Why the phase shifts for solitons on a vortex filament are so large: a theoretical explanation

The phase "jumps" for solitons interacting on a vortex filament, observed in experiments, have been unaccounted for for more than 20 years. Using explicit formulas describing the interaction of two solitons on a thin vortex filament in the localized induction approximation, we show that an appropriate choice of the parameters of the solitons leads to large phase shifts. This result does not depend on the axial flow along the filament.     

Interaction of oblique dark solitons in two-dimensional supersonic nonlinear Schrödinger flow

We investigate the collision of two oblique dark solitons in the two-dimensional supersonic nonlinear Schrödinger flow past two impenetrable obstacles. We numerically show that this collision is very similar to the dark solitons collision in the one-dimensional case. We observe that it is practically elastic and we measure the shifts of the solitons positions after their interaction.     

The collisions of two ion acoustic solitary waves in a magnetized nonextensive plasma

Using the extended Poincaré-Lighthill-Kuo (EPLK) method, the interaction between two ion acoustic solitary waves (IASWs) in a multicomponent magnetized plasma (including Tsallis nonextensive electrons) has been theoretically investigated. The analytical phase shifts of the two solitary waves after interaction are estimated. The proposed model leads to rarefactive solitons only. The effects of colliding angle, ratio of number densities of (positive/negative) ions species to the density of nonextensive electrons, ion-to-electron temperature ratio, mass ratio of the negative-to-positive ions and the electron nonextensive parameter on the phase shifts are investigated numerically. The present results show that these parameters have strong effects on the phase shifts and trajectories of the two IASWs after collision. Evidently, this model is helpful for interpreting the propagation and the oblique collision of IASWs in magnetized multicomponent plasma experiments and space observations.     

Search for carbon stars and DZ white dwarfs in SDSS spectra survey through machine learning

Carbon stars and DZ white dwarfs are two types of rare objects in the Galaxy.In this paper,we have applied the label propagation algorithm to search for these two types of stars from Data Release Eight(DR8)of the Sloan Digital Sky Survey(SDSS),which is verified to be efcient by calculating precision and recall.From nearly two million spectra including stars,galaxies and QSOs,we have found 260 new carbon stars in which 96 stars have been identified as dwarfs and 7 identified as giants,and 11 composition spectrum systems(each of them consists of a white dwarf and a carbon star).Similarly,using the label propagation method,we have obtained 29 new DZ white dwarfs from SDSS DR8.Compared with PCA reconstructed spectra,the 29 findings are typical DZ white dwarfs.We have also investigated their proper motions by comparing them with proper motion distribution of 9,374 white dwarfs,and found that they satisfy the current observed white dwarfs by SDSS generally have large proper motions.In addition,we have estimated their efective temperatures by fitting the polynomial relationship between efective temperature and g-r color of known DZ white dwarfs,and found 12 of the 29 new DZ white dwarfs are cool,in which nine are between 6,000 K and 6,600 K,and three are below 6,000 K.     

One-dimensional nonparaxial bright solitons and their coherent interactions in Kerr media

<正>The existence of one-dimensional bright Kerr solitons is investigated in Kerr media beyond the paraxial approximation. It is found that a nonparaxial soliton with no less than a minimum dimensionless width of about 0.76 can exist, which corresponds to the real width about a wavelength.Besides,the coherent interactions between two nonparaxial bright solitons in Kerr media are also investigated in detail.It is found that their separation and intensity ratio have great influence on the coherent interaction between these two solitons.Furthermore,the effect of the relative phase difference on the nonparaxial interaction is quite different from that on the paraxial interaction.Periodical breath, merging,repulsion,and energy transferring can be realized separately by choosing an appropriate initial relative phase between the coherent solitons.     

Ion-acoustic shock waves and their head-on collision in a dense electron-positron-ion quantum plasma

Ion-acoustic shock waves and their head-on collision in a dense quantum plasma comprised of electrons, positrons, and ions are studied. The extended Poincaré-Lighthill-Kuo perturbation method is used to derive the Korteweg-de Vries-Burgers equations for shock waves in this plasma. The dissipation is introduced by taking into account the kinematic viscosity among the plasma constituents. The effects of the ratio of positrons to ions unperturbation number density μ, the normalized kinematic viscosity ηi0, and the quantum Bohm potential H on the interaction and structure of the shock waves are investigated. It is found that there are integrally vertical downward movements for both the colliding shocks after their head-on collision, but there are no shifts of the postcollision trajectories (phase shifts). It is also found that these plasma parameters can significantly influence the collision and properties of the colliding shocks. The results may have relevance in dense astrophysical plasmas (such as neutron stars or white dwarfs) as well as in intense laser-solid density plasma experiments.     

