299 số bộ dữ liệu tìm thấy

Định dạng: .pdf

Kết quả lọc
  • Design and Fabrication of Driver Amplifier for Wilkinson Power Divider Operating at S Band

    1 Resources
    In this paper, we introduce an overview of microwave power transmission system (MPT) including of power transmitter, free space transmission, rectenna. Also, the paper particularly presents in detail the proposed configuration of power transmitter. The presented power amplifier, which has the output of 1W, is fabricated by using AH201. The 1-Watt amplifier plays an important role as driver amplifier in the configuration. In addtion, the 4 – way Wilkinson divider/combiner has been designed and manufactured. All simulations and experimental results will be reported
  • Buckling analysis of eccentrically stiffened functionally graded circular cylindrical thin shells under mechanical load

    1 Resources
    An analytical approach is presented to investigate the linear buckling of eccentrically stiffened functionally graded thin circular cylindrical shells subjected to axial compression, external pressure and tosional load. Based on the classical thin shell theory and the smeared stiffeners technique, the governing equations of buckling of eccentrically stiffened functionally graded circular cylindrical shells are derived. Thefunctionally graded cylindrical shells with simply supported edges are reinforced by ring and stringer stiffeners system on internal and (or) external surface. The resulting equations in the case of compressive and pressive loads are solve directly, while in the case of torsional load is solved by the Galerkin procedure to obtain the explicit expression of static critical buckling load. The obtained results show the effects of stiffeners and input factors on the buckling behavior of these structures
  • Calculation of the Hall Coefficient in Doped Semiconductor Superlattices with a Perpendicular Magnetic Field under the Influence of a Laser Radiation

    1 Resources
    We consider a model of the Hall effect when a dopedsemiconductor superlattice (DSSL) with a periodical superlattice potential in the z-direction is subjected to a crossed dc electric field (EF)  E 1 = E 1 ,0 ,0 ( ) and magnetic field  B = 0 ,0 ,B ( ) , in the presence of a laser radiation characterized by electric field  E = 0 ,E 0 sin Ωt ( ) ,0 ( ) (where E 0 and Ω are the amplitude and the frequency of the laser radiation,respectively). By using the quantum kinetic equation for electrons and considering the electron- optical phonon interaction, we obtain analytical expressions for the Hall conductivity aswell as the Hall coefficient (HC) with a dependence on B, E 1 , E 0 , Ω , the temperature Tof the system and the characteristic parameters of DSSL. The analytical results are computationallyevaluated and graphically plotted for the GaAs:Si/GaAs:Be DSSL. Numerical results show the saturation of the HC as the magnetic field or the laser radiation frequency increases. This behavior is similar to the case of low temperature in two-dimensional electron systems
  • Extending froperty of infinite direct sums of uniform modules

    1 Resources
    Let R be any ring and M = © ,e/A /i be a direct sum of uniform right R - submodules M i,i £ /. We are interested ill the question, when this module M is extendible. If the index set / is finite, this question has been studied by Harmanci and Smith Ị6). In deed, Harmanci and Smith have shown that if M = 0™=1Aft, then M is extendible if and only if every direct summand of A/ with uniform dimension 2 is an extending module, where each M t is uniform, [(), Theorem 3]. In the first part of this paper we give some conditions for A/ to be extendible, where the index set / is not necessarily finite. We show th at a module over ail arbitrary ring is extendible if it has (1 — C l) and every local direct summand is a direct summand. Moreover, properties of extending modules have been obtained. In the last part, of the paper the results have been applied to characterize quasiFrobeniüS rings and rings whose projective right modules are extendible.
  • Theoretical approach to single - mod operation of bistable fabry - perot laser comtaining staturable absorber

    1 Resources
    A theoretical approach to the optical bistability ( O B ) effect in singlemod ( Fabry- Perot lasers containing saturable absorber (LSA) is presented on the basis of the rate equations until allowance for spontaneous emission and spatial holeburning . Special attention IS paid to the case of dominant in hom ogcncous broadening in hoth Lotrn iz ia n and Gaussian models. The influence o f the m a in LSA p aram ­ eters on O B occMTcncr conditions as well as on oncurves' characteristics are invrstiyatf'd in detail.
  • Function algebra on a disk

