Articles de revues : « CHIRP INPUT »

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Liu, Weici. « Effect of initial chirp for input pulse on supercontinuum generation ». Journal of Physics : Conference Series 2029, n^o 1 (1 septembre 2021) : 012019. http://dx.doi.org/10.1088/1742-6596/2029/1/012019.

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Abstract The generation of supercontinuum spectrum is a very complex nonlinear process. Based on the nonlinear Schrodinger equation (NLSE), the effect of initial chirp on supercontinuum generation is numerically studied by split-step Fourier (SSF) method. The positive chirp and negative chirp have different effects on the supercontinuum generation. The results show that the energy distribution of supercontinuum spectrum can be improved by selecting appropriate chirp value.

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Mulsow, Jason, James J. Finneran, Madelyn G. Strahan, Dorian S. Houser et Robert F. Burkard. « Input compensation of dolphin and sea lion auditory brainstem responses using frequency-modulated up-chirps ». Journal of the Acoustical Society of America 154, n^o 2 (1 août 2023) : 739–50. http://dx.doi.org/10.1121/10.0020566.

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Frequency-modulated “chirp” stimuli that offset cochlear dispersion (i.e., input compensation) have shown promise for increasing auditory brainstem response (ABR) amplitudes relative to traditional sound stimuli. To enhance ABR methods with marine mammal species known or suspected to have low ABR signal-to-noise ratios, the present study examined the effects of broadband chirp sweep rate and level on ABR amplitude in bottlenose dolphins and California sea lions. “Optimal” chirps were designed based on previous estimates of cochlear traveling wave speeds (using high-pass subtractive masking methods) in these species. Optimal chirps increased ABR peak amplitudes by compensating for cochlear dispersion; however, chirps with similar (or higher) frequency-modulation rates produced comparable results. The optimal chirps generally increased ABR amplitudes relative to noisebursts as threshold was approached, although this was more obvious when sound pressure level was used to equate stimulus levels (as opposed to total energy). Chirps provided progressively less ABR amplitude gain (relative to noisebursts) as stimulus level increased and produced smaller ABRs at the highest levels tested in dolphins. Although it was previously hypothesized that chirps would provide larger gains in sea lions than dolphins—due to the lower traveling wave speed in the former—no such pattern was observed.

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Solyman, Ahmad AA, Hani Attar, Mohammad R. Khosravi et Baki Koyuncu. « MIMO-OFDM/OCDM low-complexity equalization under a doubly dispersive channel in wireless sensor networks ». International Journal of Distributed Sensor Networks 16, n^o 6 (juin 2020) : 155014772091295. http://dx.doi.org/10.1177/1550147720912950.

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In this article, three novel systems for wireless sensor networks based on Alamouti decoding were investigated and then compared, which are Alamouti space–time block coding multiple-input single-output/multiple-input multiple-output multicarrier modulation (MCM) system, extended orthogonal space–time block coding multiple-input single-output MCM system, and multiple-input multiple-output system. Moreover, the proposed work is applied over multiple-input multiple-output systems rather than the conventional single-antenna orthogonal chirp division multiplexing systems, based on the discrete fractional cosine transform orthogonal chirp division multiplexing system to mitigate the effect of frequency-selective and time-varying channels, using low-complexity equalizers, specifically by ignoring the intercarrier interference coming from faraway subcarriers and using the LSMR iteration algorithm to decrease the equalization complexity, mainly with long orthogonal chirp division multiplexing symbols, such as the TV symbols. The block diagrams for the proposed systems are provided to simplify the theoretical analysis by making it easier to follow. Simulation results confirm that the proposed multiple-input multiple-output and multiple-input single-output orthogonal chirp division multiplexing systems outperform the conventional multiple-input multiple-output and multiple-input single-output orthogonal frequency division multiplexing systems. Finally, the results show that orthogonal chirp division multiplexing exhibited a better channel energy behavior than classical orthogonal frequency division multiplexing, thus improving the system performance and allowing the system to decrease the equalization complexity.

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van Brederode, J. F. M., et A. J. Berger. « GAD67-GFP+ Neurons in the Nucleus of Roller. II. Subthreshold and Firing Resonance Properties ». Journal of Neurophysiology 105, n^o 1 (janvier 2011) : 249–78. http://dx.doi.org/10.1152/jn.00492.2010.

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In the companion paper we show that GAD67-GFP+ (GFP+) inhibitory neurons located in the Nucleus of Roller of the mouse brain stem can be classified into two main groups (tonic and phasic) based on their firing patterns in responses to injected depolarizing current steps. In this study we examined the responses of GFP+ cells to fluctuating sinusoidal (“chirp”) current stimuli. Membrane impedance profiles in response to chirp stimulation showed that nearly all phasic cells exhibited subthreshold resonance, whereas the majority of tonic GFP+ cells were nonresonant. In general, subthreshold resonance was associated with a relatively fast passive membrane time constant and low input resistance. In response to suprathreshold chirp current stimulation at a holding potential just below spike threshold the majority of tonic GFP+ cells fired multiple action potentials per cycle at low input frequencies (<5 Hz) and either stopped firing or were not entrained by the chirp at higher input frequencies (= tonic low-pass cells). A smaller group of phasic GFP+ cells did not fire at low input frequency but were able to phase-lock 1:1 at intermediate chirp frequencies (= band-pass cells). Spike timing reliability was tested with repeated chirp stimuli and our results show that phasic cells were able to reliably fire when they phase-locked 1:1 over a relatively broad range of input frequencies. Most tonic low-pass cells showed low reliability and poor phase-locking ability. Computer modeling suggested that these different firing resonance properties among GFP+ cells are due to differences in passive and active membrane properties and spiking mechanisms. This heterogeneity of resonance properties might serve to selectively activate subgroups of interneurons.

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Tang, Qing, et Guanshen Zhang. « Chirp encoded joint transform correlators with input scale search ». Optics Communications 107, n^o 1-2 (avril 1994) : 23–27. http://dx.doi.org/10.1016/0030-4018(94)90097-3.

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Tan, See Ling, Yu-Fu Chen, Chieh-Yu Liu, Kuo-Chung Chu et Pei-Chun Li. « Shortened neural conduction time in young adults with tinnitus as revealed by chirp-evoked auditory brainstem response ». Journal of the Acoustical Society of America 153, n^o 4 (avril 2023) : 2178–89. http://dx.doi.org/10.1121/10.0017789.

