Showing papers by "University of Iceland published in 2004"

Origin of the Overpotential for Oxygen Reduction at a Fuel-Cell Cathode

Abstract: We present a method for calculating the stability of reaction intermediates of electrochemical processes on the basis of electronic structure calculations. We used that method in combination with detailed density functional calculations to develop a detailed description of the free-energy landscape of the electrochemical oxygen reduction reaction over Pt(111) as a function of applied bias. This allowed us to identify the origin of the overpotential found for this reaction. Adsorbed oxygen and hydroxyl are found to be very stable intermediates at potentials close to equilibrium, and the calculated rate constant for the activated proton/electron transfer to adsorbed oxygen or hydroxyl can account quantitatively for the observed kinetics. On the basis of a database of calculated oxygen and hydroxyl adsorption energies, the trends in the oxygen reduction rate for a large number of different transition and noble metals can be accounted for. Alternative reaction mechanisms involving proton/electron transfer to ...

Risk factors for injuries in football.

Abstract: BackgroundThe injury risk in football is high, but little is known about causes of injury.PurposeTo identify risk factors for football injuries using a multivariate model.Study DesignProspective cohort study.MethodsParticipants were 306 male football players from the two highest divisions in Iceland. Before the 1999 football season started, the following factors were examined: height, weight, body composition, flexibility, leg extension power, jump height, peak O2 uptake, joint stability, and history of previous injury. Injuries and player exposure were recorded throughout the competitive season.ResultsOlder players were at higher risk of injury in general (odds ratio [OR] = 1.1 per year, P = 0.05). For hamstring strains, the significant risk factors were age (OR = 1.4 [1 year], P < 0.001) and previous hamstring strains (OR = 11.6, P < 0.001). For groin strains, the predictor risk factors were previous groin strains (OR = 7.3, P = 0.001) and decreased range of motion in hip abduction (OR = 0.9 [1°], P = 0...

Melanocytes and the Microphthalmia Transcription Factor Network

Abstract: ▪ Abstract The first mouse microphthalmia transcription factor (Mitf ) mutation was discovered over 60 years ago, and since then over 24 spontaneous and induced mutations have been identified at the locus. Mitf encodes a member of the Myc supergene family of basic helix-loop-helix zipper (bHLH-Zip) transcription factors. Like Myc, Mitf regulates gene expression by binding to DNA as a homodimer or as a heterodimer with another related family member, in the case of Mitf the Tfe3, Tfeb, and Tfec proteins. The study of Mitf has provided many insights into the biology of melanocytes and helped to explain how melanocyte-specific gene expression and signaling is regulated. The human homologue of MITF is mutated in patients with the pigmentary and deafness disorder Waardenburg Syndrome Type 2A (WS2A). The mouse Mitf mutations therefore serve as a model for the study of this human disease. Mutations and/or aberrant expression of several MITF family member genes have also been reported in human cancer, including me...

Experimental evidence for the existence of iron-rich metal in the Earth's lower mantle

Abstract: The oxidation state recorded by rocks from the Earth's upper mantle can be calculated from measurements of the distribution of Fe3+ and Fe2+ between the constituent minerals1,2,3. The capacity for minerals to incorporate Fe3+ may also be a significant factor controlling the oxidation state of the mantle4,5, and high-pressure experimental measurements of this property might provide important insights into the redox state of the more inaccessible deeper mantle. Here we show experimentally that the Fe3+ content of aluminous silicate perovskite, the dominant lower-mantle mineral, is independent of oxygen fugacity. High levels of Fe3+ are present in perovskite even when it is in chemical equilibrium with metallic iron. Silicate perovskite in the lower mantle will, therefore, have an Fe3+/total Fe ratio of at least 0.6, resulting in a whole-rock ratio of over ten times that of the upper mantle5,6. Consequently, the lower mantle must either be enriched in Fe3+ or Fe3+ must form by the disproportionation of Fe2+ to produce Fe3+ plus iron metal. We argue that the lower mantle contains approximately 1 wt% of a metallic iron-rich alloy. The mantle's oxidation state and siderophile element budget have probably been influenced by the presence of this alloy.

Physical fitness, injuries, and team performance in soccer.

