This study investigated the significance of semantics in computer-generated word frequency counts in response to a call for new word lists (Read, 2000; Gardner, 2007). Read claims that no corpus projects to date have produced any "definitive, stand-alone word-frequency lists" (p. 226). Many researchers are wary of the fact that the concept of a word is never clearly defined in most studies that have dealt with word frequency counts. It is clear from the research that one universally acceptable construct for the concept of word does not exist. In fact, many past word frequency counts only examine word forms without considering the word meanings and the possible effects of homography on lists. Ming-Tzu and Nation (2004) did some research on the Academic Word List (AWL) that addresses some criticisms of word-frequency lists. They evaluate the extent of homography throughout the AWL. However, words found in the AWL are often not a part of the highest frequency word-forms in English. The present study focuses on high frequency words. It evaluates a randomized sample of 46 lemmas that occur at least 1500 times in the British National Corpus (BNC). A further random sampling of 200 examples for each lemma, in context, was semantically analyzed and tallied. One hundred of these examples were from the written portion and the other 100 from the spoken portion. The list of meanings for each word was compiled using conflated WordNet senses and some additional senses. Each context was double and sometimes triple rated. The results indicate that the impact of semantic frequency versus form-based frequency is considerable. The study suggests that the presence of homography tends to be extensive in many high-frequency word forms, across major registers of the language, and within each of the four major parts of speech. It further suggests that basing frequency on semantics will considerably alter the content of a high-frequency word list.

No description available.

This thesis concerns the numerical simulation of creeping rays and their contribution to high frequency scattering problems. Creeping rays are a type of diffracted rays which are generated at the shadow line of the scatterer and propagate along geodesic paths on the scatterer surface. On a perfectly conducting convex body, they attenuate along their propagation path by tangentially shedding diffracted rays and losing energy. On a concave scatterer, they propagate on the surface and importantly, in the absence of dissipation, experience no attenuation. The study of creeping rays is important in many high frequency problems, such as design of sophisticated and conformal antennas, antenna coupling problems, radar cross section (RCS) computations and control of scattering properties of metallic structures coated with dielectric materials. First, assuming the scatterer surface can be represented by a single parameterization, we propose a new Eulerian formulation for the ray propagation problem by deriving a set of escape partial differential equations in a three-dimensional phase space. The equations are solved on a fixed computational grid using a version of fast marching algorithm. The solution to the equations contain information about all possible creeping rays. This information includes the phase and amplitude of the ray field, which are extracted by a fast post-processing. The advantage of this formulation over the standard Eulerian formulation is that we can compute multivalued solutions corresponding to crossing rays. Moreover, we are able to control the accuracy everywhere on the scatterer surface and suppress the problems with the traditional Lagrangian formulation. To compute all possible creeping rays corresponding to all shadow lines, the algorithm is of computational order O(N3 log N), with N3 being the total number of grid points in the computational phase space domain. This is expensive for computing the wave field for only one shadow line, but if the solutions are sought for many shadow lines (for many illumination angles), the phase space method is more efficient than the standard methods such as ray tracing and methods based on the eikonal equation. Next, we present a modification of the single-patch phase space method to a multiple-patch scheme in order to handle realistic problems containing scatterers with complicated geometries. In such problems, the surface is split into multiple patches where each patch has a well-defined parameterization. The escape equations are solved in each patch, individually. The creeping rays on the scatterer are then computed by connecting all individual solutions through a fast post-processing. We consider an application to mono-static radar cross section problems where creeping rays from all illumination angles must be computed. The numerical results of the fast phase space method are presented. / QC 20101119

Gold wire bonding typically uses 60 KHz ultrasonic frequency. Studies have been reported that increasing ultrasonic frequency from 60KHz to 120KHz can decrease bonding time, lower bonding temperature, and/or improve the bondability of Au metalized organic substrates. This thesis presents a systematic study of the effects of 120 KHz ultrasonic frequency on the reliability of fine pitch gold wire bonding. Two wire sizes, 25.4 and 17.8 μm in diameter (1.0 and 0.7 mil, respectively) were used. The gold wires were bonded to metalized pads over organic substrates with five different metallization. The studies were carried out using a thermosonic ball bonder that is able to easily switch from ultrasonic frequency from 60 KHz to 120 KHz by changing the ultrasonic transducer and the ultrasonic generator. Bonding parameters were optimized through design of experiment methodology for four different cases: 60 KHz with 25.4 μm wire, 60 KHz with 17.8 μm wire, 120 KHz with 25.4 μm wire, and 120 KHz with 17.8 μm wire. The integrity of wire bonds was evaluated by the wire pull and the ball bond shear tests. With the optimized bonding parameters, over 2,250 bonds were made for each frequency and wire size. The samples were then divided into three groups. The first group was subjected to temperature cycling from -55°C to +125°C with one hour per cycle for up to 1000 cycles. The second group was subject to thermal aging at 125°C for up to 1000 hours. The third group was subject to humidity at 85°C/85% relative humidity (RH) for up to 1000 hours. The bond integrity was evaluated through the wire pull and the ball shear tests immediately after bonding, and after each 150, 300, 500, and 1000 hours time interval in the reliability tests. The pull and shear data are then analyzed to compare the wire bond performance between different ultrasonic frequencies.

