Lithium Intercalation into the Excitonic Insulator Candidate Ta2NiSe5.

A new reduced phase derived from the excitonic insulator candidate Ta2NiSe5 has been synthesized via the intercalation of lithium. LiTa2NiSe5 crystallizes in the orthorhombic space group Pmnb (no. 62) with lattice parameters a = 3.50247(3) Å, b = 13.4053(4) Å, c = 15.7396(2) Å, and Z = 4, with an increase of the unit cell volume by 5.44(1)% compared with Ta2NiSe5. Significant rearrangement of the Ta-Ni-Se layers is observed, in particular a very significant relative displacement of the layers compared to the parent phase, similar to that which occurs under hydrostatic pressure. Neutron powder diffraction experiments and computational analysis confirm that Li occupies a distorted triangular prismatic site formed by Se atoms of adjacent Ta2NiSe5 layers with an average Li-Se bond length of 2.724(2) Å. Li-NMR experiments show a single Li environment at ambient temperature. Intercalation suppresses the distortion to monoclinic symmetry that occurs in Ta2NiSe5 at 328 K and that is believed to be driven by the formation of an excitonic insulating state. Magnetometry data show that the reduced phase has a smaller net diamagnetic susceptibility than Ta2NiSe5 due to the enhancement of the temperature-independent Pauli paramagnetism caused by the increased density of states at the Fermi level evident also from the calculations, consistent with the injection of electrons during intercalation and formation of a metallic phase.

Experimental and Theoretical Study of the Electronic Structures of Lanthanide Indium Perovskites LnInO3.

Ternary lanthanide indium oxides LnInO3 (Ln = La, Pr, Nd, Sm) were synthesized by high-temperature solid-state reaction and characterized by X-ray powder diffraction. Rietveld refinement of the powder patterns showed the LnInO3 materials to be orthorhombic perovskites belonging to the space group Pnma, based on almost-regular InO6 octahedra and highly distorted LnO12 polyhedra. Experimental structural data were compared with results from density functional theory (DFT) calculations employing a hybrid Hamiltonian. Valence region X-ray photoelectron and K-shell X-ray emission and absorption spectra of the LnInO3 compounds were simulated with the aid of the DFT calculations. Photoionization of lanthanide 4f orbitals gives rise to a complex final-state multiplet structure in the valence region for the 4f n compounds PrInO3, NdInO3, and SmInO3, and the overall photoemission spectral profiles were shown to be a superposition of final-state 4f n-1 terms onto the cross-section weighted partial densities of states from the other orbitals. The occupied 4f states are stabilized in moving across the series Pr-Nd-Sm. Band gaps were measured using diffuse reflectance spectroscopy. These results demonstrated that the band gap of LaInO3 is 4.32 eV, in agreement with DFT calculations. This is significantly larger than a band gap of 2.2 eV first proposed in 1967 and based on the idea that In 4d states lie above the top of the O 2p valence band. However, both DFT and X-ray spectroscopy show that In 4d is a shallow core level located well below the bottom of the valence band. Band gaps greater than 4 eV were observed for NdInO3 and SmInO3, but a lower gap of 3.6 eV for PrInO3 was shown to arise from the occupied Pr 4f states lying above the main O 2p valence band.

Fluorescent IGF-II analogues for FRET-based investigations into the binding of IGF-II to the IGF-1R.

The interaction of IGF-II with the insulin receptor (IR) and type 1 insulin-like growth factor receptor (IGF-1R) has recently been identified as potential therapeutic target for the treatment of cancer. Understanding the interactions of IGF-II with these receptors is required for the development of potential anticancer therapeutics. This work describes an efficient convergent synthesis of native IGF-II and two non-native IGF-II analogues with coumarin fluorescent probes incorporated at residues 19 and 28. These fluorescent analogues bind with nanomolar affinities to the IGF-1R and are suitable for use in fluorescence resonance energy transfer (FRET) studies. From these studies the F19Cou IGF-II and F28Cou IGF-II proteins were identified as good probes for investigating the binding interactions of IGF-II with the IGF-1R and its other high affinity binding partners.

Direct Observation of Electrostatically Driven Band Gap Renormalization in a Degenerate Perovskite Transparent Conducting Oxide.

