The 5f localization/delocalization in square and hexagonal americium monolayers: A FP-LAPW electronic structure study

The electronic and geometrical properties of bulk americium and square and hexagonal americium monolayers have been studied with the full-potential linearized augmented plane wave (FP-LAPW) method. The effects of several common approximations are examined: (1) non-spin polarization (NSP) vs. spin polarization (SP); (2) scalar-relativity (no spin-orbit coupling (NSO)) vs. full-relativity (i.e., with spin-orbit (SO) coupling included); (3) local-density approximation (LDA) vs. generalized-gradient approximation (GGA). Our results indicate that both spin polarization and spin orbit coupling play important roles in determining the geometrical and electronic properties of americium bulk and monolayers. A compression of both americium square and hexagonal monolayers compared to the americium bulk is also observed. In general, the LDA is found to underestimate the equilibrium lattice constant and give a larger total energy compared to the GGA calculations. While spin orbit coupling shows a similar effect on both square and hexagonal monolayer calculations regardless of the model, GGA versus LDA, an unusual spin polarization effect on both square and hexagonal monolayers is found in the LDA results as compared with the GGA results. The 5f delocalization transition of americium is employed to explain our observed unusual spin polarization effect. In addition, our results at the LDA level of theory indicate a possible 5f delocalization could happen in the americium surface within the same Am II (fcc crystal structure) phase, unlike the usually reported americium 5f delocalization which is associated with crystal structure change. The similarities and dissimilarities between the properties of an Am monolayer and a Pu monolayer are discussed in detail.Comment: 22 pages, 8 figure

A new solid-phase system for immunoassays

The development of a new solid-phase separation system based on silane polymers is described. A T3 radioimmunoassay (RIA) was optimized using coated tubes with polymer coatings containing hydrophilic surface aldehyde groups for antibody coupling and a T4 RIA developed on the basis of surface anilino group containing particles using a suspension method. Both RIAs offer very good performances and show the variable usability of the new separation system

A Density Functional Study of Atomic Hydrogen and Oxygen Chemisorption on the Relaxed (0001) Surface of Double Hexagonal Close Packed Americium

Ab initio total energy calculations within the framework of density functional theory have been performed for atomic hydrogen and oxygen chemisorption on the (0001) surface of double hexagonal packed americium using a full-potential all-electron linearized augmented plane wave plus local orbitals method. Chemisorption energies were optimized with respect to the distance of the adatom from the relaxed surface for three adsorption sites, namely top, bridge, and hollow hcp sites, the adlayer structure corresponding to coverage of a 0.25 monolayer in all cases. Chemisorption energies were computed at the scalar-relativistic level (no spin-orbit coupling NSOC) and at the fully relativistic level (with spin-orbit coupling SOC). The two-fold bridge adsorption site was found to be the most stable site for O at both the NSOC and SOC theoretical levels with chemisorption energies of 8.204 eV and 8.368 eV respectively, while the three-fold hollow hcp adsorption site was found to be the most stable site for H with chemisorption energies of 3.136 eV at the NSOC level and 3.217 eV at the SOC level. The respective distances of the H and O adatoms from the surface were found to be 1.196 Ang. and 1.164 Ang. Overall our calculations indicate that chemisorption energies in cases with SOC are slightly more stable than the cases with NSOC in the 0.049-0.238 eV range. The work functions and net magnetic moments respectively increased and decreased in all cases compared with the corresponding quantities of bare dhcp Am (0001) surface. The partial charges inside the muffin-tins, difference charge density distributions, and the local density of states have been used to analyze the Am-adatom bond interactions in detail. The implications of chemisorption on Am 5f electron localization-delocalization are also discussed.Comment: 9 Tables, 5 figure

Probing the 5f Electrons in Am-I by Hybrid Density Functional Theory

The ground states of the actinides and their compounds continue to be matters of considerable controversies. Experimentally, Americium-I (Am-I) is a non-magnetic dhcp metal whereas theoretically an anti-ferromagnetic ground state is predicted. We show that hybrid density functional theory, which admixes a fraction of exact Hartree-Fock (HF) exchange with approximate DFT exchange, can correctly reproduce the ground state properties of Am. In particular, for a 0.40 fraction of HF exchange we obtain a non-magnetic ground state with equilibrium atomic volume, bulk modulus, 5f electron population, and the density of electronic states all in good agreement with experimental data. We argue that the exact HF exchange corrects the overestimation of the approximate DFT exchange interaction.Comment: 1 table, 4 figures. Chemical Physics Letters, in press (2009

