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Leuchtende Blasen
摘要： Ultraschall kann in Flüssigkeiten Lichtblitze erzeugen. Diese Sonolumineszenz stammt aus implodierenden Kavitationsblasen. Das Gas in kollabierenden Blasen kann sich dabei so stark erw?rmen, dass kurzzeitig ein Plasma mit blitzartiger Lichtemission auftritt. Aus dem optischen Spektrum des Leuchtens schlie?t man auf die physikalischen Vorg?nge bei der extremen Kompression des Blaseninneren. Dabei zeigen Wolken aus Blasen und isolierte Einzelblasen, die in akustischen Stehwellen gefangen sind, unterschiedliche Eigenschaften. Isolierte Einzelblasen haben eher eine symmetrische Kugelgestalt als die sich gegenseitig beeinflussenden Wolkenblasen. Neuere Arbeiten untersuchen, wie sich im Detail Blasenbewegungen und asymmetrische Implosionen auf die Sonolumineszenz auswirken.
关键词： Implosion,Spektrum,Bjerknes-Kraft,Schwarzer K?rper,Jet,Sonolumineszenz,Kollaps,Kavitation,Hot Spot,Blasendynamik,Plasma,Blasenwolken
更新于2025-09-23 15:23:52
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Impact of strained silicon on the device performance of a bipolar charge plasma transistor
摘要： In this manuscript we analyze a unique approach to improve the performance of the bipolar charge plasma transistor (BCPT) by introducing a strained Si/SixGe1?x layer as the active device region. For charge plasma realization different metal work-function electrodes are used to induce n+ and p+ regions on undoped strained silicon-on-insulator (sSOI or SixGe1?x) to realize emitter, base, and collector regions of the BCPT. Here, by using a calibrated 2-D TCAD simulation the impact of a Si mole fraction x (in SixGe1?x) on device performance metrics is investigated. The analysis demonstrates the band gap lowering with decreasing Si content or effective strain on the Si layer, and its subsequent advantages. This work reports a significant improvement in current gain, cutoff frequency, and lower collector breakdown voltage (BVCEO) for the proposed structure over the conventional device. The effect of varying temperature on the strained Si layer and its implications on the device performance is also investigated. The analysis demonstrates a fair device-level understanding and exhibits the immense potential of the SixGe1?x material as the device layer. In addition to this, using extensive 2-D mixed-mode TCAD simulation, a considerable improvement in switching transient times are also observed compared to its conventional counterpart.
关键词： bipolar charge plasma transistor (BCPT),mole fraction,cutoff frequency (fT),current gain (β),collector breakdown voltage (BVCEO),strained Si layer,band gap lowering
更新于2025-09-23 15:23:52
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Using a commercial mini-X-ray source for calibrating Bragg crystals
摘要： In this paper we describe a procedure for calibration of Bragg crystals used for X-ray spectroscopy of laser plasmas. The method uses a relatively inexpensive commercially available X-ray source. By using the source to pump a metallic foil such as vanadium or titanium we were able to create a K-α emission source with minimal background radiation outside the desired photon energy. By using photon counting techniques with a CCD detector we were able to get absolute calibrations of curved and flat Bragg crystals in the 4–5 keV region. An important advantage of our method is that absolute calibration was not necessary either for the commercial source or the detector.
关键词： X-ray detectors and telescopes,spectroscopy and imaging,Plasma diagnostics - interferometry
更新于2025-09-23 15:23:52
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Resonant Enhancement of THz Radiation Through Vertically Aligned Carbon Nanotubes Array by Applying Wiggler Magnetic Field
摘要： The present analysis develops a novel theory of terahertz radiation generation by beating of two laser beams, incident obliquely on the array of vertically aligned carbon nanotubes (CNTs) in the presence of an external wiggler magnetic field. The array of CNTs behaves as nanoantenna to generate THz radiations. The incident lasers exert a ponderomotive force on the electrons of the CNTs to produce nonlinear oscillatory velocity, which beats with the applied wiggler magnetic field. This beating produces a nonlinear current at (ω2 ? ω1, k2 ? k1 + k0) which acts as an antenna to produce the THz radiation. We observe that when the beat frequency (ω2 ? ω1) lies near the effective plasmon frequency of the CNTs, strong THz radiation is produced due to a resonant interaction of the laser with CNT electrons. The externally applied wiggler magnetic field enhances the efficiency of THz radiation of nanoantenna by providing the necessary momentum to the generated THz radiation. We explore the impact of radius and length of nanotubes on the efficiency of THz generation. The generated THz power is enhanced at an optimum angle of incidence of lasers with an array of CNTs.
