Staying safe and visible via message sharing in online social networks

As an imperative channel for fast information propagation, online social networks (OSNs) also have their defects. One of them is the information leakage, i.e., information could be spread via OSNs to the users whom we are not willing to share with. Thus the problem of constructing a circle of trust to share information with as many friends as possible without further spreading it to unwanted targets has become a challenging research topic but still remained open. Our work is the first attempt to study the Maximum Circle of Trust problem seeking to share the information with the maximum expected number of poster’s friends such that the information spread to the unwanted targets is brought to its knees. First, we consider a special and more practical case with the two-hop information propagation and a single unwanted target. In this case, we show that this problem is NP-hard, which denies the existence of an exact polynomial-time algorithm. We thus propose a Fully Polynomial-Time Approximation Scheme (FPTAS), which can not only adjust any allowable performance error bound but also run in polynomial time with both the input size and allowed error. FPTAS is the best approximation solution one can ever wish for an NP-hard problem. We next consider the number of unwanted targets is bounded and prove that there does not exist an FPTAS in this case. Instead, we design a Polynomial-Time Approximation Scheme (PTAS) in which the allowable error can also be controlled. When the number of unwanted targets are not bounded, we provide a randomized algorithm, along with the analytical theoretical bound and inapproximaibility result. Finally, we consider a general case with many hops information propagation and further show its #P-hardness and propose an effective Iterative Circle of Trust Detection (ICTD) algorithm based on a novel greedy function. An extensive experiment on various real-world OSNs has validated the effectiveness of our proposed approximation and ICTD algorithms. Such an extensive experiment also highlights several important observations on information leakage which help to sharpen the security of OSNs in the future.     

Psychosocial correlates and depression in Vietnamese adolescents

This paper reports findings on depression in a sample of 38 Vietnamese adolescents. Hierarchical regression analysis was conducted to examine the empirical use of psychosocial variables and stressful life event measures in predicting depression. Self-esteem (Esteem) and SLEs scales were entered in blocks and explained for 68 percent of the total variance in depression (CES-D scale). Esteem accounts for 30 percent of the overall variance. The SLE block contributes another 39 percent above and beyond in the prediction of depression. Death, PTSD, and Peer stress scales were significant predictors (p<.01). The mean CES-D depression score was 16.32 (SD=10.95). A cutoff score of 16 was used to classify those adolescents who were depressed from those who were not depressed (Radloff, 1977).     

Developments in implicit leadership theory and cognitive science: Applications to improving measurement and understanding alternatives to hierarchical leadership

After reviewing key findings regarding leadership categorization theory, we develop new perspectives regarding the design of behavioral measures of leadership and the implications of shared leadership and complex adaptive leadership conceptualizations of leadership. In particular, by applying recent developments in cognitive science, we explain how an understanding of symbolic, connectionist, and embodied representations of knowledge can benefit behavioral measures of leadership. Additionally, we address some practical issues associated with the measurement of leadership and argue that ratings which tap episodic memory at the event level may be more meaningful than ratings based on semantic memory. Finally, we discuss how notions of shared leadership and of leaders as catalysts for complexity can create unique complications for leadership perceptions, coordinated behavior within a group, and the measurement of leadership.     

Nonparametric Identification of Risk Aversion in First‐Price Auctions Under Exclusion Restrictions

This paper studies the nonparametric identification of the first‐price auction model with risk averse bidders within the private value paradigm. First, we show that the benchmark model is nonindentified from observed bids. We also derive the restrictions imposed by the model on observables and show that these restrictions are weak. Second, we establish the nonparametric identification of the bidders' utility function under exclusion restrictions. Our primary exclusion restriction takes the form of an exogenous bidders' participation, leading to a latent distribution of private values that is independent of the number of bidders. The key idea is to exploit the property that the bid distribution varies with the number of bidders while the private value distribution does not. We then extend these results to endogenous bidders' participation when the exclusion restriction takes the form of instruments that do not affect the bidders' private value distribution. Though derived for a benchmark model, our results extend to more general cases such as a binding reserve price, affiliated private values, and asymmetric bidders. Last, possible estimation methods are proposed.     

