Search

Multistage reducer vibration signals have complicated spectral structures owing to the amplitude and frequency modulations of gear damage-induced vibrations and the multiplicative amplitude modulation effect caused by time-varying vibration transfer paths (in the case of local gear damage) when the multistage reducer contains both planetary and spur gears. Moreover, the difference between the vibration energies of these gears increases the difficulty of fault feature extraction when multiple failures occur in the reducer. As the meshing frequency of each gear group often varies significantly, variational mode decomposition can be performed to decompose the vibration signal according to frequency, enabling separation of the vibration signals of the spur and planetary gears. The common fault features of these gears can be extracted from the spectrum of the amplitude demodulation envelope. To verify the effectiveness of this method, we first analyzed a simulation signal, and then utilized the experimental signals from a laboratory multistage reducer for verification. In the multistage reducer simulation, we considered the amplitude and frequency modulation of the gear damage and transfer paths. In the experimental verification, we processed local faults (broken teeth) and uniform faults (uniform wear) on the sun gear and the spur gear of the planetary gear separately. [ABSTRACT FROM AUTHOR]

The use of robotic motion platforms in vehicle simulators is relatively common. However, the process of testing and tuning the so-called washout algorithms, used for motion cueing generation in motion-based vehicle simulators, is complex. This process can be reduced in cost, simplified, improved, shortened and performed safer if virtual motion platforms are used instead of real devices. This paper deals with identifying a method to perform a fast but reliable simulation of parallel mechanisms to be used for motion cueing generation. The method relies on the use of Laplacian polynomial transfer function models by means of using AM-FM bi-modulated signals as reference inputs to achieve system identification. The proposed simulation scheme is implemented and assessed using optical tracking methods by testing a real 2-DOF pitch-roll parallel robot, although the method is not intrinsically restricted to this type of device. The performance of the proposed solution is also assessed with the classical washout algorithm. Results show that the accuracy of the method is satisfactory and the performance of the proposed simulation scheme is very high, being suitable to test and tune washout algorithms. [ABSTRACT FROM AUTHOR]

This paper presents a simple method of linewidth enhancement factor (LEF) measurement of a semiconductor laser through narrowband optical frequency modulation (FM) generation by direct modulation. The narrowband optical FM is generated by using small-amplitude directcurrent modulation, thereby limiting the resultant optical intensity modulation index level typically within 10%. The LEF is found to decrease linearly with the increase in bias current of the laser diode above threshold. [ABSTRACT FROM AUTHOR]

This study investigated the psychophysical effects of distortion products in a listening task traditionally used to estimate the bandwidth of phase sensitivity. For a 2000 Hz carrier, estimates of modulation depth necessary to discriminate amplitude modulated (AM) tones and quasi-frequency modulated (QFM) were measured in a two interval forced choice task as a function modulation frequency. Temporal modulation transfer functions were often non-monotonic at modulation frequencies above 300 Hz. This was likely to be due to a spectral cue arising from the interaction of auditory distortion products and the lower sideband of the stimulus complex. When the stimulus duration was decreased from 200 ms to 20 ms, thresholds for low-frequency modulators rose to near-chance levels, whereas thresholds in the region of non-monotonicities were less affected. The decrease in stimulus duration appears to hinder the listener's ability to use temporal cues in order to discriminate between AM and QFM, whereas spectral information derived from distortion product cues appears more resilient. [ABSTRACT FROM AUTHOR]

This study used a correlational approach to clarify the mechanisms involved in modulation coding. Amplitude-modulation (AM) and frequency-modulation (FM) detection thresholds (AMDTs and FMDTs, respectively) were assessed for 70 normal-hearing listeners. In order to increase between-listeners variability in peripheral coding, participants with a wide range of age (20–70 years) were included. AMDTs and FMDTs were measured at a 5-Hz rate, using a 500-Hz sinusoidal carrier. FMDTs were also measured in the presence of an interfering AM to discourage the use of temporal-envelope cues. The results showed that AMDTs were significantly correlated with FMDTs, but not with FMDTs measured with interfering AM. FMDTs with and without interfering AM were significantly correlated with each other. This pattern of correlation proved to be robust, providing additional evidence that for low carrier frequencies, (i) low-rate AM and FM detection is based on a common code using temporal-envelope cues and (ii) low-rate FM detection is based on an additional code using cues distinct from temporal-envelope. The analyses also showed that age was correlated with FMDTs only. However, no significant difference was found when comparing the various correlations with age. Hence, the effects of age on modulation sensitivity remain unclear. [ABSTRACT FROM AUTHOR]

This paper presents an algorithm for finding carriers of frequency-modulated (FM) and amplitude-modulated (AM) electromagnetic (EM) emanations from computer systems. Computer systems create EM emanations across the RF spectrum making it difficult, error-prone, and time consuming to find the relatively few emanations that expose sensitive information. One of the most common and simplest mechanisms for information leakage occurs when an amplitude or a frequency of an existing strong signal (e.g., a processor or memory clock) is amplitude or frequency modulated by a system activity. If the system activity can be linked to sensitive information, this results in information leakage. We present an algorithm for automatically finding these AM and FM signals, demonstrate the algorithm's performance on several different types of processors and systems (desktop, laptop, and smartphone), and compare the results to an exhaustive manual search. We also verify that all signals identified by the algorithm can be traced to plausible unintentional modulation mechanisms to illustrate that these signals can potentially cause information leakage. This algorithm can be an important tool for system designers to quickly identify circuits that are leaking sensitive information. [ABSTRACT FROM PUBLISHER]

