Constant Phase Lag Research Articles

Opto-magnetic resonance single-beam magnetometer driven by vector polarized light.

In this paper, we present an analysis of the amplitude variations of the opto-magnetic resonance absorption signals obtained in a single-beam magnetometer driven by radially or azimuthally polarized light (RPL/APL). It is shown that optically polarized atoms driven by cylindrical vector beams obtained only the alignment of atomic multipole moments but not the orientation, which is in good agreement with our simulation and experimental results. In comparison with the plane polarized pump light fields, cylindrical vector beams with much more complete electric vector polarization distribution in the transverse plane, make it unlikely to create the "emptying state " (no-atom populated) among the ground-state Zeeman sublevels for any possible orientation of the applied static magnetic field. These characteristics of the RPL/APL lead to generally smaller atomic population difference and lower response intensity of the transmitted signal. The tensor decomposition of atomic polarized states and the evolution of atomic multipole moments with the sweeping radio frequency (RF) field offer the way to show the magnetic orientation sensitivity of the radially or azimuthally polarized probe light, which possess similar profiles as that of the linearly polarized light, only with a constant phase lag of about π/2 and obvious amplitude differences.

The study on transmission spectrum and TTV behaviour of the hot Jupiter WASP-12b

ABSTRACT By utilizing the 1m and 2.4m telescopes of Yunnan Observatories, we obtained 13 new photometric transit light curves of WASP-12 exoplanetary system from 2009 to 2016. The data were analysed by using the Transit Analysis Package with the aid of Markov chain Monte Carlo technique. Based on the physical parameters from previous work, we have obtained the variation of radius with wavelength and mid-transit times of WASP-12b. Compared with a set of theoretical transmission spectra, its radius variation is almost consistent with a flatten and featureless model along with a slope in the bluer band, except the weak Na signal. The flatten and featureless transmission spectrum implies a possible evidence for the absence of TiO and VO in the upper atmosphere of WASP-12b. The slope in the bluer band may result from the Rayleigh scattering caused by H2/He and there would be hazes or hydride in the upper atmosphere. Combined new mid-transit times with all of the available timing data in literature, we have found that there is a significant change in the planetary orbit, the residuals of the timing prefer the orbital decay model to the apsidal precession model and the planetary interaction-induced TTV model. We updated the decay rate as −37.14 ± 1.31 ms yr−1 and derived a slightly lower modified quality factor $Q^{^{\prime }}_{*}$ for the constant-phase lag model. Furthermore, the current observations cannot rule out the planetary interaction-induced TTV model conclusively.

Synchronous X-ray/optical quasi-periodic oscillations from the black hole LMXB MAXI J1820+070

ABSTRACT We present high-speed optical photometry from SAAO and SALT on the black hole LMXB MAXI J1820+070 (ASSASN-18ey), some of it simultaneous with NICER, Swift, and Insight-HXMT X-ray coverage. We detect optical quasi-periodic oscillations (QPOs) that move to higher frequencies as the outburst progresses, tracking both the frequency and evolution of similar X-ray QPOs previously reported. Correlated X-ray/optical data reveal a complex pattern of lags, including an anticorrelation and a sub-second lag that evolve over the first few weeks of outburst. They also show correlated components separated by a lag equal to the QPO period roughly centered on zero lag, implying that the inter-band variability is strongly and consistently affected by these QPOs at a constant phase lag of roughly ±π. The synchronization of X-ray and optical QPOs indicates that they must be produced in regions physically very close to each other; we, thus, propose that they can be explained by a precessing jet model, based on analogies with V404 Cyg and MAXI J1348−630.

