Rotation Measurements Research Articles

Generational assessment of EBSD detectors for cross-correlation-based analysis: From scintillators to direct detection

Introduced over ten years ago, cross-correlation-based electron backscatter diffraction has enabled high precision measurements of crystallographic rotations and elastic strain gradients at high spatial resolution. Since that time, there have been remarkable improvements in electron detector technology, including the advent of ultra-high speed detectors and the commercialization of direct detectors. In this study, we assess the efficacy of multiple generations of electron detectors for cross-correlation-based analysis using a single crystal Si sample as a reference. We show that, while improvements in precision are modest, there have been significant gains in the rate at which high-quality diffraction patterns can be collected. This has important implications in the size of datasets that can be collected and reduces the impact of drift and sample contamination.

Propagation effects at low frequencies seen in the LOFAR long-term monitoring of the periodically active FRB 20180916B

ABSTRACT LOFAR (LOw Frequency ARray) has previously detected bursts from the periodically active, repeating fast radio burst (FRB) source FRB 20180916B down to unprecedentedly low radio frequencies of 110 MHz. Here, we present 11 new bursts in 223 more hours of continued monitoring of FRB 20180916B in the 110–188 MHz band with LOFAR. We place new constraints on the source’s activity window $w =4.3^{+0.7}_{-0.2}$ d and phase centre $\phi _{\mathrm{c}}^{\mathrm{LOFAR}} = 0.67^{+0.03}_{-0.02}$ in its 16.33-d activity cycle, strengthening evidence for its frequency-dependent activity cycle. Propagation effects like Faraday rotation and scattering are especially pronounced at low frequencies and constrain properties of FRB 20180916B’s local environment. We track variations in scattering and time–frequency drift rates, and find no evidence for trends in time or activity phase. Faraday rotation measure (RM) variations seen between June 2021 and August 2022 show a fractional change >50 per cent with hints of flattening of the gradient of the previously reported secular trend seen at 600 MHz. The frequency-dependent window of activity at LOFAR appears stable despite the significant changes in RM, leading us to deduce that these two effects have different causes. Depolarization of and within individual bursts towards lower radio frequencies is quantified using LOFAR’s large fractional bandwidth, with some bursts showing no detectable polarization. However, the degree of depolarization seems uncorrelated to the scattering time-scales, allowing us to evaluate different depolarization models. We discuss these results in the context of models that invoke rotation, precession, or binary orbital motion to explain the periodic activity of FRB 20180916B.

Full-aperture surface reconstruction method for shift-rotation absolute measurement with tilt error suppression

We propose a new surface reconstruction method for the absolute measurement of shift rotation that can obtain a full-aperture surface distribution. Our approach reduces the effect of tilt errors on surface reconstruction by increasing the translation ratio of the test mirror. This method requires the test mirror to be measured once in situ, after translation, and after rotation. Because the known measured wavefront is a nonlinear function of the absolute surface distribution, the function of the surface distribution is linearized by performing a Taylor expansion to achieve fast surface reconstruction. Finally, a linear system of equations is constructed to solve the absolute surface distribution. The coefficient matrix is sparse and can quickly and accurately reconstruct the absolute surface distribution. In the simulation, the root mean square error (RMSE) of the reconstructed surface distribution of the method discussed in this study can reach to 0.012nm. Moreover, our method can significantly reduce the effect of tilt errors compared with typical methods, thereby yielding a new, high-precision solution for absolute measurements in interferometry.

