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Indirect, non-destructive methods to derive biophysical parameters, such as leaf area index (LAI), are of major importance for optimal grassland growth modelling and management. In this study, we compared different methods for the estimation of LAI in permanent grassland including (i) two direct methods, (ii) two indirect optical methods (AccuPAR and LAI-2200C), (iii) a proximal (field spectrometer) and a satellite remote sensing approach using Sentinel-2 (S-2) data, both based on radiative transfer modelling (RTM) of vegetation. To consider the seasonal variability of LAI sufficiently, we performed in situ measurements weekly during the entire growing season of 2018 and 2019. The RTM-based methods showed the lowest root-mean-square error (RMSE) when compared with direct green LAI measurements, which ranged from 1.68 to 7.85. The indirect optical methods resulted in higher RMSE values but in similar high correlation coefficients (r). The comparison between the indirect optical methods showed that the AccuPAR and the LAI-2200C highly correlate with a systematic underestimation of the AccuPAR in the upper range of LAI values. As expected, S-2 and the field spectrometer showed the highest correlation (RMSE: 0.40 and r: 0.95). Generally, we observed a significant influence of the seasonal changes of the canopy structure and morphology on the estimation accuracy.

The d-separation criterion detects the compatibility of a joint probability distribution with a directed acyclic graph through certain conditional independences. In this work, we study this problem in the context of categorical probability theory by introducing a categorical definition of causal models, a categorical notion of d-separation, and proving an abstract version of the d-separation criterion. This approach has two main benefits. First, categorical d-separation is a very intuitive criterion based on topological connectedness. Second, our results apply both to measure-theoretic probability (with standard Borel spaces) and beyond probability theory, including to deterministic and possibilistic networks. It therefore provides a clean proof of the equivalence of local and global Markov properties with causal compatibility for continuous and mixed random variables as well as deterministic and possibilistic variables., Comment: 42 pages, v2: more examples and an extended introduction, v3: corrected typo in Def. 4

The level of energy consumption in renovation activities of buildings has huge advantages over the demolition of old buildings and the construction of new structures. Such renovation activities are usually associated with the simultaneous strengthening of their elements, such as externally bonded carbon fibre reinforced polymer (CFRP) lamellas or sheets on vertical and horizontal surfaces as structural reinforcements. This means the process of refurbishing a building, as well as the raw materials themselves have a significant impact on CO2 emissions and energy consumption. This research paper demonstrates possibilities of replacing state of the art, highly energy-intensive CFRP lamellas with basalt fibre reinforced plastics as energy-efficient structural reinforcements for building constructions. The mechanical and thermal properties of basalt fibre reinforced polymer (BFRP) composites with variable matrix formulations are investigated. The article considers macro- and microstructures of innovative BFRP. The investigations focus on fibre–matrix interactions with different sizing formulations and their effect on the tensile strength, strain as well as modulus of elasticity.

A novel B-stage resin system is developed for the „Resin Transfer Pressing“ (RTP) process. This composite manufacturing technique makes use of nonwoven and recycled carbon fibres (rCF) that are oversaturated with a thermosetting resin. The new resin system is based on two different hardeners, allowing to easily impregnate the rCF, storing the semi-finished parts at room temperature and finally curing them via compression molding. It is shown that a commercially available resin system can be tailored to the required needs by the smart combination of state-of-the art, latent hardener systems.The present study focusses on the route for B-staging of the resin system. The viscosity for impregnation and oversaturation was adjusted to be in the range of 5 to 40 Pa·s at 60°C. The viscosity increases to above 50 Pa·s at room temperature, allowing storage and handling of the semi-finished parts and processing them whenever it is required. Choosing a proper processing temperature is important during the B-staging process to avoid any unintended activation of the second hardener, which is responsible for the final curing stage of the system.