Tidal current classification insights for search, rescue and recovery operations in the Yellow and East China Seas and Korea Strait

We investigated spatial relationships between barotropic tidal currents and tides (i.e., tidal elevations) in the tidally predominant Yellow and East China Seas and Korea Strait (YESKS) continental shelf region to understand which tidal current and tide (TCE) characteristics underpin essential insights for maritime search, rescue and recovery operations. As baseline information for such operations, tidal current types were classified using FES2014 model TCE harmonic constant data and phase lag relationships for the predominant M2 constituent, to determine maximum flood currents. In terms of surface current spatial variation, the M2 currents were classified into three types: standing, progressive, and mixed tidal waves. In addition to these horizontal patterns, Acoustic Doppler Current Profiler (ADCP) records from three stations on the west coast of Korea during summertime 2007 and wintertime 2015 were harmonically analyzed to reveal the vertical structure of M2 constituent tidal currents, including ellipse parameter gradients. M2 tidal current types were found to vary through the water column, with the maximum tidal current delayed by up to 40° (∼1.4 h) in near surface waters compared to bottom waters. M2 tidal current types also varied vertically, with changes in its ellipse phase: for example, from a near-surface mixed tidal wave to a standing tidal wave near the seabed. Finally, to explore other TCE conditions relevant to rescue and recovery operations, distributions of the age of the tide and of the tidal current ellipse were compared, with results exhibiting similar distributions for both parameters, including >1.5 days in the Yellow Sea and <1.5 days in Korea Strait. In conclusion, as demonstrated by the spatially and vertically complex tidal current type patterns found in the YESKS, detailed three dimensional understandings of TCE processes are needed to successfully support maritime search, rescue and recovery operations in this and other regions.

Implication between Geophysical Events and the Variation of Seasonal Signal Determined in GNSS Position Time Series

The seasonal signal determined by the Global Navigation Satellite System (GNSS), which is captured in the coordinate time series, exhibits annual and semi-annual periods. This signal is frequently modelled by two periodic signals with constant amplitude and phase-lag. The purpose of this study is to explore the implication of different types of geophysical events on the seasonal signal in three stages—in the time span that contains the geophysical events, before and after the geophysical event, but also the stationarity phenomena, which is analysed on approximately 200 reference stations from the EPN network since 1995. The novelty of the article is demonstrated by correlating three different types of geophysical events, such as earthquakes with a magnitude greater than 6° on the Richter scale, landslides, and volcanic activity, and analysing the variation in amplitude of the seasonal signal. The geophysical events situated within a radius of 30 km from the epicentre showed a higher seasonal value than when the timespan did not contain a geophysical event. The presence of flicker and random walk noise was computed using overlapping Hadamard variance (OHVAR) and the non-stationary behaviour of the time series of the CORS coordinates in the time frequency analysis was done using continuous wavelet transform (CWT).

Rotation Period Evolution in Low-mass Binary Stars: The Impact of Tidal Torques and Magnetic Braking

Abstract We examine how tides, stellar evolution, and magnetic braking shape the rotation period (P rot) evolution of low-mass stellar binaries up to orbital periods (P orb) of 100 days across a wide range of tidal dissipation parameters using two common equilibrium tidal models. We find that many binaries with P orb ≲ 20 days tidally lock, and most with P orb ≲ 4 days tidally lock into synchronous rotation on circularized orbits. At short P orb, tidal torques produce a population of fast rotators that single-star-only models of magnetic braking fail to produce. In many cases, we show that the competition between magnetic braking and tides produces a population of subsynchronous rotators that persists for 1 Gyr, even in short-P orb binaries, qualitatively reproducing the subsynchronous eclipsing binaries discovered in the Kepler field by Lurie et al. Both equilibrium tidal models predict that binaries can tidally interact out to P orb ≈ 80 days, while the constant phase lag tidal model predicts that binaries can tidally lock out to P orb ≈ 100 days. Tidal torques often force the P rot evolution of stellar binaries to depart from the long-term magnetic-braking-driven spin-down experienced by single stars, revealing that P rot is not a valid proxy for age in all cases, i.e., gyrochronology can underpredict ages by up to 300% unless one accounts for binarity. We suggest that accurate determinations of orbital eccentricties and P rot can be used to discriminate between which equilibrium tidal models best describe tidal interactions in low-mass binary stars.

High curvatures drive river meandering

One of the long- and widely held ideas about the dynamics of meandering rivers is that migration slows down in bends with higher curvatures. Identifying the radius of curvature at which migration is fastest is standard practice in field studies of meandering rivers. High-resolution measurements of local migration rates in time-lapse Landsat images from two rapidly migrating rivers in the Amazon Basin suggest that the variation of migration rate closely follows that of the local curvature, with a roughly constant phase lag between the two; and a quasi-linear relationship exists between curvature and migration rate if this lag is taken into account. A simple numerical model of meandering illustrates the link between curvature and migration rate and reproduces observations from the studied rivers. The implication is that meandering rivers migrate fastest at, and slightly downstream of, locations of high curvature; and one of the most important ways river migration is rejuvenated and meandering patterns are reshuffled is the generation of high-curvature bends through cutoffs.

