| 1. |
- Bai, Ru, et al.
(författare)
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Clinical characteristics and phylogenetic analysis of human enteric adenovirus type 41 (HAdV-F41) from children with gastroenteritis during SARS-CoV-2 pandemic
- 2024
-
Ingår i: Infection, Genetics and Evolution. - : Elsevier. - 1567-1348 .- 1567-7257. ; 123
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Tidskriftsartikel (refereegranskat)abstract
- Human adenovirus type 41 (HAdV-F41) usually causes pediatrics gastroenteritis. However, it was reported to be associated with the outbreaks of severe acute hepatitis of unknown aetiology (SAHUA) in pediatrics during COVID-19 pandemic. In this study, we investigated the prevalence of enteric HAdV-F41 in 37,920 paediatric gastroenteritis cases from 2017 to 2022 in Guangzhou, China. All children presented were tested negative for SARS-CoV-2 during the “zero-COVID” period. The main clinical symptom of the children was diarrhea (96.5%). No fatalities nor liver abnormal symptoms was found. In 2021, one year since the pandemic of COVID-19, the prevalence of HAdV-F41 abruptly increased from 3.71% to 8.64% (P < 0.001). All of HAdV-F41 circulating worldwide were classified into eight different subtypes (G1-G8) based on the phylogenetic clustering permutation of the four capsid genes of HAdV-F41. G3 was the predominant subtype (56.2%; 77/137). CRV5 isolates from SAHUA cases belong to this subtype, in which N312D and H335D mutations in the short fiber knob were identified in both Guangzhou and CRV5 isolates, presumably changing the virus tropism by directly interacting with the heparin sulfate (HS) receptor. Additionally, a novel recombinant G6 subtype, which is unique and only circulating in China was first identified in this study. This is the first study highlighting the prevalence of HAdV-F41 in paediatric cases of gastroenteritis during COVID-19 pandemic in China. The clinical and viral evolution finding of HAdV-F41 provide insight into the clinical characteristics of children with HAdV-F41 infections as well as the uncertain role of HAdV-F41 in the cause of SAHUA.
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| 2. |
- Huang, Xiaoyan, et al.
(författare)
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A Robust Deadbeat Predictive Current Control Method for IPMSM
- 2024
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Ingår i: IEEE Transactions on Transportation Electrification. - : Institute of Electrical and Electronics Engineers (IEEE). - 2332-7782. ; , s. 1-1
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Tidskriftsartikel (refereegranskat)abstract
- Deadbeat predictive current control (DPCC) demonstrates excellent dynamic performance. However, in practical applications, its effectiveness is degraded by parameter mismatches and inverter nonlinearities. Among the various improvement methods addressed for these issues, incremental model-based DPCC (I-DPCC) achieves zero static current error with a low computational burden but suffers from instability under parameter variation, especially when applied to interior permanent magnet synchronous motors (IPMSMs). In this paper, a robust I-DPCC (RI-DPCC) combining feedforward control is proposed for IPMSM, with an adjustable stable operation range that can be extended to twice the actual inductance or even larger. To further improve the robustness of dynamic performance, an inductance correction method is introduced to track the variation of inductance during dynamic processes. Thus, the current commands can be well tracked even when significant inductance variation occurs. With sufficient voltage margin, the dynamic processes under mismatched inductance can be shortened to four control periods. Finally, experimental results validate the effectiveness of the proposed method.
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| 3. |
- Li, Tongkuai, et al.
(författare)
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Kelvin-Helmholtz Waves and Magnetic Reconnection at the Earth's Magnetopause Under Southward Interplanetary Magnetic Field
- 2023
-
Ingår i: Geophysical Research Letters. - : American Geophysical Union (AGU). - 0094-8276 .- 1944-8007. ; 50:20
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Tidskriftsartikel (refereegranskat)abstract
- We present Magnetospheric Multiscale (MMS) observations of a K-H wave event under southward IMF conditions, accompanied by ongoing magnetic reconnection. The nonlinear K-H waves are characterized by quasi-periodic fluctuations, the presence of low-density and high-speed ions, and variations in the boundary normal vectors at both the leading and trailing edges. Our observations reveal clear evidence of on-going magnetic reconnection through the identification of Alfvenic ion jets and the escape of energetic magnetospheric electrons. Among the 36 magnetopause current-sheet crossings in this event, 19 exhibit unambiguous signatures of reconnection at both the leading (7) and trailing (12) edges. Notably, the estimated current-sheet thicknesses at both edges are comparable to the ion-inertial scale, confirming the compression effect resulting from the large-scale evolution of the K-H waves. The reconnection jets potentially contribute to the suppression of K-H growth through boundary-layer broadening and the development of complex flow and magnetic field patterns.
