Learning of Closed-Loop Motion Control

Learning motion control as a unified process of designing the reference trajectory and the controller is one of the most challenging problems in robotics. The complexity of the problem prevents most of the existing optimization algorithms from giving satisfactory results. While model-based algorithms like iterative linear-quadratic-Gaussian (iLQG) can be used to design a suitable controller for the motion control, their performance is strongly limited by the model accuracy. An inaccurate model may lead to degraded performance of the controller on the physical system. Although using machine learning approaches to learn the motion control on real systems have been proven to be effective, their performance depends on good initialization. To address these issues, this paper introduces a two-step algorithm which combines the proven performance of a model-based controller with a model-free method for compensating for model inaccuracy. The first step optimizes the problem using iLQG. Then, in the second step this controller is used to initialize the policy for our PI$^2$-01 reinforcement learning algorithm. This algorithm is a derivation of the PI$^2$ algorithm enabling more stable and faster convergence. The performance of this method is demonstrated both in simulation and experimental results

Physician decision making in selection of second-line treatments in immune thrombocytopenia in children.

Immune thrombocytopenia (ITP) is an acquired autoimmune bleeding disorder which presents with isolated thrombocytopenia and risk of hemorrhage. While most children with ITP promptly recover with or without drug therapy, ITP is persistent or chronic in others. When needed, how to select second-line therapies is not clear. ICON1, conducted within the Pediatric ITP Consortium of North America (ICON), is a prospective, observational, longitudinal cohort study of 120 children from 21 centers starting second-line treatments for ITP which examined treatment decisions. Treating physicians reported reasons for selecting therapies, ranking the top three. In a propensity weighted model, the most important factors were patient/parental preference (53%) and treatment-related factors: side effect profile (58%), long-term toxicity (54%), ease of administration (46%), possibility of remission (45%), and perceived efficacy (30%). Physician, health system, and clinical factors rarely influenced decision-making. Patient/parent preferences were selected as reasons more often in chronic ITP (85.7%) than in newly diagnosed (0%) or persistent ITP (14.3%, P = .003). Splenectomy and rituximab were chosen for the possibility of inducing long-term remission (P < .001). Oral agents, such as eltrombopag and immunosuppressants, were chosen for ease of administration and expected adherence (P < .001). Physicians chose rituximab in patients with lower expected adherence (P = .017). Treatment choice showed some physician and treatment center bias. This study illustrates the complexity and many factors involved in decision-making in selecting second-line ITP treatments, given the absence of comparative trials. It highlights shared decision-making and the need for well-conducted, comparative effectiveness studies to allow for informed discussion between patients and clinicians

Consensus Paper—ICIS Expert Meeting Basel 2009 treatment milestones in immune thrombocytopenia

The rarity of severe complications of this disease in children makes randomized clinical trials in immune thrombocytopenia (ITP) unfeasible. Therefore, the current management recommendations for ITP are largely dependent on clinical expertise and observations. As part of its discussions during the Intercontinental Cooperative ITP Study Group Expert Meeting in Basel, the Management working group recommended that the decision to treat an ITP patient be individualized and based mainly on bleeding symptoms and not on the actual platelet count number and should be supported by bleeding scores using a validated assessment tool. The group stressed the need to develop a uniform validated bleeding score system and to explore new measures to evaluate bleeding risk in thrombocytopenic patients—the role of rituximab as a splenectomy-sparing agent in resistant disease was also discussed. Given the apparently high recurrence rate to rituximab therapy in children and the drug's possible toxicity, the group felt that until more data are available, a conservative approach may be considered, reserving rituximab for patients who failed splenectomy. More studies of the effectiveness and side effects of drugs to treat refractory patients, such as TPO mimetics, cyclosporine, mycophenolate mofetil, and cytotoxic agents are required, as are long-term data on post-splenectomy complications. In the patient with either acute or chronic ITP, using a more personalized approach to treatment based on bleeding symptoms rather than platelet count should result in less toxicity and empower both physicians and families to focus on quality-of-life

Legged Robots

International audienc

An ab initio and AIM investigation into the hydration of 2-thioxanthine

<p>Abstract</p> <p>Background</p> <p>Hydration is a universal phenomenon in nature. The interactions between biomolecules and water of hydration play a pivotal role in molecular biology. 2-Thioxanthine (2TX), a thio-modified nucleic acid base, is of significant interest as a DNA inhibitor yet its interactions with hydration water have not been investigated either computationally or experimentally. Here in, we reported an <it>ab initio </it>study of the hydration of 2TX, revealing water can form seven hydrated complexes.</p> <p>Results</p> <p>Hydrogen-bond (H-bond) interactions in 1:1 complexes of 2TX with water are studied at the MP2/6-311G(d, p) and B3LYP/6-311G(d, p) levels. Seven 2TX^...H₂O hydrogen bonded complexes have been theoretically identified and reported for the first time. The proton affinities (PAs) of the O, S, and N atoms and deprotonantion enthalpies (DPEs) of different N-H bonds in 2TX are calculated, factors surrounding why the seven complexes have different hydrogen bond energies are discussed. The theoretical infrared and NMR spectra of hydrated 2TX complexes are reported to probe the characteristics of the proposed H-bonds. An improper blue-shifting H-bond with a shortened C-H bond was found in one case. NBO and AIM analysis were carried out to explain the formation of improper blue-shifting H-bonds, and the H-bonding characteristics are discussed.</p> <p>Conclusion</p> <p>2TX can interact with water by five different H-bonding regimes, N-H^...O, O-H^...N, O-H^...O, O-H^...S and C-H^...O, all of which are medium strength hydrogen bonds. The most stable H-bond complex has a closed structure with two hydrogen bonds (N(7)-H^...O and O-H^...O), whereas the least stable one has an open structure with one H-bond. The interaction energies of the studied complexes are correlated to the PA and DPE involved in H-bond formation. After formation of H-bonds, the calculated IR and NMR spectra of the 2TX-water complexes change greatly, which serves to identify the hydration of 2TX.</p

Second-line treatments in children with immune thrombocytopenia: Effect on platelet count and patient-centered outcomes

Immune thrombocytopenia (ITP) is an autoimmune bleeding disorder with isolated thrombocytopenia and hemorrhagic risk. While many children with ITP can be safely observed, treatments are often needed for various reasons, including to decrease bleeding or improve health related quality of life (HRQoL). There are a number of available second-line treatments, including rituximab, thrombopoietin-receptor agonists, oral immunosuppressive agents, and splenectomy, but data comparing treatment outcomes are lacking. ICON1 is a prospective, multi-center, observational study of 120 children starting second-line treatments for ITP designed to compare treatment outcomes including platelet count, bleeding, and HRQoL utilizing the Kids ITP Tool (KIT). While all treatments resulted in increased platelet counts, romiplostim had the most pronounced effect at 6 months (p=0.04). Only patients on romiplostim and rituximab had a significant reduction in both skin-related (84% to 48%, p=0.01 and 81% to 43%, p=0.004) and non-skin-related bleeding symptoms (58% to 14%, p=0.0001 and 54% to 17%, p=0.0006) after 1 month of treatment. HRQoL significantly improved on all treatments. However, only patients treated with eltrombopag had a median improvement in KIT scores at 1 month that met the minimal important difference (MID). Bleeding, platelet count, and HRQoL improved in each treatment group, but the extent and timing of the effect varied among treatments. These results are hypothesis generating and help to improve our understanding of the effect of each treatment on specific patient outcomes. Combined with future randomized trials, these findings will help clinicians select the optimal second-line treatment for an individual child with ITP