Local Optical Probe of Motion and Stress in a multilayer graphene NEMS

Nanoelectromechanical systems (NEMSs) are emerging nanoscale elements at the crossroads between mechanics, optics and electronics, with significant potential for actuation and sensing applications. The reduction of dimensions compared to their micronic counterparts brings new effects including sensitivity to very low mass, resonant frequencies in the radiofrequency range, mechanical non-linearities and observation of quantum mechanical effects. An important issue of NEMS is the understanding of fundamental physical properties conditioning dissipation mechanisms, known to limit mechanical quality factors and to induce aging due to material degradation. There is a need for detection methods tailored for these systems which allow probing motion and stress at the nanometer scale. Here, we show a non-invasive local optical probe for the quantitative measurement of motion and stress within a multilayer graphene NEMS provided by a combination of Fizeau interferences, Raman spectroscopy and electrostatically actuated mirror. Interferometry provides a calibrated measurement of the motion, resulting from an actuation ranging from a quasi-static load up to the mechanical resonance while Raman spectroscopy allows a purely spectral detection of mechanical resonance at the nanoscale. Such spectroscopic detection reveals the coupling between a strained nano-resonator and the energy of an inelastically scattered photon, and thus offers a new approach for optomechanics

Paraffin-enabled graphene transfer

The transfer process of as-grown graphene limits its electrical performance and reliability. Here, the authors develop a transfer approach using paraffin as a support layer and obtain wrinkle-reduced and clean large-area graphene retaining high mobility

AfriSenti: A Twitter Sentiment Analysis Benchmark for African Languages

Africa is home to over 2000 languages from over six language families and has the highest linguistic diversity among all continents. This includes 75 languages with at least one million speakers each. Yet, there is little NLP research conducted on African languages. Crucial in enabling such research is the availability of high-quality annotated datasets. In this paper, we introduce AfriSenti, which consists of 14 sentiment datasets of 110,000+ tweets in 14 African languages (Amharic, Algerian Arabic, Hausa, Igbo, Kinyarwanda, Moroccan Arabic, Mozambican Portuguese, Nigerian Pidgin, Oromo, Swahili, Tigrinya, Twi, Xitsonga, and Yor\`ub\'a) from four language families annotated by native speakers. The data is used in SemEval 2023 Task 12, the first Afro-centric SemEval shared task. We describe the data collection methodology, annotation process, and related challenges when curating each of the datasets. We conduct experiments with different sentiment classification baselines and discuss their usefulness. We hope AfriSenti enables new work on under-represented languages. The dataset is available at https://github.com/afrisenti-semeval/afrisent-semeval-2023 and can also be loaded as a huggingface datasets (https://huggingface.co/datasets/shmuhammad/AfriSenti).Comment: 15 pages, 6 Figures, 9 Table

SEARCH FOR LISTERIA MONOCYTOGENES ACCORDING TO STANDARDIZED METHOD ISO-11290-1 IN BELIEVED MILK OF COWS IN THE AREA IS ALGERIA (SETIF, BATNA & BISKRA)

252 taking away of believed milk of cows were collected starting from 9 sales outlets, distributed on three common to knowing, Bougaa (W.Sétif), Djerma (W.Batna) and Sidi Okba (W. Biskra). The results of the analysis by standardized method NF IN ISO 11290, confirmed the presence of Listeria spp (2.8%) with a prevalence of L. innocua (1.58%) and L. monocytogenes (1.19%) similar to those reported by the literature. In order to guarantee the safety of the consumer (risk of mortality = 20-30%) the search for L. monocytogenes in the dairy products is an obligation

First-principles study of an iron-based molecule grafted on graphene

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Dynamics of catalyst particle formation and multi-walled carbon nanotube growth in aerosol-assisted catalytic chemical vapor deposition

International audienceIn aerosol-assisted catalytic chemical vapor deposition (CCVD), the catalyst and carbon precursors are introduced simultaneously in the reactor. Catalyst particles are formed in situ and aligned multi-walled CNTs grow at a high rate. To scale-up the process, it is crucial to understand the chemical transformation of the precursors along the thermal gradient of the reactor, and to correlate nanotube growth with catalyst nanoparticle formation. The products synthesized along a cylindrical CVD reactor from an aerosol composed of ferrocene and toluene, as catalyst and carbon precursor, respectively, were studied. The product surface density and iron content are determined as a function of the location and the iron vapor pressure in the reactor. Samples are analyzed by electron microscopy, X-ray diffraction and Raman spectroscopy. We show the strong influence of the thermal gradient on location and rate of formation of both iron particles and CNTs, and demonstrate that catalyst particles are formed by gas phase homogeneous nucleation with a size which correlates with iron vapor pressure. They are gradually deposited on the reactor walls where nanotubes grow with an efficiency which is varying linearly with catalyst particle density. CNT crystallinity appears very high for a large range of temperature and iron content

