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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
161

Gain Flattening Design For Optical Fiber Amplifier By Long-Period Fiber Gratings

Ke, Chun-Hao 20 August 2004 (has links)
Using Long-Period Fiber Gratings as component of Gain-Flattening filter ofOptical Amplifier, and discuss spectrum of different struture of Long-Period Fiber Gratings. To investigate the spectra characteristics of Long-Period fiber Gratings for designing reference resources. Aiming at different Gain-Flattening filter uses different struture of fiber grating, and the decision of parameter of fiber grating using Genetic Algorithm. Finally delcaring the dataflow of designing filter using Long-Period Fiber Grating and conclusion.In this paper , gain flatttening Cr:YAG optical amplifier spectrum and Erbium-doped optical amplifier spectrum,one achieve 300nm bandwidth and another achieve 40nm.
162

Evaluation of the genetic gain in upland cotton during the twentieth century

Schwartz, Brian Matthew 25 April 2007 (has links)
Genetic gain studies in the past have been used to evaluate the historical improvement of different traits and give insight into what magnitudes of gain might be possible in the future. Additionally, they have been carried out to defend the role of genetics during periods of stagnant or decreasing yield trends. This study was conducted over a 2-year period (2003 and 2004) and included nine current or obsolete cotton (Gossypium hirsutum L.) cultivars grown in 5 plant densities designed to evaluate varying levels of interplant competition. Plant densities were single plant culture with plants spaced 3m x 3m, 2m x 2m, 1m x 1m, 1m x 0.3m, and two commercial populations with plants spaced 1m x 0.1m. Results were analyzed for each trait to determine whether genetic gains are interrelated with tolerance to interplant competition or strictly under genetic control. The rates of genetic gain for lint yield were highest in the 1m x 0.1m, 1m x 0.3m, and 1m x 1m treatment with slopes of 8.7, 8.2, and 7.1 kg ha-1 yr-1 respectively. The slopes were each significantly smaller in the 2m x 2m and 3m x 3m spaced populations with gains of 3.6 and 1.5 kg ha-1 yr-1 respectively, implying that for lint yield, genetic gains have been made for tolerance to interplant competition. Similarly, modern maize hybrids only out perform obsolete hybrids at higher plant densities. Genetic gain for lint yield, fiber length, fiber strength, and fiber micronaire made in the context of tolerance to interplant competition is due in large part to the excellent performance of Deltapine 491 (2002) at higher plant populations.
163

A Novel Adaptive Scheme for Widening the Stable Input Range of a Sigma-Delta Modulator

Wang, Fa-Ping 15 July 2008 (has links)
Noise shaping is one of the distinguishing characteristics of the sigma-delta modulation technique that separates it from other types of pulse-width modulation schemes. In sigma-delta modulation, unwanted noise and harmonics caused by quantization are intentionally pushed toward the high-frequency band in order to achieve high resolution data conversion within the signal bandwidth. Due to its robust, high in-band linearity, the sigma-delta modulation technique finds numerous applications in industry. Generally speaking, as the order of a sigma-delta modulator increases, the modulator performance becomes better, which unfortunately comes along with a decrease in the modulator¡¦s stable input range. This thesis presents a novel adaptive law which is capable of on-line tuning the loop filter of a sigma-delta modulator and reducing the out of band gain of the resulting noise transfer function when the modulator input is large, thereby widening the stable input range of the modulator without significant sacrifice of the performance. The simulation and experimental results prove the effectiveness of the proposed adaptive sigma-delta modulator.
164

Design of a Miniature Left-Handed Material for Gain Improvement of Antenna with Low Sensitivity to Return Loss

