Electronic states of PrCoO3_3: X-ray photoemission spectroscopy and LDA+U density of states studies

Electronic states of PrCoO$_3$ are studied using x-ray photoemission spectroscopy. Pr 3d$_{5/2}$ core level and valence band (VB) were recorded using Mg K$_\beta$ source. The core level spectrum shows that the 3d$_{5/2}$ level is split into two components of multiplicity 4 and 2, respectively due to coupling of the spin states of the hole in 3d$_{5/2}$ with Pr 4f holes spin state. The observed splitting is 4.5 eV. The VB spectrum is interpreted using density of states (DOS) calculations under LDA and LDA+U. It is noted that LDA is not sufficient to explain the observed VB spectrum. Inclusion of on-site Coulomb correlation for Co 3d electrons in LDA+U calculations gives DOS which is useful in qualitative explanation of the ground state. However, it is necessary to include interactions between Pr 4f electrons to get better agreement with experimental VB spectrum. It is seen that the VB consists of Pr 4f, Co 3d and O 2p states. Pr 4f, Co 3d and O 2p bands are highly mixed indicating strong hybridization of these three states. The band near the Fermi level has about equal contributions from Pr 4f and O 2p states with somewhat smaller contribution from Co 3d states. Thus in the Zaanen, Sawatzky, and Allen scheme PrCoO$_3$ can be considered as charge transfer insulator. The charge transfer energy $\Delta$ can be obtained using LDA DOS calculations and the Coulomb-exchange energy U' from LDA+U. The explicit values for PrCoO$_3$ are $\Delta$ = 3.9 eV and U' = 5.5 eV; the crystal field splitting and 3d bandwidth of Co ions are also found to be 2.8 and 1.8 eV, respectively.Comment: 12 pages, 7 figures; to appear J. Phys.: Condens. Matte

Classical and quantum decay of one dimensional finite wells with oscillating walls

To study the time decay laws (tdl) of quasibounded hamiltonian systems we have considered two finite potential wells with oscillating walls filled by non interacting particles. We show that the tdl can be qualitatively different for different movement of the oscillating wall at classical level according to the characteristic of trapped periodic orbits. However, the quantum dynamics do not show such differences.Comment: RevTeX, 15 pages, 14 PostScript figures, submitted to Phys. Rev.

DOPING AND BOND LENGTH CONTRIBUTIONS TO Mn K-EDGE SHIFT IN La1-xSrxMnO3 AND THEIR CORRELATION WITH ELECTRICAL TRANSPORT BEHAVIOUR.

The experimental Mn K-edge x-ray absorption spectra of La{sub 1-x}Sr{sub x}MnO{sub 3}, x = 0 - 0.7 are compared with the band structure calculations using spin polarized density functional theory. It is explicitly shown that there is a correspondence between the inflection point on the absorption edge and the center of gravity of the unoccupied Mn 4p-band. This correspondence has been used to separate the doping and size contributions to edge shift due to variation in number of electrons in valence band and Mn-O bond lengths, respectively when Sr is doped into LaMnO{sub 3}. Such separation is helpful to find the localization behavior of charge carriers and to understand the observed transport properties and type of charge carrier participating in the conduction process in these compounds

Local distortion in LaCoO3 and PrCoO3: EXAFS, XRD and XANES studies

Room temperature Co K-edge extended x-ray absorption fine structure (EXAFS), x-ray absorption near edge structure (XANES) including pre-edge and x-ray diffraction (XRD) studies are carried out on LaCoO3 and PrCoO3. The Co-O, Co-La/Pr and Co-Co bond lengths are obtained from EXAFS analysis and compared with those obtained from XRD. The EXAFS analysis of data indicates that CoO6 octahedron is distorted in both LaCoO3 and PrCoO3. Such distortion is expected in orthorhombic PrCoO3 but not in rhombohedral LaCoO3. This distortion in CoO6 octahedron is attributed to Jahn-Teller active Co3+ ion in intermediate spin state in these compounds. Higher shell studies reveal that Debye-Waller (DW) factors of Co-Pr and Co-Co bonds in PrCoO3 are more in comparison to Co-La and Co-Co bonds in LaCoO3 indicating that these bonds are structurally more disordered in PrCoO3. The comparison of Co-Co bond lengths and corresponding DW factors indicates that the structural disorder plays an important role in deciding the insulating properties of these compounds. XANES studies have shown changes in the intensities and positions of different near edge features.Comment: 22 pages, 8 figures, 2 tables. To appear in J. Phys.: Condens. Matte

