Characterization of nanoparticle transport through quartz and dolomite gravels by magnetic resonance imaging

Magnetic resonance imaging (MRI) has tremendous potential for revealing transport processes in engineered and geologic systems. Here, we utilize MRI to image nanoparticle (NP) transport through a saturated coarse-grained system. Commercially available paramagnetically tagged NPs are used; the paramagnetic tag making the NP visible to MRI. NP transport was imaged as NPs migrated through packed columns of quartz and dolomite gravel. Changes in T2-weighted image intensity were calibrated to provide fully quantitative maps of NP concentration at regular time intervals (T 2 being the spin–spin relaxation time of 1H nuclei). Transport of nanoparticles was significantly retarded in dolomite compared to quartz due to electrostatic attraction between nanoparticle and dolomite surfaces. NP concentration profiles were evaluated with the CXTFIT computer package to estimate nanoparticle transport parameters at multiple points along the length of the column. This provided temporally resolved parameters that standard breakthrough curve analysis cannot provide. Particle–surface interaction energy profiles were described through Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. While dispersion coefficients and fast deposition rate constant (k fast) were found to increase with distance, deposition rate constant (k) and collision efficiency (α) were found to decrease with distance. These length-dependant variations have significant scaling-up implications for transport models used to predict NP transport in natural and engineered coarse-grained systems, such as sustainable urban drainage systems and river beds

A Study of the Production of Neutrons for Boron Neutron Capture Therapy using a Proton Accelerator

Boron Neutron Capture Therapy (BNCT) is a binary cancer therapy particularly well-suited to treating aggressive tumours that exhibit a high degree of infiltration of the surrounding healthy tissue. Such tumours, for example of the brain and lung, provide some of the most challenging problems in oncology. The first element of the therapy is boron-10 which is preferentially introduced into the cancerous cells using a carrier compound. Boron-10 has a very high capture cross-section with the other element of the therapy, thermal neutrons, resulting in the production of a lithium nucleus and an alpha particle which destroy the cell they are created in. However, a large flux of neutrons is required and until recently the only source used was a nuclear reactor. In Birmingham, studies of an existing BNCT facility using a 2.8 MeV proton beam and a solid lithium target have found a way to increase the beam power to a sufficient level to allow clinical trials, while maintaining the target solid. In this paper, we will introduce BNCT, describe the work in Birmingham and compare with other accelerator-driven BNCT projects around the World

Impacts of extreme winter warming events on litter decomposition in a sub-Arctic heathland

Arctic climate change is expected to lead to a greater frequency of extreme winter warming events. During these events, temperatures rapidly increase to well above 0 degrees C for a number of days, which can lead to snow melt at the landscape scale, loss of insulating snow cover and warming of soils. However, upon return of cold ambient temperatures, soils can freeze deeper and may experience more freeze-thaw cycles due to the absence of a buffering snow layer. Such loss of snow cover and changes in soil temperatures may be critical for litter decomposition since a stable soil microclimate during winter (facilitated by snow cover) allows activity of soil organisms. Indeed, a substantial part of fresh litter decomposition may occur in winter. However, the impacts of extreme winter warming events on soil processes such as decomposition have never before been investigated. With this study we quantify the impacts of winter warming events on fresh litter decomposition using field simulations and lab studies. Winter warming events were simulated in sub-Arctic heathland using infrared heating lamps and soil warming cables during March (typically the period of maximum snow depth) in three consecutive years of 2007, 2008, and 2009. During the winters of 2008 and 2009, simulations were also run in January (typically a period of shallow snow cover) on separate plots. The lab study included soil cores with and without fresh litter subjected to winter-warming simulations in climate chambers. Litter decomposition of common plant species was unaffected by winter warming events simulated either in the lab (litter of Betula pubescens ssp. czerepanovii), or field (litter of Vaccinium vitis-idaea, and B. pubescens ssp. czerepanovii) with the exception of Vaccinium myrtillus (a common deciduous dwarf shrub) that showed less mass loss in response to winter warming events. Soil CO2 efflux measured in the lab study was (as expected) highly responsive to winter warming events but surprisingly fresh litter decomposition was not. Most fresh litter mass loss in the lab occurred during the first 3-4 weeks (simulating the period after litter fall). In contrast to past understanding, this suggests that winter decomposition of fresh litter is almost nonexistent and observations of substantial mass loss across the cold season seen here and in other studies may result from leaching in autumn, prior to the onset of "true" winter. Further, our findings surprisingly suggest that extreme winter warming events do not affect fresh litter decomposition. Crown Copyright (c) 2009 Published by Elsevier Ltd. All rights reserved

Survey Instrument for Gender Based Violence

This is a proposal for the design of a survey on gender-based violence across Europe. It introduces the purpose of the survey, which shapes the priorities embedded in the proposed design. It identifies the major issues involved in operationalising the concept of gender-based violence for a survey. It identifies some technical issues and how they are best addressed. The focus is on the questionnaire, largely leaving to one side the design of the survey and its strategy for issues such as sampling. This proposal draws on experience of a wide range of surveys and draws on selected parts of the architecture and questionnaire of the Crime Survey for England and Wales (CSEW), modified to fit the present priorities

