Hydrogen site occupancy and strength of forces in nano-sized metal hydrides

The dipole force components in nano-sized metal hydrides are quantitatively determined with curvature and x-ray diffraction measurements. Ab-initio density functional theory is used to calculate the dipole components and the symmetry of the strain field. The hydrogen occupancy in a 100 nm thick V film is shown to be tetrahedral with a slight asymmetry at low concentration and a transition to octahedral occupancy is shown to take place at around 0.07 [H/V] at 360 K. When the thickness of the V layer is reduced to 3 nm and biaxially strained, in a Fe_0.5V_0.5/V superlattice, the hydrogen unequivocally occupies octahedral z-like sites, even at and below concentrations of 0.02 [H/V]

Carriage of group B beta-haemolytic streptococci among pregnant women in Iceland and colonisation of their newborn infants

Neðst á síðunni er hægt að nálgast greinina í heild sinni með því að smella á hlekkinn View/OpenObjective: To determine the carrier rate of group B beta-haemolytic streptococci (GBS) of pregnant women in Iceland and the colonisation of their newborns. Material and methods: A prospective study was conducted from October 1994 until October 1997, where culture specimens for GBS were taken from vagina and rectum of pregnant women attending the prenatal clinics at the Department of Obstetrics and Gynecology, Landspitali University Hospital and the Reykjavik Health Centre. The samples were taken at 23 and 36 weeks gestation and at delivery. Culture samples were also taken from axilla, umbilical area and pharynx of their newborn infants immediately after birth. Included in the study were pregnant women born on every fourth day of each month. Carrier state was not treated during pregnancy, but Penicillin G was given i.v. at delivery if the last culture before delivery was positive and gestational age was 12 hours before delivery or the mother had a fever >38 degrees C. Results: Cultures were taken from 280 women and their children. GBS carrier rate of pregnant women in Iceland was 24.3%. Twelve newborns had GBS positive cultures. No newborn had a confirmed septicemia. Cultures from 25% of newborns, who s mothers were still GBS carriers at birth, were positive for GBS. Positive predictive value of cultures taken at 23 weeks gestation was 64% and 78% at 36 weeks. Negative predictive value was 95% and 99% respectively. Conclusion: One out of every four pregnant women in Iceland is a GBS carrier. Twentyfive percent of newborns become colonised with GBS if the mother is a GBS carrier at delivery. When screening for GBS carrier state is done cultures from both vagina and rectum is more sensitive than cultures from vagina only. At least five percent of all newborns in Iceland are therefore expected to have positive skin cultures at birth. If the mother does not have positive GBS cultures during pregnancy, the likelihood that she will give birth to a GBS colonised child is almost none.Inngangur: Blóðsýkingar hjá nýburum eru enn alvarlegt sjúkdómsástand með hárri dánartíðni. Í rannsókn á faraldsfræði blóðsýkinga meðal nýbura á Íslandi á árunum 1976 til 1995 voru blóðsýkingar staðfestar hjá tveimur af hverjum 1000 lifandi fæddum börnum og dánartíðni var 17%. Nýgengi blóðsýkinga af völdum b-hemólýtískra streptókokka af flokki B (GBS) fór verulega vaxandi á rannsóknartímabilinu og var orðið 0,9/1000 á síðustu fimm árunum. Tilgangur þessarar rannsóknar var að kanna beratíðni GBS meðal þungaðra kvenna á Íslandi og smitun nýbura í fæðingu þess vegna. Efniviður og aðferðir: Gerð var framsýn rannsókn þar sem tekin voru strok frá neðri hluta legganga og endaþarmi þungaðra kvenna á 23. og 36. viku meðgöngu svo og í fæðingu. Einnig voru tekin strok frá holhönd, nafla og koki nýburanna þegar eftir fæðingu. Úrtakið voru þungaðar konur sem fæddar voru fjórða hvern dag hvers mánaðar og komu til mæðraeftirlits á Kvennadeild Landspítalans eða Heilsuverndarstöð Reykjavíkur á tímabilinu frá október 1994 til október 1997. Ekki voru gefin sýklalyf til að uppræta berastig á meðgöngu, en hins vegar var Penisillín G gefið í æð í fæðingunni ef síðasta ræktun fyrir fæðingu var jákvæð fyrir GBS og jafnframt einu eða fleiri af eftirtöldum skilyrðum fullnægt: Meðgöngulengd 12 klukkustundum fyrir fæðingu eða hiti >38°C. Niðurstöður: Sýni voru tekin frá 280 konum. Beratíðni þungaðra kvenna hérlendis reyndist vera 24,3%. Tólf börn reyndust hafa GBS í ræktunarsýnum sem tekin voru þegar eftir fæðingu. Ekkert barn í rannsókninni fékk staðfesta blóðsýkingu. Fjórðungur (25%) barna þeirra kvenna, sem enn voru GBS berar í fæðingunni, smitaðist. Jákvætt forspárgildi GBS sýnatöku við 23 vikna meðgöngu er 64% en 78% við 36 vikna meðgöngu. Neikvætt forspárgildi er samsvarandi 95% og 99%. Ályktun: Fjórðungur þungaðra kvenna á Íslandi ber GBS í leggöngum eða endaþarmi. Tuttugu og fimm prósent barna þeirra smitast af sýklinum við fæðingu. Þannig má reikna með að 5% allra nýbura á Íslandi á umræddu tímabili hafi smitast af GBS við fæðingu. Ef verðandi móðir er ekki GBS beri samkvæmt ræktunum frá leggöngum og endaþarmi á meðgöngunni, eru hverfandi líkur á að barn hennar smitist af GBS í fæðingunni

