[1] Crustal thickness variations at the ultraslow spreading 10-16°E region of the Southwest Indian Ridge are used to constrain melt migration processes. In the study area, ridge morphology correlates with the obliquity of the ridge axis with respect to the spreading direction. A long oblique "supersegment", nearly devoid of magmatism, is flanked at either end by robust magmatic centers (Joseph Mayes Seamount and Narrowgate segment) of much lesser obliquity. Plate-driven mantle flow and temperature structure are calculated in 3-D based on the observed ridge segmentation. Melt extraction is assumed to occur in three steps: (1) vertical migration out of the melting region, (2) focusing along an inclined permeability barrier, and (3) extraction when the melt enters a region shallower than ∼35 km within 5 km of the ridge axis. No crust is predicted in our model along the oblique supersegment. The formation of Joseph Mayes Seamount is consistent with an on-axis melt anomaly induced by the local orthogonal spreading. The crustal thickness anomaly at Narrowgate results from melt extracted at a tectonic damage zone as it travels along the axis toward regions of lesser obliquity. Orthogonal spreading enhances the Narrowgate crustal thickness anomaly but is not necessary for it. The lack of a residual mantle Bouguer gravity high along the oblique supersegment can be explained by deep serpentization of the upper mantle permissible by the thermal structure of this ridge segment. Buoyancy-driven upwelling and/or mantle heterogeneities are not required to explain the extreme focusing of melt in the study area.

We present quantum observable Markov decision processes (QOMDPs), the quantum analogs of partially observable Markov decision processes (POMDPs). In a QOMDP, an agent is acting in a world where the state is represented as a quantum state and the agent can choose a superoperator to apply. This is similar to the POMDP belief state, which is a probability distribution over world states and evolves via a stochastic matrix. We show that the existence of a policy of at least a certain value has the same complexity for QOMDPs and POMDPs in the polynomial and infinite horizon cases. However, we also prove that the existence of a policy that can reach a goal state is decidable for goal POMDPs and undecidable for goal QOMDPs.

Abstract-We define the Diverse Action Manipulation (DAMA) problem in which we are given a mobile robot, a set of movable objects, and a set of diverse, possibly nonprehensile manipulation actions, and the goal is to find a sequence of actions that moves each of the objects to a goal configuration. We show that the DAMA problem can be framed as a multi-modal planning problem and describe a hierarchical algorithm that takes advantage of this multimodal nature. We also extend our earlier forward search sampling algorithm to a bi-directional version. We give results on a complicated manipulation domain and demonstrate that both new algorithms are significantly more efficient than the original, and that the hierarchical algorithm is usually much more efficient than the forward or bi-directional searches.

We present DARRT, a sampling-based algorithm for planning with multiple types of manipulation. Given a robot, a set of movable objects, and a set of actions for manipulating the objects, DARRT returns a sequence of manipulation actions that move the robot and objects from an initial configuration to a final configuration. The manipulation actions may be non-prehensile, meaning that the object is not rigidly attached to the robot, such as push, tilt, or pull. We describe a simple extension to the RRT algorithm to search the combined space of robot and objects and present an implementation of DARRT on the Willow Garage PR2 robot.

Purpose Collaborative goal setting is at the heart of person-centered rehabilitation but can be challenging, particularly in the area of aphasia. The purpose of this clinical focus article is to present a step-by-step model for forming a collaborative partnership with clients to develop an intervention plan that follows the client's lead, addresses communicative participation, and integrates multiple treatment strategies. Method We introduce the rationale and core features of a 4-step and 4-pronged process (the FOURC model) and illustrate its application through 3 cases of people with aphasia who were treated in outpatient rehabilitation. Conclusions The model invites client initiative in a clinically feasible manner while supporting the clinician's role in guiding the intervention based on professional expertise and growing familiarity with the case. Outcomes observed in case studies include strengthened motivation and improved real-life communication.