Reducing the size of bulky magnetic components (inductors and transformers) in power converters can be achieved by increasing switching frequency and applying innovative designs of magnetic components. Ferrite is the most suitable bulk magnetic material for working at high frequencies but it is difficult to fabricate novel designs of ferrite magnetic components because of the limitations of conventional fabrication methods. Additive manufacturing (AM) has the potential to make customize ferrite magnetic components. One big challenge in 3D printing ferrite magnetic components is the lack of compatible and functional ferrite materials as printers' feedstock. This work focuses on developing ferrite feedstock for 3D printing ferrite magnetic components and providing a guideline for formulating ferrite feedstock by studying the effects of materials and processing parameters on major properties of the ferrite feedstock. The ferrite feedstock should not only be processable by a 3D printer but also make functional ferrite material that can work in power converters. To meet the requirements, the following four aspects of the feedstock are considered in this study: 1. the feedstock should be sinterable to achieve high enough magnetic permeability; 2. magnetic permeability of the feedstock can be easily tailored; 3. rheological properties of the feedstock should ensure reasonable printing resolution; 4. the feedstock can print high aspect ratio structures without slumping. Based on the four major considerations and the desired properties, materials were selected for formulating the ferrite feedstock. The effects of materials and processing variables on the major properties of the ferrite feedstock need to be studied to develop a formulation guidance of the feedstock. The effects of materials fractions and the post-printing peak sintering temperature of the feedstock on maximizing magnetic permeability were studied. The peak sintering temperature had a significant impact on permeability and solid loading (SL) and solid loading excluding diluent (SLED) had smaller impacts. Densities and microstructures of the sintered ferrite cores were characterized to illustrate how the variables affect magnetic permeability. Adding sintering additives to the feedstock was selected as an easy and effective way to tailor the permeability of the ferrite feedstock. The effect of the fractions of two types of additives, SiO2 and Co3O4, on permeability of ferrite were studied. Both SiO2 and Co3O4 can effectively reduce the permeability of the ferrite. A novel multi-permeability toroid core design was 3D-printed with ferrite feedstocks having different fractions of SiO2 to demonstrate the feasibility of fabricating special designs of ferrite magnetics using feedstocks with additives. Core-loss densities of ferrite cores fabricated with feedstocks having different fractions of the two additives were also characterized since it is another important property of ferrite cores in high-frequency converters. Adding SiO2 significantly increases the core-loss density of ferrite cores while adding proper fractions of Co3O4 decreased core-loss density at low magnetic flux densities. The mechanisms of how Co3O4 affect permeability and core-loss density were discussed. The effect of the solid loading (SL) on print-line width resolution was studied by conducting line printing tests. The experiment results showed the best print-line width resolution was achieved using the feedstock with an intermediate SL. The is, which considered both viscosity of the feedstock and coagulation in the feedstock suspension, were discussed. The effect of solid loading excluding diluent (SLED) and UV illumination time on the achievable aspect ratio of printed feedstock was studied. Yield shear strength (y) of feedstocks composition versus UV-curing time were characterized. We evaluated various phenomenological models reported in the literature for predicting the critical yield shear strength (y*) required to obtain a paste structure for a certain aspect ratio. Knowing y* would help to determine the shortest time needed for UV illumination. Applying the model that best fitted to our experimental results, we developed a processing guideline that from specified magnetic permeability and dimensions of a ferrite core, would