Dissertations / Theses on the topic 'Single'

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Biological Engineering, 2018.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 77-92).
Sequencing the human genome has spurred systematic work on understanding how gene expression and genomic integrity contribute to disease. To date, 3,519 genes have been identified as the underlying cause of specific single gene disorders. However, complex diseases still pose a daunting challenge that require both an understanding of cell function as well as how the genome interacts with its cellular environment. Sequencing technologies are now routinely applied to interrogate gene variants, gene expression patterns, chromosome accessibility, among other measurements to infer gene and cell function. We build upon past work to address the challenge of targeting sequencing effort to cells and genomic loci of interest to probe the molecular mechanisms behind disease. In this thesis, we demonstrate two novel targeted sequencing methods that can enable a greater understanding of cell function. (1) The development of targeted sequencing in pooled single cell RNA-seq libraries and (2) the development of a novel sequencing approach that allows for the quantification and identification of single stranded break (SSB) locations across the genome. First, we introduce a new targeted sequencing approach to identify rare cells of interest in pooled sequence libraries. Improved throughput in single cell sequencing has enabled the transcriptional profiling of thousands of cells at once. However, due to reliance on pooled library construction methods, it is now more difficult to focus on and analyze particular cells of interest, apart from analyzing the library in its entirety. We designed multiplex PCR primers to simultaneously enrich targeted cells from a complex DNA library pool of single cells. We show how molecular enrichment can be used to efficiently target rare cell types, such as the recently identified AXL+SIGLEC6+ dendritic cell (AS DC). Next, we demonstrate a new targeted sequencing approach, called NickSeq, to locate and quantify DNA SSBs with single nucleotide resolution. SSBs are the most common form of DNA damage at an estimated 10,000 per cell per day, but there is no available method to robustly determine the exact sites of damage. SSB accumulation correlates with disease, but it is unknown how the location and amount of damage relate to health outcomes. We intentionally create a unique mutational signature at the SSB that is a fingerprint for this specific type of DNA damage when the locus is sequenced. Taken as a whole, we introduce two novel strategies to further understand cell function through studying rare cells in single cell populations and analyzing DNA SSB damage in relation to cell health. This work demonstrates that targeted sequencing approaches have promise for understanding the molecular mechanisms behind aberrant cell function, a necessary step in the prevention and treatment of disease.
by Navpreet Singh Ranu.
Ph. D.

Single-photon sources and detectors underpin the development of quantum photonic technologies. This thesis presents research into single-photon devices with a focus on telecom wavelengths. A two-channel superconducting nanowire single-photon detector (SNSPD) system was constructed and characterised. It provides free-running single-photon detection at telecom wavelengths with low dark counts and timing jitter below 90 ps FWHM. The system detection e ciency at 1310 nm is 1 % with a 1 kHz dark count rate, which was competitive when the SNSPD was built in 2009. In this work, the low timing jitter of the SNSPD was bene cial to the development of a two-photon interference experiment. Experiments were carried out with single-photon sources based on self-assembled InAs/GaAs quantum dots in micropillar cavities. Preliminary measurements of the second-order correlation function gave g(²)(τ=0) = 0.12 ± 0.04 with above-band excitation and g(²)( τ = 0) = 0:07 ± 0:05 with near-resonant excitation. These values agree with recent papers reporting improved measurements with near-resonant excitation. Irreparable damage to the sample prevented further investigation. This thesis also presents the design, construction and characterisation of a highresolution single-photon spectrometer for telecom wavelengths. The instrument, a scanning Fabry-Perot interferometer, was optimised for the characterisation of quantum photonic sources. It has a spectral resolution of 550 MHz and a free spectral range of (119.0 ± 0.4) GHz.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, June 2015.
"May 2015." Cataloged from PDF version of thesis.
Includes bibliographical references (pages 105-114).
Single Walled Carbon Nanotubes are of great interest as a semiconducting material with diameters around 1nm and length in the 100s of nm to mm range. The large aspect ratio, near-infrared wavelength bandgap and a high conductivity enable a large number of optical and optoelectronic applications inaccessible by other materials. However, carbon nanotubes as produced are heterogeneous in electronic properties that are dependent on their chirality. Small changes in geometry of the tube dramatically change the bandgap of the tube, and whether it is metallic or semiconducting. This thesis establishes the first reproducible method by which to separate a single electronic type of carbon nanotube, i.e. a single chirality. The mechanism by which this separation occurs is explored experimentally and via quantitative modelling. The thesis ends with a demonstration of the first near infrared single chirality carbon nanotube solar cell.
by Rishabh M. Jain.
Ph. D.

Quantum information is a highly interesting and fast emerging field that involves processing information encoded into quantum systems and their subsequent use in various information tasks. The use of quantum resources such as superposition and entanglement have shown to enhance information processing capabilities beyond classical means in a number of communication, information and computation tasks. In this thesis, we have used single photons to study the advantage of d-level quantum systems (qudits) for a communication task commonly known as random access codes (RACs). A successful experimental demonstration of quantum random access codes (QRACs) with four dimensions is realized to demonstrate that the higher dimensional QRACs not only outperform the classical RACs but also provide an advantage over their quantum bit (qubit) counterparts. QRACs are also studied in regards to two specific applications: certification of true randomness and for testing the non-classicality of quantum systems. A method for increased certification of generated randomness is realized for the former and a successful experimental demonstration of a test of non-classicality with arbitrarily low detection efficiency is provided for the latter. This is followed by an implementation of a QRAC in a one-path communication network consisting of preparation, transformation and measurement devices. We have shown that the distributed QRAC provides optimal success probabilities for a number of tasks. Moreover, a novel quantum protocol for the solution to the problem of dining cryptographers and anonymous veto voting is also presented. This single photon transmission based protocol provides an efficient solution, which is experimentally demonstrated for a 3-party description. Lastly, Nitrogen-Vacancy (NV) center in diamond is studied as a potential resource for single photon emission and two methods to enhance the photon collection efficiency are successfully explored. Due to this enhancement, single photons from an NV center may also be used in similar single quantum system based communication experiments.

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Manuscript. Paper 4: Manuscript. Paper 5: Manuscript.

