A note on rank-additivity

A new criterion is given for rank additivity of a collection of m × n complex matrices.     

The determination of shadowing critical angles in impact collision ion scattering spectroscopy

Critical angles for shadowing in low-energy ion scattering spectroscopy are calculated in the momentum approximation for the Thomas-Fermi-Molière potential and the Ziegler-Biersack-Littmark potential. In the relevant parameter range the results can be fitted by a formula containing five constants depending on the potential only. For a fixed projectile-target combination at a given energy the distance dependence of the critical angle is described by a simple power law. The comparison of the calculated results with experimental data shows that the inclusion of the effect of thermal vibrations on the critical angles improves the agreement between calculations and experiment significantly.     

Kumada coupling of aryl and vinyl tosylates under mild conditions

[Reaction: see text]. Aryl and alkenyl tosylates are easily prepared, inexpensive and, thus, attractive for transition-metal-catalyzed couplings, but their reactivity is low. We report examples of mild, palladium-catalyzed coupling of aryl, alkenyl, and alkyl Grignard reagents with aryl and alkenyl tosylates. The resulting biaryls, vinylarenes, and alkylarenes were isolated in good to excellent yield. These couplings were conducted with a nearly equimolar ratio of the two reactants, and many examples were conducted at room temperature.     

Eine Methode zur Bestimmung der spezifischen Radioaktivität der „freien Aminosäuren“ in Gewebeextrakten von Säugetieren

Some experiences are given with a measuring device for the determination of the specific radioactivity of ¹⁴C-labelled brain amino-acids. The apparatus consists of an automatic amino-acid analyzer combined with a flow cell filled with anthracene. The reproducibility of the method is ±5% to ±1% m.e. in the range of 1×10^?3 μCi to 5×10^?2 μCi. A quantitative determination of 3×10^?4 μCi/ml eluant is still possible.     

Stress-dependent elasticity of composite actin networks as a model for cell behavior

Networks of filamentous actin cross-linked with the actin-binding protein filamin A exhibit remarkable strain stiffening leading to an increase in differential elastic modulus by several orders of magnitude over the linear value. The variation of the frequency dependence of the differential elastic and loss moduli as a function of prestress is consistent with that observed in living cells, suggesting that cell elasticity is always measured in the nonlinear regime, and that prestress is an essential control parameter.     

A Novel Magnetic Resonance Phased-Array Coil Designed with FDTD Algorithm

Radio-frequency receiver phased-array coils in magnetic resonance imaging systems are used to pick up the signals emitted by the nuclei with high signal-to-noise ratio and a large region of sensitivity. Since the quality of obtained images strongly depends upon the correct choice of the coil geometry and position, array coils have to be designed by minimizing the mutual interaction among nearby coil elements and this is generally achieved by overlapping such adjacent elements. In this paper, we describe the use of a numerical solver based on finite-difference time-domain method to determine the optimal overlap distance, which guarantees the maximum decoupling level between the coil loops, for array coils constituted by various geometry elements. A novel array coil was designed, constituted by a couple of elliptical geometry elements in “folding” version around the animals’ spine curvature, for small animals’ imaging applications.