arXiv subjects

Jun Luo

Publications and source records attributed to Jun Luo.

At least 235 records · Page 13Linked to original sources

arXiv2018

Skyline Diagram: Efficient Space Partitioning for Skyline Queries

Skyline queries are important in many application domains. In this paper, we propose a novel structure Skyline Diagram, which given a set of points, partitions the plane into a set of regions, referred to as skyline polyominos. All query points in the same skyline polyomino have the same skyline query results. Similar to $k^{th}$-order Voronoi diagram commonly used to facilitate $k$ nearest neighbor ($k$NN) queries, skyline diagram can be used to facilitate skyline queries and many other applications. However, it may be computationally expensive to build the skyline diagram. By exploiting some interesting properties of skyline, we present several efficient algorithms for building the diagram with respect to three kinds of skyline queries, quadrant, global, and dynamic skylines. In addition, we propose an approximate skyline diagram which can significantly reduce the space cost. Experimental results on both real and synthetic datasets show that our algorithms are efficient and scalable.

cs.DB↗

arXiv2018

A Core Decomposition of Compact Sets in the Plane

A Peano continuum means a locally connected continuum. A compact metric space is called a \emph{Peano compactum} if all its components are Peano continua and if for any constant $C>0$ all but finitely many of its components are of diameter less than $C$. Given a compact set $K\subset\mathbb{C}$, there usually exist several upper semi-continuous decompositions of $K$ into subcontinua such that the quotient space, equipped with the quotient topology, is a Peano compactum. We prove that one of these decompositions is finer than all the others and call it the \emph{core decomposition of $K$ with Peano quotient}. This core decomposition gives rise to a metrizable quotient space, called the Peano model of $K$, which is shown to be determined by the topology of $K$ and hence independent of the embedding of $K$ into $\mathbb{C}$. We also construct a concrete continuum $K\subset\mathbb{R}^3$ such that the core decomposition of $K$ with Peano quotient does not exist. For specific choices of $K\subset\mathbb{C}$, the above mentioned core decomposition coincides with two models obtained recently, namely the locally connected model for unshielded planar continua (like connected Julia sets of polynomials) and the finitely Suslinian model for unshielded planar compact sets (like polynomial Julia sets that may not be connected). The study of such a core decomposition provides partial answers to several questions posed by Curry in 2010. These questions are motivated by other works, including those by Curry and his coauthors, that aim at understanding the dynamics of a rational map $f: \hat{\mathbb{C}}\rightarrow\hat{\mathbb{C}}$ restricted to its Julia set.

math.DS↗

arXiv2018

A Stackelberg Game Approach Towards Socially-Aware Incentive Mechanisms for Mobile Crowdsensing (Online report)

Mobile crowdsensing has shown a great potential to address large-scale data sensing problems by allocating sensing tasks to pervasive mobile users. The mobile users will participate in a crowdsensing platform if they can receive satisfactory reward. In this paper, to effectively and efficiently recruit sufficient number of mobile users, i.e., participants, we investigate an optimal incentive mechanism of a crowdsensing service provider. We apply a two-stage Stackelberg game to analyze the participation level of the mobile users and the optimal incentive mechanism of the crowdsensing service provider using backward induction. In order to motivate the participants, the incentive is designed by taking into account the social network effects from the underlying mobile social domain. For example, in a crowdsensing-based road traffic information sharing application, a user can get a better and accurate traffic report if more users join and share their road information. We derive the analytical expressions for the discriminatory incentive as well as the uniform incentive mechanisms. To fit into practical scenarios, we further formulate a Bayesian Stackelberg game with incomplete information to analyze the interaction between the crowdsensing service provider and mobile users, where the social structure information (the social network effects) is uncertain. The existence and uniqueness of the Bayesian Stackelberg equilibrium are validated by identifying the best response strategies of the mobile users. Numerical results corroborate the fact that the network effects tremendously stimulate higher mobile participation level and greater revenue of the crowdsensing service provider. In addition, the social structure information helps the crowdsensing service provider to achieve greater revenue gain.

