Spectrally arbitrary ray patterns

AbstractAn n×n ray pattern A is said to be spectrally arbitrary if for every monic nth degree polynomial f(x) with coefficients from C, there is a matrix in the pattern class of A such that its characteristic polynomial is f(x). In this article the authors extend the nilpotent-Jacobi method for sign patterns to ray patterns, establishing a means to show that an irreducible ray pattern and all its superpatterns are spectrally arbitrary. They use this method to establish that a particular family of n×n irreducible ray patterns with exactly 3n nonzeros is spectrally arbitrary. They then show that every n×n irreducible, spectrally arbitrary ray pattern has at least 3n-1 nonzeros

The minimum upper bound on the first ambiguous power of an irreducible, nonpowerful ray or sign pattern

AbstractLet A be an n×n irreducible ray or sign pattern matrix. If A is a sign pattern, it is shown that either A is powerful or else Ak has an ambiguous entry for some k⩽n2-2n+2, and further, sign patterns based on the Wielandt graph show that this bound is the best possible. If A is a ray pattern, partial results for the same bound are given

Ecology of Problem Individuals and the Efficacy of Selective Wildlife Management

G.S. is supported by a postgraduate research scholarship from the College of Life and Environmental Sciences of the University of Exeter. S.R. is grateful for the King Carl XVI Gustaf guest professorship that allowed him to work on this paper. We would like to thank the referees, Sasha Dall, Matthew Silk, and David Fisher for their comments on an earlier version of this manuscript.Peer reviewedPublisher PD

Analysis of N-nitrosamines in water by isotope dilution gas chromatography-electron ionisation tandem mass spectrometry

A method has been developed for the determination of eight N-nitrosamines in drinking water and treated municipal effluent. The method uses solid phase extraction (SPE), gas chromatography (GC) and analysis by tandem mass spectrometry (MS-MS) with electron ionization (EI). The target compounds are N-nitrosodimethylamine (NDMA), N-nitrosomethyethylamine (NMEA), N-nitrosodiethylamine NDEA), N-nitrosodipropylamine (NDPA), N-nitrosodi-n-butylamine (NDBuA), N-nitrosodiphenylamine (NDPhA), N-nitrosopyrrolidine (NPyr), N-nitrosopiperidine (NPip), N-nitrosomorpholine (NMorph). The use of direct isotope analogues for isotope dilution analysis of all analytes ensures accurate quantification, accounting for analytical variabilities that may occur during sample processing, extraction and instrumental analysis. Method detection levels (MDLs) were determined to describe analyte concentrations sufficient to provide a signal with 99% certainty of detection. The established MDLs for all analytes were 0.4–4 ng L−1 in a variety of aqueous matrices. Sample matrices were observed to have only a minor impact on MDLs and the method validation confirmed satisfactory method stability over intra-day and inter-day analyses of tap water and tertiary treated effluent sample

Transients drive the demographic dynamics of plant populations in variable environments

The dynamics of structured plant populations in variable environments can be decomposed into the ‘asymptotic’ growth contributed by vital rates, and ‘transient’ growth caused by deviation from stable stage structure. We apply this framework to a large, global data base of longitudinal studies of projection matrix models for plant populations. We ask, what is the relative contribution of transient boom and bust to the dynamic trajectories of plant populations in stochastic environments? Is this contribution patterned by phylogeny, growth form or the number of life stages per population and per species? We show that transients contribute nearly 50% or more to the resulting trajectories, depending on whether transient and stable contributions are partitioned according to their absolute or net contribution to population dynamics. Both transient contributions and asymptotic contributions are influenced heavily by the number of life stages modelled. We discuss whether the drivers of transients should be considered real ecological phenomena, or artefacts of study design and modelling strategy. We find no evidence for phylogenetic signal in the contribution of transients to stochastic growth, nor clear patterns related to growth form. We find a surprising tendency for plant populations to boom rather than bust in response to temporal changes in vital rates and that stochastic growth rates increase with increasing tendency to boom. Synthesis. Transient dynamics contribute significantly to stochastic population dynamics but are often overlooked in ecological and evolutionary studies that employ stochastic analyses. Better understanding of transient responses to fluctuating population structure will yield better management strategies for plant populations, and better grasp of evolutionary dynamics in the real world

Removal of trace organics by MBR treatment: the role of molecular properties

This study examined the relationship between specific molecular features of trace organic contaminants and their removal efficiencies by a laboratory scale membrane bioreactor (MBR). Removal efficiencies of 40 trace organic compounds were assessed under stable operating conditions. The reported results demonstrate an apparent correlation between chemical structures and the removal of trace organic contaminants by the laboratory scale MBR system. The removal of all 14 very hydrophobic (Log D \u3e 3.2) trace organic compounds selected in this study was consistently high and was above 85%. The occurrence and types of electron withdrawing or donating functional groups appear to be important factors governing their removal by MBR treatment. In this study, all hydrophilic and moderately hydrophobic (Log D \u3c 3.2) compounds possessing strong electron withdrawing functional groups showed removal efficiency of less than 20%. In contrast, high removal efficiencies were observed with most compounds bearing electron donating functional groups such as hydroxyl and primary amine groups. A qualitative framework for the assessment of trace organic removal by MBR treatment was proposed to provide further insights into the removal mechanisms