Lin, Kun-Hsien 24 July 2008 (has links)
In this thesis, we introduce a LHM (Left-Handed Material) with both negative permittivity and permeability. Improvement of gain antenna is achieved by utilizing the characteristics of the LHM which can focus the EM wave. We start with an analysis of electromagnetic characteristic of LHM, especially its negative index of refraction. Structures with only negative permittivity or negative permeability are also analyzed. Then, we design the structure of LHM that can reduce the sensitivity of S11 of an antenna. So that the antenna operating frequency is not changed even in the presence of the LHM. The LHM unit cell structure comes from the idea by combination of two basic SNG (Single Negative) structure. We design a unit cell whose index of refraction is negative and close to zero. Further, we combine LHM and antenna. Simulation and measurement results show that the LHM is effective. The reflection coefficient of antenna does not change much by the combination of proposed LHM. The half power beam¡Ðwidth of antenna become narrower. The antenna gain improvement can be about 3 dB or higher. Finally, the LHM has been miniaturized successfully, resulting in reduction in size by about 50%. Comparing simulation and measurement, we find the LHM is still effective. A dipole antenna is used to verify out design. The antenna gain has been enhanced and the reflection coefficient does not change much.
165

Copula models with Weibull distributions : application in fading channels.

Tseng, Tzu-chiang 23 July 2009 (has links)
In this work, copula models for fitting bivariate response data with Weibull marginal distributions are studied, which are motivated by the need of model fading channels in signal applications. The analytical expressions for the joint probability density function (p.d.f.), and joint cumulative distribution function (c.d.f.) are utilized as the bivariate distribution of the fading channels data with not necessarily identical fading parameters and average powers. The performances of outage probability employing diversity receivers, called as selection combining (SC), equal-gain combining (EGC), and maximal-ratio combining (MRC) of two diversity receivers under bivariate copula models with Weibull marginal distributions are presented. They are also compared with the results in Sagias (2005) where the data assumed to follow the bivariate Weibull distribution. It will be demonstrated that the copula models can approximate the bivariate Weibull distribution used in Sagias (2005) very closely with suitable copula model, and the computations for obtaining the performances of outage probability under SC are much simplified. Keywords and phrases: equal-gain combining, maximal-ratio combining, selection combining
166

Changes in retained weight and waist circumference during the first six months postpartum : a latent growth curve model

Cheng, Hsiu-Rong 21 October 2013 (has links)
Few studies have measured the changes of postpartum weight retention (PWR), and none of them have assessed the effect of pregnancy on waist circumference (WC) in Taiwanese women. The primary aims of this longitudinal study were to explore the changes in body weight and WC during the first six months postpartum and to identify the explanatory factors of PWR and of WC. A theoretical framework that incorporated Bandura's social learning theory and the results of a literature review was used to guide this study. Structured questionnaires were used for data collection. Postpartum body weight and WC were measured. Data were collected from May 2011 to January 2013 and analyzed using the SPSS 19.0 and Mplus 6.12. A sample of 200 healthy postpartum women was recruited from three clinics in Tainan City, Taiwan. The mean age of the women was 31.19 years, and the majority of them were married (98.0%), primiparas (56%), had a bachelor's degree (52.5%), and planned to have this pregnancy (62.5%). The mean prepregnancy body weight was 55.84 kg, and the mean GWG was 13.76 kg. About one third of the sample gained weight exceeding the GWG recommendations of the IOM. The mean PWR decreased over time from 9.13 kg at hospitalization to 2.73 kg at 6 months postpartum. Approximately 24% of the participants still retained 5 kg or more at 6 months postpartum, and about 44% of the women had at least one kind of weight-related risk--substantial PWR, overweight, or central obesity. Age, prepregnancy BMI, parity, GWG, and place for doing the month significantly affected PWR. The final latent growth curve (LGC) model of PWR explained 91.5% and 33.9% of the variance in initial status and overall change rate in PWR. Age, prepregnancy BMI, parity, GWG, and cesarean delivery significantly affected WC, which explained 84.1% and 38.1% of the variance in initial status and change rate in WC. GWG was the most influential factor in the change rate of PWR and WC. Establishing tailored recommendations for GWG for Taiwanese women is warranted. / text
167

Loss compensation in a plasmonic nanoparticle array

Miller, Shannon Marie 20 November 2013 (has links)
The problem of heavy material and radiative losses in plasmonic devices has held back their implementation for compact and high-speed data storage and interconnects. One of the most interesting solutions to this problem currently under exploration is the addition of a gain material in close proximity to the metallic nanostructures for loss compensation. Here the physics of light transport in a nanoparticle array, and the operation of gain media in contact with the structure, are described and analytically modeled. A two-dimensional array of closely spaced gold nanoparticles has been fabricated by focused ion beam milling, and its electromagnetic response in the presence or absence of a dye coating has been simulated in preparation for pump-probe optical testing. The compensation of losses via a fluorophore coating has been proven for the first time in this geometry, for a physically realized sample. / text
168

