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Showing papers by "University of Iceland published in 1991"


Journal ArticleDOI
TL;DR: In this article, it is argued that the South Iceland Seismic Zone is a transient feature, migrating sideways in response to propagation of the Eastern Volcanic Zone. But the authors do not consider the impact of the seismic and volcanic zones on the seafloor.

454 citations


Journal ArticleDOI
TL;DR: In this article, a discrete model of Euclidean quantum gravity in three dimensions based on a summation over random simplicial manifolds is proposed. But the model is not suitable for 3-D gravity.
Abstract: We consider a discrete model of Euclidean quantum gravity in three dimensions based on a summation over random simplicial manifolds. We derive some elementary properties of the model and discuss possible “matrix” models for 3-D gravity.

375 citations


Journal ArticleDOI
TL;DR: A novel group of hyperthermophilic rod-shaped motile methanogens was isolated from a hydrothermally heated deep sea sediment and from a shallow marine hydrothermal system, and a new genus is named Methanopyrus (the “methane fire”), which is not related to any of the three methanogenic lineages.
Abstract: A novel group of hyperthermophilic rod-shaped motile methanogens was isolated from a hydrothermally heated deep sea sediment (Guaymas Basin, Gulf of California) and from a shallow marine hydrothermal system (Kolbeinsey ridge, Iceland). The grew between 84 and 110°C (opt: 98°C) and from 0.2% to 4% NaCl (opt. 2%) and pH 5.5 to 7 (opt: 6.5). The isolates were obligate chemolithoautotrophes using H2/CO2 as energy and carbon sources. In the presence of sulfur, H2S was formed and cells tended to lyse. The cell wall consisted of a new type of pseudomurein containing ornithin in addition to lysine and no N-acetylglucosamine. The pseudomurein layer was covered by a detergent-sensitive protein surface layer. The core lipid consisted exclusively of phytanyl diether. The GC content of the DNA was 60 mol%. By 16S rRNA comparisons the new organisms were not related to any of the three methanogenic lineages. Based on the physiological and molecular properties of the new isolates, we describe here a new genus, which we name Methanopyrus (the “methane fire”). The type species is Methanopyrus kandleri (type strain: AV19; DSM 6324).

336 citations


Journal ArticleDOI
TL;DR: The authors argue that the subject position of PRO clauses is not properly head governed, and therefore it must not be lexicalized, irrespective of whether it is case-marked or not.
Abstract: On the basis of evidence from Icelandic I argue that PRO can be both governed and case-marked, but crucially not properly governed. Lexical arguments must be both case-marked and properly head governed, and proper head government is a strictly local relation whereas case-marking is not. As the subject position of PRO clauses is not properly head governed, it must not be lexicalized, irrespective of whether it is case-marked or not.

184 citations


Journal ArticleDOI
01 May 1991-Nature
TL;DR: The most MgO-rich lavas have the most depleted incompatible element ratios and among the least radiogenic lead isotopes recorded in Atlantic mid-ocean ridge basalts, highlighting a decoupling of the major and trace element characteristics expected of plume melts.
Abstract: Icelandic high-magnesia basalts show striking correlations between major element abundances and incompatible element and radiogenic isotope ratios. The most MgO-rich lavas have the most depleted incompatible element ratios and among the least radiogenic lead isotopes recorded in Atlantic mid-ocean-ridge basalts, highlighting a decoupling of the major and trace element characteristics expected of plume melts. This paradox can be explained by the process that mixes melts segregated from different depths of the melting column. The resulting model provides insight into the processes governing melt compositions at spreading ridges.

170 citations


Journal Article
TL;DR: It was concluded that existing theoretical perspectives on juvenile deviance do not provide an adequate account of adolescent smoking and drinking and the need to integrate existing theories into a wider explanatory framework is discussed.
Abstract: Based on a national survey of Icelandic adolescents, this study examined the various predictors of cigarette smoking and alcohol use. It was found that the use of tobacco and alcohol was related to a number of different factors: sex, residence, hours of paid work, physical activities, social network, educational performance and beliefs, and psychological distress. Further, smoking and drinking had most predictors in common. It was concluded that existing theoretical perspectives on juvenile deviance do not provide an adequate account of adolescent smoking and drinking. The need to integrate existing theories into a wider explanatory framework is discussed.

