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Graduate

Information Systems Lab Colloquium: Spy vs. Spy: Anonymous Messaging

Topic: 
Spy vs. Spy: Anonymous Messaging
Abstract / Description: 

Anonymous messaging platforms, such Secret, Whisper and Yik Yak, have emerged as important social media for sharing one's thoughts without the fear of being judged by friends, family, or the public. Further, such anonymous platforms are crucial in nations with authoritarian governments, where the right to free expression and sometimes the personal safety of the message author depends on anonymity. Current platforms offer only superficial anonymity – their centralized implementation makes them naturally vulnerable to authoritarian adversaries and/or economic incentives.

In this talk, we study the problem of designing a distributed messaging protocol that spreads the message fast while keeping the identity of the source hidden from an adversary. We present an anonymous messaging protocol, which we call adaptive diffusion, and show that it spreads fast and achieves nearly perfect obfuscation of the source for a wide range of adversaries. System issues in the implementation of the protocol are discussed.

 

Date and Time: 
Thursday, March 19, 2015 - 4:15pm to 5:15pm
Venue: 
Packard 101

Information Systems Lab Colloquium: On Landau's eigenvalue theorem and information cut-sets

Topic: 
On Landau's eigenvalue theorem and information cut-sets
Abstract / Description: 

How much information can be carried by electromagnetic radiation?

We present a variation of a theorem of Landau concerning the phase transition of the eigenvalues of a time-frequency limiting operator, and describe its application in a limiting regime where the original theorem cannot be directly applied. Using this result, we compute the number of degrees of freedom of square-integrable fields in terms of Kolmogorov's N-width and determine, up to order, the total amount of information that can be transported in time and space by electromagnetic waves, extending previous single-frequency treatments to signals of non-zero frequency bandwidth.

In closing, we also discuss how our mathematical results are related to the holographic principle of quantum gravity that has been formulated in the context of black hole thermodynamics.

Date and Time: 
Thursday, March 5, 2015 - 4:15pm to 5:15pm
Venue: 
Packard 101

Information Systems Lab Colloquium: Exploiting convex structure in aircraft design

Topic: 
Exploiting convex structure in aircraft design
Abstract / Description: 

Modern aircraft represent some of the most complex, performance-driven engineering systems ever conceived and built. Surprisingly, many high-level relationships and constraints on aircraft performance can be encoded via the feasible set of a geometric program. This observation gives us a reliable and efficient way to solve conceptual design problems. Using optimal dual variables, we can also quantify performance sensitivities, better understand tradeoffs, and guide higher fidelity analysis and optimization. We will discuss modeling techniques that have been successful in transforming aircraft design problems to GPs, ongoing research in GP modeling, fitting of GP-compatible models from data, and possible implications for design of large multidisciplinary systems.

Date and Time: 
Thursday, February 26, 2015 - 4:15pm to 5:15pm
Venue: 
Packard 101

Information Systems Lab Colloquium: If it spreads it can't hide: detecting epidemics from weak signatures

Topic: 
If it spreads it can't hide: detecting epidemics from weak signatures
Abstract / Description: 

Last week, Sanjay Shakkottai (UT Austin) talked about how external agents affect spreading properties of an epidemic -- a prediction or "forward" problem. This talk is about "inverse" problems -- what explains what we are seeing? In particular, is it an epidemic?

Specifically, we ask: can we (early) detect the spread of a new disease, or of a new kind of malware, one whose properties have not been studied, and characteristics not yet identified? We consider the problem of detecting an infection process in a network when the indication that any particular node is infected is extremely noisy -- statistically indistinguishable from everyday behavior.

Such a scenario occurs, for instance, when the only signature of a worm infecting a neighboring network node is a (rarely occurring) temporally-localized increased processor and network load (when the worm is actively spreading from one node to its neighbor). However, many other benign activities have a similar signature; further these benign activities occur frequently (as opposed to the rare occurrence of a worm infection). While it is impossible to distinguish between an infection incidence and a benign activity merely from observing a single node, we show that the spread itself can be used as a global signature of epidemic spread, and thus we can reliably distinguish between these two hypotheses (epidemic / benign activity). In addition, we explore how graph topology impacts our ability to do early detection.

Based on joint with work Chris Milling, Eli Meirom, Sanjay Shakkottai, Shie Mannor and Ariel Orda.


 

 

The Information Systems Laboratory Colloquium (ISLC) is typically held in Packard 101 every Thursday at 4:15 pm during the academic year. Refreshments are usually served after the talk.

The Colloquium is organized by graduate students Chris Fougner, Hyeji Kim, Neal Master and Dor Shaviv. To suggest speakers, please contact any of the students.

Date and Time: 
Thursday, February 19, 2015 - 4:15pm to 5:15pm
Venue: 
Packard 101

Information Systems Lab Colloquium: Spectral Embedding of k-Cliques, Graph Partitioning and k-Means

Topic: 
Spectral Embedding of k-Cliques, Graph Partitioning and k-Means
Abstract / Description: 

We introduce and study a new notion of graph partitioning, intimately connected to k-means clustering. Informally, our graph partitioning objective asks for the optimal spectral simplification of a graph as a disjoint union of k normalized cliques. It is a variant of graph decomposition into expanders (where expansion is not measured w.r.t. the induced graph). Optimizing this new objective is equivalent to clustering the effective resistance embedding of the original graph. Our approximation algorithm for the new objective is closely related to spectral clustering: it optimizes the k-means objective on a certain smoothed version of the resistive distance embedding. We also show that spectral clustering applied directly to the original graph gives guarantees for our new objective function.

