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Utilizing several instruments on 4–8 m telescopes, we have observed a large sample of objects in the mid-infrared (8–13 μm). These comprise a few evolved stars, multiple envelopes of embedded young stellar objects (YSOs) or compact H-II regions, and several sightlines through the interstellar medium (ISM). The latter is where dust resides – and is potentially modified – between its formation in evolved stellar outflows and deposition in molecular clouds. In most objects, we detect not only the well-known 9.7 μm absorption feature of amorphous silicates but also a second absorption band around 11.1 μm whose carrier is attributed to crystalline forsterite. We propose that crystalline silicates are essentially ubiquitous in the ISM and earliest phases of star formation, and are evolutionary precursors to T-Tauri and Herbig stars where such silicates have been commonly found. Modelling shows that in most YSOs, H-II regions and ISM cases, the forsterite mass fraction is between 1 and 2 per cent, suggesting that the younger phases inherit their abundance from the ISM. However, several sources show much stronger features (abundances ≥3 per cent). This suggests that significant processing, perhaps crystallization by thermal annealing, occurs early on in star formation. Most intriguing is the first detection of crystalline silicate in the diffuse ISM. We propose that our observed abundance is consistent with a mass fraction of crystalline silicates of 10–20 per cent injected into the ISM, along with commonly accepted lifetimes against their destruction, but only if cosmic ray-induced amorphization is insignificant over a few Giga years.

The MIRI instrument on the James Webb Space Telescope is equipped with detectors which are susceptible to signal disruption by the charge deposited from impacting cosmic rays. In order to quantify the degree to which the structure of MIRI will shield the detectors, we have used an opto-mechanical ray tracing approach, whereby the solid bodies in a detailed 3D model of the instrument are substituted with an absorptive glassy material. By importing this modified model into a ray tracing program (Tracepro) and then launching many rays from the detector, we have been able to generate a map of aluminium path length as a function of direction. We find that there is a minimum thickness of 2 to 3 mm over a few patches which subtend no more than 1.5 % of the sky for the worst case, imager detector. We discuss the performance of the shielding provided by the MIRI structure, concluding that this minimum thickness of aluminium is sufficient to suppress the impact of low energy protons below the level of the unavoidable flux due to high energy cosmic rays.

Objectives\ud \ud Dietary stains can be adsorbed into the dentin of teeth. Using Orange II as a model dietary stain, this study investigated the strength of its interaction with the mineral and protein components of dentin matrix and how hydrogen peroxide (H2O2) treatment influences this interaction.\ud \ud \ud Methods\ud \ud Dentin slices were prepared from human teeth and were either deproteinized (5.6% sodium hypochlorite, 12 days), demineralised (0.5 M EDTA, 3 days) or left as intact control samples. Samples were stained with Orange II for 1-168 h, during which staining intensity was quantified by image analysis. Similarly, uptake of stain by deproteinized / demineralized samples treated with 10 or 30% H2O2 was investigated. Using surface plasmon resonance technology, real-time binding kinetics were determined assessing the interaction of orange II with the dentin matrix protein constituents, collagen type I, biglycan, decorin, dentin sialoprotein and osteopontin.\ud \ud \ud Results\ud \ud Deproteinization of dentin matrix reduced the uptake of the orange II compared to the intact control. Conversely, demineralization of dentin samples increased the uptake of the dye. Treatment of samples for 48 h with H2O2 reduced subsequent uptake of the orange II. Real-time kinetic analysis indicated moderate strength of binding for Orange II with collagen type I, weak binding with decorin and biglycan and negligible binding with dentine sialoprotein and osteopontin.\ud \ud \ud Conclusion\ud \ud These results indicate a predominant role for collagen type I, which accounts for 90% of the organic protein matrix of teeth, for attracting dietary stains. Binding analyses indicate that the interaction is highly dissociable, and further binding is reduced following H2O2 treatment.\ud \ud \ud Clinical significance\ud \ud This study provides new information regarding adsorption of dietary stains into tooth dentin, suggesting that they are attracted and moderately bound to the collagen type I matrix. This study also contributes valuable information for discussion for considering the effect of H2O2 on bleaching teeth and its influence on subsequent uptake of dietary stains following whitening treatments.

