Flux Position Research Articles

The Evolution of Earth's Outer Radiation Belt Over Geomagnetic Storm Phase in Van Allen Probe Era

AbstractEarth's outer radiation belts are highly dynamic during geomagnetic storms. Using electron flux data from 226 keV to 2.6 MeV measured by the Van Allen Probes, we statistically analyzed the peak flux position and inner boundary position of the outer radiation belt across different storm phases: pre‐storm quiet time, main phase, early recovery phase, and later recovery phase. This analysis covered 196 geomagnetic storm events from October 2012 to September 2019. Our results indicate that: (a) During the pre‐storm, decreases with increasing energy. From the pre‐storm to the early recovery phase, shifts inward for energies below 1 MeV and outward for energies above 1 MeV. For all energies, converges to approximately L = 4.3–4.6 in the early recovery phase. (b) Below approximately 1 MeV, generally move inward from the main phase to the early recovery phase. Above 1 MeV, remains nearly unchanged across different storm phases. (c) The half‐width (−) of the outer belt decreases during the main phase for energies below 1 MeV and increases during the recovery phase for energies above 1.5 MeV. (d) In the early recovery phase, and at 593–742 keV show a moderate correlation with storm intensity (CC 0.7–0.8), while and at energies greater than 1.1 MeV exhibit low correlations (CC0.4) during each phase. These results confirm the complex, energy‐dependent morphology of the outer radiation belt throughout geomagnetic storm phases.

Production and radiochemical separation of Tb-161 as a feasible beta therapeutic radioisotope from reactor irradiated Gd target

Terbium-161 (161Tb) is a promising therapeutic radionuclide that has gained significant attention in the field of nuclear medicine in recent years. 161Tb has several favorable characteristics that make it a valuable candidate for targeted radionuclide therapy. The production of No-carrier-added 161Tb was carried out by the neutron activation of natural gadolinium target in the Egyptian Second Research Reactor (ETRR-2) at a thermal neutron flux position of 1.8 × 1014 ncm-2s-1. The radioactivities of 161Tb as well as coproduced Gd radioimpurities were computed theoretically by the MCNPX2.7.0 code and verified by actual measurements, where accepted discrepancies were obtained. The purification of 161Tb from irradiated Gd target was developed by Chelex-100 resin. The elution performance was studied using different eluents, and 0.1 M HNO3 was found to be the best medium to obtain a high separation efficiency of more than 92% in a short time. The eluted 161Tb was of high chemical, radiochemical, and radionuclidic purities, indicating its potential for effective application in radiopharmaceutical preparation.

Improving the coverage area and flake size of ReS2 through machine learning in APCVD

Machine learning is playing a crucial role in optimizing material synthesis, particularly in scenarios where several parameters related to growth exhibit different and significant outcomes. An example of such complexity is the growth of atomically thin semiconductors through chemical vapor deposition (CVD), where multiple parameters can influence the thermodynamics and reaction kinetics involved in the synthesis. Herein, we performed a set of orthogonal experiments, varying the key parameters such as temperature, carries gas flux and precursor position to identify the optimal conditions for maximizing covered area and the size of rhenium disulfide (ReS2) crystals. The experimental results were used to establish correlations among the three thermodynamic variables through an artificial neural network. Contour plots were then generated to visualize the impact on the coverage and flake size of the crystals. This study demonstrates the capability of machine learning to enhance the potential of CVD-growth for the integration of 2D semiconductors like ReS2at larger scales.

