Collection's Items (Sorted by Submit Date in Descending order): 1 to 20 of 465
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Authors: Vu, Duc Minh; Do, Anh Chung (2018) - The Advanced Multi-electrode Electrical Sounding method (AMES) proposed by us was introduced at VNU. Journal of Mathematics-Physics, No. 31 (3), 2015. However, the published results are mostly focused on the symmetric MC array and tested on a theoretical model. In this paper, the authors continue systematically presenting and supplementing the results obtained after the study, namely the finalization and renaming of the AMES method into the Advanced 2D Multi-electrode Electrical Exploration (AMEE) method, including MC array, data collecting and processing, and testing on theoretical model and practical application to confirm the superiority of this method.
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Authors: Hoang, Nam Nhat (2018) - Point defects in semiconductors cause many considerable behaviours of these materials. This article introduces a procedure for modelling of point defects using a structural approach often referred to as a bond-valence method. This method minimalizes the computation cost and facilitates a contruction of complex 3D images illustrating the point defects, including the charge distribution map at contact interfaces. This method also provides a convenient way to estimate the carrier density and defect locations, it visualizes a dynamics of valence relocation under thermal fluctuation
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Authors: Hoang, Nam Nhat (2018) - Point defects in semiconductors cause many considerable behaviours of these materials. This article introduces a procedure for modelling of point defects using a structural approach often referred to as a bond-valence method. This method minimalizes the computation cost and facilitates a contruction of complex 3D images illustrating the point defects, including the charge distribution map at contact interfaces. This method also provides a convenient way to estimate the carrier density and defect locations, it visualizes a dynamics of valence relocation under thermal fluctuation
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Authors: Nguyen, Thu Ha (2018) - This paper is concerned with the Bolh-Perron theorem for differential algebraic equations. We prove that the system
E(t)x'(t)=B(t)x(t), t > t0
is exponentially stable if and only if for any bounded input q, the equation
E(t)x'(t)=B(t)x(t)+q(t), t > t0
has a bounded solution.
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Authors: Phan, Van Do (2018) - Lead sodium telluroborate (LSTB) glasses doped with different concentrations of Sm3+ ions were prepared by melting method. The excitation, emission spectra and lifetimes of LSTB:Sm3+ have been investigated. The quenching of luminescence intensity happens after 0.75 mol% concentration of Sm3+ ions. The non-exponential decay curves are fitted to the Inokuti and Hirayama model to give the energy transfer parameters between Sm3+ ions. The dominant interaction mechanism for energy transfer process is dipole–dipole interaction. The energy transfer probability (WDA) increases whereas lifetime (τexp) decreases with the increase of Sm3+ concentration in glass.
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Authors: Pham, Thi Hong; Nguyen, Viet Tuyen; Tran, Thi Ha (2018) - Cu2ZnSnS4 (CZTS) is a p-type semiconductor with high absorption coefficient and direct bandgap from 1 to 1.5 eV, which is ideal for making absorber layer for solar cell. However, it is difficult to get single phase of CZTS due to the competitive formation of binary and ternary secondary phases. In this paper, we prepared CZTS nanoparticles by hydrothermal method and investigate the influence of hydrothermal temperature on the product. Raman scattering, X-ray diffraction, scanning electron microcopy, energy dispersive X-ray spectroscopy and diffusion reflective measurement were applied to characterize the products. The products are high quality nanocrystals of kesterite phase with unif...
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Authors: Nguyen, Van Thu; Luong, Thi Theu (2018) - The finite size effect causes many interesting behaviors in properties of a weakly interacting Bose gas. These behaviors were considered in one-loop approximation of quantum field theory. In this paper the influence is investigated in improved Hatree-Fock approximation, which gives more accurate results.
