arXiv subjects

Kai Zhao

Publications and source records attributed to Kai Zhao.

230 records · Page 13Linked to original sources

arXiv2016

Object Skeleton Extraction in Natural Images by Fusing Scale-associated Deep Side Outputs

Object skeleton is a useful cue for object detection, complementary to the object contour, as it provides a structural representation to describe the relationship among object parts. While object skeleton extraction in natural images is a very challenging problem, as it requires the extractor to be able to capture both local and global image context to determine the intrinsic scale of each skeleton pixel. Existing methods rely on per-pixel based multi-scale feature computation, which results in difficult modeling and high time consumption. In this paper, we present a fully convolutional network with multiple scale-associated side outputs to address this problem. By observing the relationship between the receptive field sizes of the sequential stages in the network and the skeleton scales they can capture, we introduce a scale-associated side output to each stage. We impose supervision to different stages by guiding the scale-associated side outputs toward groundtruth skeletons of different scales. The responses of the multiple scale-associated side outputs are then fused in a scale-specific way to localize skeleton pixels with multiple scales effectively. Our method achieves promising results on two skeleton extraction datasets, and significantly outperforms other competitors.

cs.CV↗

arXiv2016

Automatic City Region Analysis for Urban Routing

There are different functional regions in cities such as tourist attractions, shopping centers, workplaces and residential places. The human mobility patterns for different functional regions are different, e.g., people usually go to work during daytime on weekdays, and visit shopping centers after work. In this paper, we analyse urban human mobility patterns and infer the functions of the regions in three cities. The analysis is based on three large taxi GPS datasets in Rome, San Francisco and Beijing containing 21 million, 11 million and 17 million GPS points respectively. We categorized the city regions into four kinds of places, workplaces, entertainment places, residential places and other places. First, we provide a new quad-tree region division method based on the taxi visits. Second, we use the association rule to infer the functional regions in these three cities according to temporal human mobility patterns. Third, we show that these identified functional regions can help us deliver data in network applications, such as urban Delay Tolerant Networks (DTNs), more efficiently. The new functional-regions-based DTNs algorithm achieves up to 183% improvement in terms of delivery ratio.

cs.SI↗

arXiv2015

Correlations between the fragmentation modes and light charged particles emission in heavy ion collisions

The correlations between the shape of rapidity distribution of the yield of light charged particles and the fragmentation modes in semi-peripheral collisions for $^{70}$Zn+$^{70}$Zn, $^{64}$Zn+$^{64}$Zn and $^{64}$Ni+$^{64}$Ni at the beam energy of 35MeV/nucleon are investigated based on ImQMD05 code. Our studies show there is an interplay between the binary, ternary and multi-fragmentation break-up modes. The binary and ternary break-up modes more prefer to emit light charged particles at middle rapidity and give larger values of $R_{yield}^{mid}$ compared with the multi-fragmentation break-up mode does. The reduced rapidity distribution for the normalized yields of p, d, t, $^3$He, $^4$He and $^6$He and the corresponding values of $R_{yield}^{mid}$ can be used to estimate the probability of multi-fragmentation break-up modes. By comparing to experimental data, our results illustrate that $\ge$40\% of the collisions events belong to the multi-fragmentation break-up mode for the reactions we studied.

nucl-th↗

arXiv2015

Fusion and quasi-fission dynamics in nearly-symmetric reactions

Some nearly-symmetric fusion reactions are systematically investigated with the improved quantum molecular dynamics (ImQMD) model. By introducing two-body inelastic scattering in the Fermi constraint procedure, the stability of an individual nucleus and the description of fusion cross sections at energies near the Coulomb barrier can be further improved. Simultaneously, the quasi-fission process in $^{154}$Sm+$^{160}$Gd is also investigated with the microscopic dynamics model for the first time. We find that at energies above the Bass barrier, the fusion probability is smaller than $10^{-5}$ for this reaction, and the nuclear contact-time is generally smaller than $1500$ fm/c. From the central collisions of Sm+Gd, the neutron-rich fragments such as $^{164,165}$Gd, $^{192}$W can be produced in the ImQMD simulations, which implies that the quasi-fission reaction could be an alternative way to synthesize new neutron-rich heavy nuclei.

