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See detailSelf-reported dependence on mobile phones in young adults: A European cross-cultural empirical survey.
Lopez-Fernandez, Olatz; Kuss, Daria J.; Romo, Lucia et al

in Journal of behavioral addictions (in press)

Background and aims Despite many positive benefits, mobile phone use can be associated with harmful and detrimental behaviors. The aim of this study was twofold: to examine (a) cross-cultural patterns of ... [more ▼]

Background and aims Despite many positive benefits, mobile phone use can be associated with harmful and detrimental behaviors. The aim of this study was twofold: to examine (a) cross-cultural patterns of perceived dependence on mobile phones in ten European countries, first, grouped in four different regions (North: Finland and UK; South: Spain and Italy; East: Hungary and Poland; West: France, Belgium, Germany, and Switzerland), and second by country, and (b) how socio-demographics, geographic differences, mobile phone usage patterns, and associated activities predicted this perceived dependence. Methods A sample of 2,775 young adults (aged 18-29 years) were recruited in different European Universities who participated in an online survey. Measures included socio-demographic variables, patterns of mobile phone use, and the dependence subscale of a short version of the Problematic Mobile Phone Use Questionnaire (PMPUQ; Billieux, Van der Linden, & Rochat, 2008). Results The young adults from the Northern and Southern regions reported the heaviest use of mobile phones, whereas perceived dependence was less prevalent in the Eastern region. However, the proportion of highly dependent mobile phone users was more elevated in Belgium, UK, and France. Regression analysis identified several risk factors for increased scores on the PMPUQ dependence subscale, namely using mobile phones daily, being female, engaging in social networking, playing video games, shopping and viewing TV shows through the Internet, chatting and messaging, and using mobile phones for downloading-related activities. Discussion and conclusions Self-reported dependence on mobile phone use is influenced by frequency and specific application usage. [less ▲]

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See detailWeinhandel und Weinkonsum in der Stadt Luxemburg im 15. Jahrhundert
Pauly, Michel UL

Conference given outside the academic context (2017)

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See detailOnline deliberation: state of the art
Kies, Raphaël UL

E-print/Working paper (2017)

In the last decade, the issue of online deliberation (or web-deliberation) has gained an important visibility among the scholars in the domain of political science, political philosophy, political ... [more ▼]

In the last decade, the issue of online deliberation (or web-deliberation) has gained an important visibility among the scholars in the domain of political science, political philosophy, political communication as well as software designers. It corresponds not only to a topic of analysis – that can be broadly defined as the quantitative and qualitative assessment of the political and public debates online - but also to a democratic model of e-democracy, that aims to shape the different political usage of the web according to the deliberative values. A pertinent way to analyze this broad phenomenon is to subdivide its analysis in three sections which content is partly based on updated findings of my book Promises and Limits of web-deliberation. The first section refers to the deliberative theory on which the empirical research is based. The second section deals with the complex issue of operationalizing the deliberative theory. The last section provides an overview of the online deliberative empirical studies that were conducted this last decade by distinguishing three broad research fields: i) The studies that aim at measuring the usage of the political web-debates and the characteristics of the users; ii) The studies that identify and compare the social and political actors that offer possibilities of online debates; iii) The studies assessing the quality of deliberation in different discursive online settings and the ones aiming at defining the factors that could explain variations in web-deliberation. [less ▲]

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See detailSleep and somatic complaints in university students
Schlarb, Angelika; Claßen, Merle; Hellmann, Sara et al

in Journal of Pain Research (2017), 10

Background: Sleep problems are common among university students. Poor sleep is associated with impaired daily functioning, increased risk of psychiatric symptoms, and somatic complaints such as pain ... [more ▼]

Background: Sleep problems are common among university students. Poor sleep is associated with impaired daily functioning, increased risk of psychiatric symptoms, and somatic complaints such as pain. Previous results suggest that poor sleep exacerbates pain, which in turn negatively affects sleep. The purpose of the present study was to determine prevalence rates, comorbidity, and role of depression as a factor of moderating the relationship between sleep and physical complaints in German university students. Samples and methods: In total, 2443 German university students (65% women) completed a web survey. Self-report measures included the Pittsburg Sleep Quality Index, three modules of the Patient Health Questionnaire, and a questionnaire on the functional somatic syndromes (FSSs). Results: More than one-third (36.9%) reported poor sleep as assessed by the Pittsburgh Sleep Quality Index. Somatoform syndrome was identified in 23.5%, and the prevalence of any FSS was 12.8%. Self-reported sleep quality, sleep onset latency, sleep disturbances, use of sleep medications, and daytime dysfunctioning were significant predictors of somatoform syndrome, whereas sleep efficiency and sleep duration influenced somatic complaints indirectly. Moderate correlations were found between stress, anxiety, somatoform syndrome, depression, and overall sleep quality. The effect of somatic complaints on sleep quality was associated with the severity of depression. Anxiety shows direct effects on somatization and depression but only indirect associations with sleep quality. [less ▲]

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See detailFEUTURE EU 28 Country Report: Luxembourg
Högenauer, Anna-Lena UL

Report (2017)

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See detailPayload-based fleet optimization for rail cars in the chemical industry
Kallrath, J.; Klosterhalfen, Steffen UL; Walter, M. et al

in European Journal of Operational Research (2017), 259(1), 113-129

Rail car fleets are significant investments in the chemical industry. Therefore, chemical companies constantly try to optimize the fleets as part of major working capital optimization initiatives. We ... [more ▼]

