High-Frequency Electron-Spin-Resonance Study of the Octanuclear Ferric Wheel CsFe8_8

High-frequency ($f$ = 190 GHz) electron paramagnetic resonance (EPR) at magnetic fields up to 12 T as well as Q-band ($f$ = 34.1 GHz) EPR were performed on single crystals of the molecular wheel CsFe$_8$. In this molecule, eight Fe(III) ions, which are coupled by nearest-neighbor antiferromagnetic (AF) Heisenberg exchange interactions, form a nearly perfect ring. The angle-dependent EPR data allow for the accurate determination of the spin Hamiltonian parameters of the lowest spin multiplets with $S \leq$ 4. Furthermore, the data can well be reproduced by a dimer model with a uniaxial anisotropy term, with only two free parameters $J$ and $D$. A fit to the dimer model yields $J$ = -15(2) cm$^{-1}$ and $D$ = -0.3940(8) cm$^{-1}$. A rhombic anisotropy term is found to be negligibly small, $E$ = 0.000(2) cm$^{-1}$. The results are in excellent agreement with previous inelastic neutron scattering (INS) and high-field torque measurements. They confirm that the CsFe$_8$ molecule is an excellent experimental model of an AF Heisenberg ring. These findings are also important within the scope of further investigations on this molecule such as the exploration of recently observed magnetoelastic instabilities.Comment: 21 pages, 8 figures, accepted for publication in Inorganic Chemistr

The LRR Proteins Capricious and Tartan Mediate Cell Interactions during DV Boundary Formation in the Drosophila Wing

AbstractMechanisms to segregate cell populations play important roles in tissue patterning during animal development. Rhombomeres and compartments in the ectoderm and imaginal discs of Drosophila are examples in which initially homogenous populations of cells come to be separated by boundaries of lineage restriction. Boundary formation depends in part on signaling between the distinctly specified cell populations that comprise compartments and in part on formation of affinity boundaries that prevent intermingling of these cell populations. Here, we present evidence that two transmembrane proteins with leucine-rich repeats, known as Capricious and Tartan, contribute to formation of the affinity boundary between dorsal and ventral compartments during Drosophila wing development

The influence of topographic microstructures on the initial adhesion of L929 fibroblasts studied by single-cell force spectroscopy

Single-cell force spectroscopy was used to investigate the initial adhesion of L929 fibroblasts onto periodically grooved titanium microstructures (height ~6 μm, groove width 20 μm). The position-dependent local adhesion strength of the cells was correlated with their rheological behavior. Spherical cells exhibited a significantly lower Young’s modulus (<1 kPa) than that reported for spread cells, and their elastic properties can roughly be explained by the Hertz model for an elastic sphere. While in contact with the planar regions of the substrate, the cells started to adapt their shape through slight ventral flattening. The process was found to be independent of the applied contact force for values between 100 and 1,000 pN. The degree of flattening correlated with the adhesion strength during the first 60 s. Adhesion strength can be described by fast exponential kinetics as \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$C_{1} \left[ {1 - \exp \left( { - C_{2} \cdot t} \right)} \right]$$\end{document} with C1 = 2.34 ± 0.19 nN and C2 = 0.09 ± 0.02 s−1. A significant drop in the adhesion strength of up to 50% was found near the groove edges. The effect can be interpreted by the geometric decrease of the contact area, which indicates the inability of the fibroblasts to adapt to the shape of the substrate. Our results explain the role of the substrate’s topography in contact guidance and suggest that rheological cell properties must be considered in cell adhesion modeling

Birth Weight and Prenatal Exposure to Polychlorinated Biphenyls (PCBs) and Dichlorodiphenyldichloroethylene (DDE): A Meta-analysis within 12 European Birth Cohorts

Objectives: Exposure to high concentrations of persistent organochlorines may cause fetal toxicity, but the evidence at low exposure levels is limited. Large studies with substantial exposure contrasts and appropriate exposure assessment are warranted. Within the framework of the EU (European Union) ENRIECO (ENvironmental Health RIsks in European Birth Cohorts) and EU OBELIX (OBesogenic Endocrine disrupting chemicals: LInking prenatal eXposure to the development of obesity later in life) projects, we examined the hypothesis that the combination of polychlorinated biphenyls (PCBs) and dichlorodiphenyldichloroethylene (DDE) adversely affects birth weight

Rational design and direct fabrication of multi-walled hollow electrospun fibers with controllable structure and surface properties

Multi-walled hollow fibers with a novel architecture are fabricated through utilizing a direct,one-step tri-axial electrospinning process with a manufacturing methodology which does not require any post-treatments for the removal of core material for creating hollowness in the fiber structure. The hydrophilicity of both inner and outer layers’ solution needs to be dissimilar and carefully controlled for creating a two-walled/layered hollow fiber tructure with a sharp interface. To this end, Hansen solubility parameters are used as n index of layer solution affinity hence allowing for control of diffusion across the layers and the surface porosity whereby an ideal multi-walled hollow electrospun fiber is shown to be producible by tri-axial electrospinning process. Multi-walled hollow electrospun fibers with different inner and outer diameters and different surface morphology are successfully produced by using dissimilar material combinations for inner and outer layers (i.e., hydrophobic polymers as outer layer and hydrophilic polymer as inner layer). Upon using different material combinations for inner and outer layers, it is shown that one may control both the outer and inner diameters of the fiber. The inner layer not only acts as a barrier and thus provides an ease in the encapsulation of functional core materials of interest with different viscosities but also adds stiffness to the fiber. The structure and the surface morphology of fibers are controlled by changing applied voltage, polymer types, polymer concentration, and the evaporation rate of solvents. It is demonstrated that if the vapor pressure of the solvent for a given outer layer polymer is low, the fiber diameter decreases down to 100 nm whereas solvents with higher vapor pressure result in fibers with the outer diameter of up to 1 μm. The influence of electric field strength on the shape of Taylor cone is also monitored during the production process and the manufactured fibers are structurally investigated by relevant surface characterization techniques

Validation of different SAC305 material models calibrated on isothermal tests using in-situ TMF measurement of thermally induced shear load

In the past, a large number of material models for Sn-based solder alloys have been proposed, which are usually calibrated based on the material testing under isothermal the conditions. However, their ability to map the lifetime differences depending on the temperature rate under the field and test-lab conditions, as well as on the mean operating temperature, is still not completely investigated and validated. The novel thermo-mechanical fatigue (TMF) measurement set-up is employed for in-situ measurement of the material degradation driven by temperature cycles. The experimental system involves different materials, which impose thermally induced displacements onto the solder interconnections. The acceleration of the test duration can be controlled by the placing the sample into the loading positions with the different level of the thermally induced displacement. The measurement enables monitoring of the force-reduction and the concurrent change of displacement. In the current study, the samples comprising a real-scale geometry of the four Ball Grid Array (BGA) connections were stressed with the temperature cycles relevant for the typical lab-tests and field conditions. The level of the thermally induced shear displacement in the solder joints was significantly higher than in an Engine Control Unit ECU. Since the experimental set-up includes various geometrical and material features, an extensive FE-based sensitivity study has been performed. The simulation of the free-expanding system as well as of the system with different pre-characterized dummy samples (without solder joints) revealed the capabilities and specific mechanical behavior of the experimental set-up. Finally, for Sn96.5Ag3.0Cu0.5 solder alloy the ability of the different material formulations to reproduce the trends of the measured hysteresis was analyzed: for double power-law creep model (DPL), unified inelastic strain formulation by Anand, and unified visco-plastic model proposed by Chaboche. Their accuracies in predicting of the acceleration factor between the different temperature profiles are summarized and discussed