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Electron backscatter diffraction (EBSD) and electron channeling contrast imaging (ECCI) are used to extract crystallographic information from bulk samples, such as their crystal structure and orientation as well as the presence of any dislocation and grain boundary defects. These techniques rely on the backscattered electron signal, which has a large distribution in electron energy. Here, the influence of plasmon excitations on EBSD patterns and ECCI dislocation images is uncovered by multislice simulations including inelastic scattering. It is shown that the Kikuchi band contrast in an EBSD pattern for silicon is maximum at small energy loss (i.e., few plasmon scattering events following backscattering), consistent with previous energy-filtered EBSD measurements. On the other hand, plasmon excitation has very little effect on the ECCI image of a dislocation. These results are explained by examining the role of the characteristic plasmon scattering angle on the intrinsic contrast mechanisms in EBSD and ECCI.
We study the Balmer spectrum of the category of finite $G$-spectra for a compact Lie group $G$, extending the work for finite $G$ by Strickland, Balmer–Sanders, Barthel–Hausmann–Naumann–Nikolaus–Noel–Stapleton and others. We give a description of the underlying set of the spectrum and show that the Balmer topology is completely determined by the inclusions between the prime ideals and the topology on the space of closed subgroups of $G$. Using this, we obtain a complete description of this topology for all abelian compact Lie groups and consequently a complete classification of thick tensor ideals. For general compact Lie groups we obtain such a classification away from a finite set of primes $p$.
We have obtained long slit spectra of 3C 67 and 3C 277.1 with the HST/STIS spectrograph. We present our preliminary results on the diagnostic emission line ratios along the radio source axes in 3C 67 and 3C 277.1.
We have obtained HST/STIS long slit spectroscopy of the aligned emission line nebulae in three compact steep spectrum (CSS) radio sources — 3C 67, 3C 277.1, and 3C 303.1. We find systematic offsets (˜300–500 kms) of the emission line velocities on one or both sides of the radio sources. We also see evidence for broad lines (FWHM ˜500 kms) and complex emission line profiles. In 3C 303.1 the data are consistent with multiple components and possibly split lines. The amplitude of the velocity variations is not so large as to exclude gravitationally-induced motions. However, the complex kinematics, the lack of a signature of Keplerian rotation, and the association of the velocity variations with the radio lobes are consistent with the observed ˜300–500 kms velocities being driven by the expansion of the radio source. Acceleration of the clouds by the bow shock is plausible given the estimated densities in the clouds and the velocities observed in the much smaller compact symmetric objects and with expansion velocities estimated from spectral ageing. This conclusion is unchanged if we consider the scenario in which the cloud acceleration is dominated by the post bow shock flow.
Ni nanowires were grown in highly-ordered anodic alumina templates using pulsed electrodeposition. This technique yields completely metal-filled alumina membranes. The magnetic behavior of 100 nm period arrays of Ni nanowires with a length of 1 μ and different diameters has been characterized using SQUID magnetometry and magnetic force microscopy. Reducing the diameter from initially 50 to 25 nm while keeping the interwire distance constant leads to increasing coercive fields from 600 Oe to 1200 Oe and to increasing remanence from 30% to 100% of the hysteresis. The deposition of Ni65Fe35 gave a further improvement of the coercive fields up to 1350 Oe.
Abstract Manganese layers were deposited on polycrystalline Fe-based soft magnetic films. The magnetic domain structure of thin Fe overlayers on top these Mn films was measured by secondary electron microscopy with polarization analysis. The Fe layers show spin polarization only beyond a certain critical thickness of about 20 Å. Beyond this thickness the domain structure of the substrate starts to appear in the Fe overlayer. This delayed onset of ferromagnetic order in the Fe layers is attributed to frustration of ferromagnetic order due to the strong coupling to the antiferromagnetically ordered Mn. With increasing Fe film thickness (between 20–30 Å) the magnetization increases and shows the same domain pattern as the substrate. We find that for all Mn thicknesses studied (up to 170 Å) the Fe overlayer domain structure reproduces the substrate domain structure and the magnetization is always aligned parallel with the substrate magnetization.
