Observation of residual disorder in the centre of amorphous solid water films after pore collapse at 125 K.

The rapid structural re-organisation of porous amorphous solid water, grown to thicknesses in the range 2.5-70 µm by vapour deposition on a copper substrate at 75 K, after heating to 125 K has been found to leave a µm-wide band of residual disorder-for example, nm-sized closed pores-in the centre of the film. This layer was revealed by thinning the film by sublimation and continuously measuring the fraction of 1.5 keV positrons implanted into the film which forms ortho-positronium in the top 150 nm and decays into three gamma photons.

Structural changes in amorphous solid water films on heating to 120-140 K and 150-160 K seen by positronium annihilation spectroscopy.

Changes in the structure of amorphous solid water films, grown by vapour deposition on a copper substrate at 75 K and then held at 120 K for 10 min to effect pore collapse, have been observed in the ranges 122-139 K and 150-162 K using positronium annihilation spectroscopy. It is proposed that the former is associated with the glass transition, with an effective activation energy of 0.266(3) eV. The data for the latter, which exhibit minima suggesting the temporary introduction of molecular disorder, can be processed to yield an effective activation energy of 0.47(2) eV, and are consistent with either a structural reorganization of the crystalline lattice or a relaxation of the amorphous structure mediated by defect migration.

Structure and sublimation of water ice films grown in vacuo at 120-190 K studied by positron and positronium annihilation.

The crystalline structure of ∼ 5-20 µm water ice films grown at 165 and 172 K has been probed by measuring the fraction of positrons forming ortho-positronium (ortho-Ps) and decaying into three gamma photons. It has been established that films grown at slower rates (water vapour pressure ≥ 1 mPa) have lower concentrations of lattice defects and closed pores, which act as Ps traps, than those grown at higher rates (vapour pressure ∼ 100 mPa), evidenced by ortho-Ps diffusion lengths being approximately four times greater in the former. By varying the growth temperature between 162 and 182 K it was found that films become less disordered at temperatures above ∼ 172 K, with the ortho-Ps diffusion length rising by ∼ 60%, in this range. The sublimation energy for water ice films grown on copper has been measured to be 0.462(5) eV using the time dependence of positron annihilation parameters from 165 to 195 K, in agreement with earlier studies and with no measurable dependence on growth rate and thermal history.

Measuring the three-photon self-annihilation fraction of positronium in and above thin films: a tool for determining film morphology.

A technique is described for evaluating the fraction of positrons F incident on thin film samples which form ortho-positronium and subsequently decay into three gamma photons. The method involves the measurement of two linked phenomena: the decrease in the number of annihilation events involving the emission of two gamma photons with approximately 511 keV in the germanium detector photopeak, and the increase in the number of decays into three gamma photons with energies in the range 395-505 keV. After the application of a number of systematic corrections to the raw data, these measurements allow the determination of the absolute value of F without the need for calibration on a sample with known F values, thereby avoiding problems with changing samples of different geometries measured under different conditions.

Direct observation of electron capture and reemission by the divacancy via charge transient positron spectroscopy.

Electron capture during forward bias and reemission at zero bias by divacancies in the depletion region of a silicon diode structure at room temperature have been studied for the first time using monoenergetic positrons. The positron response increases essentially linearly with electron current, as a result of increased positron trapping by negatively charged divacancies. The measurements indicate that ≤1% of the divacancies become negatively charged in the steady state at a forward bias of 1 V. Changes in the mean positron response when applying a square wave bias to the sample (1 V forward bias and 0 V, duty cycle 1:4, times at 0 V in the range 0.1-100 µs), were consistent with a rapid conversion of doubly to singly charged divacancies (in ∼10(1) ns), followed by slower defilling of the singly charged divacancies with a time constant of ∼10(1) µs. These ac measurements allow determination of the relative populations of singly and doubly charged divacancies. The results provide confirmation of consistency between the positron's response to the silicon divacancy and previously extracted capture and emission kinetics determined through charge transient measurements and assigned to the same defect. The possibility of combining these two, orthogonal techniques suggest a promising new and powerful approach to defect spectroscopy in which the structure and electrical properties of a defect may be determined in a single measurement.

Structural and phase changes in amorphous solid water films revealed by positron beam spectroscopy.

The evolution and annealing of pores in, and the crystallization of, vapor-deposited films of amorphous solid water have been studied by using variable-energy positron annihilation spectroscopy for temperatures in the range 50-150 K. Both positron and positronium annihilation provide insight to the nature of the grown-in pores and their evolution with temperature. Crystallization of the films was observed at just below 140 K, in agreement with earlier studies, with the topmost 80 nm undergoing a transition consistent with crystallization at 90-100 K.

Coupling between positron-atom scattering channels above the first inelastic threshold.

