1,722,431 research outputs found
Hands as tools: how manual behavior shapes actions and spontaneous and task-evoked brain activity
Full text linkHumans establish interactions with external objects through stereotypical upper-limb movements. These regularities may generate probabilistic representations about the body and internal models (i.e., prior) for adaptive sensorimotor control. Recent studies show that, in the absence of any task, spontaneous brain activity patterns resemble those evoked by the execution of ecological hand movements. These observations suggest that, even at rest, the brain preserves a hand representation, likely for efficient motor control. Through hands, humans manipulate tools that can be incorporated into the body schema (i.e., brain representation of the body).
Using neuroimaging studies, we tested whether spontaneous activity patterns more strongly resemble patterns evoked by the observation of visual stimuli depicting hands vs non-hands and regular vs perturbed object-related arm and hand movements. Then, in two behavioral studies, we explored whether humans could embody a bionic tool (i.e., experience it as part of the body) and thus if this would affect behavior and the body schema. Results showed that spontaneous activity patterns code for the visual representation of human hands in somatomotor brain regions and for regular upper-limb movements in the dorsal attention network. Furthermore, we found that the virtual grafting of a bionic tool elicits a sense of embodiment like or even stronger than its natural counterpart (i.e., a virtual hand) and that tool use can alter the body representation through changes in muscular intensity and kinematics parameters.
We suggest that hand shape and regular movements are more represented in spontaneous activity than control stimuli, likely due to replay mechanisms for processing and interpreting information to which we are regularly exposed. Our studies also indicate that the natural use of bionic tools can change human behavior, opening new research and application possibilities, especially for amputees struggling to embody prosthetic limbs
A singular stochastic control problem for hydropower generation in renewable energy markets
Full text linkWe consider a singular stochastic control problem for hydroelectric power production in an energy market where the electricity spot market prices dynamics is described by a Vasicek's process, allowing also for negative prices.
We propose a hydroelectric production system that can react in two different modes when it is convenient to produce energy through an instantaneous release of water. We endow the system with the possibility of producing ``less efficiently'' when negative prices appear in the market, but it is still preferable to produce instantaneously rather than waiting for positive prices.
We defined a novel optimization problem whose performance functional exhibits a state-dependent instantaneous marginal revenue whose sign is directly affected by the sign of the prices dynamics.
We aim to maximize such functional among all the admissible control policies into the class of the adapted stochastic processes whose paths are not necessarily absolutely continuous with respect to the Lebesgue's measure but only non-decreasing, left-continuous and with finite right limits (càglàd).
We prove the Verification Theorem, allowing to characterize the value function of our singular stochastic control problem among the solutions of the associated Hamilton-Jacobi-Bellman equation which turns to be a variational inequality with state-dependent gradient constraint. The Verification Theorem sheds light on the structure of the optimal control which turns to be a purely discontinuous process that, at the first time of action, exerts all the available fuel with a single instantaneous jump.
Under some assumptions on the characteristics of our hydropower production model, we identify the value function of the optimal control problem in terms of the optimal reward function of an associated family of optimal stopping problems. We identified a unique positive boundary, separating the action and inaction regions and we showed that the optimal strategy consists in completely discharge the water reservoir as soon as the price dynamics reaches values grater or equal such optimal threshold.
We highlight the difficulties that arise when the aforementioned assumptions are replaced by other alternative hypotheses. In this more challenging context, we provide some intuitions on the tricky structure of the action and inaction regions as well as on the nature of the candidate optimal control policy
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Optimal investment and ruin probabilities
No full textWe consider an insurance company whose reserve is described by a perturbed compound Poisson risk process. The company may invest part of the reserve in a financial market index. We allow the financial risk and the insurance risk to be dependent. We study how the introduction of dependence between these two risks affects the minimization of the ruin probability as well as the optimal investment strategy. Moreover, we provide an upper bound for the ruin probability
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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