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1

Stable singlet carbenes as mimics for transition metal centers  

PubMed Central

This perspective summarizes recent results, which demonstrate that stable carbenes can activate small molecules (CO, H2, NH3 and P4) and stabilize highly reactive intermediates (main group elements in the zero oxidation state and paramagnetic species). These two tasks were previously exclusive for transition metal complexes. PMID:21743834

Martin, David; Soleilhavoup, Michele

2011-01-01

2

Cyclic (Alkyl)(Amino)Carbenes (CAACs): Stable Carbenes on the Rise.  

PubMed

Conspectus Carbenes are compounds that feature a divalent carbon atom with only six electrons in its valence shell. In the singlet state, they possess a lone pair of electrons and a vacant orbital and therefore exhibit Lewis acidic and Lewis basic properties, which explains their very high reactivity. Following the preparation by our group in 1988 of the first representative, a variety of stable carbenes are now available, the most popular being the cyclic diaminocarbenes. In this Account, we discuss another class of stable cyclic carbenes, namely, cyclic (alkyl)(amino)carbenes (CAACs), in which one of the electronegative and ?-donor amino substituents of diaminocarbenes is replaced by a ?-donating but not ?-donating alkyl group. As a consequence, CAACs are more nucleophilic (?-donating) but also more electrophilic (?-accepting) than diaminocarbenes. Additionally, the presence of a quaternary carbon in the position ? to the carbene center provides steric environments that differentiate CAACs dramatically from all other ligands. We show that the peculiar electronic and steric properties of CAACs allow for the stabilization of unusual diamagnetic and paramagnetic main group element species. As examples, we describe the preparation of room temperature stable phosphorus derivatives in which the heteroatom is in the zero oxidation state, nucleophilic boron compounds, and phosphorus-, antimony-, boron-, silicon-, and even carbon-centered neutral and cationic radicals. CAACs are also excellent ligands for transition metal complexes. The most recent application is their use for the stabilization of paramagnetic complexes, in which the metal is often in a formal zero oxidation state. Indeed, bis(CAAC)M complexes in which the metal is gold, copper, cobalt, iron, nickel, manganese, and zinc have been isolated. Depending on the metal, the majority of spin density can reside either on the metal or on the carbene carbons and the nitrogen atoms of the CAAC ligand. In contrast to diaminocarbenes, the higher basicity of CAACs makes them poor leaving groups, and thus they cannot be used for classical organocatalysis. However, because of their superior electrophilicity and smaller singlet-triplet gap, CAACs can activate small molecules at room temperature, such as CO, H2, and P4, as well as enthalpically strong bonds, such as B-H, Si-H, N-H, and P-H. Lastly, excellent results have been obtained in palladium, ruthenium, and gold catalysis. CAAC-metal complexes are extremely thermally robust, which allows for their utilization in harsh conditions. This property has been used to perform a variety of gold-catalyzed reactions in the presence of basic amines, including ammonia and hydrazine, which usually deactivate catalysts. PMID:25515548

Soleilhavoup, Michèle; Bertrand, Guy

2015-02-17

3

Stable Cyclic Carbenes and Related Species beyond Diaminocarbenes  

PubMed Central

The success of homogeneous catalysis can be attributed largely to the development of a diverse range of ligand frameworks that have been used to tune the behavior of various systems. Spectacular results in this area have been achieved using cyclic diaminocarbenes (NHCs) as a result of their strong ?-donor properties. Although it is possible to cursorily tune the structure of NHCs, any diversity is still far from matching their phosphorus-based counterparts, which is one of the great strengths of the latter. A variety of stable acyclic carbenes are known, but they are either reluctant to bind metals or they give rise to fragile metal complexes. During the last five years, new types of stable cyclic carbenes, as well as related carbon-based ligands (which are not NHCs), and which feature even stronger ?-donor properties have been developed. Their synthesis and characterization as well as the stability, electronic properties, coordination behavior, and catalytic activity of the ensuing complexes are discussed, and comparisons with their NHC cousins are made. PMID:20836099

Melaimi, Mohand; Soleilhavoup, Michèle

2011-01-01

4

Highly stable water-soluble platinum nanoparticles stabilized by hydrophilic N-heterocyclic carbenes.  

PubMed

Controlling the synthesis of stable metal nanoparticles in water is a current challenge in nanochemistry. The strategy presented herein uses sulfonated N-heterocyclic carbene (NHC) ligands to stabilize platinum nanoparticles (PtNPs) in water, under air, for an indefinite time period. The particles were prepared by thermal decomposition of a preformed molecular Pt?complex containing the NHC ligand and were then purified by dialysis and characterized by TEM, high-resolution TEM, and spectroscopic techniques. Solid-state NMR studies showed coordination of the carbene ligands to the nanoparticle surface and allowed the determination of a (13)C-(195)Pt?coupling constant for the first time in a nanosystem (940?Hz). Additionally, in one case a novel structure was formed in which platinum(II) NHC complexes form a second coordination sphere around the nanoparticle. PMID:25267410

Baquero, Edwin A; Tricard, Simon; Flores, Juan Carlos; de Jesús, Ernesto; Chaudret, Bruno

2014-11-24

5

Ultra stable self-assembled monolayers of N-heterocyclic carbenes on gold  

NASA Astrophysics Data System (ADS)

Since the first report of thiol-based self-assembled monolayers (SAMs) 30 years ago, these structures have been examined in a huge variety of applications. The oxidative and thermal instabilities of these systems are widely known, however, and are an impediment to their widespread commercial use. Here, we describe the generation of N-heterocyclic carbene (NHC)-based SAMs on gold that demonstrate considerably greater resistance to heat and chemical reagents than the thiol-based counterparts. This increased stability is related to the increased strength of the gold-carbon bond relative to that of a gold-sulfur bond, and to a different mode of bonding in the case of the carbene ligand. Once bound to gold, NHCs are not displaced by thiols or thioethers, and are stable to high temperatures, boiling water, organic solvents, pH extremes, electrochemical cycling above 0 V and 1% hydrogen peroxide. In particular, benzimidazole-derived carbenes provide films with the highest stabilities and evidence of short-range molecular ordering. Chemical derivatization can be employed to adjust the surface properties of NHC-based SAMs.

Crudden, Cathleen M.; Horton, J. Hugh; Ebralidze, Iraklii I.; Zenkina, Olena V.; McLean, Alastair B.; Drevniok, Benedict; She, Zhe; Kraatz, Heinz-Bernhard; Mosey, Nicholas J.; Seki, Tomohiro; Keske, Eric C.; Leake, Joanna D.; Rousina-Webb, Alexander; Wu, Gang

2014-05-01

6

An efficient synthetic route to stable bis(carbene)borylenes [(L1)(L2)BH].  

PubMed

Two-electron reduction of bis(carbene) boronium salts allows for the preparation of unsymmetrically substituted nucleophilic boron derivatives of type (L1)(L2)BH, which are characterized by X-ray crystallography. A single electron reduction of the same starting materials leads to the corresponding boron-centered radical cations (L1)(L2)BH?(+), X(-). PMID:24909943

Ruiz, David A; Melaimi, Mohand; Bertrand, Guy

2014-07-25

7

Redox and luminescent properties of robust and air-stable N-heterocyclic carbene group 4 metal complexes.  

PubMed

Robust and air-stable homoleptic group 4 complexes of the type M(L)2 [1-3; M = Ti, Zr, Hf; L = dianionic bis(aryloxide) N-heterocyclic carbene (NHC) ligand] were readily synthesized from the NHC proligand 1,3-bis(3,5-di-tert-butyl-2-hydroxyphenyl)imidazolinium chloride (H3L,Cl) and appropriate group 4 precursors. As deduced from cyclic voltammetry studies, the homoleptic bis-adduct zirconium and hafnium complexes 2 and 3 can also be oxidized, with up to four one-electron-oxidation signals for the zirconium derivative 2 (three reversible signals). Electron paramagnetic resonance data for the one-electron oxidation of complexes 1-3 agree with the formation of ligand-centered species. Compounds 2 and 3 are luminescent upon excitation in the absorption band at 362 nm with emissions at 485 and 534 nm with good quantum yields (? = 0.08 and 0.12) for 2 and 3, respectively. In contrast, the titanium complex 1 does not exhibit luminescent properties upon excitation in the absorption band at 310 and 395 nm. Complexes 2 and 3 constitute the first examples of emissive nonmetallocene group 4 metal complexes. PMID:24957272

Romain, Charles; Choua, Sylvie; Collin, Jean-Paul; Heinrich, Martine; Bailly, Corinne; Karmazin-Brelot, Lydia; Bellemin-Laponnaz, Stéphane; Dagorne, Samuel

2014-07-21

8

Chiral N-Heterocyclic Carbene Catalyzed Annulations of Enals and Ynals with Stable Enols: A Highly Enantioselective Coates–Claisen Rearrangement  

PubMed Central

A combination of a chiral N-heterocyclic carbene catalyst and ?,?-unsaturated aldehyde leads to a catalytically generated ?,?-unsaturated acyl azolium, which participates in a highly enantioselective annulation to give dihydropyranone products. This full account of our investigations into the scope and mechanism of this reaction reveals the critical role of both the type and substitution pattern of the chiral triazolium precatalyst in inducing and controlling the stereochemistry. In an effort to explain why stable enols such as naphthol, kojic acid, and dicarbonyl are uniquely efficient, we have postulated that this annulation occurs via a Coates-Claisen rearrangement that invokes the formation of a hemiacetal prior to a sigmatropic rearrangement. Detailed kinetic investigations of the catalytic annulation are consistent with this mechanistic postulate. PMID:22468232

Mahatthananchai, Jessada; Kaeobamrung, Juthanat; Bode, Jeffrey W.

2012-01-01

9

Shape-Controllable Formation of Poly-imidazolium Salts for Stable Palladium N-Heterocyclic Carbene Polymers  

NASA Astrophysics Data System (ADS)

The imidazolium-based main-chain organic polymers are one of promising platforms in heterogeneous catalysis, the size and outer morphology of polymer particles are known to have important effects on their physical properties and catalytic applications, but main-chain ionic polymers usually generate amorphous or spherical particles. Herein, we presented a versatile and facile synthetic route for size- and shape-controllable synthesis of main-chain poly-imidazolium particles. The wire-shaped, spherical and ribbon-shaped morphologies of poly-imidazolium particles were readily synthesized through quaternization of bis-(imidazol-1-yl)methane and 2,4,6-tris(4-(bromomethyl)phenyl)-1,3,5-triazine, and the modification of their size and morphology were realized through adjusting solvent polarity, solubility, concentration and temperatures. The direct complexation of the particles with Pd(OAc)2 produced ionic polymers containing palladium N-heterocyclic carbene units (NHCs) with intactness of original morphologies. The particle morphologies have a significant effect on catalytic performances. Wire-shaped palladium-NHC polymer shows excellent catalytic activity and recyclabilty in heterogeneous Suzuki-Miyaura cross-coupling reaction.

Zhao, Huaixia; Li, Liuyi; Wang, Yangxin; Wang, Ruihu

2014-06-01

10

Pyrido[1,2-a][1,2,4]triazol-3-ylidenes as a new family of stable annulated N-heterocyclic carbenes: synthesis, reactivity, and their application in coordination chemistry and organocatalysis.  

PubMed

General synthetic avenues to the pyrido-annulated triazolium salts with different steric and electronic properties have been developed. This architecture can be readily altered with different N-alkyl or aryl substituents at the N2 position of the triazole ring and modifications to the pyridine backbone. Deprotonation of the triazolium salts 12 with NaH led to formation of stable carbenes 11 at room temperature as clearly demonstrated through ESI mass spectra and by observation of the characteristic (13)C NMR resonance for the carbene carbon at delta = 202-208 ppm. In sharp contrast, treatment of these triazolium salts with K2CO3 led to dimerization of free carbenes 11. The dimeric enetetramine (11b)2 could react with elemental sulfur to deliver the corresponding thiourea 16 in toluene at 80 degrees C in good yield. A silver complex with the pyrido[1,2-a][1,2,4]triazol-3-ylidene is described, and the molecular structure of complex 17 was established by X-ray crystallography. The triazolium salts 12 turned out to be powerful catalysts in catalytic benzoin condensations and transesterifications at 25 degrees C. The catalytic activity was largely dependent on the steric and electronic nature of the R(1) and R(2) substituents of the triazolium salt. We rationalized that this type of triazolium-catalyzed benzoin condensations should undergo the "traditional" Breslow mechanism rather than the pathway of the dimer (11)2 as the real catalytic species. PMID:18844416

Ma, Yajun; Wei, Siping; Lan, Jingbo; Wang, Jingzhi; Xie, Rugang; You, Jingsong

2008-11-01

11

Carbene-dichlorosilylene stabilized phosphinidenes exhibiting strong intramolecular charge transfer transition.  

PubMed

The unstable species dichlorosilylene was previously stabilized by carbene. The lone pair of electrons on the silicon atom of (carbene)SiCl2 can form a coordinate bond with metal-carbonyls. Herein we report that (carbene)SiCl2 can stabilize a phosphinidene (Ar-P, a carbone analogue) with the general formula carbene?SiCl2?P-Ar (carbene = cyclic alkyl(amino) carbene (cAAC; 2) and N-heterocyclic carbene (NHC; 3)). Compounds 2 and 3 are stable, isolable, and storable at 0 °C (2) to room temperature (3) under an inert atmosphere. The crystals of 2 and 3 are dark blue and red, respectively. The intense blue color of 2 arises due to the strong intramolecular charge transfer (ICT) transition from ?Si?P??*cAAC. The electronic structure and bonding of 2, 3 were studied by theoretical calculations. The HOMO of the molecule is located on the ?Si?P bond, while the LUMO is located at the carbene moiety (cAAC or NHC). The dramatic change in color of these compounds from red (3, NHC) to blue (2, cAAC) is ascribed to the difference in energy of the LUMO within the carbenes (cAAC/NHC) due to a lower lying LUMO of cAAC. PMID:25539016

Roy, Sudipta; Stollberg, Peter; Herbst-Irmer, Regine; Stalke, Dietmar; Andrada, Diego M; Frenking, Gernot; Roesky, Herbert W

2015-01-14

12

Carbene-Stabilized Main Group Radicals and Radical Ions  

PubMed Central

Shortly after their discovery at the end of the 80s, stable singlet carbenes have been recognized as excellent ligands for transition metal based catalysts, and as organo-catalysts in their own right. At the end of the 2000s, it has been shown that they can coordinate main group elements in their zero oxidation state, and even activate small molecules. This review covers examples in the literature dealing with the most recent application of stable singlet carbenes, namely their use to stabilize radicals and radical ions that are otherwise unstable. PMID:23878717

Martin, Caleb D.; Soleilhavoup, Michele; Bertrand, Guy

2013-01-01

13

Synthesis and Properties of Chelating N-Heterocyclic Carbene Rhodium(I) Complexes: Synthetic Experiments in Current Organometallic Chemistry  

ERIC Educational Resources Information Center

The preparation and characterization of two air-stable Rh(I) complexes bearing a chelating N-heterocyclic carbene (NHC) ligand is described. The synthesis involves the preparation of a Ag(I)-NHC complex and its use as carbene transfer agent to a Rh(I) precursor. The so obtained complex can be further reacted with carbon monoxide to give the…

Mata, Jose A.; Poyatos, Macarena; Mas-Marza, Elena

2011-01-01

14

Carbene-stabilized beryllium borohydride.  

PubMed

The reaction of N-heterocyclic carbene, L:, with BeCl(2) quantitatively yields L:BeCl(2)1 (L: = :C{N(2,6-Pr(i)(2)C(6)H(3))CH}(2)). The carbene-stabilized beryllium borohydride monomer L:Be(BH(4))(2)2 is prepared by the reaction of 1 with LiBH(4). Compound 3, prepared by the reaction of 2 with Na(2)[Fe(CO)(4)]·dioxane, represents an unusual "dual reduction" of the imidazole ring (i.e., hydroboration of the C?C backbone and hydrogenation of the C2 carbene center). PMID:22670857

Gilliard, Robert J; Abraham, Mariham Y; Wang, Yuzhong; Wei, Pingrong; Xie, Yaoming; Quillian, Brandon; Schaefer, Henry F; Schleyer, Paul V R; Robinson, Gregory H

2012-06-20

15

Substitution effects on the formation of T-shaped palladium carbene and thioketone complexes from Li/Cl carbenoids.  

PubMed

The preparation of palladium thioketone and T-shaped carbene complexes by treatment of thiophosphoryl substituted Li/Cl carbenoids with a Pd(0) precursor is reported. Depending on the steric demand, the anion-stabilizing ability of the silyl moiety (by negative hyperconjugation effects) and the remaining negative charge at the carbenic carbon atom, isolation of a three-coordinate, T-shaped palladium carbene complex is possible. In contrast, insufficient charge stabilization results in the transfer of the sulfur of the thiophosphoryl moiety and thus in the formation of a thioketone complex. While the thioketones are stable compounds the carbene complexes are revealed to be highly reactive and decompose under elimination of Pd metal. Computational studies revealed that both complexes are formed by a substitution mechanism. While the ketone turned out to be the thermodynamically favored product, the carbene is kinetically favored and thus preferentially formed at low reaction temperatures. PMID:24664573

Molitor, Sebastian; Feichtner, Kai-Stephan; Kupper, Claudia; Gessner, Viktoria H

2014-08-18

16

Ruthenium Vinyl Carbene Intermediates in Enyne Metathesis  

PubMed Central

This review provides an overview of ruthenium vinyl carbene reactivity as it relates to enyne metathesis. Methods for the synthesis of metathesis-active and metathesis-inactive complexes are also summarized. Some of the early hypotheses about vinyl carbene intermediates in enyne metatheses were tested in the arena of synthetic chemistry and subsequently led to mechanistic studies. In these two areas, studies from the author's labs are described. There are still many unresolved questions in enyne metathesis that trace back to vinyl carbene reactivity. Hopefully this review will stimulate further investigation into vinyl carbene reactivity which should further refine our understanding of catalytic enyne metathesis. PMID:19590747

Diver, Steven T.

2009-01-01

17

Lewis Base Catalysts 6: Carbene Catalysts  

PubMed Central

The use of N-heterocyclic carbenes as catalysts for organic transformations has received increased attention in the past 10 years. A discussion of catalyst development and nucleophilic characteristics precedes a description of recent advancements and new reactions using N-heterocyclic carbenes in catalysis. PMID:21494949

Moore, Jennifer L.

2013-01-01

18

Exotic noble gas carbene-like ions  

NASA Astrophysics Data System (ADS)

Using a combination of theoretical techniques, this work studies the Kr2C2+ species, which has electronic, structural, and some typical chemical characteristics of carbenes, and whose ground state is singlet. Similarly to the case of traditional carbenes, Kr2C2+ is metastable and appears to be a candidate for a reactive intermediate.

Echeverri, Andrea; Moreno, Norberto; Restrepo, Albeiro; Hadad, C. Z.

2014-11-01

19

Computational Chemistry Studies on the Carbene Hydroxymethylene  

ERIC Educational Resources Information Center

A density functional theory computational chemistry exercise on the structure and vibrational spectrum of the carbene hydroxymethylene is presented. The potential energy curve for the decomposition reaction of the carbene to formaldehyde and the geometry of the transition state are explored. The results are in good agreement with recent…

Marzzacco, Charles J.; Baum, J. Clayton

2011-01-01

20

N-Heterocyclic Carbene-Catalyzed Alcohol Acetylation: An Organic Experiment Using Organocatalysis  

ERIC Educational Resources Information Center

Undergraduate students in the teaching laboratory have successfully used N-heterocyclic carbenes (NHCs) as organocatalysts for the acetylation of primary alcohols, despite the high water sensitivity of uncomplexed ("free") NHCs. The free NHC readily reacted with chloroform, resulting in an air- and moisture-stable adduct that liberates…

Morgan, John P.; Shrimp, Jonathan H.

2014-01-01

21

An overview of N-heterocyclic carbenes  

NASA Astrophysics Data System (ADS)

The successful isolation and characterization of an N-heterocyclic carbene in 1991 opened up a new class of organic compounds for investigation. From these beginnings as academic curiosities, N-heterocyclic carbenes today rank among the most powerful tools in organic chemistry, with numerous applications in commercially important processes. Here we provide a concise overview of N-heterocyclic carbenes in modern chemistry, summarizing their general properties and uses and highlighting how these features are being exploited in a selection of pioneering recent studies.

Hopkinson, Matthew N.; Richter, Christian; Schedler, Michael; Glorius, Frank

2014-06-01

22

The synthesis of ?-alkoxy and ?-aminostannanes as precursors to Novel Chromium Fischer Carbenes.  

E-print Network

??The present study involves the use of main group organometallics: organostannanes and organolithiums as precursors to chromium Fischer carbene complexes. Fischer carbenes are well stabilized… (more)

Meyer, Annalene

2012-01-01

23

N-heterocyclic carbene coordinated neutral and cationic heavier cyclopropylidenes.  

PubMed

Cyclopropylidene is a transient intermediate of the allene-propyne-cyclopropene isomerization. The incorporation of heavier Group?14 elements into the cyclopropylidene scaffold has to date been restricted to the formal replacement of the carbenic carbon atom by a base-coordinated silicon(II) center. Herein we report the synthesis and characterization of NHC-coordinated heavier cyclopropylidenes (Si2GeR3X, and Si3R3Br; X=Cl, Mes; R=Tip=2,4,6-iPr3C6H2) in which the three-membered ring is exclusively formed by silicon and germanium. In case of the chloro-substituted Si2Ge-cyclopropylidene, a stable heavier cycloprop-1-yl-2-ylidene cation is obtained by NHC-induced chloride dissociation. PMID:25060704

Jana, Anukul; Omlor, Isabell; Huch, Volker; Rzepa, Henry S; Scheschkewitz, David

2014-09-01

24

Carbene based photochemical molecular assemblies for solar driven hydrogen generation.  

PubMed

Novel photocatalysts based on ruthenium complexes with NHC (N-heterocyclic carbene)-type bridging ligands have been prepared and structurally and photophysically characterised. The identity of the NHC-unit of the bridging ligand was established unambiguously by means of X-ray structural analysis of a heterodinuclear ruthenium-silver complex. The photophysical data indicate ultrafast intersystem crossing into an emissive and a non-emissive triplet excited state after excitation of the ruthenium centre. Exceptionally high luminescence quantum yields of up to 39% and long lifetimes of up to 2 ?s are some of the triplet excited state characteristics. Preliminary studies into the visible light driven photocatalytic hydrogen formation show no induction phase and constant turnover frequencies that are independent on the concentration of the photocatalyst. In conclusion this supports the notion of a stable assembly under photocatalytic conditions. PMID:25100041

Peuntinger, Katrin; Pilz, T David; Staehle, Robert; Schaub, Markus; Kaufhold, Simon; Petermann, Lydia; Wunderlin, Markus; Görls, Helmar; Heinemann, Frank W; Li, Jing; Drewello, Thomas; Vos, Johannes G; Guldi, Dirk M; Rau, Sven

2014-09-28

25

Studies of coal structure using carbene chemistry  

SciTech Connect

The object of this grant was to react coal, derivatized forms of coal, and solvent swelled coal with carbenes (divalent carbon species) under mild conditions. These carbenes were to be prepared by treating the coal with several diazo compounds and then thermally decomposing them at relatively low temperatures (80--130{degree}C). The carbenes were to be chosen to show varying selectively toward aromatic rings containing heteroatom functionalities and toward polynuclear aromatic systems. In some instances, where selectivities toward aromatic and heteroaromatic ring systems were not known, model studies were to be carried out. Because of the generally mild conditions employed and the good selectivity anticipated, and actually observed with one particular system, it was expected that this methodology would provide structural information about the coal, along with data on the extent of occurrence and type of aromatic systems. After carbene reactions, treatment of the coal samples was to include extractions and thermolysis. Physical studies included thermogravimetric analysis, diffuse reflectance FT-IR spectroscopy, NMR ({sup 1}H and {sup 13}C) spectroscopy, gas chromatography, GC/MS and GC/FT-IR. 7 figs., 10 tabs.

Not Available

1990-01-01

26

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

27

The Reactivities of Iminoboranes with Carbenes: BN Isosteres of Carbene-Alkyne Adducts.  

PubMed

The first examples of adducts of cyclic alkyl(amino) carbenes (CAAC) and N-heterocyclic carbenes (NHCs) with iminoboranes have been synthesized and isolated at low temperature (-45?°C). The adducts show short B?N bonds and planarity at boron, mimicking the structures of the isoelectronic imine functionality. When di-tert-butyliminoborane was reacted with 1,3-bis(isopropyl)imidazol-2-ylidene (IPr), the initially formed Lewis acid-base adduct quickly rearranged to form a new carbene substituted with an aminoborane at the 4-position. Warming the iminoborane-CAAC adduct to room temperature resulted in an intramolecular cyclization to give a bicyclic 1,2-azaborilidine compound. PMID:25475584

Braunschweig, Holger; Ewing, William C; Geetharani, K; Schäfer, Marius

2015-01-26

28

Au(III)- versus Au(I)-induced cyclization: synthesis of 6-membered mesoionic carbene and acyclic (aryl)(heteroaryl) carbene complexes**  

PubMed Central

The Golden State: Selective 5-exo- and 6-endo-cyclizations of an alkynyl benzothioamide are achieved. The selectivity is controlled by the oxidation state of the gold precursor (+I or +III) yielding two new types of carbene ligand: an (aryl)(heteroaryl)carbene and a 6-membered mesoionic carbene. PMID:23169762

Ung, Gaël; Soleilhavoup, Michele

2013-01-01

29

N-Heterocyclic Carbene-Catalyzed Oxidations  

PubMed Central

N-Heterocyclic carbenes catalyze the oxidation of allylic and benzylic alcohols as well as saturated aldehydes to esters with manganese(IV) oxide in excellent yields. A variety of esters can be synthesized, including protected carboxylates. The oxidation proceeds under mild conditions, with low loadings of a simple triazolium salt pre-catalyst in the presence of base. Substrates containing potentially epimerizable centers are oxidized while preserving stereochemical integrity. The acyl triazolium intermediate generated under catalytic conditions can be employed as a chiral acylating agent in the desymmetrization of meso-diols. PMID:20161230

Maki, Brooks E.; Chan, Audrey; Phillips, Eric M.; Scheidt, Karl A.

2009-01-01

30

Chemistry of transition metal carbene complexes: nucleophilic substitution reactions of cyanamide anion to Fischer carbene complexes.  

PubMed

Rate constants for the reactions of cyanamide anion N?C-NH(-) with Fischer carbene complexes of the type (CO)(5)M=C(XR)C(6)H(4)Z with M = Cr and W, XR = SMe and OMe, Z = NMe(2), OMe, Me, H, F, Cl and CF(3) in 50% MeCN-50% water (v/v) at 25 °C are reported. N?C-NH(-) shows a much higher reactivity towards these carbene complexes than OH(-), primary aliphatic amines (e.g. n-butylamine) or secondary alicyclic amines (e.g. piperidine) but is slightly less reactive than thiolate ions (e.g. HOCH(2)CH(2)S(-)). The alkoxy carbene complexes were found to react faster than the thiomethyl derivatives, consistent with previous findings for alkoxide ion, CH(CN)(2)(-), OH(-), amine and thiolate ion nucleophiles. Hammett ? values are 3.00 ± 0.08 (k(1)) and 2.98 ± 0.08 (k(2)) for Cr-OMe-Z-N?C-NH(-) reactions and 0.94 ± 0.05 (k(1)) for Cr-SMe-Z-N?C-NH(-) reactions. The ? values for the reaction of Cr-OMe-Z and Cr-SMe-Z with CH(CN)(2)(-) and DABCO (1,4-diazabicyclo[2.2.2]octane) (in 50% MeCN-50% H(2)O (v/v) are comparable to the present reactions. The much higher reactivity and hence much higher ? value for methoxy carbene complexes over the corresponding thiomethyl derivatives is best explained by considering the substituent effects not only on the transition state (TS) but also on the reactant, and consistent with the previously observed pattern. Higher k(1)(W)/k(1)(Cr) ratios for (thiomethyl)carbene complexes as well as methoxy and ethoxycarbene complexes are related to the intrinsic rate constant which is higher for tungsten-carbene complexes than the corresponding Cr ones resulting in an enhanced ratio. This can also be explained by considering the electronegativity of Cr and W, which is higher for the latter; as a result the negative charge on the central metal atom is more localized in case of W causing destabilization of the TS and hence higher reactivity. PMID:23076623

Gangopadhyay, Sumana; Mistri, Tarun; Dolai, Malay; Alam, Rabiul; Ali, Mahammad

2013-01-14

31

Poly(fluoroalkyl acrylate)-bound ruthenium carbene complex: a fluorous and recyclable catalyst for ring-closing olefin metathesis.  

PubMed

The synthesis of a fluorous olefin metathesis catalyst derived from the Grubbs second-generation ruthenium carbene complex is described. The air stable fluorous polymer-bound ruthenium carbene complex 1 shows high reactivity in effecting the ring-closing metathesis of a broad spectrum of diene and enyne substrates leading to the formation of di-, tri-, and tetrasubstituted cyclic olefins in minimally fluorous solvent systems (PhCF3/CH2Cl2, 1:9-1:49 v/v). The catalyst can be readily separated from the reaction mixture by fluorous extraction with FC-72 and repeatedly reused. The practical advantage offered by the fluorous catalyst is demonstrated by its sequential use in up to five different metathesis reactions. PMID:14709066

Yao, Qingwei; Zhang, Yiliang

2004-01-14

32

A benzimidazole-based N-heterocyclic carbene derived from 1,10-phenanthroline.  

PubMed

[reaction: see text] A catalytically active palladium-complexed tetracyclic N-heterocyclic carbene (NHC) was prepared in three steps from commercially available 1,10-phenanthroline by using a reduction-cyclization-deprotonation sequence. The new carbene framework is a prototype for the development of a series of chiral N-heterocyclic carbenes. PMID:15387568

Metallinos, Costa; Barrett, Fred B; Chaytor, Jennifer L; Heska, Mary E A

2004-09-30

33

Fundamental spectroscopic studies of carbenes and hydrocarbon radicals  

SciTech Connect

Highly reactive carbenes and carbon-chain radicals are studied at millimeter wavelengths by observing their rotational spectra. The purpose is to provide definitive spectroscopic identification, accurate spectroscopic constants in the lowest vibrational states, and reliable structures of the key intermediates in reactions leading to aromatic hydrocarbons and soot particles in combustion.

Gottlieb, C.A.; Thaddeus, P. [Harvard Univ., Cambridge, MA (United States)

1993-12-01

34

Formal carbene insertion into C-C bond: Rh(I)-catalyzed reaction of benzocyclobutenols with diazoesters.  

PubMed

A Rh(I)-catalyzed formal carbene insertion into C-C bond of benzocyclobutenols has been realized by employing diazoesters as carbene precursors. The product indanol derivatives were obtained in good yields and in diastereoselective manner under mild reaction conditions. All-carbon quaternary center is constructed at the carbenic carbon. This catalytic reaction involves selective cleavage of C-C bond, Rh(I) carbene insertion, and intramolecular aldol reaction. PMID:24512084

Xia, Ying; Liu, Zhenxing; Liu, Zhen; Ge, Rui; Ye, Fei; Hossain, Mohammad; Zhang, Yan; Wang, Jianbo

2014-02-26

35

N-heterocyclic carbene-phosphinidyne transition metal complexes.  

