Gildun á mælistikum : hvaða orðgildi er best að nota á svarmöguleika mælikvarða?

Neðst á síðunni er hægt að nálgast greinina í heild sinni með því að smella á hlekkinn View/OpenGildunarannsókn var gerð þar sem þátttakendur voru beðnir um að meta merkingu íslenskra orðagilda sem hægt er að nota á mælistiku matskvarða. Úrtak 598 Íslendinga var tekið úr 10.000 manna netpanel sem valinn var með tilviljunaraðferð úr þjóðskrá. Alls tóku 398 þeirra þátt og var svarhlutfall því 65,9%. Þátttakendur, sem voru á aldrinum 17 til 73 ára, mátu 96 orð og orðasambönd. Erlendar rannsóknir á merkingu orðagilda voru hafðar til hliðsjónar þegar orðagildi voru valin en einnig var leitað fanga í íslenskum orðabókum. Á grundvelli niðurstaðna er hægt að velja orðagildi sem hafa nákvæma merkingu og spanna þá viðhorfavídd sem verið er að mæla með jöfnu millibili

Long time scale simulation of a grain boundary in copper

doi:10.1088/1367-2630/11/7/073034 Abstract. A general, twisted and tilted, grain boundary in copper has been simulated using the adaptive kinetic Monte Carlo method to study the atomistic structure of the non-crystalline region and the mechanism of annealing events that occur at low temperature. The simulated time interval spanned 67µs at 135 K. Similar final configurations were obtained starting from different initial structures: (i) by bringing the two grains into contact without any intermediate layer, and (ii) by inserting an amorphous region between the grains. The results obtained were analyzed with a radial distribution function and a common neighbor analysis. Annealing events leading to lowering of the energy typically involved concerted displacement of several atoms—even as many as 10 atoms displaced by more than half an Ångström. Increased local icosahedral ordering is observed in the boundary layer, but local HCP coordination was also observed. In the final low-energy configurations, the thickness of the region separating the crystalline grains corresponds to just one atomic layer, in good agreemen

Effects of hole self-trapping by polarons on transport and negative bias illumination stress in amorphous-IGZO

The effects of hole injection in amorphous-IGZO is analyzed by means of first-principles calculations. The injection of holes in the valence band tail states leads to their capture as a polaron, with high self-trapping energies (from 0.44 to 1.15 eV). Once formed, they mediate the formation of peroxides and remain localized close to the hole injection source due to the presence of a large diffusion energy barrier (of at least 0.6eV). Their diffusion mechanism can be mediated by the presence of hydrogen. The capture of these holes is correlated with the low off-current observed for a-IGZO transistors, as well as, with the difficulty to obtain a p-type conductivity. The results further support the formation of peroxides as being the root cause of Negative bias illumination stress (NBIS). The strong self-trapping substantially reduces the injection of holes from the contact and limits the creation of peroxides from a direct hole injection. In presence of light, the concentration of holes substantially rises and mediates the creation of peroxides, responsible for NBIS.Comment: 8 pages, 8 figures, to be published in Journal of Applied Physic

Ideal, Defective, and Gold--Promoted Rutile TiO2(110) Surfaces: Structures, Energies, Dynamics, and Thermodynamics from PBE+U

Extensive first principles calculations are carried out to investigate gold-promoted TiO2(110) surfaces in terms of structure optimizations, electronic structure analyses, ab initio thermodynamics calculations of surface phase diagrams, and ab initio molecular dynamics simulations. All computations rely on density functional theory in the generalized gradient approximation (PBE) and account for on-site Coulomb interactions via inclusion of a Hubbard correction, PBE+U, where U is computed from linear response theory. This approach is validated by investigating the interaction between TiO2(110) surfaces and typical probe species (H, H2O, CO). Relaxed structures and binding energies are compared to both data from the literature and plain PBE results. The main focus of the study is on the properties of gold-promoted titania surfaces and their interactions with CO. Both PBE+U and PBE optimized structures of Au adatoms adsorbed on stoichiometric and reduced TiO2 surfaces are computed, along with their electronic structure. The charge rearrangement induced by the adsorbates at the metal/oxide contact are also analyzed and discussed. By performing PBE+U ab initio molecular dynamics simulations, it is demonstrated that the diffusion of Au adatoms on the stoichiometric surface is highly anisotropic. The metal atoms migrate either along the top of the bridging oxygen rows, or around the area between these rows, from one bridging position to the next along the [001] direction. Approximate ab initio thermodynamics predicts that under O-rich conditions, structures obtained by substituting a Ti5c atom with an Au atom are thermodynamically stable over a wide range of temperatures and pressures.Comment: 20 pages, 12 figures, accepted for publication in Phys. Rev.