Impacts of off‐farm employment on welfare,food security and poverty: Evidence from rural Vietnam

How off‐farm employment can enhance welfare in terms of food consumption and poverty alleviation is a critical question facing many developing countries. This study addressed that question by pursuing two objectives: (i) to quantify the impact of off‐farm employment on rural households’ welfare, food security and poverty; and (ii) to examine the factors that affect their decision to work off‐farm. Using panel data, we estimated a difference‐in‐difference combined with a propensity score matching model. The findings show that off‐farm employment improves income, ensures food security and contributes to poverty alleviation. The results also show that age, marital status, education, labour, financial capital, land, location, market access and losses from natural disasters are significant contributing factors to the decision to participate in off‐farm employment. The findings suggest that to improve the welfare of rural households, the Vietnamese government should proceed with policies that enhance their opportunities for participation in off‐farm employment.     

“Susie Bubble is a Sign of The Times”

This essay takes as its point of critical departure the digital stardom of Susanna Lau, aka Susie Bubble, the most recognizable and respected fashion blogger in the world, in order to consider the historical formation of success in the postmillennial digital economy. By examining Lau as an embodied sign rather than an exceptional figure of success, I am concerned with the technical, cultural, and economic forces that give shape to hegemonic notions of success and the ideal subject it produces. More specifically, I hope to demonstrate the cultural frames that structure our ways of seeing and recognizing successful individuals in the post millennium by highlighting the gendered and racial construction of the ideal Web 2.0 subject. The aim of my discussion is to show that the discursive construction of Lau's success is reflective of emerging global patterns born out of the rising significance of Asians and young women (especially young Asian women) as consumers and producers in the digital economy.     

A Combined D.C. Optimization—Ellipsoidal Branch-and-Bound Algorithm for Solving Nonconvex Quadratic Programming Problems

In this paper we propose a new branch-and-bound algorithm by using an ellipsoidal partition for minimizing an indefinite quadratic function over a bounded polyhedral convex set which is not necessarily given explicitly by a system of linear inequalities and/or equalities. It is required that for this set there exists an efficient algorithm to verify whether a point is feasible, and to find a violated constraint if this point is not feasible. The algorithm is based upon the fact that the problem of minimizing an indefinite quadratic form over an ellipsoid can be efficiently solved by some available (polynomial and nonpolynomial time) algorithms. In particular, the d.c. (difference of convex functions) algorithm (DCA) with restarting procedure recently introduced by Pham Dinh Tao and L.T. Hoai An is applied to globally solving this problem. DCA is also used for locally solving the nonconvex quadratic program. It is restarted with current best feasible points in the branch-and-bound scheme, and improved them in its turn. The combined DCA-ellipsoidal branch-and-bound algorithm then enhances the convergence: it reduces considerably the upper bound and thereby a lot of ellipsoids can be eliminated from further consideration. Several numerical experiments are given.     

Optimal Nonparametric Estimation of First‐price Auctions

This paper proposes a general approach and a computationally convenient estimation procedure for the structural analysis of auction data. Considering first‐price sealed‐bid auction models within the independent private value paradigm, we show that the underlying distribution of bidders' private values is identified from observed bids and the number of actual bidders without any parametric assumptions. Using the theory of minimax, we establish the best rate of uniform convergence at which the latent density of private values can be estimated nonparametrically from available data. We then propose a two‐step kernel‐based estimator that converges at the optimal rate.     

DO TERRORIST ATTACKS IMPACT EXCHANGE RATE BEHAVIOR? NEW INTERNATIONAL EVIDENCE

This study examines whether terrorist attacks affect bilateral exchange rates. Using historical 10‐minute exchange rate data for 21 countries' currency vis‐à‐vis the U.S. dollar, we show that exchange rate returns of all countries are statistically significantly affected by terrorist attacks. Some exchange rates appreciate and some depreciate following a terrorist attack, some currencies experience exchange rate reversals while others experience a persistent effect. Generally, the effect declines but persists as terrorist attacks become stale information. (JEL F31, F37)