We have directly measured the band gap renormalization associated with the Moss-Burstein shift in the perovskite transparent conducting oxide (TCO), La-doped BaSnO_{3}, using hard x-ray photoelectron spectroscopy. We determine that the band gap renormalization is almost entirely associated with the evolution of the conduction band. Our experimental results are supported by hybrid density functional theory supercell calculations. We determine that unlike conventional TCOs where interactions with the dopant orbitals are important, the band gap renormalization in La-BaSnO_{3} is driven purely by electrostatic interactions.

On the application of the tolerance factor to inorganic and hybrid halide perovskites: a revised system.

The tolerance factor is a widely used predictor of perovskite stability. The recent interest in hybrid perovskites for use as solar cell absorbers has lead to application of the tolerance factor to these materials as a way to explain and predict structure. Here we critically assess the suitability of the tolerance factor for halide perovskites. We show that the tolerance factor fails to accurately predict the stability of the 32 known inorganic iodide perovskites, and propose an alternative method. We introduce a revised set of ionic radii for cations that is anion dependent, this revision is necessary due to increased covalency in metal-halide bonds for heavier halides compared with the metal-oxide and fluoride bonds used to calculate Shannon radii. We also employ a 2D structural map to account for the size requirements of the halide anions. Together these measures yield a simple system which may assist in the search for new hybrid and inorganic perovskites.

Determination of the nitrogen vacancy as a shallow compensating center in GaN doped with divalent metals.

We report accurate energetics of defects introduced in GaN on doping with divalent metals, focusing on the technologically important case of Mg doping, using a model that takes into consideration both the effect of hole localization and dipolar polarization of the host material, and includes a well-defined reference level. Defect formation and ionization energies show that divalent dopants are counterbalanced in GaN by nitrogen vacancies and not by holes, which explains both the difficulty in achieving p-type conductivity in GaN and the associated major spectroscopic features, including the ubiquitous 3.46 eV photoluminescence line, a characteristic of all lightly divalent-metal-doped GaN materials that has also been shown to occur in pure GaN samples. Our results give a comprehensive explanation for the observed behavior of GaN doped with low concentrations of divalent metals in good agreement with relevant experiment.

Double bubbles: a new structural motif for enhanced electron-hole separation in solids.

Electron-hole separation for novel composite systems comprised of secondary building units formed from different compounds is investigated with the aim of finding suitable materials for photocatalysis. Pure and mixed SOD and LTA superlattices of (ZnO)12 and (GaN)12, single-shell bubbles are constructed as well as core@shell single component frameworks composed of larger (ZnO)48 and (GaN)48 bubbles with each containing one smaller bubble. Enthalpies of formation for all systems are comparable with fullerenes. Hole and electron separation is achieved most efficiently by the edge sharing framework composed of (GaN)12@(ZnO)48 double bubbles, with the hole localised on the nitrogen within the smaller bubbles and the excited electron on zinc within the larger cages.

Understanding the electronic structure of IrO2 using hard-X-ray photoelectron spectroscopy and density-functional theory.

The electronic structure of IrO2 has been investigated using hard x-ray photoelectron spectroscopy and density-functional theory. Excellent agreement is observed between theory and experiment. We show that the electronic structure of IrO2 involves crystal field splitting of the iridium 5d orbitals in a distorted octahedral field. The behavior of IrO2 closely follows the theoretical predictions of Goodenough for conductive rutile-structured oxides [J. B. Goodenough, J. Solid State Chem. 3, 490 (1971).

The band structure of WO3 and non-rigid-band behaviour in Na0.67WO3 derived from soft x-ray spectroscopy and density functional theory.

The electronic structure of single-crystal WO3 and Na0.67WO3 (a sodium-tungsten bronze) has been measured using soft x-ray absorption and resonant soft x-ray emission oxygen K-edge spectroscopies. The spectral features show clear differences in energy and intensity between WO3 and Na0.67WO3. The x-ray emission spectrum of metallic Na0.67WO3 terminates in a distinct Fermi edge. The rigid-band model fails to explain the electronic structure of Na0.67WO3 in terms of a simple addition of electrons to the conduction band of WO3. Instead, Na bonding and Na 3s-O 2p hybridization need to be considered for the sodium-tungsten bronze, along with occupation of the bottom of the conduction band. Furthermore, the anisotropy in the band structure of monoclinic γ-WO3 revealed by the experimental spectra with orbital-resolved geometry is explained via density functional theory calculations. For γ-WO3 itself, good agreement is found between the experimental O K-edge spectra and the theoretical partial density of states of O 2p orbitals. Indirect and direct bandgaps of insulating WO3 are determined from extrapolating separations between spectral leading edges and accounting for the core-hole energy shift in the absorption process. The O 2p non-bonding states show upward band dispersion as a function of incident photon energy for both compounds, which is explained using the calculated band structure and experimental geometry.

