Wetting of a Stepped Platinum (211) Surface

Steps stabilize water adsorption on metal surfaces, providing favorable binding sites for water during wetting or ice nucleation, but there is limited understanding of the local water arrangements formed on such surfaces. Here we describe the structural evolution of water on the stepped Pt(211) surface using thermal desorption, low-energy electron diffraction, and scanning tunneling microscopy to probe the water structure. At low coverage water forms linear structures comprising zigzag chains along the steps that are decorated by H-bonded rings every one or two units along the terrace. Simple 2-coordinate H-bonded chains are not observed, indicating the Pt step binds too weakly to compensate entirely for a low water H-bond coordination number. As the coverage increases, water chains assemble into a disordered (2 × 1) structure, likely made up of the same narrow water chains along the steps with little or no H-bonding between adjacent structures. The chain structure disappears as water adsorption saturates the surface to form an incommensurate, disordered network of water rings of different size. Although the steps on Pt(211) clearly stabilize water adsorption and direct growth, the surface does not support the simple 1D chains previously proposed or an ordered 2D network such as seen on other surfaces. We discuss reasons for this and the factors that determine the behavior of the first water layer on stepped metal surfaces.

Clinical evaluation of deep learning and atlas-based auto-segmentation for critical organs at risk in radiation therapy

INTRODUCTION

Contouring organs at risk (OARs) is a time-intensive task that is a critical part of radiation therapy. Atlas-based automatic segmentation has shown some success at reducing this time burden on practitioners; however, this method often requires significant manual editing to reach a clinically accurate standard. Deep learning (DL) auto-segmentation has recently emerged as a promising solution. This study compares the accuracy of DL and atlas-based auto-segmentation in relation to clinical 'gold standard' reference contours.

METHODS

Ninety CT datasets (30 head and neck, 30 thoracic, 30 pelvic) were automatically contoured using both atlas and DL segmentation techniques. Sixteen critical OARs were then quantitatively measured for accuracy using the Dice similarity coefficient (DSC) and Hausdorff distance (HD). Qualitative analysis was performed to visually classify the accuracy of each structure into one of four explicitly defined categories. Additionally, the time to edit atlas and DL contours to a clinically acceptable level was recorded for a subset of 9 OARs.

RESULTS

Of the 16 OARs analysed, DL delivered statistically significant improvements over atlas segmentation in 13 OARs measured with DSC, 12 OARs measured with HD, and 12 OARs measured qualitatively. The mean editing time for the subset of DL contours was 50%, 23% and 61% faster (all P < 0.05) than that of atlas segmentation for the head and neck, thorax, and pelvis respectively.

CONCLUSIONS

Deep learning segmentation comprehensively outperformed atlas-based contouring for the majority of evaluated OARs. Improvements were observed in geometric accuracy and visual acceptability, while editing time was reduced leading to increased workflow efficiency.

Social facilitation for conservation planning: understanding fairy tern behavior and site selection in response to conspecific audio-visual cues

Simulated social facilitation techniques (e.g. decoys and call playbacks) are commonly used to attract seabirds to restored and artificially created nesting habitats. However, a lack of social stimuli and conspecific cueing at these habitats may limit the use of these sites, at least in the short term. Therefore, testing the effectiveness of simulated audio-visual cues for attracting gregarious birds is important for conservation planning. In this study, we (1) assessed whether call playback and decoys were associated with an increased likelihood of Australian fairy terns Sternula nereis nereis visiting potentially suitable nesting habitats; (2) tested their behavioral response to different cues; and (3) documented whether social facilitation had the potential to encourage colony establishment. A full cross-over study design consisting of all possible pairings of decoy and call playback treatments (control [no attractants], decoys, call playback, both decoys and playback), allocated as part of a random block design, was undertaken at 2 sites. Linear modeling suggested that call playback was important in explaining the time spent aerial prospecting as well as the maximum number of fairy terns aerial prospecting, although this only appeared to be the case for 1 of the 2 sites. Decoys, on the other hand, did not appear to have any effect on time spent aerial prospecting. The results from this study suggest that audio cues have the potential to encourage site selection by increasing social stimuli, but attractants may be required over several breeding seasons before colonies are established.

