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Ming Xu

Publications and source records attributed to Ming Xu.

At least 199 records · Page 11Linked to original sources
arXiv2014

Normal homogeneous Finsler spaces

In this paper, we study normal homogeneous Finsler spaces. We first define the notion of a normal homogeneous Finsler space, using the method of isometric submersion of Finsler metrics. Then we study the geometric properties. In particular, we establish a technique to reduce the classification of normal homogeneous Finsler spaces of positive flag curvature to an algebraic problem. The main result of this paper is a classification of positively curved normal homogeneous Finsler spaces. It turns out that a coset space $G/H$ admits a positively curved normal homogeneous Finsler metric if and only if it admits a positively curved normal homogeneous Riemannian metric. We will also give a complete description of the coset spaces admitting non-Riemannian positively curved normal homogeneous Finsler spaces.

math.DG↗
arXiv2014

Adaptive Mesh Representation and Restoration of Biomedical Images

The triangulation of images has become an active research area in recent years for its compressive representation and ease of image processing and visualization. However, little work has been done on how to faithfully recover image intensities from a triangulated mesh of an image, a process also known as image restoration or decoding from meshes. The existing methods such as linear interpolation, least-square interpolation, or interpolation based on radial basis functions (RBFs) work to some extent, but often yield blurred features (edges, corners, etc.). The main reason for this problem is due to the isotropically-defined Euclidean distance that is taken into consideration in these methods, without considering the anisotropicity of feature intensities in an image. Moreover, most existing methods use intensities defined at mesh nodes whose intensities are often ambiguously defined on or near image edges (or feature boundaries). In the current paper, a new method of restoring an image from its triangulation representation is proposed, by utilizing anisotropic radial basis functions (ARBFs). This method considers not only the geometrical (Euclidean) distances but also the local feature orientations (anisotropic intensities). Additionally, this method is based on the intensities of mesh faces instead of mesh nodes and thus provides a more robust restoration. The two strategies together guarantee excellent feature-preserving restoration of an image with arbitrary super-resolutions from its triangulation representation, as demonstrated by various experiments provided in the paper.

cs.CV↗
arXiv2014

The Landsberg equation of a Finsler space

Given a Finsler space, we introduce a system of partial differential equations, called the Landsberg equation. Based on a careful analysis of the Landsberg equation and the observation that the solution space is invariant under the linear isometries of the tangent Minkowski spaces, we prove that an $(α_1, α_2)$-metric of the Landsberg type must be a Berwald metric. This shows that the hunting for a unicorn, one of the longest standing open problem in Finsler geometry, cannot be successful even in the very broad class of $(α_1,α_2)$-metrics.

math.DG↗
arXiv2014

On the Construction of Low-Energy Cislunar and Trans-lunar Transfers Based on the Libration Points

There exist cislunar and trans-lunar libration points near the Moon, which are referred as the LL1 and LL2 points respectively and can generate the different types of low-energy trajectories transferring from Earth to Moon. The time-dependent analytic model including the gravitational forces from the Sun, Earth and Moon is employed to investigate the energy-minimal and practical transfer trajectories. However, different from the circular restricted three-body problem, the equivalent gravitational equilibria are defined according to the geometry of instantaneous Hill's boundary due to the gravitational perturbation from the Sun. The relationship between the altitudes of periapsis and eccentricities is achieved from the Poincaré mapping for all the lunar captured trajectories, which presents the statistical feature of the fuel cost and captured orbital elements rather than generating a specified Moon-captured segment. The minimum energy required by the captured trajectory on a lunar circular orbit is deduced in the spatial bi-circular model. It is presented that the asymptotical behaviors of invariant manifolds approaching to/from the libration points or halo orbits are destroyed by the solar perturbation. In fact, the energy-minimal cislunar transfer trajectory is acquired by transiting LL1 point, while the energy-minimal trans-lunar transfer trajectory is obtained by transiting LL2 point. Finally, the transfer opportunities for the practical trajectories escaped from the Earth and captured by the Moon are yielded by transiting halo orbits near LL1 and LL2 points, which can be used to generate the whole trajectories.