3C236 is the largest radio source known. It has a 39 arcmin double structure (3.0 Mpc, Ho=75 kms−1 Mpc−1) in which the SE lobe is narrow and edge-brightened and the NW lobe more diffuse and centre-brightened (Barthel et al., 1985). About half the flux density comes from a steep spectrum (α = −0.7) radio core of overall size 1.3 arcsec (2.2 kpc) located in the centre of a 17m elliptical galaxy with redshift 0.0988.
The μ–z diagram (Figure 1) plots the observed internal proper motion μ versus redshift z for 32 extragalactic radio sources associated with active galactic nuclei. The observed points fall below an upper bound which decreases with redshift; there is a statistically significant anticorrelation between redshift and internal proper motion.
We discuss VLBI observations of the bright core in the large, triple radio source 4C 34.37, associated with a quasar at z = 0.206. We have discovered superluminal motion in this quasar, which is the largest quasar known. We comment on the implications of these findings, and subsequently examine the projected size distributions of lobe and core dominated quasars in general. The results of these investigations lead us to conclude that neither superluminal motion, nor core prominence can simply be translated into an orientation of the overall radio source.
We have conducted a systematic study of the milliarcsecond structure of a complete, flux-density limited sample of strong radio sources selected at 5 GHz. We have made 5 GHz maps at two epochs of the 45 compact sources in the sample, and third-epoch observations are in progress. Our intention was to explore the full range of morphologies exhibited by compact radio sources, to search for new superluminal sources, and to determine how widespread such phenomena as parsec-scale jets, alignment of parsec-scale and kiloparsec-scale jets, and superluminal motion are. In addition, we hoped to use this well-defined sample for statistical tests of the beaming theories.
The radio source 3C205 is identified with a quasar of redshift 1.53, and is, at first glance, a standard, powerful double radio source with hotspots. Upon closer examination (MERLIN, VLA A-array), the southern lobe is seen to consist of two distinct hotspots plus some more diffuse emission, some 50 kiloparsecs from the quasar (Ho ∼ 75). The arcsecond-scale morphology and polarization structure of this hotspot complex strongly suggests that the larger and weaker off-axis secondary hotspot has been formed by outflow of material from the more compact primary hotspot (Lonsdale and Barthel 1984,6). This interpretation implies a collision between the presumed energy supply beam and something capable of deflecting the flow energy towards the secondary. Because the flow is so energetic, this obstacle would have to be both massive and dense. The main constraint on the density of the obstacle comes from measurements of the internal energy density of the compact primary hotspot coupled with model-dependent estimates for the maximum advance velocity of this feature, thus yielding a balance with the ram-pressure exerted by the obstacle medium.
A critical test of the simple relativistic beaming models is provided by the search for structural changes in the weak cores of lobe-dominated quasars. In these sources, which are expected to be close to the plane of the sky, superluminal motion should be comparatively rare. We are engaged in the study of a complete sample of 30 extended quasars (Barthel et al. 1984), ranging in projected size from 40h−1 to 200h−1 kpc (Ho = 100h, qo = 0.05). High resolution multi-epoch observations have been obtained for two objects, the quasars 1721+343 and 0742+318, at 5 GHz (1982.3, 1983.3, 1986.5) and 10.7 GHz (1986.2, 1986.5). Superluminal expansion with transverse velocities of 3.1h−1 c has been detected in the core of 1721+343, which is the largest quasar known (Barthel et al., these proceedings). No superluminal motion was found in 0742+318. The large and small scale structure of 1721+343 are shown in fig.1a,b. The spectra of the individual components point to component A as the core
Since 1977 we have been engaged on a project to survey the milliarcsecond structure and internal motions of a complete, unbiased sample of 65 radio sources (Pearson and Readhead 1984). One of the goals of the project was to discover more superluminal sources and find out how common they are. The sample contains three established superluminal sources (3C 179, 3C 345, and BL Lacertae); so far we have discovered three new superluminal quasars (0850+581, 1642+690, and 1928+738), and a fourth (3C 216) that may be superluminal. Thus at least six out of the 65 sources are superluminal, and we expect to find more as our observations proceed.
The Nuclear Radio cores of several nearby extended radio galaxies (e.g. M87, 3C236) consist not only of optically thick (< 1 pc) components, but also of emission on somewhat larger scale. As extended radio sources associated with quasars have on average stronger and more luminous radio cores (see e.g. Miley, 1980, Ann. Rev. Astron. Astrophys. 18, 165), we have started a project to study the properties of these quasar cores.
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