Rotational Modulation Research Articles

Multiscale behaviour of stellar activity and rotation of the planet host Kepler-30

Context. The Kepler-30 system consists of a G dwarf star with a rotation period of ~16 days and three planets orbiting almost coplanar with periods ranging from 29 to 143 days. Kepler-30 is a unique target with which to study stellar activity and rotation in a young solar-like star accompanied by a compact planetary system. Aims. We use about 4 yr of high-precision photometry collected by the Kepler mission to investigate the fluctuations caused by photospheric convection, stellar rotation, and starspot evolution as a function of timescale. Our main goal is to apply methods for the analysis of time-series to find the timescales of the phenomena that affect the light variations. We correlate those timescales with periodicities in the star and the planetary system. Methods. We model the flux rotational modulation induced by active regions using spot modelling and apply the Multifractal Detrending Moving Average algorithm in standard and multiscale versions to analyse the behaviour of variability and light fluctuations that can be associated with stellar convection and the evolution of magnetic fields on timescales ranging from less than 1 day up to about 35 days. The light fluctuations produced by stellar activity can be described by the multifractal Hurst index that provides a measure of their persistence. Results. The spot modelling indicates a lower limit to the relative surface differential rotation of ΔΩ∕Ω ~ 0.02 ± 0.01 and suggests a short-term cyclic variation in the starspot area with a period of ~34 days, which is close to the synodic period of 35.2 days of the planet Kepler-30b. By subtracting the two time-series of the simple aperture photometry and pre-search data conditioning Kepler pipelines, we reduce the rotational modulation and find a 23.1-day period close to the synodic period of Kepler-30c. This period also appears in the multifractal analysis as a crossover of the fluctuation functions associated with the characteristic evolutionary timescales of the active regions in Kepler-30 as confirmed by spot modelling. These procedures and methods may be greatly useful for analysing current TESS and future PLATO data.

Research on performance of rigid-hoop-reinforced multi-DOF soft actuator

In order to improve the bearing capacity of soft actuators, this article presents the development of the rigid-hoop-reinforced (spring or steel hoop) multi-DOF soft actuator. The actuator is composed of a rotary module with spring reinforcement on the silicone rubber-based body and a bending module with steel hoop reinforcement on the body. Compared with fiber-reinforced actuators, the bearing capacities of rigid-hoop-reinforced actuators made of 65Mn spring steel are improved. The radial and the axial bearing capacity for the bending module and the rotary module is raised by 29.6%, 28.2%, 30.6%, 49.6% respectively; under the same pressure, the spring-reinforced interval increases the maximum rotary angle of the rotary module, the steel hoop-reinforced interval increases the maximum bending angle of the bending module; with the same reinforcement type, the bending module with reinforcement interval of 10 mm has good bending characteristics that the bending angle changes with the pressure gently; the lower the hardness of silicone rubber base body, the better the adaptability and flexibility of the actuator, and the higher the hardness, the greater the bearing capacity of the actuator. Due to the above advantages, the rigid-hoop-reinforced multi-DOF soft actuator can be applied to medical devices which need high load-carrying capacity.

Dimerization and oligomerization of DNA-assembled building blocks for controlled multi-motion in high-order architectures

In living organisms, proteins are organized prevalently through a self-association mechanism to form dimers and oligomers, which often confer new functions at the intermolecular interfaces. Despite the progress on DNA-assembled artificial systems, endeavors have been largely paid to achieve monomeric nanostructures that mimic motor proteins for a single type of motion. Here, we demonstrate a DNA-assembled building block with rotary and walking modules, which can introduce new motion through dimerization and oligomerization. The building block is a chiral system, comprising two interacting gold nanorods to perform rotation and walking, respectively. Through dimerization, two building blocks can form a dimer to yield coordinated sliding. Further oligomerization leads to higher-order structures, containing alternating rotation and sliding dimer interfaces to impose structural twisting. Our hierarchical assembly scheme offers a design blueprint to construct DNA-assembled advanced architectures with high degrees of freedom to tailor the optical responses and regulate multi-motion on the nanoscale.

Focal impulse and rotor modulation guided ablation versus pulmonary vein isolation for atrial fibrillation: A meta-analysis of head-to-head comparative studies.

