With a view to reduce the number of components in a Static Random Access Memory (SRAM) cell, the feasibility of use of Lambda Bipolar Transistor (LBT)in the bistable element of the cell has been explored under the present study. The LBT under consideration here comprises of an enhancement mode MOSFET integrated with a parasitic bipolar transistor so as to perform as a negative resistance device. LBTs for the study have been fabricated and analysed. The devices have been shown to function at much lower voltage and current levels than those reported earlier/ and thus have been shown to be suitable for lower power applications. The issues of agreements and discrepancies of the experimental results with the original DC model of the device have been highlighted and discussed. The factors contributing to the drain current of the MOSFET in the LBT have been identified. It has also been shown that in the real case of an LBT in operation, the MOSFET in it does not function as a discrete device for the same conditions of voltages and current levels as in an LBT. As per the present study, it is assessed to be influenced by the presence of the BJT in operation and this effect is felt more at the lower current levels of operation. With a separate and tailored p-well implantation the possibility of fabrication of LBTs with a CMOS technology is established. Along with a couple of polysilicon resistors, the LBTs have been successfully made to perform in the common-collector configuration as the bistable storage element of SRAM cell (as proposed in the literature). The bistable element with the LBT in common-emitter mode also has been visualised and practically achieved with the fabricated devices. The WRITE transients for either case have been simulated for various levels of WRITE voltages and their time of hold.The speed of Writing achieved are found comparable with that of the standard SRAMs. The advantages and disadvantages of using the LBT in either mode have been highlighted and discussed. The power consumption of the bistable element with the LBT in either mode is however shown to be the same. A different approach of READING has been proposed to overcome the factors known to increase the cycle time. On the whole, under the present study, the proposal of using LBTs in the bistable storage element of the SRAM cell has been shown to be feasible. Such SRAM circuits can find possible applications in the fields where smaller circuit area is the major concern.

<p>Recrystallization kinetics, during and after hot deformation, has been investigated for decades. From these investigations several equations have been derived for describing it. The equations are often empirical or semi-empirical, i.e. they are derived for certain steel grades and are consequently only applicable to steel grades similar to these. To be able to describe the recrystallization kinetics for a variety of steel grades, more physically based models are necessary.</p><p>During rolling in hot strip mills, recrystallization enables the material to be deformed more easily and knowledge of the recrystallization kinetics is important in order to predict the required roll forces. SSAB Tunnplåt in Borlänge is a producer of low-carbon steel strips. In SSAB’s hot strip mill, rolling is conducted in a reversing roughing mill followed by a continuous finishing mill. In the reversing roughing mill the temperature is high and the inter-pass times are long. This allows for full recrystallization to occur during the inter-pass times. Due to the high temperature, the rather low strain rates and the large strains there is also a possibility for dynamic recrystallization to occur during deformation, which in turn leads to metadynamic recrystallization after deformation. In the finishing mill the temperature is lower and the inter-pass times are shorter. The lower temperature means slower recrystallization kinetics and the shorter inter-pass times could mean that there is not enough time for full recrystallization to occur. Hence, partial or no recrystallization occurs in the finishing mill, but the accumulated strain from pass to pass could lead to dynamic recrystallization and subsequently to metadynamic recrystallization.</p><p>In this work a newly developed physically based model has been used to describe the microstructural evolution of austenite. The model is based on dislocation theory where the generated dislocations during deformation provide the driving force for recrystallization. The model is built up by several submodels where the recrystallization model is one of them. The recrystallization model is based on the unified theory of continuous and discontinuous recovery, recrystallization and grain growth by Humphreys.</p><p>To verify and validate the model, rolling in the hot strip mill was modeled using process data from SSAB’s hot strip mill. In addition axisymmetric compression tests combined with relaxation was modeled using experimental results from tests conducted on a Gleeble 1500 thermomechanical simulator at Oulu University, Finland. The results show good agreement with measured data.</p>

Hemodynamic monitoring is extremely important in the accurate measurement of vital parameters. Current methods are highly invasive or noncontinuous, and require direct access to the patient’s skin. This study intends to explore the modulated magnetic signature of blood method (MMSB) to attain blood flow information. This method uses an applied magnetic field to magnetize the iron in the red blood cells and measures the disturbance to the field with a magnetic sensor [1]. Exploration will be done by experimentally studying in-vitro, as well as simulating in COMSOL the alteration of magnetic fields induced by the flow of a magnetic solution. It was found that the variation in magnetic field is due to a high magnetization of blood during slow flow and low magnetization during rapid flow. The understanding of this phenomenon can be used in order to create a portable, non-invasive, continuous, and accurate sensor to monitor the cardiovascular system.

