Detecting groundwater discharge dynamics from point-to-catchment scale in a lowland stream : Combining hydraulic and tracer methods

Acknowledgements. We would like to thank members of the Northern Rivers Institute, Aberdeen University, for helpful discussions of data. We also thank Lars Rasmussen, Jolanta Kazmierczak and Charlotte Ditlevsen for help in the field. This study is part of the Hydrology Observatory, HOBE (http://www.hobe.dk), funded by the Villum Foundation and was as well funded by the Aarhus University Research Foundation.Peer reviewedPublisher PD

Hydrothermal alteration of upper oceanic crust formed at fast spreading rates

Hydrothermal circulation plays a fundamental role in the chemical transfer from deep in the Earth’s interior to the ocean crust, the oceans and the atmosphere. It is also on of the principal mechanisms for heat transfer from the mantle to the oceans, atmosphere and ultimately, outer space. This process fundamentally influences the composition of the ocean crust during formation and aging as it spreads away from the ridge axis. However, despite much research into hydrothermal alteration of oceanic crust questions still remain including: the thermal and chemical evolution of hydrothermal fluids, the geometry of hydrothermal fluid flow, and the factors that control the nature and extent of hydrothermal alteration of oceanic crust.In this study, whole rock and secondary mineral characteristics of drilled-in situ ocean crust are used to (i) Characterise hydrothermal alteration for a range of drilled, in-situ fast spread ocean crust sites (ii) assess the factors that control hydrothermal alteration within fast spread ocean crust and (iii) assess the evolution and architecture of hydrothermal fluid.Deep Sea Drilling Project, Ocean Drilling Program, and Integrated Ocean Drilling Program Sites 504, 896, 843, 1179, 1149, 1224, 1243 and 1256 represent some the most significant penetrations into the upper portion of intermediate and fast spread crust to date. Analyses of whole rock chemical changes, Sr, O. C and S isotope systematics, petrographic observations and analysis of secondary minerals indicate that all sites underwent variable degrees of cold seawater dominated hydrothermal alteration. All these sites represent variations in the composition of the upper crust, basement topography, sedimentation rates, spreading rates, capping rocks, and age. Comparisons between these factors and style and intensity of alteration for each site indicate that spreading rate and age exherts the strongest influence on hydrothermal activity.Sites 1256 and 504 are the only sites in which both low temperature and high temperature alteration are recovered, both sites now have complete chemical and isotopic records which trace the evolution of hydrothermal fluid through the crust. Chemical and isotopic analyses of anhydrite within the ocean crust and consideration of the sulfur budget at these sites imply that the majority of hydrothermal fluid is heated to moderate temperatures (~250oC) and returns to the oceans as warm diffuse fluids at unaccounted for venting sites

Response of a particle in a one-dimensional lattice to an applied force: Dynamics of the effective mass

We study the behaviour of the expectation value of the acceleration of a particle in a one-dimensional periodic potential when an external homogeneous force is suddenly applied. The theory is formulated in terms of modified Bloch states that include the interband mixing induced by the force. This approach allows us to understand the behaviour of the wavepacket, which responds with a mass that is initially the bare mass, and subsequently oscillates around the value predicted by the effective mass. If Zener tunneling can be neglected, the expression obtained for the acceleration of the particle is valid over timescales of the order of a Bloch oscillation, which are of interest for experiments with cold atoms in optical lattices. We discuss how these oscillations can be tuned in an optical lattice for experimental detection.Comment: 15 pages, 12 figure

Nanoscale shear cohesion between cement hydrates: The role of water diffusivity under structural and electrostatic confinement

\ua9 2022 The Authors. The calcium silicate hydrate (C-S-H) controls most of the final properties of the cement paste, including its mechanical performance. It is agreed that the nanometer-sized building blocks that compose the C-S-H are the origin of the mechanical properties. In this work, we employ atomistic simulations to investigate the relaxation process of C-S-H nanoparticles subjected to shear stress. In particular, we study the stress relaxation by rearrangement of these nanoparticles via sliding adjacent C-S-H layers separated by a variable interfacial distance. The simulations show that the shear strength has its maximum at the bulk interlayer space, called perfect contact interface, and decreases sharply to low values for very short interfacial distances, coinciding with the transition from 2 to 3 water layers and beginning of the water flow. The evolution of the shear strength as a function of the temperature and ionic confinement confirms that the water diffusion controls the shear strength

From Insult to Injury: How Disputes Begin and Escalate among Adolescents and Young Adults in Medellin, Colombia

This article aims to contribute to the understanding of circumstances, causes of initiation, and process of escalation of physical disputes or fights resulting in physical injury. We analyzed data from a case-control study of perpetrators of violence between the ages of 15 to 24 (n=373) in the city of Medellín, Colombia. The findings show that 89% of conflicts resulting in injury took place in public places and most often involved males (78%). Six percent involved the consumption of alcohol, 20% reported having used illicit drugs before the initiation of the confrontation. Circa 50% of disputes began because of verbal aggression. Alcohol consumption was found to be associated with verbal aggression towards a friend or companion but not to other circumstances that start disputes. Drug use was not associated with the initiation of disputes. In 18.5% of the cases, a weapon was used while 5% of these disputes ended in a homicide. In none of the cases in which homicide was the outcome was there bystander intervention. In contrast, homicide did not result in the cases in which bystanders intervened