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Exotic states such as topological insulators, superconductors and quantum spin liquids are often challenging or impossible to create in a single material.sup.1-3. For example, it is unclear whether topological superconductivity, which has been suggested to be a key ingredient for topological quantum computing, exists in any naturally occurring material.sup.4-9. The problem can be circumvented by deliberately selecting the combination of materials in heterostructures so that the desired physics emerges from interactions between the different components.sup.1,10-15. Here we use this designer approach to fabricate van der Waals heterostructures that combine a two-dimensional (2D) ferromagnet with a superconductor, and we observe 2D topological superconductivity in the system. We use molecular-beam epitaxy to grow 2D islands of ferromagnetic chromium tribromide.sup.16 on superconducting niobium diselenide. We then use low-temperature scanning tunnelling microscopy and spectroscopy to reveal the signatures of one-dimensional Majorana edge modes. The fabricated 2D van der Waals heterostructure provides a high-quality, tunable system that can be readily integrated into device structures that use topological superconductivity. The layered heterostructures can be readily accessed by various external stimuli, potentially allowing external control of 2D topological superconductivity through electrical.sup.17, mechanical.sup.18, chemical.sup.19 or optical means.sup.20. A van der Waals structure based on a two-dimensional magnet and layered superconductor offers a potential system in which topological superconductivity could be easily tuned and integrated into devices., Author(s): Shawulienu Kezilebieke [sup.1] , Md Nurul Huda [sup.1] , Viliam Vano [sup.1] , Markus Aapro [sup.1] , Somesh C. Ganguli [sup.1] , Orlando J. Silveira [sup.1] , Szczepan Glodzik [...]

In 1928, Dirac proposed a wave equation to describe relativistic electrons.sup.1. Shortly afterwards, Klein solved a simple potential step problem for the Dirac equation and encountered an apparent paradox: the potential barrier becomes transparent when its height is larger than the electron energy. For massless particles, backscattering is completely forbidden in Klein tunnelling, leading to perfect transmission through any potential barrier.sup.2,3. The recent advent of condensed-matter systems with Dirac-like excitations, such as graphene and topological insulators, has opened up the possibility of observing Klein tunnelling experimentally.sup.4-6. In the surface states of topological insulators, fermions are bound by spin-momentum locking and are thus immune from backscattering, which is prohibited by time-reversal symmetry. Here we report the observation of perfect Andreev reflection in point-contact spectroscopy--a clear signature of Klein tunnelling and a manifestation of the underlying 'relativistic' physics of a proximity-induced superconducting state in a topological Kondo insulator. Our findings shed light on a previously overlooked aspect of topological superconductivity and can serve as the basis for a unique family of spintronic and superconducting devices, the interface transport phenomena of which are completely governed by their helical topological states. Perfect transmission of electrons through a finite potential barrier between a normal metal and a topological superconducting state is demonstrated, as evidenced by an exact doubling of conductance in point contact measurements., Author(s): Seunghun Lee [sup.1] [sup.2] , Valentin Stanev [sup.1] [sup.2] [sup.3] , Xiaohang Zhang [sup.1] [sup.2] , Drew Stasak [sup.1] , Jack Flowers [sup.1] , Joshua S. Higgins [sup.2] [sup.4] [...]

A point of a discrete object is called simple if it can be deleted from this object without altering topology. In this paper, we present new characterizations of simple points, which hold in dimensions 2, 3, and 4 and lead to efficient algorithms for detecting such points. In order to prove these characterizations, we establish two confluence properties of the collapse operation which hold in the neighborhood of a point in spaces of Iow dimension. We develop this work in the framework of cubical complexes, which provides a sound topological basis for image analysis and retrieves the main notions and results of digital topology, in particular the notion of simple point. Index Terms--Thinning, skeleton, topology preservation, simple point, cubical complex, collapse, confluence, 4D space.