prescribe the needed SLED and the minimal UV curing time for printing. The guideline was demonstrated by the successful fabrication of tall ferrite inductor cores commonly found in power converters. The main contributions of this study are listed below: 1. Designed, formulated, and characterized ferrite feedstock that not only has functionality for power electronics applications but is also compatible with a direct extrusion type 3D printer. The feedstock can be made into ferrite cores with relative permeability ranging from 10 to 500 which are much higher than those of soft ferrite feedstocks currently reported elsewhere. The packing densities of 950℃ sintered ferrite cores made from the feedstock can be as high as 95%. With the Hyrel 30M 3D-printer, the smallest nozzle orifice diameter that the feedstock can be extruded from is 0.42 mm. We demonstrated printing of the feedstock into a cylinders with a height of 18 mm and an aspect ratio of 3 without slumping issue. 2. Identified the effects of materials and processing variales on 4 major considerations of the ferrite feedstock including maximizing sintered packing density, tailoring permeability, print-line resolution, and achievable dimensions of the printed feedstock without slumping. A deeper understanding of the mechanisms of how the variables affect main properties of the feedstock was provided. 3. Provided a preparation guideline of the ferrite feedstock that prescribe feedstock formulation and UV illumination time per print-layer from the target relative permeability and dimension of a ferrite core. / Doctor of Philosophy / To reduce the size of power electronic devices, applying novel designs of ferrite magnetic components (inductors and transformers) is a promising method. While conventional fabrication methods cannot fabricate novel designs of ferrite magnetic components that have odd or intricate geometries, additive manufacturing (AM) has the potential. One big challenge in 3D printing ferrite magnetic components is the lack of compatible and functional ferrite materials as printers' feedstock. This work focuses on developing ferrite feedstock for 3D printing ferrite magnetic components and providing a guideline for formulating ferrite feedstock by studying the effects of materials and processing parameters on major properties of the ferrite feedstock. The ferrite feedstock should not only have the desired functionalities but also be suitable for printing. Major considerations and desired properties of the feedstock were discussed. Materials were selected to formulate the feedstock based on the desired properties. To develop a formulation guidance for the feedstock, the effects of materials and processing variables on the major properties of ferrite feedstock were studied. The studies included the following 4 aspects: 1. the effects of materials fractions in the feedstock and the post-printing sintering temperature of the feedstock on maximizing magnetic permeability; 2. the effect of additives in the feedstock on tailoring permeability; 3. the effect of feedstock rheology on print-line resolution; 4. the effect of materials fraction and ultraviolet light illumination time on achievable aspect ratio of printed feedstock.

High Frequency Trading (HFT) algorithms are automated feedback systems interacting with markets to maximize returns on investments. These systems have the potential to read different resolutions of market information at any given time, where Level I information is the minimal information about an equity--essentially its price--and Level II information is the full order book at that time for that equity. This paper presents a study of using Recurrent Neural Network (RNN) models to predict the spread of the DOW Industrial 30 index traded on NASDAQ, using Level I and Level II data as inputs. The results show that Level II data does not significantly improve the prediction of spread when predicting less than 100 millisecond into the future, while it is increasingly informative for spread predictions further into the future. This suggests that HFT algorithms should not attempt to make use of Level II information, and instead reallocate that computation power for improved trading performance, while slower trading algorithms may very well benefit from processing the complete order book.

