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In this paper, a novel feature-based sampling strategy for nonlinear Model Predictive Path Integral (MPPI) control is presented. Using the MPPI approach, the optimal feedback control is calculated by solving a stochastic optimal control (OCP) problem online by evaluating the weighted inference of sampled stochastic trajectories. While the MPPI algorithm can be excellently parallelized, the closed-loop performance strongly depends on the information quality of the sampled trajectories. To draw samples, a proposal density is used. The solver’s and thus, the controller’s performance is of high quality if the sampled trajectories drawn from this proposal density are located in low-cost regions of state-space. In classical MPPI control, the explored state-space is strongly constrained by assumptions that refer to the control value’s covariance matrix, which are necessary for transforming the stochastic Hamilton–Jacobi–Bellman (HJB) equation into a linear second-order partial differential equation. To achieve excellent performance even with discontinuous cost functions, in this novel approach, knowledge-based features are introduced to constitute the proposal density and thus the low-cost region of state-space for exploration. This paper addresses the question of how the performance of the MPPI algorithm can be improved using a feature-based mixture of base densities. Furthermore, the developed algorithm is applied to an autonomous vessel that follows a track and concurrently avoids collisions using an emergency braking feature. Therefore, the presented feature-based MPPI algorithm is applied and analyzed in both simulation and full-scale experiments.
Comparison of Data-Driven Modeling and Identification Approaches for a Self-Balancing Vehicle
(2023)
This paper gives a systematic comparison of different state–of–the–art modeling approaches and the corresponding parameter identification processes for a self–balancing vehicle. In detail, a nonlinear grey box model, its extension to consider friction effects, a parametric black box model based on regression neural networks, and a hybrid approach are presented. The parameters of the models are identified by solving a nonlinear least squares problem. The training, validation, and test datasets are collected in full–scale experiments using a self–balancing vehicle. The performance of the different models used for ego–motion prediction are compared in full–scale scenarios, as well. The investigated model architectures can be used to improve both, simulation environments and model–based controller design. This paper shows the upsides and downsides arising from using the different modeling approaches. Videos showing the self–balancing vehicle in action are available at: https://tinyurl.com/mvn8j7vf22nd
This paper presents the swinging up and stabilization control of a Furuta pendulum using the recently published nonlinear Model Predictive Path Integral (MPPI) approach. This algorithm is based on a path integral over stochastic trajectories and can be parallelized easily. The controller parameters are tuned offline regarding the nonlinear system dynamics and simulations. Constraints in terms of state and input are taken into account in the cost function. The presented approach sequentially computes an optimal control sequence that minimizes this optimal control problem online. The control strategy has been tested in full-scale experiments using a pendulum prototype. The investigated MPPI controller has demonstrated excellent performance in simulation for the swinging up and stabilizing task. In order to also achieve outstanding performance in a real-world experiment using a controller with limited computing power, a linear quadratic controller (LQR) is designed for the stabilization task. In this paper, the determination of the controller parameters for the MPPI algorithm is described in detail. Further, a discussion treats the advantages of the nonlinear MPPI control.
Docking Control of a Fully-Actuated Autonomous Vessel using Model Predictive Path Integral Control
(2022)
This paper presents the docking control of an autonomous vessel using the nonlinear Model Predictive Path Integral (MPPI) approach. This algorithm is based on a path integral over stochastic trajectories and can be parallelized easily. The controller parameters are tuned offline using knowledge of the system and simulations, including nonlinear state and disturbance observer. The cost function implicitly contains information regarding the surrounding of the docking position. This approach allows continuous optimization of the trajectory with respect to the system state, disturbance state and actuator dynamics. The control strategy has been tested in full-scale experiments using the solar research vessel Solgenia. The investigated MPPI controller has demonstrated excellent performance in both, simulation and real-world experiments. This paper addresses the question of how the MPPI algorithm can be applied to dock a fully-actuated vessel and what benefits its application achieves.
