published_or_final_version / abstract / Transport Policy and Planning / Master / Master of Arts in Transport Policy and Planning

A consequence of high speed rail transportation is the generation of elevated ground borne vibrations. This thesis presents several original contributions towards the prediction of these vibrations. Firstly, a new three dimensional finite element model capable of vibration prediction was developed. Its main feature was its ability to model complex track geometries while doing so through a fully coupled vehicle-tracksoil system. Model output was compared to experimental results obtained during this thesis and also to independent data sets. It was shown to predict velocity time histories, vibration frequency spectrums and international vibration descriptors with high accuracy. An appraisal of the suitability of a finite difference time domain modelling approach for railway vibration prediction was also undertaken. This resulted in the development of a new ‘higher order’ perfectly matched layers absorbing boundary condition. This condition was found to offer higher performance in comparison to current alternative absorbing boundary conditions. Field work was then undertaken on high speed lines with varying embankment conditions in Belgium and England. Vibration data was recorded up to 100m from each track and geophysical investigations were performed to determine the underlying soil properties. The results were used for numerical model validation and also to provide new insights into the effect of various embankment conditions on vibration propagation. It was found that embankments generate higher frequency excitation in comparison to nonembankment cases and that cuttings generate higher vibration levels than noncuttings. Once validated the finite element model was used to provide new insights into the effect of train speed, embankment constituent materials and railway track type on vibration levels. It was found that the shape and magnitude of ground vibration increased rapidly as the train’s speed approached the Rayleigh wave speed of the underlying soil. It was also found that ballast, slab and metal tracks produced similar levels of vibration and that stiffer embankments reduced vibration levels at distances near and far from the track. Two vibration mitigation techniques were also explored through numerical simulation. Firstly, an analysis was undertaken to determine the ability of a new modified ballast material to actively isolate vibration within the track structure. Secondly, wave barrier geometries were investigated to optimise their performance whilst minimising cost. It was found that barrier depth was the most influential parameter, whereas width had little effect. Additionally, geometry optimisation was found to result in a 95% cost saving in comparison to a base case. Using a vast array of results generated using the previously developed finite element model, a new empirical prediction model was also developed, capable of quickly assessing vibration levels across large sections of track. Unlike currently available empirical models, it was able to account for soil properties in its calculation and could predict a variety of international vibration metrics. It was shown to offer increased prediction performance in comparison to an alternative empirical model.

International Telemetering Conference Proceedings / October 30-November 02, 1995 / Riviera Hotel, Las Vegas, Nevada / There are many applications for High-speed photography, and most rely on film as the primary medium of data acquisition. One such application of interest to the military services is the study of stores separation from aircraft. This type of testing has traditionally used high-speed film to gather data, however, there are many disadvantages to using film, such as the high cost of raw film, as well as the high processing expense after it has been exposed. In addition, there is no way to review data from film until it has been processed, nor is there any way to preview in real-time other conditions such as lighting which may affect the outcome of a test event. This paper discusses the characteristics of television systems with respect to motion picture systems, the challenges of recording and transmitting pictures, as well as the nature of what the first and eventual desired systems might be.

The tremendous advancement in VLSI technologies in the past decade has fueled the need for intricate tradeoffs among speed, power dissipation and area. With gigahertz range microprocessors becoming commonplace, it is a typical design requirement to push the speed to its extreme while minimizing power dissipation and die area. Multipliers are critical components of many computational intensive circuits such as real time signal processing and arithmetic systems. The increasing demand in speed for floating-point co-processors, graphic processing units, CDMA systems and DSP chips has shaped the need for high-speed multipliers. The focus of our research for modern digital systems is two fold. The first one is to analyze a relatively unexplored logic style called MOS Current Mode Logic (MCML), which is a promising logic technique for the design of high performance arithmetic circuits with minimal power dissipation. The second one is to design high-speed arithmetic circuits, in particular, gigahertz-range multipliers that exploit the many attractive features of the MCML logic style. A small library of MCML gates that form the core components of the multiplier were designed and optimized for high-speed operation. The three 8-bit MCML multiplier architectures designed and simulated in TSMC 0.18 mm CMOS technology are: 3-2-tree architecture with ripple carry adder (Architecture I), 4-2-tree design with ripple carry adder (Architecture II) and 4-2-tree architecture with carry look-ahead adders (Architecture III). Architecture I operates with a maximum throughput of 4.76 GHz (4.76 Billion multiplications per second) and a latency of 3.78 ns. Architecture II has a maximum throughput of 3.3 GHz and a latency of 3 ns and Architecture III has a maximum throughput of 2 GHz and a latency of 3 ns. Architecture I achieves the highest throughput among the three multipliers, but it incurs the largest area and latency, in terms of clock cycle count as well as absolute delay. Although it is difficult to compare the speed of our multipliers with existing ones, due to the use of different technologies and different optimization goals, we believe our multipliers are among the fastest found in contemporary literature. / Master of Science