The vibration signals from defective rolling bearings are multi-component amplitude modulation (AM)-frequency modulation (FM) signals. Traditional envelope analysis method is based on a filter. The centre frequency and bandwidth of the filter are set according to experience. So the filter method will induce a demodulation error. This research proposes a rolling bearing fault diagnosis method based on adaptive local iterative filtering (ALIF) and envelope spectrum. The ALIF method is a new method for the analysis of non-stationary signals. It uses an iterative filters strategy together with an adaptive, data-driven filter length selection to achieve the necessary decomposition. Smooth filters with compact support from the solutions of the Fokker–Planck equations are used within the ALIF method. The ALIF method offers good performance in obtaining more accurate components of non-stationary signals and in suppressing mode mixing. The ALIF method can decompose a multi-component AM-FM signal into a number of stationary components. The envelope demodulation method is used to analyse those components containing fault information which, in turn, can reveal bearing fault features. The vibration signals from a rolling bearing with an outer race fault and an inner race fault are used to verify the proposed method. The results show that this method can effectively extract bearing fault features. [ABSTRACT FROM AUTHOR]

The coordinated tracking control for the group motion control system based on three direct-drive double-sided linear switched reluctance motors (LSRMs) is investigated in this paper. The system construction for the proposed coordinated tracking system is elaborated, including the unit system and group system design, communication configuration among unit systems, and stability and performance analysis of the group system. The coordinated control performance is concentrated on three identical LSRMs with different communication topologies. Experimental results demonstrate that necessary bidirectional interactions between the unit systems contribute to the coordination performance. The maximum dynamic tracking error within ±0.4 mm can be achieved under the sinusoidal reference of 30-mm amplitude and 0.2-Hz frequency. [ABSTRACT FROM PUBLISHER]

This paper presents a study on linear frequency modulation (LFM) pulsed signal transmission by four-dimensional (4-D) antenna arrays. LFM pulse is used as the input of 4-D antenna arrays and the influence brought by the periodic time modulation is analyzed. The relationship among pulse duration, chirp rate, sample frequency, time-modulation frequency, and propagation direction is analyzed and the restrictions to these parameters are highlighted. The transmitting and receiving structures are introduced and relevant signal processing steps are described. Numerical examples with several different time schemes, including the pulse shifting (PS) scheme and binary phase center motion (BPCM) scheme, are presented to demonstrate the effectiveness of the LFM signal transmission by 4-D arrays. Simulation results validate that original chirp signal can be correctly recovered and low sidelobe power patterns can be simultaneously achieved by 4-D antenna arrays, as long as the proposed limitations are satisfied. [ABSTRACT FROM PUBLISHER]

Cells sense external concentrations and, via biochemical signaling, respond by regulating the expression of target proteins. Both in signaling networks and gene regulation there are two main mechanisms by which the concentration can be encoded internally: amplitude modulation (AM), where the absolute concentration of an internal signaling molecule encodes the stimulus, and frequency modulation (FM), where the period between successive bursts represents the stimulus. Although both mechanisms have been observed in biological systems, the question of when it is beneficial for cells to use either AM or FM is largely unanswered. Here, we first consider a simple model for a single receptor (or ion channel), which can either signal continuously whenever a ligand is bound, or produce a burst in signaling molecule upon receptor binding. We find that bursty signaling is more accurate than continuous signaling only for sufficiently fast dynamics. This suggests that modulation based on bursts may be more common in signaling networks than in gene regulation. We then extend our model to multiple receptors, where continuous and bursty signaling are equivalent to AM and FM respectively, finding that AM is always more accurate. This implies that the reason some cells use FM is related to factors other than accuracy, such as the ability to coordinate expression of multiple genes or to implement threshold crossing mechanisms. [ABSTRACT FROM AUTHOR]

We present a detailed analysis and understanding of Kelvin probe force microscopy (KPFM) data for a system of point charges in a vacuum-dielectric tip-sample system. Explicit formulae describing the KPFM signal ΔV are derived for the two KPFM operation modes, namely amplitude modulation and frequency modulation (FM). The formulae allow for a physical interpretation of the resulting KPFM signal, reveal contributing parameters, and especially disclose an additive behavior. We numerically evaluate these equations and show exemplary KPFM slice data for a single point charge. The theoretical analysis is complemented by two-dimensional FM-KPFM maps obtained experimentally on 2,5-dihydrobenzoic acid on calcite (10.4). The molecules assemble in two coexisting phases understood as protonated and deprotonated molecules. The two-dimensional maps reveal a convex shape of the KPFM signal A V across the islands and a clear difference between the two phases is revealed. Furthermore, we apply the theoretically suggested difference strategy to extract the molecular component from the measured total KPFM signal. [ABSTRACT FROM AUTHOR]