In order to illustrate the power of our new notion, we show that approximation algorithms for our new objective can be used in a black box fashion to approximately recover a partition of a graph into k pieces given a guarantee that a good partition exists with sufficiently large gap in internal and external conductance.

Joint work with Pranjal Awasthi, Ravishankar Krishnaswamy, and Ali Kemal Sinop

Date and Time: 
Thursday, January 22, 2015 - 4:15pm to 5:15pm
Venue: 
Packard 101

Information Systems Lab Colloquium: Understanding Visual Computations in the Primate Retina

Topic: 
Understanding Visual Computations in the Primate Retina
Abstract / Description: 

Vision begins with neural computation in the retina, which sends a highly processed version of the visual world along multiple parallel pathways to the brain. Our research is focused on understanding visual computations in the primate retina and on using this information for the design of artificial retinas to treat blindness. I will describe the state of our understanding of visual computations in the retinal circuitry, with an emphasis on open problems for future exploration, and on achieving a synthetic understanding appropriate for diverse applications.

Date and Time: 
Thursday, January 29, 2015 - 4:15pm to 5:15pm
Venue: 
Packard 101

Applied Physics/Physics Colloquium: Recent Cosmology Results from the Planck Experiment

Topic: 
Recent Cosmology Results from the Planck Experiment
Abstract / Description: 

Sketched out in 1992, selected by ESA in 1996, launched in 2009, Planck delivered a first set of results on March 21, 2013, in particular a "definitive" map of the anisotropies of the Cosmic Microwave Background (CMB). The later displays minuscule variations as a function of the observing direction of the temperature of the fossil radiation around its mean temperature of 2.725K. These CMB anisotropies, of rms ~100microK, reveal the imprint of the primordial fluctuations which initiate the growth of the large scale structures of the Universe, as transformed by their evolution, in particular during the first 370 000 years. Since 2013, we analyzed twice more data and in particular the polarization information we gathered over the full course of the mission. I will describe the new results we just obtained, and in particular confront what temperature and polarization anisotropies teach us, both in terms of content of the universe and of characteristics of the primordial fluctuations.


 

Held Tuesdays at 4:15 pm, in the William R. Hewlett Teaching Center, room 200 (see map). Refreshments in the lobby of Varian Physics at 4:00 pm.

Autumn 2014/15, Committee: A. Linde (Chair), L. Hollberg, B. Macintosh & Young Lee

Date and Time: 
Tuesday, March 10, 2015 - 4:15pm to 5:15pm
Venue: 
Hewlett 200

Applied Physics/Physics Colloquium: From Stimulation to Perception: Adaptive Optics for Testing Human Vision on a Cellular Scale

Topic: 
From Stimulation to Perception: Adaptive Optics for Testing Human Vision on a Cellular Scale
Abstract / Description: 

Learning how sensory signals are transformed into perception is a challenge. In vitro preparations offer access to single cells as well as to an ever-expanding arsenal of tools to measure physiology, but come at the cost of perception. Living animals impose limitations on access (controlling the retinal stimulation, for example) and can only offer primitive measures of perception. By combining adaptive-optics micro-optical-stimulation with high-speed eye tracking in humans, we believe we can offer the best of both worlds. Adaptive optics and high-speed eye tracking allow us to control light stimulation down to the single receptor level and, since it is done in humans, we can use that in concert with sophisticated psychophysical tasks. This talk will describe the evolution of the technology that we've developed in our lab followed by an update on our ongoing efforts to learn about the neural circuits that underlie human spatial and color vision.


 

Held Tuesdays at 4:15 pm, in the William R. Hewlett Teaching Center, room 200 (see map). Refreshments in the lobby of Varian Physics at 4:00 pm.

Autumn 2014/15, Committee: A. Linde (Chair), L. Hollberg, B. Macintosh & Young Lee

Date and Time: 
Tuesday, March 3, 2015 - 4:15pm to 5:15pm
Venue: 
Hewlett 200

Applied Physics/Physics Colloquium: Laser-driven Shock Waves: From Cosmic-ray Physics to Medical Applications

Topic: 
Laser-driven Shock Waves: From Cosmic-ray Physics to Medical Applications
Abstract / Description: 

Shock waves are ubiquitous in astrophysical environments and are tightly connected with magnetic-field amplification and particle acceleration. The fast progress in high-power laser technology is bringing the study of high Mach number shocks into the realm of laboratory plasmas, where in situ measurements can be made helping us understand the fundamental kinetic processes behind shocks. I will discuss the recent progress in laser-driven shock experiments at state-of-the-art facilities like NIF and Omega and the important role that ab initio massively parallel simulations are playing in the design of these experiments and in our understanding of the plasma microphysics involved in particle acceleration and radiation emission. Finally, I will show that by controlling the laser and plasma conditions it is possible to explore different particle acceleration mechanisms, from Fermi-like processes, which are relevant in astrophysics, to the generation of high-quality ion beams for radiotherapy.


 

Held Tuesdays at 4:15 pm, in the William R. Hewlett Teaching Center, room 200 (see map). Refreshments in the lobby of Varian Physics at 4:00 pm.


Autumn 2014/15, Committee: A. Linde (Chair), L. Hollberg, B. Macintosh & Young Lee

Date and Time: 
Tuesday, February 24, 2015 - 4:15pm to 5:15pm
Venue: 
Hewlett 200

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