Waveform Symmetry Research Articles

Excitation source structural analysis of Japanese traditional singing voices

New set of voice excitation source analysis methods are applied to study Japanese traditional singing voices, especially Noh. The first method, XSX (excitation Structure extractor) is capable of visualize detailed structure of subharmonic periodicity, by using multiple dedicated periodicity detectors. The second one analyzes symmetry of the fundamental component waveform, cycle by cycle. It enables to discriminate voice onset and offset details.

Physiological and acoustic characteristics of the female music theater voice

Three Music Theater vocal qualities ("chesty belt," "twangy belt," and "legit") were investigated in female singers at their overlap range, between F#4-D5 (~370-600 Hz). Six experienced Music Theater singers performed each quality on two different vowels ([e], [ɔ]). Audio and electroglottographic (EGG) signals were recorded as well as the vocal tract impedance. In chesty belt and twangy belt, singers systematically tuned the frequency of their first vocal tract resonance (R1) to the second harmonic (2f(0)) up to C5. R1 remained lower in frequency for the legit quality. No tuning of the second vocal tract resonance (R2) was observed in any of these qualities although R2 frequency was significantly higher in both belt qualities than in legit. Closed quotient, degree of symmetry of the EGG waveform, sound pressure level (SPL) and the energy of the spectrum above 1 kHz were significantly greater in chesty belt than in legit but not significantly different between chesty belt and twangy belt qualities. A fourth quality ("mix") was explored in three singers. Different production strategies were observed for each singer, with values of spectral, glottal and vocal tract descriptors found in between those measured for legit and chesty belt qualities.

Synchronization of Swimming Microorganisms

Some microorganisms, such as spermatozoa, have been observed to synchronize their flagella when swimming in close proximity. Using a two-dimensional model we show that phase-locking can arise from hydrodynamic forces alone. In a Newtonian fluid, as a consequence of the kinematic reversibility of the field equations, there must exist front-back asymmetry in the geometry of their flagellar waveform. The time-evolution of the phase difference between co-swimming cells depends only on the nature of this geometrical asymmetry, and microorganisms can phase-lock into conformations which minimize or maximize energy dissipation. In a viscoelastic fluid the presence of polymeric stresses removes the geometrical asymmetry constraint, and therefore even symmetric swimmers synchronize. Such synchronization occurs on asymptotically faster time scales than in a Newtonian fluid, and the swimmers evolve into a stable in-phase conformation minimizing the energy dissipated in the surrounding fluid. Furthermore, we show that if we consider flexible sheets, with internal symmetric forcing instead of prescribed kinematics, they deform when interacting with each other through the fluid in such a way as to systematically break the overall waveform symmetry, thereby always evolving to an in-phase conformation where energy dissipation is minimized. These dynamics are shown to be mathematically equivalent to those obtained for prescribed waveforms in viscoelastic fluids, emphasizing the crucial role of flexibility in symmetry-breaking and synchronization - be it that of the fluid, or the swimmers themselves.

Space vector-based synchronised bus-clamping pulse width modulation algorithms for three-level voltage source inverter in overmodulation region

The main objective of the present work is to develop space vector-based synchronised bus-clamping pulse width modulation algorithms to improve total harmonic distortion and higher DC-bus utilisation of the three-level inverter in overmodulation region. The proposed algorithms can generate synchronised pulse width modulation waveforms with all possible pulse number preserving all the waveform symmetries. The results of the proposed algorithms are evaluated and compared with conventional space vector pulse width modulation algorithm. It is shown that the proposed algorithms give improved results in terms of total harmonic distortion and DC-bus utilisation than that of conventional one in overmodulation region. The proposed method is implemented and verified experimentally on a constant v/f drive fed from insulated gate bipolar transistor (IGBT)-based voltage source inverter using Motorola power PC-based embedded controller.

