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1

Early Transition Metal Alkyl and Tetrahydroborate Complexes.  

NASA Astrophysics Data System (ADS)

An investigation of early transition metal alkyl and tetrahydroborate complexes as catalytic models and ceramic precursors has been initiated. The compounds MX _2 (dmpe)_2, dmpe = 1,2-bis(dimethylphosphino)ethane, for M = Ti, V, Cr, and X = Br, I, BH_4, have been prepared. These complexes are paramagnetic and have been shown by X-ray crystallography to have trans-octahedral structures. The BH_4^{-} groups in Ti(BH_4)_2(dmpe) _2 bond to the metal in a bidentate manner. This structure is in marked contrast to the structure of the vanadium analogue, V(BH_4)_2 (dmpe)_2, which displays two unidentate BH_4^{-} groups. Alkylation of Ti(BH_4)_2 (dmpe)_2 with LiMe results in the complex TiMe_2(dmpe) _2 which is diamagnetic in both solution and solid state. Single crystal X-ray and neutron diffraction studies show that there may be strong Ti-C pi -bonding. A tetragonal compression along the C -Ti-C bond vector accounts for the observed diamegnetism. A series of complexes of the formula Ti(BH _4)_3(PR_3)_2 has been prepared where PR_3 = PMe_3, PEt_3, PMe_3Ph, and P(OMe)_3 . The X-ray crystal structure of Ti(BH _4)_3(PMe_3)_2 reveals a pseudo trigonal bipyramidal geometry in which two BH_4^{-} groups display an unusual "side-on" bonding mode. The "side-on" ligation mode has been attributed to a Jahn-Teller distortion of the orbitally degenerate d^1 ground state. In contrast, the non-Jahn-Teller susceptible vanadium analogue, V(BH_4)_3 (PMe_3)_2, possesses a nearly ideal D_{rm 3h} >=ometry with three bidentate tetrahydroborate groups. Addition of excess PMe_3 to V(BH_4)_3(PMe _3)_2<=ads to the vanadium(II) hydride -bridged dimer (V(H)(BH_4)(PMe _3)_2]_2, while addition of PMe_3 and water forms the vanadium(III) oxo dimer (V(BH_4)_2 (PMe_3)_2]_2 [mu-O) which has been structurally characterized. The compound Ti(CH_2CMe _3)_4 can be prepared by addition of Ti(OEt)_4 to LiCH_2 CMe_3. Sublimation of Ti(CH _2CMe_3)_4 over a substrate heated to 250^ circC results in the chemical vapor deposition of amorphous TiC thin films. This CVD approach has been extended to the Group 4 borides: Ti(BH_4) _3(MeOCH_2CH _2OMe) yields TiB_2 at 200^circC, while Zr(BH _4)_4 and Hf(BH_4) _4 yield ZrB_2 and HfB_2 at 250^circ C using the CVD process. The X-ray crystal structure of Ti(BH_4)_3(MeOCH _2CH_2OMe) is reported.

Jensen, James Allen

1988-06-01

2

Density functional plus dynamical mean-field theory of the metal-insulator transition in early transition-metal oxides  

NASA Astrophysics Data System (ADS)

The combination of density functional theory and single-site dynamical mean-field theory, using both Hartree and full continuous-time quantum Monte Carlo impurity solvers, is used to study the metal-insulator phase diagram of perovskite transition-metal oxides of the form ABO3 with a rare-earth ion A =Sr, La, Y and transition metal B =Ti, V, Cr. The correlated subspace is constructed from atomiclike d orbitals defined using maximally localized Wannier functions derived from the full p-d manifold; for comparison, results obtained using a projector method are also given. Paramagnetic DFT + DMFT computations using full charge self-consistency along with the standard "fully localized limit" (FLL) double counting are shown to incorrectly predict that LaTiO3, YTiO3, LaVO3, and SrMnO3 are metals. A more general examination of the dependence of physical properties on the mean p-d energy splitting, the occupancy of the correlated d states, the double-counting correction, and the lattice structure demonstrates the importance of charge-transfer physics even in the early transition-metal oxides and elucidates the factors underlying the failure of the standard approximations. If the double counting is chosen to produce a p-d splitting consistent with experimental spectra, single-site dynamical mean-field theory provides a reasonable account of the materials properties. The relation of the results to those obtained from "d-only" models in which the correlation problem is based on the frontier orbital p-d antibonding bands is determined. It is found that if an effective interaction U is properly chosen the d-only model provides a good account of the physics of the d1 and d2 materials.

Dang, Hung T.; Ai, Xinyuan; Millis, Andrew J.; Marianetti, Chris A.

2014-09-01

3

Studies of high temperature ternary phases in mixed-metal-rich early transition metal sulfide and phosphide systems  

SciTech Connect

Investigations of ternary mixed early transition metal-rich sulfide and phosphide systems resulted in the discovery of new structures and new phases. A new series of Zr and Hf - group V transition metal - sulfur K-phases was synthesized and crystallographically characterized. When the group V transition metal was Nb or Ta, the unit cell volume was larger than any previously reported K-phase. The presence of adventitious oxygen was determined in two K-phases through a combination of neutron scattering and X-ray diffraction experiments. A compound Hf{sub 10}Ta{sub 3}S{sub 3} was found to crystallize in a new-structure type similar to the known gamma brasses. This structure is unique in that it is the only reported {open_quotes}stuffed{close_quotes} gamma-brass type structure. The metal components, Hf and Ta, are larger in size and more electropositive than the metals found in normal gamma brasses (e.g. Cu and Zn) and because of the larger metallic radii, sulfur can be incorporated into the structure where it plays an integral role in stabilizing this phase relative to others. X-ray single-crystal, X-ray powder and neutron powder refinements were performed on this structure. A new structure was found in the ternary Nb-Zr-P system which has characteristics in common with many known early transition metal-rich sulfides, selenides, and phosphides. This structure has the simplest known interconnection of the basic building blocks known for this structural class. Anomalous scattering was a powerful tool for differentiating between Zr and Nb when using Mo K{alpha} X-radiation. The compounds ZrNbP and HfNbP formed in the space group Prima with the simple Co{sub 2}Si structure which is among the most common structures found for crystalline solid materials. Solid solution compounds in the Ta-Nb-P, Ta-Zr-P, Nb-Zr-P, Hf-Nb-P, and Hf-Zr-S systems were crystallographically characterized. The structural information corroborated ideas about bonding in metal-rich compounds.

Marking, G.A.

1994-01-04

4

Early diagenesis in differing depositional environments: The response of transition metals in pore water  

NASA Astrophysics Data System (ADS)

The cycling of Fe, Mn, Ni, Co, Cu, Cr, V, and Mo during early diagenesis was investigated in sediments from five different depositional environments in the California Borderland. Dissolved O 2, NO 3-, NO 2-, and SO 4- were also measured at each site to establish the position of redox boundaries pertinent to this study. Sites were chosen to allow the comparison of several parameters of potential importance to the cycling of these metals: bottom water O 2 concentration; sediment redox conditions; cycling of metal oxide carrier phases and the relative contribution of biogenic and terrigenous material to the detrital metal flux. At 10 ?M oxygen and above the sequence of terminal electron acceptor utilization was typical of pelagic sediments, differing only in scale. Under these conditions the recycling of Mn oxides resulted in an enriched layer near the interface. At bottom water 0 2 concentrations < 5 ?M Mn oxides are not recycled. Under these conditions Fe oxides and SO 42- are important oxidants. The depth of the zone of manganese oxidation with respect to the interface affects the efficiency of metal scavenging by manganese oxides. Trapping and recycling of Ni and Co with Mn oxides results in remobilization from reducing sediments and enrichment in oxic sediments. Scavenging of these metals is favored by a deep oxic zone in the sediments. In contrast, Cr, V, and Mo appear to be transported to the sediments as reduced species and are released from the sediments by oxidation. The source of the reduced species is assumed to be biogenic material. The accumulation of these metals is favored by reducing conditions in the sediments. Cu is enriched in the sediments by transport with detrital biogenic material, followed by adsorption onto sediment solids. Cu is released at the interface and rapidly removed onto the solids at all sites except the one pelagic site, at the base of the slope. The magnitude of Cu released in the slowly accumulating pelagic sediment exceeds the Cu binding capacity of the solids, resulting in pore water Cu concentrations in excess of 100 nM. In general, metal cycling associated with the early diagenesis of sediments was observed to decouple transport processes from burial processes for the transition metals measured in this study.

Shaw, Timothy J.; Gieskes, Joris M.; Jahnke, Richard A.

1990-05-01

5

Bacterial Transition Metal Homeostasis  

Microsoft Academic Search

Since details on metal cation transport proteins and on the allocation mechanisms for transition metals\\u000a are provided elsewhere in this book, I will present aspects of transition metal homeostasis in a hopefully\\u000a novel overview. We will start with a microbial look at the transition metal Periodic Table, cation speciation,\\u000a and availability in the environment. This information provides rules that might

Dietrich H. Nies

6

Synthetic and Mechanistic Investigations of Polymerization Catalyzed for Early Transition Metal Compounds  

SciTech Connect

The objectives of the research program are (1) to discover new types of chemical transformations between hydrocarbons and transition-metal compounds, (2) to investigate their mechanisms; and (3) to explore the possibilities of coupling these transformations with others to catalyze chemical reactions for the preparation of fuels, commodity chemicals and polymeric materials. A current focus is the catalytic polymerization of alpha-olefins. New and superior polymers with different microstructures and potentially very useful kinetic resolutions of abundant, racemic alpha-olefins could be realized, if sufficient control over the polymerization process could be achieved. Well defined, yttrocene catalysts have been synthesized, some with known absolute configurations, and their reactions with an isotopically chiral 1-pentene monomer have been examined. These experiments have revealed the absolute olefin facial preferences for 1-pentene addition to Y-H and Y-pentyl bonds. A new class of zirconocene catalysts having doubly-linked cyclopentadienyl ligands has been developed, which allow the preparation of polypropylenes varying from isotactic to syndiotactic. These catalysts are highly reactive, permitting the polymerization of normally unreactive monomers such as 3-substituted alpha olefins. Chiral versions effect polymerization of such racemic monomers with useful kinetic resolutions.

John E. Bercaw

2001-03-18

7

Synthesis, characterization and reactivity of early transition metal neo-pentoxides  

SciTech Connect

Titanium neo-pentoxide was isolated by the alcoholysis exchange between Ti(OCHMe{sub 2}){sub 4} and ONep. The molecule, [Ti(ONep){sub 4}]{sub 2}, was characterized using X-ray analysis and solution {sup 17}O, and {sup 47},{sup 49}Ti NMR spectroscopy. This dinuclear complex is the smallest Ti(OR){sub 4} isolated wherein each metal center is 5-coordinated. The molecule is highly soluble in standard solvents and volatile. The reactivity of this compound has been undertaken to compare with the ubiquitous Ti(O-I-Pr){sub 4}. The various compounds isolated and further NMR studies will be reported. Analogous routes to other M(ONep){sub n} will be reported as well.

Boyle, T.J.; Alam, T.M.; Scott, B.; Ziller, J.W. [Sandia National Labs., Albuquerque, NM (United States)

1997-12-31

8

Transition Metal Switchable Mirror  

SciTech Connect

The switchable-mirrors technology was developed by Tom Richardson and Jonathan Slack of Berkeley Lab's Environmental Energy Technologies Division. By using transition metals rather than the rare earth metals used in the first metal-hydride switchable mirrors, Richardson and Slack were able to lower the cost and simplify the manufacturing process. Energy performance is improved as well, because the new windows can reflect or transmit both visible and infrared light. Besides windows for offices and homes, possible applications include automobile sunroofs, signs and displays, aircraft windows, and spacecraft. More information at: http://windows.lbl.gov/materials/chromogenics/default.htm

None

2009-01-01

9

Metal to semiconductor transition in metallic transition metal dichalcogenides  

SciTech Connect

We report on tuning the electronic and magnetic properties of metallic transition metal dichalcogenides (mTMDCs) by 2D to 1D size confinement. The stability of the mTMDC monolayers and nanoribbons is demonstrated by the larger binding energy compared to the experimentally available semiconducting TMDCs. The 2D MX{sub 2} (M?=?Nb, Ta; X?=?S, Se) monolayers are non-ferromagnetic metals and mechanically softer compared to their semiconducting TMDCs counterparts. Interestingly, mTMDCs undergo metal-to-semiconductor transition when the ribbon width approaches to ?13? and ?7? for zigzag and armchair edge terminations, respectively; then these ribbons convert back to metal when the ribbon widths further decrease. Zigzag terminated nanoribbons are ferromagnetic semiconductors, and their magnetic properties can also be tuned by hydrogen edge passivation, whereas the armchair nanoribbons are non-ferromagnetic semiconductors. Our results display that the mTMDCs offer a broad range of physical properties spanning from metallic to semiconducting and non-ferromagnetic to ferromagnetic that is ideal for applications where stable narrow bandgap semiconductors with different magnetic properties are desired.

Li, Yan; Kang, Jun; Li, Jingbo, E-mail: jbli@semi.ac.cn [State Key Laboratory of Superlattice and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083 (China); Tongay, Sefaattin; Wu, Junqiao [Department of Materials Science and Engineering, University of California, Berkeley, California 94720 (United States); Yue, Qu [College of Science, National University of Defense Technology, Changsha 410073 (China)

2013-11-07

10

Selenophene transition metal complexes  

SciTech Connect

This research shows that selenophene transition metal complexes have a chemistry that is similar to their thiophene analogs. Selenophene coordination has been demonstrated and confirmed by molecular structure in both the {eta}{sup 5}- and the {eta}{sup 1}(Se)-coordination modes. The reaction chemistry of selenophene complexes closely resembles that of the analogous thiophene complexes. One major difference, however, is that selenophene is a better donor ligand than thiophene making the selenophene complexes more stable than the corresponding thiophene complexes. The {sup 77}Se NMR chemical shift values for selenophene complexes fall within distinct regions primarily depending on the coordination mode of the selenophene ligand. In the final paper, the C-H bond activation of {eta}{sup 1}(S)-bound thiophenes, {eta}{sup 1}(S)-benzothiophene and {eta}{sup 1}(Se)-bound selenophenes has been demonstrated. The deprotonation and rearrangement of the {eta}{sup 1}(E)-bound ligand to the carbon bound L-yl complex readily occurs in the presence of base. Reprotonation with a strong acid gives a carbene complex that is unreactive towards nucleophilic attack at the carbene carbon and is stable towards exposure to air. The molecular structure of [Cp(NO)(PPh{sub 3})Re(2-benzothioenylcarbene)]O{sub 3}SCF{sub 3} was determined and contains a Re-C bond with substantial double bond character. Methyl substitution for the thienylcarbene or selenylcarbene gives a carbene that rearranges thermally to give back the {eta}{sup 1}(E)-bound complex. Based on these model reactions, a new mechanism for the H/D exchange of thiophene over the hydrodesulfurization catalyst has been proposed.

White, C.J.

1994-07-27

11

Transition metals in plant photosynthesis.  

PubMed

Transition metals are involved in essential biological processes in plants since they are cofactors of metalloproteins and also act as regulator elements. Particularly, plant chloroplasts are organelles with high transition metal ion demand because metalloproteins are involved in the photosynthetic electron transport chain. The transition metal requirement of photosynthetic organisms greatly exceeds that of non-photosynthetic organisms, and either metal deficiency or metal excess strongly impacts photosynthetic functions. In chloroplasts, the transition metal ion requirement needs a homeostasis network that strictly regulates metal uptake, chelation, trafficking and storage since under some conditions metals cause toxicity. This review gives an overview of the current understanding of main features concerning the role of copper (Cu), iron (Fe), manganese (Mn) and zinc (Zn) in plant photosynthesis as well as the mechanisms involved in their homeostasis within chloroplasts. The metalloproteins functioning in photosynthetic proteins of plants as well as those proteins participating in the metal transport and metal binding assembly are reviewed. Furthermore, the role of nickel (Ni) in artificial photosynthesis will be discussed. PMID:23739807

Yruela, Inmaculada

2013-09-01

12

Transition metal nitride functional coatings  

NASA Astrophysics Data System (ADS)

During the past decade, interest in transition metal nitrides has grown considerably. Nitrides of various elements play an important role in industry, science, and technology for their interesting and useful resilient properties. For example, many transition metal nitrides based on titanium, boron, and nitrogen have stimulated commercial interest because of their extreme hardness, wear and corrosion resistance, and thermal and electrical properties. All of these features are enhanced by the resulting structures and the large degree of covalency exhibited by the transition metal-nitride bonds. Coatings of select nitrides may particularly influence physico-chemical properties in critical surface and interface regions. This article attempts to present a brief overview on transition metal-nitride research for advancement in reliable machine part manufacturing.

Navinsek, B.; Seal, Sudipta

2001-09-01

13

Early metal bis(phosphorus-stabilised)carbene chemistry.  

PubMed

Since the discovery of covalently-bound mid- and late-transition metal carbenes there has been a spectacular explosion of interest in their chemistry, but their early metal counterparts have lagged behind. In recent years, bis(phosphorus-stabilised)carbenes have emerged as valuable ligands for metals across the periodic table, and their use has in particular greatly expanded covalently-bound early metal carbene chemistry. In this tutorial review we introduce the reader to bis(phosphorus-stabilised)carbenes, and cover general preparative methods, structure and bonding features, and emerging reactivity studies of early metal derivatives (groups 1-4 and the f-elements). PMID:21321726

Liddle, Stephen T; Mills, David P; Wooles, Ashley J

2011-05-01

14

Metal-insulator transitions: Orbital control  

NASA Astrophysics Data System (ADS)

On cooling, transition metal oxides often undergo a phase change from an electrically conducting to an insulating state. Now it is shown that the metal-insulator transition temperature of vanadium dioxide thin films can be controlled by applying strain.

Mizokawa, Takashi

2013-10-01

15

Enantioselective, transition metal catalyzed cycloisomerizations.  

PubMed

This review illustrates enantioselective transition-metal promoted skeletal rearrangements of polyunsaturated substrates possessing olefin, alkyne or allene functions. These processes are classified according to the number of carbon atoms involved in the cyclization, from (1C+1C) to (2C+2C+2C) or (2C+5C) cyclizations. Thus, for instance, (1C+1C) processes are typified notably by Alder-ene type reactions taking place mainly under palladium and rhodium catalysis, in the presence of chiral phosphorus ligands. Also, rhodium, platinum, and gold promoted insertions of unsaturated carbon-carbon bonds into C-H bonds belong to this class. For each class of reactions or substrate type the best ligand-metal pairs are highlighted. Unfortunately, unlike other transition metal promoted reactions, the mechanisms of chiral induction and stereochemical pathways have not been established so far in any of these reactions. In only a few instances, qualitative heuristic models have been tentatively proposed. Although the available stereochemical information is systematically given here, the paper focuses mainly on synthetic aspects of enantioselective cycloisomerizations. PMID:22674143

Marinetti, Angela; Jullien, Hlne; Voituriez, Arnaud

2012-07-21

16

Family Perceptions of Transitions in Early Intervention  

ERIC Educational Resources Information Center

This article explores three broad themes about transitions that have emerged in a naturalistic study of experiences of families with young children with disabilities. Generalizations regarding early transitions include families going through a birth crisis have difficulty understanding all the information they are provided. Not only is their role

Lovett, David L.; Haring, Kathryn A.

2003-01-01

17

Magnetochromism in Transition Metal Oxides  

NASA Astrophysics Data System (ADS)

We discuss the discovery and mechanism of magnetic field-induced color changes in three different low-dimensional transition metal oxides: Li purple bronze, (CPA)_2CuBr_4, and Pr-substituted La_1.2Sr_1.8Mn_2O_7. In Li purple bronze, the field manipulates the density of states near E_F, altering O p to Mo d excitations. In the copper halide, the applied field rotates the CuBr4 chromophore units, yielding a strong magnetochromic effect. And in (La_0.4Pr_0.6_1.2Sr_1.8Mn_2O_7, the magnetic field acts on the Jahn-Teller-split Mn^3+ eg orbitals, with consequences of a substantial CMR effect, unusual magnetic relaxation behavior, and a change in orbital occupation.

Musfeldt, Janice; Choi, Jongwoo; Haraldsen, Jason; Woodward, Jonathan; Wei, Xing; He, Jian; Mandrus, David; Landee, Chris; Turnbull, Mark; Suryanarayanan, Ramanathanan; Revcolevschi, Alex

2004-03-01

18

Pressure-Induced Electronic Phase Transitions Transition Metal Oxides and Rare Earth Metals  

E-print Network

Pressure-Induced Electronic Phase Transitions in Transition Metal Oxides and Rare Earth Metals change us, but we start and end with family" -Anthony Brandt ii #12;Acknowledgements I would like Metal Oxides and Rare Earth Metals by Brian Ross Maddox Electron correlation can affect profound changes

Islam, M. Saif

19

Electronic structure of early transition-metal carbonyls: Gas-phase photoelectron spectroscopy of ({eta}{sup 5}-C{sub 5}H{sub 5})M(CO){sub 4} (M = V, Nb, Ta)  

SciTech Connect

Gas-phase photoelectron spectroscopy is used to investigate the bonding between early transition metals and carbonyl and cyclopentadienyl ligands. The lowest ionization energy region contains two overlapping ionizations that arise from the two orbitals that are occupied according to the formal d{sup 4} metal configuration. However, the character of these ionizations is dominated by the carbonyls rather than by the metals, as evidenced by the extensive C-O stretching vibrational progressions observed with these ionizations, by the trends in the ionization cross sections between the molecules and with different ionization sources, and by the relative lack of shifts of these ionizations with metal substitution from vanadium to niobium to tantalum or with trimethylsilyl and acetyl substitutions on the cyclopentadienyl. The second group of ionizations for these molecules corresponds to orbitals with predominantly cyclopentadienyl {pi} character that donate to empty metal d orbitals. A much larger shift of these ionizations is observed upon cyclopentadienyl substitution. The molecular structures are sensitive to the electron configurations. Both density functional theory and ab initio calculations reproduce well the geometry of the neutral molecules and also predict the geometry changes upon ionization. The first ionization, which relates to an orbital with the a{sub 1} symmetry of the metal d{sub z}{sup 2} orbital, is broad due to a substantial geometry change upon removal of an electron from this orbital. The shoulder on the cyclopentadienyl-based ionizations related to a dynamic Jahn-Teller geometrical distortion. The unusually large metal-to-carbonyl back-bonding observed in these molecules is facilitated by the interligand overlap between the four carbonyls, which substantially stabilizes the appropriate symmetry-adapted carbonyl {pi}* acceptor orbitals. The extensive carbonyl character in the valence electronic structure diminishes any trends in properties with substitutions of the metals down the group or with substitutions on the cyclopentadienyl ring.

Lichtenberger, D.L.; Fan, H.J.; Gruhn, N.E.; Bitterwolf, T.E.; Gallagher, S.

2000-05-15

20

Thermomechanical properties of 3d transition metals  

SciTech Connect

The authors have investigated the density variation of the Einstein temperatures and elastic constants of the 3d transition metals. In this respect they have employed the transition metal (TM) pair potentials involving the sp contribution with an appropriate exchange and correlation function, the d-band broadening contribution and the d-band hybridization term. These calculations are aimed at testing the TM pair potentials in generating the quasilocal and local thermomechanical properties.

Karaoglu, B.; Rahman, S.M.M. (Sultan Qaboos Univ., Muscat (Oman). Dept. of Physics)

1994-05-15

21

From Early Intervention to Early Childhood Programs: Timeline for Early Successful Transitions (TEST)  

ERIC Educational Resources Information Center

More than one million transitions between early intervention services and early childhood programs are facilitated annually for youngsters with special needs. To be successful, these transitions require planning and ongoing communication between all parties. This article substantiates the need for a timeline/checklist and provides a model of

Brandes, Joyce A.; Ormsbee, Christine K.; Haring, Kathryn A.

2007-01-01

22

Metal-insulator transition in dilute alkali-metal systems  

Microsoft Academic Search

The metal-insulator transition is studied for dilute systems of alkali metals. Using a spin-split self-consistent band-structure approach, we find the transition density, a strikingly enhanced magnetic susceptibility, and the electron effective mass. The critical density nc is found to be given by the simple relation rcs=r0+2.8. Here rcs=[3(4pinc)]13 and r0 is the model potential radius which is roughly the radius

J. H. Rose

1981-01-01

23

Desulfurization with transition metal catalysts  

Microsoft Academic Search

The principal objective of this research is to uncover new reagents and catalysts for upgrading coal-derived fuels by removing undesirable organosulfur, organonitrogen and, if feasible, oxygen components. During the sixth quarter of this two-year grant the following studies were continued: (a) evaluation of the combined desulfurizing action on SRC liquids of nickel salts and metal hydrides, especially when the reactants

Eisch

1983-01-01

24

Intermultiplet transitions in rare-earth metals  

SciTech Connect

We report here on direct observations of intermultiplet (IM) transitions in the rare-earth metals, Pr, Nd and Tb, made using the chopper spectrometers at the Intense Pulsed Neutron Source of Argonne National Laboratory. Despite hydrogen contamination of the polycrystalline samples, we have observed inelastic peaks at small Q arising from IM transitions in Pr (approx.260 MeV), Nd (approx.242 MeV) and Tb (approx.256 MeV) although the latter has not yet been observed unambiguously. Future work will investigate the energy level structure and dynamical properties of rare-earth ions in stoichiometric metallic systems. 5 refs., 3 figs.

Stirling, W.G.; McEwen, K.A.; Loong, C.K.

1985-01-01

25

Transition metal-catalyzed functionalization of pyrazines.  

PubMed

Transition metal-catalyzed reactions are generally used for carbon-carbon bond formation on pyrazines and include, but are not limited to, classical palladium-catalyzed reactions like Sonogashira, Heck, Suzuki, and Stille reactions. Also a few examples of carbon-heteroatom bond formation in pyrazines are known. This perspective reviews recent progress in the field of transition metal-catalyzed cross-coupling reactions on pyrazine systems. It deals with the most important C-C- and C-X-bond formation methodologies. PMID:23632914

Nikishkin, Nicolai I; Huskens, Jurriaan; Verboom, Willem

2013-06-14

26

Work Functions of the transition Metals and Metal Silicides  

SciTech Connect

The work functions of polycrystalline metals are often used to systematize Schottky barrier height data for rectifying contacts to semiconductors. Rectifying contacts to silicon devices are predominantly formed using conductive metal silicides with work functions which are not as well characterized as metal work functions. The present work has two objectives. First, it classifies the transition metals using correlations between the metal work function and the atomic chemical potential. Second, the available data for metal silicides is collected and interpreted using an average charge transfer (ACT) model. The ACT model accounts for the electronic hardness of the component elements in addition to their chemical potentials. New trends in the behavior of silicide work functions are identified.

Drummond, T.J.

1999-02-15

27

Upconversion Processes in Transition Metal and Rare Earth Metal Systems  

Microsoft Academic Search

The design and characterization of new luminescent materials is an active area of research. Here we present several current\\u000a topics in the area of upconversion by transition-metal and rare-earth-metal doped halide lattices. Following introduction\\u000a to the necessary background material related to upconversion mechanisms and kinetics, a series of topics are discussed which\\u000a illustrate some key areas of developing interest in

Daniel R. Gamelin; Hans U. Gdel

28

LABORATORY EXPERIMENT 6 TRANSITION METAL DETERMINATION USING  

E-print Network

, and titrate through purple to green color. Zn: Add ammonia buffer with pH 9-10 to convert all Zn(II) ions or an Erlenmeyer flask), pH is adjusted by addition of an appropriate buffer, necessary amount of suitable to be analyzed are all water soluble inorganic salts of various transition metals: Zinc, Cobalt, Nickel

Nazarenko, Alexander

29

High Pressure Synthesis of Transition Metal Carbonyls.  

ERIC Educational Resources Information Center

Presents an experiment which uses readily available starting materials and inexpensive equipment for synthesis of transition metal carbonyls at 1000 atm and which is intended to give students experience in techniques used in research and industry. Safety precautions are emphasized. (Author/SA)

Hagen, A. P.; And Others

1979-01-01

30

Mass fractionation processes of transition metal isotopes  

Microsoft Academic Search

Recent advances in mass spectrometry make it possible to utilise isotope variations of transition metals to address some important issues in solar system and biological sciences. Realisation of the potential offered by these new isotope systems however requires an adequate understanding of the factors controlling their isotope fractionation. Here we show the results of a broadly based study on copper

X. K. Zhu; Y. Guo; R. J. P. Williams; R. K. ONions; A. Matthews; N. S. Belshaw; G. W. Canters; E. C. de Waal; U. Weser; B. K. Burgess; B. Salvato

2002-01-01

31

Phonon self energy in transition metals  

NASA Astrophysics Data System (ADS)

We present ab initio calculations of the phonon self energy of transition metals obtained using second order many body perturbation theory.ootnotetextS. Narasimhan and D. Vanderbilt, Phys. Rev. B, 43, 4541 (1991) The code we have implementedootnotetextL. Chaput, A. Togo, I. Tanaka and G. Hug, submitted to Phys. Rev. B use the symmetry properties of the phonon-phonon interactions to express the self energy as a sum over irreducible triplets. It is analogous to the reduction of integration to the irreducible part of the Brillouin zone for one particle properties. The self energy of transition metals is then calculated. We show that the Peierls approximationootnotetextR. E. Peierls, Quantum Theory of Solids, Oxford University Press,1964 is in fact reasonable for bcc and fcc metals, but fails for the hcp. The decays paths of phonons producing the self energy is finally analyzed using surfaces of reciprocal space defined by conservation law.

Chaput, Laurent; Togo, Atsushi; Tanaka, Isao; Hug, Gilles

2011-03-01

32

(Electronic structure and reactivities of transition metal clusters)  

SciTech Connect

The following are reported: theoretical calculations (configuration interaction, relativistic effective core potentials, polyatomics, CASSCF); proposed theoretical studies (clusters of Cu, Ag, Au, Ni, Pt, Pd, Rh, Ir, Os, Ru; transition metal cluster ions; transition metal carbide clusters; bimetallic mixed transition metal clusters); reactivity studies on transition metal clusters (reactivity with H{sub 2}, C{sub 2}H{sub 4}, hydrocarbons; NO and CO chemisorption on surfaces). Computer facilities and codes to be used, are described. 192 refs, 13 figs.

Not Available

1992-01-01

33

Transition metal sulfur dioxide hexafluoroarsenates and hexafluoroantimonates  

Microsoft Academic Search

The preparation and characterization by X-ray crystallography of transition metal sulfur dioxide hexafluoroarsenates of the general formula [M(SO2)x](AsF6)21 (1a: M=Mn, x=2; 1c: M=Co, x=4; 1e: M=Cu, x=4) and the hexafluoroantimonate [Co(SO2)2](SbF6)23 is reported. The structural features of the compounds mentioned are compared with those of [Fe(SO2)4](AsF6)2 (1b) and [Ni(SO2)6](AsF6)2 (1d), reported previously. The structural diversity of transition metal sulfur dioxide

E Lork; R Mews; J Petersen; M Schrter; B emva

2001-01-01

34

Topological crystalline insulators in transition metal oxides.  

PubMed

Topological crystalline insulators possess electronic states protected by crystal symmetries, rather than time-reversal symmetry. We show that the transition metal oxides with heavy transition metals are able to support nontrivial band topology resulting from mirror symmetry of the lattice. As an example, we consider pyrochlore oxides of the form A2M2O7. As a function of spin-orbit coupling strength, we find two Z2 topological insulator phases can be distinguished from each other by their mirror Chern numbers, indicating a different topological crystalline insulators. We also derive an effective kp Hamiltonian, similar to the model introduced for Pb(1-x)Sn(x)Te, and discuss the effect of an on-site Hubbard interaction on the topological crystalline insulator phase using slave-rotor mean-field theory, which predicts new classes of topological quantum spin liquids. PMID:25167290

Kargarian, Mehdi; Fiete, Gregory A

2013-04-12

35

Single-layer transition metal sulfide catalysts  

DOEpatents

Transition Metal Sulfides (TMS), such as molybdenum disulfide (MoS.sub.2), are the petroleum industry's "workhorse" catalysts for upgrading heavy petroleum feedstocks and removing sulfur, nitrogen and other pollutants from fuels. We have developed an improved synthesis technique to produce SLTMS catalysts, such as molybdenum disulfide, with potentially greater activity and specificity than those currently available. Applications for this technology include heavy feed upgrading, in-situ catalysis, bio-fuel conversion and coal liquefaction.

Thoma, Steven G. (Albuquerque, NM)

2011-05-31

36

Semiconducting Al transition-metal quasicrystals  

NASA Astrophysics Data System (ADS)

We report on a class of icosahedral aluminum transition-metal (Al-TM) alloys with true semiconducting behavior. Our description of the structure of these icosahedral quasicrystals is based on the six-dimensional Katz-Gratias-Boudard (KGB) model of the face-centered-icosahedral (fci) quasicrystal and its rational approximants. The shell structure of the atomic surfaces in perpendicular space defines the chemical order of aluminum and transition-metal (TM) atoms leading to semiconducting transport properties. In transition-metal aluminides the hybridization between the Al(s,p) and transition-metal d orbitals is responsible for the formation of a semiconducting gap in the electronic spectrum. We have analyzed the electronic charge distribution and observed an enhanced charge density along the Al-TM bonds that is characteristic of covalent bonding. The existence of an energy gap in the electronic spectrum at or in the vicinity of the Fermi level is explicitly demonstrated for several low-order approximants in the hierarchy of Fibonacci approximants which converges to the icosahedral quasicrystals of the fci class, to which also the i-AlPdRe belongs. We predict existence of truly semiconducting quasicrystalline 1/1-approximants. Our results also lead to the prediction of the existence of new semiconducting quasicrystals with specified Al-TM compositions. The possibility of the existence of a semiconducting band gap suggests an explanation for the anomalously high resistivity of the icosahedral AlPdRe quasicrystals. We demonstrate that substitutional defects violating the ideal Al-TM ordering predicted by the KGB model lead to the formation of localized states in the band gap. A real sample of i-AlPdRe thus seems to be a semiconductor with a band gap filled by the localized states.

Kraj?, M.; Hafner, J.

2003-10-01

37

Lanthanoid-transition-metal bonding in bismetallocenes.  

PubMed

Bismetallocenes [Cp2 LuReCp2 ] and [Cp*2 LaReCp2 ] (Cp=cyclopentadienyl; Cp*=pentamethylcyclopentadienyl) were prepared using different synthetic strategies. Salt metathesis-performed in aromatic hydrocarbons to avoid degradation pathways caused by THF-were identified as an attractive alternative to alkane elimination. Although alkane elimination is more attractive in the sense of its less elaborate workup, the rate of the reaction shows a strong dependence on the ionic radius of Ln(3+) (Ln=lanthanide) within a given ligand set. Steric hindrance can cause a dramatic decrease in the reaction rate of alkane elimination. In this case, salt metathesis should be considered the better alternative. Covalent bonding interactions between the Ln and transition-metal (TM) cations has been quantified on the basis of the delocalization index. Its magnitude lies within the range characteristic for bonds between transition metals. Secondary interactions were identified between carbon atoms of the Cp ligand of the transition metal and the Ln cation. Model calculations clearly indicated that the size of these interactions depends on the capability of the TM atom to act as an electron donor (i.e., a Lewis base). The consequences can even be derived from structural details. The observed clear dependency of the Lu?Ru and interfragment Lu?C bonding on the THF coordination of the Lu atom points to a tunable Lewis acidity at the Ln site, which provides a method of significantly influencing the structure and the interfragment bonding. PMID:24500974

Butovskii, Mikhail V; Oelkers, Benjamin; Bauer, Tobias; Bakker, Jacinta M; Bezugly, Viktor; Wagner, Frank R; Kempe, Rhett

2014-03-01

38

Corrosion behavior of mesoporous transition metal nitrides  

SciTech Connect

Transition metal nitrides (TMN) have many desirable characteristics such as high hardness and good thermal stability under reducing conditions. This work reports an initial survey of the chemical stability of mesoporous TMNs (TM=Nb, V, Cr and Ti) in water at 80 C at neutral, acidic and alkaline pH. The mesoporous TMNs had specific surface areas of 2560 m{sup 2}/g with average pore sizes ranging from 10 to 50 nm. The high surface areas of these materials enhance the rate of corrosion per unit mass over that of a bulk material, making detection of corrosion much easier. The products were characterized by Rietveld refinement of powder X-ray diffraction (PXRD) patterns and by scanning electron microscopy (SEM). Several nitrides have corrosion rates that are, within error, not distinguishable from zero (1 /day). Of the nitrides examined, CrN appears to be the most corrosion resistant under acidic conditions. None of the nitrides studied are corrosion resistant under alkaline conditions. - Graphical abstract: Corrosion behavior of mesoporous transition metal nitrides (TM=Nb, V, Cr and Ti) in acidic and alkaline solutions at 80 C for 2 weeks. Display Omitted - highlights: Corrosion rates of mesoporous transition metal nitrides in aqueous solution is reported. The mesoporous TMNs had surface areas of 2560 m{sup 2}/g. CrN is the most corrosion resistant under the conditions studied.

Yang, Minghui, E-mail: m.yang@cornell.edu [Department of Chemistry, Cornell University, Ithaca 14853-1301, NY (United States); Allen, Amy J.; Nguyen, Minh T. [Department of Chemistry, Cornell University, Ithaca 14853-1301, NY (United States); Ralston, Walter T. [College of Chemistry, University of California, Berkeley 94720-1460, CA (United States); MacLeod, Michelle J. [Department of Chemistry, Massachusetts Institute of Technology, Cambridge 02139-4307, MA (United States); DiSalvo, Francis J., E-mail: fjd3@cornell.edu [Department of Chemistry, Cornell University, Ithaca 14853-1301, NY (United States)

2013-09-15

39

Bridging Early Services Transition Project--Outreach. Final Report.  

ERIC Educational Resources Information Center

The Bridging Early Services Transition (BEST) Project--Outreach was designed to help families, administrators, and service providers facilitate the transition of young children, birth through age 5, as they move between services and service systems including: from early intervention to special preschool services; from Head Start or preschool to

Rosenkoetter, Sharon; Shotts, Cynthia

40

Diagnostic Transitions from Childhood to Adolescence to Early Adulthood  

ERIC Educational Resources Information Center

Background: Quantifying diagnostic transitions across development is needed to estimate the long-term burden of mental illness. This study estimated patterns of diagnostic transitions from childhood to adolescence and from adolescence to early adulthood. Methods: Patterns of diagnostic transitions were estimated using data from three prospective,

Copeland, William E.; Adair, Carol E.; Smetanin, Paul; Stiff, David; Briante, Carla; Colman, Ian; Fergusson, David; Horwood, John; Poulton, Richie; Costello, E. Jane; Angold, Adrian

2013-01-01

41

Routines and Transitions: A Guide for Early Childhood Professionals  

ERIC Educational Resources Information Center

In early childhood settings, children spend over 50 percent of their time on handwashing, dressing, napping, and other routines and transitions. "Routines and Transitions" is a guide to help turn these routine daily activities into learning experiences. By using transitions wisely, providers not only help children develop skills, but also run a

Malenfont, Nicole

2006-01-01

42

Transition metal complexes as molecular machine prototypes.  

PubMed

The field of molecular machines, i.e. multicomponent systems able to undergo large amplitude motions under the action of an external signal, has experienced a spectacular development since the beginning of the 1990s. Transition metal complexes have played an important role in this context, often as components of catenanes and rotaxanes. The present tutorial review will discuss a few systems of this type, taken from the contributions of our group or from others. The stimulus responsible for the controlled motion of the machine can be chemical, electrochemical, or photochemical. Examples of these three categories will be considered. PMID:17264936

Champin, Benot; Mobian, Pierre; Sauvage, Jean-Pierre

2007-02-01

43

Photoredox laser chemistry of transition metal oxides  

NASA Astrophysics Data System (ADS)

We describe two-color laser excitation of tungsten oxide in ambient air to effect a fully reversible photoredox cycle. One color is infrared, apparently functioning as heat, and the other is visible or shorter wavelength, but not necessarily super bandgap, apparently supplying electronic excitation. In the case of either tungsten oxide or molybdenum oxide, the process can be monitored using a very strong set of Raman spectroscopic features. This process could find application in optical data storage and may be a generally useful strategy for manipulating transition metal oxides.

Osman, J. M.; Bussjager, R. J.; Nash, F.; Chaiken, J.; Villarica, R. M.

44

Transitions for Young Children: Creating Connections across Early Childhood Systems  

ERIC Educational Resources Information Center

Smooth early childhood transitions are key to ensuring positive outcomes for young children the world over--but in today's fragmented early education systems, it's difficult to ensure continuity among programs and services. Early childhood professionals will help change that with this book, the first to propose a comprehensive, practical framework

Kagan, Sharon Lynn, Ed.; Tarrant, Kate, Ed.

2010-01-01

45

High-Pressure Thermodynamic Properties of f-electron Metals, Transition Metal Oxides, and Half-Metallic Magnets  

SciTech Connect

This project involves research into the thermodynamic properties of f-electron metals, transition metal oxides, and half-metallic magnets at high pressure. These materials are ones in which the changing importance of electron-electron interactions as the distance between atoms is varied can tune the system through phase transitions from localized to delocalized electrons, from screened to unscreened magnetic moments, and from normal metal to one in which only a single spin specie can conduct. Three main thrusts are being pursued: (1) Mott transitions in transition metal oxides, (2) magnetism in half-metallic compounds, and (3) large volume-collapse transitions in f-band metals.

Scalettar, Richard T.; Pickett, Warren E.

2004-07-01

46

Transition metal abnormalities in progressive dementias.  

PubMed

Abnormal distributions of transition metals inside the brain are potential diagnostic markers for several central nervous system diseases, including Alzheimer's disease (AD), Parkinson's disease, dementia with Lewy bodies (DLB), bipolar disorders and depression. To further explore this possibility, the total concentrations of iron, zinc, copper, manganese, aluminum, chromium and cadmium were measured in post-mortem hippocampus and amygdala tissues taken from AD, DLB and Control patients. A statistically significant near fifty percent reduction in the total copper levels of AD patients was observed in both the hippocampus and amygdala. The statistical power of the hippocampus and amygdala copper analysis was found to be 86 and 74% respectively. No statistically significant deviations in the total metal concentrations were found for zinc, manganese, chromium or aluminum. Iron was found to be increased by 38% in AD amygdala tissues, but was unchanged in AD hippocampus tissues. Accounting for differences in tissue water content, as a function of both tissue type and disease state, revealed more consistencies with previous literature. To aid in the design of future experiments, the effect sizes for all tissue types and metals studied are also presented. PMID:22080191

Akatsu, Hiroyasu; Hori, Akira; Yamamoto, Takayuki; Yoshida, Mari; Mimuro, Maya; Hashizume, Yoshio; Tooyama, Ikuo; Yezdimer, Eric M

2012-04-01

47

Photoelectron spectroscopic studies on the electronic structures of transition metal clusters and transition metal oxide clusters  

NASA Astrophysics Data System (ADS)

Photoelectron spectroscopic (PES) studies have been conducted on the bare transition metal clusters: Tin/ (n = 1~65),/ Vn/ (n = 1~70),/ Crn/ (n = 1~70),/ Fen/ (n = 1~33), Con/ (n = 1~51) and Nin/ (n = 1~50). The PES spectra of these clusters are taken at several detachment photon energies ranging from the second harmonic (532 nm) to fourth harmonic (266 nm) of the YAG laser and the 193 nm from an ArF excimer laser. Transition metals are very important catalysis elements; the photoelectron spectroscopic studies on the clusters provide a powerful tool for us to understand the metal- metal bonding and their electronic structures atom by atom. The electronic structure of titanium clusters is found to become bulk-like at relative small cluster sizes. It is observed that the 3d band emerges at the eight-atom cluster beyond which the d-band broadens and evolves toward that of the bulk. The vanadium clusters show three regions of spectral evolution: molecular behavior for n = 3-12; transition from molecular to bulk- like for n = 13-17; gradual convergence to bulk for n > 17, for which a surface-like feature is observed to slowly merge into the bulk feature near n = 60. Even-odd alternations are observed in the photoelectron spectra of small Crn clusters. Density functional calculations reveal a unique dimer growth route for chromium clusters up to Cr11, at which a structural transition occurs from the dimer growth to a bulklike body-centered-cubic structure. The PES spectra of the ferromagnetic metal clusters (Fen,/ Con, and Nin) reveal interesting relationships among the electronic structures and reactivity, geometric and magnetic properties, respectively. Photoelectron spectroscopic studies on the transition metal oxide clusters are also conducted. The study on the novel molecules Mx,/ Oy, (M = Ti, V, Cr, Fe, Cu, and Ni) shows the sequential oxidation behavior of the transition metals. Information about the structures and chemical bonding of these oxide molecules is also obtained.

Wu, Hongbin

48

Structural study of supercooled liquid transition metals  

NASA Astrophysics Data System (ADS)

Local structural models for supercooled liquid transition metals (Ti, Ni, and Zr) are proposed based on a reverse Monte Carlo analysis of high-energy x-ray diffraction data taken from the electrostatically levitated liquids. The resulting structures are characterized by their bond angle distributions, Honeycutt and Andersen indices [J. Phys. Chem. 91, 4950 (1987)], and bond orientational order parameters. All analyses suggest that an icosahedral short-range order is present in these supercooled liquids, but it is distorted in liquid Ti. These results are in agreement with the observed evolution of the high-q shoulder on the second peak in the structure factor S(q ) and with an earlier analysis based on a local cluster model.

Kim, T. H.; Kelton, K. F.

2007-02-01

49

Transition-metal-mediated thiosulfinate ester synthesis  

SciTech Connect

Unlike sulfur dioxide (SO{sub 2}), the coordination and organic reaction chemistry of disulfur monoxide (S{sub 2}O) has received little attention. A few Diels-Alder reactions of simple dienes with S{sub 2}O have been reported. However, there were no reports of direct S{sub 2}O complex synthesis prior to our initial work. The authors recently published a synthesis of 4,5-diphenyl-3,6-dihydro-1,2-dithiin 1-oxide (2) which liberates S{sub 2}O via a transition-metal-assisted retro-Diels-Alder reaction. Here we report further on the unusual reactivity of 2 and its utilization in the synthesis of cyclic thiosulfinate esters.

Raseta, M.E.; Cawood, S.A.; Welker, M.E. (Wake Forest Univ., Winston-Salem, NC (USA)); Rheingold, A.L. (Univ. of Delaware, Newark (USA))

1989-10-11

50

Radiation damage of transition metal carbides  

SciTech Connect

In this grant period we have investigated electrical properties of transition metal carbides and radiation-induced defects produced by low-temperature electron irradiation in them. Special attention has been given to the composition VC[sub 0.88] in which the vacancies on the carbon sublattice of this fcc crystal order to produce a V[sub 8]C[sub 7] superlattice. The existence of this superlattice structure was found to make the crystal somewhat resistant to radiation damage at low doses and/or at ambient temperature. At larger doses significant changes in the resistivity are produced. Annealing effects were observed which we believe to be connected with the reconstitution of the superlattice structure.

Dixon, G.

1991-01-01

51

Spin-orbit damping in transition metals  

NASA Astrophysics Data System (ADS)

Magnetization dynamics are routinely described with the Landau-Lifshitz-Gilbert (LLG) equation. However, it is expected that the LLG equation fails to properly describe the large amplitude dynamics that occur during magnetization reversal. Improving switching speeds in nanoscale devices by tailoring materials requires both a qualitative understanding of the relaxation processes that contribute to damping and the ability to quantitatively calculate the resulting damping rates. We consider small amplitude LLG damping in transition metals as a prelude to approaching the more complicated mechanisms expected in complete reversal events. LLG damping rates in pure transition metal systems have non-monotonic temperature dependencies that have been empirically shown by Heinrich et al. [1] to have one part proportional to the conductivity and one part proportional to the resistivity. Kambersky [2] postulated that both contributions result from a torque between the spin and orbital moments. We have conducted first-principles calculations that validate this claim for single element systems [3]. Our calculations for Fe, Co, and Ni both qualitatively match the two trends observed in measurements and quantitatively agree with the observed damping rates. We will discuss how the spin-orbit interaction produces two contributions to damping with nearly opposite temperature dependencies and compare calculations of the damping rate versus resistivity with experimental results. [1] B. Heinrich, D.J. Meredith, and J.F. Cochran, J. Appl. Phys., 50(11), 7726 (1979). [2] V. Kambersky, Czech. J. Phys. B, 26, 1366 (1976). [3] K. Gilmore, Y.U. Idzerda, and M.D. Stiles, Phys. Rev. Lett., 99, 027204 (2007).

Gilmore, Keith

2008-03-01

52

Early Predictors of School Performance Declines at School Transition Points  

ERIC Educational Resources Information Center

This longitudinal study followed students (n = 265) from kindergarten through seventh grade and examined early social and academic predictors of school performance at two normative school transitions. Questions addressed include: (a) are there changes in students' school performance over time, especially at school transition points; (b) are

Malaspina, Diane; Rimm-Kaufman, Sara E.

2008-01-01

53

Alignment: A Missing Link in Early Childhood Transitions?  

ERIC Educational Resources Information Center

Throughout the course of life, all adults make transitions, so do young children. Because young children are more vulnerable in general and they have experienced far fewer transitions than adults, they often experience greater challenges. As a result, the field of early childhood education has historically expended much effort in understanding and

Kagan, Sharon L.; Carroll, Jude; Comer, James P.; Scott-Little, Catherine

2006-01-01

54

Density Functional Theory of Transition Metal Phthalocyanines  

NASA Astrophysics Data System (ADS)

Metal phthalocyanines (MPc's) are a family of highly stable molecules that, as a molecular solid, form organic semiconductors. They have been used in a broad range of applications, e.g., light emitting diodes, solar cells, gas sensors, thin film transistors, and even as single molecule devices. Here, we present a systematic density functional theory (DFT) study of the electronic structure of selected transition metal Pc's: CuPc, NiPc, CoPc, MnPc, and FePc. We critically assess the performance of several semi-local and hybrid exchange-correlation functionals for these systems, and compare the results to experimental photoemission data. For the low-spin systems CuPc, NiPc, and CoPc, we show that semi-local functionals fail qualitatively, primarily because of under- binding of localized orbitals due to self-interaction errors. For the intermediate-spin systems, MnPc and FePc, we show that DFT calculations are extremely sensitive to the choice of functional and basis set with respect to the obtained electronic configuration and to symmetry breaking. However, interestingly, all simulated spectra are in good agreement with experiment despite the differences in the underlying electronic configurations.

Marom, Noa; Kronik, Leeor

2009-03-01

55

Polytypism in superhard transition-metal triborides  

PubMed Central

The quest of novel compounds with special structures and unusual functionalities continues to be a central challenge to modern materials science. Even though their exact structures have puzzled scientists for decades, superhard transition-metal borides (TMBs) have long been believed to exist only in simple crystal structures. Here, we report on a polytypic phenomenon in superhard WB3 and MoB3 with a series of energetically degenerate structures due to the random stacking of metal layers amongst the interlocking boron layers. Such polytypism can create a multiphase solid-solution compound with a large number of interfaces amongst different polytypes, and these interfaces will strongly hinder the interlayer sliding movement within each polytype, thereby further increase the hardness of this particular material. Furthermore, in contrast to the conventional knowledge that intrinsically strong chemical bonds in superhard materials should lead to high lattice thermal conductivity, the polytypic TMB3 manifest anomalously low lattice thermal conductivity due to structural disorders and phonon folding. These findings promise to open a new avenue to searching for novel superhard materials with additional functionalities. PMID:24863493

Liang, Yongcheng; Yang, Jiong; Yuan, Xun; Qiu, Wujie; Zhong, Zheng; Yang, Jihui; Zhang, Wenqing

2014-01-01

56

Swedish Child Care and Early Childhood Education in Transition.  

