A study has been made of the external conversion spectrum of gamma-rays of less than 200 kev. A set of semi-empirical curves relating the photoelectric peak height to the gamma-ray intensity has been established using antimony radiators. These results will be discussed. A method of preparing thin beta sources will also be described. / Thesis / Master of Science (MSc)

Call number: LD2668 .T4 1952 K7 / Master of Science

The objective of this work is to develop essential building blocks for the lab-on-a-chip optical sensing systems with high performance. In this study, the silicon-on-insulator (SOI) platform is chosen because of its compatibility with the mature microelectronics industry for the great potential in terms of powerful data processing and massive production. Despite the impressing progress in optical sensors based on the silicon photonic technologies, two constant challenges are larger sensitivity and better selectivity. To address the first issue, we incorporate porous materials to the silicon photonics platform. Two porous materials are investigated: porous silicon and porous titania. The demonstrated travelling-wave resonators with the magnesiothermically reacted porous silicon cladding have shown significant enhancement in the sensitivity. The process is then further optimized by replacing the thermal oxide with a flowable oxide for the magnesiothermic reduction. A different approach of making porous silicon using porous anodized alumina membrane leads to better flexibility in controlling the pore size and porosity. Porous titania is successfully integrated with silicon nitride resonators. To improve the selectivity, an array of integrated optical sensors are coated with different polymers, such that each incoming gas analyte has its own signature in the collective response matrix. A multiplexed gas sensor with four polymers has been demonstrated. It also includes on chip references compensating for the adverse environmental effects. On chip spectral analysis is also very critical for lab-on-a-chip sensing systems. For that matter, based on an array of microdonut resonators, we demonstrate an 81 channel microspectrometer. The demonstrated spectrometer leads to a high spectral resolution of 0.6 nm, and a large operating bandwidth of ~ 50 nm.

The work presented in this thesis may be considered in two main parts; firstly a description of the design and operation of a display type photoelectron spectrometer. Secondly a series of experiments investigating the electronic properties of thin epitaxial films (1-5 atomic layers) of cobalt grown on a clean single crystal copper (001) substrate. Conventional angle resolved photoelectron spectrometers of the deflection type are only capable of observing one point in the (E,θ,φ) space at a time. This is often perfectly acceptable if one is concerned with optimal resolution in order to perform accurate band mapping experiments. However certain experiments are essentially impossible, for instance the observation of the emitted photocurrent over all θ,φ at the fermi energy. This is partly because of the time limitations imposed by the necessity to keep the sample atomically clean in the U.H.V. environment. Several previous workers have tackled this problem by designing spectrometers that observe large sections of θ,φ space simultaneously, for a given energy. The first part of this work concerns the design and implementation of a display type spectrometer which embodies some new and quite novel features. Thin epitaxial films of ferromagnetic materials grown on non-magnetic substrates have long been of interest. Partly as a prototypical surface for the investigation of surface magnetism, and partly for the investigation of the changes induced in the magnetic properties as the dimensionality is reduced or as the lattice size is changed. The second part of this thesis concerns experiments using three different spectroscopies on a system of this type, specifically Co on Cu(001). Firstly, a photoemission study using the display spectrometer is presented, observations of the spin-split bands as a function of wavevector parallel to the surface are shown. Secondly an Auger electron study of the growth mode of the epitaxial film, together with a LEED I/V study of the changing lattice strain as a function of film thickness are presented. Although none of these measurements directly probe the magnetism of the films, they provide very necessary information in order to understand their behaviour.

No description available.