Adsorption and dissociation of molecular oxygen on the (0001) surface of double hexagonal close packed americium

In our continuing attempts to understand theoretically various surface properties such as corrosion and potential catalytic activity of actinide surfaces in the presence of environmental gases, we report here the first ab initio study of molecular adsorption on the double hexagonal packed (dhcp) americium (0001) surface. Dissociative adsorption is found to be energetically more favorable compared to molecular adsorption. The most stable configuration corresponds to a horizontal approach molecular dissociation with the oxygen atoms occupying neighboring h3 sites, with chemisorption energies at the NSOC and SOC theoretical levels being 9.395 eV and 9.886 eV, respectively. The corresponding distances of the oxygen molecule from the surface and oxygen-oxygen distance were found to be 0.953 Ang. and 3.731 Ang., respectively. Overall our calculations indicate that chemisorption energies in cases with SOC are slightly more stable than the cases with NSOC in the 0.089-0.493 eV range. The work functions and net magnetic moments respectively increased and decreased in all cases compared with the corresponding quantities of the bare dhcp Am (0001) surface. The adsorbate-substrate interactions have been analyzed in detail using the partial charges inside the muffin-tin spheres, difference charge density distributions, and the local density of states. The effects, if any, of chemisorption on the Am 5f electron localization-delocalization characteristics in the vicinity of the Fermi level are also discussed.Comment: 6 tables, 10 figure

Female bone physiology resilience in 750-300 BP ‘Polynesian Outlier’ community

Remodelling is a fundamental biological process involved in the maintenance of bone physiology and function. We know that a range of health and lifestyle factors can impact this process in living and past societies, but there is a notable gap in bone remodelling data for populations from the Pacific Islands. We conducted the first examination of femoral cortical histology in n = 69 individuals from 750 – 300 BP Taumako in Solomon Islands, a remote ‘Polynesian Outlier’ island in Melanesia. We tested whether bone remodelling indicators differed between age-at-death groups, and biological sex validated using ancient DNA. Bone vascular canal and osteon size, vascular porosity, and localised osteon densities, corrected by femoral robusticity indices were examined. Females had statistically significantly higher vascular porosities when compared to males, but osteon densities and ratios of canal-to-osteon (~10%) did not differ between the sexes. Compared to males, the femora of Taumako females experienced higher frequencies of remodelling events, which mirrors bone health paradigms through the life-course today. However, contrary to modern populations, female femoral bone tissue did not decline with age. This matches findings in other archaeological samples, and is testament to ancient female bone physiology resilience also in the Pacific region.Introduction - The importance of bone remodelling through human life-course - Bone remodelling in archaeological humans Results - Trends in bone remodelling at Taumako Discussion - Sex-specific trends in cortical bone remodelling - Bone remodelling with age at Taumako Limitations and remarks on temporal and spatial data Conslusions Materials and Method

Female bone physiology resilience in a past Polynesian Outlier community

Remodelling is a fundamental biological process involved in the maintenance of bone physiology and function. We know that a range of health and lifestyle factors can impact this process in living and past societies, but there is a notable gap in bone remodelling data for populations from the Pacific Islands. We conducted the first examination of femoral cortical histology in 69 individuals from ca. 440–150 BP Taumako in Solomon Islands, a remote ‘Polynesian Outlier’ island in Melanesia. We tested whether bone remodelling indicators differed between age groups, and biological sex validated using ancient DNA. Bone vascular canal and osteon size, vascular porosity, and localised osteon densities, corrected by femoral robusticity indices were examined. Females had statistically significantly higher vascular porosities when compared to males, but osteon densities and ratios of canal-osteon (~ 8%) did not differ between the sexes. Our results indicate that, compared to males, localised femoral bone tissue of the Taumako females did not drastically decline with age, contrary to what is often observed in modern populations. However, our results match findings in other archaeological samples—a testament to past female bone physiology resilience, also now observed in the Pacific region.Introduction - Bone remodelling through human life‑course. - Bone remodelling in archaeological humans. Results - Femoral vascular porosity and bone remodelling indicators at Taumako. Discussion - Sex and cortical bone histology at Taumako. - The effect of age on bone histology at Taumako. Remarks on temporal and spatial bone histology data Limitations Conclusions Materials and method

