Information-theoretic lower bounds on the oracle complexity of stochastic convex optimization

Relative to the large literature on upper bounds on complexity of convex optimization, lesser attention has been paid to the fundamental hardness of these problems. Given the extensive use of convex optimization in machine learning and statistics, gaining an understanding of these complexity-theoretic issues is important. In this paper, we study the complexity of stochastic convex optimization in an oracle model of computation. We improve upon known results and obtain tight minimax complexity estimates for various function classes

Imaging, Intervention, and Workflow in Acute Ischemic Stroke: The Calgary Approach

ABSTRACT SUMMARY: Five recently published clinical trials showed dramatically higher rates of favorable functional outcome and a satisfying safety profile of endovascular treatment compared with the previous standard of care in acute ischemic stroke with proximal anterior circulation artery occlusion. Eligibility criteria within these trials varied by age, stroke severity, imaging, treatment-time window, and endovascular treatment devices. This focused review provides an overview of the trial results and explores the heterogeneity in imaging techniques, workflow, and endovascular techniques used in these trials and the consequent impact on practice. Using evidence from these trials and following a case from start to finish, this review recommends strategies that will help the appropriate patient undergo a fast, focused clinical evaluation, imaging, and intervention. ABBREVIATIONS: MR CLEAN ϭ Multicenter Randomized Clinical trial of Endovascular treatment for Acute ischemic stroke in the Netherlands; EMS ϭ Emergenc

Inverse Diffusion Theory of Photoacoustics

This paper analyzes the reconstruction of diffusion and absorption parameters in an elliptic equation from knowledge of internal data. In the application of photo-acoustics, the internal data are the amount of thermal energy deposited by high frequency radiation propagating inside a domain of interest. These data are obtained by solving an inverse wave equation, which is well-studied in the literature. We show that knowledge of two internal data based on well-chosen boundary conditions uniquely determines two constitutive parameters in diffusion and Schroedinger equations. Stability of the reconstruction is guaranteed under additional geometric constraints of strict convexity. No geometric constraints are necessary when $2n$ internal data for well-chosen boundary conditions are available, where $n$ is spatial dimension. The set of well-chosen boundary conditions is characterized in terms of appropriate complex geometrical optics (CGO) solutions.Comment: 24 page