Academic literature on the topic 'Trace Reconstruction'

Thesis: M. Eng., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2014.<br>Cataloged from PDF version of thesis.<br>Includes bibliographical references (page 95).<br>In the setting of the trace reconstruction problem, a uniform random binary sequence w [epsilon] {0, 1}n yields a collection of traces, such that each subsequence is obtained by independently deleting each bit with a public probability parameter p. In this thesis we explore a restricted version of this problem, in which each trace is a random subsequence of one of two original known sequences. Given a series of traces, we would like to device a method that allows to us to decide from which sequence, from the pair of known public sequences w, w', do all the traces come from. The question we will try to solve in this thesis is to know if such a method, operating with high probability and polynomially many samples, is possible in practice. Among other things, we show that if the two strings are drawn uniformly at random there is an algorithm that allows to efficiently distinguish with high probability the traces they produce, failing only on an exponentially small proportion of the random pairs. Additionally we explore variants of this problem and their connections with a number theoretic known as the Prouhet-Tarry-Escott problem.<br>by Aldo Pacchiano.<br>M. Eng.

This study investigated potential palaeoclimate proxies provided by rare earth element (REE) geochemistry in speleothems and in clay mineralogy of cave sediments. Speleothem and sediment samples were collected from a series of cave fill deposits that occurred with rich vertebrate fossil assemblages in and around Mount Etna National Park, Rockhampton (central coastal Queensland). The fossil deposits range from Plio- Pleistocene to Holocene in age (based on uranium/thorium dating) and appear to represent depositional environments ranging from enclosed rainforest to semi-arid grasslands. Therefore, the Mount Etna cave deposits offer the perfect opportunity to test new palaeoclimate tools as they include deposits that span a known significant climate shift on the basis of independent faunal data. The first section of this study investigates the REE distribution of the host limestone to provide baseline geochemistry for subsequent speleothem investigations. The Devonian Mount Etna Beds were found to be more complex than previous literature had documented. The studied limestone massif is overturned, highly recrystallised in parts and consists of numerous allochthonous blocks with different spatial orientations. Despite the complex geologic history of the Mount Etna Beds, Devonian seawater-like REE patterns were recovered in some parts of the limestone and baseline geochemistry was determined for the bulk limestone for comparison with speleothem REE patterns. The second part of the study focused on REE distribution in the karst system and the palaeoclimatic implications of such records. It was found that REEs have a high affinity for calcite surfaces and that REE distributions in speleothems vary between growth bands much more than along growth bands, thus providing a temporal record that may relate to environmental changes. The morphology of different speleothems (i.e., stalactites, stalagmites, and flowstones) has little bearing on REE distributions provided they are not contaminated with particulate fines. Thus, baseline knowledge developed in the study suggested that speleothems were basically comparable for assessing palaeoclimatically controlled variations in REE distributions. Speleothems from rainforest and semi-arid phases were compared and it was found that there are definable differences in REE distribution that can be attributed to climate. In particular during semiarid phases, total REE concentration decreased, LREE became more depleted, Y/Ho increased, La anomalies were more positive and Ce anomalies were more negative. This may reflect more soil development during rainforest phases and more organic particles and colloids, which are known to transport REEs, in karst waters. However, on a finer temporal scale (i.e. growth bands) within speleothems from the same climate regime, no difference was seen. It is suggested that this may be due to inadequate time for soil development changes on the time frames represented by differences in growth band density. The third part of the study was a reconnaissance investigation focused on mineralogy of clay cave sediments, illite/kaolinite ratios in particular, and the potential palaeoclimatic implications of such records. Although the sample distribution was not optimal, the preliminary results suggest that the illite/kaolinite ratio increased during cold and dry intervals, consistent with decreased chemical weathering during those times. The study provides a basic framework for future studies at differing latitudes to further constrain the parameters of the proxy. The identification of such a proxy recorded in cave sediment has broad implications as clay ratios could potentially provide a basic local climate proxy in the absence of fossil faunas and speleothem material. This study suggests that REEs distributed in speleothems may provide information about water throughput and soil formation, thus providing a potential palaeoclimate proxy. It highlights the importance of understanding the host limestone geochemistry and broadens the distribution and potential number of cave field sites as palaeoclimate information no longer relies solely on the presence of fossil faunas and or speleothems. However, additional research is required to better understand the temporal scales required for the proxies to be recognised.

A reconstruction of regional climate variability in southern West Virginia that spans the last glacial/interglacial transition is presented. Paleoclimate interpretations obtained from the 50-cm long stalagmite provide key insights regarding the timing, magnitude, and forcing mechanisms responsible for past climate variability. Stable isotopic (δ18O and δ13C) and trace element (Ba, Sr, Mg) signatures from samples contiguously milled along the growth-axis of a 230Th-dated stalagmite which grew between approximately 20 and 5 thousand years before present (kyr BP) provide critical constraints for above-cave mean annual temperature, seasonality of moisture mean annual precipitation, and potential vegetation shifts. Specifically, the stalagmite record reveals subcentennial-scale variations in the proxy records, and strong multimillennial-scale features that correlate to well-known patterns of sea-surface variability in the North Atlantic Ocean (i.e., Bond cycles). The large-scale glacial/interglacial transition is sufficiently resolved to show that regional climate changes largely paralleled climatic transitions preserved in low-latitude (Chinese monsoon records; Cariaco Basin) and high-latitude (Greenland Ice Sheet) paleo-archives. However, the Younger Dryas interval in the south-central Appalachian Mountains is not as prominent a feature as in other records.

