561 research outputs found
Environmental risk of severely Pb-contaminated riverbank sediment as a consequence of hydrometeorological perturbation
Metal mining activities have resulted in the widespread metal pollution of soils and sediments and are a worldwide health concern. Pb is often prolific in metal-mining impacted systems and has acute and chronic toxic effects. Environmental factors controlling diffuse pollution from contaminated riverbank sediment are currently seen as a âblack boxâ from a process perspective. This limits our ability to accurately predict and model releases of dissolved Pb. Previous work by the authors uncovered key mechanisms responsible for the mobilisation of dissolved Zn. The current study identifies key mechanisms controlling the mobilisation of dissolved Pb, and the environmental risk these releases pose, in response to various sequences of âriverbankâ inundation/drainage. Mesocosm experiments designed to mimic the riverbank environment were run using sediment severely contaminated with Pb, from a mining-impacted site. Results indicated that, although Pb is generally reported as less mobile than Zn, high concentrations of dissolved Pb are released in response to longer or more frequent flood events. Furthermore, the geochemical mechanisms of release for Zn and Pb were different. For Zn, mechanisms were related to reductive dissolution of Mn (hydr)oxides with higher concentrations released, at depth, over prolonged flood periods. For Pb, key mechanisms of release were related to the solubility of anglesite and the oxidation of primary mineral galena, where periodic drainage events serve to keep sediments oxic, particularly at the surface. The results are concerning because climate projections for the UK indicate a rise in the occurrence of localized heavy rainfall events that could increase flood frequency and/or duration. This study is unique in that it is the first to uncover key mechanisms responsible for dissolved Pb mobilisation from riverbank sediments. The mineralogy at the mining-impacted site is common to many sites worldwide and it is likely the mechanisms identified in this study are widespread
Localisation and disorder in the design of 2D photonic crystal devices
Photonic crystals are meta-materials that can inhibit the propagation of light in all directions for specific wavelength ranges. Material or structural defects can be introduced into the crystal to cause localised modes, providing the ability to mould the flow of light on the wavelength scale and allowing the development of miniaturised, integrated photonic devices. For this reason, photonic crystals will likely be key building blocks for future micro-optical and communication technology. In this paper, we examine the Bloch mode modelling of 2D photonic crystal structures with application to the analysis of photonic crystal waveguides and their susceptibility to disorder, which provides a framework for studying fabrication tolerances in realistic devices
Modes of Random Lasers
In conventional lasers, the optical cavity that confines the photons also
determines essential characteristics of the lasing modes such as wavelength,
emission pattern, ... In random lasers, which do not have mirrors or a
well-defined cavity, light is confined within the gain medium by means of
multiple scattering. The sharp peaks in the emission spectra of semiconductor
powders, first observed in 1999, has therefore lead to an intense debate about
the nature of the lasing modes in these so-called lasers with resonant
feedback. In this paper, we review numerical and theoretical studies aimed at
clarifying the nature of the lasing modes in disordered scattering systems with
gain. We will discuss in particular the link between random laser modes near
threshold (TLM) and the resonances or quasi-bound (QB) states of the passive
system without gain. For random lasers in the localized regime, QB states and
threshold lasing modes were found to be nearly identical within the scattering
medium. These studies were later extended to the case of more lossy systems
such as random systems in the diffusive regime where differences between
quasi-bound states and lasing modes were measured. Very recently, a theory able
to treat lasers with arbitrarily complex and open cavities such as random
lasers established that the TLM are better described in terms of the so-called
constant-flux states.Comment: Review paper submitted to Advances in Optics and Photonic
Suppression of Anderson localization in disordered metamaterials