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Tinnitus is generally considered to be caused by neuroplastic changes in the central nervous system, triggered by a loss of input from the damaged peripheral system; however, conflicting results on auditory brainstem responses (ABRs) to clicks have been reported previously in humans with tinnitus. This study aimed to compare the effect of tinnitus on ABRs to chirps with those to clicks in normal-hearing young adults with tinnitus. The results showed that the tinnitus group had no significantly poorer hearing thresholds (0.25–16 kHz), click-evoked otoacoustic emissions (1–16 kHz), and speech perception in noise (SPIN) than the control group. Although chirps evoked significantly larger wave I and V amplitudes than clicks, people with tinnitus had no significantly smaller wave I amplitudes for either stimulus. Nevertheless, adults with tinnitus exhibited significantly smaller interpeak interval (IPI) between waves I and V for chirps (IPI–chirp) but not for clicks. In addition, the IPI–chirp correlated significantly with the SPIN for individuals with tinnitus when the signal-to-noise ratio was low. The present results suggest that the chirp-evoked ABR may be a valuable clinical tool for objectively assessing the SPIN in individuals with tinnitus. Further studies should be conducted to investigate possible etiologies of tinnitus.

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Munaweera, P. C. T., et K. A. I. L. Wijewardena Gamalath. « Simulation of Pulse Propagation in Optical Fibers ». International Letters of Chemistry, Physics and Astronomy 64 (février 2016) : 159–70. http://dx.doi.org/10.18052/www.scipress.com/ilcpa.64.159.

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A theoretical model was developed for light pulses propagating in optical fibers by considering the nonlinear effects, the self-phase modulation and group velocity dispersion effects. The split step Fourier method was used to generate soliton pulses in a fiber composed of a glass core surrounded by a cladding layer. Gaussian and hyperbolic secant input pulses were used for the simulation. By varying the initial chirp, input power and nonlinear coefficient for an input Gaussian pulse at wavelength of λ =1.55μm with initial pulse width 125ps for second order dispersion β2=−20 ps2km-1, nonlinear parameter γ=3W-1kg-1and initial chirp C=−0.25 two near soliton pulses were generated for input powers P = 0.54mW and P = 0.64mW and a perfect soliton for the hyperbolic secant input pulse.

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Munaweera, P. C. T., et K. A. I. L. Wijewardena Gamalath. « Simulation of Pulse Propagation in Optical Fibers ». International Letters of Chemistry, Physics and Astronomy 64 (15 février 2016) : 159–70. http://dx.doi.org/10.56431/p-qb35f6.

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A theoretical model was developed for light pulses propagating in optical fibers by considering the nonlinear effects, the self-phase modulation and group velocity dispersion effects. The split step Fourier method was used to generate soliton pulses in a fiber composed of a glass core surrounded by a cladding layer. Gaussian and hyperbolic secant input pulses were used for the simulation. By varying the initial chirp, input power and nonlinear coefficient for an input Gaussian pulse at wavelength of λ =1.55μm with initial pulse width 125ps for second order dispersion β2=−20 ps2 km-1 , nonlinear parameter γ=3W-1kg-1 and initial chirp C=−0.25 two near soliton pulses were generated for input powers P = 0.54mW and P = 0.64mW and a perfect soliton for the hyperbolic secant input pulse.

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Zupanc, Günther K. H., et Leonard Maler. « Evoked chirping in the weakly electric fish Apteronotus leptorhynchus : a quantitative biophysical analysis ». Canadian Journal of Zoology 71, n^o 11 (1 novembre 1993) : 2301–10. http://dx.doi.org/10.1139/z93-323.

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Apteronotus leptorhynchus, a gymnotiform fish, produces highly regular electric organ discharges of 600–1000 Hz. Short-term modulations of the electric organ discharge ("chirps") were elicited by imitating the discharges of neighboring fish. Chirps displayed an increase in frequency of approximately 100 Hz, a duration of about 15 ms, and an absolute amplitude of 0.5–2 mV. Since, similar to natural conditions, chirps summated with the beat caused by interference of the fish's own electric organ discharge and the imitating discharge, the size and shape of the chirp's amplitude envelope varied greatly according to its phase relative to the beat cycle; however, the frequency of the chirp amplitude modulation was always 50–100 Hz. All 21 males examined chirped, but their rate of chirping varied considerably (range 2–59 chirps/30 s; mean 22 chirps/30 s). In contrast, only one out of nine females chirped (mean 0.25 chirps/30 s). The latency between stimulus onset and first chirp was variable and often long (range 1.0–25.0 s; median 3.3 s). We propose that chirps are not a sensory reflex but a communicatory behavior regulated by hypothalamic peptidergic input.

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Don, Manuel, Claus Elberling et Erin Maloff. « Input and Output Compensation for the Cochlear Traveling Wave Delay in Wide-Band ABR Recordings : Implications for Small Acoustic Tumor Detection ». Journal of the American Academy of Audiology 20, n^o 02 (février 2009) : 099–108. http://dx.doi.org/10.3766/jaaa.20.2.3.

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Background: The Stacked ABR (auditory brainstem response) attempts at the output of the auditory periphery to compensate for the temporal dispersion of neural activation caused by the cochlear traveling wave in response to click stimulation. Compensation can also be made at the input by using a chirp stimulus. It has been demonstrated that the Stacked ABR is sensitive to small tumors that are often missed by standard ABR latency measures. Purpose: Because a chirp stimulus requires only a single data acquisition run whereas the Stacked ABR requires six, we try to evaluate some indirect evidence justifying the use of a chirp for small tumor detection. Research Design: We compared the sensitivity and specificity of different Stacked ABRs formed by aligning the derived-band ABRs according to (1) the individual's peak latencies, (2) the group mean latencies, and (3) the modeled latencies used to develop a chirp. Results: For tumor detection with a chosen sensitivity of 95%, a relatively high specificity of 85% may be achieved with a chirp. Conclusion: It appears worthwhile to explore the actual use of a chirp because significantly shorter test and analysis times might be possible.

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Ivanov Spassov, Sevdalin. « CHIRP FILTER JAMMING IMMUNITY RESEARCH ». International Journal of Advanced Research 9, n^o 01 (31 janvier 2021) : 966–71. http://dx.doi.org/10.21474/ijar01/12377.

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The pulse compression technique uses a matched filter to extract an echo signal in the radars receiver. A model of a matched filter for a chirp signal was synthesized using the Simulink Tool of the MATLAB software. Pulse jamming and chirp jamming signals were feed to the input of the matched filter. The output signals were measured. The matched filters degree of suppression of these jamming signals was assessed. Conclusions were made about the jamming immunity of a radar operating with a Chirp matched filter.

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Javidi, Bahram, et Qing Tang. « Chirp-encoded joint transform correlators with a single input plane ». Applied Optics 33, n^o 2 (10 janvier 1994) : 227. http://dx.doi.org/10.1364/ao.33.000227.

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Varela, O., B. Alonso, I. J. Sola, J. San Román, A. Zaïr, C. Méndez et L. Roso. « Self-compression controlled by the chirp of the input pulse ». Optics Letters 35, n^o 21 (26 octobre 2010) : 3649. http://dx.doi.org/10.1364/ol.35.003649.

