Factors affecting the registration and counting of alpha tracks in solid state nuclear track detectors

In view of the fact that the radon progeny contribute the highest to the natural radiation dose to general populations, large scale and long-term measurements of radon and its progeny in the houses have been receiving considerable attention. Solid State Nuclear Track Detector (SSNTD) based systems, being the best suited for large scale passive monitoring, have been widely used for the radon gas (using a cup closed with a semi-permeable membrane) and to a limited extent, for the measurement of radon progeny (using bare mode in conjunction with the cup). These have been employed for radon mapping and indoor radon epidemiological studies with good results. In this technique, alpha tracks recorded on SSNTD films are converted to radon/thoron concentrations using corresponding conversion factors obtained from calibration experiments carried out in controlled environments. The detector response to alpha particles depends mainly on the registration efficiency of the alpha tracks on the detector films and the subsequent counting efficiency. While the former depends on the exposure design, the latter depends on the protocols followed for developing and counting of the tracks. The paper discusses on parameters like etchant temperature, stirring of the etchant and duration of etching and their influence on the etching rates on LR-115 films. Concept of break down thickness of the SSNTD film in spark counting technique is discussed with experimental results. Error estimates on measurement results as a function of background tracks of the films are also discussed in the paper.Factors affecting the registration and counting of alpha tracks in solid state nuclear track detectors K P Eappen* and Y S Mayya Environmental Assessment Division, Bhabha Atomic Research Centre, Mumbai-400 085, India E-mail : [email protected] Assessment Division, Bhabha Atomic Research Centre, Mumbai-400 085, Indi

Chemical Abundance Gradients in the Star-Forming Ring Galaxies

Ring waves of star formation, propagating outwardly in the galactic disks, leave chemical abundance gradients in their wakes. We show that the relative [Fe/O] abundance gradients in ring galaxies can be used as a tool for determining the role of the SNIa explosions in their chemical enrichment. We consider two mechanisms which can create outwardly propagating star forming rings in a purely gaseous disk -- a self-induced wave and a density wave, and demonstrate that the radial distribution of the relative [Fe/O] abundance gradients does not depend on the particular mechanism of the wave formation or on the parameters of the star-forming process. We show that the [Fe/O] profile is determined by the velocity of the wave, initial mass function, and the initial chemical composition of the star-forming gas. If the role of SNIa explosions is negligible in the chemical enrichment, the ratio [Fe/O] remains constant throughout the galactic disk with a steep gradient at the wave front. If SNIa stars are important in the production of cosmic iron, the [Fe/O] ratio has gradient in the wake of the star-forming wave with the value depending on the frequency of SNIa explosions.Comment: Uses aas2pp4.sty and epsfig.sty, 7 pages including one figure To appear in Astrophysical Journa

Multicolor Surface Photometry of Lenticulars I. The Data

We present in this paper multicolor surface and aperture photometry in the B, V, R and K' bands for a sample of 34 lenticular galaxies from the UGC catalogue. From surface photometric analysis, we obtain radial profiles of surface brightness, colors, ellipticity, position angle and the Fourier coefficients which describe the departure of isophotal shapes from purely elliptical form and find the presence of dust lanes, patches and ring like structure in several galaxies in the sample. We obtain total integrated magnitudes and colors and find that these are in good agreement with the values from the RC3 catalogue. Isophotal colors are correlated with each other, following the sequence expected for early-type galaxies. The color gradients in lenticulars are more negative than the corresponding gradients in ellipticals. There is a good correlation between B-V and B-R color gradients, and the mean gradient in the B-V, B-R and V-K' colors are -0.13+/-0.06, -0.18+/-0.06, -0.25+/-0.11 magnitude per dex in radius respectively.Comment: 18 pages, 5 figures, uses emulateapj.cls. Accepted for publication in Astronomical Journal, scheduled for February 200

Study of star formation in NGC 1084

We present UBVRI broad band, H$\alpha$ narrow band photometry of the star forming complexes in the infra-red bright galaxy NGC 1084. Results of medium resolution spectroscopy of some of the brighter complexes are also discussed. Spectroscopic data is used to better estimate the internal reddening within the galaxy which is found to be highly variable and to calculate metallicity which is close to the solar value. Diagnostic diagram identifies the shocked regions within this galaxy. The narrow band H$\alpha$ flux and its equivalent width are used to determine the star formation rates of the complexes and the distribution of ages. Star formation rates for a few of the complexes are found to be as high as 0.5 $M_{\odot}$/year. The star forming complexes lie in the age range 3 Myr to 6.5 Myr. U-B vs V-I colour-colour mixed population model created using the Starburst99 model colours is used to estimate the ages of the stellar populations present within these regions. Using this technique, it is found that the star formation in NGC 1084 has taken place in a series of short bursts over the last 40 Myr or so. It is proposed that the likely trigger for enhanced star formation is merger with a gas rich dwarf galaxy.Comment: 9 figures and 6 tables, Accepted in MNRAS for publicatio

