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S Wall

Publications and source records attributed to S Wall.

At least 19 recordsLinked to original sources
PubMed2007

The lakes of Titan.

The surface of Saturn's haze-shrouded moon Titan has long been proposed to have oceans or lakes, on the basis of the stability of liquid methane at the surface. Initial visible and radar imaging failed to find any evidence of an ocean, although abundant evidence was found that flowing liquids have existed on the surface. Here we provide definitive evidence for the presence of lakes on the surface of Titan, obtained during the Cassini Radar flyby of Titan on 22 July 2006 (T16). The radar imaging polewards of 70 degrees north shows more than 75 circular to irregular radar-dark patches, in a region where liquid methane and ethane are expected to be abundant and stable on the surface. The radar-dark patches are interpreted as lakes on the basis of their very low radar reflectivity and morphological similarities to lakes, including associated channels and location in topographic depressions. Some of the lakes do not completely fill the depressions in which they lie, and apparently dry depressions are present. We interpret this to indicate that lakes are present in a number of states, including partly dry and liquid-filled. These northern-hemisphere lakes constitute the strongest evidence yet that a condensable-liquid hydrological cycle is active in Titan's surface and atmosphere, in which the lakes are filled through rainfall and/or intersection with the subsurface 'liquid methane' table.

Journal Article↗
PubMed2006

Association between body mass index and blood pressure across three populations in Africa and Asia.

Despite a growing burden of obesity and hypertension in developing countries, there is limited information on the contribution of body mass index (BMI) to blood pressure (BP) in these populations. This study examines the association between BMI and BP in three populations across Africa and Asia. Data on BMI, BP and other background characteristics of study participants were generated using the World Health Organization STEPwise approach to surveillance (STEPS), at three demographic surveillance sites in Ethiopia, Vietnam and Indonesia. BMI and BP increased along the socioeconomic gradient across the three countries. Mean (s.d.) BMI in men varied between 19.41 (2.28) in Ethiopia to 21.17 (2.86) in Indonesia. A high prevalence of overweight/obesity was noted among Indonesian women (25%) and men (10%), whereas low BMI was widely prevalent in Ethiopia and Vietnam, ranging from 33 to 43%. Mean (s.d.) systolic BP (SBP) among men varied between 117.15 (15.35) in Ethiopia to 127.33 (17.80) in Indonesia. The prevalence of hypertension was highest among women (25%) and men (24%) in Indonesia. Mean BP levels increased with increasing BMI. The risk of hypertension was higher among population groups with overweight and obesity (BMI>/=25 kg/m(2)); odds ratio (95% confidence interval); 2.47 (1.42, 4.29) in Ethiopia, 2.67 (1.75, 4.08) in Vietnam and 7.64 (3.88, 15.0) in Indonesia. BMI was significantly and positively correlated with both SBP and DBP in all the three populations, correlation coefficient (r) ranging between 0.23 and 0.27, P<0.01. High BP exists in a background of undernutrition in populations at early stages of the epidemiologic transition.

Adult↗
PubMed2006

Tracking the motion of charges in a terahertz light field by femtosecond X-ray diffraction.

In condensed matter, light propagation near resonances is described in terms of polaritons, electro-mechanical excitations in which the time-dependent electric field is coupled to the oscillation of charged masses. This description underpins our understanding of the macroscopic optical properties of solids, liquids and plasmas, as well as of their dispersion with frequency. In ferroelectric materials, terahertz radiation propagates by driving infrared-active lattice vibrations, resulting in phonon-polariton waves. Electro-optic sampling with femtosecond optical pulses can measure the time-dependent electrical polarization, providing a phase-sensitive analogue to optical Raman scattering. Here we use femtosecond time-resolved X-ray diffraction, a phase-sensitive analogue to inelastic X-ray scattering, to measure the corresponding displacements of ions in ferroelectric lithium tantalate, LiTaO(3). Amplitude and phase of all degrees of freedom in a light field are thus directly measured in the time domain. Notably, extension of other X-ray techniques to the femtosecond timescale (for example, magnetic or anomalous scattering) would allow for studies in complex systems, where electric fields couple to multiple degrees of freedom.

Journal Article↗
PubMed2006

Titan Radar Mapper observations from Cassini's T3 fly-by.

Cassini's Titan Radar Mapper imaged the surface of Saturn's moon Titan on its February 2005 fly-by (denoted T3), collecting high-resolution synthetic-aperture radar and larger-scale radiometry and scatterometry data. These data provide the first definitive identification of impact craters on the surface of Titan, networks of fluvial channels and surficial dark streaks that may be longitudinal dunes. Here we describe this great diversity of landforms. We conclude that much of the surface thus far imaged by radar of the haze-shrouded Titan is very young, with persistent geologic activity.

