Chiral magnetic interactions induce complex spin textures including helical and conical spin spirals, as well as particle-like objects such as magnetic skyrmions and merons. These spin textures are ...the basis for innovative device paradigms and give rise to exotic topological phenomena, thus being of interest for both applied and fundamental sciences. Present key questions address the dynamics of the spin system and emergent topological defects. Here we analyse the micromagnetic dynamics in the helimagnetic phase of FeGe. By combining magnetic force microscopy, single-spin magnetometry and Landau-Lifschitz-Gilbert simulations we show that the nanoscale dynamics are governed by the depinning and subsequent motion of magnetic edge dislocations. The motion of these topologically stable objects triggers perturbations that can propagate over mesoscopic length scales. The observation of stochastic instabilities in the micromagnetic structure provides insight to the spatio-temporal dynamics of itinerant helimagnets and topological defects, and discloses open challenges regarding their technological usage.
We present Very Large Array observations of the 33 GHz radio continuum emission from 22 local ultraluminous and luminous infrared (IR) galaxies (U/LIRGs). These observations have spatial (angular) ...resolutions of 30-720 pc (0 07-0 67) in a part of the spectrum that is likely to be optically thin. This allows us to estimate the size of the energetically dominant regions. We find half-light radii from 30 pc to 1.7 kpc. The 33 GHz flux density correlates well with the IR emission, and we take these sizes as indicative of the size of the region that produces most of the energy. Combining our 33 GHz sizes with unresolved measurements, we estimate the IR luminosity and star formation rate per area and the molecular gas surface and volume densities. These quantities span a wide range (4 dex) and include some of the highest values measured for any galaxy (e.g., ). At least 13 sources appear Compton thick ( ). Consistent with previous work, contrasting these data with observations of normal disk galaxies suggests a nonlinear and likely multivalued relation between star formation rate and molecular gas surface density, though this result depends on the adopted CO-to-H2 conversion factor and the assumption that our 33 GHz sizes apply to the gas. Eleven sources appear to exceed the luminosity surface density predicted for starbursts supported by radiation pressure and supernova feedback; however, we note the need for more detailed observations of the inner disk structure. U/LIRGs with higher surface brightness exhibit stronger C ii 158 m deficits, consistent with the suggestion that high energy densities drive this phenomenon.
We present new Karl G. Jansky Very Large Array radio continuum images of the nuclei of Arp 220, the nearest ultra-luminous infrared galaxy. These new images have both the angular resolution to study ...the detailed morphologies of the two nuclei that power the galaxy merger and sensitivity to a wide range of spatial scales. At 33 GHz, we achieve a resolution of 0.081 x 0.063 and resolve the radio emission surrounding both nuclei. We conclude from the decomposition of the radio spectral energy distribution that a majority of the 33 GHz emission is synchrotron radiation. The spatial distributions of radio emission in both nuclei are well described by exponential profiles. According to the calculations, the nuclei of Arp 220 are only transparent in the frequency range ~5-350 GHz. Our results offer no clear evidence that an active galactic nucleus dominates the emission from either nucleus at 33 GHz.
Department of Psychology, Princeton University, Princeton, New Jersey
Submitted 5 May 2008;
accepted in final form 29 July 2008
A traditional view of the human motor cortex is that it contains an ...overlapping sequence of body part representations from the tongue in a ventral location to the foot in a dorsal location. In this study, high-resolution functional MRI (1.5 x 1.5 x 2 mm) was used to examine the somatotopic map in the lateral motor cortex of humans, to determine whether it followed the traditional somatotopic order or whether it contained any violations of that somatotopic order. The arm and hand representation had a complex organization in which the arm was relatively emphasized in two areas: one dorsal and the other ventral to a region that emphasized the fingers. This violation of a traditional somatotopic order suggests that the motor cortex is not merely a map of the body but is topographically shaped by other influences, perhaps including correlations in the use of body parts in the motor repertoire.
Address for reprint requests and other correspondence: M.S.A. Graziano, Dept. of Psychology, Green Hall, Princeton Univ., Princeton, NJ 08544 (E-mail: Graziano{at}princeton.edu )
We investigated the voltages obtained in a thin Pt strip on a permalloy film which was subject to inplane temperature gradients and magnetic fields. The voltages detected by thin W tips or bond wires ...showed a purely symmetric effect with respect to the external magnetic field which can be fully explained by the planar Nernst effect. To verify the influence of the contacts, measurements in vacuum and atmosphere were compared and gave similar results. We explain that a slightly inplane tilted temperature gradient only shifts the field direction dependence but does not cancel out the observed effects. Additionally, the anomalous Nernst effect could be induced by using thick Au tips which generated a heat current perpendicular to the sample plane. The effect can be manipulated by varying the temperature of the Au tips. These measurements are discussed concerning their relevance in transverse spin Seebeck effect measurements.