Empirical pulmonary vein isolation (PVI) remains the cornerstone for catheter ablation of atrial fibrillation (AF). Various ablation strategies and modalities are continually tested with the aim of improving ablation outcomes. Although focal impulse and rotor modulation (FIRM)-guided ablation is currently used as an adjunct to PVI, evidence supporting this strategy is conflicting. We sought to examine whether the utilization of FIRM-guided ablation with or without PVI is associated with a decrease in all-atrial arrhythmia recurrence as compared to PVI alone. A systematic review of PubMed, Cochrane, and Embase was performed for head-to-head study designs comparing outcomes of patients who underwent FIRM-guided ablation with or without PVI to those who underwent PVI alone. The primary efficacy endpoint was all-atrial arrhythmia recurrence. The secondary endpoints were complications rates and procedural characteristics. Overall, six studies comprising 674 patients undergoing either FIRM-guided ablation ± PVI versus PVI were included (mean age 63.4 ± 9.2, male 74%, 9% paroxysmal AF, 91% nonparoxysmal AF). After a mean follow-up of 18.8 months, FIRM-guided ablation with or without PVI was not associated with improvement in all-atrial arrhythmia recurrence rate compared to PVI alone (43.4% vs. 45.9%, risk ratio [RR]: 1.06; 95% confidence interval [CI]: 0.77-1.47; p = .70). No statistically significant difference was noted in complication rates between the two groups (RR: 1.66; 95% CI: 0.08-34.54; p = .74). In this meta-analysis of head-to-head comparison studies, FIRM-guided ablation with or without PVI did not provide any benefit in improving all-atrial arrhythmia recurrence at follow-up when compared to PVI alone.

Final results from the EU focal impulse and rotor modulation (E-FIRM) registry

Abstract Funding Acknowledgements Type of funding sources: Private company. Main funding source(s): Abbott Background The exact pathophysiology of how pulmonary vein (PV) triggers initiate or maintain episodes of atrial fibrillation (AF) has been elusive. Catheter ablation at relatively circumscribed areas of rapidly spinning rotors or very rapid focal impulse formation can significantly affect AF. Targeted ablation of these sources using Focal Impulse and Rotor Modulation (FIRM™) shows promise. Purpose To assess the safety and effectiveness of FIRM-guided procedures for the treatment of any type of symptomatic atrial fibrillation (AF). Methods Two hundred and ninety-nine subjects were enrolled in the E-FIRM Registry at 9 clinical sites in Germany and the Netherlands. Subjects were eligible if they had reported incidence of at least 2 documented episodes of symptomatic AF during the preceding 3 months and had failed at least Class I or III anti-arrhythmia drug. Data was collected at enrollment/baseline, procedure, and at 3-, 6-, and 12-month follow-up visits. Results A majority (59.5%, 178/299) had a history of previous ablation, 81.1% (133/164) in the left side, with an average of 1.5 ± 0.8 [range 0, 5] prior ablations. The primary safety endpoint was defined as freedom from procedure related Serious Adverse Events (SAEs) through 7-days and at 12-months. At 7-days, freedom from procedure related SAEs was 94.8% (257/271). At 12-months, freedom from procedure related SAEs was 84.4% (184/218). There were no deaths. Acute effectiveness success, defined as the elimination of all identified rotors, occurred in 64.0% (165/258) of treated patients. All patients for which data was reported had at least 1 rotor identified. The most common regions to find rotors were the lateral wall of the right atrium, the anterior/septal wall of the left atrium, and the posterior inferior region of the left atrium. 75.2% (194/258) of patients had at least one rotor identified in the right atrium, and 84.1% (217/258) of patients had at least one rotor identified in the left atrium. Success was defined as two sequential endpoints: single procedure freedom from AF recurrence at 3-months and single procedure freedom from AF recurrence. At 12-months, success was achieved in 46.4% (13/28) Paroxysmal, 42.9% (87/203) Persistent, and 0% (0/9) Long Standing AF subjects. Conclusions: Since acute success was reported as being achieved in only ∼2/3 of the treated subjects, it is possible that the full potential benefit of the FIRM-guided ablation was hidden in this evaluation of the full cohort. Considering the previous ablation and disease history of subjects, a single-procedure success rate at 12-months over 40% was considered a positive result. Based on these results, FIRM-guided RF ablation in conjunction with conventional RF ablation practices is both a safe and effective treatment strategy for patients with symptomatic AF.