Effects of caustic cleaning on pore size of nanofiltration membranes and their rejection of trace organic chemicals

The aim of this study was to assess the impact of caustic cleaning on the rejection of three different trace organic chemical (TrOC) groups (i.e. neutral hydrophilic, neutral hydrophobic and negatively charged) by two nanofiltration (NF) membranes ‒ namely NF270 and NF90. Chemical cleaning was simulated by exposing virgin membrane samples to commercial caustic cleaning formulations as well as sodium hydroxide solutions containing analytical grade additives such as sodium dodecyl sulfate or ethylenediaminetetraacetic acid. The membrane average pore size before and after exposure to a commercially available caustic cleaning formulation was determined based on the pore transport model. The results show that caustic chemical cleaning could cause an increase in the membrane pore size, leading to an increase in permeability and decrease in rejection of conductivity. The impact of caustic cleaning on the pore size and solute rejection was a function of the membrane active skin layer and the chemistry of the cleaning formulation. Caustic cleaning led to a small increase in pore size of the NF270 membrane and resulted in a notable increase in the permeability and salt passage. By contrast, the impact on the NF90 membrane was negligible. The influence of caustic cleaning on TrOC rejection was dependent on physical characteristics of each TrOC including their molecular size, charge, and hydrophobicity. The rejection of neutral and hydrophobic TrOC by the NF270 membrane decreased significantly after exposure to caustic cleaning formulation. However, because the rejection of negatively charged TrOC is governed mostly by electrostatic interaction, their rejection was not significantly affected by caustic cleaning

What aspects of health and wellbeing are most important to parent carers of children with disabilities?

Introduction: Parent carers of children with special educational needs or disabilities are at risk of poorer health and wellbeing outcomes because of the distinct and challenging circumstances they face. Evaluations of interventions promoting the health of parent carers should focus on measuring the aspects of health and wellbeing which are most relevant to this group. As part of a programme of research on parent carer‐focused interventions, this study aimed to understand which aspects of health and wellbeing are perceived by parent carers as most meaningful and important. Methods: A qualitative study using semistructured online interviews was conducted. A purposive sample of parent carers was interviewed about relevant health and wellbeing outcomes. Transcripts were analysed thematically. Results: Thirty parent carers were interviewed, 19 of whom had experienced a health‐promoting intervention, either as participants (n = 14) or facilitators (n = 5). Three main themes were identified: ‘self, identity and beliefs’; ‘social connections and support’ and ‘health‐promoting practices and outcomes.’ Each theme encompassed the challenges participants faced, and the changes that helped them overcome these challenges. ‘Self‐identity’ challenges focused on the overwhelming nature of the parental care role and the emotional impact of this. Changes were brought about by developing a positive mindset, increasing confidence, and reconnecting with aspects of their identity which were important to them before they became parent carers. Challenges related to ‘social connections’ reflected parent carers' isolation. Change was brought about through increased peer support and peer interactions. Parent carers experienced challenges in terms of ‘health‐promoting activities’ because they lacked free time and experienced poor physical health. Changes were brought about by engagement in health‐promoting activities of various kinds. Conclusion: Parent carers view health and wellbeing in terms of overcoming the common challenges they face as a group. These challenges reflect the ways in which their physiological and psychological needs are often unmet. Researchers interested in measuring parent carer health and wellbeing should consider the specific challenges this group face, as well as theoretical frameworks which can make sense of these challenges, such as self‐determination theory. Patient or Public Contribution: Our team carries out patient and public involvement (PPI) through a Family Faculty group facilitated by a Family Involvement Co‐ordinator (A. McD.) who is herself a parent carer. A study‐specific PPI working group was established which included members of the Family Faculty. The PPI group advised on various aspects of the research as reported in the paper. The manuscript was co‐authored by the team's Family Involvement Co‐ordinator (A. McD.)

Effects of thermal pre-treatment and recuperative thickening on the fate of trace organic contaminants during anaerobic digestion of sewage sludge

This study examined the effects of thermal pre-treatment and recuperative thickening on anaerobic digestion of sewage sludge on biogas production and removal of trace organic contaminants (TrOCs). Thermal pre-treatment and recuperative thickening resulted in approximately 15% increase in biogas production. However, the effects of thermal pretreatement and recuperative thickening on anaerobic digestion performance in respect to the removal of TrOCs were less obvious and varied widely depending on the molecular properties of each compound. Of the 40 TrOCs monitored in this study, 16 TrOCs were detected in all primary sludge samples. Removal from the aqueous phase was negligible for most of these 16 TrOCs. Caffeine and paracetamol were the only two TrOCs with a high removal from the aqueous phase. In comparison to the aqueous phase, TrOC removal from the solid phase was considerably higher. Through a mass balance calculation, it was shown that thermal pre-treatment or a combination of thermal pre-treatment and recuperative thickening could enhance the biodegradation of five persistent TrOCs, namely TCEP, verapamil, clozapine, triclosan, and triclocarban by 17-50%