Flux Density Variations Research Articles

On the Connection between Solar Surface Magnetic Flux and the Total Solar Irradiance

Abstract Solar surface magnetic flux evolution plays a dominant role in the variability of total solar irradiance (TSI). Different proxies of magnetic activity have been introduced to correlate solar variability and TSI. We present the daily strong flux densities (SFDs) and weak flux densities (WFDs) defined with three magnetic thresholds calculated from the Solar Dynamic Observatory/Helioseismic Magnetic Imager. TSI measurements are from the radiometers of the Variability of Solar Irradiance and Gravity Oscillations experiment on the Solar and Heliosphere Observatory, and sunspot area (SSA) is from the National Oceanic and Atmospheric Administration. We characterize the influence of the magnetic flux density variation on the TSI using the Pearson, Spearman, and percentage bend correlations and wavelet analysis between the TSI and the flux density. The Pearson’s correlation shows that the TSI is negatively and strongly correlated with SFD and moderately with SSA; Spearman and 20% bend correlation shows that the TSI is moderately correlated with SFD and weakly with SSA on solar maximum, but weakly correlated on solar minimum. However, the TSI is not correlated with WFD during solar maximum and minimum. The bootstrapping tests also confirm that the influence of SFD on TSI is more significant than that of SSA. Finally, a wavelet analysis supports the idea that the SFD and TSI have a causality linkage and that the SFD dominantly influences the TSI variability on the rotational timescale.

Flux density variability of 286 radio pulsars from a decade of monitoring

ABSTRACT The Parkes telescope has been monitoring 286 radio pulsars approximately monthly since 2007 at an observing frequency of 1.4 GHz. The wide dispersion measure (DM) range of the pulsar sample and the uniformity of the observing procedure make the data set extremely valuable for studies of flux density variability and the interstellar medium (ISM). Here, we present flux density measurements and modulation indices of these pulsars over this period. We derive the structure function from the light curves and discuss the contributions to it from measurement noise, intrinsic variability, and interstellar scintillation. Despite a large scatter, we show that the modulation index is inversely correlated with DM, and can be generally described by a power law with an index of ∼−0.7 covering DMs from ∼10 to 1000 cm−3 pc. We present refractive time-scales and/or lower limits for a group of 42 pulsars. These often have values significantly different from theoretical expectations, indicating the complex nature of the ISM along individual lines of sight. In particular, local structures and non-Kolmogorov density fluctuations are likely playing important roles in the observed flux density variation of many of these pulsars.

Influence of soil warming and N‐addition on sap flux density and stem radius variation in boreal stands in Quebec, Canada

AbstractClimate change is projected to intensify the global hydrological cycle and increase temperatures. Excess N deposition could limit plant productivity because of a lack of plant–soil system efficiency with reduced water availability. However, the effects of soil warming and N‐addition on tree water transport and water use remain poorly understood. This study aimed to quantify the effects of soil warming and N‐addition associated with meteorological variables on the sap flux density and stem radius variation in black spruce (Picea mariana [Mill.] B.S.P.). From 2008 to 2014, we conducted a long‐term experiment on mature trees growing in two stands (Bernatchez [BER] and Simoncouche [SIM]) at different latitudes to evaluate the effect of soil warming (H) and N‐addition. During 2014, we investigated soil and plant water status between May and August, sap flux density from July to August and stem radius variation over the whole year. At the colder, northern site (BER), we detected a significant increase in sap flux density with the H‐treatment, whereas no effect was observed at the warmer, southern site (SIM). At BER, diurnal sap flux density in H × N‐addition treatment showed a significant effect in the afternoon near the peak of day compared with the other treatments. We found no significant effects of independent single or combined factors on soil and plant water status and stem radius variation at either site. Under climate change, black spruce at more northern sites could have a better water use and storage for wood productivity than those at more southern sites.

