57 số bộ dữ liệu tìm thấy

Định dạng: Word

Kết quả lọc
  • USING THE DIRECTIONAL ANALYTIC SIGNALS OF MAGNETIC GRADIENT TENSOR TO DETERMINE BOUNDARIES OF SOURCE

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    The analytic signals of the magnetic tensor gradient in two- and three-dimensional space domain can be applied as a useful tool to estimate the depth and position of magnetic sources because their values only depend on location but magnetization direction of the sources of the magnetic anomaly. In this paper, we present results of the study for application of the combination of derivatives of directional analytic signals of the magnetic tensor gradient and maximum horizontal gradient to determine the edges of the sources through the Edge-Detector function (|ED|). Algorithms and programs written in the Matlab language have been used for testing the calculation on 3D models in correlative comparison with the method using the amplitude function of analytic signals. The calculation results showed the advantages of the |ED| function and its applicability in determing the boundaries of sources of magnetic anomaly.
  • On the Perron Effect for Exponential Stability of Differential Systems on Time Scales

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    In 2007, N. H. Du and L. H. Tien [1] shown that the exponential stability of the linear equation on time scales implies the exponential stability of the suitable small enough Lipchitz perturbed equation. In this paper, we shall prove that if the perturbation is arbitrary small order 1 then the above argument is not true which is called Perron effect.
  • AN OPPORTUNITY FOR STUDY OF MULTI-NUCLEON TRANSFER VIA 26Mg+238UAT JAEA

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    Our understanding of fission mechanism has been still limited up to date, especially, formass distribution of heavy nuclei or actinide ones. Since the heavy isotopes on theneutron-rich side of the nuclear chart cannot be accessed via capture reactions, it is thought that the mechanism can be studied via compound nuclei produced by multi-nucleon transfer reactions. A set up to measure fission properties of such compound nucleiwas developed at Japan Atomic Energy Agency. In this report we mention roles of the transfer reaction26Mg+238U and an experimental plan using the set up at JAEA tandem facility.
  • SURVEY STRUCTURES AND PHOTOLUMINESCENCE EMISSION OF ZnS MICROCRYSTALS GROWN BY THERMAL DEPOSITION

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    In this work, we report on the controlled synthesis of ZnS microstructures with high purity on Au-coated silicon substrates by thermal evaporation of ZnS powder in Ar gas ambient at atmospheric pressure. The growth mechanism is confirmed as a typical vapor–liquid–solid (VLS) process. The prepared ZnS microstructures have wurtzite (hexagonal) structures. The catalytically grown ZnS microstructures, including microwires and microbelts, are tens of micrometers in length. Energy-Dispersive X-Ray Spectroscopy [EDS] shows that the oxygen composition in the microstructures is trivial. The photoluminescence spectrum reveals strong ultraviolet emission and no other emission at room temperature also demonstrates that the ZnS microstructures are of high crystalline perfection. Optical transition from free exciton A, free exciton B are observed and analyzed through power-dependent at 10 K and temperature-dependent photoluminescence spectroscopy measurements are performed from 10 to 300 K. Our results indicate that ZnS microstructures grown by thermal evaporation, suggesting a great promise for high-efficiency light-emitting devices and lasers in the UV region.
  • Microstructural and dynamical heterogeneitycharacteristics in Al2O3- 2SiO2 liquid

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    In this paper the structural and dynamical characteristics in alumina- silicate Al2O3–2SiO2 (AS2) liquid are investigated by molecular simulation method. Structural properties are clarified through the pair radial distribution function, distribution of TOn(T= Si, Al) coordination units and distribution of partial bond angle in TOn. Furthermore the change in diffusion mechanism between low and high pressure is revealed by transition of the structural units TOx → TOx±1. At the low-pressure,liquid AS2 exhibits the dynamics heterogeneity (DH). The origin of dynamic heterogeneity is identified and liquid AS2 consists of separate mobile and immobile regions.
  • Effect of hydrothermal time on the growth of ZnO nanorods on Printed Circuit Board substrates

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    We report the direct growth of high-quality, high-density and well-aligned ZnO nanorods on cost-effective printed circuit board substrates (PCBs)by a seedless hydrothermal method. It was shown that byimplementing a galvanic cell structure in a saturated aqueous solution of zincnitrate hexahydrate (Zn[NO3]2•6H2O) and hexamethylenetetramine (C6H12N4), it can support the vertical grown of ZnO and significantly reduce the hydrothermal time. The effect of hydrothermal time on the surface morphology and the crystallinity of the synthesized ZnO nanorods werestudiedand discussed to clarify the growing mechanism of ZnO NRs by usingscanning electron microscopy (SEM), X-ray diffraction (XRD), Raman, and photoluminescence spectroscopy (PL).
  • Optical properties of PbS and Au-PbS Core-Shell Nanoparticles

