Society relies on increasingly complex software and hardware systems, hence techniques capable of proving that they behave as expected are of great and growing interest. Formal verification procedures employ mathematically sound reasoning to address this need. This thesis proposes novel techniques for the verification and falsification of expressive specifications on timed and infinite-state systems. An expressive specification language allows the description of the intended behaviour of a system via compact formal statements written at an abstraction level that eases the review process. Falsifying a specification corresponds to identifying an execution of the system that violates the property (i.e. a witness). The capability of identifying witnesses is a key feature in the iterative refinement of the design of a system, since it provides a description of how a certain error can occur. The designer can analyse the witness and take correcting actions by refining either the description of the system or its specification. The contribution of this thesis is twofold. First, we propose a semantics for Metric Temporal Logic that considers four different models of time (discrete, dense, super-discrete and super-dense). We reduce its verification problem to finding an infinite fair execution (witness) for an infinite-state system with discrete time. Second, we define a novel SMT-based algorithm to identify such witnesses. The algorithm employs a general representation of such executions that is both informative to the designer and provides sufficient structure to automate the search of a witness. We apply the proposed techniques to benchmarks taken from software, infinite-state, timed and hybrid systems. The experimental results highlight that the proposed approaches compete and often outperform specific (application tailored) techniques currently used in the state of the art.

Die Informatik ist von besonderer Bedeutung für die Gestaltung unser alltäglichen Lebensumstände und ist eine Schlüsseltechnologie des 21. Jahrhunderts. Die Fakultät für Informatik vertritt dieses Fachgebiet umfassend und kompetent mit anwendungsorientierten Schwerpunktsetzungen. In unseren Forschungsschwerpunkten - Eingebettete selbstorganisierende Systeme - Intelligente multimediale Systeme - Parallele verteilte Systeme bieten wir international wettbewerbsfähige Forschung und Entwicklung zu aktuellen Problemstellungen. Unsere Lehre basiert auf dem Leitmotiv der beständigen Erneuerung aus der Forschung. Hieraus abgeleitet bieten wir zeitgemäße Bachelor- und Masterstudiengänge mit hervorragenden Studienbedingungen. Die Fakultät hat den Anspruch eines möglichst persönlichen Umgangs zwischen Lehrkörper und Studenten. Mit der Schriftenreihe „Chemnitzer Informatik Berichte“ geben wir Einblicke in die Forschungspraxis der Fakultät. Dabei werden unterschiedliche Forschungsthemen aus den drei Forschungsschwerpunkten und allen Professuren der Fakultät vorgestellt. / Computer science, as a key technology of the 21th century, has an exceptional impact on our everyday life and living standards. The Faculty of Computer Science represents this scientific field in a comprehensive and proficient manner with an application-orientated choice of topics. In the fields of - Embedded and self-organizing systems - Intelligent multimedia systems - Parallel and distributed systems we offer research and development for current problems and challenges on an internationally competitive level. The guiding principle of our education is the continuous innovation through advances in research. Consequently, we are able to provide modern Bachelor and Master programs with excellent academic conditions. The faculty strives to provide a maximally personal interaction between students and staff. With the series of publications „Chemnitz Computer Science Reports“ we give insigths into the reasearch practice of the faculty. We present different subjects of research from the tree research fields and all of the professorships of the Faculty of Computer Science.