ERIC Educational Resources Information Center

Describes recent changes in Swedish system of child care and early childhood education and analyzes them in relation to economic and socio-political context. Argues that early childhood education is an important part of the welfare society, which itself is in a state of transition, with neo-liberal ideas and economic constraints implying financial

Kallos, Daniel; Broman, Ingegerd Tallberg

1997-01-01

57

Early-warning signals for critical transitions Marten Scheffer1  

E-print Network

such as asthma attacks1 or epileptic seizures2,3 ; in global finance, there is concern about systemic marketREVIEWS Early-warning signals for critical transitions Marten Scheffer1 , Jordi Bascompte2 difficult, work in different scientific fields is now suggesting the existence of generic early-warning

Utrecht, Universiteit

58

Transition Metal Nutrition: A Balance Between Deficiency and Toxicity  

E-print Network

359 A. Iron 359 B. Copper 369 C. Manganese and selenium 375 V. Conclusions and perspectives 376 of transition metal ions for biochemical functions is essen- tial as evidenced by the fact that metalloproteins and Clemens, 2005; 1 Commonly, "transition metal" refers to the 40 elements which belong to groups 3

Hamel, Patrice

59

The glass transition diagram in model metallic glasses  

E-print Network

We report a strain rate (equivalent to experimental observation time) induced glass transition in model SrCaYbMg(Li)Zn(Cu) metallic glasses at room temperature. A critical strain rate, equivalent to glass transition temperature, is found for the strain rate induced a glassy state to liquid-like viscoplastic state translation. The results show that the observation time, equivalent to temperature and stress, is a key parameter for the glass transition. A three-dimension glass transition phase diagram involved in time, temperature and stress in metallic glasses is established for understanding the nature of the metallic glasses.

X. Q. Gao; W. H. Wang; K. Zhao; H. Y. Bai

2013-05-22

60

Nutritional immunity: transition metals at the pathogen-host interface  

PubMed Central

Transition metals occupy an essential niche in biological systems. Their electrostatic properties stabilize substrates or reaction intermediates in the active sites of enzymes, while their heightened reactivity is harnessed for catalysis. However, the latter property renders transition metals toxic at high concentrations. Bacteria, like all living organisms, must regulate the levels of these elements to satisfy their physiological needs while avoiding harm. It is therefore not surprising that the host capitalizes on both the essentiality and toxicity of transition metals to defend against bacterial invaders. This review will discuss established and emerging paradigms in nutrient metal homeostasis at the pathogen-host interface. PMID:22796883

Hood, M. Indriati; Skaar, Eric P.

2013-01-01

61

Transition metal oxide improves overall efficiency and maintains performance with inexpensive metals.  

E-print Network

Transition metal oxide improves overall efficiency and maintains performance with inexpensive that inserting a transition metal oxide (TMO) between the lead sulfide (PbS) quantum dot (QD) layer and the metal Oxide as a Hole Extraction Layer in PbS Quantum Dot Solar Cells."Nano Letters 11, 3263 (2011). Key

62

Evaluating transition-metal catalysis in gas generation from the Permian Kupferschiefer by hydrous pyrolysis  

NASA Astrophysics Data System (ADS)

Transition metals in source rocks have been advocated as catalysts in determining extent, composition, and timing of natural gas generation (Mango, F. D. (1996) Transition metal catalysis in the generation of natural gas. Org. Geochem.24, 977-984). This controversial hypothesis may have important implications concerning gas generation in unconventional shale-gas accumulations. Although experiments have been conducted to test the metal-catalysis hypothesis, their approach and results remain equivocal in evaluating natural assemblages of transition metals and organic matter in shale. The Permian Kupferschiefer of Poland offers an excellent opportunity to test the hypothesis with immature to marginally mature shale rich in both transition metals and organic matter. Twelve subsurface samples containing similar Type-II kerogen with different amounts and types of transition metals were subjected to hydrous pyrolysis at 330 and 355 C for 72 h. The gases generated in these experiments were quantitatively collected and analyzed for molecular composition and stable isotopes. Expelled immiscible oils, reacted waters, and spent rock were also quantitatively collected. The results show that transition metals have no effect on methane yields or enrichment. ? 13C values of generated methane, ethane, propane and butanes show no systematic changes with increasing transition metals. The potential for transition metals to enhance gas generation and oil cracking was examined by looking at the ratio of the generated hydrocarbon gases to generated expelled immiscible oil (i.e., GOR), which showed no systematic change with increasing transition metals. Assuming maximum yields at 355 C for 72 h and first-order reaction rates, pseudo-rate constants for methane generation at 330 C were calculated. These rate constants showed no increase with increasing transition metals. The lack of a significant catalytic effect of transition metals on the extent, composition, and timing of natural gas generation in these experiments is attributed to the metals not occurring in the proper form or the poisoning of potential catalytic microcosms by polar-rich bitumen, which impregnates the rock matrix during the early stages of petroleum formation.

Lewan, M. D.; Kotarba, M. J.; Wi?c?aw, D.; Piestrzy?ski, A.

2008-08-01

63

Evaluating transition-metal catalysis in gas generation from the Permian Kupferschiefer by hydrous pyrolysis  

USGS Publications Warehouse

Transition metals in source rocks have been advocated as catalysts in determining extent, composition, and timing of natural gas generation (Mango, F. D. (1996) Transition metal catalysis in the generation of natural gas. Org. Geochem.24, 977984). This controversial hypothesis may have important implications concerning gas generation in unconventional shale-gas accumulations. Although experiments have been conducted to test the metal-catalysis hypothesis, their approach and results remain equivocal in evaluating natural assemblages of transition metals and organic matter in shale. The Permian Kupferschiefer of Poland offers an excellent opportunity to test the hypothesis with immature to marginally mature shale rich in both transition metals and organic matter. Twelve subsurface samples containing similar Type-II kerogen with different amounts and types of transition metals were subjected to hydrous pyrolysis at 330 and 355 C for 72 h. The gases generated in these experiments were quantitatively collected and analyzed for molecular composition and stable isotopes. Expelled immiscible oils, reacted waters, and spent rock were also quantitatively collected. The results show that transition metals have no effect on methane yields or enrichment. ?13C values of generated methane, ethane, propane and butanes show no systematic changes with increasing transition metals. The potential for transition metals to enhance gas generation and oil cracking was examined by looking at the ratio of the generated hydrocarbon gases to generated expelled immiscible oil (i.e., GOR), which showed no systematic change with increasing transition metals. Assuming maximum yields at 355 C for 72 h and first-order reaction rates, pseudo-rate constants for methane generation at 330 C were calculated. These rate constants showed no increase with increasing transition metals. The lack of a significant catalytic effect of transition metals on the extent, composition, and timing of natural gas generation in these experiments is attributed to the metals not occurring in the proper form or the poisoning of potential catalytic microcosms by polar-rich bitumen, which impregnates the rock matrix during the early stages of petroleum formation.

Lewan, M. D.; Kotarba, M. J.; Wieclaw, D.; Piestrzynski, A.

2008-01-01

64

Steam Reforming on Transition-metal Carbides from Density-functional Theory  

SciTech Connect

A screening study of the steam reforming reaction on clean and oxygen covered early transition-metal carbides surfaces is performed by means of density-functional theory calculations. It is found that carbides provide a wide spectrum of reactivities, from too reactive via suitable to too inert. Several molybdenum-based systems are identified as possible steam reforming catalysts. The findings suggest that carbides provide a playground for reactivity tuning, comparable to the one for pure metals.

Vojvodic, Aleksandra

2012-05-11

65

Fluctuation-driven electroweak phase transition. [in early universe  

NASA Technical Reports Server (NTRS)

We examine the dynamics of the electroweak phase transition in the early Universe. For Higgs masses in the range 46 less than or = M sub H less than or = 150 GeV and top quark masses less than 200 GeV, regions of symmetric and asymmetric vacuum coexist to below the critical temperature, with thermal equilibrium between the two phases maintained by fluctuations of both phases. We propose that the transition to the asymmetric vacuum is completed by percolation of these subcritical fluctuations. Our results are relevant to scenarios of baryogenesis that invoke a weakly first-order phase transition at the electroweak scale.

Gleiser, Marcelo; Kolb, Edward W.

1992-01-01

66

Chiral phase transition in lattice QCD as a metal-insulator transition  

E-print Network

We investigate the lattice QCD Dirac operator with staggered fermions at temperatures around the chiral phase transition. We present evidence of a metal-insulator transition in the low lying modes of the Dirac operator around the same temperature as the chiral phase transition. This strongly suggests the phenomenon of Anderson localization drives the QCD vacuum to the chirally symmetric phase in a way similar to a metal-insulator transition in a disordered conductor. We also discuss how Anderson localization affects the usual phenomenological treatment of phase transitions a la Ginzburg-Landau.

Antonio M. Garcia-Garcia; James C. Osborn

2006-11-17

67

Early Family Transitions and Depressive Symptom Changes from Adolescence to Early Adulthood  

ERIC Educational Resources Information Center

Some research and theory suggest that early cohabitation, parenthood, and marriage have negative long-term implications. Nevertheless, in the context of their resources and opportunities, early transitions may represent positive choices for some individuals. We studied the family and personal characteristics of young adults (N = 8,172) who did,

Booth, Alan; Rustenbach, Elisa; McHale, Susan

2008-01-01

68

Process for making transition metal nitride whiskers  

DOEpatents

A process for making metal nitrides, particularly titanium nitride whiskers, using a cyanide salt as a reducing agent for a metal compound in the presence of an alkali metal oxide. Sodium cyanide, various titanates and titanium oxide mixed with sodium oxide react to provide titanium nitride whiskers that can be used as reinforcement to ceramic composites. 1 fig., 1 tab.

Bamberger, C.E.

1988-04-12

69

Process for making transition metal nitride whiskers  

DOEpatents

A process for making metal nitrides, particularly titanium nitride whiskers, using a cyanide salt as a reducing agent for a metal compound in the presence of an alkali metal oxide. Sodium cyanide, various titanates and titanium oxide mixed with sodium oxide react to provide titanium nitride whiskers that can be used as reinforcement to ceramic composites.

Bamberger, Carlos E. (Oak Ridge, TN)

1989-01-01

70

A comprehensive comparison of transition-metal and actinyl polyoxometalates.  

PubMed

While the d(0) transition-metal POMs of Group V (V(5+), Nb(5+), Ta(5+)) and Group VI (Mo(6+), W(6+)) have been known for more than a century, the actinyl peroxide POMs, specifically those built of uranyl triperoxide or uranyl dihydroxidediperoxide polyhedra, were only realized within the last decade. While virtually every metal on the Periodic Table can form discrete clusters of some type, the actinyls are the only-in addition to the transition-metal POMs- whose chemistry is dictated by the prevalence of the 'yl' oxygen ligand. Thus this emerging structural, solution, and computational chemistry of actinide POMs warrants comparison to the mature chemistry of transition-metal POMs. This assessment between the transition-metal POMs and actinyl POMs (uranyl peroxide POMs, specifically) has provided much insight to the similarities and differences between these two chemistries. We further break down the comparison between the alkaline POMs of Nb and Ta; and the acidic POMs of V, Mo and W. This more indepth literature review and discussion reveals that while an initial evaluation suggests the actinyl POMs are more akin to the alkaline transition-metal POMs, they actually share characteristics unique to the acidic POMs as well. This tutorial review is meant to provide fodder for deriving new POM chemistries of both the familiar transition-metals and the emerging actinides, as well as fostering communication and collaboration between the two scientific communities. PMID:22695929

Nyman, May; Burns, Peter C

2012-11-21

71

Nitrene transfer reactions by late transition metal complexes  

E-print Network

This thesis presents nitrene transfer reactions that are catalyzed or mediated by late transition metal complexes. Sterically large, fluorinated supporting ligands are used to minimize potential side reactions. A new ...

Hamilton, Charles W., Ph. D. Massachusetts Institute of Technology

2007-01-01

72

Electrical properties of transition metal hydrogen complexes in silicon  

SciTech Connect

A summary is given on the electrical properties of transition-metal hydrogen complexes in silicon. Contrary to the general understanding, hydrogen leads not only to passivation of deep defect levels but also creates several new levels in the band gap due to electrically active transition-metal complexes. The author presents detailed data for Pt-H complexes and summarize briefly the results on the transition metals Ti, Co, Ni, Pd, and Ag. The introduction of hydrogen at room temperature by wet chemical etching, followed by specific annealing steps allows us to study the formation of the different complexes. In particular, depth profiles of the defect concentrations give an estimate of the number of hydrogen atoms involved in the complexes. Transition-metals binding up to four hydrogen atoms are identified.

Weber, J. [Max-Planck-Inst. fuer Festkoerperforschung, Stuttgart (Germany)

1998-12-31

73

Photochemical reductive elimination of halogen from transition metal complexes  

E-print Network

This thesis is focused on the synthesis and study of transition metal complexes that undergo halogen elimination when irradiated with UV and visible light. This chemistry is relevant for solar energy storage schemes in ...

Cook, Timothy R. (Timothy Raymond), 1982-

2010-01-01

74

Mechanisms of transition-metal gettering in silicon  

SciTech Connect

The atomic process, kinetics, and equilibrium thermodynamics underlying the gettering of transition-metal impurities in Si are reviewed from a mechanistic perspective. Methods for mathematical modeling of gettering are reviewed and illustrated. Needs for further research are discussed.

MYERS JR.,SAMUEL M.; SEIBT,M.; SCHROTER,W.

2000-03-23

75

Facilitating Family Involvement in Early Intervention to Preschool Transition  

ERIC Educational Resources Information Center

Active family involvement and important family roles in the early intervention to preschool transition have been mandated by laws, recognized by the position statements of professional organizations, and validated through evidence-based research. In order to involve families in this process, reduce stresses, and conquer the challenges families may

Pang, Yanhui

2010-01-01

76

Kansas Early Childhood Research Institute on Transitions: Executive Summary.  

ERIC Educational Resources Information Center

This executive summary reviews activities over the past 5 years of the Kansas Early Childhood Research Institute (KECRI). The Institute has addressed transition issues faced by infants and young children (and their families) who have a disability or are at risk for developmental delay. KECRI goals are stated and the importance and impact of the

Rice, Mabel L.; O'Brien, Marion

77

Structure of transition-metal-oxygen-vacancy pair centers  

Microsoft Academic Search

The microscopic structure of the Fe3+-VO and Mn2+-VO pair centers has been considered using the Newman superposition model. This model yields the EPR parameter b02 as a function of transition-metal-ion-oxygen distance d and position. It is found, for the oxide perovskites, that the transition-metal ion moves by a distance Delta=0.1 d=0.2 towards the vacancy VO. The four lateral oxygens

E. Siegel; K. A. Mller

1979-01-01

78

Electronic structure of double-perovskite transition-metal oxides  

Microsoft Academic Search

Electronic structure has been investigated by reflectivity measurement for ordered-perovskite transition-metal oxides, Sr2MMoO6 (M=Cr, Mn, Fe, and Co). The ground states of the Co and Mn compounds are paramagnetic insulators, making a sharp contrast with the ferrimagnetic metallic Sr2FeMoO6. For all the compounds, we have observed intense optical transition at ~2 eV, which has been ascribed to the charge-transfer excitation

Y. Moritomo; Sh. Xu; A. Machida; T. Akimoto; E. Nishibori; M. Takata; M. Sakata

2000-01-01

79

Improving Levine model for dielectric constants of transition metal compounds  

NASA Astrophysics Data System (ADS)

The density of states and optical properties of several transition metal compounds have been simulated using local density approximations+U. Results show that s electrons of nontransition elements in the compounds cannot be considered to have the same contribution on the number of valence electrons. In light of this observation, the parameter ? in the Levine model is improved, which leads to better prediction for dielectric constants of transition metal compounds.

Li, C.; Li, J. C.; Lian, J. S.; Jiang, Q.

2009-11-01

80

MOTHERS' PERCEPTIONS OF THE TRANSITION PROCESS FROM EARLY INTERVENTION TO EARLY CHILDHOOD SPECIAL EDUCATION: RELATED STRESSORS, SUPPORTS, AND COPING SKILLS  

Microsoft Academic Search

(ABSTRACT) This study investigated 10 mothers perceptions on the transition process, for their children with disabilities, from early intervention to early childhood special education. The issues of related stressors, supports, and coping skills were further explored. This research was guided by the ecological or systems theory. The issue of transition between the two service programs (early intervention to early childhood

Paula J. Hoover

81

Bi-phase transition diagrams of metallic thin multilayers  

SciTech Connect

Phase transitions of metallic multilayers induced by differences in interface energy are considered thermodynamically, based on a thermodynamic model for interface energy and the Goldschmidt premise for lattice contraction. Bi-phase transition diagrams of Co/Cr, Zr/Nb, Ti/Nb and Ti/Al multilayers are constructed, which are in agreement with experimental results.

Li, J.C. [Key Laboratory of Automobile Materials, Ministry of Education, and Department of Materials Science and Engineering, Jilin University, 142 RenMin Street, Changchun 130025 (China); Liu, W. [Key Laboratory of Automobile Materials, Ministry of Education, and Department of Materials Science and Engineering, Jilin University, 142 RenMin Street, Changchun 130025 (China); Jiang, Q. [Key Laboratory of Automobile Materials, Ministry of Education, and Department of Materials Science and Engineering, Jilin University, 142 RenMin Street, Changchun 130025 (China)]. E-mail: jiangq@jlu.edu.cn

2005-02-01

82

[Non-empirical interatomic potentials for transition metals]. Progress report  

SciTech Connect

The report is divided into the following sections: potential-energy functions for d-band metals, potential-energy functions for aluminides and quasicrystals, electronic structure of complex structures and quasicrystals, potential-energy functions in transition-metal oxides, applications to defect structure and mechanical properties, and basic theory of interatomic potentials.

Not Available

1993-05-01

83

[Non-empirical interatomic potentials for transition metals  

SciTech Connect

The report is divided into the following sections: potential-energy functions for d-band metals, potential-energy functions for aluminides and quasicrystals, electronic structure of complex structures and quasicrystals, potential-energy functions in transition-metal oxides, applications to defect structure and mechanical properties, and basic theory of interatomic potentials.

Not Available

1993-01-01

84

Volume variation of Gruneisen parameters of fcc transition metals  

Microsoft Academic Search

The volume variation of the Gruneisen parameters of tenfcc transition metals, up to 40% compression, has been studied on the basis of a model approach proposed by Antonovet al. The results are reasonably good for six metals except for Rh, Ag, Au and Ni when compared with available experimental and\\u000a other theoretical values. The model requires an appropriate modification for

C. V. Pandya; P. R. Vyas; T. C. Pandya; V. B. Gohel

2002-01-01

85

Melting of bcc Transition Metals and Icosahedral Clustering  

SciTech Connect

In contrast to polyvalent metals, transition metals have low melting slopes(dT/dP) that are due to partially filled d-bands that allow for a lowering of liquid phase energy through s-d electron transfer and the formation of local structures. In the case of bcc transition metals we show the apparent discrepancy of DAC melting measurements with shock melting of Mo can be understood by reexamining the shock data for V and Ta and introducing the presence of an icosahedral short range order (ISRO) melt phase.

Ross, M; Boehler, R; Japel, S

2006-05-26

86

Reactive Ion Etching of Transition-Metal Alloys  

NASA Astrophysics Data System (ADS)

For production of advanced spin-electronic devices, such as a magnetic random access memory with the higher-density memory cell, a reactive ion etching (RIE) process of transition metal alloys is the indispensable component of development, while no transition-metal compounds with the relatively high vapor pressure have been founded so far. Here, we show the RIE process of a NiFe thin film by using CH4:O2:NH3 discharge. The RIE process was designed by ab initio calculations, and the present result is the first successful demonstration of the chemical effect in the RIE process for transition-metal alloys. The relative etching ratio of NiFe against Ti as the metal mask was decreased by substituting CH4 with CHF3.

Akinaga, Hiro; Takano, Fumiyoshi; Matsumoto, Shigeno; Dio, Wilson A. T.

87

Binding and catalytic reduction of NO by transition metal aluminosilicates  

SciTech Connect

The objective of this research is to provide the scientific understanding of processes that actively and selectively reduce NO in dilute exhaust streams, as well as in concentrated streams, to N{sub 2}. Experimental studies of NO chemistry in transition metal-containing aluminosilicate catalysts are being carried out with the aim of determining the chemical rules for NO reduction on non-precious metals. The catalyst supports chosen for this investigation are A and Y zeolites, mordenite, and monoliths based on cordierite. The supported transition metal cations that were examined are principally the first row redox metals, e.g. Cr(2), Mn(II), Fe(II), Co(II), Ni(II), Cu(II), and Cu(I). The reactions of interest are the reductions of NO by H{sub 2}, CO, and CH{sub 4}, as well as the disproportionation of NO. Rare earth cations that possess redox properties were placed in the more shielded sites, e.g. Site I in Y zeolite, prior to or simultaneously with the exchange procedure with the transition metal cations. Theoretical calculations of the electronic structure of the transition metal cations in zeolitic sites were carried out by ab initio methods. The aim of this part of the research is to find the best match between the metal-based antibonding orbitals and the antibonding orbitals of the NO molecule such that the N-O bond is weakened and is readily broken. 9 refs., 4 figs., 3 tabs.

Klier, K.; Herman, R.G.; Hou, Shaolie.

1991-09-01

88

Synthesis, characterization and properties of nano-sized transition metal oxides  

Microsoft Academic Search

Chapter 1. A General introduction to the emerging field of nanomaterials is presented highlighting the category of transition metal oxides. The wide variety of structures, properties, and phenomena of transition metal oxides are stressed. Nano-sized transition metal oxides are presented as systems for fundamental and application research. Examples of individual transition metal oxides are provided. Important developments in the synthesis

Ming Yin

2005-01-01

89

[Transition metal mediated transformations of small molecules  

SciTech Connect

Work on organotransition metal chemistry, homogeneous and heterogeneous catalysis is summarized. Several cationic palladium(II) complexes with bulky phosphine or pyridine ligands were discovered that are highly selective catalysts for linear dimerization of vinyl monomers and linear polymerization of p-divinylbenzene, the reactions proceeding through a carbocationic mechanism. Our studies were continued on alternating olefin-carbon monoxide copolymers. The copolymerization reaction and reactivity of copolymers were examined. New catalytic systems for alternating copolymerization of [alpha]-olefins with CO were discovered. In the case of styrene derivatives, tactic copolymers were obtained. Poly(ethylenepyrrolediyl) derivatives were synthesized from alternating ethylene-carbon monoxide copolymer and become electronic conductors when doped with iodine. A catalytic system for direct synthesis of polyureas and polyoxamides from and diamines was also discovered. Pt metal catalyzed the oxidation of ethers, esters, and amines to carboxylic acids and the oxidation of olefins to 1,2-diols. Anaerobic and aerobic decomposition of molybdenum(VI)-oxoalkyl compounds were studied for heterogeneous oxidation of alkanes and olefins on Mo(VI)-oxide surfaces. Synthesis of polymer-trapped metal, metal oxide, and metal sulfide nanoclusters (size <1--10 nm) was studied.

Sen, A.

1992-01-01

90

Metal Selectivity Determinants in a Family of Transition Metal Transporters*  

PubMed Central

Metal tolerance proteins (MTPs) are plant members of the cation diffusion facilitator (CDF) transporter family involved in cellular metal homeostasis. Members of the CDF family are ubiquitously found in all living entities and show principal selectivity for Zn2+, Mn2+, and Fe2+. Little is known regarding metal selectivity determinants of CDFs. We identified a novel cereal member of CDFs in barley, termed HvMTP1, that localizes to the vacuolar membrane. Unlike its close relative AtMTP1, which is highly selective for Zn2+, HvMTP1 exhibits selectivity for both Zn2+ and Co2+ as assessed by its ability to suppress yeast mutant phenotypes for both metals. Expression of HvMTP1/AtMTP1 chimeras in yeast revealed a five-residue sequence within the AtMTP1 N-segment of the His-rich intracytoplasmic loop that confines specificity to Zn2+. Furthermore, mutants of AtMTP1 generated through random mutagenesis revealed residues embedded within transmembrane domain 3 that additionally specify the high degree of Zn2+ selectivity. We propose that the His-rich loop, which might play a role as a zinc chaperone, determines the identity of the metal ions that are transported. The residues within transmembrane domain 3 can also influence metal selectivity, possibly through conformational changes induced at the cation transport site located within the membrane or at the cytoplasmic C-terminal domain. PMID:22139846

Podar, Dorina; Scherer, Judith; Noordally, Zeenat; Herzyk, Pawel; Nies, Dietrich; Sanders, Dale

2012-01-01

91

Metallization and charge-transfer gap closure of transition-metal iodides under pressure  

SciTech Connect

It is shown with resistivity and near-IR absorption measurements that NiI{sub 2}, CoI{sub 2}, and FeI{sub 2} metallize under pressure by closure of the charge-transfer energy gap at pressures of 17, 10, and 23 GPa, respectively, which is close to the antiferromagnetic-diamagnetic transition in NiI{sub 2} and CoI{sub 2}. Thus, the magnetic transitions probably are caused by the metallization; in NiI{sub 2} and CoI{sub 2}, the insulator-metal transitions are first order. Moessbauer and XRD data were also collected. Figs, 46 refs.

Chen, A. Li-Chung

1993-05-01

92

Nanodisperse transition metal electrodes (NTME) for electrochemical cells  

SciTech Connect

Disclosed are transition metal electrodes for electrochemical cells using gel-state and solid-state polymers. The electrodes are suitable for use in primary and secondary cells. The electrodes (either negative electrode or positive electrode) are characterized by uniform dispersion of the transition metal at the nanoscale in the polymer. The transition metal moiety is structurally amorphous, so no capacity fade should occur due to lattice expansion/contraction mechanisms. The small grain size, amorphous structure and homogeneous distribution provide improved charge/discharge cycling performance, and a higher initial discharge rate capability. The cells can be cycled at high current densities, limited only by the electrolyte conductivity. A method of making the electrodes (positive and negative), and their usage in electrochemical cells are disclosed.

Striebel, Kathryn A.; Wen, Shi-Jie

1998-12-01

93

Nanodisperse transition metal electrodes (NTME) for electrochemical cells  

DOEpatents

Disclosed are transition metal electrodes for electrochemical cells using gel-state and solid-state polymers. The electrodes are suitable for use in primary and secondary cells. The electrodes (either negative electrode or positive electrode) are characterized by uniform dispersion of the transition metal at the nanoscale in the polymer. The transition metal moiety is structurally amorphous, so no capacity fade should occur due to lattice expansion/contraction mechanisms. The small grain size, amorphous structure and homogeneous distribution provide improved charge/discharge cycling performance, and a higher initial discharge rate capability. The cells can be cycled at high current densities, limited only by the electrolyte conductivity. A method of making the electrodes (positive and negative), and their usage in electrochemical cells are disclosed.

Striebel, Kathryn A. (Oakland, CA); Wen, Shi-Jie (Sunnyvale, CA)

2000-01-01

94

Transition metal-substituted cobalt ferrite nanoparticles for biomedical applications.  

PubMed

Transition metals of copper, zinc, chromium and nickel were substituted into cobalt ferrite nanoparticles via a sol-gel route using citric acid as a chelating agent. The microstructure and elemental composition were characterized using scanning electron microscopy combined with energy-dispersive X-ray spectroscopy. Phase analysis of transition metal-substituted cobalt ferrite nanoparticles was performed via X-ray diffraction. Surface wettability was measured using the water contact angle technique. The surface roughness of all nanoparticles was measured using profilometry. Moreover, thermogravimetric analysis and differential scanning calorimetry were performed to determine the temperature at which the decomposition and oxidation of the chelating agents took place. Results indicated that the substitution of transition metals influences strongly the microstructure, crystal structure and antibacterial property of the cobalt ferrite nanoparticles. PMID:23137676

Sanpo, Noppakun; Berndt, Christopher C; Wen, Cuie; Wang, James

2013-03-01

95

Magnetic states of transition metal impurities in silicon carbide.  

PubMed

Electronic properties of 3C silicon carbide with substitutional transition metal impurities are calculated using an ab initio full-potential linearized augmented plane wave technique. It is shown that transition metal atoms in an SiC host may exist in both magnetic and nonmagnetic states. For different impurity species, the transition from the nonmagnetic to the magnetic state and the corresponding change of the atomic magnetic moments may take place either gradually as the volume of the unit cell changes or when the energy gap between the two states is overcome. The magnetic and nonmagnetic solutions are characterized by significantly different unit cell geometries, which are analysed in detail. Magnetic ordering is studied for a number of transition metal impurities in SiC and mean-field estimates of the Curie temperature are given. Calculated densities of states are used to analyse the nature of the exchange interaction between the impurities. Some properties of transition metal impurities are compared for 3C and 4H silicon carbide substitution. PMID:21825541

Los, Andrei; Los, Victor

2009-05-20

96

Transition-metal acceptor complexes in zinc oxide  

NASA Astrophysics Data System (ADS)

The incorporation of hydrogen shallow donors gives rise to Mn2+ fine and hyperfine lines in the electron paramagnetic resonance of ZnO. This cannot be explained by recharging of isolated Mn atoms. First-principles density functional calculations reveal that transition metals readily form complexes with acceptors by a charge-transfer process or by bond formation. This mechanism has implications on both complex partners. Acceptors are neutralized and uncommon charge states of the transition metals are stabilized. Implications for dilute magnetic ZnO are discussed.

Gluba, M. A.; Nickel, N. H.

2013-02-01

97

Bias-induced insulator-metal transition in organic electronics  

NASA Astrophysics Data System (ADS)

The authors investigate the bias-induced insulator-metal transition in organic electronics devices on the basis of the Su-Schrieffer-Heeger model [W. P. Su et al., Phys. Rev. B 22, 2099 (1980)] combined with the nonequilibrium Green's function formalism. The insulator-metal transition is explained with the energy level crossover that eliminates the Peierls phase [R. Peierls, Quantum Theory of Solids (Oxford University Press, Oxford, 1955)] and delocalizes the electron states near the threshold voltage. This may account for the experimental observations on the devices that exhibit intrinsic bistable conductance switching with large on-off ratio.

Wei, J. H.; Xie, S. J.; Mei, L. M.; Yan, YiJing

2007-07-01

98

Fracture Toughness of Metallic Glasses: Ductile-to-Brittle Transition?  

E-print Network

Quantitative understanding of the fracture toughness of metallic glasses, including the associated ductile-to-brittle transitions, is not yet available. Here we use a simple model of plastic deformation in glasses, coupled to an advanced Eulerian level set formulation for solving complex free boundary problems, to calculate the fracture toughness of metallic glasses as a function of the degree of structural relaxation corresponding to different annealing times near the glass temperature. Our main result indicates the existence of an elasto-plastic crack tip instability for sufficiently relaxed glasses, resulting in a marked drop in the toughness, which we interpret as a ductile-to-brittle transition similar to experimental observations.

Rycroft, Chris H

2012-01-01

99

Synergy of polydimethylsiloxanes and late transition metal complexes  

Microsoft Academic Search

The fluxional behaviors of organosilicon groups on cyclopentadienyl derivatives were assessed in the presence and absence of late transition metal centers and, in separate work, the catalytic activity of transition metal complexes were examined in a siloxane environment. ^ Dichloro-methyl-(2,3,4,5-tetramethyl-cyclopentadienyl)-silane CpMe 4H(SiMeCl2) showed reversible variable-temperature 1H, 13C and 29Si NMR spectra without producing either Diels-Alder adducts or decomposition products. The

Masaaki Amako

2005-01-01

100

Tunable Superconducting Phase Transition in Metal-Decorated Graphene Sheets  

Microsoft Academic Search

Using typical experimental techniques it is difficult to separate the effects\\u000aof carrier density and disorder on the superconducting transition in two\\u000adimensions. Using a simple fabrication procedure based on metal layer\\u000adewetting, we have produced graphene sheets decorated with a non-percolating\\u000anetwork of nanoscale tin clusters. These metal clusters both efficiently dope\\u000athe graphene substrate and induce long-range superconducting

B. M. Kessler; . . Girit; A. Zettl; V. Bouchiat

2010-01-01

101

Peierls transition in two-dimensional metallic monophosphate tungsten bronzes  

Microsoft Academic Search

The two-dimensional metallic bronzes made of ReO3-type layers of MoO6 or WO6 octahedra present quasi-one-dimensional (1D) electronic structures along three directions of preferential overlap of the t2g transition metal orbitals. They exhibit a Peierls instability towards the formation of charge density waves (CDW) at the 2kF critical wave vector allowing to nest simultaneously the Fermi surfaces associated to two quasi-1D

P. Foury-Leylekian; J.-P. Pouget

2002-01-01

102

Charge dependence of chemisorption patterns for transition metal clusters  

Microsoft Academic Search

A method is presented for the measurement of the chemisorptive reactivity of transition metal cluster ions at near room temperature. Similar to a technique introduced previously for neutral clusters [Rev. Sci. Instrum. 56, 2123 (1985)], this cluster ion method utilizes a fast-flow reactor attached to a supersonic, laser vaporization metal cluster source, followed by time-of-flight mass spectral analysis of the

P. J. Brucat; C. L. Pettiette; S. Yang; L.-S. Zheng; M. J. Craycraft; R. E. Smalley

1986-01-01

103

The transition from population III to population II star formation in the early universe  

NASA Astrophysics Data System (ADS)

The first stars in the universe formed in a unique environment that was free of heavy elements. The lack of efficient radiative cooling in primordial gas meant that the collapse of the first star-forming cloud-cores proceeded very slowly and without fragmenting into multiple objects. This resulted in the first stars being very massive (30 [Special characters omitted.] <= M <= 300 [Special characters omitted.] ), isolated objects. When these stars died, in violent supernovae, they produced the very first heavy elements, or metals, and dispersed them into the surrounding gas. The addition of these metals changed forever the way stars formed by allowing the gas to cool much more efficiently as it collapsed. It is thought that when the chemical abundance in the next generation star-forming environments reached a critical level, the process of star-formation began producing stars that resemble those observed in the local universe, with characteristic masses of ~1 [Special characters omitted.] , instead of the behemoths of the early universe. Simulating this transition in star-formation mode requires the inclusion of the complex chemistry and radiative cooling of heavy elements, which has traditionally been too computationally expensive to be done properly in three- dimensional simulations. In this dissertation, I introduce a new method for treating the radiative cooling from metals in large-scale, three-dimensional hydrodynamic simulations that is fast, accurate, and complete in its coverage of the first 30 elements. I use this cooling method to examine the ability of metals to induce fragmentation in collapsing gas-clouds through lowering of the cooling time-scales and the creation of thermal instabilities. Comparing the cooling and dynamical time-scales within collapsing gas, I calculate that the critical metallicity, Z cr , required for fragmentation into multiple, low-mass objects is ~10 -4.2 [Special characters omitted.] , where [Special characters omitted.] denotes the metallicity of the sun. Thermal instabilities are also present in gas-clouds with metallicities, Z >= 10^-4 [Special characters omitted.] . I use the methodology introduced here to perform a series of adaptive mesh refinement hydrodynamic simulations of pre-enriched primordial star-formation with varying metallicities. For metallicities below Z cr , only massive, singular objects form, nearly identical to the metal-free case. For metallicities well above Z cr , efficient cooling rapidly lowers the gas temperature to the temperature of the cosmic microwave background (CMB), which is significantly higher in the distant past. The gas is physically unable to radiatively cool below the CMB temperature, and thus, becomes very thermally stable. For moderately high metallicities, Z >= 10 -3.5 [Special characters omitted.] , this occurs early in the evolution of the gas-cloud, when the central density is still relatively low. The resulting cloud-cores show little or no fragmentation, and have mass-scales of a few hundred [Special characters omitted.] . On the other hand, if the metallicity is only slightly above Z cr , the cloud slowly cools without ever reaching the CMB temperature. In this case, the minimum cloud temperature is achieved at much higher densities than in the high-metallicity case, resulting in mass-scales of just a few [Special characters omitted.] . This implies that not 2, but 3 star-formation modes were present in the early universe: primordial (high-mass), metallicity-regulated (low-mass), and CMB-regulated (moderate-mass). As the universe evolves to the current epoch, the CMB-regulated mode will slowly transition into the metallicity-regulated mode, as the CMB temperature gradually decreases. This suggests that the metallicity-regulated mode, which is fully dominant today, may not become so until the CMB temperature drops below the observed temperatures of molecular clouds, ~10 K, which does not occur until redshift, z ~ 2.

Smith, Britton Devon

104

The Electronic Structure of Transition Metal Coated Fullerenes  

NASA Astrophysics Data System (ADS)

Clusters composed of fullerene molecules with an outer shell of transition metal atoms in the composition C_60M_62 (M being a transition metal) have been produced with laser vaporisation techniques(F. Tast, N. Malinowski, S. Frank, M. Heinebrodt, I.M.L. Billas, and T. P. Martin, Z. Phys D 40), 351 (1997).. We have studied several of these very large systems with a parallel version of the all-electron NRLMOL cluster code. Optimized geometries of the metal encased fullerenes C_60Ti_62 and C_60V_62 are presented along with their HOMO-LUMO gaps, electron affinities, ionization energies, and cohesive energies. We compare the stability of these clusters to relaxed met-car structures (e.g. Ti_8C_12) and to relaxed rocksalt metal-carbide fragments (TiC)n with n=8 and 32. In addition to metal-coated fullerenes we consider the possibility of a trilayered structure consisting of a small shell of metal atoms enclosed by a metal coated fullerene. The nature of bonding in these systems is analyzed by studying the electronic charge distributions.

Patton, David C.; Pederson, Mark R.; Kaxiras, Efthimios

1998-03-01

105

How absorbed hydrogen affects the catalytic activity of transition metals.  

PubMed

Heterogeneous catalysis is commonly governed by surface active sites. Yet, areas just below the surface can also influence catalytic activity, for instance, when fragmentation products of catalytic feeds penetrate into catalysts. In particular, H absorbed below the surface is required for certain hydrogenation reactions on metals. Herein, we show that a sufficient concentration of subsurface hydrogen, H(sub) , may either significantly increase or decrease the bond energy and the reactivity of the adsorbed hydrogen, H(ad) , depending on the metal. We predict a representative reaction, ethyl hydrogenation, to speed up on Pd and Pt, but to slow down on Ni and Rh in the presence of H(sub) , especially on metal nanoparticles. The identified effects of subsurface H on surface reactivity are indispensable for an atomistic understanding of hydrogenation processes on transition metals and interactions of hydrogen with metals in general. PMID:25294745

Aleksandrov, Hristiyan A; Kozlov, Sergey M; Schauermann, Swetlana; Vayssilov, Georgi N; Neyman, Konstantin M

2014-12-01

106

The Electrochemical Synthesis of Transition-Metal Acetylacetonates  

ERIC Educational Resources Information Center

The electrochemical synthesis of transition-metal acetylacetonates described here can form the basis of assisting in the transformation of an entry-level laboratory course into a research-like environment where all members of a class are working on the same problem, but where each member has a personal responsibility for the synthesis and

Long, S. R.; Browning, S. R.; Lagowski, J. J.

2008-01-01

107

Strain effects in low-dimensional transition metal oxides  

Microsoft Academic Search

Transition metal oxides offer a wide spectrum of properties which provide the foundation for a broad range of potential applications. Many of these properties originate from intrinsic coupling between lattice deformation and nanoscale electronic and magnetic ordering. Lattice strain thus has a profound influence on the electrical, optical, and magnetic properties of these materials. Recent advances in materials processing have

Jinbo Cao; Junqiao Wu

2011-01-01

108

Nano Fabrication of Functional Transition Metal Oxide Thin Films  

Microsoft Academic Search

Transition metal oxide films show a rich variety of peculiar properties, such as ferroelectricity, ferromagnetism, high Tc superconductivity, colossal magnetoresistance, and so on. The method to process the oxide films down to nano scale is still under development. In this paper we introduce several techniques to process oxide films on the basis of AFM lithography and nanoimprint lithography. Using AFM

Naoki Suzuki; Hidekazu Tanaka; Yoshihiko Yanagisawa; Satoru Yamanaka; Luca Pellegrino; Bong Kuk Lee; Hea Yeon Lee; Tomoji Kawai

2008-01-01

109

Electrochemistry of transition metal single crystals with well defined surfaces  

Microsoft Academic Search

The effect of extended defects of the surface of metallic single crystals on the electrochemical processes of dissolution and formation of a new phase has been analysed. Theoretical ideas on the rearrangement of a crystal surface (phase transitions of the second kind) during the adsorption of surface-active substances are presented. The reconstruction (faceting) of the surface under the influence of

Gennadii V. Khaldeev; T. A. Syur

1992-01-01

110

Metallic phase transition investigated via terahertz time-domain spectroscopy  

E-print Network

of surface particle plasmons in- duced dipolar surface charge on the individual particles,9 the amplitudeMetallic phase transition investigated via terahertz time-domain spectroscopy K. J. Chau,a K. M; accepted 15 December 2006; published online 26 January 2007 Terahertz time-domain spectroscopy is applied

Chau, Kenneth

111

The Existence of Pure?Phase Transition Metal Hydroxy Apatites  

Microsoft Academic Search

The existence of pure?phase transition metal hydroxy apatites of zinc, copper, manganese, and cobalt could not be verified by repeated attempts to duplicate the few literature procedures reported for their preparation in aqueous solution. Variations of temperature, time of reactions, pH, and use of decomplexation also did not produce apatitic compounds. In the case of zinc, the product resulting from

Claude H. Yoder; Nathan Fedors; Natalie J. Flora; Heather Brown; Keith Hamilton; Charles D. Schaeffer Jr

2004-01-01

112

Luminescent molecular rods - transition-metal alkynyl complexes.  

PubMed

A number of transition-metal complexes have been reported to exhibit rich luminescence, usually originating from phosphorescence. Such luminescence properties of the triplet excited state with a large Stoke's shift, long lifetime, high luminescence quantum yield as well as lower excitation energy, are envisaged to serve as an ideal candidate in the area of potential applications for chemosensors, dye-sensitized solar cells, flat panel displays, optics, new materials and biological sciences. Organic alkynes (poly-ynes), with extended or conjugated?-systems and rigid structure with linear geometry, have become a significant research area due to their novel electronic and physical properties and their potential applications in nanotechnology. Owing to the presence of unsaturated sp-hybridized carbon atoms, the alkynyl unit can serve as a versatile building block in the construction of alkynyl transition-metal complexes, not only through?-bonding but also via?-bonding interactions. By incorporation of linear alkynyl groups into luminescent transition-metal complexes, the alkynyl moiety with good?-donor,?-donor and?-acceptor abilities is envisaged to tune or perturb the emission behaviors, including emission energy (color), intensity and lifetime by its role as an auxiliary ligand as well as to govern the emission origin from its direct involvement. This review summarizes recent efforts on the synthesis of luminescent rod-like alkynyl complexes with different classes of transition metals and details the effects of the introduction of alkynyl groups on the luminescence properties of the complexes. PMID:22179333

Yam, Vivian Wing-Wah; Wong, Keith Man-Chung

2005-01-01

113

Hall effect at a tunable metal-insulator transition  

E-print Network

Using a rotating magnetic field, the Hall effect in three-dimensional amorphous GdxSi1-x has been measured in the critical regime of the metal-insulator transition for a constant total magnetic field. The Hall coefficient R-0 is negative, indicating...

Teizer, Winfried; Hellman, F.; Dynes, RC.

2003-01-01

114

Epoxy nanocomposites with two-dimensional transition metal dichalcogenide additives.  

PubMed

Emerging two-dimensional (2D) materials such as transition metal dichalcogenides offer unique and hitherto unavailable opportunities to tailor the mechanical, thermal, electronic, and optical properties of polymer nanocomposites. In this study, we exfoliated bulk molybdenum disulfide (MoS2) into nanoplatelets, which were then dispersed in epoxy polymers at loading fractions of up to 1% by weight. We characterized the tensile and fracture properties of the composite and show that MoS2 nanoplatelets are highly effective at enhancing the mechanical properties of the epoxy at very low nanofiller loading fractions (below 0.2% by weight). Our results show the potential of 2D sheets of transition metal dichalcogenides as reinforcing additives in polymeric composites. Unlike graphene, transition metal dichalcogenides such as MoS2 are high band gap semiconductors and do not impart significant electrical conductivity to the epoxy matrix. For many applications, it is essential to enhance mechanical properties while also maintaining the electrical insulation properties and the high dielectric constant of the polymer material. In such applications, conductive carbon based fillers such as graphene cannot be utilized. This study demonstrates that 2D transition metal dichalcogenide additives offer an elegant solution to such class of problems. PMID:24754702

Eksik, Osman; Gao, Jian; Shojaee, S Ali; Thomas, Abhay; Chow, Philippe; Bartolucci, Stephen F; Lucca, Don A; Koratkar, Nikhil

2014-05-27

115

Polyanilinetransition metal salt complexes: insight into formation mechanisms  

Microsoft Academic Search

Two basic morphologies of emeraldine base of polyanilinetransition metal salt complex films cast from N-methylpyrrolidinone solutions are described. The first morphology consists of grains and the other consists of loose aggregates, respectively. The correlation of the film morphology with formation of precipitate in the complex solution, kinetics of solvent evaporation from the cast film, amount of solvent entrapped in the

O. P. Dimitriev; P. S. Smertenko; B. Stiller; L. Brehmer

2005-01-01

116

Transition Metal Photoredox Catalysis of Radical Thiol-Ene Reactions  

PubMed Central

We describe the anti-Markovnikov hydrothiolation of olefins using visible light absorbing transition metal photocatalysts. The key thiyl radical intermediates are generated upon quenching of photoexcited Ru*(bpz)32 with a variety of thiols. The adducts of a wide variety of olefins and thiols are formed in excellent yield (7399%). PMID:23094660

Tyson, Elizabeth L.; Ament, Michael S.

2012-01-01

117

Effect of Spin State on the Dihydrogen Binding Strength to Transition Metal Centers in Metal-Organic Frameworks  

SciTech Connect

In several recent experimental studies, it has been found that exposed transition metal (TM) sites in metal-organic frameworks (MOFs) yield the largest binding to H2 by about 10 kJ/mol. However, this binding is significantly smaller than what has been observed in the so-called Kubas molecules, also with exposed metal sites. Our ab initio calculations quantitatively account for the experimental findings and further show that the splitting and occupation of the spin orbitals in the MOF systems are the reasons for their unexpected small binding energies. We predict that the binding energy to H2 in the MOF systems can be tuned between 10 and 50 kJ/mol by using early TM elements, namely, Sc, Ti, V, Cr, and Mn.

Sun, Y. Y.; Kim, Y. H.; Zhang, S. B.

2007-01-01

118

Oxide Electronics Utilizing Ultrafast Metal-Insulator Transitions  

NASA Astrophysics Data System (ADS)

Although phase transitions have long been a centerpiece of condensed matter materials science studies, a number of recent efforts focus on potentially exploiting the resulting functional property changes in novel electronics and photonics as well as understanding emergent phenomena. This is quite timely, given a grand challenge in twenty-first-century physical sciences is related to enabling continued advances in information processing and storage beyond conventional CMOS scaling. In this brief review, we discuss synthesis of strongly correlated oxides, mechanisms of metal-insulator transitions, and exploratory electron devices that are being studied. Particular emphasis is placed on vanadium dioxide, which undergoes a sharp metal-insulator transition near room temperature at ultrafast timescales. The article begins with an introduction to metal-insulator transition in oxides, followed by a brief discussion on the mechanisms leading to the phase transition. The role of materials synthesis in influencing functional properties is discussed briefly. Recent efforts on realizing novel devices such as field effect switches, optical detectors, nonlinear circuit components, and solid-state sensors are reviewed. The article concludes with a brief discussion on future research directions that may be worth consideration.

Yang, Zheng; Ko, Changhyun; Ramanathan, Shriram

2011-08-01

119

Continuity and Respect for Diversity: Strengthening Early Transitions in Peru. Working Papers in Early Childhood Development, No. 56. Studies in Early Childhood Transitions  

ERIC Educational Resources Information Center

This working paper is part of a series on early transitions from "Young Lives," a 15-year longitudinal study of childhood poverty in Ethiopia, India, Peru and Vietnam. It explores the diverse experiences of 28 children from four contrasting communities in Peru as they start school. These detailed case studies highlight common problems: exclusion

Ames, Patricia; Rojas, Vanessa; Portugal, Tamia

2010-01-01

120

Mechanical failure and glass transition in metallic glasses  

SciTech Connect

The current majority view on the phenomenon of mechanical failure in metallic glasses appears to be that it is caused by the activity of some structural defects, such as free-volumes or shear transformation zones, and the concentration of such defects is small, only of the order of 1%. However, the recent results compel us to revise this view. Through molecular dynamics simulation it has been shown that mechanical failure is the stress-induced glass transition. According to our theory the concentration of the liquid-like sites (defects) is well over 20% at the glass transition. We suggest that the defect concentration in metallic glasses is actually very high, and percolation of such defects causes atomic avalanche and mechanical failure. In this article we discuss the glass transition, mechanical failure and viscosity from such a point of view.

Egami, Takeshi [ORNL

2011-01-01

121

Differential ability of transition metals to induce pulmonary inflammation.  

