1,720,961 research outputs found
Moiré patterns generated by stacked 2D lattices: A general algorithm to identify primitive coincidence cells
Full text linkTwo-dimensional materials on metallic surfaces or stacked one on top of the other can form a variety of moiré superstructures depending on the possible parameter and symmetry mismatch and misorientation angle. In most cases, such as incommensurate lattices or identical lattices but with a small twist angle, the common periodicity may be very large, thus making numerical simulations prohibitive. We propose here a general procedure to determine the minimal simulation cell which approximates, within a certain tolerance and a certain size, the primitive cell of the common superlattice, given the two interfacing lattices and the relative orientation angle. As case studies to validate our procedure, we report two applications of particular interest: the case of misaligned hexagonal/hexagonal identical lattices, describing a twisted graphene bilayer or a graphene monolayer grown on Ni(111), and the case of hexagonal/square lattices, describing for instance a graphene monolayer grown on Ni(100) surface. The first one, which has also analytic solutions, constitutes a solid benchmark for the algorithm; the second one shows that a very nice description of the experimental observations can be obtained also using the resulting relatively small coincidence cells
Qubit entanglement generation by Gaussian non-Markovian dynamics
Full text linkWe consider two qubits interacting with a common bosonic bath, but not directly between themselves.
We derive the (bipartite) entanglement generation conditions for Gaussian non-Markovian dynamical maps and show that they are similar as in the Markovian regime; however, they depend on different physical coefficients and hold on different time scales. Indeed, for small times, in the non-Markovian regime entanglement is possibly generated on a shorter time scale (/ t2) than in the
Markovian one (/ t). Moreover, although the singular coupling limit of non-Markovian dynamics yields Markovian ones, we show that the same limit does not lead from non-Markovian entanglement generation conditions to Markovian ones. Also, the entanglement generation conditions do not depend on the initial time for non-Markovian open dynamics resulting from couplings to bosonic
Gaussian baths, while they may depend on time for open dynamics originated by couplings to classical, stochastic Gaussian environments
Qubit entanglement generation by Gaussian non-Markovian dynamics
No full textWe consider two qubits interacting with a common bosonic bath, but not directly between themselves. We derive the (bipartite) entanglement generation conditions for Gaussian non-Markovian dynamical maps and show that they are similar as in the Markovian regime. However, they depend on different physical coefficients and hold on different time scales. Indeed, for small times, in the non-Markovian regime entanglement is possibly generated on a shorter time scale (α t2 ) than in the Markovian regime (α t). Moreover, although the singular coupling limit of non-Markovian dynamics yields Markovian ones, we show that the same limit does not lead from non-Markovian entanglement generation conditions to Markovian ones. Also, entanglement generation conditions do not depend on the initial time for non-Markovian open dynamics resulting from couplings to bosonic Gaussian baths, while they may depend on time for open dynamics originated by couplings to classical, stochastic Gaussian environments
Symmetry-induced fluctuation relations in open quantum systems
No full textWe derive a general scheme to obtain quantum fluctuation relations for dynamical observables in open quantum systems. For concreteness, we consider Markovian nonunitary dynamics that is unraveled in terms of quantum jump trajectories and exploit techniques from the theory of large deviations like the tilted ensemble and the Doob transform. Our results here generalize to open quantum system fluctuation relations previously obtained for classical Markovian systems and add to the vast literature on fluctuation relations in the quantum domain, but without resorting to the standard two-point measurement scheme. We illustrate our findings with three examples to highlight and discuss the main features of our general result
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
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
Group-based programs do not allow health improvement in fit elderly
No full textAim. The Group-Based Physical Activities (GBPA) for independent older adults, leaded in accord with guideline, are able to improve health-related physical capacities. Aim of this research is to verify how physical capacities are modified in subjects with different initial levels.
Methods. Health–related physical capacities (balance, flexibility, arms strength, endurance) and hands co-ordination were measured before and after 8 months of GBPA (1h; 2 x week, in scholastic gym) in 324 independent women (50÷88 years old). Repeated measures T-test or Wilcoxon Signed Rank Test were used to verify pre-post results. Correlation between pre-training results and pre-post variation (ΔPP) was investigated with Pearson’s r. Three groups, for every fitness test, were defined on the basis of pre–training results: Low Level Group (LLG - subjects with results lesser than mean–.5sd; Average Level Group (ALG - subjects with results better than mean–.5ds and lesser than mean+.5sd and High Level Group (HLG - subjects with results better than mean+.5sd). One and Two way ANOVA with repeated measures were used to compare ΔPP among three groups and pre-post/groups results respectively.
Results. Post training shows positive changes in all fitness capacities (2.81%÷3.61%; p<0.001). A significant low negative correlation was found from initial level and ΔPP in all fitness capacities (r=-0,14÷-0.43; P=<0.01÷<0.001). There is a statistically significant interaction between pre-post and groups in all test (P=<0.05÷<0.001). ΔPP was significantly different among the groups in all test (p=<0.05÷<0.001); LLG every improved its results (p<0.001); ALG improved in endurance, flexibility and hands co-ordination (p=<0.05÷<0.01); HLG improved in endurance and flexibility (p<0.05).
Conclusions. Data seems to confirm the effectiveness of the GBPA for older but highlights that not all participants improve their performance. Physiological and teaching hypothesis (and the combination of the two) must be evaluated
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
- …
