A high sensitivity refractometer based upon a long period grating Mach-Zehnder interferometer

A low cost interrogation scheme is demonstrated for a refractometer based on an in-line fiber long period grating (LPG) Mach–Zehnder interferometer. Using this interrogation scheme the minimum detectable change in refractive index of ?n ~ 1.8×10-6 is obtained, which is the highest resolution achieved using a fiber LPG device, and is comparable to precision techniques used in the industry including high performance liquid chromatography and ultraviolet spectroscopy.

The Single drop drying of heat-sensitive materials

The literature relating to the principles and practice of drying of materials, particularly those susceptible to thermal degradation or undesirable loss of volatile components, has been reviewed. Single droplets of heat-sensitive materials were dried whilst suspended in a horizontal wind tunnel from a specially-designed, rotating thermocouple which enabled direct observation of drying behaviour and continuous measurement of droplet temperature as drying progressed. The effects of drying air temperature and initial solids concentration on the potency of various antibiotics, viz. ampicillin, chloramphenicol, oxytetracycline, streptomycin and tetracycline, were assessed using a modified Drug Sensitivity Testing technique. Only ampicillin was heat-sensitive at temperatures above 100°C, e.g. at an air temperature of 115°C its zone diameter was reduced from 100% to 45%. Selected enzymes, viz. dextran sucrase and invertase, were also dried and their residual activities determined by High Performance Liquid Chromatography. The residual activity of dextran sucrase was rapidly reduced at temperatures above 65°C, and the residual activity of invertase reduced rapidly at temperatures above 65°C; but drying with short residence times will retain most of its activity. The performance of various skin-forming encapsulants, viz. rice and wheat starch, dextrin, coffee, skim milk, fructose, gelatine 60 and 150 Bloom, and gum arabic, was evaluated to determine their capabilities for retention of ethanol as a model volatile, under different operating conditions. The effects of initial solids concentration, air velocity and temperature were monitored for each material tested. Ethanol content was analysed by Gas Liquid Chromatography and in some cases dried crusts were removed for examination. Volatiles retention was concluded to depend in all cases upon the rate and nature of the skin formation and selective diffusion phenomena. The results provided further insight into the inter-relationship between temperature, residence time and thermal degradation of heat-sensitive materials. They should also assist in selection of the preferred dryer for such materials, and of the operating parameter to enable maximum retention of the required physico-chemical characteristics in the dried materials.

Formulation of immunomodulatory agents

Reversed-phase high-performance liquid chromatography procedures were developed for the analysis of pyrimidine-based drugs bropirimine and its derivatives (2-N-acetyl- and 2-N-propanoyl-) and for pyrimethamine and its 2/4- substituted derivatives (2, N-propanoyl and 2,4-N, N-dipropanoyl-) and its 6- substituted (methyl-, ethyl-, propyl- and isopropyl- carboxylates) analogues. Stability studies indicated that these derivatives were not sufficiently labile to act as potential prodrugs. Solubility-pH profiles were constructed from which the dissociation constants were calculated. The physicochemical properties of these compounds were studied and attempts were made to increase the poor aqueous solubility of bropirimine (35μg/mL) by prodrug synthesis, solvate formation (acetic acid, N, N-dimethylformamide and N-methylformamide) and the use of co-solvents and additives. The first two methods proved to be fruitless whereas the latter method resulted in an intravenous formulation incorporating 32mg/mL of bropirimine. An in-vitro method for the detection of precipitation was developed and the results suggested that by using low injection rates (< 0.24mL/min) and high mobile phase flow rates (> 500mL/hr) precipitation could be minimised. Differential scanning calorimetry showed that bropirimine debrominates in the presence of a number of additives commonly used in formulation work but the temperature at which this occurred were usually > 200oC. In-vitro work gave encouraging results for the possibility of rectal delivery of bropirimine but in-vivo work on rabbits showed considerable variations in the resulting plasma levels and pharmacokinetic parameters.

