2,781 research outputs found
Carborane-induced deformation of polycyclic aromatic hydrocarbons, and their intriguing emissive properties
Carboranes, C2B10H12, are bulky, icosahedral cluster compounds, with unique molecular bonding and electronic properties. Since their discovery in the middle of the 19th century, they have been studied and used in a wide range of chemical fields, with the aims of exploiting their excellent thermal and chemical stability, electron-withdrawing capability, and, more recently, their ability to act as modifiers and promotors of photoluminescence (PL). The effects of carboranes on PL have now been widely reported in the literature, but questions remain about the underlying processes dictating these behaviours. This work is an attempt to answer some of those questions.
In this thesis, the three structural isomers of carborane (ortho, meta and para) have been incorporated into a range of linear and non-linear aromatic systems, forming highly sterically strained structures. This phenomenon correlates with reduced carborane rotation, as determined by DFT and NMR investigations. All carboranes studied are fluorescent, showing local emission (LE) from the aromatic moiety, however the ortho-carborane compounds also demonstrate multi-emissive behaviour, as the carborane introduces a delocalised emissive species, associated with intramolecular charge-transfer (ICT) and twisted-ICT (TICT) states, the latter of which occurs when the carboranyl C-C bond is perpendicular to the aromatic plane. By introducing phenyl groups to ortho-carborane, it was shown that the ground state could be tuned to favour TICT formation, through favourable π-π interactions between the aromatic substituents ‘locking’ the C-C bond in the perpendicular arrangement.
Chrysene and phenanthrene-based ortho-carborane compounds were found to exhibit a peculiar, concentration-dependent, low-energy emissive peak. Through detailed temperature-dependent optical studies, these emissive excited states were assigned to excimers, the first time such species, involving a carborane in a charge-transfer state, has been observed.
In aggregated states, formed in bad solvents, the PL intensity for the meta and para-carboranes is reduced, but for the ortho-carborane compounds the intensity increases enormously, as a result of aggregation-induced emission (AIE). AIE is determined to be as a result of TICT emissive species, where the excited state is localised inside ortho-carborane, reducing non-radiative decay routes and boosting PL quantum yield. The aggregates were directly imaged with a combination of scanning and transmission electron microscopy (SEM and TEM respectively) and were found to form spherical nanoparticles, with evidence of crystallinity.Open Acces
Balancing of Resonant Differential Coils for Broadband Inductive Sensor Systems
Differential coils are frequently implemented in inductive sensing systems. They can be considered as a single coil that is made up of two or more subcoils, wound in series opposition. They can be used onthe transmit or receive side of measurement systems, and, if designed correctly, ensure no coupling between coils under background conditions. By cancelling background coupling, the receive electronics only needs to be able to measure the change in coupling produced by a target. This allows for a more efficient use of the dynamic range, and for larger receive-side amplifier gain, thereby improving SNR. When subcoils are not electrically similar, it can be hard to engineer the coil to be perfectly balanced across a wide bandwidth. This paper presents an analytical model of a resonant differential coil pair that is tested and applied on a planar metal detector for the detection of buried objects. The model demonstrates the capability to balance an arbitrary differential coil pair, which has a broad applicability across a range of inductive sensor applications such as metal detection and non-destructive testing. The method is applied to the practical system. The results show that the correction resulting from this method ensures a stable balance across a significantly enhanced bandwidth. In the case studied here, the bandwidth of the experimental system is increased from 20 kHz to 90 kHz
Stimulation of the dorsolateral prefrontal cortex impacts conflict resolution in Level-1 visual perspective taking
White Light Flare Continuum Observations with ULTRACAM
We present sub-second, continuous-coverage photometry of three flares on the
dM3.5e star, EQ Peg A, using custom continuum filters with WHT/ULTRACAM. These
data provide a new view of flare continuum emission, with each flare exhibiting
a very distinct light curve morphology. The spectral shape of flare emission
for the two large-amplitude flares is compared with synthetic ULTRACAM
measurements taken from the spectra during the large 'megaflare' event on a
similar type flare star. The white light shape during the impulsive phase of
the EQ Peg flares is consistent with the range of colors derived from the
megaflare continuum, which is known to contain a Hydrogen recombination
component and compact, blackbody-like components. Tentative evidence in the
ULTRACAM photometry is found for an anti-correlation between the emission of
these components.Comment: 8 pages, 3 figures. Proceedings of the 16th Workshop on Cool Stars,
Stellar Systems, and the Sun (PASP conference series, in press
Redescription of Anaschisma (Temnospondyli: Metoposauridae) from the Late Triassic of Wyoming and the phylogeny of the Metoposauridae