Depth dependence of coherent hemodynamics in the human head.

We report a near-infrared spectroscopy (NIRS) study of coherent hemodynamic oscillations measured on the human forehead at multiple source-detector distances (1 to 4cm). The physiological source of the coherent hemodynamics is arterial blood pressure oscillations at a frequency of 0.1Hz, induced by cyclic inflation (to a pressure of 200mmHg) and deflation of two thigh cuffs wrapped around the subject's thighs. To interpret our results, we use a recently developed hemodynamic model and a phasor representation of the oscillations of oxyhemoglobin, deoxyhemoglobin, and total hemoglobin concentrations in the tissue (phasors O, D, and T, respectively). The increase in the phase angle between D and O at larger source-detector separations is assigned to greater flow versus volume contributions and to a stronger blood flow autoregulation in deeper tissue (brain cortex) with respect to superficial tissue (scalp and skull). The relatively constant phase lag of T versus arterial blood pressure oscillations at all source-detector distances was assigned to competing effects from stronger autoregulation and smaller arterial-to-venous contributions in deeper tissue with respect to superficial tissue. We demonstrate the application of a hemodynamic model to interpret coherent hemodynamics measured with NIRS and to assess the different nature of shallow (extracerebral) versus deep (cerebral) tissue hemodynamics.

An efficient method for approximating resonance curves of weakly-damped nonlinear mechanical systems

A method is presented for tracing the locus of a specific peak in the frequency response under variation of a parameter. It is applicable to periodic, steady-state vibrations of harmonically forced nonlinear mechanical systems. It operates in the frequency domain and its central idea is to assume a constant phase lag between forcing and response. The method is validated for a two-degree-of-freedom oscillator with cubic spring and a bladed disk with shroud contact. The method provides superior computational efficiency, but is limited to weakly-damped systems. Finally, the capability to reveal isolated solution branches is highlighted.

Collective dynamics in two populations of noisy oscillators with asymmetric interactions.

We study two intertwined globally coupled networks of noisy Kuramoto phase oscillators that have the same natural frequency but differ in their perception of the mean field and their contribution to it. Such a give-and-take mechanism is given by asymmetric in- and out-coupling strengths which can be both positive and negative. We uncover in this minimal network of networks intriguing patterns of discordance, where the ensemble splits into two clusters separated by a constant phase lag. If it differs from π, then traveling wave solutions emerge. We observe a second route to traveling waves via traditional one-cluster states. Bistability is found between the various collective states. Analytical results and bifurcation diagrams are derived with a reduced system.

Spin–orbit evolution of Mercury revisited

Although it is accepted that the significant eccentricity of Mercury (0.206) favours entrapment into the 3:2 spin–orbit resonance, open are the questions of how and when the capture took place. A recent work by Makarov (Makarov, V.V. [2012]. Astrophys. J., 752, 73) has proven that trapping into this state is certain for eccentricities larger than 0.2, provided we use a realistic tidal model based on the Darwin–Kaula expansion of the tidal torque.While in Ibid. a Mercury-like planet had its eccentricity fixed, we take into account its evolution. To that end, a family of possible histories of the eccentricity is generated, based on synthetic time evolution consistent with the expected statistics of the distribution of eccentricity. We employ a model of tidal friction, which takes into account both the rheology and self-gravitation of the planet.As opposed to the commonly used constant time lag (CTL) and constant phase lag (CPL) models, the physics-based tidal model changes dramatically the statistics of the possible final spin states. First, we discover that after only one encounter with the spin–orbit 3:2 resonance this resonance becomes the most probable end-state. Second, if a capture into this (or any other) resonance takes place, the capture becomes final, several crossings of the same state being forbidden by our model. Third, within our model the trapping of Mercury happens much faster than previously believed: for most histories, 10–20Myr are sufficient. Fourth, even a weak laminar friction between the solid mantle and a molten core would most likely result in a capture in the 2:1 or even higher resonance, which is confirmed both semi-analytically and by limited numerical simulations.So the principal novelty of our paper is that the 3:2 end-state is more ancient than the same end-state obtained when the constant time lag model is employed. The swift capture justifies our treatment of Mercury as a homogeneous, unstratified body whose liquid core had not yet formed by the time of trapping.We also provide a critical analysis of the hypothesis by Wieczorek et al. (Wieczorek, M.A., Correia, A.C.M., Le Feuvre, M., Laskar, J., Rambaux, N. [2012]. Nat. Geosci., 5, 18–21) that the early Mercury might had been retrograde, whereafter it synchronised its spin and then accelerated it to the 3:2 resonance. Accurate processing of the available data on cratering does not support that hypothesis, while the employment of a realistic rheology invalidates a key element of the hypothesis, an intermediate pseudosynchronous state needed to spin-up to the 3:2 resonance.