在SDSS DR8恒星光谱中自动搜寻稀有天体

SDSS DR8海量光谱中包含许多有研究价值的稀有天体,如特殊白矮星(DZ,DQ,DC)、碳星、白矮主序双星、激变变星等,如何在海量光谱中自动搜寻稀有天体有着极其重要的意义。提出一种基于核密度估计和K-近邻(K-nearest neighbor, KNN)相结合的方法在SDSS DR8 信噪比大于5的546 383个恒星光谱中搜寻稀有天体。首先对光谱进行高斯核密度估计,选取概率最小的5 000个光谱作为稀有类,概率最大的300 000个光谱作为普通类,然后进行KNN分类,同时也将5 000个稀有光谱的K个最近邻也作为稀有的天体,结果共有21 193条光谱。为了方便分析,对这些光谱聚类后进行人工检查。这些光谱主要包括由于数据缺失、红化、流量定标不准引起的问题光谱、行星状星云、没有物理联系的光谱双星、类星体、特殊白矮星(DZ,DQ,DC)、碳星、白矮主序双星、激变变星等。通过和SIMBAD,NED,ADS及一些主要的文献交叉验证,我们新发现了3个DZ白矮星、1个白矮主序双星、2个伴星为G型星的激变变星,3个激变变星的候选体、6个DC白矮星,1个DC白矮星候选体和1个 BL Lacertae(BL lac)候选体。还发现了1个有CaⅡ三重发射线和MgⅠ发射线的DA白矮星和1个光谱上表现出发射线的晚M恒星但测光图上像是一个星云或星系。     

(1+2)维强非局域空间光孤子的相互作用

强非局域空间光孤子是指满足强非局域条件的空间孤子.在Snyder和Mitchell工作的基础上，获得了不共面对称斜入射(1+2)维强非局域空间光孤子对相互作用问题的精确解析解.结果表明，光束初始中心距离在大范围尺度内变化时，双孤子的演化都能形成类似DNA结构的稳定缠绕，这种稳定缠绕的结构与双孤子的初始相位差无关；光束中心在横截面上的投影轨迹一般是一个斜椭圆，通过改变两光束的初始中心距离和倾斜度可以控制该椭圆轨迹的变化.指出了利用(1+2)维强非局域空间光孤子的相互作用特性实现平面全光开关和全光互联的潜在可能性. 关键词： (1+2)维非局域非线性介质 空间光孤子的相互作用 全光开关 全光互联     

Non-Markovianity for a qubit system driven by a classical phase noisy laser

The nonlinear interaction between electron-acoustic shock waves in a dissipative, non-Maxwellian plasma composed of cold fluid electrons, stationary background ions, and inertialess superthermal electrons has been studied. The effects of plasma parameters on the trajectory changes (i.e., phase shifts) of shock waves after their head-on collision is our main concern. The results indicate that the interactions between shocks are different from those of solitons. Also, it is found that the occurrence and variation of trajectory shifts may be due to the combined role played by the dispersion and dissipation of the colliding nonlinear structure.     

The linear and nonlinear optical effects of white light

An overview of our research group’s experimental and theoretical developments is provided on the linear and nonlinear optical effects of white light since 2003. Their work includes the experimental researches on the white light one-dimensional photovoltaic dark spatial solitons and the waveguides and directional couplers induced by them, the circular and elliptic white-light dark spatial solitons and the white-light photorefractive phase masks, two-dimensional white-light photonic lattices and the applicati...     

Rainbow’s stars

In recent years, a growing interest in the equilibrium of compact astrophysical objects like white dwarf and neutron stars has been manifested. In particular, various modifications due to Planck-scale energy effects have been considered. In this paper we analyze the modification induced by gravity’s rainbow on the equilibrium configurations described by the Tolman–Oppenheimer–Volkoff (TOV) equation. Our purpose is to explore the possibility that the rainbow Planck-scale deformation of space-time could support the existence of different compact stars.     

