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The objective of this study is to design spacers using topology optimization in a two-dimensional (2D) crossflow reverse osmosis (RO) membrane channel in order to improve the performance of RO processes. This study is the first attempt to apply topology optimization to designing spacers in a RO membrane channel. The peiformance was evaluated based on the quantity of permeate flux penetrating both the upper and lower membrane sulfates. Here, Navier-Stokes and convection-diffusion equations were employed to calculate the permeate flux. The nine reference models, consisting of combinations of circle, rectangle, and triangle shapes and zig-zag, cavity, and submerged spacer configurations were then simulated using finite element method so that the peiformance of the model designed by topology optimization could be compared to the reference models. As a result of topology optimization with the allowable pressure drop changes in the channel, characteristics required of the spacer design were determined. The spacer design based on topology optimization was then simplified to consider manufacturability and peiformance. When the simplified design was compared to the reference models, the new design displayed a better peiformance in terms of permeate flux and wall concentration at the membrane surface. [ABSTRACT FROM AUTHOR]

Drive-by-download attacks are client-side attacks that originate from web servers clients visit. High-interaction client honeypots identify malicious web pages by directly visiting the web pages and are very useful. However, they still have shortcomings that must be addressed: long inspection time and possibility of not detecting certain attacks such as time bombs. To address these problems, we propose a new detection method to identify web pages with time bombs. The proposed method introduces a pattern-based static analysis for detecting time bombs efficiently. A high-interaction client honeypot performs the static analysis before carrying out execution-based dynamic analysis. The static analysis classifies sample web pages into two groups, the first one assumed to be time-bombs and the second one assumed to be no time-bombs. We then perform dynamic analysis for the first using sequential visitation algorithm with long classification delay and for the second using divide-and-conquer visitation algorithm with short classification delay. Experimental results demonstrate that our method is more accurate and costs less than conventional methods. [ABSTRACT FROM AUTHOR]

Distributed operating systems are designed to run over a collection of computing nodes that are spatially disseminated and communicate through a computer network. The computing nodes interact collaboratively with each other in order to pursue a common purpose. Protecting group communication between the collaborating nodes against potential attacks is one of the major challenges faced by the designers of distributed operating systems. This challenge can be effectively addressed by a group key exchange (GKE) protocol which allows a group of communicating parties to build a secure multicast channel over an insecure network. In this work, we propose a scalable GKE protocol that achieves both constant round complexity and logarithmic computation complexity. Our GKE protocol achieves its scalability by employing a complete binary tree structure combined with a so-called "nonce-chained authentication technique". Besides the scalability, our protocol features provable security against active adversaries in a well-defined communication model. [ABSTRACT FROM AUTHOR]