The results of investigations and the characteristics of a calibrator based on a vector generator are described. The application of the calibrator in the State checking schemes is considered. [ABSTRACT FROM AUTHOR]

Abstract: Frequency modulation spectroscopy (FMS) is most commonly used for trace gas detection, but its sensitivity is usually limited by the background noise attributed to residual amplitude modulation (RAM). In this paper, comprehensive theoretical analyses of FMS with and without RAM are presented. Then the measurements of RAM are experimentally verified utilizing a fiber electro-optic modulator based FMS setup. In order to reduce the RAM, a novel servo control method with its correction signal obtained from a polarization detection scheme was proposed and pure FMS signals of C2H2 gas at wavenumber of 6544.4419cm−1 are obtained. Furtherly, long-term measurements of the dispersion background signal with feedback loop on and off are performed to evaluate the stability of the instrument. Finally, this servo control method is extended into the application of Pound–Drever–Hall frequency stabilization technique to improve the locking accuracy and stability. [Copyright &y& Elsevier]

In this paper, we propose an approach for the analysis and detection of acoustic events in speech signals using the Bessel series expansion. The acoustic events analyzed are the voice onset time (VOT) and the glottal closure instants (GCIs). The hypothesis is that the Bessel functions with their damped sinusoid-like basis functions are better suited for representing the speech signals than the sinusoidal basis functions used in the conventional Fourier representation. The speech signal is band-pass filtered by choosing the appropriate range of Bessel coefficients to obtain a narrow-band signal, which is decomposed further into amplitude modulated (AM) and frequency modulated (FM) components. The discrete energy separation algorithm (DESA) is used to compute the amplitude envelope (AE) of the narrow-band AM-FM signal. Events such as the consonant and vowel beginnings in an unvoiced stop consonant vowel (SCV) and the GCIs are derived by processing the AE of the signal. The proposed approach for the detection of the VOT using the Bessel expansion is shown to perform better than the conventional Fourier representation. The performance of the proposed GCI detection method using the Bessel series expansion is compared against some of the existing methods for various noise environments and signal-to-noise ratios. [ABSTRACT FROM AUTHOR]

We study the parametric resonance in a system of two coupled quantum harmonic oscillators when the frequency of one of them (describing the field mode) is modulated at exactly twice the unperturbed eigenfrequency (the case of 'unshifted resonance'). The coordinate-momentum coupling between the two oscillators is chosen in order to simulate the dynamical Casimir effect in a cavity containing a harmonic oscillator detector (LC-contour). Analytical solutions are obtained with the aid of the multiple scales method. For the field mode and detector initially prepared in thermal squeezed states, we calculate the mean numbers of quanta in both modes, as well as the invariant squeezing coefficients, purity and photon distribution functions, analyzing the influence of coupling strength and frequency modulation depth on the dynamics of these quantities. We show that the system goes to strongly squeezed states even for high temperature initial states of the detector. Depending on the relative strength of coupling coefficient and the parametric modulation amplitude, initially separable states go to permanently entangled states or they show periodic appearance and disappearance of entanglement. [ABSTRACT FROM AUTHOR]

The frequency modulation to amplitude modulation (FM-to-AM) effect is one of the few remaining scientific issues in a large-scale laser facility which could prevent fusion ignition. A fiber-based polarization–rotation filter which consists of a fiber polarizer, a section of polarization-maintaining fiber, a half-wave plate and a polarization beam splitter is proposed to suppress the FM-to-AM effect. Theoretical analysis and experimental demonstration in the preamplifier module of the SG-III laser facility prove the effectiveness of this filter. [ABSTRACT FROM AUTHOR]

The little destruction to the deployment site and high repeatability of the Controlled Accurate Seismic Source (CASS) shows its potential for investigating seismic wave velocities in the Earth's crust. However, the difficulty in retrieving impulsive seismic waveforms from the CASS data and identifying the seismic phases substantially prevents its wide applications. For example, identification of the seismic phases and accurate measurement of travel times are essential for resolving the spatial distribution of seismic velocities in the crust. Until now, it still remains a challenging task to estimate the accurate travel times of different seismic phases from the CASS data which features extended wave trains, unlike processing of the waveforms from impulsive events such as earthquakes or explosive sources. In this study, we introduce a time-frequency analysis method to process the CASS data, and try to retrieve the seismic waveforms and identify the major seismic phases traveling through the crust. We adopt the Wigner-Ville Distribution (WVD) approach which has been used in signal detection and parameter estimation for linear frequency modulation (LFM) signals, and proves to feature the best time-frequency convergence capability. The Wigner-Hough transform (WHT) is applied to retrieve the impulsive waveforms from multi-component LFM signals, which comprise seismic phases with different arrival times. We processed the seismic data of the 40-ton CASS in the field experiment around the Xinfengjiang reservoir with the WVD and WHT methods. The results demonstrate that these methods are effective in waveform retrieval and phase identification, especially for high frequency seismic phases such as PmP and SmS with strong amplitudes in large epicenter distance of 80-120 km. Further studies are still needed to improve the accuracy on travel time estimation, so as to further promote applicability of the CASS for and imaging the seismic velocity structure. [ABSTRACT FROM AUTHOR]

