Brain Amino Acids and Biogenic Amines Under Various Atmospheric Mixtures Semiannual Report, 1 Mar. 1965 - 30 Apr. 1966

Effects of exposure to different gaseous atmospheric mixtures on free amino acids and biogenic amines in rat brain

"Wet-to-Dry" Conformational Transition of Polymer Layers Grafted to Nanoparticles in Nanocomposite

The present communication reports the first direct measurement of the conformation of a polymer corona grafted around silica nano-particles dispersed inside a nanocomposite, a matrix of the same polymer. This measurement constitutes an experimental breakthrough based on a refined combination of chemical synthesis, which permits to match the contribution of the neutron silica signal inside the composite, and the use of complementary scattering methods SANS and SAXS to extract the grafted polymer layer form factor from the inter-particles silica structure factor. The modelization of the signal of the grafted polymer on nanoparticles inside the matrix and the direct comparison with the form factor of the same particles in solution show a clear-cut change of the polymer conformation from bulk to the nanocomposite: a transition from a stretched and swollen form in solution to a Gaussian conformation in the matrix followed with a compression of a factor two of the grafted corona. In the probed range, increasing the interactions between the grafted particles (by increasing the particle volume fraction) or between the grafted and the free matrix chains (decreasing the grafted-free chain length ratio) does not influence the amplitude of the grafted brush compression. This is the first direct observation of the wet-to-dry conformational transition theoretically expected to minimize the free energy of swelling of grafted chains in interaction with free matrix chains, illustrating the competition between the mixing entropy of grafted and free chains, and the elastic deformation of the grafted chains. In addition to the experimental validation of the theoretical prediction, this result constitutes a new insight for the nderstanding of the general problem of dispersion of nanoparticles inside a polymer matrix for the design of new nanocomposites materials

Diversity of microbial eukaryotes along the West Antarctic Peninsula in austral spring

© The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Grattepanche, J.-D., Jeffrey, W., Gast, R., & Sanders, R. Diversity of microbial eukaryotes along the West Antarctic Peninsula in austral spring. Frontiers in Microbiology, 13, (2022): 844856, https://doi.org/10.3389/fmicb.2022.844856.During a cruise from October to November 2019, along the West Antarctic Peninsula, between 64.32 and 68.37°S, we assessed the diversity and composition of the active microbial eukaryotic community within three size fractions: micro- (> 20 μm), nano- (20–5 μm), and pico-size fractions (5–0.2 μm). The communities and the environmental parameters displayed latitudinal gradients, and we observed a strong similarity in the microbial eukaryotic communities as well as the environmental parameters between the sub-surface and the deep chlorophyll maximum (DCM) depths. Chlorophyll concentrations were low, and the mixed layer was shallow for most of the 17 stations sampled. The richness of the microplankton was higher in Marguerite Bay (our southernmost stations), compared to more northern stations, while the diversity for the nano- and pico-plankton was relatively stable across latitude. The microplankton communities were dominated by autotrophs, mostly diatoms, while mixotrophs (phototrophs-consuming bacteria and kleptoplastidic ciliates, mostly alveolates, and cryptophytes) were the most abundant and active members of the nano- and picoplankton communities. While phototrophy was the dominant trophic mode, heterotrophy (mixotrophy, phagotrophy, and parasitism) tended to increase southward. The samples from Marguerite Bay showed a distinct community with a high diversity of nanoplankton predators, including spirotrich ciliates, and dinoflagellates, while cryptophytes were observed elsewhere. Some lineages were significantly related—either positively or negatively—to ice coverage (e.g., positive for Pelagophyceae, negative for Spirotrichea) and temperature (e.g., positive for Cryptophyceae, negative for Spirotrichea). This suggests that climate changes will have a strong impact on the microbial eukaryotic community.This work was supported by the National Science Foundation (Grant Nos. ANT 1744767 to RS, ANT 1744663 to RG, and ANT 1744638 to WJ). This research was based, in part, upon sequencing conducted using the Rhode Island Genomics and Sequencing Center, which was supported in part by the National Science Foundation (MRI Grant No. DBI-0215393 and EPSCoR Grant Nos. 0554548 and EPS-1004057), the US Department of Agriculture (Grant Nos. 2002-34438-12688 and 2003-34438-13111), and the University of Rhode Island. This research includes calculations carried out on Temple University HPC resources supported in part by the National Science Foundation through major research instrumentation (Grant No. 1625061) and by the US Army Research Laboratory under (Contract No. W911NF-16-2-0189)

Stability of Colloidal Quasicrystals

Freezing of charge-stabilized colloidal suspensions and relative stabilities of crystals and quasicrystals are studied using thermodynamic perturbation theory. Macroion interactions are modelled by effective pair potentials combining electrostatic repulsion with polymer-depletion or van der Waals attraction. Comparing free energies -- counterion terms included -- for elementary crystals and rational approximants to icosahedral quasicrystals, parameters are identified for which one-component quasicrystals are stabilized by a compromise between packing entropy and cohesive energy.Comment: 6 pages, 4 figure

Gel transitions in colloidal suspensions

The idealized mode coupling theory (MCT) is applied to colloidal systems interacting via short-range attractive interactions of Yukawa form. At low temperatures MCT predicts a slowing down of the local dynamics and ergodicity breaking transitions. The nonergodicity transitions share many features with the colloidal gel transition, and are proposed to be the source of gelation in colloidal systems. Previous calculations of the phase diagram are complemented with additional data for shorter ranges of the attractive interaction, showing that the path of the nonergodicity transition line is then unimpeded by the gas-liquid critical curve at low temperatures. Particular attention is given to the critical nonergodicity parameters, motivated by recent experimental measurements. An asymptotic model is developed, valid for dilute systems of spheres interacting via strong short-range attractions, and is shown to capture all aspects of the low temperature MCT nonergodicity transitions.Comment: 12 pages, LaTeX, 5 eps figures, uses ioplppt.sty, to appear in J. Phys.: Condens. Matte

Silicon photomultiplier arrays - a novel photon detector for a high resolution tracker produced at FBK-irst, Italy

A silicon photomultiplier (SiPM) array has been developed at FBK-irst having 32 channels and a dimension of 8.0 x 1.1 mm^2. Each 250 um wide channel is subdivided into 5 x 22 rectangularly arranged pixels. These sensors are developed to read out a modular high resolution scintillating fiber tracker. Key properties like breakdown voltage, gain and photon detection efficiency (PDE) are found to be homogeneous over all 32 channels of an SiPM array. This could make scintillating fiber trackers with SiPM array readout a promising alternative to available tracker technologies, if noise properties and the PDE are improved