Controlling bulk conductivity in topological insulators: key role of anti-site defects.

Intrinsic topological insulators are realized by alloying Bi(2)Te(3) with Bi(2)Se(3). Angle-resolved photoemission and bulk transport measurements reveal that the Fermi level is readily tuned into the bulk bandgap. First-principles calculations of the native defect landscape highlight the key role of anti-site defects for achieving this, and predict optimal growth conditions to realize maximally resistive topological insulators.

Chemical bonding in copper-based transparent conducting oxides: CuMO2 (M = In, Ga, Sc).

The geometry and electronic structure of copper-based p-type delafossite transparent conducting oxides, CuMO(2) (M = In, Ga, Sc), are studied using the generalized gradient approximation (GGA) corrected for on-site Coulomb interactions (GGA + U). The bonding and valence band compositions of these materials are investigated, and the origins of changes in the valence band features between group 3 and group 13 cations are discussed. Analysis of the effective masses at the valence and conduction band edge explains the experimentally reported conductivity trends.

Effect of oxidation and mutation on the conformational dynamics and fibril assembly of amyloidogenic peptides derived from apolipoprotein C-II.

The oxidation of methionine residues in proteins can inhibit the self-assembly of proteins to form amyloid fibrils. For human apolipoprotein (apo) C-II the oxidation of methionine at position 60 inhibits fibril formation by the mature protein and by the core peptides apoC-II(56-76) and apoC-II(60-70). To investigate the molecular nature of these effects, we carried out fully solvated, all-atom molecular dynamics simulations of the structural changes in apoC-II(56-76) associated with substitutions of oxidized methionine (Met ox) at position 60. The results with apoC-II(56-76) (Met ox) showed less flexibility in structure, leading to a perturbation of the hydrophobic core. Valine substitution at position 60 showed an increased tendency to explore a wide range of conformational space, whereas the behavior of the Gln substitution mutant was similar to the wild-type peptide. These simulations are consistent with kinetic measurements which showed that a Met60Gln substitution within apoC-II(56-76) had little effect on the rate of fibril formation whereas substitution of Met ox or Val at position 60 lead to significant inhibition of peptide fibril formation. The effects of amino acid modification and substitutions on the kinetics of peptide fibril formation differ from the effects observed with full-length apoC-II inferring that additional mechanisms are involved in fibril formation by mature apoC-II.

Inhibition of Siah ubiquitin ligase function.

Tumor hypoxia induces the upregulation of hypoxia-inducible factor 1alpha (Hif-1alpha), which in turn induces the expression of genes including VEGF to recruit new blood vessel outgrowth, enabling tumor growth and metastasis. Interference with the Hif-1 pathway and neoangiogenesis is an attractive antitumor target. The hydroxylation of Hif-1alpha by prolyl-hydroxylase (PHD) proteins during normoxia serves as a recognition motif for its proteasomal degradation. However, under hypoxic conditions, hydroxylation is inhibited and furthermore, PHD proteins are themselves polyubiquitylated and degraded by Siah ubiquitin ligases. Our data demonstrate for the first time that inhibition of the interaction between Siah and PHD proteins using a fragment derived from a Drosophila protein (phyllopod) interferes with the PHD degradation. Furthermore, cells stably expressing the phyllopod fragment display reduced upregulation of Hif-1alpha protein levels and Hif-1-mediated gene expression under hypoxia. In a syngeneic mouse model of breast cancer, the phyllopod fragment reduced tumor growth and neoangiogenesis and prolonged survival of the mice. In addition, levels of Hif-1alpha and its target Glut-1 are reduced in tumors expressing the phyllopod fragment. These data show, in a proof-of-principle study, that Siah protein, the most upstream component of the hypoxia pathway yet identified, is a viable drug target for antitumor therapies.

Intrinsic ferromagnetism in CeO(2): dispelling the myth of vacancy site localization mediated superexchange.

