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| 2. |
- Li, Xing-Yu, et al.
(författare)
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Comparative Study of Dayside Pulsating Auroras Induced by Ultralow-Frequency Waves
- 2023
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Ingår i: Universe. - : MDPI AG. - 2218-1997. ; 9:6
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Tidskriftsartikel (refereegranskat)abstract
- Pulsating auroras are usually observed with ultralow-frequency (ULF) waves in the Pc 3-5 band (period 10-600 s). These auroras are thought to result from interactions between energetic electrons and chorus waves, but their relationship with ULF waves remains an open question. In this study, we investigated this question by conducting a comparative study on two ULF wave events with pulsating auroras observed near the magnetic footprints. Conjugate observations from the Magnetospheric Multiscale mission and the Chinese Yellow River Station were used. In both events, lower-band chorus waves were observed, which were suggested to be connected with the auroral pulsations by wavelet analysis. The intensity of these waves oscillates at the period of the ULF waves, but the physics laid behind them differs by events. During the event of 22 January 2019, compressional ULF waves changed the threshold for the whistler anisotropy instability periodically, affecting the emission of chorus waves. In the event on 10 January 2016, poloidal ULF waves modulated the chorus wave generation by regulating electron temperature anisotropy through drift resonance. ULF waves in these events may originate from perturbations in the solar wind. We highlight the role of ULF waves in the solar wind-magnetosphere-ionosphere coupling, which requires further study.
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| 3. |
- Li, Xing Yu, et al.
(författare)
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Ion Acceleration and Corresponding Bounce Echoes Induced by Electric Field Impulses: MMS Observations
- 2024
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Ingår i: Journal of Geophysical Research - Space Physics. - : American Geophysical Union (AGU). - 2169-9380 .- 2169-9402. ; 129:2
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Tidskriftsartikel (refereegranskat)abstract
- Dayside magnetosphere interactions are essential for energy and momentum transport between the solar wind and the magnetosphere. In this study, we investigate a new phenomenon within this regime. Sudden enhancements of ion fluxes followed by repeating dropouts and recoveries were observed by Magnetospheric Multiscale on 5 November 2016, which is the very end of the recovery phase from a moderate geomagnetic storm. These repetitive flux variations display energy-dispersive characteristics with periods relevant to ion bounce motion, suggesting they are corresponding echoes. Alongside the flux variations, bipolar electric field impulses originating from external sources were detected. We traced the source region of the initial injection and found it is located near the spacecraft's position. To elucidate the underlying physics, a test-particle simulation is conducted. The results reveal that radial transport resulting from impulse-induced acceleration can give rise to these echoes. Observations demonstrate dayside magnetosphere interactions are more common than we previously considered, which warrants further research.
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| 4. |
- Liu, Zhiying, et al.
(författare)
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Mobility Extraction for Nanotube TFTs
- 2011
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Ingår i: IEEE Electron Device Letters. - 0741-3106 .- 1558-0563. ; 32:7, s. 913-915
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Tidskriftsartikel (refereegranskat)abstract
- An extensive investigation of carrier mobility is presented for thin-film transistors (TFTs) with single-walled carbon nanotube (SWCNT) networks as the semiconductor channel. For TFTs particularly with low-density SWCNTs in the networks, the extracted mobility using the standard method for Si metal-oxide-semiconductor field-effect transistors is erroneous, mainly resulting from use of a parallel-plate capacitor model and assumption of the source-drain current being inversely proportional to the channel length. Large hysteresis in the transfer characteristics further complicates the extraction. By properly addressing all these challenges in this letter, a comprehensive methodology is established, leading to the extraction of mobility values that are independent of geometrical parameters.
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| 5. |
- Liu, Zhiying, et al.
(författare)
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On Gate Capacitance of Nanotube Networks
- 2011
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Ingår i: IEEE Electron Device Letters. - : IEEE. - 0741-3106 .- 1558-0563. ; 32:5, s. 641-643
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Tidskriftsartikel (refereegranskat)abstract
- This letter presents a systematic investigation of the gate capacitance C-G of thin-film transistors (TFTs) based on randomly distributed single-walled carbon nanotubes (SWCNTs) in the channel. In order to reduce false counting of SWCNTs that do not contribute to current conduction, C-G is directly measured on the TFTs using a well-established method for MOSFETs. Frequency dispersion of C-G is observed, and it is found to depend on the percolation behavior in SWCNT networks. This dependence can be accounted for using an RC transmission line model. These results are of important implications for the determination of carrier mobility in nanoparticle-based TFTs.
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| 6. |
- Luo, Jun, et al.
(författare)
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Thermal Stability and Dopant Segregation for Schottky Diodes With Ultrathin Epitaxial NiSi(2-y)
- 2011
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Ingår i: IEEE Electron Device Letters. - : Institute of Electrical and Electronics Engineers (IEEE). - 0741-3106 .- 1558-0563. ; 32:8, s. 1029-1031
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Tidskriftsartikel (refereegranskat)abstract
- The Schottky barrier height (SBH) of an ultrathin epitaxial NiSi(2-y) film grown on Si(100) is modified significantly by means of dopant segregation (DS). The DS process begins with the NiSi(2-y) formation and is followed by dopant implantation and drive-in annealing. The rapid lattice restoration and superior morphological stability upon heat treatment up to 800 degrees C allow the epitaxial NiSi(2-y) film to take full advantage of the DS process. For drive-in annealing below 750 degrees C, the effective SBH is altered to similar to 0.9-1 eV for both electrons and holes by B-DS and As-DS, respectively, without deteriorating the integrity of the NiSi(2-y) film.