High temperature gas cleaning for advanced syngas utilization:Paper # 95

Biofuels and chemicals from biomass mean the gasification of biogenic feedstocks and the synthesis via methanol, dimethylester (DME) or Fischer-Tropsch products. To prevent the sensitive synthesis catalysts from poisoning the syngas must be free of tar and particulates. The trace concentrations of S-, C1-, N-species, alkali and heavy metals must be of the order of a few ppb. Moreover maximum conversion efficiency will be achieved performing the gas cleaning above the synthesis conditions. The concept of an innovative dry HTHP syngas cleaning is presented. Based on the HT particle filtration and suitable sorption and catalysis processes for the relevant contaminants a total concept will be derived, which leads to a syngas quality required for synthesis catalysts in only 2 combined stages. The experimental setup for the HT gas cleaning behind the 60 kWtherm entrained flow gasifier REGA of the institute is described. Results from HT filter experiments in pilot scale are presented. The performance of 2 natural minerals for HC1 and H2S sorption is discussed with respect to the parameters temperature, surface and residence time. Results from lab scale investigations on low temperature tar catalysts' performance (commercial and proprietary development) are discussed finally.

A comparison of the spectral properties of high temperature annealed long period gratings inscribed by fs laser, UV and fusion-arc

Long period gratings have been inscribed in standard single mode fibre using a fs laser system, a fusion arc and a UV laser and a comparative study carried out of their thermal behaviour. The fs laser induced gratings can survive temperatures in excess of 800&deg;C, however the inscription process can induce considerable birefringence within the device. Annealing studies have been carried out showing that below 600&deg;C, all three grating types show a blue shift in their room temperature resonance wavelengths following cyclic heating, while above 600&deg;C, the UV and arc induced LPGs exhibit a red shift, with the fs LPG showing an even stronger blue shift. High temperature annealing is also shown to considerably reduce the birefringence induced by the fs inscription process.

The strength and fracture of engineering alloys at high temperature a collection of papers

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SO2 sequestration in large volcanic eruptions:high-temperature scavenging by tephra

It is well accepted that the climate impact of large explosive volcanic eruptions results from reduction of solar radiation following atmospheric conversion of magmatic SO emissions into HSO aerosols. Thus, understanding the fate of SO in the eruption plume is crucial for better assessing volcanic forcing of climate. Here we focus on the potential of tephra to interact with and remove SO gas from the eruptive plume. Scavenging of SO by tephra is generally assumed to be driven by in-plume, low-temperature reactions between HSO condensates and tephra particles. However, the importance of SO gas-tephra interaction above the dew point temperature of HSO (190-200°C) has never been constrained. Here we report the results of an experimental study where silicate glasses with representative volcanic compositions were exposed to SO in the temperature range 25-800°C. We show that above 600°C, the uptake of SO on glass exhibits optimal efficiency and emplaces surficial CaSO deposits. This reaction is sustained via Ca diffusion from the bulk to the surface of the glass particles. At 800°C, the diffusion coefficient for Ca in the glasses was in the range 10-10cms. We suggest that high temperature SO scavenging by glass-rich tephra proceeds by the same Ca diffusion-driven mechanism. Using a simple mathematical model, we estimated SO scavenging efficiencies at 800°C varying from

Microstructural degradation of aluminide coatings on single crystal nickel based superalloys during high temperature exposure

An investigation, employing edge-on transmission electron microscopy, of the microstructure of aluminide diffusion coatings on a single crystal y' strengthened nickel base super alloy is reported. An examination has been made of the effect of postcoating exposure at 1100°C on the stability of the coating matrix, a B2 type phase, nominally NiAl. Precipitation in the coating is considered with respect to both decomposition of the B2 matrix to other Ni-Al (plus titanium) phases and the formation of chromium bearing precipitates. A comparison is drawn with behaviour at lower temperatures (850-950°C). © 1995 The Institute of Materials.