PubMed

Transition metals are components of airborne particles and have been implicated in adverse health effects. The relative inflammatory potential of these metals is usually inferred from separate studies that focus on only one or a few individual metals. Comparisons of relative potency among several metals from these separate studies can be difficult. In one comprehensive study, we measured the pulmonary effects of equimolar doses of six metals in soluble form. Our purpose was to compare inflammatory potential and pulmonary toxicity among individual transition metals. Rats received saline, 0.1 or 1.0 micromol/kg of vanadium, nickel, iron(II), copper, manganese, or zinc as sulfates. Bronchoalveolar lavage (BAL) was performed at 0, 4, 16, or 48 h postinstillation. All treatments except V showed increased lactate dehydrogenase activity in BAL fluid; Cu- and Ni-exposed animals had the highest levels. Protein levels in BAL fluid were more than five times higher in Cu-exposed animals compared to other metal treatments at 16 and 48 h. At the 0.1 micromol/kg dose, only Cu induced significant neutrophilia at 16 and 48 h. For the 1.0 micromol/kg dose, all metals tested induced significant neutrophilia, with mean neutrophil numbers for Cu and Mn significantly higher compared to the other metals. At 48 h, neutrophil numbers were still elevated in all metal exposures. Only Mn caused substantial eosinophilia. At the 1.0 micromol/kg dose, only Cu induced macrophage inflammatory protein-2 (MIP-2) mRNA at 4 h. By 48 h, induction of MIP-2 mRNA was observed for all metal exposures except Cu, which subsequently returned to baseline levels. On an equimolar basis, Cu was the most proinflammatory metal, followed by Mn and Ni, while V, Fe(II), and Zn induced similar levels of inflammation. Overall, there were many similarities in the pulmonary responses of the metals we tested. However, we also observed divergent, metal-specific responses. These differential responses suggest that metals induce pulmonary inflammation by differing pathways or combinations of signals. PMID:11708899

Rice, T M; Clarke, R W; Godleski, J J; Al-Mutairi, E; Jiang, N F; Hauser, R; Paulauskis, J D

2001-11-15

122

Kentucky Early Childhood Transition Project. Evaluation Report: Quality and Impact of Transition Training and Technical Assistance Services  

ERIC Educational Resources Information Center

The Kentucky Early Childhood Transition Project (KECTP) was funded in 1992 by the Kentucky Department of Education and later expanded with support from the Kentucky Early Intervention System, to provide training and technical assistance to local communities in the state of Kentucky on effective transitions. KECTP was an outgrowth of Project STEPS,

Interdisciplinary Human Development Institute, 2002

2002-01-01

123

Quantifying covalency and metallicity in correlated compounds undergoing metal-insulator transitions  

NASA Astrophysics Data System (ADS)

The tunability of bonding character in transition-metal compounds controls phase transitions and their fascinating properties such as high-temperature superconductivity, colossal magnetoresistance, spin-charge ordering, etc. However, separating out and quantifying the roles of covalency and metallicity derived from the same set of transition-metal d and ligand p electrons remains a fundamental challenge. In this study, we use bulk-sensitive photoelectron spectroscopy and configuration-interaction calculations for quantifying the covalency and metallicity in correlated compounds. The method is applied to study the first-order temperature- (T-) dependent metal-insulator transitions (MITs) in the cubic pyrochlore ruthenates Tl2Ru2O7 and Hg2Ru2O7. Core-level spectroscopy shows drastic T-dependent modifications which are well explained by including ligand-screening and metallic-screening channels. The core-level metallic-origin features get quenched upon gap formation in valence band spectra, while ionic and covalent components remain intact across the MIT. The results establish temperature-driven Mott-Hubbard MITs in three-dimensional ruthenates and reveal three energy scales: (a) 4d electronic changes occur on the largest (eV) energy scale, (b) the band-gap energies/charge gaps (Eg160-200 meV) are intermediate, and (c) the lowest-energy scale corresponds to the transition temperature TMIT (10 meV), which is also the spin gap energy of Tl2Ru2O7 and the magnetic-ordering temperature of Hg2Ru2O7. The method is general for doping- and T-induced transitions and is valid for V2O3, CrN, La1-xSrxMnO3, La2-xSrxCuO4, etc. The obtained transition-metal-ligand (d-p) bonding energies (V45-90 kcal/mol) are consistent with thermochemical data, and with energies of typical heteronuclear covalent bonds such as C-H, C-O, C-N, etc. In contrast, the metallic-screening energies of correlated compounds form a weaker class (V*10-40 kcal/mol) but are still stronger than van der Waals and hydrogen bonding. The results identify and quantify the roles of covalency and metallicity in 3d and 4d correlated compounds undergoing metal-insulator transitions.

Chainani, Ashish; Yamamoto, Ayako; Matsunami, Masaharu; Eguchi, Ritsuko; Taguchi, Munetaka; Takata, Yasutaka; Takagi, Hidenori; Shin, Shik; Nishino, Yoshinori; Yabashi, Makina; Tamasaku, Kenji; Ishikawa, Tetsuya

2013-01-01

124

Family structure and the transition to early parenthood.  

PubMed

With the rise in out-of-wedlock childbearing and divorce in the last quarter of the twentieth century, an increasing proportion of children have been exposed to a variety of new family forms. Little research has focused on the consequences of childhood family structure for men's transition to fatherhood or on the family processes that account for the effects of family structure on the likelihood that young women and men become first-time unmarried parents, what we now call "fragile families." The data come from the linked Children and Young Adult samples of the 1979 National Longitudinal Survey of Youth (NLSY79), which provide information on the children of the women of the NLSY79 from birth until they enter young adulthood. Females growing up with a single parent and males experiencing an unstable family transition to parenthood early, particularly to nonresidential fatherhood for males. For males, the effects are strongly mediated by parenting processes and adolescent behaviors and are shaped by economic circumstances. Having experienced multiple transitions as a child is associated with a reduced likelihood that males father their first child within marriage and an increased likelihood that they become fathers within cohabitation, demonstrating how changes in family structure alter family structure patterns over time and generations. PMID:20608104

Hofferth, Sandra L; Goldscheider, Frances

2010-05-01

125

Transition-metal-catalyzed C-S bond coupling reaction.  

PubMed

Sulfur-containing molecules such as thioethers are commonly found in chemical biology, organic synthesis, and materials chemistry. While many reliable methods have been developed for preparing these compounds, harsh reaction conditions are usually required in the traditional methods. The transition metals have been applied in this field, and the palladium-catalyzed coupling of thiols with aryl halides and pseudo halides is one of the most important methods in the synthesis of thioethers. Other metals have also been used for the same purpose. Here, we summarize recent efforts in metal-catalyzed C-S bond cross-coupling reactions, focusing especially on the coupling of thiols with aryl- and vinyl halides based on different metals. PMID:24443103

Lee, Chin-Fa; Liu, Yi-Chen; Badsara, Satpal Singh

2014-03-01

126

Alkali metal ion templated transition metal formate framework materials: synthesis, crystal structures, ion migration, and magnetism.  

PubMed

Four transition metal formate coordination polymers with anionic frameworks, namely, Na[Mn(HCOO)3], K[Mn(HCOO)3], Na2[Cu3(HCOO)8], and K2[Cu5(HCOO)12], were synthesized using a mild solution chemistry approach. Multitemperature single-crystal (100-300 K) and powder X-ray diffraction studies of the compounds reveal structures of large diversity ranging from cubic chiral Na-Mn formate to triclinic Na-Cu formate. The structural variety is caused by the nature of the transition metals, the alkali metal ion templation, and the versatility of the formate group, which offers metal-metal coordination through three different O-C-O bridging modes (syn-syn, syn-anti, anti-anti) in addition to metal-metal bridging via a single oxygen atom. The two manganese(II) compounds contain mononuclear, octahedrally coordinated moieties, but the three-dimensional connectivity between the manganese octahedra is very different in the two structures. The two copper frameworks, in contrast, consist of binuclear and mononuclear moieties (Na-Cu formate) and trinuclear and mononuclear moieties (K-Cu formate), respectively. Procrystal electron density analysis of the compounds indicates one-dimensional K(+)-ion conductivity in K-Mn and K-Cu, and the nature of the proposed potassium ion migration is compared with results from similar analysis on known Na(+) and K(+) ion conductors. K-Mn and Na-Mn were tested as cathode materials, but this resulted in poor reversibility due to low conductivity or structural collapse. The magnetic properties of the compounds were studied by vibrating sample magnetometric measurements, and their thermal stabilities were determined by thermogravimetric analysis and differential thermal analysis. Despite structural differences, the metal formates that contain the same transition metal have similar magnetic properties and thermal decomposition pathways, that is, the nature of the transition metal controls the compound properties. PMID:25233266

Eikeland, Espen; Lock, Nina; Fils, Mette; Stingaciu, Marian; Shen, Yanbin; Overgaard, Jacob; Iversen, Bo Brummerstedt

2014-10-01

127

Wetting Transition of Classical Gases on Alkali Metals  

NASA Astrophysics Data System (ADS)

This talk will review recent discoveries of wetting transitions of classical gases on alkali metals. The transitions occur because the adsorption potentials on these surfaces are less attractive than those on any other surface(A. Chizmeshya, M. W. Cole, and E. Zaremba, J. Low Temp. Phys., in press.). Hence, relatively little adsorption occurs at temperature (T) close to the triple temperature. At higher T, wetting transitions are expected to occur, according to general arguments of Cahn and Ebner and Saam. Indeed, these have been found for all inert light gases on Cs and Rb. The talk will focus on recent experiments and simulations for the case of Ne, the results of which include evidence of a drying transition(G. B. Hess, M. J. Sabatini and M. H. W. Chan, Phys. Rev. Lett. 78, 1739 (1997); M. J. Bojan, M. W. Cole, J. K. Johnson, W. A. Steele and Q. Wang, J. Low Temp. Phys., in press.). Experiments are proposed to test predictions of wetting transitions for Ar and Kr on alkali metals.

Cole, Milton W.

1998-03-01

128

Cross-linking proteins with bimetallic tetracarboxylate compounds of transition metals  

DOEpatents

Stable cross-linked complexes of transition-metal tetracarboxylates and proteins are formed. The preferred transition-metal is rhodium. The protein may be collagen or an enzyme such as a proteolytic enzyme.

Kostic, Nenad M. (Ames, IA); Chen, Jian (Ames, IA)

1991-03-05

129

An Alternative Approach to the Teaching of Systematic Transition Metal Chemistry.  

ERIC Educational Resources Information Center

Presents an alternative approach to teaching Systematic Transition Metal Chemistry with the transition metal chemistry skeleton features of interest. The "skeleton" is intended as a guide to predicting the chemistry of a selected compound. (Author/SA)

Hathaway, Brian

1979-01-01

130

Cross-linking proteins with bimetallic tetracarboxylate compounds of transition metals  

DOEpatents

Stable cross-linked complexes of transition-metal tetracarboxylates and proteins are formed. The preferred transition-metal is rhodium. The protein may be collagen or an enzyme such as a proteolytic enzyme. No Drawings

Kostic, N.M.; Chen, J.

1991-03-05

131

Strain-induced semimetal-metal transition in silicene  

NASA Astrophysics Data System (ADS)

The effect of the tensile strain on the electronic structure of the silicene is studied by using first-principles density functional theory. It is found that a semimetal-metal transition occurs when an in-plane strain larger than 7.5% is applied in silicene. The downward movement of the lowest conduction band at ?-point, which originates from the weakened interaction between neighboring Si atoms, leads to the transition. The proposed mechanical control of the electronic properties will widen the application of the silicene in Si-based nanotechnology.

Liu, G.; Wu, M. S.; Ouyang, C. Y.; Xu, B.

2012-07-01

132

Holographic Polarons, the Metal-Insulator Transition and Massive Gravity  

E-print Network

Massive gravity is holographically dual to `realistic' materials with momentum relaxation. The dual graviton potential encodes the phonon dynamics and it allows for a much broader diversity than considered so far. We construct a simple family of isotropic and homogeneous materials that exhibit an interaction-driven Metal-Insulator transition. The transition is triggered by the formation of polarons -- phonon-electron quasi-bound states that dominate the conductivities, shifting the spectral weight above a mass gap. We characterize the polaron gap, width and dispersion.

Baggioli, Matteo

2014-01-01

133

Electronic and bonding analysis of hardness in pyrite-type transition-metal pernitrides  

NASA Astrophysics Data System (ADS)

Most commonly known hard transition-metal nitrides crystallize in rocksalt structure (B1). The discovery of ultraincompressible pyrite-type PtN2 10 years ago has raised a question about the cause of its exceptional mechanical properties. We answer this question by a systematic computational analysis of the pyrite-type PtN2 and other transition-metal pernitrides (MN2) with density functional theory. Apart from PtN2, the three hardest phases are found among them in the 3d transition-metal period. They are MnN2, CoN2, and NiN2, with computed Vickers hardness (HV) values of 19.9 GPa, 16.5 GPa, and 15.7 GPa, respectively. Harder than all of these is PtN2, with a HV of 23.5 GPa. We found the following trends and correlations that explain the origin of hardness in these pernitrides. (a) Charge transfer from M to N controls the length of the N-N bond, resulting in a correlation with bulk modulus, dominantly by providing Coulomb repulsion between the pairing N atoms. (b) Elastic constant C44, an indicator of mechanical stability and hardness is correlated with total density of states at EF, an indicator of metallicity. (c) Often cited monotonic variation of HV and Pugh's ratio with valence electron concentration found in rocksalt-type early transition-metal nitrides is not evident in this structure. (d) The change in M-M bond strength under a shearing strain indicated by crystal orbital Hamilton population is predictive of hardness. This is a direct connection between a specific bond and shear related mechanical properties. This panoptic view involving ionicity, metallicity, and covalency is essential to obtain a clear microscopic understanding of hardness.

Liu, Z. T. Y.; Gall, D.; Khare, S. V.

2014-10-01

134

Resonant Ultrasound Studies of Complex Transition Metal Oxides  

SciTech Connect

Department of Energy EPSCoR The University of Mississippi Award: DE-FG02-04ER46121 Resonant Ultrasound Spectroscopy Studies of Complex Transition Metal Oxides The central thrust of this DOE funded research program has been to apply resonant ultrasound spectroscopy (RUS), an elegant and efficient method for determining the elastic stiffness constants of a crystal, to the complex and poorly understood class of materials known as transition metal oxides (TMOs). Perhaps the most interesting and challenging feature of TMOs is their strongly correlated behavior in which spin, lattice, and charge degrees of freedom are strongly coupled. Elastic constants are a measure of the interatomic potentials in a crystal and are thus sensitive probes into the atomic environment. This sensitivity makes RUS an ideal tool to study the coupling of phase transition order parameters to lattice strains. The most significant result of the project has been the construction of a high temperature RUS apparatus capable of making elastic constant measurements at temperatures as high as 1000 degrees Celsius. We have designed and built novel acoustic transducers which can operate as high as 600 degrees Celsius based on lithium niobate piezoelectric elements. For measurement between 600 to 1000 C, a buffer rod system is used in which the samples under test and transducers are separated by a rod with low acoustic attenuation. The high temperature RUS system has been used to study the charge order (CO) transition in transition metal oxides for which we have discovered a new transition occurring about 35 C below the CO transition. While the CO transition exhibits a linear coupling between the strain and order parameter, this new precursor transition shows a different coupling indicating a fundamentally different mechanism. We have also begun a study, in collaboration with the Jet Propulsion Laboratory, to study novel thermoelectric materials at elevated temperatures. These materials include silicon germanium with various doping and Zintl phase materials. Such materials show promise for increased figures of merit, vital to making thermolectrics competitive with traditional power generation mechanisms.

Dr. Henry Bass; Dr. J. R. Gladden

2008-08-18

135

Novel photoinduced phase transitions in transition metal oxides and diluted magnetic semiconductors  

NASA Astrophysics Data System (ADS)

Some transition metal oxides have frustrated electronic states under multiphase competition due to strongly correlated d electrons with spin, charge, and orbital degrees of freedom and exhibit drastic responses to external stimuli such as optical excitation. Here, we present photoemission studies on Pr0.55(Ca1 - y Sr y )0.45MnO3 ( y = 0.25), SrTiO3, and Ti1 - x Co x O2 ( x = 0.05, 0.10) under laser illumination and discuss electronic structural changes induced by optical excitation in these strongly correlated oxides. We discuss the novel photoinduced phase transitions in these transition metal oxides and diluted magnetic semiconductors on the basis of polaronic pictures such as orbital, ferromagnetic, and ferroelectric polarons.

Mizokawa, Takashi

2012-10-01

136

Dynamics and Control in Complex Transition Metal Oxides  

NASA Astrophysics Data System (ADS)

Advances in the synthesis, growth, and characterization of complex transition metal oxides coupled with new experimental techniques in ultrafast optical spectroscopy have ushered in an exciting era of dynamics and control in these materials. Experiments utilizing femtosecond optical pulses can initiate and probe dynamics of the spin, lattice, orbital, and charge degrees of freedom. Major goals include (a) determining how interaction and competition between the relevant degrees of freedom determine macroscopic functionality in transition metal oxides (TMOs) and (b) searching for hidden phases in TMOs by controlling dynamic trajectories in a complex and pliable energy landscape. Advances in creating intense pulses from the far-IR spectrum through the visible spectrum enable mode-selective excitation to facilitate exploration of these possibilities. This review covers recent developments in this emerging field and presents examples that include the cuprates, manganites, and vanadates.

Zhang, J.; Averitt, R. D.

2014-07-01

137

Recent Advances in Transition Metal-Catalyzed Glycosylation  

PubMed Central

Having access to mild and operationally simple techniques for attaining carbohydrate targets will be necessary to facilitate advancement in biological, medicinal, and pharmacological research. Even with the abundance of elegant reports for generating glycosidic linkages, stereoselective construction of ?- and ?-oligosaccharides and glycoconjugates is by no means trivial. In an era where expanded awareness of the impact we are having on the environment drives the state-of-the-art, synthetic chemists are tasked with developing cleaner and more efficient reactions for achieving their transformations. This movement imparts the value that prevention of waste is always superior to its treatment or cleanup. This review will highlight recent advancement in this regard by examining strategies that employ transition metal catalysis in the synthesis of oligosaccharides and glycoconjugates. These methods are mild and effective for constructing glycosidic bonds with reduced levels of waste through utilization of sub-stoichiometric amounts of transition metals to promote the glycosylation. PMID:22924154

McKay, Matthew J.; Nguyen, Hien M.

2012-01-01

138

Wetting Transitions of Inert Gases on Alkali Metal Surfaces  

NASA Astrophysics Data System (ADS)

Theoretical and experimental discoveries have been made recently of wetting and prewetting transitions of helium and hydrogen films on alkali metal surfaces [1,2]. New experiments show anomalous nonwetting behavior of Ne on Rb and Cs [3]. Building on earlier work [4], we have done and will describe results from the first Monte Carlo simulations showing wetting transitions for classical gases on alkali metal surfaces. * Research supported by an NSF Materials Research Group grant. 1. R. B.Hallock, J. Low Temp. Phys. 101, 31, 1995 2. M. W. Cole, J. Low Temp. Phys. 101, 25, 1995. 3. G. B. Hess, M. Sabatini, and M. H. W. Chan, unpublished 4. J. E. Finn and P. A. Monson, Phys. Rev. A 39, 6402, 1989.

Bojan, M. J.; McDonald, I. A.; Cole, M. W.; Steele, W. A.

1996-03-01

139

Probing early-universe phase transitions with CMB spectral distortions  

NASA Astrophysics Data System (ADS)

Global, symmetry-breaking phase transitions in the early universe can generate scaling seed networks which lead to metric perturbations. The acoustic waves in the photon-baryon plasma sourced by these metric perturbations, when Silk damped, generate spectral distortions of the cosmic microwave background (CMB). In this work, the chemical potential distortion (? ) due to scaling seed networks is computed and the accompanying Compton y -type distortion is estimated. The specific model of choice is the O (N ) nonlinear ? -model for N ?1 , but the results remain the same order of magnitude for other scaling seeds. If CMB anisotropy constraints to the O (N ) model are saturated, the resulting chemical potential distortion ? ?2 1 0-9 .

Amin, Mustafa A.; Grin, Daniel

2014-10-01

140

Dense Electron System from Gate-Controlled Surface Metal-Insulator Transition  

E-print Network

Dense Electron System from Gate-Controlled Surface Metal- Insulator Transition Kai Liu,,, Deyi Fu modulation. A surface insulator-to-metal transition is electrostatically triggered, thereby collapsing: Vanadium dioxide, 2D electron system, electrostatic gating, metal-insulator transition Electric

Wu, Junqiao

141

Multiphase reaction diffusion in transition metal-boron systems  

Microsoft Academic Search

The formation of various diffusion layers in selected transition metal-boron systems was investigated by means of pack-boriding. Samples of commercially pure titanium, molybdenum and tantalum were packed in pre-calcined amorphous boron powder and annealed for 14 h at temperatures between 1200 and 1500C. Experiments were carried out in a high-frequency furnace in inert gas atmosphere (? 500 mbar Ar) or

J. Brandsttter; W. Lengauer

1997-01-01

142

Zwitterionic Group VIII transition metal initiators supported by olefin ligands  

DOEpatents

A zwitterionic Group VIII transition metal complex containing the simple and relatively small 3-(arylimino)-but-1-en-2-olato ligand that catalyzes the formation of polypropylene and high molecular weight polyethylene. A novel feature of this catalyst is that the active species is stabilized by a chelated olefin adduct. The present invention also provides methods of polymerizing olefin monomers using zwitterionic catalysts, particularly polypropylene and high molecular weight polyethylene.

Bazan, Guillermo C. (Goleta, CA); Chen, Yaofeng (Shanghai, CN)

2011-10-25

143

Electrical conductivity of transition metal containing crystalline zirconium phosphate materials  

Microsoft Academic Search

?-Zirconium phosphate (?-ZrP) has been prepared in various transition metal containing forms, and their structure (identified by XRD), thermal behaviour and specific surface area were determined and their electrical resistivity was measured. On the basis of experimental data, the monoclinic cell parameters for Co(II), Ni(II), Cu(II), and Zn(II) containing crystalline zirconium phosphates were calculated. They showed characteristic thermal decomposition and

L Szirtes; J Megyeri; E Kuzmann; Z Klencsr

2001-01-01

144

Tunable Superconducting Phase Transition in Metal-Decorated Graphene Sheets  

Microsoft Academic Search

We have produced graphene sheets decorated with a nonpercolating network of nanoscale tin clusters. These metal clusters both efficiently dope the graphene substrate and induce long-range superconducting correlations. We find that despite structural inhomogeneity on mesoscopic length scales (10-100 nm), this material behaves electronically as a homogenous dirty superconductor with a field-effect tuned Berezinskii-Kosterlitz-Thouless transition. Our facile self-assembly method establishes

B. M. Kessler; . . Girit; A. Zettl; V. Bouchiat

2010-01-01

145

ZnO Doped With Transition Metal Ions  

Microsoft Academic Search

Spin-dependent phenomena in ZnO may lead to devices with new or enhanced functionality, such as polarized solid-state light sources and sensitive biological and chemical sensors. In this paper, we review the experimental results on transition metal doping of ZnO and show that the material can be made with a single phase at high levels of Co incorporation (~15 at.%) and

Stephen J. Pearton; David P. Norton; M. P. Mil; Art F. Hebard; John M. Zavada; Weimin M. Chen; Irina A. Buyanova

2007-01-01

146

Superparamagnetism of transition metal nanoparticles in conducting polymer film  

NASA Astrophysics Data System (ADS)

Magnetic properties of transition metal (cobalt, iron, nickel, manganese, chromium) nanoparticles prepared by ion-exchange method in the perfluorinated sulfo-cation polymeric membrane (MF-4SK) have been investigated. While manganese and chromium in MF-4SK exhibited paramagnetic properties, cobalt, iron and nickel particles showed superparamagnetic behaviors. Our experimental evidence suggests that cobalt, iron and nickel nanoparticles in the polymer film obey a single-domain theory.

Yoon, M.; Kim, Y.; Kim, Y. M.; Yoon, H.; Volkov, V.; Avilov, A.; Park, Y. J.; Park, I.-W.

2004-05-01

147

Superparamagnetism of transition metal nanoparticles in conducting polymer film  

NASA Astrophysics Data System (ADS)

Magnetic properties of transition metal (cobalt, iron, nickel, manganese, chromium) nanoparticles prepared by ion-exchange method in the perfluorinated sulfo-cation polymeric membrane (MF-4SK) have been investigated. While manganese and chromium in MF-4SK exhibited paramagnetic properties, cobalt, iron and nickel particles showed superparamagnetic behaviors. Our experimental evidence suggests that cobalt, iron and nickel nanoparticles in the polymer film obey a single-domain theory.

Yoon, M.; Kim, Y.; Kim, Y. M.; Yoon, H.; Volkov, V.; Avilov, A.; Park, Y. J.; Park, I.-W.

148

Reductive dechlorination catalyzed by bacterial transition-metal coenzymes  

Microsoft Academic Search

The bacterial transition-metal coenzymes vitamin B (Co), coenzyme F (ni), and hematin (Fe) catalyzed the reductive dechlorination of polychlorinated ethylenes and benzenes, whereas the electron-transfer proteins four-iron ferredoxin, two-iron ferredoxin, and azurin (Cu) did not. For vitamin B and coenzyme F, reductive dechlorination rates for different classes of perchlorinated compounds had the following order: carbon tetrachloride > tetrachloroethylene > hexachlorobenzene.

Charles J. Gantzer; Lawrence P. Wackett

1991-01-01

149

The electronic Gruneisen parameter for the transition metals  

Microsoft Academic Search

A generalisation of the Lang-Ehrenreich-Heine model for the transition metals is applied to give specific formulae for their electronic Gruneisen parameters within normal band theory. Numerical values are calculated both with and without consideration of electron-phonon interaction with the aid of data from band calculations. Agreement with the experimental values available is variable but a simple framework for discussing the

G. C. Fletcher; M. Yahaya

1979-01-01

150

The influence of transition metal ions on collagen mineralization.  

PubMed

The ions in body fluid play an important role in bone formation besides being a synthesizing material. Transition metal ions Co(2+), Ni(2+), Zn(2+), Fe(3+), Mn(2+), Cu(2+), Cd(2+) and Hg(2+) doped hydroxyapatite (HAP)/collagen composites were synthesized successfully in the presence of collagen traces at mild acidic pH for the first time. However, the amount of doped Hg(2+) and Cd(2+) was relatively low. Meanwhile, through soaking the collagen sponge as a template in simulated body fluid (SBF) which contains different transition metal ions (Mn(2+), Cu(2+), Ni(2+), Co(2+), Cd(2+), Hg(2+)), bone-like HAP/collagen composites were synthesized. Hg(2+) had a certain inhibitory effect on the formation of HAP crystals on the surface of the collagen sponge while Co(2+) can promote the formation of HAP on the collagen sponge. For both HAP/collagen composites and HAP/collagen sponge, it was found that transition metal ions Mn(2+) had a significant effect on the morphology of HAP particles and could induce to form floc-like HAP particle aggregates. PMID:23498275

Jia, Mingfen; Hong, Yuanping; Duan, Shuyuan; Liu, Yongjun; Yuan, Bo; Jiang, Fengzhi

2013-05-01

151

The development of a biological interface for transition metal implants  

NASA Astrophysics Data System (ADS)

The specific goal of this research was to develop an in vitro model for a root-form endosseous dental implant that contains a periodontal ligament and that is biologically integratable into alveolar bone. This objective was based on the following two hypotheses. (1) The chemical attachment of extracellular matrix proteins to the surface of transition metals increases the number of fibroblast cells attached to the surface of the metal. (2) The chemical attachment of extracellular matrix proteins to the surface of transition metals increases the strength of the fibroblast cell attachment to the surface of the metal. The model needed to have a well-controlled surface that was reproducible. Thus, a layer of Au was deposited over a Ti base, and dithiobis(succinimidylpropionate) (DSP) a chemical containing disulfide groups was adsorbed to the Au. Next, extracellular matrix proteins which are periodontal ligament components were attached to the free end group of the chemical that was adsorbed to the Au. This surface served as an attachment substrate on which additional periodontal ligament components such as fibroblast cells could grow. From this model a new implant interface may be developed. This model was tested using the following polypeptides; collagen type I, collagen type IV, fibronectin, and poly-D-lysine. L929 cells were grown on Ti, Ti + Au, Ti + Au + polypeptide, and Ti + Au + DSP + polypeptide. After 72 hours, the live cells were stained with neutral red. The substrates were then subjected to increasing centrifugal forces. The viable stained cells were fixed onto the substrates and cells were counted. The hypotheses were proven for three polypeptides: fibronectin, collagen type I, and poly-D-lysine. The strongest attachment was found with collagen type I. Collagen type IV did not provide any advantage for attachment over uncoated transition metals.

Melton, Kim R.

152

Energy transitions in the early 21st Century  

SciTech Connect

We are in the early stages of a long and complex transition from a global economy based on fossil energy to an economy based on low carbon renewable energy. However, fossil fuel resources are abundant and widely distributed, and they will remain the dominant source of primary energy for at least the next quarter century. In the United States, displacement of coal by natural gas for electric power generation has done more to reduce CO2 emissions than all new renewables combined, and this may occur globally for the next decade or two, even if the European Union does not take advantage of its large unconventional natural gas resources. Greater energy efficiency (not including the efficiencies associated with displacement of coal by gas) will also be more important than new renewables. Cost/benefit ratios are important for sustainability of the transition, and some energy efficiency technologies and displacement of coal by natural gas have lower cost/benefit ratios than wind power, solar power or biofuels. Money spent on the large scale deployment of wind, solar and especially biofuels would be better spent on research, development and demonstration of a broader suite of technologies that would support the energy transition, with a focus on improving the cost benefit ratios of already deployed technologies and developing alternatives. Advanced nuclear reactors, engineered geothermal systems, fossil fuel recovery coupled with CO2 sequestration and pre-combustion or post-combustion decarbonation of fossil fuels with geological CO2 sequestration are among the technologies that might be more cost effective than wind, solar or biofuels, and biofuels have serious adverse societal and environment consequences.

Paul Meakin

2013-01-01

153

Templated Assembly of Metal-Anion Arrays within Layered Hosts; Synthesis and Characterization of New Transition-Metal Oxyhalide Perovskites  

E-print Network

of New Transition-Metal Oxyhalide Perovskites Gabriel Caruntu, Liliana Viciu, Leonard Spinu, Weilie Zhou Orleans, New Orleans, LA 70148-2820 ABSTRACT Ion exchange of Dion-Jacobson-type double- and triple-layered perovskites with divalent transition-metal halides leads to the templated assembly of metal-anion layers

Spinu, Leonard

154

Thermochemistry of alloys of transition metals and lanthanide metals with some IIIB and IVB elements in the periodic table  

Microsoft Academic Search

We have conducted systematic studies in this laboratory of the thermochemistry of transition metal and rare earth alloys by high temperature calorimetric methods. An overview of the thermochemistry of the alloys of the transition metals and lanthanide metals with elements in the IIIB and IVB columns of the periodic table is presented. The enthalpies of formation of most of these

S. V. Meschel; O. J. Kleppa

2001-01-01

155

Calorimetric Study of Kinetic Glass Transition in Metallic Glasses  

SciTech Connect

Differential scanning calorimetry (DSC) experiments were carried out for a bulk metallic glass (BMG), Zr{sub 41.2}Ti{sub 13.8}Cu{sub 12.5}Ni{sub 10.0}Be{sub 22.5}, below and above the glass transition temperature T{sub g}. The T{sub g} values were determined from the DSC curves. A wide range of heating rate, q = dT/dt = 0.1-100 K/min, was adopted for the experiment, and the q dependence of the apparent T{sub g} was investigated. As q was decreased, the value of T{sub g} decreased rapidly, then more slowly, and seemed to approach a constant value at low q. The experimental result of this kinetic glass transition phenomenon was analyzed on the basis of the relaxation process occurring in the transition temperature range.

Hiki, Y. [Faculty of Science, Tokyo Institute of Technology, 39-3-303 Motoyoyogi, Shibuya-ku, Tokyo 151-0062 (Japan); Takahashi, H. [Institute of Applied Beam Science, Graduate School of Science and Engineering, Ibaraki University, 4-12-1 Nakanarusawa, Hitachi 316-8511 (Japan)

2008-02-21

156

Noble metal abundances in an early Archean impact deposit  

NASA Technical Reports Server (NTRS)

Detailed analyses are reported on the concentrations of the noble metals Pd, Os, Ir, Pt, and Au in an early Archean spherule bed (S4) of probably impact origin from the lower Fig Tree Group, Barberton Greenstone Belt, South Africa. Compared to other sedimentary deposits of known or suspected impact origin, some noble metals are present in exceptionally high concentrations. Noble metal abundances are fractionated relative to abundances in chondrites with ratios of Os/Ir, Pt/Ir, Pd/Ir, and Au/Ir at only 80, 80, 41, and 2 percent of these values on CI chondrites. Although an extraterrestrial source is favored for the noble metal enrichment, the most plausible cause of the fractionation is by regional hydrothermal/metasomatic alteration.

Kyte, Frank T.; Zhou, Lei; Lowe, Donald R.

1992-01-01

157

Method for treating rare earth-transition metal scrap  

DOEpatents

Rare earth-transition metal (e.g., iron) scrap (e.g., Nd-Fe-B scrap) is flux (slag) remelted to reduce tramp non-metallic impurities, such as oxygen and nitrogen, and metallic impurities, such as Li, Na, Al, etc., picked up by the scrap from previous fabrication operations. The tramp impurities are reduced to concentrations acceptable for reuse of the treated alloy in the manufacture of end-use articles, such as permanent magnets. The scrap is electroslag or inductoslag melted using a prefused, rare earth fluoride-bearing flux of CaF.sub.2, CaCl.sub.2 or mixtures thereof or the slag resulting from practice of the thermite reduction process to make a rare earth-iron alloy.

Schmidt, Frederick A. (Ames, IA); Peterson, David T. (Ames, IA); Wheelock, John T. (Nevada, IA); Jones, Lawrence L. (Des Moines, IA)

1992-12-29

158

Method for treating rare earth-transition metal scrap  

DOEpatents

Rare earth-transition metal (e.g., iron) scrap (e.g., Nd-Fe-B scrap) is flux (slag) remelted to reduce tramp non-metallic impurities, such as oxygen and nitrogen, and metallic impurities, such as Li, Na, Al, etc., picked up by the scrap from previous fabrication operations. The tramp impurities are reduced to concentrations acceptable for reuse of the treated alloy in the manufacture of end-use articles, such as permanent magnets. The scrap is electroslag or inductoslag melted using a rare earth fluoride-bearing flux of CaF[sub 2], CaCl[sub 2] or mixtures thereof or the slag resulting from practice of the thermite reduction process to make a rare earth-iron alloy. 3 figs.

Schmidt, F.A.; Peterson, D.T.; Wheelock, J.T.; Jones, L.L.

1992-12-29

159

Capacitive network near the metal insulator transition in Vanadium Dioxide  

NASA Astrophysics Data System (ADS)

Recent infrared spectroscopy and transport measurements in nano-scaled junction of VO2 have revealed the existence of phase separation into metallic and insulating phases. Here we present Impedance spectroscopy measurements performed in high quality Vanadium dioxide (VO2) thin films for the first time. This technique allows distinguishing between the resistive and capacitive response of the VO2 films and provides the dielectric properties across the metal-insulator transition (MIT). The film capacitance exhibits an unusual increase close to the MIT which implies the formation of a capacitor network produced by the nanoscale phase separation of metallic and insulating phases. This work has been supported by AFOSR, COLCIENCIAS, CENM and Ramon y Cajal Fellowship.

Ramirez, J. G.; Patino, E. J.; Schmidt, R.; Sharoni, A.; Gomez, M. E.; Schuller, I. K.

2011-03-01

160

Synthesis, characterization and formation process of transition metal oxide nanotubes using carbon nanofibers as templates  

Microsoft Academic Search

Mono and binary transition metal oxide nanotubes could be synthesized by the immersion of carbon nanofiber templates into metal nitrate solutions and removal of the templates by heat treatment in air. The transition metal oxide nanotubes were composed of nano-crystallites of metal oxides. The functional groups on the carbon nanofiber templates were essential for the coating of these templates: they

Hitoshi Ogihara; Sadakane Masahiro; Yoshinobu Nodasaka; Wataru Ueda

2009-01-01

161

Structure of liquid transition and rare earth metals S. N. Khanna and F. Cyrot-Lackmann  

E-print Network

L-45 Structure of liquid transition and rare earth metals S. N. Khanna and F. Cyrot-Lackmann Groupe. The difference is particularly large for V, Ti, and rare earth metals which are precisely the metals where

Boyer, Edmond

162

Transition Metal Speciation in the Cell: Insights from the Chemistry of Metal Ion Receptors  

NSDL National Science Digital Library

The essential transition metal ions are avidly accumulated by cells, yet they have two faces: They are put to use as required cofactors, but they also can catalyze cytotoxic reactions. Several families of proteins are emerging that control the activity of intracellular metal ions and help confine them to vital roles. These include integral transmembrane transporters, metalloregulatory sensors, and diffusible cytoplasmic metallochaperone proteins that protect and guide metal ions to targets. It is becoming clear that many of these proteins use atypical coordination chemistry to accomplish their unique goals. The different coordination numbers, types of coordinating residues, and solvent accessibilities of these sites are providing insight into the inorganic chemistry of the cytoplasm.

Lydia Finney (Northwestern University;Department of Chemistry, Molecular Biology and Cell Biology); Thomas O'Halleron (Northwestern University;Department of Biochemistry, Molecular Biology and Cell Biology)

2003-05-09

163

Facile synthesis of mononuclear early transition-metal complexes of ?3cyclo-tetrametaphosphate ([P4O12]4-) and cyclo-trimetaphosphate ([P3O9]3-.  

PubMed

We herein report the preparation of several mononuclear-metaphosphate complexes using simple techniques and mild conditions with yields ranging from 56% to 78%. Treatment of cyclo-tetrametaphosphate ([TBA]4[P4O12]5H2O, TBA = tetra-n-butylammonium) with various metal sources including (CH3CN)3Mo(CO)3, (CH3CN)2Mo(CO)2(?(3)-C3H5)Cl, MoO2Cl2(OSMe2)2, and VOF3, leads to the clean and rapid formation of [TBA]4[(P4O12)Mo(CO)3]2H2O, [TBA]3[(P4O12)Mo(CO)2(?(3)-C3H5)], [TBA]3[(P4O12)MoO2Cl] and [TBA]3[(P4O12)VOF2]Et2O salts in isolated yields of 69, 56, 68, and 56% respectively. NMR spectroscopy, NMR simulations and single crystal X-ray studies reveal that the [P4O12](4-) anion behaves as a tridentate ligand wherein one of the metaphosphate groups is not directly bound to the metal. cyclo-Trimetaphosphate-metal complexes were prepared using a similar procedure i.e., treatment of [PPN]3[P3O9]H2O (PPN = bis(triphenylphosphine)iminium) with the metal sources (CH3CN)2Mo(CO)2(?(3)-C3H5)Cl, MoO2Cl2(OSMe2)2, MoOCl3, VOF3, WOCl4, and WO2Cl2(CH3CN)2 to produce the corresponding salts, [PPN]2[(P3O9)Mo(CO)2(?(3)-C3H5)], [PPN]2[(P3O9)MoO2Cl], [PPN]2[(P3O9)MoOCl2], [PPN]2[(P3O9)VOF2]2CH2Cl2, and [PPN]2[(P3O9)WO2Cl] in isolated yields of 78, 56, 75, 59, and 77% respectively. NMR spectroscopy, NMR simulations and single-crystal X-ray studies indicate that the trianionic ligand [P3O9](3-) in these complexes also has ?(3) connectivity. PMID:24285119

Manna, Cesar M; Nassar, Mostafa Y; Tofan, Daniel; Chakarawet, Khetpakorn; Cummins, Christopher C

2014-01-28

164

Catalytic Fusion and the Interface Between Insulators and Transition Metals  

NASA Astrophysics Data System (ADS)

Cold fusion uses a catalyzed configuration change to replace plasma fusion's need for high-energy particle collisions.1 In radiationless cold fusion, the configuration change is a coherent partitioning of deuterons into fractional pieces within a set of potential wells provided by a hosting lattice.2 The coherently partitioned matter distribution is a Bloch wave function. Alpha addition transmutations3 require active deuterium in the form of Bloch function deuterons with 2-dimensional periodic symmetry.4,5 The configuration change to Bloch form has been modeled as occurring in the interface volume between a salt and Pd metal. In Arata and Zhang radiationless cold fusion6-8 reactive deuterons are modeled by Bloch ions with 3-dimensional periodic symmetry hosted in metallic nano crystals.5 The nano crystals are isolated by salt-metal interfaces. In both cases, the fusion process is modeled as a Li-Feshbach resonance transition to an excited nucleus state, with subsequent energy transfer to a metal lattice by phonon cascade.5 The lattice structure of the deuterons is preserved in the product nucleus until the energy transfer is completed. For the 2-dimensional symmetry case, the intermediate nucleus or many-body nuclear system can sometimes be observed in "flake" lattice form, providing insight about the process.5 Research on salt-metal interfaces could facilitate cold fusion technology.

Chubb, Talbot A.

165

Critical Transitions in Early Embryonic Aortic Arch Patterning and Hemodynamics  

PubMed Central

Transformation from the bilaterally symmetric embryonic aortic arches to the mature great vessels is a complex morphogenetic process, requiring both vasculogenic and angiogenic mechanisms. Early aortic arch development occurs simultaneously with rapid changes in pulsatile blood flow, ventricular function, and downstream impedance in both invertebrate and vertebrate species. These dynamic biomechanical environmental landscapes provide critical epigenetic cues for vascular growth and remodeling. In our previous work, we examined hemodynamic loading and aortic arch growth in the chick embryo at Hamburger-Hamilton stages 18 and 24. We provided the first quantitative correlation between wall shear stress (WSS) and aortic arch diameter in the developing embryo, and observed that these two stages contained different aortic arch patterns with no inter-embryo variation. In the present study, we investigate these biomechanical events in the intermediate stage 21 to determine insights into this critical transition. We performed fluorescent dye microinjections to identify aortic arch patterns and measured diameters using both injection recordings and high-resolution optical coherence tomography. Flow and WSS were quantified with 3D computational fluid dynamics (CFD). Dye injections revealed that the transition in aortic arch pattern is not a uniform process and multiple configurations were documented at stage 21. CFD analysis showed that WSS is substantially elevated compared to both the previous (stage 18) and subsequent (stage 24) developmental time-points. These results demonstrate that acute increases in WSS are followed by a period of vascular remodeling to restore normative hemodynamic loading. Fluctuations in blood flow are one possible mechanism that impacts the timing of events such as aortic arch regression and generation, leading to the variable configurations at stage 21. Aortic arch variations noted during normal rapid vascular remodeling at stage 21 identify a temporal window of increased vulnerability to aberrant aortic arch morphogenesis with the potential for profound effects on subsequent cardiovascular morphogenesis. PMID:23555940

Kowalski, William J.; Dur, Onur; Wang, Yajuan; Patrick, Michael J.; Tinney, Joseph P.; Keller, Bradley B.; Pekkan, Kerem

2013-01-01

166

Peierls transition in two-dimensional metallic monophosphate tungsten bronzes  

NASA Astrophysics Data System (ADS)

The two-dimensional metallic bronzes made of ReO 3-type layers of MoO 6 or WO 6 octahedra present quasi-one-dimensional (1D) electronic structures along three directions of preferential overlap of the t 2g transition metal orbitals. They exhibit a Peierls instability towards the formation of charge density waves (CDW) at the 2 kF critical wave vector allowing to nest simultaneously the Fermi surfaces associated to two quasi-1D band structures out of three. The Peierls transition is achieved through a periodic lattice distortion (PLD), that we analyse, in the present work, for the monophosphate tungsten bronzes. The Peierls critical temperature decreases in presence of disorder, which breaks the electron-hole pairs forming the CDW condensate, and in presence of misfit between the PLD wave vector and the 2 kF nesting wave vector. The pair breaking effect accounts for the drop of the Peierls transition in the Na xP 4W 12O 44 ( x<1) bronzes while the misfit effect, associated to a variation of the band filling, explains quantitatively the phase diagram of the K xP 4W 8O 32 (1< x<2) bronzes.

Foury-Leylekian, P.; Pouget, J.-P.

2002-03-01

167

Early and Late Stage Metals and Sulfides in Diogenites  

NASA Technical Reports Server (NTRS)

Diogenites are typically highly brecciated orthopyroxenites that contain 84-100 vol.% orthopyroxene. Common accessory minerals include olivine, chromite, Ca-pyroxene, plagioclase, silica, troilite and Fe-Ni metal. Metal and sulfides are minor phases in diogenites with an average abundance of < 1 vol.% and 0-2 vol.% respectively. However their presence is important, as they could provide information on T-fO2-fS2 conditions and the evolution of the diogenite parent magma during crystallization and/or later metamorphism. We have examined the occurrence of Fe-Ni metal and sulfides in thin sections of several diogenites including, Johnstown, Manegaon, Roda, Shalka, Bilanga, and Tatahouine using optical microscopy and the electron microprobe. Here, we describe three features of metals and sulfides that are common in most of these diogenites. These are: i) The widespread occurrence of pentlandite associated with copper and copper sulfide minerals; ii) Textural evidence that at least some of the metal and sulfide occurring interstitially between, and as inclusions within, orthopyroxene formed from an early immiscible sulfide-oxide liquid; iii) That this sulfide- oxide liquid subsequently fractionated into assemblages containing either Fe-Ni metal, troilite, and chromite or pentlandite, troilite, and copper-bearing sulfide.

Sideras, L. C.; Domanik, K. J.; Lauretta, D. S.

2004-01-01

168

Dehydrogenation of Ammonia Borane with transition metal-doped CoB alloy catalysts  

Microsoft Academic Search

The catalytic performance of transition metal-doped Co-B ternary alloys were tested for H2 generation by hydrolysis of Ammonia Borane (AB). Chemical reduction method was used to dope Co-B catalyst with various transition metals, namely Cu, Cr, Mo, and W, using their corresponding metal salts. All transition metals induce significant promoting effects on the Co-B catalyst by increasing the H2 generation

R. Fernandes; N. Patel; A. Miotello; R. Jaiswal; D. C. Kothari

169

Environmental Effects on the Metallicities of Early-Type Galaxies  

NASA Technical Reports Server (NTRS)

We completed and published two papers in the Astrophysical Journal based on research from grant. In the first paper we analyzed nine X-ray-bright Virgo early-type galaxies observed by both ASCA and ROSAT. Through spatially resolved spectroscopy, we determined the radial temperature profiles and abundances of Mg, Si, and Fe for six galaxies. The temperature profiles are consistent with isothermal temperatures outside of cooler regions at the galaxies' centers. We present new evidence for iron abundance gradients in NGC 4472 and NGC 4649 and confirm the previous results on NGC 4636. Mg and Si abundance gradients on average are flatter than those of iron and correspond to an underabundance of ?-process elements at high Fe values, while at low iron the element ratios favor enrichment by Type II supernovae (SNe). We explain the observed trend using the metallicity dependence of SN Ia metal production and present constraints on the available theoretical modeling for low-metallicity inhibition of SNe Ia. In the second paper We analyzed nine X-ray-bright Virgo early-type galaxies observed by both ASCA and ROSAT. Through spatially resolved spectroscopy, we determined the radial temperature profiles and abundances of Mg, Si, and Fe for six galaxies. The temperature profiles are consistent with isothermal temperatures outside of cooler regions at the galaxies' centers. We present new evidence for iron abundance gradients in NGC 4472 and NGC 4649 and confirm the previous results on NGC 4636. Mg and Si abundance gradients on average are flatter than those of iron and correspond to an underabundance of ?-process elements at high Fe values, while at low iron the element ratios favor enrichment by Type I1 supernovae (SNe). We explain the observed trend using the metallicity dependence of SN Ia metal production and present constraints on the available theoretical modeling for low-metallicity inhibition of SNe Ia.

Jones, Christine; Oliversen, Ronald (Technical Monitor)

2004-01-01

170

Covalency and the metal-insulator transition in titanate and vanadate perovskites  

NASA Astrophysics Data System (ADS)

A combination of density functional and dynamical mean-field theory is applied to the perovskites SrVO3, LaTiO3, and LaVO3. We show that DFT + DMFT in conjunction with the standard fully localized-limit (FLL) double-counting predicts that LaTiO3 and LaVO3 are metals even though experimentally they are correlation-driven ("Mott") insulators. In addition, the FLL double counting implies a splitting between oxygen p and transition metal d levels, which differs from experiment. Introducing into the theory an ad hoc double counting correction, which reproduces the experimentally measured insulating gap leads also to a p-d splitting consistent with experiment if the on-site interaction U is chosen in a relatively narrow range (61 eV). The results indicate that these early transition metal oxides will serve as critical test for the formulation of a general ab initio theory of correlated electron metals.

Dang, Hung T.; Millis, Andrew J.; Marianetti, Chris A.

2014-04-01

171

Transition metal complexes of an isatinic quinolyl hydrazone  

PubMed Central

Background The importance of the isatinic quinolyl hydrazones arises from incorporating the quinoline ring with the indole ring in the same compound. Quinoline ring has therapeutic and biological activities. On the other hand, isatin (1H-indole-2,3-dione) and its derivatives exhibit a wide range of biological activities. Also, the indole ring occurs in Jasmine flowers and Orange blossoms. Recently, the physiological and biological activities of quinolyl hydrazones arise from their tendency to form metal chelates with transition metal ions. In this context, we have reported to isolate, characterize and study the biological activity of some transition metal complexes of an isatinic quinolyl hydrazone; 3-[2-(4-methyl quinolin-2-yl)hydrazono] indolin-2-one. Results Mono- and binuclear as well as dimeric chelates were obtained from the reaction of a new isatinic quinolyl hydrazone with Fe(III), Co(II), Ni(II), Cu(II), VO(II) and Pd(II) ions. The ligand showed a variety of modes of bonding viz. (NNO)2-, (NO)- and (NO) per each metal ion supporting its ambidentate and flexidentate characters. The mode of bonding and basicity of the ligand depend mainly on the type of the metal cation and its counter anion. All the obtained Pd(II)- complexes have the preferable square planar geometry (D4h- symmetry) and depend mainly on the mole ratio (M:L). Conclusion The effect of the type of the metal ion for the same anion (Cl-) is obvious from either structural diversity of the isolated complexes (Oh, Td and D4h) or the various modes of bonding. The isatinic hydrazone uses its lactim form in all complexes (Cl-) except complex 5 (SO42-) in which it uses its lactam form. The obtained Pd(II)- complexes (dimeric, mono- and binuclear) are affected by the mole ratio (M:L) and have the square planar (D4h) geometry. Also, the antimicrobial activity is highly influenced by the nature of the metal ion and the order for S. aureus bacteria is as follows: Nickel(II) > Vanadyl(II) > Cobalt(II) > Copper(II) ? Palladium(II) >> Iron(III). PMID:21708023

2011-01-01

172

Structural and Electronic Transitions in Ytterbium Metal to 202 GPa  

SciTech Connect

Ytterbium (Yb), a member of the rare earth group metals with a filled f shell and a divalent electronic character, has been studied under static high pressures in a diamond anvil cell to 202thinspthinspGPa. We report a new transformation from a face-centered-cubic structure to a hexagonal phase with 3thinspthinspatoms/cell (space group P3{sub 1}21 referred to as hP3 ) at 98{plus_minus}5 GPa . This hP3 phase is similar to that observed in trivalent neodymium and samarium at pressures near 40thinspthinspGPa. Our high pressure study thus clearly demonstrates that Yb is no longer an {open_quotes}irregular{close_quotes} member of the rare earth metals, and divalent to trivalent electronic transition is completed at megabar pressures. {copyright} {ital 1999} {ital The American Physical Society}

Chesnut, G.N.; Vohra, Y.K. [Department of Physics, University of Alabama at Birmingham (UAB), Birmingham, Alabama 35294-1170 (United States)] [Department of Physics, University of Alabama at Birmingham (UAB), Birmingham, Alabama 35294-1170 (United States)

1999-02-01

173

Computer Simulations of Wetting Transitions of Ne on Alkali Metals  

NASA Astrophysics Data System (ADS)

The wetting properties of Ne on alkali metal surfaces are investigated using grand canonical Monte Carlo simulations. The values of the well depth of the gas-surface interaction potential considered here correspond roughly to those of Ne on alkali metals(A. Chizmeshya, M. W. Cole, and E. Zaremba, J. Low Temp. Phys., in press.). For a range of temperatures extending from slightly above the bulk triple point of the gas to 0.95 of the critical temperature (depending on the interaction strength), we find (apparently first order) prewetting transitions. The simulation results are consistent (as far as they go) with the behavior studied experimentally(G. B. Hess, M. J. Sabatini and M. H. W. Chan, Phys. Rev. Lett. 78, 1739 (1997).).

