Showing papers by "University of Iceland published in 2001"

Oxygen isotope and palaeotemperature records from six Greenland ice‐core stations: Camp Century, Dye‐3, GRIP, GISP2, Renland and NorthGRIP

Abstract: Oxygen isotope variations spanning the last glacial cycle and the Holocene derived from ice-core records for six sites in Greenland (Camp Century, Dye-3, GRIP, GISP2, Renland and NorthGRIP) show strong similarities. This suggests that the dominant influence on oxygen isotope variations reflected in the ice-sheet records was regional climatic change. Differences in detail between the records probably reflect the effects of basal deformation in the ice as well as geographical gradients in atmospheric isotope ratios. Palaeotemperature estimates have been obtained from the records using three approaches: (i) inferences based on the measured relationship between mean annual δ18O of snow and of mean annual surface temperature over Greenland; (ii) modelled inversion of the borehole temperature profile constrained either by the dated isotopic profile, or (iii) by using Monte Carlo simulation techniques. The third of these approaches was adopted to reconstruct Holocene temperature variations for the Dye 3 and GRIP temperature profiles, which yields remarkably compatible results. A new record of Holocene isotope variations obtained from the NorthGRIP ice-core matches the GRIP short-term isotope record, and also shows similar long-term trends to the Dye-3 and GRIP inverted temperature data. The NorthGRIP isotope record reflects: (i) a generally stronger isotopic signal than is found in the GRIP record; (ii) several short-lived temperature fluctuations during the first 1500 yr of the Holocene; (iii) a marked cold event at ca. 8.2 ka (the ‘8.2 ka event’); (iv) optimum temperatures for the Holocene between ca. 8.6 and 4.3 ka, a signal that is 0.6‰ stronger than for the GRIP profile; (v) a clear signal for the Little Ice Age; and (vi) a clear signal of climate warming during the last century. These data suggest that the NorthGRIP stable isotope record responded in a sensitive manner to temperature fluctuations during the Holocene. Copyright © 2001 John Wiley & Sons, Ltd.

A new approach for the morphological segmentation of high-resolution satellite imagery

Abstract: A new segmentation method based on the morphological characteristic of connected components in images is proposed. Theoretical definitions of morphological leveling and morphological spectrum are used in the formal definition of a morphological characteristic. In multiscale segmentation, this characteristic is formalized through the derivative of the morphological profile. Multiscale segmentation is particularly well suited for complex image scenes such as aerial or fine resolution satellite images, where very thin, enveloped and/or nested regions must be retained. The proposed method performs well in the presence of both low radiometric contrast and relatively low spatial resolution. Those factors may produce a textural effect, a border effect, and ambiguity in the object/background distinction. Segmentation examples for satellite images are given.

The buffer effect and large-scale population regulation in migratory birds

Abstract: Buffer effects occur when sites vary in quality and fluctuations in population size are mirrored by large changes in animal numbers in poor-quality sites but only small changes in good-quality sites. Hence, the poor sites ‘buffer’ the good sites1,2, a mechanism that can potentially drive population regulation if there are demographic costs of inhabiting poor sites. Here we show that for a migratory bird this process can apply on a country-wide scale with consequences for both survival and timing of arrival on the breeding grounds (an indicator of reproductive success3,4). The Icelandic population of the black-tailed godwit, Limosa limosa islandica, wintering in Britain has increased fourfold since the 1970s (ref. 5) but rates of change within individual estuaries have varied from zero to sixfold increases. In accordance with the buffer effect, rates of increase are greater on estuaries with low initial numbers, and godwits on these sites have lower prey-intake rates, lower survival rates and arrive later in Iceland than godwits on sites with stable populations. The buffer effect can therefore be a major process influencing large-scale population regulation of migratory species.

