Research on Bending Fatigue Properties of Reinforced Macadam Foundation

Existing macadam base structures have poor resistance to bending deformation of pavement. The structural layer is challenged with serious cracking due to the long-term dynamic loads. Despite these issues, however, studies on reinforcement techniques for macadam base structure have been scarce. No reasonable and feasible method on how to improve the bending resistance of flexible base structures (e.g. macadam base structure) and prolong their bending fatigue life has yet been reported. Thus, this study proposed a method for reinforcing macadam base structures with geogrids to strengthen bending performance, anti-fatigue performance and dynamic stability of flexible base structures under different loading levels. The reinforced macadam base structure was investigated through a laboratory test of flexural-tensile strength and a three-point fatigue bending test. A cyclic loading test of reinforced and non-reinforced girder specimens was carried out under five stress levels. The effect of such a new reinforcement method in improving the bending fatigue properties of macadam base structures was analyzed by comparing the yield curves and fatigue lives of reinforced and non-reinforced specimens under different loading levels. Results demonstrate that the non-reinforced macadam base has poor bending resistance. The yield curve and fatigue life of non-reinforced specimens attenuated quickly as it approached the ultimate loading level. Non-reinforced specimens have low-cycle fatigue failures when the loads reach the 0.8 stress level and the ultimate displacement at failure is relatively small, accompanied by obvious failure surface. After geogrids are added, the fatigue life of specimens improved significantly. The yield curve shows no significant attenuation at a high loading level. The reinforced specimens can still maintain high-cycle fatigue failure under the 0.8 stress level and avoid the occurrence of low-cycle fatigue failures. Moreover, reinforced specimens can inhibit transmission of reflection cracks at midspan of cement-stabilized macadam base, delay the propagation of oblique shearing fractures close to the support, and strengthen the dynamic stability and durability of pavement structure with a macadam base. The conclusions of this study provide theoretical references to practical engineering applications of such new reinforcement technology for macadam bases

Discrete Element Simulation of Bending Deformation of Geogrid-Reinforced Macadam Base

The pavement bending deformation resistance of the existing macadam base structure is poor. The geogrid-reinforced macadam base can effectively strengthen the bending resistance of the pavement, but no international consensus has been reached at present over bending failure laws of reinforced macadam base structure. Discrete element models of semi-rigid base pavement structure, macadam base pavement structure, and geogrid-reinforced macadam base pavement structure were built based on MATDEM discrete element simulation program; loading calculation of the three models was conducted by taking their centers as loading positions; and model displacement nephogram, strain nephogram, and effects of different spans on their bending deformation were analyzed to reveal bending failure laws of reinforced macadam base and improvement effect of the geogrid on the anti-bending performance of the macadam structural layer. Finally, bending deformation laws of the three pavement structures and improvement effect of geogrid reinforcement on bending properties of the macadam base structure were established. The results show that under bending deformation of semi-rigid base, the vertical strain at the contract surface between the baseplate and soil base and horizontal strain at midspan position reach the maximum, which can easily lead to fracture and shear failure, and the macadam base layer can effectively isolate the tensile strain transmitted from bottom up. Through their own deformation, grids can transform surface pressure load into frictional resistance at the geogrid/soil interface and partial kinetic energy in the system into their own elastic potential energy to reduce the kinetic energy at the subbase layer. Geogrid reinforcement can improve the nonlinearity of macadam materials, reduce the fluctuation amplitude of the strain curve and displacement curve, lengthen the service life of the macadam base pavement structure, and improve its structural soundness under bending deformation. This study can provide a theoretical reference for numerical simulation of bending failure of geogrid-reinforced macadam base

Neuronal Circuitry Mechanisms Regulating Adult Mammalian Neurogenesis

The adult mammalian brain is a dynamic structure, capable of remodeling in response to various physiological and pathological stimuli. One dramatic example of brain plasticity is the birth and subsequent integration of newborn neurons into the existing circuitry. This process, termed adult neurogenesis, recapitulates neural developmental events in two specialized adult brain regions: the lateral ventricles of the forebrain. Recent studies have begun to delineate how the existing neuronal circuits influence the dynamic process of adult neurogenesis, from activation of quiescent neural stem cells (NSCs) to the integration and survival of newborn neurons. Here, we review recent progress toward understanding the circuit-based regulation of adult neurogenesis in the hippocampus and olfactory bulb

Molecular genetic analysis of FGFR1 signalling reveals distinct roles of MAPK and PLCγ1 activation for self-renewal of adult neural stem cells

