Repetitive Signals Research Articles

Species identity cues: possibilities for errors during vibrational communication on plant stems

The efficiency of communication depends on the ability of conspecifics to recognize and locate each other, and the environment can impose important limitations on reliability of transmitted and received information. In contrast to the 3D space of airborne sound communication, substrate-borne vibrational signals are often transmitted via 1D plant stems and leaf stalks. In such situations, discrimination between signals emitted from several sources positioned on the same side of a receiver may be difficult, as the receiver may perceive this compound signal as emanating from a single source. Here, we examined the consequences of interactions between conspecific vibrational signals emitted from 2 sources for recognition of species-specific temporal patterns. In a 1D environment on a bean plant, males of the southern green stink bug Nezara viridula perceived conspecific female song emitted in alternation from 2 sources as a compound song with a signal repetition time outside the species-specific value and male responsiveness and the number of males locating a source (conspecific female) were low. By contrast, when the conspecific song was presented together with female signals of another stinkbug Acrosternum hilare, searching activity was not significantly affected. However, when conspecific and heterospecific signals were overlapping, males made significant orientation errors and the majority located the heterospecific source. Because both outcomes, missing a conspecific female and selecting a heterospecific partner, may ultimately lead to a reduced reproductive success, the results suggest that the 1D environment encountered on plant stems and branches imposes important limitations on vibrational communication system. Copyright 2011, Oxford University Press.

Fatigue Failure Study of the Lower Suspension Vehicle Arm Using a Multiaxial Criterion of the Strain Energy Density

The objective of this study is to evaluate the potential of light alloy mechanical part use in automobile industry by studying their fatigue life using various parameters such as effect of suspension dynamic, excitation type, geometry and mechanical part weight. The studied part is the lower suspension arm made from 7075-T6 aluminium alloy. The strain density energy approach enables us to compare two same order tensor: the multiaxial and uniaxial cases. The random displacement excitation is obtained analytically from the power spectral density PSD. The force excitation is obtained by a simple normalisation of spectrum displacement. To avoid the use of Newton-Raphson method during the partial fatigue life calculation step in all mesh elements, a Matlab interface to identify the critical elements is developed. The strain energy density (SENER) signal of the critical element is corrected to remove anomalies by WAFO Matlab interface algorithm. Rainflow cycles are extracted using Markov formulation in order to calculate the number of signal repetitions to failure, which is calculated from Miner law.

A novel view of biologically active electromagnetic fields

Over the past decades, strong evidence has accumulated that low-frequency electromagnetic fields (EMFs) can be useful in treating human pathologies, such as bone fractures, soft tissue illnesses, and pain. Common strategies for the design of commercial therapeutic devices are to generate EMFs that simulate body endogenous EMFs, or EMFs that resonate with a particular biological process, such as the natural motions of ions. We recently came across a biologically active commercial EMF signal that seems to be different. The signal is generated by summing the fundamental frequencies and harmonics of several periodic base signals which remain proprietary to the company. When first examined in the time domain, the signal resembled electronic noise; however, when critically analyzed, the signal is not identical with noise. Rather, it is a highly complex waveform exhibiting a very wide range of values for the time derivative of the magnetic field density (dB/dt) and a beat frequency in the Extremely Low-Frequency range. In this paper, we speculate on the mechanism of action of this and similar signals. We consider it less likely that cells, or cell components, act like filters to extract and couple with individual signals that make up the complex EMF signal. Consequently, we favor the possibility that with the signal discussed here cells respond to the very complex signal and that the biological response can be modified by the presence of a beat in the signal, in this case a low-frequency beat. More generally, this would suggest the hypothesis that biological processes can be regulated by noise-like signals and that the effects of a noisy signal can be modified by the presence of signal repetition patterns, such as beats. Given the very small energy that signals like these can transduce into a biological system, biological effects can be expected only when the molecular processes involved are poised so that the available energy leads to molecular reactions that achieve the activation state for the reaction.

