Phase-locked Oscillator Research Articles

Impairment of odor recognition in Parkinson's disease caused by weak activations of the orbitofrontal cortex

Olfactory dysfunction and abnormalities of olfactory brain structures are found in patients with Parkinson's disease (PD), and a number of studies have reported that olfactory dysfunction is caused by abnormalities of the central olfactory systems. We previously analyzed electroencephalograms (EEGs) and respiration simultaneously in normal subjects while testing for detection and recognition of odors. We identified changes in respiration pattern in response to odor stimuli and found inspiratory phase-locked alpha oscillations (I-α). The genesis of I-α were identified in olfactory-related areas including the entorhinal cortex, hippocampus, amygdale and orbitofrontal cortex with an EEG dipole tracing method. In the present study, we used the same protocol in PD patients and compared results of PD with those of age-matched controls. All PD patients detected odor, but 5 out of 10 showed impaired odor recognition. Changes in breathing pattern associated with emotional changes during exposure to odor stimuli were not observed in PD patients. I-α waveforms were not observed; however, positive waves followed by negative waves were identified approximately 100 ms after inspiration onset. Dipoles of this component were localized in the entorhinal cortex for odor detection in all patients and in the entorhinal cortex and middle temporal gyrus for PD patients who could discriminate odors. Odor recognition in PD could be subserved by a different neural circuit from that of normal subjects, done through the temporal association cortex as a subsystem for recognizing the odor; however, the system may not be associated with the odor-induced emotions.

Evoked γ oscillations in human scalp EEG are test–retest reliable

Objective Evoked, phase-locked γ oscillations of the electroencephalogram (EEG) have been demonstrated to be modulated by both bottom-up as well as top-down factors. However, to date the test–retest reliability of these oscillations has not been studied systematically. Methods We recorded EEG activity of 12 healthy volunteers in response to stimuli of different sizes. Each participant took part in two sessions separated by two weeks in time. To obtain an estimate of the reliability of evoked γ band responses (GBRs), we compared frequency and magnitude of phase-locked EEG oscillations between sessions. Results In response to large stimuli magnitude and frequency of the evoked GBR yielded significant reliability. However, this was not the case for stimuli which were too small to evoke detectable GBRs. Conclusions The results are in accordance with studies demonstrating a dependence of γ oscillations on stimulus parameters. Significance The current findings suggest that using appropriate stimulation, the evoked γ response has sufficient test–retest reliability for use in assessing clinical changes in neurophysiological status.

Theory of mutual phase locking of spin-torque nanosized oscillators

A theory of mutual phase locking of a pair of generating magnetic nanocontacts driven by a spin-polarized current is developed using the general theory of coupled nonlinear oscillators. Expressions for the phase-locking band and for the frequency of phase-locked oscillations are derived and compared to result of experiments. It is shown that in typical experiments, where the separation $a$ between the nanocontacts lies in the interval $0.2<a<1.5\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{m}$, the coupling between the nanocontacts leading to the phase-locking effect is mainly caused by propagating spin waves radiating into the common free layer, rather than by the direct magnetodipole interaction.

Synchronization in the BCS Pairing Dynamics as a Critical Phenomenon

Fermi gas with time-dependent pairing interaction hosts several different dynamical states. Coupling between the collective BCS pairing mode and individual Cooper pair states can make the latter either synchronize or dephase. We describe transition from phase-locked undamped oscillations to Landau-damped dephased oscillations in the collisionless, dissipationless regime as a function of coupling strength. In the dephased regime, we find a second transition at which the long-time asymptotic pairing amplitude vanishes. Using a combination of numerical and analytical methods we establish a continuous (type II) character of both transitions.

Phase-locked oscillator at 3 mm waveband using high Tc superconductor mixer mounted on pulse tube crycooler

A frequency mixing and phase locking system is designed, in which electromagnetic shielding, microwave coupling, and intermediate frequency (IF) measurement arrangements are included. In lieu of liquid nitrogen, a pulse tube cryocooler is used to cool the whole system. With Josephson grain boundary junction as the mixing element, the 96th harmonic frequency mixing at 3 mm waveband is obtained, and phase-locked voltage-controlled oscillator (VCO) is realized.

