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Clumpy irregular galaxies contain 5–10 “clumps” which are hyperactive HII complexes each equivalent to 100 giant HII regions of the 30 Doradus type (Heidmann 1982). We observed one of them, Mkn 325 (= NGC 7673), with the Einstein IPC in Dec. 1980 (seq.no 10201) for 3,200 s. The reduction was made kindly by D.E. Harris. The source was localized at 23h 25m 12.2s, + 23° 18′ 25″ (1950) in agreement with the optical position, at a quite weak level (14 counts in the 1.4–2.9 kev range). Thus we could not get valuable spectral information, only that the spectrum is rather not soft. Correction for galactic absorption NH = 5 ×1020 at.cm−2 (Heyles 1975) is applied. Fits of power law spectra happen to all go through the point with flux density 4.5 ×10−5 mJy at 3.0 ×1017 Hz (1.24 kev) and they yield a flux (1.1 ± 0.3) x10−13 erg cm−2 s−1 inside 1–3 kev and an X-luminosity (2.2 ± 0.3)×1041 erg s−1 inside 0.5–4.5 kev, for a distance 49 Mpc.
The volume of work published on extragalactic astronomy in the period August 1966 – July 1969 has been large. Limitations of space have precluded the writing of an all-inclusive report; in all sections some selection has had to be made. References are given, whenever possible, by the reference numbers of the Bulletin Signalétique of the CNRS of France, with the omission of the Section number: “2” for vols. 27 to 29 and “120” for vol. 30. A reference number preceded by J is taken from the Astronomischer Jahresbericht. When no reference numbers were available, abbreviated journal references have been given.
Giant extragalactic HII regions are found in the disks of nearby spiral and irregular galaxies, in the nuclear regions of spiral and elliptical galaxies, and in a variety of peculiar and interacting systems. At radio wavelengths they may emit thermal continuum radiation from the ionized gas and/or nonthermal synchrotron radiation if high energy electrons and magnetic fields are present. In some instances line radiation from associated molecular and neutral hydrogen clouds may also be detected. Table 1 illustrates the sorts of objects in which radio HII regions are observed and indicates the range of radio parameters found. Columns 1 and 2 give the galaxy and specific HII regions within the galaxy. Column 3 is the adopted distance of the galaxy. Column 4 indicates whether the emission is thermal (T) or nonthermal (N-T); column 5 is the 20 cm luminosity, and column 6 the linear size of the radio emitting region. For thermal sources the electron density, derived from the luminosity and size, is listed in column 7. The final column gives references. Note that almost all of the observational information obtainable from radio continuum observations is contained in columns 4, 5, and 6. Very occasionally there may be additional data concerning polarization or variability.
Compact sources (compactness evidenced by flat/complex spectra) display a “flicker” in their intrinsic centimeter wavelength radiation, with an amplitude of about 2% and a characteristic time scale of a few days.
The VLA, now under construction in New Mexico, is an aperture synthesis array of twenty-seven 25-meter diameter antennas, with overall dimension of about 35 km. At 6-cm wavelength it will have resolution of 0.6 arcseconds and sensitivity of 0.1 mJy, and should be a superb instrument for radio studies of objects of large redshift. A more detailed description of the VLA has been given by Heeschen (1975).
Markarian 8, a clumpy irregular galaxy (Casini et al. 1979), was observed with the VLA at 20 cm (Mar. 19, 1981; 26 ant.) and 6 cm wavelengths (June 12, 1980; 18 ant.) The structure is alike at the two wavelengths, consisting of 3 distinct clumps imbedded in a diffuse envelope of about 40 arcsec extent. Figure 1 shows the 6 cm structure. At higher resolution the clumps break up into several components. The 20 cm structure is shown in Figure 2, which also compares the optical and radio morphologies. There is excellent general agreement, suggesting a common origin of emission in the clumps.
When comparing large numbers of TEM micrographs of insoluble additives in polymer-based nanocomposite systems, the ability to determine or estimate the dispersion quality (i.e. uniformity of size and/or spatial distribution) is often difficult. The objective of this study was to develop a method to quantify dispersions observed in TEM micrographs that enables both a numerical “ranking” to be assigned to individual dispersions as well as tabulation a multitude of images acquired over time. Several methods were reviewed and applied to a set of TEM dispersion images of an insoluble additive in polystyrene. Projected area diameter, particle area, and Euclidean distance between particle centroids were chosen from all the particle size distribution and spatial distribution parameters present in the literature, but none successfully yielded a quantitative indicator of dispersion quality for the micrographs. In contrast, generating cumulative volume percent curves for each sample appeared to be a preferred method of quantifying and comparing dispersions in TEM micrographs. The volume diameter values obtained by this method can be used for “ranking” and tabulation of dispersion quality and account for both “good” additive dispersions (i.e. those with small domains of a narrow size range around 1 μm or less) and “bad” additive dispersions (i.e. those with non-uniform domains ranging in size by several microns or more). As a result, the numerical values generated by this method can be used to quantitatively determine correlations between the dispersion quality of nanoparticles in polymer-based nanocomposite materials and various macroscale physical and/or performance properties of such materials. This method’s precision was statistically determined to decrease with increasing particle size and be heavily dependent on representative sampling.