Performance of different processing schemes in seismic noise cross-correlations

SUMMARY The estimation of the Green's function between two points on the Earth's surface by the cross-correlation of seismic noise time-series became a widely used method in seismology. In general, very long time-series (months to years) as well as massive normalization and/or data selection are necessary to obtain useful cross-correlation functions. One task of this study is to evaluate the influence of different established normalization methods on the obtained cross-correlation functions. Furthermore, we evaluate two waveform preserving time domain normalizations as well as a new fully automated data selection approach. The cross-correlation functions analysed in this study are obtained from 12 months of seismic noise recorded in 2004 at five seismic stations in the United States with station distances on a continental scale. For practical reasons, the cross-correlation functions of such long time-series are calculated by stacking the cross-correlation functions obtained from shorter time windows. We use this stacking process for the implementation of the waveform preserving time domain normalizations. The time window length is in general an important parameter of the cross-correlation processing, as it influences the normalization and data selection. Therefore, we evaluate the cross-correlation functions obtained with 47 different time window lengths between one hr and 24 hr. The time domain normalizations intend to suppress the influence of transient signals like earthquake waves as well as long-term (e.g. seasonal) amplitude variations. We compare the proposed waveform preserving time domain normalizations with the established running absolute mean normalization and the one-bit normalization. We demonstrate that a waveform preserving time domain normalization can replace a non-linear time domain normalization, if a time window length similar to the duration of the typically occurring transient signals is used. Next to the time domain normalizations also the spectral whitening in the frequency domain is evaluated. Spectral whitening is a powerful normalization to improve the emergence of broad-band signals in seismic noise cross-correlations. Nevertheless, we observe spectral whitening to depend strongly on the time window length. An unwanted amplification of a persistent microseism signal is observed on the continental scale with time windows shorter than 12 hr. Our approach of automated data selection is based on a statistical time-series classification and reliably excludes time windows with transient signals occurring contemporaneously at both sites (e.g. earthquake waves). This data selection approach is capable to replace a non-linear time domain normalization, but no improvement of the waveform symmetry or the signal-to-noise ratio of the cross-correlation functions is observed in general.

Synchronization of flexible sheets

When swimming in close proximity, some microorganisms such as spermatozoa synchronize their flagella. Previous work on swimming sheets showed that such synchronization requires a geometrical asymmetry in the flagellar waveforms. Here we inquire about a physical mechanism responsible for such symmetry breaking in nature. Using a two-dimensional model, we demonstrate that flexible sheets with symmetric internal forcing deform when interacting with each other via a thin fluid layer in such a way as to systematically break the overall waveform symmetry, thereby always evolving to an in-phase conformation where energy dissipation is minimized. This dynamics is shown to be mathematically equivalent to that obtained for prescribed waveforms in viscoelastic fluids, emphasizing the crucial role of elasticity in symmetry breaking and synchronization.

Spurious signals due to amplitude quantization in direct digital frequency synthesizers

Amplitude quantization and phase truncation are two main mechanisms which lead to the occurrence of spurious signals in direct digital frequency synthesizers (DDFSs). These signals are deterministic and periodic in the time domain, so they appear as line spectra in the frequency domain. In this paper, the discrete time versions of two types of spurious signals due to amplitude quantization in DDFSs are expressed and their time-domain characteristics are detailedly analyzed and compared. Then, the spectral properties of the amplitude-quantization spurs in the absence or presence of phase-accumulator truncation are derived by waveform symmetry and uniform-permutation estimation along with discrete Fourier transform. The effects of phase truncation and parameter variation on the amplitude-quantization spurs are studied by computer simulation. The derivation and simulation give strong insight into the spur magnitude and spectral location, and can provide theoretical and empirical supports for practical DDFS implementation and performance evaluation.