Magnetic Characterization of Ferromagnetic Alloys for High-Speed Electric Machines

High-speed electric machines operate at tens of thousands of revolutions per minute. The rotor and stator cores experience high-frequency electromagnetic fields. While the magnetic characteristics are available at 50/60 Hz, magnetic characteristics are required over a wide range of frequency due to variable speed operation of high speed motor. In this article, tests are carried out on ferromagnetic alloys over a frequency range of 1 Hz to 5 kHz and flux densities ranging from 0.1 to 2 T. The materials considered include the widely used M36 and 65C600 laminations. In applications where the rotor speed and shaft temperature are high, solid core rotors are more viable than laminated ones. Furthermore, the application requires that the shaft and active magnetic parts of the rotor be made of a single material. Hence, EN353 and EN8 are the prospective rotor materials considered. An extensive experimental study on the magnetic characteristics of these materials over a wide frequency range is reported in this article. The flux density variation over the core length at different frequencies is analyzed using finite element analysis. The results include B-H curves, static magnetisation curves, and power loss curves. The loss curves are useful to evaluate the loss density in the magnetic material at different frequencies and for various values of peak flux densities. These experimental data are essential for the analysis, design, and performance evaluation of high-speed electric machines.

An Overview of Methods and a New Three-Dimensional FEA and Analytical Hybrid Technique for Calculating AC Winding Losses in PM Machines

This article proposes a new hybrid analytical and numerical finite element (FE) based method for calculating ac eddy current losses in wire windings and demonstrates its applicability for axial flux permanent magnet electric machines. The method takes into account three-dimensional (3-D) field effects in order to achieve accurate results and yet greatly reduce computational efforts. The new 3-D FE-based method is advantageous as it employs minimum simplifications and considers the end turns in the eddy current path, the magnetic flux density variation along the effective length of coils, and the field fringing and leakage, which ultimately increases the accuracy of simulations. This study is one of the first ones to compare meticulous 3-D finite element analysis (FEA) models with more approximate, but faster solution methods, which can be employed in the optimization process. The accuracy of the 3-D FEA calculations has been confirmed through tests on a prototype axial flux permanent magnet machine. The proposed method is applicable for cases with majority of ac copper losses induced due to external magnetic flux sources, such as permanent magnets. Examples of such machines designs are coreless or open slot PM machines with conductors sizes smaller than skin depth.

Coil Positioning for Wireless Power Transfer System of Automatic Guided Vehicle Based on Magnetic Sensing.

As an auxiliary function of the wireless power transfer (WPT) system, coil positioning can solve the power and efficiency degradation during power transmission caused by misalignment of the magnetic coupler. In this paper, a Hall sensor array is used to measure the change of magnetic flux density. By comparing the multisensor data fusion results with the preset data obtained from the coil alignment, the real-time accurate positioning of the receiving coil can be realized. Firstly, the positioning model of the receiving coil is built and the variation of magnetic flux density with the coil misalignment is analyzed. Secondly, the arrangement of the Planar 8-direction symmetric sensor array and the positioning algorithm based on data fusion of magnetic flux density variations are proposed. In order to avoid coil positioning misalignment caused by the unstable magnetic field distribution which is actually affected by the change of mutual inductance during automatic guided vehicle (AGV) alignment, the constant current strategy of primary and secondary sides is proposed. Finally, the coil positioning experimental platform is built. The experimental results show that the coil positioning method proposed in this paper has high accuracy, and the positioning error is within 4 cm.

Very Long Baseline Interferometry Observations of the Proposed Radio Counterpart of an EGRET Source

We present high-resolution radio interferometric imaging observations of the radio source NVSS J182659+343113 (hereafter J1826+3431), the proposed radio counterpart of the γ-ray source, 3EG J1824+3441 detected by the Energetic Gamma Ray Experiment Telescope (EGRET) on board the Compton Gamma Ray Observatory satellite. We analyzed eight epochs of archival multi-frequency very long baseline interferometry data. We imaged the asymmetric core–jet structure of the source, and detected apparent superluminal motion in the jet. At the highest observing frequency, 15.3 GHz, the core shows high brightness temperature indicating Doppler boosting. Additionally, the radio features undergo substantial flux density variability. These findings strengthen the previous claim of the association of the blazar J1826+3431 with the possible γ-ray source, 3EG J1824+3441.

