The purpose of this study was to determine whether respiratory disturbance to posture varies as a function of the respiratory mode, i.e. thoracic or abdominal. To this aim, 10 healthy male subjects ...underwent a posturographic examination associated with a measurement of respiratory kinematics. Experimental conditions varied posture (sitting, standing) respiratory amplitude (quiet breathing, deep breathing) and respiratory mode (thoracic, abdominal). In addition to classical posturographic parameters, original peak detection algorithm and emergence parameter calculated from the Fast Fourier Transform were used to assess the respiratory component in CP displacements. Results showed that along the antero-posterior axis, time domain and frequency domain parameters were both significantly greater in thoracic breathing mode than in abdominal mode. It was concluded that respiratory kinematics have a more prominent disturbing effect on posture when they involve the rib cage rather than the abdomen.
By means of the SAETTA 3D lightning mapping array, the total lightning activity has been detected in a 240 km × 240 km square domain centred on the island of Corsica located in the West Mediterranean ...basin, and characterized by a maritime and mountainous environment, with a complex and relatively high relief. The study period covers the months from April to December of the 6 years from 2014 to 2019. Observations are reported with a horizontal resolution of 1 km and a vertical resolution of 0.1 km in terms of density of VHF sources emitted by lightning, and of number of lightning day, in plane- and vertical- projections. Vertical distributions of VHF sources are also provided monthly for the whole period and over the full domain. These 3D long term observations show that the number of lightning days is more important on the main relief of the island. The density of VHF sources exhibits a sharp maximum over the confluence area of the 3 main valleys in the center of the northern part of the island, characterized by a recurrent and vertically well developed lightning activity. The period from 11:00 UTC to 14:00 UTC in July, and in a lesser extent in June and August, is at the origin of this density maximum. This behavior is thus due to a diurnal convection. The whole lightning activity is characterized by 2 maxima in June and September. The first one is linked with the diurnal convection in phase with the maximum elevation of the Sun. The second one must be due to usual large-scale organized thunderstorm events of the fall season. The vertical distribution of VHF sources exhibits an increase in the number of VHF sources from April to August at all altitudes, as well as an increase in the altitude of the main upper peak (from 5.8 km to 10 km) and of the secondary lower peak (from 4.2 km to 6.7 km) of this distribution. From August to December, the opposite evolution appears, except that October is characterized by a strong anomaly with a single intense lower peak at 5.5 km, apparently due to 2 strong events corresponding to anomalously electrified thunderstorms. Several of these anomalously electrified thunderstorms (negative dipoles) are reported. They are all characterized by the movement of cloud cells spatially small and relatively undeveloped vertically propagating from southwest to northeast and associated with a strong transport of desert dust from the African continent. The analysis of the meteorological environment of some of the studied events allows concluding that in each of the studied cases elevated convection was triggered, above the relatively dry atmospheric boundary layer characterized by a strong convective inhibition. The low cloud liquid water content which is a key parameter of the non-inductive charging process is probably a good candidate to explain the anomalous electrification of these events.
•First 3D lightning climatology in a maritime and mountainous region.•Maximum of lightning activity mainly due to spring diurnal convection between 11:00 and 14:00 UTC.•The most intense lightning activity is located at the crossroads of the 3 main valleys.•Occurrences of anomalously electrified thunderstorms correspond to southern flows with strong transport of African dust•Convection of anomalously electrified thunderstorms triggered above the boundary layer with strong convective inhibition
In this paper, the impact of low-frequency noise sources on the gain stability of microwave amplifiers is presented. The presence of a thermally activated relaxation process is experimentally ...demonstrated. To support the experiment, a mathematical model of this additional excess noise source is proposed in the Allan variance analysis. Different microwave amplifiers are also characterized and their stability is compared with the use of the Allan variance.
Stability Analysis of an SiGe HBT-Based Active Cold Load de la Jarrige, Emilie Leynia; Escotte, Laurent; Gonneau, Eric ...
IEEE transactions on microwave theory and techniques,
02/2011, Letnik:
59, Številka:
2
Journal Article
Recenzirano
In this study, we report the results of short- and intermediate-term stability at L -band of an active cold load (ACL) realized with an SiGe heterojunction bipolar transistor. A noise injection ...radiometer has been developed to perform the measurements. A noise-equivalent delta temperature of less than 40 mK and a stability estimated to 30 mK during 90 s were obtained from Allan variance analysis. The results indicate that the variations of the ACL noise temperature correspond to the sensitivity of the measurement system. No drift was detected over one week of continuous characterization indicating that this kind of active load is very stable.
The noise behavior of microwave amplifiers operating under a large-signal condition has been studied in this paper. A Gaussian noise is added to a microwave signal and they are applied at the input ...of several amplifying devices. Experimental data show a decrease of the output noise spectral density when the power of the microwave signal at the input of the devices increases due to the compression of the amplifiers. A distortion component due to the interaction of the signal and its harmonics with the noise is also demonstrated from a simplified theoretical model. The statistical properties of the signal and the noise have also been investigated in order to verify the Gaussianity of the noise at the output of the nonlinear circuits. We have also observed that the majority of the measured devices show some variations of their additive noise versus the input power level.
The design of a high-stability radiometer is presented in this paper. It is used to characterize the stability of a microwave active cold load at L-band. The two-load radiometer takes advantage of a ...noise injection technique to improve its sensitivity. A temperature-stabilized enclosure is used to minimize gain and noise temperature fluctuations of the receiver. The radiometer sensitivity is 0.031 K and the gain fluctuations are less than 0.005 dB during 1 day. The total gain and the receiver noise temperature of the radiometer exhibit very small variations (<0.03 dB and 1 K, respectively) on the long term.
The stability of a microwave amplifier is reported in this paper. The presence of a generation-recombination noise source is investigated both in the frequency and time domains. An analytical ...expression of the Allan variance in the case of Lorentzian noise is originally determined in the time domain and agrees with previous work. The model is supported by experimental data realized at different temperatures which corroborates the presence of a thermally activated process.
In this study, results of long-term stability of an Active Cold Load (ACL), realized at L-band with an SiGe heterojunction bipolar transistor are reported. The ACL exhibits return loss higher than 35 ...dB and a noise temperature less than 66 K. A noise injection radiometer has been developed to perform the measurements. A noise-equivalent delta temperature of less than 31 mK and a stability estimated to 25 mK during 95 s were obtained from Allan variance analysis. The long-term stability measurements performed over 4 months, indicate that a maximum deviation less than 0.35 K on the noise temperature is obtained with this ACL.
The signal and noise interaction in microwave amplifiers operating under nonlinear conditions is presented in this paper. The theoretical output noise spectrum calculated from a behavioral modeling ...based on the autocorrelation function is compared to experimental data obtained from a dedicated test-set. The noise mixing with a sinusoidal signal and its harmonics is then well described for both low-pass and band-pass filtered noise. Moreover, the model is well suited to fit AM-AM characteristics and total harmonic distortion
We describe the development of multisensor antennas in a specified band of frequencies using beamforming and processing techniques. This method is based on the spatial positioning of omnidirectional ...transducers and the use of specific professing in order to maintain the directivity diagram constant over the whole frequency band of interest. The digital signal processing algorithms associated with each transducer are based on RIF filters. The corresponding coefficients of the filters are determined by optimizing the desired antenna directivity diagram. We first present the method used, then the theoretical results together with those obtained during the experiment. Finally, we present some possibilities for making the hardware part of a real-time signal processing system suitable for such an antenna.