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Al-Qahtani, Saeed, Ali Alomary et Marwan Althomali. « Transit time spectrum dependence upon ultrasound input wave types propagating through complex structures ». Journal of Umm Al-Qura University for Medical Sciences 9, n^o 1 (22 mai 2023) : 63–70. http://dx.doi.org/10.54940/ms45313008.

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Background: Ultrasound transit time spectroscopy (UTTS) has been introduced previously to characterize the propagation of ultrasound waves through complex structures such as cancellous bone to estimate bone quality and quantity. UTTS describes the propagation of ultrasonic waves through a medium with two components of differing sound speeds (e.g., bone and marrow) as a set of parallel sonic rays. The transit time spectrum (TTS) is derived via the digital deconvolution of the input and output signals. Aim: To investigate the dependence of TTS upon the type of ultrasound input wave, including four different 1 MHz ultrasound waves (pulse, chirp, tone-burst, and continuous). Methods: The presence of ischemic lesions was detected by the MDCT, transesophageal echocardiography (TEE), and non-contrast flat detector computed tomography (FDCT). The study selected the AIS patients with hyperacute stroke for less than 6 hours from July 2021 to August 2022. The CTA of cervical arteries was performed in order to determine stroke subtypes.Ten replica 3D- acrylic step-wedge models with different structure complexity were investigated. For each model and using the four types of input waves, TTS was derived and compared with calculated TTS based on the parallel sonic ray concept. Results: The results showed coefficients of determination (R2) of 0.994, 0.999, 0.90, and 1 for pulse, chirp, tone-burst and continuous signals respectively. Furthermore, solid volume fraction (SVF) was derived via TTS (TTS-SVF) and compared with the geometrically calculated SVF data of the models, yielding coefficients of determination (R2) of 0.941, 0.968, 0.489, and 0.981 for pulse, chirp, tone-burst and continuous waves, respectively. Therefore, the continuous wave provided a more accurate prediction of TTS and SVF, followed by chirp, then pulse waves. Conclusion: This study adds to the body of research supporting the validity and reliability of UTTS, as a potentially promising technique to provide a reliable in vivo estimate of bone mineral density.

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Konyukhov, A. I., et P. A. Mavrin. « Chirped soliton fission and fusion in dispersion oscillating fibers ». Laser Physics 33, n^o 1 (5 décembre 2022) : 015401. http://dx.doi.org/10.1088/1555-6611/aca4cd.

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Abstract We found that pre-chirp of initial pulses allows to control both the fission and fusion of solitons in dispersion oscillating fiber characterized by a sinusoidally varying group velocity dispersion. The fission of second order solitons and collision of two co-propagated solitons are considered. It is shown that initial chirp can prevent the resonant fission of second order soliton into two pulses propagating with different group velocities. Inelastic collision of two in-phase solitons is found can be quite different, when the chirp imposed on initial pulses. The soliton transformation reflects in the set of output eigenvalues of the Zakharov–Shabat spectral problem. Manipulation of the input pulse chirp allows to control both real and imaginary parts of the eigenvalues at the output of the fiber.

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Mitchell, Cassie S., et Robert H. Lee. « The dynamics of somatic input processing in spinal motoneurons in vivo ». Journal of Neurophysiology 105, n^o 3 (mars 2011) : 1170–78. http://dx.doi.org/10.1152/jn.00592.2010.

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Uncovering how motoneurons utilize their voltage-sensitive conductances to systematically respond to a variety of inputs is paramount to understanding synaptic integration. In this study, we examine the input dynamics and frequency-dependent characteristics of active conductances in motoneurons as viewed from the soma in the decerebrate cat. We evaluated the somatic response of the motoneuron by superimposing a voltage sinus sweep (a sine wave in which frequency increases with time, which is often referred to as a zap or chirp) at a subset of membrane holding potentials during discontinuous, single-electrode, somatic voltage-clamp. Results from both experimental and modeling data indicate that ionic conductances can respond to a wide variety of input dynamics. Notably, it appears that there is a divergence between low input conductance type S and high input conductance type FF motoneurons in their response to input frequency. Type S motoneurons generate a larger response to lower frequency input dynamics (compared with their response to higher frequencies), whereas type FF generate a larger response to higher input frequency dynamics. Functionally, these results may indicate that motoneurons on the lower end of the motor pool (i.e., recruited first) may favor steady inputs, whereas motoneurons at the higher end (i.e., recruited later) may favor input transients in producing action potentials.

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Kuzmin, M. S., V. V. Davydov et S. A. Rogov. « On the use of a multi-raster input of one-dimensional signals in two-dimensional optical correlators ». Computer Optics 43, n^o 3 (juin 2019) : 391–96. http://dx.doi.org/10.18287/2412-6179-2019-43-3-391-396.

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A mathematical description of a coherent optical correlator for the multi-raster input of long signals is given. It is shown that such an input makes it possible to reduce the value of false correlation maxima that are generally found at the output of a correlator with a single-raster input. It is shown that false maxima do not appear when processing signals with a thumbtack ambiguity function, allowing one to do without a multi-raster input. The results of the theoretical analysis are confirmed by experiments with chirp signals and M-sequence type signals.

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Ivanov Spassov, Sevdalin. « JAMMINGIMMUNITY RESEARCH OF A RADAR OPERATING WITH CHIRP SIGNAL ». International Journal of Advanced Research 8, n^o 12 (31 décembre 2020) : 731–37. http://dx.doi.org/10.21474/ijar01/12204.

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Pulse compressed signal enhances the jamming immunity of a radar operating with such a signal. The matched filter is one of the most important elements in the pulse compression technique. A model of a matched filter for a chirp signal was synthesized using the Simulink tool of the Matlab software. Interference signals were feed to the input of the matched filter and output signals were measured. The matched filters degree of suppression of these interference signals was assessed. Conclusions were made about the jamming immunity of radar operating with chirp signal.

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Ivanov Spassov, Sevdalin. « JAMMINGIMMUNITY RESEARCH OF A RADAR OPERATING WITH CHIRP SIGNAL ». International Journal of Advanced Research 8, n^o 12 (31 décembre 2020) : 731–37. http://dx.doi.org/10.21474/ijar01/12204.

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Pulse compressed signal enhances the jamming immunity of a radar operating with such a signal. The matched filter is one of the most important elements in the pulse compression technique. A model of a matched filter for a chirp signal was synthesized using the Simulink tool of the Matlab software. Interference signals were feed to the input of the matched filter and output signals were measured. The matched filters degree of suppression of these interference signals was assessed. Conclusions were made about the jamming immunity of radar operating with chirp signal.