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| 4. |
- Patel, Vivek, 1983-, et al.
(författare)
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Enhancing grain refinement and corrosion behavior in AZ31B magnesium alloy via stationary shoulder friction stir processing
- 2022
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Ingår i: Journal of Materials Research and Technology. - : Elsevier. - 2238-7854. ; 17, s. 3150-3156
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Tidskriftsartikel (refereegranskat)abstract
- Stationary shoulder friction stir processing (SSFSP) in thick AZ31B magnesium alloy was performed to refine the microstructure followed by evaluating corrosion behavior. The use of stationary shoulder exhibited low heat input and small temperature gradient across the thickness of stir zone (SZ). Moreover, smooth surface morphology with little flash was obtained. The probe-dominated SZ developed fine equiaxed uniform grain structure across the thickness of SZ, which in turn increased the corrosion resistance of SSFSPed alloy as compared to BM. SSFSPed alloy surface confirm uniform corrosion behavior with mud cracking and intergranual corrosion patterns instead of pitting corrosion in BM. This improvement in corrosion was attributed to homogenization of magnesium alloy microstructure by using low-heat-input stationary shoulder tool.
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| 5. |
- Alm, Love, et al.
(författare)
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MMS Observations of Multiscale Hall Physics in the Magnetotail
- 2019
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Ingår i: Geophysical Research Letters. - : AMER GEOPHYSICAL UNION. - 0094-8276 .- 1944-8007.
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Tidskriftsartikel (refereegranskat)abstract
- We present Magnetospheric Multiscale mission (MMS) observations of Hall physics in the magnetotail, which compared to dayside Hall physics is a relatively unexplored topic. The plasma consists of electrons, moderately cold ions (T similar to 1.5 keV) and hot ions (T similar to 20 keV). MMS can differentiate between the cold ion demagnetization region and hot ion demagnetization regions, which suggests that MMS was observing multiscale Hall physics. The observed Hall electric field is compared with a generalized Ohm's law, accounting for multiple ion populations. The cold ion population, despite its relatively high initial temperature, has a significant impact on the Hall electric field. These results show that multiscale Hall physics is relevant over a much larger temperature range than previously observed and is relevant for the whole magnetosphere as well as for other astrophysical plasma.
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| 6. |
- André, Mats, et al.
(författare)
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Magnetic reconnection and modification of the Hall physics due to cold ions at the magnetopause
- 2016
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Ingår i: Geophysical Research Letters. - : Blackwell Publishing. - 0094-8276 .- 1944-8007. ; 43:13, s. 6705-6712
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Tidskriftsartikel (refereegranskat)abstract
- Observations by the four Magnetospheric Multiscale spacecraft are used to investigate the Hall physics of a magnetopause magnetic reconnection separatrix layer. Inside this layer of currents and strong normal electric fields, cold (eV) ions of ionospheric origin can remain frozen-in together with the electrons. The cold ions reduce the Hall current. Using a generalized Ohm's law, the electric field is balanced by the sum of the terms corresponding to the Hall current, the vxB drifting cold ions, and the divergence of the electron pressure tensor. A mixture of hot and cold ions is common at the subsolar magnetopause. A mixture of length scales caused by a mixture of ion temperatures has significant effects on the Hall physics of magnetic reconnection.
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| 7. |
- Baghdadchi, Amir, 1994-, et al.