Single-photon position to time multiplexing using a fiber array

A 1 x 8 fiber array is used as the front-end of a receiver system. Each channel has a different length of fiber, resulting in each channel signal arriving at the detector at a pre-determined interval relative to a constant repetitive frequency signal. We demonstrate that these eight channels can be efficiently coupled to an individual single-photon detector such that the arrival-time of a photon in each is distinguishable from the next. Thus, we demonstrate spatial position to time information exchange, resulting in a photon-counting array using a single detector. The receiver system could be implemented in numerous applications, including time-resolved photoluminescence, low-light level spectroscopy and quantum information processing.

Effects of heterospecific and conspecific vibrational signal overlap and signal-to-noise ratio on male responsiveness inNezara viridula(L.)

Animals often communicate in environments with high levels of biotic noise that arises from the signals of other individuals. Although effects of background biotic noise on mate recognition and discrimination have been widely studied in air-born sound communication, little is known about incidental interference between signallers that use substrate-borne vibrational signals. In this study we investigated the ability of males of the southern green stink bug Nezara viridula (L.) (Heteroptera: Pentatomidae) to recognize conspecific female song in the presence of biotic noise originating from conspecific and heterospecific vibrational signals. We tested male responsiveness on a bean plant in playback experiments. One leaf was vibrated with conspecific female song, while to the other one we simultaneously applied either heterospecific female signal or various altered conspecific signals with different temporal parameters. We tested males in three levels of biotic noise, ranging from +6 dB to -6 dB and we compared male responsiveness in each treatment with response obtained in unilateral treatment with unaltered conspecific female calling song. Male responsiveness was reduced in the presence of heterospecific signals or when background noise from conspecific signals obscured the species-specific temporal pattern of conspecific female song. By contrast, the presence of two sources of conspecific female songs had a positive effect on male responsiveness, for as long as the signal repetition rate of perceived song did not differ from the species-specific value. In the presence of interfering background signals, searching activity was less affected than male signalling. Increased signal-to-noise ratio restored male responsiveness to the level expressed in unilateral stimulation with conspecific female song. The results are discussed with regard to male behavioural strategies for vibrational communication in a noisy environment.

A Photonic Method for Measuring the AM Noise of Periodic Electrical Signals

In this work, we demonstrate mode partition noise in the radio-frequency spectra of periodic signals generated using electrical pattern generators that are often used in digital optical communications and error testing. This effect makes the measurement of the amplitude modulation noise of the repetitive signal through its single sideband (SSB) power spectral density (PSD) at its fundamental frequency inaccurate. This is demonstrated for a square wave, where the dependence of the SSB PSD on the duty cycle of the signal is experimentally shown. To alleviate this ambiguity, we propose and experimentally demonstrate a photonic up-convert and down-convert method that results in invariant SSB power spectra at the signal's fundamental frequency.

High peak power eye-safe intracavity optical parametric oscillator pumped by a diode-pumped passively Q-switched ND:GGG laser

By exploiting the diode-end-pumped Nd:GGG/Cr4+:YAG laser as the pump source, a high peak power gray-trace resistance KTP intracavity optical parametric oscillator at eye-safe wavelength was first demonstrated (to our knowledge). Under the incident diode power of 10 W, the maximum average output power of 320 mW at 1567 nm was obtained with the T = 33% output coupler. The corresponding signal pulse width and repetition rate were respectively 1.4 ns and 5.8 kHz. Due to the greatly reduced pulse repetition rate and short pulse width, the signal peak power was estimated to be as high as 39.4 kW.

An eye-safe KTiAsO 4 intracavity optical parametric oscillator driven by a diode pumped composite Nd:YAG/Cr 4+:YAG laser

A mini eye-safe KTiAsO 4 intracavity optical parametric oscillator (IOPO) employing the shared cavity configuration and driven by a diode-end-pumped composite Nd:YAG/Cr 4+:YAG laser is demonstrated in this paper. Under an incident laser diode power of 11 W, a maximum average output power of 424 mW at 1534 nm was obtained. The corresponding signal pulse width and repetition rate were 1.2 ns and 16.7 kHz, respectively. The fluctuation of the average signal output power over long-term operation was found to be ±3.0%. A theoretical model for the compact IOPO was also presented in this paper.