This work focuses on the high frequency restoration of video sequences captured by a hybrid camera, using key-frames as high frequency samples. The proposed method outlines a hierarchy to the super-resolution process, and is aimed at maximizing both speed and performance. Additionally, an advanced image processing simulator (EngineX) was developed to fine tune the algorithm. / Super-resolution algorithms are designed to enhance the detail level of a particular image or video sequence. However, it is very difficult to achieve in practice due to the problem being ill-posed, and often requires regularization based on assumptions about texture or edges. The process can be aided using high-resolution key-frames such as those generated from a hybrid camera. A hybrid camera is capable of capturing footage in multiple spatial and temporal resolutions. The typical output consists of a high resolution stream captured at low frame rate, and a low resolution stream captured at a high frame rate. Key-frame based super-resolution algorithms exploit the spatial and temporal correlation between the high resolution and low resolution streams to reconstruct a high resolution and high frame rate output stream. The proposed algorithm outlines a hierarchy to the super-resolution process, combining several different classical and novel methods. A residue formulation decides which pixels are required to be further reconstructed if a particular hierarchy stage fails to provide the expected results when compared to the low resolution prior. The hierarchy includes the optical flow based estimation which warps high frequency information from adjacent key-frames to the current frame. Specialized candidate pixel selection reduces the total number of pixels considered in the NLM stage. Occlusion is handled by a final fallback stage in the hierarchy. Additionally, the running time for a CIF sequence of 30 frames has been significantly reduced to within 3 minutes by identifying which pixels require reconstruction with a particular method. A custom simulation environment implements the proposed method as well as many common image processing algorithms. EngineX provides a graphical interface where video sequences and image processing methods can be manipulated and combined. The framework allows for advanced features such as multithreading, parameter sweeping, and block level abstraction which aided the development of the proposed super-resolution algorithm. Both speed and performance were fine tuned using the simulator which is the key to its improved quality over other traditional super-resolution schemes. / Thesis / Master of Applied Science (MASc)

In today's industrial power converters, converter reliability is essential, and converter topologies are well-established. Without a doubt, the power electronic industry continues to seek efficient power delivery and high power density. Resonant converters, especially LLC converters, have been intensively studied and applied in DC-DC converters. One of the most demanding applications for LLC converters is data centers. To date, LLC Resonant converters, are deployed in many applications for improved efficiency, density, and reliability. With the introduction of WBG devices coupled with the soft switching feature, the switching frequency can be extended beyond Mega-Hertz. With the significant increase in operating frequency, complicated magnetic components can be broken down into a cellular structure, each with a few number of turns. They can be easily implemented using 4-6 layers of PCB windings. Moreover, integrating the cellular cores using flux cancellation can further improve the power density. The proposed integrated magnetics can be automated in the manufacturing process. The magnetic size is reduced at this frequency, and planar magnetics using PCB winding become more relevant. PCB magnetics feature multiple advantages over Litz wire. The benefits are summarized as follows: The labor-intensive manufacturing process can be automated, thus reduction of cost. There is much reduced CM noise by using the shield layer. They have parasitics with much-improved reproducibility in large quantities. PCB windings feature less leakage between transformer windings because of the flexibility of the winding interleaving and the reduced number of turns. There is better thermal management due to the increased surface-to-body ratio. The design has a low profile and high-power density. However, it is not without its own limitations. There are challenges for high frequency PCB-magnetic magnetic design for the LLC converter. Firstly, With the recently developed high frequency core material, a phenomenon referred to as the dimensional resonant is observed. The effects of dimensional resonance were discussed in the literature when using an unusually large core structure; however, it can be observed more frequently under high excitation frequency, particularly with integrated magnetics. This dissertation discusses the dimensional effects of core loss on a PCB-based magnetics structure. A case study is presented on a 3-kW 400-to-48-V LLC prototype running at 1 MHz. The converter utilizes a low-profile matrix of two integrated transformers with a rectangular and thin cross-section area for reduced core loss. Specific solutions