Currently, there is interest in the development of molecular-scale devices for use in quantum information processing (QIP). With this application in mind, physical studies on antiferromagnetically coupled molecular wheels [Cr7MF3(Etglu)(O2CtBu)15(phpy)], where M is a divalent metal cation (M = Mn2+, Zn2+, Ni2+) have been pursued. The heterometallic wheels contain an octagon of metal centres, which are bridged by fluoride ions, pivalate groups and a chiral N-ethyl-D-glutamine molecule which is penta-deprotonated and bound to the metal sites through all available O-donors. They are deep purple in colour and they have been named purple-Cr7M. There is antiferromagnetic coupling between adjacent metal centres, J » -8 cm-1, resulting in a non-zero net spin ground state. The spin-Hamiltonian parameters of this family have been determined.At the heterometal site of purple-Cr7M wheels there is a terminal ligand which can be substituted for a variety of N-donor organic ligands. A series of bidentate N-donor linkers has been used to link Cr7Ni wheels (each wheel Seff = 1/2) to create prototype two-qubit systems. Multi-frequency EPR spectroscopy and SQUID magnetometry has been used to extract the spin-Hamiltonian parameters of this family. It has been shown that the single wheels can be linked together electronically as well as chemically. It has been found that for the unsaturated linkers, there is a weaker interaction between Cr7Ni wheels when longer linkers are used. The strength of interaction is smaller for the saturated linkers than for the unsaturated linkers.The formation of 'green'-Cr7M wheels is different, being templated around a cation. Two new types of wheels have been studied: [tBuCONHC6H12NH2C6H12NHCOtBu][Cr7M2+F8(O2CtBu)16] and [Cs?Cr7MF8(O2CtBu)16]·0.5MeCN (where, M = Mn2+, Zn2+, Ni2+), where the former is templated around a long dialkylammonium group and the latter around a caesium cation. The effect of the templating cation on spectroscopic properties has been determined.Physical studies on a family of antiferromagnetically-coupled homometallic clusters have been pursued. They consist of cyclic arrays of homometallic Cr3+ ions in either a octametallic wheel or hexametallic horseshoes. The horseshoes have the general formula: [CrxFx+5L2x-2]n3- (where L = carboxylate). Cr3+ centres are bridged by pivalate groups and fluorides, while Cr3+ centres at the ends of the chain have terminal fluorides completing their coordination sphere. These terminal fluoride groups are labile enough to be substituted, e.g. [EtNH2][Cr6F7(O2CtBu)10(acac)2] is the product of a substitution reaction with acetylacetone.

Existing instrumental techniques must be adaptable to the analysis of novel explosives if science is to keep up with the practices of terrorists and criminals. The focus of this work has been the development of analytical techniques for the analysis of two types of novel explosives: ascorbic acid-based propellants, and improvised mixtures of concentrated hydrogen peroxide/fuel. In recent years, the use of these explosives in improvised explosive devices (IEDs) has increased. It is therefore important to develop methods which permit the identification of the nature of the original explosive from post-blast residues. Ascorbic acid-based propellants are low explosives which employ an ascorbic acid fuel source with a nitrate/perchlorate oxidizer. A method which utilized ion chromatography with indirect photometric detection was optimized for the analysis of intact propellants. Post-burn and post-blast residues if these propellants were analyzed. It was determined that the ascorbic acid fuel and nitrate oxidizer could be detected in intact propellants, as well as in the post-burn and post-blast residues. Degradation products of the nitrate and perchlorate oxidizers were also detected. With a quadrupole time-of-flight mass spectrometer (QToFMS), exact mass measurements are possible. When an HPLC instrument is coupled to a QToFMS, the combination of retention time with accurate mass measurements, mass spectral fragmentation information, and isotopic abundance patterns allows for the unequivocal identification of a target analyte. An optimized HPLC-ESI-QToFMS method was applied to the analysis of ascorbic acid-based propellants. Exact mass measurements were collected for the fuel and oxidizer anions, and their degradation products. Ascorbic acid was detected in the intact samples and half of the propellants subjected to open burning; the intact fuel molecule was not detected in any of the post-blast residue. Two methods were optimized for the analysis of trace levels of hydrogen peroxide: HPLC with fluorescence detection (HPLC-FD), and HPLC with electrochemical detection (HPLC-ED). Both techniques were extremely selective for hydrogen peroxide. Both methods were applied to the analysis of post-blast debris from improvised mixtures of concentrated hydrogen peroxide/fuel; hydrogen peroxide was detected on variety of substrates. Hydrogen peroxide was detected in the post-blast residues of the improvised explosives TATP and HMTD.

