Pub Date : 2022-09-26DOI: 10.25073/2588-1124/vnumap.4733
Dang Thi Thanh Thuy, Lương Thị Thu Thủy
We have built the research model of the dual resonant frame parameter generator based on the actual circuit diagram implemented in the laboratory to evaluate the mechanism of the dual resonant frame, two-frequency generator. The dual resonant frame parameter oscillator produces the desired frequency w2 which depends on the pump frequency and frequency w1. On the basis of the research model, we have successfully tested the mechanism of the dual-frequency transmitter, which makes it possible to manufacture RF oscillators with low phase noise, thereby improving stability. The output frequency stability w2 depends on the stability of the pump frequency and the frequency w1. Keywords: dual resonant frame, parametric generator system, pump frequency
{"title":"Study of the Dual Resonant Frame Parametric Generator","authors":"Dang Thi Thanh Thuy, Lương Thị Thu Thủy","doi":"10.25073/2588-1124/vnumap.4733","DOIUrl":"https://doi.org/10.25073/2588-1124/vnumap.4733","url":null,"abstract":"We have built the research model of the dual resonant frame parameter generator based on the actual circuit diagram implemented in the laboratory to evaluate the mechanism of the dual resonant frame, two-frequency generator. The dual resonant frame parameter oscillator produces the desired frequency w2 which depends on the pump frequency and frequency w1. On the basis of the research model, we have successfully tested the mechanism of the dual-frequency transmitter, which makes it possible to manufacture RF oscillators with low phase noise, thereby improving stability. The output frequency stability w2 depends on the stability of the pump frequency and the frequency w1. \u0000Keywords: dual resonant frame, parametric generator system, pump frequency","PeriodicalId":303178,"journal":{"name":"VNU Journal of Science: Mathematics - Physics","volume":"11 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-09-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124673221","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-09-26DOI: 10.25073/2588-1124/vnumap.4738
Nguyen Thu Nhan, Mai Thi Lan, Nguyen Thi Nam
A molecular dynamics (MD) simulation has been carried out to explore the microstructure and diffusion pathway in amorphous vanadium pentoxide (V2O5) materials at room temperature and ambient pressure. We showed that the simulated model is a mix of basic units VO5 and VO6 connected to each other via 2 or 3 bridging oxygens. In the simulated model, there exist regions without atoms (cavity) in the form of clusters or channels. We found that 87% large pores, larger than or equal to oxygen atoms, overlap to form the largest tube. Keywords: Vanadium pentoxide, amorphous, pore.
{"title":"Molecular Dynamics Simulation of Amorphous Vanadium Pentoxide","authors":"Nguyen Thu Nhan, Mai Thi Lan, Nguyen Thi Nam","doi":"10.25073/2588-1124/vnumap.4738","DOIUrl":"https://doi.org/10.25073/2588-1124/vnumap.4738","url":null,"abstract":"A molecular dynamics (MD) simulation has been carried out to explore the microstructure and diffusion pathway in amorphous vanadium pentoxide (V2O5) materials at room temperature and ambient pressure. We showed that the simulated model is a mix of basic units VO5 and VO6 connected to each other via 2 or 3 bridging oxygens. In the simulated model, there exist regions without atoms (cavity) in the form of clusters or channels. We found that 87% large pores, larger than or equal to oxygen atoms, overlap to form the largest tube. \u0000Keywords: Vanadium pentoxide, amorphous, pore.","PeriodicalId":303178,"journal":{"name":"VNU Journal of Science: Mathematics - Physics","volume":"398 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-09-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116524767","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-09-26DOI: 10.25073/2588-1124/vnumap.4699
Nguyen Thi Thao, N. Ha, Le Van Vinh
Abstract: The molecular dynamics simulations have been used to study the microstructure as well as mechanical behavior of cubic silicon nitride (c-Si3N4) under the extended deformation. The silicon nitride sample was simulated under the cooling process and high pressure. At T=300 K, dominant nitrogen (N) atoms arrange into fcc lattice, and the rest of N atoms have hexagonal close-packed (hcp) and disordered structures. The hcp and disordered N atoms gather into the narrow bands. The phonon spectra of this sample are calculated and discussed. In this work we also present a molecular dynamics prediction for the elastic moduli in strained cubic silicon nitride as functions of the volumetric strain. Young’s modulus and Poisson’s ratio are also calculated for the c-Si3N4.