The physical stability of emulsions can be related to changes in the droplet size distribution over time. Stability control of emulsions used as metal working fluids is an important factor for the machining industry due to the decreased performance of aged and broken emulsions. Results of turbidimetric spectra measurements of metal working fluids for process control purposes and emulsion stability monitoring are discussed. Metal working emulsions were artificially destabilized by admixing salts which resulted in droplet coagulation. The destabilization process was investigated by measuring the droplet size distribution and the turbidity spectra over time. The results were evaluated based on quantitative criteria proposed in the literature. The applicability of these criteria to evaluate metal working fluids during machining operations is discussed.

The continuous monitoring of the particle size distribution in particulate processes with suspensions or emulsions requires measurement techniques that can be used as in situ devices in contrast to ex situ or laboratory methods. In this context, for the evaluation of turbidimetric spectral measurements, the application of different numerical inversion algorithms is investigated with respect to the particle size distribution determination of polystyrene suspensions. A modified regularization concept consisting of a Twomey-Phillips-Regularization with an integrated nonnegative constraint and a modified L-curve criterion for the selection of the regularization parameter is used. The particle size (i.e., particle diameter) of polystyrene suspensions in the rangex=0.03–3 µm was validated via dynamic light scattering and differential centrifugal sedimentation and compared to the retrieved particle size distribution from the inverted turbidimetry measurements.

Modified natural rubber polymer hosts having low transition glass temperatures have been investigated for use in polymer electrolytes. Two types of modified natural rubber, namely 25% epoxidised natural rubber (ENR-25) and 50% epoxidised natural rubber (ENR-50) were employed in conjunction with poly(ethylene oxide), PEO. Results are reported for ionic conductivity and thermal properties for both unplasticized and plasticized polymer electrolyte systems with lithium triflate. The samples were in the form of free standing films with the thickness 0.2–0.5 mm and mixtures of ethylene carbonate (EC) and propylene carbonate (PC) were used as plasticizers. Unplasticized modified natural rubber-based systems exhibit ionic conductivities in the range 10−6 to 10−5 S cm−1 at ambient temperatures. Incorporating 100% of EC/PC by weight fraction of polymer (ENR/PEO) to the systems yielded mechanically stable films and ionic conductivities in the range of 10−4 S cm−1 at ambient temperature.

Results are presented on the performance of low-temperature, short-channel polycrystalline silicon (poly-Si) thin-film transistors (TFTs), with channel length down to 0.5 μm, and scaled gate oxide thickness down to 20 nm. Good TFT switching characteristics were obtained, and the uniformity of short-channel TFTs was shown to have a standard deviation of better then 10%, even for channel widths as small as 4 μm. The 0.5 μm TFTs have been incorporated into a 15-stage complementary pair metal-oxide-Si transistor ring oscillator, which, at a supply voltage of 3 V, operated with a delay/stage of ∼0.1 ns.

The stability of oil-in-water (O/W) emulsions used as metalworking fluids is a key factor for the economical and environmental balance of the entire metalworking process because used and broken fluids must be recycled or disposed. In this study, the ability of turbidimetric spectroscopy in the ultraviolet and visible light range to detect metalworking fluids destabilization was evaluated. Destabilization was achieved by adding calcium chloride, thus achieving accelerated aging, which leads to coalescence, creaming, and complete emulsion separation. The stability of the metalworking fluids at 5% volumetric concentration in deionized water was monitored using a spectroscopic turbidimeter composed of an optical probe for in-line measurements. Destabilization was also monitored by measuring the vertical profile of backscattered and transmitted light. The results of this offline measurement system were compared with those from the in-line spectroscopic sensor, indicating that the latter can provide local, real...

The application of a digital imaging technique to the measurement of the radii of growing spherulites in PEO and PEO 8 :Li triflate is described. The relevance of these measurements to the determination of the kinetics of crystallisation, and hence to the influence of preparation conditions on the morphology of polymer electrolyte films is discussed.

The potential influence of averaging caused by spherulite morphology on local structures deduced from EXAFS studies of crystallisable films is discussed. Evidence is presented to show that only high-melting, polymer-salt complexes interfere significantly with studies of the ionic environment within the amorphous conducting region. The possible modifications to the amorphous matrix that could result from the proximity of spherulites are considered. Results are presented for EXAFS studies of the local environment surrounding Zn in PEO n ·ZnBr 2 ( n =4, 8) prepared by three different drying procedures, at room temperature, -20°C and -70°C. Structural differences between amorphous and glassy forms were observed. The results suggest the presence of neutral ZnBr 2 entities.