One promising approach for future quantum networks is the combination of strings of trapped ions as quantum-information processors with entangled photon pairs produced by spontaneous parametric down conversion (SPDC) to establish quantum communication links between distant processing units. This work reports on experiments using a hybrid quantum-optics set-up, comprising two separate linear ion traps and a resonant SPDC photon-pair source. It demonstrates the controlled interaction of single entangled photon pairs with a single trapped 40Ca+ ion. Preparing the ion as polarization selective absorber in the main polarization bases allows for the reconstruction of the biphoton quantum state, manifesting the photon entanglement in the absorption process. Beyond that, the thesis documents the implementation of additional experimental tools enabling quantum state transfer experiments from photons to single ions. A dedicated narrowbandwidth laser system is set up, laser sequences are developed for state discrimination and state rotations of ion qubits, and for the creation and characterization of coherent superposition states, of particular importance for state-transfer schemes. Finally, detection efficiencies of single Raman photons emitted by an ion are characterized with a well controlled single-photon source, and absorption probabilities of single photons are determined with a calibrated laser beam, providing precise values to assess efficiencies for different transfer scenarios.
Un enfoque prometedor para futuras redes cuánticas es la combinación de iones atrapados con pares de fotones entrelazados que se generan por el proceso SPDC (Spontaneous Parametric Down Conversion). Los iones atrapados se utilizarán como procesadores de información cuántica. Los pares de fotones permitirán el establecimiento de enlaces de comunicación cuántica entre unidades de procesamiento distantes. En el transcurso de este trabajo, que se situa en el marco de la óptica cuántica, se han combinado dos implementaciones experimentales independientes para la realización de un experimento híbrido. Las dos partes del experimento corresponden con dos trampas de iones lineales separadas y con una fuente de pares de fotones resonantes creados por SPDC. En este experimento se demuestra la interacción controlada de pares de fotones individuales entrelazados con un ión atrapado individual de 40Ca+. La preparación del ión como absorbente selectivo de polarización en las bases de polarización principales permite la reconstrucción del estado cuántico de los pares de fotones, manifestando así su entrelazamiento a través del proceso de absorción. Además, en la tesis presente se documenta la implementación de herramientas experimentales adicionales que permitirán experimentos de transferencia de estados cuánticos de fotones a iones individuales. Así mismo, se describe el montaje de un sistema láser acondicionado con ancho de banda estrecho. Adicionalmente, se desarrollan secuencias de láser para la discriminación y la rotación de estados de qubits de iones y, para la creación y caracterización de estados de superposición coherente, especialmente importantes para varios esquemas de transferencia de estado. Por último, se caracterizan las eficiencias de detección de fotones individuales Raman emitidos por un ión con una fuente de fotones individuales bien controlada, así como también se determinan las probabilidades de absorción de fotones individuales con una fuente láser calibrada. Los valores precisos obtenidos servirán para la evaluación de la eficiencia de diferentes esquemas de transferencia.
Ein mögliches System für zukünftige Quantennetzwerke ist die Verknüpfung gefangener Ionen als Quanteninformationsprozessoren mit durch SPDC (Spontaneous Parametric Down Conversion) erzeugten verschränkten Photonenpaaren zum Aufbau von Quantenkommunikationskanälen. Diese Dissertation behandelt Experimente an einem hybriden Quantenoptikaufbau, bestehend aus zwei separaten linearen Ionenfallen und einer SPDC-Photonenpaarquelle. Sie zeigt die kontrollierte Wechselwirkung einzelner verschränkter Photonenpaare mit einem einzelnen 40Ca+ Ion. Durch Präparation des Ions als polarisationsselektiven Absorber in den drei Hauptpolarisationsbasen, wird der Zwei-Photonen-Quantenzustand rekonstruiert und somit über den Absorptionsprozess die Verschränkung der Photonenpaare nachgewiesen. Überdies dokumentiert die Arbeit die Einrichtung zusätzlicher Methoden, welche den Zustandstransfer von Photonen auf einzelne Ionen ermöglichen. Ein schmalbandiges Lasersystem wird aufgebaut, Lasersequenzen für Zustandsbestimmung und Zustandsrotationen von Ionen-Qubits und zur Erzeugung und Charakterisierung kohärenter Superpositionszustände werden entwickelt. Ferner werden mit Hilfe einer Einzelphotonenquelle Nachweiseffizienzen für einzelne, von einem Ion erzeugte, Raman-Photonen gemessen und Absorptionseffizienzen einzelner Photonen mit einer kalibrierten Laserquelle charakterisiert. Die ermittelten Werte bilden eine solide Grundlage zur Abschätzung von Erfolgswahrscheinlichkeiten geplanter Transferschemata.

A SINGLE REGRET is a murder mystery set on the post Hurricane Sandy Jersey shore. At thirteen, Jimmy Miller killed his father in retribution for murdering his mother. Twenty years later, he returns home because of the murder of his childhood best friend, Dillon Abernathy. Jimmy learns that Gavin, a classmate turned junkie, is charged with murdering Dillon, a scenario Jimmy doesn’t find plausible, so he decides to pursue leads the police won’t. Told in first person past tense, A SINGLE REGRET follows Jimmy as he unearths the secrets behind his friend’s death and also learns the truth behind the destruction of his own family. As in Dennis Lehane’s Mystic River, the novel examines how childhood ties shape perceptions in ways that are both true and false. Jimmy is forced to evaluate his own sense of bitterness and learn how to forgive his own mistakes and those of others.

This thesis presents various pipette-based techniques for resolving the electrochemical activities of single nanoentities (e.g., nanoparticles, NPs) in time and/or space. In particular, the work provides a framework for understanding the (electro)chemistry of single NPs and the development of tools to resolve them temporally and/or spatially. Through the use of the state-of-the-art instrumentation developed by the Warwick Electrochemistry & Interfaces Group (WEIG), electrochemical measurements with a “static” probe (i.e., micro-droplet electrochemical cell) have revealed detailed (temporally-resolved) information on the dynamics of the interaction of colloidal NPs (in solution) with electrode surfaces. Through careful data analysis, and supported by simulations, it has been demonstrated how current-time traces provide information on the physical dynamics of individual NPs on an electrode surface. This regime has been further applied to understand the electrodissolution of individual NPs and has revealed the complexity of the process, through carefully designed experiments and thorough quantitative analysis of large data sets. In addition, through the use of the aforementioned instrumentation, new scanning electrochemical probe microscopy (SEPM) regimes have been developed with a “dynamic” probe, providing spatial resolution. A greatly simplified nanoprobe configuration (i.e., a single channelled probe) has been proposed for simultaneous topography and electrochemical flux mapping at the nanoscale, implemented with a new scanning protocol in scanning ion conductance microscopy (SICM). This was directly applied in tandem with FEM simulations to observe and explain heterogeneities in the ion flux at and around individual catalytic NPs adhered to an inert conductive surface during catalytic turnover conditions with electrochemical activity information on surface heterogeneities at the nanoscale. Finally, to highlight the generalities of the approaches, a new configuration of scanning electrochemical microscopy (SECM) combined with SICM with a double-channelled nanoprobe has been introduced, demonstrating the simultaneous visualisation of topography and uptake rate on a biological entity (cell), which is quantified by finite element method (FEM) simulations. In this configuration the probe is multifunctional, delivering analytes to the cell surface, providing probe positional information and detecting changes in the uptake rate of electroactive molecules across the interface.