This paper compares novel methods to efficiently include input constraints using the nonlinear Model Predictive Path Integral (MPPI) approach. The MPPI algorithm solves stochastic optimal control problems and is based on sampled trajectories. MPPI results from the physical path integral framework. Sample-based algorithms are characterized by the fact that they can be computed in parallel and offer the possibility to handle discontinuous dynamics and cost functions. However, using standard MPPI the input costs in the Lagrange term have to be chosen quadratic. This fact is unfavorable for various real applications. Further, in standard nonlinear model predictive control (NMPC) approaches hard box constraints on the control input trajectory can be treated directly. In this contribution, novel architectures based on integrator action are compared. The investigated input constraint MPPI controllers were tested on an autonomous self-balancing vehicle. Therefore both, simulation and real-world experiments are presented. This paper addresses the question of how the MPPI algorithm can be further developed to consider input box constraints. Videos of the self-balancing vehicle are available at: https: https://tinyurl.com/mvn8j7vf
Recently published nonlinear model-based control
approaches achieve impressive performances in complex real-
world applications. However, due to model-plant mismatches
and unforeseen disturbances, the model-based controller’s per-
formance is limited in full-scale applications. In most applica-
tions, low-level control loops mitigate the model-plant mismatch
and the sensitivity to disturbances. But what is the influence
of these low-level control loops? In this paper, we present
the model predictive path integral (MPPI) control of a self-
balancing vehicle and investigate the influence of subordinate
control loops on closed-loop performance. Therefore, simulation
and full-scale experiments are performed and analyzed. Subor-
dinate control loops empower the MPPI controller because they
dampen the influence of disturbances, and thus improve the
model’s accuracy. This is the basis for the successful application
of model-based control approaches in real-world systems. All
in all, a model is used to design a low-level controller, then
its closed-loop behavior is determined, and this model is used
within the superimposed MPPI control loop – modeling for
control and vice versa.
The problem of vessel collisions or near-collision situations on sea, often caused by human error due to incomplete or overwhelming information, is becoming more and more important with rising maritime traffic. Approaches to supply navigators and Vessel Traffic Services with expert knowledge and suggest trajectories for all vessels to avoid collisions, are often aimed at situations where a single planner guides all vessels with perfect information. In contrast, we suggest a two-part procedure which plans trajectories using a specialised A* and negotiates trajectories until a solution is found, which is acceptable for all vessels. The solution obeys collision avoidance rules, includes a dynamic model of all vessels and negotiates trajectories to optimise globally without a global planner and extensive information disclosure. The procedure combines all components necessary to solve a multi-vessel encounter and is tested currently in simulation and on several test beds. The first results show a fast converging optimisation process which after a few negotiation rounds already produce feasible, collision free trajectories.
Growth is a key indicator of the prosperity of an economy. In today's Germany the " Gründerzeit " still describes a period of enormous economic growth. Factors that lead to growth haven't been investigated in the context of the different life cycle stages of early-stage technology ventures so far. This paper proposes a model of early-stage ventures' growth based on factors. From a theoretical angle, we look at the business from the market-based view (MBV) and the resource-based view (RBV) on strategy in the longitudinal perspective of the business life cycle. With this view we get to know what are the stage specific needs and processes of new technology based ventures in order to provide appropriate support. We tested different potential growth indicators for the model with a questionnaire-based survey which was answered by 68 high-tech entrepreneurs. The results suggest that growth factors are stage specific in their relevance. While leading to growth in one stage, certain factors evince no or even negative influence on growth in other stages. Moreover, RBV factors as seen more relevant for the growth than the MBV factors. Further research requires a large and representative population to validate the results. Keywords:-growth factors, early-stage ventures, market-based view, resources based view.
Business units are increasingly able to fuel the transformation that digitalization demands of organizations. Thereby, they can implement Shadow IT (SIT) without involving a central IT department to create flexible and innovative solutions. Self-reinforcing effects lead to an intertwinement of SIT with the organization. As a result, high complexities, redundancies, and sometimes even lock-ins occur. IT Integration suggests itself to meet these challenges. However, it can also eliminate the benefits that SIT presents. To help organizations in this area of conflict, we are conducting a literature review including a systematic search and an analysis from a systemic viewpoint using path dependency and switching costs. Our resulting conceptual framework for SIT integration drawbacks classifies the drawbacks into three dimensions. The first dimension consists of switching costs that account for the financial, procedural, and emotional drawbacks and the drawbacks from a loss of SIT benefits. The second dimension includes organizational, technical, and level-spanning criteria. The third dimension classifies the drawbacks into the global level, the local level, and the interaction between them. We contribute to the scientific discussion by introducing a systemic viewpoint to the research on shadow IT. Practitioners can use the presented criteria to collect evidence to reach an IT integration decision.