Dust is a critical component of the Earth System. The central and western Sahara (CWS) is the dustiest place on Earth during the northern hemisphere summer. Understanding patterns and causes of spatial and temporal variability of dust presence here is essential for its reliable simulation in numerical models of weather and climate. Four papers in this thesis contribute to that objective, utilising a combination of high temporal resolution satellite data and global atmospheric reanalyses for June – August 2004 – 2010 inclusive. The first paper develops an objective dust detection scheme for the CWS using data from the Spinning Enhanced Visible and Infrared Imager (SEVIRI), which are available every 15 minutes around the clock. These data have shed valuable insight on CWS dust processes, but their subjective application has to date limited their range of applications. The SEVIRI dust flag (SDF) developed here is evaluated against other widely used surface and satellite derived indicators of dustiness and it is found to reliably detect the presence of moderate-heavy dust loadings. The distribution of dust each summer is presented, revealing a high degree of interannual variability in overall dust coverage. The second paper utilises SDF to create an objective, high spatial resolution dust source map, based on the automated tracking of individual dust plumes. The most active sources are associated predominantly with palaeo-lakes and outwash plains, typically around the Saharan mountains. There is a clear intraseasonal progression of active source areas, controlled by regional climatology. The tracking scheme describes the transport trajectory of dust events following their initiation and the spatial association with deep convection at this time, revealing a clear regional divide in the relative importance of known meteorological mechanisms that drive dust emission from the dominant sources. The third paper uses an unsupervised clustering algorithm to classify maps of daily dust presence frequency and identify patterns of intraseasonal variability in CWS dust coverage. The resulting idealised dust states vary according to frequency of dust occurrence and its location, demonstrating a clear progression in preferred dust location from June – August and preferred state transitions from one day to the next. High daily dust occurrence frequency corresponds to an advanced West African Monsoon flow and low daily dust occurrence frequency corresponds to a Harmattan-dominated CWS. The overall location of the dust is linked to the location of the Sahara Heat Low, which changes as the summer progresses. The final paper addresses interannual variability in summertime dust presence frequency by comparing the 2 years with highest (2005) and lowest (2008) dust presence. The key difference is the occurrence of 3 multi-day periods in 2005 characterised by anomalously high dust presence. Case study comparison with the 3 periods of highest dust presence in 2008 identifies the anticyclonic circulation of the midtroposphere as a key control on dust duration over the CWS, dictating whether emitted dust is efficiently transported away from the CWS or whether it remains in suspension over the region for prolonged periods of time, up to several days in the anomalously dusty periods of 2005.

A lot has been said about change. For example, it is widely recognised that the only constant is change (Heraclitus, 470 BC). As such, no sensible decision can be made any longer without taking into account not only the world as it is, but the world as it will be (Isaac Asimov). As regards this, a bulk of existing researches have been aimed at understanding the triggers for change and the extent or degree to which individuals, organisations, systems or entities have to change. Generally, results from such studies vary. With specific relations to organisations, organisations are advised of the need to develop added adaptive and dynamic capabilities. One of such added adaptive and dynamic capabilities is organisational resilience. In the literature, organisational resilience has been successful linked with organisations ability to maintain long term performance. Hence, the research is not about re-examining the relationship between organisational resilience and organisations ability to maintain long term performance. This research focuses on exploring the critical success factors required to maintain long term performance and building adequate resilience into systems undergoing changes. The investigation was conducted in three phases, namely: (a) the exploratory phase; (b) the descriptive phase; and the empirical phase. The exploratory phase involved identifying the critical factors essential to maintain long term performance and at the same time build resilience into their systems after undergoing organisation-wide changes. In order to make out these critical, a pilot study was conducted. 21 persons occupying senior managerial positions in different organisations were interviewed. The interview data were transcribed, coded and analysed using coding and thematic analysis to identify five common themes, namely (a) employees readiness to support ongoing organisation-wide changes; (b) development of targeted organisational adaptive capacity; (c) the provision of individualised and social support; (d) the use of stress coping mechanisms; and (e) the existence of organisational resilience strategies. The second phase of the research entailed conducting case study research with the intention of describing the identified critical success factors. The final phase entailed conducting empirical analyses and cross case analysis. Results from the cross case study analyses indicated that both resilience building at the individual level and organisational level is needed for organisations to build in resilience into their systems especially after undergoing organisation-wide changes. Three factors (i.e. employees readiness to support ongoing organisation-wide changes, the provision of individualised and social support and the use of stress coping mechanisms) were found to be more pronounced at the individual level. The remaining two factors namely development of targeted organisational adaptive capacity and the existence of organisational resilience strategies are essentially carried out at the organisational level. The research has contributed to the current body of knowledge on how organisations can strive to maintain long term performance, especially for a country like Nigeria where there still remains a dearth of such related studies. Each of the research hypotheses were either confirmed or non confirmed. This will give the practitioners, academicians and managers of Nigerian organisations the opportunity to understand how each of the sub factors of the five critical success factors can influence on attempts to build organisational resilience. In addition, specific actions that managers can follow over the life of an organisation-wide change project that will improve the resilience of systems undergoing change. In addition, differences in how varied control factors can influence resilience building in organisations were explored and validated based on the results of the Mann Whitney test results. At the end of the thesis, recommendations for future practice and research were made. One of such is that resilience building at both levels be done concurrently and given equal prominence.

