Manufacturers of cast metal parts are interested in the development of a feedback control system for use with the Precision Sand-Casting (PSC) process. As industry demands the ability to cast more complex geometries, there are a variety of challenges that engineers have to address. Certain characteristics of the mold, such as thick-to-thin transitions, extensive horizontal or flat surfaces, and sharp corners increase the likelihood of generating defective casts due to the turbulent metal-flow during fills. Consequently, it is critical that turbulent flow behavior within the mold be minimized as much as possible. One way to enhance the quality of the fill process is to adjust the flow rate of the molten metal as it fills these critical regions of the mold. Existing systems attempt to predict the position of the metal level based on elapsed time from the beginning of the fill stage. Unfortunately, variability in several aspects of the fill process makes it very difficult to consistently predict the position of the metal front. A better approach would be to embed a sensor that can detect the melt through a lift-off distance and determine the position of the metal-front. The information from this sensor can then be used to adjust the flow rate of the aluminum as the mold is filled. This thesis presents the design of a novel non-invasive sensor monitoring system. When deployed on the factory floor, the sensing system will provide all necessary information to allow process engineers to adjust the metal flow-rate within the mold and thereby reduce the amount of scrap being produced. Moreover, the system will exhibit additional value in the research and development of future mold designs.

A compressão nas flutuações da diferença de intensidades dos feixes sinal e complementar gerados por um OPO acima do limiar foi medida já há algum tempo e constituiu um dos principais interesses nestes sistemas. Emaranhamento entre esses feixes, entretanto, ainda não foi experimentalmente demonstrado em circunstâncias normais de operação acima do limiar (feixes não-degenerados em frequência). Usando um critério de não-separabilidade entre sistemas contínuos, buscamos verificar se a variância de um par de operadores tipo EPR, a diferençaa de intensidades e a soma das fases de sinal e complementar, pode violar uma desigualdade suficiente para caracterizar emaranhamento. Após um estudo teórico, verificamos que isto pode de fato ocorrer numa região de parâmetros experimentalmente acessível. A medida não foi realizada até hoje devido à dificuldade em se medir quadratura fase, o que, neste caso, exigiria o uso de osciladores locais em frequências distintas. Motivados por isso, propomos uma montagem experimental que utiliza cavidades óticas para projetar ruído de fase em ruído de intensidade, tornando dessa forma acessível a medida de anticorrelação de fase entre sinal e complementar. Realizamos nossa proposta em caráter preliminar, obtendo resultados encorajadores, embora não conclusivos, que indicam a existência de emaranhamento. / Squeezing in the intensity difference of signal and idler beams generated by an OPO operating above threshold was observed some time ago and presented one of the major attraction of this system. Entanglement between the macroscopic fields, however, has not yet been demonstrated in normal operation conditions above threshold (non-degenerate beams). Using a non-separability criterion for continuous variables, we investigate whether the variances of a pair of EPR-like operators, difference of intensities and sum of phases of signal and idler, can violate a Bell-type inequality and hence characterize entanglement. After a theoretical study, we verified that entanglement can occur in an experimentally accessible region of parameters. This measurement was not performed to date owing to the difficulty of measuring the phase quadratures, which usually requires the use of local oscillators with slightly different frequencies. Motivated by this, we propose an experimental setup that uses optical cavities to rotate the noise ellipse of each beam, projecting phase noise into intensity noise, thus allowing the experimental access to the phase quadratures. We preliminarly implemented our proposal and obtained promising although not conclusive results, that indicate entanglement.

This dissertation presents the design of a unique prototype chemical agent detector which utilizes an array of polymer coated SAW resonators as the sensor elements. The design's particular embodiment is that of a testing platform for evaluating the utility of constructing a portable chemical agent detector, utilizing commercially available SAW resonators. It involves the consolidation of the sub-systems comprising a large laboratory development system, into a portable enclosure. A combination of design techniques, utilized to achieve an overall balance between the physical dimensions of the system and its detection performance, comprises the unique nature of the overall design of this detection system. Such techniques include; sensor power cycling, individually phase-tunable sensor oscillators, single step down conversion and the locality of the sensor's driving circuitry and sensing chamber. A frequency shift model is developed to characterize the device's response to target analytes. Reported here are the results of the preliminary tests of the detector system and the verifications of the device's operation as per the design requirements. Further, an assay of the system noise is undertaken, and the detector's limit of detection (LOD) is reported. The analytes used in this investigation were simulants of nerve and mustard gas as well as the interferent compound diesel. Among others, the following conclusions are reported: 1) that a mass loading model can adequately describe the frequency shifts of the SAW resonators utilized for sorption sensing; 2) that the quality factor of a polymer coated SAW resonator ultimately determines the noise performance of the driving oscillator; 3) that the lowest usable quality factor for the designed oscillator is 2500; 4) that the implementation of individual phase-tuning networks for each sensor in the sensor array can adequately compensate for phase variations among these sensors, and 5) that commercially available SAW resonators coated with chemo-selective polymers provide a reasonably inexpensive and reliable solution to the detection of chemical warfare agents when incorporated into a miniaturized sensing platform.

