Synchronization Timescales Research Articles

Transitory Tidal Heating and Its Impact on Cluster Isochrones

The kinetic energy in tidal flows, when converted into heat, can affect the internal structure of a star and shift its location on a color–magnitude diagram from that of standard models. In this paper we explore the impact of injecting heat into stars with masses near the main-sequence turnoff mass (1.26 M ⊙) of the open cluster M67. The heating rate is obtained from the tidal shear energy dissipation rate, which is calculated from first principles by simultaneously solving the equations that describe orbital motion and the response of a star’s layers to the gravitational, Coriolis, centrifugal, gas pressure, and viscous forces. The stellar structure models are computed with MESA. We focus on the effects of injecting heat in pulses lasting 0.01 Gyr, a time frame consistent with the synchronization timescale in binary systems. We find that the location of the tidally perturbed stars in the M67 color–magnitude diagram is shifted to significantly higher luminosities and effective temperatures than predicted by the standard model isochrone and includes locations corresponding to some of the blue straggler stars. Because tidal heating takes energy from the orbit, causing it to shrink, blue straggler stars could be merger or mass transfer progenitors, as well as products of these processes.

Centimeter-level clock synchronization and space-borne timescale generation for BDS-3 using inter-satellite link measurements

Centimeter-level clock synchronization and space-borne timescale generation for BDS-3 using inter-satellite link measurements

Development concept of inter-satellite laser communication

The relevance of this research work is dictated, among other things, by the need to ensure higher requirements for the accuracy characteristics of the navigation field created by spacecraft of the GLONASS navigation system in order to meet the high requirements for the accuracy characteristics of navigation determinations over long intervals of autonomous operation of spacecraft currently put forward by consumers. The presented concept of development uses the latest achievements of laser and radio engineering both to increase the throughput, noise immunity of transmitting information, as well as to reduce the mass and power consumption of onboard equipment, and to conduct inter-satellite range measurements and synchronization of onboard time scales of spacecraft navigation systems, including and for linking the system time scale of space navigation systems (or the group orbital time scale) to the time scale of the State standard of time and frequency. Ensuring the accurate operation of the laser guidance system in space is considered one of the critically important tasks, since its full-scale tests on Earth are almost impossible. Key experimental and also experimental works are analyzed according to the problems of constructing optical links of inter-satellite communication.

Three low-mass companions around aged stars discovered by TESS

ABSTRACT We report the discovery of three transiting low-mass companions to aged stars: a brown dwarf (TOI-2336b) and two objects near the hydrogen burning mass limit (TOI-1608b and TOI-2521b). These three systems were first identified using data from the Transiting Exoplanet Survey Satellite (TESS). TOI-2336b has a radius of 1.05 ± 0.04 RJ, a mass of 69.9 ± 2.3 MJ and an orbital period of 7.71 d. TOI-1608b has a radius of 1.21 ± 0.06 RJ, a mass of 90.7 ± 3.7 MJ and an orbital period of 2.47 d. TOI-2521b has a radius of 1.01 ± 0.04 RJ, a mass of 77.5 ± 3.3 MJ, and an orbital period of 5.56 d. We found all these low-mass companions are inflated. We fitted a relation between radius, mass, and incident flux using the sample of known transiting brown dwarfs and low-mass M dwarfs. We found a positive correlation between the flux and the radius for brown dwarfs and for low-mass stars that is weaker than the correlation observed for giant planets. We also found that TOI-1608 and TOI-2521 are very likely to be spin-orbit synchronized, leading to the unusually rapid rotation of the primary stars considering their evolutionary stages. Our estimates indicate that both systems have much shorter spin-orbit synchronization time-scales compared to their ages. These systems provide valuable insights into the evolution of stellar systems with brown dwarf and low-mass stellar companions influenced by tidal effects.

