Stroomdalgraslanden in Nederland : ontwikkeling en beheer in de Vreugderijkerwaard : veldwerkplaats rivierenlandschap Vreugderijkerwaard, 16 mei 2008

Verslag van de veldwerkplaats in de Vreugderijkerwaard, een tweeluik van excursies. Op 28 mei zijn de Millingerwaard en de Erlecomsewaard bezocht. Per gebied werden de beheersstrategieën besproken, de mate van begrazingsintensiteit voor een succesvol beheer, de dynamische verschillen per uiterwaardengebied en de verspreiding en soortensamenstelling van plantengemeenschappen. De Vreugderijkerwaard is een uiterwaard langs de IJssel, waarvan een deel al tientallen jaren in beheer is bij Natuurmonumenten. Op de oeverwal is tijdens de veldexcursie een prachtig ontwikkelde stroomdalvegetatie aangetroffen. Dit zijn de resultaten van een uitgekiend begrazingsbeheer. Ook zijn sinds enkele jaren een aantal voormalige agrarische graslanden bij het reservaat gevoegd en integraal opgenomen in de begrazing. Al na een paar jaar vestigden zich hier (massaal) enkele rode lijst- soorten. De basis voor een geslaagd beheer is de aanwezigheid van gezonde natuurlijke processen

Grayson Ligament:A Revised Description of its Anatomy and Function

PURPOSE: Grayson ligament has been described as a common pathway for digital contracture in Dupuytren disease. Its anatomical descriptions in the literature are, however, inconsistent. METHODS: We have performed a microsurgical dissection study in 20 fresh-frozen and thawed digits to revisit the anatomy of Grayson ligaments. We also performed dissections in Thiel-preserved hands to be able to study the changes in tension of the ligaments during flexion and extension of the finger. RESULTS: We found the ligaments originally described by Grayson to be the best developed part of a trabecular network of fibers, originating in continuity with the outer adventitial layer of the flexor tendon sheath and running toward their insertions into the skin in multiple planes, all volar to the neurovascular bundle. The most dorsal fibers, which cover the neurovascular bundles, form a chevron shape with its midline apex pointing distally in an extended finger. During flexion, the fibers become more transversely oriented. CONCLUSIONS: We found Grayson ligament comprises a trabecular network of fibers, instead of a ligament, with a dynamic fiber orientation on the volar side of the finger. The main function of this network of fibers seems to be the stabilization of the skin and fat pad in digit extension while the relaxation in flexion allows the skin and volar fat pad to adapt optimally to the form of the object that is held. CLINICAL RELEVANCE: The new insights in the anatomy of Grayson trabecular network of fibers may be of importance in the understanding of the pathological anatomy of Dupuytren disease

Strigolactone analogues induce suicidal seed germination of Striga spp. in soil

Striga hermonthica and Striga asiatica are obligate root parasites that cause serious problems in the production of staple cereal crops in Africa. Because of the high levels of infestation, there is an urgent need to control these weeds. A potentially useful control option is depletion of the soil seed bank by suicidal germination, which involves germination of the seeds in the absence of host plants. Suicidal germination is often mentioned in the literature, but not considered realistic, because of the alleged untimely decomposition of the stimulants in the soil, despite the fact that some encouraging results were reported around 1980. The alleged instability has prevented active research in this direction for the past 20–25 years. Five newly designed synthetic germination stimulants were investigated as candidates for suicidal germination. An important issue is the persistence of these stimulants in soil. Packets with Striga spp. seeds were put in pots with soil and then treated with aqueous solutions of the stimulants. All five compounds induced germination under these conditions, with percentages varying between 18% and 98% depending on stimulant and species. There were no noticeable signs of decomposition of the stimulants. The best performing stimulant is derived from 1-tetralone. We conclude that synthetic strigolactones analogues have excellent prospects for use in combating parasitic weeds. Further testing will be needed to evaluate whether such prospects can be realised in the field

The anatomy and function of Cleland's ligaments

The cutaneous ligaments of the digits have been recognized by anatomists for several centuries, but the best known description is that of John Cleland. Subsequent varying descriptions of their morphology have resulted in the surgical community having an imprecise view of their structure and dynamic function. We micro-dissected 24 fresh frozen fingers to analyze the individual components of Cleland's ligamentous system. Arising from the proximal interphalangeal (PIP) joint, proximal, and sometimes middle phalanx, we found strong ligaments that ran proximally (PIP-P) and distally (PIP-D). On each side of each finger there was a PIP-P ligament present, which passed obliquely from the lateral side of the proximal and sometimes middle phalanx towards its insertion into the skin at the level of the proximal phalanx. The distal (PIP-D) ligaments were found to pass obliquely distally on the radial and ulnar aspects of the digit towards cutaneous insertions around the middle phalanx. A similar arrangement exists more distally with fibres originating from the DIP joint and middle phalanx (the DIP-P pass obliquely proximally, and the DIP-D, distally). Each individual PIP ligament consisted of three different layers originating from fibres overlying the flexor tendon sheath, periosteum or joint capsule, and extensor expansion. Ligaments arising at the DIP joint had two layers equivalent to the anterior two layers of the proximal ligaments. Cleland's ligaments act as skin anchors maintaining the skin in a fixed relationship to the underlying skeleton during motion and functional tasks. They also prevent the skin from 'bagging', protect the neurovascular bundle, and create a gliding path for the lateral slips of the extensor tendon

