138 research outputs found
L-optimal transportation for Ricci flow
No full textWe introduce the notion of L-optimal transportation, and use it to construct a natural monotonic quantity for Ricci flow which includes a selection of other monotonicity results, including some key discoveries of Perelman [13] (both related to entropy and to L-length) and a recent result of McCann and the author [11]
Structural optimization of free-form reciprocal structures
No full textThis paper presents an optimization algorithm for the design of structurally efficient free-form reciprocal structures. Because of the geometric complexity of reciprocal structures, only a few structural studies have been carried out so far, and we have a limited knowledge of the relation between geometry and structural behaviour in reciprocal structures. This study takes advantage of the preceding work carried by the author on the Reciprocalizer, a software tool for the generation of reciprocal geometries. The Reciprocalizer has been included into a structural optimization algorithm for the generation of structurally efficient free-form reciprocal structures
A.C. susceptibility as a probe of low-frequency magnetic dynamics
No full textWe are grateful to EPSRC (UK) for financial support.The experimental technique of a.c. susceptibility can be used as a probe of magnetic dynamics in a wide variety of systems. Its use is restricted to the low-frequency regime and thus is sensitive to relatively slow processes. Rather than measuring the dynamics of single spins, a.c. susceptibility can be used to probe the dynamics of collective objects, such as domain walls in ferromagnets or vortex matter in superconductors. In some frustrated systems, such as spin glasses, the complex interactions lead to substantial spectral weight of fluctuations in the low-frequency regime, and thus a.c. susceptibility can play a unique role. We review the theory underlying the technique and magnetic dynamics more generally and give applications of a.c. susceptibility to a wide variety of experimental situations.Peer reviewe
Spin dynamics and field-induced magnetic phase transition in the honeycomb Kitaev magnet alpha-Li2IrO3
No full textThe deposited package contains magnetic susceptibility, muon spin relaxation, powder inelastic neutron scattering and pulsed-field magnetization data of the honeycomb Kitaev magnet alpha-Li2IrO3. The readme file inside the .zip archive contains detailed information about the individual file formats in the data archive
Local monotonicity and mean value formulas for evolving Riemannian manifolds
No full textWe derive identities for general flows of Riemannian metrics that may be regarded as local mean-value, monotonicity, or Lyapunov formulae. These generalize previous work of the first author for mean curvature flow and other nonlinear diffusions. Our results apply in particular to Ricci flow, where they yield a local monotone quantity directly analogous to Perelman's reduced volume (V) over tilde and a local identity related to Perelman's average energy F
In situ aerosol measurements taken during the 2007 COPS field campaign at the Hornisgrinde ground site
No full textCopyright @ 2011 Royal Meteorological Society.The Convective and Orographically-induced Precipitation Study (COPS) campaign was conducted during the summer of 2007. A suite of instruments housed at the top of the Hornisgrinde Mountain (1156 m) in the Black Forest region of south-west Germany provided datasets that allow an investigation into the physical, chemical and hygroscopic properties of the aerosol particles sampled during COPS. Organic mass loadings were found to dominate the aerosol composition for the majority of the project, exceeding 8 µg m−3 during a period of high pressure, high temperature, and low wind speed. The ratio of organic:sulphate sub-micron mass concentration exceeds 10:1 during the same time period. Back trajectories show air from this time-frame passing slowly over the local forest and not passing over any local anthropogenic sources. Occasional peaks in nitrate mass loadings were associated with changes in the typical wind direction from south-westerly to north-westerly where air had passed over the Stuttgart region. Size distribution data shows a dominant accumulation-mode when the measurement site was free from precipitation events. A sharp increase in ultrafine particle number concentration was seen during most days commencing around noon. The apparent growth of these particles is associated with an increase in organic mass loading, suggesting condensational growth. For the most part, with the exception of the high pressure period, the aerosol properties recorded during COPS were comparable to previous studies of continental aerosol properties.NER
The management of intelligence-assisted finite element analysis technology
No full textArtificial Intelligence (AI) approaches to Finite Element Analysis (FEA), have had tentative degrees of success over the last few years and some authors have argued that effective FEA can help in the manufacture reliability and safety aspects of engineered artefacts. The author of this paper reviews how such AI techniques have been applied and in this light, the author then uses a Fuzzy Cognitive Mapping (FCM), to develop a framework for the management of intelligence-assisted FEA
Data for Octanuclear heterobimetallic {Ni4Ln4} assemblies possessing Ln4 square grid [2×2] motifs: synthesis, structure and magnetism