Change from a regulated to deregulated structure means that, the centralized maintenance system is not valid any more. In the surveyed published literature, there is not a single model which incorporates all maintenance cost components to analyze the effect of different maintenance strategies for generator companies (GENCOs). The work enclosed in this thesis demonstrates that there is a considerable requirement for accurately modelling cost components of the maintenance model, to be used in maintenance scheduling for deregulated power system, in order to attain a superior schedule with major financial and operational impact. This research investigates and models most cost factors that affect the maintenance activities of the deregulated GENCOs, and demonstrates the utilization of the developed cost models in maintenance scheduling. It also presents the data gathering process for the developed maintenance cost model. A generator maintenance scheduling model that considers direct and indirect maintenance costs, opportunity costs (i.e. loss of customer goodwill), effective maintenance strategies, failures, and interruptions is developed. A Genetic Algorithm (GA) based approach is employed to achieve maintenance schedules to various generators maintenance scenarios. An Analytical Hierarchy Process (AHP) approach is proposed for modelling customer goodwill. The maintenance model was redeveloped under the Reliability Centred Maintenance (RCM) strategy to analyze the effect of a maintenance strategy on maintenance costs. Case studies are presented to demonstrate the utilisation of the developed models.The investigation shows that the market prices, opportunity costs and maintenance strategy have an effect on the final maintenance schedule. The research demonstrates that the cost components are critical factors to achieve an effective maintenance schedule, and they must be considered and carefully modelled in order to reflect more realistic situation for maintenance scheduling of generator units in deregulation environment.

This quantitative research study investigated the impact of organisational context on the process and success of strategic IS planning (SISP) in post-implementation information systems in Libyan organisations. A set of direct and indirect relationships were investigated in the research model. The organisational context presented as a contingent situational variable mediated by SISP process and predicted by SISP success (the criterion variable). The causality of the relationship set was developed from the contingency theory of information systems and supported by fit models in strategic management research. The study deployed multivariate analysis represented in the structural equation modelling (SEM) to develop robust construct measurements and analyse data collected from executives responsible for information systems planning in both public and private Libyan organisations. Multi-dimensional multi-items constructs were used in the path analysis model after they were extensively validated. The path analysis model represented as mediation model, where hypothesise suggest that SISP context has an impact SISP success, through the influence of the SISP process. In the model, four dimensions of the SISP context construct were found to have a significant impact on SISP success directly and indirectly through the SISP process. Two of these dimensions are components of the leadership orientation construct, namely “Creative and Controlling” leadership. The other two dimensions are “Organisation centralisation structure and the Riskiness of organisation strategies”. The environmental uncertainty and planning resource constructs were found to have no impact on SISP success in Libyan organisations. Furthermore, this study validated six out of seven dimensions of SISP process construct measurement; only five exhibited acceptable fit level in the path analysis model and all were affected by the SISP context. However, just three out of five SISP process constructs had an impact on SISP success namely “Comprehensiveness, Focus and Intuition planning process”. Different SISP processes were associated with different levels of SISP success, “Intuition” was the most effective SISP process approach. The second most effective SISP process approach was the “Focus on innovation”, followed by “Limited comprehensiveness”. The SISP success measured by the fulfilment of key objectives that has three measurements constructs namely “Analysis, Alignment, and Cooperation”. The research suggest that under the effect of organisation context the most successful SISP produced by (CIO, CEO, or top executives) who rely less on personal judgment, focus more on innovation rather than control and limit their comprehensiveness of information systems planning process.

