分类： 光学 >> 量子光学 提交时间： 2023-02-19
摘要： The overlapping of multiple beams is common in inertial confinement fusion (ICF), making the collective stimulated Brillouin scattering (SBS) with shared ion acoustic wave (IAW) potentially important because of the effectively larger laser intensities to drive the instability. In this work, based on a linear kinetic model, an exact analytic solution for the convective amplification of SBS with the shared IAW modes stimulated by two overlapped beams is presented. From this solution, effects of the wavelength difference, crossing angle, polarization states, and finite beam overlapping volume of the two laser beams on the shared IAW modes are studied. It is found that a wavelength difference of several nanometers between the laser beams has negligible effects, except for a very small crossing angle about one degree. However, the crossing angle, beam polarization states, and finite beam overlapping volume can have significant influences on the shared IAW modes. Furthermore, the out-of-plane modes, in which the wavevectors of daughter waves lie in the different planes from the two overlapped beams, are found to be important for certain polarization states and crossing angles of the laser beams with the finite beam overlapping volume. This work is helpful to comprehend and estimate the collective SBS with shared IAW in ICF experiments.
分类： 物理学 >> 核物理学 提交时间： 2016-09-13
摘要： Warped accretion disks have attracted intensive attention because of their critical role on shaping the spin of supermassive massive black holes (SMBHs) through the Bardeen-Petterson effect, a general relativistic effect that leads to final alignments or anti-alignments between black holes and warped accretion disks. We study such alignment processes by explicitly taking into account the finite sizes of accretion disks and the episodic lifetimes of AGNs that delineate the duration of gas fueling onto accretion disks. We employ an approximate global model to simulate the evolution of accretion disks, allowing to determine the gravitomagnetic torque that drives the alignments in a quite simple way. We then track down the evolutionary paths for mass and spin of black holes both in a single activity episode and over a series of episodes. Given with randomly and isotropically oriented gas fueling over episodes, we calculate the spin evolution with different episodic lifetimes and find that it is quite sensitive to the lifetimes. We therefore propose that spin distribution of SMBHs can place constraints on the episodic lifetimes of AGNs and vice versa. Applications of our results on the observed spin distributions of SMBHs and the observed episodic lifetimes of AGNs are discussed, although both the measurements at present are yet ambiguous to draw a firm conclusion. Our prescription can be easily incorporated into semi-analytic models for black hole growth and spin evolution.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： We present observations of the carbon-rich protoplanetary nebula (PPN) CRL 2688 made with the Institut de Radioastronomie Millimetrique (IRAM) 30 m telescope in the 3mm and 2mm bands. In total, 196 transition lines belonging to 38 molecular species and isotopologues are detected, among which, to our best knowledge, 153 transition lines and 13 species are the first report for this object. Additionally, in order to contribute to future research, we have collected observational data on the molecular lines of CRL 2688 from the literature and compiled them into a single unified catalog. We find that the molecular abundance of CRL 2688 cannot be explained by the standard model of a circumstellar envelope. The implications of metal-bearing molecules on circumstellar chemistry are discussed.
分类： 物理学 >> 凝聚态:结构、力学和热性能 提交时间： 2017-03-26
摘要： The vacancy-type defects induced by co-implantation of He and H ions in China Low Activation Martensitic (CLAM) steel at room temperature were investigated with a variable-energy position beam Doppler broadening spectra (DBS). The co- implantation contained two patterns: one was implanted by He ions firstly, and then followed by H-ions implantation; the other was implanted by H ions in the first place, after that followed by He-ions implantation. The S parameters of implanted samples became larger than un-implanted one under different implantation fluences, and the S parameters of pre-implanted H were larger than pre-implanted He regardless of fluence. The difference of S parameters between pre-implanted H and He decreased with increasing fluence. He-H-vacancy complex is the reason that the S parameter of pre-implanted H is higher than pre-implanted He
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Jian-Jie Qiu
Yong Zhang
Jun-ichi Nakashima
Jiang-Shui Zhang
Nico Koning
Xin-Di Tang
Yao-Ting Yan
Huan-Xue Feng
摘要： Context. IRAS 19312+1950 is an isolated infrared source that exhibits a characteristic quasi-point-symmetric morphology in the near- and mid-infrared images and is also very bright in molecular radio lines. Because of its unique observational characteristics, various observational studies have been conducted and several hypotheses have been proposed regarding its origin, which is still unclear. So far, it has been suggested that it could be a peculiar evolved star, a young stellar object, or even a red nova remnant. Regardless of which type of object it is ultimately classified as, IRAS 19312+1950 is exceptionally bright in the infrared and molecular radio lines and therefore will undoubtedly be crucial as a prototype of this kind of object having a peculiar nature or unusual evolutionary phase. Aims. This study aims to reveal the molecular composition of the central part of IRAS 19312+1950 by performing an unbiased molecular radio line survey and discussing the origin of the object from a molecular chemical point of view. Methods. We carried out a spectral line survey with the IRAM 30 m telescope towards the center of IRAS 19312+1950 in the 3 and 1.3 mm windows. Results. In total, 28 transition lines of 22 molecular species and those isotopologues are detected towards IRAS 19312+1950, some of which exhibit a broad and a narrow components. Seventeen thermal lines and 1 maser line are newly detected. The molecular species of C$^{17}$O, $^{30}$SiO, HN$^{13}$C, HC$^{18}$O$^{+}$, H$_{2}$CO, and $c$-C$_{3}$H$_{2}$ are detected for the first time in this object. Conclusions. Our results, in combination with previous studies, favor the hypothesis that IRAS 19312+1950 might be a red nova remnant, in which the progenitors that merged to become a red nova may have contained at least two evolved stars with oxygen-rich and carbon-rich chemistry, respectively.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Jian-Jie Qiu
Yong Zhang
Jun-ichi Nakashima
Jiang-Shui Zhang
Nico Koning
Xin-Di Tang
Yao-Ting Yan
Huan-Xue Feng
摘要： Context. IRAS 19312+1950 is an isolated infrared source that exhibits a characteristic quasi-point-symmetric morphology in the near- and mid-infrared images and is also very bright in molecular radio lines. Because of its unique observational characteristics, various observational studies have been conducted and several hypotheses have been proposed regarding its origin, which is still unclear. So far, it has been suggested that it could be a peculiar evolved star, a young stellar object, or even a red nova remnant. Regardless of which type of object it is ultimately classified as, IRAS 19312+1950 is exceptionally bright in the infrared and molecular radio lines and therefore will undoubtedly be crucial as a prototype of this kind of object having a peculiar nature or unusual evolutionary phase. Aims. This study aims to reveal the molecular composition of the central part of IRAS 19312+1950 by performing an unbiased molecular radio line survey and discussing the origin of the object from a molecular chemical point of view. Methods. We carried out a spectral line survey with the IRAM 30 m telescope towards the center of IRAS 19312+1950 in the 3 and 1.3 mm windows. Results. In total, 28 transition lines of 22 molecular species and those isotopologues are detected towards IRAS 19312+1950, some of which exhibit a broad and a narrow components. Seventeen thermal lines and 1 maser line are newly detected. The molecular species of C$^{17}$O, $^{30}$SiO, HN$^{13}$C, HC$^{18}$O$^{+}$, H$_{2}$CO, and $c$-C$_{3}$H$_{2}$ are detected for the first time in this object. Conclusions. Our results, in combination with previous studies, favor the hypothesis that IRAS 19312+1950 might be a red nova remnant, in which the progenitors that merged to become a red nova may have contained at least two evolved stars with oxygen-rich and carbon-rich chemistry, respectively.
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