Somato-Dendritic Morphology Predicts Physiology for Neurons That Contribute to Several Kinds of Limb Movements

It has been difficult to predict the behavioral roles of vertebrate CNS neurons based solely on their morphologies, especially for the neurons that control limb movements in adults. We examined the morphologies of spinal interneurons involved in limb movement control, using intracellular recording followed by Neurobiotin injection in the in vivo adult turtle spinal cord preparation. We report here the first description of a class of spinal interneurons whose somato-dendritic morphologies predict their robust activity during multiple forms of ipsilateral and contralateral fictive hindlimb scratching and fictive hindlimb withdrawal. These "transverse interneurons" or T cells have a mediolaterally elongated soma and a simple dendritic tree that is extensive in the transverse plane but restricted rostrocaudally. During fictive scratching, these cells display strong rhythmic modulation with higher peak firing rates than other scratch-activated interneurons. These higher peak firing rates are at least partly caused by T cells having larger phase-locked membrane potential oscillations and narrower action potentials with briefer afterhyperpolarizations than other scratch-activated interneurons. Many T cells have axon terminal arborizations in the ventral horn of the spinal cord hindlimb enlargement. Identification of this morphological and physiological class of spinal interneurons should facilitate further exploration of the mechanisms of hindlimb motor pattern selection and generation.

Multistability and stable asynchronous periodic oscillations in a multiple-delayed neural system

We consider a network of three identical neurons with multiple discrete signal transmission delays. The model for such a network is a system of nonlinear delay differential equations. After some consideration of the absolute synchronization of the system and the global attractivity of the zero solution, we present a detailed discussion about the boundaries of the stability region of the trivial solution. This allows us to determine the possible codimension one bifurcations which occur in the system. In particular, we show the existence of standard Hopf bifurcations giving rise to synchronized periodic solutions and of D 3 equivariant Hopf bifurcations giving rise to three types of periodic solutions: phase-locked, mirror-reflecting, and standing waves. Hopf–Hopf and Hopf–steady state bifurcations interactions are shown to exist and give rise to coexistence of stable synchronized and desynchronized solutions. Perturbation techniques coupled with the Floquet theory are used to determine the stability of the phase-locked oscillations.

On the conception and analysis of a 12-GHz push-push phase-locked DRO

This paper describes the design and behavior of a 12-GHz push-push dielectric resonator oscillator in a phase-locked environment. This phase-locked dielectric resonator oscillator (PLDRO) differs from conventional designs on many fronts. First, it uses a push-push oscillator for its improved phase noise and reduced fundamental frequency. Second, the phase detection is implemented at a 3-GHz IF as an alternative to detecting at RF using a sampling phase detector (PD). Finally, the push-push PLDRO is tuned via coupled microstrip lines to minimize oscillator loading. These modifications are intended to minimize the risk of PLDRO lock failures by maintaining a constant PD gain via amplifiers operating at P1dB, and by halving the DRO fundamental frequency using the push-push approach. Experimental results indicate a fundamental suppression of 27 dBc, and single-sideband phase noise densities of -105, -110, and -125 dBc/Hz at 10-kHz, 100-kHz, and 1-MHz offsets, respectively, from a 12-GHz carrier

Study of the hyperradiance from phase-locked soliton oscillators

The hyperradiance from phase-locked soliton oscillators is investigated by using a family of solutions for the unperturbed sine-Gordon equation. Analytical descriptions for the emitted power from phase-locked soliton oscillators have been obtained for the two magnetically coupled long Josephson junctions operated in single-fluxon modes. We derive an intact mathematical expression and some simulation results of space-time action for the theory for superradiance from phase-locked oscillators.

Nano-oscillators get it together

Synchronized radiation from arrays of oscillators is widely used in microwave and wireless communications. Phase-locked oscillations produced at the atomic level now pave the way for devices on the nanoscale.

