title: Oxidation of surface sediment: effects of disturbance depth and seawater flow speed

authors: Vopel, Kay

subjects: cohesive sediment

abstract: Periodic disturbance of surface sediment is a natural feature of marine environments. Following exposure to oxygenated seawater, the disturbed sediment oxidises leading to the recovery of its surface chemistry. Despite its importance for the ecology of the sediment–water interface, the dynamics of this recovery is not well known. We studied the effects of disturbance depth and seawater flow speed on the oxidation of estuarine cohesive sediment in a laboratory flume with microelectrodes. We removed surface sediment to 2 depths (5 and 50 mm) and then observed changes in sediment O₂ distribution and consumption over 1 h under conditions of slow and fast flow (3.5 and 7.5 cm s–1). Measurements were repeated 1 d later. The consumption of O₂ in the treated sediments reached a ‘quasi stable state’ within 7 h (50 mm depth) and 16 h (5 mm depth) characterised by very slow changes due to slow oxidation of reduced solids. Faster flow increased the rate at which sediment from 50 mm depth oxidised but not that of the sediment from 5 mm depth. After 20 to 24 h, sediments disturbed to 50 and 5 mm depths still differed in O₂ distribution and consumption, both from each other and from the pre-treatment sediment. Differences in the response of pore water O₂ distribution to an abrupt increase in flow speed (3.5 to 7.5 cm s–1) were also still evident at this time. Our measurements confirmed the results of previous theoretical analyses in that they indicate that the duration of the recovery of the surface sediment chemistry from disturbance and the chemical properties of the recovering sediment are controlled by the kinetics of solute and solid oxidation. Oxidation of reduced solids in disturbed sediment can result in a characteristic chemical signature at the sediment surface that lasts in the order of at least days.

text: Oxidation of surface sediment: effects of disturbance depth and seawater flow speed Periodic disturbance of surface sediment is a natural feature of marine environments. Following exposure to oxygenated seawater, the disturbed sediment oxidises leading to the recovery of its surface chemistry. Despite its importance for the ecology of the sediment–water interface, the dynamics of this recovery is not well known. We studied the effects of disturbance depth and seawater flow speed on the oxidation of estuarine cohesive sediment in a laboratory flume with microelectrodes. We removed surface sediment to 2 depths (5 and 50 mm) and then observed changes in sediment O₂ distribution and consumption over 1 h under conditions of slow and fast flow (3.5 and 7.5 cm s–1). Measurements were repeated 1 d later. The consumption of O₂ in the treated sediments reached a ‘quasi stable state’ within 7 h (50 mm depth) and 16 h (5 mm depth) characterised by very slow changes due to slow oxidation of reduced solids. Faster flow increased the rate at which sediment from 50 mm depth oxidised but not that of the sediment from 5 mm depth. After 20 to 24 h, sediments disturbed to 50 and 5 mm depths still differed in O₂ distribution and consumption, both from each other and from the pre-treatment sediment. Differences in the response of pore water O₂ distribution to an abrupt increase in flow speed (3.5 to 7.5 cm s–1) were also still evident at this time. Our measurements confirmed the results of previous theoretical analyses in that they indicate that the duration of the recovery of the surface sediment chemistry from disturbance and the chemical properties of the recovering sediment are controlled by the kinetics of solute and solid oxidation. Oxidation of reduced solids in disturbed sediment can result in a characteristic chemical signature at the sediment surface that lasts in the order of at least days.

year: 2010

title: Charge capacity characteristics of a Lithium Nickel-Cobalt-Aluminum Oxide battery show fractional-derivative behavior

authors: Wilson, Marcus T.

subjects: cs.SY

abstract: Batteries experience capacity offset where available charge depends on the
rate at which this charge is drawn. In this work we analyze the capacity offset
of a 4.8 A h lithium nickel-cobalt-aluminium oxide battery using an equivalent
circuit model of a fractional capacitor in series with a resistor. In this
case, the available charge, in theory, becomes infinite in the limit of
infinitesimal rate. We show that the fractional properties of the capacitor can
be extracted from the charge against rate plot. We then use a network of RC
elements to represent the fractional capacitor in order to simulate the data
with Matlab. We find that the fractional exponent alpha obtained in this way,
0.971, agrees with that obtained in a more traditional manner from an impedance
versus frequency plot, although the fractional capacity does not. Such an
approach demonstrates the importance of a fractional description for capacity
offset even when an element is nearly a pure capacitor and is valuable for
predictions of state-of-charge when low currents are drawn.

text: Charge capacity characteristics of a Lithium Nickel-Cobalt-Aluminum Oxide battery show fractional-derivative behavior Batteries experience capacity offset where available charge depends on the
rate at which this charge is drawn. In this work we analyze the capacity offset
of a 4.8 A h lithium nickel-cobalt-aluminium oxide battery using an equivalent
circuit model of a fractional capacitor in series with a resistor. In this
case, the available charge, in theory, becomes infinite in the limit of
infinitesimal rate. We show that the fractional properties of the capacitor can
be extracted from the charge against rate plot. We then use a network of RC
elements to represent the fractional capacitor in order to simulate the data
with Matlab. We find that the fractional exponent alpha obtained in this way,
0.971, agrees with that obtained in a more traditional manner from an impedance
versus frequency plot, although the fractional capacity does not. Such an
approach demonstrates the importance of a fractional description for capacity
offset even when an element is nearly a pure capacitor and is valuable for
predictions of state-of-charge when low currents are drawn.

year: 2021

title: An Interactive User Management System for Multilingual Documents: A case study of the Pei Jones collection

authors: Cader, Papitha

subjects: Greenstone Digital Library

abstract: Can general purpose DL software architecture be designed to provide a flexible environment that supports both the management and end-user roles through a single unified web interface? In particular we take the collected correspondence of the Māori scholar Dr. Pei Jones and undertake case study of how this approach can be applied in a practical way.

text: An Interactive User Management System for Multilingual Documents: A case study of the Pei Jones collection Can general purpose DL software architecture be designed to provide a flexible environment that supports both the management and end-user roles through a single unified web interface? In particular we take the collected correspondence of the Māori scholar Dr. Pei Jones and undertake case study of how this approach can be applied in a practical way.

year: 2012