Lazy localization using the Frozen-Time Smoother

We present a new algorithm for solving the global localization problem called Frozen-Time Smoother (FTS). Time is 'frozen', in the sense that the belief always refers to the same time instant, instead of following a moving target, like Monte Carlo Localization does. This algorithm works in the case in which global localization is formulated as a smoothing problem, and a precise estimate of the incremental motion of the robot is usually available. These assumptions correspond to the case when global localization is used to solve the loop closing problem in SLAM. We compare FTS to two Monte Carlo methods designed with the same assumptions. The experiments suggest that a naive implementation of the FTS is more efficient than an extremely optimized equivalent Monte Carlo solution. Moreover, the FTS has an intrinsic laziness: it does not need frequent updates (scans can be integrated once every many meters) and it can process data in arbitrary order. The source code and datasets are available for download

A Least-Squares Temporal Difference based method for solving resource allocation problems

Value function approximation has a central role in Approximate Dynamic Programming (ADP) to overcome the so-called curse of dimensionality associated to real stochastic processes. In this regard, we propose a novel Least-Squares Temporal Difference (LSTD) based method: the “Multi-trajectory Greedy LSTD” (MG-LSTD). It is an exploration-enhanced recursive LSTD algorithm with the policy improvement embedded within the LSTD iterations. It makes use of multi-trajectories Monte Carlo simulations in order to enhance the system state space exploration. This method is applied for solving resource allocation problems modeled via a constrained Stochastic Dynamic Programming (SDP) based framework. In particular, such problems are formulated as a set of parallel Birth–Death Processes (BDPs). Some operational scenarios are defined and solved to show the effectiveness of the proposed approach. Finally, we provide some experimental evidence on the MG-LSTD algorithm convergence properties in function of its key-parameters

Speeding-up Rao-Blackwellized SLAM

Recently, Rao-Blackwellized particle filters have become a popular tool to solve the simultaneous localization and mapping problem. This technique applies a particle filter in which each particle carries an individual map of the environment. Accordingly, a key issue is to reduce the number of particles and/or to make use of compact map representations. This paper presents an approximative but highly efficient approach to mapping with Rao-Blackwellized particle filters. Moreover, it provides a compact map model. A key advantage is that the individual particles can share large parts of the model of the environment. Furthermore, they are able to re-use an already computed proposal distribution. Both techniques substantially speed up the overall process and reduce the memory requirements. Experimental results obtained with mobile robots in large-scale indoor environments and based on published, standard datasets illustrate the advantages of our methods over previous Rao-Blackwellized mapping approaches. © 2006 IEEE

Trans Arterial Embolization of Non-variceal Upper Gastrointestinal Bleeding: Is the Use of Ethylene–Vinyl Alcohol Copolymer as Safe as Coils?

Purpose: The safety of liquid embolics over the conventional coils for the treatment of non-variceal upper gastrointestinal bleeding (UGIB) approach is still unclear. Purpose of this study is to assess the safety of ethylene–vinyl alcohol copolymer (EVOH 6%) over coils in the treatment of UGIB. Materials and Methods: All the upper gastrointestinal tract embolization procedures performed in a single center in a 6-year period were reviewed. Patients embolised with coils (Group A) versus those embolised with EVOH 6% (Group B) were compared. Technical/clinical success, bleeding recurrence, complication and mortality rates were analyzed. Results: A total 71 patients were included in the study (41 Group A and 30 Group B). Coagulopathy was present in 21% of Group A and 46% of Group B patients (p < 0.05). Technical and clinical success was 97.6 and 92.7% for Group A, and 100 and 93.3% for Group B respectively, (p > 0.05). Ten patients (17% Group A; 10% Group B) re-bled within the first 36 h and all of them were re-treated successfully with a second embolization. In Group A one major complication (bowel ischemia) occurred. No complication occurred in Group B. The survival rate in the first 30 days was 90.3% for group A and 90% for group B (p > 0.05). Conclusion: This study demonstrated EVOH 6% appears to be as safe and effective as coils in the treatment of non-variceal UGIB