Effect of processing variables and bulk composition on the surface composition of spray dried powders of a model food system

The surface composition of food powders created from spray drying solutions containing various ratios of sodium caseinate, maltodextrin and soya oil have been analysed by Electron Spectroscopy for Chemical Analysis. The results show significant enrichment of oil at the surface of particles compared to the bulk phase, and (when the non-oil components only are considered), a significant surface enrichment of sodium caseinate also. The study found evidence of high levels (80%) of surface fat even on particles of food industry grade (92.5%) sodium caseinate containing only 1% fat.

Aptamer-based surface plasmon sensor for thrombin detection

A series of surface plasmonic fibre devices were fabricated using multiple coatings deposited on a lapped section of a single mode fibre and post-fabrication UV laser irradiation processing with a phase mask, producing a surface relief grating structure. These devices showed high spectral sensitivity in the aqueous index regime ranging up to 4000 nm/RIU for wavelength and 800 dB/RIU for intensity. The devices were then coated with human thrombin binding aptamer. Several concentrations of thrombin in buffer solution were made, ranging from 1nM to 1µM. All the concentrations were detectable by the devices demonstrating that sub-nM concentrations may be monitored.

Reaction-driven surface restructuring and selectivity control in allylic alcohol catalytic aerobic oxidation over Pd

Synchronous, time-resolved DRIFTS/MS/XAS cycling studies of the vapor-phase selective aerobic oxidation of crotyl alcohol over nanoparticulate Pd have revealed surface oxide as the desired catalytically active phase, with dynamic, reaction-induced Pd redox processes controlling selective versus combustion pathways.

Bulk and surface switching in Mn-Fe-based Prussian blue analogues

Many Prussian Blue Analogues are known to show a thermally induced phase transition close to room temperature and a reversible, photo-induced phase transition at low temperatures. This work reports on magnetic measurements, X-ray photoemission and Raman spectroscopy on a particular class of these molecular heterobimetallic systems, specifically on Rb0.81Mn[Fe(CN)6]0.95_1.24H2O, Rb0.97Mn[Fe(CN)6]0.98_1.03H2O and Rb0.70Cu0.22Mn0.78[Fe(CN)6]0.86_2.05H2O, to investigate these transition phenomena both in the bulk of the material and at the sample surface. Results indicate a high degree of charge transfer in the bulk, while a substantially reduced conversion is found at the sample surface, even in case of a near perfect (Rb:Mn:Fe=1:1:1) stoichiometry. Thus, the intrinsic incompleteness of the charge transfer transition in these materials is found to be primarily due to surface reconstruction. Substitution of a large fraction of charge transfer active Mn ions by charge transfer inactive Cu ions leads to a proportional conversion reduction with respect to the maximum conversion that is still stoichiometrically possible and shows the charge transfer capability of metal centers to be quite robust upon inclusion of a neighboring impurity. Additionally, a 532 nm photo-induced metastable state, reminiscent of the high temperature Fe(III)Mn(II) ground state, is found at temperatures 50-100 K. The efficiency of photo-excitation to the metastable state is found to be maximized around 90 K. The photo-induced state is observed to relax to the low temperature Fe(II)Mn(III) ground state at a temperature of approximately 123 K.

The method of fundamental solutions for free surface Stefan problems

In this paper, free surface problems of Stefan-type for the parabolic heat equation are investigated using the method of fundamental solutions. The additional measurement necessary to determine the free surface could be a boundary temperature, a heat flux or an energy measurement. Both one- and two-phase flows are investigated. Numerical results are presented and discussed.

Effect of preparation conditions on the formation of the active phase of carbon fiber catalytic systems for the low-temperature oxidation of carbon monoxide

We studied the effects of the composition of impregnating solution and heat treatment conditions on the activity of catalytic systems for the low-temperature oxidation of CO obtained by the impregnation of Busofit carbon-fiber cloth with aqueous solutions of palladium, copper, and iron salts. The formation of an active phase in the synthesized catalysts at different stages of their preparation was examined with the use of differential thermal and thermogravimetric analyses, X-ray diffraction analysis, X-ray photoelectron spectroscopy, and elemental spectral analysis. The catalytic system prepared by the impregnation of electrochemically treated Busofit with the solutions of PdCl, FeCl, CuBr, and Cu(NO ) and activated under optimum conditions ensured 100% CO conversion under a respiratory regime at both low (0.03%) and high (0.5%) carbon monoxide contents of air. It was found that the activation of a catalytic system at elevated temperatures (170-180°C) leads to the conversion of Pd(II) into Pd(I), which was predominantly localized in a near-surface layer. The promoting action of copper nitrate consists in the formation of a crystalline phase of the rhombic atacamite CuCl(OH). The catalyst surface is finally formed under the conditions of a catalytic reaction, when a joint Pd(I)-Cu(I) active site is formed. © 2014 Pleiades Publishing, Ltd.