Ce travail est consacré à l'étude de faisabilité d'une imagerie par reconstruction de vertex (IRV) pour le contrôle qualité en temps réel de la thérapie par faisceau d'ions carbone. La détection de vertex d'interactions nucléaires repose sur la détection de particules secondaires : grâce à un dispositif de détection spatiale des fragments chargés (tracker), on peut reconstruire les trajectoires des particules émergeant du patient et les extrapoler jusqu'à leur point d'origine (le vertex)... Dans le cadre de notre étude, la position du vertex est déterminée de deux manières différentes : soit en calculant l'intersection de la trajectoire d'un fragment émergent avec celle de l'ion incident (connue grâce à l'utilisation d'un hodoscope de faisceau placé en amont du patient), soit grâce à l'intersection de la trajectoire de deux fragments émergents détectés en coïncidence. Notre étude de faisabilité de la technique repose sur l'outil de simulation GEANT4. La première partie de l'étude a consisté à valider cet outil grâce à plusieurs expériences réalisées au GANIL (Caen) et au GSI (Darmstadt) avec des ions carbone de différentes énergies dans des cibles d'eau ou de PMMA Par la suite, la comparaison des deux modes de détection des particules secondaires a montré que la technique utilisant l'hodoscope est la plus performante. Enfin, après l'optimisation des principaux paramètres de cette technique, une simulation réaliste montre qu'il est possible de mesurer le parcours des ions avec une précision millimétrique à l'échelle d'une tranche en énergie voire à l'échelle d'un voxel unique.

Ce travail est consacré à l'étude de faisabilité d'une imagerie par reconstruction de vertex (IRV) pour le contrôle qualité en temps réel de la thérapie par faisceau d'ions carbone. La détection de vertex d'interactions nucléaires repose sur la détection de particules secondaires : grâce à un dispositif de détection spatiale des fragments chargés (tracker), on peut reconstruire les trajectoires des particules émergeant du patient et les extrapoler jusqu'à leur point d'origine (le vertex)... Dans le cadre de notre étude, la position du vertex est déterminée de deux manières différentes : soit en calculant l'intersection de la trajectoire d'un fragment émergent avec celle de l'ion incident (connue grâce à l'utilisation d'un hodoscope de faisceau placé en amont du patient), soit grâce à l'intersection de la trajectoire de deux fragments émergents détectés en coïncidence. Notre étude de faisabilité de la technique repose sur l'outil de simulation GEANT4. La première partie de l'étude a consisté à valider cet outil grâce à plusieurs expériences réalisées au GANIL (Caen) et au GSI (Darmstadt) avec des ions carbone de différentes énergies dans des cibles d'eau ou de PMMA Par la suite, la comparaison des deux modes de détection des particules secondaires a montré que la technique utilisant l'hodoscope est la plus performante. Enfin, après l'optimisation des principaux paramètres de cette technique, une simulation réaliste montre qu'il est possible de mesurer le parcours des ions avec une précision millimétrique à l'échelle d'une tranche en énergie voire à l'échelle d'un voxel unique<br>This work is devoted to the feasibility study of interaction vertex imaging (IVI) for real-time quality assurance in hadrontherapy treatments with carbon ion beams. Nuclear interaction vertex detection is based on secondary particle detection: a device allows us to spatially detect charged particles (tracker), thus we can reconstruct the trajectories of particles emerging from the patient and then extrapolate their emission point (vertex). In our study, the vertex position is determined by two ways: either by calculating the intersection of the trajectory of an emerging fragment with the trajectory of the incident ion (measured by means of a beam hodoscope upstream of the patient), or with the intersection of two emerging particles trajectories detected in coincidence. Our feasibility study of this technique relies on the GEANT4 simulation tool. The first part of the study aimed to validate this tool with experiments performed at GANIL (Caen) and GSI (Darmstadt) using carbon ion beams at various energies and in various targets (water or PMMA). Secondly, the comparison of two different technics for secondary particles detection showed that the technique using the hodoscope is the most efficient. Finally, after the parameters optimization of this technique, a realistic simulation shows that it is possible to measure ion paths within millimeter precision during each energy slices. A control of each beam spot may also be possible

This thesis is an overview of the processes and procedures used in the production of my artistic practice. In my work, I explore notions such as the ambiguity of the photographic image, what constitutes an image or object as photographic, and the unexplored possibilities of the medium through surface and mark making. In addition, I draw inspiration from artists Wolfgang Tillmans, William Henry Fox Talbot, and Marco Breuer as entrance points to my conceptual interests. For viewers, my work generates an internal dialogue about the limits of the photographic medium.