Abstract: ARNASON, A., S. B. SIGURDSSON, A. GUDMUNDSSON, I. HOLME, L. ENGEBRETSEN, and R. BAHR. Physical Fitness, Injuries, and Team Performance in Soccer. Med. Sci. Sports Exerc., Vol. 36, No. 2, pp. 278 –285, 2004. Purpose: To investigate the relationship between physical fitness and team success in soccer, and to test for differences in physical fitness between different player positions. Methods: Participants were 306 male soccer players from 17 teams in the two highest divisions in Iceland. Just before the start of the 1999 soccer season, the following variables were tested: height and weight, body composition, flexibility, leg extension power, jump height, and peak O2 uptake. Injuries and player participation in matches and training were recorded through the 4-month competitive season. Team average physical fitness was compared with team success (final league standing) using a linear regression model. Physical fitness was also compared between players in different playing positions. Results: A significant relationship was found between team average jump height (countermovement jump and standing jump) and team success (P 0.009 and P 0.012, respectively). The same trend was also found for leg extension power (P 0.097), body composition (% body fat, P 0.07), and the total number of injury days per team (P 0.09). Goalkeepers demonstrated different fitness characteristics from outfield players. They were taller and heavier, more flexible in hip extension and knee flexion, and had higher leg extension power and a lower peak O2 uptake. However, only minor differences were observed between defenders, midfield players, and attackers. Conclusion: Coaches and medical support teams should pay more attention to jump and power training, as well as preventive measures and adequate rehabilitation of previous injuries to increase team success. Key Words: PHYSICAL PERFORMANCE, MAXIMAL O 2 UPTAKE, JUMPING ABILITY, LEG POWER, FLEXIBILITY, BODY COMPOSITION

Comparison of methods for finding saddle points without knowledge of the final states

Abstract: Within the harmonic approximation to transition state theory, the biggest challenge involved in finding the mechanism or rate of transitions is the location of the relevant saddle points on the multidimensional potential energy surface. The saddle point search is particularly challenging when the final state of the transition is not specified. In this article we report on a comparison of several methods for locating saddle points under these conditions and compare, in particular, the well-established rational function optimization (RFO) methods using either exact or approximate Hessians with the more recently proposed minimum mode following methods where only the minimum eigenvalue mode is found, either by the dimer or the Lanczos method. A test problem involving transitions in a seven-atom Pt island on a Pt(111) surface using a simple Morse pairwise potential function is used and the number of degrees of freedom varied by varying the number of movable atoms. In the full system, 175 atoms can move so 525 degrees of freedom need to be optimized to find the saddle points. For testing purposes, we have also restricted the number of movable atoms to 7 and 1. Our results indicate that if attempting to make a map of all relevant saddle points for a large system (as would be necessary when simulating the long time scale evolution of a thermal system) the minimum mode following methods are preferred. The minimum mode following methods are also more efficient when searching for the lowest saddle points in a large system, and if the force can be obtained cheaply. However, if only the lowest saddle points are sought and the calculation of the force is expensive but a good approximation for the Hessian at the starting position of the search can be obtained at low cost, then the RFO approaches employing an approximate Hessian represent the preferred choice. For small and medium sized systems where the force is expensive to calculate, the RFO approaches employing an approximate Hessian is also the more efficient, but when the force and Hessian can be obtained cheaply and only the lowest saddle points are sought the RFO approach using an exact Hessian is the better choice. These conclusions have been reached based on a comparison of the total computational effort needed to find the saddle points and the number of saddle points found for each of the methods. The RFO methods do not perform very well with respect to the latter aspect, but starting the searches further away from the initial minimum or using the hybrid RFO version presented here improves this behavior considerably in most cases.

