The transition to chaotic phase synchronization
NASA Astrophysics Data System (ADS)
Mosekilde, E.; Laugesen, J. L.; Zhusubaliyev, Zh. T.
2012-08-01
The transition to chaotic phase synchronization for a periodically driven spiral-type chaotic oscillator is known to involve a dense set of saddle-node bifurcations. By following the synchronization transition through the cascade of period-doubling bifurcations in a forced Rössler system, this paper describes how these saddle-node bifurcations arise and how their characteristic cyclic organisation develops. We identify the cycles that are involved in the various saddle-node bifurcations and descibe how the formation of multi-layered resonance cycles in the synchronization domain is related to the torus doubling bifurcations that take place outside this domain. By examining a physiology-based model of the blood flow regulation to the individual functional unit (nephron) of the kidney we demonstrate how a similar bifurcation structure may arise in this system as a response to a periodically varying arterial blood pressure. The paper finally discusses how an alternative transition to chaotic phase synchronization may occur in the mutual synchronization of two chaotically oscillating period-doubling systems.
Explosive transitions to synchronization in networks of phase oscillators
Leyva, I.; Navas, A.; Sendiña-Nadal, I.; Almendral, J. A.; Buldú, J. M.; Zanin, M.; Papo, D.; Boccaletti, S.
2013-01-01
The emergence of dynamical abrupt transitions in the macroscopic state of a system is currently a subject of the utmost interest. The occurrence of a first-order phase transition to synchronization of an ensemble of networked phase oscillators was reported, so far, for very particular network architectures. Here, we show how a sharp, discontinuous transition can occur, instead, as a generic feature of networks of phase oscillators. Precisely, we set conditions for the transition from unsynchronized to synchronized states to be first-order, and demonstrate how these conditions can be attained in a very wide spectrum of situations. We then show how the occurrence of such transitions is always accompanied by the spontaneous setting of frequency-degree correlation features. Third, we show that the conditions for abrupt transitions can be even softened in several cases. Finally, we discuss, as a possible application, the use of this phenomenon to express magnetic-like states of synchronization. PMID:23412391
Phase synchronization in the cochlea at transition from mechanical waves to electrical spikes
NASA Astrophysics Data System (ADS)
Bader, Rolf
2015-10-01
Measured auditory nervous spikes often show synchronization, phase-locking, or entrainment (P. Cariani, Neural Plast. 6(4), 142-172 (1999) and Kumaresana et al., J. Acoust. Soc. Am. 133(6), 4290-4310 (2013). Physiologically synchronization is found in the anteroventral cochlear nucleus (Joris et al., J. Neurophysiol. 71(3), 1022-1036 (1994)) or in the trapezoid body also between critical bandwidths (Louage et al., Auditory Signal Processing: Physiology, Psychoacoustics, and Models (Springer, New York, 2004), pp. 100-106). The effect is an enhancement of pitch detection, spatial localization, or speech intelligibility. To investigate the presence of synchronization already in the cochlea, in the present paper, a finite-difference time-domain model of the cochlea is implemented with conditions for spike excitation caused by mechanical basilar membrane displacement. This model shows synchronization already in the cochlea at the transition from mechanical waves to nerve spike excitation. Using a sound as model input consisting of ten harmonic overtones with random phase relations, the output spikes are strongly phase aligned after this transition. When using a two-sinusoidal complex as input, and altering the phase relations between the two sinusoidals, the output spikes show the higher sinusoidal shifting the phase of the lower one in its direction in a systematic way. Therefore, already during the transition from mechanical to electrical excitation within the cochlea, synchronization appears to be improving perception of pitch, speech, or localization.
Phase synchronization in the cochlea at transition from mechanical waves to electrical spikes.
Bader, Rolf
2015-10-01
Measured auditory nervous spikes often show synchronization, phase-locking, or entrainment (P. Cariani, Neural Plast. 6(4), 142-172 (1999) and Kumaresana et al., J. Acoust. Soc. Am. 133(6), 4290-4310 (2013). Physiologically synchronization is found in the anteroventral cochlear nucleus (Joris et al., J. Neurophysiol. 71(3), 1022-1036 (1994)) or in the trapezoid body also between critical bandwidths (Louage et al., Auditory Signal Processing: Physiology, Psychoacoustics, and Models (Springer, New York, 2004), pp. 100-106). The effect is an enhancement of pitch detection, spatial localization, or speech intelligibility. To investigate the presence of synchronization already in the cochlea, in the present paper, a finite-difference time-domain model of the cochlea is implemented with conditions for spike excitation caused by mechanical basilar membrane displacement. This model shows synchronization already in the cochlea at the transition from mechanical waves to nerve spike excitation. Using a sound as model input consisting of ten harmonic overtones with random phase relations, the output spikes are strongly phase aligned after this transition. When using a two-sinusoidal complex as input, and altering the phase relations between the two sinusoidals, the output spikes show the higher sinusoidal shifting the phase of the lower one in its direction in a systematic way. Therefore, already during the transition from mechanical to electrical excitation within the cochlea, synchronization appears to be improving perception of pitch, speech, or localization. PMID:26520090
Synchronization transition of identical phase oscillators in a directed small-world network.
Tönjes, Ralf; Masuda, Naoki; Kori, Hiroshi
2010-09-01
We numerically study a directed small-world network consisting of attractively coupled, identical phase oscillators. While complete synchronization is always stable, it is not always reachable from random initial conditions. Depending on the shortcut density and on the asymmetry of the phase coupling function, there exists a regime of persistent chaotic dynamics. By increasing the density of shortcuts or decreasing the asymmetry of the phase coupling function, we observe a discontinuous transition in the ability of the system to synchronize. Using a control technique, we identify the bifurcation scenario of the order parameter. We also discuss the relation between dynamics and topology and remark on the similarity of the synchronization transition to directed percolation. PMID:20887048
NASA Astrophysics Data System (ADS)
Bartsch, Ronny P.; Ivanov, Plamen Ch.
2012-02-01
Recent studies have focused on various features of cardiac and respiratory dynamics with the aim to better understand key aspects of the underlying neural control of these systems. We investigate how sleep influences cardio-respiratory coupling, and how the degree of this coupling changes with transitions across sleep stages in healthy young and elderly subjects. We analyze full night polysomnographic recordings of 189 healthy subjects (age range: 20 to 90 years). To probe cardio-respiratory coupling, we apply a novel phase synchronization analysis method to quantify the adjustment of rhythms between heartbeat and breathing signals. We investigate how cardio-respiratory synchronization changes with sleep-stage transitions and under healthy aging. We find a statistically significant difference in the degree of cardio-respiratory synchronization during different sleep stages for both young and elderly subjects and a significant decline of synchronization with age. This is a first evidence of how sleep regulation and aging influence a key nonlinear mechanism of physiologic coupling as quantified by the degree of phase synchronization between the cardiac and respiratory systems, which is of importance to develop adequate modeling approaches.
NASA Astrophysics Data System (ADS)
Teodorescu, Razvan
2009-10-01
Systems of oscillators coupled non-linearly (stochastically or not) are ubiquitous in nature and can explain many complex phenomena: coupled Josephson junction arrays, cardiac pacemaker cells, swarms or flocks of insects and birds, etc. They are know to have a non-trivial phase diagram, which includes chaotic, partially synchronized, and fully synchronized phases. A traditional model for this class of problems is the Kuramoto system of oscillators, which has been studied extensively for the last three decades. The model is a canonical example for non-equilibrium, dynamical phase transitions, so little understood in physics. From a stochastic analysis point of view, the transition is described by the large deviations principle, which offers little information on the scaling behavior near the critical point. I will discuss a special case of the model, which allows a rigorous analysis of the critical properties of the model, and reveals a new, anomalous scaling behavior in the vicinity of the critical point.
Robust spin crossover platforms with synchronized spin switch and polymer phase transition
Novio, F.; Evangelio, E.; Vazquez-Mera, N.; González-Monje, P.; Bellido, E.; Mendes, S.; Kehagias, N.; Ruiz-Molina, D.
2013-01-01
The idea of developing magnetic molecular materials into real functional electronic devices with low-cost and scalable techniques appeared with the emergence of the field several years ago. Today, even though great advances have been done with this aim, the promise of a functional device working at the micro-/nanoscale and at room temperature has unfortunately not completely materialized yet, as their use still strongly depends on the fabrication methodology of a robust device that can be handled and integrated without compromising their functionality. Here we propose the use of polymeric matrices as a platform for the development of such robust switchable structures exhibiting reproducible results independently of the dimension -from macro to micro-/nanoscale- and morphology -from thin-films to nanoparticles and nanoimprinted motives- while allowing to induce an irreversible hysteresis, reminiscent of a non-volatile memory, by synchronization with the polymer phase transition.
The prisoner's dilemma with semi-synchronous updates: evidence for a first-order phase transition
NASA Astrophysics Data System (ADS)
Ali Saif, M.; Gade, Prashant M.
2009-07-01
The emergence of cooperation in self-centered individuals has been a major puzzle in the study of evolutionary ethics. Reciprocal altruism is one of the explanations put forward and the prisoner's dilemma has been a paradigm in this context. The emergence of cooperation was demonstrated for the prisoner's dilemma on a lattice with synchronous update. However, the cooperation disappeared for asynchronous update and the general validity of the conclusions was questioned. Neither synchronous nor asynchronous updates are realistic for natural systems. In this paper, we make a detailed study of a more realistic system of semi-synchronous updates where pN agents are updated at every time instant. We observe a transition from an all-defector state to a mixed state as a function of p. Our studies indicate that despite it being a transition from an absorbing state, it is a first-order transition. Furthermore, we used a damage spreading technique to demonstrate that the transition in this system could be classified as a frozen-chaotic transition.
Noise-induced transitions in optomechanical synchronization
NASA Astrophysics Data System (ADS)
Weiss, Talitha; Kronwald, Andreas; Marquardt, Florian
2016-01-01
We study how quantum and thermal noise affects synchronization of two optomechanical limit-cycle oscillators. Classically, in the absence of noise, optomechanical systems tend to synchronize either in-phase or anti-phase. Taking into account the fundamental quantum noise, we find a regime where fluctuations drive transitions between these classical synchronization states. We investigate how this ‘mixed’ synchronization regime emerges from the noiseless system by studying the classical-to-quantum crossover and we show how the time scales of the transitions vary with the effective noise strength. In addition, we compare the effects of thermal noise to the effects of quantum noise.
Transition from synchronous to asynchronous superfluid phase slippage in an aperture array
Sato, Y.; Hoskinson, E.; Packard, R. E.
2006-10-01
We have investigated the dynamics of superfluid phase slippage in an array of apertures. The magnitude of the dissipative phase slips shows that they occur simultaneously in all the apertures when the temperature is near T{sub {lambda}}-T{approx_equal}10 mK and subsequently lose their simultaneity as the temperature is lowered. We describe three experiments to probe the mechanisms underlying the synchronous behavior. The results raise fundamental questions about the dynamics of phase slippage in a multiply connected geometry.
Spontaneous phase transition from free flow to synchronized flow in traffic on a single-lane highway
NASA Astrophysics Data System (ADS)
Jin, Cheng-Jie; Wang, Wei; Jiang, Rui; Zhang, H. M.; Wang, Hao
2013-01-01
Traffic flow complexity comes from the car-following and lane-changing behavior. Based on empirical data for individual vehicle speeds and time headways measured on a single-lane highway section, we have studied the traffic flow properties induced by pure car-following behavior. We have found that a spontaneous sudden drop in velocity could happen in a platoon of vehicles when the velocity of the leading vehicle is quite high (˜70 km/h). In contrast, when the velocity of the leading vehicle in a platoon slows down, such a spontaneous sudden drop of velocity has not been observed. Our finding indicates that traffic breakdown on a single-lane road might be a phase transition from free flow to synchronized flow (F→S transition). We have found that the flow rate within the emergent synchronized flow can be either smaller or larger than the flow rate in the free flow within which the synchronized flow propagates. Our empirical findings support Kerner's three-phase theory in which traffic breakdown is associated with an F→S transition.
Explosive synchronization transitions in complex neural networks
NASA Astrophysics Data System (ADS)
Chen, Hanshuang; He, Gang; Huang, Feng; Shen, Chuansheng; Hou, Zhonghuai
2013-09-01
It has been recently reported that explosive synchronization transitions can take place in networks of phase oscillators [Gómez-Gardeñes et al. Phys. Rev. Lett. 106, 128701 (2011)] and chaotic oscillators [Leyva et al. Phys. Rev. Lett. 108, 168702 (2012)]. Here, we investigate the effect of a microscopic correlation between the dynamics and the interacting topology of coupled FitzHugh-Nagumo oscillators on phase synchronization transition in Barabási-Albert (BA) scale-free networks and Erdös-Rényi (ER) random networks. We show that, if natural frequencies of the oscillations are positively correlated with node degrees and the width of the frequency distribution is larger than a threshold value, a strong hysteresis loop arises in the synchronization diagram of BA networks, indicating the evidence of an explosive transition towards synchronization of relaxation oscillators system. In contrast to the results in BA networks, in more homogeneous ER networks, the synchronization transition is always of continuous type regardless of the width of the frequency distribution. Moreover, we consider the effect of degree-mixing patterns on the nature of the synchronization transition, and find that the degree assortativity is unfavorable for the occurrence of such an explosive transition.
NASA Astrophysics Data System (ADS)
Parihar, Abhinav; Shukla, Nikhil; Datta, Suman; Raychowdhury, Arijit
2015-02-01
Computing with networks of synchronous oscillators has attracted wide-spread attention as novel materials and device topologies have enabled realization of compact, scalable and low-power coupled oscillatory systems. Of particular interest are compact and low-power relaxation oscillators that have been recently demonstrated using MIT (metal-insulator-transition) devices using properties of correlated oxides. Further the computational capability of pairwise coupled relaxation oscillators has also been shown to outperform traditional Boolean digital logic circuits. This paper presents an analysis of the dynamics and synchronization of a system of two such identical coupled relaxation oscillators implemented with MIT devices. We focus on two implementations of the oscillator: (a) a D-D configuration where complementary MIT devices (D) are connected in series to provide oscillations and (b) a D-R configuration where it is composed of a resistor (R) in series with a voltage-triggered state changing MIT device (D). The MIT device acts like a hysteresis resistor with different resistances in the two different states. The synchronization dynamics of such a system has been analyzed with purely charge based coupling using a resistive (RC) and a capacitive (CC) element in parallel. It is shown that in a D-D configuration symmetric, identical and capacitively coupled relaxation oscillator system synchronizes to an anti-phase locking state, whereas when coupled resistively the system locks in phase. Further, we demonstrate that for certain range of values of RC and CC, a bistable system is possible which can have potential applications in associative computing. In D-R configuration, we demonstrate the existence of rich dynamics including non-monotonic flows and complex phase relationship governed by the ratios of the coupling impedance. Finally, the developed theoretical formulations have been shown to explain experimentally measured waveforms of such pairwise coupled
Clustering versus non-clustering phase synchronizations.
Liu, Shuai; Zhan, Meng
2014-03-01
Clustering phase synchronization (CPS) is a common scenario to the global phase synchronization of coupled dynamical systems. In this work, a novel scenario, the non-clustering phase synchronization (NPS), is reported. It is found that coupled systems do not transit to the global synchronization until a certain sufficiently large coupling is attained, and there is no clustering prior to the global synchronization. To reveal the relationship between CPS and NPS, we further analyze the noise effect on coupled phase oscillators and find that the coupled oscillator system can change from CPS to NPS with the increase of noise intensity or system disorder. These findings are expected to shed light on the mechanism of various intriguing self-organized behaviors in coupled systems. PMID:24697366
Clustering versus non-clustering phase synchronizations
Liu, Shuai; Zhan, Meng
2014-03-15
Clustering phase synchronization (CPS) is a common scenario to the global phase synchronization of coupled dynamical systems. In this work, a novel scenario, the non-clustering phase synchronization (NPS), is reported. It is found that coupled systems do not transit to the global synchronization until a certain sufficiently large coupling is attained, and there is no clustering prior to the global synchronization. To reveal the relationship between CPS and NPS, we further analyze the noise effect on coupled phase oscillators and find that the coupled oscillator system can change from CPS to NPS with the increase of noise intensity or system disorder. These findings are expected to shed light on the mechanism of various intriguing self-organized behaviors in coupled systems.
NASA Astrophysics Data System (ADS)
Pikovsky, Arkady; Rosenblum, Michael; Kurths, Jürgen
2003-04-01
Preface; 1. Introduction; Part I. Synchronization Without Formulae: 2. Basic notions: the self-sustained oscillator and its phase; 3. Synchronization of a periodic oscillator by external force; 4. Synchronization of two and many oscillators; 5. Synchronization of chaotic systems; 6. Detecting synchronization in experiments; Part II. Phase Locking and Frequency Entrainment: 7. Synchronization of periodic oscillators by periodic external action; 8. Mutual synchronization of two interacting periodic oscillators; 9. Synchronization in the presence of noise; 10. Phase synchronization of chaotic systems; 11. Synchronization in oscillatory media; 12. Populations of globally coupled oscillators; Part III. Synchronization of Chaotic Systems: 13. Complete synchronization I: basic concepts; 14. Complete synchronization II: generalizations and complex systems; 15. Synchronization of complex dynamics by external forces; Appendix 1. Discovery of synchronization by Christiaan Huygens; Appendix 2. Instantaneous phase and frequency of a signal; References; Index.
NASA Astrophysics Data System (ADS)
Gitterman, Moshe
2014-09-01
In discussing phase transitions, the first thing that we have to do is to define a phase. This is a concept from thermodynamics and statistical mechanics, where a phase is defined as a homogeneous system. As a simple example, let us consider instant coffee. This consists of coffee powder dissolved in water, and after stirring it we have a homogeneous mixture, i.e., a single phase. If we add to a cup of coffee a spoonful of sugar and stir it well, we still have a single phase -- sweet coffee. However, if we add ten spoonfuls of sugar, then the contents of the cup will no longer be homogeneous, but rather a mixture of two homogeneous systems or phases, sweet liquid coffee on top and coffee-flavored wet sugar at the bottom...
Synchronization and Phase Dynamics of Oscillating Foils
NASA Astrophysics Data System (ADS)
Finkel, Cyndee L.
In this work, a two-dimensional model representing the vortices that animals produce, when they are ying/swimming, was constructed. A D{shaped cylinder and an oscillating airfoil were used to mimic these body{shed and wing{generated vortices, respectively. The parameters chosen are based on the Reynolds numbers similar to that which is observed in nature (˜10 4). In order to imitate the motion of ying/swimming, the entire system was suspended into a water channel from frictionless air{bearings. The position of the apparatus in the channel was regulated with a linear, closed loop PI controller. Thrust/drag forces were measured with strain gauges and particle image velocimetry (PIV) was used to examine the wake structure that develops. The Strouhal number of the oscillating airfoil was compared to the values observed in nature as the system transitions between the accelerated and steady states. The results suggest that self-regulation restricts the values of the Strouhal number to a certain range where no other external sensory input is necessary. As suggested by previous work, this self-regulation is a result of a limit cycle process that stems from nonlinear periodic oscillations. The limit cycles were used to examine the synchronous conditions due to the coupling of the foil and wake vortices. Noise is a factor that can mask details of the synchronization. In order to control its effect, we study the locking conditions using an analytic technique that only considers the phases. Our results show that the phase locking indices are dependent on the Strouhal value as it converges to a frequency locking ratio of ≃0:5. This indicates that synchronization occurs during cruising between the motion of the foil and the measured thrust/drag response of the uid forces. The results suggest that Strouhal number selection in steady forward natural swimming and ying is the result of a limit cycle process and not actively controlled by an organism. An implication of this is
Markers of criticality in phase synchronization
Botcharova, Maria; Farmer, Simon F.; Berthouze, Luc
2014-01-01
The concept of the brain as a critical dynamical system is very attractive because systems close to criticality are thought to maximize their dynamic range of information processing and communication. To date, there have been two key experimental observations in support of this hypothesis: (i) neuronal avalanches with power law distribution of size and (ii) long-range temporal correlations (LRTCs) in the amplitude of neural oscillations. The case for how these maximize dynamic range of information processing and communication is still being made and because a significant substrate for information coding and transmission is neural synchrony it is of interest to link synchronization measures with those of criticality. We propose a framework for characterizing criticality in synchronization based on an analysis of the moment-to-moment fluctuations of phase synchrony in terms of the presence of LRTCs. This framework relies on an estimation of the rate of change of phase difference and a set of methods we have developed to detect LRTCs. We test this framework against two classical models of criticality (Ising and Kuramoto) and recently described variants of these models aimed to more closely represent human brain dynamics. From these simulations we determine the parameters at which these systems show evidence of LRTCs in phase synchronization. We demonstrate proof of principle by analysing pairs of human simultaneous EEG and EMG time series, suggesting that LRTCs of corticomuscular phase synchronization can be detected in the resting state and experimentally manipulated. The existence of LRTCs in fluctuations of phase synchronization suggests that these fluctuations are governed by non-local behavior, with all scales contributing to system behavior. This has important implications regarding the conditions under which one should expect to see LRTCs in phase synchronization. Specifically, brain resting states may exhibit LRTCs reflecting a state of readiness facilitating
Synchronization transition in gap-junction-coupled leech neurons
NASA Astrophysics Data System (ADS)
Wang, Qingyun; Duan, Zhisheng; Feng, Zhaosheng; Chen, Guanrong; Lu, Qishao
2008-07-01
Real neurons can exhibit various types of firings including tonic spiking, bursting as well as silent state, which are frequently observed in neuronal electrophysiological experiments. More interestingly, it is found that neurons can demonstrate the co-existing mode of stable tonic spiking and bursting, which depends on initial conditions. In this paper, synchronization in gap-junction-coupled neurons with co-existing attractors of spiking and bursting firings is investigated as the coupling strength gets increased. Synchronization transitions can be identified by means of the bifurcation diagram and the correlation coefficient. It is illustrated that the coupled neurons can exhibit different types of synchronization transitions between spiking and bursting when the coupling strength increases. In the course of synchronization transitions, an intermittent synchronization can be observed. These results may be instructive to understand synchronization transitions in neuronal systems.
Phase synchronization of neuronal noise in mouse hippocampal epileptiform dynamics.
Serletis, Demitre; Carlen, Peter L; Valiante, Taufik A; Bardakjian, Berj L
2013-02-01
Organized brain activity is the result of dynamical, segregated neuronal signals that may be used to investigate synchronization effects using sophisticated neuroengineering techniques. Phase synchrony analysis, in particular, has emerged as a promising methodology to study transient and frequency-specific coupling effects across multi-site signals. In this study, we investigated phase synchronization in intracellular recordings of interictal and ictal epileptiform events recorded from pairs of cells in the whole (intact) mouse hippocampus. In particular, we focused our analysis on the background noise-like activity (NLA), previously reported to exhibit complex neurodynamical properties. Our results show evidence for increased linear and nonlinear phase coupling in NLA across three frequency bands [theta (4-10 Hz), beta (12-30 Hz) and gamma (30-80 Hz)] in the ictal compared to interictal state dynamics. We also present qualitative and statistical evidence for increased phase synchronization in the theta, beta and gamma frequency bands from paired recordings of ictal NLA. Overall, our results validate the use of background NLA in the neurodynamical study of epileptiform transitions and suggest that what is considered "neuronal noise" is amenable to synchronization effects in the spatiotemporal domain. PMID:23273129
Phase synchronization of instrumental music signals
NASA Astrophysics Data System (ADS)
Mukherjee, Sayan; Palit, Sanjay Kumar; Banerjee, Santo; Ariffin, M. R. K.; Bhattacharya, D. K.
2014-06-01
Signal analysis is one of the finest scientific techniques in communication theory. Some quantitative and qualitative measures describe the pattern of a music signal, vary from one to another. Same musical recital, when played by different instrumentalists, generates different types of music patterns. The reason behind various patterns is the psycho-acoustic measures - Dynamics, Timber, Tonality and Rhythm, varies in each time. However, the psycho-acoustic study of the music signals does not reveal any idea about the similarity between the signals. For such cases, study of synchronization of long-term nonlinear dynamics may provide effective results. In this context, phase synchronization (PS) is one of the measures to show synchronization between two non-identical signals. In fact, it is very critical to investigate any other kind of synchronization for experimental condition, because those are completely non identical signals. Also, there exists equivalence between the phases and the distances of the diagonal line in Recurrence plot (RP) of the signals, which is quantifiable by the recurrence quantification measure τ-recurrence rate. This paper considers two nonlinear music signals based on same raga played by two eminent sitar instrumentalists as two non-identical sources. The psycho-acoustic study shows how the Dynamics, Timber, Tonality and Rhythm vary for the two music signals. Then, long term analysis in the form of phase space reconstruction is performed, which reveals the chaotic phase spaces for both the signals. From the RP of both the phase spaces, τ-recurrence rate is calculated. Finally by the correlation of normalized tau-recurrence rate of their 3D phase spaces and the PS of the two music signals has been established. The numerical results well support the analysis.
Synchronization of phase oscillators with frequency-weighted coupling
NASA Astrophysics Data System (ADS)
Xu, Can; Sun, Yuting; Gao, Jian; Qiu, Tian; Zheng, Zhigang; Guan, Shuguang
2016-02-01
Recently, the first-order synchronization transition has been studied in systems of coupled phase oscillators. In this paper, we propose a framework to investigate the synchronization in the frequency-weighted Kuramoto model with all-to-all couplings. A rigorous mean-field analysis is implemented to predict the possible steady states. Furthermore, a detailed linear stability analysis proves that the incoherent state is only neutrally stable below the synchronization threshold. Nevertheless, interestingly, the amplitude of the order parameter decays exponentially (at least for short time) in this regime, resembling the Landau damping effect in plasma physics. Moreover, the explicit expression for the critical coupling strength is determined by both the mean-field method and linear operator theory. The mechanism of bifurcation for the incoherent state near the critical point is further revealed by the amplitude expansion theory, which shows that the oscillating standing wave state could also occur in this model for certain frequency distributions. Our theoretical analysis and numerical results are consistent with each other, which can help us understand the synchronization transition in general networks with heterogenous couplings.
Synchronization of phase oscillators with frequency-weighted coupling.
Xu, Can; Sun, Yuting; Gao, Jian; Qiu, Tian; Zheng, Zhigang; Guan, Shuguang
2016-01-01
Recently, the first-order synchronization transition has been studied in systems of coupled phase oscillators. In this paper, we propose a framework to investigate the synchronization in the frequency-weighted Kuramoto model with all-to-all couplings. A rigorous mean-field analysis is implemented to predict the possible steady states. Furthermore, a detailed linear stability analysis proves that the incoherent state is only neutrally stable below the synchronization threshold. Nevertheless, interestingly, the amplitude of the order parameter decays exponentially (at least for short time) in this regime, resembling the Landau damping effect in plasma physics. Moreover, the explicit expression for the critical coupling strength is determined by both the mean-field method and linear operator theory. The mechanism of bifurcation for the incoherent state near the critical point is further revealed by the amplitude expansion theory, which shows that the oscillating standing wave state could also occur in this model for certain frequency distributions. Our theoretical analysis and numerical results are consistent with each other, which can help us understand the synchronization transition in general networks with heterogeneous couplings. PMID:26903110
Synchronization of phase oscillators with frequency-weighted coupling
Xu, Can; Sun, Yuting; Gao, Jian; Qiu, Tian; Zheng, Zhigang; Guan, Shuguang
2016-01-01
Recently, the first-order synchronization transition has been studied in systems of coupled phase oscillators. In this paper, we propose a framework to investigate the synchronization in the frequency-weighted Kuramoto model with all-to-all couplings. A rigorous mean-field analysis is implemented to predict the possible steady states. Furthermore, a detailed linear stability analysis proves that the incoherent state is only neutrally stable below the synchronization threshold. Nevertheless, interestingly, the amplitude of the order parameter decays exponentially (at least for short time) in this regime, resembling the Landau damping effect in plasma physics. Moreover, the explicit expression for the critical coupling strength is determined by both the mean-field method and linear operator theory. The mechanism of bifurcation for the incoherent state near the critical point is further revealed by the amplitude expansion theory, which shows that the oscillating standing wave state could also occur in this model for certain frequency distributions. Our theoretical analysis and numerical results are consistent with each other, which can help us understand the synchronization transition in general networks with heterogenous couplings. PMID:26903110
Multivariate singular spectrum analysis and the road to phase synchronization
NASA Astrophysics Data System (ADS)
Groth, Andreas; Ghil, Michael
2010-05-01
Singular spectrum analysis (SSA) and multivariate SSA (M-SSA) are based on the classical work of Kosambi (1943), Loeve (1945) and Karhunen (1946) and are closely related to principal component analysis. They have been introduced into information theory by Bertero, Pike and co-workers (1982, 1984) and into dynamical systems analysis by Broomhead and King (1986a,b). Ghil, Vautard and associates have applied SSA and M-SSA to the temporal and spatio-temporal analysis of short and noisy time series in climate dynamics and other fields in the geosciences since the late 1980s. M-SSA provides insight into the unknown or partially known dynamics of the underlying system by decomposing the delay-coordinate phase space of a given multivariate time series into a set of data-adaptive orthonormal components. These components can be classified essentially into trends, oscillatory patterns and noise, and allow one to reconstruct a robust "skeleton" of the dynamical system's structure. For an overview we refer to Ghil et al. (Rev. Geophys., 2002). In this talk, we present M-SSA in the context of synchronization analysis and illustrate its ability to unveil information about the mechanisms behind the adjustment of rhythms in coupled dynamical systems. The focus of the talk is on the special case of phase synchronization between coupled chaotic oscillators (Rosenblum et al., PRL, 1996). Several ways of measuring phase synchronization are in use, and the robust definition of a reasonable phase for each oscillator is critical in each of them. We illustrate here the advantages of M-SSA in the automatic identification of oscillatory modes and in drawing conclusions about the transition to phase synchronization. Without using any a priori definition of a suitable phase, we show that M-SSA is able to detect phase synchronization in a chain of coupled chaotic oscillators (Osipov et al., PRE, 1996). Recently, Muller et al. (PRE, 2005) and Allefeld et al. (Intl. J. Bif. Chaos, 2007) have
NASA Astrophysics Data System (ADS)
Gu, Hua-Guang; Chen, Sheng-Gen; Li, Yu-Ye
2015-05-01
We investigated the synchronization dynamics of a coupled neuronal system composed of two identical Chay model neurons. The Chay model showed coexisting period-1 and period-2 bursting patterns as a parameter and initial values are varied. We simulated multiple periodic and chaotic bursting patterns with non-(NS), burst phase (BS), spike phase (SS), complete (CS), and lag synchronization states. When the coexisting behavior is near period-2 bursting, the transitions of synchronization states of the coupled system follows very complex transitions that begins with transitions between BS and SS, moves to transitions between CS and SS, and to CS. Most initial values lead to the CS state of period-2 bursting while only a few lead to the CS state of period-1 bursting. When the coexisting behavior is near period-1 bursting, the transitions begin with NS, move to transitions between SS and BS, to transitions between SS and CS, and then to CS. Most initial values lead to the CS state of period-1 bursting but a few lead to the CS state of period-2 bursting. The BS was identified as chaos synchronization. The patterns for NS and transitions between BS and SS are insensitive to initial values. The patterns for transitions between CS and SS and the CS state are sensitive to them. The number of spikes per burst of non-CS bursting increases with increasing coupling strength. These results not only reveal the initial value- and parameter-dependent synchronization transitions of coupled systems with coexisting behaviors, but also facilitate interpretation of various bursting patterns and synchronization transitions generated in the nervous system with weak coupling strength. Project supported by the National Natural Science Foundation of China (Grant Nos. 11372224 and 11402039) and the Fundamental Research Funds for Central Universities designated to Tongji University (Grant No. 1330219127).
