Properties such as chemical robustness, potential for synthetic tunability, and superior electron-accepting character describe the chromophore perylene-3,4,9,10-tetracarboxylic diimide (PDI) and have enabled its penetration into organic photovoltaics. The ability to extend what is already a large aromatic core allows for synthesis of graphene ribbon PDI oligomers. Functionalization with polar and ionic groups leads to liquid crystalline phases or immense supramolecular architectures. Significantly, PDI dianions can survive in water for two months with no decomposition, an important property for charge storage materials. We realized the potential of PDI as an efficient negative-side material for Redox Flow Batteries (RFBs). The synthetic tunability of PDI allowed for screening of several derivatives with side chains that enhanced solubility in polar solvents. The optimized molecule, PDI[TFSI]2, dissolved in acetonitrile up to 0.5 M. For the positive-side, we synthesized the ferrocene oil [Fc4] in high yield. The large hydrodynamic radii of PDI[TFSI]2 and [Fc4] preclude their ability to cross a size exclusion membrane, which is a cheap alternative to the typical RFB membranes. We show that this cellulose-based membrane can support high voltages in excess of 3 V and extreme temperatures (−20 to 110 °C). We assembled a cell with 0.4 M electron concentration with negligible capacity loss for over 450 cycles (>74 days). Such concentration and stability are among the highest values reported in redox flow batteries with organic electrolytes. Oxidative photocyclizations of PDI onto acenes administer regiochemistry that favors helical products, albeit with a small number of overlapping π-bonded atoms. We achieved an oxidative photocyclization of PDI onto phenanthrene to form the [7]helicenes PPDHa and PPDHb with 20 overlapping π-bonded atoms, as well as a partially planar molecule 5HPP. Higher temperature increases the ratio of PPDHa:5HPP. Calculations reveal that these molecules contain ~20 kcal/mol more strain than planar analogs, and single crystals show bending of the PDI units from their favored planarity. The PPDH molecules display a new electronic transition in their UV-Vis spectra that sets them apart from monomer PDI and other PDI helicenes. Spectroelectrochemical measurements confirm that PPDHb accepts four electrons. Compared to a naphthyl-fused PDI helicene with only 10 overlapping π-bonded atoms, the PPDH molecules have a heightened ability to delocalize the first added electron.

Han-bing Ji. / Thesis (Ph.D.)--Chinese University of Hong Kong, 1996. / Includes bibliographical references (p. 160-163). / Microfiche. Ann Arbor, Mich.: UMI, 1998. 2 microfiches ; 11 x 15 cm.

