摘要 :
Electrogram analysis is important in clinical and experimental settings. Activation recovery interval (ARI) has been used to measure ventricular action potential duration (APD) but its suitability for the atria has not been addre...
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Electrogram analysis is important in clinical and experimental settings. Activation recovery interval (ARI) has been used to measure ventricular action potential duration (APD) but its suitability for the atria has not been addressed. Mapping of atrial repolarization may be especially important during nerve stimulation since large heterogenous APD changes may manifest. This study assessed the utility of estimating APD in the atria using electrograms. A computer model of the atria was used to compute electrograms. Two different atrial waveforms were used, as well as two ventricular. APD was modulated with an acetylcholine- (ACh) dependent potassium channel and varying the spatial ACh distribution. ARI was computed, as well as the area under the repolarization wave (ATa). APD was measured by four methods. Atrial electrograms were also compared to monophasic action potentials recorded from a dog. ARI computed from atrial action potentials was not very precise, with errors ranging over 30 ms. Determining changes in APD induced by changing [ACh] yielded larger errors. Conversely, ventricular action potentials produced ARIs that very closely correlated with APD, and changes in APD . Positive ATa indicated regions of shortened APD, and islands of ACh release were clearly demarcated by ATa polarity. Experimentally, ARI was able to detect changes in APD, but did not measure APD well. The faster rate of ventricular repolarization produces larger currents that are less susceptible to electrotonic coupling effects, improving correlation with APD. ARI most closely correlated with APD measured as a fixed threshold above rest. Atrial APs produce electrograms that can be used to detect changes in APD. This may be improved by decreasing coupling. The ATa is a robust measure for precisely identifying spatial APD heterogeneities.
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This paper presents a localized information processing approach for long-term, online structural health monitoring (SHM) using wireless sensor networks (WSNs). Based on the embedded AR-ARX method, each sensor independently calcul...
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This paper presents a localized information processing approach for long-term, online structural health monitoring (SHM) using wireless sensor networks (WSNs). Based on the embedded AR-ARX method, each sensor independently calculates a statistical damage-sensitive coefficient using the measured acceleration data during each monitoring period. A nonlinear programming formulation is developed to identify damage presence, localize damage position, and quantify damage severity from the damage-sensitive coefficients in the whole sensing field. By limiting each sensor to exchange information among its neighboring sensors only, a localized near-optimal algorithm is proposed to reduce communication costs, thus alleviating the channel interference and prolonging the network lifetime. Simulation results on a steel frame structure prove the effectiveness of the proposed algorithm.
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Filtering of plasmas by curved solenoidal ducts is well established as a method of removing macroparticles. By analyzing the interactions of planar probes with the drifting plasma of the cathodic arc, new insights have been obtain...
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Filtering of plasmas by curved solenoidal ducts is well established as a method of removing macroparticles. By analyzing the interactions of planar probes with the drifting plasma of the cathodic arc, new insights have been obtained into the operation of these ducts. Theoretical modeling of these interactions suggests, and experiment confirms, that the use of a separate biased electrode on the inside of the duct gives enhanced transmission without drawing excessive electron current. Theoretical modeling of a negatively biased planar electrode lying parallel to the drift velocity as well as experiment both show that ions are captured effectively onto the electrode producing a macroparticle free film at good deposition rates. The application of pulsed high voltage to the substrate placed at the exit of the duct is treated theoretically, and a model is proposed which gives a good agreement with the experimental concentration profile for a silicon surface coated and simultaneously implanted with titanium.
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Traffic has always been the infrastructure of national economic and social development. With the pace of urbanization unprecedented speedup and the increase of vehicle possessions, traffic congestion has become a big problem in mo...
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Traffic has always been the infrastructure of national economic and social development. With the pace of urbanization unprecedented speedup and the increase of vehicle possessions, traffic congestion has become a big problem in modern cities. Regional traffic guidance system provides traffic information for road travelers in pre-trip and in on-trip,and guides travelers to change travel modes, choose travel routes, and save travel time to take full advantage of road network resources.
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There is clear evidence that creep damage in power plant steels is associated with grain boundary precipitates. These particles provide favourable nucleation sites for grain boundary cavities and microcracks. The formation of M23C...
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There is clear evidence that creep damage in power plant steels is associated with grain boundary precipitates. These particles provide favourable nucleation sites for grain boundary cavities and microcracks. The formation of M23C6 carbides as grain boundary precipitates can also lead to grain boundary chromium depleted zones which are susceptible to corrosive attack. Such precipitates are the causing loss of creep life in the later stages of creep because of their very high coarsening rate. Through Monte Carlo based grain boundary precipitation kinetics models, combined with continuum creep damage modelling it is predicted that improvements in creep behaviour of power plant steels can be achieved by increasing the proportion of MX type particles. Studies of a Hf containing steel have produced improvements in both creep and corrosion properties of 9%Cr steels. Hf has been ion implanted into thin foils of a 9 wt-%Cr ferritic steel to study its effect on precipitation. Two new types of precipitates are formed, Hf carbide, (an MX type precipitate) and a Cr-V rich nitride, with the formula M2N. The Hf carbide particles were identified using convergent beam diffraction techniques, and micro-analysis. The nanosized particles are present in much higher volume fractions when compared to VN volume fractions in conventional power plant ferritic steels. Furthermore it is confirmed that the Hf causes the removal of M23C6 grain boundary precipitates. This has led to an increased concentration of Cr within the matrix, reduced chromium depleted zones at grain boundaries, and increased resistance to intergranular corrosion cracking.
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Measurements of microwave oscillations in resistive-gate MESFET contiguous-domain oscillator devices are discussed. Oscillation frequencies in the ranges from 22 to 30 GHz and 37 to 42 GHz are observed independently of the device ...
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Measurements of microwave oscillations in resistive-gate MESFET contiguous-domain oscillator devices are discussed. Oscillation frequencies in the ranges from 22 to 30 GHz and 37 to 42 GHz are observed independently of the device length, and frequency can be tuned during operation by varying the source-to-gate voltage. Evidence suggests that the observed signals are harmonics of a fundamental signal in the range from 11 to 15 GHz. While the possibility that conventional transit-time Gunn domain propagation is occurring in this frequency range cannot be ruled out, the fact that frequency is independent of channel length suggests that contiguous domains are forming, at least in the longer devices. Because of its structure, the resistive-gate MESFET oscillator can be easily incorporated into MESFET integrated circuits for MMIC (monolithic microwave integrated circuit) applications.
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Summary form only given. The authors report the first observation of microwave oscillation in the contiguous domain oscillator (CDO). Computer simulations indicate that, if the channel field V/sub GG//L is in the regime of negativ...
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Summary form only given. The authors report the first observation of microwave oscillation in the contiguous domain oscillator (CDO). Computer simulations indicate that, if the channel field V/sub GG//L is in the regime of negative differential mobility for electrons in GaAs, a contiguous sequence of charge domains will form spontaneously along the entire length of the channel, continuously drifting into the drain. Experimental devices were fabricated using a standard ion-implanted MESFET process, modified to include a WSiN resistive gate. The gate resistivity is 30 k Omega /sq, channel doping is 1.2*10/sup 17/ cm/sup -3/, and channel thickness is 150 nm. Channel widths range from 200 to 400 mu m and lengths from 10 to 50 mu m. Devices were mounted in a waveguide insertion unit, and operation was characterized between 26 and 140 GHz using a Tektronix 2755P spectrum analyzer. Modulation of the oscillation frequency by the gate-to-source V/sub G1-s/ was observed, as predicted by the computer simulation.
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