{"title":"Structural and Mechanical Properties of Cubic Silicon Nitride: A Molecular Dynamics Study","authors":"Nguyen Thi Thao, N. Ha, Le Van Vinh","doi":"10.25073/2588-1124/vnumap.4699","DOIUrl":"https://doi.org/10.25073/2588-1124/vnumap.4699","url":null,"abstract":"Abstract: The molecular dynamics simulations have been used to study the microstructure as well as mechanical behavior of cubic silicon nitride (c-Si3N4) under the extended deformation. The silicon nitride sample was simulated under the cooling process and high pressure. At T=300 K, dominant nitrogen (N) atoms arrange into fcc lattice, and the rest of N atoms have hexagonal close-packed (hcp) and disordered structures. The hcp and disordered N atoms gather into the narrow bands. The phonon spectra of this sample are calculated and discussed. In this work we also present a molecular dynamics prediction for the elastic moduli in strained cubic silicon nitride as functions of the volumetric strain. Young’s modulus and Poisson’s ratio are also calculated for the c-Si3N4. \u0000 ","PeriodicalId":303178,"journal":{"name":"VNU Journal of Science: Mathematics - Physics","volume":"72 2 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-09-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"134460703","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-09-26DOI: 10.25073/2588-1124/vnumap.4707
Tran Le Hung, Nguyen Dinh Duc
The dynamical responses of railway track has been carried out by different ways. In this work, by developing an analytical model for the ballasted railway track which includes two rails connected to the railway sleeper, a fast method to calculated the dynamic responses of the two rails is presented. The rail is modelled as the infinite beams posed on the periodically supports which are rested on a viscoelastic foundation. We consider the dynamic equation in the steady-state of rails subjected to the moving loads. By using Fourier transform together the periodically conditions, a relation between the reaction force and the beam displacement in the frequency domain has been demonstrated. Then, by performing this relation into the dynamic equation of sleeper laying on viscoelastic foundation, the dynamic responses of the two rails can be obtained with a help of Green’s function. The numerical example demonstrates the effect of the support on the beam responses.
{"title":"Calculation of the Dynamic Responses of Rails Subjected to Moving Loads on Ballasted Railway Track","authors":"Tran Le Hung, Nguyen Dinh Duc","doi":"10.25073/2588-1124/vnumap.4707","DOIUrl":"https://doi.org/10.25073/2588-1124/vnumap.4707","url":null,"abstract":"The dynamical responses of railway track has been carried out by different ways. In this work, by developing an analytical model for the ballasted railway track which includes two rails connected to the railway sleeper, a fast method to calculated the dynamic responses of the two rails is presented. The rail is modelled as the infinite beams posed on the periodically supports which are rested on a viscoelastic foundation. We consider the dynamic equation in the steady-state of rails subjected to the moving loads. By using Fourier transform together the periodically conditions, a relation between the reaction force and the beam displacement in the frequency domain has been demonstrated. Then, by performing this relation into the dynamic equation of sleeper laying on viscoelastic foundation, the dynamic responses of the two rails can be obtained with a help of Green’s function. The numerical example demonstrates the effect of the support on the beam responses. \u0000 ","PeriodicalId":303178,"journal":{"name":"VNU Journal of Science: Mathematics - Physics","volume":"10 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-09-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127427454","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-09-26DOI: 10.25073/2588-1124/vnumap.4720
Nguyen Thu Ha, Lê Anh Tuấn
This work is concerned with the Hardy inequalityon time scales. It finds the condition for the existence of a constant C such that where p is a fixed number satisfying .
这项工作涉及时间尺度上的哈代不等式。它找到常数C存在的条件使得p是一个固定的数满足。
{"title":"Hardy’s Inequality on Time Scale","authors":"Nguyen Thu Ha, Lê Anh Tuấn","doi":"10.25073/2588-1124/vnumap.4720","DOIUrl":"https://doi.org/10.25073/2588-1124/vnumap.4720","url":null,"abstract":"This work is concerned with the Hardy inequalityon time scales. It finds the condition for the existence of a constant C such that \u0000where p is a fixed number satisfying . \u0000 \u0000 ","PeriodicalId":303178,"journal":{"name":"VNU Journal of Science: Mathematics - Physics","volume":"2 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-09-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124402158","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-09-26DOI: 10.25073/2588-1124/vnumap.4722
Vu Thi Huong
We consider a class of multi-dimensional stochastic differential equations driven by fractional Brownian motion with Hurst index . In particular, the drift coefficient blows up at 0. We first prove that this equation has a unique positive solution, and then propose a semi-implicit Euler approximation scheme for the equation, and finally show that it is also positive, and study its rate of convergence.
