Peter J Heard

A simple device to allow enhanced bandwidths at 850 nm in multimode fibre links for gigabit LANs

Summary form only given. There is currently much interest in gigabit/s datacommunication links for computer LANs. However, due to the low modal bandwidth of installed multimode fibre (MMF), the achievable link lengths are limited. At an operating wavelength of 1300 nm, greater link lengths can be achieved with mode conditioning patch cords which generate an offset launch into the MMF. However, at the alternative operating wavelength of 850 nm, there is currently no equivalent low cost commercial method available that allows restricted mode launch to be achieved. Therefore, there is considerable interest in developing techniques for generating conditioned launch in MMF which can be implemented in a cost-effective manner. A device has been previously reported that used focused ion beam etching to suppress the emission at the centre of the output aperture. However, this technique requires additional processing steps and results in non planar devices. This paper therefore demonstrates a simpler approach for enhancing the performance of these links.

Small Fermi Surface Pockets in Underdoped High Temperature Superconductors: Observation of Shubnikov-de Haas Oscillations in YBa2Cu4O8

A. F. Bangura, J. D. Fletcher, A. Carrington, J. Levallois, M. Nardone, B. Vignolle , P. J. Heard, N. Doiron-Leyraud, D. LeBoeuf, L. Taillefer, S. Adachi, C. Proust and N. E. Hussey H. H. Wills Physics Laboratory, University of Bristol, Tyndall Avenue, BS8 1TL, United Kingdom. Laboratoire National des Champs Magnétiques Pulsés, UMR CNRS-UPS-INSA 5147, Toulouse, France. Département de physique and RQMP, Université de Sherbrooke, Sherbrooke, J1K 2R1, Canada. and Superconducting Research Laboratory, International Superconductivity Center, Shinonome 1-10-13, Tokyo 135, Japan. (Dated: February 1, 2008)

Dry Hybrid Lipid−Silica Microcapsules Engineered from Submicron Lipid Droplets and Nanoparticles as a Novel Delivery System for Poorly Soluble Drugs

We report on the fabrication and characterization of dry hybrid lipid-silica nanoparticle based microcapsules with an internal porous matrix structure for encapsulation of poorly soluble drugs, and their delivery properties (in vitro release and lipolysis and in vivo pharmacokinetics demonstrated for indomethacin as a model drug). Microcapsules were prepared by spray drying of Pickering o/w emulsions containing either negatively or positively charged lipophilic surfactant in the oil phase and hydrophilic silica nanoparticles in the aqueous phase. Effective microcapsule formation is critically dependent on the interfacial structure of the nanoparticle containing emulsions, which are in turn controlled by the surfactant charge and the nanoparticle to lipid ratio. Microcapsules (containing 50-85% oil) can be prepared with 10 times fewer silica nanoparticles when a droplet-nanoparticle charge neutralizing mechanism is operative. Cross-sectional SEM imaging has confirmed the internal porous matrix structure and identified pore sizes in the range 20-100 nm, which is in agreement with BET average pore diameters determined from gas adsorption experiments. Differential scanning calorimetry and X-ray diffraction analysis have confirmed that the model drug indomethacin remains in a noncrystalline form during storage under accelerated conditions (40 degrees C, 75% RH). Dissolution studies revealed a 2-5-fold increase in dissolution efficiency and significantly reduced the time taken to achieve 50% of drug dissolution values (> or =2- or 10-fold) for indomethacin formulated as microcapsules in comparison to o/w submicron emulsions and pure drug, respectively. Orally dosed in vivo studies in rats have confirmed superior pharmacokinetics for the microcapsules. Specifically, the fasted state absolute bioavailability (F) was statistically higher (93.07 +/- 5.09%) (p < 0.05) than for aqueous suspension (53.54 +/- 2.91%) and o/w submicron emulsion (64.57 +/- 2.11%). The microcapsules also showed the highest maximum plasma concentration (C(max)) among the investigated formulations (p < 0.05). In vitro lipolysis showed statistically higher (p < 0.05) fasted digestion (75.8% after 5 min) and drug solubilization (98% after 5 min) in digestive products for microcapsules than o/w emulsions. The hybrid lipid-silica microcapsules improve oral absorption by enhancing lipolysis and drug dissolution.