High stability multiplexed fiber interferometer and its application on absolute displacement measurement and on-line surface metrology

We propose a self-reference multiplexed fibre interferometer (MFI) by using a tunable laser and fibre Bragg grating (FBG). The optical measurement system multiplexes two Michelson fibre interferometers with shared optical path in the main part of optical system. One fibre optic interferometer is used as a reference interferometer to monitor and control the high accuracy of the measurement system under environmental perturbations. The other is used as a measurement interferometer to obtain information from the target. An active phase tracking homodyne (APTH) technique is applied for signal processing to achieve high resolution. MFI can be utilised for high precision absolute displacement measurement with different combination of wavelengths from the tuneable laser. By means of Wavelength-Division-Multiplexing (WDM) technique, MFI is also capable of realising on-line surface measurement, in which traditional stylus scanning is replaced by spatial light-wave scanning so as to greatly improve the measurement speed and robustness.

Investigation of some critical aspects of on-line surface measurement by a wavelength-division-multiplexing technique

Some critical aspects of a new kind of on-line measurement technique for micro and nanoscale surface measurements are described. This attempts to use spatial light-wave scanning to replace mechanical stylus scanning, and an optical fibre interferometer to replace optically bulky interferometers for measuring the surfaces. The basic principle is based on measuring the phase shift of a reflected optical signal. Wavelength-division-multiplexing and fibre Bragg grating techniques are used to carry out wavelength-to-field transformation and phase-to-depth detection, allowing a large dynamic measurement ratio (range/resolution) and high signal-to-noise ratio with remote access. In effect the paper consists of two parts: multiplexed fibre interferometry and remote on-machine surface detection sensor (an optical dispersive probe). This paper aims to investigate the metrology properties of a multiplexed fibre interferometer and to verify its feasibility by both theoretical and experimental studies. Two types of optical probes, using a dispersive prism and a blazed grating, respectively, are introduced to realize wavelength-to-spatial scanning.

Generation and performance of localised surface plasmons utilising nano-scale structured multi-layered thin films deposited upon D-shaped optical fiber

A new generation of surface plasmonic optical fibre sensors is fabricated using multiple coatings deposited on a lapped section of a single mode fibre. Post-deposition UV laser irradiation using a phase mask produces a nano-scaled surface relief grating structure, resembling nano-wires. The overall length of the individual corrugations is approximately 14 μm with an average full width half maximum of 100 nm. Evidence is presented to show that these surface structures result from material compaction created by the silicon dioxide and germanium layers in the multi-layered coating and the surface topology is capable of supporting localised surface plasmons. The coating compaction induces a strain gradient into the D-shaped optical fibre that generates an asymmetric periodic refractive index profile which enhances the coupling of the light from the core of the fibre to plasmons on the surface of the coating. Experimental data are presented that show changes in spectral characteristics after UV processing and that the performance of the sensors increases from that of their pre-UV irradiation state. The enhanced performance is illustrated with regards to change in external refractive index and demonstrates high spectral sensitivities in gaseous and aqueous index regimes ranging up to 4000 nm/RIU for wavelength and 800 dB/RIU for intensity. The devices generate surface plasmons over a very large wavelength range, (visible to 2 μm) depending on the polarization state of the illuminating light. © 2013 SPIE.

Physical characteristics of localized surface plasmons resulting from nano-scale structured multi-layer thin films deposited on D-shaped optical fiber

Novel surface plasmonic optical fiber sensors have been fabricated using multiple coatings deposited on a lapped section of a single mode fiber. UV laser irradiation processing with a phase mask produces a nano-scaled surface relief grating structure resembling nano-wires. The resulting individual corrugations produced by material compaction are approximately 20 μm long with an average width at half maximum of 100 nm and generate localized surface plasmons. Experimental data are presented that show changes in the spectral characteristics after UV processing, coupled with an overall increase in the sensitivity of the devices to surrounding refractive index. Evidence is presented that there is an optimum UV dosage (48 joules) over which no significant additional optical change is observed. The devices are characterized with regards to change in refractive index, where significantly high spectral sensitivities in the aqueous index regime are found, ranging up to 4000 nm/RIU for wavelength and 800 dB/RIU for intensity. © 2013 Optical Society of America.

