Self-Consistent Cluster Embedding Calculation Method and the Electronic Structure of Nickel Oxide and Cobalt Oxide.

We present a self-consistent cluster embedding method to study the electronic structure of solids by ab initio, local spin density functional calculations. A theoretical discussion from the viewpoint of total energy is given, and a definition of the total energy for an embedded cluster is introduced. We have constructed a general LCGO cluster-embedding program package, and developed a procedure to simulate the spin disordered states with local antiferromagnetic (AF) order. The electronic structures of NiO and CoO are studied by this method with a high quality basis set. The two materials show similar antiferromagnetic insulating ground states with both localized and band properties: A small energy gap separates the well localized unoccupied and occupied 3d orbitals. Each 3d orbital is attached to a particular cation. Two diffuse oxygen 2p bands are below the 3d levels; empty oxygen 3s bands are above the 3d levels. Calculations show that the excited 3d electrons are also well localized. We propose a new explanation of the insulating nature for transition-metal monoxides which can explain both NiO and CoO consistently: The overlap of excited 3d electrons is too small to form a metallic band, but the overlap is sufficient for the hole to migrate through the crystal. In this sense, both NiO and CoO are charge transfer insulators with gaps of about 4 and 5 ev (mostly from oxygen ion to cation), respectively. The spin magnetic moments of both ions and the Neel temperatures of NiO and CoO are calculated directly. The theoretical simulations of the paramagnetic phases for both materials show that the electronic structure in the local AF pairs is independent of long-range spin order. Our theoretical results lead to a natural interpretation of almost all experimental data

Finite-time estimation for linear time-delay systems via homogeneous method

International audienceThis paper presents a finite-time observer for linear time-delay systems with commensurate delay. Unlike the existing observers in the literature which converge asymptotically, the proposed observer provides a finite-time estimation. This is realized by using the well-known homogeneous technique, and the results are also extended to investigate the estimation problem for linear time-delay systems with unknown inputs. Simulation results are presented in order to illustrate the feasibility of the proposed method

A nonlinear Luenberger-like observer for nonlinear singular systems

International audienceThis paper investigates observer design problem for a large class of nonlinear singular systems with multiple outputs. We firstly regularize the singular system by injecting the derivative of outputs into the system. Then differential geometric method is applied to transform the regularized system into a simple normal form, for which a Luenberger-like observer is proposed

Hyphal Development in Candida albicans Requires Two Temporally Linked Changes in Promoter Chromatin for Initiation and Maintenance

Phenotypic plasticity is common in development. For Candida albicans, the most common cause of invasive fungal infections in humans, morphological plasticity is its defining feature and is critical for its pathogenesis. Unlike other fungal pathogens that exist primarily in either yeast or hyphal forms, C. albicans is able to switch reversibly between yeast and hyphal growth forms in response to environmental cues. Although many regulators have been found involved in hyphal development, the mechanisms of regulating hyphal development and plasticity of dimorphism remain unclear. Here we show that hyphal development involves two sequential regulations of the promoter chromatin of hypha-specific genes. Initiation requires a rapid but temporary disappearance of the Nrg1 transcriptional repressor of hyphal morphogenesis via activation of the cAMP-PKA pathway. Maintenance requires promoter recruitment of Hda1 histone deacetylase under reduced Tor1 (target of rapamycin) signaling. Hda1 deacetylates a subunit of the NuA4 histone acetyltransferase module, leading to eviction of the NuA4 acetyltransferase module and blockage of Nrg1 access to promoters of hypha-specific genes. Promoter recruitment of Hda1 for hyphal maintenance happens only during the period when Nrg1 is gone. The sequential regulation of hyphal development by the activation of the cAMP-PKA pathway and reduced Tor1 signaling provides a molecular mechanism for plasticity of dimorphism and how C. albicans adapts to the varied host environments in pathogenesis. Such temporally linked regulation of promoter chromatin by different signaling pathways provides a unique mechanism for integrating multiple signals during development and cell fate specification