The Impact of Insomnia on Cognitive Functioning in Older Adults

Abstract: OBJECTIVES: To examine whether self-reported symptoms of insomnia independently increase risk of cognitive decline in older adults. DESIGN: Longitudinal cohort study. SETTING: The four sites of the Established Populations for Epidemiologic Studies of the Elderly. PARTICIPANTS: Six thousand four hundred forty-four community-dwelling men and women age 65 and older who had no more than one error on the Short Portable Mental Status Questionnaire (SPMSQ) at baseline and an in-person interview at the third annual follow-up (FU3). MEASUREMENTS: Insomnia was defined as report of trouble falling asleep or waking up too early most of the time. Cognitive decline was defined as two or more errors on the SPMSQ at FU3. Logistic regression was used to determine risk of cognitive decline associated with insomnia, controlling for demographic, behavioral, and health-related factors. Analyses were stratified by sex and depressed mood. RESULTS: Among nondepressed men, those reporting symptoms of insomnia at both baseline and FU3 had an adjusted odds ratio (OR) of 1.49 (95% CI = 1.03–2.14) for cognitive decline, relative to those with no insomnia at FU3. Men with insomnia at FU3 only were not at increased risk (OR = 1.16, 95% CI = 0.82–1.65). These relationships were not found in women. Men and women with depressive symptoms at FU3 were at increased risk for cognitive decline independent of insomnia. CONCLUSION: Chronic insomnia independently predicts incident cognitive decline in older men. More sensitive measures of cognitive performance may identify more subtle declines and may confirm whether insomnia is associated with cognitive decline in women. J Am Geriatr Soc 49:1185–1189, 2001.

In Vitro Killing of Candida albicans by Fatty Acids and Monoglycerides

Abstract: The susceptibility of Candida albicans to several fatty acids and their 1-monoglycerides was tested with a short inactivation time, and ultrathin sections were studied by transmission electron microscopy (TEM) after treatment with capric acid. The results show that capric acid, a 10-carbon saturated fatty acid, causes the fastest and most effective killing of all three strains of C. albicans tested, leaving the cytoplasm disorganized and shrunken because of a disrupted or disintegrated plasma membrane. Lauric acid, a 12-carbon saturated fatty acid, was the most active at lower concentrations and after a longer incubation time.

Fertilizing potential of volcanic ash in ocean surface water

Abstract: The fertilization potential of newly erupted and well-preserved ash from the 2000 Hekla eruption in Iceland was measured for the first time by flow-through experiments. As previously shown, (1) the North Atlantic Ocean, including the subarctic seas surrounding Iceland, is the largest net sink of the world’s oceans for atmospheric CO 2, owing to biological drawdown during summer; (2) almost complete consumption of phosphate in chlorophyll-rich areas of the North Atlantic Ocean might limit primary production; and (3) in the southern Pacific Ocean and parts of the equatorial Pacific Ocean iron might limit primary production. We found through laboratory experiments that volcanic ash exposed to seawater initially releases large amounts of adsorbed phosphate, 1.7 mmol·g 21 ·h 21 ; iron, 37.0 mmol·g 21 ·h 21 ; silica, 49.5 mmol·g 21 h 21 ; and manganese, 1.7 mmol·g 21 ·h 21 . Dissolution of acid aerosols adsorbed to the surface of the ash caused the high initial release of major and trace elements. Because of the instantaneous dissolution of adsorbed components when newly erupted volcanic ash comes in contact with the ocean surface water, macronutrients and ‘‘bioactive’’ trace metals are released fast enough to become available to support primary production.

The therapeutic effects of retinal laser treatment and vitrectomy. A theory based on oxygen and vascular physiology.

Abstract: The physiologic mechanism of photocoagulation can been seen in the following steps. The physical light energy is absorbed in the melanin of the retinal pigment epithelium. The adjacent photoreceptors are destroyed and are replaced by a glial scar and the oxygen consumption of the outer retina is reduced. Oxygen that normally diffuses from the choriocapillaris into the retina can now diffuse through the laser scars in the photoreceptor layer without being consumed in the mitochondria of the photoreceptors. This oxygen flux reaches the inner retina to relieve inner retinal hypoxia and raise the oxygen tension. As a result, the retinal arteries constrict and the bloodflow decreases. Hypoxia relief reduces production of growth factors such as VEGF and neovascularization is reduced or stopped. Vasoconstriction increases arteriolar resistance, decreases hydrostatic pressure in capillaries and venules and reduces edema formation according to Starling's law. Vitrectomy also improves retinal oxygenation by allowing oxygen and other nutrients to be transported in water currents in the vitreous cavity from well oxygenated to ischemic areas of the retina. Vitrectomy and retinal photocoagulation both improve retinal oxygenation and both reduce diabetic macular edema and retinal neovascularization.

