Search

This research examines the feasibility of using synchronization signals broadcasted by currently deployed fifth generation (5G) cellular networks to determine the position of a static receiver. The main focus lies on the analysis of synchronization among the base stations of a real 5G network in Milan, Italy, as this has a major impact on the accuracy of localization based on time of arrival measurements. Understanding such properties, indeed, is fundamental to characterize the clock drifts and implement compensation strategies as well as to identify the direct communication beam. The paper shows how the clock errors, i.e., inaccurate synchronization, among 5G base stations exhibit a significant bias, which is detrimental for precise cellular positioning. By compensating the synchronization errors of devices' clocks, we demonstrate that it is in principle possible to localize a static user with an accuracy of approximately 8–10 m in non-obstructed visibility conditions, for urban and rural scenarios, using the deployed 5G network operating at 3.68 GHz and relying on broadcast signals as defined by 5G Release 15 standard. This work has been funded by the European Space Agency (ESA) Navigation Innovation and Support Program (NAVISP) Element 2 pillar which aims at improving the competitiveness of the industry of the participating States in the global Positioning, Navigation and Timing (PNT) market. [ABSTRACT FROM AUTHOR]

The rapid development of multi-satellite formations requires inter-satellite radio frequency (RF) measurement to be both precise and scalable. The navigation estimation of multi-satellite formations using a unified time reference demands the simultaneous RF measurement of the inter-satellite range and time difference. However, high-precision inter-satellite RF ranging and time difference measurements are investigated separately in existing studies. Different from the conventional two-way ranging (TWR) method, which is limited by its reliance on a high-performance atomic clock and navigation ephemeris, asymmetric double-sided two-way ranging (ADS-TWR)-based inter-satellite measurement schemes can eliminate such reliance while ensuring measurement precision and scalability. However, ADS-TWR was originally proposed for ranging-only applications. In this study, by fully exploiting the time-division non-coherent measurement characteristic of ADS-TWR, a joint RF measurement method is proposed to obtain the inter-satellite range and time difference simultaneously. Moreover, a multi-satellite clock synchronization scheme is proposed based on the joint measurement method. The experimental results show that when inter-satellite ranges are hundreds of kilometers, the joint measurement system has a centimeter-level accuracy for ranging and a hundred-picosecond-level accuracy for time difference measurement, and the maximum clock synchronization error was only about 1 ns. [ABSTRACT FROM AUTHOR]

The article discusses the importance of understanding follicular dynamics in bovine reproduction. It emphasizes that the ovarian cycle does not depend on a follicle starting to grow immediately after ovulation, but rather on waves of follicular growth. It is mentioned that a deep knowledge of the estrous cycle and follicular dynamics is essential for optimizing reproductive management. The article also mentions the importance of ultrasound in detecting changes in the ovaries during these phases of the estrous cycle. Additionally, it describes the characteristics of the uterus in different stages of the cow's estrous cycle and how ultrasound can be useful in evaluating these uterine characteristics. [Extracted from the article]

This letter addresses the time-of-arrival based localization problem when the source and sensors are not synchronized, whereby an unknown transmission time is introduced. A non-convex weighted least squares (WLS) minimization problem is first formulated to jointly estimate the source position and the unknown transmission time by transforming the measurement model, and then semidefinite relaxation is applied to relax the WLS problem as a convex semidefinite program (SDP). The relaxed SDP problem is always tight and thus the optimal solution of the WLS problem can always be obtained. The proposed method is then extended to the moving source localization scenario, where the source velocity is assumed to be a constant for a sufficiently small observation period. Simulation results show that the proposed method is able to reach the Cramer-Rao lower bound accuracy when the noise is not very large. [ABSTRACT FROM AUTHOR]

PNT (positioning, navigation, and timing) is the core functional part of kinds of wireless sensor network, which can provide high-precision timing and positioning services for cooperative work systems. Unfortunately, the mature wireless PNT schemes are generally based on GNSS and other auxiliary sources to complete the high accuracy synchronization process, which cannot be applied to GNSS degraded and denied environments such as mines, underground application. In order to solve the application problem of high-precision wireless PNT, Hybsync—a novel non-GNSS-aided wireless PNT architecture, is proposed in this paper, which integrates the information from the UWB communication, inertial sensor, and camera to achieve great PNT performance. Hybsync improves the accuracy of time deviation measurement by collecting and recording timestamps in hardware layer, and with the coarse/fine synchronization two-phase calibration, Hybsync greatly improves the accuracy of time deviation adjustment, thus providing accurate time information for the whole system. Besides, Hybsync uses the VINS framework to further integrate the real-time information of IMU and camera to complete the multinode positioning service. Under the premise that the cost is much lower than existing solutions, Hybsync can provide nanosecond-level clock synchronization and centimeter-level positioning. Experiments prove that Hybsync supports high-precision clock synchronization and positioning of more than 10 nodes; the maximum clock synchronization error is 3 ns, and the positioning error is 7 cm. It can provide accurate time and position services for cooperative work systems under complex and GNSS-denied conditions. [ABSTRACT FROM AUTHOR]

