324,207 research outputs found
First principles calculations of vacancy–vacancy interactions in nickel: thermal expansion effects
No full textThe energetic properties of the divacancy defect in fcc nickel are studied by ab initio calculations based on density functional theory. The formation and binding enthalpies of the divacancy in the first (1nn), second (2nn) and third (3nn) nearest-neighbor configurations are presented. Results show that the 1nn divacancy configuration is the most stable with a formation enthalpy H2vf of 2.71 eV and a small binding energy H2vb of 0.03 eV. In the 2nn configuration, the monovacancy–monovacancy interaction is repulsive, and it vanishes in the 3nn configuration. The migration process of the divacancy in its stable configuration is studied. We find that the divacancy migrates in the (111) plane by successive rotational steps of 60°. The corresponding migration enthalpy H2vm is predicted to be 0.59 eV, about half of that found for the monovacancy. For a better comparison of our results with high temperature experimental data, we have analyzed the effects of thermal expansion. Our results show that the inclusion of thermal expansion allows us to reproduce satisfactorily the experimental predictions
First-principles study of diffusion and interactions of vacancies and hydrogen in hcp-titanium
No full textWe present a study of the stability of n-vacancies (Vn) and hydrogens in the hexagonal close-packed titanium system computed by means of first-principles calculations. In this work, performed by using the generalized gradient approximation of density functional theory, we focused on the formation energies and the processes of migration of these defects. In the first part, the calculated formation energy of the monovacancy presents a disagreement with experimental data, as already mentioned in the literature. The activation energy is underestimated by almost 20%. The stability of compact divacancies was then studied. We show that a divacancy is more stable than a monovacancy if their migration energies are of the same order of magnitude. We also predict that the migration process in the basal plane of the divacancy is controlled by an intermediate state corresponding to a body-centered triangle(BO site). The case of the trivacancies is finally considered from an energetic point of view. In the second part, the insertion of hydrogen and the processes of its migration are discussed. We obtain a satisfactory agreement with experimental measurements. The chemical nature of the interactions between hydrogen and titanium are discussed, and we show that the H-atom presents an anionic behavior in the metal. The trapping energy of hydrogen in a monovacancy as a function of the number of hydrogen atoms is finally presented
Diffusive author(s), cohesive author: Analysis of S/N (1994)
No full textThis study indicates the ways in which various aspects of the author(s) are brought forth in Dumb type’s performance art, the S/N production. Previous research has suggested a non-hierarchical organization of Dumb type and the absence of a “privileged author” in Dumb type’s collaborative work, S/N. However, the results that I have investigated from member’s interviews on the creative process of S/N along with my analysis of the recorded images of S/N, indicate a different aspect of the author(s). First, S/N was created through, so to speak, the collective ideas of the members of Dumb type. Further, S/N has at least nine quotations from previous performances, installations, and printed writings, besides the work-in-progress technique. Explicating one of the “author functions” as given by Michel Foucault, each text has plural subjects of the author. However, it has been revealed from members’ interviews that Teiji Furuhashi had a decision-making role in selecting the members’ ideas within the performance. Since then, S/N has had plural subjects of creation; however, Furuhashi is one of the subjects of creation along with the “privileged author.” S/N has plural authors (diffusive authors) yet at the same time, it has a “privileged author,” Teiji Furuhashi (cohesive author)
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe 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
Impact of lattice vibrations on equation of state of the hardest boron phase
No full textAn accurate equation of state (EOS) is determined for the high-pressure orthorhombic phase of boron, B(28), experimentally as well as from ab initio calculations. The unique feature of our experiment is that it is carried out on the single crystal of B(28). In theory, we take into consideration the lattice vibrations, often neglected in first-principles simulations. We show that the phonon contribution has a profound effect on the EOS of B(28), giving rise to anomalously low values of the pressure derivative of the bulk modulus and greatly improving the agreement between theory and experiment.Original Publication:Eyvas Isaev, Sergey Simak, Arkady Mikhaylushkin, Yu. Kh. Vekilov, E. Yu. Zarechnaya, L. Dubrovinsky, N. Dubrovinskaia, M. Merlini, M. Hanfland and Igor Abrikosov, Impact of lattice vibrations on equation of state of the hardest boron phase, 2011, Physical Review B. Condensed Matter and Materials Physics, (83), 13, 132106.http://dx.doi.org/10.1103/PhysRevB.83.132106Copyright: American Physical Societyhttp://www.aps.org
ОБРАБОТКА НЕПРЕРЫВНЫХ И ДИСКРЕТИЗИРОВАННЫХ СИГНАЛОВ МЕТОДОМ S-ПРЕОБРАЗОВАНИЙ В БАЗИСЕ СМЕЩЕННЫХ ПОЛИНОМОВ ЛЕЖАНДРА
No full textДля аналитической аппроксимации и последующей обработки непрерывных и
дискретизированных сигналов, заданных на конечном интервале изменения аргумента и сопровождаемых высокочастотными помехами и ошибками измерений применен метод S-преобразования. В качестве системы базисных функций использована система ортогональных полиномов Лежандра, приведенных к интервалу определения сигналов.
Выведены выражения для определения операционной матрицы интегрирования целого и дробного порядков в базисе смещенных полиномов Лежандра. Приведены примеры последующей обработки аппроксимированных сигналов (низкочастотной фильтрации, определения производных различных целых и дробных (по Капуто и Риману–Лиувиллю) порядков). Вычислительные эксперименты выполнены в программной среде системы Mathematica®.
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A. V. Vasуliev, V. V. Vasylyev, L. A. Simak
Continuous and sampled signal processing via S-transform method based on shifted Legendre polynomials The S-transform is applied to the analytical approximation and the subsequent processing of continuous and sampled signals defined on a finite interval of the argument and followed by highfrequency noise and measurement errors. The system of orthogonal Legendre polynomials defined on approximation interval is used as a system of base functions. The expressions for the operational matrix of integration of the integer and fractional orders in the basis of the shifted Legendre
polynomials have been derived. Examples of postprocessing of the approximated signals (low-pass filtering, evolution of derivative of various integer and fractional orders in Caputo and Riemann– Liouville sense) are given. Computer experiments are performed in the software environment of Mathematica®
Dispelling the Myths Behind First-author Citation Counts
No full textWe 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
Author's address:
No full textCan archives of audiovisual TV interviews be used to make authors more visible to students, and thereby reduce the learning gap between native and non-native language speakers in college classes? We examined students in a college course who learned about one scholar's ideas through watching an audiovisual TV interview (i.e., visible author format) and about another scholar's ideas through reading a formal text description (i.e., invisible author format). For the invisible author, native language speakers scored significantly higher than the non-native language speakers on a corresponding exam question (i.e., a cognitive measure), generated more words on the exam question (i.e., a motivational measure), and mentioned the author's name more often in answering the exam question (i.e., an affective measure). For the visible author, the groups did not differ on any of these measures. These findings provide evidence for the idea that making the author visible through audiovisual TV interviews can eliminate the learning gap between native and non-native language speakers. 3 Universities around the world serve students who are non-native speakers of th
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