Metoposaurids are non-marine temnospondyls that are among the most common constituents of Late Triassic deposits, but despite their abundance, the evolutionary relationships of the group are poorly resolved and have not been fully addressed with modern phylogenetic methods. The genus Anaschisma is one of a number of poorly resolved metoposaurid taxa and was erected to describe two species from the Popo Agie Formation (Carnian) in Wyoming: Anaschisma browni and Anaschisma brachygnatha. Since being named, the genus has been repeatedly synonymized and separated with other taxa in the context of broader revisions of the Metoposauridae. At present, Anaschisma is considered to be an indeterminate metoposaurid. Extensive descriptive work of metoposaurids since the erection of Anaschisma in 1905 and the last taxonomic review of the clade in 1993, including the naming of several new taxa and the reappraisal of several others, has generated a sufficiently detailed database through which to re-evaluate the taxonomy of the Metoposauridae as part of the analysis of phylogenetic relationships of Anaschisma. Here we reappraise and redescribe the holotypes of A. browni and A. brachygnatha to determine their taxonomic status and relationships in the context of an updated and revised metoposaurid phylogenetic framework. Anaschisma browni and Anaschisma brachygnatha are synonymized under the former species, as all previously listed diagnostic differences are compatible with intraspecific variation. Additionally, the well-known Koskinonodon perfectus is found to be a junior synonym of Anaschisma browni, which takes taxonomic precedence given its earlier description. Poor phylogenetic resolution of the Metoposauridae is likely the product of marked morphological conservatism within the clade and limited character sampling, although some patterns of regional clustering are apparent from the analysis
Oocyte-follicle interactions
The ovarian follicle is an individual functional unit that provides the optimal environment for the oocyte within to develop. This thesis outlines the research in the field of ovarian follicular dynamics that has already been established, and further develops these findings to explore in greater detail the relationship between the oocyte and its environment, both in an in vitro and in vivo setting, using a variety of species. The first major research area involved studying the role of oocyte-secreted factors, which was examined using a series of dose response experiments. These were performed using an ovine granulosa cell culture model, and elucidated a possible role for a collaborative action of BMP15 and GDF9 in the promotion of oestradiol synthesis, while inhibiting production of progesterone in this species. This finding was then further investigated using an ovine in vivo immune-neutralisation study, the endocrine and histological results of which confirmed these findings in a proportion of these animals, although this study was limited by the animals appearing to have been in seasonal anoestrus.
The second major topic that was investigated was based around the ovarian microenvironment, in terms of angiogenesis and hypoxia. Again, ovine granulosa cell cultures were used, in this instance to examine the effect of hypoxic conditions on steroid hormone production. These experiments indicated that somatic cell steroid hormone production is likely to be compromised by a hypoxic environment, and therefore that the provision of oxygen through a local blood supply may be a vital requirement for these cells.
To investigate the relevance of studying ovarian blood supply and physiology in a clinical setting, perfusion studies were carried out based on a series of bovine phantom experiments, which were used to study the effect of varying flow rate on the parameters routinely measured using this technology. The routine clinical ultrasonographic methods of ovarian assessment such as 4D ViewTM, SonoAVCTM and VOCAL were also examined, based on bovine phantom experiments, revealing possible weaknesses in the data provided by ultrasound that are increasingly relied upon in the clinical setting.
Finally, a clinical trial was carried out to try and encompass all of the findings of the in vitro and in vivo work, in order to place these theories into context in a human IVF setting. This work was unfortunately limited severely by a lack of patient numbers, but some interesting results were observed with regard to oocyte developmental potential relationships with follicular fluid and somatic cell factors, as well as ultrasound measures of peri-follicular blood supply
Close relationship partners of impartial altruists do not report diminished relationship quality and are similarly altruistic
Impartial altruism is often considered a moral ideal but is rare in practice. Instead, generosity typically decreases as social distance increases, a phenomenon termed social discounting. Most people prefer this partiality in their close relationships and view impartial altruists as poorer relationship partners. This suggests real-world impartial altruism may be rare because it reduces—or is perceived to reduce—the quality of close relationships. To investigate this, we compared patterns of generosity and social relationship quality in a rare sample of individuals who had engaged in extraordinary real-world impartial altruism (altruistic kidney donors; n = 59) and their closest friend or family member (n = 59) to controls (n = 71) and their closest others (n = 71). We designed a direct test of third-party social discounting, which experimentally confirmed real-world altruists’ impartiality, finding that they are more likely than controls to split resources evenly between close and distant others rather than favoring close others. However, we found no statistically significant association between impartial altruism and social relationship quality. Instead, we found that altruists’ close others also show more impartiality than controls. This suggests value homophily (shared moral values) among altruists, which may represent a protective factor for close relationships in the context of impartial altruism
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