In this paper, fast fixed-time (FDT) synchronization of T--S fuzzy (TSF) complex networks (CNs) is considered. The given control schemes can make the CNs synchronize with the given isolated system more fleetly than the most of existing results. By constructing comparison system and applying new analytical techniques, sufficient conditions are established to derive fast FDT synchronization speedily. In order to give some comparisons, FDT synchronization of the considered CNs is also presented by designing FDT fuzzy controller. Numerical examples are given to illustrate our new results. [ABSTRACT FROM AUTHOR]

Based on the topological characteristics of small-world networks, a nonlinear sliding mode controller is designed to minimize the effects of internal parameter uncertainties. To qualify the effects of uncertain parameters in the response networks, some effective recognition rates are designed so as to achieve a steady value in the extremely fast simulation time period. Meanwhile, the Fisher-Kolmogorov and Burgers spatiotemporal chaotic systems are selected as the network nodes for constructing a drive and a response network, respectively. The simulation results confirm that the developed sliding mode could realize the effective synchronization problem between the spatiotemporal networks, and the outer synchronization is still achieved timely even when the connection probability of the small-world networks changes. [ABSTRACT FROM AUTHOR]

Clock skew compensation is essential for accurate time synchronization in wireless networks. However, contemporary clock skew estimation is based on inaccurate transmission time measurement, which makes credible estimation challenging. Based on one-way broadcast synchronization, this article presents a novel maximum likelihood estimation (MLE) with an innovative implementation to minimize the clock skew estimation error caused by delay. A multiple one-way broadcast model is developed for observation and set collection, while the distribution of actual delay is discussed. A clock skew MLE based on Gaussian delay is then proposed and its Cramer–Rao lower bound provided. The developed MLE is independent of the clock offset estimation, and requires only two synchronization periods to generate an accurate estimation. Extensive experimental results indicate that the performance of the proposed MLE is better than the methods popularly used in existing time synchronization protocols. [ABSTRACT FROM AUTHOR]

The impedance spectrum of dynamic systems is time-dependent. Fast impedance changes take place, e.g., in living cardiovascular and pulmonary systems. Measurements must be as short as possible to avoid significant impedance changes during the spectral analysis, and as long as possible to enlarge the excitation energy for obtaining the highest signal-to-noise ratio (SNR). The authors propose to use chirp waveforms for excitation (perturbation) signals thanks to their scalability. Separate and almost independent scalability of chirps both in time and frequency domains gave us a possibility to find the best compromise between the controversial requirements between spectral bandwidth, measurement time, and allowed SNR. The chirp wave excitation can include thousands of cycles when the impedance changes are slow. However, it can contain only some cycles, also a single cycle or even a part of it, if the speed of impedance variations is very high. The excitation bandwidth is maintained at the expense of the reduction in excitation energy. The authors show how to generate the chirps with different duration but the same bandwidth up to some MHz and how to use these signals in the time-dependent impedance spectroscopy. [ABSTRACT FROM AUTHOR]

Shared memory is widely used for inter-process communication. The shared memory abstraction allows computation to be decoupled from communication, which offers benefits, including portability and ease of programming. To enable shared memory access by processes that are on different machines, distributed shared memory (DSM) can be employed. However, DSM systems can suffer from thrashing: while different processes update certain hot data items, the largest amount of effort is spent on data synchronization, and little progress is made by each process. To avoid interference between processes during data updating while providing shared memory at page granularity, more time is reserved for a writer to hold a page in a traditional manner. In this paper, we report on complex thrashing, which can explain why extending the time of holding a page might not be sufficient to control thrashing. To increase the throughput, we propose a thrashing control mechanism that allows each process to update a set of pages during a period of time, where the pages compose a logical area. Because of the isolation of areas, updates on different areas can be performed concurrently. To allow the areas to be fairly well used, each process is assigned with a random priority for thrashing control. The thrashing control mechanism is implemented on a Linux-based DSM system. Performance results show that the execution time of the applications that are apt to cause system thrashing can be significantly reduced by our approach. [ABSTRACT FROM AUTHOR]