Experimentally determined cross sections for the elastic scattering of positrons by argon and xenon atoms have been found to exhibit a steplike increase at the first inelastic threshold energy--i.e., that for positronium formation. Rather than supporting the existence of a cusplike behavior predicted theoretically, this feature, which is more pronounced for xenon, suggests the existence of an intermediate virtual positronium state which enhances the elastic interaction probability.

Activation energies for the formation and evaporation of vacancy clusters in silicon.

The thermal evolution of vacancy-type defects in Czochralski (Cz-) and epitaxially grown (epi-) silicon has been investigated using variable-energy positron annihilation spectroscopy. Heating at 300-500 degrees C caused rapid migration of divacancies and clustering of the resulting defects with activation energies of 2.1(2) and 2.7(7) eV in epi- and Cz-Si. Clustering occurred more rapidly in Cz-Si, attributed to the seeding effect of impurities. Heating at 500-640 degrees C annealed the clusters with activation energies of 3.9(3) and 3.6(3) eV in epi- and Cz-Si, linked to the vacancy-cluster binding energy.

Monovacancy and interstitial migration in ion-implanted silicon.

The migration of monovacancies (V0) and self-interstitials (I) has been observed in ion-implanted low-doped float-zone silicon by variable-energy positron annihilation spectroscopy. V0 and I were created by the in situ implantation of approximately 20 keV helium ions below 50 K. Monitoring the time evolution of the vacancy response during isothermal heating enabled the measurement of activation energies for I and V(0) [corrected] migration of 0.078(7) and 0.46(28) eV, respectively. In highly As-doped Si, partial V annihilation occurs via free I migration, with a second stage of annealing, probably associated with V-As complexes, above room temperature.

The sound of death rattle I: are relatives distressed by hearing this sound?

BACKGROUND: Death rattle is the noisy, rattling breathing that occurs in many dying patients. Health professionals intervene because the sound is said to distress attendant relatives. We found no formal study to confirm or refute relatives' distress, so we decided to ask the relatives. METHOD: Face-to-face semi-structured interviews with 27 bereaved relatives to investigate their experience of terminal care and what their response had been to the sound of death rattle if this had occurred. Interview transcripts were subjected to thematic content analysis. RESULTS: We found that almost half of the 12 relatives who had heard the sound of death rattle had been distressed by it. The others were either neutral about the sound or found it a helpful signal of impending death. CONCLUSION: We confirmed that some relatives do find it distressing to hear the sound of death rattle. However, our expectation that relatives are universally disturbed by this sound was unfounded. There is no justification for a 'blanket' approach to therapeutic intervention when death rattle occurs. A better understanding is required of how relatives make sense of the sound of death rattle.

The sound of death rattle II: how do relatives interpret the sound?

BACKGROUND: In an earlier study, we found that some bereaved relatives (five out of 12 interviewed) found it distressing to hear the sound of death rattle, but the remainder did not. In this paper, we report a second study in which we explored how a different group of relatives interpreted the sound of death rattle when they heard it. METHOD: We conducted face-to-face semi-structured interviews with 25 bereaved relatives using the principles of grounded theory. RESULTS: Seventeen of the 25 bereaved relatives interviewed had heard the sound of death rattle. Ten relatives were distressed by the sound, but seven were not. Some relatives regarded the sound of death rattle as a useful warning sign that death was imminent. Their interpretation of the sound was influenced by the patient's appearance, being less concerned if the patient was not obviously disturbed. Relatives were distressed when they thought that the sound of death rattle indicated that the patient might be drowning or choking. These concerns were reinforced by seeing fluid dribble from the dying patient's mouth. CONCLUSION: This study confirms the previous finding that not all relatives are distressed by the sound of death rattle. It also demonstrates that relatives interpret the sound in a variety of ways, some matter of fact and some distressing. We suggest that effective communication is helpful in uncovering relatives' interpretation of death rattle and dispelling unwarranted fears.

Falklands War veterans' perceptions of social support and the reconciliation of traumatic memories.

The current paper focused on the role social support plays in the reconciliation of traumatic memories. Four currently serving, male Royal Marines ranging from 40-42 years participated in semi-structured one-to-one interviews that explored perceptions of social support. Using thematic analysis, comradeship was found to be important in terms of maintaining support networks. However, this resource was used to avoid the reconciliation of traumatic memories. Social support from family members was sought when veterans were reassured that relatives would understand their experiences, and could support reconciliation. The importance of positive societal reaction was also emphasized. The paper concludes by highlighting the potential for early life reconciliation of traumatic war memories through the creation of a meaningful personal narrative.

Quantifying the level of under-detection of Trypanosoma brucei rhodesiense sleeping sickness cases.

