arXiv subjects

Rui Li

Publications and source records attributed to Rui Li.

At least 523 records · Page 29Linked to original sources

arXiv2018

Structural and magnetic properties of CeZnAl$_3$ single crystals

We have synthesized single crystals of CeZnAl$_3$, which is a new member of the family of the Ce-based intermetallics Ce$TX_3$ ($T$ = transition metal, $X$= Si, Ge, Al), crystallizing in the non-centrosymmetric tetragonal BaNiSn$_3$-type structure. Magnetization, specific heat and resistivity measurements all show that CeZnAl$_3$ orders magnetically below around 4.4 K. Furthermore, magnetization measurements exhibit a hysteresis loop at low temperatures and fields, indicating the presence of a ferromagnetic component in the magnetic state. This points to a different nature of the magnetism in CeZnAl$_3$ compared to the other isostructural Ce$T$Al$_3$ compounds. Resistivity measurements under pressures up to 1.8 GPa show a moderate suppression of the ordering temperature with pressure, suggesting that measurements to higher pressures are required to look for quantum critical behavior.

cond-mat.str-el↗

arXiv2018

The discrepancy between Einstein mass and dynamical mass for SIS and power-law mass models

We investigate the discrepancy between the two-dimensional projected lensing mass and the dynam- ical mass for an ensemble of 97 strong gravitational lensing systems discovered by the Sloan Lens ACS (SLACS) Survey, the BOSS Emission-Line Lens Survey (BELLS), and the BELLS for GALaxy-Lyα EmitteR sYs- tems (BELLS GALLERY) Survey. We fit the lensing data to obtain the Einstein mass, and use the velocity dispersion of the lensing galaxies provided by the Sloan Digital Sky Survey (SDSS) to get the projected dynamical mass within the Einstein radius by assuming the power-law mass approximation. The discrepancy is found to be obvious and quantified by Bayesian analysis. For the singular isothermal sphere (SIS) mass model, we obtain that the Einstein mass is 20.7% more than the dynamical mass, and the discrepancy increases with the redshift of the lensing galaxies. For more general power-law mass model, the discrepancy still exists within 1σ credible region. The main reason of the the discrepancy could be mass contamination, including all invisible masses along the line of sight. In addition, the measurement errors and the approximation of the mass models could lead to part of the discrepancy.

astro-ph.GA↗

arXiv2018

Energy spectrum, the spin polarization, and the optical selection rules of the Kronig-Penney superlattice model with spin-orbit coupling

The Kronig-Penney model, an exactly solvable one-dimensional model of crystal in solid physics, shows how the allowed and forbidden bands are formed in solids. In this paper, we study this model in the presence of both strong spin-orbit coupling and the Zeeman field. We analytically obtain four transcendental equations that represent an implicit relation between the energy and the Bloch wavevector. Solving these four transcendental equations, we obtain the spin-orbital bands exactly. In addition to the usual band gap opened at the boundary of the Brillouin zone, a much larger spin-orbital band gap is also opened at some special sites inside the Brillouin zone. The $x$-component of the spin-polarization vector is an even function of the Bloch wavevector, while the $z$-component of the spin-polarization vector is an odd function of the Bloch wavevector. At the band edges, the optical transition rates between adjacent bands are nonzero.

cond-mat.mes-hall↗

arXiv2017

Paving the Way to Smart Micro Energy Internet: Concepts, Design Principles, and Engineering Practices

The energy internet is one of the most promising future energy infrastructures that could both enhance energy efficiency and improve its operating flexibility. Analogous to the micro-grid, the micro energy internet emphasizes the distribution level and demand side. This paper proposes concepts and design principles of a smart micro energy internet for accommodating micro-grids, distributed poly-generation systems, energy storage facilities, and associated energy distribution infrastructures. Since the dispatch and control system of the smart micro energy internet is responsible for external disturbances, it should be able to approach a satisfactory operating point while supporting multiple criteria, such as safety, economy, and environmental protection. To realize the vision of a smart micro energy internet, an engineering game theory based energy management system with self-approaching-optimum capability is investigated. Based on the proposed concepts, design principles, and energy management system, this paper presents a prototype of China's first conceptual solar-based smart micro energy internet, established in Qinghai University.

math.OC↗

arXiv2017

An perturbation-iteration method for multi-peak solitons in nonlocal nonlinear media

