Time-domain modeling of high-frequency electromagnetic wave propagation, overhead wires, and earth

Prediction of radiated fields from transmission lines has not previously been studied from a panoptical power system perspective. The application of BPL technologies to overhead transmission lines would benefit greatly from an ability to simulate real power system environments, not limited to the transmission lines themselves. Presently circuitbased transmission line models used by EMTP-type programs utilize Carson’s formula for a waveguide parallel to an interface. This formula is not valid for calculations at high frequencies, considering effects of earth return currents. This thesis explains the challenges of developing such improved models, explores an approach to combining circuit-based and electromagnetics modeling to predict radiated fields from transmission lines, exposes inadequacies of simulation tools, and suggests methods of extending the validity of transmission line models into very high frequency ranges. Electromagnetics programs are commonly used to study radiated fields from transmission lines. However, an approach is proposed here which is also able to incorporate the components of a power system through the combined use of EMTP-type models. Carson’s formulas address the series impedance of electrical conductors above and parallel to the earth. These equations have been analyzed to show their inherent assumptions and what the implications are. Additionally, the lack of validity into higher frequencies has been demonstrated, showing the need to replace Carson’s formulas for these types of studies. This body of work leads to several conclusions about the relatively new study of BPL. Foremost, there is a gap in modeling capabilities which has been bridged through integration of circuit-based and electromagnetics modeling, allowing more realistic prediction of BPL performance and radiated fields. The proposed approach is limited in its scope of validity due to the formulas used by EMTP-type software. To extend the range of validity, a new set of equations must be identified and implemented in the approach. Several potential methods of implementation have been explored. Though an appropriate set of equations has not yet been identified, further research in this area will benefit from a clear depiction of the next important steps and how they can be accomplished. Prediction of radiated fields from transmission lines has not previously been studied from a panoptical power system perspective. The application of BPL technologies to overhead transmission lines would benefit greatly from an ability to simulate real power system environments, not limited to the transmission lines themselves. Presently circuitbased transmission line models used by EMTP-type programs utilize Carson’s formula for a waveguide parallel to an interface. This formula is not valid for calculations at high frequencies, considering effects of earth return currents. This thesis explains the challenges of developing such improved models, explores an approach to combining circuit-based and electromagnetics modeling to predict radiated fields from transmission lines, exposes inadequacies of simulation tools, and suggests methods of extending the validity of transmission line models into very high frequency ranges. Electromagnetics programs are commonly used to study radiated fields from transmission lines. However, an approach is proposed here which is also able to incorporate the components of a power system through the combined use of EMTP-type models. Carson’s formulas address the series impedance of electrical conductors above and parallel to the earth. These equations have been analyzed to show their inherent assumptions and what the implications are. Additionally, the lack of validity into higher frequencies has been demonstrated, showing the need to replace Carson’s formulas for these types of studies. This body of work leads to several conclusions about the relatively new study of BPL. Foremost, there is a gap in modeling capabilities which has been bridged through integration of circuit-based and electromagnetics modeling, allowing more realistic prediction of BPL performance and radiated fields. The proposed approach is limited in its scope of validity due to the formulas used by EMTP-type software. To extend the range of validity, a new set of equations must be identified and implemented in the approach. Several potential methods of implementation have been explored. Though an appropriate set of equations has not yet been identified, further research in this area will benefit from a clear depiction of the next important steps and how they can be accomplished.

Statistical analysis of personal radiofrequency electromagnetic field measurements with nondetects

Exposimeters are increasingly applied in bioelectromagnetic research to determine personal radiofrequency electromagnetic field (RF-EMF) exposure. The main advantages of exposimeter measurements are their convenient handling for study participants and the large amount of personal exposure data, which can be obtained for several RF-EMF sources. However, the large proportion of measurements below the detection limit is a challenge for data analysis. With the robust ROS (regression on order statistics) method, summary statistics can be calculated by fitting an assumed distribution to the observed data. We used a preliminary sample of 109 weekly exposimeter measurements from the QUALIFEX study to compare summary statistics computed by robust ROS with a naïve approach, where values below the detection limit were replaced by the value of the detection limit. For the total RF-EMF exposure, differences between the naïve approach and the robust ROS were moderate for the 90th percentile and the arithmetic mean. However, exposure contributions from minor RF-EMF sources were considerably overestimated with the naïve approach. This results in an underestimation of the exposure range in the population, which may bias the evaluation of potential exposure-response associations. We conclude from our analyses that summary statistics of exposimeter data calculated by robust ROS are more reliable and more informative than estimates based on a naïve approach. Nevertheless, estimates of source-specific medians or even lower percentiles depend on the assumed data distribution and should be considered with caution.