In response to the ever-increasing global energy demand and the need to move away from non-renewable and CO2-emitting fossil fuels as the primary energy production method, renewable energy sources have become more and more viable as energy production methods. However, given the unreliable and instantaneous nature of these energy sources, reliable, renewable energy storage methods are required. Hydrogen is an excellent candidate as a chemical energy store, as it is highly abundant, relatively easily produced as diatomic hydrogen (including from water electrolysis), and only produces water upon its complete combustion. Hydrogen also has the highest gravimetric energy density of any known chemical fuel, meaning that not very much of it is required relative to other chemical fuels. However, hydrogen gas is incredibly sparse, and therefore hydrogen has a very low volumetric energy density, making storage of the material a key challenge in the development of the so-called “hydrogen economy”. Most commonly, hydrogen is stored by compressing it to 70 MPa. However, this technique has a number of flaws, including the high expense of strong tanks (and in the case of light duty vehicles, lightweight materials are also required), and the inherent safety risks that high pressure, highly flammable gas poses. One of the alternatives to compression is to store hydrogen by adsorption, which uses high surface area materials to densify hydrogen via the formation of weak physical bonds. This research line is well developed, and a number of different materials has been created that show good potential as hydrogen storage materials, such as activated carbons and metal organic frameworks. However, the vast majority of materials developed for this purpose are tailored only with the hydrogen uptake in mind, which can cause issues as the focus of development shifts from small scale tests to full tank scale. One adsorptive that shows a number of highly useful engineering properties on the large scale, such as good thermal resistance and solution processability, is the polymer of intrinsic microporosity PIM-1. This material can be processed into a number of morphologies without losing porosity, and shows good thermal and mechanical resistance. However, its adsorption capacity is rather limited, with the BET surface area generally reported in the 700 – 800 m2 g-1 range, and hydrogen uptake of 1.45 wt% at 77 K and 1 MPa. This thesis presents two separate studies on attempting to improve the hydrogen uptake of PIM-1 without adversely affecting the material properties that make it attractive. The first of these was the creation of mixed-matrix-membrane style composite films solution cast from PIM-1 and the metal organic framework MIL-101. PIM-1 proved slightly difficult to synthesise consistently with high molecular weight, but MIL-101 is an easy hydrothermal synthesis. Film casting was successfully performed, producing flat, homogeneous films that maintained the MOF crystallinity. These materials were tested for their thermal properties – thermal decompositions proceeded according to the rule of mixtures of the two starting materials, whilst an increasing concentration of MOF was shown to decrease the specific heat capacity. Both PIM-1 and MIL-101 were shown to adsorb nitrogen as previously reported. The composites showed increasing uptake with MIL-101 content, but at a lower rate than the rule of mixtures. This was a common theme for the N2 (77 K), CO2 (293 K) and low pressure H2 isotherms performed. High pressure isotherms up to 17 MPa were performed on PIM-1 for the first time, showing a maximum excess uptake of 1.8 wt% on the powder and 1.6 wt% on the film, both at 77 K. The composites showed improved uptake with increasing MIL-101, but the maximum uptakes did not meet the rule of mixtures. The uptakes at the highest pressure did, however. Multiple temperature isotherm sets were performed on the PIM-1 film and powder, as well as the 30 wt% composite. These data sets were hampered largely by machine faults, but contained sufficient valuable data to be able to proceed with parameter fitting. The sensitivity of the isotherms produced in this study to the value of skeletal density is also examined closely. The second theme of improved H2 uptake in PIM-1 was to carbonise the material. TGA studies on PIM-1 showed good thermal stability in anoxic conditions, and TGA twinned with mass spectroscopy was able to confirm a previously proposed mechanism of thermal decomposition. Carbonised and activated PIM-1 film samples, and a carbonised powder, were produced using physical activation methods. The adsorption performance of the carbons was disappointing, as the uptakes of N2 and H2 (< 0.1 MPa) were reduced post-carbonisation, with little recovery in the activated film. CO2 uptakes were improved, however. High pressure H2 isotherms on both the carbonised and activated films showed unusual ‘stepping’ behaviour in the adsorption curve, but maximum uptakes for both (1.0 – 1.3 wt%) were less than that seen for PIM-1 alone. Parameter fitting was performed on all of the high pressure H2 isotherms performed in this study, using a method previously proposed by the Mays group. The parameter fits all showed effective hydrogen densification in the adsorbate layer, although the repeatability of parameter values, and the smoothness of the parameters as a function of temperature were undermined by the low quality of some of the isotherms. Using the parameters acquired, it was possible to calculate the isosteric enthalpy of adsorption for PIM-1 powder (-9.5 kJ mol-1), film (- 8.0 kJ mol-1) and the 30 wt% composite (-9.3 kJ mol-1). The stored and deliverable hydrogen contained within tanks featuring the tested materials were estimated, although only the MIL-101 powder on its own competes with other hydrogen storage adsorbents currently reported.

One of the main challenges in the implementation of renewable energy is the mismatch between supply and demand. Energy storage has been identified as one of the solutions to the mismatch problem. Among various storage technologies, thermal energy storage (TES) is foreseen to have a significant role to achieve a low carbon energy systems because of the large share of thermal energy demand and its relatively low cost. However, integrating TES into energy systems requires careful design and implementation since otherwise potential financial and environmental savings may not be achieved. Computational-based design tools are ubiquitous in the design process of modern energy systems and can be broadly categorised into two methodologies: optimisation and simulation. In both cases, designing an energy system with storage technology is significantly more complicated than those without, mainly due to the coupling of variables between time steps. This thesis is concerned with two facets of the application of TES in energy systems. First, the role of TES in improving the performance of renewable-based domestic heating systems. Second, the implementation of optimisation and simulation tools in the design of energy systems with integrated TES. They are addressed by examining two case studies that illustrate the spatial and temporal variance of energy systems: a single dwelling heat pump system with a hot water tank, and a solar district heating system with a borehole thermal energy storage. In the single dwelling case study, the technical and financial benefits of TES installation in a heat pump system are illustrated by the optimisation model. A simulation model which utilises the optimisation results is developed to assess the accuracy of the optimisation results and the potential interaction between the two methodologies. The solar district heating case study is utilised to highlight the potential of a time decomposition technique, the multiple time grids method, in reducing the computational time in the operational optimisation of the system. Furthermore, the case study is also employed to illustrate the potential of installing a similar system in the UK. The latter study was performed by developing a validated simulation model of the solar district heating system. The findings of the analyses reported in this thesis exemplify the potential of TES in a domestic and community-level heating system in the UK. They also provide a basis for recommendations on the improved use of optimisation and simulation tools in the design process of energy systems.