Organizations deploy a plethora of information technology (IT) systems. Various types of enterprise systems (ES) may coexist with the shadow IT systems (SITS) implemented by individual business units without the involvement of the IT department. The associated redundancy of SITS and ES suggests their integration. After integration, however, organization may find it challenging to retain the flexibility and innovation that the development of SITS offers the business. In this study, we conduct a literature review on IT systems integration. This review and the specific characteristics of SITS then serve to define SITS integration, derive guidelines for the integration decision, the phases preceding and following integration, and the integration process itself. SITS and ES integration can profit from existing knowledge of integration benefits, costs, and of the available technologies. Our study offers IT decision makers an insight into the specifics of SITS integration, and provides a basis for future SITS research.
Shadow information technology systems (SITS) coexist with formal enterprise systems in organisations. SITS pose risks but also increase flexibility of business units. Practice shows that SITS emerge, despite that Enterprise Architecture Management (EAM) aims at controling all IT systems in an organization. Studies acknowledge this problem in general. However, they neither show the specific influencing areas of SITS nor provide approaches to address them. To close this gap, we use a literature review to analyse examples of practical SITS and their interference with EAM concerns. Thus, we find that they hinder especially transparency, reduction of EA complexity and governance. Research has focused on achieving transparency, governing the evolution of the EA but lacks strategies for reducing complexity. This study contributes to research and practice by uncovering the main influencing areas of SITS on EAM, as well as by laying a foundation for future research on this topic.
Business units are increasingly able to fuel the transformation that digitalization demands of organizations. Thereby, they implement Shadow IT (SIT) to create flexible and innovative solutions. However, the individual implementation of SIT leads to high complexities and redundancies. Integration suggests itself to meet these challenges but can also eliminate the described benefits. In this emergent research, we develop propositions for a conceptual decision framework, that balances the benefits and drawbacks of an integration of SIT using a literature review as well as a multiple-case study. We thereby integrate the perspective of the overall organization as well as the specific business unit. We then pose six propositions regarding SIT integration that will serve to evaluate our conceptual framework in future research.
ERP systems integrate a major part of all business processes and organizations include them in their IT service management. Besides these formal systems, there are additional systems that are rather stand-alone and not included in the IT management tasks. These so-called ‘shadow systems’ also support business processes but hinder a high enterprise integration. Shadow systems appear during their explicit detection or during software maintenance projects such as enhancements or release changes of enterprise systems. Organizations then have to decide if and to what extent they integrate the identified shadow systems into their ERP systems. For this decision, organizations have to compare the capabilities of each identified shadow system with their ERP systems. Based on multiple-case studies, we provide a dependency approach to enable their comparison. We derive categories for different stages of the dependency and base insights into integration possibilities on these stages. Our results show that 64% of the shadow systems in our case studies are related to ERP systems. This means that they share parts or all of their data and/or functionality with the ERP system. Our research contributes to the field of integration as well as to the discussion about shadow systems.
This paper presents the goals, service design approach, and the results of the project “Accessible Tourism around Lake Constance”, which is currently run by different universities, industrial partners and selected hotels in Switzerland, Germany and Austria. In the 1st phase, interviews with different persons with disabilities and elderly persons have been conducted to identify the barriers and pains faced by tourists who want to spend their holidays in the region of Lake Constance as well as possible assistive technologies that help to overcome these barriers. The analysis of the interviews shows that one third of the pains and barriers are due to missing, insufficient, wrong or inaccessible information about the
accessibility of the accommodation, surroundings, and points of interests during the planning phase of the holidays. Digital assistive technologies hence play a
major role in bridging this information gap. In the 2nd phase so-called Hotel-Living-Labs (HLL) have been established where the identified assistive technologies
can be evaluated. Based on these HLLs an overall service for accessible holidays has been designed and developed. In the last phase, this service has been implemented
based on the HLLs as well as the identified assistive technologies and is currently field tested with tourists with disabilities from the three participated countries.
The main challenge in Bayesian models is to determine the posterior for the model parameters. Already, in models with only one or few parameters, the analytical posterior can only be determined in special settings. In Bayesian neural networks, variational inference is widely used to approximate difficult-to-compute posteriors by variational distributions. Usually, Gaussians are used as variational distributions (Gaussian-VI) which limits the quality of the approximation due to their limited flexibility. Transformation models on the other hand are flexible enough to fit any distribution. Here we present transformation model-based variational inference (TM-VI) and demonstrate that it allows to accurately approximate complex posteriors in models with one parameter and also works in a mean-field fashion for multi-parameter models like neural networks.
