High-resolution permeability determination and two-dimensional porewater flow in sandy sediment

A new, inexpensive method is proposed to measure permeability in natural sandy sediment with high spatial resolution. This methodology allows for a reconstruction of the vertical permeability anisotropy in natural sediments, with a depth resolution of a few millimeters. Thus, the possible intrusion depth of advective flow over the water-sediment interface of sandy sediments can be deduced. Shipboard measurements on five natural sandy sediment cores taken from North Sea sediments are used to demonstrate that both the direction and magnitude of the second-order permeability tensor can be calculated from direct measurements using this method. This presents a major improvement over previous methods particularly in the context of quantifying flow and reaction in permeable sediments.info:eu-repo/semantics/publishedVersio

Effect of Glacial/Interglacial Recharge Conditions on Flow of Meteoric Water Through Deep Orogenic Faults: Insights Into the Geothermal System at Grimsel Pass, Switzerland

Many meteoric-recharged, fault-hosted geothermal systems in amagmatic orogenic belts have been active through the Pleistocene glacial/interglacial climate fluctuations. The effects of climate-induced recharge variations on fluid flow patterns and residence times of the thermal waters are complex and may influence how the geothermal and mineralization potential of the systems are evaluated. We report systematic thermal-hydraulic simulations designed to reveal the effects of recharge variations, using a model patterned on the orogenic geothermal system at Grimsel Pass in the Swiss Alps. Previous studies have shown that fault-bounded circulation of meteoric water is driven to depths of ∼10 km by the high alpine topography. Simulations suggest that the current single-pass flow is typical of interglacial periods, during which (a) meteoric recharge into the fault is high (above tens of centimeters per year), (b) conditions are at or somewhat below the critical Rayleigh number, and (c) hydraulic connectivity along the fault plane is extensive (an extent of at least 10 km into increasingly higher terrain is required to explain the 10 km penetration depth). The subcritical condition constrains the bulk fault permeability to <1e-14 m2. In contrast, the limited recharge during the numerous Pleistocene glaciation events likely induced a layered flow system, with single-pass flow confined to shallow depths while non-Rayleigh convection occurred deeper in the fault. The same layering can be observed at low aspect ratios (length/depth) of the fault plane, when the available recharge area limits flux through the fault

Unbalanced allocations

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mathematics, 2010.Cataloged from PDF version of thesis.Includes bibliographical references (p. 65).Recently, there has been much research on processes that are mostly random, but also have a small amount of deterministic choice; e.g., Achlioptas processes on graphs. This thesis builds on the balanced allocation algorithm first described by Azar, Broder, Karlin and Upfal. Their algorithm (and its relatives) uses randomness and some choice to distribute balls into bins in a balanced way. Here is a description of the opposite family of algorithms, with an analysis of exactly how unbalanced the distribution can become.by Amanda E. Redlich.Ph.D

Growing Stronger: Strength Training for Older Adults

In choosing to read this book, you have taken the first step on a journey toward greater strength and vitality. Growing Stronger was written for you—the older adult who wants to grow stronger, healthier, more active, and more independent. You may be inactive or only mildly active at the moment. You may know that regular exercise is important for your health and well-being and want to get started on a program of physical activity. But you may feel that you don’t have the necessary information. Perhaps you are concerned that because of your age or health problems physical activity may not be safe for you. Or perhaps you have had trouble finding or staying with a suitable program. This book gives you a safe, simple, and highly effective exercise program based on the principles of strength training. Studies at laboratories around the world have shown that strength training benefits women and men of all ages and all levels of fitness. According to Physical Activity and Health: A Report of the Surgeon General (1996), experts agree that aerobic activities should be supplemented with strength-developing exercises at least twice per week

Large effect of irradiance on hydrogen isotope fractionation of alkenones in <i>Emiliania huxleyi</i>

The hydrogen isotopic (dD) composition of long-chain alkenones produced by certain haptophyte algae has been suggested as a potential proxy for reconstructing paleo sea surface salinity. However, environmental parameters other than salinity may also affect the dD of alkenones. We investigated the impact of the level of irradiance on hydrogen isotopic fractionation of alkenones versus growth water by cultivating two strains of the cosmopolitan haptophyte Emiliania huxleyi at different light intensities. The hydrogen isotope fractionation decreased by approximately 40‰ when irradiance was increased from 15 to 200 µmol photons m-2 s-1 above which it was relatively constant. The response is likely a direct effect of photosystem I and II activity as the relationship of the fractionation factor a versus light intensity can be described by an Eilers–Peeters photosynthesis model. This irradiance effect is in agreement with published dD data of alkenones derived from suspended particulate matter collected from different depths in the photic zone of the Gulf of California and the eastern tropical North Pacific. However, haptophyte algae tend to bloom at relatively high light intensities (>500 µmol photons m-2 s-1) occurring at the sea surface, at which hydrogen isotope fractionation is relatively constant and not affected by changes in light intensity. Alkenones accumulating in the sediment are likely mostly derived from these surface water haptophyte blooms, when the largest amount of biomass is produced. Therefore, the observed irradiance effect is unlikely to affect the applicability of the hydrogen isotopic composition of sedimentary long chain alkenones as a proxy for paleosalinit