Chromium at High Pressures: Weak Coupling and Strong Fluctuations in an Itinerant Antiferromagnet

The spin- and charge-density-wave order parameters of the itinerant antiferromagnet chromium are measured directly with non-resonant x-ray diffraction as the system is driven towards its quantum critical point with high pressure using a diamond anvil cell. The exponential decrease of the spin and charge diffraction intensities with pressure confirms the harmonic scaling of spin and charge, while the evolution of the incommensurate ordering vector provides important insight into the difference between pressure and chemical doping as means of driving quantum phase transitions. Measurement of the charge density wave over more than two orders of magnitude of diffraction intensity provides the clearest demonstration to date of a weakly-coupled, BCS-like ground state. Evidence for the coexistence of this weakly-coupled ground state with high-energy excitations and pseudogap formation above the ordering temperature in chromium, the charge-ordered perovskite manganites, and the blue bronzes, among other such systems, raises fundamental questions about the distinctions between weak and strong coupling.Comment: 11 pages, 9 figures (8 in color

Analysis of antenal sensilla patterns of Rhodnius prolixus from Colombia and Venezuela

Antennal sensilla patterns were used to analyze population variation of domestic Rhodnius prolixus from six departments and states representing three biogeographical regions of Colombia and Venezuela. Discriminant analysis of the patterns of mechanoreceptors and of three types of chemoreceptors on the pedicel and flagellar segments showed clear differentiation between R. prolixus populations east and west of the Andean Cordillera. The distribution of thick and thin-walled trichoids on the second flagellar segment also showed correlation with latitude, but this was not seen in the patterns of other sensilla. The results of the sensilla patterns appear to be reflecting biogeographic features or population isolation rather than characters associated with different habitats and lend support to the idea that domestic R. prolixus originated in the eastern region of the Andes.Fil: Esteban, Lyda. Universidad Industrial de Santander; ColombiaFil: Angulo, Víctor Manuel. Universidad Industrial de Santander; ColombiaFil: Dora Feliciangeli, M.. Universidad de Carabobo; VenezuelaFil: Catala, Silvia Susana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja. - Universidad Nacional de La Rioja. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja. - Universidad Nacional de Catamarca. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja. - Secretaría de Industria y Minería. Servicio Geológico Minero Argentino. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja. - Provincia de La Rioja. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja; Argentin

Pasture Management in the US Midwest – An Assessment of Current Practices and Future Opportunities

Managed grazing offers significant potential to improve the sustainability of livestock farms in the US Midwest, however the benefits of managed grazing are largely influenced by the management practices employed on farm. The objective of this study was to gain an understanding of current grazing practices on Midwest farms and to identify the knowledge and support needs of graziers. A total of 185 responses were received from a range of different enterprises including dairy, beef, and sheep production. Results show a substantial degree of variation in grazing management practices between respondents and highlights significant scope for improvement on farms particularly in the areas of pasture measurement and budgeting, and grazing infrastructure. Reported benefits of managed grazing included lower environmental impact, better pasture and animal performance, better animal health and welfare, and lower costs. Challenges with managed grazing included time and labor input, maintaining pasture quantity and quality during the grazing season, adverse weather conditions such as excessive rain and drought, and animal health challenges such as heat stress, parasites and in some cases coyotes. The study highlighted opportunities for research and extension providers to better support farmers with information and advice and identified knowledge gaps in areas such as pasture species selection, soil fertility, grazing infrastructure, pasture budgeting, legumes, and pasture measurement. The study successfully gained an insight into graziers in the Midwest, the outputs of which, will be valuable to a number of key stakeholders going forward, including researchers, extension agents, farmers and policy makers

The carbon cycle in Mexico: past, present and future of C stocks and fluxes

PublishedThe Supplement related to this article is available online at doi:10.5194/bg-13-223-2016-supplement.We modeled the carbon (C) cycle in Mexico with a process-based approach. We used different available products (satellite data, field measurements, models and flux towers) to estimate C stocks and fluxes in the country at three different time frames: present (defined as the period 2000–2005), the past century (1901–2000) and the remainder of this century (2010–2100). Our estimate of the gross primary productivity (GPP) for the country was 2137 ± 1023 TgC yr−1 and a total C stock of 34 506 ± 7483 TgC, with 20 347 ± 4622 TgC in vegetation and 14 159 ± 3861 in the soil. Contrary to other current estimates for recent decades, our results showed that Mexico was a C sink over the period 1990–2009 (+31 TgC yr−1) and that C accumulation over the last century amounted to 1210 ± 1040 TgC. We attributed this sink to the CO2 fertilization effect on GPP, which led to an increase of 3408 ± 1060 TgC, while both climate and land use reduced the country C stocks by −458 ± 1001 and −1740 ± 878 TgC, respectively. Under different future scenarios, the C sink will likely continue over the 21st century, with decreasing C uptake as the climate forcing becomes more extreme. Our work provides valuable insights on relevant driving processes of the C cycle such as the role of drought in drylands (e.g., grasslands and shrublands) and the impact of climate change on the mean residence time of soil C in tropical ecosystems.The lead author (G. Murray-Tortarolo) thanks CONACYT-CECTI, the University of Exeter and Secretaría de Educación Pública (SEP) for their funding of this project. The authors extend their thanks to Carlos Ortiz Solorio and to the Colegio de Posgraduados for the field soil data and to the Alianza Redd+ Mexico for the field biomass data. This project would not have been possible without the valuable data from the CMIP5 models. A. Arneth, G. Murray-Tortarolo, A. Wiltshire and S. Sitch acknowledge the support of the European Commission-funded project LULCC4C (grant no. 603542). A. Wiltshire was partsupported by the Joint UK DECC/Defra Met Office Hadley Centre Climate Programme (GA01101)

