An efficient method of FIR filtering based on impulse responserounding

A new method of implementing efficient FIR filters is presented. It involves approximation of an equiripple FIR by a rounding operation and application of the derived impulse response by a simple recursive equation. The technique is extremely efficient for lowpass, highpass, bandpass, and bandstop filters with sharp transitions and low edge frequencies     

Values in educating for citizenship: sources, influences and assessment

This article considers social factors that have led to concerns regarding disaffection and disengagement of young people. The introduction of Citizenship Education in the United Kingdom is seeking to redress conditions of apathy and cynicism about public life. While the indirect transmission of values in relation to democracy and citizenship could previously be relied upon at an implicit level, both the growing diversity of values in society, and the way that values feature in changing concepts of citizenship, require that they be examined and articulated explicitly. The influence of values has been acknowledged in corporate culture and is considered to be a crucial factor in managing educational change. However, the external imposition of values implied by citizenship education appears paternalistic and unrealistic considering the diversity inherent in a multiracial and multicultural society. Rather, the challenge presented to schools lies in taking a framework of democratic values to expose every aspect of education to re-examination. With the values of citizenship and democracy underpinning and directing practice in institutions, citizenship education can become an agenda for democratic change.     

Fabrication and characterization of transducer elements in two-dimensional arrays for medical ultrasound imaging

Some of the problems of developing a two-dimensional (2-D) transducer array for medical imaging are examined. The fabrication of a 2-D array material consisting of lead zirconate titanate (PZT) elements separated by epoxy is discussed. Ultrasound pulses and transmitted radiation patterns from individual elements in the arrays are measured. A diffraction theory for the continuous wave pressure field of a 2-D array element is generalized to include both electrical and acoustical cross-coupling between elements. This theory can be fit to model the measured radiation patterns of 2-D array elements, giving an indication of the level of cross-coupling in the array, and the velocity of the acoustic cross-coupling wave. Improvements in bandwidth and cross-coupling resulting from the inclusion of a front acoustic matching layer are demonstrated, and the effects of including a lossy backing material on the array are discussed. A broadband electrical matching network is described, and pulse-echo waveforms and insertion loss from a 2-D array element are measured.     

Impact of transient chemistry on the corrosion potential of a steam turbine disc steel

The adoption of two-shifting in coal-fired power generation (switching from on-load to off-load conditions on a daily basis and off-load for the weekend) results in regular cycling of the solution chemistry of the condensed steam on the turbine discs. A first stage investigation has been made of the effect of such chemistry cycling on the corrosion potential of the disc steel. The corrosion potential is typically about +0.05 V (SCE) in off-load chemistry (aerated pure water) and below −0.6 V (SCE) in on-load chemistry (deaerated solution containing chloride or chloride and sulphate anions). The critical observation was the sluggish response of the corrosion potential upon restoration of deaerated on-load conditions with the implication of a likely increase in pit and stress corrosion crack development.     

Adjustable Voltage and Frequency Polyphase Sine Wave Signal Generator

An adjustable-voltage adjustable-frequency polyphase reversible-phase sequence sine wave signal generator is described. This signal generator develops the reference waveforms, in this case sine waves, that are required in the control circuits of certain types of static dc to ac inverters and ac to ac cycloconverters. Digital and linear integrated circuits together with passive components are used to generrate the output signals. The output frequency is adjustable from 0 to 500 hertz; the output voltage is adjustable from 0 to 20 volts peak-to-peak. The phase sequence is reversible on command. The theory of operation together with steady-state and transient performance data are presented.     

Mathematical modelling of the electrochemistry in corrosion fatigue cracks in steel corroding in marine environments

A mathematical model has been developed to describe the mass transport and electrochemical conditions in a corrosion fatigue crack in steel in 3.5% NaCl and in sea water for both freely corroding and anodic polarization conditions. Mass transport by advection (fluid flow induced by the movement of the crack walls), diffusion and ion migration was considered. Anodic and cathodic processes, hydrolysis reactions (including hydrolysis of alloying elements) and buffering reactions were included in the model. The pH value developed within the crack at a temperature of 5°C was between 7.0 and 8.5 for a wide range of conditions, with the maximum value controlled by the buffering associated with deposition of ferrous hydroxide. The lower pH values corresponded to relatively high ferrous ion concentration and were obtained for combinations of high R values (minimum/maximum load) and low frequencies for which convective mixing with the bulk solution was minimized. The presence of chromium in the steel at the 1 wt% level had only a small effect on the crack tip pH value in deep cracks but could lower the pH considerably (to about 4.0) in very shallow cracks (2.5 × 10⁻² cm) if the potential was about −600 mV(SCE). The potential drop in the crack was relatively small (<30 mV) for a wide range of conditions at the free corrosion potential for structural steel in sea water ( −690 mV(SCE)) but increased markedly with anodic polarization with the effect most pronounced for deep cracks. Comparison of the model predictions with experimental measurements showed very good agreement with respect to crack tip pH and potential.     

Challenges in modelling the evolution of stress corrosion cracks from pits

The evolution of stress corrosion cracks from pits is important in many industrial applications but continues to be a challenge in both measurement and prediction. Life prediction in these circumstances has to account for pit growth kinetics, the conditions for the transition from pits to cracks, and the growth rate of cracks in the short and long crack domain. An example of importance is the performance of steam turbine rotors in power generation. Although stress corrosion failures are comparatively rare, the consequences can be severe and occasionally catastrophic. Consequently, considerable effort is being focused on evaluating the effect of operational variables on pitting and crack growth and in developing an improved basis for structural integrity assessment. A preliminary mathematical model based on deterministic equations with statistically variable input parameters was developed for simulating the evolution of the pit depth distribution at different exposure times, and the transformation to stress corrosion cracks was based on the Kondo criteria. The model predicted some features of the damage well but recent novel measurements of the evolution of stress corrosion cracks from pits combined with finite element analysis of the strain distribution suggest that the transition from a pit to a crack is more complex than can be accounted for by the Kondo approach.     

Broadly tunable deep blue laser based on a star-shaped oligofluorene truxene

We report amplified spontaneous emission (ASE) and optically pumped deep-blue-emitting distributed feedback (DFB) lasers based on a star-shaped oligofluorene truxene molecule. A low ASE threshold of 2.1 kW/cm² at 439 nm was achieved. The material exhibits a high net gain of 38 cm^?1 and also low optical loss coefficient of 3.5 cm^?1. Second-order DFB lasers show tuning of the emission wavelength from 422 to 473 nm, and a minimum threshold density of 515 W/cm². This is the broadest tuning range (51 nm) reported for organic deep-blue/blue lasing materials.     

Quantitative proton MRS assessment of citrate heterogeneity in normal prostate

Water-suppressed proton spectra of the two major anatomical regions of the normal prostate were acquired with a commercial phased-array multicoil. The spectra demonstrated excellent signal-to-noise ratio and spectral resolution allowing identification of peaks from choline, creatine, and amino acids, as well as a major peak from citrate. Quantification of the citrate peak using tissue water as an internal concentration reference revealed a marked variability among different volunteers. In each case, citrate was consistently twofold to threefold greater in the peripheral zone than in the central gland. The results demonstrate heterogeneity of citrate within the prostate and suggest significant differences in the cytology and hormonal control of citrate synthesis among individuals.