Geometric selection in two-dimensional crystal aggregates

The simultaneous growth of randomly oriented crystals nucleated at a surface rapidly produces a coarsely crystalline radial or columnar aggregate possessing a strong preferred shape and lattice orientation. Such textures are common in natural crystalline aggregates and are considered to arise because those crystals having their fastest growth direction normal to the initial substrate outdistance and eventually eliminate their less favorably oriented neighbors. In its simplest form the process of elimination is a purely geometric phenomenon. Detailed analysis and computer simulation of textural changes accompanying geometric selection in random two dimensional needlelike crystal aggregates demonstrate that selection initially proceeds exceedingly rapidly but slows drastically once roughly 90 percent of the crystals originally present are eliminated. Subsequent decrease in crystal density is inversely proportional to the square root of the distance from the initial substrate. Increases in crystal size larger than one or two orders of magnitude are thus unlikely to arise in natural crystalline aggregates in which only simple geometric selection is involved.     

PCB-containing paint and plaster caused extreme PCB-concentrations in biota from the Sørfjord (Western Norway)--a case study

The Sørfjord (Western Norway) has a long history of industry and pollution, and has been monitored for several decades. The environmental monitoring has comprised analyses of different contaminants in sea water, mussel, fish, seaweed and sediments. Measurements of polychlorinated biphenyls (PCBs) in blue mussels (Mytilus edulis) some 17 years ago indicated a local source. In 2001 severe concentrations were measured in blue mussels and further investigations disclosed the primary source of PCBs in the Sørfjord. In 2002, extreme PCB-concentrations were found in cod (Gadus morhua) from the same area. However, no induction of EROD activity was detected, indicating the limitations of this assay as marker for PCB contamination. A future scientific challenge will be to understand the specific mechanisms and effects of such PCB accumulation in fish.     

Participatory modeling in dairy farm systems: a method for building consensual environmental sustainability using seasonal climate forecasts

Dairy farmers face increasing pressure to decrease environmental impact while remaining economically viable. Adaptation of farm management practices in response to seasonal climate forecasts may be one means of achieving these objectives. This paper describes the interactive and iterative process by which farmers, researchers, extension agents, regulatory agencies, and other stakeholders collaborated to create, calibrate, and validate the Dynamic North Florida Dairy Farm model (DyNoFlo), a whole-farm decision support system to decrease nitrogen leaching while maintaining profitability under variable climate conditions. Participatory modeling may enhance the creation of adoptable and adaptable user-friendly models that include environmental, economic and biophysical components. By providing farmers, policy makers, and other stakeholders with a more holistic view of current practices, common ground among them was more easily identified and collaboration was fostered. Farmer values included willingness to be good environmental stewards when they are profitable. The participatory research and development process enhanced understanding of and potential adaptation to seasonal climate variability conditioned to the El Niño Southern Oscillation (ENSO) phases in light of increasing environmental regulations and economic challenges. Adoption of the collaboratively-developed DyNoFlo is expected to be higher than usual because stakeholders feel greater ownership of the final product.     

Magnetic zones of Mars: Deformation‐controlled origin of magnetic anomalies

Abstract— Intense magnetic anomalies over Martian surface suggest preservation of large volumes of very old crust (>3 Gyr) that formed in the presence of a global magnetic field. The global distribution of the magnetic intensities observed above the Martian crust suggests a division into three zones. Zone 1 is where the magnetic signature is negligible or of relatively low intensity at Mars Global Surveyor (MGS) satellite mapping altitude (400 km). Zone 2 is the region of intermediate crustal magnetic amplitudes and zone 3 is where the highest magnetic intensities are measured. Crater demagnetization near zone 3 reveals the presence of rocks with both high magnetic intensity and coercivity. Magnetic analyses of terrestrial rocks show that compositional banding in orogenic zones significantly enhances both magnetic coercivity and thermal remanent magnetization (TRM) efficiency. Such enhancement offers a novel explanation for the anomalously large intensities inferred of magnetic sources on Mars. We propose that both large magnetic coercivity and intensity near the South Pole is indicative of the presence of a large degree of deformation. Associated compositional zoning creates conditions for large scale magnetic anisotropy allowing magnetic minerals to acquire magnetization more efficiently, thereby causing the distinct magnetic signatures in zone 3, expressed by intense magnetic anomalies. We use a simple model to verify the magnetic enhancement. We hypothesize that magnetically enhanced zone would reside over the down welling plume at the time of magnetization acquisition.     

