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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.
1

A Temporal White Noise Analysis for Extracting the Impulse Response Function of the Human Electroretinogram

Zele, A., Feigle, B., Kambhampati, P., Aher, A., McKeefry, Declan J., Parry, Neil R.A., Maguire, John, Murray, I.J., Kremers, Jan January 2017 (has links)
Yes / Purpose: We introduce a method for determining the impulse response function (IRF) of the ERG derived from responses to temporal white noise (TWN) stimuli. Methods: This white noise ERG (wnERG) was recorded in participants with normal trichromatic vision to full-field (Ganzfeld) and 39.38 diameter focal stimuli at mesopic and photopic mean luminances and at different TWN contrasts. The IRF was obtained by cross-correlating the TWN stimulus with the wnERG. Results: We show that wnERG recordings are highly repeatable, with good signal-tonoise ratio, and do not lead to blink artifacts. The wnERG resembles a flash ERG waveform with an initial negativity (N1) followed by a positivity (P1), with amplitudes that are linearly related to stimulus contrast. These N1 and N1-P1 components showed commonalties in implicit times with the a- and b-waves of flash ERGs. There was a clear transition from rod- to cone-driven wnERGs at ~1 photopic cd.m 2. We infer that oscillatory potentials found with the flash ERG, but not the wnERG, may reflect retinal nonlinearities due to the compression of energy into a short time period during a stimulus flash. Conclusion: The wnERG provides a new approach to study the physiology of the retina using a stimulation method with adaptation and contrast conditions similar to natural scenes to allow for independent variation of stimulus strength and mean luminance, which is not possible with the conventional flash ERG. Translational Relevance: The white noise ERG methodology will be of benefit for clinical studies and animal models in the evaluation of hypotheses related to cellular redundancy to understand the effects of disease on specific visual pathways.
2

Spatial resolution limits for the reconstruction of acoustic source distribution by inverse techniques

Kim, Youngtae January 2002 (has links)
No description available.
3

The Estimation of the RapidScat Spatial Response Function

Bury, Samuel Gary 01 April 2018 (has links)
RapidScat is a pencil-beam wind scatterometer which operated from September 2014 to August 2016. Mounted aboard the International Space Station (ISS), RapidScat experiences significant altitude and attitude variations over its dataset. These variations need to be properly accounted for to ensure accurate calibration and to produce high resolution scatterometer images. Both the antenna pose and the one-way antenna pattern need to be validated. The spatial response function (SRF) is the two-way antenna pattern for a scatterometer combined with the processing and filtering done in the radar system electronics, and is dominated by the two-way pattern. To verify the pointing of the RapidScat antenna, the RapidScat SRF is estimated using on-orbit data. A rank reduced least squares estimate is used, which was developed previously for the Oceansat-2 (OSCAT) scatterometer [1]. This algorithm uses a small, isolated island as a delta function to sample the SRF. The island used is Rarotonga Island of the Cook Islands. The previously developed algorithm is updated to estimate the SRF in terms of beam azimuth and elevation angle rather than in kilometers on the ground. The angle-based coordinate system promotes greater understanding of how the SRF responds to biases and errors in antenna geometry. The estimation process is simulated to verify its accuracy by calculating the SRF for several thousand measurements in the region of Rarotonga. The calculated SRFs are multiplied by a corresponding synthetically created surface and integrated to yield simulated backscatter measurements, with added white noise. The SRF estimation algorithm is then performed. The results of the simulation show that the SRF estimation process yields a close estimate of the original SRF. The antenna pointing is validated by introducing a fixed offset in azimuth angle into the simulation and observing that the SRF is correspondingly shifted in the azimuth-elevation grid. The SRF computed from real data shows that there is an azimuth rotation angle bias of about 0.263 degrees for the inner beam and about 0.244 degrees for the outer beam. Since the SRF is dominated by the two-way antenna pattern, it can be modeled as the product of two identical one-way antenna patterns which are slightly offset from each other due to antenna rotation during the transmit/receive cycle. A method is developed based on this model to derive the one-way antenna pattern from the estimated SRF. Using a Taylor series expansion the one-way antenna pattern is computed from the SRF. The derived pattern recovers the SRF with small error, but there is significant error in the inferred one-way pattern when compared to the pre-launch estimated RapidScat one-way antenna pattern.
4

The Effect of Bonner Sphere Borehole Orientation on Neutron Detector Response

Brittingham, John Macdougall 01 December 2010 (has links)
This thesis investigates the differences in Bonner Sphere detector response for anisotropic neutron fields as a function of borehole orientation. Monte Carlo simulations using MCNPX were used to calculate the difference for a borehole oriented directly behind a unidirectional neutron field and one in which the borehole is normal to the neutron flux. The differences in detector response depend on the size of the Bonner Sphere and the energy of the incident flux, which could introduce significant error in the determination of the neutron field’s energy spectrum.
5

