A pulsed NMR study of He adsorbed on bare and 4He preplated MCM-41 using DC SUID detection

This thesis describes two low field NMR and vapour pressure experiments of helium adsorbed in the pores of the mesoporous powder substrate MCM-41 at temperatures down to 1.5K. A sensitive broadband DC SQUID based spectrometer was developed to facilitate these measurements with a coupled energy sensitivity of 30 h at 1.5K. NMR relaxation times T1 and T∗ 2 were measured as a function of temperature for frequencies from 80 to 240 kHz. MCM-41 is an amorphous silica formed of a hexagonal array of straight regular pores. For our sample the pore diameter is 2.3 nm and length is ∼ 300 nm, equal to the grain size. The substrate was characterised by 4He vapour pressure isotherms performed using an in-situ pressure gauge with a resolution of 1 μbar. Layer completion and full pores were determined from the isothermal compressibility of the adsorbed film. In the first NMR experiment 3He was adsorbed onto the bare pore walls of MCM-41 from coverages approaching monolayer completion up to full pores. The adsorbed helium was found to form a 2D film which exhibited significant motional narrowing of the NMR line at low temperatures due to quantum tunnelling. In the second experiment the substrate was initially preplated with just over a monolayer of 4He before a low 3He coverage of 0.01 monolayer was added. Subsequently the preplating coverage was varied whilst the 3He coverage was held constant at 0.02 monolayer. Under these stringent conditions a transition to a quasi-1D state is expected to occur at temperatures below 100mK where Luttinger liquid behaviour is predicted. Nuclear magnetic resonance is a powerful tool for probing the necessary dynamic and magnetic properties of systems to determine the Luttinger liquid parameters. The 3He in this helium mixtures experiment was also found to behave as a 2D film, where at these low coverages the relaxation times were independent of the 3He density. A correlation was found between the relaxation times and the isothermal compressibility of the film. The results of the NMR experiments have been used to make proposals on the design and fabrication of a new experiment with a coolable cell capable of reaching temperatures low enough to observe a transition to 1D. Cooling this substrate to temperatures far below 1K is not trivial and low resonant frequencies are required to avoid excessively heating the sample during NMR pulsing.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

A meta-analytic review of stand-alone interventions to improve body image

Objective Numerous stand-alone interventions to improve body image have been developed. The present review used meta-analysis to estimate the effectiveness of such interventions, and to identify the specific change techniques that lead to improvement in body image. Methods The inclusion criteria were that (a) the intervention was stand-alone (i.e., solely focused on improving body image), (b) a control group was used, (c) participants were randomly assigned to conditions, and (d) at least one pretest and one posttest measure of body image was taken. Effect sizes were meta-analysed and moderator analyses were conducted. A taxonomy of 48 change techniques used in interventions targeted at body image was developed; all interventions were coded using this taxonomy. Results The literature search identified 62 tests of interventions (N = 3,846). Interventions produced a small-to-medium improvement in body image (d+ = 0.38), a small-to-medium reduction in beauty ideal internalisation (d+ = -0.37), and a large reduction in social comparison tendencies (d+ = -0.72). However, the effect size for body image was inflated by bias both within and across studies, and was reliable but of small magnitude once corrections for bias were applied. Effect sizes for the other outcomes were no longer reliable once corrections for bias were applied. Several features of the sample, intervention, and methodology moderated intervention effects. Twelve change techniques were associated with improvements in body image, and three techniques were contra-indicated. Conclusions The findings show that interventions engender only small improvements in body image, and underline the need for large-scale, high-quality trials in this area. The review identifies effective techniques that could be deployed in future interventions

Evidence for a Spatially Modulated Superfluid Phase of ³He under Confinement

In superfluid $^3$He-B confined in a slab geometry, domain walls between regions of different order parameter orientation are predicted to be energetically stable. Formation of the spatially-modulated superfluid stripe phase has been proposed. We confined $^3$He in a 1.1 $\mu$m high microfluidic cavity and cooled it into the B phase at low pressure, where the stripe phase is predicted. We measured the surface-induced order parameter distortion with NMR, sensitive to the formation of domains. The results rule out the stripe phase, but are consistent with 2D modulated superfluid order.Comment: 9 pages, 9 figure

