The GLARE Survey – II. Faint z≈ 6 Lyα line emitters in the HUDF

The galaxy population at   z ≈ 6  has been the subject of intense study in recent years, culminating in the Hubble Ultra Deep Field (HUDF) – the deepest imaging survey yet. A large number of high-redshift galaxy candidates have been identified within the HUDF, but until now analysis of their properties has been hampered by the difficulty of obtaining spectroscopic redshifts for these faint galaxies. Our 'Gemini Lyman-Alpha at Reionization Era' (GLARE) project has been designed to undertake spectroscopic follow-up of faint  ( z ' < 28.5)  i '-drop galaxies at   z ≈ 6  in the HUDF. In a previous paper we presented preliminary results from the first 7.5 h of data from GLARE. In this paper we detail the complete survey. We have now obtained 36 h of spectroscopy on a single GMOS slitmask from Gemini-South, with a spectral resolution of  λ/Δλ_FWHM≈ 1000  . We identify five strong Lyα emitters at   z > 5.5  , and a further nine possible line emitters with detections at lower significance. We also place tight constraints on the equivalent width of Lyα emission for a further ten i '-drop galaxies and examine the equivalent width distribution of this faint spectroscopic sample of   z ≈ 6  galaxies. We find that the fraction of galaxies with little or no emission is similar to that at   z ≈ 3  , but that the   z ≈ 6  population has a tail of sources with high rest-frame equivalent widths. Possible explanations for this effect include a tendency towards stronger line emission in faint sources, which may arise from extreme youth or low metallicity in the Lyman-break population at high redshift, or possibly a top-heavy initial mass function.     

RETRACTED ARTICLE: Aspect Sensitivity Considerations in Interpreting Radar Meteor Range-Spread Trail Echo Durations

Earth, Moon, and Planets -     

The expected detection of dust emission from high-redshift Lyman α galaxies

Recent results have shown that a substantial fraction of high-redshift Lyman α (Lyα) galaxies contain considerable amounts of dust. This implies that Lyα galaxies are not primordial, as has been thought in the past. However, this dust has not been directly detected in emission; rather it has been inferred based on extinction estimates from rest-frame ultraviolet (UV) and optical observations. This can be tricky, as both dust and old stars redden galactic spectra at the wavelengths used to infer dust. Measuring dust emission directly from these galaxies is thus a more accurate way to estimate the total dust mass, giving us real physical information on the stellar populations and interstellar medium enrichment. New generation instruments, such as the Atacama Large Millimeter Array and Sub-Millimeter Array, should be able to detect dust emission from some of these galaxies in the submillimeter. Using measurements of the UV spectral slopes, we derive far-infrared flux predictions for of a sample of  23 z ≥ 4  Lyα galaxies. We find that in only a few hours, we can detect dust emission from 39 ± 22 per cent of our Lyα galaxies. Comparing these results to those found from a sample of 21 Lyman break galaxies (LBGs), we find that LBGs are on average 60 per cent more likely to be detected than Lyα galaxies, implying that they are more dusty, and thus indicating an evolutionary difference between these objects. These observations will provide better constraints on dust in these galaxies than those derived from their UV and optical fluxes alone. Undeniable proof of dust in these galaxies could explain the larger than expected Lyα equivalent widths seen in many Lyα galaxies today.     

Base uplifting analysis of flexibly supported liquid-storage tanks

An approximate method is presented for the analysis of earthquake induced uplifting in base plates of unanchored liquid-storage tanks that are supported directly on flexible soil foundations. The method takes due account of the non-linearities arising from the continuous variation of base contact area, membrane action and plastic yielding in the base plate. First, an ‘exact’ solution is presented for a uniformly loaded flexibly supported prismatic beam, uplifted by a concentrated force applied at one end. A series of such beams are later used in an approximate model of the base plate. The method is highly efficient and believed to be accurate for the level of uplifts encountered in practice. The results are presented for a range of foundation stiffness, representing loose sandy soils to rigid concrete mat. It is shown that, for the same overturning base moment, the flexibly supported tanks, in comparison with the rigidly supported tanks, experience significantly smaller axial compressive stress, but larger base uplift, foundation penetration, plastic rotation at plate boundary and hoop compressive stress in the tank wall.     

