Experimental investigation of paraffin-based fuels for hybrid rocket propulsion

Solid fuels for hybrid rockets were characterized in the framework of a research project aimed to develop a new generation of solid fuels, combining at the same time good mechanical and ballistic properties. Original techniques were implemented in order to improve paraffin-based fuels. The first strengthening technique involves the use of a polyurethane foam (PUF); a second technique is based on thermoplastic polymers mixed at molecular level with the paraffin binder. A ballistic characterization of paraffin-based hybrid rocket solid fuels was performed, considering pure wax-based fuels and fuels doped with suitable metal additives. Nano-Al powders and metal hydrides (magnesium hydride (MgH2), lithium aluminum hydride (LiAlH4 )) were used as fillers in paraffin matrices. The results of this investigation show a strong correlation between the measured viscosity of the melted paraffin layer and the regression rate: a decrease of viscosity increases the regression rate. This trend is due to the increasing development of entrainment phenomena, which strongly increase the regression rate. Addition of LiAlH4 (mass fraction 10%) can further increase the regression rate up to 378% with respect to the pure HTPB regression rate, taken as baseline reference fuel. The highest regression rates were found for the Solid Wax (SW) composition, added with 5% MgH2 mass fraction; at 350 kg/(m2s) oxygen mass flux, the measured regression rate, averaged in space and time, was 2.5 mm/s, which is approximately five times higher than that of the pure HTPB composition. Compositions added with nanosized aluminum powders were compared with those added with MgH2, using gel or solid wax

NIGER-DELTA: ENVIRONMENT, OGONI CRISIS AND THE STATE

Among the well agreed-on benefits of a guideline computerisation, with respect to the traditional text format, there are the disambiguation, the possibility of looking at the guideline at different levels of detail and the possibility of generating patient-tailored suggestions. Nevertheless, the connection of guidelines with patient records is still a challenging problem, as well as their effective integration into the clinical workflow. In this paper, we describe the evolution of our environment for representing and running guidelines. The main new features concern the choice of a commercial product as the middle layer with the electronic patient record, the consequent possibility of gathering information from different legacy systems, and the extension of this "virtual medical record" to the storage of process data. This last feature allows managing exceptions, i.e. decisions that do not comply with guidelines

Bimacrocyclic Effect in Anion Recognition by a Copper(II) Bicyclam Complex

The dicopper(II) complex of the bimacrocyclic ligand α,α′-bis(5,7-dimethyl-1,4,8,11-tetraazacyclotetradecan-6-yl)-o-xylene, 2, interacts with selected anions in dimethyl sulfoxide solution according to two different modes: (i) halides (Cl-, Br-, and I-) and N3- coordinate the two metal centers at the same time between the two macrocyclic subunits that face each other and (ii) anionic species that do not fit the bridging coordination mode (e.g., NCO-, SCN-, CH3COO-, NO3-, and H2PO4-) interact with copper(II) ions only at the "external" positions or their interaction is too weak to be detected. Occurrence of the bridging interaction is demonstrated by X-ray crystallographic studies performed on the adduct formed by [Cu2(2)]4+ with azide and by electron paramagnetic resonance investigation, as the anion coordination between the two copper(II) centers induces spin-spin coupling. Isothermal titration calorimetry experiments performed on [Cu2(2)]4+ and, for comparison, on [(5,7-dimethyl-6-benzyl-1,4,8,11-tetraazacyclotetradecane)copper(II)], representing the mononuclear analogue, allowed determination of thermodynamic parameters (log K, ΔH, and TΔS) associated with the considered complex/anion equilibria. Thermodynamic data showed that adducts formed by [Cu2(2)]4+ with halides and azide benefit from an extra stability that can be explained on the basis of the anion advantage of simultaneously binding the two metal centers, i.e., in terms of the bimacrocyclic effect

Loss of heterozygosity at the 5,10-methylenetetrahydrofolate reductase locus in human ovarian carcinomas.

The high-affinity folate-binding protein (FBP) is primarily involved in the uptake of the 5-methyltetrahydrofolate, and its expression may be physiologically regulated by the intracellular folate content. The overexpression of FBP on the cell surface of ovarian carcinoma cells may be responsible for an increased folate uptake. We tested the hypothesis of the existence of a defect in the 5, 10-methylenetetrahydrofolate reductase (MTHFR) in ovarian tumours that could cause reduced intracellular regeneration of the 5-methyltetrahydrofolate and induce increased FBP expression. No sequence mutations were found in the MTHFR gene, but allelic deletions of this gene were frequently detected in ovarian tumours (59%). Chromosomal losses appeared to be confined to the 1p36.3 region to which the MTHFR gene maps. Although it cannot be stated that MTHFR is the target gene of the chromosomal loss involving the 1p36.3 region, a correlation between loss of heterozygosity at this locus and decrease in MTHFR activity was shown, suggesting a role of these allelic deletions in generating a biochemical defect in folate metabolism. Further studies are needed to assess further the relationship between MTHFR and FBP overexpression, but the demonstration of the alteration of a key metabolic enzyme of the folate cycle in a subset of human ovarian tumours is in accordance with the hypothesis of an altered folate metabolism in these neoplasias and might be exploited for therapeutic purposes