Topological Analysis

Map-matching algorithms integrate positioning data with spatial road network data (roadway centrelines) to identify the correct link on which a vehicle is travelling and to determine the location of a vehicle on a link. A map-matching algorithm could be used as a key component to improve the performance of systems that support the navigation function of intelligent transport systems (ITS). The required horizontal positioning accuracy of such ITS applications is in the range of 1 m to 40 m (95%) with relatively stringent requirements placed on integrity (quality), continuity and system availability. A number of map-matching algorithms have been developed by researchers around the world using different techniques such as topological analysis of spatial road network data, probabilistic theory, Kalman filter, fuzzy logic, and belief theory. The performances of these algorithms have improved over the years due to the application of advanced techniques in the map matching processes and improvements in the quality of both positioning and spatial road network data. However, these algorithms are not always capable of supporting ITS applications with high required navigation performance, especially in difficult and complex environments such as dense urban areas. This suggests that research should be directed at identifying any constraints and limitations of existing map matching algorithms as a prerequisite for the formulation of algorithm improvements. The objectives of this paper are thus to uncover the constraints and limitations by an in-depth literature review and to recommend ideas to address them. This paper also highlights the potential impacts of the forthcoming European Galileo system and the European Geostationary Overlay Service (EGNOS) on the performance of map matching algorithms. Although not addressed in detail, the paper also presents some ideas for monitoring the integrity of mapmatching algorithms. The map-matching algorithms considered in this paper are generic and do not assume knowledge of 'future' information (i.e. based on either cost or time). Clearly, such data would result in relatively simple map-matching algorithms.

... in which xi denotes the space and spin coordinates of the electron labeled i. For a single determinental wave function (ie ... the basins of these attractors, 0.55, is higher than for a double or a single CC bond in the ab-sence of conjugation, indicating a noticeable delocalization. ...

In this study we concentrate on qualitative topological analysis of the local behavior of the space of natural images. To this end, we use a space of 3 by 3 high-contrast patches M. We develop a theoretical model for the high-density 2-dimensional submanifold of M showing that it has the topology of the Klein bottle. Using our topological software package PLEX we experimentally verify our theoretical conclusions. We use polynomial representation to give coordinatization to various subspaces of M. We find the bestfitting embedding of the Klein bottle into the ambient space of M. Our results are currently being used in developing a compression algorithm based on a Klein bottle dictionary.

The Niemann-Pick C1 (NPC1) protein is predicted to be a polytopic glycoprotein, and it contains a region with extensive homology to the sterol-sensing domains (SSD) of 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMG-R) and sterol regulatory element binding protein cleavage-activating protein (SCAP). To aid the functional characterization of NPC1, a model of NPC1 topology was evaluated by expression of epitope-tagged NPC1 proteins and investigation of epitope accessibility in selectively permeabilized cells. These results were further confirmed by expression of NPC1 and identification of glycosylated domains that are located in the lumen of the endoplasmic reticulum. Our data indicate that this glycoprotein contains 13 transmembrane domains, 3 large and 4 small luminal loops, 6 small cytoplasmic loops, and a cytoplasmic tail. Furthermore, our data show that the putative SSD of NPC1 is oriented in the same manner as those of HMG-R and SCAP, providing strong evidence that this domain is functionally important.

To develop and investigate detailed mathematical models of metabolic processes is one of the primary challenges in systems biology. However, despite considerable advance in the topological analysis of metabolic networks, kinetic modeling is still often severely hampered by inadequate knowledge of the enzyme-kinetic rate laws and their associated parameter values. Here we propose a method that aims to give a quantitative account of the dynamical capabilities of a metabolic system, without requiring any explicit information about the functional form of the rate equations. Our approach is based on constructing a local linear model at each point in parameter space, such that each element of the model is either directly experimentally accessible or amenable to a straightforward biochemical interpretation. This ensemble of local linear models, encompassing all possible explicit kinetic models, then allows for a statistical exploration of the comprehensive parameter space. The method is exemplified on two paradigmatic metabolic systems: the glycolytic pathway of yeast and a realistic-scale representation of the photosynthetic Calvin cycle.

