Influence of indenter shape on nanoindentation: an atomistic study

Lai, Chia-Wei,Chen, Chuin-Shan Techno-Press 2013 Interaction and multiscale mechanics Vol.6 No.3

The influence of indenter geometry on nanoindentation was studied using a static molecular dynamics simulation. Dislocation nucleation, dislocation locks, and dislocation movements during nanoindentation into Al (001) were studied. Spherical, rectangular, and Berkovich indenters were modeled to study the material behaviors and dislocation activities induced by their different shapes. We found that the elastic responses for the three cases agreed well with those predicted from elastic contact theory. Complicated stress fields were generated by the rectangular and Berkovich indenters, leading to a few uncommon nucleation and dislocation processes. The calculated mean critical resolved shear stresses for the Berkovich and rectangular indenters were lower than the theoretical strength. In the Berkovich indenter case, an amorphous region was observed directly below the indenter tip. In the rectangular indenter case, we observed that some dislocation loops nucleated on the plane. Furthermore, a prismatic loop originating from inside the material glided upward to create a mesa on the indenting surface. We observed an unusual softening phenomenon in the rectangular indenter case and proposed that heterogeneously nucleating dislocations are responsible for this.

Enterochromaffin Cells–Gut Microbiota Crosstalk: Underpinning the Symptoms, Pathogenesis, and Pharmacotherapy in Disorders of Gut-Brain Interaction

Lai Wei,Rajan Singh,Uday C Ghoshal 대한소화기 기능성질환·운동학회 2022 Journal of Neurogastroenterology and Motility (JNM Vol.28 No.3

Disorders of gut-brain interaction (DGBIs) are common conditions in community and clinical practice. As specialized enteroendocrine cells, enterochromaffin (EC) cells produce up to 95% of total body serotonin and coordinate luminal and basolateral communication in the gastrointestinal (GI) tract. EC cells affect a broad range of gut physiological processes, such as motility, absorption, secretion, chemo/mechanosensation, and pathologies, including visceral hypersensitivity, immune dysfunction, and impaired gastrointestinal barrier function. We aim to review EC cell and serotonin-mediated physiology and pathophysiology with particular emphasis on DGBIs. We explored the knowledge gap and attempted to suggest new perspectives of physiological and pathophysiological insights of DGBIs, such as (1) functional heterogeneity of regionally distributed EC cells throughout the entire GI tract; (2) potential pathophysiological mechanisms mediated by EC cell defect in DGBIs; (3) cellular and molecular mechanisms characterizing EC cells and gut microbiota bidirectional communication; (4) differential modulation of EC cells through GI segment-specific gut microbiota; (5) uncover whether crosstalk between EC cells and (i) luminal contents; (ii) enteric nervous system; and (iii) central nervous system are core mechanisms modulating gut-brain homeostasis; and (6) explore the therapeutic modalities for physiological and pathophysiological mechanisms mediated through EC cells. Insights discussed in this review will fuel the conception and realization of pathophysiological mechanisms and therapeutic clues to improve the management and clinical care of DGBIs.

Using Adaptive Bandwidth Allocation Approach to Defend DDoS Attacks

Wei-Shen Lai,Chu-Hsing Lin,Jung-Chun Liu,Hsun-Chi Huang,Tsung-Che Yang 보안공학연구지원센터 2008 International Journal of Software Engineering and Vol.2 No.4

Denial of service attacks occur when the attacks are from a single host, whereas distributed denial of service attacks occur when multiple affected systems flood the bandwidth or resources of a targeted system. Although it is not possible to exempt entirely from denial of service or distributed denial of service attacks, we can limit the malicious user by controlling the traffic flow. In the paper, we propose to monitor the traffic pattern in order to alleviate distributed denial of service attacks. A bandwidth allocation policy will be adopted to assign normal users to a high priority queue and suspected attackers to a low priority queue. Simulations conducted in network simulator of our proposed priority queue-based scheme shows its effectiveness in blocking attacking traffic while maintaining constant flows for legitimate traffic.

