Abstract
Magnetic reconnection, breaking and reorganization of magnetic field topology, is a fundamental process for rapid release of magnetic energy into plasmas that occurs pervasively throughout ...the universe. In natural circumstances, the plasma properties on either side of the reconnection layer are almost asymmetric, in particular for the collision rates that critically determine the underlying reconnection mechanism. To date, all laboratory experiments on magnetic reconnections have been limited to purely collisional or collisionless regimes. Here, we report a well-designed experimental investigation on magnetic reconnections in a hybrid collisional-collisionless regime by interactions between laser-ablated copper and plastic plasmas. We directly observe the topology evolutions of the whole process of this asymmetric magnetic reconnection by highly-resolved proton radiography. Through this, we show that the growth rate of tearing instability in such a hybrid regime is still extremely large, resulting in rapid formation of multiple plasmoids and generation of plasmoid-dominated current sheet.
Interfacial magnetic field structures induced by transverse electron-scale shear instability (mushroom instability) are found to be strongly associated with electron and ion dynamics, which in turn ...will influence the development of the instability itself. We find that high-frequency electron oscillations are excited normal to the shear interface. Also, on a larger time scale, the bulk of the ions are gradually separated under the influence of local magnetic fields, eventually reaching an equilibrium related to the initial shear conditions. We present a theoretical model of this behavior. Such separation on the scale of the electron skin depth will prevent different ions from mixing and will thereafter restrain the growth of higher-order instabilities. We also analyze the role of electron thermal motion in the generation of the magnetic field, and we find an increase in the instability growth rate with increasing plasma temperature. These results have potential for providing a more realistic description of relativistic plasma flows.
Powerful lasers interacting with solid targets can generate intense electromagnetic
pulses (EMPs). In this study, EMPs produced by a pulsed laser (1 ps, 100 J) shooting at CH
targets doped with ...different titanium (Ti) contents at the XG-III laser facility are
measured and analyzed. The results demonstrate that the intensity of EMPs first increases
with Ti doping content from 1% to 7% and then decreases. The electron spectra show that
EMP emission is closely related to the hot electrons ejected from the target surface,
which is confirmed by an analysis based on the target–holder–ground equivalent antenna
model. The conclusions of this study provide a new approach to achieve tunable EMP
radiation by adjusting the metal content of solid targets, and will also help in
understanding the mechanism of EMP generation and ejection of hot electrons during laser
coupling with targets.
Background: To compare the outcomes of totally thoracoscopic technique (TTS) vs. right anterolateral thoracotomy technique (RALT) in female patients undergoing minimal invasive atrial septal defect ...(ASD) correction.Methods: From March 2011 to January 2013, 125 female patients underwent minimally invasive atrial septal defect closure, of whom 62 patients were in the TTS group and 63 were in the RALT group.Results: Procedures were performed successfully in all patients without in-hospital mortality or major complications. cardiopulmonary bypass (CPB) time were 48.95 ± 15.63 min in TTS group, 31.4 ± 8.04 min in RALT group (p <0.001); the cross-clamp time were 26.92 ± 11.84 min in TTS group and 18.51 ± 6.11 min in RALT group (p <0.001). The length of incision in RALT group (6.02 ± 1.03 cm) was longer than TTS group (5.31 ± 0.68 cm) and the difference was significant (p <0.001). The overall satisfaction rate for the cosmetic results of TTS was 100% and was 96.83% (61/63 patients) in RALT patients. During follow-up, all patients in TTS group were satisfied expect two patients complained that scar was too long at groin. Reasons for a lower score in RALT group included the long scar in the chest; a RALT incision that was located too medially (coming off the bra line) and asymmetrical breast development.Conclusions: Both TTS and RALT are valid and reliable cosmetic surgical techniques for repairing ASDs in female patients. Both techniques allow excellent cosmetic and functional results in most female patients. The totally thoracoscopic technique may gain shorter incision and cosmetic results compared with RALT.
The results of a commissioning experiment on the SILEX-Ⅱ laser facility (formerly known as CAEP-PW) are reported. SILEX-Ⅱ is a complete optical parametric chirped-pulse amplification laser facility. ...The peak power reached about 1 PW in a 30 fs pulse duration during the experiment. The laser contrast was better than 1010 at 20 ps ahead of the main pulse. In the basic laser foil target interaction, a set of experimental data were collected, including spatially resolved x-ray emission, the image of the coherent transition radiation, the harmonic spectra in the direction of reflection, the energy spectra and beam profile of accelerated protons, hot-electron spectra, and transmitted laser energy fraction and spatial distribution. The experimental results show that the laser intensity reached 5 × 1020 W/cm2 within a 5.8 µm focus (FWHM). Significant laser transmission did not occur when the thickness of the CH foil was equal to or greater than 50 nm. The maximum energy of the accelerated protons in the target normal direction was roughly unchanged when the target thickness varied between 50 nm and 15 µm. The maximum proton energy via the target normal sheath field acceleration mechanism was about 21 MeV. We expect the on-target laser intensity to reach 1022 W/cm2 in the near future, after optimization of the laser focus and upgrade of the laser power to 3 PW.
