TY  - JOUR
A1  - Ulmer, Jessica
A1  - Braun, Sebastian
A1  - Cheng, Chi-Tsun
A1  - Dowey, Steve
A1  - Wollert, Jörg
T1  - Gamification of virtual reality assembly training: Effects of a combined point and level system on motivation and training results
JF  - International Journal of Human-Computer Studies
N2  - Virtual Reality (VR) offers novel possibilities for remote training regardless of the availability of the actual equipment, the presence of specialists, and the training locations. Research shows that training environments that adapt to users' preferences and performance can promote more effective learning. However, the observed results can hardly be traced back to specific adaptive measures but the whole new training approach. This study analyzes the effects of a combined point and leveling VR-based gamification system on assembly training targeting specific training outcomes and users' motivations. The Gamified-VR-Group with 26 subjects received the gamified training, and the Non-Gamified-VR-Group with 27 subjects received the alternative without gamified elements. Both groups conducted their VR training at least three times before assembling the actual structure. The study found that a level system that gradually increases the difficulty and error probability in VR can significantly lower real-world error rates, self-corrections, and support usages. According to our study, a high error occurrence at the highest training level reduced the Gamified-VR-Group's feeling of competence compared to the Non-Gamified-VR-Group, but at the same time also led to lower error probabilities in real-life. It is concluded that a level system with a variable task difficulty should be combined with carefully balanced positive and negative feedback messages. This way, better learning results, and an improved self-evaluation can be achieved while not causing significant impacts on the participants' feeling of competence.
KW  - Gamification
KW  - Virtual reality
KW  - Assembly
KW  - User study
KW  - Level system
Y1  - 2022
U6  - https://doi.org/10.1016/j.ijhcs.2022.102854
SN  - 1071-5819
VL  - 165
IS  - Art. No. 102854
PB  - Elsevier
CY  - Amsterdam
ER  - 
TY  - JOUR
A1  - Dachwald, Bernd
T1  - Optimization of very-low-thrust trajectories using evolutionary neurocontrol
JF  - Acta Astronautica
N2  - Searching optimal interplanetary trajectories for low-thrust spacecraft is usually a difficult and time-consuming task that involves much experience and expert knowledge in astrodynamics and optimal control theory. This is because the convergence behavior of traditional local optimizers, which are based on numerical optimal control methods, depends on an adequate initial guess, which is often hard to find, especially for very-low-thrust trajectories that necessitate many revolutions around the sun. The obtained solutions are typically close to the initial guess that is rarely close to the (unknown) global optimum. Within this paper, trajectory optimization problems are attacked from the perspective of artificial intelligence and machine learning. Inspired by natural archetypes, a smart global method for low-thrust trajectory optimization is proposed that fuses artificial neural networks and evolutionary algorithms into so-called evolutionary neurocontrollers. This novel method runs without an initial guess and does not require the attendance of an expert in astrodynamics and optimal control theory. This paper details how evolutionary neurocontrol works and how it could be implemented. The performance of the method is assessed for three different interplanetary missions with a thrust to mass ratio <0.15mN/kg (solar sail and nuclear electric).
Y1  - 2005
SN  - 1879-2030
VL  - 57
IS  - 2-8
SP  - 175
EP  - 185
PB  - Elsevier
CY  - Amsterdam [u.a.]
ER  - 
TY  - JOUR
A1  - Loeb, Horst Wolfgang
A1  - Schartner, Karl-Heinz
A1  - Dachwald, Bernd
A1  - Ohndorf, Andreas
A1  - Seboldt, Wolfgang
T1  - Interstellar heliopause probe
JF  - Труды МАИ
N2  - There is common agreement within the scientific community that in order to understand our local galactic environment it will be necessary to send a spacecraft into the region beyond the solar wind termination shock. Considering distances of 200 AU for a new mission, one needs a spacecraft traveling at a speed of close to 10 AU/yr in order to keep the mission duration in the range of less than 25 yrs, a transfer time postulated by European Space Agency (ESA). Two propulsion options for the mission have been proposed and discussed so far: the solar sail propulsion and the ballistic/radioisotope-electric propulsion (REP). As a further alternative, we here investigate a combination of solar-electric propulsion (SEP) and REP. The SEP stage consists of six 22-cms diameter RIT-22 ion thrusters working with a high specific impulse of 7377 s corresponding to a positive grid voltage of 5 kV. Solar power of 53 kW at begin of mission (BOM) is provided by a lightweight solar array.