Poster
Pitting susceptibility of metastable austenitic stainless steels as a function of surface conditions
(2019)
Fachvortrag auf der 10th International European Stainless Steel Conference and 6th European Duplex Stainless Steel Conference (ESSC & DUPLEX 2019), 30.09. – 02.10.2019, Vienna, Austria
Fachvortrag auf dem Swiss Tribology Symposium, 12.11.2019, Hightechzentrum Aargau, Brugg, Schweiz
The electrochemical behavior for different surface conditions and different degrees of deformation of metastable austenitic stainless steel AISI 304 UNS S30400 were studied using critical pitting potential and electrochemical noise measurements. The influence on corrosion resistance by using different abrasives (silicon carbide and corundum) for surface finish by grinding is illustrated. For the characterization of local defects and surface topography, scanning electron microscopy (SEM) and tactile measurements were used. An inverse correlation between occurrence of local defects on the surface and critical pitting potential was found by using image processing. Therefore, gray scale values of different surfaces were compared. The influence of mass content of α'-martensite on the corrosion resistance is shown by comparing different qualities of surface finish. For smooth machined surfaces it can be shown that an increasing numbers of strain induced martensite is decreasing the corrosion resistance lightly. For low abrasive machining an inverse correlation between the critical pitting potential and surface roughness is given. However, for higher abrasive machining parameters, this correlation could not be found.
Pitting susceptibility of metastable austenitic stainless steels as a function of surface conditions
(2019)
The influence of surface roughness and local defects on pitting susceptibility of type 304 (UNS S30400) and type 301 (UNS S30100) in chloride solution were investigated. Because the mechanical properties can be regarded as decisive for the achieved surface quality, different properties of the base material were obtained by cold rolling the metastable austenites. This was done before the surfaces were finished. Therefor the surfaces were treated by different grinding parameters to generate different surface conditions and different defects. As a reference, different standardised surface finishes were used.
By using and comparing different methods for the characterization of surface roughness and surface texture, it is possible to find a relationship between the quantity and characteristics of local defects on the one hand and pitting susceptibility on the other hand. For the machining parameters used, a ranking of the influencing factors on the corrosion resistance achieved could be determined.
The automated application of software-based solutions for estimating the pitting susceptibility of machined surfaces and components will be discussed using concrete examples.
Botswana is a country in southern Africa with rich mineral resources, which has built its economy on mining. Due to challenges in the upcoming years caused by climate and demographic change, it aims to move away from a resource-based economy to a knowledge-based economy in the long term. In order to support the
process, the Maun Science Park, a centre for research and development is planned to be created in Maun, a town on the edge of the Okavango Delta. The project is initiated by the “International Resilience and Sustainability Partnership” (inRES), a non-governmental organization. The project is currently in the initiation phase.
The purpose of this thesis is to determine a cost framework with exemplary developer calculation and sensitivity analysis for the Maun Science Park Project in Botswana. Therefor, a source research was performed in a first step. Based on this, interviews were conducted with members of the inRES. Based on the data
obtained and further assumptions, a cost framework for the different project phases of the MSP project was established. Subsequently, a developer calculation
was exemplarily carried out on the basis of the project phase 2 and a sensitivity analysis was performed.
During the interviews, data was collected on the different project phases. It became clear that the interview partners had partly inconsistent perceptions
about different project phases. The calculation can be used as a basis for further calculation at the time of concretization of the planning data.
This research project has been awarded as part of the research competition organized by Connect2Recover, which is a global initiative by the International Telecommunication Union (ITU) with the priority of reinforcing and strengthening the digital infrastructure and ecosystems of developing countries. Carried out by an international and transdisciplinary research consortium, the project sets out to analyze the prospects of digital federation and data sharing within the context of Botswana. Considering the country’s stage of economic and digital development, the project team identified Botswana’s smallholder agricultural sector as the most important area of digital transformation given the development need of the country’s primary sector.
Derived from semi-structured interviews, a focus group, as well as secondary research, the project team developed a digital transformation roadmap based on three development stages: (a) crowdfarming pilot, (b) crowdfarming marketplace, and (c) digital ecosystem for smallholder agriculture. Based on a detailed review of Botswana’s smallholder agriculture and the government’s digitalization strategy, the report envisions each phase, especially the pilot project, in terms of a minimal viable product. This is to consider the low level of digital penetration of Botswana’s primary sector, while providing an incentive to connect smallholders with consumers, traders, and retailers.
