Publications

We develop a matched signal detection (MSD) theory for signals with an intrinsic structure described by a weighted graph. Hypothesis tests are formulated under different signal models. In the simplest scenario, we assume that the signal is deterministic with noise in a subspace spanned by a subset of eigenvectors of the graph Laplacian. The conventional matched subspace detection can be easily extended to this case. Furthermore, we study signals with certain level of smoothness. The test turns out to be a weighted energy detector, when the noise variance is negligible. More generally, we presume that the signal follows a prior distribution, which could be learnt from training data. The test statistic is then the difference of signal variations on associated graph structures, if an Ising model is adopted. Effectiveness of the MSD on graph is evaluated both by simulation and real data. We apply it to the network classification problem of Alzheimer’s disease (AD) particularly. The preliminary results demonstrate that our approach is able to exploit the sub-manifold structure of the data, and therefore achieve a better performance than the traditional principle component analysis (PCA).

Here's a look at what's coming up in the May 2013 issue of JoVE - The Journal of Visualized Experiments.

test test abstract

The global economy has a chronic shortage of safe assets which lies behind many recent macroeconomic imbalances. This paper provides a simple model of the Safe Asset Mechanism (SAM), its recessionary safety traps, and its policy antidotes. Public debt plays a central role in SAM as long as the government has spare fiscal capacity to back safe asset production. We show that Quantitative Easing type policies have positive effects on spreads and output. In contrast, Operation Twist type policies, where the duration of public debt held by the public is reduced, can be counterproductive. Monetary policy commitments work if they support future bad states of nature. All these policies depend on fiscal capacity. Once the latter runs out, short term cyclical policy becomes ineffective. In contrast, credible long run fiscal consolidation relaxes the fiscal capacity constraint and enhances the effectiveness of short term policy. An economy that is near its scal limits is susceptible to runs on its public debt and to destabilizing feedback loops.