The influence of chemical composition on models of Type Ia supernovae

Type Ia supernovae are bright stellar explosions distinguished by standardizable light curves that allow for their use as distance indicators for cosmological studies. Despite the highly successful use of these events in this capacity, many fundamental questions remain. Contemporary research investigates how properties of the progenitor system that follow from the host galaxy such as composition and age influence the brightness of an event with the goal of better understanding and assessing the intrinsic scatter in the brightness. We provide an overview of these supernovae and proposed progenitor systems, all of which involve one or more compact stars known as white dwarfs. We describe contemporary research investigating how the composition and structure of the progenitor white dwarf systematically influences the explosion outcome assuming the progenitor is a single white dwarf that has gained mass from a companion. We present results illustrating some of these systematic effects from our research.     

Overtaking collisions of oblique isothermal ion-acoustic multisolitons in ultra-relativistic degenerate dense magnetoplasmas

Overtaking collisions of oblique isothermal ion-acoustic multisolitons are studied in an ultra-relativistic degenerate dense magnetoplasma, containing non-degenerate inertial warm ions and ultra-relativistic degenerate inertialess electrons and positrons. A non-linear Korteweg-de Vries (KdV) equation describing oblique isothermal ion-acoustic solitons (OIIASs) in such a plasma model is derived. By applying Hirota's bilinear method (HBM), the overtaking collisions of oblique isothermal ion-acoustic multisoliton solutions are investigated. An in-depth discussion shows that the amplitude, the width, and the phase shift of isothermal ion-acoustic multisolitons increase as the obliqueness and the chemical potential of electrons increase. The deviation of the trajectories decreases with increasing concentration of fermions and the ion cyclotron frequency. The present finding of this study is applicable in compact objects, such as white dwarfs and neutron stars, having degenerate ultra-relativistic dense electrons and positrons.     

Is it possible to explore Peccei-Quinn axions from frequency-dependence radiation dimming?

We explore how the Peccei-Quinn (PQ) axion parameter space can be constrained by the frequency-dependence dimming of radiation from astrophysical objects. To do so we perform accurate calculations of photon-axion conversion in the presence of a variable magnetic field. We propose several tests where the PQ axion parameter space can be explored with current and future astronomical surveys: the observed spectra of isolated neutron stars, occultations of background objects by white dwarfs and neutron stars, the light-curves of eclipsing binaries containing a white dwarf. We find that the lack of dimming of the light-curve of a detached eclipsing white dwarf binary recently observed, leads to relevant constraints on the photon-axion conversion. Current surveys designed for Earth-like planet searches are well matched to strengthen and improve the constraints on the PQ axion using astrophysical objects radiation dimming.     

亚强非局域空间光孤子的相互作用

研究了亚强非局域空间光孤子的相互作用规律,从光线方程出发得到了孤子光束中心的演化性质以及相互作用周期的解析解.发现亚强非局域条件下孤子的初始间距和非局域特征长度的关系对孤子的相互作用周期有很大的影响,在斜入射时存在一个最大入射角, 小于这个角度孤子才会吸引.数值模拟验证了理论解析的结果. 关键词： 亚强非局域 相互作用 空间光孤子 全光开关     

Interactions of ion acoustic multi-soliton and rogue wave with Bohm quantum potential in degenerate plasma

This work investigates the interactions among solitons and their consequences in the production of rogue waves in an unmagnetized plasmas composing non-relativistic as well as relativistic degenerate electrons and positrons, and inertial non-relativistic helium ions. The extended Poincare′–Lighthill–Kuo(PLK) method is employed to derive the two-sided Korteweg–de Vries(Kd V) equations with their corresponding phase shifts. The nonlinear Schr o¨dinger equation(NLSE) is obtained from the modified Kd V(m Kd V) equation, which allows one to study the properties of the rogue waves. It is found that the Fermi temperature and quantum mechanical effects become pronounced due to the quantum diffraction of electrons and positrons in the plasmas. The densities and temperatures of the helium ions, degenerate electrons and positrons, and quantum parameters strongly modify the electrostatic ion acoustic resonances and their corresponding phase shifts due to the interactions among solitons and produce rogue waves in the plasma.     

