On the evaluation of seismic response of structures by nonlinear static methods

In the most recent seismic codes, the assessment of the seismic response of structures may be carried out by comparing the displacement capacity, provided by nonlinear static analysis, with the displacement demand. In many cases the code approach is based on the N2 method proposed by Fajfar, which evaluates the displacement demand by defining, as an intermediate step, a single degree‐of‐freedom (SDOF) system equivalent to the examined structure. Other codes suggest simpler approaches, which do not require equivalent SDOF systems, but they give slightly different estimation of the seismic displacement demand. The paper points out the differences between the methods and suggests an operative approach that provides the same accuracy as the N2 method without requiring the evaluation of an equivalent SDOF system. A wide parametric investigation allows an accurate comparison of the different methods and demonstrates the effectiveness of the proposed operative approach. Copyright © 2009 John Wiley & Sons, Ltd.     

The measurement of the decorrelation function in underground muon pairs as a probe of primary cosmic ray interactions

We discuss the measurement of the average angle within pairs of muons detected in underground experiments versus their relative distance, as a tool for studying primary Cosmic Ray interactions. We propose to call Φ(d) “decorrelation” function. Under simplifying approximation, the decorrelation function can be computed analytically to show its dependence on details of cosmic ray interactions as well as on the propagation in the rock. We argue that this new measurement is useful in a real experiment, complementing traditional ones like the decoherence function.     

Seasonal dynamics of inorganic nutrients and phytoplankton biomass in the NW Alboran Sea

The seasonal dynamics of inorganic nutrients and phytoplankton biomass (chlorophyll a), and its relation with hydrological features, was studied in the NW Alboran Sea during four cruises conducted in February, April, July and October 2002. In the upper layers, the seasonal pattern of nutrient concentrations and their molar ratios (N:Si:P) was greatly influenced by hydrological conditions. The higher nutrient concentrations were observed during the spring cruise (2.54 μM NO₃⁻, 0.21 μM PO₄³⁻ and 1.55 μM Si(OH)₄, on average), coinciding with the increase of salinity due to upwelling induced by westerlies. The lowest nutrient concentrations were observed during summer (<0.54 μM NO₃⁻, 0.13 μM PO₄³⁻ and 0.75 μM Si(OH)₄, on average), when the lower salinities were detected. Nutrient molar ratios (N:Si:P) followed the same seasonal pattern as nutrient distribution. During all the cruises, the ratio N:P in the top 20 m was lower than 16:1, indicating a NO₃⁻ deficiency relative to PO₄³⁻. The N:P ratio increased with depth, reaching values higher than 16:1 in the deeper layers (200–300 m). The N:Si ratio in the top 20 m was lower than 1:1, excepting during spring when N:Si ratios higher than 1:1 were observed in some stations due to the upwelling event. The N:Si ratio increased with depth, showing a maximum at 50–100 m (>1.5:1), which indicates a shift towards Si-deficiency in these layers. The Si:P ratio was much lower than 16:1 throughout the water column during the four cruises. In general, the spatial and seasonal variation of phytoplankton biomass showed a strong coupling with hydrological and chemical fields. The higher chlorophyll a concentrations at the depth of the chlorophyll maximum were found in April (2.57 mg m⁻³ on average), while the lowest phytoplankton biomass corresponded to the winter cruise (0.74 mg m⁻³ on average). The low nitrate concentrations together with the low N:P ratios found in the upper layers (top 20 m) during the winter, summer and autumn cruises suggest that N-limitation could occur in these layers during great part of the year. However, N-limitation during the spring cruise was temporally overcome by nutrient enrichment caused by an intense wind-driven upwelling event.     