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    Lead sulfide (PbS)and Au-PbS core-shell nanoparticles were successfully synthesized using the sonochemical method at room temperature. The morphology of the synthesized particles was characterized by FESEM and TEM images. Pure fcc phase of PbS and Au crystal structures was examined and confirmed by XRD patterns. The quantum confinement effect plays a crucial role in blue-shifting the absorption edge and the band gap energy of both solid PbS nanoparticles and a thin spherical PbS shell toward shorter wavelength region in comparison to those of PbS bulk.Due to the high refractive index of PbS shell, Surface Plasmon Resonance (SPR) peak of Au nanocores is significantly red-shifted by roughly 80 nm toward the longer wavelength region. More sophisticate experimental data and some adequate theoretical models are needed to fully explain the matters.
  • Synthesis and Optical Properties of Cu2O and Au-Cu2O core-shell particles

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    Cuprous oxide (Cu2O) and Au-Cu2O core-shell nanoparticles were successfully synthesized using the chemical reduction method. The morphology of the synthesized pure Cu2Oparticles can be controlled by varying the amount of reducing agent NH2OH.HCl. Due to their similar crystal structure and relatively small lattice mismatch Cu2O particles are nucleated and locally undergo an epitaxial growth on the surface of the multi-faceted Au seed resulting in a stellated icosahedra Au-Cu2O core-shell particle. The extinction spectrum of Cu2O particles offew hundred-nm in size is dominated by light scattering, while that of the stellated icosahedra Au-Cu2O core-shell particles exhibits the interband absorption of the Cu2O shell only. The interband absorption peak undergoes a blue shift as the shell gets thinner. No prominent SPR of the Au nanocore was observed due to a rather thick Cu2O shell.
  • Epitaxial-like growthof solution-processed PbZr0.4Ti0.6O3 thin film on single-crystal Nb-doped SrTiO3 substrate

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    PbZr0.4Ti0.6O3 (PZT) thin films have been conventionally fabricated on traditional silicon substrates with a platinum bottom electrode; however, as a consequence of unit cell mismatch,the films are difficult to form as an epitaxial-like growth. Hence, PZT films deposited on single-crystal niobium doped SrTiO3(111) substrates (Nb:STO) are promising to solve this issue thanks to the similar perovskite structure between PZT and STO. Essentially, Nb:STO material is a conductor, playing a part in bothbottom electrode andepitaxial substrate. In this work, 200-nm-thick PZT films were successfully fabricated on Nb:STO substrates by a solution process.One obtained thatPZT(111) peak started to appear on the Nb:STO substrate at a low annealing temperature of 450oC. Also, scanning electron microscopy observation showssmooth and homogeneous surface of PZT films on Nb:STO substrate with no grain boundary, which evidences for epitaxial-like growth of PZT thin films. Remnant polarization of 6µC/cm2 and leakage current of 8×10-8 A were obtained at applied voltage of 5 V.
  • PHOTOLUMINESCENCE EMISSION OF Cu DOPED ZnS MICROSTRUCTURES SYNTHESIZED BY THERMAL EVAPORATION

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    Cu doped ZnS microstructures were prepared by the thermal evaporation method using ZnS powder and CuCl2.2H2O powder as precusor materials. The microstructures was characterized by using X-ray diffraction (XRD) analysis. The XRD studies indicated that there are two phases (ZnS and ZnO) at the undoped sample, but most of the samples are only having wurtzite (hexagonal) phase of ZnS after doping. The photoluminescence emission and photoluminescence excitation of ZnS and Cu2+ doped ZnS microstructures have been studied. The photoluminescence excitation spectra of ZnS microstructures is presented around 374 nm. By doping of Cu2+ ion, the absorption wavelength is shifted towards the lower wavelength being an evidence for an increasing band gap. The emission spectrum of pure ZnS has a green emission band centred at around 520 nm. By doping Cu2+ ion, the peak of the green band in the luminescence spectra were transferred to 516 nm and appeared a strong blue peak at 440 nm. The reasons of these will be discussed in this paper.
  • Synthesis and optical properties of ZnAl2O4/Al2O3 - Cr3+ composite materials