123 citations


Journal ArticleDOI
01 Jun 1991-Geology
TL;DR: In this article, the isotopes of volcanic rocks from Hekla and in a few samples from Askja and Krafla volcanic centers in Iceland have been determined, showing that the silicic rocks cannot be derived from fractional crystallization of a more primitive magma.
Abstract: Th, Sr, Nd, and O isotopes have been determined in a suite of volcanic rocks from Hekla and in a few samples from Askja and Krafla volcanic centers in Iceland. Although {sup 87}Sr/{sup 86}Sr and {sup 143}Nd/{sup 144}Nd ratios are nearly the same for all compositions at Hekla, the ({sup 230}Th/{sup 232}Th) ratios differ and thus clearly show that the silicic rocks cannot be derived from fractional crystallization of a more primitive magma. Similar results are obtained for the Krafla and Askja volcanic centers, where the {delta}{sup 18}O values are much lower in the silicic magma than in the mafic magma. These data suggest that large volumes of silicic rocks in central volcanoes of the neovolcanic zones in Iceland are produced by partial melting of the underlying crust.

120 citations


Journal ArticleDOI
TL;DR: Kinetic properties were examined and the cod enzymes found to be more active towards both ester and amide (N-benzoyl-tyrosine-p-nitroanilide) substrates, indicative of an adaptive response towards the low temperature environment in which the cod lives.
Abstract: 1. 1. Two chymotrypsins with isoelectric points pI 6.2 and 5.8 were purified from the pyloric caeca of Atlantic cod using a phenyl-Sepharose column and chromatofocusing chromatography. The apparent molecular weight was 26,000 as judged by SDS-polyacrylamide gel electrophoresis and gel filtration. 2. 2. The cod enzymes differed from bovine chymotrypsin in having a slightly higher molecular weight and more acidic pI points. N-terminal amino acid sequence analysis of cod chymotrypsin B showed considerable similarity with bovine chymotrypsin. 3. 3. Heat stability and stability towards acidic pH were reduced in the cod enzymes. Generally, the cod and bovine chymotrypsins responded similarly to various protease inhibitors. However, the cod chymotrypsins were less sensitive to aprotinin inhibition but more sensitive towards soybean trypsin inhibitor and cysteine. 4. 4. Kinetic properties were examined and the cod enzymes found to be more active towards both ester (N-benzoyl-tyrosine ethyl ester) and amide (N-benzoyl-tyrosine-p-nitroanilide) substrates. The observed differences in kinetic properties are indicative of an adaptive response towards the low temperature environment in which the cod lives.

117 citations


Book ChapterDOI
17 Jun 1991
TL;DR: It is shown how the value of various parameters of graphs connected to sparse matrix factorization and other applications can be approximated using an algorithm of Leighton et al. that finds vertex separators of graphs.
Abstract: We show how the value of various parameters of graphs connected to sparse matrix factorization and other applications can be approximated using an algorithm of Leighton et al. that finds vertex separators of graphs. The approximate values of the parameters, which include minimum front size, treewidth, pathwidth, and minimum elimination tree height, are no more than O(log n) (minimum front size and treewidth) and O(log2n) (pathwidth and minimum elimination tree height) times the optimal values. In addition we examine the existence of bounded approximation algorithms for the parameters, and show that unless P = NP, there are no absolute approximation algorithms for them.

95 citations


Journal ArticleDOI
TL;DR: The Sveinagja graben as mentioned in this paper is an example of a large-scale tension fracture in the Holocene basaltic lava flows of the rift zone in Northeast Iceland.

86 citations


Journal ArticleDOI
TL;DR: Icelandic Arctic charr show greater affinity to charr from the British Isles than those from North America supporting their current taxonomic distinction.
Abstract: Restriction fragment length polymorphisms in mitochondrial DNA (mtDNA) were examined in progeny of four sympatric morphs of Arctic charr (Salvelinus alpinus L.) from Thingvallavatn, Iceland. The mtDNA analysis with 46 hexanucleotide restriction enzymes indicates that the Thingvallavatn morphs are very closely related. Sequence divergence was less than 0.2% between any of the five clones detected. Although not significant, the topology of the mtDNA UPGMA dendogram was similar to that from a previous allozyme survey. Icelandic Arctic charr show greater affinity to charr from the British Isles than those from North America supporting their current taxonomic distinction.

