Flux Density Variations Research Articles

Core–sheath structured polystyrene‐ethylene‐butene‐styrene/carbon nanotubes/carbonyl iron particlecomposite fiber with high stretchability for strain and magnetic field dual‐mode sensing

AbstractTo meet the requirement of high stretchability, high sensitivity, and multifunction for flexible sensors, core–sheath structured polystyrene‐ethylene‐butene‐styrene (SEBS)/carbon nanotubes (CNTs)/carbonyl iron particle (CIP) fiber with SEBS/CNTs as the sheath and SEBS/CIP as the core was prepared through wet spinning. The contents of CNTs and CIP in the composite fiber were adjusted by changing the extrusion speed of the SEBS/CNTs and SEBS/CIP spinning solutions. The morphology, electromechanical sensing, and magnetic precepting performances of the fiber were studied. The SEBS/CNTs/CIP fiber sensor showed high stretchability with a maximum strain sensing range of 0%–216.9%, high sensitivity with a gauge factor (GF) of up to 1068.28, as well as excellent durability. In addition, the SEBS/CNTs/CIP fiber sensor exhibited excellent magnetic sensing performance by changing the relative resistance of 35.2% with a magnetic flux density variation of 1.2 T. The applications of SEBS/CNTs/CIP fiber in stretchable circuits, human body motion monitoring, and magnetic field perception were demonstrated.Highlights SEBS/CNTs/CIP fiber for strain and magnetic field sensing was fabricated. The SEBS/CNTs/CIP fiber sensor could sense 216.9% strain with GF up to 1068.28. Relative resistance of SEBS/CNTs/CIP fiber sensor changed by 35.2% under 1.2 T. SEBS/CNTs/CIP fiber was used in human motion monitoring and magnetic perception.

Signatures of a spinning supermassive black hole binary on the mas-scale jet of the quasar S5 1928+738 based on 25 yr of VLBI data

ABSTRACT In a previous work, we have identified the spin of the dominant black hole of a binary from its jet properties. Analysing Very Long Baseline Array (VLBA) observations of the quasar S5 1928+738, taken at 15-GHz during 43 epochs between 1995.96 and 2013.06, we showed that the inclination angle variation of the inner (<2 mas) jet symmetry axis naturally decomposes into a periodic and a monotonic contribution. The former emerges due to the Keplerian orbital evolution, while the latter is interpreted as the signature of the spin-orbit precession of the jet emitting black hole. In this paper, we revisit the analysis of the quasar S5 1928+738 by including new 15-GHz VLBA observations extending over 29 additional epochs, between 2013.34 and 2020.89. The extended data set confirms our previous findings which are further supported by the flux density variation of the jet. By applying an enhanced jet precession model that can handle arbitrary spin orientations κ with respect to the orbital angular momentum of a binary supermassive black hole system, we estimate the binary mass ratio as ν = 0.21 ± 0.04 for κ = 0 (i.e. when the spin direction is perpendicular to the orbital plane) and as ν = 0.32 ± 0.07 for κ = π/2 (i.e. when the spin lies in the orbital plane). We estimate more precisely the spin precession velocity, halving its uncertainty from $(-0.05\pm 0.02)$ to $(-0.04\pm 0.01)^{\circ }\, \mathrm{yr}^{-1}$.

Understanding the radio emission from ϵ Eridani

Some solar-type stars are known to present faint, time-variable radio continuum emission whose nature is not clearly established. We report on Jansky Very Large Array observations of the nearby star ϵ Eridani at 10.0 and 33.0 GHz. We find that this star has flux density variations on scales down to days, hours, and minutes. On 2020 April 15 it exhibited a radio pulse at 10.0 GHz with a total duration of about 20 min and a peak four times larger than the plateau of 40 μJy present in that epoch. We were able to model the time behavior of this radio pulse in terms of the radiation from shocks ramming into the stellar wind. Such shocks can be produced by the wind interaction of violently expanding gas heated suddenly by energetic electrons from a stellar flare, similar to the observed solar flares. Because of the large temperature needed in the working surface to produce the observed emission, this has to be nonthermal. It could be gyrosynchrotron or synchrotron emission. Unfortunately, the spectral index or polarization measurements from the radio pulse do not have a high enough signal-to-noise ratio to allow us to determine its nature.