DEVELOPMENT OF A PREDICTIVE COMBUSTION MODEL OF A SPARK IGNITED ENGINE WITH GASOLINE DIRECT INJECTION, VARIABLE VALVE TIMING, DURATION AND LIFT TECHNOLOGIES

There is a need by engine manufactures for computationally efficient and accurate predictive combustion modeling tools for integration in engine simulation software for the assessment of combustion system hardware designs and early development of engine calibrations. This thesis discusses the process for the development and validation of a combustion modeling tool for Gasoline Direct Injected Spark Ignited Engine with variable valve timing, lift and duration valvetrain hardware from experimental data. Data was correlated and regressed from accepted methods for calculating the turbulent flow and flame propagation characteristics for an internal combustion engine. A non-linear regression modeling method was utilized to develop a combustion model to determine the fuel mass burn rate at multiple points during the combustion process. The computational fluid dynamic software Converge ©, was used to simulate and correlate the 3-D combustion system, port and piston geometry to the turbulent flow development within the cylinder to properly predict the experimental data turbulent flow parameters through the intake, compression and expansion processes. The engine simulation software GT-Power © is then used to determine the 1-D flow characteristics of the engine hardware being tested to correlate the regressed combustion modeling tool to experimental data to determine accuracy. The results of the combustion modeling tool show accurate trends capturing the combustion sensitivities to turbulent flow, thermodynamic and internal residual effects with changes in intake and exhaust valve timing, lift and duration.

OPTIMAL SHAPE IN ELECTROMAGNETIC SCATTERING BY SMALL ASPHERICAL PARTICLES

We consider the question of optimal shapes, e.g., those causing minimal extinction among all shapes of equal volume. Guided by the isoperimetric property of a sphere, relevant in the geometrical optics limit of scattering by large particles, we examine an analogous question in the low frequency (electrostatics) approximation, seeking to disentangle electric and geometric contributions. To that end, we survey the literature on shape functionals and focus on ellipsoids, giving a simple proof of spherical optimality for the coated ellipsoidal particle. Monotonic increase with asphericity in the low frequency regime for orientation-averaged induced dipole moments and scattering cross-sections is also shown. Additional physical insight is obtained from the Rayleigh-Gans (transparent) limit and eccentricity expansions. We propose connecting low and high frequency regime in a single minimum principle valid for all size parameters, provided that reasonable size distributions of randomly oriented aspherical particles wash out the resonances for intermediate size parameters. This proposal is further supported by the sum rule for integrated extinction.

EXPERIMENTAL AND COMPUTATIONAL STUDIES OF ELECTROMAGNETIC CLOAKING AT MICROWAVES

An invisibility cloak is a device that can hide the target by enclosing it from the incident radiation. This intriguing device has attracted a lot of attention since it was first implemented at a microwave frequency in 2006. However, the problems of existing cloak designs prevent them from being widely applied in practice. In this dissertation, we try to remove or alleviate the three constraints for practical applications imposed by loosy cloaking media, high implementation complexity, and small size of hidden objects compared to the incident wavelength. To facilitate cloaking design and experimental characterization, several devices and relevant techniques for measuring the complex permittivity of dielectric materials at microwave frequencies are developed. In particular, a unique parallel plate waveguide chamber has been set up to automatically map the electromagnetic (EM) field distribution for wave propagation through the resonator arrays and cloaking structures. The total scattering cross section of the cloaking structures was derived based on the measured scattering field by using this apparatus. To overcome the adverse effects of lossy cloaking media, microwave cloaks composed of identical dielectric resonators made of low loss ceramic materials are designed and implemented. The effective permeability dispersion was provided by tailoring dielectric resonator filling fractions. The cloak performances had been verified by full-wave simulation of true multi-resonator structures and experimental measurements of the fabricated prototypes. With the aim to reduce the implementation complexity caused by metamaterials employment for cloaking, we proposed to design 2-D cylindrical cloaks and 3-D spherical cloaks by using multi-layer ordinary dielectric material (εr>1) coating. Genetic algorithm was employed to optimize the dielectric profiles of the cloaking shells to provide the minimum scattering cross sections of the cloaked targets. The designed cloaks can be easily scaled to various operating frequencies. The simulation results show that the multi-layer cylindrical cloak essentially outperforms the similarly sized metamaterials-based cloak designed by using the transformation optics-based reduced parameters. For the designed spherical cloak, the simulated scattering pattern shows that the total scattering cross section is greatly reduced. In addition, the scattering in specific directions could be significantly reduced. It is shown that the cloaking efficiency for larger targets could be improved by employing lossy materials in the shell. At last, we propose to hide a target inside a waveguide structure filled with only epsilon near zero materials, which are easy to implement in practice. The cloaking efficiency of this method, which was found to increase for large targets, has been confirmed both theoretically and by simulations.