Water Dissociation and Hydroxyl Formation on Ni(110)

Nickel is an active catalyst for hydrogenation and re-forming reactions, with the reactions showing a strong dependence on the surface exposed. Here, we describe the mixed hydroxyl-water phases formed during water dissociation on Ni(110) using scanning tunneling microscopy and low-current low-energy electron diffraction. Water dissociation starts between 150 and 180 K as the H-bond structure evolves from linear one-dimensional (1D) chains of intact water into a two-dimensional (2D) network containing short rows of face-sharing hexagonal rings. As further water desorbs, the hexagonal rows adopt a local (2 × 3) arrangement, forming small, disordered domains separated by strain relief features. Decomposition of this phase occurs near 220 K to form linear 1D structures consisting of flat, zigzag water chains, with each water stabilized by donating one H to hydroxyl to form a branched chain structure. The OH-H₂O chains repel each other, with the saturation layer ordering into a (2 0, 1 4) structure that decomposes to OH near 245 K as further water desorbs. The structure of the mixed OH/H₂O phases is discussed and contrasted with those found on the related Cu(110) surface, with the differences attributed to strain in the 2D H-bond network caused by the short Ni lattice spacing and strong bond to OH/H₂O.

Hydration of a 2D Supramolecular Assembly: Bitartrate on Cu(110)

Hydration layers play a key role in many technical and biological systems, but our understanding of these structures remains very limited. Here, we investigate the molecular processes driving hydration of a chiral metal–organic surface, bitartrate on Cu(110), which consists of hydrogen-bonded bitartrate rows separated by exposed Cu. Initially water decorates the metal channels, hydrogen bonding to the exposed O ligands that bind bitartrate to Cu, but does not wet the bitartrate rows. At higher temperature, water inserts into the structure, breaks the existing intermolecular hydrogen bonds, and changes the adsorption site and footprint. Calculations show this process is driven by the creation of stable adsorption sites between the carboxylate ligands, to allow hydration of O–Cu ligands within the interior of the structure. This work suggests that hydration of polar metal–adsorbate ligands will be a dominant factor in many systems during surface hydration or self-assembly from solution.

Formation of Linear Water Chains on Ni(110)

Materials that bind strongly to water structure the contact layer, modifying its chemical and physical properties in a manner that depends on the symmetry and reactivity of the surface. Although detailed models have been developed for several inert surfaces, much less is known about reactive surfaces, particularly those with a symmetry different from that of ice. Here we investigate water adsorption on a rectangular surface, Ni(110), an active re-forming catalyst that interacts strongly with water. Instead of forming a network of H-bonded cyclic rings, water forms flat 1D water chains, leaving half the Ni atoms exposed. Second layer water also follows the surface symmetry, forming chains of alternating pentamer and heptamer rings in preference to an extended 2D structure. This behavior is different from that found on other surfaces studied previously and is driven by the short lattice spacing of the solid and the strength of the Ni-water bond.

Strain Relief during Ice Growth on a Hexagonal Template

Heterogeneous ice nucleation at solid surfaces impacts many areas of science, from environmental processes, such as precipitation, to microbiological systems and food processing, but the microscopic mechanisms underpinning nucleation remain unclear. Discussion of ice growth has often focused around the role of the surface in templating the structure of water, forcing the first layer to adopt the registry of the underlying substrate rather than that of ice. To grow a thick ice film, water in the first few ice layers must accommodate this strain, but understanding how this occurs requires detailed molecular-scale information that is lacking. Here we combine scanning tunneling microscopy, low-energy electron diffraction, and work-function measurements with electronic structure calculations to investigate the initial stages of ice growth on a Pt alloy surface, having a lattice spacing 6% larger than ice. Although the first layer of water forms a strictly commensurate hexagonal network, this behavior does not extend to the second layer. Instead, water forms a 2D structure containing extended defect rows made from face-sharing pentamer and octamer rings. The defect rows allow the majority of second-layer water to remain commensurate with the solid surface while compensating lateral strain by increasing the water density close to that of an ice surface. The observation of octamer-pentamer rows in ice films formed on several surfaces suggests that the octamer-pentamer defect motif acts as a flexible strain relief mechanism in thin ice films, providing a mechanism that is not available during the growth of strained films in other materials, such as semiconductors.

