Transverse Magnetic Anisotropy in Mn12-acetate: Direct Determination by Inelastic Neutron Scattering

A high resolution inelastic neutron scattering (INS) study of fully deuterated Mn$_{12}$-acetate provides the most accurate spin Hamiltonian parameters for this prototype single molecule magnet so far. The Mn$_{12}$-clusters deviate from axial symmetry, a non-zero rhombic term in the model Hamiltonian leading to excellent agreement with observed positions and intensities of the INS peaks. The following parameter set provides the best agreement with the experimental data: $D=-0.0570(1)$ meV, $B_{4}^0=-2.78(7)\cdot 10^{-6}$ meV, $B_{4}^4=-3.2(6)\cdot 10^{-6}$ meV and $\mid$\textit{E}$\mid =6.8(15)\cdot 10^{-4}$ meV. Crystal dislocations are not the likely cause of the symmetry lowering. Rather, this study lends strong support to a recently proposed model, which is based on the presence of several molecular isomers with distinct spin Hamiltonian parameters.Comment: 4 pages, 4 figure

Real time, confocal imaging of Ca2+ waves in arterially perfused rat hearts

Objective: The aim of this study was to characterize the spatio-temporal dynamics of slow Ca2+ waves (SCW's) with cellular resolution in the arterially-perfused rat heart. Methods: Wister rat hearts were Langendorff-perfused with Tyrode solution containing bovine-albumine and Dextran. The heart was loaded with the Ca2+ sensitive dye Fluo-3 AM. Intracellular fluorescence changes reflecting changes in [Ca2+]i were recorded from subepicardial tissue layers using a slit hole confocal microscope with an image intensified video camera system at image rates of up to 50/s. Results: SCW's appeared spontaneously during cardiac rest or after trains of electrical stimuli. They were initiated preferentially in the center third of the cell and propagated to the cell borders, suggesting a relation between the cell nucleus and wave initiation. They were suppressed by Ca2+ transients and their probability of occurrence increased with the Ca2+ resting level. Propagation velocity within myocytes (40 to 180 μm/s) decreased with the resting Ca2+ level. Intercellular propagation was mostly confined to two or three cells and occurred bi-directionally. Intercellular unidirectional conduction block and facilitation of SCW's was occasionally observed. On average 10 to 20% of cells showed non-synchronized simultaneous SCW's within a given area in the myocardium. Conclusions: SCW's occurring at increased levels of [Ca2+]i in normoxic or ischemic conditions are mostly confined to two or three cells in the ventricular myocardium. Spatio-temporal summation of changes in membrane potential caused by individual SCW's may underlie the generation of triggered electrical ectopic impulse

Photothermal excitation of microcantilevers in liquid: effect of the excitation laser position on temperature and vibrational amplitude

Demands to improve the sensitivity and measurement speed of dynamic scanning force microscopy and cantilever sensing applications necessitate the development of smaller cantilever sensors. As a result, methods to directly drive cantilevers, such as photothermal or magnetic excitation, are gaining in importance. Presented is a report on the effect of photothermal excitation of microcantilevers on the increase in steady-state temperature and the dynamics of higher mode vibrations. First, the local temperature increase upon continuous irradiation with laser light at different positions along the cantilever was measured and compared with finite element analysis data. The temperature increase was highest when the heating laser was positioned at the free end of the cantilever. Next, the laser intensity was modulated to drive higher flexural modes to resonance. The dependence of the cantilever dynamics on the excitation laser position was assessed and was in good agreement with the analytical expressions. An optimal position to simultaneously excite all flexural modes of vibration with negligible heating was found at the clamped end of the cantilever. The reports findings are essential for optimisation of the excitation efficiency to minimise the rise in temperature and avoid damaging delicate samples or functionalisation layers

Pressure Dependence of the Magnetic Anisotropy in the "Single-Molecule Magnet" [Mn4O3Br(OAc)3(dbm)3]