Doppler-beaming in theKeplerlight curve of LHS 6343 A

Context. Kepler observations revealed a brown dwarf eclipsing the M-type star LHS 6343 A with a period of 12.71 days. In addition, an out-of-eclipse light modulation with the same period and a relative semi-amplitude of 2 x 10^-4 was observed showing an almost constant phase lag to the eclipses produced by the brown dwarf. In a previous work, we concluded that this was due to the light modulation induced by photospheric active regions in LHS 6343 A. Aims. In the present work, we prove that most of the out-of-eclipse light modulation is caused by the Doppler-beaming induced by the orbital motion of the primary star. Methods. We introduce a model of the Doppler-beaming for an eccentric orbit and also considered the ellipsoidal effect. The data were fitted using a Bayesian approach implemented through a Monte Carlo Markov chain method. Model residuals were analysed by searching for periodicities using a Lomb-Scargle periodogram. Results. For the first seven quarters of Kepler observations and the orbit previously derived from the radial velocity measurements, we show that the light modulation of the system outside eclipses is dominated by the Doppler-beaming effect. A period search performed on the residuals shows a significant periodicity of 42.5 +- 3.2 days with a false-alarm probability of 5 x 10^-4, probably associated with the rotational modulation of the primary component.

SUPERORBITAL MODULATION OF X-RAY EMISSION FROM GAMMA-RAY BINARY LSI +61 303

We report the discovery of a systematic constant time lag between the X-ray and radio flares of the gamma-ray binary LSI +61 303, persistent over long, multi-year, time scale. Using the data of monitoring of the system by RXTE we show that the orbital phase of X-ray flares from the source varies from $\phi_X\simeq 0.35$ to $\phi_X\simeq 0.75$ on the superorbital 4.6 yr time scale. Simultaneous radio observations show that periodic radio flares always lag the X-ray flare by $\Delta\phi_{X-R}\simeq 0.2$. We propose that the constant phase lag corresponds to the time of flight of the high-energy particle filled plasma blobs from inside the binary to the radio emission region at the distance ~10 times the binary separation distance. We put forward a hypothesis that the X-ray bursts correspond to the moments of formation of plasma blobs inside the binary system.

Uncertainties in tidal theory: Implications for bloated hot Jupiters

AbstractThanks to the combination of transit photometry and radial velocity doppler measurements, we are now able to constrain theoretical models of the structure and evolution of objects in the whole mass range between icy giants and stars, including the giant planet/brown dwarf overlapping mass regime (Leconte et al. 2009). In the giant planet mass range, the significant fraction of planets showing a larger radius than predicted by the models suggests that a missing physical mechanism which is either injecting energy in the deep convective zone or reducing the net outward thermal flux is taking place in these objects. Several possibilities have been suggested for such a mechanism: •downward transport of kinetic energy originating from strong winds generated at the planet's surface (Showman &amp; Guillot 2002),•enhanced opacity sources in hot-Jupiter atmospheres (Burrows et al. 2007),•ohmic dissipation in the ionized atmosphere (Batygin &amp; Stevenson 2010),•(inefficient) layered or oscillatory convection in the planet's interior (Chabrier &amp; Baraffe 2007),•Tidal heating due to circularization of the orbit, as originally suggested by Bodenheimer, Lin &amp; Mardling (2001). Here we first review the differences between current models of tidal evolution and their uncertainties. We then revisit the viability of the tidal heating hypothesis using a tidal model which treats properly the highly eccentric and misaligned orbits commonly encountered in exoplanetary systems. We stress again that the low order expansions in eccentricity often used in constant phase lag tidal models (i.e. constant Q) necessarily yields incorrect results as soon as the (present or initial) eccentricity exceeds ~ 0.2, as can be rigorously demonstrated from Kepler's equations.