(författare)
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Ductilization and grain refinement of AA7075-T651 alloy via stationary shoulder friction stir processing
- 2023
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Ingår i: Journal of Materials Research and Technology. - 2238-7854 .- 2214-0697. ; 27, s. 5360-5367
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Tidskriftsartikel (refereegranskat)abstract
- This study investigates the microstructural evolution, mechanical properties, and fracture behavior of AA7075-T651 aluminium alloy subjected to stationary shoulder friction stir processing (SSFSP). SSFSP samples were produced at three different rotational speeds in a range of 600–1000 rpm. The results reveal that SSFSP leads to a uniform grain refinement within the Stir Zone (SZ), reducing the grain size to approximately 2–3 μm from the initial 15 μm in the base material (BM) irrespective of the probe rotational speeds. After SSFSP, the elongation increased by over 50 % at the cost of 10 % reduction in the ultimate tensile strength for all samples. It was worth to note that variations in tool rotational speed exhibited minimal influence on the microstructure and mechanical properties, offering wide range of probe rotational speeds. This could be attributed to the use of non-rotating shoulder with prob dominated microstructure in the SZ. Fractographic analysis confirmed the ductile nature of fractures, revealing development of fine dimples due to grain refinement. This work underscores the effectiveness of SSFSP in achieving significant grain refinement followed by drastic increase in ductility, which offers valuable insights for using stationary shoulder at wider range of rotational speed.
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| 8. |
- Das, Subhash, et al.
(författare)
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Experimental investigation on welding of 2.25 Cr-1.0 Mo steel with regulated metal deposition and GMAW technique incorporating metal-cored wires
- 2021
-
Ingår i: Journal of Materials Research and Technology. - : Elsevier Editora Ltda. - 2238-7854. ; 15, s. 1007-1016
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Tidskriftsartikel (refereegranskat)abstract
- The regulated Metal Deposition (RMD) process is a variant of the gas metal arc welding process (GMAW), which was developed to effectively control the metal transfer in the short-circuiting mode. The process is fundamentally a modified short-circuit GMAW process wherein a uniform droplet deposition, making it easier for the welder to control the puddle and hence achieve an enhanced quality of welded joints. In the present study, the RMD technique has been established for the low alloy steel grade 2.25 Cr - 1.0 Mo particularly for depositing the root pass on a 10 mm thick joint. In addition to this, the RMD technique is attempted with metal-cored wires to enhance the deposition rates and hence productivity. The joint fill-up is further attempted with the GMAW technique using metal-cored wires and analysed. The weldments were subjected to post-weld heat treatment followed by mechanical and metallurgical characterization. Mechanical characterization such as tensile properties, impact properties, bend test as well as all weld tensile properties of the weld joint was evaluated and found to be acceptable. The ductile to brittle transition temperature (DBTT) testing was carried out by breaking series of impact specimen till negative temperatures. The DBTT temperature for the weld joint was found well below -30°C which indicated the strength and soundness of the welded joint. Optical microscopy and scanning electron microscopy was carried out for and favourable results were achieved in microanalysis. The study proposes the use of metal-cored wires for potential applications in the welding of high thickness joints for enhancing the overall productivity.
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| 9. |
- Dokgo, Kyunghwan, et al.
(författare)
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High-Frequency Waves Driven by Agyrotropic Electrons Near the Electron Diffusion Region
- 2020
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Ingår i: Geophysical Research Letters. - : AMER GEOPHYSICAL UNION. - 0094-8276 .- 1944-8007. ; 47:5
-
Tidskriftsartikel (refereegranskat)abstract
- National Aeronautics and Space Administration's Magnetosphere Multiscale mission reveals that agyrotropic electrons and intense waves are prevalently present in the electron diffusion region. Prompted by two distinct Magnetosphere Multiscale observations, this letter investigates by theoretical means and the properties of agyrotropic electron beam-plasma instability and explains the origin of different structures in the wave spectra. The difference is owing to the fact that in one instance, a continuous beam mode is excited, while in the other, discrete Bernstein modes are excited, and the excitation of one mode versus the other depends on physical input parameters, which are consistent with observations. Analyses of dispersion relations show that the growing mode becomes discrete when the maximum growth rate is lower than the electron cyclotron frequency. Making use of particle-in-cell simulations, we found that the broadening angle Delta in the gyroangle space is also an important factor controlling the growth rate. Ramifications of the present finding are also discussed. Plain Language Summary Magnetospheric Multiscale mission has observed magnetic reconnection process, which converts magnetic energy to kinetic energy of charged particles. Extremely rapid time scale data reveal that electron scale high-frequency waves exist near the electron diffusion region of magnetic reconnection. Recently, two different types of waves observed; one is discrete electron-Bernstein waves, and the other is continuous beam modes. In this study, we formulated a unified theory for both types of waves. Comparing Magnetosphere Multiscale observations, the theory, and particle-in-cell simulations, this study shows that the same cause (agyrotropic electrons) can make two different wave structures depending on plasma parameters. The condition that the maximum growth rate of instabilities equals the electron cyclotron frequency can be considered as a threshold of the transition from discrete electron Bernstein waves to continuous beam modes.