Theoretical study of kinks on screw dislocation in silicon

Theoretical calculations of the structure, formation and migration of kinks on a non-dissociated screw dislocation in silicon have been carried out using density functional theory calculations as well as calculations based on interatomic potential functions. The results show that the structure of a single kink is characterized by a narrow core and highly stretched bonds between some of the atoms. The formation energy of a single kink ranges from 0.9 to 1.36 eV, and is of the same order as that for kinks on partial dislocations. However, the kinks migrate almost freely along the line of an undissociated dislocation unlike what is found for partial dislocations. The effect of stress has also been investigated in order to compare with previous silicon deformation experiments which have been carried out at low temperature and high stress. The energy barrier associated with the formation of a stable kink pair becomes as low as 0.65 eV for an applied stress on the order of 1 GPa, indicating that displacements of screw dislocations likely occur via thermally activated formation of kink pairs at room temperature

Structure and stability of small H clusters on graphene

The structure and stability of small hydrogen clusters adsorbed on graphene is studied by means of Density Functional Theory (DFT) calculations. Clusters containing up to six H atoms are investigated systematically -- the clusters having either all H atoms on one side of the graphene sheet (\textit{cis}-clusters) or having the H atoms on both sides in an alternating manner (\textit{trans}-cluster). The most stable cis-clusters found have H atoms in ortho- and para-positions with respect to each other (two H's on neighboring or diagonally opposite carbon positions within one carbon hexagon) while the most stable trans-clusters found have H atoms in ortho-trans-positions with respect to each other (two H's on neighboring carbon positions, but on opposite sides of the graphene). Very stable trans-clusters with 13-22 H atoms were identified by optimizing the number of H atoms in ortho-trans-positions and thereby the number of closed, H-covered carbon hexagons. For the cis-clusters, the associative H$_2$ desorption was investigated. Generally, the desorption with the lowest activation energy proceeds via para-cis-dimer states, i.e.\ involving somewhere in the H clusters two H atoms that are positioned on opposite sites within one carbon hexagon. H$_2$ desorption from clusters lacking such H pairs is calculated to occur via hydrogen diffusion causing the formation of para-cis-dimer states. Studying the diffusion events showed a strong dependence of the diffusion energy barriers on the reaction energies and a general odd-even dependence on the number of H atoms in the cis-clusters.Comment: 11 pages, 11 figures, to appear in Phys. Rev.

Equilibrium shape and dislocation nucleation in strained epitaxial nanoislands

We study numerically the equilibrium shapes, shape transitions and dislocation nucleation of small strained epitaxial islands with a two-dimensional atomistic model, using simple interatomic pair potentials. We first map out the phase diagram for the equilibrium island shapes as a function of island size (up to N = 105 atoms) and lattice misfit with the substrate and show that nanoscopic islands have four generic equilibrium shapes, in contrast with predictions from the continuum theory of elasticity. For increasing substrate-adsorbate attraction, we find islands that form on top of a finite wetting layer as observed in Stranski-Krastanow growth. We also investigate energy barriers and transition paths for transitions between different shapes of the islands and for dislocation nucleation in initially coherent islands. In particular, we find that dislocations nucleate spontaneously at the edges of the adsorbate-substrate interface above a critical size or lattice misfit.Comment: 4 pages, 3 figures, uses wrapfig.sty and epsfig.st

Stress release mechanisms for Cu on Pd(111) in the submonolayer and monolayer regimes

We study the strain relaxation mechanisms of Cu on Pd(111) up to the monolayer regime using two different computational methodologies, basin-hopping global optimization and energy minimization with a repulsive bias potential. Our numerical results are consistent with experimentally observed layer-by-layer growth mode. However, we find that the structure of the Cu layer is not fully pseudomorphic even at low coverages. Instead, the Cu adsorbates forms fcc and hcp stacking domains, separated by partial misfit dislocations. We also estimate the minimum energy path and energy barriers for transitions from the ideal epitaxial state to the fcc-hcp domain pattern.Comment: 4 pages, 4 figure

Self-learning Kinetic Monte-Carlo method: application to Cu(111)

