Pseudoactive bridge for separation of R and C in a practical capacitive/conductive transducer

An effective and unique method of measuring independently the variations of resistive and capacitive constituents of a practical capacitive transducer using an improved pseudo-active bridge is described. The impedance change in some types of transducers may be due to changes in resistance and/or capacitance either way. Separation of changes in resistance and capacitance results in a better understanding of the transduced variable. The active bridge which separates the changes is suitable for online determination of the two changes.     

Surface contours in the axi-symmetric upsetting of solid cylinders

Surface flow contours during the axi-symmetric upsetting of aluminium, Sn-Pb eutectic alloy and Plasticine have been studied as a function of the extent of deformation, frictional condition and height-to-diameter ratio. The roughness of the end faces after upsetting has also been measured. The results have been explained in terms of the changes in the frictional condition, the strain-rate sensitivity and the local strain rate and it is concluded (a) that cold upsetting of a material of negligible strain-rate sensitivity gives rise to a parabolically-shaped barrel, (b) that hot upsetting the Sn-Pb alloy specimens of height-to-diameter ratio 1.5 results in a linear increase in diameter from the top to the bottom of specimens, due to a linear decrease in strain rate in the same direction, (c) that hot compression of Plasticine specimens and Sn-Pb alloy specimens of height-to-diameter ratio 2.0 leads to complex shape changes which cannot be predicted using the present knowledge concerning the upsetting of strain-rate sensitive materials and (d) that the greater increase in roughness following significant compression of the end faces of lubricated specimens, compared with that observed for unlubricated specimens, is due to enhanced surface metal flow with a decrease in frictional constraints.     

Room-temperature forming limit diagram and tensile behaviour up to 200° C of an AI-Ca-Zn superplastic alloy

The forming limit diagram and strain distribution under punch stretching at room temperature of an AI-Ca-Zn (superplastic) alloy have been evaluated. Tensile behaviour up to 200° C is reported. The fracture surfaces have been examined by scanning electron microscopy and the results are analysed to support the failure criterion proposed earlier by Marciniaket al.     

Glycoform composition of serum gonadotrophins through the normal menstrual cycle and in the post-menopausal state

The heterogeneity of follicle stimulating hormone (FSH) and luteinizing hormone (LH) was investigated in five women aged 29.4 +/- 3.2 years (mean +/- SD) throughout their menstrual cycles and in five post-menopausal women aged 53.8 +/- 5.6 years. Chromatofocusing (pH range 7-4) revealed menstrual cycle stage- and postmenopausal-related differences in the serum gonadotrophin charge. There were differences in the proportion of FSH with an isoelectric point (pl) > 4.3 across phases of the menstrual cycle (P = 0.019): midcycle (MC) 50%; early to mid-follicular (EMF) 36%; late follicular (LF) 37%, luteal (L) 29% and following the menopause (PM) 17%. There was no significant difference in the proportion of LH with pl > 6.55 between midcycle (53%) and EMF, LF or L phases (36, 43 and 32% respectively); although all were greater than that found in the menopause (13%). Concanavalin A chromatography revealed less (P < 0.005) complex FSH and LH glycoforms at midcycle (63 and 13%) than in the EMF, LF and L phases (90 and 18; 90 and 20 and 93 and 24% respectively). Menopausal gonadotrophins were least complex (FSH 34%, LH 4%). There was a direct relationship between serum FSH and FSH pl/complexity, and less acidic FSH was associated with reduced FSH complexity. Increased oestradiol was associated with basic FSH isoforms during the menstrual cycle and reduced follicular phase FSH complexity. We conclude that changes in gonadotrophin glycoforms occur through the menstrual cycle which are related to changes in the prevailing steroid environment. Following the menopause oestrogenic loss resulted in acidic, relatively simple glycoforms.     

Accelerometer type cardiac transducer for detection of low-levelheart sounds

The authors compare several different cardiac transducers and describe the development of a low-mass, accelerometer-type cardiac transducer which fulfils these objectives. The accelerometer weighs approximately 5 g and has a theoretical sensitivity of 125 mV/g in the frequency range 200-800 Hz. The basic design allows for easy modification of sensitivity and resonant frequency. This transducer has been effective in detecting sound associated with turbulent blood flow in partially occluded coronary arteries     

Numerical analysis of pressure transients in bubbly two-phase mixtures by explicit-implicit methods

Summary The one-dimensional equations for transient two-phase flow are a system of nonlinear hyperbolic partial differential equations, expressible, under certain assumptions, in conservation form. Inasmuch as the use of the method of characteristics becomes complicated if shock waves are present, it is easier to follow a gas-dynamics approach and employ one of the available procedures for solving one-dimensional systems of conservation equations. A recently introduced technique, due to McGuire and Morris [1, see also 12] and known as an Explicit-Implicit method, is used here for a simple boundary-value problem of wave propagation in bubbly two-phase mixtures, and is found to be simple and versatile. A comparison of this method with the well-known Lax-Wendroff (two-step) scheme demonstrates that shock fronts are simulated better, oscillations behind the shocks are smoothable by parameter adjustment, and computation time is reduced when the Explicit-Implicit method is employed.     

Fast and scalable wireless handoffs in support of mobile Internet audio

Future internetworks will include large numbers of portable devices moving among small wireless cells. We propose a hierarchical mobility management scheme for such networks. Our scheme exploits locality in user mobility to restrict handoff processing to the vicinity of a mobile node. It thus reduces handoff latency and the load on the internetwork. Our design is based on the Internet Protocol (IP) and is compatible with the Mobile IP standard. We also present experimental results for the lowest level of the hierarchy. We implemented our local handoff mechanism on Unix-based portable computers and base stations, and evaluated its performance on a WaveLAN network. These experiments show that our handoffs are fast enough to avoid noticeable disruptions in interactive audio traffic. For example, our handoff protocol completes less than 10 milliseconds after a mobile node initiates it. Our mechanism also recovers from packet losses suffered during the transition from one cell to another. This work helps extend Internet telephony and teleconferencing to mobile devices that communicate over wireless networks. This revised version was published online in June 2006 with corrections to the Cover Date.     

A direct second-variational method for unconstrained optimal control problems

A direct second-variational algorithm is proposed for the iterative solution of optimal control problems in continuous, as well as discrete, systems. While the classical method using the Riccati transformation is shown to follow from the direct method, the latter has certain promising features in terms of structural simplicity, ease of programming, and substantial reduction in computation time. The process involves a predictor-corrector algorithm for a forward sweep in the state equations, followed by a backwards sweep in the adjoint equations. Applied to discrete systems, this method functions under conditions less stringent than in the classical scheme. Linearized quasioptimal feedback control is examined from the point of view of the direct method and a scheme for successive improvement in quasi-optimal policy is proposed for systems that suffer small perturbations from a given optimal trajectory.     

A method for estimating the optimum load resistance of a silicon solar cell used in terrestrial power applications

Solar intensity undergoes significant changes from dawn to dusk. Further, the power output of a silicon solar cell is a function of the load resistance. A load resistance (R_m) giving maximum conversi n efficiency at mid-day becomes less efficient at other times of the day under reduced intensity levels. The load resistance must be optimised to derive maximum overall power output for the whole day, taking intensity variations into account. A method for estimating the optimum load resistance (R_opt) is presented here. It is also shown that considerable improvement in the output of a terrestrial power system could be achieved at solar intensities 100 MW cm².