Explosive Synchronization Transitions in Scale-Free Networks
NASA Astrophysics Data System (ADS)
Gómez-Gardeñes, Jesús; Gómez, Sergio; Arenas, Alex; Moreno, Yamir
2011-03-01
Explosive collective phenomena have attracted much attention since the discovery of an explosive percolation transition. In this Letter, we demonstrate how an explosive transition shows up in the synchronization of scale-free networks by incorporating a microscopic correlation between the structural and the dynamical properties of the system. The characteristics of the explosive transition are analytically studied in a star graph reproducing the results obtained in synthetic networks. Our findings represent the first abrupt synchronization transition in complex networks and provide a deeper understanding of the microscopic roots of explosive critical phenomena.
Holographic magnetic phase transition
Lifschytz, Gilad; Lippert, Matthew
2009-09-15
We study four-dimensional interacting fermions in a strong magnetic field, using the holographic Sakai-Sugimoto model of intersecting D4- and D8-branes in the deconfined, chiral-symmetric parallel phase. We find that as the magnetic field is varied, while staying in the parallel phase, the fermions exhibit a first-order phase transition in which their magnetization jumps discontinuously. Properties of this transition are consistent with a picture in which some of the fermions jump to the lowest Landau level. Similarities to known magnetic phase transitions are discussed.
Burst synchronization transitions in a neuronal network of subnetworks
NASA Astrophysics Data System (ADS)
Sun, Xiaojuan; Lei, Jinzhi; Perc, Matjaž; Kurths, Jürgen; Chen, Guanrong
2011-03-01
In this paper, the transitions of burst synchronization are explored in a neuronal network consisting of subnetworks. The studied network is composed of electrically coupled bursting Hindmarsh-Rose neurons. Numerical results show that two types of burst synchronization transitions can be induced not only by the variations of intra- and intercoupling strengths but also by changing the probability of random links between different subnetworks and the number of subnetworks. Furthermore, we find that the underlying mechanisms for these two bursting synchronization transitions are different: one is due to the change of spike numbers per burst, while the other is caused by the change of the bursting type. Considering that changes in the coupling strengths and neuronal connections are closely interlaced with brain plasticity, the presented results could have important implications for the role of the brain plasticity in some functional behavior that are associated with synchronization.
Synthesis and evaluation of phase detectors for active bit synchronizers
NASA Technical Reports Server (NTRS)
Mcbride, A. L.
1974-01-01
Self-synchronizing digital data communication systems usually use active or phase-locked loop (PLL) bit synchronizers. The three main elements of PLL synchronizers are the phase detector, loop filter, and the voltage controlled oscillator. Of these three elements, phase detector synthesis is the main source of difficulty, particularly when the received signals are demodulated square-wave signals. A phase detector synthesis technique is reviewed that provides a physically realizable design for bit synchronizer phase detectors. The development is based upon nonlinear recursive estimation methods. The phase detector portion of the algorithm is isolated and analyzed.
Synchronous Phase-Resolving Flash Range Imaging
NASA Technical Reports Server (NTRS)
Pain, Bedabrata; Hancock, Bruce
2007-01-01
An apparatus, now undergoing development, for range imaging based on measurement of the round-trip phase delay of a pulsed laser beam is described. The apparatus would operate in a staring mode. A pulsed laser would illuminate a target. Laser light reflected from the target would be imaged on a verylarge- scale integrated (VLSI)-circuit image detector, each pixel of which would contain a photodetector and a phase-measuring circuit. The round-trip travel time for the reflected laser light incident on each pixel, and thus the distance to the portion of the target imaged in that pixel, would be measured in terms of the phase difference between (1) the photodetector output pulse and (2) a local-oscillator signal that would have a frequency between 10 and 20 MHz and that would be synchronized with the laser-pulse-triggering signal.
Phase synchronized quasiperiodicity in power electronic inverter systems
NASA Astrophysics Data System (ADS)
Zhusubaliyev, Zhanybai T.; Mosekilde, Erik; Andriyanov, Alexey I.; Shein, Vladimir V.
2014-02-01
The development of switch-mode operated power electronic converter systems has provided a broad range of new effective approaches to the conversion of electric power. In this paper we describe the transitions from regular periodic operation to quasiperiodicity and high-periodic resonance behavior that can be observed in a pulse-width modulated DC/AC converter operating with high feedback gain. We demonstrate the occurrence of two different types of torus birth bifurcations and present a series of phase portraits illustrating the appearance of phase-synchronized quasiperiodicity. Our numerical findings are verified through comparison with an experimental inverter system. The results shed light on the transitions to quasiperiodicity and to various forms of three-frequency dynamics in non-smooth systems.
Network-complement transitions, symmetries, and cluster synchronization
NASA Astrophysics Data System (ADS)
Nishikawa, Takashi; Motter, Adilson E.
2016-09-01
Synchronization in networks of coupled oscillators is known to be largely determined by the spectral and symmetry properties of the interaction network. Here, we leverage this relation to study a class of networks for which the threshold coupling strength for global synchronization is the lowest among all networks with the same number of nodes and links. These networks, defined as being uniform, complete, and multi-partite (UCM), appear at each of an infinite sequence of network-complement transitions in a larger class of networks characterized by having near-optimal thresholds for global synchronization. We show that the distinct symmetry structure of the UCM networks, which by design are optimized for global synchronizability, often leads to formation of clusters of synchronous oscillators, and that such states can coexist with the state of global synchronization.
Photoinduced phase transitions.
Bennemann, K H
2011-02-23
Optically induced ultrafast electronic excitations with sufficiently long lifetimes may cause strong effects on phase transitions like structural and nonmetal→metal ones and on supercooling, supersaturation, etc. Examples are the transitions diamond→graphite, graphite→graphene, non-metal→metal, solid→liquid and vapor→liquid, solid. Photoinduced formation of graphene and water condensation of saturated or supersaturated vapor due to increased bonding amongst water molecules are of particular interest. These nonequilibrium transitions are an ultrafast response, on a few hundred fs time scale, to the fast low to large energy electronic excitations. The energy of the photons is converted into electronic energy via electronic excitations changing the cohesive energy. This changes the chemical potential controlling the phase transition. In view of the advances in laser optics photon induced transitions are expected to become an active area in nonequilibrium physics and phase transition dynamics. Conservation laws like energy or angular momentum conservation control the time during which the transitions occur. Since the photon induced effects result from weakening or strengthening of the bonding between the atoms or molecules transitions like solid/liquid, etc can be shifted in both directions. Photoinduced transitions will be discussed from a unified point of view. PMID:21411879
Sharp versus smooth synchronization transition of locally coupled oscillators
NASA Astrophysics Data System (ADS)
Ciszak, M.; Montina, A.; Arecchi, F. T.
2008-07-01
We provide a general condition for the occurrence of a sudden transition to synchronization in an array of oscillators mutually coupled via the nearest neighbors. At the onset of synchronization a specific constraint must be fulfilled: precisely, the response time of a single system to signals from the adjacent sites must be smaller than the refractory period. We verify this criterion in some models for neuronal dynamics, namely, in excitable systems driven by noise as well as in chaotic oscillators.
The comfortable driving model revisited: traffic phases and phase transitions
NASA Astrophysics Data System (ADS)
Knorr, Florian; Schreckenberg, Michael
2013-07-01
We study the spatiotemporal patterns resulting from different boundary conditions for a microscopic traffic model and contrast them with empirical results. By evaluating the time series of local measurements, the local traffic states are assigned to the different traffic phases of Kerner’s three-phase traffic theory. For this classification we use the rule-based FOTO-method, which provides ‘hard’ rules for this assignment. Using this approach, our analysis shows that the model is indeed able to reproduce three qualitatively different traffic phases: free flow (F), synchronized traffic (S), and wide moving jams (J). In addition, we investigate the likelihood of transitions between the three traffic phases. We show that a transition from free flow to a wide moving jam often involves an intermediate transition: first from free flow to synchronized flow and then from synchronized flow to a wide moving jam. This is supported by the fact that the so-called F → S transition (from free flow to synchronized traffic) is much more likely than a direct F → J transition. The model under consideration has a functional relationship between traffic flow and traffic density. The fundamental hypothesis of the three-phase traffic theory, however, postulates that the steady states of synchronized flow occupy a two-dimensional region in the flow-density plane. Due to the obvious discrepancy between the model investigated here and the postulate of the three-phase traffic theory, the good agreement that we found could not be expected. For a more detailed analysis, we also studied vehicle dynamics at a microscopic level and provide a comparison of real detector data with simulated data of the identical highway segment.
On precision of wavelet phase synchronization of chaotic systems
Postnikov, E. B.
2007-10-15
It is shown that time-scale synchronization of chaotic systems with ill-defined conventional phase is achieved by using wavelet transforms with center frequencies above a certain threshold value. It is found that the possibility of synchronization detection by introducing a wavelet phase is related to diffusion averaging of the analyzed signals.
NASA Astrophysics Data System (ADS)
Anderson, Gregory Wayne
An analytic treatment of the one Higgs doublet, electroweak phase transition is given. The phase transition is first order, occurs by the nucleation of thin walled bubbles, and completes at a temperature where the order parameter,
Anderson, G.W.
1991-09-16
An analytic treatment of the one Higgs doublet, electroweak phase transition is given. The phase transition is first order, occurs by the nucleation of thin walled bubbles and completes at a temperature where the order parameter, {l angle}{phi}{r angle}{sub T} is significantly smaller than it is when the origin becomes absolutely unstable. The rate of anomalous baryon number violation is an exponentially function of {l angle}{phi}{r angle}{sub T}. In very minimal extensions of the standard model it is quite easy to increase {l angle}{phi}{r angle}{sub T} so that anomalous baryon number violation is suppressed after completion of the phase transition. Hence baryogenesis at the electroweak phase transition is tenable in minimal of the standard model. In some cases additional phase transitions are possible. For a light Higgs boson, when the top quark mass is sufficiently large, the state where the Higgs field has a vacuum expectation value {l angle}{phi}{r angle} = 246 GeV is not the true minimum of the Higgs potential. When this is the case, and when the top quark mass exceeds some critical value, thermal fluctuations in the early universe would have rendered the state {l angle}{phi}{r angle} = 246 GeV unstable. The requirement that the state {l angle}{phi}{r angle} = 246 GeV is sufficiently long lived constrains the masses of the Higgs boson and the top quark. Finally, we consider whether local phase transitions can be induced by heavy particles which act as seeds for deformations in the scalar field.
Anderson, G.W.
1991-09-16
An analytic treatment of the one Higgs doublet, electroweak phase transition is given. The phase transition is first order, occurs by the nucleation of thin walled bubbles and completes at a temperature where the order parameter, {l_angle}{phi}{r_angle}{sub T} is significantly smaller than it is when the origin becomes absolutely unstable. The rate of anomalous baryon number violation is an exponentially function of {l_angle}{phi}{r_angle}{sub T}. In very minimal extensions of the standard model it is quite easy to increase {l_angle}{phi}{r_angle}{sub T} so that anomalous baryon number violation is suppressed after completion of the phase transition. Hence baryogenesis at the electroweak phase transition is tenable in minimal of the standard model. In some cases additional phase transitions are possible. For a light Higgs boson, when the top quark mass is sufficiently large, the state where the Higgs field has a vacuum expectation value {l_angle}{phi}{r_angle} = 246 GeV is not the true minimum of the Higgs potential. When this is the case, and when the top quark mass exceeds some critical value, thermal fluctuations in the early universe would have rendered the state {l_angle}{phi}{r_angle} = 246 GeV unstable. The requirement that the state {l_angle}{phi}{r_angle} = 246 GeV is sufficiently long lived constrains the masses of the Higgs boson and the top quark. Finally, we consider whether local phase transitions can be induced by heavy particles which act as seeds for deformations in the scalar field.
Detection of Nonverbal Synchronization through Phase Difference in Human Communication
Kwon, Jinhwan; Ogawa, Ken-ichiro; Ono, Eisuke; Miyake, Yoshihiro
2015-01-01
Nonverbal communication is an important factor in human communication, and body movement synchronization in particular is an important part of nonverbal communication. Some researchers have analyzed body movement synchronization by focusing on changes in the amplitude of body movements. However, the definition of “body movement synchronization” is still unclear. From a theoretical viewpoint, phase difference is the most important factor in synchronization analysis. Therefore, there is a need to measure the synchronization of body movements using phase difference. The purpose of this study was to provide a quantitative definition of the phase difference distribution for detecting body movement synchronization in human communication. The phase difference distribution was characterized using four statistical measurements: density, mean phase difference, standard deviation (SD) and kurtosis. To confirm the effectiveness of our definition, we applied it to human communication in which the roles of speaker and listener were defined. Specifically, we examined the difference in the phase difference distribution between two different communication situations: face-to-face communication with visual interaction and remote communication with unidirectional visual perception. Participant pairs performed a task supposing lecture in the face-to-face communication condition and in the remote communication condition via television. Throughout the lecture task, we extracted a set of phase differences from the time-series data of the acceleration norm of head nodding motions between two participants. Statistical analyses of the phase difference distribution revealed the characteristics of head nodding synchronization. Although the mean phase differences in synchronized head nods did not differ significantly between the conditions, there were significant differences in the densities, the SDs and the kurtoses of the phase difference distributions of synchronized head nods. These
String mediated phase transitions
NASA Technical Reports Server (NTRS)
Copeland, ED; Haws, D.; Rivers, R.; Holbraad, S.
1988-01-01
It is demonstrated from first principles how the existence of string-like structures can cause a system to undergo a phase transition. In particular, the role of topologically stable cosmic string in the restoration of spontaneously broken symmetries is emphasized. How the thermodynamic properties of strings alter when stiffness and nearest neighbor string-string interactions are included is discussed.
NASA Technical Reports Server (NTRS)
Maestrello, Lucio
2002-01-01
Acoustic and turbulent boundary layer flow loadings over a flexible structure are used to study the spatial-temporal dynamics of the response of the structure. The stability of the spatial synchronization and desynchronization by an active external force is investigated with an array of coupled transducers on the structure. In the synchronous state, the structural phase is locked, which leads to the formation of spatial patterns while the amplitude peaks exhibit chaotic behaviors. Large amplitude, spatially symmetric loading is superimposed on broadband, but in the desynchronized state, the spectrum broadens and the phase space is lost. The resulting pattern bears a striking resemblance to phase turbulence. The transition is achieved by using a low power external actuator to trigger broadband behaviors from the knowledge of the external acoustic load inducing synchronization. The changes are made favorably and efficiently to alter the frequency distribution of power, not the total power level. Before synchronization effects are seen, the panel response to the turbulent boundary layer loading is discontinuously spatio-temporally correlated. The stability develops from different competing wavelengths; the spatial scale is significantly shorter than when forced with the superimposed external sound. When the external sound level decreases and the synchronized phases are lost, changes in the character of the spectra can be linked to the occurrence of spatial phase transition. These changes can develop broadband response. Synchronized responses of fuselage structure panels have been observed in subsonic and supersonic aircraft; results from two flights tests are discussed.
NASA Astrophysics Data System (ADS)
Belan, S.
2015-12-01
Decentralized control of autonomous phase oscillators integrated into networked systems is of great interest for many technological applications, from clock synchronization in sensor nets to coordinated motion in swarm robotics. In the simplest distributed synchronization scheme, each oscillator updates its phase from time to time to a new value equal to the average of its present phase and the phases of its neighbors. Here we describe the resulting synchronization dynamics within a mean-field model where the update actions of different oscillators are completely asynchronous. In particular, it is shown how the steady-state level of synchrony depends on noise intensity and frequency diversity for any given rate of updates. The central part of the analysis is devoted to the case when the correction rate positively correlates with the degree of macroscopic coherence. We demonstrate that depending on relation between correction rate and phase coherence the oscillators may exhibit both continuous and discontinuous transition from incoherence to synchrony upon the change of interaction constant. To illustrate our analytical results, numerical simulations have been performed for a large population of phase oscillators with the proposed type of coupling.
Belan, S
2015-12-01
Decentralized control of autonomous phase oscillators integrated into networked systems is of great interest for many technological applications, from clock synchronization in sensor nets to coordinated motion in swarm robotics. In the simplest distributed synchronization scheme, each oscillator updates its phase from time to time to a new value equal to the average of its present phase and the phases of its neighbors. Here we describe the resulting synchronization dynamics within a mean-field model where the update actions of different oscillators are completely asynchronous. In particular, it is shown how the steady-state level of synchrony depends on noise intensity and frequency diversity for any given rate of updates. The central part of the analysis is devoted to the case when the correction rate positively correlates with the degree of macroscopic coherence. We demonstrate that depending on relation between correction rate and phase coherence the oscillators may exhibit both continuous and discontinuous transition from incoherence to synchrony upon the change of interaction constant. To illustrate our analytical results, numerical simulations have been performed for a large population of phase oscillators with the proposed type of coupling. PMID:26764777
NASA Astrophysics Data System (ADS)
Yu, Wen; Wood, Kevin B.
2015-06-01
We study the dynamics of phase synchronization in growing populations of discrete phase oscillatory systems when the division process is coupled to the distribution of oscillator phases. Using mean-field theory, linear-stability analysis, and numerical simulations, we demonstrate that coupling between population growth and synchrony can lead to a wide range of dynamical behavior, including extinction of synchronized oscillations, the emergence of asynchronous states with unequal state (phase) distributions, bistability between oscillatory and asynchronous states or between two asynchronous states, a switch between continuous (supercritical) and discontinuous (subcritical) transitions, and modulation of the frequency of bulk oscillations.
Emergence and Phase Transitions
NASA Astrophysics Data System (ADS)
Sikkema, Arnold
2006-05-01
Phase transitions are well defined in physics through concepts such as spontaneous symmetry breaking, order parameter, entropy, and critical exponents. But emergence --- also exhibiting whole-part relations (such as top-down influence), unpredictability, and insensitivity to microscopic detail --- is a loosely-defined concept being used in many disciplines, particularly in psychology, biology, philosophy, as well as in physics[1,2]. I will review the concepts of emergence as used in the various fields and consider the extent to which the methods of phase transitions can clarify the usefulness of the concept of emergence both within the discipline of physics and beyond.1. Robert B. Laughlin, A Different Universe: Reinventing Physics from the Bottom Down (New York: Basic Books, 2005). 2. George F.R. Ellis, ``Physics and the Real World'', Physics Today, vol. 58, no. 7 (July 2005) pp. 49-54.
Coupling among three chemical oscillators: Synchronization, phase death, and frustration
NASA Astrophysics Data System (ADS)
Yoshimoto, Minoru; Yoshikawa, Kenichi; Mori, Yoshihito
1993-02-01
Various modes in three coupled chemical oscillators in a triangular arrangement were observed. As a well-defined nonlinear oscillator, the Belousov-Zhabotinsky reaction was studied in a continuous-flow stirred tank reactor (CSTR). Coupling among CSTR's was performed by mass exchange. The coupling strength was quantitatively controlled by changing the flow rate of reacting solutions among the three CSTR's using peristaltic pumps between each pair of the reactors. As a key parameter to control the model of coupling, we changed the symmetry of the interaction between the oscillators. In the case of the symmetric coupling, a quasiperiodic state or a biperiodic mode, an all-death mode and two kinds of synchronized modes appeared, depending on the coupling strength. On the other hand, under the asymmetric coupling, a quasiperiodic state or a biperiodic mode, an all death mode and four kinds of synchronized modes appeared. Those modes have been discussed in relation to the idea of ``frustration'' in the Ising spin system, where the three-phase mode appears as a transition from the Ising spin system to the XY spin system.
Separation of synchronous sources through phase locked matrix factorization.
Almeida, Miguel S B; Vigário, Ricardo; Bioucas-Dias, José
2014-10-01
In this paper, we study the separation of synchronous sources (SSS) problem, which deals with the separation of sources whose phases are synchronous. This problem cannot be addressed through independent component analysis methods because synchronous sources are statistically dependent. We present a two-step algorithm, called phase locked matrix factorization (PLMF), to perform SSS. We also show that SSS is identifiable under some assumptions and that any global minimum of PLMFs cost function is a desirable solution for SSS. We extensively study the algorithm on simulated data and conclude that it can perform SSS with various numbers of sources and sensors and with various phase lags between the sources, both in the ideal (i.e., perfectly synchronous and nonnoisy) case, and with various levels of additive noise in the observed signals and of phase jitter in the sources. PMID:25291741
Application of Soft Computing in Coherent Communications Phase Synchronization
NASA Technical Reports Server (NTRS)
Drake, Jeffrey T.; Prasad, Nadipuram R.
2000-01-01
The use of soft computing techniques in coherent communications phase synchronization provides an alternative to analytical or hard computing methods. This paper discusses a novel use of Adaptive Neuro-Fuzzy Inference Systems (ANFIS) for phase synchronization in coherent communications systems utilizing Multiple Phase Shift Keying (MPSK) modulation. A brief overview of the M-PSK digital communications bandpass modulation technique is presented and it's requisite need for phase synchronization is discussed. We briefly describe the hybrid platform developed by Jang that incorporates fuzzy/neural structures namely the, Adaptive Neuro-Fuzzy Interference Systems (ANFIS). We then discuss application of ANFIS to phase estimation for M-PSK. The modeling of both explicit, and implicit phase estimation schemes for M-PSK symbols with unknown structure are discussed. Performance results from simulation of the above scheme is presented.
Chaotic phase synchronization in small-world networks of bursting neurons
NASA Astrophysics Data System (ADS)
Yu, Haitao; Wang, Jiang; Deng, Bin; Wei, Xile; Wong, Y. K.; Chan, W. L.; Tsang, K. M.; Yu, Ziqi
2011-03-01
We investigate the chaotic phase synchronization in a system of coupled bursting neurons in small-world networks. A transition to mutual phase synchronization takes place on the bursting time scale of coupled oscillators, while on the spiking time scale, they behave asynchronously. It is shown that phase synchronization is largely facilitated by a large fraction of shortcuts, but saturates when it exceeds a critical value. We also study the external chaotic phase synchronization of bursting oscillators in the small-world network by a periodic driving signal applied to a single neuron. It is demonstrated that there exists an optimal small-world topology, resulting in the largest peak value of frequency locking interval in the parameter plane, where bursting synchronization is maintained, even with the external driving. The width of this interval increases with the driving amplitude, but decrease rapidly with the network size. We infer that the externally applied driving parameters outside the frequency locking region can effectively suppress pathologically synchronized rhythms of bursting neurons in the brain.
Phase transitions in semidefinite relaxations
Javanmard, Adel; Montanari, Andrea; Ricci-Tersenghi, Federico
2016-01-01
Statistical inference problems arising within signal processing, data mining, and machine learning naturally give rise to hard combinatorial optimization problems. These problems become intractable when the dimensionality of the data is large, as is often the case for modern datasets. A popular idea is to construct convex relaxations of these combinatorial problems, which can be solved efficiently for large-scale datasets. Semidefinite programming (SDP) relaxations are among the most powerful methods in this family and are surprisingly well suited for a broad range of problems where data take the form of matrices or graphs. It has been observed several times that when the statistical noise is small enough, SDP relaxations correctly detect the underlying combinatorial structures. In this paper we develop asymptotic predictions for several detection thresholds, as well as for the estimation error above these thresholds. We study some classical SDP relaxations for statistical problems motivated by graph synchronization and community detection in networks. We map these optimization problems to statistical mechanics models with vector spins and use nonrigorous techniques from statistical mechanics to characterize the corresponding phase transitions. Our results clarify the effectiveness of SDP relaxations in solving high-dimensional statistical problems. PMID:27001856
Phase transitions in semidefinite relaxations.
Javanmard, Adel; Montanari, Andrea; Ricci-Tersenghi, Federico
2016-04-19
Statistical inference problems arising within signal processing, data mining, and machine learning naturally give rise to hard combinatorial optimization problems. These problems become intractable when the dimensionality of the data is large, as is often the case for modern datasets. A popular idea is to construct convex relaxations of these combinatorial problems, which can be solved efficiently for large-scale datasets. Semidefinite programming (SDP) relaxations are among the most powerful methods in this family and are surprisingly well suited for a broad range of problems where data take the form of matrices or graphs. It has been observed several times that when the statistical noise is small enough, SDP relaxations correctly detect the underlying combinatorial structures. In this paper we develop asymptotic predictions for several detection thresholds, as well as for the estimation error above these thresholds. We study some classical SDP relaxations for statistical problems motivated by graph synchronization and community detection in networks. We map these optimization problems to statistical mechanics models with vector spins and use nonrigorous techniques from statistical mechanics to characterize the corresponding phase transitions. Our results clarify the effectiveness of SDP relaxations in solving high-dimensional statistical problems. PMID:27001856
Thermodynamics aspects of noise-induced phase synchronization
NASA Astrophysics Data System (ADS)
Pinto, Pedro D.; Oliveira, Fernando A.; Penna, André L. A.
2016-05-01
In this article, we present an approach for the thermodynamics of phase oscillators induced by an internal multiplicative noise. We analytically derive the free energy, entropy, internal energy, and specific heat. In this framework, the formulation of the first law of thermodynamics requires the definition of a synchronization field acting on the phase oscillators. By introducing the synchronization field, we have consistently obtained the susceptibility and analyzed its behavior. This allows us to characterize distinct phases in the system, which we have denoted as synchronized and parasynchronized phases, in analogy with magnetism. The system also shows a rich complex behavior, exhibiting ideal gas characteristics for low temperatures and susceptibility anomalies that are similar to those present in complex fluids such as water.
Thermodynamics aspects of noise-induced phase synchronization.
Pinto, Pedro D; Oliveira, Fernando A; Penna, André L A
2016-05-01
In this article, we present an approach for the thermodynamics of phase oscillators induced by an internal multiplicative noise. We analytically derive the free energy, entropy, internal energy, and specific heat. In this framework, the formulation of the first law of thermodynamics requires the definition of a synchronization field acting on the phase oscillators. By introducing the synchronization field, we have consistently obtained the susceptibility and analyzed its behavior. This allows us to characterize distinct phases in the system, which we have denoted as synchronized and parasynchronized phases, in analogy with magnetism. The system also shows a rich complex behavior, exhibiting ideal gas characteristics for low temperatures and susceptibility anomalies that are similar to those present in complex fluids such as water. PMID:27300893
A synchronous phase detection system for an optical interferometric sensor
NASA Astrophysics Data System (ADS)
Bush, I. J.
1982-05-01
A system has been developed to accurately detect phase produced in optical interferometric sensors. The system employs optical heterodyning, and it synchronously detects optical phase by feeding an error signal back to a phase modulator in the reference leg of the interferometer. This system is seen to have properties similar to a phase-locked loop used for the demodulation of FM signals. The system model is second order and nonlinear, but a linear approximation serves to accurately describe the system in synchronous operation and is corroborated with well-matched empirical data. The complete model is simulated via computer techniques and is needed to describe the system's parameters that lead to loss and reacquisition of synchronization.
Segregation induced by phase synchronization in a bidisperse granular layer
NASA Astrophysics Data System (ADS)
Wang, Tai-Yuan; Hong, T. M.