Influence of Asymmetrical Waveform on Low-Cycle Fatigue Life of Micro Solder Joint

The effects of waveform symmetry on the low-cycle fatigue life of the Sn-3.0Ag-0.5Cu alloy have been investigated, using micro solder joint specimens with approximately the same volume of solder as is used in actual products. Focusing on crack initiation life, fatigue tests on Sn-Ag-Cu micro solder joints using asymmetrical triangular waveforms revealed no significant reduction in fatigue life. A slight reduction in fatigue life at low strain ranges caused by an increase in the fatigue ductility exponent, which is the result of a weakening microstructure due to loads applied at high temperature for long testing time, was observed. This was due to the fact that grain boundary damage, which has been reported in large-size specimens subjected to asymmetrical triangular waveforms, does not occur in Sn-Ag-Cu micro size solder joints with only a small number of crystal grain boundaries.

Space Vector Sequence Investigation and Synchronization Methods for Active Front-End Rectifiers in High-Power Current-Source Drives

Space vector pulsewidth modulation (PWM) schemes for the active front end of a high-power drive normally produce low-order and suborder harmonics due to the low switching frequency and the drifting of synchronization between the PWM waveform and the rectifier input frequency. To provide a synchronized PWM and achieve the best harmonic performance, different space vector sequences suitable for a current-source converter are investigated in this paper. Details on how to achieve the waveform symmetries with a minimum switching frequency for each sequence are discussed. A thorough comparison of the harmonic performance of different space vector sequences is carried out. An optimum space vector modulation method by switching between two best sequences is proposed to achieve the best line-current total harmonic distortion with reduced switching losses. In addition, two synchronization methods, namely a PWM frame regulation method and a direct digital phase-locked loop synchronization method, are proposed. Both methods are equally effective in providing tight synchronization of the PWM waveform with the rectifier input frequency. The work has been verified in simulation and experiment.

A thin‐film field‐emission cathode with Pt or Au interlayer between insulator and Zn0.75Mg0.25O

AbstractThe cover picture illustrates a modified design for field emission cathodes proposed by Zengmei Wang and Dejie Li in their Original Paper [1] in the current issue. By introducing an additional interlayer, they were able to significantly improve the symmetry of the cathode's transmission current waveform while maintaining a stable and uniform electron emission.The sketch in the lower part depicts the layer sequence Al/Ta2O5/(Pt or Au)/Zn0.75Mg0.25O/Pt–Au–Ag, where a Pt or Au interlayer is introduced between the insulator (Ta2O5) and semiconductor (Zn0.75Mg0.25O) layers, in order to effectively control the interfacial electron energy state distribution. The resulting transmission current waveforms become completely symmetric (left curves in upper part) in comparison to those of the cathode without metal interlayer (right curves).The first author of the article currently is a Ph.D. candidate at the Electronic Engineering Department of Tsinghua University (Beijing, P.R. China) who is working on electron emission cathodes made of thin films, including discontinuous films.

Waveform Symmetry during the Habituation Process of Sympathetic Skin Response

Waveform Symmetry during the Habituation Process of Sympathetic Skin Response

Design of push-push and triple-push oscillators for reducing 1/f noise upconversion

In this paper, 1/f noise upconversion in push-push and triple-push oscillators is studied, and the design requirements for minimizing 1/f noise upconversion are presented. In push-push oscillators, the presence of the large second harmonic components may degrade the waveform symmetry of the oscillation waveforms, leading to the significant 1/f noise upconversion. To minimize 1/f noise upconversion in push-push oscillators, the phases of Fourier coefficients of all harmonics need to be equal. In triple-push oscillators, the waveform symmetry can easily be achieved by eliminating all even harmonic components. The experimental results show that around 15-dB phase-noise improvement at 100-kHz offset frequency can be obtained by satisfying the waveform symmetry condition in push-push and triple-push oscillators.

Independently Driven DG MOSFETs for Mixed-Signal Circuits: Part II—Applications on Cross-Coupled Feedback and Harmonics Generation

Circuit applications utilizing the tight quasi-static and nonquasi-static channel coupling in independently driven double-gate (IDDG) MOSFETs are presented. The performances of cross-coupled differential amplifiers and mixers with IDDG are compared with those of the SDDG counterparts. The quasi-static coupling in IDDG increases output voltage swing and improves voltage waveform symmetry in the cross-coupled differential amplifier. The nonquasi-static coupling in IDDG provides fast feedback in the differential amplifiers, and allows higher frequencies in the input signals for harmonic generation in mixers. We have identified plausible advantages in IDDG that cannot be readily implemented by SDDG, which justifies the fabrication cost and parasitic capacitance penalty of IDDG.