In mammals, the central circadian clock is located in the hypothalamus, coordinating peripheral clocks with neuronal and endocrine signals. It has been shown that circadian clock genes and proteins continue their rhythmic expression in peripheral cells and tissues independent of central clock. The rhythm continues even in the immortalized cell lines, but intercellular coordination is impaired. Cell lines are good mediators for studying cancer-related pathways and circadian rhythm relationships. However, it should first be shown that rhythmic gene expression continues. Some mediators are used to achieve intercellular synchronization. The aim of this study was to investigate the role of strong synchronization initiators, FBS, and dexamethasone, on the expression of the PER2 clock gene in the HT-29 colon cancer cell line. For this purpose; following FBS or dexamethasone administration, HT-29 cells were harvested at 6 different times to isolate RNA and the PER2 and ACTB gene expressions were quantified by real-time PCR assay. The results were evaluated by Linear Cosinor analysis. When the change in mRNA expression of the PER2 gene was compared to the ACTB reference gene, it was shown that rhythmic expression was achieved with both initiators. According to the Cosinor analysis, a significant rhythmic change was observed in both 18 and 24 hour periods. However, in the synchronization with dexamethasone, the confidence interval in the time Period was also significant in the 24 hour period. In this study, it was determined that the initiators may vary in the calculation of circadian Periods which was carried out with two different initiators in HT-29 cell line. [ABSTRACT FROM AUTHOR]

This paper addresses the intermittent pinning synchronization problem of spatial diffusion coupled reaction–diffusion neural networks (RDNNs). Initially, the synchronization error signals are quantized before transmission to save both channel resource and control cost. Subsequently, utilizing intermittent pinning control scheme, only a small fraction of network nodes are selected to be controlled in various time periods, which further reduces the control cost. On the basis of the constructed controller, sufficient conditions that guarantee the synchronization of the coupled RDNNs are derived via Lyapunov direct method. Finally, the efficacy of the developed control approach is demonstrated by numerical simulation studies of three examples. [ABSTRACT FROM AUTHOR]

The transient dynamics of phase-locking in serially connected nanopillar spin-torque oscillators (STOs) is studied both analytically and numerically. A variety of transient behaviors are observed stemming from the high oscillator nonlinearity and the interplay between the damping to coupling strength ratio and the phase delay of the coupling. Non-Adlerian (ringing) dynamics is found to be the main regime of synchronization where the synchronization time depends strongly on the phase delay. Somewhat nonintuitively, sufficiently strong coupling can also destabilize the system, destroying the synchronized regime even for identical STOs. This transient behavior is also found to dominate when the STOs have different frequencies. These results highlight fundamental issues that must be considered in the design of serially synchronized STOs. [ABSTRACT FROM AUTHOR]

We present a novel clock synchronization algorithm and prove tight upper and lower bounds on the worst-case clock skew that may occur between any two participants in any given distributed system. More importantly, the worst-case clock skew between neighboring nodes is (asymptotically) at most a factor of two larger than the best possible bound. While previous results solely focused on the dependency of the skew bounds on the network diameter, we prove that our techniques are optimal also with respect to the maximum clock drift, the uncertainty in message delays, and the imposed bounds on the clock rates. The presented results all hold in a general model where both the clock drifts and the message delays may vary arbitrarily within pre-specified bounds. Furthermore, our algorithm exhibits a number of other highly desirable properties. First, the algorithm ensures that the clock values remain in an affine linear envelope of real time. A better worst-case bound on the accuracy with respect to real time cannot be achieved in the absence of an external timer. Second, the algorithm minimizes the number and size of messages that need to be exchanged in a given time period. Moreover, only a small number of bits must be stored locally for each neighbor. Finally, our algorithm can easily be adapted for a variety of other prominent synchronization models. [ABSTRACT FROM AUTHOR]

Stimulated Brillouin scattering pulse compression of a 2.5 ns laser into a 175 ps pulse using a fused quartz is demonstrated without optical damage. The synchronization and the time jitter between the initial and the compressed pulses were measured (σ<80 ps) and analyzed numerically. [ABSTRACT FROM AUTHOR]

A medium-energy synchrotron capable of accelerating all-ion species is proposed. The accelerator employs a strong focusing lattice for ion-beam guiding and induction acceleration for acceleration and longitudinal capture, which is driven by a switching power supply. All ions, including cluster ions in their possible and arbitrary charge state, are accelerated in a single accelerator. Since the switching power supply employing solid-state switching elements is energized by a trigger signal, which is generated from a bunch monitor signal produced by a circulating ion bunch, the induction acceleration always synchronizes with the bunch circulation. This feature enables the realization of an almost injector-free synchrotron. [ABSTRACT FROM AUTHOR]

