TY - JOUR
AU - Ma, Xuekai
AU - Kartashov, YV
AU - Kavokin, A
AU - Schumacher, Stefan
ID - 20586
IS - 20
JF - Optics Letters
SN - 0146-9592
TI - Chiral condensates in a polariton hexagonal ring.
VL - 45
ER -
TY - JOUR
AU - von Bardeleben, H. J.
AU - Rauls, E.
AU - Gerstmann, Uwe
ID - 40444
IS - 18
JF - Physical Review B
SN - 2469-9950
TI - Carbon vacancy-related centers in 3C-silicon carbide: Negative-U properties and structural transformation
VL - 101
ER -
TY - JOUR
AB -
EPR spectroscopy reveals the universality class and dynamic effects of the [NH4][Zn(HCOO)3] hybrid formate framework.
AU - Navickas, Marius
AU - Giriūnas, Laisvydas
AU - Kalendra, Vidmantas
AU - Biktagirov, Timur
AU - Gerstmann, Uwe
AU - Schmidt, Wolf Gero
AU - Mączka, Mirosław
AU - Pöppl, Andreas
AU - Banys, Jūras
AU - Šimėnas, Mantas
ID - 17070
JF - Physical Chemistry Chemical Physics
SN - 1463-9076
TI - Electron paramagnetic resonance study of ferroelectric phase transition and dynamic effects in a Mn2+ doped [NH4][Zn(HCOO)3] hybrid formate framework
VL - 22
ER -
TY - JOUR
AU - Biktagirov, Timur
AU - Gerstmann, Uwe
ID - 29745
IS - 2
JF - Physical Review Research
KW - General Engineering
SN - 2643-1564
TI - Spin-orbit driven electrical manipulation of the zero-field splitting in high-spin centers in solids
VL - 2
ER -
TY - JOUR
AB - Density-functional theory calculations of (TiO2)n clusters (n = 1–5) in the gas phase and adsorbed on pristine graphene as well as graphene quantum dots are presented. The cluster adsorption is found to be dominated by van der Waals forces. The electronic structure and in particular the excitation energies of the bare clusters and the TiO2/graphene composites are found to vary largely in dependence on the size of the respective constituents. This holds in particular for the energy and the spatial localization of the highest occupied and lowest unoccupied molecular orbitals. In addition to a substantial gap narrowing, a pronounced separation of photoexcited electrons and holes is predicted in some instances. This is expected to prolong the lifetime of photoexcited carriers. Altogether, TiO2/graphene composites are predicted to be promising photocatalysts with improved electronic and photocatalytic properties compared to bulk TiO2.
AU - Badalov, Sabuhi
AU - Wilhelm, René
AU - Schmidt, Wolf Gero
ID - 19189
JF - Journal of Computational Chemistry
SN - 0192-8651
TI - Photocatalytic properties of graphene‐supported titania clusters from density‐functional theory
ER -
TY - JOUR
AB - AbstractSemiconductor quantum dots are excellent candidates for ultrafast coherent manipulation of qubits by laser pulses on picosecond timescales or even faster. In inhomogeneous ensembles a macroscopic optical polarization decays rapidly due to dephasing, which, however, is reversible in photon echoes carrying complete information about the coherent ensemble dynamics. Control of the echo emission time is mandatory for applications. Here, we propose a concept to reach this goal. In a two-pulse photon echo sequence, we apply an additional resonant control pulse with multiple of 2π area. Depending on its arrival time, the control slows down dephasing or rephasing of the exciton ensemble during its action. We demonstrate for self-assembled (In,Ga)As quantum dots that the photon echo emission time can be retarded or advanced by up to 5 ps relative to its nominal appearance time without control. This versatile protocol may be used to obtain significantly longer temporal shifts for suitably tailored control pulses.
AU - Kosarev, Alexander N.
AU - Rose, Hendrik
AU - Poltavtsev, Sergey V.
AU - Reichelt, Matthias
AU - Schneider, Christian
AU - Kamp, Martin
AU - Höfling, Sven
AU - Bayer, Manfred
AU - Meier, Torsten
AU - Akimov, Ilya A.
ID - 20773
IS - 1
JF - Communications Physics
SN - 2399-3650
TI - Accurate photon echo timing by optical freezing of exciton dephasing and rephasing in quantum dots
VL - 3
ER -
TY - JOUR
AB - Vortices are topological objects representing the circular motion of a fluid. With their additional degree of freedom, the vorticity, they have been widely investigated in many physical systems and different materials for fundamental interest and for applications in data storage and information processing. Vortices have also been observed in non-equilibrium exciton-polariton condensates in planar semiconductor microcavities. There they appear spontaneously or can be created and pinned in space using ring-shaped optical excitation profiles. However, using the vortex state for information processing not only requires creation of a vortex but also efficient control over the vortex after its creation. Here we demonstrate a simple approach to control and switch a localized polariton vortex between opposite states. In our scheme, both the optical control of vorticity and its detection through the orbital angular momentum of the emitted light are implemented in a robust and practical manner.
