Transport properties of the azimuthal magnetorotational instability

The magnetorotational instability (MRI) is thought to be a powerful source of turbulence in Keplerian accretion disks. Motivated by recent laboratory experiments, we study the MRI driven by an azimuthal magnetic field in an electrically conducting fluid sheared between two concentric rotating cylinders. By adjusting the rotation rates of the cylinders, we approximate angular velocity profiles ω ∝ r q . We perform direct numerical simulations of a steep profile close to the Rayleigh line q & −2 and a quasiKeplerian profile q ≈ −3/2 and cover wide ranges of Reynolds (Re ≤ 4 · 104 ) and magnetic Prandtl numbers (0 ≤ Pm ≤ 1). In the quasi-Keplerian case, the onset of instability depends on the magnetic Reynolds number, with Rmc ≈ 50, and angular momentum transport scales as √ PmRe2 in the turbulent regime. The ratio of Maxwell to Reynolds stresses is set by Rm. At the onset of instability both stresses have similar magnitude, whereas the Reynolds stress vanishes or becomes even negative as Rm increases. For the profile close to the Rayleigh line, the instability shares these properties as long as Pm & 0.1, but exhibits a markedly different character if Pm → 0, where the onset of instability is governed by the Reynolds number, with Rec ≈ 1250, transport is via Reynolds stresses and scales as Re2 . At intermediate Pm = 0.01 we observe a continuous transition from one regime to the other, with a crossover at Rm = O(100). Our results give a comprehensive picture of angular momentum transport of the MRI with an imposed azimuthal field

Kharkiv region of Ukraine in the aspect of a polycentric development model

This article is devoted to the analysis of a model of regional development of Kharkiv region of Ukraine, which is monocentric, and the rationale for the formation of polycentrism in the region. The city of Kharkiv and urban areas as centers of growth in the region are considered in the articl

Mapping the properties of blue compact dwarf galaxies: integral field spectroscopy with PMAS

(Abridged) We perform integral field spectroscopy of a sample of Blue compact dwarf (BCD) galaxies with the aim of analyzing their morphology, the spatial distribution of some of their physical properties (excitation, extinction, and electron density) and their relationship with the distribution and evolutionary state of the stellar populations. Integral field spectroscopy observations of the sample galaxies were carried out with the Potsdam Multi-Aperture Spectrophotometer (PMAS) at the 3.5 m telescope at Calar Alto Observatory. An area 16 arcsec x 16 arcsec in size was mapped with a spatial sampling of 1 arcsec x 1 arcsec. We obtained data in the 3590-6996 Angstroms spectral range, with a linear dispersion of 3.2 Angstroms per pixel. From these data we built two-dimensional maps of the flux of the most prominent emission lines, of two continuum bands, of the most relevant line ratios, and of the gas velocity field. Integrated spectra of the most prominent star-forming regions and of whole objects within the FOV were used to derive their physical parameters and the gas metal abundances. Six galaxies display the same morphology both in emission line and in continuum maps; only in two objects, Mrk 32 and Tololo 1434+032, the distributions of the ionized gas and of the stars differ considerably. In general the different excitation maps for a same object display the same pattern and trace the star-forming regions, as expected for objects ionized by hot stars; only the outer regions of Mrk 32, I Zw 123 and I Zw 159 display higher [SII]/Halpha values, suggestive of shocks. Six galaxies display an inhomogeneous dust distribution. Regarding the kinematics, Mrk 750, Mrk 206 and I Zw 159 display a clear rotation pattern, while in Mrk 32, Mrk 475 and I Zw 123 the velocity fields are flat.Comment: 27 pages, 11 figures; Accepted for publication in A&