PubMed

The N-heterocyclic carbene-phosphinidene adduct IPr?PSiMe3 is introduced as a synthon for the preparation of terminal carbene-phosphinidyne transition metal complexes of the type [(IPr?P)MLn ] (MLn =(?(6) -p-cymene)RuCl) and (?(5) -C5 Me5 )RhCl). Their spectroscopic and structural characteristics, namely low-field (31) P?NMR chemical shifts and short metal-phosphorus bonds, show their similarity with arylphosphinidene complexes. The formally mononegative IPr?P ligand is also capable of bridging two or three metal atoms as demonstrated by the preparation of bi- and trimetallic RuAu, RhAu, Rh2 , and Rh2 Au complexes. PMID:25287885

Doddi, Adinarayana; Bockfeld, Dirk; Bannenberg, Thomas; Jones, Peter G; Tamm, Matthias

2014-12-01

36

N-Heterocyclic Carbene Complexes in Additions to Multiple Bonds  

NASA Astrophysics Data System (ADS)

The use of N-heterocyclic carbene (NHC) complexes as homogeneous catalysts in addition reactions across carbon-carbon double and triple bonds and carbon-heteroatom double bonds is described. The discussion is focused on the description of the catalytic systems, their current mechanistic understanding and occasionally the relevant organometallic chemistry. The reaction types covered include hydrogenation, transfer hydrogenation, hydrosilylation, hydroboration and diboration, hydroamination, hydrothiolation, hydration, hydroarylation, allylic substitution, addition, chloroesterification and chloroacylation.

Danopoulos, Andreas A.

37

The halocarbenes: model systems for understanding the spectroscopy, dynamics and chemistry of carbenes  

Microsoft Academic Search

We review recent studies of the spectroscopy and dynamics of halocarbenes :CXY (X = H, F, Cl, Br, I; Y = F, Cl, Br, I), which are set forth as model systems for understanding the spectroscopy, photochemistry and photophysics of carbenes, and benchmarks for comparing experiment and theory concerning carbene singlet–triplet gaps and spin–orbit coupling from the limit of mixing

Scott H. Kable; Scott A. Reid; Trevor J. Sears

2009-01-01

38

Activation of carbon dioxide and carbon disulfide by a scandium N-heterocyclic carbene complex.  

PubMed

A Sc NHC complex readily activates three equivalents of CO2 showing 'Frustrated Lewis Pair' type reactivity with each metal-carbene bond, but whilst CS2 is also activated by the labile carbenes, no metal involvement is observed. PMID:24162511

Arnold, Polly L; Marr, Isobel A; Zlatogorsky, Sergey; Bellabarba, Ronan; Tooze, Robert P

2014-01-01

39

Volume 123, number 4 CHEMICAL PHYSICS LETTERS 17 January 1986 ELECTRONIC STATES OF CHROMIUM CARBENE IONS  

E-print Network

Volume 123, number 4 CHEMICAL PHYSICS LETTERS 17 January 1986 ELECTRONIC STATES OF CHROMIUM CARBENE,4] that the chromium carbene ion, CrCg, can be generated by reaction of electronically excited Cr+ with methane: Cr. Chromium ions are formed from 150 eV electron impact ionization of Cr(CD),. Reaction of excited-state Cr

Goddard III, William A.

40

The Depolymerization of Poly(Ethylene Terephthalate) (PET) Using N-Heterocyclic Carbenes from Ionic Liquids  

ERIC Educational Resources Information Center

The depolymerization of the plastic polyethylene terephthalate (PET or PETE) is described in this laboratory procedure. The transesterification reaction used to depolymerize PET employs a highly efficient N-heterocyclic carbene catalyst derived from a commercially available imidazolium ionic liquid. N-heterocyclic carbenes are potent nucleophilic…

Kamber, Nahrain E.; Tsujii, Yasuhito; Keets, Kate; Waymouth, Robert M.; Pratt, Russell C.; Nyce, Gregory W.; Hedrick, James L.

2010-01-01

41

Singlet 2-adamantylidene--an ambiphilic foiled carbene stabilized by hyperconjugation.  

PubMed

The EDA-NOCV analysis shows that the singlet 2-adamantylidene is a foiled-type carbene stabilized by the hyperconjugative interaction of one pair of the vicinal C-C ?-MOs with the empty p-orbital on the carbene carbon atom. The high proton affinity and hydride affinity indicate the ambiphilic nature of 2-adamantylidene. PMID:23939037

Rojisha, Vallyanga Chalil; Nijesh, Karikkeeriyil; De, Susmita; Parameswaran, Pattiyil

2013-10-01

42

1,2-migration in N-phosphano functionalized N-heterocyclic carbenes.  

PubMed

1,2-Migration of the phosphano-group to the carbene center in N-phosphano functionalized N-heterocyclic carbenes has been studied by density functional theory (DFT) calculations. An intramolecular mechanism with a three-center transition state structure seems to be most plausible for the isolated carbenes, while an intermolecular pathway catalyzed by azolium salts may be preferable for a migration proceeding in the course of generating the carbenes in situ. Our calculations show that amino-substitution at the phosphorus atom and an enhanced nucleophilicity of the heterocycle scaffold facilitate the phosphorus shift. Calculated singlet-triplet energy gaps do not correlate with thermodynamic stability of the studied carbenes and their disposition toward the 1,2-rearrangement. © 2014 Wiley Periodicals, Inc. PMID:25363134

Kirilchuk, Andrey A; Yurchenko, Aleksandr A; Kostyuk, Aleksandr N; Rozhenko, Alexander B

2015-01-01

43

On the stability of perfluoroalkyl-substituted singlet carbenes: a coupled-cluster quantum chemical study.  

PubMed

A series of trifluoromethyl-substituted carbenes R-C(:)-CF3 (R = NMe2, OMe, F, PMe2, P(NMe2)2, P(N(Pr-i)2)2, SMe, Cl); (dimethylamino)(perfluoroalkyl)carbenes Me2N-C(:)-R (R = CF3, C2F5, n-C3F7, i-C3F7, and t-C4F9) and symmetrically substituted carbenes R-C(:)-R (R = NMe2, OMe, F, PMe2, SMe, Cl) have been investigated by means of quantum chemistry methods. Different levels of approximation were used, including the CCSD(T) approach also known in quantum chemistry as the "golden standard", in combination with three different basis sets (TZVP, cc-pVDZ, cc-pVTZ). Relative stabilities of carbenes have been estimated using the differences between the singlet and triplet ground state energies (?EST) and energies of the hydrogenation reaction for the singlet and triplet ground states of the carbenes. The latter seem to correlate better with stability of carbenes than the ?EST values. The (13)C NMR chemical shifts of the methylidene carbon indicate the more high-field chemical shift values in the known, isolable carbenes compared to the unstable ones. This is the first report on the expected chemical shifts in the highly unstable singlet carbenes. Using these criteria, some carbene structures from the studied series (as, for instance, Me2N-C(:)-CF3, Me2N-C(:)-C3F7-i) are proposed as good candidates for the experimental preparation. PMID:24471524

Rozhenko, Alexander B; Schoeller, Wolfgang W; Leszczynski, Jerzy

2014-02-27

44

N-heterocyclic carbene Pt(II) complexes from caffeine: synthesis, structures and photoluminescent properties.  

PubMed

The caffeine-derived N-heterocyclic carbene (NHC) complex [Pt(II)(C^N)(NHC)Cl] (C^N = 2-phenylpyridine), 4 has the opposite stereochemistry and a shorter Pt-C(carbene) bond compared to that of an analogous benzimidazole-derived N,N-heterocyclic carbene (NNHC) Pt complex 2. These suggest a lower trans influence of pyridyl N compared to cyclometallated carbon and an increased Pt-NHC ?-backbonding because of decreased ?-donation resulting from conjugation to the electron deficient pyrimidine of caffeine. Complex 4 has a lower emission quantum yield (?) and is blue-shifted into the green region of the visible spectrum relative to non-carbene Pt(II) cyclometalated complex 5. PMID:21409198

Hu, Jian Jin; Bai, Shi-Qiang; Yeh, Hsiu Hsuan; Young, David J; Chi, Yun; Hor, T S Andy

2011-05-01

45

Small molecule activation using electropositive metal N-heterocyclic carbene complexes   

E-print Network

The versatility of N-heterocyclic carbenes (NHCs) is demonstrated by numerous practical applications in homogeneous transition metal catalysis, organocatalysis and materials science. There remains a paucity of electropositive ...

Turner, Zoe Rose

2011-06-27

46

Silver, mercury and ruthenium complexes of N-heterocyclic carbene linked cyclophanes.  

E-print Network

??This thesis describes the synthesis and isolation of silver, mercury, ruthenium and palladium complexes of bidentate N-heterocyclic carbenes (NHCs), derived from imidazolium-linked cyclophanes and related… (more)

Anwarul Haque, Rosenani S. M.

2007-01-01

47

Synthetic and catalytic studies of Group 11 N-heterocyclic carbene complexes  

E-print Network

This thesis presents the synthesis, structure and reactivity of two-coordinate Group 11 metal complexes, supported by N-heterocyclic carbene (NHC) ligands. The NHC ligand was found to stabilize monomeric, terminal fluoride ...

Laitar, David S. (David Stephen)

2006-01-01

48

Characterization of Tunable Radical Metal-Carbenes: Key Intermediates in Catalytic Cyclopropanation  

PubMed Central

A new class of radical metal-carbene complex has been characterized as having Fischer-like orbital interactions and adjacent ? acceptor stabilization. Density Functional Theory (DFT) along with Natural Bond Orbital (NBO) analysis and Charge Decomposition Analysis (CDA) has given insight into the electronics of this catalytic intermediate in an open-shell cobalt-porphyrin, [Co(Por)], system. The complex has a single bond from the metal to the carbene and has radical character with localized spin density on the carbene carbon. In addition, the carbene carbon is found to be nucleophilic and “tunable” through the introduction of different ?-carbon substituents. Finally, based on these findings, rational design strategies are proposed which should lead to the enhancement of catalytic activity. PMID:21643517

Belof, Jonathan L.; Cioce, Christian R.; Xu, Xue; Zhang, X. Peter; Space, Brian; Woodcock, H. Lee

2011-01-01

49

Stable Heterocyclopentane-1,3-diyls.  

PubMed

Diphosphadiazanediyl, [(?-NR)P]2 (R=Ter=2,6-dimesitylphenyl), is known to readily activate small molecules with multiple bonds. CO is an especially intriguing species for activation, because either 1,1- or 1,2-bridging mode would lead to a [1.1.1]bicycle or a carbene, respectively. The activation of CO with diphosphadiazanediyl already occurs at ambient temperatures (1?bar, 25?°C). However, CO is involved in an unprecedented ring expansion reaction under preservation of the biradical character, which leads to the formation of the first stable cyclopentane-1,3-diyl analogue displaying photochromic molecular switch characteristics. PMID:25604347

Hinz, Alexander; Schulz, Axel; Villinger, Alexander

2015-02-23

50

Quantitative description of structural effects on the stability of gold(I) carbenes.  

PubMed

The gas-phase bond-dissociation energies of a SO2 -imidazolylidene leaving group of three gold(I) benzyl imidazolium sulfone complexes are reported (E0 =46.6±1.7, 49.6±1.7, and 48.9±2.1?kcal?mol(-1) ). Although these energies are similar to each other, they are reproducibly distinguishable. The energy-resolved collision-induced dissociation experiments of the three [L]-gold(I) (L=ligand) carbene precursor complexes were performed by using a modified tandem mass spectrometer. The measurements quantitatively describe the structural and electronic effects a p-methoxy substituent on the benzyl fragment, and trans [NHC] and [P] gold ligands, have towards gold carbene formation. Evidence for the formation of the electrophilic gold carbene in solution was obtained through the stoichiometric and catalytic cyclopropanation of olefins under thermal conditions. The observed cyclopropane yields are dependent on the rate of gold carbene formation, which in turn is influenced by the ligand and substituent. The donation of electron density to the carbene carbon by the p-methoxy benzyl substituent and [NHC] ligand stabilizes the gold carbene intermediate and lowers the dissociation barrier. Through the careful comparison of gas-phase and solution chemistry, the results suggest that even gas-phase leaving-group bond-dissociation energy differences of 2-3?kcal?mol(-1) enormously affect the rate of gold carbene formation in solution, especially when there are competing reactions. The thermal decay of the gold carbene precursor complex was observed to follow first-order kinetics, whereas cyclopropanation was found to follow pseudo-first-order kinetics. Density-functional-theory calculations at the M06-L and BP86-D3 levels of theory were used to confirm the observed gas-phase reactivity and model the measured bond-dissociation energies. PMID:25236486

Ringger, David H; Kobylianskii, Ilia J; Serra, Daniel; Chen, Peter

2014-10-27

51

Oxidative Addition at a Carbene Center: Synthesis of an Iminoboryl-CAAC Adduct.  

PubMed

The reaction of a cyclic (alkyl)(amino)carbene (CAAC) with dichloro- and dibromobis(trimethylsilyl)aminoborane results in the formation of haloiminoborane-CAAC adducts. When the iodo analogue is used, an oxidative addition at the carbene center affords a cationic iminoboryl-CAAC adduct, featuring a boron-nitrogen triple bond. Similar salts are also obtained by halide abstraction from the chloro- and bromoiminoborane-CAAC adducts. The reactivity of all of these compounds towards CO2 is discussed. PMID:25414006

Dahcheh, Fatme; Stephan, Douglas W; Bertrand, Guy

2015-01-01

52

Computational assessment of non-heteroatom-stabilized carbene complexes reactivity: formation of oxazine derivatives.  

PubMed

A complete DFT-level mechanism elucidation of the two-step reaction of non-heteroatom-stabilized carbenes with imines, followed by addition of alkynes to yield oxazine derivatives, is presented. These compounds show different reactivity than the equivalent Fischer carbene complexes. A rationale of the experimental outcome is presented together with some suggestion for increasing the scope of the reaction, with special attention to the solvent effects in the regioselectivity. PMID:25389797

Funes-Ardoiz, Ignacio; Sampedro, Diego

2014-12-01

53

N-heterocyclic carbene-main-group chemistry: a rapidly evolving field.  

PubMed

This Award Article targets the evolving, yet surprisingly fruitful, chemistry of N-heterocyclic carbenes with low-oxidation-state main-group elements. Specifically, the chemistry of carbene-stabilized diatomic allotropes, diborenes, gallium octahedra, beryllium borohydride, and a host of related compounds will be presented. Providing a valuable historical perspective, the foundational work concerning the organometallic chemistry of gallium with sterically demanding m-terphenyl ligands from this laboratory will also be discussed. PMID:25343222

Wang, Yuzhong; Robinson, Gregory H

2014-11-17

54

N-Heterocyclic carbene metal complexes: photoluminescence and applications.  

PubMed

This review covers the advances made in the synthesis of luminescent transition metal complexes containing N-heterocyclic carbene (NHC) ligands. The presence of a high field strength ligand such as an NHC in the complexes gives rise to high energy emissions, and consequently, to the desired blue colour needed for OLED applications. Furthermore, the great versatility of NHC ligands for structural modifications, together with the use of other ancillary ligands in the complex, provides numerous possibilities for the synthesis of phosphorescent materials, with emission colours over the entire visible spectra and potential future applications in fields such as photochemical water-splitting, chemosensors, dye-sensitised solar cells, oxygen sensors, and medicine. PMID:24604135

Visbal, Renso; Gimeno, M Concepción

2014-05-21

55

Reactivity of a frustrated lewis pair and small-molecule activation by an isolable Arduengo carbene-B{3,5-(CF3)2C6H3}3 complex.  

PubMed

Tris[3,5-bis(trifluoromethyl)phenyl]borane reacts with the sterically demanding Arduengo carbenes 1,3-di-tert-butylimidazolin-2-ylidene and 1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene to form isolable normal adducts. In the case of 1,3-di-tert-butylimidazolin-2-ylidene, the adduct exhibits dynamic behaviour in solution and frustrated-Lewis-pair (FLP) reactivity. Fast cleavage of dihydrogen and THF, the C-H activation of phenylacetylene, and carbon dioxide fixation were achieved by using solutions of this adduct in benzene. This adduct is stable at room temperature in the absence of suitable substrates; however, thermal rearrangement into an abnormal carbene-borane adduct can be observed. In contrast, the 1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene adduct exhibits no evidence of FLP reactivity or of dissociation in solution. DFT calculations confirmed the experimental behaviour and stability of these carbene-borane adducts. PMID:23150467

Kolychev, Eugene L; Bannenberg, Thomas; Freytag, Matthias; Daniliuc, Constantin G; Jones, Peter G; Tamm, Matthias

2012-12-21

56

Synthesis of the first radiolabeled 188Re N-heterocyclic carbene complex and initial studies on its potential use in radiopharmaceutical applications.  

PubMed

A novel approach towards the synthesis of radiolabeled organometallic rhenium complexes is presented. We successfully synthesized and analyzed the first (188)Re-labeled N-heterocyclic biscarbene complex, trans-dioxobis(1,1'-methylene-bis(3,3'-diisopropylimidazolium-2-ylidene))(188)rhenium(V) hexafluorophosphate ((188)Re-4) via transmetalation using an air-stable and moisture-stable silver(I) biscarbene complex. In order to assess the viability of this complex as a potential lead structure for in vivo applications, the stability of the (188)Re-NHC complex was tested in physiologically relevant media. Ultimately, our studies illustrate that the complex we synthesized dissociates rapidly and is therefore unsuitable for use in radiopharmaceuticals. However, it is clear that the transmetalation approach we have developed is a rapid, robust, and mild method for the synthesis of new (188)Re-labeled carbene complexes. PMID:24889257

Wagner, Thomas; Zeglis, Brian M; Groveman, Sam; Hille, Claudia; Pöthig, Alexander; Francesconi, Lynn C; Herrmann, Wolfgang A; Kühn, Fritz E; Reiner, Thomas

2014-06-15

57

A diruthenium ?-carbido complex that shows singlet-carbene-like reactivity.  

PubMed

Low-temperature deprotonation of the cationic ?-methylidyne complex [(Cp*Ru)2(?-NPh)(?-CH)][BF4] (Cp* = ?(5)-C5Me5) with KN(SiMe3)2 affords a thermally unstable ?-carbido complex [(Cp*Ru)2(?-NPh)(?-C)] (2), as evidenced by trapping experiments with elemental S or Se and (13)C NMR spectroscopic observation. The reactivity of 2 toward CO2, Ph2S(+)CH2(-), EtOH, and an intramolecular C-H bond indicates that the ?-carbido carbon in 2 has an ambiphilic (nucleophilic and electrophilic) nature consistent with the formulation of 2 as the first example of a transition-metal-substituted singlet carbene. DFT study suggests that the Ru substituents in 2 are stronger ?-donor and weaker ?-donor to the carbene center than amino substituents in N-heterocyclic carbenes. PMID:25365114

Takemoto, Shin; Ohata, Jun; Umetani, Kento; Yamaguchi, Masahiro; Matsuzaka, Hiroyuki

2014-11-12

58

Synthesis and antimicrobial studies of silver N-heterocyclic carbene complexes bearing a methyl benzoate substituent  

PubMed Central

Due to the properties of silver as an antimicrobial, our research group has synthesized many different silver carbene complexes. Two new silver N-heterocyclic carbene complexes derived from 4,5-dichloroimidazole and theobromine bearing methyl benzoate substituents were synthesized by in situ carbene formation using silver acetate as the base in the reaction. The new compounds were fully characterized by several methods including NMR spectroscopy and X-ray crystallography. Preliminary antimicrobial efficacy studies against Pseudomonas aeruginosa, Staphylococcus aureus, and Escherichia coli were conducted. The results of this study demonstrated antimicrobial efficacy of the two complexes comparable to silver nitrate, showing their potential for use in the treatment of bacterial infections. PMID:21218156

Knapp, Amanda R.; Panzner, Matthew J.; Medvetz, Doug A.; Wright, Brian D.; Tessier, Claire A.; Youngs, Wiley J.

2010-01-01

59

A Continuum of Progress: Applications of N-Hetereocyclic Carbene Catalysis in Total Synthesis  

PubMed Central

N-Heterocyclic carbene (NHC) catalyzed transformations have emerged as powerful tactics for the construction of complex molecules. Since Stetter’s report in 1975 of the total synthesis of cis-jasmon and dihydrojasmon by using carbene catalysis, the use of NHCs in total synthesis has grown rapidly, particularly over the last decade. This renaissance is undoubtedly due to the recent developments in NHC-catalyzed reactions, including new benzoin, Stetter, homoenolate, and aroylation processes. These transformations employ typical as well as Umpolung types of bond disconnections and have served as the key step in several new total syntheses. This Minireview highlights these reports and captures the excitement and emerging synthetic utility of carbene catalysis in total synthesis. PMID:23074146

Izquierdo, Javier; Hutson, Gerri E.; Cohen, Daniel T.; Scheidt, Karl A.

2013-01-01

60

A Non-Diazo Approach to ?-Oxo Gold Carbenes via Gold-Catalyzed Alkyne Oxidation  

PubMed Central

For the past dozen years, homogeneous gold catalysis has evolved from a little known topic in organic synthesis to a fully blown research field of significant importance to synthetic practitioners, due to its novel reactivities and reaction modes. Cationic gold(I) complexes are powerful soft Lewis acids that can activate alkynes and allenes toward efficient attack by nucleophiles, leading to the generation of alkenyl gold intermediates. Some of the most versatile aspects of gold catalysis involve the generation of gold carbene intermediates, which occurs through the approach of an electrophile to the distal end of the alkenyl gold moiety, and their diverse transformations thereafter. On the other hand, ?-oxo metal carbene/carbenoids are highly versatile intermediates in organic synthesis and can undergo various synthetically challenging yet highly valuable transformations such as C–H insertion, ylide formation, and cyclopropanation reactions. Metal-catalyzed dediazotizations of diazo carbonyl compounds are the principle and most reliable strategy to access them. Unfortunately, the substrates contain a highly energetic diazo moiety and are potentially explosive. Moreover, chemists need to use energetic reagents to prepare them, putting further constrains on operational safety. In this Account, we show that the unique access to the gold carbene species in homogeneous gold catalysis offers an opportunity to generate ?-oxo gold carbenes if both nucleophile and electrophile are oxygen. Hence, this approach would enable readily available and safer alkynes to replace hazardous ?-diazo carbonyl compounds as precursors in the realm of gold carbene chemistry. For the past several years, we have demonstrated that alkynes can indeed effectively serve as precursors to versatile ?-oxo gold carbenes. In our initial study, we showed that a tethered sulfoxide can be a suitable oxidant, which in some cases leads to the formation of ?-oxo gold carbene intermediates. The intermolecular approach offers excellent synthetic flexibility because no tethering of the oxidant is required, and its reduced form is not tangled with the product. We were the first research group to develop this strategy, through the use of pyridine/quinolone N-oxides as the external oxidants. In this manner, we can effectively make a C–C triple bond a surrogate of an ?-diazo carbonyl moiety in various gold catalyses. With terminal alkynes, we demonstrated that we can efficiently trap exclusively formed terminal carbene centers by internal nucleophiles en route to the formation of cyclic products, including strained oxetan-3-ones and azetidin-3-ones, and by external nucleophiles when a P,N-bidentate ligand is coordinated to gold. With internal alkynes, we generated synthetically useful regioselectivities in the generation of the ?-oxo gold carbene moiety, which enables expedient formation of versatile enone products. Other research groups have also applied this strategy en route to versatile synthetic methods. The ?-oxo gold carbenes appear to be more electrophilic than their Rh counterpart, which many chemists have focused on in a large array of excellent work on metal carbene chemistry. The ease of accessing the reactive gold carbenes opens up a vast area for developing new synthetic methods that would be distinctively different from the known Rh chemistry and promises to generate a new round of “gold rush”. PMID:24428596

2015-01-01

61

Rotational spectrum and theoretical structure of the carbene HC4N  

NASA Astrophysics Data System (ADS)

Following a high-level coupled cluster calculation, the rotational spectrum of the bent HC4N singlet carbene was detected in a supersonic molecular beam by Fourier transform microwave spectroscopy. The three rotational constants, the leading centrifugal distortion constants, and two nitrogen hyperfine coupling constants were determined to high accuracy. The rotational constants agree with those calculated ab initio to better than 0.5%. Like the isoelectronic C5H2 carbene of similar structure, HC4N was found to have fairly large centrifugal distortion and a large inertial defect. The calculated dipole moment of HC4N is 2.95 D.

McCarthy, M. C.; Apponi, A. J.; Gordon, V. D.; Gottlieb, C. A.; Thaddeus, P.; Daniel Crawford, T.; Stanton, John F.

1999-10-01

62

Gold(I) Carbenes by Retro-Buchner Reaction: Generation and Fate  

PubMed Central

The fate of the aryl gold(I) carbenes generated by retro-Buchner reaction of ortho-substituted 7-aryl-1,3,5-cycloheptatrienes is dependent on the constitution of the ortho substituent. Indenes and fluorenes are obtained by intramolecular reaction of highly electrophilic gold(I) carbenes with alkenes and arenes. According to density functional theory calculations, the gold-catalyzed retro-Buchner process occurs stepwise, although the two carbon–carbon cleavages occur on a rather flat potential energy surface. PMID:24358986

2013-01-01

63

Stereoselective 1,3-Insertions of Rhodium(II) Azavinyl Carbenes  

PubMed Central

Rhodium(II) azavinyl carbenes, conveniently generated from 1-sulfonyl-1,2,3-triazoles, undergo a facile, mild and convergent formal 1,3-insertion into N–H and O–H bonds of primary and secondary amides, various alcohols, and carboxylic acids to afford a wide range of vicinally bis-functionalized Z-olefins with perfect regio- and stereoselectively. Utilizing the distinctive functionality installed through these reactions, a number of subsequent rearrangements and cyclizations expand the repertoire of valuable organic building blocks constructed by reactions of transition metal carbene complexes, including ?-allenyl ketones and amino-substituted heterocycles. PMID:24295389

Chuprakov, Stepan; Worrell, Brady T.; Selander, Nicklas; Sit, Rakesh K.; Fokin, Valery V.

2014-01-01

64

Two-coordinate Fe? and Co? complexes supported by cyclic (alkyl)(amino)carbenes.  

PubMed

The CAAC [CAAC=cyclic (alkyl)(amino)carbene] family of carbene ligands have shown promise in stabilizing unusually low-coordination number transition-metal complexes in low formal oxidation states. Here we extend this narrative by demonstrating their utility in affording access to the first examples of two-coordinate formal Fe(0) and Co(0) [(CAAC)2M] complexes, prepared by reduction of their corresponding two-coordinate cationic Fe(I) and Co(I) precursors. The stability of these species arises from the strong ?-donating and ?-accepting properties of the supporting CAAC ligands, in addition to steric protection. PMID:24953342

Ung, Gaël; Rittle, Jonathan; Soleilhavoup, Michele; Bertrand, Guy; Peters, Jonas C

2014-08-01

65

Intermolecular Dynamic Kinetic Resolution Cooperatively Catalyzed by an N-Heterocyclic Carbene and a Lewis Acid.  

PubMed

The ubiquitous structure of ?-lactones makes the development of new methods for their enantioselective and stereoselective synthesis an important ongoing challenge. The intermolecular dynamic kinetic resolution (DKR) of ?-halo-?-ketoesters cooperatively catalyzed by an N-heterocyclic carbene and a Lewis acid generates two contiguous stereocenters with remarkable diastereoselectivity through an oxidation/lactonization sequence. PMID:25447028

Wu, Zijun; Li, Fangyi; Wang, Jian

2014-11-28

66

How to make the ?0?2 singlet the ground state of carbenes.  

PubMed

Successful strategies have previously been developed to stabilize the ?(2)?(0) singlet states of carbenes, relative to ?(1)?(1) triplet states. However, little or no attention has been paid to the stabilization of the ?(0)?(2) singlet states. We present two simple strategies to stabilize the ?(0)?(2) singlet states of carbenes, relative to both the ?(2)?(0) singlet and ?(1)?(1) triplet states. These strategies consist of destabilization of the carbene ? orbital by two, adjacent, sp(2) nitrogen lone pairs of electrons and stabilization of the carbene 2p-? orbital by incorporating it into a five-membered ring, containing two double bonds, or into a six-membered ring, containing two double bonds and a sixth atom that has a low-lying empty ? orbital. B3LYP, CASPT2, and CCSD(T) calculations have been performed in order to assess the success of these strategies in creating derivatives of cyclopenta-2,4-dienylidene and cyclohexa-2,5-dienylidene with ?(0)?(6) singlet ground states. Differences between the calculated geometries and binding energies of the Xe complexes of the ?(0)?(6) singlet ground state of 2,5-diazacyclopentadienylidene (5) and the ?(2)?(0) singlet states of CH2 and CF2 are discussed. PMID:24007553

Chen, Bo; Rogachev, Andrey Yu; Hrovat, David A; Hoffmann, Roald; Borden, Weston Thatcher

2013-09-18

67

Hydrogenations at room temperature and atmospheric pressure with mesoionic carbene-stabilized borenium catalysts.  

PubMed

1,2,3-Triazolylidene-based mesoionic carbene boranes have been synthesized in a convenient one-pot protocol from the corresponding 1,2,3-triazolium salts, base, and borane. Borenium ions are obtained by hydride abstraction and serve as catalysts in mild hydrogenation reactions of imines and unsaturated N-heterocycles at ambient pressure and temperature. PMID:25586407

Eisenberger, Patrick; Bestvater, Brian P; Keske, Eric C; Crudden, Cathleen M

2015-02-16

68

Sterically driven synthesis of ruthenium and ruthenium-silver N-heterocyclic carbene complexes.  

PubMed

A straightforward and efficient synthetic route to novel Ru N-heterocyclic carbene (NHC) complexes by transmetallation of non-bulky silver NHC to ruthenium dicarbonyl tetraarylcyclopentadienone is described. The same procedure with sterically demanding NHC leads to unprecedented heterobimetallic Ru-Ag(NHC) complexes. PMID:25338159

Cesari, C; Conti, S; Zacchini, S; Zanotti, V; Cassani, M C; Mazzoni, R

2014-12-14

69

Mild and rational synthesis of palladium complexes comprising C(4)-bound N-heterocyclic carbenes.  

PubMed

Oxidative addition of pyridyl-functionalised 4-iodoimidazolium salts to palladium(0) gives catalytically active complexes in which the N-heterocyclic carbene is bound to the palladium(II) centre in a non-classical bonding mode via C(4). PMID:17283796

Kluser, Evelyne; Neels, Antonia; Albrecht, Martin

2006-11-21

70

Olefin Cyclopropanation and Carbon-Hydrogen Amination via Carbene and Nitrene  

E-print Network

Olefin Cyclopropanation and Carbon- Hydrogen Amination via Carbene and Nitrene Transfers Catalyzed ACKNOWLEDGEMENTS To my mentor and role model, Frances Arnold, whose career is proof that novel and useful research stages of this research project. To my parents and my brothers for their unconditional support. To Renata

Winfree, Erik

71

N-Heterocyclic Carbene Metal Complexes: Synthesis, Kinetics, Reactivity, and Recycling With Polymers  

E-print Network

the nature of NHC-silver(I) complexes. The NHC-silver(I) complex is an important synthetic intermediate as it can be used to prepare other NHC-metal complexes through transmetallation. The carbene carbon of an NHC-silver(I) complex in 13C NMR spectra...

