Adaptation of psychrophilic and psychrotrophic sulfate-reducing bacteria to permanently cold marine environments

The potential for sulfate reduction at low temperatures was examined in two different cold marine sediments, Mariager Fjord (Denmark), which is permanently cold (3 to 6 degrees C) but surrounded by seasonally warmer environments, and the Weddell Sea (Antarctica), which is permanently below 0 degrees C. The rates of sulfate reduction were measured by the (SO42-)-S-35 tracer technique at different experimental temperatures in sediment slurries, In sediment slurries from Mariager Fjord, sulfate reduction showed a mesophilic temperature response which was comparable to that of other temperate environments, In sediment slurries from Antarctica, the metabolic activity of psychrotrophic bacteria was observed with a respiration optimum at 18 to 19 degrees C during short-term incubations, However, over a 1-week incubation, the highest respiration rate was observed at 12.5 degrees C. Growth of the bacterial population at the optimal growth temperature could be an explanation for the low temperature optimum of the measured sulfate reduction, The potential for sulfate reduction was highest at temperatures well above the in situ temperature in all experiments, The results frorn sediment incubations were compared with those obtained from pure cultures of sulfate-reducing bacteria by using the psychrotrophic strain Itk10 and the mesophilic strain ak30. The psychrotrophic strain reduced sulfate optimally at 28 degrees C in short-term incubations, even though it could not grow at temperatures above 24 degrees C. Furthermore, this strain showed its highest growth yield between 0 and 12 degrees C. In contrast, the mesophilic strain ak30 respired and grew optimally and showed its highest growth yield at 30 to 35 degrees C

Codend selectivity of the Danish seine investigated by the trouser trawl method

During June 1986 codend selectivity of the Danish seine was measured using both diamond mesh codends and square mesh codends. Comparisons between different codends were made by the trouser trawl method, having two parallel 12 m codends with either different meshshape or different meshsize. A special construction panel in front were ("trousers") with an 8 m lang vertical used for dividing the extension piece/rear belly into two equal parts

Height and spread of the Danish seine

Height and spread of trawls is successfully measured by the wireless "Scanmar" system. Several experiments made by fishermen have shown that this system will not work on the Danish seine. A modified version of the "Scanmar" system have been tested for geometrical measurements on the Danish seine. During May 1987 a total of 11 valid hauls were made by two different types of Danish seines on fishing grounds in Northern Norway. Hauling and fishing procedures were carried out as in the normal, commercial fishery. The measurements clearly demonstrated that it is possible to control the geometry of the Danish seine throughout the haul by this modified version of the "Scanmar" system. In addition to read the height and spread of the net, it was possible to detect whenever a rope got fastened around rocks, and to see when it loosened again. Signals from the height and spread sensors were lost for shorter periods during the haul. Using this (modified version of the) system, the skipper will get continuous information about the geometry of the Danish seine, and thereby know exactly when to start hauling the ropes and when to change the hauling speed, in order to keep a steady/continous closing of the wings

Locally class-presentable and class-accessible categories

We generalize the concepts of locally presentable and accessible categories. Our framework includes such categories as small presheaves over large categories and ind-categories. This generalization is intended for applications in the abstract homotopy theory

The atmospheric effects of stratospheric aircraft: A current consensus

In the early 1970's, a fleet of supersonic aircraft flying in the lower stratosphere was proposed. A large fleet was never built for economic, political, and environmental reasons. Technological improvements may make it economically feasible to develop supersonic aircraft for current markets. Some key results of earlier scientific programs designed to assess the impact of aircraft emissions on stratospheric ozone are reviewed, and factors that must be considered to assess the environmental impact of aircraft exhaust are discussed. These include the amount of nitrogen oxides injected in the stratosphere, horizontal transport, and stratosphere/troposphere assessment models are presented. Areas in which improvements in scientific understanding and model representation must be made to reduce the uncertainty in model calculations are identified

Prevalence of intracranial artery stenosis in a general population using 3D-time of flight magnetic resonance angiography