"Counterpart" method for abundance determinations in HII regions

We suggest a new way of the determining abundances and electron temperatures in HII regions from strong emission lines. Our approach is based on the standard assumption that HII regions with similar intensities of strong emission lines have similar physical properties and abundances. A "counterpart" for a studied HII region may be chosen among HII regions with well-measured abundances (reference HII regions) by comparison of carefully chosen combinations of strong line intensities. Then the abundances in the investigated HII region can be assumed to be the same as that in its counterpart. In other words, we suggest to determine the abundances in HII regions "by precedent". To get more reliable abundances for the considered HII region, a number of reference HII regions is selected and then the abundances in the target HII region is estimated through extra-/interpolation. We will refer to this method of abundance determination as the counterpart method or, for brevity, the C method. We define a sample of reference HII regions and verify the validity of the C method. We find that this method produces reliable abundances. Finally, the C method is used to obtain the radial abundance distributions in the extended discs of the spiral galaxies M83, NGC4625 and NGC 628.Comment: 21 pages, 11 figures, accepted for publication in the MNRA

Super Star Clusters in the Blue Dwarf Galaxy UM 462

I present optical observations of the Blue Compact Dwarf Galaxy UM 462. The images of this galaxy show several bright compact sources. A careful study of these sources has revealed their nature of young Super Star Clusters. The ages determined from the analysis of the stellar continuum and $H\alpha$ are between few and few tens Myr. The total star formation taking place into the clusters is about 0.05 $\mathrm{M_{\odot}/yr}$. The clusters seem to be located at the edges of two large round-like structures, possibly shells originated in a previous episode of star formation. The sizes of the shells compare well with the ages of the clusters. Evidence for the presence of an evolved underlying stellar population is found.Comment: 8 pages, 6 figure

An Exploratory Assessment of Applying Risk Management Practices to Engineered Nanomaterials

The widespread industrial application of nanotechnology has increased the number of workers exposed to engineered nanomaterials (ENMs), but it is not clear to what extent prevention guidance is practiced. Our aim was to explore the extent that companies manufacturing and/or using ENMs apply risk assessment and management measures. Thirty-four companies were surveyed with an international 35-item questionnaire investigating company and workforce features, types of ENM handled, and risk evaluation and preventive measures adopted. Among participating companies, 62% had a maximum of 10 employees. Metal-based nanomaterials were most frequently identified (73%). Environmental monitoring was performed by 41% of the companies, while engineering exposure controls were approximately reported by 50%. Information and training programs were indicated by 85% of the sample, only 9% performed specific health surveillance for ENM workers. Personal protective equipment primarily included gloves (100%) and eye/face protection (94%). This small-scale assessment can contribute to the limited amount of published literature on the topic. Future investigations should include a greater number of companies to better represent ENM workplaces and a direct access to industrial settings to collect information on site. Finally, deeper attention should be paid to define standardized frameworks for ENM risk assessment that may guide nano-specific preventive actions

Consumer credit in comparative perspective

We review the literature in sociology and related fields on the fast global growth of consumer credit and debt and the possible explanations for this expansion. We describe the ways people interact with the strongly segmented consumer credit system around the world—more specifically, the way they access credit and the way they are held accountable for their debt. We then report on research on two areas in which consumer credit is consequential: its effects on social relations and on physical and mental health. Throughout the article, we point out national variations and discuss explanations for these differences. We conclude with a brief discussion of the future tasks and challenges of comparative research on consumer credit.Accepted manuscrip

New insights to the photometric structure of Blue Compact Dwarf Galaxies from deep Near-Infrared studies: II. The sample of northern BCDs

This paper is part of a series of publications which present a systematic study of Blue Compact Dwarf (BCD) Galaxies in the Near Infrared (NIR). Compared to the visible light, NIR data allow a better separation of the starburst emission from the light distribution of the old stellar low-surface brightness (LSB) host galaxy. We analyze deep NIR broad band images of a sample of 11 BCDs, observed with the Calar Alto 3.6m telescope. This work enlarges the samples presented in preceding papers of this study (Noeske et al. 2003, Cairos et al. 2003) by BCDs of the most common morphological type, displaying a regular elliptical LSB host galaxy. The data presented here allow the detection and quantitative study of the extended stellar LSB host galaxy in all sample BCDs. The NIR surface brightness profiles (SBPs) of the LSB host galaxies agree at large galactocentric radii with those from optical studies, showing also an exponential intensity decrease and compatible scale lengths. Similar to Noeske et al. (2003), we find centrally flattening exponential (type V) SBPs of the host galaxy for several BCDs. Such SBPs remain mostly undetected in optical bands, due to the comparatively stronger starburst emission at these wavelengths. We apply a modified exponential distribution to decompose and quantitatively analyze SBPs of LSB hosts with a type V intensity distribution. We present the results of the surface photometry and the decomposition of SBPs, and discuss individual objects with respect to morphological details of their star-forming regions.Comment: 18 pages, 11 figures; accepted for publication in Astronomy & Astrophysics; postscript file with full resolution images available at http://www.ucolick.org/~kai/PUB/noeske_nirbcds_2.ps.g