A microseismic experiment in Abu Dhabi,United Arab Emirates: implications for carbonate reservoir monitoring

A microseismic experiment utilizing a single downhole array of eight 3-component receivers was conducted in an offshore oilfield in the emirate of Abu Dhabi in the United Arab Emirates. The Lower Cretaceous Thamama Group is the major carbonate reservoir in the field producing from six zones. Microseismic data was acquired in conjunction with gas injections that took place in the Thamama IV A and IV B reservoirs during 9 days of acquisition. The aim of the experiment was to monitor the microseismic activity arising in the carbonate reservoirs as a result of gas injection. A total of 103 microseismic events were detected from two of the receivers. For the majority of these events, there were no well-defined P wave arrivals, probably due to the presence of strong background noise and the very weak microseismic signals. The results from this experiment indicate that the detected events are probably related to the microseismic activities caused by the gas injection within the Thamama IV B reservoir. Therefore, downhole microseismic monitoring methods can potentially provide valuable information about the fracture systems within the carbonate reservoirs of Abu Dhabi's oilfields.     

Effect of turbulence and inorganic carbon supply on growth ofDunaliella viridis Teodoresco

Turbulence is known to enhance growth in microalgae. We studied the possible effects of the extra inorganic carbon supplied to the cultures when air bubbling is the source of turbulence. A set of experiments was carried out to separate the effects of the subsidiary action of agitation on growth from those due to possible carbon enrichment from air CO₂ when air bubbling was the source of mixing. It was found that air bubbling does not induce an increase of the concentration of inorganic carbon in HCO ₃ ^– -enriched growth media, and that no differences appear between air-bubbled and CO₂-free air-bubbled cultures. On the other hand, photosynthetic O₂ was accumulated in the medium in non-mixed cultures, which showed higher respiration and lower photosynthetic rates, probably due to photoinhibition induced by oversaturation of O₂. Growth rate, maximal cell density and photosynthetic efficiency were higher in aerated cultures than in non-aerated ones.     

Jobs and the Single Parent: An Analysis of Accessibility to Employment in Toronto

Abstract

In this article, we undertake an analysis of accessibility to jobs from the perspective of single-parent household members. Individuals in this demographic segment are of interest due to the fact they often face the double burden of household and employment responsibilities. A case study of the city of Toronto in Canada, an urban area that has seen an increase in absolute and relative numbers of single-parent households in recent years, is presented. Analysis is based on the application of relative accessibility deprivation indicators (RADI), which are calculated using model-based estimates of distance traveled for various population segments, as well as employment data for the city and its surroundings. The results of the analysis indicate that there are substantial differences in the levels of accessibility to jobs between members of single-parent households, in particular females, and members of other types of households.     

On the use of NOAA's storm surge model,SLOSH, in managing coastal hazards — the experience in Puerto Rico

A numerical-dynamic, tropical storm surge model, SLOSH (Sea, Land, and Overland Surges from Hurricanes), was originally developed for real-time forecasting of hurricane storm surges on continental shelves, across inland water bodies and along coastlines and for inland routing of water -either from the sea or from inland water bodies. The model is two-dimensional, covering water bodies and inundated terrain. In the present version available at the University of Puerto Rico a curvilinear, polar coordinate grid scheme is used. The grid cells are approximately 3.2 × 3.2 km in size.The model has been used in a revision of all coastal Flood Insurance Rate Maps (FIRM) for Puerto Rico and the U.S. Virgin Islands, and in hurricane evacuation studies. The FIRM's, since they are based on the 100 year stillwater elevation, are also used by the state Planning Board for regulatory purposes. The hurricane evacuation studies are used by emergency planners and personnel to assign shelters, escape routes, and delimit coastal zones that need to be evacuated during a hurricane threat.Recently, the acquisition of data from hurricane Hugo has allowed the first comparison of model results and observations for Puerto Rico and the other islands.     