This research presents a level set-based topology optimization for electromagnetic problems dealing with geometrical shape derivatives and topological design. The shape derivative is computed by an adjoint variable method to avoid numerous sensitivity evaluations. A level set function interpolated into a fixed initial domain is evolved by using the Hamilton-Jacobi equation. The moving free boundaries (dynamic interfaces) represented in the level set model determine the optimal shape via the topological changes. In order to improve efficiency of level set evolution, a radial basis function (RBF) is introduced. The optimization technique is illustrated with 2-D example captured from 3-D level set configuration and the resulting optimum shape is compared to conventional topology optimization. Index Terms--Gradient-based optimization, level set (LS) method, radial basis function, shape derivative, topology optimization.

Modeling from silhouettes is a popular and useful topic in computer vision. Many methods exist to compute the surface of the visual hull from silhouettes, but few address the problem of ensuring good topological properties of the surface, such as manifoldness. This paper provides an efficient algorithm to compute such a surface in the form of a polyhedral mesh. It relies on a small number of geometric operations to compute a visual hull polyhedron in a single pass. Such simplicity enables the algorithm to combine the advantages of being fast, producing pixel-exact surfaces, and repeatably yield manifold and watertight polyhedra in general experimental conditions with real data, as verified with all data sets tested. The algorithm is fully described, its complexity analyzed, and the modeling results given. Index Terms--Modeling from multiple views, modeling from silhouettes, shape from silhouettes, 3D reconstruction, visual hull.

A new differential topology featuring a stacked multiloop inductor with and without patterned ground shields (PGSs) is described for silicon-based radio-frequency integrated circuits (RFICs). The hybrid method could be used as a promising technique for developing new silicon-based passive devices used in RFICs.

In the following years power levels of 20 kW to 50 kW will be demanded by the telecommunication satellites. It is not possible to keep 0.5 kW modules with up to 100 modules in parallel and, therefore, higher power modules must be used. A higher bus voltage seems also necessary and any voltage below 150 V and above 100 V could meet the needs. In addition, new optimized topologies that process only a part of the total power delivery can be employed to improve the efficiency. In this article, design guidelines and experimental results of a high efficiency battery discharge regulator (BDR) module based on parallel power processing are given.

To meet the stringent transient response requirements of a voltage regulator (VR) at high slew rate load current while keeping high VR efficiency, this paper proposes a new topology: active transient voltage compensator (ATVC). ATVC only engages in transient periods operating at several MHZ to handle ac current and main VR operates at low switching frequency for better efficiency mainly providing dc current. ATVC injects a very high slew rate current in step up load and recovers energy in step down load. With introduction of a transformer, ATVC significantly reduces its conduction and switching losses due to the reduced current. Also, the new topology reduces the number of VR bulk capacitors while keeping the same output impedance. A built prototype and detailed experimental results verify the theoretical analysis. Index Terms--Active transient voltage compensator (ATVC), high slew rate, load line, synchronous buck converter, voltage regulator (VR).

This paper proposes a novel synthesis methodology to generate integrated zero-voltage-transition (ZVT) topologies, as well as to systematize the topologies that are already known. An approach is presented to classify single-pole ZVT converters. This approach can be expanded to multipole systems, such as polyphase inverters and rectifiers, uninterruptible power supplies, and variable-speed drives. The connections among several presented topologies are easily seen by means of the general diagrams that are shown in this paper. Analysis and understanding of the advantages, disadvantages, merits, and limitations of each converter are made easier since these converters are obtained from a common approach that is presented in this paper. Index Terms--Circuit synthesis, lossless circuits, switching circuits.

This paper looks at the performance of photovoltaic modules in nonideal conditions and proposes topologies to minimize the degradation of performance caused by these conditions. It is found that the peak power point of a module is significantly decreased due to only the slightest shading of the module, and that this effect is propagated through other nonshaded modules connected in series with the shaded one. Based on this result, two topologies for parallel module connections have been outlined. In addition, dc/dc converter technologies, which are necessary to the design, are compared by way of their dynamic models, frequency characteristics, and component cost. Out of this comparison, a recommendation has been made. Index Terms--DC-DC power conversion, modeling, photovoltaic power systems, topology, voltage control.

To solve the problem of multi-period capacity expansion in local access telecommunication network, a method that uses heuristics and tree topology is presented.