Su, Haw-Lih

2012-10-19

72

N-heterocyclic carbene catalyzed reactions of ?-bromo-?,?-unsaturated aldehydes/?,?-dibromoaldehydes with 1,3-dinucleophilic reagents.  

PubMed

Carbenes ring true: N-Heterocyclic carbene (NHC) catalyzed reactions of ?-bromo-?,?-unsaturated aldehydes/?,?-dibromoaldehydes with 1,3-dinucleophilic reagents, such as 1,3-dicarbonyl compounds, ?-enamino ketones, and ?-enamino esters through umpolung processes gave functionalized 3,4-dihydropyranones and 3,4-dihydropyridinones. The availability of the starting materials, lack of external oxidant, and usefulness of the products make this strategy attractive. PMID:22259126

Yao, Changsheng; Wang, Donglin; Lu, Jun; Li, Tuanjie; Jiao, Weihui; Yu, Chenxia

2012-02-13

73

Synthesis, characterization and catalytic activity of saturated and unsaturated N-heterocyclic carbene iridium(i) complexes.  

PubMed

Both saturated and unsaturated N-benzyl substituted heterocyclic carbene (NHC) iridum(i) complexes were synthesized. The unsaturated carbene complex [(un-NHC-Bn)Ir(CO)(2)Cl] in the cis form was prepared via the carbene transfer from the corresponding silver complex to [Ir(COD)(2)Cl](2) followed by ligand substitution with CO, whereas the saturated complex was obtained via the transfer from (sat-NHC-Bn)W(CO)(5). The treatment of phosphines with (NHC)Ir(CO)(2)Cl complexes yielded the products with the phosphine ligand trans to the carbene moiety via substitution. X-Ray structural determination shows that distances of Ir-C((carbene)) in both (un-NHC-Bn)Ir(CO)(PR(3))Cl and (un-NHC-Bn)Ir(CO)(PR(3))Cl are essentially the same. Analyses of spectroscopic and crystal structural data of iridium complexes [(NHC)Ir(CO)(PR(3))Cl] and Vaska's complex show similar corresponding data in both types of complexes, suggesting that the studied NHC ligands and phosphines have similar bonding with Ir(i) metal center. All iridium complexes studied in this work illustrated their catalytically activity on N-alkylation of amine with alcohol via hydrogen transfer reduction. It appears no dramatic difference on the catalytic activity among these iridium carbene complexes; but the saturated carbene complex (sat-NHC-Bn)Ir(CO)(PR(3))Cl appears to be slightly more active. For example, the reaction of benzyl alcohol with aniline in the presence of catalyst (1 mol%) under basic conditions at 100 degrees C provided the secondary amine (N-benzylaniline) in 96% yield. PMID:19156280

Chang, Yung-Hung; Fu, Ching-Feng; Liu, Yi-Hong; Peng, Shei-Ming; Chen, Jwu-Ting; Liu, Shiuh-Tzung

2009-02-01

74

Metathesis copolymerization of norbornene with tert-Butylacetylene initiated by a tungsten carbene complex  

Microsoft Academic Search

Metathesis copolymerization of norbornene (NBE) with tert-butylacetylene (t-BA) at a feed ratio of 1:1 initiated by a tungsten carbene complex was investigated under various conditions. Results obtained from time-conversion curves indicated that the reactivity of tert-butylacetylene was several times greater than that of norbornene. The copolymer was obtained in a higher yield and a larger molar mass in the solvent

Der-Jang Liaw; Hao-Hsien Chiang; Bing-Hung Jin; En-Tang Kang

1996-01-01

75

NHC?SiCl4 : An Ambivalent Carbene-Transfer Reagent.  

PubMed

The addition of BCl3 to the carbene-transfer reagent NHC?SiCl4 (NHC=1,3-dimethylimidazolidin-2-ylidene) gave the tetra- and pentacoordinate trichlorosilicon(IV) cations [(NHC)SiCl3 ](+) and [(NHC)2 SiCl3 ](+) with tetrachloroborate as counterion. This is in contrast to previous reactions, in which NHC?SiCl4 served as a transfer reagent for the NHC ligand. The addition of BF3 ?OEt2 , on the other hand, gave NHC?BF3 as the product of NHC transfer. In addition, the highly Lewis acidic bis(pentafluoroethyl)silane (C2 F5 )2 SiCl2 was treated with NHC?SiCl4 . In acetonitrile, the cationic silicon(IV) complexes [(NHC)SiCl3 ](+) and [(NHC)2 SiCl3 ](+) were detected with [(C2 F5 )SiCl3 ](-) as counterion. A similar result was already reported for the reaction of NHC?SiCl4 with (C2 F5 )2 SiH2 , which gave [(NHC)2 SiCl2 H][(C2 F5 )SiCl3 ]. If the reaction medium was changed to dichloromethane, the products of carbene transfer, NHC?Si(C2 F5 )2 Cl2 and NHC?Si(C2 F5 )2 ClH, respectively, were obtained instead. The formation of the latter species is a result of chloride/hydride metathesis. These compounds may serve as valuable precursors for electron-poor silylenes. Furthermore, the reactivity of NHC?SiCl4 towards phosphines is discussed. The carbene complex NHC?PCl3 shows similar reactivity to NHC?SiCl4 , and may even serve as a carbene-transfer reagent as well. PMID:25363673

Böttcher, Tobias; Steinhauer, Simon; Lewis-Alleyne, Lesley C; Neumann, Beate; Stammler, Hans-Georg; Bassil, Bassem S; Röschenthaler, Gerd-Volker; Hoge, Berthold

2015-01-01

76

N-heterocyclic carbene-catalyzed hydroacylation of unactivated double bonds.  

PubMed

An intramolecular N-heterocyclic carbene (NHC)-catalyzed hydroacylation of unactivated double bonds is reported. Systematic variation of the catalyst structure revealed an N-mesitylthiazolylidene annulated with a seven-membered ring to be especially reactive. This NHC enables a unique C-C bond-forming reaction to afford substituted chroman-4-ones in moderate to excellent yields, even ones containing all-carbon quaternary centers. PMID:19807174

Hirano, Keiichi; Biju, Akkattu T; Piel, Isabel; Glorius, Frank

2009-10-14

77

Ruthenium-catalyzed synthesis of functional conjugated dienes via addition of two carbene units to alkynes.  

PubMed

The reaction of a variety of alkynes with N(2)CHSiMe(3), in the presence of Cp*RuCl(cod) as the catalyst precursor, leads to the general formation of functional conjugated dienes. This selective formation results from the ruthenium-catalyzed creation of two carbon-carbon double bonds in a single step under mild conditions. Terminal alkynes produce 1,4-bistrimethylsilylbuta-1,3-dienes with Z stereoselectivity for the less hindered double bond whereas disubstituted alkynes favor E-configuration for the same double bond. Diynes react also as monoalkynes, and only one triple bond is transformed to give disilylated dienynes. The reaction can be applied to the in situ desilylation in methanol and formation of monosilylated dienes. The catalytic formation of 1,4-bisfunctional buta-1,3-dienes can also take place with N(2)CHCO(2)Et and N(2)CHPh. The reaction can be understood by addition of two carbene units to triple bonds. An initial [2 + 2] addition of the Ru=CHSiMe(3) bond with the alkyne triple bond leads to an alkenyl ruthenium-carbene species capable of coordinating a second carbene unit to produce conjugated dienes. PMID:20459106

Le Paih, Jacques; Vovard-Le Bray, Chloé; Dérien, Sylvie; Dixneuf, Pierre H

2010-06-01

78

Role of quantum mechanical tunneling on the ?-effect of silicon on carbenes in 3-trimethylsilylcyclobutylidene.  

PubMed

Quantum mechanical tunneling (QMT) is increasingly being realized as an important phenomenon that can enhance the rate of reactions even at room temperature. Recently, the ability of a trimethylsilane (TMS) group to activate 1,3-H shift to a carbene from a ?-position has been demonstrated. Direct dynamical calculations (using canonical varitational transition state theory) inclusive of small curvature tunneling (CVT-SCT) show that QMT plays a decisive role in such 1,3-hydrogen migration in both the presence and absence of TMS. The presence of a TMS group reduces the activation energy of 1,3-H shift reaction via 1,3-equatorial interaction of the TMS group with the carbene. Tunneling across the smaller barrier enhances the overall forward rate of the reaction. The Arrhenius plot for the reaction shows substantial curvature in comparison to the CVT mechanism at room temperature. Arrhenius plots for the kinetic isotope effects (KIEs) for the ?-deuterated and per deuterated 3-trimethylsilylcyclobutylidene also show strong deviations from the classical over the barrier mechanism. The magnitude of the KIE is suggestive of QMT from the vibrational excited states of the carbenes. PMID:24467461

Karmakar, Sharmistha; Datta, Ayan

2014-03-01

79

A Carbene-Stabilized Gold(I) Fluoride: Synthesis and David S. Laitar, Peter Muller, Thomas G. Gray,* and Joseph P. Sadighi*  

E-print Network

A Carbene-Stabilized Gold(I) Fluoride: Synthesis and Theory David S. Laitar, Peter Mu¨ller, Thomas, 2005 Summary: The first isolable gold(I) fluoride complex, stabilized by an N-heterocyclic carbene (NHC/d interactions between fluoride and gold(I) and indicate a substantial negative charge on fluorine. Fluoride

Müller, Peter

80

Fascinating frontiers of N/O-functionalized N-heterocyclic carbene chemistry: from chemical catalysis to biomedical applications.  

PubMed

The in vogue N-heterocyclic carbenes (NHCs) have attracted attention largely for its new found popularity in chemical catalysis and also for displaying promising traits in biomedical applications. The current perspective provides an account of our efforts in exploring the utility of N/O-functionalized N-heterocyclic carbenes in these two areas. On the catalysis front, we have employed the N/O-functionalized N-heterocyclic carbene based precatalysts for the C-C and C-N bond forming reactions like the Suzuki-Miyaura, Sonogashira and Hiyama cross-couplings, the base-free Michael addition, the alkene and alkyne hydroamination reactions and the ring-opening polymerization (ROP) of L-lactides that produce biodegradable polylactide polymers while on the biomedical application front, the anticancer and antimicrobial properties of these N/O-functionalized N-heterocyclic carbene complexes were evaluated. Towards this objective, the N-heterocyclic carbene chemistry of a variety of transition metals like Ag, Au, Ni and Pd has been investigated. PMID:20495733

John, Alex; Ghosh, Prasenjit

2010-08-21

81

Cationic bis-N-heterocyclic carbene (NHC) ruthenium complex: structure and application as latent catalyst in olefin metathesis.  

PubMed

An unexpected cationic bis-N-heterocyclic carbene (NHC) benzylidene ether based ruthenium complex (2 a) was prepared through the double incorporation of an unsymmetrical unsaturated N-heterocyclic carbene (U2 -NHC) ligand that bore an N-substituted cyclododecyl side chain. The isolation and full characterization (including X-ray diffraction studies) of key synthetic intermediates along with theoretical calculations allowed us to understand the mechanism of the overall cationization process. Finally, the newly developed complex 2 a displayed interesting latent behavior during ring-closing metathesis, which could be "switched on" under acidic conditions. PMID:25212827

Rouen, Mathieu; Queval, Pierre; Falivene, Laura; Allard, Jessica; Toupet, Loïc; Crévisy, Christophe; Caijo, Frédéric; Baslé, Olivier; Cavallo, Luigi; Mauduit, Marc

2014-10-13

82

Oxyanion steering and CH-? interactions as key elements in an N-heterocyclic carbene-catalyzed [4 + 2] cycloaddition.  

PubMed

The N-heterocyclic carbene catalyzed [4 + 2] cycloaddition has been shown to give ?,?-unsaturated ?-lactones in excellent enantio- and diastereoselectivity. However, preliminary computational studies of the geometry of the intermediate enolate rendered ambiguous both the origins of selectivity and the reaction pathway. Here, we show that a concerted, but highly asynchronous, Diels-Alder reaction occurs rather than the stepwise Michael-type or Claisen-type pathways. In addition, two crucial interactions are identified that enable high selectivity: an oxyanion-steering mechanism and a CH-? interaction. The calculations accurately predict the enantioselectivity of a number of N-heterocyclic carbene catalysts in the hetero-Diels-Alder reaction. PMID:22765294

Allen, Scott E; Mahatthananchai, Jessada; Bode, Jeffrey W; Kozlowski, Marisa C

2012-07-25

83

Gold-catalyzed tandem cycloisomerization/functionalization of in situ generated ?-oxo gold carbenes in water.  

PubMed

A gold-catalyzed tandem cycloisomerization/functionalization of in situ generated ?-oxo gold carbenes in water has been developed, which provides ready access to highly functionalized indole derivatives from o-alkynyl anilines and ynamides. Importantly, gold serves dual catalytic roles to mediate both the cycloisomerization of o-alkynyl anilines and the intermolecular oxidation of ynamides at the same time, thus providing a new type of concurrent tandem catalysis. The use of readily available starting materials, a simple procedure, and mild reaction conditions are other notable features of this method. PMID:25229883

Shen, Cang-Hai; Li, Long; Zhang, Wei; Liu, Shuang; Shu, Chao; Xie, Yun-Er; Yu, Yong-Fei; Ye, Long-Wu

2014-10-01

84

Conformational analysis of N , N ?-dinaphthyl heterocyclic carbenes: imidazol-2-ylidenes and imidazolin-2-ylidenes  

Microsoft Academic Search

\\u000a Abstract  The paths connecting the stationary points of tesseract (four-dimensional hypercube) have been explored. The minimum energy\\u000a conformations and the different transition states of N,N?-dinaphthyl imidazol-2-ylidenes and imidazolin-2-ylidenes have been calculated. The available experimental results were conveniently\\u000a reproduced. The dimerization of carbenes to enetetramines has also been calculated.\\u000a \\u000a \\u000a \\u000a \\u000a Graphical abstract   

Ibon Alkorta; José Elguero

85

Complexes of borane and N-heterocyclic carbenes: a new class of radical hydrogen atom donor.  

PubMed

Calculations suggest that complexes of borane with N-heterocyclic carbenes (NHC) have B-H bond dissocation energies more then 20 kcal/mol less than free borane, diborane, borane-THF, and related complexes. Values are in the range of popular radical hydrogen atom donors like tin hydrides (70-80 kcal/mol). The resulting prediction that NHC borane complexes could be used as radical hydrogen atom donors was verified by radical deoxygenations of xanthates by using either AIBN or triethylborane as initiator. PMID:18611014

Ueng, Shau-Hua; Brahmi, Malika Makhlouf; Derat, Etienne; Fensterbank, Louis; Lacôte, Emmanuel; Malacria, Max; Curran, Dennis P

2008-08-01

86

Optimized Syntheses of Cyclopentadienyl Nickel Chloride Compounds Containing "N"-Heterocyclic Carbene Ligands for Short Laboratory Periods  

ERIC Educational Resources Information Center

Experiments are described for the preparation of imidazolium chloride precursors to "N"-heterocyclic carbenes and their cyclopentadienyl nickel chloride derivatives. The syntheses have been optimized for second- and third-year undergraduate laboratories that have a maximum programmed length of three hours per week. The experiments are flexible and…

Cooke, Jason; Lightbody, Owen C.

2011-01-01

87

Conformational Analysis of Olefin-Carbene Ruthenium Metathesis Diego Benitez, Ekaterina Tkatchouk, and William A. Goddard III*  

E-print Network

Conformational Analysis of Olefin-Carbene Ruthenium Metathesis Catalysts Diego Benitez, Ekaterina of acenaphthalene. Ruthenium-catalyzed olefin metathesis1 has become a power- ful tool for forming organic carbon-Fock exchange) functional, the relative ruthenium tricyclohexylphosphine (PCy3) bond dissociation energies

Goddard III, William A.

88

Bis-mixed-carbene ruthenium-thiolate-alkylidene complexes: synthesis and olefin metathesis activity.  

PubMed

A series of bis-carbene Ru-hydride species, including (IMes)(Im(OMe)2)(PPh3)RuHCl () and (SIMes)(Me2Im(OMe)2)(PPh3)RuHCl () were prepared and subsequently shown to react with aryl-vinyl-sulfides to give the bis-carbene-alkylidene complexes: Im(OMe)2(SIMes)RuCl(SR)([double bond, length as m-dash]CHCH3) (R = p-FC6H4 (), p-(NO2)C6H4 ()), Im(OMe)2(IMes)RuCl([double bond, length as m-dash]CHCH3)(SPh) (), Me2Im(OMe)2(SIMes)RuCl([double bond, length as m-dash]CHCH3)(SPh) (), Im(OMe)2(SIMes)(F5C6S)RuCl([double bond, length as m-dash]CHR) (R = C4H9 (), C5H11 ()). The activity of these species in the standard Grubbs' tests for ring-opening metathesis polymerization, ring-closing and cross-metathesis are reported. Although these thiolate derivatives are shown to exhibit modest metathesis activities, the reactivity is enhanced in the presence of BCl3. PMID:25462569

Dahcheh, Fatme; Stephan, Douglas W

2014-12-23

89

Imidazolium hydrogen carbonates versus imidazolium carboxylates as organic precatalysts for N-heterocyclic carbene catalyzed reactions.  

PubMed

Imidazolium-2-carboxylates (NHC-CO(2) adducts, 3) and (benz)imidazolium hydrogen carbonates ([NHC(H)][HCO(3)], 4) were independently employed as organic precatalysts for various molecular N-heterocyclic carbene (NHC) catalyzed reactions. NHC-CO(2) adducts were obtained by carboxylation in THF of related free NHCs (2), while the synthesis of [NHC(H)][HCO(3)] precursors was directly achieved by anion metathesis of imidazolium halides (1) using potassium hydrogen carbonate (KHCO(3)) in methanolic solution, without the need for the prior preparation of free carbenes. Thermogravimetric analysis (TGA) and TGA coupled with mass spectrometry (TGA-MS) of most [NHC(H)][HCO(3)] precursors 4 showed a degradation profile in stages, with either a concomitant or a stepwise release of H(2)O and CO(2), between 108 and 280 °C, depending on the nature of the azolium and substituents. In solution, NHC generation from both [NHC(H)][HCO(3)] salts and NHC-CO(2) adducts could be achieved at room temperature, most likely by a simple solvation effect. Both types of precursors proved efficient for organocatalyzed molecular reactions, including cyanosilylation, benzoin condensation, and transesterification reactions. The catalytic efficiencies of NHC-CO(2) adducts 3 were found to be approximately 3 times higher than those of their [NHC(H)][HCO(3)] counterparts 4. PMID:23092332

Fèvre, Maréva; Coupillaud, Paul; Miqueu, Karinne; Sotiropoulos, Jean-Marc; Vignolle, Joan; Taton, Daniel

2012-11-16

90

Intramolecular cyclotrimerization of triynes catalyzed by N-heterocyclic carbene-CoCl2/Zn or -FeCl3/Zn.  

PubMed

[reaction: see text] Triynes 1 could effectively be cyclotrimerized to annulated benzenes 2 by treatment with a catalytic amount of zinc powder, N-heterocyclic carbene, and CoCl(2) or FeCl(3). PMID:15987206

Saino, Naoko; Kogure, Daisuke; Okamoto, Sentaro

2005-07-01

91

Di- and Trinuclear Gold Complexes of Diphenylphosphinoethyl-Functionalised Imidazolium Salts and their N-Heterocyclic Carbenes: Synthesis and Photophysical Properties.  

PubMed

Diphenylphosphinoethyl-functionalised imidazolium salts and their silver-carbene complexes were used to synthesise a series of di- and trinuclear gold complexes through ligand exchange and transmetallation, respectively. Besides a few positively charged macrocyclic compounds with different anions (both with and without activation of the carbene function), we were able to obtain neutral polynuclear complexes by varying the gold precursor. The synthesised gold complexes show a variety of photophysical properties, including bright white photoluminescence at ambient temperature. PMID:25377172

Bestgen, Sebastian; Gamer, Michael T; Lebedkin, Sergei; Kappes, Manfred M; Roesky, Peter W

2015-01-01

92

Ambient Stable Zwitterionic Perylene Bisimide-Centered Radical.  

PubMed

The unexpected introduction of a cationic imidazolium substituent in the 2-position of a tetrachloro-substituted perylene-3,4:9,10-tetracarboxylic acid bisimide (PBI) by the reaction of PBI-Cl4 1 with the N-heterocyclic carbene 1,3-di-iso-propyl-imidazolin-2-ylidene ((i) Pr2 Im 2) enables the isolation of an ambient stable zwitterionic radical. The remarkable stability of this unprecedented PBI-centered radical facilitates the complete characterization by several spectroscopic methods as well as single crystal structure analysis. Redox studies revealed that (i) Pr2 Im-PBI-Cl4 4 can be transferred reversibly to the corresponding anion and cation, respectively, even on a preparative scale. PMID:25393879

Schmidt, David; Bialas, David; Würthner, Frank

2014-11-12

93

Spectral, structural, and electrochemical properties of ruthenium porphyrin diaryl and aryl(alkoxycarbonyl) carbene complexes: influence of carbene substituents, porphyrin substituents, and trans-axial ligands.  

PubMed

A wide variety of ruthenium porphyrin carbene complexes, including [Ru(tpfpp)(CR(1)R(2))] (CR(1)R(2) = C(p-C(6)H(4)Cl)(2) 1 b, C(p-C(6)H(4)Me)(2) 1 c, C(p-C(6)H(4)OMe)(2) 1 d, C(CO(2)Me)(2) 1 e, C(p-C(6)H(4)NO(2))CO(2)Me 1 f, C(p-C(6)H(4)OMe)CO(2)Me 1 g, C(CH==CHPh)CO(2)CH(2)(CH==CH)(2)CH(3) 1 h), [Ru(por)(CPh(2))] (por=tdcpp 2 a, 4-Br-tpp 2 b, 4-Cl-tpp 2 c, 4-F-tpp 2 d, tpp 2 e, ttp 2 f, 4-MeO-tpp 2 g, tmp 2 h, 3,4,5-MeO-tpp 2 i), [Ru(por)[C(Ph)CO(2)Et

Li, Yan; Huang, Jie-Sheng; Xu, Guo-Bao; Zhu, Nianyong; Zhou, Zhong-Yuan; Che, Chi-Ming; Wong, Kwok-Yin

2004-07-19

94

Isolation of an imino-N-heterocyclic carbene/germanium(0) adduct: a mesoionic germylene equivalent.  

PubMed

An autoionization of germanium dichloride/dioxane complex with an imino-N-heterocyclic carbene ligand (L) afforded a novel germyliumylidene ion, [(L)GeCl](+)[GeCl3](-), which was fully characterized. Reduction of the germyliumylidene ion with potassium graphite produced a cyclic species [(L)Ge], which can be viewed as both a Ge(0) species and a mesoionic germylene. X-ray diffraction analysis and computational studies revealed one of the lone pairs on the Ge atom is involved in the ??system on the GeC2N2 five-membered ring. It was also confirmed that the nucleophilic behavior of [(L)Ge] as a two lone-pair donor. PMID:25283638

Su, Bochao; Ganguly, Rakesh; Li, Yongxin; Kinjo, Rei

2014-11-24

95

Evidence for the cyclic CN2 carbene in the gas phase.  

PubMed

3-Halodiazirine-3-carboxylic acids (c-CN2XCOOH, X = Cl or Br) were prepared from their esters and converted to the corresponding sodium salts. Collision-induced dissociation (CID) of the carboxylate ions led exclusively to the loss of CO2 and the resulting c-CN2X(-) ions dissociated to c-CN2 carbene at low energies. The bond dissociation energy (BDE) for c-CN2Br(-) was found to be less than 8 kcal/mol using CID of the anion generated by electrospray ionization of the carboxylate. The analogous difluoro system (CF2XCOOH/CF2X(-)/CF2) exhibits similar dissociative behavior. All experimental BDEs are in very good agreement with MP4/aug-cc-pVTZ calculations. PMID:25296289

Hanzlová, Eva; Vá?a, Ji?í; Shaffer, Christopher J; Roithová, Jana; Martin?, Tomáš

2014-10-17

96

Proton-induced generation of remote N-heterocyclic carbene-ru complexes.  

PubMed

The proton-induced Ru?C bond variation, which was previously found to be relevant in the water oxidation, has been investigated by using cyclometalated ruthenium complexes with three phenanthroline (phen) isomers. The designed complexes, [Ru(bpy)2 (1,5-phen)](+) ([2](+) ), [Ru(bpy)2 (1,6-phen)](+) ([3](+) ), and [Ru(bpy)2 (1,7-phen)](+) ([4](+) ) were newly synthesized and their structural and electronic properties were analyzed by various spectroscopy and theoretical protocols. Protonation of [4](+) triggered profound electronic structural change to form remote N-heterocyclic carbene (rNHC), whereas protonation of [2](+) and [3](+) did not affect their structures. It was found that changes in the electronic structure of phen beyond classical resonance forms control the rNHC behavior. The present study provides new insights into the ligand design of related ruthenium catalysts. PMID:25382152

Fukushima, Takashi; Fukuda, Ryoichi; Kobayashi, Katsuaki; Caramori, Giovanni F; Frenking, Gernot; Ehara, Masahiro; Tanaka, Koji

2015-01-01

97

Electrocatalytic Reduction of CO2 with Palladium Bis-N-heterocyclic Carbene Pincer Complexes.  

PubMed

A series of pyridine- and lutidine-linked bis-N-heterocyclic carbene (NHC) palladium pincer complexes were electrochemically characterized and screened for CO2 reduction capability with 2,2,2-trifluoroethanol, acetic acid, or 2,2,2-trifluoroacetic acid (TFA) as proton sources. The lutidine-linked pincer complexes electrocatalytically reduce CO2 to CO at potentials as low as -1.6 V versus Ag/AgNO3 in the presence of TFA. The one-electron reduction of these complexes is shown to be chemically reversible, yielding a monometallic species, with density functional theory studies indicating charge storage on the redox-active ligand, thus addressing a major source of deactivation in earlier triphosphine electrocatalysts. PMID:25337973

Therrien, Jeffrey A; Wolf, Michael O; Patrick, Brian O

2014-12-15

98

Exploiting Acyl and Enol Azolium Intermediates via NHeterocyclic Carbene Catalyzed Reactions of Alpha-Reducible Aldehydes  

PubMed Central

N-heterocyclic carbenes are well known for their role in catalyzing benzoin and Stetter reactions: the generation of acyl anion equivalents from simple aldehydes to react with a variety of electrophiles. However, when an aldehyde bearing a leaving group or unsaturation adjacent to the acyl anion equivalent is subjected to an NHC, a new avenue of reactivity is unlocked, leading to a number of novel transformations which can generate highly complex products from simple starting materials, many of which are assembled through unconventional bond disconnections. The field of these new reactions - those utilizing ?-reducible aldehydes to access previously unexplored catalytic intermediates – has expanded rapidly in the past eight years. This review aims to provide the reader with a historical perspective on the underlying discoveries that led to the current state of the art, a mechanistic description of these reactions, and a summary of the recent advances in this area. PMID:23538785

Vora, Harit U.; Wheeler, Philip

2013-01-01

99

Cyclic Alkyl Amino Carbene (CAAC) Ruthenium Complexes as Remarkably Active Catalysts for Ethenolysis.  

PubMed

An expanded family of ruthenium-based metathesis catalysts bearing cyclic alkyl amino carbene (CAAC) ligands was prepared. These catalysts exhibited exceptional activity in the ethenolysis of the seed-oil derivative methyl oleate. In many cases, catalyst turnover numbers (TONs) of more than 100?000 were achieved, at a catalyst loading of only 3?ppm. Remarkably, the most active catalyst system was able to achieve a TON of 340?000, at a catalyst loading of only 1?ppm. This is the first time a series of metathesis catalysts has exhibited such high performance in cross-metathesis reactions employing ethylene gas, with activities sufficient to render ethenolysis applicable to the industrial-scale production of linear ?-olefins (LAOs) and other terminal-olefin products. PMID:25522160

Marx, Vanessa M; Sullivan, Alexandra H; Melaimi, Mohand; Virgil, Scott C; Keitz, Benjamin K; Weinberger, David S; Bertrand, Guy; Grubbs, Robert H

2015-02-01

100

Systematic strategy for designing immidazolium containing precursors to produce N-heterocyclic carbenes: a DFT study.  

PubMed

A series of cationic N-heterocyclic carbene (NHC) precursors that can be utilized as fluorescent chemosensors for carbon dioxide capture were investigated by density functional theory (DFT) calculations. Activation energy barriers for the reactions of the cationic NHC precursors and hydrogen carbonate (HCO3(-)) based on intrinsic reaction coordinate (IRC) profiles as well as proton affinity of the precursors were compared. The calculated proton affinity of 1-ethyl-3-methylimidazol-2-yliene was in good agreement with experimental one within the margin of error. We clarified main factors to lower the activation energy barrier based on the correlation among the number of N-heterocyclic functional group, aromatic ring size, and structural characteristics for the candidate compounds. On the basis of the results, it was verified that some of our model systems spontaneously generate NHCs without any specific catalyst. PMID:25594878

Baek, Kyung Yup; Jo, Ji Hye; Moon, Jong Hun; Yoon, Juyoung; Lee, Jin Yong

2015-02-01

101

N-heterocyclic carbene formation induced fluorescent and colorimetric sensing of fluoride using perimidinium derivatives.  