Risk of breast cancer in female flight attendants: a population-based study (Iceland)

Abstract: Objectives: To study whether increased cancer risk, particularly of cancer types previously related to radiation, was found among cabin attendants, using employment time as a surrogate of exposure to cosmic radiation. Methods: A cohort of 1690 cabin attendants, 158 men and 1532 women from the Icelandic Cabin Crew Association and two airline companies in Iceland, was established. Cancer sites were ascertained between 1955 and 1997 by follow-up in a cancer registry. The personal identification number of each subject was used in record linkage to population-based registers containing vital and emigration status, reproductive factors and histologically verified cancer diagnosis. Standardized incidence rates (SIR) of different cancer sites in relation to employment time and year of hiring were calculated, as well as predictive values of breast cancer risk for evaluating possible confounding due to reproductive factors. Results: The total number of person-years was 27,148. Among the women, 64 cancers were observed whereas 51.63 were expected (SIR 1.2, 95% CI 1.0–1.6), and significantly increased risk for malignant melanoma (SIR 3.0, 95% CI 1.2–6.2) was found. Significantly increased risks of overall cancers (SIR 1.3, 95% CI 1.0–1.8) and breast cancer (SIR 1.6, 95% CI 1.0–2.4) were observed among the female cabin attendants when 15 years lag time was applied. Those hired in 1971 or later had the heaviest exposure to cosmic radiation at a young age and had significantly increased risk of overall cancer (SIR 2.8, 95% CI 1.4–4.9) and breast cancer (SIR 4.1, 95% CI 1.7–8.5). Predictive values calculated on the basis of reproductive factors among the cabin attendants and the population, and risk of breast cancer were 1.0 for parous vs. nulliparous, 1.0 for number of children, and 1.1 for age at birth of first child. Conclusion: The increased risk of breast cancer and malignant melanoma among cabin attendants seems to be occupationally related. The part played by occupational exposures, i.e. cosmic radiation, disturbance of the circadian rhythm, and electromagnetic fields or combination of these factors in the etiology of breast cancer among the cabin crew, is still a puzzle as confounding due to parity appears to be ruled out. The relationship between the sunbathing habits of the cabin crew and the increased risk of malignant melanoma needs to be clarified. There is also an urgent need to elucidate the importance of these findings for today's aviation.

Killing of Gram-positive cocci by fatty acids and monoglycerides.

Abstract: The susceptibilities of three Gram-positive cocci to medium-chain saturated and long-chain unsaturated fatty acids and their one-monoglycerides were studied. The bacteria were incubated with equal volumes of lipid solutions for 10 min. Lauric acid, palmitoleic acid and monocaprin reduced the number of CFU by 6.0 log10 or greater at 5 mM concentration for streptococci of group A (GAS) and group B (GBS). When further compared at lower concentrations and after longer incubation time monocaprin proved to be the most active. Capric acid showed the highest activity against Staphylococcus aureus at 10 mM. However, at lower concentrations monocaprin was the only lipid that showed significant activity against S. aureus. The mode of action of monocaprin against GBS was studied by a novel two-color fluorescent assay of bacterial viability and by electron microscopy. The results indicate that the bacteria are killed by disintegration of the cell membrane by the lipid, leaving the bacterial cell wall intact. The highly lethal effect of monocaprin indicates that this lipid might be useful as a microbicidal agent for prevention and treatment of infections caused by these bacteria.

Electronegativity of low-pressure high-density oxygen discharges

Abstract: We use a global (volume averaged) model to study the presence of negative ions and metastable species in low-pressure high-density oxygen discharges. We find the negative oxygen ion O- to be the dominant negative ion in the discharge, the density of the negative ion O2- to be small and the density of the negative ion O-3 to be negligible in the pressure range of interest, 1-100?mTorr. Dissociative attachment of the oxygen molecule in the ground-state O2(3?g-) and the metastable oxygen molecule O2(a1?g) are the dominating channels for the creation of the negative oxygen ion O-. At low pressure (<5?mTorr) recombination involving O- and O+ ions is the main loss channel for O- ions. At higher pressure, the detachment on O(3P) becomes the main loss channel for the O- ion. The creation of O-2 is mainly through dissociative attachment of ozone O3. Ozone is almost entirely created through detachment by the collision of O- with the metastable oxygen molecule O2(a1?g). The creation of O-2 is thus greatly influenced by this detachment process and neglecting the detachment has a significant influence on the density of O-2 ions. At low pressure (<10?mTorr) the O-2 ion is mainly lost through recombination while at higher pressure the charge transfer to form O2 is the dominating loss process.