Disrupting the pathological synchronous firing patterns of neurons with high frequency stimulation is a common treatment for Parkinsonian symptoms and epileptic seizures when pharmaceutical drugs fail. In this paper, our goal is to design a desynchronization strategy for large networks of spiking neurons such that the neuronal activity of the network remains in the desynchronized regime for a long period of time after the removal of the stimulation. We develop a novel "Forced Temporal-Spike Time Stimulation (FTSTS)" strategy that harnesses the spike-timing dependent plasticity to control the synchronization of neural activity in the network by forcing the neurons in the network to artificially fire in a specific temporal pattern. Our strategy modulates the synaptic strengths of selective synapses to achieve a desired synchrony of neural activity in the network. Our simulation results show that the FTSTS strategy can effectively synchronize or desynchronize neural activity in large spiking neuron networks and keep them in the desired state for a long period of time after the removal of the external stimulation. Using simulations, we demonstrate the robustness of our strategy in desynchronizing neural activity of networks against uncertainties in the designed stimulation pulses and network parameters. Additionally, we show in simulation, how our strategy could be incorporated within the existing desynchronization strategies to improve their overall efficacy in desynchronizing large networks. Our proposed strategy provides complete control over the synchronization of neurons in large networks and can be used to either synchronize or desynchronize neural activity based on specific applications. Moreover, it can be incorporated within other desynchronization strategies to improve the efficacy of existing therapies for numerous neurological and psychiatric disorders associated with pathological synchronization. [ABSTRACT FROM AUTHOR]

Time synchronization is a challenging problem for wireless sensor networks, as clocks deviate and sensor measurements need to be associated with the reference clock time they took place. In Internet of Things (IoT) environments, crucial factors like energy, robustness, limited capabilities and extreme ambient conditions (e.g., when nodes are deployed in soil) lead researchers to consider various schemes of relaxing the synchronization requirements. In this paper, a lightweight synchronization algorithm is proposed for wireless sensor networks, focusing on synchronizing the particular measurements in a per hop basis as they are transmitted encapsulated in data packets towards the sink node. The aim is to synchronize data measurements instead of node clocks, and thereby, induce negligible extra overhead, since extra messages and re-synchronization periods are not required. The analysis of the proposed algorithm regarding time deviation and the corresponding variance shows a dependency on residual time (i.e., the particular time period a data packet remains within a node), distance (i.e., the number of hops between the sink node and the sensor node that sensed the data in the first place) and the average skew deviation value. Various simulations were carried out aiming to exhibit thoroughly the effectiveness of the proposed algorithm, as well as the validation of the analytical results. Findings from a comparison between the proposed algorithm and a traditional synchronization algorithm along with their simulation results show that the proposed algorithm can be a suitable solution for demanding environments like IoT systems. [ABSTRACT FROM AUTHOR]

When listening to music, humans can easily identify and move to the beat. Numerous experimental studies have identified brain regions that may be involved with beat perception and representation. Several theoretical and algorithmic approaches have been proposed to account for this ability. Related to, but different from the issue of how we perceive a beat, is the question of how we learn to generate and hold a beat. In this paper, we introduce a neuronal framework for a beat generator that is capable of learning isochronous rhythms over a range of frequencies that are relevant to music and speech. Our approach combines ideas from error-correction and entrainment models to investigate the dynamics of how a biophysically-based neuronal network model synchronizes its period and phase to match that of an external stimulus. The model makes novel use of on-going faster gamma rhythms to form a set of discrete clocks that provide estimates, but not exact information, of how well the beat generator spike times match those of a stimulus sequence. The beat generator is endowed with plasticity allowing it to quickly learn and thereby adjust its spike times to achieve synchronization. Our model makes generalizable predictions about the existence of asymmetries in the synchronization process, as well as specific predictions about resynchronization times after changes in stimulus tempo or phase. Analysis of the model demonstrates that accurate rhythmic time keeping can be achieved over a range of frequencies relevant to music, in a manner that is robust to changes in parameters and to the presence of noise. [ABSTRACT FROM AUTHOR]

Highlights • The hippocampus generates ordered spike sequences to support memory functions. • However, not all synchronized spike sequences contain similar ensemble pattern. • Some synchronized events include non-spatial pyramidal cells. • Non-ordered spike sequences may play functional roles in enriching brain functions. Abstract The hippocampal network generates synchronized spikes of a large population of pyramidal neurons associated with sharp-wave ripples in local field potential signals. Ample evidence demonstrates that the synchronized spikes are created by sequential activation of hippocampal place cells that correspond to the animal's past or future trajectories and are hypothesized to play instrumental roles in mnemonic functions. However, not all place-cell spike sequences are precisely organized, and some sequences are composed of spikes from non-spatial cells, implying that not all hippocampal synchronized events directly replicate learned behavioral episodes. While less attention has been given to such non-ordered spike sequences, variable and dynamic selection of active neuronal assemblies may be optimal mechanisms for rapidly reorganizing functional circuits and self-developing novel representations to enable flexible decision-making processes. We recently showed that specific neurons, including both spatial and non-spatial cells, are preferentially recruited in synchronous events for particular time periods, suggesting that there are temporally fluctuating background states of the hippocampal network that determine active neuronal ensembles. Based on recent reports, this review discusses potential roles of the low-fidelity, heterogeneous repertoire of synchronized spike sequences of hippocampal neurons. [ABSTRACT FROM AUTHOR]

