Remediation of Contaminated Soils by Solvent Flushing

Solvent flushing is a potential technique for remediating a waste disposal/spill site contaminated with organic chemicals. This technique involves the injection of a solvent mixture (e.g., water plus alcohols) that enhances contaminant solubility, reduces the retardation factor, and increases the release rates of the contaminants. A simulation model is developed to predict contaminant elution curves during solvent flushing for the case of one‐dimensional, steady flow through a contaminated medium. Column experiments are conducted with a Eustis fine sand that is initially equilibrated with an aqueous naphthalene solution, and then eluted with different methanol‐water mixtures to remove the naphthalene. The model simulations, based on parameter values estimated from literature data, agree well with the measured elution profiles. Solvent flushing experiments, where the soil was initially equilibrated with a solution of naphthalene and anthracene, show that compounds with different retardation factors are separated at low cosolvent contents, while coelution of the compounds occurs at higher contents. In general, the smaller the retardation factor in water and the higher the cosolvent fraction, the faster the contaminant is recovered. The presence of nonequilibrium conditions, soil heterogeneity, and type of cosolvent will influence the time required to recover the contaminant.\u

Mechanical fluidity of fully suspended biological cells

Mechanical characteristics of single biological cells are used to identify and possibly leverage interesting differences among cells or cell populations. Fluidity---hysteresivity normalized to the extremes of an elastic solid or a viscous liquid---can be extracted from, and compared among, multiple rheological measurements of cells: creep compliance vs. time, complex modulus vs. frequency, and phase lag vs. frequency. With multiple strategies available for acquisition of this nondimensional property, fluidity may serve as a useful and robust parameter for distinguishing cell populations, and for understanding the physical origins of deformability in soft matter. Here, for three disparate eukaryotic cell types deformed in the suspended state via optical stretching, we examine the dependence of fluidity on chemical and environmental influences around a time scale of 1 s. We find that fluidity estimates are consistent in the time and the frequency domains under a structural damping (power-law or fractional derivative)model, but not under an equivalent-complexity lumpedcomponent (spring-dashpot) model; the latter predicts spurious time constants. Although fluidity is suppressed by chemical crosslinking, we find that adenosine triphosphate (ATP) depletion in the cell does not measurably alter the parameter, and thus conclude that active ATP-driven events are not a crucial enabler of fluidity during linear viscoelastic deformation of a suspended cell. Finally, by using the capacity of optical stretching to produce near-instantaneous increases in cell temperature, we establish that fluidity increases with temperature---now measured in a fully suspended, sortable cell without the complicating factor of cell-substratum adhesion

Driver-pressure-impact and response-recovery chains in European rivers: observed and predicted effects on BQEs

The report presented in the following is part of the outcome of WISER’s river Workpackage WP5.1 and as such part of the module on aquatic ecosystem management and restoration. The ultimate goal of WP5.1 is to provide guidance on best practice restoration and management to the practitioners in River Basin Management. Therefore, a series of analyses was undertaken, each of which used a part of the WP5.1 database in order to track two major pathways of biological response: 1) the response of riverine biota to environmental pressures (degradation) and 2) the response of biota to the reduction of these impacts (restoration). This report attempts to provide empirical evidence on the environment-biota relationships for both pathways

Simple methods for assessing groundwater resources in low permeability areas of Africa

In many areas throughout Africa, a staggering proportion of wells and boreholes fail. Failure can occur for a number of reasons – inadequate maintenance and community involvement, poor engineering or a lack of water. Often it can be difficult to work out the exact reason after the event. However, in many geological environments the impacts of poorly sited and designed boreholes and wells are a major concern to funding agencies, implementing institutions and local communities. In such areas, good supplies of groundwater cannot be found everywhere, and boreholes and wells must be sited and designed carefully to make use of the available groundwater. To appropriately site and design water sources, the groundwater resources of an area need first to be investigated to understand how water occurs in the ground. In this manual we present some techniques that allow a quick assessment of groundwater resources without requiring much expertise or expense. Some of the techniques are old and established while others are new. However, all techniques have been tested by BGS (and others) in assessing groundwater resources in Africa. This manual does not claim to be a detailed textbook for hydrogeologists – there are enough already (see reading list at the end of the chapter). Rather it is meant as a practicalaid for those involved in the practice of rural water supply, particularly in Africa. Little training or equipment is required for the tests and they can all be carried out in a short space of time. The manual is divided into six sections. The first gives an overview of the groundwater resources of sub-Saharan Africa (SSA) and discusses the scope and detail of investigations required in different geological environments. The remaining chapters describe simple techniques for assessing groundwater resources, from basic reconnaissance to assessing the yield of a borehole. In the appendix are summary sheets of the most common techniques which can be photocopied and used in the field

Modeling Bank Loan LGD of Corporate and SME Segments: A Case Study

Loss given default (LGD) is one of key parameters to estimate credit risk in an internal rating based approach considered in The New Basel Capital Accord. The aim of this paper is to find determinants of LGD using a set of firm loan micro-data of an anonymous Czech commercial bank. The authors find that LGD is driven primarily by the period of loan origination, relative value of collateral, loan size and length of business relationship. Different models employed in their analysis provide similar results; in more complex models, log-log models appear to perform better, implying an asymmetric response of the dependent variable.credit risk, loss given default, fractional responses, ordinal regression, quasi-maximum likelihood estimator

Adaptation kinetics in bacterial chemotaxis

Cells of Escherichia coli, tethered to glass by a single flagellum, were subjected to constant flow of a medium containing the attractant alpha-methyl-DL-aspartate. The concentration of this chemical was varied with a programmable mixing apparatus over a range spanning the dissociation constant of the chemoreceptor at rates comparable to those experienced by cells swimming in spatial gradients. When an exponentially increasing ramp was turned on (a ramp that increases the chemoreceptor occupancy linearly), the rotational bias of the cells (the fraction of time spent spinning counterclockwise) changed rapidly to a higher stable level, which persisted for the duration of the ramp. The change in bias increased with ramp rate, i.e., with the time rate of change of chemoreceptor occupancy. This behavior can be accounted for by a model for adaptation involving proportional control, in which the flagellar motors respond to an error signal proportional to the difference between the current occupancy and the occupancy averaged over the recent past. Distributions of clockwise and counterclockwise rotation intervals were found to be exponential. This result cannot be explained by a response regular model in which transitions between rotational states are generated by threshold crossings of a regular subject to statistical fluctuation; this mechanism generates distributions with far too many long events. However, the data can be fit by a model in which transitions between rotational states are governed by first-order rate constants. The error signal acts as a bias regulator, controlling the values of these constants

Ageing of Natural Rubber under Stress

We report a dynamical-mechanical study of stress relaxation at small deformation in a natural (polyisoprene) rubber well above its glass transition temperature Tg. We find that an almost complete relaxation of stress takes place over very long periods of time, even though the elastic network integrity is fully retained. The relaxation rate and the long-time equilibrium modulus are sensitive functions of temperature which do not follow time-temperature superposition. Many characteristic features of non-ergodic ageing response are apparent at both short and very long times. We interpret the observed behaviour in terms of the properties of rubber crosslinks, capable of isomerisation under stress, and relate the results to recent models of soft glassy rheology.Comment: Latex 2e (EPJ style), 5 EPS figure