Probing the Efficiency of Tidal Synchronization in Outspiralling Double White Dwarf Binaries with LISA

Compact-object binaries including a white dwarf component are unique among gravitational-wave sources because their evolution is governed not just by general relativity and tides, but also by mass transfer. While the black hole and neutron star binaries observed with ground-based gravitational-wave detectors are driven to inspiral due to the emission of gravitational radiation—manifesting as a “chirp-like” gravitational-wave signal—the astrophysical processes at work in double white dwarf (DWD) systems can cause the inspiral to stall and even reverse into an outspiral. The dynamics of the DWD outspiral thus encode information about tides, which tell us about the behavior of electron-degenerate matter. We carry out a population study to determine the effect of the strength of tides on the distributions of the DWD binary parameters that the Laser Interferometer Space Antenna (LISA) will be able to constrain. We find that the strength of tidal coupling parameterized via the tidal synchronization timescale at the onset of mass transfer affects the distribution of gravitational-wave frequencies and frequency derivatives for detectably mass-transferring DWD systems. Using a hierarchical Bayesian framework informed by binary population synthesis simulations, we demonstrate how this parameter can be inferred using LISA observations. By measuring the population properties of DWDs, LISA will be able to probe the behavior of electron-degenerate matter.

Prolonged Intrinsic Neural Timescales Dissociate from Phase Coherence in Schizophrenia.

Input processing in the brain is mediated by phase synchronization and intrinsic neural timescales, both of which have been implicated in schizophrenia. Their relationship remains unclear, though. Recruiting a schizophrenia EEG sample from the B-SNIP consortium dataset (n = 134, 70 schizophrenia patients, 64 controls), we investigate phase synchronization, as measured by intertrial phase coherence (ITPC), and intrinsic neural timescales, as measured by the autocorrelation window (ACW) during both the rest and oddball-task states. The main goal of our paper was to investigate whether reported shifts from shorter to longer timescales are related to decreased ITPC. Our findings show (i) decreases in both theta and alpha ITPC in response to both standard and deviant tones; and (iii) a negative correlation of ITPC and ACW in healthy subjects while such correlation is no longer present in SCZ participants. Together, we demonstrate evidence of abnormally long intrinsic neural timescales (ACW) in resting-state EEG of schizophrenia as well as their dissociation from phase synchronization (ITPC). Our data suggest that, during input processing, the resting state's abnormally long intrinsic neural timescales tilt the balance of temporal segregation and integration towards the latter. That results in temporal imprecision with decreased phase synchronization in response to inputs. Our findings provide further evidence for a basic temporal disturbance in schizophrenia on the different timescales (longer ACW and shorter ITPC), which, in the future, might be able to explain common symptoms related to the temporal experience in schizophrenia, for example temporal fragmentation.

Synchronization of time scales switched complex networks via impulsive couplings

We investigate the asymptotic synchronization problem of switched complex networks (SCNs) on time scales. Switches are made by a following time sequence with a dwell time constraint. By designing a Lyapunov function and a matrix inequality, self‐synchronizing criteria for SCNs are derived based on time scales theory. An impulsive coupling approach is designed to control links between nodes at the impulsive time. It is shown that the non‐synchronized SCNs can be synchronized by impulsive coupling with interval constraint. Three simulations on different time scales verify the effectiveness of our conclusions.

Apsidal motion and absolute parameters of GV Nor and V881 Sco based on mid-resolution spectroscopy and TESS photometry

ABSTRACT The veracity of stellar evolution models and theoretical internal structure constants may be subjected to stringent tests by using physical parameters obtained from spectroscopic and photometric observations of eclipsing binary systems that exhibit apsidal motion. Two eclipsing binary stars from the southern hemisphere with no prior published spectroscopic analyses were selected for this study: GV Nor and V881 Sco. Spectroscopic observations of these two eccentric binary systems were made at the South African Astronomical Observatory (SAAO) in 2018 and 2019, and their mid-resolution spectra were obtained. The radial velocities were measured using the cross-correlation method as well as by disentangling the spectra. The rotational broadening of the disentangled spectra of the components was also determined. The absolute parameters of these two systems were obtained by analyzing the SAAO-based spectroscopic data in conjunction with photometric data from Transiting Exoplanet Survey Satellite. Apsidal motion parameters for these two eccentric binary systems were calculated by analysing eclipse timing variations. Granada and Padova evolution models indicated ages of 340 ± 35 Myr for GV Nor and 760 ± 15 Myr for V881 Sco, in agreement with the observational results. The theoretical internal structure constants estimated from the Granada models were compatible with the observational values within the error limits. However, for both systems, it was found that their circularization and synchronization timescales were shorter than their respective evolutionary ages. Therefore, the fact that the components rotate faster than their synchronized values and still have rather large eccentric orbits (e ∼ 0.11) challenges present theories of circularization and spin–orbit synchronization.

