Pressure-dependent calibration of the OH and HO2 channels of a FAGE HOx instrument using the Highly Instrumented Reactor for Atmospheric Chemistry (HIRAC)

The calibration of field instruments used to measure concentrations of OH and HO2 worldwide has traditionally relied on a single method utilising the photolysis of water vapour in air in a flow tube at atmospheric pressure. Here the calibration of two FAGE (fluorescence assay by gaseous expansion) apparatuses designed for HOx (OH and HO2) measurements have been investigated as a function of external pressure using two different laser systems. The conventional method of generating known concentrations of HOx from H2O vapour photolysis in a turbulent flow tube impinging just outside the FAGE sample inlet has been used to study instrument sensitivity as a function of internal fluorescence cell pressure (1.8-3.8 mbar). An increase in the calibration constants CHO and CHO2 with pressure was observed, and an empirical linear regression of the data was used to describe the trends, with ΔCHO Combining double low line (17 ± 11) % and ΔCHO2 Combining double low line (31.6 ± 4.4)% increase per millibar air (uncertainties quoted to 2σ). Presented here are the first direct measurements of the FAGE calibration constants as a function of external pressure (440-1000 mbar) in a controlled environment using the University of Leeds HIRAC chamber (Highly Instrumented Reactor for Atmospheric Chemistry). Two methods were used: the temporal decay of hydrocarbons for calibration of OH, and the kinetics of the second-order recombination of HO2 for HO2 calibrations. Over comparable conditions for the FAGE cell, the two alternative methods are in good agreement with the conventional method, with the average ratio of calibration factors (conventional : alternative) across the entire pressure range, COH(conv)/COH(alt) Combining double low line 1.19 ± 0.26 and CHO2(conv)/CHO2(alt) Combining double low line 0.96 ± 0.18 (2σ). These alternative calibration methods currently have comparable systematic uncertainties to the conventional method: ∼ 28% and ∼ 41% for the alternative OH and HO2 calibration methods respectively compared to 35% for the H2O vapour photolysis method; ways in which these can be reduced in the future are discussed. The good agreement between the very different methods of calibration leads to increased confidence in HOx field measurements and particularly in aircraft-based HOx measurements, where there are substantial variations in external pressure, and assumptions are made regarding loss rates on inlets as a function of pressure

Heterogeneous Ice Nucleation by Soufriere Hills Volcanic Ash Immersed in Water Droplets

Fine particles of ash emitted during volcanic eruptions may sporadically influence cloud properties on a regional or global scale as well as influencing the dynamics of volcanic clouds and the subsequent dispersion of volcanic aerosol and gases. It has been shown that volcanic ash can trigger ice nucleation, but ash from relatively few volcanoes has been studied for its ice nucleating ability. In this study we quantify the efficiency with which ash from the Soufriere Hills volcano on Montserrat nucleates ice when immersed in supercooled water droplets. Using an ash sample from the 11th February 2010 eruption, we report ice nucleating efficiencies from 246 to 265 K. This wide range of temperatures was achieved using two separate droplet freezing instruments, one employing nanolitre droplets, the other using microlitre droplets. Soufriere Hills volcanic ash was significantly more efficient than all other ash samples that have been previously examined. At present the reasons for these differences are not understood, but may be related to mineralogy, amorphous content and surface chemistry

Ice nucleation by fertile soil dusts: Relative importance of mineral and biogenic components

Agricultural dust emissions have been estimated to contribute around 20% to the global dust burden. In contrast to dusts from arid source regions, the ice-nucleating abilities of which have been relatively well studied, soil dusts from fertile sources often contain a substantial fraction of organic matter. Using an experimental methodology which is sensitive to a wide range of ice nucleation efficiencies, we have characterised the immersion mode ice-nucleating activities of dusts (d<11 μ m) extracted from fertile soils collected at four locations around England. By controlling droplet sizes, which ranged in volume from 10 to 10 L (concentration=0.02 to 0.1 wt% dust), we have been able to determine the ice nucleation behaviour of soil dust particles at temperatures ranging from 267K (-6°C) down to the homogeneous limit of freezing at about 237K (-36°C). At temperatures above 258K (-15°C) we find that the ice-nucleating activity of soil dusts is diminished by heat treatment or digestion with hydrogen peroxide, suggesting that a major fraction of the ice nuclei stems from biogenic components in the soil. However, below 258 K, we find that the ice active site densities tend towards those expected from the mineral components in the soils, suggesting that the inorganic fraction of soil dusts, in particular the K-feldspar fraction, becomes increasingly important in the initiation of the ice phase at lower temperatures. We conclude that dusts from agricultural activities could contribute significantly to atmospheric IN concentrations, if such dusts exhibit similar activities to those observed in the current laboratory study

