The sensor based manipulation of irregularly shaped objects with special application to the semiconductor industry

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1998.Includes bibliographical references (leaves 91-94).by Vivek Anand Sujan.S.M

Dynamic Pricing for Vehicle Ferries: using Packing and Simulation to Optimize Revenues

We propose an heuristic approach to the vehicle ferry revenue management problem, where the aim is to maximize the revenue obtained from the sale of vehicle tickets by varying the prices charged to different vehicle types, each occupying a different amount of deck space. Customers arrive and purchase tickets according to their vehicle type and their willingness-to-pay, which typically increases over time because customers purchasing tickets closer to departure tend to accept higher prices. The optimization problem can be solved using dynamic programming but the possible states in the selling season are the set of all feasible vehicle mixes that fit onto the ferry. This makes the problem intractable as the number of vehicle types and ferry size increases. We propose a state space reduction, which uses a vehicle ferry loading simulator to map each vehicle mix to a remaining-space state. This reduces the state space of the dynamic program. Our approach allows the value function to be approximated rapidly and accurately with a relatively coarse discretization of states. We present simulations of the selling season using this reduced state space to validate the method. The vehicle ferry loading simulator was developed in collaboration with a vehicle ferry company and addresses real-world constraints such as manoeuvrability, elevator access, strategic parking gaps, vehicle height constraints and ease of implementation of the packing solutions

Understanding Gas and Energy Storage in Geological Formations with Molecular Simulations

Methane (CH4), the cleanest burning fossil fuel, has the potential to solve the energy crisis owing to the growing population and geopolitical tensions. Whilst highly calorific, realising its potential requires efficient storage solutions, which are safe and less energy-intensive during production and transportation. On the other hand, carbon dioxide (CO2), the by-product of human activities, exacerbates global heating driving climate change. CH4 is abundant in natural systems, in the form of gas hydrate and trapped gas within geological formations. The primary aim of this project was to learn how Nature could store such a large quantity of CH4 and how we can potentially extract and replace the in-place CH4 with atmospheric CO2, thereby reducing greenhouse gas emissions. We studied this question by applying molecular dynamics (MD) and Monte Carlo (MC) simulation techniques. Such techniques allow us to understand the behaviour of confined fluids, i.e., within the micropores of silica and kerogen matrices. Our simulations showed that CH4 hydrate in confinement could form under milder conditions than required, deviating from the typical methane-water phase diagram, complementing experimental observations. This research can contribute to artificial gas hydrate production via porous materials for gas storage. Besides that, the creation of 3D kerogen models via simulated annealing has enabled us to understand how maturity level affects the structural heterogeneity of the matrices and, ultimately CH4 diffusion. Immature and overmature kerogen types were identified to having fast CH4 diffusion. Subsequently, our proof-of-concept study demonstrated the feasibility of recovering CH4 via supercritical CO2 injection into kerogens. Insights from our study also explained why full recovery of CH4 is impossible. A pseudo-second-order rate law can predict the kinetics of such a process and the replacement quantity. A higher CO2 input required than the CH4 recovered highlights the possibility of achieving a net-zero future via geological CO2 sequestration

Quantum phases in frustrated strongly correlated 2-D systems

The strong Coulomb repulsion between charge carriers in a system with one electron per site can lead to a full localization of the electrons. The resulting state is called a Mott insulating state. The interplay between the physics of Mott insulators and of unconventional superconductors has been a focus in condensed matter physics for a long time. Although it has frequently been argued that the proximity to a Mott insulating phase is responsible for the emergence of unconventional superconductivity, little progress has been made in obtaining a convincing microscopic theory. Due to the strong electron-electron (e-e) interaction involved in Mott insulators, mean field theory is not a reliable tool. Thus other nonperturbative methods, including the Resonating Valence Bond (RVB) variational theory, have been developed. Recently experimental results showing that a spin liquid state, which is a Mott insulator without long range magnetic order, can undergo a pressure induced transition into an unconventional superconducting state has helped to sharpen this question. This experimental observation demonstrates that the onset of unconventional superconductivity doesn\u27t require magnetic ordering. The RVB picture serves perfectly in this context since it starts with a nonmagnetic state. The major goal of this thesis is to investigate the unconventional electronic and magnetic properties of a superconductor close to a Mott insulating phase. Particular emphasis is given to frustrated systems where the role of quantum frustration is known to be strong and where the Mott insulator is not magnetically ordered. Specifically we study models relevant to two frustrated quantum spin systems.;One material of interest is kappa - (ET)2 Cu 2 (CN)3, an organic superconductor. Its spin-liquid ground state can be tuned by pressure into an unconventional superconducting state. We propose a new variational wavefunction by introducing nonlocal correlation effects into the usual partially projected Gutzwiller wavefunction. We successfully find a superconducting state of d-wave pairing symmetry sandwiched between a metallic state and a spin liquid state around some critical onsite repulsion U. We also find strong Fermi surface renormalization when superconductivity starts to emerge.;The other material of interest is SrCu2 ( BO3)2 whose ground state is known to be a singlet dimer state. We derive a multiband BCS wavefunction and apply onto it the full Gutzwiller projection. We show that the obtained trial wavefunction can give the exact ground state energy to the undoped system. We then find that the physical properties are dramatically different for the electron and hole doped cases. We find, for the hole doped case, a plaquette d-wave pairing pattern and enhanced superconductivity due to this pairing inhomogeneity; while for the electron doped case, we find a strange metallic state