We have developed a novel fully self-aligned top gate amorphous silicon thin-film transistor, which shows excellent transistor characteristics. Self-alignment is achieved by patterning the gate electrode and then etching the silicon nitride gate insulator, followed by silicidation and ion implantation of the exposed a-Si in the contact regions. We obtain a long channel saturated mobility of 0.9 cm/sup 2/ V/sup -1/ s/sup -1/, while for channel lengths of 6 /spl mu/m, we obtain an effective mobility of 0.6 cm/sup 2/ V/sup -1/ s/sup -1/, in the saturated region and 0.5 cm/sup 2/ V/sup -1/ s/sup -1/, in the linear region. This high level of performance, together with the negligible parasitic capacitance of the self-aligned structure, makes this transistor suitable for new demanding applications in active matrix liquid crystal displays and large area X-ray image sensors.

A technique developed by Scharmer & Carlsson for finding accurate solutions to the multi-level line transfer problem in the presence of velocity fields has been adapted for modelling the submillimetre emission spectra of molecular clouds. Line profiles for transitions up to J=20−19 in CO and J=5−4 in HCO+ can be modelled for slab or spherically symmetric atmospheres exhibiting spatial variations in temperature, density and bulk velocity. The technique is used to reproduce the published observed profiles of HCO+, CO and its isotopes, using a single physical model of the Bok globule B335.

Michelle is a 7 to 25 μm imager and spectrometer built by the UKATC for operation on the UKIRT (3.8m) and Gemini-North (8m) telescopes on Mauna Kea. Its spectroscopic capability is provided by a long-slit spectrometer. We illustrate Michelle’s performance at high spectral resolutions with observations that were taken using the echelle during its first year of operations on UKIRT. These include the detection of water vapour absorption features in the atmosphere of the bright M star β Pegasi.

Source-gated transistors (SGTs) have been made in thin layers of polysilicon formed by excimer laser crystallization of amorphous silicon. It is shown that the main features of the SGT, namely a low saturation voltage and high output impedance can be obtained in poly-silicon. Furthermore the nature of the source barrier enabled it to be pulled down by the influence of the gate to low values giving small activation energies for current transport and reduced temperature sensitivity in the on-state.

Modified natural rubber (NR) polymer hosts having low transition glass temperatures have been investigated. Three types of modified NR, namely 25% epoxidised NR (ENR-25), 50% ENR (ENR-50) and polymethyl methacrylate grafted NR (MG-49) were employed. Results are reported for ionic conductivity and thermal properties for both unplasticised and plasticised polymer electrolyte systems. The samples were in the form of free standing films with the thickness 0.2–0.5 mm and mixtures of ethylene carbonate (EC) and propylene carbonate (PC) were used as plasticisers. Unplasticised modified NR based systems exhibit ionic conductivities in 10 −6 –10 −5 S cm −1 range at ambient temperatures. Incorporating 50–100% of EC/PC by weight to the systems yielded mechanically stable films and ionic conductivities in 10 −4 –10 −3 S cm −1 range at ambient temperature. The thermal event of the systems has displayed an increasing trend of transition glass temperature at elevated salt concentration whereas incorporation of EC and PC into the systems leads to marked reduction in their T g values.

We have developed a fully self-aligned amorphous silicon TFT technology, which is suitable for large area image sensors and active matrix displays. Self-alignment is achieved by defining the top nitride by back exposure and then forming source and drain contacts by ionimplantation and silicidation. We incorporate a low resistance gate metallisation process, by using Al metal, capped by Cr. We have compared the process of forming the silicide after the ion-implantation step, with a new process of forming the silicide first and then implanting through the formed silicide. We find a significant advantage to the latter method, where we can achieve a higher doping level and reduced contact resistance. We have therefore optimised our process based on this method. Transistor characteristics as a function of channel length for both methods show the improved contact resistance, obtained with the latter method. We obtain field effect mobilities of 0.7cm2V−1s−1, measured in the saturated region, for a channel length of 8μm.

We present first results on the performance of flat dynamic x-ray detectors (FDXD) based on arrays of amorphous silicon thin film transistors (TFT) with charge storage capacitances and lead oxide as x-ray photoconductor. In order to increase the “active area” of every pixel, the layout of the array has been made in a multilevel arrangement, where the charge collecting electrode is separated from the underlying electronics by a thick insulating layer. This allows for a geometrical overlap of the pixel electrodes and TFTs. PbO has been chosen as the x-ray sensing material due to its very high x-ray sensitivity. The relevant detector properties of evaporated PbO layers are described along with results obtained on first FDXD devices with PbO.

