Stable Phase Relationship Research Articles

A consistent map in the medial entorhinal cortex supports spatial memory

The medial entorhinal cortex (MEC) is hypothesized to function as a cognitive map for memory-guided navigation. How this map develops during learning and influences memory remains unclear. By imaging MEC calcium dynamics while mice successfully learned a novel virtual environment over ten days, we discovered that the dynamics gradually became more spatially consistent and then stabilized. Additionally, grid cells in the MEC not only exhibited improved spatial tuning consistency, but also maintained stable phase relationships, suggesting a network mechanism involving synaptic plasticity and rigid recurrent connectivity to shape grid cell activity during learning. Increased c-Fos expression in the MEC in novel environments further supports the induction of synaptic plasticity. Unsuccessful learning lacked these activity features, indicating that a consistent map is specific for effective spatial memory. Finally, optogenetically disrupting spatial consistency of the map impaired memory-guided navigation in a well-learned environment. Thus, we demonstrate that the establishment of a spatially consistent MEC map across learning both correlates with, and is necessary for, successful spatial memory.

Co/Bi2Se3 interfacial reactions and Bi-Co-Se phase equilibria

BackgroundBi2Se3 holds significant importance in thermoelectric applications, and Co is considered a promising candidate for use as a barrier layer. This study investigates the interfacial reactions between Co and Bi2Se3, along with the phase equilibria within the Bi-Co-Se system, to provide fundamental insights. MethodsThe Bi-Co-Se alloys and Bi2Se3 substrates were prepared with pure constituent elements. The Co/Bi2Se3 couples were formed by electroplating Co onto the Bi2Se3 substrates, followed by subjecting them to reactions at 400℃ and 500℃. Significant findingsIsothermal sections of the Bi-Co-Se phase equilibria at 400 °C and 500 °C have been proposed based on key ternary experimental results and phase diagrams of its three constituent binary systems. No ternary compounds were observed. The stable phases and phase relationships are similar at both 400℃ and 500℃, except for the instability of Co9Se8 at 500℃. Significant interfacial reactions were observed in the Co/Bi2Se3 couples reacted at 400℃ and 500℃. These results suggest that Co alone may not serve as a suitable barrier layer for Bi2Se3 at temperatures exceeding 400 °C. The reaction path at 400℃ is Co/Co1-ꭓSe/(Bi2)m(Bi2Se3)n/Bi2Se3, with Se as the dominant diffusion species. Se atoms migrate towards Co to form the Co1-ꭓSe phase and leave a Se-depleted Bi2Se3 behind to form (Bi2)m(Bi2Se3)n. Unexpected liquation occurred in the Co/Bi2Se3 couple reacted at 500℃. This liquation resulted from the rapid outward diffusion of Se from the Bi2Se3, leading to the emergence of bismuth from the Se-depleted Bi2Se3 and its transformation into a molten state.

Quantifying the scale-dependent relationships of PM2.5 and O3 on meteorological factors and their influencing factors in the Beijing-Tianjin-Hebei region and surrounding areas

To investigate the variations of PM2.5 and O3 and their synergistic effects with influencing factors at different time scales, we employed Bayesian estimator of abrupt seasonal and trend change to analyze the nonlinear variation process of PM2.5 and O3. Wavelet coherence and multiple wavelet coherence were utilized to quantify the coupling oscillation relationships of PM2.5 and O3 on single/multiple meteorological factors in the time-frequency domain. Furthermore, we combined this analysis with the partial wavelet coherence to quantitatively evaluate the influence of atmospheric teleconnection factors on the response relationships. The results obtained from this comprehensive analysis are as follows: (1) The seasonal component of PM2.5 exhibited a change point, which was most likely to occur in January 2017. The trend component showed a discontinuous decline and had a change point, which was most likely to appear in February 2017. The seasonal component of O3 did not exhibit a change point, while the trend component showed a discontinuous rise with two change points, which were most likely to occur in July 2018 and May 2017. (2) The phase and coherence relationships of PM2.5 and O3 on meteorological factors varied across different time scales. Stable phase relationships were observed on both small- and large-time scales, whereas no stable phase relationship was formed on medium scales. On all-time scales, sunshine duration was the best single variable for explaining PM2.5 variations and precipitation was the best single variable explaining O3 variations. When compared to single meteorological factors, the combination of multiple meteorological factors significantly improved the ability to explain variations in PM2.5 and O3 on small-time scales. (3) Atmospheric teleconnection factors were important driving factors affecting the response relationships of PM2.5 and O3 on meteorological factors and they had greater impact on the relationship at medium-time scales compared to small- and large-time scales.