Y1  - 2012
IS  - 60
SP  - 2
EP  - 2
PB  - Moskauer Staatliches Luftfahrtinstitut (МАИ)
CY  - Moskau
ER  - 
TY  - JOUR
A1  - Valero, Daniel
A1  - Bung, Daniel Bernhard
A1  - Erpicum, Sebastien
A1  - Peltier, Yann
A1  - Dewals, Benjamin
T1  - Unsteady shallow meandering flows in rectangular reservoirs: a modal analysis of URANS modelling
JF  - Journal of Hydro-environment Research
N2  - Shallow flows are common in natural and human-made environments. Even for simple rectangular shallow reservoirs, recent laboratory experiments show that the developing flow fields are particularly complex, involving large-scale turbulent structures. For specific combinations of reservoir size and hydraulic conditions, a meandering jet can be observed. While some aspects of this pseudo-2D flow pattern can be reproduced using a 2D numerical model, new 3D simulations, based on the unsteady Reynolds-Averaged Navier-Stokes equations, show consistent advantages as presented herein. A Proper Orthogonal Decomposition was used to characterize the four most energetic modes of the meandering jet at the free surface level, allowing comparison against experimental data and 2D (depth-averaged) numerical results. Three different isotropic eddy viscosity models (RNG k-ε, k-ε, k-ω) were tested. The 3D models accurately predicted the frequency of the modes, whereas the amplitudes of the modes and associated energy were damped for the friction-dominant cases and augmented for non-frictional ones. The performance of the three turbulence models remained essentially similar, with slightly better predictions by RNG k-ε model in the case with the highest Reynolds number. Finally, the Q-criterion was used to identify vortices and study their dynamics, assisting on the identification of the differences between: i) the three-dimensional phenomenon (here reproduced), ii) its two-dimensional footprint in the free surface (experimental observations) and iii) the depth-averaged case (represented by 2D models).
KW  - coherent structures
KW  - hydraulic modelling
KW  - model performance
KW  - Proper Orthogonal Decomposition
KW  - Q-criterion
Y1  - 2022
U6  - https://doi.org/10.1016/j.jher.2022.03.002
SN  - 1570-6443
IS  - In Press
PB  - Elsevier
CY  - Amsterdam
ER  - 
TY  - JOUR
A1  - Bhattarai, Aroj
A1  - Horbach, Andreas
A1  - Staat, Manfred
A1  - Kowalczyk, Wojciech
A1  - Tran, Thanh Ngoc
T1  - Virgin passive colon biomechanics and a literature review of active contraction constitutive models
JF  - Biomechanics
N2  - The objective of this paper is to present our findings on the biomechanical aspects of the virgin passive anisotropic hyperelasticity of the porcine colon based on equibiaxial tensile experiments. Firstly, the characterization of the intestine tissues is discussed for a nearly incompressible hyperelastic fiber-reinforced Holzapfel–Gasser–Ogden constitutive model in virgin passive loading conditions. The stability of the evaluated material parameters is checked for the polyconvexity of the adopted strain energy function using positive eigenvalue constraints of the Hessian matrix with MATLAB. The constitutive material description of the intestine with two collagen fibers in the submucosal and muscular layer each has been implemented in the FORTRAN platform of the commercial finite element software LS-DYNA, and two equibiaxial tensile simulations are presented to validate the results with the optical strain images obtained from the experiments. Furthermore, this paper also reviews the existing models of the active smooth muscle cells, but these models have not been computationally studied here. The review part shows that the constitutive models originally developed for the active contraction of skeletal muscle based on Hill’s three-element model, Murphy’s four-state cross-bridge chemical kinetic model and Huxley’s sliding-filament hypothesis, which are mainly used for arteries, are appropriate for numerical contraction numerical analysis of the large intestine.
