The Influence of Numerical and Observational Errors on the Likelihood of an ARMA Series

Formulae are established describing how the round-off and observational errors influence the reduced likelihood function, as a step towards providing guidelines for such likelihood computations in a time series context. Error bounds are set up for Ali's method.     

An investigation of shear-induced mixing in the PSAN/PMMA blend

We investigate experimentally the effect of steady-state simple shear flow on the miscibility of a 60–40 poly(styrene-co-acrylonitrile) with poly(methyl-methacrylate) (PSAN/PMMA) blend. Thin disks, containing 60% w/w PSAN, are thermoformed from blend pellets made by mixing PSAN and PMMA granules in a co-rotating, fully-intermeshing twin-screw extruder. These disks are sheared at constant shear rate in a cone-and-plate mechanical spectrometer at fixed temperatures within the quiescent two-phase region. At the end of each shearing experiment the sample is quenched and its morphology investigated first visually for optical transparency (cloudiness being an indicator of a phase-separated blend) and then using transmission electron microscopy (TEM). Results indicate that upon imposition of a shear rate as low as 0.1s^?1 the 60–40 blend remains miscible even at temperatures up to 7K within the (quiescent) two-phase region. These observations are in agreement with theoretical predictions of the phase diagram under shear, based on the concept of a modified Gibbs free energy of mixing. The TEM results concerning the morphology of the phase-separated blends are also discussed.     

Synthesis and nonlinear optical properties of PMMA copolymers having novel benzoxazole chromophores attached with various electron-withdrawing groups

For improvements of thermal stability and nonlinear optical (NLO) activity of chromophores, we newly synthesized a series of NLO chromophores incorporating aromatic benzoxazole unit as a π-conjugated bridge with various electron-withdrawing groups, such as nitrophenyl, nitrothiophene, nitrofuran, dicyanovinylphenyl, and nitrophenylethenyl group. Polymethylmethacrylate copolymers (PMBz) containing these benzoxazole chromophores were synthesized and their properties were investigated by thermogravimetry and ultraviolet-visible spectroscopy. The PMBz copolymers exhibited better thermal and ultraviolet stabilities than the corresponding copolymer with general stilbene chromophores (PMSt). Moreover, temporal stability of nonlinear optical coefficient (d₃₃) of PMBz copolymer increased in comparison with that of PMSt. The copolymer with benzoxazole–nitrothiophene chromophores had the largest d₃₃ value of 153 pm/V (at 1.064 mm) and nonresonant d₃₃ calculated by the two-level model was 21.3 pm/V.     

Engineered human carboxypeptidase B enzymes that hydrolyse hippuryl-L- glutamic acid: reversed-polarity mutants

Variants of human pancreatic carboxypeptidase B (HCPB), with specificityfor hydrolysis of C-terminal glutamic acid and aspartic acid, were preparedby site-directed mutagenesis of the human gene and expressed in theperiplasm of Escherichia coli. By changing residues in the lining of theS1' pocket of the enzyme, it was possible to reverse the substratespecificity to give variants able to hydrolyse prior to C- terminal acidicamino acid residues instead of the normal C-terminal basic residues. Thiswas achieved by mutating Asp253 at the base of the S1' specificity pocket,which normally interacts with the basic side- chain of the substrate, toeither Lys or Arg. The resulting enzymes had the desired reversed polarityand enzyme activity was improved significantly with further mutations atresidue 251. The [G251T,D253K]HCPB double mutant was 100 times more activeagainst hippuryl-L-glutamic acid (hipp-Glu) as substrate than was thesingle mutant, [D253K]HCPB. Triple mutants, containing additional changesat Ala248, had improved activity against hipp-Glu substrate when position251 was Asn. These reversed-polarity mutants of a human enzyme have thepotential to be used in antibody-directed enzyme prodrug therapy of cancer.     

222Rn concentrations in greenhouses in Aomori Prefecture, Japan

Greenhouses are possible places with high 222Rn concentrations, since soil, the source of 222Rn, is directly exposed inside them. To examine this point, 222Rn concentrations in 28 greenhouses at five locations in Aomori Prefecture were measured for approximately 1 year with passive Rn detectors. For 1 week, measurements of 222Rn concentration and working level were also carried out with active detectors to get equilibrium factors and the ratio of 222Rn concentration in working time to non-working time in selected greenhouses. The geometric mean of annual 222Rn concentrations in greenhouses was 13 Bq m-3, and the same as that in dwellings and lower than that in indoor workplaces in the prefecture. However, variation of the 222Rn concentrations was far larger than in other environments, and ranged from the lowest level in outdoor workplaces to the highest level in indoor workplaces. Significant seasonal variation was also observed in 222Rn concentrations. The mean effective dose from 222Rn and its progenies was estimated to be 0.047 mSv year-1 for a farmer working in a greenhouse.     

Aerodynamic separation of disperse minerals and materials

The paper sums up experimental studies on aerodynamic separation of disperse-type rocks with special reference to beneficiation of Callovian clays and reports the natural radionuclide content of various minerals and materials. Basically new, competitive designs of aerodynamic separators are reported. Translated from Ogneupory i Tekhnicheskaya Keramika, No. 1, pp. 27–29, January, 1998.     

The anthropogenic nitrogen cycle in the Netherlands

Results of a study on the nitrogen flows in the Netherlands are presented for three different years. The details given for 1995 are preliminary. The data are derived from a material balance sheet investigation. The objective of the study is to present a complete, integrated and accurate overview of nitrogen losses from the anthropogenic nitrogen cycle in the country with respect to present and possible future nitrous oxide emissions. Losses are analyzed in terms of economic sources and the recipient environmental compartments. The nitrogen losses account for about 25% of the total nitrogen input in the anthropogenic nitrogen cycle. Most of the losses occur in agriculture (67%), whereas industry, traffic and households each contribute about 10% to the total nitrogen loss. About 15% of the total nitrogen input in the national economy ends up in the environment, where it gives rise to adverse effects as the eutrophication of fresh surface water and the contamination of ground water with nitrate. A comparison of the results for different years shows that little progress has been made in emission reductions so far. Ammonia emissions have been reduced, but at the expense of an increase of the nitrogen input to agricultural soils.     

Catalysis of H2, CO and alkane oxidation–combustion over Pt/Silica catalysts: evidence of coupling and promotion

Results are presented on the oxidative–combustion reactions of H₂, CO, methane and propane over polycrystalline-powdered silica-supported catalysts containing Pt (and possibly oxide promoters, e.g. MnO₂, etc.) and the coupling of different combustion processes and also heterogeneous–homogeneous reactions. The Pt/silica catalysts appear to mature with use. Catalysed combustions take place, as expected, at far lower temperatures and with smaller activation energies than the homogeneous reactions. The role of added or intermediate (i.e. produced by alkane partial oxidation or steam reforming) H₂ in accelerating and lowering the temperatures of catalysed alkane combustions and hence minimising NO_x emission is considered with regard to the dispersion of the Pt, as is bifurcative–hysteretic combustion in the catalysed reaction, prevalent for CO, but less certain for H₂ or alkanes. CO decelerates the catalysed combustion of hydrogen on supported Pt (and may also do this for alkane combustion). Whether the acceleration due to intermediate H₂ in alkane combustion exceeds the deceleration due to intermediate CO remains to be seen, but it may be that the water–gas shift reaction moves the advantage to H₂. Further study by in situ methods will be needed to optimise and understand this coupling so that it can be used to maximise efficient alkane-catalysed combustion with minimum NO_x production. This should also lead to higher turnover numbers (which are at present quite low for propane-catalysed combustion).