Characterization of Lateral and Longitudinal Mode Competition in Blue InGaN Broad‐Ridge Laser Diodes

In blue GaN‐based laser diodes with a 40 μm broad‐ridge waveguide, lateral modes of different order are selectively observed by high‐resolution spectroscopy combined with lateral near‐field scanning. Longitudinal mode clusters contribute to different lateral modes, close above the threshold current. Longitudinal mode competition is observed in each longitudinal mode cluster as intensity modulation and wavelength shift, repeating itself with a frequency of around 60–80 MHz. Despite the spectral separation of the different clusters and different lateral mode order, the mode competition processes share the same frequency and show a stable phase relation, especially at low currents. This indicates coupling of separate mode clusters via the charge carrier density. Due to the lateral modes occurring at separate wavelengths, lateral–longitudinal mode competition is found, which not only causes spectral effects but also time‐dependent periodic variations in the lateral near field.

Towards phase-stabilized Fourier domain mode-locked frequency combs

Fourier domain mode-locked (FDML) lasers are some of the fastest wavelength-swept light sources, and used in many applications like optical coherence tomography (OCT), OCT endoscopy, Raman microscopy, light detection and ranging, and two-photon microscopy. For a deeper understanding of the underlying laser physics, it is crucial to investigate the light field evolution of the FDML laser and to clarify whether the FDML laser provides a frequency comb structure. In this case, the FDML would output a coherent sweep in frequency with a stable phase relation between output colours. To get access to the phase of the light field, a beat signal measurement with a stable, monochromatic laser is performed. Here we show experimental evidence of a well-defined phase evolution and a comb-like structure of the FDML laser. This is in agreement with numerical simulations. This insight will enable new applications in jitter-free spectral-scanning, coherent, synthetic THz-generation and as metrological time-frequency ruler.

Theoretical study of the Fourier-transform analysis of heterodyne comb-emission measurements

Enforcing stable phase relations among all laser comb modes is a powerful way to control broad-band emitted radiation with only two actuators. This is an established technique for pulsed mode-locked lasers covering even more than an octave with several thousand modes. Recently, generation of combs has been demonstrated in miniaturized sources, like microresonators for the near-infrared and quantum cascade lasers for the mid- and far-infrared region. Despite the lack of a thorough theoretical background, these sources have been recently characterized by a Fourier-transform analysis of comb emission (FACE). This technique is suitable for comb characterization in any spectral region and regardless of the temporal emission profile. Here we provide a comprehensive and complete FACE theoretical framework, clarifying the details of the data analysis, giving access to more detailed results, and improving the overall reach of the technique itself. This will foster a widespread use of this approach for a full characterization of any comb emission.

GeoPS: An interactive visual computing tool for thermodynamic modelling of phase equilibria

AbstractThe availability of thermodynamic data for geologically relevant phases has made practical the calculation of stable phase relations throughout the mantle and crust of terrestrial planets. GeoPS (http://www.geops.org) is a program designed for this purpose in which both input and output are done through an intuitive graphical user interface. GeoPS provides a wide range of phase equilibrium calculations based on a novel Gibbs energy minimization algorithm. The algorithm provides for exceptionally robust and computationally efficient solution to the phase equilibrium problem by successive alternation between a linear programming step to identify stable phase compositions and a non‐linear programming step to refine the compositions estimated during the linear programming. Applications include calculation of various types of phase diagrams and path‐dependent phase fractionation. By combining an easy‐to‐use graphical user interface with a robust and efficient solver, GeoPS makes phase equilibrium modelling accessible to researchers and students with minimal training and provides a powerful tool for understanding natural phase relations and for planning experimental work.

A Complex-Valued Oscillatory Neural Network for Storage and Retrieval of Multidimensional Aperiodic Signals.