cs.GT↗

arXiv2018

Eclipse: Practicability Beyond kNN and Skyline

The $k$ nearest neighbor ($k$NN) query is a fundamental problem in databases. Given a set of multidimensional data points and a query point, $k$NN returns the $k$ nearest neighbors based on a scoring function such as weighted sum given an attribute weight vector. However, the attribute weight vector can be difficult to specify in practice. Skyline returns the points including all possible nearest neighbors without requiring the exact attribute weight vector or a scoring function but the number of returned points can be prohibitively large for practical use. In this paper, we propose a novel \emph{eclipse} definition which provides a more flexible and customizable definition than the classic $1$NN and skyline. In eclipse, users can specify a range of attribute weights and control the number of returned points. We show that both $1$NN and skyline are instantiations of eclipse. To compute eclipse points, we propose a baseline algorithm with time complexity of $O(n^22^{d-1})$, and an improved $O(n\log ^{d-1}n)$ time transformation-based algorithm by transforming the eclipse problem to the skyline problem, where $n$ is the number of points and $d$ is the number of dimensions. Furthermore, we propose a novel index-based algorithm utilizing duality transform with much better efficiency. The experimental results on the real NBA dataset and the synthetic datasets demonstrate the effectiveness and efficiency of our eclipse algorithms.

cs.DB↗

arXiv2018

A Novel Method for Extrinsic Calibration of Multiple RGB-D Cameras Using Descriptor-Based Patterns

This letter presents a novel method to estimate the relative poses between RGB-D cameras with minimal overlapping fields of view in a panoramic RGB-D camera system. This calibration problem is relevant to applications such as indoor 3D mapping and robot navigation that can benefit from a 360$^\circ$ field of view using RGB-D cameras. The proposed approach relies on descriptor-based patterns to provide well-matched 2D keypoints in the case of a minimal overlapping field of view between cameras. Integrating the matched 2D keypoints with corresponding depth values, a set of 3D matched keypoints are constructed to calibrate multiple RGB-D cameras. Experiments validated the accuracy and efficiency of the proposed calibration approach, both superior to those of existing methods (800 ms vs. 5 seconds; rotation error of 0.56 degrees vs. 1.6 degrees; and translation error of 1.80 cm vs. 2.5 cm.

eess.IV↗

arXiv2018

A Socially-Aware Incentive Mechanism for Mobile Crowdsensing Service Market

Mobile Crowdsensing has shown a great potential to address large-scale problems by allocating sensing tasks to pervasive Mobile Users (MUs). The MUs will participate in a Crowdsensing platform if they can receive satisfactory reward. In this paper, in order to effectively and efficiently recruit sufficient MUs, i.e., participants, we investigate an optimal reward mechanism of the monopoly Crowdsensing Service Provider (CSP). We model the rewarding and participating as a two-stage game, and analyze the MUs' participation level and the CSP's optimal reward mechanism using backward induction. At the same time, the reward is designed taking the underlying social network effects amid the mobile social network into account, for motivating the participants. Namely, one MU will obtain additional benefits from information contributed or shared by local neighbours in social networks. We derive the analytical expressions for the discriminatory reward as well as uniform reward with complete information, and approximations of reward incentive with incomplete information. Performance evaluation reveals that the network effects tremendously stimulate higher mobile participation level and greater revenue of the CSP. In addition, the discriminatory reward enables the CSP to extract greater surplus from this Crowdsensing service market.

cs.GT↗

arXiv2018

Ricci-flat graphs with girth four

Lin-Lu-Yau introduced an interesting notion of Ricci curvature for graphs and obtained a complete characterization for all Ricci-flat graphs with girth at least five [1]. In this paper, we propose a concrete approach to construct an infinite family of distinct Ricci-flat graphs of girth four with edge-disjoint 4-cycles and completely characterize all Ricci-flat graphs of girth four with vertex-disjoint 4-cycles.