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Lan, Xiang, Min Zhang et Jin-Xing Li. « OFDM Chirp Waveform Design Based on Subchirp Bandwidth Overlap and Segmented Transmitting for Low Correlation Interference in MIMO Radar ». Sensors 19, n^o 12 (14 juin 2019) : 2696. http://dx.doi.org/10.3390/s19122696.

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There are some special merits for the orthogonal frequency division multiplexing (OFDM) chirp waveform as multiple input multiple output (MIMO) signals. This signal has high range resolution, good Doppler tolerance, and constant modulus superiority since it exploits a full bandwidth and is based on chirp signals. The correlation sidelobe peaks level are critical for the detection requirement of MIMO radar signals, however conventional OFDM chirp signals produce high autocorrelation sidelobe peaks (ASP) and cross-correlation peaks (CP), which reduces detection performance. In this paper, we explore the structure of OFDM chirp signals’ autocorrelation function and proposed a scheme to reduce the designed signal’s ASP by a designing suitable range of subchirp bandwidth and a segmented transmit-receive mode. Next, we explore a suitable range of interval between the chirp rates of each two signals to reduce the CP. The simulation of designed signals verifies the effectiveness of the proposed methods in the reduction of ASP and CP, with the correlation performance being compared with recent relate studies. In addition, the multiple signals detection and one-dimensional range image simulation show the good detection performance of a designed signal in MIMO radar detection.

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Stewart, Shania, Ha H. Nguyen, Robert Barton et Jerome Henry. « Reducing the Cost of Implementing Filters in LoRa Devices ». Sensors 19, n^o 18 (19 septembre 2019) : 4037. http://dx.doi.org/10.3390/s19184037.

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This paper presents two methods to optimize LoRa (Low-Power Long-Range) devices so that implementing multiplier-less pulse shaping filters is more economical. Basic chirp waveforms can be generated more efficiently using the method of chirp segmentation so that only a quarter of the samples needs to be stored in the ROM. Quantization can also be applied to the basic chirp samples in order to reduce the number of unique input values to the filter, which in turn reduces the size of the lookup table for multiplier-less filter implementation. Various tests were performed on a simulated LoRa system in order to evaluate the impact of the quantization error on the system performance. By examining the occupied bandwidth, fast Fourier transform used for symbol demodulation, and bit-error rates, it is shown that even performing a high level of quantization does not cause significant performance degradation. Therefore, the memory requirements of LoRa devices can be significantly reduced by using the methods of chirp segmentation and quantization so as to improve the feasibility of implementing multiplier-less filters in LoRa devices.

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Schöneich, Stefan, et Berthold Hedwig. « Feedforward discharges couple the singing central pattern generator and ventilation central pattern generator in the cricket abdominal central nervous system ». Journal of Comparative Physiology A 205, n^o 6 (5 novembre 2019) : 881–95. http://dx.doi.org/10.1007/s00359-019-01377-7.

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Abstract We investigated the central nervous coordination between singing motor activity and abdominal ventilatory pumping in crickets. Fictive singing, with sensory feedback removed, was elicited by eserine-microinjection into the brain, and the motor activity underlying singing and abdominal ventilation was recorded with extracellular electrodes. During singing, expiratory abdominal muscle activity is tightly phase coupled to the chirping pattern. Occasional temporary desynchronization of the two motor patterns indicate discrete central pattern generator (CPG) networks that can operate independently. Intracellular recordings revealed a sub-threshold depolarization in phase with the ventilatory cycle in a singing-CPG interneuron, and in a ventilation-CPG interneuron an excitatory input in phase with each syllable of the chirps. Inhibitory synaptic inputs coupled to the syllables of the singing motor pattern were present in another ventilatory interneuron, which is not part of the ventilation-CPG. Our recordings suggest that the two centrally generated motor patterns are coordinated by reciprocal feedforward discharges from the singing-CPG to the ventilation-CPG and vice versa. Consequently, expiratory contraction of the abdomen usually occurs in phase with the chirps and ventilation accelerates during singing due to entrainment by the faster chirp cycle.

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Cheng, Wenhai, Qunying Zhang, Wei Lu, Haiying Wang et Xiaojun Liu. « An Efficient Digital Channelized Receiver for Low SNR and Wideband Chirp Signals Detection ». Applied Sciences 13, n^o 5 (27 février 2023) : 3080. http://dx.doi.org/10.3390/app13053080.

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Synthetic aperture radar (SAR) is essential for obtaining intelligence in modern information warfare. Wideband chirp signals with a low signal-to-noise ratio (SNR) are widely used in SAR. Intercepting low-SNR wideband chirp signals is of great significance for anti-SAR reconnaissance. Digital channelization technology is an effective means to intercept wideband signals. The existing digital channelization methods have the following problems: the contradiction of reception blind zone and signal spectrum aliasing, high computational complexity, and low estimating accuracy for chirp signals with a low SNR. This paper proposes a non-critical sampling digital channelized receiver architecture to intercept chirp signals. The receiver architecture has no blind zone in channel division and no aliasing of signal spectrum in the channel, which can provide reliable instantaneous frequency measurements. An adaptive threshold generation algorithm is proposed to detect signals without prior information. In addition, an improved instantaneous frequency measurement (IFM) algorithm is proposed, improving low SNR chirp signals’ frequency estimation accuracy. Moreover, a simple channel arbitration logic is proposed to complete the cross-channel combination of wideband signals. Simulations show that the proposed receiver architecture is reliable and robust for low SNR and wideband chirp signal detection. When the input SNR is 0 dB, the absolute frequency root-mean-square error (RMSE) of bandwidth and the center frequency is 0.57 MHz and 1.05 MHz, respectively. This frequency accuracy is great for radio frequency (RF) wideband systems.

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Rahman, M. S., et G. F. Gott. « A Comparative Study of the Outputs of a Chirp-Matched Filter and a Dispersive Line for the Matched Input Chirp Signal ». IETE Journal of Research 42, n^o 6 (novembre 1996) : 401–7. http://dx.doi.org/10.1080/03772063.1996.11415949.

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Deng, Zhixiang, et Meng Zhang. « Dynamics of Dispersive Wave Generation in Gas-Filled Photonic Crystal Fiber with the Normal Dispersion ». Advances in Condensed Matter Physics 2017 (2017) : 1–9. http://dx.doi.org/10.1155/2017/1268230.