Generalised max entropy classifiers

In this paper we propose a generalised maximum-entropy classification framework, in which the empirical expectation of the feature functions is bounded by the lower and upper expectations associated with the lower and upper probabilities associated with a belief measure. This generalised setting permits a more cautious appreciation of the information content of a training set. We analytically derive the KarushKuhn-Tucker conditions for the generalised max-entropy classifier in the case in which a Shannon-like entropy is adopted

Shallow-water hydrothermal venting linked to the Palaeocene–Eocene Thermal Maximum

The Palaeocene–Eocene Thermal Maximum (PETM) was a global warming event of 5–6 °C around 56 million years ago caused by input of carbon into the ocean and atmosphere. Hydrothermal venting of greenhouse gases produced in contact aureoles surrounding magmatic intrusions in the North Atlantic Igneous Province have been proposed to play a key role in the PETM carbon-cycle perturbation, but the precise timing, magnitude and climatic impact of such venting remains uncertain. Here we present seismic data and the results of a five-borehole transect sampling the crater of a hydrothermal vent complex in the Northeast Atlantic. Stable carbon isotope stratigraphy and dinoflagellate cyst biostratigraphy reveal a negative carbon isotope excursion coincident with the appearance of the index taxon Apectodinium augustum in the vent crater, firmly tying the infill to the PETM. The shape of the crater and stratified sediments suggests large-scale explosive gas release during the initial phase of vent formation followed by rapid, but largely undisturbed, diatomite-rich infill. Moreover, we show that these vents erupted in very shallow water across the North Atlantic Igneous Province, such that volatile emissions would have entered the atmosphere almost directly without oxidation to CO2 and at the onset of the PETM

iAggregator: Multidimensional Relevance Aggregation Based on a Fuzzy Operator

International audienceRecently, an increasing number of information retrieval studies have triggered a resurgence of interest in redefining the algorithmic estimation of relevance, which implies a shift from topical to multidimensional relevance assessment. A key underlying aspect that emerged when addressing this concept is the aggregation of the relevance assessments related to each of the considered dimensions. The most commonly adopted forms of aggregation are based on classical weighted means and linear combination schemes to address this issue. Although some initiatives were recently proposed, none was concerned with considering the inherent dependencies and interactions existing among the relevance criteria, as is the case in many real-life applications. In this article, we present a new fuzzy-based operator, called iAggregator, for multidimensional relevance aggregation. Its main originality, beyond its ability to model interactions between different relevance criteria, lies in its generalization of many classical aggregation functions. To validate our proposal, we apply our operator within a tweet search task. Experiments using a standard benchmark, namely, Text REtrieval Conference Microblog,1 emphasize the relevance of our contribution when compared with traditional aggregation schemes. In addition, it outperforms state-of-the-art aggregation operators such as the Scoring and the And prioritized operators as well as some representative learning-to-rank algorithms

The Role of Sensorimotor Difficulties in Autism Spectrum Conditions

AbstractIn addition to difficulties in social communication, current diagnostic criteria for autism spectrum conditions (ASC) also incorporate sensorimotor difficulties; repetitive motor movements and atypical reactivity to sensory input (APA, 2013). This paper explores whether sensorimotor difficulties are associated with the development and maintenance of symptoms in ASC. Firstly, studies have shown difficulties coordinating sensory input into planning and executing movement effectively in ASC. Secondly, studies have shown associations between sensory reactivity and motor coordination with core ASC symptoms, suggesting these areas each strongly influence the development of social and communication skills. Thirdly, studies have begun to demonstrate that sensorimotor difficulties in ASC could account for reduced social attention early in development, with a cascading effect on later social, communicative and emotional development. These results suggest that sensorimotor difficulties not only contribute to non-social difficulties such as narrow circumscribed interests, but also to the development of social behaviours such as effectively coordinating eye contact with speech and gesture, interpreting others’ behaviour and responding appropriately. Further research is needed to explore the link between sensory and motor difficulties in ASC, and their contribution to the development and maintenance of ASC