Ice Nucleation on a Corrugated Surface

Heterogeneous ice nucleation is a key process in many environmental and technical fields and is of particular importance in modeling atmospheric behavior and the Earth's climate. Despite an improved understanding of how water binds at solid surfaces, no clear picture has emerged to describe how 3D ice grows from the first water layer, nor what makes a particular surface efficient at nucleating bulk ice. This study reports how water at a corrugated, hydrophilic/hydrophobic surface restructures from a complex 2D network, optimized to match the solid surface, to grow into a continuous ice film. Unlike the water networks formed on plane surfaces, the corrugated Cu(511) surface stabilizes a buckled hexagonal wetting layer containing both hydrogen acceptor and donor sites. First layer water is able to relax into an "icelike" arrangement as further water is deposited, creating an array of donor and acceptor sites with the correct spacing and corrugation to stabilize second layer ice and allow continued commensurate multilayer ice growth. Comparison to previous studies of flat surfaces indicates nanoscale corrugation strongly favors ice nucleation, implying surface corrugation will be an important aspect of the surface morphology on other natural or engineered surfaces.

The reactivity of water and OH on Pt-Ni(111) films

Bimetallic Pt catalysts are of interest as water redox catalysts in low temperature fuel cells. Here we compare water and hydroxyl adsorption on Pt-Ni(111) films and a PtNi(111) alloy surface with the behaviour on the pure metals. Whereas water adsorbs and desorbs intact from close packed Pt and Ni, it dissociates on PtNi surfaces to form adsorbed hydroxyl and hydrogen. Reactivity to water increases in the order Pt(111) < monolayer Pt-Ni(111) < multilayer (2-6 ML) Pt-Ni(111) ∼ PtNi(111) surface alloy and does not scale directly with the Pt strain. Hydroxyl can also be formed by reaction with pre-adsorbed O and is less stable than on pure Pt, decomposing to water and O in a broad peak near 180 K, 20 K lower than on Pt(111). The reduced stability of OH on Pt-Ni(111) films is common to all the PtNi surfaces and consistent with bimetallic PtNi surfaces showing less blocking by OH during the oxygen reduction reaction.

The Mayak Worker Dosimetry System (MWDS-2013): A Bayesian Analysis to Quantify Pulmonary Binding of Plutonium in Lungs Using Historic Beagle Dog Data

The revised human respiratory tract model, published in Part 1 of the International Commission on Radiological Protection's (ICRP) report on Occupational Intakes of Radionuclides (OIR), includes a bound fraction, fb, to represent radionuclides that have become chemically bound in the lungs following dissolution of particulates in lung fluid. Bound radionuclides are not subject to particle transport clearance but can be absorbed to blood at a rate, sb. The occurrence of long-term binding of plutonium can greatly increase lung doses, particularly if it occurs in the bronchial and bronchiolar regions. However, there has been little evidence that currently supports the existence of a long-term bound state for plutonium. The present work describes the analysis of measurements of lung data obtained from a life span study of Beagle dogs that were exposed by inhalation to different concentrations of plutonium-239 (239Pu) nitrate aerosol at Pacific Northwest Laboratories, USA. The data have been analysed to assess whether a bound state was required to explain the data. A Bayesian approach was adopted for the analysis that accounts for uncertainties in model parameter values, including uncertainties in the rates of particle transport clearance. Furthermore, it performs the analysis using two different modelling hypotheses: a model based on the current ICRP human respiratory tract model and its treatment of alveolar particle transport clearance; and a model of particle transport clearance that is based on the updated model developed by ICRP to calculate dose coefficients for the OIR. The current model better represents clearance in dogs at early times (up to 1 year following intake) and the latter better represents retention at greater times (>5 years following intake). The results indicate that a long-term bound fraction of between 0.16 and 1.1%, with a mean value of between 0.24 and 0.8% (depending on the model) is required to explain the data.

Chiral segregation driven by a dynamical response of the adsorption footprint to the local adsorption environment: bitartrate on Cu(110)

Bitartrate, a strongly bound chiral modifier, is able to restructure its adsorption footprint on Cu(110) in response to local adsorbates.

Water at Interfaces

The interfaces of neat water and aqueous solutions play a prominent role in many technological processes and in the environment. Examples of aqueous interfaces are ultrathin water films that cover most hydrophilic surfaces under ambient relative humidities, the liquid/solid interface which drives many electrochemical reactions, and the liquid/vapor interface, which governs the uptake and release of trace gases by the oceans and cloud droplets. In this article we review some of the recent experimental and theoretical advances in our knowledge of the properties of aqueous interfaces and discuss open questions and gaps in our understanding.