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The absence of Raman and unique pressure-tunable dispersion is the characteristic feature of gas-filled photonic crystal fiber (PCF), and its zero dispersion points can be extended to the near-infrared by increasing gas pressure. The generation of dispersive wave (DW) in the normal group velocity dispersion (GVD) region of PCF is investigated. It is demonstrated that considering the self-steepening (SS) and introducing the chirp of the initial input pulse are two suitable means to control the DW generation. The SS enhances the relative average intensity of blue-shift DW while weakening that of red-shift DW. The required propagation distance of DW emission is markedly varied by introducing the frequency chirp. Manipulating DW generation in gas-filled PCF by the combined effects of either SS or chirp and three-order dispersion (TOD) provides a method for a concentrated transfer of energy into the targeted wavelengths.

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Zhu, Qiuming, Xinglin Liu, Xuefeng Yin, Xiaomin Chen et Cuiwei Xue. « A Novel Simulator of Nonstationary Random MIMO Channels in Rayleigh Fading Scenarios ». International Journal of Antennas and Propagation 2016 (2016) : 1–9. http://dx.doi.org/10.1155/2016/3492591.

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For simulations of nonstationary multiple-input multiple-output (MIMO) Rayleigh fading channels in time-variant scattering environments, a novel channel simulator is proposed based on the superposition of chirp signals. This new method has the advantages of low complexity and implementation simplicity as the sum of sinusoids (SOS) method. In order to reproduce realistic time varying statistics for dynamic channels, an efficient parameter computation method is also proposed for updating the frequency parameters of employed chirp signals. Simulation results indicate that the proposed simulator is effective in generating nonstationary MIMO channels with close approximation of the time-variant statistical characteristics in accordance with the expected theoretical counterparts.

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Dafydd, Ifan, et Zahra Sharif Khodaei. « Laser Vibrometer Imaging of Delamination Interaction with Lamb Waves Using a Chirp Excitation Method ». Key Engineering Materials 754 (septembre 2017) : 375–78. http://dx.doi.org/10.4028/www.scientific.net/kem.754.375.

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One method that has shown great potential in visualising and characterising the interaction of guided waves with damage in composites is Laser Vibrometry. A Laser Doppler Vibrometer (LDV) can be used to produce 2D wavefield images of guided Lamb waves but a single scan is very time consuming and normally multiple scans are required at various frequencies in order to determine the best input signal. This paper demonstrates the use of a chirp excitation method requiring only a single scan and a post-processing algorithm to obtain results corresponding to any narrowband signal within the frequency range of the chirp signal. The method was used on an artificially delaminated composite panel and showed that the S0 mode, dominant at higher frequencies, mainly caused mode conversions whilst the A0 mode, dominant at lower frequencies, mainly caused a change in phase and amplitude across the delaminationOne method that has shown great potential in visualising and characterising the interaction of guided waves with damage in composites is Laser Vibrometry. A Laser Doppler Vibrometer (LDV) can be used to produce 2D wavefield images of guided Lamb waves but a single scan is very time consuming and normally multiple scans are required at various frequencies in order to determine the best input signal. This paper demonstrates the use of a chirp excitation method requiring only a single scan and a post-processing algorithm to obtain results corresponding to any narrowband signal within the frequency range of the chirp signal. The method was used on an artificially delaminated composite panel and showed that the S0 mode, dominant at higher frequencies, mainly caused mode conversions whilst the A0 mode, dominant at lower frequencies, mainly caused a change in phase and amplitude across the delamination.

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Lan, Xuegang, Tao Wan, Kaili Jiang, Ying Xiong et Bin Tang. « Intelligent Recognition of Chirp Radar Deceptive Jamming Based on Multi-Pulse Information Fusion ». Sensors 21, n^o 8 (11 avril 2021) : 2693. http://dx.doi.org/10.3390/s21082693.

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The perception of jamming types is very important for protecting our radar in complex electromagnetic environments. Radar active deceptive jamming based on digital radio frequency memory (DRFM) has a high coherence with the target echo, which confuses the information of the target echo and achieves the effect of hiding the real target. Traditional deceptive jamming recognition methods need to extract complex features and artificially set classification thresholds, which is inefficient. The existing neural network-based jamming identification methods still follow the pattern of signal modulation-type identification, so there are fewer types of jamming that can be identified, and the identification accuracy is low in the case of low jamming-to-noise ratios (JNR). This paper studies the input of jamming recognition networks and proposes an improved intelligent identification method for chirp radar deceptive jamming. This method fuses three short-time Fourier transform time–frequency graphs disturbed by three consecutive pulse periods into a new graph as the input of the convolutional neural network (CNN). Using a CNN to classify the time–frequency image has realized the recognition of a variety of common deceptive jamming techniques. Similarly, by changing the network input, the original signal is used to replace the echo signal, which improves the accuracy of the jamming recognition in the case of a low JNR.

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Milián, Carles, Amélie Jarnac, Yohann Brelet, Vytautas Jukna, Aurélien Houard, André Mysyrowicz et Arnaud Couairon. « Effect of input pulse chirp on nonlinear energy deposition and plasma excitation in water ». Journal of the Optical Society of America B 31, n^o 11 (22 octobre 2014) : 2829. http://dx.doi.org/10.1364/josab.31.002829.

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Zhang, Bo, Jinglong Han, Haiwei Yun et Xiaomao Chen. « Nonlinear Aeroelastic System Identification Based on Neural Network ». Applied Sciences 8, n^o 10 (15 octobre 2018) : 1916. http://dx.doi.org/10.3390/app8101916.

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This paper focuses on the nonlinear aeroelastic system identification method based on an artificial neural network (ANN) that uses time-delay and feedback elements. A typical two-dimensional wing section with control surface is modelled to illustrate the proposed identification algorithm. The response of the system, which applies a sine-chirp input signal on the control surface, is computed by time-marching-integration. A time-delay recurrent neural network (TDRNN) is employed and trained to predict the pitch angle of the system. The chirp and sine excitation signals are used to verify the identified system. Estimation results of the trained neural network are compared with numerical simulation values. Two types of structural nonlinearity are studied, cubic-spring and friction. The results indicate that the TDRNN can approach the nonlinear aeroelastic system exactly.

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Hemant, Somen Adhikary et Mousumi Basu. « Generation of Parabolic pulse by nonlinear pulse reshaping inside a Silicon on Insulator (SOI) Waveguide ». Journal of Physics : Conference Series 2357, n^o 1 (1 octobre 2022) : 012010. http://dx.doi.org/10.1088/1742-6596/2357/1/012010.

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In recent times, silicon photonics attracts a lot of attraction of researchers. It is the technology that converts many functions of the circuit on the thumb-size chip. Nowadays, various types of technology platforms are being used to design photonic integrated circuits using various materials such as high index glass, semiconductors, polymers, and silicon. In our work, we have used silicon to design rectangular silicon on Insulator (SOI) buried waveguide. This type of waveguide has shown great potential in the field of pulse reshaping. We have used the effective index method for the calculation of group velocity dispersion and nonlinearity. Though the two-photon absorption and free-carrier generation contribute significantly to loss parameters, the highly nonlinear buried waveguide is found to be capable of reshaping super-Gaussian pulse input into a parabolic shape. Moreover, the values of input chirp, pulse width, and peak power are further optimized for the generation of a high-quality parabolic pulse at shorter lengths. The length required for pulse reshaping is much less when compared to optical fibers. Thus, our design waveguide has potential in the domain of pulse generation, signal processing, and many more.