Spectral Energy Distributions of Southern Binary X-Ray Sources

The rapid variability of X-ray binaries (XRBs) produces a wide range of X-ray states that are linked to activity across the electromagnetic spectrum. It is particularly challenging to study a sample of sources large enough to include all types in their various states, and to cover the full range of frequencies that show flux density variations. Simultaneous observations with many telescopes are necessary. In this project, we monitor 48 XRBs with seven telescopes across the electromagnetic spectrum from 5 × 109 to 1019 Hz, including ground-based radio, IR, and optical observatories, and five instruments on two spacecraft over a 1 week period. We construct spectral energy distributions and matching X-ray color–intensity diagrams for 20 sources that have the most extensive detections. Our observations are consistent with several models of expected behavior proposed for the different classes: we detect no significant radio emission from pulsars or atoll sources, but we do detect radio emission from Z sources in the normal or horizontal branch, and from black holes in the high/soft, low/hard, and quiescent states. The survey data provide useful constraints for more detailed models predicting behavior from the different classes of sources.

From binary to singular: The AGN PSO J334.2028+1.4075 under the high-resolution scope

Context. PSO J334.2028+1.4075 (PSO J334) is a luminous quasar located at redshift z = 2.06. The source gained attention when periodic flux density variations were discovered in its optical light curve. These variations were initially interpreted as the variability due to the orbital motion of a supermassive black hole binary (SMBHB) residing in a single circumbinary accretion disk. The orbital separation was determined to be 0.006 pc with an in-spiral time of 7 yr in the rest frame of PSO J334. These findings suggested the quasar could be in the gravitational wave emitting phase of its merger and so extended multiwavelength observations were commenced. However, subsequent observations provided evidence against the binary hypothesis as no optical periodicity was found on extended time baselines. On the other hand, detailed radio analysis with the Karl G. Jansky Very Large Array (VLA) and the Very Long Baseline Array (VLBA) revealed a lobe-dominated quasar at kiloparsec scales, and possibly a precessing jet, which could retain PSO J334 as a binary SMBH candidate. Aims. We aim to study both the large- and small-scale radio structures in PSO J334 to provide additional evidence for or against the binary scenario. Methods. We observed the source at 1.7 GHz with the European Very Long Baseline Interferometry Network (EVN), and at 1.5 and 6.2 GHz with the VLA, at frequencies that complement the previous radio interferometric study. Results. Our images reveal a single component at parsec scales slightly resolved in the southeast-northwest direction and a lobe-dominated quasar at kiloparsec scales with a complex structure. The source morphology and polarization in our VLA maps suggest that the jet is interacting with dense clumps of the ambient medium. While we also observe a misalignment between the inner jet and the outer lobes, we suggest that this is due to the restarted nature of the radio jet activity and the possible presence of a warped accretion disk rather than due to the perturbing effects of a companion SMBH. Conclusions. Our analysis suggests that PSO J334 is most likely a jetted active galactic nucleus with a single SMBH, and there is no clear evidence of a binary SMBH system in its central engine.

Comparison and Analysis of Electromagnetic Characteristics of Basic Structure of Wireless Power Coil for Permanent Magnet Motors in Electric Vehicles

The purpose of this paper is to compare and analyze the electromagnetic characteristics of the basic structure of the coil in the electromagnetic coupling mechanism for the wireless power supply of permanent magnet motors in electric vehicles. The electromagnetic coupling mechanism is one of the key technologies for wireless power transmission and the coil structure plays a key role in the transmission performance of the coupling mechanism, and different structures can achieve different performances. The central objective of coil structure studies is to investigate how the coupling coefficient can be increased to achieve greater transmitted power and higher efficiency. In this paper, we investigate two basic coil configurations, circular and square, by studying their flux density variations when used as transmitting coils and their electromagnetic coupling characteristics when used as receiving coils. Three couplers consisting of circular and square coils are also analyzed in simulations and experiments are carried out on couplings containing circular and square coils of the same area. The results of the study show that the qualitative analysis, simulation analysis and experimental results are in high agreement. The results of this paper are an important reference for the design and optimization of wireless power coils for permanent magnet motors in electric vehicles.

