The gravitational perturbation spectrum in linear satellite theory

A new method for calculating the perturbation spectrum in the framework of Kaula's linear satellite theory (LST) is introduced. The novelty of this approach consists in using recent results on the spectral decomposition of the perturbation frequencies in LST to provide a closed formulation for the amplitude and the phase of each line in the perturbation spectrum. The theory presented here can be applied to perturbations in the elements or in the radial and transverse directions due to the geopotential or to the tides. Separate algorithms are developed for application to orbits with circulating or frozen perigee.     

Ostreopsis cf. ovata bloom in the northern Adriatic Sea during summer 2009: ecology, molecular characterization and toxin profile

Intense blooms of the benthic dinoflagellate Ostreopsis cf. ovata have occurred in the northern Adriatic Sea since 2006. These blooms are associated with noxious effects on human health and with the mortality of benthic organisms because of the production of palytoxin-like compounds. The O. cf. ovata bloom and its relationships with nutrient concentrations at two stations on the Conero Riviera (northern Adriatic Sea) were investigated in the summer of 2009. O. cf. ovata developed from August to November, with the highest abundances in September (1.3 × 10⁶ cells g⁻¹ fw corresponding to 63.8 × 10³ cells cm⁻²). The presence of the single O. cf. ovata genotype was confirmed by a PCR assay. Bloom developed when the seawater temperature was decreasing. Nutrient concentrations did not seem to affect bloom dynamics. Toxin analysis performed by high resolution liquid chromatography-mass spectrometry revealed a high total toxin content (up to 75 pg cell⁻¹), including putative palytoxin and all the ovatoxins known so far.     

On the use of the autocorrelation function: the constraint of using frequency band-limited signals for monitoring relative velocity changes

Correlations of seismic noise are commonly used to monitor temporal variations of relative seismic velocity in period ranges from 1 s up to 100 s. Of particular interest is the detection of small changes in the order of 0.01–0.1 % in propagation speeds. Measuring such small differences can, however, be significantly biased by temporal variations in the properties of the noise sources within the corresponding frequency band. Using synthetic data, we show that apparent relative velocity variations might appear only due to changes in the amplitude and frequency content caused by source variations. Removing such unwanted effects by applying narrow bandpass filters in the preprocessing restricts the high-resolution analysis of any signal due to Gabor’s uncertainty limit, i.e., the correlation function suffers a limited resolution to time delay estimates for small correlation times, low-frequency ranges, and in narrow frequency bands. Better understanding of spatiotemporal noise source properties and the theoretical limitations of time–frequency analysis is critical for accurate and reliable passive monitoring.     

Seismic performance of masonry walls retrofitted with steel reinforced grout

An innovative solution for the seismic protection of existing masonry structures is proposed and investigated through shake table tests on a natural scale wall assemblage. After a former test series carried out without reinforcement, the specimen was retrofitted using Steel Reinforced Grout. The strengthening system comprises horizontal strips of ultra‐high strength steel cords, externally bonded to the masonry with hydraulic lime mortar, and connectors to transversal walls, applied within the thickness of the plaster layer. In order to assess the seismic performance of the retrofitted wall, natural accelerograms were applied with increasing intensity up to failure. Test results provide a deep understanding of the effectiveness of mortar‐based composites for improving the out‐of‐plane seismic capacity of masonry walls, in comparison with traditional reinforcements with steel tie‐bars. The structural implications of the proposed solution in terms of dynamic properties and damage development under earthquake loads are also discussed.Copyright © 2015 John Wiley & Sons, Ltd.     