The project team has been successful in receiving commitment from actual smallholder farmers, the farmer association and government, as well as support for the idea of developing a crowdfarming marketplace as a novel production model and, eventually, a digital agriculture ecosystem for smallholder farmers, livestock producers, and agricultural technology companies and start-ups. The report is a proposal for a phase-one pilot project with the objective to advance smallholder agribusiness in Botswana.
There was hardly another development which influenced the life on earth as much as the development of the communication technology in the last decades. The advantages of mobile communication brought the branch enormeous growth rates. However, for some years an increasing saturation has been looming in the markets especially in the developed nations and new marketing strategies are needed in order for companies to be able to distance themselves from their competitors. Against the background of this situation ICT companies all over the world started to look for new growth opportunities and found them in the so called “emerging markets” of the developing nations. To exploit this potential will be the one central challenge for the mobile communication industry for the next years. With this book I want to direct the gaze of all readers towards these markets which hold an enormous potential for the whole industry. Furthermore, I want to introduce some generic strategic approaches which can help firms to successfully participate in these markets.
Today we live in a world that is characterized by a constantly changing environment. During the last decade, this highly volatile environment forced companies to implement strategies that identify, track and minimise the risks that entrepreneurial activity entails. Unfortunately, risks only account for a part of the insecurity that is connected to future events. The other and not inferior part of this insecurity consists of possible positive developments – so called opportunities. Due to this reason in economic science and in practice the opinion aggravates that solely focusing on risks is not sufficient to fully exploit the potential of markets and companies. In the 16th century, the Dutch Renaissance humanist scholar Desiderius Erasmus (1466-1536) said: “It is well known that among the blind, the one-eyed man is king.” Transferring this statement in the context of Risk Management, the conclusion becomes apparent: The environmental uncertainty that surrounds entrepreneurial actions includes both opportunities and threats. As commonly practiced though, Risk Management tools only address threats. While this approach is surely better than doing nothing, it still can be seen as a major weakness of the traditional Risk Management approach. Nevertheless, in terms of Erasmus, this approach represents the one-eyed man when compared with the blind. To continue this metaphor a little further, it is possible to conclude that the one-eyed king could be easily relieved of his crown by introducing an emperor who is able to see with two eyes. Although this problem is well known in economic science, up to know only little scientific focus was shifted towards the systematic identification and management of opportunities. In fact, most of the present literature focuses on the identification and handling of risk and even though much of the recently published literature captures the term opportunity, none of it proposes a solid idea of following up on the approach. Still, facing the defiances of the present economic environment, it is not sufficient for companies to focus their attention on reducing risks. Instead, it is imperative to deal with the subject of Opportunity Management as well. With this paper, I want to undermine the importance of Opportunity Management for all companies independently of their size or branch that they operate in. Thereby, this paper is dedicated to all managers who strive to improve the professionalism of their companies in terms of strategic thinking. Furthermore, I hope that this paper can facilitate a practical implementation of a working Opportunity Management System.
The exposure to the light has a great influence on human beings in their everyday life. Various lighting sources produce light that reaches the human eye and influences a rhythmic release of melatonin hormone, that is a sleep promoting factor.
Since the development of new technologies provides more control over illuminance, this work uses an IoT based lighting system to set up dim and bright scenarios. A small study has been performed on the influence of illuminance on sleep latency. The system consists of different light bulbs, sensors and a central bridge which are interconnected like a mesh network. Also, a mobile app has been developed, that allows to adjust the lighting in various rooms. With the help of a ferro-electret sensor, like applied in sleep monitoring systems, a subject’s sleep was monitored. The sensor is placed below the mattress and it collects data, which is stored and processed in a cloud or in other alternative locations.
The research was conducted on healthy young subjects after being previously exposed to the preconfigured illuminance for at least three hours before bedtime. The results indicate correlation between sleep onset latency and exposure to different illuminance before bedtime. In a dimmed environment, the subject fell asleep in average 28% faster compared to the brighter environment.
AbstractSanctions encompass a wide set of policy instruments restricting cross‐border economic activities. In this paper, we study how different types of sanctions affect the export behavior of firms to the targeted countries. We combine Danish register data, including information on firm‐destination‐specific exports, with information on sanctions imposed by Denmark from the Global Sanctions Database. Our data allow us to study firms' export behavior in 62 sanctioned countries, amounting to a total of 453 country‐years with sanctions over the period 2000–2015. Methodologically, we apply a two‐stage estimation strategy to properly account for multilateral resistance terms. We find that, on average, sanctions lead to a significant reduction in firms' destination‐specific exports and a significant increase in firms' probability to exit the destination. Next, we study heterogeneity in the effects of sanctions across (i) sanction types and sanction packages, (ii) the objectives of sanctions, and (iii) countries subject to sanctions. Results confirm that the effects of sanctions on firms' export behavior vary considerably across these three dimensions.
