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  • Engineering General  (3)
  • GASTRIC ELECTRICAL ACTIVITY  (3)
  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Digestive diseases and sciences 42 (1997), S. 1154-1157 
    ISSN: 1573-2568
    Keywords: ELECTROGASTROGRAMS ; GASTRIC ELECTRICAL ACTIVITY ; POWER DYNAMICS
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract This study was undertaken to investigate thecorrelation between power dynamics of gastric electricalactivity (GEA) assessed with different recordingtechniques. A total of seven eight-channel 1-hr combined recordings were obtained from three subjects infive consecutive postoperative days. Four channels wererecorded from bipolar electrodes implanted into thegastric antral wall, and four channels wereelectrogastrographic (EGG). Six pairs of bipolar electrodes wereinserted into the antral wall (three anterior; threeposterior) of 16 anaesthetized dogs. Fourteen-channel(six internal GEA and eight EGG) 1/2-hr recordings were obtained from each dog. Sets of powervalues calculated from channel pairs (internal, EGG ormixed) were cross-correlated and the significance of theobtained correlation coefficients was examined (P 〈 0.05). The majority of powercorrelations of internal GEA channel pairs, and those ofmixed (internal GEA-EGG) channel pairs wereinsignificant. These findings question the claims thatEGG power dynamics mirrors the power dynamics of internalGEA.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Digestive diseases and sciences 43 (1998), S. 953-956 
    ISSN: 1573-2568
    Keywords: GASTRIC ELECTRICAL ACTIVITY ; ELECTROGASTROGRAPHY ; RANDOMNESS
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract This study was undertaken to investigate thedynamics of the level of randomness in gastricelectrical signals. Combined recordings of internalgastric electrical activity (GEA) and electrogastrograms(EGG) were obtained from 16 unconscious dogs and twopostoperative patients. The signals were amplified usingspecially designed amplifiers with flexible frequencyrange and were digitized with 10-Hz sampling frequency. The 4.27-min portions of the digitalsignals were subjected to a previously described turningpoint test for randomness. The distributions of thenumber of turning points (NTP) in successive time intervals calculated from all GEA signalswere compared to the estimated NTP distribution of arandom signal. NTP dynamics of internal GEA signals wasalso correlated to the NTP dynamics of cutaneous EGG. In five of 16 recordings from the dogs andin two of the 14 recordings from the patients, NTPvalues calculated from some internal GEA channelsexceeded the 1% probability level for entering thenormal NTP distribution of a random signal (P 〉0.01). In all measurements the distributions of the NTPvalues recorded from cutaneous EGG channels weresignificantly different (P 〈 0.01) from the NTPdistribution of a random signal. There was significantcorrelation (P 〈 0.01) between the NTP dynamics ofinternal GEA and EGG. The level of randomness ininternal GEA recorded with the short-distance bipolartechnique is substantially higher than that in cutaneousEGG, probably due to the occurrence of spike activity.Although the level of randomness in EGG is affected bymany external factors, its dynamics correlated significantly with the level of randomness ininternal GEA.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1573-2568
    Keywords: GASTRIC ELECTRICAL ACTIVITY ; ELECTROGASTROGRAPHY ; RANDOMNESS ; GASTRIC ELECTRICAL UNCOUPLING
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Gastric electrical uncoupling is the lack ofelectrical synchronization in different parts of thestomach. The aim of this study was to investigate theimpact of gastric electrical uncoupling on the level of randomness of canine electrogastrograms(EGG). Electrogastrograms were obtained from 11unconscious acute dogs. Gastric electrical uncouplingwas produced surgically by performing two consecutivecircumferential cuts through the entire thickness of thegastric muscle layer. Three separate 1/2-hreight-channel bipolar EGGs were obtained from each dogin the basal state and after each cut. The signals wereamplified using amplifiers with a flexible frequencyrange, digitized with 10-Hz sampling frequency, and4.27-min portions of the digital EGGs weResubjected toa turning point test for randomness. The number of turning points (NTPs) was determined fromsuccessive time intervals calculated from all EGGchannels. Distributions of NTPs were calculated for eachdog. An average NTPs (ANTP) for each dog in a givenstate (basal, after the first cut, and after thesecond cut) was calculated from the ANTPs of allchannels. In six of 11 dogs the ANTP were greater afterthe first cut. The number rose to nine of 11 dogs after the second cut. In only 45% of the dogs werethe ANTP distributions significantly different (P 〈0.01) after the first cut (sensitivity 45%). After thesecond cut the sensitivity rose to 64%. In two specific EGG channels NTP distribution wassignificantly different (P 〈 0.01) in nine of 11 dogs(sensitivity: 82% ) after the second cut. The dynamicsof the level of randomness in EGG can be indicative of severe gastric electrical uncoupling. SomeEGG channel configurations are moResensitive thanoThers in recognizing gastric electricaluncoupling.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 38 (1995), S. 1149-1170 