An perturbation-iteration method is developed for the computation of the Hermite-Gaussian-like solitons with arbitrary peak numbers in nonlocal nonlinear media. This method is based on the perturbed model of the Schrödinger equation for the harmonic oscillator, in which the minimum perturbation is obtained by the iteration. This method takes a few tens of iteration loops to achieve enough high accuracy, and the initial condition is fixed to the Hermite-Gaussian function. The method we developed might also be extended to the numerical integration of the Schrödinger equations in any type of potentials.

physics.optics↗

arXiv2017

A novel energy-based phase field model for ferrodroplet deformation and breakup in a uniform magnetic field

In this paper, we propose a novel, thermodynamically consistent phase field model to simulate the deformation and breakup of a ferrodroplet that is immersed in a viscous medium and subject to an applied uniform magnetic field. Instead of using the magnetic body force in the traditional Rosensweig model, the key idea of this model is to propose a new magnetic energy that enables direct effects of the magnetic field on the interface evolution. The model can thereby be derived from the variational principle via minimizing the free energy of the total system. This energy based modeling idea can be easily extended to include more external fields in a convenient and consistent way for more complicated applications involving multiple external fields. We validate the model by performing a series of numerical simulations, including the comparison with analytic solutions, the investigation of the effect of different types of magnetic fields, the dynamical behaviors of the ferrodroplet breakup under the strong magnetic field, magnetic/velocity/pressure field distributions, the magnetic energy density, and the inertial phenomenon, etc.

physics.flu-dyn↗

arXiv2017

Laboratory Investigations of Titan Haze Formation: In Situ Measurement of Gas and Particle Composition

Prior to the arrival of Cassini-Huygens, aerosol production in Titan's atmosphere was believed to begin in the stratosphere where chemical processes are predominantly initiated by FUV radiation. However, measurements taken by Cassini UVIS and CAPS indicate that haze formation initiates in the thermosphere where there is a greater flux of EUV photons and energetic particles available to initiate chemical reactions, including the destruction of N2. The discovery of previously unpredicted nitrogen species in Titan's atmosphere by Cassini INMS indicates that nitrogen participates in the chemistry to a much greater extent than was appreciated before Cassini. The degree of nitrogen in the haze is important for understanding the diversity of molecules present in Titan's atmosphere and on its surface. We have conducted a series of simulation experiments using either spark discharge or FUV photons to initiate chemistry in CH4/N2 gas mixtures (0.01% CH4/99.99% N2 to 10% CH4/90% N2). We obtained in situ real-time measurements using an HR-ToF-AMS to measure the particle composition as a function of particle size and a PIT-MS to measure the composition of gas phase products. These two techniques allow us to investigate the effect of energy source and initial CH4 concentration on the degree of nitrogen incorporation in both the gas and solid phase products. The results presented here confirm that FUV photons produce not only solid phase nitrogen bearing products but also gas phase nitrogen species. We find that in both the gas and solid phase, nitrogen is found in nitriles rather than amines and both the gas phase and solid phase products are composed primarily of molecules with a low degree of aromaticity. The UV experiments reproduce the absolute abundances measured in Titan's stratosphere for a number of gas phase species including C4H2, C6H6, HCN, CH3CN, HC3N, and C2H5CN. [Edited for length]

astro-ph.EP↗

arXiv2017

Finite-size corrections to quantized particle transport in topological charge pumps

We investigate the quantization of adiabatic charge transport in the insulating ground state of finite systems. Topological charge pumps are used in experiments as an indicator of topological order. In the thermodynamic limit the transport can be related to a topological Berry phase and is thus strictly quantized. This is no longer true for finite systems. We derive finite-size corrections to the transport both for non-interacting and interacting systems and relate them to analytic properties of the single- and many-body Berry curvature. We find that they depend on the details of experimental realizations of the pumps. While they can be non-negligible even in large systems, a proper choice of the pumping protocol can suppress these corrections.

cond-mat.quant-gas↗

arXiv2017

More on products of Baire spaces

New results on the Baire product problem are presented. It is shown that an arbitrary product of almost locally ccc Baire spaces is Baire; moreover, the product of a Baire space and a 1st countable space which is $β$-unfavorable in the strong Choquet game is Baire.

math.GN↗

arXiv2017

Approximate Quantum Adders with Genetic Algorithms: An IBM Quantum Experience

It has been proven that quantum adders are forbidden by the laws of quantum mechanics. We analyze theoretical proposals for the implementation of approximate quantum adders and optimize them by means of genetic algorithms, improving previous protocols in terms of efficiency and fidelity. Furthermore, we experimentally realize a suitable approximate quantum adder with the cloud quantum computing facilities provided by IBM Quantum Experience. The development of approximate quantum adders enhances the toolbox of quantum information protocols, paving the way for novel applications in quantum technologies.

