Quantitative imaging of concentrated suspensions under flow

We review recent advances in imaging the flow of concentrated suspensions, focussing on the use of confocal microscopy to obtain time-resolved information on the single-particle level in these systems. After motivating the need for quantitative (confocal) imaging in suspension rheology, we briefly describe the particles, sample environments, microscopy tools and analysis algorithms needed to perform this kind of experiments. The second part of the review focusses on microscopic aspects of the flow of concentrated model hard-sphere-like suspensions, and the relation to non-linear rheological phenomena such as yielding, shear localization, wall slip and shear-induced ordering. Both Brownian and non-Brownian systems will be described. We show how quantitative imaging can improve our understanding of the connection between microscopic dynamics and bulk flow.Comment: Review on imaging hard-sphere suspensions, incl summary of methodology. Submitted for special volume 'High Solid Dispersions' ed. M. Cloitre, Vol. xx of 'Advances and Polymer Science' (Springer, Berlin, 2009); 22 pages, 16 fig

Surface Modifications by Field Induced Diffusion

By applying a voltage pulse to a scanning tunneling microscope tip the surface under the tip will be modified. We have in this paper taken a closer look at the model of electric field induced surface diffusion of adatoms including the van der Waals force as a contribution in formations of a mound on a surface. The dipole moment of an adatom is the sum of the surface induced dipole moment (which is constant) and the dipole moment due to electric field polarisation which depends on the strength and polarity of the electric field. The electric field is analytically modelled by a point charge over an infinite conducting flat surface. From this we calculate the force that cause adatoms to migrate. The calculated force is small for voltage used, typical 1 pN, but due to thermal vibration adatoms are hopping on the surface and even a small net force can be significant in the drift of adatoms. In this way we obtain a novel formula for a polarity dependent threshold voltage for mound formation on the surface for positive tip. Knowing the voltage of the pulse we then can calculate the radius of the formed mound. A threshold electric field for mound formation of about 2 V/nm is calculated. In addition, we found that van der Waals force is of importance for shorter distances and its contribution to the radial force on the adatoms has to be considered for distances smaller than 1.5 nm for commonly used voltages

The Adaptor Molecule Nck Localizes the WAVE Complex to Promote Actin Polymerization during CEACAM3-Mediated Phagocytosis of Bacteria

Background: CEACAM3 is a granulocyte receptor mediating the opsonin-independent recognition and phagocytosis of human-restricted CEACAM-binding bacteria. CEACAM3 function depends on an intracellular immunoreceptor tyrosine-based activation motif (ITAM)-like sequence that is tyrosine phosphorylated by Src family kinases upon receptor engagement. The phosphorylated ITAM-like sequence triggers GTP-loading of Rac by directly associating with the guanine nucleotide exchange factor (GEF) Vav. Rac stimulation in turn is critical for actin cytoskeleton rearrangements that generate lamellipodial protrusions and lead to bacterial uptake. Principal Findings: In our present study we provide biochemical and microscopic evidence that the adaptor proteins Nck1 and Nck2, but not CrkL, Grb2 or SLP-76, bind to tyrosine phosphorylated CEACAM3. The association is phosphorylation-dependent and requires the Nck SH2 domain. Overexpression of the isolated Nck1 SH2 domain, RNAi-mediated knock-down of Nck1, or genetic deletion of Nck1 and Nck2 interfere with CEACAM3-mediated bacterial internalization and with the formation of lamellipodial protrusions. Nck is constitutively associated with WAVE2 and directs the actin nucleation promoting WAVE complex to tyrosine phosphorylated CEACAM3. In turn, dominant-negative WAVE2 as well as shRNA-mediated knock-down of WAVE2 or the WAVE-complex component Nap1 reduce internalization of bacteria. Conclusions: Our results provide novel mechanistic insight into CEACAM3-initiated phagocytosis. We suggest that the CEACAM3 ITAM-like sequence is optimized to co-ordinate a minimal set of cellular factors needed to efficiently trigger actin-based lamellipodial protrusions and rapid pathogen engulfment

A comparative study of non-covalent encapsulation methods for organic dyes into silica nanoparticles

