No description available.

What information is used by the visual system to detect patterns? A standard model hypothesizes that both spatial frequency and orientation information are processed by independent channels, meaning there is no summation among channels. Despite consensus among researchers on how the visual system sums spatial frequency and orientation information there are data in the literature (Kersten, 1987) that ostensibly contradict the standard model. To resolve this conflict, we measured the efficiency of spatial frequency and orientation of filtered noise. To learn what information the visual system uses when detecting filtered noise, we applied a technique that can determine the information used to detect and discriminate filtered visual noise. In Chapter 2 the detection of spatial frequency filtered noise is not only efficient but remains so with stimulus uncertainty and extremely brief (10ms) stimulus duration. When the spatial frequency channel used was measured, we found a fixed bandwidth channel as the spatial frequency of the pattern was increased. To test the standard model, we implemented simulations of the standard model and contrary to the interpretation, the standard model could predict detection of spatial frequency filtered noise. Chapter 3 used spatial frequency filtered noise to relate the detection and discrimination of filtered visual noise. A simple rule relates what information observers use to detect and discriminate spatial frequency filtered noise. Chapter 4 extends the work of Chapter 2 to orientation information and found that orientation filtered noise is detected efficiently. We again measured what information observers used and found that, unlike SF filtered noise, observers use orientation in a flexible or adjustable manner. / Thesis / Doctor of Philosophy (PhD)

The electrical activity recorded from the human colon could play an important role in analyzing the pattern of contractions under different physiologic or experimental states. In general, the frequency of the electrical activity is extremely irregular and time-varying. Its analysis requires a technique that considers variations in both time and frequency domains. The research undertaken was to analyze time-frequency variations of the human colonic electrical activity, to implement positive time- frequency distribution techniques in a computer system and to analyze theoretical signals using this technique to characterize a kernel function. Our results show that the uncertainty coefficient together with the marginal conditions and the average of the conditional PTFD in time and also in frequency can be applied to determine which kernel function and c-value were appropriate for calculating the PTFD of a sinusoidal signal. The selected kernel function constituted a comparative template of signals with similar characteristics. We found that those results were useful in analyzing the time- frequency variations of the electrical activity recorded in the human colon. The comparison of relative contributions of frequency bands showed that the band with the highest values during the pre- and interprandial period was 30-40 cpm suggesting an important role in the generation of bursts of these signals. The numerical results suggested that a meal can induce changes in the relative importance of frequencies below 10 cpm and a significant change in the 30-40 cpm band. In addition, a computer program of the Chakravarti method was implemented to calculate the Fourier transform of nonperiodical signals. This program was part of the computer program system developed to compute the PTFD of theoretical and experimental signals. / Thesis / Master of Engineering (MEngr)

No / In the past fifty years it has been clearly identified that the presence of biological tissues effect the performance of the antenna and considerable effort has been made to improve the characteristics of the mobile phone antenna's but very less effort has been put in to evaluate the effects of the radio frequency and energy absorption by the biological organisms and their effect. In this work as part of a bigger work package we have evaluated the effects of the handset orientation on the values of SAR and radiation efficiency as well as the effect of the distance upon these values. The study has produced some very interesting results showing that the most common way of holding the mobile phone i.e. microphone close to the mouth produces the highest SAR values.

Two algorithms for estimating the frequency and power of the carriers of 20 GHz and 30 GHz satellite signals are compared. Both algorithms operate on a prefiltered sequence generated by lowpass filtering followed by signal decimation for the purpose of sampling rate reduction. The lowpass filtering is accomplished via the overlap-add method of FIR filtering using the FFT. Carrier frequency prediction and tracking is accomplished with a Kalman predictor, for which the frequency drift process is modeled via polynomial extrapolation. The Kalman predictor operates on frequency measurements provided by one of two frequency estimators. One of the frequency estimation algorithms, a refinement of the DFT-automatic frequency control technique, uses the Chirp-Transform algorithm in its aim for the maximum likelihood estimate of frequency and power. The averaged periodogram is computed from the prefiltered sequence and is used to measure the frequency of the drifting frequency signal as well as its power. One of the disadvantages of this algorithm is the bias present in the estimation of power. The bias can be removed only with knowledge of the noise power. The algorithm has the advantage of being almost exclusively a convolution and therefore is accomplished with minimal computation via the FFT. An alternative parametric approach to frequency estimation is also investigated. In this approach the weighted least-squares modified Yule-Walker method of autoregressive model estimation is used on the prefiltered sequence to yield frequency estimates. Power estimation is accomplished next via modal decomposition of the estimated correlation sequence. The advantage of this approach is that for slowly varying frequency drift paths (24 hour cycle) the frequency estimates exhibit MSE approximately 3 dB less than the Chirp-Transform algorithm over a wide range of SNR. There are two disadvantages to the parametric algorithm. First the parametric algorithm estimates power with MSE approximately 2 dB greater than the nonparametric algorithm. Secondly the algorithm is more complicated than the nonparametric Chirp-Transform algorithm because it requires matrix inversions and the determination of the roots of a polynomial. For the digital beacon receiver problem investigated here both algorithms perform similarly in two important respects. First both algorithms can lock onto a carrier signal whose frequency is drifting at the rate of 5 Hertz per second in a noise environment corresponding to a 15 dB/Hz SNR. Secondly both algorithms can make unbiased frequency estimates of the carrier signal allowing the receiver to track the carrier at 7 dB/Hz SNR. Both algorithms attain the Cramer-Rao bound for estimation of constant frequency sinusoids. For a simulated satellite signal with maximum frequency drift of 5 Hertz per second the Kalman frequency predictor is able to reduce the problem to nearly that of the constant frequency case so that the resulting performance corresponds to the Cramer-Rao bound for estimation of constant frequency sinusoids. Where computational considerations are critical the nonparametric algorithm is preferred. In fact, unless the superior accuracy of the frequency prediction afforded by the parametric algorithm is paramount, the nonparametric algorithm is to be chosen. / Master of Science