Recurrent neural networks with associative memory properties are typically based on fixed-point dynamics, which is fundamentally distinct from the oscillatory dynamics of the brain. There have been proposals for oscillatory associative memories, but here too, in the majority of cases, only binary patterns are stored as oscillatory states in the network. Oscillatory neural network models typically operate at a single/common frequency. At multiple frequencies, even a pair of oscillators with real coupling exhibits rich dynamics of Arnold tongues, not easily harnessed to achieve reliable memory storage and retrieval. Since real brain dynamics comprises of a wide range of spectral components, there is a need for oscillatory neural network models that operate at multiple frequencies. We propose an oscillatory neural network that can model multiple time series simultaneously by performing a Fourier-like decomposition of the signals. We show that these enhanced properties of a network of Hopf oscillators become possible by operating in the complex-variable domain. In this model, the single neural oscillator is modeled as a Hopf oscillator, with adaptive frequency and dynamics described over the complex domain. We propose a novel form of coupling, dubbed “power coupling,” between complex Hopf oscillators. With power coupling, expressed naturally only in the complex-variable domain, it is possible to achieve stable (normalized) phase relationships in a network of multifrequency oscillators. Network connections are trained either by Hebb-like learning or by delta rule, adapted to the complex domain. The network is capable of modeling N-channel electroencephalogram time series with high accuracy and shows the potential as an effective model of large-scale brain dynamics.

Polyrhythmic multifrequency synchronization in coupled oscillators with exactly solvable attractors

While stable polyrhythmic multifrequency [Formula: see text] dynamics has traditionally been an important element in music performance, recently, this type of dynamics has been discovered in the human brain in terms of elementary temporal neural activity patterns. In this context, the canonical-dissipative systems framework is a promising modeling approach due to its two key features to bridge the gap between classical mechanics and life sciences, on the one hand, and to provide analytical or semi-analytical solutions, on the other hand. Within this framework, a family of testbed models is constructed that exhibit [Formula: see text] multifrequency limit cycle attractors describing two components oscillating with frequencies at [Formula: see text] ratios and stable polyrhythmic phase relationships. The attractors are super-integrable due to the existence of third invariants of motion for all [Formula: see text] ratios. Strikingly, all [Formula: see text] attractors models satisfy the same generic bifurcation diagram. The study generalizes earlier work on super-integrable systems, on the one hand, and canonical-dissipative limit cycle oscillators, on the other hand. Explicit worked-out models for 1[Formula: see text]:[Formula: see text]4 and 2[Formula: see text]:[Formula: see text]3 frequency ratios are presented.

Adaptation to unstable coordination patterns in individual and joint actions.

Previous research on interlimb coordination has shown that some coordination patterns are more stable than others, and function as attractors in the space of possible phase relations between different rhythmic movements. The canonical coordination patterns, i.e. the two most stable phase relations, are in-phase (0 degree) and anti-phase (180 degrees). Yet, musicians are able to perform other coordination patterns in intrapersonal as well as in interpersonal coordination with remarkable precision. This raises the question of how music experts manage to produce these unstable patterns of movement coordination. In the current study, we invited participants with at least five years of training on a musical instrument. We used an adaptation paradigm to address two factors that may facilitate producing unstable coordination patterns. First, we investigated adaptation in different coordination settings, to test the hypothesis that the lower coupling strength between individuals during joint performance makes it easier to achieve stability outside of the canonical patterns than the stronger coupling during individual bimanual performance. Second, we investigated whether adding to the structure of action effects may support achieving unstable coordination patterns, both intra- and inter-individually. The structure of action effects was strengthened by adding a melodic contour to the action effects, a measure that has been shown to improve the acquisition of bimanual coordination skills. Adaptation performance was measured both in terms of asynchrony and variability thereof. As predicted, we found that producing unstable patterns benefitted from the weaker coupling during joint performance. Surprisingly, the structure of action effects did not help with achieving unstable coordination patterns.

Effects of footedness and stance asymmetry confirm an inter-leg metastable coordination dynamics of standing posture

We investigated the patterns of coordination between the left and right legs that support the task of maintaining an upright standing posture. We used cross-wavelet analyses to assess coordination between the centers of pressure under the left and right feet. We recruited participants with a lateralized functional preference for their right leg, and we manipulated whether these participants stood with symmetric/asymmetric stances and whether their eyes were open or closed. Our hypotheses were derived from the Haken-Kelso-Bunz (HKB) model of interlimb coordination dynamics. Consistent with HKB model predictions, we observed (1) coordination taking the form of metastable, transient epochs of stable phase relations, (2) preferences for in-phase and anti-phase coordination patterns, and (3) changes in pattern stability and phase leads associated with both stance asymmetry and right-side lateral preference. The form and stability of observed coordination patterns were mediated by the availability of visual information. Our findings confirm the existence of a metastable coordination dynamic associated with the task of maintaining upright stance. We discuss the implications of these findings in the context of evaluating the utility of the HKB model for understanding the functional organization of the posture system.