X-ray diffraction study of the evolution of Fe-filled multiwalled carbon nanotubes under pressure

International audienceWe present in situ high pressure X-ray diffraction experiments on multi-walled carbon nanotubes (MWNTs) filled with iron-based nanowires. In addition to our diffraction results, we provide a detailed characterization of our samples in terms of nanotube length, iron contents, nanotube number of walls and radial dimension. Both carbon nanotubes and encapsulated iron-based nanowires were found to be stable under high pressure conditions, in contrast with previous experiments performed on Fe-filled MWNTs where structural transitions of nanotubes and Fe3C nanowires were recorded around 9 GPa. We point out the importance of providing a complete structural characterization of the studied material and we propose an explanation for the contradictory results found in the literature based on different structural characteristics of the samples and on recent results on the non-hydrostaticity of some pressure transmitting media

Affinity for MgADP and force of unbinding from actin of myosin purified from tonic and phasic smooth muscle

Smooth muscle is unique in its ability to maintain force at low MgATP consumption. This property, called the latch state, is more prominent in tonic than phasic smooth muscle. Studies performed at the muscle strip level have suggested that myosin from tonic muscle has a greater affinity for MgADP and therefore remains attached to actin longer than myosin from phasic muscle, allowing for cross-bridge dephosphorylation and latch-bridge formation. An alternative hypothesis is that after dephosphorylation, myosin reattaches to actin and maintains force. We investigated these fundamental properties of smooth muscle at the molecular level. We used an in vitro motility assay to measure actin filament velocity (νmax) when propelled by myosin purified from phasic or tonic muscle at increasing [MgADP]. Myosin was 25% thiophosphorylated and 75% unphosphorylated to approximate in vivo conditions. The slope of νmax versus [MgADP] was significantly greater for tonic (−0.51 ± 0.04) than phasic muscle myosin (−0.15 ± 0.04), demonstrating the greater MgADP affinity of myosin from tonic muscle. We then used a laser trap assay to measure the unbinding force from actin of populations of unphosphorylated tonic and phasic muscle myosin. Both myosin types attached to actin, and their unbinding force (0.092 ± 0.022 pN for phasic muscle and 0.084 ± 0.017 pN for tonic muscle) was not statistically different. We conclude that the greater affinity for MgADP of tonic muscle myosin and the reattachment of dephosphorylated myosin to actin may both contribute to the latch state

Quantitative evaluation of multi-walled carbon nanotube uptake in wheat and rapeseed

International audienceEnvironmental contamination with carbon nanotubes would lead to plant exposure and particularly exposure of agricultural crops. The only quantitative exposure data available to date which can be used for risk assessment comes from computer modeling. The aim of this study was to provide quantitative data relative to multi-walled carbon nanotube (MWCNT) uptake and distribution in agricultural crops, and to correlate accumulation data with impact on plant development and physiology. Roots of wheat and rapeseed were exposed in hydroponics to uniformly C-14-radiolabeled MWCNTs. Radioimaging, transmission electron microscopy and raman spectroscopy were used to identify CNT distribution. Radioactivity counting made it possible absolute quantification of CNT accumulation in plant leaves. Impact of CNTs on seed germination, root elongation, plant biomass, evapotranspiration, chlorophyll, thiobarbituric acid reactive species and H2O2 contents was evaluated. We demonstrate that less than 0.005% of the applied MWCNT dose is taken up by plant roots and translocated to the leaves. This accumulation does not impact plant development and physiology. In addition, it does not induce any modifications in photosynthetic activity nor cause oxidative stress in plant leaves. Our results suggest that if environmental contamination occurs and MWCNTs are in the same physicochemical state than the ones used in the present article, MWCNT transfer to the food chain via food crops would be very low

Tunable intertube spacing in single-walled carbon nanotube bundles.

International audienceThe structure of ternary compounds involving alkali, tetrahydrofuran (THF) and single-walled carbon nanotubes have been investigated using neutron diffraction (ND). Hydrogen-deuterium substitution in THF, as well as the study of different alkali-based compounds, allow a layered structure around the nanotubes to be determined. ND results indicate that the alkali cations form a monolayer surrounding each tube of the bundle, while THF molecules intercalate between the decorated tubes and at the surface of the bundles. In spite of this insertion, the triangular bundle structure is preserved, albeit with a much larger lattice parameter, which depends on the size of the inserted cation