Effects of Workrate and Seat Position on Frontal Plane Knee Biomechanics in Recumbent Cycling

In cycling study, most of the research focused on the sagittal plane lower extremity biomechanics and upright cycling. However, few of them paid attention to the frontal plane and recumbent cycling. Internal knee abduction moment (KAbM), on the frontal plane, has been shown to be an effective predictor of knee osteoarthritis (OA), and recumbent bicycle has become the newest popular tool of rehabilitation. The purpose of this study was to examine the effects of different workrates and seat positions on knee frontal plane biomechanics during stationary recumbent cycling. Thirteen participants took part in the study. 6 total conditions of one-minute cycling at the cadence of 80 RPM were assigned to each participant: pedaling at “flexed”, “optimal” and “extended” seat positions (largest knee extension angle of 10-20 degrees, 20-30 degrees, and 30-40 degrees, respectively) with 60 and 100 W of workrate. A 3D motion analysis system and a pair of custom-made instrumented pedals were used to collect kinematic and kinetic data

Degradation of High Voltage Glass Fiber-Reinforced Polymer Matrix Composites by Aggressive Environmental Conditions

Polymer matrix composites reinforced with either E glass or ECR glass fibers-reinforced are used in a variety of high voltage electrical applications because of their advantages like lower weight and cost. However, they can be damaged by aggressive in-service conditions such as high temperature, ultraviolet radiation, moisture, ozone and corrosive environments. Different degradation mechanisms can develop in high voltage PMCs under those extreme environments, which, in turn, can affect the long term structural durability of the composites. A set of PMCs reinforced with ECR-glass and E-glass fibers embedded in four different resins has been investigated in this study. In addition, two PMC systems with surface coatings were also tested. The composites were supplied to the project by a US high voltage equipment manufacturer. The composites were subjected in four different tests to the individual and combined effects of UV radiation, elevated temperature, moisture, and nitric acid solutions. The surface degradation of the composites was subsequently analyzed using optical and scanning electron microscopy (SEM) techniques. Fourier transform infrared spectroscopy (FTIR) techniques are used to analyze chemical structure of the composites

A Generalized Alternating Method for Bilevel Learning under the Polyak-{\L}ojasiewicz Condition

Bilevel optimization has recently regained interest owing to its applications in emerging machine learning fields such as hyperparameter optimization, meta-learning, and reinforcement learning. Recent results have shown that simple alternating (implicit) gradient-based algorithms can match the convergence rate of single-level gradient descent (GD) when addressing bilevel problems with a strongly convex lower-level objective. However, it remains unclear whether this result can be generalized to bilevel problems beyond this basic setting. In this paper, we first introduce a stationary metric for the considered bilevel problems, which generalizes the existing metric, for a nonconvex lower-level objective that satisfies the Polyak-{\L}ojasiewicz (PL) condition. We then propose a Generalized ALternating mEthod for bilevel opTimization (GALET) tailored to BLO with convex PL LL problem and establish that GALET achieves an $\epsilon$-stationary point for the considered problem within $\tilde{\cal O}(\epsilon^{-1})$ iterations, which matches the iteration complexity of GD for single-level smooth nonconvex problems.Comment: Camera ready versio

The Washback Effect of Reformed CET 6 Listening Comprehension Test

In China, the English Test Band 6 (CET6) is a national test that is used to assess the English proficiency of test-takers by the state with unified questions, unified fees, and unified organization of tests. It is held twice a year. This test has had a great impact on college students and college teachers. It was introduced in 1978. In 2016, the Ministry of Education reformed CET-6, especially in listening tests. The reformed listening test not only brings scenes and dialogues closer to daily life but also emphasizes the examination of students' comprehensive English listening and speaking ability. From the perspective of learners, this paper draws on the theoretical models and empirical results of washback at home and abroad and studies the backwash of the reformed English CET-6 listening to learners' listening learning through a questionnaire. To do the survey, the paper was surveyed by quantitative research methods with 60 samples in several public universities. After the collection and analysis of data, the authors have affirmed and determined this test has a significant washback effect on student learning

