Testing cosmic opacity from SNe Ia and Hubble parameter through three cosmological-model-independent methods

We use the newly published 28 observational Hubble parameter data ($H(z)$) and current largest SNe Ia samples (Union2.1) to test whether the universe is transparent. Three cosmological-model-independent methods (nearby SNe Ia method, interpolation method and smoothing method) are proposed through comparing opacity-free distance modulus from Hubble parameter data and opacity-dependent distance modulus from SNe Ia . Two parameterizations, $\tau(z)=2\epsilon z$ and $\tau(z)=(1+z)^{2\epsilon}-1$ are adopted for the optical depth associated to the cosmic absorption. We find that the results are not sensitive to the methods and parameterizations. Our results support a transparent universe.Comment: 11 pages, 8 figures, 1 table, PLB(in press

Temporal similarity metrics for latent network reconstruction: The role of time-lag decay

When investigating the spreading of a piece of information or the diffusion of an innovation, we often lack information on the underlying propagation network. Reconstructing the hidden propagation paths based on the observed diffusion process is a challenging problem which has recently attracted attention from diverse research fields. To address this reconstruction problem, based on static similarity metrics commonly used in the link prediction literature, we introduce new node-node temporal similarity metrics. The new metrics take as input the time-series of multiple independent spreading processes, based on the hypothesis that two nodes are more likely to be connected if they were often infected at similar points in time. This hypothesis is implemented by introducing a time-lag function which penalizes distant infection times. We find that the choice of this time-lag strongly affects the metrics' reconstruction accuracy, depending on the network's clustering coefficient and we provide an extensive comparative analysis of static and temporal similarity metrics for network reconstruction. Our findings shed new light on the notion of similarity between pairs of nodes in complex networks

Optical and Gamma-Ray Variability Behaviors of 3C 454.3 from 2006 to 2011

We present our photometric monitoring of a flat spectrum radio quasar (FSRQ) 3C 454.3 at Yunnan observatories from 2006 to 2011. We find that the optical color of 3C 454.3 shows obvious redder-when-brighter trend, which reaches a saturation stage when the source is brighter than 15.15 mag at V band. We perform a simulation with multiple values of disk luminosity and spectral index to reproduce the magnitude-color diagram. The results show that the contamination caused by the disk radiation alone is difficult to produce the observed color variability. The variability properties during the outburst in December 2009 are also compared with $\gamma$-ray data derived from Fermi $\gamma$-ray space telescope. The flux variation of these two bands follow a linear relation with $F_{\gamma} \propto F_R^{1.14\pm0.07}$, which provides an observational evidence for external Compton process in 3C 454.3. Meanwhile, this flux correlation indicates that electron injection is the main mechanism for variability origin. We also explore the variation of the flux ratio $F_{\gamma}/F_R$ and the detailed structures in the lightcurves, and discuss some possible origins for the detailed variability behaviors.Comment: accepted for publication in The Astrophysical Journal, 5 figures, 2 table

HIP-KNEE control for gait assistance with Powered Knee Orthosis

A Powered Knee Orthosis (PKO) was developed for the elderly and patients with disordered gait to regain normal walking. In order to enhance the PKO performance and reduce system complexity especially for people with muscle weakness in their knee joints, an algorithm named HIP-KNEE control is proposed. This algorithm is based on the analysis of kinematic gait model, and the desired knee joint angle (KNEE) is estimated from the measurements of hip joint angle (HIP). The relationship between HIP and KNEE is modeled as a polynomial, which can be easily implemented to an embedded controller for real-time control. This control method is suitable to subjects with good function in hip joint, and it can provide help in walking without special training. An Inertia Measurement Units (IMU) is used for obtaining HIP input, and integrated with a footswitch for checking the heel condition; the gait assistance performance can be further improved

Experimental studies on kinematics and kinetics of walking with an assistive knee brace

Assistive knee brace is a species of wearable lower extremity exoskeletons. Such assistive equipment can enhance people's strength and provide desired locomotion to have advantages over wheelchairs, which are commonly used for patients with mobility disorders. However, the integration between the assistive knee brace and the user is challenging as inaccurate alignments may adversely affect the biomechanics of the knee joint. The goal of this study is to evaluate the changes between normal walking and walking with an assistive knee brace in "off" mode. The assistive knee brace was developed by integrating a multifunctional actuator with a custom-made knee-ankle-foot orthosis in order to minimize excessive shifting and to improve alignment to the knee joint. Spatial and temporal gait parameters, joint kinematics and joint kinetics parameters were compared. In general, the observed results showed that most of the gait parameters were not affected when walking with the knee brace. The only significant differences were found in knee flexion and knee rotational motions. These results indicated that walking with the developed knee brace provided minimal hindrance to the user and assured that assistive torque can be applied to the knee joint

Gait analysis for designing a new assistive knee brace

Assistive knee brace is a species of wearable lower extremity exoskeletons. In this research, an assistive knee brace was developed by integrating a multifunctional actuator with a custom-made knee-ankle-foot orthosis. In the study, the location of the actuator is moved up to the lateral side of the hip, instead of knee joint. Waist belt and shoulder belt are appended on the knee brace. This paper aimed to improve the design of the assistive knee braces through gait analysis. By walking with the knee braces, the spatial and temporal gait parameters, joint kinematics and joint kinetics parameters were evaluated, and the changes from normal walking were compared as well. The experimental results showed that walking with the developed knee brace provided minimal hindrance to the wearer. © 2011 IEEE