Atomic Scale Microscopy of Zr-based Bulk Metallic Glasses Processed by Various Routes

Bulk metallic glasses (BMGs) exhibit a rare combination of strength and toughness that is difficult to achieve by other materials. These properties make them favourable for a diverse range of engineering applications. However, their disordered amorphous structure invokes catastrophic failure with shear bands localisation, limiting their industrial development as structural materials. Moreover, it is not yet clear how to quantitatively link their microstructural features to processing and mechanical properties. The aim of this thesis was to quantitatively analyse the structural features contributing to local hardness variations in thermomechanically processed zirconium (Zr)-based BMGs. Advanced atom probe tomography (APT) techniques were used to observe structural and chemical changes in these BMGs. APT operational parameters were optimised and tested for robust data outcomes. APT cluster analysis was effectively utilised in the characterisation of nanoscale heterogeneities in the BMG microstructure. The chemical composition of the nanoscale heterogeneities was roughly Zr27Cu29Al21Ni19Nb4 (at. %) in Zr63.96Cu13.36Ni10.29Al11.04Nb1.25 (at. %), and Zr22Cu29Al17Ni23Ti9 (at. %) in Zr52.5Cu17.9Ni14.6Al10Ti5 (at. %). Their chemistry was experimentally reported herein for the first time. Additionally, an ab-initio molecular dynamic (AIMD) simulation was used to simulate the atomistic distribution in a Zr-based BMG. Clusters observed in APT assigned as MRO regions were found synonymous to the shear band nucleation zones. Beyond the novel methodological rigor introduced here, the findings provide a new, independent validation of the inverse correlation between local hardness and size of the MRO regions, with their chemical compositions, providing a novel handle on the quest for understanding microstructure- property-processing relationship in BMGs

X-ray structure of the Na+-coupled Glycine-Betaine symporter BetP from Corynebacterium glutamicum

Cellular membranes are important sites of interaction between cells and their environment. Among the multitude of macromolecular complexes embedded in these membranes, transporters play a particularly important role. These integral membrane proteins perform a number of vital functions that enable cell adaptation to changing environmental conditions. Osmotic stress is a major external stimulus for cells. Bacteria are frequently exposed to either hyperosmotic or hypoosmotic stress. Typical conditions for soil bacteria, such as Corynebacterium glutamicum, vary between dryness and sudden rainfall. Physical stimuli caused by osmotic stress have to be sensed and used to activate appropriate response mechanisms. Hypoosmotic stress causes immediate and uncontrolled influx of water. Cells counteract by instantly opening mechanosensitive channels, which act as emergency valves leading to fast efflux of small solutes out of the cell, therebydiminishing the osmotic gradient across the cell membrane. Hyperosmotic stress, on the other hand, results in water efflux. This is counterbalanced by an accumulation of small, osmotically active solutes in the cytoplasm, the so-called compatible solutes. They comprise a large variety of substances, including amino acids (proline), amino acid derivatives (betaine, ectoine), oligosaccharides (trehalose), and heterosides (glucosylglycerol). Osmoregulated transporters sense intracellular osmotic pressure and respond to hyperosmotic stress by facilitating the inward translocation of compatible solutes across the cell membrane, to restore normal hydration levels. This work presents the first X-ray structure of a member of the Betaine-Choline-Carnitine-Transporter (BCCT) family, BetP. This Na+-coupled symporter from Corynebacterium glutamicum is a highly effective osmoregulated and specific uptake system for glycine-betaine. X-ray structure determination was achieved using single wavelength anomalous dispersion (SAD) of selenium atoms. Selenium was incorporated into the protein during its expression in methione auxotrophic E. coli cells, grown in media supplemented with selenomethionine. SAD data with anomalous signal up to 5 Å led to the detection of 39 selenium sites, which were used to calculate the initial electron density map of the protein. Medium resolution and high data anisotropy made the structure determination of BetP a challenging task. A specific strategy for data anisotropy correction and a combination of various crystallographic programs were necessary to obtain an interpretable electron density map suitable for model building. The crystal structure of BetP shows a trimer with glycine-betaine bound in a three-fold cation-pi interaction built by conserved tryptophan residues. The bound substrate is occluded from both sides of the membrane and aromatic side chains line its transport pathway. Very interestingly, the structure reveals that the alpha-helical C-terminal domain, for which a chemo- and osmosensory function was elucidated by biochemical methods, interacts with cytoplasmic loops of an adjacent monomer. These unexpected monomer-monomer interactions are thought to be crucial for the activation mechanism of BetP, and a new atomic model combing biochemical results with the crystal structure is proposed. BetP is shown to have the same overall fold as three unrelated Na+-coupled symporters. While these were crystallised in either the outward- or inward-facing conformation, BetP reveals a unique intermediate state, opening new perspectives on the alternating access mechanism of transport

