Nonlinear viscoelastic dynamics of nano-confined water

The viscoelastic dynamics of nano-confined water is studied by means of atomic force microscopy (AFM). We observe a nonlinear viscoelastic behavior remarkably similar to that widely observed in metastable complex fluids. We show that the origin of the measured nonlinear viscoelasticity in nano-confined water is a strain rate dependent relaxation time and slow dynamics. By measuring the viscoelastic modulus at different frequencies and strains, we find that the intrinsic relaxation time of nano-confined water is in the range 0.1-0.0001 s, orders of magnitude longer than that of bulk water, and comparable to the dielectric relaxation time measured in supercooled water at 170-210 K.Comment: 4 Figure

Drought Response Mechanisms and Adaptation: An Analysis of Strategies Adopted by Wine Grape Farmers in the Western Cape

This thesis examines the response mechanisms and adaptation strategies adopted by grapevine farmers to counteract the effects of the 2015-2018 Western Cape drought, which was characterised as particularly rare and severe. The challenges that emerged during the drought within the study area were exacerbated by the increasing competition over water resources between urban and agriculture users, as investment to supply water to urban users are expected to bring more economic and social value than investments in water supply for agriculture. The study responds to the dearth of literature on climate change adaptation strategies by grapevine farmers in South Africa. Using information from 27 open-ended, face to face interviews conducted with grapevine farmers operating in the Berg River catchment area, as well as an analysis of existing economic and weather data, the research sought to understand the effects of the water stress on grapevine production, the main cause of yield loss and the key drivers of farmers’ behaviour shifts. Analysis of industry production performance from 2015 to 2018 and observed rainfall from 2015 to 2017 suggests that water stress remains the key factor influencing grapevine yields. The water stress was also found to have catalysed later ripening of red varieties, higher pH levels in the wine and the introduction of emergency pruning methods to reduce water use, which in turn led to uneven budding budding due to pruning methods, later ripening of red varieties, higher pH levels in the wine. It was also found that the depleting quality of the Berg River water led to reduced yield, as well as heightened financial and psychological stress. The research identifies a portfolio of long-term and short-term adaptation options pursued by farmers in the study area, entailing reduced water consumption and increased water efficiency. The research identified that the drought induced farmers to suspend or reduce plant replacement. However, this behavior cannot be explained simply as responses to climate change, but that this is linked to the low profitability of the local wine grape industry. Most farmers adopted incremental measures rather than transformative strategies, where the major barriers to transformative adaptation included uncertainty regarding climate trends, limited financial capacity for large investments, the belief in grapevine drought resilience and the cultural attachment to viticulture

Nanopatterning spin-textures: A route to reconfigurable magnonics

Magnonics is envisioned to enable highly efficient data transport and processing, by exploiting propagating perturbations in the spin-texture of magnetic materials. Despite the demonstrations of a plethora of proof-of-principle devices, the efficient excitation, transport and manipulation of spin-waves at the nanoscale is still an open challenge. Recently, we demonstrated that the spin-wave excitation and propagation can be controlled by nanopatterning reconfigurable spin-textures in a continuous exchange biased ferromagnetic film. Here, we show that by patterning 90° stripe-shaped magnetic domains, we spatially modulate the spin-wave excitation in a continuous film, and that by applying an external magnetic field we can reversibly â\u80\u9cswitch-offâ\u80\u9d the spin-wave excitation. This opens the way to the use of nanopatterned spin-textures, such as domains and domain walls, for exciting and manipulating magnons in reconfigurable nanocircuits

The LMS-GT instrument – a new perspective for quantification with the LIMS-TOF measurement technique

In this contribution we present the design and first measurement results obtained with a new highperformance laser ablation and ionisation (LIMS) mass spectrometer for solid sample analysis named “LMS-GT”, combining high mass- and high spatial resolving powers. The instrument consists of a fs-laser ablation ion source coupled to a time-of-flight (TOF) mass spectrometer that provides measurements with a mass resolution (m/Dm) of 10 000 at full width half max and more over a wide mass range. This resolution enables the separation of the most important isobaric interferences between clusters, molecules and multiple charged ions. Thereby it enables significant improvements of the quantitative analysis of complex samples with the LIMS-TOF technique. The instrument performance is demonstrated by analysis of measurements conducted on various NIST standard reference materials (SRMs). Using these samples we determined detection limits in the ppm range and below, and relative sensitivity coefficients (RSCs), in the range between 0.1 and 10

A˚\r{A}-Indentation for non-destructive elastic moduli measurements of supported ultra-hard ultra-thin films and nanostructures

During conventional nanoindentation measurements, the indentation depths are usually larger than 1-10 nm, which hinders the ability to study ultra-thin films ($<$ 10 nm) and supported atomically thin two-dimensional (2D) materials. Here, we discuss the development of modulated \r{A}-indentation to achieve sub-\r{A} indentation depths during force-indentation measurements while also imaging materials with nanoscale resolution. Modulated nanoindentation (MoNI) was originally invented to measure the radial elasticity of multi-walled nanotubes. Now, by using extremely small amplitude oscillations ($\ll$ 1 \r{A}) at high frequency, and stiff cantilevers, we show how modulated nano/\r{A}-indentation (MoNI/\r{A}I) enables non-destructive measurements of the contact stiffness and indentation modulus of ultra-thin ultra-stiff films, including CVD diamond films (modulus $\sim$ 1000 GPa), as well as the transverse modulus of 2D materials. Our analysis demonstrates that in presence of a standard laboratory noise floor, the signal to noise ratio of MoNI/\r{A}I implemented with a commercial atomic force microscope (AFM) is such that a dynamic range of 80 dB $-$ achievable with commercial Lock-in amplifiers $-$ is sufficient to observe superior indentation curves, having indentation depths as small as 0.3 \r{A}, resolution in indentation $<$ 0.05 \r{A}, and in normal load $<$ 0.5 nN. Being implemented on a standard AFM, this method has the potential for a broad applicability.Comment: 37 pages, 12 figure

Global conservation status assessment of the threatened aquatic plant genus Baldellia (Alismataceae): challenges and limitations

In this study, the aquatic monocot Baldellia (Alismataceae) is used as a model for evaluating the general hindrances and shortfalls in the global conservation status assessment of a threatened taxon. Our study clearly shows that Linnean shortfalls (uncertainty in the number of species and taxonomy) and the Wallacean shortfall (fragmentary knowledge regarding distribution) form the basis for all other hindrances. We demonstrate that even in Europe, which has traditionally been very well investigated, between 60 and 75% of regions or countries possess no detailed distribution maps and/or data banks for Baldellia spp. Furthermore, between 50 and 60% of regions do not have any published red list category. Thus, only general conclusions concerning the global conservation status of the three Baldellia taxa are possible—a global assessment of conservation status for B. ranunculoides subsp. repens is nearly impossible. Baldellia ranunculoides s.str. shows a strong decline in practically all regions of its natural range, and thus it is probably the most threatened species in the genus. Baldellia alpestris is the least threatened species in the genus, even though it is a narrow endemic. Our case study clearly shows the need for reinforced coordination of research and conservation activities as well as an urgent need for data accessibility regarding taxonomic, chorological and conservation studies of endangered specie