nucl-th↗

arXiv2015

Macroscopic and direct light propulsion of bulk graphene material

It has been a great challenge to achieve the direct light manipulation of matter on a bulk scale. In this work, the direct light propulsion of matter was observed on a macroscopic scale for the first time using a bulk graphene based material. The unique structure and properties of graphene and the morphology of the bulk graphene material make it capable of not only absorbing light at various wavelengths but also emitting energetic electrons efficiently enough to drive the bulk material following Newtonian mechanics. Thus, the unique photonic and electronic properties of individual graphene sheets are manifested in the response of the bulk state. These results offer an exciting opportunity to bring about bulk scale light manipulation with the potential to realize long-sought proposals in areas such as the solar sail and space transportation driven directly by sunlight.

physics.optics↗

arXiv2015

Explaining the Power-law Distribution of Human Mobility Through Transportation Modality Decomposition

Human mobility has been empirically observed to exhibit Levy flight characteristics and behaviour with power-law distributed jump size. The fundamental mechanisms behind this behaviour has not yet been fully explained. In this paper, we analyze urban human mobility and we propose to explain the Levy walk behaviour observed in human mobility patterns by decomposing them into different classes according to the different transportation modes, such as Walk/Run, Bicycle, Train/Subway or Car/Taxi/Bus. Our analysis is based on two real-life GPS datasets containing approximately 10 and 20 million GPS samples with transportation mode information. We show that human mobility can be modelled as a mixture of different transportation modes, and that these single movement patterns can be approximated by a lognormal distribution rather than a power-law distribution. Then, we demonstrate that the mixture of the decomposed lognormal flight distributions associated with each modality is a power-law distribution, providing an explanation to the emergence of Levy Walk patterns that characterize human mobility patterns.

physics.soc-ph↗

arXiv2014

Type-Driven Incremental Semantic Parsing with Polymorphism

Semantic parsing has made significant progress, but most current semantic parsers are extremely slow (CKY-based) and rather primitive in representation. We introduce three new techniques to tackle these problems. First, we design the first linear-time incremental shift-reduce-style semantic parsing algorithm which is more efficient than conventional cubic-time bottom-up semantic parsers. Second, our parser, being type-driven instead of syntax-driven, uses type-checking to decide the direction of reduction, which eliminates the need for a syntactic grammar such as CCG. Third, to fully exploit the power of type-driven semantic parsing beyond simple types (such as entities and truth values), we borrow from programming language theory the concepts of subtype polymorphism and parametric polymorphism to enrich the type system in order to better guide the parsing. Our system learns very accurate parses in GeoQuery, Jobs and Atis domains.

cs.CL↗

arXiv2014

Systematic study of 16O-induced fusions with the improved quantum molecular dynamics model

The heavy-ion fusion reactions with 16O bombarding on 62Ni, 65Cu, 74Ge, 148Nd, 180Hf, 186W, 208Pb, 238U are systematically investigated with the improved quantum molecular dynamics (ImQMD) model. The fusion cross sections at energies near and above the Coulomb barriers can be reasonably well reproduced by using this semi-classical microscopic transport model with the parameter sets SkP* and IQ3a. The dynamical nucleus-nucleus potentials and the influence of Fermi constraint on the fusion process are also studied simultaneously. In addition to the mean field, the Fermi constraint also plays a key role for the reliable description of fusion process and for improving the stability of fragments in heavy-ion collisions.

nucl-th↗

arXiv2013

n+1 Dimensional Gravity duals to quantum criticalities with spontaneous symmetry breaking

We reexamine the charged AdS domain wall solution to the Einstein-Abelian-Higgs model proposed by Gubser et al as holographic superconductors at quantum critical points and comment on their statement about the uniqueness of gravity solutions. We generalize their explorations from 3+1 dimensions to arbitrary $n+1$Ds and find that the $n+1\geqslant5$D charged AdS domain walls are unstable against electric perturbations.