Comparative analysis of various materials for linear switched reluctance motor applied in railways

Linear switched reluctance motors (LSRM) are a very important and one of the most researched motors for applications in railways due to its robust structure, superior efficiency, lower mass production cost and superior tolerance towards faults. The study of electromagnetic properties plays a pertinent role in the selection of materials for linear switched reluctance motor. In this work a Finite element method (FEM) based tool is used for visualizing the electromagnetic field (magnetic flux) within the LSRM. The ANSYS maxwell software is used for obtaining the magnetic flux density variation in various materials. Based on the electromagnetic analysis of different materials obtained using the ANSYS software, the selection of material suitable for design of motor for implementation in railways application is made. The electromagnetic analysis between the stator and the translator is investigated and based upon this the selection of material is made. The magnetic flux between the stator and rotor teeth are analyzed during both the instants of alignment and unalignment. Various materials namely Cobalt, Steel 1008 and Samarium Cobalt (SmCo4) are tested and analyzed using the FEM based ANSYS software.

A VLBI Proper Motion Analysis of the Recoiling Supermassive Black Hole Candidate Mrk 1018

Mrk 1018 is a nearby changing-look active galactic nucleus (AGN) that has oscillated between spectral Type 1.9 and Type 1 over a period of 40 yr. Recently, a recoiling supermassive black hole (rSMBH) scenario has been proposed to explain the spectral and flux variability observed in this AGN. Detections of rSMBHs are important for understanding the processes by which SMBH binaries merge and how rSMBHs influence their galactic environment through feedback mechanisms. However, conclusive identification of any rSMBHs has remained elusive to date. In this paper, we present an analysis of 6.5 yr of multifrequency Very Long Baseline Array monitoring of Mrk 1018. We find that the radio emission is compact down to 2.4 pc, and it displays flux density and spectral variability over the length of our campaign, typical of a flat-spectrum radio core. We observe proper motion in RA of the radio core at −36.4 ± 8.6 μas yr−1 (4.2σ), or 0.10c ± 0.02c at the redshift of Mrk 1018. No significant proper motion is found in DEC (31.3 ± 25.1 μas yr−1). We discuss possible physical mechanisms driving the proper motion, including an rSMBH. We conclude that the apparent velocity we observe of the VLBI radio core is too high to reconcile with theoretical predictions of rSMBH velocities and that the proper motion is most likely dominated by an unresolved, outflowing jet component. Future observations may yet reveal the true nature of Mrk 1018. However, our observations are not able to confirm it as a true rSMBH.

The radio monitoring of the microquasar GRS 1915+105 with FAST

We report radio observations of the Galactic microquasar GRS 1915+105 with the Five-hundred-meter Aperture Spherical radio Telescope (FAST) in the band of 1.0−1.5 GHz. The observations were performed in 2020 with a total duration of ∼ 3.5 hours. In this work, we developed the pipeline to perform the calibration of the radio flux density and polarization for the persistent emitting radio source GRS 1915+105. The flux densities of the source during each observation are relatively stable, with the maximum fluctuation in flux density less than 40 mJy in one observation. And the linear polarization is between 20-30%, the polarization position angle is around 89.5∘, and the circular polarization is small and likely to be slightly left polarized. With the linear fitting of the polarization angles, we get a flat rotation measure of ∼ -0.5 rad⋅m−2. Meanwhile, the derived spectral index is near a constant for each observation of α∼−(0.4−0.3), indicating an optically thick emission source. The small variations of flux densities and flat rotation measure imply that GRS 1915+105 is likely in a plateau state during the FAST observations.

