Stochastic methods for the prediction of strata behaviour

Summary A two-dimensional finite difference computer program, with the facility to represent stratified material by means of a mesh of mass points with different material properties in each square of the mesh, is adapted to run on a mesh whose material properties are selected stochastically from a specified distribution. The program uses an iterative method to solve the equations of equilibrium, giving estimates of displacements and stresses.Lattices of normally distributed (zero mean, unit variance) random values are produced: lattices of statistically independent values and lattices whose values are spatially correlated, to give the effect of gradual variations resulting in regions of positive values and regions of negative values.These lattices are used to generate the material properties: Young's modulus, Poisson's ratio and density. Each property has a specified mean and standard deviation for each material in the model, and the precise values for each mass point are calculated from the relevant lattices.A simple model with a square opening is used to investigate the effect of this stochastic generation of material properties, by comparison of stresses and displacements near the opening for runs of the program with (1) deterministic and (2) stochastic properties.Similar lattices of random values are used to introduce a stochastic element in the criterion for failure of materials. This is applied to a more realistic simulation of a mining situation, where Mohr's Criterion is used, with a stochastic component, to determine whether failure has occurred at each point of the mesh.     

Decomposition algorithms for system reliability estimation with applications to interdependent lifeline networks

Reliability and risk assessment of lifeline systems call for efficient methods that integrate hazard and interdependencies. Such methods are computationally challenged when the probabilistic response of systems is tied to multiple events, as performance quantification requires a large catalog of ground motions. Available methods to address this issue use catalog reductions and importance sampling. However, besides comparisons against baseline Monte Carlo trials in select cases, there is no guarantee that such methods will perform or scale well in practice. This paper proposes a new efficient method for reliability assessment of interdependent lifeline systems, termed RAILS, that considers systemic performance and is particularly effective when dealing with large catalogs of events. RAILS uses the state‐space partition method to estimate systemic reliability with theoretical bounds and, for the first time, supports cyclic interdependencies among lifeline systems. Recycling computations across an entire seismic catalog with RAILS considerably reduces the number of system performance evaluations in seismic performance studies. Also, when performance estimate bounds are not tight, we adopt an importance and stratified sampling method that in our computational experiments is various orders of magnitude more efficient than crude Monte Carlo. We assess the efficiency of RAILS using synthetic networks and illustrate its application to quantify the seismic risk of realistic yet streamlined systems hypothetically located in the San Francisco Bay Region.     

Queer Farmland: Land Access Strategies for Small-Scale Agriculture

Farmers struggle to afford farmland because competing land uses raise prices higher than what farmers earn, especially in small-scale and sustainable agriculture. Farmers often depend on an intimate partner’s income or labor to access land, yet few studies investigate sexual relationships in farmland access. I interrogate how sexuality shapes land access for small-scale agriculture through participant observation and interviews with 25 queer farmers in New England. I find that queer farmers’ sexual identities and relationships influence where they farm, who they live and work with, how they afford the land, and how they learn to farm. I argue that finding land, labor, credit, and knowledge are intertwined, heteronormative processes of capital accumulation shaped by racism and sexism. Queer farmers’ experiences navigating heteronormativity suggest the relevance of sexuality to land conservation and food justice, limits of organizing land access through sexual relationships, and alternatives to the “family farm.”     

Quantifying the EEJ current with ground-based ionosonde inferred vertical E × B drifts in the morning hours over Ilorin,West Africa

The relationship between the ground-based inferred vertical E × B drifts, Vz, and the magnetic equatorial electrojet current during the year of solar minima was presented. Both the diurnal and seasonal Vz variations are positively directed during the daytime and negative at nighttime. The evening time pre-reversal enhancement occurs around 19:00 LT. The fairly strong linear relationship between the electrojet current strength and Vz exhibited higher correlations during the daytime (06:00–16:00 LT). The maximum morning time proxy parameter described by E = [d (ΔH _ILR)/dt]_max in the morning hours, indicating the east-west electric field in the EEJ, corresponds reasonably well with the E × B drift and, hence, can be used as a proxy parameter for representing Vz in the morning hours. The daytime EEJ magnitude seasonal changes are connected with a change in conductivity emerging from the action of turbulence and divergence of momentum flux. These waves above the dynamo region are suggested to lead to partial counter electrojet during the equinoctial months.     

The Magnitude and Proximate Cause of Ice-Sheet Growth Since 35,000 yr B.P.