hep-th↗

arXiv2010

A UI Design Case Study and a Prototype of a Travel Search Engine

We review a case study of a UI design project for a complete travel search engine system prototype for regular and corporate users. We discuss various usage scenarios, guidelines, and so for, and put them into a web-based prototype with screenshots and the like. We combined into our prototype the best features found at the time (2002) on most travel-like sites and added more to them as a part of our research. We conducted feasibility studies, review common design guidelines and Nelson's heuristics while constructing this work. The prototype is itself open-source, but has no backend functionality, as the focus is the user-centered design of such a system. While the prototype is mostly static, some dynamic activity is present through the use of PHP.

cs.SE↗

arXiv2009

The Study of Mass Distribution of products in 7.0 AMeV U238+U238 Collisions

Within the Improved Quantum Molecular Dynamics (ImQMD) Model incorporating the statistical decay Model, the reactions of U238+U238 at the energy of 7.0 AMeV have been studied. The charge, mass and excitation energy distributions of primary fragments are investigated within the ImQMD model and de-excitation processes of those primary fragments are described by the statistical decay model. The mass distribution of the final products in U238+U238 collisions is obtained and compared with the recent experimental data.

nucl-th↗

arXiv2009

Mass parameters for relative and neck collective motions in heavy ion fusion reactions

Mass parameters for the relative and neck motions in fusion reactions of symmetric systems $^{90}$Zr+$^{90}$Zr, $^{110}$Pd+$^{110}$Pd, and $^{138}$Ba+$^{138}$Ba are studied by means of a microscopic transport model. The shape of the nuclear system is determined by an equi-density surface obtained from the density distribution of the system. The relative and neck motions are then studied and the mass parameters for these two motions are deduced. The mass parameter for the relative motion is around the reduced mass when the reaction partners are at the separated configuration and increases with decrease of the distance between two reaction partners after the touching configuration. The mass parameter for the neck motion first decreases slightly up to the touching configuration and then increases with the neck width, and its magnitude is from less than tenth to several times more than the total mass of the system. The mass parameters obtained from the microscopic transport model are larger than the ones obtained from the hydrodynamic model and smaller than those obtained from the linear response function theory. The mass parameters for both motions depend on the reaction systems, but the one for the relative motion depends on the incompressibility of the EoS more obviously than that for neck motion.

nucl-th↗

arXiv2007

Fusion-fission reactions with modified Woods-Saxon potential

A modified Woods-Saxon potential model is proposed for a unified description of the entrance channel fusion barrier and the fission barrier of fusion-fission reactions based on the Skyrme energy-density functional approach. The fusion excitation functions of 120 reactions have been systematically studied. The fusion (capture) cross sections are well described with the calculated potential and an empirical barrier distribution. Incorporating a statistical model (HIVAP code) for describing the decay of the compound nucleus, the evaporation residue (and fission) cross sections of 51 fusion-fission reactions have been systematically investigated. Optimal values of some key parameters of the HIVAP code are obtained based on the experimental data of these reactions. The experimental data are reasonably well reproduced by the calculated results. The upper and lower confidence limits of the systematic errors of the calculated results are given.

nucl-th↗

arXiv2005

Commutators of integral operators with variable kernels on Hardy spaces

Let $\T (0\leq α<n)$ be the singular and fractional integrals with variable kernel $Ω(x,z)$, and $[b,\T]$ be the commutator generated by $\T$ and a Lipschitz function $b$. In this paper, the authors study the boundedness of $[b,\T]$ on the Hardy spaces, under some assumptions such as the $L^r$-Dini condition. Similar results and the weak type estimates at the end-point cases are also given for the homogeneous convolution operators $\tT (0\leq α<n)$. The smoothness conditions imposed on $\tOmega$ are weaker than the corresponding known results.

math.CA↗