Timing system based on customized frequency White Rabbit network in SHINE

Shanghai HIgh repetition rate XFEL aNd Extreme light facility (SHINE) is China's first hard X-ray FEL light source, which is expected to provide cutting-edge research methods for scientific research. To achieve the design target of SHINE, a high-precision timing system synchronized with the RF synchronization system of the accelerator is required, which could provide trigger signals and bunch ID for equipment on the accelerator, beamlines, and experimental stations so that those devices can be triggered in the correct sequence. This paper proposes a timing system based on WR technology that uses the RF signal from the synchronization system of SHINE as a reference and realizes the broadcasting of RF synchronization clock, including frequency and timescale, through an optical fiber network, achieving a timing accuracy of 8 picoseconds in the four-level network. Two enhanced timing applications, including the machine clock fanout and the random-event trigger distribution, are developed based on the RF timing benchmark. The scheme provides high-precision distribution of RF timing signal and general hardware interface, which can simplify the network structure and is expected to be extended to other large-scale physical accelerator facilities.

Binary mixtures of locally coupled mobile oscillators.

Synchronized behavior in a system of coupled dynamic objects is a fascinating example of an emerged cooperative phenomena which has been observed in systems as diverse as a group of insects, neural networks, or networks of computers. In many instances, however, the synchronization is undesired because it may lead to system malfunctioning, as in the case of Alzheimer's and Parkinson's diseases, for example. Recent studies of static networks of oscillators have shown that the presence of a small fraction of so-called contrarian oscillators can suppress the undesired network synchronization. On the other hand, it is also known that the mobility of the oscillators can significantly impact their synchronization dynamics. Here, we combine these two ideas-the oscillator mobility and the presence of heterogeneous interactions-and study numerically binary mixtures of phase oscillators performing two-dimensional random walks. Within the framework of a generalized Kuramoto model, we introduce two phase-coupling schemes. The first one is invariant when the types of any two oscillators are swapped, while the second model is not. We demonstrate that the symmetric model does not allow for a complete suppression of the synchronized state. However, it provides means for a robust control of the synchronization timescale by varying the overall number density and the composition of the mixture and the strength of the off-diagonal Kuramoto coupling constant. Instead, the asymmetric model predicts that the coherent state can be eliminated within a subpopulation of normal oscillators and evoked within a subpopulation of the contrarians.

KIC 5359678: a detached eclipsing binary with starspots

ABSTRACT We study the detached eclipsing binary, KIC 5359678, with starspot modulation using the high-quality Kepler photometry and LAMOST spectroscopy. The phoebe model, optimal for this binary, reveals that this system is a circular detached binary, composed of two F-type main-sequence stars. The masses and radii of the primary and the secondary are M1 = 1.31 ± 0.05 M⊙, R1 = 1.52 ± 0.04 R⊙, M2 = 1.12 ± 0.04 M⊙, and R2 = 1.05 ± 0.06 R⊙, respectively. The age of this binary is estimated to be about 2 Gyr, a value much longer than the synchronization time-scale of 17.8 Myr. The residuals of light curves show quasi-sinusoidal signals, which could be induced by starspots. We apply autocorrelation function analysis on the out-of-eclipse residuals and find that the spot with rotational period close to the orbital period, while, the decay time-scale of starspots is longer than that on the single stars with the same temperature, period range, and rms scatter. A two-starspot model is adopted to fit the signals with two-dip pattern, whose result shows that the longitude decreases with time.