Nature, Power, and Growth

Abstract: This essay reviews the relationship between natural-resource abundance and economic growth around the world, and presents some new results. The principal reasons why resource-based production can inhibit economic growth over long periods are traced to the Dutch disease, neglect of education, rent seeking, and economic policy failures. Across a large number of countries in the period from 1965 to 1998, the share of the primary sector in the labour force is shown to be inversely related to exports, domestic and foreign investment, and education, and directly related to external debt, import protection, corruption, and income inequality. The cross-sectional data show, moreover, that the share of the primary sector in the labour force is inversely related to per capita growth across countries. None of this lies in the nature of things, however. What seems to matter for economic growth is not the abundance of natural resources per se, but rather the quality of their management, and of economic management and institutions in general.

Nature, Power, and Growth

Abstract: This essay reviews the relationship between natural-resource abundance and economic growth around the world, and presents some new results. The principal reasons why resource-based production can inhibit economic growth over long periods are traced to the Dutch disease, neglect of education, rent seeking, and economic policy failures. Across a large number of countries in the period from 1965 to 1998, the share of the primary sector in the labour force is shown to be inversely related to exports, domestic and foreign investment, and education, and directly related to external debt, import protection, corruption, and income inequality. The cross-sectional data show, moreover, that the share of the primary sector in the labour force is inversely related to per capita growth across countries. None of this lies in the nature of things, however. What seems to matter for economic growth is not the abundance of natural resources per se, but rather the quality of their management, and of economic management and institutions in general.

Estimating uncertainty in fish stock assessment and forecasting

Abstract: A variety of tools are available to quantify uncertainty in age-structured fish stock assessments and in management forecasts. These tools are based on particular choices for the underlying population dynamics model, the aspects of the assessment considered uncertain, and the approach for assessing uncertainty (Bayes, frequentist or likelihood). The current state of the art is advancing rapidly as a consequence of the availability of increased computational power, but there remains little consistency in the choices made for assessments and forecasts. This can be explained by several factors including the specifics of the species under consideration, the purpose for which the analysis is conducted and the institutional framework within which the methods are developed and used, including the availability and customary usage of software tools. Little testing of either the methods or their assumptions has yet been done. Thus, it is not possible to argue either that the methods perform well or perform poorly or that any particular conditioning choices are more appropriate in general terms than others. Despite much recent progress, fisheries science has yet to identify a means for identifying appropriate conditioning choices such that the probability distributions which are calculated for management purposes do adequately represent the probabilities of eventual real outcomes. Therefore, we conclude that increased focus should be placed on testing and carefully examining the choices made when conducting these analyses, and that more attention must be given to examining the sensitivity to alternative assumptions and model structures. Provision of advice concerning uncertainty in stock assessments should include consideration of such sensitivities, and should use model-averaging methods, decision tables or management procedure simulations in cases where advice is strongly sensitive to model assumptions.

On the effect of the electron energy distribution on the plasma parameters of an argon discharge : a global (volume-averaged) model study

Abstract: On the effect of the electron energy distribution on the plasma parameters of argon discharge : A global (volume averaged) model study

Macrobenthic invertebrate richness and composition along a latitudinal gradient of European glacier‐fed streams

Abstract: 1. The influence of 11 environmental variables on benthic macroinvertebrate communities was examined in seven glacier-fed European streams ranging from Svalbard in the north to the Pyrenees in the south. Between 4 and 11 near-pristine reaches were studied on each stream in 1996–97. 2. Taxonomic richness, measured at the family or subfamily (for Chironomidae) levels for insects and higher levels for non-insects, increased with latitude from Svalbard (3 taxa) to the Pyrenees (29 taxa). 3. A Generalized Additive Model (GAM) incorporating channel stability [Pfankuch Index (PFAN)], tractive force, Froude number (FROU), water conductivity (COND), suspended solids (SUSP) concentration, and maximum temperature explained 79% of the total deviance of the taxonomic richness per reach. Water temperature and the PFAN of stability made the highest contribution to this deviance. In the model, richness response to temperature was positive linear, whereas the response to the PFAN was bell-shaped with an optimum at an intermediate level of stability. 4. Generalized Additive Models calculated for the 16 most frequent taxa explained between 25 (Tipulidae) and 79% (Heptageniidae) of the deviance. In 10 models, more than 50% of the deviance was explained and 11 models had cross-validation correlation ratios above 0.5. Maximum temperature, the PFAN, SUSP and tractive force (TRAC) were the most frequently incorporated explanatory variables. Season and substrate characteristics were very rarely incorporated. 5. Our results highlight the strong deterministic nature of zoobenthic communities in glacier-fed streams and the prominent role of water temperature and substrate stability in determining longitudinal patterns of macroinvertebrate community structure. The GAMs are proposed as a tool for predicting changes of zoobenthic communities in glacier-fed streams under climate or hydrological change scenarios.