The Solid Sorbent Technology (SST) is a breakthrough technology which separates CO2 from flue gas in a continuous Temperature Swing Adsorption (TSA) fluidized bed process using solid adsorbent. The technology simultaneously delivers > 90% CO2 capture efficiency and > 95% CO2 purity with low to no process related emissions and at lower capture costs compared to state-of-the-art liquid amines technology. This paper will discuss results of a 900 h piloting campaign using Lewatit VP OC 1065 adsorbent and its impact on the cost comparison with liquid amines technology. The successful operation of the pilot plant and finalization of the test campaign marked the progression of the technology readiness level from TRL4 to TRL6.

The toughening performance of hybridized core-shell rubber particles and block copolymers on bulk epoxy and epoxy based carbon fibre reinforced composites was investigated. The results reveal that the interlaminar fracture toughness of the fibre reinforced laminates increased by more than 300% due to an enhanced fibre-matrix adhesion because of a combination of BCP and CSR particles. However, no synergistic improvement of the fracture mechanics properties of the bulk materials was found. Thereby, the critical energy release rate of the bulk and fibre reinforced materials is related to the interparticle distance to particle size ratio of the modifiers in the bulk/matrix systems and the plastic zone size. Furthermore, the fibre volume content of the CFRP influences the final BCP phase morphology, and thus the fracture toughness.

This study focused on the examination of unsaturated polyester resin based continuous glass filament mat reinforced composites (GFRP) and the modification by core-shell rubber particles (CSR). The goal was to evaluate the effect of CSR toughening on processability, mechanical properties and impact strength as well as the interaction with inorganic color particles in the submicron range on the GFRP. The interlaminar fracture toughness GIc of the modified GFRP was improved by about 20% compared to the neat GFRP by using only 2 wt-% of the CSR modifier, while only marginally increasing the viscosity of the reactive mixture. The responsible mechanisms were found to be local shear yielding of the matrix and an improved fiber-matrix adhesion. The hybridization of inorganic color particles and CSR reduced the interlaminar fracture toughness of the laminate, which could be ascribed to the formation of pores due to the introduction of the oxide particles. However, the impact behavior of the GFRP was positively affected.

This study systematically investigates the influence of a Polymethylmethacrylate-block-Polybutylacrylate-block-Polymethylmethacrylate (PMMA-b-PBuA-b-PMMA) triblock copolymer (BCP) on the flexural properties, the static fracture toughness and especially the resistance to fatigue crack propagation (FCP) of a cycloaliphatic amine cured bisphenol A based epoxy resin (EP). The results show that already small concentrations of BCP can significantly improve fracture toughness and the resistance to fatigue crack propagation. Crack growth rate as well as the Paris' law exponent m were considerably reduced from m = 15.5 of the neat epoxy to m = 8.1 for the BCP toughened materials. Simultaneously, the resistance to fatigue crack propagation was found to increase drastically from a critical stress intensity factor range ΔKIc of 0.39 MPam to 0.81 MPam. Fractography and structural analysis reveal that the improved resistance to fatigue crack propagation correlates to crack shielding and zone shielding mechanisms caused by the synergistic interaction of BCP-rich domains and dispersed nanometer sized, presumably BCP-rich particles in epoxy-rich regions. POLYM. ENG. SCI., 2017. © 2017 Society of Plastics Engineers

The benefit of fiber-reinforced composites originates from the interaction between the fiber reinforcement and the matrix. This interplay controls many of its mechanical properties and is of utmost importance to enable its unique performance as a lightweight material. However, measuring the fiber−matrix interphase strength with micromechanical tests, like the Broutman test, is challenging, due to the many, often unknown boundary conditions. Therefore, this study uses state-of-the-art, high-resolution X-ray computed microtomography (XRM) as a tool to investigate post mortem the failure mechanisms of single carbon fibers within an epoxy matrix. This was conducted at the example of single carbon fiber Broutman test specimens. The capabilities of today’s XRM analysis were shown in comparison to classically obtained light microscopy. A simple finite element model was used to enhance the understanding of the observed fracture patterns. In total, this research reveals the possibilities and limitations of XRM to visualize and assess compression-induced single fiber fracture patterns. Furthermore, comparing two different matrix systems with each other illustrates that the failure mechanisms originate from differences in the fiber−matrix interphases. The carbon fiber seems to fail due to brittleness under compression stress. Observation of the fiber slippage and deformed small fracture pieces between the fragments suggests a nonzero stress state at the fragment ends after fiber failure. Even more, these results demonstrate the usefulness of XRM as an additional tool for the characterization of the fiber−matrix interphase.

