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Fahrnberger G.,University of Hagen
Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) | Year: 2014

Many companies have thought about using external hosting solutions. Cloud computing as such a solution attracts prospective users who want to avoid initial costs and standing expenses with the underlying pay-as-you-use model. The outsourcing of sensitive information implies security risks, like eavesdropping and sabotage, for them as soon as they pass any unconfident area. If an outhouse hosting solution serves as data storage only, then an end-to-end cryptosystem without the necessity of having homomorphic properties comes up with the answer. Moreover, secure computations on the encrypted data need the use of more complex cryptosystems. SecureString 1.0 [3] and SecureString 2.0 [4] were proposed as such complex cryptosystems that focus on computing on encrypted character strings in untrustworthy environments (like clouds). While SecureString 1.0 offered a too inflexible approach, SecureString 2.0 as its improvement was introduced textually at a high level only so far. This paper contributes to foster the understanding of SecureString 2.0 by providing performance analysis for its supported operations plus formal definitions, theorems and proofs. © 2014 Springer International Publishing Switzerland.

Bortfeldt A.,University of Hagen | Homberger J.,Stuttgart University of Applied Sciences
Computers and Operations Research | Year: 2013

The Vehicle Routing and Loading Problem (VRLP) results by combining vehicle routing, possibly with time windows, and three-dimensional loading. Some packing constraints of high practical relevance, among them an unloading sequence constraint and a support constraint, are also part of the VRLP. Different formulations of the VRLP are considered and the issue is discussed under which circumstances routing and packing should be tackled as a combined task. A two-stage heuristic is presented following a packing first, routing second approach, i.e. the packing of goods and the routing of vehicles is done in two strictly separated stages. High quality results are achieved in short computation times for the 46 VRLP instances recently introduced by Moura and Oliveira. Moreover 120 new large benchmark instances including up to 1000 customers and 50,000 boxes are introduced and results for these instances are also reported. © 2012 Elsevier Ltd.

Weihrauch K.,University of Hagen
Logical Methods in Computer Science | Year: 2013

This article continues the study of computable elementary topology started by the author and T. Grubba in 2009 and extends the author's 2010 study of axioms of computable separation. Several computable T3- and Tychonoff separation axioms are introduced and their logical relation is investigated. A number of implications between these axioms are proved and several implications are excluded by counter examples, however, many questions have not yet been answered. Known results on computable metrization of T3-spaces from M. Schr̈oder (1998) and T. Grubba, M. Schr̈oder and the author (2007) are proved under uniform assumptions and with partly simpler proofs, in particular, the theorem that every computably regular computable topological space with non-empty base elements can be embedded into a computable metric space. Most of the computable separation axioms remain true for finite products of spaces. © K. Weihrauch.

Forster F.,University of Hagen | Bortfeldt A.,University of Hagen
Computers and Operations Research | Year: 2012

In the container relocation problem (CRP) n items are given that belong to G different item groups (g=1,..,G). The items are piled up in up to S stacks with a maximum stack height H. A move can either shift one item from the top of a stack to the top of another one (relocation) or pick an item from the top of a stack and entirely remove it (remove). A move of the latter type is only feasible if the group index of the item is minimum compared to all remaining items in all stacks. A move sequence of minimum length has to be determined that removes all items from the stacks. The CRP occurs frequently in container terminals of seaports. It has to be solved when containers, piled up in stacks, need to be transported to a ship or to trucks in a predefined sequence. This article presents a heuristic tree search procedure for the CRP. The procedure is compared to all known solution approaches for the CRP and turns out to be very competitive. © 2011 Elsevier Ltd.

Bortfeldt A.,University of Hagen
Computers and Operations Research | Year: 2012

The capacitated vehicle routing problem with three-dimensional loading constraints combines capacitated vehicle routing and three-dimensional loading with additional packing constraints concerning, for example, unloading operations. An efficient hybrid algorithm including a tabu search algorithm for routing and a tree search algorithm for loading is introduced. Computational results are presented for all publicly available test instances. Most of the best solutions previously reported in literature have been improved while the computational effort is drastically reduced compared to other methods. © 2011 Elsevier Ltd.