Topological methods have recently been developed for the analysis of dissipative dynamical systems that operate in the chaotic regime. They were originally developed for three-dimensional dissipative dynamical systems, but they are applicable to all ''low-dimensional'' dynamical systems. These are systems for which the flow rapidly relaxes to a three-dimensional subspace of phase space. Equivalently, the associated attractor has Lyapunov dimension

Information in the cortex is thought to be represented by the joint activity of neurons. Here we describe how fundamental questions about neural representation can be cast in terms of the topological structure of population activity. A new method, based on the concept of persistent homology, is introduced and applied to the study of population activity in primary visual cortex (V1). We found that the topological structure of activity patterns when the cortex is spontaneously active is similar to those evoked by natural image stimulation and consistent with the topology of a two sphere. We discuss how this structure could emerge from the functional organization of orientation and spatial frequency maps and their mutual relationship. Our findings extend prior results on the relationship between spontaneous and evoked activity in V1 and illustrates how computational topology can help tackle elementary questions about the representation of information in the nervous system.

Osteoporosis is a disease characterized by bone volume loss and architectural deterioration. The majority of work aimed at evaluating the structural implications of the disease has been performed based on stereologic analysis of histomorphometric sections. Only recently noninvasive imaging methods have emerged that provide sufficient resolution to resolve individual trabeculae. In this article, we apply digital topological analysis (DTA) to magnetic resonance microimages (-MRI) of the radius obtained at 137 ؋ 137 ؋ 350 m 3 voxel size in a cohort of 79 women of widely varying bone mineral density (BMD) and vertebral deformity status. DTA is a new method that allows unambiguous determination of the three-dimensional (3D) topology of each voxel in a trabecular bone network. The analysis involves generation of a bone volume fraction map, which is subjected to subvoxel processing to alleviate partial volume blurring, followed by thresholding and skeletonization. The skeletonized images contain only surfaces, profiles, curves, and their mutual junctions as the remnants of trabecular plates and rods after skeletonization. DTA parameters were compared with integral BMD in the lumbar spine and femur as well as MR-derived bone volume fraction (BV/TV). Vertebral deformities were determined based on sagittal MRIs of the spine with a semiautomatic method and the number of deformities counted after threshold setting. DTA structural indices were found the strongest discriminators of subjects with deformities from those without deformities. Subjects with deformities (n ‫؍‬ 29) had lower topological surface (SURF) density (p < 0.0005) and surface-to-curve ratio (SCR; a measure of the ratio of platelike to rodlike trabeculae; p < 0.0005) than those without. Profile interior (PI) density, a measure of intact trabecular rods, was also lower in the deformity group (p < 0.0001). These data provide the first in vivo evidence for the structural implications inherent in postmenopausal osteoporosis accompanying bone loss, that is, the conversion of trabecular plates to rods and disruption of rods due to repeated osteoclastic resorption. (J Bone Miner Res 2001;16:1520 -1531)

The network paradigm is increasingly used to describe the topology and dynamics of complex systems. Here, we review the results of the topological analysis of protein structures as molecular networks describing their small-world character, and the role of hubs and central network elements in governing enzyme activity, allosteric regulation, protein motor function, signal transduction and protein stability. We summarize available data how central network elements are enriched in active centers and ligand binding sites directing the dynamics of the entire protein. We assess the feasibility of conformational and energy networks to simplify the vast complexity of rugged energy landscapes and to predict protein folding and dynamics. Finally, we suggest that modular analysis, novel centrality measures, hierarchical representation of networks and the analysis of network dynamics will soon lead to an expansion of this field.

In recent years, the maturation of microarray technology has allowed the genomewide analysis of gene expression patterns to identify tissue-specific and ubiquitously expressed ('housekeeping') genes. We have performed a functional and topological analysis of housekeeping and tissue-specific networks to identify universally necessary biological processes, and those unique to or characteristic of particular tissues.

We use the theory of complex networks in order to quantitatively characterize the formation of communities in a particular financial market. The system is composed by different banks exchanging on a daily basis loans and debts of liquidity. Through topological analysis and by means of a model of network growth we can determine the formation of different group of banks characterized by different business strategy. The model based on Pareto's Law makes no use of growth or preferential attachment and it reproduces correctly all the various statistical properties of the system. We believe that this network modeling of the market could be an efficient way to evaluate the impact of different policies in the market of liquidity.