Forward masking of sinusoidal frequency modulation (FM) was measured with three types of maskers: FM, amplitude modulation (AM), and a masker created by combining the magnitude spectrum of an FM tone with random component phases. For the signal FM rates used (5, 20, and 40 Hz), an FM masker raised detection thresholds in terms of frequency deviation by a factor of about 5 relative to without a masker. The AM masker produced a much smaller effect, suggesting that FM-to-AM conversion did not contribute substantially to the FM forward masking. The modulation depth of an FM masker had a nonmonotonic effect, with maximal masking observed at an intermediate value within the range of possible depths, while the random-phase FM masker produced less masking, arguing against a spectrally-based explanation for FM forward masking. Broad FM-rate selectivity for forward masking was observed for both 4-kHz and 500-Hz carriers. Thresholds measured as a function of the masker-signal delay showed slow recovery from FM forward masking, with residual masking for delays up to 500 ms. The FM forward-masking effect resembles that observed for AM [Wojtczak and Viemeister (2005). J. Acoust. Soc. Am. 188, 3198-3210] and may reflect modulation-rate selective neural adaptation to FM. [ABSTRACT FROM AUTHOR]

Gearboxes usually run under fluctuating load conditions during service, however most of papers available in the literature describe models of gearboxes under stationary load conditions. Main task of published papers is fault modeling for their detection. Considering real situation from industry, the assumption of stationarity of load conditions cannot be longer kept. Vibration signals issued from monitoring in maintenance operations differ from mentioned models (due to load non-stationarity) and may be difficult to analyze which lead to erroneous diagnosis of the system. The objective of this paper is to study the influence of time varying load conditions on a gearbox dynamic behavior. To investigate this, a simple spur gear system without defects is modeled. It is subjected to a time varying load. The speed-torque characteristic of the driving motor is considered. The load variation induces speed variation, which causes a variation in the gearmesh stiffness period. Computer simulation shows deep amplitude modulations with sidebands that don't differ from those obtained when there is a defective tooth. In order to put in evidence the time varying load effects, Short Time Fourier Transform and then Smoothed Wigner-Ville distribution are used. Results show that the last one is well suited for the studied case. The experimental validation presented at the end of the paper confirms the obtained results. Such results offer useful information when diagnosing gear transmissions by avoiding confusing conclusions from vibration signals. [ABSTRACT FROM AUTHOR]

The article presents a study which describes the first recordings of narwhals in winter in West Greenland. The study used an Offshore Acoustics hydrophone to collect data and a Sony TCD-D7 Digital Audio Tape (DAT) recorder. Results show that each sound produced by narwhals were classified as either tonal frequency modulated (FM) or pulsed (amplitude modulated).

An approach for surface potential imaging based on half-harmonic band excitation (BE) in Kelvin probe force microscopy is demonstrated. Using linear and half-harmonic BE enables quantitative correction of the cantilever transfer function. Half-harmonic band excitation Kelvin probe force microscopy (HBE KPFM) thus allows quantitative separation of surface potential and topographic contributions to the signal, obviating the primary sources of topographic cross-talk. HBE KPFM imaging and voltage spectroscopy methods are illustrated for several model systems. [ABSTRACT FROM AUTHOR]

In this article, a new model to predict the amplitude reduction of the interference harmonics in power supplies with parallel topology is presented when the switching frequency modulation with variable delay (VDFM) technique is applied. The VDFM method consists of combining the interleaving and switching frequency modulation (SFM) techniques. The new model presented has been evaluated in a multichannel buck converter, operating with different numbers of converters when a triangular modulation profile is used. Theoretical study and experimental results show the influence of the number of converters and the modulation parameters with regard to electromagnetic interference reduction. From the new model presented, it is possible to predict the value of modulation parameters and the numbers of converters in order to satisfy the required attenuation regarding the electromagnetic compatibility directives, when a triangular modulation profile is used. [ABSTRACT FROM PUBLISHER]

Underwater acoustic (UWA) channels exhibit time-varying fading statistics, thus a coded modulation scheme optimally designed for a specific model (e.g., Rayleigh fading) will perform poorly when the channel statistics change. Exploiting diversity via coded modulation is a robust approach to improve the reliability of the acoustic link in a variety of channel conditions. Two coded modulation schemes drawn from the terrestrial radio literature are compared in terms of their bit error rate (BER). The first scheme combines trellis coded modulation (TCM) based on an 8-phase-shift keying (8-PSK) signal set and symbol interleaving. The second scheme is based on bit-interleaved coded modulation (BICM), which includes a convolutional encoder, a bit interleaver, and a 16-quadrature-amplitude-modulation (16-QAM) signal set. These schemes, which are designed to have the same bit rate and decoding complexity, are tested under two scenarios. In the first scenario, a single-input–multiple-output (SIMO) system is implemented by means of orthogonal frequency-division multiplexing (OFDM) modulation. In the second scenario, a multiple-input–multiple-output (MIMO) system is implemented and each of the coded modulation scheme is coupled with a 3/4-rate space–time block code (STBC) before applying OFDM. Analyzing both simulated and experimental data, the following results, which also hold for terrestrial radio, are confirmed: coded modulation schemes emphasizing higher Hamming distance (such as BICM) yield a lower error rate when spatial diversity is very limited (first scenario). On the other hand, coded modulation schemes emphasizing higher free Euclidean distance (such as TCM) demonstrate a lower error rate when spatial diversity is sufficiently high (second scenario). [ABSTRACT FROM PUBLISHER]