Journal Article↗
PubMed2006

The sand seas of Titan: Cassini RADAR observations of longitudinal dunes.

The most recent Cassini RADAR images of Titan show widespread regions (up to 1500 kilometers by 200 kilometers) of near-parallel radar-dark linear features that appear to be seas of longitudinal dunes similar to those seen in the Namib desert on Earth. The Ku-band (2.17-centimeter wavelength) images show approximately 100-meter ridges consistent with duneforms and reveal flow interactions with underlying hills. The distribution and orientation of the dunes support a model of fluctuating surface winds of approximately 0.5 meter per second resulting from the combination of an eastward flow with a variable tidal wind. The existence of dunes also requires geological processes that create sand-sized (100- to 300-micrometer) particulates and a lack of persistent equatorial surface liquids to act as sand traps.

Extraterrestrial Environment↗
PubMed2006

Gender differences in prevalence and socioeconomic determinants of hypertension: findings from the WHO STEPs survey in a rural community of Vietnam.

In Vietnam, hypertension was estimated to cause a large number of deaths in hospitals. However, population-based knowledge about the magnitude of hypertension in Vietnam and its relationship with socioeconomic status, especially in the rural communities, still remains scarce. This paper, taking advantage of a study on noncommunicable disease (NCD) risk factors in Bavi district, Vietnam, using the WHO STEPs approach, estimates the prevalence of hypertension in the setting and examines its association with some socioeconomic factors. A representative sample comprising 2000 adults aged 25-64 years were selected randomly and surveyed in 2002. The JNC VII criteria for hypertension were used. Socioeconomic status of the study subjects was estimated by assessing their education, occupation and economic conditions. Descriptive techniques and multivariate logistic regression were used. The prevalence of hypertension was 14.1%. Of hypertensives, only 17.4% were aware of their hypertensive status. Men were hypertensive more often than women and age was positively associated with hypertension. The association between hypertension and socioeconomic status was complex and differed between men and women. Among men, those with lower educational and occupational status but who were richer were more likely to be hypertensive. More women with lower occupational and economic status were hypertensive.

Adult↗
PubMed2005

Cassini radar views the surface of Titan.

The Cassini Titan Radar Mapper imaged about 1% of Titan's surface at a resolution of approximately 0.5 kilometer, and larger areas of the globe in lower resolution modes. The images reveal a complex surface, with areas of low relief and a variety of geologic features suggestive of dome-like volcanic constructs, flows, and sinuous channels. The surface appears to be young, with few impact craters. Scattering and dielectric properties are consistent with porous ice or organics. Dark patches in the radar images show high brightness temperatures and high emissivity and are consistent with frozen hydrocarbons.

Atmosphere↗
PubMed2005

Dose rate calculations for a reconnaissance vehicle.

A Chemical Nuclear Reconnaissance System (CNRS) has been developed by the British Ministry of Defence to make chemical and radiation measurements on contaminated terrain using appropriate sensors and recording equipment installed in a land rover. A research programme is under way to develop and validate a predictive capability to calculate the build-up of contamination on the vehicle, radiation detector performance and dose rates to the occupants of the vehicle. This paper describes the geometric model of the vehicle and the methodology used for calculations of detector response. Calculated dose rates obtained using the MCBEND Monte Carlo radiation transport computer code in adjoint mode are presented. These address the transient response of the detectors as the vehicle passes through a contaminated area. Calculated dose rates were found to agree with the measured data to be within the experimental uncertainties, thus giving confidence in the shielding model of the vehicle and its application to other scenarios.

Automobiles↗
PubMed2003

Nithsdale Schizophrenia Surveys 24: sexual dysfunction. Case-control study.

BACKGROUND: That sexual dysfunction occurs in schizophrenia is not in doubt. Previous studies have had weaknesses such as the use of selected populations or the absence of a control group. AIMS: To measure rates of sexual dysfunction in people with schizophrenia compared with the general population. METHOD: Sexual dysfunction was assessed by a self-completed gender-specific questionnaire. Ninety-eight (73%) of 135 persons with schizophrenia and 81 (71%) of 114 persons recruited as controls returned the questionnaire. RESULTS: At least one sexual dysfunction was reported by 82% of men and 96% of women with schizophrenia. Male patients reported less desire for sex, were less likely to achieve and maintain an erection, were more likely to ejaculate more quickly and were less satisfied with the intensity of their orgasms. Female patients reported less enjoyment than the control group. Sexual dysfunction in female patients was associated with negative schizophrenic symptoms and general psychopathology. There was no association between sexual dysfunction and type of antipsychotic medication. CONCLUSIONS: People with schizophrenia report much higher rates of sexual dysfunction than do the general population. Men and women with schizophrenia have a different pattern of sexual dysfunction.

