arXiv subjects

K. Li

Publications and source records attributed to K. Li.

At least 91 records · Page 5Linked to original sources

arXiv2014

The first photometric analysis of the near contact binary IR Cas

The first photometric analysis of IR Cas was carried out based on the new observed BVRI light curves. The symmetric light curves and nearly flat secondary minimum indicate that very precise photometric results can be determined. We found that IR Cas is a near contact binary with the primary component filling its Roche lobe. An analysis of the O-C diagram based on all available times of light minimum reveals evidence for a periodic change with a semiamplitude of 0.0153 days and a period of 39.7 years superimposed on a secular decrease at a rate of dp/dt=-1.28(\pm0.09)\times10^{-7} d yr^{-1}. The most reasonable explanation for the periodic change is the light time-travel effect due to a third body. The period decrease may be caused by mass transfer from the primary component to the secondary. With the decreasing period, IR Cas would eventually evolve into a contact system.

astro-ph.SR↗

arXiv2014

Discovery of a W UMa type binary GSC 03553-00845

When observing the transiting extrasolar planets, we discovered a new W UMa type binary GSC 03553-00845. Following observation was carried out using the 1m telescope at Weihai Observatory of Shandong University. Complete BVR light curves were determined. Using the W-D program, we analyzed the light curves. Photometric solution reveals that GSC 03553-00845 is a W-subtype W UMa type binary with a mass ratio of q=2.904, it is an overcontact binary system by a contact degree of f=29.5% with a small temperature difference between the components (ΔT=206 K indicating a good thermal contact between the components. More observation of GSC 03553-00845 is needed in order to analyze the light curve variation and orbital period change.

astro-ph.SR↗

arXiv2013

Nonlinear modes and symmetries in linearly-coupled pairs of PT-invariant dimers

The subject of the work are pairs of linearly coupled PT-symmetric dimers. Two different settings are introduced, namely, straight-coupled dimers, where each gain site is linearly coupled to one gain and one loss site, and cross-coupled dimers, with each gain site coupled to two lossy ones. The latter pair with equal coupling coefficients represents a "PT-hypersymmetric" quadrimer. We find symmetric and antisymmetric solutions in these systems, chiefly in an analytical form, and explore the existence, stability and dynamical behavior of such solutions by means of numerical methods. We thus identify bifurcations occurring in the systems, including spontaneous symmetry breaking and saddle-center bifurcations. Simulations demonstrate that evolution of unstable branches typically leads to blowup. However, in some cases unstable modes rearrange into stable ones.

nlin.PS↗

arXiv2013

${\cal PT}$-symmetric coupler with $χ^{(2)}$ nonlinearity

We introduce the notion of a ${\cal PT}$-symmetric dimer with a $χ^{(2)}$ nonlinearity. Similarly to the Kerr case, we argue that such a nonlinearity should be accessible in a pair of optical waveguides with quadratic nonlinearity and gain and loss, respectively. An interesting feature of the problem is that because of the two harmonics, there exist in general two distinct gain/loss parameters, different values of which are considered herein. We find a number of traits that appear to be absent in the more standard cubic case. For instance, bifurcations of nonlinear modes from the linear solutions occur in two different ways depending on whether the first or the second harmonic amplitude is vanishing in the underlying linear eigenvector. Moreover, a host of interesting bifurcation phenomena appear to occur including saddle-center and pitchfork bifurcations which our parametric variations elucidate. The existence and stability analysis of the stationary solutions is corroborated by numerical time-evolution simulations exploring the evolution of the different configurations, when unstable.

physics.optics↗

arXiv2013

Collectivity evolution in the neutron-rich Pd isotopes towards the N=82 shell closure

The neutron-rich, even-even 122,124,126Pd isotopes has been studied via in-beam gamma-ray spectroscopy at the RIKEN Radioactive Isotope Beam Factory. Excited states at 499(9), 590(11), and 686(17) keV were found in the three isotopes, which we assign to the respective 2+ -> 0+ decays. In addition, a candidate for the 4+ state at 1164(20) keV was observed in 122Pd. The resulting Ex(2+) systematics are essentially similar to those of the Xe (Z=54) isotopic chain and theoretical prediction by IBM-2, suggesting no serious shell quenching in the Pd isotopes in the vicinity of N=82.