Noise in frequency-modulation dynamic force microscopy

Analytical expressions for the noise affecting the different signals of interest in frequency-modulation dynamic force microscopy are derived. Two noise sources are considered, the thermomechanical noise of the cantilever and the noise of the deflection sensor. It is shown that distinguishing between amplitude and phase noise is crucial for a good understanding of the instrument. When the tip is far from the sample surface, in the absence of any tip-substrate interaction, the system reduces to two independent feedback loops, the first one maintaining the amplitude at a set point value and the other one keeping a constant phase lag between the tip oscillation and the cantilever excitation force. Closer to the surface, in the presence of tip-substrate interaction, these two loops become coupled to an extent that is determined by the nonlinear character of the cantilever oscillation induced by this interaction. The approximations introduced in deriving these analytical expressions are validated by numerical simulations and a comparison with experimental measurements is proposed. This modeling of the noise in frequency-modulation dynamic force microscopy allows us to derive most of the previously published results in a clear and unified framework. In addition, it demonstrates that the oscillator nonlinearities play an essential role in determining the noise level of the instrument, an effect that was not considered before.

Prototype and Applications for Asynchronous Rotation of Magnetic Microspheres

Magnetic microsphere suspended in a fluid aligns its magnetic moment with external magnetic field and follows a rotating external field with a constant phase lag. While this is true for low enough driving frequencies, the dynamics of the rotation change above some critical frequency and the particle rotates asynchronously with the driving field. This nonlinear response of the microsphere depends on physical parameters such as the magnetic moment and the size of the particle as well as the viscosity of the surrounding fluid.Asynchronous rotation of magnetic microspheres has many applications including magnetic particle characterization, viscosity measurements in small amounts of fluid, and pathogen detection. The technique enables continuous sensing of the sample which allows for real time viscosity measurements and single cell growth analysis.One of our technological and research goals is to develop a portable, easy to use and low power device that utilizes a magnetic field to asynchronously rotate magnetic particles. Owing to the platform technology nature of the method, the prototype setup explained in this poster can be utilized in many applications with minor modifications. Asynchronous rotation analysis can be done using off the shelf magnetic particles (usually used for magnetic separation) or custom made Janus particles (MagMoons) depending on the application. This poster will discuss progress toward this device as well as the applications of asynchronous rotation of magnetic microspheres.

Model-Based Real-Time Dynamic Power Factor Measurement in AC Resistance Spot Welding With an Embedded ANN

Today, real-time measurement of dynamic power factor in resistance spot welding (RSW) is of increasing importance. On the basis of the welding transformer circuit model, a new method is proposed to measure the peak angle of the welding current and then calculate the dynamic power factor in each half-wave. The tailored sensing and computing system ensures that the measuring method possesses a real-time computational capacity with satisfying accuracy. Since the power factor cannot be represented via an explicit function with respect to measurable parameters, the traditional method(s) has to approximate the power factor angle with a constant phase lag angle and fails to detect its dynamic characteristics. An offline-trained embedded artificial neural network (ANN) successfully realizes the real-time implicit function calculation or estimation. A digital-signal-processor-based RSW monitoring system is developed to perform ANN computation. Experimental results indicate that the proposed method is applicable for measuring the dynamic power factor in single-phase half-wave controlled rectifier circuits