The availability of low-power wide area networks solutions opens new scenario in many application sectors. Among these technologies, long-range wide area network (LoRaWAN) was originally designed for consumer internet-of-things systems, but now it is investigated for distributed measurement systems applied to more demanding applications, including industry. In order to fulfill real-time requirements, the LoRaWAN end devices (EDs) are frequently requested to share a common timebase (i.e., to be synchronized). This paper deals with the tradeoff between the desired synchronization uncertainty and the energy available in the ED, which is usually battery powered. A new approach based on two algorithms for a posteriori synchronization and uncertainty estimation is proposed. After experimental validation of the proposed algorithms, a set of optimal energy/uncertainty tradeoff curves is obtained with the help of a specific tradeoff algorithm. Finally, the proposed tradeoff methodology is applied to two use cases concerning the design of: an industrial time division multiple access system and a predictive maintenance framework. [ABSTRACT FROM AUTHOR]

A malicious attack on a safety‐critical system can derive in an undesired behavior of the system that may result in a failure. In this case, the reliability of the device is decreased, and it might affect directly to safety. Therefore, the security is also an essential issue to consider in the design of safety‐critical systems. The main problem when safety and security are considered is to make them work together without interfering each other. A safety‐critical device needs to be certified following standards like IEC‐61508, and any security mechanisms must not affect this certification. This paper describes a system that integrates safety and security mechanisms to improve reliability without affecting safety certification. With the aim of reaching the required safety level, a redundant system is considered. This system is an n out of m distributed and synchronized voter. The synchronization method is based on the precision time protocol (IEEE‐1588) allowing that all devices on a local network have the same time. [ABSTRACT FROM AUTHOR]

Abstract This paper investigates the anti-unwinding finite-time attitude synchronization control problem for Spacecraft formation flying with external disturbances. Two finite-time controllers are designed based on rotation matrix and terminal sliding mode method. By designing a novel sliding mode surface, the first controller is developed when the upper bound of the external disturbances can be exactly known. However, this value is not always available in reality. In addition, the direct use of the upper bound of the external disturbances can result in the chattering problem. For the purpose of overcoming the disadvantage of the first controller, a modified control law is proposed, in which the adaptive law is applied to estimate the unknown value online. Theoretical analysis and numerical simulations are presented to demonstrate the validity of the proposed controllers. Highlights • Two finite-time attitude synchronization controllers are proposed for spacecraft. • A novel terminal sliding mode surface is proposed. • The proposed adaptive law can ensure finite-time stability for the spacecraft system. [ABSTRACT FROM AUTHOR]

Highlights • Psychological counseling showed better working alliances than chatting. • Interpersonal brain synchronization (IBS) increased during psychological counseling. • The IBS correlated with the bond of working alliance. Abstract The mechanisms underlying behavioral synchrony during psychological counseling are not clear. Recent research has provided evidence that pervasive synchrony is associated with interpersonal brain synchronization (IBS) and possibly contributes to the positive working alliance—the degree to which the counseling dyads engage in collaborative and purposive work. Our study explored the IBS between the clients and the counselors using functional near-infrared spectroscopy (fNIRS)-based hyperscanning. Thirty-four participants (as clients) were randomly assigned either to the psychological counseling group or to the chatting group; three female professional counselors provided them with 40 minutes of psychological counseling or chatting. We found better working alliances and increased IBS in the right temporo-parietal junction (rTPJ) between clients and counselors during psychological counseling (versus chatting). Such IBS also correlated with the bond of working alliance. To our knowledge, our work represents the first demonstration of fNIRS-hyperscanning measurements for synchronous brain activity between the clients and counselors. This study refines the neural explanation of behavioral synchrony during psychological counseling. [ABSTRACT FROM AUTHOR]

Time-slotted channel hopping (TSCH), which can enable highly reliable and low-power wireless mesh networks, is the cornerstone of current industrial wireless standards. In a TSCH network, all nodes must maintain high-precision synchronization. If an adversary launches a time-synchronization attack on a TSCH network, the entire network communication system can be paralyzed. Thus, time-synchronization security is a key problem in this network. In this article, time synchronization is divided into single-hop pairwise, clusterwise, and three-level multihop according to the network scope. We deeply analyze their security vulnerabilities due to the TSCH technology itself and its high-precision synchronization requirements and identify the specific attacks; then, we propose corresponding security countermeasures. Finally, we built a test bed using 16 OpenMoteSTM nodes and the OpenWSN software to evaluate the performance of the proposed scheme. The experimental results showed that serious security vulnerabilities exist in time-synchronization protocols, and the proposed countermeasures can successfully defend against the attacks. [ABSTRACT FROM AUTHOR]

