715 research outputs found
An efficient algorithm for learning with semi-bandit feedback
We consider the problem of online combinatorial optimization under
semi-bandit feedback. The goal of the learner is to sequentially select its
actions from a combinatorial decision set so as to minimize its cumulative
loss. We propose a learning algorithm for this problem based on combining the
Follow-the-Perturbed-Leader (FPL) prediction method with a novel loss
estimation procedure called Geometric Resampling (GR). Contrary to previous
solutions, the resulting algorithm can be efficiently implemented for any
decision set where efficient offline combinatorial optimization is possible at
all. Assuming that the elements of the decision set can be described with
d-dimensional binary vectors with at most m non-zero entries, we show that the
expected regret of our algorithm after T rounds is O(m sqrt(dT log d)). As a
side result, we also improve the best known regret bounds for FPL in the full
information setting to O(m^(3/2) sqrt(T log d)), gaining a factor of sqrt(d/m)
over previous bounds for this algorithm.Comment: submitted to ALT 201
Unusual Low-Temperature Phase in VO Nanoparticles
We present a systematic investigation of the crystal and electronic structure
and the magnetic properties above and below the metal-insulator transition of
ball-milled VO nanoparticles and VO microparticles. For this research,
we performed a Rietveld analysis of synchrotron radiation x-ray diffraction
data, O x-ray absorption spectroscopy, V resonant inelastic x-ray
scattering, and magnetic susceptibility measurements. This study reveals an
unusual low-temperature phase that involves the formation of an elongated and
less-tilted V-V pair, a narrowed energy gap, and an induced paramagnetic
contribution from the nanoparticles. We show that the change in the crystal
structure is consistent with the change in the electronic states around the
Fermi level, which leads us to suggest that the Peierls mechanism contributes
to the energy splitting of the state. Furthermore, we find that the
high-temperature rutile structure of the nanoparticles is almost identical to
that of the microparticles.Comment: 7 pages, 8 figures, 2 table
Treatment with biologic agents in child and adolescent
OBJETIVO: Revisar os mecanismos fisiopatológicos e novos alvos terapêuticos, os agentes biológicos disponíveis, principais indicações e a evidência científica atual para o uso de terapias biológicas na população pediátrica. FONTES DE DADOS: Pesquisa na base de dados Medline e SciELO, nas línguas inglesa e portuguesa, entre 2000 e 2009. As palavras-chave usadas foram "agentes biológicos", "crianças" e "adolescentes". SÍNTESE DOS DADOS: Os agentes biológicos são uma importante opção terapêutica para tratar as doenças autoimunes refratárias às terapias convencionais na infância e na adolescência. Com exceção da artrite idiopática juvenil, a maioria dos estudos em outras doenças autoimunes não é controlada. CONCLUSÕES: Os agentes biológicos têm demonstrado eficácia no tratamento de doenças autoimunes pediátricas como artrite idiopática juvenil, miopatias idiopáticas inflamatórias, lúpus eritematoso juvenil, vasculites, uveítes crônicas, doenças inflamatórias intestinais e púrpura trombocitopênica imune crônica, assim como no linfoma não-Hodgkin. Considerando-se o custo elevado e os potenciais eventos adversos, o uso desses agentes deve ser individualizado e acompanhado por especialista.OBJECTIVE: To review the physiopathology and new therapeutical targets, the available biologic agents, the main indications and the current scientific evidence for the use of biological therapies in the pediatric population. DATA SOURCES: A bibliographical search was obtained from Medline and SciELO databases in English and Portuguese from 2000 to 2009. The key-words included were "biologic agent", "children" and "adolescent". DATA SYNTHESIS: Biologic agents are important therapeutic options to treat refractory autoimmune diseases to conventional therapies in childhood and adolescence. Excluding juvenile idiopathic arthritis, the majority of studies in other autoimmune diseases are uncontrolled trials. CONCLUSIONS: Biologic agents have shown efficacy in the treatment of pediatric autoimmune diseases such as juvenile idiopathic arthritis, idiopathic inflammatory myositis, juvenile systemic lupus erythematosus, vasculitis, chronic uveitis, inflammatory bowel diseases, and chronic immune thrombocytopenic purpura, as well as in non-Hodgkin lymphoma. Considering the high cost and the potential adverse events, the choice to use them must be individualized and followed by a specialist
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