Journal ArticleDOI
TL;DR: In this article, a 30 km long profile, extending from 3 million year-old Pleistocene rocks to the Holocene rocks of the rift zone in southwest Iceland, is dissected by 443 dikes and 156 normal faults.

Book ChapterDOI
TL;DR: Microbial killing by milk lipids is due primarily to free fatty acids (FFAs) and monoglycerides (MGs) released from milk triglycerides by lipases and can be duplicated using purified FFAs and MGs8,9.
Abstract: Milk lipids are not only nutrients but also non-immunoglobulin protective factors1–3. The lipids in human milk do not initially have antimicrobial activity, but become antiviral2, antibacteria14,5 and antiprotozoal6 in vitro following storage and in vivo following digestion in the gastrointestinal tract of the milk-fed infant2,5,7. Microbial killing by milk lipids is due primarily to free fatty acids (FFAs) and monoglycerides (MGs) released from milk triglycerides by lipases and can be duplicated using purified FFAs and MGs8,9.

Journal ArticleDOI
TL;DR: This paper describes how the scenario aggregation principle can be combined with approximate solutions of the individual scenario problems, resulting in a computationally efficient algorithm where two individual Lagrangian-based procedures are merged into one.
Abstract: This paper describes how the scenario aggregation principle can be combined with approximate solutions of the individual scenario problems, resulting in a computationally efficient algorithm where two individual Lagrangian-based procedures are merged into one. Computational results are given for an example from fisheries management. Numerical experiments indicate that only crude scenario solutions are needed.

Journal ArticleDOI
TL;DR: In this article, the authors reviewed and matched the results of post-mortem examinations with death certificates from 433 autopsied hospital patients and found significant discrepancies between the two documents were observed in 50% of patients.
Abstract: The death certificate is an important source of data on disease incidence, prevalence and mortality. It should therefore be as accurate and complete as possible. Death certificates from 433 autopsied hospital patients were reviewed and matched against the results of post-mortem examinations. Significant discrepancies between the two documents were observed in 50% of patients. In 25%, the immediate cause of death was incorrectly stated on the certificate, having been assigned to a different organ system in the majority of those cases. In 33%, there was disagreement on major disease other than the immediate cause of death. In 9%, the death certificate was signed before the autopsy was performed. The extent of disagreement was largely independent of whether the certificate was signed before or after the autopsy. We conclude that: (1) there is a significant discrepancy between autopsy diagnoses and entries on death certificates; (2) disagreement is not due to unavailability of autopsy data at the time of completion of the certificate; (3) death certificates should be completed or amended utilizing data gained at autopsy.

Journal ArticleDOI
TL;DR: In this article, the chemical and isotopic composition of fumarole and geothermal well gases has been studied along a 15 km section of a subaerial spreading center (Hengill area, southwest Iceland).

Journal ArticleDOI
TL;DR: Etude des oscillations collectives longitudinales d'un gaz d'electrons bidimensionnel (2DEG) confine sur un disque (point quantique) dans un champ magnetique perpendiculaire constant changent lorsque l'on fait varier le potentiel de confinement and le nombre d-electrons.
Abstract: We investigate the longitudinal collective oscillations of a two-dimensional interacting electron gas (2DEG) confined to a disk (quantum dot) in a perpendicular constant magnetic field. We show how the exact results known for a parabolically confined 2DEG change when the confining potential and the electron number are varied. Considering reasonable corrections to a parabolic confinement potential, we are able to explain all features of the far-infrared spectrum of quantum dots observed in recent experiments.

