Identification of a class of nonlinear state-space models using RPEtechniques

The RPE (recursive prediction error) method in state-space form is developed in the nonlinear systems and extended to include the exact form of a nonlinearity, thus enabling structure preservation for certain classes of nonlinear systems. Both the discrete and the continuous-discrete versions of the algorithm in an innovations model are investigated, and a nonlinear simulation example shows a quite convincing performance of the filter as combined parameter and state estimator     

Optical networks for local loop applications

Some of the options for optical technology within the local loop environment are examined. In particular, passive shared access networks have been considered in some detail. These networks show great promise for delivering existing telephone services to small to medium business customers (4-30 lines) economically by the early 1990s. Extending fiber to the home will also be possible by virtue of a similar passive network infrastructure for customers requiring new broadband services beyond the single telephone line. For one-line plain old telephone service (POTS) customers, an intermediate approach of terminating the fiber network at the final network distribution point, with copper retained for the final leg, may be used prior to the provision of broadband services. A key feature of the passive optical network architecture is the use of wavelength-division multiplexing (WDM) as an upgrade strategy, allowing graceful upgrading from telephone services to multichannel high-definition television (HDTV) on gigabit/second bearers and full two-way switched broadband services employing wavelength routing across the network     

Boosting nitrification by membrane-attached biofilm.

Nitrification is a key step for reliable biological nitrogen removal. In order to enhance nitrification in the activated sludge (AS) process, membrane-attached biofilm (MAB) was incorporated in a conventional activated sludge tank. Simultaneous organic carbon removal and nitrification of the MAB incorporated activated sludge (AS + MAB) process was investigated with continuous wastewater treatment. The effluent TOC concentration of AS and the AS + MAB processes were about 6.3 mg/L and 7.9 mg/L, respectively. The TOC removal efficiency of both AS and AS + MAB were above 95% during the wastewater treatment, indicating excellent organic carbon removal performance in both processes. Little nitrification occurred in the AS process. On the contrary, successful nitrification was obtained with the AS + MAB process with nitrification efficiency of about 90%. The volumetric and surface nitrification rates were about 0.14 g/Ld and 6.5 g/m2d, respectively. The results clearly demonstrated that nitrification in the conventional AS process was boosted by MAB. Furthermore, the microfaunal population in the AS + MAB process was different from that in the AS process. The high concentration of rotifers in the AS + MAB process was expected to decrease the generation of excess sludge in the process.     

Kinematic nonuniqueness of elastoplastic structures

Lack of uniqueness of the kinematic solution of structures, analyzed as an assemblage of discretized elements assuming nonholonomic linearly-elastic/perfectly-plastic behaviour and a linearized yield surface, is studied. The occurrence of an elastoplastic mechanism leads to nonuniqueness; an elastoplastic mechanism is defined as a kinematically-admissible strain rate field made up of an admissible elastoplastic solution of the governing conditions and an add-on variable component consisting of a linear combination of plastic (collapse) mechanisms. The scalar multipliers of this linear combination are bounded, except at plastic collapse in which case the elastoplastic mechanism degenerates to a plastic mechanism. In the space of loads, the load paths that could coexist with nonuniqueness are restricted to a hyperplane or a crease of intersection of hyperplanes, defined by the equilibrium equations arising from the associated plastic mechanisms of the elastoplastic mechanism. The difference between any two competing displacement vectors would be normal to that hyperplane or crease, in the same manner plastic strain rates are to the yield surface according to the flow rule.     