Effects of variable viscosity and rotation modulation on ferroconvection

Effects of variable viscosity and rotation modulation on ferroconvection

Time-domain Modulation of HD 189733 Activities by Its Planet

Abstract Star–planet interaction can be studied by analyzing exoplanetary orbit and stellar rotation modulations of the transit emissions from exoplanetary systems. Here we carry out a time-domain analysis of the multiband activities of the HD 189733 star–planet system observed in X-ray, atomic lines, and broadband spectra reported in the literature. We find that the number of activities occuring at beat angles (of the planetary orbit and the stellar rotation) concentrating on a sector with a width of 108° are significantly larger than expected from a uniform distribution of activities, which indicates the existence of a major stellar active magnetic field region. The concentration of activities in this active magnetic field region shows their possible origins from the magnetic field interaction between HD 189733 and its close planet HD 189733 b.

Angular momentum transport by magnetoconvection and the magnetic modulation of the solar differential rotation

In order to explain the variance of the solar rotation law during the activity minima and maxima, the angular momentum transport by rotating magnetoconvection is simulated in a convective box penetrated by an inclined azimuthal magnetic field. Turbulence-induced kinetic and magnetic stresses and the Lorentz force of the large-scale magnetic background field are the basic transporters of angular momentum. Without rotation, the sign of the magnetic stresses naturally depends on the signs of the field components as positive (negative) BθBϕ transport the angular momentum poleward (equatorward). For fast enough rotation, however, the turbulence-originated Reynolds stresses start to dominate the transport of the angular momentum flux. The simulations show that positive ratios of the two meridional magnetic field components to the azimuthal field reduce the inward radial as well as the equatorward latitudinal transport, which result from hydrodynamic calculations. Only for BθBϕ > 0 (generated by solar-type rotation laws with an accelerated equator) does the magnetic-influenced rotation at the solar surface prove to be flatter than the nonmagnetic profile together with the observed slight spin-down of the equator. The latter phenomenon does not appear for antisolar rotation with polar vortex as well as for rotation laws with prevailing radial shear.

New constraints on the planetary system around the young active star AU Mic

AU Microscopii (AU Mic) is a young, active star whose transiting planet was recently detected. Here, we report our analysis of its TESS light curve, where we modeled the BY Draconis type quasi-periodic rotational modulation by starspots simultaneously to the flaring activity and planetary transits. We measured a flare occurrence rate in AU Mic of 6.35 flares per day for flares with amplitudes in the range of 0.06% < fmax < 1.5% of the star flux. We employed a Bayesian Markov chain Monte Carlo analysis to model the five transits of AU Mic b observed by TESS, improving the constraints on the planetary parameters. The measured planet-to-star effective radius ratio of Rp∕R⋆ = 0.0496 ± 0.0007 implies a physical radius of 4.07 ± 0.17 R⊕ and a planet density of 1.4 ± 0.4 g cm−3, confirming that AU Mic b is a Neptune-size moderately inflated planet. While a single feature possibly due to a second planet was previously reported in the former TESS data, we report the detection of two additional transit-like events in the new TESS observations of July 2020. This represents substantial evidence for a second planet (AU Mic c) in the system. We analyzed its three available transits and obtained an orbital period of 18.859019 ± 0.000016 d and a planetary radius of 3.24 ± 0.16 R⊕, which defines AU Mic c as a warm Neptune-size planet with an expected mass in the range of 2.2 M⊕ < Mc < 25.0 M⊕, estimated from the population of exoplanets of similar sizes. The two planets in the AU Mic system are in near 9:4 mean-motion resonance. We show that this configuration is dynamically stable and should produce transit-timing variations (TTV). Our non-detection of significant TTV in AU Mic b suggests an upper limit for the mass of AU Mic c of <7 M⊕, indicating that this planet is also likely to be inflated. As a young multi-planet system with at least two transiting planets, AU Mic becomes a key system for the study of atmospheres of infant planets and of planet-planet and planet-disk dynamics at the early stages of planetary evolution.

Subregional modulation of axial flow fans to reduce condensate supercooling of air-cooled steam condenser in cold days

For the air-cooled steam condensers (ACSCs) in the power station, the power consumption of axial flow fans accounts for a large proportion of the auxiliary power, which can be optimized by their rotational speed modulation. In this work, the subregional modulation strategies of axial flow fans in cold days are studied to reduce the supercooling of condensate in ACSCs as much as possible. For the steam-side and air-side heat transfer coupling in ACSCs, the macro heat exchanger model is adopted with the steam thermo-flow process solved, where the water phase state change is characterized by the steam enthalpy. Besides, the exhausted steam condensation in the down-flow bundles and the residual steam condensation in the up-flow bundles are both taken into consideration. Under the working conditions of choking turbine back pressure for an ideal power generating efficiency, the inlet temperature and flow rate of cooling air for each condenser cell are obtained, the condensate outlet temperature of the up-flow bundles and the total fan power consumption are calculated in terms of different modulation methods. The results show that the subregional modulation is superior to the uniform modulation with the maximum power conservation of 362.8 kW, which can be recommended in the practical operation of axial flow fans for ACSCs in winter.