2008-12-01
We propose an alternative segregation mechanism where the species-dependent interactions are dynamically induced by the phase synchronization of beads. Based on this scenario, we report an alternative segregation among beads of different restitution coefficients by molecular dynamics simulations. Since the beads are of equal size and mass, this is not related to the Brazilian-nut effect, nor can it be explained by the depletion force. Instead, this phenomenon derives from the phase synchronization, a concept which helps us determine the criteria for segregation and the phase boundaries that agree excellently with the simulation results.
More About the Phase-Synchronized Enhancement Method
NASA Technical Reports Server (NTRS)
Jong, Jen-Yi
2004-01-01
A report presents further details regarding the subject matter of "Phase-Synchronized Enhancement Method for Engine Diagnostics" (MFS-26435), NASA Tech Briefs, Vol. 22, No. 1 (January 1998), page 54. To recapitulate: The phase-synchronized enhancement method (PSEM) involves the digital resampling of a quasi-periodic signal in synchronism with the instantaneous phase of one of its spectral components. This resampling transforms the quasi-periodic signal into a periodic one more amenable to analysis. It is particularly useful for diagnosis of a rotating machine through analysis of vibration spectra that include components at the fundamental and harmonics of a slightly fluctuating rotation frequency. The report discusses the machinery-signal-analysis problem, outlines the PSEM algorithms, presents the mathematical basis of the PSEM, and presents examples of application of the PSEM in some computational simulations.
NASA Astrophysics Data System (ADS)
Gu, Hua-Guang; Li, Yu-Ye; Jia, Bing; Chen, Guan-Rong
2013-08-01
A firing pattern transition is simulated in the Leech neuron model, firstly from bursting to co-existence of spiking and bursting and then to spiking. The attraction domain of spiking and bursting for three different parameter values are calculated. Synchronization transition processes of two coupled Leech neurons, one is bursting and the other the co-existing spiking, are simulated for the three parameters. The three synchronization processes appear similar as the coupling strength increases, beginning from non-synchronization to complete synchronization through a complex dynamical procedure, but their detailed processes are different depending on the parameter values. The transition procedure is complex and the complete synchronization is in bursting for larger parameter values, while the process is simple with complete synchronization of spiking for smaller values. The potential relationship between complete synchronization and the attraction domain is also discussed. The results are instructive to understanding the synchronization behaviors of the coupled neuronal system with co-existing attractors.
Quantum phase transition in space
Damski, Bogdan; Zurek, Wojciech H
2008-01-01
A quantum phase transition between the symmetric (polar) phase and the phase with broken symmetry can be induced in a ferromagnetic spin-1 Bose-Einstein condensate in space (rather than in time). We consider such a phase transition and show that the transition region in the vicinity of the critical point exhibits scalings that reflect a compromise between the rate at which the transition is imposed (i.e., the gradient of the control parameter) and the scaling of the divergent healing length in the critical region. Our results suggest a method for the direct measurement of the scaling exponent {nu}.
Explosive synchronization as a process of explosive percolation in dynamical phase space
Zhang, Xiyun; Zou, Yong; Boccaletti, S.; Liu, Zonghua
2014-01-01
Explosive synchronization and explosive percolation are currently two independent phenomena occurring in complex networks, where the former takes place in dynamical phase space while the latter in configuration space. It has been revealed that the mechanism of EP can be explained by the Achlioptas process, where the formation of a giant component is controlled by a suppressive rule. We here introduce an equivalent suppressive rule for ES. Before the critical point of ES, the suppressive rule induces the presence of multiple, small sized, synchronized clusters, while inducing the abrupt formation of a giant cluster of synchronized oscillators at the critical coupling strength. We also show how the explosive character of ES degrades into a second-order phase transition when the suppressive rule is broken. These results suggest that our suppressive rule can be considered as a dynamical counterpart of the Achlioptas process, indicating that ES and EP can be unified into a same framework. PMID:24903808
Repulsive Synchronization in an Array of Phase Oscillators
NASA Astrophysics Data System (ADS)
Tsimring, L. S.; Rulkov, N. F.; Larsen, M. L.; Gabbay, M.
2005-06-01
We study the dynamics of a repulsively coupled array of phase oscillators. For an array of globally coupled identical oscillators, repulsive coupling results in a family of synchronized regimes characterized by zero mean field. If the number of oscillators is sufficiently large, phase locking among oscillators is destroyed, independently of the coupling strength, when the oscillators’ natural frequencies are not the same. In locally coupled networks, however, phase locking occurs even for nonidentical oscillators when the coupling strength is sufficiently strong.
Theory of antiferroelectric phase transitions
NASA Astrophysics Data System (ADS)
Tolédano, Pierre; Guennou, Mael
2016-07-01
At variance with structural ferroic phase transitions which give rise to macroscopic tensors coupled to macroscopic fields, criteria defining antiferroelectric (AFE) phase transitions are still under discussion due to the absence of specific symmetry properties characterizing their existence. They are recognized by the proximity of a ferroelectric (FE) phase induced under applied electric field, with a double hysteresis loop relating the induced polarization to the electric field and a typical anomaly of the dielectric permittivity. Here, we show that there exist indeed symmetry criteria defining AFE transitions. They relate the local symmetry of the polar crystallographic sites emerging at an AFE phase transition with the macroscopic symmetry of the AFE phase. The dielectric properties of AFE transitions are deduced from a Landau theoretical model in which ferroelectric and ferrielectric phases are shown to stabilize as the result of specific symmetry-allowed couplings of the AFE order parameter with the field-induced polarization.
Estimating the phase of synchronized oscillators
NASA Astrophysics Data System (ADS)
Revzen, Shai; Guckenheimer, John M.
2008-11-01
The state of a collection of phase-locked oscillators is determined by a single phase variable or cyclic coordinate. This paper presents a computational method, Phaser, for estimating the phase of phase-locked oscillators from limited amounts of multivariate data in the presence of noise and measurement errors. Measurements are assumed to be a collection of multidimensional time series. Each series consists of several cycles of the same or similar systems. The oscillators within each system are not assumed to be identical. Using measurements of the noise covariance for the multivariate input, data from the individual oscillators in the system are combined to reduce the variance of phase estimates for the whole system. The efficacy of the algorithm is demonstrated on experimental and model data from biomechanics of cockroach running and on simulated oscillators with varying levels of noise.
Phase Transitions for Suspension Flows
NASA Astrophysics Data System (ADS)
Iommi, Godofredo; Jordan, Thomas
2013-06-01
This paper is devoted to studying the thermodynamic formalism for suspension flows defined over countable alphabets. We are mostly interested in the regularity properties of the pressure function. We establish conditions for the pressure function to be real analytic or to exhibit a phase transition. We also construct an example of a potential for which the pressure has countably many phase transitions.
Brains swinging in concert: cortical phase synchronization while playing guitar
Lindenberger, Ulman; Li, Shu-Chen; Gruber, Walter; Müller, Viktor
2009-01-01
Background Brains interact with the world through actions that are implemented by sensory and motor processes. A substantial part of these interactions consists in synchronized goal-directed actions involving two or more individuals. Hyperscanning techniques for assessing fMRI simultaneously from two individuals have been developed. However, EEG recordings that permit the assessment of synchronized neuronal activities at much higher levels of temporal resolution have not yet been simultaneously assessed in multiple individuals and analyzed in the time-frequency domain. In this study, we simultaneously recorded EEG from the brains of each of eight pairs of guitarists playing a short melody together to explore the extent and the functional significance of synchronized cortical activity in the course of interpersonally coordinated actions. Results By applying synchronization algorithms to intra- and interbrain analyses, we found that phase synchronization both within and between brains increased significantly during the periods of (i) preparatory metronome tempo setting and (ii) coordinated play onset. Phase alignment extracted from within-brain dynamics was related to behavioral play onset asynchrony between guitarists. Conclusion Our findings show that interpersonally coordinated actions are preceded and accompanied by between-brain oscillatory couplings. Presumably, these couplings reflect similarities in the temporal properties of the individuals' percepts and actions. Whether between-brain oscillatory couplings play a causal role in initiating and maintaining interpersonal action coordination needs to be clarified by further research. PMID:19292892
Phase transitions in disordered systems
NASA Astrophysics Data System (ADS)
Hrahsheh, Fawaz Y.
Disorder can have a wide variety of consequences for the physics of phase transitions. Some transitions remain unchanged in the presence of disorder while others are completely destroyed. In this thesis we study the effects of disorder on several classical and quantum phase transitions in condensed matter systems. After a brief introduction, we study the ferromagnetic phase transition in a randomly layered Heisenberg magnet using large-scale Monte-Carlo simulations. Our results provide numerical evidence for the exotic infinite-randomness scenario. We study classical and quantum smeared phase transitions in substitutional alloys A1-xBx. Our results show that the disorder completely destroys the phase transition with a pronounced tail of the ordered phase developing for all compositions x < 1. In addition, we find that short-ranged disorder correlations can have a dramatic effect on the transition. Moreover, we show an experimental realization of the composition-tuned ferromagnetic-to-paramagnetic quantum phase transition in Sr1-xCa xRuO3. We investigate the effects of disorder on first-order quantum phase transitions on the example of the N-color quantum Ashkin-Teller model. By means of a strong disorder renormalization group, we demonstrate that disorder rounds the first-order transition to a continuous one for both weak and strong coupling between the colors. Finally, we investigate the superfluid-insulator quantum phase transition of one-dimensional bosons with off-diagonal disorder by means of large-scale Monte-Carlo simulations. Beyond a critical disorder strength, we find nonuniversal, disorder dependent critical behavior.
Fluctuation driven electroweak phase transition
NASA Technical Reports Server (NTRS)
Gleiser, Marcelo; Kolb, Edward W.
1991-01-01
We examine the dynamics of the electroweak phase transition in the early Universe. For Higgs masses in the range 46 less than or = M sub H less than or = 150 GeV and top quark masses less than 200 GeV, regions of symmetric and asymmetric vacuum coexist to below the critical temperature, with thermal equilibrium between the two phases maintained by fluctuations of both phases. We propose that the transition to the asymmetric vacuum is completed by percolation of these subcritical fluctuations. Our results are relevant to scenarios of baryogenesis that invoke a weakly first-order phase transition at the electroweak scale.
Transition of Bery Phase and Pancharatnam Phase and Phase Change
NASA Astrophysics Data System (ADS)
Fu, Guolan; Pan, Hui; Wang, Zisheng
2016-07-01
Berry Phase and time-dependent Pancharatnam phase are investigated for nuclear spin polarization in a liquid by a rotation magnetic field, where two-state mixture effect is exactly included in the geometric phases. We find that when the system of nuclear spin polarization is in the unpolarized state, the transitive phenomena of both Berry phase and Pancharatnam phase are taken place. For the polarized system, in contrast, such a transition is not taken place. It is obvious that the transitions of geometric phase correspond to the phase change of physical system.
Synchronization of coupled Boolean phase oscillators
NASA Astrophysics Data System (ADS)
Rosin, David P.; Rontani, Damien; Gauthier, Daniel J.
2014-04-01
We design, characterize, and couple Boolean phase oscillators that include state-dependent feedback delay. The state-dependent delay allows us to realize an adjustable coupling strength, even though only Boolean signals are exchanged. Specifically, increasing the coupling strength via the range of state-dependent delay leads to larger locking ranges in uni- and bidirectional coupling of oscillators in both experiment and numerical simulation with a piecewise switching model. In the unidirectional coupling scheme, we unveil asymmetric triangular-shaped locking regions (Arnold tongues) that appear at multiples of the natural frequency of the oscillators. This extends observations of a single locking region reported in previous studies. In the bidirectional coupling scheme, we map out a symmetric locking region in the parameter space of frequency detuning and coupling strength. Because of the large scalability of our setup, our observations constitute a first step towards realizing large-scale networks of coupled oscillators to address fundamental questions on the dynamical properties of networks in a new experimental setting.
Cavagnoli, Rafael; Menezes, Debora P.; Providencia, Constanca
2009-06-03
In the present work we study the hadron-quarkphase transition with boson condensation by investigating the binodal surface and extending it to finite temperature in order to mimic the QCD phase diagram.
Clustering and phase synchronization in populations of coupled phase oscillators
NASA Astrophysics Data System (ADS)
Cascallares, Guadalupe; Gleiser, Pablo M.
2015-10-01
In many species daily rhythms are endogenously generated by groups of coupled neurons that play the role of a circadian pacemaker. The adaptation of the circadian clock to environmental and seasonal changes has been proposed to be regulated by a dual oscillator system. In order to gain insight into this model, we analyzed the synchronization properties of two fully coupled groups of Kuramoto oscillators. Each group has an internal coupling parameter and the interaction between the two groups can be controlled by two parameters allowing for symmetric or non-symmetric coupling. We show that even for such a simple model counterintuitive behaviours take place, such as a global decrease in synchrony when the coupling between the groups is increased. Through a detailed analysis of the local synchronization processes we explain this behaviour.
Experimentally determined chaotic phase synchronization in a neuronal system
Makarenko, Vladimir; Llinás, Rodolfo
1998-01-01
Mathematical analysis of the subthreshold oscillatory properties of inferior olivary neurons in vitro indicates that the oscillation is nonlinear and supports low dimensional chaotic dynamics. This property leads to the generation of complex functional states that can be attained rapidly via phase coherence that conform to the category of “generalized synchronization.” Functionally, this translates into neuronal ensemble properties that can support maximum functional permissiveness and that rapidly can transform into robustly determined multicellular coherence. PMID:9861041
Holographic approach to phase transitions
Franco, Sebastian; Garcia-Garcia, Antonio M.; Rodriguez-Gomez, Diego
2010-02-15
We provide a description of phase transitions at finite temperature in strongly coupled field theories using holography. For this purpose, we introduce a general class of gravity duals to superconducting theories that exhibit various types of phase transitions (first or second order with both mean and non-mean field behavior) as parameters in their Lagrangian are changed. Moreover the size and strength of the conductivity coherence peak can also be controlled. Our results suggest that certain parameters in the gravitational dual control the interactions responsible for binding the condensate and the magnitude of its fluctuations close to the transition.
NASA Astrophysics Data System (ADS)
Watanabe, Takamitsu
2013-03-01
As exemplified by power grids and large-scale brain networks, some functions of networks consisting of phase oscillators rely on not only frequency synchronization, but also phase synchronization among the oscillators. Nevertheless, even after the oscillators reach frequency-synchronized status, the phase synchronization is not always accomplished because the phase difference among the oscillators is often trapped at non-zero constant values. Such phase difference potentially results in inefficient transfer of power or information among the oscillators, and avoids proper and efficient functioning of the networks. In the present study, we newly define synchronization cost by using the phase difference among the frequency-synchronized oscillators, and investigate the optimal network structure with the minimum synchronization cost through rewiring-based optimization. By using the Kuramoto model, we demonstrate that the cost is minimized in a network with a rich-club topology, which comprises the densely-connected center nodes and low-degree peripheral nodes connecting with the center module. We also show that the network topology is characterized by its bimodal degree distribution, which is quantified by Wolfson’s polarization index.
Siclari, Francesca; Bernardi, Giulio; Riedner, Brady A.; LaRocque, Joshua J.; Benca, Ruth M.; Tononi, Giulio
2014-01-01
Objectives: To assess how the characteristics of slow waves and spindles change in the falling-asleep process. Design: Participants undergoing overnight high-density electroencephalographic recordings were awakened at 15- to 30-min intervals. One hundred forty-one falling-asleep periods were analyzed at the scalp and source level. Setting: Sleep laboratory. Participants: Six healthy participants. Interventions: Serial awakenings. Results: The number and amplitude of slow waves followed two dissociated, intersecting courses during the transition to sleep: slow wave number increased slowly at the beginning and rapidly at the end of the falling-asleep period, whereas amplitude at first increased rapidly and then decreased linearly. Most slow waves occurring early in the transition to sleep had a large amplitude, a steep slope, involved broad regions of the cortex, predominated over frontomedial regions, and preferentially originated from the sensorimotor and the posteromedial parietal cortex. Most slow waves occurring later had a smaller amplitude and slope, involved more circumscribed parts of the cortex, and had more evenly distributed origins. Spindles were initially sparse, fast, and involved few cortical regions, then became more numerous and slower, and involved more areas. Conclusions: Our results provide evidence for two types of slow waves, which follow dissociated temporal courses in the transition to sleep and have distinct cortical origins and distributions. We hypothesize that these two types of slow waves result from two distinct synchronization processes: (1) a “bottom-up,” subcorticocortical, arousal system-dependent process that predominates in the early phase and leads to type I slow waves, and (2) a “horizontal,” corticocortical synchronization process that predominates in the late phase and leads to type II slow waves. The dissociation between these two synchronization processes in time and space suggests that they may be differentially
Perfect phase correction in synchronization with slow auditory sequences.
Repp, Bruno H
2008-09-01
Phase correction during synchronization (finger tapping) with an isochronous auditory sequence is typically imperfect, requiring several taps to complete. However, two independent hypotheses predict that phase correction should approach perfection when the sequence tempo is slow. The present results confirm this prediction. The experiment used a phase perturbation method and a group of musically trained participants. As the sequence interonset interval increased from 300 to 1200 ms, the phase correction response to perturbations increased and approached instantaneous phase resetting between 700 and 1200 ms, depending on the individual. A possible explanation of this finding is that emergent timing of the periodic finger movement vanishes as the movement frequency decreases and thus ceases to compete with event-based timing. PMID:18782711
Phase transitions in traffic flow on multilane roads
NASA Astrophysics Data System (ADS)
Kerner, Boris S.; Klenov, Sergey L.
2009-11-01
Based on empirical and numerical analyses of vehicular traffic, the physics of spatiotemporal phase transitions in traffic flow on multilane roads is revealed. The complex dynamics of moving jams observed in single vehicle data measured by video cameras on American highways is explained by the nucleation-interruption effect in synchronized flow, i.e., the spontaneous nucleation of a narrow moving jam with the subsequent jam dissolution. We find that (i) lane changing, vehicle merging from on-ramps, and vehicle leaving to off-ramps result in different traffic phases—free flow, synchronized flow, and wide moving jams—occurring and coexisting in different road lanes as well as in diverse phase transitions between the traffic phases; (ii) in synchronized flow, the phase transitions are responsible for a non-regular moving jam dynamics that explains measured single vehicle data: moving jams emerge and dissolve randomly at various road locations in different lanes; (iii) the phase transitions result also in diverse expanded general congested patterns occurring at closely located bottlenecks.
Wu, Yanan; Gong, Yubing; Wang, Qi
2015-04-01
In this paper, we numerically study the effect of autapse on the synchronization of Newman-Watts small-world Hodgkin-Huxley neuron network. It is found that the neurons exhibit synchronization transitions as autaptic self-feedback delay is varied, and the phenomenon becomes strongest when autaptic self-feedback strength is optimal. This phenomenon also changes with the change of coupling strength and network randomness and become strongest when they are optimal. There are similar synchronization transitions for electrical and chemical autapse, but the synchronization transitions for chemical autapse occur more frequently and are stronger than those for electrical synapse. The underlying mechanisms are briefly discussed in quality. These results show that autaptic activity plays a subtle role in the synchronization of the neuronal network. These findings may find potential implications of autapse for the information processing and transmission in neural systems. PMID:25933661
NASA Astrophysics Data System (ADS)
Wu, Yanan; Gong, Yubing; Wang, Qi
2015-04-01
In this paper, we numerically study the effect of autapse on the synchronization of Newman-Watts small-world Hodgkin-Huxley neuron network. It is found that the neurons exhibit synchronization transitions as autaptic self-feedback delay is varied, and the phenomenon becomes strongest when autaptic self-feedback strength is optimal. This phenomenon also changes with the change of coupling strength and network randomness and become strongest when they are optimal. There are similar synchronization transitions for electrical and chemical autapse, but the synchronization transitions for chemical autapse occur more frequently and are stronger than those for electrical synapse. The underlying mechanisms are briefly discussed in quality. These results show that autaptic activity plays a subtle role in the synchronization of the neuronal network. These findings may find potential implications of autapse for the information processing and transmission in neural systems.
Synchronous, alternating, and phase-locked stridulation by a tropical katydid.
Sismondo, E
1990-07-01
In the field the chirps of neighboring Mecopoda sp. (Orthoptera, Tettigoniidae, and Mecopodinae) males are normally synchronized, but between more distant individuals the chirps are either synchronous or regularly alternating. The phase response to single-stimulus chirps depends on both the phase and the intensity of the stimulus. Iteration of the Poincaré map of the phase response predicts a variety of phase-locked synchronization regimes, incuding period-doubling bifurcations, in close agreement with experimental observations. The versatile acoustic behavior of Mecopoda encompasses most of the phenomena found in other synchronizing insects and thus provides a general model of insect synchronization behavior. PMID:17787627
Phase transitions in nuclear matter
Glendenning, N.K.
1984-11-01
The rather general circumstances under which a phase transition in hadronic matter at finite temperature to an abnormal phase in which baryon effective masses become small and in which copious baryon-antibaryon pairs appear is emphasized. A preview is also given of a soliton model of dense matter, in which at a density of about seven times nuclear density, matter ceases to be a color insulator and becomes increasingly color conducting. 22 references.
Noise-Enhanced Phase Synchronization in Excitable Media
Neiman, Alexander; Schimansky-Geier, Lutz; Cornell-Bell, Ann
1999-12-06
We study the response of one- and two-dimensional excitable media to external spatiotemporal noise in terms of synchronization. The media are modeled by a finite-size lattice of locally coupled nonidentical units of the FitzHugh-Nagumo type driven by additive noise. We show that at nonzero noise level the behavior of the system becomes extremely ordered which is manifested by entrainment of the mean frequencies and by stochastic phase locking of distant oscillators in the lattice. (c) 1999 The American Physical Society.
Phase-synchronous detection of coherent and incoherent nonlinear signals
NASA Astrophysics Data System (ADS)
Karki, Khadga Jung; Kringle, Loni; Marcus, Andrew H.; Pullerits, Tõnu
2016-01-01
The nonlinear optical response of a material system contains detailed information about its electronic structure. Standard approaches to nonlinear spectroscopy often use multiple beams crossed in a sample, and detect the wave vector matched polarization in transmission. Here, we apply a phase-synchronous digital detection scheme using an excitation geometry with two phase-modulated collinear ultrafast pulses. This scheme can be used to efficiently detect nonlinear coherent signals and incoherent signals, such as higher harmonics and multiphoton fluorescence and photocurrent, from various systems including a photocell device. We present theory and experiment to demonstrate that when the phase of each laser pulse is modulated at the frequency {φ }1 and {φ }2, respectively, nonlinear signals can be isolated at the frequencies n({φ }2-{φ }1), where n=0,1,2,\\ldots . This approach holds promise for performing nonlinear spectroscopic measurements under low-signal conditions.
NASA Astrophysics Data System (ADS)
Wang, Qi; Gong, Yubing; Wu, Yanan
2015-04-01
Autapse is a special synapse that connects a neuron to itself. In this work, we numerically study the effect of chemical autapse on the synchronization of Newman-Watts Hodgkin-Huxley neuron network with time delays. It is found that the neurons exhibit synchronization transitions as autaptic self-feedback delay is varied, and the phenomenon enhances when autaptic self-feedback strength increases. Moreover, this phenomenon becomes strongest when network time delay or coupling strength is optimal. It is also found that the synchronization transitions by network time delay can be enhanced by autaptic activity and become strongest when autaptic delay is optimal. These results show that autaptic delayed self-feedback activity can intermittently enhance and reduce the synchronization of the neuronal network and hence plays an important role in regulating the synchronization of the neurons. These findings could find potential implications for the information processing and transmission in neural systems.
GENERAL: A Possible Population-Driven Phase Transition in Cicada Chorus
NASA Astrophysics Data System (ADS)
Gu, Si-Yuan; Jin, Yu-Liang; Zhao, Xiao-Xue; Huang, Ji-Ping
2009-06-01
We investigate the collective synchronization of cicada chirping. Using both experimental and phenomenological numerical techniques, here we show that the onset of a periodic two-state acoustic synchronous behavior in cicada chorus depends on a critical size of population Nc = 21, above which a typical chorus state appears periodically with a 30 second-silence state in between, and further clarify its possibility concerning a new class of phase transition, which is unusually driven by population. This work has relevance to acoustic synchronization and to general physics of phase transition.
NASA Astrophysics Data System (ADS)
Liu, Chen; Wang, Jiang; Yu, Haitao; Deng, Bin; Wei, Xile; Tsang, Kaiming; Chan, Wailok
2013-09-01
The combined effects of the information transmission delay and the ratio of the electrical and chemical synapses on the synchronization transitions in the hybrid modular neuronal network are investigated in this paper. Numerical results show that the synchronization of neuron activities can be either promoted or destroyed as the information transmission delay increases, irrespective of the probability of electrical synapses in the hybrid-synaptic network. Interestingly, when the number of the electrical synapses exceeds a certain level, further increasing its proportion can obviously enhance the spatiotemporal synchronization transitions. Moreover, the coupling strength has a significant effect on the synchronization transition. The dominated type of the synapse always has a more profound effect on the emergency of the synchronous behaviors. Furthermore, the results of the modular neuronal network structures demonstrate that excessive partitioning of the modular network may result in the dramatic detriment of neuronal synchronization. Considering that information transmission delays are inevitable in intra- and inter-neuronal networks communication, the obtained results may have important implications for the exploration of the synchronization mechanism underlying several neural system diseases such as Parkinson's Disease.
Non-equilibrium phase transitions
Mottola, E.; Cooper, F.M.; Bishop, A.R.; Habib, S.; Kluger, Y.; Jensen, N.G.
1998-12-31
This is the final report of a one-year, Laboratory Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). Non-equilibrium phase transitions play a central role in a very broad range of scientific areas, ranging from nuclear, particle, and astrophysics to condensed matter physics and the material and biological sciences. The aim of this project was to explore the path to a deeper and more fundamental understanding of the common physical principles underlying the complex real time dynamics of phase transitions. The main emphasis was on the development of general theoretical tools to deal with non-equilibrium processes, and of numerical methods robust enough to capture the time-evolving structures that occur in actual experimental situations. Specific applications to Laboratory multidivisional efforts in relativistic heavy-ion physics (transition to a new phase of nuclear matter consisting of a quark-gluon plasma) and layered high-temperature superconductors (critical currents and flux flow at the National High Magnetic Field Laboratory) were undertaken.
Phase Transitions in Dipalmitoylphosphatidylcholine Monolayers.
Zuo, Yi Y; Chen, Rimei; Wang, Xianju; Yang, Jinlong; Policova, Zdenka; Neumann, A Wilhelm
2016-08-23
A self-assembled phospholipid monolayer at an air-water interface is a well-defined model system for studying surface thermodynamics, membrane biophysics, thin-film materials, and colloidal soft matter. Here we report a study of two-dimensional phase transitions in the dipalmitoylphosphatidylcholine (DPPC) monolayer at the air-water interface using a newly developed methodology called constrained drop surfactometry (CDS). CDS is superior to the classical Langmuir balance in its capacity for rigorous temperature control and leak-proof environments, thus making it an ideal alternative to the Langmuir balance for studying lipid polymorphism. In addition, we have developed a novel Langmuir-Blodgett (LB) transfer technique that allows the direct transfer of lipid monolayers from the droplet surface under well-controlled conditions. This LB transfer technique permits the direct visualization of phase coexistence in the DPPC monolayer. With these technological advances, we found that the two-dimensional phase behavior of the DPPC monolayer is analogous to the three-dimensional phase transition of a pure substance. This study has implications in the fundamental understanding of surface thermodynamics as well as applications such as self-assembled monolayers and pulmonary surfactant biophysics. PMID:27479299
Synchronization in area-preserving maps: Effects of mixed phase space and coherent structures
NASA Astrophysics Data System (ADS)
Mahata, Sasibhusan; Das, Swetamber; Gupte, Neelima
2016-06-01
The problem of synchronization of coupled Hamiltonian systems presents interesting features due to the mixed nature (regular and chaotic) of the phase space. We study these features by examining the synchronization of unidirectionally coupled area-preserving maps coupled by the Pecora-Caroll method. The master stability function approach is used to study the stability of the synchronous state and to identify the percentage of synchronizing initial conditions. The transient to synchronization shows intermittency with an associated power law. The mixed nature of the phase space of the studied map has notable effects on the synchronization times as is seen in the case of the standard map. Using finite-time Lyapunov exponent analysis, we show that the synchronization of the maps occurs in the neighborhood of invariant curves in the phase space. The phase differences of the coevolving trajectories show intermittency effects, due to the existence of stable periodic orbits contributing locally stable directions in the synchronizing neighborhoods. Furthermore, the value of the nonlinearity parameter, as well as the location of the initial conditions play an important role in the distribution of synchronization times. We examine drive response combinations which are chaotic-chaotic, chaotic-regular, regular-chaotic, and regular-regular. A range of scaling behavior is seen for these cases, including situations where the distributions show a power-law tail, indicating long synchronization times for at least some of the synchronizing trajectories. The introduction of coherent structures in the system changes the situation drastically. The distribution of synchronization times crosses over to exponential behavior, indicating shorter synchronization times, and the number of initial conditions which synchronize increases significantly, indicating an enhancement in the basin of synchronization. We discuss the implications of our results.
Synchronization in area-preserving maps: Effects of mixed phase space and coherent structures.