We present a novel way of performing kinetic Monte Carlo simulations which does not require an {\it a priori} list of diffusion processes and their associated energetics and reaction rates. Rather, at any time during the simulation, energetics for all possible (single or multi-atom) processes, within a specific interaction range, are either computed accurately using a saddle point search procedure, or retrieved from a database in which previously encountered processes are stored. This self-learning procedure enhances the speed of the simulations along with a substantial gain in reliability because of the inclusion of many-particle processes. Accompanying results from the application of the method to the case of two-dimensional Cu adatom-cluster diffusion and coalescence on Cu(111) with detailed statistics of involved atomistic processes and contributing diffusion coefficients attest to the suitability of the method for the purpose.Comment: 18 pages, 9 figure

Study of medications use of elderly admitted to acute care hospital

Neðst á síðunni er hægt að nálgast greinina í heild sinni með því að smella á hlekkinn View/OpenObjective: The prevalence of diseases increases with age and so does use of medications. Thus illness related to medications use does also become more prevalent. This study aims at evaluating medications of elderly people admitted to an acute care hospital, and demonstrate adverse reactions and quality indicators. Material and methods: This is a study of patients 75 years of age and older admitted acutely to internalmedicine at the Reykjavik Hospital over a three month period in the spring of 1995. All medications and diagnoses were registered and the medical records reviewed. The contribution of adverse medication effects to the admission was assessed. Quality of treatment was evaluated according to evidence based medicine for the diagnoses chosen. The study included 208 individuals, 133 women and 75 men with the mean age of 82.4 years. Results: Mean length of stay for women was 19.9 days and men 15.2 days. Number of drugs on admission and discharge ranged from 0 to 18. The mean number of drugs were for women 5.8 and 6.9 and men 6.6 and 7.7 on admission and discharge, respectively. In 16 cases or 7.7% it was judged that there was a high likelihood of the admission being due to an adverse effect. Potential drug interactions according to a computer software package were not judged to be of clinical importance in any case. Conclusions: Treatment for coronary heart disease, heart failure, osteoporosis, insomnia and long term prednisolon treatment is not completely optimal according to evidence based medicine. The results of this study indicate that treatment could be improved for example with use of clinical guidelines.Tilgangur: Með hækkandi aldri vex algengi sjúkdóma og jafnframt lyfjanotkun. Veikindi sem tengjast lyfjanotkun verða því tíðari meðal aldraðra. Rannsóknin lýsir lyfjanotkun aldraðra á bráðasjúkrahúsi, aukaverkunum og gæðavísum. Efniviður og aðferðir: Þessi rannsókn tekur til allra aldraðra, 75 ára og eldri, sem lögðust inn brátt á lyflækningadeildir Borgarspítalans á þriggja mánaða tímabili vorið 1995. Öll lyf og allar sjúkdómsgreiningar voru skráð og sjúkraskrár yfirfarnar. Lagt var mat á það hvort lyfjanotkun ætti þátt í innlögn. Gæði lyfjameðferðar voru metin meðal annars með tilliti til fyrri og núverandi sjúkdómsgreininga. Niðurstöður: Könnunin náði til 208 einstaklinga, 133 kvenna og 75 karla á aldrinum 75 til 98 ára, meðalaldur 82,4 ár. Meðallegudagar kvennanna voru 19,9 dagar og karlanna 15,2 dagar. Skráður fjöldi lyfja við innskrift var á bilinu 0 til 18 lyf og við útskrift mest 18. Meðalfjöldi lyfja hjá konum við innskrift var 5,8 lyf og við útskrift 6,9. Karlar höfðu 6,6 lyf við innskrift að meðaltali og 7,7 við útskrift. Í 16 tilvikum eða 7,7% voru taldar miklar líkur á að sjúklingur hefði lagst inn vegna aukaverkana lyfja. Engin vísbending um milliverkun samkvæmt tölvuútskrift reyndist hafa klíníska þýðingu að mati höfunda. Ályktanir: Aldraðir sem leggjast inn á bráðasjúkrahús eru á fjölda lyfja og eiga aukaverkanir lyfja nokkurn þátt í innlögnum. Hvað varðar meðferð á kransæðasjúkdómi, hjartabilun, beinþynningu, svefntruflunum og langtímameðferð með sykursterum kom fram að all nokkuð vantar upp á að bestu meðferð, samkvæmt niðurstöðum rannsókna, sé beitt. Niðurstöður rannsóknarinnar, ásamt þeim grófu gæðavísum sem beitt var, benda til að gera megi betur til dæmis með klínískum leiðbeiningum