Shifting from presumptive to test-based management of malaria - technical basis and implications for malaria control in Ghana

The presumptive approach was the World Health Organisation (WHO) recommended to the management of malaria for many years and this was incorporated into syndromic guidelines such as the Integrated Management of Childhood Illnesses (IMCI). In early 2010 however, WHO issued revised treatment guidelines that call for a shift from the presumptive to the test-based approach. Practically, this implies that in all suspected cases, the diagnosis of uncomplicated malaria should be confirmed using rapid test before treatment is initiated. This revision effectively brings to an end an era of clinical practice that span several years. Its implementation has important implications for the health systems in malaria-endemic countries. On the basis of research in Ghana and other countries, and evidence from program work, the Ghana National Malaria Control Program has issued revised national treatment guidelines that call for implementation of test-based management of malaria in all cases, and across all age groups. This article reviews the evidence and the technical basis for the shift to test-based management and examines the implications for malaria control in Ghana.

The role of lattice parameter in water adsorption and wetting of a solid surface

Reducing the lattice parameter of a Sn–metal surface alloy below the O–O separation of ice disrupts the flat wetting layer, causing the first layer to buckle and instead form ice clusters.

A randomized, comparative study of two regimens of β-artemether for the treatment of uncomplicated,Plasmodium falciparummalaria, in northern Ghana

In Ghana, wide-spread resistance to chloroquine has necessitated the drug's replacement as the first-line treatment for malaria, both to increase the likelihood of cure and to reduce transmission. To see if beta-artemether could be a suitable alternative to chloroquine, 223 adults (aged > or = 15 years) with uncomplicated, Plasmodium falciparum malaria were each given a total dose of 480 mg beta-artemether over 4 or 5 days. The patients were randomly allocated to receive an initial, loading dose of 80 or 160 mg, and were checked on days 1, 2, 3, 4 (or 5), 7 and 14, for fever clearance and any adverse events. Blood samples collected on days 0, 4 (or 5), 7 and 14 were smeared so that levels of parasitaemia could be evaluated. Haemoglobin concentrations on days 0 and 14 were also determined. In terms of the clinical cure 'rates' estimated in the intention-to-treat analysis (92.5% v. 97.4%) and the evaluability analysis (98.9% v. 100%), and of the frequency of parasitological cure by day 14 (97.0% v. 96.5%), the patients given an initial dose of 80 mg were similar to those given 160 mg as the loading dose. The regimen with the 160-mg loading dose appears as safe and as effective as the regimen with an initial dose of 80 mg. Since the regimen with the higher loading dose is shorter and involves fewer treatments than the other regimen, it would probably be associated with better compliance.

Infant illness spanning the antenatal to early neonatal continuum in rural northern Ghana: local perceptions, beliefs and practices

OBJECTIVE

To explore community understanding of perinatal illness in northern Ghana.

STUDY DESIGN

A cross-sectional descriptive study design.

RESULT

253 community members participated in in-depth interviews and focus group discussions, including women with newborn infants, grandmothers and health care providers. Four overarching themes emerged: (1) Local understanding of illness affects treatment practices. Respondents recognized danger signs of illness spanning antenatal to early neonatal periods. Understanding of causation often had a distinctly local flavor, and thus treatment sometimes differed from mainstream recommendations; (2) Mothers are frequently blamed for their infant's illness; (3) Healthcare decisions regarding infant care are often influenced by community members aside from the infant's mother and (4) Confidence in healthcare providers is issue-specific, and many households use a blended approach to meet their health needs.

CONCLUSION

Despite widespread recognition of danger signs and reported intentions to treat ill infants through the formal health care system, traditional approaches to perinatal illness remain common. Interventions need to be aligned with community perceptions if they are to succeed.

Urban-rural differences in the nature and prevalence of mental ill-health in adults with intellectual disabilities

BACKGROUND

In the general population there are statistically significant urban-rural differences in the rate of common mental disorders. In people with intellectual disability (ID) no study has attempted to address this issue.

AIMS

To compare the prevalence of mental illness, autism spectrum disorder (ASD) and behaviour disorder in people with ID living in urban areas with those living in rural areas.

METHODS

Cross-sectional study of 2713 individuals registered with an ID service. Participants were assigned to urban or rural groups using the Department for Environment Food and Rural Affairs rural/urban local authority classification for their district. The main outcome variable was a clinical diagnosis of mental illness, ASD and behaviour disorder. Differences between diagnoses of mental illness in urban and rural areas were evaluated using the chi-squared test for the difference in two independent proportions.