Inspiratory phase‐locked alpha oscillation in human olfaction: source generators estimated by a dipole tracing method

Olfactory perception and related emotions are largely dependent on inspiration. We acquired simultaneous respiration and electroencephalographic recordings during pleasant odour and unpleasant odour stimulation. We sought to identify changes in respiratory pattern, inspiratory-related potentials and location of dipoles estimated from the potentials. Electroencephalographic recording was triggered by inspiration onset. Respiratory frequency decreased at pleasant odour recognition, and it increased at unpleasant odour detection and recognition. O2 consumption records showed that these changes were not due to metabolic demand. During olfactory stimulation, inspiratory phase-locked alpha oscillation (I-alpha) was found in the averaged potential triggered by inspiration onset. I-alpha was observed at both pleasant odour and unpleasant odour detection and recognition, but it was not seen in the inspiration-triggered potentials of normal air breathing. Electroencephalographic dipole tracing identified the location of dipoles from the I-alpha in the limbic area and the cortex; the entorhinal cortex, hippocampus, amygdala, premotor area and centroposterior orbitofrontal cortex subserve odour detection, and the rostromedial orbitofrontal cortex subserves odour recognition. We suggest that the I-alpha in our study originated from the olfactory cortex in the forebrain and was phase-locked to inspiration.

Optimization of the Phase-Locked Flux-Flow Oscillator for the submm Integrated Receiver

The Superconducting Integrated Receiver (SIR) comprises in one chip a planar antenna integrated with an SIS mixer, a superconducting Flux Flow Oscillator (FFO) acting as Local Oscillator (LO) and a second SIS harmonic mixer (HM) for FFO phase locking. Free-running FFO linewidth well below 10 MHz is required to ensure phase-locked operation of an SIR. Comprehensive experimental study of the Nb-AlOx-Nb FFO linewidth and other main parameters has been carried out in order to achieve this goal. Essential dependence of the FFO linewidth on its width and idle region dimension has been found. It makes possible an optimization of the FFO design and selection of the best FFO parameters for practical operation of the SIR.

On the intrinsic time scales involved in synchronization: A data-driven approach

We address the problem of detecting, from scalar observations, the time scales involved in synchronization of complex oscillators with several spectral components. Using a recent data-driven procedure for analyzing nonlinear and nonstationary signals [Huang, Proc. R. Soc. London A 454, 903 (1998)], we decompose a time series in distinct oscillation modes which may display a time varying spectrum. When applied to coupled oscillators with multiple time scales, we found that motions are captured in a finite number of phase-locked oscillations. Further, in the synchronized state distinct phenomena as phase slips, anti-phase or perfect phase locking can be simultaneously observed at specific time scales. This fully data-driven approach (without a priori choice of filters or basis functions) is tested on numerical examples and illustrated on electric intracranial signals recorded from an epileptic patient. Implications for the study of the build-up of synchronized states in nonstationary and noisy systems are pointed out.

Silicon resonant accelerometer with electronic compensation of input-output cross-talk

A resonant accelerometer manufactured in silicon bulk micromachining with electrothermal excitation and piezoresistive detection is presented. The structure is a seismic mass supported by two parallel flexure hinges as a doubly-sustained cantilever, with a resonating microbeam located between the hinges. The acceleration normal to the chip plane induces an axial stress in the microbeam and, in turn, a proportional change in the microbeam resonant frequency. Beam resonant frequency of around 70 kHz and acceleration sensitivity of 35 Hz/g over the range 0–3 kHz were measured on prototypes, in accordance with analytical calculations and simulations. The microbeam operates unsealed at atmospheric pressure, therefore a comparatively low quality factor results due to air damping. In this condition, the effect of the input-output cross-talk was found to be significant. The cross-talk is analyzed and modeled, and an electronic active compensation is proposed. The compensated sensor was inserted into a phase-locked loop oscillator and tested. Reported experimental results show that the sensor performs in excellent agreement with the theoretical predictions.