    1 Resources
    In this paper we prove the theorem, on approxim ation of continous func ­ tion algebra on a disk. This result is an extension of the Werner *8 one
  • Effect of Temperature on Ultrasonic Velocities, Attenuations, Reflection and Transmission Coefficients between Motor Oil and Carbon Steel Estimated by Pulse-echo Technique of Ultrasonic Testing Method

    1 Resources
    In this research,the dependence of the velocities and the absorption coefficients of ultrasonic waves propagated in 1018 low carbon steel on temperature range from 0 o C to 50 o C was investigated. The coefficients of the temperature dependence of the ultrasonic longitudinal wave and ultrasonic shear wave were estimated to be-0.8 m/s. o C and -0.44m/s. o C, respectively. The acoustic impedances of this carbon steel were also investigated and effected much by temperature. Simultaneous, the effect of temperature on the acoustic impedances and ultrasonic attenuations of the motor oil was also determined. As the results, reflection and transmission coefficients at the interface between the carbon steel and motor oil were estimated. It is concluded that the ultrasonic attenuation of the motor oil isone of the main reasons for the behavior of the ultrasonic absorption coefficients propagated in the steel sample.
  • Adapting Learning Activities for Teaching Know-How in Adaptive Course Generation System

    1 Resources
    In our previous work, we have built an adaptive course generation system (ACGS) [1] to adapt a learning path for learning goals. In this paper we describe learning activity is represented in the learner model and domain model to teach learners how to get through course content based on learner’s knowledge. Therefore, our model aim is to develop Bayesian Network learner model to manage overlay knowledge model and adapt learning activities based on a task model. In addition, an implementation of this model with the course topic about computer science domain for third year students is also described
  • Crystallographic Structural and Magnetic Propertiesof FePt Nanoparticles

    1 Resources
    Fe 60Pt 40nanoparticles have been successfully prepared by sonochemistry method from the solution of Fe(C2H3O2)2and H 2PtCl 6. The as-prepared sample then has been annealed at temperatures from 450 o C to 650 o C. Annealed samples have ordered L1ophase with face-centered tetragonal (fct) structure and show hard magnetic properties. The nanoparticles annealed at 550 o C show highest coervicity of 4.36 kOe measured at room temperature. The annealed-temperature dependence of the coercivity is consistent with theappearance of the order phase L1 oin the samples.
  • Song song hóa thuật toán so khớp mẫu QuickSearch trong NIDS sử dụng mô hình chia sẻ bộ nhớ trên OpenMP và PThreads

    1 Resources
    Thực hiện song song hóa thuật toán so khớp mẫu QuickSearch sử dụng mô hình chia sẻ bộ nhớ trên OpenMP và PThreads nhằm nâng cao hiệu năng và tốc độ xử lý gói tin trong NIDS với các tập luật của Snort
  • Optical Properties of Zn-based Semiconductor Nanoparticles and Application in Two-barcode Encryption

    1 Resources
    Mn-doped ZnS (ZnS/Mn) nanoparticles synthesized bysono-chemical co-precipitation are combined with ZnO nanoparticles synthesized by sol-gel method for application in two-barcode encryption. Nanoparticles are mixed together in different mass proportions of ZnO: ZnS/Mn respectively being 5: 1, 10: 1, 15: 1, 20: 1, 25: 1.30 : 1 and 35: 1, before being pressed in 1 cm diameter, 1 mm thick KBr pellets. The photoluminescence (PL) of the tablet shows that the mass proportion of two materials could be distinghuished by the proportion of the PL intensities at 515 nm and 600 nm, which promises potential manufacturing ability two-substant/two-barcode information storage systems for civil security applications.
  • Some results of interfacing the r-r coincidence spectrometer and computer

    1 Resources
    The construction of the spectro meter based on SACP method (Surm nation of Am ­ plitudes of coinciding of pulses) has lead to the need of the interface card to exchange data with computer. The interface card has been completed at the faculty of technology. Vietn am National University Hanoi. With simple design, the card worked completely stability in the long work period. Many measuring experiments with this card have been done at Dalat nuclear research Institute. Processing independently, the results of experiments at Hanoi and Dubna pointed out the good operation of the spectro meter and the interface card.
  • Nghiên cứu sơ bộ hiện trạng và đềxuất giải pháp bảo tồn các loài thực vật bị đe dọa tuyệt chủng tại Khu bảo tồn thiên nhiên Hang Kia - Pà Cò, tỉnh Hòa Bình

