The dune size distribution and scaling relations of barchan dune fields

Barchan dunes emerge as a collective phenomena involving the generation of thousands of them in so called barchan dune fields. By measuring the size and position of dunes in Moroccan barchan dune fields, we find that these dunes tend to distribute uniformly in space and follow an unique size distribution function. We introduce an analytical mean-field approach to show that this empirical size distribution emerges from the interplay of dune collisions and sand flux balance, the two simplest mechanisms for size selection. The analytical model also predicts a scaling relation between the fundamental macroscopic properties characterizing a dune field, namely the inter-dune spacing and the first and second moments of the dune size distribution.     

Lymphangioma of the right kidney in an infant boy

A 9-month-old boy with a primary cystic lymphangioma of the right kidney is reported. The clinical and radiological features favored a malignant tumor. Histology revealed the lesion to be a lymphangioma; the diagnosis was confirmed by immunohistochemistry and chemical analysis of the intracystic fluid. Lymphangiomas of the kidney are rare in adults; they are even rarer in infants and children. Nevertheless, renal lymphangiomas should be considered in the differential diagnosis of multicystic, unilateral renal masses, independent of the age of the patient.     

Comparative studies of pyruvate kinase from PSE and normal pig muscles

A fast breakdown of glycogen is observed in muscles of stress-susceptible pigs leading to pale, soft and exudative (PSE) meat. We report a comparative study of pyruvate kinase from muscles of normal and PSE-prone pigs. Compared with the enzyme from normal muscle, pyruvate kinase isolated from PSE muscle shows a five times lower Michaelis constant,K _m, for phosphoenol pyruvate and a more than ten times higherk _cat/K _m value. The pH dependency of the enzymatic activity is shifted to more acidic values for pyruvate kinase from PSE muscles. According to isoelectric focusing, pyruvate kinase from PSE muscle consists of three isoforms, while only two isoforms are detectable in pyruvate kinase preparations from normal pigs. The various isoforms were isolated by preparative isoelectric focusing and their steady-state properties were compared. Isoform 3, which is found only in PSE muscle, shows a 10-fold higher specific activity, a 30-fold lowerK _m value and a 100-fold increasedk _cat/K _m value for phosphoenol pyruvate as compared to isoform 1. The presence of isoform 3 in PSE muscle appears to be responsible for the high activity of this enzyme under the more acidic conditions prevailing in PSE muscle. In vitro phosphorylation and dephosphorylation experiments using total enzyme and purified isoenzyme 1 suggest that isoforms 2 and 3 arise from isoform 1 by phosphorylation. Thus protein phosphorylation seems to be responsible for the shift in activity of pyruvate kinase, a key enzyme of glycolysis, under the acidic conditions of PSE muscles.     

25th Anniversary Article: A Soft Future: From Robots and Sensor Skin to Energy Harvesters

Scientists are exploring elastic and soft forms of robots, electronic skin and energy harvesters, dreaming to mimic nature and to enable novel applications in wide fields, from consumer and mobile appliances to biomedical systems, sports and healthcare. All conceivable classes of materials with a wide range of mechanical, physical and chemical properties are employed, from liquids and gels to organic and inorganic solids. Functionalities never seen before are achieved. In this review we discuss soft robots which allow actuation with several degrees of freedom. We show that different actuation mechanisms lead to similar actuators, capable of complex and smooth movements in 3d space. We introduce latest research examples in sensor skin development and discuss ultraflexible electronic circuits, light emitting diodes and solar cells as examples. Additional functionalities of sensor skin, such as visual sensors inspired by animal eyes, camouflage, self‐cleaning and healing and on‐skin energy storage and generation are briefly reviewed. Finally, we discuss a paradigm change in energy harvesting, away from hard energy generators to soft ones based on dielectric elastomers. Such systems are shown to work with high energy of conversion, making them potentially interesting for harvesting mechanical energy from human gait, winds and ocean waves.     

Small-molecule vacuum processed melamine-C60, organic field-effect transistors

The transfer of benchtop knowledge into large scale industrial production processes represents a challenge in the field of organic electronics. Large scale industrial production of organic electronics is envisioned as roll to roll (R2R) processing which nowadays comprises usually solution-based large area printing steps. The search for a fast and reliable fabrication process able to accommodate the deposition of both insulator and semiconductor layers in a single step is still under way. Here we report on the fabrication of organic field effect transistors comprising only evaporable small molecules. Moreover, both the gate dielectric (melamine) and the semiconductor (C₆₀) are deposited in successive steps without breaking the vacuum in the evaporation chamber. The material characteristics of evaporated melamine thin films as well as their dielectric properties are investigated, suggesting the applicability of vacuum processed melamine for gate dielectric layer in OFETs. The transistor fabrication and its transfer and output characteristics are presented along with observations that lead to the fabrication of stable and virtually hysteresis-free transistors. The extremely low price of precursor materials and the ease of fabrication recommend the evaporation processes as alternative methods for a large scale, R2R production of organic field effect transistors.     

Effects of different storage conditions on quality related porphyrin fluorescence signatures of pork slices

This study evaluated the potential of fluorescence as an indicator of pork quality by determining the effects of various conditions on fluorescence signatures (excitation at 420 nm, emission at 550-750 nm).Storage of porcine musculus longissimus dorsi in PE bags led to a clear increase in porphyrin fluorescence intensity after approx. 10 d post mortem. Modified gas atmosphere (70% O₂, 30% CO₂) inhibited the fluorescence emission of zinc protoporphyrin and protoporphyrin IX due to quenching by oxygen. Bleaching processes caused similar effects by halogen light exposure during meat storage. However, already formed signals could not be manipulated by oxygen or halogen light. Storage under vacuum reduced the quenching effects and resulted in increased fluorescence intensities. Freezing and thawing of meat samples delayed and reduced the increase in fluorescence intensity. Only minor effects could be detected at long-term frozen storage for two months.Consequently porphyrin fluorescence analysis is a potential means to indicate changes of pork quality and remaining shelf life.     

Vacuum-processed polyethylene as a dielectric for low operating voltage organic field effect transistors

We report on the fabrication and performance of vacuum-processed organic field effect transistors utilizing evaporated low-density polyethylene (LD-PE) as a dielectric layer. With C₆₀ as the organic semiconductor, we demonstrate low operating voltage transistors with field effect mobilities in excess of 4 cm²/Vs. Devices with pentacene showed a mobility of 0.16 cm²/Vs. Devices using tyrian Purple as semiconductor show low-voltage ambipolar operation with equal electron and hole mobilities of ～0.3 cm²/Vs. These devices demonstrate low hysteresis and operational stability over at least several months. Grazing-angle infrared spectroscopy of evaporated thin films shows that the structure of the polyethylene is similar to solution-cast films. We report also on the morphological and dielectric properties of these films. Our experiments demonstrate that polyethylene is a stable dielectric supporting both hole and electron channels.