Stan, G.; Bojan, M. J.; Cole, M. W.; Steele, W. A.

1998-03-01

174

Metal-insulator transition by holographic charge density waves.  

PubMed

We construct a gravity dual for charge density waves (CDWs) in which the translational symmetry along one spatial direction is spontaneously broken. Our linear perturbation calculation on the gravity side produces the frequency dependence of the optical conductivity, which exhibits the two familiar features of CDWs, namely, the pinned collective mode and gapped single-particle excitation. These two features indicate that our gravity dual also provides a new mechanism to implement the metal to insulator phase transition by CDWs, which is further confirmed by the fact that dc conductivity decreases with the decreased temperature below the critical temperature. PMID:25215974

Ling, Yi; Niu, Chao; Wu, Jian-Pin; Xian, Zhuo-Yu; Zhang, Hongbao

2014-08-29

175

Cross-plane thermal properties of transition metal dichalcogenides  

SciTech Connect

In this work, we explore the thermal properties of hexagonal transition metal dichalcogenide compounds with different average atomic masses but equivalent microstructures. Thermal conductivity values of sputtered thin films were compared to bulk crystals. The comparison revealed a >10 fold reduction in thin film thermal conductivity. Structural analysis of the films revealed a turbostratic structure with domain sizes on the order of 5-10 nm. Estimates of phonon scattering lengths at domain boundaries based on computationally derived group velocities were consistent with the observed film microstructure, and accounted for the reduction in thermal conductivity compared to values for bulk crystals.

Muratore, C. [Department of Chemical and Materials Engineering, University of Dayton, Dayton, Ohio 45469 (United States) [Department of Chemical and Materials Engineering, University of Dayton, Dayton, Ohio 45469 (United States); Materials and Manufacturing Directorate, Air Force Research Laboratory, Wright-Patterson AFB, Ohio 45433 (United States); Varshney, V. [Materials and Manufacturing Directorate, Air Force Research Laboratory, Wright-Patterson AFB, Ohio 45433 (United States) [Materials and Manufacturing Directorate, Air Force Research Laboratory, Wright-Patterson AFB, Ohio 45433 (United States); Universal Technology Corporation, Dayton, Ohio 45432 (United States); Gengler, J. J. [Materials and Manufacturing Directorate, Air Force Research Laboratory, Wright-Patterson AFB, Ohio 45433 (United States) [Materials and Manufacturing Directorate, Air Force Research Laboratory, Wright-Patterson AFB, Ohio 45433 (United States); Spectral Energies LLC, Dayton, Ohio 45431 (United States); Hu, J. J.; Bultman, J. E. [Materials and Manufacturing Directorate, Air Force Research Laboratory, Wright-Patterson AFB, Ohio 45433 (United States) [Materials and Manufacturing Directorate, Air Force Research Laboratory, Wright-Patterson AFB, Ohio 45433 (United States); University of Dayton Research Institute, Dayton, Ohio 45469 (United States); Smith, T. M. [Department of Materials Science and Engineering, Ohio State University, Columbus, Ohio 43210 (United States)] [Department of Materials Science and Engineering, Ohio State University, Columbus, Ohio 43210 (United States); Shamberger, P. J.; Roy, A. K.; Voevodin, A. A. [Materials and Manufacturing Directorate, Air Force Research Laboratory, Wright-Patterson AFB, Ohio 45433 (United States)] [Materials and Manufacturing Directorate, Air Force Research Laboratory, Wright-Patterson AFB, Ohio 45433 (United States); Qiu, B.; Ruan, X. [Department of Mechanical Engineering and Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana 47907 (United States)] [Department of Mechanical Engineering and Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana 47907 (United States)

2013-02-25

176

Metal-Insulator Transition in Graphene on Boron Nitride  

NASA Astrophysics Data System (ADS)

Electrons in graphene aligned with hexagonal boron nitride are modeled by Dirac fermions in a correlated random-mass landscape subject to a scalar- and vector-potential disorder. We find that the system is insulating in the commensurate phase since the average mass deviates from zero. At the transition the mean mass is vanishing and electronic conduction in a finite sample can be described by a critical percolation along zero-mass lines. In this case graphene at the Dirac point is in a critical state with the conductivity ?3 e2/h. In the incommensurate phase the system behaves as a symplectic metal.

Titov, M.; Katsnelson, M. I.

2014-08-01

177

Metal-Insulator Transition by Holographic Charge Density Waves  

NASA Astrophysics Data System (ADS)

We construct a gravity dual for charge density waves (CDWs) in which the translational symmetry along one spatial direction is spontaneously broken. Our linear perturbation calculation on the gravity side produces the frequency dependence of the optical conductivity, which exhibits the two familiar features of CDWs, namely, the pinned collective mode and gapped single-particle excitation. These two features indicate that our gravity dual also provides a new mechanism to implement the metal to insulator phase transition by CDWs, which is further confirmed by the fact that dc conductivity decreases with the decreased temperature below the critical temperature.

Ling, Yi; Niu, Chao; Wu, Jian-Pin; Xian, Zhuo-Yu; Zhang, Hongbao

2014-08-01

178

Ionically-mediated electromechanical hysteresis in transition metal oxides  

SciTech Connect

Electromechanical activity, remanent polarization states, and hysteresis loops in paraelectric TiO2 and SrTiO3 are observed. The coupling between the ionic dynamics and incipient ferroelectricity in these materials is analyzed using extended Ginsburg Landau Devonshire (GLD) theory. The possible origins of electromechanical coupling including ionic dynamics, surface-charge induced electrostriction, and ionically-induced ferroelectricity are identified. For the latter, the ionic contribution can change the sign of first order GLD expansion coefficient, rendering material effectively ferroelectric. These studies provide possible explanation for ferroelectric-like behavior in centrosymmetric transition metal oxides.

Kim, Yunseok [ORNL] [ORNL; Kumar, Amit [ORNL] [ORNL; Jesse, Stephen [ORNL] [ORNL; Kalinin, Sergei V [ORNL] [ORNL

2012-01-01

179

Valley photothermoelectric effects in transition-metal dichalcogenides  

NASA Astrophysics Data System (ADS)

We theoretically investigate photothermoelectric effects, i.e., the photoenabled versions of the Seebeck and Nernst effects in monolayer transition metal dichalcogenides (TMDCs) using semiclassical transport theory. We find that monolayer TMDCs subjected to circular polarized light show anomalous thermoelectric properties as a result of strong spin-orbit interaction and broken inversion symmetry. The Seebeck coefficient for photogenerated carriers is relatively large and changes its sign at a critical carrier density. In addition, a nontrivial photo-Nernst effect emerges in the absence of an external magnetic field or magnetic moments.

Konabe, Satoru; Yamamoto, Takahiro

2014-08-01

180

Exploring Transition Metal Catalyzed Reactions via AB Initio Reaction Pathways  

NASA Astrophysics Data System (ADS)

The study and prediction of chemical reactivity is one of the most influential contributions of quantum chemistry. A central concept in the theoretical treatment of chemical reactions is the reaction pathway, which can be quite difficult to integrate accurately and efficiently. This talk will outline our developments in the integration of these pathways on ab initio potential energy surfaces. We will also describe results from recent studies on the kinetics of transition metal catalyzed reactions, including the importance of vibrational coupling to the reaction coordinate and the role of this coupling in catalytic rate enhancement.

Hratchian, Hrant P.

2011-06-01

181

Rare earth-transition metal scrap treatment method  

DOEpatents

Rare earth-transition metal (e.g. iron) scrap (e.g. Nd-Fe-B scrap) is melted to reduce the levels of tramp oxygen and nitrogen impurities therein. The tramp impurities are reduced in the melt by virtue of the reaction of the tramp impurities and the rare earth to form dross on the melt. The purified melt is separated from the dross for reuse. The oxygen and nitrogen of the melt are reduced to levels acceptable for reuse of the treated alloy in the manufacture of end-use articles, such as permanent magnets. 3 figs.

Schmidt, F.A.; Peterson, D.T.; Wheelock, J.T.; Jones, L.L.; Lincoln, L.P.

1992-02-11

182

Rare earth-transition metal scrap treatment method  

DOEpatents

Rare earth-transition metal (e.g. iron) scrap (e.g. Nd-Fe-B scrap) is melted to reduce the levels of tramp oxygen and nitrogen impurities therein. The tramp impurities are reduced in the melt by virtue of the reaction of the tramp impurities and the rare earth to form dross on the melt. The purified melt is separated from the dross for reuse. The oxygen and nitrogen of the melt are reduced to levels acceptable for reuse of the treated alloy in the manufacture of end-use articles, such as permanent magnets.

Schmidt, Frederick A. (Ames, IA); Peterson, David T. (Ames, IA); Wheelock, John T. (Nevada, IA); Jones, Lawrence L. (Des Moines, IA); Lincoln, Lanny P. (Woodward, IA)

1992-02-11

183

Metal-insulator transition in pyrochlore Eu2Ir2O7 studied by infrared spectroscopy  

NASA Astrophysics Data System (ADS)

The large family of pyrochlores with formula A2B2C7 attracted a lot of early attention due to strong geometric magnetic frustration. Recent band structure calculations predict that the iridate pyrochlores A2Ir2O7 may have nontrivial topological states. We will report the results of an infrared spectroscopic study of the metal-insulator transition in Eu2Ir2O7 single crystal and Y2Ir2O7 polycrystal. We will report the broad band IR reflection as a function of temperature for an overview of the M-I transition and the low frequency transmission which is more sensitive for detection of a 10 meV gap[1] and other possible excitations. We will discuss possible implications of the semimetal Weyl states. [1] J.J. Ishikawa et al., Phys. Rev. B 85, 245109 (2012).

Sushkov, Andrei; Drew, Dennis; Ishikawa, Jun; Nakatsuji, Satoru; Luo, Xuan; Cheong, Sang-Wook

2013-03-01

184

Parents' Marital Distress, Divorce, and Remarriage: Links with Daughters' Early Family Formation Transitions  

ERIC Educational Resources Information Center

The authors used data from the Add Health study to estimate the effects of parents' marital status and relationship distress on daughters' early family formation transitions. Outcomes included traditional transitions (marriage and marital births) and nontraditional transitions (cohabitation and nonmarital births). Relationship distress among

Amato, Paul R.; Kane, Jennifer B.

2011-01-01

185

Study of the spray to globular transition in gas metal arc welding: a spectroscopic investigation  

E-print Network

Study of the spray to globular transition in gas metal arc welding: a spectroscopic investigation of the spray to globular transition in gas metal arc welding: a spectroscopic investigation F Valensi1.iop.org/JPhysD/46/224005 Abstract The gas metal arc welding (GMAW) process is strongly influenced by the composition

186

Transition-metal-catalyzed oxidation of metallic Sn in NiO/SnO2 nanocomposite.  

PubMed

It is well accepted that metallic tin as a discharge (reduction) product of SnO(x) cannot be electrochemically oxidized below 3.00?V versus Li(+)/Li(0) due to the high stability of Li2O, though a similar oxidation can usually occur for a transition metal formed from the corresponding oxide. In this work, nanosized Ni2 SnO4 and NiO/SnO2 nanocomposite were synthesized by coprecipitation reactions and subsequent heat treatment. Owing to the catalytic effect of nanosized metallic nickel, metallic tin can be electrochemically oxidized to SnO2 below 3.00?V. As a result, the reversible lithium-storage capacities of the nanocomposite reach 970?mAh?g(-1) or above, much higher than the theoretical capacity (ca. 750?mAh?g(-1)) of SnO2, NiO, or their composites. These findings extend the well-known electrochemical conversion reaction to non-transition-metal compounds and may have important applications, for example, in constructing high-capacity electrode materials and efficient catalysts. PMID:24648283

Hua, Chunxiu; Fang, Xiangpeng; Wang, Zhaoxiang; Chen, Liquan

2014-04-25

187

Nanostructured transition metal oxides for energy storage and conversion  

NASA Astrophysics Data System (ADS)

Lithium-ion batteries, supercapacitors and photovoltaic devices have been widely considered as the three major promising alternatives of fossil fuels facing upcoming depletion to power the 21th century. The conventional film configuration of electrochemical electrodes hardly fulfills the high energy and efficiency requirements because heavy electroactive material deposition restricts ion diffusion path, and lowers power density and fault tolerance. In this thesis, I demonstrate that novel nanoarchitectured transition metal oxides (TMOs), e.g. MnO2, V2O 5, and ZnO, and their relevant nanocomposites were designed, fabricated and assembled into devices to deliver superior electrochemical performances such as high energy and power densities, and rate capacity. These improvements could be attributed to the significant enhancement of surface area, shortened ion diffusion distances and facile penetration of electrolyte solution into open structures of networks as well as to the pseudocapacitance domination. The utilization of ForcespinningRTM, a newly developed nanofiber processing technology, for large-scale energy storage and conversion applications is emphasized. This process simplifies the tedious multi-step hybridization synthesis and facilitates the contradiction between the micro-batch production and the ease of large-scale manufacturing. Key Words: Transition metal oxides, energy storage and conversion, ForcespinningRTM, pseudocapacitance domination, high rate capacity

Li, Qiang

188

Metal-Insulator Transitions in Crystalline Phase Change Materials  

NASA Astrophysics Data System (ADS)

Phase-change materials are capable of undergoing fast and reversible transitions between amorphous and crystalline phase upon heating and have been exploited in data storage applications based on the strong optical/electrical contrast between the two phases. Recently, compelling evidence for a metal-insulator transition (MIT) solely due to disorder has been observed in the crystalline PCM Ge1Sb2Te4 (GST) and similar compounds: upon annealing at temperatures T below 548K, the system exhibits insulating behavior due to Anderson localization; at higher T, it shows metallic behavior. In contrast to the MITs observed in other systems such as P-doped Si, in GST correlation effects do not play a role and the MIT occurs at fixed stoichiometry. In this work, we present a Density Functional Theory study of this effect. We consider a set of very large models of GST containing one to several thousand atoms and different degree of disorder. We identify the microscopic mechanism that localizes the electron wavefunctions near the Fermi energy in the insulating phase: these states are localized inside regions having large vacancy consequent dissolution of these vacancy clusters. These results could help to develop new device based on multiple resistance states.

Zhang, Wei; Thiess, Alexander; Zalden, Peter; Zeller, Rudolf; Dederichs, Peter; Raty, Jean-Yves; Wuttig, Matthias; Blgel, Stefan; Mazzarello, Riccardo

2013-03-01

189

EPR monitoring of redox processes in transition metal oxide catalysts.  

PubMed

Transition metal oxides (TMO) are widely used as catalysts of a number of catalytic reactions, mainly of redox nature. This is due to the unique ability of transition metal ions to change easily their oxidation state, coordination, and/or arrangement of the coordination polyhedra. At present, the only abundant, direct information available about paramagnetic centers formed during interaction of the reagents with the TMO surface stems from EPR studies. This technique is very sensitive and allows detection of very small concentration of paramagnetic sites. Moreover, analysis of the EPR spectrum offers a direct approach to the determination of symmetry and electronic structure of the centers concerned. Such information is of particular value for understanding the operating reduction/reoxidation mechanisms, with immediate implications for solid-state structural studies, catalysis and so forth. The present work shows two aspects of the use of EPR for monitoring of redox processes with the participation of TMO: a) investigation of the reaction kinetics and b) description of the individual active sites involved in the catalytically important redox processes. The presented examples include: a) kinetic descriptions (including mathematical models) of reduction and oxidation processes in the vanadia-molybdena catalysts occurring upon interaction with propene and oxygen, b) identification of paramagnetic centers formed in the reduced molybdena, c) analysis of the butene interaction with a nickel catalyst, and d) description of the radical oxygen species on the surface of manganese-containing catalysts. PMID:23686922

Labanowska, M

2001-12-17

190

Selective transformations of cyclopentadienyl ligands of transition-metal and rare-earth metal complexes.  

PubMed

Cyclopentadienyl and substituted cyclopentadienyl ligands are observed in a wide range of organometallic complexes. In addition to serving as ancillary ligands, these ligands have come into their own as intermediates in organometallic reactions, and shown many unique reaction modes involving ring C-H, C-C and C=C bond cleavages. This feature article summarizes the progressive development of cyclopentadienyl-based reactions of metallocene complexes of transition metals and rare-earth metals, with the aim of further developing the fundamental modes of reactivity of such systems together with their synthetic applications. PMID:23323264

Liu, Ruiting; Zhou, Xigeng

2013-04-21

191

Orbital-dependent singlet dimers and orbital-selective Peierls transitions in transition-metal compounds  

NASA Astrophysics Data System (ADS)

We show that in transition-metal compounds containing structural metal dimers there may exist in the presence of different orbitals a special state with partial formation of singlets by electrons on one orbital, while others are effectively decoupled and may give, e.g., long-range magnetic order or stay paramagnetic. A similar situation can be realized in dimers spontaneously formed at structural phase transitions, which can be called the orbital-selective Peierls transition. This can occur in the case of strongly nonuniform hopping integrals for different orbitals and small intra-atomic Hund's rule coupling JH. Yet another consequence of this picture is that for an odd number of electrons per dimer there exists competition between the double-exchange mechanism of ferromagnetism and the formation of a singlet dimer by the electron on one orbital, with the remaining electrons giving a net spin of a dimer. The first case is realized for strong Hund's rule coupling, typical for 3d compounds, whereas the second is more plausible for 4d-5d compounds. We discuss some implications of these phenomena, and consider examples of real systems, in which the orbital-selective phase seems to be realized.

Streltsov, Sergey V.; Khomskii, Daniel I.

2014-04-01

192

Metal semiconductor phase transition in vanadium dioxide nanocrystals  

NASA Astrophysics Data System (ADS)

The goal of this research was to improve the understanding of the submicron VO2 formation in the near surface of a host material and to explore the possibility of size effects in the mechanics of the semiconductor to metal phase transition as well as in the optical properties of VO2. By means of ion implantation and thermal processing, we were able to produce variable-sized nanoscale VO2 precipitates embedded in SiO 2. The transition temperatures were found to be correlated with the size of the precipitates, in such a way that for smaller particles, both transitions were thermally delayed. A review of the energy barriers and other features involved in the transition, led us to conclude that regardless of that exact mechanism, the phase transition must proceed in a heterogeneous fashion. Smaller particles were expected to have a lower chance of containing a nucleation site and thus, they need a greater thermal driving force in order to activate them. VO2 precipitates were not only controlled in size but as an unexpected result they turned out to be produced in elongated shapes oriented mainly along the implanted surface. This morphology, which was explained in terms of the Bravais-Friedel law of crystal growth, allowed us to understand the optical properties of the precipitates. We concluded that the optical behavior shown by the particles in the SiO2 matrix, was result of a surface plasmon resonance due to the dielectric confinement and metallic character of the VO2 in the high temperature phase. Beside these contributions to material and physical sciences, we have shown that established results for VO2 doping can be applicable to our submicron particles. We were able to successfully control the width of the hysteresis loop by adding Ti ions before the precipitation. We also reached lower switching temperatures by implanting small quantities of W. Ion implantation also proved to be an easy and convenient way to incorporate VO2 nanoparticles into an optical fiber and thin film Si/SiO2 technologies.

Lopez Noriega, Rene

193

Metal Oxide Resistive Switching: Evolution of the Density of States Across the Metal-Insulator Transition  

NASA Astrophysics Data System (ADS)

We report the study of gold-SrTiO3 (STO)-gold memristors where the doping concentration in STO can be fine-tuned through electric field migration of oxygen vacancies. In this tunnel junction device, the evolution of the density of states (DOS) can be followed continuously across the metal-insulator transition (MIT). At very low dopant concentration, the junction displays characteristic signatures of discrete dopant levels. As the dopant concentration increases, the semiconductor band gap fills in but a soft Coulomb gap remains. At even higher doping, a transition to a metallic state occurs where the DOS at the Fermi level becomes finite and Altshuler-Aronov corrections to the DOS are observed. At the critical point of the MIT, the DOS scales linearly with energy N(?)?, the possible signature of multifractality.

Mottaghizadeh, A.; Yu, Q.; Lang, P. L.; Zimmers, A.; Aubin, H.

2014-02-01

194

Spectroscopic Studies of Diatomic Transition Metal Oxides and Fluorides.  

NASA Astrophysics Data System (ADS)

Wavelength selected fluorescence excitation spectroscopy (WSFES) techniques and ligand field theory (LFT) calculations have been applied to the following transition metal diatomics: CeO, UO, LaF, YF, ScF, HfO, TiO, and ZrO. All of the rotational spectra recorded for these molecules were at a resolution of 0.03 cm^{-1}, and, with few exceptions, Omega assignments for electronic states were unambiguously determined from observations of the first lines in at least two rotational branches. Accurate term energies and rotational constants are reported. Thirty one electronic transitions of CeO were recorded, and all of the sixteen states that correlate with rm Ce^{2+}(4f6s)O^ {2-} were characterized. The results are in good accord with a ligand field theory model of the low-lying states. New assignments were established for four previously observed transitions, and spectra for three new excited states were analyzed. LFT calculations have been used in an attempt to provide configurational assignments for the excited states (including those from previous studies). Twenty two states are tentatively assigned to the rm Ce^{2+}(4f6p)O ^{2-} configuration. Twelve others are tentatively assigned to rm Ce^ {2+}(4f5d)O^{2-}.. Rotation-electronic interactions between states of the 4f6s configuration of CeO, mediated by the operator {-}B(R)( J^+ cdot J_sp{a}{-}+ J^-cdot J_sp{a} {+}), have been calculated. Second-order perturbation theory was used to account for the effect of heterogeneous interactions on the rotation constants within a single configuration. Thirty-three electronic transitions of UO were analyzed, and nine low-lying electronic states that correlated with either rm U^{2+}(5f ^37s)O^{2-} or rm U^{2+}(5f^27s^2)O ^{2-} were characterized. Ligand field theory calculations were also used in an attempt to provide configurational assignments for the excited states of UO and ThO. Experimentally derived values for Delta B_sp{0} {0}(nl/n^' l^') parameters were used to predict the electronic structures of UO and UO^+.. Eight electronic transitions of LaF and nine transitions of YF were studied. LFT calculations (and in the case of LaF, hyperfine constants) were used to suggest electronic configurational assignments for the excited states of these molecules. WSFE spectra of the 0-0 and 1-1 bands of the ScF F^1Phi-A^1 Delta transition were observed, and perturbations in the F^1Phi state, caused by interactions with the h^3Pi_2 state, were analyzed. Using a method based on Franck-Condon factors, the vibrational numbering in the perturbing h^3Pi_2 state was estimated. The 5698 A band of HfO has been re examined. The wavelength-resolved fluorescence excitation technique was used to record the (2,0) band of the C ^3Delta_3-a^1 Delta transition, and the (2,3) and (2,4) bands of the C^3Delta_3 -X^3Delta_3 electronic transition of TiO. The (0,0) bands of the satellite e^3 Pi_1-a^3Delta _1 and e^3Pi_2 -a^3Delta_2 transitions of ZrO were investigated, and these data were combined with previous high resolution analyses of the ZrO beta-system and with the analysis of the intercombination e^3Pi_1 -X^1Sigma ^+ transition to obtain accurate term energies for the triplet states of ^{90 }Zr^{16}O. (Abstract shortened by UMI.).

McCord, John Edward

195

Density functional calculation of transition metal adatom adsorption on graphene.  

PubMed

The functionalization of graphene (a single graphite layer) by the addition of transition metal atoms of Mn, Fe and Co to its surface has been investigated computationally using density functional theory. In the calculation, the graphene surface supercell was constructed from a single layer of graphite (0001) surface separated by vertical vacuum layers 2nm thick. We found that the center of the hexagonal ring formed by carbon from graphene is the most stable site for Mn, Fe, Co to stay after optimization. The calculated spin-polarized band structures of the graphene encapsulating the Mn adatom indicate that the conduction bands are modified and move down due to the coupling between the Mn atom and graphene. For Fe adsorbed on the graphene surface, it is semi-half-metallic, and the spin polarization P is found to be 100%. The system of Coadatom on graphene exhibits metallic electronic structure due to the density of states (DOS) peak at the band center with both majority and minority spins. Local density of states analyses indicate a larger promotion of 4s electrons into the 3d state in Fe and Co, resulting in lower local moments compared to an Mn adatom on the graphite surface. PMID:21694226

Mao, Yuliang; Yuan, Jianmei; Zhong, Jianxin

2008-03-19

196

Characteristics of thermal decomposition products of rare earth, alkali earth metal and transition metal p -toluenesulfonates  

Microsoft Academic Search

Summary A series of alkali earth (Ca, Ba), lanthanide (La, Ce, Pr, Nd,) and transition metal (Fe, Mn, Co, Ni, Cu, Zn, Cd) p-toluenesulfonates were synthesized. Thermal analysis, infrared spectrophotometry, and XRD powder diffraction patterns were employed to characterize the final thermal decomposition products. By heating in dynamic air atmosphere at 30-850C, it has been found that the alkali earth

Z.-L. Sun

2005-01-01

197

Environmental Effects on the Metallicities of Early-Type Galaxies  

NASA Technical Reports Server (NTRS)

In this multi-year project to investigate the metal enrichment of early-type galaxies, we have used ROSAT, ASCA and now Chandra observations to study samples of galaxies. We have published two papers and a third paper that incorporates Chandra archival observations is nearing completion. Below, we briefly describe our findings. Our first paper "SN IA Enrichment in Virgo Early-type Galaxies from ROSAT and ASCA Observations" was published in the Astrophysical Journal (vol 539, 603) reported on the properties of nine X-ray bright elliptical galaxies in the Virgo cluster observed by ROSAT and ASCA. We measured iron abundance gradients as a function of radius in three galaxies. We found that the magnesium and silicon abundance gradients were in general flatter than those of iron. We suggest this is due to a metallicity dependence in the metal production rates of SN Ia's. We calculate SN Ia rates in the center of these galaxies that are comparable to those measured optically. Our second paper "ASCA Observations of Groups at Radii of Low Overdensity: Implications for Cosmic Preheating" also was published in the Astrophysical Journal (vol 578, 74). This paper reported on the ASCA spectroscopy of nine groups of galaxies. We found that the entropy profile in groups is driven by nongravitational heating processes, and could be explained by a short period of preheating by galactic winds. The third paper (in preparation) uses a sample of about 200 galaxies from both ROSAT and Chandra observations. In this paper we characterize both the nuclear and the extended X-ray emission for this sample. We will use these observations to determine the "on-time" of the X-ray emitting AGN and the fraction of "fossil groups" as well as to investigate how large AGN outbursts can sweep the galaxy of its hot ISM, thus leading to changes in the ISM metal enrichment.

Oliversen, Ronald J. (Technical Monitor); Jones, Christine

2004-01-01

198

Insulator-to-metal transition in vanadium sesquioxide: does the Mott criterion work in this case?  

Microsoft Academic Search

It is shown that the Mott criterion expressed by the simple relation aB(nc)???0.25 turns out to be quite successful in describing metalinsulator phase transitions not only in heavily doped semiconductors, but also in transition metal oxides such as VO2 and V2O3. It is found in this article that, in the case of a high-temperature transition paramagnetic insulator paramagnetic metal

Alexander Pergament; Genrikh Stefanovich

2012-01-01

199

Insulator-to-metal transition in vanadium sesquioxide: does the Mott criterion work in this case?  

Microsoft Academic Search

It is shown that the Mott criterion expressed by the simple relation aB(nc)???0.25 turns out to be quite successful in describing metalinsulator phase transitions not only in heavily doped semiconductors, but also in transition metal oxides such as VO2 and V2O3. It is found in this article that, in the case of a high-temperature transition paramagnetic insulator paramagnetic metal

Alexander Pergament; Genrikh Stefanovich

2011-01-01

200

Charge-transfer gap closure in transition-metal halides under pressure  

SciTech Connect

Insulator-to-metal transition induced by pressure has been studied in three transition metal iodides: NiI{sub 2}, CoI{sub 2} and FeI{sub 2} using optical absorption and resistivity measurements at room temperature. Comparisons between the results obtained by these two techniques suggested that the closure of the charge-transfer gap is the principal mechanism responsible for the insulator-to-metal transition in these materials.

Chen, A.L.; Yu, P.Y.

1995-01-01

201

Phase Transitions in Transition Metal Monooxides: Interplay Between Structural, Magnetic, and Electronic Properties  

Microsoft Academic Search

The iron monoxide Fe1-xO (wustite) is an important member of the highly correlated transition metal monoxide group which includes NiO, CoO, and MnO, and is also an end-member component of the (Mg,Fe)O solid solution, the most abundant non-silicate oxide in the Earth. At ambient conditions wustite exists in a cubic fcc-based rock-salt structure with a nonstoichiometric formula Fe1-xO. At low

L. S. Dubrovinsky; I. Y. Kantor; A. P. Kantor; C. McCammon; W. Crichton; I. N. Goncharenko

2005-01-01

202

Graphene nucleation on transition metal surface: structure transformation and role of the metal step edge.  

PubMed

The nucleation of graphene on a transition metal surface, either on a terrace or near a step edge, is systematically explored using density functional theory calculations and applying the two-dimensional (2D) crystal nucleation theory. Careful optimization of the supported carbon clusters, C(N) (with size N ranging from 1 to 24), on the Ni(111) surface indicates a ground state structure transformation from a one-dimensional C chain to a 2D sp(2) C network at N ? 10-12. Furthermore, the crucial parameters controlling graphene growth on the metal surface, nucleation barrier, nucleus size, and nucleation rate on a terrace or near a step edge are calculated. In agreement with numerous experimental observations, our analysis shows that graphene nucleation near a metal step edge is superior to that on a terrace. On the basis of our analysis, we propose the use of graphene seeds to synthesize high-quality graphene in large area. PMID:21384854

Gao, Junfeng; Yip, Joanne; Zhao, Jijun; Yakobson, Boris I; Ding, Feng

2011-04-01

203

Quantum Spin Liquids and the Metal-Insulator Transition in Doped Semiconductors  

E-print Network

We describe a new possible route to the metal-insulator transition in doped semiconductors such as Si:P or Si:B. We explore the possibility that the loss of metallic transport occurs through Mott localization of electrons ...

Potter, Andrew Cole

204

Electrochemical lithiation and delithiation for control of magnetic properties of nanoscale transition metal oxides  

E-print Network

Transition metal oxides comprise a fascinating class of materials displaying a variety of magnetic and electronic properties, ranging from half-metallic ferromagnets like CrO2, ferrimagnetic semiconductors like Fey's, and ...

Sivakumar, Vikram

2008-01-01

205

Dense organic-inorganic framework materials containing transition metal ions  

NASA Astrophysics Data System (ADS)

Hybrid inorganic-organic framework materials built upon metal cations and polyfunctional anionic ligands have arrived at the forefront of chemical research, boasting unique properties that derive from their diverse structures. The majority of these compounds are prepared through mild hydrothermal or solvothermal synthesis, at temperatures below 225C. There has been a great deal of emphasis on porous coordination polymers, or "metal-organic frameworks" (MOFs), which exhibit a wide range of useful sorption and catalytic properties, but there is growing interest in a second class of hybrid frameworks which are denser and often have extended inorganic connectivity, which may be thought of as hybrid metal oxides. These denser compounds provide access to more oxide-like properties such as magnetism, along with improved thermal stability. The flourishing diversity of structures and dimensionalities seen in these materials has led to their growth into a major field of research. Here, the hydrothermal syntheses and crystal structures of fourteen new hybrid framework materials are reported, and additional properties are measured for several of them. The terminology used to describe this class of materials is laid out, and a classification scheme is introduced based on the dimensionalities of their structures. While a combinatorial approach for new compound discovery is often used, strategies for rational synthesis are also discussed. A family of isostructural 3,4,5-trihydroxybenzoate (gallate) hybrid frameworks of the first-row transition metals is produced, with chiral structures imparted by helical packing arrangements. Complex magnetic behavior is characterized in a pillared layered cobalt ethanedisulfonate, the structure of which features intricate metal-oxygen-metal connectivity. Frameworks of new, sometimes unreported, ligand molecules are created through the reactivities of aspartic acid and 5-hydroxyisophthalic acid under hydrothermal conditions. A family of two-ligand frameworks are created using 5-hydroxyisophthalic acid and 4,4'-bipyridyl, which form very different structures when reacted with Mn, Ni, Cu and Zn. Finally, reactions of Cu and Zn together with these two ligands lead to a family of four- and five-component hybrid frameworks showing even greater degrees of structural complexity.

Feller, Russell Kenneth

206

Global Transcriptome and Deletome Profiles of Yeast Exposed to Transition Metals  

Microsoft Academic Search

A variety of pathologies are associated with exposure to supraphysiological concentrations of essential metals and to non-essential metals and metalloids. The molecular mechanisms linking metal exposure to human pathologies have not been clearly defined. To address these gaps in our understanding of the molecular biology of transition metals, the genomic effects of exposure to Group IB (copper, silver), IIB (zinc,

Yong Hwan Jin; Paul E. Dunlap; Sandra J. McBride; Hanan Al-Refai; Pierre R. Bushel; Jonathan H. Freedman

2008-01-01

207

Three-particle approximation for transition-metal oxides  

NASA Astrophysics Data System (ADS)

Quasiparticle spectra are calculated for NiO and CuO on the basis of band structures obtained within the ab initio self-interaction-corrected local-spin density (SIC-LSD) and LSD+U approximations. On-site Coulomb correlations are described by a multiband Hubbard model, which is treated within Igarashi's three-particle approximation. The transition-metal d-state spectral weight is split into a main dnL peak and a dn-1 satellite. We show that mean-field band structures in this way can lead to a good description of the experimental photoemission spectra of these compounds. The validity of the three-particle approach is investigated, and it is concluded that the method is best suited for a system which is well orbitally polarized on the mean-field level.

Lgsgaard, J.; Svane, A.

1997-02-01

208

The Role of Carbon in Catalytically Stabilized Transition Metal Sulfides  

SciTech Connect

Since WWII considerable progress has been made in understanding the basis for the activity and the selectivity of molybdenum and tungsten based hydrotreating catalysts. Recently, the focus of investigation has turned to the structure of the catalytically stabilized active catalyst. The surface of the catalytically stabilized MoS2 has been shown to be carbided with the formula MoSxCy under hydrotreating conditions. In this paper we review the basis for this finding and present new data extending the concept to the promoted TMS (transition metal sulfides) systems CoMoC and NiMoC. Freshly sulfided CoMoS and NiMoS catalyst have a strong tendency to form the carbided surface phases from any available carbon source.

Kelty,S.; Berhault, G.; Chianelli, R.

2007-01-01

209

Exchange coupling in transition metal monoxides: Electronic structure calculations  

SciTech Connect

An ab initio study of magnetic-exchange interactions in antiferromagnetic and strongly correlated 3d transition metal monoxides is presented. Their electronic structure is calculated using the local self-interaction correction approach, implemented within the Korringa-Kohn-Rostoker band-structure method, which is based on multiple scattering theory. The Heisenberg exchange constants are evaluated with the magnetic force theorem. Based on these the corresponding Neel temperatures TN and spin-wave dispersions are calculated. The Neel temperatures are obtained using mean-field approximation, random-phase approximation and Monte Carlo simulations. The pressure dependence of TN is investigated using exchange constants calculated for different lattice constants. All the calculated results are compared to experimental data.

Fischer, Guntram [University Halle-Wittenberg, Halle Germany; Daene, Markus W [ORNL; Ernst, Arthur [Max Planck Institute of Microstructure Physics; Bruno, Patrick [European Synchrotron Radiation Facility (ESRF); Lueders, Martin [Daresbury Laboratory, UK; Szotek, Zdzislawa [Daresbury Laboratory, UK; Temmerman, Walter M [Daresbury Laboratory, UK; Wolfam, Hergert [Martin-Luther University Halle-Wittenberg

2009-01-01

210

Radiation damage of transition metal carbides. Final technical report  

SciTech Connect

In this grant period we have investigated electrical properties of transition metal carbides and radiation-induced defects produced by low-temperature electron irradiation in them. Special attention has been given to the composition VC{sub 0.88} in which the vacancies on the carbon sublattice of this fcc crystal order to produce a V{sub 8}C{sub 7} superlattice. The existence of this superlattice structure was found to make the crystal somewhat resistant to radiation damage at low doses and/or at ambient temperature. At larger doses significant changes in the resistivity are produced. Annealing effects were observed which we believe to be connected with the reconstitution of the superlattice structure.

Dixon, G.

1991-12-31

211

A new ligand field approach to linear transition metal dihalides  

NASA Astrophysics Data System (ADS)

We have performed theoretical multiconfigurational calculations of the molecular energy levels based on two axial ligand field models and determined the model parameters to reproduce ab initio energies of TiCl2, TiF2, VCl2, and VF2. We develop two extensions to ligand field theory (LFT) for linear transition metal dihalides, which are incorrectly described by standard LFT. The standard LFT is augmented (1) by including the ligand induced hybridization of the d(?) orbital with the 4s orbital or (2) by using a different radial part for the d(?) orbital. Both models reproduce the energies of the first electronic states in very good agreement with numerical multireference configuration interaction results. Furthermore the model parameters are very close to experimental known Racah parameters describing the term energies of Ti2+ and V2+.

Vogel, M.; Weber, W.; Wenzel, W.

2006-07-01

212

Early transitional metal alkyl, alkylidene, and alkylidyne chemistry  

E-print Network

CHAPTER 1. Zirconium and hafnium complexes of several new unsymmetric diamide ligands have been prepared and their proficiency in olefin polymerization reactions evaluated. The first set of supporting ligands examined are ...

Tonzetich, Zachary John

2007-01-01

213

Transition metal catalysis in the generation of petroleum and natural gas. Final report  

SciTech Connect

This project originated on the premise that natural gas could be formed catalytically in the earth rather than thermally as commonly believed. The intention was to test this hypothetical view and to explore generally the role of sedimentary metals in the generation of light hydrocarbons (C1 - C9). We showed the metalliferous source rocks are indeed catalytic in the generation of natural gas. Various metal compounds in the pure state show the same levels of catalytic activity as sedimentary rocks and the products are identical. Nickel is particularly active among the early transition metals and is projected to remain catalytically robust at all stages of catagenesis. Nickel oxide promotes the formation of n-alkanes in addition to natural gas (NG), demonstrating the full scope of the hypothetical catalytic process: The composition of catalytic gas duplicates the entire range of natural gas, from so-called wet gas to dry gas (60 to 95+ wt % methane), while gas generated thermally is consistently depleted in methane (10 to 60 wt % methane). These results support the view that metal catalysis is a major pathway through which natural gas is formed in the earth.

Mango, F.D.

1997-01-21

214

Metal-insulator transition in doped semiconductors without impurity compensation  

NASA Astrophysics Data System (ADS)

The purpose of this work is to study the metal-insulator transition in doped semiconductors without impurity compensation, ruling out an ambiguity due to inhomogeneous distribution of impurities. The value of the conductivity critical exponent has been examined both in zero magnetic field and magnetic fields. In order to avoid the inhomogeneous distribution of impurities and impurity compensation, the samples were prepared by neutron-transmutation doping (NTD) of isotopically enriched germanium 70. (Gallium 71 acceptors were produced.) Gallium concentration of the sample closest to the critical point for the transition is only 0.04% larger than the critical concentration. Electrical conductivity of the samples was measured down to 20 mK, and magnetic fields up to 8 T were applied perpendicular to the current direction. It has been fully confirmed that the conductivity critical exponent in zero magnetic field is 0.5 in doped semiconductors without impurity compensation. This result does not satisfy Chayes et al.'s inequality if the Wegner relation derived for systems without interactions is assumed, and hence, calls for serious theoretical examinations on the point whether the Wegner relation applies or not to doped semiconductors where both disorder and electron-electron interaction are important. A different value 1.1 of the exponent has been found in magnetic fields, which supports a picture that the exponent varies depending on the universality class to which the system belongs.

Watanabe, Michio

215

Antiferromagnetic Metal and Mott Transition on Shastry-Sutherland Lattice  

PubMed Central

The Shastry-Sutherland lattice, one of the simplest systems with geometrical frustration, which has an exact eigenstate by putting singlets on diagonal bonds, can be realized in a group of layered compounds and raises both theoretical and experimental interest. Most of the previous studies on the Shastry-Sutherland lattice are focusing on the Heisenberg model. Here we opt for the Hubbard model to calculate phase diagrams over a wide range of interaction parameters, and show the competing effects of interaction, frustration and temperature. At low temperature, frustration is shown to favor a paramagnetic metallic ground state, while interaction drives the system to an antiferromagnetic insulator phase. Between these two phases, there are an antiferromagnetic metal phase and a paramagnetic insulator phase (which should consist of a small plaquette phase and a dimer phase) resulting from the competition of the frustration and the interaction. Our results may shed light on more exhaustive studies about quantum phase transitions in geometrically frustrated systems. PMID:24777282

Liu, Hai-Di; Chen, Yao-Hua; Lin, Heng-Fu; Tao, Hong-Shuai; Liu, Wu-Ming

2014-01-01

216

Antiferromagnetic metal and Mott transition on Shastry-Sutherland lattice.  

PubMed

The Shastry-Sutherland lattice, one of the simplest systems with geometrical frustration, which has an exact eigenstate by putting singlets on diagonal bonds, can be realized in a group of layered compounds and raises both theoretical and experimental interest. Most of the previous studies on the Shastry-Sutherland lattice are focusing on the Heisenberg model. Here we opt for the Hubbard model to calculate phase diagrams over a wide range of interaction parameters, and show the competing effects of interaction, frustration and temperature. At low temperature, frustration is shown to favor a paramagnetic metallic ground state, while interaction drives the system to an antiferromagnetic insulator phase. Between these two phases, there are an antiferromagnetic metal phase and a paramagnetic insulator phase (which should consist of a small plaquette phase and a dimer phase) resulting from the competition of the frustration and the interaction. Our results may shed light on more exhaustive studies about quantum phase transitions in geometrically frustrated systems. PMID:24777282

Liu, Hai-Di; Chen, Yao-Hua; Lin, Heng-Fu; Tao, Hong-Shuai; Liu, Wu-Ming

2014-01-01

217

Group 7 transition metal complexes with N-heterocyclic carbenes.  

PubMed

This tutorial review summarizes all works and highlights recent advances published in the growing field of group 7 N-heterocyclic carbene (NHC) complexes. It provides a valuable source for all scientists that are interested in conducting research with new compounds bearing these metals. The article provides an overview of all manganese NHC complexes that are known to date. There are a lot of examples where manganese NHC complexes show unpredicted behaviour during synthesis, very different from other transition metal NHC complexes and their higher homologues rhenium and technetium. These differences are depicted and discussed. Furthermore, the chemistry of technetium NHC compounds and their chemical behaviour are discussed. To date published work on technetium NHC chemistry has been restricted to the oxidation state +v. It was found that such compounds are very reactive but show great stability in dry air. Their radioactivity makes such compounds interesting candidates for radiochemical applications. Since most group 7 NHC chemistry was conducted on rhenium NHC complexes, this tutorial review highlights the chemical behaviour of such compounds. Rhenium(i) complexes reveal luminescent properties, making them interesting candidates for applications ranging from biological markers to organic light-emitting diodes (OLEDs). Another interesting feature is the radioactivity of some compounds, which makes them excellent candidates for radiopharmaceutical research; hence their synthesis and reactivity are discussed. PMID:23475206

Hock, Sebastian J; Schaper, Lars-Arne; Herrmann, Wolfgang A; Khn, Fritz E

2013-06-21

218

Topological superconductivity at the edge of transition-metal dichalcogenides  

NASA Astrophysics Data System (ADS)

Time-reversal breaking topological superconductors are new states of matter which can support Majorana zero modes at the edge. In this Rapid Communication, we propose a different realization of one-dimensional topological superconductivity and Majorana zero modes. The proposed system consists of a monolayer of transition-metal dichalcogenides MX2 (M =Mo,W; X =S,Se) on top of a superconducting substrate. Based on first-principles calculations, we show that a zigzag edge of the monolayer MX2 terminated by a metal atom M has edge states with strong spin-orbit coupling and spontaneous magnetization. By proximity coupling with a superconducting substrate, topological superconductivity can be induced at such an edge. We propose NbS2 as a natural choice of substrate, and estimate the proximity induced superconducting gap based on first-principles calculation and a low energy effective model. As an experimental consequence of our theory, we predict that Majorana zero modes can be detected at the 120 corner of a MX2 flake in proximity to a superconducting substrate.

Xu, Gang; Wang, Jing; Yan, Binghai; Qi, Xiao-Liang

2014-09-01

219

Strong electron correlations in biomimetic transition metal molecules  

NASA Astrophysics Data System (ADS)

The first-row transition metals (Fe, Co, V,...) are key players in the active sites of proteins and enzymes responsible for diverse biological processes such as NO regulation and photosynthesis. Many small transition metal complexes possess chemical coordination environments in the vicinity of the metal atom that are reminiscent of these active sites. We have studied the electronic structure of these molecules and discussed the relevance for their biological analogues. The specific question on which we wish to focus is: Do strong correlations (resulting from the localized character of the TM 3d-orbitals) contribute significantly to the reaction energetics of these molecules and, if so, can these effects be observed by experiment? To accomplish these ends we focus on the cobalt valence tautomer molecules and the phenomenon of electron transfer in aqueous hexaammine cobalt ions. We utilize theoretical methods in order to study the cobalt valence tautomer molecules which undergo an interconversion with temperature that is reminiscent of the changes in structure and spin that the heme group experiences as the result of Fe-ligand interactions. We perform fully ab initio calculations using the GGA implementation of density functional theory with the computer code SIESTA. In addition, a simple Anderson Impurity Model has been employed that more properly accounts for the Coulomb interaction among the 3d electrons on the cobalt atom. The calculated Co K x-ray absorption near-edge spectra XANES agrees well with experimental data and a prediction for the Co L-edge XAS that could be tested in future experiments is also presented. We believe that there are structures in both spectra that may only be explained by a strong admixture of configurations. It is conjectured that strong electron correlations help explain the non-Arrhenius rate behavior observed in the high-spin to low-spin relaxation rate at low temperatures. Work on electron-transfer in CoNH32 +/3+6aq using these methods is discussed. Relevant physics for single complexes is presented and then the Born-Oppenheimer potential energy surface for the bridged Co2+ and Co3+ complexes is plotted. The electronic transfer matrix element HDA is extracted directly from the surface topography. Finally there are comments on how a mechanism similar to valence tautomerism might be relevant for iron-poryphrin groups that are present in the active sites of many metalloproteins such as myoglobin and cytochrome oxidase.

Labute, Montiago Xavier

220

Magnetic Phenomena and Ballistic Transport in Monatomic Transition Metal Nanowires  

NASA Astrophysics Data System (ADS)

I will address the general issue of possible magnetism in ultimately thin, vacuum suspended monatomic transition metal nanowires, and of its eventual consequences on ballistic conductance. First I will show, based on zero-temperature electronic structure calculations, that magnetism will generally occur in 4d nanowires made of Rh, Ru, and Pd, and also in 5d nanowires made of Pt,Os as well as of Ir under stress [1]. Magnetization magnitudes obtained are stress dependent, and roughly in the order of 1/2 Bohr magneton per atom at zero stress. This apparent resurgence of Hund's rule magnetism, usually quenched in these transition metals in bulk, can be attributed to d-band narrowing in the nanowire, accompanied by a slightly more effective emptying of the d-bands in favor of s-bands than in the bulk metal. In addition Pd exemplifies a case where 1-dimensional band edge singularities represent the factor that triggers awake an otherwise dormant Hund's rule magnetism. Analysis of the band structures of the wires indicates that the onset of magnetism should generally reduce, although not by much, the number of conducting bands crossing the Fermi level. This in turn suggests that ballistic conductance through the wires should also be affected by magnetism, at least at zero temperature. Conductance calculations based on an extension of the complex band structure method to ultrasoft pseudopotentials [2] are presently under way, to describe that. A discussion of the expected nanowire conductance in connection with experimental data will also be given, particularly in connection with fractional conductance peaks recently reported. We show that magnetization reversals inside the nanowire[3] could in principle lead to fractional conductance. However, some such fractional peaks were seen at room temperature and zero field [4], where nanowire magnetism seems unlikely to survive. Their origin is disputed [5] and remains unclear at the moment. Work done in collaboration with A. Delin, A. Dal Corso, A. Smogunov, and R. Weht. Work sponsored by EU contract HPMF-CT-2000-00827 (Marie Curie fellowship), STINT and NFR of Sweden, and by MIUR COFIN, MIUR FIRB of Italy. [1] A. Delin and E. Tosatti, cond-mat/0305658; A. Delin, E. Tosatti, R. Weht, cond-mat/0307737. [2] A. Smogunov, A. dal Corso and E. Tosatti, cond-mat/0305308, and in preparation. [3] A. Smogunov, A. dal Corso and E. Tosatti, Surface Science 507, 609 (2002). [4] V. Rodrigues, J. Bettini, P.C. Silva, and D. Ugarte, Phys. Rev. Lett. 91, 096801 (2003). [5] C. Untiedt, D.M.T. Dekker, D. Djukic, J.M. van Ruitenbeek,cond-mat/0309622.

Tosatti, Erio

2004-03-01

221

The Transition Process: The Early Years of Being a Teacher  

Microsoft Academic Search

Becoming a teacher involves a transition from pre-service training into the profession of teaching. This transition brings about a shift in role orientation and an epistemological move from knowing about teaching through formal study to knowing how to teach by confronting the daily challenges of the school and classroom (FeimanNemser, 2000). According to Feiman-Neimser, becoming a teacher requires the development

Zachariah O. Wanzare

222

Deviance as an antecedent and consequence of early transitions to adulthood: mediating effects and moderating conditions  

E-print Network

, were used to estimate Structural Equation Models, testing the unmediated and mediated relationships between adolescent deviance, early timing of transitions to adult roles, and adult deviance. First, a simplified three latent variable model...

Halim, Shaheen

2005-08-29

223

Reactivity and Spectroscopic Studies of Selected Transition Metal Clusters.  

NASA Astrophysics Data System (ADS)

Reactions of the group 5 transition-metal clusters (V_{rm n}, Nb _{rm n}, and Ta_ {rm n}) have been investigated in the gas-phase by using a fast-flow chemical reactor. Dissociative chemisorption of D_ 2 and N _ 2 is found to be size selective for these bare metal clusters, as well as for the cluster monoxides V_{rm n}O and Ta _{rm n}O and monocarbides V_{rm n}C. The effect of a single atomic impurity (C or O) decreases for clusters larger than 10 atoms and becomes negligible for clusters larger than 15-20 atoms. This loss of sensitivity to impurities is consistent with the loss of cluster size specificity, which occurs in the same size range. Evidence of structural isomerism is found for Nb_ 9, Nb_{11}, Nb _{12}, and Ta_ {12} which react with N_ 2 with biexponential reaction kinetics. The rate of chemisorption with ethane (C_ 2H _ 6) displays a steady increase with cluster size for V_{rm n} and Nb_{rm n}, but Ta_{rm n} clusters are only slightly reactive. Finally, the rate of addition of a second ligand to a metal cluster is considered, and examples are analyzed for the Nb_{ rm n}N_ 2 + N _ 2 case. Resonant two photon ionization spectroscopy has been used to investigate the optical spectra of jet-cooled MoO. By coupling the technique to a time-of-flight mass spectrometer, spectra of all isotopic species of MoO have been separately recorded. The observed spectra establish the ground state of MoO as ^ 5Pi_ {rm r}, deriving from the 2 delta^{2}12sigma^{1 }6pi^ 1 molecular configuration. Transitions from this ground state to the excited 2delta ^{1}12sigma^{1}6 pi^ 2, A^' ^ 5Delta_{rm r}; 2delta^{2}6 pi^{1}13sigma^ 1; B ^ 5Pi_{rm r} ; and 2delta^{1}12 sigma^{1}6pi^{1 }13sigma^ 1, B^ ' ^ 5Pi_{ rm r} states have been located, rotationally resolved, and anlayzed. Numerous other weak transitions have been observed in the visible, many of which must be due to S = 1 >=ts X^ 5Pi_{rm r} intercombinations. Several strong transitions are observed in the near infrared where the 2delta^{2}12sigma ^{1}13sigma^ 1, ^ 5Sigma^ - >=ts X ^ 5Pi and 2 delta^{2}6pi^ 2, A ^ 5Sigma^ + >=ts X ^ 5Pi band systems are expected. The general electronic structure of MoO is shown to be quite analogous to that of its congener, CrO, and the pattern of molecular orbitial energies is also quite comparable to that found for NbO.

