Enhanced dynamic nuclear polarization via swept microwave frequency combs

Dynamic Nuclear Polarization (DNP) has enabled enormous gains in magnetic resonance signals and led to vastly accelerated NMR/MRI imaging and spectroscopy. Unlike conventional cw-techniques, DNP methods that exploit the full electron spectrum are appealing since they allow direct participation of all electrons in the hyperpolarization process. Such methods typically entail sweeps of microwave radiation over the broad electron linewidth to excite DNP, but are often inefficient because the sweeps, constrained by adiabaticity requirements, are slow. In this paper we develop a technique to overcome the DNP bottlenecks set by the slow sweeps, employing a swept microwave frequency comb that increases the effective number of polarization transfer events while respecting adiabaticity constraints. This allows a multiplicative gain in DNP enhancement, scaling with the number of comb frequencies and limited only by the hyperfine-mediated electron linewidth. We demonstrate the technique for the optical hyperpolarization of 13C nuclei in powdered microdiamonds at low fields, increasing the DNP enhancement from 30 to 100 measured with respect to the thermal signal at 7T. For low concentrations of broad linewidth electron radicals, e.g. TEMPO, these multiplicative gains could exceed an order of magnitude.Comment: Contains supplementary inf

Multi-function power electronic interface for hybrid mini-grid systems

In the past five years, global interest regarding the development of renewable energy technologies has significantly increased. The conventional electric power generation methods sourced from fossil fuels is now problematic, from both the supply and emission points of view. Fossil fuels are non-renewable limited resources that have taken millions of years to form; eventually they will be exhausted and the current cost of automotive fuel is evidence of them becoming diminished. The carbon dioxide emissions created through the energy conversion process are causing an increase in the overall atmospheric concentrations, which through global warming may have serious consequences for humanity.Natural sources of energy production can be derived from the Sun through the use of solar and wind generation methods. Converting these sources to electricity requires the technology of power electronics, the central area of research for this dissertation. Solar energy can most easily be harnessed through the photo-electric effect which creates DC electricity. However, the majority of electric loads and transmission require AC electricity. The inverter is the electronic device required for this power conversion. Wind turbines usually create variable voltage and frequency AC that is rectified to DC and then converted to grid type AC through an inverter.Voltage source inverters, their topologies and control are investigated within this dissertation. Voltage control methods are adopted for both stand-alone and grid connected techniques where control of active and reactive power is required. Current control techniques in the form of PI and hysteresis are applied to allow novel interfaces between generation sources to be achieved. Accurate control of the power electronics allows an enhancement in the power production from the renewable energy source. The power electronic device of the DC-DC converter, either buck or boost is controlled to allow the renewable resource to operate at its optimum power point. The control aspects and algorithms of these converters are central to this research. The solar algorithms of perturb and observe, and incremental conductance are developed with the latter being more favourable to changing levels of irradiation. The author draws a parallel between rapidly changing solar conditions with normally changing wind states. This analogy with an understanding of the mechanics of PMSG allows a novel wind MPPT algorithm to be developed which is simulated in PSIM. Methods to analyse the usefulness of the algorithm are developed and general conclusions are drawn.Another aim central to the research is the efficient combination of renewable energy sources into a single reliable power system. This forms the multi-function aspect of the research. The interconnection of the sources on the AC or DC sides is investigated for both stand-alone and grid connected topologies. A requirement of the stand-alone system is to provide power when no renewable resources are available causing some form of energy storage to be utilised. Conventional batteries are used, causing the VC-VSI to become bi-directional allowing charging. This is simulated in PSIM and demonstrated as part of the Denmark and Eco Beach projects. Many differing topologies of stand alone, grid connected and edge of grid systems are developed, simulated and some are demonstrated.While investigating the currently used topologies the author invents the novel complimentary hybrid system concept. This idea allows a single inverter to be used to feed energy from either the wind or solar resource. With careful engineering of the PV array and wind turbine characteristics only a small loss of energy is caused, deemed the crossover loss. This original concept is mathematically modelled, simulated and demonstrated with results presented from the Denmark project. The strength of this idea is from the quite complimentary nature of wind and solar resources, for only a small proportion of the year are high solar and strong wind conditions occurring simultaneously.Compared to a solar resource, the wind resource is much more complicated to model. An analysis of readily available wind source data is presented with a statistical analysis of the scaling methods; a novel box and whiskers plot is used to convey this information. New software is presented to allow a more accurate and digital model of a power curve to be recreated, allowing a more precise annual energy generation calculation. For various wind turbines a capacity factor analysis is presented with its disadvantages explained. To overcome these issues the concepts of economic efficiency and conversion efficiency are explained. These prevent some of the typical methods to enhance the standard capacity factor expression. The combination of these three methods allows selection of the most suitable wind turbine for a site.The concept of a mini-grid is an isolated power generation and distribution system, which can have its renewable energy sources, centralised or decentralised. The methods used to coalesce conventional generation with renewable energy technology forms another key piece of this research. A design methodology for the development of a hybrid power system is created with examples used from projects attributed to the author. The harmonising of the renewable energy sources with the conventional generation while providing a stable and robust grid is explained in detail with respect to the generator loading and control. The careful control of the renewable resource output is shown to allow a greater overall penetration of renewable energy into the network while continuing network stability. The concept of frequency shift control is presented, simulated and demonstrated with reference to the Eco Beach project. This project epitomises much of the research that has been presented in this dissertation. It combines centralised and decentralised inverters, with battery storage and the control of diesel generators. An overall controller dictates the optimum times to charge or draw from the battery based upon the local environmental and time of day variables. Finally, the monitoring aspects of this project are representative of a future smart grid where loads may be shed on demand through under frequency or direct control