The formulation of network models from global protein studies is essential to understand the functioning of organisms. Network models of the proteome enable the application of Complex Network Analysis, a quantitative framework to investigate large complex networks using techniques from graph theory, statistical physics, dynamical systems and other fields. This approach has provided many insights into the functional organization of the proteome so far and will likely continue to do so. Currently, several network concepts have emerged in the field of proteomics. It is important to highlight the differences between these concepts, since different representations allow different insights into functional organization. One such concept is the protein interaction network, which contains proteins as nodes and undirected edges representing the occurrence of binding in large-scale protein-protein interaction studies. A second concept is the protein-signaling network, in which the nodes correspond to levels of post-translationally modified forms of proteins and directed edges to causal effects through post-translational modification, such as phosphorylation. Several other network concepts were introduced for proteomics. Although all formulated as networks, the concepts represent widely different physical systems. Therefore caution should be taken when applying relevant topological analysis. We review recent literature formulating and analyzing such networks.

Background: Approximately 1 out of every 100 individuals has some form of venous insufficiency, which can lead to chronic venous disease and Venous Leg Ulcer (VLU). There are known underlying pathologies which contribute to the chronic nature of VLU including biofilm phenotype infections.

The atoms in molecules (AIM) theory may be used to derive atomic charges, atomic volumes and molecular dipole moments from the charge density. The theory is applied to theoretical periodic Hartree±Fock (PHF), density-functional (DFT) and experimental X-ray densities of p-nitroaniline using the program TOPOND and a newly developed program, TOPXD, for topological analysis of densities described by the Coppens±Hansen multipole formalism. Results show that, like dipole moments derived directly from the multipole re®nement, AIMderived atomic and molecular moments are dependent on the multipole model used. As expected, large differences are found between charges derived from the monopole parameters and those from AIM analysis of the experimental model density. Differences between the H -restricted multipole model (KRMM) and the unrestricted multipole model (UMM) results are preserved in the AIM analysis. The enhancement of the molecular dipole moment of p-nitroaniline in the solid state is con®rmed by both experiment and theory but the experimental dipole moment is in much better agreement with theoretical periodic Hartree± Fock and, especially, periodic DFT (PDFT) data when KRMM is used in the re®nement. The AIM analysis allows a rigorous de®nition of the charges of the atoms in molecules and provides a realistic basis for comparison between molecules and between experiment and theory.

Recently, imaging techniques have become available which permit non-destructive analysis of the three-dimensional (3D) architecture of trabecular bone (TB), which forms a network of interconnected plates and rods. Most osteoporotic fractures occur at locations rich in TB, which has spurred the search for architectural parameters as determinants of bone strength. In this paper, we present a new approach to quantitative characterization of the 3D micro-architecture of TB, based on digital topology. The method classifies each voxel of the 3D structure based on the connectivity information of neighboring voxels. Following conversion of the 3D digital image to a skeletonized surface representation containing only one-and two-dimensional structures, each voxel is classified as a curve, surface, or junction. The method has been validated by means of synthesized images and has subsequently been applied to TB images from the human wrist. The topological parameters were found to predict Young's modulus for uniaxial loading; specifically, the surface-to-curve ratio was found to be the single strongest predictor of Young's modulus (r 2 = 0.69). Finally, the method has been applied to TB images from a group of patients showing very large variations in topological parameters that parallel much smaller changes in bone volume fraction.

Vector fields can present complex structural behavior, especially in turbulent computational fluid dynamics. The topological analysis of these datasets reduces the information but one is usually still left with too many details for interpretation. In this paper, we present a simplification approach that removes pairs of critical points from the dataset, based on relevance measures. In contrast to earlier methods, no grid changes are necessary since the whole method uses small local changes of the vector values defining the vector field. An interpretation in terms of bifurcations underlines the continuous, natural flavor of the algorithm.

We have applied topological methods to analyze chaotic time series data from the Belousov-Zhabotinskii reaction. First, the periodic orbits shadowed by the data set were identified. Next, a three-dimensional embedding without self-intersections was constructed from the data set. The topological structure of that flow was visualized by constructing a branched manifold such that every periodic orbit in the flow could be held by the branched manifold. The branched manifold, or induced template, was computed using the three lowest-period orbits. The organization of the higher-period orbits predicted by this induced template was compared with the organization of the orbits reconstructed from the data set with excellent results. The consequences of the presence of certain knots found in the data are discussed.