This dissertation describes the techniques involved in using a fiber optic coupled spectrometer to do multiple object spectroscopy of astronomical objects. The Medusa spectrograph, with optical fibers fixed in a focal plane aperture plate, was used to study clusters of galaxies via velocity distributions. Some relevant problems in the study of the structure and dynamics of clusters of galaxies are outlined as motivation for building a multiple fiber spectrometer. The history of fiber optic spectroscopy in astronomy is presented along with an outlook for the future. The results and experience gained from the Medusa spectrograph are used to design a second generation instrument. The MX Spectrometer uses optical fibers which are positioned remotely under computer control. These fibers are optically matched to the telescope and spectrograph optics to achieve optimum performance. The transmission, flexibility, and image scrambling properties of step-index silica fibers allow efficient reformatting of multiple objects into the spectrometer entrance aperature. By allowing spectra of 32 objects to be obtained simultaneously, the MX Spectrometer will make an order of magnitude increase in the quantity of spectroscopic data that can be recorded with a large telescope. Mechanical, control, and optical elements of the MX design are discussed. Telescope and fiber parameters influencing the design of the fishermen-around-the-pond mobile fiber head are detailed. Results of testing the stepper motor driven fiber positioner probes are described. The algorithm for controlling the motion of 32 positioners in the telescope focal plane without collisions is outlined. Detector performance and spectrometer efficiency are considered for both the Medusa and MX systems. The use of a Charge Coupled Device (CCD) array detector provides increased quantum efficiency, dynamic range, and stability, as well as allowing digital sky subtraction. Microlenses and their use in correctly coupling optical fibers to the telescope and spectrograph are discussed. In particular, the pupil-imaging technique for microlens matching to fibers is introduced.

The work of this thesis is to investigate new techniques for Integral Field Spectroscopy (IPS) to make the most efficient use of modem large telescopes. Most of the work described is aimed at the FMOS for the SUBARU 8m telescope. Although this is primarily a system for Multiple Object Spectroscopy (MOS) employing single fibres, there is an option to include a multiple-IFS (MIPS) system. Much of this thesis is therefore aimed at the design and prototyping of critical systems for both the IPS and MOS modes of this instrument. The basic theory of IFU design is discussed first. Some particular problems are described and their soludons presented. The design of the MIPS system is described together with the construction and testing of a prototype deployable IFU. The assembly of the pickoff/fore-optics, microlens array and fibre bundle and their testing are described in detail. The estimated performance of the complete module is presented together with suggestions for improving the system efficiency which is currently limited by the performance of the microlens array. The prototyping of the MIPS system is supported by an extensive programme of testing of candidate microlens arrays. Another critical aspect of the instrument is the ability to disconnect the (IPS and MOS) fibre input which is installed on a removable prime focus top-end ring from the spectrographs which are mounted elsewhere on the telescope. This requires high-performance multiple fibre connectors. The designs of connectors for the MOS and IPS modes are described. Results from the testing of a prototype for the MOS mode are presented. This work is supported by a mathematical model of the coupling efficiency which takes into account optical aberrations and alignment errors. The final critical aspect of FMOS which has been investigated is the design of the spectrographs. The baseline system operates in the near-infrared (NIR) but an additional visible channel is an option. Efficient designs for both the visible and NIR systems are presented. The design of the NIR spectrograph presents challenges in the choice of materials for the doublet and triplet lenses employed. The choice of material and the combinations in which they can be used are described. This thesis shows that all these critical aspects of FMOS have good solutions that will result in good performance of the whole instrument. For the multiple IFU system, the prototype demonstrates acceptable performance which can be made excellent by the use of a better microlens array. The multiple fibre connector prototype already indicates excellent performance. Finally, the spectrograph designs presented should result in high efficiency and good image quality.

Sonification is the process of mapping non-musical data to sound. The field is comprised of three key areas of research: (1) psychological research in perception and cognition, (2) the development of tools, and (3) sonification design and application. The goals of this research were twofold: (1) To provide insights to the development of sonification tools within the programming environment Max for use in further sonification/interdisciplinary research, as well as (2) provide a framework for a musical sonification system. The sonification system discussed was developed to audify spectrometry data, with the purpose of better understanding how multi-purpose systems can be easily modified to suit a particular need. Since all sonification systems may become context specific to the data they audify, a system was developed in the programming language Max that is both modular and responsive to the parameterization of data to create musical outcomes. The trends and phenomena of spectral data in the field of spectroscopy are plotted musically through the system and further enhanced by processes that associate descriptors of said data with compositional idioms, rhythmically, melodically, and harmonically. This process was achieved in Max by creating a modular system that handles the importing and formatting of spectral data (or any data in an array format) to send that data to a variety of subprograms for sonification. Subprograms handle timing and duration, diatonic melody, harmony, and timbral aspects including synthesis and audio effects. These systems are accessible both at a high level for novice users, as well as within the Max environment for more nuanced modification to support further research.