Mahata, Sasibhusan; Das, Swetamber; Gupte, Neelima
2016-06-01
The problem of synchronization of coupled Hamiltonian systems presents interesting features due to the mixed nature (regular and chaotic) of the phase space. We study these features by examining the synchronization of unidirectionally coupled area-preserving maps coupled by the Pecora-Caroll method. The master stability function approach is used to study the stability of the synchronous state and to identify the percentage of synchronizing initial conditions. The transient to synchronization shows intermittency with an associated power law. The mixed nature of the phase space of the studied map has notable effects on the synchronization times as is seen in the case of the standard map. Using finite-time Lyapunov exponent analysis, we show that the synchronization of the maps occurs in the neighborhood of invariant curves in the phase space. The phase differences of the coevolving trajectories show intermittency effects, due to the existence of stable periodic orbits contributing locally stable directions in the synchronizing neighborhoods. Furthermore, the value of the nonlinearity parameter, as well as the location of the initial conditions play an important role in the distribution of synchronization times. We examine drive response combinations which are chaotic-chaotic, chaotic-regular, regular-chaotic, and regular-regular. A range of scaling behavior is seen for these cases, including situations where the distributions show a power-law tail, indicating long synchronization times for at least some of the synchronizing trajectories. The introduction of coherent structures in the system changes the situation drastically. The distribution of synchronization times crosses over to exponential behavior, indicating shorter synchronization times, and the number of initial conditions which synchronize increases significantly, indicating an enhancement in the basin of synchronization. We discuss the implications of our results. PMID:27415260
Phase-Synchronization Early Epileptic Seizure Detector VLSI Architecture.
Abdelhalim, K; Smolyakov, V; Genov, R
2011-10-01
A low-power VLSI processor architecture that computes in real time the magnitude and phase-synchronization of two input neural signals is presented. The processor is a part of an envisioned closed-loop implantable microsystem for adaptive neural stimulation. The architecture uses three CORDIC processing cores that require shift-and-add operations but no multiplication. The 10-bit processor synthesized and prototyped in a standard 1.2 V 0.13 μm CMOS technology utilizes 41,000 logic gates. It dissipates 3.6 μW per input pair, and provides 1.7 kS/s per-channel throughput when clocked at 2.5 MHz. The power scales linearly with the number of input channels or the sampling rate. The efficacy of the processor in early epileptic seizure detection is validated on human intracranial EEG data. PMID:23852175
Polarized gravitational waves from cosmological phase transitions
NASA Astrophysics Data System (ADS)
Kisslinger, Leonard; Kahniashvili, Tina
2015-08-01
We estimate the degree of circular polarization for the gravitational waves generated during the electroweak and QCD phase transitions from the kinetic and magnetic helicity generated by bubble collisions during those cosmological phase transitions.
Transition from winnerless competition to synchronization in time-delayed neuronal motifs
NASA Astrophysics Data System (ADS)
Zhang, X.; Li, P. J.; Wu, F. P.; Wu, W. J.; Jiang, M.; Chen, L.; Qi, G. X.; Huang, H. B.
2012-03-01
The dynamics of brain functional motifs are studied. It is shown that different rhythms can occur in the motifs when time delay is taken into account. These rhythms include synchronization, winnerless competition (WLC) and "two plus one" (TPO). The main discovery is that the transition from WLC to synchronization can be induced simply by time delay. It is also concluded that some medium time delay is needed to achieve WLC in the realistic case. The motifs composed of heterogeneous neurons are also considered.
Phase transition dynamics and gravitational waves
Megevand, Ariel
2009-04-20
During a first-order phase transition, gravitational radiation is generated either by bubble collisions or by turbulence. For phase transitions which took place at the electroweak scale and beyond, the signal is expected to be within the sensitivity range of planned interferometers such as LISA or BBO. We review the generation of gravitational waves in a first-order phase transition and discuss the dependence of the spectrum on the dynamics of the phase transition.
Methods, systems and apparatus for synchronous current regulation of a five-phase machine
Gallegos-Lopez, Gabriel; Perisic, Milun
2012-10-09
Methods, systems and apparatus are provided for controlling operation of and regulating current provided to a five-phase machine when one or more phases has experienced a fault or has failed. In one implementation, the disclosed embodiments can be used to synchronously regulate current in a vector controlled motor drive system that includes a five-phase AC machine, a five-phase inverter module coupled to the five-phase AC machine, and a synchronous current regulator.
Phase locked loop synchronization for direct detection optical PPM communication systems
NASA Technical Reports Server (NTRS)
Chen, C. C.; Gardner, C. S.
1985-01-01
Receiver timing synchronization of an optical pulse position modulation (PPM) communication system can be achieved using a phase locked loop (PLL) if the photodetector output is properly processed. The synchronization performance is shown to improve with increasing signal power and decreasing loop bandwidth. Bit error rate (BER) of the PLL synchronized PPM system is analyzed and compared to that for the perfectly synchronized system. It is shown that the increase in signal power needed to compensate for the imperfect synchronization is small (less than 0.1 dB) for loop bandwidths less than 0.1% of the slot frequency.
Brain Performance versus Phase Transitions
NASA Astrophysics Data System (ADS)
Torres, Joaquín J.; Marro, J.
2015-07-01
We here illustrate how a well-founded study of the brain may originate in assuming analogies with phase-transition phenomena. Analyzing to what extent a weak signal endures in noisy environments, we identify the underlying mechanisms, and it results a description of how the excitability associated to (non-equilibrium) phase changes and criticality optimizes the processing of the signal. Our setting is a network of integrate-and-fire nodes in which connections are heterogeneous with rapid time-varying intensities mimicking fatigue and potentiation. Emergence then becomes quite robust against wiring topology modification—in fact, we considered from a fully connected network to the Homo sapiens connectome—showing the essential role of synaptic flickering on computations. We also suggest how to experimentally disclose significant changes during actual brain operation.
Steady-State Visual Evoked Potentials and Phase Synchronization in Migraine Patients
NASA Astrophysics Data System (ADS)
Angelini, L.; Tommaso, M. De; Guido, M.; Hu, K.; Ivanov, P. Ch.; Marinazzo, D.; Nardulli, G.; Nitti, L.; Pellicoro, M.; Pierro, C.; Stramaglia, S.
2004-07-01
We investigate phase synchronization in EEG recordings from migraine patients. We use the analytic signal technique, based on the Hilbert transform, and find that migraine brains are characterized by enhanced alpha band phase synchronization in the presence of visual stimuli. Our findings show that migraine patients have an overactive regulatory mechanism that renders them more sensitive to external stimuli.
Analysis of phase synchronization of chaotic oscillations in terms of symbolic CTQ-analysis
NASA Astrophysics Data System (ADS)
Makarenko, A. V.
2016-02-01
The application of symbolic CTQ-analysis for studying synchronization of chaotic oscillations is considered. This approach differs substantially from its analogs since it makes it possible to diagnose and measure quantitatively the characteristics of intermittency regimes in synchronization of chaotic systems and, hence, to analyzer the temporal structure of synchronization. The application of the symbolic analysis apparatus based on the T alphabet to systems with phase locking and synchronization of time scales is demonstrated for the first time. As an example, a complex system of two mutually coupled nonidentical Rössler oscillators in the helical chaos regime with attractors having an ill-conditioned phase is considered. The results show that the method considered here makes it possible to reliably diagnose synchronism sooner than a phase locking and/or time-scale synchronization threshold is detected.
Work and quantum phase transitions: quantum latency.
Mascarenhas, E; Bragança, H; Dorner, R; França Santos, M; Vedral, V; Modi, K; Goold, J
2014-06-01
We study the physics of quantum phase transitions from the perspective of nonequilibrium thermodynamics. For first-order quantum phase transitions, we find that the average work done per quench in crossing the critical point is discontinuous. This leads us to introduce the quantum latent work in analogy with the classical latent heat of first order classical phase transitions. For second order quantum phase transitions the irreversible work is closely related to the fidelity susceptibility for weak sudden quenches of the system Hamiltonian. We demonstrate our ideas with numerical simulations of first, second, and infinite order phase transitions in various spin chain models. PMID:25019721
NASA Astrophysics Data System (ADS)
Barois, T.; Perisanu, S.; Vincent, P.; Purcell, S. T.; Ayari, A.
2014-08-01
Synchronization has been reported for a wide range of self-oscillating systems. However, even though it has been predicted theoretically for several decades, the experimental realization of phase self-oscillation, sometimes called phase trapping, in the high driving regime has been studied only recently. We explored in detail the phase dynamics in a synchronized field emission SiC nanoelectromechanical system with intrinsic feedback. A richer variety of phase behavior has been unambiguously identified, implying phase modulation and inertia. This synchronization regime is expected to have implications for the comprehension of the dynamics of interacting self-oscillating networks and for the generation of frequency modulated signals at the nanoscale.
Phase synchronization of diffusively coupled Rössler oscillators with funnel attractors
NASA Astrophysics Data System (ADS)
Yang, H. L.
2001-08-01
Recently, an antiphase phase-synchronized state in a system of diffusively coupled Rössler oscillators has been reported [Gang Hu et al., Phys. Rev. Lett. 85, 3377 (2000)]. In the current paper this antiphase state is explored in detail. Our interests are concentrated on the comparison with the normal in-phase phase-synchronized state for phase-coherent oscillators and the effect of the lattice size. Our main results are that (i) this antiphase synchronization is only for funnel Rössler attractors and cannot be observed in a system of coupled phase-coherent oscillators; (ii) it can be observed only for intermediate values of the lattice size while it disappears for quite low or large values of the lattice size; and (iii) it is different from the in-phase phase-synchronized state of phase-coherent oscillators in many respects.
Joint Carrier-Phase Synchronization and LDPC Decoding
NASA Technical Reports Server (NTRS)
Simon, Marvin; Valles, Esteban
2009-01-01
A method has been proposed to increase the degree of synchronization of a radio receiver with the phase of a suppressed carrier signal modulated with a binary- phase-shift-keying (BPSK) or quaternary- phase-shift-keying (QPSK) signal representing a low-density parity-check (LDPC) code. This method is an extended version of the method described in Using LDPC Code Constraints to Aid Recovery of Symbol Timing (NPO-43112), NASA Tech Briefs, Vol. 32, No. 10 (October 2008), page 54. Both methods and the receiver architectures in which they would be implemented belong to a class of timing- recovery methods and corresponding receiver architectures characterized as pilotless in that they do not require transmission and reception of pilot signals. The proposed method calls for the use of what is known in the art as soft decision feedback to remove the modulation from a replica of the incoming signal prior to feeding this replica to a phase-locked loop (PLL) or other carrier-tracking stage in the receiver. Soft decision feedback refers to suitably processed versions of intermediate results of iterative computations involved in the LDPC decoding process. Unlike a related prior method in which hard decision feedback (the final sequence of decoded symbols) is used to remove the modulation, the proposed method does not require estimation of the decoder error probability. In a basic digital implementation of the proposed method, the incoming signal (having carrier phase theta theta (sub c) plus noise would first be converted to inphase (I) and quadrature (Q) baseband signals by mixing it with I and Q signals at the carrier frequency [wc/(2 pi)] generated by a local oscillator. The resulting demodulated signals would be processed through one-symbol-period integrate and- dump filters, the outputs of which would be sampled and held, then multiplied by a soft-decision version of the baseband modulated signal. The resulting I and Q products consist of terms proportional to the cosine
Effect of phase response curve skew on synchronization with and without conduction delays.
Canavier, Carmen C; Wang, Shuoguo; Chandrasekaran, Lakshmi
2013-01-01
A central problem in cortical processing including sensory binding and attentional gating is how neurons can synchronize their responses with zero or near-zero time lag. For a spontaneously firing neuron, an input from another neuron can delay or advance the next spike by different amounts depending upon the timing of the input relative to the previous spike. This information constitutes the phase response curve (PRC). We present a simple graphical method for determining the effect of PRC shape on synchronization tendencies and illustrate it using type 1 PRCs, which consist entirely of advances (delays) in response to excitation (inhibition). We obtained the following generic solutions for type 1 PRCs, which include the pulse-coupled leaky integrate and fire model. For pairs with mutual excitation, exact synchrony can be stable for strong coupling because of the stabilizing effect of the causal limit region of the PRC in which an input triggers a spike immediately upon arrival. However, synchrony is unstable for short delays, because delayed inputs arrive during a refractory period and cannot trigger an immediate spike. Right skew destabilizes antiphase and enables modes with time lags that grow as the conduction delay is increased. Therefore, right skew favors near synchrony at short conduction delays and a gradual transition between synchrony and antiphase for pairs coupled by mutual excitation. For pairs with mutual inhibition, zero time lag synchrony is stable for conduction delays ranging from zero to a substantial fraction of the period for pairs. However, for right skew there is a preferred antiphase mode at short delays. In contrast to mutual excitation, left skew destabilizes antiphase for mutual inhibition so that synchrony dominates at short delays as well. These pairwise synchronization tendencies constrain the synchronization properties of neurons embedded in larger networks. PMID:24376399
Nonequilibrium dynamics of phase transitions
NASA Astrophysics Data System (ADS)
Gagne, Carmen Jeanne
2001-11-01
Phase transitions occur in such diverse and important systems as ferromagnets, liquid crystals and the early Universe. The dynamics of phase transitions such as these have been studied for decades, but the analytical models still need a great deal of improvement before they can adequately describe all time stages and regions under the coexistence curve. Numerical studies can supplement these analytical theories, but they need to accurately describe the continuum equations that they are intended to solve. This thesis describes a method for removing the lattice- spacing and renormalization-mass dependence of Langevin simulations of phase mixing in (2 + 1)-dimensional asymmetric Ginzburg-Landau models with short-ranged interactions. Also, the spread in the order parameter near the critical value of the control parameter due to critical slowing down is used to more accurately determine this value of the control parameter in these simulations. In addition, a new method is proposed for quantifying the departure from equilibrium. The method explores the behavior of the rate of change of the momentum-integrated structure function, ΔStot( t), as it evolves in time. As an illustration, we examine a (1 + 1)-dimensional model of a stochastic Ginzburg-Landau model at varying cooling rates. We show that ΔStot(t) displays a peak which scales with cooling time-scale as t1/2q in the over-damped limit and t1/3q in the underdamped limit. The peak amplitude was found to scale with cooling time-scale as t6/5q in all viscosities studied.
NASA Astrophysics Data System (ADS)
Moskalenko, O. I.; Koronovskii, A. A.; Hramov, A. E.; Zhuravlev, M. O.
2016-04-01
A method for determining the degree of synchronization of intermittent phase synchronization regime from a time series has been proposed on the basis of estimating the zero conditional Lyapunov exponent. The efficiency of the method has been tested on model systems near the boundary of the appearance of the synchronous regime. The method has been used to determine the degree of synchronization between various regions of the brain of rats of the WAG/Rij line having a genetic predisposition to epilepsy.
QCD Phase Transitions, Volume 15
Schaefer, T.; Shuryak, E.
1999-03-20
The title of the workshop, ''The QCD Phase Transitions'', in fact happened to be too narrow for its real contents. It would be more accurate to say that it was devoted to different phases of QCD and QCD-related gauge theories, with strong emphasis on discussion of the underlying non-perturbative mechanisms which manifest themselves as all those phases. Before we go to specifics, let us emphasize one important aspect of the present status of non-perturbative Quantum Field Theory in general. It remains true that its studies do not get attention proportional to the intellectual challenge they deserve, and that the theorists working on it remain very fragmented. The efforts to create Theory of Everything including Quantum Gravity have attracted the lion share of attention and young talent. Nevertheless, in the last few years there was also a tremendous progress and even some shift of attention toward emphasis on the unity of non-perturbative phenomena. For example, we have seen some efforts to connect the lessons from recent progress in Supersymmetric theories with that in QCD, as derived from phenomenology and lattice. Another example is Maldacena conjecture and related development, which connect three things together, string theory, super-gravity and the (N=4) supersymmetric gauge theory. Although the progress mentioned is remarkable by itself, if we would listen to each other more we may have chance to strengthen the field and reach better understanding of the spectacular non-perturbative physics.
NASA Astrophysics Data System (ADS)
Wang, Bao-Ying; Gong, Yu-Bing
2015-11-01
We numerically study the effect of the channel noise on the spiking synchronization of a scale-free Hodgkin-Huxley neuron network with time delays. It is found that the time delay can induce synchronization transitions at an intermediate and proper channel noise intensity, and the synchronization transitions become strongest when the channel noise intensity is optimal. The neurons can also exhibit synchronization transitions as the channel noise intensity is varied, and this phenomenon is enhanced at around the time delays that can induce the synchronization transitions. It is also found that the synchronization transitions induced by the channel noise are dependent on the coupling strength and the network average degree, and there is an optimal coupling strength or network average degree with which the synchronization transitions become strongest. These results show that by inducing synchronization transitions, the channel noise has a big regulation effect on the synchronization of the neuronal network. These findings could find potential implications for the information transmission in neural systems. Project supported by the Natural Science Foundation of Shandong Province of China (Grant No. ZR2012AM013).
Dynamics of a Quantum Phase Transition
Zurek, Wojciech H.; Dorner, Uwe; Zoller, Peter
2005-09-02
We present two approaches to the dynamics of a quench-induced phase transition in the quantum Ising model. One follows the standard treatment of thermodynamic second order phase transitions but applies it to the quantum phase transitions. The other approach is quantum, and uses Landau-Zener formula for transition probabilities in avoided level crossings. We show that predictions of the two approaches of how the density of defects scales with the quench rate are compatible, and discuss the ensuing insights into the dynamics of quantum phase transitions.
Phase Transition of Diluted Magnetic Semiconductor
NASA Astrophysics Data System (ADS)
Li, M. K.; Lee, S. J.; Yuldashev, S. U.; Ihm, G.; Kang, T. W.
2011-12-01
Three types of phase transitions in diluted magnetic semiconductor, first-order, second-order and mixed-order, are found in theory. Especially the mixed type transition shows two steps transition and novel specific heat property. Specific heat properties disclose a possible meta ferromagnetic phase confirmed by the experimental qualitative result.
Smith, Stephen F.; Moore, James A.
2011-02-01
Systems and methods are described for carrier phase synchronization for improved AM and TV broadcast reception. A method includes synchronizing the phase of a carrier frequency of a broadcast signal with the phase of a remote reference frequency. An apparatus includes a receiver to detect the phase of a reference signal; a phase comparator coupled to the reference signal-phase receiver; a voltage controlled oscillator coupled to the phase comparator; and a phase-controlled radio frequency output coupled to the voltage controlled oscillator.
Smith, Stephen F; Moore, James A
2009-09-08
Systems and methods are described for carrier phase synchronization for improved AM and TV broadcast reception. A method includes synchronizing the phase of a carrier frequency of a broadcast signal with the phase of a remote reference frequency. An apparatus includes a receiver to detect the phase of a reference signal; a phase comparator coupled to the reference signal-phase receiver; a voltage controlled oscillator coupled to the phase comparator; and a phase-controlled radio frequency output coupled to the voltage controlled oscillator.
Cloud regimes as phase transitions
NASA Astrophysics Data System (ADS)
Stechmann, Samuel N.; Hottovy, Scott
2016-06-01
Clouds are repeatedly identified as a leading source of uncertainty in future climate predictions. Of particular importance are stratocumulus clouds, which can appear as either (i) closed cells that reflect solar radiation back to space or (ii) open cells that allow solar radiation to reach the Earth's surface. Here we show that these clouds regimes -- open versus closed cells -- fit the paradigm of a phase transition. In addition, this paradigm characterizes pockets of open cells as the interface between the open- and closed-cell regimes, and it identifies shallow cumulus clouds as a regime of higher variability. This behavior can be understood using an idealized model for the dynamics of atmospheric water as a stochastic diffusion process. With this new conceptual viewpoint, ideas from statistical mechanics could potentially be used for understanding uncertainties related to clouds in the climate system and climate predictions.
NASA Astrophysics Data System (ADS)
Wang, Qi; Gong, Yubing; Xie, Huijuan
2016-05-01
In neural networks, there exist both synaptic delays among different neurons and autaptic self-feedback delays in a neuron itself. In this paper, we study synchronization transitions induced by synaptic and autaptic delays in scale-free neuron networks, mainly exploring how these two time delays affect synchronization transitions induced by each other. It is found that the synchronization transitions induced by synaptic (autaptic) delay are intermittently enhanced when autaptic (synaptic) delay is varied. There are optimal autaptic strength and synaptic coupling strength by which the synchronization transitions induced by autaptic and synaptic delays become strongest. The underlying mechanisms are briefly discussed in terms of the relationships of autaptic delay, synaptic delay, and inter-burst interval. These results show that synaptic and autaptic delays could contribute to each other and enhance synchronization transitions in the neuronal networks. This implies that autaptic and synaptic delays could play a vital role for the information transmission in neural systems.
Phase Response Synchronization in Neuronal Population with Time-Varying Coupling Strength
Jiao, Xianfa; Zhao, Wanyu; Cao, Jinde
2015-01-01
We present the dynamic model of global coupled neuronal population subject to external stimulus by the use of phase sensitivity function. We investigate the effect of time-varying coupling strength on the synchronized phase response of neural population subjected to external harmonic stimulus. For a time-periodic coupling strength, we found that the stimulus with increasing intensity or frequency can reinforce the phase response synchronization in neuronal population of the weakly coupled neural oscillators, and the neuronal population with stronger coupling strength has good adaptability to stimulus. When we consider the dynamics of coupling strength, we found that a strong stimulus can quickly cause the synchronization in the neuronal population, the degree of synchronization grows with the increasing stimulus intensity, and the period of synchronized oscillation induced by external stimulation is related to stimulus frequency. PMID:26640514
Resonance Assisted Synchronization of Coupled Oscillators: Frequency Locking without Phase Locking
NASA Astrophysics Data System (ADS)
Thévenin, J.; Romanelli, M.; Vallet, M.; Brunel, M.; Erneux, T.
2011-09-01
Frequency locking without phase locking of two coupled nonlinear oscillators is experimentally demonstrated. This synchronization regime is found for two coupled laser modes, beyond the phase-locking range fixed by Adler’s equation, because of a resonance mechanism. Specifically, we show that the amplitudes of the two modes exhibit strong fluctuations that produce average frequency synchronization, even if the instantaneous phases are unlocked. The experimental results are in good agreement with a theoretical model.
Nielsen, Olaf
2016-01-01
A well-characterized S phase, a unicellular lifestyle, and a plethora of mutations in key components of DNA metabolism make fission yeast a particularly attractive system in which to study DNA replication. However, synchronization of passage through a normal S phase has proved challenging. This protocol describes how combining nitrogen starvation with M-factor mating pheromone treatment presents a highly effective method for synchronizing passage through an ostensibly normal S phase. PMID:27587782
NASA Astrophysics Data System (ADS)
Ogawa, Yutaro; Ikeda, Akira; Kotani, Kiyoshi; Jimbo, Yasuhiko
In this study, we propose the EEG phase synchronization analysis including not only the average strength of the synchronization but also the distribution and directions under the conditions that evoked emotion by musical stimuli. The experiment is performed with the two different musical stimuli that evoke happiness or sadness for 150 seconds. It is found that the average strength of synchronization indicates no difference between the right side and the left side of the frontal lobe during the happy stimulus, the distribution and directions indicate significant differences. Therefore, proposed analysis is useful for detecting emotional condition because it provides information that cannot be obtained only by the average strength of synchronization.
NASA Technical Reports Server (NTRS)
Natarajan, Suresh; Gardner, C. S.
1987-01-01
Receiver timing synchronization of an optical Pulse-Position Modulation (PPM) communication system can be achieved using a phased-locked loop (PLL), provided the photodetector output is suitably processed. The magnitude of the PLL phase error is a good indicator of the timing error at the receiver decoder. The statistics of the phase error are investigated while varying several key system parameters such as PPM order, signal and background strengths, and PPL bandwidth. A practical optical communication system utilizing a laser diode transmitter and an avalanche photodiode in the receiver is described, and the sampled phase error data are presented. A linear regression analysis is applied to the data to obtain estimates of the relational constants involving the phase error variance and incident signal power.
NASA Astrophysics Data System (ADS)
Jia, Bing
2014-05-01
The coexistence of a resting condition and period-1 firing near a subcritical Hopf bifurcation point, lying between the monostable resting condition and period-1 firing, is often observed in neurons of the central nervous systems. Near such a bifurcation point in the Morris—Lecar (ML) model, the attraction domain of the resting condition decreases while that of the coexisting period-1 firing increases as the bifurcation parameter value increases. With the increase of the coupling strength, and parameter and initial value dependent synchronization transition processes from non-synchronization to compete synchronization are simulated in two coupled ML neurons with coexisting behaviors: one neuron chosen as the resting condition and the other the coexisting period-1 firing. The complete synchronization is either a resting condition or period-1 firing dependent on the initial values of period-1 firing when the bifurcation parameter value is small or middle and is period-1 firing when the parameter value is large. As the bifurcation parameter value increases, the probability of the initial values of a period-1 firing neuron that lead to complete synchronization of period-1 firing increases, while that leading to complete synchronization of the resting condition decreases. It shows that the attraction domain of a coexisting behavior is larger, the probability of initial values leading to complete synchronization of this behavior is higher. The bifurcations of the coupled system are investigated and discussed. The results reveal the complex dynamics of synchronization behaviors of the coupled system composed of neurons with the coexisting resting condition and period-1 firing, and are helpful to further identify the dynamics of the spatiotemporal behaviors of the central nervous system.
Construction of the Lyapunov Spectrum in a Chaotic System Displaying Phase Synchronization
NASA Astrophysics Data System (ADS)
De Carlo, Leonardo; Gentile, Guido; Giuliani, Alessandro
2016-06-01
We consider a three-dimensional chaotic system consisting of the suspension of Arnold's cat map coupled with a clock via a weak dissipative interaction. We show that the coupled system displays a synchronization phenomenon, in the sense that the relative phase between the suspension flow and the clock locks to a special value, thus making the motion fall onto a lower dimensional attractor. More specifically, we construct the attractive invariant manifold, of dimension smaller than three, using a convergent perturbative expansion. Moreover, we compute via convergent series the Lyapunov exponents, including notably the central one. The result generalizes a previous construction of the attractive invariant manifold in a similar but simpler model. The main novelty of the current construction relies in the computation of the Lyapunov spectrum, which consists of non-trivial analytic exponents. Some conjectures about a possible smoothening transition of the attractor as the coupling is increased are also discussed.
Lowet, Eric; Roberts, Mark J.; Bonizzi, Pietro; Karel, Joël; De Weerd, Peter
2016-01-01
Synchronization or phase-locking between oscillating neuronal groups is considered to be important for coordination of information among cortical networks. Spectral coherence is a commonly used approach to quantify phase locking between neural signals. We systematically explored the validity of spectral coherence measures for quantifying synchronization among neural oscillators. To that aim, we simulated coupled oscillatory signals that exhibited synchronization dynamics using an abstract phase-oscillator model as well as interacting gamma-generating spiking neural networks. We found that, within a large parameter range, the spectral coherence measure deviated substantially from the expected phase-locking. Moreover, spectral coherence did not converge to the expected value with increasing signal-to-noise ratio. We found that spectral coherence particularly failed when oscillators were in the partially (intermittent) synchronized state, which we expect to be the most likely state for neural synchronization. The failure was due to the fast frequency and amplitude changes induced by synchronization forces. We then investigated whether spectral coherence reflected the information flow among networks measured by transfer entropy (TE) of spike trains. We found that spectral coherence failed to robustly reflect changes in synchrony-mediated information flow between neural networks in many instances. As an alternative approach we explored a phase-locking value (PLV) method based on the reconstruction of the instantaneous phase. As one approach for reconstructing instantaneous phase, we used the Hilbert Transform (HT) preceded by Singular Spectrum Decomposition (SSD) of the signal. PLV estimates have broad applicability as they do not rely on stationarity, and, unlike spectral coherence, they enable more accurate estimations of oscillatory synchronization across a wide range of different synchronization regimes, and better tracking of synchronization-mediated information
Lowet, Eric; Roberts, Mark J; Bonizzi, Pietro; Karel, Joël; De Weerd, Peter
2016-01-01
Synchronization or phase-locking between oscillating neuronal groups is considered to be important for coordination of information among cortical networks. Spectral coherence is a commonly used approach to quantify phase locking between neural signals. We systematically explored the validity of spectral coherence measures for quantifying synchronization among neural oscillators. To that aim, we simulated coupled oscillatory signals that exhibited synchronization dynamics using an abstract phase-oscillator model as well as interacting gamma-generating spiking neural networks. We found that, within a large parameter range, the spectral coherence measure deviated substantially from the expected phase-locking. Moreover, spectral coherence did not converge to the expected value with increasing signal-to-noise ratio. We found that spectral coherence particularly failed when oscillators were in the partially (intermittent) synchronized state, which we expect to be the most likely state for neural synchronization. The failure was due to the fast frequency and amplitude changes induced by synchronization forces. We then investigated whether spectral coherence reflected the information flow among networks measured by transfer entropy (TE) of spike trains. We found that spectral coherence failed to robustly reflect changes in synchrony-mediated information flow between neural networks in many instances. As an alternative approach we explored a phase-locking value (PLV) method based on the reconstruction of the instantaneous phase. As one approach for reconstructing instantaneous phase, we used the Hilbert Transform (HT) preceded by Singular Spectrum Decomposition (SSD) of the signal. PLV estimates have broad applicability as they do not rely on stationarity, and, unlike spectral coherence, they enable more accurate estimations of oscillatory synchronization across a wide range of different synchronization regimes, and better tracking of synchronization-mediated information
GENERAL: Complete and phase synchronization in a heterogeneous small-world neuronal network
NASA Astrophysics Data System (ADS)
Han, Fang; Lu, Qi-Shao; Wiercigroch, Marian; Ji, Quan-Bao
2009-02-01
Synchronous firing of neurons is thought to be important for information communication in neuronal networks. This paper investigates the complete and phase synchronization in a heterogeneous small-world chaotic Hindmarsh-Rose neuronal network. The effects of various network parameters on synchronization behaviour are discussed with some biological explanations. Complete synchronization of small-world neuronal networks is studied theoretically by the master stability function method. It is shown that the coupling strength necessary for complete or phase synchronization decreases with the neuron number, the node degree and the connection density are increased. The effect of heterogeneity of neuronal networks is also considered and it is found that the network heterogeneity has an adverse effect on synchrony.
