Principles of Branching Morphology and Anatomy in Arborescent Monocotyledons and Columnar Cacti as Concept Generators for Branched Fiber‐Reinforced Composites

The branching of arborescent (tree‐like) monocotyledonous plants of the genus Dracaena or of columnar cacti differ considerably from that observed in other dicotyledonous or gymnosperm trees. The investigated ramifications exhibit distinctive morphological and anatomical features. In arborescent monocotyledons the side branches are attached to the main stem by a fiber‐reinforced tissue newly formed during secondary growth, clasping the main stem and finally resulting in a “flange‐mounted” structure. In the case of columnar cacti the most obvious feature is the pronounced constriction at the attachment point of the branches that is also mirrored in the lignified vascular tissue. One might argue that these characteristic morphological and anatomical features in regions exposed to high mechanical stresses represent structural weaknesses. However, the outer shape and the inner structures of the ramifications cause considerable stability and structural integrity of the stem‐branch connection under static and dynamic loading. Our results allow concluding that load‐adaptation in ramified plant structures is a result of a combination of optimization in outer shape and fiber arrangement within the ramifications. Numerical methods simulating the mechanical behavior based on data obtained from the studied plants support this assumption. A deeper understanding of the outer shape of the connection between shoot and branch as well as of the arrangement of the lignified vascular tissues in the branching region, may contribute toward alternative concepts for branched technical light‐weight‐structures. In particular for braided fiber‐reinforced composites this biomimetic approach might help to keep the demand on the available design space as small as possible.     

Direct numerical study of hypersonic flow about a swept parabolic body

Direct numerical simulations (DNS) of hypersonic flow about a swept parabolic body have been performed to study the global stability of flow in the leading-edge region of a swept blunt body. Previous stability investigations have been based on local models but have not fully succeeded in reproducing the established experimental findings. The current flow configuration represents a more realistic model and is thus expected to resolve some of the remaining questions. However, novel approaches like DNS-based global stability theory are necessary for such flow models and are employed in this study. As a result, boundary-layer modes have been identified by different but complementary techniques as the dominant instability mechanism. The DNS starting with small-amplitude white noise provide further evidence for the presence of non-modal effects which may be important in the subcritical regime. From a methodological point of view, the potential for quantitative flow analysis by combining numerical simulations with advanced iterative techniques represents a promising direction for investigating the governing physical processes of complex flows.     

On the internal structure of weakly nonlinear bores in laminar high Reynolds number flow

The paper deals with the internal structure of hydraulic jumps in near-critical single-layer flows which replaces the discontinuities predicted by hydraulic theory if viscous effects acting inside a thin laminar boundary layer are properly accounted for. In the limit of large Reynolds number this leads to a structure problem formed by the classical triple-deck equations supplemented with a novel nonlinear interaction relationship which allows for the passage through the critical state. Hydraulic jumps are shown to represent eigensolutions of the structure problem where this passage is achieved by the local thickening of the boundary layer which acts as a viscous hump. The effects of detuning and dispersion due to streamline curvature and surface tension on the internal structure of hydraulic jumps are studied in detail. In addition, the interaction of hydraulic jumps with surface mounted obstacles is investigated.     

Competing topological phases in few-layer graphene

We investigate the effect of spin-orbit coupling on the band structure of graphene-based two-dimensional Dirac fermion gases in the quantum Hall regime. Taking monolayer graphene as our first candidate, we show that a quantum phase transition between two distinct topological states—the quantum Hall and the quantum spin Hall phases—can be driven by simply tuning the Fermi level with a gate voltage. This transition is characterized by the existence of a chiral spin-polarized edge state propagating along the interface separating the two topological phases. We then apply our analysis to the more difficult case of bilayer graphene. Unlike in monolayer graphene, spin-orbit coupling by itself has indeed been predicted to be unsuccessful in driving bilayer graphene into a topological phase, due to the existence of an even number of pairs of spin-polarized edge states. While we show that this remains the case in the quantum Hall regime, we point out that by additionally breaking the layer inversion symmetry, a non-trivial quantum spin Hall phase can re-emerge in bilayer graphene at low energy. We consider two different symmetry-breaking mechanisms: inducing spin-orbit coupling only in the upper layer, and applying a perpendicular electric field. In both cases, the presence at low energy of an odd number of pairs of edge states can be driven by an exchange field. The related situation in trilayer graphene is also discussed.     

Visualization of immune cell infiltration in experimental viral myocarditis by 19F MRI in vivo

Objective

This paper introduces a new approach permitting for the first time a specific, non-invasive diagnosis of myocarditis by visualizing the infiltration of immune cells into the myocardium.