This article presents a versatile, rigorous, and efficient methodology for extracting various geometric and topological parameters of 3D discrete porous media. The new approach takes advantage of the morphological skeleton of the pore structure-a lower dimensional representation of the pore space akin to the topological "deformation retract." The skeleton is derived by a fully parallel thinning algorithm that fulfils two essential requirements: it generates a medial axis and preserves the connectivity of the pore space. Topological analysis is accomplished by classifying all skeleton points as node or link (branch) points according to the concept of λ-adjacency in 3D discrete space. In this manner, node coordination number and link length distributions are directly obtained from the skeleton. Pore necks (throats) are identified through a search for minima in the hydraulic radius of individual pore space channels outlined by skeleton links. In addition to the determination of the size distribution of the constrictions (pore necks) that control nonwetting phase invasion, improved estimates of the distributions of effective hydraulic and electric conductivity of individual pore space channels are obtained. Furthermore, erection of planes at the location of pore necks results in partitioning of the pore space into its constituent pores. This enables the characterization of the pore space in terms of a pore volume distribution. The new methodology is illustrated by application to a regular cubic pore network and irregularly shaped 2D and 3D pore networks generated by stochastic simulation. In the latter case, important new results are obtained concerning the sensitivity of geometric and topological properties of the microstructure to the parameters of stochastic simulation, namely, the porosity and correlation function. It is found that model porous media reconstructed from the same porosity and correlation function can exhibit marked differences in geometry and connectivity, which correlate with differences in specific surface area. C 2000 Academic Press

Extended Hückel Molecular Orbital (EHMO) calculations were carried out on octahedral transition metal clusters with general formula [M6X8 i Y6 a ] (M = Molybdenum; X and Y = π-Donor Ligands) in order to rationalize their electronic structure. In these species the optimal metallic electron (ME) count is of 24 but for many clusters experimentally synthesized, the ME count can vary from 20 to 48 without dramatically altering the architecture of the octahedral cluster. Herein are reported the geometrical parameters and electronic properties, of a series of clusters with 20 to 24 valence electrons per cluster. The calculated characteristics for all the considered structures are in excellent agreement with the experimental ones and requires to learn more about the relationships that exist between their structural arrangement and electronic properties especially the number of electrons available for metal-metal bonding in M6 octahedral clusters.

Central venous catheters are widely used in clinical practice; however, complications such as venous thrombosis or infection are frequent. The physical and biological effects of a coating procedure designed to improve the blood-contacting properties of polyurethane central venous catheters (CVCs) were studied. The surface atomic composition of poly(vinyl pyrrolidone) (PVP)-coated or uncoated Pellethane@ single lumen CVCs was characterized by electron spectroscopy for chemical analysis (ESCA), which confirmed the presence of an oxygen-rich PVP layer on the former material. Topological analysis of both single and triple lumen CVCs by scanning force microscopy (SFM) revealed a very smooth surface in PVP-coated catheters compared to the more frequent surface irregularities found either in uncoated Pellethane@ or in four additional randomly selected, commercially available triple lumen polyurethane CVCs. The PVP-coated Pellethane@ showed a strong reduction in either fibrinogen or fibronectin adsorption compared to all other PVP-free polyurethane CVCs. This decreased protein adsorption led to a proportional reduction in protein-mediated adhesion of either Staphylococcus aureus or Staphy/ococcus epidermidis and in the binding of a monoclonal antibody directed against the cell-binding domain of fibronectin. Increased surface smoothness and hydrophilic properties of polyurethane CVCs might decrease the risk of bacterial colonization and infection.

The paper presents a qualitative analysis of the following systems of n differential equations: xi = xixj-xi ~",= 1 xrxs (] = i-1 + n6il and s = r-1 + n6rl), which show cyclic symmetry. These dynamical systems are of particular interest in the theory of selforganization and biological evolution as well as for application to other fields.

A silver/Coomassie brilliant blue R-250 staining technique that permits a color-coded differentiation of erythrocyte membrane proteins, sialoglycoproteins, and lipids in a single one-dimensional NaDodSO4/polyacrylamide gel has been described. Gels stained first with silver stain and then with Coomassie blue (CB) showed the characteristic blue staining of all conventional CB-sensitive membrane polypeptides, whereas periodic acid-Schiff reagent-sensitive sialoglycoproteins and lipids stained yellow. Several yellow Ag-stained bands corresponding to major and minor sialoglycoproteins were detected at Mr x 10-3 of 88, 72, 65, 41, 35, 31, 28, 24, and 20. Neuraminidase treatment of intact erythrocytes caused shifts in the electrophoretic mobilities of several yellowstained bands without affecting the CB-stained polypeptide pattern. These observations afforded evidence that the yellowstaining bands were sialoglycoproteins and lipids. The doublestaining technique was used in a topological analysis of the membrane surface of the erythrocyte using protease digestion and selective solubilization. Trypsin cleaved the yellow bands at Mr 88,000 and 41,000. Membrane-associated cleavage products were noted at Mr 58,000 and 38,000. Pronase treatment of intact cells gave membrane-associated cleavage products at Mr 38,000 (yellow) and two CB-stained bands at Mr 58,000 and 60,000. These results suggested that the double-staining technique may be applicable in compositional and topological analyses of other biological membranes.