An in-phase filter-based flux observation strategy for sensorless control of PMSMs

Due to the complexity of determining the initial rotor flux and detecting errors, conventional rotor flux observation methods are easily affected by direct current (DC) components and harmonics. To address this issue, this paper proposes an in-phase filter (IPF)-based rotor flux observation strategy for sensorless control of permanent magnet synchronous machines (PMSMs). The core components of the IPF consist of a double second-order generalized integrator (DSOGI) and a phase angle compensation transfer function (PACTF). The DSOGI provides a accurate electrical angular frequency, while the PACTF implements a phase correction to the vq′ signals. By employing IPF structure, accurate observations for rotor flux, electronic speed, and rotor position are achieved, which can be effectively used in the sensorless control of PMSMs, eliminating the need for magnitude and phase compensations. Finally, the proposed observation strategy is applied to an experimental bench of a PMSM, and its effectiveness is illustrated by experimental results. From experimental results, it can be concluded that the IPF is significantly better than the LPF, and 5% more accurate than the observer based on cascade second-order generalized integral(CSOGI) overall.

Vortex Fiber Nulling for Exoplanet Observations: First Direct Detection of M Dwarf Companions around HIP 21543, HIP 94666, and HIP 50319

Vortex fiber nulling (VFN) is a technique for detecting and characterizing faint companions at small separations from their host star. A near-infrared (∼2.3 μm) VFN demonstrator mode was deployed on the Keck Planet Imager and Characterizer (KPIC) instrument at the Keck Observatory and presented earlier. In this Letter, we present the first VFN companion detections. Three targets, HIP 21543 Ab, HIP 94666 Ab, and HIP 50319 B, were detected with host–companion flux ratios between 70 and 430 at and within one diffraction beamwidth (λ/D). We complement the spectra from KPIC VFN with flux ratio and position measurements from the CHARA Array to validate the VFN results and provide a more complete characterization of the targets. This Letter reports the first direct detection of these three M dwarf companions, yielding their first spectra and flux ratios. Our observations provide measurements of bulk properties such as effective temperatures, radial velocities, and vsini , and verify the accuracy of the published orbits. These detections corroborate earlier predictions of the KPIC VFN performance, demonstrating that the instrument mode is ready for science observations.

Experimental investigation on heat transfer characteristics of an annual jet flame in a pore-array spray gun

Oxyacetylene ablation is widely used to assess high-temperature thermal protection materials. This study investigated the heat transfer characteristics of an oxyacetylene spray gun structured with pore arrays for long-term ablation. The effects of oxyacetylene test parameters (Reynolds number (Re), equivalence ratio (φ), and ablation distance (H)) on the flame shape and heat flux distribution were studied to explore heat transfer behavior. Subsequently, ablation experiments were performed to verify the heat transfer characteristics under different operating conditions. The following conclusions were obtained: (1) The flame shape is characterized by the base flame, flame neck, and main flame, depending on the mixedness of the inner and outer jets. (2) The position of peak heat flux occurred in the radial direction, and the peak heat flux reached 4792 kW/m2 when the Reynolds number, impingement distance, and equivalence ratio were 77700, 20 mm, and 0.72, respectively. (3) The suggested ablation distance is Hs = (57.65–61.98) × [MR]−0.56 (MR: momentum ratio). This study provides useful data for high-enthalpy, long-duration ablation.

Optimum active power tracking based control of brushless doubly-fed reluctance generator tied to renewable microgrid

Among all the existing wind energy generators (WEG), a brushless doubly-fed reluctance generator (BDFRG) is the better option in terms of maintenance cost and constructional simplicity. For more adaptability, the efficiency of the BDFRG can be improved through proper control mechanisms. Therefore, this paper presents an optimum active power tracking-based control technique for BDFRG for minimum losses. Copper loss of the machine is considered to be the objective function for the proposed optimization technique. However, one issue found to be the major in all the existing controllers is the accuracy of sensor less control of the BDFRG. Therefore, this paper proposes an accurate model reference adaptive system (MRAS) based sensor less mechanism for computation of BDFRG secondary winding flux position. The no sensitivity of the proposed technique to the machine parameter variation and hence the accuracy, catch-on-fly, and non-inclusion of integrator and differentiators and hence less burden on the processor makes the proposed scheme robust. The control scheme is practically implemented with a 2.5 kW BDFRG using MATLAB/Simulink platform.