We have developed a new amorphous silicon image sensor technology using a matrix array of amorphous silicon thin film transistors and photodiodes, where the amorphous silicon nip photodiode is fabricated on top of a thick insulating layer, on top of the thin film transistor array. We call this ‘diode on top’ technology or DOTTY. The active diode area can be as high as 93%, compared to 50% for our conventional photodiode-TFT technology. This leads to a higher signal to noise performance, which is important for medical X-ray applications.

The dream of an all-solid state large area x-ray image sensor with digital readout and full dynamic performance will most probably find a first realization in 2D thin-film amorphous silicon arrays. In this paper we address in particular the evaluation of the limits of the signal/noise ratio in this concept. Using small prototype detectors measurements of MTF and noise power spectra have been made as a function of x-ray dose. The results are given in terms of the detective quantum efficiency as a function of dose and spatial frequency. We further present an analysis of the different noise sources and their dependence on the detector parameters, and we provide estimates on the maximum signals that may be achieved per unit dose. The intrinsic lag of the amorphous silicon photodiodes causes a second problem area with this type of x-ray detectors. Especially in radiography/fluoroscopy mixed applications, memory effects may not be negligible.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

(PEO)n:ZnX2 (X = I, Br) complexes were formed at room temperature with values ofn ranging from 8 to 30. Differential scanning calorimetry (DSC) results indicate that none of them contained any crystalline phases that can be associated with the formation of a complex (i.e. it can be assumed that all the salt is in the amorphous phase). EXAFS studies carried out on these samples suggest that the zinc cation is co-ordinated to two of the halide ions and, in addition, to 4 oxygen atoms whereX = I and 6 oxygen atoms whereX = Br. The DSC results confirm that the zinc cation is in an environment independent of overall stoichiometry, as the glass transition temperatures of the samples were found to be similar throughout. By comparing these with those of annealed samples (made by heating the above samples to 150°C and cooling to −80°C at 320°C min−1) it was found that the stoichiometry of the amorphous phase was roughly 6∶1 forX=I and 8∶1 forX = Br.

Solutions of living oligomers of α-methylstyrene in THF age in two ways. In “decay” the UV-visible absorption of the anion slowly disappears but in “transformation” the peak at 340 nm is replaced by a new one at 430 nm. Decay follows first-order kinetics, while transformation depends upon a photochemical process and requires the presence of excess monomer. This monomer is consumed in a second-order reaction to produce an intermediate from which new anions are formed.

Studies on PEO/LiCF 3 SO 3 polymeric electrolytes using polarising microscopy, SEM/EDX, DSC and complex plane analysis show that thin electrolyte films prepared by slow evaporation from CH 3 CN solution are spherulitic in nature. More than one type of spherulite is present across the composition range and each spherulite type contains both amorphous and crystalline regions. The structural behaviour on heating and cooling is discussed with particular reference to electrolyte films of overall composition PEO 20 :LiCF 3 SO 3 . For these high ratio triflate films, in contrast to similar PEO/LiClO 4 films, high melting salt-rich regions are unexpectedly present in conjunction with low melting, low salt spherulites. No evidence is found for the presence of pure PEO spherulites, but the low melting spherulites may have a crystalline skeleton of pure PEO. Evidence is presented for the dependence of conductivity on thermal history.

The living anions of oligomeric α-methalystyrene in THF transform to a new anion in the presence of excess monomer and UV light. Kinetic results have demonstrated that one step in this process is the second-order disappearance of monomer to form a dimeric intermediate. We have attempted to prepare this intermediate. Contrary to other reports, no hydrogen was liberated on terminating the reactions mixture with water, and an oily liquid which was identified as 1-methyl-1,3-diphenyl-cyclopentane was isolated. However, this is not the intermediate; the true intermediate is 2,5-diphenylhex-1-ene and under the conditions of the reaction the former compound is formed from this by a cyclization reaction.

The compounds Eu x ZrSe 1.95 have been prepared by reaction of the zirconium diselenide and europium metal using the liquid ammonia technique. The 1T structural type of pristine ZrSe 1.95 is apparently retained for x lying in the range 0–0.40 (+/− 0.02). For x>0.40, Eu amide is formed. No significant change in the cell parameter values related to size effects is observed as x increases. From magnetic susceptibility measurements together with Mossbauer spectroscopy, discrete Eu 2+ and Eu 3+ valence states are evidenced. The question whether these compounds are real intercalation compounds is discussed.

Solutions of the dimer dianion of 1,1-diphenylethene in tetrahydrofuran have been found to decay but not to transform on storage or on exposure to u.v. light.