Towards robust steganalysis: binary classifiers and large, heterogeneous data

The security of a steganography system is defined by our ability to detect it. It is of no surprise then that steganography and steganalysis both depend heavily on the accuracy and robustness of our detectors. This is especially true when real-world data is considered, due to its heterogeneity. The difficulty of such data manifests itself in a penalty that has periodically been reported to affect the performance of detectors built on binary classifiers; this is known as cover source mismatch. It remains unclear how the performance drop that is associated with cover source mismatch is mitigated or even measured. In this thesis we aim to show a robust methodology to empirically measure its effects on the detection accuracy of steganalysis classifiers. Some basic machine-learning based methods, which take their origin in domain adaptation, are proposed to counter it. Specifically, we test two hypotheses through an empirical investigation. First, that linear classifiers are more robust than non-linear classifiers to cover source mismatch in real-world data and, second, that linear classifiers are so robust that given sufficiently large mismatched training data they can equal the performance of any classifier trained on small matched data. With the help of theory we draw several nontrivial conclusions based on our results. The penalty from cover source mismatch may, in fact, be a combination of two types of error; estimation error and adaptation error. We show that relatedness between training and test data, as well as the choice of classifier, both have an impact on adaptation error, which, as we argue, ultimately defines a detector's robustness. This provides a novel framework for reasoning about what is required to improve the robustness of steganalysis detectors. Whilst our empirical results may be viewed as the first step towards this goal, we show that our approach provides clear advantages over earlier methods. To our knowledge this is the first study of this scale and structure

Non-suicidal self-injury in adolescence: a longitudinal study of the relationship between NSSI, psychological distress and perceived parenting

Objective: The present study investigates whether either adolescents' psychological distress and/or perceived parenting predicted the occurrence of NSSI. Furthermore, the consequences of NSSI are examined in a three-wave longitudinal study. Design: The sample at time 1 (age 12) consisted of 1396 adolescent reports and 1438 parent reports. At time 2 (age 13), 827 adolescent reports and 936 parent reports were obtained. Time 3 (age 14) included 754 adolescent reports and 790 parent reports. Psychological distress of adolescents was measured using the Strengths and Difficulties Questionnaire. Perceived parenting behaviors were examined by the Parental Behavior Scale and the Psychological Control Scale. Results: A total of 10% of the adolescents engaged in NSSI at least once before age 15. Higher psychological distress of adolescents at time 1 was associated with the presence of NSSI at time 2 or 3. The association between psychological distress at time 1 and perception of decreased parental rule setting at time 3 was mediated by the presence of NSSI at time 2. Conclusions: The present study showed that psychological distress at age 12 predicts NSSI over time and that parental awareness of NSSI changes the perception of parenting behaviors. (C) 2014 The Foundation for Professionals in Services for Adolescents. Published by Elsevier Ltd. All rights reserved

Web-based intervention for developing long-term health literacy of individuals : Possibilities and limitations

Publisher Copyright: © by Aira Aija Krumiņa 2016.Web-based interventions (WBI) are purposefully developed online programs designed for wide range of users (clients, patients, health care specialists, as well as medical practitioners) which allow obtaining and using information on various issues related to health maintenance and improvement. On the basis of the analysis of scientific literature, the article provides an overview of WBI types and components, as well as a structural model of WBI and its user in the context of environment factors. The possibilities of using WBI for developing long-term health literacy of individuals are specified. By summarising the main advantages and limitations of using WBI, the possible suggestions for the WBI use and development are offered.publishersversionPeer reviewe

Impact of COVID-19 pandemic on mental health: an international study

20 páginasLa pandemia de COVID-19 desencadenó confinamientos gubernamentales generalizados. El impacto de estos confinamientos en la salud mental no se comprende adecuadamente. Por un lado, estos cambios drásticos en las rutinas diarias podrían ser perjudiciales para la salud mental. Por otro lado, es posible que no se perciban de forma negativa, especialmente porque toda la población se vio afectada

Prospects of controlling the propagation of high-power THz radiation by passive optical elements including 3D printed

Optical properties of different commercial plastics for fused deposition modeling 3D printing are defined at room temperature in the spectral range 0.2˗1.2 THz. We compare absorption coefficients and refractive index of ABS, PETG, and SBS printed 1-4 mm plates. Different types of optical elements for controlling high-power THz radiation are studied. A comparison is made of the efficiency of attenuation of linearly polarized THz radiation with homemade band-pass polarizers obtained by etching copper from a flexible polyimide substrate. Filters and polarizers created using 3D printing or by deposition of polymer matrix with magnetic particles under external field are cost-effective and can be easily changed or replaced. Comparison between plastic insets, filters based on magnetic particles, and polyimide film filters are made

Prospects of controlling the propagation of high power THz radiation by passive optical elements including 3D printed

Different types of optical elements for controlling high power THz radiation were studied. Controlling was performed utilizing amplitude modulation of the electric field and effective spatial modulation of the complex dielectric susceptibility in the volume of the THz filter. We make a comparison of attenuation efficiency of various options of 3D printed filters when ABS filament is mixed with perovskite microparticles. Another type of filter was obtained by the deposition of magnetic particles in the presence of an external magnetic field in a transparent polymer matrix. Industrial isotropic cut-off filters based on layered meta structures have also been investigated. A comparison is made of the efficiency of attenuation of linearly polarized THz radiation with homemade band-pass polarizers obtained by etching copper from a flexible polyimide substrate and industrial filters. Filters and polarizers created using 3D printing, or by deposition of polymer matrix with magnetic particles under external field, are attractive cost effective elements

Aspects for efficient wide spectral band THz generation via CO2 laser down conversion

Detailed model study of THz generation by CO2 laser down-conversion in pure and solid solution crystals GaSe1-xSx is carried out for the first time. Both forward and backward collinear interactions of common (eo-e, oe-e, oe-o, oo-e, ee-o) and original (ee-e, oo-o) types are considered. Possibility of realization, phase matching angles and figure of merits are estimated for line mixing within 9 μm and 10 μm emission bands, as well between them. Dispersion properties of o- and e-wave refractive indices and absorption coefficients for GaSe, GaS and GaSe1-xSx crystals were preliminary measured by THz-TDS, approximated in the equation form and then used in the study. Estimated results are presented in the form of 3-D figures that are suitable for rapid analyses of DFG parameters. The most efficient type of interaction is eo-o type. Optimally doped (x = 0.09-0.13) GaSe1-xSx crystals are from 4 to 5 times more efficient at limit pump intensity than not doped GaSe crystals

About enhanced access control using FIDO2 authentication and attributes

In this paper a joint use of the FIDO2 specifi cation and attribute-based access control with support for reading attributes from electronic documents is proposed. Existing solutions and implementation options are reviewed. This provides an opportunity to improve access control methods to information and resources