Background: Data on prevalence of intracranial artery stenosis (ICAS) in Western populations is sparse. The aim of the study was to assess the prevalence and risk factors for ICAS in a mainly Caucasian general population. Methods: We assessed the prevalence of ICAS in 1847 men and women aged 40 to 84 years who participated in a cross-sectional population-based study, using 3-dimensional time-of-flight 3 Tesla magnetic resonance angiography. ICAS was defined as a focal luminal flow diameter reduction of ≥50 %. The association between cardiovascular risk factor levels and ICAS was assessed by multivariable regression analysis. Results: The overall prevalence of ICAS was 6.0 % (95 % confidence interval (CI) 5.0–7.2), 4.3 % (95 % CI 3.1–5.7) in women and 8.0 % (95 % CI 6.3–10.0) in men. The prevalence increased by age from 0.8 % in 40-54 years age group to 15.2 % in the 75-84 years age group. The majority of stenoses was located to the internal carotid artery (52.2 %), followed by the posterior circulation (33.1 %), the middle cerebral artery (10.8 %) and the anterior cerebral artery (3.8 %). The risk of ICAS was independently associated with higher age, male sex, hypertension, hyperlipidemia, diabetes mellitus, current smoking and higher BMI. Conclusions: The prevalence of ICAS in a general population of Caucasians was relatively high and similar to the prevalence of extracranial internal carotid artery stenosis in previous population-based studies

Prevalence of unruptured intracranial aneurysms: impact of different definitions-the Tromsø Study

Background - Management of incidental unruptured intracranial aneurysms (UIAs) remains challenging and depends on their risk of rupture, estimated from the assumed prevalence of aneurysms and the incidence of aneurysmal subarachnoid haemorrhage. Reported prevalence varies, and consistent criteria for definition of UIAs are lacking. We aimed to study the prevalence of UIAs in a general population according to different definitions of aneurysm. Methods - Cross-sectional population-based study using 3-dimensional time-of-flight 3 Tesla MR angiography to identify size, type and location of UIAs in 1862 adults aged 40–84 years. Size was measured as the maximal distance between any two points in the aneurysm sac. Prevalence was estimated for different diameter cutoffs (≥1, 2 and 3 mm) with and without inclusion of extradural aneurysms. Results - The overall prevalence of intradural saccular aneurysms ≥2 mm was 6.6% (95% CI 5.4% to 7.6%), 7.5% (95% CI 5.9% to 9.2%) in women and 5.5% (95% CI 4.1% to 7.2%) in men. Depending on the definition of an aneurysm, the overall prevalence ranged from 3.8% (95% CI 3.0% to 4.8%) for intradural aneurysms ≥3 mm to 8.3% (95% CI 7.1% to 9.7%) when both intradural and extradural aneurysms ≥1 mm were included. Conclusion - Prevalence in this study was higher than previously observed in other Western populations and was substantially influenced by definitions according to size and extradural or intradural location. The high prevalence of UIAs sized <5 mm may suggest lower rupture risk than previously estimated. Consensus on more robust and consistent radiological definitions of UIAs is warranted

Twenty years of European mountain permafrost dynamics-the PACE legacy

This paper reviews and analyses the past 20 years of change and variability of European mountain permafrost in response to climate change based on time series of ground temperatures along a south-north transect of deep boreholes from Sierra Nevada in Spain (37°N) to Svalbard (78°N), established between 1998 and 2000 during the EU-funded PACE (Permafrost and Climate in Europe) project. In Sierra Nevada (at the Veleta Peak), no permafrost is encountered. All other boreholes are drilled in permafrost. Results show that permafrost warmed at all sites down to depths of 50 m or more. The warming at a 20 m depth varied between 1.5 °C on Svalbard and 0.4 °C in the Alps. Warming rates tend to be less pronounced in the warm permafrost boreholes, which is partly due to latent heat effects at more ice-rich sites with ground temperatures close to 0 °C. At most sites, the air temperature at 2 m height showed a smaller increase than the near-ground-surface temperature, leading to an increase of surface offsets (SOs). The active layer thickness (ALT) increased at all sites between c. 10% and 200% with respect to the start of the study period, with the largest changes observed in the European Alps. Multi-temporal electrical resistivity tomography (ERT) carried out at six sites showed a decrease in electrical resistivity, independently supporting our conclusion of ground ice degradation and higher unfrozen water content