Ab-initio investigation of phonon dispersion and anomalies in palladium

In recent years, palladium has proven to be a crucial component for devices ranging from nanotube field effect transistors to advanced hydrogen storage devices. In this work, I examine the phonon dispersion of fcc Pd using first principle calculations based on density functional perturbation theory. While several groups in the past have studied the acoustic properties of palladium, this is the first study to reproduce the phonon dispersion and associated anomaly with high accuracy and no adjustable parameters. In particular, I focus on the Kohn anomaly in the [110] direction.Comment: 19 pages, preprint format, 7 figures, added new figures and discussio

Magnetic structure of Yb2Pt2Pb: Ising moments on the Shastry-Sutherland lattice.

Neutron diffraction measurements were carried out on single crystals and powders of Yb2Pt2Pb, where Yb moments form two interpenetrating planar sublattices of orthogonal dimers, a geometry known as Shastry-Sutherland lattice, and are stacked along the c axis in a ladder geometry. Yb2Pt2Pb orders antiferromagnetically at TN=2.07K, and the magnetic structure determined from these measurements features the interleaving of two orthogonal sublattices into a 5×5×1 magnetic supercell that is based on stripes with moments perpendicular to the dimer bonds, which are along (110) and (−110). Magnetic fields applied along (110) or (−110) suppress the antiferromagnetic peaks from an individual sublattice, but leave the orthogonal sublattice unaffected, evidence for the Ising character of the Yb moments in Yb2Pt2Pb that is supported by point charge calculations. Specific heat, magnetic susceptibility, and electrical resistivity measurements concur with neutron elastic scattering results that the longitudinal critical fluctuations are gapped with ΔE≃0.07meV

Isospin Physics in Heavy-Ion Collisions at Intermediate Energies

In nuclear collisions induced by stable or radioactive neutron-rich nuclei a transient state of nuclear matter with an appreciable isospin asymmetry as well as thermal and compressional excitation can be created. This offers the possibility to study the properties of nuclear matter in the region between symmetric nuclear matter and pure neutron matter. In this review, we discuss recent theoretical studies of the equation of state of isospin-asymmetric nuclear matter and its relations to the properties of neutron stars and radioactive nuclei. Chemical and mechanical instabilities as well as the liquid-gas phase transition in asymmetric nuclear matter are investigated. The in-medium nucleon-nucleon cross sections at different isospin states are reviewed as they affect significantly the dynamics of heavy ion collisions induced by radioactive beams. We then discuss an isospin-dependent transport model, which includes different mean-field potentials and cross sections for the proton and neutron, and its application to these reactions. Furthermore, we review the comparisons between theoretical predictions and available experimental data. In particular, we discuss the study of nuclear stopping in terms of isospin equilibration, the dependence of nuclear collective flow and balance energy on the isospin-dependent nuclear equation of state and cross sections, the isospin dependence of total nuclear reaction cross sections, and the role of isospin in preequilibrium nucleon emissions and subthreshold pion production.Comment: 101 pages with embedded epsf figures, review article for "International Journal of Modern Physics E: Nuclear Physics". Send request for a hard copy to 1/author

The key role of bismuth in the magnetoelastic transitions of Ba3BiIr2O9 and Ba3BiRu2O9 as revealed by chemical doping

The key role played by bismuth in an average intermediate oxidation state in the magnetoelastic spin-gap compounds Ba3BiRu2O9 and Ba3BiIr2O9 has been confirmed by systematically replacing bismuth with La3+ and Ce4+. Through a combination of powder diffraction (neutron and synchrotron), X-ray absorption spectroscopy, and magnetic properties measurements, we show that Ru/Ir cations in Ba3BiRu2O9 and Ba3BiIr2O9 have oxidation states between +4 and +4.5, suggesting that Bi cations exist in an unusual average oxidation state intermediate between the conventional +3 and +5 states (which is confirmed by the Bi L3-edge spectrum of Ba3BiRu2O9). Precise measurements of lattice parameters from synchrotron diffraction are consistent with the presence of intermediate oxidation state bismuth cations throughout the doping ranges. We find that relatively small amounts of doping (~10 at%) on the bismuth site suppress and then completely eliminate the sharp structural and magnetic transitions observed in pure Ba3BiRu2O9 and Ba3BiIr2O9, strongly suggesting that the unstable electronic state of bismuth plays a critical role in the behaviour of these materials