Immunopathogenic mechanisms in psoriasis

Abstract: Psoriasis is a common autoimmune skin disease characterized by T cell-mediated hyperproliferation of keratinocytes. The disease has a strong but complex genetic background with a concordance of approximately 60% in monozygotic twins, and recent linkage and high resolution association studies indicate that HLA-Cw*0602 is itself a major susceptibility allele for psoriasis. Patients carrying this allele have been shown to have different clinical features and earlier age of disease onset, and patients homozygous for this allele have about 2.5 times higher disease risk than heterozygotes. Published data indicate that CD8+ T cells may play a major effector role in psoriasis. Epidermal infiltration of predominantly oligoclonal CD8+ T cells, and probably also of CD4+ T cells in the dermis, is a striking feature of chronic psoriasis lesions, indicating that these cells are responding to specific antigens. We argue that CD4+ T cells are essential for initiating and maintaining the pathogenic process of psoriasis but that cross-primed CD8+ T cells are the main effector cells responding to antigens in the HLA-Cw*0602 binding pocket of keratinocytes. It is further proposed that CD8+ T cells are involved in the control of the Th1 polarization, which is observed in psoriasis lesions, through a complex interplay between CD4+, CD8+ T cells and cross-presenting dendritic cells. It is also suggested that spontaneous remissions or fluctuations in disease activity may be determined by a balance within the lesions between effector and suppressor CD4+ and CD8+ T cells.

Internet site for European strong-motion data

Abstract: The Internet Site for European Strong-Motion Data (ISESD) provides unlimited free access to over 2,000 strong-motion records of earthquakes from Europe, the Mediterranean and the Middle East (EMME). Four mirror sites of ISESD have been operating since 26th March 2002. The URLs of these sites are: www.isesd.cv.ic.ac.uk, smbase.itsak.gr, seismo.univ.trieste.it and www.isesd.hi.is. ISESD provides a basis for improved dissemination of strong-motion data in EMME. There are a number of future improvements to ISESD which would improve its usefulness to seismologists, earthquake engineers and insurance specialists.

Boundary entropy of one-dimensional quantum systems at low temperature.

Abstract: The boundary beta function generates the renormalization group acting on the universality classes of one-dimensional quantum systems with boundary which are critical in the bulk but not critical at the boundary. We prove a gradient formula for the boundary beta function, expressing it as the gradient of the boundary entropy s at fixed nonzero temperature. The gradient formula implies that s decreases under renormalization, except at critical points (where it stays constant). At a critical point, the number exp((s) is the "ground-state degeneracy," g, of Affleck and Ludwig, so we have proved their long-standing conjecture that g decreases under renormalization, from critical point to critical point. The gradient formula also implies that s decreases with temperature, except at critical points, where it is independent of temperature. It remains open whether the boundary entropy is always bounded below.

Routes of transmission and consequences of small ruminant lentiviruses (SRLVs) infection and eradication schemes.

Abstract: Small ruminant lentiviruses (SRLV = maedi-visna in sheep and caprine arthritis encephalitis in goats) are distributed throughout most countries of the world, particularly Europe. Laboratories from 16 European countries established collaborations within the framework of a COST (CO-operation in the field of Scientific and Technical Research) action sponsored by the European Union in order to (i) better organize their research programmes on SRLVs and (ii) to coordinate efforts to combat these two diseases. After five years, a consensus conference--the first one in the veterinary medicine field--concluded the work of this network of laboratories by reviewing the present position and discussing three important questions in the field of SRLVs: routes of transmission, consequences of infection and potential role of eradication programmes at either a European or local level, according to the situation in each country or region. This paper brings together existing information regarding these questions and identifies areas for future research.

Role of cyclodextrins in improving oral drug delivery

Abstract: The use of high-throughput screening and similar techniques in drug discovery has put a number of evolutionary pressures on drug candidates such that over time there is a tendency for them to increase in molecular weight, increase in log K(octanol/water) and decrease in water solubility. These trends provide an ever-increasing series of challenges for the drug formulator to generate effective, orally bioavailable dosage forms. An important tool in this regard is the use of cyclodextrins, especially chemically modified cyclodextrins. These starch derivatives interact via dynamic complex formation and other mechanisms in a way that camouflages undesirable physicochemical properties, including low aqueous solubility, poor dissolution rate and limited drug stability. Through these effects, cyclodextrins and their derivatives have become popular modalities for increasing oral bioavailability and absorption rate. These actions have positioned cyclodextrins as important enabling and functional excipients. This review aims to assess the use of cyclodextrins in oral and other administration routes in the context of the Biopharmaceutical Classification Systems (BCS), a US FDA-based characterization approach that bins drugs based on solubility and permeability features. Specifically, a framework based on Fickian theory as well as the Noyes-Whiney relationship is constructed to assess where cyclodextrins are likely to be useful and where their use is probably not justified. This working model is examined in the context of a number of published examples in which cyclodextrins have been applied to class I, II, III, and IV drugs and drug candidates.

