Universitätsbibliothek
Weimar Open Access

Rapid advancements of modern technologies put high demands on mathematical modelling of engineering systems. Typically, systems are no longer “simple” objects, but rather coupled systems involving multiphysics phenomena, the modelling of which involves coupling of models that describe different phenomena. After constructing a mathematical model, it is essential to analyse the correctness of the coupled models and to detect modelling errors compromising the final modelling result. Broadly, there are two classes of modelling errors: (a) errors related to abstract modelling, eg, conceptual errors concerning the coherence of a model as a whole and (b) errors related to concrete modelling or instance modelling, eg, questions of approximation quality and implementation. Instance modelling errors, on the one hand, are relatively well understood. Abstract modelling errors, on the other, are not appropriately addressed by modern modelling methodologies. The aim of this paper is to initiate a discussion on abstract approaches and their usability for mathematical modelling of engineering systems with the goal of making it possible to catch conceptual modelling errors early and automatically by computer assistant tools. To that end, we argue that it is necessary to identify and employ suitable mathematical abstractions to capture an accurate conceptual description of the process of modelling engineering systems.

Die in diesem Tagungsband zusammengeführten Beiträge beschäftigen sich mit dem Spannungsfeld, das sich zwischen externen Förderprogrammen, Veränderungsprojekten und den Zielen, Strukturen und Bedingungen der jeweiligen Hochschule ergibt. In diesem Spannungsfeld kommt es unweigerlich zu Reibungen, da vorhandene Strukturen und Ziele in Konflikt mit neuen Vorhaben und Ideen geraten. Ein Teil der Projekte stellt allein durch ihr finanzielles Volumen und die daraus resultierende Wirkkraft die tradierten Verhältnisse zwischen Lehre, Forschung und den wissenschaftsstützenden Bereichen in Frage und teils auf den Kopf. Die leitenden Fragen der Tagung und der hier versammelten Beiträge waren daher: Wie bringen Hochschulen ihre individuellen Ziele mit denen der bundesweiten Programme oder länderspezfifischer Fördermaßnahmen überein? Wie gehen Hochschulen mit ihren Projekten um? Wie vollzieht sich Veränderung an den Hochschulen? Und schließlich: Was bleibt von den Impulsen, die Projekte setzen? Die in diesem Tagungsband versammelten Beiträge geben darauf erste, auf dem bisherigen Erfahrungswissen basierende Antworten. Sie setzen sich intensiv mit den Faktoren auseinander, die den Erfolg von Veränderungsprozessen und Projekten befördern oder behindern können und leiten daraus Empfehlungen für Gestaltungsprozesse an Hochschulen ab.

During the previous decades, the upcoming demand for security in the digital world, e.g., the Internet, lead to numerous groundbreaking research topics in the field of cryptography. This thesis focuses on the design and analysis of cryptographic primitives and schemes to be used for authentication of data and communication endpoints, i.e., users. It is structured into three parts, where we present the first freely scalable multi-block-length block-cipher-based compression function (Counter-bDM) in the first part. The presented design is accompanied by a thorough security analysis regarding its preimage and collision security. The second and major part is devoted to password hashing. It is motivated by the large amount of leaked password during the last years and our discovery of side-channel attacks on scrypt – the first modern password scrambler that allowed to parameterize the amount of memory required to compute a password hash. After summarizing which properties we expect from a modern password scrambler, we (1) describe a cache-timing attack on scrypt based on its password-dependent memory-access pattern and (2) outline an additional attack vector – garbage-collector attacks – that exploits optimization which may disregard to overwrite the internally used memory. Based on our observations, we introduce Catena – the first memory-demanding password-scrambling framework that allows a password-independent memory-access pattern for resistance to the aforementioned attacks. Catena was submitted to the Password Hashing Competition (PHC) and, after two years of rigorous analysis, ended up as a finalist gaining special recognition for its agile framework approach and side-channel resistance. We provide six instances of Catena suitable for a variety of applications. We close the second part of this thesis with an overview of modern password scramblers regarding their functional, security, and general properties; supported by a brief analysis of their resistance to garbage-collector attacks. The third part of this thesis is dedicated to the integrity (authenticity of data) of nonce-based authenticated encryption schemes (NAE). We introduce the so-called j-IV-Collision Attack, allowing to obtain an upper bound for an adversary that is provided with a first successful forgery and tries to efficiently compute j additional forgeries for a particular NAE scheme (in short: reforgeability). Additionally, we introduce the corresponding security notion j-INT-CTXT and provide a comparative analysis (regarding j-INT-CTXT security) of the third-round submission to the CAESAR competition and the four classical and widely used NAE schemes CWC, CCM, EAX, and GCM.