Using high-resolution electron microscopy, anisotropic elasticity calculations, and image simulations, typical contrast was identified for the a → pure edge threading dislocations in GaN layers grown by molecular-beam epitaxy on sapphire. Their atomic structure was found to exhibit 5/7, or 8 atom cycles. The two configurations were observed at a similar frequency for isolated dislocations and low-angle boundaries. Coincidence grain boundaries have been studied and they are all made of a → pure-edge dislocations with the above identified atomic structures. A topological analysis of high-angle boundaries has been carried out in order to determine the defect content at the interfaces. The defects introduced on deviation from coincidence are associated with steps and their Burgers vectors correspond to the smallest vectors of the displacement shift complete set. At the interfaces, defect free steps, which belong to the sides or diagonal of the coincident site lattice unit cell, have been found to occur. The reconstruction of some boundaries was only possible by taking into account the occurrence of structural units which exhibit 4-atom ring cycles for the dislocation cores. In nonsymmetric interfaces, a new structural unit made of 5/4/7 atom rings has been found to constitute the core of one grain boundary dislocation.

Zinc complexes (ZnL 2 ) with bidentate N,O-donor Schiff bases (HL = HSH1, HSH2, HSH3) derivatives of salicylaldehyde and para-substituted anilines were synthesized and fully characterized. The crystallographic parameters of HSH2 and ZnL 2 were refined. Low temperature X-ray diffraction analysis including topological analysis of electron density function for crystals of ZnL 2 reveals that the geometrical parameters of all investigated compounds as well as the charges in chelate rings of complexes remain almost unchanged upon variation of the substituents (R) in para-position of the aniline fragment, going from -CH 3 (HSH1) to -N(CH 3 ) 2 (HSH2) and -OCH 3 (HSH3). Zinc complexes are thermally stable up to ∼190 • C as shown by thermogravimetric analysis under nitrogen atmosphere. The photoluminescent (PL) properties of HL and ZnL 2 were investigated in the solid state while its absorption spectra were measured in methanol. The theoretical calculation of the investigated compounds confirmed firstly the existence of enol-imine and keto-enamine tautomeric forms; and secondly the influence of the introduction of R on the PL properties of the compounds. The study of excited state dynamics of ZnL 2 in the solid state shows bi-exponential fluorescence decays and relatively high PL quantum yield, making them potentially adequate for being used as manifold optical materials. The interpretation of photophysical properties are substantiated by DFT and TD-DFT theoretical calculations of the Schiff bases and zinc complex species.

In this work, the average bifurcation value of the electron localization function (ELF) of both σ (ELFσ) and π (ELFπ) contributions was used to construct an aromaticity scale for chemical compounds. We have validated the scale with a series of well-known molecules and then used it to evaluate global aromaticity on aluminum based clusters, which present σ aromaticity and π antiaromaticity. The proposed scaled predicts an overall antiaromatic character for the Al 4 4moiety.

The increasing demand for real-time applications (video conferencing, Internet telephony -VoIP-etc.) delivered over Internet networks requires stringent Quality of Service (QoS) guarantees. Internet traffic routing based on a Best-effort basis can hardly support these QoS requirements. This article argues that Internet services providers should form strategic alliances to coordinate their investments in a newgeneration infrastructure and provide innovative services with QoS guarantees. This is supported by a topological analysis of the interconnection agreements among top-level Internet providers and by the lessons derived from alliances forged in the airline and card-based payment sectors. We conclude that on the Internet, the optimal organizational form should be a centralized alliance with a hub-and-spoke network structure.

Missense mutations as well as a null allele of the human glycine receptor ␣1 subunit gene GLRA1 result in the neurological disorder hyperekplexia [startle disease, stiff baby syndrome, Mendelian Inheritance in Man (MIM) #149400]. In a pedigree showing dominant transmission of hyperekplexia, we identified a novel point mutation C1128A of GLRA1. This mutation encodes an amino acid substitution (P250T) in the cytoplasmic loop linking transmembrane regions M1 and M2 of the mature ␣1 polypeptide. After recombinant expression, homomeric ␣1 P250T subunit channels showed a strong reduction of maximum whole-cell chloride currents and an altered desensitiza-tion, consistent with a prolonged recovery from desensitization. Apparent glycine binding was less affected, yielding an approximately fivefold increase in K i values. Topological analysis predicts that the substitution of proline 250 leads to the loss of an angular polypeptide structure, thereby destabilizing open channel conformations. Thus, the novel GLRA1 mutant allele P250T defines an intracellular determinant of glycine receptor channel gating.

