52,844 research outputs found
A Survey of Positioning Systems Using Visible LED Lights
© 2018 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.As Global Positioning System (GPS) cannot provide satisfying performance in indoor environments, indoor positioning technology, which utilizes indoor wireless signals instead of GPS signals, has grown rapidly in recent years. Meanwhile, visible light communication (VLC) using light devices such as light emitting diodes (LEDs) has been deemed to be a promising candidate in the heterogeneous wireless networks that may collaborate with radio frequencies (RF) wireless networks. In particular, light-fidelity has a great potential for deployment in future indoor environments because of its high throughput and security advantages. This paper provides a comprehensive study of a novel positioning technology based on visible white LED lights, which has attracted much attention from both academia and industry. The essential characteristics and principles of this system are deeply discussed, and relevant positioning algorithms and designs are classified and elaborated. This paper undertakes a thorough investigation into current LED-based indoor positioning systems and compares their performance through many aspects, such as test environment, accuracy, and cost. It presents indoor hybrid positioning systems among VLC and other systems (e.g., inertial sensors and RF systems). We also review and classify outdoor VLC positioning applications for the first time. Finally, this paper surveys major advances as well as open issues, challenges, and future research directions in VLC positioning systems.Peer reviewe
Synchronization in an array of linearly stochastically coupled networks with time delays
This is the post print version of the article. The official published version can be obtained from the link - Copyright 2007 Elsevier LtdIn this paper, the complete synchronization problem is investigated in an array of linearly stochastically coupled identical networks with time delays. The stochastic coupling term, which can reflect a more realistic dynamical behavior of coupled systems in practice, is introduced to model a coupled system, and the influence from the stochastic noises on the array of coupled delayed neural networks is studied thoroughly. Based on a simple adaptive feedback control scheme and some stochastic analysis techniques, several sufficient conditions are developed to guarantee the synchronization in an array of linearly stochastically coupled neural networks with time delays. Finally, an illustrate example with numerical simulations is exploited to show the effectiveness of the theoretical results.This work was jointly supported by the National Natural Science Foundation of China under Grant 60574043, the Royal Society of the United Kingdom, the Natural Science Foundation of Jiangsu Province of China under Grant BK2006093, and International Joint Project funded by NSFC and the Royal Society of the United Kingdom
Profiles of thermal line emission from advection dominated accretion flows
Recently, Narayan & Raymond (1999) proposed that the thermal emission lines
from the hot plasma in advection dominated accretion flows (ADAFs) are
potentially observable with the next generation of X-ray observatories, with
which the physical properties of some X-ray sources can be probed. In ADAFs,
the temperature of the ion is so high that the thermal broadening of the line
is important. We calculate the profiles of thermal line emission from ADAFs, in
which both the thermal and Doppler broadening have been considered. It is found
that the double-peaked profiles are present for high inclination angles between
the axis of disk and the line of sight. The double-peaked profiles are smeared
in low inclination cases, and completely disappear while the inclination angle
is less than , where the thermal and turbulent broadening dominated
on the line profiles. We also note that the thermal line profile is affected by
the location of the transition radius of ADAF. The self-similar
height-integrated disk structure and the emissivity with power-law dependence
of radius are adopted in our calculations. The results obtained in this work
can be used as a diagnosis on the future X-ray observations of the thermal
lines. Some important physical quantities of ADAFs could be inferred from
future thermal line observations.Comment: 7 page
Numerical simulation of solid tumor blood perfusion and drug delivery during the “vascular normalization window” with antiangiogenic therapy
This Article is provided by the Brunel Open Access Publishing Fund - Copyright @ 2011 Hindawi PublishingTo investigate the influence of vascular normalization on solid tumor blood perfusion and drug delivery, we used the generated blood vessel network for simulations. Considering the hemodynamic parameters changing after antiangiogenic therapies, the results show that the interstitial fluid pressure (IFP) in tumor tissue domain decreases while the pressure gradient increases during the normalization window. The decreased IFP results in more efficient delivery of conventional drugs to the targeted cancer cells. The outcome of therapies will improve if the antiangiogenic therapies and conventional therapies are carefully scheduled