Magnetic state of plutonium ion in metallic Pu and its compounds

By LDA+U method with spin-orbit coupling (LDA+U+SO) the magnetic state and electronic structure have been investigated for plutonium in \delta and \alpha phases and for Pu compounds: PuN, PuCoGa5, PuRh2, PuSi2, PuTe, and PuSb. For metallic plutonium in both phases in agreement with experiment a nonmagnetic ground state was found with Pu ions in f^6 configuration with zero values of spin, orbital, and total moments. This result is determined by a strong spin-orbit coupling in 5f shell that gives in LDA calculation a pronounced splitting of 5f states on f^{5/2} and f^{7/2} subbands. A Fermi level is in a pseudogap between them, so that f^{5/2} subshell is already nearly completely filled with six electrons before Coulomb correlation effects were taken into account. The competition between spin-orbit coupling and exchange (Hund) interaction (favoring magnetic ground state) in 5f shell is so delicately balanced, that a small increase (less than 15%) of exchange interaction parameter value from J_H=0.48eV obtained in constrain LDA calculation would result in a magnetic ground state with nonzero spin and orbital moment values. For Pu compounds investigated in the present work, predominantly f^6 configuration with nonzero magnetic moments was found in PuCoGa5, PuSi2, and PuTe, while PuN, PuRh2, and PuSb have f^5 configuration with sizeable magnetic moment values. Whereas pure jj coupling scheme was found to be valid for metallic plutonium, intermediate coupling scheme is needed to describe 5f shell in Pu compounds. The results of our calculations show that both spin-orbit coupling and exchange interaction terms in the Hamiltonian must be treated in a general matrix form for Pu and its compounds.Comment: 20 pages, LaTeX; changed discussion on reference pape

Patient-reported experiences of cancer care related to the COVID-19 pandemic in Switzerland.

This study aims to describe the experience of Swiss oncological patients during the COVID-19 pandemic. A national multi-center study including five hospitals covering the three main language regions of Switzerland was conducted between March and July 2021. Patients with melanoma, breast, lung, or colon cancer receiving active systemic anti-cancer treatment at the time of the COVID-19 pandemic were included. We conducted semi-structured telephone or onsite interviews alongside the administration of distress and resilience-validated questionnaires. Thematic analysis was performed for the qualitative data and descriptive statistics for the quantitative data. Sixty-two cancer patients with a mean age of 61 (SD=14) (58% female) were interviewed. Based on the interviews, we identified that the experience of having cancer during the COVID-19 pandemic was related to five dimensions: psychological, social, support, healthcare, and vaccination. Three themes transverse the five dimensions: (a) needs, (b) positive changes, and (c) phases of the pandemic. In general, patients did not experience delays or disruptions in their cancer treatment nor felt additionally burdened by the pandemic. Lockdown and isolation were reported as mixed experiences (positive and negative), and access to vaccination reassured patients against the risk of infection and instilled hope to return to normalcy. Additionally, we found low distress levels (M=2.9; SD=2.5) and high resilience scores (M=7; SD=1.3) in these patients. Swiss patients with cancer did not express major needs or disruptions in their care during this period of the COVID-19 pandemic. Results identify the mixed experiences of patients and highlight the high resilience levels

On the Convergence of the Electronic Structure Properties of the FCC Americium (001) Surface

Electronic and magnetic properties of the fcc Americium (001) surface have been investigated via full-potential all-electron density-functional electronic structure calculations at both scalar and fully relativistic levels. Effects of various theoretical approximations on the fcc Am (001) surface properties have been thoroughly examined. The ground state of fcc Am (001) surface is found to be anti-ferromagnetic with spin-orbit coupling included (AFM-SO). At the ground state, the magnetic moment of fcc Am (001) surface is predicted to be zero. Our current study predicts the semi-infinite surface energy and the work function for fcc Am (001) surface at the ground state to be approximately 0.82 J/m2 and 2.93 eV respectively. In addition, the quantum size effects of surface energy and work function on the fcc Am (001) surface have been examined up to 7 layers at various theoretical levels. Results indicate that a three layer film surface model may be sufficient for future atomic and molecular adsorption studies on the fcc Am (001) surface, if the primary quantity of interest is the chemisorption energy.Comment: 34 pages, 9 figure