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Authors: Ha, Thanh Tung; Nguyen, Cong Hau; Nguyen, Tan Phat; Lam, Quang Vinh (2018) - In this study, we have prepared and investigated the optical properties of the TiO2/CdS:Mn2+/CdSe photoanode as the function of Mn2+ doping concentration and thickness. The results show that the peaks of the UV-Vis spectra shifted toward longer wavelength while Mn2+ doping concentrations or thickness of the films were changed. The main cause of the red-shifting in UV-Vis spectra may come from the increasing of photoanode light-harvesting capacity. In addition, the results also demonstrated by the boosting performance of quantum dots sensitized solar cells from 2.07% for TiO2/CdS/CdSe photoanode to 2.5% for TiO2/CdS:Mn2+/CdSe photoanode.
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Authors: Le, Quang Thao; Dinh, Thi Hai; Tran, Thanh Ha (2018) - This paper presents a low cost Wireless Sensor Network using TCP/IP to use Ethernet configuration and hybrid networks to extend range or improve connectivity in distant areas, in particular is agriculture. The system is designed with soil moisture sensor based on Atmega8L and Nordic nRF24L01 to monitor environmental parameter. Moreover, to make data available globally, we have connected the wireless sensor network to GSM/GPRS. The system not only uses a low power but also has a compact size and applies advantages of TCP/IP
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Authors: Trinh, Thi Loan; Nguyen, Ngoc Long (2018) - Anatase TiO2 powders doped with different amounts of Cu2+ ions (0, 0.5, 1.0 and 4 mol%) were successfully synthesized by sol-gel method from precursors of TiCl4, (CH3COO)2Cu. Effect of Cu2+ concentrations on the structural and optical properties of TiO2 host was investigated by X-ray diffraction, Raman spectroscopy and diffuse reflection spectroscopy. The XRD analysis showed that the doped samples exhibit anatase single phase at annealing temperature 600 oC. The Cu2+ contents did not affect on the lattice of TiO2 hot, but affected on positions of these Raman modes. The band gap of the TiO2:Cu2+ was decreased with the increase of doping concentration.
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Authors: Leuangtakoun, Somsavath; Bui, Thi Hong; Bui, Van Loat; Phan, Viet Cuong (2018) - This paper presented the method of determining the radioactivity of 40K, 226Ra and 232Th in soil samples by gamma-ray spectrometer using NaI (Tl) scintillation detector. The radioactivity of each isotope is calculated based on the net count rate in the energy window characteristic for the 40K, 226Ra and 232Th radioisotopes respectively. We have determined activity concentrations of the natural radionuclides 226Ra,232Th and 40K in 15 soil samples collected around gold mines of Khamkeut district, Bolikhamxay Province, Laos. The average activity concentrations of the natural radionuclides 226Ra, 232Th and 40K are 46.58 ± 7.36 , 71.19 ± 5.42 and 574.62 ± 25.02 Bq.kg-1, respectively...
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Authors: Luong, Thi Kim Phuong (2018) - To enhance the photoluminescence effeciency of the Ge film, we can apply a tensile strain or n doping in the Ge epilayers for modifying it’s energy band gap structure. In this work, we combine both electron doping method from Sb source and inducing a tensile strain in Ge films. Sb doped Ge grown on Si(100) substrate by molecular beam epitaxy technique. The dependence of photoluminescence intensity on the substrate temperature in the range of 130-240oC and on the Sb source temperature from 240 to 300oC are investigated. The active electron concentration obtained up to 2.5x1019cm-3. The tensile strain level in the Sb-doped Ge epilayers is twice larger than that of the P-doped Ge films u...
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Authors: Luong, Duy Thanh (2018) - Theoretical models have been developed to calculate the zeta potential based on the solution of the linearized approximation of the Poisson-Boltzmann equation (PB). The approximation is only valid for the small magnitude of the surface potential. However, the surface potential available in published experimental data normally does not satisfy that condition. Therefore, the complete analytical solution to the PB equation (nonlinear equation) needs to be considered. In this work, the comparison between the linearized and nonlinear solutions has been performed. The results show that the linearized solution always overestimates the absolute value of the electric potential in the electric ...
