13979 research outputs found
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25 Jahre Forschung am S-DALINAC
Get PDFAls am 18. Oktober 1991 der »Supraleitende Darmstädter Linear-Accelerator«, kurz S-DALINAC, mit einem Festakt eingeweiht wurde, begann eine neue Epoche der Grundlagenforschung an der TH Darmstadt
Vor 100 Jahren: Eduard Sonne (1828 - 1917)
Get PDFEduard Sonne, mit vollem Namen Eduard Heinrich Christian Sonne, war einer der ersten Direktoren der Technischen Hochschule Darmstadt und Professor für Ingenieurwissenschaften. Er wurde am 13. November 1828 in Ilfeld, einer Kleinstadt etwa 75 Kilometer nordwestlich von Weimar, geboren
Eugen Kogon – kritischer Vordenker und unruhiger Geist
Get PDFEugen Kogon (*2. Februar 1903) war eine der bedeutendsten Persönlichkeiten der TU Darmstadt und gilt als intellektueller Gründervater der Bundesrepublik Deutschland. Zudem war er ein Vordenker für ein geeintes Europa und setzte sich zugleich für eine Aussöhnung zwischen Ost und West ein. Kogon starb am 24. Dezember 1987
Sustainable Production of Medium-Chain Fatty Acids from Fresh Leachates in the District of Abidjan: Study of the Feasibility of the Process and Environmental Benefits
Get PDFLeachate management remains a major environmental challenge, especially in rapidly urbanizing cities of developing countries. Traditionally considered toxic and useless, it is a sustainable organic resource with the potential for high-value biochemical production through bioprocessing. This study investigated the characteristics of fresh leachates from three solid waste transfer stations (SWTS) in the Abidjan district, Côte d’Ivoire, and assessed their potential as substrates for medium-chain fatty acid (MCFA) production via microbial chain elongation. The MCFA synthesis was carried out in anaerobic bioreactors operated under methanogenesis inhibition conditions. The leachates from Bingerville, Abobo-Dokui, and Yopougon exhibited acidic and high organic content, particularly volatile fatty acids (VFAs), key precursors for MCFA synthesis. High concentrations of microbial communities associated with chain elongation were observed, including Clostridium (sulphite-reducing), Lactobacillus, Bacillus, and Pseudomonas (greater than 5 log10 CFU/mL). MCFA production ranged from 5 to 10 g/L, mainly C6, C7, and C8, with compositional variation depending on the SWTS. Notably, leachates from higher-income areas demonstrated higher MCFA productivity compared to those from lower-income areas. These findings highlight the potential of fresh SWTS leachates in the Abidjan district for sustainable MCFA production, paving the way for industrial applications
Data-driven modelling of touch-down bearing forces
Get PDFTo reduce CO2 emissions, the share of renewable energies in the grid increases. At the same time, many sectors like the transport and the building sector are changing to be powered by electricity. Especially electric cars demand high peaks in current from the grid. Storage is needed to balance demand and supply of electric energy. Flywheels can be part of the solution as they can be charged and discharged with high power and do not suffer from losing significant capacity even after thousands of cycles. Minimum loss of energy is crucial for a flywheel therefor active magnetic bearings (AMB) are used. If a malfunction of the AMB occurs the rotor falls into a touch-down bearing (TDB). To decide whether further maintenance in case of a drop-down event is needed information about the forces stressing the TDB is important. To avoid costs for physical sensors soft sensors are a suitable solution. In this research, a data-driven soft sensor based on recurrent neural networks is created to calculate the forces during the drop-down event. As input data only the position of the rotor is used. A test rig with physical sensors applied to every TDB supplies the force data to train, validate, and test the soft sensor model. Three different network architectures are compared. The results show that the sensor can calculate whether the rotor hits a TDB and is also capable of predicting the peaks in the force signal
Experimental Assessment of the Effects of Gas Composition on Volatile Flames of Coal and Biomass Particles in Oxyfuel Combustion Using Multi-Parameter Optical Diagnostics
Get PDFThis experimental study examines the particle-level combustion behavior of high-volatile bituminous coal and walnut shell particles in oxyfuel environments, with a particular focus on the gas-phase ignition characteristics and the structural development of volatile flames. Particles with similar size and shape distributions (a median diameter of about 126 µm and an aspect ratio of around 1.5) are combusted in hot flows generated using lean, flat flames, where the oxygen mole fraction is systematically varied in both CO₂/O₂ and N₂/O₂ atmospheres while maintaining comparable gas temperatures and particle heating rates. The investigation employs a high-speed multi-camera diagnostic system combining laser-induced fluorescence of OH, diffuse backlight-illumination, and Mie scattering to simultaneously measure the particle size, shape, and velocity; the ignition delay time; and the volatile flame dynamics during early-stage volatile combustion. Advanced detection algorithms enable the extraction of these multiple parameters from spatiotemporally synchronized measurements. The results reveal that the ignition delay time decreases with an increasing oxygen mole fraction up to 30 vol%, beyond which point further oxygen enrichment no longer accelerates the ignition, as