Closed-Loop Control of Constrained Flapping Wing Micro Air Vehicles

Micro air vehicles are vehicles with a maximum dimension of 15 cm or less, so they are ideal in confined spaces such as indoors, urban canyons, and caves. Considerable research has been invested in the areas of unsteady and low Reynolds number aerodynamics, as well as techniques to fabricate small scale prototypes. Control of these vehicles has been less studied, and most control techniques proposed have only been implemented within simulations without concern for power requirements, sensors and observers, or actual hardware demonstrations. In this work, power requirements while using a piezo-driven, resonant flapping wing control scheme, Bi-harmonic Amplitude and Bias Modulation, were studied. In addition, the power efficiency versus flapping frequency was studied and shown to be maximized while flapping at the piezo-driven system\u27s resonance. Then prototype hardware of varying designs was used to capture the impact of a specific component of the flapping wing micro air vehicle, the passive rotation joint. Finally, closed-loop control of different constrained configurations was demonstrated using the resonant flapping Bi-harmonic Amplitude and Bias Modulation scheme with the optimized hardware. This work is important in the development and understanding of eventual free-flight capable flapping wing micro air vehicle

Breathy, Resonant, Pressed - Automatic Detection Of Phonation Mode From Audio Recordings of Singing

In this paper we present an experiment on automatic detection of phonation modes from recordings of sustained sung vowels. We created an open dataset specifically for this experiment, containing recordings of nine vowels from multiple languages, sung by a female singer on all pitches in her vocal range in phonation modes breathy, neutral, flow (resonant) and pressed. The dataset is available under a Creative Commons license at . First, glottal flow waveform is estimated via inverse filtering (IAIF) from audio recordings. Then six parameters of the glottal flow waveform are calculated. A 4-class Support Vector Machine classifier is constructed to separate these features into phonation mode classes. We automated the IAIF approach by computing the values of the input arguments – lip radiation and formant count – leading to the best-performing SVM classifiers (average classification accuracy over 60%), yielding a physical model for the articulation of the vowels. We examine the steps needed to generalise and extend the experimental work presented in this paper in order to apply this method in ethnomusicological investigations

Tunable lenses: Dynamic characterization and fine-tuned control for high-speed applications