quant-ph↗

arXiv2017

Preference-driven Similarity Join

Similarity join, which can find similar objects (e.g., products, names, addresses) across different sources, is powerful in dealing with variety in big data, especially web data. Threshold-driven similarity join, which has been extensively studied in the past, assumes that a user is able to specify a similarity threshold, and then focuses on how to efficiently return the object pairs whose similarities pass the threshold. We argue that the assumption about a well set similarity threshold may not be valid for two reasons. The optimal thresholds for different similarity join tasks may vary a lot. Moreover, the end-to-end time spent on similarity join is likely to be dominated by a back-and-forth threshold-tuning process. In response, we propose preference-driven similarity join. The key idea is to provide several result-set preferences, rather than a range of thresholds, for a user to choose from. Intuitively, a result-set preference can be considered as an objective function to capture a user's preference on a similarity join result. Once a preference is chosen, we automatically compute the similarity join result optimizing the preference objective. As the proof of concept, we devise two useful preferences and propose a novel preference-driven similarity join framework coupled with effective optimization techniques. Our approaches are evaluated on four real-world web datasets from a diverse range of application scenarios. The experiments show that preference-driven similarity join can achieve high-quality results without a tedious threshold-tuning process.

cs.DB↗

arXiv2017

Exploring the Brown Dwarf Desert: New Substellar Companions from the SDSS-III MARVELS Survey

Planet searches using the radial velocity technique show a paucity of companions to solar-type stars within ~5 AU in the mass range of ~10 - 80 M$_{\text{Jup}}$. This deficit, known as the brown dwarf desert, currently has no conclusive explanation. New substellar companions in this region help asses the reality of the desert and provide insight to the formation and evolution of these objects. Here we present 10 new brown dwarf and two low-mass stellar companion candidates around solar-type stars from the Multi-object APO Radial-Velocity Exoplanet Large-Area Survey (MARVELS) of the Sloan Digital Sky Survey III (SDSS-III). These companions were selected from processed MARVELS data using the latest University of Florida Two Dimensional (UF2D) pipeline, which shows significant improvement and reduction of systematic errors over previous pipelines. The 10 brown dwarf companions range in mass from ~13 to 76 M$_{\text{Jup}}$ and have orbital radii of less than 1 AU. The two stellar companions have minimum masses of ~98 and 100 M$_{\text{Jup}}$. The host stars of the MARVELS brown dwarf sample have a mean metallicity of [Fe/H] = 0.03 $\pm$ 0.08 dex. Given our stellar sample we estimate the brown dwarf occurrence rate around solar-type stars with periods less than ~300 days to be ~0.56%.

astro-ph.SR↗

arXiv2016

Very Low-Mass Stellar and Substellar Companions to Solar-like Stars From MARVELS VI: A Giant Planet and a Brown Dwarf Candidate in a Close Binary System HD 87646

We report the detections of a giant planet (MARVELS-7b) and a brown dwarf candidate (MARVELS-7c) around the primary star in the close binary system, HD 87646. It is the first close binary system with more than one substellar circum-primary companion discovered to the best of our knowledge. The detection of this giant planet was accomplished using the first multi-object Doppler instrument (KeckET) at the Sloan Digital Sky Survey (SDSS) telescope. Subsequent radial velocity observations using ET at Kitt Peak National Observatory, HRS at HET, the "Classic" spectrograph at the Automatic Spectroscopic Telescope at Fairborn Observatory, and MARVELS from SDSS-III confirmed this giant planet discovery and revealed the existence of a long-period brown dwarf in this binary. HD 87646 is a close binary with a separation of $\sim22$ AU between the two stars, estimated using the Hipparcos catalogue and our newly acquired AO image from PALAO on the 200-inch Hale Telescope at Palomar. The primary star in the binary, HD 87646A, has Teff = 5770$\pm$80K, log(g)=4.1$\pm$0.1 and [Fe/H] = $-0.17\pm0.08$. The derived minimum masses of the two substellar companions of HD 87646A are 12.4$\pm$0.7M$_{\rm Jup}$ and 57.0$\pm3.7$M$_{\rm Jup}$. The periods are 13.481$\pm$0.001 days and 674$\pm$4 days and the measured eccentricities are 0.05$\pm$0.02 and 0.50$\pm$0.02 respectively. Our dynamical simulations show the system is stable if the binary orbit has a large semi-major axis and a low eccentricity, which can be verified with future astrometry observations.