Computer-assisted assessment of segmental bimaxillary surgery using voxel- and surface-based registration: A comparative study

The purpose of the present study was to compare the precision and reliability of voxel- and surface-based registration for computer-assisted assessment of the surgical accuracy and postoperative stability of segmental bimaxillary surgery. Three-dimensional translational and rotational measurements were performed by two observers using voxel- and surface-based registration. The precision and reliability of the measurements were calculated by the mean absolute differences (MAD) and intraclass correlation coefficients (ICC) at 95 % confidence intervals. A paired t-test or the non-parametric equivalent, Wilcoxon signed-rank test, was applied to statistically evaluate whether the precision of voxel- and surface-based registration was statistically significantly different (p < 0.05). Voxel-based registration had high precision (MAD <0.44 mm/0.92°) and excellent reliability, ICC [0.82–1.00]. The precision of surface-based registration was lower (MAD <0.56 mm/1.45°) and the reliability ranged from poor to excellent for the different bone segments, ICC [0.33–1.00]. Both registration techniques had high precision and excellent reliability for the assessment of the surgical accuracy, and the error margin of both techniques was clinical irrelevant. However, the increased precision of voxel-based registration was statistically significant (p < 0.05) for the maxillary segments and the chin, and the stability measurement error (ranging up to 1.58 mm and 4.46°) introduced by surface-based registration may be considered clinical relevant for these bone segments. Within the limitations of the present comparative study, voxel-based registration generally exhibited higher precision and reliability than surface-based registration for the surgical accuracy and postoperative stability assessment of segmental bimaxillary surgery.

Enhancing nitrogen use efficiency and plant productivity in long-term precrop/crop rotation and fertilization management

ContextLong-term experiments are an important tool to investigate the effects of crop rotation and fertilization measures under climate change conditions. However, there are few studies on nitrogen use efficiency (NUE) of crops in long-term cropping systems in Europe, but no consolidate studies in Germany. ObjectiveWe analyzed a long-term experiment established in 1982 to observe the role of legumes on total nitrogen uptake, NUE, agronomic efficiency, nitrogen response index and N recovery efficiency compared to fallow land and cereals in a crop rotation over the long-term. MethodsThe experiment included five different precrops (fallow land, maize, oat, field bean and clover mulch) in combination with four levels of fertilization (control, PK, PK+N with reduced dosage, and PK+N with full dosage followed by three years of cereal cultivation (winter wheat, winter rye, summer barley) in all treatments. The field trial was conducted as a fully factorial split plot design, with spatially randomized field repetitions in four blocks. ResultsLong-term mineral NPK fertilization improved the N uptake of winter wheat (185.7 kg N ha−1), winter rye (152.2 kg N ha−1) and summer barley (92.2 kg N ha−1) when the higher level of fertilization (NPK 100%) was implemented. A year-round application of clover mulch as green manure in the rotational system resulted in higher NUE (up to 37%) compared to fallow land after 40 years. Crop rotation with oat and maize (100% cereals) led to lower NUE (up to 30%) compared to fallow land. Clover mulch (198%), field bean (155%), fallow land (148%) and maize (119%) significantly increased the N uptake of wheat compared to oat in 2015. Over time, the agronomic efficiency was increased. This increase was 4 or 5 times higher in the 9th and 10th crop rotation compared to the beginning of the experiment (in 1983). Nitrogen response index of clover mulch was approximately 33–37% lower than fallow land at the beginning of the experiment in 1983 and 45–50% lower over the 40 years. N recovery efficiency values of winter wheat (94%), winter rye (66%) and summer barley (46%) increased within the 10th crop rotation compared to the beginning of the long-term experiment. ConclusionsCombining clover mulch as a green manure with mineral fertilizer has greater potential to improve NUE and crop productivity by increasing soil N availability. ImplicationsOur study highlights the importance of evaluating agronomic management practices in long-term field experiments to understand their sustainable effects.

Gas-phase Ortho-to-para Ratio of Formaldehyde Formed at Low Temperatures in Laboratory Ices

The ortho-to-para ratio (OPR) of formaldehyde (H2CO) has been used as a probe to estimate the formation temperature of molecules in interstellar, circumstellar, and cometary environments, relying on the assumption that nuclear spin conversion is extremely slow, preserving the OPR from molecular formation. An OPR for H2CO less than 3 corresponds to a spin temperature below 30 K and has been proposed to result from formation at low temperatures within an ice, whereas an OPR of 3 is interpreted as arising from warmer formation in the gas phase. In spite of this common assumption, there is no laboratory evidence in the literature to date in support of it. Here, in the first study of its kind for H2CO, we report rotational spectroscopy measurements of the OPR of H2CO sublimated after its formation in methanol (CH3OH) ice samples that were photolyzed by ultraviolet light at 10, 15, 20, and 40 K. None of the measured OPR values correlated with the ice formation temperature.