Övervikt och fetma under graviditet

Blixt, Anne-Sofie, Mejerblad, Maria January 2008 (has links)
ABSTRACT Overweight and obesity is an increasing problem worldwide although high-income countries take a leed. High BMI during pregnancy and delivery constitute to many risks for both the mother and her outcome. Intervention programmes with the purpose to get the pregnant women to eat healthier and to excercise more are now working out in many different shapes. The effect of these activities varies. The aim of this study was to investigate if interventions during pregnancy, with women who’s BMI are 25 or more, affects health of the mother and her expected child, delivery outcome and self estimated health. The design of this study was quantitative. A total of 163 women participated in this study who took place i two cities in Sweden. All of the women gave birth at the same hospital. 96 of the women participated in the intervention group and 69 in the comparison group. Data was analyzed using SPSS. The results shows that most of the women (60 percent), choose not to participate in water aerobics. The results of the women who used a stepcounter showed that the women were more active during early pregnancy than later on. Results showed that there was a significantly increased risk for complications during delivery if the women had gained more than seven kilograms during pregnancy. Overweight women who had a weight gain of more than seven kilograms also had an increased risk for delivering large babies (more than 4000 gram), compared with those who gained less. There were no difference in self estimated health between the groups. The results of the study shows that a weight gain less than eight kilograms is positively associated with less complications during pregnancy. Women should be helped to get motivated to live a healthy and active life during pregnancy. What motivates pregnant women towards healthier living needs to be examined further.
169

Computational Gains Via a Discretization of the Parameter Space in Individual Level Models of Infectious Disease

FANG, XUAN 13 January 2012 (has links)
The Bayesian Markov Chain Monte Carlo(MCMC) approach to inference is commonly used to estimate the parameters in spatial infectious disease models. However, such MCMC analyses can pose a hefty computational burden. Here we present new method to reduce the computing time cost in such MCMC analyses and study its usefulness. This method is based a round the discretization of the spatial parameters in the infectious disease model. A normal approximation of the posterior density of the output from the original model will be compared to that of the modified model, using the Kullback-Leibler(KL) divergence measure.
170

Psychosocial Processes Influencing Weight Management Among Persons Newly Prescribed Atypical Antipsychotic Medications

Xiao, Sarah 08 September 2010 (has links)
PURPOSE: To generate a theory of the psychosocial processes influencing weight management among persons newly prescribed atypical antipsychotic medications. RESEARCH QUESTIONS: 1. What influences weight management in persons with first-episode psychosis who are newly prescribed atypical antipsychotic medications? 2. How is weight management facilitated in persons with first-episode psychosis who are newly prescribed atypical antipsychotic medications? 3. What psychosocial processes impede weight management in persons with first-episode psychosis who are newly prescribed atypical antipsychotic medications? METHODS: A qualitative, grounded theory research design was used to guide the study. Semi-structured interviews were the method of data collection and analysis was performed using constant comparison. SAMPLE & SETTING: A sample of 10 participants with first-episode psychosis prescribed atypical antipsychotics for at least eight weeks and six participants with a diagnosis of chronic schizophrenia who have been taking atypical antipsychotic medication for at least three years were obtained from an Outpatient Psychiatric program using theoretical sampling. FINDINGS: Contextual factors influencing weight management were: accessibility to resources, unstructured lifestyle, and others’ perception of their weight. Conditions influencing weight management were: rapid weight gain, insatiable hunger, and a lack of motivation boosters. Participants’ early responses to actions influencing weight gain management included discontinuing medications, choosing lower calorie foods, using walking in daily activities as exercise, accepting weight gain, and trying to manage weight but giving up. The consequences revealed from data analysis were contemplating weight management and not trying, as the barriers to weight management substantially exceeded the facilitators and many procrastinated in taking on any weight management strategies. CONCLUSION: The theoretical framework developed in this study can assist with the understanding and management of weight gain among this unique population. / Thesis (Master, Nursing) -- Queen's University, 2010-09-06 00:12:11.781

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