Improved flux linkage observer for position estimation of permanent magnet synchronous linear motor

Abstract. With the development of motor technology, sensorless control attracts more and more attention. In this paper, an improved flux linkage observer is proposed to overcome issues including inaccurate initial positions and sampling noise. The voltage and current models are combined, and a sliding-mode observer is designed based on the hybrid model to obtain the compensation voltage. Therefore, the estimated flux linkage after compensation can greatly resist the influence caused by inaccurate initial positions or sampling noise. Phase-locked loop technology is used to process the estimated flux linkage to get the stable estimated speed and position. The proposed scheme has a simple structure and only one parameter. It is easy to use and adjust in practice. The simulation and experimental results verify that the proposed algorithm is effective, and the estimated flux linkage and position is accurate with an inaccurate initial position.

On the shock wave boundary layer interaction in slightly rarefied gas

The shock wave and boundary layer interaction (SWBLI) plays an important role in the design of hypersonic vehicles. However, discrepancies between the numerical results of high-temperature gas dynamics and experiment data have not been fully addressed. It is believed that the rarefaction effects are important in SWBLI, but the systematic analysis of the temperature-jump boundary conditions and the role of translational/rotational/vibrational heat conductivities are lacking. In this paper, we derive the three-temperature Navier–Stokes–Fourier (NSF) equations from the gas kinetic theory, with special attention paid to the components of heat conductivity. With proper temperature-jump boundary conditions, we simulate the SWBLI in the double cone experiment. Our numerical results show that, when the three heat conductivities are properly recovered, the NSF equations can capture the position and peak value of the surface heat flux, in both low- and high-enthalpy inflow conditions. Moreover, the separation bubble induced by the separated shock and the reattachment point induced by impact between transmitted shock and boundary layer are found to agree with the experimental measurement.

Bearing capacity factor for strip foundations on unsaturated clay

ABSTRACT The matric suction in unsaturated soil depends on the type of soil and various flux conditions i.e., infiltration, evaporation and no flow. The shear strength of unsaturated soil changes with change in matric suction leading to varying resistance of soil under various flow conditions. In this study, the bearing capacity of strip foundations resting over unsaturated clay considering variation of matric suction with depth for different surface flux conditions and position of water table, has been obtained using finite element lower bound limit analysis. Modified Mohr-Coulomb yield criteria based on unified effective stress approach has been employed to incorporate the contribution of matric suction stress to the failure condition. A non-dimensional bearing capacity factor was introduced to estimate the bearing capacity of strip foundations and presented as a function of different influencing parameters such as foundation width, water table depth, soil properties, various flow conditions and their flow rate, and surcharge pressure. The influence of variation of unit weight of soil in the unsaturated zone, air entry and pore size distribution parameters, residual degree of saturation of soil, specific gravity of soil solids, and foundation-soil interface roughness on the bearing capacity has also been examined and found to be insignificant.

Improved Sensorless Operation of Double Inverter Fed Wound Rotor Induction Machine With Seamless Mode Transitions

The performance of a sensorless induction motor drive depends on the accuracy in estimating the flux position from the supply voltage and machine parameters. Accurate estimation of flux position at low speed operation is difficult due to the low supply frequency. In a double inverter fed induction motor drive, the low speed operation can be obtained by maintaining the relative frequency between stator and rotor supply <bold xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">voltage</b> without reducing the individual supply frequency to a very low value. In this paper, a novel frequency profile for the stator and rotor supplies of a DFIM drive is proposed, in which the minimum supply frequency of any side inverter is around 0.5 p.u. for the whole speed range of operation. With this proposed scheme, the zero speed operation of the drive is obtained by maintaining both the stator and rotor supply frequencies as 1.0 p.u.. To achieve this, the DFIM is required to be operated as a squirrel cage induction motor for certain speed range. The control scheme for both the stator and rotor side inverters along with seamless mode transitions are also presented. In this DFIM drive, the required motor power is only 50 % of the rated load power and the total <bold xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">volt-ampere (VA)</b> rating of the two inverters is same as that of a conventional squirrel cage induction motor drive. Experimental studies are carried out on a 45 <bold xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">kW</b> wound rotor induction machine to validate the control scheme with the proposed frequency profile and results are presented.