Sulfides in mantle peridotites from Penghu Islands, Taiwan: Melt percolation, PGE fractionation, and the lithospheric evolution of the South China block

Major elements, highly siderophile elements (HSE) and Re-Os isotope ratios were analysed in situ on individual sulfide grains in spinel peridotite xenoliths hosted by Miocene intraplate basalts from the Penghu Islands, Taiwan. The xenoliths represent texturally and compositionally different mantle domains, and the geochemical characteristics of the sulfides show changes in HSE distribution and Re-Os isotope systematics, produced as their host rocks were metasomatised by percolating fluids/melts. In prophyroclastic and partly metasomatised peridotites from the Kueipi (KP) locality, the sulfides have subchondritic to superchondritic ¹⁸⁷Re/¹⁸⁸Os and ¹⁸⁷Os/¹⁸⁸Os ratios. Many of these sulfides reflect fluid/melt interaction with residual MSS and/or crystallization of fractionated sulfide melts, which produced high contents of Cu and PPGEs and high Re/Os; inferred melt/rock ratios are low. In contrast, sulfides in equigranular and extensively metasomatised peridotites from the Tungchiyu (TCY) locality are mainly more sulfur-rich Ni-(Co)-rich MSS, with subchondritic to chondritic ¹⁸⁷Os/¹⁸⁸Os and subchondritic ¹⁸⁷Re/¹⁸⁸Os. These sulfides are interpreted as products of interaction between pre-existing MSS and percolating silicate melts. Melt/rock ratios were high and the percolating melt was less differentiated than the melt that percolated the KP peridotites. Sulfides in a TCY pyroxenite are mainly MSS; they have the lowest HSE contents, subchondritic to superchondritic ¹⁸⁷Os/¹⁸⁸Os and subchondritic ¹⁸⁷Re/¹⁸⁸Os, and may have precipitated from sulfide melts that segregated from basaltic melts under S-saturated conditions. In most sulfides melt percolation appears to have induced fractionation among the HSEs and disturbed Re-Os isotope compositions. Despite the metasomatic effects, rare residual MSS, sulfides that from crystallised sulfide melts and sulfides modified by addition of Re (with no evidence for Os addition) can still provide useful chronological information. Such sulfides yield T_RD age peaks of 1.9, 1.7-1.6, 1.4-1.3 and 0.9-0.8 Ga, which may record the timing of melt extraction and/or metasomatic events in the mantle. These periods are contemporaneous with the major crustal events recorded by U-Pb dates and Nd and Hf model ages in the overlying crust. This close correspondence indicates that the sulfide T_RD ages reflect the timing of lithosphere-scale tectonothermal events (such as melting and metasomatism) that affected both the lithospheric mantle and the overlying crust. The sulfide T_RD ages, taken together with the crustal data, suggest that most of the Cathaysia block had formed at least by Paleo-Proterozoic time, and that some domains are Archean in age.     

Thallium isotopes as a potential tracer for the origin of cratonic eclogites

Cratonic eclogites are inferred to originate either from subducted ocean crust or mantle melts accreted onto the roots of continents. These models have different implications for the growth of continents, but it is currently difficult to determine the origin of individual eclogite suites.Upper ocean crust altered at low temperatures and marine sediments both display high thallium (Tl) concentrations and strongly fractionated Tl isotope signatures relative to the ambient upper mantle. In this study we carry out the first examination of the suitability of Tl isotopes as a tracer for an ocean-crust origin of cratonic eclogites. We have analysed the Tl isotope composition of clinopyroxene and garnet in six eclogites from the Kaalvallei and Bellsbank kimberlite pipes in South Africa. Minerals were pre-cleaned with an HCl leaching technique and the leachates display variably light Tl isotope ratios. These most likely reflect low-temperature hydrothermal alteration occurring after eruption of the kimberlite that carried the eclogites to the surface.The leached mineral pairs all display identical Tl isotope ratios, strongly suggesting that the source of the analysed Tl is identical for each mineral pair. It is, however, not possible to exclude the possibility that the analysed Tl originates from kimberlitic material that was not removed by the cleaning procedure.Only one of the six samples exhibits a Tl isotope composition different from ambient mantle. Assuming that the Tl isotope signatures indeed represent the eclogite minerals and not any form of contamination, the Tl isotope composition in this sample is consistent with containing a minor component (<3%) of ocean crust altered at low temperatures.Thallium isotopes may become one of the most sensitive indicators for the presence of low-T altered ocean crust because of the stark contrast in Tl concentration and isotopic composition between the mantle and altered ocean crust. In fact, no other chemical or isotopic tracer could have provided an indication that any of the samples studied here had a subduction origin. However, much work is still required before it becomes clear if Tl isotope measurements are a viable means to establish the origin of cratonic eclogites.     