The Owens Valley Radio Observatory 40-m telescope has been monitoring the 15-GHz radio flux density of over 1200 blazars since 2008. The 15-GHz light curve of the flat spectrum radio quasar ...J1359+4011 shows a strong and persistent quasi-periodic oscillation. The time-scale of the oscillation varies between 120 and 150 d over an ∼4 year time span. We interpret this as the active galactic nucleus mass-scaled analogue of low-frequency quasi-periodic oscillations from Galactic microquasars or as evidence of modulation of the accretion flow by thermal instabilities in the 'inner' accretion disc.
Parsec-scale VLBA images of BL Lac at 15 GHz show that the jet contains a permanent quasi-stationary emission feature 0.26 mas (0.34 pc projected) from the core, along with numerous moving features. ...In projection, the tracks of the moving features cluster around an axis at a position angle of - 166degrees.6 that connects the core with the standing feature. The moving features appear to emanate from the standing feature in a manner strikingly similar to the results of numerical two-dimensional relativistic magneto-hydrodynamic (RMHD) simulations in which moving shocks are generated at a recollimation shock (RCS). Because of this, and the close analogy to the jet feature HST-1 in M87, we identify the standing feature in BL Lac as an RCS. We assume that the magnetic field dominates the dynamics in the jet, and that the field is predominantly toroidal. From this we suggest that the moving features are compressions established by slow and fast mode magneto-acoustic MHD waves. We illustrate the situation with a simple model in which the slowest moving feature is a slow-mode wave, and the fastest feature is a fast-mode wave. In the model, the beam has Lorentz factor Gamma super(gal) sub(beam) approximately 3.5 in the frame of the host galaxy and the fast mode wave has Lorentz factor Gamma super(beam) sub(Fwave) approximately 1.6 in the frame of the beam. This gives a maximum apparent speed for the moving features, beta sub(app) = v sub(app)/c = 10. In this model the Lorentz factor of the pattern in the galaxy frame is approximately three times larger than that of the beam itself.
Pyrolytic lignins have been obtained from pyrolysis oil as fine homogeneous powder by a novel precipitation method. The paper presents results obtained for various pyrolytic lignins of pyrolysis oils ...from different fast pyrolysis processes. They were subjected to various physico-chemical characterization methods. Analysis methods comprise chromatography, spectroscopy and wet chemical techniques. FTIR data indicate that a changing oxygen content mainly effects the intensity of carbonyl absorption bands. Therefore, FTIR analysis is valuable as a fast analytical method to elucidate aging processes of pyrolysis oil. Analytical pyrolysis combined with GC/MS, FTIR data, and results of functional group analysis show pyrolytic lignin to be similar to technical lignins.
Hexagonal manganites are among the most intensively studied multiferroics, exhibit unusual geometrically driven ferroelectricity and magnetoelectric couplings, and form domains and domain walls with ...intriguing functional properties. In order to study these electronic correlation phenomena and develop a comprehensive understanding about the underlying physics, the availability of high-quality single-crystals is crucial. In particular, different members of the RMnO3 (R=Sc, Y, In, Dy to Lu) family require different growth condition in order to achieve stoichiometric single-phase crystals. Here, we report on the growth of high-quality ErMnO3 single crystals with dimensions of 5mm in diameter and up to 60mm in length using the pressurized floating-zone technique. We present Laue diffraction, piezoresponse force microscopy, and conductive atomic force microscopy data, reflecting the quality of our single crystals regarding the structure, as well as electronic properties on the level of domains and domain walls.
•High-quality hexagonal ErMnO3 single-crystals are grown by the pressurized floating-zone method.•The growth pressure is up to 0.8MPa in any step of the growth.•The method effectively prevents the volatilization of manganese from melt during crystal growth and hence makes it possible to grow stoichiometric single crystals.•The piezoresponse force microscopy, and conductive atomic force microscopy data, reflected the quality of our single-crystals regarding the structure, as well as electronic properties on the level of domains and domain walls.
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