Optical phase dynamics in mutually coupled diode laser systems exhibiting power synchronization
NASA Astrophysics Data System (ADS)
Pal, Vishwa; Prasad, Awadhesh; Ghosh, R.
2011-12-01
We probe the physical mechanism behind the known phenomenon of power synchronization of two diode lasers that are mutually coupled via their delayed optical fields. In a diode laser, the amplitude and the phase of the optical field are coupled by the so-called linewidth enhancement factor, α. In this work, we explore the role of optical phases of the electric fields in amplitude (and hence power) synchronization through α in such mutually delay-coupled diode laser systems. Our numerical results show that the synchronization of optical phases drives the powers of lasers to synchronized death regimes. We also find that as α varies for different diode lasers, the system goes through a sequence of in-phase amplitude-death states. Within the windows between successive amplitude-death regions, the cross-correlation between the field amplitudes exhibits a universal power-law behaviour with respect to α.
Phase transitions in the web of science
NASA Astrophysics Data System (ADS)
Phillips, J. C.
2015-06-01
The Internet age is changing the structure of science, and affecting interdisciplinary interactions. Publication profiles connecting mathematics with molecular biology and condensed matter physics over the last 40 years exhibit common phase transitions indicative of the critical role played by specific interdisciplinary interactions. The strengths of the phase transitions quantify the importance of interdisciplinary interactions.
Analysis of Nuclear Quantum Phase Transitions
Li, Z. P.; Meng, J.; Niksic, T.; Vretenar, D.; Lalazissis, G. A.; Ring, P.
2009-08-26
A microscopic analysis, based on nuclear energy density functionals, is presented for shape phase transitions in Nd isotopes. Low-lying excitation spectra and transition probabilities are calculated starting from a five-dimensional Hamiltonian, with parameters determined by constrained relativistic mean-field calculations for triaxial shapes. The results reproduce available data, and show that there is an abrupt change of structure at N = 90, that corresponds to a first-order quantum phase transition between spherical and axially deformed shapes.
Quantum phase transitions in disordered magnets
NASA Astrophysics Data System (ADS)
Nozadze, David
We study the effects of quenched weak disorder on quantum phase transitions in disordered magnets. The presence of disorder in the system can lead to a variety of exotic phenomena, e.g., the smearing of transitions or quantum Griffiths singularities. Phase transitions are smeared if individual spatial regions can order independently of the bulk system. In paper I, we study smeared quantum phase transitions in binary alloys A1-xBx that are tuned by changing the composition x. We show that in this case the ordered phase is extended over all compositions x < 1. We also study the composition dependence of observables. In paper II, we investigate the influence of spatial disorder correlations on smeared phase transitions. As an experimental example, we demonstrate in paper III, that the composition-driven ferromagnetic-toparamagnetic quantum phase transition in Sr1-xCaxRuO3 is smeared. When individual spatial regions cannot order but fluctuate slowly, the phase transition is characterized by strong singularities in the quantum Griffiths phase. In paper IV, we develop a theory of the quantum Griffiths phases in disordered ferromagnetic metals. We show that the quantum Griffiths singularities are stronger than the usual power-law quantum Griffiths singularities in insulating magnets. In paper V, we present an efficient numerical method for studying quantum phase transitions in disordered systems with O(N) order parameter symmetry in the large-N limit. Our algorithm solves iteratively the large-N self-consistent equations for the renormalized distances from criticality. Paper VI is devoted to the study of transport properties in the quantum Griffiths phase associated with the antiferromagnetic quantum phase transition in a metal. We find unusual behavior of transport properties which is in contrast to the normal Fermi-liquid behavior.
Exploring structural phase transitions of ion crystals
Yan, L. L.; Wan, W.; Chen, L.; Zhou, F.; Gong, S. J.; Tong, X.; Feng, M.
2016-01-01
Phase transitions have been a research focus in many-body physics over past decades. Cold ions, under strong Coulomb repulsion, provide a repealing paradigm of exploring phase transitions in stable confinement by electromagnetic field. We demonstrate various conformations of up to sixteen laser-cooled 40Ca+ ion crystals in a home-built surface-electrode trap, where besides the usually mentioned structural phase transition from the linear to the zigzag, two additional phase transitions to more complicated two-dimensional configurations are identified. The experimental observation agrees well with the numerical simulation. Heating due to micromotion of the ions is analysed by comparison of the numerical simulation with the experimental observation. Our investigation implies very rich and complicated many-body behaviour in the trapped-ion systems and provides effective mechanism for further exploring quantum phase transitions and quantum information processing with ultracold trapped ions. PMID:26865229
Pressure-induced phase transition in pentacene
NASA Astrophysics Data System (ADS)
Farina, L.; Brillante, A.; Della Valle, R. G.; Venuti, E.; Amboage, M.; Syassen, K.
2003-07-01
We have recently studied two solid phases of bulk pentacene (polymorphs H and C) by means of lattice phonon Raman spectroscopy. The assignment, previously based on lattice dynamics calculations alone, is now verified by X-ray diffraction measurements, conclusively confirming the existence of both polymorphs. Furthermore, Raman phonon spectra indicate a pressure-induced phase transition where the polymorph C (lower density phase) transforms to the H form (higher density phase). The onset pressure for the phase transition is only 0.2 GPa. The phase change is irreversible.
Microscopic Description of Nuclear Quantum Phase Transitions
Niksic, T.; Vretenar, D.; Lalazissis, G. A.; Ring, P.
2007-08-31
The relativistic mean-field framework, extended to include correlations related to restoration of broken symmetries and to fluctuations of the quadrupole deformation, is applied to a study of shape transitions in Nd isotopes. It is demonstrated that the microscopic self-consistent approach, based on global effective interactions, can describe not only general features of transitions between spherical and deformed nuclei, but also the singular properties of excitation spectra and transition rates at the critical point of quantum shape phase transition.
Phase-dependent forcing and synchronization in the three-sphere model of Chlamydomonas
NASA Astrophysics Data System (ADS)
Bennett, Rachel R.; Golestanian, Ramin
2013-07-01
The green alga Chlamydomonas swims with synchronized beating of its two flagella, and is experimentally observed to exhibit run-and-tumble behaviour similar to bacteria. Recently, we studied a simple hydrodynamic three-sphere model of Chlamydomonas with a phase-dependent driving force that can produce run-and-tumble behaviour when intrinsic noise is added, due to the nonlinear mechanics of the system. Here, we consider the noiseless case and explore numerically the parameter space in the driving force profiles, which determine whether or not the synchronized state evolves from a given initial condition, as well as the stability of the synchronized state. We find that phase-dependent forcing, or a beat pattern, is necessary for stable synchronization in the geometry we work with. The phase-dependent forcing allows this simple model of Chlamydomonas to produce a rich variety of behaviours.
NASA Technical Reports Server (NTRS)
Drake, Jeffrey T.; Prasad, Nadipuram R.
1999-01-01
This paper surveys recent advances in communications that utilize soft computing approaches to phase synchronization. Soft computing, as opposed to hard computing, is a collection of complementary methodologies that act in producing the most desirable control, decision, or estimation strategies. Recently, the communications area has explored the use of the principal constituents of soft computing, namely, fuzzy logic, neural networks, and genetic algorithms, for modeling, control, and most recently for the estimation of phase in phase-coherent communications. If the receiver in a digital communications system is phase-coherent, as is often the case, phase synchronization is required. Synchronization thus requires estimation and/or control at the receiver of an unknown or random phase offset.
NASA Astrophysics Data System (ADS)
Jalili, Mahdi
2013-03-01
In this paper, we investigated phase synchronization in delayed dynamical networks. Non-identical spiking Hindmarsh-Rose neurons were considered as individual dynamical systems and coupled through a number of network structures such as scale-free, Erdős-Rényi, and modular. The individual neurons were coupled through excitatory chemical synapses with uniform or distributed time delays. The profile of spike phase synchrony was different when the delay was uniform across the edges as compared to the case when it was distributed, i.e., different delays for the edges. When an identical transmission delay was considered, a quasi-periodic pattern was observed in the spike phase synchrony. There were specific values of delay where the phase synchronization reached to its peaks. The behavior of the phase synchronization in the networks with non-uniform delays was different with the former case, where the phase synchrony decreased as distributed delays introduced to the networks.
Phase transitions in QCD and string theory
NASA Astrophysics Data System (ADS)
Campell, Bruce A.; Ellis, John; Kalara, S.; Nanopoulos, D. V.; Olive, Keith A.
1991-02-01
We develop a unified effective field theory approach to the high-temperature phase transitions in QCD and string theory, incorporating winding modes (time-like Polyakov loops, vortices) as well as low-mass states (pseudoscalar mesons and glueballs, matter and dilaton supermultiplets). Anomalous scale invariance and the Z3 structure of the centre of SU(3) decree a first-order phase transition with simultaneous deconfinement and Polyakov loop condensation in QCD, whereas string vortex condensation is a second-order phase transition breaking a Z2 symmetry. We argue that vortex condensation is accompanied by a dilaton phase transition to a strong coupling regime, and comment on the possible role of soliton degrees of freedom in the high-temperature string phase. On leave of absence from the School of Physics & Astronomy, University of Minnesota, Minneapolis, Minnesota, USA.
Time concurrency/phase-time synchronization in digital communications networks
NASA Technical Reports Server (NTRS)
Kihara, Masami; Imaoka, Atsushi
1990-01-01
Digital communications networks have the intrinsic capability of time synchronization which makes it possible for networks to supply time signals to some applications and services. A practical estimation method for the time concurrency on terrestrial networks is presented. By using this method, time concurrency capability of the Nippon Telegraph and Telephone Corporation (NTT) digital communications network is estimated to be better than 300 ns rms at an advanced level, and 20 ns rms at final level.
Kim, Sung-Phil; Kang, Jae-Hwan; Choe, Seong-Hyun; Jeong, Ji Woon; Kim, Hyun Taek; Yun, Kyongsik; Jeong, Jaeseung; Lee, Seung-Hwan
2012-08-01
To the extent that recognition memory relies on interactions among widely distributed neural assemblies across the brain, phase synchronization between brain rhythms may play an important role in meditating those interactions. As the theta rhythm is known to modulate in power during the recognition memory process, we aimed to determine how the phase synchronization of the theta rhythms across the brain changes with recognition memory. Fourteen human participants performed a visual object recognition task in a virtual reality environment. Electroencephalograms were recorded from the scalp of the participants while they either recognized objects that had been presented previously or identified new objects. From the electroencephalogram recordings, we analyzed the phase-locking value of the theta rhythms, which indicates the degree of phase synchronization. We found that the overall phase-locking value recorded during the recognition of previously viewed objects was greater than that recorded during the identification of new objects. Specifically, the theta rhythms became strongly synchronized between the frontal and the left parietal areas during the recognition of previously viewed objects. These results suggest that the recognition memory process may involve an interaction between the frontal and the left parietal cortical regions mediated by theta phase synchronization. PMID:22610314
Phase transitions and convection in icy satellites
NASA Technical Reports Server (NTRS)
Bercovici, D.; Schubert, G.; Reynolds, R. T.
1986-01-01
The effects of solid-solid phase changes on subsolidus convection in the large icy moons of the outer solar system are considered. Phase transitions affect convection via processes that distort the phase change boundary and/or influence buoyancy through thermal expansion. Linear stability analyses are carried out for ice layers with a phase change at the midplane. Two exothermic phase transitions (ice I - ice II, ice VI - ice VIII) and two endothermic transitions (ice I - ice III, ice II - ice V) are considered. For the exothermic cases, the phase change can either impede or enhance whole-layer convection. For the endothermic cases, the phse change always inhibits whole-layer convective overturn and tends to enforce two-layer convection. These results play some constraints on possible models of icy satellite evolution and structure.
Adaptive Phase Synchronization Techniques for Unbalanced and Distorted Three-Phase Voltage System
NASA Astrophysics Data System (ADS)
Woinowsky-Krieger, Alexis
Interfacing and operating AC power electronic systems requires rapid and accurate estimation of the phase angle of the power source, and specifically of the positive sequence of the three-phase utility grid voltage. This is needed to ensure reliable operation of the power control devices and of the resulting power flow. However, the quality of this information is undermined by various distortions and unbalanced conditions of the three-phase grid voltage. Phase estimation and power control can both be performed in real time by a DSP, but a DSP typically has limited computational resources, especially in regards to speed and memory, which motivates the search for computationally efficient algorithms to accomplish these tasks. In contrast to conventional PLL techniques, recent approaches have used adaptive amplitude estimation to enhance the acquisition of the phase information, resulting in faster response and improved performance. This thesis presents a novel technique to estimate the phase of the positive sequence of a three-phase voltage in the presence of frequency variations and unbalanced conditions, referred to as hybrid negative sequence adaptive synchronous amplitude estimation with PLL, or H-NSASAE-PLL. The key feature consists of a feedback structure which embeds a positive sequence PLL and an adaptive synchronous negative sequence estimator to enhance the performance of the PLL. The resulting benefits include faster estimation of the phase of the positive sequence under unbalanced conditions with zero steady state error, simplified tuning of PLL parameters to address a wide range of application requirements, robust performance with respect to distortions and PLL parameters, a structure of minimal dynamical order (fifth) to estimate the main signal parameters of interest, simplified discretization, and reduced computational costs, making the proposed technique suitable for real time execution on a DSP. The H-NSASAE-PLL is developed in the Matlab
Phase transition phenomenon: A compound measure analysis
NASA Astrophysics Data System (ADS)
Kang, Bo Soo; Park, Chanhi; Ryu, Doojin; Song, Wonho
2015-06-01
This study investigates the well-documented phenomenon of phase transition in financial markets using combined information from both return and volume changes within short time intervals. We suggest a new measure for the phase transition behaviour of markets, calculated as a return distribution conditional on local variance in volume imbalance, and show that this measure successfully captures phase transition behaviour under various conditions. We analyse the intraday trade and quote dataset from the KOSPI 200 index futures, which includes detailed information on the original order size and the type of each initiating investor. We find that among these two competing factors, the submitted order size yields more explanatory power on the phenomenon of market phase transition than the investor type.
Critical behaviours of contact near phase transitions
Chen, Y.-Y.; Jiang, Y.-Z.; Guan, X.-W.; Zhou, Qi
2014-01-01
A central quantity of importance for ultracold atoms is contact, which measures two-body correlations at short distances in dilute systems. It appears in universal relations among thermodynamic quantities, such as large momentum tails, energy and dynamic structure factors, through the renowned Tan relations. However, a conceptual question remains open as to whether or not contact can signify phase transitions that are insensitive to short-range physics. Here we show that, near a continuous classical or quantum phase transition, contact exhibits a variety of critical behaviours, including scaling laws and critical exponents that are uniquely determined by the universality class of the phase transition, and a constant contact per particle. We also use a prototypical exactly solvable model to demonstrate these critical behaviours in one-dimensional strongly interacting fermions. Our work establishes an intrinsic connection between the universality of dilute many-body systems and universal critical phenomena near a phase transition. PMID:25346226
Swing Amplification of Galactic Spiral Arms: Phase Synchronization of Stellar Epicycle Motion
NASA Astrophysics Data System (ADS)
Michikoshi, Shugo; Kokubo, Eiichiro
2016-06-01
We revisit the swing amplification model of galactic spiral arms proposed by Toomre. We describe the derivation of the perturbation equation in detail and investigate the amplification process of stellar spirals. We find that the elementary process of the swing amplification is the phase synchronization of the stellar epicycle motion. Regardless of the initial epicycle phase, the epicycle phases of stars in a spiral are synchronized during the amplification. Based on the phase synchronization, we explain the dependence of the pitch angle of spirals on the epicycle frequency. We find the most amplified spiral mode and calculate its pitch angle, wavelengths, and amplification factor, which are consistent with those obtained by the more rigorous model based on the Boltzmann equation by Julian & Toomre.
Thermal Phase Transitions in Finite Quantum Systems
Dean, D.J.
2001-10-18
In this Proceedings, the author will describe the behavior of two different quantum-mechanical systems as a function of increasing temperature. While these systems are somewhat different, the questions addressed are very similar, namely, how does one describe transitions in phase of a finite many-body system; how does one recognize these transitions in practical calculations; and how may one obtain the order of the transition.
Phase transition model for community detection
NASA Astrophysics Data System (ADS)
Wu, Jianshe; Lu, Rui; Jiao, Licheng; Liu, Fang; Yu, Xin; Wang, Da; Sun, Bo
2013-03-01
Motivated by social and biological interactions, a novel type of phase transition model is provided in order to investigate the emergence of the clustering phenomenon in networks. The model has two types of interactions: one is attractive and the other is repulsive. In each iteration, the phase of a node (or an agent) moves toward the average phase of its neighbors and moves away from the average phase of its non-neighbors. The velocities of the two types of phase transition are controlled by two parameters, respectively. It is found that the phase transition phenomenon is closely related to the topological structure of the underlying network, and thus can be applied to identify its communities and overlapping groups. By giving each node of the network a randomly generated initial phase and updating these phases by the phase transition model until they reach stability, one or two communities will be detected according to the nodes’ stable phases, confusable nodes are moved into a set named Of. By removing the detected communities and the nodes in Of, another one or two communities will be detected by an iteration of the algorithm, …. In this way, all communities and the overlapping nodes are detected. Simulations on both real-world networks and the LFR benchmark graphs have verified the efficiency of the proposed scheme.
Nuclear binding near a quantum phase transition
NASA Astrophysics Data System (ADS)
Lee, Dean
2016-03-01
I review recent ab initio results by the Nuclear Lattice Effective Field Theory Collaboration showing that nature lies close to a quantum phase transition between an alpha-particle gas and nuclear liquid. I discuss the control parameter of this transition and the implications for clustering in nuclei and improving ab initio nuclear structure calculations.
Phase transitions three-component superfluid
NASA Astrophysics Data System (ADS)
Carlstrom, Johan; Babaev, Egor
2014-03-01
We discuss phase transitions in three-component models of superfluidity and superconductivity. We present Monte Carlo simulations showing that for certain types of inter-component interactions, these systems exhibit novel types of first order phase transitions that are driven by spin-waves. Supported by NSF CAREER Award DMR-0955902, Knut and Alice Wallenberg Foundation through the Royal Swedish Academy of Sciences andSwedish Research Council.
Persistent homology analysis of phase transitions
NASA Astrophysics Data System (ADS)
Donato, Irene; Gori, Matteo; Pettini, Marco; Petri, Giovanni; De Nigris, Sarah; Franzosi, Roberto; Vaccarino, Francesco
2016-05-01
Persistent homology analysis, a recently developed computational method in algebraic topology, is applied to the study of the phase transitions undergone by the so-called mean-field XY model and by the ϕ4 lattice model, respectively. For both models the relationship between phase transitions and the topological properties of certain submanifolds of configuration space are exactly known. It turns out that these a priori known facts are clearly retrieved by persistent homology analysis of dynamically sampled submanifolds of configuration space.
Modelling of phase transitions: do it yourself
NASA Astrophysics Data System (ADS)
Medved', I.; Huckaby, D. A.; Trník, A.; Valovičová, L'
2013-01-01
We present the basics of a powerful contemporary statistical mechanical technique that can be used by students to explore first-order phase transitions by themselves and for models of their own construction. The technique is a generalization of the well-known Peierls argument and is applicable to various models on a lattice. We illustrate the technique with the help of two simple models that were recently used to simulate phase transitions on surfaces.
In-phase synchronization of array laser using intra-Talbot-cavity second harmonic generation
NASA Astrophysics Data System (ADS)
Hirosawa, Kenichi; Shohda, Fumio; Yanagisawa, Takayuki; Kannari, Fumihiko
2015-02-01
Talbot cavity is passive method to synchronize the phase of array lasers. Because the Talbot cavity does not need any electrical feedback systems, we believe that Talbot cavity is the most suitable technique to combine a considerable number of laser array into a compact system. A well-known drawback of the Talbot cavity is that it can produce out-phased array and their far-field image has 2-peak profile. To solve this drawback, we developed a frequency doubled laser array based on intra-Talbot-cavity second harmonic generation. Basic concept is second harmonic generation of the out-phased array generated from the Talbot cavity. Because the second harmonic wave is generated proportionally to the square of the fundamental wave, out-phase flips to in-phase. Our Talbot cavity is composed of a pumping 808-nm laser diode array with 15 emitters, an Nd:YVO4 planar waveguide, a PPLN planar waveguide, an f =10 cylindrical lens, and an output coupler (high reflection for 1064 nm and high transition to 532 nm). The pump laser beams are directly launched into the Nd:YVO4. The fundamental wave (1064 nm) oscillates between the Nd:YVO4 and the output coupler and generates second harmonic wave (532 nm) at the PPLN placed next to the Nd:YVO4. The round-trip optical path of the cavity length is set to 1/2 Talbot length so that Talbot cavity forms for the fundamental wave. As a result, we obtained 1-peak far-field image of second harmonic wave from the intra-Talbot-cavity second harmonic generation.
Higgs couplings and electroweak phase transition
NASA Astrophysics Data System (ADS)
Katz, Andrey; Perelstein, Maxim
2014-07-01
We argue that extensions of the Standard Model (SM) with a strongly first-order electroweak phase transition generically predict significant deviations of the Higgs couplings to gluons, photons, and Z bosons from their SM values. Precise experimental measurements of the Higgs couplings at the LHC and at the proposed next-generation facilities will allow for a robust test of the phase transition dynamics. To illustrate this point, in this paper we focus on the scenario in which loops of a new scalar field are responsible for the first-order phase transition, and study a selection of benchmark models with various SM gauge quantum numbers of the new scalar. We find that the current LHC measurement of the Higgs coupling to gluons already excludes the possibility of a first-order phase transition induced by a scalar in a sextet, or larger, representation of the SU(3) c . Future LHC experiments (including HL-LHC) will be able to definitively probe the case when the new scalar is a color triplet. If the new scalar is not colored, an electron-positron Higgs factory, such as the proposed ILC or TLEP, would be required to test the nature of the phase transition. The extremely precise measurement of the Higgsstrahlung cross section possible at such machines will allow for a comprehensive and definitive probe of the possibility of a first-order electroweak phase transition in all models we considered, including the case when the new scalar is a pure gauge singlet.
Contemporary Research of Dynamically Induced Phase Transitions
NASA Astrophysics Data System (ADS)
Hull, Lawrence
2015-06-01
Dynamically induced phase transitions in metals, within the present discussion, are those that take place within a time scale characteristic of the shock waves and any reflections or rarefactions involved in the loading structure along with associated plastic flow. Contemporary topics of interest include the influence of loading wave shape, the effect of shear produced by directionality of the loading relative to the sample dimensions and initial velocity field, and the loading duration (kinetic effects, hysteresis) on the appearance and longevity of a transformed phase. These topics often arise while considering the loading of parts of various shapes with high explosives, are typically two or three-dimensional, and are often selected because of the potential of the transformed phase to significantly modify the motion. In this paper, we look at current work on phase transitions in metals influenced by shear reported in the literature, and relate recent work conducted at Los Alamos on iron's epsilon phase transition that indicates a significant response to shear produced by reflected elastic waves. A brief discussion of criteria for the occurrence of stress induced phase transitions is provided. Closing remarks regard certain physical processes, such as fragmentation and jet formation, which may be strongly influenced by phase transitions. Supported by the DoD/DOE Joint Munitions Technology Development Program.
Supercooling and phase coexistence in cosmological phase transitions
Megevand, Ariel; Sanchez, Alejandro D.
2008-03-15
Cosmological phase transitions are predicted by particle physics models, and have a variety of important cosmological consequences, which depend strongly on the dynamics of the transition. In this work we investigate in detail the general features of the development of a first-order phase transition. We find thermodynamical constraints on some quantities that determine the dynamics, namely, the latent heat, the radiation energy density, and the false-vacuum energy density. Using a simple model with a Higgs field, we study numerically the amount and duration of supercooling and the subsequent reheating and phase coexistence. We analyze the dependence of the dynamics on the different parameters of the model, namely, the energy scale, the number of degrees of freedom, and the couplings of the scalar field with bosons and fermions. We also inspect the implications for the cosmological outcomes of the phase transition.
Continuous and discontinuous topological quantum phase transitions
NASA Astrophysics Data System (ADS)
Roy, Bitan; Goswami, Pallab; Sau, Jay D.
2016-07-01
The continuous quantum phase transition between noninteracting, time-reversal symmetric topological and trivial insulators in three dimensions is described by the massless Dirac fermion. We address the stability of this quantum critical point against short range electronic interactions by using renormalization group analysis and mean field theory. For sufficiently weak interactions, we show that the nature of the direct transition remains unchanged. Beyond a critical strength of interactions we find that either (i) there is a direct first order transition between two time reversal symmetric insulators or (ii) the direct transition is eliminated by an intervening time reversal and inversion odd "axionic" insulator. We also demonstrate the existence of an interaction driven first order quantum phase transition between topological and trivial gapped states in lower dimensions.
Phase synchronization of non-Abelian oscillators on small-world networks
NASA Astrophysics Data System (ADS)
Gu, Zhi-Ming; Zhao, Ming; Zhou, Tao; Zhu, Chen-Ping; Wang, Bing-Hong
2007-02-01
In this Letter, by extending the concept of Kuramoto oscillator to the left-invariant flow on general Lie group, we investigate the generalized phase synchronization on networks. The analyses and simulations of some typical dynamical systems on Watts Strogatz networks are given, including the n-dimensional torus, the identity component of 3-dimensional general linear group, the special unitary group, and the special orthogonal group. In all cases, the greater disorder of networks will predict better synchronizability, and the small-world effect ensures the global synchronization for sufficiently large coupling strength. The collective synchronized behaviors of many dynamical systems, such as the integrable systems, the two-state quantum systems and the top systems, can be described by the present phase synchronization frame. In addition, it is intuitive that the low-dimensional systems are more easily to synchronize, however, to our surprise, we found that the high-dimensional systems display obviously synchronized behaviors in regular networks, while these phenomena cannot be observed in low-dimensional systems.
Monoclinic phases arising across thermal inter-ferroelectric phase transitions
NASA Astrophysics Data System (ADS)
Gu, Yijia; Xue, Fei; Lei, Shiming; Lummen, Tom T. A.; Wang, Jianjun; Gopalan, Venkatraman; Chen, Long-Qing
2014-07-01
Thermotropic phase boundaries (TPBs), as thermal analogs of morphotropic phase boundaries (MPBs), are associated with the thermal inter-ferroelectric phase transitions. Similar to an MPB, a TPB exhibits a characteristically flattened energy profile which favors polarization rotation, thus giving rise to a structurally bridging low-symmetry phase. We report on the kinetic process of thermal inter-ferroelectric phase transitions in BaTiO3 and KNbO3 using the phase-field method. The domain structures are found to play key roles in stabilizing the monoclinic phase. In simple domain structures, the monoclinic phase is a transient phase and cannot be stabilized into its neighboring phase regimes. However, by introducing structural inhomogeneity (orthogonal in-plane domain twins), we found that the monoclinic phase can be stabilized over a range of over 100 K across the transition. As a result, the piezoelectric properties are enhanced due to the stabilized monoclinic phase. In addition to the emergence of new piezoelectric components with monoclinic symmetry, most of the original components present in the tetragonal symmetry also show substantial enhancement with the rotation of polarization.
Thermochromic phase transitions in two aromatic tetrachlorocuprates
NASA Astrophysics Data System (ADS)
Mostafa, M. Fareed; Abdel-Kader, M. M.; Arafat, S. S.; Kandeel, E. M.
1991-06-01
Bis(para-toluidinium)2 tetrachlorocuprate and bis(para-chloroanilinium)2 tetrachlorocuprate crystallize in a perovskite-related layer structure. The former crystallizes in an orthorhombic unit cell with a = 6.911 Å, b = 7.052 Å and c = 33.182 Å. It undergoes a thermochromic first order phase transition from a yellow low temperature phase to a dark orange high temperature phase at T = 300 ± 3K with a 10° thermal hysteresis. The latter compound undergoes two thermochromic transitions expressed by the relation. Orange Phase (I) rightleftarrows294 K Yellow Phase (II) rightleftarrows214K Green Phase (III). Both compounds are ferromagnetic at low temperture with exchange interactions J/k = 17.5° and 20° for the two compounds respectively.
Random fields at a nonequilibrium phase transition.
