Occurrence Of Nonlinear Phenomena Research Articles

Singing more, singing harsher: occurrence of nonlinear phenomena in a primate' song.

Nonlinear phenomena (NLP) in animal vocalizations arise from irregularities in the oscillation of the vocal folds. Various non-mutually exclusive hypotheses have been put forward to explain the occurrence of NLP, from adaptive to physiological ones. Non-human primates often display NLP in their vocalizations, yet the communicative role of these features, if any, is still unclear. We here investigate the occurrence of NLP in the song of a singing primate, the indri (Indri indri),testing for the effect of sex, age, season, and duration of the vocal display on their emission. Our results show that NLP occurrence in indri depends on phonation, i.e., the cumulative duration of all the units emitted by an individual, and that NLP have higher probability to be emitted in the later stages of the song, probably due to the fatigue indris may experience while singing. Furthermore, NLP happen earlier in the vocal display of adult females than in that of the adult males, and this is probably due to the fact that fatigue occurs earlier in the former because of a greater contribution within the song. Our findings suggest, therefore, that indris may be subjected to physiological constraints during the singing process which may impair the production of harmonic sounds. However, indris may still benefit from emitting NLP by strengthening the loudness of their signals for better advertising their presence to the neighboring conspecific groups.

Siberian crane chick calls reflect their thermal state

Chicks can convey information about their needs with calls. But it is still unknown if there are any universal need indicators in chick vocalizations. Previous studies have shown that in some species vocal activity and/or temporal-frequency variables of calls are related to the chick state, whereas other studies did not confirm it. Here, we tested experimentally whether vocal activity and temporal-frequency variables of calls change with cooling. We studied 10 human-raised Siberian crane (Grus leucogeranus) chicks at 3–15 days of age. We found that the cooled chicks produced calls higher in fundamental frequency and power variables, longer in duration and at a higher calling rate than in the control chicks. However, we did not find significant changes in level of entropy and occurrence of non-linear phenomena in chick calls recorded during the experimental cooling. We suggest that the level of vocal activity is a universal indicator of need for warmth in precocial and semi-precocial birds (e.g. cranes), but not in altricial ones. We also assume that coding of needs via temporal-frequency variables of calls is typical in species whose adults could not confuse their chicks with other chicks. Siberian cranes stay on separate territories during their breeding season, so parents do not need to check individuality of their offspring in the home area. In this case, all call characteristics are available for other purposes and serve to communicate chicks’ vital needs.

Design and implementation of closed-loop control system for buck converter using different techniques

Comparing between different techniques for the design and implementation of closed-loop control systems for buck converters is carried out. Controllers used for this comparison are integral, proportional plus integral (PI) controllers and artificial intelligence are represented in fuzzy logic controller (FLC) and tuned fuzzy logic controller (TFLC). Design and implementation of a control system demand the role of effective techniques that offer simple and pragmatic solutions in society to meet the performance requirements despite system disturbances and uncertainties [1]. The occurrence of nonlinear phenomena in buck converters makes their analysis and control difficult [2]. Classical linear techniques have stability limitations around the operating points [1]–[3]. Hence digital and nonlinear stabilizing control methods must be applied to ensure large-signal stability [3]. Fuzzy control has also been employed to control buck converters because of its simplicity, simplicity of design and simplicity of implementation [4], [5]–[10]. Fuzzy controllers are easily suited to nonlinear time-variant systems and do not require an accurate mathematical model for the system being controlled. They are usually designed based on expert knowledge of the converters [5]. In this survey, the design procedures of integral, proportional plus integral, fuzzy logic, and tuned fuzzy logic controllers are presented.

Non-linear phenomena in little spotted kiwi calls

Non-linear phenomena (NLP) in vocalizations may have adaptive functions, such as increasing acoustic impact or conveying fitness or identity information. Yet despite their potential to impart behavioural information, these spectral features have not been studied in most bird species and many genera. This applies to the New Zealand kiwi (Apterygidae), with NLP-like features indicated in one species, but not explored further. Yet as nocturnal and cryptic birds heavily reliant on vocal communication, kiwi are ideal species in which to assess the function of these structures. Furthermore, kiwi are acoustically typical but taxonomically and ecologically unique among birds, so can provide an important reference for determining the behavioural relevance of NLP in other bird species. We have assessed the occurrence of NLP in little spotted kiwi (Apteryx owenii) calls, in the first detailed study of such features in a ratite. NLP in the form of subharmonics are common in this species. We tested for possible adaptive functions of these features by comparing their occurrence with call spectral parameters and conditions. Subharmonics increased with frequency and during calls produced in territorial contexts, indicating that these features may provide acoustic impact, possibly to convey aggression or fitness information. Our results also suggest that NLP are unlikely to provide identification information in this kiwi species.

Nonlinear dynamic phenomena in a SDOF model of cable net

The dynamic behavior of the simplest possible cable net is studied in this paper, consisting of two crossing cables in perpendicular vertical planes, having the same span and opposite sags. A concentrated mass is attached at the central node, and only the vertical translational degree of freedom is assumed as active. First, the static behavior is explored up to the load level that causes tensile cable failure. Then, the dynamic response is investigated for different resonant conditions and is found to give significantly larger amplitudes with respect to the static ones, even for loading frequencies away from the eigenfrequency of the system. In order to derive analytical solutions, the equation of motion is simplified and the cable net is proved to be a Duffing oscillator. For the simplified problem, the occurrence of nonlinear phenomena is verified analytically, such as bending of the response curve, jump phenomena, instability regions, dependence on the initial conditions, and superharmonic and subharmonic resonances. These phenomena are also detected by means of numerical analyses. A comparison between the exact model and the simplified one shows that the analytical solution of the Duffing equation describes the dynamic behavior of the cable net with satisfactory accuracy.