Pulsed field magnetization of a rectangular Y–Ba–Cu–O bulk, single grain superconductor assembly

The practical magnetization of arrays of multiple single grain, bulk high temperature superconductors is essential for practical applications, such as trapped flux rotating machines, magnetic resonance imaging and nuclear magnetic resonance. We report a systematic investigation of the pulsed field magnetization (PFM) of a bulk assembly consisting of two rectangular Y–Ba–Cu–O bulk single grains, in close proximity, at various temperatures. The measurements of the dynamic variation of the magnetic flux density, supported by numerical analysis, reveal that the induced screening currents during the rise of a pulsed field may greatly enhance the flux density in the region of the junction leading to uneven flux penetration and to an increased likelihood of flux jumps in this region. Such coupling between field and current promotes magnetic flux penetration and improves the peak trapped field from 3.01 T for a bulk single grain to 3.11 T for the bulk assembly at 30 K, improving the magnetization efficiency from 80% to 90%. The peak trapped field was further enhanced to 3.39 T and 3.31 T for the single bulk single grain and the bulk assembly, respectively, by employing a two-step multi-pulse PFM process.

Obscuring Environment and X-Ray Variability of Compact Symmetric Objects Unveiled with XMM-Newton and NuSTAR

Compact symmetric objects (CSOs) show radio features such as jets, lobes, and hot spots, which are contained within their host galaxies, and likely represent a recent radio activity. A subpopulation of CSOs with high intrinsic X-ray column densities has been inferred from shallow, soft X-ray band exposures, and observed to cluster in the linear radio size versus 5 GHz radio power plane, which suggests that a dense circumnuclear medium may dramatically influence the growth of compact radio structures. Here, we report on the first detection of two CSOs, 2021+614 and J1511+0518, at energies above 10 keV with NuSTAR. We model the NuSTAR data jointly with the new XMM-Newton data of J1511+0518, and with the archival XMM-Newton data of 2021+614. A toroidal reprocessor model fits the data well and allows us to robustly confirm the X-ray properties of the CSO absorbers and continuum. In both sources, we find intrinsic X-ray absorbing column densities in excess of 1023 cm−2, hard photon indices of the primary emission, Γ ∼ 1.4–1.7, Fe Kα line emission, and variability of the intrinsic X-ray flux density on the timescale of years. The studied X-ray continua are dominated by the primary power-law emission at energies above 3 keV, and by the scattered component at energies below 3 keV. An additional soft X-ray component, modeled with a hot, collisionally ionized plasma with temperature kT ∼ 1 keV, is required by the XMM-Newton data in J1511+0518, which is corroborated by the tentative evidence for the extension in the archival Chandra image of the source.

Time-dependent visibility modelling of a relativistic jet in the X-ray binary MAXI J1803−298

ABSTRACT Tracking the motions of transient jets launched by low-mass X-ray binaries (LMXBs) is critical for determining the moment of jet ejection, and identifying any corresponding signatures in the accretion flow. However, these jets are often highly variable and can travel across the resolution element of an image within a single observation, violating a fundamental assumption of aperture synthesis. We present a novel approach in which we directly fit a single time-dependent model to the full set of interferometer visibilities, where we explicitly parametrize the motion and flux density variability of the emission components, to minimize the number of free parameters in the fit, while leveraging information from the full observation. This technique allows us to detect and characterize faint, fast-moving sources, for which the standard time binning technique is inadequate. We validate our technique with synthetic observations, before applying it to three Very Long Baseline Array (VLBA) observations of the black hole candidate LMXB MAXI J1803−298 during its 2021 outburst. We measured the proper motion of a discrete jet component to be 1.37 ± 0.14 mas h−1, and thus we infer an ejection date of MJD $59348.08_{-0.06}^{+0.05}$, which occurs just after the peak of a radio flare observed by the Australia Telescope Compact Array (ATCA) and the Atacama Large Millimeter/Sub-Millimeter Array (ALMA), while MAXI J1803−298 was in the intermediate state. Further development of these new VLBI analysis techniques will lead to more precise measurements of jet ejection dates, which, combined with dense, simultaneous multiwavelength monitoring, will allow for clearer identification of jet ejection signatures in the accretion flow.