2D Eigenvalue Problems I: Existence and Number of Solutions

A two dimensional eigenvalue problem (2DEVP) of a Hermitian matrix pair $(A, C)$ is introduced in this paper. The 2DEVP can be viewed as a linear algebraic formulation of the well-known eigenvalue optimization problem of the parameter matrix $H(\mu) = A - \mu C$. We present fundamental properties of the 2DEVP such as the existence, the necessary and sufficient condition for the finite number of 2D-eigenvalues and variational characterizations. We use eigenvalue optimization problems from the quadratic constrained quadratic program and the computation of distance to instability to show their connections with the 2DEVP and new insights of these problems derived from the properties of the 2DEVP.Comment: 24 pages, 5 figure

Synergistic Environmental Aging of Glass Reinforced Polymer Composites

Synergistic effects involved in the environmental degradation of Glass Reinforced Polymer (GRP) composites were examined and a novel synergistic aging model was proposed in this study. Six GRPs based on glass fibers with four different polymer resins and six pure polymer thermoplastic resins were exposed either individually or in combination to ultraviolet (UV) radiation, water condensation and elevated temperature for approximately 1000 h. The composites and polymers were monitored for weight changes as a function of time and their surfaces were examined after the tests using optical and scanning electron microscopes (SEM). Photodegradation of the polymer matrices was analyzed by Fourier Transform Infrared Spectroscopy (FTIR) techniques. A comparison of weight changes of polymer composites degraded by UVA and UVB was also presented. It has been shown that the selected aging conditions created noticeable synergistic effects causing extensive erosion of the polymer matrices of the tested composites which appeared to be much stronger under the combined actions than under individual exposures. However, synergetic aging of pure polymers was not as obvious as in the tested GRPs with the exception of the PVC resin. Based on the synergistic aging mechanisms observed on the surfaces of the tested GRPs, a new model of synergistic aging of polymers under UV and water condensation was proposed. The model includes numerical simulations of UV radiation, numerical simulations of hydrodynamic effects, and complex particle removal analyses. In the UV radiation modeling part of the simulations, flat and sinusoidal polymer surfaces were numerically modeled for their UV damage as a function of UV intensity, surface topography, and exposure time. The results showed that UV damage on uneven polymer surfaces reduces their surface roughness making them planar and that the degradation rates are the largest at the tips of the local heights of the surfaces. This was subsequently verified experimentally by exposing neat epoxy specimens to UV and by precisely monitoring their surface topography as a function of time. In the hydrodynamic portion, viscous shear stresses generated by slowly moving water were determined on uneven polymer surfaces as a function of surface morphology, flow rates, and volumetric forces. In the particle removal portion of the analysis, a new micro-particle removal mechanism was suggested by comparing the adhesion forces calculated using the Johnson-Kendall-Roberts (JKR) model and the Hamaker approach with the drag forces created by slow water flows. Subsequently, the particle removal mechanism was verified on an inclined unidirectional glass/epoxy surface with randomly distributed epoxy particles subjected to a gravitational flow of water. It has been shown that the movement of polymer particles on polymer/composite surfaces depends very strongly on particle sizes, water velocity, and surface morphology. The analysis of adhesion forces between particles and polymer surfaces was further enhanced by introducing the surface roughness effects for both the polymer surfaces and the particles. The interactions were simulated by using the Rumpf, Rabinovich, Kumar, and the modified Rabinovich models as a function of nano roughness and micro roughness of substrate surfaces, nano roughness of micro roughness of particles, particle size and the number of contact points. Adhesion forces between irregular particles and irregular surfaces were also analyzed for their effects on the critical sizes of particle which could be removed from different rough surfaces by shear stresses generated by slowly moving water. It has been shown that the polymer surfaces with irregular nano/micro structure characteristics significantly reduced their interactions with deposited rough particles. The critical sizes of rough particles that could be removed by water flows were found to be significantly smaller than for smooth particles removed from flat surfaces