In boreal summer, satellite measurements show that the central Sahara is the dustiest region of the planet. However, ground-based observations of the central Sahara have been limited to its outer edges, leaving a void in observations approximately 1 million km² in area. The Fennec Project has been the first campaign to instrument this remote but climatologically important region. This thesis uses these new observations to detect and explain the atmospheric mechanisms that make the central Sahara the summer global dust maximum. Four atmospheric mechanisms are found to cause dust storms in the central Sahara in June 2011 and June 2012. These are cold pool outflows, low-level jets (LLJs), monsoon surges and dry convective plumes. Dust may be emitted locally by these phenomena, or be advected, principally by cold pools. In both field seasons, dust emission by cold pool outflows is the most important dust mechanism, causing roughly half of the total dust loadings at the Fennec supersite of Bordj-Badji Mokhtar (BBM), the closest station to the dust maximum. The second most important mechanism is dust advection by cold pools (roughly 30% dust at BBM), followed by dust emission by monsoon surges, LLJs and finally dry convective plumes (only 2% dust at BBM). Although June 2012 was significantly more dusty than June 2011, the relative importance of the different atmospheric dust mechanisms at BBM did not change. At the automatic weather stations (AWSs) across the remote desert, cold pools and LLJs are by far the most frequently detected atmospheric dust mechanisms. LLJs are particularly common in the Atlantic Inflow in western Mauritania and in the north-easterly Harmattan in western Algeria. Cold pools are much more frequent at BBM, the station under the greatest moist monsoon influence, than at the AWSs to the north. Detection of advected dust is a particular difficulty without dedicated dust-detection instrumentation or human observers (e.g. at the AWSs). Detection of dust emission mechanisms can be very successful with only routine ground observations and satellite measurements, but quantifying the associated dust burden without dedicated dust instruments is problematic. The choice of instrumentation for dust measurement is crucial. Because cold pool outflows - the most important dust mechanism - frequently occur at night or under cloud, sun photometers miss about half of cold pool dust. Lidars have the advantage of providing height resolved dust profiles, but they suffer from attenuation in thick dust. The nephelometer proved to be the most reliable dust instrument. Although LLJs occurred on 21/28 mornings at BBM in June 2011, only five of these jets led to dust emission. Calculations of momentum exchanges through the atmospheric column show that momentum mix-down from the jet core is the cause of dust emission on these occasions, but that the LLJ has to be particularly strong (≥ 16 m s^-1) to result in dust emission at the surface. Met Office Africa-LAM underestimates monsoon LLJ wind profiles and ERA-Interim reanalysis underestimates both monsoon and Harmattan LLJ wind profiles. At the surface, the Met Office Africa-LAM and GLOBAL models significantly underpredict the frequency of observed wind speeds &gt6 m s^-1. This will cause them to significantly underestimate dust emission, as emission is a threshold process proportional to the cube of wind speed. A particularly interesting implication of the research presented here is that the central Sahara is likely much more dusty than previously thought. This is because almost all of the techniques currently used to study dust in the region are systematically biased to result in underestimates of dust burden. Cold pools are the most important dust mechanism but, since they rarely occur during the daytime or in cloud-free conditions they are often missed by sun photometers. Many will be missed by satellites that cannot retrieve below cloud and satellites that pass over the Sahara in daylight hours (e.g. the A-train). A commonly-used satellite dust detection algorithm often misses dust under moist (i.e. cold pool) conditions. Cold pools cannot be simulated by models without explicit convection, which requires very high spatial resolution. Finally, the numerical models assessed here significantly underpredict the frequency of wind speeds over the dust emission threshold. The Sahara is probably much dustier than current estimates suggest.

