587 research outputs found
Control Of Nonh=holonomic Systems
Many real-world electrical and mechanical systems have velocity-dependent constraints in their dynamic models. For example, car-like robots, unmanned aerial vehicles, autonomous underwater vehicles and hopping robots, etc. Most of these systems can be transformed into a chained form, which is considered as a canonical form of these nonholonomic systems. Hence, study of chained systems ensure their wide applicability. This thesis studied the problem of continuous feed-back control of the chained systems while pursuing inverse optimality and exponential convergence rates, as well as the feed-back stabilization problem under input saturation constraints. These studies are based on global singularity-free state transformations and controls are synthesized from resulting linear systems. Then, the application of optimal motion planning and dynamic tracking control of nonholonomic autonomous underwater vehicles is considered. The obtained trajectories satisfy the boundary conditions and the vehicles\u27 kinematic model, hence it is smooth and feasible. A collision avoidance criteria is set up to handle the dynamic environments. The resulting controls are in closed forms and suitable for real-time implementations. Further, dynamic tracking controls are developed through the Lyapunov second method and back-stepping technique based on a NPS AUV II model. In what follows, the application of cooperative surveillance and formation control of a group of nonholonomic robots is investigated. A designing scheme is proposed to achieves a rigid formation along a circular trajectory or any arbitrary trajectories. The controllers are decentralized and are able to avoid internal and external collisions. Computer simulations are provided to verify the effectiveness of these designs
Traveling Waves of Modified Leslie-Gower Predator-prey Systems
The spreading phenomena in modified Leslie-Gower reaction-diffusion
predator-prey systems are the topic of this paper. We mainly study the
existence of two different types of traveling waves. Be specific, with the aid
of the upper and lower solutions method, we establish the existence of
traveling wave connecting the prey-present state and the coexistence state or
the prey-present state and the prey-free state by constructing different and
appropriate Lyapunov functions. Moreover, for traveling wave connecting the
prey-present state and the prey-free state, we gain more monotonicity
information on wave profile based on the asymptotic behavior at negative
infinite. Finally, our results are applied to modified Leslie-Gower system with
Holling II type or Lotka-Volterra type, and then a novel Lyapunov function is
constructed for the latter, which further enhances our results. Meanwhile, some
numerical simulations are carried to support our results
A sufficient condition on successful invasion by the predator
In this paper, we provide a sufficient condition on successful invasion by
the predator. Specially, we obtain the persistence of traveling wave solutions
of predator-prey system, in which the predator can survive without the
predation of the prey. This proof heavily depends on comparison principle of
scalar monostable equation, the rescaling method and phase-plane analysis
Traveling Wave in a Ratio-dependent Holling-Tanner System with Nonlocal Diffusion and Strong Allee Effect
In this paper, a ratio-dependent Holling-Tanner system with nonlocal
diffusion is taken into account, where the prey is subject to a strong Allee
effect. To be special, by applying Schauder's fixed point theorem and iterative
technique, we provide a general theory on the existence of traveling waves for
such system. Then appropriate upper and lower solutions and a novel sequence,
similar to squeeze method, are constructed to demonstrate the existence of
traveling waves for c>c*. Moreover, the existence of traveling wave for c=c* is
also established by spreading speed theory and comparison principle. Finally,
the nonexistence of traveling waves for c<c* is investigated, and the minimal
wave speed then is determined
A Novel Genetic Variant in Long Non-coding RNA Gene NEXN-AS1 is Associated with Risk of Lung Cancer