Journal ArticleDOI
TL;DR: A Pleistocene subaqueous, volcanic sequence in South Iceland consists of flows of basaltic hyaloclastite and lava with interbedded sedimentary diamictite units as discussed by the authors.
Abstract: A Pleistocene subaqueous, volcanic sequence in South Iceland consists of flows of basaltic hyaloclastite and lava with interbedded sedimentary diamictite units. Emplacement occurred on a distal submarine shelf in drowned valleys along the southern coast of Iceland. The higher sea level was caused by eustatic sea-level change, probably towards the end of a glaciation. This sequence, nearly 700 m thick, rests unconformably on eroded flatlying lavas and sedimentary rocks of likely Tertiary age. A Standard Depositional Unit, describing the flows of hyaloclastite, starts with compact columnar-jointed basalt overlain by cubejointed basalt, and/or pillow lava. This in turn is overlain by thick unstructured hyaloclastite containing aligned basalt lobes, and bedded hyaloclastite at the top. A similar lithofacies succession is valid for proximal to distal locations. The flows were produced by repeated voluminous extrusions of basaltic lava from subaquatic fissures on the Eastern Rift Zone of Iceland. The fissures are assumed to lie in the same general area as the 1783 Laki fissure which produced 12 km3 of basaltic lava. Due to very high extrusion rates, the effective water/melt ratio was low, preventing optimal fragmentation of the melt. The result was a heterogeneous mass of hyaloclastite and fluid melt which moved “en masse” downslope with the melt at the bottom of the flow and increasingly vesicular hyaloclastite fragments above. The upper and distal parts of the flow moved as low-concentration turbulent suspensions that deposited bedded hyaloclastite.

Journal ArticleDOI
TL;DR: The growth pattern of the bacterium at primary isolation was characterized by a prolonged lag phase followed by a relatively growth in one week from microscopic to macroscopic size of the colonies.
Abstract: . Cultivation plates for the primary isolation of Renibacterium salmoninarum were incubated for 12 or more weeks over 3.5 years. The incubation time for sample of two groups of Atlantic salmon, Salmo solar L., broodfish on a selective agar medium is reported. Samples turned positive over a long time-span. but the longest incubation time recorded for growth of the bacterium was 19 week. In one group, 79% of all positive samples form fish with macroscopic signs of bacterial kidney disease were positive after 6 weeks of incubation and the highest incidence of positive samples occured during the sixth week. From covertly infected fish within the same group.42% of sample were positive after 6 weeks of incubation, and the highest incidence of positive sample occured during the sixth and the ninth weeks of incubation. The growth pattern of the bacterium at primary isolation was characterized by a prolonged lag phase followed by a relatively growth in one week from microscopic to macroscopic size of the colonies.

Journal ArticleDOI
TL;DR: The most primitive olivine cores (Fo 90.0-91.7) are probably derived from a peridotitic mantle as mentioned in this paper, which is the case for all pyroxene and much of the olivines in the lavas.
Abstract: The picritic Maelifell pillow lava series contains olivine macrocrysts (Fo 83.0–91.7) and microphenocrysts (Fo 86.8–88.5), resorbed Cr−Al endiopside, ± plagioclase, and microphenocrysts of Cr-spinel. The most primitive olivine cores (Fo 90–91.7) are probably derived from a peridotitic mantle. Gabbroic adcumulus xenoliths in the lavas contain plagioclase, Cr−Al endiopside and olivine (Fo 85.5–87.5) which overlap compositionally with lava minerals, ± Cr-spinel. This suggests that all pyroxene and much of the olivine ± feldspar in the lavas are xenocrysts. Olivines from the pillow lavas and from the gabbroic xenoliths contain inclusions of Cr-spinel, silicate glass and pure or nearly pure CO2. Early (type 1) silicate melt inclusions which occur in lava-olivine only, have crystalized 0.1 to 4 vol.% daughter spinel and unknown amounts of olivine during pre-eruptive cooling. Later (type 2) glass inclusions in olivine from the lavas do not contain daughter minerals; similar type 2 inclusions also occur in the xenoliths. High-temperature microthermometry at buffered oxygen fugacity (fO2) gives a plagioclaseout temperature of about 1230°C for both types of silicate melt inclusions; this was interpreted as the liquidus temperature for type 2 inclusions. Molar volumes of undisturbed CO2 inclusions in olivine from both lavas and xenoliths correspond to a depth of trapping of 7–10 km (2.2–3.0 kbar) at 1230°C. This is interpreted as a minimum depth to a partially molten layer near the crust/mantle boundary in the rift zone. The xenoliths are thus probably derived from a layered olivine-gabbro complex similar to those occurring in ophiolite complexes.

