Structural analysis of Aleksinac oil shale kerogen by high-resolution solid-state C n.m.r. spectroscopy

A sample of kerogen from Aleksinac oil shale was examined by high-resolution solid-state ¹³C n.m.r. spectroscopy. The presence and relative proportions of kerogen structural units were estimated using a combination of NQS and T_1C methods with a peak-synthesis technique applied to the ¹³C CP—MAS spectrum. Relaxation parameters from these experiments were used to estimate differences in relative ‘mobility’ of various structural units. The kerogen was found to be highly aliphatic and to contain 79% long-chain aliphatic plus alicyclic structures, as well as 9% aromatic structures. These findings are in good agreement with the characterization of the same kerogen from its oxidation products.     

HYDRODYNAMIC STUDIES IN FISCHER-TROPSCH DERIVED WAXES IN A BUBBLE COLUMN

Gas hold-up and Sauter mean bubble diameter measurements were made in a 0.051 m diameter by 3 m long glass bubble column in the system, nitrogen-molten wax, with three different waxes (paraffin wax FT-300, Sasol's Arge wax and Mobil's reactor wax). Paraffin wax has a tendency to foam and gas hold-up is a strong function of gas distributor type, temperature and start-up procedure, whereas the reactor waxes do not foam and are much less affected by these variables, In experiments at 265°C with a 1.85 mm single hole orifice plate distributor the gas hold-ups were nearly the same for all three waxes. However, significant differences in Sauter mean bubble diameters were obtained in experiments with different waxes; FT-300 wax produced the smallest Sauter mean bubble diameters whereas Mobil's reactor wax produced the largest bubbles. Addition of 1-octadecanol and octadecanoic acid (up to 10wt%) to the FT-300 paraffin wax caused an increase in gas hold-up and a delay in the foam break-up in runs at 265°C with the 1.85 mm orifice plate distributor.     

Condensed phase decomposition and gas phase combustion of hydrazinium nitroformate

This paper presents the results of a series of experiments on the condensed phase decomposition and the gas phase combustion of hydrazinium nitroformate (HNF). The experiments include SEM analysis of quenched samples that showed evidence of the formation of a foam layer. FTIR spectrometry and mass spectrometry provide details on species formation during decomposition and combustion. The analysis of the results led to the identification of probable overall reactions in the low pressure regime around 0.1 MPa. It is found that decomposition of HNF takes place through formation of ammonium nitroformate, and through dissociative vaporisation. The gas phase near the surface of burning HNF is expected to contain a large amount of hydrazine, ammonia and nitrogen dioxide (as a decomposition product of nitroform). The primary reaction zone of the HNF flame is then associated with the exothermic reactions of these species. The resulting nitrogen oxide is subsequently reduced to molecular nitrogen in the secondary flame.     

Redundancy resolution through local optimization: A review

Kinematically redundant manipulator arms and other robotic mechanisms provide a means for solving sophisticated motion tasks but require complex research on both mechanical and control problems. So far, many works have been published on kinematic redundancy, however, a systemization is missing. In this article an attempt for such a systemization is presented. It has been limited to methods for redundancy resolution through local optimization. Until now, these methods are most widely used, and it is expected also that they will prevail in the near future. A classification is suggested and the performance capabilities of the methods are discussed and compared. Two reference tables are provided; One of them lists references for different problems on kinematic redundancy as: mechanical design, dexterity measures, multicriteria optimization, global optimization, control design and computational considerations. The other table displays existing publications classified according to the application area of redundant robotic-mechanisms.     

Long-period fibre grating formation with 264 nm femtosecondradiation

A new approach for producing long period fibre gratings by exposure of the optical fibre to high-intensity femosecond pulses λ = 264 nm is presented. Different types of fibres were investigated and it was found that strong attenuation peaks (16-28 dB) can be induced in H₂-loaded fibres     

Storage of trachea for X-ray microanalytical studies of tracheal submucosal glands

Previous studies have suggested that penicillin-resistant pneumococcal isolates (especially those with MIC > 1 microgram/mL) usually are clonally related. To test this hypothesis, the molecular epidemiology of 29 clinical isolates of penicillin-resistant pneumococci (of which 83% were also resistant to either cefotaxime or ceftriaxone) collected in central Taiwan was investigated by pulsed field gel electrophoresis. Twenty-seven distinct patterns were identified. Our results indicate that an increase in penicillin-resistant S. pneumoniae between April 1993 and June 1994 in central Taiwan is not due to the clonal dissemination of a limited number of epidemic strains.     

Experimental and clinical correlation in acute pancreatitis pathogenesis

Pathological aspects in 100 cases of operated A.P. different in severity are not strictly related to aetiological conditions. Clinical observations have suggested some components of pathogenesis: obstruction of bilio-pancreatic inflow in duodenum at the beginning of the attack, bilio-pancreatic reflux on cholangiograms, strong secretory digestive stimulation before attack. Some experimental animals models (dogs) which can mimic pathogenic mechanism (obstruction of pancreatic flow, common bilio-pancreatic duct, closed duodenal loop, acute cholecystitis) have revealed characteristic pathological changes depending on the initiating process. Our conclusion that severity of pathological changes in A.P. are determined by the initiating mechanisms which may differ in some aetiological condition or may be common for different ones.     

Potential of proton-enhanced 13C n.m.r. for the classification of kerogens

High resolution n.m.r. spectroscopy, involving the technique of cross-polarization, along with magicangle spinning, was used in the structural characterization of eight kerogens of different origins, selected to represent the three types of kerogens (types I–III evolution paths). The influence of cross-polarization dynamics on the sensitivity of the method and the ratio of individual fractions in the spectrum was studied in more detail. It is suggested that an analysis of the influence of the mixing time is necessary prior to definitive characterization of any sample. Good separation of signals in aliphatic, aromatic, and carboxylic regions was achieved. The general correlation between the ¹³C n.m.r. structural characteristics and the classification based on ultimate analysis of the kerogens (types I–III, van Krevelen atomic H/C vs. O/C diagrams) was found to be satisfactory. The structural features of kerogens derived from ¹³C n.m.r. analysis agreed quite well with characteristics constituting the above mentioned classification. The ¹³C n.m.r. method used in this paper may be considered promising in the classification of kerogens.