the process becomes limited by the volatile release rate. In contrast, the reactivity of volatile flames shows continuous enhancement with an increasing oxygen mole fraction, indicating non-premixed flame behavior governed by the diffusion of oxygen toward the particles. The analysis of the flame stand-off distance demonstrates that volatile flames burn closer to the particles at higher oxygen mole fractions, consistent with the expected scaling of O₂ diffusion with its partial pressure. Notably, walnut shell and coal particles exhibit remarkably similar ignition delay times, volatile flame sizes, and OH-LIF intensities. The substitution of N₂ with CO₂ produces minimal differences, suggesting that for 126 µm particles under high-heating-rate conditions, the relatively small variations in the heat capacity and O₂ diffusivity between these diluents have negligible effects on the homogeneous combustion phenomena observed
Waveguide based acoustic levitation device for moving objects in a large volume
Get PDFMoving objects contactlessly in a large addressable
3D space usually requires moving parts of an acoustic levitation
device or running optimization algorithms in conjunction with
it. We propose a computationally lightweight approach to trap
objects in a narrowed beam and transport them in a 3D volume
within by a stationary setup. This is achieved by attaching an
ultrasonic phased array to a 3D-printed acoustic waveguide,
which reduces the inter-element spacing of the array to half of its
emitted wavelength. This allows electronically steering the sound
beam of the ultrasonic phased array while reducing the near-field
length and grating lobes at the same time. By combining those
capabilities with a concave reflector, we can move multiple objects
in a spherical cone at the same time. Up to twelve objects can be
levitated for an apex angle of 80°. The absolute positioning error
is below 7° and has a standard deviation of 1.29°. Some nodes in
the center of the acoustic levitator can also be steered inside an
apex angle of 120°. With this levitation device, we demonstrate
the benefits of combining passive and active means of shaping a
sound field to manipulate acoustically levitated objects
A 220 kHz Air-Coupled Spiral Ultrasonic Phased Array Using Waveguides
Get PDFThe freedom of air-coupled phased array design
is restricted due to the size constraints of off-the-shelf transducers.
Waveguides can be a solution, because they allow to
design the element aperture as well as the array aperture
independently of transducer sizes. Recent work (Rutsch et al.
2021) has demonstrated the feasibility of air-coupled waveguides
at frequencies around 40 kHz for phased arrays. This work
explores the use of waveguides at a higher frequency of 220 kHz
with commercially available piezoelectric ultrasonic transducers
for creating air-coupled phased arrays, since higher frequency
allows higher resolution. We employ tapered, cylindrical 3Dprinted
waveguides of equal lengths in an arc shape, with
each 220 kHz transducer individually controllable for 3D beam
steering. A spiral arrangement of the transducers is chosen for
its lower maximum side lobe level and independence of the λ/2
criterion. The point spread function of the resulting phased array
is characterized in an anechoic chamber. Results confirm the
feasibility of the waveguided phased array at 220 kHz, with a
-3 dB main lobe width of 9° and a maximum side lobe level
of -10 dB. Therefore the waveguide approach is feasible even at
higher frequencies such as 220 kHz for selecting the aperture
independent of the transducer
Wem gehört die Sprache? - Bibliotheken im Zeitalter einer schreibenden KI
Get PDFDiskussion der Frage, ob KI die im Netz oder anderweitig publizierten Sprachwerke frei nutzen darf. Ausgangspunkt ist die Frage, wem die Sprache gehört und worin sich menschliches vom Lernen der KI unterscheidet. Relevant wird die Frage für Bibliotheken in der Nutzung der KI, aber auch der Bereitstellung von Texten für die KI und ggf. Sammlung bzw. Rekonstruktion von Texten der K
Unlocking Electrostrain in Plastically Deformed Barium Titanate
Get PDFAchieving substantial electrostrain alongside a large effective piezoelectric strain coefficient (d₃₃*) in piezoelectric materials remains a formidable challenge for advanced actuator applications. Here, a straightforward approach to enhance these properties by strategically designing the domain structure and controlling the domain switching through the introduction of arrays of ordered {100} dislocations is proposed. This dislocation engineering yields an intrinsic lock‐in steady–state electrostrain of 0.69% at a low field of 10 kV cm⁻¹ without external stress and an output strain energy density of 5.24 J cm⁻³ in single‐crystal BaTiO₃, outperforming the benchmark piezoceramics and relaxor ferroelectric single‐crystals. Additionally, applying a compression stress of 6 MPa fully unlocks electrostrains exceeding 1%, yielding a remarkable d₃₃* value over 10 000 pm V⁻¹ and achieving a record‐high strain energy density of 11.67 J cm⁻³. Optical and transmission electron microscopy, paired with laboratory and synchrotron X‐ray diffraction, is employed to rationalize the observed electrostrain. Phase‐field simulations further elucidate the impact of charged dislocations on domain nucleation and domain switching. These findings present an effective and sustainable strategy for developing high‐performance, lead‐free piezoelectric materials without the need for additional chemical elements, offering immense potential for actuator technologies