Interstellar scintillation of an extreme scintillator: PKS B1144−379

ABSTRACT The University of Tasmania Ceduna radio telescope has been used to investigate rapid variability in the radio flux density of the BL Lac object PKS B1144−379 at 6.7 GHz. High-cadence monitoring of this extreme scintillator was carried out over a period of approximately 9 yr, between 2003 and 2011. We have used structure functions created from the intensity time-series to determine the characteristic time-scale of the variability. The characteristic time-scale is consistently observed to increase during certain periods of each year, demonstrating the annual cycle expected for scintillation through an interstellar scattering screen. The best-fitting annual cycle model for each year suggests that the scintillation pattern has an anisotropic structure and that the upper limit of its scattering screen is at a distance of ∼0.84 kpc. Higher anisotropy in some of the annual cycle fits suggests that changes in the intrinsic source structure might be influencing the variability time-scale. We found a prominent annual cycle is only present in the variability time-scale for certain years, where other evidence suggests that the core is compact. From our measurements, we calculated that the core angular size varied between 5.65 and 15.90 μas (0.05–0.13 pc). The core component was found to be at its most compact during two flares in the total flux density, which were observed in 2005 and 2008. We conclude that the long-term variability in the radio flux density of PKS B1144−379 is due to intrinsic changes in the source and that these affect our ability to measure an annual cycle in its variability time-scale.

A New High-Frequency Iron Loss Model Including Additional Iron Losses due to Punching and Burrs’ Connection

A variable magnetic permeability is introduced to the skin effect coefficient to reflect the influence of flux density variation on eddy current losses. The evaluation results show that the new iron loss model can cover a wide range of frequencies without using piecewise functions. Two types of punched edges are defined and the additional iron losses are tested, separated, and modeled, so that the punching and burrs’ connection effects on iron losses can be considered more accurately. The iron loss model proposed in this article is very useful for a more accurate design of high-speed motors including the punching effects.

Nocturnal sap flow is mainly caused by stem refilling rather than nocturnal transpiration for Acer truncatum in urban environment

Nocturnal sap flow is an important part of plant sap flow, while it is usually regarded as negligible. Consequently, the aim of this study was to measure nocturnal stem sap flow of Acer truncatum and to determine its driving force in an urban green space. Stomatal aperture was measured using surface impression method in a typical clear day of August. Sap flux density was monitored by a thermal diffusive probe system from July to October. Meanwhile, wind speed (WS), relative humidity, air temperature, precipitation and total solar radiation were monitored by an automatic weather station. We found nocturnal stomatal aperture was about 32% of mid-morning, and nocturnal sap flux density was significantly and positively affected by WS and vapor pressure deficit (VPD) (P < 0.001), while nocturnal sap flow volume was significantly and positively related to diurnal sap flow volume (R2 = 0.30, P < 0.001).The explanation of VPD and WS to nocturnal sap flux density was less than that of diurnal sap flow. The relationship between nocturnal sap flux density and VPD separated into two distinct models. When VPD≥0.10 kPa, nocturnal sap flux density was significantly and positively correlated with VPD (R2 = 0.53, P < 0.001), while there was a significant negative correlation between sap flux density and VPD when VPD<0.10 kPa (R2 = 0.18, P < 0.001). The variation of sap flux density showed different patterns in different weather conditions. During a clear night, sap flux density showed a decreasing trend with VPD and WS, while sap flux density only showed a similar trend to precipitation during rainfall. We suggest nocturnal sap flow of Acer truncatum is regulated by nocturnal transpiration and stem refilling, and stem refilling is the fundamental force while transpiration promotes sap flow, and the volume is restricted by soil moisture, stem storage water volume, and the water status of the previous day.

Study of Diameter, Depth and Variation of Relative Flux Density of Moon’s Craters

In this work, we have selected three craters Mutus, Mutus C and Nearch of the satellite Moon. The fits images were taken from Meade 16- inch LX200GPS Schmidt- Cassegrain Telescope on June 20, 2018 from National observatory located at Nagarkot, Nepal. To find the diameter, number of lines were drawn across the craters and distance of them were determined in pixel size from Aladin V 2.5 software. By using shadow length method, the height of two craters (Mutus and Nearch) were determined and compared with the published one. In addition to this, variations of relative flux density, Gaussian trend distribution of flux were studied.

