1,721,048 research outputs found
Non-equilibrium Thermodynamics of Piecewise Deterministic Markov Processes
No full textWe consider a class of stochastic dynamical systems, called piecewise deterministic
Markov processes, with states (x, σ) ∈ × , being a region in Rd or the
d-dimensional torus, being a finite set. The continuous variable x follows a piecewise
deterministic dynamics, the discrete variable σ evolves by a stochastic jump dynamics
and the two resulting evolutions are fully-coupled. We study stationarity, reversibility
and time-reversal symmetries of the process. Increasing the frequency of the σ-jumps,
the system behaves asymptotically as deterministic and we investigate the structure of its
fluctuations (i.e. deviations from the asymptotic behavior), recovering in a non Markovian
frame results obtained by Bertini et al. (Phys. Rev. Lett. 87(4):040601, 2001; J. Stat.
Phys. 107(3–4):635–675, 2002; J. Stat. Mech. P07014, 2007; Preprint available online at
http://www.arxiv.org/abs/0807.4457, 2008), in the context of Markovian stochastic interacting
particle systems. Finally, we discuss a Gallavotti–Cohen-type symmetry relation with
involution map different from time-reversal
Averaging and large deviation principles for fully--coupled piecewise deterministic Markov processes and applications to molecular motors
No full textAveraging and large deviation principles for fully-coupled pieceweise deterministic Markov processes and applications to molecular motors
No full textWe consider Piecewise Deterministic Markov Processes (PDMPs) with a
finite set of discrete states. In the regime of fast jumps between discrete states, we prove
a law of large number and a large deviation principle. In the regime of fast and slow
jumps, we analyze a coarse–grained process associated to the original one and prove its
convergence to a new PDMP with effective force fields and jump rates. In all the above
cases, the continuous variables evolve slowly according to ODEs. Finally, we discuss some
applications related to the mechanochemical cycle of macromolecules, including strained–
dependent power–stroke molecular motors. Our analysis covers the case of fully–coupled
slow and fast motions
STM investigation of the alpha-Sn/Si(111) phase at 120 K
No full textLow-temperature (120 K) scanning tunneling microscopy experiments on the one-third of a monolayer alpha-Sn/Si(111) surface have clearly shown that both the substrate and the defect density have an effect on the charge density wave transition from a root 3 x root 3 to a 3 x 3 structure, reported for the isoelectronic system Sn/Ge(111). Both systems show that defects generate exponentially (temperature-dependent) damped electronic disturbances. At room temperature this perturbation decays rapidly at the second-nearest neighbors of the defects while at 120 K its decay length increases to about 11 Angstrom [compared with 50 Angstrom for Sn/Ge(111)], clearly affecting the defect neighbors up to the third coordination shell. In contrast to the Sn/Ge(111) system, there is no sign of a phase transition down to 120 K. At 120 K the high defective surface clearly shows localized 3 x 3 symmetry domains, whilst the vast majority of the low defective surface retains its root 3 x root 3 symmetry. The role of defect-to-defect correlation in originating opposite-phase 3 x 3 symmetry patterns is discussed. An advantage of the Sn/Si(111) system is that the defect density can be controlled; in this study, from a low value of 1% to a high value of 20%. (C) 2000 Elsevier Science B.V. All rights reserved
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
Characterization of Oscillations during Flow Boiling of Water in Parallel Microchannels
No full textSeveral challenges coexist in the field of flow boiling in microchannels, ranging from high superheat required for boiling incipience to boiling instabilities and early dryouts. The aim of this study is to mitigate or solve some of the challenges and develop an image-processing algorithm for analysis of boiling oscillations in multiple parallel channels. The experimental results were acquired on an array of 64 parallel 25×25 μm microchannels using a synchronized high-speed visualization and measuring system. The small cross section of the microchannels allowed only the formation of annular two-phase flow, and a computer algorithm was developed for tracking the meniscus oscillations during boiling. The applied image analysis focuses on reliability with the simultaneous use of brightness variation and brightness derivative along with image subtraction. Moreover, the images were preprocessed to determine the number of microchannels and their orientation with applying different filtering and Radon transformations. The data extracted from the visualization helped determine the peak-to-peak amplitudes and fundamental frequencies of the oscillating meniscus. The results exhibit lower amplitudes and higher fundamental frequencies with increasing heat flux. The mass flux was kept constant at 83 kg/m2s, whereas the heat flux varied from 150 kW/m2 to 250 kW/m2. The amplitudes and the fundamental frequencies of the meniscus oscillations determine the length and duration of microchannel with periodically alternating liquid and vapor phases
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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