A meshless method for an inverse two-phase one-dimensional nonlinear Stefan problem

We extend a meshless method of fundamental solutions recently proposed by the authors for the one-dimensional two-phase inverse linear Stefan problem, to the nonlinear case. In this latter situation the free surface is also considered unknown which is more realistic from the practical point of view. Building on the earlier work, the solution is approximated in each phase by a linear combination of fundamental solutions to the heat equation. The implementation and analysis are more complicated in the present situation since one needs to deal with a nonlinear minimization problem to identify the free surface. Furthermore, the inverse problem is ill-posed since small errors in the input measured data can cause large deviations in the desired solution. Therefore, regularization needs to be incorporated in the objective function which is minimized in order to obtain a stable solution. Numerical results are presented and discussed. © 2014 IMACS.

Microstructural study of aluminide surface coatings on single crystal nickel base superalloy substrates

Aluminide diffusion coatings are frequently employed to enhance the oxidation resistance of nickel base superalloys. However, there is a concern that the presence of an aluminide coating could influence the properties of the coated superalloy, especially in respect of fatigue behaviour. To understand the nature of the effects of surface coatings on the fatigue properties of superalloys, an understanding of microstructural development within both the coating and the coating/substrate interfacial zone during high temperature fatigue testing is necessary. This paper is concerned with microstructural changes in aluminide diffusion coatings on single crystal γ′ strengthened superalloy substrates during the course of high temperature fatigue testing. The 'edge on' transmission electron microscopy technique is employed to study cross-sections of two stage (aluminization plus diffusion treatment) coated superalloy samples. The paper examines the degradation of the coating produced by phase transformations induced by loss of aluminum from the coating and/or aging of the coating. Aluminum removal both by interdiffusion with the substrate and by oxidation of the coating surface is considered. Microstructural development in the portion of the substrate influenced by interdiffusion with the coating is also discussed.

Dynamic complexity of chaotic transitions in high-dimensional classical dynamics:Leu-Enkephalin folding

Leu-Enkephalin in explicit water is simulated using classical molecular dynamics. A ß-turn transition is investigated by calculating the topological complexity (in the "computational mechanics" framework [J. P. Crutchfield and K. Young, Phys. Rev. Lett., 63, 105 (1989)]) of the dynamics of both the peptide and the neighbouring water molecules. The complexity of the atomic trajectories of the (relatively short) simulations used in this study reflect the degree of phase space mixing in the system. It is demonstrated that the dynamic complexity of the hydrogen atoms of the peptide and almost all of the hydrogens of the neighbouring waters exhibit a minimum precisely at the moment of the ß-turn transition. This indicates the appearance of simplified periodic patterns in the atomic motion, which could correspond to high-dimensional tori in the phase space. It is hypothesized that this behaviour is the manifestation of the effect described in the approach to molecular transitions by Komatsuzaki and Berry [T. Komatsuzaki and R.S. Berry, Adv. Chem. Phys., 123, 79 (2002)], where a "quasi-regular" dynamics at the transition is suggested. Therefore, for the first time, the less chaotic character of the folding transition in a realistic molecular system is demonstrated. © Springer-Verlag Berlin Heidelberg 2006.

Surface catalysed Suzuki-Miyaura cross-coupling by Pd nanoparticles:an operando XAS study

Size-controlled, catalytically active PVP-stabilised Pd nanoparticles have been studied by operando liquid phase XAS during the Suzuki cross-coupling of iodonanisole and phenylboronic acid in MeOH-toluene using KOMe base. XAS reveals nanoparticles are stable to metal leaching throughout the reaction, with surface density Pd defect sites directly implicated in the catalytic cycle. The efficacy of popular selective chemical and structural poisons for distinguishing heterogeneous and homogeneous contributions in Pd catalysed cross-couplings is also explored. © 2010 The Royal Society of Chemistry.

Femtosecond laser inscribed phase masks for fibre Bragg grating sensor inscription

We present femtosecond laser inscribed phase masks for the inscription of Bragg gratings in optical fibres. The principal advantage is the flexibility afforded by the femtosecond laser inscription, where sub-surface structures define the phase mask period and mask properties. The masks are used to produce fibre Bragg gratings having different orders according to the phase mask period. The work demonstrates the incredible flexibility of femtosecond lasers for the rapid prototyping of complex and reproducible mask structures. We also consider three-beam interference effects, a consequence of the zeroth-order component present in addition to higher-order diffraction components. © 2012 SPIE.