To formally quantify the level of under-detection of Trypanosoma brucei rhodesiense sleeping sickness (SS) during an epidemic in Uganda, a decision tree (under-detection) model was developed; concurrently, to quantify the subset of undetected cases that sought health care but were not diagnosed, a deterministic (subset) model was developed. The values of the under-detection model parameters were estimated from previously published records of the duration of symptoms prior to presentation and the ratio of early to late stage cases in 760 SS patients presenting at LIRI hospital, Tororo, Uganda during the 1988--1990 epidemic of SS. For the observed early to late stage ratio of 0.47, we estimate that the proportion of under-detection in the catchment area of LIRI hospital was 0.39 (95% CI 0.37--0.41) i.e. 39% of cases are not reported. Based on this value, it is calculated that for every one reported death of SS, 12.0 (95% CI 11.0--13.0) deaths went undetected in the LIRI hospital catchment area - i.e. 92% of deaths are not reported. The deterministic (subset) model structured on the possible routes of a SS infection to either diagnosis or death through the health system or out of it, showed that of a total of 73 undetected deaths, 62 (CI 60-64) (85%) entered the healthcare system but were not diagnosed, and 11 (CI 11--12) died without seeking health care from a recognized health unit. The measure of early to late stage presentation provides a tractable measure to determine the level of rhodesiense SS under-detection and to gauge the effects of interventions aimed at increasing treatment coverage.

A burgeoning epidemic of sleeping sickness in Uganda.

The epidemic of Trypanosoma brucei rhodesiense sleeping sickness in eastern Uganda, which began in 1998 as a result of movements of the livestock reservoir of the parasite, has continued to spread. An additional 133 000 people have been put at risk of infection in Kaberamaido, another newly affected district. The few resources committed to control interventions in Soroti district have failed to contain the epidemic. The high prevalence of the parasite in cattle presents a significant risk for transmission to human beings and further spread of this neglected zoonotic disease. Targeted interventions are urgently needed to control epidemics and reduce the high mortality resulting from sleeping sickness.

The epidemiology of animal bite injuries in Uganda and projections of the burden of rabies.

OBJECTIVES: Rabies is a global problem, although it is often under-reported in developing countries. We aimed at describing the profile of patients presenting to health centres with animal bite injuries in Uganda, and use a predictive model to estimate the mortality of rabies at a national level. METHODS: We conducted a passive surveillance study in Uganda based in a random sample of health centres supplied with rabies vaccine to determine the characteristics of bite injury patients and establish the age and sex profiles of patients, the site of bites and their severity, wound management techniques and details of the vaccination course given. We also applied a decision tree model to the data to estimate the rabies mortality from the bite injury data using an established protocol. RESULTS: We found that most patients are bitten by dogs, and that a considerable proportion of these are young children, who are at greater risk of developing rabies in the absence of treatment due to the location of the bites they receive. From conservative parameter estimates, we estimate that in the absence of post-exposure prophylaxis (PET), 592 (95% CI 345-920) deaths would occur, and that if one dose of PET is sufficient for protection following a rabid animal bite, 20 (95% CI 5-50) deaths would occur annually. If a complete course of PET is required for protection following a rabid animal bite, up to 210 (95% CI 115-359) deaths would occur, as 41% of patients did not complete their course of PET. CONCLUSIONS: Active animal bite surveillance studies are required to improve our mortality estimates and determine the true burden of rabies in the Ugandan population. We emphasize the need for small-scale active case detection studies and improved data on the recognition of rabies in dogs as inputs for improving national-level estimates of rabies mortality.

Estimating medium- and long-term trends in malaria transmission by using serological markers of malaria exposure.

The implementation and evaluation of malaria control programs would be greatly facilitated by new tools for the rapid assessment of malaria transmission intensity. Because acquisition and maintenance of antimalarial antibodies depend on exposure to malaria infection, such antibodies might be used as proxy measures of transmission intensity. We have compared the prevalence of IgG antibodies with three Plasmodium falciparum asexual stage antigens in individuals of all ages living at varying altitudes encompassing a range of transmission intensities from hyper- to hypoendemic in northeastern Tanzania, with alternative measures of transmission intensity. The prevalence of antibodies to merozoite surface protein-1(19) was significantly more closely correlated with altitude than either point-prevalence malaria parasitemia or single measures of hemoglobin concentration. Analysis of age-specific seroprevalence rates enabled differentiation of recent (seasonal) changes in transmission intensity from longer-term transmission trends and, using a mathematical model of the annual rate of seroconversion, estimation of the longevity of the antibody response. Thus, serological tools allow us to detect variations in malaria transmission over time. Such tools will be invaluable for monitoring trends in malaria endemicity and the effectiveness of malaria control programs.

Spatial and temporal risk factors for the early detection of Trypanosoma brucei rhodesiense sleeping sickness patients in Tororo and Busia districts, Uganda.

