295 research outputs found
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 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 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 /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,
, 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 emitting gas
within NGC4753. The current star formation rate of NGC4753, averaged over past
, 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
Factors affecting the registration and counting of alpha tracks in solid state nuclear track detectors
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
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