nucl-ex↗

arXiv2013

Revisiting the PT-symmetric Trimer: Bifurcations, Ghost States and Associated Dynamics

In this paper, we revisit one of the prototypical PT-symmetric oligomers, namely the trimer. We find all the relevant branches of "regular" solutions and analyze the bifurcations and instabilities thereof. Our work generalizes the formulation that was proposed recently in the case of dimers for the so-called "ghost states" of trimers, which we also identify and connect to symmetry-breaking bifurcations from the regular states. We also examine the dynamics of unstable trimers, as well as those of the ghost states in the parametric regime where the latter are found to exist. Finally, we present the current state of the art for optical experiments in PT-symmetric trimers, as well as experimental results in a gain-loss-gain three channel waveguide structure.

quant-ph↗

arXiv2013

A frequency determination method for digitized NMR signals

We present a high precision frequency determination method for digitized NMR FID signals. The method employs high precision numerical integration rather than simple summation as in many other techniques. With no independent knowledge of the other parameters of a NMR FID signal (phase $ϕ$, amplitude $A$, and transverse relaxation time $T_{2}$) this method can determine the signal frequency $f_{0}$ with a precision of $1/(8π^{2}f_{0}^{2}T_{2}^{2})$ if the observation time $T$ is long enough. The method is especially convenient when the detailed shape of the observed FT NMR spectrum is not well defined. When $T_{2}$ is $+\infty$ and the signal becomes pure sinusoidal, the precision of the method is $3/(2π^{2}f_{0}^{2}T^{2})$ which is one order more precise than a typical frequency counter. Analysis of this method shows that the integration reduces the noise by bandwidth narrowing as in a lock-in amplifier, and no extra signal filters are needed. For a pure sinusoidal signal we find from numerical simulations that the noise-induced error in this method reaches the Cramer-Rao Lower Band(CRLB) on frequency determination. For the damped sinusoidal case of most interest, the noise-induced error is found to be within a factor of 2 of CRLB when the measurement time $T$ is a few times larger than $T_{2}$.We discuss possible improvements for the precision of this method.

physics.comp-ph↗

arXiv2013

Parity-time symmetric optical coupler with birefringent arms

In this work, we propose a PT-symmetric coupler whose arms are birefringent waveguides as a realistic physical model which leads to a so-called quadrimer i.e., a four complex field setting. We seek stationary solutions of the resulting linear and nonlinear model, identifying its linear point of PT symmetry breaking and examining the corresponding nonlinear solutions that persist up to this point, as well as, so-called, ghost states that bifurcate from them. We obtain the relevant symmetry breaking bifurcations and numerically follow the associated dynamics which give rise to growth/decay even within the PT-symmetric phase. Our obtained stationary nonlinear solutions are found to terminate in saddle-center bifurcations which are analogous to the linear PT-phase transition.

quant-ph↗

arXiv2012

Linear and Nonlinear PT-symmetric Oligomers: A Dynamical Systems Analysis

In the present work we focus on the cases of two-site (dimer) and three-site (trimer) configurations, i.e. oligomers, respecting the parity-time (PT) symmetry, i.e., with a spatially odd gain-loss profile. We examine different types of solutions of such configurations with linear and nonlinear gain/loss profiles. Solutions beyond the linear PT-symmetry critical point as well as solutions with asymmetric linearization eigenvalues are found in both the nonlinear dimer and trimer. The latter feature is absent in linear PT-symmetric trimers, while both of them are absent in linear PT symmetric dimers. Furthermore, nonlinear gain/loss terms enable the existence of both symmetric and asymmetric solution profiles (and of bifurcations between them), while only symmetric solutions are present in the linear PT-symmetric dimers and trimers. The linear stability analysis around the obtained solutions is discussed and their dynamical evolution is explored by means of direct numerical simulations. Finally, a brief discussion is also given of recent progress in the context of PT-symmetric quadrimers.