Many digital signal processing and real-time streaming systems are modeled using dataflow graphs, such as Synchronous Dataflow (SDF) and Cyclo-static Dataflow (CSDF) graphs that allow static analysis and optimization techniques. However, mapping of such descriptions into tightly constrained real-time implementations requires optimization of resource sharing, buffering and scheduling across a multi-dimensional latency-throughput-area objective space. This requires techniques that can find the Pareto-optimal set of implementations for the designer to choose from. In this work, we address the problem of multi-objective mapping and scheduling of SDF and CSDF graphs onto heterogeneous multi-processor platforms. Building on previous work, this thesis extends existing two-stage hybrid heuristics that combine an evolutionary algorithm with an integer linear programming (ILP) model to jointly optimize throughput, area and latency for SDF graphs. The primary contributions of this work include: (1) extension of the ILP model to support CSDFGs with additional buffer size optimizations; (2) a further optimization in the ILP-based scheduling model to achieve a runtime speedup of almost a factor of 10 compared to the existing SDFG formulation; (3) a list scheduling heuristic that replaces the ILP model in the hybrid heuristic to generate Pareto-optimal solutions at significantly decreased runtime while maintaining near-optimality of the solutions within an acceptable gap of 10% when compared to its ILP counterparts. The list scheduling heuristic presented in this work is based on existing modulo scheduling approaches for software pipelining in the compiler domain, but has been extended by introducing a new concept of mobility-based rescheduling before resorting to backtracking. It has been proved in this work that if mobility-based rescheduling is performed, the number of required backtrackings and hence overall complexity and runtime is less. / text

Software forking---creating a variant product by copying and modifying an existing project---is often considered an ad hoc, low cost alternative to principled product line development. To maintain forked projects, developers need to manually port existing features or bug-fixes from one project to another. Such manual porting is not only tedious but also error-prone. When the contexts of the ported code vary, developers often have to adapt the ported code to fit its surroundings. Faulty adaptations or inconsistent updates of the ported code could potentially introduce subtle inconsistencies in the codebase. To build a deeper understanding to cross-system porting and porting related errors, this dissertation investigates: (1) How can we identify ported code from software version histories? (2) What is the overhead of cross-system porting required to maintain forked projects? (3) What is the extent and characteristics of porting errors that occur in practice? and (4) How can we detect and characterize potential porting errors? As a first step towards assessing the overhead of cross-system porting, we implement REPERTOIRE, a tool to analyze repeated work of cross-system porting across peer projects. REPERTOIRE can detect ported edits between program patches with high accuracy of 94% precision and 84% recall. Using REPERTOIRE, we study the temporal, spatial, and developer dimensions of cross-system porting using 18 years of parallel evolution history of the BSD product family. Our study finds that cross-system porting happens periodically and the porting rate does not necessarily decrease over time. The upkeep work of porting changes from peer projects is significant and currently, porting practice seems to heavily depend on developers doing their porting job on time. Analyzing version histories of Linux and FreeBSD, we derive five categories of porting errors, including incorrect control- and data-flow, code redundancy, and inconsistent identifier and token renamings. Leveraging this categorization, we design a static control- and data-dependence analysis technique, SPA, to detect and characterize porting inconsistencies. SPA detects porting inconsistencies with 65% to 73% precision and 90% recall, and identify inconsistency types with 58% to 63% precision and 92% recall on average. In a comparison with two existing error detection tools, SPA outperforms them with 14% to 17% better precision. / text

