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Sharan Raja

Publications and source records attributed to Sharan Raja.

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Adversarial Attacks Against Deep Learning Systems for ICD-9 Code Assignment

Manual annotation of ICD-9 codes is a time consuming and error-prone process. Deep learning based systems tackling the problem of automated ICD-9 coding have achieved competitive performance. Given the increased proliferation of electronic medical records, such automated systems are expected to eventually replace human coders. In this work, we investigate how a simple typo-based adversarial attack strategy can impact the performance of state-of-the-art models for the task of predicting the top 50 most frequent ICD-9 codes from discharge summaries. Preliminary results indicate that a malicious adversary, using gradient information, can craft specific perturbations, that appear as regular human typos, for less than 3% of words in the discharge summary to significantly affect the performance of the baseline model.

cs.LG

On the brachistochrone of a fluid-filled cylinder

We discuss a fluid dynamic variant of the classical Bernoulli's brachistochrone problem. The classical brachistochrone for a non-dissipative particle is governed by maximization of the particle's kinetic energy resulting in a cycloid. We consider a variant where the particle is replaced by a bottle filled with a viscous fluid and attempt to identify the shape of a curve connecting two points along which the bottle would move in the shortest time. We derive the system of integro-differential equations governing system dynamics for a given shape of the curve. Using these equations, we pose the brachistochrone problem invoking optimal control formalism and show that (in general) the curve deviates from a cycloid. This is due to the fact that increasing the rate of change of bottle kinetic energy is accompanied by increased viscous dissipation. We show that the bottle motion is governed by a balance between the desire to minimize travel time and the need to reach the end point in the face of increased dissipation. The trade-off between these two physical forces plays a vital role in determining the brachistochrone of a fluid-filled cylinder. We show that in the two limits of either vanishing or high viscosity, the brachistochrone for this problem reduces to a cycloid. An intermediate viscosity range is identified where the fluid brachistochrone is non-cycloidal. Finally, we show relevance of these results to the dynamics of a rolling liquid marble.

physics.flu-dyn