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| 7. |
- Beal, Jacob, et al.
(författare)
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Robust estimation of bacterial cell count from optical density
- 2020
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Ingår i: Communications Biology. - : Springer Science and Business Media LLC. - 2399-3642. ; 3:1
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Tidskriftsartikel (refereegranskat)abstract
- Optical density (OD) is widely used to estimate the density of cells in liquid culture, but cannot be compared between instruments without a standardized calibration protocol and is challenging to relate to actual cell count. We address this with an interlaboratory study comparing three simple, low-cost, and highly accessible OD calibration protocols across 244 laboratories, applied to eight strains of constitutive GFP-expressing E. coli. Based on our results, we recommend calibrating OD to estimated cell count using serial dilution of silica microspheres, which produces highly precise calibration (95.5% of residuals <1.2-fold), is easily assessed for quality control, also assesses instrument effective linear range, and can be combined with fluorescence calibration to obtain units of Molecules of Equivalent Fluorescein (MEFL) per cell, allowing direct comparison and data fusion with flow cytometry measurements: in our study, fluorescence per cell measurements showed only a 1.07-fold mean difference between plate reader and flow cytometry data.
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| 8. |
- Georgiev, Boris, et al.
(författare)
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A Universal Power-law Prescription for Variability from Synthetic Images of Black Hole Accretion Flows
- 2022
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Ingår i: Astrophysical Journal Letters. - : American Astronomical Society. - 2041-8213 .- 2041-8205. ; 930:2
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Tidskriftsartikel (refereegranskat)abstract
- We present a framework for characterizing the spatiotemporal power spectrum of the variability expected from the horizon-scale emission structure around supermassive black holes, and we apply this framework to a library of general relativistic magnetohydrodynamic (GRMHD) simulations and associated general relativistic ray-traced images relevant for Event Horizon Telescope (EHT) observations of Sgr A*. We find that the variability power spectrum is generically a red-noise process in both the temporal and spatial dimensions, with the peak in power occurring on the longest timescales and largest spatial scales. When both the time-averaged source structure and the spatially integrated light-curve variability are removed, the residual power spectrum exhibits a universal broken power-law behavior. On small spatial frequencies, the residual power spectrum rises as the square of the spatial frequency and is proportional to the variance in the centroid of emission. Beyond some peak in variability power, the residual power spectrum falls as that of the time-averaged source structure, which is similar across simulations; this behavior can be naturally explained if the variability arises from a multiplicative random field that has a steeper high-frequency power-law index than that of the time-averaged source structure. We briefly explore the ability of power spectral variability studies to constrain physical parameters relevant for the GRMHD simulations, which can be scaled to provide predictions for black holes in a range of systems in the optically thin regime. We present specific expectations for the behavior of the M87* and Sgr A* accretion flows as observed by the EHT.
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| 9. |
- Li, Xing-Yu, et al.
(författare)
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ULF Wave-Induced Ion Pitch Angle Evolution in the Dayside Outer Magnetosphere
- 2022
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Ingår i: Geophysical Research Letters. - : American Geophysical Union (AGU). - 0094-8276 .- 1944-8007. ; 49:8
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Tidskriftsartikel (refereegranskat)abstract
- Drift-bounce resonance between ultralow frequency (ULF) waves and ions is essential for ion energization in the magnetosphere. Here, we present the first comprehensive study of drift-bounce resonance in the dayside outer magnetosphere, where off-equatorial magnetic field minima would strongly distort ions' bounce and drift motion. A generalized theory is proposed, in which the effects of off-equatorial minima, time-evolving fields and ion bounce motion are taken into account. In consequence of these effects, ion pitch angle distributions undergo dramatic changes. In the presence of off-equatorial minima, the time-of-flight effect of ion bounce motion forms latitude-dependent dispersions besides "paw-track shaped" structures, while evolving wave fields cause time-dependent phase shifts in "paw-tracks." All the predicted signatures have been confirmed by 5 years of Magnetospheric Multiscale spacecraft data and numerical simulations. These results allow us to better understand the interactions between ULF waves and thermal ion species in global magnetospheric dynamics.
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| 10. |
- Luo, Jun, et al.
(författare)
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Effects of Carbon on Schottky Barrier Heights of NiSi Modified by Dopant Segregation
- 2009
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Ingår i: IEEE Electron Device Letters. - : Institute of Electrical and Electronics Engineers (IEEE). - 0741-3106 .- 1558-0563. ; 30:6, s. 608-610
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Tidskriftsartikel (refereegranskat)abstract
- The presence of carbon at the interface between NiSi and Si has been found to participate in the process of modification of effective Schottky barrier heights using the dopant segregation (DS) method. Carbon alone results in an increased phi(bn) from 0.7 to above 0.9 eV. Boron diffusion in NiSi is inhibited by carbon, and no B-DS at the NiSi/Si interface occurs below 600 degrees C. Above this temperature, B-DS at this interface is evident thus keeping phi(bn) high. The presence of interfacial carbon leads to an increased interfacial As concentration resulting in beneficial effects in tuning phi(bn) above 1.0 eV by As-DS.
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