math.CO↗

arXiv2018

Competition effects of multiple quantum paths in an atom interferometer

We present an observation of competition effect among multiple quantum paths in a Raman-type Mach-Zehnder atom interferometer. By measuring the contrast of interference fringes, the competition effect among multiple interference paths is experimentally investigated. Due to the phase competition, the contrast periodically oscillates when modulating either the phase or the interrogation time between Raman pulses. The multiple quantum paths form because of the imperfect population transfer efficiency in stimulated Raman transitions, and are verified by modulating the duration of Raman pulses. The contrast could be optimized by suppressing the phase competition.

physics.atom-ph↗

arXiv2018

Construction of all-in-focus images assisted by depth sensing

Multi-focus image fusion is a technique for obtaining an all-in-focus image in which all objects are in focus to extend the limited depth of field (DoF) of an imaging system. Different from traditional RGB-based methods, this paper presents a new multi-focus image fusion method assisted by depth sensing. In this work, a depth sensor is used together with a color camera to capture images of a scene. A graph-based segmentation algorithm is used to segment the depth map from the depth sensor, and the segmented regions are used to guide a focus algorithm to locate in-focus image blocks from among multi-focus source images to construct the reference all-in-focus image. Five test scenes and six evaluation metrics were used to compare the proposed method and representative state-of-the-art algorithms. Experimental results quantitatively demonstrate that this method outperforms existing methods in both speed and quality (in terms of comprehensive fusion metrics). The generated images can potentially be used as reference all-in-focus images.

cs.CV↗

arXiv2018

Structural phase transition, precursory electronic anomaly and strong-coupling superconductivity in quasi-skutterudite (Sr$_{1-x}$Ca$_{x}$)$_{3}$Ir$_{4}$Sn$_{13}$ and Ca$_{3}$Rh$_{4}$Sn$_{13}$

The interplay between superconductivity and structural phase transition has attracted enormous interests in recent years. For example, in Fe-pnictide high temperature superconductors, quantum fluctuations in association with structural phase transition have been proposed to lead to many novel physical properties and even the superconductivity itself. Here we report a finding that the quasi-skutterudite superconductors (Sr$_{1-x}$Ca$_{x}$)$_{3}$Ir$_{4}$Sn$_{13}$ ($x$ = 0, 0.5, 1) and Ca$_{3}$Rh$_{4}$Sn$_{13}$ show some unusual properties similar to the Fe-pnictides, through $^{119}$Sn nuclear magnetic resonance (NMR) measurements. In (Sr$_{1-x}$Ca$_{x}$)$_{3}$Ir$_{4}$Sn$_{13}$, the NMR linewidth increases below a temperature $T^*$ that is higher than the structural phase transition temperature $T_{\rm s}$. The spin-lattice relaxation rate ($1/T_1$) divided by temperature ($T$), $1/T_1T$, and the Knight shift $K$ increase with decreasing $T$ down to $T^*$, but start to decrease below $T^*$ and followed by more distinct changes at $T_{\rm s}$. In contrast, none of the anomalies was observed in Ca$_{3}$Rh$_{4}$Sn$_{13}$ that does not undergo a structural phase transition. The precursory phenomenon above structural phase transition resembles that occurs in Fe-pnictides. In the superconducting state of Ca$_{3}$Ir$_{4}$Sn$_{13}$, $1/T_{1}$ decays as ${\rm exp}(-Δ/k_{\rm B}T)$ with a large gap $Δ= 2.21 k_{\rm B}T_{\rm c}$, yet without a Hebel-Slichter coherence peak, which indicate strong-coupling superconductivity. Our results provide new insight into the relationship between superconductivity and the electronic-structure change associated with structural phase transition.