Methemoglobin Suppression in a 0.3 Tesla Magnet: An In Vitro and In Vivo Study

The aim of this study was to design a pulse sequence that suppresses methemoglobin and is applicable in a 0.3-T permanent magnet. Blood samples were collected from six healthy volunteers. Magnetic resonance imaging was performed with a 0.3-T scanner until the typical signal intensities of methemoglobin were obtained. Each blood sample was then scanned using repetition times of 300, 600, 900, 1200, 1500, and 1800 ms and a constant echo time of 20 ms. All other parameters (field of view, slice thickness, matrix, and number of signal averages) were kept constant for all six sequences. Signal intensities and repetition time data were used to calculate the T1 relaxation time of extracellular methemoglobin. T1 was determined by ordinary least square regression according to the equation S =k(1 - e(-repetition time/T1)), where S is signal intensity and k is the proportional constant. A short tau inversion recovery sequence with an inversion time calculated from the T1 value of methemoglobin was used on fat, water, and methemoglobin blood samples and in 11 patients diagnosed with subacute brain hemorrhages. The inversion time was calculated as ln2 T1 (tissue), where T1 is the relaxation time of extracellular methemoglobin to be suppressed. The T1 relaxation time of extracellular methemoglobin was determined to be 231.24 +/- 9.068 ms, and inversion time was calculated to be 160 +/- 6.67 msec. Application of an inversion time of 160 ms showed complete suppression on extracellular methemoglobin blood samples and all of the 11 subjects. A methemoglobin suppression technique using an inversion time of 160 +/- 6.67 ms is applicable in a 0.3-T permanent magnet.

Broadband Time-Domain Measurement System for the Characterization of Nonlinear Microwave Devices With Memory

This paper describes a novel fully calibrated four channel broadband time-domain measurement system for the characterization of nonlinear microwave devices with memory. The hardware architecture of the proposed time-domain measurement system is based on a wideband sub-sampling principle. The sampling heads work at a high strobe signal repetition frequency that can be tuned between 357-536 MHz. We achieve a 40-GHz RF frequency bandwidth and a 160-MHz IF bandwidth. This instrument enables the measurement of carrier and envelope waveforms at both ports of nonlinear microwave devices driven by broadband modulated multicarriers. The test-bench is applied to the cross modulation characterization of a 15-W GaN HEMT CREE <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S</i> -band power amplifier with memory due to different biasing circuit configurations. The amplifier under test is driven by the sum of a large-signal modulated carrier (double-sideband amplitude modulation at 3.6 GHz) and a small single-tone signal at a 110-MHz offset frequency. Our significant contribution comes from the capability of the measurement system to record the time-domain waveforms of several nonadjacent modulated signals on a similar time equivalent scale for different cases of memory effects of the power amplifier under test.

Efficient GTR-KTP IOPO driven by a diode-pumped Nd:YAG/Cr4+:YAG laser with the shared cavity configuration

An efficient eye-safe GTR-KTP IOPO with the shared cavity configuration and excited by a diode-end-pumped composite Nd:YAG/Cr4+:YAG laser was demonstrated. Under the incident LD power of 8.4 W, the maximum average output power of 900 mW at 1572 nm was obtained with the T=33% output coupler, corresponding to a diode-to-signal conversion efficiency of 10.7%. The corresponding signal pulse width and repetition rate were respectively 2.2 ns and 12 kHz, with the peak power and single pulse energy estimated to be 34.1 kW and 75 µJ, respectively. The instability of the average signal output power over hours-long operation was found to be 2.0%. As for the common KTP IOPO at the same pump condition and cavity design, a lower average output power of 640 mW with a longer pulse width of 4.6 ns was obtained. The corresponding diode-to-signal conversion efficiency was reduced by 28.8% compared with that obtained in GTR-KTP IOPO. A theoretical model for the compact GTR-KTP IOPO was also presented in this paper. Theoretical analysis on the pulse characteristics of the signal was performed, which showed a good agreement with that obtained experimentally.

