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16 results on '"Walker, Tristan"'

1. LAMP: Learning a Motion Policy to Repeatedly Navigate in an Uncertain Environment

Author

Tsang, Florence, Walker, Tristan, MacDonald, Ryan A., Sadeghi, Armin, and Smith, Stephen L.

Subjects
Computer Science - Robotics
Abstract

Mobile robots are often tasked with repeatedly navigating through an environment whose traversability changes over time. These changes may exhibit some hidden structure, which can be learned. Many studies consider reactive algorithms for online planning, however, these algorithms do not take advantage of the past executions of the navigation task for future tasks. In this paper, we formalize the problem of minimizing the total expected cost to perform multiple start-to-goal navigation tasks on a roadmap by introducing the Learned Reactive Planning Problem. We propose a method that captures information from past executions to learn a motion policy to handle obstacles that the robot has seen before. We propose the LAMP framework, which integrates the generated motion policy with an existing navigation stack. Finally, an extensive set of experiments in simulated and real-world environments show that the proposed method outperforms the state-of-the-art algorithms by 10% to 40% in terms of expected time to travel from start to goal. We also evaluate the robustness of the proposed method in the presence of localization and mapping errors on a real robot.

Published
2020

4. Predictive Dead Reckoning for Online Peer-to-Peer Games

Author

Walker, Tristan, Gilhuly, Barry, Sadeghi, Armin, Delbosc, Matt, and Smith, Stephen L.

Abstract

In online peer-to-peer games, players send periodic updates to each other and each player must locally reconstruct the position of their opponents in between these updates. In scenarios where players are driving cars, high speeds produce more pronounced errors in local replication of online opponents. In this work, we propose a new method of replicating opponents with less data sent and up to 45% less error compared to the state-of-the-art. We use a neural network-based approach to predict an opponent's position, combined with a path tracking controller from the field of mobile robotics, to produce smooth, believable trajectories for opponents' vehicles. We also propose a neural network-based approach to predict a replicated opponent's trajectory following a collision with a static obstacle.

Published
2024
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6. LAMP: Learning a Motion Policy to Repeatedly Navigate in an Uncertain Environment.

Author

Tsang, Florence, Walker, Tristan, MacDonald, Ryan A., Sadeghi, Armin, and Smith, Stephen L.

Subjects
*ONLINE algorithms, *MOBILE robots, *LAMPS, *TIME travel, *PRODUCTION planning
Abstract

Mobile robots are often tasked with repeatedly navigating through an environment whose traversability changes over time. These changes may exhibit some hidden structure, which can be learned. Many studies consider reactive algorithms for online planning, however, these algorithms do not take advantage of the past executions of the navigation task for future tasks. In this article, we formalize the problem of minimizing the total expected cost to perform multiple start-to-goal navigation tasks on a roadmap by introducing the learned reactive planning problem. We propose a method that captures information from past executions to learn a motion policy to handle obstacles that the robot has seen before. We propose the LAMP framework, which integrates the generated motion policy with an existing navigation stack. Finally, an extensive set of experiments in simulated and real-world environments show that the proposed method outperforms the state-of-the-art algorithms by 10% to 40% in terms of expected time to travel from start to goal. We also evaluate the robustness of the proposed method in the presence of localization and mapping errors on a real robot. [ABSTRACT FROM AUTHOR]

Published
2022
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8. The association of infiltrating lymphocytes in androgen ablation induced apoptosis of prostate tumours

Author

Walker, Tristan J.

Abstract

Prostate cancer has a high incidence and mortality rate, with currently no curative treatment for advanced disease. Both the gland and the tumour are androgen dependent; therefore, the removal of androgens, known clinically as hormone ablation therapy, is the most effective treatment, and is thought to force secretory epithelial cells, as well as the cancerous tissue, to undergo apoptosis. Unfortunately, the effects of the hormone ablative therapy are temporary and prostate cancer will recur in an untreatable androgen independent phenotype. The underlying molecular mechanisms involved in prostate cancer progression and the effects of androgen ablation are poorly understood, and the process by which the cancer is cleared, post-androgen ablation, has never been clearly elucidated. This study proposes that, contrary to present theorem, androgen ablation itself is insufficient to induce apoptosis; rather, the apoptotic reaction is facilitated by immune factors including the presence of immune cells at the tumour site. Observational data was used in conjunction with microarray experiments and immunohistochemistry to identify underlying gene expression and immune cell components of tumours grown in hosts with varying states of immunocompentency. We demonstrate that the immunocompetency of the host affects the rate of tumour regression post androgen ablation. Our results show that a tumour in a host with a functional immune system will regress faster and reach its nadir point sooner than in B- or T-cell deficient animals. Furthermore, lymphocyte infiltration significantly changes at the point at which the tumour reaches its lowest point. This correlates with gene expression studies showing a shift towards up-regulating genes related to antigen presentation and immune function. Immunohistochemistry on human tissue samples analyzed from radical prostatectomies also show a marked increase in lymphocyte infiltration post androgen ablation. A better understanding of the tumour environment and effecter immune factors present will provide additional clinical strategies and therapeutic targets to better facilitate androgen ablation therapy.

Published
2005
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13. How I Got the Idea for My Startup.

Author

Ryan, Kevin J. and Walker, Tristan

Subjects
*CRITICAL success factor
Abstract

The article shares the experience of Tristan Walker, the former director of business development at Foursquare and entrepreneur-in-residence at Andreessen Horowitz, on how he got the idea of his startup company Walker and Co. which was launched in 2013.

Published
2016

15. Wheelchair user dragged by bus slams 6-month ban for driver.

Author

Peter Walker ;Tristan Kirk

Abstract

A WHEELCHAIR user injured by a double-decker bus at a zebra crossing today hit out at the driver's six-month ban from the road saying "it should have been for life". [ABSTRACT FROM PUBLISHER]

Published
2016

16. Bloomberg Studio 1.0. Black leadership matters

Author

Bloomberg Television News, production company., Lampkin, Stephanie, interviewee., Bennett, Chris, interviewee., Abuzeid, Iman, interviewee., Walker, Tristan, 1984- interviewee., and Chang, Emily, interviewer.

Published
2020

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