Polyfluorinated Aromatic Systems for Liquid Crystal Display Applications

This thesis is concerned with the syntheses of a range of polyfluorinated biphenyl ether derivatives for use as dopants in commercial LC materials, so that overall display performance may be improved. Reactions of hexa– and penta–fluorobenzene with sodium phenoxide in polar aprotic solvents (MeCN, THF) and under mild reaction conditions (45–50 °C, 4–65 h) afford moderate yields of pentafluorophenoxybenzene and 1,2,4,5–tetrafluoro–3–phenoxybenzene, respectively. SNAr reactions of sodium phenoxide with less electrophilic 1,2,3,4–tetra– and 1,2,3,5–tetra–fluorobenzene under microwave irradiation (150 °C, 30 mins) furnish good yields of 1,2,4–trifluoro–3–phenoxybenzene and 1,2,5–trifluoro–3–phenoxybenzene, respectively. Similar SNAr methodology is used to access a series of 1,2,4,5–tetra– and 1,2,4–tri–fluoro–3–(4–n–alkylphenoxy)benzene derivatives in good yield. A two–step SNAr–hydrodebromination procedure to access trifluorophenoxybenzene systems from highly electrophilic dibromotetrafluorobenzene derivatives is also developed, and provides a practical synthetic route to 1,2,4–trifluoro–5–phenoxybenzene. Finally, a three–step SNAr–diazotisation–reductive diazotisation pathway is developed for the syntheses of difluorophenoxybenzene derivatives, which are not accessible by direct SNAr reactions of sodium phenoxide with corresponding trifluorobenzene derivatives. The use of these polyfluorinated biphenyl ether systems as dopants for LC materials is assessed by a range of electro–optical measurements. Highly fluorinated nitrobenzene systems are compatible substrates for palladium–catalysed Suzuki–Miyaura and Heck–type cross–coupling reactions involving C–F bond activation. Cross–coupling reactions of pentafluoronitrobenzene with a range of boronic acids and protected ester equivalents bearing electron–withdrawing or electron–donating substituents in the meta– and para– positions, with respect to the C–B bond, are described. For example, Reaction of pentafluoronitrobenzene with 5,5–dimethyl–2–phenyl–1,3,2–dioxaborinane in the presence of catalytic quantities of Pd(PPh3)4 and using KF/alumina as the preferred base (DMF, 150 °C, 15 mins, μW) affords 2,3,4,5–tetrafluoro–6–nitrobiphenyl in good yield (80 %). The nitro group is crucial to the success of the cross–coupling processes and is believed to facilitate the oxidative addition step by directing the palladium catalyst into the adjacent C–F bond by a predominantly SNAr–type mechanism

The solubility of gases in aqueous alcohols

Extensive measurements have been made of the solubilities of the five gases helium, hydrogen, argon, oxygen, and carbon dioxide, in ethanol/water and in t-butanol/water mixtures over the whole of their concentration range, and throughout the temperature interval 4°C to 61°C. The measurements were carried out by the less usual flowing-film technique, which has been described in detail. It depends on the rapid establishment of equilibrium between a gas and its solvent while the liquid flows in a stable, thin film down the walls of a tube enclosing the gas. Results were reproducible, corroborated at relevant points by results obtained by other workers from the other more common mixing techniques. These solubility measurements were used to investigate the effects of foreign molecules on the structure of liquid water. To this end standard thermodynamic functions were calculated for each of the solubilities, having programmed a computer to carry out the arithmetic. Graphs were drawn to show the relationship of the functions to the gas dissolved, the alcohol mixed with the water, and the temperature. Most information was obtained from the enthalpy and entropy changes in the systems, and certain features of their dependence on the concentration of the alcohol. A mixture model for water structure has been described, and some aspects of it elucidated. The size of any molecule introduced into water has been shown to be an important factor in its influence on the water structure. A quantitative estimate has been made of the effect of temperature on the mole fraction of water molecules which are completely hydrogen-bonded, called "icebergs" or "clusters". An estimate has also been made of the relative amounts of different-sized clusters at various temperatures, and it has been concluded that as the temperature rises, there is a selective and progressive destruction of the largest clusters. Finally, a mechanism has been suggested for the stabilisation of clusters by added solute molecules, which depends on their efficiency at preventing thermal disruption of the clusters