Cinematographic observation of the deformation of an antibubble when a spark-induced cavitation bubble oscillates in its vicinity

An antibubble is the opposite of a soap bubble: a thin spherical gas shell containing liquid inside and surrounded by liquid outside. The dynamic behaviour of antibubbles when a spark-induced cavitation bubble oscillates in their vicinity is studied using a high-speed video camera. It is found that the rupture process of antibubble impacted by shock wave is different from that of antibubble due to aging or puncture. There is a stable phase relationship between the cavitation bubble deformation and the antibubble deformation. The non-uniformity of the thickness of the gas film strongly influences the rupture process of the antibubble. The antibubbles will split horizontally into two parts, and the gas in the gas film of antibubbles will move and gather to the point where the air film is thickest, and then divide into two gas bubbles. The dynamics of antibubble deformation under the impact of primary shock wave and secondary shock wave induced by the growth and collapse of cavitation bubble is analysed.

Entrainment of the Circadian Clock of the Enteric Bacterium Klebsiella aerogenes by Temperature Cycles.

SummaryThe gastrointestinal bacterium Klebsiella (née Enterobacter) aerogenes expresses an endogenously generated, temperature-compensated circadian rhythm in swarming motility. We hypothesized that this rhythm may be synchronized/entrained in vivo by body temperature (TB). To determine entrainment, cultures expressing bioluminescence were exposed to temperature cycles of 1°C (35°C–36°C) or 3°C (34°C–37°C) in amplitude at periods (T-cycles) of T = 22, T = 24, or T = 28 h. Bacteria entrained to all T-cycles at both amplitudes and with stable phase relationships. A high-amplitude phase response curve (PRC) in response to 1-h pulses of 3°C temperature spike (34°C–37°C) at different circadian phases was constructed, revealing a Type-0 phase resetting paradigm. Furthermore, real-time bioluminescence imaging revealed a spatiotemporal pattern to the circadian rhythm. These data are consistent with the hypothesis that the K. aerogenes circadian clock entrains to its host via detection of and phase shifting to the daily pattern of TB.

Temporal evolution of beta bursts in the parkinsonian cortical and basal ganglia network

Beta frequency oscillations (15 to 35 Hz) in cortical and basal ganglia circuits become abnormally synchronized in Parkinson's disease (PD). How excessive beta oscillations emerge in these circuits is unclear. We addressed this issue by defining the firing properties of basal ganglia neurons around the emergence of cortical beta bursts (β bursts), transient (50 to 350 ms) increases in the beta amplitude of cortical signals. In PD patients, the phase locking of background spiking activity in the subthalamic nucleus (STN) to frontal electroencephalograms preceded the onset and followed the temporal profile of cortical β bursts, with conditions of synchronization consistent within and across bursts. Neuronal ensemble recordings in multiple basal ganglia structures of parkinsonian rats revealed that these dynamics were recapitulated in STN, but also in external globus pallidus and striatum. The onset of consistent phase-locking conditions was preceded by abrupt phase slips between cortical and basal ganglia ensemble signals. Single-unit recordings demonstrated that ensemble-level properties of synchronization were not underlain by changes in firing rate but, rather, by the timing of action potentials in relation to cortical oscillation phase. Notably, the preferred angle of phase-locked action potential firing in each basal ganglia structure was shifted during burst initiation, then maintained stable phase relations during the burst. Subthalamic, pallidal, and striatal neurons engaged and disengaged with cortical β bursts to different extents and timings. The temporal evolution of cortical and basal ganglia synchronization is cell type-selective, which could be key for the generation/ maintenance of excessive beta oscillations in parkinsonism.