cond-mat.supr-con↗

arXiv2018

Peano Model for Planar Compacta and a Lemma by Beardon

It is known that, among all the monotone decompositions of a planar compact set K with Peano hyperspaces, there exists a unique one that is finer than all the others. We call it the "core decomposition" of K with Peano hyperspace. The resulted hyperspace under quotient topology will be referred to as the "Peano model" for K. We show that the core decomposition is independent of the embedding of K into the plane. Given a rational function f with degree at least 2 that is independent of K. A well known result by Beardon says that the pre-image for any element d of the core decomposition has finitely many components, each of which is mapped by f onto d. We show that those components belong to the core decomposition of L, the pre-image of K under the above mentioned rational map f. This provides an affirmative answer to Question 5.4 proposed by Curry (MR2642461) and extends earlier partial results by Blokh-Curry-Oversteegen (MR2737795 and MR3008890), when K is assumed to be unshielded and the rational map f is assumed to be a polynomial, under which K is completely invariant. The previous result is also connected with a well known Factor Theorem developed by Whyburn. We also introduce a lambda function from K to the set of non-negative integers, such that this function is constantly zero if and only if K is a Peano space. This function and its maximum are topologically invariant, while its level set at zero is of particular interest. For instance, when K is the Mandelbrot set we find close relations between the level set at zero and the hyperbolic components. Further discussions on the lambda function can be expected.

math.DS↗

arXiv2018

Every component of a fractal square is a Peano continuum

This paper concerns the local connectedness of components of self-similar sets. Given an equal partition of the unit square into n*n small squares, we may choose arbitrarily two or more of them and form an iterated function system. The attractor F resulted from this IFS is called a fractal square. We prove that every component of F is locally connected. The same result for three-dimensional analogues of F does not hold.

math.GN↗

arXiv2017

Calibration of atomic trajectories in a large-area dual-atom-interferometer gyroscope

We propose and demonstrate a method for calibrating atomic trajectories in a large-area dual-atom-interferometer gyroscope. The atom trajectories are monitored by modulating and delaying the Raman transition, and they are precisely calibrated by controlling the laser orientation and the bias magnetic field. To improve the immunity to the gravity effect and the common phase noise, the symmetry and the overlapping of two large-area atomic interference loops are optimized by calibrating the atomic trajectories and by aligning the Raman-laser orientations. The dual-atom-interferometer gyroscope is applied in the measurement of the Earth rotation. The sensitivity is $1.2\times10^{-6}$ rad/s/$\sqrt{Hz}$, and the long-term stability is $6.2\times10^{-8}$ rad/s $@$ $2000$ s.

physics.atom-ph↗

arXiv2017

Effect of aging and Mn substitution on anisotropy of third generation piezoelectrics

We predict a new candidate high-temperature high-pressure structure of FeSiO$_3$ with space-group symmetry Cmmm by applying an evolutionary algorithm within DFT+U that we call post-perovskite II (PPv-II). An exhaustive search found no other competitive candidate structures with ABO$_3$ composition. We compared the X-ray diffraction (XRD) pattern of FeSiO$_3$ PPv-II with experimental results of the recently reported "H-phase" of (Fe,Mg)SiO$_3$. The intensities and positions of two main X-ray diffraction peaks of PPv-II FeSiO$_3$ compare well with those of the H-phase. We also calculated the static equation of state, the enthalpy and the bulk modulus of the PPv-II phase and compared it with those of perovskite (Pv) and post-perovskite (PPv) phases of FeSiO$_3$. According to the static DFT+U computations the PPv-II phase of FeSiO$_3$ is less stable than Pv and PPv phases under lower mantle pressure conditions at T=0 K and has a higher volume. PPv-II may be entropically stabilized, and may be a stable phase in Earth's lower mantle, coexisting with {α-PbO$_2$ (Columbite-structure) silica and perovskite, or with magnesiowustite and/or ferropericlase, depending on bulk composition.