PubMed

In this study, two perimidinium derivatives (1 and 2) were designed, synthesized, and developed as efficient fluorescent and colorimetric chemodosisensors for F(-) in DMSO or more competitive media (DMSO containing 10?% water). In the presence of F(-) , the yellow and non-fluorescent solution of 1/2 became colourless and exhibited strong blue fluorescence. This unique spectroscopic behaviour of 1/2 towards F(-) was attributed to the formation of N-heterocyclic carbene deprotonated by F(-) , which immediately reacted with water to give a colourless and fluorescent carbinol. Interestingly, it was found that this carbinol intermediate was unstable and further underwent a redox disproportionation to generate two other optically changed compounds. All the proposed mechanisms for the sensing process have been carefully confirmed by experiments. PMID:25346203

Zhang, Dawei; Yang, Haiqiang; Martinez, Alexandre; Jamieson, Kelsey; Dutasta, Jean-Pierre; Gao, Guohua

2014-12-15

102

Dimerisation, rhodium complex formation and rearrangements of N-heterocyclic carbenes of indazoles  

PubMed Central

Summary Deprotonation of indazolium salts at low temperatures gives N-heterocyclic carbenes of indazoles (indazol-3-ylidenes) which can be trapped as rhodium complexes (X-ray analysis). In the absence of Rh, the indazol-3-ylidenes spontaneously dimerize under ring cleavage of one of the N,N-bonds and ring closure to an indazole–indole spiro compound which possesses an exocyclic imine group. The E/Z isomers of the imines can be separated by column chromatography when methanol is used as eluent. We present results of a single crystal X-ray analysis of one of the E-isomers, which equilibrate in solution as well as in the solid state. Heating of the indazole–indole spiro compounds results in the formation of quinazolines by a ring-cleavage/ring-closure sequence (X-ray analysis). Results of DFT calculations are presented. PMID:24778738

Guan, Zong; Namyslo, Jan C; Drafz, Martin H H; Nieger, Martin

2014-01-01

103

Highly Stereoselective Synthesis of Cyclopentanes bearing Four Stereocenters by a Rhodium Carbene–Initiated Domino Sequence  

PubMed Central

Stereoselective synthesis of a cyclopentane nucleus by convergent annulations constitutes a significant challenge for synthetic chemists. Though a number of biologically relevant cyclopentane natural products are known, more often than not, the cyclopentane core is assembled in a stepwise fashion due to lack of efficient annulation strategies. Herein, we report the rhodium-catalyzed reactions of vinyldiazoacetates with (E)-1,3-disubstituted 2-butenols generate cyclopentanes, containing four new stereogenic centers with very high levels of stereoselectivity (99% ee, >97 : 3 dr). The reaction proceeds by a carbene–initiated domino sequence consisting of five distinct steps: rhodium–bound oxonium ylide formation, [2,3]-sigmatropic rearrangement, oxy-Cope rearrangement, enol–keto tautomerization, and finally an intramolecular carbonyl ene reaction. A systematic study is presented detailing how to control chirality transfer in each of the four stereo-defining steps of the cascade, consummating in the development of a highly stereoselective process. PMID:25082301

Parr, Brendan T.; Davies, Huw M. L.

2014-01-01

104

Photolysis of 4-chlororesorcinol in water: competitive formation of a singlet ketene and a triplet carbene.  

PubMed

Research on photoinduced reactions of halogenated phenols is of interest for environmental photochemistry and for synthetic organic chemistry. Previous studies have uncovered interesting mechanistic features, including ring contraction from benzene to cyclopentadiene from ortho derivatives and two-electron processes forming carbocations and carbenes from para derivatives. In the present work, we studied the aqueous photochemistry of 4-chlororesorcinol (1), which combines the conformational properties of both types of derivatives, using nanosecond transient absorption spectroscopy and photoproduct analysis. The absorption spectra obtained upon pulsed laser excitation of 1 showed the occurrence of both o-Cl and p-Cl elimination, the first observed transients being the ketene 3-hydroxy-6-fulvenone (2, ?(max) = 255 nm) and the carbene 2-hydroxy-4-oxo-2,5-cyclohexadienylidene (3, ?(max) = 405 and 395 nm). The reactivities of 2 and 3, the spectra of the secondary transients and the analysis of the final products showed that the two HCl elimination pathways take place concurrently. Most probably, the bifurcation step is the competition between intersystem crossing on the molecular level and o-Cl elimination on the singlet surface; p-Cl elimination proceeds on the triplet surface. Remarkably, the quantum yield of p-Cl elimination from 1 is lower by one order of magnitude compared to that found in para-halogenated phenols, while that of o-Cl elimination from 1 is comparable to ortho-halogenated phenol. To explain this result, we propose that o-Cl elimination is the major deactivation step, forming an intermediate singlet cation which is able to recombine to ground state 1, thereby limiting the observed photochemical quantum yields. PMID:20859579

Richard, Claire; Krajnik, Paul; Grabner, Gottfried

2010-11-14

105

A search for thermal isomerization of olefins to carbenes: Thermal generations of the silicon-nitrogen double bond  

SciTech Connect

The first part of this thesis will search for the thermal isomerization of olefins to carbenes which is predicted to be a high energy process by calculations and has only been observed in a few strained olefins. The possibility of thermal isomerization of simple olefins to carbenes will be explored. Substitution of a silyl group on the double bond of an olefin allows a potential intermediate which has a {beta}-radical to the silyl group during the cis-trans isomerization. The effects of a trimethylsilyl group on this isomerization are the subject of this study. The second part of this thesis will include the generation and chemistry of intermediates containing a silicon-nitrogen double bond. The isomerization of parent silanimine to the aminosilylene was calculated to be a high energy process. New approaches to the silicon-nitrogen double bond will also be presented. 92 refs., 12 figs., 11 tabs.

Zhang, Xianping.

1990-09-21

106

Role of gold(I) ?-oxo carbenes in the oxidation reactions of alkynes catalyzed by gold(I) complexes.  

PubMed

The gas phase structures of gold(I) complexes formed by intermolecular oxidation of selected terminal (phenylacetylene) and internal alkynes (2-butyne, 1-phenylpropyne, diphenylacetylene) were investigated using tandem mass spectrometry and ion spectroscopy in conjunction with quantum-chemical calculations. The experiments demonstrated that the primarily formed ?-gold(I) vinyloxypyridinium complexes readily undergo rearrangement, dependent on their substituents, to either gold(I) ?-oxo carbenenoids (a synthetic surrogate of the ?-oxo carbenes) or pyridine adducts of gold(I) enone complexes in the condensed phase and that the existence of naked ?-oxo carbenes is highly improbable. Isotopic labeling experiments performed with the reaction mixtures clearly linked the species that exist in solution to the ions transferred to the gas phase. The ions were then fully characterized by CID experiments and IRMPD spectroscopy. The conclusions based on the experimental observations perfectly correspond with the results from quantum-chemical calculations. PMID:25068382

Schulz, Ji?í; Jašíková, Lucie; Skríba, Anton; Roithová, Jana

2014-08-13

107

Efficient synthesis strategies by application of transition metal-catalyzed carbene/nitrene insertions into C-H bonds.  

PubMed

Transition metal-catalyzed insertion of carbenes and nitrenes into C-H bonds has become a powerful tool for the construction of C-C and C-N bonds in the synthesis of complex natural products. In this Highlight, a selection of syntheses are detailed involving the implementation of C-H insertion reactions leading to strategies marked by improved efficiency. PMID:24589531

Egger, Julian; Carreira, Erick M

2014-04-01

108

Preparation of a N-Heterocyclic Carbene Nickel(II) Complex: Synthetic Experiments in Current Organic and Organometallic Chemistry  

ERIC Educational Resources Information Center

A four-part experiment that leads to the synthesis of a cyclopentadienyl chloro-nickel(II) complex bearing a N-heterocyclic carbene (NHC) ligand is presented. In the first part, the preparation of 1,3-bis-(2,4,6-trimethylphenyl)imidazolium chloride (IMes[middle dot]HCl) in a one-pot procedure by reaction of 2,4,6-trimethylaniline with…

Ritleng, Vincent; Brenner, Eric; Chetcuti, Michael J.

2008-01-01

109

Catalytic boracarboxylation of alkynes with diborane and carbon dioxide by an N-heterocyclic carbene copper catalyst.  

PubMed

By the use of an N-heterocyclic carbene copper(I) complex as a catalyst, the boracarboxylation of various alkynes (e.g., diaryl alkynes, aryl/alkyl alkynes, and phenylacetylene) with a diborane compound and carbon dioxide has been achieved for the first time, affording the ?,?-unsaturated ?-boralactone derivatives regio- and stereoselectively via a borylcupration/carboxylation cascade. Some important reaction intermediates were isolated and structurally characterized to clarify the reaction mechanism. PMID:22909063

Zhang, Liang; Cheng, Jianhua; Carry, Béatrice; Hou, Zhaomin

2012-09-01

110

N-Heterocyclic carbene-palladium(II)-1-methylimidazole complex catalyzed Mizoroki-Heck reaction of aryl chlorides with styrenes.  

PubMed

A well-defined N-heterocyclic carbene-palladium(II)-1-methylimidazole [NHC-Pd(II)-Im] complex 1 was found to be an effective catalyst for the Mizoroki-Heck reaction of a variety of aryl chlorides with styrenes. Both activated and deactivated aryl chlorides work well to give the corresponding coupling products in good to excellent yields by using tetrabutylammonium bromide (TBAB) as the ionic liquid. PMID:23209531

Gao, Ting-Ting; Jin, Ai-Ping; Shao, Li-Xiong

2012-01-01

111

N-Heterocyclic carbene–palladium(II)-1-methylimidazole complex catalyzed Mizoroki–Heck reaction of aryl chlorides with styrenes  

PubMed Central

Summary A well-defined N-heterocyclic carbene–palladium(II)-1-methylimidazole [NHC-Pd(II)-Im] complex 1 was found to be an effective catalyst for the Mizoroki–Heck reaction of a variety of aryl chlorides with styrenes. Both activated and deactivated aryl chlorides work well to give the corresponding coupling products in good to excellent yields by using tetrabutylammonium bromide (TBAB) as the ionic liquid. PMID:23209531

Gao, Ting-Ting; Jin, Ai-Ping

2012-01-01

112

Multicomponent synthesis of chiral bidentate unsymmetrical unsaturated N-heterocyclic carbenes: copper-catalyzed asymmetric c?c bond formation.  

PubMed

A multicomponent strategy was applied to the synthesis of chiral bidentate unsaturated hydroxyalkyl- and carboxyalkyl-N-heterocyclic carbene (NHC) precursors. The newly developed low-cost chiral ligands derived from amino alcohols and amino acids were evaluated in copper-catalyzed asymmetric conjugated addition and asymmetric allylic alkylation, which afforded the desired tertiary and quaternary carbon stereocenters with excellent regio- and enantioselectivities (up to 99:1 e.r.). PMID:25421857

Jahier-Diallo, Claire; Morin, Marie S T; Queval, Pierre; Rouen, Mathieu; Artur, Isabelle; Querard, Pierre; Toupet, Loic; Crévisy, Christophe; Baslé, Olivier; Mauduit, Marc

2015-01-12

113

Gold (I) N-heterocyclic carbene complex inhibits mouse melanoma growth by p53 upregulation  

PubMed Central

Background Cancer treatment using gold (I) complexes is becoming popular. In this study, a gold (I) N-heterocyclic complex designated as complex 3 was synthesized, its cytotoxicity was examined, and its anti-melanoma activity was evaluated in vitro and in vivo. Methods Viability of cancer cells was determined by MTT assay upon treatment with various concentrations of a gold (I) N-heterocyclic carbene complex (complex 3) in a dose and time dependent manner. Mouse melanoma cells B16F10 were selected for further apoptotic studies, including flowcytometric analysis of annexin binding, cell cycle arrest, intracellular ROS generation and loss in the mitochondrial membrane potential. ELISA based assays were done for caspase activities and western blots for determining the expression of various survival and apoptotic proteins. Immunocytology was performed to visualize the translocation of p53 to the nucleus. B16F10 cells were inoculated into mice and post tumor formation, complex 3 was administered. Immunohistology was performed to determine the expressions of p53, p21, NF-?B (p65 and p50), MMP-9 and VEGF. Student’s t test was used for determining statistical significance. The survival rate data were analyzed by Kaplan-Meier plots. Results Complex 3 markedly inhibited the growth of HCT 116, HepG2, and A549, and induced apoptosis in B16F10 cells with nuclear condensation, DNA fragmentation, externalization of phosphatidylserine, activation of caspase 3 and caspase 9, PARP cleavage, downregulation of Bcl-2, upregulation of Bax, cytosolic cytochrome c elevation, ROS generation, and mitochondrial membrane potential loss indicating the involvement of an intrinsic mitochondrial death pathway. Further, upregulation of p53, p-p53 (ser 15) and p21 indicated the role of p53 in complex 3 mediated apoptosis. The complex reduced tumor size, and caused upregulation of p53 and p21 along with downregulation of NF-?B (p65 and p50), VEGF and MMP-9. These results suggest that it induced anti-melanoma effect in vitro and in vivo by modulating p53 and other apoptotic factors. Conclusions The gold (I) N-heterocyclic carbene complex (C22H26N6AuO2PF6) designated as complex 3 induced ROS and p53 dependent apoptosis in B16F10 cells involving the mitochondrial death pathway along with suppression of melanoma tumor growth by regulating the levels of pro and anti apoptotic factors (p53, p21, NF-?B, VEGF and MMP-9). PMID:24625085

2014-01-01

114

Nanofiber composites containing N-heterocyclic carbene complexes with antimicrobial activity  

PubMed Central

This report concerns nanofiber composites that incorporate N-heterocyclic carbenes and the use of such composites for testing antimicrobial and antifungal activities. The nanofiber composites were produced by electrospinning mixtures of the gold chloride or gold acetate complexes of a bis(imino)acenaphthene (BIAN)-supported NHC with aqueous solutions of polyvinyl alcohol (PVA). The products were characterized by scanning-electron microscopy, which revealed that nanofibers in the range of 250–300 nm had been produced. The biological activities of the nanofiber composites were tested against two Gram-positive bacteria, six Gram-negative bacteria, and two fungal strains. No activity was evident against the fungal strains. However, the gold chloride complex was found to be active against all the Gram-positive pathogens and one of the Gram-negative pathogens. It was also found that the activity of the produced nanofibers was localized and that no release of the bioactive compound from the nanofibers was evident. The demonstrated antimicrobial activities of these novel nanofiber composites render them potentially useful as wound dressings. PMID:22745545

Elzatahry, Ahmed A; Al-Enizi, Abdullah M; Elsayed, Elsayed Ahmed; Butorac, Rachel R; Al-Deyab, Salem S; Wadaan, Mohammad AM; Cowley, Alan H

2012-01-01

115

N-Heterocyclic Carbenes: Versatile Second Cyclometalated Ligands for Neutral Iridium(III) Heteroleptic Complexes.  

PubMed

With 2-(2,4-difluorophenyl)pyridine (dfppy) as the first cyclometalated ligand and different monoanionic N-heterocyclic carbenes (NHCs) as the second cyclometalated ligands, 16 blue or greenish-blue neutral iridium(III) phosphorescent complexes, (dfppy)2Ir(NHC), were synthesized efficiently. The obtained Ir(III) complexes display typical phosphorescence of 455-485 nm with quantum yields up to 0.73. By modifying the phenyl moiety in the NHCs with electron-withdrawing substituents (e.g., -F or -CF3) or replacing it with N-heteroaromatic rings (pyridine or pyrimidine), the HOMO-LUMO gaps are broadened, and the emissions shift to the more blue region accordingly. Furthermore, to extend the application scope of NHCs as the second cyclometalated ligands, five other Ir(III) complexes from blue to red were synthesized with different first cyclometalated ligands. Finally, the organic light-emitting diodes using one blue emitter exhibit a maximum current efficiency of 37.83 cd A(-1), an external quantum efficiency of 10.3%, and a maximum luminance of 8709 cd m(-2). Our results demonstrate that NHCs as the second cyclometalated ligands are good candidates for the achievement of efficient phosphorescent Ir(III) complexes and corresponding devices. PMID:25495711

Li, Tian-Yi; Liang, Xiao; Zhou, Liang; Wu, Chen; Zhang, Song; Liu, Xuan; Lu, Guang-Zhao; Xue, Li-Sha; Zheng, You-Xuan; Zuo, Jing-Lin

2015-01-01

116

Cytotoxic gold(I) N-heterocyclic carbene complexes with phosphane ligands as potent enzyme inhibitors.  

PubMed

Organometallic gold complexes with N-heterocyclic carbene (NHC) ligands have been demonstrating promising properties as novel anticancer agents. Gold(I) NHC complexes containing different phosphanes as secondary ligands were shown to trigger strong cytotoxic effects in cancer cells, and their effective uptake into the cells was quantified by atomic absorption spectroscopy. Moreover, the new compounds strongly inhibited the activity of the seleno-enzyme thioredoxin reductase (TrxR) and of the zinc-finger enzyme poly(ADP-ribose) polymerase?1 (PARP-1). In the case of TrxR inhibition, their activity depended clearly on the size of the alkyl/aryl residues of phosphorus atoms. Density functional theory (DFT) calculations showed that the Au-P bond of the triphenylphosphane complex [Au(I) (NHC)(PPh3 )]I had a lower bond dissociation energy compared to trialkylphosphane complexes [Au(I) (NHC)(PR3 )]I, indicating a higher kinetic reactivity of this particular compound. In fact, [Au(I) (NHC)(PPh3 )]I triggered an enhanced inhibitory activity against PARP-1. PMID:24677779

Rubbiani, Riccardo; Salassa, Luca; de Almeida, Andreia; Casini, Angela; Ott, Ingo

2014-06-01

117

Relativistic effects in the cationic platinum carbene PtCH + 2  

NASA Astrophysics Data System (ADS)

Fully relativistic four-component Dirac-Fock Coulomb calculations in conjunction with a second-order perturbational estimate for the correlation energy have been performed in benchmark calculations on geometric and electronic structures as well as the binding energy of the cationic platinum carbene complex PtCH+2. The relativistic stabilization of this species amounts to as much as 50 kcal/mol and the combination of relativistic and correlation effects shorten the Pt-C bond length by nearly 1 bohr, changing the bond order from one to two. The relative importance of spin-free and spin-dependent relativistic effects on the geometry, the electronic structure, and the binding energy is evaluated by comparison to the Douglas-Kroll method. Relativistic effective core potentials are shown to describe the spin-free effects reliably. The best theoretical estimate for the bond dissociation energy underestimates the experimental value by 13% due to truncation errors in the one- and n-particle space treatments. The mixed Hartree-Fock/density-functional method Becke3-Lee-Yang-Parr performs surprisingly well with respect to the structure and binding energy of the target molecule.

Heinemann, Christoph; Schwarz, Helmut; Koch, Wolfram; Dyall, Kenneth G.

1996-03-01

118

A highly conjugated benzimidazole carbene-based ruthenium sensitizer for dye-sensitized solar cells.  

PubMed

A new type of carbene-based ruthenium sensitizer, CB104, with a highly conjugated ancillary ligand, diphenylvinylthiophene-substituted benzimidazolepyridine, was designed and developed for dye-sensitized solar cell applications. The influence of the thiophene antenna on the performance of the cell anchored with CB104 was investigated. Compared with the dye CBTR, the conjugated thiophene in the ancillary ligand of CB104 enhanced the molar extinction coefficient of the intraligand ?-?* transition and the intensity of the lower energy metal-to-ligand charge-transfer band. However, the incident photon-to-current conversion efficiency spectrum of the cell anchored with CB104 (0.15?mM) showed a maximum of 63?% at 420?nm. The cell sensitized with the dye CB104 attained a power conversion efficiency of 7.30?%, which was lower than that of the cell with nonconjugated sensitizer CBTR (8.92?%) under the same fabrication conditions. The variation in the performance of these two dyes demonstrated that elongating the conjugated light-harvesting antenna resulted in the reduction of short-circuit photocurrent density, which might have been due to the aggregation of dye molecules. In the presence of a coabsorbate, chenodeoxycholic acid, the CB104-sensitized cell exhibited an enhanced photocurrent density and achieved a photovoltaic efficiency of 8.36?%. PMID:23832840

Ho, Shih-Yu; Su, Chaochin; Li, Chung-Yen; Prabakaran, Kumaresan; Shen, Ming-Tai; Chen, Ying-Fan; Chang, Wei-Chun; Tingare, Yogesh S; Akula, Suribabu; Tsai, Sheng-Han; Li, Wen-Ren

2013-09-01

119

Mechanism of ultrasound scission of a silver-carbene coordination polymer.  

PubMed

Scission of a supramolecular polymer-metal complex can be carried out using collapsing cavitation bubbles created by ultrasound. Although the most plausible scission mechanism of the coordinative bonds is through mechanical force, the influence of radicals and high hot-spot temperatures on scission has to be considered. A silver(I)-N-heterocyclic carbene complex was exposed to 20 kHz ultrasound in argon, nitrogen, methane, and isobutane saturated toluene. Scission percentages were almost equal under argon, nitrogen, and methane. Radical production differs by a factor of 10 under these gases, indicating that radical production is not a significant contributor to the scission process. A model to describe the displacement of the bubble wall, strain rates, and temperature in the gas shows that critical strain rates for coil-to-stretch transition, needed for scission, are achieved at reactor temperatures of 298 K, an acoustic pressure of 1.2 × 10(5) Pa, and an acoustic frequency of 20 kHz. Lower scission percentages were measured under isobutane, which also shows lower strain rates in model simulations. The activation of the polymer-metal complexes in toluene under the influence of ultrasound occurs through mechanical force. PMID:21827184

Rooze, Joost; Groote, Ramon; Jakobs, Robert T M; Sijbesma, Rint P; van Iersel, Maikel M; Rebrov, Evgeny V; Schouten, Jaap C; Keurentjes, Jos T F

2011-09-29

120

Stereoelectronic effects in C-H bond oxidation reactions of Ni(I) N-heterocyclic carbene complexes.  

PubMed

Activation of O2 by the three-coordinate Ni(I) ring-expanded N-heterocyclic carbene complexes Ni(RE-NHC)(PPh3)Br (RE-NHC = 6-Mes, 1; 7-Mes, 2) produced the structurally characterized dimeric Ni(II) complexes Ni(6-Mes)(Br)(?-OH)(?-O-6-Mes')NiBr (3) and Ni(7-Mes)(Br)(?-OH)(?-O-7-Mes')NiBr (4) containing oxidized ortho-mesityl groups from one of the carbene ligands. NMR and mass spectrometry provided evidence for further oxidation in solution to afford bis-?-aryloxy compounds; the 6-Mes derivative was isolated, and its structure was verified. Low-temperature UV-visible spectroscopy showed that the reaction between 1 and O2 was too fast even at ca. -80 °C to yield any observable intermediates and also supported the formation of more than one oxidation product. Addition of O2 to Ni(I) precursors containing a less electron-donating diamidocarbene (6-MesDAC, 7) or less bulky 6- or 7-membered ring diaminocarbene ligands (6- or 7-o-Tol; 8 and 9) proceeded quite differently, affording phosphine and carbene oxidation products (Ni(O?PPh3)2Br2 and (6-MesDAC)?O) and the mononuclear Ni(II) dibromide complexes (Ni(6-o-Tol)(PPh3)Br2 (10) and (Ni(7-o-Tol)(PPh3)Br2 (11)) respectively. Electrochemical measurements on the five Ni(I) precursors show significantly higher redox potentials for 1 and 2, the complexes that undergo oxygen atom transfer from O2. PMID:24972307

Poulten, Rebecca C; López, Isidoro; Llobet, Antoni; Mahon, Mary F; Whittlesey, Michael K

2014-07-21

121

Domino Michael addition-carbene rearrangement-cyclization reaction of 1-alkynyl(aryl)-lambda3-bromanes with 2-mercapto-1,3-benzazoles.  

PubMed

Exposure of 1-alkynyl[p-(trifluoromethyl)phenyl](tetrafluoroborato)-lambda3-bromanes to 2-mercaptobenzimidazole or benzothiazole in dichloromethane at 0 degrees C under argon resulted in a domino Michael addition-carbene rearrangement-cyclization reaction to produce directly tricyclic heterocycles in high yields, whereas the reaction with 2-mercaptobenzoxazole afforded 1-alkynyl sulfides. PMID:16220178

Ochiai, Masahito; Tada, Norihiro

2005-10-28

122

Controlled CO release using photochemical, thermal and electrochemical approaches from the amino carbene complex [(CO)?CrC(NC?H?)CH?].  

PubMed

Multimodal photo, thermal and electrochemical approaches toward CO release from the amino carbene complex [(CO)5CrC(NC4H8)CH3] is reported. Picosecond time resolved infrared spectroscopy was used to probe the photo-induced early state dynamics leading to CO release, and DFT calculations confirmed that CO release occurs from a singlet excited state. PMID:25188765

McMahon, Suzanne; Rochford, Jonathan; Halpin, Yvonne; Manton, Jennifer C; Harvey, Emma C; Greetham, Gregory M; Clark, Ian P; Rooney, A Denise; Long, Conor; Pryce, Mary T

2014-10-21

123

Rhenium and technetium tricarbonyl complexes of N-heterocyclic carbene ligands.  

PubMed

A strategy for the conjugation of N-heterocyclic carbene (NHC) ligands to biomolecules via amide bond formation is described. Both 1-(2-pyridyl)imidazolium or 1-(2-pyridyl)benzimidazolium salts functionalized with a pendant carboxylic acid group were prepared and coupled to glycine benzyl ester using 1-ethyl-3-(3-(dimethylamino)propyl)carbodiimide. A series of 10 rhenium(I) tricarbonyl complexes of the form [ReX(CO)3(?N)] (?N is a bidentate NHC ligand, and X is a monodentate anionic ligand: Cl(-), RCO2(-)) were synthesized via a Ag2O transmetalation protocol from the Re(I) precursor compound Re(CO)5Cl. The synthesized azolium salts and Re(I) complexes were characterized by elemental analysis and by (1)H and (13)C NMR spectroscopy, and the molecular structures for one imidazolium salt and seven Re(I) complexes were determined by single-crystal X-ray diffraction. (1)H NMR and mass spectrometry studies for an acetonitrile-d3 solution of [ReCl(CO)3(1-(2-pyridyl)-3-methylimidazolylidene)] show that the monodentate chloride ligand is labile and exchanges with this solvent yielding a cationic acetonitrile adduct. For the first time the labeling of an NHC ligand with technetium-99m is reported. Rapid Tc-99m labeling was achieved by heating the imidazolium salt 1-(2-pyridyl)-3-methylimidazolium iodide and Ag2O in methanol, followed by the addition of fac-[(99m)Tc(OH2)3(CO)3](+). To confirm the structure of the (99m)Tc-labeled complex, the equivalent (99)Tc complex was prepared, and mass spectrometric studies showed that the formed Tc complexes are of the form [(99m/99)Tc(CH3CN)(CO)3(1-(2-pyridyl)-3-methylimidazolylidene)](+) with an acetonitrile molecule coordinated to the metal center. PMID:25280253

Chan, Chung Ying; Pellegrini, Paul A; Greguric, Ivan; Barnard, Peter J

2014-10-20

124

Aerosolized Antimicrobial Agents Based on Degradable Dextran Nanoparticles Loaded with Silver Carbene Complexes  

PubMed Central

Degradable acetalated dextran (Ac-DEX) nanoparticles were prepared and loaded with a hydrophobic silver carbene complex (SCC) by a single-emulsion process. The resulting particles were characterized for morphology and size distribution using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and dynamic light scattering (DLS). The average particle size and particle size distribution were found to be a function of the ratio of the organic phase to the surfactant containing aqueous phase with a 1:5 volume ratio of Ac-DEX CH2Cl2 (organic): PBS (aqueous) being optimal for the formulation of nanoparticles with an average size of 100 ± 40 nm and a low polydispersity. The SCC loading was found to increase with an increase in the SCC quantity in the initial feed used during particle formulation up to 30% (w/w); however, the encapsulation efficiency was observed to be the best at a feed ratio of 20% (w/w). In vitro efficacy testing of the SCC loaded Ac-DEX nanoparticles demonstrated their activity against both Gram-negative and Gram-positive bacteria; the nanoparticles inhibited the growth of every bacterial species tested. As expected, a higher concentration of drug was required to inhibit bacterial growth when the drug was encapsulated within the nanoparticle formulations compared with the free drug illustrating the desired depot release. Compared with free drug, the Ac-DEX nanoparticles were much more readily suspended in an aqueous phase and subsequently aerosolized, thus providing an effective method of pulmonary drug delivery. PMID:23025592

Ornelas-Megiatto, Cátia; Shah, Parth N.; Wich, Peter R.; Cohen, Jessica L.; Tagaev, Jasur A.; Smolen, Justin A.; Wright, Brian D.; Panzner, Matthew J.; Youngs, Wiley J.; Fréchet, Jean M. J.; Cannon, Carolyn L.

2012-01-01

125

Aerosolized antimicrobial agents based on degradable dextran nanoparticles loaded with silver carbene complexes.  

PubMed

Degradable acetalated dextran (Ac-DEX) nanoparticles were prepared and loaded with a hydrophobic silver carbene complex (SCC) by a single-emulsion process. The resulting particles were characterized for morphology and size distribution using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and dynamic light scattering (DLS). The average particle size and particle size distribution were found to be a function of the ratio of the organic phase to the surfactant containing aqueous phase with a 1:5 volume ratio of Ac-DEX CH(2)Cl(2) (organic):PBS (aqueous) being optimal for the formulation of nanoparticles with an average size of 100 ± 40 nm and a low polydispersity. The SCC loading was found to increase with an increase in the SCC quantity in the initial feed used during particle formulation up to 30% (w/w); however, the encapsulation efficiency was observed to be the best at a feed ratio of 20% (w/w). In vitro efficacy testing of the SCC loaded Ac-DEX nanoparticles demonstrated their activity against both Gram-negative and Gram-positive bacteria; the nanoparticles inhibited the growth of every bacterial species tested. As expected, a higher concentration of drug was required to inhibit bacterial growth when the drug was encapsulated within the nanoparticle formulations compared with the free drug illustrating the desired depot release. Compared with free drug, the Ac-DEX nanoparticles were much more readily suspended in an aqueous phase and subsequently aerosolized, thus providing an effective method of pulmonary drug delivery. PMID:23025592

Ornelas-Megiatto, Cátia; Shah, Parth N; Wich, Peter R; Cohen, Jessica L; Tagaev, Jasur A; Smolen, Justin A; Wright, Brian D; Panzner, Matthew J; Youngs, Wiley J; Fréchet, Jean M J; Cannon, Carolyn L

2012-11-01

126

Chelated Bis-N-heterocyclic Carbene Platinum and Palladium Units as Tunable Components of Multinuclear Complexes.  