Recent advances in Quaternary paleoclimate research using Antarctic blue ice

<p indent="0mm">Remarkable scientific discoveries have been made from the studies of ice cores drilled in polar ice sheets and mountain ice caps. These samples serve as the most accurate archives of the past atmospheric composition thus far. Two milestone achievements of ice cores include a continuous record of atmospheric greenhouse gas concentrations over the past eight glacial cycles (800 ka) and the discovery of abrupt climate change events on millennial timescale, both made possible by deep drilling in polar ice sheets. Yet, this conventional approach of deep drilling is faced with challenges from prohibitive logistical and operational cost and limited sample supply, particularly with greater depth. To address these challenges, shallow coring in blue ice areas has emerged as an appealing alternative. Two significant advances have been recently achieved from blue ice studies. Ice older than <sc>800 ka</sc> from the Allan Hills Blue Ice Area was discovered and the trapped gases inside the ice allow, for the first time, for the direct observation of atmospheric carbon dioxide concentrations (pCO₂) before <sc>800 ka.</sc> The data show no long-term decline in atmospheric pCO₂, and consequently, the Mid-Pleistocene Transition is not the result of cooling resulting from a decreasing pCO₂. Moreover, large-volume samples retrieved by a large-diameter ice drill (“Blue Ice Drill”) in the Taylor Glacier Blue Ice Area allow for novel geochemical analyses such as the radiocarbon (¹⁴C) content of methane (CH₄). The ¹⁴C of CH₄ trapped in the Taylor Glacier ice suggests that old carbon reservoirs were not responsible for the deglacial rise of CH₄ in the last glacial cycle. Another example of new geochemical methods enabled by the unprecedented sample availability offered by the blue ice areas is the elemental ratios of xenon, krypton, and nitrogen which are sensitive to the mean ocean temperature (MOT). Taylor Glacier ice samples dating back to the penultimate glacial period record <sc>1.1±0.3°C</sc> warmer-than-modern MOT values at <sc>129 ka</sc>, near the end of the penultimate deglaciation. Despite these advances, several challenges and limits remain. First, to accurately establish a chronology for the blue ice samples requires methods of absolute dating, which have considerable uncertainties at present. A precise chronology can be established via timescale synchronization with existing deep ice cores only when the blue ice is younger than <sc>800 ka.</sc> Second, the original deposition site of the blue ice field is not always known, complicating the interpretations of climate proxies that are sensitive to depositional environments such as the stable water isotopes of the ice. Third, glacial flows disrupt the chronology of the ice and could lead to the incomplete and biased preservation of climate signals. In light of these issues and shortcomings, stratigraphically continuous ice cores cannot be fully replaced by temporally discrete samples from the blue ice areas, although blue ice records hold the potentials to provide snapshots of the critical intervals of the Quaternary climate. Future progress in blue ice research may be made in three directions: (1) The prospecting of new blue ice fields and identification of blue ice areas containing the climate records of key understudied intervals; (2) numerical simulations of glacial dynamics to better the interpretation of blue ice records; and (3) the development of novel analytical techniques that reveal new climate information.

A quantitative in-depth analysis of the prototype sdB+BD system SDSS J08205+0008 revisited in the Gaia era

ABSTRACT Subdwarf B stars are core-helium-burning stars located on the extreme horizontal branch (EHB). Extensive mass loss on the red giant branch is necessary to form them. It has been proposed that substellar companions could lead to the required mass loss when they are engulfed in the envelope of the red giant star. J08205+0008 was the first example of a hot subdwarf star with a close, substellar companion candidate to be found. Here, we perform an in-depth re-analysis of this important system with much higher quality data allowing additional analysis methods. From the higher resolution spectra obtained with ESO-VLT/XSHOOTER, we derive the chemical abundances of the hot subdwarf as well as its rotational velocity. Using the Gaia parallax and a fit to the spectral energy distribution in the secondary eclipse, tight constraints to the radius of the hot subdwarf are derived. From a long-term photometric campaign, we detected a significant period decrease of $-3.2(8)\times 10^{-12} \, \rm dd^{-1}$. This can be explained by the non-synchronized hot subdwarf star being spun up by tidal interactions forcing it to become synchronized. From the rate of period decrease we could derive the synchronization time-scale to be 4 Myr, much smaller than the lifetime on EHB. By combining all different methods, we could constrain the hot subdwarf to a mass of $0.39\!-\!0.50\, \rm M_\odot$ and a radius of $R_{\rm sdB}=0.194\pm 0.008\, \rm R_\odot$, and the companion to $0.061\!-\!0.071\rm \, M_\odot$ with a radius of $R_{\rm comp}=0.092 \pm 0.005\, \rm R_\odot$, below the hydrogen-burning limit. We therefore confirm that the companion is most likely a massive brown dwarf.