High-Performance Field-Effect Transistor-Type Sensors Based on Nanoscopically Engineered Organic Semiconductors

Department of Energy EngineeringSensors based on organic field-effect transistor (OFET) platforms show great promise for use in chemical and biological sensors due to their prominent advantages, including high sensitivity, light-weight, low-cost, simple platforms, and flexible applications. Functional properties of active organic semiconductor layers can be tailored by material design or/and surface functionalization to enhance selectivity. To date, a large number of sensors for chemical and biogenic substances have used high-cost immobilization methods and high-end technologies. OFET-based sensors are particularly attractive for applications in simple, cost-effective, high-performance electronics. Furthermore, the sensitivity, selectivity, response time, stability, reproducibility, and limit of detection of sensors can be optimized by choosing or engineering more suitable fabrication techniques and materials for the active layers. Such on-demand, structure-engineered, and surface-engineered organic semiconducting layers are highly desirable for the practical uses of OFETs. In my thesis, commendable molecular engineering, process engineering and interface engineering are highlighted to demonstrate the feasibility of high-performance nanoscopically engineered organic-transistor-based sensors. Here, I begin with an introduction to OFET and organic sensors, with an emphasis on the organic semiconductor engineering strategies in chapter 1. In detail, in chapter 1, typical properties of organic semiconductors, a discussion of OFET operation, and a working principles of this OFET-type sensors are introduced. Chapter 2 presents molecular engineering strategies to enable the fabrication of n-channel-dominant ambipolar OFETs. The electrical charge transport through fluorine-substituted semiconducting materials is investigated. These investigations are easily applied to demonstrate complementary inverters with a reasonable performance. In chapter 3, I focus on the device design and fabrication of high mobility OFETs made by using organic???organic heterointerface. Pentacene is used as an active layer above, and m-bis(triphenylsilyl)benzene is used as the bottom layer. Sequential evaporation process without breaking vacuum of these materials results in high-quality organic semiconductor thin films with far fewer grain boundaries. In addition, the pentacene film exhibits myriad nanometre-sized pores in the organic layers. This surprising structure, the pore-rich structure improves the sensitivity of organic-transistor-based chemical sensors. This approach demonstrates a conceptually novel methodology for the fabrication of ???structurally engineered??? organic semiconducting thin films and our work has a significant impact in the fields of materials science as well as organic electronics. Furthermore, organic semiconductor engineering strategies to improve sensitivity and selectivity for biogenic substances by direct semiconductor surface functionalization and to enhance sensitivity and selectivity towards psychostimulants by modification with specific selective sensing layer are given in chapter 4 and 5, respectively. In chapter 4, highly sensitive organic-transistor-based sensors that can selectively detect a neurotransmitter acetylcholine without enzyme immobilization are fabricated using organic thin films functionalized with a synthetic receptor, a cucurbit[6]uril (CB[6]) derivative. The liquid-phase sensing experiments are successfully performed by using organic semiconductor layer with high operational stability in water. The findings provide a low-cost, simple, and feasible method for the fabrication of high-performance water-stable sensors for biogenic substances. In addition, the results obtained herein describe the first demonstration of acetylcholine sensing without any enzymatic reactions using the synthetic receptor-functionalized OFET-platform. In chapter 5, the direct detection of amphetamine-type-stimulants (ATS) is suggested for the illicit and designer drugs sensing OFET platforms. Their novel sensing system and sensing mechanism are studied using other CB homologues, a cucurbit[7]uril (CB[7]) derivative decorated OFET-based sensors. By synergistic combination of a highly selective synthetic host molecule and a highly sensitive OFET device, the first ATS sensors with specific synthetic receptor-engineered OFET-platform are demonstrated flexible polymer substrates. These sensors in physiological buffer system and even in urine samples show highly sensitive sensing behaviors.ope