by Chan Chi Wai. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1997. / Includes bibliographical references (leaves [89]-91). / Abstract --- p.ii / List of Tables --- p.vii / List of Figures --- p.viii / Chapter 1 --- Introduction --- p.1 / Chapter 2 --- Background Information And Scope of Thesis --- p.6 / Chapter 2.1 --- Related Work --- p.6 / Chapter 2.2 --- Scope of Thesis --- p.10 / Chapter 3 --- System Architecture and Design Principle --- p.12 / Chapter 3.1 --- Overall System Architecture --- p.12 / Chapter 3.2 --- Entry Term Construct and Thesaurus Frame --- p.14 / Chapter 3.2.1 --- Semantic Classification --- p.15 / Chapter 3.2.2 --- "Word, Entry Term and Semanteme" --- p.17 / Chapter 3.2.3 --- Relationship Type and Relationship Link --- p.19 / Chapter 3.3 --- Thesaurus Module and Maintenance Module --- p.22 / Chapter 3.4 --- Data Structure --- p.22 / Chapter 3.4.1 --- Semantic Classification Tree --- p.24 / Chapter 3.4.2 --- Entry Term Construct --- p.24 / Chapter 3.4.3 --- Thesaurus Frame --- p.26 / Chapter 4 --- Relationship Inference --- p.28 / Chapter 4.1 --- Study on a Traverse of Two Relationship Links --- p.29 / Chapter 4.2 --- Grammar of the Relationship Inference Rules Definition --- p.33 / Chapter 4.3 --- Implementation Detail and API of Relationship Inference --- p.35 / Chapter 4.4 --- Evaluation on Relationship Inference --- p.39 / Chapter 5 --- Weight Schemes --- p.41 / Chapter 5.1 --- Thesaurus Frame Construction and Relationship Type Definition --- p.42 / Chapter 5.2 --- Two Kinds of Relationship Types --- p.44 / Chapter 5.3 --- Evaluation on different Weighting Scheme Formulas --- p.46 / Chapter 5.4 --- Term Ranking --- p.57 / Chapter 5.5 --- Normalization on Semantic Distance --- p.62 / Chapter 6 --- User Interface and API --- p.66 / Chapter 6.1 --- User Interface --- p.66 / Chapter 6.2 --- API --- p.74 / Chapter 6.2.1 --- Thesaurus Management --- p.75 / Chapter 6.2.2 --- Semantic Classifications --- p.76 / Chapter 6.2.3 --- Entry Terms --- p.77 / Chapter 6.2.4 --- Semantemes --- p.79 / Chapter 6.2.5 --- Relationship Types and Relationship Links --- p.80 / Chapter 6.2.6 --- Weighting Schemes --- p.83 / Chapter 7 --- Conclusion --- p.86 / Reference --- p.89 / Chapter A --- System Installation --- p.92 / Chapter A.1 --- File Organization of TheSys --- p.92 / Chapter A. 1.1 --- API Source Codes (THESYS/API) --- p.93 / Chapter A. 1.2 --- Header Files (THESYS/include) --- p.94 / Chapter A. 1.3 --- Interface Source Codes and Library (THESYS/UI and THESYS/lib) --- p.95 / Chapter A. 1.4 --- System Generated Files --- p.96 / Chapter A.2 --- Setup TheSys with its User Interfaces --- p.97 / Chapter A.3 --- Employ TheSys with Customized Applications --- p.97 / Chapter B --- API Description --- p.99 / Chapter B.1 --- Thesaurus Management --- p.102 / Chapter B.2 --- Semantic Classifications --- p.107 / Chapter B.3 --- Entry Terms --- p.116 / Chapter B.4 --- Semanemes --- p.123 / Chapter B.5 --- Relationship Types and Relationship Links --- p.130 / Chapter B.6 --- Relationship Inference --- p.141 / Chapter B.7 --- Weighting Schemes --- p.145

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Typescript, etc. / Digitized by Kansas Correctional Industries

