<p>Sudden death from arrhythmia is a major cause of mortality in the United States. Unfortunately, no current diagnostic test can accurately predict risk for sudden arrhythmic death. Because ventricular arrhythmias often result from abnormalities of repolarization, assessment of myocardial repolarization using the electrocardiogram (ECG) can aid in prediction of arrhythmia risk. Non-linear, rate-dependent changes in myocardial repolarization can promote the development of arrhythmia, but few studies examine how these dynamic changes in repolarization affect the ECG. This dissertation describes the use of a computer model to investigate the effect of dynamic changes in myocardial repolarization on the ECG T wave.</p><p>To simulate action potential conduction from the endocardium to the epicardium of the free wall of the canine left ventricle, 1-dimensional multicellular computer fiber models were created. Each fiber model was composed of endocardial, midmyocardial, and epicardial cells. For each cell type, existing mathematical models were modified to approximate experimental data for four types of dynamic repolarization behavior: (1) dynamic restitution, the response to steady-state pacing; (2) S1-S2 restitution, the response to a premature or postmature stimulus; (3) short-term memory (STM), the response to an abrupt change in pacing rate; and (4) repolarization alternans, beat-to-beat alternation in cellular repolarization time. Repolarization times were obtained from endocardial, midmyocardial, and epicardial regions in the fiber model and compared to parameters measured from a computed transmural ECG.</p><p>Spatial differences in repolarization created two voltage gradients that influenced the ECG: an endocardial-midmyocardial (endo-mid) gradient and a midmyocardial-epicardial (mid-epi) gradient. Epicardial dynamic restitution changes altered the mid-epi gradient, influencing the rising phase of the ECG T wave, and endocardial dynamic restitution changes altered the endo-mid gradient, influencing the falling phase of the T wave. Changes in epicardial or endocardial repolarization due to S1-S2 restitution or STM caused transient changes in the rising or falling phase of the T wave, respectively.</p><p>During repolarization alternans, an alternating, asymmetric distribution of extracellular potential around the fiber influenced the measurement of T-wave alternans (TWA) in the ECG. Presence of a resistive barrier in the fiber model altered the magnitude of repolarization alternans as well as the TWA amplitude in the ECG with effects dependent on barrier location. The resistive barrier also modified the relationship between cellular repolarization alternans magnitude and TWA amplitude.</p><p>The results presented in this dissertation explain basic mechanisms by which dynamic changes in myocardial repolarization affect the ECG T wave. These mechanisms form the foundation for the development of techniques to identify arrhythmogenic, dynamic changes in the myocardium using the ECG. Future studies in higher-dimensional, more complex models will build upon these results by considering the influence of additional voltage gradients, more realistic tissue geometries, and heterogeneities in the volume conductor.</p> / Dissertation

These studies were designed to evaluate the relationships between residual feed intake (RFI) and performance of growing heifers and Brahman cows. Residual feed intake was determined for 77 heifers of diverse breedtypes (Angus, Brahman, Hereford, Holstein, Jersey and F1 crosses) during both the pre- and post-pubertal periods. Heifers were individually fed and allowed ad libitum access to feed for 84 +/- 6 d during the prepubertal feeding trial and 90 +/- 4 d during the post-pubertal feeding trial. Brahmaninfluenced heifers had lower RFI than heifers without Brahman influence during both the pre-pubertal (P < 0.05) and post-pubertal (P < 0.0001) periods. Residual feed intake determined during the pre-pubertal period was only a moderate predictor (r = 0.48; P < 0.0001) of RFI determined during the post-pubertal period. Residual feed intake was determined for 38 Bonsmara heifers over a 70-d feeding period. Heifers were fed a high roughage diet at 2.65% of body weight (BW). Weekly blood serum samples were analyzed for progesterone concentration by radioimmunoassay (RIA) to determine puberty. There were no observed differences between efficient and inefficient heifers for performance traits, age at puberty or conception, or cumulative achievement of puberty and conception. The postpartum performance of Brahman primiparous (n=16) and multiparous (n=38) cows previously evaluated postweaning for RFI was investigated. Females were weighed and evaluated for body condition score (BCS) at 28-d intervals prior to the start of the 2008 calving season. Weekly weights and BCS were collected beginning 21 d after calving. Blood serum samples were also collected weekly for progesterone analysis by radioimmunoassay (RIA), non-esterified fatty acid (NEFA) analysis by enzymatic colorimetry, and insulin-like growth factor-I (IGF-I) analysis by RIA. Females were exposed to vasectomized marker bulls after calving to aid in estrus detection. Eight and ten d following observed estrus, females were evaluated using ultrasonography via rectal palpation to determine the presence of a corpus luteum (CL). Efficient cows exhibited estrus, developed functional corpora lutea, and exhibited estrus with CL formation earlier (P < 0.05) than inefficient cows. Furthermore, a greater percentage (P < 0.05) of efficient than inefficient cows were pregnant at the end of the breeding season.