The individual vulnerabilities of hosts on a network can be combined by an attacker to gain access that would not be possible if the hosts were not interconnected. Currently available tools report vulnerabilities in isolation and in the context of individual hosts in a network. Topological vulnerability analysis (TVA) extends this by searching for sequences of interdependent vulnerabilities, distributed among the various network hosts. Model checking has been applied to the analysis of this problem with some interesting initial results. However previous efforts did not take into account a realistic representation of network connectivity. These models were enough to demonstrate the usefulness of the model checking approach but would not be sufficient to analyze real-world network security problems. This paper presents a modem of network connectivity at multiple levels of the TCP/IP stack appropriate for use in a model checker. With this enhancement, it is possible to represent realistic networks including common network security devices such as firewalls, filtering routers, and switches.

We review three general approaches to determining the topology of integral cytoplasmic membrane proteins. (i) Inspection of the amino acid sequence and use of algorithms to predict membrane spanning segments allows the construction of topological models. For many proteins, the mere identification of such segments and an analysis of the distribution of basic amino acids in hydrophilic domains leads to correct structure predictions. For others, additional factors must come into play in determining topology. (ii) Gene fusion analysis of membrane proteins, in many cases, leads to complete topological models. Such analyses have been

We report here that the inward-rectifying potassium channels KAT1 and AKT2 were functionally expressed in K + uptake-deficient Escherichia coli . Immunological assays showed that KAT1 was translocated into the cell membrane of E. coli . Functional assays suggested that KAT1 was inserted topologically correctly into the cell membrane. In control experiments, the inactive point mutation in KAT1, T256R, did not complement for K + uptake in E. coli . The inward-rectifying K + channels of plants share a common hydrophobic domain comprising at least six membrane-spanning segments (S1–S6). The finding that a K + channel can be expressed in bacteria was further exploited to determine the KAT1 membrane topology by a gene fusion approach using the bacterial reporter enzymes, alkaline phosphatase, which is active only in the periplasm, and β-galactosidase. The enzyme activity from the alkaline phosphatase and β-galactosidase fusion plasmid showed that the widely predicted S1, S2, S5, and S6 se...

The mechanical competence of trabecular bone is significantly determined, next to material density, by its three-dimensional (3D) structure. Recent advances in micromagnetic resonance imaging (A-MRI) acquisition and processing techniques allow the 3D trabecular structure to be analyzed in vivo at peripheral sites such as the distal radius and tibia. The practicality of A-MRI-based noninvasive virtual bone biopsy (VBB) for longitudinal studies of patients hinges on the reproducibility of the derived structural parameters, which largely determine the size of the effect that can be detected at a given power and significance level. In this paper, the reproducibility of A-MRI-derived trabecular bone structure measures was examined by performing repeat studies in six healthy subjects in whom the distal aspects of the radius and tibia were scanned with a 3D spin-echo sequence at 137 Â 137 Â 410 Am 3 voxel size. Bone volume fraction (BV/TV) and digital topological analysis (DTA) structural parameters including the topological bone surface-to-curve ratio (SCR) and topological erosion index (TEI) were evaluated after subjecting the raw images to a cascade of processing steps. The average coefficient of variation was 4 -7% and was comparable for the two anatomic sites and for all parameters measured. The reliability expressed in terms of the intraclass correlation coefficient ranged from 0.95 to 0.97 in the radius and 0.68 to 0.92 in the tibia. Error analysis based on simulations suggests involuntary patient motion, primarily rotation, to be the chief source of imprecision, followed by failure to accurately match the analysis volumes in repeat studies. D 2004 Elsevier Inc. All rights reserved.