Event Horizon Telescope imaging of the archetypal blazar 3C 279 at an extreme 20 microarcsecond resolution

3C 279 is an archetypal blazar with a prominent radio jet that show broadband flux density variability across the entire electromagnetic spectrum. We use an ultra-high angular resolution technique – global Very Long Baseline Interferometry (VLBI) at 1.3 mm (230 GHz) – to resolve the innermost jet of 3C 279 in order to study its fine-scale morphology close to the jet base where highly variableγ-ray emission is thought to originate, according to various models. The source was observed during four days in April 2017 with the Event Horizon Telescope at 230 GHz, including the phased Atacama Large Millimeter/submillimeter Array (ALMA), at an angular resolution of ∼20 μas (at a redshift ofz = 0.536 this corresponds to ∼0.13 pc ∼ 1700 Schwarzschild radii with a black hole massMBH = 8 × 108 M⊙). Imaging and model-fitting techniques were applied to the data to parameterize the fine-scale source structure and its variation. We find a multicomponent inner jet morphology with the northernmost component elongated perpendicular to the direction of the jet, as imaged at longer wavelengths. The elongated nuclear structure is consistent on all four observing days and across different imaging methods and model-fitting techniques, and therefore appears robust. Owing to its compactness and brightness, we associate the northern nuclear structure as the VLBI “core”. This morphology can be interpreted as either a broad resolved jet base or a spatially bent jet. We also find significant day-to-day variations in the closure phases, which appear most pronounced on the triangles with the longest baselines. Our analysis shows that this variation is related to a systematic change of the source structure. Two inner jet components move non-radially at apparent speeds of ∼15 cand ∼20 c(∼1.3 and ∼1.7 μas day−1, respectively), which more strongly supports the scenario of traveling shocks or instabilities in a bent, possibly rotating jet. The observed apparent speeds are also coincident with the 3C 279 large-scale jet kinematics observed at longer (cm) wavelengths, suggesting no significant jet acceleration between the 1.3 mm core and the outer jet. The intrinsic brightness temperature of the jet components are ≲1010K, a magnitude or more lower than typical values seen at ≥7 mm wavelengths. The low brightness temperature and morphological complexity suggest that the core region of 3C 279 becomes optically thin at short (mm) wavelengths.

Dynamic Stiffness Analysis and Experimental Verification of Axial Magnetic Bearing Based on Air Gap Flux Variation in Magnetically Suspended Molecular Pump

Current and displacement stiffness are important parameters of axial magnetic bearing (AMB) and are usually considered as constants for the control system. However, in actual dynamic work situations, time-varying force leads to time-varying currents and air gap with a specific frequency, which makes the stiffness of appear decrease and even worsens control performance for the whole system. In this paper, an AMB dynamic stiffness model considering the flux variation across the air gap due to frequency is established to obtain the accurate dynamic stiffness. The dynamic stiffness characteristics are analyzed by means of the dynamic equivalent magnetic circuit method. The analytical results show that the amplitude of current and displacement stiffness decreases with frequency increasing. Moreover, compared with the stiffness model without considering the variation of flux density across the air gap, the improved dynamic stiffness results are closer to the actual results. Through the dynamic stiffness measurement method of AMB, experiments of AMB in magnetically suspended molecular pump (MSMP) are carried out and the experimental results are consistent with theoretical analysis results. This paper proposes the dynamic stiffness model of axial magnetic bearing considering the variation of flux density across the air gap, which improves the accuracy of the AMB stiffness analysis.