Water and methanol are common solvents used in liquid chromatographic (LC) separations. It is highly desirable to model .the interactions of these solvents in order to better understand the nature of analyte solvation and its effect on retention. Therefore, structure and frequencies of complexes of these solvent molecules have been studied from a theoretical perspective as a first step in this direction. Specifically, cluster structures have been optimized at the RHF and MP2 levels in various flexible basis sets and with the counterpoise correction for basis set superposition error, and trends in the structure and binding energies of several clusters are described. Good agreement wasobtained for the water dimer with the experimental value for the binding energy of D20 using MP2 energies from 6-3 11G**/6-3 l+G** basis sets in conjunction with counterpoise optimizations and full counterpoise corrections. In this investigation harmonic frequencies have been calculated and corrected for the effects of anharmonicity by several methods, two of which are original. The first new method fits a Morse potential function to the energy computed along each normal mode. A second new method is based on fitting a quartic polynomial to energies computed along each normal mode. In cases where the quartic potential function is not very different from the harmonic well, a second order perturbation formula provides a reasonable approximation to the anharmonic vibrational frequencies. When the quartic potential is very far from the harmonic potential, a variational treatment of the vibrations is required. We find that the Morse method delivers reasonable estimates of frequencies of anharmonic motions at lower cost than multi-point potential mapping/multiple geometry optimization/Taylor series methods, and is more successful at predicting intermolecular frequencies than the anharmonic VSCF methods found in GAMESS software. Variational calculations using the quartic polynomials produce estimates of frequencies comparable to the more costly VSCF method. Both the Morse method and polynomial method are very fast computationally relative to these and other methods found in the literature.

In this work, a programmable frequency divider suitable for millimeter wave phase-lock loops is presented. The frequency divider has been implemented in a 90 nm standard CMOS technology. To the extent of maximizing the operative input frequency, the higher frequency digital blocks of the frequency divider have been realized using dynamic precharge-evaluation logic. Moreover, a non-conventional method to implement non-power-of-2 division ratios has been used for the higher frequency divider stages (input stages).

No description available.

This thesis describes a non-magnetic mass spectrometer incorporating the following components: a heated filament source, an electrostatic energy analyser, and a time-of-flight velocity analyser. The last component measures the time required for an ion to go between two small condensers by means of a radio frequency voltage applied to the condensers. If an ion passes successively through both condensers when the field in them is zero, it is collected and detected. It is then possible to relate the e/m to the frequency of the applied voltage when the energy of the ion and the distance between the centres of the condensers is known. Theory is presented which permits the calculation of resolution and current intensities. The values so obtained are realized experimentally. / Thesis / Master of Science (MSc)

Ces travaux de thèse portent principalement sur la génération de signal d'horloge haute fréquence. Dans un premier temps, la faisabilité d'un oscillateur à base de BAW y est démontrée par la conception d'un circuit en technologie CMOS 65 nm. Les deux principales innovations sont les performances en terme de stabilité (bruit de phase de -128dBc/Hz à 100kHz de la porteuse) et en précision (implémentation d'une banque de capacités ayant un pas de 0.4ppm) de l'oscillateur. Sa consommation est optimisée (0.9mW). Il est suivi d'un diviseur faible bruit (-140dBc/Hz à 100kHz de la porteuse) délivrant un signal à 500MHz. Dans un second temps, les imperfections des résonateurs BAW sont analysées. Une procédure de calibration comprenant une calibration initiale et une calibration en boucle ouverte est alors proposée. Cette dernière repose sur l'identification et l'utilisation d'un modèle comportemental du dispositif, régulièrement mis à jour grâce à un filtre de Kalman. Une précision de 0.4 ppm est atteinte / This thesis deals with the gigahertz range reference frequency generation. In a first part, this document presents the design of a 500 MHz oscillator in a 65 nm CMOS process using a 2 GHz Bulk Acoustic Wave resonator. A digital frequency control is implemented using a switched capacitor bank in parallel to the resonator. The tuning range is up to 500 kHz with a minimum step of 200 Hz. The oscillator core uses a differential topology and is designed for low phase noise (-128 dBc/Hz at 100 kHz offset) at low power consumption (0.9 mW). It is followed by a low noise divider which provides a 500 MHz output with a phase noise of -139 dBc/Hz at 100 kHz offset from the carrier. In a second part, we consider a method for the calibration of a BAW based frequency reference. In fact, the frequency variations of a BAW oscillator against process, supply, temperature and aging effects make difficult its use as a frequency reference. We propose here a method based on Kalman filtering to identify with high precision a behavioral model of this BAW reference, thus enabling its use in an open loop frequency tuning. A precision of 0.4 ppm is achieved