The magnitude of late Wisconsinan (post-35,000 yr B.P.) ice-sheet growth in the Northern Hemisphere is not well known. Ice volume at 35,000 yr B.P. may have been as little as 20% or as much as 70% of the volume present at the last glacial maximum (LGM). A conservative evaluation of glacial–geologic, sea level, and benthic δ¹⁸O data indicates that ice volume at 35,000 yr B.P. was approximately 50% of that extant at the LGM (20,000 yr B.P.); that is, it doubled in about 15,000 yr. On the basis of literature for the North Atlantic and a sea-surface temperature (SST) data compilation, it appears that this rapid growth may have been forced by low-to-mid-latitude SST warming in both the Atlantic and Pacific Oceans, with attendant increased moisture transport to high latitudes. The SST ice-sheet growth notion also explains the apparent synchroneity of late Wisconsinan mountain glaciation in both hemispheres.     

Book reviews

Natural Resources Research -     

Patterns of Chemical Changes During Environmental Alteration of Hydrocarbon Fuels

This paper discusses major environmental alteration processes and describes a set of chemical tests that have been developed to monitor compositional changes in hydrocarbon fuels released into the environment. The methods examine various homologous series of hydrocarbons including straight chain (paraffins or n-alkanes), branched chain (isoparaffins or isoprenoids), alicyclic (naphthenes or alkylated cyclohexanes), polycyclic (steranes and terpanes), and aromatic structures (benzene, toluene, ethylbenzene. xylenes, alkylated benzenes, polycyclic aromatic hydrocarbons, and aromatic steranes). Each one of these groups of hydrocarbons has a different tolerance to environmental alteration by evaporation, dissolution (water washing), and biodegradation. When used as an analytical system on environmental samples, the data obtained provide information on fuel type recognition patterns and on degradation levels of the various fuels, allowing for an estimate of residence time.     

Contrasting the tropical responses to zonally asymmetric extratropical and tropical thermal forcing

The mechanism is investigated by which extratropical thermal forcing with a finite zonal extent produces global impact. The goal is to understand the near-global response to a weakened Atlantic meridional overturning circulation suggested by paleoclimate data and modeling studies. An atmospheric model coupled to an aquaplanet slab mixed layer ocean, in which the unperturbed climate is zonally symmetric, is perturbed by prescribing cooling of the mixed layer in the Northern Hemisphere and heating of equal magnitude in the Southern Hemisphere, over some finite range of longitudes. In the case of heating/cooling confined to the extratropics, the zonally asymmetric forcing is homogenized by midlatitude westerlies and extratropical eddies before passing on to the tropics, inducing a zonally symmetric tropical response. In addition, the zonal mean responses vary little as the zonal extent of the forced region is changed, holding the zonal mean heating fixed, implying little impact of stationary eddies on the zonal mean. In contrast, when the heating/cooling is confined to the tropics, the zonally asymmetric forcing produces a highly localized response with slight westward extension, due to advection by mean easterly trade winds. Regardless of the forcing location, neither the spatial structure nor the zonal mean responses are strongly affected by wind–evaporation–sea surface temperature feedback.     

Egg capsule hatch rate and incubation duration of the California market squid,Doryteuthis (= Loligo) opalescens: insights from laboratory manipulations

Egg capsules of the squid Doryteuthis (= Loligo) opalescens were reared in the laboratory to assess the dependence of time‐to‐hatching (incubation time) and hatching success rate on temperature and light regime. Both incubation time and hatch duration were found to be inversely related to temperature. More than 96% of paralarvae hatch from eggs reared at temperatures between 9 and 14 °C. Hatch rate drops below 90% in warmer and colder water. No eggs hatch below 7 °C, and the upper limit of viability is near 25 °C. The vast majority (91%) of hatchlings emerged during the dark phase of the photoperiod. Egg capsules reared at 13.4 °C with a supposedly commensal polychaete, Capitella ovincola, had a slightly higher hatch rate than those without the annelid. Because eggs are naturally laid closely together, crowding was hypothesized to cause decreased ventilation and a lower hatch rate. Crowding was tested by placing two capsules (rather than one) into the small incubation chambers (50 ml). This treatment did not result in a lower hatch rate at 13.4 °C, but at 21.4 °C it decreased the hatch rate by 20%. Brood incubation duration is related to temperature by the equation: Incubation (days) = 14.97 + 177.40 × exp(?0.119 × Temperature –°C) (χ² = 282.5, P = 0.001). Stable isotope analysis confirmed that C. ovincola worms eat the capsule matrix, not the paralarvae. These polychaetes had a δ¹⁵N value of 12.79‰versus 12.06‰ for squid paralarvae, and 10.54‰ for the gelatinous matrix of egg capsules. This fractionation factor ε of 2.25‰ is consistent with marine food webs. Provision of nutrients and shelter for the annelids and increased hatch rate for the squid embryos suggests a symbiotic relationship between these organisms.