RESULTS

No differences were observed between gender, age and level of ID of service users based on their place of residence. But more people from an ethnic minority background were living in urban areas than rural areas. No differences were observed in the overall prevalence of mental illness by place of residence. However, the results showed that ASD was more common in people living in rural areas.

CONCLUSIONS

We found these results surprising and at odds with the majority of studies carried out in the general population and propose several reasons for the differences found. We believe that the results and further studies in this area will help inform health service provision for those with ID who live in different geographical areas.

A molecular perspective of water at metal interfaces

Water/solid interfaces are relevant to a broad range of physicochemical phenomena and technological processes such as corrosion, lubrication, heterogeneous catalysis and electrochemistry. Although many fields have contributed to rapid progress in the fundamental knowledge of water at interfaces, detailed molecular-level understanding of water/solid interfaces comes mainly from studies on flat metal substrates. These studies have recently shown that a remarkably rich variety of structures form at the interface between water and even seemingly simple flat surfaces. In this Review we discuss the most exciting work in this area, in particular the emerging physical insight and general concepts about how water binds to metal surfaces. We also provide a perspective on outstanding problems, challenges and open questions.

Strain relief and disorder in commensurate water layers formed on Pd(111)

Water adsorbs and desorbs intact on Pd(111), forming a hydrogen-bonded wetting layer whose structure we examine by low energy electron diffraction (LEED) and He atom scattering (HAS). LEED shows that water forms commensurate (√3 × √3)R30° clusters that aggregate into a partially ordered, approximately (7 × 7) superstructure as the layer completes. HAS indicates that the water layer remains disordered on a local (approximately 10 Å) scale. Based on workfunction measurements and density functional theory simulations we propose that water forms small, flat domains of a commensurate (√3 × √3)R30° water network, separated by disordered domain boundaries containing largely H-down water. This arrangement allows the water layer to adapt its density and relieve the lateral strain associated with adsorbing water in the optimum flat atop adsorption site. We discuss different possibilities for the structure of these domain walls and compare this strain relief mechanism to the highly ordered, large unit cell structures formed on surfaces such as Pt(111).

Review of Antenatal-Linked Voluntary Counseling and HIV Testing in Sub-Saharan Africa: Lessons and Options for Ghana

SummaryVoluntary counselling and HIV testing has become an integral part of HIV prevention and care programs in many countries in sub-Saharan Africa. A number of interventions offer potential to reduce mother-to-child HIV transmission. These interventions, including antenatal and or intrapartum administration of antiretroviral drugs require the integration of voluntary counselling and HIV testing for pregnant women into antenatal care. Ghana's strategic framework for HIV control calls for the integration of voluntary counselling and HIV testing to antenatal care nationwide. It sets as target, the year 2005 when VCT would be widely available and accessible in the country. This paper reviews medline-indexed publications on antenatal-linked VCT programs of sub-Saharan Africa. Four critical themes were used in the medline search. These are acceptability, rates of return for test, disclosure of results vis-à-vis confidentiality and cost effectiveness. The growing consensuses on these issues are discussed in relations to the findings of a recent study conducted among 270 pregnant women in Navrongo in the Kassena-Nankana district of northern Ghana. Suggestions are made to guide the on-going pilot VCT and prevention of mother-to-child programs in Ghana. It is also suggested on the basis of the review and the findings of the Navrongo study that Ghana should explore options likely to promote universal access and overall acceptability. These include couple counselling, guarantee of confidentiality, free testing and continuum of care for mothers who are test positive.

Trends in the prevalence of female genital mutilation and its effect on delivery outcomes in the kassena-nankana district of northern ghana

Summary

RATIONAL

Female genital mutilation (FGM) is prevalent in northern Ghana, as the practice is seen as a passage rite to women adulthood and thus undertaken just before marriage.

OBJECTIVES

We determined the changes in trend of FGM in deliveries at the Navrongo War Memorial hospital, and compared the outcomes and FGM status.

DESIGN

Retrospective extraction and analysis of delivery data at the hospital from 1(st) January 1996 to 31(st) December 2003.

