Unsupervised Anomaly Detection with Rejection

Anomaly detection aims at detecting unexpected behaviours in the data. Because anomaly detection is usually an unsupervised task, traditional anomaly detectors learn a decision boundary by employing heuristics based on intuitions, which are hard to verify in practice. This introduces some uncertainty, especially close to the decision boundary, that may reduce the user trust in the detector's predictions. A way to combat this is by allowing the detector to reject examples with high uncertainty (Learning to Reject). This requires employing a confidence metric that captures the distance to the decision boundary and setting a rejection threshold to reject low-confidence predictions. However, selecting a proper metric and setting the rejection threshold without labels are challenging tasks. In this paper, we solve these challenges by setting a constant rejection threshold on the stability metric computed by ExCeeD. Our insight relies on a theoretical analysis of such a metric. Moreover, setting a constant threshold results in strong guarantees: we estimate the test rejection rate, and derive a theoretical upper bound for both the rejection rate and the expected prediction cost. Experimentally, we show that our method outperforms some metric-based methods

Estimating the Contamination Factor's Distribution in Unsupervised Anomaly Detection

Anomaly detection methods identify examples that do not follow the expected behaviour, typically in an unsupervised fashion, by assigning real-valued anomaly scores to the examples based on various heuristics. These scores need to be transformed into actual predictions by thresholding, so that the proportion of examples marked as anomalies equals the expected proportion of anomalies, called contamination factor. Unfortunately, there are no good methods for estimating the contamination factor itself. We address this need from a Bayesian perspective, introducing a method for estimating the posterior distribution of the contamination factor of a given unlabeled dataset. We leverage on outputs of several anomaly detectors as a representation that already captures the basic notion of anomalousness and estimate the contamination using a specific mixture formulation. Empirically on 22 datasets, we show that the estimated distribution is well-calibrated and that setting the threshold using the posterior mean improves the anomaly detectors' performance over several alternative methods. All code is publicly available for full reproducibility

Electrochemical Approaches for the Synthesis and Characterization of Innovative Electrode Materials

The synthesis of nanoscale catalysts is a cornerstone technology to meet the current energy challenges, spanning in a wide range of applications from fuel cell efficiency to pollutant degradation [1]. On this regard, electrocatalysis is a field of particular interest and one of the most promising, owing to the ability of electrochemical methods to study the reaction mechanisms and electron transfer (ET) dynamics at a molecular level, at the electrode surface. With the rapid advances in nanostructure synthesis, new nanoscale catalysts and novel catalytic properties continue to emerge [2]. Often, nanoscale catalysts are used on electrodes, where the electrode modifies the kinetics of the process reducing the overpotential, hence performing electrocatalysis. The development and use of new electrodic materials and modified electrodes in the field of applied electrochemistry, energy and organic electrosynthesis is today an important way to obtain catalysts with controlled structure and morphology, and reactions with high selectivity. Control over a variety of physical and chemical phenomena ranging from catalysis to electron transfer is often achieved through the extensive use of modified surfaces. There are basically two possibilities for the modification of an electrode surface, (i) to alter its structure or (ii) to modifiy its composition (or both) [3]. The emergence of fuel cell technology has created a new tool for the generation of new catalysts to replace the expensive and rare platinum, which contributes to over 55% of the total costs. Reducing the Pt loading (particularly in the cathode catalyst layer) without compromising the fuel cell performance is an effective strategy to meet the cost requirements for its commercialization. In addition, the design of novel electrocatalysts requires not only reducing the amount of Pt used, but also enhancing catalytic activity and durability. In fuel cells (FCs), the oxygen reduction reaction (ORR) is the reaction occurring at the cathode. ORR in a typical PEM fuel cell is a slow reaction; using the state-of art platinum catalysts the overpotential of ORR is found to be 300 mV higher than that of the oxidation reaction at the anode [4]. Ideally, the standard cell potential, E0cell, is 1.23 V with a negative Gibbs free energy, implying a spontaneous reaction that can be utilised as an electrical energy generator. Practically, however, the cell potential is less than 1.23 V due to an overpotential in the cell, primarily related to the oxygen reduction reaction at the cathode, which is kinetically sluggish because a large amount of energy is needed to break the strong oxygen-oxygen double bond during the process. For example, Nitrogen-doped carbon and its composites possess a great potential for fuel cell catalyst applications, especially at the oxygen reduction reaction. The ORR mechanisms of nitrogen-doped carbon catalysts seem to involve adsorption of oxygen [5] at the partially polarised carbon atoms adjacent to the nitrogen dopants, in contrast to the mechanism at metal catalysts (i.e. Pt, Pd), which utilise d-bands to form bonds with oxygen. Indeed, in the field of organic electrocatalysis, a topic of great interest is the behaviour of catalytic electrode materials for the reduction of organic halides [6]. In fact, the choice of electrode materials is often crucial for the success of electrochemical reactions in order to achieve selective reactions. In our own experience, some electrode materials such as Ag, Cu or Pd in organic solvents (MeCN, DMF, etc.) showed extraordinary catalytic properties for the electroreduction of organic halides [7]. This allows not only the reduction of the substrates at more positive potentials, but also makes possible modification of the reaction mechanism and selectivity [8]. It is thus of great interest to find new catalytic materials to create more favourable conditions for electrochemical processes. Therefore, it is of primary importance to characterize decisive parameters influencing the reactivity and the selectivity of a catalytic surface, in order to use this knowledge for the systematic design of better catalysts. The parameters influencing the electrocatalytic properties of nanoparticles [9,10] can be: (i) particle size, (ii) particle dispersion, (iii) density of low-coordinated surface atoms and (iv) effect of the substrate material. In order to evaluate these parameters, model surfaces without chemical and morphological defects (HOPG) and monolayer nanostructures deposited on them must be investigated. Usually, the modified electrodes are built from an inert support, such as graphite (HOPG), glassy carbon (GC) or mesoporous carbon (MC), on which metal nanoparticles are deposited. These supports are very interesting because, like all carbon-based supports, they have chemical stability, wide potential window and low background current. This PhD thesis project intends to prepare and characterize different carbon materials, before and after doping with heteroatoms (particularly Nitrogen), with aim of investigating their catalytic properties in the ORR and in the reduction of organic halides. After that, we will try to deposit metal nanoparticles prepared by evaporation in ultra-high-vacuum (UHV), or by electrochemical and chemical means, to compare the results achieved using the three deposition methods and gain a better indication about the possibility to device a real electro-catalyst in the different fields described above. The first task includes the research for the best experimental conditions to obtain the new electrode materials. To this end, UHV conditions will be investigated to synthetize N-HOPG and N-GC, whereas chemical synthesis followed by annealing will be used to prepare N-MC. After evaluation of the chemical and morphological properties of the materials, the second goal is to investigate their catalytic properties toward the electrochemical reduction reactions of oxygen and organic halides, reactions that can be influenced by solvent, pH, supporting electrolyte, working potential and electron transfer mechanism. The physical and chemical characterizations will be carried out using Cyclic Voltammetry (CV), Rotating Disk Electrode (RDE), X-ray Photoelectron Spectroscopy (XPS), Transmission and Scanning Electron Microscopy (TEM, SEM) and Brunauer-Emmett-Teller theory (BET)