Comparison of two or more failure time distributions based on interval-censored data is tested by extension of log-rank test proposed by Sun (1996, 2001, 2004). Furthermore, Chang (2004) verified that the proposed test statistics are approximately chi-cquare with degrees of freedom p-1 after constants factor adjustment which can be obtained from simulations. In this paper we approach in a different way to estimate the adjustment factor of a given interval-censored data by applying the bootstrap technique to the test statistics. Simulation results indicate that the bootstrap technique performs well on those test statistics except the one proposed in 1996. By using chi-square goodness of fit test, we found that Sun's test in 1996 is significantly far from any chi-square.

¡@¡@In recent year, orthogonal frequency division multiplexing ¡]OFDM¡^ technology has been widely used in high-speed communication systems. One primary reason for the popularity of OFDM is its ability to provide good performance in multi-path channels than the other systems through the use of Guard interval(GI). By using the Guard interval, it can convert these inter-symbol interference (ISI) channels into ISI-free channels. But Guard interval without any information will caused inter-channel interference. In order to solve this problem, a guard interval using cyclic prefix (CP) is inserted to avoid inter-symbol interference from the adjacent symbols and inter-channel interference from other sub-channels. However, using long cyclic prefix will decrease the transmission rate, reduce the spectral efficiency, and increase the signal-to-noise power ratio¡]SNR¡^loss. If we choose a shorter one, the channel length may be longer than the cyclic prefix. The interference caused by insufficient cyclic prefix can seriously degrade the performance of OFDM systems. In order to solve this problem, a time domain equalizer¡]TEQ¡^is usually used in the receiver to shorten the channel length of OFDM transmission system, and therefore minimize the ISI and ICI. However, because of its high complexity, the optimum design of TEQ is hard to realize. ¡@¡@So we use an iterative channel estimation technique between time domain and frequency domain to mitigate the ISI and ICI which is caused by insufficient cyclic prefix. The iterative technique can remove ISI and hold the circular convolution property. By utilizing the iterative technique we can improve the channel estimation performance as the OFDM symbol used sufficient cyclic prefix. ¡@¡@In the computer simulations, we consider the worst case that the OFDM symbol is transmitted without guard interval. The results show that our proposed method can effectively suppress residual ISI. The comparison between our proposed method including both proposed channel estimation¡]PCE¡^and proposed data demodulation¡]PDD¡^, decision feedback channel estimation¡]DFCE¡^, avoid ISI preamble channel estimation¡]AISIP¡^, and residual ISI cancellation¡]RISIC¡^algorithm are made in this thesis. Finally, the performance improvement of the proposed algorithm under several channel conditions is considered and compared with other algorithms.

The aim of this study is to understand students¡¦ solutions (to problems related to time, time interval, and time unit conversion) and to analyze their common errors and possible causes. Students¡¦ problem-solving strategies and error types were also categorized and used as a reference for improvement in teaching and a scaffold for supporting students' learning. Findings in this research were three: 1. Distinction between time and interval. Students were performing better in the concept of interval than in the concept of time. They also performed well in total time consumed and in daily life problems such as clock time. However, problems with longer text description would make it harder for students to do problem solving in the concept of time and interval. 2. Problem-solving types. The problem-solving types ranked by the frequency are: (1) processing larger units first; (2) converting time from high scale to low scale and vice-versa; (3) using fractions; (4) using decimals; and (5) using addition. 3. Error types: The error types presented by students in solving time-related problems include: (1) interference of the decimal; (2) interference between non-decimal time conversion systems; (3) insufficient knowledge about division; (4) unclear concept about high and low scales of time; (5) incorrect calculation; (6) influence of the clock dial structure; (7) incorrect problem-solving strategy; (8) misjudgment of keywords; and (9) ignorance of problem conditions.

Thesis (M.S. in C.E.E.)--School of Civil and Environmental Engineering, Georgia Institute of Technology, 2004. Directed by Rafi Muhanna. / Includes bibliographical references (leaves 125-126).