Mandibular third molar removal: Risk indicators for extended operation time, postoperative pain, and complications

Abstract: Objectives The aim of this study was to identify risk indicators for extended operation time and postoperative complications after removal of mandibular third molars. Study design There were 388 molars included in the study. The teeth were removed using the buccal approach under local anesthesia. Four hours postoperatively the patient recorded his or her pain perception on a visual analogue scale (VAS). After surgery a surgeon recorded parameters regarding the tooth and if the mandibular nerve had been visible during the operation. One week postoperatively the postoperative pain and complications were recorded. Logistic regression models were made to identify risk indicators for extended operation time, postoperative pain, and complications. Results Females were at higher risk for postoperative pain and dry socket than males. Older patients were at higher risk for extended operation time than younger patients. Radiographically fully impacted molars increased the risk of postoperative general infection. If the nerve was visible during surgery there was a higher risk of a high VAS score, postoperative pain, and general infection than if the nerve had not been visible. Conclusion Several indicators were found to increase the risk of postoperative complications, but a visible alveolar inferior nerve during the operation was repeatedly found to be the highest single risk indicator.

Exploiting spectral and spatial information in hyperspectral urban data with high resolution

Abstract: Very high resolution hyperspectral data should be very useful to provide detailed maps of urban land cover. In order to provide such maps, both accurate and precise classification tools need, however, to be developed. In this letter, new methods for classification of hyperspectral remote sensing data are investigated, with the primary focus on multiple classifications and spatial analysis to improve mapping accuracy in urban areas. In particular, we compare spatial reclassification and mathematical morphology approaches. We show results for classification of DAIS data over the town of Pavia, in northern Italy. Classification maps of two test areas are given, and the overall and individual class accuracies are analyzed with respect to the parameters of the proposed classification procedures.

The Strengths and Difficulties Questionnaire in the Nordic countries

Abstract: Background: The Strengths and Difficulties Questionnaire (SDQ) has been translated into the different Nordic languages between 1996 and 2003. During the past few years, SDQs have been completed for nearly 100,000 children and adolescents in population-based studies as well as in clinical samples. The largest studies have been performed in Norway and Denmark, and in these countries the diagnostic interview DAWBA has also been used in conjunction with the SDQ. Aims: In addition to a brief overview of past and ongoing SDQ work in Sweden, Finland, Norway, Denmark, and Iceland, we present scale means and standard deviations from selected community studies with comparable age groups, including parental reports for 7, 9 and 11 year-old children and self-reports of 13 and 15 year-olds. Conclusions: The descriptive statistics suggest that the distributions of SDQ scores are very similar across the Nordic countries. Further collaborative efforts in establishing norms and evaluating the validity of the SDQ as a screening instrument are encouraged.

Swift identification of dark gamma-ray bursts

Abstract: We present an optical flux vs. X-ray flux diagram for all known gamma-ray bursts (GRBs) for which an X-ray afterglow has been detected. We propose an operational definition of dark bursts as those bursts that are optically subluminous with respect to the fireball model, i.e., which have an optical-to-X-ray spectral indexOX < 0.5. Out of a sample of 52 GRBs we identify 5 dark bursts. The definition and diagram serve as a simple and quick diagnostic tool for identifying dark GRBs based on limited information, particularly useful for early and objective identification of dark GRBs observed with the Swift satellite. Subject headings: dust, extinction — galaxies: high-redshift — gamma rays: bursts large differences in localisation accuracies, localisation time since the onset of the burst, and search strate- gies. Moreover, effects of observing conditions (e.g., lu- nar phase) have generally not been taken into account in statistical studies. In many cases, GRBs have been con- sidered dark if no OA was detected, irrespective of how inefficient the search was. In fact, there is no generally accepted criterion for when a GRB is considered dark. With the launch of the Swift satellite it will be essential to have a quick diagnostic tool to flag dark bursts for im- mediate and/or detailed follow-up (including the near-IR bands) to ensure homogeneity of samples. In this Let- ter we present a GRB diagram of the optical flux (Fopt) vs. the X-ray flux (FX) and propose that those bursts which are optically subluminous with respect to the fire- ball model, i.e., which have an optical-to-X-ray spectral indexOX < 0.5, be defined as dark.