One important skill for engineers is the ability of optimizing their experiments. On their job they will often spend a lot more time designing and improving an experimental setup compared to running the actual experiment itself. Is it possible to teach this complex task in physics labs? A method for reaching this goal is proposed an example is given and discussed.
RELOAD
(2015)
Vortrag auf dem Doktorandenkolloquium des Kooperativen Promotionskollegs der HTWG, 09.07.2015
When designing drying processes for sensitive biological foodstuffs like fruit or vegetables, energy and time efficiency as well as product quality are gaining more and more importance. These all are greatly influenced by the different drying parameters (e.g. air temperature, air velocity and dew point temperature) in the process. In sterilization of food products the cooking value is widely used as a cross-link between these parameters. In a similar way, the so-called cumulated thermal load (CTL) was introduced for drying processes. This was possible because most quality changes mainly depend on drying air temperature and drying time. In a first approach, the CTL was therefore defined as the time integral of the surface temperature of agricultural products. When conducting experiments with mangoes and pineapples, however, it was found that the CTL as it was used had to be adjusted to a more practical form. So the definition of the CTL was improved and the behaviour of the adjusted CTL (CTLad) was investigated in the drying of pineapples and mangoes. On the basis of these experiments and the work that had been done on the cooking value, it was found, that more optimization on the CTLad had to be done to be able to compare a great variety of different products as well as different quality parameters.
In modern fruit processing technology, non-destructive quality measuring techniques aresought for determining and controlling changes in the optical, structural, and chemical properties of theproducts. In this context, changes inside the product can be measured during processing. Especiallyfor industrial use, fast, precise, but robust methods are particularly important to obtain high-qualityproducts. In this work, a newly developed multi-spectral imaging system was implemented andadapted for drying processes. Further it was investigated if the system could be used to link changesin the surface spectral reflectance during mango drying with changes in moisture content andcontents of chemical components. This was achieved by recovering the spectral reflectance frommulti-spectral image data and comparing the spectral changes with changes of the total soluble solids(TSS), pH-value and the relative moisture contentxwbof the products. In a first step, the camera wasmodified to be used in drying, then the changes in the spectra and quality criteria during mangodrying were measured. For this, mango slices were dried at air temperatures of 40–80◦C and relativeair humidities of 5%–30%. Samples were analyzed and pictures were taken with the multi-spectralimaging system. The quality criteria were then predicted from spectral data. It could be shown thatthe newly developed multi-spectral imaging system can be used for quality control in fruit drying.There are strong indications as well, that it can be employed for the prediction of chemical qualitycriteria of mangoes during drying. This way, quality changes can be monitored inline during theprocess using only one single measuring device.
Efficient privacy-preserving configurationless service discovery supporting multi-link networks
(2017)
Data is the pollution problem of the information age, and protecting privacy is the environmental challenge — this quotation from Bruce Schneier laconically illustrates the importance of protecting privacy. Protecting privacy — as well as protecting our planet — is fundamental for humankind. Privacy is a basic human right, stated in the 12th article of the United Nations’ Universal Declaration of Human Rights. The necessity to protect human rights is unquestionable. Nothing ever threatened privacy on a scale comparable to today’s interconnected computers. Ranging from small sensors over smart phones and notebooks to large compute clusters, they collect, generate and evaluate vast amounts of data. Often, this data is distributed via the network, not only rendering it accessible to addressees, but also — if not properly secured — to malevolent parties. Like a toxic gas, this data billows through networks and suffocates privacy. This thesis takes on the challenge of protecting privacy in the area of configurationless service discovery. Configurationless service discovery is a basis for user-friendly applications. It brings great benefits, allowing the configurationless network setup for various kinds of applications; e.g. for communicating, sharing documents and collaborating, or using infrastructure devices like printers. However, while today’s various protocols provide some means of privacy protection, typical configurationless service discovery solutions do not even consider privacy. As configurationless service discovery solutions are ubiquitous and run on almost every smart device, their privacy problems affect almost everyone. The quotation aligns very well with configurationless service discovery. Typically, configurationless service discovery solutions realize configurationlessness by using cleartext multicast messages literally polluting the local network and suffocating privacy. Messages containing private cleartext data are sent to everyone, even if they are only relevant for a few users. The typical means for mitigating the network pollution problem caused by multicast per se, regardless of the privacy aspects, is confining multicast messages to a single network link or to the access network of a WiFi access point; institutions often even completely deactivate multicast. While this mitigates the privacy problem, it also strongly scales configurationless service discovery down, either confining it or rendering it completely unusable. In this thesis, we provide an efficient configurationless service discovery framework that protects the users’ privacy. It further reduces the network pollution by reducing the number of necessary multicast messages and offers a mode of operation that is completely independent of multicast. Introducing a multicast independent mode of operation, we also address the problem of the limited range in which services are discoverable. Our framework comprises components for device pairing, privacy-preserving service discovery, and multi-link scaling. These components are independent and — while usable in a completely separated way — are meant to be used as an integrated framework as they work seamlessly together. Based on our device pairing and privacy-preserving service discovery components, we published IETF Internet drafts specifying a privacy extension for DNS service discovery over multicast DNS, a wildly used protocol stack for configurationless service discovery. As our drafts have already been adopted by the dnssd working group, they are likely to become standards.