Estimation of static and dynamic petrophysical properties of multi-layer hydrocarbon reservoirs is crucial for the assessment of storage and flow capacities, compartmentalization, and for best primary or enhanced recovery practices. Interactive numerical simulation to reproduce field logs and core data is a reliable procedure to estimate static and dynamic petrophysical properties of complex rock formations. Previously, Voss et al. (2009) introduced the concept of Common Stratigraphic Framework (CSF) to construct and cross-validate multi-layer static/dynamic petrophysical models by invoking the interactive, numerical simulation of well logs both before and after invasion. This thesis documents the successful implementation of the CSF concept to examine and quantify the effects of mud-filtrate invasion on apparent resistivity, nuclear, and magnetic resonance logs acquired in San Martin, Cashiriari and Pagoreni gas fields in Camisea, Peru. Conventional petrophysical interpretation methods yield abnormally high estimates of water saturation in some of the reservoir units that produce gas with null water influx. This anomalous behavior is due to relatively low values of deep apparent electrical resistivity, and has otherwise been attributed to the presence of clay-coating grains and/or electrically conductive grain minerals. On the other hand, electrical resistivity logs exhibit substantial invasion effects as evidenced by the separation of apparent resistivity logs (both LWD and wireline) with multiple radial lengths of investigation. In extreme cases, apparent resistivity logs “stack” because of very deep invasion. We diagnose and quantify invasion effects on resistivity and nuclear logs with interactive numerical modeling before and after invasion. The assimilation of such effects in the interpretation consistently decreases previous estimates of water saturation to those of irreducible water saturation inferred from core data. It is shown that capillary pressure effects are responsible for the difference in separation of resistivity curves in some of the reservoir units. The final multi-layer CSF is in agreement with gas production measurements and permits reliable flow predictions to assist in reservoir engineering and production studies. / text

This thesis presents a comprehensive study of the compressive response of hexagonal honeycomb panels from the initial elastic regime to a fully crushed state. Expanded aluminum alloy honeycomb panels with a cell size of 0.375 in (9.53 mm), a relative density of 0.026, and a height of 0.625 in (15.9 mm) are laterally compressed quasi statically between rigid platens under displacement control. The cells buckle elastically and collapse at a higher stress due to inelastic action. Deformation then first localizes at mid-height and the cells crush by progressive formation of folds; associated with each fold family is a stress undulation. The response densifies when the whole panel height is consumed by folds. The buckling, collapse, and crushing events are simulated numerically using finite element models involving periodic domains of a single or several characteristic cells. The models idealize the microstructure as hexagonal, with double walls in one direction. The nonlinear behavior is initiated by elastic buckling while inelastic collapse that leads to the localization observed in the experiments occurs at a significantly higher load. The collapse stress is found to be mildly sensitive to various problem imperfections. For the particular honeycomb studied, the collapse stress is 67% higher than the buckling stress. It was also shown that all aspects of the compressive behavior can be reproduced numerically using periodic domains with a fine mesh capable of capturing the complexity of the folds. The calculated buckling stress is reduced when considering periodic square domains as the compatibility of the buckles between neighboring cells tends to make the structure more compliant. The mode consisting of three half waves is observed in every simulation but its amplitude is seen to be accented at the center of the domains. The calculated crushing response is shown to better resemble measured ones when a 4x4 cell domain is used, which is smoother and reproduces decays in the amplitude of load peaks. However, the average crushing stress can be captured with engineering accuracy even from a single cell domain. / text