Broadband terahertz polarization converter with anomalous reflection based on phase gradient metasurface

In order to expand the application situation of the polarization converter in terahertz band, a broadband polarization converter based on phase gradient metasurface is proposed for simultaneously manipulating the polarization and the wavefront of the reflected wave in terahertz region. Consisting of six different “H”-shaped resonators which can tune the phase and the polarization respectively, the polarization converter is able to deflect the normally incident terahertz wave with an anomalous reflection angle while changing the polarization. Geometric rotation and resonant frequency modulation constitute the phase variation of the unit, which can be superimposed on each other without interference. The simulation results show that the reflecting angle from 0.40 to 0.60 THz varies from 39° to 22° with side lobe level lower than −14 dB. Specific elucidation for high polarization conversion ratio is discussed through reflection phase and resonant branch analysis. Compared to the conventional polarization converter, the proposed one has an advantage in propagation manipulating, which reveals its potential application in THz detection, imaging and sensing, etc.

A structure scheme to reduce the influence of the accelerometer inner lever-arm effect on tri-axis inertial navigation systems

The accelerometer inner lever-arm effect is a significant error source for high-precision inertial navigation systems (INSs) and has a marked influence on the speed accuracy—a critical technical index of high-precision weapon systems. Rotation modulation technology is widely applied to reduce the errors of high-precision INS. However, this method fails to work for the inner lever-arm effect. Furthermore, variations in the rotation angular velocity and acceleration during modulation alter the inner lever-arm effect, further complicating the compensation of errors. System self-calibration is currently the principle method adopted to deal with the inner lever-arm effect, yet calculation errors result in residual estimations at the millimeter-level for the inner lever-arm. Such a residual will cause obvious speed errors for high-precision INS, which typically turns over the inertial measurement unit via the rotation modulation. This consequently makes it difficult to fully meet the requirements of high-precision weapon systems. In the current paper, we propose an accelerometer geometric space scheme based on the calculations and structural characteristics of a tri-axis INS. Through a simple structure arrangement, we demonstrate the complete theoretical elimination of the inner lever-arm effect in the absence of complex calibration and compensation processes. The only residual error of the inner lever-arm in the proposed scheme is the accumulated geometric tolerance with a value less than 0.2 mm. Semi-physical simulation results reveal the ability of our scheme to directly reduce the magnitude of the system speed error from 10−2 to 10−5. Moreover, the speed fluctuation disappears during the modulation rolling process, thus fully meeting the requirements of high-precision weapon systems.

Ultra-compact X-ray binaries as dual-line gravitational-wave sources

ABSTRACT By virtue of their sub-hour orbital periods, ultra-compact X-ray binaries are promising sources for the space-borne gravitational-wave interferometers LISA, Taiji, and TianQin. Some of these systems contain a neutron star primary, whose spin period can be measured directly via pulse timing, or indirectly through rotational modulations of burst phenomena. It is pointed out here that since actively accreting stars, with spin frequencies in the hundreds of Hz, may continuously emit appreciable gravitational waves due to the presence of accretion-built mountains, toroidal magnetic fields, and/or r-mode oscillations, such binaries are also candidate sources for ground-based interferometers. Two Galactic systems (4U 1728−34 and 4U 1820−30) are identified as being potentially detectable by both LISA and aLIGO simultaneously: a dual-line detection of this sort could provide percent-level constraints on the mass, radius, and internal magnetic field strength of the neutron star. With the Einstein Telescope, we find that at least four of the known ultra-compact binaries become dual-line visible.

Spots and Flares in Hot Main Sequence Stars Observed by Kepler, K2, and TESS

About 22,000 Kepler stars, 7,000 K2 stars, and nearly 60,000 TESS stars from sectors 1–24 have been classified according to variability type. A large proportion of stars of all spectral types appear to have periods in their light curves consistent with the expected rotation periods. A previous analysis of A- and late B-type stars suggests that these stars are indeed rotational variables. In this paper we have accumulated data to show that rotational modulation is present in about 30–40% of A- and B-type stars. A search for flares in TESS A- and B-type stars resulted in the detection of 102 flares in 57 stars. Analysis of flare energies show that the source of the flares cannot be a cool dwarf companion nor a F/G giant. The realization that a considerable fraction of A- and B-type stars are active indicates that a revision of current concepts regarding hot star envelopes is required.