The complexity matching effect refers to a maximization of information exchange, when interacting systems share similar complexities. Additionally, interacting systems tend to attune their complexities in order to enhance their coordination. This effect has been observed in a number of synchronization experiments, and interpreted as a transfer of multifractality between systems. Finally, it has been shown that when two systems of different complexity levels interact, this transfer of multifractality operates from the most complex system to the less complex, yielding an increase of complexity in the latter. This theoretical framework inspired the present experiment that tested the possible restoration of complexity in older people. In young and healthy participants, walking is known to present 1/ f fluctuations, reflecting the complexity of the locomotion system, providing walkers with both stability and adaptability. In contrast walking tends to present a more disordered dynamics in older people, and this whitening was shown to correlate with fall propensity. We hypothesized that if an aged participant walked in close synchrony with a young companion, the complexity matching effect should result in the restoration of complexity in the former. Older participants were involved in a prolonged training program of synchronized walking, with a young experimenter. Synchronization within the dyads was dominated by complexity matching. We observed a restoration of complexity in participants after 3 weeks, and this effect was persistent 2 weeks after the end of the training session. This work presents the first demonstration of a restoration of complexity in deficient systems. [ABSTRACT FROM AUTHOR]

Abstract In this paper, global exponential synchronization of multiple coupled inertial memristive neural networks with time-varying delay is investigated. First, by choosing suitable variable substitution, the inertial memristive neural networks are transformed into first-order differential equations. Next, a novel coupling scheme with linear diffusive term and discontinuous sign function term depending on the first order derivative of state variables is introduced. Based on this coupling scheme, several sufficient conditions for global exponential synchronization of multiple inertial memristive neural networks are derived by using Lyapunov stability theory and some inequality techniques. Finally, several numerical examples are presented to substantiate the effectiveness of the theoretical results. [ABSTRACT FROM AUTHOR]

This paper proposed a precise time synchronization method between schedulers of real‐time operating systems by communicating time stamps over a network. An NTP‐based communication protocol was used to measure the time offset between nodes. To minimize the measurement error, a light‐weight network stack called RT‐Messenger was used instead of common transmission control protocol/Internet protocol (TCP/IP) stack. Also, a Kalman filter was introduced to eliminate such error and to estimate time offset and drift. Furthermore, a real‐time scheduler in RTAI/Linux (where RTAI is real‐time application interface) was modified to compensate the time difference using the estimated offset and drift. The time compensation of a scheduler clock affects the next resume times for real‐time tasks. Therefore, a recalculation process of next resume times for all real‐time tasks and a reordering process of real‐time task queue were added to the real‐time scheduler. To validate the proposed method, time differences of resume times for two real‐time tasks on different nodes were measured under various experimental conditions. The results confirm that the resume time differences were successfully kept lower than 400 ns with 300 ns standard deviation under the condition of observation period at 1 s and correction period at 10 s. [ABSTRACT FROM AUTHOR]

In this paper, a frequency synthesizer, based on a type-2, third order phase locked loop (PLL), covering the frequency range of 0.9-5.4 GHz using three voltage controlled oscillators, is implemented using a 0.13-μm CMOS technology. The PLL has three modes of operation—a high bandwidth mode, a low bandwidth mode and a dynamic mode, in which the bandwidth dynamically changes from a low to a high value, during a frequency jump, and reverts back to low value, once the PLL settles. With a proper choice of bandwidth and timing synchronization during a frequency jump, a worst-case settling time of 3-μs has been obtained, which is one of the lowest in reported literature. The input clock of the PLL is set to 100 MHz, but it can go as low as 25 MHz without having any effect on its settling time. The PLL consumes 24 mW of power and occupies 0.8 mm2 of active area.This PLL is expected to be specially useful in wide-bandwidth cognitive radios that require large and fast transitions in the frequency of operation. [ABSTRACT FROM AUTHOR]

In this paper, finite-time inner synchronization of coupled systems on a network with time delay and distributed delay (CSNTD) is investigated. And here, time delay and distributed delay are both taken into consideration when modelling a realistic network. Different from common feedback control, the controller we design is quantized, which is more realistic and reasonable. By using Lyapunov method and Kirchhoff’s Matrix Tree Theorem, some sufficient criteria are derived to guarantee finite-time inner synchronization of CSNTD. It should be underlined that the method is first applied to studying the issue of finite-time inner synchronization of CSNTD and the synchronization time we obtain has a close relationship with the topological structure of the network. Moreover, to verify our theoretical results, we present an application to coupled oscillators with time delay and distributed delay, and a sufficient criterion is obtained. Ultimately, a numerical example is given to verify the validity and feasibility of theoretical results. [ABSTRACT FROM AUTHOR]

