Kevin T. Moore

Bio: Kevin T. Moore is an academic researcher from Lawrence Livermore National Laboratory. The author has contributed to research in topics: Spectroscopy & Absorption spectroscopy. The author has an hindex of 21, co-authored 51 publications receiving 1397 citations.

Nature of the 5f states in actinide metals

Abstract: Actinide elements produce a plethora of interesting physical behaviors due to the $5f$ states. This review compiles and analyzes progress in the understanding of the electronic and magnetic structure of the $5f$ states in actinide metals. Particular interest is given to electron energy-loss spectroscopy and many-electron atomic spectral calculations, since there is now an appreciable library of core $d\ensuremath{\rightarrow}\text{valence}$ $f$ transitions for Th, U, Np, Pu, Am, and Cm. These results are interwoven and discussed against published experimental data, such as x-ray photoemission and absorption spectroscopy, transport measurements, and electron, x-ray, and neutron diffraction, as well as theoretical results, such as density-functional theory and dynamical mean-field theory.

Applicability of the spin-orbit sum rule for the actinide 5f states.

Abstract: The branching ratio of core-valence transitions in x-ray absorption spectroscopy and electron energy loss spectroscopy is linearly related to the expectation value of the spin-orbit operator of the valence states. Here, we analyze the measured branching ratio of the N{sub 4,5} edges acquired by electron energy-loss spectroscopy in a transmission electron microscope, and synchrotron-radiation-based x-ray absorption. Results show that the spin-orbit sum rule can be applied to actinide 5f states, where the accuracy can be increased using the correction term obtained from atomic many-electron calculations.

Competition between delocalization and spin-orbit splitting in the actinide 5f states

Abstract: Synchrotron-radiation-based x-ray absorption, electron energy-loss spectroscopy in a transmission electron microscope, multielectronic atomic spectral simulations, and improved first-principles calculations (generalized gradient approximation in the local density approximation) have been used to investigate the electronic structure of the light actinides: $\ensuremath{\alpha}\text{\ensuremath{-}}\mathrm{Th}$, $\ensuremath{\alpha}\text{\ensuremath{-}}\mathrm{U}$, and $\ensuremath{\alpha}\text{\ensuremath{-}}\mathrm{Pu}$. It will be shown that the spin-orbit interaction can be used as a measure of the degree of localization of valence electrons in a material. The spin-orbit interaction in the light actinide metals $\ensuremath{\alpha}\text{\ensuremath{-}}\mathrm{Th}$, $\ensuremath{\alpha}\text{\ensuremath{-}}\mathrm{U}$, and $\ensuremath{\alpha}\text{\ensuremath{-}}\mathrm{Pu}$, has been determined using the branching ratio of the white line peaks of the ${N}_{4,5}$ edges, which correspond to $4d\ensuremath{\rightarrow}5f$ transitions. Examination of the branching ratios and spin-orbit interaction shows that the apparent spin-orbit splitting is partially quenched in $\ensuremath{\alpha}\text{\ensuremath{-}}\mathrm{U}$, but is strongly dominant in $\ensuremath{\alpha}\text{\ensuremath{-}}\mathrm{Pu}$. These results are fully quantified using the sum rule. This picture of the actinide $5f$ electronic structure is confirmed by comparison with the results of electronic structure calculations for $\ensuremath{\alpha}\text{\ensuremath{-}}\mathrm{Th}$, $\ensuremath{\alpha}\text{\ensuremath{-}}\mathrm{U}$, and $\ensuremath{\alpha}\text{\ensuremath{-}}\mathrm{Pu}$, which in turn are supported by a previous bremsstrahlung isochromat spectroscopy experiment.

Oxidation and aging in U and Pu probed by spin-orbit sum rule analysis: Indications for covalent metal-oxide bonds

Abstract: Transmission electron microscopy is used to acquire electron energy-loss spectra from phase-specific regions of Pu and U metal, PuO{sub 2} and UO{sub 2}, and aged, self-irradiated Pu metal. The N{sub 4,5} (4d {yields} 5f) spectra are analyzed using the spin-orbit sum rule. Our results show that the technique is sensitive enough to detect changes in the branching ratio of the white-line peaks between the metal and dioxide of both U and Pu. There is a small change in the branching ratio between different Pu metals, and the data trends as would be expected for varying f electron localization, i.e., {alpha}-Pu, {delta}-Pu, aged {delta}-Pu. Moreover, our results suggest that the metal-oxide bonds in UO{sub 2} and PuO{sub 2} are strongly covalent in nature and do not exhibit an integer valence change as would be expected from purely ionic bonding.

Failure of Russell-Saunders coupling in the 5f states of plutonium.

Abstract: Using high energy-electron energy loss spectroscopy, transmission electron microscopy, and synchrotron-radiation-based x-ray absorption spectroscopy, we provide the first experimental evidence that Russell-Saunders (LS) coupling fails for the 5f states of Pu. These results support the assumption that only the use of jj or intermediate coupling is appropriate for the 5f states of Pu. High energy-electron energy loss spectroscopy experiments were performed by use of a transmission electron microscope and are coupled with image and diffraction data; therefore, the measurements are completely phase specific.