Ljósameðferð við nýburagulu í heimahúsi. Kerfisbundin fræðileg samantekt

Bakgrunnur: Nýburagula greinist hjá 50–60% lifandi fæddra barna á fyrstu vikunni. Alvarleg nýburagula greinist hjá 10% nýbura og er ein algengasta ástæða endurinnlagna á sjúkrahús á nýburaskeiði. Ljósameðferð hófst sem meðferð við nýburagulu á sjötta áratugnum og í upphafi þess níunda fór hún að færast í heimahús í Bandaríkjunum undir nánu eftirliti heilbrigðisstarfsfólks. Í kjölfarið hefur ljósameðferð heima breiðst út og er nú framkvæmd víðs vegar um heim þrátt fyrir litla gagnreynda þekkingu á öryggi og árangri. Ýmsar vísbendingar eru þó um að ljósameðferð heima sé örugg og árangursrík. Tilgangur: Kanna hvort gagnreynd þekking sé fyrir hendi og styðji þá tilgátu að ljósameðferð í heimahúsi sé jafn örugg og árangursrík og innan spítala. Byggt á fyrirliggjandi þekkingu verður gerð tillaga að drögum að verklagsreglum um ljósameðferð nýbura í heimahúsi. Aðferðir: Gerð var kerfisbundin fræðileg samantekt yfir allar þær rannsóknir sem fundust við heimildaleit. Þar sem meðferðin er lítið rannsökuð var ákveðið að hafa engin tímamörk á birtingu rannsóknargreina. Eftirfarandi leitarorð voru notuð: newborn, hyperbilirubinemia, home phototherapy, home og phototherapy. Niðurstöður: Alls fundust 11 rannsóknir með fjórum rannsóknarsniðum. Rannsóknirnar könnuðu langflestar árangur og öryggi ljósameðferðar í heimahúsi, en einnig var skoðað álag á mæðrum, brjóstagjöf og viðhorf foreldra. Helstu niðurstöður sýndu að hvorki var marktækur munur á lækkun gallrauðagilda milli daga né tímalengdar í ljósameðferð. Einnig benda niðurstöður til þess að ljósameðferð heima dregur úr streitu hjá foreldrum, hefur jákvæð áhrif á brjóstagjöf og eflir tengslamyndun. Ályktun: Ætla má að ljósameðferð heima sé jafn örugg og árangursrík og á sjúkrahúsi. Ávinningur þess að hafa meðferðina í heimahúsi virðist vera til góðs fyrir fjölskyldur á margan hátt. Niðurstöðurnar gefa gjarnan vísbendingar en eru ekki alltaf tölfræðilega marktækar vegna smæðar þeirra og hve fáar þær eru. Þörf er á vönduðum rannsóknum og gerð tillögu að verklagi er mikilvægur liður fyrir það. Lykilorð: nýburagula, ljósameðferð, heimaBackground: Neonatal jaundice is diagnosed in 50–60% of neonates in the first week. Severe neonatal jaundice is diagnosed in about 10% of neonates and is the most common reason for rehospitalization. Phototherapy began as a treatment for neonatal jaundice in the 1960s, and in the early 1980s, American physicians began to bring the treatment home under close supervision. As a result, phototherapy at home has spread and is now practiced around the world despite little evidence-based knowledge of safety and efficacy. However, there are various indications that phototherapy at home is safe and effective. Purpose: To assess whether evidence is available and support the hypothesis that home phototherapy is as safe and effective as in a hospital. Design a guideline for home phototherapy. Methods: A systematic review was made of all the research found. As the treatment is little researched, it was decided to have no time limit for publishing research articles. The following keywords were used: newborn, hyperbilirubinemia, home phototherapy, home and phototherapy. Results: A total of 11 studies with four research designs were found. Most studies focus on effectiveness and safety of phototherapy at home, but also examined the stress on mothers, breastfeeding and parental attitudes. The main results showed that there was no significant difference in the reduction of bilirubin values between days or the duration of phototherapy. The results also indicate that home phototherapy reduces parental stress, has a positive effect on breastfeeding and promotes bonding. Conclusion: It can be assumed that phototherapy at home is as safe and effective as in a hospital. The benefits of having the treatment at home seem to benefit families in many ways. The results give clues but are not always statistically significant due to their small size and how few they are. Therefore, further research is needed and a guideline is an important part of that. Keywords: neonatal jaundice, home, phototherap