are presented. % Secondly, The matrix transformer is suitable for an LLC converter with high output current. However, the matrix transformer also increases the core size and core losses. The core loss degrades the LLC converter's light load and peak efficiency. In this dissertation, We discuss the design process and implementation of the DC-DC stage of the power supply unit for narrow range 48 V data center bus architecture. The optimization takes into account the number of elemental transformers, number of transformer turns, switching frequency, and transformer dimensions, namely winding width and core cross-section area. The optimization process results in a nearly 99% efficient 400-to-48-V LLC with a very high-power density and low profile fully integrated on PCB. A matrix of four transformers is used to reduce the termination loss of the secondary synchronous rectifier and achieve better thermal management. The number of secondary turns is optimized to achieve the best trade-off between winding loss, core loss, and power density. Another challenge arises for magnetic integration when multiple magnetic components with different characteristics come together. For instance, in the case of a transformer and an inductor on the same PCB. The PCB transformer is designed with perfectly interleaved primary and secondary layers to utilize the full PCB layer thickness. As a rule of thumb, the transformer winding layer is designed within 1 to 2 times the skin depth. On the other hand, the inductor's winding lacks interleaving and suffers from high MMF stress on layers. This makes the inductor prone to high eddy currents and eddy loss. Furthermore, this dissertation addresses the challenges associated with the high winding and core loss in the Integrated Transformer-Inductor (ITL). To overcome these challenges, we propose an improved winding design of the ITL by utilizing idle shielding layers for inductor integration within the matrix transformer. This method offers full printed circuit board (PCB) utilization, where all layers are consumed as winding, resulting in a significant reduction in the winding loss of the ITL. Moreover, we propose an improved core structure of the ITL that offers better flux distribution of the leakage flux within the magnetic core. This method reduces the core loss by more than 50% compared to the conventional core structure. We demonstrate the effectiveness of our proposed concepts by presenting the design of the ITL used in a high-efficiency, high-power-density 3-kW 400-to-48-V LLC module. The proposed converter achieves a peak efficiency of 98.7% and a power density of 1500 W/in3. This dissertation presents the concept of matrix inductors to solve such problems. A matrix of four resonant inductors is also designed to reduce the proximity effect between inductor windings and reduce inductor PCB winding loss. The matrix inductor provides a solution for high thermal stress in PCB-based inductors and reduces the inter-winding capacitance between inductor layers. This dissertation solves the challenges in magnetic design in high-frequency DC-DC converters in offline power supplies and data centers. This includes the transformer and inductor of the LLC converter. With the academic contribution in this dissertation, Wide-bandgap devices WBG can be successfully utilized in high-frequency DC-DC converters with Mega-Hertz switching frequency to achieve high efficiency, high power density, and automated manufacturing. The cost will be reduced, and the performance will be improved significantly. / Doctor of Philosophy / Industrial power converters need to be reliable and efficient to meet the power industry's demand for efficient power delivery and high power density. Research should focus on improving existing converter designs to improve fabrication, efficiency, and reliability. Resonant converters have been found to be effective in power conversion, especially in data centers where energy consumption is high. Three-element Resonant converters (LLC) are already used to improve efficiency, density, and reliability. By using Wide Bandgap devices and soft switching, the switching frequency can be extended beyond MHz, simplifying magnetic components and improving power density. The proposed integrated magnetics can be automated during the manufacturing process, further improving power density. At higher frequencies, planar magnetic components made with PCB winding are more effective than Litz wire. They are cheaper to make because of automation, have less common-mode noise, and are more reproducible in large quantities. PCB winding also has a low profile, high-power density, and better thermal management. However, it is not without its own limitations. There are challenges for high frequency PCB-magnetic magnetic design for the LLC converter. Firstly, With the recently developed high frequency core material, a phenomenon referred to as the dimensional resonant is observed. The effects of dimensional resonance were discussed in the literature when using an unusually large core structure; however, it can be observed more frequently under high excitation frequency, particularly with integrated magnetics. This dissertation discusses the effects of core loss on a PCB-based magnetics structure and presents