Path planning with user route preference - A reward surface approximation approach using orthogonal Legendre polynomials

As self driving cars become more ubiquitous, users would look for natural ways of informing the car AI about their personal choice of routes. This choice is not always dictated by straightforward logic such as shortest distance or shortest time, and can be influenced by hidden factors, such as comfort and familiarity. This paper presents a path learning algorithm for such applications, where from limited positive demonstrations, an autonomous agent learns the user's path preference and honors that choice in its route planning, but has the capability to adopt alternate routes, if the original choice(s) become impractical. The learning problem is modeled as a Markov decision process. The states (way-points) and actions (to move from one way-point to another) are pre-defined according to the existing network of paths between the origin and destination and the user's demonstration is assumed to be a sample of the preferred path. The underlying reward function which captures the essence of the demonstration is computed using an inverse reinforcement learning algorithm and from that the entire path mirroring the expert's demonstration is extracted. To alleviate the problem of state space explosion when dealing with a large state space, the reward function is approximated using a set of orthogonal polynomial basis functions with a fixed number of coefficients regardless of the size of the state space. A six fold reduction in total learning time is achieved compared to using simple basis functions, that has dimensionality equal to the number of distinct states

Haptic-Guided Teleoperation of a 7-DoF Collaborative Robot Arm With an Identical Twin Master

In this article, we describe two techniques to enable haptic-guided teleoperation using 7-DoF cobot arms as master and slave devices. A shortcoming of using cobots as master-slave systems is the lack of force feedback at the master side. However, recent developments in cobot technologies have brought in affordable, flexible, and safe torque-controlled robot arms, which can be programmed to generate force feedback to mimic the operation of a haptic device. In this article, we use two Franka Emika Panda robot arms as a twin master-slave system to enable haptic-guided teleoperation. We propose a two layer mechanism to implement force feedback due to 1) object interactions in the slave workspace, and 2) virtual forces, e.g. those that can repel from static obstacles in the remote environment or provide task-related guidance forces. We present two different approaches for force rendering and conduct an experimental study to evaluate the performance and usability of these approaches in comparison to teleoperation without haptic guidance. Our results indicate that the proposed joint torque coupling method for rendering task forces improves energy requirements during haptic guided telemanipulation, providing realistic force feedback by accurately matching the slave torque readings at the master side

Transverse magnetic focussing of heavy holes in a (100) GaAs quantum well

We perform magnetic focussing of high mobility holes confined in a shallow GaAs/Al0.33Ga0.67As quantum well grown on a (100) GaAs substrate. We observe ballistic focussing of holes over a path length of up to 4.9µm with a large number of focussing peaks. We show that additional structure on the focussing peaks can be caused by a combination of the finite width of the injector QPC and Shubnikov-de Haas oscillations. These results pave the way to studies of spin-dependent magnetic focussing and spin relaxation lengths in 2D hole systems without complications of crystal anisotropies and anisotropic g-tensors.We thank Scott Liles, Samuel Bladwell, Oleg Sushkov and Ulrich Zülicke for numerous discussions. This project was supported by the Australian Research Council (ARC) DP Scheme and the EPSRC (UK). Devices were fabricated using facilities at the UNSW Node of Australian National Fabrication Facility (ANFF).This is the final version of the article. It first appeared from IOP via http://dx.doi.org/10.1088/0268-1242/30/10/10200

Applying Markov decision process to understand driving decisions using basic safety messages data

While a number of studies have investigated driving behaviors, detailed microscopic driving data has only recently become available for analysis. Through Basic Safety Message (BSM) data from the Michigan Safety Pilot Program, this study applies a Markov Decision Process (MDP) framework to understand driving behavior in terms of acceleration, deceleration and maintaining speed decisions. Personally Revealed Choices (PRC) that maximize the expected sum of rewards for individual drivers are obtained by analyzing detailed data from 120 trips and the application of MDP. Specifically, this paper defines states based on the number of objects around the host vehicle and the distance to the front object. Given the states, individual drivers’ reward functions are estimated using the multinomial logit model and used in the MDP framework. Optimal policies (i.e. PRC) are obtained through a value iteration algorithm. The results show that as the number of objects increases around a host vehicle, the driver prefer to accelerate in order to escape the crowdedness around them. In addition, when trips are segmented based on the level of crowdedness, increased levels of trip crowdedness results in a fewer number of drivers accelerating because the traffic conditions constrain them to maintaining constant speed or deceleration. One potential application of this study is to generate short-term predictive driver decision information through historical driving performance, which can be used to warn a host vehicle driver when the person substantially deviates from their own historical PRC. This information could also be disseminated to surrounding vehicles as well, enabling them to foresee the states and actions of other drivers and potentially avoid collisions

Noncollinear paramagnetism of a GaAs two-dimensional hole system.