Adult↗
PubMed2002

The role of demographic surveillance systems (DSS) in assessing the health of communities: an example from rural Ethiopia.

Longitudinal demographic surveillance systems (DSSs) in selected populations can provide important information in situations where routine health information is incomplete or absent, particularly in developing countries. The Butajira Rural Health Project is one such example, initiated in rural Ethiopia in 1987. DSSs rely on regular community-based surveillance as a means of vital event registration, among a sufficient population base to draw meaningful conclusions about rates and trends in relatively rare events such as maternal death. Enquiries into specific health problems can also then use this framework to quantify particular issues or evaluate interventions. Demographic characteristics and trends for a rural Ethiopian population over a 10-y period are presented as an illustration of the DSS approach, based on 336 000 person-years observed. Overall life expectancy at birth was 50 y. Demographic parameters generally showed modest trends towards improvement over the 10-y period. The DSS approach is useful in characterising populations at the community level over a period of time, providing important information for health planning and intervention. Methodological issues underlying this approach need further exploration and development.

Adolescent↗
PubMed2002

De novo GLI3 mutation in acrocallosal syndrome: broadening the phenotypic spectrum of GLI3 defects and overlap with murine models.

Acrocallosal syndrome (ACS) is characterised by postaxial polydactyly, hallux duplication, macrocephaly, and absence of the corpus callosum, usually with severe developmental delay. The condition overlaps with Greig cephalopolysyndactyly syndrome (GCPS), an autosomal dominant disorder that results from mutations in the GLI3 gene. Here we report a child with agenesis of the corpus callosum and severe retardation, both cardinal features of ACS and rare in GCPS, who has a mutation in GLI3. Since others have excluded GLI3 in ACS, we suggest that ACS may represent a heterogeneous group of disorders that, in some cases, may result from a mutation in GLI3 and represent a severe, allelic form of GCPS. The finding is important for counselling families with suspected ACS.

Abnormalities, Multiple↗
PubMed2002

The impact of neonatal mortality on subsequent survival in rural Ethiopia.

In countries where most deliveries occur at home and most available information is hospital-based, accurate information on neonatal mortality is difficult to obtain. This study was conducted in a rural community in Ethiopia that has been under monthly demographic surveillance since 1987. The analysis in this paper was based on data collected in the 1st decade (1987-96) and this database was used to calculate mortality incidence rates and analyse survival. The overall neonatal mortality rate was 27/1000 live births (95% CI 24.5-29.5). The rates in the early and late neonatal periods were 20 and 8/1000 live births, respectively (95% CIs 18.0-22.9 and 6.6-9.4). The mortality incidence rates show that, every day, three of every 1000 newborns die in their 1st week of life. Neonatal mortality accounted for 43% of infant mortality. If all neonates survived the 1st week of life, life expectancy would increase by 1 year. Increased risk of neonatal mortality was found to be associated with living in a rural lowland area, twin births and male gender. This paper also addresses the need for further identification of the complex environmental and behavioural risk factors for neonatal mortality and for instituting appropriate and affordable interventions to reduce neonatal mortality.

Developing Countries↗
PubMed2001

Are serum anticonvulsant levels in people with epilepsy appropriately monitored?

The medical care of people with epilepsy has often been described as being poor, although objective markers for the quality of epilepsy care are lacking. This paper describes the results of using a simple quality marker, appropriate measuring of serum anticonvulsant levels, in assessing the quality of epilepsy care. The checking of serum phenytoin levels in certain clinical circumstances is advocated, whereas the checking of serum sodium valproate levels is not generally supported. A total of 1254 people with epilepsy in the community had their medical records examined for evidence of checking of anticonvulsant levels and 1204 of these individuals completed questionnaires about their epilepsy and its treatment. Of those on phenytoin, only 26% to 47% had phenytoin levels checked appropriately; 23% of patients on sodium valproate were inappropriately having their serum levels checked. The only clinical or organizational factor that predicted whether checking of serum phenytoin levels was performed was whether or not patients reported three common phenytoin side-effects but this still showed a small effect size (odds ratio 2.4).

Anticonvulsants↗
PubMed2001

Design issues in the combination of international data from two rural community cardiovascular intervention programs.

OBJECTIVES: To compare and contrast two rural cardiovascular community intervention programs (CCIP) in northern Sweden and the US by discussing the methods used to select and combine similar data from two separately designed and implemented CCIP in order to describe and evaluate their effectiveness in reducing cardiovascular risk. METHODS: Two rural intervention populations and their reference populations were compared. A comparison was made of the intensity and duration of the intervention programs using an overall intervention intensity score. Population-based surveys were conducted at 5-year intervals in both countries. The methods used for data pooling and comparison are described. A description of statistical analyses using a mixed analysis of variance model is provided. RESULTS: The data were pooled. taking into consideration comparable ages. New variables were created in order to define the relationship between similar data that did not permit direct comparison. CONCLUSIONS: Combination and comparison of international data from two programs allowed evaluation of community intervention programs that were developed independently for similar communities. The effectiveness of interventions can be compared using such methods.

