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Wheatstone bridge has long been used in many strain-gauge based measuring instruments including the local displacement transducer. In this paper, an alternative circuit to the Wheatstone bridge, Anderson loop, for local displacement transducers is examined. Local displacement transducers were manufactured in an identical fashion but with different circuitries. In both circuitries, similar gain and filter were applied to the output signals. An identical experimental setup for both Anderson loop and Wheatstone bridge local displacement transducers was used in the evaluation, and, therefore, any differences in performances of the local displacement transducers are attributed to the circuitry. The range of displacement examined for the local displacement transducer was 0.4 mm. Self-heating of the strain gauges was found to occur regardless of the circuitry used when a high input current was used in the local displacement transducer with Anderson loop or a high input voltage was used in the local displacement transducer with Wheatstone bridge. The effects of self-heating of strain gauges are only evident in long duration tests. The local displacement transducer with Anderson loop was found to be twice as sensitive as that with Wheatstone bridge for similar input current. Furthermore, the local displacement transducer with Anderson loop outperformed the local displacement transducer with Wheatstone bridge in terms of lower deviation, hysteresis and repeatability errors.

The sorption characteristics of citric acid modified wood to remove copper and lead ions from aqueous solution under batch conditions have been investigated. Sorption was pH dependent with increasing uptake at higher pH values. The kinetics of sorption for both ions was rapid with 90% sorption taking place within the first 60 min regardless of its initial concentration. Sorption can be explained by a second-order kinetics model from which the rate constant, the equilibrium sorption capacity and the initial rate were calculated. From these parameters, the predictive models for Cu and Pb sorbed ( q t) in time t and at an initial concentration ( C o) are given by q t= C o t[0.31 C o−2.29+(0.04 C o+5.19) t] and q t= C o t/[0.06 C o−6.59+(0.01 C o+4.48) t] for Cu and Pb, respectively. Using these models the predicted and experimental uptakes of Cu and Pb were compared and discussed. Maximum sorption capacities of modified wood under present experimental conditions were 23.70 and 82.64 mg/g for Cu and Pb, respectively. However, for untreated wood the corresponding values were 2.56 and 7.71 mg/g indicating a tenfold increase in sorption upon citric acid modification. Ethylene diamine tetraacetic acid and nitrilotriacetic acid complexed with both ions render sorption less favorably. However, salicylic acid had little influence. In a binary system, Pb ions were more favorably sorbed than Cu ions which could be due to the larger ionic radius of the former ions.

A plug-in digital repetitive learning (RC) controller is proposed to eliminate periodic tracking errors in constant-voltage constant-frequency (CVCF) pulse-width modulated (PWM) DC/AC converter systems. The design of the RC controller is systematically developed and the stability analysis of the overall system is discussed. The periodic errors are forced toward zero asymptotically and the total harmonics distortion (THD) of the output voltage is substantially reduced under parameter uncertainties and load disturbances. Simulation and experimental results are provided to illustrate the validity of the proposed scheme.

A recent study [J. Opt. Soc. Am. A15, 2720 (1998)] showed that the eikonal equation can be generalized to include higher-order terms that can describe the dispersion of a pulse in a linear medium. In this companion paper, the formalism of this generalized eikonal approximation is investigated for stationary waves in both linear and nonlinear media. A local refractive index can be defined that includes higher-order terms in the form of the second derivatives of the amplitude of the wave. It is shown that wave phenomena such as diffraction, self-focusing, and self-trapping of a finite beam in linear and nonlinear media can be derived naturally as a result of the differences in the local refractive indices that arise from the spatial variation of the wave amplitude and the nonlinearity of the medium. This formalism can be readily extended to the study of other complex electromagnetic wave-propagation phenomena in both linear and nonlinear media.