A System for One- and Two-Way Comparisons of Time Scales Using Stimulated Raman Scattering

Problems requiring high-precision comparisons and synchronization of time scales (TS) of remote time and frequency standards are analyzed. The prospects of using fiber-optic communication lines to solve these problems are considered. Data on maximum operating distances and accuracy characteristics of TS comparison systems using fiber-optic communication lines are given. It is shown that the range of existing systems is not sufficient for solving a number of relevant problems. A method for amplifying optical signals in an optical fiber using the stimulated Raman scattering (SRS) effect is proposed. The application of the Raman amplifier in telecommunication systems is considered. A method is suggested for using SRS to amplify the optical signals of TS comparison systems. A scheme is proposed for a system of one- and two-way TS comparisons of distant objects using signal amplification based on the SRS effect realized using two-way counter-pumping. The operational principle of the system is described along with the procedure for determining the divergence in the TS of remote objects. The results of estimating the error and range of systems of one- and two-way comparisons of time scales using the Raman amplifier are presented. It is shown that the implementation of Raman amplification in the equipment of such systems will allow their range to be increased by more than three times without reducing system accuracy.

A system of one- and two-way comparisons of time scales using stimulated Raman scattering

Problems requiring high-precision comparisons and synchronization of time scales of remote time and frequency standards are considered. The prospects of using fiber-optic communication lines to solve these problems are considered. Data on maximum operating distances and accuracy characteristics of time scale comparison systems using fiber-optic communication lines are given. It is shown that the range of existing systems is not enough to solve a number of problems. A method for amplifying optical signals in an optical fiber using the effect of stimulated Raman scattering is considered. The application of the Raman amplifier in telecommunication systems is considered. A method is proposed for using the effect of stimulated Raman scattering (SRS) to amplify the optical signals of time scale comparison systems. A scheme is proposed for a system of one- and two-way comparisons of time scales of distant objects, using signal amplification based on the SRS effect realized using two-way counter-pumping. The principle of the system’s operation and the procedure for determining the divergence in the time scales of remote objects are described. The results of estimation of the error and range of systems of one- and two-way comparisons of time scales using Raman amplifier are presented. It is shown that the implementation of Raman-amplification in the equipment of such systems will allow more than three times to increase their range without reducing the accuracy of the systems.

УСТАНОВКА ДЛЯ ИЗМЕРЕНИЙ ЗАДЕРЖЕК РАСПРОСТРАНЕНИЯ СИГНАЛОВ В ОПТИЧЕСКИХ ЭЛЕМЕНТАХ

The results of the development of an installation for measuring signal propagation delays in optical elements and optical fibers are presented. Measuring the delays of signal propagation in optical elements and optical fibers required for the development of various instruments, in particular, the development of fiber-optic systems, the synchronization time scales for complexes of metrological support of the global navigation satellite system GLONASS and measuring means of ground-based GLONASS, the development of metrological maintenance of fiber-optic communication systems, the development radiophonic systems (e.g., phased arrays with fiber-optical channels, measuring systems with remote antennas). It is shown that the installation allows to implement phase and pulse methods for measuring signal propagation delays introduced by optical elements, as well as a modified pulse method designed to determine the delays in optical elements with a large signal attenuation, when the accuracy of measurements by other methods is reduced due to the increasing influence of noise measuring equipment. The developed method is based on registration of the pulse shape with the help of analog-to-digital Converter, the approximation was a data taking into account information about the original form of pulses to reduce random error caused by the influence of noise, and subsequent determination of temporal characteristics of pulses using parameters approximating functions. The application of the developed method for various forms of laser pulses is considered, the scheme of the installation implementing these methods is presented, and the results of experimental studies of the installation are presented. It is shown that the modified pulse method allows to reduce the measurement error of signal propagation delays in optical fibers and optical elements by 15–20% or more, depending on the introduced attenuation, and the installation for measuring signal propagation delays can be used to control the characteristics of optical fibers and optical elements of various fiber-optic systems.