Particle Size and Loading Effects on Particle-Laden Flow with Mono-sized Droplets

( Wei Hsiang Lai ),( Wei Fu Lu ),( Keh Chin Chang ) 한국액체미립화학회 2010 한국액체미립화학회 학술강연회 논문집 Vol.2010 No.-

Turbulence modulation is an interaction between phases that occurs in multiphase flow, and turbulence intensity traditionally can be represented as an indicator of turbulence modulation. Many researchers paid attention on the subject, but no coincident conclusion can be proposed. A general cognition is that larger particles induced wake to enhance the fluid turbulence intensity and smaller particles suppressed the fluid turbulence intensity since the fluid eddy imparted energy to the smaller particle. Here, the authors orderly changed particle size of dispersed phase and mass loading ratio (LR) to study the change on fluid turbulence intensity. Mono-dispersed droplets with a narrow size distribution were used to load into a homogeneous turbulence to investigate the turbulence modulation. Particle Dynamic Analyzer (PDA) was used to measure the particle (droplets and tracers) dynamic information. The particle concentration effect can be significantly observed. After coupling particle concentration and particle wetting area (πd2), a linear relationship can be obtained and it represents the turbulence modulation dominated the dilute two-phase flow as our expectation.

Investigation of in-train stability and safety assessment for railway vehicles during braking

Lai Wei,Jing Zeng,Qunsheng Wang 대한기계학회 2016 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.30 No.4

In-train stability of railway vehicles has becoming a major concern for railway vehicles, which refers to the jackknifing behavior of couplers under large in-train forces. For the train to train rescue scenario, braking induced impacts from couplers can adversely affect the dynamic performance of the coupled train. It is indicated from field tests that in-train forces if combined with large rotational angles of couplers can produce vertical components, which will further lead to the interference of adjacent carbodies and structural damages. In this paper, the dynamic model of the train and coupler system is developed. The model verifications are conducted by comparing the calculated responses with the tested results. The safety indices are formulated on the basis of which the running safety of the coupled train is evaluated. The propelling test in the laboratory is conducted to reproduce the coupler jackknifing behavior. The quasi-static analysis and anti-jackknifing mechanism under compressing in-train forces are analysed. Parametric studies are then conducted to propose some limitations for the application of train to train rescue. It is indicated from numerical and testing results that the decrease of the braking deceleration or a limitation of the free rotational angle of couplers is beneficial to lower the amplitude of braking induced impacts.

Efficient Cluster Radius and Transmission Ranges in Corona-based Wireless Sensor Networks

( Wei Kuang Lai ),( Chung-shuo Fan ),( Chin-shiuh Shieh ) 한국인터넷정보학회 2014 KSII Transactions on Internet and Information Syst Vol.8 No.4

In wireless sensor networks (WSNs), hierarchical clustering is an efficient approach for lower energy consumption and extended network lifetime. In cluster-based multi-hop communications, a cluster head (CH) closer to the sink is loaded heavier than those CHs farther away from the sink. In order to balance the energy consumption among CHs, we development a novel cluster-based routing protocol for corona-structured wireless sensor networks. Based on the relaying traffic of each CH conveys, adequate radius for each corona can be determined through nearly balanced energy depletion analysis, which leads to balanced energy consumption among CHs. Simulation results demonstrate that our clustering approach effectively improves the network lifetime, residual energy and reduces the number of CH rotations in comparison with the MLCRA protocols.