The origin of the strongest magnetic fields in dwarfs

White dwarfs have frozen in magnetic fields ranging from below the measurable limit of about 3×10³ to 10⁹ G. White dwarfs with surface magnetic fields in excess of 1 MG are found as isolated single stars and relatively more often in magnetic cataclysmic variables. Some 1253 white dwarfs with a detached low-mass main-sequence companion have been identified in the Sloan Digital Sky Survey (SDSS) but none of these shows sufficient evidence for Zeeman splitting of hydrogen lines for a magnetic field in excess of 1 MG. If such high magnetic fields in white dwarfs result from the isolated evolution of a single star then there should be the same fraction of high field white dwarfs among this SDSS binary sample as among single stars. Thus, we deduce that the origin of such high magnetic fields must be intimately tied to the formation of cataclysmic variables (CVs). The formation of a CV must involve orbital shrinkage from giant star to main-sequence star dimensions. It is believed that this shrinkage occurs as the low-mass companion and the white dwarf spiral together inside a common envelope. CVs emerge as very close but detached binary stars that are then brought together by magnetic braking or gravitational radiation. We propose that the smaller the orbital separation at the end of the common envelope phase, the stronger the magnetic field. The magnetic cataclysmic variables (MCVs) originate from those common envelope systems that almost merge. Those common envelope systems that do merge are the progenitors of the single high field white dwarfs. Thus all highly magnetic white dwarfs, be they single stars or the components of MCVs, have a binary origin. This accounts for the relative dearth of single white dwarfs with fields of 10⁴–10⁶ G. Such intermediate-field white dwarfs are found preferentially in cataclysmic variables. The bias towards higher masses for highly magnetic white dwarfs is expected if a fraction of these form when two degenerate cores merge in a common envelope. From the space density of single highly magnetic white dwarfs we estimate that about three times as many common envelope events lead to a merged core as to a cataclysmic variable.     

Obliquely propagating ion-acoustic shock waves in a degenerate quantum plasma

A theoretical investigation has been carried out on the propagation of non-linear ion-acoustic shock waves (IASHWs) in a magnetized degenerate quantum plasma system composed of inertial non-relativistic positively charged light and heavy ions, inertialess non-relativistically or ultra-relativistically degenerate electrons and positrons. The reductive perturbation method has been employed to derive the Burgers' equation. It has been observed that under consideration, our plasma model supports only positive potential shock structure. It is also found that the amplitude and steepness of the IASHWs have been significantly modified by the variation of ion kinematic viscosity, oblique angle, number density, and charge state of the plasma species. The results of our present investigation will be helpful for understanding the propagation of IASHWs in white dwarfs and neutron stars.     

Interaction phenomena and effect of higher order dispersion on electron acoustic solitary waves in weakly relativistic regimes

The interaction phenomena of electron acoustic solitary waves (EASWs) and the higher order correction of Korteweg‐de Vries (KdV) equations (KdVEs) have investigated in unmagnetized collisionless plasma system consisting of relativistic cold electrons and electron beams, non‐relativistic Maxwellian hot electrons and stationary ions. To understand the physical issues concerned, the two‐sided KdVEs using extended Poincaré‐Lighthill‐Kue (ePLK) method are derived taking the higher order correction into consideration. The analyses reveal that the widths and amplitudes of EASWs (as obtain from KdVEs) are decreasing with plasma parameters. The plasma parameters are responsible for the modification of KdV‐soliton structure. It is found that the narrowness of width and the steepness of dip of the solitons become more pronounced and the electric field behaves like semi‐kink solitons due to the higher order correction of KdVEs. Dip shape rarefactive soliton becomes pronounced by plasma parameters. The phase shifts of EASWs are also enhanced due to the effects of plasma species temperatures and density ratios.     

Interaction properties of complex modified Korteweg-de Vries (mKdV) solitons

Interaction properties of complex solitons are studied for the two U(1)-invariant integrable generalizations of the modified Korteweg-de Vries (mKdV) equation, given by the Hirota equation and the Sasa-Satsuma equation, which share the same traveling wave (single-soliton) solution having a sech profile characterized by a constant speed and a constant phase angle. For both equations, nonlinear interactions in which a fast soliton collides with a slow soliton are shown to be described by 2-soliton solutions that can have three different types of interaction profile, depending on the speed ratio and the relative phase angle of the individual solitons. In all cases, the shapes and speeds of the solitons are found to be preserved apart from a shift in position such that their center of momentum moves at a constant speed. Moreover, for the Hirota equation, the phase angles of the fast and slow solitons are found to remain unchanged, while, for the Sasa-Satsuma equation, the phase angles are shown to undergo a shift such that the relative phase between the fast and slow solitons changes sign.