Shear wave sensors for viscoelastic properties

AbstractElectromechanical resonators are sensitive to the properties of the surrounding medium due to interaction forces onto the surface caused by motions in the medium. In the present contribution, fully metallic Lorentz force resonators exhibiting in-plane oscillation are used to excite shear waves to measure the linear viscoelastic storage and loss-moduli at specific frequencies in the kHz range of complex fluids (e.g. aqueous polymeric solutions). Reflected shear waves in a well defined gap are employed to extend the measurement range as well as the capability to measure at multiple frequencies. Numerical methods and reduced order models are employed to solve for the velocity field and interaction forces to determine the required quantities from the measured frequency response

Miniaturized high frequency plate resonators for rheometric applications

Conventional rotational rheometers are typically limited to around 100Hz. In order to extent the frequency domain, a couple of methods have been proposed [1]. These are however typically stand alone instruments and only a few have been commercially available. In the present work we pursue an approach aimed at miniaturizing in-plane plate resonators for possible add-on integration into standard rheometers. The lithographically structured plates have primary mechanical resonance frequencies up to 10 kHz. Lorentz force excitation and an inductive readout mechanism allow the measurement of the frequency response by monitoring the electrical two port behavior [2]. The fluid-structure interaction is dominated by decaying shear waves with penetration depths of typically a few to tens of micrometers, exact values depend on the mass density and viscoelastic moduli. The resonance frequency and damping are sensitive to the fluid forces and therefore can be used to measure the rheological properties of liquids. In our work, we will present the modeling approach including the eigenmode solution of the mechanical resonance, the fluid-structure interaction, and the electrical equivalent circuit describing the excitation and readout mechanisms. The theoretical model is verified using a set of low to intermediate viscosity liquids demonstrating the measurement technique and consistency of the modeling approach. For an aqueous silica suspension it is shown that the resonator damping is determined by the steady shear viscosity. This result is compared to measurements obtained with a high frequency quartz thickness shear mode sensor where the high-frequency viscosity determines the damping. Further experiments will focus on the behavior in non-Newtonian (viscoelastic) media and the effect of a reflecting wall placed at a distance below the shear-wave penetration depth. [1] Kirschenmann et al, Rheol. Acta 41, 2002 [2] Reichel et al, submitted to Sens. and Act. A, Elsevier, 2009status: publishe

Viscoelasticity Sensor with Resonance Tuning and Low-Cost Interface

AbstractElectromechanical resonators are sensitive to the material parameters of a surrounding medium and therefore can be used as sensors for viscoelastic properties and density. In our recent work, we presented a metallic plate resonator excited by Lorentz forces in a permanent magnetic field. We improved the interface circuitry by using signal transformers, so that it is now possible to make accurate measurements using a commonly available low-cost audio- interface. Beside that, the necessary sample volume is reduced to a maximum of 50μl, so that a drop of liquid covers the sensitive area. Using a reflector parallel to the oscillation plane, standing waves in the gap could be generated. A desirable feature of resonator sensors is tunability over a significant frequency range. We investigated mechanisms to change the resonance frequency, e.g. an electric current that induces thermal stress. These advancements pave the way for a versatile low-cost, easy-to-use solution to measure viscoelastic properties in numerous applications

A Conceptual Framework for Choosing Target Species for Wildlife-Inclusive Urban Design

Recent research has highlighted the significance of cities for biodiversity, making them important places for conservation in their own right. Current conservation approaches in cities are mostly defensive. Thus, they focus on remnant pockets of natural areas or try to protect particular species that occur in the built environment. These approaches are vulnerable to further urban development and do not create habitats. An alternative strategy is to make wildlife an integral part of urban development and thereby create a new habitat in the built-up area. Here we address the challenge of choosing target species for such wildlife-inclusive urban design. The starting point of our conceptual framework is the regional species pool, which can be obtained from geo-referenced species data. The existing habitat types on and around the development site and dispersal barriers limit the species numbers to the local species potential. In the next step, the site’s potential for each species is analyzed—how can it be upgraded to host species given the planned development and the life-cycle of the species? For the final choice of target species, traits related to the human–animal interaction are considered. We suggest that stakeholders will be involved in the final species selection. Our approach differs from existing practice, such as expert choice of priority species, by (1) representing an open process where many species are potential targets of conservation, (2) the involvement of stakeholders in a participatory way. Our approach can also be used at larger spatial scales such as quarters or entire cities

Monitoring Early Zeolite Formation via in situ Electrochemical Impedance Spectroscopy