The possibility of creating a scaleable quantum network by interconverting photonic and atomic qubits shows great promise. The fundamental requirement for such a network is deterministic control over the emission and absorption of photons from single atoms. This thesis reports on the experi-mental construction of a photon source that can emit single-photons with arbitrary spatio-temporal shape, phase, and frequency. The photon source itself is a strongly-coupled atom cavity system based on a single ⁸⁷ Rb atom within a macroscopic high-finesse Fabry-Perot cavity. It operates intermittently for periods of up to 100µs, with single-photon repetition rates of 1.0 MHz and an efficiency of almost 80%. Atoms are loaded into the cavity using an atomic fountain, with the upper turning point near the centre of the cavity mode. This ensures long interaction times without any disturbances introduced by trapping potentials. The photons’ indistinguishability was tested, with a two-photon Hong-Ou-Mandel visibility of 87%. This ability to both generate, and control, the photons’ properties, for example producing photons with symmetric or multi-peaked spatio-temporal shapes, allows for the production of photons in an n-time-bin superposition state where each time-bin has an arbitrarily defined amplitude and phase. These photons can be used as photonic qubits, qutrits and qquads, and their properties have been tested using a small linear-optics network.

Das Neuron ist das zentrale Element in der Informationsverarbeitung im Nervensystem. In dieser Arbeit werden verschiedene Aspekte der Spikegenerierung sowohl theoretisch als auch experimentell untersucht. Phasen-Rotatoren verschiedener Komplexität werden zur Vorhersage von Spikezeitpunkten vorgestellt. Die Kennlinie eines Neurons wird dabei als wichtiger Parameter für diese Modelle verwendet, damit diese leicht auf echte Neurone anwendbar sind. Die Phasenantwortkurve als ein zweiter wichtiger Aspekt der Spikedynamik wird zur Erweiterung der Modelle verwendet. Solange ein Neuron in seinem überschwelligen Bereich gereizt wird, erweisen sich die Phasenrotatoren als gute Beschreibung des Spikeverhaltens. Es wird jedoch gezeigt, daß bei einer Stimulierung mit Strömen, die um die Schwelle des Neurons herum fluktuieren, diese Modelle, genauso wie alle anderen eindimensionalen Modelle einschließlich des Intergrate-and-fire Neurons, versagen. Feuerraten Adaptation kann in vielen Neuronen beobachtet werden. Es wird ein allgemeines phänomenologisches Modell für die Feuerrate adaptierender Neurone aus den Eigenschaften verschiedene Ionenströme, die Adaptation verursachen, hergeleitet. Dieses Modell ist durch die Kennlinien und einer Adaptations-Zeitkonstanten vollständig definiert. Mit Hilfe des Modells können die Eigenschaften der Adaptation als Hochpassfilter quantifiziert werden. Weiterhin wird die Rolle der Adaptation bei der Unterdrückung von Hintergrundrauschen diskutiert. Sowohl die Phasenrotatoren als auch das Adaptationsmodell werden an auditorischen Rezeptorzellen der Wanderheuschrecke und dem AN1, ein primäres auditorisches Interneuron der Grille {Teleogryllus oceanicus}, getestet. In beiden Fällen stimmen die Modelle gut mit den experimentelle Daten überein. Es wird mit Hilfe der Modelle gezeigt, daß Adaptation in den Rezeptorzellen durch Ionenströme des Spikegenerators verursacht wird, während in dem Interneuron der Eingang schon adaptatiert. Zusätzlich wird der Einfluß der Feuerraten-Adaptation auf die Gesangserkennung analysiert.
The single neuron is the basic element of information processing in nervous systems. In this thesis several properties of the dynamics of the generation of spikes are investigated theoretically as well as experimentally. Phase oscillators of different complexity are introduced as models to predict the timing of spikes. The neuron's intensity-response curve is used as a basic parameter in these models to make them easily applicable to real neurons. As a second important aspect of the spiking dynamics, the neuron's phase-resetting curve is used to extend the models. The phase oscillators turn out to be a good approximation of the spiking behavior of a neuron as long as it is stimulated in its super-threshold regime. However, it is shown by comparison with conductance-based models that these models, as well as all other one-dimensional models including the common integrate-and-fire model, fail, if the neuron is stimulated with currents fluctuating around its threshold. Spike-frequency adaptation is a common feature of many neurons. For various ionic currents, as a possible reason for adaptation, a general phenomenological model for the firing rate of adapting neurons is derived from their biophysical properties. This model is defined by the neuron's intensity-response curves and an adaptation time-constant. By means of this model the high-pass properties of spike-frequency adaptation can be quantified. Also the role of adaptation in supression of background noise is discussed. Both the phase oscillators and the adaptation-model are tested on auditory receptor neurons of locusts and the AN1, a primary auditory interneuron of the cricket {Teleogryllus oceanicus}. In both cases the models are in good agreement with the experimental data. By means of the models it is shown that adaptation in the receptor neurons is caused by ionic currents of the spike generator while in the interneuron it is the input which is already adapting. In addition, the influence of spike-frequency adaptation on the recognition of courtship songs is analysed.

This study researched the meaning of being single among 24 college-age adults of The Church of Jesus Christ of Latter-day Saints (i.e., Mormons). It examined influences on the construction of meanings of singlehood, gender patterns regarding the meaning of singlehood, and pressures on L.D.S. singles to date and marry. The most important finding was that positive attitudes toward singlehood are more prevalent than negative or ambivalent attitudes. Families, as gate-keepers and transmitters of cultural information about singlehood and marriage, and the L.D.S. religion were the strongest influences on the development of meanings of singlehood. Families and religion mutually influence one another and meanings of singlehood, and supportive friends helped singles feel that they are not alone. Although there was more variation within than between gender accounts of singlehood, important patterns in construction of attitudes were also discovered. Participants felt both external and internal pressures to date and marry.

