectively, and Arrhenius plot between creep rate and temperature yielded a creep activation energy of 576 kJ mol−1. Cavities were found to be mainly on the triple grain junctions. Diffusion coupled with grain boundary sliding and accompanied by the formation of wedge-shaped cavities was identified as the dominant creep mechanism. 相似文献
The assembly of hybrid nanomaterials has opened up a new direction for the construction of high-performance anodes for lithium-ion batteries (LIBs). In this work, we present a straightforward, eco-friendly, one-step hydrothermal protocol for the synthesis of a new type of Fe2O3-SnO2/graphene hybrid, in which zero-dimensional (0D) SnO2 nanoparticles with an average diameter of 8 nm and one-dimensional (1D) Fe2O3 nanorods with a length of ~150 nm are homogeneously attached onto two-dimensional (2D) reduced graphene oxide nanosheets, generating a unique point-line-plane (0D-1D-2D) architecture. The achieved Fe2O3-SnO2/graphene exhibits a well-defined morphology, a uniform size, and good monodispersity. As anode materials for LIBs, the hybrids exhibit a remarkable reversible capacity of 1,530 mA·g?1 at a current density of 100 mA·g?1 after 200 cycles, as well as a high rate capability of 615 mAh·g?1 at 2,000 mA·g?1. Detailed characterizations reveal that the superior lithium-storage capacity and good cycle stability of the hybrids arise from their peculiar hybrid nanostructure and conductive graphene matrix, as well as the synergistic interaction among the components.
For Gd2CuO4, a new symmetry-forbidden phonon for the tetragonal T structure is observed. This implies that oxygen in the CuO2 plane is locally distorted along the CuO2 plane. Such distortion has never been observed for other T-type superconductors, which show superconductivity by Ce doping. The disappearance of superconductivity for Gd can be correlated with the appearance of the distortion due to oxygen in the CuO2 plane. 相似文献
2D β‐Ga2O3 nanosheets, as fundamental materials, have great potential in next generations of ultraviolet transparent electrodes, high‐temperature gas sensors, solar‐blind photodetectors, and power devices, while their synthesis and growth with high crystalline quality and well‐controlled orientation have not been reported yet. The present study demonstrates how to grow single‐crystalline ultrathin quasi‐hexagonal β‐Ga2O3 nanosheets with nanowire seeds and proposes a hierarchy‐oriented growth mechanism. The hierarchy‐oriented growth is initiated by epitaxial growth of a single‐crystalline β‐Ga2O3 nanowire on a GaN nanocrystal and followed by homoepitaxial growth of quasi‐hexagonal (010) β‐Ga2O3 nanosheets. The undoped 2D (010) β‐Ga2O3 nanosheet field effect transistor has a field‐effect electron mobility of 38 cm2 V?1 s?1 and an on/off current ratio of 107 with an average subthreshold swing of 150 mV dec?1. The from‐nanowires‐to‐nanosheets technique paves a novel way to fabricate nanosheets, which has great impact on the field of nanomaterial synthesis and growth and the area of nanoelectronics as well. 相似文献
The169Tm enhanced NMR in TmBa2Cu3O6+x (x=0.5, 0.6) at temperatures below 4.2K and the63Cu(1) NQR in YBa2Cu3O6.5 at temperatures above 4.2K are used to study properties of intrinsic paramagnetic centers incorporated into superconducting materials. The spin-lattice relaxation of thulium and copper nuclei reveals three types of paramagnetic centers to be present in oxygen-deficient 1-2-3 superconductors, those are (1) two-level ones with a spin S=1/2, localized outside CuO2 bilayers, (2) singlet-ground-state paramagnetic centers with an integer spin S1 in CuO2 bilayers, and (3) exchange copper-oxygen clusters with a half-integer spin S5/2, localized in a nearest neighborhood of CuOx basal plane at boundaries of superconducting OrthoII microdomains. 相似文献
The syntheses of nanosize magnetite particles by wet-chemical oxidation of Fe2+ have been extensively investigated. In the present investigation the nanosize magnetite particles were synthesised without using the Fe(II) precursor. This was achieved by γ-irradiation of water-in-oil microemulsion containing only the Fe(III) precursor. The corresponding phase transformations were monitored. Microemulsions (pH 12.5) were γ-irradiated at a relatively high dose rate of 22 kGy/h. Upon 1 h of γ-irradiation the XRD pattern of the precipitate showed goethite and unidentified low-intensity peaks. Upon 6 h of γ-irradiation, reductive conditions were achieved and substoichiometric magnetite (Fe2.71O4) particles with insignificant amount of goethite particles found in the precipitate. Hydrated electrons , organic