Resuspension of the aortic valve in acute type A dissection: long-term results

BACKGROUND AND AIM OF THE STUDY: Preservation of the aortic valve during the repair of acute type A aortic dissection (AADA) is a viable option to prevent lifelong oral anticoagulation. The study aim was to assess aortic valve function following resuspension and supracoronary ascending aortic grafting. METHODS: Among a collective of 210 consecutive patients undergoing surgery for AADA, 140 (66.7%) with resuspension of the aortic valve and supracoronary ascending graft were analyzed. Of these patients, 83 (59.3%) had a complete follow up (mean 61.2 +/- 40.8 months), with 65 of the subgroup (78.3%) being followed by computed tomography scanning and echocardiography. RESULTS: Reoperation due to severe aortic valve regurgitation was required in seven patients (10.8%). The perioperative characteristics were similar in these patients; notably, no significant difference was evident with regards to the aortic annulus diameter and the severity of regurgitation at the time of surgery. The left ventricular mass index was significantly higher in patients requiring reoperation due to aortic valve regurgitation (219.3 +/- 146.6 versus 123.9 +/- 146.6 g/m2; p <0.05). None of the patients died as a result of reoperation. CONCLUSION: The long-term functional results following resuspension of the aortic valve in AADA were very good. A close echocardiographic follow up was necessary, as reoperation of the aortic valve was required in more than 10% of the collective, with an average follow up of five years. Reoperation was mainly related to secondary dilatation of the aortic root.

[Treatment of the aortic valve and ascending aorta. The significance of reconstructive methods on the aortic root]

BACKGROUND AND OBJECTIVE: The standard surgical repair of disease of the aortic valve and the ascending aorta has been combined replacement, which includes the disadvantage of inserting a mechanical valve. We have investigated an individualized approach which preserves the native valve. PATIENTS AND METHODS: Between October 1995 and October 1997, a consecutive total of 101 patients (72 men, 29 women, aged 21-83 years) underwent operations for disease of the ascending aorta: aortic dissection type A in 34 patients, aneurysmal dilatation in 67. Dilatation of the aortic arch was associated with aortic regurgitation in 58 patients. There were 11 patients with aortic valve stenosis or previously implanted aortic valve prosthesis among a total of 46 whose aortic valve was replaced (group II). Supracommissural aortic replacement with a Dacron tube was performed in 16 patients (group I) with normal valve cusps and an aortic root diameter < 3.5 cm. In 28 patients with an aortic root diameter of 3.5-5.0 cm the aortic root was remodelled (group III). Resuspension of the native aortic valve was undertaken in 11 patients with aortic root dilatation of > 5.0 cm (group IV). RESULTS: Operative intervention was electively performed in 72 patients, without any death. Of 29 patients operated as an emergency for acute type A dissection four died (14%). In 55 of the 58 patients with aortic regurgitation in proved possible to preserve native aortic valve (95%). In the early postoperative phase and after an average follow-up time of 11.8 months, transthoracic echocardiography demonstrated good aortic valve function, except in one patient each of groups III and IV who developed aortic regurgitation grades I or II. CONCLUSION: The described individualized approach makes it possible to preserve the native aortic valve in most patients with aortic regurgitation, at a low risk. Follow-up observations so far indicate good results of the reconstruction.

Valve reconstruction or replacement for long-term biopsy-induced tricuspid regurgitation following heart transplantation

Tricuspid regurgitation following heart transplantation can become a severe problem in a subset of patients, where medical therapy fails. Operative findings are described and results of subsequent results with surgical intervention including repair and replacement are analysed. Although follow-up is short, tricuspid replacement seems superior to reconstruction following heart transplantation. Best results are obtained, if replacement is performed, before right ventricular function deteriorates.

Tricuspid valve regurgitation attributable to endomyocardial biopsies and rejection in heart transplantation

In the present report the prevalence, severity, and risk factors of tricuspid valve regurgitation (TR) in 251 heart transplant recipients have been analyzed retrospectively. Tricuspid valve function was studied by color-flow Doppler echocardiogram and annual heart catheterization. The presence or severity of TR was graded on a scale from 0 (no TR) to 4 (severe). Additional postoperative data included rate of rejection, number of endomyocardial biopsies, incidence of transplant vasculopathy, and preoperative and postoperative hemodynamics. The incidence of grade 3 TR increases from 5% at 1 year to 50% at 4 years after transplantation. Multivariate analysis showed rate of rejection and donor heart weight to be significant risk factors. The ischemic intervals as well as the preoperative and postoperative pulmonary hemodynamics did not affect the severity or prevalence of TR. These results indicate that various factors appear to have an impact on the development of TR and that the prevalence might be lowered by a reduction of the number of biopsies performed and when possible, oversizing of donor hearts.