Ultrasound for Fracture Healing: Current Evidence

Low-intensity pulsed ultrasound (LIPUS) is a relatively new technique for the acceleration of fracture healing in fresh fractures and nonunions. It has a frequency of 1.5 MHz, a signal burst width of 200 micros, a signal repetition frequency of 1 kHz, and an intensity of 30 mW/cm2. In 1994 and 1997, two milestone double-blind randomized controlled trials revealed the benefits of LIPUS for the acceleration of fracture healing in the tibia and radius. They showed that LIPUS accelerated the fracture healing rate from 24% to 42% for fresh fractures. Some literature, however, has shown no positive effects. The beneficial effect of acceleration of fracture healing by LIPUS is considered to be larger in the group of patients or fractures with potentially negative factors for fracture healing. The incidence of delayed union and nonunion is 5% to 10% of all fractures. For delayed union and nonunion, the overall success rate of LIPUS therapy is approximately 67% (humerus), 90% (radius/radius-ulna), 82% (femur), and 87% (tibia/tibia-fibula). LIPUS likely has the ability to enhance maturation of the callus in distraction osteogenesis and reduce the healing index. The critical role of LIPUS for fracture healing is still unknown because of the heterogeneity of results in clinical trials for fresh fractures and the lack of controlled trials for delayed unions and nonunions.

Real-time full-field arbitrary optical waveform measurement

The development of a real-time optical waveform measurement technique with quantum-limited sensitivity, unlimited record lengths and an instantaneous bandwidth scalable to terahertz frequencies would be beneficial in the investigation of many ultrafast optical phenomena. Currently, full-field (amplitude and phase) optical measurements with a bandwidth greater than 100 GHz require repetitive signals to facilitate equivalent-time sampling methods or are single-shot in nature with limited time records. Here, we demonstrate a bandwidth- and time-record scalable measurement that performs parallel coherent detection on spectral slices of arbitrary optical waveforms in the 1.55 µm telecommunications band. External balanced photodetection and high-speed digitizers record the in-phase and quadrature-phase components of each demodulated spectral slice, and digital signal processing reconstructs the signal waveform. The approach is passive, extendable to other regions of the optical spectrum, and can be implemented as a single silicon photonic integrated circuit. A measurement scheme that is capable of recording the amplitude and phase of arbitrary shaped optical waveforms with a bandwidth of up to 160 GHz is presented. The approach is compatible with integration on a silicon photonic chip and could aid the study of transient ultrafast phenomena.

Bayesian phase tracking for multiple pulse signals

The problem of estimating the frequencies and phases of two superimposed pulse-like, repetitive signals is considered. A method of solving this problem based on Bayesian (i.e., sequential Monte-Carlo or particle) filtering is presented. The particular problem motivating the technique is estimation of the rate of maternal and foetal heartbeats, although the technique is applicable to other domains. Aspects of the problem leading to the solution are discussed, and the performance of the proposed technique is presented on both simulated signals and real heart signals. The resulting frequency estimator has very similar functionality to a phase-locked loop, and so the performance measure used is the time to lose phase lock. The estimator is also analysed in terms of the posterior Cramér–Rao bound on the phase estimation accuracy.

Current Control for Single-Phase Active Filter Based on Multirate PWM

The shunt active filter, which is connected to power systems in parallel with the load, is considered as a current source. However, the shunt active filter is actually realized by current control using the voltage source type inverter. Authors applied multirate perfect tracking control (PTC) to current control for the shunt active filter. Although conventional single-rate deadbeat control could not guarantee zero tracking error for arbitrary reference signals, the proposed multirate control can achieve perfect tracking at every sampling point. In this paper, we propose a novel method to generate repetitive compensation signals. Simulations and experiments are shown to verify the effectiveness of the proposed method.

