Periodic oscillations in feedback systems with combined pulse modulation

This paper presents a systematic method of investigating the existence of limit cycle oscillations in feedback systems with combined integral pulse frequency-pulse width (IPF-P/V) modulation. The method is based on the non-linear discrete equivalence of the continuous feedback system containing the IPF-PW modulator.

Development of novel NMR pulse sequences

To elucidate the structures of orgamc molecules in solution using pulse FT NMR, heteronuclear pulse sequence experiments to probe carbon-13 (13C) and proton (1H) spin systems are invaluable. The one-dimensional insensitive nucleus detected PENDANT experiment finds popular use for structure determination via one-bond 13C-1H scalar couplings. PENDANT facilitates the desired increase in 13C signal-to-noise ratio, and unlike many other pulse sequence experiments (e.g., refocused INEPT and DEPT), allows the simultaneous detection of 13C quaternary nuclei. The tlrst chapter herein details the characterisation of PENDANT and the successful rectification of spectral anomalies that occur when it is used without proton broadband decoupling. Multiple-bond (long-range) l3C-1H scalar coupling correlations can yield important bonding information. When the molecule under scrutiny is devoid of proton spectral crowding, and more sensitive 'inverse' pulse sequence experiments are not available, one may use insensitive nucleus detected long-range selective one-dimensional correlation methods, rather than more time consuming and insensitive multidimensional analogues. To this end a novel long-range selective one-dimensional correlation pulse sequence experiment has been invented. Based on PENDANT, the new experiment is shown to rival the popular selective INEPT technique because it can determine the same correlations while simultaneously detecting isolated 13C quaternary nuclei. INEPT cannot facilitate this, potentially leaving other important quaternary nuclei undetected. The novel sequence has been modified further to yield a second novel experiment that simultaneously yields selective 13C transient nOe data. Consequently, the need to perform the two experiments back-to-back is conveniently removed, and the experimental time reduced. Finally, the SNARE pulse sequence was further developed. SNARE facilitates the reduction of experimental time by accelerating the relaxation of protons upon which pulse sequences, to which SNARE is appended, relies. It is shown, contrary to the original publication, that reiaxation time savings can be derived from negative nOes.

Utilização de pulsos de radiofrequência fortemente modulados no processamento de informação quântica via ressonância magnética nuclear

Nesta dissertação apresentamos um trabalho de desenvolvimento e utilização de pulsos de radiofreqüência modulados simultaneamente em freqüência, amplitude e fase (pulsos fortemente modulados, SMP, do inglês Strongly Modulated Pulses) para criar estados iniciais e executar operações unitárias que servem como blocos básicos para processamento da informação quântica utilizando Ressonância Magnética Nuclear (RMN). As implementações experimentais foram realizas em um sistema de 3 q-bits constituído por spins nucleares de Césio 133 (spin nuclear 7/2) em uma amostra de cristal líquido em fase nemática. Os pulsos SMP´s foram construídos teoricamente utilizando um programa especialmente desenvolvido para esse fim, sendo o mesmo baseado no processo de otimização numérica Simplex Nelder-Mead. Através deste programa, os pulsos SMP foram otimizados de modo a executarem as operações lógicas desejadas com durações consideravelmente menores que aquelas realizadas usando o procedimento usual de RMN, ou seja, seqüências de pulsos e evoluções livres. Isso tem a vantagem de reduzir os efeitos de descoerência decorrentes da relaxação do sistema. Os conceitos teóricos envolvidos na criação dos SMPs são apresentados e as principais dificuldades (experimentais e teóricas) que podem surgir devido ao uso desses procedimentos são discutidas. Como exemplos de aplicação, foram produzidos os estados pseudo-puros usados como estados iniciais de operações lógicas em RMN, bem como operações lógicas que foram posteriormente aplicadas aos mesmos. Utilizando os SMP\'s também foi possível realizar experimentalmente os algoritmos quânticos de Grover e Deutsch-Jozsa para 3 q-bits. A fidelidade das implementações experimentais foi determinadas utilizando as matrizes densidade experimentais obtidas utilizando um método de tomografia da matriz densidade previamente desenvolvido.