Hamrick, Yoon Mi Lee

1990-01-01

224

Axially Engineered Metal-Insulator Phase Transition by Graded Doping VO2 Nanowires  

E-print Network

Axially Engineered Metal-Insulator Phase Transition by Graded Doping VO2 Nanowires Sangwook Lee Supporting Information ABSTRACT: The abrupt first-order metal-insulator phase transition in single level of tungsten. We also demonstrate the potential of these NWs for thermal sensing and actuation

Wu, Junqiao

225

Tight-binding study of anomalous Hall effect in ferromagnetic 3d transition metals  

Microsoft Academic Search

Anomalous Hall conductivity in ferromagnetic 3d transition metals is calculated using realistic tight-binding models assuming the intrinsic origin of the effect. The order of magnitude and sign of the obtained results are found to agree with experimental and previous theoretical results, supporting the intrinsic origin of the anomalous Hall effect in ferromagnetic 3d transition metals. Furthermore, it is shown that

T. Naito; D. S. Hirashima; H. Kontani

2010-01-01

226

Photofragment spectroscopy of covalently bound transition metal complexes: a window into CH and CC bond  

E-print Network

Photofragment spectroscopy of covalently bound transition metal complexes: a window into C­H and C­C bond activation by transition metal ions RICARDO B. METZ* Department of Chemistry, University­H and C­C bonds in hydrocarbons. In this review, we discuss our studies of the electronic spectroscopy

Metz, Ricardo B.

227

ThermoElectricity at Low Temperatures. IX. The Transition Metals as Solute and Solvent  

Microsoft Academic Search

Transition metals (in particular Cr, Mn, Fe, Co and Ni) present as solutes give rise to highly anomalous thermo-electric powers and unusual resistive behaviour at very low temperatures. Following an outline of the theories which have been proposed to account for this behaviour, experimental data are presented on alloys of gold as parent metal with transition element solutes down to

D. K. C. MacDonald; W. B. Pearson; I. M. Templeton

1962-01-01

228

Structure and thermodynamic properties of liquid transition metals: An embedded-atom-method approach  

Microsoft Academic Search

We have obtained the volume term and effective pair potentials for liquid transition metals using the embedded-atom method (EAM). The EAM embedding functions are fitted to bulk solid-state properties: the experimental Voigt average bulk and shear moduli and sublimation energies. The same fitting procedure is used for all the transition metals. This potential is used in conjunction with the variational

G. M. Bhuiyan; M. Silbert; M. J. Stott

1996-01-01

229

XAFS Studies of Transition Metal and Halogen Biomaterials in Invertebrate Tools  

E-print Network

XAFS Studies of Transition Metal and Halogen Biomaterials in Invertebrate Tools Y. Taoad , J of brominated aromatic amino acid-derived organic components in these biomaterials. Calculated Debye, invertebrate tools, biomaterials PACS: 87.64.Fb INTRODUCTION There exists a large amount of transition metals

Scott, Robert A.

230

Chemical synthetic strategy for single-layer transition-metal chalcogenides.  

PubMed

A solution-phase synthetic protocol to form two-dimensional (2D) single-layer transition-metal chalcogenides (TMCs) has long been sought; however, such efforts have been plagued with the spontaneous formation of multilayer sheets. In this study, we discovered a solution-phase synthetic protocol, called "diluted chalcogen continuous influx (DCCI)", where controlling the chalcogen source influx (e.g., H2S) during its reaction with the transition-metal halide precursor is the critical parameter for the formation of single-layer sheets as examined for the cases of group IV TMCs. The continuous influx of dilute H2S throughout the entire growth period is necessary for large sheet formation through the exclusive a- and b-axial growth processes. By contrast, the burst influx of highly concentrated H2S in the early stages of the growth process forms multilayer TMC nanodiscs. Our DCCI protocol is a new synthetic concept for single-layer TMCs and, in principle, can be operative for wide range of TMC nanosheets. PMID:25313652

Yoo, Dongwon; Kim, Minkyoung; Jeong, Sohee; Han, Jeonghee; Cheon, Jinwoo

2014-10-22

231

Infusing Early Intervention for Substance Use Into Community Mental Health Services for Transitioning Youth  

Microsoft Academic Search

The treatment of transitioning youth (ages 1625) diagnosed with co-occurring mental health and substance abuse problems has been the focus of numerous research and practice efforts. However, far less attention has been devoted to intervening early to address alcohol and other drug (AOD) use, which has the potential to contribute to the numerous challenges transitioning youth with emotional or behavioral

Sarah A. Taylor; Elizabeth K. Anthony

2011-01-01

232

Kindergarten Transition: Does Family Involvement Make a Difference in Children's Early School Adjustment?  

ERIC Educational Resources Information Center

Kindergarten transition is a critical experience for children because of its potential long-term impact on school performance. Recognizing this impact, the field of early childhood education has been making great efforts to facilitate children's smooth transition to kindergarten through various approaches. One of the most widely accepted

Kang, Jean

2010-01-01

233

Ligational behavior of Schiff bases towards transition metal ion and metalation effect on their antibacterial activity  

NASA Astrophysics Data System (ADS)

New Schiff bases pyrazine-2-carboxylicacid (phenyl-pyridin-2-yl-methylene)-hydrazide (Hpch-bp) HL1 and pyrazine-2-carboxylicacid (pyridin-2-ylmethylene)-hydrazide (Hpch-pc) HL2 derived from condensation of pyrazine carboxylic hydrazide (Hpch) with 2-benzoyl pyridine (bp) or pyridine 2-carbaldehyde (pc) and their transition metal complexes of type ML(1-2)2 have been synthesized, where M = Mn(II), Co(II), Ni(II), Cu(II) and Zn(II). Characterization of ligands and their metal complexes was carried out by elemental analysis, conductimetric studies, magnetic susceptibility, spectroscopic techniques (IR, UV-VIS, NMR, ESR, Mass) and thermogravimetric analysis. The physico-chemical studies revealed octahedral geometry or distorted octahedral geometry around metal ion. These azomethine Schiff base ligands acted as tridentate ? coordinating through carbonyl, azomethine and pyridine nitrogen present in the ligand. The thermodynamic and thermal properties of the complexes have been investigated and it was observed on the basis of these studies that thermal stability of complexes follows the order Mn < Zn < Cu < Co < Ni. The ligands and their complexes were tested for in vitro antibacterial activity at different concentrations against bacteria viz. Gram positive Bacillus subtilis, Micrococcus luteus and Gram negative Pseudomonas aeruginosa, Pseudomonas mendocina. A marked enhancement in biocidal activity of the ligands under similar experimental conditions was observed as a consequence of coordination with metal ions. The trend of growth inhibition in the complexes was found to be in the order: Cu > Mn > Ni > Co > Zn.

Devi, Jai; Batra, Nisha; Malhotra, Rajesh

2012-11-01

234

Environmental Effects on the Metallicities of Early-Type Galaxies  

NASA Technical Reports Server (NTRS)

We have completed and published two papers based on research from this grant. Our first paper "SN IA Enrichment in Virgo Early-type Galaxies from ROSAT and ASCA Observations" was published in the Astrophysical Journal (vol 539,603) reported on the properties of nine X-ray bright elliptical galaxies in the Virgo cluster observed by ROSAT and ASCA. We measured iron abundance gradients as a function of radius in three galaxies. We found that the magnesium and silicon abundance gradients were in general flatter than those of iron. We suggest this is due to a metallicity dependence in the metal production rates of SN Ia's. We calculate SN Ia rates in the center of these galaxies that are comparable to those measured optically. Our second paper "ASCA Observations of Groups at Radii of Low Overdensity: Implications for Cosmic Preheating" also was published in the Astrophysical Journal (vol 578, 74). This paper reported on the ASCA spectroscopy of nine groups of galaxies. We found that the entropy profile in groups is driven by nongravitational heating processes, and could be explained by a short period of preheating by galactic winds.

Jones, Christine; Oliversen, Ronald J. (Technical Monitor)

2003-01-01

235

A Qualitative Study of Early Family Histories and Transitions of Homeless Youth  

ERIC Educational Resources Information Center

Using intensive qualitative interviews with 40 homeless youth, this study examined their early family histories for abuse, neglect, and other family problems and the number and types of transitions that youth experienced. Multiple forms of child maltreatment, family alcoholism, drug use, and criminal activity characterized early family histories

Tyler, Kimberly A.

2006-01-01

236

Fingerprints of spin-orbital entanglement in transition metal oxides  

E-print Network

The concept of spin-orbital entanglement on superexchange bonds in transition metal oxides is introduced and explained on several examples. It is shown that spin-orbital entanglement in superexchange models destabilizes the long-range (spin and orbital) order and may lead either to a disordered spin-liquid state or to novel phases at low temperature which arise from strongly frustrated interactions. Such novel ground states cannot be described within the conventionally used mean field theory which separates spin and orbital degrees of freedom. Even in cases where the ground states are disentangled, spin-orbital entanglement occurs in excited states and may become crucial for a correct description of physical properties at finite temperature. As an important example of this behaviour we present spin-orbital entanglement in the $R$VO$_3$ perovskites, with $R$=La,Pr,...,Yb,Lu, where such finite temperature properties of these compounds can be understood only using entangled states: ($i$) thermal evolution of the optical spectral weights, ($ii$) the dependence of transition temperatures for the onset of orbital and magnetic order on the ionic radius in the phase diagram of the $R$VO$_3$ perovskites, and ($iii$) dimerization observed in the magnon spectra for the $C$-type antiferromagnetic phase of YVO$_3$. Finally, it is shown that joint spin-orbital excitations in an ordered phase with coexisting antiferromagnetic and alternating orbital order introduces topological constraints for the hole propagation and will thus radically modify transport properties in doped Mott insulators where hole motion implies simultaneous spin and orbital excitations.

Andrzej M. Ole?

2012-07-12

237

Photoluminescence properties of Jahn-Teller transition-metal ions  

NASA Astrophysics Data System (ADS)

This work investigates the influence of electron-phonon coupling associated with E ?e and T ?e Jahn-Teller (JT) effect in different transition-metal (TM) ions on de-excitation phenomena through nonradiative multiphonon relaxation, i.e., photoluminescence (PL) quenching. We developed a configurational curve model which is able to predict from the absorption spectrum whether a given JT-TM ion is PL or quenched. The prediction is made on the basis of an adapted Dexter-Klick-Russell parameter for JT systems, defined in terms of spectroscopic parameters through ?JT=??eabs/Eabs, where ?eabs refers to the splitting of the parent octahedral Eg states by the JT distortion in E ?e (? =3/4) or T ?e (? =1/4), and Eabs is the energy of the first absorption band involving electronic transition between Eg and T2g. We show that PL in any JT-TM ion occurs whenever ?JT<0.1 or is quenched if ?JT>0.2. This result is noteworthy since it allows us to establish structural requirements for the JT-TM ion and the host crystal to be PL. Although PL properties of materials containing TM ions depend on a variety of structural factors such as the electronic configuration, the site symmetry, and the crystal field produced by neighboring atoms, the present model achieves this goal through a simple spectroscopic parameter: ?JT. In this work we correlated the PL properties of different sixfold-coordinated JT systems such as Ti3+, Cu2+, Mn3+, Cr2+, Fe2+, Co3+, and Ni3+ in halides and oxides with ?JT obtained from their respective absorption spectra. From this analysis we conclude that depending on the nature of the JT coupling and its strength, PL is either strongly favored or quenched in T ?e while it is mostly quenched in E ?e systems due to the larger JT distortion.

Sanz-Ortiz, Marta N.; Rodrguez, Fernando

2009-09-01

238

Nanocrystalline transition metal ferrites: Synthesis, characterization and surface functionalization  

NASA Astrophysics Data System (ADS)

In this thesis, a new synthetic methodology for the high yield synthesis of spinel-type transition metal ferrite nanoparticles has been developed. This approach is based on the complexation of the first-row transition metal cations with diethylene glycol (DEG) followed by the hydrolysis of the resulting chelate iron alkoxide complexes in the presence of an alkaline hydroxide. Due to the passivation of their surfaces with DEG molecules, the as-prepared nanoparticles are stable against agglomeration and can be easily dispersed in polar protic solvents (water, alcohols, etc.). Alternatively, a postsynthesis passivation with carboxylate ions can render the iron oxide nanocrystals highly dispersible in non-polar solvents. Optimization of the reaction conditions suggested that the size of the nanocrystals could be controlled by changing the complexing strength of the reaction medium. This hypothesis was verified in the case of the Fe3O4 nanoparticles: their sizes vary from 5.7 nm when the reaction is performed in neat diethylene glycol to 16.8 nm in N-methyl diethanolamine (NMDEA), whereas a 1:1 (%wt) mixture of these solvents yields nanocrystals with an average size of and 12.7 nm. A detailed characterization by using a wide variety of techniques, including powder X-Ray diffraction, IR spectroscopy, thermogravimetric analysis (TGA), transmission electron microscopy (TEM) and 1H-NMR spectrometry was performed in order to elucidate the composition and the morphology of the variable-sized iron oxide nanoparticles. Both finite size and interparticle interaction effects were identified to influence the magnetic behavior of the oleate-capped nanosized particles. At low temperatures the Fe3O 4 nanocrystals exhibit a ferromagnetic behavior with blocking temperatures which increase with the average particle size, whereas at room temperature, except for the largest nanoparticles, they undergo a superparamagnetic relaxation. We exploited the high surface reactivity of the 10 nm Fe3O 4 nanoparticles to attach 2-3 nm gold grains to their surfaces through a simple, two-step chemically controlled procedure. By chemically bonding bioactive molecules to the attached Au nanoparticles these novel nanoarchitectures open up new opportunities for the implementation of the magnetic nanoparticles as a platform for various applications in the biomedical field.

Caruntu, Daniela

239

Explicitly correlated composite thermochemistry of transition metal species.  

PubMed

Atomization energies were calculated using explicitly correlated coupled cluster methods with correlation consistent basis sets for a series of 19 small molecules containing 3d transition metal atoms. The atomization energies were calculated using a modified Feller-Peterson-Dixon approach in which CCSD(T) complete basis set (CBS) limits were obtained using extrapolations of aVTZ?aVQZ CCSD(T)-F12b correlation energies, and then a series of additive contributions for relativity, core correlation, higher order correlation, and zero-point vibrations were included. The frozen-core CBS limits calculated with F12 methods closely matched the more computational expensive conventional awCVQZ?awCV5Z CBS extrapolations, with a mean unsigned deviation of just 0.1 kcal?mol. In particular, the CCSD(T?)-F12b?aVDZ and aVTZ atomization energies were more accurate on average than the conventional CCSD(T)?aVQZ and aV5Z results, respectively. In several cases the effects of higher order correlation beyond CCSD(T), as judged by CCSDT and CCSDT(Q)? calculations, were greater than 1 kcal?mol, reaching 4.5 kcal?mol for CrO3. For the 16 molecules of this study with experimental uncertainties of ?3.5 kcal?mol or less, the final composite heats of formation have a mean unsigned deviation (MUD) from experiment of just 1.3 kcal?mol, which is slightly smaller than the average of the experimental uncertainties, 1.8?kcal?mol. The root mean square deviation (RMS) is only slightly larger at 1.7 kcal?mol. Without the contributions due to higher order correlation effects, the MUD and RMS rise to 2.1 and 2.8?kcal?mol, respectively. To facilitate the F12 calculations, new (aug-)cc-pVnZ?MP2Fit (n = Q, 5) and (aug-)cc-pwCVTZ?MP2Fit auxiliary basis sets were also developed for the transition metal atoms. PMID:24028112

Bross, David H; Hill, J Grant; Werner, H-J; Peterson, Kirk A

2013-09-01

240

Metal-Insulator Transition in Dilute 2D Electron and Hole Gases  

Microsoft Academic Search

\\u000a The existence of a critical metal-insulator transition in two-dimensional (2D) systems has been a subject of great debate\\u000a over the last few decades. The scaling theory of electron localisation [1] predicts a critical metal-to-insulator transition with increasing disorder only in 3D, and no such transition in 2D. According\\u000a to this theory, the resistance of a 2D sample should monotonically increase

A. K. Savchenko

241

The Mass-Metallicity Gradient Relation of Early-Type Galaxies  

NASA Astrophysics Data System (ADS)

We present a newly observed relation between galaxy mass and radial metallicity gradients of early-type galaxies. Our sample of 51 early-type galaxies encompasses a comprehensive mass range from dwarfs to brightest cluster galaxies. The metallicity gradients are measured out to one effective radius by comparing nearly all of the Lick absorption-line indices to recent models of single stellar populations. The relation shows very different behavior at low and high masses, with a sharp transition being seen at a mass of ~3.5 1010 M sun (velocity dispersion of ~140 km s-1, MB ~ -19). Low-mass galaxies form a tight relation with mass, such that metallicity gradients become shallower with decreasing mass and positive at the very low mass end. Above the mass transition point several massive galaxies have steeper gradients, but a clear downturn is visible marked by a broad scatter. The results are interpreted in comparison with competing model predictions. We find that an early star-forming collapse could have acted as the main mechanism for the formation of low-mass galaxies, with star formation efficiency increasing with galactic mass. The high-mass downturn could be a consequence of merging and the observed larger scatter a natural result of different merger properties. These results suggest that galaxies above the mass threshold of ~3.5 1010 M sun might have formed initially by mergers of gas-rich disk galaxies and then subsequently evolved via dry merger events. The varying efficiency of the dissipative merger-induced starburst and feedback processes have shaped the radial metallicity gradients in these high-mass systems. Based on observations obtained at the Gemini observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the NSF in behalf of the Gemini partnership: the National Science Foundation (United States), the Particle Physics and Astronomy Research Council (United Kingdom), the National Research Council (Canada), CONICYT (Chile), the Australian Research Council (Australia), CNPq (Brazil), and CONICET (Argentina).

Spolaor, Max; Proctor, Robert N.; Forbes, Duncan A.; Couch, Warrick J.

2009-02-01

242

Transition metal activation and functionalization of carbon-hydrogen bonds  

SciTech Connect

We are investigating the fundamental thermodynamic and kinetic factors that influence carbon-hydrogen bond activation at homogeneous transition metal centers and the conversion of hydrocarbons into functionalized products of potential use to the chemical industry. Advances have been made in both understanding the interactions of hydrocarbons with metals and in the functionalization of hydrocarbons. We have found that RhCl(PR{sub 3}){sub 2}(CNR) complexes can catalyze the insertion of isonitriles into the C-H bonds or arenes upon photolysis. The mechanism of these reactions was found to proceed by way of initial phosphine dissociation, followed by C-H activation and isonitrile insertion. We have also examined reactions of a series of arenes with (C{sub 5}Me{sub 5})Rh(PMe{sub 3})PhH and begun to map out the kinetic and thermodynamic preferences for arene coordination. The effects of resonance, specifically the differences in the Hueckel energies of the bound vs free ligand, are now believed to fully control the C-H activation/{eta}{sup 2}-coordination equilibria. We have begun to examine the reactions of rhodium isonitrile pyrazolylborates for alkane and arene C-H bond activation. A new, labile, carbodiimide precursor has been developed for these studies. We have completed studies of the reactions of (C{sub 5}Me{sub 5})Rh(PMe{sub 3})H{sub 2} with D{sub 2} and PMe{sub 3} that indicate that both {eta}{sup 5} {yields} {eta}{sup 3} ring slippage and metal to ring hydride migration occur more facilely than thermal reductive elimination of H{sub 2}. We have examined the reactions of heterocycles with (C{sub 5}Me{sub 5})Rh(PMe{sub 3})PhH and found that pyrrole and furan undergo C-H or N-H activation. Thiophene, however, undergoes C-S bond oxidative addition, and the mechanism of activation has been shown to proceed through sulfur coordination prior to C-S insertion.

Jones, W.D.

1992-06-01

243

Discovering the electronic circuit diagram of life: structural relationships among transition metal binding sites in oxidoreductases.  

PubMed

Oxidoreductases play a central role in catalysing enzymatic electron-transfer reactions across the tree of life. To first order, the equilibrium thermodynamic properties of these proteins are governed by protein folds associated with specific transition metals and ligands at the active site. A global analysis of holoenzyme structures and functions suggests that there are fewer than approximately 500 fundamental oxidoreductases, which can be further clustered into 35 unique groups. These catalysts evolved in prokaryotes early in the Earth's history and are largely responsible for the emergence of non-equilibrium biogeochemical cycles on the planet's surface. Although the evolutionary history of the amino acid sequences in the oxidoreductases is very difficult to reconstruct due to gene duplication and horizontal gene transfer, the evolution of the folds in the catalytic sites can potentially be used to infer the history of these enzymes. Using a novel, yet simple analysis of the secondary structures associated with the ligands in oxidoreductases, we developed a structural phylogeny of these enzymes. The results of this 'composome' analysis suggest an early split from a basal set of a small group of proteins dominated by loop structures into two families of oxidoreductases, one dominated by ?-helices and the second by ?-sheets. The structural evolutionary patterns in both clades trace redox gradients and increased hydrogen bond energy in the active sites. The overall pattern suggests that the evolution of the oxidoreductases led to decreased entropy in the transition metal folds over approximately 2.5 billion years, allowing the enzymes to use increasingly oxidized substrates with high specificity. PMID:23754810

Kim, J Dongun; Senn, Stefan; Harel, Arye; Jelen, Benjamin I; Falkowski, Paul G

2013-07-19

244

The Early College Challenge: Navigating Disadvantaged Students' Transition to College  

ERIC Educational Resources Information Center

Successful early college high schools (ECHSs) are formed through partnerships between high schools and colleges (usually community colleges). Think of it as preparation through acceleration. ECHSs enroll disadvantaged students who have not excelled with ordinary grade-level academic content and have them take college courses while still in high

Rosenbaum, James E.; Becker, Kelly Iwanaga

2011-01-01

245

Metal-insulator transitions in IZO, IGZO, and ITZO films  

NASA Astrophysics Data System (ADS)

In this study, we measured the low-temperature resistivity of amorphous two- and three-dimensional (2D and 3D) indium-zinc oxide, indium-gallium-zinc oxide, and indium-tin-zinc oxide films with a wide range of carrier densities. To determine their critical characteristics at the metal-insulator transition (MIT), we used the Ioffe-Regel criterion. We found that the MIT occurs in a narrow range between k F ? = 0.13 and k F ? = 0.25, where k F and ? are the Fermi wave number and electron mean free path, respectively. For films in the insulating region, we analyzed ? ( T ) using a procedure proposed by Zabrodskii and Zinov'eva. This analysis confirmed the occurrence of Mott and Efros-Shklovskii (ES) variable-range hopping. The materials studied show crossover behavior from exp(TMott/T)1/4 or exp(TMott/T)1/3 for Mott hopping conduction to exp(TES/T)1/2 for ES hopping conduction with decreasing temperature. For both 2D and 3D materials, we found that the relationship between TMott and TES satisfies TES ? TMott2/3.

Makise, Kazumasa; Hidaka, Kazuya; Ezaki, Syohei; Asano, Takayuki; Shinozaki, Bunju; Tomai, Shigekazu; Yano, Koki; Nakamura, Hiroaki

2014-10-01

246

Thermomagnetic switching in amorphous rare-earth transition metal alloys  

SciTech Connect

Conditions for writing and erasure have been investigated for different amorphous rare-earth transition metal alloys using a simple temperature distribution evaluated for a three-layer structure. The radial and time dependence of the magnetic parameters relevant for the switching process have been calculated by means of the mean-field theory based on experimental data of the saturation magnetization, uniaxial anisotropy, and the coercivity, for alloys of composition (Gd,Tb)/sub 1-//sub x/Fe/sub x/ and Tb/sub 1-//sub x/(Fe,Co)/sub x/. From the radial profiles of the coercive field, maximum domain diameters are extracted in the limit of large domain velocities. Domain-wall stabilities are calculated from the force equation for writing and erasure conditions as a function of applied field yielding margins for stable domains and collapse fields. In addition to bubblelike domains, ring domain configurations are considered, which imply the possibility of direct overwrite for alloys with a compensation temperature above ambient temperature. The switching with a continuous read power level is discussed.

Hansen, P.

1987-07-01

247

Structural, electrical and magnetic properties of transition metal nickel oxides  

NASA Astrophysics Data System (ADS)

Neutron powder diffraction, high pressure, magnetic susceptibility, and heat capacity measurements, as well as x-ray powder diffraction and iodometric titration, have been conducted on transition metal nickel oxides (TMOs), representative Ruddlesden-Popper (RP) phases Lan+1NinO3n+1 (n = 1, 2, ..., infinity) and hole-doped La2-xSr xNiO4 (0 ? x ? 1.2). The first complete study of La 2-xSrxNiO4 (0 ? x ? 1.2) and La n+1NinO3n+1 (n = 2 and 3) phases under high pressure is produced. Strong direct experimental evidence for polaron dominated electrical conduction in these charge transfer (CT) gap La2-xSr xNiO4 compounds is provided. Temperature evolution of the crystal structure of La2-xSrxNiO4 (x = 1/4 and 1/3) is revealed through neutron powder diffraction, structural relationships among n = 1, 2, and 3 phases are exhibited, and charge density wave (CDW) in multilayer Lan+1NinO3n+1 phases is strongly suggested. No superconductivity is observed at pressures up to 1.6 GPa and temperatures down to 4.2 K.

Wu, Guoqing

248

Dislocations and Plasticity in bcc Transition Metals at High Pressure  

SciTech Connect

Using first-principles electronic structure calculations, quantum-based atomistic simulations and atomistically informed dislocation dynamics (DD) simulations, we have studied individual dislocation behavior and the multiscale modeling of single-crystal plasticity in the prototype bcc transition metals Ta, Mo and V under both ambient and high pressure conditions. The primary focus in this work is on the pressure-dependent structure, mobility and interaction of a/2<111> screw dislocations, which dominate the plastic deformation properties of these materials. At the electronic scale, first-principles calculations of elasticity, ideal strength and generalized stacking fault energy surfaces have been used to validate quantum-based multi-ion interatomic potentials. At the atomistic scale, these potentials have been used in flexible Green's function boundary condition simulations to study the core structure, Peierls stress {tau}{sub P}, thermally activated kink-pair formation and mobility below {tau}{sub P}, and phonon-drag mobility above {tau}{sub P}. These results have then been distilled into analytic velocity laws and used directly in predictive microscale DD simulations of flow stress and resolved yield stress over wide ranges of pressure, temperature and strain rate.

Yang, L H; Tang, M; Moriarty, J A

2009-01-23

249

Valency configuration of transition metal impurities in ZnO  

SciTech Connect

We use the self-interaction corrected local spin-density approximation to investigate the ground state valency configuration of transition metal (TM=Mn, Co) impurities in n- and p-type ZnO. We find that in pure Zn{sub 1-x}TM{sub x}O, the localized TM{sup 2+} configuration is energetically favored over the itinerant d-electron configuration of the local spin density (LSD) picture. Our calculations indicate furthermore that the (+/0) donor level is situated in the ZnO gap. Consequently, for n-type conditions, with the Fermi energy {epsilon}F close to the conduction band minimum, TM remains in the 2+ charge state, while for p-type conditions, with {epsilon}F close to the valence band maximum, the 3+ charge state is energetically preferred. In the latter scenario, modeled here by co-doping with N, the additional delocalized d-electron charge transfers into the entire states at the top of the valence band, and hole carriers will only exist, if the N concentration exceeds the TM impurity concentration.

Petit, Leon [ORNL; Schulthess, Thomas C [ORNL; Svane, Axel [University of Aarhus, Denmark; Temmerman, Walter M [Daresbury Laboratory, UK; Szotek, Zdzislawa [Daresbury Laboratory, UK; Janotti, Anderson [University of California, Santa Barbara

2006-01-01

250

Ionic bonding of transition-metal halides: A spectroscopic approach  

NASA Astrophysics Data System (ADS)

The dielectric theory of the chemical bond has been applied to crystals with either Cd(OH)2 or CdCl2 structure, namely to layered Mn, Fe, Co, and Ni dihalides (MX2) with octahedral coordination, in order to evaluate the fractional ionic character fi for this class of insulators. The crystalline spectroscopic energy gap Eg has been measured via the optical data, related to the dominant exciton peaks ?, and then evaluated either through the Phillips model (EPhillipsg) or the measured dielectric constant ?1(0) in the framework of the Penn model (EPenng). The obtained scales of ionicities, fi or fDTi, ranging from fi~=0.72 of NiI2 to fi~=0.80 of MnCl2 are then compared to the ionicity scale fXPSi based on x-ray photoelectron spectroscopy. For transition-metal chlorides, for which photoemission spectra are available, the different ionicity scales are in good agreement. Furthermore, the ionicity parameters scale rather well with the ionicity trend given by the fitted values of the net charge Z, the electrostatic parameter for dealing with crystals not completely ionic. The overall agreement between the spectroscopically determined ionicity, the structural, thermochemical, and electronic properties of these compounds seems to indicate that the dielectric theory of Phillips and Van Vechten can be successfully applied to layered materials with reduced ionicity and open d-shell configuration.

Thomas, J.; Pollini, I.

1985-08-01

251

Defect-induced semiconductor to metal transition in graphene monoxide.  

PubMed

This study investigates the influence of point defects on the geometric and electronic structure of graphene monoxide (GMO) via density functional theory calculations. In aspects of defect formation energy, GMOs with oxygen vacancies and bridge interstitial defects are more likely to form when compared to GMOs with defects such as carbon vacancies and hollow interstitial defects. It was also found that the oxygen vacancy or the hollow interstitial defect induces local tensile strain around the defective site and this strain increases the band gap energy of the defective GMO. In addition, the band gaps of GMO with carbon vacancies or bridge interstitial defects decreased mainly due to the dangling bonds, not due to the strain effect. It is noted that the dangling bond derived from the defects forms the defect-level in the band gap of GMO. The semiconductor to metal transition by the band gap change (0-0.7 eV) implies the possibility for band gap engineering of GMO by vacancies and interstitial defects. PMID:24886723

Woo, Jungwook; Yun, Kyung-Han; Cho, Sung Beom; Chung, Yong-Chae

2014-07-14

252

Transition radiation in metal-metal multilayer nanostructures as a medical source of hard x-ray radiation  

E-print Network

Transition radiation in metal-metal multilayer nanostructures as a medical source of hard x at developing an x-ray source for medical applications, which is based on using low-energy relativistic in mind, we have considered also the unwanted effects due to bremsstrahlung radiation, absorption

Kaplan, Alexander

253

Methods for Detecting Early Warnings of Critical Transitions in Time Series Illustrated Using Simulated Ecological Data  

PubMed Central

Many dynamical systems, including lakes, organisms, ocean circulation patterns, or financial markets, are now thought to have tipping points where critical transitions to a contrasting state can happen. Because critical transitions can occur unexpectedly and are difficult to manage, there is a need for methods that can be used to identify when a critical transition is approaching. Recent theory shows that we can identify the proximity of a system to a critical transition using a variety of so-called early warning signals, and successful empirical examples suggest a potential for practical applicability. However, while the range of proposed methods for predicting critical transitions is rapidly expanding, opinions on their practical use differ widely, and there is no comparative study that tests the limitations of the different methods to identify approaching critical transitions using time-series data. Here, we summarize a range of currently available early warning methods and apply them to two simulated time series that are typical of systems undergoing a critical transition. In addition to a methodological guide, our work offers a practical toolbox that may be used in a wide range of fields to help detect early warning signals of critical transitions in time series data. PMID:22815897

Dakos, Vasilis; Carpenter, Stephen R.; Brock, William A.; Ellison, Aaron M.; Guttal, Vishwesha; Ives, Anthony R.; Kefi, Sonia; Livina, Valerie; Seekell, David A.; van Nes, Egbert H.; Scheffer, Marten

2012-01-01

254

Oligomeric rare-earth metal cluster complexes with endohedral transition metal atoms  

NASA Astrophysics Data System (ADS)

Comproportionation reactions of rare-earth metal trihalides (RX3) with the respective rare-earth metals (R) and transition metals (T) led to the formation of 22 oligomeric R cluster halides encapsulating T, in 19 cases for the first time. The structures of these compounds were determined by single-crystal X-ray diffraction and are composed of trimers ({T3R11}X15-type, P63/m), tetramers ({T4R16}X28{R4} (P-43m), {T4R16}X20 (P42/nnm), {T4R16}X24(RX3)4 (I41/a) and {T4R16}X23 (C2/m) types of structure) and pentamers ({Ru5La14}2Br39, Cc) of {TRr}n (n=2-5) clusters. These oligomers are further enveloped by inner (Xi) as well as outer (Xa) halido ligands, which possess diverse functionalities and interconnect like oligomers through i-i, i-a and/or a-i bridges. The general features of the crystal structures for these new compounds are discussed and compared to literature entries as well as different structure types with oligomeric T centered R clusters. Dimers and tetramers originating from the aggregation of {TR6} octahedra via common edges are more frequent than trimers and pentamers, in which the {TRr} clusters share common faces.

Steinberg, Simon; Zimmermann, Sina; Brhmann, Matthias; Meyer, Eva; Rustige, Christian; Wolberg, Marike; Daub, Kathrin; Bell, Thomas; Meyer, Gerd

2014-11-01

255

Theory of elastic phase transitions in metals at high pressures. Application to vanadium  

SciTech Connect

Structural transformations in elementary metals under high pressures are considered using the Landau theory of phase transitions, in which the finite strain tensor components play the role of the order parameter. As an example, the phase transition in vanadium observed at a pressure of 69 GPa is analyzed. It is shown that it is a first-order elastic phase transition, which is close to a second-order transition.

Krasil'nikov, O. M., E-mail: omkras@mail.ru; Vekilov, Yu. Kh.; Isaev, E. I.; Bondarenko, N. G. [National Research Technological University MISiS (Russian Federation)

2011-02-15

256

Recent advances in transition metal-catalyzed Csp2-monofluoro-, difluoro-, perfluoromethylation and trifluoromethylthiolation  

PubMed Central

Summary In the last few years, transition metal-mediated reactions have joined the toolbox of chemists working in the field of fluorination for Life-Science oriented research. The successful execution of transition metal-catalyzed carbonfluorine bond formation has become a landmark achievement in fluorine chemistry. This rapidly growing research field has been the subject of some excellent reviews. Our approach focuses exclusively on transition metal-catalyzed reactions that allow the introduction of CFH2, CF2H, CnF2 n +1 and SCF3 groups onto sp carbon atoms. Transformations are discussed according to the reaction-type and the metal employed. The review will not extend to conventional non-transition metal methods to these fluorinated groups. PMID:24367416

Landelle, Gregory; Panossian, Armen; Pazenok, Sergiy; Vors, Jean-Pierre

2013-01-01

257

Ligational behavior of Schiff bases towards transition metal ion and metalation effect on their antibacterial activity.  

PubMed

New Schiff bases pyrazine-2-carboxylicacid (phenyl-pyridin-2-yl-methylene)-hydrazide (Hpch-bp) HL(1) and pyrazine-2-carboxylicacid (pyridin-2-ylmethylene)-hydrazide (Hpch-pc) HL(2) derived from condensation of pyrazine carboxylic hydrazide (Hpch) with 2-benzoyl pyridine (bp) or pyridine 2-carbaldehyde (pc) and their transition metal complexes of type ML((1-2)2) have been synthesized, where M=Mn(II), Co(II), Ni(II), Cu(II) and Zn(II). Characterization of ligands and their metal complexes was carried out by elemental analysis, conductimetric studies, magnetic susceptibility, spectroscopic techniques (IR, UV-VIS, NMR, ESR, Mass) and thermogravimetric analysis. The physico-chemical studies revealed octahedral geometry or distorted octahedral geometry around metal ion. These azomethine Schiff base ligands acted as tridentate coordinating through carbonyl, azomethine and pyridine nitrogen present in the ligand. The thermodynamic and thermal properties of the complexes have been investigated and it was observed on the basis of these studies that thermal stability of complexes follows the order Mnmetal ions. The trend of growth inhibition in the complexes was found to be in the order: Cu>Mn>Ni>Co>Zn. PMID:22813991

Devi, Jai; Batra, Nisha; Malhotra, Rajesh

2012-11-01

258

Comprehensive study of the metal-insulator transition in pulsed laser deposited epitaxial VO2 thin films  

E-print Network

Comprehensive study of the metal-insulator transition in pulsed laser deposited epitaxial VO2 thin properties of high-quality VO2 thin films across its metal-insulator phase transition. Detailed x along three equivalent crystallographic directions. Across the metal-insulator transition

Wu, Junqiao

259

Observations of Electron Irradiation Effects at Transition Metal Oxide Surfaces.  

NASA Astrophysics Data System (ADS)

In this dissertation the effects of electron irradiation on several maximally-valent transition-metal oxides have been investigated using a combination of surface profile imaging, selected-area-electron diffraction, optical diffractograms, and electron-energy-loss spectroscopy. It was found that the surfaces of TiO_2, Nb _2O_5, V_2 O_5 and Ti_2 Nb_{10}O _{29} were reduced to the corresponding binary oxide phase inside a 400keV high-resolution electron microscope during observation at high magnification and high current density (5-50A/cm^2). These reduced surface phases, which are all based on cubic rock -salt structures, grow with a well-defined three-dimensional epitaxial relationship with the bulk oxide. Certain structural features of the epitaxy were found to be common to the oxides studied and computer-drawn models of the crystalline structures were used to gain insight into the atomic rearrangements which took place during the monoxide growth. In the case of WO_3, for which no stable monoxide phase has been reported, the striking similarity in the epitaxial growth of a surface phase led to the proposal of a novel monoxide phase. The metallic conductivity of each of these monoxide phases was considered to be significant in terms of the mechanism which is proposed to initiate the electron-stimulated-desorption of oxygen from the original oxides. Evidence for a current density threshold for the accumulation of the monoxide phase and observation of recrystallization below this threshold are reported. In contrast, in response to extremely high-current density irradiation (10 ^3-10^4A/cm ^2), the surfaces of these oxides developed sputter pits and were reduced beyond the monoxide phase. These observations were repeated for TiO_2 in a ultra-high-vacuum microscope. Secondary electron images, high-angle annular dark-field images and EELS confirmed that the improved vacuum did not affect substantially the beam-induced reactions.

McCartney, Martha Rogers

260

The metal-insulator transition in VO2 studied using terahertz apertureless near-field microscopy  

NASA Astrophysics Data System (ADS)

We have studied the metal-insulator transition in a vanadium dioxide (VO2) thin film using terahertz apertureless near-field optical microscopy. We observe a variation of the terahertz amplitude due to the phase transition induced by an applied voltage across the sample. The change of the terahertz signal is related to the abrupt change of the conductivity of the VO2 film at the metal-insulator transition. The subwavelength spatial resolution of this near-field microscopy makes it possible to detect signatures of micron-scale metallic domains in inhomogeneous VO2 thin films.

Zhan, Hui; Astley, Victoria; Hvasta, Michael; Deibel, Jason A.; Mittleman, Daniel M.; Lim, Yong-Sik

2007-10-01

261

Structural and Electrochemical Characterization of Lithium Transition Metal Phosphates  

NASA Astrophysics Data System (ADS)

The lithium ion battery has emerged as one of the most promising hybrid vehicle energy storage systems of the future. Of the potential cathode chemistries explored, lithium transition metal phosphates have generated a significant amount of interest due to their low-cost precursors, potential ease of synthesis, stability, and their environmentally friendly nature. This is in contrast to layered oxide systems such as LiCoO2, which have long been considered state of the art, but are now being reevaluated due to their structural instability at elevated temperatures, and higher cost. In particular, LiFePO4 has an operating potential comparable to those batteries available on the market (3.5V vs. Li/Li+), and higher theoretical specific capacity (170mAh/g vs. that of LiCoO2 which is 140mAh/g). The manganese analog to LiFePO4, LiMnPO4, exhibits a higher operating potential (4.1V v Li/Li+), and the same theoretical capacity, however Li-ion diffusion through this structure is much more rate limited and its theoretical capacity cannot be realized at rates suitable for commercial applications. The purpose of this work was threefold: 1) To explore the impact of Fe substitution on Mn sites in LiMnPO 4. 2) To examine the effects of alterations to the particle/electrolyte interface on rate capability. 3) To explore a novel fabrication route for LiMnPO4 using microwaves, and determine an optimal power and time combination for best performance. The coexistence of Fe and Mn on the transition metal site M, of LiMPO 4 resulted in an improved apparent Li-ion diffusivity in both Fe and Mn regimes as compared to that observed for LiFePO4 and LiMnPO 4 respectively. Calculations made from two different analysis methods, cyclic voltammetry (CV) and galvanostatic intermittent titration (GITT) drew this same conclusion. The signature characteristics observed from the CVs pertaining to single and dual phase reactions led to a delithiation model of LiFe0.5Mn0.5PO4 proposing the localization of half the Li atoms with Fe and half with Mn. Following this work, pure LiMnPO 4 was explored. LiMnPO4 was successfully fabricated using rapid, solid state microwave irradiation. Three classes of materials were prepared to study the effects of particle size, carbon coating, and electrolytic environment on rate capability. Reduction in particle size, carbon coating, and the aqueous electrolyte environment provided the most favorable conditions for performance enhancement. Based on the initial promising results of solid state microwave synthesis, further studies were conducted to optimize irradiation parameters. C-LiMnPO 4 fabricated at 200W for 5.0 minutes demonstrated the most superior rate capability. This material attained its full theoretical specific capacity, showing promise for the advancement of materials fabricated via this method.

Hashambhoy, Ayesha Maria

262

IR analysis of polyvinylidene fluoride doped with transition metal halides  

NASA Astrophysics Data System (ADS)

Pure and doped polyvinylidene fluoride (PVDF) films were prepared by casting. Films with various concentrations of transition metal halides TMHs (AlCl3, ZnCl2, and CoCl2) were prepared. The microstructure and physical properties of these films were studied by IR analysis. The two factors affecting the interaction between the PVDF and MHs are (i) the dopant weight fraction (Hc) (0.05% -30%) by weght, and (ii) precasting time (tpc) which is the time during which the PVDF pellets are maintained solved with the halides added before casting. From the IR quantitative analysis, it is evident that the addition of the three MH to the undoped PVDF film makes ?-phase as the dominant crystalline structures in the doped films without the need for mechanical drawing treatment. The precasting time plays a role for new crystalline structures to appear which becomes strong for CoCl2 doping, moderate in ZnCl2 doping and weak in AlCl3 doping. This phase is maximum for the relatively low doping levels < 5%. The stability of these structures in the samples doped with CoCl2 is high compared to the doping with ZnCl2 and AlCl3. This result is extremely important hence the ?-phase is that one which is electrically active compared with the other two phases and it is needed in all the samples used in the useful applications of the PVF2 films. Remembering, that ?-phase is obtained in the crystallization from melt samples by the uneasy mechanical stress and elevated temperature, it becomes evident the importance of the present result.

El Hefnawy, Somia M.; Aboelkher, Mervet M.; Abdelkader, H.

2009-05-01

263

Transition Metal Ions: Charge Carriers that Mediate the Electron Capture Dissociation Pathways of Peptides  

NASA Astrophysics Data System (ADS)

Electron capture dissociation (ECD) of model peptides adducted with first row divalent transition metal ions, including Mn2+, Fe2+, Co2+, Ni2+, Cu2+, and Zn2+, were investigated. Model peptides with general sequence of ZGGGXGGGZ were used as probes to unveil the ECD mechanism of metalated peptides, where X is either V or W; and Z is either R or N. Peptides metalated with different divalent transition metal ions were found to generate different ECD tandem mass spectra. ECD spectra of peptides metalated by Mn2+ and Zn2+ were similar to those generated by ECD of peptides adducted with alkaline earth metal ions. Series of c-/ z-type fragment ions with and without metal ions were observed. ECD of Fe2+, Co2+, and Ni2+ adducted peptides yielded abundant metalated a-/ y-type fragment ions; whereas ECD of Cu2+ adducted peptides generated predominantly metalated b-/ y-type fragment ions. From the present experimental results, it was postulated that electronic configuration of metal ions is an important factor in determining the ECD behavior of the metalated peptides. Due presumably to the stability of the electronic configuration, metal ions with fully-filled (i.e., Zn2+) and half filled (i.e., Mn2+) d-orbitals might not capture the incoming electron. Dissociation of the metal ions adducted peptides would proceed through the usual ECD channel(s) via "hot-hydrogen" or "superbase" intermediates, to form series of c-/z - fragments. For other transition metal ions studied, reduction of the metal ions might occur preferentially. The energy liberated by the metal ion reduction would provide enough internal energy to generate the "slow-heating" type of fragment ions, i.e., metalated a-/y- fragments and metalated b-/y- fragments.

Chen, Xiangfeng; Fung, Yi Man Eva; Chan, Wai Yi Kelly; Wong, Pui Shuen; Yeung, Hoi Sze; Chan, T.-W. Dominic

2011-12-01

264

Broken symmetry and strangeness of the semiconductor impurity band metal-insulator transition  

PubMed Central

The filamentary model of the metal-insulator transition in randomly doped semiconductor impurity bands is geometrically equivalent to similar models for continuous transitions in dilute antiferromagnets and even to the ? transition in liquid He, but the critical behaviors are different. The origin of these differences lies in two factors: quantum statistics and the presence of long range Coulomb forces on both sides of the transition in the electrical case. In the latter case, in addition to the main transition, there are two satellite transitions associated with disappearance of the filamentary structure in both insulating and metallic phases. These two satellite transitions were first identified by Fritzsche in 1958, and their physical origin is explained here in geometrical and topological terms that facilitate calculation of critical exponents. PMID:9636137

Phillips, J. C.

1998-01-01

265

Properties of molecular beam epitaxy grown Eu{sub x}(transition metal){sub y} films (transition metals: Mn, Cr)  

SciTech Connect

The electronic and crystallographic structures, as well as the magnetic properties, of Eu{sub x}(transition metal){sub y} (transition metals: Mn, Cr) thin films grown by molecular beam epitaxy were studied. Relative changes of the Eu/Mn and Eu/Cr ratios derived from the XPS lines, as well as x-ray reflectivity, indicate mixing of the Eu/Mn and Eu/Cr layers. Valency transitions from Eu{sup 2+} to Eu{sup 3+} were observed in both systems for most studied stoichiometries. A transition to a magnetically ordered phase was observed at 15 K, 40 K, and 62 K for selected films in the Eu-Mn system, and at 50 K for the film with a Eu/Cr ratio of 0.5.

Balin, K. [A. Chelkowski Institute of Physics, University of Silesia, Katowice, 40-007 (Poland); Center for Magnetism and Magnetic Nanostructures, University of Colorado at Colorado Springs, Colorado Springs, Colorado 80918 (United States); Nowak, A. [A. Chelkowski Institute of Physics, University of Silesia, Katowice, 40-007 (Poland); Laboratoire de Physique de l'Etat Condense, University du Maine, Le Mans Cedex, 72085 (France); Gibaud, A. [Laboratoire de Physique de l'Etat Condense, University du Maine, Le Mans Cedex, 72085 (France); Szade, J. [A. Chelkowski Institute of Physics, University of Silesia, Katowice, 40-007 (Poland); Celinski, Z. [Center for Magnetism and Magnetic Nanostructures, University of Colorado at Colorado Springs, Colorado Springs, Colorado 80918 (United States)

2011-04-01

266

Equity and Quality? Challenges for Early Childhood and Primary Education in Ethiopia, India and Peru. Working Papers in Early Childhood Development, No. 55. Studies in Early Childhood Transitions  

ERIC Educational Resources Information Center

Part of the "Studies in Early Transitions" series, this Working Paper draws on interviews and observations carried out as part of "Young Lives", a 15-year longitudinal study of childhood poverty in Ethiopia, India, Peru and Vietnam based at the University of Oxford's Department of International Development. This paper focuses on the challenges of

Woodhead, Martin; Ames, Patricia; Vennam, Uma; Abebe, Workneh; Streuli, Natalia

2009-01-01

267

Tunable metal-insulator transitions in bilayer graphene by thermal annealing  

NASA Astrophysics Data System (ADS)

Tunable and highly reproducible metal-insulator transitions have been observed in bilayer graphene upon thermal annealing at 400 K under high vacuum conditions. Before annealing, the sample is metallic in the whole temperature regime of study. Upon annealing, the conductivity changes from metallic to that of an insulator and the transition temperature is a function of annealing time. The pristine metallic state can be reinstated by exposing to air thereby inducing changes in the electronic properties by adsorbing water vapor, which makes graphene a technologically promising material for sensor applications.

Kalon, Gopinadhan; Shin, Young Jun; Yang, Hyunsoo

2011-06-01

268

Compositional dependence of elastic moduli for transition-metal oxide spinels  

NASA Astrophysics Data System (ADS)

Spinel phases (AB2O4) are common non-silicate oxides in the Earth's crust and upper mantle. A characteristic of this mineral group is the ability to host a wide range of transition metals. Here we summarize the influence of transition metals (Fe, Zn, and Mn) on the pressure dependence of elastic moduli of related spinels (magnetite, gahnite, and franklinite) using GHz-ultrasonic interferometry. Measurements were carried out up to 10 GPa in diamond-anvil cells using hydrostatic pressure media. Transition metals with unfilled 3d orbitals strongly influence the elastic properties of spinels. Franklinite (Zn,Mn)Fe2O4 and magnetite Fe3O4 with transition metals on both A and B cation sites exhibit pressure-induced mode softening of C44, whereas C44 of gahnite(ZnAl2O4) and spinel (MgAl2O4) exhibit positive pressure derivatives of the shear moduli. Spinels with two transition elements tend to undergo phase changes at a lower pressure than those with none or only one transition metal. Along the Mn-Zn solid solution, the variation of moduli with composition is non-linear, and a mid-range franklinite composition studied here shows a minimum in C44 compared with either end-member: MnFe2O 4 or ZnFe2O4. In general, the linear variation of sound velocity with density (Birch's Law) is followed by spinels, however spinels containing only one or no transition metals follow a distinct slope from those containing transition metals on both A and B sites. The Cauchy relation, 0.5(C12 - C44) = P is fulfilled by spinels with only one or no transition metals, suggesting that that Coulomb interactions dominate. Spinels with two transition metals fail to meet the Cauchy relation, indicating strong directional dependence and covalent character of bonding. The bonding character of transition metals is crucial to understanding the elastic behavior of natural and synthetic spinel solid solutions containing transition metals.