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| 10. |
- Dokgo, Kyunghwan, et al.
(författare)
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The Effects of Upper-Hybrid Waves on Energy Dissipation in the Electron Diffusion Region
- 2020
-
Ingår i: Geophysical Research Letters. - : AMER GEOPHYSICAL UNION. - 0094-8276 .- 1944-8007. ; 47:19
-
Tidskriftsartikel (refereegranskat)abstract
- Using a two-dimensional particle-in-cell simulation, we investigate the effects and roles of upper-hybrid waves (UHW) near the electron diffusion region (EDR). The energy dissipation via the wave-particle interaction in our simulation agrees withJ center dot E(')measured by magnetospheric multiscale (MMS) spacecraft. It means that UHW contributes to the local energy dissipation. As a result of wave-particle interactions, plasma parameters which determine the larger-scale energy dissipation in the EDR are changed. They-directional current decreases while the pressure tensorP(yz)increases/decreases when the agyrotropic beam density is low/high, where(x, y, z)-coordinates correspond the(L, M, N)-boundary coordinates. Because the reconnection electric field comes from- partial differential P-yz/ partial differential z, our result implies that UHW plays an additional role in affecting larger-scale energy dissipation in the EDR by changing plasma parameters. We provide a simple diagram that shows how the UHW activities change the profiles of plasma parameters near the EDR comparing cases with and without UHW.
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| 11. |
- Harwani, Deepika, et al.
(författare)
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Developing superplasticity in magnesium alloys with the help of friction stir processing and its variants : A review
- 2021
-
Ingår i: Journal of Materials Research and Technology. - : Elsevier. - 2238-7854. ; 12, s. 2055-2075
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Tidskriftsartikel (refereegranskat)abstract
- Friction stir processing (FSP), an adaption of the solid-state joining process friction stir welding (FSW), is now a widely recognized severe plastic deformation (SPD) technique. It induces microstructural refinement in the metallic materials which enhances their formability and other mechanical properties. Dynamic recrystallization occurs during the stirring phase which leads to reduction in the grain size and texture modification. Breaking up of the intermetallics and precipitates with their homogeneous distribution in the matrix is also accompanied. This further improves the material's ability to attain maximum ductility during plastic deformation at higher temperatures, resulting in very large uniform elongations (>200%) termed as ‘superplasticity’. Optimization of FSP parameters activates superplastic behaviour in different magnesium alloys at low temperatures and high strain rates. It has become the focal point of the recent researches owing to its huge potential in the light-weight structural applications. In addition to the essential aspects of superplasticity, this article highlights the major explorations in the area of superplasticity of magnesium alloys using FSP method and it's recently developed variants.
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| 12. |
- He, Jiansen, et al.
(författare)
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Direct Measurement of the Dissipation Rate Spectrum around Ion Kinetic Scales in Space Plasma Turbulence
- 2019
-
Ingår i: Astrophysical Journal. - : IOP PUBLISHING LTD. - 0004-637X .- 1538-4357. ; 880:2
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Tidskriftsartikel (refereegranskat)abstract
- The energy of turbulence in the universe, which cascades from large fluid scales to small kinetic scales, is believed to be dissipated through conversion to thermal or nonthermal kinetic energy. However, identifying the dissipation processes and measuring the dissipation rate in turbulence remain challenging. Based on unprecedented high-quality measurements of space plasma turbulence by the Magnetospheric Multiscale mission, we propose a novel approach to measure the scale-dependent spectrum of the energy conversion rate between the fluctuating electromagnetic energy and plasma kinetic energy. The energy conversion rate spectrum is found to show a positive bulge around the ion kinetic scale, which clearly indicates the dissipation of the turbulent energy. The energy dissipation rate around the ion scale is estimated to be 0.5 x 10(6) J kg(-1) s(-1). This work provides basic information on local dissipation in magnetosheath turbulence and sets up a new paradigm for studying the dissipation of universal plasma turbulence.