Dust Properties of NGC4753

We report BVR surface photometry of a lenticular galaxy, NGC4753 with prominent dust lanes. We have used the multicolor broadband photometry to study dust-extinction as a function of wavelength and derived the extinction curve. We find the extinction curve of NGC 4753 to be similar to the Galactic extinction curve in the visible region which implies that the sizes of dust grains responsible for optical extinction are similar to those in our Galaxy. We derive dust mass from optical extinction as well as from the far infrared fluxes observed with IRAS. The ratio of the two dust masses, $\frac{M_{d,IRAS}}{M_{d,optical}}$, is 2.28 for NGC 4753, which is significantly lower than the value of 8.4 \pm 1.3 found previously for a large sample of elliptical galaxies. The total mass of the observed dust within NGC4753 is about a factor of 10 higher than the mass of dust expected from loss of mass from red giant stars and destruction by sputtering and grain-grain collisions in low velocity shocks, and sputtering in supernova driven blast waves. We find evidence for the coexistence of dust and H$\alpha$ emitting gas within NGC4753. The current star formation rate of NGC4753, averaged over past $2\times10^{6} yr$, is estimated to be less than 0.21M_{\sun}yr^{-1}. A substantial amount of dust within NGC4753 exists in the form of cirrus.Comment: 15 pages, 8 jpeg figures, 5 tables in one file, AASTEX style, Accepted for publication in the Astronomical Journal, 1999 Augus

"Then you get a teacher" - Guidelines for excellence in teaching

Background: Current literature calls for the explicit teaching to health-science educators of the skills, knowledge and dispositions that are required for successful teaching in higher education. Aims: This paper draws on evidence from an Oral Hygiene department at a South African university in order to illustrate these teaching-competency needs. Insights from the evidence are synthesised with current literature regarding best teaching practice, in support of an appropriate framework for the development of teaching competencies to health-science educators. Description: A qualitative approach, using a case study, was adopted. The cohort comprised fifteen students in the first-year Oral Hygiene cohort class and the ten educators who taught their programme. Data was collected through semistructured interviews and open-ended questionnaires. The topics that emerged from the combined analysis of the interviews and the questionnaires were organised into a grid so that common themes could be identified. Current literature regarding teaching and learning was used as a framework for interpreting the empirical evidence, from which three categories emerged. The first category included suggestions from students regarding what to do to teach better. A review of the literature indicates that these competencies can be effectively learnt from self-help guides. The second category included requests for skills development. Literature review suggests that these might effectively be learnt from single-event workshops facilitated by more able peers. Responses in the final category highlighted the need for an underpinning theory of teaching and learning, and signalled the need for a more theoretically grounded and detailed approach to teacher development. Conclusion: The framework developed from the empirical study and current literature makes it possible for individual clinical teachers, and staff developers, to construct teaching-competency development plans that are pertinent to individual teachers’ needs, relevant and practical, educationally sound, and cost-effective in terms of time and effort

An evaluation of thoron (and radon) equilibrium factorclose towalls based on long-term measurements in dwellings

Thoron gas and its progeny behave quite differently in room environments, owing to the difference in their half-lives; therefore, it is important to measure simultaneously gas and progeny concentrations to estimate the time-integrated equilibrium factor. Furthermore, thoron concentration strongly depends on the distance from the source, i.e. generally walls in indoor environments. In the present work, therefore, the measurements of both thoron and radon gas and their progeny concentrations were consistently carried out close to the walls, in 43 dwellings located in the Sokobanja municipality, Serbia. Three different types of instruments have been used in the present survey to measure the time-integrated thoron and radon gas and their progeny concentrations simultaneously. The equilibrium factor for thoron measured ‘close to the wall’, FW Tn, ranged from 0.001 to 0.077 with a geometric mean (GM) [geometric standard deviation (GSD)] of 0.006 (2.2), whereas the equilibrium factor for radon, FRn, ranged from 0.06 to 0.95 with a GM (GSD) of 0.23 (2.0)

mTOR Is Essential for the Proteotoxic Stress Response, HSF1 Activation and Heat Shock Protein Synthesis

The target of rapamycin (TOR) is a high molecular weight protein kinase that regulates many processes in cells in response to mitogens and variations in nutrient availability. Here we have shown that mTOR in human tissue culture cells plays a key role in responses to proteotoxic stress and that reduction in mTOR levels by RNA interference leads to increase sensitivity to heat shock. This effect was accompanied by a drastic reduction in ability to synthesize heat shock proteins (HSP), including Hsp70, Hsp90 and Hsp110. As HSP transcription is regulated by heat shock transcription factor 1 (HSF1), we examined whether mTOR could directly phosphorylate this factor. Indeed, we determined that mTOR could directly phosphorylate HSF1 on serine 326, a key residue in transcriptional activation. HSF1 was phosphorylated on S326 immediately after heat shock and was triggered by other cell stressors including proteasome inhibitors and sodium arsenite. Null mutation of S326 to alanine led to loss of ability to activate an HSF1-regulated promoter-reporter construct, indicating a direct role for mTOR and S326 in transcriptional regulation of HSP genes during stress. As mTOR is known to exist in at least two intracellular complexes, mTORC1 and mTOR2 we examined which complex might interact with HSF1. Indeed mTORC1 inhibitor rapamycin prevented HSF1-S326 phosphorylation, suggesting that this complex is involved in HSF1 regulation in stress. Our experiments therefore suggest a key role for mTORC1 in transcriptional responses to proteotoxic stress