A genome-wide scan for preeclampsia in the Netherlands.

Abstract: Preeclampsia, hallmarked by de novo hypertension and proteinuria in pregnancy, has a familial tendency. Recently, a large Icelandic genome-wide scan provided evidence for a maternal susceptibility locus for preeclampsia on chromosome 2p13 which was confirmed by a genome scan from Australia and New Zealand (NZ). The current study reports on a genome-wide scan of Dutch affected sib-pair families. In total 67 Dutch affected sib-pair families, comprising at least two siblings with proteinuric preeclampsia, eclampsia or HELLP-syndrome, were typed for 293 polymorphic markers throughout the genome and linkage analysis was performed. The highest allele sharing lod score of 1.99 was seen on chromosome 12q at 109.5 cM. Two peaks overlapped in the same regions between the Dutch and Icelandic genome-wide scan at chromosome 3p and chromosome 15q. No overlap was seen on 2p. Re-analysis in 38 families without HELLP-syndrome (preeclampsia families) and 34 families with at least one sibling with HELLP syndrome (HELLP families), revealed two peaks with suggestive evidence for linkage in the non-HELLP families on chromosome 10q (lod score 2.38, D10S1432, 93.9 cM) and 22q (lod score 2.41, D22S685, 32.4 cM). The peak on 12q appeared to be associated with HELLP syndrome; it increased to a lod score of 2.1 in the HELLP families and almost disappeared in the preeclampsia families. A nominal peak on chromosome 11 in the preeclampsia families showed overlap with the second highest peak in the Australian/NZ study. Results from our Dutch genome-wide scan indicate that HELLP syndrome might have a different genetic background than preeclampsia.

Polysaccharides from lichens : Structural characteristics and biological activity

Abstract: Lichens have been used for medicinal purposes throughout the ages, and beneficial claims have to some extent been correlated with their polysaccharide content. Of 13,500 lichen species growing worldwide, less than 100 species have been investigated for polysaccharide content. Lichen polysaccharides are mainly of three different structural types: beta-glucans, alpha-glucans, and galactomannans. In addition, a few complex heteroglycans have recently been described, such as thamnolan, a water-soluble, immunologically active heteroglycan with a novel rhamnopyranosylgalactofuranan type of structure. A number of investigations have been carried out on biological effects of lichen polysaccharides, most notably antitumour, immunomodulating, antiviral, and memory-enhancing effects. The current review summarizes present knowledge on the structural characteristics and biological activity of lichen polysaccrides.

The afterglow of the short/intermediate-duration gamma-ray burst GRB 000301C: A jet at z = 2:04 ?;??;???

Abstract: We present Ulysses and NEAR data from the detection of the short or intermediate duration (2 s) gamma-ray burst GRB000301C (2000 March 1.41 UT). The gamma-ray burst (GRB) was localised by the Inter Planetary Network (IPN) and RXTE to an area of 50 arcmin^2. A fading optical counterpart was subsequently discovered with the Nordic Optical Telescope (NOT) about 42h after the burst. The GRB lies at the border between the long-soft and the short-hard classes of GRBs. If GRB000301C belongs to the latter class, this would be the first detection of an afterglow to a short-hard burst. We present UBRI and JHK photometry from the time of the discovery until 11 days after the burst. Finally, we present spectroscopic observations of the optical afterglow obtained with the ESO VLT Antu telescope 4 and 5 days after the burst. The optical light curve is consistent with being achromatic from 2 to 11 days after the burst and exhibits a break. A broken power-law fit yields a shallow pre-break decay power-law slope of a_1=-0.72+-0.06, a break time of t_b=4.39+-0.26 days after the burst, and a post-break slope of a_2=-2.29+-0.17, which is best explained by a sideways expanding jet in an ambient medium of constant mean density. In the optical spectrum we find absorption features that are consistent with FeII, CIV, CII, SiII and Ly-a at a redshift of 2.0404+-0.0008. We find evidence for a curved shape of the spectral energy distribution of the observed afterglow. It is best fitted with a power-law spectral distribution with index b ~ -0.7 reddened by an SMC-like extinction law with A_V~0.1 mag. Based on the Ly-a absorption line we estimate the HI column density to be log(N(HI))=21.2+-0.5. This is the first direct indication of a connection between GRB host galaxies and Damped Ly-a Absorbers.