Barghathi, Hatem; Vojta, Thomas
2012-10-26
We study nonequilibrium phase transitions in the presence of disorder that locally breaks the symmetry between two equivalent macroscopic states. In low-dimensional equilibrium systems, such random-field disorder is known to have dramatic effects: it prevents spontaneous symmetry breaking and completely destroys the phase transition. In contrast, we show that the phase transition of the one-dimensional generalized contact process persists in the presence of random-field disorder. The ultraslow dynamics in the symmetry-broken phase is described by a Sinai walk of the domain walls between two different absorbing states. We discuss the generality and limitations of our theory, and we illustrate our results by large-scale Monte Carlo simulations. PMID:23215170
NASA Astrophysics Data System (ADS)
Hata, Shigefumi; Arai, Kensuke; Galán, Roberto F.; Nakao, Hiroya
2011-07-01
We consider optimization of phase response curves for stochastic synchronization of noninteracting limit-cycle oscillators by common Poisson impulsive signals. The optimal functional shape for sufficiently weak signals is sinusoidal, but can differ for stronger signals. By solving the Euler-Lagrange equation associated with the minimization of the Lyapunov exponent characterizing synchronization efficiency, the optimal phase response curve is obtained. We show that the optimal shape mutates from a sinusoid to a sawtooth as the constraint on its squared amplitude is varied.
Closed-loop carrier phase synchronization techniques motivated by likelihood functions
NASA Technical Reports Server (NTRS)
Tsou, H.; Hinedi, S.; Simon, M.
1994-01-01
This article reexamines the notion of closed-loop carrier phase synchronization motivated by the theory of maximum a posteriori phase estimation with emphasis on the development of new structures based on both maximum-likelihood and average-likelihood functions. The criterion of performance used for comparison of all the closed-loop structures discussed is the mean-squared phase error for a fixed-loop bandwidth.
NASA Astrophysics Data System (ADS)
Lombard, L.; Bellanger, C.; Canat, G.; Mugnier, L.; Cassaing, F.; Michau, V.; Bourdon, P.; Primot, J.
2015-10-01
Active coherent beam combination (CBC) of femtosecond pulses requires knowledge of the absolute phase between all the optical pulses: pulse synchronization and phase locking are both mandatory and must be measured and controlled. To assess controller requirements, we study fiber amplifier phase noise for various packaging and power levels. The main contributors are thermal noise (with large amplitude phase noise and frequencies below 5 Hz) and vibrations (with low amplitude phase noise and frequencies from 5 Hz to 2 kHz), leading to a woofer/tweeter pair of actuator. The amplifier packaging is of major importance: a simple PID model shows that in order to achieve a residual phase error of λ/100, the required controller bandwidth ranges from 0.5 Hz to 1 kHz, mostly depending on amplifier packaging. We also shortly review common phase locking techniques either based on pupil-plane sensor or focal-plane sensor. Common focal-plane techniques as SPGD or LOCSET are not directly compatible with pulsed femtosecond operation. Pupil-plane fringe-sensor techniques are more promising and route towards collective synchronization for femtosecond regime are proposed. Following the example of telescope interferometry, the final system might include both a pupil-plane, fringe-sensor and a focal-plane phase-diversity sensor, with pupil-plane sensor for synchronization and phase lock, and focal-plane sensor to control and maintain required focalized beam quality.
Phase transitions at high pressure in tetracyanoethylene
NASA Astrophysics Data System (ADS)
Mukhopadhyay, R.; Deb, S. K.; Das, Amitabh; Chaplot, S. L.
2009-11-01
We report in situ x-ray diffraction studies in tetracyanoethylene (TCNE) at high pressure using diamond anvil cell (DAC) at Elettra synchrotron source, Trieste, Italy. Experiments were performed with both the polymorphic phases (monoclinic and cubic) of TCNE as the starting phase. While starting with monoclinic (the high temperature stable) TCNE, it was found that the Bragg peaks get broadened with increase of pressure and above 5 GPa only few broad peaks remained to be observed. On release of pressure from 6.4 GPa, when the sample started turning black, the diffraction pattern at ambient pressure corresponds to cubic, the other crystalline phase of TCNE. Results reconfirm the monoclinic to cubic transition at high pressure but via an intermediate 'disordered' phase. This settles a number of conflicting issues. TCNE represents only system, which undergoes transition from one crystalline to another crystalline phase via a 'disordered' metastable phase at high pressure. When the starting phase was cubic (the low temperature stable) no apparent phase transition was observed up to 10.8 GPa.
Shaping Crystal-Crystal Phase Transitions
NASA Astrophysics Data System (ADS)
Du, Xiyu; van Anders, Greg; Dshemuchadse, Julia; Glotzer, Sharon
Previous computational and experimental studies have shown self-assembled structure depends strongly on building block shape. New synthesis techniques have led to building blocks with reconfigurable shape and it has been demonstrated that building block reconfiguration can induce bulk structural reconfiguration. However, we do not understand systematically how this transition happens as a function of building block shape. Using a recently developed ``digital alchemy'' framework, we study the thermodynamics of shape-driven crystal-crystal transitions. We find examples of shape-driven bulk reconfiguration that are accompanied by first-order phase transitions, and bulk reconfiguration that occurs without any thermodynamic phase transition. Our results suggest that for well-chosen shapes and structures, there exist facile means of bulk reconfiguration, and that shape-driven bulk reconfiguration provides a viable mechanism for developing functional materials.
Phase transitions in multiplicative competitive processes
Shimazaki, Hideaki; Niebur, Ernst
2005-07-01
We introduce a discrete multiplicative process as a generic model of competition. Players with different abilities successively join the game and compete for finite resources. Emergence of dominant players and evolutionary development occur as a phase transition. The competitive dynamics underlying this transition is understood from a formal analogy to statistical mechanics. The theory is applicable to bacterial competition, predicting novel population dynamics near criticality.
Friction forces on phase transition fronts
Mégevand, Ariel
2013-07-01
In cosmological first-order phase transitions, the microscopic interaction of the phase transition fronts with non-equilibrium plasma particles manifests itself macroscopically as friction forces. In general, it is a nontrivial problem to compute these forces, and only two limits have been studied, namely, that of very slow walls and, more recently, ultra-relativistic walls which run away. In this paper we consider ultra-relativistic velocities and show that stationary solutions still exist when the parameters allow the existence of runaway walls. Hence, we discuss the necessary and sufficient conditions for the fronts to actually run away. We also propose a phenomenological model for the friction, which interpolates between the non-relativistic and ultra-relativistic values. Thus, the friction depends on two friction coefficients which can be calculated for specific models. We then study the velocity of phase transition fronts as a function of the friction parameters, the thermodynamic parameters, and the amount of supercooling.
Quantum phase transitions with dynamical flavors
NASA Astrophysics Data System (ADS)
Bea, Yago; Jokela, Niko; Ramallo, Alfonso V.
2016-07-01
We study the properties of a D6-brane probe in the Aharony-Bergman-Jafferis-Maldacena (ABJM) background with smeared massless dynamical quarks in the Veneziano limit. Working at zero temperature and nonvanishing charge density, we show that the system undergoes a quantum phase transition in which the topology of the brane embedding changes from a black hole to a Minkowski embedding. In the unflavored background the phase transition is of second order and takes place when the charge density vanishes. We determine the corresponding critical exponents and show that the scaling behavior near the quantum critical point has multiplicative logarithmic corrections. In the background with dynamical quarks the phase transition is of first order and occurs at nonzero charge density. In this case we compute the discontinuity of several physical quantities as functions of the number Nf of unquenched quarks of the background.
Gong, Hai-Qing; Liang, Pei-Ji; Zhang, Pu-Ming; Lu, Qin-Chi
2016-01-01
The synchronization among the activities of neural populations in functional regions is one of the most important electrophysiological phenomena in epileptic brains. The spatiotemporal dynamics of phase synchronization was investigated to reveal the reciprocal interaction between different functional regions during epileptogenesis. Local field potentials (LFPs) were recorded simultaneously from the basolateral amygdala (BLA), the cornu ammonis 1 of hippocampus (CA1) and the mediodorsal nucleus of thalamus (MDT) in the mouse amygdala-kindling models during the development of epileptic seizures. The synchronization of LFPs was quantified between BLA, CA1 and MDT using phase-locking value (PLV). During amygdala kindling, behavioral changes (from stage 0 to stage 5) of mice were accompanied by after-discharges (ADs) of similar waveforms appearing almost simultaneously in CA1, MDT, as well as BLA. AD durations were positively related to the intensity of seizures. During seizures at stages 1~2, PLVs remained relatively low and increased dramatically shortly after the termination of the seizures; by contrast, for stages 3~5, PLVs remained a relatively low level during the initial period but increased dramatically before the seizure termination. And in the theta band, the degree of PLV enhancement was positively associated with seizure intensity. The results suggested that during epileptogenesis, the functional regions were kept desynchronized rather than hyper-synchronized during either the initial or the entire period of the seizures; so different dynamic patterns of phase synchronization may be involved in different periods of the epileptogenesis, and this might also reflect that during seizures at different stages, the mechanisms underlying the dynamics of phase synchronization were different. PMID:27100891
Late-time cosmological phase transitions
Schramm, D.N. Fermi National Accelerator Lab., Batavia, IL )
1990-11-01
It is shown that the potential galaxy formation and large-scale structure problems of objects existing at high redshifts (Z {approx gt} 5), structures existing on scales of 100M pc as well as velocity flows on such scales, and minimal microwave anisotropies ({Delta}T/T) {approx lt} 10{sup {minus}5} can be solved if the seeds needed to generate structure form in a vacuum phase transition after decoupling. It is argued that the basic physics of such a phase transition is no more exotic than that utilized in the more traditional GUT scale phase transitions, and that, just as in the GUT case, significant random gaussian fluctuations and/or topological defects can form. Scale lengths of {approximately}100M pc for large-scale structure as well as {approximately}1 M pc for galaxy formation occur naturally. Possible support for new physics that might be associated with such a late-time transition comes from the preliminary results of the SAGE solar neutrino experiment, implying neutrino flavor mixing with values similar to those required for a late-time transition. It is also noted that a see-saw model for the neutrino masses might also imply a tau neutrino mass that is an ideal hot dark matter candidate. However, in general either hot or cold dark matter can be consistent with a late-time transition. 47 refs., 2 figs.
Late-time cosmological phase transitions
NASA Technical Reports Server (NTRS)
Schramm, David N.
1991-01-01
It is shown that the potential galaxy formation and large scale structure problems of objects existing at high redshifts (Z approx. greater than 5), structures existing on scales of 100 M pc as well as velocity flows on such scales, and minimal microwave anisotropies ((Delta)T/T) (approx. less than 10(exp -5)) can be solved if the seeds needed to generate structure form in a vacuum phase transition after decoupling. It is argued that the basic physics of such a phase transition is no more exotic than that utilized in the more traditional GUT scale phase transitions, and that, just as in the GUT case, significant random Gaussian fluctuations and/or topological defects can form. Scale lengths of approx. 100 M pc for large scale structure as well as approx. 1 M pc for galaxy formation occur naturally. Possible support for new physics that might be associated with such a late-time transition comes from the preliminary results of the SAGE solar neutrino experiment, implying neutrino flavor mixing with values similar to those required for a late-time transition. It is also noted that a see-saw model for the neutrino masses might also imply a tau neutrino mass that is an ideal hot dark matter candidate. However, in general either hot or cold dark matter can be consistent with a late-time transition.
Phase synchronization of multiple klystrons in RF system
Kwon, S.; Regan, A.; Wang, Y.M.; Rohlev, T.
1998-12-31
The Low Energy Demonstration Accelerator (LEDA) being constructed at Los Alamos National Laboratory will serve as the prototype for the low energy section of the Acceleration Production of Tritium (APT) accelerator. The first LEDA RF system includes three, 1.2 MW, 350 MHz, continuous wave, klystrons driving a radio frequency quadrupole (RFQ). A phase control loop is necessary for each individual klystron in order to guarantee the phase matching of these klystrons. To meet this objective, they propose adaptive PI controllers which are based on simple adaptive control. These controllers guarantee not only phase matching but also amplitude matching.
Synchronization and Spin-Flop Transitions for a Mean-Field XY Model in Random Field
NASA Astrophysics Data System (ADS)
Collet, Francesca; Ruszel, Wioletta
2016-08-01
We characterize the phase space for the infinite volume limit of a ferromagnetic mean-field XY model in a random field pointing in one direction with two symmetric values. We determine the stationary solutions and detect possible phase transitions in the interaction strength for fixed random field intensity. We show that at low temperature magnetic ordering appears perpendicularly to the field. The latter situation corresponds to a spin-flop transition.
Shape phase transitions and critical points
Alonso, C. E.; Arias, J. M.; Fortunato, L.; Vitturi, A.
2009-05-04
We investigate different aspects connected with shape phase transitions in nuclei and the possible occurrence of dynamical symmetries at the critical points. We discuss in particular the behaviour of the neighbour odd nuclei at the vicinity of the critical points in the even nuclei. We consider both the case of the transition from the vibrational behaviour to the gamma-unstable deformation (characterized within the collective Bohr hamiltonian by the E(5) critical point symmetry) and the case of the transition from the vibrational behaviour to the stable axial deformation (characterized by the X(5) symmetry). The odd particle is assumed to be moving in the three single particle orbitals j = 1/2,3/2,5/2, a set of orbitals that is known to lead to possible supersymmetric cases. The coupling of the odd particle to the Bohr hamiltonian does lead in fact in the former case at the critical point to the E(5/12) boson-fermion dynamical symmetry. An alternative approach to the two shape transitions is based on the Interacting Boson Fermion Model. In this case suitably parametrized boson-fermion hamiltonians can describe the evolution of the odd system along the shape transitions. At the critical points both energy spectra and electromagnetic transitions were found to display characteristic patterns similar to those displayed by the even nuclei at the corresponding critical point. The behaviour of the odd nuclei can therefore be seen as necessary complementary signatures of the occurrence of the phase transitions.
Network traffic behaviour near phase transition point
NASA Astrophysics Data System (ADS)
Lawniczak, A. T.; Tang, X.
2006-03-01
We explore packet traffic dynamics in a data network model near phase transition point from free flow to congestion. The model of data network is an abstraction of the Network Layer of the OSI (Open Systems Interconnect) Reference Model of packet switching networks. The Network Layer is responsible for routing packets across the network from their sources to their destinations and for control of congestion in data networks. Using the model we investigate spatio-temporal packets traffic dynamics near the phase transition point for various network connection topologies, and static and adaptive routing algorithms. We present selected simulation results and analyze them.
Solid-liquid phase transition in argon
NASA Technical Reports Server (NTRS)
Tsang, T.; Tang, H. T.
1978-01-01
Starting from the Lennard-Jones interatomic potential, a modified cell theory has been used to describe the solid-liquid phase transition in argon. The cell-size variations may be evaluated by a self-consistent condition. With the inclusion of cell-size variations, the transition temperature, the solid and liquid densities, and the liquid-phase radial-distribution functions have been calculated. These ab initio results are in satisfactory agreement with molecular-dynamics calculations as well as experimental data on argon.
Phase transition in loop quantum gravity
NASA Astrophysics Data System (ADS)
Mäkelä, Jarmo
2016-04-01
We point out that with a specific counting of states loop quantum gravity implies that black holes perform a phase transition at a certain characteristic temperature TC . In this phase transition the punctures of the spin network on the stretched horizon of the black hole jump, in effect, from the vacuum to the excited states. The characteristic temperature TC may be regarded as the lowest possible temperature of the hole. From the point of view of a distant observer at rest with respect to the hole, the characteristic temperature TC corresponds to the Hawking temperature of the hole.
Queueing phase transition: theory of translation.
Romano, M Carmen; Thiel, Marco; Stansfield, Ian; Grebogi, Celso
2009-05-15
We study the current of particles on a lattice, where to each site a different hopping probability has been associated and the particles can move only in one direction. We show that the queueing of the particles behind a slow site can lead to a first-order phase transition, and derive analytical expressions for the configuration of slow sites for this to happen. We apply this stochastic model to describe the translation of mRNAs. We show that the first-order phase transition, uncovered in this work, is the process responsible for the classification of the proteins having different biological functions. PMID:19519001
Holographic endpoint of spatially modulated phase transition
Ooguri, Hirosi; Park, Chang-Soon
2010-12-15
In a previous paper [S. Nakamura, H. Ooguri, and C. S. Park, Phys. Rev. D 81, 044018 (2010)], we showed that the Reissner-Nordstroem black hole in the five-dimensional anti-de Sitter space coupled to the Maxwell theory with the Chern-Simons term is unstable when the Chern-Simons coupling is sufficiently large. In the dual conformal field theory, the instability suggests a spatially modulated phase transition. In this paper, we construct and analyze nonlinear solutions which describe the endpoint of this phase transition. In the limit where the Chern-Simons coupling is large, we find that the phase transition is of the second order with the mean field critical exponent. However, the dispersion relation with the Van Hove singularity enhances quantum corrections in the bulk, and we argue that this changes the order of the phase transition from the second to the first. We compute linear response functions in the nonlinear solution and find an infinite off-diagonal DC conductivity in the new phase.
Seasonal Synchronization of Diapause Phases in Aedes albopictus (Diptera: Culicidae)
Lacour, Guillaume; Chanaud, Lionel; L’Ambert, Grégory; Hance, Thierry
2015-01-01
In temperate areas, population dynamics of the invasive Asian tiger mosquito Aedes albopictus are strongly affected by winter. The work we present here analyzes the adaptive synchronization of the diapause process in the wintry generation of A. albopictus, where the egg stage is exposed to adverse winter conditions. The seasonal pattern of egg laying activity of a French Mediterranean population of the Asian tiger mosquito was monitored weekly for 2 years with ovitraps. The field diapause incidence and the critical photoperiod (CPP, i.e. the maternal day length inducing diapause in 50% of the eggs), were determined by hatching experiments on the collected eggs. The period of diapause termination was estimated by a field survey of the first hatchings for both years. The CPP is equal to 13.5 hours of light and occurs in the field on the 25th of August. Thus, it is on September 11th, 17 days after the CPP, that 50% of the eggs are in a prediapause stage in the field. The egg diapause rate increases rapidly during September, whereas the mean number of eggs laid decreases sharply after mid-September. Surprisingly, after having reached a peak of 95% at the end of September, from mid-October the diapause incidence declined and stayed below 50%. Indeed, both years the diapause initiates before the rapid decrease of the environmental temperature. This leaves a sufficient period of time to the complete development of one generation of A. albopictus with effective induction of diapause in the laid eggs. The very first larvae hatched were sampled both years in the first half of March. With 20 to 26 weeks in the egg stage and about 7 weeks in the larval stages, the first annual generation spends a long time in immature stages. On a practical point of view, this long development time represents a wide window for eggs and larvae control in early spring. PMID:26683460
Transition to turbulence in pipe flow as a phase transition
NASA Astrophysics Data System (ADS)
Vasudevan, Mukund; Hof, Björn
2015-11-01
In pipe flow, turbulence first arises in the form of localized turbulent patches called puffs. The flow undergoes a transition to sustained turbulence via spatio-temporal intermittency, with puffs splitting, decaying and merging in the background laminar flow. However, the due to mean advection of the puffs and the long timescales involved (~107 advective time units), it is not possible to study the transition in typical laboratory set-ups. So far, it has only been possible to indirectly estimate the critical point for the transition. Here, we exploit the stochastic memoryless nature of the puff decay and splitting processes to construct a pipe flow set-up, that is periodic in a statistical sense. It then becomes possible to study the flow for sufficiently long times and characterize the transition in detail. We present measurements of the turbulent fraction as a function of Reynolds number which in turn allows a direct estimate of the critical point. We present evidence that the transition has features of a phase transition of second order.
On configurational weak phase transitions in graphene
NASA Astrophysics Data System (ADS)
Sfyris, Dimitris
2016-07-01
We report a study on configurational weak phase transitions for a freestanding monolayer graphene. Firstly, we characterize weak transformation neighborhoods by suitably bounding the metric components. Then, we distinguish between structural and configurational phase changes and elaborate on the second class of them. We evaluate the irreducible invariant subspaces corresponding to these phase changes and lay down symmetry-breaking as well as symmetry-preserving stretches. In the reduced bifurcation diagram, symmetry-preserving stretches are related to a turning point with a change of stability but not of symmetry. Symmetry-breaking stretches are related to a first-order weak phase transition. We evaluate symmetry-breaking stretches as well as their generating cosets. The reduced bifurcation diagram consists of three transcritical bifurcating curves which are all unstable but can be stabilized producing a subcritical bifurcation. We, also, shortly comment on the hysteretical behavior that might appear in this case.
Black Hole Phase Transition in Massive Gravity
NASA Astrophysics Data System (ADS)
Ning, Shou-Li; Liu, Wen-Biao
2016-07-01
In massive gravity, some new phenomena of black hole phase transition are found. There are more than one critical points under appropriate parameter values and the Gibbs free energy near critical points also has some new properties. Moreover, the Maxwell equal area rule is also investigated and the coexistence curve of the black hole is given.
Hysteresis in the phase transition of chocolate
NASA Astrophysics Data System (ADS)
Ren, Ruilong; Lu, Qunfeng; Lin, Sihua; Dong, Xiaoyan; Fu, Hao; Wu, Shaoyi; Wu, Minghe; Teng, Baohua
2016-01-01
We designed an experiment to reproduce the hysteresis phenomenon of chocolate appearing in the heating and cooling process, and then established a model to relate the solidification degree to the order parameter. Based on the Landau-Devonshire theory, our model gave a description of the hysteresis phenomenon in chocolate, which lays the foundations for the study of the phase transition behavior of chocolate.
Dual condensate and QCD phase transition
Zhang Bo; Bruckmann, Falk; Fodor, Zoltan; Szabo, Kalman K.; Gattringer, Christof
2011-05-23
The dual condensate is a new QCD phase transition order parameter, which connnects confinement and chiral symmetry breaking as different mass limits. We discuss the relation between the fermion spectrum at general boundary conditions and the dual condensate and show numerical results for the latter from unquenched SU(3) lattice configurations.
Theory and phenomenology of electroweak phase transitions
NASA Astrophysics Data System (ADS)
Patel, Hiren H.
An open problem in cosmology is to explain the origin of baryon abundance implied by observational cosmology. Among the many proposed explanations, electroweak baryogenesis is particularly attractive in that its ingredients is discoverable by modern experiments. The analysis of the electroweak phase transition in the early universe comprises an integral component within the larger study of electroweak baryogenesis. In this work, I make a detailed investigation of the conventional analysis of the electroweak phase transition commonly found in literature, and explicitly demonstrate that results are not independent of the choice of gauge. In its place, I provide a manifestly gauge-independent method for the analysis, review sources of theoretical and numerical uncertainties, and explore avenues for further development. Next, I explore the dynamics of the electroweak phase transition in two minimal extensions of the Standard Model of particle physics. Within these simple models, I describe a novel pattern of electroweak symmetry breaking favorable for baryogenesis that can serve as a paradigm for phase transition analysis in more complicated models.
Chaos: Butterflies also Generate Phase Transitions
NASA Astrophysics Data System (ADS)
Leplaideur, Renaud
2015-10-01
We exhibit examples of mixing subshifts of finite type and of continuous potentials such that there are phase transitions but the pressure is always strictly convex. More surprisingly, we show that the pressure can be analytic on some interval although there exist several equilibrium states.
Application of epidemic models to phase transitions
NASA Astrophysics Data System (ADS)
Bilge, A. H.; Pekcan, Ö.; Gürol, M. V.
2012-11-01
The Susceptible-Infected-Recovered (SIR) and Susceptible-Exposed-Infected-Recovered (SEIR) models describe the spread of epidemics in a society. In the typical case, the ratio of the susceptible individuals fall from a value S 0 close to 1 to a final value Sf , while the ratio of recovered individuals rise from 0 to Rf = 1 - Sf . The sharp passage from the level zero to the level Rf allows also the modeling of phase transitions by the number of "recovered" individuals R(t) of the SIR or SEIR model. In this article, we model the sol-gel transition for polyacrylamide-sodium alginate (SA) composite with different concentrations of SA as SIR and SEIR dynamical systems by solving the corresponding differential equations numerically and we show that the phase transitions of "classical" and "percolation" types are represented, respectively, by the SEIR and SIR models.
Double-Diffusive Layers and Phase Transitions
NASA Astrophysics Data System (ADS)
Dude, Sabine; Hansen, Ulrich
2015-04-01
Researching the thermal evolution of the Earth's mantle on numerical base is very challenging. During the last decade different approaches are put forward in oder to understand the picture of the today's Earth's mantle. One way is to incorporate all the known features and physics (plate tectonics, phase transitions, CMB-topography, ...) into numerical models and make them as complex (or 'complete') as possible to capture Earth's mantle processes and surface signals. Another way is, to take a step back and look at less complex models which account for single processes and their interaction and evolution. With these 'simpler' models one is able look in detail into the physical processes and dependencies on certain parameters. Since the knowledge of slab stagnation in the transitions zone of the Earth's mantle the question whether the mantle is or at least has been layered to some degree is still under debate. On this basis we address two important features that lead to layered mantle convection and may affect each other and with this the thermal evolution of the mantle. It is commonly known the main mantle mineral olivine pass through various phase changes with depth [1]. Detailed numerical studies had been carried out to ascertain the influence on convective motion and planetary evolution [2]. It is still heavily discussed whether the endothermic phase change at 660km depth can lead an isolated lower mantle. Most of the numerical studies favour a model which has phases of layering that are disrupted by catastrophic events. In the last years double-diffusive convection has also been intensively studied with regard to planetary mantle evolution such as pile formation and core-mantle boundary topography [3]. However, another striking feature still posing open questions are evolving layers self-organised from a previous non layered state. Considering a chemical component that influences the density of a fluid in addition to the temperature leads to dynamical phenomena
EEG alpha phase shifts during transition from wakefulness to drowsiness.
Kalauzi, Aleksandar; Vuckovic, Aleksandra; Bojić, Tijana
2012-12-01
Phases of alpha oscillations recorded by EEG were typically studied in the context of event or task related experiments, rarely during spontaneous alpha activity and in different brain states. During wake-to-drowsy transition they change unevenly, depending on the brain region. To explore their dynamics, we recorded ten adult healthy individuals in these two states. Alpha waves were treated as stable frequency and variable amplitude signals with one carrier frequency (CF). A method for calculating their CF phase shifts (CFPS) and CF phase potentials (CFPP) was developed and verified on surrogate signals as more accurate than phase shifts of Fourier components. Probability density estimate (PDE) of CFPS, CFPP and CF phase locking showed that frontal and fronto-temporal areas of the cortex underwent more extensive changes than posterior regions. The greatest differences were found between pairs of channels involving F7, F8, F3 and F4 (PDE of CFPS); F7, F8, T3 and T4 (CFPP); F7, F8, F3, F4, C3, C4 and T3 (decrease in CF phase locking). A topographic distribution of channels with above the average phase locking in the wake state revealed two separate regions occupying anterior and posterior brain areas (with intra regional and inter hemispheric connections). These regions merged and became mutually phase locked longitudinally in the drowsy state. Changes occurring primarily in the frontal and fronto-temporal regions correlated with an early decrease of alertness. Areas of increased phase locking might be correlated with topography of synchronous neuronal assemblies conceptualized within neural correlates of consciousness. PMID:22580156
NASA Astrophysics Data System (ADS)
Megam Ngouonkadi, Elie B.; Nono, Martial Kabong; Tamba, Victor Kamdoum; Fotsin, Hilaire B.
2015-11-01
Diffusive electrical connections in neuronal networks are instantaneous, while excitatory or inhibitory couplings through chemical synapses contain a transmission time-delay. Moreover, chemical synapses are nonlinear dynamical systems whose behavior can be described by nonlinear differential equations. In this work, neuronal networks with diffusive electrical couplings and time-delayed dynamic chemical couplings are considered. We investigate the effects of distributed time delays on phase synchronization of bursting neurons. We observe that in both excitatory and Inhibitory chemical connections, the phase synchronization might be enhanced when time-delay is taken into account. This distributed time delay can induce a variety of phase-coherent dynamical behaviors. We also study the collective dynamics of network of bursting neurons. The network model presents the so-called Small-World property, encompassing neurons whose dynamics have two time scales (fast and slow time scales). The neuron parameters in such Small-World network, are supposed to be slightly different such that, there may be synchronization of the bursting (slow) activity if the coupling strengths are large enough. Bounds for the critical coupling strengths to obtain burst synchronization in terms of the network structure are given. Our studies show that the network synchronizability is improved, as its heterogeneity is reduced. The roles of synaptic parameters, more precisely those of the coupling strengths and the network size are also investigated.
NASA Astrophysics Data System (ADS)
Yu, Dan; Yang, Jun-Zhong
2014-02-01
A recent study has found an explosive synchronization in a Kurammoto model on scale-free networks when the natural frequencies of oscillators are equal to their degrees. In this work, we introduce a quantity to characterize the correlation between the structural and the dynamical properties and investigate the impacts of the correlation on the synchronization transition in the Kuramoto model on scale-free networks. We find that the synchronization transition may be either a continuous one or a discontinuous one depending on the correlation and that strong correlation always postpones both the transitions from the incoherent state to a synchronous one and the transition from a synchronous state to the incoherent one. We find that the dependence of the synchronization transition on the correlation is also valid for other types of distributions of natural frequency.
Nonuniversal surface behavior of dynamic phase transitions.
