Test of conformal gravity with astrophysical observations

Since it can describe the rotation curves of galaxies without dark matter and can give rise to accelerated expansion, conformal gravity attracts much attention recently. As a theory of modified gravity, it is important to test conformal gravity with astrophysical observations. Here we constrain conformal gravity with SNIa and Hubble parameter data and investigate whether it suffers from an age problem with the age of APM~08279+5255. We find conformal gravity can accommodate the age of APM~08279+5255 at 3 $\sigma$ deviation, unlike most of dark energy models which suffer from an age problem.Comment: 6 pages, 2 figure

Disorder Induced Anomalous Hall Effect in Type-I Weyl Metals: Connection between the Kubo-Streda Formula in the Spin and Chiral basis

We study the anomalous Hall effect (AHE) in tilted Weyl metals with Gaussian disorder under the Kubo-Streda formalism in this work. To separate the three different contributions, namely the intrinsic, side jump and skew scattering, it's usually considered necessary to go to the eigenband (chiral) basis of the Kubo-Streda formula. However, it's more straight-forward to compute the total Hall current in the spin basis. For the reason, we develop a systematic and transparent scheme to separate the three different contributions in the spin basis by building a one-to-one correspondence between the Feynmann diagrams of the different contributions in the chiral basis and the products of the symmetric and anti-symmetric part of the polarization operator in the spin basis. We obtain the three contributions of the AHE in type-I Weyl metals with our scheme and compared the difference with the semi-classical Boltzmann equation approach. Our scheme is applicable for general anomalous Hall systems with Gaussian disorder, and is especially useful for anisotropic systems for which both the semi-classical approach and the Kubo-Streda formula in the chiral basis encounter diffculties in computing the disorder induced anomalous Hall effect.Comment: 15 pages, 5figure

The return of river life—Urban river ecosystem restoration based on biodiversity enhancement

Biodiversity is the immune system of river ecological health. Restoration and improvement of urban river biodiversity and return of life to river are the main goals and important tasks of river ecosystem restoration. Taking Wuyuan River located in Xiuying District, Haikou city as the research object, based on the ecological environment and biodiversity background before river restoration, the design technology and practice of Wuyuan River ecosystem restoration were discussed, and four strategies of ecological restoration were put forward: 1) River ecological restoration—Three-dimensional ecological space reconstruction. 2) Riparian ecological restoration—Flexible ecological riparian design. 3) River-wetland synergy—River-wetland complex construction. 4) Multi-functional habitat restoration—Life landscape river reconstruction. Based on the goal of biodiversity improvement, the innovative path and mode of urban river ecosystem restoration were explored from the perspective of life landscape river restoration. Finally, the biodiversity of Wuyuan River after restoration was evaluated. The results showed that the habitat types of Wuyuan River after restoration were diverse, the habitat quality was good, and the improvement effect of biodiversity was obvious. The practice of ecological restoration shows that urban river ecological restoration aimed at the improvement of biodiversity is more conducive to the overall protection of urban river ecosystem and the optimization and improvement of river landscape quality

Passive Radio Frequency-based 3D Indoor Positioning System via Ensemble Learning

Passive radio frequency (PRF)-based indoor positioning systems (IPS) have attracted researchers' attention due to their low price, easy and customizable configuration, and non-invasive design. This paper proposes a PRF-based three-dimensional (3D) indoor positioning system (PIPS), which is able to use signals of opportunity (SoOP) for positioning and also capture a scenario signature. PIPS passively monitors SoOPs containing scenario signatures through a single receiver. Moreover, PIPS leverages the Dynamic Data Driven Applications System (DDDAS) framework to devise and customize the sampling frequency, enabling the system to use the most impacted frequency band as the rated frequency band. Various regression methods within three ensemble learning strategies are used to train and predict the receiver position. The PRF spectrum of 60 positions is collected in the experimental scenario, and three criteria are applied to evaluate the performance of PIPS. Experimental results show that the proposed PIPS possesses the advantages of high accuracy, configurability, and robustness.Comment: DDDAS 202

Developing a Low-Cost Force Treadmill via Dynamic Modeling

By incorporating force transducers into treadmills, force platform-instrumented treadmills (commonly called force treadmills) can collect large amounts of gait data and enable the ground reaction force (GRF) to be calculated. However, the high cost of force treadmills has limited their adoption. This paper proposes a low-cost force treadmill system with force sensors installed underneath a standard exercise treadmill. It identifies and compensates for the force transmission dynamics from the actual GRF applied on the treadmill track surface to the force transmitted to the force sensors underneath the treadmill body. This study also proposes a testing procedure to assess the GRF measurement accuracy of force treadmills. Using this procedure in estimating the GRF of “walk-on-the-spot motion,” it was found that the total harmonic distortion of the tested force treadmill system was about 1.69%, demonstrating the effectiveness of the approach

Assessing Postural Stability Via the Correlation Patterns of Vertical Ground Reaction Force Components

Background Many methods have been proposed to assess the stability of human postural balance by using a force plate. While most of these approaches characterize postural stability by extracting features from the trajectory of the center of pressure (COP), this work develops stability measures derived from components of the ground reaction force (GRF). Methods In comparison with previous GRF-based approaches that extract stability features from the GRF resultant force, this study proposes three feature sets derived from the correlation patterns among the vertical GRF (VGRF) components. The first and second feature sets quantitatively assess the strength and changing speed of the correlation patterns, respectively. The third feature set is used to quantify the stabilizing effect of the GRF coordination patterns on the COP. Results In addition to experimentally demonstrating the reliability of the proposed features, the efficacy of the proposed features has also been tested by using them to classify two age groups (18–24 and 65–73 years) in quiet standing. The experimental results show that the proposed features are considerably more sensitive to aging than one of the most effective conventional COP features and two recently proposed COM features. Conclusions By extracting information from the correlation patterns of the VGRF components, this study proposes three sets of features to assess human postural stability during quiet standing. As demonstrated by the experimental results, the proposed features are not only robust to inter-trial variability but also more accurate than the tested COP and COM features in classifying the older and younger age groups. An additional advantage of the proposed approach is that it reduces the force sensing requirement from 3D to 1D, substantially reducing the cost of the force plate measurement system