Archives for 2013

Today I read a paper titled “Geometric Models of Rolling-Shutter Cameras”

The abstract is:
Cameras with rolling shutters are becoming more common as low-power, low-cost CMOS sensors are being used more frequently in cameras.

The rolling shutter means that not all scanlines are exposed over the same time interval.

The effects of a rolling shutter are noticeable when either the camera or objects in the scene are moving and can lead to systematic biases in projection estimation.

We develop a general projection equation for a rolling shutter camera and show how it is affected by different types of camera motion.

In the case of fronto-parallel motion, we show how that camera can be modeled as an X-slit camera.

We also develop approximate projection equations for a non-zero angular velocity about the optical axis and approximate the projection equation for a constant velocity screw motion.

We demonstrate how the rolling shutter effects the projective geometry of the camera and in turn the structure-from-motion.

Today I read a paper titled “User Interface for Volume Rendering in Virtual Reality Environments”

The abstract is:
Volume Rendering applications require sophisticated user interaction for the definition and refinement of transfer functions.

Traditional 2D desktop user interface elements have been developed to solve this task, but such concepts do not map well to the interaction devices available in Virtual Reality environments.

In this paper, we propose an intuitive user interface for Volume Rendering specifically designed for Virtual Reality environments.

The proposed interface allows transfer function design and refinement based on intuitive two-handed operation of Wand-like controllers.

Additional interaction modes such as navigation and clip plane manipulation are supported as well.

The system is implemented using the Sony PlayStation Move controller system.

This choice is based on controller device capabilities as well as application and environment constraints.

Initial results document the potential of our approach.

Today I read a paper titled “Reinforced communication and social navigation: remember your friends and remember yourself”

The abstract is:
In social systems, people communicate with each other and form groups based on their interests.

The pattern of interactions, the network, and the ideas that flow on the network naturally evolve together.

Researchers use simple models to capture the feedback between changing network patterns and ideas on the network, but little is understood about the role of past events in the feedback process.

Here we introduce a simple agent-based model to study the coupling between peoples’ ideas and social networks, and better understand the role of history in dynamic social networks.

We measure how information about ideas can be recovered from information about network structure and, the other way around, how information about network structure can be recovered from information about ideas.

We find that it is in general easier to recover ideas from the network structure than vice versa.

Today I read a paper titled “Single-window Integrated Development Environment”

The abstract is:
This paper addresses the problem of IDE interface complexity by introducing single-window graphical user interface.

This approach lies in removing additional child windows from IDE, thus allowing a user to keep only text editor window open.

We describe an abstract model of IDE GUI that is based on most popular modern integrated environments and has generalized user interface parts.

Then this abstract model is reorganized into single windowed interface model: access to common IDE functions is provided from the code editing window while utility windows are removed without loss of IDE functionality.

After that the implementation of single-window GUI on KDevelop 4 is described.

And finally tool views and usability of several well- known IDEs are surveyed.

Today I read a paper titled “Cops and Invisible Robbers: the Cost of Drunkenness”

The abstract is:
We examine a version of the Cops and Robber (CR) game in which the robber is invisible, i.e., the cops do not know his location until they capture him.

Apparently this game (CiR) has received little attention in the CR literature.

We examine two variants: in the first the robber is adversarial (he actively tries to avoid capture); in the second he is drunk (he performs a random walk).

Our goal in this paper is to study the invisible Cost of Drunkenness (iCOD), which is defined as the ratio ct_i(G)/dct_i(G), with ct_i(G) and dct_i(G) being the expected capture times in the adversarial and drunk CiR variants, respectively.

We show that these capture times are well defined, using game theory for the adversarial case and partially observable Markov decision processes (POMDP) for the drunk case.

We give exact asymptotic values of iCOD for several special graph families such as $d$-regular trees, give some bounds for grids, and provide general upper and lower bounds for general classes of graphs.

We also give an infinite family of graphs showing that iCOD can be arbitrarily close to any value in [2,infinty).

Finally, we briefly examine one more CiR variant, in which the robber is invisible and “infinitely fast”; we argue that this variant is significantly different from the Graph Search game, despite several similarities between the two games.

Today I read a paper titled “Opinion fluctuations and disagreement in social networks”

The abstract is:
We study a tractable opinion dynamics model that generates long-run disagreements and persistent opinion fluctuations.

Our model involves an inhomogeneous stochastic gossip process of continuous opinion dynamics in a society consisting of two types of agents: regular agents, who update their beliefs according to information that they receive from their social neighbors; and stubborn agents, who never update their opinions.

When the society contains stubborn agents with different opinions, the belief dynamics never lead to a consensus (among the regular agents).

Instead, beliefs in the society fail to converge almost surely, the belief profile keeps on fluctuating in an ergodic fashion, and it converges in law to a non-degenerate random vector.

The structure of the network and the location of the stubborn agents within it shape the opinion dynamics.

The expected belief vector evolves according to an ordinary differential equation coinciding with the Kolmogorov backward equation of a continuous-time Markov chain with absorbing states corresponding to the stubborn agents and converges to a harmonic vector, with every regular agent’s value being the weighted average of its neighbors’ values, and boundary conditions corresponding to the stubborn agents’.

Expected cross-products of the agents’ beliefs allow for a similar characterization in terms of coupled Markov chains on the network.