Entrainment of the Circadian Clock of the Enteric Bacterium <i>Klebsiella aerogenes</i> by Temperature Cycles

We have previously shown that the gastrointestinal bacterium, Klebsiella (nee Enterobacter) aerogenes, expresses an endogenously generated and temperature-compensated circadian rhythm in swarming motility and gene expression. As a human gastrointestinal commensal, we hypothesized that this circadian rhythm may be synchronized/entrained in vivo by the daily rhythm in body temperature (TB). Cultures of K. aerogenes transformed to express a plasmid containing luxCDABE with a MotA promoter exhibited rhythms in bioluminescence and in spatial distribution on the culture dish with a circadian period (τ). To determine entrainment, cultures were exposed to temperature cycles of 1o (35oC-36oC) or 3oC (34oC-37oC) in amplitude and cycles with varying periods (T cycles) of T=22 hours, T=24 hours, or T=28 hours. Bacteria entrained to all 3 T cycles at both temperature amplitudes with stable phase relationships (Ψ) to the Zeitgebers. To better understand the nature of this entrainment, a phase response curve (PRC) was constructed in response to 1 hr. pulses of 3oC increase in temperature (34oC-37oC) at different circadian phases (Φ) of the bioluminescence rhythm. A very high amplitude PRC, with small phase shifts (ΔΦ) during subjective day, large phase delays (-ΔΦ) during early subjective night, and large phase advances (+ΔΦ) during late subjective night was constructed, explaining the entrainment patterns of these bacteria. A phase transition curve (PTC) revealed a Type 0 PRC. To determine whether spatial patterns of bioluminescence rhythms contributed to the overall circadian organization of K. aerogenes, cultures were imaged for 2.5 days in a cooled CCD camera system, revealing a spatiotemporal pattern the circadian rhythmicity. These data are consistent with the hypothesis that the K. aerogenes circadian clock entrains to its host via detection of and phase-shifting to the daily pattern of TB.

Coupled actuators with a mechanically synchronized phase during MR elastography: A phantom feasibility study

AbstractIntroductionMagnetic resonance elastography (MRE) is an MR imaging method for the quantification of spatial stiffness of soft tissues using mechanically induced dynamic shear waves. In some applications, the penetration of shear waves can be limited through attenuation and shadowing of the waves. In order to increase the actuator performance, we present a dual driver approach to compensate for shear wave attenuation and to achieve better coverage over the entire region of interest.Materials and Methods(a) We designed pneumatic turbines that created a sinusoidal centrifugal force due to an eccentric weight. Two turbines were connected in‐phase with each eccentric weight having the same angular position relative to its pivot point. (b) We developed a tissue elasticity mimicking abdominal phantom. (c) The phantom served as a test object to investigate the feasibility to generate shear waves at two surface origins with the dual actuator system and to compare it against a single actuation setup.Results and DiscussionA stable phase relationship of the shear waves generated by the turbines was achieved as the positions of the eccentric weights were mechanically fixed. The abdominal phantom yielded sufficient MR signal. Liver and rib cage were clearly visible in MR imaging. The shear waves generated by the dual turbine propagated through the region of interest. Our turbine design is reproducible through 3D printing and can be integrated into existing clinical equipment for 1.5 T and 3 T scanners.

Temporal characteristics of quantum cascade laser frequency modulated combs in long wave infrared and THz regions.

We consider here a time domain model representing the dynamics of quantum cascade lasers (QCLs) generating frequency combs (FCs) in both THz and long wave infrared (LWIR λ = 8-12µm) spectral ranges. Using common specifications for these QCLs we confirm that the free running laser enters a regime of operation yielding a pseudo-randomly frequency modulated (FM) radiation in the time domain corresponding to FCs with stable phase relations in the frequency domain. We provide an explanation for this unusual behavior as a consequence of competition for the most efficient regime of operation. Expanding the model previously developed in [Opt. Eng. 57(1), 011009 (2017)] we analyze the performance of realistic THz and LWIR QCLs and show, despite the vastly different scale of many parameters, that both types of lasers offer very similar characteristics, namely FM operation with an FM period commensurate with the gain recovery time and an FM amplitude comparable with the gain bandwidth. We also identify the true culprit behind pseudo-random dynamics of the FM comb to be spatial hole burning, rather than the more pervasive spectral hole burning.