Crystallization and Luminescence Properties of Polypropylene Fiber Containing Rare Earth Aluminates and a Sorbital Derivative Nucleating Agent

Wei-Jen Lai,Kuo-Chung Cheng 한국섬유공학회 2018 Fibers and polymers Vol.19 No.1

Polypropylene (PP) fibers with a sorbital derivative nucleating agent (SDN) and rare earth aluminates (SrAl2O4:Eu2+,Dy3+) were prepared via melt compounding and melt-spinning. Non-isothermal crystallization kinetics and luminescence properties of PP and luminous PP fibers were studied by differential scanning calorimetry (DSC), polarized optical microscopy (POM), and decay of the afterglow test. The crystallization temperature determined by DSC increasedwith the addition of the nucleating agent during the cooling process from 200 oC. The Jeziorny model successfully described the non-isothermal crystallization behavior of the luminous PP with various SDN contents. The crystal grain size and morphology of the sample with the SDN was different from that without nucleating agent. The luminous PP fabric having high initial brightness intensity, approximately 461 mcd g-1m-2, can be prepared with addition of 10 wt% of rare earthaluminates and 0.5 % of SDN.

I-SEAD: A Secure Routing Protocol for Mobile Ad Hoc Networks

Wei-Shen Lai,Chu-Hsing Lin,Jung-Chun Liu,Yen-Lin Huang,Mei-Chun Chou 보안공학연구지원센터 2008 International Journal of Multimedia and Ubiquitous Vol.3 No.4

Ad hoc networks are highly dynamic routing networks cooperated by a collection of wireless mobile hosts without any assistance of a centralized access point. Secure Efficient Ad hoc Distance Vector (SEAD) is a proactive routing protocol, based on the design of Destination Sequenced Distance Vector routing protocol (DSDV). SEAD provides a robust protocol against attackers trying to create incorrect routing state in the other node. However, it does not provide a way to prevent an attacker from tampering the next hop or the destination field in route update. In this paper, we propose an I-SEAD protocol to solve the problem. A series of simulation experiments are conducted to evaluate the performance.

Numerical Method with High Real-time Property Based on Shortest Path Algorithm for Optimal Control

Wei Liao,Xiaohui Wei,Jizhou Lai,Hao Sun 제어·로봇·시스템학회 2021 International Journal of Control, Automation, and Vol.19 No.6

A numerical method consisting of an off-line part and an on-line part for optimal control problems is proposed in this paper. In the off-line part, the state space is discretized into a Cartesian grid structure and then define a graph over all grid points by connecting two points if the Euclidean norm between them is closer than a positive number called adjacent radius, the minimum cost between them is estimated using difference method and stored in a matrix. After that the matrix is updated by a shortest path algorithm and a matrix holding the information of the shortest paths between any two grid points is generated. In the on-line part, the optimal control vector at each time step can be generated by reading data from the matrix according to the current state and target state and doing some simple calculations. Since there is no need to do a lot of calculation in the on-line part, this method can satisfy the real-time requirements in some engineering control problems. We prove that the solution of the proposed method converge to the analytical solution when the adjacent radius and the grid size tend to zero and the grid size tend is a higher order infinitesimal of the adjacent radius. At the end of this paper, some numerical examples are taken to illustrate the effectiveness of the proposed method.

Ethanol and Water Atomization of Like- and Unlike-Doublet Impinging Jets

( Wei Hsiang Lai ),( Shun Jie Yang ),( Wen Non Huang ) 한국액체미립화학회 2005 한국액체미립화학회 학술강연회 논문집 Vol.2005 No.-

The objective of the present study is to further investigate the general influence of the physical properties and environment effects on the mean drop size generated by like- and unlike-doublet impinging jets with 95% ethanol and purified water. The orifice of the injector element are 0.3, 0.5, and 0.7 mm in diameter, with depth-to-diameter ratio of 10, the impinging angle is set to be 60°, 90° and 120° respectively. In order to measure the mean drop size, the jet velocity is varied from 2 m/s to 30 m/s, the environment pressure is designated as 1, 2, 5 and 9 bar. Results show that in liquid shape mode, the larger impinging angle, the lower jet velocity threshold of mode transition is observed. Regarding the liquid film size, an empirical equation can be used to calculate the ψ angle, and the equation induced by Ibrahim et al.(1991) can figure out the film length by multiply a constant, which is related to the viscosity. The SMD of unlike-doublet impinging is highly influenced by the surface tension. High ambient pressure has no effect on film size, but it causes the liquid shape change mode in lower jet velocity.