Plate convergence measured by GPS across the Sundaland/Philippine Sea Plate deformed boundary: the Philippines and eastern Indonesia

The western boundary of the Philippine Sea (PH) Plate in the Philippines and eastern Indonesia corresponds to a wide deformation zone that includes the stretched continental margin of Sundaland, the Philippine Mobile Belt (PMB), extending from Luzon to the Molucca Sea, and a mosaic of continental blocks around the PH/Australia/Sunda triple junction. The GPS GEODYSSEA data are used to decipher the present kinematics of this complex area. In the Philippines, the overall scheme is quite simple: two opposing rotations on either side of the left-lateral Philippine Fault, clockwise to the southwest and counterclockwise to the northeast, transfer 55 per cent of the PH/Sundaland convergence from the Manila Trench to the northwest to the Philippine Trench to the southeast. Further south, 80 per cent of the PH/Sunda convergence is absorbed in the double subduction system of the Molucca Sea and less than 20 per cent along both continental margins of northern Borneo. Finally, within the triple junction area between the Sundaland, PH and Australia plates, from Sulawesi to Irian Jaya, preferential subduction of the Celebes Sea induces clockwise rotation of the Sulu block, which is escaping toward the diminishing Celebes Sea oceanic space from the eastward-advancing PH Plate. To the south, we identify an undeformed Banda block that rotates counterclockwise with respect to Australia and clockwise with respect to Sundaland. The kinematics of this block can be defined and enable us to compute the rates of southward subduction of the Banda block within the Flores Trench and of eastward convergence of the Makassar Straits with the Banda block. The analysis made in this paper confirms that this deformation is compatible with the eastward motion of Sundaland with respect to Eurasia determined by the GEODYSSEA programme but is not compatible with the assumption that Sundaland belongs to Eurasia, as was often assumed prior to this study.     

Carbon isotopic fractionation in macroalgae from Cádiz Bay (Southern Spain): Comparison with other bio-geographic regions

The ¹³C signature of forty-five macroalgal species from intertidal zones at Cádiz Bay was analysed in order to research the extension of diffusive vs. non-diffusive utilisation of dissolved inorganic carbon (DIC) and to perform a comparison with data published for other bio-geographic regions. The ∂¹³C values ranged from −6.8‰ to −33‰, although the span of variation was different depending on the taxa. Thus, ∂¹³C for Chlorophyta varied from −7‰ (Codium adhaerens) to −29.6‰ (Flabellia petiolata), while all the Phaeophyceae (excepting Padina pavonica with ∂¹³C higher than −10‰) had values between −10‰, and −20‰. The widest variation range was recorded in Rhodophyta, from values above −10‰ (Liagora viscida) to values lower than −30‰ obtained in three species belonging to the subclass Rhodymeniophycidae. Accordingly, the mean ∂¹³C value calculated for red algae (−20.2‰) was significantly lower than that for brown (−15.9‰) and green algae (−15.6‰). Most of the analysed red algae were species inhabiting crevices and the low intertidal fringe which explains that, on average, the shaded-habitat species had a ∂¹³C value lower than those growing fully exposed to sun (i.e. in rockpools or at the upper intertidal zone). The comparison between the capacity for non-diffusive use of DIC (i.e. active or facilitated transport of HCO₃⁻ and/or CO₂) and the ∂¹³C values reveals that values more negative than −30‰ indicate that photosynthesis is dependent on CO₂ diffusive entry, whereas values above this threshold would not indicate necessary the operation of a non-diffusive DIC transport mechanism. Furthermore, external carbonic anhydrase activity (_extCA) and ∂¹³C values were negatively correlated indicating that the higher the dependence of the photosynthesis on the CO₂ supplied from HCO₃⁻ via _extCA, the lower the ∂¹³C in the algal material. The comparison between the ∂¹³C values obtained for the analysed species and those published for species inhabiting other bio-geographic areas (warm-temperate, cold and polar) suggests that globally (at least for the red and brown algae) the non-diffusive entry of DIC is more widely spread among the species from Cádiz Bay than among those of polar regions. If it is assumed that non-diffusive use of DIC implies saturation of photosynthesis at the present-day CO₂ concentration in seawater, our data indicate that the potential impact of the acidification on photosynthesis in the seaweed communities will be different depending on the latitude.