A Decade of Radial-velocity Monitoring of Vega and New Limits on the Presence of Planets

Abstract We present an analysis of 1524 spectra of Vega spanning 10 yr, in which we search for periodic radial-velocity variations. A signal with a periodicity of 0.676 day and a semi-amplitude of ∼10 m s−1 is consistent with the rotation period measured over much shorter time spans by previous spectroscopic and spectropolarimetric studies, confirming the presence of surface features on this A0 star. The activity signal appears to evolve on long timescales, which may indicate the presence of failed fossil magnetic fields on Vega. TESS data reveal Vega’s photometric rotational modulation for the first time, with a total amplitude of only 10 ppm. A comparison of the spectroscopic and photometric amplitudes suggests that the surface features may be dominated by bright plages rather than dark spots. For the shortest orbital periods, transit and radial-velocity injection recovery tests exclude the presence of transiting planets larger than 2 R ⊕ and most non-transiting giant planets. At long periods, we combine our radial velocities with direct imaging from the literature to produce detection limits for Vegan planets and brown dwarfs out to distances of 15 au. Finally, we detect a candidate radial-velocity signal with a period of 2.43 days and a semi-amplitude of 6 m s−1. If caused by an orbiting companion, its minimum mass would be ∼20 M ⊕; because of Vega’s pole-on orientation, this would correspond to a Jovian planet if the orbit is aligned with the stellar spin. We discuss the prospects for confirmation of this candidate planet.

ROOSTER: a machine-learning analysis tool for Kepler stellar rotation periods

In order to understand stellar evolution, it is crucial to efficiently determine stellar surface rotation periods. Indeed, while they are of great importance in stellar models, angular momentum transport processes inside stars are still poorly understood today. Surface rotation, which is linked to the age of the star, is one of the constraints needed to improve the way those processes are modelled. Statistics of the surface rotation periods for a large sample of stars of different spectral types are thus necessary. An efficient tool to automatically determine reliable rotation periods is needed when dealing with large samples of stellar photometric datasets. The objective of this work is to develop such a tool. For this purpose, machine learning classifiers constitute relevant bases to build our new methodology. Random forest learning abilities are exploited to automate the extraction of rotation periods in Kepler light curves. Rotation periods and complementary parameters are obtained via three different methods: a wavelet analysis, the autocorrelation function of the light curve, and the composite spectrum. We trained three different classifiers: one to detect if rotational modulations are present in the light curve, one to flag close binary or classical pulsators candidates that can bias our rotation period determination, and finally one classifier to provide the final rotation period. We tested our machine learning pipeline on 23 431 stars of the Kepler K and M dwarf reference rotation catalogue for which 60% of the stars have been visually inspected. For the sample of 21 707 stars where all the input parameters are provided to the algorithm, 94.2% of them are correctly classified (as rotating or not). Among the stars that have a rotation period in the reference catalogue, the machine learning provides a period that agrees within 10% of the reference value for 95.3% of the stars. Moreover, the yield of correct rotation periods is raised to 99.5% after visually inspecting 25.2% of the stars. Over the two main analysis steps, rotation classification and period selection, the pipeline yields a global agreement with the reference values of 92.1% and 96.9% before and after visual inspection. Random forest classifiers are efficient tools to determine reliable rotation periods in large samples of stars. The methodology presented here could be easily adapted to extract surface rotation periods for stars with different spectral types or observed by other instruments such as K2, TESS or by PLATO in the near future.

Activity of TRAPPIST-1 analogue stars observed with TESS

As more exoplanets are being discovered around ultracool dwarfs, understanding their magnetic activity -- and the implications for habitability -- is of prime importance. To find stellar flares and photometric signatures related to starspots, continuous monitoring is necessary, which can be achieved with spaceborn observatories like the Transiting Exoplanet Survey Satellite (TESS). We present an analysis of TRAPPIST-1 like ultracool dwarfs with TESS full-frame image photometry from the first two years of the primary mission. A volume-limited sample up to 50 pc is constructed consisting of 339 stars closer than 0.5 mag to TRAPPIST-1 on the Gaia colour-magnitude diagram. The 30-min cadence TESS light curves of 248 stars were analysed, searching for flares and rotational modulation caused by starspots. The composite flare frequency distribution of the 94 identified flares shows a power law index similar to TRAPPIST-1, and contains flares up to $E_\mathrm{TESS} = 3 \times 10^{33}$ erg. Rotational periods shorter than 5 days were determined for 42 stars, sampling the regime of fast rotators. The ages of 88 stars from the sample were estimated using kinematic information. A weak correlation between rotational period and age is observed, which is consistent with magnetic braking.

