Distribution of Dangling Ends on the Incipient Percolation Cluster

We study numerically and by scaling arguments the probability P(M)dM that a given dangling end of the incipient percolation cluster has a mass between M and M + dM. We find by scaling arguments that P(M) decays with a power law, P(M)~M^(-(1+k)), with an exponent k=dBf/df, where df and dBf are the fractal dimensions of the cluster and its backbone, respectively. Our numerical results yield k=0.83 in d=2 and k=0.74 in d=3 in very good agreement with theory.Comment: proceedings of the conference "Percolation and Disordered Systems: *Theory and Applications*", Giessen (Germany) 1998, see http://ory.ph.biu.ac.il/PERCOLATION98/ , 4 pages, 3 figures, in press, will be published in Physica

Resource-efficient high-dimensional entanglement detection via symmetric projections

We introduce two families of criteria for detecting and quantifying the entanglement of a bipartite quantum state of arbitrary local dimension. The first is based on measurements in mutually unbiased bases and the second is based on equiangular measurements. Both criteria give a qualitative result in terms of the state's entanglement dimension and a quantitative result in terms of its fidelity with the maximally entangled state. The criteria are universally applicable since no assumptions on the state are required. Moreover, the experimenter can control the trade-off between resource-efficiency and noise-tolerance by selecting the number of measurements performed. For paradigmatic noise models, we show that only a small number of measurements are necessary to achieve nearly-optimal detection in any dimension. The number of global product projections scales only linearly in the local dimension, thus paving the way for detection and quantification of very high-dimensional entanglement.Comment: 6+2 page

The Dispersion Calculator: A Free Software for Calculating Dispersion Curves of Guided Waves

The nondestructive inspection of components by means of guided waves is an emerging technology in fields like aerospace or pipeline construction and maintenance. The guided waves' capability of propagating many meters in a structure is utilized for swift inspection tasks as well as structural health monitoring. The German Aerospace Center uses Lamb waves for the quality assurance of large-scale aerospace vehicle components made from carbon composites. However, the use of guided waves in NDT requires knowledge of the dispersion curves. DISPERSE is the most renown software for the calculation of dispersion curves. This paper presents the open source Dispersion Calculator (DC). The MATLAB® -based DC is an interactive and fully validated software for the computation of dispersion curves and mode shapes of guided waves in isotropic plates and multilayered anisotropic composites. Damping caused by viscoelasticity and fluid-loading can be considered. DC features the capability of calculating laminates consisting of several hundreds of layers so that even the largest specimens, like rocket booster pressure vessels, can be calculated. This is made possible through the implementation of the stiffness matrix method. DC is also able to distinguish the different mode families, like symmetric, antisymmetric, and nonsymmetric Lamb, shear horizontal, and Scholte waves, depending on the symmetry and coupling properties of a given layup. Lastly, DC features a highly efficient and robust dispersion curve tracing algorithm. DC is available at GitHub, and it has gained many users world-wide since its initial release in 2018

Automatisierte Qualitätssicherung von CFK-Bauteilen mittels luftgekoppeltem Ultraschall

To this day, carbon fiber reinforced plastic (CFRP)-components are used in aerospace only to a minor degree, because its fabrication is much more expensive than production of metallic components, which is due to the high amount of handcraft that is involved. Therefore, it is the aim of the German Aerospace Center to automate the production process of CFRP by using robots. An important part of the production process is quality assurance. One of the methods that are used at DLR is non-destructive inspection (NDI) by using air-coupled ultrasonic testing (ACU-testing). In contrast to water-coupled ultrasonic testing, this method is completely contactless and allows for inspection of CFRP-components with high amount of porosity of a few percent. ACU-testing is going to be automated as well and, in another effort, be integrated into the automated production process. The acquired data from ACU-testing could then be used for optimization of the production process. Despite its high potential as an NDI-method, ACU-testing facilities for reflection measurements exist only in laboratories. Thus, it is another aim of DLR to improve the method to a degree, where it can be introduced into industrial sites. For this purpose, reflection measurements on test components and a pressure vessel were carried out with an ACU-testing device. In the course of those experiments the degree of automation of the NDI-method was increased step by step

Air-coupled ultrasonic inspection of thermoplastic composite structures for aerospace vehicles

