SACOC: A spectral-based ACO clustering algorithm

The application of ACO-based algorithms in data mining is growing over the last few years and several supervised and unsupervised learning algorithms have been developed using this bio-inspired approach. Most recent works concerning unsupervised learning have been focused on clustering, where ACO-based techniques have showed a great potential. At the same time, new clustering techniques that seek the continuity of data, specially focused on spectral-based approaches in opposition to classical centroid-based approaches, have attracted an increasing research interest–an area still under study by ACO clustering techniques. This work presents a hybrid spectral-based ACO clustering algorithm inspired by the ACO Clustering (ACOC) algorithm. The proposed approach combines ACOC with the spectral Laplacian to generate a new search space for the algorithm in order to obtain more promising solutions. The new algorithm, called SACOC, has been compared against well-known algorithms (K-means and Spectral Clustering) and with ACOC. The experiments measure the accuracy of the algorithm for both synthetic datasets and real-world datasets extracted from the UCI Machine Learning Repository

Numerically flat Higgs vector bundles

After providing a suitable definition of numerical effectiveness for Higgs bundles, and a related notion of numerical flatness, in this paper we prove, together with some side results, that all Chern classes of a Higgs-numerically flat Higgs bundle vanish, and that a Higgs bundle is Higgs-numerically flat if and only if it is has a filtration whose quotients are flat stable Higgs bundles. We also study the relation between these numerical properties of Higgs bundles and (semi)stability.Comment: 11 page

Time-stepping approach for solving upper-bound problems: Application to two-dimensional Rayleigh-Benard convection

An alternative computational procedure for numerically solving a class of variational problems arising from rigorous upper-bound analysis of forced-dissipative infinite-dimensional nonlinear dynamical systems, including the Navier-Stokes and Oberbeck-Boussinesq equations, is analyzed and applied to Rayleigh-Benard convection. A proof that the only steady state to which this numerical algorithm can converge is the required global optimal of the relevant variational problem is given for three canonical flow configurations. In contrast with most other numerical schemes for computing the optimal bounds on transported quantities (e.g., heat or momentum) within the "background field" variational framework, which employ variants of Newton's method and hence require very accurate initial iterates, the new computational method is easy to implement and, crucially, does not require numerical continuation. The algorithm is used to determine the optimal background-method bound on the heat transport enhancement factor, i.e., the Nusselt number (Nu), as a function of the Rayleigh number (Ra), Prandtl number (Pr), and domain aspect ratio L in two-dimensional Rayleigh-Benard convection between stress-free isothermal boundaries (Rayleigh's original 1916 model of convection). The result of the computation is significant because analyses, laboratory experiments, and numerical simulations have suggested a range of exponents alpha and beta in the presumed Nu similar to (PrRa beta)-Ra-alpha scaling relation. The computations clearly show that for Ra <= 10(10) at fixed L = 2 root 2, Nu <= 0.106Pr(0)Ra(5/12), which indicates that molecular transport cannot generally be neglected in the "ultimate" high-Ra regime.NSF DMS-0928098 DMS-1515161 DMS-0927587 PHY-1205219Simons FoundationNSFONRInstitute for Computational Engineering and Sciences (ICES

Evaluation Approach for an Effective Blockchain Implementation in an Accounting Environment

Blockchain has the potential to revolutionize accounting transactions in the same way the Internet revolutionized the collection and dissemination of information. Nonetheless, like the Internet, blockchain technology is a double-edged sword offering tremendous benefits but also drawbacks. The literature points to inadequacies in blockchain implementations, particularly when evaluating and selecting controls to help ensure an effective blockchain implementation in organizations. This research develops an approach that not only addresses the inadequacies identified in the literature, but also prompts organizations to a more precise evaluation and selection of controls to achieve effective blockchain implementation. The approach uses Desirability Functions to quantify the desirability of each control after considering its benefits and drawbacks, providing organizations with an objective metric when assessing and selecting controls. Through a case assessment exercise, the approach proved successful in providing accurate evaluation, ranking, and potential selection of controls for organizations to consider when implementing blockchain accounting technology

Psychological Therapists’ Wellbeing in the Context of IAPT-NHS: A Foucauldian Discourse Analysis

This study set out to gain in depth and critical understanding of how psychological therapists working in IAPT-NHS services construct the concept of their wellbeing at work. Foucauldian Discourse Analysis (FDA) was used to identify the available discourses mobilised by these practitioners and map out their impact on subjectivity and practice, as well as the role of the specific NHS-IAPT context. Ten psychological therapists working in IAPT services across two East London NHS Trusts were interviewed, using a semi-structured interview which also featured a visual task to elicit information. The interview narratives were analysed using FDA through the lens of a moderate social constructionist position. The analysis identified four main discursive constructions of wellbeing: (1) wellbeing as an individual responsibility; (2) wellbeing as a collective responsibility; (3) wellbeing as self-actualisation; and (4) wellbeing as productivity. Each presented a picture of duality and contradiction, delineated by the subject positions made available. Notably, for the first two constructions, the subject positions of responsible and irresponsible alternated between the individual and the service, with particular impact on the ability to voice wellbeing difficulties at work. Subject positions of the good/ideal therapist and the good employee, corresponding to the latter two constructions, were mediated by the introduction of IAPT as a sub-context. IAPT was constructed as an inflexible, target-driven system in which participants seemed unable to hold both the good/ideal therapist and good employee position, resulting in a constant tension that seemed to only be resolved by giving up one of the two positions. The conclusion addresses the benefits of approaching the issue of psychological therapists’ wellbeing at work beyond the individualistic, neoliberal perspective, with particular recommendations to: (1) direct more funding to protect the NHS’s therapeutic function, preventing further expansion of the market discourse into mental health services; (2) promote congruence between policies and practices at work, aligned with a collectivist perspective of wellbeing where both the individual and the system share responsibility and support; and (3) increase IAPT’s flexibility to adapt appropriately to diversity

Variational bounds on the energy dissipation rate in body-forced shear flow

A new variational problem for upper bounds on the rate of energy dissipation in body-forced shear flows is formulated by including a balance parameter in the derivation from the Navier-Stokes equations. The resulting min-max problem is investigated computationally, producing new estimates that quantitatively improve previously obtained rigorous bounds. The results are compared with data from direct numerical simulations.Comment: 15 pages, 7 figure

Research on nonlinear and quantum optics at the photonics and quantum information group of the University of Valladolid

We outline the main research lines in Nonlinear and Quantum Optics of the Group of Photonics and Quantum Information at the University of Valladolid. These works focus on Optical Solitons, Quantum Information using Photonic Technologies and the development of new materials for Nonlinar Optics. The investigations on optical solitons cover both temporal solitons in dispersion managed fiber links and nonparaxial spatial solitons as described by the Nonlinear Helmholtz Equation. Within the Quantum Information research lines of the group, the studies address new photonic schemes for quantum computation and the multiplexing of quantum data. The investigations of the group are, to a large extent, based on intensive and parallel computations. Some associated numerical techniques for the development of the activities described are briefly sketched