A newly developed relativistic Vlasov code is introduced. The governing Vlasov-Maxwell equation system is solved numerically in one-dimensional space and three-dimensional momentum space. Spherical ...coordinate system is adopted to characterize the momentum variables for its potential advantage on reducing computational cost. The resulting Vlasov equation is split into two advection equations with respect to position and momentum, respectively. They are solved with a conservative finite volume scheme, together with techniques suppressing numerical oscillations at sharp interfaces. Relativistic longitudinal plasma oscillations are investigated for different plasma temperatures and wave numbers. Results from code simulations are in good agreement with the existing theories.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, SIK, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
The low-mode shell asymmetry and high-mode hot spot mixing appear to be the main reasons for the performance degradation of the National Ignition Facility (NIF) implosion experiments. The effects of ...the mode coupling between low-mode P2 radiation flux asymmetry and intermediate-mode L = 24 capsule roughness on the implosion performance of ignition capsule are investigated by two-dimensional radiation hydrodynamic simulations. It is shown that the amplitudes of new modes generated by the mode coupling are in good agreement with the second-order mode coupling equation during the acceleration phase. The later flow field not only shows large areal density P2 asymmetry in the main fuel, but also generates large-amplitude spikes and bubbles. In the deceleration phase, the increasing mode coupling generates more new modes, and the perturbation spectrum on the hot spot boundary is mainly from the strong mode interactions rather than the initial perturbation conditions. The combination of the low-mode and high-mode perturbations breaks up the capsule shell, resulting in a significant reduction of the hot spot temperature and implosion performance.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
In order to study the laser plasma instabilities (LPIs) in the context of some novel six-side laser-driven indirect designs like the six-cylinder-port hohlraum and the three-axis cylindrical ...hohlraum, where the laser beams inject in hohlraum with a large angle. LPI experiments in cylindrical hohlraum with only outer beams were designed and performed based on the current laser arrangement condition of SGIII laser facility for the first time. Stimulated Brillouin backscatter (SBS) was found to be the dominant instability with high instantaneous reflectivity in experiments. A typical feature was obtained in the time-resolved spectra of SBS, which maintained similar for different laser intensities of the interaction beam. The experimental data are analyzed by the hydrodynamic simulations combined with HLIP code, which is based on the ray-tracing model. By analysis of experimental data, it is argued that the mixture of gas and Au in the region of their interface is important to SBS, which indicates the need for the mixture model between the filled gas and the high Z plasma from hohlraum wall in the hydrodynamic simulations. Nonlinear saturation of SBS as well as the smoothed beam are also discussed here. Our effective considerations of the ions pervasion effect and the smoothed beam provide utilitarian ways for improvement of the current ray-tracing method.
The Schiff bases N-(5-phenylthiazole-2-yl)-2-hydroxylnaphthaldehydehydrazone (1), N-(4′-chloro-5-phenylthiazole-2-yl)-2-hydroxylnaphthaldehydehydrazone (2), and ...N-(4′-nitro-5-phenylthiazole-2-yl)-2-hydroxylnaphthaldehydehydrazone (3) were synthesized. These compounds were characterized by using IR, 1H NMR, 13C NMR, and MS. The photochromism of the compounds was investigated by IR and UV-visible spectrometry which is time variable under irradiation of 254 nm UV light. The thermochromism of the compounds was studied using temperature-variable IR, UV-visible spectrometry, TG, and differential scanning calorimetry (DSC). The results suggested that compound 2 showed thermochromism properties and compounds 2 and 3 displayed photochromism properties. The relationship between the substituents species and photochromic or thermochromic properties of these compounds was revealed as well.
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FZAB, GIS, IJS, IZUM, KILJ, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBMB, UL, UM, UPUK
A novel method based on hybrid feature is proposed for human action recognition in video image sequences, which includes two stages of feature extraction and action recognition. Firstly, we use ...adaptive background subtraction algorithm to extract global silhouette feature and optical flow model to extract local optical flow feature. Then we combine global silhouette feature vector and local optical flow feature vector to form a hybrid feature vector. Secondly, in order to improve the recognition accuracy, we use an optimized Multiple Instance Learning algorithm to recognize human actions, in which an Iterative Querying Heuristic (IQH) optimization algorithm is used to train the Multiple Instance Learning model. We demonstrate that our hybrid feature-based action representation can effectively classify novel actions on two different data sets. Experiments show that our results are comparable to, and significantly better than, the results of two state-of-the-art approaches on these data sets, which meets the requirements of stable, reliable, high precision, and anti-interference ability and so forth.
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FZAB, GIS, IJS, IZUM, KILJ, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBMB, UL, UM, UPUK
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