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| 13. |
- He, Jiansen, et al.
(författare)
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Observations of Rapidly Growing Whistler Waves in Front of Space Plasma Shock due to Resonance Interaction between Fluctuating Electron Velocity Distributions and Electromagnetic Fields
- 2022
-
Ingår i: Astrophysical Journal. - : Institute of Physics Publishing (IOPP). - 0004-637X .- 1538-4357. ; 941:2
-
Tidskriftsartikel (refereegranskat)abstract
- The whistler-mode wave extending from the fast-magnetosonic wave branch is a fundamental perturbation of electromagnetic fields and plasmas in various environments including planetary space, laboratory, and astrophysics. The origin and evolution of the waves is a long-standing question due to the limited instrumental capability in resolving highly variable plasma and electromagnetic fields. Here, we analyze observational data with a high time resolution from the Magnetospheric Multiscale spacecraft in front of the terrestrial bow shock (e.g., foreshock). We develop a novel approach to extract the three-dimensional fluctuating electron velocity distributions (delta f (e)( V )) from their background (f (e0)( V )), and have successfully captured the coherent resonance between fluctuating electrons (delta f (e)( V )) and wavelike electromagnetic fields (delta B , delta E ) at an unprecedentedly high frequency (>1 Hz) for investigating wave-particle interactions. We provide that the unstable whistler wave grows rapidly over a timescale that is much shorter than the proton gyro-period. Regarding the energy origin for the waves, we find the ion distributions consisting of the solar wind ion flows and the ion beams reflected from the shock play crucial roles in providing the free energy and determining the eigenmode disturbances of fields and electrons. The quantification of wave growth rate and the characterization of wave-particle interactions for the instability driver can significantly advance the understandings of wave evolution and energy conversion between multisource multispecies particles and wave electromagnetic fields.
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| 14. |
- Khotyaintsev, Yuri V., et al.
(författare)
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Electron jet of asymmetric reconnection
- 2016
-
Ingår i: Geophysical Research Letters. - : Blackwell Publishing. - 0094-8276 .- 1944-8007. ; 43:11, s. 5571-5580
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Tidskriftsartikel (refereegranskat)abstract
- We present Magnetospheric Multiscale observations of an electron-scale current sheet and electron outflow jet for asymmetric reconnection with guide field at the subsolar magnetopause. The electron jet observed within the reconnection region has an electron Mach number of 0.35 and is associated with electron agyrotropy. The jet is unstable to an electrostatic instability which generates intense waves with E-vertical bar amplitudes reaching up to 300mVm(-1) and potentials up to 20% of the electron thermal energy. We see evidence of interaction between the waves and the electron beam, leading to quick thermalization of the beam and stabilization of the instability. The wave phase speed is comparable to the ion thermal speed, suggesting that the instability is of Buneman type, and therefore introduces electron-ion drag and leads to braking of the electron flow. Our observations demonstrate that electrostatic turbulence plays an important role in the electron-scale physics of asymmetric reconnection.
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| 15. |
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| 16. |
- Li, Miao, et al.
(författare)
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Unmanned aerial vehicle scheduling problem for traffic monitoring
- 2018
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Ingår i: Computers and Industrial Engineering. - : Elsevier BV. - 0360-8352. ; 122, s. 15-23
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Tidskriftsartikel (refereegranskat)abstract
- For more accurate multiple-period real-time monitoring of road traffic, this paper investigates the unmanned aerial vehicle scheduling problem with uncertain demands. A mixed integer programming model is designed for this problem by combining the capacitated arc routing problem with the inventory routing problem. A local branching based solution method is developed to solve the model. A case study which applies this model to the road traffic in Shanghai is performed. In addition, numerical experiments are conducted to validate the effectiveness of the proposed model and the efficiency of the proposed solution method.