The anisotropy splitting in the ground state of the single-molecule magnet [Mn4O3Br(OAc)3(dbm)3] is studied by inelastic neutron scattering as a function of hydrostatic pressure. This allows a tuning of the anisotropy and thus the energy barrier for slow magnetisation relaxation at low temperatures. The value of the negative axial anisotropy parameter $D_{\rm cluster}$ changes from -0.0627(1) meV at ambient to -0.0603(3) meV at 12 kbar pressure, and in the same pressure range the height of the energy barrier between up and down spins is reduced from 1.260(5) meV to 1.213(9) meV. Since the $\rm Mn-Br$ bond is significantly softer and thus more compressible than the $\rm Mn-O$ bonds, pressure induces a tilt of the single ion Mn$^{3+}$ anisotropy axes, resulting in the net reduction of the axial cluster anisotropy.Comment: 4 pages, 3 figure

Array based real-time measurement of fluid viscosities and mass-densities to monitor biological filament formation

Liquid mass density and viscosity are fundamental characteristics of fluids. Their quantification by means of classical viscosity and density meters has several drawbacks: (i) the liquid-density and the viscosity cannot be measured simultaneously, (ii) sample volumes in the mL-range are consumed, (iii) the measurements cannot be multiplexed, and, (iv) the quantifications are time-consuming (minutes). Nano-mechanical transducers promise to overcome these limitations. We use fully clamped, gold coated silicon-nitride membranes with a thickness of 200 nm to measure liquid viscosity and density of samples of 1 L volumes residing above the membrane in a miniature well. Photo-thermal actuation is used to excite the membrane, and an optical deflection system measures the response. From the response spectra, the eigenfrequency (f) and the quality (Q) factor are extracted and used to determine liquid density and viscosity by applying a three-point calibrated, simplified lumped model. We tested the system using calibrated solutions with viscosities in the range of 1-219 mPa s and mass densities between 998 kg m(-3) and 1235 kg m(-3). Real-time measurements were performed that characterize the polymerization of G-actin to F-actin filaments. The method presented promises to overcome the aforementioned limitations and thereby enables the real-time characterization of sub-L sample volumes in a multiplexed manner

Allergologische Diagnostik von Überempfindlichkeitsreaktionen auf Arzneimittel

Überempfindlichkeitsreaktionen auf Arzneimittel müssen ausreichend geklärt werden mit dem Ziel, den Auslöser zu identifizieren. Die Anamnese umfasst neben der allgemeinen Anamnese auch Informationen zu angewandten Arzneimitteln, zur Klassifikation und zu den Umständen der Reaktion. Hauttests erfolgen bei allen Reaktionen mit Symptomen allergischer Überempfindlichkeiten mit geeigneten Testkonzentrationen, möglichst zwischen 4 Wochen und 6 Monate nach Abheilung der Reaktion durch Pricktest, Intrakutantest, Epikutantest oder Photopatchtest. Validierte Tests zum Nachweis spezifischer IgE-Antikörper im Serum sind nur für wenige Arzneistoffe (vor allem Betalaktamantibiotika) verfügbar; andere immunologische Labormethoden, z.B. der Basophilen-Aktivierungstest, werden nur in ausgewählten Fällen angewendet. Provokationstests sind indiziert, wenn der Auslöser durch bisherige Untersuchungen nicht mit Sicherheit identifiziert werden kann. Die Bewertung der Ergebnisse von Provokationstests sollte möglichst anhand objektiver Parameter erfolgen. Das Ergebnis der abschließenden Gesamtbeurteilung wird mit dem Patienten ausführlich besprochen und in einem Allergiepass niedergeleg

Allergologische Diagnostik von Überempfindlichkeitsreaktionen auf Arzneimittel

Drug hypersensitivity reactions have to be tested to identify the culprit substance. The history includes the general information and specific data concerning used drugs, the classification and circumstances of the reaction. Skin tests are performed in all hypersensitivity reactions with allergic symptoms. Tests should be done between four weeks and six months after clearance of the symptoms by performing skin prick test, intradermal test, patch test or photopatch test. Validated tests for the detection of specific IgE antibodies in the serum are available for only few drugs, especially betalactam antibiotics. Other laboratory tests, e.g., the basophil activation test are done only in special cases. Provocation tests are indicated, if the culprit drug cannot be identified by the above mentioned tests. If possible, the evaluation of provocation tests should rely on objective parameters. The concluding assessment will be discussed with the patient and will be documented in an allergy pass