    1 Resources
    Ở Khu bảo tồn thiên nhiên Hang Kia - Pà Cò đã phát hiện được 52 loài thực vật đang bị đe doạ tuyệt chủng thuộc 3 ngành thực vật bậc cao có mạch là Ngọc lan, Thông và Dương xỉ. Trong đó, có 41 loài thực vật được ghi trong Sách Đỏ Việt Nam (2007), 29 loài được xếp trong Nghị định 32/2006/NĐ-CP, và 2 loài được xếp trong danh lục đỏ thế giới IUCN (2012.2). Hầu hết chúng cần được nghiên cứu nhân giống, gây trồng, bảo tồn và phát triển. Hai nhóm giải pháp để bảo tồn các loài thực vật bị đe dọa tuyệt chủng ởKhu bảo tồn thiên nhiên Hang Kia - Pà Cò là giải pháp về quản lý, bảo vệ rừng và giải pháp về giám sát và bảo tồn đa dạng sinh học
  • Tối ưu hóa quy trình phân tích đồng thời các anion vô cơ trong mẫu nước môi trường sử dụng hệ điện di mao quản vận hành bằng tay kết hợp với detectơ độ dẫn không tiếp xúc

    1 Resources
    Quy trình phân tích đồng thời cảphốt phát và các anion cơbản khác trong nước như clorua, nitrat, nitrit và sunphat trong nước sửdụng hệ điện di mao quản vận hành bằng tay kết hợp detector độdẫn không tiếp xúc đã được tối ưu hóa. Các điều kiện tối ưu cho quá trình phân tích là: hệ đệm 50 mM Tris/50 mM MOPS ởpH 7,7, mao quản PEEK và áp thế-15kV. Giới hạn phát hiện của cảnăm anion đều tương đối thấp từ5 đến 15 µM với độlặp (5 -10%) và độthu hồi (95- 112%) tốt. Kết quảphân tích một sốmẫu thực cho thấy tương quan cao giữa phương pháp điện di mao quản đã phát triển và phương pháp đối chứng bằng sắc ký ion
  • Diffusion sorption experiment for studying transport propertiesof 137 Cs and 85 Sr in soil

    1 Resources
    The radionuclides released from nuclear weapon tests during the 1960’s and from nuclear industries may still endanger the terrestrial environment. Therefore, a diffusion-sorption experim ent has been carried out t .0 study the behaviour of the radionu­ clides that are of interest in safety assessments in the environmental radioactivity field such as vi7C s and 90S r. T he system s studied were as close as possible to those encountered in the field. T h e experimental data were evaluated by numerical analysis, incorporating lin­ ear and nonlinear sorption m odels (six sorption isotherm m odels). T h is procedure enables us to calculate the sorption parameters of different sorption isotherm models. T h e parameters determ inated were the diffusion and sorption properties of cesium and strontium in an Orthic Podsol soil (Germany).
  • Satellite Tracking Control System Using Fuzzy PID Controller

    1 Resources
    This paper presents the results of study, design and manufacture of a searching and satellite auto-tracking system used for mobile receiver. This system applies both the traditional proportional integral derivative (PID) control and the fuzzy PID control methods. Firstly, the PID controller was designed by Ziegler-Nichols tuning method to obtain control parameters. Then, a fuzzy controller was applied to tuning online parameters of the PID controller. In order to apply for mobile satellite receiver, the tracking controlsystem has been designed, fabricated on a PCB board. Simulated and experimental results indicate that the system performances obtain from applying the fuzzy PID controller was better than traditional PID controller
  • Study on influence of substrate and exposure coffosive environment on adhesion ability of a modified polyethylenelined on blasted steel substrate

