Dynamics of semi-flexible polymer solutions in the highly entangled regime

We present experimental evidence that the effective medium approximation (EMA), developed by D.C. Morse [Phys. Rev. E {\bf 63}, 031502, (2001)], provides the correct scaling law of the macroscopic plateau modulus $G^{0}\propto\rho^{4/3}L^{-1/3}_{p}$ (where $\rho$ is the contour length per unit volume and $L_{p}$ is the persistence length) of semi-flexible polymer solutions, in the highly entangled concentration regime. Competing theories, including a self-consistent binary collision approximation (BCA), have instead predicted $G^{0}\propto\rho^{7/5}L^{-1/5}_{p}$. We have tested both the EMA and BCA scaling predictions using actin filament (F-actin) solutions which permit experimental control of $L_p$ independently of other parameters. A combination of passive video particle tracking microrheology and dynamic light scattering yields independent measurements of the elastic modulus $G$ and $L_{p}$ respectively. Thus we can distinguish between the two proposed laws, in contrast to previous experimental studies, which focus on the (less discriminating) concentration functionality of $G$.Comment: 4 pages, 6 figures, Phys. Rev. Lett. (accepted

Structure, mineralogy, and microbial diversity of geothermal spring microbialites associated with a deep oil drilling in Romania

© 2015 Coman, Chiriac, Robeson, Ionescu, Dragos, Barbu-Tudoran, Andrei, Banciu, Sicora and Podar. Modern mineral deposits play an important role in evolutionary studies by providing clues to the formation of ancient lithified microbial communities. Here we report the presence of microbialite-forming microbial mats in different microenvironments at 32°C, 49°C, and 65°C around the geothermal spring from an abandoned oil drill in Ciocaia, Romania. The mineralogy and the macro- and microstructure of the microbialites were investigated, together with their microbial diversity based on a 16S rRNA gene amplicon sequencing approach. The calcium carbonate is deposited mainly in the form of calcite. At 32°C and 49°C, the microbialites show a laminated structure with visible microbial mat-carbonate crystal interactions. At 65°C, the mineral deposit is clotted, without obvious organic residues. Partial 16S rRNA gene amplicon sequencing showed that the relative abundance of the phylum Archaea was low at 32°C (1%. The dominant bacterial groups at 32°C were Cyanobacteria, Gammaproteobacteria, Firmicutes, Bacteroidetes, Chloroflexi, Thermi, Actinobacteria, Planctomycetes, and Defferibacteres. At 49°C, there was a striking dominance of the Gammaproteobacteria, followed by Firmicutes, Bacteroidetes, and Armantimonadetes. The 65°C sample was dominated by Betaproteobacteria, Firmicutes, [OP1], Defferibacteres, Thermi, Thermotogae, [EM3], and Nitrospirae. Several groups from Proteobacteria and Firmicutes, together with Halobacteria and Melainabacteria were described for the first time in calcium carbonate deposits. Overall, the spring from Ciocaia emerges as a valuable site to probe microbes-minerals interrelationships along thermal and geochemical gradients

Influence of microstructure on the interphase exchange coupling of Nd2Fe14B + 10 wt%α-Fe nanocomposites obtained at different milling energies

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Electrochemical Detection of Lead Ions with Ordered Mesoporous Silica–Modified Glassy Carbon Electrodes

The development of methods for lead ion determination in various biological and environmental samples is both necessary and challenging. In this context, considering the properties of both SBA-15 and MCM-41 mesoporous materials and the role of NH2-functional groups grafted on the silica surface (SBA-15-NH2 and MCM-41-NH2), the aim of the study was to investigate the electrochemical detection of Pb2+ by means of silica-modified glassy carbon electrodes (GCEs). The square wave anodic stripping voltammetry (SWASV) was used to characterize the modified electrodes with four different samples of ordered mesoporous silica (OMS) powders, mentioned above. Additionally, scanning electron microscopy (SEM) was used to characterize these modifiers. Pb2+ exhibits a well-defined oxidation peak (around − 0.5 V vs. Ag/AgCl/KClsat) and high peak current at either bare or OMS-modified glassy carbon electrodes, but the best response was recorded in the case of GC/SBA-15-NH2-modified electrode in 0.1 M acetate buffer. The performance of the prepared electrodes is highlighted by good analytical parameters (satisfies the requirements of low cost and rapid results), which recommends them to be used for real sample analysis

