Papers.

Remote incremental linking for energy-efficient reprogramming of sensor networks

Flexible Application Rights Management in a Pervasive Environment

Reversible Fault-Tolerant Logic

It is now widely accepted that the CMOS technology implementing irreversible logic may hit a scaling limit beyond 2016, and that the increased power dissipation is a major limiting factor. Reversible computing can potentially require arbitrarily small amounts of energy. Recently several nano-scale devices which have the potential to scale, and which naturally perform reversible logic, have emerged. This paper addresses several fundamental issues that need to be addressed before any nano-scale reversible computing systems can be realized, including reliability and performance trade-offs and architecture optimization. Many nano-scale devices are limited to only near neighbor interactions, requiring careful optimization of circuits. We provide efficient fault-tolerant (FT) circuits when restricted to both 2D and 1D. Finally, we compute bounds on the entropy (and hence, heat) generated by our FT circuits and provide quantitative estimates on how large can we make our circuits before we lose any advantage over irreversible computing.

Cruz: Application-Transparent Distributed Checkpoint-Restart on Standard Operating Systems

PathScale InfiniPath: A First Look

Matching distributed systems to their environment using dissipative structures

On LQG Control Across a Stochastic Packet-Dropping Link

Motion Planning with Wireless Network Constraints

Multiple power-law structures in heterogeneous complex networks

Stopping gluinos

Cosmological particle production and the precision of the WKB approximation

Particle production by slow-changing gravitational fields is usually described using quantum field theory in curved spacetime. Calculations require a definition of the vacuum state, which can be given using the adiabatic (WKB) approximation. I investigate the best attainable precision of the resulting approximate definition of the particle number. The standard WKB ansatz yields a divergent asymptotic series in the adiabatic parameter. I derive a novel formula for the optimal number of terms in that series and demonstrate that the error of the optimally truncated WKB series is exponentially small. This precision is still insufficient to describe particle production from vacuum, which is typically also exponentially small. An adequately precise approximation can be found by improving the WKB ansatz through perturbation theory. I show quantitatively that the fundamentally unavoidable imprecision in the definition of particle number in a time-dependent background is equal to the particle production expected to occur during that epoch. The results are illustrated by analytic and numerical examples.

Limits on split supersymmetry from gluino cosmology

Drawing conformal diagrams for a fractal landscape

Generic models of cosmological inflation and the recently proposed scenarios of a recycling universe and the string theory landscape predict spacetimes whose global geometry is a stochastic, self-similar fractal. To visualize the complicated causal structure of such a universe, one usually draws a conformal (Carter-Penrose) diagram. I develop a new method for drawing conformal diagrams, applicable to arbitrary 1+1-dimensional spacetimes. This method is based on a qualitative analysis of intersecting lightrays and thus avoids the need for explicit transformations of the spacetime metric. To demonstrate the power and simplicity of this method, I present derivations of diagrams for spacetimes of varying complication. I then apply the lightray method to three different models of an eternally inflating universe (scalar-field inflation, recycling universe, and string theory landscape) involving the nucleation of nested asymptotically flat, de Sitter and/or anti-de Sitter bubbles. I show that the resulting diagrams contain a characteristic fractal arrangement of lines.

Time-reparametrization invariance in eternal inflation

I address some recently raised issues regarding the time-parametrization dependence in stochastic descriptions of eternal inflation. To clarify the role of the choice of the time gauge, I show examples of gauge-dependent as well as gauge-independent statements about physical observables in eternally inflating spacetimes. In particular, the relative abundance of thermalized and inflating regions is highly gauge-dependent. The unbounded growth of the 3-volume of the inflating regions is found in certain time gauges, such as the proper time or the scale factor gauge. Yet in the same spacetimes there exist time foliations with a finite and monotonically decreasing 3-volume, which I demonstrate by an explicit construction. I also show that there exists no "correct" choice of the time gauge that would yield an unbiased stationary probability distribution for observables in thermalized regions.

N-flation

Probabilities in the inflationary multiverse

Inflationary cosmology leads to the picture of a "multiverse," involving an infinite number of (spatially infinite) post-inflationary thermalized regions, called pocket universes. In the context of theories with many vacua, such as the landscape of string theory, the effective constants of Nature are randomized by quantum processes during inflation. We discuss an analytic estimate for the volume distribution of the constants within each pocket universe. This is based on the conjecture that the field distribution is approximately ergodic in the diffusion regime, when the dynamics of the fields is dominated by quantum fluctuations (rather than by the classical drift). We then propose a method for determining the relative abundances of different types of pocket universes. Both ingredients are combined into an expression for the distribution of the constants in pocket universes of all types.