Fiber-based broadband detection of a rotational object with superposed vortices

Recently, the rotational Doppler effect has attracted broad attention in detecting rotational motion. However, the presently proposed detection techniques based on the rotational Doppler effect are generally configured relying on discrete components in free space, resulting in cumbersome and inflexible systems, which brings challenges to practical applications. In this paper, we demonstrate a fiber-based configuration on rotational Doppler measurements for the detection of a rotational object using an ultra-broadband mode-selective coupler to convert the superposed vortices. Remarkably, the results show the broadband operating range of the fiber-based measurement system intuitively through wavelength scanning. The refinement of rotational Doppler detection techniques is of great significance for lowering the cost, reducing system complexity, improving system integration, and industrial manufacturing. This fiber-based scheme might be a promising candidate for facilitating the rotational Doppler effect applied as novel motion monitoring and sensing equipment in engineering and industry.

The spectroscopic investigation of broad C I and C II lines emitted from pulsed atmospheric pressure gas discharge source in argon and argon‑hydrogen mixture

The spectroscopic investigation of pulsed atmospheric pressure needle-to-cylinder (NTC) gas discharge source with graphite cathode in argon and argon‑hydrogen mixture is performed. Numerous C2 molecular bands, of interest for rotational temperature Trot measurement, are recorded in the optical region of NTC discharge spectrum. Due to strong interference with C2 bands, the full set of C I and C II lines are not recorded. Nevertheless, we succeeded to obtain the spectra of broad C I multiplet at 477.0 nm, C II 274.7 nm line, and C II doublet at 283.7 nm. In addition, the hill-shaped-spectrum is recorded in the range 709–714 nm which is most probably the superposition of broad C II lines. Applying the appropriate fitting function on C II lines, the Stark broadening full-width-at-half-maximum (FWHM) is obtained and electron number density Ne estimated. The gas temperature Tg = 3500–4500 K, an important parameter for Ne diagnostics, is estimated from Trot calculated using C2, CH and CN molecular bands in the course of this study. The Ne ≈ 3 × 1016 cm−3 and Ne ≈ 1.5 × 1017 cm−3 are determined, which is consistent with our previous study with brass and stainless steel cathode NTC gas discharge.

Suppressing the false magnetic field in beam-splitting Faraday rotation measurement.

In laser-plasma experiments, the beam-splitting Faraday rotation measurement is usually used for mapping the magnetic field. Due to the geometric characteristics of the beam-splitting configuration, the split beams are not always incident normally on the image plane, and their spots have different shapes and intensity distributions. Ignoring these issues will inevitably introduce errors in polarization calculation and then generate large false magnetic fields. We introduced the restoration method to recover the spots and suppress the false magnetic field. We applied this method to ZEMAX simulation data and Shenguang-II experimental data. Compared to the method of directly overlaying the spots, it can reduce the average false magnetic field by about 50%. And the false magnetic field at the edge of the spot is reduced by one order of magnitude. We can highly improve the accuracy of the magnetic field measurement with the Faraday rotation method.