astro-ph.EP↗

arXiv2016

Patch-based Texture Synthesis for Image Inpainting

Image inpaiting is an important task in image processing and vision. In this paper, we develop a general method for patch-based image inpainting by synthesizing new textures from existing one. A novel framework is introduced to find several optimal candidate patches and generate a new texture patch in the process. We form it as an optimization problem that identifies the potential patches for synthesis from an coarse-to-fine manner. We use the texture descriptor as a clue in searching for matching patches from the known region. To ensure the structure faithful to the original image, a geometric constraint metric is formally defined that is applied directly to the patch synthesis procedure. We extensively conducted our experiments on a wide range of testing images on various scenarios and contents by arbitrarily specifying the target the regions for inference followed by using existing evaluation metrics to verify its texture coherency and structural consistency. Our results demonstrate the high accuracy and desirable output that can be potentially used for numerous applications: object removal, background subtraction, and image retrieval.

cs.CV↗

arXiv2016

Hyperfine interaction mediated electric-dipole spin resonance: the role of frequency modulation

The electron spin in a semiconductor quantum dot can be coherently controlled by an external electric field, an effect called electric-dipole spin resonance (EDSR). Several mechanisms can give rise to the EDSR effect, among which there is a hyperfine mechanism, where the spin-electric coupling is mediated by the electron-nucleus hyperfine interaction. Here, we investigate the influence of frequency modulation (FM) on the spin-flip efficiency. Our results reveal that FM plays an important role in the hyperfine mechanism. Without FM, the electric field almost cannot flip the electron spin; the spin-flip probability is only about 20%. While under FM, the spin-flip probability can be improved to approximately 70%. In particular, we find that the modulation amplitude has a lower bound, which is related to the width of the fluctuated hyperfine field.

cond-mat.mes-hall↗

arXiv2016

Skolem Sequence Based Self-adaptive Broadcast Protocol in Cognitive Radio Networks

The base station (BS) in a multi-channel cognitive radio (CR) network has to broadcast to secondary (or unlicensed) receivers/users on more than one broadcast channels via channel hopping (CH), because a single broadcast channel can be reclaimed by the primary (or licensed) user, leading to broadcast failures. Meanwhile, a secondary receiver needs to synchronize its clock with the BS's clock to avoid broadcast failures caused by the possible clock drift between the CH sequences of the secondary receiver and the BS. In this paper, we propose a CH-based broadcast protocol called SASS, which enables a BS to successfully broadcast to secondary receivers over multiple broadcast channels via channel hopping. Specifically, the CH sequences are constructed on basis of a mathematical construct---the Self-Adaptive Skolem sequence. Moreover, each secondary receiver under SASS is able to adaptively synchronize its clock with that of the BS without any information exchanges, regardless of any amount of clock drift.

cs.NI↗

arXiv2015

Survival analysis, the infinite Gaussian mixture model, FDG-PET and non-imaging data in the prediction of progression from mild cognitive impairment

We present a method to discover interesting brain regions in [18F] fluorodeoxyglucose positron emission tomography (PET) scans, showing also the benefits when PET scans are in combined use with non-imaging variables. The discriminative brain regions facilitate a better understanding of Alzheimer's disease (AD) progression, and they can also be used for predicting conversion from mild cognitive impairment (MCI) to AD. A survival analysis(Cox regression) and infinite Gaussian mixture model (IGMM) are introduced to identify the informative brain regions, which can be further used to make a prediction of conversion (in two years) from MCI to AD using only the baseline PET scan. Further, the predictive accuracy can be enhanced when non-imaging variables are used together with identified informative brain voxels. The results suggest that PET scan imaging data is more predictive than other non-imaging data, revealing even better performance when both imaging and non-imaging data are combined.

q-bio.NC↗

arXiv2015

An exactly solvable model for a strongly spin-orbit-coupled nanowire quantum dot

In the presence of spin-orbit coupling, quantum models for semiconductor materials are generally not exactly solvable. As a result, understanding of the strong spin-orbit coupling effects in these systems remains poor. Here we develop an analytical method to solve the one-dimensional hard-wall quantum dot problem in the presence of strong spin-orbit coupling and magnetic field, which allows us to obtain exact eigenenergies and eigenstates of a single electron. With the help of the exact solution, we demonstrate some unique effects from the strong spin-orbit coupling in a semiconductor quantum dot, in particular the anisotropy of the electron g-factor and its tunability.

cond-mat.mes-hall↗