We have studied a new optical sensor characterized by performances that will extend the capabilities of several new physical investigation techniques. Our imaging device is based on a two-dimensional array of Single Photon Avalanche Diode (SPAD), sensitive to the single photon with a subnanosecond timing precision. It is able to perform a continuous photon acquisition without the necessity to break to perform the readout process. Moreover it is not damageable by intense light sources. The proposed solution constitutes a step forward for all Time Correlated Single Photon Counting analysis, as Fluorescence Lifetime Imaging Microscopy, Dynamic Light Scattering, 3D Camera, Particle Imaging Velocimetry and Adaptive Optics. An electric characterization of the single SPAD has been carried out to perform multiple readout strategies, and an electric model has been used to perform the simulation of different two-dimensional electric array configurations. We have also deeply studied the source of the counting distortion of the single passive quenched SPAD and have been able to extend the dynamic range of four order of magnitude and to use the dead time saturation as a compression feature for data produced by our imaging sensor. The dead time compensation laws established in Literature have been extended over the steady state analysis to include the time dependent source and any type of dead time. The acquisition electronics, the sensor calibration and the imaging reconstruction algorithm have been performed on a working prototype. The device has been tested with many experimental setups, developed to evaluate the features and the limits of our technological solutions.
Abbiamo studiato un nuovo sensore ottico caratterizzato da prestazioni che estenderanno le funzionalita' di molte nuove tecniche di indagine fisica. Il nostro dispositivo si basa su una matrice bidimensionale di Single Photon Avalanche Diode (SPAD), in grado di fornire il tempo di arrivo di ogni singolo fotone con una precisione del decimo di nanosecondo. Il nostro apparato e' in grado di acquisire là ¢ arrivo dei fotoni con continuita', senza interruzioni dovute al processo di lettura, ed e' inoltre resistente a fonti di luce eccessiva che costituiscono una limitazione per i normali dispositivi a singolo fotone. La soluzione proposta costituisce un passo in avanti per tutte le analisi basate sulla correlazione temporale a singolo fotone, come la Fluorescence Lifetime Imaging Microscopy, Dynamic Light Scattering, 3D Camera, Particle Imaging Velocimetry e Adaptive Optics. Grazie allo studio delle caratteristiche elettriche del singolo SPAD e' stato possibile individuare varie strategie di lettura. Il modello elettrico sviluppato e' stato inoltre utilizzato per simulare diverse configurazioni elettriche della matrici bidimensionali di sensori. Abbiamo studiato le caratteristiche funzionali del singolo SPAD ponendo l'attenzione sui fenomeni che alterano la linearita' di ri-sposta, siamo stati cosi' in grado di estendere di quattro ordini di grandezza il suo intervallo di utilizzo, e di utilizzare la saturazione come una funzione di compressione dei dati prodotti dal sensore. Le equazioni presentate estendono la correzione degli effetti del tempo morto, gia' presenti in letteratura, dallà ¢ analisi del caso stazionario a quello delle sorgenti variabili nel tempo, e sono inoltre estendibili a qualunque configurazione di tempo morto. La produzione di un prototipo funzionante ha compreso inoltre la realizzazione dell'elettronica di acquisizione, dell'algoritmo di calibrazione del sensore e di ricostruzione delle immagini. Il dispositivo e' stato testato realizzando diversi esperimenti, che hanno permesso di valutare le caratteristiche e i limiti delle soluzioni tecnologiche adottate.