New insights into the anatomy at the palmodigital junction in Dupuytren's disease:the palmodigital spiralling sheet

The anatomy in the region of the palmodigital junction has been relatively little studied, but it is very relevant for the surgical treatment of Dupuytren's disease. To study the microanatomy of the palmodigital junction, we dissected 26 cadaveric digits from 13 human cadaveric hands using microsurgical techniques. The dynamics of the different ligaments were studied in three hands preserved by Thiel's method. We found a structure, which we propose to name the 'palmodigital spiralling sheet' (PSS), which has not been described before. It has a spiralling course around the neurovascular bundle giving rise to a neurovascular tunnel distally in the palm of the hand. It is formed proximally by fibres from the pretendinous band and the intrinsic muscle fascias and distally is in continuity with Cleland's and Grayson's ligaments. As such it connects the palmar and digital fascias. Its spiralling course stabilizes the neurovascular bundle in the healthy hand, but can displace it in Dupuytren's disease, which may contribute to the development of spiral cords

Resonant tunnelling features in the transport spectroscopy of quantum dots

We present a review of features due to resonant tunnelling in transport spectroscopy experiments on quantum dots and single donors. The review covers features attributable to intrinsic properties of the dot as well as extrinsic effects, with a focus on the most common operating conditions. We describe several phenomena that can lead to apparently identical signatures in a bias spectroscopy measurement, with the aim of providing experimental methods to distinguish between their different physical origins. The correct classification of the resonant tunnelling features is an essential requirement to understand the details of the confining potential or predict the performance of the dot for quantum information processing.Comment: 18 pages, 7 figures. Short review article submitted to Nanotechnology, special issue on 'Quantum Science and Technology at the Nanoscale

Horizontal Translational Failures of Levees Due to Water Filled Gaps

A peat levee at Wilnis in The Netherlands suddenly failed at the end of the relatively dry summer of 2003. On Monday, 29 August 2005, Hurricane Katrina struck the U.S. gulf coast and breached, among other failures, the 17th Street Canal. These failures triggered large research programs. In the Wilnis case, it was eventually deduced that the 5-m horizontal translation of the levee was triggered by a combination of reduced weight by evaporation, shrinkage and cracking of the peat material, and an increased head in the sand layer under the dike. A key factor in the 17th Street Canal failure was the formation of a gap between the wall and the levee fill on the canal side of the fill. Due to climate change, more extreme dry and wet periods, land subsidence, and increasing sea and river levels, the horizontal shifting due to cracking is becoming more significant in the safety assessments of levees. In this paper, aspects of horizontal failures during extreme dry or wet periods are elaborated. First, a geo-hydrologic design procedure to assess the consequences of droughts for cracked peat levees is presented. The design procedure is then validated with measurements of a peat levee, the Middelburgsekade, and extreme water table positions that are likely to occur once in a period of 400 years that have been predicted for this levee. Furthermore, the most dangerous cracks for the Wilnis case are indicated. Next, the performance of levees and floodwalls during Hurricane Katrina are presented. Finally, the failure of the 17th Street Canal breach in New Orleans is described in detail. Conclusions are drawn related to horizontal failures and location of cracks during extreme weather condition

Strong coupling between single-electron tunneling and nano-mechanical motion

Nanoscale resonators that oscillate at high frequencies are useful in many measurement applications. We studied a high-quality mechanical resonator made from a suspended carbon nanotube driven into motion by applying a periodic radio frequency potential using a nearby antenna. Single-electron charge fluctuations created periodic modulations of the mechanical resonance frequency. A quality factor exceeding 10^5 allows the detection of a shift in resonance frequency caused by the addition of a single-electron charge on the nanotube. Additional evidence for the strong coupling of mechanical motion and electron tunneling is provided by an energy transfer to the electrons causing mechanical damping and unusual nonlinear behavior. We also discovered that a direct current through the nanotube spontaneously drives the mechanical resonator, exerting a force that is coherent with the high-frequency resonant mechanical motion.Comment: Main text 12 pages, 4 Figures, Supplement 13 pages, 6 Figure