Sensitivity of the NMR density matrix to pulse sequence parameters : a simplified analytic approach

We present a formalism for the analysis of sensitivity of nuclear magnetic resonance pulse sequences to variations of pulse sequence parameters, such as radiofrequency pulses, gradient pulses or evolution delays. The formalism enables the calculation of compact, analytic expressions for the derivatives of the density matrix and the observed signal with respect to the parameters varied. The analysis is based on two constructs computed in the course of modified density-matrix simulations: the error interrogation operators and error commutators. The approach presented is consequently named the Error Commutator Formalism (ECF). It is used to evaluate the sensitivity of the density matrix to parameter variation based on the simulations carried out for the ideal parameters, obviating the need for finite-difference calculations of signal errors. The ECF analysis therefore carries a computational cost comparable to a single density-matrix or product-operator simulation. Its application is illustrated using a number of examples from basic NMR spectroscopy. We show that the strength of the ECF is its ability to provide analytic insights into the propagation of errors through pulse sequences and the behaviour of signal errors under phase cycling. Furthermore, the approach is algorithmic and easily amenable to implementation in the form of a programming code. It is envisaged that it could be incorporated into standard NMR product-operator simulation packages.

Integrable high order UWB pulse photonic generator based on cross phase modulation in a SOA-MZI

We propose and experimentally demonstrate a potentially integrable optical scheme to generate high order UWB pulses. The technique is based on exploiting the cross phase modulation generated in an InGaAsP Mach-Zehnder interferometer containing integrated semiconductor optical amplifiers, and is also adaptable to different pulse modulation formats through an optical processing unit which allows to control of the amplitude, polarity and time delay of the generated taps.

Novel ultra-wideband pulse spectrum modulation scheme

Current ultra-wideband communication systems use short narrow timed pulse sequences to transmit information. Some disadvantages of UWB communication systems are its interference of other conventional wireless systems and its reliance on time hopping schemes for multiple access. This paper presents a novel UWB data modulation scheme based on pulse shaping. This modulation scheme adds more flexibility for data modulation in UWB communication systems. The modulation scheme encodes data in both the timing and frequency spectrum of the transmitted pulse. This has the potential to improve data throughput rates and to lower interference between UWB and narrowband systems.

Operator's and organizational maintenance manual : pulse form restorer TD-12l8/G (NSN 5820-01-145-4938).

"5 March 1985."

A high voltage power converter with a frequency and voltage controller

A high voltage power converter is presented in this paper and is based on a Capacitor-Diode Voltage Multiplier (CDVM) supplied through an inverter. This power converter has the capabilities of generating variable high DC voltage with improved transient response. The simulation results which are presented in this paper verify that due to its fast transient response, this converter can be used as a high DC voltage source in many applications.

Structure and dynamics of protein excited states with millisecond lifetimes

An in-depth understanding of biological processes often requires detailed atomic resolution structures of the molecules involved. However in solution where most of these processes occur the conformation of biomolecules like RNA, DNA and proteins is not static but fluctuates. Routinely used structural techniques like X-ray crystallography, NMR spectroscopy and cryo-electron microscopy have almost always been used to determine the structure of the dominant conformation or obtain an average structure of the biomolecule in solution with very little detailed information regarding the dynamics of these molecules in solution. Over the last few years, NMR based methods have been developed to study the dynamics of these biomolecules in solution in a site-specific manner with the aim of generating structures of the different conformations that these molecules can adopt in solution. One powerful technique is the Carr-Purcell-Meiboom-Gill (CPMG) relaxation dispersion experiment, which can be used to detect and characterize protein excited states that are populated for as less as 0.5% of the time with ∼0.5–10 millisecond lifetimes. Due to recent advances in NMR pulse sequences and labeling methodology, it is now possible to determine the structures of these transiently populated excited states with millisecond lifetimes by obtaining accurate chemical shifts, residual dipolar couplings (RDCs) and residual chemical shift anisotropies (RCSAs) of these excited states. In these excited states the dynamics of some methyl containing residues can also be studied.