Antarctic Circumpolar Current response to zonally averaged winds

Coherence analysis techniques are used to compare Southern Ocean wind forcing with Antarctic Circumpolar Current transport. Winds are derived from five different products: ERS winds that have been bin‐averaged, weekly gridded ERS winds produced by the Centre ERS d'Archivage et de Traitement, 5 day winds from the Special Sensor Microwave Imager, analysis winds from the European Centre for Medium‐Range Weather Forecasts, and reanalysis winds from the National Centers for Environmental Prediction. Barotropic transport is estimated from the pressure difference between bottom pressure gauges deployed on either side of Drake Passage by Proudman Oceanographic Laboratory as part of the World Ocean Circulation Experiment. Surface transport is estimated from TOPEX altimetry. Results indicate that transport and wind forcing are coherent over a broad range of frequencies, corresponding to time periods of roughly 10–256 days. Highest coherences occur for winds at latitudes on the south side of Drake Passage. Barotropic ocean transport lags wind forcing not by a constant time interval but by a constant phase lag of about one eighteenth of a cycle at a broad range of frequencies, suggesting that the oceanic response to wind is controlled by both the tendency term and a frequency‐dependent viscous process. Surface transport lags by a longer phase interval. Wind stress curl north of Drake Passage is more coherent with transport than is wind stress curl in the latitudes of Drake Passage. Ocean transport lags wind stress curl, suggesting that transport fluctuations are not governed by a simple Sverdrupian vorticity balance. Like the observations, general circulation model transports from the Parallel Ocean Program and from the Parallel Ocean Climate Model are coherent with wind stress from the south side of Drake Passage and with wind stress curl from latitudes north of Drake Passage. Unlike the observations, model transport and bottom pressure vary almost simultaneously with the wind and do not replicate the observed phase lags, implying that the effective model viscosity may be too large.

Coordination of spinal locomotor activity in the lamprey: long-distance coupling of spinal oscillators.

The extent and strength of long-distance coupling between locomotor networks in the rostral and caudal spinal cord of larval lamprey were examined with in vitro brain/spinal cord preparations, in which spinal locomotor activity was initiated by chemical microstimulation in the brain, as well as with computer modeling. When locomotor activity and short-distance coupling were blocked in the middle spinal cord for at least 40 segments, burst activity in the rostral and caudal spinal cord was still coupled 1:1, indicating that long-distance coupling is extensive. However, in the absence of short-distance coupling, intersegmental phase lags were not constant but decreased significantly with increasing cycle times, suggesting that long-distance coupling maintains a relatively constant delay rather than a constant phase lag between rostral and caudal bursts. In addition, under these conditions, intersegmental phase lags, measured between rostral and caudal burst activity, were significantly less than normal, and the decrease was greater for longer distances between rostral and caudal locomotor networks. The above result could be mimicked by a computer model consisting of pairs of oscillators in the rostral, middle, and caudal spinal cord that were connected by short- and long-distance coupling. With short-distance coupling blocked in the middle spinal cord, strychnine was applied to either the rostral or caudal spinal cord to convert the pattern locally from right-left alternation to synchronous burst activity. Synchronous burst activity in the rostral spinal cord resulted in a reduction in right-left phase values for burst activity in the caudal cord. These results also could be mimicked by the computer model. Strychnine-induced synchronous burst activity in the caudal spinal cord did not appear to alter the right-left phase values of rostral burst activity. Taken together, the experimental and modeling results suggest that the descending and ascending components of long-distance coupling, although producing qualitatively different effects, are comparatively weak. In particular, the descending component of long-distance coupling appears to become progressively weaker with increasing distance between two given regions of spinal cord. Therefore, short-distance coupling probably contributes substantially to normal rostrocaudal phase lags for locomotor activity along the spinal cord. However, short-distance coupling may be more extensive than "nearest neighbor coupling."

Behaviour of Leaky Surface Acoustic Wave Propagation at Discontinuous Region of Periodic Grating

This paper describes the leaky surface acoustic wave (LSAW) propagation characteristics at a discontinuous region in a grating structure. First, the dispersion relation of LSAWs propagating under a multielectrode-type grating is analysed. Then, the LSAW propagation on the discontinuous region is characterised by simply assuming that the LSAW behaviour under periodic part of the structure is identical with that under a totally periodic grating structure. It is concluded that the phase lag considerably decreases at the discontinuous region. This suggests that the energy storing effect may be weakened at the region where the periodic structure is broken. The simulation of one-port LSAW resonators shows that device performances are sufficiently evaluated only by taking account of the constant phase lag for a simulation tool based on the coupling-of-modes theory.