The 'form finding' methods for tension structures may be classified into two different groups: the linear and nonlinear methods. One of the linear methods is the force density method (FDM). In this paper advantage is taken of an important property of the FDM by which knowledge of the initial position of the nonfixed nodes of the structure is not needed, only the connectivity of the nodes is necessary for the solution of the problem. Accordingly, a new mapping method is presented that is based on topology, in contrast to the mapping methods used so far that are based exclusively on geometry. The most important contribution of this new approach is that due to mapping in topology, an initial guess of the equilibrium position is not needed as part of the solution process. The ease of implementation is also shown in this paper, along with future research that may improve this new idea. Several examples are presented that illustrate the applicability of this new method. DOI: 10.1061/(ASCE)0733-9445(2006)132:6(970) CE Database subject headings: Mapping: Tension structures: Nonlinear analysis.

It has recently been demonstrated that many biological networks exhibit a 'scale-free' topology, for which the probability of observing a node with a certain number of edges (k) follows a power law: i.e., p(k) ~ [k.sup.-[gamma]]. This observation has been reproduced by evolutionary models. Here we consider the network of protein-protein interactions (PPIs) and demonstrate that two published independent measurements of these interactions produce graphs that are only weakly correlated with one another despite their strikingly similar topology. We then propose a physical model based on the fundamental principle that (de)solvation is a major physical factor in PPIs. This model reproduces not only the scale-free nature of such graphs but also a number of higher-order correlations in these networks. A key support of the model is provided by the discovery of a significant correlation between the number of interactions made by a protein and the fraction of hydrophobic residues on its surface. The model presented in this paper represents a physical model for experimentally determined PPIs that comprehensively reproduces the topological features of interaction networks. These results have profound implications for understanding not only PPIs but also other types of scale-free networks. biological networks | hydrophobic effect | scale-free networks

This work demonstrates the successful synthesis of path generating compliant mechanisms by the process of topology and shape design optimization. As geometric topology variation of continuum structures is difficult to treat and analysis of the displacement path or trajectory of such structures is computationally intensive, a highly effective and efficient optimal design procedure is needed. This paper describes the use of a recently developed morphological geometric representation scheme coupled with an evolutionary algorithm to synthesize the mechanism. The scheme uses arrangements of skeleton and 'flesh' to define structural geometry, which facilitates transmission of topological/shape characteristics across generations in the evolutionary process and will not render any geometrically invalid designs. The evolutionary algorithm solves the problem as a discrete optimization problem, with a proficient constraint handling capability. [DOI: 10.1115/1.1480818]

Nonpolluting and polluting compounds can be differentiated with the basis of molecular topology and the use of observations of pesticide occurrence in groundwater in the United States. The application of molecular approaches for understanding pollution at the molecular level to risk assessment and agricultural development is examined.

Abstract: We study n-dimensional complete intersections of 'sufficiently high' multidegree in CP.sup.n + k ,\ n 3 , with fixed number and, possibly, position of singularities. In the case of quadratic singularities, we give a topological description of such a complete intersection by decomposing it into a connected sum of special form. In this case, the diffeomorphism type of the variety is determined by its dimension, multidegree, and the number of singular points. Bibliography: 5 titles. Article History: Registration Date: 20/10/2004

Abstract: Several combinatorial geometry properties of convex compact sets are proved by topological methods. It is proved that if K .sub.1,... ,K .sub.n-1 are convex compacta in R.sup.n , then there is an (n-2)-plane E.sup.n such that for each i=1,2,... ,n-1 there exist three (two orthogonal) hyperplanes containing E and dividing .sub.Ki into six (four) parts of equal volume. It is also proved that for every two bounded continuous distributions of masses in R.sup.3 centrally symmetric with respect to the origin there are three planes dividing both masses into eight equal parts. Bibliography: 9 titles. Article History: Registration Date: 20/10/2004

