Influence of carbon and nitrogen on electronic structure and hyperfine interactions in fcc iron-based alloys

Carbon and nitrogen austenites, modeled by Fe8N and Fe8C superstructures are studied by full-potential LAPW method. Structure parameters, electronic and magnetic properties as well as hyperfine interaction parameters are obtained. Calculations prove that Fe-C austenite can be successfully modeled by ordered Fe8C superstructure. The results show that chemical Fe-C bond in Fe8C has higher covalent part than in Fe8N. Detailed analysis of electric field gradient formation for both systems is performed. The calculation of electric field gradient allow us to carry out a good interpretation of Moessbauer spectra for Fe-C and Fe-N systems.Comment: 8 pages, 3 figures, IOP-style LaTeX, submitted to J. Phys. Condens. Matte

Differential clearance rates of microbial phylotypes by four appendicularian species

Appendicularians are abundant planktonic filter feeders that play a significant role in the pelagic food web due to their high clearance rates. Their diet and feeding rates have typically been measured as bulk chlorophyll or cell removal, with some attention given to prey size but no differentiation between the microbial phylotypes. Using a combination ofin situand laboratory incubations with flow cytometry and next-generation sequencing, we found species-specific differences in clearance rates and diet compositions of 4 common species:Oikopleura albicans,O. fusiformis,O. longicauda, andO. dioica. WhileO. albicansmost efficiently removed nano-eukaryotic algae, the other smaller species preferentially removed micron-sized pico-eukaryotic algae. Pico- and nano-eukaryotic cells constituted the major food source of the studied appendicularians despite their occurrence in oligotrophic water dominated by prokaryotic cells. Across species, pico- and nano-planktonic microalgae biomass comprised 45 to 75% of the appendicularian diets. Although non-photosynthetic bacteria were removed at lower rates than all other prey groups, their total contribution to the appendicularian diet was not trivial, representing 5 to 19% of the planktonic carbon in the appendicularian diet; pico-cyanobacteria contributed an additional 9 to 18%. Removal rates and efficiencies of pico-eukaryotes were higher than those of prokaryotes of similar size. Strikingly different clearance rates were observed for different prokaryotic phylotypes, indicating that factors other than size are involved in determining the capturability of the cells. Collectively, our findings provide additional evidence for differential retention of microbial prey among mucous-mesh grazers and its substantial effect on the upper-ocean microbial community.</jats:p

Excitonic absorption and emission in diamond near the edge of fundamental absorption

The study of optical absorption of CVD diamond near the fundamental absorption edge was performed in the temperature range of 87-296 K. At temperatures lower than 195 K the absorption was practically constant. At higher temperatures the sharp increase of absorption took place. This sharp increase was attributed to the sharp enrichment of the phonon spectrum. Same phonon modes have different contributions to the negative and the positive branches of freeexciton absorption. For the negative branch (phonon absorption) the TA-mode dominated. For the positive branch (phonon emission) the TO-mode dominated. The possibility of diamond-based cathodoluminescent UV-sources at 235 nm was demonstrated

Shear Lag Sutures: Improved Suture Repair through the use of Adhesives

Conventional surgical suture is mechanically limited by the ability of the suture to transfer load to tissue at suture anchor points. Sutures coated with adhesives can improve mechanical load transfer beyond the range of performance of existing suture methods, thereby strengthening orthopaedic repairs and decreasing the risk of failure. The mechanical properties of suitable adhesives were identified using a shear lag model. Examination of the design space for an optimal adhesive demonstrated requirements for strong adhesion and low stiffness to maximize strength. As a proof of concept, cyanoacrylate-coated sutures were used to perform a clinically relevant flexor digitorum profundus tendon repair in cadaver tissue. Even with this non-ideal adhesive, the maximum load resisted by repaired cadaveric canine flexor tendon increased by ∼ 17.0% compared to standard repairs without adhesive. To rapidly assess adhesive binding to tendon, we additionally developed a lap shear test method using bovine deep digital flexor tendons as the adherends. Further study is needed to develop a strongly adherent, compliant adhesive within the optimal design space described by the model