Improving Current Transformer-Based Energy Extraction From AC Power Lines by Manipulating Magnetic Field

This article presents a novel method to improve energy scavenging from ac power lines under magnetic saturation conditions. The extracted power level of a conventional magnetic energy harvester is limited by the maximum flux density of the magnetic core. When a magnetic core is clamped on ac power lines, the flux density in the core is proportional to the magnetic field strength around the power line. Choosing a high-permeability core has the advantage of harvesting more energy for a given primary current. The flux density in such a core could reach its maximum value when the magnetic field increases. In this scenario, very little energy can be harvested since flux density variation in the core is small. Here we introduce an artificial magnetic field by adding an additional control coil to manipulate the magnetic field of power lines. A power management circuit is employed to store the energy harvested by the control coil and feed it back to the harvester to generate a counter magnetic field. As a result, the core will not be easily driven into the saturation region; hence, more energy can be harvested. Experimental results show that the proposed energy harvester can harvest an average power of 283 mW on a 50 Hz 10 Arms power line (2.34 mW/cm3/Arms), which is increased by 45% compared with the device without the control coil. This new method could provide a promising solution for smart grid monitoring and other industrial sensing applications.

Effect of Magnetostriction on Localised Flux Density in Toroidal Amorphous Cores Due To Bending Stress

Application of a force causes a localized bending stress, which results in a change in the domain structure and therefore a variation in induced voltages are occurred across search coils uniformly wound on this area. The magnetostriction of amorphous ribbons vary with their compositions. Two types of amorphous ribbon were used to analyse the variation of localised flux density with different flux density and frequency levels. Amorphous toroidal transducers were made from high and near zero magnetostrictive Metglas® as-cast amorphous ribbons, which were Fe-based 2605SA1 and Co-based 2705X respectively. Measurements were carried out to confirm the influence of applying force and frequency on output characteristic of the transducer due to their magnetostriction. A force was applied to the toroidal core in steps of 20 from 0 to 500 g-force. The transducer under the test were sinusoidally magnetised over the frequency range from 1 to 10 kHz and flux density levels of 50, 100 and 150 mT. The variation in the induced voltage of search coils located at 0º and 90º was very significant with applied stress, while it was less pronounced located at 45º with applied stress on the Fe-based toroidal core and the applying force is not effective on 2705X amorphous ribbon. This investigation highlights the influence of localised bending stress on flux density in amorphous ribbon cores due to its magnetostriction. Key words: Amorphous ribbon core, magnetostriction, flux distribution. DOI: 10.7176/JSTR/6-07-13

Spitzer Observations of the Predicted Eddington Flare from Blazar OJ 287

Abstract Binary black hole (BH) central engine description for the unique blazar OJ 287 predicted that the next secondary BH impact-induced bremsstrahlung flare should peak on 2019 July 31. This prediction was based on detailed general relativistic modeling of the secondary BH trajectory around the primary BH and its accretion disk. The expected flare was termed the Eddington flare to commemorate the centennial celebrations of now-famous solar eclipse observations to test general relativity by Sir Arthur Eddington. We analyze the multi-epoch Spitzer observations of the expected flare between 2019 July 31 and 2019 September 6, as well as baseline observations during 2019 February–March. Observed Spitzer flux density variations during the predicted outburst time display a strong similarity with the observed optical pericenter flare from OJ 287 during 2007 September. The predicted flare appears comparable to the 2007 flare after subtracting the expected higher base-level Spitzer flux densities at 3.55 and 4.49 μm compared to the optical R-band. Comparing the 2019 and 2007 outburst lightcurves and the previously calculated predictions, we find that the Eddington flare arrived within 4 hr of the predicted time. Our Spitzer observations are well consistent with the presence of a nano-Hertz gravitational-wave emitting spinning massive binary BH that inspirals along a general relativistic eccentric orbit in OJ 287. These multi-epoch Spitzer observations provide a parametric constraint on the celebrated BH no-hair theorem.

Three-Dimensional Structured Dual-Mode Flexible Sensors for Highly Sensitive Tactile Perception and Noncontact Sensing.