{"title":"Euler Approximation for A Class of Singular Multi-Dimensional SDEs Driven by an Additive Fractional Noise","authors":"Vu Thi Huong","doi":"10.25073/2588-1124/vnumap.4722","DOIUrl":"https://doi.org/10.25073/2588-1124/vnumap.4722","url":null,"abstract":"We consider a class of multi-dimensional stochastic differential equations driven by fractional Brownian motion with Hurst index . In particular, the drift coefficient blows up at 0. We first prove that this equation has a unique positive solution, and then propose a semi-implicit Euler approximation scheme for the equation, and finally show that it is also positive, and study its rate of convergence. \u0000 ","PeriodicalId":303178,"journal":{"name":"VNU Journal of Science: Mathematics - Physics","volume":"41 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-09-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"114874489","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-09-26DOI: 10.25073/2588-1124/vnumap.4710
Nguyen Thu Hang, N. V. Tan
The aim of this work is to study the tail distribution of the Cox–Ingersoll–Ross (CIR) model driven by fractional Brownian motion. We first prove the existence and uniqueness of the solution. Then based on the techniques of Malliavin calculus and a result established recently in [1], we obtain an explicit estimate for tail distributions.
{"title":"Tail Distribution Estimates of Fractional CIR Model","authors":"Nguyen Thu Hang, N. V. Tan","doi":"10.25073/2588-1124/vnumap.4710","DOIUrl":"https://doi.org/10.25073/2588-1124/vnumap.4710","url":null,"abstract":"The aim of this work is to study the tail distribution of the Cox–Ingersoll–Ross (CIR) model driven by fractional Brownian motion. We first prove the existence and uniqueness of the solution. Then based on the techniques of Malliavin calculus and a result established recently in [1], we obtain an explicit estimate for tail distributions. \u0000 ","PeriodicalId":303178,"journal":{"name":"VNU Journal of Science: Mathematics - Physics","volume":"12 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-09-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122264452","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-09-26DOI: 10.25073/2588-1124/vnumap.4705
Nenuwe Oyindenyifa Nelson, Omagbemı Oghogho
Half-Heusler (hH) alloys are an intriguing class of materials with significant potential for applications in spintronics, thermoelectrics, optoelectronics, and magnetoelectronics due to their unique adjustable properties. In this work, we have investigated the structural, thermodynamic, mechanical, and electronic properties of RuVZ (Z: As, Bi, Sb) half-Heusler materials using the density functional theory (DFT) as implemented in the quantum espresso computational suite. The structural, thermodynamic, and mechanical properties were also predicted using the linear response density functional perturbation theory. We observed that the hH alloys are non-magnetic semiconductors and have an indirect narrow band gap. The band gap values and lattice constants for RuVSb and RuVAs cubic crystals are consistent with published reports. RuVBi has a lattice constant of 6.18 and a band gap of 0.16 eV. The elastic parameter results obtained satisfy Born's stability requirements, suggesting mechanical stability of the hH materials. All three alloys are found to be ductile. The RuVZ alloys obey the Dulong-Petit law at heat capacity of 74.7, 74.5, and 74.3 J mol-1K-1 and temperatures of 556, 754, and 775 K, respectively. The Debye temperature of 353.75K suggests that the RuVAs alloy is the hardest, with a significant Debye sound velocity (2997.12 m/s) and will have high thermal conductivity.
{"title":"DFT based Investigation of Structural, Thermodynamic, Mechanical and Electronic Properties of RuVZ (Z: As, Bi, Sb) Half-Heusler Semiconductors","authors":"Nenuwe Oyindenyifa Nelson, Omagbemı Oghogho","doi":"10.25073/2588-1124/vnumap.4705","DOIUrl":"https://doi.org/10.25073/2588-1124/vnumap.4705","url":null,"abstract":"Half-Heusler (hH) alloys are an intriguing class of materials with significant potential for applications in spintronics, thermoelectrics, optoelectronics, and magnetoelectronics due to their unique adjustable properties. In this work, we have investigated the structural, thermodynamic, mechanical, and electronic properties of RuVZ (Z: As, Bi, Sb) half-Heusler materials using the density functional theory (DFT) as implemented in the quantum espresso computational suite. The structural, thermodynamic, and mechanical properties were also predicted using the linear response density functional perturbation theory. We observed that the hH alloys are non-magnetic semiconductors and have an indirect narrow band gap. The band gap values and lattice constants for RuVSb and RuVAs cubic crystals are consistent with published reports. RuVBi has a lattice constant of 6.18 and a band gap of 0.16 eV. The elastic parameter results obtained satisfy Born's stability requirements, suggesting mechanical stability of the hH materials. All three alloys are found to be ductile. The RuVZ alloys obey the Dulong-Petit law at heat capacity of 74.7, 74.5, and 74.3 J mol-1K-1 and temperatures of 556, 754, and 775 K, respectively. The Debye temperature of 353.75K suggests that the RuVAs alloy is the hardest, with a significant Debye sound velocity (2997.12 m/s) and will have high thermal conductivity. \u0000 ","PeriodicalId":303178,"journal":{"name":"VNU Journal of Science: Mathematics - Physics","volume":"55 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-09-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115071249","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-09-26DOI: 10.25073/2588-1124/vnumap.4706
Cao Huy Phuong, V. Hùng
Temperature and pressure dependence of lattice constants of a cubic Strontium Titanate (SrTiO3) has been investigated using the statistical moment method. The lattice constants at various temperatures is derived in closed analytic form by including the anharmonic effects of the lattice vibrations explicitly. The potential with the partial charge model and Morse function is used. The numerical lattice constants at high temperatures by the statistical moment method are in good and reasonable agreement with the other theories and the experimental data. Variations of the lattice parameter of SrTiO3 with the temperature are obtained at 1 atm, 8.2 GPa, and 15.2 GPa. Increasing of the lattice constants with increasing temperature is due to enhancing atomic anharmonic fluctuations in SrTiO3 lattice crystal at higher temperature. A decrease of the lattice constants with increasing pressure can be demonstrated by the reduction of atomic vibrations in SrTiO3 crystal lattice at higher pressures.