We have carried out a study of risk factors for early detection of Trypanosoma brucei rhodesiense sleeping sickness. Records of sleeping sickness patients from 1987 to 2001 from Tororo and Busia districts in Uganda were reviewed for their village of origin and clinical stage (early or late). All villages that reported sleeping sickness and fixed post-diagnostic sleeping sickness health units in Tororo and Busia districts were geo-referenced. The spatial distribution of early and late stage patient detection by health units was analysed using Geographical Information Systems (GIS). Of 1316 sleeping sickness patients admitted at the Livestock Health Research Institute and Busolwe hospitals and Lumino health centre from Tororo and Busia districts, 471 (35.8%) were early stage, 825 (62.7%) were late stage, while 20 (1.5%) were not staged. Five hundred and eighty-five (44.5%) came from within a 10 km radius of the reporting health units. After multivariate analysis, the proportion of early stage patients detected was found to be significantly associated with patients originating from within a 10 km radius of the health unit (P < 0.01), with adults (>19 years) (P < 0.01), and with annual parish incidence (P < 0.01). Application of GIS and the early to late stages ratio are an informative and powerful means of determining efficiency of surveillance of sleeping sickness.

Assessing the patterns of health-seeking behaviour and awareness among sleeping-sickness patients in eastern Uganda.

For those with sleeping sickness, the consequences of delayed diagnosis include poor prognosis at treatment and an increased risk of tsetse infection. Data on their socio-demographic and clinical characteristics, health-seeking behaviour and delays in presentation and diagnosis were collected from 119 diagnosed cases of rhodesiense sleeping sickness in eastern Uganda. The median total delay, from onset of the illness to diagnosis, was 60 days. The median service-provider delay (30 days) was markedly longer than the median patient delay (17 days). Each of these delays was, however, considerable and independently associated with patients presenting with late-stage sleepiness, giving odds ratios and (95% confidence intervals) of 7.29 (3.10-17.14) and 2.98 (1.38-6.43), respectively. A blood examination at the first visit was also associated with the service-provider delay (odds ratio = 0.45; 95% confidence interval = 0.22-0.95). Most of the patients (77.4%) had either been referred to the local sleeping-sickness hospital by other members of their community or presented at the hospital on their own initiative; few had been referred by other components of the local health system. The results are disappointing, not only in showing long delays in diagnosis (and therefore in treatment) but also in indicating that much of the delay is attributable to the service provider failing to diagnose sleeping sickness among symptomatic individuals.

Reanalyzing the 1900-1920 sleeping sickness epidemic in Uganda.

Sleeping sickness has long been a major public health problem in Uganda. From 1900 to 1920, more than 250,000 people died in an epidemic that affected the southern part of the country, particularly the Busoga region. The epidemic has traditionally been ascribed to Trypanosoma brucei gambiense, a parasite now confined to central and western Africa. The Busoga region still reports sleeping sickness, although it is caused by T.b. rhodesiense, commonly believed to have spread to Uganda from Zambia in the 1940s. Our analysis of clinical data recorded in the early 1900s shows that the clinical course of sleeping sickness cases during the 1900-1920 epidemic in Uganda was markedly different from T.b. gambiense cases, but similar to T.b. rhodesiense. These findings suggest that T.b. rhodesiense was present in Uganda and contributed to the epidemic. The historic context is reassessed in the light of these data.

A comparative study on the clinical, parasitological and molecular diagnosis of bovine trypanosomosis in Uganda.

The clinical, parasitological and molecular diagnosis of bovine trypanosomosis were compared using samples from 250 zebu cattle exposed to natural trypanosome challenge in Uganda. Clinical examination, molecular and parasitological diagnoses detected 184 (73.6%), 96 (38.4%) and 36 (14.4%) as diseased, respectively. The sensitivity and specificity of clinical examination were 87.5% and 35%, and 78 % and 27 % based on molecular and parasitological diagnoses, as gold standards, respectively. Of the 33, 3, 13 and 12 parasitological-positive cattle that had Trypanosoma brucei, Trypanosoma congolense, Trypanosoma vivax or mixed infections, 78 %, 33 %, 84 % and 100 % respectively manifested clinical signs. Of the 24, 89, 12, 3, 6 and 27 cattle detected by molecular diagnosis to have mixed infections, T. brucei, T. vivax, T. congolense forest-, Savannah- and Tsavo-type, 100%, 83%, 91%, 100%, 67% and 81 % had clinical signs, respectively. In conclusion, treatment of cattle based on clinical examination may clear up to 87.5 % or 78 % of the cases that would be positive by either molecular or parasitological diagnosis, respectively. Under field conditions, in the absence of simple and portable diagnostic tools or access to laboratory facilities, veterinarians could rely on clinical diagnosis to screen and treat cases of bovine trypanosomosis presented by farmers before confirmatory diagnosis in diagnostic centres for few unclear cases is sought.