An approach of understanding acid volcanics and tuffaceous volcaniclastics from field studies: A case from Tadpatri Formation,Proterozoic Cuddapah basin,Andhra Pradesh,India

The lower stratigraphic part of the Cuddapah basin is marked by mafic and felsic volcanism. Tadpatri Formation consists of a greater variety of rock types due to bimodal volcanism in the upper part. Presence of bimodal volcanism is an indication of continental rift setting. Various genetic processes involved in the formation of such volcanic sequence result in original textures which are classified into volcaniclastic and coherent categories. Detailed and systematic field works in Tadpatri–Tonduru transect of SW Cuddapah basin have provided information on the physical processes producing this diversity of rock types. Felsic volcanism is manifested here with features as finger print of past rhyolite-dacite eruptions. Acid volcanics, tuffs and associated shale of Tadpatri Formation are studied and mapped in the field. With supporting subordinate studies on geochemistry, mineralogy and petrogenesis of the volcanics to validate field features accurately, it is understood that volcanism was associated with rifting and shallow marine environmental condition. Four facies (i.e., surge, flow, fall and resedimented volcaniclastic) are demarcated to describe stratigraphic units and volcanic history of the mapped area. The present contribution focuses on the fundamental characterization and categorization of field-based features diagnostic of silica-rich volcanic activities in the Tadpatri Formation.     

Response spectrum of incompatible acceleration,velocity and displacement histories

The ground motions induced by an earthquake are expressed by the histories of acceleration, velocity and displacement. It is generally assumed that the acceleration, velocity and displacement histories contain identical information, i.e. the velocity history is obtained by integration of the acceleration history, and the displacement history is obtained by integration of the velocity history. However, this is not always true. In conventional processing of ground motion histories, additional corrections are applied to the velocity and displacement histories, which are not reflected in the acceleration history. As a result, the three ground motion histories contain slightly different information, or they are not fully compatible with one another. The structural response computed from the acceleration history, therefore, does not correspond to the processed velocity and displacement histories. The purpose of this paper is to underscore the engineering difficulties associated with incompatible histories and to provide a method of computing the response spectrum, which is compatible with the acceleration, velocity and displacement histories. Copyright © 2001 John Wiley & Sons, Ltd.     

FTIR spectra of hydroxyls and dehydroxylation kinetics mechanism in montmorillonite

The application of Fourier transform infrared (FTIR) spectroscopy to the analysis of the hydroxyl groups bands' intensities of montmorillonite from Texas shows four regions of intensity loss rate for thermally shocked samples at 290<T<1100 K for 24 h. The first three regions are associated with the dehydroxylation process; while the fourth region suggests the loss of the remaining (～10%) hydroxyls via thermal dissociation into hydrogen atoms and oxygen centers. The dehydroxylation process appears to be homogeneous with adjacent trans OH ions interacting to form H₂O molecules below the hexagonal hole or cavity. The vibrational analysis of the stretching and bending modes of water and hydroxyl groups at 290<T<553 K indicates not only that water is desorbed in this range, resulting in the perturbation of the octahedral hydroxyl structure due to the close approach of exchangeable cations to the hexagonal holes, but also that surface hydroxyls and AlFe³⁺-OH groups are dehydroxylated. AT 553<T< 773 K, the intensity loss of AlAl-OH and AlMg-OH groups almost varies linearly as a function of thermal shock temperature with the AlMg-OH vibration disappearing at T> 673 K. However, what is surprising is the persistence of very weak water stretching (～3470 cm^?1) and bending (～1628 cm^?1) vibrations at 553<T<773 K. It is speculated that this water, formed because of dehydroxylation, is trapped in the hexagonal cavities of the dehydrated montmorillonite lattice. However, conclusive evidence will require surface-sensitive spectroscopic measurements as this water could also be adsorbed on the external surfaces of processed samples. In the range 773<T<823 K, the main dehydroxylation of the AlAl-OH group results, and this reaction induces structural transformations in the montmorillonite lattice. FTIR measurements at 803 K for 0<t< 25 h were used to determine the kinetics mechanism of dehydroxylation in montmorillonite from Texas. The experimental data was tested, using diffusion controlled as well as six decomposition models to ascertain the kinetics mechanism of the AlAl-OH group's dehydroxylation. It appears that the dehydroxylation process can be described by the contracting spherical movement model rather than by a diffusion controlled model, suggesting surface nucleation, growth over the surface, and then advancement of the dehydroxylated/hydroxylated interface toward the center of the montmorillonite particles.     

Seismic induced soil gas radon anomalies observed at multiparametric geophysical observatory,Tezpur (Eastern Himalaya), India: an appraisal of probable model for earthquake forecasting based on peak of radon anomalies

Natural Hazards - We applied multiple linear regressions to scrutinize the maximum variability produced in soil gas radon (Rn-222) by pressure, temperature and rainfall. Statistical methodologies...