Tunable lenses are becoming ubiquitous, in applications including microscopy, optical coherence tomography, computer vision, quality control, and presbyopic corrections. Many applications require an accurate control of the optical power of the lens in response to a time-dependent input waveform. We present a fast focimeter (3.8 KHz) to characterize the dynamic response of tunable lenses, which was demonstrated on different lens models. We found that the temporal response is repetitive and linear, which allowed the development of a robust compensation strategy based on the optimization of the input wave, using a linear time-invariant model. To our knowledge, this work presents the first procedure for a direct characterization of the transient response of tunable lenses and for compensation of their temporal distortions, and broadens the potential of tunable lenses also in high-speed applicationsVA and EL acknowledge financial support from Comunidad de Madrid and Marie Curie Action of the European Union FP7/2007-2013 COFUND 291820; XB from Comunidad de Madrid Doctorado Industrial IND2017/BMD-7670; EL from Spanish Government Ramon y Cajal Program RyC-2016-21125; EG from Spanish Government Torres-Quevedo Program PTQ-15-07432; LS from EU H2020 SME Innovation Associate GA-739882; EG from EIT Health; SM from ERC Grant Agreement ERC-2011-AdC 294099 and Spanish Government Grants FIS2014-56643-R; SM and CD from Spanish Government Grant FIS2017-84753-R; and CD from DTS16-0012

Recommendations for reporting ion mobility Mass Spectrometry measurements

Here we present a guide to ion mobility mass spectrometry experiments, which covers both linear and nonlinear methods: what is measured, how the measurements are done, and how to report the results, including the uncertainties of mobility and collision cross section values. The guide aims to clarify some possibly confusing concepts, and the reporting recommendations should help researchers, authors and reviewers to contribute comprehensive reports, so that the ion mobility data can be reused more confidently. Starting from the concept of the definition of the measurand, we emphasize that (i) mobility values (K0) depend intrinsically on ion structure, the nature of the bath gas, temperature, and E/N; (ii) ion mobility does not measure molecular surfaces directly, but collision cross section (CCS) values are derived from mobility values using a physical model; (iii) methods relying on calibration are empirical (and thus may provide method‐dependent results) only if the gas nature, temperature or E/N cannot match those of the primary method. Our analysis highlights the urgency of a community effort toward establishing primary standards and reference materials for ion mobility, and provides recommendations to do so. © 2019 The Authors. Mass Spectrometry Reviews Published by Wiley Periodicals, Inc