Model-based reconstruction of the time response of electrochemical air pollutant monitors to rapidly varying concentrations

Electrochemical sensors are commonly used to measure concentrations of gaseous air pollutants in real time, especially for personal exposure investigations. The monitors are small, portable, and have suitable response times for estimating time-averaged concentrations. However, for transient exposures to air pollutants lasting only seconds to minutes, a non-instantaneous time response can cause measured values to diverge from actual input concentrations, especially when the pollutant fluctuations are pronounced and rapid. Using 38 Langan carbon monoxide (CO) monitors, which can be set to log data every 2 s, we found electrochemical sensor response times of 30-50 s. We derived a simple model based on Fick's Law to reconstruct a close to accurate time series from logged data. Starting with experimentally measured data for repetitive step input signals of alternating high and low CO concentrations, we were able to reconstruct a much improved 2-s concentration time series using the model. We also utilized the model to examine errors in monitor measurements for different averaging times. By selecting the averaging time based on the response time of the monitor, the error between actual and measured pollutant levels can be minimized. The methodology presented in this study is useful when aiming to accurately determine a time series of rapidly time-varying concentrations, such as for locations close to an active point source or near moving traffic.

Iterative Learning Model Predictive Control for a Class of Continuous/Batch Processes

An iterative learning model predictive control (ILMPC) technique is applied to a class of continuous/batch processes. Such processes are characterized by the operations of batch processes generating periodic strong disturbances to the continuous processes and traditional regulatory controllers are unable to eliminate these periodic disturbances. ILMPC integrates the feature of iterative learning control (ILC) handling repetitive signal and the flexibility of model predictive control (MPC). By on-line monitoring the operation status of batch processes, an event-driven iterative learning algorithm for batch repetitive disturbances is initiated and the soft constraints are adjusted timely as the feasible region is away from the desired operating zone. The results of an industrial application show that the proposed ILMPC method is effective for a class of continuous/batch processes.

High-rate groupwise STBC using low-complexity SIC based receiver

In this paper, using diagonal signal repetition with Alamouti code employed as building blocks, we propose a high-rate groupwise space-time block code (GSTBC) which can be effectively decoded by a low-complexity successive interference cancellation (SIC) based receiver. The proposed GSTBC and SIC based receiver are jointly designed such that the diversity repetition in a GSTBC can induce the dimension expansion to suppress interfering signals as well as to obtain diversity gain. Our proposed scheme can be easily applied to the case of large number of antennas while keeping a reasonably low complexity at the receiver. It is found that the required minimum number of receive antennas is only two for the SIC based receiver to avoid the error floor in performance. The simulation results show that the proposed GSTBC with SIC based receiver obtains a near maximum likelihood (ML) performance while having a significant performance gain over other codes equipped with linear decoders.

Pulsed eddy current testing with variable duty cycle on rivet joints

In pulsed eddy current testing, repetitive excitation signals with different duty cycles have different spectral representations. This work studies the influence of duty cycle on the ability to detect holes and EDM notches beneath rivet heads in subsurface layers of stratified samples. Feature patterns for the integrity of rivet joints are proposed and verified. The proposed method has the added advantage in that no reference sample is needed while employing multiple pulse measurements, with different pulse widths. Experimental testing and modelling approaches are discussed in connection with defect depth quantification, which can be extended to the quantification of complex defects.

Auditory Streaming of Amplitude-Modulated Sounds in the Songbird Forebrain

Streaming in auditory scene analysis refers to the perceptual grouping of multiple interleaved sounds having similar characteristics while sounds with different characteristics are segregated. In human perception, auditory streaming occurs on the basis of temporal features of sounds such as the rate of amplitude modulation. We present results from multiunit recordings in the auditory forebrain of awake European starlings (Sturnus vulgaris) on the representation of sinusoidally amplitude modulated (SAM) tones to investigate the effect of temporal envelope structure on neural stream segregation. Different types of rate modulation transfer functions in response to SAM tones were observed. The strongest responses were found for modulation frequencies (fmod) <160 Hz. The streaming stimulus consisted of sequences of alternating SAM tones with the same carrier frequency but differing in fmod (ABA-ABA-ABA-...). A signals had a modulation frequency evoking a large excitation, whereas the fmod of B signals was <or=4 octaves higher. Synchrony of B signal responses to the modulation decreased as fmod increased. Spike rate in response to B signals dropped as fmod increased. Faster signal repetition resulted in fewer spikes, suggesting the contribution of forward suppression to the response that may be due to both signals having similar spectral energy and that is not related to the temporal pattern of modulation. These two effects are additive and may provide the basis for a more separated representation of A and B signals by two populations of neurons that can be viewed as a neuronal correlate of segregated streams.