University of California

About: University of California is a education organization based out in Oakland, California, United States. It is known for research contribution in the topics: Population & Layer (electronics). The organization has 55175 authors who have published 52933 publications receiving 1491169 citations. The organization is also known as: UC & University of California System.

Electron correlation methods based on the random phase approximation

Abstract: In the past decade, the random phase approximation (RPA) has emerged as a promising post-Kohn–Sham method to treat electron correlation in molecules, surfaces, and solids. In this review, we explain how RPA arises naturally as a zero-order approximation from the adiabatic connection and the fluctuation-dissipation theorem in a density functional context. This is contrasted to RPA with exchange (RPAX) in a post-Hartree–Fock context. In both methods, RPA and RPAX, the correlation energy may be expressed as a sum over zero-point energies of harmonic oscillators representing collective electronic excitations, consistent with the physical picture originally proposed by Bohm and Pines. The extra factor 1/2 in the RPAX case is rigorously derived. Approaches beyond RPA are briefly summarized. We also review computational strategies implementing RPA. The combination of auxiliary expansions and imaginary frequency integration methods has lead to recent progress in this field, making RPA calculations affordable for systems with over 100 atoms. Finally, we summarize benchmark applications of RPA to various molecular and solid-state properties, including relative energies of conformers, reaction energies involving weak and covalent interactions, diatomic potential energy curves, ionization potentials and electron affinities, surface adsorption energies, bulk cohesive energies and lattice constants. RPA barrier heights for an extended benchmark set are presented. RPA is an order of magnitude more accurate than semi-local functionals such as B3LYP for non-covalent interactions rivaling the best empirically parametrized methods. Larger but systematic errors are observed for processes that do not conserve the number of electron pairs, such as atomization and ionization.

Gene regulation during cold stress acclimation in plants.

Abstract: Cold stress adversely affects plant growth and development and thus limits crop productivity. Diverse plant species tolerate cold stress to a varying degree, which depends on reprogramming gene expression to modify their physiology, metabolism, and growth. Cold signal in plants is transmitted to activate CBF-dependent (C-repeat/drought-responsive element binding factor-dependent) and CBF-independent transcriptional pathway, of which CBF-dependent pathway activates CBF regulon. CBF transcription factor genes are induced by the constitutively expressed ICE1 (inducer of CBF expression 1) by binding to the CBF promoter. ICE1-CBF cold response pathway is conserved in diverse plant species. Transgenic analysis in different plant species revealed that cold tolerance can be significantly enhanced by genetic engineering CBF pathway. Posttranscriptional regulation at pre-mRNA processing and export from nucleus plays a role in cold acclimation. Small noncoding RNAs, namely micro-RNAs (miRNAs) and small interfering RNAs (siRNAs), are emerging as key players of posttranscriptional gene silencing. Cold stress-regulated miRNAs have been identified in Arabidopsis and rice. In this chapter, recent advances on cold stress signaling and tolerance are highlighted.

Multi-wavelength cross-connect optical switch

Abstract: A cross-connect switch for fiber-optic communication networks employing a wavelength dispersive element, such as a grating, and a stack of regular (non-wavelength selective) cross bar switches using two-dimensional arrays of micromachined, electrically actuated, individually-tiltable, controlled deflection micro-mirrors for providing multiport switching capability for a plurality of wavelengths. Using a one-dimensional micromirror array, a fiber-optic based MEMS switched spectrometer that does not require mechanical motion of bulk components or large diode arrays can be constructed with readout capability for WDM network diagnosis or for general purpose spectroscopic applications.