No full textOctanuclear heterobimetallic complexes, [Ln4Ni4(H3L)4(µ3-OH)4(µ2-OH)4]4Cl·xH2O·yCHCl3 (Dy3+ , x = 30.6, y = 2 (1); Tb3+ , x = 28, y = 0 (2) ; Gd3+ , x = 25.3, y = 0 (3); Ho3+ , x = 30.6, y = 3 (4)) (H5L = N1, N3-bis(6-formyl-2-(hydroxymethyl)
-4-methylphenol) diethylenetriamine) are reported. These are assembled by the cumulative coordination action of four doubly deprotonated compartmental ligands, [H3L] 2- , along with eight exogenous –OH ligands. Within the core of these complexes, four Ln3+ are distributed to the four corners of a perfect square grid while four Ni2+ are projected away from the plane of the Ln4 unit. Each of the four Ni2+ possesses distorted octahedral geometry while all the Ln3+ are crystallographically equivalent and are present in an elongated square antiprism geometry. The magnetic properties of compound 3 are dominated by an easy-plane single-ion anisotropy of the Ni2+ ions [DNi = 6.7(7) K] and dipolar interactions between Gd3+ centers. Detailed ac magnetometry reveals the presence of distinct temperature-dependent out-of-phase signals for compounds 1 and 2, indicative of slow magnetic relaxation. Magnetochemical analysis of complex 1 implies the 3d and the 4f metal ions are engaged in ferromagnetic interactions with SMM behavior, while dc magnetometry of compound 2 is suggestive of an antiferromagnetic Ni-Tb spin-exchange with slow magnetic relaxation due to a field-induced level crossing. Compound 4 exhibits an easy-plane single-ion anisotropy for the Ho3+ ions and weak interactions between spin centers
Octanuclear heterobimetallic {Ni4Ln4} assemblies possessing Ln4 square grid [2×2] motifs : synthesis, structure and magnetism
No full textOctanuclear heterobimetallic complexes, [Ln4Ni4(H3L)4(µ3-OH)4(µ2-OH)4]4Cl·xH2O·yCHCl3 (Dy3+ , x = 30.6, y = 2 (1); Tb3+ , x = 28, y = 0 (2) ; Gd3+ , x = 25.3, y = 0 (3); Ho3+ , x = 30.6, y = 3 (4)) (H5L = N1, N3-bis(6-formyl-2-(hydroxymethyl)
-4-methylphenol) diethylenetriamine) are reported. These are assembled by the cumulative coordination action of four doubly deprotonated compartmental ligands, [H3L] 2- , along with eight exogenous –OH ligands. Within the core of these complexes, four Ln3+ are distributed to the four corners of a perfect square grid while four Ni2+ are projected away from the plane of the Ln4 unit. Each of the four Ni2+ possesses distorted octahedral geometry while all the Ln3+ are crystallographically equivalent and are present in an elongated square antiprism geometry. The magnetic properties of compound 3 are dominated by an easy-plane single-ion anisotropy of the Ni2+ ions [DNi = 6.7(7) K] and dipolar interactions between Gd3+ centers. Detailed ac magnetometry reveals the presence of distinct temperature-dependent out-of-phase signals for compounds 1 and 2, indicative of slow magnetic relaxation. Magnetochemical analysis of complex 1 implies the 3d and the 4f metal ions are engaged in ferromagnetic interactions with SMM behavior, while dc magnetometry of compound 2 is suggestive of an antiferromagnetic Ni-Tb spin-exchange with slow magnetic relaxation due to a field-induced level crossing. Compound 4 exhibits an easy-plane single-ion anisotropy for the Ho3+ ions and weak interactions between spin centers
Virtual peer tutoring as an aid for the course "Matemáticas Básicas", a study case
No full textEl presente trabajo tiene como propósito diseñar una propuesta de tutorías académicas entre pares, mediadas por herramientas virtuales; esta propuesta fue implementada en el curso de Matemáticas Básicas del semestre 2020-1 de la Universidad Nacional, sede Medellín.
Para evaluar los resultados, se tomaron elementos de la investigación cualitativa y por medio de un estudio de casos, se observaron cinco estudiantes a partir de tres unidades de análisis: la acción, la reflexión y el error como oportunidad de aprendizaje.
Las tutorías entre pares, se realizaron a través de encuentros sincrónicos por videoconferencias, se planificaron de acuerdo con las variables organizativas propuestas por Topping y se desarrollaron teniendo en cuenta sus principios respecto a este tipo de acompañamiento académico. De acuerdo a los resultados obtenidos, se observó que la estrategia permitió disminuir los porcentajes de pérdida del curso, así como el fortalecimiento de estrategias y habilidades académicas que les permiten a los estudiantes abordar los contenidos de las matemáticas universitarias de una forma más adecuada.The intention of the present work is to propose a virtual peer tutoring scheme, which was applied to the course Basic mathematics for the 2020-1 term at the National University of Colombia, at Medellín. To evaluate the results, five cases were studied by taking elements of qualitative research in three analysis units: action, reflection and failure as a learning opportunity.
The peer tutoring sessions were synchronously delivered by means of videoconferences; these were planned according to the organizational variables proposed by Keith Topping and were developed subject to the principles about this type of academic accompaniment proposed by the same author. According to the results, not only a lower reprobation rate of the course was observed, but also the strengthen of strategies and academic abilities that help students tackle the contents in an adequate manner.Maestrí
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