PubMed

Heterometallic trinuclear M2M' complexes (M = Rh, Ir; M' = Pt, Pd) containing a platinum or palladium moiety with chelated bis-N-heterocyclic carbene ligands, [(MCp*)2{M'(bisNHC-Cn-R)}(?3-S)2](BPh4)2 (M = Rh, Ir; M' = Pt, Pd; bisNHC-Cn-R = methylene-, ethylene-, or propylene-bridged bis(N-alkyl-imidazolylidene)), were synthesized by reacting bis(hydrosulfido)platinum(II) or palladium(II) complexs with bisNHC-Cn-R and hydroxo-bridged dinuclear complexes [(MCp*)2(?-OH)3](BPh4), whose dinuclear structures remained intact during the formation of the trinuclear complexes, which was confirmed by using electrospray mass spectrometry and NMR spectroscopy. The heterometallic trinuclear M2M' complexes with a variety of alkylene bridges in bisNHC-Cn-R showed two reversible reduction waves in the cyclic voltammogram, and the second reduction potentials were affected by the alkylene chain lengths, which caused different dihedral angles between the imidazolylidene rings and the coordination plane of the platinum or palladium center. The M2M' complexes, except for those containing the platinum unit with the ethylene-bridged bisNHC ligands, showed dynamic behavior in solution due to the flapping wing motion of the NHC ligand moieties. Although activation parameters obtained from line-shape analyses on variable-temperature NMR spectra of the complexes suggested that the flapping wing motion occurred without bond cleavage, large negative ?S(‡) values were obtained for the complexes with the palladium unit with the ethylene-bridged ligand, suggesting that the Pd-Ccarbene bond cleavage, accompanied by coordination of solvent molecules, occurred. PMID:25563064

Maeda, Yuri; Hashimoto, Hideki; Kinoshita, Isamu; Nishioka, Takanori

2015-01-20

127

A versatile approach for the immobilization of amines via copper-free “click” reaction between azido self-assembled monolayer and alkynyl Fischer carbene complex. Application to the detection of staphylococcal enterotoxin A antibody  

Microsoft Academic Search

A copper-free “click” reaction between an azido-terminated self-assembled monolayer (SAM) chemisorbed on planar gold-coated glass sensors and an alkynyl Fischer carbene complex yielded functionalized surfaces onto which facile and swift grafting of amine-containing molecules was achieved via aminolysis of the Fischer carbene moieties. The course of this process was conveniently monitored by Polarization-Modulation Infrared Reflection-Absorption Spectroscopy (PM-IRRAS), contact angle measurements

Pratima Srivastava; Amitabha Sarkar; Sudeshna Sawoo; Amarnath Chakraborty; Piyali Dutta; Othman Bouloussa; Christophe Méthivier; Claire-Marie Pradier; Souhir Boujday; Michèle Salmain

2011-01-01

128

Au(I) and Au(III) complexes of a sterically bulky benzimidazole-derived N-heterocyclic carbene  

Microsoft Academic Search

The reaction of [AuCl(SMe2)] with in situ generated [AgCl(iPr2-bimy)] (iPr2-bimy=1,3-diisopropylbenzimidazolin-2-ylidene), which in turn was obtained by the reaction of Ag2O with 1,3-diisopropylbenzimidazolium bromide (iPr2-bimyH+Br?, A), afforded the monocarbene Au(I) complex [AuCl(iPr2-bimy)] (1). Subsequent reaction of 1 and the ligand precursor iPr2-bimyH+BF4?, (B) in acetone in the presence of K2CO3 yielded the bis(carbene) complex [Au(iPr2-bimy)2]BF4 (2) as a white powder in

Ramasamy Jothibasu; Han Vinh Huynh; Lip Lin Koh

2008-01-01

129

Electronic structure and slow magnetic relaxation of low-coordinate cyclic alkyl(amino) carbene stabilized iron(I) complexes.  

PubMed

Cyclic alkyl(amino) carbene stabilized two- and three-coordinate Fe(I) complexes, (cAAC)2FeCl (2) and [(cAAC)2Fe][B(C6F5)4] (3), respectively, were prepared and thoroughly studied by a bouquet of analytical techniques as well as theoretical calculations. Magnetic susceptibility and Mössbauer spectroscopy reveal the +1 oxidation state and S = 3/2 spin ground state of iron in both compounds. 2 and 3 show slow magnetic relaxation typical for single molecule magnets under an applied direct current magnetic field. The high-frequency EPR measurements confirm the S = 3/2 ground state with a large, positive zero-field splitting (?20.4 cm(-1)) and reveal easy plane anisotropy for compound 2. CASSCF/CASPT2/RASSI-SO ab initio calculations using the MOLCAS program package support the experimental results. PMID:25072104

Samuel, Prinson P; Mondal, Kartik Chandra; Amin Sk, Nurul; Roesky, Herbert W; Carl, Elena; Neufeld, Roman; Stalke, Dietmar; Demeshko, Serhiy; Meyer, Franc; Ungur, Liviu; Chibotaru, Liviu F; Christian, Jonathan; Ramachandran, Vasanth; van Tol, Johan; Dalal, Naresh S

2014-08-27

130

The stable marriage problem  

Microsoft Academic Search

The original work of Gale and Shapley on an assignment method using the stable marriage criterion has been extended to find all the stable marriage assignments. The algorithm derived for finding all the stable marriage assignments is proved to satisfy all the conditions of the problem. Algorithm 411 applies to this paper.

D. G. McVitie; L. B. Wilson

1971-01-01

131

Coupling of Fischer carbene complexes with conjugated enediynes featuring radical traps; Novel structure and reactivity features of chromium complexed arene diradical species  

PubMed Central

The reaction of Fischer carbene complexes with conjugated enediynes that feature a pendant alkene group has been examined. The reaction proceeds through carbene-alkyne coupling to generate an enyne-ketene intermediate. This intermediate then undergoes Moore cyclization to generate a chromium complexed arene diradical, which then undergoes cyclization with the pendant alkene group. The radical cyclization prefers the 6-endo mode unless radical-stabilizing groups are present to favor the 5-exo mode. The intermediate diradical species were evaluated computationally in both the singlet and triplet configurations. Arene triplet diradicals feature minimal spin density at oxygen and delocalization to chromium. The 6-endo cyclization product was kinetically and thermodynamically favored. PMID:19838290

Zhang, Yi; Irshaidat, Tareq; Wang, Haixia; Waynant, Kris V.; Wang, Haobin; Herndon, James W.

2008-01-01

132

An Electronic Rationale for Observed Initiation Rates in Ruthenium-Mediated Olefin Metathesis: Charge Donation in Phosphine And N-Heterocyclic Carbene Ligands  

SciTech Connect

Ru K-edge XAS data indicate that second generation ruthenium-based olefin metathesis precatalysts (L = N-heterocyclic carbene) possess a more electron-deficient metal center than in the corresponding first generation species (L = tricyclohexylphosphine). This surprising effect is also observed from DFT calculations and provides a simple rationale for the slow phosphine dissociation kinetics previously noted for second-generation metathesis precatalysts.

Getty, K.; Delgado-Jaime, M.U.; Kennepohl, P.

2009-06-01

133

Exploring a unique reactivity of N-heterocyclic carbenes (NHC) in rhodium(III)-catalyzed intermolecular C-H activation/annulation.  

PubMed

Disclosed herein is the unique conjugative role of N-heterocyclic carbene (NHC) ligands as a directing group in aromatic C-H activation, coupled with a facile NHC-alkenyl annulative reductive elimination which guided the Rh(III)-catalyzed intermolecular annulations of imidazolium salts and alkynes under ambient conditions leading to structurally important imidazo[1,2-a]quinolinium motifs. PMID:25331451

Ghorai, Debasish; Choudhury, Joyanta

2014-12-14

134

N-heterocyclic carbene catalyzed annulation of benzofuran-2,3-diones and enals: a concise synthesis of spiro-bis-lactone.  

PubMed

The N-heterocyclic carbene catalyzed annulation of benzofuran-2,3-diones and enals via homoenolate intermediates is described. The reaction provided a direct and efficient method for the synthesis of spiro-bis-lactones. The ketone-carbonyl group annulated products and the ester-carbonyl group annulated products can be obtained as major products with good yields by convenient catalyst regulation. Furthermore, commercially available thiazolium salt can also catalyze this reaction with modest yield. PMID:23868545

Wang, Ze-Dong; Wang, Feng; Li, Xin; Cheng, Jin-Pei

2013-09-14

135

On the mechanism of N-heterocyclic carbene-catalyzed reactions involving acyl azoliums.  

PubMed

Catalytic reactions promoted by N-heterocyclic carbenes (NHCs) have exploded in popularity since 2004 when several reports described new fundamental reactions that extended beyond the long-studied generation of acyl anion equivalents. These new NHC-catalyzed reactions allow chemists to generate unique reactive species from otherwise inert starting materials, all under simple, mild reaction conditions and with exceptional selectivities. In analogy to transition metal catalysis, the use of NHCs has introduced a new set of elementary steps that operate via discrete reactive species, including acyl anion, homoenolate, and enolate equivalents, usually generated by oxidation state reorganization ("redox neutral" reactions). Nearly all NHC-catalyzed reactions offer operationally simple reactions, proceed at room temperature without the need for stringent exclusion of air, and do not generate reaction byproducts. Variation of the catalyst or reaction conditions can profoundly influence reaction outcomes, and researchers can tune the desired selectivities through careful choice of NHC precursor and base. The catalytically generated homoenolate and enolate equivalents are nucleophilic species. In contrast, the catalytically generated acyl azolium and ?,?-unsaturated acyl azoliums are electrophilic cationic species with unique and unprecedented chemistry. For example, when generated catalytically, these species transformed an ?-functionalized aldehyde to an ester under redox neutral conditions without coupling reagents or waste. In addition to providing new approaches to catalytic esterifications, acyl azoliums offer unique reactivities that chemists can exploit for selective reactions. This Account focuses on the discovery and mechanistic investigation of the catalytic generation of acyl azoliums and ?,?-unsaturated acyl azoliums. These chemical species are fascinating, and their catalytic generation is an important development. Studies of their unusual chemistry, however, date back to the intense investigation of thiamine-dependent enzymatic processes in the 1960s. Acyl azoliums are remarkably reactive in acylation chemistry and are unusually chemoselective. These two properties have led to a new wave of reactions such as redox esterification reaction (1) and the catalytic kinetic resolution of challenging substrates (i.e., 3). Our group and others have also developed methods to generate and exploit ?,?-unsaturated acyl azoliums, which have facilitated new C-C bond-forming annulations, including a catalytic, enantioselective variant of the Claisen rearrangement (2). From essentially one class of catalysts, the N-mesityl derived triazolium salts, researchers can easily prepare highly enantioenriched dihydropyranones and dihydropyridinones. Although this field is now one of the most explored areas of enantioselective C-C bond forming reactions, many mechanistic details remained unsolved and in dispute. In this Account, we address the mechanistic inquiries about the characterization of the unsaturated acyl triazolium species and its kinetic profile under catalytically relevant conditions. We also provide explanations for the requirement and effect of the N-mesityl group in NHC catalysis based on detailed experimental data within given specific reactions or conditions. We hope that our studies provide a roadmap for catalyst design/selection and new reaction discovery based on a fundamental understanding of the mechanistic course of NHC reactions. PMID:24410291

Mahatthananchai, Jessada; Bode, Jeffrey W

2014-02-18

136

Cooperativity of anion⋯? and ?⋯? interactions regulates the self-assembly of a series of carbene proligands: Towards quantitative analysis of intermolecular interactions with Hirshfeld surface  

NASA Astrophysics Data System (ADS)

The cooperative effect of weak non-covalent forces between anions and electron deficient aromatics by ?⋯? stacking of a series of carbene proligands (1-3) have been thoroughly explored by crystallographic studies. Structural analysis revealed that the anion⋯? and ?⋯? interactions along with intermolecular hydrogen bonding mutually cooperate to facilitate the assembling of the supramolecular framework. The ?⋯? and corresponding anion⋯? interactions have been investigated in the title carbene proligands despite their association with counter ions. The presence of the anion in the vicinity of the ?-system leads to the formation of anion⋯?/?⋯?/?⋯anion network for an inductive stabilization of the assemblies. To assess the dimensionality of the supramolecular framework consolidated by cooperative anion⋯?/?⋯? interactions and hydrogen bonding, different substituent effects in the carbene backbone have been considered to tune these interactions. These facts show that the supramolecular framework based on these cooperative weak forces may be robust enough for application in molecular recognition. The investigation of close intermolecular interactions between the molecules via Hirshfeld surface analyses is presented in order to reveal subtle differences and similarities in the crystal structures. The decomposition of the fingerprint plot area provides a percentage of each intermolecular interaction, allowing for a quantified analysis of close contacts within each crystal.

Samanta, Tapastaru; Dey, Lingaraj; Dinda, Joydev; Chattopadhyay, Shyamal Kumar; Seth, Saikat Kumar

2014-06-01

137

[3,3]-Sigmatropic Rearrangement vs. Carbene Formation in Gold-Catalyzed Transformations of Alkynyl Aryl Sulfoxides: Mechanistic Studies and Expanded Reaction Scope  

PubMed Central

Gold-catalyzed intramolecular oxidation of terminal alkynes with an arenesulfinyl group as the tethered oxidant is a reaction in gold chemistry of high impact, as it introduced to the field the highly-valued concept of gold carbene generation via alkyne oxidation. The proposed intermediacy of ?-oxo gold carbenes in these reactions, however, has never been substantiated. Detailed experimental studies suggest that the involvement of such reactive intermediates in the formation of dihydrobenzothiepinones is highly unlikely. Instead, a [3,3]-sigmatropic rearrangement of the initial cyclization intermediate offers a reaction path that can readily explain the high reaction efficiency and the lack of sulfonium formation. With internal alkyne substrates, however, the generation of a gold carbene species becomes competitive with the [3,3]-sigmatropic rearrangement. This reactive intermediate, nevertheless, does not proceed to afford the Friedel-Crafts type cyclization product. Extensive Density Functional Theory studies support the mechanistic conclusion that the cyclized product is formed via an intramolecular [3,3]-sigmatropic rearrangement instead of the previously proposed Friedel-Crafts type cyclization. With the new mechanistic insight, the product scope of this versatile formation of mid-sized sulfur-containing cycloalkenones has been expanded readily to various dihydrobenzothiocinones, a tetrahydrobenzocyclononenone, and even those without the entanglement of a fused benzene ring. Besides gold, Hg(OTf)2 can be an effective catalyst, thereby offering a cheap alternative for this intramolecular redox reaction. PMID:23731178

Lu, Biao; Li, Yuxue; Wang, Youliang; Aue, Donald H.; Luo, Yingdong; Zhang, Liming

2013-01-01

138

INVERSE STABLE SUBORDINATORS  

PubMed Central

The inverse stable subordinator provides a probability model for time-fractional differential equations, and leads to explicit solution formulae. This paper reviews properties of the inverse stable subordinator, and applications to a variety of problems in mathematics and physics. Several different governing equations for the inverse stable subordinator have been proposed in the literature. This paper also shows how these equations can be reconciled. PMID:25045216

MEERSCHAERT, MARK M.; STRAKA, PETER

2013-01-01

139

Novel benzyl-substituted N-heterocyclic carbene-silver acetate complexes: synthesis, cytotoxicity and antibacterial studies.  

PubMed

From the reaction of 1-methylimidazole (1a), 4,5-dichloro-1H-imidazole (1b(I)) and 1-methylbenzimidazole (1c) with p-cyanobenzyl bromide (2a), non-symmetrically substituted N-heterocyclic carbene (NHC) [(3a-c)] precursors, 5,6-dimethyl-1H-benzimidazole (1d) and 4,5-diphenyl-1H-imidazole (1e) with p-cyanobenzyl bromide (2a) and benzyl bromide (2b), symmetrically substituted N-heterocyclic carbene (NHC) [(3d-f)] precursors were synthesised. These NHC-precursors were then reacted with silver(i) acetate to yield the NHC-silver complexes (1-methyl-3-(4-cyanobenzyl)imidazole-2-ylidene)silver(i)acetate (4a), (4,5-dichloro-1-(4-cyanobenzyl)-3-methyl)imidazole-2-ylidene)silver(i)acetate (4b), (1-methyl-3-(4-cyanobenzyl)benzimidazole-2-ylidene)silver(i)acetate (4c), (1,3-bis(4-cyanobenzyl)5,6-dimethylbenzimidazole-2-ylidene) silver(i) acetate (4d), (1,3-dibenzyl-5,6-dimethylbenzimidazole-2-ylidene) silver(i) acetate (4e) and (1,3-dibenzyl-4,5-diphenylimidazol-2-ylidene) silver(i) acetate (4f) respectively. Three NHC-precursors 3c-e and four NHC-silver complexes 4b and 4d-f were characterised by single crystal X-ray diffraction. Preliminary in vitro antibacterial activity of the NHC-precursors and NHC-silver complexes was investigated against Gram-positive bacteria Staphylococcus aureus, and Gram-negative bacteria Escherichia coli using the qualitative Kirby-Bauer disk-diffusion method. NHC-silver complexes have shown very high antibacterial activity compared to the NHC-precursors. All six NHC-silver complexes were tested for their cytotoxicity through MTT based in vitro tests on the human renal-cancer cell line Caki-1 in order to determine their IC?? values. NHC-silver complexes 4a-f were found to have IC?? values of 6.2 (±1.0), 7.7 (±1.6), 1.2 (±0.6), 10.8 (±1.9), 24.2 (±1.8) and 13.6 (±1.0) ?M, respectively. These values represent improved cytotoxicity against Caki-1, most notably for 4c, which is a three times more cytotoxic than cisplatin (IC?? value = 3.3 ?M) itself. PMID:21135954

Patil, Siddappa; Deally, Anthony; Gleeson, Brendan; Müller-Bunz, Helge; Paradisi, Francesca; Tacke, Matthias

2011-01-01

140

Metal Complexes of a Boron-Dipyrromethene (BODIPY)-Tagged N-Heterocyclic Carbene (NHC) as Luminescent Carbon Monoxide Chemodosimeters.  

PubMed

Several metal complexes with a boron dipyrromethene (BODIPY)-functionalized N-heterocyclic carbene (NHC) ligand 4 were synthesized. The fluorescence in [(4)(SIMes)RuCl2 (ind)] complex is quenched (?=0.003), it is weak in [(4)PdI2 (Clpy)] (?=0.033), and strong in [(4)AuI] (?=0.70). The BODIPY-tagged complexes can experience pronounced changes in the brightness of the fluorophore upon ligand-exchange and ligand-dissociation reactions. Complexes [(4)MX(1,5-cyclooctadiene)] (M=Rh, Ir; X=Cl, I; ?=0.008-0.016) are converted into strongly fluorescent complexes [(4)MX(CO)2 ] (?=0.53-0.70) upon reaction with carbon monoxide. The unquenching of the Rh and Ir complexes appears to be a consequence of the decreased electron density at Rh or Ir in the carbonyl complexes. In contrast, the substitution of an iodo ligand in [(4)AuI] by an electron-rich thiolate decreases the brightness of the BODIPY fluorophore, rendering the BODIPY as a highly sensitive probe for changes in the coordination sphere of the transition metal. PMID:25487747

Kos, Pavlo; Plenio, Herbert

2014-12-01

141

Traditional and ion-pair halogen-bonded complexes between chlorine and bromine derivatives and a nitrogen-heterocyclic carbene.  

PubMed

A theoretical study of the halogen-bonded complexes (A-X···C) formed between halogenated derivatives (A-X; A = F, Cl, Br, CN, CCH, CF3, CH3, H; and X = Cl, Br) and a nitrogen heterocyclic carbene, 1,3-dimethylimidazole-2-ylidene (MeIC) has been performed using MP2/aug'-cc-pVDZ level of theory. Two types of A-X:MeIC complexes, called here type-I and -II, were found and characterized. The first group is described by long C-X distances and small binding energies (8-54 kJ·mol(-1)). In general, these complexes show the traditional behavior of systems containing halogen-bonding interactions. The second type is characterized by short C-X distances and large binding energies (148-200 kJ·mol(-1)), and on the basis of the topological analysis of the electron density, they correspond to ion-pair halogen-bonded complexes. These complexes can be seen as the interaction between two charged fragments: A(-) and (+)[X-CIMe] with a high electrostatic contribution in the binding energy. The charge transfer between lone pair A(LP) to the ?* orbital of C-X bond is also identified as a significant stabilizing interaction in type-II complexes. PMID:25188812

Donoso-Tauda, Oscar; Jaque, Pablo; Elguero, José; Alkorta, Ibon

2014-10-01

142

Non-covalent interactions in coinage metal complexes of 1,2,4-triazole-based N-heterocyclic carbenes.  

PubMed

Seven coinage metal(I) complexes bearing two different triazole-based N-heterocyclic carbene (NHC) ligands, [1-tert-butyl-4-{2-[(N,N-dimethylamino)methyl]phenyl}-3-phenyl-1H-1,2,4-triazol-4-ium-5-ide and 1-tert-butyl-4-(4-methylphenyl)-3-phenyl-1H-1,2,4-triazol-4-ium-5-ide], were synthesized and fully characterized in solution by NMR spectroscopy as well as in the solid state by X-ray diffraction techniques. Furthermore, the XRD analysis showed that the bidentate coordination of the amino group substituted NHC ligand, previously observed for rhodium and palladium complexes, does not take place in the solid state structure of Au(I) complexes with various halide ligands. Nevertheless, the formation of sets of two head-to-tail oriented monomers aggregated via a weak metallophilic contact was revealed for both NHC ligands as well as for all three coinage metals with different halides. These experimental data correlate quite well with the previously published theoretical study on related complexes. PMID:25189129

Turek, Jan; Panov, Illia; Švec, Petr; R?ži?ková, Zde?ka; R?ži?ka, Aleš

2014-11-01

143

Expanded-ring N-heterocyclic carbenes efficiently stabilize gold(I) cations, leading to high activity in ?-acid-catalyzed cyclizations.  

PubMed

A series of six- and seven-membered expanded-ring N-heterocyclic carbene (er-NHC) gold(I) complexes has been synthesized using different synthetic approaches. Complexes with weakly coordinating anions [(er-NHC)AuX] (X(-) = BF4(-), NTf2(-), OTf(-)) were generated in solution. According to their (13)C?NMR spectra, the ionic character of the complexes increases in the order X(-) = Cl(-) < NTf2(-) < OTf(-) < BF4(-). Additional factors for stabilization of the cationic complexes are expansion of the NHC ring and the attachment of bulky substituents at the nitrogen atoms. These er-NHCs are bulkier ligands and stronger electron donors than conventional NHCs as well as phosphines and sulfides and provide more stabilization of [(L)Au(+)] cations. A comparative study has been carried out of the catalytic activities of five-, six-, and seven-membered carbene complexes [(NHC)AuX], [(Ph3 P)AuX], [(Me2S)AuX], and inorganic compounds of gold in model reactions of indole and benzofuran synthesis. It was found that increased ionic character of the complexes was correlated with increased catalytic activity in the cyclization reactions. As a result, we developed an unprecedentedly active monoligand cationic [(THD-Dipp)Au]BF4 (1,3-bis(2,6-diisopropylphenyl)-3,4,5,6-tetrahydrodiazepin-2-ylidene gold(I) tetrafluoroborate) catalyst bearing seven-membered-ring carbene and bulky Dipp substituents. Quantitative yields of cyclized products were attained in several minutes at room temperature at 1?mol?% catalyst loadings. The experimental observations were rationalized and fully supported by DFT calculations. PMID:24682976

Morozov, Oleg S; Lunchev, Andrey V; Bush, Alexander A; Tukov, Aleksandr A; Asachenko, Andrey F; Khrustalev, Victor N; Zalesskiy, Sergey S; Ananikov, Valentine P; Nechaev, Mikhail S

2014-05-12

144

Gold(III) N-heterocyclic carbene complexes mediated synthesis of ?-enaminones from 1,3-dicarbonyl compounds and aliphatic amines.  

PubMed

A series of gold(III) N-heterocyclic carbene complexes [1-(R(1))-3-(R(2))imidazol-2-ylidene]AuBr(3) [R(1) = i-Pr, R(2) = CH(2)Ph (1c); R(1) = mesityl, R(2) = CH(2)Ph (2c); R(1) = i-Pr, R(2) = CH(2)COt-Bu (3c), and R(1) = t-Bu, R(2) = CH(2)COt-Bu (4c)] act as effective precatalysts in the synthesis of ?-enaminones from 1,3-dicarbonyl compounds and primary amines under ambient conditions. Specifically the 1c-4c complexes efficiently catalyzed the condensation of a variety of cyclic as well as acyclic 1,3-dicarbonyl compounds, namely, acetyl acetone, benzoylacetone, 2-acetylcyclopentanone, and ethyl-2-oxocyclopentanecarboxylate with primary aliphatic amines, viz., methylamine, ethylamine, n-propylamine, i-propylamine, and n-butylamine, yielding ?-enamines at room temperature. Interestingly enough, the more electrophilic gold(III) 1c-4c complexes exhibited superior activity in comparison to the gold(I) counterparts 1b-4b. A comparison along a representative 4a-c series further underscored the importance of gold in the reaction as both the gold(I) 4b and gold(III) 4c complexes were more effective than the silver analogue 4a. The density functional theory (DFT) study revealed that the strong ?-donating nature of the N-heterocyclic carbene ligand results in a strong C(carbene)-Au(III) interaction in the 1c-4c complexes. PMID:21254751

Samantaray, Manoja K; Dash, Chandrakanta; Shaikh, Mobin M; Pang, Keliang; Butcher, Ray J; Ghosh, Prasenjit

2011-03-01

145

Unimolecular reaction mechanism of an imidazolin-2-ylidene: an iPEPICO study on the complex dissociation of an Arduengo-type carbene.  

PubMed

The photoionization and dissociative photoionization of Im(iPr)2, 1,3-diisopropylimidazolin-2-ylidene, was investigated by imaging photoelectron photoion coincidence (iPEPICO) with vacuum ultraviolet (VUV) synchrotron radiation. A lone-pair electron of the carbene carbon atom is removed upon ionization and the molecular geometry changes significantly. Only 0.5 eV above the adiabatic ionization energy, IEad =7.52±0.1 eV, the carbene cation fragments, yielding propene or a methyl radical in parallel dissociation reactions with appearance energies of 8.22 and 8.17 eV, respectively. Both reaction channels appear at almost the same photon energy, suggesting a shared transition state. This is confirmed by calculations, which reveal the rate-determining step as hydrogen-atom migration from the isopropyl group to the carbene carbon center forming a resonance-stabilized imidazolium ion. Above 10.5 eV, analogous sequential dissociation channels open up. The first propene-loss fragment ion dissociates further and another methyl or propene is abstracted. Again, a resonance-stabilized imidazolium ion acts as intermediate. The aromaticity of the system is enhanced even in vertical ionization. Indeed, the coincidence technique confirms that a real imidazolium ion is produced by hydrogen transfer over a small barrier. The simple analysis of the breakdown diagram yields all the clues to disentangle the complex dissociative photoionization mechanism of this intermediate-sized molecule. Photoelectron photoion coincidence is a promising tool to unveil the fragmentation mechanism of larger molecules in mass spectrometry. PMID:23553670

Hemberger, Patrick; Bodi, Andras; Gerber, Thomas; Würtemberger, Max; Radius, Udo

2013-05-27

146

N-Heterocyclic carbene-palladium(II)-1-methylimidazole complex catalyzed Suzuki-Miyaura coupling of benzylic chlorides with arylboronic acids or potassium phenyltrifluoroborate in neat water.  

PubMed

An easily available N-heterocyclic carbene-palladium(II)-1-methylimidazole complex showed efficient catalytic activity in the Suzuki-Miyaura coupling of benzylic chlorides with arylboronic acids or potassium phenyltrifluoroborate in neat water under mild conditions, providing an alternative method for the synthesis of diarylmethane derivatives, which widely exist in molecules with pharmaceutical activities and are also frequently found as subunits in supramolecules. Under the optimal conditions, all reactions performed well to give the desired products in moderate to almost quantitative yields in an environmentally benign medium within 12 h, extending their applications toward potentially industrial processes. PMID:23381388

Zhang, Yun; Feng, Meng-Ting; Lu, Jian-Mei

2013-04-14

147

Quinone-annulated N-heterocyclic carbene-transition-metal complexes: observation of pi-backbonding using FT-IR spectroscopy and cyclic voltammetry.  

PubMed

A new N-heterocyclic carbene architecture comprising a 1,4-naphthoquinone annulated to 1,3-dimesitylimidazolylidene (NpQ-NHC) was synthesized in two high yielding steps from commercially available starting materials. The free NpQ-NHC was characterized (solution and solid-state) and was used to synthesize various Rh and Ag complexes that ranged in pi-electron density. Enabled by the quinone moiety, the pi-systems of these complexes were analyzed using infrared spectroscopy and cyclic voltammetry. In contrast to previous reports, pi-backbonding was found to be non-negligible and was directly influenced by the metal's electronic character. PMID:17177396

Sanderson, Matthew D; Kamplain, Justin W; Bielawski, Christopher W

2006-12-27

148

How stable are the 'stable ancient shields'?  

NASA Astrophysics Data System (ADS)

"Archean cratons are relatively flat, stable regions of the crust that have remained undeformed since the Precambrian, forming the ancient cores of the continents" (King, EPSL, 2005). While this type of statement is supported by a wealth of constraints in the case of episodes of thoroughgoing ductile deformation affecting shield regions of Archean and also Peleoproterozoic age, a growing amount of research indicates that shields are not nearly as structurally stable within the broad field of environmental conditions leading to brittle deformation. In fact, old crystalline basements usually present compelling evidence of long brittle deformation histories, often very complex and challenging to unfold. Recent structural and geochronological studies point to a significant mechanical instability of the shield areas, wherein large volumes of 'stable' rocks actually can become saturated with fractures and brittle faults soon after regional cooling exhumes them to below c. 300-350° C. How cold, rigid and therefore strong shields respond to applied stresses remains, however, still poorly investigated and understood. This in turn precludes a better definition of the shallow rheological properties of large, old crystalline blocks. In particular, we do not yet have good constraints on the mechanisms of mechanical reactivation that control the partial (if not total) accommodation of new deformational episodes by preexisting structures, which remains a key to untangle brittle histories lasting several hundred Myr. In our analysis, we use the Svecofennian Shield (SS) as an example of a supposedly 'stable' region with Archean nucleii and Paleoproterozoic cratonic areas to show how it is possible to unravel the details of brittle histories spanning more than 1.5 Gyr. New structural and geochronological results from Finland are integrated with a review of existing data from Sweden to explore how the effects of far-field stresses are partitioned within a shield, which was growing progressively saturated with fractures as time passed from its initial consolidation. The comparison of time-constrained paleostress data derived from three different locations of the shield shows a remarkably similar stress evolution through time, despite the different geological frameworks of the investigated areas. This suggests that the southern SS has behaved as a coherent rigid crustal block since the Late Mesoproterozoic. By that time, the SS had already reached structural maturity with respect to the saturation of brittle structural features. Therefore, structural reactivation rather than generation of new faults and fractures is the key mechanism that has controlled the mechanical evolution of the shield and that will steer its future evolution within the brittle regime. Comparable brittle structural histories within parts of the shield that are far apart also imply that far-field stresses can propagate over large distances and can lead to similar deformational histories, with the local geological conditions only playing a second-order role on the final brittle strain pattern recorded by the rock.