Journal ArticleDOI
TL;DR: In this article, the relationship between inflation, economic growth and external debt is reconsidered, and various channels through which increased inflation tends to reduce growth and raise foreign indebtedness over time and declining growth tends to amplify both inflation and debt.
Abstract: This paper reconsiders the relationship between inflation, economic growth and external debt, and discusses various channels through which (a) increased inflation tends to reduce growth and raise foreign indebtedness over time and (b) declining growth tends to amplify both inflation and debt. Based on a simple model of the simultaneous determination of inflation and growth, a non-parametric statistical comparison of the growth record and external indebtedness of high- and low-inflation economies reveals significantly slower growth and greater debts in the high-inflation economies since 1973. The observed growth differential indicates that the real costs of inflation over time may be high for individual countries as well as for the world economy as a whole.(This abstract was borrowed from another version of this item.)

Journal ArticleDOI
TL;DR: It is suggested that hormones defending the extracellular volume and composition are regulated close to zero input and output of both NaCl and water, regardless of whether they are NaCl conserving or free-water conserving.
Abstract: The plasma levels of four osmoregulatory hormones and their target ion-transport systems in the lower intestines of the domestic fowl were determined in order to elucidate their interrelationship and their setpoints in relation to NaCl intake. White Plymouth Rock hens were adapted to six intake levels of NaCl (0.20 +/- 0.02-24.7 +/- 1.9 mmoles Na+.kg bw-1.day-1) for 6 weeks. The Na+ absorption and the Cl- secretion of colon and coprodeum were characterized in vitro by the effects of hexoses, amino acids, amiloride, and theophylline on the short-circuit current (SCC) and electrical potential difference (PD). The NaCl-conserving system of the adult chicken is set at low intake levels of NaCl as the 80% range (quantized by non-linear, logistic regression analyses) of the change in the plasma [ALDO], the amiloride-inhibitable Na+ absorption of coprodeum and colon (delta SCC), occurred from 0.18 to 2.3, from 0.9 to 4.3, and from 1.2 to 7.3 mmoles Na+.kg bw-1.day-1, respectively. These results demonstrate that the amiloride-inhibitable Na+ absorption of coprodeum is more closely linked to plasma [ALDO] than that of colon. The aminoacid-Na+ coabsorption of colon increased over exactly the same range of Na+ intake as the colonic amiloride-inhibitable Na+ absorption decreased, whereas the hexose-Na+ coabsorption increased at higher levels of Na+ coabsorption increased at higher levels of Na+ intake, from 2 to 11 mmoles Na+.kg bw-1.day-1. Both these Na+ absorption types had reached their maximums at 24.7 mmoles Na+.kg bw-1.day-1, whereas the plasma [AVT] and plasma [PRL], although significantly increased, apparently had not; their 80% range of change occurred from 9.9 to 99 mmoles Na+.kg bw-1.day-1, and the main changes in plasma osmolality were predicted to occur from 5.4 to 107 mmoles Na+.kg bw-1.day-1. These results suggest that these colonic and hormonal variables conserve osmotically-free water and operate at high NaCl intake. The theophylline-induced colonic Cl- secretion did not change with NaCl intake, whereas the stimulation of SCC in coprodeum decreased with increasing NaCl intake: the main change occurred between 0 and 3.2 mmoles Na+.kg bw-1.day-1. Thus, all ion-transport capacity (although the nature of the Na+ transport changes). It is suggested that hormones defending the extracellular volume and composition are regulated close to zero input and output of both NaCl and water, regardless of whether they are NaCl conserving or free-water conserving.(ABSTRACT TRUNCATED AT 400 WORDS)

Journal ArticleDOI
TL;DR: The results indicated unusually large iron stores in the adult Icelandic population and significantly larger iron Stores in the rural compared to the urban population, and measures to improve the iron balance in urban premenopausal women cannot include increased iron fortification of food but must be more directed towards the target group.