Publication Skills Development in the Sciences: Decision Support for Effective Program Design

Frente al incremento de la presión en investigadores científicos a escribir artículos para revistas indexadas, hacen falta estudios sobre maneras rentables de diseñar programas de formación que responden a variables contextuales, entre ellos la lengua materna de los participantes. En este estudio proponemos una matriz de cuatro escalas descriptivas para la clasificación de grupos de formación, basada en el análisis detallado de talleres impartidos por equipos interdisciplinarios en una amplia gama de contextos institucionales y lingüísticos utilizando un enfoque colaborativo basado en el análisis de géneros y la lingüística de corpus. La clasificación resultante de los participantes y el contexto permite la optimización del equipo de formación y la toma de decisiones eficaces sobre el diseño del programa.In the face of expanding pressure for science researchers to write articles for refereed journals, research is needed on ways to design cost-effective training programs that respond to contextual variables including language backgrounds. Here we propose a matrix of four descriptor scales for classifying groups to be trained, based on detailed analysis of workshops taught by interdisciplinary teams in a wide range of institutional and linguistic contexts using a collaborative approach grounded in genre analysis and corpus linguistics. The resulting classification of participants and context enable optimisation of the training team and effective decision-making about program design

The color of a Dalmatian's spots: Linkage evidence to support the TYRP1 gene

BACKGROUND: The distinctive coat pattern of a Dalmatian is the result of the interaction of several loci. While the encoded function of these genes is not fully understood, it is known the Piebald, Ticking, and Flecking loci interact to produce the Dalmatian's classic pigmented spots on a white background. The color of the pigmented spots in purebred Dalmatians can either be black or liver, but the locus responsible for color determination is unknown. Studies have been conducted to determine the underlying genes involved in coat color determination in the dog, e.g., in the Labrador Retriever, but none to date have addressed black versus liver in the Dalmatian. RESULTS: A genome scan was conducted in a multi-generational kindred of Dalmatians segregating black and liver spot color. Linkage analysis was performed using a total of 113 polymorphic microsatellite markers from the kindred. Linkage was found between spot color and a single microsatellite marker, FH2319 (LOD = 12.5) on chromosome 11. CONCLUSION: The TYRP1 (Brown) locus is located at position 50.1 Mb on chromosome 11, which is approximately 0.4 Mb from marker FH2319. Given the recent characterization of TYRP1 genetic variations in the dog and the linkage evidence reported here, TYRP1 is likely responsible for the spot color variation of black versus liver seen in the Dalmatian

Heterogeneity in ess transcriptional organization and variable contribution of the Ess/Type VII protein secretion system to virulence across closely related <em>Staphylocccus aureus </em>strains

The Type VII protein secretion system, found in Gram-positive bacteria, secretes small proteins, containing a conserved W-x-G amino acid sequence motif, to the growth medium. Staphylococcus aureus has a conserved Type VII secretion system, termed Ess, which is dispensable for laboratory growth but required for virulence. In this study we show that there are unexpected differences in the organization of the ess gene cluster between closely related strains of S. aureus. We further show that in laboratory growth medium different strains of S. aureus secrete the EsxA and EsxC substrate proteins at different growth points, and that the Ess system in strain Newman is inactive under these conditions. Systematic deletion analysis in S. aureus RN6390 is consistent with the EsaA, EsaB, EssA, EssB, EssC and EsxA proteins comprising core components of the secretion machinery in this strain. Finally we demonstrate that the Ess secretion machinery of two S. aureus strains, RN6390 and COL, is important for nasal colonization and virulence in the murine lung pneumonia model. Surprisingly, however, the secretion system plays no role in the virulence of strain SA113 under the same conditions

Amyloid Precursor Proteins Are Dynamically Trafficked and Processed during Neuronal Development