Failure behaviour of glass-microballoons/thermoset-matrix syntactic foams subject to hydrostatic loading

This investigation deals with a lightweight syntactic foam constituted by an epoxy matrix filled with polydispersed glass microballoons up to 75% volume fraction. We present experimental results on hydrostatic loading which demonstrate the possibility of different failure modalities depending on whether the surface of the composite is painted/coated or not. In order to explain this peculiar behaviour, we develop a three-dimensional Finite Element (FE) micromechanical model. The model enables a detailed analysis of the stress diffusion from the external surface, subject to uniform pressure, through an appropriately thick layer of composite. The FE model includes 300 randomly placed microballoons and accounts for their polydispersion, in terms of both size and radius ratio. The FE model is first validated by comparing its prediction on the elastic moduli with experimental findings and accurate analytical homogenisation techniques. Towards modelling failure, we adopt a structural criterion for the glass microballoons, as recently proposed by our group. The criterion assumes brittle failure when the average elastic strain energy density reaches a critical value. On the basis of the effective strength measured under uniaxial stress, we identify different critical values for selected types of microballoons constituting the filler employed in the syntactic foam under investigation. Finally, the new micromechanical model, through a detailed analysis of the collapsed microballoons and the matrix stress state, allows us to demonstrate the influence of the paint/coating on the syntactic foam failure

Critical storm thresholds for significant morphological changes and damage along the Emilia-Romagna coastline, Italy

n/

Test-Driven Design of an Active Dual-Polarized Log-Periodic Antenna for the Square Kilometre Array

An active dual-polarized Log-Periodic antenna has been designed to meet the requirements of the low-frequency (50 - 350 MHz) radio telescope of the Square Kilometre Array (SKA). The integration of antenna and low noise amplifier has been conceived in order to achieve a high degree of testability. This aspect has been found to be crucial to obtain a smooth frequency response compatible with the SKA science cases. The design has also been driven by other factors such as the large-volume production (more than 130 000 antennas will be built) and the environmental conditions of the harsh Australian desert. A specific verification approach based on both wideband radiometric spectral and spatial measurements in relevant laboratory and in-situ conditions has been developed. Electromagnetic analyses and experimental results exhibit a very good agreement. In December 2019, this antenna was part of the reference solution for the System Critical Design Review of the SKA

Disposición en la adolescencia a llevar a cabo distintas prácticas sexuales homosexuales