Reef status in the Rasfari region (North Malé Atoll,Maldives) five years before the mass mortality event of 1998

The Maldives was severely hit by massive coral bleaching and subsequent mortality in 1998. The results of reef monitoring in the following years have supported contrasting views about their recovery potential, partly because of the scarcity of information on the situation before 1998. Quantitative data on coral assemblages collected in 1993 in the Rasfari region (North Malé Atoll) may provide a base-line for the evaluation of the present status of the Maldivian reefs. Five years before the 1998 mortality, most coral communities appeared to be similar, in terms of both coral cover and growth-form composition, to those described in 1958 and 1964, notwithstanding increased human pressure and local events such as minor bleaching episodes in 1987 and crown-of-thorns starfish (COTS) attacks in 1989. Three lessons can be learnt from these results to help to understand the present situation, some ten years after the 1998 mass mortality. First, Maldivian reefs proved in the past to be capable of maintaining flourishing coral life despite various disturbances. Second, four years had been sufficient for complete reef recovery after a (minor) bleaching event. Third, recovery after both COTS attack and bleaching follows a predictable path suggesting that the presence of a three-dimensional community structure, which should reduce post settlement mortality of coral recruits, is essential for rapid coral recovery. As coral recruitment remains high and large tabular Acropora colonies are now reappearing, it is expected that Maldivian reefs should return to their original condition within the next few years.     

Changes in Venice Lagoon dynamics due to construction of mobile barriers

The MoSE project (construction of mobile barrier to safeguard the Lagoon of Venice) entails changes to the structure of the lagoon's inlets. This could have consequences for the areas near the inlets and for the dynamics of the lagoon ecosystem as a whole. In order to predict the effects of the proposed alterations on the hydrodynamics of the lagoon, a well-tested hydrodynamic-dispersion model was applied. Simulations were carried out considering both idealised and realistic tide and wind scenarios.     

Global photometric properties of Asteroid (4) Vesta observed with Dawn Framing Camera

Dawn spacecraft orbited Vesta for more than one year and collected a huge volume of multispectral, high-resolution data in the visible wavelengths with the Framing Camera. We present a detailed disk-integrated and disk-resolved photometric analysis using the Framing Camera images with the Minnaert model and the Hapke model, and report our results about the global photometric properties of Vesta. The photometric properties of Vesta show weak or no dependence on wavelengths, except for the albedo. At 554 nm, the global average geometric albedo of Vesta is 0.38 ± 0.04, and the Bond albedo range is 0.20 ± 0.02. The bolometric Bond albedo is 0.18 ± 0.01. The phase function of Vesta is similar to those of S-type asteroids. Vesta’s surface shows a single-peaked albedo distribution with a full-width-half-max ∼17% relative to the global average. This width is much smaller than the full range of albedos (from ∼0.55× to >2× global average) in localized bright and dark areas of a few tens of km in sizes, and is probably a consequence of significant regolith mixing on the global scale. Rheasilvia basin is ∼10% brighter than the global average. The phase reddening of Vesta measured from Dawn Framing Camera images is comparable or slightly stronger than that of Eros as measured by the Near Earth Asteroid Rendezvous mission, but weaker than previous measurements based on ground-based observations of Vesta and laboratory measurements of HED meteorites. The photometric behaviors of Vesta are best described by the Hapke model and the Akimov disk-function, when compared with the Minnaert model, Lommel–Seeliger model, and Lommel–Seeliger–Lambertian model. The traditional approach for photometric correction is validated for Vesta for >99% of its surface where reflectance is within ±30% of global average.     

First observations of the Na exosphere of Mercury with the high-resolution spectrograph of the 3.5M Telescopio Nazionale Galileo

Analysis of three spectra of the exosphere of Mercury in the Na-D lines are presented. Spectra were secured with the high-resolution spectrograph (SARG) of the 3.5 M Telescopio Nazionale Galileo (TNG, located on the Roque de los Muchachos, Canaries) on the evenings of August 23 and 24, 2002. Spectra have resolution ; the slit length was 26.7”. The Na column abundances range from 4.3 to with the highest abundances being close to the illuminated limb. Our observations at true anomaly angles (TAA) from 171°to 174°show the traces of the emission lines to be strongly peaked at the illuminated limb, supportive of recent modeling that shows thermal desorption to be a strong factor in determining the distribution of Na about the planet.