Reichmann, H. J.; Jacobsen, S. D.; Boffa Ballaran, T.

2012-12-01

269

UPTAKE OF METAL IONS BY A NEW CHELATING ION-EXCHANGE RESIN. PART 2: ACID DEPENDENCIES OF TRANSITION AND POST-TRANSITION METAL IONS  

Microsoft Academic Search

Diphonixis a new dual-mechanism polyfunctional resin containing sulfonic and gem-diphosphonic acid groups. In Part 1 of this series the effectiveness of Diphonix in removing actinide ions from very acidic solutions was demonstrated. In this paper we report on the uptake of various transition and post-transition metal ions with Diphonix and two other resins for comparison. The results show that Diphonix

R. Chiarizia; E. P. Horwitz; R. C. Gatrone; S. D. Alexandratos; A. Q. Trochimczuk; D. W. Crick

1993-01-01

270

Conducting polymer-metal hybrid materials: Towards tunable redox control over transition metal properties?  

NASA Astrophysics Data System (ADS)

Terthienyl-based redox-switchable hemilabile ligands, 3' -(2-diphenylphosphinoethyl)-5,5?-dimethyl-2,2 ': 5',2?-terthiophene and 3'-(2-diphenylphosphinoethyl)-2,2':5,2 ?-terthiophene have been synthesized and fully characterized. Mononuclear, dinuclear, and polymeric Ru(II) complexes formed from these ligands demonstrate that this class of ligand provides electrochemical control over the electronic properties, coordination environments, and reactivities of bound transition metals. Specifically, [CpRuCO(kappa2-3 '-(2-diphenylphosphinoethyl)-5,5?-dimethyl-2,2 ':5',2?-terthiophene)][B(C 6H3-3,5-(CF3)2)4] ( 4a) exhibits a three order of magnitude increase in binding affinity for acetonitrile upon terthienyl-based oxidation. FT-IR spectroelectrochemical experiments on 4a indicate that terthienyl-based oxidation removes electron density from the metal center, equivalent to approximately 11--17% of the electronic change that occurs upon direct oxidation of Ru(II) to Ru(III) in analogous complexes. The FT-IR spectroelectrochemical responses of 4a were compared to those of dimeric and polymeric analogues of 4a. The spectroelectrochemistry of the dimer is consistent with two, sequential, one-electron ligand-based oxidations, compared to only one in 4a. In contrast, the polymer exhibits spectroelectrochemical behavior similar to that of 4a. The polymer spectroelectrochemistry shows changes in the metal center electronic properties between two different states, reflective of two discrete oxidation states of the polymeric ligand backbone. We propose that the polymer backbone does not allow one to vary the electronic properties of the metal center through a continuous range of oxidation states due to charge localization within the metallated films. The oxidation state dependent coordination chemistries of 4a and 4a + with a variety of substrates were studied. Dip-Pen Nanolithography (DPN) has been used to deposit monolayer-based resists with micron to sub-100 nm dimensions on the surfaces of Au/Ti/Si trilayer substrates. These resists have been used with wet chemical etchants to remove the unprotected substrate layers, resulting in three-dimensional solid-state features with comparable dimensions. This work demonstrates the potential of using DPN for a variety of solid-state nanolithography applications.

Weinberger, Dana Alise

2000-10-01

271

Controlled synthesis of transition metal/conducting polymer nanocomposites  

NASA Astrophysics Data System (ADS)

A novel displacement reaction has been observed to occur between conducting polymers (CP) and metal salts which can be used to fabricate nanostructured CP-metal composites in a one-pot manner. Vanadium pentoxide (V 2O5) nanofiber is used during the synthesis as the reactive seeds to induce the nanofibril CP-metal network formation. The CP-metal nanocomposites exhibit excellent sensory properties for hydrogen peroxide (H2O2) detection, where both high sensitivity and a low detection limit can be obtained. The sensory performance of the CP-metal composite can be further enhanced by a facile microwave treatment. It is believed that the CP-metal nanofibril network can be converted to a carbon-metal network by a microwave-induced carbonization process and result in the sensory enhancement.

Liu, Zhen; Liu, Yang; Zhang, Lin; Poyraz, Selcuk; Lu, Ning; Kim, Moon; Smith, James; Wang, Xiaolong; Yu, Yajiao; Zhang, Xinyu

2012-08-01

272

Group theory analysis of phonons in two-dimensional transition metal dichalcogenides  

E-print Network

Transition metal dichalcogenides (TMDCs) have emerged as a new two-dimensional material's field since the monolayer and few-layer limits show different properties when compared to each other and to their respective bulk ...

Ribeiro-Soares, J.

273

Single crystal particles of a mesoporous mixed transition metal oxide with a wormhole structure.  

PubMed

A new type of mesoporous mixed transition metal oxide of Nb and Ta (NbTa-TIT-1) has been prepared through a two-step calcination, which consists of single crystal particles with wormhole mesoporous structure. PMID:12240191

Lee, B; Lu, D; Kondo, J N; Domen, K

2001-10-21

274

Solid-state NMR concepts for the investigation of supported transition metal catalysts and nanoparticles.  

PubMed

In recent years, solid-state NMR spectroscopy has evolved into an important characterization tool for the study of solid catalysts and chemical processes on their surface. This interest is mainly triggered by the need of environmentally benign organic transformations ("green chemistry"), which has resulted in a large number of new catalytically active hybrid materials, which are organized on the meso- and nanoscale. Typical examples of these catalysts are supported homogeneous transition metal catalysts or transition metal nanoparticles (MNPs). Solid-state NMR spectroscopy is able to characterize both the structures of these materials and the chemical processes on the catalytic surface. This article presents recent trends both on the characterization of immobilized homogeneous transition metal catalysts and on the characterization of surface species on transition metal surfaces. PMID:23972428

Gutmann, Torsten; Grnberg, Anna; Rothermel, Niels; Werner, Mayke; Srour, Mohamad; Abdulhussain, Safaa; Tan, Shulin; Xu, Yeping; Breitzke, Hergen; Buntkowsky, Gerd

2013-01-01

275

Electron Spin Resonance of Tetrahedral Transition Metal Oxyanions (MO4n-) in Solids.  

ERIC Educational Resources Information Center

Outlines general principles in observing sharp electron spin resonance (ESR) lines in the solid state by incorporating the transition metal ion of interest into an isostructural diamagnetic host material in small concentration. Examples of some recent studies are described. (CS)

Greenblatt, M.

1980-01-01

276

Superelastic metal-insulator phase transition in single-crystal VO[subscript 2] nanobeams  

E-print Network

We investigated external-stress-induced metal-insulator phase transitions in cantilevered single-crystal VO[subscript 2] nanobeams at variable temperatures using a combined theoretical and experimental approach. An atomic ...

Fan, W.

277

Activation of methane by transition metal-substituted aluminophosphate molecular sieves  

DOEpatents

Aluminophosphate molecular sieves substituted with cobalt, manganese or iron and having the AlPO.sub.4 -34 or AlPO.sub.4 -5, or related AlPO.sub.4 structure activate methane starting at approximately 350.degree. C. Between 400.degree. and 500.degree. C. and at methane pressures .ltoreq.1 atmosphere the rate of methane conversion increases steadily with typical conversion efficiencies at 500.degree. C. approaching 50% and selectivity to the production of C.sub.2+ hydrocarbons approaching 100%. The activation mechanism is based on reduction of the transition metal(III) form of the molecular sieve to the transition metal(II) form with accompanying oxidative dehydrogenation of the methane. Reoxidation of the - transition metal(II) form to the transition metal(III) form can be done either chemically (e.g., using O.sub.2) or electrochemically.

Iton, Lennox E. (Downers Grove, IL); Maroni, Victor A. (Naperville, IL)

1991-01-01

278

Multi-body forces and the energetics of transition metals, alloys, and semiconductors  

SciTech Connect

Progress over the past year is divided into 3 areas: potential-energy functions for transition-metal aluminides; electronic structure and energetics of complex structures and quasicrystals; and ceramic materials (PdO, PtO).

Carlsson, A.E.

1992-01-01

279

Transition metal gettering studies and simulation for the optimization of silicon photovoltaic device processing  

E-print Network

We use what is known about transition metal (TM) defect thermodynamic driving forces and kinetic responses to make predictive simulation of gettering during solar cell fabrication possible. We have developed a simulator ...

Smith, Aime Louise, 1971-

2002-01-01

280

Selective exchange of divalent transition metal ions in cryptomelane-type manganic acid with tunnel structure  

SciTech Connect

The ion-exchange selectivity of divalent transition metal ions on cryptomelane-type manganic acid (CMA) with tunnel structure has been studied using the distribution coefficients ([ital K][sub [ital d

Tsuji, M. (Department of Chemistry, Faculty of Science, Tokyo Institute of Technology, 2-12-1, O-okayama, Meguro-ku, Tokyo 152 (Japan)); Komarneni, S. (Materials Research Laboratory and Department of Agronomy, The Pennsylvania State University, University Park, Pennsylvania 16802-4801 (United States))

1993-03-01

281

Effective Charge Transfer Distances in Cyanide-Bridged Mixed-Valence Transition Metal Complexes  

E-print Network

Effective Charge Transfer Distances in Cyanide-Bridged Mixed-Valence Transition Metal Complexes theory (Oh; Boxer J. Am. Chem. Soc. 1990, 112, 8161). Stark spectra are reported for a series of cyanide

Boxer, Steven G.

282

Strong Bond Activation with Late Transition-Metal Pincer Complexes as a Foundation for Potential Catalysis  

E-print Network

. Transition metal carbene and carbyne complexes are of great interest because of their role in a wide variety of catalytic reactions. Our work has resulted in the isolation of a rhodium(I) difluorocarbene. Reaction of the rhodium difluorocarbene complex...

Zhu, Yanjun

2012-07-16

283

Theoretical studies of transition metal surfaces as electrocatalysts for oxygen electroreduction  

E-print Network

are actively researched. Platinum alloys with different transition metals (for example: Ni, Co and Fe) have shown improved activity over pure Pt. The design of a Pt-free catalysts is also highly desirable, and different alternatives including metalloporphyrins...

Lamas, Eduardo J.

2007-09-17

284

Polar alignment of ?-shaped basic building units within transition metal oxide fluoride materials.  

PubMed

A series of pseudosymmetrical structures of formula K10(M2OnF11-n)3X (M = V and Nb, n = 2, X = (F2Cl)1/3, Br, Br4/2,I4/2; M = Mo, n = 4, X = Cl, Br4/2, I4/2) illustrates generation of polar structures with the use of ?-shaped basic building units (BBUs). For a compound to belong to a polar space group, dipole moments of individual species must be partially aligned. Incorporation of d(0) early transition metal polyhedral BBUs into structures is a common method to create polar structures, owing to the second-order Jahn-Teller distortion these polyhedra contain. Less attention has been spent examining how to align the polar moments of BBUs. To address alignment, we present a study on previously reported bimetallic BBUs and synthesized compounds K10(M2OnF11-n)3X. These materials differ in their (non)centrosymmetry despite chemical and structural similarities. The vanadium compounds are centrosymmetric (space groups P3m1 or C2/m) while the niobium and molybdenum heterotypes are noncentrosymmetric (Pmn21). The difference in symmetry occurs owing to the presence of linear, bimetallic BBUs or ?-shaped bimetallic BBUs and related packing effects. These ?-shaped BBUs form as a consequence of the coordination environment around the bridging anion of the metal oxide fluoride BBUs. PMID:24328163

Holland, Michael; Donakowski, Martin D; Pozzi, Eric A; Rasmussen, Andrew M; Tran, Thanh Thao; Pease-Dodson, Shannon E; Halasyamani, P Shiv; Seideman, Tamar; Van Duyne, Richard P; Poeppelmeier, Kenneth R

2014-01-01

285

Role of Thermal Heating on the Voltage Induced Insulator-Metal Transition in VO2  

NASA Astrophysics Data System (ADS)

We show that the main mechanism for the dc voltage or dc current induced insulator-metal transition in vanadium dioxide VO2 is due to local Joule heating and not a purely electronic effect. This tour de force experiment was accomplished by using the fluorescence spectra of rare-earth doped micron sized particles as local temperature sensors. As the insulator-metal transition is induced by a dc voltage or dc current, the local temperature reaches the transition temperature indicating that Joule heating plays a predominant role. This has critical implications for the understanding of the dc voltage or dc current induced insulator-metal transition and has a direct impact on applications which use dc voltage or dc current to externally drive the transition.

Zimmers, A.; Aigouy, L.; Mortier, M.; Sharoni, A.; Wang, Siming; West, K. G.; Ramirez, J. G.; Schuller, Ivan K.

2013-02-01

286

Role of thermal heating on the voltage induced insulator-metal transition in VO2.  

PubMed

We show that the main mechanism for the dc voltage or dc current induced insulator-metal transition in vanadium dioxide VO(2) is due to local Joule heating and not a purely electronic effect. This "tour de force" experiment was accomplished by using the fluorescence spectra of rare-earth doped micron sized particles as local temperature sensors. As the insulator-metal transition is induced by a dc voltage or dc current, the local temperature reaches the transition temperature indicating that Joule heating plays a predominant role. This has critical implications for the understanding of the dc voltage or dc current induced insulator-metal transition and has a direct impact on applications which use dc voltage or dc current to externally drive the transition. PMID:23414038

Zimmers, A; Aigouy, L; Mortier, M; Sharoni, A; Wang, Siming; West, K G; Ramirez, J G; Schuller, Ivan K

2013-02-01

287

Studies of transition metals/metal compounds by high temperature mass spectroscopy and laser vaporization techniques  

SciTech Connect

The high temperature/laser vaporization experiment used to obtain thermochemical data for transition metals and metal compounds is described. High-temperature equilibrium reactions involving transition metals and oxygen were studied. Results include the determination of the enthalpy, [Delta]H, for the gaseous equilibrium OsO[sub 4] (g) [r equilibrium] OsO[sub 3] (g) + 1/2 O[sub 2] (g) over 1139-1471 K, resulting in a second-law heat of reaction [Delta]H[sub 305] (II) = 38.5 [+-] 3.3 kcal mol [sup [minus]1], which yields the standard enthalphy [Delta]H[sub 298] (II) = 39.2 [+-] 3.3 kcal mol[sup [minus]1] and a third-law heat of reaction [Delta]H[sub 298] (III) = 45.2 [+-] 1.7 kcal mol[sup [minus]1]. An average standard enthalpy of [Delta]H[sub 298](II) and [Delta]H[sub 298](III), 42 [+-] 7 kcal mol[sup [minus]1] is reported for the equilibrium. The heat of formation for gaseous OsO[sub 3] is [Delta][sub f]H[degrees][sub 298](OsO[sub 3]) = 39 [+-] 7 kcal mol[sup [minus]1], leading to a bond energy for O-OSO[sub 3] of 101 [+-] 7 kcal mol[sup [minus]1]. The ionization potentials for OsO[sub 3] and OsO[sub 4] were found to be 11.4 [+-] 0.2 and 12.3 [+-] 0.2 eV. Equilibrium reactions involving Ni(g) + 1/2O[sub 2](g)[r equilibrium] NiO(g) and Zn(g) + 1/2O[sub 2](g) [r equilibrium] ZnO(g) were studied. The [Delta][sub f]H[degrees][sub 298](II,III)[NiO(g)] and D[degrees][sub 0] (II,III)[NiO (g)] determined reinforce literature values. A lower limit for the standard heat of formation for ZnO(g) is determined based on the detection limit. The laser vaporization experiment replaced the Knudsen cell with a disc of a material is irradiated by a pulsed laser beam, Neutral and ionic atom beams of kinetic energy 3-300 eV are generated. The neutral atom's energy can be controlled with the laser power. Initial results of studies done on copper, nickel, zinc and related oxide, sulfide, bromide, and chloride salts are discussed.

Thiem, T.L.

1993-01-01

288

Biological interaction between transition metals (Ag, Cd and Hg), selenide/sulfide and selenoprotein P.  

PubMed

The interaction between transition metals (Ag+, Cd2+ and Hg2+) and selenium (Se) in the bloodstream was studied in vitro by means of the HPLC--inductively coupled argon plasma-mass spectrometry (ICP MS) method. Transition metal ions and selenide (produced in vitro from selenite in the presence of glutathione) or sulfide (Na2S) formed a (metal-Se/S) complex, which then bound to a plasma protein, selenoprotein P (Sel P), to form a ternary complex, (metal-Se/S)-Sel P. The molar ratios of metals to Se were 1:1 for Hg/Se and Cd/Se, but either 1:1 or 2:1 for Ag/Se, depending on the ratio of their doses. The results indicate that the interaction between transition metals and Se occurs through the general mechanism, i.e., transition metal ions and selenide form the unit complex (metal-Se)n, and then the complex binds to selenoprotein P to form the ternary complex (metal-Se)nm--seleno-protein P in the bloodstream. PMID:9833321

Sasakura, C; Suzuki, K T

1998-09-01

289

Transitions in the nuclear age: late adolescence to early adulthood.  

PubMed

College students, subjects in a 1983 study on reaction to that threat of nuclear war, participated in a follow-up study to investigate the changes that occur from late adolescence to early adulthood. The 41 subjects again completed the Nuclear War Attitude Survey (NWAS II) and, additionally, a second questionnaire and to 1 to 2 1/2 hour individual interview during which they were asked to explain changes in their answers to the NWAS II. Compared to their previous responses to the NWAS II, the responses of these young adults showed statistically significant decreases in the frequency they reported thinking about the possibility of nuclear war, their estimation of the likelihood of a nuclear war, and their intention to contact the news media to express their views. The researchers hypothesize that the major reasons for changes in response were (1) developmental differences, (2) the campus culture, (3) the political climate, (4) the media climate and (5) lack of engagement with the democratic process. PMID:2708600

Van Hoorn, J; Le Veck, P; French, P

1989-03-01

290

Inverse correlation between cohesive energy and thermal expansion coefficient in liquid transition metal alloys  

NASA Astrophysics Data System (ADS)

The volume expansion coefficients (?) of twenty-five glass-forming transition metal alloy liquids, measured using the electrostatic levitation technique, are reported. An inverse correlation between ? and the cohesive energy is found. The predicted values of ? from this relationship agree reasonably well with the published data for thirty other transition metal and alloy liquids; some disagreement was found for a few alloys containing significant amounts of group III and IV elements. A theoretical argument for this empirical relationship is presented.

Gangopadhyay, A. K.; Bendert, J. C.; Mauro, N. A.; Kelton, K. F.

2012-09-01

291

Electron transport studies in single transition metal ions doped borophosphate glasses  

Microsoft Academic Search

Three series of boro-phosphate glasses doped with single transition metal ions, Cuo, Fe2O3 and CoO have been prepared by melt quenching method and investigated for room temperature density and dc electrical conductivity in the temperature range from 325 to 600K. The density increased with increasing transition metal ions concentration in all the three series. The measured conductivities were in the

B. Vijaya kumar; T. Sankarappa; Santoshkumar; S. S. Veena

2009-01-01

292

Bridged transition-metal complexes and uses thereof for hydrogen separation, storage and hydrogenation  

DOEpatents

The present invention constitutes a class of organometallic complexes which reversibly react with hydrogen to form dihydrides and processes by which these compounds can be utilized. The class includes bimetallic complexes in which two cyclopentadienyl rings are bridged together and also separately .pi.-bonded to two transition metal atoms. The transition metals are believed to bond with the hydrogen in forming the dihydride. Transition metals such as Fe, Mn or Co may be employed in the complexes although Cr constitutes the preferred metal. A multiple number of ancilliary ligands such as CO are bonded to the metal atoms in the complexes. Alkyl groups and the like may be substituted on the cyclopentadienyl rings. These organometallic compounds may be used in absorption/desorption systems and in facilitated transport membrane systems for storing and separating out H.sub.2 from mixed gas streams such as the product gas from coal gasification processes.

Lilga, Michael A. (Richland, WA); Hallen, Richard T. (Richland, WA)

1991-01-01

293

Bridged transition-metal complexes and uses thereof for hydrogen separation, storage and hydrogenation  

DOEpatents

The present invention constitutes a class of organometallic complexes which reversibly react with hydrogen to form dihydrides and processes by which these compounds can be utilized. The class includes bimetallic complexes in which two cyclopentadienyl rings are bridged together and also separately [pi]-bonded to two transition metal atoms. The transition metals are believed to bond with the hydrogen in forming the dihydride. Transition metals such as Fe, Mn or Co may be employed in the complexes although Cr constitutes the preferred metal. A multiple number of ancillary ligands such as CO are bonded to the metal atoms in the complexes. Alkyl groups and the like may be substituted on the cyclopentadienyl rings. These organometallic compounds may be used in absorption/desorption systems and in facilitated transport membrane systems for storing and separating out H[sub 2] from mixed gas streams such as the product gas from coal gasification processes. 3 figures.

Lilga, M.A.; Hallen, R.T.

1991-10-15

294

Bridged transition-metal complexes and uses thereof for hydrogen separation, storage and hydrogenation  

DOEpatents

The present invention constitutes a class of organometallic complexes which reversibly react with hydrogen to form dihydrides and processes by which these compounds can be utilized. The class includes bimetallic complexes in which two cyclopentadienyl rings are bridged together and also separately [pi]-bonded to two transition metal atoms. The transition metals are believed to bond with the hydrogen in forming the dihydride. Transition metals such as Fe, Mn or Co may be employed in the complexes although Cr constitutes the preferred metal. A multiple number of ancillary ligands such as CO are bonded to the metal atoms in the complexes. Alkyl groups and the like may be substituted on the cyclopentadienyl rings. These organometallic compounds may be used in absorption/desorption systems and in facilitated transport membrane systems for storing and separating out H[sub 2] from mixed gas streams such as the producer gas from coal gasification processes. 3 figs.

Lilga, M.A.; Hallen, R.T.

1990-08-28

295

Bridged transition-metal complexes and uses thereof for hydrogen separation, storage and hydrogenation  

DOEpatents

The present invention constitutes a class of organometallic complexes which reversibly react with hydrogen to form dihydrides and processes by which these compounds can be utilized. The class includes bimetallic complexes in which two cyclopentadienyl rings are bridged together and also separately .pi.-bonded to two transition metal atoms. The transition metals are believed to bond with the hydrogen in forming the dihydride. Transition metals such as Fe, Mn or Co may be employed in the complexes although Cr constitutes the preferred metal. A multiple number of ancilliary ligands such as CO are bonded to the metal atoms in the complexes. Alkyl groups and the like may be substituted on the cyclopentadienyl rings. These organometallic compounds may be used in absorption/desorption systems and in facilitated transport membrane systems for storing and separating out H.sub.2 from mixed gas streams such as the produce gas from coal gasification processes.

Lilga, Michael A. (Richland, WA); Hallen, Richard T. (Richland, WA)

1990-01-01

296

Structural and magnetic properties of a variety of transition metal incorporated DNA double helices.  

PubMed

By using density functional theory calculations, the structural, energetic, magnetic, and optical properties for a variety of transition metal (M = Mn, Fe, Co, Ni and Cu) ions incorporated modified-DNA (M-DNA) double helices has been investigated. The DNA is modified with either hydroxypyridone (H) or bis(salicylaldehyde)ethylenediamine (S-en) metalated bases. We find the formation of extended M-O network leading to the ferromagnetic interactions for the case of H-DNA for all the metal ions. More ordered stacking arrangement was found for S-en-DNA. We calculate the exchange coupling constant (J) considering Heisenberg Hamiltonian for quantitative description of magnetic interactions. The ferromagnetic and antiferromagnetic interactions are obtained by varying different transition metal ions. The extent of the magnetic interaction depends on the number of transition metal ions. Optical profiles show peaks below 2?eV, a clear signature of spin-spin coupling. PMID:24382746

Samanta, Pralok K; Pati, Swapan K

2014-02-01

297

Magnetic and Lattice Interaction in 3d Transition Metal Compounds  

NASA Astrophysics Data System (ADS)

Available from UMI in association with The British Library. The importance and nature of magnetic and lattice degrees of freedom and their interaction in transition metal magnets has been investigated. As an example of localised behaviour, Heusler alloys in which the magnetic moment was confined to Mn atoms were chosen, e.g. Pd_2MnIn. The manganese atoms are separated by more than 4.6A. By systematically changing Pd for either Ag or Au the electron concentration can be varied in a continuous manner. Dependent upon the electron concentration several different antiferromagnetic structures consistent with an fcc lattice are observed at low temperatures. The type of magnetic order gives rise to distinct lattice distortion characteristic of the magnetic symmetry. A wide range of bulk measurements was carried out to characterise the materials, e.g. X-ray, neutron diffraction, magnetic susceptibility and specific heat (using both pulse and continuous heating techniques). The magnetic structures were, in some instances, frustrated as may be expected for antiferromagnetism on an fcc lattice. As an example of itinerant behaviour the Fe-Ni system was chosen. rm Fe_{1 -x}Ni_ x alloy systems have long been of considerable interest since rm Fe_ {65}Ni_{35} shows an anomalously small thermal expansion below T_ {rm c}. Numerous experiments have been carried out to understand this phenomenon, the Invar effect. The effect is most pronounced close to the composition defining the phase boundary between the bcc and fcc structures. The interplay between the magnetic and lattice degrees of freedom were investigated on an atomic scale using inelastic polarised neutron scattering. The polarisation dependence of the magneto vibrational scattering of the one phonon cross-sections has been investigated as a continuous function of q throughout the Brillouin zone in the Invar alloy rm Fe_{65 }Ni_{35}, and in two other FeNi samples out side the Invar region. The magneto vibrational scattering is strongly dependent on the energy and wave vector of the phonon, indicating that the effective magnetic moments are reduced as the phonon energy increases. The results also show the presence of a "forbidden" phonon mode propagating in the (001) direction. The "forbidden" mode was identified as being the transverse (001) phonon. (Abstract shortened by UMI.).

Jassim, Ishmaeel Khalil

298

Transition metal deposition on graphene and carbon nanotubes.  

PubMed

We present a combined theoretical and experimental comparative study of the deposition of five different metals on perfect and defective graphene and multi-walled carbon nanotubes (MWNTs): Ti, Ni, Pd, Pt and Au. Atomistic modelling successfully provides a comprehensive picture of surface binding, diffusion and aggregation properties for these metals, highlighting some fundamental differences in their surface chemical and electronic behaviour. We correlate these theoretical results with experimental TEM images of metal deposited MWCNTs. PMID:19908511

Suarez-Martinez, Irene; Felten, Alexandre; Pireaux, Jean Jacques; Bittencourt, Carla; Ewels, Christopher P

2009-10-01

299

Study of Transition Probability of Low States of Alkali Metal Atoms with WBEPM Theory  

Microsoft Academic Search

In this paper, a theory, called Weakest Bound Electron Potential Model Theory, is employed to study the transition probability of low states of Na, K, Rb and Cs. The parameters are determined by solving the coupled equations: concerning energy ? and the radial expectation value nl of the weakest bound electron. Some transition probabilities of alkali metal atoms are given

Nengwu Zheng; Tao Wang; Tao Zhou; Yujie Sun; Wei Su; Yi Zhang

1999-01-01

300

Realization of tunable photonic crystals based on the metal insulator transition of VO2  

Microsoft Academic Search

The feasibility of an electrically programmable photonic crystal (PC) is investigated theoretically based on the metal-insulator transition of vanadium dioxide (VO2). We propose a slab structure based on VO2 whose dielectric properties can be modulated by selectively applying the bias on a lithographically defined array of gate electrodes to induce the phase transition. So, unlike the ordinary PCs, wave propagation

D. Xiao; K. W. Kim; J. M. Zavada; G. Lazzi

2006-01-01

301

Photoelectron spectra of transition-metal carbonyl complexes: comparison with the spectra of adsorbed CO  

Microsoft Academic Search

(Received 27 January 1978) The uv and x-ray photoelectron spectra of carbon monoxide and transition-metal (TM) carbonyl complexes have been studied. The systematic changes in these spectra were recorded as the number of metal atoms in the complexes was increased and as the bonding configuration of the CO changed. The observations on TM carbonyl complexes are compared to the spectra

E. W. Plummer; W. R. Salaneck; J. S. Miller

1978-01-01

302

Manipulation of a Schlenk Line: Preparation of Tetrahydrofuran Complexes of Transition-Metal Chlorides  

ERIC Educational Resources Information Center

Before taking an inorganic laboratory course few students have experience handling air-sensitive materials using Schlenk techniques. This exercise introduces them to techniques they will employ in later syntheses. The procedure involves the formation of anhydrous tetrahydrofuran complexes of transition-metal chlorides from metal-chloride hydrates;

Davis, Craig M.; Curran, Kelly A.

2007-01-01

303

Spatial Patterns of Soil Heavy Metals in Urban-Rural Transition Zone of Beijing1  

Microsoft Academic Search

To identify the main sources responsible for soil heavy metal contamination, 70 topsoils were sampled from the Daxing County in the urban-rural transition zone of Beijing. The concentrations of heavy metals Cu, Zn, Pb, Cr, Cd, Ni, As, Se, Hg, and Co; the soil texture; and the organic matter content were determined for each soil sample. Descriptive statistics and geostatistics

HU Ke-Lid; F ZHANG; H LI; F HUANG; B LI

2006-01-01

304

Cationic and neutral transition metal complexes with a tetramethylfulvene or trimethylallyldiene ligand  

Microsoft Academic Search

Published data on the synthesis and chemical properties of complexes of Group 4-10 transition metals (d elements) with eta 6-tetramethylfulvene and eta7-trimethylallyldiene ligands, formed from the pentamethylcyclopentadienyl complexes of these metals, are described systematically. A description of the structures of these complexes in terms of a \\

Arkadii Z. Kreindlin; Margarita I. Rybinskaya

2004-01-01

305

First-row transition metal dichalcogenide catalysts for hydrogen evolution reaction  

E-print Network

First-row transition metal dichalcogenide catalysts for hydrogen evolution reaction Desheng Kong­4 State-of-the-art hydrogen evolution reaction (HER) catalysts contain noble metals such as Pt expand and enrich the family of high performance HER catalysts. The efficient generation of hydrogen

Cui, Yi

306

Integrated FIA\\/HPLC method for preconcentration and determination of transition metal ions  

Microsoft Academic Search

SummaryAn automatic method based on the combination of a flow injection (FI) manifold with a liquid chromatograph has been developed for the enrichment and determination of transition metal ions in water samples. Alternatively, the FI configuration can be used as a screening system for the determination of the total concentration of heavy metals. Two-parameter expressions for calibration graphs involving preconcentration

P. Richter; J. M. Fernndez-Romero; M. D. Luque de Castro; M. Valcrcel

1992-01-01

307

Synthesis of transition-metal phosphides from oxidic precursors by reduction in hydrogen plasma  

SciTech Connect

A series of transition metal phosphides, including MoP, WP, CoP, Co{sub 2}P, and Ni{sub 2}P, were synthesized from their oxidic precursors by means of hydrogen plasma reduction under mild conditions. The effects of reduction conditions, such as metal to phosphorus molar ratio, power input, and reduction time, on the synthesis of metal phosphides were investigated. The products were identified by means of XRD characterization. It is indicated that metal phosphides were readily synthesized stoichiometrically from their oxides in hydrogen plasma under mild conditions. - Graphical abstract: Metal phosphides were obtained stoichiometrically from their oxidic precursors by hydrogen plasma reaction under mild conditions.

Guan Jie [Department of Catalytic Chemistry and Engineering, State Key Laboratory of Fine Chemicals, Dalian University of Technology, Dalian 116012 (China); Wang Yao [Liaoning Key Laboratory of Petrochemical Technology and Equipments, Dalian University of Technology, Dalian 116012 (China); Qin Minglei; Yang Ying [Department of Catalytic Chemistry and Engineering, State Key Laboratory of Fine Chemicals, Dalian University of Technology, Dalian 116012 (China); Li Xiang [Department of Catalytic Chemistry and Engineering, State Key Laboratory of Fine Chemicals, Dalian University of Technology, Dalian 116012 (China); Liaoning Key Laboratory of Petrochemical Technology and Equipments, Dalian University of Technology, Dalian 116012 (China); Wang Anjie, E-mail: ajwang@dlut.edu.c [Department of Catalytic Chemistry and Engineering, State Key Laboratory of Fine Chemicals, Dalian University of Technology, Dalian 116012 (China); Liaoning Key Laboratory of Petrochemical Technology and Equipments, Dalian University of Technology, Dalian 116012 (China)

2009-06-15

308

Transition metal ions at the crossroads of mucosal immunity and microbial pathogenesis  

PubMed Central

Transition metal ions are essential micronutrients for all living organisms. In mammals, these ions are often protein-bound and sequestered within cells, limiting their availability to microbes. Moreover, in response to infection, mammalian hosts further reduce the availability of metal nutrients by activating epithelial cells and recruiting neutrophils, both of which release metal-binding proteins with antimicrobial function. Microorganisms, in turn, have evolved sophisticated systems to overcome these limitations and acquire the metal ions essential for their growth. Here we review some of the mechanisms employed by the host and by pathogenic microorganisms to compete for transition metal ions, with a discussion of how evading nutritional immunity benefits pathogens. Furthermore, we provide new insights on the mechanisms of host-microbe competition for metal ions in the mucosa, particularly in the inflamed gut. PMID:24478990

Diaz-Ochoa, Vladimir E.; Jellbauer, Stefan; Klaus, Suzi; Raffatellu, Manuela

2013-01-01

309

The Experience of Parents as Their Children with Developmental Disabilities Transition from Early Intervention to Kindergarten  

ERIC Educational Resources Information Center

Despite recognition of the importance of parent involvement to enable meaningful inclusion of young children with developmental disabilities in education contexts, few Canadian studies have reported how parents experience this collaboration. Recent research suggests that the transition process is critical to the early school experiences of

Villeneuve, Michelle; Chatenoud, Celine; Hutchinson, Nancy L.; Minnes, Patricia; Perry, Adrienne; Dionne, Carmen; Frankel, Elaine B.; Isaacs, Barry; Loh, Alvin; Versnel, Joan; Weiss, Jonathan

2013-01-01

310

Developmental tasks of early adulthood transitions in University life an inner world perspective.  

E-print Network

1 Developmental tasks of early adulthood ­ transitions in University life ­ an inner world perspective. Biddy Youell, Head of Child and Adolescent Psychotherapy, Tavistock and Portman NHS Foundation an overview of the developmental tasks which face older adolescents...young adults...and will attempt

Stevenson, Mark

311

Mexican American Birthweight and Child Overweight: Unraveling a Possible Early Life Course Health Transition  

ERIC Educational Resources Information Center

Mexican American children have a weight distribution that categorizes them as relatively healthy at birth but relatively unhealthy by age 3. This early life course transition in health based on weight raises the question of whether Mexican American children "outgrow" the epidemiologic paradox of favorable birth outcomes despite social disadvantage

Hamilton, Erin R.; Teitler, Julien O.; Reichman, Nancy E.

2011-01-01

312

A Stage-Sequential Model of Reading Transitions: Evidence from the Early Childhood Longitudinal Study  

ERIC Educational Resources Information Center

This study uses latent transition analysis to examine reading development across the kindergarten and 1st-grade year. Data include poverty status and dichotomous measures of reading at 4 time points for a large sample of children within the Early Childhood Longitudinal Study. In each of 4 waves of the study, 5 latent classes were represented in

Kaplan, David; Walpole, Sharon

2005-01-01

313

Insulator-metal transition of highly compressed carbon disulfide  

SciTech Connect

We present integrated spectral, structural, resistance, and theoretical evidences for simple molecular CS{sub 2} transformations to an insulating black polymer with threefold carbon atoms at 9 GPa, then to a semiconducting polymer above 30 GPa, and finally to a metallic solid above 50 GPa. The metallic phase is a highly disordered three-dimensional network structure with fourfold carbon atoms at the carbon-sulfur distance of {approx}1.70 {angstrom}. Based on first-principles calculations, we present two plausible structures for the metallic phase: {alpha}-chalcopyrite and tridymite, both of which exhibit metallic ground states and disordered diffraction features similar to that measured. We also present the phase and chemical transformation diagram for carbon disulfide, showing a large stability field of the metallic phase to 100 GPa and 800 K.

Dias, Ranga P.; Yoo, Choong-Shik; Kim, Minseob; Tse, John S. (WSU); (Saskatchewan)

2012-04-24

314

Terahertz-field-induced insulator-to-metal transition in vanadium dioxide metamaterial.  

PubMed

Electron-electron interactions can render an otherwise conducting material insulating, with the insulator-metal phase transition in correlated-electron materials being the canonical macroscopic manifestation of the competition between charge-carrier itinerancy and localization. The transition can arise from underlying microscopic interactions among the charge, lattice, orbital and spin degrees of freedom, the complexity of which leads to multiple phase-transition pathways. For example, in many transition metal oxides, the insulator-metal transition has been achieved with external stimuli, including temperature, light, electric field, mechanical strain or magnetic field. Vanadium dioxide is particularly intriguing because both the lattice and on-site Coulomb repulsion contribute to the insulator-to-metal transition at 340?K (ref. 8). Thus, although the precise microscopic origin of the phase transition remains elusive, vanadium dioxide serves as a testbed for correlated-electron phase-transition dynamics. Here we report the observation of an insulator-metal transition in vanadium dioxide induced by a terahertz electric field. This is achieved using metamaterial-enhanced picosecond, high-field terahertz pulses to reduce the Coulomb-induced potential barrier for carrier transport. A nonlinear metamaterial response is observed through the phase transition, demonstrating that high-field terahertz pulses provide alternative pathways to induce collective electronic and structural rearrangements. The metamaterial resonators play a dual role, providing sub-wavelength field enhancement that locally drives the nonlinear response, and global sensitivity to the local changes, thereby enabling macroscopic observation of the dynamics. This methodology provides a powerful platform to investigate low-energy dynamics in condensed matter and, further, demonstrates that integration of metamaterials with complex matter is a viable pathway to realize functional nonlinear electromagnetic composites. PMID:22801506

Liu, Mengkun; Hwang, Harold Y; Tao, Hu; Strikwerda, Andrew C; Fan, Kebin; Keiser, George R; Sternbach, Aaron J; West, Kevin G; Kittiwatanakul, Salinporn; Lu, Jiwei; Wolf, Stuart A; Omenetto, Fiorenzo G; Zhang, Xin; Nelson, Keith A; Averitt, Richard D

2012-07-19

315

Adsorption of alkali, alkaline-earth, and 3d transition metal atoms on silicene  

NASA Astrophysics Data System (ADS)

The adsorption characteristics of alkali, alkaline-earth, and transition metal adatoms on silicene, a graphene-like monolayer structure of silicon are analyzed by means of first-principles calculations. In contrast to graphene, interaction between the metal atoms and the silicene surface is quite strong due to its highly reactive buckled hexagonal structure. In addition to structural properties, we also calculate the electronic band dispersion, net magnetic moment, charge transfer, work function, and dipole moment of the metal adsorbed silicene sheets. Alkali metals, Li, Na, and K, adsorb to hollow sites without any lattice distortion. As a consequence of the significant charge transfer from alkalis to silicene, metalization of silicene takes place. Trends directly related to atomic size, adsorption height, work function, and dipole moment of the silicene/alkali adatom system are also revealed. We found that the adsorption of alkaline-earth metals on silicene is entirely different from their adsorption on graphene. The adsorption of Be, Mg, and Ca turns silicene into a narrow gap semiconductor. Adsorption characteristics of eight transition metals Ti, V, Cr, Mn, Fe, Co, Mo, and W are also investigated. As a result of their partially occupied d orbital, transition metals show diverse structural, electronic, and magnetic properties. Upon the adsorption of transition metals, depending on the adatom type and atomic radius, the system can exhibit metal, half-metal, and semiconducting behavior. For all metal adsorbates, the direction of the charge transfer is from adsorbate to silicene, because of its high surface reactivity. Our results indicate that the reactive crystal structure of silicene provides a rich playground for functionalization at nanoscale.

Sahin, H.; Peeters, F. M.

2013-02-01

316

Phase Diagram of Coulomb Interactions across the Metal-Insulator Transition in Si:B  

Microsoft Academic Search

Measurements of the single-particle density of states (DOS) near T=0 K in Si:B are used to construct an energy-density phase diagram of Coulomb interactions across the critical density nc of the metal-insulator transition. Insulators and metals are found to be distinguishable only below a phase boundary ?*(|n\\/nc-1|) determined by the Coulomb energy. Above ?* is a mixed state where metals

Mark Lee

2004-01-01

317

Parents' Marital Distress, Divorce, and Remarriage: Links with Daughters' Early Family Formation Transitions  

PubMed Central

We used data from the Add Health study to estimate the effects of parents marital status and relationship distress on daughters early family formation transitions. Outcomes included traditional transitions (marriage and marital births) and nontraditional transitions (cohabitation and nonmarital births). Relationship distress among continuously married parents was not related to any outcome. Offspring with single parents and remarried parents had an elevated risk of nonmarital births and nonmarital cohabitation. Offspring with remarried parents with a high-distress relationship had an elevated risk of early marriages and marital births. These results, combined with analyses of mediating variables, provide the strongest support for a modeling perspective, although some support also was found for a perspective based on escape from stress. PMID:21785523

Amato, Paul R.; Kane, Jennifer B.

2011-01-01

318

Parents' Marital Distress, Divorce, and Remarriage: Links with Daughters' Early Family Formation Transitions.  

PubMed

We used data from the Add Health study to estimate the effects of parents' marital status and relationship distress on daughters' early family formation transitions. Outcomes included traditional transitions (marriage and marital births) and nontraditional transitions (cohabitation and nonmarital births). Relationship distress among continuously married parents was not related to any outcome. Offspring with single parents and remarried parents had an elevated risk of nonmarital births and nonmarital cohabitation. Offspring with remarried parents with a high-distress relationship had an elevated risk of early marriages and marital births. These results, combined with analyses of mediating variables, provide the strongest support for a modeling perspective, although some support also was found for a perspective based on escape from stress. PMID:21785523

Amato, Paul R; Kane, Jennifer B

2011-08-01

319

Modulation of hydride formation energies in transition metal doped Mg by alteration of spin state  

NASA Astrophysics Data System (ADS)

Coupled cluster and density functional theory calculations have been used to assess the role of the transition metal spin state upon the energetic favorability of hydride formation within small, transition metal doped, magnesium clusters. The spin state is found to modulate the occupation of bonding and anti-bonding orbitals, thus having a large effect upon both geometric and energetic parameters. This chemical description provides a potential theoretical basis for unexplained experimental observations, and indicates a mechanism for using an external magnetic field to control the thermodynamics of H2 sorption and desorption in metal hydrides.

Ozkanlar, Abdullah; Samuels, Alex; Clark, Aurora E.

2013-02-01

320

Theory of quantum metal to superconductor transitions in highly conducting systems  

SciTech Connect

We derive the theory of the quantum (zero temperature) superconductor to metal transition in disordered materials when the resistance of the normal metal near criticality is small compared to the quantum of resistivity. This can occur most readily in situations in which 'Anderson's theorem' does not apply. We explicitly study the transition in superconductor-metal composites, in an swave superconducting film in the presence of a magnetic field, and in a low temperature disordered d-wave superconductor. Near the point of the transition, the distribution of the superconducting order parameter is highly inhomogeneous. To describe this situation we employ a procedure which is similar to that introduced by Mott for description of the temperature dependence of the variable range hopping conduction. As the system approaches the point of the transition from the metal to the superconductor, the conductivity of the system diverges, and the Wiedemann-Franz law is violated. In the case of d-wave (or other exotic) superconductors we predict the existence of (at least) two sequential transitions as a function of increasing disorder: a d-wave to s-wave, and then an s-wave to metal transition.

Spivak, B.

2010-04-06

321

All-Valence Electron CNDO Calculations on Transition Metal Complexes  

Microsoft Academic Search

The CNDO-II approximate SCF molecular orbital method is extended to include molecules containing atoms of the first transition series. Valence orbitals explicitly considered in the transition atoms are 3d, 4s, and 4p. Calculations are reported for the monoxides of Sc, Ti, V, and Cu, using three sets of orbital exponents. The results are compared, where possible, with those obtained by

D. W. Clack; N. S. Hush; J. R. Yandle

1972-01-01

322

Photoluminescence response of colloidal quantum dots on VO2 film across metal to insulator transition  

PubMed Central

We have proposed a method to probe metal to insulator transition in VO2 measuring photoluminescence response of colloidal quantum dots deposited on the VO2 film. In addition to linear luminescence intensity decrease with temperature that is well known for quantum dots, temperature ranges with enhanced photoluminescence changes have been found during phase transition in the oxide. Corresponding temperature derived from luminescence dependence on temperature closely correlates with that from resistance measurement during heating. The supporting reflectance data point out that photoluminescence response mimics a reflectance change in VO2 across metal to insulator transition. Time-resolved photoluminescence study did not reveal any significant change of luminescence lifetime of deposited quantum dots under metal to insulator transition. It is a strong argument in favor of the proposed explanation based on the reflectance data. PACS 71.30. + h; 73.21.La; 78.47.jd

2014-01-01

323

Gas-phase activation of methane by ligated transition-metal cations  

PubMed Central

Motivated by the search for ways of a more efficient usage of the large, unexploited resources of methane, recent progress in the gas-phase activation of methane by ligated transition-metal ions is discussed. Mass spectrometric experiments demonstrate that the ligands can crucially influence both reactivity and selectivity of transition-metal cations in bond-activation processes, and the most reactive species derive from combinations of transition metals with the electronegative elements fluorine, oxygen, and chlorine. Furthermore, the collected knowledge about intramolecular kinetic isotope effects associated with the activation of CH(D) bonds of methane can be used to distinguish the nature of the bond activation as a mere hydrogen-abstraction, a metal-assisted mechanism or more complex reactions such as formation of insertion intermediates or ?-bond metathesis. PMID:18955709

Schroder, Detlef; Schwarz, Helmut

2008-01-01

324

Metal Transport and Chemical Heterogeneity in Early Star Forming Systems  

E-print Network

To constrain the properties of the first stars with the chemical abundance patterns observed in metal-poor stars, one must identify any non-trivial effects that the hydrodynamics of metal dispersal can imprint on the abundances. We use realistic cosmological hydrodynamic simulations to quantify the distribution of metals resulting from one Population III supernova and from a small number of such supernovae. Overall, supernova ejecta remain highly inhomogeneous throughout the simulations. When the supernova bubbles collapse, quasi-virialized metal-enriched clouds, fed by fallback from the bubbles and by streaming of metal-free gas from the cosmic web, grow in the centers of the dark matter halos. Partial turbulent homogenization on scales resolved in the simulation is observed in the clouds, and the vortical time scales are short enough to ensure true homogenization on subgrid scales. However, the abundances in the clouds differ from the gross yields of the supernovae. Continuing the simulations until the clou...

Ritter, Jeremy S; Safranek-Shrader, Chalence; Milosavljevic, Milos; Bromm, Volker

2014-01-01

325

First-principles study of hydrogen dissociation and diffusion on transition metal-doped Mg(0 0 0 1) surfaces  

NASA Astrophysics Data System (ADS)

First-principles calculations within the density functional theory (DFT) have been carried out to study hydrogen molecules dissociation and diffusion on clean and transition metals (TMs) doped Mg(0 0 0 1) surfaces following Pozzo et al. work. Firstly, the stability of Mg(0 0 0 1) surface doped with transition metals atom has been studied. The results showed that transition metals on the left of the table tend to substitute Mg in the second layer, while the other transition metals prefer to substitute Mg in the first layer. Secondly, we studied hydrogen molecules dissociation and diffusion on clean and Mg(0 0 0 1) surfaces which the transition metal atoms substituted both in the first layer and second layer. When transition metal atoms substitute in the first layer, the results agree with the Pozzo et al. result; when transition metal atoms substitute in the second layer, the results showed that the transition metals on the left of the periodic table impact on the dissociation barriers is less. However, for the transition metals (Mn, Fe, Co, Ni) on the right, there is a great impact on the barriers. The transition metals doped surfaces bind the dissociated H atoms loosely, making them easily diffused. The results further reveal that the Fe dopant on the Mg surface is the best choice for H2 dissociation and hydrogen storage.

Wang, Zhiwen; Guo, Xinjun; Wu, Mingyi; Sun, Qiang; Jia, Yu

2014-06-01

326

Mitochondrial morphology transition is an early indicator of subsequent cell death in Arabidopsis.  

PubMed

Mitochondrial morphology and dynamics were investigated during the onset of cell death in Arabidopsis thaliana. Cell death was induced by either chemical (reactive oxygen species (ROS)) or physical (heat) shock. Changes in mitochondrial morphology in leaf tissue, or isolated protoplasts, each expressing mitochondrial-targeted green fluorescent protein (GFP), were observed by epifluorescence microscopy, and quantified. Chemical induction of ROS production, or a mild heat shock, caused a rapid and consistent change in mitochondrial morphology (termed the mitochondrial morphology transition) that preceded cell death. Treatment of protoplasts with a cell-permeable superoxide dismutase analogue, TEMPOL, blocked this morphology change. Incubation of protoplasts in micromolar concentrations of the calcium channel-blocker lanthanum chloride, or the permeability transition pore inhibitor cyclosporin A, prevented both the mitochondrial morphology transition and subsequent cell death. It is concluded that the observed mitochondrial morphology transition is an early and specific indicator of cell death and is a necessary component of the cell death process. PMID:17986180

Scott, Iain; Logan, David C

2008-01-01

327

Unravelling the switching mechanisms in electric field induced insulator-metal transitions in VO2 nanobeams  

NASA Astrophysics Data System (ADS)

We studied insulator-metal transitions in VO2 nanobeams for both abrupt and gradual changes in applied electric fields. Based on the observations, the Poole-Frenkel effect explained the abrupt transition, while the gradual case is found to be dominated by the Joule heating phenomenon. We also carried out power model and finite element method based simulations which supported the Joule heating phenomena for gradual transition. An in-principle demonstration of the Poole-Frenkel effect, performed using a square voltage pulse of 1 s duration, further confirms the proposed insulator-metal transition mechanism with a switching time in the order of 100 ns. Finally, conductivity variations introduced via rapid thermal annealing at various temperatures validate the roles of both Joule heating and Poole-Frenkel mechanisms in the transitions.

Rathi, Servin; Park, Jin-Hyung; Lee, In-yeal; Baik, Jeong Min; Yi, Kyung Soo; Kim, Gil-Ho

2014-07-01

328

Sickle blade life-history and the transition to agriculture: an early Neolithic case study from Southwest Asia  

E-print Network

Sickle blade life-history and the transition to agriculture: an early Neolithic case study from Department of Biology, Hamilton College, Clinton, NY, USA a r t i c l e i n f o Article history: Received 14 t In Southwest Asia, sickle blades first appear early in the sequence of the transition to agriculture

Kohler, Tim A.

329

Caregivers' Experience during Their Children's Transition Process from Early Childhood Special Education Services to School-Aged Special Education Services  

ERIC Educational Resources Information Center

This study investigates caregivers' perceptions of the transition process for children transitioning from Early Childhood Special Education (ECSE) to School Age Special Education services (SA). Interest in this topic developed during the researcher's 18 years of experience as an Itinerant Early Childhood Special Education Teacher during which she

Hicks, Linda Yvonne

2011-01-01

330

Bridging Early Services for Children with Special Needs and Their Families: A Practical Guide for Transition Planning.  