Journal ArticleDOI
TL;DR: A study that revealed reductions in vehicle speeding following the posting of percentages of drivers not speeding on a sign at roadside is replicated to offer possible explanations for the failure of feedback posting to reduce speed in the U.S.
Abstract: We replicated a study by Van Houten, Nau, and Marini (1980) that had revealed reductions in vehicle speeding following the posting of percentages of drivers not speeding on a sign at roadside. Our subjects were drivers entering a residential area where the speed limit changed from 90 km/hr (55.9 mph) to 60 km/hr (37.3 mph). A total of 4,409 vehicle speeds were taken from two observation sessions per day for 20 consecutive weekdays. The intervention consisted of a single posting condition, in which a hypothetical daily percentage of drivers not speeding was posted on a feedback sign, followed by a double posting condition, in which a sign posting a best result was erected beyond the feedback sign. Results revealed a significant speed reduction from an average of 69.0 km/hr (42.9 mph) during baseline to 63.4 km/hr (39.4 mph) during single posting. Average speed during double posting was 62.9 km/hr (39.1 mph). The percentage of drivers exceeding 70 km/hr (43.5 mph) dropped from 41.0 during baseline to 20.5 during single posting. The significant speed reductions add to the generality of findings of similar studies in Canada and Israel and offer possible explanations for the failure of feedback posting to reduce speed in the U.S.

Journal ArticleDOI
TL;DR: The stability study of 1 in various pH buffers indicated the base-catalyzed hydrolysis of the acyloxyalkyl linkage and the hydration of the 5,6 double bond of the dihydropyridine as the main degradation processes.
Abstract: A dihydropyridine ↔ pyridinium salt redox carrier-based chemical delivery system for benzylpenicillin (1) was complexed with 2-hydroxypropyl-β-cyclodextrin (HPCD). The solubility of the lipophilic 1, which is incompatible with aqueous formulations, was dramatically increased and showed a linear dependency on the HPCD concentration. The degree of incorporation was 20 mg of 1 per g of complex. The stability study of 1 in various pH buffers indicated the base-catalyzed hydrolysis of the acyloxyalkyl linkage and the hydration of the 5,6 double bond of the dihydropyridine as the main degradation processes. The overall loss of 1, which follows first-order kinetics, was not influenced by changes in ionic strength and elimination of oxygen from the reaction medium. The HPCD complex of 1, which has a stability constant of 720–940 M−1, stabilized the chemical delivery system. The influence of the temperature on the stability of 1 is also discussed.

Journal ArticleDOI
TL;DR: In this article, the problem of efficient management of common property ocean fish fisheries is considered and a particular management method based on individual property rights in the fishery and discussed in the paper is not only capable of restoring economic efficiency in valuable ocean fisheries, but also extremely informationally efficient in the sense that very little centralized collection of information is required for its operation.

Journal ArticleDOI
TL;DR: A congruency is found between statements about needs of parents of hospitalized 2- to 6-year-olds in the literature and the needs ofParents expressed by parents themselves and pediatric health care professionals on the other hand.
Abstract: The present study uses a qualitative approach to explore and identify areas of needs among parents of 2- to 6-year-old children who are hospitalized. An extensive literature review and informal in-depth interviews with five parents and six pediatric health care professionals were analyzed by content to develop a representative list of statements about needs. Six groups of needs were recognized: (a) the need to be able to trust doctors and nurses, (b) the need for information, (c) needs related to other family members, (d) a need to feel that they are trusted, (e) needs related to human and physical resources, and (e) the need for support and guidance. A congruency is found between statements about needs of parents of hospitalized 2- to 6-year-olds in the literature on the one hand and the needs of parents expressed by parents themselves and pediatric health care professionals on the other hand.

Journal ArticleDOI
TL;DR: A detailed foraminiferal stratigraphy for the Plio-Pleistocene sequence of the Central North Sea region is presented in this article, where the boundary between Early and Middle Pleistocene occurs at a depth of about 210 m in the borehole.

Journal ArticleDOI
TL;DR: In this paper, a multicolor map of geomagnetic field intensity anomalies over the island and its surroundings was produced, based on data from a 1968-1980 aeromagnetic survey of Iceland and a 1972-1973 marine magnetic survey of a part of the shelf around Iceland.

Journal ArticleDOI
TL;DR: This short note discusses some structural properties of the progressive hedging algorithm, based on the finite case, but allows for event trees that are unbalanced and where the nodes can have a varying number of children.
Abstract: This short note discusses some structural properties of the progressive hedging algorithm. It is based on the finite case, but allows for event trees that are unbalanced and where the nodes can have a varying number of children. Generic procedures and a generic record definition for the algorithms are presented.