Huba M.,Slovak University of Technology in Bratislava | Huba M.,University of Hagen
Journal of Process Control | Year: 2013

This paper analyses the optimal nominal tuning of a new modification of predictive disturbance observer (PDO) based filtered PI control (PDO FPI) applied to a first order plus dead time (FOPDT) plant with exactly known parameters. The impacts of applied filters on optimal controller tuning and on achievable closed loop performance are evaluated first of all. The limits of achievable performance are compared with those of traditional two degree of freedom (2DOF) PI control, with both controllers tuned by the multiple real dominant pole method. This comparison shows the potential of PDO FPI control to improve tracking and regulatory dynamics significantly, permitting the Pareto-like servo/regulator trade-off of 2DOF PI control to be removed. Two PDO FPI tuning approaches are proposed, allowing optimal filter degree and time constants to be evaluated. The first tuning scenario considers optimization of closed loop performance expressed in terms of the Integral of the Absolute Error (IAE) weighted alternatively by the relative total variance TV1 of the control signal. This is carried out by changing the filter order n under the constraint that a constant position of the dominant closed loop pole is maintained. This keeps the dynamics of the setpoint step responses almost unchanged. In the second tuning scenario the optimization is carried out under a constraint on constant speed of disturbance step responses. All the main results are then numerically checked for the integral first order plant with dead time by the performance portrait (PP) method. The analysis presented here shows that the new PDO FPI structure substantially enriches the spectrum of controllers applicable to simple control tasks. © 2013 Elsevier Ltd.

Huba M.,Slovak University of Technology in Bratislava | Huba M.,University of Hagen
Journal of Process Control | Year: 2013

This paper considers PI controller tuning for the Integral Plus Dead Time (IPDT) plant subject to constraints on tolerable deviations from ideal shapes and guaranteeing minimal combined IAE (Integral of Absolute Error) measure composed of weighted IAE values of the setpoint and disturbance step responses. As the ideal responses at the plant output, monotonic (MO) transients are chosen. This implies one-pulse (1P) responses consisting of two monotonic intervals at the plant input. Optimal nominal tunings for the most important situations regarding the servo/regulation trade-off are determined by the newly developed Matlab/Simulink tool based on the performance portrait (PP) method. Generated results confirm Pareto-like limits of performance achievable under PI control and are used in classifying traditional tuning approaches into the setpoint and disturbance oriented ones. Principles of robust PP based tuning are briefly illustrated and conditions of invariance of the closed loop performance against the dead time uncertainty are formulated and checked by simulation.© 2013 Elsevier Ltd. All rights reserved.

Fahrnberger G.,University of Hagen
Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) | Year: 2013

Many organizations today are turning towards the contemporary concept of Cloud Computing, which entails the transfer of their applications (processing both sensitive and non-sensitive data) into online repositories or clouds. Encryption schemes based on homomorphic functions can provide the technology required to protect the confidentiality of this data. Their limitation, however, lies in their ability to process numeric values only. This paper, therefore, is focused on proposing a new encryption scheme relying on character string splitting and ciphering with additional components on the user and cloud side to support querying and modifying character string functions. Ultimately, what eventuates is an environment where a cloud is unaware of the contents of any input character strings, and of the output data during processing. © 2013 Springer-Verlag Berlin Heidelberg.

Imec and University of Hagen | Date: 2010-01-12

The present invention is related to a photovoltaic device, the device comprising a first layer of a first semiconductor material of a first conductivity type, a second layer of a second semiconductor material of the opposite conductivity type of the first layer, and a third layer of a third porous semiconductor material situated between the first layer and the second layer. The present invention also provides a method for producing the photovoltaic device.

News Article | February 15, 2017
Site: www.newscientist.com

Ever felt hungry and angry at the same time? There’s evidence that “hanger” is a real phenomenon, one that can affect your work and relationships. The main reason we become more irritable when hungry is because our blood glucose level drops. This can make it difficult for us to concentrate, and more likely to snap at those around us. Low blood sugar also triggers the release of stress-related hormones like cortisol and adrenaline, as well as a chemical called neuropeptide Y, which has been found to make people behave more aggressively towards those around them. This can all have an alarming effect on how you feel about other people – even those you love. A classic study of married couples asked them to stick pins into “voodoo dolls” that represented their loved ones, to reflect how angry they felt towards them. The volunteers then competed against their spouse in a game, in which the winner could blast loud noise through the loser’s headphones. The researchers tracked the participants’ blood glucose levels throughout. They found that when people had lower sugar levels, the longer the blasts of unpleasant noise they subjected their spouse to, and the more pins they stuck into their dolls. But while being hungry really does change your behaviour, the effects of hanger have sometimes been overstated. One study that attracted attention a few years ago found that judges are less likely to set lenient sentences the closer it gets to lunch. However, the findings from this study have never been replicated, and a newer analysis by Andreas Glöckner at the University of Hagen, in Germany, has suggested an alternative explanation. Harsher sentences may in fact be more likely towards the end of the morning because judges schedule simpler cases for this time. More complicated, lengthier cases carry a risk of running over into their lunch break. “Simulations show that the direct causal effects of eating on favourable rulings is overestimated by at least 23 per cent,” says Glöckner. We won’t know for certain what causes the nasty judge effect until more research is done. But one thing is clear – it certainly isn’t advisable to make important decisions on an empty stomach.

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