ERIC Educational Resources Information Center

This volume presents a comprehensive plan for transition of children with special needs and their families between infant or early intervention services and preschool services, and between preschool services and kindergarten. It aims to help in bridging these services to minimize the stress and increase the promise of early childhood transitions.

Rosenkoetter, Sharon E.; And Others

331

Mechanical properties, glass transition temperature, and bond enthalpy trends of high metalloid Fe-based bulk metallic glasses  

E-print Network

-based bulk metallic glasses X. J. Gu,1 S. Joseph Poon,1,a Gary J. Shiflet,2 and Michael Widom3 1 Department transition temperatures Tg of Fe­Cr­Mo­P­C­B bulk metallic glasses containing up to 27 at. % metalloids have. The findings are relevant to understanding ductility and glass transition of metallic glasses. © 2008 American

Widom, Michael

332

The deformation units in metallic glasses revealed by stress-induced localized glass transition  

NASA Astrophysics Data System (ADS)

We report that even in quasi-static cyclic compressions in the apparent elastic regimes of the bulk metallic glasses, the precisely measured stress-strain curve presents a mechanical hysteresis loop, which is commonly perceived to occur only in high-frequency dynamic tests. A phenomenological viscoelastic model is established to explain the hysteresis loop and demonstrate the evolutions of the viscous zones in metallic glasses during the cyclic compression. The declining of the viscosity of the viscous zones to at least 1 1012 Pa s when stress applied indicates that stress-induced localized glass to supercooled liquid transition occurs. We show that the deformation units of metallic glasses are evolved from the intrinsic heterogeneous defects in metallic glasses under stress and the evolution is a manifestation of the stress-induced localized glass transition. Our study might provide a new insight into the atomic-scale mechanisms of plastic deformation of metallic glasses.

Huo, L. S.; Ma, J.; Ke, H. B.; Bai, H. Y.; Zhao, D. Q.; Wang, W. H.

2012-06-01

333

Ternary rare earth and actinoid transition metal carbides viewed as carbometalates  

SciTech Connect

Ternary carbides A{sub x}T{sub y}C{sub z} (A=rare earth metals and actinoids; T=transition metals) with monoatomic species C{sup 4-} as structural entities are classified according to the criteria (i) metal to carbon ratio, (ii) coordination number of the transition metal by carbon atoms, and (iii) the dimensionality of the anionic network [T{sub y}C{sub z}]{sup n-}. Two groups are clearly distinguishable, depending on the metal to carbon ratio. Those where this ratio is equal to or smaller than 2 may be viewed as carbometalates, thus extending the sequence of complex anions from fluoro-, oxo-, and nitridometalates to carbometalates. The second group, metal-rich carbides with metal to carbon ratios equal to or larger than 4 is better viewed as typical intermetallics (''interstitial carbides''). The chemical bonding properties have been investigated by analyzing the Crystal Orbital Hamilton Population (COHP). The chemical bonding situation with respect to individual T-C bonds is similar in both classes. The main difference is the larger number of metal-metal bonds in the crystal structures of the metal-rich carbides.

Dashjav, Enkhtsetseg [Max-Planck-Institut fuer Chemische Physik fester Stoffe, Noethnitzer Strasse 40, D-01187 Dresden (Germany); Kreiner, Guido [Max-Planck-Institut fuer Chemische Physik fester Stoffe, Noethnitzer Strasse 40, D-01187 Dresden (Germany); Schnelle, Walter [Max-Planck-Institut fuer Chemische Physik fester Stoffe, Noethnitzer Strasse 40, D-01187 Dresden (Germany); Wagner, Frank R. [Max-Planck-Institut fuer Chemische Physik fester Stoffe, Noethnitzer Strasse 40, D-01187 Dresden (Germany); Kniep, Ruediger [Max-Planck-Institut fuer Chemische Physik fester Stoffe, Noethnitzer Strasse 40, D-01187 Dresden (Germany)], E-mail: Kniep@cpfs.mpg.de; Jeitschko, Wolfgang [Institut fuer Anorganische und Analytische Chemie, Universitaet Muenster, Wilhelm-Klemm-Strasse 8, D-48149 Muenster (Germany)], E-mail: jeitsch@uni-muenster.de

2007-02-15

334

Solid-state complexes of poly(alpha-amino acid)s and transition metal chlorides  

NASA Astrophysics Data System (ADS)

Poly(4-vinyl pyridine) (P4VP) and dichlorotricarbonyl ruthenium(II) dimer are shown via fourier transform infrared (FTIR) analysis and group theory to form coordination crosslinks. The crosslinks occur by coordination of two pyridine groups to each Rusp{2+} metal center. As the percentage of dimer is increased, FTIR shows evidence of metal pendant groups in addition to the coordination crosslinks. Quantitative measurements from FTIR spectra are used to correlate the number of crosslinks with the amount of dimer present in the mixture. Poly(L-histidine) (PHIS) and poly(L-lysine) (PLYS) are shown to have glass transition temperatures when heated in the solid state. These transition temperatures at 169spC for PHIS and 178spC have never been reported in the literature. When combined with several first-row transition metal ions (Cosp{2+},\\ Nisp{2+},\\ Cusp{2+},\\ Znsp{2+}) PHIS forms coordination crosslinks. Differential scanning calorimetry (DSC) shows an increase in glass transition temperature for metal/PHIS complexes, with the greatest enhancement (6.9spC/mol% metal salt) from nickel chloride. FTIR shows evidence of coordination to both the histidine side chains and to the amide group in the backbone of PHIS. When combined with two second-row metal ions (Rusp{2+},\\ Pdsp{2+}) coordination crosslinks also form, with only histidine side chains involved in the crosslinking. Glass transition temperature is enhanced by 11.5spC/mol% metal salt with dichlorobisacetonitrile palladium(II). PLYS does not form coordination crosslinks in the presence of the same first-row metal ions. However, thermal and spectral data suggest a metal salts form pendant groups on the polymer chain via the carbonyl oxygen in the backbone. This metal-polymer coordination causes disruption of hydrogen bonding resulting in a decrease in the glass transition temperature with the addition of metal salts. Statistical models illustrate that ligand field stabilization is an important parameter for the prediction of a change in Tg when metal ions are added to the polymer. Statistical models also confirm that the mechanism, which changes Tg and the spectral data in PLYS/metal blends, is different than the mechanism suggested for PHIS and P4VP complexes.

McCurdie, Mary Pat

335

A general holographic metal/superconductor phase transition model  

E-print Network

We study the scalar condensation of a general holographic superconductor model in AdS black hole background away from the probe limit. We find the model parameters together with the scalar mass and backreaction can determine the order of phase transitions completely. In addition, we observe two types of discontinuities of the scalar operator in the case of first order phase transitions. We analyze in detail the effects of the scalar mass and backreaction on the formation of discontinuities and arrive at an approximate relation between the threshold model parameters. Furthermore, we obtain superconductor solutions corresponding to higher energy states and examine the stability of these superconductor solutions.

Peng, Yan

2014-01-01

336

A general holographic metal/superconductor phase transition model  

E-print Network

We study the scalar condensation of a general holographic superconductor model in AdS black hole background away from the probe limit. We find the model parameters together with the scalar mass and backreaction can determine the order of phase transitions completely. In addition, we observe two types of discontinuities of the scalar operator in the case of first order phase transitions. We analyze in detail the effects of the scalar mass and backreaction on the formation of discontinuities and arrive at an approximate relation between the threshold model parameters. Furthermore, we obtain superconductor solutions corresponding to higher energy states and examine the stability of these superconductor solutions.

Yan Peng; Yunqi Liu

2014-10-27

337

Catastrophic phase transitions and early warnings in a spatial ecological model  

NASA Astrophysics Data System (ADS)

Gradual changes in exploitation, nutrient loading, etc produce shifts between alternative stable states (ASS) in ecosystems which, quite often, are not smooth but abrupt or catastrophic. Early warnings of such catastrophic regime shifts are fundamental for designing management protocols for ecosystems. Here we study the spatial version of a popular ecological model, involving a logistically growing single species subject to exploitation, which is known to exhibit ASS. Spatial heterogeneity is introduced by a carrying capacity parameter varying from cell to cell in a regular lattice. Transport of biomass among cells is included in the form of diffusion. We investigate whether different quantities from statistical mechanicslike the variance, the two-point correlation function and the patchinessmay serve as early warnings of catastrophic phase transitions between the ASS. In particular, we find that the patch-size distribution follows a power law when the system is close to the catastrophic transition. We also provide links between spatial and temporal indicators and analyse how the interplay between diffusion and spatial heterogeneity may affect the earliness of each of the observables. We find that possible remedial procedures, which can be followed after these early signals, become more effective as the diffusion becomes lower. Finally, we comment on similarities of and differences between these catastrophic shifts and paradigmatic thermodynamic phase transitions like the liquid-vapour change of state for a fluid like water.

Fernndez, A.; Fort, H.

2009-09-01

338

Barium distributions in teeth reveal early life dietary transitions in primates  

PubMed Central

Early life dietary transitions reflect fundamental aspects of primate evolution and are important determinants of health in contemporary human populations1,2. Weaning is critical to developmental and reproductive rates; early weaning can have detrimental health effects but enables shorter inter-birth intervals, which influences population growth3. Uncovering early life dietary history in fossils is hampered by the absence of prospectively-validated biomarkers that are not modified during fossilisation4. Here we show that major dietary shifts in early life manifest as compositional variations in dental tissues. Teeth from human children and captive macaques, with prospectively-recorded diet histories, demonstrate that barium (Ba) distributions accurately reflect dietary transitions from the introduction of mothers milk and through the weaning process. We also document transitions in a Middle Palaeolithic juvenile Neanderthal, which shows a pattern of exclusive breastfeeding for seven months, followed by seven months of supplementation. After this point, Ba levels in enamel returned to baseline prenatal levels, suggesting an abrupt cessation of breastfeeding at 1.2 years of age. Integration of Ba spatial distributions and histological mapping of tooth formation enables novel studies of the evolution of human life history, dietary ontogeny in wild primates, and human health investigations through accurate reconstructions of breastfeeding history. PMID:23698370

Austin, Christine; Smith, Tanya M.; Bradman, Asa; Hinde, Katie; Joannes-Boyau, Renaud; Bishop, David; Hare, Dominic J.; Doble, Philip; Eskenazi, Brenda; Arora, Manish

2013-01-01

339

[Transition metal mediated transformations of small molecules]. Progress report  

SciTech Connect

Work on organotransition metal chemistry, homogeneous and heterogeneous catalysis is summarized. Several cationic palladium(II) complexes with bulky phosphine or pyridine ligands were discovered that are highly selective catalysts for linear dimerization of vinyl monomers and linear polymerization of p-divinylbenzene, the reactions proceeding through a carbocationic mechanism. Our studies were continued on alternating olefin-carbon monoxide copolymers. The copolymerization reaction and reactivity of copolymers were examined. New catalytic systems for alternating copolymerization of {alpha}-olefins with CO were discovered. In the case of styrene derivatives, tactic copolymers were obtained. Poly(ethylenepyrrolediyl) derivatives were synthesized from alternating ethylene-carbon monoxide copolymer and become electronic conductors when doped with iodine. A catalytic system for direct synthesis of polyureas and polyoxamides from and diamines was also discovered. Pt metal catalyzed the oxidation of ethers, esters, and amines to carboxylic acids and the oxidation of olefins to 1,2-diols. Anaerobic and aerobic decomposition of molybdenum(VI)-oxoalkyl compounds were studied for heterogeneous oxidation of alkanes and olefins on Mo(VI)-oxide surfaces. Synthesis of polymer-trapped metal, metal oxide, and metal sulfide nanoclusters (size <1--10 nm) was studied.

Sen, A.

1992-10-01

340

A Model of Metallicity Evolution in the Early Universe  

Microsoft Academic Search

We apply the phenomenological model used to explain the abundances of Fe and\\u000ar-process elements in very metal-poor stars in the Galaxy to [Fe\\/H] of damped\\u000aLy alpha systems. It is assumed that the first stars formed after the Big Bang\\u000awere very massive and promptly enriched the interstellar medium to [Fe\\/H] ~ -3,\\u000aat which metallicity formation of normal

G. J. Wasserburg; Y.-Z. Qian

2000-01-01

341

X-ray induced insulator-metal transitions in CMR manganites  

SciTech Connect

In this work the authors report a study of the photoinduced insulator-to-metal transition in manganese oxide perovskites of the formula Pr{sub 1{minus}x}Ca{sub x}MnO{sub 3}. The transition is closely related to the magnetic field induced insulator-to-metal transition (CMR effect) observed in these materials. It is accompanied by a dramatic change in the magnetic properties and lattice structure: the material changes from an insulating charge-ordered canted antiferromagnet to a ferromagnetic metal. The authors present an investigation of the transport and structural properties of these materials over the course of the transition (which usually takes about an hour to complete). The current-voltage characteristics exhibited by the material during the transition are highly nonlinear, indicating a large inhomogeneity of the transitional state. Possible practical applications of this novel type of transition are briefly discussed. They also report a high resolution X-ray diffraction study of the charge ordering in these materials. The temperature dependent charge ordering structure observed in these compounds is more complex than previously reported.

Kiryukhin, V.; Casa, D.; Keimer, B. [Princeton Univ., NJ (United States). Dept. of Physics; Hill, J.P.; Vigliante, A. [Brookhaven National Lab., Upton, NY (United States). Dept. of Physics; Tomioka, Y. [Joint Research Center for Atom Technology, Tsukuba, Ibaraki (Japan); Tokura, Y. [Joint Research Center for Atom Technology, Tsukuba, Ibaraki (Japan)]|[Univ. of Tokyo (Japan). Dept. of Applied Physics

1997-12-01

342

Normal variations in the isotopic composition of metabolically relevant transition metals in human blood  

NASA Astrophysics Data System (ADS)

Cu, Fe and Zn are transition metals with great catalytic, structural and regulating importance in the human body. Hence, an aberrant metabolism of these elements can have serious implications on the health of a person. It is assumed that, due to differences in isotope fractionation, the isotopic composition of these elements in whole blood of patients can be different from that in blood of healthy subjects. Therefore, isotopic analysis of the element affected by the disease can be a promising approach for early diagnosis. A method for isotopic analysis of Cu, Fe and Zn in human whole blood was developed. The simultaneous chromatographic isolation of these elements and the conditions for isotope ratio measurement via multi-collector ICP - mass spectrometry (MC-ICP-MS) were optimized. So far, only whole blood of supposedly healthy volunteers (reference population) was analyzed. Results for Fe confirmed the known differences in isotopic composition between male and female blood. It is also shown that other parameters can have influence as well, e.g., the isotopic composition of Zn seems to be governed by the diet.

Van Heghe, L.; Cloquet, C.; Vanhaecke, F.

2012-04-01

343

Enhancement of Platinum Cathode Catalysis by Addition of Transition Metals  

ERIC Educational Resources Information Center

The sluggish kinetics of oxygen reduction reaction (ORR) contributes significantly to the loss of cathode overpotential in fuel cells, thus requiring high loadings of platinum (Pt), which is an expensive metal with limited supply. However, Pt and Pt-based alloys are still the best available electrocatalysts for ORR thus far. The research presented

Duong, Hung Tuan

2009-01-01

344

A high-performance liquid chromatography method for determining transition metal content in proteins.  

PubMed

Transition metals are common components of cellular proteins and the detailed study of metalloproteins necessitates the identification and quantification of bound metal ions. Screening for metals is also an informative step in the initial characterization of the numerous unknown and unclassified proteins now coming through the proteomic pipeline. We have developed a high-performance liquid chromatography method for the quantitative determination of the most prevalent biological transition metals: manganese, iron, cobalt, nickel, copper, and zinc. The method is accurate and simple and can be adapted for automated high-throughput studies. The metal analysis involves acid hydrolysis to release the metal ions into solution, followed by ion separation on a mixed-bead ion-exchange column and absorbance detection after postcolumn derivatization with the metallochromic indicator 4-(2-pyridylazo)resorcinol. The potential interferences by common components of protein solutions were investigated. The metal content of a variety of metalloproteins was analyzed and the data were compared to data obtained from inductively coupled plasma-atomic emission spectroscopy. The sensitivity of the assay allows for the detection of 0.1-0.8 nmol, depending on the metal. The amount of protein required is governed by the size of the protein and the fraction of protein with metal bound. For routine analysis 50 microg was used but for many proteins 10 microg would be sufficient. The advantages, disadvantages, and possible applications of this method are discussed. PMID:15519577

Atanassova, Anelia; Lam, Robert; Zamble, Deborah B

2004-12-01

345

First-principles prediction of half-metallic ferromagnetism in five transition-metal chalcogenides: The case of rocksalt structure  

NASA Astrophysics Data System (ADS)

Motivated by the experimental synthesis of bulk rocksalt MnS, MnSe, and MnTe, we show with first-principles calculations that among all transition-metal pnictides and chalcogenides with rocksalt structure CrTe, VPo, and CrPo are truly half-metallic ferromagnets, and both VTe and CrSe exhibit nearly half-metallicity. Importantly, for these five half-metallic compounds, the rocksalt phase is energetically more stable than the zinc-blende and wurtzite ones, and the total energy differences between the rocksalt and ground-state NiAs phases are very small (0.06-0.43 eV/f.u.) and comparable with that of experimental MnTe (0.24 eV/f.u.), thus like rocksalt manganese chalcogenides, these five rocksalt half-metals would be realized in the form of bulk or at list thin films for spintronic applications. In addition, we study the (111) surface properties of rocksalt CrPo and find both Cr- and Po-terminated (111) surfaces retain the bulk half-metallicity. We also reveal that the spin-orbit coupling has very weak effect on the half-metallicity of rocksalt CrSe, VTe, and CrTe, and the spin polarizations are still high for rocksalt VPo and CrPo although the spin-orbit coupling affects greatly their half-metallicities.

Gao, G. Y.; Yao, Kai-Lun

2012-06-01

346

First-principles prediction of half-metallic ferromagnetism in five transition-metal chalcogenides: The case of rocksalt structure  

NASA Astrophysics Data System (ADS)

Motivated by the experimental synthesis of bulk rocksalt MnS, MnSe, and MnTe, we show with first-principles calculations that among all transition-metal pnictides and chalcogenides with rocksalt structure CrTe, VPo, and CrPo are truly half-metallic ferromagnets, and both VTe and CrSe exhibit nearly half-metallicity. Importantly, for these five half-metallic compounds, the rocksalt phase is energetically more stable than the zinc-blende and wurtzite ones, and the total energy differences between the rocksalt and ground-state NiAs phases are very small (0.06-0.43 eV/f.u.) and comparable with that of experimental MnTe (0.24 eV/f.u.), thus like rocksalt manganese chalcogenides, these five rocksalt half-metals would be realized in the form of bulk or at list thin films for spintronic applications. In addition, we study the (111) surface properties of rocksalt CrPo and find both Cr- and Po-terminated (111) surfaces retain the bulk half-metallicity. We also reveal that the spin-orbit coupling has very weak effect on the half-metallicity of rocksalt CrSe, VTe, and CrTe, and the spin polarizations are still high for rocksalt VPo and CrPo although the spin-orbit coupling affects greatly their half-metallicities.

Gao, G. Y.; Yao, Kai-Lun

2012-05-01

347

Transition metal (Mn, Fe, Co, Ni)-doped graphene hybrids for electrocatalysis.  

PubMed

The development of electrocatalysts is crucial for renewable energy applications. Metal-doped graphene hybrid materials have been explored for this purpose, however, with much focus on noble metals, which are limited by their low availability and high costs. Transition metals may serve as promising alternatives. Here, transition metal-doped graphene hybrids were synthesized by a simple and scalable method. Metal-doped graphite oxide precursors were thermally exfoliated in either hydrogen or nitrogen atmosphere; by changing exfoliation atmospheres from inert to reductive, we produced materials with different degrees of oxidation. Effects of the presence of metal nanoparticles and exfoliation atmosphere on the morphology and electrocatalytic activity of the hybrid materials were investigated using electron microscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and cyclic voltammetry. Doping of graphene with transition metal nanoparticles of the 4th?period significantly influenced the electrocatalysis of compounds important in energy production and storage applications, with hybrid materials exfoliated in nitrogen atmosphere displaying superior performance over those exfoliated in hydrogen atmosphere. Moreover, nickel-doped graphene hybrids displayed outstanding electrocatalytic activities towards reduction of O2 when compared to bare graphenes. These findings may be exploited in the research field of renewable energy. PMID:23495248

Toh, Rou Jun; Poh, Hwee Ling; Sofer, Zden?k; Pumera, Martin

2013-06-01

348

METAL-NON METAL TRANSITIONS /N RARE EARTH COMPOUNDS. EXPERIMENT AND THEORK /.  

E-print Network

, superconductivity, electron-phonon and band theory, to name a few. 2. Properties of normal rare earth metals. - Before discussing rare earth valence instabilities, three relevant general features of rare earth metals

Paris-Sud XI, Université de

349

Prebiotic coordination chemistry: The potential role of transition-metal complexes in the chemical evolution  

NASA Technical Reports Server (NTRS)

In approaching the extremely involved and complex problem of the origin of life, consideration of the coordination chemistry appeared not only as a possibility but as a necessity. The first model experiments appear to be promising because of prebiotic-type synthesis by means of transition-metal complexes. It is especially significant that in some instances various types of vitally important substances (nucleic bases, amino acids) are formed simultaneously. There is ground to hope that systematic studies in this field will clarify the role of transition-metal complexes in the organizatorial phase of chemical evolution. It is obvious that researchers working in the fields of the chemistry of cyano and carbonyl complexes, and of the catalytic effect of transition-metal complexes are best suited to study these aspects of the attractive and interesting problem of the origin of life.

Beck, M.

1979-01-01

350

STABILITY IN BCC TRANSITION METALS: MADELUNG AND BAND-ENERGY EFFECTS DUE TO ALLOYING  

SciTech Connect

The phase stability of the bcc Group VB (V, Nb, and Ta) transition metals is explored by first-principles electronic-structure calculations. Alloying with a small amount of a neighboring metal can either stabilize or destabilize the bcc phase. This counterintuitive behavior is explained by competing mechanisms that dominate depending on particular dopand. We show that band-structure effects dictate stability when a particular Group VB metal is alloyed with its nearest neighbors within the same d-transition series. In this case, the neighbor with less (to the left) and more (to the right) d electrons, destabilize and stabilize bcc, respectively. When alloying with neighbors of different d-transition series, electrostatic Madelung energy dominates over the band energy and always stabilizes the bcc phase.

Landa, A; Soderlind, P; Ruban, A; Peil, O; Vitos, L

2009-08-28

351

Band gap tuning in transition metal oxides by site-specific substitution  

DOEpatents

A transition metal oxide insulator composition having a tuned band gap includes a transition metal oxide having a perovskite or a perovskite-like crystalline structure. The transition metal oxide includes at least one first element selected form the group of Bi, Ca, Ba, Sr, Li, Na, Mg, K, Pb, and Pr; and at least one second element selected from the group of Ti, Al, V, Cr, Mn, Fe, Co, Ni, Cu, Zr, Nb, Mo, Ru, Rh, Hf, Ta, W, Re, Os, Ir, and Pt. At least one correlated insulator is integrated into the crystalline structure, including REMO.sub.3, wherein RE is at least one Rare Earth element, and wherein M is at least one element selected from the group of Co, V, Cr, Ni, Mn, and Fe. The composition is characterized by a band gap of less of 4.5 eV.

Lee, Ho Nyung; Chisholm, Jr., Matthew F; Jellison, Jr., Gerald Earle; Singh, David J; Choi, Woo Seok

2013-12-24

352

Electronic Excitations and Insulator-Metal Transition in Poly(3-hexylthiophene) Organic Field-Effect Transistors  

E-print Network

We carry out a comprehensive theoretical and experimental study of charge injection in Poly(3-hexylthiophene) (P3HT) to determine the most likely scenario for metal-insulator transition in this system. We calculate the optical absorption frequencies corresponding to a polaron and a bipolaron lattice in P3HT. We also analyze the electronic excitations for three possible scenarios under which a first-- or a second--order metal--insulator transition can occur in doped P3HT. These theoretical scenarios are compared with data from infrared absorption spectroscopy on P3HT thin film field-effect transistors (FET). Our measurements and theoretical predictions suggest that charge-induced localized states in P3HT FETs are bipolarons and that the highest doping level achieved in our experiments approaches that required for a first-order metal--insulator transition.

N. Sai; Z. Q. Li; M. C. Martin; D. N. Basov; M. Di Ventra

2006-11-10

353

Bonds Between Metal Atoms: A New Mode of Transition Metal Chemistry.  

ERIC Educational Resources Information Center

Discusses polynuclear metal clusters (containing two or more metal atoms bonded to one another as well as to nonmetallic elements), including their formation and applications. Studies of bonds between metal atoms reveal superconductors, organic-reaction catalysts, and photosensitive complexes that may play a role in solar energy. (JN)

Cotton, F. Albert; Chisholm, Malcolm H.

1982-01-01

354

Global transcriptome and deletome profiles of yeast exposed to transition metals.  

PubMed

A variety of pathologies are associated with exposure to supraphysiological concentrations of essential metals and to non-essential metals and metalloids. The molecular mechanisms linking metal exposure to human pathologies have not been clearly defined. To address these gaps in our understanding of the molecular biology of transition metals, the genomic effects of exposure to Group IB (copper, silver), IIB (zinc, cadmium, mercury), VIA (chromium), and VB (arsenic) elements on the yeast Saccharomyces cerevisiae were examined. Two comprehensive sets of metal-responsive genomic profiles were generated following exposure to equi-toxic concentrations of metal: one that provides information on the transcriptional changes associated with metal exposure (transcriptome), and a second that provides information on the relationship between the expression of approximately 4,700 non-essential genes and sensitivity to metal exposure (deletome). Approximately 22% of the genome was affected by exposure to at least one metal. Principal component and cluster analyses suggest that the chemical properties of the metal are major determinants in defining the expression profile. Furthermore, cells may have developed common or convergent regulatory mechanisms to accommodate metal exposure. The transcriptome and deletome had 22 genes in common, however, comparison between Gene Ontology biological processes for the two gene sets revealed that metal stress adaptation and detoxification categories were commonly enriched. Analysis of the transcriptome and deletome identified several evolutionarily conserved, signal transduction pathways that may be involved in regulating the responses to metal exposure. In this study, we identified genes and cognate signaling pathways that respond to exposure to essential and non-essential metals. In addition, genes that are essential for survival in the presence of these metals were identified. This information will contribute to our understanding of the molecular mechanism by which organisms respond to metal stress, and could lead to an understanding of the connection between environmental stress and signal transduction pathways. PMID:18437200

Jin, Yong Hwan; Dunlap, Paul E; McBride, Sandra J; Al-Refai, Hanan; Bushel, Pierre R; Freedman, Jonathan H

2008-04-01

355

Global Transcriptome and Deletome Profiles of Yeast Exposed to Transition Metals  

PubMed Central

A variety of pathologies are associated with exposure to supraphysiological concentrations of essential metals and to non-essential metals and metalloids. The molecular mechanisms linking metal exposure to human pathologies have not been clearly defined. To address these gaps in our understanding of the molecular biology of transition metals, the genomic effects of exposure to Group IB (copper, silver), IIB (zinc, cadmium, mercury), VIA (chromium), and VB (arsenic) elements on the yeast Saccharomyces cerevisiae were examined. Two comprehensive sets of metal-responsive genomic profiles were generated following exposure to equi-toxic concentrations of metal: one that provides information on the transcriptional changes associated with metal exposure (transcriptome), and a second that provides information on the relationship between the expression of ?4,700 non-essential genes and sensitivity to metal exposure (deletome). Approximately 22% of the genome was affected by exposure to at least one metal. Principal component and cluster analyses suggest that the chemical properties of the metal are major determinants in defining the expression profile. Furthermore, cells may have developed common or convergent regulatory mechanisms to accommodate metal exposure. The transcriptome and deletome had 22 genes in common, however, comparison between Gene Ontology biological processes for the two gene sets revealed that metal stress adaptation and detoxification categories were commonly enriched. Analysis of the transcriptome and deletome identified several evolutionarily conserved, signal transduction pathways that may be involved in regulating the responses to metal exposure. In this study, we identified genes and cognate signaling pathways that respond to exposure to essential and non-essential metals. In addition, genes that are essential for survival in the presence of these metals were identified. This information will contribute to our understanding of the molecular mechanism by which organisms respond to metal stress, and could lead to an understanding of the connection between environmental stress and signal transduction pathways. PMID:18437200

Jin, Yong Hwan; Dunlap, Paul E.; McBride, Sandra J.; Al-Refai, Hanan; Bushel, Pierre R.; Freedman, Jonathan H.

2008-01-01

356

Transition-metal-free highly chemo- and regioselective arylation of unactivated arenes with aryl halides over recyclable heterogeneous catalysts.  

PubMed

A novel heterogeneous catalysis system using metal-organic frameworks as catalyst demonstrated excellent chemo- and regioselectivity for the direct arylation of unactivated arenes with aryl iodides/bromides without the assistance of any transition metals. PMID:22227601

Liu, Hongli; Yin, Biaolin; Gao, Zhiqiang; Li, Yingwei; Jiang, Huanfeng

2012-02-14

357

On the behavior of Bronsted-Evans-Polanyi Relations for Transition Metal Oxides  

SciTech Connect

Versatile Broensted-Evans-Polanyi (BEP) relations are found from density functional theory for a wide range of transition metal oxides including rutiles and perovskites. For oxides, the relation depends on the type of oxide, the active site and the dissociating molecule. The slope of the BEP relation is strongly coupled to the adsorbate geometry in the transition state. If it is final state-like the dissociative chemisorption energy can be considered as a descriptor for the dissociation. If it is initial state-like, on the other hand, the dissociative chemisorption energy is not suitable as descriptor for the dissociation. Dissociation of molecules with strong intramolecular bonds belong to the former and molecules with weak intramolecular bonds to the latter group. We show, for the prototype system La-perovskites, that there is a 'cyclic' behavior in the transition state characteristics upon change of the active transition metal of the oxide.

Vojvodic, Aleksandra

2011-08-22

358

PROLONGED INTRAVENOUS THERAPY VERSUS EARLY TRANSITION TO ORAL ANTIMICROBIAL THERAPY FOR ACUTE OSTEOMYELITIS IN CHILDREN  

PubMed Central

OBJECTIVES Early transition from intravenous to oral antimicrobial therapy for acute osteomyelitis in children has been suggested as a safe and effective alternative to traditional prolonged intravenous therapy via central venous catheter, but no studies have directly compared these two treatment modalities. We sought to compare the effectiveness of early transition from intravenous to oral antimicrobial therapy vs. prolonged intravenous antimicrobial therapy for the treatment of children with acute osteomyelitis. METHODS We conducted a retrospective cohort study of children ages 2 months to 17 years diagnosed with acute osteomyelitis between 2000 and 2005 at 29 free-standing childrens hospitals in the United States to confirm the extent of variation in use of early transition to oral therapy. We used a propensity scores to adjust for potential differences between children treated with prolonged intravenous therapy, and logistic regression to model the association of outcome (treatment failure rates within 6 months of diagnosis and difference in the mode of therapy within hospitals and across hospitals. RESULTS Of the 1969 children who met inclusion criteria, 1021 received prolonged intravenous therapy and 948 received oral therapy. Use of prolonged intravenous therapy varied significantly across hospitals (10% to 95%, P<0.001). The treatment failure rate was 5% (54 of 1021) in the prolonged intravenous therapy group and 4% (38 of 948) in the oral therapy group. There was no significant association between treatment failure and the mode of antimicrobial therapy (adjusted odds ratio=0.77, 95% confidence interval=0.49 to 1.22). Thirty-five children (3.4%) in the prolonged intravenous therapy group were readmitted for a catheter-associated complication. CONCLUSIONS Treatment of acute osteomyelitis with early transition to oral therapy is not associated with a higher risk of treatment failures and avoids the risks of prolonged intravenous therapy through central venous catheters. PMID:19171632

Zaoutis, Theoklis; Localio, A. Russell; Leckerman, Kateri; Saddlemire, Stephanie; Bertoch, David; Keren, Ron

2013-01-01

359

Transition metal surface passivation induced graphene edge reconstruction.  

PubMed

In vacuum, the bare zigzag (zz) edge of graphene is reconstructed into a line of pentagon-heptagon pairs, while the pristine armchair (ac) edge is retained. Our first-principle explorations of graphene edges on three metal surfaces [Cu(111), Co(111), and Ni(111)] indicate an opposite tendency, that is, the pristine zz edge is energetically favorable and the reconstructed ac edge with dangling C atoms is highly stable on Co(111) and Ni(111) surfaces. Insightful analysis shows that passivation of the graphene edge by metal surfaces is responsible for the dramatic differences. Beyond this, the unique edge configuration has a significant impact on the graphene CVD growth behavior. PMID:22420470

Gao, Junfeng; Zhao, Jijun; Ding, Feng

2012-04-11

360

Synthesis of heterocycles through transition-metal-catalyzed isomerization reactions.  

PubMed

Metal-catalyzed isomerization of N- and O-allylic systems is emerging as an effective method to form synthetically useful iminium and oxocarbenium intermediates. In the presence of tethered nucleophiles, several recent examples illuminate this approach as a powerful strategy for the synthesis of structurally complex and diverse heterocycles. In this Concept article, we attempt to cover this area of research through a selection of recent versatile examples. PMID:24924616

Ishoey, Mette; Nielsen, Thomas E

2014-07-14

361

Trace Metals in the Early Ocean, Biological Implications, and Evolving Biospheric Redox  

NASA Astrophysics Data System (ADS)

Dissolved molybdenum abounds in modern, oxygen-rich seawater as the highly soluble molybdate ion. But this trace metal, also a nutrient essential to phytoplankton productivity, was not always so readily available. Several periods of the geologic past are noted for being euxinic (i.e., oxygen-poor and sulfide-rich) at regional or perhaps even global scales. During the Proterozoic in particular, numerous euxinic settings may have persisted in the ocean for a billion years or more following the initial rise of oxygen in the atmosphere. Under such conditions, Mo is sequestered efficiently, and corresponding limitation in the oceanic inventory may have impacted nitrogen fixation by prokaryotes, as well as uptake of fixed nitrogen by early eukaryotes. Mo is essential for nitrogen fixation and nitrate assimilation as a cofactor for nitrogenase and assimilatory nitrate reductase enzymes, respectively. Evidence for analogous limitations is emerging for portions of the Paleozoic and Mesozoic, but the potential impacts have not yet been considered. In each case, the critical arguments hang on our ability (1) to estimate oceanic extents of oxygen-poor, sulfide-rich settings for the time slice of interest and (2) to discriminate Mo drawdown in the global ocean from that occurring locally within individual basins. Traditional and emerging approaches for distinguishing local from global ancient anoxia/euxinia will be highlighted with an eye toward estimating the impact on availability of Mo and other bioessential, redox-sensitive transition metals. The context for this exploration will be the long history of evolving redox in the ocean and atmosphere from the Archean forward. The Phanerozoic examples are also associated with major biotic extinction events, and our understanding of the relationships among the primary drivers of extinction, widespread euxinic conditions, and the impact of micronutrient availability during extinction and recovery remains nascent.

Lyons, T. W.; Scott, C.; Gill, B. C.; Anbar, A. D.

2008-12-01

362

Density of States Scaling at the Semimetal to Metal Transition in Three Dimensional Topological Insulators  

NASA Astrophysics Data System (ADS)

The quantum phase transition between the three dimensional Dirac semimetal and the diffusive metal can be induced by increasing disorder. Taking the system of a disordered Z2 topological insulator as an important example, we compute the single particle density of states by the kernel polynomial method. We focus on three regions: the Dirac semimetal at the phase boundary between two topologically distinct phases, the tricritical point of the two topological insulator phases and the diffusive metal, and the diffusive metal lying at strong disorder. The density of states obeys a novel single parameter scaling, collapsing onto two branches of a universal scaling function, which correspond to the Dirac semimetal and the diffusive metal. The diverging length scale critical exponent ? and the dynamical critical exponent z are estimated, and found to differ significantly from those for the conventional Anderson transition. Critical behavior of experimentally observable quantities near and at the tricritical point is also discussed.

Kobayashi, Koji; Ohtsuki, Tomi; Imura, Ken-Ichiro; Herbut, Igor F.

2014-01-01

363

Electronic and structural transformations near the insulator-to-metal transition in vanadium dioxide  

Microsoft Academic Search

Vanadium dioxide (VO2) undergoes an insulator-to-metal transition (IMT) at T 340 K accompanied by a change in the lattice structure. Numerous studies of this phase transition in VO2 have focused either on the electronic change or on the structural change. The interplay between the electronic and lattice degrees of freedom has been relatively unexplored. In previous work using scanning near-field

M. M. Qazilbash; A. Tripathi; A. Frenzel; O. G. Shpyrko; D. N. Basov; M. V. Holt; J. M. Maser; Byung-Gyu Chae; Bong-Jun Kim; Hyun-Tak Kim

2010-01-01

364

Vibrational-electronic interaction in the infrared circular dichroism spectra of transition-metal complexes  

NASA Astrophysics Data System (ADS)

The circular dichroism spectra of the quasi-tetrahedral complexes of transition-metal ions with (-)-spartein, [M( l-sp)Cl 2], over the C-H stretching vibration range, show an optical activity which is weak in the Zn(II) case, but enhanced in the Co(II) and Ni(II) analogues through the coupling of the sharp vibrational transition with underlying broad d-d electronic excitation.

Barnett, C. J.; Drake, A. F.; Kuroda, R.; Mason, S. F.; Savage, S.

1980-02-01

365

Ultra-fast diffusion mechanism of the late 3d transition metal impurities in silicon  

Microsoft Academic Search

Based upon ab initio electronic structure calculations with super-cells and an FLAPW method, we discuss the mechanism of the ultra-fast diffusion and the reduction of the migration barriers of the late 3d transition atom impurities of Co, Ni and Cu in silicon. The reduction mechanism of the migration barriers of the late 3d transition metal impurities is due to the

Y. Kamon; H. Harima; A. Yanase; H. Katayama-Yoshida

2001-01-01

366

Mesoscopic Metal-Insulator Transition at Ferroelastic Domain Walls in VO2  

Microsoft Academic Search

The novel phenomena induced by symmetry breaking at homointerfaces between ferroic variants in ferroelectric and ferroelastic materials have attracted recently much attention. Using variable temperature scanning microwave microscopy, we demonstrate the mesoscopic strain-induced metal-insulator phase transitions in the vicinity of ferroelastic domain walls in the semiconductive VO2 that nucleated at temperatures as much as 10-12 C below bulk transition, resulting

Keith M Jones; Sergei V Kalinin; Andrei Kolmakov; Igor A. Lukyanchuk; Vincent Meunier; Roger Proksch; William Allison Shelton Jr; Evgheni Strelcov; Alexander Tselev

2010-01-01

367

How does quantum confinement influence the electronic structure of transition metal sulfides TmS2  

E-print Network

Bulk MoS2, a prototypical layered transition-metal dichalcogenide, is an indirect band gap semiconductor. Reducing its size to a monolayer, MoS2 undergoes a transition to the direct band semiconductor. We support this experimental observation by first principles calculations and show that quantum confinement in layered d-electron dichalcogenides results in tuning the electronic structure at the nanoscale. We further studied the properties of related TmS2 nanolayers (Tm = W, Nb, Re) and show that the isotopological WS2 exhibits similar electronic properties, while NbS2 and ReS2 remain metallic independent on size.

Kuc, Agnieszka; Heine, Thomas

2011-01-01

368

Investigation of metal-insulator like transition through the ab initio density matrix renormalization group approach  

E-print Network

We have studied the Metal-Insulator like Transition (MIT) in lithium and beryllium ring-shaped clusters through ab initio Density Matrix Renormalization Group (DMRG) method. Performing accurate calculations for different interatomic distances and using Quantum Information Theory (QIT) we investigated the changes occurring in the wavefunction between a metallic-like state and an insulating state built from free atoms. We also discuss entanglement and relevant excitations among the molecular orbitals in the Li and Be rings and show that the transition bond length can be detected using orbital entropy functions. Also, the effect of different orbital basis on the effectiveness of the DMRG procedure is analyzed comparing the convergence behavior.

Fertitta, E; Barcza, G; Legeza,

2014-01-01

369

Pairwise chemical interactions of charged transition-metal impurities in insulators  

NASA Astrophysics Data System (ADS)

We report the pairwise chemical interaction and the direct d-d interactions of substitutional 3d transition-metal impurities in various insulator hosts for various charged conditions by first-principles calculations. Our calculations show that for nearest-neighbor impurity pairs, the direct d-d interactions play an important role in the binding of the impurities and the degree of these interactions increases as the defect charge state is varied from positive to negative. This allows for direct control of the transition-metal impurity clustering and possible secondary phase formation by n- or p-type doping.

Fujita, Takeshi; Raebiger, Hannes

2014-10-01

370

Insulator-to-metal transition in heavily Ti-doped silicon thin film  

NASA Astrophysics Data System (ADS)

The hydrogenated amorphous silicon thin films with heavily Ti doping were deposited by combination of hot-wire chemical vapor deposition and magnetron sputtering. The sheet resistance for as-deposited heavily Ti-doped amorphous silicon thin films exhibits typical semiconductor features. However, the electrical properties of crystallized Ti-doped silicon thin film by pulse laser melting shows the metal-like behavior, which indicates the happening of an insulator-to-metal transition with the crystallization process. The transition implies the formation of an intermediate band originated from the Ti deep levels.

Zhou, Yurong; Liu, Fengzhen; Zhu, Meifang; Song, Xiaohui; Zhang, Ping

2013-06-01

371

Nanoscale structural evolution of electrically driven insulator to metal transition in vanadium dioxide  

SciTech Connect

The structural evolution of tensile strained vanadium dioxide thin films was examined across the electrically driven insulator-to-metal transition by nanoscale hard X-ray diffraction. A metallic filament with rutile (R) structure was found to be the dominant conduction pathway for an electrically driven transition, while the majority of the channel area remained in the monoclinic M1 phase. The filament dimensions were estimated using simultaneous electrical probing and nanoscale X-ray diffraction. Analysis revealed that the width of the conducting channel can be tuned externally using resistive loads in series, enabling the M1/R phase ratio in the phase coexistence regime to be tuned.

Freeman, Eugene, E-mail: exf181@psu.edu; Shukla, Nikhil; Datta, Suman [Department of Electrical Engineering, Pennsylvania State University, University Park, Pennsylvania 16802 (United States)] [Department of Electrical Engineering, Pennsylvania State University, University Park, Pennsylvania 16802 (United States); Stone, Greg; Engel-Herbert, Roman; Gopalan, Venkatraman [Department of Materials Science and Engineering, Pennsylvania State University, University Park, Pennsylvania 16802 (United States)] [Department of Materials Science and Engineering, Pennsylvania State University, University Park, Pennsylvania 16802 (United States); Paik, Hanjong [Department of Materials Science and Engineering, Cornell University, Ithaca, New York 14853 (United States)] [Department of Materials Science and Engineering, Cornell University, Ithaca, New York 14853 (United States); Moyer, Jarrett A. [Department of Physics and Frederick Seitz Materials Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801 (United States)] [Department of Physics and Frederick Seitz Materials Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801 (United States); Cai, Zhonghou; Wen, Haidan [Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439 (United States)] [Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439 (United States); Schlom, Darrell G. [Department of Materials Science and Engineering, Cornell University, Ithaca, New York 14853 (United States) [Department of Materials Science and Engineering, Cornell University, Ithaca, New York 14853 (United States); Kavli Institute at Cornell for Nanoscale Science, Ithaca, New York 14853 (United States)

2013-12-23

372

Transition Metal Oxide Core-Shell Nanowires: Generic Synthesis and Transport Studies  

Microsoft Academic Search

A generic non-equilibrium synthesis technique has been developed to produce novel transition metal oxide nanowires, including YBa2Cu3O6.66, La0.67Ca0.33MnO3, PbZr0.58Ti0.42O3, and Fe3O4. Key to our success is the growth of vertically aligned single-crystalline MgO nanowires, which worked as excellent templates for epitaxial deposition of the desired transition metal oxides and led to high-quality core-shell nanowires. Transport studies on La0.67Ca0.33MnO3 nanowires have

Song Han; Chao Li; Zuqin Liu; Bo Lei; Daihua Zhang; Wu Jin; Xiaolei Liu; Tao Tang; Chongwu Zhou

2004-01-01

373

Quantum molecular dynamics simulations for the nonmetal-to-metal transition in fluid helium.  

PubMed

We have performed quantum molecular dynamics simulations for dense helium to study the nonmetal-to-metal transition at high pressures. We present new results for the equation of state and the Hugoniot curve in the warm dense matter region. The optical conductivity is calculated via the Kubo-Greenwood formula from which the dc conductivity is derived. The nonmetal-to-metal transition is identified at about 1 g/cm(3). We compare with experimental results as well as with other theoretical approaches, especially with predictions of chemical models. PMID:17677615

Kietzmann, Andr; Holst, Bastian; Redmer, Ronald; Desjarlais, Michael P; Mattsson, Thomas R

2007-05-11

374

Quantum Molecular Dynamics Simulations for the Nonmetal-to-Metal Transition in Fluid Helium  

SciTech Connect

We have performed quantum molecular dynamics simulations for dense helium to study the nonmetal-to-metal transition at high pressures. We present new results for the equation of state and the Hugoniot curve in the warm dense matter region. The optical conductivity is calculated via the Kubo-Greenwood formula from which the dc conductivity is derived. The nonmetal-to-metal transition is identified at about 1 g/cm{sup 3}. We compare with experimental results as well as with other theoretical approaches, especially with predictions of chemical models.

Kietzmann, Andre; Holst, Bastian; Redmer, Ronald; Desjarlais, Michael P.; Mattsson, Thomas R. [Universitaet Rostock, Institut fuer Physik, D-18051 Rostock (Germany); Pulsed Power Sciences Center, Sandia National Laboratories, Albuquerque, New Mexico 87185-1186 (United States)

2007-05-11

375

Bacterial Transition Metal P1B-ATPases, Transport Mechanism and Roles in Virulence  

PubMed Central

P1B-type ATPases are polytopic membrane proteins that couple the hydrolysis of ATP to the efflux of cytoplasmic transition metals. This article reviews recent progress in our understanding of the structure and function of these proteins in bacteria. These are members of the P-type superfamily of transport ATPases. Cu+-ATPases are the most frequently observed and best-characterized members of this group of transporters. However, bacterial genomes show diverse arrays of P1B-type ATPases with a range of substrates (Cu+, Zn2+, Co2+). Furthermore, because of the structural similarities among transitions metals, these proteins can also transport non-physiological substrates (Cu2+, Cd2+, Pb2+, Au+, Ag+). P1B-type ATPases have six or eight transmembrane segments (TM) with metal coordinating amino acids in three core TMs flanking the cytoplasmic domain responsible for ATP binding and hydrolysis. In addition, regulatory cytoplasmic metal binding domains are present in most P1B-type ATPases. Central to the transport mechanism is the binding of the uncomplexed metal to these proteins when cytoplasmic substrates are bound to chaperone and chelating molecules. Metal binding to regulatory sites is through a reversible metal exchange among chaperones and cytoplasmic metal binding domains. In contrast, the chaperone-mediated metal delivery to transport sites appears as a largely irreversible event. P1B-ATPases have two overarching physiological functions: to maintain cytoplasmic metal levels and to provide metals for the periplasmic assembly of metalloproteins. Recent studies have shown that both roles are critical for bacterial virulence, since P1B-ATPases appear key to overcome high phagosomal metal levels and are required for the assembly of periplasmic and secreted metalloproteins that are essential for survival in extreme oxidant environments. PMID:21999638

Argello, Jos M.; Gonzlez-Guerrero, Manuel; Raimunda, Daniel

2011-01-01

376

A Transition Metal Complex (Venus Flytrap Cluster) for Radioimmunodetection and Radioimmunotherapy  

Microsoft Academic Search

A novel transition metal complex, Venus flytrap cluster (VFC), is described for the preparation of radiolabeled antibodies. VFC contained 57Co, which was held tightly between the faces of two covalently bridged carborane ligands by cluster bonding of the metal with appropriate ligand orbitals. Anti-carcinoembryonic antigen monoclonal antibody T84.66 was conjugated to 57Co-VFC with full retention of immunological activity. Biodistribution studies

Raymond J. Paxton; Barbara G. Beatty; M. Frederick Hawthorne; Aravamuthan Varadarajan; Lawrence E. Williams; Frederick L. Curtis; Carolyn B. Knobler; J. David Beatty; John E. Shiveley

1991-01-01

377

A transition metal complex (Venus flytrap cluster) for radioimmunodetection and radioimmunotherapy  

Microsoft Academic Search

A novel transition metal complex, Venus flytrap cluster (VFC), is described for the preparation of radiolabeled antibodies. VFC contained ⁵⁷Co, which was held tightly between the faces of two covalently bridged carborane ligands by cluster bonding of the metal with appropriate ligand orbitals. Anti-carcinoembryonic antigen monoclonal antibody T84,66 was conjugated to ⁵⁷Co-VFC with full retention of immunological activity. Biodistribution studies

R. J. Paxton; F. L. Curtis; J. E. Shively; B. G. Beatty; L. E. Williams; J. D. Beatty; M. F. Hawthorne; A. Varadarajan; C. B. Knobler

1991-01-01

378

Satellites in X-Ray Photoelectron Spectra of Transition-Metal Compounds  

Microsoft Academic Search

Appearance of satellite lines in the X-ray photoelectron emission from the 2p-shell of the metal ion transition-metal compounds are ascribed to the increase of covalency due to the creation of an inner-core hole. For this argument a simple two-configuration model is used, which reveals a shortcoming once ab initio calculations of the line positions and intensities are attempted. The molecular-orbital

Susumu Asada; Satoru Sugano

1976-01-01

379

Surface-State Electrical Conductivity at a Metal-Insulator Transition On Silicon  

Microsoft Academic Search

A quasi-one-dimensional metallic Si(111)-(41)-In surface was investigated by a newly developed temperature-variable microscopic four-point probe method combined with insitu electron diffraction in ultrahigh vacuum. We have succeeded, for the first time, in detecting directly a surface metal-insulator transition around 130K as a dramatic change of electrical conductivity through the surface states. An energy gap of 300 meV at the low-temperature

Takehiro Tanikawa; Iwao Matsuda; Taizo Kanagawa; Shuji Hasegawa

2004-01-01

380

Thermochemistry of binary alloys of lanthanum with 3 d -transition metals  

Microsoft Academic Search

The enthalpy of mixing for liquid binary alloys of lanthanum with 3d-transition metals (Sc, Ti, V, Cr, and Fe) is determined\\u000a by a calorimetric method within the field of compositions rich in lanthanum. Data for the partial enthalpy of mixing in the\\u000a La-3d-metal system with infinite dilution demonstrates a complex relationship of a change in it in the series of

V. V. Berezutskii; N. I. Usenko; M. I. Ivanov

2006-01-01

381

Structure and Stability of Substitutional Metallofullerenes of the First?Row Transition Metals  

Microsoft Academic Search

A DFT investigation of substitutional metallofullerenes MC59 (M=ScNi) shows that they are drop?shaped, with the deviation from spherical structure depending on the size of the metal atom. The metal atomic radius, however, seems to be unimportant for the stability of the metallofullerenes. In general, the stability increases toward the right?hand side of the transition series, commensurate with the higher electronegativities

Manuel Sparta; Vidar. R. Jensen; Knut J. Brve

2006-01-01

382

Investigation of surface properties of liquid transition metals: Surface tension and surface entropy  

Microsoft Academic Search

In the present study, surface properties namely surface tension and surface entropy of liquid transition metals have been reported. The surface entropy of liquid Fe, Co and Ni metals has been investigated using the expression derived by Gosh et al. [R.C. Gosh, A.Z. Ziauddin Ahmed, G.M. Bhuiyan, Eur. Phys. J. B 56 (2007) 177]. To describe interionic interaction the pseudopotential

S. D. Korkmaz

2010-01-01

383

Early Identification of Special Educational Needs and the Definition of "At Risk": The Early Years Transition and Special Educational Needs (EYTSEN) Project  

ERIC Educational Resources Information Center

Education in the early years is a key element in the Government's current strategy. Recently, the Department for Education and Skills (DfES) funded a major study of Effective Provision of Pre-School Education (EPPE). The Early Years Transition and Special Educational Needs (EYTSEN) Project developed from the EPPE research and was also funded by

Taggart, Brenda; Sammons, Pam; Smees, Rebecca; Sylva, Kathy; Melhuish, Edward; Siraj-Blatchford, Iram; Elliot, Karen; Lunt, Ingrid

2006-01-01

384

Alkali cation specific adsorption onto fcc(111) transition metal electrodes.  