The goal of this dissertation is to present new and improved techniques for fully automatic verification of sequential and concurrent software libraries. In most cases, automatic software verification is plagued by undecidability, while in many others it suffers from prohibitively high computational complexity. Model checking -- a highly successful technique used for verifying finite state hardware circuits against logical specifications -- has been less widely adapted for software, as software verification tends to involve reasoning about potentially infinite state-spaces. Two of the biggest culprits responsible for making software model checking hard are heap-allocated data structures and concurrency. In the first part of this dissertation, we study the problem of verifying shape properties of sequential data structure libraries. Such libraries are implemented as collections of methods that manipulate the underlying data structure. Examples of such methods include: methods to insert, delete, and update data values of nodes in linked lists, binary trees, and directed acyclic graphs; methods to reverse linked lists; and methods to rotate balanced trees. Well-written methods are accompanied by documentation that specifies the observational behavior of these methods in terms of pre/post-conditions. A pre-condition [phi] for a method M characterizes the state of a data structure before the method acts on it, and the post-condition [psi] characterizes the state of the data structure after the method has terminated. In a certain sense, we can view the method as a function that operates on an input data structure, producing an output data structure. Examples of such pre/post-conditions include shape properties such as acyclicity, sorted-ness, tree-ness, reachability of particular data values, and reachability of pointer values, and data structure-specific properties such as: "no red node has a red child'', and "there is no node with data value 'a' in the data structure''. Moreover, methods are often expected not to violate certain safety properties such as the absence of dangling pointers, absence of null pointer dereferences, and absence of memory leaks. We often assume such specifications as implicit, and say that a method is incorrect if it violates such specifications. We model data structures as directed graphs, and use the two terms interchangeably. Verifying correctness of methods operating on graphs is an instance of the parameterized verification problem: for every input graph that satisfies [phi], we wish to ensure that the corresponding output graph satisfies [psi]. Control structures such as loops and recursion allow an arbitrary method to simulate a Turing Machine. Hence, the parameterized verification problem for arbitrary methods is undecidable. One of the main contributions of this dissertation is in identifying mathematical conditions on a programming language fragment for which parameterized verification is not only decidable, but also efficient from a complexity perspective. The decidable fragment we consider can be broadly sub-divided into two categories: the class of iterative methods, or methods which use loops as a control flow construct to traverse a data structure, and the class of recursive methods, or methods that use recursion to traverse the data structure. We show that for an iterative method operating on a directed graph, if we are guaranteed that if the number of destructive updates that a method performs is bounded (by a constant, i.e., O(1)), and is guaranteed to terminate, then the correctness of the method can be checked in time polynomial in the size of the method and its specifications. Further, we provide a well-defined syntactic fragment for recursive methods operating on tree-like data structures, which assures that any method in this fragment can be verified in time polynomial in the size of the method and its specifications. Our approach draws on the theory of tree automata, and we show that parameterized correctness can be reduced to emptiness of finite-state, nondeterministic tree automata that operate on infinite trees. We then leverage efficient algorithms for checking the emptiness of such tree automata to obtain a tractable verification framework. Our prototype tool demonstrates the low theoretical complexity of our technique by efficiently verifying common methods that operate on data structures. In the second part of the dissertation, we tackle another obstacle for tractable software verification: concurrency. In particular, we explore application of a static analysis technique based on interprocedural dataflow analysis to predict and document deadlocks in concurrent libraries, and analyze deadlocks in clients that use such libraries. The kind of deadlocks that we focus result from circular dependencies in the acquisition of shared resources (such as locks). Well-written applications that use several locks implicitly assume a certain partial order in which locks are acquired by threads. A cycle in the lock acquisition order is an indicator of a possible deadlock within the application. Methods in object-oriented concurrent libraries often encapsulate internal synchronization details. As a result of information hiding, clients calling the library methods may cause thread safety violations by invoking methods in a manner that violates the partial ordering between lock acquisitions that is implicit within the library. Given a concurrent library, we present a technique for inferring interface contracts that speciy permissible concurrent method calls and patterns of aliasing among method arguments that guarantee deadlock-free execution for the methods in the library. The contracts also help client developers by documenting required assumptions about the library methods. Alternatively, the contracts can be statically enforced in the client code to detect potential deadlocks in the client. Our technique combines static analysis with a symbolic encoding for tracking lock dependencies, allowing us to synthesize contracts using a satisfiability modulo theories (SMT) solver. Additionally, we investigate extensions of our technique to reason about deadlocks in libraries that employ signalling primitives such as wait-notify for cooperative synchronization. We demonstrate its scalability and efficiency with a prototype tool that analyzed over a million lines of code for some widely-used open-source Java libraries in less than 50 minutes. Furthermore, the contracts inferred by our approach have been able to pinpoint real bugs, i.e. deadlocks that have been reported by users of these libraries. / text