<p>U radu su istražene mogućnosti za razvoj modela za izbor<br />lokacije proizvodnih sistema. Razvijen je model za izbor<br />lokacije proizvodnih sistema i verifikovan u studiji<br />slučaja na teritoriji AP Vojvodine i opštine Inđija.<br />Posebno značajan rezultat je fazi ekspertni sistem za<br />analizu kriterijuma odlučivanja, geografski informacioni<br />sistem za skrining i prostorni sistem za podršku u izboru<br />lokacije proizvodnih sistema.</p> / <p>This paper examines the possibilities of model development for<br />production systems site selection. Developed model for production<br />systems site selection is presented and tested in case study of AP<br />Vojvodina and Indjija municipality. A particularly important result is<br />developed fuzzy expert system for factor analysis, geographic<br />information system for screening and spatial decision support system.</p>

A teoria sobre as capacidades dinâmicas acolhe influências de várias teorias que a antecederam no campo da economia, da teoria das organizações e da estratégia. Em função dessas influências variadas, seu construto central, a capacidade dinâmica, tornou-se complexo e multifacetado. Vários autores especulam acerca da natureza e da evolução das capacidades dinâmicas. A percepção que se tem a partir das definições fornecidas pelos autores seminais é de que a natureza das capacidades dinâmicas é sistêmica e evolutiva. Em particular, é perceptível a afinidade do conceito de capacidades dinâmicas com duas abordagens sistêmicas específicas: o modelo do sistema viável (viable system model, VSM) e a metodologia sistêmica soft (soft systems methodology, SSM). Entretanto, apesar dessa aparente afinidade das capacidades dinâmicas com a visão sistêmica, estudos que relacionem os dois domínios da literatura são muito raros. Praticamente inexistem trabalhos que apliquem o VSM ou a SSM no estudo ou na administração de capacidades dinâmicas. O objetivo desta pesquisa é investigar a natureza e a evolução das capacidades dinâmicas sob uma perspectiva sistêmico-evolutiva. Como descrever a natureza das capacidades dinâmicas segundo uma perspectiva sistêmico-evolutiva? Como operacionalizar uma abordagem de administração evolutiva de capacidades dinâmicas através de metodologias sistêmicas como o VSM e a SSM? Essas são as perguntas que orientam este estudo. Através de revisão narrativa de literatura, a visão de capacidades dinâmicas e as teorias que a influenciaram foram analisadas e relacionadas com a visão sistêmica. Além disso, na falta de artigos que relacionassem os dois domínios da literatura, empreendeu-se uma revisão integrativa de literatura com artigos que tratam sobre a construção, desenvolvimento, evolução, obtenção, manutenção, mobilização e gerenciamento de capacidades dinâmicas. Esses artigos foram submetidos à análise categorial, uma variante da análise de conteúdo, para verificar a ocorrência de temas relacionados ao VSM e à SSM. Como resultado da revisão narrativa, demonstrou-se que a visão de capacidades dinâmicas está intimamente relacionada com a visão sistêmica, inclusive com o VSM e a SSM. Essa relação é uma herança da relação que as teorias que influenciaram a visão de capacidades dinâmicas já possuíam com a visão sistêmica. A revisão integrativa de literatura com análise de conteúdo permitiu concluir que (1) as capacidades dinâmicas têm, de fato, uma natureza evolutiva, (2) a intervenção da administração tem um papel importante na construção e na evolução de capacidades dinâmicas, e (3) essa intervenção pode ocorrer de duas maneiras básicas, que se chamou de evolução por projeto e evolução por aprendizagem, que se relacionou, respectivamente, às abordagens do VSM e da SSM. As descobertas da pesquisa foram sintetizadas em um modelo sistêmico evolutivo de organização que possui múltiplas vistas: um modelo hierárquico de administração de recursos e capacidades, um modelo recursivo de competências, um modelo recursivo de capacidades, um modelo de evolução de capacidades e um modelo de administração evolutiva baseado no VSM e na SSM. A pesquisa oferece uma contribuição teórica, no que diz respeito à compreensão da natureza sistêmica das capacidades dinâmicas. A pesquisa também oferece uma contribuição prática, ao propor a administração evolutiva, operacionalizada através do VSM e da SSM, como uma abordagem para o gerenciamento das capacidades dinâmicas. / The theory of dynamic capabilities gathers influences from several theories that preceded it in the fields of economics, organizational theory and strategy. Due to these varied influences, its core construct, the dynamic capability, ended up to become complex and multifaceted. Several authors speculate about the nature and the evolution of dynamic capabilities. The perception that we have from the definitions provided by the seminal authors is that the nature of dynamic capabilities is systemic and evolutionary. In particular, it is noticeable the affinity of the dynamic capability concept with two specific systems approaches: the viable system model (VSM) and the soft systems methodology (SSM). However, despite this seemingly affinity of dynamic capabilities with systems approach, studies that relate