Thesis (M.A.)--Boston University / PLEASE NOTE: Boston University Libraries did not receive an Authorization To Manage form for this thesis or dissertation. It is therefore not openly accessible, though it may be available by request. If you are the author or principal advisor of this work and would like to request open access for it, please contact us at open-help@bu.edu. Thank you. / The general theory of the operation of a mass spectrometer is described with particular attention to the second order focusing. The equations wherever applicable are used for a symmetrical type, 90° deflection mass spectrometer with a radius of 4.6 centimeters. Since errors in the magnetic field are more serious (by a factor of 2) than errors in the electrostatic potential, a current regulator is constructed which can correct an error signal to few parts in 10^3. The beam is provided by surface ionization and the analysis of possible masses is limited by such factors as ionization potential, maximum magnetic field, and accelerating potential. A few mass spectra are given with voltage scanning, and the results are analyzed in terms of the equations derived in part I. The Bediasite sample used for analysis is from the Grimes County, Texas, and such elements as Fe, Si, Al, Mg, Na, Ne, O, N, and possibly Ti and carbon have been identified in its spectrum. The existence of elements with high ionization potential is explained to be due to a discharge process in the ionization chamber. The experimental duration of peaks due to Ne, 0, N is about 2 hours with N the most intense and Ne the least intense element. These peaks seem to be the contents of the microscopic bubbles present in the sample. The presence of neon oxygen, and helium has been confirmed by the spectroscopic analysis of O'Keefe, Dunning, and Lowman. Helium was not recorded due to the limited range of the accelerating power supply. It is suggested that in order to carry out the research further, some improvements be made on the instrument. / 2031-01-01

