The STEREO/PLASTIC response to solar wind ions (Flight measurements and models)

The Plasma and Supra-Thermal Ion Composition (PLASTIC) instrument is one of four experiment packages on board of the two identical STEREO spacecraft A and B, which were successfully launched from Cape Canaveral on 26 October 2006. During the two years of the nominal STEREO mission, PLASTIC is providing us with the plasma characteristics of protons, alpha particles, and heavy ions. PLASTIC will also provide key diagnostic measurements in the form of the mass and charge state composition of heavy ions. Three measurements (E/qk, time of flight, ESSD) from the pulse height raw data are used to characterize the solar wind ions from the solar wind sector, and part of the suprathermal particles from the wide-angle partition with respect to mass, atomic number and charge state. In this paper, we present a new method for flight data analysis based on simulations of the PLASTIC response to solar wind ions. We present the response of the entrance system / energy analyzer in an analytical form. Based on stopping power theory, we use an analytical expression for the energy loss of the ions when they pass through a thin carbon foil. This allows us to model analytically the response of the time of flight mass spectrometer to solar wind ions. Thus we present a new version of the analytical response of the solid state detectors to solar wind ions. Various important parameters needed for our models were derived, based on calibration data and on the first flight measurements obtained from STEREO-A. We used information from each measured event that is registered in full resolution in the Pulse Height Analysis words and we derived a new algorithm for the analysis of both existing and future data sets of a similar nature which was tested and works well. This algorithm allows us to obtain, for each measured event, the mass, atomic number and charge state in the correct physical units. Finally, an important criterion was developed for filtering our Fe raw flight data set from the pulse height data without discriminating charge states.

Analysis of polygonal cracking patterns in chloride-bearing terrains on Mars: Indicators of ancient playa settings

The ancient southern highlands on Mars (~3.5 Gyr old) contain > 600 regions that display spectral evidence in the infrared for the presence of chloride-bearing materials. Many of these locations were previously reported to display polygonal cracking patterns. We studied more than 80 of the chloride-bearing terrains using high-resolution (0.25-0.5 m/pixel) images, as well as near-infrared spectral data, to characterize the surface textures and the associated cracking patterns and mineralogies. Our study indicates that ~75% of the studied locations display polygonal cracks that resemble desiccation cracks, while some resemble salt expansion/thrust polygons. Furthermore, we detect, spectrally, the presence of smectites in association with ~30% of the studied fractured terrains. We note that smectites are a special class of swelling clay minerals that can induce formation of large desiccation cracks. As such, we suggest that the cracking patterns are indicative of the presence of smectite phyllosilicates even in the absence of spectral confirmation. Our results suggest that many chloride-bearing terrains have a lacustrine origin and a geologic setting similar to playas on Earth. Such locations would have contained ephemeral lakes that may have undergone repeated cycles of desiccation and recharging by a near-surface fluctuating water table in order to account for the salt-phyllosilicates associations. These results have notable implications for the ancient hydrology of Mars. We propose that the morphologies and sizes of the polygonal cracks can be used as paleoenvironmental, as well as lithological, indicators that could be helpful in planning future missions.

From transient to steady state deformation and grain size: A thermodynamic approach using elasto-visco-plastic numerical modeling

Numerical simulation experiments give insight into the evolving energy partitioning during high-strain torsion experiments of calcite. Our numerical experiments are designed to derive a generic macroscopic grain size sensitive flow law capable of describing the full evolution from the transient regime to steady state. The transient regime is crucial for understanding the importance of micro structural processes that may lead to strain localization phenomena in deforming materials. This is particularly important in geological and geodynamic applications where the phenomenon of strain localization happens outside the time frame that can be observed under controlled laboratory conditions. Ourmethod is based on an extension of the paleowattmeter approach to the transient regime. We add an empirical hardening law using the Ramberg-Osgood approximation and assess the experiments by an evolution test function of stored over dissipated energy (lambda factor). Parameter studies of, strain hardening, dislocation creep parameter, strain rates, temperature, and lambda factor as well asmesh sensitivity are presented to explore the sensitivity of the newly derived transient/steady state flow law. Our analysis can be seen as one of the first steps in a hybrid computational-laboratory-field modeling workflow. The analysis could be improved through independent verifications by thermographic analysis in physical laboratory experiments to independently assess lambda factor evolution under laboratory conditions.

