Local cluster aggregation models of explosive percolation

We introduce perhaps the simplest models of graph evolution with choice that demonstrate discontinuous percolation transitions and can be analyzed via mathematical evolution equations. These models are local, in the sense that at each step of the process one edge is selected from a small set of potential edges sharing common vertices and added to the graph. We show that the evolution can be accurately described by a system of differential equations and that such models exhibit the discontinuous emergence of the giant component. Yet, they also obey scaling behaviors characteristic of continuous transitions, with scaling exponents that differ from the classic Erdos-Renyi model.Comment: Final version as appearing in PR

Parallel Implementations of Cellular Automata for Traffic Models

The Biham-Middleton-Levine (BML) traffic model is a simple two-dimensional, discrete Cellular Automaton (CA) that has been used to study self-organization and phase transitions arising in traffic flows. From the computational point of view, the BML model exhibits the usual features of discrete CA, where the state of the automaton are updated according to simple rules that depend on the state of each cell and its neighbors. In this paper we study the impact of various optimizations for speeding up CA computations by using the BML model as a case study. In particular, we describe and analyze the impact of several parallel implementations that rely on CPU features, such as multiple cores or SIMD instructions, and on GPUs. Experimental evaluation provides quantitative measures of the payoff of each technique in terms of speedup with respect to a plain serial implementation. Our findings show that the performance gap between CPU and GPU implementations of the BML traffic model can be reduced by clever exploitation of all CPU features

The Prison Houses of Knowledge: Activist scholarship and revolution in the era of “globalization”

The rise of new social movements has produced an emerging discourse on activist scholarship. There is considerable ambiguity about what the term means. In this article I draw on my work as a trade unionist, political activist, and activist lawyer in Mumbai, and later as a social justice activist in New Zealand to reflect on the meaning of activist scholarship, interrogate the institutional contexts for knowledge, and the relationship of knowledge to emancipatory structural social transformations. Although based on personal experiences, this article provides a theoretically oriented meta-analysis of activist scholarship.La montée des nouveaux mouvements sociaux a provoqué l’émergence d’un discours novateur sur l’activisme étudiant. Il persiste cependant une grande ambiguïté quand à la signification de ce terme. Dans cet article, je m’inspire de mes travaux comme militante syndicale, activiste politique et avocate engagée à Mumbai, ainsi que de mon expérience en tant que activiste en justice sociale en Nouvelle-Zélande pour réfléchir sur le sens à donner à l’activisme étudiant, m’interroger sur les contextes institutionnels du savoir, et sur la relation existant entre le savoir et les transformations structurelles d’émancipation. Bien que prenant appui sur mes expériences personnelles, cet article étaye une méta-analyse théorique de l’activisme étudiant

Assessment of Medium-Sized Ontario Municipalities’ Hiring Practices

This paper examines whether municipalities incorporate equitable principles within their hiring practices and policies. An anonymous online survey was administered to the chief administrative officers, city managers, and human resources personnel of medium-sized municipalities in Ontario working in the capacity of senior level management, as these individuals are known to be the most knowledgeable about hiring practices and employment equity initiatives. The findings demonstrate that, generally speaking, mid-sized Ontario municipalities are not incorporating strategies within their recruitment and selection processes that work towards reducing employment barriers for designated groups

Maritain’s Philosophy of Education and Christian Religious Education

Catholic schools invest much time and energy in writing mission statements that express the common values, beliefs, and goals of the Church community. This article explores the philosophical foundation supporting our mission by analyzing the work of the Catholic philosopher Jacques Maritain. While often labeled dismissively as a new-Thomist, Maritain’s thought offers a cogent, philosophically balanced view of education that is highly congruent with Catholic theology. Arguing that Catholic schools are more than just institutions staffed by Catholics, the author reasons that all education, if the truth be told, is in some form a religious education, and that good teachers create schools that invite students to grow in the life of the mind

Avatar captcha : telling computers and humans apart via face classification and mouse dynamics.

Bots are malicious, automated computer programs that execute malicious scripts and predefined functions on an affected computer. They pose cybersecurity threats and are one of the most sophisticated and common types of cybercrime tools today. They spread viruses, generate spam, steal personal sensitive information, rig online polls and commit other types of online crime and fraud. They sneak into unprotected systems through the Internet by seeking vulnerable entry points. They access the system’s resources like a human user does. Now the question arises how do we counter this? How do we prevent bots and on the other hand allow human users to access the system resources? One solution is by designing a CAPTCHA (Completely Automated Public Turing Tests to tell Computers and Humans Apart), a program that can generate and grade tests that most humans can pass but computers cannot. It is used as a tool to distinguish humans from malicious bots. They are a class of Human Interactive Proofs (HIPs) meant to be easily solvable by humans and economically infeasible for computers. Text CAPTCHAs are very popular and commonly used. For each challenge, they generate a sequence of alphabets by distorting standard fonts, requesting users to identify them and type them out. However, they are vulnerable to character segmentation attacks by bots, English language dependent and are increasingly becoming too complex for people to solve. A solution to this is to design Image CAPTCHAs that use images instead of text and require users to identify certain images to solve the challenges. They are user-friendly and convenient for human users and a much more challenging problem for bots to solve. In today’s Internet world the role of user profiling or user identification has gained a lot of significance. Identity thefts, etc. can be prevented by providing authorized access to resources. To achieve timely response to a security breach frequent user verification is needed. However, this process must be passive, transparent and non-obtrusive. In order for such a system to be practical it must be accurate, efficient and difficult to forge. Behavioral biometric systems are usually less prominent however, they provide numerous and significant advantages over traditional biometric systems. Collection of behavior data is non-obtrusive and cost-effective as it requires no special hardware. While these systems are not unique enough to provide reliable human identification, they have shown to be highly accurate in identity verification. In accomplishing everyday tasks, human beings use different styles, strategies, apply unique skills and knowledge, etc. These define the behavioral traits of the user. Behavioral biometrics attempts to quantify these traits to profile users and establish their identity. Human computer interaction (HCI)-based biometrics comprise of interaction strategies and styles between a human and a computer. These unique user traits are quantified to build profiles for identification. A specific category of HCI-based biometrics is based on recording human interactions with mouse as the input device and is known as Mouse Dynamics. By monitoring the mouse usage activities produced by a user during interaction with the GUI, a unique profile can be created for that user that can help identify him/her. Mouse-based verification approaches do not record sensitive user credentials like usernames and passwords. Thus, they avoid privacy issues. An image CAPTCHA is proposed that incorporates Mouse Dynamics to help fortify it. It displays random images obtained from Yahoo’s Flickr. To solve the challenge the user must identify and select a certain class of images. Two theme-based challenges have been designed. They are Avatar CAPTCHA and Zoo CAPTCHA. The former displays human and avatar faces whereas the latter displays different animal species. In addition to the dynamically selected images, while attempting to solve the CAPTCHA, the way each user interacts with the mouse i.e. mouse clicks, mouse movements, mouse cursor screen co-ordinates, etc. are recorded nonobtrusively at regular time intervals. These recorded mouse movements constitute the Mouse Dynamics Signature (MDS) of the user. This MDS provides an additional secure technique to segregate humans from bots. The security of the CAPTCHA is tested by an adversary executing a mouse bot attempting to solve the CAPTCHA challenges