Numerical study of a scramjet isolator performance under different sidewall compression angles

Scramjet engines, also known as supersonic combustion ramjet engines, are frequently regarded as a compelling alternative for launching payloads into Earth's orbit. These air-breathing engines have streamlined designs with minimal movement of components. However, the successful design of scramjet engines necessitates overcoming various challenges such as managing the high heat fluxes and pressure loads exerted on the engine walls. Additionally, addressing issues such as shockwave-boundary-layer interactions and the potential occurrence of choked flow within the isolator channel are critical considerations during the scramjet design process. Therefore, this study aims to evaluate sidewall compression in the isolator region to deal with the high heat fluxes and pressure loads inside the scramjet isolator. In addition, this work also investigates how the variation in the angle of attack influences the mass flow rate of the intake and at which range of the angle of attack the intake becomes choked. The CFD analyses include contour images of properties such as Mach number, total pressure, heat flux, and pressure distribution on the walls, and the calculation of performance parameters, including the analysis of the second law of thermodynamics. The study involved varying the compression angle within the range of 4° to 10°. The results of this study demonstrate that implementing sidewall compression in the isolator region allows for the effective management of the position of the heat flux and pressure peaks on the upper wall of the isolator. Regarding the pressure distribution along the upper wall of the isolator, the 10°case presented a pressure peak of approximately 130000 Pa while the 4°case presented 155000 Pa. In addition to this significant decrease in the pressure peak value, its location also changed, with an increase of approximately 8 mm downstream of the isolator by decreasing the compression angle from 10° to 4°. This engineering approach presents a viable solution for mitigating the challenges posed by high heat flux and pressure loads in the intake section. The cost of applying such a solution is to decrease the intake performance – a decrease of approximately 30 % in the isentropic efficiency when comparing a case with no sidewall compression with the sidewall compression cases. In the choked flow study, angles of attack ranging from 4 to 30°were considered. The analysis shows that the choked-flow condition gradually occurs as the angle of attack increases beyond 4°, owing to the shock-on-lip condition. The results at approximately 20° indicate that the isolator becomes completely choked once the mass flow rate abruptly decreases – from around 0.30 to 0.15 Kg/s when comparing the 20°-of-AoA case with the 30° one. This work aims to contribute to the early phase of engine design by avoiding critical failures in the scramjet structure owing to aerodynamic load, thermal stress, and engine unstart.

Surface features of strongly heated bulk tungsten divertor plates at ASDEX Upgrade

• Horizontal cracks and humps at the surface were observed at ASDEX Upgrade solid tungsten divertor plates. • Recrystallization and grain growth is found at these locations. • High thermal stress due to temperature gradients is discussed to produce these cracks. • He bubble formation in tungsten is discusses as source of the surface humps. Solid tungsten tiles exposed at the outer strike point module of the ASDEX Upgrade divertor show cracks parallel to surface in the bulk and humps at the surface. At ASDEX Upgrade these horizontal cracks were observed for the first time. About 10 % of all tiles exhibit protrusions originated by horizontal cracks about 3-5 mm below the surface. The position of this damage coincidence with the location of highest deposited energy, which varies for the different tiles due to the mounting. The tungsten at the locations of the horizontal cracks exhibits recrystallization and grain growth, presumably due to the worse thermal contact caused by the horizontal cracks. Although, the operation of AUG was not hampered by these damages, these tiles had to be exchanged preventing progression of these damages. High thermal stress due to temperature gradients is discussed to originate these cracks. Additionally, humps are found at the surface at the position of high heat flux. Their occurrence seems to be related to the increased number of high power discharges. Focused ion beam prepared cross sections indicate pores and cavities in and below these humps. This finding is discussed in the view of He bubble formation in tungsten.