A comparative study of the chemisorption of the isoelectronic species CO and CN À on Rh, Ni, Pd and Pt(1 1 1) surfaces has been performed using the cluster model approach and the density functional theory. The CO bond is weakened whereas the CN À one is strengthened upon chemisorption in agreement with experimental evidence based on shifts to lower or higher frequencies, respectively, with respect the vibrational frequency of the free adsorbate. The details of the chemisorption bond have been studied using different techniques including a topological analysis of the electron localization function and the projection orbitals method. Finally, a correlation between the substrate-adsorbate charge transfer and the frequency shift has been found. Ó

The task of systematically choosing the s e t t i n the relays in a protection scheme is facilitated by the identification of a suitable break point set and the corresponding relative sequence matrix. The concept of functional dependency is used as a means o f developing algorithms for the accomplishment of these sub-tasks. These algorithms are seen to be computationally more efficient than the existing algorithms of the graph theoretic schemes.

Full-potential linearized augmented plane waves (FPLAPW) calculations have been used to determine the equilibrium properties and elastic constants of the chalcopyrite phase of AgGaSe 2 . The topological analysis of the electron density shows a clear polar bonding, with the integrated basin charges revealing a clear dominance of the covalent over the ionic character. The bonding analysis also provides a partition of the bulk modulus and compressibility into atomic contributions. Se is seen to dominate the global behavior (B ¼51.2 GPa), with a local bulk modulus intermediate between the values of the other two atoms: 44.8 (Ga), 51.1 (Se), and 56.6 GPa (Ag).

We used x-ray nanotomography to characterize the three-dimensional 3D morphology and topology of dealloyed nanoporous gold after coarsening. The interface shape distribution obtained from the nanotomography measurement shows that the coarsening does not proceed by bulk ...

Nanostructured skutterudite Co 1Ϫx Ni x Sb 3 has been synthesized by chemical alloying with Ni substitution for Co up to 27.5 at. %. High concentration of grain boundaries provided by nanostructuring is expected to lower the thermal conductivity of thermoelectric materials and could thus increase their thermoelectric dimensionless figure-of-merit ZT. Material preparation comprises two key stages, coprecipitation of the precursor, and thermal processing to produce the skutterudite. By modeling the chemistry of the metal ions in aqueous solution, optimum coprecipitation conditions were achieved. The precipitated precursor consists of a solid solution of the different intermediate compounds, and exhibits high reactivity. Calcination and reduction of the precursor resulted in the alloying of these elements and in the formation of skutterudite at a temperature as low as 723-773 K. Unfilled CoSb 3 skutterudites were prepared by chemical precipitation from aqueous solutions to achieve powders with a very small grain size ͑ϳ40 nm͒. Compacted samples were produced from this powder by uniaxial pressing under various conditions. Thermal conductivity, electrical resistivity and Seebeck coefficient of the resulting compacts were measured in a temperature range from 150 to 575 K. Measurement procedures were standardized for absolute accuracy and reproducibility between the DLR, Cologne and NEDO, Cardiff Laboratories. It was found that the thermal conductivity can be decreased by almost an order of magnitude at the highest concentration of grain boundaries compared to highly annealed CoSb 3 . Scanning Seebeck microthermoprobe examination, facilitated spatially resolved measurement of Seebeck coefficient S, providing information on samples' homogeneity and on its effect on local S. Indications on the formation of an additional Ni containing phase were found. The electronic structure of Ni-doped skutterudites has been investigated by means of fully periodic density functional theory calculations and a topological analysis of the resulting electron densities. Ni substitution for Co doubles the electronic charge transfer from the pnicogen ring to the metal frame and fills the region of the CoSb 3 band gap with occupied states, thus explaining the increase of electrical conductivity observed experimentally. The effect of the Ni substitution on the thermal conductivity is analyzed. The a͒ Electronic Downloaded 16 Jan 2003 to 130.237.66.192. Redistribution subject to AIP license or copyright, see http://ojps.aip.org/japo/japcr.jsp

The electronic reorganization along the [3+2] cycloaddition (32CA) reaction of the simplest azomethine ylide (AY) with ethylene has been studied using the topological analysis of the ELF at the B3LYP/6-31G(d) level of theory. This 32CA reaction, which has a negligible barrier (1.2 kcal/mol), takes place through a synchronous concerted transition state structure. The analysis of the ELF stresses that the pseudo-diradical character of the AY is responsible for the large reactivity of this species. Only the two non-bonding electrons located at the terminal carbon atoms of the AY and the two electrons of ethylene are involved in this 32CA reaction. This cycloaddition, certainly not a pericyclic electron reorganization, may be electronically classified as [2n + 2 ] process.

... of entire VOI after subvoxel processing clearly showing the tubular highly directed plate-likearchitecture of the ... as empirical measures of structural competence, for example, to distinguish subjects with and without osteoporotic fractures, where densitometric ... [54] in the form of a ...