PubMed

The presence of alkali cations in electrolyte solutions is known to impact the rate of electrocatalytic reactions, though the mechanism of such impact is not conclusively determined. We use density functional theory (DFT) to examine the specific adsorption of alkali cations to fcc(111) electrode surfaces, as specific adsorption may block catalyst sites or otherwise impact surface catalytic chemistry. Solvation of the cation-metal surface structure was investigated using explicit water models. Computed equilibrium potentials for alkali cation adsorption suggest that alkali and alkaline earth cations will specifically adsorb onto Pt(111) and Pd(111) surfaces in the potential range of hydrogen oxidation and hydrogen evolution catalysis in alkaline solutions. PMID:24722828

Mills, J N; McCrum, I T; Janik, M J

2014-07-21

385

Transition metal catalysis in the generation of petroleum and natural gas. Final report, September 1, 1992--October 31, 1995  

SciTech Connect

This project originated on the premise that natural gas could be formed catalytically in the earth rather than thermally as commonly believed. The intention was to test this hypothetical view and to explore generally the role of sedimentary metals in the generation of light hydrocarbons (C1 - C9). We showed the metalliferous source rocks are indeed catalytic in the generation of natural gas. Various metal compounds in the pure state show the same levels of catalytic activity as sedimentary rocks and the products are identical. Nickel is particularly active among the early transition metals and is projected to remain catalytically robust at all stages of catagenesis. Nickel oxide promotes the formation of n-alkanes in addition to natural gas (NG), demonstrating the full scope of the hypothetical catalytic process. The composition of catalytic gas duplicates the entire range of natural gas, from so-called wet gas to dry gas (60 to 95+ wt % methane), while gas generated thermally is consistently depleted in methane (10 to 60 wt % methane). These results support the view that metal catalysis is a major pathway through which natural gas is formed in the earth.

Mango, F.D.

1997-01-21

386

Reduction of an electronically unsaturated transition-metal. eta. sup 2 -acyl complex. Arene formation from deoxygenative acyl coupling with a cyclopentadienyl ligand  

SciTech Connect

{eta}{sup 2}-Acyl ligands are common products from carbonylation of early-transition-metal, lanthanide, and actinide alkyls and have been studied primarily from a synthetic or structural rather than a reactivity perspective. Our interests in mid-valent, mono({eta}-C{sub 5}R{sub 5}) early-metal chemistry and in the comparative structure/reactivity of organometallic functional groups in complexes with different metal valencies led us to examine whether an electronically unsaturated {eta}{sup 2}-acyl complex would deinsert, rearrange to a ketene hydride, have altered {eta}{sup 2}-interaction and reactivity, or undergo structural rearrangement upon reduction. We have discovered an example of the latter, specifically that {eta}{sup 2}-acyl reduction can lead to deoxygenative coupling with a cyclopentadienyl C{sub ring}-C{sub ring} bond.

Meyer, T.Y.; Messerle, L. (Univ. of Iowa, Iowa City (USA))

1990-05-23

387

Sharp semiconductor-to-metal transition of VO{sub 2} thin films on glass substrates  

SciTech Connect

Outstanding phase transition properties of vanadium dioxide (VO{sub 2}) thin films on amorphous glass were achieved and compared with the ones grown on c-cut sapphire and Si (111) substrates, all by pulsed laser deposition. The films on glass substrate exhibit a sharp semiconductor-to-metal transition (?4.3?C) at a near bulk transition temperature of ?68.4?C with an electrical resistance change as high as 3.2??10{sup 3} times. The excellent phase transition properties of the films on glass substrate are correlated with the large grain size and low defects density achieved. The phase transition properties of VO{sub 2} films on c-cut sapphire and Si (111) substrates were found to be limited by the high defect density.

Jian, Jie; Chen, Aiping [Department of Electrical and Computer Engineering, Texas A and M University, College Station, Texas 77843-3128 (United States); Zhang, Wenrui [Material Science and Engineering Program, Texas A and M University, College Station, Texas 77843-3128 (United States); Wang, Haiyan, E-mail: wangh@ece.tamu.edu [Department of Electrical and Computer Engineering, Texas A and M University, College Station, Texas 77843-3128 (United States); Material Science and Engineering Program, Texas A and M University, College Station, Texas 77843-3128 (United States)

2013-12-28

388

Binding and activation of N2O at transition-metal centers: recent mechanistic insights.  

PubMed

No laughing matter, nitrous oxide's role in stratospheric ozone depletion and as a greenhouse gas has stimulated great interest in developing and understanding its decomposition, particularly through the use of transition-metal promoters. Recent advances in our understanding of the reaction pathways for N(2)O reduction by metal ions in the gas phase and in heterogeneous, homogeneous, and biological catalytic systems have provided provocative ideas about the structure and properties of metal N(2)O adducts and derived intermediates. These ideas are likely to inform efforts to design more effective catalysts for N(2)O remediation. PMID:20058284

Tolman, William B

2010-02-01

389

Phase Diagram of Coulomb Interactions across the Metal-Insulator Transition in Si:B  

NASA Astrophysics Data System (ADS)

Measurements of the single-particle density of states (DOS) near T=0 K in Si:B are used to construct an energy-density phase diagram of Coulomb interactions across the critical density nc of the metal-insulator transition. Insulators and metals are found to be distinguishable only below a phase boundary ?*(|n/nc-1|) determined by the Coulomb energy. Above ?* is a mixed state where metals and insulators equidistant from nc cannot be distinguished from their DOS structure. The data imply a diverging screening radius at nc, which may signal an interaction-driven thermodynamic state change.

Lee, Mark

2004-12-01

390

Reentrant insulator-metal transition in the half-filled Hubbard model  

SciTech Connect

Using the {ital d}={infinity} or local-approximation approach to the half-filled Hubbard model on a compressible lattice, we present a detailed study of the transport and structural properties near the paramagnetic metal-insulator transition. The results describe qualitatively most of the observed data in V{sub 2}O{sub 3}, including the metal-insulator-metal crossover [Kuwamoto {ital et} {ital al}., Phys. Rev. B {bold 22}, 2626 (1980)]. In addition, we discuss an interesting and intrinsic reentrance feature in the resistivity of the half-filled Hubbard model at high temperatures.

Majumdar, P.; Krishnamurthy, H.R. [Department of Physics, Indian Institute of Science, Bangalore 560 012 (India)] [Department of Physics, Indian Institute of Science, Bangalore 560 012 (India)

1995-08-15

391

Elucidation of Proton-Assisted Fluxionality in Transition-Metal Oxide Clusters  

NASA Astrophysics Data System (ADS)

The phenomenon of fluxionality in the reactions of transition-metal oxide clusters provides many opportunities in various industrial and catalytic processes. We present an electronic structure investigation of the fluxionality pathways when anionic W3O6- and Mo3O6- clusters react with three small molecules - water, ammonia and hydrogen sulfide. The presentation features a detailed understanding of (a) how the fluxionality pathway occurs and (b) the various factors that affect the fluxionality pathway - such as the metal, different spin-states and the nature of the non-metal in the reacting small molecule.

Ramabhadran, Raghunath O.; Mayhall, Nicholas J.; Becher, Edwin L. Becher, Iii; Chowdhury, Arefin; Raghavachari(s), Krishnan

2012-06-01

392

Wetting transitions of Ne on alkali metal surfaces  

NASA Astrophysics Data System (ADS)

In relation to the Ne-Ne interatomic potential well depth, the adsorption potential of Ne on Cs is weaker than that of any other simple gas on any other surface. Hence the wetting temperature is expected to be higher (relative to the critical temperature) than that for any other known adsorption system. This expectation, based on a simple energy/entropy balance argument(E. Cheng, M. W. Cole, W. F. Saam and J. Treiner, Phys. Rev. B48,18214 (1993)) has been borne out in recent experiments of Hess et al(G. B. Hess, M. J. Sabatini and M. H. W. Chan,submitted to Phys. Rev.). We report here the results of grand canonical Monte Carlo simulations which find the simple argument to be qualitatively accurate. Our results imply a prewetting transition for Ne on Li and complete nonwetting of Ne on Cs. The case of a Rb surface is under investigation.

Bojan, M. J.; Cole, M. W.; Steele, W. A.

1997-03-01

393

Recycling of rare earth metals from rare earth-transition metal alloy scrap by liquid metal extraction  

Microsoft Academic Search

A method is described for treating rare earth metal-bearing scrap, waste or other material (e.g. Nd--Fe--B or Dy--Tb--Fe scrap) to recover the rare earth metal comprising melting the rare earth metal-bearing material, melting a Group IIA metal extractant, such as Mg, Ca, or Ba, in which the rare earth is soluble in the molten state, and contacting the melted material

T. W. Ellis; F. A. Schmidt

1995-01-01

394

Recycling of rare earth metals from rare earth-transition metal alloy scrap by liquid metal extraction  

Microsoft Academic Search

Method of treating rare earth metal-bearing scrap, waste or other material (e.g. Nd--Fe--B or Dy--Tb--Fe scrap) to recover the rare earth metal comprising melting the rare earth metal-bearing material, melting a Group IIA metal extractant, such as Mg, Ca, or Ba, in which the rare earth is soluble in the molten state, and contacting the melted material and melted extractant

Timothy W. Ellis; Frederick A. Schmidt

1995-01-01

395

18-Electron rule inspired Zintl-like ions composed of all transition metals.  

PubMed

Zintl phase compounds constitute a unique class of compounds composed of metal cations and covalently bonded multiply charged cluster anions. Potential applications of these materials in solution chemistry and thermoelectric materials have given rise to renewed interest in the search for new Zintl ions. Up to now these ions have been mostly composed of group 13, 14, and 15 post-transition metal elements and no Zintl ions composed of all transition metal elements are known. Using gradient corrected density functional theory we show that the 18-electron rule can be applied to design a new class of Zintl-like ions composed of all transition metal atoms. We demonstrate this possibility by using Ti@Au12(2-) and Ni@Au6(2-) di-anions as examples of Zintl-like ions. Predictive capability of our approach is demonstrated by showing that FeH6(4-) in an already synthesized complex metal hydride, Mg2FeH6, is a Zintl-like ion, satisfying the 18-electron rule. We also show that novel Zintl phase compounds can be formed by using all transition metal Zintl-like ions as building blocks. For example, a two-dimensional periodic structure of Na2[Ti@Au12] is semiconducting and nonmagnetic while a one-dimensional periodic structure of Mg[Ti@Au12] is metallic and ferromagnetic. Our results open the door to the design and synthesis of a new class of Zintl-like ions and compounds with potential for applications. PMID:25139391

Zhou, Jian; Giri, Santanab; Jena, Purusottam

2014-10-01

396

Electrical permittivity driven metal-insulator transition in heterostructures of nonpolar Mott and band insulators  

NASA Astrophysics Data System (ADS)

Metallic interfaces between insulating perovskites are often observed in heterostructures combining polar and nonpolar materials. In these systems, the polar discontinuity across the interface may drive an electronic reconstruction inducing free carriers at the interface. Here, we theoretically show that a metallic interface between a Mott and a band insulator can also form in the absence of a polar discontinuity. The condition for the appearance of such a metallic state is consistent with the classical Mott criterion: the metallic state is stable if the screening length falls below the effective Bohr radius of a particle-hole pair. In this case, the metallic state bears a remarkable similarity to the one found in polar/nonpolar heterostructures. On the other hand, if the screening length approaches the size of the effective Bohr radius, particles and holes are bound to each other resulting in an overall insulating phase. We analyze this metal-insulator transition, which is tunable by the dielectric constant, in the framework of the slave-boson mean-field theory for a lattice model with both on-site and long-range Coulomb interactions. We discuss ground-state properties and transport coefficients, which we derive in the relaxation-time approximation. Interestingly, we find that the metal-insulator transition is accompanied by a strong enhancement of the Seebeck coefficient in the band-insulator region in the vicinity of the interface. The implications of our theoretical findings for various experimental systems such as nonpolar (110) interfaces are also discussed.

Omori, Yukiko; Regg, Andreas; Sigrist, Manfred

2014-10-01

397

New laser dye systems based on transition metal complexes  

NASA Astrophysics Data System (ADS)

Excited state properties of luminescent ruthenium (II) complexes and their interactions with laser dyes, other metal complexes, and oxygen have been studied in both homogeneous and surfactant containing solutions and in solid polymer matrices. Low cost experimental tools have been developed to facilitate these studies. These include a low cost temperature controller, a simple deoxygenation cell for surfactant solutions, and a low frequency computerized lockin amplifier. Also, new quantum counters for light intensity measurements have been developed. Energy transfer from ruthenium (II) complexes to a variety of rhodamine and oxazine laser dyes has been demonstrated in both homogeneous solutions and in surfactant-assisted ones. Singlet energy transfer efficiencies from the charge transfer (CT) sensitizing state of the Ru(II) complex to the laser dyes in homogeneous solutions are unity, and in surfactant-assisted systems efficiencies are 45-75% at concentrations of 10-5M.

Demas, J. N.

1982-05-01

398

Role of transition metal exporters in virulence: the example of Neisseria meningitidis  

PubMed Central

Transition metals such as iron, manganese, and zinc are essential micronutrients for bacteria. However, at high concentration, they can generate non-functional proteins or toxic compounds. Metal metabolism is therefore regulated to prevent shortage or overload, both of which can impair cell survival. In addition, equilibrium among these metals has to be tightly controlled to avoid molecular replacement in the active site of enzymes. Bacteria must actively maintain intracellular metal concentrations to meet physiological needs within the context of the local environment. When intracellular buffering capacity is reached, they rely primarily on membrane-localized exporters to maintain metal homeostasis. Recently, several groups have characterized new export systems and emphasized their importance in the virulence of several pathogens. This article discusses the role of export systems as general virulence determinants. Furthermore, it highlights the contribution of these exporters in pathogens emergence with emphasis on the human nasopharyngeal colonizer Neisseria meningitidis. PMID:24392357

Guilhen, Cyril; Taha, Muhamed-Kheir; Veyrier, Frdric J.

2013-01-01

399

Adhesion and friction of transition metals in contact with nonmetallic hard materials  

NASA Technical Reports Server (NTRS)

Sliding friction experiments were conducted with the metals yttrium, titanium, tantalum, zirconium, vanadium, neodymium, iron, cobalt, nickel, tungsten, platinum, rhenium, ruthenium, and rhodium in sliding contact with single crystal diamond, silicon carbide, pyrolytic boron nitride, and ferrite. Auger electron spectroscopy analysis was conducted with the metals and nonmetals to determine the surface chemistry and the degree of surface cleanliness. The results of the investigation indicate the adhesion and friction of the transition metals in contact with diamond, silicon carbide, boron nitride, and ferrite are related to the relative chemical activity of the metals. The more chemically active the metal, the higher the coefficient of friction and the greater amount of transfer to the nonmetals.

Miyoshi, K.; Buckley, D. H.

1981-01-01

400

Intrinsic and extrinsic properties of rare earth-transition metal compounds and permanent magnets  

Microsoft Academic Search

The revolutionary progress made in the field of permanent magnets over the past 25 years has been almost entirely due to a concentrated research effort in the field of rare earth-transition metal compounds. This paper discusses the unique intrinsic properties of such compounds as precursors for permanent magnets, and outlines possible coercivity mechanisms and their relationship with microstructure in the

J. P. Gavigan; D. Givord

1990-01-01

401

The hard-magnetic properties of rare earth-transition metal alloys  

Microsoft Academic Search

The intermetallic phases formed between the rare earth metals (R) and the elements of the 3-d transition series are a large group of new substances with interesting magnetic properties. They have been studied intensely in the last decade. Their properties are reviewed with a view toward their usefulness for permanent magnets. Some aspects of the recently developed magnets based on

KARL J. STRNAT

1972-01-01

402

Oxygen vacancies in transition metal and rare earth oxides: Current state of understanding and remaining challenges  

Microsoft Academic Search

Defects at transition metal (TM) and rare earth (RE) oxide surfaces, neutral oxygen vacancies in particular, play a major role in a variety of technological applications. This is the motivation of numerous studies of partially reduced oxide surfaces. We review, discuss, and compare theoretical data for structural and electronic properties and energetic quantities related to the formation of oxygen defects

M. Vernica Ganduglia-Pirovano; Alexander Hofmann; Joachim Sauer

2007-01-01

403

Transition metal ion capture using functional mesoporous carbon made with 1,10-phenanthroline?  

PubMed Central

Functional mesoporous carbon has been built using 1,10-phenanthroline as the fundamental building block, resulting in a nanoporous, high surface area sorbent capable of selectively binding transition metal ions. This material had a specific surface area of 870 m2/g, an average pore size of about 30 , and contained as much as 8.2 wt% N. Under acidic conditions, where the 1,10-phenanthroline ligand is protonated, this material was found to be an effective anion exchange material for transition metal anions like PdCl42- and H2VO41-. 1,10-Phenanthroline functionalized mesoporous carbon (Phen-FMC) was found to have a high affinity for Cu(II), even down to a pH of 1. At pHs above 5, Phen-FMC was found to bind a variety of transition metal cations (e.g. Co(II), Ni(II), Zn(II), etc.) from filtered ground water, river water and seawater. Phen-FMC displayed rapid sorption kinetics with Co(II) in filtered river water, reaching equilibrium in less than an hour, and easily lowering the [Co(II)] to sub-ppb levels. Phen-FMC was found to be more effective for transition metal ion capture than ion-exchange resin or activated carbon. PMID:23762013

Chouyyok, Wilaiwan; Yantasee, Wassana; Shin, Yongsoon; Grudzien, Rafal M.; Fryxell, Glen E.

2012-01-01

404

Filtrates & Residues: Hemoglobinometry--A Biochemistry Experiment that Utilizes the Principles of Transition Metal Chemistry.  

ERIC Educational Resources Information Center

Describes a chemistry experiment dealing with hemoglobinometry that can apply to transition metal chemistry, colorimetry, and biochemistry. Provides a detailed description of the experimental procedure, including discussions of the preparation of the cyanide reagent, colorimetric measurements, and waste disposal and treatment. (TW)

Giuliano, Vincenzo; Rieck, John Paul

1987-01-01

405

First-principles study on transition metal-doped anatase TiO2  

NASA Astrophysics Data System (ADS)

The electronic structures, formation energies, and band edge positions of anatase TiO2 doped with transition metals have been analyzed by ab initio band calculations based on the density functional theory with the planewave ultrasoft pseudopotential method. The model structures of transition metal-doped TiO2 were constructed by using the 24-atom 2 1 1 supercell of anatase TiO2 with one Ti atom replaced by a transition metal atom. The results indicate that most transition metal doping can narrow the band gap of TiO2, lead to the improvement in the photoreactivity of TiO2, and simultaneously maintain strong redox potential. Under O-rich growth condition, the preparation of Co-, Cr-, and Ni-doped TiO2 becomes relatively easy in the experiment due to their negative impurity formation energies, which suggests that these doping systems are easy to obtain and with good stability. The theoretical calculations could provide meaningful guides to develop more active photocatalysts with visible light response.

Wang, Yaqin; Zhang, Ruirui; Li, Jianbao; Li, Liangliang; Lin, Shiwei

2014-01-01

406

Microwave response near zero magnetic field in transition-metal-doped silicate glasses  

E-print Network

Microwave response near zero magnetic field in transition-metal-doped silicate glasses R. R- and iron-doped Na2O­CaO­MgO­SiO2 glasses with phase opposite to the normal Mn 2 and Fe 3 paramagnetic signals. The response can be described as magneto-induced microwave conductivity in the dielectric glass

Glebov, Leon

407

Dependence of the insulator-metal transition in EuO on magnetic order  

NASA Astrophysics Data System (ADS)

The Hall coefficient in an EuO sample which exhibited an isulator-metal transition was measured at T ? 4 Tc in fields up to 150 kOe. The results indicate that the activation energy does not vary linearly with magnetization, contrary to the conclusion of Penney et al.

Shapira, Y.; Foner, S.; Reed, T. B.; Birecki, H.; Stanley, H. E.

1972-10-01

408

A numerical calculation of the orbital magnetic susceptibility for BCC 3d series transition metals  

Microsoft Academic Search

The generalised orbital magnetic susceptibility chi (q) given by Hebborn and March (1976) is numerically calculated at small wave vectors q in order to estimate the uniform orbital magnetic susceptibility chi orb given by Hebborn and Sondheimer (1960) from the extrapolation of chi (q) to q=0. For BCC 3d series transition metals the dependence on the electron per atom ratio

M. Yasui; M. Shimizu

1979-01-01

409

The Effect of the Electron Correlation on (1\\/T)orb in Ferromagnetic Transition Metals  

Microsoft Academic Search

By making use of the many band Hamiltonian, the effect of the electron correlation on (1\\/T1)orb for ferromagnetic metals is investigated by solving the Green function within RPA. It is found that only the contribution from the interband transition is affected by the electron correlation. For the case of the saturated ferromagnets, it is found that the electron correlation enhances

Syozo Maeda; Eijiro Haga

1974-01-01

410

A possibility to obtain room temperature ferromagnetism by transition metal doping of ZnO nanoparticles  

Microsoft Academic Search

Based on the s-d model and using a Green's function technique, we have studied the influence of transition metal doping effects on different properties such as magnetization M, Curie temperature TC, and coercive field Hc of ZnO nanoparticles. We have shown that the experimentally obtained room temperature ferromagnetism is an intrinsic property and can be due to doping effects in

J. M. Wesselinowa; A. T. Apostolov

2010-01-01

411

The First Precise Molecular Structure of a Monomeric Transition Metal Cyanide, Copper(I) Cyanide  

E-print Network

The First Precise Molecular Structure of a Monomeric Transition Metal Cyanide, Copper(I) Cyanide, Arizona 85721 Received September 27, 2001 Abstract: Copper(I) cyanide is an important reagent in organic, organometallic, and supramolecular chemistry because of both the copper center and the versatile cyanide ligand

Ziurys, Lucy M.

412

THE EXTRACTION OF CITRATE AND TARTRATE COMPLEXES OF THE TRANSITION METALS  

Microsoft Academic Search

The citrate and tartrate complexes of the transition metals palladium, ; vanadium, uranium, iron, bismuth, gold, and cerium can be separated as ; substituted ammonium salts by liquid-liquid extraction from aqueous solutions ; with organic solvents. The citrate complex of rhodium and the tartrate complex ; of zirconium can be extracted in a similar manner. The organic solvent and the

Ziegler

1959-01-01

413

A Spectromicroscopic Study of 3d Transition Metal Interactions with Humic Acid; A bright  

E-print Network

A Spectromicroscopic Study of 3d Transition Metal Interactions with Humic Acid; A bright future for Humic Acid Research? (S02- nachtegaal174813-Oral) Abstract: It is important to understand groups of humic acid. Soft X-ray microscopy was applied to map the distribution of carbon containing

Sparks, Donald L.

414

Chemistry of Sulfur Oxides on Transition Metals. II. Thermodynamics of Sulfur Oxides on Platinum(111)  

E-print Network

Chemistry of Sulfur Oxides on Transition Metals. II. Thermodynamics of Sulfur Oxides on Platinum at the highest coverages and sulfur oxidation states. Calculated vibrational spectra are used to assign observed the preferred SOx species on Pt(111), consistent with observation. I. Introduction The chemistry of sulfur

Lin, Xi

415

Aging Effects across the Metal-Insulator Transition in Two Dimensions J. Jaroszynski and Dragana Popovic*  

E-print Network

Aging Effects across the Metal-Insulator Transition in Two Dimensions J. Jaroszyn´ski and Dragana, USA (Received 17 August 2007; published 19 November 2007) Aging effects in the relaxations) while full aging is observed in the insulating regime, there are significant departures from full aging

Popovic, Dragana

416

Super hard cubic phases of period VI transition metal nitrides: First principles investigation  

E-print Network

Super hard cubic phases of period VI transition metal nitrides: First principles investigation S July 2008 Keywords: Coatings Elastic properties Hardness Nitrides We report a systematic studyN in rocksalt phase has a bulk modulus of 380 GPa making them candidates for super hardness. Based on the bulk

Khare, Sanjay V.

417

X-ray Absorption Spectroscopy of Transition Metal-Magnesium Hydride Thin Films  

E-print Network

of the chemical and physical changes that accompany the optical transitions is essential for optimizing changes in both reflectance and transmittance on exposure to hydrogen gas. Changes in electronic structure reflect both reversible and irreversible changes in the metal environments. A significant shift

418

Kinetic, chemical and mechanical factors affecting mechanical alloying of Nibcc transition metal mixtures  

Microsoft Academic Search

The influence of enthalpy of mixing and elemental mechanical characteristics on the kinetics of mechanical alloying (MA) of 80 at.% Ni-20 at.% bcc transition metals (Fe, Cr, W, Nb, and Ta) has been studied. The features and structures of milled powders were characterized by X-ray diffraction, optical microscopy, and particle size analysis. Powder caking of the grinding media in

A. N Streletskii; T. H Courtney

2000-01-01

419

H-Solid State NMR Studies of Tunneling Phenomena and Isotope Effects in Transition Metal Dihydrides  

Microsoft Academic Search

In many transition metal dihydrides and dihydrogen complexes the hydrogens are relatively weakly bound and exhibit a fairly high mobility, in particular with respect to their mutual exchange. Part of this high mobility is due to the exchange symmetry of the two hydrogens, which causes an energy splitting into even and odd spatial energy eigenfunctions, resulting in the typical coherent

Gerd Buntkowsky; Hans-Heinrich Limbach

2006-01-01

420

The Transition State for Metal-Catalyzed Dehalogenation: C-I Bond Cleavage on Ag(111)  

E-print Network

is the dissociation of carbon-iodine bonds which is used to create stable alkyl groups on many metal surfaces.3 picture of the nature of the transition state for carbon-iodine and carbon-chlorine bond cleavage on both- fluorocarbons (CFCs) into hydrofluorocarbons (HFCs).1,2 The most commonly studied catalyst

Gellman, Andrew J.

421

A systems view of haloarchaeal strategies to withstand stress from transition metals  

PubMed Central

Given that transition metals are essential cofactors in central biological processes, misallocation of the wrong metal ion to a metalloprotein can have resounding and often detrimental effects on diverse aspects of cellular physiology. Therefore, in an attempt to characterize unique and shared responses to chemically similar metals, we have reconstructed physiological behaviors of Halobacterium NRC-1, an archaeal halophile, in sublethal levels of Mn(II), Fe(II), Co(II), Ni(II), Cu(II), and Zn(II). Over 20% of all genes responded transiently within minutes of exposure to Fe(II), perhaps reflecting immediate large-scale physiological adjustments to maintain homeostasis. At steady state, each transition metal induced growth arrest, attempts to minimize oxidative stress, toxic ion scavenging, increased protein turnover and DNA repair, and modulation of active ion transport. While several of these constitute generalized stress responses, up-regulation of active efflux of Co(II), Ni(II), Cu(II), and Zn(II), down-regulation of Mn(II) uptake and up-regulation of Fe(II) chelation, confer resistance to the respective metals. We have synthesized all of these discoveries into a unified systems-level model to provide an integrated perspective of responses to six transition metals with emphasis on experimentally verified regulatory mechanisms. Finally, through comparisons across global transcriptional responses to different metals, we provide insights into putative in vivo metal selectivity of metalloregulatory proteins and demonstrate that a systems approach can help rapidly unravel novel metabolic potential and regulatory programs of poorly studied organisms. PMID:16751342

Kaur, Amardeep; Pan, Min; Meislin, Megan; Facciotti, Marc T.; El-Gewely, Raafat; Baliga, Nitin S.

2006-01-01

422

Identifying the isolated transition metal ions\\/oxides in molecular sieves and on oxide supports by UV resonance Raman spectroscopy  

Microsoft Academic Search

Isolated transition metal ions\\/oxides in molecular sieves and on surfaces are a class of active sites for selective oxidation of hydrocarbons. Identifying the active sites and their coordination structure is vital to understanding their essential role played in catalysis and designing and synthesizing more active and selective catalysts. The isolated transition metal ions in the framework of molecular sieves (e.g.,

2003-01-01

423

Insulator to correlated metal transition in V_1-xMo_xO_2  

SciTech Connect

The change from metallic to insulating states is one of the most dramatic transitions that solids undergo on cooling or chemical doping. Many materials display this transition, but only a handful have the right combination of crystal structure and physical properties to serve as model systems. VO{sub 2} is one of those materials. Using Mo as a chemical dopant in VO{sub 2}, we find unanticipated phenomenology for both the electronic and structural characteristics of the resulting insulator to metal transition. The results support a complex, previously proposed scenario involving the coexistence of both electron repulsion and electron pairing for yielding an insulator in VO{sub 2}, but not simply; many issues are raised about local versus itinerant behavior and structure-property correlations in this most iconic ofdoped correlated electron systems.

Klimczuk, Tomasz [Los Alamos National Laboratory; Ronning, Filip [Los Alamos National Laboratory; Holman, Katherine [PRINCETON UNIV; Mcqueen, Tyrel M [PRINCETON UNIV; Williams, Anthony J [PRINDCETON UNIV; Stephens, P W [BNL; Zandbergen, Henny W [DELFT INSTIT OF TECH; Xu, Q [DELFT INSTIT OF TECH; Cava, Robert J [PRINCETON UNIV

2009-01-01

424

Postfabrication Annealing Effects on Insulator-Metal Transitions in VO2 Thin-Film Devices.  

PubMed

In order to investigate the metal-insulator transition characteristics of VO2 devices annealed in reducing atmosphere after device fabrication at various temperature, electrical, chemical, and thermal characteristics are measured and analyzed. It is found that the sheet resistance and the insulator-metal transition point, induced by both voltage and thermal, decrease when the devices are annealed from 200 to 500 C. The V 2p3/2 peak variation in X-ray photoelectron spectroscopy (XPS) characterization verifies the reduction of thin-films. A decrease of the transition temperature from voltage hysteresis measurements further endorse the reducing effects of the annealing on VO2 thin-film. PMID:25343172

Rathi, Servin; Lee, In-Yeal; Park, Jin-Hyung; Kim, Bong-Jun; Kim, Hyun-Tak; Kim, Gil-Ho

2014-11-26

425

Transition-metal-doped chalcogenide glasses for broadband near-infrared sources  

NASA Astrophysics Data System (ADS)

In this paper we report the spectroscopic data for samples of 0.031% iron, 0.017% nickel, 0.01% chromium and 0.017% cobalt (molar) doped gallium lanthanum sulphide (GLS) glass. Photoluminescence (PL) with a full width half maximum (FWHM) of around 500 nm and peaking between 1120 nm and 1460 nm is observed when excited using wavelengths of 850 nm and 1064 nm. The emission lifetime for nickel-doped GLS at 300 K was measured to be 40 ?s. Photoluminescence excitation (PLE) peaks for chromium-doped GLS at 700 nm and 1020 nm have been observed. By comparisons of our spectroscopic data to that of transition metals doped into other hosts we determine the oxidation states of the transition metal ions and propose transitions for the observed spectroscopic peaks.

Hughes, Mark A.; Aronson, Jonathan E.; Brocklesby, William S.; Shepherd, David P.; Hewak, Daniel W.; Curry, Richard J.

2004-12-01

426

A gastropod toxin selectively slows early transitions in the Shaker K channel's activation pathway.  

PubMed

A toxin from a marine gastropod's defensive mucus, a disulfide-linked dimer of 6-bromo-2-mercaptotryptamine (BrMT), was found to inhibit voltage-gated potassium channels by a novel mechanism. Voltage-clamp experiments with Shaker K channels reveal that externally applied BrMT slows channel opening but not closing. BrMT slows K channel activation in a graded fashion: channels activate progressively slower as the concentration of BrMT is increased. Analysis of single-channel activity indicates that once a channel opens, the unitary conductance and bursting behavior are essentially normal in BrMT. Paralleling its effects against channel opening, BrMT greatly slows the kinetics of ON, but not OFF, gating currents. BrMT was found to slow early activation transitions but not the final opening transition of the Shaker ILT mutant, and can be used to pharmacologically distinguish early from late gating steps. This novel toxin thus inhibits activation of Shaker K channels by specifically slowing early movement of their voltage sensors, thereby hindering channel opening. A model of BrMT action is developed that suggests BrMT rapidly binds to and stabilizes resting channel conformations. PMID:15148327

Sack, Jon T; Aldrich, Richard W; Gilly, William F

2004-06-01

427

Tuning the phase transition in transition-metal-based magnetocaloric compounds  

NASA Astrophysics Data System (ADS)

Neutron-diffraction experiments on the (Mn,Fe)2(P,Si)-type compounds have shown a site preference of Si atoms in the hexagonal structure. The degree of ordering of Si depends on the Si/P ratio, while it is independent of the Mn/Fe ratio. The ferromagnetic-paramagnetic magnetoelastic transition is closely related to the size of the magnetic moment on the 3f site. A preferred occupation of Si atoms on the 2c site stabilizes and decreases the magnetic moment on the 3f and 3g site, respectively, which is supported by our first-principles density functional theory calculations. This effect, together with the contribution from the Si substitution-induced changes in the interatomic distances, leads to a phase transition that is tunable in temperature and degree of first order in Mn1.25Fe0.70P1-xSix compounds. These results provide us with further insight into the relationship between the magnetoelastic phase transition and the local atomic coordination.

Miao, X. F.; Caron, L.; Roy, P.; Dung, N. H.; Zhang, L.; Kockelmann, W. A.; de Groot, R. A.; van Dijk, N. H.; Brck, E.

2014-05-01

428

A Transition Metal Complex (Venus Flytrap Cluster) for Radioimmunodetection and Radioimmunotherapy  

NASA Astrophysics Data System (ADS)

A novel transition metal complex, Venus flytrap cluster (VFC), is described for the preparation of radiolabeled antibodies. VFC contained 57Co, which was held tightly between the faces of two covalently bridged carborane ligands by cluster bonding of the metal with appropriate ligand orbitals. Anti-carcinoembryonic antigen monoclonal antibody T84.66 was conjugated to 57Co-VFC with full retention of immunological activity. Biodistribution studies in nude mice bearing carcinoembryonic antigen-producing tumors showed excellent tumor localization of 57Co-VFC-T84.66. The accumulation of radionuclide in normal liver was low and independent of dose, which may reflect the stability of the radionuclide complex. These results presage the use of VFC systems for binding transition metals that are clinically useful for radio-immunodiagnosis and radioimmunotherapy.

Paxton, Raymond J.; Beatty, Barbara G.; Hawthorne, M. Frederick; Varadarajan, Aravamuthan; Williams, Lawrence E.; Curtis, Frederick L.; Knobler, Carolyn B.; Beatty, J. David; Shiveley, John E.

1991-04-01

429

A transition metal complex (Venus flytrap cluster) for radioimmunodetection and radioimmunotherapy  

SciTech Connect

A novel transition metal complex, Venus flytrap cluster (VFC), is described for the preparation of radiolabeled antibodies. VFC contained {sup 57}Co, which was held tightly between the faces of two covalently bridged carborane ligands by cluster bonding of the metal with appropriate ligand orbitals. Anti-carcinoembryonic antigen monoclonal antibody T84,66 was conjugated to {sup 57}Co-VFC with full retention of immunological activity. Biodistribution studies in nude mice bearing carcinoembryonic antigen-producing tumors showed excellent tumor localization of {sup 57}Co-VFC-T84.66. The accumulation of radionuclide in normal liver was low and independent of dose, which may reflect the stability of the radionuclide complex. These results presage the use of VFC systems for binding transition metals that are clinically useful for radioimmunodiagnosis and radioimmunotherapy.

Paxton, R.J.; Curtis, F.L.; Shively, J.E. (Beckman Research Inst. of the City of Hope, Duarte, CA (United States)); Beatty, B.G.; Williams, L.E.; Beatty, J.D. (City of Hope National Medical Center, Duarte, CA (United States)); Hawthorne, M.F.; Varadarajan, A.; Knobler, C.B. (Univ. of California, Los Angeles (United States))

1991-04-15

430

Holographic entanglement entropy in metal/superconductor phase transition with Born-Infeld electrodynamics  

E-print Network

We investigate the holographic entanglement entropy in the metal/superconductor phase transition for the Born-Infeld electrodynamics with full backreaction and note that the entropy is a good probe to study the properties of the phase transition. For the operator $$, we find that the entanglement entropy decreases (or increases) with the increase of the Born-Infeld parameter $b$ in the metal (or superconducting) phase. For the operator $$, we observe that, with the increase of the Born-Infeld parameter, the entanglement entropy in the metal phase decreases monotonously but the entropy in the superconducting phase first increases and forms a peak at some threshold $b_{T}$, then decreases continuously, which implies that there is some kind of the significant reorganization of the degrees of freedom. Moreover, the value of $b_{T}$ becomes smaller as the width of the subsystem $A$ decreases.

Yao, Weiping

2014-01-01

431

Holographic entanglement entropy in metal/superconductor phase transition with Born-Infeld electrodynamics  

E-print Network

We investigate the holographic entanglement entropy in the metal/superconductor phase transition for the Born-Infeld electrodynamics with full backreaction and note that the entropy is a good probe to study the properties of the phase transition. For the operator $$, we find that the entanglement entropy decreases (or increases) with the increase of the Born-Infeld parameter $b$ in the metal (or superconducting) phase. For the operator $$, we observe that, with the increase of the Born-Infeld parameter, the entanglement entropy in the metal phase decreases monotonously but the entropy in the superconducting phase first increases and forms a peak at some threshold $b_{T}$, then decreases continuously. Moreover, the value of $b_{T}$ becomes smaller as the width of the subsystem $A$ decreases.

Weiping Yao; Jiliang Jing

2014-08-06

432

Thermodynamical Study of (DMe-DCQNI) 2Cu System - Mechanism of Reentrant Metal-Insulator Transition -  

NASA Astrophysics Data System (ADS)

We have experimentally studied the mechanism of reentrantmetal-insulator-metal transition of DCNQI-Cu system. Measurements ofspecific heat and latent heat were carried out by thermal relaxation(0.5metallic and insulating phases and succeededto draw the phase diagram that reproduces the experimental resultquite well. We conclude that the free energy change of free electrons(metallic phase) to localized electrons with spin 1/2 (insulatingphase) is essential to drive the anomalous phase transition in thissystem. Contribution of lattice system is also clarified.

Nishio, Yutaka; Tamura, Masafumi; Kajita, Koji; Aonuma, Shuji; Sawa, Hiroshi; Kato, Reizo; Kobayashi, Hayao

2000-05-01

433

Status in calculating electronic excited States in transition metal oxides from first principles.  

PubMed

Characterization of excitations in transition metal oxides is a crucial step in the development of these materials for photonic and optoelectronic applications. However, many transition metal oxides are considered to be strongly correlated materials, and their complex electronic structure is challenging to model with many established quantum mechanical techniques. We review state-of-the-art first-principles methods to calculate charged and neutral excited states in extended materials, and discuss their application to transition metal oxides. We briefly discuss developments in density functional theory (DFT) to calculate fundamental band gaps, and introduce time-dependent DFT, which can model neutral excitations. Charged excitations can be described within the framework of many-body perturbation theory based on Green's functions techniques, which predominantly employs the GW approximation to the self-energy to facilitate a feasible solution to the quasiparticle equations. We review the various implementations of the GW approximation and evaluate each approach in its calculation of fundamental band gaps of many transition metal oxides. We also briefly review the related Bethe-Salpeter equation (BSE), which introduces an electron-hole interaction between GW-derived quasiparticles to describe accurately neutral excitations. Embedded correlated wavefunction theory is another framework used to model localized neutral or charged excitations in extended materials. Here, the electronic structure of a small cluster is modeled within correlated wavefunction theory, while its coupling to its environment is represented by an embedding potential. We review a number of techniques to represent this background potential, including electrostatic representations and electron density-based methods, and evaluate their application to transition metal oxides. PMID:24488486

Bendavid, Leah Isseroff; Carter, Emily Ann

2014-01-01

434

Transition metal-chelating surfactant micelle templates for facile synthesis of mesoporous silica nanoparticles  

SciTech Connect

Highly ordered mesoporous silica nanoparticles with tunable morphology and pore-size are prepared by the use of a transition metal-chelating surfactant micelle complex using Co{sup 2+}, Ni{sup 2+}, Cu{sup 2+}, and Zn{sup 2+} ions. These metal ions formed a metal-P123 micelle complex in an aqueous solution, while the metal ions are chelated to the hydrophilic domain such as the poly(ethylene oxide) group of a P123 surfactant. The different complexation abilities of the utilized transition metal ions play an important role in determining the formation of nano-sized ordered MSNs due to the different stabilization constant of the metal-P123 complex. Consequently, from a particle length of 1700 nm in the original mesoporous silica materials, the particle length of ordered MSNs through the metal-chelating P123 micelle templates can be reduced to a range of 180-800 nm. Furthermore, the variation of pore size shows a slight change from 8.8 to 6.6 nm. In particular, the Cu{sup 2+}-chelated MSNs show only decreased particle size to 180 nm. The stability constants for the metal-P123 complex are calculated on the basis of molar conductance measurements in order to elucidate the formation mechanism of MSNs by the metal-chelating P123 complex templates. In addition, solid-state {sup 29}Si, {sup 13}C-NMR and ICP-OES measurements are used for quantitative characterization reveal that the utilized metal ions affect only the formation of a metal-P123 complex in a micelle as a template. - Graphical abstract: Metal-chelating surfactant micelle templates support a simple and facile preparations of size-tunable ordered MSNs. Black-Small-Square Highlights: Black-Right-Pointing-Pointer Facile preparation of mesoporous silica nanoparticles (MSNs) was achieved by metal-chelating surfactant micelle complex using Co{sup 2+}, Ni{sup 2+}, Cu{sup 2+}, and Zn{sup 2+} ions. Black-Right-Pointing-Pointer Different complexation of metal ions plays an important role in determining the formation of nano-sized ordered MSNs. Black-Right-Pointing-Pointer Systematic characterization of the synthesized materials was achieved by solid-state {sup 29}Si and {sup 13}C-NMR techniques, BET, FT-IR, and XPS. Black-Right-Pointing-Pointer Stability constants for the metal-P123 complex are calculated on the basis of molar conductance measurements in order to elucidate the formation mechanism.

Lee, Hye Sun [Korea Institute of Ceramic Engineering and Technology, Seoul 153-801 (Korea, Republic of); Department of Materials Science and Engineering, Yonsei University, Seoul 120-749 (Korea, Republic of); Kim, Won Hee; Lee, Jin Hyung [Korea Institute of Ceramic Engineering and Technology, Seoul 153-801 (Korea, Republic of); Choi, Doo Jin [Department of Materials Science and Engineering, Yonsei University, Seoul 120-749 (Korea, Republic of); Jeong, Young-Keun [National Core Research Center for Hybrid Materials Solution, Pusan National University, Pusan 609-735 (Korea, Republic of); Chang, Jeong Ho, E-mail: jhchang@kicet.re.kr [Korea Institute of Ceramic Engineering and Technology, Seoul 153-801 (Korea, Republic of)

2012-01-15

435

Nanopatterning of transition metal surfaces via electrochemical dimple array formation.  

PubMed

Nanoscale surface patterning is of great importance for applications ranging from catalysts to biomaterials. We show the formation of ordered nanoscale dimple arrays on titanium, tungsten, and zirconium during electropolishing, demonstrating versatility of a process previously only reported for tantalum. This is a rare example of an electrochemical pattern formation process that can be translated to other materials. The dimpled surfaces have been characterized with scanning electron microscopy, transmission electron microscopy, atomic force microscopy, and X-ray photoelectron spectroscopy, and electrochemical conditions were optimized for each material. While conditions for titanium and tungsten resemble those for tantalum, zirconium requires a different type of electrolyte. Given the appropriate electropolishing chemistry, formation of these patterns should be possible on any metal surface. The process is very robust on homogeneous surfaces, but sensitive to inhomogeneities in chemical composition, such as in the case of differentially etched alloys. An alternative process for some materials such as platinum is the coating of a dimpled substrate with a thin film of the required material. PMID:19206279

Singh, Sherdeep; Barden, Warren R T; Kruse, Peter

2008-12-23

436

EPR investigations of mesoporous silica doped with metal transitions ions  

NASA Astrophysics Data System (ADS)

Electron paramagnetic resonance (EPR) experiments were performed on mesoporous silica powders in which (1,4,8,11-tetraazacyclotetradecane) cyclam groups were incorporated. These functionalised groups allow an easy binding with copper and nickel ions. Comparative studies are carried out on samples functionalised by cyclam groups located either inside the pores or in the walls of the mesoporous structures. Copper and nickel EPR parameters, including g-tensors and hyperfine components are determined and relevant electronic, magnetic and structural information are obtained. The EPR spectra intensities and line-widths are investigated on the temperature range [4 K,300 K] to clarify the relative dispersion or agglomeration of the doping ions in the matrices as well as their possible thermally activated mobility and ions pairing. As a support of the experimental EPR investigations, numerical simulations of the geometry of metallic ion environments and their electronic properties are carried out and discussed. The possibility of dynamic Jahn Teller (JT) effect in the temperature range [200, 60 K] is discussed for the nickel doped matrices where the low temperature quenched JT configuration is thought to favour the formation of Ni3+ pairs.

Kassiba, A.; Makowska-Janusik, M.; Alauzun, J.; Kafrouni, W.; Mehdi, A.; Rey, C.; Corriu, R. J.; Gibaud, A.

2006-04-01

437

Translation repressors, an RNA helicase, and developmental cues control RNP phase transitions during early development.  

PubMed

Like membranous organelles, large-scale coassembly of macromolecules can organize functions in cells. Ribonucleoproteins (RNPs) can form liquid or solid aggregates, but control and consequences of these RNP states in living, developing tissue are poorly understood. Here, we show that regulated RNP factor interactions drive transitions among diffuse, semiliquid, or solid states to modulate RNP sorting and exchange in the Caenorhabditis elegans oocyte cytoplasm. Translation repressors induce an intrinsic capacity of RNP components to coassemble into either large semiliquids or solid lattices, whereas a conserved RNA helicase prevents polymerization into nondynamic solids. Developmental cues dramatically alter both fluidity and sorting within large RNP assemblies, inducing a transition from RNP segregation in quiescent oocytes to dynamic exchange in the early embryo. Therefore, large-scale organization of gene expression extends to the cytoplasm, where regulation of supramolecular states imparts specific patterns of RNP dynamics. PMID:24176641

Hubstenberger, Arnaud; Noble, Scott L; Cameron, Cristiana; Evans, Thomas C

2013-10-28

438

Translation Repressors, an RNA Helicase, and Developmental Cues Control RNP Phase Transitions during Early Development  

PubMed Central

SUMMARY Like membranous organelles, large-scale coassembly of macromolecules can organize functions in cells. Ribonucleoproteins (RNPs) can form liquid or solid aggregates, but control and consequences of these RNP states in living, developing tissue are poorly understood. Here, we show that regulated RNP factor interactions drive transitions among diffuse, semiliquid, or solid states to modulate RNP sorting and exchange in the Caenorhabditis elegans oocyte cytoplasm. Translation repressors induce an intrinsic capacity of RNP components to coassemble into either large semiliquids or solid lattices, whereas a conserved RNA helicase prevents polymerization into nondynamic solids. Developmental cues dramatically alter both fluidity and sorting within large RNP assemblies, inducing a transition from RNP segregation in quiescent oocytes to dynamic exchange in the early embryo. Therefore, large-scale organization of gene expression extends to the cytoplasm, where regulation of supramolecular states imparts specific patterns of RNP dynamics. PMID:24176641

Hubstenberger, Arnaud; Noble, Scott L.; Cameron, Cristiana; Evans, Thomas C.

2013-01-01

439

Asymmetric photoredox transition-metal catalysis activated by visible light.  

PubMed

Asymmetric catalysis is seen as one of the most economical strategies to satisfy the growing demand for enantiomerically pure small molecules in the fine chemical and pharmaceutical industries. And visible light has been recognized as an environmentally friendly and sustainable form of energy for triggering chemical transformations and catalytic chemical processes. For these reasons, visible-light-driven catalytic asymmetric chemistry is a subject of enormous current interest. Photoredox catalysis provides the opportunity to generate highly reactive radical ion intermediates with often unusual or unconventional reactivities under surprisingly mild reaction conditions. In such systems, photoactivated sensitizers initiate a single electron transfer from (or to) a closed-shell organic molecule to produce radical cations or radical anions whose reactivities are then exploited for interesting or unusual chemical transformations. However, the high reactivity of photoexcited substrates, intermediate radical ions or radicals, and the low activation barriers for follow-up reactions provide significant hurdles for the development of efficient catalytic photochemical processes that work under stereochemical control and provide chiral molecules in an asymmetric fashion. Here we report a highly efficient asymmetric catalyst that uses visible light for the necessary molecular activation, thereby combining asymmetric catalysis and photocatalysis. We show that a chiral iridium complex can serve as a sensitizer for photoredox catalysis and at the same time provide very effective asymmetric induction for the enantioselective alkylation of 2-acyl imidazoles. This new asymmetric photoredox catalyst, in which the metal centre simultaneously serves as the exclusive source of chirality, the catalytically active Lewis acid centre, and the photoredox centre, offers new opportunities for the 'green' synthesis of non-racemic chiral molecules. PMID:25373679

Huo, Haohua; Shen, Xiaodong; Wang, Chuanyong; Zhang, Lilu; Rse, Philipp; Chen, Liang-An; Harms, Klaus; Marsch, Michael; Hilt, Gerhard; Meggers, Eric

2014-11-01

440

DFT-GGA errors in NO chemisorption energies on (111) transition metal surfaces  

NASA Astrophysics Data System (ADS)

We investigate whether well-known DFT-GGA errors in predicting the chemisorption energy (Echem) of CO on transition metal surfaces manifest in analogous NO chemisorption systems. While widely investigated in the case of CO/