2,109 research outputs found
Ab-Initio Calculation of Molecular Aggregation Effects: a Coumarin-343 Case Study
We present time-dependent density functional theory (TDDFT) calculations for
single and dimerized Coumarin-343 molecules in order to investigate the quantum
mechanical effects of chromophore aggregation in extended systems designed to
function as a new generation of sensors and light-harvesting devices. Using the
single-chromophore results, we describe the construction of effective
Hamiltonians to predict the excitonic properties of aggregate systems. We
compare the electronic coupling properties predicted by such effective
Hamiltonians to those obtained from TDDFT calculations of dimers, and to the
coupling predicted by the transition density cube (TDC) method. We determine
the accuracy of the dipole-dipole approximation and TDC with respect to the
separation distance and orientation of the dimers. In particular, we
investigate the effects of including Coulomb coupling terms ignored in the
typical tight-binding effective Hamiltonian. We also examine effects of orbital
relaxation which cannot be captured by either of these models
ENV-654: NUMERICAL MODELLING OF SMOULDERING COMBUSTION TO OPTIMIZE EX SITU SOIL TREATMENT SYSTEM DESIGN
There is widespread soil contamination at thousands of cites in Canada resulting from the historical improper storage and disposal of industrial liquids (Story et al., 2014). Large financial resources are allocated to remediation efforts due to the human and environmental health risks associated with exposure to such contamination, with over $582 million CAN spent on remediation in 2014-15 by the Canadian government alone (Treasury Board of Canada, 2016). Our scientific understanding of site remediation has evolved greatly over the past decades and it is now widely accepted that remediation of the contaminant source zone is necessary to achieve a high level of long-term remediation (Kueper et al., 2014). Non-aqueous phase liquids, or NAPLS, are one of the most prevalent contaminants at contaminated sites and are challenging to remediate due to their highly recalcitrant nature (Kueper et al., 2003). Although many remediation technologies have been developed over the past decades, the challenge in source zone remediation of NAPLs persists.
The application of smouldering combustion to treat NAPL contaminated soils has been proven as an effective technology with both the laboratory experiments and applied in situ at a field site (Switzer et al., 2009, Pironi et al., 2011, Switzer et al, 2014, Salman et al., 2015, Scholes et al., 2015). This technology, titled “Self-sustaining treatment for active remediation”, or STAR, utilizes the high calorific value of NAPLs to ignite and sustain a smouldering oxidation reaction, effectively destroying the contaminant in the process. A phenomenological model developed by MacPhee et al. (2012) uniquely combined a multiphase flow model, perimeter expansion model, and analytical expression for the forward smouldering front velocity. This model is able to predict the propagation of the reaction front in response to the interplay between a heterogeneous distribution of permeability and the time-dependent distribution of air flux. After subsequent calibration by Hasan et al. (2014), the model was shown to correctly predict the ultimate extent and time of remediation during treatment for 2D lab scale experiments
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Biogeochemical cycles and biodiversity as key drivers of ecosystem services provided by soils
Soils play a pivotal role in major global biogeochemical cycles (carbon, nutrient, and water), while hosting the largest diversity of organisms on land. Because of this, soils deliver fundamental ecosystem services, and management to change a soil process in support of one ecosystem service can either provide co-benefits to other services or result in trade-offs. In this critical review, we report the state-of-the-art understanding concerning the biogeochemical cycles and biodiversity in soil, and relate these to the provisioning, regulating, supporting, and cultural ecosystem services which they underpin. We then outline key knowledge gaps and research challenges, before providing recommendations for management activities to support the continued delivery of ecosystem services from soils. We conclude that, although soils are complex, there are still knowledge gaps, and fundamental research is still needed to better understand the relationships between different facets of soils and the array of ecosystem services they underpin, enough is known to implement best practices now. There is a tendency among soil scientists to dwell on the complexity and knowledge gaps rather than to focus on what we do know and how this knowledge can be put to use to improve the delivery of ecosystem services. A significant challenge is to find effective ways to share knowledge with soil managers and policy makers so that best management can be implemented. A key element of this knowledge exchange must be to raise awareness of the ecosystems services underpinned by soils and thus the natural capital they provide. We know enough to start moving in the right direction while we conduct research to fill in our knowledge gaps. The lasting legacy of the International Year of Soils in 2015 should be for soil scientists to work together with policy makers and land managers to put soils at the centre of environmental policy making and land management decisions.</p
Financial correlations at ultra-high frequency: theoretical models and empirical estimation
A detailed analysis of correlation between stock returns at high frequency is
compared with simple models of random walks. We focus in particular on the
dependence of correlations on time scales - the so-called Epps effect. This
provides a characterization of stochastic models of stock price returns which
is appropriate at very high frequency.Comment: 22 pages, 8 figures, 1 table, version to appear in EPJ
Exciton bimolecular annihilation dynamics in supramolecular nanostructures of conjugated oligomers
We present femtosecond transient absorption measurements on -conjugated
supramolecular assemblies in a high pump fluence regime.