대규모 인구 모델과 단일 가슴 착용형 장치를 활용한 비침습적 연속 동맥 혈압 모니터링 시스템

학위논문 (박사) -- 서울대학교 대학원 : 공과대학 협동과정 바이오엔지니어링전공, 2021. 2. 김희찬.최근 수십 년 동안 비침습적 연속 혈압 모니터링에 대한 필요성이 점차 대두되면서 맥파 전달 시간, 맥파 도달 시간, 또는 광용적맥파의 파형으로부터 추출된 다양한 특징들을 이용한 혈압 추정 연구들이 전세계적으로 활발하게 진행되었다. 하지만 대부분의 연구들은 국제 혈압 표준을 만족시키지 못하는 매우 적은 수의 피험자들 만을 대상으로 주로 혈압 추정 모델을 개발 및 검증하였기 때문에 성능의 정확도가 적절하게 검증되지 못했다는 한계점이 있었고, 또한 혈압 추정 파라미터 추출을 위한 생체 신호들을 측정하기 위해 대부분 두 개 이상의 모듈을 필요로 하면서 실용성 측면에서 한계점이 있었다. 첫 번째 연구는 대규모 생체신호 데이터베이스들을 분석함으로써 임상적으로 허용 가능한 수준의 정확도가 적절히 검증된 혈압 추정 모델을 개발하는 것을 목적으로 진행되었다. 본 연구에서는 1376명의 수술 중 환자들의 약 250만 심박 주기에 대해 측정된 두 가지 비침습적 생체신호인 심전도와 광용적맥파를 활용한 혈압 추정 방식들을 분석하였다. 맥파 도달 시간, 심박수, 그리고 다양한 광용적맥파 파형 피처들을 포함하는 총 42 종류의 파라미터들을 대상으로 피처 선택 기법들을 적용한 결과, 28개의 피처들이 혈압 추정 파라미터로 결정되었고, 특히 두 가지 광용적맥파 피처들이 기존에 혈압 추정 파라미터로 가장 주요하게 활용되었던 맥파 도달 시간보다 우월한 파라미터들로 분석되었다. 선정된 파라미터들을 활용하여 혈압의 낮은 주파수 성분을 인공신경망으로 모델링하고, 높은 주파수 성분을 순환신경망으로 모델링 한 결과, 수축기 혈압 에러율 0.05 ± 6.92 mmHg와 이완기 혈압 에러율 -0.05 ± 3.99 mmHg 정도의 높은 정확도를 달성하였다. 또 다른 생체신호 데이터베이스에서 추출한 334명의 중환자들을 대상으로 모델을 외부 검증했을 때 유사한 결과를 획득하면서 세 가지 대표적 혈압 측정 장비 기준들을 모두 만족시켰다. 해당 결과를 통해 제안된 혈압 추정 모델이 1000명 이상의 다양한 피험자들을 대상으로 적용 가능함을 확인하였다. 두 번째 연구는 일상 생활 중 장기간 모니터링이 가능한 단일 착용형 혈압 모니터링 시스템을 개발하는 것을 목적으로 진행되었다. 대부분의 기존 혈압 추정 연구들은 혈압 추정 파라미터 추출을 위해 필요한 생체신호들을 측정하기 위해 두 군데 이상의 신체 지점에 두 개 이상의 모듈을 부착하는 등 실용성 측면에서 한계를 나타냈다. 이를 해결하기 위해 본 연구에서는 심전도와 광용적맥파를 동시에 연속적으로 측정하는 단일 가슴 착용형 디바이스를 개발하였고, 개발된 디바이스를 대상으로 총 25명의 건강한 피험자들로부터 데이터를 획득하였다. 손가락에서 측정된 광용적맥파와 가슴에서 측정된 광용적맥파 간 파형의 특성에 유의미한 차이가 있기 때문에 가슴에서 측정된 광용적맥파에서 추출된 피처들을 대응되는 손가락에서 측정된 광용적맥파 피처들로 특성을 변환하는 전달 함수 모델을 개발하였다. 25명으로부터 획득한 데이터에 전달 함수 모델을 적용시킨 후 혈압 추정 모델을 검증한 결과, 수축기 혈압 에러율 0.54 ± 7.47 mmHg와 이완기 혈압 에러율 0.29 ± 4.33 mmHg로 나타나면서 세 가지 혈압 측정 장비 기준들을 모두 만족시켰다. 결론적으로 본 연구에서는 임상적으로 허용 가능한 수준의 정확도로 장기간 일상 생활이 가능한 비침습적 연속 동맥 혈압 모니터링 시스템을 개발하고 다수의 데이터셋을 대상으로 검증함으로써 고혈압 조기 진단 및 예방을 위한 모바일 헬스케어 서비스의 가능성을 확인하였다.As non-invasive continuous blood pressure monitoring (NCBPM) has gained wide attraction in the recent decades, many studies on blood pressure (BP) estimation using pulse transit time (PTT), pulse arrival time (PAT), and characteristics extracted from the morphology of photoplethysmogram (PPG) waveform as indicators of BP have been conducted. However, most of the studies have used small homogeneous subject pools to generate models of BP, which led to inconsistent results in terms of accuracy. Furthermore, the previously proposed modalities to measure BP indicators are questionable in terms of practicality, and lack the potential for being utilized in daily life. The first goal of this thesis is to develop a BP estimation model with clinically valid accuracy using a large pool of heterogeneous subjects undergoing various surgeries. This study presents analyses of BP estimation methods using 2.4 million cardiac cycles of two commonly used non-invasive biosignals, electrocardiogram (ECG) and PPG, from 1376 surgical patients. Feature selection methods were used to determine the best subset of predictors from a total of 42 including PAT, heart rate, and various PPG morphology features. BP estimation models were constructed using linear regression, random forest, artificial neural network (ANN), and recurrent neural network (RNN), and the performances were evaluated. 