astro-ph.EP↗
arXiv2014

$(α_1,α_2)$-Spaces and Clifford-Wolf Homogeneity

In this paper, we introduce a new type of Finsler metrics, called $(α_1,α_2)$-metrics. We define the notion of the good datum of a homogeneous $(α_1,α_2)$-metric and use that to study the geometric properties. In particular, we give a formula of the S-curvature and deduce a condition for the S-curvature to be vanishing identically. Moreover, we consider the restrictive Clifford-Wolf homogeneity of left invariant $(α_1,α_2)$-metrics on compact connected simple Lie groups. We prove that, in some special cases, a restrictively Clifford-Wolf homogeneous $(α_1,α_2)$-metric must be Riemannian. An unexpected interesting observation contained in the proof reveals the fact that the S-curvature may play an important role in the study of Clifford-Wolf homogeneity in Finsler geometry.

math.DG↗
arXiv2013

Clifford-Wolf homogeneous left invariant $(α,β)$-metrics on compact semi-simple Lie groups

Let $(M,F)$ be a connected Finsler space. An isometry of $(M,F)$ is called a Clifford-Wolf translation (or simply CW-translation) if it moves all points the same distance. The compact Finsler space $(M,F)$ is called restrictively Clifford-Wolf homogeneous (restrictively CW-homogeneous) if for any two sufficiently close points $x_1,x_2\in M$, there exists a CW-translation $σ$ such that $σ(x_1)=x_2$. In this paper, we define the good normalized datum for a homogeneous non-Riemannian $(α,β)$-space, and use it to study the restrictive CW-homogeneity of left invariant $(α,β)$-metrics on a compact connected semisimple Lie group. We prove that a left invariant restrictively CW-homogeneous $(α,β)$-metric on a compact semisimple Lie group must be of the Randers type. This gives a complete classification of left invariant $(α,β)$-metrics on compact semi-simple Lie groups which are restrictively Clifford-Wolf homogeneous.

math.DG↗
arXiv2013

Clifford-Wolf homogeneous Finsler metrics on spheres

An isometry of a Finsler space is called Clifford-Wolf translation (CW-translation) if it moves all points the same distance. A Finsler space $(M, F)$ is called Clifford-Wolf homogeneous (CW-homogeneous) if for any $x, y\in M$ there is a CW-translation $σ$ such that $σ(x)=y$. We prove that if $F$ is a homogeneous Finsler metric on the sphere $S^n$ such that $(S^n, F)$ is CW-homogeneous, then $F$ must be a Randers metric. This gives a complete classification of CW-homogeneous Finsler metrics on spheres.

math.DG↗
arXiv2013

Killing frames and S-curvature of homogeneous Finsler spaces

In this paper, we first deduce a formula of S-curvature of homogeneous Finsler spaces in terms of Killing vector fields. Then we prove that a homogeneous Finsler space has isotropic S-curvature if and only if it has vanishing S-curvature. In the special case that the homogeneous Finsler space is a Randers space, we give an explicit formula which coincides with the previous formula obtained by the second author using other methods.

math.DG↗
arXiv2013

Comparison of Thermal Neutron Detection Efficiency of $^{6}$Li Scintillation Glass and $^{3}$He Gas Proportional Tube

We report on a comparison study of the $^{3}$He gas proportional tube and the $^{6}$Li incorporated scintillation glasses on thermal neutron detection efficiency. Both $^{3}$He and $^{6}$Li are used commonly for thermal neutron detection because of their high neutron capture absorption coefficient. By using a neutron source $^{252}$Cf and a paraffin moderator in an alignment system, we can get a small beam of thermal neutrons. A flash ADC is used to measure the thermal neutron spectrum of each detector, and the detected number of events is determined from the spectrum, then we can calculate the detection efficiency of different detectors. Meanwhile, the experiment have been modeled with GEANT4 to validate the results against the Monte Carlo simulation.

physics.ins-det↗
arXiv2012

Clifford-Wolf homogeneous Randers spaces

A Clifford-Wolf translation of a connected Finsler space is an isometry which moves each point the same distance. A Finsler space $(M, F)$ is called Clifford-Wolf homogeneous if for any two points $x_1, x_2\in M$ there is a Clifford-Wolf translation $ρ$ such that $ρ(x_1)=x_2$. In this paper, we give a complete classification of connected simply connected Clifford-Wolf homogeneous Randers spaces.

math.DG↗
arXiv2012

Clifford-Wolf translations of Homogeneous Randers spheres

In this paper, we study Clifford-Wolf translations of homogeneous Randers metrics on spheres. It turns out that we can present a complete description of all the Clifford-Wolf translations of all the homogeneous Randers metrics on spheres. The most important point of this paper is that a new phenomena surfaces. Namely, we find that there are some CW-homogeneous Randers spaces which are essentially not symmetric. This is a great difference compared to Riemannian geometry, where any CW-homogeneous Riemannian manifold must be locally symmetric.