quant-ph↗

arXiv2012

Well-developed deformation in 42Si

Excited states in 38,40,42Si nuclei have been studied via in-beam gamma-ray spectroscopy with multi-nucleon removal reactions. Intense radioactive beams of 40S and 44S provided at the new facility of the RIKEN Radioactive Isotope Beam Factory enabled gamma-gamma coincidence measurements. A prominent gamma line observed with an energy of 742(8) keV in 42Si confirms the 2+ state reported in an earlier study. Among the gamma lines observed in coincidence with the 2+ -> 0+ transition, the most probable candidate for the transition from the yrast 4+ state was identified, leading to a 4+_1 energy of 2173(14) keV. The energy ratio of 2.93(5) between the 2+_1 and 4+_1 states indicates well-developed deformation in 42Si at N=28 and Z=14. Also for 38,40Si energy ratios with values of 2.09(5) and 2.56(5) were obtained. Together with the ratio for 42Si, the results show a rapid deformation development of Si isotopes from N=24 to N=28.

nucl-ex↗

arXiv2012

PT-symmetric Double Well Potentials Revisited: Bifurcations, Stability and Dynamics

In this work we analyze PT-symmetric double-well potentials based on a two-mode picture. We reduce the problem into a PT-symmetric dimer and illustrate that the latter has effectively two fundamental bifurcations, a pitchfork (symmetry-breaking bifurcation) and a saddle-center one, which is the nonlinear analog of the PT-phase-transition. It is shown that the symmetry breaking leads to ghost states (amounting to growth or decay); although these states are not true solutions of the original continuum problem, the system's dynamics closely follows them, at least in its metastable evolution. Past the second bifurcation, there are no longer states of the original continuum system. Nevertheless, the solutions can be analytically continued to yield a new pair of branches, which is also identified and dynamically examined. Our explicit analytical results for the dimer are directly compared to the full continuum problem, yielding a good agreement.

nlin.PS↗

arXiv2012

Intrinsic localized modes in coupled DNLS equations from the anti-continuum limit

In the present work, we generalize earlier considerations for intrinsic localized modes consisting of a few excited sites, as developed in the one-component discrete nonlinear Schrodinger equation model, to the case of two-component systems. We consider all the different combinations of "up" (zero phase) and "down" (π phase) site excitations and are able to compute not only the corresponding existence curves, but also the eigenvalue dependences of the small eigenvalues potentially responsible for instabilities, as a function of the nonlinear parameters of the model representing the self/cross phase modulation in optics and the scattering length ratios in the case of matter waves in optical lattices. We corroborate these analytical predictions by means of direct numerical computations. We infer that all the modes which bear two adjacent nodes with the same phase are unstable in the two component case and the only solutions that may be linear stable are ones where each set of adjacent nodes, in each component is out of phase.

nlin.PS↗

arXiv2012

Controlling fast electron beam divergence using two laser pulses

This paper describes the first experimental demonstration of the guiding of a relativistic electron beam in a solid target using two co-linear, relativistically intense, picosecond laser pulses. The first pulse creates a magnetic field which guides the higher current fast electron beam generated by the second pulse. The effects of intensity ratio, delay, total energy and intrinsic pre-pulse are examined. Thermal and Kα imaging showed reduced emission size, increased peak emission and increased total emission at delays of 4 - 6 ps, an intensity ratio of 10 : 1 (second:first) and a total energy of 186 J. In comparison to a single, high contrast shot, the inferred fast electron divergence is reduced by 2.7 times, while the fast electron current density is increased by a factor of 1.8. The enhancements are reproduced with modelling and are shown to be due to the self-generation of magnetic fields. Such a scheme could be of considerable benefit to fast ignition inertial fusion.

