A study of the student training program of the Veterans Administration Hospital, Bedford, Massachusetts

Thesis (M.S.)--Boston University, 1947. This item was digitized by the Internet Archive

Numerical simulation and data-driven analysis of infrared detector performance

Infrared detectors are a critical technology frequently used in commercial, military, and scientific settings. Research and development of modern infrared detectors is driven by finding new ways to reduce the system's size, weight, power, and cost while adding new functionalities without lowering performance. Physics-based numerical models can be instrumental in lowering the cost of developing such advances. This dissertation presents three main contributions to further the predictive modeling of infrared photodetectors. First, motivated by recent demonstrations of small-pitch focal plane arrays for infrared imaging---5 μm for SWIR and 10 to 15 μm for MWIR/LWIR---we use physics-based numerical simulations to assess the implications on dark current, quantum efficiency, specific detectivity, and modulation transfer function in SWIR InGaAs FPAs. From the results, we propose a new pixel sub-architecture aimed toward lowering dark current and improving MTF. Second, we present a methodology for simulating the capacitance-voltage (C-V) characteristics of nBn photodetectors. For junction-based semiconductor devices, C-V profiling is a common technique for non-destructively characterizing semiconductor layers in metal-insulator-semiconductor devices by using well-established analytical relations. However, this type of analysis cannot be directly applied to the barrier detector’s unique architecture and the formalism must be modified. To this end, we present a modified analytical formalism based on metal-oxide-semiconductor theory, and a methodology using the drift-diffusion method; both are used to explore the role of the device architectural properties on determining the C-V characteristics. Last, we present several cases of applying neural networks to nBn photodetector figures of merit. We use artificial neural networks as surrogate model for the capacitance-voltage, current-voltage, and quantum efficiency to explore the multi-dimensional parameter space to assess parameter-performance correlations and determine the global role of each feature in shaping each characteristic without the need for additional simulations. Moreover, using inspiration from image recognition, we demonstrate that a convolutional neural network can be trained to analyze a C-V characteristic to yield more information about a device than what would be possible from a conventional analysis

Resource Management for Realtime Traffic in Intranets

Um in IP-basierten Intranets die Integration von Daten- und Kommunikationsdiensten voranzutreiben, wurde eine skalierbare Ressourcenmanagement-Architektur entwickelt. Sie basiert auf der funktionalen Trennung von Paketverarbeitung und Ressourcenreservierung und kann flexibel an eine Dienststeuerung und das darunter liegende Netz angebunden werden. Dadurch ist sie leicht in eine bestehende Systemumgebung einzuführen. Aufbauend auf der Messung und Charakterisierung von echtzeitkritischen IP-Verkehren und Zugangskontrollverfahren wurden eine zentralisierte Systemarchitektur und ein Reservierungsprotokoll entworfen, prototypisch realisiert und getestet.This thesis describes a novel resource management architecture for IP-based intranets. The architecture is designed to facilitate the integration of realtime services in data networks. The technical concept is based on the functional separation of packet processing and resource reservation. It enables flexible interworkingwith various service control entities and underlying network technologies. The components of the architecture can easily be introduced in an existing intranet environment. On the basis of measurements and chracterization of realtime critical IP-traffic appropriate call admission control algorithms are selected. In a second step, the system architecture and a reservation protocol was developed, prototypical impelemented and evaluated in several testbeds

Low temperature, authigenic illite and carbonates in a mixed dolomite-clastic lagoonal and pedogenic setting, Spanish Central System, Spain