Abstract: A novel method for feature extraction from the frequency modulation (FM) in speech signals is proposed for robust speech recognition. To exploit of the multistream speech recognizers, each stream should compensate for the shortcomings of the other streams. In this light, FM features are promising as complemental features of amplitude modulation (AM). In order to extract effective features from FM patterns, we applied the proposed feature extraction method by the data-driven modulation analysis of instantaneous frequency. By evaluating the frequency responses of the temporal filters obtained by the proposed method, we confirmed that the modulation observed around 4Hz is important for the discrimination of FM patterns, as in the case of AM features. We evaluated the robustness of our method by performing noisy speech recognition experiments. We confirmed that our FM features can improve the noise robustness of speech recognizers even when the FM features are not combined with conventional AM and/or spectral envelope features. We also performed multistream speech recognition experiments. The experimental results show that combination of the conventional AM system and proposed FM system reduced word error by 43.6% at 10 dB SNR as compared to the baseline MFCC system and by 20.2% as compared to the conventional AM system. We investigated the complementarity of the AM and FM features by performing speech recognition experiments in artificial noisy environments. We found the FM features to be robust to wide-band noise, which certainly degrades the performance of AM features. Further, we evaluated the efficiency of multiconditional training. Although the performance of the proposed combination method was degraded by multiconditional training, we confirmed that the performance of the proposed FM method improved. Through a series of experiments, we confirmed that our FM features can be used as independent features as well as complemental features. [Copyright &y& Elsevier]

Sensory experience during development can modify the CNS and alter adult perceptual skills. While this principle draws support from deprivation or chronic stimulus exposure studies, the effect of training is addressed only in adults. Here, we asked whether a brief period of training during development can exert a unique impact on adult perceptual skills. Juvenile gerbils were trained to detect amplitude modulation (AM), a stimulus feature elemental to animal communication sounds. When the performance of these juvenile-trained animals was subsequently assessed in adulthood, it was superior to a control group that received an identical regimen of training as adults. The juvenile-trained animals displayed significantly betterAMdetection thresholds. This was not observed in an adult group that received only exposure to AM stimuli as juveniles. To determine whether enhanced adult performance was due solely to learning the conditioned avoidance procedure, juveniles were trained on frequency modulation (FM) detection, and subsequently assessed on AM detection as adults. These animals displayed significantly poorer AM detection thresholds than all other groups. Thus, training on a specific auditory task (AM detection) during development provided a benefit to performance on that task in adulthood, whereas an identical training regimen in adulthood did not bring about this enhancement. In contrast, there was a cost, in adulthood, following developmental training on a different task (FM detection). Together, the results demonstrate a period of heightened sensitivity in the developing CNS such that behavioral training in juveniles has a unique impact on adult behavioral capabilities. [ABSTRACT FROM AUTHOR]

We obtained linear solutions for the frequency and amplitude modulations of the El Niño-Southern Oscillation (ENSO) by the annual cycle using a modified harmonic oscillator equation. The frequency modulation by the annual cycle was capable of changing the ENSO phases and dominant frequency, but could not modify the ENSO amplitude. On the other hand, the amplitude modulation by the annual cycle intensifies the ENSO variability and also induces seasonal amplitude locking. The intensification rate of the ENSO amplitude with respect to the annual cycle becomes less sensitive in low-frequency regime of ENSO. [ABSTRACT FROM AUTHOR]

Frequency modulation detection limens (FMDLs) were measured for carrier frequencies (fc) of 1000, 4000, and 6000 Hz, using modulation frequencies (fm) of 2 and 10 Hz and levels of 20 and 60 dB sensation level (SL), both with and without random amplitude modulation (AM), applied in all intervals of a forced-choice trial. The AM was intended to disrupt excitation-pattern cues. At 60 dB SL, the deleterious effect of the AM was smaller for fm = 2 than for fm = 10 Hz for fc = 1000 and 4000 Hz, respectively, while for fc = 6000 Hz the deleterious effect was large and similar for the two values of fm. This is consistent with the idea that, for fc below about 5000 Hz and fm = 2 Hz, frequency modulation can be detected via changes in phase locking over time. However, at 20 dB SL, the deleterious effect of the added AM for fc = 1000 and 4000 Hz was similar for the two values of fm, while for fc = 6000 Hz, the deleterious effect of the AM was greater for fm = 10 than for fm = 2 Hz. It is suggested that, at low SLs, the auditory filters become relatively sharp and phase locking weakens, so that excitation-pattern cues influence FMDLs even for low fc and low fm. [ABSTRACT FROM AUTHOR]