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| 17. |
- Li, Wenya, et al.
(författare)
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Kinetic evidence of magnetic reconnection due to Kelvin-Helmholtz waves
- 2016
-
Ingår i: Geophysical Research Letters. - : Blackwell Publishing. - 0094-8276 .- 1944-8007. ; 43:11, s. 5635-5643
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Tidskriftsartikel (refereegranskat)abstract
- The Kelvin-Helmholtz (KH) instability at the Earth's magnetopause is predominantly excited during northward interplanetary magnetic field (IMF). Magnetic reconnection due to KH waves has been suggested as one of the mechanisms to transfer solar wind plasma into the magnetosphere. We investigate KH waves observed at the magnetopause by the Magnetospheric Multiscale (MMS) mission; in particular, we study the trailing edges of KH waves with Alfvenic ion jets. We observe gradual mixing of magnetospheric and magnetosheath ions at the boundary layer. The magnetospheric electrons with energy up to 80keV are observed on the magnetosheath side of the jets, which indicates that they escape into the magnetosheath through reconnected magnetic field lines. At the same time, the low-energy (below 100eV) magnetosheath electrons enter the magnetosphere and are heated in the field-aligned direction at the high-density edge of the jets. Our observations provide unambiguous kinetic evidence for ongoing reconnection due to KH waves.
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| 18. |
- Li, Wenya, et al.
(författare)
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Upper-Hybrid Waves Driven by Meandering Electrons Around Magnetic Reconnection X Line
- 2021
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Ingår i: Geophysical Research Letters. - : American Geophysical Union (AGU). - 0094-8276 .- 1944-8007. ; 48:16
-
Tidskriftsartikel (refereegranskat)abstract
- Magnetic reconnection is a fundamental process in collisionless space plasma environment, and plasma waves relevant to the kinetic interactions can have a significant impact on the multiscale behavior of reconnection. Here, we present Magnetospheric Multiscale (MMS) observations during an encounter of an X line of symmetric magnetic reconnection in the magnetotail. The X line is characterized by reversals of ion and electron jets and electromagnetic fields, agyrotropic electron velocity distribution functions (VDFs), and an electron-scale current sheet. MMS observe large-amplitude nonlinear upper-hybrid (UH) waves on both sides of the neutral line, and the wave amplitudes have highly localized distribution along the normal direction. The inbound meandering electrons drive the UH waves, releasing the free energy stored from the reconnection electric field along the meandering trajectories. The interaction between the meandering electrons and the UH waves may modify the balance of the reconnection electric field around the X line. Plain Language Summary The electron-scale kinetic physics in the electron diffusion region (EDR) controls how magnetic field lines break and reconnect. Electron crescent, an indicator of EDR, can drive high-frequency electrostatic waves around EDR. For the first time, the upper-hybrid (UH) waves are observed on both sides of the X line and we show the direct association between the UH waves and the reconnection electric field. The strong wave-electron interaction can change the electron-scale dynamics and may modify the reconnection electric field. This study demonstrates that the UH waves may play an important role in controlling the reconnection rate.
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| 19. |
- Li, Wenya Y., et al.
(författare)
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Cold Ionospheric Ions in the Magnetic Reconnection Outflow Region
- 2017
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Ingår i: Journal of Geophysical Research - Space Physics. - : Blackwell Publishing. - 2169-9380 .- 2169-9402. ; 122:10, s. 10,194-10,202
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Tidskriftsartikel (refereegranskat)abstract
- Magnetosheath plasma usually determines properties of asymmetric magnetic reconnection at the subsolar region of Earth's magnetopause. However, cold plasma that originated from the ionosphere can also reach the magnetopause and modify the kinetic physics of asymmetric reconnection. We present a magnetopause crossing with high-density (10–60 cm−3) cold ions and ongoing reconnection from the observation of the Magnetospheric Multiscale (MMS) spacecraft. The magnetopause crossing is estimated to be 300 ion inertial lengths south of the X line. Two distinct ion populations are observed on the magnetosheath edge of the ion jet. One population with high parallel velocities (200–300 km/s) is identified to be cold ion beams, and the other population is the magnetosheath ions. In the deHoffman-Teller frame, the field-aligned magnetosheath ions are Alfvénic and move toward the jet region, while the field-aligned cold ion beams move toward the magnetosheath boundary layer, with much lower speeds. These cold ion beams are suggested to be from the cold ions entering the jet close to the X line. This is the first observation of the cold ionospheric ions in the reconnection outflow region, including the reconnection jet and the magnetosheath boundary layer.