关键词： THz radiation,Carbon nanotubes,Antenna theory,Wiggler magnetic field,Plasma,Nanotechnology
更新于2025-09-23 15:23:52
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Mechanistic reaction pathway for hexafluoropropylene oxide pulsed plasma deposition of PTFE-like films
摘要： The pulsed plasma deposition of PTFE-like thin films using hexafluoropropylene oxide (HFPO) precursor has been investigated by time-resolved in situ mass spectrometry. Electron-impact and electron-attachment ionisation modes have been employed to monitor neutral plasma species; whilst electrical discharge negative and positive ions have been detected by switching-off the mass spectrometer electron-impact ionisation source. The relative concentrations of neutral versus ionic plasma species were found to rise for shorter pulse duty cycles. Mechanistically, HFPO molecules undergo pulsed plasma-initiated decomposition to form difluorocarbene (:CF2) radical species, and these can combine to form tetrafluoroethylene (CF2=CF2) molecules, which subsequently polymerise leading to the growth of PTFE-like ([–CF2–]n) perfluoroalkyl chains. Shorter pulsed plasma duty cycles enhance the growth of linear PTFE-like perfluoroalkyl chains.
关键词： pulsed plasma,PTFE,mechanistic reaction pathway,nanofilms
更新于2025-09-23 15:23:52
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Stomatal response to blue light in crassulacean acid metabolism plants <i>Kalanchoe pinnata</i> and <i>Kalanchoe daigremontiana</i>
摘要： Blue light (BL) is a fundamental cue for stomatal opening in both C3 and C4 plants. However, it is unknown whether crassulacean acid metabolism (CAM) plants open their stomata in response to BL. We investigated stomatal BL responses in the obligate CAM plants Kalanchoe pinnata and Kalanchoe daigremontiana that characteristically open their stomata at night and close them for part of the day, as contrasted with C3 and C4 plants. Stomata opened in response to weak BL superimposed on background red light in both intact leaves and detached epidermal peels of K. pinnata and K. daigremontiana. BL-dependent stomatal opening was completely inhibited by tautomycin and vanadate, which repress type 1 protein phosphatase and plasma membrane H+-ATPase, respectively. The plasma membrane H+-ATPase activator fusicoccin (FC) induced stomatal opening in the dark. Both BL and FC induced phosphorylation of the guard cell plasma membrane H+-ATPase in K. pinnata. These results indicate that BL-dependent stomatal opening occurs in the obligate CAM plants K. pinnata and K. daigremontiana independently of photosynthetic CO2 assimilation mode.
关键词： phototropins,CAM plants,plasma membrane H+-ATPase,stomatal opening,blue light,signal transduction
更新于2025-09-23 15:23:52
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The effect of pre-annealing and post-annealing on the transparency of MgAl2O4, prepared by slip casting and spark plasma sintering (SPS)
摘要： The aim of this paper is to investigate the effect of slip casting process and the annealing before and after sintering to achieve a transparent MgAl2O4. To remove contaminants such as carbon from the structure of shaped spinel bodies, at first, the samples were annealed at temperature of 800 °C, 900 °C and 1000 °C for 2 h and then sintered at 1400 °C. By annealing the sample before sintering at 900 °C, the transmission increased (15% at IR region and 10% at visible region). Although by annealing the samples, the amount of carbon contamination reduced. Annealing the samples after sintering also had some desirable results. The samples annealed at temperature of 1200 °C for a time of 3, 5 and 10 h. The darkness of samples reduced due to the removal of carbon impurities and the sample was annealed at 1200 °C for 5 h had the most transparency in the visible and infrared regions.