RESULTS

Of the 5071 deliveries, about 29% (1466/5071) were associated with FGM. The highest prevalence (95% CI) of 61.5% (50.9, 71.2) was in women aged 40 years and above, and the lowest of 14.4% (11.7, 17.0) was in women below 20 years. The all-age prevalence of FGM showed a significant decline (p-value for linear trend < 0.01) from 35.2% in 1996 to 21.1% in 2003. About 6% (89/1466) of mothers with FGM had stillbirths compared with about 3% (123/3605) of mothers without FGM. Again FGM was associated with 8.2% (120/1466) caesarean section rate compared with 6.7% (241/3605) in mothers without FGM. Mean birth weight and frequency of low birth weights were not significantly associated with FGM status.

CONCLUSION

Although there is a high rate of FGM among mothers in the district and is associated with a higher proportion of stillbirths and caesarean sections, practice has shown a significant decline in the district in recent years due to the prevailing campaigns and intervention studies. There is therefore the need to sustain the ongoing intervention efforts.

Tailoring the structure of water at a metal surface: a structural analysis of the water bilayer formed on an alloy template

Recent studies show that structures based on the traditional "icelike" water bilayer are not stable on flat transition metal surfaces and, instead, more complex wetting layers are formed. Here we show that an ordered bilayer can be formed on a SnPt(111) alloy template and determine the structure of the water layer by low energy electron diffraction. Close agreement is found between experiment and the structure calculated by density functional theory. Corrugation of the alloy surface allows only alternate water molecules to chemisorb, stabilizing the H-down water bilayer by reducing the metal-hydrogen repulsion compared to a flat surface.

c(2×2) water-hydroxyl layer on Cu(110): a wetting layer stabilized by Bjerrum defects

Understanding the composition and stability of mixed water-hydroxyl layers is a key step in describing wetting and how surfaces respond to redox processes. Here we show that, instead of forming a complete hydrogen bonding network, structures containing an excess of water over hydroxyl are stabilized on Cu(110) by forming a distorted hexagonal network of water-hydroxyl trimers containing Bjerrum defects. This arrangement maximizes the number of strong bonds formed by water donation to OH and provides uncoordinated OH groups able to hydrogen bond multilayer water and nucleate growth.

The Efficacies of 3,4,3-LIHOPO and DTPA for Enhancing the Excretion of Plutonium and Americium from the Rat: Comparison with Other Siderophore Analogues

With DTPA as a comparison, the siderophore analogue code named 3,4,3-LIHOPO has been tested for its ability to remove 238Pu and 241Am from rats after their inhalation or intravenous injection as nitrate. The most effective treatment regimen for inhaled Pu was the repeated administration of 30 mumol kg-1 3,4,3-LIHOPO. By 7 days after exposure, the Pu contents of the lungs and total body were reduced respectively to 2 and 4% of those in untreated animals. These values were six and three times less than when DTPA was administered using the same protocol. For inhaled Am, 3,4,3-LIHOPO and DTPA were considered equally effective, the lung and total body contents being reduced respectively to 13 and 10% of those in controls. Some animals showed slight degenerative changes in the liver and proximal tubules of the kidneys after the repeated administration of 30 mumol kg-1 of 3,4,3-LIHOPO; however these changes were less marked than after DTPA treatment. After the intravenous injection of Pu, the most effective regimen was the single administration of 3 mumol kg-1 3,4,3-LIHOPO. The body content at 7 days was reduced to 7% controls compared with 19% after the repeated administration of 30 mumol kg-1 DTPA. At a dosage of 30 mumol kg-1, 3,4,3-LIHOPO was less effective owing to the higher retention of Pu in the liver. With repeated dosages of 30 mumol kg-1 3,4,3-LIHOPO was more effective than DTPA for the decorporation of Am; the body contents were 16 and 31% of those in controls respectively. Importantly, the body content was still reduced to 28% of control after a single administration of 3 mumol kg-1. The ligand 3,4,3-LIHOPO, which is also superior to other siderophore analogues, could represent a most significant development in the decorporation of Pu and Am.

Comparative absorption parameters of Pu and Am from PuO2and mixed oxide aerosols measured afterin vitrodissolution test and inhalation in rats

PURPOSE

To compare specific absorption parameter values obtained from in vitro dissolution studies (this paper) and in vivo experiments (data published by Ramounet et al, 2000) and to determine their influence on Dose Per Unit Intake (DPUI) calculations.

