5,032 research outputs found
Combinatorial curvature flows for generalized hyperbolic circle packings
Generalized circle packings were introduced in \cite{Ba-Hu-Sun} as a
generalization of tangential circle packings in hyperbolic background geometry.
In this paper, we introduce the combinatorial Calabi flow, fractional
combinatorial Calabi flow and combinatorial -th Calabi flow for generalized
hyperbolic circle packings. We establish several equivalent conditions
regarding the longtime behaviors of these flows. This provides effective
algorithms for finding the generalized circle packings with prescribed total
geodesic curvatures
Circle packings and total geodesic curvatures in hyperbolic background geometry
In this paper, we study a new type of circle packings in hyperbolic
background geometry. Horocycles and hypercycles are also considered in this
packing. We give the existence and rigidity of this type of circle packing with
conical singularities in terms of the total geodesic curvature. Moreover, we
introduce the combinatorial curvature flow on surfaces to find the desired
circle packing with the prescribed total geodesic curvature
Rigidity of bordered polyhedral surfaces
This paper investigates the rigidity of bordered polyhedral surfaces. Using
the variational principle, we show that bordered polyhedral surfaces are
determined by boundary value and discrete curvatures on the interior. As a
corollary, we reprove the classical result that two Euclidean cyclic polygons
(or hyperbolic cyclic polygons) are congruent if the lengths of their sides are
equal
Pickup Coil Spacing Effects on Eddy Current Reflection Probe Sensitivity
Differential probes have existed for many years and have been produced in a variety of configurations. The common feature of these diverse probes is that they detect an ac magnetic field gradient, but it is the desired direction of gradient detection that results in the numerous design variations [1,2,3]. The probes commonly used in a production shop for nondestructive testing (NDT) are invariably wound on ferrite cores because of the increased sensitivity that results from the use of high magnetic permeability core materials. However, recent advances in the theory of flawfield interactions have stimulated interest in the use of air core probes [4,5]. The use of air core coils in the detector helps to minimize the complexity of the calculations and leaves the experimenter with very adequate tools for verification studies. This theoretical work has been a critical element in the development of quantitative eddy current measurements
Aharonov-Bohm interference in topological insulator nanoribbons
Topological insulators represent novel phases of quantum matter with an
insulating bulk gap and gapless edges or surface states. The two-dimensional
topological insulator phase was predicted in HgTe quantum wells and confirmed
by transport measurements. Recently, Bi2Se3 and related materials have been
proposed as three-dimensional topological insulators with a single Dirac cone
on the surface and verified by angle-resolved photoemission spectroscopy
experiments. Here, we show unambiguous transport evidence of topological
surface states through periodic quantum interference effects in layered
single-crystalline Bi2Se3 nanoribbons. Pronounced Aharonov-Bohm oscillations in
the magnetoresistance clearly demonstrate the coverage of two-dimensional
electrons on the entire surface, as expected from the topological nature of the
surface states. The dominance of the primary h/e oscillation and its
temperature dependence demonstrate the robustness of these electronic states.
Our results suggest that topological insulator nanoribbons afford novel
promising materials for future spintronic devices at room temperature.Comment: 5 pages, 4 figures, RevTex forma
Suicide ideation of individuals in online social networks
Suicide explains the largest number of death tolls among Japanese adolescents
in their twenties and thirties. Suicide is also a major cause of death for
adolescents in many other countries. Although social isolation has been
implicated to influence the tendency to suicidal behavior, the impact of social
isolation on suicide in the context of explicit social networks of individuals
is scarcely explored. To address this question, we examined a large data set
obtained from a social networking service dominant in Japan. The social network
is composed of a set of friendship ties between pairs of users created by
mutual endorsement. We carried out the logistic regression to identify users'
characteristics, both related and unrelated to social networks, which
contribute to suicide ideation. We defined suicide ideation of a user as the
membership to at least one active user-defined community related to suicide. We
found that the number of communities to which a user belongs to, the
intransitivity (i.e., paucity of triangles including the user), and the
fraction of suicidal neighbors in the social network, contributed the most to
suicide ideation in this order. Other characteristics including the age and
gender contributed little to suicide ideation. We also found qualitatively the
same results for depressive symptoms.Comment: 4 figures, 9 table
History of clinical transplantation
The emergence of transplantation has seen the development of increasingly potent immunosuppressive agents, progressively better methods of tissue and organ preservation, refinements in histocompatibility matching, and numerous innovations is surgical techniques. Such efforts in combination ultimately made it possible to successfully engraft all of the organs and bone marrow cells in humans. At a more fundamental level, however, the transplantation enterprise hinged on two seminal turning points. The first was the recognition by Billingham, Brent, and Medawar in 1953 that it was possible to induce chimerism-associated neonatal tolerance deliberately. This discovery escalated over the next 15 years to the first successful bone marrow transplantations in humans in 1968. The second turning point was the demonstration during the early 1960s that canine and human organ allografts could self-induce tolerance with the aid of immunosuppression. By the end of 1962, however, it had been incorrectly concluded that turning points one and two involved different immune mechanisms. The error was not corrected until well into the 1990s. In this historical account, the vast literature that sprang up during the intervening 30 years has been summarized. Although admirably documenting empiric progress in clinical transplantation, its failure to explain organ allograft acceptance predestined organ recipients to lifetime immunosuppression and precluded fundamental changes in the treatment policies. After it was discovered in 1992 that long-surviving organ transplant recipient had persistent microchimerism, it was possible to see the mechanistic commonality of organ and bone marrow transplantation. A clarifying central principle of immunology could then be synthesized with which to guide efforts to induce tolerance systematically to human tissues and perhaps ultimately to xenografts
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