D-branes, KK-theory and duality on noncommutative spaces

We present a new categorical classification framework for D-brane charges on noncommutative manifolds using methods of bivariant K-theory. We describe several applications including an explicit formula for D-brane charge in cyclic homology, a refinement of open string T-duality, and a general criterion for cancellation of global worldsheet anomalies

Materials from renewable resources based on furan monomers and furan chemistry: work in progress

The polymerisation of furan monomers and the exploitation of some of the chemical peculiarities of the furan heterocycle have generated a wide diversity of macromolecular materials based on renewable resources. We present here recent contributions to this field, including ongoing studies on the synthesis and characterisation of novel furan polyesters and on the application of the Diels-Alder reaction to the preparation of linear and branched thermally reversible polyadducts

Accessibility in Metrô Rio prior to the 2016 Olympic and Paralympic games.

ABSTRACT:The city of Rio de Janeiro, Brazil hosted the 2016 Olympic and Paralympic Games which brought forth an enormous influx of tourists to a large populated city. This study, analyzed accessibility of the Metrô Line 1 of the subway system in preparation for the games. Photo-based research was used to investigate the Metrô Rio services. Findings suggest that the subway system in the city of Rio de Janeiro, is accessible; however, improvement is needed in the areas of communication, through standardization of language used to describe equipment and accommodations, the standardization of signage and equipment, standardization of navigational logic patterns, and predictability of barriers and services for patrons. A tension was also identified between services provided with assistance and services that promote independence for users with disabilities. Results will help transit agencies to consider accessibility features for all patrons.RESUMO:O Rio de Janeiro foi cidade-sede dos Jogos Olímpicos e Paraolímpicos de 2016, evento que gerou um enorme fluxo de turistas em uma cidade bastante populosa. O presente estudo analisou a acessibilidade do Metrô Linha 1 do sistema metrofer­roviário em preparação para os jogos. A investigação utilizou-se do registro fotográ­fico para averiguar os serviços do Metrô Rio. Os resultados sugerem que o sistemade metrô do Rio de Janeiro é acessível; porém, são necessárias melhorias nas áreas de comunicação por meio da padronização da linguagem utilizada para descrever os equipamentos e espaços, da padronização da sinalização e dos equipamentos oferecidos, da uniformização dos modelos de locomoção e do aumento de previsi­bilidade dos obstáculos e dos serviços oferecidos aos usuários. Também foi iden­tificada uma tensão entre os serviços que se apoiam na assistência e serviços que promovem a independência para os usuários portadores de deficiência. Os resulta­dos auxiliarão agências de transporte a considerar características de acessibilidade para todos os usuários

Mothers’ perceptions of family centred care in neonatal intensive care units

Objective To explore mothers’ perceptions of family centred care (FCC) in neonatal intensive care units (NICUs) in England. Design The qualitative experiences of 12 mothers from three NICUs in the UK were elicited using individual interviews. A thematic network analysis was conducted on the transcribed interviews Main outcome measures A central global theme supported by a number of organizing themes were developed reflecting the views of the mothers and their experiences of FCC. Results A global theme of “Finding My Place” was identified, supported by six organizing themes: Mothering in Limbo; Deference to the Experts; Anxious Surveillance; Muted Relations, Power Struggles and Consistently Inconsistent. Mothers experienced a state of liminality and were acutely sensitive to power struggles, awkward relationships and inconsistencies in care. To try to maintain their equilibrium and protect their baby they formed deferential relationships with health professionals and remained in a state of anxious surveillance. Conclusions This study illustrates that despite the rhetoric around the practice of FCC in NICUs, there was little in the mother's narratives to support this. It is of the utmost importance to minimize the consequences of the liminal experience, to improve staff–mother interactions and to facilitate mothers’ opportunities to be primary caregivers

Analysis on the evolution process of BFW-like model with explosive percolation of multiple giant components

Recently, the modified BFW model on random graph [Phys. Rev. Lett., 106, 115701 (2011)], which shows a strongly discontinuous percolation transition with multiple giant components, has attracted much attention from physicists, statisticians and materials scientists. In this paper, by establishing the theoretical expression of evolution equations on the modified BFW model, the steady-state and evolution process are analyzed and a close correspondence is built between the values of parameter \alpha and the number of giant components in steady-states, which fits very well with the numerical simulations. In fact, with the value of \alpha decreasing to 0.25, the error between theoretical and numerical results is smaller than 4% and trends to 0 rapidly. Furthermore, the sizes of giant components for different evolution strategies can also be obtained by solving some constraints derived from the evolution equations. The analysis of the steady-state and evolution process is of great help to explain why the percolation of modified BFW model is explosive and how explosive it is.Comment: 12 pages, 5 figure