Probing the strongly correlated magnetic state of Co2C nanoparticles at low temperatures using μSR

Co2C nanoparticles (NPs) are amongst transition metal carbides whose magnetic properties have not been well explored. An earlier study (Roy et al 2021 J. Phys.: Condens. Matter 33 375804) showed that a pellet made from Co2C NPs exhibits exchange bias (EB) effect below a temperature, T EB = 50 K and a spin glass (SG) feature emerges below T SG = 5 K. In the current study we use magnetic, electrical transport, specific heat, and muon spin rotation (μSR) measurements to explore further the magnetic properties of a pellet made with 40 nm diameter pure Co2C NPs. We uncover the onset of Kondo localization at Kondo temperature T K (= 40.1 K), which is close to the onset temperature (T EB) of the EB effect. A crossover from the Kondo-screened scenario to the Ruderman–Kittel–Kasuya–Yosida interaction-dominated regime is also observed for T < T K. Temperature-dependent specific heat measurement further supports the Kondo localization scenario in the pellet and shows the heavy fermionic nature of the strongly correlated electronic state in Co2C. The zero field μSR asymmetry spectra in the low-temperature regime are characterized by two distinct fast and slow relaxation rates. The spectra show the absence of long-range magnetic order in the sample. However, our analysis suggests the NPs-pellet shows the presence of a dominant magnetically disordered fraction and a smaller fraction with short-range order. Muons in the disordered fraction exhibit a slower relaxation rate, while muons in the smaller fraction with short-range order exhibit a faster relaxation rate. We observe an increase in this fast relaxation rate between T EB and T SG. This increase below T EB ∼ 50 K suggests a slowing down of the fluctuating local magnetic environment around muons. Transverse field-μSR asymmetry spectra show the emergence of a stable, multi-peaked local magnetic field distribution in the pellet below T EB. Longitudinal field μSR spectra shows distinct changes in the dynamics of fluctuations suggesting the presence of a frozen glassy like state below 6 K. Based on our results, we suggest that below T EB, the pellet of Co2C NPs develops a magnetic interface that separates the two magnetic fractions; one is a disordered fraction, and the other is a fraction with short-range order. The exchange interaction that sets in below T EB at the interface couples the two fractions, leading to a suppression of the fluctuations. With the suppression of magnetic fluctuations below T EB, strong correlation effects in the electronic state of Co2C lead to Kondo localization.

Single-shot vector magnetic measurements using synchronous coherent population trapping resonance in a feedback compensation system

We demonstrate a real-time, single-shot vector magnetic measurement technique using synchronous coherent population trapping (SCPT) in an apparatus consisting of a small rubidium vapor cell. Vector modality of our magnetometer is enabled by designing a feedback system based on performing a peak-lock on a particularly strong 2ΩL magnetic resonance produced in the SCPT spectrum and compensating the external magnetic field via a three-axis field coil. With its current design, this magnetometer exhibits high sensitivities of approximately 155, 129, and 57pT/Hz in measuring the magnetic field vector components along the (x,y,z) axes. Sensitivities closer to the shot-noise limit can be achieved in the future by reducing the technical noise of our equipment and by employing a differential detection and polarization rotation measurement scheme in our system.

THE MUSCULOSKELETAL PROFILE OF FEMALE ADOLESCENT ELITE WATER POLO PLAYERS AND THE FACTORS AFFECTING THROWING PERFORMANCE

The musculoskeletal (MSK) profiles of water polo players and other overhead athletes has been shown to relate to injury and throwing performance (TP). There have been no robust studies conducted on the MSK profiles and the variables affecting TP amongst female, adolescent, elite water polo players.A prospective quantitative cohort design was conducted amongst eighty-three female adolescent, elite water polo players (range 14–19 years). All participants filled out the Kerlan-Jobe Orthopaedic Clinic questionnaire, followed by a battery of screening tests aimed to identify possible MSK factors affecting TP. Pain provocation tests, range of motion (ROM), upward scapula rotation (USR), strength and pectoralis minor length measurements were all included. Participants also performed throwing speed (TS) and throwing accuracy (TA) tests.All the data collected were grouped together and analysed using SPSS 28.0. The condition for statistical significance was set as p &lt;0.05. Multi-collinearity was tested for among variables to find out inter-variable correlations. Finally, a multiple regression analysis was performed.The mean KJOC score was 82.55 ± 14.96. 26.5% tested positive for at least one of the impingement tests. The MSK profile revealed decreased internal rotation ROM, increased external rotation ROM, a downwardly rotated scapula, weak external rotators, weak serratus anterior strength, strong lower trapezius and gluteus medius strength and a shorter pectoralis minor length all on the dominant side.Age, pectoralis minor length, upper trapezius and serratus anterior strength as well as upward scapula rotation were all positively correlated with TS, while sitting height, upper trapezius and serratus anterior strength and glenohumeral internal rotation ROM were positively correlated with TA.Multiple MSK parameters were found to be related to TS and TA in elite, adolescent water polo players.

