The attachment strategy of English ivy: a complex mechanism acting on several hierarchical levels

English ivy (Hedera helix L.) is able to grow on vertical substrates such as trees, rocks and house plaster, thereby attaching so firmly to the surface that when removed by force typically whole pieces of the climbing substrate are torn off. The structural details of the attachment process are not yet entirely understood. We studied the attachment process of English ivy in detail and suggest a four-phase process to describe the attachment strategy: (i) initial physical contact, (ii) form closure of the root with the substrate, (iii) chemical adhesion, and (iv) shape changes of the root hairs and form-closure with the substrate. These four phases and their variations play an important role in the attachment to differently structured surfaces. We demonstrate that, in English ivy, different mechanisms work together to allow the plant''s attachment to various climbing substrates and reveal the importance of micro-fibril orientation in the root hairs for the attachment based on structural changes at the subcellular level.     

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Carbide and nanocomposite thin films in the Ti-Pt-C system

Thin films in the Ti-Pt-C system were deposited by non-reactive, DC-magnetron sputtering. Samples were characterised using X-ray photoelectron spectroscopy, X-ray diffraction, and transmission electron microscopy. A previously not reported metastable solid solution carbide, (Ti_1 − xPt_x)C_y with a Pt/Ti ratio of up to 0.43 was observed. This solid solution phase was present both as single phase in polycrystalline samples, and together with amorphous carbon (a-C) in nanocomposite samples. Annealing of nanocomposite samples leads to the decomposition of the solid solution phase and the formation of a nc-TiC_x/a-C/nc-Pt nanocomposite. Test sensors for automotive gas exhausts manufactured from such a three-phase material suffer from complete oxidation of the coating at 400 °C with no observed sensor activity.     

Solid-state diffusion as an efficient doping method for silicon nanowires and nanowire field effect transistors

In this work we investigate doping by solid-state diffusion from a doped oxide layer, obtained by plasma-enhanced chemical vapor deposition (PECVD), as a means for selectively doping silicon nanowires (NWs). We demonstrate both n-type (phosphorous) and p-type (boron) doping up to concentrations of 10(20) cm(-3), and find that this doping mechanism is more efficient for NWs as opposed to planar substrates. We observe no diameter dependence in the range of 25 to 80 nm, which signifies that the NWs are uniformly doped. The drive-in temperature (800-950?°C) can be used to adjust the actual doping concentration in the range 2 × 10(18) to 10(20) cm(-3). Furthermore, we have fabricated NMOS and PMOS devices to show the versatility of this approach and the possibility of achieving segmented doping of NWs. The devices show high I(on)/I(off) ratios of around 10(7) and, especially for the PMOS, good saturation behavior and low hysteresis.     

Extending EDCA with distributed resource reservation for QoS guarantees

In this paper we describe how the contention-based medium access mechanism of 802.11e, EDCA, can be enhanced in order to allow stations to reserve medium access for their real-time applications with QoS requirements. We present our proposed scheme, which is called EDCA with resource reservation (EDCA/RR), and describe how it can be extended in order to be used in wireless multi-hop networks. EDCA/RR operates in a completely distributed manner and manages to provide deterministic, contention-free medium access, making it an attractive scheme for wireless networks.     

Power output estimation and experimental validation for piezoelectric energy harvesting systems

Many modern devices especially for ubiquitous computing or wireless sensor networks need a long life energy source. Batteries or accumulators are often an insufficient solution. Low frequency vibrations can be found in the most technical facilities or even in the human movements. Even while these vibrations are neither wanted nor used in the most times, they enable us to generate electrical energy. Piezoelectric flexural transducers are a promising choice for utilizing the vibrations for energy harvesting. There are two major influences on the amount of generated energy. First there is the frequency behavior of the piezoelectric transducers, for optimal power output the transducer should be driven in resonance. Second, the energy output is highly dependent on the electrical load of the connected application. Both circumstances, working frequency and electrical load, typically are boundary conditions for the development of the generator. Therefore, it is necessary to handpick the type of piezoelectric elements. To meet the requirements of development engineers, a model based design method for energy harvesting systems is needed. As a first step towards such a method, this work proposes a model for the estimations of the power output of piezoelectric flexural transducers. For the validation of this model an experiment is described in detail. The results of the model and the experiments are compared.     

Stress‐Dependent Elastic Properties of Porous Microcracked Ceramics

Although ceramics are considered linear elastic materials, we have observed a non‐linear pseudo‐elastic behavior in porous cellular microcracked ceramics such as β‐eucryptite. This is attributed to the evolution of microstructure in these materials. This behavior is particularly different from that of non‐microcracked ceramics such as silicon carbide. It is shown that in microcracked materials two processes, namely stiffening and softening, always compete when a compressive external load is applied. The first regime is attributed to microcrack closure, and the second to microcracks opening, i.e. to a damage introduced by the applied stress. On the other hand rather a continuous damage is observed in the non‐microcracked case. A comparison has been done between the microscopic (as measured by neutron diffraction) and the macroscopic stress‐strain response. Also, it has been found that at constant load a significant strain relaxation occurs, which has two timescales, possibly driven by the two phenomena quoted above. Indeed, no such relaxation is observed for non‐microcracked SiC. Implications of these findings are discussed.     

Reduced pyruvate decarboxylase and increased glycerol-3-phosphate dehydrogenase [NAD+] levels enhance glycerol production in Saccharomyces cerevisiae

This investigation deals with factors affecting the production of glycerol in Saccharomyces cerevisiae. In particular, the impact of reduced pyruvate-decarboxylase (PDC) and increased NAD-dependent glycerol-3-phosphate dehydrogenase (GPD) levels was studied. The glycerol yield was 4·7 times (a pdc mutant exhibiting 19% of normal PDC activity) and 6·5 times (a strain exhibiting 20-fold increased GPD activity resulting from overexpression of GPD1 gene) that of the wild type. In the strain carrying both enzyme activity alterations, the glycerol yield was 8·1 times higher than that of the wild type. In all cases, the substantial increase in glycerol yield was associated with a reduction in ethanol yield and a higher by-product formation. The rate of glycerol formation in the pdc mutant was, due to a slower rate of glucose catabolism, only twice that of the wild type, and was increased by GPD1 overexpression to three times that of the wild-type level. Overexpression of GPD1 in the wild-type background, however, led to a six- to seven-fold increase in the rate of glycerol formation. The experimental work clearly demonstrates the rate-limiting role of GPD in glycerol formation in S. cerevisiae.