Riego, Patricia; Berger, Andreas
2015-06-01
We have studied the dynamic phase transition (DPT) of the kinetic Ising model in systems with surfaces within the mean-field approximation. Varying the surface exchange coupling strength J(s), the amplitude of the externally applied oscillating field h(0), and its period P, we explore the dynamic behavior of the layer-dependent magnetization and the associated DPTs. The surface phase diagram shows several features that resemble those of the equilibrium case, with an extraordinary bulk transition and a surface transition for high J(s) values, independent from the value of h(0). For low J(s), however, h(0) is found to be a crucial parameter that leads to nonuniversal surface behavior at the ordinary bulk transition point. Specifically, we observed here a bulk-supported surface DPT for high field amplitudes h(0) and correspondingly short critical periods P(c), whereas this surface transition simultaneous to the bulk one is suppressed for slow critical dynamics occurring for low values of h(0). The suppression of the DPT for low h(0) not only occurs for the topmost surface layer, but also affects a significant number of subsurface layers. We find that the key physical quantity that explains this nonuniversal behavior is the time correlation between the dynamic surface and bulk magnetizations at the bulk critical point. This time correlation has to pass a threshold value to trigger a bulk-induced DPT in the surface layers. Otherwise, dynamic phase transitions are absent at the surface in stark contrast to the equilibrium behavior of the corresponding thermodynamic Ising model. Also, we have analyzed the penetration depth of the dynamically ordered phase for the surface DPT that occurs for large J(s) values. Here we find that the penetration depth depends strongly on J(s) and behaves identically to the corresponding equilibrium Ising model. PMID:26172695
Chandrasekar, A; Rakkiyappan, R; Cao, Jinde
2015-10-01
This paper studies the impulsive synchronization of Markovian jumping randomly coupled neural networks with partly unknown transition probabilities via multiple integral approach. The array of neural networks are coupled in a random fashion which is governed by Bernoulli random variable. The aim of this paper is to obtain the synchronization criteria, which is suitable for both exactly known and partly unknown transition probabilities such that the coupled neural network is synchronized with mixed time-delay. The considered impulsive effects can be synchronized at partly unknown transition probabilities. Besides, a multiple integral approach is also proposed to strengthen the Markovian jumping randomly coupled neural networks with partly unknown transition probabilities. By making use of Kronecker product and some useful integral inequalities, a novel Lyapunov-Krasovskii functional was designed for handling the coupled neural network with mixed delay and then impulsive synchronization criteria are solvable in a set of linear matrix inequalities. Finally, numerical examples are presented to illustrate the effectiveness and advantages of the theoretical results. PMID:26210982
Frequency synchronization and phase locking of CO/sub 2/ lasers
Leeb, W.R.; Philipp, H.K.; Scholtz, A.L.; Bonek, E.
1982-10-01
Employing the principle of a phase-locked loop (PLL) we have synchronized the frequency and phase of two CO/sub 2/ lasers. The laser acting as voltage controlled oscillator is tuned both by electro-optic and piezoelectric means. A cooled photodiode serves as the phase detector. The main loop parameters, natural frequency ..omega../sub n/ and damping factor zeta, have been measured. The small phase jitter in the error signal obtained will allow application of such an optical PLL in homodyne receivers at 10 ..mu..m.
NASA Astrophysics Data System (ADS)
Atlas, Dogan A.
1990-01-01
This thesis study presents the design/analysis considerations, fundamental performance limitations and the experimental set-up of an optical phase-locked loop which is employed in phase-shift keying homodyne and synchronous heterodyne optical fiber communication system experiments. From an optical communication systems point of view, the characteristics of the lightwave sources to be used are important to investigate. Therefore, frequency modulation, frequency noise and intensity noise characteristics of 1320-nm (227 THz) laser-diode-pumped miniature Nd:YAG ring lasers have been investigated. The modulation and noise properties of these lasers are characterized both qualitatively and quantitatively. For applications such as optical phase-locking, phase-shift keying homodyne and synchronous heterodyne optical fiber and optical free -space communication systems, subcarrier multiplexing systems, and microwave phase array antennas diode-pumped Nd:YAG lasers are excellent lightwave sources. The reasons that make these lasers attractive candidates for such a variety of applications include the narrow laser linewidth, the uniformly flat frequency modulation response and the wide frequency modulation bandwidth. A stable second-order optical phase-locked loop has been constructed using two Nd:YAG lasers and a balanced optical receiver. The loop is designed so that the local oscillator laser locks to the frequency/phase variations of the transmitter laser. The frequency/phase tracking performance of the loop is limited by the quantum phase noise and mainly by the frequency drift induced by the temperature variations of both the transmitter and local oscillator laser cavities. Using the loop, optical phase -shift keying homodyne communication system experiments are demonstrated at modulation rates of 140 Mb/s and 2 Gb/s. The receiver sensitivity at 140 Mb/s is 25 photons/bit which is the highest sensitivity reported to date with any optical communication system. An optical
Phase transitions and chaos in long-range models of coupled oscillators
NASA Astrophysics Data System (ADS)
Miritello, G.; Pluchino, A.; Rapisarda, A.
2009-01-01
We study the chaotic behavior of the synchronization phase transition in the Kuramoto model. We discuss the relationship with analogous features found in the Hamiltonian mean-field (HMF) model. Our numerical results support the connection between the two models, which can be considered as limiting cases (dissipative and conservative, respectively) of a more general dynamical system of damped/driven coupled pendula. We also show that, in the Kuramoto model, the shape of the phase transition and the largest Lyapunov exponent behavior are strongly dependent on the distribution of the natural frequencies.
NASA Astrophysics Data System (ADS)
Huang, Xu-Hui; Hu, Gang
2014-10-01
Phase transitions widely exist in nature and occur when some control parameters are changed. In neural systems, their macroscopic states are represented by the activity states of neuron populations, and phase transitions between different activity states are closely related to corresponding functions in the brain. In particular, phase transitions to some rhythmic synchronous firing states play significant roles on diverse brain functions and disfunctions, such as encoding rhythmical external stimuli, epileptic seizure, etc. However, in previous studies, phase transitions in neuronal networks are almost driven by network parameters (e.g., external stimuli), and there has been no investigation about the transitions between typical activity states of neuronal networks in a self-organized way by applying plastic connection weights. In this paper, we discuss phase transitions in electrically coupled and lattice-based small-world neuronal networks (LBSW networks) under spike-timing-dependent plasticity (STDP). By applying STDP on all electrical synapses, various known and novel phase transitions could emerge in LBSW networks, particularly, the phenomenon of self-organized phase transitions (SOPTs): repeated transitions between synchronous and asynchronous firing states. We further explore the mechanics generating SOPTs on the basis of synaptic weight dynamics.
Phase transitions in nonequilibrium traffic theory
Zhang, H.M.
2000-02-01
This paper uses the center difference scheme of Lax-Friedrichs to numerically solve a newly developed continuum traffic flow theory and the kinematic theory of Lighthill and Whitham, and Richards, and it studies the flow-concentration phase transitions in flow containing both shock and rarefaction waves. A homogeneous road with finite length was modeled by both theories. Numerical simulations show that both theories yield nearly identical results for two representative Riemann problems--one has a shock solution and the other a rarefaction wave solution. Their phase transition curves, however, are different: those derived from the new theory have two branches--one for acceleration flow and one for deceleration flow, whereas those derived from the LWR theory comprise a single curve--the equilibrium curve. The phase transition curves in the shock case agree well with certain experimental observations but disagree with others. This disagreement may be resolved by studying transitions among nonequilibrium states, which awaits further development of a more accurate finite difference approximation of the nonequilibrium theory.
Phase transition theory of sprite halo
NASA Astrophysics Data System (ADS)
Hiraki, Yasutaka
2010-04-01
We present the phase transition theory for sprite halo using measurable lightning parameters (charge moment and discharge time) on the basis of steady state thermodynamics. A halo is located at the upper part of the tree-like structure of a sprite and is produced through electron impact excitation of neutral species under the lightning-induced electric field. We proposed in our previous studies that the occurrence criteria for halos and sprites are characterized by the above lightning parameters, and additionally, the intensity of a halo weakens rapidly with an increase in the discharge time T. We assume that this phenomenon is quite similar to the phase transition between the vapor and the liquid states of water; here the analogy is between the accelerated electrons and the water molecules. We demonstrate analytically a phase transition for a simply modeled halo based on the quasistatic theory of lightning-induced electric field. Choosing the luminosity of a halo as an order parameter, we show that it has a dependence of T-0.25 - Tc-0.25 near the critical point Tc, which is characteristic of the phase transition. Furthermore, the critical time scale Tc ≈ 5.5 ms is provided naturally from our modeling and is somewhat larger than the typical time scale of the halo luminosity in observations. We consider that this kind of formalism is useful in understanding the detailed relationship between lightning activity and occurrence of halos. We discuss this point for future observations along with the possibilities of the transition model of column and carrot structures.
Understanding topological phase transition in monolayer transition metal dichalcogenides
NASA Astrophysics Data System (ADS)
Choe, Duk-Hyun; Sung, Ha-Jun; Chang, K. J.
2016-03-01
Despite considerable interest in layered transition metal dichalcogenides (TMDs), such as M X2 with M =(Mo ,W ) and X =(S ,Se ,Te ) , the physical origin of their topological nature is still poorly understood. In the conventional view of topological phase transition (TPT), the nontrivial topology of electron bands in TMDs is caused by the band inversion between metal d - and chalcogen p -orbital bands where the former is pulled down below the latter. Here, we show that, in TMDs, the TPT is entirely different from the conventional speculation. In particular, M S2 and M S e2 exhibits the opposite behavior of TPT such that the chalcogen p -orbital band moves down below the metal d -orbital band. More interestingly, in M T e2 , the band inversion occurs between the metal d -orbital bands. Our findings cast doubts on the common view of TPT and provide clear guidelines for understanding the topological nature in new topological materials to be discovered.
Topological phase transition in layered transition metal dichalcogenides
NASA Astrophysics Data System (ADS)
Choe, Duk-Hyun; Sung, Ha-Jun; Chang, Kee Joo
Despite considerable interests in transition metal dichalcogenides (TMDs), such as MX2 with M = (Mo, W) and X = (S, Se, Te), the physical origin of their topological nature is still in its infancy. The conventional view of topological phase transition (TPT) in TMDs is that the band inversion occurs between the metal d and chalcogen p orbital bands. More precisely, the former is pulled down below the latter. Here we introduce an explicit scheme for analyzing TPT in topological materials and find that the TPT in TMDs is different from the conventional speculation. When the 1T phase undergoes a structural transformation to the 1T' phase in monolayer MX2, the band topology changes from trivial to non-trivial, leading to the TPT. We discuss the exact role of the metal d and chalcogen p orbital bands during the TPT. Our finding would provide clear guidelines for understanding the topological nature not only in TMDs but also in other topological materials yet to be explored.
NASA Astrophysics Data System (ADS)
Radhakrishnan, Srinivasan; Duvvuru, Arjun; Sultornsanee, Sivarit; Kamarthi, Sagar
2016-02-01
The cross correlation coefficient has been widely applied in financial time series analysis, in specific, for understanding chaotic behaviour in terms of stock price and index movements during crisis periods. To better understand time series correlation dynamics, the cross correlation matrices are represented as networks, in which a node stands for an individual time series and a link indicates cross correlation between a pair of nodes. These networks are converted into simpler trees using different schemes. In this context, Minimum Spanning Trees (MST) are the most favoured tree structures because of their ability to preserve all the nodes and thereby retain essential information imbued in the network. Although cross correlations underlying MSTs capture essential information, they do not faithfully capture dynamic behaviour embedded in the time series data of financial systems because cross correlation is a reliable measure only if the relationship between the time series is linear. To address the issue, this work investigates a new measure called phase synchronization (PS) for establishing correlations among different time series which relate to one another, linearly or nonlinearly. In this approach the strength of a link between a pair of time series (nodes) is determined by the level of phase synchronization between them. We compare the performance of phase synchronization based MST with cross correlation based MST along selected network measures across temporal frame that includes economically good and crisis periods. We observe agreement in the directionality of the results across these two methods. They show similar trends, upward or downward, when comparing selected network measures. Though both the methods give similar trends, the phase synchronization based MST is a more reliable representation of the dynamic behaviour of financial systems than the cross correlation based MST because of the former's ability to quantify nonlinear relationships among time
Phase Transitions in Models of Bird Flocking
NASA Astrophysics Data System (ADS)
Christodoulidi, H.; van der Weele, K.; Antonopoulos, Ch. G.; Bountis, T.
2014-12-01
The aim of the present paper is to elucidate the transition from collective to random behavior exhibited by various mathematical models of bird flocking. In particular, we compare Vicsek's model [Vicsek et al., Phys. Rev. Lett. 75, 1226-1229 (1995)] with one based on topological considerations. The latter model is found to exhibit a first order phase transition from flocking to decoherence, as the "noise parameter" of the problem is increased, whereas Vicsek's model gives a second order transition. Refining the topological model in such a way that birds are influenced mostly by the birds in front of them, less by the ones at their sides and not at all by those behind them (because they do not see them), we find a behavior that lies in between the two models. Finally, we propose a novel mechanism for preserving the flock's cohesion, without imposing artificial boundary conditions or attractive forces.
Phase transition to turbulence in a pipe
NASA Astrophysics Data System (ADS)
Goldenfeld, Nigel
Leo Kadanoff taught us much about phase transitions, turbulence and collective behavior. Here I explore the transition to turbulence in a pipe, showing how a collective mode determines the universality class. Near the transition, turbulent puffs decay either directly or through splitting, with characteristic time-scales that exhibit a super-exponential dependence on Reynolds number. Direct numerical simulations reveal that a collective mode, a so-called zonal flow emerges at large scales, activated by anisotropic turbulent fluctuations, as represented by Reynolds stress. This zonal flow imposes a shear on the turbulent fluctuations that tends to suppress their anisotropy, leading to a Landau theory of predator-prey type, in the directed percolation universality class. Stochastic simulations of this model reproduce the functional form and phenomenology of pipe flow experiments. Talk based on work performed with Hong-Yan Shih and Tsung-Lin Hsieh. This work was partially supported by the National Science Foundation through Grant NSF-DMR-1044901.
Phase transitions in soft-committee machines
NASA Astrophysics Data System (ADS)
Biehl, M.; Schlösser, E.; Ahr, M.
1998-10-01
Equilibrium statistical physics is applied to the off-line training of layered neural networks with differentiable activation functions. A first analysis of soft-committee machines with an arbitrary number (K) of hidden units and continuous weights learning a perfectly matching rule is performed. Our results are exact in the limit of high training temperatures (β → 0). For K = 2 we find a second-order phase transition from unspecialized to specialized student configurations at a critical size P of the training set, whereas for K >= 3 the transition is first order. The limit K → ∞ can be performed analytically, the transition occurs after presenting on the order of NK/β examples. However, an unspecialized metastable state persists up to P propto NK2/β.
Song, Zhiwen; Wu, Ye; Liu, Weiqing; Xiao, Jinghua
2015-01-01
It has recently been observed in numerical simulations that the phases of two coupled nonlinear oscillators can become locked into an irrational ratio, exhibiting the phenomenon of irrational phase synchronization (IPS) [Phys. Rev. E 69, 056228 (2004)]. Here, using two coupled nonidentical periodic mechanical metronomes, we revisit this interesting phenomenon through experimental studies. It is demonstrated that under suitable couplings, the phases of the metronomes indeed can become locked into irrational ratios. Numerical simulations confirm the experimental observations and also reveal that in the IPS state, the system dynamics are chaotic. Our studies provide a solid step toward further studies of IPS. PMID:25786222
Gravitational Waves from a Dark Phase Transition.
Schwaller, Pedro
2015-10-30
In this work, we show that a large class of models with a composite dark sector undergo a strong first order phase transition in the early Universe, which could lead to a detectable gravitational wave signal. We summarize the basic conditions for a strong first order phase transition for SU(N) dark sectors with n_{f} flavors, calculate the gravitational wave spectrum and show that, depending on the dark confinement scale, it can be detected at eLISA or in pulsar timing array experiments. The gravitational wave signal provides a unique test of the gravitational interactions of a dark sector, and we discuss the complementarity with conventional searches for new dark sectors. The discussion includes the twin Higgs and strongly interacting massive particle models as well as symmetric and asymmetric composite dark matter scenarios. PMID:26565451
Phase transition in the countdown problem.
Lacasa, Lucas; Luque, Bartolo
2012-07-01
We present a combinatorial decision problem, inspired by the celebrated quiz show called Countdown, that involves the computation of a given target number T from a set of k randomly chosen integers along with a set of arithmetic operations. We find that the probability of winning the game evidences a threshold phenomenon that can be understood in the terms of an algorithmic phase transition as a function of the set size k. Numerical simulations show that such probability sharply transitions from zero to one at some critical value of the control parameter, hence separating the algorithm's parameter space in different phases. We also find that the system is maximally efficient close to the critical point. We derive analytical expressions that match the numerical results for finite size and permit us to extrapolate the behavior in the thermodynamic limit. PMID:23005354
Evolution of structure during phase transitions
Martin, J.E.; Wilcoxon, J.P.; Anderson, R.A.
1996-03-01
Nanostructured materials can be synthesized by utilizing the domain growth that accompanies first-order phase separation. Structural control can be achieved by appropriately selecting the quench depth and the quench time, but in order to do this in a mindful fashion one must understand the kinetics of domain growth. The authors have completed detailed light scattering studies of the evolution of structure in both temperature- and field-quenched phase transitions in two and three dimensional systems. They have studied these systems in the quiescent state and in shear and have developed theoretical models that account for the experimental results.
Structural phase transitions in monolayer molybdenum dichalcogenides
NASA Astrophysics Data System (ADS)
Choe, Duk-Hyun; Sung, Ha June; Chang, Kee Joo
2015-03-01
The recent discovery of two-dimensional materials such as graphene and transition metal dichalcogenides (TMDs) has provided opportunities to develop ultimate thin channel devices. In contrast to graphene, the existence of moderate band gap and strong spin-orbit coupling gives rise to exotic electronic properties which vary with layer thickness, lattice structure, and symmetry. TMDs commonly appear in two structures with distinct symmetries, trigonal prismatic 2H and octahedral 1T phases which are semiconducting and metallic, respectively. In this work, we investigate the structural and electronic properties of monolayer molybdenum dichalcogenides (MoX2, where X = S, Se, Te) through first-principles density functional calculations. We find a tendency that the semiconducting 2H phase is more stable than the metallic 1T phase. We show that a spontaneous symmetry breaking of 1T phase leads to various distorted octahedral (1T') phases, thus inducing a metal-to-semiconductor transition. We discuss the effects of carrier doping on the structural stability and the modification of the electronic structure. This work was supported by the National Research Foundation of Korea (NRF) under Grant No. NRF-2005-0093845 and Samsung Science and Technology Foundation under Grant No. SSTFBA1401-08.
Phase transitions in Nowak Sznajd opinion dynamics
NASA Astrophysics Data System (ADS)
Wołoszyn, Maciej; Stauffer, Dietrich; Kułakowski, Krzysztof
2007-05-01
The Nowak modification of the Sznajd opinion dynamics model on the square lattice assumes that with probability β the opinions flip due to mass-media advertising from down to up, and vice versa. Besides, with probability α the Sznajd rule applies that a neighbour pair agreeing in its two opinions convinces all its six neighbours of that opinion. Our Monte Carlo simulations and mean-field theory find sharp phase transitions in the parameter space.
Phase Transitions in Delaunay Potts Models
NASA Astrophysics Data System (ADS)
Adams, Stefan; Eyers, Michael
2016-01-01
We establish phase transitions for certain classes of continuum Delaunay multi-type particle systems (continuum Potts models) with infinite range repulsive interaction between particles of different type. In one class of the Delaunay Potts models studied the repulsive interaction is a triangle (multi-body) interaction whereas in the second class the interaction is between pairs (edges) of the Delaunay graph. The result for the edge model is an extension of finite range results in Bertin et al. (J Stat Phys 114(1-2):79-100, 2004) for the Delaunay graph and in Georgii and Häggström (Commun Math Phys 181:507-528, 1996) for continuum Potts models to an infinite range repulsion decaying with the edge length. This is a proof of an old conjecture of Lebowitz and Lieb. The repulsive triangle interactions have infinite range as well and depend on the underlying geometry and thus are a first step towards studying phase transitions for geometry-dependent multi-body systems. Our approach involves a Delaunay random-cluster representation analogous to the Fortuin-Kasteleyn representation of the Potts model. The phase transitions manifest themselves in the percolation of the corresponding random-cluster model. Our proofs rely on recent studies (Dereudre et al. in Probab Theory Relat Fields 153:643-670, 2012) of Gibbs measures for geometry-dependent interactions.
Generalized phase transitions in Lovelock gravity
NASA Astrophysics Data System (ADS)
Camanho, Xián O.; Edelstein, José D.; Giribet, Gastón; Gomberoff, Andrés
2014-09-01
We investigate a novel mechanism for phase transitions that is a distinctive feature of higher-curvature gravity theories. For definiteness, we bound ourselves to the case of Lovelock gravities. These theories are known to have several branches of asymptotically anti-de Sitter solutions. Here, extending our previous work, we show that phase transitions among some of these branches are driven by a thermalon configuration: a bubble separating two regions of different effective cosmological constants, generically hosting a black hole in the interior. Above some critical temperature, this thermalon configuration is preferred with respect to the finite-temperature anti-de Sitter space, triggering a sophisticated version of the Hawking-Page transition. After being created, the unstable bubble configuration can in general dynamically change the asymptotic cosmological constant. While this phenomenon already occurs in the case of a gravity action with square curvature terms, we point out that in the case of Lovelock theory with cubic (and higher) terms new effects appear. For instance, the theory may admit more than one type of bubble and branches that are in principle free of pathologies may also decay through the thermalon mechanism. We also find ranges of the gravitational couplings for which the theory becomes sick. These add up to previously found restrictions to impose tighter constraints on higher-curvature gravities. The results of this paper point to an intricate phase diagram which might accommodate similarly rich behavior in the dual conformal field theory side.
Phase transitions in planar bilayer membranes.
White, S H
1975-01-01
Temperature-dependent structural changes in planar bilayer membranes formed from glycerol monooleate (GMO) dispersed in various n-alkane solvents (C12-C17) have been studied using precise measurements of specific geometric capacitance (Cg). Cg generally increases as temperature (T) decreases. A change in the slope of Cg(T) occurs between 15 and 18 degrees C for all solvent systems examined. Measurements of the interfacial tension (gamma) of the bulk GMO-alkane dispersions against 0.1 M NaCl show that gamma generally decreases with decreasing temperature. The data can be fitted with two straight lines of different slope which intersect on the average at 17 degrees C. Pagano et al. (1973, Science (Wash. D.C.). 181:557) have shown using calorimetry that GMO has a phase transition at about 15 degrees C. Thus, the changes in Cg and gamma with temperature are likely to result from a GMO phase transition. A second structural change is observed to occur between 5 and 10 degrees C which has not been detected calorimetrically. Calculations of Cg based on various estimates of the hydrocarbon dielectric coefficient (epsilon-b) and/or hydrocarbon thickness (delta-b) leads to models for the structure of the bilayer above and below the phase transition temperature. PMID:1111634
Bursting frequency versus phase synchronization in time-delayed neuron networks
NASA Astrophysics Data System (ADS)
Nordenfelt, Anders; Used, Javier; Sanjuán, Miguel A. F.
2013-05-01
We investigate the dependence of the average bursting frequency on time delay for neuron networks with randomly distributed time-delayed chemical synapses. The result is compared with the corresponding curve for the phase synchronization and it turns out that, in some intervals, these have a very similar shape and appear as almost mirror images of each other. We have analyzed both the map-based chaotic Rulkov model and the continuous Hindmarsh-Rose model, yielding the same conclusions. In order to gain further insight, we also analyzed time-delayed Kuramoto models displaying an overall behavior similar to that observed on the neuron network models. For the Kuramoto models, we were able to derive analytical formulas providing an implicit functional relationship between the mean frequency and the phase synchronization. These formulas suggest a strong dependence between those two measures, which could explain the similarities in shape between the curves.
Lowet, Eric; Roberts, Mark; Hadjipapas, Avgis; Peter, Alina; van der Eerden, Jan; De Weerd, Peter
2015-01-01
Fine-scale temporal organization of cortical activity in the gamma range (∼25–80Hz) may play a significant role in information processing, for example by neural grouping (‘binding’) and phase coding. Recent experimental studies have shown that the precise frequency of gamma oscillations varies with input drive (e.g. visual contrast) and that it can differ among nearby cortical locations. This has challenged theories assuming widespread gamma synchronization at a fixed common frequency. In the present study, we investigated which principles govern gamma synchronization in the presence of input-dependent frequency modulations and whether they are detrimental for meaningful input-dependent gamma-mediated temporal organization. To this aim, we constructed a biophysically realistic excitatory-inhibitory network able to express different oscillation frequencies at nearby spatial locations. Similarly to cortical networks, the model was topographically organized with spatially local connectivity and spatially-varying input drive. We analyzed gamma synchronization with respect to phase-locking, phase-relations and frequency differences, and quantified the stimulus-related information represented by gamma phase and frequency. By stepwise simplification of our models, we found that the gamma-mediated temporal organization could be reduced to basic synchronization principles of weakly coupled oscillators, where input drive determines the intrinsic (natural) frequency of oscillators. The gamma phase-locking, the precise phase relation and the emergent (measurable) frequencies were determined by two principal factors: the detuning (intrinsic frequency difference, i.e. local input difference) and the coupling strength. In addition to frequency coding, gamma phase contained complementary stimulus information. Crucially, the phase code reflected input differences, but not the absolute input level. This property of relative input-to-phase conversion, contrasting with latency
Phase Transitions in Model Active Systems
NASA Astrophysics Data System (ADS)
Redner, Gabriel S.
The amazing collective behaviors of active systems such as bird flocks, schools of fish, and colonies of microorganisms have long amazed scientists and laypeople alike. Understanding the physics of such systems is challenging due to their far-from-equilibrium dynamics, as well as the extreme diversity in their ingredients, relevant time- and length-scales, and emergent phenomenology. To make progress, one can categorize active systems by the symmetries of their constituent particles, as well as how activity is expressed. In this work, we examine two categories of active systems, and explore their phase behavior in detail. First, we study systems of self-propelled spherical particles moving in two dimensions. Despite the absence of an aligning interaction, this system displays complex emergent dynamics, including phase separation into a dense active solid and dilute gas. Using simulations and analytic modeling, we quantify the phase diagram and separation kinetics. We show that this nonequilibrium phase transition is analogous to an equilibrium vapor-liquid system, with binodal and spinodal curves and a critical point. We also characterize the dense active solid phase, a unique material which exhibits the structural signatures of a crystalline solid near the crystal-hexatic transition point, as well as anomalous dynamics including superdiffusive motion on intermediate timescales. We also explore the role of interparticle attraction in this system. We demonstrate that attraction drastically changes the phase diagram, which contains two distinct phase-separated regions and is reentrant as a function of propulsion speed. We interpret this complex situation with a simple kinetic model, which builds from the observed microdynamics of individual particles to a full description of the macroscopic phase behavior. We also study active nematics, liquid crystals driven out of equilibrium by energy-dissipating active stresses. The equilibrium nematic state is unstable in these
Liao, Fuyuan; Jan, Yih-Kuen
2012-01-01
The study of skin microcirculation may be used to assess risk for pressure ulcers. It is observed that local heating not only causes an increase in blood flow of the heated skin but also in the adjacent non-heated skin. The underlying physiological mechanism of this indirect vasodilation of the non-heated skin remains unclear. We hypothesized that blood flow oscillations (BFO) in the adjacent non-heated skin area synchronize with BFO in the heated skin, thus inducing a vasodilatory response. We investigated BFO in the heated and adjacent non-heated skin (12.1±1.2 cm distance) on the sacrum in 12 healthy participants. The ensemble empirical mode decomposition (EEMD) was used to decompose blood flow signals into a set of intrinsic mode functions (IMFs), and the IMFs with power spectra over the frequency range of 0.0095–0.02 Hz, 0.02–0.05 Hz, and 0.05–0.15 Hz were chosen as the characteristic components corresponding to metabolic, neurogenic, and myogenic regulations, respectively. Then, the instantaneous phase of the characteristic components was calculated using the Hilbert transform. From the time series of phase difference between a pair of characteristic components, the epochs of phase synchronization were detected. The results showed that myogenic and neurogenic BFO exhibit self-phase synchronization during the slower vasodilation of the heated skin. In the non-heated skin, the degree of synchronization of BFO is associated with the changes in blood flow. PMID:22936012
Schwartz, Christopher E.; Lambert, Elisabeth; Medow, Marvin S.
2013-01-01
Withdrawal of muscle sympathetic nerve activity (MSNA) may not be necessary for the precipitous fall of peripheral arterial resistance and arterial pressure (AP) during vasovagal syncope (VVS). We tested the hypothesis that the MSNA-AP baroreflex entrainment is disrupted before VVS regardless of MSNA withdrawal using the phase synchronization between blood pressure and MSNA during head-up tilt (HUT) to measure reflex coupling. We studied eight VVS subjects and eight healthy control subjects. Heart rate, AP, and MSNA were measured during supine baseline and at early, mid, late, and syncope stages of HUT. Phase synchronization indexes, measuring time-dependent differences between MSNA and AP phases, were computed. Directionality indexes, indicating the influence of AP on MSNA (neural arc) and MSNA on AP (peripheral arc), were computed. Heart rate was greater in VVS compared with control subjects during early, mid, and late stages of HUT and significantly declined at syncope (P = 0.04). AP significantly decreased during mid, late, and syncope stages of tilt in VVS subjects only (P = 0.001). MSNA was not significantly different between groups during HUT (P = 0.700). However, the phase synchronization index significantly decreased during mid and late stages in VVS subjects but not in control subjects (P < .001). In addition, the neural arc was significantly affected more than the peripheral arc before syncope. In conclusion, VVS is accompanied by a loss of the synchronous AP-MSNA relationship with or without a loss in MSNA at faint. This provides insight into the mechanisms behind the loss of vasoconstriction and drop in AP independent of MSNA at the time of vasovagal faint. PMID:23934851
Waves of Cdk1 Activity in S Phase Synchronize the Cell Cycle in Drosophila Embryos.