Proteolytic processing of the Amyloid Precursor Protein (APP) produces beta-amyloid (Aβ) peptide fragments that accumulate in Alzheimer’s Disease (AD), but APP may also regulate multiple aspects of neuronal development, albeit via mechanisms that are not well understood. APP is a member of a family of transmembrane glycoproteins expressed by all higher organisms, including two mammalian orthologs (APLP1 and APLP2) that have complicated investigations into the specific activities of APP. By comparison, insects express only a single APP-related protein (APP-Like, or APPL) that contains the same protein interaction domains identified in APP. However, unlike its mammalian orthologs, APPL is only expressed by neurons, greatly simplifying an analysis of its functions in vivo. Like APP, APPL is processed by secretases to generate a similar array of extracellular and intracellular cleavage fragments, as well as an Aβ-like fragment that can induce neurotoxic responses in the brain. Exploiting the complementary advantages of two insect models (Drosophila melanogaster and Manduca sexta), we have investigated the regulation of APPL trafficking and processing with respect to different aspects of neuronal development. By comparing the behavior of endogenously expressed APPL with fluorescently tagged versions of APPL and APP, we have shown that some full-length protein is consistently trafficked into the most motile regions of developing neurons both in vitro and in vivo. Concurrently, much of the holoprotein is rapidly processed into N- and C-terminal fragments that undergo bi-directional transport within distinct vesicle populations. Unexpectedly, we also discovered that APPL can be transiently sequestered into an amphisome-like compartment in developing neurons, while manipulations targeting APPL cleavage altered their motile behavior in cultured embryos. These data suggest that multiple mechanisms restrict the bioavailability of the holoprotein to regulate APPL-dependent responses within the nervous system. Lastly, targeted expression of our double-tagged constructs (combined with time-lapse imaging) revealed that APP family proteins are subject to complex patterns of trafficking and processing that vary dramatically between different neuronal subtypes. In combination, our results provide a new perspective on how the regulation of APP family proteins can be modulated to accommodate a variety of cell type-specific responses within the embryonic and adult nervous system

Critical Issues For Understanding Particle Acceleration in Impulsive Solar Flares

This paper, a review of the present status of existing models for particle acceleration during impulsive solar flares, was inspired by a week-long workshop held in the Fall of 1993 at NASA Goddard Space Flight Center. Recent observations from Yohkoh and the Compton Gamma Ray Observatory, and a reanalysis of older observations from the Solar Maximum Mission, have led to important new results concerning the location, timing, and efficiency of particle acceleration in flares. These are summarized in the first part of the review. Particle acceleration processes are then discussed, with;particular emphasis on new developments in stochastic acceleration by magnetohydrodynamic waves and direct electric field acceleration by both sub- and super-Dreicer electric fields. Finally, issues that arise when these mechanisms are incorporated into the large-scale flare structure are considered. Stochastic and super-Dreicer acceleration may occur either in a single large coronal reconnection site or at multiple \u27\u27fragmented\u27\u27 energy release sites. Sub-Dreicer acceleration requires a highly filamented coronal current pattern. A particular issue that needs to be confronted by all theories is the apparent need for large magnetic field strengths in the flare energy release region

The gamma-ray giant flare from SGR1806-20: Evidence for crustal cracking via initial timescales

We report here on serendipitous observations of the intense gamma-ray flare from SGR 1806-20 that occured on 27 December 2004. Unique data from the Cluster and Double Star-2 satellites, designed to study the Earth's magnetosphere, provide the first observational evidence of three separate timescales within the early (first 100ms) phases of this class of events. These observations reveal that, in addition to the initial very steep (<0.25ms) X-ray onset, there is firstly a 4.9ms exponential rise timescale followed by a continued exponential rise in intensity on a timescale of 70ms. These three timescales are a prominent feature of current theoretical models including the timescale (several ms) for fracture propagation in the crust of the neutron star.Comment: 10 pages including 2 figures Ap J Letters in press, May 200

Implications of the 2019–2020 megafires for the biogeography and conservation of Australian vegetation

Australia's 2019–2020 'Black Summer' bushfires burnt more than 8 million hectares of vegetation across the south-east of the continent, an event unprecedented in the last 200 years. Here we report the impacts of these fires on vascular plant species and communities. Using a map of the fires generated from remotely sensed hotspot data we show that, across 11 Australian bioregions, 17 major native vegetation groups were severely burnt, and up to 67–83% of globally significant rainforests and eucalypt forests and woodlands. Based on geocoded species occurrence data we estimate that >50% of known populations or ranges of 816 native vascular plant species were burnt during the fires, including more than 100 species with geographic ranges more than 500 km across. Habitat and fire response data show that most affected species are resilient to fire. However, the massive biogeographic, demographic and taxonomic breadth of impacts of the 2019–2020 fires may leave some ecosystems, particularly relictual Gondwanan rainforests, susceptible to regeneration failure and landscape-scale decline