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    Zinc aluminate - alumina (ZnAl2O4/Al2O3) systems doped with Cr3+ different concentrations were synthesized by sol-gel method. The samples were characterized by X-ray diffraction (XRD), photoluminescence (PL) and photoluminescence excitation (PLE) spectra. The results showed that Cr3+ dopant concentration had a significant effect on the lattice constants of ZnAl2O4/Al2O3 composite and their luminescence characteristics. When increasing Cr3+ contents, the lattice constants of both the ZnAl2O4 and α-Al2O3 crystals increase. For the samples with low Cr3+ dopant concentrations, the PL spectra mainly consist of sharp lines assigned to the 2E(2G)→4A2(4F) transitions of Cr3+ ions located in strong octahedral field of the ZnAl2O4 and α-Al2O3 crystals. With increasing Cr3+ concentration, in the PL spectra appears very broad emission band in the long-wavelength side, which originates from the 4T2(4F)→4A2(4F) transitions within the Cr3+ ions located in the weak octahedral sites of the ZnAl2O4 and α-Al2O3 crystals.
  • High-pressure EXAFS Debye-Waller factors of metals

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    The anharmonic correlated Debye model has been developed to investigate the pressure effects on the extended X-ray absorption fine structure (EXAFS) Debye-Waller factors of metals. The recent well-established Grüneisen parameter expressions have been applied to formulate the pressure-dependent analytical expressions of the effective spring constant, correlated Debye frequency and temperature. Combing with the anharmonic correlated Debye model, the expression of EXAFS Debye–Waller factor under pressure can be derived. Numerical calculations, performed for Fe and Cu metals show reasonable agreement with experiments.
  • First-principles Calculations on Electronic Properties of LaNiO3 in Solid Oxide Fuel Cell Cathodes

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    First-principles calculations based on the density functional theory are used to study the electronic structure of LaNiO3 perovskite for application of cathode material in solid oxide fuel cell. Our results show that bulk LaNiO3 exhibits metallic behavior. For 1x1x1 LaNiO3 unit cell, increasing in-plane strain leads to the increase in the density of states (DOS) at the Fermi level. On the other hand, the DOS at the Fermi level for 2x2x2 LaNiO3 supercell first increases with the strain up to 3% and then decreases for larger values of the strain. The difference between the electronic structure of the 2x2x2 supercell and that of the 1x1x1 unit cell is attributed to the rotations of NiO6 octahedra.
  • Synthesis, Magnetic Properties and Enhanced Photoluminescence of Fe3O4-ZnO Heterostructure Multifunc Nanoparticles

    2 Resources
    In this paper, Fe3O4-ZnO heterostructure multifunctional nanoparticles (NPs) were successfully prepared in aqueous solution by ultrasound assisted thermolysis. First, iron oxide (Fe3O4) magnetic NPs were prepared by co-precipitation method. The Fe3O4 NPs were modified by 3-aminopropyltriethoxysilane (APTES) to have free amine (-NH2) groups on their surface, then, Zn2+ ions were added and stirred to adsorb onto the surface of Fe3O4-NH2 NPs in alkaline solution at a pH of 11. This solution was decomposed through thermolysis in ultrasound bath. The results of measurements show that photoluminescence of Fe3O4-ZnO heterostructure multifunctional NPs was enhanced in visible light at 565 nm wavelength to allow detection, labeling, diagnosis, and therapy in biomedicine. Moreover, they exhibit superparamagnetic properties of Fe3O4 with high saturation magnetization (MS), which can be used for seperation application in biomedicine under an external magnetic field.
  • INVESTIGATION OF MAGNETO-PHONON RESONANCE IN GRAPHENE MONOLAYERS

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    In this work, utilising the linear response theory we calculate the magneto conductivity (MC) in graphene monolayers, subjected to a static perpendicular magnetic field. The interaction of Dirac fermions with optical phonon via deformation potential is taken into account at high temperature. The dependence of the MC on the magnetic field shows resonant peaks that describe transitions of electrons between Landau levels via the resonant scattering with optical phonons. The effect of temperature on the MC is also obtained and discussed.
  • Bounded generalized random linear operators

    1 Resources
    In this paper we are concerned with bounded generalized random linear operators. It is shown that each bounded generalized random linear operator can be seen as a set-valued random variable. The prop¬erties of some special bounded generalized random linear operators and the random resolvent set of generalized random linear operators are in-vestigated.
  • ANALYSIS OF HEAT TRANSFER IN THE VVER-1200 REACTOR’S HEAT CHANNEL

    1 Resources
    In early 2015, the Government of Vietname has decided to choose VVER-1200 Russian-made technology for building at the Nuclear Power Plant in Ninh Thuan 1, this is the advanced reactor generation III + and the only one has been completed for the first time in the world in August 2016. Vietnam is facing a major challenge, which is how to ensure the acquired technology transfer process, then the safe operation of thisunit. This article analyzes some of the heat changes occur in reactor when there are changes of the heatflux. This is an issue directly related to the workof predictingincidents and give ways to fix the problem when the plant is in conditions such as startup, normal and abnormaloperations.For analysis, the authors used CFD methods, this is a very modern method and have high reliability. The results received have fit well when compared with the safety analysis report of Rosatom published.
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