Reliable assessment of static and dynamic petrophysical properties of hydrocarbon-bearing reservoirs is critical for estimating hydrocarbon reserves, identifying good production zones, and planning hydro-fracturing jobs. Conventional well-log interpretation methods are adequate to estimate static petrophysical properties (i.e., porosity and water saturation) in formations consisting of thick beds. However, they are not as reliable when estimating dynamic petrophysical properties such as absolute permeability, movable hydrocarbon saturation, and saturation-dependent capillary pressure and relative permeability. Additionally, conventional well-log interpretation methods do not take into account shoulder-bed effects, radial distribution of fluid saturations due to mud-filtrate invasion, and differences in the volume of investigation of the various measurements involved in the calculations. This dissertation introduces new quantitative methods for petrophysical and compositional evaluation of water- and hydrocarbon-bearing formations based on the combined numerical simulation and nonlinear joint inversion of conventional well logs. Specific interpretation problems considered are those associated with (a) complex mineral compositions, (b) mud-filtrate invasion, and (c) shoulder-bed effects. Conventional well logs considered in the study include density, photoelectric factor (PEF), neutron porosity, gamma-ray (GR), and electrical resistivity. Depending on the application, estimations yield static petrophysical properties, dynamic petrophysical properties, and volumetric/weight concentrations of mineral constituents. Assessment of total organic carbon (TOC) is also possible in the case of hydrocarbon-bearing shale. Interpretation methods introduced in this dissertation start with the detection of bed boundaries and population of multi-layer petrophysical properties with conventional petrophysical interpretation results or core/X-Ray Diffraction (XRD) data. Differences between well logs and their numerical simulations are minimized to estimate final layer-by-layer formation properties. In doing so, the interpretation explicitly takes into account (a) differences in the volume of investigation of the various well logs involved, (b) the process of mud-filtrate invasion, and (c) the assumed rock-physics model. Synthetic examples verify the accuracy and reliability of the introduced interpretation methods and quantify the uncertainty of estimated properties due to noisy data and incorrect bed boundaries. Several field examples describe the successful application of the methods on (a) the assessment of residual hydrocarbon saturation in a tight-gas sand formation invaded with water-base mud (WBM) and a hydrocarbon-bearing siliciclastic formation invaded with oil-base mud (OBM), (b) estimation of dynamic petrophysical properties of water-bearing sands invaded with OBM, (c) estimation of porosity and volumetric concentrations of mineral and fluid constituents in carbonate formations, and (d) estimation of TOC, total porosity, total water saturation, and volumetric concentrations of mineral constituents in the Haynesville shale-gas formation. Comparison of results against those obtained with conventional petrophysical interpretation methods, commercial multi-mineral solvers, and core/XRD data confirm the advantages and flexibility of the new interpretation techniques introduced in this dissertation for the quantification of petrophysical and compositional properties in a variety of rock formations. / text

Understanding static and dynamic nonlinear behavior of pipes and risers is crucial for the design aspects in offshore engineering fields. In this work, we examine two nonlinear problems in offshore engineering field: vortex Induced vibration of straight horizontal pipes, and boundary layer static solution of inclined risers. In the first study, we analyze the effect of the internal velocity of straight horizontal pipe and obtain the vortex induced vibration forces via coupling the pipe equation of motion with the recently modified Van Der Pol oscillator governing the lift coefficient. Our numerical results are obtained for two different pipe configurations: hinged-hinged, and clamped- clamped. The results show that the internal velocity reduces the vibration and the oscillation amplitudes. Also, it is shown that the clamped-clamped pipe configuration offers a wider range of internal velocities before buckling instability occurs. The results also demonstrate the effect of the end condition on the amplitudes of vibration. In the second study, we develop a boundary layer perturbation static solution to govern and simulate the static behavior of inclined risers. In the boundary layer analysis, we take in consideration the effects of the axial stretch, applied tension, and internal velocity. Our numerical simulation results show good agreement with the exact solutions for special cases. In addition, our developed method overcomes the mathematical and numerical limitations of the previous methods used before.