Materials and methods

The feasibility of this approach is shown in a murine model of viral myocarditis. Our study uses biochemically inert perfluorocarbons (PFCs) known to be taken up by circulating monocytes/macrophages after intravenous injection.

Results

In vivo ¹⁹F MRI at 9.4 T demonstrated that PFC-loaded immune cells infiltrate into inflamed myocardial areas. Because of the lack of any fluorine background in the body, detected ¹⁹F signals of PFCs are highly specific as confirmed ex vivo by flow cytometry and histology.

Conclusion

Since PFCs are a family of compounds previously used clinically as blood substitutes, the technique described in our paper holds the potential as a new imaging modality for the diagnosis of myocarditis in man.     

Quantification and localization of contrast agents using delta relaxation enhanced magnetic resonance at 1.5?T

Object

Delta relaxation enhanced magnetic resonance (dreMR) is a new imaging technique based on the idea of cycling the magnetic field B ₀ during an imaging sequence. The method determines the field dependency of the relaxation rate (relaxation dispersion dR ₁/dB). This quantity is of particular interest in contrast agent imaging because the parameter can be used to determine contrast agent concentrations and increases the ability to localize the contrast agent.

Materials and methods

In this paper dreMR imaging was implemented on a clinical 1.5?T MR scanner combining conventional MR imaging with fast field-cycling. Two improvements to dreMR theory are presented describing the quantification of contrast agent concentrations from dreMR data and a correction for field-cycling with finite ramp times.

Results

Experiments demonstrate the use of the extended theory and show the measurement of contrast agent concentrations with the dreMR method. A second experiment performs localization of a contrast agent with a significant improvement in comparison to conventional imaging.

Conclusion

dreMR imaging has been extended by a method to quantify contrast agent concentrations and improved for field-cycling with finite ramp times. Robust localization of contrast agents using dreMR imaging has been performed in a sample where conventional imaging delivers inconclusive results.     

Ozone Differentially Affects Perception of Plant Volatiles in Western Honey Bees

Floral scents play a key role in mediating plant-pollinator interactions. Volatile organic compounds (VOCs) emitted by flowers are used by flower visitors as olfactory cues to locate flowers, both from a distance and at close range. More recently it has been demonstrated that reactive molecules such as ozone can modify or degrade VOCs, and this may impair the communication between plants and their pollinators. However, it is not known whether such reactive molecules also may affect the olfactory system of pollinators, and thus not only influence signal transmission but perception of the signal. In this study, we used electroantennographic measurements to determine the effect of increased levels of ozone on antennal responses in western honey bees (Apis mellifera L.). Linalool and 2-phenylethanol, both known to be involved in location of flowers by the bees, and (Z)-3-hexenyl acetate, a widespread green leaf volatile also detected by bees, were used. The results showed that ozone affected antennal responses to the different substances differently. Ozone decreased antennal responses to (Z)-3-hexenyl acetate, whereas responses to linalool and 2-phenylethanol were not influenced by ozone. Overall, the study does not provide evidence that pollination by honey bees is impaired by damage in the olfactory system of the bees caused by increased levels of ozone, at least when linalool and 2-phenylethanol are the attractive signals. However, the results also suggest that ozone can change the overall perception of an odor blend. This might have negative effects in pollination systems and other organismic interactions mediated by specific ratios of compounds.     

The Chemical Evolution of the La<Subscript>0.6</Subscript>Sr<Subscript>0.4</Subscript>CoO<Subscript>3−δ</Subscript> Surface Under SOFC Operating Conditions and Its Implications for Electrochemical Oxygen Exchange Activity

Owing to its extraordinary high activity for catalysing the oxygen exchange reaction, strontium doped LaCoO₃ (LSC) is one of the most promising materials for solid oxide fuel cell (SOFC) cathodes. However, under SOFC operating conditions this material suffers from performance degradation. This loss of electrochemical activity has been extensively studied in the past and an accumulation of strontium at the LSC surface has been shown to be responsible for most of the degradation effects. The present study sheds further light onto LSC surface changes also occurring under SOFC operating conditions. In-situ near ambient pressure X-ray photoelectron spectroscopy measurements were conducted at temperatures between 400 and 790 °C. Simultaneously, electrochemical impedance measurements were performed to characterise the catalytic activity of the LSC electrode surface for O₂ reduction. This combination allowed a correlation of the loss in electro-catalytic activity with the appearance of an additional La-containing Sr-oxide species at the LSC surface. This additional Sr-oxide species preferentially covers electrochemically active Co sites at the surface, and thus very effectively decreases the oxygen exchange performance of LSC. Formation of precipitates, in contrast, was found to play a less important role for the electrochemical degradation of LSC.