Adult↗
PubMed2001

The Norsjö-Cooperstown healthy heart project: a case study combining data from different studies without the use of meta-analysis.

OBJECTIVES: This paper aims to develop and describe a method for combining. comparing, and maximizing the statistical power of two longitudinal studies of risk factors for cardiovascular disease that did not have identical data collection methodologies. METHODS: Subjects from a 1986 cross-sectional study (n = 180) were pair-matched with subjects of corresponding gender and age (+5 years) from a 1990 cross-sectional study. The methodology is described and results are calculated for various measures of cardiovascular risk or risk factors (e.g. cholesterol. Finnish Risk Score). RESULTS: Box's test of equality and symmetry of covariance matrices gave chi-square values of 223.8 and 710.0 for two cardiovascular risk factors (cholesterol and cardiac risk score, respectively); these values were highly significant (p=0.0001) For the North Karelia Risk Score, repeated measures ANOVA revealed a borderline significant interaction for treatment by time (p=0.054) and a significant interaction for treatment by time by country (p=0.035). These probabilities compared favorably with a randomized blocks model. CONCLUSIONS: Creation of a synthetic longitudinal control group resulted in a statistically valid ANOVA model that increased the statistical power of the study.

Adult↗
PubMed2001

Different outcomes for different interventions with different focus!--A cross-country comparison of community interventions in rural Swedish and US populations.

OBJECTIVES: There is a need among healthcare providers to acquire more knowledge about small-scale and low budget community intervention programmes. This paper compares risk factor outcomes in Swedish and US intervention programmes for the prevention of cardiovascular disease (CVD). The aim was to explore how different intervention programme profiles affect outcome. METHODS: Using a quasi-experimental design, trends in risk factors and estimated CVD risk in two intervention areas (Norsjö. Sweden and Otsego-Schoharie County, New York state) are compared with those in reference areas (Northern Sweden region and Herkimer County, New York state) using serial cross-sectional studies and panel studies. RESULTS: The programmes were able to achieve significant changes in CVD risk factors that the local communities recognized as major concerns: changing eating habits in the Swedish population and reducing smoking in the US population. For the Swedish cross-sectional follow-up study cholesterol reduction was 12%, compared to 5% in the reference population (p for trend differences <0.000). The significantly higher estimated CVD risk (as assessed by risk scores) at baseline in the intervention population was below that of the Swedish reference population after 5 years of intervention. The Swedish panel study provided the same results. In the US, both the serial cross-sectional and panel studies showed a > 10% decline in smoking prevalence in the intervention population, while it increased slightly in the reference population. When pooling the serial cross-sectional studies the estimated risk reduction (using the Framingham risk equation) was significantly greater in the intervention populations compared to the reference populations. CONCLUSIONS: The overall pattern of risk reduction is consistent and suggests that the two different models of rural county intervention can contribute to significant risk reduction. The Swedish programme had its greatest effect on reduction of serum cholesterol levels whereas the US programme had its greatest effect on smoking prevention and cessation. These outcomes are consistent with programmatic emphases. Socially less privileged groups in these rural areas benefited as much or more from the interventions as those with greater social resources.

Adult↗
PubMed2001

Can a sustainable community intervention reduce the health gap?--10-year evaluation of a Swedish community intervention program for the prevention of cardiovascular disease.

OBJECTIVES: This paper evaluates the 10-year outcomes of a Northern Sweden community intervention program for the prevention of cardiovascular disease (CVD), with special reference to the social patterning of risk development. METHODS: Using a quasi-experimental design, trends in risk factors and predicted mortality in an intervention area (Norsjö municipality) are compared with those in a reference area (Northern Sweden region) by repeated independent cross-sectional surveys. RESULTS: There were significant differences in changes in total cholesterol level and systolic blood pressure between the intervention and reference populations. The predicted coronary heart disease mortality (based on the North Karelia risk equation). after adjustment for age and education, was reduced by 36% in the intervention area and by 1% in the reference area. CONCLUSIONS: We conclude that a long-term community-based CVD prevention program which combines population and individual strategies can substantially promote a health shift in CVD risk in a high risk rural population. When evaluated for different social strata, we found no signs of an increasing health gap between socially privileged and less privileged groups. Socially less-privileged groups benefited the most from the present prevention program.

Adult↗