cond-mat.mtrl-sci↗

arXiv2017

Fibers and local connectedness of planar continua

We describe non-locally connected planar continua via the concepts of fiber and numerical scale. Given a continuum $X\subset\mathbb{C}$ and $x\in\partial X$, we show that the set of points $y\in \partial X$ that cannot be separated from $x$ by any finite set $C\subset \partial X$ is a continuum. This continuum is called the {\em modified fiber} $F_x^*$ of $X$ at $x$. If $x\in X^o$, we set $F^*_x=\{x\}$. For $x\in X$, we show that $F_x^*=\{x\}$ implies that $X$ is locally connected at $x$. We also give a concrete planar continuum $X$, which is locally connected at a point $x\in X$ while the fiber $F_x^*$ is not trivial. The scale $\ell^*(X)$ of non-local connectedness is then the least integer $p$ (or $\infty$ if such an integer does not exist) such that for each $x\in X$ there exist $k\le p+1$ subcontinua $$X=N_0\supset N_1\supset N_2\supset\cdots\supset N_{k}=\{x\}$$ such that $N_{i}$ is a fiber of $N_{i-1}$ for $1\le i\le k$. If $X\subset\mathbb{C}$ is an unshielded continuum or a continuum whose complement has finitely many components, we obtain that local connectedness of $X$ is equivalent to the statement $\ell^*(X)=0$. We discuss the relation of our concepts to the works of Schleicher (1999) and Kiwi (2004). We further define an equivalence relation $\sim$ based on the fibers and show that the quotient space $X/\sim$ is a locally connected continuum. For connected Julia sets of polynomials and more generally for unshielded continua, we obtain that every prime end impression is contained in a fiber. Finally, we apply our results to examples from the literature and construct for each $n\ge1$ concrete examples of path connected continua $X_n$ with $\ell^*(X_n)=n$.

math.GN↗

arXiv2016

Measurable signatures of quantum mechanics in a classical spacetime

We propose an optomechanics experiment that can search for signatures of a fundamentally classical theory of gravity and in particular of the many-body Schroedinger-Newton (SN) equation, which governs the evolution of a crystal under a self-gravitational field. The SN equation predicts that the dynamics of a macroscopic mechanical oscillator's center of mass wavefunction differ from the predictions of standard quantum mechanics. This difference is largest for low-frequency oscillators, and for materials, such as Tungsten or Osmium, with small quantum fluctuations of the constituent atoms around their lattice equilibrium sites. Light probes the motion of these oscillators and is eventually measured in order to extract valuable information on the pendulum's dynamics. Due to the non-linearity contained in the SN equation, we analyze the fluctuations of measurement results differently than standard quantum mechanics. We revisit how to model a thermal bath, and the wavefunction collapse postulate, resulting in two prescriptions for analyzing the quantum measurement of the light. We demonstrate that both predict features, in the outgoing light's phase fluctuations' spectrum, which are separate from classical thermal fluctuations and quantum shot noise, and which can be clearly resolved with state of the art technology.

quant-ph↗

arXiv2016

Enhanced sensitivity to Lorentz invariance violations in short-range gravity experiments

Recently, first limits on putative Lorentz invariance violation coefficients in the pure gravity sector were determined by the reanalysis of short-range gravity experiments. Such experiments search for new physics at sidereal frequencies. They are not, however, designed to optimize the signal strength of a Lorentz invariance violation force; in fact the Lorentz violating signal is suppressed in the planar test mass geometry employed in those experiments. We describe a short-range torsion pendulum experiment with enhanced sensitivity to possible Lorentz violating signals. A periodic, striped test mass geometry is used to augment the signal. Careful arrangement of the phases of the striped patterns on opposite ends of the pendulum further enhances the signal while simultaneously suppressing the Newtonian background.

gr-qc↗

arXiv2016

Combined search for Lorentz violation in short-range gravity

Short-range experiments testing the gravitational inverse-square law at the submillimeter scale offer uniquely sensitive probes of Lorentz invariance. A combined analysis of results from the short-range gravity experiments HUST-2015, HUST-2011, IU-2012, and IU-2002 permits the first independent measurements of the 14 nonrelativistic coefficients for Lorentz violation in the pure-gravity sector at the level of $10^{-9}$ m$^2$, improving by an order of magnitude the sensitivity to numerous types of Lorentz violation involving quadratic curvature derivatives and curvature couplings.

gr-qc↗