Quantitative acoustic analysis of the vocal repertoire of the golden rocket frog (Anomaloglossus beebei)

This study describes the vocal repertoire of the Guyanan golden rocket frog, Anomaloglossus beebei, a bromeliad specialist with biparental care. Using multivariate analyses of nine call properties, as well as the occurrence of nonlinear phenomena, three signal types were distinguished-advertisement, courtship, and aggressive calls. Although all three call types were composed of a short series of rapidly repeated pulses, advertisement calls were produced at higher amplitudes and had longer pulse durations than both courtship calls and aggressive calls. Courtship calls exhibited lower dominant frequencies than both advertisement and aggressive calls, which had similar dominant frequencies. Aggressive calls had more pulses per call, had longer intervals between calls, and occasionally contained one or two introductory pulses preceding the pulsed call. Several acoustic properties predicted aspects of the signaler's body size and condition. Our study demonstrates the reliability of human observers to differentiate the multiple call types of A. beebei based on hearing calls and observing the social context in which they are produced under field conditions.

Diversity of the Vocal Signals of Concave‐Eared Torrent Frogs (Odorrana tormota): Evidence for Individual Signatures

AbstractMale concave‐eared torrent frogs (Odorrana tormota) have an unusually large call repertoire and have been shown to communicate ultrasonically. We investigated the individual specificity of male advertisement calls in order to explore the acoustic bases of individual recognition, which was demonstrated in an accompanying study. Vocalizations of 15 marked males were recorded in the field. A quantitative analysis of the signals revealed eight basic call‐types. Two of them (the single‐ and multi‐note long‐calls) were investigated in more detail. Long‐calls were characterized by pronounced and varying frequency modulation patterns, and abundant occurrence of nonlinear phenomena (NLP), i.e., frequency jumps, subharmonics, biphonations and deterministic chaos. The occurrence of NLP was predictable from the contour of the fundamental frequency in the harmonic segment preceding the onset of the NLP, and this prediction showed individual‐specific patterns. Fifteen acoustic variables of the long calls were measured, all of which were significantly different among individuals, except biphonic segment duration. Discriminant function analysis (DFA) showed that 54.6% of the calls could be correctly assigned to individual frogs. The correct classification was above chance level, suggesting that individual specificity of calls underlie the ability of males to behaviorally discriminate the vocal signals of their neighbors from those of strangers, a remarkable feat for a frog species with a diverse vocal repertoire. The DFA classification results were lower than those for other anurans, however. We hypothesize that there is a tradeoff between an increase in the fundamental frequency of vocalizations to avoid masking by low‐frequency ambient background noise, and a decrease in individual‐specific vocal tract information extractable from the signal.

The Origin of Nonlinear Phenomena in TCR-SVC Associated With Parametric Excitation of Intrinsic Oscillation and External Excitation

This paper focuses on anomalous nonlinear phenomena in a thyristor controlled reactor-static var compensator (TCR-SVC) system, called switching time bifurcation, and clarifies the relationship between the occurrence of nonlinear phenomenon and the intrinsic characteristics of the circuit equation with switching function. The occurrence of nonlinear phenomenon in a TCR-SVC system cannot be predicted when the dynamics of the circuit related to the switching action is neglected. Therefore, this paper considers the dynamics related to the switching operations in the analysis of nonlinear phenomena. The parametric excitation of circuit is discussed in relation to the homogeneous expression of the circuit equation. This paper indicates that the homogeneous equation of the TCR-SVC system results in Hill's equation, and it can be approximated as Mathieu's equation. The occurrence of nonlinear phenomena in the system is evaluated using the characteristics of Mathieu's equation. The anomalous nonlinear phenomena occur when the natural frequency of Mathieu's equation coincides with the frequency of the ac voltage in a TCR-SVC system. The parametric excitation is also confirmed through the characteristics of Hill's equation. This study clarified the interaction between the switching dynamics of the circuit and its external excitation, and clued the occurrence of nonlinear phenomena in the circuit. The proposed procedure can also be applied to the analysis for other switching converter circuits with periodic excitation source.

Shifting nonlinear phenomena in a DC–DC converter using a fuzzy logic controller

The occurrence of nonlinear phenomena in DC–DC power converters makes their analysis and control difficult. We propose a converter model that takes into account the internal resistances of the converter elements. A fuzzy logic controller is then used to shift the nonlinear phenomena outside the operating domain, and to ensure current regulation over a wide range of parameters. To validate the achieved performance, a comparative study is presented.

Nonlinear dynamics in HVDC systems

Voltage instability in AC power systems has been widely studied from a nonlinear dynamical system perspective. In contrast, this approach for HVDC systems is of recent origin and rudimentary, therefore much basic work in this area remains to be developed. Thus this work presents a comprehensive and fundamental analysis of the nonlinear phenomena in HVDC systems. In particular the conditions for occurrence of nonlinear phenomena are derived analytically for a basic and enhanced dynamic HVDC system models, These results consequently identify: (i) the various system and HVDC control parameters which influence the nonlinear behaviour; (ii) oscillatory instability in HVDC systems as a feasible voltage collapse mechanism; and (iii) the explicit relationship between the quasi-static and dynamic conditions for aperiodic voltage collapse.

Nonlinear modeling and bifurcations in the boost converter

The occurrence of nonlinear phenomena like subharmonics and chaos in power electronic circuits has been reported recently. In this paper, the authors investigate these phenomena in the current-mode-controlled boost power converter. A nonlinear model in the form of a mapping from one point of observation to the next has been derived. The map has a closed form even when the parasitic elements are included. The bifurcation behavior of the boost power converter has been investigated with the help of this discrete model.