In this thesis, single-molecule experiments using LOT are employed to extract accurate information about the thermodynamics and kinetics of various molecular systems, with special emphasis on the elastic properties of single-stranded DNA (ssDNA). The thesis is divided in three parts. Part I provides a general description of the research field as well as the main theoretical framework for the basic concepts that will be developed in parts II and III. In Chapter 2 the miniTweezers and the experimental setup used throughout the thesis is described, as well as the physical basis of its working mechanisms, introducing the phenomenon of optical trapping. Chapter 3 contains a brief introduction of the biomolecules of study in this thesis, with an explanation of their historical discoveries, as well as their structure and function. The main focus of this chapter is on ssDNA, which is the main object of study of the thesis. Chapter 4 introduces the polymer models that are widely used in describing the elasticity of nucleic acids and proteins. Specifically, the Freely-Jointed Chain and Worm-Like Chain models are presented. Part II deals with the elasticity of single-stranded DNA. This is the main part of the thesis, and it includes chapters 5-7. Chapter 5 is about the study of the elasticity of ideal ssDNA chain, i.e. the one that can be modelled as ideal polymers (presented in Chapter 4). The study of the elasticity of different DNA sequences is presented. The blocking-splint oligo technique is described, a experimental technique developed for studying the elasticity of short (tens of bases) DNA molecules. This study shows the need of using extensible models to succesfully describe ssDNA elasticity over a large range of forces, which explains the previous discrepancies on the elastic parameters obtained in different studies. We also provide an explanation for the required extensibility of the model: a transition experienced at the nucleotide level: a change in DNA sugar pucker conformation. A simple two-states model is introduced and preeliminary results regarding its energetics are presented. The characterization of the ssDNA elasticity is central for the works developed in the following chapters. Chapter 6 studies the stacking-unstacking transition for ssDNA, previously observed for certain sequences (mainly purine-rich ones). Several molecules, with different degrees of stacking, are studied by obtaining their force extension curves (FECs). A cooperative helix-coil model including heterogeneity is developed and used to fit the obtained FECs, allowing to obtain elastic parameters to describe the stacked chain. The salt dependence of the unstacking transition is also measured by studying two of the sequences by varying the salt concentration over two decades. The free energy of formation of dsDNA duplexes depends on the salt concentration. The obtained salt dependence on the stacking free-energy of ssDNA provides a possible explanation for the salt dependence of duplex formation. Chapter 7 deals with the non-specific structures that arise at low forces and high salt concentration when pulling ssDNA molecules longer than $\sim 100$ bases. A helix-coil model with cooperativity is proposed and used to extract some mean-field characteristics of these structures. 8 different sequences are studied, characterizing their elasticity and deviation from the ideal elastic behaviour. The results for a $14$kb molecule for 3 decades of varying \ce{NaCl} and \ce{MgCl2} are also shown. All experimental FECs are fitted to the helix-coil model. The model can be used to predict the formation of secondary structures at zero force. A comparison between the predicted structures from the model and those obtained from Mfold is also investigated. Part III contains two studies which also need of the correct determination of ssDNA elasticity. In Chapter 8, we study the interaction between the RecQ helicase from E. coli and DNA, i.e. how the RecQ unwinds double-stranded DNA molecules, releasing single-stranded DNA. We obtain some of its kinematic properties as well as study the entropy production of the system using the Fluctuation Theorem. In Chapter 9, the effect of DNA mismatches, i.e. non complementary base pairing, on the stability of DNA is studied. To do so, two types of experiments on several DNA sequences are performed: stretching and releasing the molecule by moving the optical trap (pulling experiments) and monitoring the folding/unfolding of the molecule passively (hopping experiments).
En aquesta tesi hem realitzat experiments fent servir pinces òptiques per tal d’extreure informació precisa sobre les propietats termodinàmiques i cinètiques de diferents sistemes moleculars, posant especial èmfasi en les propietats elàstiques de la cadena simple d’ADN (ssDNA, pel seu acrònim en anglès). La tesi es troba dividida en tres parts. A la primera part s’introdueix de forma general el camp de recerca dels experiments de molècula única, així com s’expliquen els conceptes més bàsics que es desenvoluparan en les parts II i III. La configuració experimental emprada al llarg de tota la tesi, les pinces òptiques, s’introdueix al capítol 2. Per a fer-ho, s’expliquen els principis físics de funcionament de les pinces, que es basen en l’atrapament òptic. Breument, la focalització d’un feix de llum d’alta intensitat permet atrapar i exercir forces en micropartícules dielèctriques (pilotes fetes de plàstic de la mida d’un bacteri), que són recobertes químicament de manera que la molècula d’estudi pot estirar-se, de forma individual, repetides vegades. El capítol 3 conté una breu introducció a les biomolècules que apareixen en aquesta tesi, amb una breu explicació de la seva descoberta, així com la seva estructura i funció (íntimament relacionades). Ens centrem en la descripció de la ssDNA que és el principal objecte d’estudi de la tesi. Al capítol 4 s’introdueixen els models de polímers que s’empren habitualment per a descriure l’elasticitat d’àcids nucleics i proteïnes. En concret, es descriuen els models de la Freely-Jointed Chain i la Worm-Like Chain. La Part II tracta de l’elasticitat de la ssDNA, i inclou els capítols 5, 6 i 7. El capítol 5 es basa en la caracterització de l’elasticitat de la cadena ideal de ssDNA, és a dir, aquella que pot ser modelitzada pels polímers ideals introduïts en el capítol 4. S’estudia l’elasticitat de diferents seqüències de ssDNA, introduint un nou mètode experimental, blocking-splint oligo, per tal d’ampliar el rang de forces estudiat habitualment en molècules curtes (d’una longitud de desenes de bases) de ssDNA. L’estudi mostra la necessitat d’emprar models elàstics extensibles per a la correcte caracterització de l’elasticitat de ssDNA, que explica les discrepàncies existents entre els paràmetres elàstics trobats a la literatura. També hipotetitzem que l’extensibilitat del model pot ser explicada gràcies a la transició experimentada a nivell de nucleòtids: el canvi que experimenta la distància interfosfat de l’ADN es veu modificada segons quina sigui la configuració de l’anell de desoxiribosa. Tot i que és un fenomen molt més conegut en la cadena doble d’ADN, l’apilament-desapilament de bases també s’ha observat en certes seqüències de ssDNA (especialment les que són riques en contingut de purines). Al capítol 6 s’estudien quatre molècules amb un grau d’apilament diferent a partir de les seves corbes força-extensió (FECs). Es desenvolupa un model helix-coil (hèlix-cabdell) per tal d’ajustar les FECs, fet que permet d’obtenir, indirectament, les propietats elàstiques de la cadena apilada. També s’estudia la dependència d’aquesta transició variant la concentració de sal dels experiments en més de dos ordres de magnitud. A través d’aquests experiments, trobem una dependència amb la concentració de sal de l’energia lliure de formació de l’apilament de la ssDNA, fet que ens permet explicar, parcialment, la dependència que es troba en la literatura per la hibridació de la cadena doble d’ADN. El capítol 7 tracta de la formació d’estructures no específiques que apareixen a forces baixes i a concentració de sal alta per a molècules de ssDNA de més de ~100bases. Es proposa un model helix-coil amb cooperativitat per tal de caracteritzar propietats de camp mitjà de les estructures estudiades. S’estudien vuit seqüències diferents, entre 120 i ~14000 bases, i es caracteritza el seu desviament respecte de la corba elàstica ideal amb el model. També s’estudia la dependència de l’estructura secundària de la ssDNA en funció de la concentració de la sal. Analitzant experiments variant la concentració de MgCl2 i NaCl, aconseguim reproduir les FECs a partir de fer dependre els paràmetres del model amb la sal. Finalment, el model desenvolupat ens permet predir la formació d’estructura secundària a força zero (fet que no podem detectar directament a partir d’experiments d’espectroscopia de forces). Es comparen les previsions del model amb les trobades per Mfold, trobant una compatibilitat per als resultats per a molècules de de menys de 1000 bases. La darrera part se centra en col·laboracions que he fet durant a tesi i que necessiten una determinació precisa de les propietats elàstiques de la ssDNA. Al capítol 8 s’estudia la interacció entre l’helicasa del bacteri E. coli i l’ADN, que s’encarrega d’obrir la cadena doble d’ADN, alliberant ssDNA. S’extreuen les seves propietats cinètiques, com la velocitat de translocació – obtenim, independentment de la força aplicada, d’uns 50bp/s, d’acord amb la literatura –. També n’estudiem les seves propietats termodinàmiques, a partir del Teorema de Fluctuació. Finalment, al capítol 9 s’estudien els efectes de certs defectes en molècules d’ADN. A partir d’experiments fora de l’equilibri s’extrau la penalització que suposa per a la hibridització d’ADN la presència d’aquestes bases no complementàries (és a dir, que no són enllaços de A-T o G-C).

This paper considers two major issues in the evolution of the European Union, the Single Market and the Single Currency. The first chapter deals with the projected effects of the 1992 Programme, and the second chapter deals with the collapse of the Exchange Rate Mechanism of the European Monetary System and examines the prospects for European Monetary Union given this collapse. The third chapter revolves around the concept of Central Banking under Monetary Union and focuses on the European Monetary Institute and the European System of Central Banks. Chapter four presents data regarding the progress of the European Union towards the target of the Single Currency, as well as other macroeconomic indicators.

Cell-substrate interactions are important to study for development of accurate in vitro research platforms.  Recently it has been demonstrated that physical microenvironment of cells directly affects cellular motility and cytoskeletal arrangement.  Specifically, previous studies have explored the role of material stiffness (Young\'s modulus: N/m2) on cell behavior including attachment, spreading, migration, cytoskeleton arrangement (stress fiber and focal adhesion distribution) and differentiation.
In this study using our recently described non-electrospinning fiber manufacturing platform, customized scaffolds of suspended nanofibers are developed to study single cell behavior in a tunable structural stiffness (N/m) environment.  Suspended fibers of three different diameters (400, 700 and 1200 nm) are deposited in aligned configurations in two lengths of 1 and 2 mm using the previously described STEP (Spinneret based Tunable Engineered Parameters) platform.  These fibers present a gradient of structural stiffness to the cells at constant material stiffness.   Single cells attached to fibers are constrained to move along the fiber axis and with increase in structural stiffness are observed to spread to longer lengths, put out longer focal adhesions, have elongated nucleus with decreased migration rates. Furthermore, more than 60% of cell population is observed to migrate from areas of low to high structural stiffness. Additionally dividing cells are observed to round up and daughter cells are observed to migrate away from each other after division. Interestingly, dividing rounded cells are found to be anchored to the fibers through thin protrusions emanating from the focal adhesion sites.
These results indicate a substrate stiffness sensing mechanism that goes beyond the traditionally accepted modulus sensing that cells have been shown to respond to previously.  From this work, the importance of structural stiffness in cellular mechanosensing at the single cell-nanofiber scaled warrants consideration of the above factors in accurate design of scaffolds in future.  