The electrophilic/nucleophilic behavior of dimethyl 2,3-dimethylenesuccinate 1, an electron-deficient 2,3disubstituted 1,3-butadiene, in polar Diels-Alder reactions has been studied using DFT methods at the B3LYP/ 6-31G(d) level of theory. The electronic nature of bonding of the transition structures involved in the cycloaddition reactions of the diene 1 toward the nucleophilically activated dienophile 6 and the strong electrophilically activated dienophile 7 has been carefully examined within the natural bond orbital (NBO) and the topological analysis of the electron localization function (ELF) frameworks. Additionally, a study of the global electrophilicity pattern of the reagents at the ground state was performed. This evidence allows us to rationalize the participation of electron-deficient 2-susbtituted and 2,3-disubstituted 1,3-butadienes as nucleophiles in polar Diels-Alder reactions.

We describe an MRI-based system for topological analysis followed by measurements of topographic features for the human cerebral cortex that takes as its starting point volumetric segmentation data. This permits interoperation between volume-based and surface-based topographic analysis and extends the functionality of many existing segmentation schemes. We demonstrate the utility of these operations in individual as well as to group analysis. The methodology integrates analyses of cortical segmentation data generated by manual and semiautomated volumetric morphometry routines (such as the program cardviews) with the procedures of the FreeSurfer program to generate a cortical ribbon of the cerebrum and perform cortical topographic measurements (including thickness, surface area and curvature) in individual subjects as well as in subject populations. This system allows the computation of topographical cortical measurements for segmentation data generated from manual and semi-automated volumetric sources other than FreeSurfer. These measurements can be regionally specific and integrated with systems of cortical parcellation that subdivides the neocortex into gyral-based parcellation units (PUs). This system of topographical analysis of the cerebral cortex is consistent with current views of cortical development and neural systems organization of the human and non-human primate brain. D

A new approach is presented for the development of quantitative structure-property relations (QSPR) based on the extraction of relevant molecular features with self-organizing maps and the use of a modified fuzzy-ARTMAP classifier for variable prediction. The present methodology is demonstrated for the development of a QSPR for the aqueous-phase infinite dilution activity coefficient ␥ ϱ , based on a data set of 325 diverse organic compounds. The QSPR was developed using a set of 11 molecular descriptors (four connectivities v 1-4 , Coulomb self-similarity measure, electron-nuclear attraction, dipole moment, sum of atomic numbers, number of filled levels, average polarizability, and nuclear-nuclear repulsion). The final set of molecular descriptors was selected from an initial pool of 23 topological and quantum chemical descriptors, including six molecular quantum similarity measures, by means of a topological analysis of self-organization of the data set. Additional interpolated information to enhance the training of the neural system was obtained from the self-organization analysis. The resulting fuzzy-ARTMAP-based QSPRs performed with errors that were on the average seven times smaller compared to previous published models. The use of only four molecular quantum similarity measures proved to be sufficient for building a ln␥ ϱ fuzzy-ARTMAP-based QSPR with reasonable accuracy.

A high-resolution, low-temperature X-ray diffraction data set on DL-histidine, collected with a CCD detector, is used in the analysis of molecular bonding and intermolecular interactions. The molecular dipole moment in the crystal is enhanced relative to that from HF and DFT calculations. Topological properties of the molecular electron density differ from theory for the polar bonds but generally agree well for the C-C bonds in the molecule. A major aim of the study is the evaluation of the electrostatic contribution to the intermolecular interactions from the experimental density. The electrostatic interaction energies between pairs of neighboring molecules, as calculated from the experimental density, compare reasonably well with the total interaction energies from supermolecule calculations. The agreement is somewhat improved by the addition of nonelectrostatic repulsion and dispersive terms, which together contribute much less than the electrostatic energy. The electrostatic interaction energy calculated from the CHARMM point-charge force field is often close to the values derived from the experimental charge density, though exceptions occur. In an alternative approach, the topology of the intermolecular charge density is related to the intermolecular interaction energy. The latter approach makes use of a density functional by Abramov (Acta Crystallogr. 1997, A53, 264-272) and a relation between the potential energy density at the bond critical point and the hydrogen bond dissociation energy (Espinosa, et al.

Methods of topological analysis of the experimental electron density reconstructed from X-ray diffraction data are described. Their advantages and drawbacks are discussed and the results for organic and inorganic crystalline solids are presented.