Regionalized tissue fluidization is required for epithelial gap closure during insect gastrulation

Many animal embryos pull and close an epithelial sheet around the ellipsoidal egg surface during a gastrulation process known as epiboly. The ovoidal geometry dictates that the epithelial sheet first expands and subsequently compacts. Moreover, the spreading epithelium is mechanically stressed and this stress needs to be released. Here we show that during extraembryonic tissue (serosa) epiboly in the insect Tribolium castaneum, the non-proliferative serosa becomes regionalized into a solid-like dorsal region with larger non-rearranging cells, and a more fluid-like ventral region surrounding the leading edge with smaller cells undergoing intercalations. Our results suggest that a heterogeneous actomyosin cable contributes to the fluidization of the leading edge by driving sequential eviction and intercalation of individual cells away from the serosa margin. Since this developmental solution utilized during epiboly resembles the mechanism of wound healing, we propose actomyosin cable-driven local tissue fluidization as a conserved morphogenetic module for closure of epithelial gaps

A study of transition metal K-edge x-ray absorption spectra of LaBO3 (B=Mn, Fe, Co, Ni), La2CuO4 and SrMnO3 using partial density of states

The transition metal K-edge x-ray absorption near edge structure (XANES) studies have been carried on LaBO3 (B=Mn, Fe, Co, Ni), La2CuO4 and SrMnO3 compounds. The theoretical spectra have been calculated using transition metal (TM) 4p density of states (DOS) obtained from full-potential LMTO density functional theory. The exchange-correlation functional used in this calculation is taken under local density approximation (LDA). The comparison of experimental spectra with the calculated ones indicates that single-particle transitions under LDA are sufficient to generate all the observed XANES including those which have earlier been attributed to many-body shake-up transitions and core-hole potentials. The present study reveals that all the experimentally observed features are mainly due to distribution in TM 4p DOS influenced by hybridization with other orbitals. Specifically, for LaMnO3, the feature earlier attributed to shake-up process is seen to arise from hybridization of Mn 4p with La 6p and O 2p orbitals; in La2CuO4 the features attributed to core hole potential correspond to hybridization of Cu 4p with La 6p, La 5d and O 2p orbitals. To see the effect of inhomogeneous electronic charge distribution and on-site Coulomb and exchange interaction (U) on the XANES of these compounds generalized-gradient approximation and U corrections are incorporated in the calculations. These corrections do not generate any new features in the spectra but affect the detailed intensity and positions of some of the features.Comment: 23 pages, 8 figures. To appear in J. Phys.: Condens. Matte

Genotype and functional correlates of disease phenotype in deficiency of adenosine deaminase 2 (DADA2)

BACKGROUND Deficiency of adenosine deaminase 2 (DADA2) is a syndrome with pleiotropic manifestations including vasculitis and hematologic compromise. A systematic definition of the relationship between ADA2 mutations and clinical phenotype remains unavailable. OBJECTIVE We tested whether the impact of ADA2 mutations on enzyme function correlates with clinical presentation. METHODS DADA2 patients with severe hematologic manifestations were compared with vasculitis-predominant patients. Enzymatic activity was assessed using expression constructs reflecting all 53 missense, nonsense, insertion and deletion genotypes from 152 patients across the DADA2 spectrum. RESULTS We identified DADA2 patients presenting with pure red cell aplasia (PRCA, n = 5) or bone marrow failure syndrome (BMF, n = 10). Most patients did not exhibit features of vasculitis. Recurrent infection, hepatosplenomegaly and gingivitis were common in patients with BMF, of whom half died from infection. Unlike DADA2 patients with vasculitis, patients with PRCA and BMF proved largely refractory to tumor necrosis factor inhibitors. ADA2 variants associated with vasculitis predominantly reflected missense mutations with at least 3% residual enzymatic activity. By contrast, PRCA and BMF were associated with missense mutations with minimal residual enzyme activity, nonsense variants, and insertions / deletions resulting in complete loss of function. CONCLUSION Functional interrogation of ADA2 mutations reveals an association of subtotal function loss with vasculitis, typically responsive to TNF blockade, whereas more extensive loss is observed in hematologic disease which may be refractory to treatment. These findings establish a genotype-phenotype spectrum in DADA2