We experimentally investigate the synchronization of driven metronomes using a servo motor to impose external control. We show that a driven metronome will only synchronize in a narrow range near its own frequency; when we introduce coupling between metronomes, we can widen the range of frequencies over which a metronome will synchronize to the external input. Using these features, we design a signal to synchronize a population of dissimilar metronomes; separately we design a signal to selectively synchronize a subpopulation of metronomes within a heterogeneous population. [ABSTRACT FROM AUTHOR]

In this paper we investigate the possibilities and scenarios of synchronization under the influence of parameters of structure that couples oscillators. The research is based on a simple model of two pendula with van der Pol damping type, suspended on a horizontally oscillating beam. The regions of existence and co-existence of different synchronization patterns are shown, and typical bifurcation scenarios between types of model’s responses are presented. The behavior of each pendulum is analyzed, and the reasons of bifurcations are explained using the energy balance method. Moreover, we investigate the basins of attraction of considered system, exhibiting their complicated structure along with statistical study on attractors’ occurrence. Our results are presented for simple one parameter variation, as well as for group of parameters varied, when the influence of coupling structure’s parameters on appearance of observed patterns is studied. Our results refer to a simple and typical mechanical model of coupled oscillators, emphasizing their universality in dynamical systems of engineering type. [ABSTRACT FROM AUTHOR]

The article presents a study on the nature of biological clocks. In this report, Ruth Henoch, associate science editor for Rand McNally and Co., suggests that the clock is a biochemical timer linking organism and environment. Based on scientific findings, peaks and troughs in the cycle are geared to the organism's habitual routine. And, with its ability to rephase or reset itself in response to the changes in the environment, this biological clock becomes the adaptive link between the organism and its environment. Also, understanding the basis of this chemical synchronization provides insights into the nature of sleep-active cycles.

Abstract In order to take full advantage of the hardware benefits by using redundant drive mechanisms, both synchronizing motions of the two actuators and avoiding excessive internal forces are vital to the smooth operations of dual drive gantry systems. However, almost all existing control schemes focus on pure motion synchronization only and the latter has been essentially ignored. Thus, even if the synchronization errors are kept within a small enough range, “pull and drag” phenomena could still exhibit due to the near-rigid physical coupling crossbeam and the consequent large internal forces. In this paper, a three-level synchronization control scheme based on adaptive thrust allocation is proposed to achieve not only better synchronized motion performance but also simultaneous regulation of internal forces. The overall control algorithm is composed of the motion tracking (Level I), the adjustable thrust allocation (Level II) and the on-line recursive least squares estimation (Level III), which is capable of achieving excellent internal force regulation and synchronization performance even when the distribution of system load cannot be priori known exactly in implementation or suffers from variations. Simulation and experimental results verify the effectiveness of the proposed synchronization control scheme based on adaptive thrust allocation in practical applications. [ABSTRACT FROM AUTHOR]

Inhibitory synchronization is commonly observed and may play some important functional roles in excitatory/inhibitory (E/I) neuronal networks. The firing rate contrast enhancement is a general feature of information processing in sensory pathways, and a new mechanism of contrast enhancement by inhibitory synchronization in E/I neuronal networks is investigated in this paper. Inspired by the firing rate contrast enhancement phenomenon by the lateral feed-forward inhibition, we reveal that the firing rate contrast enhancement could also occur by recurrent inhibition in E/I networks. It is further found that the synchronized inhibitory neurons act as a global inhibition which can enhance the firing rate contrast of excitatory neurons globally in synchronized E/I networks, even in partially synchronous states. Therefore, the firing rate contrast enhancement might be an important function of inhibitory synchronization and might facilitate information transmission in neural systems. [ABSTRACT FROM AUTHOR]

Spiking patterns and synchronization dynamics of thalamic neurons along the sleep-wake cycle are studied in a minimal model of four coupled conductance-based neurons. The model simulates two thalamic neurons coupled via a gap junction and driven by a synaptic input from a two-neuron model of sleep regulation by the hypothalamus. In accord with experimental data, the model shows that during sleep, when hypothalamic wake-active neurons are silent, the thalamic neurons discharge bursts of spikes. During wake, the excitatory synaptic input from the hypothalamus drives the coupled thalamic neurons to a state of tonic firing (single spikes). In the deterministic case, the thalamic neurons synchronize in-phase in the bursting regime but demonstrate multi-stability of out-of-phase, in-phase, and asynchronous states in the tonic firing. However, along the sleep-wake cycle, once the neurons synchronize in-phase during sleep (bursting), they stay synchronized in wake (tonic firing). It is thus found that noise is needed to reproduce the experimentally observed transitions between synchronized bursting during sleep and asynchronous tonic firing during wake. Overall, synchronization of bursting is found to be more robust to noise than synchronization of tonic firing, where a small disturbance is sufficient to desynchronize the thalamic neurons. The model predicts that the transitions between sleep and wake happen via chaos because a single thalamic neuron exhibits chaos between regular bursting and tonic activity. The results of this study suggest that the sleep- and wake-related dynamics in the thalamus may be generated at a level of gap junction-coupled clusters of thalamic neurons driven from the hypothalamus which would then propagate throughout the thalamus and cortex via axonal long-range connections. [ABSTRACT FROM AUTHOR]