Specific-heat evidence for strong electron correlations in the thermoelectric material (Na,Ca)Co_{2}O_{4}

The specific heat of (Na,Ca)Co_{2}O_{4} is measured at low-temperatures to determine the magnitude of the electronic specific-heat coefficient \gamma, in an attempt to gain an insight into the origin of the unusually large thermoelectric power of this compound. It is found that \gamma is as large as 48 mJ/molK^2, which is an order of magnitude larger than \gamma of simple metals. This indicates that (Na,Ca)Co_{2}O_{4} is a strongly-correlated electron system, where the strong correlation probably comes from the low-dimensionality and the frustrated spin structure. We discuss how the large thermopower and its dependence on Ca doping can be understood with the strong electron correlations.Comment: 5 pages, 4 figures, accepted for publication in Phys. Rev.

Mg/Ti multilayers: structural, optical and hydrogen absorption properties

Mg-Ti alloys have uncommon optical and hydrogen absorbing properties, originating from a "spinodal-like" microstructure with a small degree of chemical short-range order in the atoms distribution. In the present study we artificially engineer short-range order by depositing Pd-capped Mg/Ti multilayers with different periodicities and characterize them both structurally and optically. Notwithstanding the large lattice parameter mismatch between Mg and Ti, the as-deposited metallic multilayers show good structural coherence. Upon exposure to H2 gas a two-step hydrogenation process occurs, with the Ti layers forming the hydride before Mg. From in-situ measurements of the bilayer thickness L at different hydrogen pressures, we observe large out-of-plane expansions of the Mg and Ti layers upon hydrogenation, indicating strong plastic deformations in the films and a consequent shortening of the coherence length. Upon unloading at room temperature in air, hydrogen atoms remain trapped in the Ti layers due to kinetic constraints. Such loading/unloading sequence can be explained in terms of the different thermodynamic properties of hydrogen in Mg and Ti, as shown by diffusion calculations on a model multilayered systems. Absorption isotherms measured by hydrogenography can be interpreted as a result of the elastic clamping arising from strongly bonded Mg/Pd and broken Mg/Ti interfaces

Metal-insulator transition in EuO

It is shown that the spectacular metal-insulator transition in Eu-rich EuO can be simulated within an extended Kondo lattice model. The different orders of magnitude of the jump in resistivity in dependence on the concentration of oxygen vacancies as well as the low-temperature resistance minimum in high-resistivity samples are reproduced quantitatively. The huge colossal magnetoresistance (CMR) is calculated and discussed

Thermoelectric Response Near the Density Driven Mott Transition

We investigate the thermoelectric response of correlated electron systems near the density driven Mott transition using the dynamical mean field theory.Comment: 4 pages, 2 embedded figure

Radon precursor studies in Iceland

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Theory of Thermoelectric Power in High-Tc Superconductors

We present a microscopic theory for the thermoelectric power (TEP) in high-Tc cuprates. Based on the general expression for the TEP, we perform the calculation of the TEP for a square lattice Hubbard model including all the vertex corrections necessary to satisfy the conservation laws. In the present study, characteristic anomalous temperature and doping dependences of the TEP in high-Tc cuprates, which have been a long-standing problem of high-Tc cuprates, are well reproduced for both hole- and electron-doped systems, except for the heavily under-doped case. According to the present analysis, the strong momentum and energy dependences of the self-energy due to the strong antiferromagnetic fluctuations play an essential role in reproducing experimental anomalies of the TEP.Comment: 5 pages, 8 figures, to appear in J. Phys. Soc. Jpn. 70 (2001) No.10. Figure 2 has been revise