Effect of rehabilitation worker input on visual function outcomes in individuals with low vision: study protocol for a randomised controlled trial

BACKGROUND: Visual Rehabilitation Officers help people with a visual impairment maintain their independence. This intervention adopts a flexible, goal-centred approach, which may include training in mobility, use of optical and non-optical aids, and performance of activities of daily living. Although Visual Rehabilitation Officers are an integral part of the low vision service in the United Kingdom, evidence that they are effective is lacking. The purpose of this exploratory trial is to estimate the impact of a Visual Rehabilitation Officer on self-reported visual function, psychosocial and quality-of-life outcomes in individuals with low vision. METHODS/DESIGN: In this exploratory, assessor-masked, parallel group, randomised controlled trial, participants will be allocated either to receive home visits from a Visual Rehabilitation Officer (n = 30) or to a waiting list control group (n = 30) in a 1:1 ratio. Adult volunteers with a visual impairment, who have been identified as needing rehabilitation officer input by a social worker, will take part. Those with an urgent need for a Visual Rehabilitation Officer or who have a cognitive impairment will be excluded. The primary outcome measure will be self-reported visual function (48-item Veterans Affairs Low Vision Visual Functioning Questionnaire). Secondary outcome measures will include psychological and quality-of-life metrics: the Patient Health Questionnaire (PHQ-9), the Warwick-Edinburgh Mental Well-being Scale (WEMWBS), the Adjustment to Age-related Visual Loss Scale (AVL-12), the Standardised Health-related Quality of Life Questionnaire (EQ-5D) and the UCLA Loneliness Scale. The interviewer collecting the outcomes will be masked to the group allocations. The analysis will be undertaken on a complete case and intention-to-treat basis. Analysis of covariance (ANCOVA) will be applied to follow-up questionnaire scores, with the baseline score as a covariate. DISCUSSION: This trial is expected to provide robust effect size estimates of the intervention effect. The data will be used to design a large-scale randomised controlled trial to evaluate fully the Visual Rehabilitation Officer intervention. A rigorous evaluation of Rehabilitation Officer input is vital to direct a future low vision rehabilitation strategy and to help direct government resources. TRIAL REGISTRATION: The trial was registered with ( ISRCTN44807874 ) on 9 March 2015

Plasmodium vivax Tryptophan-Rich Antigen PvTRAg33.5 Contains Alpha Helical Structure and Multidomain Architecture

Tryptophan-rich proteins from several malarial parasites have been identified where they play an important role in host-parasite interaction. Structural characterization of these proteins is needed to develop them as therapeutic targets. Here, we describe a novel Plasmodium vivax tryptophan-rich protein named PvTRAg33.5. It is expressed by blood stage(s) of the parasite and its gene contains two exons. The exon 1 encodes for a 23 amino acids long putative signal peptide which is likely to be cleaved off whereas the exon 2 encodes for the mature protein of 252 amino acids. The mature protein contains B-cell epitopes which were recognized by the human immune system during P.vivax infection. The PvTRAg33.5 contains 24 (9.5%) tryptophan residues and six motifs whose patterns were similar among tryptophan-rich proteins. The modeled structure of the PvTRAg33.5 consists of a multidomain architecture which is stabilized by the presence of large number of tryptophan residues. The recombinant PvTRAg33.5 showed predominantly α helical structure and alpha helix to beta sheet transition at pH below 4.5. Protein acquires an irreversible non-native state at temperature more than 50°C at neutral pH. Its secondary and tertiary structures remain stable in the presence of 35% alcohol but these structures are destabilized at higher alcohol concentrations due to the disturbance of hydrophobic interactions between tryptophanyl residues. These structural changes in the protein might occur during its translocation to interact with other proteins at its final destination for biological function such as erythrocyte invasion