Cyclotron harmonic emission in a Penning discharge

Microwave noise emission at the harmonics of the electron cyclotron frequency from the magnetized plasma column of a Penning discharge is investigated experimentally. The harmonic emission spectrum is observed using oxygen gas in a variety of discharge configurations. It is found that grid stabilization of the plasma column has very little effect on the emission spectrum. Measurements of the shape and location of the harmonic emission lines are described in detail. On the basis of a microwave interferometer measurement of the electron density, it is concluded that the existence of a hybrid layer somewhere on the plasma column is a necessary condition for the observation of harmonic emission. The relaxation time and the cathode voltage dependence of the harmonic emission are investigated using a pulse modulation technique. It is found that the emission intensity increases rapidly with the magnitude of the cathode voltage and that the relaxation time decreases with increasing neutral gas pressure. High intensity nonharmonic radiation is observed and identified as resulting from a beam-plasma wave instability thereby eliminating the same instability as a possible source of the harmonic emission. It is found that the collective experimental results are in reasonable agreement with the single particle electrostatic radiation theory of Canobbio and Croci.

冷却储存实验环功率源的设计与计算

RF system of HIRFL-CSRe(cooling storage experimental ring)was designed by ourselves and manufactured domestically,which operates in the frequency range of 0.5~2.0 MHz at first and second harmonic modes.Based on detailed engineering calculation,the design of RF generator was completed.It will work not only in CW mode but also in the mode of ramping pulse modulation,and the maximum power is up to 70 kW.It satisfies the requirement of 10 kV maximum deceleration voltage to capture the irradiative beam and decel...中文摘要：对兰州重离子加速器冷却储存环实验环(CSRe)的高频系统功率源的设计作了详细的工程计算,工作频率范围为0.5～2.0MHz,工作于基波及二次谐波模式,发射机不仅能工作于点频连续波模式,而且还可以工作在扫频调制模式,输出最大功率达到70kW。满足最高加速或减速电压10kV的设计要求,能够用于捕获放射性次级束并将束流的能量从400MeV/u减速到30MeV/u。

Variable impedance LED matrix control system for lamps in PV applications

The interest in LED lighting has been growing recently due to the high efficacy, lifelime and ruggedness that this technology offers. However the key element to guarantee those parameters with these new electronic devices is to keep under control the working temperature of the semiconductor crystal. This paper propases a LED lamp design that fulfils the requ irements of a PV lighting systems, whose main quality criteria is reliability. It uses directly as a power supply a non·stabilized constant voltage source, as batteries. An electronic control architecture is used to regulate the current applied to the LEO matri)( according to their temperature and the voltage output value of the batteries with two pulse modulation signals (PWM) signals. The first one connects and disconnects the LEOs to the power supply and the second one connects and disconnects several emitters to the electric circuit changing its overall impedance. A prototype of the LEO lamp has been implemented and tested at different temperaturas and battery voltages.

Very short-term plasticity in hippocampal synapses

Hippocampal pyramidal neurons often fire in bursts of action potentials with short interspike intervals (2–10 msec). These high-frequency bursts may play a critical role in the functional behavior of hippocampal neurons, but synaptic plasticity at such short times has not been carefully studied. To study synaptic modulation at very short time intervals, we applied pairs of stimuli with interpulse intervals ranging from 7 to 50 msec to CA1 synapses isolated by the method of minimal stimulation in hippocampal slices. We have identified three components of short-term paired-pulse modulation, including (i) a form of synaptic depression manifested after a prior exocytotic event, (ii) a form of synaptic depression that does not depend on a prior exocytotic event and that we postulate is based on inactivation of presynaptic N-type Ca2+ channels, and (iii) a dependence of paired-pulse facilitation on the exocytotic history of the synapse.

Variable time-scale information processing

With the extensive use of pulse modulation methods in telecommunications, much work has been done in the search for a better utilisation of the transmission channel.The present research is an extension of these investigations. A new modulation method, 'Variable Time-Scale Information Processing', (VTSIP), is proposed.The basic principles of this system have been established, and the main advantages and disadvantages investigated. With the proposed system, comparison circuits detect the instants at which the input signal voltage crosses predetermined amplitude levels.The time intervals between these occurrences are measured digitally and the results are temporarily stored, before being transmitted.After reception, an inverse process enables the original signal to be reconstituted.The advantage of this system is that the irregularities in the rate of information contained in the input signal are smoothed out before transmission, allowing the use of a smaller transmission bandwidth. A disadvantage of the system is the time delay necessarily introduced by the storage process.Another disadvantage is a type of distortion caused by the finite store capacity.A simulation of the system has been made using a standard speech signal, to make some assessment of this distortion. It is concluded that the new system should be an improvement on existing pulse transmission systems, allowing the use of a smaller transmission bandwidth, but introducing a time delay.