We study wave propagation in mixed, 1D disordered stacks of alternating right- and left-handed layers and reveal that the introduction of metamaterials substantially suppresses Anderson localization. At long wavelengths, the localization length in mixed stacks is orders of magnitude larger than for normal structures, proportional to the sixth power of the wavelength, in contrast to the usual quadratic wavelength dependence of normal systems. Suppression of localization is also exemplified in long-wavelength resonances which largely disappear when left-handed materials are introduced. © 2007 The American Physical Society
Modes of random lasers
In conventional lasers, the optical cavity that confines the photons also determines essential characteristics of the lasing modes such as wavelength, emission pattern, directivity, and polarization. In random lasers, which do not have mirrors or a well-defined cavity, light is confined within the gain medium by means of multiple scattering. The sharp peaks in the emission spectra of semiconductor powders, first observed in 1999, has therefore lead to an intense debate about the nature of the lasing modes in these so-called lasers with resonant feedback. We review numerical and theoretical studies aimed at clarifying the nature of the lasing modes in disordered scattering systems with gain. The past decade has witnessed the emergence of the idea that even the low-Q resonances of such open systems could play a role similar to the cavity modes of a conventional laser and produce sharp lasing peaks. We focus here on the nearthreshold single-mode lasing regime where nonlinear effects associated with gain saturation and mode competition can be neglected.We discuss in particular the link between random laser modes near threshold and the resonances or quasi-bound (QB) states of the passive system without gain. For random lasers in the localized (strong scattering) regime, QB states and threshold lasing modes were found to be nearly identical within the scattering medium. These studies were later extended to the case of more lossy systems such as random systems in the diffusive regime, where it was observed that increasing the openness of such systems eventually resulted in measurable and increasing differences between quasi-bound states and lasing modes. Very recently, a theory able to treat lasers with arbitrarily complex and open cavities such as random lasers established that the threshold lasing modes are in fact distinct from QB states of the passive system and are better described in terms of a new class of states, the so-called constant-flux states. The correspondence between QB states and lasing modes is found to improve in the strong scattering limit, confirming the validity of initial work in the strong scattering limit. © 2010 Optical Society of America
The proper name as starting point for basic reading skills
Does alphabetic-phonetic writing start with the proper name and how does the name affect reading and writing skills? Sixty 4- to 5Âœ-year-old children from middle SES families with Dutch as their first language wrote their proper name and named letters. For each child we created unique sets of words with and without the childâs first letter of the name to test spelling skills and phonemic sensitivity. Name writing correlated with childrenâs knowledge of the first letter of the name and phonemic sensitivity for the sound of the first letter of the name. Hierarchical regression analysis makes plausible that both knowledge of the first letterâs name and phonemic sensitivity for this letter explain why name writing results in phonetic spelling with the name letter. Practical implications of the findings are discussed
RNAseq Analyses Identify Tumor Necrosis Factor-Mediated Inflammation as a Major Abnormality in ALS Spinal Cord
ALS is a rapidly progressive, devastating neurodegenerative illness of adults that produces disabling weakness and spasticity arising from death of lower and upper motor neurons. No meaningful therapies exist to slow ALS progression, and molecular insights into pathogenesis and progression are sorely needed. In that context, we used high-depth, next generation RNA sequencing (RNAseq, Illumina) to define gene network abnormalities in RNA samples depleted of rRNA and isolated from cervical spinal cord sections of 7 ALS and 8 CTL samples. We aligned \u3e50 million 2X150 bp paired-end sequences/sample to the hg19 human genome and applied three different algorithms (Cuffdiff2, DEseq2, EdgeR) for identification of differentially expressed genes (DEGâs). Ingenuity Pathways Analysis (IPA) and Weighted Gene Co-expression Network Analysis (WGCNA) identified inflammatory processes as significantly elevated in our ALS samples, with tumor necrosis factor (TNF) found to be a major pathway regulator (IPA) and TNFα-induced protein 2 (TNFAIP2) as a major network âhubâ gene (WGCNA). Using the oPOSSUM algorithm, we