Anomalous phase synchronization describes a synchronization phenomenon occurring even for the weakly coupled network and characterized by a non-monotonous dependence of the synchronization strength on the coupling strength. Its existence may support a theoretical framework to some neurological diseases, such as Parkinson's and some episodes of seizure behavior generated by epilepsy. Despite the success of controlling or suppressing the anomalous phase synchronization in neural networks applying external perturbations or inducing ambient changes, the origin of the anomalous phase synchronization as well as the mechanisms behind the suppression is not completely known. Here, we consider networks composed of N = 2000 coupled neurons in a small-world topology for two well known neuron models, namely, the Hodgkin-Huxley-like and the Hindmarsh-Rose models, both displaying the anomalous phase synchronization regime. We show that the anomalous phase synchronization may be related to the individual behavior of the coupled neurons; particularly, we identify a strong correlation between the behavior of the inter-bursting-intervals of the neurons, what we call neuron variability, to the ability of the network to depict anomalous phase synchronization. We corroborate the ideas showing that external perturbations or ambient parameter changes that eliminate anomalous phase synchronization and at the same time promote small changes in the individual dynamics of the neurons, such that an increasing individual variability of neurons implies a decrease of anomalous phase synchronization. Finally, we demonstrate that this effect can be quantified using a well known recurrence quantifier, the "determinism." Moreover, the results obtained by the determinism are based on only the mean field potential of the network, turning these measures more suitable to be used in experimental situations. [ABSTRACT FROM AUTHOR]

This paper investigates robust exponential synchronization for stochastic delayed neural networks with reaction-diffusion terms and Markovian jumping parameters driven by infinite dimensional Wiener processes. The novelty of this paper lives in the use of a new Lyapunov-Krasovskii functional and Poincaré inequality to present some criteria for robust exponential synchronization in terms of linear matrix inequalities (LMIs) and matrix measure under Robin boundary conditions. Finally, two numerical examples are provided to illustrate the effectiveness of the easily verifiable synchronization LMIs in MATLAB toolbox. [ABSTRACT FROM AUTHOR]

This paper discusses the problem of adaptive finite-time synchronization for neutral type dynamical network model with double derivative coupling. Based on the Lyapunov functional theory, inequality theorem, and adaptive control technique, some synchronization criteria of neutral type dynamical network are established by using adaptive finite-time control, which is different from the existence of finite-time synchronization of neutral type network using LMI and matrix equality constraint methods. Moreover, when the dynamics nodes of the neutral type network contain delay or no delay, the control gain of the response network are also provided. Finally, the effectiveness of the synchronization criteria proposed in this paper is verified by numerical simulations. [ABSTRACT FROM AUTHOR]

This paper investigates fixed-time synchronization of coupled neural networks with discontinuous activation functions and nonidentical perturbations under the framework of Filippov solution. In order to overcome uncertainties of the Filippov solution and the effects of nonidentical perturbations, 1-norm based techniques are developed. By designing new state feedback controllers, constructing new Lyapunov functional, and utilizing differential inclusion theory, several sufficient conditions are obtained to ensure that the coupled discontinuous neural networks (CDNNs) to be synchronized in a fixed settling time. Results of this paper improve corresponding ones which only finite-time synchronization can be achieved for CDNNs. Finally, numerical simulations are offered to verify the effectiveness of the theoretical analysis. [ABSTRACT FROM AUTHOR]

The output synchronisation of two deterministic Boolean networks coupled in the master-slave configuration is studied. First, under the algebraic framework of logical systems, an auxiliary system is constructed. Second, core input-state cycles are generalised and an algorithm is given to calculate these cycles. Third, based on core input-state cycles of the newly constructed auxiliary system, a necessary and sufficient existence condition is derived for a synchronising state feedback controller. Furthermore, a constructive method is provided to get feasible state feedback controllers when the existence condition obtained above is satisfied. Finally, an illustrative example is provided to verify the effectiveness and superiority of the presented results. [ABSTRACT FROM AUTHOR]