AU - Meier, Torsten
AU - Ma, Xuekai
AU - Berger, Bernd
AU - Aßmann, Marc
AU - Driben, Rodislav
AU - Schneider, Christian
AU - Höfling, Sven
AU - Schumacher, Stefan
ID - 43747
IS - 1
JF - Nature communications
TI - Realization of all-optical vortex switching in exciton-polariton condensates
VL - 11
ER -
TY - CONF
AU - Hannes, Wolf-Rüdiger
AU - Meier, Torsten
ED - Betz, Markus
ED - Elezzabi, Abdulhakem Y.
ID - 20770
SN - 9781510633193
T2 - Ultrafast Phenomena and Nanophotonics XXIV
TI - k.p-based multiband simulations of non-degenerate two-photon absorption in bulk GaAs
VL - 11278
ER -
TY - JOUR
AU - Hannes, W.-R.
AU - Trautmann, Alexander
AU - Stein, M.
AU - Schäfer, F.
AU - Koch, M.
AU - Meier, Torsten
ID - 20563
IS - 7
JF - Physical Review B
TI - Strongly nonresonant four-wave mixing in semiconductors
VL - 101
ER -
TY - JOUR
AU - Song, Xiaohong
AU - Yang, Shidong
AU - Zuo, Ruixin
AU - Meier, Torsten
AU - Yang, Weifeng
ID - 20772
JF - Physical Review A
SN - 2469-9926
TI - Enhanced high-order harmonic generation in semiconductors by excitation with multicolor pulses
VL - 101
ER -
TY - JOUR
AU - Bocchini, Adriana
AU - Eigner, Christof
AU - Silberhorn, Christine
AU - Schmidt, Wolf Gero
AU - Gerstmann, Uwe
ID - 20682
JF - Phys. Rev. Materials
TI - Understanding gray track formation in KTP: Ti^3+ centers studied from first principles
VL - 4
ER -
TY - CONF
AU - Müller, Inez
ID - 44159
SN - 978-3-86205-600-2
TI - Generationelle und gesellschaftliche Differenzen im wiedervereinigten Deutschland - "Der neunzigste Geburtstag. Ein ländliches Idyll" von Günter de Bruyn in postkolonialer Lesart.
VL - 11
ER -
TY - JOUR
AU - Müller, Inez
ID - 44160
JF - Peter Weiss Jahrbuch
SN - 978-3-86110-748-4
TI - Transmediale und transkulturelle Schreibweisen im Exil der Gegenwart - Prosa und Lyrik syrischer Autoren in Europa
VL - 28
ER -
TY - CHAP
AU - Moritzer, Elmar
AU - Hüttner, M.
AU - Henning, Bernd
AU - Webersen, Manuel
ID - 24479
T2 - Advances in Polymer Processing 2020
TI - The Influence of Hydrothermal Aging on the Material Properties of Continuous Fiber-Reinforced Thermoplastics and its Non-Destructive Characterization
ER -
TY - JOUR
AU - Grabo, Matti
AU - Staggenborg, Christoph
AU - Philippi, Kai Alexander
AU - Kenig, Eugeny
ID - 22266
JF - Frontiers in Energy Research
SN - 2296-598X
TI - Modeling and Optimization of Rectangular Latent Heat Storage Elements in an Air-Guided Heat Storage System
VL - 8
ER -
TY - JOUR
AB - The influence of latent heat storage elements on the cooling performance and the temperature rise time of household refrigerating appliances is studied experimentally in the context of the “new global refriger- ator standard”IEC 62552:2015. In addition to the daily energy consumption, this international standard- ization introduced performance tests for cooling capacity and temperature rise time. While the cooling capacity has long been anchored in various test procedures of consumer organizations, the temperature rise time, which has only been tested on freezers so far, will be a decisive factor in the future. Moreover, the need for so-called "smart appliances" that may balance power consumption is increasing since such devices may compensate the volatility of renewable energies and thus stabilize the power grid. Against this background, eight commercial household refrigerators and refrigerator-freezers are equipped with polymer-bound phase change materials (PCM) and their performance is determined under the new stan- dard test conditions. The results show that the introduction of PCM increases the cooling capacity by up to 33 % and also increases the temperature rise time by up to 145 %, without affecting power consump- tion, as compared to the unmodified refrigeration appliances.
AU - Sonnenrein, Gerrit
AU - Baumhögger, Elmar
AU - Elsner, Andreas
AU - Morbach, A.
AU - Neukötter, Moritz
AU - Paul, Andreas
AU - Vrabec, J.
