Effects of a temperature-dependent rheology on large scale continental extension

The effects of a temperature-dependent rheology on large-scale continental extension are investigated using a thin viscous sheet model. A vertically-averaged rheology is used that is consistent with laboratory experiments on power-law creep of olivine and that depends exponentially on temperature. Results of the calculations depend principally on two parameters: the Peclet number, which describes the relative rates of advection and diffusion of heat, and a dimensionless activation energy, which controls the temperature dependence of the rheology. At short times following the beginning of extension, deformation occurs with negligible change in temperature, so that only small changes in lithospheric strength occur due to attenuation of the lithosphere. However, after a certain critical time interval, thermal diffusion lowers temperatures in the lithosphere, strongly increasing lithospheric strength and slowing the rate of extension. This critical time depends principally on the Peclet number and is short compared with the thermal time constant of the lithosphere. The strength changes cause the locus of high extensional strain rates to shift with time from regions of high strain to regions of low strain. Results of the calculations are compared with observations from the Aegean, where maximum extensional strains are found in the south, near Crete, but maximum present-day strain rates are largest about 300 km further north

Formation of oriented particles in an amorphous host: ZnS nanocrystals in silicon

Processes for incorporating randomly oriented crystalline precipitates in an amorphous host can be traced back to the 17th century when Cassius produced “gold ruby” glass. In this glass, octahedral colloidal precipitates of gold scatter light by the Mie process to produce a deep red color. In contrast to gold ruby glass, we describe a type of material in which the crystalline precipitates are crystallographically aligned in a coherent manner—even though they are dispersed in an amorphous matrix. Ion implantation and thermal processing are first used to form zinc sulfide nanocrystals that are coherently oriented with respect to a crystalline Si host. The Si is then amorphized by ion irradiation leaving the highly radiation-resistant ZnS precipitates in an aligned crystalline state. The process is anticipated to find applications in the creation of surfaces with unique optoelectronic properties. © 1999 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/69678/2/APPLAB-74-5-697-1.pd

Targeting drought-tolerant maize varieties in southern Africa: a geospatial crop modeling approach using big data

Maize is a major staple food crop in southern Africa and stress tolerant improved varieties have the potential to increase productivity, enhance livelihoods and reduce food insecurity. This study uses big data in refining the geospatial targeting of new drought-tolerant (DT) maize varieties in Malawi, Mozambique, Zambia, and Zimbabwe. Results indicate that more than 1.0 million hectares (Mha) of maize in the study countries is exposed to a seasonal drought frequency exceeding 20% while an additional 1.6 Mha experience a drought occurrence of 10–20%. Spatial modeling indicates that new DT varieties could give a yield advantage of 5–40% over the commercial check variety across drought environments while crop management and input costs are kept equal. Results indicate a huge potential for DT maize seed production and marketing in the study countries. The study demonstrates how big data and analytical tools enhance the targeting and uptake of new agricultural technologies for boosting rural livelihoods, agribusiness development and food security in developing countries

Tortillas on the roaster: Central America’s maize–bean systems and the changing climate

Maize and beans are a vital component of human diets and culture in Central America. More than a million smallholder families grow these crops for subsistence, producing 70% of the maize and 100% of the beans consumed locally. Average yields are low, however – 1.5 t/ha for maize and 0.7 t/ha for beans – on the approximately 2.5 million hectares of land sown to these crops (40% of the total area harvested) in El Salvador, Guatemala, Honduras, and Nicaragua. In the years to come, a harsher climate together with soil degradation1, widespread poverty, and rural people’s limited access to services and infrastructure will pose challenging obstacles to production. By 2025, these pressures could result in total annual losses of maize and bean production in the four countries of around 350,000 t – with a gross production value of around US$120 million. To ward off this threat to the food security of some 100,000 households, effective adaptation strategies must be developed in collaboration with stakeholders in the maize and bean value chains. These strategies require strong public support and must draw on both scientific and community knowledge

Penalty finite element approximations of the stationary power- law Stokes problem

Finite element approximations of the stationary power-law Stokes problem using penalty formulation are considered. A priori error estimates under appropriate smoothness assumptions on the solutions are established without assuming a discrete version of the BB condition. Numerical solutions are presented by implementing a nonlinear conjugate gradient metho

Tortillas en el comal: los sistemas de maíz y fríjol de América Central y el cambio climático