Master of Science

Single-channel recordings (SCR) and single-molecule Fluorescence (SMF) are invaluable tools for studying membrane proteins. Combining these two techniques would allow for structural dynamics to be correlated with function at the single-molecule level. However, the different requirements of SCR and SMF measurements present a long-standing challenge. Droplet interface bilayers (DIBs) are a model membrane system in which parallelisation of such measurements is possible using optical single-channel recording to resolve the conductance of multiple proteins simultaneously. In this project, two approaches were evaluated for obtaining simultaneous measurements in DIBs: the first sought to report on structural changes associated with a gating bacterial mechanosensitive channel, MscS; the second sought to resolve kinetics of the spontaneous β-barrel folding mechanism. For both approaches, functional, labelled protiens were produced and characterised using ensemble measurements to confirm that the state-transition of interest was accompanied by a change in fluorescent signal. Characterisation of MscS in DIBs revealed that control of lateral tension (a requirement to stimulate mechanosensitive channel gating) posed a major experimental challenge, rendering further pursuit of this candidate impossible. However in the case of β-barrel folding, the single-molecule fluorescence alone revealed a rare but fast transition from a membrane-associated unfolded to a folded state. While further work is needed to fully exploit simultaneous measurements, significant progress towards this goal is presented in this work, in particular the development of reagents, experimental procedures and analytical tools.

[Ce travail concerne le développement des mémoires à un électron de type SET/SEM pour les technologies CMOS silicium. Le premier chapitre du manuscrit est consacré à la présentation d' une revue bibliographique des phénomènes apparaissant dans les nanodispositifs électroniques (effets quantiques, blocage de Coulomb) de type transistors et mémoires à un électron. Dans le deuxième chapitre, nous nous intéressons aux diffë rents modèles électriques proposés pour les SETs. Grâce à des simulations numériques développées sous SPICE, nous avons approfondi notre compréhension du fonctionnement des SETs dans quelques exemples d'applications. Il s' agissait notamment de comparer les modèles dans le cas de SETs métalliques et semiconducteurs. Le troisième chapitre concerne la définition de l' architecture mémoire à un électron de type SET/SEM que nous proposons d'étudier. Après avoir présenté le concept de la structure SET/SEM, et expliqué le principe de fonctionnement dans les modes de lecture et de programmation, nous détaillons les résultats de simulations des caractéristiques du dispositif proposé. Après avoir opté pour une mémoire utilisant deux îlots métalliques pour les opérations de stockage de charge et de lecture respectivement, nous avons utilisé le logiciel SIMON afi n de proposer une architecture optimisée. Les travaux de simulations de l'architecture SET/SEM nous ont permis de calculer les éléments de circuits du modèle électrique équivalent permettant un fonctionnement optimal de la mémoire. Un aspect fondamental pour cette étude était en effet d'optimiser le décalage OVg des caractéristiques Ig-Vg observé lors de l' injection d'électrons uniques dans le point mémoire. Finalement, nous avons démontré qu'un décalage de quelques dizaines de m V/ électron était possible dans notre architecture. Dans le quatrième chapitre, nous présentons une étude détaillée des mécanismes de transport dans le bloc de mémorisation. Un modèle électrique de la cinétique de charge et décharge a été utilisé en prenant en compte l'effet du champ électrique. Finalement, nous avons étudié l' influence des paramètres technologiques comme les épaisseurs d'oxyde et la surface de l' îlot de mémorisation afin de proposer un dimensionnement de l'architecture SET/SEM. Ces simulations faites dans un premier temps à partir du système Ti / Tiüx utilisé dans la technologie nanodamascène développée à l'Université de Sherbrooke, ont pu dans un second temps être étendues à d'autres systèmes de matériaux afin de pro poser les matériaux présentant les meilleurs temps de rétention théoriques. Après avoir comparé les simulations d'îlots métalliques en Pt, Au, TiSi2, NiSi et Ti, nos travaux montrent que titane associé au Ti02 présente les meilleurs temps de rétention à 85% y compris à des températures aussi élevées que 430K qui représente actuellement la température maximale de fonctionnement des SETs réalisés à l'uni versité de Sherbrooke. ]
[This work concerns the study of SET/SEM single electron memories for CMOS technologies. The first part presents a review of quantum and Coulomb blockade effects in electronic nanodevices. In a second part, we present the main electrical models proposed for single electron devices. A comparison between semiconductor-based and metall ic-based single electron transistors. The third part of the thesis presents the SET/SEM memory structure on the basis of SIMON simulations. The device consists on the coupling of a metallic SET operating at high temperature with a metalli c memory node. Finnaly, an optimized memory device has been proposed in the Ti/Tiüx system. The proposed memory is able to write and erase a discrete number of electrons varying from 0 to 7 at room temperature. This opens the possibility of multilevel memory circuits. Finally, we have studied the data retenti on performances of the memory in the last part of this thesis. After the first simulations with the Ti/Tiüx materials system, we have simulated various metallic systems such as Pt, Au, TiSi2, and NiSi. We have shown that finally, the Ti/Ti02 systems gives the best data retention performances even at high temperatures, up to 430K. . ]

Thesis (M. Arch.)--University of Hong Kong, 1996.
Includes special report study entitled: Precast concrete system : its application in Buildingrenovation and addition. Includes bibliographical references.