Abstract: We study the global topological structure of hypersurfaces in CP.sup.n + 1 , n 3 , with quadratic singularities and prescribed set of singular points. Under certain restrictions on the degree, we give a precise topological description of such a hypersurface by decomposing it into a connected sum of special form. In this case, the diffeomorphism type of the hypersurface is determined by the dimension, degree, and the number of singular points. Bibliography: 14 titles. Article History: Registration Date: 20/10/2004

Byline: A. V. Vologodskii (1) Keywords: circular DNA; DNA topology; DNA knots; DNA links; DNA simulation Abstract: A distinctive feature of closed circular DNA molecules is their particular topological state, which cannot be altered by any conformational rearrangement short of breaking at least one strand. This topological constraint opens unique possibilities for experimental studies of the distributions of topological states created in different ways. Primarily, the equilibrium distributions of topological properties are considered in the review. It is described how such distributions can be obtained and measured experimentally, and how they can be computed. Comparison of the calculated and measured equilibrium distributions over the linking number of complementary strands, equilibrium fractions of knots and links formed by circular molecules has provided much valuable information about the properties of the double helix. Study of the steady-state fraction of knots and links created by type II DNA topoisomerases has revealed a surprising property of the enzymes: their ability to reduce these fractions considerably below the equilibrium level. Author Affiliation: (1) Department of Chemistry, New York University, NY, 10003, USA Article History: Registration Date: 08/10/2004

Abstract: Three theorems on approximation of plane sections of convex bodies by affine-regular polygons, ellipses, or circles are proved by topological means. In particular, it is proved that if K is a convex body in [].sup.3 (resp., [].sup.4), then for every interior point O of K there is a plane cross section of K through O which is circumscribed about an affine-regular hexagon (resp., octagon) with center O. Bibliography: 8 titles. Article History: Registration Date: 10/07/2000 Received Date: 24/04/1996 Article note: Translated from Zapiski Nauchnykh Seminarov POMI, Vol. 246, 1997, pp. 174--183. Translated by N. Yu. Netsvetaev.

Simulation experiments demonstrate predicting the relative retention times of 10 alkane isomers based on their topology in a helium-squalane gas-liquid chromatographic system.

A visual odometer developed for autonomous helicopter flight is discussed with consideration of the philosophy behind it, its tracking algorithm and implementation. The odometer can find approximate position by visually locking on and tracking objects on the ground and test flight data are given..

Byline: Daniel Druckman (1), Jennifer Martin (1), Susan Allen Nan (1), Dimostenis Yagcioglu (1) Keywords: comparative analysis; international negotiations; multidimensional scaling; negotiating objectives; Pew case studies; profiles of negotiation Abstract: Results from statistical analyses of 30 cases of international negotiations supported Ikle's typology of negotiating objectives. The cases, sampled from the collection of Pew Case Studies in International Affairs, were distinguished in terms of five objectives: innovation, redistribution, extension, normalization, and side effects. In addition, a sixth objective was identified: negotiations concerning the creation of multilateral regimes. These cases focused on issues that surfaced on the international agenda during the 1980s. Each type had a relatively distinct profile based on such aspects of negotiation as the number of parties and issues, bargaining strategies, media exposure, stability of the process, and types of outcomes. The methodology contributes to the state-of-the art in comparative analysis and the results have implications for the development of middle-range theories of negotiation. They also contribute to practice, by enabling negotiators to evaluate future cases in terms of knowledge about past cases. Author Affiliation: (1) Institute for Conflict Analysis and Resolution, George Mason University, Fairfax, VA, 22030-4444, USA Article History: Registration Date: 29/09/2004

In the maximum parsimony (MP) and minimum evolution (ME) methods of phylogenetic inference, evolutionary trees are constructed by searching for the topology that shows the minimum number of mutational changes required (M) and the smallest sum of branch lengths (S), respectively, whereas in the maximum likelihood (ML) method the topology showing the highest maximum likelihood (A) of observing a given data set is chosen. However, the theoretical basis of the optimization principle remains unclear. We therefore examined the relationships of M, S, and A for the MP, ME, and ML trees with those for the true tree by using computer simulation. The results show that M and S are generally greater for the true tree than for the MP and ME trees when the number of nucleotides examined (n) is relatively small, whereas A is generally lower for the true tree than for the ML tree. This finding indicates that the optimization principle tends to give incorrect topologies when n is small. To deal with this disturbing property of the optimization principle, we suggest that more attention should be given to testing the statistical reliability of an estimated tree rather than to finding the optimal tree with excessive efforts. When a reliability test is conducted, simplified MP, ME, and ML algorithms such as the neighbor-joining method generally give conclusions about phylogenetic inference very similar to those obtained by the more extensive tree search algorithms.