KW  - virgin passive
KW  - strain energy function
KW  - smooth muscle contraction
KW  - viscoelasticity
KW  - damage
Y1  - 2022
U6  - https://doi.org/10.3390/biomechanics2020013
SN  - 2673-7078
VL  - 2
IS  - 2
SP  - 138
EP  - 157
PB  - MDPI
CY  - Basel
ER  - 
TY  - JOUR
A1  - Golland, Alexander
A1  - Engling, Christoph
T1  - a-i3/BSI Symposium 2014: Sicherheit von Daten und Identitäten angesichts NSA und Big Data
JF  - DSB Datenschutz-Berater
Y1  - 2014
SN  - 0170-7256
VL  - 38
IS  - 7-8
SP  - 165
EP  - 166
PB  - DFV Mediengruppe
CY  - Frankfurt a.M.
ER  - 
TY  - JOUR
A1  - Peloni, Alessandro
A1  - Ceriotti, Matteo
A1  - Dachwald, Bernd
T1  - Solar-sail trajectory design for a multiple near-earth-asteroid rendezvous mission
JF  - Journal of Guidance, Control, and Dynamics
N2  - The scientific interest for near-Earth asteroids as well as the interest in potentially hazardous asteroids from the perspective of planetary defense led the space community to focus on near-Earth asteroid mission studies. A multiple near-Earth asteroid rendezvous mission with close-up observations of several objects can help to improve the characterization of these asteroids. This work explores the design of a solar-sail spacecraft for such a mission, focusing on the search of possible sequences of encounters and the trajectory optimization. This is done in two sequential steps: a sequence search by means of a simplified trajectory model and a set of heuristic rules based on astrodynamics, and a subsequent optimization phase. A shape-based approach for solar sailing has been developed and is used for the first phase. The effectiveness of the proposed approach is demonstrated through a fully optimized multiple near-Earth asteroid rendezvous mission. The results show that it is possible to visit five near-Earth asteroids within 10 years with near-term solar-sail technology.
Y1  - 2016
U6  - https://doi.org/10.2514/1.G000470
SN  - 0731-5090
VL  - 39
IS  - 12
SP  - 2712
EP  - 2724
PB  - AIAA
CY  - Reston, Va.
ER  - 
TY  - JOUR
A1  - Golland, Alexander
T1  - Datenschutz durch modulare Zertifizierung: Trusted Cloud-Pilotprojekt bringt neuen Ansatz
JF  - DSB Datenschutz-Berater
Y1  - 2014
SN  - 0170-7256
VL  - 38
IS  - 10
SP  - 213
EP  - 215
PB  - DFV Mediengruppe
CY  - Frankfurt a.M.
ER  - 
TY  - JOUR
A1  - Golland, Alexander
A1  - Engling, Christoph
T1  - Offene und geschlossene WLAN: Rechtliche Hürden bei Betrieb eines öffentlichen Internetzugangs
JF  - DSB Datenschutz-Berater
Y1  - 2015
SN  - 0170-7256
VL  - 39
IS  - 5
SP  - 102
EP  - 103
PB  - DFV Mediengruppe
CY  - Frankfurt a.M.
ER  - 
TY  - JOUR
A1  - Golland, Alexander
A1  - Kriegesmann, Torben
ED  - Härting, Niko
T1  - Der Schutz virtueller Identitäten durch die DSGVO
JF  - PinG Privacy in Germany
N2  - Die Frage des Schutzes von virtuellen Identitäten ist – insbesondere bei Online-Medien – von elementarer Bedeutung: Ihre Beantwortung entscheidet über die Anwendbarkeit des Datenschutzrechts auf vermeintlich anonyme Nutzerprofile im Internet. Eine differenzierte Auseinandersetzung mit der Problematik, ob und unter welchen Umständen virtuelle Identitäten dem Datenschutzrecht unterfallen, fehlt bislang. Der vorliegende Beitrag gibt einen Überblick über den Schutz virtueller Identitäten und zeigt Ansätze auf, mittels derer bestimmt werden kann, wann virtuelle Identitäten nach Inkrafttreten der DSGVO durch das Datenschutzrecht geschützt werden.
Y1  - 2017
SN  - 2197-1862
U6  - https://doi.org/10.37307/j.2196-9817.2017.02.03
VL  - 5
IS  - 2
SP  - 45
EP  - 50
PB  - Erich Schmidt Verlag
CY  - Berlin
ER  -