The self-assembly, elasticity, and dynamics of cardiac thin filaments^☆

Solutions of intact cardiac thin filaments were examined with transmission electron microscopy, dynamic light scattering (DLS), and particle-tracking microrheology. The filaments self-assembled in solution with a bell-shaped distribution of contour lengths that contained a population of filaments of much greater length than the in vivo sarcomere size (∼1 μm) due to a one-dimensional annealing process. Dynamic semiflexible modes were found in DLS measurements at fast timescales (12.5 ns–0.0001 s). The bending modulus of the fibers is found to be in the range 4.5–16 × 10<sup>−27</sup> Jm and is weakly dependent on calcium concentration (with Ca<sup>2+</sup> ≥ without Ca<sup>2+</sup>). Good quantitative agreement was found for the values of the fiber diameter calculated from transmission electron microscopy and from the initial decay of DLS correlation functions: 9.9 nm and 9.7 nm with and without Ca<sup>2+</sup>, respectively. In contrast, at slower timescales and high polymer concentrations, microrheology indicates that the cardiac filaments act as short rods in solution according to the predictions of the Doi-Edwards chopsticks model (viscosity, η ∼c<sup>3</sup>, where c is the polymer concentration). This differs from the semiflexible behavior of long synthetic actin filaments at comparable polymer concentrations and timescales (elastic shear modulus, G′ ∼ c1.4, tightly entangled) and is due to the relative ratio of the contour lengths (∼30). The scaling dependence of the elastic shear modulus on the frequency (ω) for cardiac thin filaments is G′ ∼ω<sup>3/4 ± 0.03</sup>, which is thought to arise from flexural modes of the filaments

Continuity and diversity of Roman pottery production at Famars (northern France) in the 2nd–4th centuries AD: insights from the pottery waste

© 2020, Springer-Verlag GmbH Germany, part of Springer Nature. Grey and cream ware were widely produced and traded in Roman towns in Northern France (a region known as Civitas Nerviorum). A large production centre of grey and cream ware in northern France was Famars, where 15 pottery kilns functioned between the 2nd and 4th centuries ad. In order to identify the raw materials and to reconstruct the technology of grey and cream ware produced at Famars, 51 sherds found in the pottery waste, associated with kilns, were investigated by means of optical microscopy, X-ray fluorescence spectrometry, cold field emission scanning electron microscopy and electron microprobe analysis. The optical microscopy analysis allowed to define the Quartz (Qz), Microfossil-Glauconite (MFG) and Quartz-Microfossil-Glauconite (QzMFG) petrographic groups, as well as the Quartz + Argillaceous Rocks Fragments (QZ + ARF), Microfossil-Glauconite Fine (MFG Fine) and Microfossil-Glauconite + Chamotte (MFG + Chm) variants. The defining components for all groups are quartz, glauconite pellets and microfossils, but in variable proportions. The chemical data support the optical microscopy analysis and reveal the differences between the petrographic groups: Qz sherds are rich in Si and Fe, whereas MFG sherds contain more Ca, Al and K. Firing phases, as seen in scanning electron microscopy analysis, include glass, melilite, clinopyroxene and an Fe aluminosilicate. The matrix of most sherds of the MFG and QzMFG groups shows low sintering and initial vitrification, while the matrix of the Qz group displays mostly extensive and continuous vitrification. The results permitted to identify two kinds of raw materials, most likely originating from local georesources. One raw material, with high Si and Fe, was fired in a reducing kiln atmosphere in order to produce grey ware, while the other, with high Ca, Al and K, was fired in oxidising conditions in order to produce cream ware