Dynamics of seismic impacts in base-isolated buildings

A systematic study is made of the effects of seismic impacts between the base of an isolated building and the surrounding retaining wall. The analysis is performed without using gap elements or assuming values of the coefficient of restitution and the duration of impact. The analysis captures the effects of wave travel along the height of the building and of the associated energy loss. It poses no numerical difficulties. Results show that for elastic systems the base shear generated by impacts can be higher than the weight of the building; base shear increases with increase in the stiffness of the retaining wall, stiffness of the building and the mass of the base mat. A significant fraction of the initial kinetic energy of the system is lost by impacts; energy loss increases with increase in the stiffness of the retaining wall, system damping and mass of the base mat. © 1997 John Wiley & Sons, Ltd.     

Reliability analysis of shallow foundation in the vicinity of the existing buried conduit

ABSTRACT

The present study proposes reliability-based approach for assessing the performance of shallow foundation placed in the vicinity of an existing buried flexible pipe or utility tunnel. Performance function for the reliability analysis is defined in terms of % bearing capacity loss in the load carrying capacity of the shallow foundation due to the presence of buried flexible pipe or utility tunnel, and, allowable bearing capacity loss in load carrying capacity that can be tolerated. For the reliability analysis, an explicit functional relationship between input variables, such as geotechnical parameters of in situ soil as well as material properties of pipe, and, output response, i.e. % bearing capacity loss in load carrying capacity of foundation soil is needed. Using concept of response surface methodology (RSM) combined with the results of the numerical analysis; such an explicit functional relationship is easily established. Thereafter, reliability analysis can be performed, conveniently, using standard First Order Second Moment (FOSM) approach and performance of the foundation soil system with buried flexible pipe, present in the vicinity, can be assessed in terms of an index, popularly known as ‘reliability index (β)’.     

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.     

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.     

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.