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Bakar, M. A. A., D. A. Green et A. V. Metcalfe. « Comparison of Spectral and Wavelet Estimators of Transfer Function for Linear Systems ». East Asian Journal on Applied Mathematics 2, n^o 3 (août 2012) : 214–37. http://dx.doi.org/10.4208/eajam.170512.270712a.

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AbstractWe compare spectral and wavelet estimators of the response amplitude operator (RAO) of a linear system, with various input signals and added noise scenarios. The comparison is based on a model of a heaving buoy wave energy device (HBWED), which oscillates vertically as a single mode of vibration linear system. HBWEDs and other single degree of freedom wave energy devices such as oscillating wave surge convertors (OWSC) are currently deployed in the ocean, making such devices important systems to both model and analyse in some detail. The results of the comparison relate to any linear system. It was found that the wavelet estimator of the RAO offers no advantage over the spectral estimators if both input and response time series data are noise free and long time series are available. If there is noise on only the response time series, only the wavelet estimator or the spectral estimator that uses the cross-spectrum of the input and response signals in the numerator should be used. For the case of noise on only the input time series, only the spectral estimator that uses the cross-spectrum in the denominator gives a sensible estimate of the RAO. If both the input and response signals are corrupted with noise, a modification to both the input and response spectrum estimates can provide a good estimator of the RAO. A combination of wavelet and spectral methods is introduced as an alternative RAO estimator. The conclusions apply for autoregressive emulators of sea surface elevation, impulse, and pseudorandom binary sequences (PRBS) inputs. However, a wavelet estimator is needed in the special case of a chirp input where the signal has a continuously varying frequency.

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Chang, Hsiu-Chen, Patrick Roblin, Yunsik Hahn, Jose I. Martinez-Lopez et Chenyu Liang. « CW and Modulated Input Second Harmonic Injection for Efficiency Enhancement in Broadband Power Amplifiers ». Electronics 10, n^o 20 (14 octobre 2021) : 2507. http://dx.doi.org/10.3390/electronics10202507.

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The second-harmonic input impedance plays a critical role on the performance of GaN power amplifiers. In a recent paper, a drain efficiency enhancement for a continuous-mode power amplifiers was reported to be achieved using active broadband second-harmonic injection at the PA input. In this paper, the strategy for selecting the second-harmonic input impedance and the necessity for using active injection in such broadband PAs are discussed in detail. Additionally, the methodology for designing an embedded broadband diplexer in the input matching network is reported. Finally, the importance of the phase of the second-harmonic signal injected is demonstrated for both CW and modulated signals using both simulation and measurement, respectively. The effectiveness of the CW and modulated active second-harmonic injection methodology presented here are validated by previously reported measurements that demonstrated an average drain efficiency improvement of 9.4% from 1.3 to 2.4 GHz for CW signals and of 9.7% at 2 GHz for a frequency-modulated 30 MHz chirp radar signal.

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Li, Jing Jiao, Dong An, Jiao Wang et Chao Qun Rong. « Speech Endpoint Detection in Noisy Environment Based on the Ensemble Empirical Mode Decomposition ». Advanced Engineering Forum 2-3 (décembre 2011) : 135–39. http://dx.doi.org/10.4028/www.scientific.net/aef.2-3.135.

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Speech endpoint detection is one of the key problems in the practical application of speech recognition system. In this paper, speech signal contained chirp is decomposed into several intrinsic mode function (IMF) with the method of ensemble empirical mode decomposition (EEMD). At the same time, it eliminates the modal mix superposition phenomenon which usually comes out in processing speech signal with the algorithm of empirical mode decomposition (EMD). After that, selects IMFs contained major noise through the adaptive algorithm. Finally, the IMFs and speech signal contained chirp are input into the independent component analysis (ICA) and pure voice signal is separated out. The accuracy of speech endpoint detection can be improved in this way. The result shows that the new speech endpoint detection method proposed above is effective, and has strong anti-noises ability, especially suitable for the speech endpoint detection in low SNR.

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Zhao, Quan, Ling Tong et Bo Gao. « Advanced Chirp Transform Spectrometer with Novel Digital Pulse Compression Method for Spectrum Detection ». Applied Sciences 11, n^o 3 (21 janvier 2021) : 960. http://dx.doi.org/10.3390/app11030960.

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Based on chirp transform and pulse compression technology, chirp transform spectrometers (CTSs) can be used to perform high-resolution and real-time spectrum measurements. Nowadays, they are widely applied for weather and astronomical observations. The surface acoustic wave (SAW) filter is a key device for pulse compression. The system performance is significantly affected by the dispersion characteristics match and the large insertion loss of the SAW filters. In this paper, a linear phase sampling and accumulating (LPSA) algorithm was developed to replace the matched filter for fast pulse compression. By selecting and accumulating the sampling points satisfying a specific periodic phase distribution, the intermediate frequency (IF) chirp signal carrying the information of the input signal could be detected and compressed. Spectrum measurements across the entire operational bandwidth could be performed by shifting the fixed sampling points in the time domain. A two-stage frequency resolution subdivision method was also developed for the fast pulse compression of the sparse spectrum, which was shown to significantly improve the calculation speed. The simulation and experiment results demonstrate that the LPSA method can realize fast pulse compression with adequate high amplitude accuracy and frequency resolution. Compared to existing digital pulse compression technology, this method can significantly reduce the number of required calculations, especially for measurements of sparse signals.

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Takayama, Takuya, Masayuki Sugano, Yukinobu Tokieda et Hiroki Sugawara. « Hybrid SIMO and MIMO sparse array radar ». International Journal of Microwave and Wireless Technologies 6, n^o 3-4 (15 avril 2014) : 389–95. http://dx.doi.org/10.1017/s1759078714000154.

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This paper clarifies what we benefit from single-input–multiple-output (SIMO) or multiple-input–multiple-output (MIMO) radar. We have developed an X-band sparse array imaging radar system capable of operating at both SIMO and MIMO modes. The hybrid radar modes are realized without any modification in hardware, but simply by switching the scheme of waveform generation and post-processing. A comparison has been made between the SIMO mode adopting a chirp pulse waveform and the MIMO mode based on the code-division multiple access method using the Gold-coded pulse waveform. Mutually complementary properties between the SIMO and MIMO modes in terms of the cost of computation, the ease of array calibration, and the detectability of targets are clarified through simulations and an experiment.