When mobile devices at the network edge want to communicate with each other, they too often depend on the availability of faraway resources. For direct communication, feasible user-friendly service discovery is essential. DNS Service Discovery over Multicast DNS (DNS-SD/mDNS) is widely used for configurationless service discovery in local networks, due inno small part to the fact that it is based on the well establishedDNS, and efficient in small networks. In our research, we enhance DNS-SD/mDNS providing versatility, user control, efficiency, and privacy, while maintaining the deployment simplicity and backward compatibility. These enhancements are necessary to make it a solid, flexible foundationfor device communication in the edge of the Internet. In this paper, we focus on providing multi-link capabilities and scalable scopes for DNS-SD while being mindful of both user-friendliness and efficiency. We propose DNS-SD over StatelessDNS (DNS-SD/sDNS), a solution that allows configurationless service discovery in arbitrary self-named scopes - largely independentof the physical network layout - by leveraging ourStateless DNS technique and the Raft consensus algorithm.
This paper compares the surface morphology of differently finished austenitic stainless steel AISI 316L, also in combination with low temperature carburization. Milled and tumbled surfaces were analyzed by means of corrosion resistance and surface morphology. The results of potentiodynamic measurements show that professional grinding operations with SiC and Al2O3 always lead to a better corrosion resistance of low temperature carburized surfaces compared to the untreated reference in the used acidified chloride solution. Big influence on the corrosion resistance of vibratory ground or tumbled surfaces has the amount of plastic deformation while machining, that has to be kept low for austenitic stainless steels. Due to the high ductility, plastic deformation can lead to the formation of meta stable pits that can be initiation points of corrosion. The formation of meta stable pits can be aggravated by low temperature diffusion processes.
With the increased deployment of biometric authentication systems, some security concerns have also arisen. In particular, presentation attacks directed to the capture device pose a severe threat. In order to prevent them, liveness features such as the blood flow can be utilised to develop presentation attack detection (PAD) mechanisms. In this context, laser speckle contrast imaging (LSCI) is a technology widely used in biomedical applications in order to visualise blood flow. We therefore propose a fingerprint PAD method based on textural information extracted from pre-processed LSCI images. Subsequently, a support vector machine is used for classification. In the experiments conducted on a database comprising 32 different artefacts, the results show that the proposed approach classifies correctly all bona fides. However, the LSCI technology experiences difficulties with thin and transparent overlay attacks.
Continuous range queries are a common means to handle mobile clients in high-density areas. Most existing approaches focus on settings in which the range queries for location-based services are mostly static whereas the mobile clients in the ranges move. We focus on a category called Dynamic Real-Time Range Queries (DRRQ) assuming that both, clients requested by the query and the inquirers, are mobile. In consequence, the query parameters results continuously change. This leads to two requirements: the ability to deal with an arbitrary high number of mobile nodes (scalability) and the real-time delivery of range query results. In this paper we present the highly decentralized solution Adaptive Quad Streaming (AQS) for the requirements of DRRQs. AQS approximates the query results in favor of a controlled real-time delivery and guaranteed scalability. While prior works commonly optimizes data structures on servers, we use AQS to focus on a highly distributed cell structure without data structures automatically adapting to changing client distributions. Instead of the commonly used request-response approach, we apply a lightweight streaming method in which no bidirectional communication and no storage or maintenance of queries are required at all.
