There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

Deposits of clastic carbonate-dominated (calciclastic) sedimentary slope systems in the rock record have been identified mostly as linearly-consistent carbonate apron deposits, even though most ancient clastic carbonate slope deposits fit the submarine fan systems better. Calciclastic submarine fans are consequently rarely described and are poorly understood. Subsequently, very little is known especially in mud-dominated calciclastic submarine fan systems. Presented in this study are a sedimentological core and petrographic characterisation of samples from eleven boreholes from the Lower Carboniferous of Bowland Basin (Northwest England) that reveals a >250 m thick calciturbidite complex deposited in a calciclastic submarine fan setting. Seven facies are recognised from core and thin section characterisation and are grouped into three carbonate turbidite sequences. They include: 1) Calciturbidites, comprising mostly of highto low-density, wavy-laminated bioclast-rich facies; 2) low-density densite mudstones which are characterised by planar laminated and unlaminated muddominated facies; and 3) Calcidebrites which are muddy or hyper-concentrated debrisflow deposits occurring as poorly-sorted, chaotic, mud-supported floatstones. These

Phd by thesis

PEEK Biomaterials in Trauma, Orthopedic, and Spinal Implants

Conductive polymers: towards a smart biomaterial for tissue engineering.

Epoxies are widely used materials, especially in high voltage insulation for its mechanical and dielectric properties. Boron Nitride is an attractive filler because of its high insulating properties associated with a high thermal conductivity. Nanometric Silica used as filler is actually widely studied in the literature and enhancement of dielectric breakdown and insulating properties has been shown. Using a combination of these two fillers in an epoxy matrix may produce a new material with improved properties. Samples containing only micrometric filler (Boron Nitride), only nanometric filler (Silica) and both fillers were prepared by gravity moulding. A pure epoxy sample was also prepared to quantify the enhancement properties. Broadband Dielectric Spectroscopy was used to study the influence of nanoparticles on the relaxation mechanisms in the composites. An additional relaxation peak was highlighted for samples containing nanosilica between the local β relaxation, associated with crankshaft motions of the hydroxylether groups, and the main α relaxation, corresponding to glass transition cooperative movements. This relaxation phenomenon was found to be associated with the water bounded at the surface of the silica particles. Further relaxation investigation will be performed to clarify the influence of water, its state and its role.

Dielectric properties of Boron Nitride and silica epoxy composites

Research on polymer nanocomposites promises to create a new class of materials with enhanced dielectric properties. This paper reports on the study of polystyrene systems filled with hexagonal boron nitride (BN) nanoparticles. The polymer nanocomposite materials were produced using a solvent blending procedure, where some of the materials were produced using dichloromethane (DCM) as the solvent and others using isopropyl alcohol (IPA). The breakdown strength was measured at different loading levels; the breakdown strength was found to decrease at the 5 wt% loading level, but increased again with 10 wt% and higher loadings of BN. The effect of exfoliation by solvent choice and sonication on the breakdown strength was investigated; sonication in IPA produced the best results. However, micrographs obtained from the scanning electron microscope show no apparent change of the dispersion of BN in the sonicated systems with the different solvents.

/pdf/the-effect-of-exfoliation-on-the-breakdown-strength-of-252crry8nf.pdf

The effect of exfoliation on the breakdown strength of polystyrene boron nitride composites

This paper takes a novel approach to the problem of characterising electrical ageing in solid dielectrics through ex-situ experiments that seek to reproduce the chemistry of electrical treeing in bulk. Plaque specimens of a range of polymers, including polyethylene, polystyrene, polyether ether ketone and silicone rubber, were subjected to surface ageing via corona discharge in air or in a closed cell where the atmosphere can be controlled and adjusted. The residual products on both the sample surface and the high voltage electrode were characterised by Raman microprobe spectroscopy and the resulting fingerprints were compared with those previously identified within electrical trees. Analysis of the electrodes aged in air and nitrogen revealed varying evidence of sp2 hybridized carbon, and fluorescence, both of which are products previously associated with the processes involved in electrical treeing. The significance of the results is discussed with respect to electrical treeing.

Surface ageing of dielectric materials in a controlled atmosphere: A Raman microprobe study

In the present paper, DC current of polyethylene nanocomposites containing different nanosilica loading ratios, either the untreated or the surface treated using the trimethoxy(propyl)silane coupling agent has been investigated. TGA was used to identify the true loading concentration in the samples and the nanofillers dispersion was studied using SEM. A range of electric field from 10 kV/mm to 50 kV/mm were applied It has been found that two dynamic processes are involved in the current observed over a period of 3 hours. The initial process was dominated by trap filling where a decreasing current versus time was observed. The second process was related to the transient space charge limited current in the unfilled sample but taken over by the effect of nanofillers that shows a continuous current increase versus time rather than peaking. The exact mechanism responsible for the increasing current is not known yet. The influence of surface treatment of the nanofillers on the current is significant, resulting in a lower current comparing with the untreated samples. A current dip has been observed for samples with lower loading concentration, supporting the deep trap concept.

/pdf/dc-current-in-nanosilica-based-polyethylene-nanocomposites-2r04m22i55.pdf

DC current in nanosilica-based polyethylene nanocomposites

There is a wide range of commercial applications that utilize epoxy resin as a main insulation material. Recent studies revealed that changing the molecular structure in epoxy/anhydride systems, by the introduction of a reactive diluent, can significantly improve the electrical properties. This research is of interest for high voltage applications, because the introduction of these reactive modifiers may provide a means of tailoring the dielectric properties of epoxy resins, such as permittivity and conductivity. The results reported in this work reveal that the addition of a reactive diluents greatly affects the glass transition temperature, Tg, the permittivity, the DC conductivity and the breakdown strength. This can be explained through the reactive diluent leading to a significant modification of the epoxy network, whereby changed free volume caused by the presence of small branches alters the properties of the system. Therefore, the concept described, in principle, may be used to varying material properties in a controlled manner to tailor the properties of epoxy resins.

/pdf/change-in-the-electrical-properties-due-to-modification-of-3j5vcbf4jg.pdf

Alun S. Vaughan

Papers

Dielectric properties of Boron Nitride and silica epoxy composites

The effect of exfoliation on the breakdown strength of polystyrene boron nitride composites

Surface ageing of dielectric materials in a controlled atmosphere: A Raman microprobe study

DC current in nanosilica-based polyethylene nanocomposites

Change in the electrical properties due to modification of the epoxy network structure using reactive diluents