Lung cancer etiology is multifactorial, and growing evidence has indicated that long non-coding RNAs (lncRNAs) are important players in lung carcinogenesis. We performed a large-scale meta-analysis of690,564 SNPs in 15,531 autosomal lncRNAs by using datasets from six previously published genome-wideassociation studies (GWASs) from the Transdisciplinary Research in Cancer of the Lung (TRICL) consortiumin populations of European ancestry. Previously unreported significant SNPs (P value \u3c 1 × 10−7) were further validated in two additional independent lung cancer GWAS datasets from Harvard University anddeCODE. In the final meta-analysis of all eight GWAS datasets with 17,153 cases and 239,337 controls, a novel risk SNP rs114020893 in the lncRNA NEXN-AS1 region at 1p31.1 remained statistically significant(odds ratio = 1.17; 95% confidence interval = 1.11–1.24; P = 8.31 × 10−9). In further in silico analysis,rs114020893 was predicted to change the secondary structure of the lncRNA. Our finding indicates that SNP rs114020893 of NEXN-AS1 at 1p31.1 may contribute to lung cancer susceptibility
Swing surfaces and holographic entanglement beyond AdS/CFT
We propose a holographic entanglement entropy prescription for general states
and regions in two models of holography beyond AdS/CFT known as flat/BMSFT
and (W)AdS/WCFT. Flat/BMSFT is a candidate of holography for
asymptotically flat three-dimensional spacetimes, while (W)AdS/WCFT is
relevant in the study of black holes in the real world. In particular, the
boundary theories are examples of quantum field theories that feature an
infinite dimensional symmetry group but break Lorentz invariance. Our
holographic entanglement entropy proposal is given by the area of a swing
surface that consists of ropes, which are null geodesics emanating from the
entangling surface at the boundary, and a bench, which is a spacelike geodesic
connecting the ropes. The proposal is supported by an extension of the
Lewkowycz-Maldacena argument, reproduces previous results based on the Rindler
method, and satisfies the first law of entanglement entropy.Comment: 45 pages, 4 figures; v2: corrected typos and added comments on strong
subadditivity, matches published versio
Beam Squint Assisted User Localization in Near-Field Integrated Sensing and Communications Systems
Integrated sensing and communication (ISAC) has been regarded as a key
technology for 6G wireless communications, in which large-scale multiple input
and multiple output (MIMO) array with higher and wider frequency bands will be
adopted. However, recent studies show that the beam squint phenomenon can not
be ignored in wideband MIMO system, which generally deteriorates the
communications performance. In this paper, we find that with the aid of
true-time-delay lines (TTDs), the range and trajectory of the beam squint in
near-field communications systems can be freely controlled, and hence it is
possible to reversely utilize the beam squint for user localization. We derive
the trajectory equation for near-field beam squint points and design a way to
control such trajectory. With the proposed design, beamforming from different
subcarriers would purposely point to different angles and different distances,
such that users from different positions would receive the maximum power at
different subcarriers. Hence, one can simply localize multiple users from the
beam squint effect in frequency domain, and thus reduce the beam sweeping
overhead as compared to the conventional time domain beam search based
approach. Furthermore, we utilize the phase difference of the maximum power
subcarriers received by the user at different frequencies in several times beam
sweeping to obtain a more accurate distance estimation result, ultimately
realizing high accuracy and low beam sweeping overhead user localization.
Simulation results demonstrate the effectiveness of the proposed schemes.Comment: This paper has been accepted by IEEE Transactions on Wireless
Communications (TWC) on 18 September 202
Modular Hamiltonians in flat holography and (W)AdS/WCFT
We study several aspects of holographic entanglement in two models known as
flat/BMSFT and (W)AdS/WCFT. These are two examples of holography beyond
AdS/CFT where the the boundary field theories are not Lorentz invariant but
still feature an infinite set of local symmetries. In the first example,
BMS-invariant field theories (BMSFTs) are conjectured to provide a holographic
description of quantum gravity in asymptotically flat three-dimensional
spacetimes; while in the second example, warped conformal field theories
(WCFTs) are proposed to describe quantum gravity in warped AdS or AdS
backgrounds with Dirichlet-Neumann boundary conditions. In particular, we
derive the modular Hamiltonian for single intervals in both BMSFTs and WCFTs
and find the holographic duals in the bulk using the covariant formulation of
gravitational charges. We also extend the first law of entanglement entropy to
these models of non-AdS holography and discuss the bound on "modular chaos"
introduced recently in the context of the AdS/CFT correspondence.Comment: 46 pages, 3 figures; v2: corrected typos, matches published versio
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