Mathematics and Physics : [477]

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Collection's Items (Sorted by Submit Date in Descending order): 1 to 20 of 477
  • item.jpg
  • Article


  • Authors: Pham, Van Thu (2018)

  • This paper presents the investigation on the buckling of three-phase orthotropic composite plates used in shipbuilding subjected to mechanical loads by analytical approach. The basic equations are established based on the Classical Plate Theory. The analytical method is used to obtain the expressions of critical loads of the three-phase composite plate. The results in the article are compared to the results obtained by other authors to validate the reliability of the present method. The approach in this direction is for. The effects of fiber and particle volume fraction, material and geometrical parameters on the critical load of three-phase composite plates are discussed in detail.

  • item.jpg
  • Article


  • Authors: Pham, Thi Linh (2018)

  • In this paper, the index-1 notion for arbitrarily switched discrete-time linear singular systems (SDLS) has been introduced. Based on the Bohl exponents of SDLS as well as properties of associated positive switched systems, some necessary and sufficient conditions have been established for exponential stability.

  • item.jpg
  • Article


  • Authors: Nguyen, Thi Yen Mai; Nguyen, Thi Ha (2018)

  • Copper nanodisks (Cu NDs) of 50 nm were prepared on square-inch anodic aluminum oxide substrates by sputtering method. The samples were annealed at 450oC, then the walls of AAO substrates were lift off in a solution of acid phosphoric. The 2D arrays of Cu NDs were fabricated in high quality. Morphology of the substrates were observed by scanning electron microscopy. Surface plasmon resonance absorption was observed with different peaks in the range of 400-1400nm wavelengths that means the substrate is promising for SERS application. To demonstrate, we observed Raman spectrum of Rhodamine 6G using the enhancement effect of the substrate.

  • item.jpg
  • Article


  • Authors: Pham, Quoc Trieu; Hoang, Nam Nhat (2018)

  • The year 2019 marks 45 years in the development of Deep Level Transient Spectroscopy (DLTS) - the signal processing method for determination of overalpping deep levels in semiconductors. From its introduction in 1974 by David Lang (D.V. Lang, J. Appl. Phys. 45, 1974, p.3023) to this date the DLTS method has undergone many changes and modifications: some were purely theoretical speculations, some were to also include new experimental arrangement and technique. This paper provides almost complete review on DLTS, focusing on the main three approaches widely used today. We also summarize the development of this method in the Faculty of Physics, VNU-Hanoi University of Sciences

  • item.jpg
  • Article


  • Authors: Bui, Thi Hang (2018)

  • Fe2O3@C material was prepared by one-step hydrothermal method for use as a negative electrode in an iron-air battery. The structure of Fe2O3@C was determined by X-ray diffraction (XRD) measurement while their morphology was observed by scanning electron microscopy (SEM). The electrochemical properties of the Fe2O3@C electrode in alkaline solution were investigated using cyclic voltammetry (CV) measurement. The results showed that Fe2O3@C material with α-Fe2O3 structure and amorphous carbon were successfully synthesized by one-step hydrothermal method. CV measurements indicate that the redox reaction rate of the Fe2O3@C electrode is higher than that of the Fe2O3@AB electrode using comm...

  • item.jpg
  • Article


  • Authors: Mai, Thi Lan; Tran, Thu Thuy; Le, Thi Hong Lien; Le, Van Vinh (2018)

  • We have studied structure of silica glass at different pressures and temperature of 300K by using Molecular Dynamics simulation (MD) method. The model consists of 6000 atoms (2000 Si, 4000 O atoms) with the periodic boundary condition. We applied the Morse-Stretch potentials which describe the pairwise interactions between ions for SiO2 system. There is structural phase transformation from tetrahedra (SiO4) to octahedra (SiO6) network structure. There is splitting in the Si-Si pair radial distribution function (PRDF) at high pressure (100 GPa). The original of this splitting relates to the edge- and face-sharing bonds. The new second peak of the O-O PRDF at the high pressure originate...

  • item.jpg
  • Article


  • Authors: Vu, Thi Hoai Huong; Dao, Thi Thuy Nguyet; Nguyen, Phuc Duong (2018)

  • This study examines the effect of substituted concentration on the structure and magnetic properties of Y3Fe5-xInxO12 (x = 0.1 ÷ 0.7) powder samples prepared using the sol-gel method. The morphological properties of the samples were analysed using XRD, SEM. The single phase of garnet was obtained in x = 0.1 ÷ 0.6 samples. The lattice parameters of the samples exhibit a linear increase with the increasing In3+ content, which can be explained by a substitution of In3+ ions for Fe3+ ions, considering the larger ionic radius of In3+ compared with that of Fe3+. Crystallite sizes were determined via the XRD data which are of 38 – 49 nm while the particle sizes were estimated from SEM images...