solutions, including a case study on a 3-kW 400-to-48 V LLC prototype running at 1 MHz. Another challenge arises for magnetic integration when multiple magnetic components with different characteristics come together. For instance, in the case of a transformer and an inductor on the same PCB. The PCB transformer is designed with perfectly interleaved winding and low Ohmic loss. On the other hand, the inductor's winding lacks interleaving and suffers from a high proximity field. This makes the inductor prone to high eddy currents and eddy loss. This dissertation presents the concept of matrix inductors to solve such problems. A matrix of four resonant inductors is also designed to reduce the proximity effect between inductor windings and reduce inductor PCB winding loss. The matrix inductor provides a solution for high thermal stress in PCB-based inductors and reduces the inter-winding capacitance between inductor layers. Furthermore, this dissertation addresses the challenges associated with the high winding and core loss in the Integrated Transformer-Inductor (ITL). To overcome these challenges, we propose an improved winding design of the ITL by utilizing idle shielding layers for inductor integration within the matrix transformer. This method offers full printed circuit board (PCB) utilization, where all layers are consumed as winding, resulting in a significant reduction in the winding loss of the ITL. Moreover, we propose an improved core structure of the ITL that reduces the core loss by more than 50% compared to the conventional core structure. We demonstrate the effectiveness of our proposed concepts on a high-efficiency, high-power-density 3-kW 400-to-48-V LLC module. The proposed converter achieves a peak efficiency of 98.7% and a power density of 1500 W/in3. This dissertation solves the challenges in magnetic design in high-frequency DC-DC converters in offline power supplies and data centers. This includes the transformer and inductor of the LLC converter. With the academic contribution in this dissertation, Wide-bandgap devices WBG can be successfully utilized in high-frequency DC-DC converters with Mega-Hertz switching frequency to achieve high efficiency, high power density, and automated manufacturing. The cost will be reduced, and the performance will be improved significantly.

When the cochlea is stimulated with two primary tones (f1 and f2) some of the energy is reflected back and propagates via the middle ear into the outer ear. Due to cochlear nonlinearities, distortion product otoacoustic emissions (DPOAEs), may be detected by a probe microphone sealed in the ear canal. Reduced DPOAEs may indicate subclinical cochlear lesions. The relationship between hearing sensitivity and the strength of DPOAEs is debatable, especially in the extended high frequency (EHF) region (≥8 kHz). Monitoring cochlea function corresponding to the EHF range is important for detecting early stages of hearing loss, which typically begins above 8 kHz. Complex interactions of high-frequency pure-tones in the ear canal result in standing waves that increases test-retest variability of DPOAEs measured for f2≥6 kHz. The aim of the project was to evaluate reliability of DPOAEs measured up to 12 kHz with a system used routinely in audiology clinics. Thirty-one adults (age, 18-30 yrs) with normal middle-ear function and normal hearing thresholds in the conventional region (≤8 kHz) participated. The EHF audiometry was performed for frequencies up to 16 kHz. The DPOAE data were collected for the f2 frequency varied from 1.5 to 12 kHz, twice for each ear with the probe removed and then repositioned after the first test. The EHF audiometric data of four participants showed elevated thresholds. Their DPOAEs were reduced or absent for f2≥9 kHz, i.e., supporting the sensitivity of DPOAEs for cochlear hearing loss above the conventional audiometry frequency range. Mean and standard deviations of DPOAE levels were calculated separately for the left and the right ears of subjects with normal EHF thresholds. There were no differences between mean DPOAE values in the left and the right ears. The intersubject variability of the DPOAE levels was moderate (SD≈6 dB or lower) but it increased significantly in the 12-kHz region, per the F-test for variances, possibly due to 1. effects of standing waves on the high-frequency DPOAE reliability and/or 2. subclinical pathology in the most basal portion (i.e., high-frequency region) of the cochlea. For each ear, absolute values of differences between test/retest levels of detectable DPOAEs were calculated. ANOVA showed the main effect of frequency for the data collected in the left and the right ears. Post-hoc analyses indicated that test/retest variability of DPOAEs was rather constant for f2 frequencies up to 10 kHz, but a statistically significant increase of test/retest variability for f2 of 11 and 12 kHz was found. This aspect needs to be considered when using DPOAE tests for longitudinal monitoring of cochlear function in the basal portion. Nevertheless, combining behavioral thresholds with DPOAEs collected for the EHF range is vital for detecting the initial stage of the cochlear pathology corresponding to the high-frequency region, e.g., due to ototoxicity or aging of the cochlea.

No description available.