Analysis of rotational Doppler shift with multi-ring vortex beams.

Vortex beams (VBs) with orbital angular momentum have shown great potential in the detection of transverse rotational motion of spatial targets which is undetectable in the classical radar scheme. However, most of the reported rotational Doppler measurements based on VBs can only be realized under ideal experimental conditions. The long-range detection is still a challenge. The detection distance based on rotational Doppler effect (RDE) is mainly limited by the scattered signal's signal-to-noise ratio (SNR). In this work, we investigated the influence of multi-ring vortex beams (MVBs) on the rotational Doppler frequency spectrum of scattered light from an object based on RDE and proposed a method of SNR enhancement of RDE signal. Firstly, different types of MVBs composed of a set of single-ring VBs with the same topological charge and different radii are designed, including multi-ring Laguerre Gaussian beam (MLGB), multi-ring perfect vortex beams (MPVB), and high-order Laguerre Gaussian beam (HLGB). Then, the influence of the number of rings and radial radius interval on the intensity profiles of MVBs and rotational Doppler frequency spectra under aligned and misaligned conditions is studied in detail. And the reasons why different types of MVBs lead to different SNR enhancement effectiveness with the increase of rings are also analyzed theoretically. Finally, proof-of-concept experiments were conducted to verify the effectiveness of the SNR enhancement method for RDE signals. The results showed that the amplitudes of the Doppler spectra generated by the MLGB and MPVB are improved substantially with the increase of rings, but the enhancement effect caused by the former is superior to the latter. The gain of HLGB on the RDE signal is the lowest. This study provides a useful reference for the optimization of rotational Doppler detection systems and may be of great application value in telemetry, long-range communication and optical imaging.

A multidirectional ultralow-frequency rotational energy harvester: Modeling and characterization

Energy harvesting under ultralow-frequency rotation is challenging, especially for frequencies below 1 Hz. This paper proposes a highly robust multidirectional ultralow-frequency rotational energy harvester (MUREH). The impact force generated by periodic gravity provides double excitation for the harvester at ultralow frequencies. The piezoelectric cantilever beam resonates at the intrinsic frequency under ultralow-frequency excitation, achieving frequency up-conversion and energy harvesting abilities under 1 Hz. An electromechanical coupling model is developed to analyze the influence of crucial parameters. Uniaxial and triaxial rotation measurements characterize the performance of the MUREH. At optimum conditions, the MUREH’s root mean square voltage is 4.995 V at 0.8 Hz. The adaptability of attitude randomness is verified by triaxial rotation experiments, with an output of not less than 77 % when tilted less than 45°. Under frequent disturbances, 66 % power is maintained, demonstrating high robustness.

Rotational Speed Measurement of a Shaft Using Infrared Sensor with NI Data Acquisition system and LabVIEW

Rotational speed measurement is the process of determining the number of rotations completed in a unit time. Generally, it is measured in Hertz, radians per second and rotations per minute (RPM). Rotational speed measurement is very critical parameter in condition monitoring, speed control, and supervision of rotational equipment like generators and turbines. This paper presents an alternate method of measuring the speed of a shaft using one of the cheapest infrared sensors available in Nepalese market. The principle of measurement of speed is on the basis of reflected and absorbed infrared light which is acquired using data acquisition unit of National Instrument. The signal processing has been carried out in a LabVIEW program and speed of shaft has been verified using the other optical sensors.