Temporal and spatial variability of personal exposure to radio frequency electromagnetic fields

BACKGROUND: Little is known about the population's exposure to radio frequency electromagnetic fields (RF-EMF) in industrialized countries. OBJECTIVES: To examine levels of exposure and the importance of different RF-EMF sources and settings in a sample of volunteers living in a Swiss city. METHODS: RF-EMF exposure of 166 volunteers from Basel, Switzerland, was measured with personal exposure meters (exposimeters). Participants carried an exposimeter for 1 week (two separate weeks in 32 participants) and completed an activity diary. Mean values were calculated using the robust regression on order statistics (ROS) method. RESULTS: Mean weekly exposure to all RF-EMF sources was 0.13 mW/m(2) (0.22 V/m) (range of individual means 0.014-0.881 mW/m(2)). Exposure was mainly due to mobile phone base stations (32.0%), mobile phone handsets (29.1%) and digital enhanced cordless telecommunications (DECT) phones (22.7%). Persons owning a DECT phone (total mean 0.15 mW/m(2)) or mobile phone (0.14 mW/m(2)) were exposed more than those not owning a DECT or mobile phone (0.10 mW/m(2)). Mean values were highest in trains (1.16 mW/m(2)), airports (0.74 mW/m(2)) and tramways or buses (0.36 mW/m(2)), and higher during daytime (0.16 mW/m(2)) than nighttime (0.08 mW/m(2)). The Spearman correlation coefficient between mean exposure in the first and second week was 0.61. CONCLUSIONS: Exposure to RF-EMF varied considerably between persons and locations but was fairly consistent within persons. Mobile phone handsets, mobile phone base stations and cordless phones were important sources of exposure in urban Switzerland.

Persistent diastolic dysfunction late after valve replacement in severe aortic regurgitation

BACKGROUND: Regression of left ventricular (LV) hypertrophy with normalization of diastolic function has been reported in patients with aortic stenosis late after aortic valve replacement (AVR). The purpose of the present study was to evaluate the effect of AVR on LV function and structure in chronic aortic regurgitation early and late after AVR. METHODS AND RESULTS: Twenty-six patients were included in the present analysis. Eleven patients with severe aortic regurgitation were studied before, early (21 months) and late (89 months) after AVR through the use of LV biplane angiograms, high-fidelity pressure measurements, and LV endomyocardial biopsies. Fifteen healthy subjects were used as controls. LV systolic function was determined from biplane ejection fraction and midwall fractional shortening. LV diastolic function was calculated from the time constant of LV relaxation, peak filling rates, and myocardial stiffness constant. LV structure was assessed from muscle fiber diameter, interstitial fibrosis, and fibrous content. LV muscle mass decreased significantly by 38% early and 55% late after surgery. Ejection fraction was significantly reduced preoperatively and did not change after AVR (P=NS). LV relaxation was significantly prolonged before surgery (89+/-28 ms) but was normalized late after AVR (42+/-14 ms). Early and late peak filling rates were increased preoperatively but normalized postoperatively. Diastolic stiffness constant was increased before surgery (22+/-6 versus 9+/-3 in control subjects; P=0.0003) and remained elevated early and late after AVR (23+/-4; P=0.002). Muscle fiber diameter decreased significantly after AVR but remained increased at late follow-up. Interstitial fibrosis was increased preoperatively and increased even further early but decreased late after AVR. Fibrosis was positively linearly correlated to myocardial stiffness and inversely correlated to LV ejection fraction. CONCLUSIONS: Patients with aortic regurgitation show normalization of macroscopic LV hypertrophy late after AVR, although fiber hypertrophy persists. These changes in LV myocardial structure late after AVR are accompanied by a change in passive elastic properties with persistent diastolic dysfunction.

Clinical and hemodynamic predictors of natriuretic peptide elevation among aortic valve disease patients

We investigated the relative contribution of hemodynamic and clinical factors to serum natriuretic peptide elevation in seventy-one patients with either aortic stenosis or aortic regurgitation. We found that pulmonary hypertension, heart failure and renal failure are the most powerful independent predictors of natriuretic peptide elevation in patients with aortic valve disease, irrespective of the type or severity of valvular lesion itself.