1,721,094 research outputs found
Quantum-dot Carnot engine at maximum power
Full text linkpeer reviewedWe evaluate the efficiency at maximum power of a quantum-dot Carnot heat engine. The universal values of
the coefficients at the linear and quadratic order in the temperature gradient are reproduced. Curzon-Ahlborn
efficiency is recovered in the limit of weak dissipation
Fluctuation theorem for entropy production during effusion of an ideal gas with momentum transfer
No full textWe derive an exact expression for entropy production during effusion of an ideal gas driven by momentum transfer in addition to energy and particle flux. Following the treatment in CLEUREN [Phys. Rev. E 74, 021117 (2006)], we construct a master equation formulation of the process and explicitly verify the thermodynamic fluctuation theorem, thereby directly exhibiting its extended applicability to particle flows and hence to hydrodynamic systems
Effects of disorder on synchronization of discrete phase-coupled oscillators
No full textWe study synchronization in populations of phase-coupled stochastic three-state oscillators characterized by a distribution of transition rates. We present results on an exactly solvable dimer as well as a systematic characterization of globally connected arrays of N types of oscillators (N=2,3,4) by exploring the linear stability of the nonsynchronous fixed point. We also provide results for globally coupled arrays where the transition rate of each unit is drawn from a uniform distribution of finite width. Even in the presence of transition rate disorder, numerical and analytical results point to a single phase transition to macroscopic synchrony at a critical value of the coupling strength. Numerical simulations make possible further characterization of the synchronized arrays
Effects of disorder on synchronization of discrete phase-coupled oscillators
No full textWe study synchronization in populations of phase-coupled stochastic three-state oscillators characterized by a distribution of transition rates. We present results on an exactly solvable dimer as well as a systematic characterization of globally connected arrays of N types of oscillators (N=2,3,4) by exploring the linear stability of the nonsynchronous fixed point. We also provide results for globally coupled arrays where the transition rate of each unit is drawn from a uniform distribution of finite width. Even in the presence of transition rate disorder, numerical and analytical results point to a single phase transition to macroscopic synchrony at a critical value of the coupling strength. Numerical simulations make possible further characterization of the synchronized arrays
Entropy production as correlation between system and reservoir
Full text linkpeer reviewedWe derive an exact (classical and quantum) expression for the
entropy production of a finite system placed in contact with one or several
finite reservoirs, each of which is initially described by a canonical equilibrium
distribution. Although the total entropy of system plus reservoirs is conserved,
we show that system entropy production is always positive and is a direct
measure of system–reservoir correlations and/or entanglements. Using an
exactly solvable quantum model, we illustrate our novel interpretation of the
Second Law in a microscopically reversible finite-size setting, with strong
coupling between the system and the reservoirs. With this model, we also
explicitly show the approach of our exact formulation to the standard description
of irreversibility in the limit of a large reservoir
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
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Effects of Channel Noise on Neural Networks
Full text linkThe human brain contains on the order of neurons with each neuron having on the order of synaptic connections with other neurons. Within each neuron, there are protein channels that dictate when ions can flow through them. It is the flow of these ions that is the basis for action potential generation, and these action potentials are the source of neural communication and information. These channels exist in various configurations some of which are conducting (``open'') and some of which are non-conducting (``closed''). Moreover, these channels can stochastically switch between the open and closed states. It is nothing short of remarkable that the brain functions as it does despite the randomness present within each neuron.What role these microscopic fluctuations, herein known as channel noise, have on macroscopic neural network properties is an open area of neuroscience that has generated a great deal of interest in recent years due to the advancement of computational methods. In this thesis, we first introduce the Hodgkin-Huxley model and mathematical equations which incorporate this channel noise in the Hodgkin-Huxley model. We then study the role of channel noise on properties of small neural networks which begins in Chapter 3. The first property we will look at is how channel noise affects the timing of the first action potential after stimulus onset. This property, known as first spike latency, is believed to be a coding mechanism used by neurons to communicate information between stimuli and brain processing. We will then look at the role of channel noise on neural synchronization. Abnormal synchronization has been strongly correlated with a number of neural disorders such as Alzheimer's disease and Parkinson's disease.One area of research in neuroscience that is of fundamental interest is the relationship between neural spiking and cognitive processing. For this thesis, in addition to the small neural network models for first spike latency and synchronization, we will consider a recently developed model for cognition and study the model's behavior when subjected to noise. We will conclude with a brief summary of the results obtained as well as discuss ways to extend the research to larger neural network systems
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
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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