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| 20. |
- Ling, Yiming, et al.
(författare)
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Observations of Kelvin-Helmholtz Waves in the Earth's Magnetotail Near the Lunar Orbit
- 2018
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Ingår i: Journal of Geophysical Research - Space Physics. - 2169-9380 .- 2169-9402. ; 123:5, s. 3836-3847
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Tidskriftsartikel (refereegranskat)abstract
- Kelvin‐Helmholtz waves (KHWs), which have been widely observed at the magnetopause in the region near the Earth, play an essential role in the transport of solar wind plasma and energy into the magnetosphere under dominantly northward interplanetary magnetic field (IMF) conditions. In this study, we present simultaneous observations of KHWs under the northward IMF observed by both the Acceleration, Reconnection, Turbulence, and Electrodynamics of Moon's Interaction with the Sun (ARTEMIS) spacecraft in the Earth's magnetotail around the lunar orbit (at X ~ −50RE, Y ~ 30RE, dusk side) and the Geotail in the near‐Earth space (at X ~ −5RE, Y ~ −10RE, dawn side). The KHWs are quantitatively characterized by their dominant period, phase velocity, and wavelength, utilizing wavelet analysis and an approximation of their center‐of‐mass velocity. Our results suggest that the phase velocity and spatial scale of KHWs may increase as they propagate along the boundary layer toward the tail. Alternatively, the differences between the ARTEMIS and Geotail observations may indicate the possibility of dawn‐dusk asymmetry in the excited KHWs in this study. Our results strongly evidence the existence of the development of KHWs in terms of their wave frequency and scale size in the magnetotail and provide insight to the time evolution of KHWs along the magnetopause.
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| 21. |
- Lu, S. W., et al.
(författare)
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Prolonged Kelvin-Helmholtz Waves at Dawn and Dusk Flank Magnetopause : Simultaneous Observations by MMS and THEMIS
- 2019
-
Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 875:1
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Tidskriftsartikel (refereegranskat)abstract
- The Kelvin-Helmholtz (K-H) waves predominantly excited at the Earth's low-latitude magnetopause were suggested to be dawn-dusk asymmetric. We report a prolonged simultaneous observations of the K-H waves on the dawn and dusk magnetopause by Magnetospheric Multiscale (MMS) and THEMIS-A (THA) spacecraft, respectively. The quasi-periodic K-H waves on both flanks have unambiguous low-density and high-speed patterns. The wave periods vary gradually on both flanks, with similar average periods (303 ± 107 s for MMS and 266 ± 102 s for THA). The lag time between the variations of the wave periods is close to the wave propagation time from THA to MMS, which suggests that the K-H waves generate and propagate quasi-symmetrically on both flanks. Larger local magnetic shear angles are observed on the trailing edges by MMS than by THA, which is probably due to the strong magnetic field distortion during the tailward propagation. The increased magnetic shear may excite magnetic reconnection, thus contributing to the formation of the low-latitude boundary layer.
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| 22. |
- Nakamura, T. K. M., et al.
(författare)
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Turbulent mass transfer caused by vortex induced reconnection in collisionless magnetospheric plasmas
- 2017
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Ingår i: Nature Communications. - : NATURE PUBLISHING GROUP. - 2041-1723. ; 8
-
Tidskriftsartikel (refereegranskat)abstract
- Magnetic reconnection is believed to be the main driver to transport solar wind into the Earth's magnetosphere when the magnetopause features a large magnetic shear. However, even when the magnetic shear is too small for spontaneous reconnection, the Kelvin-Helmholtz instability driven by a super-Alfvenic velocity shear is expected to facilitate the transport. Although previous kinetic simulations have demonstrated that the non-linear vortex flows from the Kelvin-Helmholtz instability gives rise to vortex-induced reconnection and resulting plasma transport, the system sizes of these simulations were too small to allow the reconnection to evolve much beyond the electron scale as recently observed by the Magnetospheric Multiscale (MMS) spacecraft. Here, based on a large-scale kinetic simulation and its comparison with MMS observations, we show for the first time that ion-scale jets from vortex-induced reconnection rapidly decay through self-generated turbulence, leading to a mass transfer rate nearly one order higher than previous expectations for the Kelvin-Helmholtz instability.
