Photochemical dissolution of radionuclides from marine sediment

Laboratory experiments were carried out to assess the role of photochemical reactions upon the dissolution of ^{239 + 240}pu and ²⁴¹Am from marine sediment in sea water. Supplementary information was obtained by comparing their behaviour with that of ⁵⁴Mn under similar experimental conditions. Irradiation from natural sunlight resulted in more than a ten-fold increase in the extent of ^{239 + 240}Pu desorption relative to that observed in the dark. Remobilisation of ⁵⁴Mn from sediment was also enhanced by natural sunlight, albeit to a lesser extent than ^{239 + 240}Pu, whilst the behaviour of ²⁴¹Am was largely unaffected. Data for concentrations of dissolved ^{239 + 240}Pu(IV) and ^{239 + 240}Pu(V) species showed that only the oxidised form was significantly affected by irradiation, indicating remobilisation occurs as a result of photooxidation reactions. Further experiments were carried out using artificial light sources to establish the influence of wavelength. Data from these investigations indicated ^{239 + 240}Pu photooxidation (hence desorption) was a function of both light intensity and wavelength. Remobilisation decreased concomitant with light intensity but increased as the wavelength decreased. Similar trends were observed for photoreduction of ⁵⁴Mn, although differences were less pronounced than those observed for ^{239 + 240}Pu.     

Lateral stability of a submarine flexible hoseline

The lateral stability of a submarine hoseline in a slowly varying current is investigated. If the current force overcomes the sea bottom resistance, the hose segment is assumed to slide on the sea bottom without twisting. The stability is evaluated in terms of lateral deflections, hose tensions, and anchor loads. The behavior of a hoseline in a variable current is simulated based on nonlinear cable-like response to lift and Morison-type drag forces. Principles and the numerical algorithm of the simulation model are briefly summarized. A parametric analysis is conducted to study the influence on the hose response of the physical parameters considered in the simulation model. The results indicate that, for a practical hoseline, the most critical parameters are: the segment length-to-span ratio, the axial rigidity of the hose, the hose size, and the current velocity. The sea bottom resistance is negligible from a design point of view.     

Chandra smells a RRAT

“Rotating RAdio Transients” (RRATs) are a newly discovered astronomical phenomenon, characterised by occasional brief radio bursts, with average intervals between bursts ranging from minutes to hours. The burst spacings allow identification of periodicities, which fall in the range 0.4 to 7 seconds. The RRATs thus seem to be rotating neutron stars, albeit with properties very different from the rest of the population. We here present the serendipitous detection with the Chandra X-ray Observatory of a bright point-like X-ray source coincident with one of the RRATs. We discuss the temporal and spectral properties of this X-ray emission, consider counterparts in other wavebands, and interpret these results in the context of possible explanations for the RRAT population. B.M.G. acknowledges the support of NASA through LTSA grant NAG5-13023 and of an Alfred P. Sloan Fellowship.     

A characteristic observable signature of preferred-frame effects in relativistic binary pulsars

In this paper, we develop a consistent, phenomenological methodology to measure preferred-frame effects (PFEs) in binary pulsars that exhibit a high rate of periastron advance. We show that in these systems the existence of a preferred frame for gravity leads to an observable characteristic 'signature' in the timing data, which uniquely identifies this effect. We expand the standard Damour–Deruelle timing formula to incorporate this 'signature' and show how this new PFE timing model can be used to either measure or constrain the parameters related to a violation of the local Lorentz invariance of gravity in the strong internal fields of neutron stars. In particular, we demonstrate that in the presence of PFEs we expect a set of the new timing parameters to have a unique relationship that can be measured and tested incontrovertibly. This new methodology is applied to the Double Pulsar, which turns out to be the ideal test system for this kind of experiment. The currently available data set allows us only to study the impact of PFEs on the orbital precession rate,     , providing limits that are, at the moment, clearly less stringent than existing limits on PFE strong-field parameters. However, simulations show that the constraints improve fast in the coming years, allowing us to study all new PFE timing parameters and to check for the unique relationship between them. Finally, we show how a combination of several suitable systems in a PFE antenna array , expected to be available, for instance, with the Square Kilometre Array (SKA), provides full sensitivity to possible violations of local Lorentz invariance in strong gravitational fields in all directions of the sky. This PFE antenna array may eventually allow us to determine the direction of a preferred frame should it exist.     