Ramond-Ramond Fields, Fractional Branes and Orbifold Differential K-Theory

We study D-branes and Ramond-Ramond fields on global orbifolds of Type II string theory with vanishing H-flux using methods of equivariant K-theory and K-homology. We illustrate how Bredon equivariant cohomology naturally realizes stringy orbifold cohomology. We emphasize its role as the correct cohomological tool which captures known features of the low-energy effective field theory, and which provides new consistency conditions for fractional D-branes and Ramond-Ramond fields on orbifolds. We use an equivariant Chern character from equivariant K-theory to Bredon cohomology to define new Ramond-Ramond couplings of D-branes which generalize previous examples. We propose a definition for groups of differential characters associated to equivariant K-theory. We derive a Dirac quantization rule for Ramond-Ramond fluxes, and study flat Ramond-Ramond potentials on orbifolds.Comment: 46 pages; v2: typos correcte

Fluxes, Brane Charges and Chern Morphisms of Hyperbolic Geometry

The purpose of this paper is to provide the reader with a collection of results which can be found in the mathematical literature and to apply them to hyperbolic spaces that may have a role in physical theories. Specifically we apply K-theory methods for the calculation of brane charges and RR-fields on hyperbolic spaces (and orbifolds thereof). It is known that by tensoring K-groups with the rationals, K-theory can be mapped to rational cohomology by means of the Chern character isomorphisms. The Chern character allows one to relate the analytic Dirac index with a topological index, which can be expressed in terms of cohomological characteristic classes. We obtain explicit formulas for Chern character, spectral invariants, and the index of a twisted Dirac operator associated with real hyperbolic spaces. Some notes for a bivariant version of topological K-theory (KK-theory) with its connection to the index of the twisted Dirac operator and twisted cohomology of hyperbolic spaces are given. Finally we concentrate on lower K-groups useful for description of torsion charges.Comment: 26 pages, no figures, LATEX. To appear in the Classical and Quantum Gravit

Correlation functions in the two-dimensional random-field Ising model

Transfer-matrix methods are used to study the probability distributions of spin-spin correlation functions $G$ in the two-dimensional random-field Ising model, on long strips of width $L = 3 - 15$ sites, for binary field distributions at generic distance $R$, temperature $T$ and field intensity $h_0$. For moderately high $T$, and $h_0$ of the order of magnitude used in most experiments, the distributions are singly-peaked, though rather asymmetric. For low temperatures the single-peaked shape deteriorates, crossing over towards a double-$\delta$ ground-state structure. A connection is obtained between the probability distribution for correlation functions and the underlying distribution of accumulated field fluctuations. Analytical expressions are in good agreement with numerical results for $R/L \gtrsim 1$, low $T$, $h_0$ not too small, and near G=1. From a finite-size {\it ansatz} at $T=T_c (h_0=0)$, $h_0 \to 0$, averaged correlation functions are predicted to scale with $L^y h_0$, $y =7/8$. From numerical data we estimate y=0.875 \pm 0.025$, in excellent agreement with theory. In the same region, the RMS relative width$W$of the probability distributions varies for fixed$R/L=1$as$W \sim h_0^{\kappa} f(L h_0^u)$with$\kappa \simeq 0.45$,$u \simeq 0.8$;$f(x)$appears to saturate when$x \to \infty$, thus implying$W \sim h_0^{\kappa}$in$d=2$.Comment: RevTeX code for 8 pages, 7 eps figures, to appear in Physical Review E (1999

KO-Homology and Type I String Theory

We study the classification of D-branes and Ramond-Ramond fields in Type I string theory by developing a geometric description of KO-homology. We define an analytic version of KO-homology using KK-theory of real C*-algebras, and construct explicitly the isomorphism between geometric and analytic KO-homology. The construction involves recasting the Cl(n)-index theorem and a certain geometric invariant into a homological framework which is used, along with a definition of the real Chern character in KO-homology, to derive cohomological index formulas. We show that this invariant also naturally assigns torsion charges to non-BPS states in Type I string theory, in the construction of classes of D-branes in terms of topological KO-cycles. The formalism naturally captures the coupling of Ramond-Ramond fields to background D-branes which cancel global anomalies in the string theory path integral. We show that this is related to a physical interpretation of bivariant KK-theory in terms of decay processes on spacetime-filling branes. We also provide a construction of the holonomies of Ramond-Ramond fields in Type II string theory in terms of topological K-chains.Comment: 40 pages; v4: Clarifying comments added, more detailed proof of main isomorphism theorem given; Final version to be published in Reviews in Mathematical Physic

Avoiding catastrophic failure in correlated networks of networks

Networks in nature do not act in isolation but instead exchange information, and depend on each other to function properly. An incipient theory of Networks of Networks have shown that connected random networks may very easily result in abrupt failures. This theoretical finding bares an intrinsic paradox: If natural systems organize in interconnected networks, how can they be so stable? Here we provide a solution to this conundrum, showing that the stability of a system of networks relies on the relation between the internal structure of a network and its pattern of connections to other networks. Specifically, we demonstrate that if network inter-connections are provided by hubs of the network and if there is a moderate degree of convergence of inter-network connection the systems of network are stable and robust to failure. We test this theoretical prediction in two independent experiments of functional brain networks (in task- and resting states) which show that brain networks are connected with a topology that maximizes stability according to the theory.Comment: 40 pages, 7 figure