ID - 21514
JF - International Journal of Refrigeration
SN - 0140-7007
TI - Improving the performance of household refrigerating appliances through the integration of phase change materials in the context of the new global refrigerator standard IEC 62552:2015
VL - 119
ER -
TY - JOUR
AB - Despite the omnipresence of household refrigeration appliances, there is still a lack of knowledge about their agerelated efficiency loss over time. Past studies provide basic evidence for increasing electricity consumption of cooling appliances with ageing but fail to investigate the associated technical wear. Concentrating on the degradation of the thermal insulation, we first determined the ageing process of sealed samples of polyurethane rigid foam by investigating changes in cell gas composition and thermal conductivity over time. Simultaneously, the main challenge was to develop an approach that investigates the age-related efficiency loss of the insulation without its destruction. This testing procedure is referred to as the Bonn method. The non-destructive Bonn method was applied to varying refrigerator models in a series of successive experiments to evaluate the insulation degradation over time. Subsequently, the physical relationship between the test value of the Bonn method and the heat transfer through the multi-layered compartment walls of domestic refrigeration appliances was established, ultimately characterising the degrading insulation in terms of increasing heat transfer. Our results give substantiated evidence that the efficiency loss of cooling appliances is greatly influenced by insulation degradation over time. The ageing of sealed samples of polyurethane rigid foam indicates a large initial increase of thermal conductivity by 15% within the first year, corresponding to a change in cell gas composition. These results are in line with those of the Bonn method, emphasising an increasing heat flow through the multi-layered compartment walls of domestic refrigerators with ageing. Therewith, the present study is of significance to a wide range of stakeholders and forms the basis for future research.
AU - Hueppe, Christian
AU - Geppert, Jasmin
AU - Stamminger, Rainer
AU - Wagner, Hendrik
AU - Hoelscher, Heike
AU - Vrabec, Jadran
AU - Paul, Andreas
AU - Elsner, Andreas
AU - Becker, Wolfgang
AU - Gries, Ulrich
AU - Freiberger, Alfred
ID - 21512
JF - Applied Thermal Engineering
SN - 1359-4311
TI - Age-related efficiency loss of household refrigeration appliances: Development of an approach to measure the degradation of insulation properties
VL - 173
ER -
TY - GEN
AB - Due to the trend towards lightweight design in car body development mechanical joining technologies become increasingly important. These techniques allow for the joining of dissimilar materials and thus enable multi-material design, while thermic joining methods reach their limits. Semi-tubular self-piercing riveting is an important mechanical joining technology. The rivet production, however, is costly and time-consuming, as the process consists of several process steps including the heat treatment and coating of the rivets in order to achieve an adequate strength and corrosion resistance. The use of high nitrogen steel as rivet material leads to the possibility of reducing process steps and hence increasing the efficiency of the process. However, the high tool loads being expected due to the high strain hardening of the material are a major challenge during the rivet production. Thus, there is a need for appropriate forming strategies, such as the manufacturing of the rivets at elevated temperatures. Prior investigations led to the conclusion that forming already at 200 °C results in a distinct reduction of the yield strength. To create a deeper understanding of the forming behaviour of high nitrogen steel at elevated temperatures, compression tests were conducted in a temperature range between room temperature and 200 °C. The determined true stress – true strain curves are the basis for the further process and tool design of the rivet production. Another key factor for the rivet manufacturing at elevated temperatures is the influence of the process temperature on the tribological conditions. For this reason, ring compression tests at room temperature and 200 °C are carried out. The friction factors are determined on the basis of calibration curves resulting from the numerical analysis of the ring compression process. The investigations indicate that the friction factor at 200 °C is significantly higher compared to room temperature. This essential fact has to be taken into account for the process and tool design for the rivet production using high nitrogen steel.
ED - Kuball, Clara-Maria
ED - Jung, R
ED - Uhe, Benedikt
ED - Meschut, Gerson
ED - Merklein, Marion
ID - 19974
KW - High nitrogen steel
KW - Self-piercing riveting
KW - Joining by forming
KW - Bulk forming
KW - Strain hardening
TI - Influence of the process temperature on the forming behaviour and the friction during bulk forming of high nitrogen steel
VL - 1
ER -
TY - JOUR
AB - As a result of lightweight design, increased use is being made of high-strength steel and aluminium in car bodies. Self-piercing riveting is an established technique for joining these materials. The dissimilar properties of the two materials have led to a number of different rivet geometries in the past. Each rivet geometry fulfils the requirements of the materials within a limited range. In the present investigation, an improved rivet geometry is developed, which permits the reliable joining of two material combinations that could only be joined by two different rivet geometries up until now. Material combination 1 consists of high-strength steel on both sides, while material combination 2 comprises aluminium on the punch side and high-strength steel on the die side. The material flow and the stress and strain conditions prevailing during the joining process are analysed by means of numerical simulation. The rivet geometry is then improved step-by-step on the basis of this analysis. Finally, the improved rivet geometry is manufactured and the findings of the investigation are verified in experimental joining tests.
AU - Uhe, Benedikt
AU - Kuball, Clara-Maria
AU - Merklein, Marion
AU - Meschut, Gerson
ID - 19973
JF - Production Engineering
KW - Self-piercing riveting
KW - Joining technology
KW - Rivet geometry
KW - Multi-material design
KW - High-strength steel
KW - Aluminium
TI - Improvement of a rivet geometry for the self-piercing riveting of high-strength steel and multi-material joints
VL - 14
ER -
TY - JOUR
AU - Tinkloh, Steffen Rainer
AU - Wu, Tao
AU - Tröster, Thomas
AU - Niendorf, Thomas
ID - 15945
JF - Composite Structures
SN - 0263-8223
TI - A micromechanical-based finite element simulation of process-induced residual stresses in metal-CFRP-hybrid structures
VL - 238
ER -