Drainage And Sedimentary Response Of The Northern Andes And The Pebas System To Miocene Strike-slip Tectonics: A Source To Sink Study Of The Magdalena Basin

Miocene strike-slip tectonics was responsible for creating and closing short-lived (ca. 6 Ma) passages and the emergence of isolated topography in the Northern Andes. These geological events likely influenced the migration and/or isolation of biological populations. To better understand the paleogeography of the Miocene hinterland and foreland regions in the Northern Andes, we conducted a source-to-sink approach in the Magdalena Basin. This basin is located between the Central and Eastern Cordilleras of Colombia and contains an ample Miocene record, which includes Lower Miocene fine-grained strata and Middle Miocene to Pliocene coarsening-up strata. Our study presents a new data set that includes detrital U–Pb zircon ages (15 samples), sandstone petrography (45 samples) and low-temperature thermochronology from the Southern Central Cordillera (19 dates); which together with previously published data were used to construct a paleogeographical model of the Miocene hinterland and foreland regions in the Northern Andes. The evolution of the Magdalena Basin during the Miocene was characterized by playa and permanent lake systems at ca. 17.5 Ma, which may be related to a marine incursion into NW South America and western Amazonia. The appearance of Eocene to Miocene volcanic sources in the Honda Group after ca. 16 Ma suggests the development of fluvial passages, which connected the Pacific with the western Amazonia and Caribbean regions. These passages were synchronous with a time of Miocene exhumation and topographic growth (ca. 16 to 10 Ma) in the Central Cordillera and the transition from lacustrine to fluvial deposition in the Magdalena Basin. Middle to Late Miocene strike-slip deformation promoted by oblique plate convergence and the oblique collision of the Panamá-Chocó Block likely explains the synchronous along-strike fragmentation and exhumation in the Central Cordillera

Influence of Atomic Surface Structure on the Activity of Ag for the Electrochemical Reduction of CO 2 to CO

The present work was undertaken to elucidate the facet-dependent activity of Ag for the electrochemical reduction of CO to CO. To this end, CO reduction was investigated over Ag thin films with (111), (100), and (110) orientations prepared via epitaxial growth on single-crystal Si wafers with the same crystallographic orientations. This preparation technique yielded larger area electrodes than can be achieved using single-crystals, which enabled the electrocatalytic activity of the corresponding Ag surfaces to be quantified in the Tafel regime. The Ag(110) thin films exhibited higher CO evolution activity compared to the Ag(111) and Ag(100) thin films, consistent with previous single-crystal studies. Density functional theory calculations suggest that CO reduction to CO is strongly facet-dependent, and that steps are more active than highly coordinated terraces. This is the result of both a higher binding energy of the key intermediate COOH as well as an enhanced double-layer electric field stabilization over undercoordinated surface atoms located at step edge defects. As a consequence, step edge defects likely dominate the CO reduction activity observed over the Ag(111) and Ag(100) thin films. The higher activity observed over the Ag(110) thin film is then related to the larger density of undercoordinated sites compared to the Ag(111) and Ag(100) thin films. Our conclusion that undercoordinated sites dominate the CO reduction activity observed over close-packed surfaces highlights the need to consider the contribution of such defects in studies of single-crystal electrodes. 2 2 2 2

Informal rental housing in Colombia: an essential option for low-income households

Around the world, rental housing is frequently seen as secondary to home ownership; yet it plays a crucial role in many countries. In particular, rental housing in urban informal neighbourhoods has a critical but consistently overlooked role in housing the most vulnerable households in the Global South. If better policy and practice are to be pursued, there is a need for improved data on rental housing in urban informal settlements, and in particular, better understanding of ‘the lived experiences of the poor’. This paper responds to these empirical gaps in debates on informality and rental housing with qualitative research on residents’ experiences of informal rented housing in two Colombian cities, Bogotá and Cali. The paper frames informal rental housing as an essential option for diverse low-income households for whom ownership is not accessible or attractive. In this way, it also contributes to policy and theoretical debates calling for a better understanding of the dynamics, possibilities and potential of informal housing