Deposition and properties of amorphous carbon phosphide films

a Abstract Radio frequency plasma deposition has been used to deposit phosphorus doped diamond-like carbon (DLC) films on Si and quartz substrates, using a gas mixture consisting of CH with additions of 0-90% PH . XPS studies reveal that the films contain 43

Etching characteristics of LiNbO3 in reactive ion etching and inductively coupled plasma

The etching characteristics of congruent LiNbO3 single crystals including doped LiNbO3 and proton-changed LiNbO3 have been studied in reactive ion etching (RIE) and inductively coupled plasma (ICP) etching tools, using different recipes of gas mixtures. The effects of parameters including working pressure, RIE power, and ICP power are investigated and analyzed by measurement of etching depth, selectivity, uniformity, etched surface state, and sidewall profile by means of focused ion beam etching, energy-dispersive x-ray analysis, secondary ion mass spectroscopy, scanning electron microscopy, and surface profilometry. The effects of a sample carrier wafer coating have also been investigated. Optimized processes with high etching rates, good mask selectivity, and a near-vertical profile have been achieved. Ridge waveguides on proton-exchanged LiNbO3 have been fabricated and optically measured.

Thermal mapping of defects in AlGaN∕GaN heterostructure field-effect transistors using micro-Raman spectroscopy

We illustrate the use of micro-Raman mapping to study the local effect of defects on device temperature in active AlGaN∕GaN heterostructure field-effect transistors. Significant temperature rises in active devices, 50–100% above average device temperatures, were identified in the vicinity of defects. Measured temperature distributions were compared to finite difference simulations. Reduced thermal conductivity in the defect vicinity was found to be responsible for the local temperature rises in these devices, combined with possible changes in the current flow distribution.

The extraction of uranium from groundwaters on iron surfaces

The observation of uranium remediation from groundwater onto mild-steel surfaces is reported. Mechanisms for uranium immobilization are proposed.

Mode control in vertical-cavity surface-emitting lasers by post-processing using focused ion-beam etching

Single-mode emission is achieved in previously multimode gain-guided vertical-cavity surface-emitting lasers (VCSELs) by localized modification of the mirror reflectivity using focused ion-beam etching. Reflectivity engineering is also demonstrated to suppress transverse mode emission in an oxide-confined device, reducing the spectral width from 1.2 nm to less than 0.5 nm.

Hybrid lipid–silica microcapsules engineered by phase coacervation of Pickering emulsions to enhance lipid hydrolysis

We report on the fabrication of dry hybrid lipid-silica microcapsules for enhanced lipid hydrolysis using Pickering emulsion templates formed by interfacial nanoparticle-emulsifier electrostatic interaction. The microcapsules are produced by controlled precipitation of emulsion droplets by oppositely charged silica nanoparticles at room temperature. Microcapsule formation is driven by the interfacial structure of the initial Pickering emulsion, which is in turn controlled by the nanoparticle to lipid ratio. In the region of charge reversed, precipitated and aggregated droplets, droplet-nanoparticle networks have been identified by freeze-fracture SEM imaging. The microcapsules have diameters in the range 20-50 mum and contain approximately 65% oil distributed within an internal matrix structure composed of a labyrinth of interconnected pores approximately 20-100 nm. Pore distribution and diameters depend on the silica to nanoparticle ratio that in turn determines droplet coating and stability. The microcapsules facilitate enhanced lipid hydrolysis kinetics, i.e. their pseudo first-order rate constant for lipid hydrolysis is approximately 3 times greater than for equivalent submicron lipid droplets. This behaviour is attributed to the increased oil surface area within the microcapsule due to the specific porous structure that causes rapid release of submicron and micron size oil droplets. The simple route for fabrication of porous microcapsule morphologies may present new opportunities for applications in encapsulation, delivery, coatings, and catalysis.

Investigation into the distribution of ink components throughout printed coated paper: Part 2: Utilising XPS and SIMS

Abstract To maximise the performance of the offset litho printing process it is essential to have an understanding of the spatial arrangement of ink pigment and resin within a dry ink film. This arrangement has an effect on properties such as gloss, roughness and colour density. In the current study, the composition of a magenta process ink film printed onto kaolin coated paper substrates having different pore sizes and densities is investigated. Surface analytical techniques such as X-ray photoelectron spectroscopy (XPS) along with secondary ion mass spectroscopy (SIMS) are useful for investigating this chemical distribution in the ink film. Gentle ion etching was carried out in the z -direction through the ink film into the kaolin substrate to enable a continuous chemical analysis to be obtained. In all cases, both techniques clearly showed the presence of a hydrocarbon resin on the surface of the ink film. It was estimated that the resin thickness was approximately 35–50 nm. XPS gave some evidence that this resin thickness varied with coating porosity and ink film thickness. An initial model for this system is given and results compared with the optical and roughness measurements discussed in part 1 of this paper. SIMS showed that the ink pigment–kaolin interface was rough and it was concluded that this was due to the micro roughness of the kaolin coating. Comparison of the SIMS ink–paper interface with the micro roughness of the coating showed that none of the ink pigment penetrated into the paper coating layer. By comparison, ink films printed onto model non-porous substrates such as a polyester film showed a sharp ink–substrate interface.