動力學解耦(DD) 是一種源於核磁共振(NMR) 的技術。通過快速地控制量子系統， DD可以把不需要的耦合抑制。它可以用來保護處於噪音環境中的量于系統或者用來測量環境噪音譜，甚至它可以用來測量單分子的核磁共振信號。 / 在論文的第一部分，我們主要研究和設計DD技術來保護量子系統。(i)我們提出最套DD來保護量子算符，例如嵌套Uhrig DD (NUDD)。NUDD保護一個相互正交算符集(MOOS); 通過保護這個MOOS算符集， NUDD可以保護所有由MOOS生成的算符。對於量子比特系統，任何一個物理量都可以由NUDD保護;而且，NUDD可以通過單量子比特的操作實現。由於對於單量子比特系統， NUDD 剛好是內層含有偶數階UDD 的quadratic DD (QDD). 所以我們證明了內層含有偶數階UDD 的QDD可以達到設計上所期待的效能。隨著解耦階數的增長， NUDD 只需要多項式增長的脈衝數目，而以前的最套DD(CDD)則要指數增長的脈衝數目。基於保護MOOS 的DD可以用一種通用的有限寬度的服衝代替理想的瞬時脈衝，這種非瞬時的脈衝只會引起正比於脈衝寬度的二階小量的誤差。(ii) 我們也證明了，如果一個動態操控方法能夠以一定的控制精度O(TN +1 )控制一個與不依賴於時間的通屬量子庫耦合的量子系統，那麼它也能夠以同樣階數的精度控制含時的這類系統。這裡T是很短的控制時間。這個結果拓展了各種普適量子控制方法的應用範圍，使它們也可以用於含時系統。(iii) 一個量子系統如果和一個無限大的環境耦合，它會受到馬科夫噪音的影響。這種噪音的關聯函數對於時間的級數展開會有奇數項。我們證明，對於這種噪音， DD不會特別有效，因為退相干只能被DD抑制到一定的階數(以時間的級數展開的階數計算)。在這種噪音下，我們做了DD 的脈衝優化。我們發現，當脈衝比較少的時候，它和UDD序列一樣，但當脈衝比較多的時候，它接近於Carr-Purcell-Meiboom-Gill(CPMG)序列 。對於關聯函數對時間的級數展開含有線性項的情況， CPMG序列在時間很短的情況下是最優的。我們也得到了外加約束條件的做衝序列優化方程組，通過解這方程組，我們得到了一些DD序列，它們可以完全消去由非均勻展寬導致的退相干。(iv) 我們通過一個例子演示了，如果我們不能解析地優化量子控制方案，遺傳算法是很有用的。遺傳算法可以有效地得到優化的控制方案。對比以前的控制方案，我們通過遺傳算法得到的控制方案在性能上好很多。 / 在論文的第二部分，我們提出用原子干涉技術和動力學解捐助〈衝技術來選擇性地測量隨時間變化的引力場。通過惆整脈衝序列的時間，我們可以提取特定頻率下的信號或者噪音譜。我們得到了通用的相移公式。這些公式對於任意的π 脈衝序列都適用。當引力場的漲落對於光子的頻率的變化可以忽略的時候，由引力場引起的相位差和序列時間T的二次方成正比，或者對於某個測量頻率，相位差和脈衝數N成正比。對於引力波探測，這個相位差和自永衝數N的平方成正比，所以，對比於以前的π/2一π一π/2序列，我們的方法提供了額外的N²倍信號放大。 / Dynamical decoupling (DD) is a technique originated from the spin echo techniques in nuclear magnetic resonance (NMR). DD can average out unwanted couplings through fast control on the quantum systems. It has applications in protection of quantum systems from noisy environments, measurements of environmental noise spectra, and even NMR of single molecule. / In the first part of this thesis, we study and design DD techniques for quantum system preservation. (i) We propose nested DD, such as nested Uhrig DD (NUDD), for protection of system operators. NUDD protects a set of mutually orthogonal operators (a MOOS) and hence all system operators generated by the MOOS. For multiqubit systems, any physical quantities can be protected, and NUDD can be implemented by single-qubit operations. For single-qubit systems NUDD reduces to quadratic DD (QDD) with even-order UDD on the inner level. Thus we have proved the validity of QDD with even-order DD on the inner level. NUDD achieves a desired decoupling order with only a polynomial increase in the number of pulses, with exponential saving of the number of pulses as compared with concatenated DD (CDD) of the same decoupling order. DD based on protection of a MOOS can be implemented with pulses of finite amplitude, up to an error in the second order of the pulse durations. (ii) We also establish that if a scheme can control a time-independent system arbitrarily coupled to a generic finite bath over a short period oftime T with control precision O(T[superscript N]⁺¹), it can also realize the control with the same order of precision on smoothly time-dependent systems. This result extends the validity of various universal dynamical control schemes to arbitrary analytically time-dependent systems. (iii) A quantum systems coupled to infinite baths feels a Markovian noise. The short-time correlation function expansion of this noise has odd-order expansion terms. We proof that in this case DD is not very efficient and the decoherence can be suppressed only to some order in short-time T. In the optimization of pulse sequence for a qubit under dephasing due to Markovian noise, the optimal sequences coincide the Uhrig DD sequence when the number N of pulses is small, and they resemble Carr-Purcell-Meiboom-Gill (CPMG) sequences when N is large. For a special case, if the short-time correlation function expansion has a linear term in time, the CPMG sequences are optimal in short-time limit. We have also derived the optimizing equations for suppressing decoherence with arbitrary constraints, and have obtained optimized sequences that can also perfectly eliminate the decoherence due to inhomogeneous broadening. (iv) When analytic results is not possible, we demonstrate that genetic algorithm may be useful by showing an optimized quantum control which has much better performance than the previous results. / In the second part, we combine atom interferometry and dynamical decoupling pulse sequences to selectively measure time-dependent gravitational fields. Using the pulse sequences, we can extract signals or noise with certain frequencies by tuning the timing of the sequences. We obtain the general phase-shift formulas for arbitrary π pulse sequences. When the effect of gravity fluctuations on the light is not considered in the interferometers, the phase shift due to gravitational fields scales quadratically with the duration time T of pulse sequences or linearly with the number N of pulses for a given detection frequency. For gravitational wave detection, the phase shift due to the spacetime fluctuations scales quadratic ally with the number N of pulses, N²-fold enhancement over the traditional π/2-π-π/2 sequences. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Wang, Zhenyu = 信息處理和頻譜測定中的量子相干動態操控 / 王振宇. / "December 2011." / Thesis (Ph.D.)--Chinese University of Hong Kong, 2012. / Includes bibliographical references (leaves 100-112). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese. / Wang, Zhenyu = Xin xi chu li he pin pu ce ding zhong de liang zi xiang gan dong tai cao kong / Wang Zhenyu. / Abstract --- p.iii / Acknowledgment --- p.vii / List of Figures --- p.xiii / List of Appendices --- p.xiv / Chapter 1 --- Introduction and Outline --- p.1 / Chapter I --- Dynamical Control of Quantum Coherence / Chapter 2 --- Introduction --- p.5 / Chapter 3 --- Decoherence and Dynamical Control --- p.11 / Chapter 3.1 --- Quantum decoherence --- p.11 / Chapter 3.1.1 --- Semiclassical picture of decoherence --- p.12 / Chapter 3.1.2 --- Quantum picture of decoherence --- p.13 / Chapter 3.2 --- Dynamical control of open quantum systems --- p.14 / Chapter 3.3 --- Protection of system operators --- p.15 / Chapter 4 --- Dynamical Oecoupling for Quantum Systems --- p.19 / Chapter 4.1 --- Dynamical decoupling for a qubit --- p.19 / Chapter 4.1.1 --- A semiclassical model --- p.19 / Chapter 4.1.1.1 --- Filter functions --- p.21 / Chapter 4.1.2 --- Geometrical view of decoherence and control --- p.22 / Chapter 4.1.3 --- Uhrig dynamical decoupling (UDD) --- p.25 / Chapter 4.2 --- Nested dynamical decoupling for quantum systems --- p.26 / Chapter 4.2.1 --- Mutually orthogonal operation set --- p.26 / Chapter 4.2.2 --- Lowest-order protection of system operators --- p.29 / Chapter 4.2.3 --- Higher-order protection by nesting and concatenation --- p.31 / Chapter 4.2.4 --- Higher-order protection by nested UDD (NUDD) --- p.33 / Chapter 4.2.4.1 --- A theorem on UDD control of time-dependent systerns --- p.34 / Chapter 4.2.4.2 --- Nested Uhrig dynamical decoupling (NUDD) --- p.37 / Chapter 4.2.5 --- Pulses of finite amplitude --- p.39 / Chapter 5 --- Dynamical Control for Time-Dependent Hamiltonians --- p.43 / Chapter 5.1 --- Universal control of time-independent systems --- p.44 / Chapter 5.2 --- Time-dependence in interaction frames --- p.44 / Chapter 5.3 --- Generalization to time-dependent systems --- p.45 / Chapter 6 --- Dynamical Decoupling for Noise Spectra with Soft Cutoff --- p.49 / Chapter 6.1 --- Decoherence functions in frequency domain --- p.50 / Chapter 6.2 --- Performance of dynamical decoupling against noise with soft highfrequency cutoff --- p.53 / Chapter 6.3 --- Relation between noise correlation and high-frequency cutoff --- p.54 / Chapter 6.4 --- Sequence optimization --- p.57 / Chapter 6.4.1 --- Short-time optimization --- p.57 / Chapter 6.4.2 --- Optimization with constraints --- p.59 / Chapter 7 --- Design of Optimal Control by Genetic Algorithm --- p.64 / Chapter 8 --- Summary and Discussions --- p.69 / Chapter II --- Dynamical Decoupling for Gravitational Spectrometry / Chapter 9 --- Introduction --- p.73 / Chapter 10 --- Selective Detection of Gravitational Field by Dynamical Decoupling --- p.75 / Chapter 10.1 --- Atom interferometry --- p.75 / Chapter 10.2 --- Phase shift calculation --- p.76 / Chapter 10.2.1 --- Path phase Δφ[subscript path] --- p.79 / Chapter 10.2.2 --- Laser phase Δφ[subscript laser] --- p.80 / Chapter 10.3 --- Spectroscopy by dynamical decoupling --- p.82 / Chapter 10.4 --- Effects due to gravity gradient --- p.85 / Chapter 11 --- Gravitational Wave Antenna by Dynamical Decoupling --- p.89 / Chapter 11.1 --- Configuration and simple understanding --- p.89 / Chapter 11.1.1 --- Path phase --- p.93 / Chapter 11.1.2 --- Laser phase --- p.95 / Chapter 11.2 --- Gravitational wave signal --- p.96 / Chapter 12 --- Summary and Discussions --- p.99 / Bibliography --- p.100