En términos generales, la flexoelectricidad es la respuesta de la polarización a un gradiente de deformación. A diferencia del efecto piezoeléctrico, este efecto está presente en todos los materiales independientemente de su estructura cristalina. En esta tesis doctoral, hemos estudiado la polarización inducida por deformación en cristales dieléctricos y semiconductores, la cual surge desde dos mecanismos: flexoelectricidad macroscópica y flexoelectricidad superficial. Los dos mecanismos son del mismo orden en dieléctricos normales y hasta ahora sus respectivas contribuciones han sido indistinguibles entre ellas. La investigación desarrollada en esta tesis muestra que es posible separar las dos contribuciones, además de mostrar que la deformación induce reorientación de las nanoregiones polares las cuales también pueden incrementar el coeficiente flexoelectrico efectivo sobre el valor intrínseco. La polarización puede ser generada por la separación de las cargas enlazadas entre los átomos o la celda unidad, pero también por la separación de cargas superficiales debido a las cargas libres. Hasta ahora cuando se refiere a flexoelectricidad, únicamente es tomada en cuenta la respuesta de las cargas enlazadas; sin embargo, en esta tesis doctoral se ha reportado que la polarización debida a las cargas libres también pueden contribuir, generando una gran respuesta flexoeléctrica efectiva en materiales semiconductores. Antes de esta investigación, habían numerosas controversias respecto a la verdadera magnitud del coeficiente flexoelectrico y el origen de la discrepancia entre los valores predichos teóricamente y experimentalmente. En el presente trabajo hemos buscado dilucidar esta situación y cuantificar el valor intrínseco del coeficiente flexoelectrico e identificar el origen de contribuciones adicionales a este. El mensaje principal de esta tesis es que el coeficiente macroscópico flexoeléctrico efectivo permanece en valores relativamente pequeño con un riguroso límite superior de f ≈ 10V para el coeficiente de flexoacoplo de incluso los mejores materiales, pero hay otra gran cantidad de fenómenos de polarización inducida debida a gradientes de deformación que pueden incrementar la respuesta total de este: nanoregiones polares, piezoelectricidad superficial y movimiento de cargas libres son las tres que hemos identificado, pero no descartamos la existencia de otras. Entre estos, la incorporación de cargas libres a la respuesta flexoeléctrica total en semiconductores es cuantitativamente la más grande y la más prometedora dando lugar a aplicaciones macroscópicas debida a su elevada magnitud del coeficiente flexoeléctrico y permitiendo a su vez que compita con la piezoelectricidad.
In general terms, flexoelectricity is the response of polarization to a strain gradient. In contrast to the piezoelectric effect, this effect is present in all materials regardless of their crystal structure. In this doctoral dissertation, we studied the bending-induced polarization in dielectric and semiconductor single crystals that arises from two mechanisms: bulk flexoelectricity and surface flexoelectricity. Both mechanisms are of the same order in ordinary dielectrics and, before this work, their respective contributions were considered indistinguishable one from another. The research in this thesis shows that it is possible to separate the two contributions. Additionally, we show that bending-induced reorientation of polar nanoregions can also enhance the effective flexoelectric coefficients well above the intrinsic value. Polarization can be generated by dielectric separation of bound charge within atoms or unit cells, but also by a space charge separation of free carriers. Until now, when referring to flexoelectricity, only the response from bound charge was taken into account; however, in this thesis dissertation we report that free charge also can also contribute, generating very big effective flexoelectric responses in semiconductor materials. Before this research, there were numerous controversies regarding the true magnitude of flexoelectricity and the origin of discrepancies between theoretically predicted values and actual experimentally measured ones. The present work has seeked to address this situation by quantifying the true value of the intrinsic flexoelectiricy and identifying the origin of additional contributions. The take-home message from this thesis is that true bulk flexoelectricity remains a relatively small effect with a stringent upper bound of f ≈10V for the flexocoupling coefficient of even the best materials, but that there are a number of other gradient-induced polarization phenomena that can greatly enhance the total response: polar nanoregions, surface piezoelectricity and movement of free charges are the three we have identified, but we do not discard the existence of others. Among these, the incorporation of free carriers to the total flexoelectric response in semiconductors is quantitatively the largest, and it also offers most promising route to elevating flexoelectricity to a level where it can compete with piezoelectricity even in bulk applications.

Electron Transfer (ET) is undoubtedly one of the most important processes in life. Molecularly well-defined ET pathways in complex protein ensembles play a vital role in biological processes such as cell respiration or photosynthesis. The fundamental understanding of ET processes in biology is important not only to understand such key natural processes but also to advance in the design of biomolecule/electrode interfaces for Bioelectronic applications. The development of new techniques such as scanning probe microscopies (SPM) played a key role. In particular, the electrochemical scanning tunnelling microscopy (EC-STM) has been exploited to in situ monitor the ET rate as a function of the applied potential of individual metalloproteins immobilized on an Au electrode thanks to the single-molecule spatial resolution and the electrochemical gate capabilities. Azurin from Pseudomonas aeruginosa is a widely studied redox protein model both in bulk and at the single molecule level. Its globular structure contains a coordinated copper ion, which makes the protein capable of exchanging electrons by switching its redox state (Cu I/II) and supports its role as a soluble electron carrier in the respiratory chain of bacteria. In this thesis, we will show our advances on the design and characterization of single-protein devices using a Cu-Azurin metalloprotein model. We have demonstrated transistor like-behaviour in an electrochemically-gated single-protein wire that operates at very low voltages thanks to the Cu-Azurin redox properties. It was demonstrated that the conductance varies depending on the redox state of the Cu centre, having its maximum value at the redox-midpoint. We have also analysed the spontaneous formation of single-Azurin electrical contacts through the monitored current when the two ECSTM electrodes were placed at a fixed distance. Discrete switching events for the conductance were observed, whose frequency depends on the applied electrochemical conditions and, therefore, they were univocally ascribed to discrete changes in the redox state of the trapped protein. In order to tailor the charge transport behaviour of the single-protein wire, we have synthesized several mutants of the protein by exploiting point-site bioengineering schemes at different positions of the protein second coordination sphere. Our results show that we can rationally change the transport mechanism of the single-protein device by studying the effect of the specific residue modification on the particular ET pathways in the protein backbone.
La transferencia de electrones (ET) es uno de los procesos más importantes de la vida. La comprensión fundamental de los procesos de ET en biología es importante no sólo para comprender tales procesos naturales claves, sino también para avanzar en el diseño de interfaces biomolécula / electrodo para aplicaciones bioelectrónicas. En particular, se ha explotado la microscopía de efecto túnel con control electroquímico (EC-STM) para monitorizar in situ la constante de ET en función del potencial aplicado de las metaloproteínas. La Azurina de Pseudomonas aeruginosa es un modelo de proteína redox ampliamente estudiado, tanto en ‘bulk’ como a nivel de una sola proteina. Su estructura globular contiene un ion de cobre coordinado, que hace que la proteína sea capaz de intercambiar electrones cambiando su estado redox (Cu I/II). Este ion es el responsable de su rol como portador de electrones en la cadena respiratoria de las bacterias. En esta tesis, mostraremos nuestros avances en el diseño y caracterización de dispositivos de una sola proteína utilizando un modelo de metaloproteína Cu-Azurin. Hemos demostrado un comportamiento similar a un transistor en un hilo electroquímico de una sola proteína que funciona a muy bajos voltajes gracias a las propiedades redox de Cu-Azurin. Se demostró que la conductancia varía dependiendo del estado redox del centro de Cu, teniendo su valor máximo en el punto medio redox. También hemos analizado la formación espontánea de los contactos eléctricos de Azurin única a través de la corriente monitorizada cuando los dos electrodos ECSTM se colocaron a una distancia fija. Se observaron eventos discretos de conmutación para la conductancia, cuya frecuencia depende de las condiciones electroquímicas aplicadas y, por lo tanto, se atribuyeron unívocamente cambios discretos en el estado redox de la proteína atrapada. Con el fin de adaptar el comportamiento de transporte de carga de la unión uniproteica, hemos sintetizado varios mutantes de la misma proteína mediante bioingeniería en diferentes posiciones de la proteína. Nuestros resultados muestran que podemos cambiar racionalmente el mecanismo de transporte del dispositivo de una sola proteína mediante el estudio del efecto de la modificación de residuos específicos en las vías ET particular en el esqueleto de la proteína.