The circadian clock orchestrates metabolism and cell division and imposes important consequences to health and diseases, such as obesity, diabetes, and cancer. It is well established that phosphorylation-dependent circadian rhythms are the result of circadian clock protein interactions, which regulate many intercellular processes according to time of day. The phosphorylation-dependent circadian rhythm undergoes a succession of phases: Phosphorylation Phase → Transition Phase → Dephosphorylation Phase. Each phase induces the next phase. However, the mechanism of each phase and how the phosphorylation and dephosphorylation phases are prevented from interfering with each other remain elusive. In this research, we used a newly developed isotopic labeling strategy in combination with a new type of nuclear magnetic resornance (NMR) experiment to obtain the structural and dynamic information of the cyanobacterial KaiABC oscillator system. This system is uniquely suited for the mechanistic studies: mixing KaiA, KaiB KaiC, and ATP generates a self-sustained ~24 h rhythm of KaiC phosphorylation in vitro. Our data strongly suggest that the dynamic states of KaiC underpin the timing mechanism of cyanobacterial oscillator.

The recent discovery that a spin-polarized current can exert a large torque on a ferromagnet, through direct transfer of spin angular momentum, offers the possibility of electrical current controlled manipulation of magnetic moment in nanoscale magnetic device structures. This so-called spin torque effect holds great promise for two applications, namely, spin torque oscillators (STOs) for wireless communication and radar communication, and spin transfer torque RAM (STT-RAM) for data/information storage.   The STO is a nanosized spintronic device capable of microwave generation at frequencies in the 1-65 GHz range with high quality factors. Although the STO is very promising for future telecommunication, two major shortcomings have to be addressed before it can truly find practical use as a radio-frequency device. Firstly, its very limited output power has to be significantly improved. One possibility is the synchronization of two or more STOs to both increase the microwave power and further increase the signal quality. Synchronization of serially connected STOs has been suggested in this thesis. In this configuration, synchronization relies on phase locking between the STOs and their self-generated alternating current. While this locking mechanism is intrinsically quite weak, we find that the locking range of two serially connected spin-valve STOs can be enhanced by over two orders of magnitude by adjusting the circuit I-V phase to that of an intrinsic preferred phase shift between the STO and an alternating current. More recently, we have also studied the phase-locking of STOs based on magnetic tunnel junctions (MTJ-STO) to meet the power specifications of actual application where the rf output levels should be above 0 dBm (1 mW). In addition to the spin torque terms present in GMR spin valves, MTJs also exhibit a significant perpendicular spin torque component with a quite complex dependence on both material choices and applied junction bias. We find that the perpendicular torque component modifies the intrinsic preferred I-V phase shift in single MTJ-STOs in such a way that serially connected STOs synchronize much more readily without the need for additional circuitry to change the I-V phase.   Secondly, equal attention has been focused on removing the applied magnetic field for STO operation, which requires bulky components and will limit the miniaturization of STO-based devices. Various attempts have been made to realize STOs operating in zero magnetic field. By using a tilted (oblique angle) polarizer (fixed layer) instead of an in-plane polarizer (standard STO), we show zero field operation over a very wide polarizer angle range without sacrificing output signal. In addition, the polarizer angle introduces an entirely new degree of freedom to any spin torque device and opens up for a wide range of additional phenomena.   The STT-RAM has advantages over other types of memories including conventional MRAM in terms of power consumption, speed, and scalability. We use a set of simulation tools to carry out a systematic study on the subject of micromagnetic switching processes of a device for STT-RAM application. We find that the non-zero k spin wave modes play an important role in the experimentally measured switching phase boundary. These may result in telegraph transitions among different spin-wave states, and be related to the back-hopping phenomena where the switching probability will decrease with increasing bias in tunnel junctions. / QC 20100819

A hybrid operational amplifier compensation technique using Miller and multipath compensation is presented for multi-stage amplifier designs. Unconditional stability is achieved by the means of pole-zero cancellation where left-half zeros cancel out the non-dominant poles of the operational amplifier. The compensation technique is stable over process, temperature, and voltage variations. Compared to conventional Miller-compensation, the proposed compensation technique exhibits improved settling response for operational amplifiers with the same gain, bandwidth, power, and area. For the same settling time, the proposed compensation technique will require less area and consume less power than conventional Miller-compensation. Furthermore, the proposed technique exhibits improved output slew rate and lower noise over the conventional Miller-compensation technique. Two-stage operational amplifiers were designed in a 0.18µm CMOS process using the proposed technique and conventional Miller-compensated technique. The design procedure for the two-stage amplifier is applicable for higher-order amplifier designs. The amplifiers were incorporated into a switched-capacitor oscillator where the oscillation harmonics are dependent on the settling behaviour of the op amps. The superior settling response of the proposed compensation technique results in a improved output waveform from the oscillator.