Hitherto zeolite formation is not fully understood. Although electrochemical impedance spectroscopy has proven to be a versatile tool for characterizing ionic solutions, it was never used for monitoring zeolite growth. We show here that EIS can quantitatively monitor zeolite formation, especially during crucial early steps where other methods fall short.crosscheck: This document is CrossCheck deposited related_data: Supplementary Information identifier: E. Breynaert (ORCID) copyright_licence: The Royal Society of Chemistry has an exclusive publication licence for this journal copyright_licence: This article is freely available. This article is licensed under a Creative Commons Attribution 3.0 Unported Licence (CC BY 3.0) history: Received 3 February 2016; Accepted 19 March 2016; Accepted Manuscript published 21 March 2016; Advance Article published 29 March 2016; Version of Record published 7 April 2016status: publishe

Revisiting Silicalite-1 Nucleation in Clear Solution by Electrochemical Impedance Spectroscopy

EIS was used to detect and investigate nucleation in silicalite-1 clear solutions. Whereas zeolite nucleation was previously assumed to be a step event, inducing a sharp discontinuity around a Si/OH ratio of 1, complex bulk conductivity measurements at elevated temperatures reveal a gradual decay of the conductivity with increased silicon concentrations. Inverse Laplace transformation of the complex conductivity allows to observe the chemical exchange phenomena governing nano-aggregate formation. At low temperatures, the fast exchange between dissociated ions and ion pairs leads to a gradual decay of the conductivity with increasing silicon content. Upon heating, the exchange rate is slower and the residence time of ion pairs inside the nano-aggregates is increasing, facilitating the crystallization process. This results in a bilinear chemical exchange and gives rise to the discontinuity at the Si/OH ratio of 1, as observed by Fedeyko et al. EIS allows to observe slow chemical exchange processes occurring in zeolite precursors. Up to now, such processes could only be observed using techniques such as nuclear magnetic or electron paramagnetic resonance spectroscopy. In addition, EIS enables the quantification of interfacial processes via the double-layer capacitance. The electrical double layer thickness, derived from the double-layer capacitance, shows a similar gradual decay and confirms that the onset of nano-aggregate formation is indeed not narrowly defined.status: publishe

Designing wildlife-inclusive cities that support human-animal co-existence

In an urbanizing world there is an increasing priority for making cities nature-inclusive environments. Cities offer places for human-wildlife experiences, and thus for broad societal support of biodiversity conservation. Cities also depend on ecosystem services provided by biodiversity to remain healthy, liveable places. Although biodiversity is frequently addressed in urban green infrastructure plans, it often is not an integral topic in city planning, urban design and housing development. As a result, wildlife-rich urban green is often lacking in those parts of the cities where people live and work. Here, we introduce the concept of ‘wildlife-inclusive urban design’ for the built-up area of cities that integrates animal needs into the urban planning and design process. To identify key features that determine the success of wildlife-inclusive urban design, we evaluated lessons learnt from existing best practices. These were collected during an international workshop with architects, landscape practitioners, ecological consultants, conservationists and urban ecologists. We propose that features of successful wildlife-inclusive urban design projects are: 1) interdisciplinary design teams that involve ecologists early on, 2) consideration of the entire life-cycle of target species, 3) post-occupancy monitoring and evaluation with feedback to communicate best practices, and 4) stakeholder involvement and participatory approaches. We propose how wildlife-inclusive urban design could be included into the different steps of the urban planning cycle. We conclude that following these principles will facilitate incorporation of wildlife-inclusive urban design into urban planning and design and enable urban environments where humans and animals can thrive in the built-up areas.</p

Genome-wide association studies with proteomics data reveal genes important for synthesis, transport and packaging of globulins in legume seeds

Improving nutritional seed quality is an important challenge in grain legume breeding. However, the genes controlling the differential accumulation of globulins, which are major contributors to seed nutritional value in legumes, remain largely unknown. We combined a search for protein quantity loci with genome-wide association studies on the abundance of 7S and 11S globulins in seeds of the model legume species Medicago truncatula. Identified genomic regions and genes carrying polymorphisms linked to globulin variations were then cross-compared with pea (Pisum sativum), leading to the identification of candidate genes for the regulation of globulin abundance in this crop. Key candidates identified include genes involved in transcription, chromatin remodeling, post-translational modifications, transport and targeting of proteins to storage vacuoles. Inference of a gene coexpression network of 12 candidate transcription factors and globulin genes revealed the transcription factor ABA-insensitive 5 (ABI5) as a highly connected hub. Characterization of loss-of-function abi5 mutants in pea uncovered a role for ABI5 in controlling the relative abundance of vicilin, a sulfur-poor 7S globulin, in pea seeds. This demonstrates the feasibility of using genome-wide association studies in M. truncatula to reveal genes that can be modulated to improve seed nutritional value