math.DG↗
arXiv2012

Clifford-Wolf translations of left invariant Randers metrics on compact Lie groups

A Clifford-Wolf translation of a connected Finsler space is an isometry which moves each point the sam distance. A Finsler space $(M, F)$ is called Clifford-Wolf homogeneous if for any two point $x_1, x_2\in M$ there is a Clifford-Wolf translation $ρ$ such that $ρ(x_1)=x_2$. In this paper, we study Clifford-Wolf translations of left invariant Randers metrics on compact Lie groups. The mian result is that a left invariant Randers metric on a connected compact simple Lie group is Clifford-Wolf homogeneous if and only if the indicatrix of the metric is a round sphere with respect to a bi-invariant Riemannian metric. This presents a large number of examples of non-reversible Finsler metrics which are Clifford-Wolf homogeneous.

math.DG↗
arXiv2012

Clifford-Wolf Translations of Finsler spaces

In this paper, we study Clifford-Wolf translations of Finsler spaces. We first give a characterization of Clifford-Wolf translations of Finsler spaces in terms of Killing vector fields. In particular, we show that there is a natural correspondence between Clifford-Wolf translations and the Killing vector fields of constant length. In the special case of homogeneous Randers spaces, we give some explicit sufficient and necessary conditions for an isometry to be a Clifford-Wolf translation. Finally, we construct some explicit examples to explain some of the results of this paper.

math.DG↗
arXiv2010

A High-confidence Cyber-Physical Alarm System: Design and Implementation

Most traditional alarm systems cannot address security threats in a satisfactory manner. To alleviate this problem, we developed a high-confidence cyber-physical alarm system (CPAS), a new kind of alarm systems. This system establishes the connection of the Internet (i.e. TCP/IP) through GPRS/CDMA/3G. It achieves mutual communication control among terminal equipments, human machine interfaces and users by using the existing mobile communication network. The CPAS will enable the transformation in alarm mode from traditional one-way alarm to two-way alarm. The system has been successfully applied in practice. The results show that the CPAS could avoid false alarms and satisfy residents' security needs.

cs.DC↗
arXiv2010

Design and Implementation of a Wireless Sensor Network for Smart Homes

Wireless sensor networks (WSNs) have become indispensable to the realization of smart homes. The objective of this paper is to develop such a WSN that can be used to construct smart home systems. The focus is on the design and implementation of the wireless sensor node and the coordinator based on ZigBee technology. A monitoring system is built by taking advantage of the GPRS network. To support multi-hop communications, an improved routing algorithm based on the Dijkstra algorithm is presented. Preliminary simulations have been conducted to evaluate the performance of the algorithm.

cs.NI↗
arXiv2009

Long-term Continuous Energy Injection in the Afterglow of GRB 060729

A long plateau phase and an amazing brightness have been observed in the Xray afterglow of GRB 060729. This peculiar light curve is likely due to long-term energy injection in external shock. Here we present a detailed numerical study on the energy injection process of magnetic dipole radiation from a strongly magnetized millisecond pulsar and model the multi-band afterglow observations. It is found that this model can successfully explain the long plateaus in the observed X-ray and optical afterglow light curves. The sharp break following the plateaus should be due to the rapid decline of the emission power of the central pulsar. At an even late time (~5*10^6s), an obvious jet break appears, which implies a relatively large half opening angle of theta~0.3 for the GRB ejecta. Due to the energy injection, the Lorentz factor of the outflow is still larger than two 10^7s post the GRB trigger, making the X-ray afterglow of this burst detectable by Chandra even 642 days after the burst.

astro-ph.HE↗
arXiv2009

A model for the optical flares from the Galactic tran-sient SWIFT J195509+261406

The Galactic hard X-ray transient SWIFT J195509+261406 was first observed as a gamma-ray burst GRB 070610. Within 3 days after the burst, more than forty optical flares had been observed. Here we propose that this peculiar event should be associated with a white dwarf. The hard X-ray burst itself may be triggered by the collision between two planets orbiting the white dwarf. Some cracked frag-ments produced in the collision then fall onto the surface of the white dwarf in several days, giving birth to the observed optical flares via cyclotron radiation. Our model can satisfactorily explain the basic features of the observations.

astro-ph.HE↗