We have performed transport measurements in tilted magnetic fields in a two-dimensional hole system grown on the surface of a (311)A GaAs crystal. A striking asymmetry of Shubnikov-de Haas oscillations occurs upon reversing the in-plane component of the magnetic field along the low-symmetry [2[over ¯]33] axis. As usual, the magnetoconductance oscillations are symmetric with respect to reversal of the in-plane field component aligned with the high-symmetry [011[over ¯]] axis. Our observations demonstrate that an in-plane magnetic field can generate an out-of-plane component of magnetization in a low-symmetry hole system, creating new possibilities for spin manipulation.This work was supported by the Australian Research Council (ARC) under the DP scheme and by the NSF under Grant No. DMR-1310199. ARH acknowledges an ARC DOR award.This is the accepted manuscript. The final version is available from APS at http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.113.236401

Haptic-Guided Shared Control Grasping for Collision-Free Manipulation

We propose a haptic-guided shared control system that provides an operator with force cues during reach-to-grasp phase of tele-manipulation. The force cues inform the operator of grasping configuration which allows collision-free autonomous post-grasp movements. Previous studies showed haptic guided shared control significantly reduces the complexities of the teleoperation. We propose two architectures of shared control in which the operator is informed about (1) the local gradient of the collision cost, and (2) the grasping configuration suitable for collision-free movements of an aimed pick-and-place task. We demonstrate the efficiency of our proposed shared control systems by a series of experiments with Franka Emika robot. Our experimental results illustrate our shared control systems successfully inform the operator of predicted collisions between the robot and an obstacle in the robot's workspace. We learned that informing the operator of the global information about the grasping configuration associated with minimum collision cost of post-grasp movements results in a reach-to-grasp time much shorter than the case in which the operator is informed about the local-gradient information of the collision cost

Organic aerosol formation downwind from the Deepwater Horizon oil spill.

A large fraction of atmospheric aerosols are derived from organic compounds with various volatilities. A National Oceanic and Atmospheric Administration (NOAA) WP-3D research aircraft made airborne measurements of the gaseous and aerosol composition of air over the Deepwater Horizon (DWH) oil spill in the Gulf of Mexico that occurred from April to August 2010. A narrow plume of hydrocarbons was observed downwind of DWH that is attributed to the evaporation of fresh oil on the sea surface. A much wider plume with high concentrations of organic aerosol (>25 micrograms per cubic meter) was attributed to the formation of secondary organic aerosol (SOA) from unmeasured, less volatile hydrocarbons that were emitted from a wider area around DWH. These observations provide direct and compelling evidence for the importance of formation of SOA from less volatile hydrocarbons

Carrier-mediated magnetoelectricity in complex oxide heterostructures

While tremendous success has been achieved to date in creating both single phase and composite magnetoelectric materials, the quintessential electric-field control of magnetism remains elusive. In this work, we demonstrate a linear magnetoelectric effect which arises from a novel carrier-mediated mechanism, and is a universal feature of the interface between a dielectric and a spin-polarized metal. Using first-principles density functional calculations, we illustrate this effect at the SrRuO$_3$/SrTiO$_3$ interface and describe its origin. To formally quantify the magnetic response of such an interface to an applied electric field, we introduce and define the concept of spin capacitance. In addition to its magnetoelectric and spin capacitive behavior, the interface displays a spatial coexistence of magnetism and dielectric polarization suggesting a route to a new type of interfacial multiferroic

Differential light-induced responses in sectorial inherited retinal degeneration.

Retinitis pigmentosa (RP) is a group of genetically and clinically heterogeneous inherited degenerative retinopathies caused by abnormalities of photoreceptors or retinal pigment epithelium in the retina leading to progressive sight loss. Rhodopsin is the prototypical G-protein-coupled receptor located in the vertebrate retina and is responsible for dim light vision. Here, novel M39R and N55K variants were identified as causing an intriguing sector phenotype of RP in affected patients, with selective degeneration in the inferior retina. To gain insights into the molecular aspects associated with this sector RP phenotype, whose molecular mechanism remains elusive, the mutations were constructed by site-directed mutagenesis, expressed in heterologous systems, and studied by biochemical, spectroscopic, and functional assays. M39R and N55K opsins had variable degrees of chromophore regeneration when compared with WT opsin but showed no gross structural misfolding or altered trafficking. M39R showed a faster rate for transducin activation than WT rhodopsin with a faster metarhodopsinII decay, whereas N55K presented a reduced activation rate and an altered photobleaching pattern. N55K also showed an altered retinal release from the opsin binding pocket upon light exposure, affecting its optimal functional response. Our data suggest that these sector RP mutations cause different protein phenotypes that may be related to their different clinical progression. Overall, these findings illuminate the molecular mechanisms of sector RP associated with rhodopsin mutations

Orexinergic Input to Dopaminergic Neurons of the Human Ventral Tegmental Area

The mesolimbic reward pathway arising from dopaminergic (DA) neurons of the ventral tegmental area (VTA) has been strongly implicated in reward processing and drug abuse. In rodents, behaviors associated with this projection are profoundly influenced by an orexinergic input from the lateral hypothalamus to the VTA. Because the existence and significance of an analogous orexigenic regulatory mechanism acting in the human VTA have been elusive, here we addressed the possibility that orexinergic neurons provide direct input to DA neurons of the human VTA. Dual-label immunohistochemistry was used and orexinergic projections to the VTA and to DA neurons of the neighboring substantia nigra (SN) were analyzed comparatively in adult male humans and rats. Orexin B-immunoreactive (IR) axons apposed to tyrosine hydroxylase (TH)-IR DA and to non-DA neurons were scarce in the VTA and SN of both species. In the VTA, 15.062.8% of TH-IR perikarya in humans and 3.260.3% in rats received orexin B-IR afferent contacts. On average, 0.2460.05 and 0.0560.005 orexinergic appositions per TH-IR perikaryon were detected in humans and rats, respectively. The majority(86–88%) of randomly encountered orexinergic contacts targeted the dendritic compartment of DA neurons. Finally, DA neurons of the SN also received orexinergic innervation in both species. Based on the observation of five times heavierorexinergic input to TH-IR neurons of the human, compared with the rat, VTA, we propose that orexinergic mechanism acting in the VTA may play just as important roles in reward processing and drug abuse in humans, as already established well in rodents