Spherical Code Key Distribution Protocols for Qubits

Recently spherical codes were introduced as potentially more capable ensembles for quantum key distribution. Here we develop specific key creation protocols for the two qubit-based spherical codes, the trine and tetrahedron, and analyze them in the context of a suitably-tailored intercept/resend attack, both in standard form, and a ``gentler'' version whose back-action on the quantum state is weaker. When compared to the standard unbiased basis protocols, BB84 and six-state, two distinct advantages are found. First, they offer improved tolerance of eavesdropping, the trine besting its counterpart BB84 and the tetrahedron the six-state protocol. Second, the key error rate may be computed from the sift rate of the protocol itself, removing the need to sacrifice key bits for this purpose. This simplifies the protocol and improves the overall key rate.Comment: 4 pages revtex, 2 figures; clarified security analysis. Final version for publicatio

Polarization and frequency disentanglement of photons via stochastic polarization mode dispersion

We investigate the quantum decoherence of frequency and polarization variables of photons via polarization mode dispersion in optical fibers. By observing the analogy between the propagation equation of the field and the Schr\"odinger equation, we develop a master equation under Markovian approximation and analytically solve for the field density matrix. We identify distinct decay behaviors for the polarization and frequency variables for single-photon and two-photon states. For the single photon case, purity functions indicate that complete decoherence for each variable is possible only for infinite fiber length. For entangled two-photon states passing through separate fibers, entanglement associated with each variable can be completely destroyed after characteristic finite propagation distances. In particular, we show that frequency disentanglement is independent of the initial polarization status. For propagation of two photons in a common fiber, the evolution of a polarization singlet state is addressed. We show that while complete polarization disentanglement occurs at a finite propagation distance, frequency entanglement could survive at any finite distance for gaussian states.Comment: 2 figure

Accumulation of entanglement in a continuous variable memory

We study the accumulation of entanglement in a memory device built out of two continuous variable (CV) systems. We address the case of a qubit mediating an indirect joint interaction between the CV systems. We show that, in striking contrast with respect to registers built out of bidimensional Hilbert spaces, entanglement superior to a single ebit can be efficiently accumulated in the memory, even though no entangled resource is used. We study the protocol in an immediately implementable setup, assessing the effects of the main imperfections.Comment: 4 pages, 3 figures, RevTeX

Persistent reduction of segment growth and photosynthesis in a widespread and important sub-Arctic moss species after cessation of three years of experimental winter warming

1. Winter is a period of dormancy for plants of cold environments. However, winter climate is changing, leading to an increasing frequency of stochastic warm periods (winter warming events) and concomitant reductions in snow cover. These conditions can break dormancy for some plants and expose them to freeze-and-thaw stress. Mosses are a major component of high latitude ecosystems, yet the longer-term impacts of such winter warming events on mosses remain unknown. 2. In order to determine the longer-term legacy effects of winter warming events on mosses, we undertook a simulation of these events over three consecutive winters in a sub-Arctic dwarf shrub-dominated open woodland. The mat-forming feathermoss Hylocomium splendens (the most abundant cryptogam in this system), is one of the most widespread Arctic and boreal mosses and plays a key functional role in ecosystems. We studied the ecophysiological performance of this moss during the summers of the experimental period (2007-2009) and in the following years (2010-2013). 3. We show that the previously reported warming-induced reduction in segment growth and photosynthesis during the experimental years was persistent. Four years after the last event, photosynthesis and segment growth were still 30 and 36 % lower than control levels, which was only a slight improvement from 44 and 43 % four years earlier. Winter warming did not affect segment symmetry. During the years after the last simulated event, in both warmed and control plots, chlorophyll fluorescence and segment growth, but not net photosynthesis, increased slightly. The increases were probably driven by increased summer rainfall over the study years, highlighting the sensitivity of this moss to rainfall change. 4. Overall, the legacy effects shown here demonstrate that this widespread and important moss is likely to be significantly disadvantaged in a future sub-Arctic climate where frequent winter warming events may become the norm. Given the key importance of mosses for soil insulation, shelter and carbon sequestration in high-latitude regions, such persistent impacts may ultimately affect important ecosystem functions

Persistent reduction of segment growth and photosynthesis in a widespread and important sub-Arctic moss species after cessation of three years of experimental winter warming

1. Winter is a period of dormancy for plants of cold environments. However, winter climate is changing, leading to an increasing frequency of stochastic warm periods (winter warming events) and concomitant reductions in snow cover. These conditions can break dormancy for some plants and expose them to freeze-and-thaw stress. Mosses are a major component of high latitude ecosystems, yet the longer-term impacts of such winter warming events on mosses remain unknown. 2. In order to determine the longer-term legacy effects of winter warming events on mosses, we undertook a simulation of these events over three consecutive winters in a sub-Arctic dwarf shrub-dominated open woodland. The mat-forming feathermoss Hylocomium splendens (the most abundant cryptogam in this system), is one of the most widespread Arctic and boreal mosses and plays a key functional role in ecosystems. We studied the ecophysiological performance of this moss during the summers of the experimental period (2007-2009) and in the following years (2010-2013). 3. We show that the previously reported warming-induced reduction in segment growth and photosynthesis during the experimental years was persistent. Four years after the last event, photosynthesis and segment growth were still 30 and 36 % lower than control levels, which was only a slight improvement from 44 and 43 % four years earlier. Winter warming did not affect segment symmetry. During the years after the last simulated event, in both warmed and control plots, chlorophyll fluorescence and segment growth, but not net photosynthesis, increased slightly. The increases were probably driven by increased summer rainfall over the study years, highlighting the sensitivity of this moss to rainfall change. 4. Overall, the legacy effects shown here demonstrate that this widespread and important moss is likely to be significantly disadvantaged in a future sub-Arctic climate where frequent winter warming events may become the norm. Given the key importance of mosses for soil insulation, shelter and carbon sequestration in high-latitude regions, such persistent impacts may ultimately affect important ecosystem functions