Rail car fleets are significant investments in the chemical industry. Therefore, chemical companies constantly try to optimize the fleets as part of major working capital optimization initiatives. We study a complex rail car fleet optimization problem observed at BASF and an approach to tackle the problem in a sequential way. We develop a mixed integer non-linear programming model to derive suggestions to the questions: (i) How many different rail car sizes in terms of volume are appropriate and what are their optimal volumes? and (ii) For each volume, what is the optimal number of rail cars of this size? The model formulation takes into account various real-world restrictions concerning the volume and weight of the rail cars as well as the tracks that they run on. We propose two solution methods. First, we reformulate the non-linear terms, which results in a mixed integer linear programming (MILP) model. This model can be solved in a reasonable amount of time, if the number of different rail car sizes is small (2 or 3). Second, we develop a two-step approach that uses an enumeration scheme in the first stage to find good initial solutions that are fed into the MILP formulation in the second stage. This approach solves the model for larger numbers of different rail car sizes (4 or 5). Through the fleet redesign BASF has realized cost savings of nearly 2 million euros so far. [less ▲]

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See detailInvited talk - Übergangsentscheidungen in Luxemburg
Krolak-Schwerdt, Sabine UL; Pit, Ineke UL; Glock, Sabine et al

Conference given outside the academic context (2016)

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See detailIm Gespräch mit Paul Benneworth
Epping, Elisabeth UL; Benneworth, Paul

in Institut für Innovation und Technik (Ed.) Neue Formen der Kooperation in regionalen Innovationssystemen (2015)

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See detailOperations Research in BASF's Supply Chain Operations
Blackburn, Robert; Kallrath, Josef; Klosterhalfen, Steffen UL

in International Transactions in Operational Research (2015), 22

In this paper, we highlight the application of operations research (OR) at BASF in the area of supply chain management (SCM) by using selected examples with annual cost savings ranging between several ... [more ▼]

In this paper, we highlight the application of operations research (OR) at BASF in the area of supply chain management (SCM) by using selected examples with annual cost savings ranging between several hundred thousand and several million euros. We address special characteristics of the process industry that should be dealt with and identify future research needs. The examples cover strategic, tactical, and operational topics encountered at BASF. We share our lessons learned, based on our experience from past OR projects in SCM, about challenges as well as benefits of standard and tailor-made OR solutions. In general, we find that the special characteristics often call for a modification or enhancement of standard OR models. Providing appropriate solutions therefore requires a joint effort of SCM, IT, and OR experts. [less ▲]

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See detailInvited keynote - 50th Anniversary resume, outlook and discussion: Classification society and data science
Wishart, David; Bock, Hans-Hermann; Hand, David et al

Scientific Conference (2014, July)

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See detailStrategic Safety Stock Placement in Supply Networks with Static Dual Supply
Klosterhalfen, Steffen UL; Minner, Stefan; Willems, Sean

in Manufacturing & Service Operations Management (2014), 16(2), 204-219

Many real-world supply networks source required materials from multiple suppliers. Existing multiechelon inventory optimization approaches either restrict their scope to multiple supply sources in two ... [more ▼]

Many real-world supply networks source required materials from multiple suppliers. Existing multiechelon inventory optimization approaches either restrict their scope to multiple supply sources in two-echelon systems or single suppliers in multiechelon systems. We develop an exact mathematical model for static dual supply in a general acyclic N-echelon network structure, which builds on the guaranteed-service framework for safety stock optimization. It is assumed that the suppliers are allocated static fractions of demand. We prove that for normally distributed demand an extreme point property holds. We present a real example from the industrial electronics industry consisting of five echelons and three dual-sourced materials. This example forms the basis for a numerical analysis. Compared with the only previously published approximate solution, our exact approach results in considerable cost savings because the exact model captures inventory pooling in a way that the approximation is unable to do. For a set of test problems, total safety stock cost savings are 9.1%, on average. [less ▲]

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See detailRail Car Fleet Design: Optimization of Structure and Size
Klosterhalfen, Steffen UL; Kallrath, J.; Fischer, G.

in International Journal of Production Economics (2014), 157

We develop a model to determine the optimal structure and size of a rail car fleet at a chemical company under uncertainty in demand and travel times as well as substitution between rail car types. First ... [more ▼]

We develop a model to determine the optimal structure and size of a rail car fleet at a chemical company under uncertainty in demand and travel times as well as substitution between rail car types. First, we formulate an MILP model that accounts for the substitution relations between the types and minimizes the total direct rail car cost under given rail car availability constraints and a predefined maximum number of types. Second, based on the fleet structure obtained by the MILP model, the fleet size is computed by using an approximation from inventory theory that considers the existing uncertainties. Compared to the current approach of the rail car fleet management team, the model produces a reduction in safety stock of 120 rail cars and thus direct cost savings of 8% as well as further indirect cost savings due to a smaller number of rail car types, which reduces the switching effort of the rail cars on the storage tracks. [less ▲]

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See detailInvited talk - Schulübergangsentscheidung in Luxemburg
Krolak-Schwerdt, Sabine UL

Conference given outside the academic context (2013)

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See detailDiscussant - Session 5
Krolak-Schwerdt, Sabine UL

Scientific Conference (2013, November)

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See detailPanel discussion - Challenges in measuring methodology
Cao, Li; Fox, Jean-Paul; Hambleton, Ronald K. et al

Scientific Conference (2013, November)

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See detailInvited talk - Diagnostische Kompetenzen
Gräsel, Cornelia; Krolak-Schwerdt, Sabine UL

Scientific Conference (2013, October)

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See detailTeacher judgment accuracy
Krolak-Schwerdt, Sabine UL

Scientific Conference (2013, July)

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