Coping with bullying in the workplace: the effect of gender, age and type of bullying

Abstract: A study of bullying, victimisation and the coping strategies employed to tackle it is presented in the first study of bullying in the workplace conducted in Iceland. Participants were 398 members of a union of store and office workers and members of a national organisation of bank-employees. A factor analysis of bullying items identified two factors: general bullying and work-related bullying. Males score higher on both factors, but when asked directly if they have been bullied or not, no significant gender difference appears. A measure of coping strategies when faced with bullying is presented. A factor analysis and multidimensional scaling of these strategies identified four clusters: assertive response, seek help, avoidance and do nothing. These can be arranged on a passive vs. active dimension, which may reflect the severity or duration of the bullying situation. Multiple regressions indicate that males seek help less and use avoidance less than females, and males are more likely to use assertive stra...

Large retrotransposon derivatives : abundant, conserved but nonautonomous retroelements of barley and related genomes

Abstract: Retroviruses and LTR retrotransposons comprise two long-terminal repeats (LTRs) bounding a central domain that encodes the products needed for reverse transcription, packaging, and integration into the genome. We describe a group of retrotransposons in 13 species and four genera of the grass tribe Triticeae, including barley, with long, approximately 4.4-kb LTRs formerly called Sukkula elements. The approximately 3.5-kb central domains include reverse transcriptase priming sites and are conserved in sequence but contain no open reading frames encoding typical retrotransposon proteins. However, they specify well-conserved RNA secondary structures. These features describe a novel group of elements, called LARDs or large retrotransposon derivatives (LARDs). These appear to be members of the gypsy class of LTR retrotransposons. Although apparently nonautonomous, LARDs appear to be transcribed and can be recombinationally mapped due to the polymorphism of their insertion sites. They are dispersed throughout the genome in an estimated 1.3 x 10(3) full-length copies and 1.16 x 10(4) solo LTRs, indicating frequent recombinational loss of internal domains as demonstrated also for the BARE-1 barley retrotransposon.

Mitochondrial Cytochrome b DNA Variation in the High-Fecundity Atlantic Cod: Trans-Atlantic Clines and Shallow Gene Genealogy

Abstract: An analysis of sequence variation of 250 bp of the mitochondrial cytochrome b gene of 1278 Atlantic cod Gadus morhua ranging from Newfoundland to the Baltic shows four high-frequency (>8%) haplotypes and a number of rare and singleton haplotypes. Variation is primarily synonymous mutations. Natural selection acting directly on these variants is either absent or very weak. Common haplotypes show regular trans-Atlantic clines in frequencies and each of them reaches its highest frequency in a particular country. A shallow multifurcating constellation gene genealogy implies young age and recent turnover of polymorphism. Haplotypes characterizing populations at opposite ends of the geographic distribution in Newfoundland and the Baltic are mutationally closest together. The haplotypes are young and have risen rapidly in frequency. Observed differentiation among countries is due primarily to clinal variation. Hypotheses of historical isolation and polymorphisms balanced by local selection and gene flow are unlikely. Instead the results are explained by demic selection of mitochondria carried by highly fit females winning reproductive sweepstakes. By inference the Atlantic cod, a very high-fecundity vertebrate, is characterized by a high variance of offspring number and strong natural selection that leads to very low effective to actual population sizes.

Swift Identification of Dark Gamma-Ray Bursts

Abstract: We present an optical flux vs. X-ray flux diagram for all known gamma-ray bursts (GRBs) for which an X-ray afterglow has been detected. We propose an operational definition of dark bursts as those bursts that are optically subluminous with respect to the fireball model, i.e., which have an optical-to-X-ray spectral index beta_OX < 0.5. Out of a sample of 52 GRBs we identify 5 dark bursts. The definition and diagram serve as a simple and quick diagnostic tool for identifying dark GRBs based on limited information, particularly useful for early and objective identification of dark GRBs observed with the Swift satellite.

Relationship between dental erosion, soft drink consumption, and gastroesophageal reflux among Icelanders.

