Supersolid phases in the one dimensional extended soft core Bosonic Hubbard model

We present results of Quantum Monte Carlo simulations for the soft core extended bosonic Hubbard model in one dimension exhibiting the presence of supersolid phases similar to those recently found in two dimensions. We find that in one and two dimensions, the insulator-supersolid transition has dynamic critical exponent z=2 whereas the first order insulator-superfluid transition in two dimensions is replaced by a continuous transition with z=1 in one dimension. We present evidence that this transition is in the Kosterlitz-Thouless universality class and discuss the mechanism behind this difference. The simultaneous presence of two types of quasi long range order results in two soliton-like dips in the excitation spectrum.Comment: 4 pages, 5 figure

Thermal phase diagrams of columnar liquid crystals

In order to understand the possible sequence of transitions from the disordered columnar phase to the helical phase in hexa(hexylthio)triphenylene (HHTT), we study a three-dimensional planar model with octupolar interactions inscribed on a triangular lattice of columns. We obtain thermal phase diagrams using a mean-field approximation and Monte Carlo simulations. These two approaches give similar results, namely, in the quasi one-dimensional regime, as the temperature is lowered, the columns order with a linear polarization, whereas helical phases develop at lower temperatures. The helicity patterns of the helical phases are determined by the exact nature of the frustration in the system, itself related to the octupolar nature of the molecules.Comment: 12 pages, 9 figures, ReVTe

Propagation dynamics on networks featuring complex topologies

Analytical description of propagation phenomena on random networks has flourished in recent years, yet more complex systems have mainly been studied through numerical means. In this paper, a mean-field description is used to coherently couple the dynamics of the network elements (nodes, vertices, individuals...) on the one hand and their recurrent topological patterns (subgraphs, groups...) on the other hand. In a SIS model of epidemic spread on social networks with community structure, this approach yields a set of ODEs for the time evolution of the system, as well as analytical solutions for the epidemic threshold and equilibria. The results obtained are in good agreement with numerical simulations and reproduce random networks behavior in the appropriate limits which highlights the influence of topology on the processes. Finally, it is demonstrated that our model predicts higher epidemic thresholds for clustered structures than for equivalent random topologies in the case of networks with zero degree correlation.Comment: 10 pages, 5 figures, 1 Appendix. Published in Phys. Rev. E (mistakes in the PRE version are corrected here

Universal nonlinear infection kernel from heterogeneous exposure on higher-order networks

The colocation of individuals in different environments is an important prerequisite for exposure to infectious diseases on a social network. Standard epidemic models fail to capture the potential complexity of this scenario by (1) neglecting the higher-order structure of contacts which typically occur through environments like workplaces, restaurants, and households; and by (2) assuming a linear relationship between the exposure to infected contacts and the risk of infection. Here, we leverage a hypergraph model to embrace the heterogeneity of environments and the heterogeneity of individual participation in these environments. We find that combining heterogeneous exposure with the concept of minimal infective dose induces a universal nonlinear relationship between infected contacts and infection risk. Under nonlinear infection kernels, conventional epidemic wisdom breaks down with the emergence of discontinuous transitions, super-exponential spread, and hysteresis

Pair formation and collapse in imbalanced Fermion populations with unequal masses

We present an exact Quantum Monte Carlo study of the effect of unequal masses on pair formation in Fermionic systems with population imbalance loaded into optical lattices. We have considered three forms of the attractive interaction and find in all cases that the system is unstable and collapses as the mass difference increases and that the ground state becomes an inhomogeneous collapsed state. We also address the question of canonical vs grand canonical ensemble and its role, if any, in stabilizing certain phases

A shadowing problem in the detection of overlapping communities: lifting the resolution limit through a cascading procedure

Community detection is the process of assigning nodes and links in significant communities (e.g. clusters, function modules) and its development has led to a better understanding of complex networks. When applied to sizable networks, we argue that most detection algorithms correctly identify prominent communities, but fail to do so across multiple scales. As a result, a significant fraction of the network is left uncharted. We show that this problem stems from larger or denser communities overshadowing smaller or sparser ones, and that this effect accounts for most of the undetected communities and unassigned links. We propose a generic cascading approach to community detection that circumvents the problem. Using real and artificial network datasets with three widely used community detection algorithms, we show how a simple cascading procedure allows for the detection of the missing communities. This work highlights a new detection limit of community structure, and we hope that our approach can inspire better community detection algorithms.Comment: 14 pages, 12 figures + supporting information (5 pages, 6 tables, 3 figures