A New Approach to Estimate the Incidence of the Corporate Income Tax

Vasquez-Ruiz, Harold A. 12 April 2012 (has links)
After Harberger published his influential paper in 1962, many authors have assessed empirically whether the incidence of the corporate income tax (CIT) falls on capital owners, consumers, or workers (Krzyzaniak and Musgrave, 1963; Gordon, 1967; Arulampalam et al., 2008). Today, there is little agreement among economists about who bears the incidence of the CIT (Gruber, 2007; Harberger, 2008a,b). The reason for the little convincing evidence is that the econometric models used in the literature ignore that the factors that motivate changes in corporate tax policy are sometimes correlated with other developments in the economy and disentangling those effects from exogenous policy changes requires tremendous effort. Using annual information at the industry level for the United States, I propose to investigate the consequences of exogenous changes in corporate tax policy. The identification of these exogenous events follows the work of Romer and Romer (2009, 2010), who provide an extensive analysis of the U.S. federal tax legislation using narrative records from presidential speeches and congressional reports, among other documentations. The results validate the original predictions from Harberger (1995, 2008a). That is, in the short-term, capital owners bear the full burden of the tax. Over time, however, capital owners are able to shift this burden either by raising consumers' goods prices, or decreasing workers' wages. The magnitude of these e ects depends on the degree of capital intensity as well as the access to international markets and the availability of substitutes for the industry under consideration.
6

Economic Policy Effect in Quterly-dependence VAR model: Empirical Analysis of Taiwanese cases

Liu, Chun-I 30 June 2010 (has links)
abtract This paper uses a seasonal dependence VAR model that is proposed by Olivei and Tenreyro in the year 2007.We are to assess whether the effect of a policy exogenous shock differs according to the quarter in which the shock occur. We consider Taiwan as a small open economy with flourishing international trade; the effect of exchange rate is viewed as an important transmission channel in monetary transmission mechanism. First part, we consider domestic monetary policy shock how to influence macroeconomic variables. Second part, the United State is powerful around the world. The Fed policies whether affect Taiwan macroeconomic or not. Finally, discuss an exogenous shock on the exchange rate to impact Taiwan macroeconomic.
7

The Analysis of Long-run Real Exchange Rate in Japan

Liu, Ya-chun 26 July 2010 (has links)
Purchasing Power Parity (PPP) has been regarded as the most important theory to explain the exchange rate movement based on relative price levels of two countries. After 1973, more and more countries were taking the floating exchange rate system, and the real exchange is testing out to be a non-stationary time seriess. This would be some real factors to have an effect on the real exchange rate. In the article, We study how these possible factors change the real exchange rate and make use of Wu et.al (2008) and Lee (2010)¡¦s local projection to estimate the impulse responses under the non-stationary time series which has cointegration vectors, and then we compare the difference between the impulse response in conventional VAR and the impulse response in Local Projection. The emprical model we use is the smae one as in Zhou (1995) and Wang and Dunne (2003), and the rule of the data is the same as in Wang and Dunne (2003). Finally, we get the consistent conclusion with Wu et.al (2008), Zhou (1995) and Wang and Dunne (2003).
8

The Impulse Response Analysis of General Inference on Cointegration Vector for Non-Stationary Process by Local Projection

Lin, Meng-wei 26 July 2010 (has links)
Jorda (2005) proposed the new method to estimate impulse response functions by local projection. The new method, local projection, can avoid the misspecification problem. That is, local projections are robust to misspecification of the data generating process (DGP). Wu, Lee, and Wang (2008) extended the Jorda¡¦s local projection from stationary time series I(0) to non-stationary time series I(1). It makes the local projection be a more generally applicative method for the Macroeconomic. In the article, I relax the cointegration vector which assumed to be known in the Wu, Lee, and Wang (2008) and Lee(2010). From the inference of Johansen (1995) I can get the property of super-consistent between £] and ˆ £] in the cointegration vector. I use the above condition and OLS to estimate impulse response functions, and in the asymptotic theorem, the cointegration vectors which assumed to be known or estimated by Johansen MLE are both get the consistent coefficients of impulse responses.
9

The Impact of The Monetary Polciy in Taiwan-A FAVAR Model Approach

Chu, I-Ching 19 July 2011 (has links)
This paper applies a Factor-Augmented VAR model proposed by Bernanke, Boivin and Eliasz (2005) to measure the impact of the monetary policy in Taiwan. Our empirical results show that, first, the more the factors added in the benchmark VAR, the more we can explain the price puzzle problem. Second, the effect of the tightening in the monetary policy (the increase in the interbank overnight lending rate) is inconsistent with the results expected by the credit channel.
10

History matching pressure response functions from production data

Ibrahim, Mazher Hassan 17 February 2005 (has links)
This dissertation presents several new techniques for the analysis of the long-term production performance of tight gas wells. The main objectives of this work are to determine pressure response function for long-term production for a the slightly compressible liquid case, to determine the original gas in place (OGIP) during pseudosteady state (PSS), to determine OGIP in the transient period, and to determine the effects of these parameters on linear flow in gas wells. Several methods are available in the industry to analyze the production performance of gas wells. One common method is superposition time. This method has the advantage of being able to analyze variable-rate and variable-pressure data, which is usually the nature of field data. However, this method has its shortcomings. In this work, simulation and field cases illustrate the shortcomings of superposition. I present a new normalized pseudotime plotting function for use in the superposition method to smooth field data and more accurately calculate OGIP. The use of this normalized pseudotime is particularly important in the analysis of highly depleted reservoirs with large change in total compressibility where the superposition errors are largest. The new tangent method presented here can calculate the OGIP with current reservoir properties for both constant rate and bottomhole flowing pressure (pwf) production. In this approach pressure-dependent permeability data can be integrated into a modified real gas pseudopressure,m(p), which linearizes the reservoir flow equations and provides correct values for permeability and skin factor. But if the customary real-gas pseudopressure, m(p) is used instead, erroneous values for permeability and skin factor will be calculated. This method uses an exponential equation form for permeability vs. pressure drop. Simulation and field examples confirm that the new correction factor for the rate dependent problem improves the linear model for both PSS and transient period, whether plotted on square-root of time or superposition plots.

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