This work reports a three-dimensional (3D) structured multifunctional sensor by connecting a magnetowhisker with a superflexible patterned skin film. Composed of percolation networks of silver nanowires, the patterned skin film is integrated via a simple template manufacturing method without increasing the complexity and sacrificing the flexibility. The as-prepared 3D structured sensor can realize the multimodal detection of out-of-plane tactile stimuli and details of noncontact environmental obstacles in multiple directions. Here, the sensor's perception behaviors on compression, pulling, magnetic field, sound waves, airflow, water level, water flow, and backwash are presented. Furthermore, the 3D structured sensor obtains outstanding mechanical robustness and stability for 8000 cycles, excellent sensitivity (12 800% when the applied pulling displacement was 3.5 mm; 152% T-1 when the magnetic flux density variation was 40.6 mT), ultrahigh response time, and ultrahigh recovery time (∼5 ms), which may meet the industrial sensing requirement for artificial tactile electronics. Facile manufacturing processes and outstanding multimodal sensing characteristics make the 3D structured sensor to possess great potential to be implemented in the next-generation intelligent bionic equipment or systems.

Development of Electromagnet for Laboratory Water Treatment Experiments

Water is said to be magnetized when it flows across the magnetic field and magnetized water finds its application in many areas of life. Despite the numerous benefits of magnetized water, very little works have been reported on the development of magnet for water magnetizer application. In most of the reported works, the detailed theoretical analysis and design procedure required for the development of the magnet was not accounted for; hence the need for the present study. Electromagnetic means of producing flux density is considered in this study due to its advantage of flux density variation, which is not achievable with the use of its permanent magnet counterparts. The design equation of short electromagnet was derived from the existing equations of coil magnetic flux density and then used for the air core electromagnet design. The variation of the magnetic flux density with the distance between two electromagnets was empirically investigated. The performance of the developed electromagnet is satisfactory, as the flux density varies between 814.6 and 510G corresponding to the gap (0 - 4cm) between the coils (i.e., water pipe diameter). Keywords— Air core, Coils, Iron core, Magnetic flux density, Magnetized water

Rotor UMP characteristics and vibration properties in synchronous generator due to 3D static air‐gap eccentricity faults

In this article, the qualitative theoretical derivation, together with finite element analysis and experimental studies are presented to investigate the unbalanced magnetic pull (UMP) as well as the rotor vibration characteristics. Differently from previous studies, this study focuses on the UMP/vibration not only under the normal and the conventional radial rotor eccentricity conditions but also for three-dimensional (3D) hybrid static air-gap eccentricity (SAGE) cases which are composed of both the radial SAGE and the axial SAGE. The detailed UMP expressions before and after each SAGE, are first deduced based on the analysis of the magnetic flux density variation. Then, the 3D finite element calculation and the experimental study are carried out on the CS-5 prototype generator which has two poles and a rated speed of 3000 rpm in order to validate the proposed theoretical analysis. It is shown that the DC component and the even harmonics of the radial UMP/vibration, especially the second harmonic, increase under the SAGE conditions. Specifically, the increment of the radial SAGE increases both the radial and the axial UMPs/vibrations, while the growth of the axial SAGE increases the axial UMP/vibration but meanwhile reduces the radial UMP/vibration.

A Decade of Multiwavelength Observations of the TeV Blazar 1ES 1215+303: Extreme Shift of the Synchrotron Peak Frequency and Long-term Optical–Gamma-Ray Flux Increase

Abstract Blazars are known for their variability on a wide range of timescales at all wavelengths. Most studies of TeV gamma-ray blazars focus on short timescales, especially during flares. With a decade of observations from the Fermi-LAT and VERITAS, we present an extensive study of the long-term multiwavelength radio-to-gamma-ray flux-density variability, with the addition of a couple of short-time radio-structure and optical polarization observations of the blazar 1ES 1215+303 (z = 0.130), with a focus on its gamma-ray emission from 100 MeV to 30 TeV. Multiple strong GeV gamma-ray flares, a long-term increase in the gamma-ray and optical flux baseline, and a linear correlation between these two bands are observed over the ten-year period. Typical HBL behaviors are identified in the radio morphology and broadband spectrum of the source. Three stationary features in the innermost jet are resolved by Very Long Baseline Array at 43.1, 22.2, and 15.3 GHz. We employ a two-component synchrotron self-Compton model to describe different flux states of the source, including the epoch during which an extreme shift in energy of the synchrotron peak frequency from infrared to soft X-rays is observed.