Spark ignition (SI) and compression ignition (CI) engine fuels are characterized by standards developed in 1927 and 1932, respectively. Over the course of these years, modern engines have drastically changed their operating conditions; however, these fuel indexes are still used today with no significant change to their definition. The requirements for fuels in future advanced engines, employing low temperature combustion (LTC) concepts, may be somewhere between gasoline and diesel in terms of their autoignition characteristics. With this focus, this study examines methodologies to bridge the gap between those fuels classified between gasoline and diesel. First, the ignition delay times (IDTs) at various temperatures obtained from an ignition quality tester (IQT), was correlated with the octane index (OI), an anti-knock scale combining the effect of the operating condition and the anti-knock quality of the fuel given by the RON/MON. This study was extended to introduce a new concept of IDT sensitivity (IDS) in an IQT. It was observed that IDS could be correlated with fuel octane sensitivity (OS = RON − MON), offering an additional methodology to estimate RON/MON with an IQT. Chemical kinetics are most sensitive to fuel molecular structure; remarkable progress has been made in covering high carbon-number fuels, relevant to gasoline fuels, for better understanding of the chemical processes that lead to engine knock. To this end, a methodology to relate IDTs calculated from homogeneous batch-reactor simulations with gasoline fuel indexes was developed. This methodology enabled correlation of a kinetic property (i.e., IDT) with RON/MON values. The influence of various components present in gasolines, and their anti-knock quality, was investigated. A spinning band distillation system was utilized to separate the components of various gasolines. Ignition quality and the functional group distribution of various boiling ranges were investigated with an IQT and 1H nuclear magnetic resonance (NMR) spectroscopy. Finally, the importance of physical and chemical fuel properties in fuel stratification in LTC engine concepts was undertaken in a CI engine with a multi hole solid-cone injector. The findings suggest that the physical properties of fuel played a dominant role when fuel stratification occurred in the engine combustion chamber.

abstract: The efficiency of spacecraft’s solar cells reduces over the course of their operation. Traditionally, they are configured to extract maximum power at the end of their life and not have a system which dynamically extracts the maximum power over their entire life. This work demonstrates the benefit of dynamic re-configuration of spacecraft’s solar arrays to access the full power available from the solar panels throughout their lifetime. This dynamic re-configuration is achieved using enhancement mode GaN devices as the switches due to their low Ron and small footprint. This work discusses hardware Implementation challenges and a prototype board is designed using components-off-the-shelf (COTS) to study the behavior of photovoltaic (PV) panels with different configurations of switches between 5 PV cells. The measurement results from the board proves the feasibility of the idea, showing the power improvements of having the switch structure. The measurement results are used to simulate a 1kW satellite system and understand practical trade-offs of this idea in actual satellite power systems. Additionally, this work also presents the implementation of CMOS controller integrated circuit (IC) in 0.18um technology. The CMOS controller IC includes switched-capacitor converters in open loop to provide the floating voltages required to drive the GaN switches. Each CMOS controller IC can drive 10 switches in series and parallel combination. Furthermore, the designed controller IC is expected to operate under 300MRad of total dose radiation, thus enabling the controller modules to be placed on the solar cell wings of the satellites. / Dissertation/Thesis / Masters Thesis Electrical Engineering 2019