Utilizing EOS method to support diagnosis and treatment implementation in physiotherapy

Objective. The aim of this study is to describe the EOS method in correlation with other imaging studies within the field of medical diagnostics and demonstrate its utility in the diagnosis and implementation of treatment in physiotherapy. Materials and methods. This article utilizes available literature on medical imaging, including the EOS method. Additionally, the second part of the article illustrates the usefulness of EOS examination through a patient case study in the process of diagnosis and treatment in physiotherapy. Conclusions. The patient case example presented in this article demonstrates the utility of EOS examination as a supportive tool in the process of diagnosis and treatment within physiotherapy. The EOS equipment, complemented by integrated software, provides measurements of individual bone lengths, joint rotations, and axes and angles within the skeletal structure of the examined patient. The 3D visualization allows for assessing the functional state of the individual with a lower radiation dose compared to X-rays and computed tomography, making it conducive to frequent utilization in analyzing changes during the treatment process.

Does Rotation and Anterior Translation Persist as Residual Instability in the Knee after Anterior Cruciate Ligament Reconstruction? (Evaluation of Coronal Lateral Collateral Ligament Sign, Tibial Rotation, and Translation Measurements in Postoperative MRI).

Purpose: The aim of this study was to evaluate the presence of residual instability in the knee after ACL reconstruction through the analysis of MRI findings. Methods: This study included patients who underwent isolated ACL reconstruction between December 2019 and December 2021, and had preoperative and postoperative MRI, clinical scores, and postoperative isokinetic measurements. The anterior tibial translation (ATT) distance, coronal lateral collateral ligament (LCL) sign, and femorotibial rotation (FTR) angle were compared preoperatively and postoperatively. The correlation between the changes in preoperative-postoperative measurements and postoperative measurements with clinical scores and isokinetic measurements was examined. The clinical outcomes were compared based on the presence of a postoperative coronal LCL sign. Inclusion criteria were set as follows: the time between the ACL rupture and surgery being 6 months, availability of preoperative and postoperative clinical scores, and objective determination of muscle strength using isokinetic dynamometer device measurements. Patients with a history of previous knee surgery, additional ligament injuries other than the ACL, evidence of osteoarthritis on direct radiographs, cartilage injuries lower limb deformities, and contralateral knee injuries were excluded from this study. Results: This study included 32 patients. After ACL reconstruction, there were no significant changes in the ATT distance (preoperatively: 6.5 ± 3.9 mm, postoperatively: 5.7 ± 3.2 mm) and FTR angle (preoperatively: 5.4° ± 2.9, postoperatively: 5.2° ± 3.5) compared to the preoperative measurements (p > 0.05). The clinical measurements were compared based on the presence of a postoperative coronal LCL sign (observed in 17 patients, not observed in 15 patients), and no significant differences were found for all parameters (p > 0.05). There were no observed correlations between postoperative FTR angle, postoperative ATT distance, FTR angle change, and ATT distance change values with postoperative clinical scores (p > 0.05). Significant correlations were observed between the high strength ratios generated at an angular velocity of 60° and a parameters FTR angle and ATT distance (p-values: 0.028, 0.019, and r-values: -0.389, -0.413, respectively). Conclusions: Despite undergoing ACL reconstruction, no significant changes were observed in the indirect MRI findings (ATT distance, coronal LCL sign, and FTR angle). These results suggest that postoperative residual tibiofemoral rotation and tibial anterior translation may persist; however, they do not seem to have a direct impact on clinical scores. Furthermore, the increase in tibial translation and rotation could potentially negatively affect the flexion torque compared to the extension torque in movements requiring high torque at low angular velocities.