MATERIALS AND METHODS

Experiments were performed on plutonium oxide (PuO2) and two Mixed Oxide (MOx) preparations containing 5% Pu (w/w) made according to the industrial process in vitro using a static test and in vivo after rat inhalation.

RESULTS

Behaviour of Pu and Am shows, in vitro, at shorter times, a greater rapid dissolution fraction f(r) for Pu (factor 10) and Am (factor 2) with MOx powders compared with PuO2, whereas in vivo results show a greater fraction f(r) for Pu (factor 5) and Am (factor 15) with PuO2 compared with MOx powders. This phenomenon has not been observed for slow dissolution absorption parameter s(s). The in vivo parameters for Pu and Am in these materials were very close to the default values recommended by International Commission for Radiological Protection for default Type S.

CONCLUSIONS

Results obtained have shown that solubility of Pu from the mixed oxide was higher than that of Pu from PuO2. Nevertheless, no significant difference was observed between the three compounds in the corresponding dose coefficients in vivo or in vitro. Therefore, for these particular compounds, variation in the chemical composition of the aerosols had no significant influence on DPUI. Consequently, in vitro, the dissolution test can provide a good estimate of the in vivo behaviour. Studies of variation of % Pu (w/w) from MOx are in progress in our laboratory to confirm these conclusions.

A one-dimensional ice structure built from pentagons

Heterogeneous ice nucleation has a key role in fields as diverse as atmospheric chemistry and biology. Ice nucleation on metal surfaces affords an opportunity to watch this process unfold at the molecular scale on a well-defined, planar interface. A common feature of structural models for such films is that they are built from hexagonal arrangements of molecules. Here we show, through a combination of scanning tunnelling microscopy, infrared spectroscopy and density-functional theory, that about 1-nm-wide ice chains that nucleate on Cu(110) are not built from hexagons, but instead are built from a face-sharing arrangement of water pentagons. The pentagon structure is favoured over others because it maximizes the water-metal bonding while maintaining a strong hydrogen-bonding network. It reveals an unanticipated structural adaptability of water-ice films, demonstrating that the presence of the substrate can be sufficient to favour non-hexagonal structural units.

Order and disorder in the wetting layer on Ru(0001)

The growth of an intact water monolayer on Ru(0001) has been investigated by comparing the ordering of O and Ru, determined by low-energy electron diffraction (LEED), with that of the top layer of O and H, as probed by He atom scattering (HAS). Although LEED shows that water forms an extended commensurate (square root 3 x square root 3) R30 degrees structure as the coverage approaches 0.67 monolayer, the HAS distributions are insensitive to the exact water coverage and show a very low specular reflectivity, indicating a disordered water layer. The angular profile from a D2O monolayer shows a broad diffuse peak in the angular scattering distribution at a momentum exchange similar to the position of the second-order (1/3, 1/3) peaks, but the maxima show little variation with scattering azimuth. H2O shows a slightly higher He reflectivity and more clearly resolved angular structure, with broad, faint peaks appearing close to the first-order diffraction positions. The origin of this disorder is discussed based on density functional calculations for the monolayer which find that water forms chains of flat and H-down molecules within a hexagonal hydrogen-bonding network, rather than the ice bilayer usually assumed. This arrangement leads to long-range order in the O location, but disorder in the O height and the proton orientation. We discuss how this combination of lateral order in the adsorption site, but disorder in the water orientation, is reflected in the sharp square root 3 LEED pattern but diffuse, broad peaks in He scattering.

What are the Technical and Allocative Efficiencies of Public Health Centres in Ghana?

INTRODUCTION

Health systems in developing countries including Ghana are faced with critical resource constraints in pursuing the goal of improving the health status of the population. The constrained ability to adequately meet health care needs is exacerbated by inefficiency in the health care systems, especially within public health centres.

METHODS

The study used Data Envelopment Analysis (DEA) method, to calculate the technical and allocative efficiency of 113 randomly sampled health centres. A logistic regression model was also applied on whether a health centre was technically efficient or not to determine the factors that significantly influence the efficiency of health centres.

FINDINGS

The findings showed that 78% of health centres were technically inefficient and so were using resources that they did not actually need. Eight-eight percent were also allocatively inefficient. The overall efficiency, (product of the technical and allocative efficiency), was also calculated and over 90% of the health centres were inefficient. The results of a logistic regression analysis show that newer health centres and those which receive incentives were more likely to be technically efficient compared to older health centres and those who did receive incentives.