Mapping Luminous Blue Compact Galaxies with VIRUS-P: morphology, line ratios and kinematics

[abridged] We carry out an integral field spectroscopy (IFS) study of a sample of luminous BCGs, with the aim to probe the morphology, kinematics, dust extinction and excitation mechanisms of their warm interstellar medium (ISM). IFS data for five luminous BCGs were obtained using VIRUS-P, the prototype instrument for the Visible Integral Field Replicable Unit Spectrograph, attached to the 2.7m Harlan J. Smith Telescope at the McDonald Observatory. VIRUS-P consists of a square array of 247 optical fibers, which covers a 109"x109" field of view, with a spatial sampling of 4.2" and a 0.3 filling factor. We observed in the 3550-5850 Angstrom spectral range, with a resolution of 5 A FWHM. From these data we built two-dimensional maps of the continuum and the most prominent emission-lines ([OII]3727, Hgamma, Hbeta and [OIII]5007), and investigate the morphology of diagnostic emission-line ratios and the extinction patterns in the ISM as well as stellar and gas kinematics. Additionally, from integrated spectra we infer total line fluxes and luminosity-weighted extinction coefficients and gas-phase metallicities. All galaxies exhibit an overall regular morphology in the stellar continuum, while their warm ISM morphology is more complex: in II Zw 33 and Mrk 314, the star-forming regions are aligned along a chain-structure; Haro 1, NGC 4670 and III Zw 102 display several salient features, such as extended gaseous filaments and bubbles. A significant intrinsic absorption by dust is present in all galaxies, the most extreme case being III Zw 102. Our data reveal a manifold of kinematical patterns, from overall regular gas and stellar rotation to complex velocity fields produced by structurally and kinematically distinct components.Comment: Accepted for publication in A&A. 16 pages, 10 figure

The Importance of Nebular Continuum and Line Emission in Observations of Young Massive Star Clusters

In this spectroscopic study of infant massive star clusters, we find that continuum emission from ionized gas rivals the stellar luminosity at optical wavelengths. In addition, we find that nebular line emission is significant in many commonly used broad-band HST filters including the F814W I-band, the F555W V-band and the F435W B-band. Two young massive clusters (YMCs) in NGC 4449 were targeted for spectroscopic observations after Reines et al. (2008a) discovered an F814W I-band excess in their photometric study of radio-detected clusters in the galaxy. The spectra were obtained with the Dual Imaging Spectrograph on the 3.5 m APO telescope. We supplement these data with HST and SDSS photometry. By comparing our data to the Starburst99 and GALEV models, we find that nebular continuum emission competes with the stellar light in our observations and that the relative contribution is largest in the U- and I-bands, where the Balmer and Paschen jumps are located. The spectra also exhibit strong line emission including the [SIII] 9069,9532 lines in the HST F814W I-band. We find that the combination of nebular continuum and line emission can account for the F814W I-band excess found by Reines et al. (2008a). In an effort to provide a benchmark for estimating the impact of ionized gas emission on photometric observations of YMCs, we compute the relative contributions of the stellar continuum, nebular continuum, and emission lines to the total flux of a 3 Myr-old cluster through various HST filter/instrument combinations, including filters in the WFC3. We urge caution when comparing observations of YMCs to evolutionary synthesis models since nebular emission can have a large impact on magnitudes and colors of young (< 5 Myr) clusters, significantly affecting inferred properties such as ages, masses and extinctions. (Abridged)Comment: 13 pages, 11 figures, Accepted for Publication in Ap