The optical behaviour of BL Lacertae at its maximum brightness levels: a blend of geometry and energetics

ABSTRACT In 2021 BL Lacertae underwent an extraordinary activity phase, which was intensively followed by the Whole Earth Blazar Telescope (WEBT) Collaboration. We present the WEBT optical data in the BVRI bands acquired at 36 observatories around the world. In mid-2021 the source showed its historical maximum, with R = 11.14. The light curves display many episodes of intraday variability, whose amplitude increases with source brightness, in agreement with a geometrical interpretation of the long-term flux behaviour. This is also supported by the long-term spectral variability, with an almost achromatic trend with brightness. In contrast, short-term variations are found to be strongly chromatic and are ascribed to energetic processes in the jet. We also analyse the optical polarimetric behaviour, finding evidence of a strong correlation between the intrinsic fast variations in flux density and those in polarization degree, with a time delay of about 13 h. This suggests a common physical origin. The overall behaviour of the source can be interpreted as the result of two mechanisms: variability on time-scales greater than several days is likely produced by orientation effects, while either shock waves propagating in the jet, or magnetic reconnection, possibly induced by kink instabilities in the jet, can explain variability on shorter time-scales. The latter scenario could also account for the appearance of quasi-periodic oscillations, with periods from a few days to a few hours, during outbursts, when the jet is more closely aligned with our line of sight and the time-scales are shortened by relativistic effects.

Radio and mid-infrared properties of the blazar J1419–0838

The radio quasar NVSS J141922−083830 (J1419−0838) was initially classified as an uncategorised blazar-type object, following its detection in the gamma -ray band with the Fermi space telescope. Later, using multi-waveband observations and modeling, its was found to be a flat-spectrum radio quasar (FSRQ). However, its radio emission has never been discussed in depth in the literature. Here we present a detailed analysis on the radio properties of J1419−0838 using archival interferometric imaging data at pc and kpc scales. We conclude that the flux density variations, the flat radio spectrum, the compact nature of the quasar structure at all scales, and the relativistic Doppler enhancement of the radio emission all support the previous classification as an FSRQ. We also investigated the short- and long-term mid-infrared (MIR) light curve of the quasar based on observations by the Wide-field Infrared Survey Explorer satellite, and found that there is significant variability on time-scales of days as well as years. Comparison of the MIR light curve to the times of previously reported gamma -ray and optical flares shows no clear correlation between the events at different wavebands.

A novel micromechanical method for nonlinear analysis of magnetostrictive composites

In this paper, a novel micromechanical modeling framework is presented to investigate mechanical properties of a multiphase magnetostrictive composite subjected to a multi-field coupling environment. To this end, a nonlinear constitutive equation with consideration of mechanical-magneto-thermal condition is proposed. Parametric elements are used to discretize a representative volume element (RVE) of the material to obtain local stress distribution. The macroscopic strain responses of the magnetostrictive material under magnetic field loading are predicated considering local equilibrium and using the homogenization technique. Numerical results are compared with the available experimental data. In general, the proposed method offers a useful tool to study the effects of external pre-stress, ambient temperature and fiber volume fraction on the overall characteristics of fiber reinforced magnetostrictive composites. The numerical results show that the nonlinear variations of strain and flux density are closely related to the magnetization intensity.

The Radio Structure of the γ-Ray Narrow-line Seyfert 1 Galaxy SDSS J211852.96-073227.5

The γ-ray narrow-line Seyfert 1 (NLS1) galaxies can be considered to be the third class of γ-ray active galactic nuclei possessing relativistic jets. In this paper, we present multi-band high-resolution Very Long Baseline Array (VLBA) images of the γ-ray NLS1, SDSS J211852.96-073227.5 (J2118-0732, z = 0.26). We find a core-jet radio morphology and significant flux density variations in the radio core. The high brightness temperature estimated from VLBA images and core variability demonstrate that it exhibits substantial relativistic beaming effects. By considering radio emission in several bands, we find that the source has an inverted spectrum above 1 GHz but a steep spectrum at low frequencies ranging from 74 MHz–1 GHz; these may arise from the present activity and the old diffuse/extended emission, respectively. The core-jet morphology, significant flux density variations, and beaming effect make J2118-0732 resemble a blazar. Considering the low mass of its central black hole and the ongoing merger environment, J2118-0732 may represent a low-mass, low-power counterpart of blazars, and may finally evolve into a blazar.