radicals and hydrogen gas as radiolytic products were responsible for the reductive dissolution of iron oxide in the microemulsion and the reduction Fe3+ → Fe2+. Upon 18 h of γ-irradiation the precipitate exhibited dual behaviour, it was a more oxidised product than the precipitate obtained after 6 h of γ-irradiation, but it contained magnetite particles in a more reduced form (Fe2.93O4). It was presumed that the reduction and oxidation processes existed as concurrent competitive processes in the microemulsion. After 18 h of γ-irradiation the pH of the medium shifted from the alkaline to the acidic range. The high dose rate of 22 kGy/h was directly responsible for this shift to the acidic range. At a slightly acidic pH a further reduction of Fe3+ → Fe2+ resulted in the formation of more stoichiometric magnetite particles, whereas the oxidation conditions in the acidic medium permitted the oxidation Fe2+ → Fe3+. The Fe3+ was much less soluble in the acidic medium and it hydrolysed and recrystallised as goethite. The γ-irradiation of the microemulsion for 25 h at a lower dose rate of 16 kGy/h produced pure substoichiometric nanosize magnetite particles of about 25 nm in size and with the stoichiometry of Fe2.83O4. 相似文献
Efficient white polymer light-emitting diodes based on the polymer blend of poly(2-(4′-(diphenylamino)phenylenevinyl)-1,4-phenylene-alt-9,9-n-dihexylfluorene-2,7-diyl) doped with poly{2-[3′,5′-bis(2?-ethylhexyloxy) benzyloxy]-1,4-phenylenevinylene}-co-poly(2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene) were fabricated. The electroluminescence (EL) spectrum is easily controlled by changing the dopant concentration. A white light emission was realized on the device with the dopant concentration of 0.194‰ and the emission light is less sensitive to the applied voltage in a wide voltage range. The maximum luminance and the maximum EL efficiency of the single-layer device were 2330 cd/m2 and 0.29 cd/A, respectively. By introducing an Alq3 layer as an electron transporting and hole blocking layer, the overall performance of the double layer device was dramatically improved, the maximum luminance and the maximum EL efficiency reached 3300 cd/m2 and 2.37 cd/A, respectively. 相似文献
In this preview we consider implications from the recent AGILE γ-ray detection of the BL Lac 0716+714 in September–October 2007, marked by two intense flaring episodes reaching peak fluxes of 200×10−8 photons cm−2 s−1 in the energy range 0.1–10 GeV. The source shows no evidence of emission lines or disk radiation, related to any surrounding gas; its pure non-thermal radiation is effectively represented in terms of the synchrotron-self Compton radiation in the Thomson regime, also supported by the observed quadratic relation of the γ-ray to the X-ray flux variations. With source parameters so derived, we find a total jet power of about 4×1045 erg s−1, that makes 0716+714 one of the brightest gas-poor BL Lacs so far detected at γ-ray energies. Thus it provides an ideal benchmark to compare its intrinsic luminosity with the top power extractable from a maximally rotating black-hole via the Blandford–Znajek mechanism. With a mass close to 5×108M for the associated BH, we find the source to remain close to the Blandford–Znajek threshold during the flare. Other gas-poor but weaker BL Lacs remain well below the threshold. These findings and those expected from FERMI will provide a powerful test of GR at work. 相似文献
In this research, β-CaSiO3 particles were surface modified with dodecyl alcohol, and Poly-(DL-lactic acid) (PDLLA)/modified β-CaSiO3 composite films were fabricated with a homogenous dispersion of β-CaSiO3 particles in the PDLLA matrix. The aim of the study was to investigate the properties of the composite films before and after hydrolytic treatment. SEM images showed retained homogenous dispersion of β-CaSiO3 particles after hydrolysis and tensile test also showed maintained mechanical property. Simulated body fluid (SBF) incubation experiment suggested that hydrolytic treatment did not affect the formation of hydroxyapatite on the surface of the composite films. The hydrophilicity of the composites was greatly recovered (from 69.82° to 50.28°) after hydrolysis. In addition, cells cultured on composite films after hydrolysis presented the highest cell proliferation rate and differentiation level. All of these results suggested that the surface modification of silicate particles with dodecyl alcohol along with reversible hydrolytic treatment was an effective and feasible approach to fabricate polymer/silicate composite materials with improved properties. 相似文献