Switching and diffusion models for gene regulation networks
We analyze a hierarchy of three regimes for modeling gene regulation. The most complete model is a continuous time, discrete state space, Markov jump process. An intermediate 'switch plus diffusion' model takes the form of a stochastic differential equation driven by an independent continuous time Markov switch. In the third 'switch plus ODE' model the switch remains but the diffusion is removed. The latter two models allow for multi-scale simulation where, for the sake of computational efficiency, system components are treated differently according to their abundance. The 'switch plus ODE' regime was proposed by Paszek (Modeling stochasticity in gene regulation: characterization in the terms of the underlying distribution function, Bulletin of Mathematical Biology, 2007), who analyzed the steady state behavior, showing that the mean was preserved but the variance only approximated that of the full model. Here, we show that the tools of stochastic calculus can be used to analyze first and second moments for all time. A technical issue to be addressed is that the state space for the discrete-valued switch is infinite. We show that the new 'switch plus diffusion' regime preserves the biologically relevant measures of mean and variance, whereas the 'switch plus ODE' model uniformly underestimates the variance in the protein level. We also show that, for biologically relevant parameters, the transient behaviour can differ significantly from the steady state, justifying our time-dependent analysis. Extra computational results are also given for a protein dimerization model that is beyond the scope of the current analysis
Orbitally-driven Behavior: Mott Transition, Quantum Oscillations and Colossal Magnetoresistance in Bilayered Ca3Ru2O7
We report recent transport and thermodynamic experiments over a wide range of
temperatures for the Mott-like system Ca3Ru2O7 at high magnetic fields, B, up
to 30 T. This work reveals a rich and highly anisotropic phase diagram, where
applying B along the a-, b-, and c-axis leads to vastly different behavior. A
fully spin-polarized state via a first order metamagnetic transition is
obtained for B||a, and colossal magnetoresistance is seen for B||b, and quantum
oscillations in the resistivity are observed for B||c, respectively. The
interplay of the lattice, orbital and spin degrees of freedom are believed to
give rise to this strongly anisotropic behavior.Comment: 26 pages and 8 figure
Multiband effects on the conductivity for a multiband Hubbard model
The newly discovered iron-based superconductors have attracted lots of
interests, and the corresponding theoretical studies suggest that the system
should have six bands. In this paper, we study the multiband effects on the
conductivity based on the exact solutions of one-dimensional two-band Hubbard
model. We find that the orbital degree of freedom might enhance the critical
value of on-site interaction of the transition from a metal to an
insulator. This observation is helpful to understand why undoped High-
superconductors are usually insulators, while recently discovered iron-based
superconductors are metal. Our results imply that the orbital degree of freedom
in the latter cases might play an essential role.Comment: 4 pages, 5 figure
Recommended from our members
On the exceptional damage-tolerance of gradient metallic materials
An experimental study is described on the fracture toughness and micro-mechanisms associated with the initiation and propagation of cracks in metallic nickel containing marked gradients in grain size, ranging from ∼30 nm to ∼4 μm. Specifically, cracks are grown in a gradient structured (GS) nickel with grain-size gradient ranging from the coarse macro-scale to nano-scale (CG → NG) and vice versa (NG → CG), with the measured crack-resistance R-curves compared to the corresponding behavior in uniform nano-grained (NG) and coarse-grained (CG) materials. It is found that the gradient structures display a much-improved combination of high strength and toughness compared to uniform grain-sized materials. However, based on J-integral measurements in the gradient materials, the crack-initiation toughness is far higher for cracks grown in the direction of the coarse-to-nano grained gradient than vice versa, a result which we ascribe primarily to excessive crack-tip blunting in the coarse-grained microstructure. Both gradient structures, however, display marked rising R-curve behavior with exceptional crack-growth toughnesses exceeding 200 MPa.m½
- …