NON-INVASIVE IDENTIFICATION OF PHYSIOLOGICALLY SIGNIFICANT PUMPING STATES IN IMPLANTABLE ROTARY BLOOD PUMPS USED AS LEFT VENTRICULAR ASSIST DEVICES

Non-invasive detection of dangerous pumping states is important for the control of rotary blood pumps. The VentrAssistTM LVAD, is an implantable centrifugal rotary blood pump (iRBP), the impeller supported by a hydrodynamic bearing. In-vitro (pulsatile mock-loop) and ex-vivo (acute sheep) experiments (N=3) were conducted. By perturbing system parameters of the pulsatile mock loop and by physiological intervention through pharmacological or mechanical methods in the ovine experiments, and by varying iRBP impeller speed, it was possible to transition through five physiologically significant pumping states. These states were defined as regurgitant pump flow, ventricular ejection, continuous aortic valve closure, partial sucking of the ventricle, and total ventricular collapse, states confirmed in the experiments through observation and through implanting of additional flow and pressure sensors. Using instantaneous impeller speed and pump input power, we investigated the detection of these states without the use of additional sensors. Indices based on pump flow, flow amplitude and flow waveform symmetry were analyzed using classification and regression tree methods. The classification tree derived from the in-vitro experiments was applied to the ex-vivo data with perfect accuracy (0% false positives and negatives in predicting the pumping states). These data indicate that the state detection methods may be a valuable mechanism in optimal LVAD control and operational diagnosis

Frequency dependence on bias current in 5 GHz CMOS VCOs: impact on tuning range and flicker noise upconversion

The tuning curve of an LC-tuned voltage-controlled oscillator (VCO) substantially deviates from the ideal curve 1//spl radic/(LC(V)) when a varactor with an abrupt C(V) characteristic is adopted and the full oscillator swing is applied directly across the varactor. The tuning curve becomes strongly dependent on the oscillator bias current. As a result, the practical tuning range is reduced and the upconverted flicker noise of the bias current dominates the 1/f/sup 3/ close-in phase noise, even if the waveform symmetry has been assured. A first-order estimation of the tuning curve for MOS-varactor-tuned VCOs is provided. Based on this result, a simplified phase-noise model for double cross-coupled VCOs is derived. This model can be easily adapted to cover other LC-tuned oscillator topologies. The theoretical analyses are experimentally validated with a 0.25 /spl mu/m CMOS fully integrated VCO for 5 GHz wireless LAN receivers. By eliminating the bias current generator in a second oscillator, the close-in phase noise improves by 10 dB and features -70 dBc/Hz at 10 kHz offset. The 1/f/sup 2/ noise is -132 dBc/Hz at 3 MHz offset. The tuning range spans from 4.6 to 5.7 GHz (21%) and the current consumption is 2.9 mA.

Two novel synchronized bus-clamping PWM strategies based on space vector approach for high power drives

Two synchronized bus-clamping pulse width modulation (PWM) strategies based on the space vector approach are proposed for high-power induction motor drives. The two strategies together can produce PWM waveforms with any odd pulse number, preserving the waveform symmetries. The proposed strategies operate upto the six-step mode, maintaining the proportionality between the reference magnitude and the fundamental voltage generated throughout. These two strategies lead to lesser harmonic distortion as well as lesser peak current over the conventional space vector strategy (CSVS) in the high speed ranges of constant V/F drives. The reduction in the harmonic distortion over CSVS subject to a given maximum switching frequency (F/sub SW(MAX)/) of the inverter is demonstrated theoretically as well as experimentally for F/sub SW(MAX)/=750 Hz and 450 Hz, both with and without overmodulation. The best reduction in the distortion is as high as 30% to 50% in the different cases considered. Further, these two PWM strategies are also useful in reducing the switching frequency of the inverter over sine-triangle PWM and CSVS subject to an upper limit on the harmonic distortion.