Vertical distribution and diel patterns of zooplankton abundance and biomass at Conch Reef, Florida Keys (USA)

Zooplankton play an important role in the trophic dynamics of coral reef ecosystems. Detailed vertical and temporal distribution and biomass of zooplankton were evaluated at four heights off the bottom and at six times throughout the diel cycle over a coral reef in the Florida Keys (USA). Zooplankton abundance averaged 4396 ± 1949 SD individuals m−3, but temporal and spatial distributions varied for individual zooplankton taxa by time of day and by height off the bottom. Copepods comprised 93–96% of the abundance in the samples. Taxon-based zooplankton CHN values paired with abundance data were used to estimate biomass. Average daily biomass ranged from 3.1 to 21.4 mg C m−3 and differed by both height off the bottom and by time of day. While copepods were the numerically dominant organisms, their contribution to biomass was only 35% of the total zooplankton biomass. Our findings provide important support for the new emerging paradigm of how zooplankton are distributed over reefs

Methyl 1-methyl-1H-1,2,3-triazole-4-carboxyl­ate

The title mol­ecule, C5H7N3O2, has an almost planar conformation, with a maximum deviation of 0.043 (3) Å, except for the methyl H atoms. In the crystal structure, inter­molecular C—H⋯O hydrogen bonds link the mol­ecules into layers parallel to the bc plane. Inter­molecular π–π stacking inter­actions [centroid–centroid distances = 3.685 (2) and 3.697 (2) Å] are observed between the parallel triazole rings

Nanoscale integrin cluster dynamics controls cellular mechanosensing via FAKY397 phosphorylation

Transduction of extracellular matrix mechanics affects cell migration, proliferation, and differentiation. While this mechanotransduction is known to depend on the regulation of focal adhesion kinase phosphorylation on Y397 (FAKpY397), the mechanism remains elusive. To address this, we developed a mathematical model to test the hypothesis that FAKpY397-based mechanosensing arises from the dynamics of nanoscale integrin clustering, stiffness-dependent disassembly of integrin clusters, and FAKY397 phosphorylation within integrin clusters. Modeling results predicted that integrin clustering dynamics governs how cells convert substrate stiffness to FAKpY397, and hence governs how different cell types transduce mechanical signals. Existing experiments on MDCK cells and HT1080 cells, as well as our new experiments on 3T3 fibroblasts, confirmed our predictions and supported our model. Our results suggest a new pathway by which integrin clusters enable cells to calibrate responses to their mechanical microenvironment

Protein-free formation of bone-like apatite: New insights into the key role of carbonation

International audienceThe nanometer-sized plate-like morphology of bone mineral is necessary for proper bone mechanics and physiology. However, mechanisms regulating the morphology of these mineral nanocrystals remain unclear. The dominant hypothesis attributes the size and shape regulation to organic-mineral interactions. Here, we present data supporting the hypothesis that physicochemical effects of carbonate integration within the apatite lattice control the morphology, size, and mechanics of bioapatite mineral crystals. Carbonated apatites synthesized in the absence of organic molecules presented plate-like morphologies and nanoscale crystallite dimensions. Experimentally-determined crystallite size, lattice spacing, solubility and atomic order were modified by carbonate concentration. Molecular dynamics (MD) simulations and density functional theory (DFT) calculations predicted changes in surface energy and elastic moduli with carbonate concentration. Combining these results with a scaling law predicted the experimentally observed scaling of size and energetics with carbonate concentration. The experiments and models describe a clear mechanism by which crystal dimensions are controlled by carbonate substitution. Furthermore, the results demonstrate that carbonate substitution is sufficient to drive the formation of bone-like crystallites. This new understanding points to pathways for biomimetic synthesis of novel, nanostructured biomaterials