The asymptotic theory of eikonal approximation permits electromagnetic fields to be described locally in terms of plane waves and the trajectory to be described as space–time rays. Properties of these space–time rays in a dispersive medium can be studied through the effective index of refraction defined by the higher-order space–time eikonal equation. From the analysis it is shown that the diffraction effects due to the finite size of the beam and the dispersion effects due to the finite pulse width can be treated in a unified manner in the generalized space–time eikonal equation. The space–time rays of a Gaussian pulse in a dispersive medium can be readily solved analytically and shown to provide results similar to those obtained by the Fourier transformation method.

The potential of carbonized spent bleaching earth (CSBE) to remove/reduce acid and basic dyes in aqueous solution was investigated. Results show that CSBE was more effective in removing basic dyes. Parameters like pH, initial concentration, agitation rate, contact time and temperature which affect the sorption process were studied. As determined from Langmuir isotherms the maximum sorption capacities of CSBE for Basic Blue 3 and Methylene Blue were 102.6 and 94.5 mg/g respectively. Hence CSBE could be a useful sorbent in the treatment of baisc dyes in wastewater.

Biomass of non-living dried water hyacinth roots, Eichhornia crassipes, showed high sorption for copper from aqueous solutions. Maximum sorption was 20.90 mg Cu/g as determined from Langmuir isotherm. Several factors affecting sorption were investigated. They include effect of pH, initial concentrations, presence of chelators and other metals. The feasibility of removing copper from electroplating waste using this material in a packed-bed system was also discussed.

The removal of trivalent chromium from synthetic solution by hexane-extracted spent bleaching earth was investigated on a laboratory scale under various conditions. Data obtained followed the Langmuir isotherm for the Cr(III)-hexane extracted spent bleaching earth. Maximum sorption was calculated to be 9.48 mg/g at room temperature.

A major variable to consider in the production of biologicals from mammalian cell cultures is the mode of operation, be it a batch, continuous, perfusion, fed-batch or other production method. The final choice must consider a number of fundamental and economic issues. Here we present some antibody production data from different cell lines using different modes of production and discuss the important factors for consideration in choosing a production strategy. It was found that the productivity of batch cultures was lower than that obtained in continuous and perfused cultures, but that productivity could be improved by implementing suitable feeding strategies. The antibody productivity of one cell line, MCL1, during exponential phase was not affected by media type or glucose level. The maximum productivity of two cell lines in continuous culture was found to occur at dilution rates below the maximum, from 0.019 to 0.030 hr-1.

Three different hybridoma cell lines, grown in serum-free media with different levels of Pluronic F-68, were subjected to a shear force of 0.6 N m-2. Some protective effect due to the polymer was found, indicating it to be a potentially useful adjuvant in serum-free media. Other observations of liquid and gas effects at the reactor level have been included here. A discussion of the difference between suspension and microcarrier cultures, in relation to hydrodynamic effects, is included.

While laser beams are essential for endoscopic photodynamic therapy (PDT), many types of superficial tumors can be treated effectively using incoherent light sources which are appropriately filtered. This paper reports on clinical trials using simple and effective red light sources modified from an overhead projector and a surgical headlamp with fiber optic output. More than 1 W of effective red light can be obtained and used effectively in the palliative control of large superficial lesions in initial trial cases of three types of malignancies. The use of simple light sources for the treatment of superficial tumors avoids the technical complexities associated with laser sources and enables ready observations of treatment response. Such clinical trials should be conducted extensively in the development of PDT as a viable cancer treatment modality prior to the development of endoscopic procedures.

In photodynamic therapy (PDT), red light is administered 24 - 72 hours post intravenous (i.v.) injection of hematoporphyrin derivatives (HpD). In an earlier animal model study, more effective therapeutic response was obtained when red light irradiation was carried out 15 mins after the injection of HpD. The effectiveness of this immediate PDT protocol has been correlated to the high serum level of HpD immediately after administration and the destruction of the microcirculation system as the dominant tumor destruction mechanism. This study examines the pharmacokinetics and the serum levels of HpD in rats and also in human patients. Such data can assist in defining the optimum time delay for light irradiation in the PDT of cancer.