Solution of the Lambda modes problem of a nuclear power reactor using an h-p finite element method

Lambda modes of a nuclear power reactor have interest in reactor physics since they have been used to develop modal methods and to study BWR reactor instabilities. An h–p-Adaptation finite element method has been implemented to compute the dominant modes the fundamental mode and the next subcritical modes of a nuclear reactor. The performance of this method has been studied in three benchmark problems, a homogeneous 2D reactor, the 2D BIBLIS reactor and the 3D IAEA reactor.This work has been partially supported by the Spanish Ministerio de Ciencia e Innovacion under project ENE2011-22823, the Generalitat Valenciana under projects PROMETEO/2010/039 and ACOMP/2013/237, and the Universitat Politecnica de Valencia under project UPPTE/2012/118.Vidal Ferràndiz, A.; Fayez Moustafa Moawad, R.; Ginestar Peiro, D.; Verdú Martín, GJ. (2014). Solution of the Lambda modes problem of a nuclear power reactor using an h-p finite element method. Annals of Nuclear Energy. 72:338-349. https://doi.org/10.1016/j.anucene.2014.05.026S3383497

Kondo screening and Magnetism at Interfaces

The nature of magnetic order and transport properties near surfaces is a topic of great current interest. Here we model metal-insulator interfaces with a multi-layer system governed by a tight-binding Hamiltonian in which the interaction is non-zero on one set of adjacent planes and zero on another. As the interface hybridization is tuned, magnetic and metallic properties undergo an evolution that reflects the competition between anti-ferromagnetism and (Kondo) singlet formation in a scenario similar to that occurring in heavy-fermion materials. For a few-layer system at intermediate hybridization, a Kondo insulating phase results where magnetic order and conductivity are suppressed in all layers. As more insulating layers are added, magnetic order is restored in all correlated layers except that at the interface. Residual signs of Kondo physics are however evident in the bulk as a substantial reduction of the order parameter in the 2-3 layers immediately adjacent to the interfacial one. We find no signature of long range magnetic order in the metalli

The eSMAF: a software for the assessment and follow-up of functional autonomy in geriatrics

BACKGROUND: Functional status or disability forms the core of most assessment instruments used to identify mix and level of resources and services needed by older adults who possess common characteristics. The Functional Autonomy Measurement System (SMAF) is a 29-item scale measuring functional ability in five different areas. It has been recommended for use for home care, for allocation of chronic beds, for developing care plans in institutional settings and for epidemiological and evaluative studies. The SMAF can also be used with a case-mix classification system (Iso-SMAF) to allocate resources based on patients' functional autonomy characteristics. The objective of this project was to develop a software version of the SMAF to facilitate the evaluation of the functional status of older adults in health services research and to optimize the clinical decision-making process. RESULTS: The eSMAF was developed over an 24-month period using a modified waterfall software engineering process. Requirements and functional specifications were determined using focus groups of stakeholders. Different versions of the software were iteratively field-tested in clinical and research environments and software adaptations made accordingly. User documentation and online help were created to assist the deployment of the software. The software is available in French or English versions under a 30-day unregistered demonstration license or a free restricted registered academic license. It can be used locally on a Windows-based PC or over a network to input SMAF data into a database, search and aggregate client data according to clinical and/or administrative criteria, and generate summary or detailed reports of selected data sets for print or export to another database. CONCLUSION: In the last year, the software has been successfully deployed in the clinical workflow of different institutions in research and clinical applications. The software performed relatively well in terms of stability and performance. Barriers to implementation included antiquated computer hardware, low computer literacy and access to IT support. Key factors for the deployment of the software included standardization of the workflow, user training and support

Superconductivity and antiferromagnetism in a hard-core boson spin-1 model in two dimensions

A model of hard-core bosons and spin-1 sites with single-ion anisotropy is proposed to approximately describe hole pairs moving in a background of singlets and triplets with the aim of exploring the relationship between superconductivity and antiferromagnetism. The properties of this model at zero temperature were investigated using quantum Monte Carlo techniques. The most important feature found is the suppression of superconductivity, as long range coherence of preformed pairs, due to the presence of both antiferromagnetism and $S^z=\pm 1$ excitations. Indications of charge ordered and other phases are also discussed.Comment: One figure, one reference, adde