    1 Resources
    This paper presents a study of the adhesion ability of a modified polyethylene (sPE) lined on blasted steel substrate. Effects of pre-treatment of the substrate surface, the exposure environments, and elevated temperature on the adhesion shength, adhesion energy was conducted. A peel analysis model was established to calculate adhesion energy (fracture energy) ofthe sPE lined on the substrate from the peel data. The dumbbell tensile test was conducted at the rate of 50 mnr/min. as similar to the rate of peel test to find out the parameters using for the model. Adhesion ability of the sPE lined on the different pre-treafinent surface substrates was investigated. The Standard specimens showed the highest peel strength-adhesion energy. The adhesion energy result (2657.5 J/mz) for the Very low roughness specimens (smooth surface) was considered to the chemical bonding energy between the rhodifier/polymer and the metal oxides/metal crossing the interface. The peel strength of lined virgin PE for these substrates was also measured. The value of 743.2 Jlm2...
  • Structural and Optical Properties of Samarium DopedCalcium Fluoride Nanoparticles Synthesized By Co-Precipitation Technique

    1 Resources
    CaF2 nanoparticles doped with 0, 1, 2, 3, 4 and 5 mol% Sm 3+ were prepared by co-precipitation method. These nanoparticles were studied by X-ray diffraction (XRD), transmission electron microscopy (TEM), photoluminescence (PL), photoluminescence excitation (PLE) spectra, energy-dispersive X-ray spectroscopy (EDS)and diffuse reflective spectra. The XRD patterns indicate cubic structure of CaF 2 and no other impurities. TEM images show that CaF 2 nanoparticles have size varying from 15 to 20 nm. The photoluminescence spectra show 4 peaks at 566 nm, 604 nm, 645 nm and 704 nm, which are assigned to different transitions from the 4 G(4)5/2 excited state to the 6 HJ with J = 5/2; 7/2; 9/2 and 11/2 ground states of Sm 3+ ions. The PLE spectra show 8 lines, which are attributed to the absorption transitions from the 6 H5/2ground state to the 4 H(1)9/2, 4 D(2)3/2, 6 P 7/2, 4 F(3) 7/2, 6 P 5/2, 4 M17/2, 4 I(3)13/2 and 4 M15/2 excited states. Six lines among eight excitation lines were observed in the diffuse reflection spectra
  • Study on the characteristics and catalytic properties of PI/SBA-I5 in the selective oxidation of D-Glucose

    1 Resources
    In this work, platinum nanoparticles were dispersed on SBA-15 mesoporous material by incipient wetness method and the synthesized materials were characterizedby XRD, TEM, EDX spectoscopies and N2 adsorption-desorption isotherm measurement. The results indicated that 2D hexagonal ordered structure of SBA-15 was still maintained after grafting Pt on SBA-15 support and platinum nanoparticles existed both inside and outside the pore channels of SBA-15 material. Catalytic activity of these materials was tested in the aqueous phase D-glucose oxidation as a model reactiop. The reaction was carried out in a glass reactor at atrnospheric presslue, 80"C, air flow rate 20mVminute, at pH 9. The results from IIPLC-RID method showed that the pH has a profound effect in the platinum-catalyzed oxidation of glucose and high conversion of D-glucose with the highest selectivity to D-gluconic acid was performed with I%PVSBA-IS catalvst.
  • Occurrences of microcystis spp. and microcystins in some cyanobacterial blooms in freshwater bodies in Vietnam

    1 Resources
    This paper reporb the analyses of cyanobacteia Microcystrs spp. and toxin occlurence in bloom samples from some freshwater bodies in Vietnam. Six species of Microcystis (M. aeraginosa, M. botrys, M. pannifurmis, M. wessenbergii, M. flos-aquae and M. protocystis) were identified in 8 bloom samples collected from Lake Tri An (Ddng Nai province), Lake Bien Ho and Lake Duc An (Gia Lai Province), Cua Ngan, Dap Da, Nhu Y, Ho Mung sites (Thua Thien Hue Province), Lake Hoan Kiem (Ha Noi). The results of the quantitative analyses of Microcystl's spp. and screening of microcystin by ELISA in the water are presented. The cell density of Microcystis spp. ranged from I lxl03 to 624,5x103 cellV ml-r and M. aeruginosa as the dominating species. In the water samples, microcystins detected by ELISA varied between 5.854 and 17.966 ng ml-r. The results from toxin analyses showed thet there was no correlation between the total biomass of Microcystis and microcystins concentration in the same sample
Bạn cũng có thể truy cập cơ quan đăng ký này bằng Giao diện lập trình ứng dụng (xem Văn bản API).