28 features out of 42 were determined as suitable for BP estimation, in particular two PPG morphology features outperformed PAT, which has been conventionally seen as the best non-invasive indicator of BP. By modelling the low frequency component of BP using ANN and the high frequency component using RNN with the selected predictors, mean errors of 0.05 ± 6.92 mmHg for systolic blood pressure (SBP), and -0.05 ± 3.99 mmHg for diastolic blood pressure (DBP) were achieved. External validation of the model using another biosignal database consisting of 334 intensive care unit patients led to similar results, satisfying three international standards concerning the accuracy of BP monitors. The results indicate that the proposed method can be applied to large number of subjects and various subject phenotypes. The second goal of this thesis is to develop a wearable BP monitoring system, which facilitates NCBPM in daily life. Most previous studies used two or more modules with bulky electrodes to measure biosignals such as ECG and PPG for extracting BP indicators. In this study, a single wireless chest-worn device measuring ECG and PPG simultaneously was developed. Biosignal data from 25 healthy subjects measured by the developed device were acquired, and the BP estimation model developed above was tested on this data after applying a transfer function mapping the chest PPG morphology features to the corresponding finger PPG morphology features. The model yielded mean errors of 0.54 ± 7.47 mmHg for SBP, and 0.29 ± 4.33 mmHg for DBP, again satisfying the three standards for the accuracy of BP monitors. The results indicate that the proposed system can be a stepping stone to the realization of mobile NCBPM in daily life. In conclusion, the clinical validity of the proposed system was checked in three different datasets, and it is a practical solution to NCBPM due to its non-occlusive form as a single wearable device.Abstract i Contents iv List of Tables vii List of Figures viii Chapter 1 General Introduction 1 1.1 Need for Non-invasive Continuous Blood Pressure Monitoring (NCBPM) 2 1.2 Previous Studies for NCBPM 5 1.3 Issues with Previous Studies 9 1.4 Thesis Objectives 12 Chapter 2 Non-invasive Continuous Arterial Blood Pressure Estimation Model in Large Population 14 2.1 Introduction 15 2.1.1 Electrocardiogram (ECG) and Photoplethysmogram (PPG) Features for Blood Pressure (BP) Estimation 15 2.1.2 Description of Surgical Biosignal Databases 16 2.2 Feature Analysis 19 2.2.1 Data Acquisition and Data Pre-processing 19 2.2.2 Feature Extraction 25 2.2.3 Feature Selection 35 2.3 Construction of the BP Estimation Models 44 2.3.1 Frequency Component Separation 44 2.3.2 Modelling Algorithms 47 2.3.3 Summary of Training and Validation 52 2.4 Results and Discussion 54 2.4.1 Feature Analysis 54 2.4.1.1 Pulse Arrival Time versus Pulse Transit Time 54 2.4.1.2 Feature Selection 57 2.4.2 Optimization of the BP Estimation Models 63 2.4.2.1 Frequency Component Separation 63 2.4.2.2 Modelling Algorithms 66 2.4.2.3 Comparison against Different Modelling Settings 68 2.4.3 Performance of the Best-case BP Estimation Model 69 2.4.4 Limitations 75 2.5 Conclusion 78 Chapter 3 Development of the Single Chest-worn Device for Non-invasive Continuous Arterial Blood Pressure Monitoring 80 3.1 Introduction 81 3.2 Development of the Single Chest-worn Device 84 3.2.1 Hardware Development 84 3.2.2 Software Development 90 3.2.3 Clinical Trial 92 3.3 Development of the Transfer Function 95 3.3.1 Finger PPG versus Chest PPG 95 3.3.2 The Concept of the Transfer Function 97 3.3.3 Data Acquisition for Modelling of the Transfer Function 98 3.4 Results and Discussion 100 3.4.1 Construction of the Transfer Function 100 3.4.2 Test of the BP Estimation Model 101 3.4.3 Comparison with the Previous Study using the Single Chest-worn Device 104 3.4.4 Limitations 106 3.5 Conclusion 108 Chapter 4 Thesis Summary and Future Direction 109 4.1 Summary and Contributions 110 4.2 Future Work 113 Bibliography 115 Abstract in Korean 129 Acknowledgement 132Docto