Numerous luminophores may be encapsulated into silica nanoparticles (< 100 nm) using the reverse microemulsion process. Nevertheless, the behaviour and effect of such luminescent molecules appear to have been much less studied and may possibly prevent the encapsulation process from occurring. Such nanospheres represent attractive nanoplatforms for the development of biotargeted biocompatible luminescent tracers. Physical and chemical properties of the encapsulated molecules may be affected by the nanomatrix. This study examines the synthesis of different types of dispersed silica nanoparticles, the ability of the selected luminophores towards incorporation into the silica matrix of those nanoobjects as well as the photophysical properties of the produced dye-doped silica nanoparticles. The nanoparticles present mean diameters between 40 and 60 nm as shown by TEM analysis. Mainly, the photophysical characteristics of the dyes are retained upon their encapsulation into the silica matrix, leading to fluorescent silica nanoparticles. This feature article surveys recent research progress on the fabrication strategies of these dye-doped silica nanoparticles

Strategies for Controlled Placement of Nanoscale Building Blocks

The capability of placing individual nanoscale building blocks on exact substrate locations in a controlled manner is one of the key requirements to realize future electronic, optical, and magnetic devices and sensors that are composed of such blocks. This article reviews some important advances in the strategies for controlled placement of nanoscale building blocks. In particular, we will overview template assisted placement that utilizes physical, molecular, or electrostatic templates, DNA-programmed assembly, placement using dielectrophoresis, approaches for non-close-packed assembly of spherical particles, and recent development of focused placement schemes including electrostatic funneling, focused placement via molecular gradient patterns, electrodynamic focusing of charged aerosols, and others

HELIOS CJ app: The decentralization of the citizen journalism

The decentralization of Social Media applications has gained importance in the last years. In this direction, the HELIOS project has been proposed in order to provide a decentralized platform for social applications. Among these several social applications, the Journalism field is considered an important use case. The main problem which needs to be addressed is preventing the spread of fake news and ensuring the authenticity of the literature for end readers. Furthermore, with the rise of Citizen Journalism, the way of how people can participate to share information is changed. In this paper, we present the HELIOS Citizen Journalism App (CJ) developed in the context of the HELIOS project. The CJ App allows users to contribute content anonymously, based on blockchain technology. After publishing the content via the app, the content is available to publishers for further distribution, on a decentralized P2P and IPFS-based network storage. Furthermore, by making a donation for particular content, the CJ also receives remuneration. In this paper, we show the architecture of the App by describing its components and how it works

Improving the efficiency of rock phosphate on high pH soils: Results from participatory research in India

High soil pH levels may limit the availability of phosphorous (P) to crops. In organic farming, the use of synthetic P fertilizers is not allowed. Application of rock phosphate (RP) to crops is one of the alternatives for organic production. However, RP application shows little effect on high pH soils, because the P is not transformed into plant-available forms under alkaline soil conditions. Aiming at the development of locally adapted solutions, we followed a Participatory Technology Development approach, making use of the local knowledge to identify current practices and associated problems by conducting focus group discussions with organic farmers. Farmers stated that they are facing challenges with a P limitation in their cotton-based production systems. In 2011-12, on-station trials with maize, green gram and wheat investigated the potential of several locally available materials to solubilize RP (phosphorus solubilizing bacteria (PSB), tamarind fruits, local vinegar from mahua trees (Madhuca longifolia), butter milk (BM), incubating RP into compost). The results of these trials showed that the two most promising options for solubilizing RP were BM and Mahua Vinegar (MV). Further on-station trials in 2012-13 investigated the effects of BM and MV more closely, focusing on incubation periods and ratios of RP:acidifying liquids. Another study looked at technologies for improved farm yard manure (FYM) management. Results suggested that acidulating RP with BM for a period of one week in a ratio BM:RP = 10:1 leads to a good solubilization of RP. Furthermore, the so-called “shaded shallow-pit system”, which was favored by local farmers, best conserved the quality of FYM as a fertilizer. Subsequently, the information of the two studies was combined, and the production of RP-enriched FYM (RP-FYM) by five local lead farmers was initiated in 2012. The RP-FYM produced was distributed to associated farmers (4 per lead farmer) to set up several on-farm trials with cotton and soybean in 2013-14. Results showed an increase of soybean grain and seed cotton yields in the RP-FYM treatment of 40% (1’548 kg ha-1 to 2’163 kg ha-1) and 41% (1’170 kg ha-1 to 1’646 kg ha-1), respectively, as compared to farmers’ practices across a range of farms and soils. To further elaborate on the limiting factors in the production systems, future research will explore the specific effects of P as a part of the RP-FYM fertilizer complex. Potential improvements to the RP-FYM technology such as its combination with wood ash and/or PSB will also be explored. Furthermore, the socioeconomic sustainability of the technology needs to be addressed more thoroughly in order to elucidate potential constraints for adoption