Introducción: La orientación sexual es el deseo/atracción hacia personas del mismo o diferente sexo. Actualmente, se aconseja su evaluación a través de un continuo. Según nuestra experiencia en este campo, existe, ocasionalmente, una mayor o menor disposición a tener relaciones con personas del mismo sexo en función de una determinada práctica sexual. El objetivo de este estudio ha sido llevar a cabo un aná- lisis de esta predisposición en población adolescente. Método: La muestra incluía 400 alumnos (50,5 % chicas y 49,5 % chicos), entre 14 y 18 años (m = 16,39; dt ±1,12), procedentes de distintos institutos de la Comunidad Valenciana. Los participantes cumplimentaron el cuestionario de intereses y prácticas sexuales (Unisexsida, 2014) de 5 ítems. Para este estudio se utilizaron dos ítems: orientación sexual autodefinida y disposición hacia prácticas sexuales con personas del mismo sexo. Resultados: Se observaron diferencias significativas entre chicos y chicas respecto a su disposición a dar besos en los labios, abrazos y caricias desnudos a personas del mismo sexo, siendo mayor en el caso de las adolescentes. Entre la población de adolescentes que se consideran heterosexuales, un 4,5 % y un 59,9 % se encuentra dispuesto a realizar ciertas prácticas con personas del mismo sexo. En esta población existen diferencias significativas entre chicas y chicos respecto a su disposición a dar besos en los labios, abrazos y caricias desnudos y dejarse masturbar por personas de su mismo sexo. Conclusiones: Estos resultados enfatizan la necesidad de dejar de considerar la orientación sexual como una categoría estanca, de manera que refleje la diversidad afectivo-sexual.Introduction: Sexual orientation is defined as the desire/sexual attraction to people of the same or opposite sex. Currently, its evaluation is advised through a continuum. Ac- cording to our experience in this field, there is occasionally more or less willingness to have sex with the same sex depending on a particular sexual practice. The aim of this study was to analyse this predisposition in an adolescent population. Method: The sam- ple included 400 students (50.5% female, 49.5% male), aged 14-18 years (M=16.39; SD±1.12), from different high schools in the Valencian Community (Spain). Participants completed the questionnaire Sexual Interests and Practices (Unisexsida, 2014) with five items, although only the first (self-reported sexual orientation) and the last (disposition towards different sexual practices with the same sex) items were used. Results: Signifi- cant gender differences were found in their willingness to kiss on the lips or to hug and caress naked people of the same sex, which were higher for females. In the adolescent population who considered themselves heterosexuals, from 4.5% to 59.9% were willing to undertake certain practices with persons of their same sex. Significant gender differ- ences were also found in this same population as to their willingness to kiss on the lips, hug and caress, and be masturbated by, persons of the same sex. Conclusions: These results stress the need to stop considering sexual orientation as a tight category to reflect sexual diversity

Effects of wild boar grazing on the yield of summer truffle (Tuscany, Italy)

The research presented here seeks to describe the impact of wild boar to a natural truffle ground of Tuber aestivum Vittad. on Monte Amiata (Tuscany – Italy). Pedoclimatic analyses indicated that the selected area could be considered suitable for the truffle production. Then classification of the vegetation of a Quercus cerris forest was carried out exploring the possibility of the BACI (Before-After-Control-Impact) sampling design. Finally 10 plots were selected, half of which have been fenced. For the first time the impact of wild boar was evaluated by estimating the surface area turned over by its activity. Moreover in each plot the number and weight of summer truffles was performed every 10 days during the fruiting period (June-November 2006-2008). The hypothesis that the presence of Sus scrofa has a strong negative influence on truffle harvesting has been amply confirmed by the data presented here, given the large increase of fruiting bodies of the summer truffle collected in the fenced plots. Consequently the destructive behaviour of the wild boar imply not only an ecological but also an economic damage in areas in which non-wood forest products are an important source of income

Hydrologic control on natural land subsidence in the shallow coastal aquifer of the Ravenna coast, Italy

Abstract. Multiple processes contributing to natural land subsidence in a shallow coastal aquifer near Ravenna (Italy) were identified by analysing the relationships among different data set time series (water table level, rainfall, land reclamation drainage, sea level, etc.) and establishing the correlations with vertical ground motion observed at a high-resolution settlement gauge. Our study highlights the presence of three deformation components related to different processes controlling land subsidence: elastic, delayed-elastic, and irreversible (plastic) components. The elastic and delayed-elastic components are closely related to water table fluctuations that change the effective stress in two portions of the coastal aquifer at a daily (in the sandy unconfined portion) and seasonal time scales (in the layered clay-rich semi-confined prodelta portion), respectively. The irreversible component represents the trend in the land subsidence time series and is due to primary consolidation (pore pressure dissipation) of the fine-grained prodelta levels above where the settlement gauge is located. The amplitudes of the elastic component can be up to 0.2–0.3 mm whereas the amplitude of the delayed-elastic component reaches 0.89 mm. The primary consolidation rate of deformation is 0.9 mm yr−1 and constrains the likely age of prodelta sediments deposition to 1300–2800 years before present. The delayed-elastic subsidence rate has similar magnitude to that due to primary consolidation and is connected to poroelastic effects in the prodelta sequence following seasonal variations in water table. Our findings are important for planning land subsidence management and monitoring strategies especially where the surface aquifer structure is heterogeneous due to different depositional settings. The natural land subsidence rate in the Holocene sediments of the shallow coastal aquifer of Ravenna (North eastern Italy) that we measured in this study accounts for 10 %–20 % of the total current land subsidence rate observed in this portion of Ravenna coastal area (10–20 mm yr−1)