Modeling of the Structure of Disordered Metallic Alloys and Its Transformation Under Thermal Forcing

The morphology of disordered binary metallic alloys is investigated. The structure of disordered binary metallic alloys is modeled as a randomly close packed (RCP) assembly of atoms. It was observed through a 2-D binary hard sphere experiment that RCP structure can be modeled as a mixture of nano-crystallites and glassy matter. We define the degree of crystallinity as the fraction of atoms contained in nano-crystallites in an RCP medium. Nano-crystallites by size in a crystallite size distribution were determined experimentally to define the morphology of the RCP medium. Both the degree of crystallinity and the crystallite size distribution have been found to be determined by the composition of a given binary mixture. A 2-D Monte Carlo simulation was developed in order to replicate the RCP structure observed in the experiment which is then extended to cases of arbitrary composition. Crystallites were assumed to be spherical with isotropic cross sections. The number of atoms in an individual crystallite in 2-D is simply transformed into the number of atoms in 3-D; we then obtain the crystallite size distribution in 3-D. This experiment accounts for the contribution from the repulsive core of the inter-atomic potential. The attractive part of the potential is recovered by constructing spherical nano-crystallites of a given radius from a crystalline specimen of each given alloy. A structural model of a disordered alloy is thus obtained.With the basic structure of the RCP medium defined, the response to heating would be in the form of changes to the crystallite size distribution. This was first investigated in a hard sphere mechanical oven experiment. The experimental setup consists of a 2-D cell which is driven by two independent stepper motors. The motors drive a binary RCP bed of spheres on a slightly tilted plane according to a chaotic algorithmm. The motors are driven at four different speed settings. The RCP medium was analyzed using a sequence of digital images taken of the beds. The bursts of images provide a Gaussian distribution of particle speeds in x and y directions thus giving rise to the notion of temperature. This temperature scales with the motor speed settings. The measured average degree of crystallinity is found to decrease as the effective temperature was raised suggesting that nano-crystallites dissociate under thermal forcing. The evolution of a specimen\u27s structure is calculated rigorously by means of the law of mass action formalism. A system of thermal dissociation reaction equations is written out for the set of nano-crystallites according to the 3-D crystallite size distribution. The equilibrium treatment is justified because the energy differences between metastable RCP structures fall within kT. Thermal dissociation of one surface atom at a time is assumed because the energy cost in dissociation of a surface atom on a nano-crystallite is significantly less than that of a multi atom cluster. The full set of reaction equations cover all possible dissociation steps, which may amount to several thousand for a disordered alloy specimen. The primary determining factor in each of these dissociation equations is the dissociation potential or the amount of attractive energy needed to remove a surface atom on a nano-crystallite of a given size. The attractive potential between atoms is calculated using a Lennard-Jones potential between a pair of atoms for which quantum chemistry calculations exist in the literature. All interactions impinged on the surface atom by all other atoms in a crystallite are summed. As the nano-crystallites dissociate due to heating, the structure of the alloy changes, and this leads to modifications of alloy\u27s transport properties. The model is found to predict the melting temperature of various disordered binary alloys as well as refractory metals in good agreement with known data. The structure model for disordered binary alloys gives an excellent characterization of the alloy morphology. It therefore provides fruitful avenues for making predictions about how thermophysical properties of disordered binary alloys change as the alloy temperature is raised by heating

Eleventh European Powder Diffraction Conference. Warsaw, September 19-22, 2008

Zeitschrift für Kristallographie. Supplement Volume 30 presents the complete Proceedings of all contributions to the XI European Powder Diffraction Conference in Warsaw 2008: Method Development and Application,Instrumental, Software Development, Materials. Supplement Series of Zeitschrift für Kristallographie publishes Proceedings and Abstracts of international conferences on the interdisciplinary field of crystallography