The focus of this thesis is on systems that employ both flash and magnetic disks as storage media. Considering the widely disparate I/O costs of flash disks currently on the market, our approach is a cost-aware one: we explore techniques that exploit the I/O costs of the underlying storage devices to improve I/O performance. We also study the asymmetric I/O properties of magnetic and flash disks and propose algorithms that take advantage of this asymmetry. Our work is geared towards database systems; however, most of the ideas presented in this thesis can be generalised to any data-intensive application. For the case of low-end, inexpensive flash devices with large capacities, we propose using them at the same level of the memory hierarchy as magnetic disks. In such setups, we study the problem of data placement, that is, on which type of storage medium each data page should be stored. We present a family of online algorithms that can be used to dynamically decide the optimal placement of each page. Our algorithms adapt to changing workloads for maximum I/O efficiency. We found that substantial performance benefits can be gained with such a design, especially for queries touching large sets of pages with read-intensive workloads. Moving one level higher in the storage hierarchy, we study the problem of buffer allocation in databases that store data across multiple storage devices. We present our novel approach to per-device memory allocation, under which both the I/O costs of the storage devices and the cache behaviour of the data stored on each medium determine the size of the main memory buffers that will be allocated to each device. Towards informed decisions, we found that the ability to predict the cache behaviour of devices under various cache sizes is of paramount importance. In light of this, we study the problem of efficiently tracking the hit ratio curve for each device and introduce a lowoverhead technique that provides high accuracy. The price and performance characteristics of high-end flash disks make them perfectly suitable for use as caches between the main memory and the magnetic disk(s) of a storage system. In this context, we primarily focus on the problem of deciding which data should be placed in the flash cache of a system: how the data flows from one level of the memory hierarchy to the others is crucial for the performance of such a system. Considering such decisions, we found that the I/O costs of the flash cache play a major role. We also study several implementation issues such as the optimal size of flash pages and the properties of the page directory of a flash cache. Finally, we explore sorting in external memory using external merge-sort, as the latter employs access patterns that can take full advantage of the I/O characteristics of flash memory. We study the problem of sorting hierarchical data, as such is necessary for a wide variety of applications including archiving scientific data and dealing with large XML datasets. The proposed algorithm efficiently exploits the hierarchical structure in order to minimize the number of disk accesses and optimise the utilization of available memory. Our proposals are not specific to sorting over flash memory: the presented techniques are highly efficient over magnetic disks as well.

Theories of lexical storage differ in how entries are encoded in the lexicon. Exemplar-based accounts posit that lexical items are stored with detailed acoustic information, while abstract accounts argue that fine acoustic detail is removed and an item is stored in more basic phonological units. These separate accounts make distinct predictions about cross-linguistic and bilingual perception. Studies asking participants to compare non-native vowels have shown that people tend to associate multiple non-native phonemes to a single L1 phoneme when the contrast between the two does not exist in the L1. However, several studies have shown that the ability to discriminate sounds is never lost. A line of research has focused on how bilinguals perceive contrasts in their second language. One such study, Pallier et al. (2001) looked at early bilinguals of Spanish and Catalan, testing whether the native Spanish speakers, who were highly proficient in Catalan, perceived certain Catalan minimal pairs as homophones. Importantly, the contrasts of these minimal pairs were exclusive to Catalan. The native Spanish bilinguals heard pairs such as /neta/-/nεta/ in an audio-only lexical decision task (LDT), and showed responses to the second item that were not significantly different from actual item repetitions (i.e., /neta/-/neta/). These results were taken as evidence in favor of abstractionist models of lexical storage. This study was based on Pallier et al, (2001), examining instead the perceptions of heritage speakers of Spanish (HSSs) in the U.S., children of native Spanish speakers who get early and sustained exposure to their second language, English. Unlike the bilinguals studied in Pallier et al., heritage bilinguals receive little linguistic or social support for development of their first language. The L1 proficiency of adult heritage bilinguals varies considerably. In this study, a group of these HSSs participated in an LDT testing their perception of English-exclusive phonemic vowel contrasts (i.e., peak-pick). It was hypothesized that, like Pallier et al.'s highly proficient bilinguals, HSSs would show responses to the second item of these minimal pairs as if it were a repetition of the first. Results of the LDT did not confirm the hypothesis. The heritage Spanish speakers did not perform significantly differently from the native English controls on English-specific contrasts (p = .065), and it was found that the native English speakers showed higher priming on these minimal pairs than HSSs. These results run counter to those of previous studies, and may disfavor an abstract account of lexical storage. At the very least, the construct validity of this methodology is questionable when the control and experimental participants reverse hypothesized behavior.

As California continues to integrate more renewable energy into its electrical system, the state has experienced a corresponding rise in photovoltaic system installations. PV arrays are a unique source of power generation in that they are affected by the location of the sun, shading, and temperature changes. These characteristics make solar one of the most highly variable forms of renewable energy. In order to improve solar power’s consistency, PV systems require a supplemental source of power. The primary focus of this paper is to determine if distributed energy storage systems can be used to reduce the effect of solar intermittency. This paper examines the test data and system specifications of an experimental DESS. The benefits of using a DESS in a PV system are further studied using computer simulation modeling. This paper also shows through computer simulations how a maximum power point tracker can increase a PV array’s power output. The results of this thesis demonstrate that DESS’s are capable of smoothing out highly variable load profiles caused by intermittent solar power.