Efficiency of frost-cracking processes through space and time: An example from the eastern Italian Alps

It is widely accepted that climate has a strong impact and exerts important feedbacks on erosional processes and sediment transport mechanisms. However, the extent at which climate influences erosion is still a matter of debate. In this paper we test whether frost-cracking processes and related temperature variations can influence the sediment production and surface erosion in a small catchment situated in the eastern Italian Alps. To this extent, we first present a geomorphic map of the region that we complement with published 10Be-based denudation rates. We then apply a preexisting heat-flow model in order to analyze the variations of the frost-cracking intensity (FCI) in the study area, which could have controlled the sediment production in the basin. Finally, we compare the model results with the pattern of denudation rates and Quaternary deposits in the geomorphic map. The model results, combined with field observations, mapping, and quantitative geomorphic analyses, reveal that frost-cracking processes have had a primary role in the production of sediment where the intensity of sediment supply has been dictated and limited by the combined effect of temperature variations and conditions of bedrock preservation. These results highlight the importance of a yet poorly understood process for the production of sediment in mountain areas.

Bone-added periodontal plastic surgery: a new approach in esthetic dentistry

This article proposes a combined technique including bone grafting, connective tissue graft, and coronally advanced flap to create some space for simultaneous bone regrowth and root coverage. A 23 year-old female was referred to our private clinic with a severe class II Miller recession and lack of attached gingiva. The suggested treatment plan comprised of root coverage combined with xenograft bone particles. The grafted area healed well and full coverage was achieved at 12-month follow-up visit. Bone-added periodontal plastic surgery can be considered as a practical procedure for management of deep gingival recession without buccal bone plate.

Black Degradable Plastic Mulch Evaluation

Black polyethylene plastic mulch provides many benefits to fruit and vegetable producers. It increases earliness by increasing spring soil temperatures, conserves soil moisture, and reduces pesticide usage by decreasing weed and disease pressure. Furthermore, during seasons of high precipitation, it protects fertilizer from leaching below the root zone. Unfortunately, polyethylene mulches do not degrade and must be removed from the field and discarded each season. This is a labor-intensive process whether it is done mechanically or by hand. Several degradable plastic mulches have been developed that are designed to be incorporated into the soil profile, eliminating the need for removal, with no negative impact on soil quality or health. However, these degradable plastics often do not meet degradation expectations (either degrade too quickly or degrade incompletely and require manual removal). The objective of this project was to evaluate several degradable mulches for storage life, ease of use, and influence on tomato production.

A numerical discrete element study on the influence of an embedded viscoelastic-plastic layer at different viscosity values

The major aim of this study was to examine the influence of an embedded viscoelastic-plastic layer at different viscosity values on accretionary wedges at subduction zones. To quantify the effects of the layer viscosity, we analysed the wedge geometry, accretion mode, thrust systems and mass transport pattern. Therefore, we developed a numerical 2D 'sandbox' model utilising the Discrete Element Method. Starting with a simple pure Mohr Coulomb sequence, we added an embedded viscoelastic-plastic layer within the brittle, undeformed 'sediment' package. This layer followed Burger's rheology, which simulates the creep behaviour of natural rocks, such as evaporites. This layer got thrusted and folded during the subduction process. The testing of different bulk viscosity values, from 1 × 10**13 to 1 × 10**14 (Pa s), revealed a certain range where an active detachment evolved within the viscoelastic-plastic layer that decoupled the over- and the underlying brittle strata. This mid-level detachment caused the evolution of a frontally accreted wedge above it and a long underthrusted and subsequently basally accreted sequence beneath it. Both sequences were characterised by specific mass transport patterns depending on the used viscosity value. With decreasing bulk viscosities, thrust systems above this weak mid-level detachment became increasingly symmetrical and the particle uplift was reduced, as would be expected for a salt controlled forearc in nature. Simultaneously, antiformal stacking was favoured over hinterland dipping in the lower brittle layer and overturning of the uplifted material increased. Hence, we validated that the viscosity of an embedded detachment strongly influences the whole wedge mechanics, both the respective lower slope and the upper slope duplex, shown by e.g. the mass transport pattern.

Concentrations of floating plastic debris in the Mediterranean Sea measured during MedSeA-2013 cruise

Floating plastic debris sampled in surface waters of the Mediterranean Sea in May 2013 on board the Spanish R/V Angeles Alvariño. Geographical coordinates and dates of sampling are available in the dataset. Surface plastic concentrations derived from net tows were adjusted in relation to wind speed following the vertical-distribution model proposed by Kukulta et al. (2012, doi:10.1029/2012GL051116).

The number of plastic particles found in estuarine sediment and water samples of five estuaries, Durban, KwaZulu-Natal, South Africa

Widespread disposal of plastics negatively affects biotic and abiotic components of marine systems. Monitoring plastics transitioning through estuaries is vital in assessing terrestrial inputs to oceanic environments. Data on microplastics (particles <= 5mm) in estuaries are scant. This study determined microplastic levels within five estuaries along the Durban coastline and on intervening beaches. Plastics were isolated from estuarine sediment, beach sediment and the surface water of each estuary and characterised. Sediment at the Bayhead area of Durban Harbour was found to contain the highest average plastic concentrations (745.40 ± 129.72 particles per 500ml). Overall an attenuating concentration trend away from the city center was found. Fragments composed the largest percent of plastics (59 %) found in Bayhead, whereas fibers dominated other estuaries (Mdloti - 66 %, uMgeni - 38 %, Isipingo - 45 % and iLovu - 53 %). Plastic particle concentration in estuarine sediment generally increased from larger to smaller size classes. If high input and high retention in the harbour is coupled with high organic and metal pollutant loads, this area can become (if not already) a major environmental hazard.