both realms of the literature are very scarce. There are practically no studies that apply the VSM or SSM in the study or the management of dynamic capabilities. The goal of the present research is to investigate the nature and the evolution of dynamic capabilities under a systemic-evolutionary approach. How to conceive the nature of dynamic capabilities according to a systemic-evolutionary perspective? How to operationalize an evolutionary management approach to dynamic capabilities by using systems methodologies such as the VSM and SSM? These are the questions that drive this research. By means of a narrative literature review, the dynamic capabilities view and the theories that influenced it were analyzed and related with systems thinking. In addition, given the lack of articles that relate both realms of the literature, an integrative literature review was undertaken with articles that address the construction, development, evolution, attainment, maintenance, deployment and management of dynamic capabilities. These articles were submitted to categorical analysis, a variation of content analysis, to verify the occurrence of themes related to the VSM and SSM. As a result of the narrative literature review, we showed that the dynamic capabilities view is closely related to the systems thinking, including to the VSM and SSM. This relation in an inheritance of the relation that the theories that influenced the dynamic capabilities view already had with systems thinking. The integrative literature review with content analysis led to the conclusion that (1) the dynamic capabilities do have an evolutionary nature, (2) the intervention of management has an important role in building and evolving dynamic capabilities, and (3) this intervention can take two basic approaches, that we named evolution by design and evolution by learning, which we respectively related to the approaches of the VSM and SSM. The findings of the research were synthesized in a evolutionary system model of the organization that has several multiple views: a hierarchical model for resources management, a recursive model of competences, a recursive model of capabilities, a capabilities evolution model and a model for evolutionary management based on the VSM and SSM. The research provides a theoretical contribution, which regards the understanding of the systemic nature of dynamic capabilities. The research also provides a practical contribution, as it proposes evolutionary management, operationalized by applying the VSM and SSM, as an approach to the management of the dynamic capabilities.

Thema der Arbeit sind die Phänomene Risiko und Krise als Herausforderung für das Kommunikationsmanagement von Organisationen in Wirtschaft Politik und Gesellschaft. Das Ziel ist ein theoretisch begründeter Handlungsrahmen, der als Grundlage für operative Maßnahmen der Risiko- und Krisenkommunikation dienen soll. Nach Klärung der Begriffe und kommunikativen Bedingungen geht es dabei um die Betrachtung von Risiko- und Krisenkommunikation als Spielhandlung. Es werden Verlaufsstrukturen aufgezeigt, die weitgehend auch die Handlungsspielräume der Akteure und deren Erwartungen sowie die der Zuschauer bestimmen. Neben einer kritischen Auseinandersetzung mit vorliegenden Modellen des Management von Risiko- und Krisenkommunikation liefert die Arbeit Ergebnisse einer standardisierten schriftlichen Befragung von Kommunikationsfachleuten aus dem Bereich der Unternehmenskommunikation. Ein wichtiges Ziel ist dabei, die offensichtlichen Differenzen in der Einschätzung zwischen Theorie und Praxis aufzudecken und zu quantifizieren. Den übergeordneten Handlungsrahmen der Risiko- und Krisenkommunikation bilden schließlich Überlegungen zur Bestandserhaltung und Anschlußfähigkeit von Kommunikationssystemen. Neben geeigneten Prozessen, Ritualen und Verfahren spielen Aspekte der Imagepflege dabei eine wichtige Rolle. / The phenomena risk and crisis as challenges facing the management of communications processes in business, politics, and society provide the subject for this work, the goal of which is a theoretically-based framework laying the groundwork for operative measures in communications with respect to risk and crisis situations. Having first defined relevant terms and conditions for communication, the work analyses risk and crisis communications from the standpoint of a game and illustrates the structures created as the game runs its course. These structures are crucial elements in determining not only participants' but also observers' freedom to act and the expectations they develop. In addition to a critical discussion of available models for the management of risk and crisis communications, the work contains the results of a standardized written polling of experts in the field of corporate communications. Crucial goals of this research were to identify and quantify apparent differences in the assessment of theory and practice. Observations as to how to maintain and ensure the continuation of communication systems provide the overlying framework for risk and crisis communications, for which aspects of image preservation, together with processes, rituals, and procedures, play an important role.