A New Natural Secondary Reference Material for Garnet U-Pb Dating by TIMS and LA-ICP-MS

Gem quality andradite-rich garnet (IUC-1), obtained from the Miocene trachyte dome near Ankara city (Turkey), has been identified as a potential natural secondary reference material for U-Pb dating. In this study, U-Pb dating was performed in five different laboratories using isotope dilution TIMS and laser ablation ICP-MS to determine the homogeneity of euhedral garnet crystals. The U-Pb ID-TIMS data for IUC-1 yielded ²⁰⁷Pb/²³⁵U and ²⁰⁶Pb/²³⁸U ages of 20.9 ± 0.4 and 20.6 ± 0.8 Ma respectively, and these values are consistent with U-Pb LA-ICP-MS analyses, in which different garnet crystals yielded ages of 20.8 ± 0.1, 20.7 ± 0.1, 20.7 ± 0.2 and 20.2 ± 0.1 Ma. An andradite (IUC-2) from the Serçeören wollastonite skarn (Turkey) can be used as a secondary reference material provided detailed imaging of the crystals is undertaken. ID-TIMS data yielded ²⁰⁷Pb/²³⁵U and ²⁰⁶Pb/²³⁸U ages of 20.4 ± 0.4 and 20.9 ± 1.0 Ma respectively, and yielded U-Pb ages on different grains of 20.5 ± 0.1, 20.7 ± 1.0, 20.8 ± 1.7 and 20.9 ± 1.6 Ma. The assigned weighted mean age of IUC-1 (20.4 ± 0.5 Ma, 2s) is proposed as a 2023 reference value. IUC-1 garnet is expected to contribute significantly to rapidly developing garnet geochronology in the near future.     

An operational framework for communicating flood warnings to indigenous farmers in southern Nigeria: a systems thinking analysis

GeoJournal - In March 2012, the Nigerian meteorological agency forecasted massive flooding for parts of the country, with the displacement of large parts of the population as a consequence. Delta...     

Modeling effects of multinode wells on solute transport

Long-screen wells or long open boreholes with intraborehole flow potentially provide pathways for contaminants to move from one location to another in a ground water flow system. Such wells also can perturb a flow field so that the well will not provide water samples that are representative of ground water quality a short distance away from the well. A methodology is presented to accurately and efficiently simulate solute transport in ground water systems that include wells longer than the grid spacing used in a simulation model of the system and hence are connected to multiple nodes of the grid. The methods are implemented in a MODFLOW-compatible solute-transport model and use MODFLOW's Multi-Node Well Package but are generic and can be readily implemented in other solute-transport models. For nonpumping multinode wells (used to simulate open boreholes or observation wells, for example) and for low-rate pumping wells (in which the flow between the well and the ground water system is not unidirectional), a simple routing and local mixing model was developed to calculate nodal concentrations within the borehole. For high-rate pumping multinode wells (either withdrawal or injection, in which flow between the well and the ground water system is in the same direction at all well nodes), complete and instantaneous mixing in the wellbore of all inflows is assumed.     

Does Collinder 236 host a Cepheid calibrator?

Photoelectric UBV photometry and star counts are presented for the previously unstudied open cluster Collinder 236, supplemented by observations for stars near the Cepheid WZ Car. Collinder 236 is typical of groups associated with Cepheids, with an evolutionary age of  (3.2 ± 1.1) × 10⁷ yr  , but it is  1944 ± 71  pc distant, only half the predicted distance to WZ Car. The cluster is reddened by   E ( B − V ) ≃ 0.26  , and has nuclear and coronal radii of   r _n≃ 2 arcmin (1.1 pc)  and   R _c≃ 8 arcmin (4.5 pc)  , respectively. The Cepheid is not a member of Collinder 236 on the basis of location beyond the cluster tidal radius and implied distance, but its space reddening can be established as   E ( B − V ) = 0.268 ± 0.006  s.e. from five adjacent stars. Period changes in WZ Car studied with the aid of archival data are revised. The period of WZ Car is increasing, its rate of  +8.27 ± 0.19 s yr⁻¹  being consistent with a third crossing of the instability strip.