The HI content of extremely metal-deficient blue compact dwarf galaxies

We have obtained new HI observations with the 100m Green Bank Telescope (GBT) for a sample of 29 extremely metal-deficient star-forming Blue Compact Dwarf (BCD) galaxies, selected from the Sloan Digital Sky Survey spectral data base to be extremely metal-deficient (12+logO/H<7.6). Neutral hydrogen was detected in 28 galaxies, a 97% detection rate. Combining the HI data with SDSS optical spectra for the BCD sample and adding complementary galaxy samples from the literature to extend the metallicity and mass ranges, we have studied how the HI content of a galaxy varies with various global galaxian properties. There is a clear trend of increasing gas mass fraction with decreasing metallicity, mass and luminosity. We obtain the relation M(HI)/L(g)~L(g)^{-0.3}, in agreement with previous studies based on samples with a smaller luminosity range. The median gas mass fraction f(gas) for the GBT sample is equal to 0.94 while the mean gas mass fraction is 0.90+/-0.15, with a lower limit of ~0.65. The HI depletion time is independent of metallicity, with a large scatter around the median value of 3.4 Gyr. The ratio of the baryonic mass to the dynamical mass of the metal-deficient BCDs varies from 0.05 to 0.80, with a median value of ~0.2. About 65% of the BCDs in our sample have an effective yield larger than the true yield, implying that the neutral gas envelope in BCDs is more metal-deficient by a factor of 1.5-20, as compared to the ionized gas.Comment: 21 pages, 13 figures, accepted for publication in MNRA

Evaluation of a composite mobile holographic nondestructive test system

A simplified theoretical model for the interpretation of the double-exposure holographic interference fringe loci due to the general three-dimensional displacements was derived for the specific composite mobile holographic nondestructive test system. The model, representing a good approximation to a more tedious theoretical result, predicts that a combination of in-plane and out-of-plane displacements of the surface will produce concentric circular-shaped fringe patterns with locations of their center affected by the displacements. Appropriate experiments were designed and carried out for the test of the validity of the theory. These experiments include the taking of double-exposure holograms of in-plane translations and combined in-plane and out-of-plane translations. The simplified model agreed quite well with the experimental results. Experimentally observed effects due to the curvature of the test plate and the variations of the angles of incidence of the laser light suggest that in order for the simplified model to be able to predict the test results more accurately, incidence and reflection of the laser light should be chosen as nearly perpendicular to the surface of the tested object as possible

Endogenous and Exogenous Time Pressure: Interactions with Mathematics Anxiety in Explaining Arithmetic Performance

Eighty adults performed mental arithmetic under endogenous (time limit) or exogenous (presence of a clock) time pressure. Results demonstrated a significant interaction between math anxiety and endogenous pressure: error rates were significantly greater among high math anxious individuals when given a time limit. A significant interaction was observed between exogenous time pressure and math anxiety: performance of low math anxious individuals was reduced when a clock was present. Effects were only present in response to problems involving a carry operation, supporting previous findings that math anxiety may be particularly detrimental on math problems that rely more on working memory resources. The findings suggest that the type of time pressure may need to be taken into account when designing assessments.N/

How does star formation proceed in the circumnuclear starburst ring of NGC 6951?

Gas inflowing along stellar bars is often stalled at the location of circumnuclear rings, that form an effective reservoir for massive star formation and thus shape the central regions of galaxies. However, how exactly star formation is proceeding within these circumnuclear starburst rings is subject of debate. Two main scenarios for this process have been put forward: In the first the onset of star formation is regulated by the total amount of gas present in the ring with star forming starting once a mass threshold has reached in a `random' position within the ring like `popcorn'. In the second star formation preferentially takes place near the locations where the gas enters the ring. This scenario has been dubbed `pearls-on-a-string'. Here we combine new optical IFU data covering the full stellar bar with existing multi-wavelength data to study in detail the 580 pc radius circumnuclear starburst ring in the nearby spiral galaxy NGC 6951. Using HST archival data together with Sauron and Oasis IFU data, we derive the ages and stellar masses of star clusters as well as the total stellar content of the central region. Adding information on the molecular gas distribution, stellar and gaseous dynamics and extinction, we find that the circumnuclear ring in NGC 6951 is ~1-1.5 Gyr old and has been forming stars for most of that time. We see evidence for preferred sites of star formation within the ring, consistent with the `pearls-on-a-string' scenario, when focusing on the youngest stellar populations. Due to the ring's longevity this signature is washed out when older stellar populations are included in the analysis.Comment: accepted for publication in A&A, 15 page

Evidence for CO2-rich fluids in rocks from the type charnockite area near Pallavaram, Tamil Nadu

Fluid inclusion and mineral chemistry data was presented for samples from the type charnockite area near Pallavaram (Tamil Nadu, India). The results indicate the presence of a dense CO2 fluid phase, but the data cannot distinguish between influx of this fluid from elsewhere or localized migration of CO2-rich fluids associated with dehydration melting

Comparison between seasonal pumped-storage and conventional reservoir dams from the water, energy and land nexus perspective

Renewable sources of energy are providing an increasing share of the electricity generation mix, but their intermittency drives a need for energy storage. At the same time, water resources are increasingly scarce due to changes in demand, such as from population growth, supply side pressures such as climate change and governance challenges relating to poor management. Large storage reservoirs are used for water management and for energy storage. However, some existing and proposed hydropower reservoirs require vast areas of land and have considerable social and environmental impacts. Growing concerns on water and energy storage from a water-energy-land nexus approach motivated this study. Our objective is to compare how energy and water storage services, such as hydropower generation, electricity grid and water management, are provided with Seasonal Pumped-Storage (SPS) and Conventional Reservoir Dams (CRD) plants. Our case study region is Brazil, a country with extensive hydropower capacity and development plans, for which we compare the cost, land requirement and social impacts between CRD and potential SPS plants. Whilst seasonal pumped-storage have higher capital costs than conventional reservoir dams, given the much lower land requirements and evaporative losses, they are a valuable water and energy storage alternative especially in locations with plain topography and high evaporation. Results show that if Sobradinho CRD was built today it would result in a $USD 1.46 billion loss, on the other hand, Muquém SPS plant would result in a$USD 0.67b revenue