analyzed transcription factors (TF) controlling expression of the nine DEG/hub genes in the ALS samples and identified TFâs involved in inflammation (NFkB, REL, NFkB1) and macrophage function (NR1H2::RXRA heterodimer). Transient expression in human iPSC-derived motor neurons of TNFAIP2 (also a DEG identified by all three algorithms) reduced cell viability and induced caspase 3/7 activation. Using high-density RNAseq, multiple algorithms for DEG identification, and an unsupervised gene co-expression network approach, we identified significant elevation of inflammatory processes in ALS spinal cord with TNF as a major regulatory molecule. Overexpression of the DEG TNFAIP2 in human motor neurons, the population most vulnerable to die in ALS, increased cell death and caspase 3/7 activation. We propose that therapies targeted to reduce inflammatory TNFα signaling may be helpful in ALS patients
Risk factors for pressure sores in adult patients with myelomeningocele â a questionnaire-based study
BACKGROUND: Myelomeningocele (MMC) is a part of a complex neural tube defect and a disorder of the cerebrospinal fluid system. Pressure sores are a frequent complication for patients with MMC. Little is known about the risk factors for pressure sores in adults with MMC. The aim of this study was to investigate an association between the presence of pressure sores and other patient characteristics, in order to develop an improved strategy for the management of sores. METHODS: A structured questionnaire regarding sores, medical condition, function and living factors was designed and sent to the 193 patients with MMC registered in the year 2003 at TRS, a National Centre for Rare Disorders in Norway. RESULTS: Out of 193 total, 87 patients participated and 71 patients (82%) reported sores; 26 (30%) at the time of the interview and 45 (52%) during the last 5 years. Sores were mostly localized on toes and feet and occurred exclusively in regions with reduced or missing sensibility. A significant association was found between sores and memory deficit (p = 0.02), Arnold Chiari malformation (p = 0.02) and a record of previous sores (p = 0.004). Sores were not significantly associated with hydrocephalus, syringomyelia, nutrition, body mass index, smoking, physical activity, employment or living together with other persons. Some patients (18, 21%) reported skin inspection by others and the remainder relied on self-inspection. CONCLUSION: Patients with sensory deficit, memory problems, and Arnold Chiari malformation had a higher risk of having pressure sores. This patient group needs improved skin inspection routines and sore treatment
Bereavement help-seeking following an 'expected' death: a cross-sectional randomised face-to-face population survey
© 2008 Currow et al; licensee BioMed Central Ltd.
This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.Background :
This study examines the prevalence and nature of bereavement help-seeking among the population who experienced an "expected" death in the five years before their survey response. Such whole population data are not limited by identification through previous access to specific services nor practitioners.
Methods :
In a randomised, cross-sectional, state-wide population-based survey, 6034 people over two years completed face-to-face interviews in South Australia by trained interviewers using piloted questions (74.2% participation rate). Respondent demographics, type of grief help sought, and circumstantial characteristics were collected. Uni- and multi-variate logistic regression models were created.
Results :
One in three people (1965/6034) had experienced an 'expected' death of someone close to them in the last five years. Thirteen per cent sought help for their grief from one or more: friend/family members (10.7%); grief counselors (2.2%); spiritual advisers (1.9%); nurses/doctors (1.5%). Twenty five respondents (1.3%) had not sought, but would have valued help with their grief.
In multi-variate regression modeling, those who sought professional help (3.4% of the bereaved) had provided more intense care (OR 5.39; CI 1.94 to14.98; p < 0.001), identified that they were less able to 'move on' with their lives (OR 7.08; CI 2.49 to 20.13; p = 0.001) and were more likely not to be in full- or part-time work (OR 3.75; CI 2.31 â 11.82; p = 0.024; Nagelkerke's R2 = 0.33).
Conclusion :
These data provide a whole-of-population baseline of bereavement help-seeking. The uniquely identified group who wished they had sought help is one where potentially significant health gains could be made as we seek to understand better any improved health outcomes as a result of involving bereavement services
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