Capping of an Extremely Soft Neutralised Uranium Tailings − A Case History in Environmental Geomechanics

The environmental regulation for Ranger Uranium Mine, in the Northern Territory, Australia, requires the stored tailings (irrespective of where they are finally stored, whether in a tailings dam or in mined-out pits) be capped safely to minimise contamination, erosion and radon gas emission, and also to enable the site to be rehabilitated through revegetation. The hydraulically deposited neutralised tailings in the existing tailings dam have a ‘gel-like’ structure which hinders the consolidation process. Consequently, the in situ tailings have a high water content, low permeability and extremely low shear strength. The present paper describes the case history of a successful capping trial constructed on these extremely soft tailings. Environmental geotechnical issues are highlighted and investigated. Results, especially the characteristics of the tailings observed during the construction and subsequent monitoring, are also discussed

The Merti aquifer (Kenya), a sustainable water resource for the Dadaab refugee camps and local communities?

The Merti aquifer (Kenya) is the only permanent water resource for the supply of the Dadaab refugee camps and local community. Risk of well salinisation and water level depletion has led to the concerns regarding sustainability of groundwater management. A methodology was developed to quantify groundwater recharge, based on hydrogeological data analysis, linking river discharge rates to groundwater recharge by combining remote sensing techniques with surface/groundwater numerical modelling. Also, the risk of salinisation of wells was assessed by means of numerical modelling combined with data provided from a groundwater monitoring network. Groundwater recharge estimates yielded 50 to 100 times higher values than previous studies, suggesting a multi-layered aquifer system. Since abstractions are concentrated within only one aquifer horizon of the system, they were found to be close to recharge rates. Hence, groundwater prospection of deeper horizons could reveal a potential for new groundwater resources in the area

Bias-Dependent Generation and Quenching of Defects in Pentacene

We describe a defect in pentacene single crystals that is created by bias stress and persists at room temperature for an hour in the dark but only seconds with 420nm illumination. The defect gives rise to a hole trap at Ev + 0.38eV and causes metastable transport effects at room temperature. Creation and decay rates of the hole trap have a 0.67eV activation energy with a small (108 s-1) prefactor, suggesting that atomic motion plays a key role in the generation and quenching process.Comment: 10 pages, 3 figure

Femscan -The development of the image dissector to a tube with femtosecond time resolution

ABSTRACT The Image Dissector was one of the firsts all electronic TV tubes and was described by Farnsworth in 1934. (Ref 1). Fifty years later, in 1983, more modern image dissectors were used to measure the electron bunch lengths in synchrotrons. The advent of modern computers and high-speed electronics enables these rather elderly tubes to be used in exciting new applications. This paper described how we have adapted the image dissector to enable the development of low cost instruments with exceptional bandwidth, sensitivity and sampling rate for optical signals

Suppression of hole-hole scattering in GaAs/AlGaAs heterostructures under uniaxial compression

Resistance, magnetoresistance and their temperature dependencies have been investigated in the 2D hole gas at a [001] p-GaAs/Al$_{0.5}$Ga$_{0.5}$As heterointerface under [110] uniaxial compression. Analysis performed in the frame of hole-hole scattering between carriers in the two spin splitted subbands of the ground heavy hole state indicates, that h-h scattering is strongly suppressed by uniaxial compression. The decay time $\tau_{01}$ of the relative momentum reveals 4.5 times increase at a uniaxial compression of 1.3 kbar.Comment: 5 pages, 3 figures. submitted to Phys.Rev.

Beam tests of a large-scale TORCH time-of-flight demonstrator

The TORCH time-of-flight detector is designed to provide particle identification in the momentum range 2-10 GeV/c over large areas. The detector exploits prompt Cherenkov light produced by charged particles traversing a 10 mm thick quartz plate. The photons propagate via total internal reflection and are focused onto a detector plane comprising position-sensitive Micro-Channel Plate Photo-Multiplier Tubes (MCP-PMT) detectors. The goal is to achieve a single-photon timing resolution of 70 ps, giving a timing precision of 15 ps per charged particle by combining the information from around 30 detected photons. The MCP-PMT detectors have been developed with a commercial partner (Photek Ltd, UK), leading to the delivery of a square tube of active area 53 $\times$ 53mm$^2$ with a granularity of 8 $\times$ 128 pixels equivalent. A large-scale demonstrator of TORCH, having a quartz plate of dimensions 660 $\times$ 1250 $\times$ 10 mm$^3$ and read out by a pair of MCP-PMTs with custom readout electronics, has been verified in a test beam campaign at the CERN PS. Preliminary results indicate that the required performance is close to being achieved. The anticipated performance of a full-scale TORCH detector at the LHCb experiment is presented.Comment: 12 pages, 7 figures, Paper submitted to Nuclear Instruments & Methods in Physics Research, Section A - Special Issue VCI 201

Gynecological cancers: an alternative approach to healing

Grief and hope are two conflicting emotions that a patient recently diagnosed with cancer has to master. The real challenge for gynecologic oncologists is how to reach out. Conventional wisdom states that offering patients focus and belief when combating cancer in their lives allows them to embrace hope with greater confidence, which minimizes their grief. Three pictorial models are presented: ‘4-cusp approach’ model used at the initial consultation; ‘tapestry of bereavement or landscape of grief’ model at the postsurgery consultation; and ‘Venn-diagram’ model at any time during patient management. We have applied these models in our practice and believe that they can act as a fulcrum for the patient, the family and healthcare team around which therapy should be centered., Grief and hope are two emotions that a patient faces if diagnosed with cancer. The real challenge for the doctor is how to reach out and help the patient through this process. A doctor's role may be to offer focus and belief to the patient which may allow her to embrace hope with greater confidence. This will hopefully lessen the grief. We present three models which we believe can play a crucial part: ‘4-cusp approach’ used at the initial consultation; ‘tapestry of bereavement or landscape of grief model’ at the postsurgery consultation; and ‘Venn-diagram model’ at any time during care

Realistic performance prediction in nanostructured solar cells as a function of nanostructure dimensionality and density

The behavior of quantum dot, quantum wire, and quantum well InAs/GaAs solar cells is studied with a very simplified model based on experimental results in order to assess their performance as a function of the low bandgap material volume fraction fLOW. The efficiency of structured devices is found to exceed the efficiency of a non-structured GaAs cell, in particular under concentration, when fLOW is high; this condition is easier to achieve with quantum wells. If three different quasi Fermi levels appear with quantum dots the efficiency can be much higher