A Micropower Adaptive Linear Transform Vector Quantiser

Micropower signal classification and compression are becoming important requirements for implantable cardioverter defibrillators although they are currently limited by power and computational constraints. This paper describes an integrated circuit that facilitates Intracardiac Electrogram (ICEG) classification and compression of 30 dimensional analogue vectors while consuming a maximum of 2.5 W power for a heart rate of 60 beats per minute (1 vector per second) from a 3.3 V supply. This represents a significant advance on previous work which achieved ultra low power supervised morphology classification [6] since the templated matching scheme used in this chip enables unsupervised blind classification of abnormal rhythms and the computational support for low bit rate data compression. The adaptive template matching scheme used is tolerant to amplitude variations, and inter- and intra-sample time shifts. Micropower performance is achieved using CMOS analogue circuits biased in weak inversion in order to minimise energy per computation. Results from the fabricated chip demonstrate the impact of the amplitude and shift tolerance on ICEG data and performance for blind classification of an abnormal rhythm in five heart patients. For four out of the five patients, no false negative classifications and a worst case of 11% false positive classifications were made.     

Symbolic analysis of large-scale networks using a hierarchical signal flowgraph approach

This paper presents an approach suitable for the symbolic analysis of large-scale active networks. The method depends on the partitioning of the network into smaller networks which are then symbolically analyzed noniteratively using the Mason's signal flowgraph models of each partition. The resulting solutions, which are reduced signal flowgraphs (transfer functions) for the subnetworks are then hierarchically combined to produce the final solution or solutions (transfer functions) for the entire system. The advantage of such an approach is the reduction in the number of symbolic terms compared to the conventional approaches, and the ability to analyze hybrid systems consisting of electrical and nonelectrical parts. The result of the analysis is a series of equations that have an upward hierarchical dependency on each other.     

Nondestructive detection of flaws in material using transducer arrays

In this paper, we describe a system which uses array filters for processing the recordings of an array of transducers for the purpose of locating possible flaws in the material being tested nondestructively. When applied, in order to focus the array outputs at a point inside the material, these filters are able to attenuate, very effectively, interfering residual energy scattered from adjacent flaws, as well as random noise. If there is a flaw at the point of focus, the summed output of the filters will have a large signal at a delay time corresponding to the total travel time for this point; otherwise the output will consist mainly of residual random noise. Thus, the location of flaws or even microflaws in material may be achieved by simple threshold detection.     

Looking back: KDKA [radio station]

At 8:00 p.m., 2 November 1920, KDKA of East Pittsburgh, Pennsylvania began broadcasting the Harding-Cox presidential election returns. With a power output of 100 watts, the transmitter's signals reached homes several hundred miles from the world's first commercial radio station. Its great success led its owner, the Westinghouse Electric and Manufacturing Company, to increase its power output by 10-fold within one year. By the end of 1923, KDKA was heard regularly all over the United States as well as some parts of Europe, South America and the Hawaiian Islands     

Numerical modelling and mechanical behaviour analysis of ancient tunnel masonry structures

As with all older construction, ancient tunnels feature particular characteristics, especially as regards past construction methods, geometrical design considerations and the set of construction materials used. Old tunnels usually display a unique vaulted section shape built with masonry. The present paper proposes two numerical models of an old tunnel supported by masonry; these models were developed by the well-known Universal Distinct Element Code (UDEC). A masonry mechanical behaviour analysis and numerical simulation of the masonry ageing phenomenon will also be addressed by means of an experimental design to study the influence of masonry block physical properties on the mechanical behaviour of masonry structures in old tunnels.     

Epoxy–lignin polyblends. III. Thermal properties and infrared analysis

Differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and IR analysis were performed on a nonviscous epoxy polymer system (EP) with Kraft lignin (L) up to 20%. Mixtures of EP with similar amounts of silica (S) as in EP–L polyblends were used as a reference system for the analyses performed. EP–L polyblends cured at room temperature exhibit a single T_g, a fact characteristic for the monophasic systems. One-step tensile storage modulus vs. temperature curves, and related one-peak tensile loss modulus vs. temperature curves were found for all the EP–L polyblends. At about 30°C the tensile storage modulus of EP does not change in the presence of lignin in amounts up to 20% by weight. All these showed that L is miscible with EP and it does not affect the crosslinking at room temperature. IR spectra led to similar conclusions. The gradual decrease of the peak values of tan δ with the amount of L in polyblends is due to an increase in the tensile storage modulus and a decrease of the tensile loss modulus at temperatures close to T_g. This fact is explained by a stronger bond between EP and L, which could be formed at higher temperatures. The DSC and DMA data are in agreement with the mechanical properties of EP–L polyblends, which were reported previously.     

Game theory applied to dynamic duopoly problems with production constraints

In this paper an application of differential game theory in the area of microeconomics is presented. The problem considered is that of a dynamic duopoly where two firms each limited by a maximum capacity of production, share the same market, and try simultaneously but independently to maximize their profits over a certain planning horizon. While the static duopoly theory does not address itself to the question of the process by which changes in the price are brought about, but only compares the prices before and after the change takes place, the dynamic market theory, considered in this paper, allows for an analysis of how the price changes with time and what trajectory it follows. Necessary conditions for the existence of a Nash equilibrium solution in the general case are discussed and more specific results for the special case of linear demand and quadratic cost functions are developed.     

Failure and Dilatancy Properties of Sand at Relatively Low Stresses

Analysis of geotechnical problems concerned by low confinement such as design of shallow foundations and analysis of slope stability and soil liquefaction requires modeling of the soil behavior at low stresses. This note includes a laboratory study of the behavior of Hostun RF sand at low cell pressure (20–50?kPa). Isotropic and triaxial compression drained tests were performed. Drained tests show that both failure and dilatancy angles at low stresses are stress dependent. The contractive/dilative phase transition is observed for loose sand, which may result from the overconsolidated nature of this sand for low values of cell pressure.