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Veljković, Marija, Ana Mančić, Daniela Milović et Aleksandra Maluckov. « Numerical study of high intensity events in the supercontinuum generation in the presence of input chirp ». Optik 196 (novembre 2019) : 163180. http://dx.doi.org/10.1016/j.ijleo.2019.163180.

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Bhamidipati, J. K. P., K. C. Durbhakula et A. N. Caruso. « A dynamically tunable discrete-element transmission line pulse generator ». AIP Advances 13, n^o 4 (1 avril 2023) : 045205. http://dx.doi.org/10.1063/5.0125277.

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The Frozen Wave Generator (FWG) is a megawatt-class radio frequency pulse forming network that converts DC input up to ones-of-GHz center frequency ( f c) by superposing an ensemble of alternately charged reactive storage elements. In this work, we demonstrate an all-solid-state, dynamically tunable, and chirp-capable FWG using the lumped-element transmission line (LETL) topology. A 12-segment LETL-FWG switched using a MOSFET is demonstrated and directly compared with a literature standard coaxial-based system. Comparison metrics for pulse width ( tpulse) are studied as a function of the transmission line length and respective LC parameters. The chirp- and dynamic-tuning-capability as well as the high volumetric power density of the system are demonstrated by comparing the predicted and measured bandwidth, rise-time, pulse width, and delay-time from a 7.5 × 30 × 3 cm3 printed circuit board. The experiment resulted in dynamically tunable pulse trains with 15–24 ns pulse widths (40–80 MHz) and >35% conversion efficiency and an ∼80% reduction in volume compared to vacuum-relativistic pulsers in the same peak power class.

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Adhikary, Somen, et Mousumi Basu. « Nonlinear pulse reshaping in a typically designed silicon-on-insulator waveguide and its application to generate a high repetition rate pulse train ». Journal of Optics 23, n^o 12 (25 novembre 2021) : 125506. http://dx.doi.org/10.1088/2040-8986/ac34e5.

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Abstract A silicon-on-insulator (SOI) planar waveguide is designed with a small group velocity dispersion (β 2) ∼2.212 (ps2 m−1) and a quite high nonlinear coefficient (γ) of ∼360.57 (W−1 m−1). The designed waveguide is capable of reshaping a super-Gaussian input optical pulse into a parabolic pulse (PP), without any use of external gain. The same waveguide with a relatively longer length can also generate a triangular pulse (TP) by using a positive chirp at the input. In both cases, PP and TP are created at a much shorter optimum length (L opt) of a few millimeters when compared to previously reported works on normal dispersion optical fibers. The interaction of a pulse pair inside such an SOI waveguide is investigated, for the first time as per our knowledge to generate a high-frequency (∼4.8 THz) pulse train, while lower repetition rate (∼180 GHz) pulses are used at the input. This study as a whole enables potential device applications in the domains of tunable high frequency (THz) pulse generators, optical signal processing, and many more.

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Ivanov Spassov, Sevdalin. « SIMULATION MODELING OF THE INTERFERENCE IMMUNITY OF THE RADARS OPERATING WITH COMPRESSED SIGNAL ». International Journal of Advanced Research 8, n^o 12 (31 décembre 2020) : 799–804. http://dx.doi.org/10.21474/ijar01/12216.

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The immunity to the interference of a radar operating with a pulse compression signal is an important feature. The matched filter is one of the elements of the radar, providing resistance to interference. A model of a matched filter to chirp signal has synthesized using the Simulink tool of the Matlab software. Two types of interference signals have fed to the matched filter input, and the output signals are measured. The matched filters degree of suppression against these two interference signals has been assessed. Inferences about the interference immunity of the radars operating with compressed signals have been made.

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Li Gang, Liu Hong-Jie, Lu Feng, Wen Xian-Lun, He Ying-Ling, Zhang Fa-Qiang et Dai Zeng-Hai. « Investigation on the influences of linear chirp with different input pulse intensities on BaF2 cross-polarized wave generation ». Acta Physica Sinica 64, n^o 2 (2015) : 020602. http://dx.doi.org/10.7498/aps.64.020602.

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Mandeng, Lucien Mandeng, Clement Tchawoua, Hippolyte Tagwo, Mourad Zghal, Rim Cherif et Alidou Mohamadou. « Role of the Input Profile Asymmetry and the Chirp on the Propagation in Highly Dispersive and Nonlinear Fibers ». Journal of Lightwave Technology 34, n^o 24 (15 décembre 2016) : 5635–41. http://dx.doi.org/10.1109/jlt.2016.2624699.

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Sarotama, Afrias, et Benyamin Kusumoputro. « System Identification of UAV Alap-Alap Using Back Propagation Neural Network ». Applied Mechanics and Materials 373-375 (août 2013) : 1212–19. http://dx.doi.org/10.4028/www.scientific.net/amm.373-375.1212.

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A good model is necessary in order to design a controller of a system off-line. It is especially beneficial in the implementation of new advanced control schemes in Unmanned Aerial Vehicle (UAV). Considering the safety and benefit of an off-line tuning of the UAV controllers, this paper identifies a dynamic MIMO UAV nonlinear system which is derived based on the collection of input-output data taken from a test flights (36250 samples data). These input-output sample flight data are grouped into two flight data sets. The first flight data set, a chirp signal, is used for training the neural network in order to determine parameters (weights) for the network. Validation of the network is performed using the second data set, which is not used for training, and is a representation of UAV circular flight movement. An artificial neural network is trained using the training data set and thereafter the network is excited by the second set input data set. The predicted outputs based on our proposed Neural Network model is similar to the desired outputs (roll, pitch and yaw) which has been produced by real UAV system.

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Paun, Maria-Alexandra, Vladimir-Alexandru Paun et Viorel-Puiu Paun. « Electrical Signal Modeling in Cochlear Implants. Study of Temperature and Humidity Effects ». Micromachines 12, n^o 7 (30 juin 2021) : 785. http://dx.doi.org/10.3390/mi12070785.

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The present paper discusses the climatic effects of humidity and temperature on cochlear implant functioning and the quality of the electrical sound signal. MATLAB Simulink simulations were prepared, offering insights into signal behavior under such climatic parameter changes. A simulation setup of the cochlear implant was developed, where a source type selection was used to change between a voice recording and a “chirp” sound. In addition, a DC blocking filter was applied to the input signal. A simulation code, with the application of the climatic influence via the air attenuation function, was developed. Thereby, the attenuation of temperature and humidity in the sound atmospheric circulation of the input signal, at T = 0 °C and RH = 0% and at T = 36 °C and RH = 40% was graphically represented. The results of the electrical pulse generator for each of the eight channels, with the IIR filter, Gaussian noise, temperature variation, humidity influence, and control of denoise block activity, were thus obtained.