Viola, Giulio; Mattila, Jussi

2014-05-01

149

Synthesis of Well-Defined Copper "N"-Heterocyclic Carbene Complexes and Their Use as Catalysts for a "Click Reaction": A Multistep Experiment that Emphasizes the Role of Catalysis in Green Chemistry  

ERIC Educational Resources Information Center

A multistep experiment for an advanced synthesis lab course that incorporates topics in organic-inorganic synthesis and catalysis and highlights green chemistry principles was developed. Students synthesized two "N"-heterocyclic carbene ligands, used them to prepare two well-defined copper(I) complexes and subsequently utilized the complexes as…

Ison, Elon A.; Ison, Ana

2012-01-01

150

Mixed N-Heterocyclic Carbene-Bis(oxazolinyl)borato Rhodium and Iridium Complexes in Photochemical and Thermal Oxidative Addition Reactions  

SciTech Connect

In order to facilitate oxidative addition chemistry of fac-coordinated rhodium(I) and iridium(I) compounds, carbene–bis(oxazolinyl)phenylborate proligands have been synthesized and reacted with organometallic precursors. Two proligands, PhB(OxMe2)2(ImtBuH) (H[1]; OxMe2 = 4,4-dimethyl-2-oxazoline; ImtBuH = 1-tert-butylimidazole) and PhB(OxMe2)2(ImMesH) (H[2]; ImMesH = 1-mesitylimidazole), are deprotonated with potassium benzyl to generate K[1] and K[2], and these potassium compounds serve as reagents for the synthesis of a series of rhodium and iridium complexes. Cyclooctadiene and dicarbonyl compounds {PhB(OxMe2)2ImtBu}Rh(?4-C8H12) (3), {PhB(OxMe2)2ImMes}Rh(?4-C8H12) (4), {PhB(OxMe2)2ImMes}Rh(CO)2 (5), {PhB(OxMe2)2ImMes}Ir(?4-C8H12) (6), and {PhB(OxMe2)2ImMes}Ir(CO)2 (7) are synthesized along with ToMM(?4-C8H12) (M = Rh (8); M = Ir (9); ToM = tris(4,4-dimethyl-2-oxazolinyl)phenylborate). The spectroscopic and structural properties and reactivity of this series of compounds show electronic and steric effects of substituents on the imidazole (tert-butyl vs mesityl), effects of replacing an oxazoline in ToM with a carbene donor, and the influence of the donor ligand (CO vs C8H12). The reactions of K[2] and [M(?-Cl)(?2-C8H14)2]2 (M = Rh, Ir) provide {?4-PhB(OxMe2)2ImMes?CH2}Rh(?-H)(?-Cl)Rh(?2-C8H14)2 (10) and {PhB(OxMe2)2ImMes}IrH(?3-C8H13) (11). In the former compound, a spontaneous oxidative addition of a mesityl ortho-methyl to give a mixed-valent dirhodium species is observed, while the iridium compound forms a monometallic allyl hydride. Photochemical reactions of dicarbonyl compounds 5 and 7 result in C–H bond oxidative addition providing the compounds {?4-PhB(OxMe2)2ImMes?CH2}RhH(CO) (12) and {PhB(OxMe2)2ImMes}IrH(Ph)CO (13). In 12, oxidative addition results in cyclometalation of the mesityl ortho-methyl similar to 10, whereas the iridium compound reacts with the benzene solvent to give a rare crystallographically characterized cis-[Ir](H)(Ph) complex. Alternatively, the rhodium carbonyl 5 or iridium isocyanide {PhB(OxMe2)2ImMes}Ir(CO)CNtBu (15) reacts with PhSiH3 in the dark to form the silyl compound {PhB(OxMe2)2ImMes}RhH(SiH2Ph)CO (14) or {PhB(OxMe2)2ImMes}IrH(SiH2Ph)CNtBu (17). These examples demonstrate the enhanced thermal reactivity of {PhB(OxMe2)2ImMes}-supported iridium and rhodium carbonyl compounds in comparison to tris(oxazolinyl)borate, tris(pyrazolyl)borate, and cyclopentadienyl-supported compounds.

Xu, Songchen [Ames Laboratory; Manna, Kuntal [Ames Laboratory; Ellern, Arkady [Ames Laboratory; Sadow, Aaron D [Ames Laboratory

2014-12-08

151

Cyclodimerization versus polymerization of methyl methacrylate induced by N-heterocyclic carbenes: a combined experimental and theoretical study.  

PubMed

The activation behavior of two N-heterocyclic carbenes (NHCs), namely, 1,3-bis(isopropyl)imidazol-2-ylidene(NHCiPr) and 1,3-bis(tert-butyl) imidazol-2-ylidene (NHCtBu), as organic nucleophiles in the reaction with methyl methacrylate (MMA) is described. NHCtBu allows the polymerization of MMA in DMF at room temperature and in toluene at 50?°C, whereas NHCiPr reacts with two molecules of MMA, forming an unprecedented imidazolium-enolate cyclodimer (NHCiPr/MMA=1:2). It is proposed that the reaction mechanism occurs by initial 1,4-nucleophilic addition of NHCiPr to MMA, generating a zwitterionic enolate 2, followed by addition of 2 to a second MMA molecule, forming a linear imidazolium-enolate 3 (NHCiPr/MMA=1:2). Proton transfer, generating intermediate 5, followed by cyclization and release of methanol yielded the aforementioned zwitterionic cyclodimer 1:2 adduct 7, the molecular structure of which has been established by NMR spectroscopy, X-ray diffraction, and mass spectrometry. This unexpected difference between NHCtBu and NHCiPr in the reaction with MMA (polymerization and cyclodimerization, respectively) can be rationalized by using DFT calculations. In particular, the nature of the NHC strongly influences the cyclodimerization pathway, the cyclization of 5 and the release of methanol are the discriminating step and limiting step, respectively. In the case of NHCtBu, both steps are strongly disfavoured compared with that of NHCiPr (energetic difference of around 14 and 9?kcal?mol(-1), respectively), preventing the cyclization mechanism from a kinetic viewpoint. Moreover, addition of a third molecule of MMA in the polymerization pathway results in a lower activation barrier than that of the limiting step in the cyclodimerization pathway (difference of around 14?kcal?mol(-1)), in agreement with the formation of polymethyl methacrylate (PMMA) by using NHCtBu as nucleophile. PMID:24604823

Nzahou Ottou, Winnie; Bourichon, Damien; Vignolle, Joan; Wirotius, Anne-Laure; Robert, Fredéric; Landais, Yannick; Sotiropoulos, Jean-Marc; Miqueu, Karinne; Taton, Daniel

2014-04-01

152

Dimers of N-heterocyclic carbene copper, silver, and gold halides: probing metallophilic interactions through electron density based concepts.  

PubMed

Homobimetallic metallophilic interactions between copper, silver, and gold-based [(NHC)MX]-type complexes (NHC=N-heterocyclic carbene, i.e, 1,3,4-trimethyl-4,5-dihydro-1H-1,2,4-triazol-5-ylidene; X=F, Cl, Br, I) were investigated by means of ab initio interaction energies, Ziegler-Rauk-type energy-decomposition analysis, the natural orbital for chemical valence (NOCV) framework, and the noncovalent interaction (NCI) index. It was found that the dimers of these complexes predominantly adopt a head-to-tail arrangement with typical M???M distance of 3.04-3.64?Å, in good agreement with the experimental X-ray structure determined for [{(NHC)AuCl}2 ], which has an Au???Au distance of 3.33?Å. The interaction energies between silver- and gold-based monomers are calculated to be about -25?kcal?mol(-1) , whereas that for the Cu congener is significantly lower (-19.7?kcal?mol(-1) ). With the inclusion of thermal and solvent contributions, both of which are destabilizing, by about 15 and 8?kcal?mol(-1) , respectively, an equilibrium process is predicted for the formation of dimer complexes. Energy-decomposition analysis revealed a dominant electrostatic contribution to the interaction energy, besides significantly stabilizing dispersion and orbital interactions. This electrostatic contribution is rationalized by NHC(?(+) )???halogen(?(-) ) interactions between monomers, as demonstrated by electrostatic potentials and derived charges. The dominant NOCV orbital indicates weakening of the ? backdonation in the monomers on dimer formation, whereas the second most dominant NOCV represents an electron-density deformation according to the formation of a very weak M???M bond. One of the characteristic signals found in the reduced density gradient versus electron density diagram corresponds to the noncovalent interactions between the metal centers of the monomers in the NCI plots, which is the manifestation of metallophilic interaction. PMID:24339216

Pinter, Balazs; Broeckaert, Lies; Turek, Jan; R?ži?ka, Aleš; De Proft, Frank

2014-01-13

153

Angina Pectoris (Stable Angina)  

MedlinePLUS

... But, with physical exertion—like walking up a hill or climbing stairs—the heart works harder and needs more oxygen. Symptoms of Stable Angina - The pain or discomfort: Occurs when the heart must work harder, usually during physical exertion Doesn't come as a surprise, and episodes of pain ...

154

Stable isotope studies  

SciTech Connect

The research has been in four general areas: (1) correlation of isotope effects with molecular forces and molecular structures, (2) correlation of zero-point energy and its isotope effects with molecular structure and molecular forces, (3) vapor pressure isotope effects, and (4) fractionation of stable isotopes. 73 refs, 38 figs, 29 tabs.

Ishida, T.

1992-01-01

155

The ketimide ligand is not just an inert spectator: heteroallene insertion reactivity of an actinide-ketimide linkage in a thorium carbene amide ketimide complex.  

PubMed

The ketimide anion R2C=N(-) is an important class of chemically robust ligand that binds strongly to metal ions and is considered ideal for supporting reactive metal fragments due to its inert spectator nature; this contrasts with R2N(-) amides that exhibit a wide range of reactivities. Here, we report the synthesis and characterization of a rare example of an actinide ketimide complex [Th(BIPM(TMS)){N(SiMe3)2}(N=CPh2)] [2, BIPM(TMS)=C(PPh2NSiMe3)2]. Complex 2 contains Th=C(carbene), Th-N(amide) and Th-N(ketimide) linkages, thereby presenting the opportunity to probe the preferential reactivity of these linkages. Importantly, reactivity studies of 2 with unsaturated substrates shows that insertion reactions occur preferentially at the Th-N(ketimide) bond rather than at the Th=C(carbene) or Th-N(amide) bonds. This overturns the established view that metal-ketimide linkages are purely inert spectators. PMID:25044515

Lu, Erli; Lewis, William; Blake, Alexander J; Liddle, Stephen T

2014-08-25

156

Stable Charged Cosmic Strings  

SciTech Connect

We study the quantum stabilization of a cosmic string by a heavy fermion doublet in a reduced version of the standard model. We show that charged strings, obtained by populating fermionic bound state levels, become stable if the electroweak bosons are coupled to a fermion that is less than twice as heavy as the top quark. This result suggests that extraordinarily large fermion masses or unrealistic couplings are not required to bind a cosmic string in the standard model. Numerically we find the most favorable string profile to be a simple trough in the Higgs vacuum expectation value of radius {approx_equal}10{sup -18} m. The vacuum remains stable in our model, because neutral strings are not energetically favored.

Weigel, H. [Physics Department, Stellenbosch University, Matieland 7602 (South Africa); Quandt, M. [Institute for Theoretical Physics, Tuebingen University, D-72076 Tuebingen (Germany); Graham, N. [Department of Physics, Middlebury College , Middlebury, Vermont 05753 (United States)

2011-03-11

157

Thermally stable laminating resins  

NASA Technical Reports Server (NTRS)

Improved thermally stable laminating resins were developed based on the addition-type pyrolytic polymerization. Detailed monomer and polymer synthesis and characterization studies identified formulations which facilitate press molding processing and autoclave fabrication of glass and graphite fiber reinforced composites. A specific resin formulation, termed P10P was utilized to prepare a Courtaulds HMS reinforced simulated airfoil demonstration part by an autoclave molding process.

Jones, R. J.; Vaughan, R. W.; Burns, E. A.

1972-01-01

158

Iridium(III) Hydrido N-Heterocyclic Carbene–Phosphine Complexes as Catalysts in Magnetization Transfer Reactions  

PubMed Central

The hyperpolarization (HP) method signal amplification by reversible exchange (SABRE) uses para-hydrogen to sensitize substrate detection by NMR. The catalyst systems [Ir(H)2(IMes)(MeCN)2(R)]BF4 and [Ir(H)2(IMes)(py)2(R)]BF4 [py = pyridine; R = PCy3 or PPh3; IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene], which contain both an electron-donating N-heterocyclic carbene and a phosphine, are used here to catalyze SABRE. They react with acetonitrile and pyridine to produce [Ir(H)2(NCMe)(py)(IMes)(PPh3)]BF4 and [Ir(H)2(NCMe)(py)(IMes)(PCy3)]BF4, complexes that undergo ligand exchange on a time scale commensurate with observation of the SABRE effect, which is illustrated here by the observation of both pyridine and acetonitrile HP. In this study, the required symmetry breaking that underpins SABRE is provided for by the use of chemical inequivalence rather than the previously reported magnetic inequivalence. As a consequence, we show that the ligand sphere of the polarization transfer catalyst itself becomes hyperpolarized and hence that the high-sensitivity detection of a number of reaction intermediates is possible. These species include [Ir(H)2(NCMe)(py)(IMes)(PPh3)]BF4, [Ir(H)2(MeOH)(py)(IMes)(PPh3)]BF4, and [Ir(H)2(NCMe)(py)2(PPh3)]BF4. Studies are also described that employ the deuterium-labeled substrates CD3CN and C5D5N, and the labeled ligands P(C6D5)3 and IMes-d22, to demonstrate that dramatically improved levels of HP can be achieved as a consequence of reducing proton dilution and hence polarization wastage. By a combination of these studies with experiments in which the magnetic field experienced by the sample at the point of polarization transfer is varied, confirmation of the resonance assignments is achieved. Furthermore, when [Ir(H)2(pyridine-h5)(pyridine-d5)(IMes)(PPh3)]BF4 is examined, its hydride ligand signals are shown to become visible through para-hydrogen-induced polarization rather than SABRE. PMID:24215616

2013-01-01

159

Colorado Plateau Stable Isotope Laboratory  

NSDL National Science Digital Library

This website, hosted by Northern Arizona University, describes stable isotopes. The site defines stable isotopes and how to measure them, and lists their research applications. Many of the advances in ecology and environmental sciences in the past decade have relied on stable isotopes.

Colorado Plateau Stable Isotope Laboratory (CPSIL); University, Northern A.

160

Bi-stable optical actuator  

DOEpatents

The present invention is a bi-stable optical actuator device that is depowered in both stable positions. A bearing is used to transfer motion and smoothly transition from one state to another. The optical actuator device may be maintained in a stable position either by gravity or a restraining device.

Holdener, Fred R. (Tracy, CA); Boyd, Robert D. (Livermore, CA)

2000-01-01

161

Ruthenium-porphyrin-catalyzed diastereoselective intramolecular alkyl carbene insertion into c?h bonds of alkyl diazomethanes generated in situ from N-tosylhydrazones.  

PubMed

With a ruthenium-porphyrin catalyst, alkyl diazomethanes generated in situ from N-tosylhydrazones efficiently underwent intramolecular C(sp(3) )?H insertion of an alkyl carbene to give substituted tetrahydrofurans and pyrrolidines in up to 99?% yield and with up to 99:1 cis selectivity. The reaction displays good tolerance of many functionalities, and the procedure is simple without the need for slow addition with a syringe pump. From a synthetic point of view, the C?H insertion of N-tosylhydrazones can be viewed as reductive coupling between a C?O bond and a C?H bond to form a new C?C bond, since N-tosylhydrazones can be readily prepared from carbonyl compounds. This reaction was successfully applied in a concise synthesis of (±)-pseudoheliotridane. PMID:25319195

Reddy, Annapureddy Rajasekar; Zhou, Cong-Ying; Guo, Zhen; Wei, Jinhu; Che, Chi-Ming

2014-12-15

162

Reaction of an N-Heterocyclic Carbene-Stabilized Silicon(II) Monohydride with Alkynes: [2+2+1] Cycloaddition versus Hydrogen Abstraction.  

PubMed

An in depth study of the reactivity of an N-heterocyclic carbene (NHC)-stabilized silylene monohydride with alkynes is reported. The reaction of silylene monohydride 1, tBu3 Si(H)Si?NHC, with diphenylacetylene afforded silole 2, tBu3 Si(H)Si(C4 Ph4 ). The density functional theory (DFT) calculations for the reaction mechanism of the [2+2+1] cycloaddition revealed that the NHC played a major part stabilizing zwitterionic transition states and intermediates to assist the cyclization pathway. A significantly different outcome was observed, when silylene monohydride 1 was treated with phenylacetylene, which gave rise to supersilyl substituted 1-alkenyl-1-alkynylsilane 3, tBu3 Si(H)Si(CH?CHPh)(C?CPh). Mechanistic investigations using an isotope labelling technique and DFT calculations suggest that this reaction occurs through a similar zwitterionic intermediate and subsequent hydrogen abstraction from a second molecule of phenylacetylene. PMID:25413306

Eisenhut, Carsten; Szilvási, Tibor; Breit, Nora C; Inoue, Shigeyoshi

2015-01-26

163

The antimicrobial efficacy of sustained release silver–carbene complex-loaded l-tyrosine polyphosphate nanoparticles: Characterization, in vitro and in vivo studies  

PubMed Central

The pressing need to treat multi-drug resistant bacteria in the chronically infected lungs of cystic fibrosis (CF) patients has given rise to novel nebulized antimicrobials. We have synthesized a silver–carbene complex (SCC10) active against a variety of bacterial strains associated with CF and chronic lung infections. Our studies have demonstrated that SCC10-loaded into l-tyrosine polyphosphate nanoparticles (LTP NPs) exhibits excellent antimicrobial activity in vitro and in vivo against the CF relevant bacteria Pseudomonas aeruginosa. Encapsulation of SCC10 in LTP NPs provides sustained release of the antimicrobial over the course of several days translating into efficacious results in vivo with only two administered doses over a 72 h period. PMID:19395021

Hindi, Khadijah M.; Ditto, Andrew J.; Panzner, Matthew J.; Medvetz, Douglas A.; Han, Daniel S.; Hovis, Christine E.; Hilliard, Julia K.; Taylor, Jane B.; Yun, Yang H.; Cannon, Carolyn L.; Youngs, Wiley J.

2009-01-01

164

Marginally Stable Nuclear Burning  

NASA Technical Reports Server (NTRS)

Thermonuclear X-ray bursts result from unstable nuclear burning of the material accreted on neutron stars in some low mass X-ray binaries (LMXBs). Theory predicts that close to the boundary of stability oscillatory burning can occur. This marginally stable regime has so far been identified in only a small number of sources. We present Rossi X-ray Timing Explorer (RXTE) observations of the bursting, high- inclination LMXB 4U 1323-619 that reveal for the first time in this source the signature of marginally stable burning. The source was observed during two successive RXTE orbits for approximately 5 ksec beginning at 10:14:01 UTC on March 28, 2011. Significant mHz quasi- periodic oscillations (QPO) at a frequency of 8.1 mHz are detected for approximately 1600 s from the beginning of the observation until the occurrence of a thermonuclear X-ray burst at 10:42:22 UTC. The mHz oscillations are not detected following the X-ray burst. The average fractional rms amplitude of the mHz QPOs is 6.4% (3 - 20 keV), and the amplitude increases to about 8% below 10 keV.This phenomenology is strikingly similar to that seen in the LMXB 4U 1636-53. Indeed, the frequency of the mHz QPOs in 4U 1323-619 prior to the X-ray burst is very similar to the transition frequency between mHz QPO and bursts found in 4U 1636-53 by Altamirano et al. (2008). These results strongly suggest that the observed QPOs in 4U 1323-619 are, like those in 4U 1636-53, due to marginally stable nuclear burning. We also explore the dependence of the energy spectrum on the oscillation phase, and we place the present observations within the context of the spectral evolution of the accretion-powered flux from the source.

Strohmayer, Tod E.; Altamirano, D.

2012-01-01

165

Visible-light photoredox catalysis: selective reduction of carbon dioxide to carbon monoxide by a nickel N-heterocyclic carbene-isoquinoline complex.  

PubMed

The solar-driven reduction of carbon dioxide to value-added chemical fuels is a longstanding challenge in the fields of catalysis, energy science, and green chemistry. In order to develop effective CO2 fixation, several key considerations must be balanced, including (1) catalyst selectivity for promoting CO2 reduction over competing hydrogen generation from proton reduction, (2) visible-light harvesting that matches the solar spectrum, and (3) the use of cheap and earth-abundant catalytic components. In this report, we present the synthesis and characterization of a new family of earth-abundant nickel complexes supported by N-heterocyclic carbene-amine ligands that exhibit high selectivity and activity for the electrocatalytic and photocatalytic conversion of CO2 to CO. Systematic changes in the carbene and amine donors of the ligand have been surveyed, and [Ni((Pr)bimiq1)](2+) (1c, where (Pr)bimiq1 = bis(3-(imidazolyl)isoquinolinyl)propane) emerges as a catalyst for electrochemical reduction of CO2 with the lowest cathodic onset potential (E(cat) = -1.2 V vs SCE). Using this earth-abundant catalyst with Ir(ppy)3 (where ppy = 2-phenylpyridine) and an electron donor, we have developed a visible-light photoredox system for the catalytic conversion of CO2 to CO that proceeds with high selectivity and activity and achieves turnover numbers and turnover frequencies reaching 98,000 and 3.9 s(-1), respectively. Further studies reveal that the overall efficiency of this solar-to-fuel cycle may be limited by the formation of the active Ni catalyst and/or the chemical reduction of CO2 to CO at the reduced nickel center and provide a starting point for improved photoredox systems for sustainable carbon-neutral energy conversion. PMID:24033186

Thoi, V Sara; Kornienko, Nikolay; Margarit, Charles G; Yang, Peidong; Chang, Christopher J

2013-09-25

166

Stable local oscillator microcircuit.  

SciTech Connect

This report gives a description of the development of a Stable Local Oscillator (StaLO) Microcircuit. The StaLO accepts a 100MHz input signal and produces output signals at 1.2, 3.3, and 3.6 GHz. The circuit is built as a multi-chip module (MCM), since it makes use of integrated circuit technologies in silicon and lithium niobate as well as discrete passive components. The StaLO uses a comb generator followed by surface acoustic wave (SAW) filters. The comb generator creates a set of harmonic components of the 100MHz input signal. The SAW filters are narrow bandpass filters that are used to select the desired component and reject all others. The resulting circuit has very low sideband power levels and low phase noise (both less than -40dBc) that is limited primarily by the phase noise level of the input signal.

Brocato, Robert Wesley

2006-10-01

167

Stable angina pectoris.  

PubMed

The stable coronary artery disease (SCAD) population is a heterogeneous group of patients both for clinical presentations and for different underlying mechanisms. The recent European Society of Cardiology guidelines extensively review SCAD from its definition to patients' diagnostic and therapeutic management. In this review, we deal with five topics that, in our opinion, represent the most intriguing, novel and/or clinically relevant aspects of this complex coronary condition. Firstly, we deal with a peculiar SCAD population: patients with angina and 'normal' coronary arteries. Secondly, we reinforce the clinical importance of a diagnostic approach based on the pretest probability of disease. Thirdly, we review and critically discuss the novel pharmacological therapies for SCAD patients. Finally, we analyse the results of the most recent clinical trials comparing revascularization versus optimal medical therapy in SCAD patients and review the currently recommended use of intracoronary functional evaluation of stenosis. PMID:24838374

Valgimigli, Marco; Biscaglia, Simone

2014-07-01

168

Angina (chronic stable)  

PubMed Central

Introduction Stable angina is usually caused by coronary atherosclerosis, and affects up to 16% of men and 10% of women aged 65–74 years in the UK. Risk factors include hypertension, elevated serum cholesterol levels, smoking, physical inactivity, and overweight. People with angina are at increased risk of other cardiovascular events and mortality compared with people without angina. Among people not thought to need coronary artery revascularisation, annual mortality is 1–2% and the annual non-fatal myocardial infarction (MI) rate is 2–3%. Methods and outcomes We conducted a systematic review and aimed to answer the following clinical question: What are effects of long-term drug treatment for stable angina? We searched: Medline, Embase, The Cochrane Library, and other important databases up to June 2007 (BMJ Clinical Evidence reviews are updated periodically, please check our website for the most up-to-date version of this review). We included harms alerts from relevant organisations such as the US Food and Drug Administration (FDA) and the UK Medicines and Healthcare products Regulatory Agency (MHRA). Results We found nine systematic reviews, RCTs, or observational studies that met our inclusion criteria. We performed a GRADE evaluation of the quality of evidence for interventions. Conclusions In this systematic review we present information relating to the long-term effectiveness and safety of the following interventions: beta-blockers, calcium channel blockers, long-acting nitrates, potassium channel openers, combinations of these anti-anginal drug treatments and the use of these anti-anginal drug treatment as an adjunct to existing therapies. PMID:19445795

2008-01-01

169

Stable umbral chromospheric structures  

NASA Astrophysics Data System (ADS)

Aims: We seek to understand the morphology of the chromosphere in sunspot umbra. We investigate if the horizontal structures observed in the spectral core of the Ca II H line are ephemeral visuals caused by the shock dynamics of more stable structures, and examine their relationship with observables in the H-alpha line. Methods: Filtergrams in the core of the Ca II H and H-alpha lines as observed with the Swedish 1-m Solar Telescope are employed. We utilise a technique that creates composite images and tracks the flash propagation horizontally. Results: We find 0.?15 wide horizontal structures, in all of the three target sunspots, for every flash where the seeing is moderate to good. Discrete dark structures are identified that are stable for at least two umbral flashes, as well as systems of structures that live for up to 24 min. We find cases of extremely extended structures with similar stability, with one such structure showing an extent of 5''. Some of these structures have a correspondence in H-alpha, but we were unable to find a one-to-one correspondence for every occurrence. If the dark streaks are formed at the same heights as umbral flashes, there are systems of structures with strong departures from the vertical for all three analysed sunspots. Conclusions: Long-lived Ca II H filamentary horizontal structures are a common and likely ever-present feature in the umbra of sunspots. If the magnetic field in the chromosphere of the umbra is indeed aligned with the structures, then the present theoretical understanding of the typical umbra needs to be revisited. Movies associated to Figs. 3 and 4 are available in electronic form at http://www.aanda.org

Henriques, V. M. J.; Scullion, E.; Mathioudakis, M.; Kiselman, D.; Gallagher, P. T.; Keenan, F. P.

2015-02-01

170

Stable string bit models  

NASA Astrophysics Data System (ADS)

In string bit models, the superstring emerges as a very long chain of "bits," in which s fermionic degrees of freedom contribute positively to the ground state energy in a way to exactly cancel the destabilizing negative contributions of d=s bosonic degrees of freedom. We propose that the physics of string formation be studied nonperturbatively in the class of string bit models in which s>d, so that a long chain is stable, in contrast to the marginally stable (s=d=8) superstring chain. We focus on the simplest of these models with s=1 and d=0, in which the string bits live in zero space dimensions. The string bit creation operators are N×N matrices. We choose a Hamiltonian such that the large N limit produces a string moving in one space dimension, with excitations corresponding to one Grassmann light-cone world sheet field (s=1) and no bosonic world sheet field (d=0). We study this model at finite N to assess the role of the large N limit in the emergence of the spatial dimension. Our results suggest that stringlike states with large bit number M may not exist for N?(M-1)/2. If this is correct, one can have finite chains of string bits, but not a continuous string, at finite N. Only for extremely large N can such chains behave approximately like a continuous string, in which case there will also be the (approximate) emergence of a new spatial dimension. In string bit models designed to produce a critical superstring at N=?, we can then expect only approximate Lorentz invariance at finite N, with violations of order 1/N2.

Sun, Songge; Thorn, Charles B.

2014-05-01

171

Construct validity of Stable-2000 and Stable-2007 scores.  

PubMed

We addressed the construct validity of Stable-2000 and Stable-2007 scores by examining correlations between selected items and validated independent measures of relevant constructs in samples of convicted sex offenders. In Study 1, the Child Molester Attitudes item of the Stable-2000 shared 23% of the variance with a self-report measure of beliefs supportive of child molestation, r(19) = .48. The Deviant Sexual Interests items of the Stable-2000 and Stable-2007 shared 7% to 66% of the variance, respectively, with an offense-history-based measure of pedophilic interests, r(18) = .27 for the Stable-2000 and r(11) = .81 for the Stable-2007. In Study 2, the Lovers/Intimate Partners, General Social Rejection/Loneliness, Rapist Attitudes, and Child Molester Attitudes items of the Stable-2000 shared 4% to 19% of the variance with self-report measures of, respectively, intimacy, r(90) = -.44; loneliness, r(88) = .34; beliefs supportive of rape, r(72) = .21; and beliefs supportive of child molestation, r(78) = .36. The results generally suggest that the Stable items examined are associated with measures of similar constructs; however, the degree of convergence was lower than expected. More systematic and comprehensive research is needed to examine convergence of the Stable items with other relevant measures and additional aspects of construct validity. Such efforts will provide a clearer understanding of dynamic risk factors, appropriate areas of focus for treatment efforts, and, more generally, why some sex offenders recidivate. PMID:21543623

Nunes, Kevin L; Babchishin, Kelly M

2012-02-01

172

Tris(carbene)borate ligands featuring imidazole-2-ylidene, benzimidazol-2-ylidene and 1,3,4-triazol-2-ylidene donors. Evaluation of donor properties in four-coordinate {NiNO}10 complexes  

PubMed Central

The synthesis and characterization of new tris(carbene)borate ligand precursors containing substituted benzimidazol-2-ylidene and 1,3,4-triazol-2-ylidene donor groups, as well as a new tris(imidazol-2-ylidene)borate ligand precursor are reported. The relative donor strength of the tris(carbene)borate ligands have been evaluated by the position of ?(NO) in four-coordinate {NiNO}10 complexes, and follows the order: imidazol-2-ylidene > benzimidazol-2-ylidene > 1,3,4-triazol-2-ylidene. There is a large variation in ?(NO), suggesting these ligands to have a wide range of donor strengths while maintaining a consistent ligand topology. All ligands are stronger donors than Tp* and Cp*. PMID:23140462

Muñoz, Salvador B.; Foster, Wallace K.; Lin, Hsiu-Jung; Margarit, Charles G.; Dickie, Diane A.

2012-01-01

173

Bis-N-heterocyclic carbene (NHC) stabilized ?6-arene iron(0) complexes: synthesis, structure, reactivity, and catalytic activity.  