Deneke, Victoria E; Melbinger, Anna; Vergassola, Massimo; Di Talia, Stefano
2016-08-22
Embryos of most metazoans undergo rapid and synchronous cell cycles following fertilization. While diffusion is too slow for synchronization of mitosis across large spatial scales, waves of Cdk1 activity represent a possible process of synchronization. However, the mechanisms regulating Cdk1 waves during embryonic development remain poorly understood. Using biosensors of Cdk1 and Chk1 activities, we dissect the regulation of Cdk1 waves in the Drosophila syncytial blastoderm. We show that Cdk1 waves are not controlled by the mitotic switch but by a double-negative feedback between Cdk1 and Chk1. Using mathematical modeling and surgical ligations, we demonstrate a fundamental distinction between S phase Cdk1 waves, which propagate as active trigger waves in an excitable medium, and mitotic Cdk1 waves, which propagate as passive phase waves. Our findings show that in Drosophila embryos, Cdk1 positive feedback serves primarily to ensure the rapid onset of mitosis, while wave propagation is regulated by S phase events. PMID:27554859
Structural phase transition in evolving networks.
Kim, Sang-Woo; Noh, Jae Dong
2009-08-01
A network as a substrate for dynamic processes may have its own dynamics. We propose a model for networks which evolve together with diffusing particles through a coupled dynamics and investigate emerging structural property. The model consists of an undirected weighted network of fixed mean degree and randomly diffusing particles of fixed density. The weight w of an edge increases by the amount of traffics through its connecting nodes or decreases by a constant factor. Edges are removed with the probability P(rew)=1/(1+w) and replaced by new ones having w=0 at random locations. We find that the model exhibits a structural phase transition between the homogeneous phase characterized by an exponentially decaying degree distribution and the heterogeneous phase characterized by the presence of hubs. The hubs emerge as a consequence of a positive feedback between the particle and the edge dynamics. PMID:19792212
Polymer physics of intracellular phase transitions
NASA Astrophysics Data System (ADS)
Brangwynne, Clifford P.; Tompa, Peter; Pappu, Rohit V.
2015-11-01
Intracellular organelles are either membrane-bound vesicles or membrane-less compartments that are made up of proteins and RNA. These organelles play key biological roles, by compartmentalizing the cell to enable spatiotemporal control of biological reactions. Recent studies suggest that membrane-less intracellular compartments are multicomponent viscous liquid droplets that form via phase separation. Proteins that have an intrinsic tendency for being conformationally heterogeneous seem to be the main drivers of liquid-liquid phase separation in the cell. These findings highlight the relevance of classical concepts from the physics of polymeric phase transitions for understanding the assembly of intracellular membrane-less compartments. However, applying these concepts is challenging, given the heteropolymeric nature of protein sequences, the complex intracellular environment, and non-equilibrium features intrinsic to cells. This provides new opportunities for adapting established theories and for the emergence of new physics.
Phase transitions of ɛ-HNIW in compound systems
NASA Astrophysics Data System (ADS)
Zhang, Jing-yuan; Guo, Xue-yong; Jiao, Qing-jie; Zhang, Pu
2016-05-01
The heat-induced phase transitions of ɛ-HNIW, both neat and coated with various additives used in plastic bonded explosives, were investigated using powder X-ray diffraction and differential scanning calorimetry. It was found that ɛ-HNIW, after being held at 70°C for 60h, remained in the ɛ-phase. Applying other conditions, various phase transition parameters were determined, including Tc (the critical phase transition temperature), T50 (the temperature at which 50% of the phase transition is complete) and T180 (the percentage of γ-HNIW present in samples heated to 180°C). According to the above three parameters, additives were divided into three categories: those that delay phase transition, those that raise the critical temperature and the transition rate, and those that promote the phase transition. Based on the above data, a phase transition mechanism is proposed.
Quantum Phase Transitions in Antiferromagnets and Superfluids
NASA Astrophysics Data System (ADS)
Sachdev, Subir
2000-03-01
A general introduction to the non-zero temperature dynamic and transport properties of low-dimensional systems near a quantum phase transition shall be presented. Basic results will be reviewed in the context of experiments on the spin-ladder compounds. Recent large N computations (M. Vojta and S. Sachdev, Phys. Rev. Lett. 83), 3916 (1999) on an extended t-J model motivate a global scenario of the quantum phases and transitions in the high temperature superconductors, and connections will be made to numerous experiments. A universal theory (S. Sachdev, C. Buragohain, and M. Vojta, Science, in press M. Vojta, C. Buragohain, and S. Sachdev, cond- mat/9912020) of quantum impurities in spin-gap antiferromagnets near a magnetic ordering transition will be compared quantitatively to experiments on Zn doped Y Ba2 Cu3 O7 (Fong et al.), Phys. Rev. Lett. 82, 1939 (1999)
Thin film phase transition materials development program
NASA Astrophysics Data System (ADS)
Case, W. E.
1985-04-01
A number of application concepts have emerged based on the idea that a phase transition thin film such as vanadium dioxide provides a high resolution, two-dimensional format for switching, recording, and processing optical signals. These applications range from high density optical disk recording systems and optical data processing to laser protection devices, infrared FLIRS and seekers, laser radar systems and IR scene simulators. All application candidates have a potential for providing either a totally new capability, an improved performance, a lower cost, or combinations of the three. Probably of greatest significance is the emergence of agile sensor concepts arising out of some of the film's special properties. These are represented by the above FLIRs, seekers and laser radar systems. A three year research program has been completed to advance the state-of-the-art in the preparation and characterization of selected thin film phase transition materials. The objectives of the program were: (1) to expand the data base and improve operational characteristics of Vought prepared vanadium dioxide thin films, (2) to evolve process chemistry and subsequently characterize several new program materials, including rare-earth chalcogenides, organic semiconductor charge complexes, alloys of transition metal oxides, and metal-insulator cermets, and (3) to spin-off new applications and concepts.
Transitional Bubble in Periodic Flow Phase Shift
NASA Technical Reports Server (NTRS)
Talan, M.; Hourmouziadis, Jean
2004-01-01
One particular characteristic observed in unsteady shear layers is the phase shift relative to the main flow. In attached boundary layers this will have an effect both on the instantaneous skin friction and heat transfer. In separation bubbles the contribution to the drag is dominated by the pressure distribution. However, the most significant effect appears to be the phase shift on the transition process. Unsteady transition behaviour may determine the bursting of the bubble resulting in an un-recoverable full separation. An early analysis of the phase shift was performed by Stokes for the incompressible boundary layer of an oscillating wall and an oscillating main flow. An amplitude overshoot within the shear layer as well as a phase shift were observed that can be attributed to the relatively slow diffusion of viscous stresses compared to the fast change of pressure. Experiments in a low speed facility with the boundary layer of a flat plate were evaluated in respect to phase shift. A pressure distribution similar to that on the suction surface of a turbomachinery aerofoil was superimposed generating a typical transitional separation bubble. A periodically unsteady main flow in the suction type wind tunnel was introduced via a rotating flap downstream of the test section. The experiments covered a range of the three similarity parameters of momentum-loss-thickness Reynolds-number of 92 to 226 and Strouhal-number (reduced frequency) of 0.0001 to 0.0004 at the separation point, and an amplitude range up to 19 %. The free stream turbulence level was less than 1% .Upstream of the separation point the phase shift in the laminar boundary layer does not appear to be affected significantly bay either of the three parameters. The trend perpendicular to the wall is similar to the Stokes analysis. The problem scales well with the wave velocity introduced by Stokes, however, the lag of the main flow near the wall is less than indicated analytically. The separation point
Exploiting phase transitions for fusion optimization problems
NASA Astrophysics Data System (ADS)
Svenson, Pontus
2005-05-01
Many optimization problems that arise in multi-target tracking and fusion applications are known to be NP-complete, ie, believed to have worst-case complexities that are exponential in problem size. Recently, many such NP-complete problems have been shown to display threshold phenomena: it is possible to define a parameter such that the probability of a random problem instance having a solution jumps from 1 to 0 at a specific value of the parameter. It is also found that the amount of resources needed to solve the problem instance peaks at the transition point. Among the problems found to display this behavior are graph coloring (aka clustering, relevant for multi-target tracking), satisfiability (which occurs in resource allocation and planning problem), and the travelling salesperson problem. Physicists studying these problems have found intriguing similarities to phase transitions in spin models of statistical mechanics. Many methods previously used to analyze spin glasses have been used to explain some of the properties of the behavior at the transition point. It turns out that the transition happens because the fitness landscape of the problem changes as the parameter is varied. Some algorithms have been introduced that exploit this knowledge of the structure of the fitness landscape. In this paper, we review some of the experimental and theoretical work on threshold phenomena in optimization problems and indicate how optimization problems from tracking and sensor resource allocation could be analyzed using these results.
Phase transitions in least-effort communications
NASA Astrophysics Data System (ADS)
Prokopenko, Mikhail; Ay, Nihat; Obst, Oliver; Polani, Daniel
2010-11-01
We critically examine a model that attempts to explain the emergence of power laws (e.g., Zipf's law) in human language. The model is based on the principle of least effort in communications—specifically, the overall effort is balanced between the speaker effort and listener effort, with some trade-off. It has been shown that an information-theoretic interpretation of this principle is sufficiently rich to explain the emergence of Zipf's law in the vicinity of the transition between referentially useless systems (one signal for all referable objects) and indexical reference systems (one signal per object). The phase transition is defined in the space of communication accuracy (information content) expressed in terms of the trade-off parameter. Our study explicitly solves the continuous optimization problem, subsuming a recent, more specific result obtained within a discrete space. The obtained results contrast Zipf's law found by heuristic search (that attained only local minima) in the vicinity of the transition between referentially useless systems and indexical reference systems, with an inverse-factorial (sub-logarithmic) law found at the transition that corresponds to global minima. The inverse-factorial law is observed to be the most representative frequency distribution among optimal solutions.
Western Wind and Solar Integration Study Phase 3A: Low Levels of Synchronous Generation
Miller, Nicholas W.; Leonardi, Bruno; D'Aquila, Robert; Clark, Kara
2015-11-17
The stability of the North American electric power grids under conditions of high penetrations of wind and solar is a significant concern and possible impediment to reaching renewable energy goals. The 33% wind and solar annual energy penetration considered in this study results in substantial changes to the characteristics of the bulk power system. This includes different power flow patterns, different commitment and dispatch of existing synchronous generation, and different dynamic behavior from wind and solar generation. The Western Wind and Solar Integration Study (WWSIS), sponsored by the U.S. Department of Energy, is one of the largest regional solar and wind integration studies to date. In multiple phases, it has explored different aspects of the question: Can we integrate large amounts of wind and solar energy into the electric power system of the West? The work reported here focused on the impact of low levels of synchronous generation on the transient stability performance in one part of the region in which wind generation has displaced synchronous thermal generation under highly stressed, weak system conditions. It is essentially an extension of WWSIS-3. Transient stability, the ability of the power system to maintain synchronism among all elements following disturbances, is a major constraint on operations in many grids, including the western U.S. and Texas systems. These constraints primarily concern the performance of the large-scale bulk power system. But grid-wide stability concerns with high penetrations of wind and solar are still not thoroughly understood. This work focuses on 'traditional' fundamental frequency stability issues, such as maintaining synchronism, frequency, and voltage. The objectives of this study are to better understand the implications of low levels of synchronous generation and a weak grid on overall system performance by: 1) Investigating the Western Interconnection under conditions of both high renewable generation (e
Phase transitions of Dirac electrons in bismuth.
Li, Lu; Checkelsky, J G; Hor, Y S; Uher, C; Hebard, A F; Cava, R J; Ong, N P
2008-07-25
The Dirac Hamiltonian, which successfully describes relativistic fermions, applies equally well to electrons in solids with linear energy dispersion, for example, in bismuth and graphene. A characteristic of these materials is that a magnetic field less than 10 tesla suffices to force the Dirac electrons into the lowest Landau level, with resultant strong enhancement of the Coulomb interaction energy. Moreover, the Dirac electrons usually come with multiple flavors or valley degeneracy. These ingredients favor transitions to a collective state with novel quantum properties in large field. By using torque magnetometry, we have investigated the magnetization of bismuth to fields of 31 tesla. We report the observation of sharp field-induced phase transitions into a state with striking magnetic anisotropy, consistent with the breaking of the threefold valley degeneracy. PMID:18653888
Dynamical phase transitions in quantum mechanics
NASA Astrophysics Data System (ADS)
Rotter, Ingrid
2012-02-01
The nucleus is described as an open many-body quantum system with a non-Hermitian Hamilton operator the eigenvalues of which are complex, in general. The eigenvalues may cross in the complex plane (exceptional points), the phases of the eigenfunctions are not rigid in approaching the crossing points and the widths bifurcate. By varying only one parameter, the eigenvalue trajectories usually avoid crossing and width bifurcation occurs at the critical value of avoided crossing. An analog spectroscopic redistribution takes place for discrete states below the particle decay threshold. By this means, a dynamical phase transition occurs in the many-level system starting at a critical value of the level density. Hence the properties of the low-lying nuclear states (described well by the shell model) and those of highly excited nuclear states (described by random ensembles) differ fundamentally from one another. The statement of Niels Bohr on the collective features of compound nucleus states at high level density is therefore not in contradiction to the shell-model description of nuclear (and atomic) states at low level density. Dynamical phase transitions are observed experimentally in different quantum mechanical systems by varying one or two parameters.
Topological Phase Transition without Gap Closing
Ezawa, Motohiko; Tanaka, Yukio; Nagaosa, Naoto
2013-01-01
Topological phase transition is accompanied with a change of topological numbers. According to the bulk-edge correspondence, the gap closing and the breakdown of the adiabaticity are necessary at the phase transition point to make the topological number ill-defined. However, the gap closing is not always needed. In this paper, we show that two topological distinct phases can be continuously connected without gap closing, provided the symmetry of the system changes during the process. Here we propose the generic principles how this is possible by demonstrating various examples such as 1D polyacetylene with the charge-density-wave order, 2D silicene with the antiferromagnetic order, 2D silicene or quantum well made of HgTe with superconducting proximity effects and 3D superconductor Cu doped Bi2Se3. It is argued that such an unusual phenomenon can occur when we detour around the gap closing point provided the connection of the topological numbers is lost along the detour path. PMID:24071900
Finitely Generated Multifractals Can Display Phase Transitions
NASA Astrophysics Data System (ADS)
Huillet, Thierrey; Jeannet, Bernard
1996-02-01
A new class of multifractal objects (“skewed” multifractals) is introduced, the mutiplicative generator of which has a finite number of branches of different real-valued depths. Both microscopic and macroscopic scales are represented by such objects, each of these corresponding to a specific thermodynamical regime. In the “diluted” regime, the partition function Z_t is exactly renormalizable which means in the sequel, as is the case in the general multifractal theory, that t^{-1} log Z_t as a non trivial limit as t tends to infinity. In the “condensed” one the partition function converges. Details about the transition between these two regimes are given. Une nouvelle classe de “multifractales” est introduite, pour laquelle le générateur présente un nombre fini de branches de longueur variable à valeurs réelles. Les échelles macroscopiques et microscopiques sont représentables par de tels objets, chacune d'elles correspondant à un régime thermodynamique spécifique. Dans la phase “diluée”, la fonction de partition Z_t est exactement renormalisable, en ce sens (classique) que la limite quand trightarrow infty de t^{-1} log Z_t est non triviale. Dans la phase “condensée” la fonction de partition converge. Les détails thermodynamiques concernant cette transition de phase sont fournis.
Phase transitions of nuclear matter beyond mean field theory
Tran Huu Phat; Nguyen Tuan Anh; Nguyen Van Long; Le Viet Hoa
2007-10-15
The Cornwall-Jackiw-Tomboulis (CJT) effective action approach is applied to study the phase transition of nuclear matter modeled by the four-nucleon interaction. It is shown that in the Hartree-Fock approximation (HFA) a first-order phase transition takes place at low temperature, whereas the phase transition is of second order at higher temperature.
Jahn-Teller solitons, structural phase transitions, and phase separation.
Clougherty, Dennis P
2006-02-01
It is demonstrated that under common conditions a molecular solid subject to Jahn-Teller interactions supports stable Q-ball-like nontopological solitons. Such solitons represent a localized lump of excess electric charge in periodic motion accompanied by a time-dependent shape distortion of a set of adjacent molecules. The motion of the distortion can correspond to a true rotation or to a pseudorotation about the symmetric shape configuration. These solitons are stable for Jahn-Teller coupling strengths below a critical value; however, as the Jahn-Teller coupling approaches this critical value, the size of the soliton diverges signaling an incipient structural phase transition. The soliton phase mimics features commonly attributed to phase separation in complex solids. PMID:16486846
Jahn-Teller Solitons, Structural Phase Transitions, and Phase Separation
NASA Astrophysics Data System (ADS)
Clougherty, Dennis P.
2006-02-01
It is demonstrated that under common conditions a molecular solid subject to Jahn-Teller interactions supports stable Q-ball-like nontopological solitons. Such solitons represent a localized lump of excess electric charge in periodic motion accompanied by a time-dependent shape distortion of a set of adjacent molecules. The motion of the distortion can correspond to a true rotation or to a pseudorotation about the symmetric shape configuration. These solitons are stable for Jahn-Teller coupling strengths below a critical value; however, as the Jahn-Teller coupling approaches this critical value, the size of the soliton diverges signaling an incipient structural phase transition. The soliton phase mimics features commonly attributed to phase separation in complex solids.
Phases and phase transitions in the algebraic microscopic shell model
NASA Astrophysics Data System (ADS)
Georgieva, A. I.; Drumev, K. P.
2016-01-01
We explore the dynamical symmetries of the shell model number conserving algebra, which define three types of pairing and quadrupole phases, with the aim to obtain the prevailing phase or phase transition for the real nuclear systems in a single shell. This is achieved by establishing a correspondence between each of the pairing bases with the Elliott's SU(3) basis that describes collective rotation of nuclear systems. This allows for a complete classification of the basis states of different number of particles in all the limiting cases. The probability distribution of the SU(3) basis states within theirs corresponding pairing states is also obtained. The relative strengths of dynamically symmetric quadrupole-quadrupole interaction in respect to the isoscalar, isovector and total pairing interactions define a control parameter, which estimates the importance of each term of the Hamiltonian in the correct reproduction of the experimental data for the considered nuclei.
Swarms, phase transitions, and collective intelligence
Millonas, M.M.
1992-12-31
A model of the collective behavior of a large number of locally acting organisms is proposed. The model is intended to be realistic, but turns out to fit naturally into the category of connectionist models, Like all connectionist models, its properties can be divided into the categories of structure, dynamics, and learning. The space in which the organisms move is discretized, and is modeled by a lattice of nodes, or cells. Each cell hag a specified volume, and is connected to other cells in the space in a definite way. Organisms move probabilistically between local cells in this space, but with weights dependent on local morphogenic substances, or morphogens. The morphogens are in turn are effected by the passage of an organism. The evolution of the morphogens, and the corresponding constitutes of the organisms constitutes the collective behavior of the group. The generic properties of such systems are analyzed, and a number of results are obtained. The model has various types of phase transitions and self-organizing properties controlled both by the level of the noise, and other parameters. It is hoped that the present mode; might serve as a paradigmatic example of a complex cooperative system in nature. In particular this model can be used to explore the relation of phase transitions to at least three important issues encountered in artificial life. Firstly, that of emergence as complex adaptive behavior. Secondly, as an exploration of second order phase transitions in biological systems. Lastly, to derive behavioral criteria for the evolution of collective behavior in social organisms. The model is then applied to the specific case of ants moving on a lattice. The local behavior of the ants is inspired by the actual behavior observed in the laboratory, and analytic results for the collective behavior are compared to the corresponding laboratory results. Monte carlo simulations are used as illustrations.
Swarms, phase transitions, and collective intelligence
Millonas, M.M. . Dept. of Physics)
1992-01-01
A model of the collective behavior of a large number of locally acting organisms is proposed. The model is intended to be realistic, but turns out to fit naturally into the category of connectionist models, Like all connectionist models, its properties can be divided into the categories of structure, dynamics, and learning. The space in which the organisms move is discretized, and is modeled by a lattice of nodes, or cells. Each cell hag a specified volume, and is connected to other cells in the space in a definite way. Organisms move probabilistically between local cells in this space, but with weights dependent on local morphogenic substances, or morphogens. The morphogens are in turn are effected by the passage of an organism. The evolution of the morphogens, and the corresponding constitutes of the organisms constitutes the collective behavior of the group. The generic properties of such systems are analyzed, and a number of results are obtained. The model has various types of phase transitions and self-organizing properties controlled both by the level of the noise, and other parameters. It is hoped that the present mode; might serve as a paradigmatic example of a complex cooperative system in nature. In particular this model can be used to explore the relation of phase transitions to at least three important issues encountered in artificial life. Firstly, that of emergence as complex adaptive behavior. Secondly, as an exploration of second order phase transitions in biological systems. Lastly, to derive behavioral criteria for the evolution of collective behavior in social organisms. The model is then applied to the specific case of ants moving on a lattice. The local behavior of the ants is inspired by the actual behavior observed in the laboratory, and analytic results for the collective behavior are compared to the corresponding laboratory results. Monte carlo simulations are used as illustrations.
Is ``metamictization`` of zircon a phase transition?
Salje, E.K.H.; Chrosch, J.; Ewing, R.C.
1999-07-01
Metamictization is the transition from the crystalline to an aperiodic or amorphous state due to alpha-decay event damage from constituent radionuclides ({sup 238}U, {sup 235}U, and {sup 232}Th) and their daughters. However, this transformation in minerals is part of a larger class of radiation-induced transformations to the amorphous state that has received considerable recent attention as a result of ion- and electron-beam experiments on metals, intermetallics, simple oxides, and complex ceramics and minerals. Diffuse X-ray scattering from single crystals of metamict zircon reveals residual crystallinity even at high fluences (up to 7.2 {times} 10{sup 18} {alpha}-decay events/g). The experimental evidence does not suggest that radiation-induced amorphization is a phase transition. The observations are in good agreement with a nonconvergent, heterogeneous model of amorphization in which damage production is a random process of cascade formation and overlap at increasing fluence. Instead of an amorphization transition, the existence of a percolation transition is postulated. At the level of radiation damage near the percolation point, the heterogeneous strain broadening of X-ray diffraction profiles is reduced whereas the particle-size broadening increases. Simultaneously, the macroscopic swelling of the zircon becomes larger than the maximum expansion of the unit-cell parameters. A suitable empirical parameter that characterizes this transition is the flux, D{sub s}, at which the macroscopic expansion is identical to the maximum expansion of the crystallographic unit cell. In zircon, D{sub s} = 3.5{center_dot}10{sup 18} {alpha}-decay events/g.
Evolutionary Phase Transitions in Random Environments.
Skanata, Antun; Kussell, Edo
2016-07-15
We present analytical results for long-term growth rates of structured populations in randomly fluctuating environments, which we apply to predict how cellular response networks evolve. We show that networks which respond rapidly to a stimulus will evolve phenotypic memory exclusively under random (i.e., nonperiodic) environments. We identify the evolutionary phase diagram for simple response networks, which we show can exhibit both continuous and discontinuous transitions. Our approach enables exact analysis of diverse evolutionary systems, from viral epidemics to emergence of drug resistance. PMID:27472146
Evolutionary Phase Transitions in Random Environments
NASA Astrophysics Data System (ADS)
Skanata, Antun; Kussell, Edo
2016-07-01
We present analytical results for long-term growth rates of structured populations in randomly fluctuating environments, which we apply to predict how cellular response networks evolve. We show that networks which respond rapidly to a stimulus will evolve phenotypic memory exclusively under random (i.e., nonperiodic) environments. We identify the evolutionary phase diagram for simple response networks, which we show can exhibit both continuous and discontinuous transitions. Our approach enables exact analysis of diverse evolutionary systems, from viral epidemics to emergence of drug resistance.
Berry phase transition in twisted bilayer graphene
NASA Astrophysics Data System (ADS)
Rode, Johannes C.; Smirnov, Dmitri; Schmidt, Hennrik; Haug, Rolf J.
2016-09-01
The electronic dispersion of a graphene bilayer is highly dependent on rotational mismatch between layers and can be further manipulated by electrical gating. This allows for an unprecedented control over electronic properties and opens up the possibility of flexible band structure engineering. Here we present novel magnetotransport data in a twisted bilayer, crossing the energetic border between decoupled monolayers and coupled bilayer. In addition a transition in Berry phase between π and 2π is observed at intermediate magnetic fields. Analysis of Fermi velocities and gate induced charge carrier densities suggests an important role of strong layer asymmetry for the observed phenomena.
Quantum coherence and quantum phase transitions
Li, Yan-Chao; Lin, Hai-Qing
2016-01-01
We study the connections between local quantum coherence (LQC) based on Wigner-Yanase skew information and quantum phase transitions (QPTs). When applied on the one-dimensional Hubbard, XY spin chain with three-spin interaction, and Su-Schrieffer-Heeger models, the LQC and its derivatives are used successfully to detect different types of QPTs in these spin and fermionic systems. Furthermore, the LQC is effective as the quantum discord (QD) in detecting QPTs at finite temperatures, where the entanglement has lost its effectiveness. We also demonstrate that the LQC can exhibit different behaviors in many forms compared with the QD. PMID:27193057
Bound entanglement in quantum phase transitions
Baghbanzadeh, S.; Alipour, S.; Rezakhani, A. T.
2010-04-15
We investigate quantum phase transitions in which a change in the type of entanglement from bound entanglement to either free entanglement or separability may occur. In particular, we present a theoretical method to construct a class of quantum spin-chain Hamiltonians that exhibit this type of quantum criticality. Given parameter-dependent two-site reduced density matrices (with prescribed entanglement properties), we lay out a reverse construction for a compatible pure state for the whole system, as well as a class of Hamiltonians for which this pure state is a ground state. This construction is illustrated through several examples.
Quantum coherence and quantum phase transitions
NASA Astrophysics Data System (ADS)
Li, Yan-Chao; Lin, Hai-Qing
2016-05-01
We study the connections between local quantum coherence (LQC) based on Wigner-Yanase skew information and quantum phase transitions (QPTs). When applied on the one-dimensional Hubbard, XY spin chain with three-spin interaction, and Su-Schrieffer-Heeger models, the LQC and its derivatives are used successfully to detect different types of QPTs in these spin and fermionic systems. Furthermore, the LQC is effective as the quantum discord (QD) in detecting QPTs at finite temperatures, where the entanglement has lost its effectiveness. We also demonstrate that the LQC can exhibit different behaviors in many forms compared with the QD.
Quantum coherence and quantum phase transitions.
Li, Yan-Chao; Lin, Hai-Qing
2016-01-01
We study the connections between local quantum coherence (LQC) based on Wigner-Yanase skew information and quantum phase transitions (QPTs). When applied on the one-dimensional Hubbard, XY spin chain with three-spin interaction, and Su-Schrieffer-Heeger models, the LQC and its derivatives are used successfully to detect different types of QPTs in these spin and fermionic systems. Furthermore, the LQC is effective as the quantum discord (QD) in detecting QPTs at finite temperatures, where the entanglement has lost its effectiveness. We also demonstrate that the LQC can exhibit different behaviors in many forms compared with the QD. PMID:27193057
Ayeni, Joseph O; Audibert, Agnès; Fichelson, Pierre; Srayko, Martin; Gho, Michel; Campbell, Shelagh D
2016-04-01
Developmentally regulated cell cycle arrest is a fundamental feature of neurogenesis, whose significance is poorly understood. DuringDrosophilasensory organ (SO) development, primary progenitor (pI) cells arrest in G2 phase for precisely defined periods. Upon re-entering the cell cycle in response to developmental signals, these G2-arrested precursor cells divide and generate specialized neuronal and non-neuronal cells. To study how G2 phase arrest affects SO lineage specification, we forced pI cells to divide prematurely. This produced SOs with normal neuronal lineages but supernumerary non-neuronal cell types because prematurely dividing pI cells generate a secondary pI cell that produces a complete SO and an external precursor cell that undergoes amplification divisions. pI cells are therefore able to undergo self-renewal before transit to a terminal mode of division. Regulation of G2 phase arrest thus serves a dual role in SO development: preventing progenitor self-renewal and synchronizing cell division with developmental signals. Cell cycle arrest in G2 phase temporally coordinates the precursor cell proliferation potential with terminal cell fate determination to ensure formation of organs with a normal set of sensory cells. PMID:26893341
Phase transitions in fluids and biological systems
NASA Astrophysics Data System (ADS)
Sipos, Maksim
metric to 16S rRNA metagenomic studies of 6 vertebrate gastrointestinal microbiomes and find that they assembled through a highly non-neutral process. I then consider a phase transition that may occur in nutrient-poor environments such as ocean surface waters. In these systems, I find that the experimentally observed genome streamlining, specialization and opportunism may well be generic statistical phenomena.