Long-term variation of the sap flow to tree diameter relation in a temperate poplar forest

Understanding the relationship between trunk sap flow and tree diameter is crucial for tree-stand transpiration upscaling and sap flow measurement strategy design, because of well-known tree-to-tree variations in sap flow metrics. However, whether and how this relationship will vary intra- and inter-annually, and the underlying mechanisms, are still poorly understood. We measured the sap flow of 126 trees throughout a six-year experiment (2016–2021) in a temperate poplar (Populus tomentosa) forest with five irrigation management regimes. Simultaneously, we also monitored meteorological factors, leaf area indices, and soil water contents. There was a great variability of both sap flux (SF) and sap flux density (SFD) across trees, and this variability tended to be larger in older stands. Patterns of the relationships between SF, SFD, and diameter at breast height (DBH) changed markedly from year to year. A nonlinear positive correlation (P < 0.001) between SF and DBH was found, except in 2016 when canopy closure did not occur. In contrast, no correlations between SFD and DBH were observed in most years, but their correlations became positive and linear in two wet years (2018, 2021) (P < 0.05). The power (Q) of DBH to explain tree-to-tree sap flow variations exhibited enormous change on both intra- and inter-annual scales, underpinned by different mechanisms. The potential transpiration demand of trees mainly determined the intra-annual variation of Q, but its effect depended on stand development, whereas the environmental water supply mostly controlled the inter-annual variation of Q. Based on these results, we provide some recommendations on sap flow measurement and stand transpiration estimation for pure tree plantations in water-limited regions. Our findings should assist the accurate prediction of stand water use in plantation forests of both poplar and other tree species.

Study of pulsar flux density and its variability with Parkes data archive

ABSTRACT We present average flux density measurements of 151 radio pulsars at 1.4 GHz with the Parkes ‘Murriyang’ radio telescope. We recommend our results be included in the next version of the Australia Telescope National Facility Pulsar Catalogue. The large sample of pulsars together with their wide dispersion measure (DM) range makes this data set useful for studying variability of flux density, pulsar spectra, and interstellar medium (ISM). We derive the modulation indices and structure-function from the flux density time series for 95 and 54 pulsars, respectively. We suggest the modulation index also be included in the next version of the pulsar catalogue to manifest the variability of pulsar flux density. The modulation index of flow density and DM are negatively correlated. The refractive scintillation (RISS) time-scales or its lower bound for a set of 15 pulsars are derived. They are very different from theoretical expectations, implying the complicated properties of the ISM along different lines of sight. The structure-function for other pulsars is flat. The RISS parameters for some of these pulsars possibly could be derived with different observing strategies in the future.

The RATAN-600 Multi-Frequency Catalogue of Blazars—BLcat

In this paper we present the RATAN-600 multi-frequency catalogue of blazars, an updated version of the BLcat: the RATAN-600 multi-frequency catalogue of BL Lacertae objects. The main novelty in the catalogue is an extension of the sample with flat-spectrum radio quasars (FSRQs), thus currently it contains more than 1700 blazars of different types. The main feature of the BLcat is a compilation of radio continuum data for blazars based on the RATAN-600 quasi-simultaneous measurements at frequencies of 1.1, 2.3, 4.7, 7.7/8.2, 11.2, and 21.7/22.3 GHz. We additionally supplement the catalogue with the radio data from external sources to provide an opportunity to more complete study of radio spectra and radio light curves. For the convenience of users, we developed tools to calculate the spectral index, variability index, and radio luminosity. We briefly describe basic radio properties of blazar subsamples of the catalogue: spectral classification, spectral indices, flux density variability, and radio luminosity.

Discovery of circular polarization of the 6.7 GHz methanol maser in G33.641-0.228

AbstractThe 6.7 GHz methanol maser emitted by a high-mass star forming region G33.641-0.228 is known to exhibit fast flux density variability on timescales of less than one day. The mechanism of this variability, called burst, has not been known. We observed the circular polarization of this maser. As a result, we found that only the spectral components representing burst exhibit strong circular polarization exceeding 10%. This suggests that the two phenomena of the burst and circular polarization are related to each other.