Microscale machining processes modifying component surfaces are applied in various fields: from drive technology through plant engineering to medical technology. The impact of the fine structures formed in the material on its behavior and mechanical properties need to be investigated in more detail. Besides the examination of the cyclic and quasi-static behavior of micromachined samples, analysing the near-surface microstructure and the hardness is of great importance. The nanoindentation allows for the determination of local mechanical properties in small analysis volumes. Its applicability to determine the hardness in micromachined near-surface areas including the metallographic preparation for commercially pure titanium is presented in this work.

The effect of the hybridization of a triblock copolymer and a rigid TiO2 nanofiller on the tensile, fracture mechanics and thermo-mechanical properties of bisphenol F based epoxy resin were studied. The self-assembling block copolymer, constituted of a center block of poly (butyl acrylate) and two side blocks of poly (methyl) methacrylate-co-polar co-monomer was used as a soft filler, and TiO2 nanoparticles were employed as rigid modifiers. Toughening solely by block copolymers (BCP&rsquo, s) led to the highest fracture toughness and fracture energy in the study, KIc = 2.18 MPa&middot, m1/2 and GIc = 1.58 kJ/m2. This corresponds to a 4- and 16-fold improvement, respectively, over the neat reference epoxy system. However, a reduction of 15% of the tensile strength was observed. The hybrid nanocomposites, containing the same absolute amounts of modifiers, showed a maximum value of KIc = 1.72 MPa&middot, m1/2 and GIc = 0.90 kJ/m2. Yet, only a minor reduction of 4% of the tensile strength was observed. The fracture toughness and fracture energy were co-related to the plastic zone size for all the modified systems. Finally, the analysis of the fracture surfaces revealed the toughening mechanisms of the nanocomposites.

Self-assembling block-copolymers allow the easy manufacturing of nanocomposites due to the thermodynamically driven in situ formation of nanosized phases in thermosetting resins during the curing process. Complex mechanical dispersion processes can be avoided. The current study investigates the effect of a block-copolymer on the fatigue crack propagation resistance of a cycloaliphatic amine cured epoxy resin. It was found that a small amount of MAM triblock-copolymer significantly increases the resistance to fatigue crack propagation of epoxy. Crack growth rate and the Paris law exponent for fatigue-crack growth were considerably reduced from m=15.5 of the neat epoxy to m=8.1 of the nanocomposite.To identify the related reinforcing and fracture mechanisms structural analyses of the fractured surfaces were performed by scanning electron microscope. Characteristic features were identified to be deformation, debonding and fracture of the nano-phases as well as crack pinning. However, the highest resistance a...

Several physically inspired problems have been proven undecidable; examples are the spectral gap problem and the membership problem for quantum correlations. Most of these results rely on reductions from a handful of undecidable problems, such as the halting problem, the tiling problem, the Post correspondence problem or the matrix mortality problem. All these problems have a common property: they have an NP-hard bounded version. This work establishes a relation between undecidable unbounded problems and their bounded NP-hard versions. Specifically, we show that NP-hardness of a bounded version follows easily from the reduction of the unbounded problems. This leads to new and simpler proofs of the NP-hardness of bounded version of the Post correspondence problem, the matrix mortality problem, the positivity of matrix product operators, the reachability problem, the tiling problem, and the ground state energy problem. This work sheds light on the intractability of problems in theoretical physics and on the computational consequences of bounding a parameter., 10 pages and 7 pages of appendices, 8 figures; v2,v3: minor changes