Edge-to-Stem Variability in Wet-Canopy Evaporation From an Urban Tree Row

Evaporation from wet-canopy (\(E_\mathrm{C}\)) and stem (\(E_\mathrm{S}\)) surfaces during rainfall represents a significant portion of municipal-to-global scale hydrologic cycles. For urban ecosystems, \(E_\mathrm{C}\) and \(E_\mathrm{S}\) dynamics play valuable roles in stormwater management. Despite this, canopy-interception loss studies typically ignore crown-scale variability in \(E_\mathrm{C}\) and assume (with few indirect data) that \(E_\mathrm{S}\) is generally \({<}2\%\) of total wet-canopy evaporation. We test these common assumptions for the first time with a spatially-distributed network of in-canopy meteorological monitoring and 45 surface temperature sensors in an urban Pinus elliottii tree row to estimate \(E_\mathrm{C}\) and \(E_\mathrm{S}\) under the assumption that crown surfaces behave as “wet bulbs”. From December 2015 through July 2016, 33 saturated crown periods (195 h of 5-min observations) were isolated from storms for determination of 5-min evaporation rates ranging from negligible to 0.67 \(\hbox {mm h}^{-1}\). Mean \(E_\mathrm{S}\) (0.10 \(\hbox {mm h}^{-1}\)) was significantly lower (\(p < 0.01\)) than mean \(E_\mathrm{C}\) (0.16 \(\hbox {mm h}^{-1}\)). But, \(E_\mathrm{S}\) values often equalled \(E_\mathrm{C}\) and, when scaled to trunk area using terrestrial lidar, accounted for 8–13% (inter-quartile range) of total wet-crown evaporation (\(E_\mathrm{S}+E_\mathrm{C}\) scaled to surface area). \(E_\mathrm{S}\) contributions to total wet-crown evaporation maximized at 33%, showing a general underestimate (by 2–17 times) of this quantity in the literature. Moreover, results suggest wet-crown evaporation from urban tree rows can be adequately estimated by simply assuming saturated tree surfaces behave as wet bulbs, avoiding problematic assumptions associated with other physically-based methods.     

First encounter with a live male blanket octopus: The world's most sexually size‐dimorphic large animal

The first encounter with a live male blanket octopus, Tremoctopus violaceus Chiaie, 1830, illustrates the most extreme example of sexual size‐dimorphism in a non‐microscopic animal. Females attain sizes of up to 2 m long—almost 2 orders of magnitude larger than the 2.4‐cm‐long male. Weight ratios between the sexes are at least 10 000:1 and are likely to reach 40 000:1. Sexual selection and the unique defensive strategy of carrying cnidarian stinging tentacles may both have contributed to the evolution of this extreme size‐dimorphism. Such dimorphism is not seen in any other animal remotely as large.     

Seismic demand models for probabilistic risk analysis of near fault vertical ground motion effects on ordinary highway bridges

The influence of vertical ground motions on the seismic response of highway bridges is not very well understood. Recent studies suggest that vertical ground motions can substantially increase force and moment demands on bridge columns and girders and cannot be overlooked in seismic design of bridge structures. For an evaluation of vertical ground motion effects on the response of single‐bent two‐span highway bridges, a systematic study combining the critical engineering demand parameters (EDPs) and ground motion intensity measures (IMs) is required. Results of a parametric study examining a range of highway bridge configurations subjected to selected sets of horizontal and vertical ground motions are used to determine the structural parameters that are significantly amplified by the vertical excitations. The amplification in these parameters is modeled using simple equations that are functions of horizontal and vertical spectral accelerations at the corresponding horizontal and vertical fundamental periods of the bridge. This paper describes the derivation of seismic demand models developed for typical highway overcrossings by incorporating critical EDPs and combined effects of horizontal and vertical ground motion IMs depending on the type of the parameter and the period of the structure. These models may be used individually as risk‐based design tools to determine the probability of exceeding the critical levels of EDP for pre‐determined levels of ground shaking or may be included explicitly in probabilistic seismic risk assessments. Copyright © 2011 John Wiley & Sons, Ltd.