International Telemetering Conference Proceedings / October 26-29, 1992 / Town and Country Hotel and Convention Center, San Diego, California / SAIC, under contract with the Air Force Wright Laboratory, has developed and demonstrated a prototype High Speed Avionics Data Instrumentation System (HADIS). The HADIS system is designed to operate in both the laboratory and in an airborne environment. This paper briefly describes the features of the system including its ability to collect and record data at up to 13.25 MBytes per second, its ability to provide real-time processing of the data, and its ability to rapidly reconfigure its interfaces based on field programmable gate arrays. The paper discusses the need for multiple data paths within the system to allow parallel operations to take place, the need for dedicated access to the recorder subsystem, and methods for allowing selective recording based on the information content of the data. The effort was sponsored by the Test Facility Working Group to provide a common data collection system for Air Force logistics and test and evaluation facilities. The design is owned by the government and may be cost-effectively used by any government agency.

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Thesis. 1976. B.S.--Massachusetts Institute of Technology. Dept. of Physics. / Microfiche copy available in Archives and Science. / Bibliography: leaves 36-37. / B.S.

This thesis deals with the development of high speed InPmesa HBT’s with power gain cut—off frequencies up toand above 300 GHz, with high current density and low collectordischarging times. Key developments are Pd—based base ohmics yielding basecontact resistances as low as 10 Ωµm2, base—collector grades to enable to use ofInP in the collector, and an increase in the maximum currentdensity through collector design and thermal optimization.HBT’s with a linear doping gradient in the base are forthe first time reported and compared to HBT’s with abandgap graded base. The effect of degenerate base doping issimulated, as well as the base transit time. Key results include a DHBT with a 215 nm thick collector andan fτ= 280GHz, and fmax=400 GHz. This represents the highest fmaxreported for a mesa HBT. Results also include aDHBT with a 150 nm thick collector and an fτ= 300 GHz, and fmax=280 GHz. The maximum operating current densityhas been increased to above 10 mAµm while maintaining fτand fmax≥ 200 GHz. A mesa DHBT process with and as much yield and simplicity aspossible has been developed, while maintaining or pushingworld—class performance.

<p>This thesis deals with the development of high speed InPmesa HBT’s with power gain cut—off frequencies up toand above 300 GHz, with high current density and low collectordischarging times.</p><p>Key developments are Pd—based base ohmics yielding basecontact resistances as low as 10 Ωµm², base—collector grades to enable to use ofInP in the collector, and an increase in the maximum currentdensity through collector design and thermal optimization.HBT’s with a linear doping gradient in the base are forthe first time reported and compared to HBT’s with abandgap graded base. The effect of degenerate base doping issimulated, as well as the base transit time.</p><p>Key results include a DHBT with a 215 nm thick collector andan f_τ= 280GHz, and f_max=400 GHz. This represents the highest f_maxreported for a mesa HBT. Results also include aDHBT with a 150 nm thick collector and an f_τ= 300 GHz, and f_max=280 GHz. The maximum operating current densityhas been increased to above 10 mAµm while maintaining f_τand f_max≥ 200 GHz.</p><p>A mesa DHBT process with and as much yield and simplicity aspossible has been developed, while maintaining or pushingworld—class performance.</p>