AM-FM models analyse an image in terms of amplitude (AM) and frequency modulated (FM) sinusoids. In this study, the authors present detection and tracking of single and multiple objects in video sequences using AM-FM features. The authors use the particle filtering framework for estimating the motion parameters. The single object tracking algorithm uses an affine motion model and a subspace-based appearance model. The multiple object tracking algorithm, which is a logical extension of single object tracking, can handle varying number of interacting objects. The performance of both single and multiple object tracking is illustrated on real-world videos. [ABSTRACT FROM AUTHOR]

Ultrasonic vibration generates a sensation of sound via bone-conduction. This phenomenon is called bone-conducted ultrasonic (BCU) hearing. Complex sounds can also be perceived by amplitude-modulating a BCU stimulus (AM-BCU). The influence of the modulation frequency on the sensitivity to detecting amplitude modulation of sinusoidal carriers of 10, 20, and 30 kHz was examined to clarify the characteristics of the perception of amplitude modulation over the sonic or audio-frequency range and the ultrasonic range. In addition, the detection sensitivity for single-sideband modulation for a 20 kHz carrier was measured. Temporal modulation transfer functions (TMTFs) obtained at each carrier frequency suggest that the auditory system has the ability to process timing information in the envelopes of AM-BCUs at lower modulation frequencies, as is the case with audio-frequency sounds. The possible influence of peripheral filtering on the shape of the TMTF at higher frequencies was examined. [ABSTRACT FROM AUTHOR]

Abstract: Many natural sounds such as speech contain concurrent amplitude and frequency modulation (AM and FM), with the FM components often in the form of directional frequency sweeps or glides. Most studies of modulation coding, however, have employed one modulation type in stationary carriers, and in cases where mixed-modulation sounds have been used, the FM component has typically been confined to an extremely narrow range within a critical band. The current study examined the ability to detect AM signals carried by broad logarithmic frequency sweeps using a 2-alternative forced-choice adaptive psychophysical design. AM-detection thresholds were measured as a function of signal modulation rate and carrier sweep frequency region. Thresholds for detection of AM in a sweep carrier ranged from −8dB for an AM rate of 8Hz to −30dB at 128Hz. Compared to thresholds obtained for stationary carriers (pure tones and filtered Gaussian noise), detection of AM carried by frequency sweeps substantially declined at low (12dB at 8Hz) but not high modulation rates. Several trends in the data, including sweep- versus stationary-carrier threshold patterns and effects of frequency region were predicted from a modulation filterbank model with an envelope-correlation decision statistic. [Copyright &y& Elsevier]

This paper describes the responses of brainstem lateral line units in goldfish, Carassius auratus, to constant-amplitude and to amplitude-modulated sinusoidal water motions. If stimulated with constant amplitude sinusoidal water motions, units responded with phasic (50%) or with sustained (50%) increases in dicharge rate. Based on isodisplacement curves, units preferred low (33 Hz, 12.5%), mid (50 Hz, 10% and 100 Hz, 30%) or high (200 Hz, 47.5%) frequencies. In most units, responses were weakly phase locked to the carrier frequency. However, at a carrier frequency of 50Hz or 100 Hz, a substantial proportion of the units exhibited strong phase locking. If stimulated with amplitude-modulated water motions, units responded with a burst of discharge to each modulation cycle, that is, units phase locked to the amplitude modulation frequency. Response properties of brainstem units were in many respects comparable to those of midbrain units, suggesting that they emerge first in the lateral line brainstem. [ABSTRACT FROM AUTHOR]

The envelope order spectrum based on the generalized demodulation time-frequency analysis is proposed and applied to the processing of the gear instantaneous signal in this paper. The generalized demodulation time-frequency analysis approach that is a new signal processing method can decompose a multi-component signal into some single-component signals whose instantaneous frequencies possess physics sense. While each single-component signal can be amplitude and frequency modulated signal, the generalized demodulation time-frequency analysis approach is very applicable for processing the multi-component amplitude and frequency modulated signals. When fault occurs in gear, the gear vibration signal in the start-stop process shows the multi-component amplitude and frequency modulated characteristics. In the method of envelope order spectrum based on the generalized demodulation time-frequency analysis, firstly the multi-component signal is decomposed into some single-component signals by using the generalized demodulation time-frequency analysis method; secondly the envelope analysis is applied to each single-component signal; thirdly each envelope signal is resampled in angle-domain; finally the spectrum analysis is applied to each resampled signal and the envelope order spectrum can be obtained. Furthermore, the gear work state can be identified according to the envelope order spectrum. The analysis results from the simulated and experimental signals show the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

Abstract: Scanning probe imaging in a shear force mode allows for the characterization of in-plane surface properties. In a standard AFM, shear force imaging can be realized by the torsional resonance mode. In order to investigate the imaging conditions on mineral surfaces, a torsional resonance mode atomic force microscope was operated in amplitude (AM) and frequency modulation (FM) feedback. Freshly cleaved chlorite was investigated, which showed brucite-like and talc-like surface areas. In constant amplitude FM mode, a slight variation in energy dissipation was observed between both surfaces. Amplitude and frequency vs. distance curves revealed that the tip was in repulsive contact with the specimen during imaging. [Copyright &y& Elsevier]