Composites have become the most important type of material used in the manufacturing of aerospace vehicle components. One focus of the German Aerospace Center is to develop cost-efficient manufacturing processes for large-scale composite components such as liquid hydrogen tanks, rocket booster pressure vessels, and aircraft fuselages. To enable a high degree of automation in the manufacturing, robot-assisted tape-laying processes with flash lamp consolidation of thermoplastic prepregs are preferred. Nondestructive inspection is crucial to monitor manufacturing quality, and various forms of ultrasonic inspection have become standard. Air-coupled ultrasonic inspection is applied at the German Aerospace Center, and since access to the component is usually available only from one side, Lamb waves are excited and detected in focused slanted reflection mode. Like the manufacturing process, air-coupled ultrasonic inspection has been automated as well to avoid a significant pause during or after manufacturing. The paper demonstrates the robot-assisted air-coupled ultrasonic inspection of a liquid hydrogen tank. The robotic program is generated using offline programming software, based on the topography of a CAD model of the hydrogen tank. The inspection is carried out by scanning the component while ultrasonic pulses are triggered on a regular grid. The ultrasonic A-scans together with the measurement coordinates are monitored simultaneously. The data are used to generate and evaluate a three-dimensional C-sca

Towards deep generation of guided wave representations for composite materials

Laminated composite materials are widely used in most fields of engineering. Wave propagation analysis plays an essential role in understanding the short-duration transient response of composite structures. The forward physics-based models are utilized to map from elastic properties space to wave propagation behavior in a laminated composite material. Due to the high-frequency, multi-modal, and dispersive nature of the guided waves, the physics-based simulations are computationally demanding. It makes property prediction, generation, and material design problems more challenging. In this work, a forward physics-based simulator such as the stiffness matrix method is utilized to collect group velocities of guided waves for a set of composite materials. A variational autoencoder (VAE)-based deep generative model is proposed for the generation of new and realistic polar group velocity representations. It is observed that the deep generator is able to reconstruct unseen representations with very low mean square reconstruction error. Global Monte Carlo and directional equally-spaced samplers are used to sample the continuous, complete and organized low-dimensional latent space of VAE. The sampled point is fed into the trained decoder to generate new polar representations. The network has shown exceptional generation capabilities. It is also seen that the latent space forms a conceptual space where different directions and regions show inherent patterns related to the generated representations and their corresponding material properties

Technical studies for operations with real-time communications in robotic missions

Robotic telepresence operations between earth and space are of high research value for science as they enable operators on ground to perform physical tasks in space without the need of human presence. Real-Time telepresence with haptic-feedback and stereoscopic imaging, however, poses new requirements to physical parameters of the communication channel like loss, delay and jitter as well as to the protocols spoken between the participants. To meet the new requirements, past robotic missions like ROKVISS chose to use specialized and dedicated communication channels while bypassing the established ground station network infrastructure. However, performing robotic and standard TM/TC operations in parallel was impossible because the Space Link could only be locked by either of the communication chains. For future missions, we present a setup that multiplexes robotic science data and standard TM/TC into one physical channel. Real-time requirements are met because the setup makes use of several FPGAs that forward UDP packets in synchronization with a common master clock. We present test results and test measurements of this technology and compare the proposed setup to a software based solution. Furthermore we present general approaches, tools and techniques for real-time related tasks. Finally we discuss the use of Space Link and Space Link Extension protocols in the communication chain and their impact on the real-time requirements. Operational aspects of the new setup and protocols are discussed as well

Tracking trauma-induced structural and functional changes above the level of spinal cord injury

PURPOSE OF REVIEW: This review will highlight the latest findings from neuroimaging studies that track structural and functional changes within the central nervous system at both the brain and spinal cord levels following acute human spinal cord injury (SCI). The putative, underlying biological mechanisms of structural change (e.g. degradation of neural tissue) rostral to the lesion site will be discussed in relation to animal models of SCI and their potential value in clinical studies of human SCI. RECENT FINDINGS: Recent prospective studies in human acute SCI have begun to reveal the time-course, spatial distribution and extent of structural changes following an acute SCI and their relation to functional outcome. Adaptive changes in sensory and motor pathways above the level of the lesion have prognostic value and complement clinical readouts. SUMMARY: The introduction of sensitive neuroimaging biomarkers will be an essential step forward in the implementation of interventional trials in which proof-of-concept is currently limited to clinical readouts, but more responsive measures are required to improve the sensitivity of clinical trials

Extra Fructose in the Growth Medium Fuels Lipogenesis of Adipocytes

Fructose in excessive amounts exerts negative effects on insulin sensitivity, blood pressure, and liver metabolism. These adverse outcomes were attributed to its disturbances of key metabolic pathways in the liver. Recently, possible consequences of high fructose levels directly on adipocytes in vivo have been considered. We have cultured adipocytes in growth media containing 1 g/L fructose additionally to glucose and monitored the cells fate. Cells developed lipid vesicles much earlier with fructose and showed altered kinetics of the expression of mRNAs involved in lipogenesis and hexose uptake. Adiponectin secretion, too, peaked earlier in fructose containing media than in media with glucose only. From these data it can be speculated that similar effects of fructose containing diets happen in vivo also. Apart from toxic action on liver cells, adipocytes might be stimulated to take up extra fructose and generate new lipid vesicles, further dysregulating energy homeostasis