Deep Synoptic Array Science: Implications of Faraday Rotation Measures of Fast Radio Bursts Localized to Host Galaxies

Faraday rotation measures (RMs) of fast radio bursts (FRBs) offer the prospect of directly measuring extragalactic magnetic fields. We present an analysis of the RMs of 10 as yet nonrepeating FRBs detected and localized to host galaxies with robust redshift measurements by the 63-antenna prototype of the Deep Synoptic Array (DSA-110). We combine this sample with published RMs of 15 localized FRBs, nine of which are repeating sources. For each FRB in the combined sample, we estimate the host-galaxy dispersion measure (DM) contributions and extragalactic RM. We find compelling evidence that the extragalactic components of FRB RMs are often dominated by contributions from the host-galaxy interstellar medium (ISM). Specifically, we find that both repeating and as yet nonrepeating FRBs show a correlation between the host DM and host RM in the rest frame, and we find an anticorrelation between extragalactic RM (in the observer frame) and redshift for nonrepeaters, as expected if the magnetized plasma is in the host galaxy. Important exceptions to the ISM origin include a dense, magnetized circumburst medium in some repeating FRBs, and the intracluster medium of host or intervening galaxy clusters. We find that the estimated ISM magnetic-field strengths, , are characteristically ∼1–2 μG larger than those inferred from Galactic radio pulsars. This suggests either increased ISM magnetization in FRB hosts in comparison with the Milky Way, or that FRBs preferentially reside in regions of increased magnetic-field strength within their hosts.

Turbulent Structure in Supernova Remnants G46.8−0.3 and G39.2−0.3 from THOR Polarimetry

We present the continued analysis of polarization and Faraday rotation for the supernova remnants (SNRs) G46.8−0.3 and G39.2−0.3 in L-band (1–2 GHz) radio continuum in The H i/OH/Recombination line (THOR) survey. In this work, we present our investigation of Faraday depth fluctuations from angular scales comparable to the size of the SNRs down to scales less than our 16″ beam (≲0.7 pc) from Faraday dispersion (σ ϕ ). From THOR, we find median σ ϕ of 15.9 ± 3.2 rad m−2 for G46.8−0.3 and 17.6 ± 1.6 rad m−2 for G39.2−0.3. When comparing to polarization at 6 cm, we find evidence for σ ϕ ≳ 30 rad m−2 in localized regions where we detect no polarization in THOR. We combine Faraday depth dispersion with the rotation measure (RM) structure function (SF) and find evidence for a break in the SF on scales less than the THOR beam. We estimate the RM SF of the foreground interstellar medium using the SF of extragalactic radio sources and pulsars to find that the RM fluctuations we measure originate within the SNRs for all but the largest angular scales.

A Comprehensive Analysis of Repeating Fast Radio Bursts

Nearly 700 fast radio burst (FRB) sources have been detected so far, of which 29 are found to burst out repeatedly. Although a firm connection between at least some FRBs and magnetars has been established, the trigger mechanism and radiation process in these enigmatic phenomena are still highly controversial. In this study, we build a sample of 16 repeating FRBs from which at least five bursts have been detected, including the most active four repeaters of FRBs 20121102A, 20180916B, 20190520B, and 20201124A. Various key parameters of their bursts are collected from the literature, which include the arrival time, pulse width, dispersion measure (DM), Faraday rotation measure (RM), bandwidth, waiting time, peak flux, and fluence. The distribution and time evolution of these parameters are investigated. Potential correlations between various parameter pairs are also extensively explored. The behaviors of different repeaters are then compared. It is found that the DM of FRB 20121102A seems to increase continuously on a long timescale. While the DM of most repeaters varies in a narrow range of ±3 cm−3 pc, FRB 20190520B is found to have a large variation range of ±12 cm−3 pc. The RM evolves with time in a much more chaotic behavior in different repeaters. A linear correlation is found between the absolute mean RM and DMHost, which may provide a method to estimate the redshift of FRBs. Generally, the waiting time shows a similar bimodal distribution for the active repeating sources. The implications of these features to the underlying physics are discussed.