We present StarWatch, our application for real-time analysis of radio astronomical data in Virtual Environment. Serving as an interface to radio astronomical databases or being applied to live data from the radio telescopes, the application supports various data filters measuring signal-to-noise ratio (SNR), Doppler's drift, degree of signal localization on celestial sphere and other useful tools for signal extraction and classification. Originally designed for the database of narrow band signals from SETI Institute (setilive.org), the application has been recently extended for the detection of wide band periodic signals, necessary for the search of pulsars. We will also address the detection of week signals possessing arbitrary waveforms and present several data filters suitable for this purpose.

Urban and building energy simulation models are usually driven by typical meteorological year (TMY) weather data often in a TMY2 or EPW format. However, the locations where these historical datasets were collected (usually airports) generally do not represent the local, site specific micro-climates that cities develop. In this paper, a humid sub-tropical climate context has been considered. An idealised “urban unit model” of 250 m radius is being presented as a method of adapting commonly available weather data files to the local micro-climate. This idealised “urban unit model” is based on the main thermal and morphological characteristics of nine sites with residential/institutional (university) use in Hangzhou, China. The area of the urban unit was determined by the region of influence on the air temperature signal at the centre of the unit. Air temperature and relative humidity were monitored and the characteristics of the surroundings assessed (eg green-space, blue-space, built form). The “urban unit model” was then implemented into micro-climatic simulations using a Computational Fluid Dynamics – Surface Energy Balance analysis tool (ENVI-met, Version 4). The “urban unit model” approach used here in the simulations delivered results with performance evaluation indices comparable to previously published work (for air temperature; RMSE <1, index of agreement d > 0.9). The micro-climatic simulation results were then used to adapt the air temperature and relative humidity of the TMY file for Hangzhou to represent the local, site specific morphology under three different weather forcing cases, (ie cloudy/rainy weather (Group 1), clear sky, average weather conditions (Group 2) and clear sky, hot weather (Group 3)). Following model validation, two scenarios (domestic and non-domestic building use) were developed to assess building heating and cooling loads against the business as usual case of using typical meteorological year data files. The final “urban weather projections” obtained from the simulations with the “urban unit model” were used to compare the degree days amongst the reference TMY file, the TMY file with a bulk UHI offset and the TMY file adapted for the site-specific micro-climate (TMY-UWP). The comparison shows that Heating Degree Days (HDD) of the TMY file (1598 days) decreased by 6 % in the “TMY + UHI” case and 13 % in the “TMY-UWP” case showing that the local specific micro-climate is attributed with an additional 7 % (ie from 6 to 13 %) reduction in relation to the bulk UHI effect in the city. The Cooling Degree Days (CDD) from the “TMY + UHI” file are 17 % more than the reference TMY (207 days) and the use of the “TMY-UWP” file results to an additional 14 % increase in comparison with the “TMY + UHI” file (ie from 17 to 31 %). This difference between the TMY-UWP and the TMY + UHI files is a reflection of the thermal characteristics of the specific urban morphology of the studied sites compared to the wider city. A dynamic thermal simulation tool (TRNSYS) was used to calculate the heating and cooling load demand change in a domestic and a non-domestic building scenario. The heating and cooling loads calculated with the adapted TMY-UWP file show that in both scenarios there is an increase by approximately 20 % of the cooling load and a 20 % decrease of the heating load. If typical COP values for a reversible air-conditioning system are 2.0 for heating and 3.5 for cooling then the total electricity consumption estimated with the use of the “urbanised” TMY-UWP file will be decreased by 11 % in comparison with the “business as usual” (ie reference TMY) case. Overall, it was found that the proposed method is appropriate for urban and building energy performance simulations in humid sub-tropical climate cities such as Hangzhou, addressing some of the shortfalls of current simulation weather data sets such as the TMY.