Dynamic Real-Time Range Queries (DRRQ) are a common means to handle mobile clients in high-density areas where both, clients requested by the query and the inquirers, are mobile. In contrast to the very well-known continuous range queries, only a few approaches, such as Adaptive Quad Streaming (AQS), address the mandatory scalability and real-time requirements of these so-called ad-hoc mobility challenges. In this paper we present the highly decentralized solution Adaptive Quad Streaming Flexible (AQSflex) as an extension of the already existing more theoretical AQS approach. Beside a highly distributed cell structure without data structures and a lightweight streaming communication, we use a multi-cell-assignment on limited pool resources instead of an idealistic unlimited cell-per-server assignment. The described experimental results show the potential of our local capacity balancing scheme for cell handover in a strongly decentralized setting. Leafs of a cell hierarchy define a kind of self-optimizing fuzzy edge for the processing resources in high-density systems without any centralized controlling or cloud component.
Location-aware mobile devices are becoming increasingly popular and GPS sensors are built into nearly every portable unit with computational capabilities. At the same time, the emergence of location-aware virtual services and ideas calls for new efficient spatial real-time queries. Communication latency in mobile environments interacting with high decentralization and the need of scalability in high-density systems with immense client counts leads to major challenges. In this paper we describe a decentralized architecture for continuous range queries in settings in which both, the requested and the requesting clients, are mobile. While prior works commonly use a request-response approach we provide a stream-based adaptive grid solution dealing with arbitrary high client counts and improving communication latency that meets given hard real-time constraints.
adidas and Reebok
(2016)
Lidar sensors are widely used for environmental perception on autonomous robot vehicles (ARV). The field of view (FOV) of Lidar sensors can be reshaped by positioning plane mirrors in their vicinity. Mirror setups can especially improve the FOV for ground detection of ARVs with 2D-Lidar sensors. This paper presents an overview of several geometric designs and their strengths for certain vehicle types. Additionally, a new and easy-to-implement calibration procedure for setups of 2D-Lidar sensors with mirrors is presented to determine precise mirror orientations and positions, using a single flat calibration object with a pre-aligned simple fiducial marker. Measurement data from a prototype vehicle with a 2D-Lidar with a 2 m range using this new calibration procedure are presented. We show that the calibrated mirror orientations are accurate to less than 0.6° in this short range, which is a significant improvement over the orientation angles taken directly from the CAD. The accuracy of the point cloud data improved, and no significant decrease in distance noise was introduced. We deduced general guidelines for successful calibration setups using our method. In conclusion, a 2D-Lidar sensor and two plane mirrors calibrated with this method are a cost-effective and accurate way for robot engineers to improve the environmental perception of ARVs.
This thesis presents the development of two different state-feedback controllers to solve the trajectory tracking problem, where the vessel needs to reach and follow a time-varying reference trajectory. This motion problem was addressed to a real-scaled fully actuated surface vessel, whose dynamic model had unknown hydrodynamic and propulsion parameters that were identified by applying an experimental maneuver-based identification process. This dynamic model was then used to develop the controllers. The first one was the backstepping controller, which was designed with a local exponential stability proof. For the NMPC, the controller was developed to minimize the tracking error, considering the thrusters’ constraints. Moreover, both controllers considered the thruster allocation problem and counteracted environmental disturbance forces such as current, waves and wind.The effectiveness of these approaches was verified in simulation using Matlab/Simulink and GRAMPC (in the case of the NMPC), and in experimental scenarios, where they were applied to the vessel, performing docking maneuvers at the Rhine River in Constance (Germany).
The trajectory tracking problem for a fully-actuated real-scaled surface vessel is addressed in this paper by designing a backstepping controller with a multivariable integral action, considering the thruster allocation problem. The performance and robustness of this controller are evaluated in simulation, taking into account environmental disturbance forces and modeling mismatch, using a docking maneuver as a reference trajectory. Furthermore, a comparison between the backstepping controller and a nonlinear position PID-Control with flatness based-feedforward is also analyzed.
The trajectory tracking problem for a real-scaled fully-actuated surface vessel is addressed in this paper. A nonlinear model predictive control (NMPC) scheme was designed to track a reference trajectory, considering state and input constraints, and environmental disturbances, which were assumed to be constant over the prediction horizon. The controller was tested by performing docking maneuvers using the real-scaled research vessel from the University of Applied Sciences Konstanz at the Rhine river in Germany. A comparison between the experimental results and the simulated ones was analyzed to validate the NMPC controller.