Thermodynamic assessment of binary erythritol-xylitol phase diagram for phase change materials design

Here, the erythritol-xylitol binary system was thermodynamically optimized based on available experimental phase equilibrium data, to explore compositions suitable as phase change materials (PCMs) for thermal energy storage (TES). A previous experimental study revealed that erythritol-xylitol was a partially isomorphous system with a eutectic. In the thermodynamic evaluation, the CALPHAD method was employed coupling the phase diagram and thermodynamic property information. There, both unary and binary systems’ experimental data were taken into account, and all phases were described using the substitutional solution model. Finally, a self-consistent thermodynamic description for the erythritol-xylitol system was achieved. The calculated eutectic point is at 76.7°C and 26.8mol% erythritol, agreeing well with the experimental data. The calculated phase diagram better-verifies the systems’ solidus and the solvus, disclosing the stable phase relations. Based on the Gibbs energy minimization, phase diagrams can be predicted for the binary and higher order systems, provided the component subsystems are thermodynamically assessed beforehand. In conclusion, to move forward beyond e.g. non-isomorphous simple eutectic systems, methods using Gibbs free energy minimization from a fundamental point-of-view such as CALPHAD are essential.

Synchronization of the mammalian central and peripheral circadian clocks

The circadian clock is an endogenous, self-sustained biological rhythm. Different organisms possess different period of the circadian clock, ranging from 20 to 28 h. Synchronizations of the circadian clock contribute to the organisms’ fitness. This synchrony refers not only to the synchronization between the body clock and the environment, but also to that between the central and peripheral clocks. The synchronization is a process that the organism’s circadian clock is reset by the outside environment. Being synchronized often makes the organism oscillate in a period of 24 h, that of the earth’s rotation. More importantly, being synchronized changes the phase of the organism’s clock, for example activity onset, to a stable phase relationship to the environmental time cues, like the sunrise. Pittendrigh had raised the phase response curve (PRC) model to explain how light synchronizes the circadian clock by phase shifting the clock. His PRC model successfully predicts entrainment on the basis of period changes. Light pulse is considered as the most effective zeitgeber that can synchronize an organism’s circadian clock. Phase response curves show distinct similarities from diverse organisms, including both diurnal and nocturnal animals. Better understanding on these synchronizations are built on recent advances in the following aspects, the molecular feedback loops, the novel photoreceptor melanopsin and its expressing cells, and the hierarchical structures constituting the mammalian clock system. This review summarizes recent progresses on topics of the synchronizations of both the body clock and the environment, and the central and peripheral clocks. It discusses how light and food cues mediate the synchronization of the clock system, followed with introducing main human disorders in which desynchronized body clocks are involved. Light pulse transmits the environmental time cues to the suprachiasmatic nucleus (SCN) through the retino-hypothalamic tract (RHT). SCN is located in the hypothalamus and serves as the central oscillator in mammals. Food is another important zeitgeber that synchronizes the circadian clock. Feeding behavior passes the timing information to the central oscillator, SCN, by taking advantages of the circulating hormones and metabolites. After receiving information from either light or food, SCN integrates the information and passes them along to peripheral clocks that locate in different organs, finally reaching to a coherent circadian system for the entire multicellular organism. Therefore, this review offers basic knowledge to further researches on the clock synchronization, and expects people understand that keeping our body clocks in synchrony is important to our health.

Features of Pc5 pulsations in the geomagnetic field, auroral luminosity, and Riometer absorption

Simultaneous morning Pc5 pulsations (f ~ 3–5 mHz) in the geomagnetic field, aurora intensities (in the 557.7 and 630.0 nm oxygen emissions and the 471.0 nm nitrogen emission), and riometer absorption, were studied based on the CARISMA, CANMOS, and NORSTAR network data for the event of January 1, 2000. According to the GOES-8 satellite observations, these Pc5 geomagnetic pulsations are observed as incompressible Alfven waves with toroidal polarization in the magnetosphere. Although the Pc5 pulsation frequencies in auroras, the geomagnetic field, and riometer absorption are close to one another, stable phase relationships are not observed between them. Far from all trains of geomagnetic Pc5 pulsations are accompanied by corresponding auroral pulsations; consequently, geomagnetic pulsations are primary with respect to auroral pulsations. Both geomagnetic and auroral pulsations propagate poleward, and the frequency decreases with increasing geomagnetic latitude. When auroral Pc5 pulsations appear, the ratio of the 557.7/630.0 nm emission intensity sharply increases, which indicates that auroral pulsations result from not simply modulated particle precipitation but also an additional periodic acceleration of auroral electrons by the wave field. A high correlation is not observed between Pc5 pulsations in auroras and the riometer absorption, which indicates that these pulsations have a common source but different generation mechanisms. Auroral luminosity modulation is supposedly related to the interaction between Alfven waves and the region with the field-aligned potential drop above the auroral ionosphere, and riometer absorption modulation is caused by the scattering of energetic electrons by VLF noise pulsations.