Self-Sensing Six-Phase PMSM Drive Based on Back-EMF Measurement

This paper presents a novel procedure for the emergency sensorless operation of a six-phase electric drive. More degrees of freedom provided by multiphase technology have been utilized to determine the rotor flux position. The proposed technique is based on the direct measurement of the back EMF generated on a disconnected three-phase winding of a six-phase permanent-magnet synchronous machine (PMSM). The method is suitable for the emergency operation of an electric drive in the case of speed/position sensor failure. The proposed solution has been verified utilizing a six-phase permanent-magnet synchronous machine with a displacement of 30° between two three-phase sets of the stator winding and a power of 1 kW.

A Unidirectional Voltage Vector Preselection Strategy for Optimizing Model Predictive Torque Control With Discrete Space Vector Modulation of IPMSM

Discrete space vector modulation (DSVM) is employed to synthesize large number of voltage vectors (VVs) to improve the steady-state performance of predictive torque control (PTC). However, enumerating all the VVs in the prediction process increases the computation load of the motor drive. To address this issue, this article proposes a unidirectional VV preselection (UVVP) method for optimizing the performance of DSVM-based PTC of ac motors. The proposed UVVP method divides both voltage space vector diagram (VSVD) and flux space trajectory into twelve 30° based sectors to reduce the impact of candidate VVs with negative effects. At each flux position, the UVVP strategy can restrict the nearest candidate VVs in the 30° based VSVD region within the circular flux trajectory. This is achieved by using the speed direction to avoid the candidate VVs, which are in the same flux sector for reverse flux rotation, hence resulting in significant flux and torque ripple reduction. The main benefit of the proposed method is its simplicity since it only requires the flux sector and speed information as well as it can generate the VV enumerations online while ensuring the reduction of computation burden.

Energy-saving actuation signal for magnetorheological valve train by leveraging hysteresis effect

• Analysis of electromagnetic hysteresis effect in magnetorheological valve train. • Customized pulse actuation signal for leveraging the hysteresis effect in magnetorheological valve train. • Pulse signal optimization for energy saving operation of VVL that improves the engine efficiency. • Customized pulse signal saves actuation energy of magnetorheological valve train. Smart, adaptive, and effective magnetorheological (MR) technology-based devices are replacing conventional brakes, clutches, valves, and dampers. MR valve improves engine performance by enabling variable valve actuation. Constructing an MR valve train is simpler than other active valve systems. However, similar to other electromagnetic valves, the MR valve train consumes considerable electrical energy in controlling the resistance force of the MR fluid such that the valve can remain partially open or fully closed. Thus, an engine equipped with an MR valve expends additional fuel for the actuation of the valve system. In this study, instead of conventional direct current (DC) actuation, an energy-saving customized pulse (CP) signal is proposed for valve actuation by leveraging the electromagnetic hysteresis effect. The applied CP signal causes fluctuations in the generated magnetic flux, resistance force, and consequent valve position. Therefore, the variation in MR resistance force at various duty cycles and negative half cycles was investigated and compared with the required force to perform variable valve lift (VVL). Simulations indicated that a 35% duty cycle with 75% current during the negative half cycle was able to maintain the required force but results in negligible deviation in the resistance force which doesn’t affect the VVL operation. Therefore, the proposed method is advantageous over conventional DC input, conferring actuation energy-savings of approximately 28%.