{"title":"Influence of Temperature and Pressure on the Lattice Constant of SrTiO3 Perovskite by the Statistical Moment Method with Improved Interatomic Potential","authors":"Cao Huy Phuong, V. Hùng","doi":"10.25073/2588-1124/vnumap.4706","DOIUrl":"https://doi.org/10.25073/2588-1124/vnumap.4706","url":null,"abstract":"Temperature and pressure dependence of lattice constants of a cubic Strontium Titanate (SrTiO3) has been investigated using the statistical moment method. The lattice constants at various temperatures is derived in closed analytic form by including the anharmonic effects of the lattice vibrations explicitly. The potential with the partial charge model and Morse function is used. The numerical lattice constants at high temperatures by the statistical moment method are in good and reasonable agreement with the other theories and the experimental data. Variations of the lattice parameter of SrTiO3 with the temperature are obtained at 1 atm, 8.2 GPa, and 15.2 GPa. Increasing of the lattice constants with increasing temperature is due to enhancing atomic anharmonic fluctuations in SrTiO3 lattice crystal at higher temperature. A decrease of the lattice constants with increasing pressure can be demonstrated by the reduction of atomic vibrations in SrTiO3 crystal lattice at higher pressures. \u0000 ","PeriodicalId":303178,"journal":{"name":"VNU Journal of Science: Mathematics - Physics","volume":"51 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-09-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130277622","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-09-26DOI: 10.25073/2588-1124/vnumap.4708
Tran Trong Duc, Bui Hong Van, Nguyen The Binh
Abstract: Gold (Au) and silver (Ag) nanoparticles were synthesized by laser ablation in water. The average sizes of Au and Ag nanoparticles are 18,4 nm and 21,8 nm respectively. ZnS:Mn2+ nanoparticles with average size of 3-5 nm were prepared by a co-precipitation method. The photoluminescence of ZnS:Mn2+solution in mixture with Au (Ag) nanoparticle colloids was investigated. The quenching effect on Mn2+ emission at 601 nm band were observed in the presence of the Au and Ag nanoparticles while the D-A emission at 445 nm band was enhanced and blue shifted by Au nanoparticles . The results and discussion are presented in this report.
{"title":"Photoluminescence enhancement and quenching of ZnS:Mn2+ in the presence of Au and Ag nanoparticles synthesized by pulse laser ablation in solution.","authors":"Tran Trong Duc, Bui Hong Van, Nguyen The Binh","doi":"10.25073/2588-1124/vnumap.4708","DOIUrl":"https://doi.org/10.25073/2588-1124/vnumap.4708","url":null,"abstract":"Abstract: Gold (Au) and silver (Ag) nanoparticles were synthesized by laser ablation in water. The average sizes of Au and Ag nanoparticles are 18,4 nm and 21,8 nm respectively. ZnS:Mn2+ nanoparticles with average size of 3-5 nm were prepared by a co-precipitation method. The photoluminescence of ZnS:Mn2+solution in mixture with Au (Ag) nanoparticle colloids was investigated. The quenching effect on Mn2+ emission at 601 nm band were observed in the presence of the Au and Ag nanoparticles while the D-A emission at 445 nm band was enhanced and blue shifted by Au nanoparticles . The results and discussion are presented in this report. \u0000 ","PeriodicalId":303178,"journal":{"name":"VNU Journal of Science: Mathematics - Physics","volume":"57 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-09-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"134519650","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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