29,904 research outputs found
ATP as a presynaptic modulator
© 2000 Elsevier Science Inc.There is considerable evidence that ATP acts as a fast transmitter or co-transmitter in autonomic and sensory nerves mostly through activation of ionotropic P2X receptors but also through metabotropic P2Y receptors. By analogy, the observations that ATP is released from stimulated central nervous
system (CNS) nerve terminals and that responses to exogenously added ATP can be recorded in central neurons, lead to the proposal that ATP might also be a fast transmitter in the CNS. However, in spite of
the robust expression of P2 receptor mRNA and binding to P2 receptors in the CNS, the demonstration of central purinergic transmission has mostly remained elusive. We now review evidence to suggest that ATP may also act presynaptically rather than solely postsynaptically in the nervous system.Fundação Ciência e Tecnologia and European nio
An empirical evaluation of imbalanced data strategies from a practitioner's point of view
This research tested the following well known strategies to deal with binary
imbalanced data on 82 different real life data sets (sampled to imbalance rates
of 5%, 3%, 1%, and 0.1%): class weight, SMOTE, Underbagging, and a baseline
(just the base classifier). As base classifiers we used SVM with RBF kernel,
random forests, and gradient boosting machines and we measured the quality of
the resulting classifier using 6 different metrics (Area under the curve,
Accuracy, F-measure, G-mean, Matthew's correlation coefficient and Balanced
accuracy). The best strategy strongly depends on the metric used to measure the
quality of the classifier. For AUC and accuracy class weight and the baseline
perform better; for F-measure and MCC, SMOTE performs better; and for G-mean
and balanced accuracy, underbagging
Control of wavepacket spreading in nonlinear finite disordered lattices
In the absence of nonlinearity all normal modes (NMs) of a chain with
disorder are spatially localized (Anderson localization). We study the action
of nonlinearity, whose strength is ramped linearly in time. It leads to a
spreading of a wavepacket due to interaction with and population of distant
NMs. Eventually the nonlinearity induced frequency shifts take over, and the
wavepacket becomes selftrapped. On finite chains a critical ramping speed is
obtained, which separates delocalized final states from localized ones. The
critical value depends on the strength of disorder and is largest when the
localization length matches the system size.Comment: 7 pages, 4 figures, submitted to PR
Slavnov and Gaudin-Korepin Formulas for Models without Symmetry: the Twisted XXX Chain
We consider the XXX spin- Heisenberg chain on the circle with an
arbitrary twist. We characterize its spectral problem using the modified
algebraic Bethe anstaz and study the scalar product between the Bethe vector
and its dual. We obtain modified Slavnov and Gaudin-Korepin formulas for the
model. Thus we provide a first example of such formulas for quantum integrable
models without symmetry characterized by an inhomogenous Baxter
T-Q equation
A Non-Reductionist Solution to the Problem of Social Causation
The thesis of the causal closure of the physical world renders mental and social causation philosophically problematic. In The Construction of Social Reality, John Searle offers a partial solution to the problem of the causal efficacy of social and institutional facts by an appeal to the notion of the Background, or, as I will argue, by an appeal to its physical components. Since Searle's solution refers to physical facts in order to explain social causation, it does not seem to differ from the solution offered by reductive physicalists to the problem of mental causation. In this paper, I will discuss both responses to these two problems of higher-order causation. As a result of this investigation, the paper offers an account of how and to what extent does Searle's solution solve the problem of the causal efficacy of social facts, without implying their reducibility to physical facts
Massive color-octet bosons and the charge asymmetries of top quarks at hadron colliders
Several models predict the existence of heavy colored resonances decaying to
top quarks in the TeV energy range that might be discovered at the LHC. In some
of those models, moreover, a sizable charge asymmetry of top versus antitop
quarks might be generated. The detection of these exotic resonances, however,
requires selecting data samples where the top and the antitop quarks are highly
boosted, which is experimentally very challenging. We asses that the
measurement of the top quark charge asymmetry at the LHC is very sensitive to
the existence of excited states of the gluon with axial-vector couplings to
quarks. We use a toy model with general flavour independent couplings, and show
that a signal can be detected with relatively not too energetic top and antitop
quarks. We also compare the results with the asymmetry predicted by QCD, and
show that its highest statistical significance is achieved with data samples of
top-antitop quark pairs of low invariant masses.Comment: 20 page
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