A 5‐GHz injection‐locked phase‐locked loop

AbstractIn this paper, we introduce a 5‐GHz injection‐locked phase‐locked loop (ILPLL). A new method is presented for accurate analysis of the phase‐noise performance of the proposed system. Furthermore, comparison with other phase‐noise‐estimation techniques demonstrates that our method provides an accurate characterization of any ILPLL topology. The theoretical and calculation results show an improved performance for phase noise, locking range, and power consumption compared to conventional phase‐locked loops (PLLs) and injection‐locked oscillators (ILOs). Furthermore, we demonstrate the pulling behavior of the injected oscillator and examine the obtained results. To verify the presented analysis, a 5‐GHz prototype has been implemented, which achieves −119‐dBc/Hz at 100‐KHz frequency offset, producing +4.5 dBm of output power and consuming 9 mA at 3 V. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 46: 80–84, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20907

Direct comparison between phase locked oscillator and direct resonance oscillator in the noncontact atomic force microscopy under ultrahigh vacuum

I have demonstrated the advantage of the phase locked oscillator (PLO) over the conventional direct resonance oscillator (DRO) in noncontact mode atomic force microscopy (AFM) under ultrahigh vacuum. Direct comparison between PLO and DRO has been made in terms of background noise level, temporal response, and stability. Compared to the DRO method without phase coherence, the experimental results show that the PLO method is more effective in reducing the noise level and enhancing the stability over all force regimes in UHV noncontact AFM. The noise reduction and stability enhancement in PLO indicate the important role of the phase coherent effect in improving the capability of noncontact imaging in UHV.

Chimera States for Coupled Oscillators

Arrays of identical oscillators can display a remarkable spatiotemporal pattern in which phase-locked oscillators coexist with drifting ones. Discovered two years ago, such "chimera states" are believed to be impossible for locally or globally coupled systems; they are peculiar to the intermediate case of nonlocal coupling. Here we present an exact solution for this state, for a ring of phase oscillators coupled by a cosine kernel. We show that the stable chimera state bifurcates from a spatially modulated drift state, and dies in a saddle-node bifurcation with an unstable chimera state.

A study of injection locking and pulling in oscillators

Injection locking characteristics of oscillators are derived and a graphical analysis is presented that describes injection pulling in time and frequency domains. An identity obtained from phase and envelope equations is used to express the requisite oscillator nonlinearity and interpret phase noise reduction. The behavior of phase-locked oscillators under injection pulling is also formulated.

Upgrade Procedure for the Delingha 13.7-m Telescope

The 13.7-m millimeter-wave radio telescope of Purple Mountain Observatory operates at 3200-m above the sea level near Delingha, Qinghai Province, China. Equipped with a superconducting SIS receiver, the telescope is used in the millimeter-wave band ranging from 85 to 115 GHz. An upgrade procedure is reported here which includes a superconducting SIS receiver, a new phase-locked local oscillator, a dedicated multi-line backend system, and a new control system based on industrial computer with PCI bus. With the dedicated multi-line backend system, the CO and isotopic lines around 110 GHz are obtained simultaneously. In recent years, scientific activities with this telescope have been focused on studies of Galactic molecular clouds and star formation regions, including surveys of molecular lines from IRAS sources and large-scale map of molecular clouds. Other programs include studies of the circumstellar envelope of late-type stars and interaction of Galactic supernova remnants with dense molecular gas.

Gamma band responses to target and non-target auditory stimuli in humans

We studied the EEG oscillatory changes in the gamma band during auditory oddball paradigms in two different conditions (counting targets and reading). A time–frequency analysis was performed for standard and target stimuli. The study revealed an early (26–59 ms) phase-locked oscillation. Around 200 ms, a non-phase locked response was found for standard and target stimuli in temporal posterior electrodes. At about 360 ms, a phase-locked oscillation was observed only after target stimuli in the “counting targets” condition. During the “reading” task this late activity was not found, and energy increases were lower than during “counting” task. The early oscillation may be related to the sensory processing of the stimuli. The response around 200 ms may be involved in auditory mismatch and/or memory retrieval, and late activity is probably a P300-related response. Attention enhances all these activities.