  • item.jpg
  • Article


  • Authors: Dinh, Khac Huy; Nguyen, Phuc Duong; To, Thanh Loan; Hoang, Manh Chung; Nguyen, Kim Thanh; Vu, Van Khai (2018)

  • NiFe2O4/ZnO core-shell nanocomposites were prepared by two-step methodology. First, NiFe2O4 nanoparticles as the cores were synthesized by using hydrothermal method, and then modified by sodium citrate. After that ZnO as the shell was coated on modified NiFe2O4 nanoparticles by two different chemical methods including hydrothermal and co-precipitation. The formation, crystal structure, morphology and magnetic properties of the uncoated and coated samples were investigated by using X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy and vibrating sample magnetometer. It was shown that the core nanoparticles are single phase of NiFe2O4 with cubic spi...

  • item.jpg
  • Article


  • Authors: Nguyen, Thi Thanh Ha; Phan, Quan; Tran, Van Hong; Le, Van Vinh (2018)

  • We perform a molecular dynamics simulation to study the microstructure and dynamical properties in large silica model at liquid state. The models consisting of 19998 atoms were constructed under a wide range of pressure (0-20 GPa) and at 3500K temperature. Structural characteristics were clarified through the pair radial distribution function (PRDF), the distribution of SiOx coordination units and network structure. The result shows that these liquids consist of identical units SiO4, SiO5 and SiO6 and have common partial O―Si―O angle distribution. Furthermore, the major change in the diffusion mechanism under pressure is also considered and discussed

  • item.jpg
  • Article


  • Authors: Luong, Duy Thanh (2018)

  • A model for the effective excess charge in a capillary as well as in porous media is developed for arbitrary pore scales. The prediction of the model is then compared with another published model that is limited for a thin electric double layer (EDL) assumption. The comparison shows that there is a deviation between two models depending on the ratio of capillary/pore radius and the Debye length. The reasons for the deviation between two models are not only due to the thin EDL assumption to get electrical potential and charge distribution in pores but also to some other approximations for integral evaluations. The results suggest that the model developed in this work can be used...

  • item.jpg
  • Article


  • Authors: Le, Nhu Thuc (2018)

  • The change in other two fermion processes is called Bhabha process. In this paper, we discuss the Bhabha process e e e e   in the Randall –Sundrum (RS). We caculated the cross section for photon , boson Z, radion and Higgs h exchange and evaluated exchange contributions of the Bhabha process in detail.

  • item.jpg
  • Article


  • 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.

  • item.jpg
  • Article


  • 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

  • item.jpg
  • Article


  • 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

  • item.jpg
  • Article


  • 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.

  • item.jpg
  • Article


  • 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.

  • item.jpg
  • Article


  • 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...

  • item.jpg
  • Article


  • 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.

Collection's Items (Sorted by Submit Date in Descending order): 1 to 20 of 477

Mathematics and Physics : [477]

Follow this collection to receive daily e-mail notification of new additions
Collection's Items (Sorted by Submit Date in Descending order): 1 to 20 of 477
  • item.jpg
  • Article


  • Authors: Pham, Van Thu (2018)

  • This paper presents the investigation on the buckling of three-phase orthotropic composite plates used in shipbuilding subjected to mechanical loads by analytical approach. The basic equations are established based on the Classical Plate Theory. The analytical method is used to obtain the expressions of critical loads of the three-phase composite plate. The results in the article are compared to the results obtained by other authors to validate the reliability of the present method. The approach in this direction is for. The effects of fiber and particle volume fraction, material and geometrical parameters on the critical load of three-phase composite plates are discussed in detail.

  • item.jpg
  • Article


  • Authors: Pham, Thi Linh (2018)

  • In this paper, the index-1 notion for arbitrarily switched discrete-time linear singular systems (SDLS) has been introduced. Based on the Bohl exponents of SDLS as well as properties of associated positive switched systems, some necessary and sufficient conditions have been established for exponential stability.

  • item.jpg
  • Article


  • Authors: Nguyen, Thi Yen Mai; Nguyen, Thi Ha (2018)

  • Copper nanodisks (Cu NDs) of 50 nm were prepared on square-inch anodic aluminum oxide substrates by sputtering method. The samples were annealed at 450oC, then the walls of AAO substrates were lift off in a solution of acid phosphoric. The 2D arrays of Cu NDs were fabricated in high quality. Morphology of the substrates were observed by scanning electron microscopy. Surface plasmon resonance absorption was observed with different peaks in the range of 400-1400nm wavelengths that means the substrate is promising for SERS application. To demonstrate, we observed Raman spectrum of Rhodamine 6G using the enhancement effect of the substrate.

  • item.jpg
  • Article


  • Authors: Pham, Quoc Trieu; Hoang, Nam Nhat (2018)

  • The year 2019 marks 45 years in the development of Deep Level Transient Spectroscopy (DLTS) - the signal processing method for determination of overalpping deep levels in semiconductors. From its introduction in 1974 by David Lang (D.V. Lang, J. Appl. Phys. 45, 1974, p.3023) to this date the DLTS method has undergone many changes and modifications: some were purely theoretical speculations, some were to also include new experimental arrangement and technique. This paper provides almost complete review on DLTS, focusing on the main three approaches widely used today. We also summarize the development of this method in the Faculty of Physics, VNU-Hanoi University of Sciences

  • item.jpg
  • Article


  • Authors: Bui, Thi Hang (2018)

  • Fe2O3@C material was prepared by one-step hydrothermal method for use as a negative electrode in an iron-air battery. The structure of Fe2O3@C was determined by X-ray diffraction (XRD) measurement while their morphology was observed by scanning electron microscopy (SEM). The electrochemical properties of the Fe2O3@C electrode in alkaline solution were investigated using cyclic voltammetry (CV) measurement. The results showed that Fe2O3@C material with α-Fe2O3 structure and amorphous carbon were successfully synthesized by one-step hydrothermal method. CV measurements indicate that the redox reaction rate of the Fe2O3@C electrode is higher than that of the Fe2O3@AB electrode using comm...