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Lin, Yueguan, Yida Fan, Chenglong Jiang, Zhiqiang Wang et Weizeng Shao. « MIMO SAR Using Orthogonal Coding : Design, Performance Analysis, and Verifications ». International Journal of Antennas and Propagation 2015 (2015) : 1–10. http://dx.doi.org/10.1155/2015/629506.

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Multiple-input multiple-output (MIMO) synthetic aperture radar (SAR) is a promising technology in radar imaging which provides a better balance of azimuth resolution and swath width compared with traditional single-input single-output (SISO) SAR. It has the potential to help scientists and engineers to design ambitious SAR system with higher resolution and wider swath. This paper studies the principle of MIMO SAR using orthogonal coding waveform and then provides the performance analysis in resolution and swath width. By using orthogonal coding waveform, lower channel interference is obtained, which makes MIMO SAR achieve wider unambiguous range swath and lower azimuth ambiguity. Simulations are carried out by means of the system parameters of real spaceborne SAR platform. A ground-based MIMO SAR imaging system with up and down chirp modulation is also designed. The performances of MIMO SAR and SISO SAR are compared, and the validity and advantage of MIMO SAR are verified.

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Rakesh Kumar, V., Kamalesh Jana, Indranuj Dey, K. Chandra Vardhan, Amit D. Lad, Jeffrey M. Brown, Mette B. Gaarde, Arnaud Couairon et G. Ravindra Kumar. « Spectral and intensity control of high energy terahertz radiation from bulk liquids ». Journal of Physics D : Applied Physics 55, n^o 9 (23 novembre 2021) : 095107. http://dx.doi.org/10.1088/1361-6463/ac3455.

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Abstract High power, broadband terahertz (THz) radiation from liquids, excited by intense, femtosecond 800 nm laser pulses has been demonstrated recently, overturning the long held belief that liquids would not give such emission due to their absorption in the THz region. Given the widespread interest in the use of THz radiation for several applications and the energy and bandwidth limitations of existing sources, liquids are expected to attract great attention in the future. While the emission at tens of microjoules from liquids is very promising, it is important to explore whether control of the THz flux and spectrum is achievable by manipulating the laser or liquid parameters. In this paper we present results on manipulating the spectrum of THz radiation from liquids by chirping the input laser pulse and optimizing the THz output energy by laser chirp as well as optimizing the focal position. We demonstrate tunability by varying the chirp of the laser pulse and show that the THz emission predominantly comes from the region near the end of the liquid path, consistent with the absorption of THz radiation by liquids. This control gives us an opportunity to tune the THz radiation to suit experimental needs. We present simulations that support the results.

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Xue, Weiqi, Yaohui Chen, Filip Öhman et Jesper Mørk. « The role of input chirp on phase shifters based on slow and fast light effects in semiconductor optical amplifiers ». Optics Express 17, n^o 3 (22 janvier 2009) : 1404. http://dx.doi.org/10.1364/oe.17.001404.

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Kalybek, Maksat, Mateusz Bocian, Wojciech Pakos, Jacek Grosel et Nikolaos Nikitas. « Performance of Camera-Based Vibration Monitoring Systems in Input-Output Modal Identification Using Shaker Excitation ». Remote Sensing 13, n^o 17 (1 septembre 2021) : 3471. http://dx.doi.org/10.3390/rs13173471.

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Despite significant advances in the development of high-resolution digital cameras in the last couple of decades, their potential remains largely unexplored in the context of input-output modal identification. However, these remote sensors could greatly improve the efficacy of experimental dynamic characterisation of civil engineering structures. To this end, this study provides early evidence of the applicability of camera-based vibration monitoring systems in classical experimental modal analysis using an electromechanical shaker. A pseudo-random and sine chirp excitation is applied to a scaled model of a cable-stayed bridge at varying levels of intensity. The performance of vibration monitoring systems, consisting of a consumer-grade digital camera and two image processing algorithms, is analysed relative to that of a system based on accelerometry. A full set of modal parameters is considered in this process, including modal frequency, damping, mass and mode shapes. It is shown that the camera-based vibration monitoring systems can provide high accuracy results, although their effective application requires consideration of a number of issues related to the sensitivity, nature of the excitation force, and signal and image processing. Based on these findings, suggestions for best practice are provided to aid in the implementation of camera-based vibration monitoring systems in experimental modal analysis.

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Ghosh, Binoy Krishna, Dipankar Ghosh et Mousumi Basu. « Generation of stable temporal doublet by a single-mode silicon core optical fiber ». Journal of Optics 24, n^o 5 (31 mars 2022) : 055503. http://dx.doi.org/10.1088/2040-8986/ac5b50.

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Abstract A highly nonlinear single mode anomalous dispersion silicon-core fiber is designed and optimized at the operating wavelength of 2.2 µm for the purpose of generating stable temporal pulse doublets. To designate the output pulse pair as a perfect Gaussian doublet, two new parameters, dissimilarity factor ( ρ g ) and co-similarity index (μ cs) are introduced. Different input pulse parameters such as power, pulse width and chirp are optimized to obtain Gaussian temporal doublets at the shortest optimum length (∼few cm) which is sufficiently smaller in comparison to silica fibers reported earlier. The output pulse pairs remain as a doublet for quite a good stability length. In view of serving practical purposes, the possibilities of fluctuations of input power and pulse width are included to investigate the changes in stability length and effective repetition rate (ERR). The change in ERR along the fiber length produces a remarkable change in free carrier concentration in core, which has also been taken into account for the first time as per our knowledge to obtain the temporal pulse doublet in the so designed Si-core fiber.

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Krishna, B. Murali, B. T. Krishna et K. Babulu. « Hardware Implementation of Stockwell Transform and Smoothed Pseudo Wigner Ville Distribution Transform on FPGA using CORDIC Algorithm ». International Journal of Recent Technology and Engineering (IJRTE) 10, n^o 5 (30 janvier 2022) : 57–60. http://dx.doi.org/10.35940/ijrte.e6705.0110522.

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A comparison of linear and quadratic transform implementation on field programmable gate array (FPGA) is presented. Popular linear transform namely Stockwell Transform and Smoothed Pseudo Wigner Ville Distribution (SPWVD) transform from Quadratic transforms is considered for the implementation on FPGA. Both the transforms are coded in Verilog hardware description language (Verilog HDL). Complex calculations of transformation are performed by using CORDIC algorithm. From FPGA family, Spartan-6 is chosen as hardware device to implement. Synthetic chirp signal is taken as input to test the both designed transforms. Summary of hardware resource utilization on Spartan-6 for both the transforms is presented. Finally, it is observed that both the transforms S-Transform and SPWVD are computed with low elapsed time with respect to MATLAB simulation.

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