(Thesis: M.Sc.Eng.) PLEASE NOTE: Boston University Libraries did not receive an Authorization To Manage form for this thesis or dissertation. It is therefore not openly accessible, though it may be available by request. If you are the author or principal advisor of this work and would like to request open access for it, please contact us at open-help@bu.edu. Thank you. / In recent years, the effects of process variation have become increasingly more severe as technology has been scaling down in lithographic dimension. This problem also has affected the operation of the MINS IC (Multi-Input Neural Sensor) designed at Boston University by Dr. Lu Wang. This MINS chip was designed for use in both in-vitro and in-vivo applications of measuring and recording neural action potentials and local field potentials in the brains of animals. The MINS chip has been tested and is fully functional, however, with a serious problem of output level shifting from input-to-input due to process variation. This thesis will focus on the study of the effect of process variation on the MINS chip and a proposed method for process variation correction. The effect of process variation on the MINS chip is an extremely serious issue, given the large amount of gain required to sense and record neural signals, especially local field potentials, which have an input voltage of the order of 10-100 μV. The previous version of the printed circuit board designed to correct for process variation can center the output between the upper and lower rails by measuring the required column bias current independently for each of 256 inputs individually and storing these on an FPGA. However, this process variation correction procedure has jeopardized the ability to scan at the required rate in order to record action potentials (spikes). This thesis has two parts: The first part includes the study of the effects of process variation on the functionality of the 8HP MINS chip by doing Gaussian distribution analysis. The second part is the design of a new printed circuit board to increase the speed of the process variation correction procedure in scan mode, and as a goal, to center the output level in both stop mode and scan mode. The study of the effects of process variation on MINS utilizes circuit simulations with the IBM 8HP device models and design kit, using extracted models based on the MINS chip layout. According to the Monte Carlo sampling analysis, only 12 out of 200 samples are showing output level to be around center, with 65% of the samples having output voltage at upper and lower rails. What is more, as the study of 1000 cases shows, a column bias current of about 105uA and/or a bias voltage of 1.212 V, with 3σ to be 3.798uA and 0.131V respectively, is needed to center the output. A new developed version of the variation correction PCB has been designed and fabricated, utilizing a charge pump methodology to quickly charge up (or discharge) the large stabilization capacitor (4.7μF) placed on the Ibias0 node for stability, on the existing MINS PCB. Given that the Ibias0 current on MINS is only around 100μA, a large current of the order of 250-500mA is used in order to achieve the desired scan rate on the chip. A ping-pong approach is used, having two 4.7μF capacitors so that one can be readied while the other is being used for the testing. This PCB design also includes the needed controls with comparators and logic to terminate the charging/discharging operation at the exact correct voltage on the Ibias0 node, for each of the 256 inputs. On this new board, the required voltage at the Ibias0 node (Vbias0) to center the output, instead of Ibias0, will be measured and stored for each of 256 inputs in both stop mode and scan mode. / 2031-01-01

Several modern marine engines use multiple injectors for lower heat losses and higher efficiency. However, the heavy-duty vehicles still apply a single injector per cylinder. This work investigates how multiple injectors can be operated in compression ignition heavy-duty engines along with potential benefits from such concepts. The studies aimed to avoid high boundary gas temperatures by having two injectors at the rim of the bowl, in addition to the standard injector. A longer injector-wall distance reduces the amount of hot gases at the boundaries for reduced convective heat losses. Additional degrees of freedom also follows from an increased number of injectors to simplify combustion control. The thesis included CFD simulations, metal engine experiments, and optical engine diagnostics to investigate the efficiency –and emission benefits for two –and three-injector concepts compared to the single-injector approach. The CFD simulations aimed to set beneficial spray angles and chamber geometries for reduced heat losses and reasonable emission levels with and without swirl at different load conditions. A flat bowl with two injectors reduced the heat losses by 4.2 %-points resulting in a direct efficiency increase of 1.9 %-points at middle-load conditions. Metal engine studies confirmed the simulation results by testing two -and three-injector concepts. The higher three-injector flow rate raised efficiency and diminished heat losses while providing low nitric oxide levels. Thus, three injectors lessen the typical trade-off between efficiency and nitric oxides. The thesis further performed single-injector optical engine experiments to investigate combustion control limitations. The results concluded that high soot levels occur from the multiple injections used to achieve isobaric combustion. These high soot levels followed by injecting into fuel-rich zones, which can be avoided by using multiple injectors. Finally, the thesis provides a multiple injector design suitable for heavy-duty production engines.

No description available.

No description available.