Intrinsic ferromagnetism in CeO(2) is a source of controversy in the literature and has been linked to the excess electrons left over upon oxygen vacancy formation on Ce sites neighbouring the vacancy. A recent theoretical study (Han et al 2009 Phys. Rev. B 79 100403) concluded that increased vacancy concentration changes the localization behaviour of CeO(2), resulting in some degree of charge localization in the vacancy site itself, which leads to superexchange and polarization effects that enhance the stability of ferromagnetism. In this report, we show conclusively that oxygen vacancy concentrations of up to 12.5% do not cause localization in the vacancy site, and that this is not responsible for any enhanced ferromagnetism. Investigation of oxygen vacancies on the (111), (110) and (100) low index surfaces also show no evidence for ferromagnetic preference.

The role of performance measures for improving quality in managed care organizations.

OBJECTIVES: To understand how managed care plans use performance measures for quality improvement and to identify the strengths and weaknesses of currently used standardized performance measures such as the Health Plan Employer Data and Information Set (HEDIS) and the Consumer Assessment of Health Plans (CAHPS) survey. DATA SOURCES/STUDY SETTING: Representatives (chief executive officers, medical directors, and quality-improvement directors) from 24 health plans in four states were surveyed. The overall response rate was 58.3 percent, with a mean of 1.8 respondents per plan. STUDY DESIGN: This exploratory qualitative research used a purposive sample of respondents. Two study authors conducted separate one-hour tape-recorded telephone interviews with multiple respondents from each health plan. PRINCIPAL FINDINGS: All managed care organizations interviewed use performance measures for quality improvement but the degree and sophistication of use varies. Many of our respondent plans use performance measures to target quality-improvement initiatives, evaluate current performance, establish goals for quality improvement, identify the root cause of problems, and monitor performance. CONCLUSION: Performance measures are used for quality improvement in addition to informing external constituents, but additional research is needed to understand how the benefits of measurement can be maximized.

Are managed care plans organizing for quality?

This article examines the degree to which managed care organizations (MCOs) are reorganizing to take responsibility for the quality of care and service they provide. Specifically, factors prompting plans to focus on quality improvement (QI) and how they may be building the capacity to improve quality are considered. The authors' analysis is based on executive interviews with the plan medical directors, QI directors, and chief executive officers (CEOs) in a sample of 24 health plans. The overall response rate was 58.3 percent (medical director = 62.5 percent, QI director = 79.2 percent, CEO = 33.3 percent). The authors queried respondents about (1) perceived drivers and obstacles to the development of an effective QI program, (2) plan organizational structure for QI, and (3) technical capacities for data collection, management, and performance measurement. The results suggest that MCOs are responding to outside pressures to engage in QI. They are reorganizing their management structures and more slowly and tentatively are building technical capacity for QI.

Differentiating between difficult-to-remediate and readily remediated poor readers: more evidence against the IQ-achievement discrepancy definition of reading disability.

In this article we discuss research bearing on the traditional use of the IQ-achievement discrepancy to define specific reading disability. We initially review the evidence presented by Rutter and Yule (1975) in support of this practice, and then discuss results from subsequent studies that have questioned the reliability of their findings. We also discuss results from more recent studies demonstrating that the IQ-achievement discrepancy does not reliably distinguish poor from normal readers, whereas language-based measures do reliably distinguish these groups. We highlight results from a study we recently completed, in which it was found that IQ scores did not differentiate between poor readers who were found to be readily remediated and poor readers who were difficult to remediate. In view of the convergent evidence against the use of IQ scores to define specific reading disability, we suggest that the IQ-achievement discrepancy definition of this disorder be discarded.

Transcriptional activation of the cloned Heliothis virescens (Lepidoptera) ecdysone receptor (HvEcR) by muristeroneA.

Ecdysteroids play an important role during insect development. We report here the isolation and characterisation of an Ecdysone receptor (EcR) homologue from Heliothis virescens (HvEcR) and present evidence supporting the HvEcR active role as an active component of the native insect receptor. Alignment of the deduced amino acid sequence of HvEcR with those of EcRs from other species confirmed its membership of this family and showed that it is closely related to the B1 isoform of Drosophila melanogaster. Northern blot analysis showed that two transcripts (6.0 and 6.5 kb) were recognised by a probe spanning the DNA and ligand binding domains of the HvEcR. Genomic Southern blots showed that the HvEcR is encoded by a single copy gene. Two lines of evidence towards the functional activity of the HvEcR are presented. In vitro transcribed and translated HvEcR showed specific binding to hsp27 and pall response elements in the presence of CfUSP. Stable expression of HvEcR in 293 cells induced reporter gene activity in the presence of muristeroneA in a dose dependant manner while dexamethasone failed to activate.