Influence of Al₂O₃ Nanoparticle Addition on a UV Cured Polyacrylate for 3D Inkjet Printing

The brittleness of acrylic photopolymers, frequently used in 3D Inkjet printing, limits their utilization in structural applications. In this study, a process was developed for the production and characterization of an alumina-enhanced nanocomposite with improved mechanical properties for Inkjet printing. Ceramic nanoparticles with an average primary particle size (APPS) of 16 nm and 31 nm, which was assessed via high-resolution scanning electron microscopy (HRSEM), were functionalized with 3.43 and 5.59 mg/m2 3-(trimethoxysilyl)propyl methacrylate (MPS), respectively, while being ground in a ball mill. The suspensions of the modified fillers in a newly formulated acrylic mixture showed viscosities of 14 and 7 mPa∙s at the printing temperature of 60 °C. Ink-jetting tests were conducted successfully without clogging the printing nozzles. Tensile tests of casted specimens showed an improvement of the tensile strength and elongation at break in composites filled with 31 nm by 10.7% and 74.9%, respectively, relative to the unfilled polymer

Spectral analysis of 3D MHD models of coronal structures

We study extreme-ultraviolet emission line spectra derived from three-dimensional magnetohydrodynamic models of structures in the corona. In order to investigate the effects of increased magnetic activity at photospheric levels in a numerical experiment, a much higher magnetic flux density is applied at photospheric levels as compared to the Sun. Thus, we can expect our results to highlight the differences between the Sun and more active, but still solar-like stars. We discuss signatures seen in extreme-ultraviolet emission lines synthesized from these models and compare them to signatures found in the spatial distribution and temporal evolution of Doppler shifts in lines formed in the transition region and corona. This is of major interest to test the quality of the underlying magnetohydrodynamic model to heat the corona, i.e. currents in the corona driven by photospheric motions (flux braiding).Comment: 10 pages, 3 figure

Remote sensing of geomorphodiversity linked to biodiversity — part III: traits, processes and remote sensing characteristics

Remote sensing (RS) enables a cost-effective, extensive, continuous and standardized monitoring of traits and trait variations of geomorphology and its processes, from the local to the continental scale. To implement and better understand RS techniques and the spectral indicators derived from them in the monitoring of geomorphology, this paper presents a new perspective for the definition and recording of five characteristics of geomorphodiversity with RS, namely: geomorphic genesis diversity, geomorphic trait diversity, geomorphic structural diversity, geomorphic taxonomic diversity, and geomorphic functional diversity. In this respect, geomorphic trait diversity is the cornerstone and is essential for recording the other four characteristics using RS technologies. All five characteristics are discussed in detail in this paper and reinforced with numerous examples from various RS technologies. Methods for classifying the five characteristics of geomorphodiversity using RS, as well as the constraints of monitoring the diversity of geomorphology using RS, are discussed. RS-aided techniques that can be used for monitoring geomorphodiversity in regimes with changing land-use intensity are presented. Further, new approaches of geomorphic traits that enable the monitoring of geomorphodiversity through the valorisation of RS data from multiple missions are discussed as well as the ecosystem integrity approach. Likewise, the approach of monitoring the five characteristics of geomorphodiversity recording with RS is discussed, as are existing approaches for recording spectral geomorhic traits/ trait variation approach and indicators, along with approaches for assessing geomorphodiversity. It is shown that there is no comparable approach with which to define and record the five characteristics of geomorphodiversity using only RS data in the literature. Finally, the importance of the digitization process and the use of data science for research in the field of geomorphology in the 21st century is elucidated and discussed

Resistance seam welding of carbon fiber semi-finished products

The DLR preforming process for non-crimped-fabrics (ncf) as part of the RTM-Process chain consists of automated draping, a new binder activation process through electrical resistance heating, consolidation inside a membrane press and trimming of the preform to net shape. On the ncf a powder binder is applied. During the process of binder activation the binder powder is heated under pressure until it melts and then cooled down. As a result plies can be fixed to each other respectivly consolidated. Consolidation with the help of a membrane press is energy inefficient and time consuming, since membrane and tool are heated as well. In this paper it is investigated whether a roll electrode has the ability to replace a conventional consolidation press. Since a roll electrode applies heat and pressure at the same time a consolidation is possible. In this process the carbon fibers are heated by an electric current. In contrast to state of the art electrical resistance heating, the voltage is applied in through-thickness direction. In order to have a homogeneous temperature distribution the parameters pressure, roll width, number of fiber layers and activation speed was varied in a full-factorial experimental plan. Ultrasonic fine-trimming of roll-electrode consolidated preforms was investigated. Also the fiber volume content of the preform was measured with the help of a laser light sheet sensor and compared to specimen of a consolidation press

Effects, classification and mitigation of external interference in IEEE 802.15.4-based wireless sensor networks at 2.4 GHz

The IEEE Standard 802.15.4 de nes the low power wireless transmission technology behind Wireless Sensor Networks (WSNs) and ZigBee. Since IEEE 802.15.4 is a low power technology, the mitigation of interference is vital to conserve energy and to extend the lifetime of devices. Most of the IEEE 802.15.4 radios operate in the crowded 2.4 GHz frequency band, which is also used by many other technologies. A complete study of the common sources of external interference, namely IEEE 802.11-based Wireless Local Area Networks (WLANs), Bluetooth and microwave ovens, is provided. The effects of these coexisting technologies on IEEE 802.15.4 are investigated and the modeling of the interference is discussed. The possibilities of Energy Detection (ED) (the feature behind Received Signal Strength Indication (RSSI)) and certain Clear Channel Assessments (CCAs) are evaluated. Based on the CCAs, a lightweight interference classi cation algorithm is presented to classify the common external sources of interference in the 2.4 GHz frequency band without demodulation of the inteferers' signals. As the classification algorithm relies on time patterns instead of spectral features, it has no need to change the channel. Thus, it allows the radio both to stay connected to the channel and to receive while the interferer is classified. Furthermore, interference mitigation strategies are reviewed and evaluated with respect to their effectiveness to overcome the three external sources of interference. By combining the interference classification algorithm and the chosen mitigation strategies, Interference-Aware, Self-Adapting (IASA) Medium Access Control (MAC) is developed. This smart interference-mitigating MAC protocol is implemented in ContikiOS and evaluated

Competition at the wireless sensor network MAC layer: low power probing interfering with X-MAC

Wireless Sensor Networks (WSNs) combine sensors with computer networks and enable very dense, in-situ and live measurements of data over a large area. Since this emerging technology has the potential to be embedded almost everywhere for numberless applications, interference between different networks can become a serious issue. For most WSNs, it is assumed today that the network medium access is non-competitive. On the basis of X-MAC interfered by Low Power Probing, this paper shows the danger and the effects of different sensor networks communicating on a single wireless channel of the 2.4 GHz band, which is used by the IEEE 802.15.4 standard

Bewertung des Preformprozesses mit Hilfe der optischen Verformungsmessung

The preforming of carbon fiber semi-finished parts is responsible for a major share of the total costs at RTM processes. In order to identify the areas with the highest degree of deformation, an optical forming analysis was used. One requirement for this measurement technique is the application of a regular grid of red dots. Therefore different methods for the application have been investigated and automated. Furthermore the integration of the optical camera into the process has been achieved. As a result the measuring process could be automated. In a final step the measuring technology was validated at the automated preforming process of an aircraft fuselage frame segment