    ISSN: 0029-5981
    Keywords: material design ; structural optimization ; multiple loads ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: An extension of recent work1 on the simultaneous optimization of material and structure to address the design of structures under multiple loading conditions is presented. Material properties are represented in the most general form possible, namely, as elements of the unrestricted set of positive-semi-definite constitutive tensors of a linearly elastic continuum. Existence of solutions can be shown when the objective is a weighted average of compliances and a resource constraint measured as the 2-norm or the trace of the constitutive tensors is included. The optimized material properties can be derived analytically. The optimization of the layout of the material leads to a sizing problem of structural optimization involving a non-linear, non-smooth elasticity analysis. The computational solution of this problem is discussed and illustrated with examples.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 38 (1995), S. 3483-3495 
    ISSN: 0029-5981
    Keywords: discretized Green's functions ; multiple scattering ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: Discretization of boundary integral equations leads to large full systems of algebraic equations, in practice. Partitioning is a method for solving such systems by breaking them down into smaller systems. It may be viewed merely as a technique from linear algebra. However, it is profitable to view it as arising directly from partitions of the boundary; these partitions could be natural (such as two separate boundaries) but they need not be. We investigate partitioning in the context of multiple scattering of acoustic waves by two sound-hard obstacles (the ideas extend to other physical situations). Specifically, we make a connection between partitioning and the use of the exact Green's function for a single obstacle in isolation. This suggests computing the action of this Green's function once-and-for-all, storing it (perhaps on a compact disc), and then using it to solve other problems in which the second obstacle is altered. One example of this approach is computing the stress distribution around a cavity of a standard-but-complicated shape inside a structure whose shape is varied. The theoretical foundation for these ideas is given, as well as a connection with the use of generalized Born series for multiple-scattering problems. Important distinctions between the partitioning/Green's function idea in this paper and seemingly similar ideas such as substructuring, multi-zoning, and domain decomposition are made.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 39 (1996), S. 687-704 
    ISSN: 0029-5981
    Keywords: boundary element methods ; Cauchy principal-value integrals ; Hadamard finite-part integrals ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: Hypersingular integrals are guaranteed to exist at a point x only if the density function f in the integrand satisfies certain conditions in a neighbourhood of x. It is well known that a sufficient condition is that f has a Hölder-continuous first derivative. This is a stringent condition, especially when it is incorporated into boundary-element methods for solving hypersingular integral equations. This paper is concerned with finding weaker conditions for the existence of one-dimensional Hadamard finite-part integrals: it is shown that it is sufficient for the even part of f (with respect to x) to have a Hölder-continuous first derivative - the odd part is allowed to be discontinuous. A similar condition is obtained for Cauchy principal-value integrals. These simple results have non-trivial consequences. They are applied to the calculation of the tangential derivative of a single-layer potential and to the normal derivative of a double-layer potential. Particular attention is paid to discontinuous densities and to discontinuous boundary conditions. Also, despite the weaker sufficient conditions, it is reaffirmed that, for hypersingular integral equations, collocation at a point x at the junction between two standard conforming boundary elements is not permissible, theoretically. Various modifications to the definition of finite-part integral are explored.
    Type of Medium: Electronic Resource
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