Developing a short-term comparative optimization forecasting model for operational units’ strategic planning

Data drain for peer active units operating in the same sector is a major factor that prevents policy makers from developing flawless strategic plans for their organisation. This study introduces a hybrid model that incorporates a purely deterministic method, Data Envelopment Analysis (DEA), and a semi-parametric technique, Artificial Neural Networks (ANNs), to provide a strategic planning tool for efficiency optimization applicable to short-term lag of data availability. For consecutive time instances, t and t+1, the developed DEANN model returns optimum “regression-type” input and output levels for every sample operational unit, even for the fully efficient ones, that may decide to alter the levels of the efficiency determinants, respecting the t-time efficiency frontier.Forecasting, Optimization, Efficiency, Data Envelopment Analysis (DEA), Artificial Neural Networks (ANN), Adaptive Techniques

Nonlinear static and dynamic analysis of mixed cable elements

This paper presents a family of finite elements for the nonlinear static and dynamic analysis of cables based on a mixed variational formulation in curvilinear coordinates and finite deformations. This formulation identifies stress measures, in the form of axial forces, and conjugate deformation measures for the nonlinear catenary problem. The continuity requirements lead to two distinct implementations: one with a continuous axial force distribution and one with a discontinuous. Two examples from the literature on nonlinear cable analysis are used to validate the proposed formulation for St VenantKirchhoff elastic materials. These studies show that displacements and axial forces are captured with high accuracy for both the static and the dynamic case

A Coordinated Approach to Channel Estimation in Large-scale Multiple-antenna Systems

This paper addresses the problem of channel estimation in multi-cell interference-limited cellular networks. We consider systems employing multiple antennas and are interested in both the finite and large-scale antenna number regimes (so-called "massive MIMO"). Such systems deal with the multi-cell interference by way of per-cell beamforming applied at each base station. Channel estimation in such networks, which is known to be hampered by the pilot contamination effect, constitute a major bottleneck for overall performance. We present a novel approach which tackles this problem by enabling a low-rate coordination between cells during the channel estimation phase itself. The coordination makes use of the additional second-order statistical information about the user channels, which are shown to offer a powerful way of discriminating across interfering users with even strongly correlated pilot sequences. Importantly, we demonstrate analytically that in the large-number-of-antennas regime, the pilot contamination effect is made to vanish completely under certain conditions on the channel covariance. Gains over the conventional channel estimation framework are confirmed by our simulations for even small antenna array sizes.Comment: 10 pages, 6 figures, to appear in IEEE Journal on Selected Areas in Communication

MEC-aware Cell Association for 5G Heterogeneous Networks

The need for efficient use of network resources is continuously increasing with the grow of traffic demand, however, current mobile systems have been planned and deployed so far with the mere aim of enhancing radio coverage and capacity. Unfortunately, this approach is not sustainable anymore, as 5G communication systems will have to cope with huge amounts of traffic, heterogeneous in terms of latency among other Qualityof- Service (QoS) requirements. Moreover, the advent of Multiaccess Edge Computing (MEC) brings up the need to more efficiently plan and dimension network deployment by means of jointly exploiting the available radio and processing resources. From this standpoint, advanced cell association of users can play a key role for 5G systems. Focusing on a Heterogeneous Network (HetNet), this paper proposes a comparison between state-of-the-art (i.e., radio-only) and MEC-aware cell association rules, taking the scenario of task offloading in the Uplink (UL) as an example. Numerical evaluations show that the proposed cell association rule provides nearly 60% latency reduction, as compared to its standard, radio-exclusive counterpart.Comment: 2018 IEEE Wireless Communications and Networking Conference Workshops (WCNCW): The First Workshop on Control and management of Vertical slicing including the Edge and Fog Systems (COMPASS

3D beam-column finite element under non-uniform shear stress distribution due to shear and torsion

The paper discusses the application of a 2-node, three-dimensional (3D) beam-column finite element with an enhanced fiber cross-section model to the inelastic response analysis of concrete members. The element accounts for the local distribution of strains and stresses under the coupling of axial, flexural, shear, and torsional effects with an enriched kinematic description that accounts for the out-of-plane deformations of the cross-section. To this end the warping displacements are interpolated with the addition of a variable number of local degrees of freedom. The material response is governed by a 3D nonlinear stress-strain relation with damage that describes the degrading mechanisms of typical engineering materials under the coupling of normal and shear stresses. The element formulation is validated by comparing the numerical results with measured data from the response of two prismatic concrete beams under torsional loading and with standard beam formulations

Μελέτη των μηχανισμών οξείδωσης Χρωμίου στα φυσικά νερά των Ψαχνών Ευβοίας

Εθνικό Μετσόβιο Πολυτεχνείο--Μεταπτυχιακή Εργασία. Διεπιστημονικό-Διατμηματικό Πρόγραμμα Μεταπτυχιακών Σπουδών (Δ.Π.Μ.Σ.) “Περιβάλλον και Ανάπτυξη

A rare case of ascending colon actinomycosis mimicking cancer

BACKGROUND: Actinomycosis is a rare inflammatory disease caused by an anaerobic bacterium that can rarely affect the large intestine. CASE PRESENTATION: We present a rare case of a cecum and ascending colon actinomycosis in a 72 years old woman, mimicking clinically a malignant inflammatory tumor of the right colon. The patient complained of right lower quadrant pain. Although our first thought was a peri-appendiceal abscess, CT scan suggested a right colon tumor. The patient underwent a right colectomy and the histological examination of the specimen revealed colon actinomycosis. CONCLUSIONS: Preoperative diagnosis in colon actinomycosis is difficult to achieve. Treatment of choice is antibiotics administration. A review of the possible pathogenesis and therapeutic modalities is also presented

Common macro factors and currency premia

We study the role of domestic and global factors in the payoffs of portfolios mimicking carry, dollar-carry, and momentum strategies. Using factors summarizing large data sets of macroeconomic and financial variables, we find that global equity-market factors are predictive for carry-trade returns, whereas U.S. inflation and consumption variables drive dollar-carry-trade payoffs, momentum returns are predominantly driven by U.S. inflation factors, and global factors capture the countercyclical nature of currency premia. We also find predictability in the exchange-rate component of each strategy and demonstrate strong economic value for risk-averse investors with mean-variance preferences, regardless of base currency