Electrostatic Discharge (ESD) phenomenon is a common phenomenon in daily life and it could damage the integrated circuit throughout the whole cycle of product from the manufacturing. Several ESD stress models and test methods have been used to reproduce ESD events and characterize ESD protection device's performance. The basic ESD stress models are: Human Body Model (HBM), Machine Model (MM), and Charged Device Model (CDM). On-chip ESD protection devices are widely used to discharge ESD current and limit the overstress voltage under different ESD events. Some effective ESD protection devices were reported for low speed circuit applications such as analog ICs or digital ICs in CMOS process. On the contrast, only a few ESD protection devices available for radio frequency integrated circuits (RF ICs). ESD protection for RF ICs is more challenging than traditional low speed CMOS ESD protection design because of the facts that: (1) Process limitation: High-performance RF ICs are typically fabricated in compound semiconductor process such as GaAs pHEMT and SiGe HBT process. And some proved effective ESD devices (e.g. SCR) are not able to be fabricated in those processes due to process limitation. Moreover, compound semiconductor process has lower thermal conductivity which will worsen its ESD damage immunity. (2) Parasitic capacitance limitation: Even for RF CMOS process, the inherent parasitic capacitance of ESD protection devices is a big concern. Therefore, this dissertation will contribute on ESD protection designs for RF ICs in all the major processes including GaAs pHEMT, SiGe BiCMOS and standard CMOS. iv The ESD protection for RF ICs in GaAs pHEMT process is very difficult, and the typical HBM protection level is below 1-kV HBM level. The first part of our work is to analyze pHEMT's snapback, post-snapback saturation and thermal failure under ESD stress using TLP-like Sentaurus TCAD simulation. The snapback is caused by virtual bipolar transistor due to large electron-hole pairs impacted near drain region. Postsnapback saturation is caused by temperature-induced mobility degradation due to IIIV compound semiconductor materials' poor thermal conductivity. And thermal failure is found to be caused by hot spot located in pHEMT's InGaAs layer. Understanding of these physical mechanisms is critical to design effective ESD protection device in GaAs pHEMT process. Several novel ESD protection devices were designed in 0.5um GaAs pHEMT process. The multi-gate pHEMT based ESD protection devices in both enhancementmode and depletion-mode were reported and characterized then. Due to the multiple current paths available in the multi-gate pHEMT, the new ESD protection clamp showed significantly improved ESD performances over the conventional single-gate pHEMT ESD clamp, including higher current discharge capability, lower on-state resistance, and smaller voltage transient. We proposed another further enhanced ESD protection clamp based on a novel drain-less, multi-gate pHEMT in a 0.5um GaAs pHEMT technology. Based on Barth 4002 TLP measurement results, the ESD protection devices proposed in this chapter can improve the ESD level from 1-kV (0.6 A It2) to up to 8-kV ( > 5.2 A It2) under HBM. v Then we optimized SiGe-based silicon controlled rectifiers (SiGe SCR) in SiGe BiCMOS process. SiGe SCR is considered a good candidate ESD protection device in this process. But the possible slow turn-on issue under CDM ESD events is the major concern. In order to optimize the turn-on performance of SiGe SCR against CDM ESD, the Barth 4012 very fast TLP (vfTLP) and vfTLP-like TCAD simulation were used for characterization and analysis. It was demonstrated that a SiGe SCR implemented with a P PLUG layer and minimal PNP base width can supply the smallest peak voltage and fastest response time which is resulted from the fact that the impact ionization region and effective base width in the SiGe SCR were reduced due to the presence of the P PLUG layer. This work demonstrated a practical approach for designing optimum ESD protection solutions for the low-voltage/radio frequency integrated circuits in SiGe BiCMOS process. In the end, we optimized SCRs in standard silicon-based CMOS process to supply protection for high speed/radio-frequency ICs. SCR is again considered the best for its excellent current handling ability. But the parasitic capacitance of SCRs needs to be reduced to limit SCR's impact to RF performance. We proposed a novel SCR-based ESD structure and characterize it experimentally for the design of effective ESD protection in high-frequency CMOS based integrated circuits. The proposed SCR-based ESD protection device showed a much lower parasitic capacitance and better ESD performance than the conventional SCR and a low-capacitance SCR reported in the literature. The physics underlying the low capacitance was explained by measurements using HP 4284 capacitance meter. vi Throughout the dissertation work, all the measurements are mainly conducted using Barth 4002 transimission line pulsing (TLP) and Barth 4012 very fast transmission line pulsing (vfTLP) testers. All the simulation was performed using Sentaurus TCAD tool from Synopsys.

In Part I, the design of an ASIC control chip for a forward active clamp converter is presented. Integration of the control and drive circuit into one IC chip results in higher power density, higher reliability for the converter module. The designed ASIC control chip uses a 2.0 um N well Analog CMOS process, and is fabricated at MOSIS. The design procedures of the ASIC chip are explained, and experimental results are presented. Part II of the thesis focuses on the numerical investigation of several integratable lateral power devices. Lateral power devices are used in power IC designs because of their compatibility with analog & digital IC process. To obtain devices with high current density, large safe operating area, fast response and low cost is highly desirable for power ICs. In Part II of this thesis, several lateral power devices are discussed and simulated, including lateral IGBT, lateral MCT and double gate lateral MCTs. It is shown that lateral IGBT and lateral MCTs are good candidates for power IC applications. / Master of Science