Comfort limits for asymmetric thermal radiation

Groups of 32 and 16 subjects of both sexes were exposed in an environmental chamber to radiant asymmetry caused by a cool wall, a warm wall, and a cool ceiling. Each subject was tested individually while seated and clothed at 0.6 clo. During each 3.5-hour experiment the subject was exposed to six radiant temperature asymmetries. He was asked whether and where he experienced any local cool or warm sensation, and whether it was felt to be uncomfortable. During the entire experiment he was kept thermally neutral by changing the air temperature according to his wishes.For cool walls, warm walls, and cool ceilings curves have been established showing the percentage of dissatisfied subjects as a function of the radiant asymmetry. Radiant asymmetry at a warm wall caused less discomfort than a cool wall. A cool ceiling caused less discomfort than a warm ceiling. Accepting that 5% of the subjects may feel uncomfortable. a radiant temperature asymmetry of 10°C is allowable at a cool wall, 23°C at a warm wall, and 14°C under a cool ceiling. A previous study showed that 4°C is allowable under a warm ceiling. Radiant asymmetry had no significant impact on the operative temperatures preferred by the subjects. No significant differences were observed between the responses of men and women exposed to radiant asymmetry.     

Quantitative determination of aflatoxin B1 in chick liver

A method for the rapid and quantitative determination of aflatoxin B1 from small quantities of liver, around 1-2 g, is described. The extraction procedure involves acidification to pH 2 of the aqueous liver homogenates, extraction with chloroform: acetone and HPLC-fluorimetric detection after derivatization with trifluoroacetic acid. Quantitative recovery of aflatoxin B1 from chick liver was achieved and detection at levels of 0.2-1 ppb was proved feasible. The aflatoxin B1 concentration in chick liver after oral administration is also shown.     

Hydrologic regionalisation impacts on wet-weather control selection.

Continuous simulation is performed using the US Environmental Protection Agency (USEPA) Storm Water Management Model (SWMM) to evaluate regional differences around the United States in hydrologic and water quality performance of wet-weather controls. Controls are characterised as being limited by peak inflow rate (i.e. any device with little or no storage, such as screens, filters and some proprietary devices) or by storage capacity (e.g., ponds, tanks). For flow-limited devices, results are presented in the form of percentage of annual runoff volume captured (passing through the device) for a given inflow capacity. For storage-limited devices, results are presented in two forms: percentage of annual runoff volume captured as a function of unit basin size and drawdown (drain) time, and as a percentage of total suspended solids captured, for the same two variables. Regional differences are apparent, driven mainly by variations in rainfall patterns around the country.     

THEORETICAL STUDY OF A NEW MATERIAL FOR FILTERS: AEROGELS

Aerogels are highly porous materials made by removing the liquid phase of a dilute suspension of solids by taking off the vapor under super-critical temperature and pressure conditions. The aerogel structure has a skeleton of nanometer-size elements forming pores that are tens of nanometers in dimension. In some cases the structure of the aerogel arises from clusters having fractal geometry. The collection efficiency and pressure drop for such material is predicted here from models in the literature. A quality factor is used to compare aerogel material with other filter materials. The quality factor relating gas filtration efficiency with pressure drop is predicted to be unusually high for these materials in comparison with other common fibrous filter media, predicting lower flow resistance for aerogels at equivalent particle collection efficiency levels.     

Toughening of Dental Porcelain by Tetragonal ZrO2 Additions

The effect on mechanical behavior of ZrO₂ additions to a dental porcelain was investigated. The ZrO₂ was introduced into the glassy matrix phase of the porcelain by refritting the all-glass porcelain constituent. X-ray diffraction indicated that a sizeable fraction of the ZrO₂ was retained in the tetragonal form after the porcelain was fired. Zirconia additions to the porcelain produced substantial improvements in fracture toughness, strength, and thermal shock resistance.     

Pesticide monitoring programme of the Ministry of Health of Brazil

The structure of the recently introduced Brazilian government programme for monitoring pesticide residues in six major agricultural products is described. Residues found from the analysis of samples of tomatoes and strawberries are discussed in detail. The much greater frequency of detection of pesticide residues, many of which are not approved for use in Brazil, in produce being sold on the domestic market, as opposed to that produced for export, is of major concern. It is perceived that this new monitoring programme will become permanent and be used to underpin enforcement actions that will need to be taken to reduce the numbers of incidents of illegal residues occurring, particularly in fresh fruits and vegetables.