Improvements on Activation Functions in ANN: An Overview

Activation functions are an essential part of artificial neural networks. Over the years, researches have been done to seek for new functions that perform better. There are several mainstream activation functions, such as sigmoid and ReLU, which are widely used across the decades. At the meantime, many modified versions of these functions are also proposed by researchers in order to further improve the performance. In this paper, limitations of the mainstream activation functions, as well as the main characteristics and relative performances of their modifications, are discussed

On the Impact of Wireless Jamming on the Distributed Secondary Microgrid Control

The secondary control in direct current microgrids (MGs) is used to restore the voltage deviations caused by the primary droop control, where the latter is implemented locally in each distributed generator and reacts to load variations. Numerous recent works propose to implement the secondary control in a distributed fashion, relying on a communication system to achieve consensus among MG units. This paper shows that, if the system is not designed to cope with adversary communication impairments, then a malicious attacker can apply a simple jamming of a few units of the MG and thus compromise the secondary MG control. Compared to other denial-of-service attacks that are oriented against the tertiary control, such as economic dispatch, the attack on the secondary control presented here can be more severe, as it disrupts the basic functionality of the MG

Experimental Evaluation and Modeling of Photocatalytic Oxidation Air Cleaners

Heterogeneous ultraviolet photocatalytic oxidation (UV-PCO), as a promising advanced oxidation technology, has been suggested as an alternative and energy efficient method to improve indoor air quality (IAQ) through the photocatalytic degradation of indoor air pollutants. However, the complicated PCO reaction mechanisms and unexpected intermediates still need to be further explored in order for this technology to be successfully applied in mechanically ventilated buildings. Two main objectives of this study include the development of methodologies to evaluate the performance of PCO systems and the development of a reliable mathematical model to fully simulate the performance of these systems. A pilot four-parallel duct system was set-up to equitably and thoroughly evaluate the performance of UV-PCO air cleaners under the conditions relevant to the actual applications for a wide range of indoor air pollutants. This study investigated the UV-PCO removal efficiency of two types of air filters (fiberglass fibers coated with TiO2 (TiO2/FGFs) and carbon cloth fibers loaded with TiO2 (TiO2/CCFs)) under ultraviolet C (UVC) and vacuum ultraviolet (VUV) illumination. A systematic parametric evaluation of the effects of various kinetic parameters, such as types of pollutants, inlet concentration, airflow rate, light intensity, and relative humidity that influence the PCO performance, was conducted. In addition, gas-phase ozonation with a variety of chemical compounds was first examined when ozone was produced by VUV. Moreover, the formation of by-products generated from incomplete conversion was investigated to evaluate its impact on IAQ. A time-dependent model was proposed for predicting the performance of an in-duct PCO air cleaner under the conditions relevant to the actual applications. A comprehensive model was developed by integrating light scattering model, reaction kinetic model, mass balance as well as optional ozonation model. The UV-PCO model and the UV-PCO ozonation integrated model were validated with experimental results; there was a good agreement between the model prediction and the experiment result. The relative rate-limiting process between physical interactions and photochemical interactions was fully investigated through simulation analysis. Depending on the physical properties of the catalyst, reactor geometries, operation conditions, as well as environmental conditions, the photochemical reaction occurring on the fixed active sites at the catalyst surface is the dominating process for this PCO system

Modeling and Simulation of Concentric and Eccentric Tube Continuum Robots

Unlike conventional manipulators where the robot is actuated at discrete joints, continuum robots are actuated continuously in smooth curves. These robots are often dexterous and compact, allowing them to operate in constrained environments during minimally invasive medical interventions. Since the unconventional robot structure often consists of elastic or flexible materials, the corresponding kinematics formulation is significantly more challenging to derive and simulate. This thesis introduces two different but related continuum robot designs: the concentric tube robot (CTR) and the eccentric tube robot (ETR). These designs utilize multiple pre-curved and superelastic nitinol tubes to actuate the robot. This mechanism also leads to an undesirable behavior called snapping . Based on Cosserat Rod theory, two separate kinematics models are derived, solved, and simulated for CTR and ETR. Additionally, an ETR prototype is designed and constructed for experimental validation. Compared to the simulation, the measured average tip error is about 3.8% of the robot length