313 research outputs found
Safe Controller Optimization for Quadrotors with Gaussian Processes
One of the most fundamental problems when designing controllers for dynamic
systems is the tuning of the controller parameters. Typically, a model of the
system is used to obtain an initial controller, but ultimately the controller
parameters must be tuned manually on the real system to achieve the best
performance. To avoid this manual tuning step, methods from machine learning,
such as Bayesian optimization, have been used. However, as these methods
evaluate different controller parameters on the real system, safety-critical
system failures may happen. In this paper, we overcome this problem by
applying, for the first time, a recently developed safe optimization algorithm,
SafeOpt, to the problem of automatic controller parameter tuning. Given an
initial, low-performance controller, SafeOpt automatically optimizes the
parameters of a control law while guaranteeing safety. It models the underlying
performance measure as a Gaussian process and only explores new controller
parameters whose performance lies above a safe performance threshold with high
probability. Experimental results on a quadrotor vehicle indicate that the
proposed method enables fast, automatic, and safe optimization of controller
parameters without human intervention.Comment: IEEE International Conference on Robotics and Automation, 2016. 6
pages, 4 figures. A video of the experiments can be found at
http://tiny.cc/icra16_video . A Python implementation of the algorithm is
available at https://github.com/befelix/SafeOp
A Study of Medical Negligence Claiming in Scotland
Published version made available in accordance with the Publisher's Policy. © Crown copyright 2012
You may re-use this information (not including logos) free of charge in any format or
medium, under the terms of the Open Government Licence. To view this licence,
visit http://www.nationalarchives.gov.uk/doc/open-government-licence/ or write to the
Information Policy Team, The National Archives, Kew, London TW9 4DU, or e-mail:
[email protected]
No-Regret Bayesian Optimization with Unknown Hyperparameters
Bayesian optimization (BO) based on Gaussian process models is a powerful
paradigm to optimize black-box functions that are expensive to evaluate. While
several BO algorithms provably converge to the global optimum of the unknown
function, they assume that the hyperparameters of the kernel are known in
advance. This is not the case in practice and misspecification often causes
these algorithms to converge to poor local optima. In this paper, we present
the first BO algorithm that is provably no-regret and converges to the optimum
without knowledge of the hyperparameters. During optimization we slowly adapt
the hyperparameters of stationary kernels and thereby expand the associated
function class over time, so that the BO algorithm considers more complex
function candidates. Based on the theoretical insights, we propose several
practical algorithms that achieve the empirical sample efficiency of BO with
online hyperparameter estimation, but retain theoretical convergence
guarantees. We evaluate our method on several benchmark problems
“He did everything he possibly could for me…” Medical malpractice claimants’ experiences of legal services
Teoria multicultural em trabalhos acadêmicos e sua relação com as práticas pedagógicas
The present article aims to investigate how the theory multiculturalism is presented in the academic works available in the CAPES Portal and the possible relation of these works with the pedagogical practices. In the first part of the work a systematized bibliographical review was carried out, followed by a search with period criteria, considering the moment in which the discussions regarding the multiculturalism in Brazil surface. And, finally, the selected papers were analyzed, seeking support in several authors such as Hall (2003), MacLaren (2000), Silva (2000), among others. Although it is a theme already established in the academic universe, the analysis reveals, that this subject still deserves to be researched, especially in relation to the discussion of multiculturalism and its articulation with pedagogical practices, so that so that it contributes to provide researchers and teachers whit reflection processes that allow the construction of a more just and democratic education.O presente artigo tem por objetivo investigar como o multiculturalismo se apresenta nos trabalhos acadêmicos disponíveis no Portal CAPES e a possível relação destes trabalhos com as práticas pedagógicas. Na primeira parte do trabalho efetuou-se uma revisão bibliográfica sistematizada, em seguida realizou-se uma busca com critérios de período, considerando o momento em que se afloram as discussões sobre o multiculturalismo no Brasil. E, por fim, foram analisados os trabalhos selecionados buscando respaldo em vários autores. Ainda que seja um tema já instituído no universo acadêmico, as pesquisas disponíveis revelam que ainda merece ser mais pesquisado, sobretudo em relação à discussão do multiculturalismo e sua articulação às práticas pedagógicas, de modo que contribua para propiciar, a pesquisadores e professores, processos de reflexão que permitam construir uma educação mais justa e democrática
Endolithic Algae Affect Modern Coral Carbonate Morphology and Chemistry
While burial diagenetic processes of tropical corals are well investigated, current knowledge about factors initiating early diagenesis remains fragmentary. In the present study, we focus on recent Porites microatolls, growing in the intertidal zone. This growth form represents a model organism for elevated sea surface temperatures (SSTs) and provides important but rare archives for changes close to the seawater/atmosphere interface with exceptional precision on sea level reconstruction. As other coral growth forms, microatolls are prone to the colonization by endolithic green algae. In this case, the algae can facilitate earliest diagenetic alteration of the coral skeleton. Algae metabolic activity not only results in secondary coral porosity due to boring activities, but may also initiate reprecipitation of secondary aragonite within coral pore space, a process not exclusively restricted to microatoll settings. In the samples of this initial study, we quantified a mass transfer from primary to secondary aragonite of around 4% within endolithic green algae bands. Using δ 18 O, δ 13 C, Sr/Ca, U/Ca, Mg/Ca, and Li/Mg systematics suggests that the secondary aragonite precipitation followed abiotic precipitation principles. According to their individual distribution coefficients, the different isotope and element ratios showed variable sensitivity to the presence of secondary aragonite in bulk samples, with implications for microatoll-based SST reconstructions. The secondary precipitates formed on an organic template, presumably originating from endolithic green algae activity. Based on laboratory experiments with the green algae Ostreobium quekettii, we propose a conceptual model that secondary aragonite formation is potentially accelerated by an active intracellular calcium transport through the algal thallus from the location of dissolution into coral pore spaces. The combined high-resolution imaging and geochemical approach applied in this study shows that endolithic algae can possibly act as a main driver for earliest diagenesis of coral aragonite starting already during a coral’s life span
Development of a Bead-Based Multiplex Assay for the Analysis of the Serological Response against the Six Pathogens HAV, HBV, HCV, CMV, T. gondii, and H. pylori
The spread of infectious diseases and vaccination history are common subjects of epidemiological and immunological research studies. Multiplexed serological assays are useful tools for assessing both current and previous infections as well as vaccination efficacy. We developed a serological multi-pathogen assay for hepatitis A, B and C virus, cytomegalovirus (CMV), Toxoplasma gondii, and Helicobacter pylori using a bead-based multiplex assay format. The multi-pathogen assay consisting of 15 antigens was utilized for the analysis of the serological response in elderly individuals of an influenza vaccination study (n = 34). The technical assay validation revealed a mean intra-assay precision of coefficient of variation (CV) = 3.2 ± 1.5% and a mean inter-assay precision of CV = 8.2 ± 5.3% across all 15 antigens and all tested samples, indicating a robust test system. Furthermore, the assay shows high sensitivities (ranging between 94% and 100%) and specificities (ranging between 93% and 100%) for the different pathogens. The highest seroprevalence rates in our cohort were observed for hepatitis A virus (HAV; 73.5%), followed by CMV (70.6%), T. gondii (67.6%) and H. pylori (32.4%). Seroprevalences for hepatitis B virus (HBV, 8.8%) and hepatitis C virus (HCV, 0%) were low. The seroprevalences observed in our study were similar to those from other population-based studies in Germany. In summary, we conclude that our multiplex serological assay represents a suitable tool for epidemiological studies
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