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Authors: Nguyen, Van Nghia; Nguyen, Duy Hung (2018) - 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 w...
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Authors: Luong, Duy Thanh (2018) - Measurements of the zeta potential in sandpacks saturated with monovalent electrolytes at six different electrolyte concentrations have been reported. The values we record are classified into two groups based on the magnitude of the zeta potential: group 1 (samples S1 and S2) and group 2 (samples S3 and S4). The measured zeta potential in magnitude in group 1 is much smaller than that in group 2 and in literature at the same electrolyte concentration. The reason for a big variation of the zeta potential between group 1 and group 2 may be due to the difference in technique of making sand particles of different size leading to change of particle surface properties. Consequently, the zet...
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Authors: Ha, Phi (2018) - The stability analysis of linear time invariant delay differential- algebraic equations (DDAEs) is analyzed. Examples are delivered to demonstrate that the eigenvalue-based approach to analyze the exponential stability of dynamical systems is not valid for an arbitrarily high index system, and hence, a new concept of weak exponential stability (w.e.s) is proposed. Then, we characterize the w.e.s in term of a spectral condition for some special classes of DDAEs.
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Authors: Nguyen, Quang Hoa; Bui, Nguyen Quoc Trinh (2018) - Lanthanum nickel oxide LaNiO3 (LNO) isextensively known as one of typical perovskite-structured materials with metallic conductivity, which is suitable for the electrode application in electronic devices such as transistors or solar cells. Since LNO is a low-cost material and a simple fabrication process, it has been attracted much attention for commercialization. In this paper, we have focused on optimizing the fabrication process of LNO thin films on SiO2/Sisubstrate and Al foil by using asolution process. The crystal structure and surface morphology were characterized by using X-ray diffraction and field-emission scanning electron microscopy (FE-SEM), respectively. It was found tha...
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Authors: Bui, Thi Hang (2018) - To find the suitable materials for Fe/air battery anode, in this study Fe2O3 electrodes were prepared using Fe2O3 nanoparticles. The size and morphology of Fe2O3 material were observed by scanning electron microscope (SEM). The electrochemical properties of the Fe2O3 electrode in alkaline solution were investigated by using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The effects of K2S additive in electrolyte solution on the electrochemical characteristics of Fe2O3 electrodes were also investigated. The obtained results show that the additive strongly affected on the impedance, redox reaction rate and cyclability of Fe2O3 electrode
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Authors: Nguyen, Xuan Sang; Le, Phuoc Sang; Nguyen, Minh Quan; Nguyen, Huu Tho (2018) - Herein we study point defects and correlation to photoluminescence in ZnO nanorod. ZnO mirco/nanorod structure was successfully fabricated by co-precipitation method with highly homogeneous characteristics. When ion Mn+2 introduced into ZnO structure, the d-spacing distance of ZnO was increased from 0.248 nm to 0.295 nm due to the larger ionic radius of Mn2+ in comparison to Zn2+. The photoluminescence emission evolution of ZnO through doping and annealing processes hinted the relation of point defect transformations. We found that zinc interstitial, zinc vacancy and its related defects were responsible mainly for photoluminescence emission in annealing and/or Mn2+ doped samples.
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Authors: Ho, Thi Doan; Vuong, Van Hiep; Nguyen, Khac Thuan; Do, Thi Kim Anh (2018) - The TbTSn compounds (T = Pt, Rh) have been prepared by arc-melting in purified Ar atmosphere. Crystal structures were studied by X-ray powder diffraction. The Rietveld analysis shows the single phase in hexagonal ZrNiAl-type structure for TbPtSn and TbRhSn compounds. Magnetic properties and specific heat measured by mean of Physical Properties Measurement System (PPMS) demonstrated the phase magnetic transition at Néel temperature TN.
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Collection's Items (Sorted by Submit Date in Descending order): 1 to 20 of 465