Scheduled Voluntary Wheel Running Activity Modulates Free-Running Circadian Body Temperature Rhythms in Octodon degus

Entrainment of the circadian pacemaker to nonphotic stimuli, such as scheduled wheel-running activity, is well characterized in nocturnal rodents, but little is known about activity-dependent entrainment in diurnal or crepuscular species. In the present study, effects of scheduled voluntary wheel-running activity on circadian timekeeping were investigated in Octodon degus, a hystricomorph rodent that exhibits robust crepuscular patterns of wakefulness. When housed in constant darkness, O. degus exhibited circadian rhythms in wheel-running activity and body temperature (Tb) with an average period length (tau) of 23.39 +/- 0.11 h. When wheel running was restricted to a fixed 2-h schedule every 24 h, tau increased on average 0.39 +/- 0.09 h but did not result in steady-state entrainment. Instead, relative coordination between the fixed running schedule and circadian timing was observed. Tau was greatest when scheduled wheel running occurred at CT 20.5 (0.4 h greater than DD baseline tau). Scheduled running activity also influenced Tb waveform symmetry, reflecting concomitant changes in the circadian activity-rest ratio (alpha:rho). Aftereffects of the scheduled wheel-running paradigm were also observed. In 2 animals, tau lengthened from 23.20 and 23.80 h to 24.14 and 24.15 h, respectively, and remained relatively stable for approximately 1 month during the wheel schedule. Although behavioral activity appears to be a weak zeitgeber in this species, these data suggest that nonphotic stimuli can phase delay the circadian pacemaker in O. degus at similar times of the day as in nocturnal hamsters and mice, and in humans.

Overmodulation algorithm for space vector modulated inverters and its application to low switching frequency PWM techniques

An overmodulation algorithm is applied to four recently proposed space vector-based synchronised PWM strategies, to extend their range of operation and enhance the DC bus utilisation. The waveform symmetries and the proportionality between the reference magnitude and the fundamental voltage generated are also maintained in the overmodulation zone. It is shown that the relationship between the control variable and the fundamental voltage generated differs widely with the strategy and the pulse number used in low switching frequency PWM techniques unlike that at high switching frequencies. As a result the boundaries between any two consecutive zones of modulation and the maximum modulation index also vary with the strategy and the pulse number used. Cases where operation is possible up to the six-step mode are distinguished from those cases where it is not. The performance of the different strategies is evaluated. It is shown theoretically as well as experimentally that the bus-clamping PWM strategies perform better than the conventional space vector strategy in the overmodulation zone.

Synchronised PWM strategies based on space vector approach. Part 1: Principles of waveform generation

The authors deal with space-vector-based generation of synchronised three-phase PWM waveforms with three-phase, half-wave and quarter-wave symmetries. The necessary and sufficient conditions for synchronisation and the waveform symmetries are brought out in terms of the inverter states. These conditions are applied to the conventional and modified forms of space vector modulation to generate synchronised PWM waveforms with all the symmetries. Further, the necessary conditions governing the numbers of switchings of the different phases in any given sector to maintain the symmetries are identified. These rules are used to develop two new clamping strategies, namely the asymmetric zero-changing strategy and the boundary sampling strategy, which exploit the flexible features of space vector methods like double-switching of a phase and clamping of two phases in a sampling period. Typical waveforms corresponding to the different strategies are presented along with their theoretical and experimental spectra. The performance assessment of these strategies and their application to drives are dealt with in Part 2.

Waveform symmetry properties and phase noise inoscillators

The authors formalise and expand an empirically observed waveform symmetry condition which minimises the transformation of low-frequency noise into the close-in phase noise spectrum of an electrical oscillator. The result provides an insight into the impact of waveform symmetry on the phase noise performance of electrical oscillators.