A guide to the crystallographic analysis of icosahedral viruses

Determining the structure of an icosahedral virus crystal by X-ray diffraction follows very much the same course as conventional protein crystallography. The major differences arise from the relatively large sizes of the particles, which significantly affect the data collection process, data processing and management, and later, the refinement of a model. Most of the other differences are due to the high 5 3 2 point group symmetry of icosahedral viruses. This alters dramatically the means by which initial phases are obtained by molecular substitution, extended to higher resolution by electron density averaging and density modification, and the refinement of the structure in the light of high non-crystallographic symmetry. In this review, we attempt to lead the investigator through the various steps involved in solving the structure of a virus crystal. These steps include the purification of viruses, their crystallization, the recording of X-ray diffraction data, and its reduction to structure amplitudes. It further addresses the problems attending phase determination and ultimately the refinement of a model. Finally, we describe the unique properties of virus crystals and the factors that influence their physical and diffraction properties

Platform for Plasmodium vivax vaccine discovery and development

Plasmodium vivax is the most prevalent malaria parasite on the American continent. It generates a global burden of 80-100 million cases annually and represents a tremendous public health problem, particularly in the American and Asian continents. A malaria vaccine would be considered the most cost-effective measure against this vector-borne disease and it would contribute to a reduction in malaria cases and to eventual eradication. Although significant progress has been achieved in the search for Plasmodium falciparum antigens that could be used in a vaccine, limited progress has been made in the search for P. vivax components that might be eligible for vaccine development. This is primarily due to the lack of in vitro cultures to serve as an antigen source and to inadequate funding. While the most advanced P. falciparum vaccine candidate is currently being tested in Phase III trials in Africa, the most advanced P. vivax candidates have only advanced to Phase I trials. Herein, we describe the overall strategy and progress in P. vivax vaccine research, from antigen discovery to preclinical and clinical development and we discuss the regional potential of Latin America to develop a comprehensive platform for vaccine development

The crystal structure of ice under mesospheric conditions

Ice clouds form in the summer high latitude mesopause region, which is the coldest part of the Earth's atmosphere. At these very low temperatures (<150K) ice can exist in metastable forms, but the nature of these ices remains poorly understood. In this paper we show that ice which is grown at mesospherically relevant temperatures does not have a structure corresponding to the well-known hexagonal form or the metastable cubic form. Instead, the ice which forms under mesospheric conditions is a material in which cubic and hexagonal sequences of ice are randomly arranged to produce stacking disordered ice (ice Isd). The structure of this ice is in the trigonal crystal system, rather than the cubic or hexagonal systems, and is expected to produce crystals with aspect ratios consistent with lidar observations

Stacking disorder in ice I

Traditionally, ice I was considered to exist in two well-defined crystalline forms at ambient pressure: stable hexagonal ice (ice Ih) and metastable cubic ice (ice Ic). However, it is becoming increasingly evident that what has been called cubic ice in the past does not have a structure consistent with the cubic crystal system. Instead, it is a stacking-disordered material containing cubic sequences interlaced with hexagonal sequences, which is termed stacking-disordered ice (ice Isd). In this article, we summarise previous work on ice with stacking disorder including ice that was called cubic ice in the past. We also present new experimental data which shows that ice which crystallises after heterogeneous nucleation in water droplets containing solid inclusions also contains stacking disorder even at freezing temperatures of around -15 °C. This supports the results from molecular simulations, that the structure of ice that crystallises initially from supercooled water is always stacking-disordered and that this metastable ice can transform to the stable hexagonal phase subject to the kinetics of recrystallization. We also show that stacking disorder in ice which forms from water droplets is quantitatively distinct from ice made via other routes. The emerging picture of ice I is that of a very complex material which frequently contains stacking disorder and this stacking disorder can vary in complexity depending on the route of formation and thermal history