PubMed

Reaction of FeCl2 with the chelating bis-N-heterocyclic carbene (NHC) bis-(N-Dipp-imidazole-2-ylidene)methylene (abbreviated {((Dipp)C:)2CH2}) (Dipp = 2,6-di-isopropylphenyl) affords the complex [FeCl2{((Dipp)C:)2CH2}] (1) in high yield. Reduction of complex 1 with excess KC8 with a 10-fold molar excess of PMe3 affords the Fe(II) complex [FeH{((Dipp)C:)2CH2}(PMe3)(?(2)-PMe2CH2)] (2) as a mixture of three stereoisomers. Complex 2, the first example of any iron(II) complex bearing mutually an NHC and PMe3 ligand, is likely obtained from the in situ, reductively generated 16 VE Fe(0) complex, [Fe{((Dipp)C:)2CH2}(PMe3)2] (2'), following intramolecular C-H activation of one of the phosphorus-bound CH3 groups. Complex 2 is unstable in aromatic solvents and forms, via a novel synthetic transformation involving intramolecular reductive elimination and concomitant PMe3 elimination, the Fe (0) arene complex [Fe{((Dipp)C:)2CH2}(?(6)-C6D6)] (4-d6) in C6D6. Complex 4-d6 represents the first example of an NHC stabilized iron (0) arene complex. The transformation from 2 to 4-d6 can be accelerated at higher temperature and at 60 °C forms immediately. Alternatively, the reduction of 1 in the presence of toluene or benzene affords the complexes [Fe{((Dipp)C:)2CH2}(?(6)-C7H8)] (3) and [Fe{((Dipp)C:)2CH2}(?(6)-C6H6)] (4), selectively and in good yields. DFT calculations characterizing the bonding situation in 3 and 4 reveal similar energies of the HOMO and LUMO orbitals, with the LUMO orbital of both complexes located on the Dipp rings of the bis-NHC. The HOMO orbital reflects a ?-back-bonding interaction between the Fe(0) center and the chelating NHC ligand, while the HOMO-1 is associated with the arene interaction with the Fe(0) site. The calculations do not suggest any noninnocence of the coordinated arene in either complex. Moreover, the (57)Fe Mössbauer spectrum of 4 at 80K exhibits parameters (? = 0.43 mm·s(-1); ?EQ = 1.37 mm·s(-1)) which are consistent with a five-coordinate Fe(0) system, rendering 3 and 4 the first examples of well-defined authentic Fe(0)-?(6)-arene complexes of the type [Fe(?(6)-arene)L2] (L = ?(1 or 2) neutral ligand, mono or bidentate). Some reactivitiy studies of 3 are also reported: The reaction of 3 with excess CO selectively yields the five-coordinate piano-stool complex [Fe{((Dipp)C:)2CH2}(CO)3] (6) in near quantitative yields, while the reaction of complex 3 with C6D6 under heating affords by toluene elimination 4-d6. The catalytic ability of 4 was also investigated with respect to amide reduction to amines, for a variety of substrates using Ph2SiH2 as a hydride source. In all cases good to excellent yields to the corresponding amines were obtained. The use of 4 as a precatalyst represents the first example of a well-defined Fe(0) complex to effect this catalytic process. PMID:24195449

Blom, Burgert; Tan, Gengwen; Enthaler, Stephan; Inoue, Shigeyoshi; Epping, Jan Dirk; Driess, Matthias

2013-12-01

174

Stable face representations  

PubMed Central

Photographs are often used to establish the identity of an individual or to verify that they are who they claim to be. Yet, recent research shows that it is surprisingly difficult to match a photo to a face. Neither humans nor machines can perform this task reliably. Although human perceivers are good at matching familiar faces, performance with unfamiliar faces is strikingly poor. The situation is no better for automatic face recognition systems. In practical settings, automatic systems have been consistently disappointing. In this review, we suggest that failure to distinguish between familiar and unfamiliar face processing has led to unrealistic expectations about face identification in applied settings. We also argue that a photograph is not necessarily a reliable indicator of facial appearance, and develop our proposal that summary statistics can provide more stable face representations. In particular, we show that image averaging stabilizes facial appearance by diluting aspects of the image that vary between snapshots of the same person. We review evidence that the resulting images can outperform photographs in both behavioural experiments and computer simulations, and outline promising directions for future research. PMID:21536553

Jenkins, Rob; Burton, A. Mike

2011-01-01

175

Stable Black Families. Final Report.  

ERIC Educational Resources Information Center

This document is the final report of a study conducted to determine what factors contribute to strong Black family life and how these strong families solve problems, in order to add to the knowledge base on stable families so as to enhance practical intervention with families in need, and to identify models of self-help strategies used by stable…

Gary, Lawrence E.; And Others

176

Stable Spheromaks with Profile Control  

SciTech Connect

A spheromak equilibrium with zero edge current is shown to be stable to both ideal MHD and tearing modes that normally produce Taylor relaxation in gun-injected spheromaks. This stable equilibrium differs from the stable Taylor state in that the current density j falls to zero at the wall. Estimates indicate that this current profile could be sustained by non-inductive current drive at acceptable power levels. Stability is determined using the NIMROD code for linear stability analysis. Non-linear NIMROD calculations with non-inductive current drive could point the way to improved fusion reactors.

Fowler, T K; Jayakumar, R

2008-01-29

177

Synthesis of a stable adduct of dialane(4) (Al2H4) via hydrogenation of a magnesium(I) dimer.  

PubMed

The desorption of dihydrogen from magnesium(II) hydride, MgH2 (containing 7.6 wt% H), is reversible. MgH2 therefore holds promise as a hydrogen storage material in devices powered by fuel cells. We believed that dimeric magnesium(I) dimers (LMgMgL, L=?-diketiminate) could find use as soluble models to aid the study of the mechanisms and/or kinetics of the hydrogenation of magnesium and its alloys. Here, we show that LMgMgL can be readily hydrogenated to yield LMg(µ-H)2MgL by treatment with aluminium(III) hydride complexes. In one case, hydrogenation was reversed by treating LMg(µ-H)2MgL with potassium metal. The hydrogenation by-products are the first thermally stable, neutral aluminium(II) hydride complexes to be produced, one of which, [{(IPr)(H)2Al}2] (IPr=:C[{(C6H3-i-Pr(2)-2,6)NCH}2]), is an N-heterocyclic carbene adduct of the elusive parent dialane4 (Al2H4). A computational analysis of this compound is presented. PMID:20861903

Bonyhady, Simon J; Collis, David; Frenking, Gernot; Holzmann, Nicole; Jones, Cameron; Stasch, Andreas

2010-10-01

178

Earthquakes in stable continental crust  

SciTech Connect

Earthquakes can strike even in stable crust, well away from the familiar earthquake zones at the edges of tectonic plates, but their mere occurrence is both a source of concern in planning critical facilities such as nuclear power plants. The authors sought answers to two major questions: Just how much seismic activity does take place within the stable parts of continents And are there specific geologic features that make some areas of stable crust particularly susceptible to earthquakes They began by studying North America alone, but it soon became clear that the fairly short record of these rare events on a single continent would not provide enough data for reliable analysis. Hence, they decided to substitute space for time--to survey earthquake frequency and distribution in stable continental areas worldwide. This paper discusses their findings.

Johnson, A.C.; Kanter, L.R. (Memphis State Univ., TN (USA))

1990-03-01

179

Earthquakes in Stable Continental Crust.  

ERIC Educational Resources Information Center

Discussed are some of the reasons for earthquakes which occur in stable crust away from familiar zones at the ends of tectonic plates. Crust stability and the reactivation of old faults are described using examples from India and Australia. (CW)

Johnston, Arch C.; Kanter, Lisa R.

1990-01-01

180

Distributed Weighted Stable Marriage Problem  

NASA Astrophysics Data System (ADS)

The Stable Matching problem was introduced by Gale and Shapley in 1962. The input for the stable matching problem is a complete bipartite K n,n graph together with a ranking for each node. Its output is a matching that does not contain a blocking pair, where a blocking pair is a pair of elements that are not matched together but rank each other higher than they rank their current mates. In this work we study the Distributed Weighted Stable Matching problem. The input to the Weighted Stable Matching problem is a complete bipartite K n,n graph and a weight function W. The ranking of each node is determined by W, i.e. node v prefers node u 1 over node u 2 if W((v,u 1)) > W((v, u 2)). Using this ranking we can solve the original Stable Matching problem. We consider two different communication models: the billboard model and the full distributed model. In the billboard model, we assume that there is a public billboard and each participant can write one message on it in each time step. In the distributed model, we assume that each node can send O(logn) bits on each edge of the K n,n . In the billboard model we prove a somewhat surprising tight bound: any algorithm that solves the Stable Matching problem requires at least n - 1 rounds. We provide an algorithm that meets this bound. In the distributed communication model we provide an algorithm named intermediation agencies algorithm, in short (IAA), that solves the Distributed Weighted Stable Marriage problem in O(sqrt{n}) rounds. This is the first sub-linear distributed algorithm that solves some subcase of the general Stable Marriage problem.

Amira, Nir; Giladi, Ran; Lotker, Zvi

181

Shedding light on the photophysical properties of iridium(III) complexes with N-heterocyclic carbene ligands from a theoretical viewpoint.  

PubMed

The phosphorescent efficiencies of the Ir(III) carbene complexes 1-3 with wide-range color tuning were focused on in this work. A DFT/TDDFT (density functional theory/time-dependent density functional theory) investigation on the geometries in the ground and lowest triplet excited states, the frontier molecular orbitals, the absorption spectra, and d-orbital splittings of 1-3 were provided to get a better understanding of structure–property relationships. Importantly, to shed light on the difference in phosphorescent quantum yields for 1-3, radiative decay constants as well as zero-field-splitting parameters were calculated based on the estimation of spin–orbit coupling (SOC) matrix elements denoted as T(?1)|H(SOC)|S(n). The results show that, for any complex, the radiative decay rates in the three substates (namely, T(x), T(y), and T(z0) are not equal, and the largest radiative rates of 1-3 are all located in x substates with values of 1.0764 × 10(4), 0.8231 × 10(4), and 1.9596 × 10(4) s(–1), respectively. Moreover, for 3 with the highest quantum efficiency, we make efforts to modify it through varying substituents and substituent positions not only to achieve blue shift in the emission but also to obtain improved triplet energy. PMID:24844441

Wang, Li; Wu, Yong; Geng, Yun; Wu, Jie; Zhu, Dong-Xia; Su, Zhong-Min

2014-07-10

182

DFT investigation on mechanisms and stereoselectivities of [2 + 2 + 2] multimolecular cycloaddition of ketenes and carbon disulfide catalyzed by N-heterocyclic carbenes.  

PubMed

The first theoretical investigation using density functional theory (DFT) methods to study the detailed reaction mechanisms of stereoselective [2 + 2 + 2] multimolecular cycloaddition of ketene (two molecules) and carbon disulfide (CS2, one molecule) which is catalyzed by N-heterocyclic carbene (NHC) is presented in this paper. The calculated results indicate that this reaction occurs through four steps: the complexation of NHC with ketene (channel 1a) rather than with CS2 (channel 1b), addition of CS2 (channel 2b) but not dimerization of ketene (channel 2a), formal [4 + 2] cycloaddition with a second molecule of ketene (channel 3a) rather than intramolecular [2 + 2] cycloaddition (channel 3b), and finally regeneration of NHC. The second step is revealed to be the rate-determining step. Moreover, the stereoselectivities associated with the chiral carbon center and the carbon double bond are predicted to be respectively determined in the second and third steps and respectively R and E configurations dominated, which are in good agreement with the experimental results. Furthermore, the possible mechanisms of the identical [2 + 2 + 2] cycloaddition catalyzed by N,N-dimethylpyridin-4-amine (DMAP) have also been investigated to help understand the ring closure mechanism proceeding in the third step. PMID:24188481

Zhang, Wen-Jing; Wei, Dong-Hui; Tang, Ming-Sheng

2013-12-01

183

Stepwise Strategy to Cyclometallated Pt(II) Complexes with N-Heterocyclic Carbene Ligands: A Luminescence Study on New ?-Diketonate Complexes.  

PubMed

The imidazolium salt 3-methyl-1-(naphthalen-2-yl)-1H-imidazolium iodide (2) has been treated with silver(I) oxide and [{Pt(?-Cl)(?(3) -2-Me-C3 H4 )}2 ] (?(3) -2-Me-C3 H4 =?(3) -2-methylallyl) to give the intermediate N-heterocyclic carbene complex [PtCl(?(3) -2-Me-C3 H4 )(H$\\widehat{CC}$*-?C*)] (3) (H$\\widehat{CC}$*-?C*=3-methyl-1-(naphthalen-2-yl)-1H-imidazol-2-ylidene). Compound 3 undergoes regiospecific cyclometallation at the naphthyl ring of the NHC ligand to give the five-membered platinacycle compound [{Pt(?-Cl)($\\widehat{CC}$*)}2 ] (4). Chlorine abstraction from 4 with ?-diketonate Tl derivatives rendered the corresponding neutral compounds [Pt($\\widehat{CC}$*)(L-O,O')] {L=acac (HL=acetylacetone) 5, phacac (HL=1,3-diphenyl-1,3-propanedione) 6, hfacac (HL=hexafluoroacetylacetone) 7}. All of the compounds (3-7) were fully characterized by standard spectroscopic and analytical methods. X-ray diffraction studies were performed on 5-7, revealing short Pt?Pt and ?-? interactions in the solid-state structure. The influence of the R-substituents of the ?-diketonate ligand on the photophysical properties and the use of the most efficient emitter, 5, as phosphor converter has also been studied. PMID:25412763

Fuertes, Sara; García, Hector; Perálvarez, Mariano; Hertog, Wim; Carreras, Josep; Sicilia, Violeta

2015-01-19

184

Intramolecular C?H/O?H Bond Cleavage with Water and Alcohol Using a Phosphine-Free Ruthenium Carbene NCN Pincer Complex.  

PubMed

Transition metal complexes that exhibit metal-ligand cooperative reactivity could be suitable candidates for applications in water splitting. Ideally, the ligands around the metal should not contain oxidizable donor atoms, such as phosphines. With this goal in mind, we report new phosphine-free ruthenium NCN pincer complexes with a central N-heterocyclic carbene donor and methylpyridyl N-donors. Reaction with base generates a neutral, dearomatized alkoxo-amido complex, which has been structurally and spectroscopically characterized. The tert-butoxide ligand facilitates regioselective, intramolecular proton transfer through a C?H/O?H bond cleavage process occurring at room temperature. Kinetic and thermodynamic data have been obtained by VT NMR experiments; DFT calculations support the observed behavior. Isolation and structural characterization of a doubly dearomatized phosphine complex also strongly supports our mechanistic proposal. The alkoxo-amido complex reacts with water to form a dearomatized ruthenium hydroxide complex, a first step towards phosphine-free metal-ligand cooperative water splitting. PMID:25266279

Prokopchuk, Demyan E; Tsui, Brian T H; Lough, Alan J; Morris, Robert H

2014-12-15

185

Synthesis of tridentate 2,6-bis(imino)pyridyl ruthenium(II) complexes with N-heterocyclic carbene ligands: activation of imidazolium salts.  

PubMed

Low-valent Ru(0) complexes, [?(2)-N3]Ru(?(6)-Ar) (1) or {[N3]Ru}2(?-N2) (2), where Ar = C6H6 or C6H5Me, and [N3] = 2,6-(2,4,6-(CH3)3C6H2N?CCH3)2C5H3N, activate C-H bonds in imidazolium salts to produce bis(imino)pyridyl ruthenium-(imidazolidin-2-ylidene) complexes, [N3]Ru(H)(X)(NHC) (4) (X = halides and tosylate). Formation of 4 is most likely to proceed via C-H oxidative addition, followed by anion coordination, which is expected to be a useful pathway in synthesizing new complexes with both N-heterocyclic carbene (NHC) and hydride ligands. A zwitterionic ruthenium complex with an ylidic ligand, bis(imino)pyridyl ruthenium-(2-methyleneimidazoline) complex, 7, was also successfully isolated and fully characterized. The (1)H NMR spectra and the solid-state structure confirm that complex 7 is an ylidic transition-metal complex with both NHC and hydride ligands, which was formed through the activation of imidazolium salts. PMID:25337998

Yoo, Hyojong; Berry, Donald H

2014-11-01

186

WEIGHTED GRASSMANNIANS AND STABLE HYPERPLANE ARRANGEMENTS  

E-print Network

generalization of (1) Hassett's weighted stable curves, and (2) Hacking-Keel-Tevelev's stable hyperplane's moduli M0, of weighted stable n-pointed curves [Has03], and (2) Hacking-Keel-Tevelev's moduli M(r, n

Alexeev, Valery

187

Multi-stable cylindrical lattices  

NASA Astrophysics Data System (ADS)

We present a cylindrical lattice structure that mimics the behaviour of the virus bacteriophage T4 in having two (or more) stable states which differ in their radii and length. While the virus achieves bistability through molecular mechanisms we use composite materials to exploit the interplay between pre-stress, material properties and structural geometry. We demonstrate (computationally) that multi-stability is a robust phenomenon. We also show (analytically) that it is possible to choose the design variables so that the energy is independent of the radius, thus resulting in every state of the structure being stable.

Pirrera, Alberto; Lachenal, Xavier; Daynes, Stephen; Weaver, Paul M.; Chenchiah, Isaac V.

2013-11-01

188

A Stable Local Limit Theorem  

Microsoft Academic Search

Conditions are given which imply that the partial sums of a sequence of independent integer-valued random variables, suitably normalized, converge in distribution to a stable law of exponent $\\\\alpha, 0 < \\\\alpha < 2$, and imply as well that a strong version of the corresponding local limit theorem holds.

J. Mineka

1974-01-01

189

Bayesian stable isotope mixing models  

EPA Science Inventory

In this paper we review recent advances in Stable Isotope Mixing Models (SIMMs) and place them into an over-arching Bayesian statistical framework which allows for several useful extensions. SIMMs are used to quantify the proportional contributions of various sources to a mixtur...

190

Achieving Biologically Stable Drinking Water  

Microsoft Academic Search

Biologically stable water does not promote the growth of microorganisms during its distribution. This article combines microbiological theory and European practice to demonstrate how biological processes within a water treatment plant can remove the organic and inorganic substrates that cause or contribute to biological instability. Theory and practice indicate that ammonium and manganese ions and biodegradable organic compounds can be

Bruce E. Rittmann; Vernon L. Snoeyink

1984-01-01

191

Synthesis and Characterization of Amphiphilic Cyclic Diblock Copolypeptoids from N-Heterocyclic Carbene-Mediated Zwitterionic Polymerization of N-Substituted N-carboxyanhydride  

PubMed Central

N-Heterocyclic carbene (NHC)-mediated ring-opening polymerization of N-decylN-carboxylanhydride monomer (De-NCA) has been shown to occur in a controlled manner, yielding cyclic poly(N-decyl-glycine)s (c-PNDGs) with polymer molecular weights (MW) between 4.8 and 31 kg·mol?1 and narrow molecular weight distributions (PDI < 1.15). The reaction exhibits pseudo-first order kinetics with respect to monomer concentration. The polymer MW increases linearly with conversion, consistent with a living polymerization. ESI MS and SEC analysesconfirm the cyclic architectures of the forming polymers. DSC and WAXS studies reveal that the c-PNDG homopolymers are highly crystalline with two prominent first order transitions at 72–79°C (Tm,1) and 166–177°C (Tm,2), which have been attributed to the side chain and main chain melting respectively. A series of amphiphilic cyclic diblock copolypeptoids [i.e.,poly(N-methyl-glycine)-b-poly(N-decyl-glycine) (c-PNMG-b-PNDG)] with variable molecular weight and composition was synthesized by sequential NHC-mediated polymerization of the corresponding N-methyl N-carboxyanhydride (Me-NCA) and De-NCA monomers. 1H NMR analysis reveals that adjusting the initial monomer to NHC molar ratio can readily control the block copolymer chain length and composition. Time-lapsed light scattering and cryogenic transmission electron microscopy (cryo-TEM) analysis of c-PNDG-b-PNMG samples revealed that the amphiphilic cyclic block copolypeptoids self-assemble into spherical micelles that reorganize into micron-long cylindrical micelles with uniform diameter in room temperature methanol over the course of several days. An identical morphological transition has also been noted for the linear analogs, which occurs more rapidly than for the cyclic copolypeptoids. We tentatively attribute this difference to the different crystallization kinetics of the solvophobic block (i.e., PNDG) in the cyclic and linear block copolypeptoids. PMID:22247571

Lee, Chang-Uk; Smart, Thomas P.; Guo, Li; Epps, Thomas H.; Zhang, Donghui

2011-01-01

192

Bis-N-Heterocyclic Carbene Palladium(IV) Tetrachloride Complexes: Synthesis, Reactivity and Mechanisms of Direct Chlorinations and Oxidations of Organic Substrates  

PubMed Central

This paper describes the preparation and isolation of novel octahedral CH2-bridged bis-(N-heterocyclic carbene)palladium(IV) tetrachlorides of the general formula LPdIVCl4 [L = (NHC)CH2(NHC)] from LPdIICl2 and Cl2. In intermolecular, non-chelation controlled transformations LPdIVCl4 reacted with alkenes and alkynes to 1,2-dichlorination adducts. Aromatic, benzylic, and aliphatic CH-bonds were converted into C-Cl bonds. Detailed mechanistic investigations in the dichlorinations of alkenes were conducted on the 18VE PdIV-complex. Positive solvent effects as well as kinetic measurements probing the impact of cyclohexene- and chloride concentrations on the rate of alkene chlorination, support a PdIV-Cl ionization in the first step. Product stereochemistry and product distributions from various alkenes also support Cl+-transfer from the pentacoordinated PdIV-intermediate LPdIVCl3+ to olefins. 1-hexene/3-hexene competition experiments rule out both the formation of ?-complexes along the reaction coordinate as well as in situ generated Cl2 from a reductive elimination process. Instead, a ligand-mediated direct Cl+-transfer from LPdIVCl3+ to the ?-system is likely to occur. Similarly, C-H bond chlorinations proceed via an electrophilic process with in situ formed LPdIVCl3+. The presence of a large excess of added Cl? slows down cyclohexene chlorination while the presence of stoichiometric amounts of chloride accelerates both PdIV-Cl ionization and Cl+-transfer from LPdIVCl3+. 1H NMR titrations, T1 relaxation time measurements, binding isotherms and Job plot analysis point to the formation of a trifurcated Cl?…H-C bond in the NHC-ligand periphery as a supramolecular cause for the accelerated chemical events involving the metal center. PMID:21247150

McCall, A. Scott; Wang, Hongwang; Desper, John M.; Kraft, Stefan

2014-01-01

193

Synthesis and characterization of a triphenyl-substituted radical and an unprecedented formation of a carbene-functionalized quinodimethane.  

PubMed

The trichlorosilylcarbene monoradical (Cy-cAAC?·)SiCl3 (1) was directly converted to (Cy-cAAC?·)SiPh3 (2) by substitution of the three chlorine atoms with phenyl groups without affecting the radical center adjacent to the silicon atom. In addition to the structure determination, compound 2 was studied by EPR spectroscopy and DFT calculations. The three hyperfine lines in the EPR spectrum of 2 are due to the coupling with (14)N nucleus. Functionalized 1,4-quinodimethane Me2-cAAC=C6H4=CPh2 (7) was isolated, whereas carbon analogue of radical 2 was targeted. Cyclic voltammogram of 7 indicated that a stable radical-anion 7??·-, as well as a radical-cation 7??·+, can be prepared. Theoretical calculations showed that one-electron ionization energy and electron affinity of 7 are 5.1 and 0.7?eV?mol(-1), respectively. PMID:24664879

Mondal, Kartik Chandra; Samuel, Prinson P; Roesky, Herbert W; Niepötter, Benedikt; Herbst-Irmer, Regine; Stalke, Dietmar; Ehret, Fabian; Kaim, Wolfgang; Maity, Bholanath; Koley, Debasis

2014-07-21

194

Palladium complexes of abnormal N-heterocyclic carbenes as precatalysts for the much preferred Cu-free and amine-free Sonogashira coupling in air in a mixed-aqueous medium.  

PubMed

A series of new PEPPSI (Pyridine Enhanced Precatalyst Preparation Stabilization and Initiation) themed precatalysts of abnormal N-heterocyclic carbenes for the highly desirable Cu-free and amine-free Sonogashira coupling in air in a mixed-aqueous medium is reported. Specifically, the PEPPSI themed (NHC)PdI2(pyridine) type precatalysts, 1b-4b, efficiently carried out the highly convenient Cu-free and amine-free Sonogashira coupling of aryl bromides and iodides with terminal acetylenes in air in a mixed aqueous medium. Complexes, 1b-4b, were synthesized by the direct reaction of the corresponding imidazo[1,2-a]pyridinium iodide salts, 1a-4a, with PdCl2 in pyridine in the presence of K2CO3 as a base while the imidazo[1,2-a]pyridinium iodide salts, 1a-4a, were in turn synthesized by the alkylation reactions of the respective imidazo[1,2-a]pyridine derivatives with alkyl iodides. The density functional theory (DFT) studies revealed that these imidazol-3-ylidene[1,2-a]pyridine derived abnormal carbenes are strongly sigma-donating and consequently significantly weaken the catalytically important labile trans pyridine ligand in 1b-4b. PMID:20023883

John, Alex; Shaikh, Mobin M; Ghosh, Prasenjit

2009-12-21

195

Effect of chelating ring size in catalytic ketone hydrogenation: facile synthesis of ruthenium(II) precatalysts containing an N-heterocyclic carbene with a primary amine donor for ketone hydrogenation and a DFT study of mechanisms.  

PubMed

A half-sandwich ruthenium(II) complex, [Ru(?(6)-p-cymene)(C-NH(2))Cl]PF(6) (4·PF(6)), containing an N-heterocyclic carbene (NHC) with a primary amine donor (C-NH(2)) which chelates through the carbene carbon and the amine nitrogen to form a 6-membered ring was synthesized in a one-pot reaction starting from a primary-amine functionalized imidazolium salt 2. Complex 4·PF(6) catalyzed the hydrogenation of ketones using 2-propanol or H(2) as the reductant. A maximum turnover frequency of 1062 h(-1) and a turnover number of 1140 at 5 h were achieved for the transfer hydrogenation of 3'-chloroacetophenone in 2-propanol at 75 °C. A cationic hydride-amine complex 5, [Ru(?(6)-p-cymene)(C-NH(2))H]PF(6), was synthesized, and this reacted very slowly with acetophenone unless first activated by an alkoxide base. Computational studies by DFT methods suggested that the poor reactivity of the hydride-amine complex 5 was attributed to a large barrier for the transfer of its H(+)/H(-) couple to a ketone for bifunctional catalysis. An inner-sphere mechanism, which involves a decoordinated amine group of the C-NH(2) ligand, was computed to be a feasible energetic pathway in comparison to the computed outer-sphere bifunctional mechanism. This explains the catalytic activity and selectivity that is observed for the newly synthesized ruthenium(II) catalysts. PMID:22728720

Ohara, Hisashi; O, Wylie W N; Lough, Alan J; Morris, Robert H

2012-08-01

196

LP based approach to optimal stable matchings  

SciTech Connect

We study the classical stable marriage and stable roommates problems using a polyhedral approach. We propose a new LP formulation for the stable roommates problem. This formulation is non-empty if and only if the underlying roommates problem has a stable matching. Furthermore, for certain special weight functions on the edges, we construct a 2-approximation algorithm for the optimal stable roommates problem. Our technique uses a crucial geometry of the fractional solutions in this formulation. For the stable marriage problem, we show that a related geometry allows us to express any fractional solution in the stable marriage polytope as convex combination of stable marriage solutions. This leads to a genuinely simple proof of the integrality of the stable marriage polytope. Based on these ideas, we devise a heuristic to solve the optimal stable roommates problem. The heuristic combines the power of rounding and cutting-plane methods. We present some computational results based on preliminary implementations of this heuristic.

Teo, Chung-Piaw [National Univ. of Singapore (Singapore); Sethuraman, J.

1997-06-01

197

Stable Carbon and Nitrogen Isotopic  

Microsoft Academic Search

The perennially ice-covered lakes in the McMurdo Dry Valleys, Antarctica, are part of the coldest and driest ecosystem on earth. To understand lacustrine carbon and nitrogen cycling in this end-member ecosystem, and to define paleolimnological proxies for ice-covered lakes, we measured the stable carbon and nitrogen isotopic composition of particulate organic matter (POM) and benthic organic matter (BOM) within the

Jennifer Lawson; PETER T. DORAN; Fabien Kenig; DAVID J. DES MARAIS; JOHN C. PRISCU

2004-01-01

198

Advanced Thermally Stable Jet Fuels  

SciTech Connect

The Penn State program in advanced thermally stable jet fuels has five components: 1) development of mechanisms of degradation and solids formation; 2) quantitative measurement of growth of sub-micrometer and micrometer-sized particles during thermal stressing; 3) characterization of carbonaceous deposits by various instrumental and microscopic methods; 4) elucidation of the role of additives in retarding the formation of carbonaceous solids; and 5) assessment of the potential of producing high yields of cycloalkanes and hydroaromatics from coal.

A. Boehman; C. Song; H. H. Schobert; M. M. Coleman; P. G. Hatcher; S. Eser

1998-01-01

199

Stable polymorph of morphine1  

PubMed Central

In the stable polymorph of the title compound, C17H19NO3 [systematic name: (5?,6?)-7,8-didehydro-4,5-ep­oxy-17-methyl­morphinan-3,6-diol], the mol­ecular conformation is in agreement with the characteristics of previously reported morphine forms. The molecule displays the typical T-shape and its piperidine ring adopts a slightly distorted chair conformation. Inter­molecular O—H?O hydrogen bonds link the mol­ecules into helical chains parallel to the b axis. Intra­molecular O—H?O hydrogen bonds are also observed. PMID:23476407

Gelbrich, Thomas; Braun, Doris E.; Griesser, Ulrich J.

2013-01-01

200

Mechanism of Ni N-heterocyclic carbene catalyst for C-O bond hydrogenolysis of diphenyl ether: a density functional study.  

PubMed

Catalysts for aromatic C-O bond activation can potentially be used for the lignin degradation process. We investigated the mechanisms of C-O bond hydrogenolysis of diphenyl ether (PhOPh) by the nickel N-heterocyclic carbene (Ni-SIPr) complex to produce benzene and phenol as products. Our calculations revealed that diphenyl ether is not only a substrate, but also serves as a ligand to stabilize the Ni-SIPr complex. The Ni(SIPr)(?(6)-PhOPh) complex is initially formed before rearranging to Ni(SIPr)(?(2)-PhOPh), the active species for C-O bond activation. The catalytic reaction has three steps: (i) oxidative addition of Ni(SIPr)(?(2)-PhOPh) to form [Ni(SIPr)(OPh)(Ph)](0), (ii) ?-complex-assisted metathesis, in which H2 binds to the nickel to form [Ni(SIPr)(OPh)(Ph)(H2)](0), and then benzene (or phenol) is eliminated, and (iii) reductive elimination of phenol (or benzene) and the binding of PhOPh to regenerate Ni(SIPr)(?(2)-PhOPh). As the rate determining step is the oxidative addition step (+24 kcal mol(-1)), we also calculated the free energy barriers for the oxidative addition of diaryl ether containing a trifluoromethyl electron withdrawing group (PhOC6H4CF3) and found that C-O bond activation at the carbon adjacent to the aryl ring that contains the electron withdrawing substituent is preferred. This is in agreement with the experimental results, in that the major products are phenol and trifluoromethylbenzene. Moreover, the hydrogenation of benzene via Ni(SIPr)(?(2)-C6H6) requires a high energy barrier (+39 kcal mol(-1)); correspondingly, the hydrogenation products, e.g. cyclohexane and cyclohexadiene, were not observed in the experiment. Understanding the reaction mechanisms of the nickel catalysts for C-O bond hydrogenolysis of diphenyl ether will guide the development of catalytic systems for aromatic C-O bond activation to achieve the highest possible selectivity and efficiency. PMID:25355042

Sawatlon, Boodsarin; Wititsuwannakul, Taveechai; Tantirungrotechai, Yuthana; Surawatanawong, Panida

2014-12-28

201

Silver(I) complexes of mono- and bidentate N-heterocyclic carbene ligands: Synthesis, crystal structures, and in vitro antibacterial and anticancer studies.  