Quantum-dot (QD) lasers exhibit many useful properties such as low threshold current, temperature and feedback insensitivity, chirpless behavior, and low linewidth enhancement factor (αH-factor). Although many breakthroughs have been demonstrated, the maximum modulation bandwidth remains limited in QD devices, and a strong damping of the modulation response is usually observed pointing out the role of gain compression. This paper investigates the influence of the gain compression in a 1.3-µm InAs-GaAs QD laser and its consequences on the above-threshold αH-factor. A model is used to explain the dependence of the αH-factor with the injected current and is compared with AM/FM experiments. Finally, it is shown that the higher the maximum gain, the lower the effects of gain compression and the lower the αH-factor. This analysis can be useful for designing chirpless QD lasers with improved modulation bandwidth as well as for isolator-free transmission under direct modulation. [ABSTRACT FROM AUTHOR]

Abstract: Simultaneous amplitude modulation of the exciting light beam with two different frequencies enables the excitation of two acoustic modes of a resonant photoacoustic cell. The photoacoustic amplitudes at both resonance frequencies and the corresponding photoacoustic amplitude ratio are obtained continuously without changing the modulation frequency. The photoacoustic mode amplitude ratio is affected neither by intensity fluctuations of the light source nor by microphone or electronics drifts and is a measure of the gas concentration. The simultaneous acquisition of signals at both resonance frequencies with the dual-modulation scheme reduces drifts on the timescale needed to obtain the PA amplitude ratio. As an example acetone measurements using this new dual-modulation photoacoustic scheme are presented. A detection limit of 90ppmm−1 is reached with a simple heated black-body as infrared light source. [Copyright &y& Elsevier]

This paper provides an analysis of the impact of amplitude modulated blocking signals on receiver performance due to device nonlinearity. Using a standard polynomial model of nonlinearity, we derive limitations on the receiver SNR capabilities, depending on the blocking signal modulation statistical properties. The phenomena that we focus on are cross-modulation due to odd-order nonlinearity and amplitude demodulation due to even-order nonlinearity. The results are then detailed for two types of blocking signal modulations: GSMJEDGE modified 8PSK and UTRAIFDD uplink HPSK. [ABSTRACT FROM AUTHOR]

Laser experiments performed on two SiGe voltage controlled oscillator (VCO) circuit topologies show different output spectrums. Analytical models demonstrate that spectral response is determined by design features that impact modulated amplitude or frequency characteristic of transient signals. Further analysis of the two circuits shows the DC bias condition dependence on the topology during laser strikes, which is the main cause of the frequency and amplitude modulation of the transient output signal. [ABSTRACT FROM AUTHOR]

This letter addresses the effect of timing synchronization errors that are introduced by an erroneous detection of the start of an orthogonal frequency-division multiplexing (OFDM) symbol. Such errors degrade the performance of an OFDM receiver by introducing intercarrier interference (ICI) and intersymbol interference (ISI). They can occur due to either an erroneous initial frame synchronization or a change in the power delay profile of the channel. In this letter, we provide a mathematical analysis of the effect of timing errors on the performance of an OFDM receiver in a frequency-selective fading environment. We find exact formulas for the power of interference terms and the resulting average signal-to-interference ratio. We further extend the analysis to the subsample level. Our results show the nonsymmetric effect of timing errors on the performance of an OFDM system. Finally, simulation results confirm the analysis. [ABSTRACT FROM AUTHOR]

Self-assembled pi-conjugated oligomer nanowires have been investigated by frequency modulation atomic force microscopy and amplitude modulation Kelvin probe force microscopy under ultra high vacuum. The distance dependence of the contact potential difference (CPD) has been analyzed by combining high resolution imaging with distance-spectroscopy measurements. It is shown that the apparition of a damping contrast characterizes the onset of short range electrostatic (SRE) forces, which are responsible for the occurrence of local CPD (LCPD) modulations correlated with the molecular lattice. By working at the onset of the damping contrast, the tip-surface separation can be adjusted to minimize the contribution of SRE forces to the measured CPD. [ABSTRACT FROM AUTHOR]

We demonstrate a two-dimensional imaging technique that uses a tomographic image reconstruction algorithm of object projections measured with a single photodetector. By imposing a spatially varying amplitude modulation on the illumination beam, the lateral projections of the object are encoded in the electronic spectrum of the signal from a single-element photodetector. [ABSTRACT FROM AUTHOR]

An optically induced fast wavelength shift is demonstrated in a standard middle infrared (MIR) quantum cascade laser (QCL) by illuminating the front facet with a femtosecond (fs) near infrared (NIR) laser, allowing fast optical frequency modulation (FM) for free space optical communication (FSOC) and FM spectroscopy. Using an etalon as a narrow band-pass wavelength filter, the wavelength modulation (WM) was clearly observed at frequencies up to 1.67 GHz. This approach can also be used for wavelength conversion and might be extended to QCLs operating in different wavelength regions. [ABSTRACT FROM AUTHOR]