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

Abstract: 抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

A topological Dirac insulator in a quantum spin Hall phase

Abstract: When electrons are subject to a large external magnetic field, the conventional charge quantum Hall effect dictates that an electronic excitation gap is generated in the sample bulk, but metallic conduction is permitted at the boundary. Recent theoretical models suggest that certain bulk insulators with large spin-orbit interactions may also naturally support conducting topological boundary states in the quantum limit, which opens up the possibility for studying unusual quantum Hall-like phenomena in zero external magnetic fields. Bulk Bi(1-x)Sb(x) single crystals are predicted to be prime candidates for one such unusual Hall phase of matter known as the topological insulator. The hallmark of a topological insulator is the existence of metallic surface states that are higher-dimensional analogues of the edge states that characterize a quantum spin Hall insulator. In addition to its interesting boundary states, the bulk of Bi(1-x)Sb(x) is predicted to exhibit three-dimensional Dirac particles, another topic of heightened current interest following the new findings in two-dimensional graphene and charge quantum Hall fractionalization observed in pure bismuth. However, despite numerous transport and magnetic measurements on the Bi(1-x)Sb(x) family since the 1960s, no direct evidence of either topological Hall states or bulk Dirac particles has been found. Here, using incident-photon-energy-modulated angle-resolved photoemission spectroscopy (IPEM-ARPES), we report the direct observation of massive Dirac particles in the bulk of Bi(0.9)Sb(0.1), locate the Kramers points at the sample's boundary and provide a comprehensive mapping of the Dirac insulator's gapless surface electron bands. These findings taken together suggest that the observed surface state on the boundary of the bulk insulator is a realization of the 'topological metal'. They also suggest that this material has potential application in developing next-generation quantum computing devices that may incorporate 'light-like' bulk carriers and spin-textured surface currents.

Topological surface states protected from backscattering by chiral spin texture

Abstract: Topological insulators are a new class of insulators in which a bulk gap for electronic excitations is generated because of the strong spin–orbit coupling inherent to these systems. These materials are distinguished from ordinary insulators by the presence of gapless metallic surface states, resembling chiral edge modes in quantum Hall systems, but with unconventional spin textures. A key predicted feature of such spin-textured boundary states is their insensitivity to spin-independent scattering, which is thought to protect them from backscattering and localization. Recently, experimental and theoretical efforts have provided strong evidence for the existence of both two- and three-dimensional classes of such topological insulator materials in semiconductor quantum well structures and several bismuth-based compounds, but so far experiments have not probed the sensitivity of these chiral states to scattering. Here we use scanning tunnelling spectroscopy and angle-resolved photoemission spectroscopy to visualize the gapless surface states in the three-dimensional topological insulator Bi_(1-x)Sb_x, and examine in detail the influence of scattering from disorder caused by random alloying in this compound. We show that, despite strong atomic scale disorder, backscattering between states of opposite momentum and opposite spin is absent. Our observations demonstrate that the chiral nature of these states protects the spin of the carriers. These chiral states are therefore potentially useful for spin-based electronics, in which long spin coherence is critical, and also for quantum computing applications, where topological protection can enable fault-tolerant information processing.

Desk handbook phase diagrams for binary alloys

Abstract: Get the phase diagram information you need at a price you can afford. Key Features: Peer reviewed by the Japanese Committee for Alloy Phase Diagrams. Updated through April 2000. Total number of diagrams = 2,332 (605 are new of greatly revised diagrams; among these 171 are not in Binary Alloy Phase Diagrams, 2nd Edition). Approximately 600 crystal structure tables of systems for which phase diagrams are unknown. You've been asking for a simple book containing just binary phase diagrams and crystal structure data. Desk Handbook: Phase Diagrams for Binary Alloys meets this need, and it presents the most current information. Updates the previous print compilation of binary phase diagrams by 10 years. Presents diagrams in consistent size. Shows the principal axis in atomic per cent, with a secondary axis in weight per cent. Includes an introductory article on phase diagrams and their use. Gives reference to the original literature source. This volume is the latest outgrowth of the phase diagram activity in which ASM International has been involved since 1978.

Superconducting phases of f -electron compounds

Abstract: Intermetallic compounds containing $f$-electron elements display a wealth of superconducting phases, which are prime candidates for unconventional pairing with complex order parameter symmetries. For instance, superconductivity has been found at the border of magnetic order as well as deep within ferromagnetically and antiferromagnetically ordered states, suggesting that magnetism may promote rather than destroy superconductivity. Superconducting phases near valence transitions or in the vicinity of magnetopolar order are candidates for new superconductive pairing interactions such as fluctuations of the conduction electron density or the crystal electric field, respectively. The experimental status of the study of the superconducting phases of $f$-electron compounds is reviewed.