El maíz y el fríjol son un componente vital de las dietas alimenticias de los humanos y la cultura en América Central. Más de un millón de familias de pequeños agricultores siembran estos cultivos para su subsistencia y producen el 70% del maíz y 100% del fríjol que se consume localmente. Sin embargo, los rendimientos promedio son bajos —1.5 t/ha para maíz y 0.7 t/ha para fríjol — en las cerca de 2.5 millones de hectáreas de tierra sembradas con estos cultivos (40% del área total cosechada) en El Salvador, Guatemala, Honduras y Nicaragua. En los próximos años, el cambio climático junto con la degradación del suelo, la pobreza generalizada y el acceso limitado de la población rural a servicios e infraestructura plantearán obstáculos desafiantes para la producción. Para el 2025, estas presiones podrían producir pérdidas anuales totales de la producción de maíz y fríjol en los cuatro países de alrededor de 350.000 t — con un valor bruto de producción cercano a US$120 millones. Para detener esta amenaza para la seguridad alimentaria de alrededor de 100.000 hogares, se deben desarrollar unas estrategias de adaptación efectivas en colaboración con los interesados directos de las cadenas de valor del maíz y el fríjol. Estas estrategias requieren un apoyo público firme y deben aprovechar tanto el conocimiento científico como el saber de las comunidades

Wheat Blast: A Disease Spreading by Intercontinental Jumps and Its Management Strategies

Wheat blast (WB) caused by Magnaporthe oryzae pathotype Triticum (MoT) is an important fungal disease in tropical and subtropical wheat production regions. The disease was initially identified in Brazil in 1985, and it subsequently spread to some major wheat-producing areas of the country as well as several South American countries such as Bolivia, Paraguay, and Argentina. In recent years, WB has been introduced to Bangladesh and Zambia via international wheat trade, threatening wheat production in South Asia and Southern Africa with the possible further spreading in these two continents. Resistance source is mostly limited to 2NS carriers, which are being eroded by newly emerged MoT isolates, demonstrating an urgent need for identification and utilization of non-2NS resistance sources. Fungicides are also being heavily relied on to manage WB that resulted in increasing fungal resistance, which should be addressed by utilization of new fungicides or rotating different fungicides. Additionally, quarantine measures, cultural practices, non-fungicidal chemical treatment, disease forecasting, biocontrol etc., are also effective components of integrated WB management, which could be used in combination with varietal resistance and fungicides to obtain reasonable management of this disease

Present-day stress orientations and tectonic provinces of the NW Borneo collisional margin

Extent: 15p.Borehole failure observed on image and dipmeter logs from 55 petroleum wells across the NW Borneo collisional margin were used to determine maximum horizontal stress (σH) orientations; combined with seismic and outcrop data, they define seven tectonic provinces. The Baram Delta–Deepwater Fold-Thrust Belt exhibits three tectonic provinces: its inner shelf inverted province (σH is NW-SE, margin-normal), its outer shelf extension province (σH is NE-SW, margin-parallel), and its slope to basin floor compression province (σH is NW-SE, margin-normal). In the inverted province, σH reflects inversion of deltaic normal faults. The σH orientations in the extension and compression provinces reflect deltaic gravitational tectonics. The shale and minibasin provinces have been recognized in offshore Sabah. In the shale province, σH is N010°E, which aligns around the boundary of a massif of mobile shale. Currently, no data are available to determine σH in the minibasin province. In the Balingian province, σH is ESE-WNW, reflecting ESE absolute Sunda plate motions due to the absence of a thick detachment seen elsewhere in NW Borneo. The Central Luconia province demonstrates poorly constrained and variable σH orientations. These seven provinces result from the heterogeneous structural and stratigraphic development of the NW Borneo margin and formed due to complex collisional tectonics and the varied distribution and thicknesses of stratigraphic packages.Rosalind C. King, Mark R. P. Tingay, Richard R. Hillis, Christopher K. Morley, and James Clar

Sexually transmitted infections: challenges ahead.

WHO estimated that nearly 1 million people become infected every day with any of four curable sexually transmitted infections (STIs): chlamydia, gonorrhoea, syphilis, and trichomoniasis. Despite their high global incidence, STIs remain a neglected area of research. In this Commission, we have prioritised five areas that represent particular challenges in STI treatment and control. Chlamydia remains the most commonly diagnosed bacterial STI in high-income countries despite widespread testing recommendations, sensitive and specific non-invasive testing techniques, and cheap effective therapy. We discuss the challenges for chlamydia control and evidence to support a shift from the current focus on infection-based screening to improved management of diagnosed cases and of chlamydial morbidity, such as pelvic inflammatory disease. The emergence and spread of antimicrobial resistance in Neisseria gonorrhoeae is globally recognised. We review current and potential future control and treatment strategies, with a focus on novel antimicrobials. Bacterial vaginosis is the most common vaginal disorder in women, but current treatments are associated with frequent recurrence. Recurrence after treatment might relate to evidence that suggests sexual transmission is integral to the pathogenesis of bacterial vaginosis, which has substantial implications for the development of effective management approaches. STIs disproportionately affect low-income and middle-income countries. We review strategies for case management, focusing on point-of-care tests that hold considerable potential for improving STI control. Lastly, STIs in men who have sex with men have increased since the late 1990s. We discuss the contribution of new biomedical HIV prevention strategies and risk compensation. Overall, this Commission aims to enhance the understanding of some of the key challenges facing the field of STIs, and outlines new approaches to improve the clinical management of STIs and public health