SIMAC: semantic interaction with music audio contents

Joeq: A virtual machine and compiler infrastructure

The optimality of a control band policy

A massively parallel particle-in-cell code for the simulation of field-emitter based electron sources

Advances in information retrieval: An introduction to the special issue

Dynamics of the Chilean Web structure

An adaptive overflow technique for B-trees

A Gradient Topology for Master-Slave Replication in Peer-to-Peer Environments

Applications of Web Query Mining

Collaborative Machine Learning

Database and Information Retrieval Techniques for XML

Semantic Web Services for Activity-Based Computing

Experimental Analysis of a Fast Intersection Algorithm for Sorted Sequences

Using Datalog with Binary Decision Diagrams for Program Analysis

Reflection Analysis for Java

The Bittorrent P2P File-Sharing System: Measurements and Analysis

Scanning Objects in the Wild: Assessing an Object Triggered Information System

Banshee: A Scalable Constraint-Based Analysis Toolkit

The Essence of Data Access in C-omega

Emergent Consensus in Decentralised Systems Using Collaborative Reinforcement Learning

Let Your CyberAlter Ego Share Information and Manage Spam

Almost all of us have multiple cyberspace identities, and these cyberalter egos are networked together to form a vast cyberspace social network. This network is distinct from the world-wideweb (WWW), which is being queried and mined to the tune of billions of dollars everyday, and until recently, has gone largely unexplored. Empirically, the cyberspace social networks have been found to possess many of the same complex features that characterize its real counterparts, including scalefree degree distributions, low diameter, and extensive connectivity. We show that these topological features make the latent networks particularly suitable for explorations and management via localonly messaging protocols. Cyberalter egos can communicate via their direct links (i.e., using only their own address books) and set up a highly decentralized and scalable message passing network that can allow large-scale sharing of information and data. As one particular example of such collaborative systems, we provide a design of a spam filtering system, and our large-scale simulations show that the system achieves a spam detection rate close to 100%, while the false positive rate is kept around zero. This system of letting cyberalter egos network among themselves has several advantages over other recent proposals for collaborative spam filtering: (i) It uses an already existing network, created by the same social dynamics that govern our daily lives, and no dedicated peerto-peer (P2P) systems or centralized server-based systems need be constructed; (ii) It utilizes a percolation search algorithm (which can be viewed as mimicking how rumor is spread in a social network) that makes the query-generated traffic scalable; (iii) The network has a built in trust system (just as in social networks) that can be used to thwart malicious attacks; and (iv) It can be implemented right now as a plugin to popular email programs, such as MS Outlook, Eudora, and Sendmail.

A Practical Approach to Joint Network-Source Coding

Joint Network-Source Coding: An Achievable Region with Diversity Routing

Essential Incompleteness of Arithmetic Verified by Coq

Disaster Management in Scale-Free Networks: Recovery from and Protection Against Intentional Attacks

Near-optimal Nonmyopic Value of Information in Graphical Models

A fundamental issue in real-world systems, such as sensor networks, is the selection of observations which most effectively reduce uncertainty. More specifically, we address the long standing problem of nonmyopically selecting the most informative subset of variables in a graphical model. We present the first efficient randomized algorithm providing a constant factor (1 - 1/e – e) approximation guarantee for any e > 0 with high confidence. The algorithm leverages the theory of submodular functions, in combination with a polynomial bound on sample complexity. We furthermore prove that no polynomial time algorithm can provide a constant factor approximation better than (1 - 1/e) unless P = NP. Finally, we provide extensive evidence of the effectiveness of our method on two complex real-world datasets.

Wi-Fi Walkman: A wireless handhold that shares and recommends music on peer-to-peer networks

Visualizing the Structural Signature of Social Roles

Una herramienta de minería de consultas para el diseño del contenido y la estructura de un sitio Web

Un modelo de integración de conceptos institucionales en una plataforma de programación de agentes

Um novo retrato da Web brasileira

Trickle: A Userland Bandwidth Shaper for UNIX-like Systems

Towards formal evaluation of collaborative work

The syntax of case and agreement : its relationship to morphology and argument structure