Abstract: The aim of this study was to determine the prevalence of dental erosion in young Icelandic adults (19-22 years old) and patients with gastroesophageal reflux disease (GERD), in relation to their soft drink consumption and gastroesophageal reflux. Eighty subjects (40 males and 40 females), comprising 57 young adults (mean age 21 +/- 2 years) and 23 GERD patients (mean age 35 +/- 10 years), were enrolled in this study. All subjects answered a detailed frequency questionnaire of soft drink consumption and participated in a clinical examination. Erosion was scored for incisor and molar teeth separately. No significant difference was observed in the prevalence of dental erosion between young adults and GERD patients. However, by combining the two study groups a three-fold higher risk of having erosion in molars or incisors was found for subjects drinking Coca-Cola three times a week or more often ( p < 0.05). Additionally, significantly higher erosion scores were found in molars among subjects drinking more than 1 litre of carbonated drinks (all brands) per week ( p < 0.05). It is concluded that the frequency of soft drink consumption is a strong risk factor in the development of dental erosion.

Community care in Europe. The Aged in Home Care project (AdHOC)

Abstract: Background and aims: Community care for older people is increasing dramatically in most European countries as the preferred option to hospital andlong-term care. While there has been a rapid expansion in Evidence-Based Medicine, apart from studies of specific interventions such as home visiting and hospital at home (specialist visits or hospital services provided to people in their own homes in the community), there is little evidence of characteristics of the recipients of community care services or the organisation of services that produce the best outcomes for them and their informal carers. The AdHOC Study was designed to compare outcomes of different models of community care using a structured comparison of services and a comprehensive standardised assessment instrument across 11 European countries. This paper describes the study and baseline data. Methods: 4,500 people 65 years and older already receiving home care services within the urban areas selected in each country were randomly sampled. They were assessed with the MDS-HC (Minimum Data Set-Home Care) instrument, containing over 300 items, including socio-demographic, physical and cognitive characteristics of patients as well as medical diagnoses and medications received. These data were linked to information on the setting, services structures and services utilization, including use of hospital and long-term care. After baseline assessment, patients were re-evaluated at 6 months with an abbreviated version of the instrument, and then at the end of one year. Data collection was performed by specially-trained personnel. In this paper, socio-demographics, physical and cognitive function and provision of hours of formal care are compared between countries at baseline. Results: The final study sample comprised 3,785 patients; mean age was 82±7.2 years, 74.2% were females. Marital and living status reflected close family relationships in southern Europe relative to Nordic countries, where 5 times as many patients live alone. Recipients of community care in France and Italy are characterised by very high physical and cognitive impairment compared with those in northern Europe, who have comparatively little impairment in Activities of Daily Living and cognitive function. The provision of formal care to people with similar dependency varies extremely widely with very little formal care in Italy and more than double the average across all levels of dependency in the UK. Conclusions: The AdHOC study, by virtue of the use of a common comprehensive standardised assessment instrument, is a unique tool in examining older recipients of community care services in European countries and their widely varied organisation. The extreme differences seen in dependency and hours of care illustrate the probable contribution the study will make to developing an evidence based on the structure, quantity and targeting of community care, which will have major policy implications.

Extensive sharing of chloroplast haplotypes among European birches indicates hybridization among Betula pendula, B. pubescens and B. nana.

Abstract: Extensive sharing of chloroplast haplotypes among the silver birch, Betula pendula Roth., the downy birch, B. pubescens Ehrh., and the dwarf birch, B. nana L., was discovered using polymerase chain reaction-restriction fragment length polymporphism markers. The geographical component of the genetic variation was stronger than the species component: the species were not significantly different while 11% of the variation could be attributed to differentiation between the two main regions studied, Scandinavia and western Russia. All haplotypes occurring in more than 2% of the individuals were shared among the species and the introgression ratios were quite large: 0.79 between B. pubescens and B. pendula and 0.67 between B. pubescens and B. nana. The data also indicate that B. pendula individuals are more similar to sympatric B. pubescens than to B. pendula individuals from nearby forests. However, this trend is not as pronounced when B. pubescens is considered, suggesting that introgression is not symmetrical. The haplotype sharing among the three Betula species is most likely caused by hybridization and subsequent cytoplasmic introgression.