Enhancing magneto-optic effects in two-dimensional magnets by thin-film interference

The magneto-optic Kerr effect is a powerful tool for measuring magnetism in thin films at microscopic scales, as was recently demonstrated by the major role it played in the discovery of two-dimensional (2D) ferromagnetism in monolayer CrI3 and Cr2Ge2Te6. These 2D magnets are often stacked with other 2D materials in van der Waals heterostructures on a SiO2/Si substrate, giving rise to thin-film interference. This can strongly affect magneto-optical measurements but is often not taken into account in experiments. Here, we show that thin-film interference can be used to engineer the magneto-optical signals of 2D magnetic materials and optimize them for a given experiment or setup. Using the transfer matrix method, we analyze the magneto-optical signals from realistic systems composed of van der Waals heterostructures on SiO2/Si substrates, using CrI3 as a prototypical 2D magnet, and hexagonal boron nitride to encapsulate this air-sensitive layer. We observe a strong modulation of the Kerr rotation and ellipticity, reaching several tens to hundreds of milliradians, as a function of the illumination wavelength, and the thickness of SiO2 and layers composing the van der Waals heterostructure. Similar results are obtained in heterostructures composed by other 2D magnets, such as CrCl3, CrBr3, and Cr2Ge2Te6. Designing samples for the optimal trade-off between magnitude of the magneto-optical signals and intensity of the reflected light should result in a higher sensitivity and shorter measurement times. Therefore, we expect that careful sample engineering, taking into account thin-film interference effects, will further the knowledge of magnetization in low-dimensional structures.

Mid-term Periodicities in Solar Radio Emission Corresponding to Sunspot Number During Solar Cycle 23

We present a systematic time-series analysis of solar radio emission in nine different frequencies to compare with that of daily sunspot number (SSN) during Solar Cycle 23 (1996–2009). Owing to the contribution from quiet-sun emission, the total solar fluxes in microwaves do not decrease as significantly as the sunspot number does during 2006 to 2009. Lomb–Scargle (LS) and wavelet analysis techniques are employed to infer the various periodicities present in the time-series data. False alarm probability (FAP) levels are estimated by the use of background mean power spectrum in the global wavelet spectrum. The LS periodogram contains resolved period peaks, some of which are below FAP levels, for example a well-known rotational period. These peaks are assessed with global significance levels of the wavelet analysis. In all the data sets, the period for solar rotational modulation (26–31 days) is present. The periodogram for the SSN presents Rieger type periods (130–180 days), mid-term periods (300–400 days) and long-term periods (430–850 days). These periods in north and south are not similar, especially long term periods are missing in SSN data of the southern hemisphere. Corresponding to the SSN periodicities, Rieger and near Rieger type of oscillations (130–180 days), quasi-biennial periodicities in the range of 1.2 to 3 years were detected in the time-series data of radio frequencies. Several of these detected periods fall in the range of the periods that are suggested to be connected with magneto-Rossby wave spherical harmonics. Our analysis found reduced power levels in the LS periodograms of low frequencies because of the fact that these low frequency emissions originate higher up in the corona with diminishing contrast to small scale structures.

Research on initial alignment method of vehicle-mounted SINS based on reverse navigation

In order to improve the alignment accuracy and speed of vehicle-mounted SINS, an initial alignment scheme of “inertial solidification alignment + Kalman filter fine alignment based on reverse navigation” is proposed in this paper. Firstly, an inertial solidification alignment algorithm is derived, the initial alignment problem is transformed into Wahba problem, and the optimal attitude matrix at the initial moment is obtained by singular value decomposition algorithm. The inertial solidification alignment algorithm is more concise and intuitive than the traditional alignment algorithm of geocentric inertial coordinate system. Then, we analyzed the effectiveness of rotation modulation technology to improve alignment accuracy theoretically and proved it by simulation. And it is pointed out that the application platform space is limited and the system cost is increased when using this technology. Furthermore, in order to overcome the shortcomings of using rotation modulation technology, a Kalman filter algorithm based on reverse navigation is derived. By reusing the data stored during the inertial solidification alignment, the alignment time is extended equivalently, the initial attitude error is reduced and the attitude calculation accuracy after forward navigation is improved, higher precision alignment is realized. Finally, the effectiveness of the initial alignment scheme is verified by simulation.