Large algebraic connectivity fluctuations in spatial network ensembles imply a predictive advantage from node location information

A Random Geometric Graph (RGG) ensemble is defined by the disordered distribution of its node locations. We investigate how this randomness drives sample-to-sample fluctuations in the dynamical properties of these graphs. We study the distributional properties of the algebraic connectivity which is informative of diffusion and synchronization timescales in graphs. We use numerical simulations to provide the first characterisation of the algebraic connectivity distribution for RGG ensembles. We find that the algebraic connectivity can show fluctuations relative to its mean on the order of $30 \%$, even for relatively large RGG ensembles ($N=10^5$). We explore the factors driving these fluctuations for RGG ensembles with different choices of dimensionality, boundary conditions and node distributions. Within a given ensemble, the algebraic connectivity can covary with the minimum degree and can also be affected by the presence of density inhomogeneities in the nodal distribution. We also derive a closed-form expression for the expected algebraic connectivity for RGGs with periodic boundary conditions for general dimension.

Tidal Interactions of Close Hot Subdwarf Binaries

Over half of all observed hot subdwarf B (sdB) stars are found in binaries, and over half of these are found in close configurations with orbital periods of 10$ \,\rm{d}$ or less. In order to estimate the companion masses in these predominantly single-lined systems, tidal locking has frequently been assumed for sdB binaries with periods less than half a day. Observed non-synchronicity of a number of close sdB binaries challenges that assumption and hence provides an ideal testbed for tidal theory. We solve the second-order differential equations for detailed 1D stellar models of sdB stars to obtain the tidal dissipation strength and hence to estimate the tidal synchronization time-scale owing to Zahn's dynamical tide. The results indicate synchronization time-scales longer than the sdB lifetime in all observed cases. Further, we examine the roles of convective overshooting and convective dissipation in the core of sdB stars and find no theoretical framework in which tidally-induced synchronization should occur.

Synchronizing early Eocene deep-sea and continental records – cyclostratigraphic age models for the Bighorn Basin Coring Project drill cores

Abstract. A consistent chronostratigraphic framework is required to understand the effect of major paleoclimate perturbations on both marine and terrestrial ecosystems. Transient global warming events in the early Eocene, at 56–54 Ma, show the impact of large-scale carbon input into the ocean–atmosphere system. Here we provide the first timescale synchronization of continental and marine deposits spanning the Paleocene–Eocene Thermal Maximum (PETM) and the interval just prior to the Eocene Thermal Maximum 2 (ETM-2). Cyclic variations in geochemical data come from continental drill cores of the Bighorn Basin Coring Project (BBCP, Wyoming, USA) and from marine deep-sea drilling deposits retrieved by the Ocean Drilling Program (ODP). Both are dominated by eccentricity-modulated precession cycles used to construct a common cyclostratigraphic framework. Integration of age models results in a revised astrochronology for the PETM in deep-sea records that is now generally consistent with independent 3He age models. The duration of the PETM is estimated at ∼ 200 kyr for the carbon isotope excursion and ∼ 120 kyr for the associated pelagic clay layer. A common terrestrial and marine age model shows a concurrent major change in marine and terrestrial biota ∼ 200 kyr before ETM-2. In the Bighorn Basin, the change is referred to as Biohorizon B and represents a period of significant mammalian turnover and immigration, separating the upper Haplomylus–Ectocion Range Zone from the Bunophorus Interval Zone and approximating the Wa-4–Wa-5 land mammal zone boundary. In sediments from ODP Site 1262 (Walvis Ridge), major changes in the biota at this time are documented by the radiation of a “second generation” of apical spine-bearing sphenolith species (e.g., S. radians and S. editus), the emergence of T. orthostylus, and the marked decline of D. multiradiatus.

Метод определения разности задержек распространения по оптическому волокну импульсов лазерного излучения систем сравнений и синхронизации шкал времени

Метод определения разности задержек распространения по оптическому волокну импульсов лазерного излучения систем сравнений и синхронизации шкал времени