The layer of the Earth’s atmosphere known as the ionosphere presents a significant obstacle to global satellite navigation systems (GNSS) due to its ability to introduce errors. To address this ...challenge, various navigation systems have introduced new signals designed to minimize the errors caused by the ionosphere. These signals not only aid in error reduction but also facilitate the examination of electron content behavior. This study focuses on the analysis of vTEC plots obtained from RINEX data collected at the INEG station in Aguascalientes, Mexico, from 2011 to 2018, with a particular emphasis on highly intense geomagnetic storms characterized by values below −100 nT. Our analysis of these plots employed the Probability Density Function (PDF), which allows for the graphical representation of data distribution. This distribution is then examined in conjunction with the station’s Total Electron Content (TEC) values and the Dst index during the corresponding geomagnetic storm events. The findings establish the correlation between each of these parameters during such events.
Towards Adversarial Malware Detection Maiorca, Davide; Biggio, Battista; Giacinto, Giorgio
ACM computing surveys,
07/2020, Letnik:
52, Številka:
4
Journal Article
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Malware still constitutes a major threat in the cybersecurity landscape, also due to the widespread use of infection vectors such as documents. These infection vectors hide embedded malicious code to ...the victim users, facilitating the use of social engineering techniques to infect their machines. Research showed that machine-learning algorithms provide effective detection mechanisms against such threats, but the existence of an arms race in adversarial settings has recently challenged such systems. In this work, we focus on malware embedded in PDF files as a representative case of such an arms race. We start by providing a comprehensive taxonomy of the different approaches used to generate PDF malware and of the corresponding learning-based detection systems. We then categorize threats specifically targeted against learning-based PDF malware detectors using a well-established framework in the field of adversarial machine learning. This framework allows us to categorize known vulnerabilities of learning-based PDF malware detectors and to identify novel attacks that may threaten such systems, along with the potential defense mechanisms that can mitigate the impact of such threats. We conclude the article by discussing how such findings highlight promising research directions towards tackling the more general challenge of designing robust malware detectors in adversarial settings.
The name of the third author of the article by Koch et al. Acta Cryst. (2021). A77, 611–636 is corrected.
Corrigendum to the article by Koch et al. Acta Cryst. (2021). A77, 611–636.
In this study, a general frame of the forward and inverse structural uncertainty propagations (UPs) based on the dimension reduction (DR) method and the derivative lambda probability density function ...(λ-PDF) is proposed to handle arbitrary probability distribution. For the forward UP, a DR method is applied to decompose a multivariable system into multiple univariate subsystems and a derivative λ-PDF is adopted to transform the arbitrary probability distribution of each subsystem. Then, the statistical moments and a fitting region are mathematically derived to analyze the fitting ability of the derivative λ-PDF. According to whether the kurtosis–skewness point lies in or out the fitting region, two different strategies combining the Gauss–Gegenbauer quadrature are proposed to implement the forward propagation. Compared with the conventional methods, the proposed method has advantages in higher accuracy, stability and efficiency. For the inverse propagation, because the unknown variable may be arbitrary distribution, the general frame based on the derivative λ-PDF and the Gauss–Gegenbauer quadrature are utilized to convert the uncertainty propagation into multiple deterministic calculations. Based on this, optimization method is adopted to accurately obtain the statistical moments and PDFs of the unknown stochastic variables. Five examples are provided to verify the accuracy and efficiency of the proposed general frame for the forward and inverse UPs.
•A general frame is proposed to realize forward and inverse uncertainty propagations.•Arbitrary mono-peak PDFs are represented by the derivative λ-PDF.•A fitting region is derived to analyze the fitting ability of the derivative λ-PDF.•The forward UP with arbitrary PDFs is solved by Gauss-Gegenbauer quadrature and DR.•PDFs of the unknown variables are accurately estimated by inverse UP.
In this study, the structural phase transitions are investigated as a function of composition and temperature for polycrystalline x(Ba0.7Ca0.3)TiO3-(1 − x)Ba(Zr0.2Ti0.8)O3 (x = 0.40, 0.45, 0.50, ...0.55, and 0.60) through a combination of Raman spectroscopy, synchrotron X-ray diffraction, and dielectric spectroscopy. The aim is to gain insight into the complex phase boundary region responsible for the excellent electromechanical properties. The results demonstrate the correlation between local site substitutions based on the stoichiometric variations to the microstructure and dielectric properties. The dielectric response has been correlated with the BCT/BZT content displaying a maximum depending on the phase content. Additionally, in situ temperature-dependent Raman, permittivity, and pair distribution function (PDF) studies were performed from −60 °C to 130 °C to highlight the structure and phase evolution. In particular, the in situ temperature-dependent Raman measurements reveal sudden discontinuities in the vibrational modes that correspond to the structural changes in the perovskite structure. Therefore, the results of the permittivity response, based on the average of a large volume, are consistent with the local structural changes obtained by other techniques. Indeed, correlations of Raman, X-ray diffraction, and PDFs obtained from synchrotron X-ray total scattering data, along with permittivity measurements allowed the identification of the discrete ferro- to paraelectric phase transitions and a more robust characterization. The rotation and distortion of the octahedral caused by oxygen displacement are driving forces behind symmetry changes and phase transitions, explaining the mechanism of polymorphic phase transition based on A- and B-site substitution. Therefore, this work provides a comprehensive understanding of temperature and composition-dependent phase transitions in BCZT.
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•The polymorphic phase transitions in BCZT ceramics are investigated as a function of composition and temperature.•The mechanism of polymorphic phase transition is explained based on A and B site substitution.•Variations in octahedra distortion due to the Ti/Zr substitution explain the symmetry change as a function of composition.•in situ T-dependent Raman data show sudden discontinuities in the vibrational modes that agree with the phase transitions.•Symmetry in BCZT can be estimated using three-phase transition equations based on barycenter of Raman stretching mode.
Data reduction and correction steps and processed data reproducibility in the emerging single‐crystal total‐scattering‐based technique of three‐dimensional differential atomic pair distribution ...function (3D‐ΔPDF) analysis are explored. All steps from sample measurement to data processing are outlined using a crystal of CuIr2S4 as an example, studied in a setup equipped with a high‐energy X‐ray beam and a flat‐panel area detector. Computational overhead as pertains to data sampling and the associated data‐processing steps is also discussed. Various aspects of the final 3D‐ΔPDF reproducibility are explicitly tested by varying the data‐processing order and included steps, and by carrying out a crystal‐to‐crystal data comparison. Situations in which the 3D‐ΔPDF is robust are identified, and caution against a few particular cases which can lead to inconsistent 3D‐ΔPDFs is noted. Although not all the approaches applied herein will be valid across all systems, and a more in‐depth analysis of some of the effects of the data‐processing steps may still needed, the methods collected herein represent the start of a more systematic discussion about data processing and corrections in this field.
Data reduction and processing as related to single‐crystal diffuse scattering and 3D‐ΔPDF experiments are explored.
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