A series of production and perception experiments investigating the prosody and well-formedness of special sentences, called Wide Focus Partial Fronting (WFPF), which consist of only one prosodic phrase and a unique initial accented argument, are reported on here. The results help us to decide between different models of German prosody. The absence of pitch height difference on the accent of the sentence speaks in favor of a relative model of prosody, in which accents are scaled relative to each other, and against models in which pitch accents are scaled in an absolute way. The results also speak for a model in which syntax, but not information structure, influences the prosodic phrasing. Finally, perception experiments show that the prosodic structure of sentences with a marked word order needs to be presented for grammaticality judgments. Presentation of written material only is not enough, and falsifies the results.

The goal of the project was to create an extension to Internet Explorer forStatens Tjänstepensionsverk (SPV) which would give the staff the experience ofSingle sign-on (SSO) to external web service providers as well as manage andupdate their passwords in a secure manner. The survey focused on the providersPalasso, ProCompetence and Wera. The extension was created as a BrowserHelper Object (BHO) with C# in .NET. The solution was implemented as aCOM object in a DLL-file that was running in-process with the browser. Theprogram used a locally stored XML file containing URLs, usernames andencrypted passwords to the providers. When a user came to a login page theprogram collected the HTML elements on the page and populated them withdata from the file and logged in the user. Encryption and decryption was solvedwith a symmetric key that was stored in the program. In the XML file was alsothe date for the latest update of the password. If one month had passed, theprogram either gave the user an indication that the password needed to beupdated, or updated it automatically with a new generated password, dependingon the provider. The conclusion was that the extension worked as planned butthat there were improvements to be made regarding the possibility to add newsites to the system. The project also included an analysis of alternative optionsto solve the problem using JavaScript, Add-in Express, or via a portal page. Theconclusion was that none of these were an equally powerful tool as a BHO.

The world of the 20-21st century is one of rapid change - for family life, for our work environments, in friendship structures and general attitudes about ourselves. We question who we are and our values. We seek to understand ourselves more fully as individuals and as groups within a world of flux. Within this context a significant change that has taken place in the church is the growing emergence of people remaining single for a variety of reasons. I understand that the term 'single' denotes that group of baptised Christians who have never married and who have chosen to remain single or who continue to affirm their singleness but not foreclosing on the possibility of marriage. As with any change, the transition that is required is never easy. Raymond Brown (1979) touched upon this type of transition and movement for change in society when he said that more and more are finding the single life-style suitable as new territory in which to dwell. They see the structures of society beginning to shift. They see a growing awareness on the part of many people toward an acceptance of single adulthood. This growing awareness has also been paralleled within the thinking of the church. However, many single men and women 'generally feel that the church has geared its ministry toward those who are married and towards nuclear family units'. The reflection by Brown reflects my own thought about being single, particularly with regard to single people and their being church. I will argue in this thesis that being single has theological value as a way of living out one's baptismal call to follow Christ in work, relationships, in attitudes and values. This thesis represents a critical search in, my own need for self-understanding as a single person together with other single people as I believe we contribute to our society and to our Christian calling. At the beginning of Mark's gospel Jesus' baptism is recorded as a prelude to his ministry: It was at this time that Jesus came from Nazareth in Galilee and was baptised in the Jordan by John. No sooner had he come up out of the water than he saw the heavens torn apart and the Spirit, like a dove, descending on him. And a voice came from heaven, 'You are my Son, the Beloved; my favour rests on you' (Mark 1:9-11). Jesus' baptism is the impetus and is at the heart of his ministry for a mission that is favoured by God. Likewise, baptism is at the heart of the single person's way of living for Christ. Further, the sentiments of Paul in Ephesians 3: 14-21 serve as a goal for all Christians which includes single men and women. Paul speaks about a unique relationship with Christ, one based on love and openness to Christ. This, then, is what I pray, kneeling before the Father, from whom every family, whether spiritual or natural, takes its name: Out of his infinite glory, may he give you the power through his Spirit for your hidden self to grow strong, so that Christ may live in your hearts through faith, and then, planted in love and built on love, you will with all the saints have strength to grasp the breadth and the length, the height and the depth; until, knowing the love of Christ, which is beyond all knowledge, you are filled with the utter fullness of God. Glory be to him whose power, working in us, can do infinitely more than we can ask or imagine; glory be to him from generation to generation in the Church and in Christ Jesus for ever and ever. Amen. Jesus' baptism as depicted in Mark together with Paul's thoughts concerning the reception of the power of the Spirit for our hidden selves to grow in love and faith and journeying with others in the Christian tradition, represent the underlying theological attitude of this thesis about the single person. The single person by the nature of his or her baptism, is called to follow Christ - to grow in personal stature as one who is open to the presence of Christ in and through the events of daily life. Integral to this baptismal call is the need to challenge those constructs which don't enhance and give voice to the single person within the church. I consider that one such construct is the notion of 'vocation' as it has been used traditionally in the church's thinking for its self-understanding. In this regard, it is my contention that 'vocation' is about following Christ in and through baptism. How one lives one's life is his or her career choice; how one lives in response to Christ - whether as married or single, priest or religious. It is our primary vocation to follow Christ as promised at baptism. The chosen definition, however, ought not to exclude those Christians who, for reasons beyond their control, for example find themselves living the single life because of their separation from their partner or are widowed, although the primary thrust of the definition will focus on those Christians who continue to affirm their choice for the single way of life. The term Church here is explained by Lumen Gentium 9: 'This was to be the new People of God. For, those who believe in Christ, who are reborn not from a perishable but from an imperishable seed through the Word of the living God (cf. 1 Pet. 1:23), not from the flesh but from water and the Holy Spirit (cf. Jn. 3:5-6), are finally established as 'a chosen race, a royal priesthood, a holy nation, a purchased people.' This definition has been chosen as it articulates a point of view about the people who comprise the church. In particular the definition speaks of the 'signs' of baptism - water and the Holy Spirit. It is these signs that characterise those called by God through baptism to be the people of God, the purchased people. I argue that the sacrament of baptism is what characterises all in the church irrespective of their state. The primary methodology for our critical examination of the meaning of the single state is by case study. The Case Study method will allow me to elaborate upon a developmental theological perspective from within the Vatican Council documents. By this method I examine the single state from within the ecclesial as well as a sociological understanding. Secondly a dialectical approach will enable me to argue the case for the single state as a valid way of life. From this I aim to highlight the single state and its key attributes as well as to provide a personal perspective about single living. Further, this secondary method allows me to highlight the way in which single people contribute to, and are a part of the life of the church. This twofold methodology enables me to look at the particular issue of the single state within the wider context of the church, and to argue for the significance of the part to the whole.