We prove that, in large-scale societies which are highly fluid, meaning that the product of the mixing time of the Markov chain on the graph describing the social network and the relative size of the linkages to stubborn agents vanishes as the population size grows large, a condition of \emph{homogeneous influence} emerges, whereby the stationary beliefs’ marginal distributions of most of the regular agents have approximately equal first and second moments.

Today I read a paper titled “Egomunities, Exploring Socially Cohesive Person-based Communities”

The abstract is:
In the last few years, there has been a great interest in detecting overlapping communities in complex networks, which is understood as dense groups of nodes featuring a low outbound density.

To date, most methods used to compute such communities stem from the field of disjoint community detection by either extending the concept of modularity to an overlapping context or by attempting to decompose the whole set of nodes into several possibly overlapping subsets.

In this report we take an orthogonal approach by introducing a metric, the cohesion, rooted in sociological considerations.

The cohesion quantifies the community-ness of one given set of nodes, based on the notions of triangles – triplets of connected nodes – and weak ties, instead of the classical view using only edge density.

A set of nodes has a high cohesion if it features a high density of triangles and intersects few triangles with the rest of the network.

As such, we introduce a numerical characterization of communities: sets of nodes featuring a high cohesion.

We then present a new approach to the problem of overlapping communities by introducing the concept of ego-munities, which are subjective communities centered around a given node, specifically inside its neighborhood.

We build upon the cohesion to construct a heuristic algorithm which outputs a node’s ego-munities by attempting to maximize their cohesion.

We illustrate the pertinence of our method with a detailed description of one person’s ego-munities among Facebook friends.

We finally conclude by describing promising applications of ego-munities such as information inference and interest recommendations, and present a possible extension to cohesion in the case of weighted networks.

Today I read a paper titled “Effect of Embedding Watermark on Compression of the Digital Images”

The abstract is:
Image Compression plays a very important role in image processing especially when we are to send the image on the internet.

The threat to the information on the internet increases and image is no exception.

Generally the image is sent on the internet as the compressed image to optimally use the bandwidth of the network.

But as we are on the network, at any intermediate level the image can be changed intentionally or unintentionally.

To make sure that the correct image is being delivered at the other end we embed the water mark to the image.

The watermarked image is then compressed and sent on the network.

When the image is decompressed at the other end we can extract the watermark and make sure that the image is the same that was sent by the other end.

Though watermarking the image increases the size of the uncompressed image but that has to done to achieve the high degree of robustness i.e.

how an image sustains the attacks on it.

The present paper is an attempt to make transmission of the images secure from the intermediate attacks by applying the generally used compression transforms.

Today I read a paper titled “Can virtual reality predict body part discomfort and performance of people in realistic world for assembling tasks?”

The abstract is:
This paper presents our work on relationship of evaluation results between virtual environment (VE) and realistic environment (RE) for assembling tasks.

Evaluation results consist of subjective results (BPD and RPE) and objective results (posture and physical performance).

Same tasks were performed with same experimental configurations and evaluation results were measured in RE and VE respectively.

Then these evaluation results were compared.

Slight difference of posture between VE and RE was found but not great difference of effect on people according to conventional ergonomics posture assessment method.

Correlation of BPD and performance results between VE and RE are found by linear regression method.

Moreover, results of BPD, physical performance, and RPE in VE are higher than that in RE with significant difference.

Furthermore, these results indicates that subjects feel more discomfort and fatigue in VE than RE because of additional effort required in VE.

Today I read a paper titled “Signed Networks in Social Media”

The abstract is:
Relations between users on social media sites often reflect a mixture of positive (friendly) and negative (antagonistic) interactions.

In contrast to the bulk of research on social networks that has focused almost exclusively on positive interpretations of links between people, we study how the interplay between positive and negative relationships affects the structure of on-line social networks.

We connect our analyses to theories of signed networks from social psychology.

We find that the classical theory of structural balance tends to capture certain common patterns of interaction, but that it is also at odds with some of the fundamental phenomena we observe — particularly related to the evolving, directed nature of these on-line networks.

We then develop an alternate theory of status that better explains the observed edge signs and provides insights into the underlying social mechanisms.

Our work provides one of the first large-scale evaluations of theories of signed networks using on-line datasets, as well as providing a perspective for reasoning about social media sites.

Today I read a paper titled “A Decomposition Approach to Multi-Vehicle Cooperative Control”

The abstract is:
We present methods that generate cooperative strategies for multi-vehicle control problems using a decomposition approach.

By introducing a set of tasks to be completed by the team of vehicles and a task execution method for each vehicle, we decomposed the problem into a combinatorial component and a continuous component.

The continuous component of the problem is captured by task execution, and the combinatorial component is captured by task assignment.

In this paper, we present a solver for task assignment that generates near-optimal assignments quickly and can be used in real-time applications.

To motivate our methods, we apply them to an adversarial game between two teams of vehicles.

One team is governed by simple rules and the other by our algorithms.

In our study of this game we found phase transitions, showing that the task assignment problem is most difficult to solve when the capabilities of the adversaries are comparable.

Finally, we implement our algorithms in a multi-level architecture with a variable replanning rate at each level to provide feedback on a dynamically changing and uncertain environment.