Oligo(\emph{p}-phenylenevinylene) monofunctionalized with
ureido-\emph{s}-triazine (MOPV) self-assembles into chiral stacks in dodecane
solution below 75C at a concentration of M. We
observe exciton bimolecular annihilation in MOPV stacks at high excitation
fluence, indicated by the fluence-dependent decay of B-exciton
spectral signatures, and by the sub-linear fluence dependence of time- and
wavelength-integrated photoluminescence (PL) intensity. These two
characteristics are much less pronounced in MOPV solution where the phase
equilibrium is shifted significantly away from supramolecular assembly,
slightly below the transition temperature. A mesoscopic rate-equation model is
applied to extract the bimolecular annihilation rate constant from the
excitation fluence dependence of transient absorption and PL signals. The
results demonstrate that the bimolecular annihilation rate is very high with a
square-root dependence in time. The exciton annihilation results from a
combination of fast exciton diffusion and resonance energy transfer. The
supramolecular nanostructures studied here have electronic properties that are
intermediate between molecular aggregates and polymeric semiconductors
Transparency, trust and minimizing burden to increase recruitment and retentio in trials: A systematic review
Objective: To describe patient perspectives on recruitment and retention in clinical trials. Study Design and Setting: Systematic review of qualitative studies that reported the perspective of adult patients with any health condition who accepted or declined to participate in clinical trials. Results: Sixty-three articles involving 1681 adult patients were included. Six themes were identified. Four themes reflected barriers: ambiguity of context and benefit – patients were unaware of the research question and felt pressured in making decisions; lacking awareness of opportunities – some believed health professionals obscured trials opportunities, or felt confused because of language barriers; wary of added burden – patients were without capacity because of sickness or competing priorities; and skepticism, fear and mistrust – patients feared loss of privacy, were suspicious of doctor's motivation, afraid of being a guinea pig, and disengaged from not knowing outcomes. Two themes captured facilitators: building confidence – patients hoped for better treatment, were supported from family members and trusted medical staff; and social gains and belonging to the community – altruism, a sense of belonging and peer encouragement motivated participation in trials. Conclusion: Improving the visibility and transparency of trials, supporting informed decision making, minimizing burden, and ensuring confidence and trust may improve patient participation in trials
Angular sensitivity of blowfly photoreceptors: intracellular measurements and wave-optical predictions
The angular sensitivity of blowfly photoreceptors was measured in detail at wavelengths λ = 355, 494 and 588 nm.
The measured curves often showed numerous sidebands, indicating the importance of diffraction by the facet lens.
The shape of the angular sensitivity profile is dependent on wavelength. The main peak of the angular sensitivities at the shorter wavelengths was flattened. This phenomenon as well as the overall shape of the main peak can be quantitatively described by a wave-optical theory using realistic values for the optical parameters of the lens-photoreceptor system.
At a constant response level of 6 mV (almost dark adapted), the visual acuity of the peripheral cells R1-6 is at longer wavelengths mainly diffraction limited, while at shorter wavelengths the visual acuity is limited by the waveguide properties of the rhabdomere.
Closure of the pupil narrows the angular sensitivity profile at the shorter wavelengths. This effect can be fully described by assuming that the intracellular pupil progressively absorbs light from the higher order modes.
In light-adapted cells R1-6 the visual acuity is mainly diffraction limited at all wavelengths.
The views of general practitioners and practice nurses towards the barriers and facilitators of proactive, internet-based chlamydia screening for reaching young heterosexual men
Background:
Chlamydia trachomatis is a common bacterial sexually transmitted infection (STI), which disproportionately affects young people under 25 years. Commonly, more women are offered screening than men. This study obtained the views of general practitioners and practice nurses towards Internet-based screening and assessed levels of support for the development of proactive screening targeting young heterosexual men via the Internet.
Methods:
Semi-structured telephone interviews with 10 general practitioners and 8 practice nurses, across Central Scotland. Topics covered: experience of screening heterosexual men for chlamydia, views on the use of the Internet as a way to reach young men for chlamydia screening, beliefs about the potential barriers and facilitators to Internet-based screening. Transcripts from audio recordings were analysed with Framework Analysis, using QSR NVivo10.
Results:
Experiences of chlamydia screening were almost exclusively with women, driven by the nature of consultations and ease of raising sexual health issues with female patients; few practice nurses reported seeing men during consultations. All participants spoke in favour of Internet-based screening for young men. Participants reported ease of access and convenience as potential facilitators of an Internet-based approach but anonymity and confidentiality could be potential barriers and facilitators to the success of an Internet approach to screening. Concerns over practical issues as well as those pertaining to gender and socio-cultural issues were raised.
Conclusions:
Awareness of key barriers and facilitators, such as confidentiality, practicality and socio-cultural influences, will inform the development of an Internet-based approach to screening. However, this approach may have its limits in terms of being able to tackle wider social and cultural barriers, along with shifts in young people's and health professionals' attitudes towards screening. Nevertheless, employing innovative efforts as part of a multi-faceted approach is required to ensure effective interventions reach the policy agenda
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