Branched polymers can show new properties, including high solublity and low density, leading to new applications. Hyperbranched materials are easily prepared through one-step reactions of ABchi monomers. However the rate of branching or polydispersity (PDI) and polymerization (DP) are difficult to control. Hydrogen bonding between hydroxy groups and crown ether has been proposed as a driving force for threading, and the concept is expanded for use in a novel strategy to overcome limitations associated with classical methods, through the syntheses of mechanically linked branched and network polyurethanes.

Byline: Michel Rerat (1), Michel Gelize (1), Daniel Liotard (2) Abstract: The whole sets of critical points of analytical functions corresponding to the longarange twoabody interaction between two, three and four dipole vectors set at the vertices of several polygons are determined using topology theorems. Betti numbers associated to the configuration spaces are first obtained, then stationary points are located via an analytical gradient method till the Morse inequalities are checked. Author Affiliation: (1) Laboratoire de Chimie Structurale, Universite de Pau, Fa64000, Pau, France (2) Laboratoire de PhysicoaChimie Theorique, Universite de Bordeaux I, Fa33405, Talence, France Article History: Registration Date: 11/09/2004

New mathematical techniques in the field of topology and improvements in computational abilities of computers enable the use of knot theory and braid theory to fluid flows. An example of this application is in the estimation of the stored energy in the magnetic fields in the solar atmosphere.

A theoretical framework is provided for addressing k-terminal reliability problems and a reliability expression is obtained for computing the probability of an acyclic monotone (S,t)-graph being operational. The use of local domination parameters reduces the system level of consideration to the element level. This provides a unifying understanding of the combinatorial nature of some results based on the domination theory.

Abstract algebra and topology are two methods of key importance for the in depth understanding of mathematics in a simplified way. Their applications in the development and research of complex problems in various streams of mathematics are given. The abstract algebraic and topological approaches converge in classical algebraic function theory but are otherwise disparate approaches.

This paper describes a method of verifying the consistency (i.e., agreement) between the topology and geometry of boundary representation (B-rep) solid models of mechanical components. This verification is well-suited for implementation as an algorithm and has been implemented as such in a polyhedral boundary representation solid modeling system (Jablokow, 1989). This technique and algorithm is important in the design of mechanical components for design documentation, integration with analysis and manufacturing applications, and design data exchange between solid modeling systems. Information regarding boundary representations has typically divided into the geometry and topology. It is important that the two are consistent for a valid solid model. In this work the genus of a solid model of an object is calculated topologically and geometrically and then compared to verify the consistency of the solid model. The genus of an object gives insight as to the geometric complexity of the object. This is equivalent to verifying the Gauss-Bonnet Theorem for the model, and is discussed in the paper.

A new topological method of determining possible bridging modes and connectivity patterns for a given formula was presented. The formula facilitated the prediction of potentially new conformations for the cluster molecules MmQnLt containing four-coordinate metal sites and Qu2,3,4 bridging modes. Additionally, the method allowed the formation of an organizational framework for all involved structures.

The traditional approach to the mathematical theory of dynamic programming incorporates an abstract contraction property known as Lipschitz condition. Biconvergence is a suggested alternative approach that embodies an abstract topological condition on both the utility function and the intertemporal production correspondence. Biconvergence is easier to test, and results are less difficult to interpret.

Twenty combinatorial examples are provided for deriving the asymptotics of the coefficients of multivariate generating functions using concepts of topology, complex variables and algebra. Functions derived by the transfer matrix method, kernel method and Lagrange inversion method are discussed.