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| 23. |
- Patel, Vivek, 1983-, et al.
(författare)
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A novel approach to measure three-dimensional surface topography for stationary shoulder friction stir processing
- 2021
-
Ingår i: Journal of Materials Research and Technology. - : Elsevier. - 2238-7854. ; 15, s. 5608-5614
-
Tidskriftsartikel (refereegranskat)abstract
- We demonstrate a stationary shoulder friction stir processing (SSFSP) to produce smooth surface finish due to non-rotating action of the shoulder. The present work aims to investigate surface topography of high strength AA7075 aluminum alloy processed by SSFSP at different rotational speeds. The unique approach of 3D surface mapping under high-end digital microscopy carried out to evaluate qualitative as well as quantitative surface behavior of the processed region. The surface topography indicated the little amount of flash generation on the processed zone, while 3D mapping of the surface quantified the surface roughness in longitudinal (PD) as well as transverse direction (ND) of the processing zone. Surface analysis confirmed that amount of flash generation was relied on tool rotational speed. The overall surface roughness characterized by average and peak values in both the directions, demonstrating better surface finish in ND at the higher tool rotation, while better uniformity in PD.
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| 24. |
- Rana, Harikrishna, et al.
(författare)
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Augmentation of weld penetration by flux assisted TIG welding and its distinct variants for oxygen free copper
- 2021
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Ingår i: Journal of Materials Research and Technology. - : Elsevier. - 2238-7854. ; 10, s. 138-151
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Tidskriftsartikel (refereegranskat)abstract
- A comparative study to investigate the influences of single component fluxes on the depth-to-width ratio (DWR) of oxygen free copper was carried out with novel variants of tungsten inert gas (TIG) welding namely Activated TIG (A-TIG), Flux Bounded TIG (FB-TIG) and Flux Zoned TIG (FB-TIG) processes. The experiments to identify the fluxes delivering the higher DWRs in A-TIG welding among thirteen distinct fluxes were followed by the trials with FB-TIG and FZ-TIG employing those identified DWR fluxes. The fluxes which outperformed with all the techniques were MoO3 & MgO. Reversed Marangoni and arc constriction mechanisms were perceived to be opt for such an increase in DWR. Metallurgical characterization of the weldment indicated distinct grain morphologies and certain defects as well in the weld zones. The FZ-TIG welding is postulated to surpass all the techniques in terms of bringing about the upmost weld penetration.
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| 25. |
- Tang, B. -B, et al.
(författare)
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Crescent-Shaped Electron Distributions at the Nonreconnecting Magnetopause : Magnetospheric Multiscale Observations
- 2019
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Ingår i: Geophysical Research Letters. - : AMER GEOPHYSICAL UNION. - 0094-8276 .- 1944-8007. ; 46:6, s. 3024-3032
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Tidskriftsartikel (refereegranskat)abstract
- Crescent‐shaped electron distributions perpendicular to the magnetic field are an important indicator of the electron diffusion region in magnetic reconnection. They can be formed by the electron finite gyroradius effect at plasma boundaries or by demagnetized electron motion. In this study, we present Magnetospheric Multiscale mission observations of electron crescents at the flank magnetopause on 20 September 2017, where reconnection signatures are not observed. These agyrotropic electron distributions are generated by electron gyromotion at the thin electron‐scale magnetic boundaries of a magnetic minimum after magnetic curvature scattering. The variation of their angular range in the perpendicular plane is in good agreement with predictions. Upper hybrid waves are observed to accompany the electron crescents at all four Magnetospheric Multiscale spacecraft as a result of the beam‐plasma instability associated with these agyrotropic electron distributions. This study suggests electron crescents can be more frequently formed at the magnetopause.
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