Before going into service, high tensile steel chains are subjected to a manufacturing test load that causes plastic deformation and profoundly affects the chain's mechanical properties, particularly under fatigue loading. The residual stresses thus introduced have been calculated by the finite element method and compared with neutron diffraction measurements. Satisfactory agreement has been obtained.MST/1155

The in vivo uptake of Tc-99m-labelled HpD in a murine tumour has been investigated using nuclear imaging techniques. Eighty-four per cent of the palpable tumours were visualized with good contrast resolution. The peak tumour-to-surrounding-normal-tissue ratio of 5:1 was at 4 h post-injection indicating the optimum time of imaging. The high level of HpD in the blood-pool component of the tumour could indicate that photodynamic therapy administered within 2 h after intravenous injection (‘early PDT’) could lead to damage of tumour vasculature and tumour necrosis. The therapeutic response achieved by this early method needs to be investigated.

From continuous culture studies it has been shown that the protein concentrations of strains of Z. mobilis (62–68%) were appreciably higher than for the yeast S.uvarum (45–50%). The DNA and RNA contents were similar for the two species. Comparison of the essential amino acids indicated that Z.mobilis did not exhibit the deficiency in methionine which was apparent in the yeast. Such a study of the macromolecular composition of cells of Z.mobilis is important in assessing its by-product nutritional value for animal feed supplementation.

The chlorophyll (CHL) content in palm oil extracted from oil palm fruits, Elaeis guineensis, at various stages of ripeness was determined. It was found that oils from ripe fruits of the same age contained different levels of CHL. In addition it was noted that fruits from palms planted at the centre and those at the edge of the field seemed to ripen at different rates. Those at the centre of the field contained higher levels of CHL when compared with those of the same age produced at the edge of the field. This phenomenon could be due to topographical effects whereby the palms at the edge of the field were exposed to much more sunlight. This probably hastened the process of fruit ripening. A survey on CHL levels in commercial CPO samples supplied by mills showed the presence of CHL in all samples analysed. The range observed was between 250 and 1800 μg kg^-1 with a mean value of 930±107 μg kg^-1. This implied wide variations in the ripeness of palm fruits processed by the mills. ©1997 SCI

Studies were carried out to assess the capability of a moss, Calymperes delessertii Besch, to remove copper from solution. Both batch and column experiments were performed, taking into account such parameters as pH, sorbent dosage, copper concentration, presence of other metal ions, temperature, contact time, column height and flow'rate. The results show that the moss is an efficient sorbent for copper removal and the mechanism is mainly an ion-exchange process.

The sorption of Cr(VI) from synthetic solution and electroplating waste by quaternized rice hulls was investigated under laboratory conditions to assess its potential in removing Cr(VI). The results show that quaternized rice hulls provided higher sorption capacity and a more workable pH range as compared to the untreated rice hulls. From the Langmuir isotherm the maximum sorption capacity of Cr(VI) was 32.3 mg/g at pH 4.82 at 25° C. Column studies showed that Cr(VI) and Cu(ll) from electroplating waste could be successfully removed or reduced using a combination of untreated and quaternized rice hulls. The effect of different anions on the sorption capacity of quarternized rice hulls was discussed.

Equilibrium sorption of copper and related heavy metal cations by dye-coated moss, Calymperes delessertii, Desch. was investigated under various conditions. Parameters studied include contact time, different initial concentrations, pH, presence of chelators and other metal cations. Results showed that modification through dye-coating improved the sorption capacity of the moss. The application of such a system to electroplating waste is discussed.

This paper describes the setup of a precise thrust stand based on torsional pendulum design for characterizing the performance of microthrusters. Calibration has been carried out by using an improved version of electrostatic calibrator, which produces a wide range of accurate and repeatable calibration force. After the calibration, the thrust stand can resolve constant force from 40uN to 3.4mN and impulse bit from 7uNs to 340uNs. The usefulness of the thrust stand has been demonstrated by measuring the performance of two different microthrusters: a pulsed plasma thruster that produces impulse bit of 23.15uNs and a vaporizing liquid microthruster that produces steady state thrust of 633.5uN.