A prerequisite for the perception of motion in primates is the transformation of varying intensities of light on the retina into an estimation of position, direction and speed of coherent objects. The neuro-computational mechanisms relevant for object feature encoding have been thoroughly explored, with many neurally plausible models able to represent static visual scenes. However, motion estimation requires the comparison of successive scenes through time. Precisely how the necessary neural dynamics arise and how other related neural system components interoperate have yet to be shown in a large-scale, biologically realistic simulation. The proposed model simulates a spiking neural network computation for representing object velocities in cortical areas V1 and middle temporal area (MT). The essential neural dynamics, hypothesized to reside in networks of V1 simple cells, are implemented through recurrent population connections that generate oscillating spatiotemporal tunings. These oscillators produce a resonance response when stimuli move in an appropriate manner in their receptive fields. The simulation shows close agreement between the predicted and actual impulse responses from V1 simple cells using an ideal stimulus. By integrating the activities of like V1 simple cells over space, a local measure of visual pattern velocity can be produced. This measure is also the linear weight of an associated velocity in a retinotopic map of optical flow. As a demonstration, the classic motion stimuli of drifting sinusoidal gratings and variably coherent dots are used as test stimuli and optical flow maps are generated. Vector field representations of this structure may serve as inputs for perception and decision making processes in later brain areas.

The objectives of this research lie in the area of millimeter and submillimeter wave signal generation and are directed into two paths that are separate, but related. The first involves the development of a W-Band oscillator using Raytheon's Metamorphic High Electron Mobility Transistor (MHEMT) substrate. The second involves the development of silicon formed rectangular waveguide to replace metallic waveguide, ultimately to be used in THz signal source circuits. An exploration of two different topologies for a W-Band oscillator design utilizing Raytheon s MHEMT substrate is presented. This material will demonstrate the reasoning behind the topology selection and the approach of the design. An evaluation of this first ever W-Band MHEMT oscillator will be presented demonstrating its performance capabilities. Finally, an oscillator design will be presented extending the first successful MHEMT W-Band design. The area of Silicon rectangular waveguide with is covered. A design approach of the silicon waveguide will be discussed. The technology used to fabricate and package the silicon waveguide will be explained. The results of the very first 400 GHz silicon waveguide will be shown and the future efforts will be covered. A silicon micromachined waveguide multiplier using an HBV diode circuit is constructed and successfully demonstrated with an output frequency of 261 GHz, showing little difference between using micromachined waveguide and metal waveguide. Lastly, a power combining frequency multiplier is developed utilizing HBV diodes with an output of 260 GHz. The input and output sections are created using branch line couplers. The results showed good power generation as compared to a single diode multiplier.

Quadrature LO signal is a key element in many of the RF transceivers which tend to dominate today’s wireless communication technology. The design of a quadrature LC VCO with better phase noise and lower power consumption forms the core of this work. This thesis investigates a coupling mechanism to implement a quadrature voltage controlled oscillator using indirect injection method. The coupling network in this QVCO couples the two LC cores with their super-harmonic and it recycles its bias current back into the LC tank such that the power consumed by the coupling network is insignificant. This recycled current enables the oscillator to achieve higher amplitude of oscillation for the same power consumption compared to conventional design, hence assuring better phase noise. Mathematical analysis has been done to study the mechanism of quadrature operation and mismatch effects of devices on the quadrature phase error of the proposed QVCO. The proposed quadrature LC VCO is designed in TSMC 0.18 μm technology. It is tunable from 2.61 GHz - 2.85 GHz with sensitivity of 240 MHz/V. Its worst case phase noise is -120 dBc/Hz at 1 MHz offset. The total layout area is 1.41 mm^2 and the QVCO core totally draws 3 mA current from 1.8 V supply.

In this research we consider synchronization of oscillators. We use mechanical metronomes that are coupled through a mechanical medium. We investigate the problem for three different cases: 1) In passive coupling of two oscillators, the coupling medium is a one degree of freedom passive mechanical basis. The analysis of the system is supported by simulations of the proposed model and experimental results. 2) In another case, the oscillator is forced by an external input while the input is also affected by the oscillator. This feedback loop introduces dynamics to the whole system. For realization, we place the mechanical metronome on a one degree of freedom moving base. The movements of the base are a function of a feedback from the phase of the metronome. We study a family of functions for the reactions of the base and their impact on the behavior of the metronome. 3) We consider two metronomes located on a moving base. In this case the two metronomes oscillate and as the base is not freely moving, they are not directly coupled to each other. Now based on the feedbacks from the vision system, the base moves and hence the phases of the metronomes are affected by these movements. We study the space of possibilities for the movements of the base and consider impacts of the base movement on the synchronization of metronomes. We also show how such a system evolves in time.