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Barbey H.-P.,FH Bielefeld
Proceedings - 27th European Conference on Modelling and Simulation, ECMS 2013 | Year: 2013

The bullwhip effect has been well known since many years and often takes place in supply chains. It is caused by wrong order policy in real systems. The bullwhip effect can be demonstrated easily through the beer game. It was developed by the MIT in the 60s. All stages of the supply chain operate independently. The only decisions that can be taken in the particular stages of this simulation game are the size of the orders. This beer game was depicted as a simulation with two additional simple control algorithms for the decision of the order quantities. The first algorithm set the time to compensate a difference in the inventory to a specific value, in the second algorithm the quantity of the order is limited. Both algorithms were taken to compensate a sudden and steady increase of the orders. Both control algorithms generated a bullwhip effect. The limited duration strategy for compensation a difference in the inventory led to rising orders in the upstream stages. The limited order strategy led to an increasing time to compensate a difference in the inventories of the upstream stages. The limited duration strategy was applied to an ordering behavior with a linear trend und to a random ordering behavior. For the linear trend it has been found that the shorter the time for compensation the lower the difference to the nominal stock and the higher the bullwhip effect in the stages upstream. In contrast to that for random orders the time for compensation has to be longer to minimize the bullwhip effect. That is why the setting of the closed-loop control of the stocks in supply chains is an optimization problem. It can only be solved for a real supply chain, if the ordering behavior of the customer is known. © ECMS Webjøm Rekdalsbakken.


Schulz M.,FH Bielefeld | Gray R.,University of the West of England | Abderhalden C.,University of Bern | Behrens J.,Martin Luther University of Halle Wittenberg
Schizophrenia Research | Year: 2013

Background: Non-adherence with antipsychotic medication is common in patients with schizophrenia. Aims: To establish the efficacy of adherence therapy (AT) compared to treatment as usual (TAU) in improving medication compliance in patients following an acute episode of schizophrenia. Method: The study was designed as a parallel group, single blind, randomised controlled trial. Fieldwork was conducted in four centres (3 in Germany and 1 in Switzerland) and involved a total of 161 patients. Patients received 8 sessions of AT in addition to treatment as usual. The main outcomes of this study were adherence and psychopathology at 12. weeks post discharge follow up. Results: In total 80 patients received AT and 57 TAU. Intention-to-treat analysis included all randomised patients. Psychopathology, as determined using the PANSS-total, improved in the AT compared to TAU group by a mean of - 6.16 points 12. weeks after discharge from hospital (p < .05). AT had no significant effects on patients' adherence, treatment attitudes or functioning. No significant adverse events were reported. Conclusion: AT improves psychopathology in patients recovering from an acute episode of schizophrenia. © 2013 Elsevier B.V.


Hamelmann F.U.,FH Bielefeld
Journal of Physics: Conference Series | Year: 2016

Zinc oxide is known as a mineral since 1810, but it came to scientific interest after its optoelectronic properties found to be tuneable by p-type doping. Since the late 1980's the number of publications increased exponentially. All thin film deposition technologies, including sol-gel and spray pyrolysis, are able to produce ZnO films. However, for outstanding properties and specific doping, only chemical vapor deposition and physical vapor deposition have shown so far satisfying results in terms of high conductivity and high transparency. In this paper the different possibilities for doping will be discussed, some important applications of doped ZnO thin films will be presented. The deposition technologies used for industrial applications are shown in this paper. Especially sputtering of aluminium doped Zinc Oxide (ZnO:Al or AZO) and LPCVD of boron doped Zinc Oxide (ZnO:B or BZO) are used for the commercial production of transparent conductive oxide films on glass used for thin film photovoltaic cells. For this special application the typical process development for large area deposition is presented, with the important trade-off between optical properties (transparency and ability for light scattering) and electrical properties (conductivity). Also, the long term stability of doped ZnO films is important for applications, humidity in the ambient is often the reason for degradation of the films. The differences between the mentioned materials are presented.


Bamberg S.,FH Bielefeld | Rees J.,Bielefeld University
Transportation Research Part A: Policy and Practice | Year: 2017

Personal travel planning (PTP) is generally regarded as an effective approach to voluntary travel behavior change in the domain of transportation research. However, this view has recently been challenged by findings from another research domain, public health research, reporting little or no effect of PTP-based interventions. We argue that these conflicting results regarding the effectiveness of PTP-based measures are due to different understandings of which research designs should be used: Transportation research tends to be based on large-scale quasi-experimental designs whereas public health research tends to favor experimental designs such as randomized control trials (RCTs). Consequently, we argue, the discrepancy may at least partly be resolved by a more nuanced position on what empirical evidence really matters when evaluating if an intervention is effective or not. In the empirical part of the paper, we meta-analytically re-analyze ten quasi-experimental PTP evaluation studies and report an experimental RCT-based study testing the effectiveness of a PTP strategy implemented in a major German city. Including all information in one meta-analytical synthesis yields a standardized effect size estimate of Cohen's h = 0.12, documenting a small but reliable effect of PTP interventions. When implementing a PTP like one of those analyzed in this paper, in other words, we can expect an average reduction of the car modal split share of about 5 percentage points. We close by discussing the implications of our results for future PTP evaluation studies and the dispute about what kind of empirical evidence really matters when evaluating the effectiveness of PTP measures. © 2017 Elsevier Ltd