The paper addresses the problem of designing and building a stable molecular based oscillator which can be controlled in terms of both amplitude and frequency. A study of previous oscillators of this type showed that they are inherently unstable. To overcome this problem a design was chosen which is based on Lotka–Voltera dynamics. An important aspect of the work was the use of what we term the Engineering Cycle; that is, the cycle of system specification, design, modelling, implementation, and testing and validation. The Lotka–Voltera dynamic, in the context of a predation oscillator, amounts to a predator–prey approach. This is the basis of the oscillator design. The oscillator was designed and detailed modelling undertaken to establish the modes of the dynamic; how it could be tuned for stability; and how to control its amplitude and frequency. The biological implementation of the design was undertaken using a number of BioBricks from the MIT registry (http://parts.mit.edu/registry/index.php/Main_Page), together with a number of parts which we designed and built. [ABSTRACT FROM AUTHOR]

In drive testing, pseudorandom data is very often used to avoid biasing results to a particular pattern, e.g., constant frequency. Using the readback signal to measure flying height modulation (FHM) is the most convenient method, but available methods need a special data pattern. In this paper, we present a method that can be used to measure FHM from a pseudorandom readback signal. The method was applied to measure the FHM due to slider-lubricant impact during read. The obtained FHM is a half-sinusoidal-like pulse with about 40 nm amplitude and 4 µs width that is very similar to results measured on spin-stand tests by using a laser Doppler vibrometer (LDV). [ABSTRACT FROM AUTHOR]

The conversion of the frequency modulated pulse induced from frequency modulation (FM) to amplitude modulation (AM) by the polarization mode dispersion (PMD) is theoretically and experimentally investigated. When there is no polarizer at the output end of a fiber system, the amplitude modulation depth is stable by 8%. Random amplitude modulation is observed when a polarizer is placed at the output end of the fiber system. The observed minimum and maximum modulation depths in our experiment are 5% and 80%, respectively. Simulation results show that the amplitude modulation is stable by 4% induced mainly by group velocity dispersion (GVD) when there is no polarizer, and the amplitude modulation depth displays the random variation character induced by the GVD and PMD. Lastly, a new fiber system scheme is proposed and little amplitude modulation is observed at the top of the output pulse. [ABSTRACT FROM AUTHOR]

The article reports on a study conducted in Columbia, Missouri, concerning the detection and identification of nonlinearities through amplitude and frequency modulation analysis. By the use of a sliding-window fitting (SWF) method, it depicts the physical implications of the proposed method as well as other methods for data processing and transformation. It notes that SWF utilizes windowed regular harmonics and function orthogonality to extract time-localized regular and distorted harmonics.

The influence of short-range electrostatic forces on the measured local contact potential difference (CPD) by means of amplitude-modulation and frequency-modulation Kelvin probe force microscopy (AM- and FM-KPFM) is discussed on the base of numerical and analytical descriptions of both methods. The goal of this work is to help in interpreting recent experimental results reporting atomically resolved CPD images, in particular on bulk insulating samples. The discussion is carried out on the basis of spectroscopic curves. The expression of the bias-dependent electrostatic force is derived from a previous work and is estimated between a tip with simple geometry and the (001) facet of a perfect alkali halide single crystal. The force, with a short-range character, scales as a second-order polynomial function of the bias voltage. It is stated that the linear term is responsible for the occurrence of the atomic-scale CPD contrast, while the quadratic one, involving the sample polarization, accounts for the detected signal by the KPFM methods. Nevertheless, analytical and numerical approaches stress the influence of the linear term on the measured CPD which intrinsically hinders the possibility to perform quantitative CPD measurements, but also makes the measured ''pseudo-CPD'' strongly deviating from the surface potential. Hence, in the short-range regime, AM- or FM-KPFM measurements neither reflect the CPD nor the local surface potential, but rather an effective value which is convoluted by the geometric parameters of the tip, the so-called local CPD. It is also stated that the local CPD measured by means of AM- or FM-KPFM differs when sub-nanometer vibration amplitudes of the cantilever are used. Otherwise, AM- and FM-KPFM measurements should be almost similar. At last, the influence of long-range, capacitive, electrostatic forces is discussed in conjunction with the short-range ones. This allows us to draw conclusions regarding the distance dependence of the local CPD which then exhibits a resonant behavior as a function of the tip-surface separation. This phenomenon is expected to play a role in the KPFM imaging process. [ABSTRACT FROM AUTHOR]

There has been increasing focus on the use of Kelvin probe force microscopy (KPFM) for the determination of local electronic structure in recent years, especially in systems where other methods, such as scanning tunnelling microscopy/spectroscopy, may be intractable. We have examined three methods for determining the local apparent contact potential difference (CPD): frequency modulation KPFM (FM-KPFM), amplitude modulation KPFM (AM-KPFM), and frequency shift-bias spectroscopy, on a test system of 3,4,9,10-perylene tetracarboxylic dianhydride (PTCDA) on NaCl, an example of an organic semiconductor on a bulk insulating substrate. We will discuss the influence of the bias modulation on the apparent CPD measurement by FM-KPFM compared to the DC-bias spectroscopy method, and provide a comparison of AM-KPFM, AM-slope detection KPFM and FM-KPFM imaging resolution and accuracy. We will also discuss the distance dependence of the CPD as measured by FM-KPFM for both the PTCDA organic deposit and the NaCl substrate. [ABSTRACT FROM AUTHOR]