<p>Abstract</p> <p>Background</p> <p>Neural stem cells (NSCs) are present in the adult mammalian brain and sustain life-long adult neurogenesis in the dentate gyrus of the hippocampus. In culture, fibroblast growth factor-2 (FGF-2) is sufficient to maintain the self-renewal of adult NSCs derived from the adult rat hippocampus. The underlying signalling mechanism is not fully understood.</p> <p>Results</p> <p>In the established adult rat NSC culture, FGF-2 promotes self-renewal by increasing proliferation and inhibiting spontaneous differentiation of adult NSCs, accompanied with activation of MAPK and PLC pathways. Using a molecular genetic approach, we demonstrate that activation of FGF receptor 1 (FGFR1), largely through two key cytoplasmic amino acid residues that are linked to MAPK and PLC activation, suffices to promote adult NSC self-renewal. The canonical MAPK, Erk1/2 activation, is both required and sufficient for the NSC expansion and anti-differentiation effects of FGF-2. In contrast, PLC activation is integral to the maintenance of adult NSC characteristics, including the full capacity for neuronal and oligodendroglial differentiation.</p> <p>Conclusion</p> <p>These studies reveal two amino acid residues in FGFR1 with linked downstream intracellular signal transduction pathways that are essential for maintaining adult NSC self-renewal. The findings provide novel insights into the molecular mechanism regulating adult NSC self-renewal, and pose implications for using these cells in potential therapeutic applications.</p

Analytical and computational method of structure-borne noise and shock resistance of gear system

An approach to synthetically evaluate structure-borne noise and shock resistance of gear system is proposed. Firstly, dynamic finite element mesh model of gear system which includes shafts, bearings, gears and housing is established by using spring element, tetrahedral element and hexahedral element. Then dynamic finite element analysis model of gear system is gotten by loading the dynamic excitation force which can be calculated via the computation program of gear pair stiffness excitation, error excitation and impact excitation onto the tooth meshing line as boundary conditions. And the dynamic response of gear system is analyzed by using modal superposition method, and the vibration response experimental study of gear system is performed on the gearbox test-bed. The comparative analysis shows that computational results of the vibration response are in good agreement with the data of experiment tests and it could verify the rationality of dynamic finite element mesh model of gear system. Finally, taking acceleration shock excitation load into account on the basis of the dynamic finite element mesh model, the impact response of gear system is solved, and the shock resistance is analyzed based on the strength decision criterion

Radial glial cells in the adult dentate gyrus : What are they and where do they come from?

Peer reviewedPublisher PD

Causal-Based Supervision of Attention in Graph Neural Network: A Better and Simpler Choice towards Powerful Attention

Recent years have witnessed the great potential of attention mechanism in graph representation learning. However, while variants of attention-based GNNs are setting new benchmarks for numerous real-world datasets, recent works have pointed out that their induced attentions are less robust and generalizable against noisy graphs due to lack of direct supervision. In this paper, we present a new framework which utilizes the tool of causality to provide a powerful supervision signal for the learning process of attention functions. Specifically, we estimate the direct causal effect of attention to the final prediction, and then maximize such effect to guide attention attending to more meaningful neighbors. Our method can serve as a plug-and-play module for any canonical attention-based GNNs in an end-to-end fashion. Extensive experiments on a wide range of benchmark datasets illustrated that, by directly supervising attention functions, the model is able to converge faster with a clearer decision boundary, and thus yields better performances

Model Order Reduction of Aeroservoelastic Model of Flexible Aircraft

This paper presents a holistic model order reduction (MOR) methodology and framework that integrates key technological elements of sequential model reduction, consistent model representation, and model interpolation for constructing high-quality linear parameter-varying (LPV) aeroservoelastic (ASE) reduced order models (ROMs) of flexible aircraft. The sequential MOR encapsulates a suite of reduction techniques, such as truncation and residualization, modal reduction, and balanced realization and truncation to achieve optimal ROMs at grid points across the flight envelope. The consistence in state representation among local ROMs is obtained by the novel method of common subspace reprojection. Model interpolation is then exploited to stitch ROMs at grid points to build a global LPV ASE ROM feasible to arbitrary flight condition. The MOR method is applied to the X-56A MUTT vehicle with flexible wing being tested at NASA/AFRC for flutter suppression and gust load alleviation. Our studies demonstrated that relative to the fullorder model, our X-56A ROM can accurately and reliably capture vehicles dynamics at various flight conditions in the target frequency regime while the number of states in ROM can be reduced by 10X (from 180 to 19), and hence, holds great promise for robust ASE controller synthesis and novel vehicle design