Fischer W.,FH Bielefeld
Frontiers of Physics in China | Year: 2011

The diffusive scaling is studied based on pomeron loop equations in the fixed coupling case. At Y ≫ YDS, the gluon number fluctuations become important, the geometric scaling is replaced by the diffusive scaling. In the diffusive scaling regime, the deep inelastic scattering (DIS) total scattering cross-section is a function of single variable [1/(r2Qs2(x))]/√DY. We show that the deep inelastic scattering experimental data lie on a single curve, which seems to indicate the existence of the diffusive scaling phenomenology in the deep inelastic scattering. © 2011 Higher Education Press and Springer-Verlag Berlin Heidelberg.


Hamelmann F.U.,FH Bielefeld
Journal of Physics: Conference Series | Year: 2014

This paper show results from the development of transparent conductive oxides (TCO's) on large areas for the use as front electrode in thin film silicon solar modules. It is focused on two types of zinc oxide, which are cheap to produce and scalable to a substrate size up to 6 m2. Low pressure CVD with temperatures below 200°C can be used for the deposition of boron doped ZnO with a native surface texture for good light scattering, while sputtered aluminum doped ZnO needs a post deposition treatment in an acid bath for a rough surface. The paper presents optical and electrical characterization of large area samples, and also results about long term stability of the ZnO samples with respect to the so called TCO corrosion.


Weicht J.A.,FH Bielefeld | Hamelmann F.U.,FH Bielefeld | Behrens G.,FH Bielefeld
Journal of Physics: Conference Series | Year: 2014

For analyzing the long-term behavior of thin film a-Si/μc-Si photovoltaic modules, it is important to observe the light-induced degradation (LID) in dependence of the temperature for the parameters of the one-diode model for solar cells. According to the IEC 61646 standard, the impact of LID on module parameters of these thin film cells is determined at a constant temperature of 50°C with an irradiation of 1000 W/m2 at open circuit conditions. Previous papers examined the LID of thin film a-Si cells with different temperatures and some others are about a-Si/μc-Si. In these previous papers not all parameters of the one-diode model are examined. We observed the serial resistance (Rs), parallel resistance (Rp), short circuit current (Isc), open circuit voltage (Uoc), the maximum power point (MPP: Umpp, Impp and Pmpp) and the diode factor (n). Since the main reason for the LID of silicon-based thin films is the Staebler Wronski effect in the a-Si part of the cell, the temperature dependence of the healing of defects for all parameters of the one-diode model is also taken into account. We are also measuring modules with different kind of transparent conductive oxides: In a-Si thin film solar cells fluorine-doped tin oxide (FTO) is used and for thin film solar cells of a-Si/μc-Si boron- doped zinc oxide is used. In our work we describe an approach for transferring the parameters of a one-diode model for tandem thin film solar cells into the one-diode model for each part of the solar cell. The measurement of degradation and regeneration at higher temperatures is the necessary base for optimization of the different silicon-based thin films in warm hot climate.


Pross S.,FH Bielefeld
Journal of integrative bioinformatics | Year: 2011

Biological systems are often very complex so that an appropriate formalism is needed for modeling their behavior. Hybrid Petri Nets, consisting of time-discrete Petri Net elements as well as continuous ones, have proven to be ideal for this task. Therefore, a new Petri Net library was implemented based on the object-oriented modeling language Modelica which allows the modeling of discrete, stochastic and continuous Petri Net elements by differential, algebraic and discrete equations. An appropriate Modelica-tool performs the hybrid simulation with discrete events and the solution of continuous differential equations. A special sub-library contains so-called wrappers for specific reactions to simplify the modeling process. The Modelica-models can be connected to Simulink-models for parameter optimization, sensitivity analysis and stochastic simulation in Matlab. The present paper illustrates the implementation of the Petri Net component models, their usage within the modeling process and the coupling between the Modelica-tool Dymola and Matlab/Simulink. The application is demonstrated by modeling the metabolism of Chinese Hamster Ovary Cells.


Thiels C.,FH Bielefeld
British Journal of Psychiatry | Year: 2013

In mid-19th-century Germany the conviction that 'mental disease is brain disease' was accompanied by a call for social reform in psychiatry. During neurology training, future psychiatrists often encounter patients with mental disorders rarely seen in psychiatric departments and learn how to avoid misdiagnosing brain diseases as mental disorders.


Tamm U.,FH Bielefeld
2015 Information Theory and Applications Workshop, ITA 2015 - Conference Proceedings | Year: 2015

Integer codes correcting a single error in the maximum metric are considered. This corresponds to a packing of tori by cubes. For an asymmetric error of size one these cubes have side length 2 and the problem can be shown to be equivalent to finding zero-error codes for cycles in the sense of Shannon and Lovasz. For side length greater 3 the equivalence of single error correcting integer codes and zero-error codes does not hold any more. © 2015 IEEE.

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