Wave-induced changes in seaweed toughness entail plastic modifications in snail traits maintaining consumption efficacy, link to supplementary material

1. Environmental stress can influence species traits and performance considerably. Using a seaweed-snail system from NW (Nova Scotia) and NE (Helgoland) Atlantic rocky shores, we examined how physical stress (wave exposure) modulates traits in the seaweed Fucus vesiculosus and indirectly in its main consumer, the periwinkle Littorina obtusata. 2. In both regions, algal tissue toughness increased with wave exposure. Reciprocal-transplant experiments showed that tissue toughness adjusts plastically to the prevailing level of wave exposure. 3. Choice experiments tested the feeding preference of snails from sheltered, exposed, and very exposed habitats for algae from such wave exposures. Snails from exposed and very exposed habitats consumed algal tissues at similar rates irrespective of the exposure of origin of the algae. However, snails from sheltered habitats consumed less algal tissues from very exposed habitats than tissues from sheltered and exposed habitats. Choice assays using reconstituted algal food (triturated during preparation) identified high thallus toughness as the explanation for the low preference of snails from sheltered habitats for algae from very exposed habitats. 4. Ultrastructural analyses of radulae indicated that rachidian teeth were longest and the number of cusps in lateral teeth (grazing-relevant traits) was highest in snails from very exposed habitats, suggesting that radulae are best suited to rupture tough algal tissues in such snails. 5. No-choice feeding experiments revealed that these radular traits are also phenotypically plastic, as they adjust to the toughness of the algal food. 6. Synthesis. This study indicates that the observed plasticity in the feeding ability of snails is mediated by wave exposure through phenotypic plasticity in the tissue toughness of algae. Thus, plasticity in consumers and their resource species may reduce the potential effects of physical stress on their interaction.

Impact And Explosive Loads On Concrete Buildings Using Shell And Beam Type Elements

The threat of impact or explosive loads is regrettably a scenario to be taken into account in the design of lifeline or critical civilian buildings. These are often made of concrete and not specifically designed for military threats. Numerical simulation of such cases may be undertaken with the aid of state of the art explicit dynamic codes, however several difficult challenges are inherent to such models: the material modeling for the concrete anisotropic failure, consideration of reinforcement bars and important structural details, adequate modeling of pressure waves from explosions in complex geometries, and efficient solution to models of complete buildings which can realistically assess failure modes. In this work we employ LS-Dyna for calculation, with Lagrangian finite elements and explicit time integration. Reinforced concrete may be represented in a fairly accurate fashion with recent models such as CSCM model [1] and segregated rebars constrained within the continuum mesh. However, such models cannot be realistically employed for complete models of large buildings, due to limitations of time and computer resources. The use of structural beam and shell elements for this purpose would be the obvious solution, with much lower computational cost. However, this modeling requires careful calibration in order to reproduce adequately the highly nonlinear response of structural concrete members, including bending with and without compression, cracking or plastic crushing, plastic deformation of reinforcement, erosion of vanished elements etc. The main objective of this work is to provide a strategy for modeling such scenarios based on structural elements, using available material models for structural elements [2] and techniques to include the reinforcement in a realistic way. These models are calibrated against fully three-dimensional models and shown to be accurate enough. At the same time they provide the basis for realistic simulation of impact and explosion on full-scale buildings

Parametric study of the expansive joint model for cracking of concrete due to rebar corrosion

Un modelo numérico llamado elemento junta expansiva fue programado para simular la expansión mecánica del óxido y estudiar la fisuración en el hormigón circundante. El elemento junta expansiva trabaja con elementos finitos con fisura cohesiva embebida adaptable para simular la fractura del hormigón según el modelo de fisura cohesiva. Se ha comprobado que el modelo reproduce correctamente el patrón de fisuración del hormigón que se obtiene en ensayos de corrosión acelerada. En este trabajo, se realiza un estudio paramétrico del elemento junta expansiva para establecer los límites de los parámetros constitutivos del óxido. Se simula una cierta expansión variando los valores de los parámetros del óxido y se estudian la apertura de fisura y las tensiones resultantes en el hormigón. Se determina el rango de valores para los que los resultados de las simulaciones son prácticamente iguales, con el menor número posible de iteraciones.