关键词： Spark plasma sintering,Slip casting,MgAl2O4,Annealing,Transparency
更新于2025-09-23 15:23:52
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Controlling the relativistic self-focusing of Hermite-cosh-Gaussian beams in plasma
摘要： The purpose of current study was to find the effects of Hermite-cosh-Gaussian (HChG) beam characteristics on the relativistic self-focusing. The Self-focusing Parameter (SFP), for mode indexes of m=0, 1, and 2 is proposed which provides a basis for achieving the nonlinear self-focusing dependencies on the beam characteristics. The dissimilar nonlinear self-focusing dependencies of different mode indexes on the initial intensity and decentered parameter of HChG beam are founded. The predictions of SFP model are then validated by investigating the beam focusing/diverging along the propagation axis and the exact conformity is observed. The results of introduced model can by applied for HChG beams with higher mode indexes, the Hermite Gaussian and cosh-Gaussian beams.
关键词： Hermite-cosh-Gaussian beam,mode indices,Decentered parameter,Plasma,Relativistic self-focusing
更新于2025-09-23 15:23:52
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Photoluminescence properties of Er3+/Yb3+ doped ZrO2 coatings formed by plasma electrolytic oxidation
摘要： In the present work, down- and up-conversion photoluminescence properties of Er3+/Yb3+ doped ZrO2 coatings formed by plasma electrolytic oxidation of zirconium in electrolyte containing Er2O3 and Yb2O3 particles were investigated. Down-conversion PL analysis shows that emission spectra of ZrO2:Er3+/Yb3+ coatings excited with 280 nm radiation are composed of broad PL band related to ZrO2 host and bands assigned to f-f transitions of Er3+. The main PL emission bands of Er3+ at around 548 nm and 560 nm are related to 4S3/2→4I15/2 transition. PL excitation spectra monitored at 548 nm feature broad band in the region from 250 nm to 350 nm which is associated with the electron transfer transition from 2p orbital of O2? to 4f orbital of Er3+ and transitions of ZrO2. On the other hand, bands in PL excitation spectra ranging from 350 nm to 535 nm are related to 4f transitions of the Er3+ from the ground state 4I15/2 to higher energy levels. Down-conversion PL intensity decreases with increasing concentration of Yb3+ in coating due to energy transfer from Er3+ to Yb3+. ZrO2:Er3+/Yb3+ coatings show intense green (4S3/2→4I15/2) and red (4F9/2→4I15/2) up-conversion PL emission under the excitation with a 980 nm diode laser. With increasing Yb3+ concentration red up-conversion PL intensity increases more rapidly with respect to green emission, because red up-conversion PL intensity strongly depends on Yb3+ concentration, i.e. 4F9/2 state of Er3+ is directly excited by energy transfer from excited Yb3+.
关键词： up-conversion,Photoluminescence,Er3+/Yb3+,Down-conversion,Plasma electrolytic oxidation
更新于2025-09-23 15:23:52
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[IEEE 2018 International IEEE Conference and workshop in óbuda on Electrical and Power Engineering (CANDO-EPE) - Budapest, Hungary (2018.11.20-2018.11.21)] 2018 International IEEE Conference and Workshop in óbuda on Electrical and Power Engineering (CANDO-EPE) - Plasma ignition and current control considerations for magnetron sputtering power supplies
摘要： Physical vapor deposition processes require different types of special power supplies for the ignition and sustaining of the plasma inside the sputtering chamber. The paper identifies some requirements for the design of a pulsed DC converter. Experiments have been carried out to identify the current-voltage characteristics of the vacuum chamber with the supply of different gases, and gas mixtures in the usable pressure domain. The vacuum chamber was supplied with voltage and current impulse trains with various parameters in order to acquire relevant data regarding the gas breakdown in pulsed power mode. A power electronic converter topology and control routine has been proposed, which is suitable for plasma ignition and discharge current control. The proof of concept has been demonstrated with the help of the magnetron sputtering chamber supplied by a test circuit.
关键词： current control,power electronic converter,plasma ignition,magnetron sputtering
更新于2025-09-23 15:23:52