Ultra-wideband Outdoor Communication Characteristics with and without Traffic

[[abstract]]The BER performance for ultra-wideband (UWB) outdoor communication in LOS and NLOS environments with and without traffic is investigated. We obtain the impulse responses of the UWB outdoor environment by both 2.5D SBR-Image method and inverse Fourier transform techniques. The 2.5D SBR-Image method is first considered for two-dimensional environment simulated without heights of obstacles by ray tubes. Then, heights of the obstacles are taken into consideration between the transmitters and receivers. If the height of ray is lower than that of obstacles, the ray is neglected for the receivers. This effectively reduces the simulating time. By using the impulse response of multipath channels, the BER performance for binary pulse amplitude modulation communications over the radio UWB system is evaluated. We have performed computer simulations in LOS and NLOS environments with and without traffic in dense building areas. Numerical results have shown that the multipath effect caused by moving vehicles in the outdoor LOS and NLOS environments has a great impact on BER performance. Rake receivers are used to improve the outage probability. The relationship between traffic and BER performance is investigated; meanwhile, the characteristics of LOS and NLOS outdoor UWB environments are analyzed. Our investigation results can help improve planning and design of the UWB system.[[notice]]補正完畢[[incitationindex]]SCI[[booktype]]電子

A Comparative Study on Spin-Orbit Torque Efficiencies from W/ferromagnetic and W/ferrimagnetic Heterostructures

It has been shown that W in its resistive form possesses the largest spin-Hall ratio among all heavy transition metals, which makes it a good candidate for generating efficient dampinglike spin-orbit torque (DL-SOT) acting upon adjacent ferromagnetic or ferrimagnetic (FM) layer. Here we provide a systematic study on the spin transport properties of W/FM magnetic heterostructures with the FM layer being ferromagnetic Co$_{20}$Fe$_{60}$B$_{20}$ or ferrimagnetic Co$_{63}$Tb$_{37}$ with perpendicular magnetic anisotropy. The DL-SOT efficiency $|\xi_{DL}|$, which is characterized by a current-induced hysteresis loop shift method, is found to be correlated to the microstructure of W buffer layer in both W/Co$_{20}$Fe$_{60}$B$_{20}$ and W/Co$_{63}$Tb$_{37}$ systems. Maximum values of $|\xi_{DL}|\approx 0.144$ and $|\xi_{DL}|\approx 0.116$ are achieved when the W layer is partially amorphous in the W/Co$_{20}$Fe$_{60}$B$_{20}$ and W/Co$_{63}$Tb$_{37}$ heterostructures, respectively. Our results suggest that the spin Hall effect from resistive phase of W can be utilized to effectively control both ferromagnetic and ferrimagnetic layers through a DL-SOT mechanism

Multi-time analysis of CMOS circuits

Transient simulation of circuits with widely separated time constants and fast periodic excitations is not efficient because a long simulation period with small time steps is required. One approach to simulate the transient behaviour more efficiently is known as the Multi Partial Differential Equation (MPDE). In the MPDE the system ordinary differential equations that describe a circuit is transformed into a system of partial differential equations with two time variables, one for the fast periodic variations and another for the slow transient evolution. This method has been implemented in a general-purpose circuit simulator program named Carrot. This thesis presents progress towards the development that simulator. The main contributions of this thesis are the implementation and validation of MOSFET models in the simulator and the study of the performance of the MPDE approach (as currently implemented in Carrot) applied to complex CMOS circuits. An overview of concepts relevant for this work is presented, followed by a detailed description of the MOSFET model implementation. Next, the design of an integrated CMOS ring voltage-controlled oscillator is presented. This is followed by simulation case studies. The simulation results indicate that the MPDE approach can achieve orders of magnitude of improvement in simulation speed compared to regular transient analysis. This thesis concludes with recommendations for future research

Scanning Near-shore Intertidal Terrain Using Ground LiDAR

Intertidal zone refers to the area under and above the water during high and low tides. Traditionally, this zone is not within the scope of land management authorities. Moreover, in accordance with principals set out by existing plans, intertidal zones are excluded from management zones. Boundaries should therefore be set at the land and sea border. Traditionally, methods in determining this have included the traditional theodolite (total station) method, mapping and aerial photography (photogrammetry). However, existing operational restrictions lower efficiency, in addition to increasing time and operational costs. Therefore this paper explores the practicality of a user- friendly, ground-based high resolution laser scanning technology. This method offers easy operation and high-density characteristics with an instrument platform that can be installed on elevated rooftops. High accuracy and resolution is achieved using a stop-and-go method producing Digital Terrain Model (DTM) data. The range of the completed data is 61km in length, 2.5km in width, and -0.5m depth, with a sampling error of approximately ±2cm. Through the implementation discussed in this research, accurate information about the changes of topography in intertidal areas can be obtained

Directed diffraction without negative refraction

Using the FDTD method, we investigate the electromagnetic propagation in two-dimensional photonic crystals, formed by parallel air cylinders in a dielectric medium. The corresponding frequency band structure is computed using the standard plane-wave expansion method. It is shown that within partial bandgaps, waves tend to bend away from the forbidden directions. This phenomenon perhaps need not be explained in terms of negative refraction or `superlensing' behavior, contrast to what has been conjectured.Comment: 3 pages, 4 figure

Controlled Heterogeneous Nucleation and Growth of Germanium Quantum Dots on Nanopatterned Silicon Dioxide and Silicon Nitride Substrates

Controlled heterogeneous nucleation and growth of Ge quantum dots (QDs) are demonstrated on SiO_2/Si_3N_4 substrates by means of a novel fabrication process of thermally oxidizing nanopatterned SiGe layers. The otherwise random self-assembly process for QDs is shown to be strongly influenced by the nanopatterning in determining both the location and size of the QDs. Ostwald ripening processes are observed under further annealing at the oxidation temperature. Both nanopattern oxidation and Ostwald ripening offer additional mechanisms for lithography for controlling the size and placement of the QDs