Sociodemographic differences in patterns of sedentary and physically active behavior in older children and adolescents.

Abstract: UNLABELLED Numerous studies have found that involvement in moderate-intensity and strenuous activity has positive effects on health. This study considered the prevalence of different aspects of physical activity and sedentary behavior in 11-16-y-olds based on a representative national survey of 3270 Icelandic primary schoolchildren (91% response rate). All-day sedentary behavior was extremely rare ( or = 3 times per week) during school or leisure time, thanks largely to school physical education. Only 39% were physically active (> or = 3 times per week) during leisure time, and only 29% engaged in regular (> or = 3 times per week) leisure time strenuous exercise. Girls were more sedentary, less leisure time physically active, and less involved in leisure time strenuous exercise. Sedentary behavior increased and physically active behavior decreased with age, especially after early adolescence. However, there were no age differences in strenuous leisure time exercise. Upper-class students were less sedentary and more physically active during leisure time than working-class students. Finally, rural students were more sedentary during leisure time, and less physically active than students from urban areas. An interaction was found between age and residence when predicting leisure time physical activity, indicating that the inverse age-activity relationship in urban areas is partly reversed in rural areas. CONCLUSION Compulsory school physical education frequently failed to translate into voluntary physical involvement. Sociodemographic differences in physical activity were greater during leisure time, than during school and leisure time combined.

Geochemistry, dispersal, volumes and chronology of Holocene silicic tephra layers from the Katla volcanic system, Iceland

Abstract: At least 12 silicic tephra layers (SILK tephras) erupted between ca 6600 and ca 1675 yr BP from the Katla volcanic system, have been identified in southern Iceland In addition to providing significant new knowledge on the Holocene volcanism of the Katla system which typically produces basaltic tephra, the SILK tephras form distinct and precise isochronous marker horizons in a climatically sensitive location close to both the atmospheric and marine polar fronts With one exception the SILK tephras have a narrow compositional range, with SiO2 between 63 and 67% Geochemically they are indistinguishable from ocean transported pumice found on beaches in the North Atlantic region, although they differ significantly from the silicic component of the North Atlantic Ash Zone One (NAAZO) Volumes of airborne SILK tephra range from 005 to 03 km3 We present new isopach maps of the six largest layers and demonstrate that they originate within the Katla caldera The apparently stable magma system conditions that produced the SILK tephras may have been established as a consequence of the eruption of the silicic component of NAAZO (ca 103 ka) and disrupted by another large-scale event, the tenth century ad Eldgja eruption (ca 1 ka) Despite the current long repose, silicic activity of this type may occur again in the future, presenting hitherto unknown hazards Copyright © 2001 John Wiley & Sons, Ltd

Routine activities in social context: A closer look at the role of opportunity in deviant behavior

Abstract: Present versions of the routine activity approach to deviant behavior do not account for the social context of situational motivation and opportunity. Using concepts from social bonding and differential association theories, we argue that the patterning of routine activities is guided in part by the same factors that cause deviant behavior, namely differential social relations. We extend the routine activity approach by arguing that the effect of routine activities on deviant behavior is contingent on people's differential social relations. Based on cross-sectional survey data from a nationally representative sample of Icelandic adolescents, our findings support these claims. First, there is a considerable decrease in the effect of our routine activities indicator (unstructured peer interaction in the absence of authority figures) on both violent behavior and property offending when we control for differential social relations, namely bonding with conventional agents and associations with deviant peers. S...