physics.plasm-ph↗

arXiv2012

Optical flares and flaring oscillations on the M-type eclipsing binary CU Cnc

We report here the discovery of an optical flare observed in R band from the red-dwarf eclipsing binary CU Cnc whose component stars are at the upper boundary of full convection (M1=0.43 and M2=0.4M0, M0 is the solar mass). The amplitude of the flare is the largest among those detected in R band (~0.52mag) and the duration time is about 73 minutes. As those observed on the Sun, quasi-periodic oscillations were seen during and after the flare. Three more R-band flares were found by follow up monitoring. In total, this binary was monitored photometrically by using R filter for 79.9 hours, which reveals a R-band flare rate about 0.05 flares per hour. These detections together with other strong chromospheric and coronal activities, i.e., very strong H_alpha and H_beta emission features and an EUV and X-ray source, indicate that it has very strong magnetic activity. Therefore, the apparent faintness (~1.4 magnitude in V) of CU Cnc compared with other single red dwarfs of the same mass can be plausibly explained by the high coverage of the dark spots.

astro-ph.SR↗

arXiv2011

Detection of a planetary system orbiting the eclipsing polar HU Aqr

Using the precise times of mid-egress of the eclipsing polar HU Aqr, we discovered that this polar is orbited by two or more giant planets. The two planets detected so far have masses of at least 5.9 and 4.5\,M_{Jup}. Their respective distances from the polar are 3.6 AU and 5.4 AU with periods of 6.54 and 11.96 years, respectively. The observed rate of period decrease derived from the downward parabolic change in O-C curve is a factor 15 larger than the value expected for gravitational radiation. This indicates that it may be only a part of a long-period cyclic variation, revealing the presence of one more planet. It is interesting to note that the two detected circumbinary planets follow the Titus-Bode law of solar planets with n=5 and 6. We estimate that another 10 years of observations will reveal the presence of the predicted third planet.

astro-ph.SR↗

arXiv2011

PT-Symmetric Oligomers: Analytical Solutions, Linear Stability and Nonlinear Dynamics

In the present work we focus on the case of (few-site) configurations respecting the PT-symmetry. We examine the case of such "oligomers" with not only 2-sites, as in earlier works, but also the cases of 3- and 4-sites. While in the former case of recent experimental interest, the picture of existing stationary solutions and their stability is fairly straightforward, the latter cases reveal a considerable additional complexity of solutions, including ones that exist past the linear PT-breaking point in the case of the trimer, and more complex, even asymmetric solutions in the case of the quadrimer with nontrivial spectral and dynamical properties. Both the linear stability and the nonlinear dynamical properties of the obtained solutions are discussed.

nlin.PS↗

arXiv2010

Exploring the "Island of Inversion" by in-beam gamma-ray spectroscopy of the neutron-rich sodium isotopes 31,32,33Na

The structure of the neutron rich sodium isotopes 31,32,33Na was investigated by means of in-beam gammaray spectroscopy following one-neutron knockout and inelastic scattering of radioactive beams provided by the RIKEN Radioactive Ion Beam Factory. The secondary beams were selected and separated by the fragment separator BigRIPS and incident at ~240 meV/u on a natural carbon (secondary) target, which was surrounded by the DALI2 array to detect coincident de-excitation gammarays. Scattered particles were identified by the spectrometer ZeroDegree. In 31Na, a new decay gammaray was observed in coincidence with the known (5/2+)-> 3/2(+) transition, while for 32,33Na excited states are reported for the first time. From a comparison to state-of-the-art shell model calculations it is concluded that the newly observed excited state in 31Na belongs to a rotational band formed by a 2p2h intruder configuration within the "Island of Inversion".

nucl-ex↗

arXiv2009

Spin Order and Excitations in Triangular Antiferromagnet La2Ca2MnO7

We report a spin S = 3/2 triangular antiferromagnet with nearest-neighbor coupling J = 0.29 meV in La2Ca2MnO7. A genuinely two-dimensional, three-sublattice order develops below 2.80 K << the Weiss constant (25 K). The spin excitations deviate substantially from linear spin-wave theory, suggesting that magnon breakdown occurs in the material. Such a breakdown has been anticipated in recent theoretical studies, although the excitation spectrum remains to be accounted for.

cond-mat.str-el↗