  • item.jpg
  • Article


  • Authors: Mai, Thi Lan; Tran, Thu Thuy; Le, Thi Hong Lien; Le, Van Vinh (2018)

  • We have studied structure of silica glass at different pressures and temperature of 300K by using Molecular Dynamics simulation (MD) method. The model consists of 6000 atoms (2000 Si, 4000 O atoms) with the periodic boundary condition. We applied the Morse-Stretch potentials which describe the pairwise interactions between ions for SiO2 system. There is structural phase transformation from tetrahedra (SiO4) to octahedra (SiO6) network structure. There is splitting in the Si-Si pair radial distribution function (PRDF) at high pressure (100 GPa). The original of this splitting relates to the edge- and face-sharing bonds. The new second peak of the O-O PRDF at the high pressure originate...

  • item.jpg
  • Article


  • Authors: Vu, Thi Hoai Huong; Dao, Thi Thuy Nguyet; Nguyen, Phuc Duong (2018)

  • This study examines the effect of substituted concentration on the structure and magnetic properties of Y3Fe5-xInxO12 (x = 0.1 ÷ 0.7) powder samples prepared using the sol-gel method. The morphological properties of the samples were analysed using XRD, SEM. The single phase of garnet was obtained in x = 0.1 ÷ 0.6 samples. The lattice parameters of the samples exhibit a linear increase with the increasing In3+ content, which can be explained by a substitution of In3+ ions for Fe3+ ions, considering the larger ionic radius of In3+ compared with that of Fe3+. Crystallite sizes were determined via the XRD data which are of 38 – 49 nm while the particle sizes were estimated from SEM images...

  • item.jpg
  • Article


  • Authors: Dinh, Khac Huy; Nguyen, Phuc Duong; To, Thanh Loan; Hoang, Manh Chung; Nguyen, Kim Thanh; Vu, Van Khai (2018)

  • NiFe2O4/ZnO core-shell nanocomposites were prepared by two-step methodology. First, NiFe2O4 nanoparticles as the cores were synthesized by using hydrothermal method, and then modified by sodium citrate. After that ZnO as the shell was coated on modified NiFe2O4 nanoparticles by two different chemical methods including hydrothermal and co-precipitation. The formation, crystal structure, morphology and magnetic properties of the uncoated and coated samples were investigated by using X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy and vibrating sample magnetometer. It was shown that the core nanoparticles are single phase of NiFe2O4 with cubic spi...

  • item.jpg
  • Article


  • Authors: Nguyen, Thi Thanh Ha; Phan, Quan; Tran, Van Hong; Le, Van Vinh (2018)

  • We perform a molecular dynamics simulation to study the microstructure and dynamical properties in large silica model at liquid state. The models consisting of 19998 atoms were constructed under a wide range of pressure (0-20 GPa) and at 3500K temperature. Structural characteristics were clarified through the pair radial distribution function (PRDF), the distribution of SiOx coordination units and network structure. The result shows that these liquids consist of identical units SiO4, SiO5 and SiO6 and have common partial O―Si―O angle distribution. Furthermore, the major change in the diffusion mechanism under pressure is also considered and discussed

  • item.jpg
  • Article


  • Authors: Luong, Duy Thanh (2018)

  • A model for the effective excess charge in a capillary as well as in porous media is developed for arbitrary pore scales. The prediction of the model is then compared with another published model that is limited for a thin electric double layer (EDL) assumption. The comparison shows that there is a deviation between two models depending on the ratio of capillary/pore radius and the Debye length. The reasons for the deviation between two models are not only due to the thin EDL assumption to get electrical potential and charge distribution in pores but also to some other approximations for integral evaluations. The results suggest that the model developed in this work can be used...

  • item.jpg
  • Article


  • Authors: Le, Nhu Thuc (2018)

  • The change in other two fermion processes is called Bhabha process. In this paper, we discuss the Bhabha process e e e e   in the Randall –Sundrum (RS). We caculated the cross section for photon , boson Z, radion and Higgs h exchange and evaluated exchange contributions of the Bhabha process in detail.

  • item.jpg
  • Article


  • 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.

  • item.jpg
  • Article


  • 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

  • item.jpg
  • Article


  • 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

  • item.jpg
  • Article


  • 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.

  • item.jpg
  • Article


  • 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.

  • item.jpg
  • Article


  • 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...

  • item.jpg
  • Article


  • 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.

Collection's Items (Sorted by Submit Date in Descending order): 1 to 20 of 477