Ferromagnetic resonance investigation of nanocrystalline FeCuNbSiB

An elaborate line-shape analysis of the ferromagnetic resonance (FMR) spectra taken in the temperature range 100 K to 350 K on amorphous FeCuNbSiB alloys before and after nanocrystallizing them reveals that in the nanocrystalline state, (i) spin wave stiffness (D) is enhanced while the saturation magnetization,M _S, is reduced, (ii) both the ‘in-plane’ anisotropy field,H _K, as well as the FMR line-width scale with MS, (iii) the single-ion anisotropy of spin-orbit plus crystal field origin dominates over the twoion anisotropy of dipolar origin and (iv) multi-magnon scattering contributions to FMR line-width become important in some cases     

Horizons in 2+1-dimensional collapse of particles

A simple, geometrical construction is given for three-dimensional spacetimes with negative cosmological constant that contain two particles colliding head-on. Depending on parameters like particle masses and distance, the combined geometry will be that of a particle, or of a black hole. In the black hole case the horizon is calculated. It is found that the horizon typically starts at a point and spreads into a closed curve with corners, which propagate along spacelike caustics and disappear as the horizon passes the particles.      

Optical and magnetotransport properties of the Nd<Subscript>0.55</Subscript>Sr<Subscript>0.45</Subscript>MnO<Subscript>3</Subscript>-Sm<Subscript>0.55</Subscript>Sr<Subscript>0.45</Subscript>MnO<Subscript>3</Subscript> heterostructure

The effects of magnetotransmission and magnetoresistance in a film heterostructure composed of manganite layers with different Curie temperatures have been analyzed. High sensitivity of optical methods to the presence of different magnetic phases in the bulk of the material has been shown.     

Electrical imaging of neuronal activity by multi-transistor-array (MTA) recording at 7.8 μm resolution

We report on a novel method for two-dimensional electrical mapping of neuronal activity using a 1 mm² array of 16384 sensor field-effect transistors fabricated by an extended CMOS (complementary metal oxide silicon) technology. The contact from neurons to chip is made by an insulating oxide on the chip surface that provides a purely capacitive drive of the sensor transistors. As a test system for multi-transistor-array (MTA) recording we use cultured neurons from the pond snail. We present electrical maps of an individual neuron and of a small neuronal network at a resolution of 7.8 m. MTA recording provides a tool for imaging the network dynamics of cultured nerve cells and brain slices for studies in neurobiology and biosensorics. Supplementary material to this paper is available in electronic form on Springers server at http://dx.doi.org/10.1007/s00339-004-2991-5PACS 87.17.Nn, 87.80.Xa, 73.40.Mr     

Colossal room-temperature magnetoresistance in thin La<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Ag<Subscript>y</Subscript>MnO<Subscript>3</Subscript> epitaxial films

The first thin La_1?xAg_yMnO₃ epitaxial films (_y ≤ x) were grown on SrTiO₃ (110) substrates with silver present in the ionized state (Ag⁺) only. The Curie temperatures T_C of the compositions with x = y = 0.05, x = y = 0.1, and x = 0.3 and y = 0.27 crystallizing in the hexagonal structure \(R\bar 3c\) above or close to room temperature. The temperature dependences of electrical resistivity ρ and of magnetoresistance ¦Δρ/ρ/¦ = ¦(ρ_H ? ρ _H = 0)/ρ_H=0¦ pass through maxima near T_C, with the magnetoresistance being negative and reaching colossal values of ～7–20% in a magnetic field H = 8.2 kOe not only at T_C but also at room temperature. The magnetic moment per formula unit as derived from the saturation magnetization at T = 5 K is substantially smaller than expected for complete ferromagnetic ordering. The magnetization in fields of up to 6 kOe depends on the actual sample cooling conditions, and the hysteresis loop of a field-cooled sample is displaced along the H axis by ΔH. The above properties can be accounted for by the fact that the films are in a two-phase magnetic (ferromagnetic-antiferromagnetic) state induced by strong s-d exchange. The maximum value of Δ H was used to calculate the energy of exchange coupling between the ferromagnetic and antiferromagnetic parts of a sample.     

Studies of material constitutive behavior using perturbation growth in explosive and magnetically driven liner systems

This paper discusses a collaborative research program aimed at the development of improved constitutive modeling capability, in particular, the development of a model validated over a wide range of strain rates (from quasistatic to 10⁶ s⁻¹). This program includes experimental, theoretical, and numerical components. The experimental part of the program includes both planar and cylindrical manifestations of the perturbation growth method. The theoretical part of the program is focused on the development of a model that considers all the necessary physical aspects and, at the same time, is compatible with standard numerical methods for solving the governing field equations. The numerical part of the program is focused on model implementation (in an appropriate continuum mechanics code) and validation. All three parts of the program are coupled. This paper will discuss the experimental program, the development of a new model, and show some results comparing various model predictions to experimental data. The text was submitted by the authors in English.     

Relativistic α-particles emitted in Fe-emulsion interactions at 1.7A GeV

Relativistic α-particles have been studied in 423 interactions of Fe in emulsion at 1.7A GeV. Comparisons of the observed angular distribution with that from ¹⁶O-emulsion reactions at 2.1A GeV reveal that more α-particles are observed at large angles in the Fe-emulsion reactions. The α-particles at large angles cannot be explained by fragmentation from a clean-cut spectator. Comparison of the experimental data with moving relativistic Boltzmann distributions shows that a single Boltzmann distribution cannot fit the fragmentation peak and the tail simultaneously. A thermal source (fireball) explaining the tail part of the distribution needs to be formed by a mechanism other than a simple clean-cut participant-spectator process. A large transverse momentum transfer to the spectator before fragmentation may explain the tail.     

Fluorescent polymer particles by emulsion and miniemulsion polymerization

We describe the synthesis and characterization of latex particles labeled with a brightly fluorescent yellow dye (HY) based on the benzothioxanthene ring structure. Three dye derivatives were synthesized with different spacers connecting the HY nucleus to a methacrylate group. For one of the dyes (HY2CMA, r_A), we show that the reactivity ratios with styrene (r_A = 0.71, r_B = 0.25) and butyl methacrylate (r_A = 0.87, r_B = 0.14) should lead to random dye incorporation if the amount of dye in the feed is small. Seeded emulsion polymerization fails to lead to significant dye incorporation unless large amounts of nonionic surfactant are present. In contrast, miniemulsion polymerization worked well to yield latex particles of polystyrene, poly(butyl methacrylate), and poly(methyl methacrylate) with high monomer conversion and essentially quantitative dye incorporation. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 766–778, 2003     

Ein einschliessungssatz für H-flächen in Riemannschen Mannigfaltigkeiten

In this paper an inclusion theorem of HEINZ and HILDEBRANDT is generalized to H-surfaces in Riemannian manifolds. Furthermore an isoperimetric inequality and an estimate of the number of branch points of H-surfaces are given.

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Diese Arbeit wurde durch Mittel der Deutschen Forschungsgemeinschaft unterstützt.