CONCLUSION

The results broadly point to grave inefficiency in the health care delivery system of the health centres and that lots of resources could be saved if measures were put in place to curb the waste. Incentives to health centres were found to be major motivating factors to the promotion of efficiency.

Internal dosimetry: towards harmonisation and coordination of research

The CONRAD Project is a Coordinated Network for Radiation Dosimetry funded by the European Commission 6th Framework Programme. The activities developed within CONRAD Work Package 5 ('Coordination of Research on Internal Dosimetry') have contributed to improve the harmonisation and reliability in the assessment of internal doses. The tasks carried out included a study of uncertainties and the refinement of the IDEAS Guidelines associated with the evaluation of doses after intakes of radionuclides. The implementation and quality assurance of new biokinetic models for dose assessment and the first attempt to develop a generic dosimetric model for DTPA therapy are important WP5 achievements. Applications of voxel phantoms and Monte Carlo simulations for the assessment of intakes from in vivo measurements were also considered. A Nuclear Emergency Monitoring Network (EUREMON) has been established for the interpretation of monitoring data after accidental or deliberate releases of radionuclides. Finally, WP5 group has worked on the update of the existing IDEAS bibliographic, internal contamination and case evaluation databases. A summary of CONRAD WP5 objectives and results is presented here.

In vitro dissolution of tritium-loaded particles from the JET fusion machine

With the experimental evolution of fusion power the levels of tritium used will increase as will the potential for human exposure. Tritium-loaded carbon particles produced during the experimental operation of the Joint European Torus fusion tokamak have been characterised in terms of size, elemental composition and specific activity of tritium elsewhere. The aim of this study was to characterise the dissolution of tritium from these particles in order to derive dose coefficients for this material and provide guidance on monitoring procedures should it be inhaled accidentally. The dissolution of tritium was measured for 100 d in lung serum simulant from two batches of materials, SG1 and SG2, which were obtained from carbon tiles originating from different positions in the reactor. Retention over this period followed a three-component exponential. About 1-5% dissolved within a minute, and up to a further 20% dissolved over 100 d for the SG1 materials but <1% for the SG2 materials. Dissolution between the SG1 materials varied greatly, whereas the SG2 materials were similar. As a result of this variability, the assessed dose from urinary excretion could be in error by up to two orders of magnitude depending on the material inhaled. It is recommended that (i) the dissolution is measured for a wider range of materials, preferably dusts collected in working areas, and (ii) in vivo studies are performed to characterise fully the urine excretion of tritium from these materials. This information could be used to provide improved guidance on dose assessment after special or routine monitoring, taking account of the likely variation of particle size and biological retention half times.

Comparative repeatability of guide-pin axis positioning in computer-assisted and manual femoral head resurfacing arthroplasty

The orientation of the femoral component in hip resurfacing arthroplasty affects the likelihood of loosening and fracture. Computer-assisted surgery has been shown to improve significantly the surgeon's ability to achieve a desired position and orientation; nevertheless, both bias and variability in positioning remain and can potentially be improved. The authors recently developed a computer-assisted surgical (CAS) technique to guide the placement of the pin used in femoral head resurfacing arthroplasty and showed that it produced significantly less variation than a typical manual technique in varus/valgus placement relative to a pre-operatively determined surgical plan while taking a comparable amount of time. In the present study, the repeatability of both the CAS and manual techniques is evaluated in order to estimate the relative contributions to overall variability of surgical technique (CAS versus manual), surgeon experience (novice versus experienced), and other sources of variability (e.g. across specimens and across surgeons). This will enable further improvements in the accuracy of CAS techniques.

Three residents/fellows new to femoral head resurfacing and three experienced hip arthroplasty surgeons performed 20-30 repetitions of each of the CAS and manual techniques on at least one of four cadaveric femur specimens. The CAS system had markedly better repeatability (1.2°) in varus/valgus placement relative to the manual technique (2.8°), slightly worse repeatability in version (4.4° versus 3.2°), markedly better repeatability in mid-neck placement (0.7 mm versus 2.5 mm), no significant dependence on surgeon skill level (in contrast to the manual technique), and took significantly less time (50 s versus 123 s). Proposed improvements to the version measurement process showed potential for reducing the standard deviation by almost two thirds.

This study supports the use of CAS for femoral head resurfacing as it is quicker than the manual technique, independent of surgeon experience, and demonstrates improved repeatability.