The aim of this study was to further our understanding of the pedogenic and lacustrine modification of clay minerals. Some of these modifications are of special interest because they constitute reverse weathering reactions, rare in surface environments, and because there is not yet an accurate assessment of their global relevance in mineralogical and geochemical cycles. For this study, two sections from the Central System in Spain were selected. Both are sections through the Uppper Cenomanian-Turonian mixed clastic and carbonate succession, containing both calcite and dolomite, in the Sierra de Guadarrama. Mid-Turonian sea level fall resulted in the formation of a coastal plain environment in which extensive pedogenesis occurred around saline lagoons. The mineralogical changes that have occurred as a result of sedimentation in saline lagoons and as a consequence of pedogenesis are described. Textural relationships indicate that the dolomite cement pre-dates the calcite. Silicate minerals are represented by quartz, kaolinite, illite-smectite, illite, minor plagioclase and alkali feldspar, and trace chlorite and palygorskite. There is a positive correlation between the intensity of pedogenesis and the proportion of illite in the clay assemblage in one of the sections, indicating pedogenic illitisation. In this section, the intensity of the illitisation process increases up, reaching a maximum where pedogenesis is most intense in the middle part, and then decreases as marine influence increases towards the top of the Alcorlo Formation and the overlying marine Tranquera Formation. The clay assemblages are consistent with a slow transformation process from 42 kaolinite to illite by way of illite-smectite, taking place under surface conditions. The illitisation process has resulted in a less Fe-rich, more Mg-, and Al-rich illite than the majority of previously documented cases in the near surface. Formation of Al-rich illite is not therefore restricted to the deep subsurface. The mechanism for low temperature illitisation involves enhanced layer charge resulting from Mg2+ substitution for Al3+ (or Fe3+) and Fe3+ to Fe2+ reduction. Mg2+ enrichment may have occurred principally in saline lagoons or lakes, while Fe3+ to Fe2+ reduction occurred as a result of wetting and drying in a pedogenic environment. So far as it has been possible to establish, this dual mechanism has not previously been documented. This study indicates clearly that the dolomite and calcite are authigenic cements that precipitated in a clastic sediment, probably soon after deposition. Dolomitisation and Mg enrichment of the clay may have occurred at the same time. Seawater is the most probable source of Mg

Measurements of differential cross-sections in four-lepton events in 13 TeV proton-proton collisions with the ATLAS detector

Artículo escrito por un elevado número de autores, solo se referencian el que aparece en primer lugar, el nombre del grupo de colaboración, si le hubiere, y los autores pertenecientes a la UA

Search for pair production of third-generation scalar leptoquarks decaying into a top quark and a tau-lepton in pp collisions at √s=13 TeV with the ATLAS detector

Artículo escrito por un elevado número de autores, solo se referencian el que aparece en primer lugar, el nombre del grupo de colaboración, si le hubiere, y los autores pertenecientes a la UA

Does the nucleation of clay minerals control the rate of diagenesis in sandstones?

Nucleation is much more important for clay minerals than for other authigenic cements as clay crystals are very small, so that a very large number of clay crystals must be nucleated. The role of this difficult kinetic step in the diagenesis of sandstones has not been considered adequately as a rate-determining process. The relationship between pore-fluid supersaturation and the rate of nucleation of a mineral is very different from the relationship between supersaturation and the rate of crystal enlargement; thus the two processes will act at very different rates. A diagenetic model that predicts clay-mineral formation but omits the nucleation stage may make unreliable predictions. This may account partially for the discrepancy between numerical simulations of CO2 injection that predict high degrees of reaction between the CO2 and the host rock, and the results of studies of natural analogues that have much lower degrees of reaction

Measurements of top-quark pair single- and double-differential cross-sections in the all-hadronic channel in pp collisions at √s = 13 TeV using the ATLAS detector

Artículo escrito por un elevado número de autores, solo se referencian el que aparece en primer lugar, el nombre del grupo de colaboración, si le hubiere, y los autores pertenecientes a la UA

Measurement of hadronic event shapes in high-pT multijet final states at √s = 13 TeV with the ATLAS detecto

Artículo escrito por un elevado número de autores, solo se referencian el que aparece en primer lugar, el nombre del grupo de colaboración, si le hubiere, y los autores pertenecientes a la UA

Authigenic illite within northern and central North Sea oilfield sandstones: evidence for post-growth alteration

It has been previously reported that late diagenetic fibrous illite, separated out from oilfield sandstones for dating by the K-Ar method, has systematically shown an increasing K-content with burial depth in the UK northern and central North Sea. This is surprising as fibrous illite is believed to form rapidly, in response to a geological event such as oil charging, and to retain its composition during subsequent burial. If the composition of the illite is related to present-day conditions, rather than the conditions of initial formation, then argon loss may have occurred, making K-Ar ages of questionable validity. Variations in crystal chemistry of the illite and their fundamental particle size and shape (length/width) distribution suggest alteration of the illite from the time of formation. The extent to which K-Ar ages of illite might need to be re-interpreted as a result of this post-formation alteration is not quantifiable at present; however there is evidence to suggest that the ages may be interpreted in terms of burial models involving both crystal nucleation and growth, and that a high proportion of Ar within the crystals may be retained during post-growth recrystallization