CYCLICITY IN THE CERREJON FORMATION

El patrón de sedimentación de la Formación Cerrejón es característicamente repetitivo y monótono. Presenta un espesor estratigráfico de aproximadamente 1000 m y una longitud en rumbo de al menos 30 km a lo largo del Valle del Cesar - Ranchería. Esta monotonía ha sido utilizada para definir ocho asociaciones de litofacies y tres secuencias típicas con las que es posible describir la totalidad de esta unidad. El arreglo vertical de dichas asociaciones de litofacies permite establecer los patrones de apilamiento, pero no el mecanismo generador de la repetición y arreglo vertical de estos ciclos. Este estudio pretende reconocer patrones de ciclicidad y así establecer las posibles relaciones causales de estos ciclos, para lo cual se utilizó modelamiento sintético como primera aproximación. Los resultados de este modelamiento sugieren que con subsidencia tectónica, tasas de sedimentación constantes y una variación rítmica en el nivel de base puede reproducirse el patrón progradacional puntuado de la Formación Cerrejón. Únicamente subsidencia tectónica o termal, compactación diferencial, o fenómenos autocíclicos podrían difícilmente generar el patrón observado en tal extensión regional. Palabras clave: Patrones ciclo, monotonía, modelamiento sintético, subsidencia tectónica        The Cerrejon Formation exhibits a stacking pattern characteristically repetitive and monotonous. It has a stratigraphic thickness of about 1000 m and a strike-length of at least 30 km through Cesar - Ranchería Valley. This monotony has been used to define eight lithofacies assemblages, and three typical sequences that describe the entire unit. The vertical arrangement of these lithofacies assemblages allows the recognition of stacking patterns, but not the mechanisms that generated the repetition and the vertical arrangement of these patterns. This study aims to identify cyclicity in the record and to establish a possible causal relationship for these patterns. To do this, forward modeling was used and preliminarily indicates that the punctuated progradational pattern observed in the Cerrejón Formation can be simulated keeping constant tectonic subsidence, sedimentation rates, and forcing a base level oscillation. Only tectonic or thermal subsidence, differential compaction or autocyclic phenomena could not easily generate the observed pattern on such regional extension. Key words: Cycle patterns, monotony, forward modelling, tectonic subsidence. &nbsp

CYCLICITY IN THE CERREJON FORMATION

El patrón de sedimentación de la Formación Cerrejón es característicamente repetitivo y monótono. Presenta un espesor estratigráfico de aproximadamente 1000 m y una longitud en rumbo de al menos 30 km a lo largo del Valle del Cesar - Ranchería. Esta monotonía ha sido utilizada para definir ocho asociaciones de litofacies y tres secuencias típicas con las que es posible describir la totalidad de esta unidad. El arreglo vertical de dichas asociaciones de litofacies permite establecer los patrones de apilamiento, pero no el mecanismo generador de la repetición y arreglo vertical de estos ciclos. Este estudio pretende reconocer patrones de ciclicidad y así establecer las posibles relaciones causales de estos ciclos, para lo cual se utilizó modelamiento sintético como primera aproximación. Los resultados de este modelamiento sugieren que con subsidencia tectónica, tasas de sedimentación constantes y una variación rítmica en el nivel de base puede reproducirse el patrón progradacional puntuado de la Formación Cerrejón. Únicamente subsidencia tectónica o termal, compactación diferencial, o fenómenos autocíclicos podrían difícilmente generar el patrón observado en tal extensión regional. Palabras clave: Patrones ciclo, monotonía, modelamiento sintético, subsidencia tectónica        The Cerrejon Formation exhibits a stacking pattern characteristically repetitive and monotonous. It has a stratigraphic thickness of about 1000 m and a strike-length of at least 30 km through Cesar - Ranchería Valley. This monotony has been used to define eight lithofacies assemblages, and three typical sequences that describe the entire unit. The vertical arrangement of these lithofacies assemblages allows the recognition of stacking patterns, but not the mechanisms that generated the repetition and the vertical arrangement of these patterns. This study aims to identify cyclicity in the record and to establish a possible causal relationship for these patterns. To do this, forward modeling was used and preliminarily indicates that the punctuated progradational pattern observed in the Cerrejón Formation can be simulated keeping constant tectonic subsidence, sedimentation rates, and forcing a base level oscillation. Only tectonic or thermal subsidence, differential compaction or autocyclic phenomena could not easily generate the observed pattern on such regional extension. Key words: Cycle patterns, monotony, forward modelling, tectonic subsidence. &nbsp