Thermal and Structural Analysis and its Effect on Beam-Wave Interaction for 170-GHz, 1-MW Gyrotron Cavity

In this paper thermal and structural analysis for 170 GHz, 1 MW gyrotron interaction cavity and the effect of structural deformation on beam wave interaction is presented. Finite element analysis codes ANSYS has been used for the thermal and structural analysis. Electromagnetic simulator-MAGIC, a Particle-in-Cell (PIC) code, has been used to carry out the effect of the radial expansion of the interaction cavity on beam wave interaction. The change in output power and resonant frequency for operating mode TE_34,10 due to thermal expansion is 10 kW and 0.07 GHz, respectively. These values are under the tolerance limit of power and frequency of the gyrotron. The major variation is found in the power growth stability time.     

Design of single-stage depressed collector for 42 GHz, 200 kW gyrotron

A single stage depressed collector has been designed to dissipate the spent electron energy of 45 keV. This results in an increase of overall efficiency of 42 GHz, 200 kW gyrotron from 33% to 57%. The design of depressed collector has taken into account the performance on several sectors such as maximum beam spread, minimum power dissipation including the effect of high voltage and thermal efficiency. Different computer codes have been used in order to design this particular collector. The simulated efficiency of the single stage depressed collector is 63%.     

Reduced Rank Technique for Joint Channel Estimation and Joint Data Detection in TD-SCDMA Systems

In time division-synchronous code division multiple access systems, the channel estimation for multiple subscribers requires the computation of very complicated algorithms through short training sequences. This situation causes mismodeling of the actual channels and introduces significant errors in the detected data of multiple users. This paper presents a novel channel estimation method with low complexity, which relies on reducing the rank order of the total channel matrix H. We exploit the rank deficient of H to reduce the number of parameters that characterizes this matrix. The adopted reduced rank technique is based on singular value decomposition algorithm. Equations for reduced rank-joint channel estimation (JCE) are derived and compared against traditional full rank-joint channel estimators: least square (LS) or Steiner, enhanced LS, and minimum mean square error algorithms. Simulation results of the normalized mean square error for the above mentioned estimators showed the superiority of reduced rank estimators. Multi-user joint data detectors based linear equalizers are used to suppress inter-symbol interference and mitigate intra-cell multiple access interference. The detectors: zero forcing block linear equalizer and minimum mean square error block linear equalizer algorithms are considered in this paper to recover the data. The results of bit error rate simulation have shown that reduced rank-JCE based detectors have an improvement by 5 dB lower than other traditional full rank-JCE based detectors.     

A joint PHY/MAC cross-layer design for UWB under power control

Power control (PC) is a critical parameter for the design and evaluation of UWB-based WPAN networks due to its distributed control nature and non-fixed topology. The main issues in UWB PC are the channel gain fluctuations induced by indoor channel fluctuation and interference arising from narrowband systems. In this paper we introduce a joint PHY/MAC technique for DS-UWB power control design by exploiting the high time resolution of the UWB signal for channel gain improvement and mitigate the narrowband interference to reduce transmitted power. The results indicate that the proposed approach achieves better BER and throughput over previous works.     

TEM study of RTD structure fabricated with epi-Si/γ-Al2O3 heterostructure

Fabrication of γ-Al₂O₃/epi-Si/γ-Al₂O₃/Si-sub resonant tunneling diode structure has been performed and interfacial and crystalline quality of the fabricated RTD structure were characterized by high resolution transmission electron microscopy. Multiple layer structure formation with atomically flat interfaces was confirmed. The γ-Al₂O₃ layer on Si-sub was observed highly crystalline and oriented along the orientation of the Si substrate. But the epi-Si layer was not smoothly crystalline over the whole specimen and also crystallinity varies from place to place. The epitaxial Si layer was observed to be strained due to the difference in thermal expansion coefficient and the lattice mismatch between γ-Al₂O₃ and silicon.     

Stabilization of anatase phase by uncompensated Ga-V co-doping in TiO2: A structural phase transition,grain growth and optical property study

Uncompensated Ga-V co-doped TiO₂ samples have been prepared by modified sol-gel process. Inhibition of phase transition due to co-doping is confirmed by X-ray diffraction measurement. Activation of phase transition increases from 120?kJ/mol (x?=?0) to 240?kJ/mol (x?=?0.046) due to Ga-V incorporation. In anatase phase, lattice constant increases by the effect of Ga³⁺ interstitials. This results in inhibition of phase transition. Anatase phase becomes stable up to ~ 650?°C in co-doped sample whereas for pure TiO₂ phase transition starts in between 450 and 500?°C. High-resolution transmission electron microscope image shows particle size decreases in anatase phase due to co-doping. Increasing strain due to Ga-V incorporation results in reducing crystallite size. Brunauer–Emmett–Teller analysis shows that surface increases from 4.55?m²/g (pure TiO₂) to 96.53?m²/g (x?=?0.046) by Ga-V incorporation. In rutile phase, grain growth process is enhanced mainly due to the effect of Vanadium and particles show a rod-like structure with majority {110} facets. Bandgap decreases in both phases and reduced to visible light region. For charge balance in uncompensated Ga-V co-doped sample, structural distortion created in the lattice by combining effect of substitution, interstitials and oxygen vacancies, which results in stabilization of anatase phase and reducing of bandgap.     

Development of Cooling System for Gyrotron Collector

In this paper, the development of cooling system for 42 GHz, 200 kW gyrotron collector is presented. The design of the cooling duct has been finalized after different analyses such as, the fluid analysis, the thermal analysis, the structural analysis, etc. All analyses have been carried out by ANSYS software and the development of the cooling system based on the final design is performed.     

Application of fuzzy control algorithms for electric vehicle antilock braking/traction control systems

The application of fuzzy-based control strategies has gained enormous recognition as an approach for the rapid development of effective controllers for nonlinear time-variant systems. This paper describes the preliminary research and implementation of a fuzzy logic based controller to control the wheel slip for electric vehicle antilock braking systems (ABSs). As the dynamics of the braking systems are highly nonlinear and time variant, fuzzy control offers potential as an important tool for development of robust traction control. Simulation studies are employed to derive an initial rule base that is then tested on an experimental test facility representing the dynamics of a braking system. The test facility is composed of an induction machine load operating in the generating region. It is shown that the torque-slip characteristics of an induction motor provides a convenient platform for simulating a variety of tire/road /spl mu/-/spl sigma/ driving conditions, negating the initial requirement for skid-pan trials when developing algorithms. The fuzzy membership functions were subsequently refined by analysis of the data acquired from the test facility while simulating operation at a high coefficient of friction. The robustness of the fuzzy-logic slip regulator is further tested by applying the resulting controller over a wide range of operating conditions. The results indicate that ABS/traction control may substantially improve longitudinal performance and offer significant potential for optimal control of driven wheels, especially under icy conditions where classical ABS/traction control schemes are constrained to operate very conservatively.