Recent research suggests that [beta]-hydroxy-[beta]-methylbutyrate (HMB), a metabolite of leucine (Leu), increases muscle mass and attenuates muscle damage during resistance training. Although Leu acts as a potent stimulator of protein synthesis, HMB, but not Leu, has been reported to be effective in suppressing proteolysis in skeletal muscle. However, mechanisms for the effects of HMB on cell signaling pathways controlling muscle protein turnover during rest and after endurance exercise are still poorly understood. Furthermore, the effects of HMB on cell signaling pathways controlling protein synthesis and degradation under normal in vivo conditions warrant further investigation. For optimal gains in muscle mass, the appropriate type and amount of protein (PRO) is required for positive protein balance to occur in skeletal muscle. Therefore, this dissertation was designed to determine the effect of HMB, PRO and Leu, individually and in combination, on the regulation of cellular signaling pathways controlling muscle protein turnover during sedentary and post-exercise conditions. Study 1 demonstrated that, compared with HMB and PRO alone, the combination of HMB and PRO was more effective in activating the mTOR signaling pathway, which controls protein synthesis, and inhibiting FOXO3A, a major regulator of the ubiquitin-proteasome proteolytic signaling pathway. Study 2 demonstrated that, compared with its individual components, a novel HMB/PRO/Leu supplement better activated protein-synthetic signals and inhibited proteolytic signals in skeletal muscle, and these effects were better sustained. Finally, Study 3 demonstrated that adding Leu to PRO-enriched mixtures after exercise additively activated protein-synthetic signals in a fiber type-specific manner, and adding HMB clearly inhibited proteolytic signaling proteins. Furthermore, provision of an HMB/PRO/Leu supplement after exercise was found to favorably modulate signaling pathways controlling both protein synthesis and degradation. Taken together, the results of these studies suggest that a novel nutrient supplement, composed of HMB, Leu and PRO, additively enhances the intracellular signaling proteins controlling protein synthesis and attenuates signaling proteins controlling proteolysis in skeletal muscle during sedentary and post-exercise recovery. Therefore, such a supplement may be beneficial for both athletic and therapeutic purposes. / text

Intermittent power sources such as wind and solar are increasingly penetrating electrical grids, mainly motivated by global warming concerns and government policies. These intermittent and non-dispatchable sources of power affect the operation and control of the power system because of the uncertainties associated with their output power. Depending on the penetration level of intermittent sources of power, the electric grid may experience considerable changes in power flows and synchronizing torques associated with system stability, because of the variability of the power injections, among several other factors. Thus, adequate and efficient techniques are required to properly analyze the system stability under such uncertainties. A variety of methods are available in the literature to perform power flow, transient, and voltage stability analyses considering uncertainties associated with electrical parameters. Some of these methods are computationally inefficient and require assumptions regarding the probability density functions (pdfs) of the uncertain variables that may be unrealistic in some cases. Thus, this thesis proposes computationally efficient Affine Arithmetic (AA)-based approaches for voltage and transient stability assessment of power systems, considering uncertainties associated with power injections due to intermittent sources of power. In the proposed AA-based methods, the estimation of the output power of the intermittent sources and their associated uncertainty are modeled as intervals, without any need for assumptions regarding pdfs. This is a more desirable characteristic when dealing with intermittent sources of power, since the pdfs of the output power depends on the planning horizon and prediction method, among several other factors. The proposed AA-based approaches take into account the correlations among variables, thus avoiding error explosions attributed to other self-validated techniques such as Interval Arithmetic (IA).

Thesis (Ph. D.)--University of Wisconsin--Madison, 1970. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliography.

In a mobile robotic system, the interaction with the surrounding environment is essential in order to complete tasks such as localisation and mapping. This interaction can only be conducted by means of sensors that permit the accumulation of a large amount of information from several sources. However, this information is useless without adequate interpretation; thus, in order to accurately determine the positioning of the robot, it is necessary to identify and characterise landmarks in the environment required to serve as anchoring points for both localisation and mapping. Having constructed the map, an accurate analysis of the information gathered is vital. In this manner, this work is focused on two main aspects of any mobile robotic system: first, the detection and characterisation of highly descriptive landmarks by using image and point cloud processing techniques; and second, the geometrical and spatial analysis of the information gathered from the environment. For the former, two novel techniques based on image processing and geometrical analysis are presented; for the latter, a guaranteed technique for the parameter estimation of primitive shapes using interval analysis is proposed.