Speed Tracking for IFOC Induction Motor Speed Control Using Hybrid Sensorless Speed Estimator Based on Flux Error for Electric Vehicles Application

This paper presents hybrid sensorless speed tracking by an indirect field-oriented control (IFOC) for an induction motor (IM). The sensorless model is based on an improved virtual estimation topology model to predict the virtual speed and flux of the IM using stator current components. The hybrid sensorless model, defined as a modification of voltage with a rotor flux-oriented current model, was also implemented with proportional-integral (PI) control for comparison with the conventional voltage model (CVM). The suggested adaptive mechanism for PI control in the hybrid estimator was able to compensate for the back-EMF error from the rotor flux-oriented current model into the voltage model and change the air gap flux of the IM. An accurate rotor flux position was estimated and used to estimate the speed with low speed error. This IFOC model, with various speed change references, was tested in a simulation environment by using the MATLAB/Simulink program. The proposed hybrid estimator was tested in two different EV operations, which were reverse and forward operations. The effectiveness of the proposed estimator was analyzed for its transient and steady-state performances based on settling time, recovery time and the overshoot and speed error percentages. All the results were in good agreement in terms of the stability of the speed and current controller with minimum speed error obtained, where the average errors were 0.08% and 0.16% for high speed and lower speed, respectively.

Effects of longitudinal wind and sidewall restriction on downstream radiative heat flux and temperature rise distribution in tunnel fires

This paper presents an experimental study on downstream radiative heat flux and temperature rise distribution of tunnel fires under the combined effects of longitudinal wind and sidewall restriction. Two fire locations, i.e., centerline fire and sidewall fire, were considered, and the wind speeds were varied between 0 and 3 m/s. The results show that under smaller ventilation velocity, the downstream radiative heat flux of sidewall fire is larger than that of centerline fire. As the ventilation velocity increases, the radiative heat flux of two fire locations both firstly increase and then decrease with increasing distance. The position of the peak radiative heat flux depends on the evolution of the flame drag and moves away from the fire center with increasing wind speed and heat release rate (HRR). Based on the solid flame assumption, thermal radiation models are proposed and validated by experimental results. A similar spacial distribution trend was observed for temperature rise with varying fire locations and wind speeds. The distance from peak temperature rise to fire center is related to the flame drag front and increases with HRR and ventilation velocity. Finally, correlations for peak temperature rise, its locations and the temperature rise attenuation beyond the peak value were established.

The nature of the radio source detected towards the exoplanet system 1RXS1609.1−210524

ABSTRACT Several studies have been carried out to detect radio emissions from known exoplanets. Some of these studies have resulted in tentative detections of radio sources near the position of known exoplanets. One such planet/brown dwarf around which a radio source was detected is 1RXS1609.1−210524 (hereafter 1RX) b. A radio source near 1RX was detected with the TIFR GMRT Sky Survey (TGSS) at 150 MHz and the NRAO VLA Sky Survey (NVSS) at 1.4 GHz. However, since these surveys’ spatial resolution was low, it was not possible to ascertain whether the radio emission originated from the system or a background source. This work presents results from the 1RX field’s targeted observations at 150, 325, and 610 MHz with Giant Meterwave Radio Telescope (GMRT). These observations have a higher angular resolution as compared to TGSS and NVSS. I detected the radio source near the position of 1RX at all frequencies with GMRT. I further used the Very Large Array Sky Survey (VLASS) data at 3 GHz to determine the flux density and position at high frequency. With the targeted GMRT observations and observations from VLASS, I show that the radio emission does not originate from the 1RX b but is from a background source about ∼13 arcsec away from the host star. Further, no radio emission was detected from the position of 1RX.

Improvement of a design of the molten salt fast reactor

This study provides an improved design of molten salt fast reactors to reduce the maximum magnitude velocity in the core. The results indicated that the improved design reduces the magnitude velocity with acceptable hot spot temperature where the maximum magnitude velocity is nearly equal to 4.59 m/s and the temperature of the hot spot is greater than the outlet temperature by 9°. The performed analyses are used to adjust the amount of fissile material started for keff = 1. Neutron flux and delayed Neutron distribution study where the position of the maximum Neutron flux is in the center and the position of the maximum thermal flux is in a fertile blanket. Simulations of unprotected loss of heat sink, unprotected loss of flow, unprotected transient overpower, and Unprotected over-cooling are performed and discussed with new geometry. Due to the negative reactive feedback, it is clear that MSFR has a high safety potential.