PubMed

A series of benzimidazole-based N-heterocyclic carbene (NHC) proligands {1-benzyl-3-(2-methylbenzyl)-benzimidazolium bromide/hexafluorophosphate (1/4), 1,3-bis(2-methylbenzyl)-benzimidazolium bromide/hexafluorophosphate (2/5) and 1,3-bis(3-(2-methylbenzyl)-benzimidazolium-1-ylmethylbenzene dibromide/dihexafluorophosphate (3/6)} has been synthesized by the successive N-alkylation method. Ag complexes {1-benzyl-3-(2-methylbenzyl)-benzimidazol-2-ylidenesilver(I) hexafluorophosphate (7), 1,3-bis(2-methylbenzyl)-benzimidazol-2-ylidenesilver(I) hexafluorophosphate (8) and 1,3-bis(3-(2-methylbenzyl)-benzimidazol-2-ylidene)-1-ylmethylbenzene disilver(I) dihexafluorophosphate (9)} of NHC ligands have been synthesized by the treatment of benzimidazolium salts with Ag2O at mild reaction conditions. Both, NHC proligands and Ag-NHC complexes have been characterized by (1)H and (13)C{(1)H} NMR and FTIR spectroscopy and elemental analysis technique. Additionally, the structure of the NHC proligand 5 and the mononuclear Ag complexes 7 and 8 has been elucidated by the single crystal X-ray diffraction analysis. Both the complexes exhibit the same general structural motif with linear coordination geometry around the Ag centre having two NHC ligands. Preliminary in vitro antibacterial potentials of reported compounds against a Gram negative (Escherichia coli) and a Gram positive (Bacillus subtilis) bacteria evidenced the higher activity of mononuclear silver(I) complexes. The anticancer studies against the human derived colorectal cancer (HCT 116) and colorectal adenocarcinoma (HT29) cell lines using the MTT assay method, revealed the higher activity of Ag-NHC complexes. The benzimidazolium salts 4-6 and Ag-NHC complexes 7-9 displayed the following IC50 values against the HCT 116 and HT29 cell lines, respectively, 31.8 ± 1.9, 15.2 ± 1.5, 4.8 ± 0.6, 10.5 ± 1.0, 18.7 ± 1.6, 1.20 ± 0.3 and 245.0 ± 4.6, 8.7 ± 0.8, 146.1 ± 3.1, 7.6 ± 0.7, 5.5 ± 0.8, 103.0 ± 2.3 ?M. PMID:25461313

Haque, Rosenani A; Choo, Sze Yii; Budagumpi, Srinivasa; Iqbal, Muhammad Adnan; Al-Ashraf Abdullah, Amirul

2015-01-27

202

Brief Announcement: Distributed Almost Stable Marriage  

E-print Network

1 Brief Announcement: Distributed Almost Stable Marriage Patrik Floréen, Petteri Kaski, Valentin: Distributed Almost Stable Marriage Patrik Floréen, Petteri Kaski, Valentin Polishchuk, Jukka Suomela Helsinki

Suomela, Jukka

203

Persistence Length of Stable Microtubules  

NASA Astrophysics Data System (ADS)

Microtubules are a vital component of the cytoskeleton. As the most rigid of the cytoskeleton filaments, they give shape and support to the cell. They are also essential for intracellular traffic by providing the roadways onto which organelles are transported, and they are required to reorganize during cellular division. To perform its function in the cell, the microtubule must be rigid yet dynamic. We are interested in how the mechanical properties of stable microtubules change over time. Some "stable" microtubules of the cell are recycled after days, such as in the axons of neurons or the cilia and flagella. We measured the persistence length of freely fluctuating taxol-stabilized microtubules over the span of a week and analyzed them via Fourier decomposition. As measured on a daily basis, the persistence length is independent of the contour length. Although measured over the span of the week, the accuracy of the measurement and the persistence length varies. We also studied how fluorescently-labeling the microtubule affects the persistence length and observed that a higher labeling ratio corresponded to greater flexibility.

Hawkins, Taviare; Mirigian, Matthew; Selcuk Yasar, M.; Ross, Jennifer

2011-03-01

204

Stable Imaging for Astronomy (SIA)  

NASA Astrophysics Data System (ADS)

One of the most challenging fields of astronomical instrumentation is probably high-contrast imaging since it ultimately combines ultra-high sensitivity at low flux and the ability to cope with photon flux contrasts of several hundreds of millions or even more. These two aspects implicitly require that high-contrast instruments should be highly stable in the sense of the reproducibility of their measurements at different times, but also, continuously stable over time. In most high contrast instruments or experiments, their sensitivity is broken after at most tens of minutes of operation due to uncontrolled and unknown behaviour of the whole experiment regarding the environmental conditions. In this paper, we introduce a general approach of an exhaustive stability study for high-contrast imaging that has been initiated at Lagrange Laboratory, Observatoire de la Côte d'Azur (OCA). On a practical ground, one of the fundamental issues of this study is the metrology, which is the basis of all reproducible measurements. We describe a small experiment designed to understand the behaviour of one of our ultra-precise metrology tools (a commercial sub-nanometric 3-way interferometer) and derive the conditions under which its operation delivers reliable results. The approach will apply to the high-contrast imaging test-bench SPEED, under development at OCA.

Beaulieu, Mathilde; Ottogalli, Sebastien; Preis, Olivier; Bresson, Yves; Rivet, Jean-Pierre; Abe, Lyu; Vakili, Farrokh

2014-07-01

205

Stable marriage with general preferences Extended Abstract  

E-print Network

Stable marriage with general preferences Extended Abstract Linda Farczadi, Konstantinos Georgiou of the classical stable marriage problem. In our model, the preferences on one side of the partition are given is practically well-motivated, and as we show, encompasses the well studied hard variant of stable marriage where

Könemann, Jochen

206

Stable marriage problems with quantitative preferences  

E-print Network

Stable marriage problems with quantitative preferences Maria Silvia Pini, Francesca Rossi, K. Brent Venable, and Toby Walsh Abstract The stable marriage problem is a well-known problem of matching men, to matching students to schools or more generally to any two-sided market. In the classical stable marriage

Rossi, Francesca

207

EXCEPTIONALLY SMALL BALLS IN STABLE TREES  

E-print Network

EXCEPTIONALLY SMALL BALLS IN STABLE TREES Thomas Duquesne Guanying Wang November 14, 2011 Abstract The -stable trees are random measured compact metric spaces that appear as the scaling limit of Galton-Watson trees whose offspring distribution lies in a -stable domain, (1, 2]. They form a specific class

Paris-Sud XI, Université de

208

Uses of stable isotopes in fish ecology  

EPA Science Inventory

Analyses of fish tissues (other than otoliths) for stable isotope ratios can provide substantial information on fish ecology, including physiological ecology. Stable isotopes of nitrogen and carbon frequently are used to determine the mix of diet sources for consumers. Stable i...

209

Stable massive particles at colliders  

SciTech Connect

We review the theoretical motivations and experimental status of searches for stable massive particles (SMPs) which could be sufficiently long-lived as to be directly detected at collider experiments. The discovery of such particles would address a number of important questions in modern physics including the origin and composition of dark matter in the universe and the unification of the fundamental forces. This review describes the techniques used in SMP-searches at collider experiments and the limits so far obtained on the production of SMPs which possess various colour, electric and magnetic charge quantum numbers. We also describe theoretical scenarios which predict SMPs, the phenomenology needed to model their production at colliders and interactions with matter. In addition, the interplay between collider searches and open questions in cosmology such as dark matter composition are addressed.

Fairbairn, M.; /Stockholm U.; Kraan, A.C.; /Pennsylvania U.; Milstead, D.A.; /Stockholm U.; Sjostrand, T.; /Lund U.; Skands, P.; /Fermilab; Sloan, T.; /Lancaster U.; ,

2006-11-01

210

Dimensionally stable metallic hydride composition  

DOEpatents

A stable, metallic hydride composition and a process for making such a composition. The composition comprises a uniformly blended mixture of a metal hydride, kieselguhr, and a ballast metal, all in the form of particles. The composition is made by subjecting a metal hydride to one or more hydrogen absorption/desorption cycles to disintegrate the hydride particles to less than approximately 100 microns in size. The particles are partly oxidized, then blended with the ballast metal and the kieselguhr to form a uniform mixture. The mixture is compressed into pellets and calcined. Preferably, the mixture includes approximately 10 vol. % or more kieselguhr and approximately 50 vol. % or more ballast. Metal hydrides that can be used in the composition include Zr, Ti, V, Nb, Pd, as well as binary, tertiary, and more complex alloys of La, Al, Cu, Ti, Co, Ni, Fe, Zr, Mg, Ca, Mn, and mixtures and other combinations thereof. Ballast metals include Al, Cu and Ni.

Heung, Leung K. (Aiken, SC)

1994-01-01

211

Stable density stratification solar pond  

NASA Technical Reports Server (NTRS)

A stable density-stratification solar pond for use in the collection and storage of solar thermal energy including a container having a first section characterized by an internal wall of a substantially cylindrical configuration and a second section having an internal wall of a substantially truncated conical configuration surmounting the first section in coaxial alignment therewith, the second section of said container being characterized by a base of a diameter substantially equal to the diameter of the first section and a truncated apex defining a solar energy acceptance opening is discussed. A body of immiscible liquids is disposed within the container and comprises a lower portion substantially filling the first section of the container and an upper portion substantially filling the second section of the container, said lower portion being an aqueous based liquid of a darker color than the upper portion and of a greater density. A protective cover plate is removably provided for covering the acceptance opening.

Lansing, F. L. (inventor)

1985-01-01

212

Synthesis, structural characterization of benzimidazole-functionalized Ni(II) and Hg(II) N-heterocyclic carbene complexes and their applications as efficient catalysts for Friedel–Crafts alkylations  

Microsoft Academic Search

[Ni(L1)2](PF6)2 (3a, L1 = 3-(1-ethyl-1H-benzimidazol-2-yl)methyl)-1-((6-methylpyridin-2-yl)methyl)imidazolyl-idene), [Ni(L2)2(CH3CN)](PF6)2 (3b, L2 = 3-(1-ethyl-1H-benzimidazol-2-yl)methyl)-1-((6-methylpyridin-2-yl)-methyl)benzimidazolylidene), and [Hg(L1)2(CH3CN)2](PF6)2 (4) have been successfully prepared and fully characterized by NMR, ESI-MS spectroscopy, and X-ray diffraction analysis. The nickel complexes reveal a square-planar structure with two carbene ligands and benzimidazole groups at the cis configuration. The nickel complex 3b has been proved to be a highly efficient catalyst for Friedel–Crafts alkylation of indoles

Guoli Huang; Hongsheng Sun; Xiaojie Qiu; Yingzhong Shen; Juli Jiang; Leyong Wang

2011-01-01

213

Concerted amidation of activated esters: reaction path and origins of selectivity in the kinetic resolution of cyclic amines via N-heterocyclic carbenes and hydroxamic acid cocatalyzed acyl transfer.  

PubMed

The N-heterocyclic carbene and hydroxamic acid cocatalyzed kinetic resolution of cyclic amines generates enantioenriched amines and amides with selectivity factors up to 127. In this report, a quantum mechanical study of the reaction mechanism indicates that the selectivity-determining aminolysis step occurs via a novel concerted pathway in which the hydroxamic acid plays a key role in directing proton transfer from the incoming amine. This modality was found to be general in amide bond formation from a number of activated esters including those generated from HOBt and HOAt, reagents that are broadly used in peptide coupling. For the kinetic resolution, the proposed model accurately predicts the faster reacting enantiomer. A breakdown of the steric and electronic control elements shows that a gearing effect in the transition state is responsible for the observed selectivity. PMID:25050843

Allen, Scott E; Hsieh, Sheng-Ying; Gutierrez, Osvaldo; Bode, Jeffrey W; Kozlowski, Marisa C

2014-08-20

214

Templating an N-heterocyclic carbene (NHC)-cyclometalated Cp*Ir(III)-based oxidation precatalyst on a pendant coordination platform: assessment of the oxidative behavior via electrochemical, spectroscopic and catalytic probes.  

PubMed

The coordination of metalloligands to derive modified properties of the metal functionality is one of the interesting strategies practiced in materials chemistry and catalysis. In this work, a pendant terpyridine ligand has been utilized for templating a Cp*Ir(III)(NHC)-based (NHC = N-heterocyclic carbene) oxidation precatalyst to assess its modified oxidative behavior via electrochemical, UV-vis spectroscopic, and catalytic probes. These studies suggested that the coordination-template enhances the electron-deficiency at the Ir(III) redox center and affects the nature of the oxidized high-valent Ir-oxo species during chemical oxidation. Moreover, both the premodified and postmodified Cp*Ir(III)(NHC)-based complexes were found to be equally efficient in catalytic sp(3) C-H oxidation reactions with NaIO4 as a mild sacrificial oxidant. PMID:25415183

Gupta, Suraj K; Choudhury, Joyanta

2015-01-21

215

Helical metal cage of silver(I) and mercury(II)-N-heterocyclic carbene complexes of 1,4-phenylene-bis{imidazo[1,5-a]pyridine-4-iumhexaflurophosphate}  

NASA Astrophysics Data System (ADS)

Novel N-heterocyclic carbene (NHC) architecture of 1,4-phenylene-bis{imidazo[1,5-a]pyridine-4 iumhexaflurophosphate}, [1(HPF6)2] has been synthesized in two steps from commercially available starting materials. The p-phylene bridged free annulated imidazolium salt has been synthesized and characterized both in solution and solid-state and has been used to synthesize silver(I) and mercury(II)-NHC complexes using the basic metal precursors. The [Ag2(1)2][PF6]2 (2) was synthesized using [1(HPF6)2] by Ag2O method in acceptable yield. The dinuclear Hg(II) complex [Hg2(1)2][PF6]4 (3) consisting of two biscarbene ligand has been synthesized from Hg(OAc)2 and [1(HPF6)2]. The helical nature of Hg(II)-NHC (3) has been established from solid state X-ray structure.

Rana, Bidyut Kumar; Bertolasi, Valerio; Pal, Satyanarayan; Mitra, Partha; Dinda, Joydev

2013-10-01

216

Primary amino-functionalized N-heterocyclic carbene ligands as support for Au(I)···Au(I) interactions: structural, electrochemical, spectroscopic and computational studies of the dinuclear [Au2(NH2(CH2)2imMe)2][NO3]2.  

PubMed

The N-heterocyclic carbene (NHC) precursor, 1-(2-aminoethyl)-3-methylimidazolium nitrate, [NH(2)(CH(2))(2)imMe)]NO(3) ([3][NO(3)]) reacted with Ag(2)CO(3) in dimethyl sulfoxide readily yielding a Ag(I)-(NHC-NH(2)) complex presenting limited stability in solution. The in situ carbene transfer reaction of the latter with [Au(tht)Cl] afforded the first example of a dinuclear gold(I) complex [Au(2)(NH(2)(CH(2))(2)imMe)(2)][NO(3)](2) ([5][NO(3)](2)) bearing a primary amino-functionalized NHC ligand. The complex has been characterized by NMR, mass spectrometry, X-ray crystallography and cyclic voltammetry; the electrochemical behaviour and photophysical properties of [5][NO(3)](2) have been also investigated and the experimental data have been compared with density functional theory (DFT) and Time Dependent (TDDFT) calculations. Single-crystal structural studies showed that the Au(I)-carbene compound contains dinuclear (AuL)(2) cations in which pairs of gold(I) centres are linked by a pair of bridging ligands, with a Au···Au aurophilic contact of 3.2332(17) Å that is maintained in solution as documented by the DFT calculations. Complex [5][NO(3)](2) is photoluminescent in solution at room temperature and the high energy emission peak at 410 nm is remarkably shifted with respect to the absorption band centered at 260 nm. PMID:22218374

Ballarin, Barbara; Busetto, Luigi; Cassani, Maria Cristina; Femoni, Cristina; Ferrari, Anna Maria; Miletto, Ivana; Caputo, Giuseppe

2012-02-28

217

Stable Isotopes and M&Ms  

NSDL National Science Digital Library

Students are often confused by the concepts of stable isotope signatures and conventional notation. This activity is designed to introduce students to the del notation (isotopic signature), fractionation, and end member mixing of stable isotopes using familiar objects disguised as isotopes. The activity does not explain the physical manifestation of why isotopic fractionation occurs, but does explain the concepts that one easily observes when interpreting stable isotope data sets.

De Jesus, Roman

218

Suppression of Stable Flies on Cattle  

E-print Network

. Management To suppress stable fly populations efficient- ly, producers should use an integrated pest management (IPM) approach. IPM relies on Figure 1. Adult stable fly (Photo courtesy of Bart Drees, Texas Cooperative Extension). E-212 7/04 three tactics... of the winter, the sites where hay bales have been placed become ideal sta- ble fly breeding areas (Fig. 3). To reduce stable fly populations on the range, implement the same cultural practices as for confined animal facilities. Another tactic for confined...

Tomberlin, Jeffery K.

2004-07-01

219

Packing and Hausdorff Measures of Stable Trees  

Microsoft Academic Search

\\u000a In this paper we discuss Hausdorff and packing measures of random continuous trees called stable trees. Stable trees form\\u000a a specific class of Lévy trees (introduced by Le Gall and Le Jan in [33]) that contains Aldous’s continuum random tree which\\u000a corresponds to the Brownian case. We provide results for the whole stable trees and for their level sets that

Thomas Duquesne

2010-01-01

220

Ultraviolet and thermally stable polymer compositions  

NASA Technical Reports Server (NTRS)

Copolymers, produced from aromatic substituted aromatic azine-siloxane compositions, are thermally stable, solar ultraviolet light non-degradable by wavelengths shorter than those reaching earth surface.

Adamson, M. J.; Gloria, H. R.; Goldsberry, R. E.; Reinisch, R. F.

1972-01-01

221

Advanced thermally stable jet fuels  

SciTech Connect

The Pennsylvania State University program in advanced thermally stable coal-based jet fuels has five broad objectives: (1) Development of mechanisms of degradation and solids formation; (2) Quantitative measurement of growth of sub-micrometer and micrometer-sized particles suspended in fuels during thermal stressing; (3) Characterization of carbonaceous deposits by various instrumental and microscopic methods; (4) Elucidation of the role of additives in retarding the formation of carbonaceous solids; (5) Assessment of the potential of production of high yields of cycloalkanes by direct liquefaction of coal. Future high-Mach aircraft will place severe thermal demands on jet fuels, requiring the development of novel, hybrid fuel mixtures capable of withstanding temperatures in the range of 400--500 C. In the new aircraft, jet fuel will serve as both an energy source and a heat sink for cooling the airframe, engine, and system components. The ultimate development of such advanced fuels requires a thorough understanding of the thermal decomposition behavior of jet fuels under supercritical conditions. Considering that jet fuels consist of hundreds of compounds, this task must begin with a study of the thermal degradation behavior of select model compounds under supercritical conditions. The research performed by The Pennsylvania State University was focused on five major tasks that reflect the objectives stated above: Task 1: Investigation of the Quantitative Degradation of Fuels; Task 2: Investigation of Incipient Deposition; Task 3: Characterization of Solid Gums, Sediments, and Carbonaceous Deposits; Task 4: Coal-Based Fuel Stabilization Studies; and Task 5: Exploratory Studies on the Direct Conversion of Coal to High Quality Jet Fuels. The major findings of each of these tasks are presented in this executive summary. A description of the sub-tasks performed under each of these tasks and the findings of those studies are provided in the remainder of this volume (Sections 1 through 5).

Schobert, H.H.

1999-01-31

222

Stable, intelligible ultrasonic strain imaging  

PubMed Central

Background Freehand quasistatic strain imaging can reveal qualitative information about tissue stiffness with good spatial accuracy. Clinical trials, however, repeatedly cite instability and variable signal-to-noise ratio as significant drawbacks. Methods This study investigates three post-processing strategies for quasistatic strain imaging. Normalisation divides the strain by an estimate of the stress field, the intention being to reduce sensitivity to variable applied stress. Persistence aims to improve the signal-to-noise ratio by time-averaging multiple frames. The persistence scheme presented in this article operates at the pixel level, weighting each frame’s contribution by an estimate of the strain precision. Precision-based display presents the clinician with an image in which regions of indeterminate strain are obscured behind a colour wash. This is achieved using estimates of strain precision that are faithfully propagated through the various stages of signal processing. Results and discussion The post-processing strategy is evaluated qualitatively on scans of a breast biopsy phantom and in vivo head and neck examinations. Strain images processed in this manner are observed to benefit from improved stability and signal-to-noise ratio. There are, however, limitations. In unusual though conceivable circumstances, the normalisation procedure might suppress genuine stiffness variations evident in the unprocessed strain images. In different circumstances, the raw strain images might fail to capture significant stiffness variations, a situation that no amount of post-processing can improve. Conclusion The clinical utility of freehand quasistatic strain imaging can be improved by normalisation, precision-weighted pixel-level persistence and precision-based display. The resulting images are stable and generally exhibit a better signal-to-noise ratio than any of the original, unprocessed strain images. PMID:21151829

Gee, Andrew; Lindop, Joel; Treece, Graham; Prager, Richard; Freeman, Susan

2010-01-01

223

Adaptive Stable Marriage Algorithms John Dabney  

E-print Network

Adaptive Stable Marriage Algorithms John Dabney School of Computing Clemson University jdabney(n2 ) worst-case time to solve a stable marriage problem instance with n men and n women, a trivial O marriage algorithm -- an algo- rithm whose running time is of the form O(n + k), where k describes

Dean, Brian C.

224

Inapproximability Results on Stable Marriage Problems  

E-print Network

Inapproximability Results on Stable Marriage Problems Magn´us Halld´orsson1 , Kazuo Iwama2 marriage problem has received considerable at- tention both due to its practical applications as well' variants. 1 Introduction An instance of the original stable marriage problem (SM) [5] consists of N men

Halldórsson, Magnús M.

225

Stable grasp planning by evolutionary programming  

Microsoft Academic Search

This paper deals with the problem of synthesis of stable grasp by multifingered hands. First, a mathematical description of the problem is formulated. The grasp to be synthesized should satisfy equilibrium conditions and unilateral frictional constraints. In addition, it should be stable against disturbances applied to the object. Two types of stability conditions, contact stability and Lyapunov stability, are taken

Yoshiaki Katada; Mikhail Svinin; Kazuhiro Ohkura; Kanji Ueda

2001-01-01

226

Optimization of Stable Grasps by Evolutionary Programming  

Microsoft Academic Search

This paper deals with the problem of synthesis of stable grasp by multi-fingered hands. First, a mathematical descrip- tion of the problem is formulated. The grasp to be synthesized should satisfy equilibrium conditions and unilateral frictional constraints. It should also be stable against disturbances ap- plied to the object. Two types of stability conditions, con- tact stability and Lyapunov stability,

Y. Katada; M. Svinin; K. Ohkura; K. Ueda

2001-01-01

227

Bone stable isotope studies in archaeology  

Microsoft Academic Search

Stable isotope ratios of carbon and nitrogen in bone have become increasingly frequent inclusions in archaeological reports over the past few decades. The majority of such studies has been done in North America, where the use of marine foods and the introduction of maize have been monitored. Similar questions have been addressed in Mesoamerica and South America. In Europe, stable

Margaret J. Schoeninger; Katherine Moore

1992-01-01

228

Biological Populations with Nonoverlapping Generations: Stable Points, Stable Cycles, and Chaos  

E-print Network

situations (for example, in 13-year periodical cicadas), population growth takes place at dis- creteBiological Populations with Nonoverlapping Generations: Stable Points, Stable Cycles, and Chaos populations with nonoverlapping generations can exhibit a remarkable spectrum of dynamical behavior, from

Seoane, Javier

229

Structure of acid-stable carmine.  

PubMed

Acid-stable carmine has recently been distributed in the U.S. market because of its good acid stability, but it is not permitted in Japan. We analyzed and determined the structure of the major pigment in acid-stable carmine, in order to establish an analytical method for it. Carminic acid was transformed into a different type of pigment, named acid-stable carmine, through amination when heated in ammonia solution. The features of the structure were clarified using a model compound, purpurin, in which the orientation of hydroxyl groups on the A ring of the anthraquinone skeleton is the same as that of carminic acid. By spectroscopic means and the synthesis of acid-stable carmine and purpurin derivatives, the structure of the major pigment in acid-stable carmine was established as 4-aminocarminic acid, a novel compound. PMID:11998314

Sugimoto, Naoki; Kawasaki, Yoko; Sato, Kyoko; Aoki, Hiromitsu; Ichi, Takahito; Koda, Takatoshi; Yamazaki, Takeshi; Maitani, Tamio

2002-02-01

230

The frequency distribution of mechanically stable packings  

NASA Astrophysics Data System (ADS)

We generate mechanically stable packings of soft particles in 2D using an algorithm in which we successively grow or shrink purely repulsive grains and minimize the total energy at each step until particles are just at contact and at rest. We focus on small systems of up to 20 particles, and thus we are able to enumerate nearly all of the possible mechanically stable packings. Complete enumeration allows us to factorize the probability distribution, P(?), for obtaining a mechanically stable state at packing fraction ? into algorithm-dependent and independent contributions, ?(?) and ?(?). ?(?) is the probability density to obtain a distinct mechanically stable packing at ?, while ?(?) is the frequency with which each distinct state occurs. We found several remarkable features of the frequency distribution. For example, the frequency averaged over bins of width d? grows exponentially with increasing packing fraction. In addition, distinct mechanically stable packings within d? can occur with frequencies that differ by orders of magnitude. We also add thermal fluctuations to these stable configurations to understand the relationship between the frequency and shape of the potential landscape near the stable configurations.

Gao, Guo-Jie; Blawzdziewicz, Jerzy; O'Hern, Corey

2006-03-01

231

Generating Mammalian Stable Cell Lines by Electroporation  

PubMed Central

Expression of functional, recombinant mammalian proteins often requires expression in mammalian cells (see Single Cell Cloning of a Stable Mammalian Cell Line). If the expressed protein needs to be made frequently, it can be best to generate a stable cell line instead of performing repeated transient transfections into mammalian cells. Here, we describe a method to generate stable cell lines via electroporation followed by selection steps. This protocol will be limited to the CHO dhfr– Urlaub et al. (1983) and LEC1 cell lines, which in our experience perform the best with this method. PMID:24011048

Longo, Patti A.; Kavran, Jennifer M.; Kim, Min-Sung; Leahy, Daniel J.

2014-01-01

232

Bi-stable optical element actuator device  

DOEpatents

The present invention is a bistable optical element actuator device utilizing a powered means to move an actuation arm, to which an optical element is attached, between two stable positions. A non-powered means holds the actuation arm in either of the two stable positions. The optical element may be a electromagnetic (EM) radiation or particle source, an instrument, or EM radiation or particle transmissive reflective or absorptive elements. A bearing is used to transfer motion and smoothly transition the actuation arm between the two stable positions.

Holdener, Fred R. (Tracy, CA); Boyd, Robert D. (Livermore, CA)

2002-01-01

233

Evolutionary Origin of Asymptotically Stable Consensus  

PubMed Central

Consensus is widely observed in nature as well as in society. Up to now, many works have focused on what kind of (and how) isolated single structures lead to consensus, while the dynamics of consensus in interdependent populations remains unclear, although interactive structures are everywhere. For such consensus in interdependent populations, we refer that the fraction of population adopting a specified strategy is the same across different interactive structures. A two-strategy game as a conflict is adopted to explore how natural selection affects the consensus in such interdependent populations. It is shown that when selection is absent, all the consensus states are stable, but none are evolutionarily stable. In other words, the final consensus state can go back and forth from one to another. When selection is present, there is only a small number of stable consensus state which are evolutionarily stable. Our study highlights the importance of evolution on stabilizing consensus in interdependent populations. PMID:24699444

Tang, Chang-Bing; Wu, Bin; Wang, Jian-Bo; Li, Xiang

2014-01-01

234

Stable Manifolds as Thresholds for Multipulse Excitability  

E-print Network

)], Electrodynamic convection in liquid crystals [Peacock et al, J. Fluid Mech. 432 (2001)], Food chains in predator, Nonlinearity 18 (2005), 1095-1120.] PA/BK/HO - Stable manifolds and excitability ­ p. #12;Menu for today

Doedel, Eusebius

235

Stable Isotope Signatures for Microbial Forensics  

SciTech Connect

The isotopic distribution of the atoms composing the molecules of microorganisms is a function of the substrates used by the organisms. The stable isotope content of an organism is fixed so long as no further substrate consumption and biosynthesis occurs, while the radioactive isotopic content decays over time. The distribution of stable isotopes of C, N, O and H in heterotrophic microorganisms is a direct function of the culture medium, and therefore the stable isotope composition can be used to associate samples with potential culture media and also with one another. The 14C content depends upon the 14C content, and therefore the age, of the organic components of the culture medium, as well as on the age of the culture itself. Stable isotope signatures can thus be used for sample matching, to associate cultures with specific growth media, and to predict characteristics of growth media.

Kreuzer, Helen W.

2012-01-03

236

AIAA 20020227 On Constructing Stable Perfectly  

E-print Network

AIAA 2002­0227 On Constructing Stable Perfectly Matched Layers as an Absorbing Boundary Condition, Virginia 23529 40th AIAA Aerospace Sciences Meeting and Exhibit 14-17 January 2002/Reno, NV For permission

Hu, Fang Q.

237

Thermally Stable Piezoelectric and Pyroelectric Polymers  

NASA Technical Reports Server (NTRS)

A class of thermally stable piezoelectric and pyroelectric polymers, and an improved method of making them, have been invented. These polymers can be used as substrates for a wide variety of electromechanical transducers, sensors, and actuators.

Simpson, Joycelyn O.; St. Clair, Terry L.

2006-01-01

238

DNA modifications: Another stable base in DNA  

NASA Astrophysics Data System (ADS)

Oxidation of 5-methylcytosine has been proposed to mediate active and passive DNA demethylation. Tracking the history of DNA modifications has now provided the first solid evidence that 5-hydroxymethylcytosine is a stable epigenetic modification.

Brazauskas, Pijus; Kriaucionis, Skirmantas

2014-12-01

239

Stable vector bundles and string theory  

SciTech Connect

In [4], Braun, He, Ovrut and Pantev proposed a model of string theory (based on the Calabi-Yau 3-fold X) whose low energy limit predicts certain properties of the Standard Model of particle Physics. This model depends on two vector bundles that have to be stable. We calculate the ample cone of X, and prove that one of them is stable, and the other one is not.

Gomez, Tomas L.; Sols, Ignacio [ICMAT (CSIC-UAM-UC3M-UCM), Serrano 113bis, 28006 Madrid (Spain); Facultad de Ciencias Matematicas, Universidad Complutense de Madrid, 28040 Madrid (Spain); Lukic, Sergio [Mathematics Department, Imperial College, London SW7 (United Kingdom)

2009-05-06

240

Synthesis and characterization of various ruthenium small molecules and metallopolymers for potential use in photovoltaic devices and luminescence properties of N-heterocyclic carbenes and trifluoro methylated tris(pyrazolyl)borate silver (I) acid-base adducts  

NASA Astrophysics Data System (ADS)

This thesis with its 66 pages, 1 table, 29 figures and 47 references, deals with two major topics involving structure and properties of selected metal complexes and their use in electronic devices. The first chapter discusses the development of ruthenium-based metallopolymer and small molecular complexes toward possible utilization as active materials for solar cells. Such complexes have been found to be good "black absorbers" with solid-state absorption that spans the entire visible region into the near-infrared, representing an impressive overlap with the solar radiation that is more favorable than common molecular solar cell active materials. The second chapter includes photophysical studies of different metallo N-heterocyclic carbenes and acid-base adducts comprising fluorinated tris(pyrazolyl)borate silver(I) complexes coordinated to different solvent and aromatic molecules. These species have been investigated and found to exhibit unusual photophysical properties, including metal-free phosphorescence at room temperature with high quantum yield, multi-color emission from a single compound, and selective sensing of temperature and hazardous vapors.

Chitikuri, Shylaja

241

The complexity of the certification of properties of Stable Marriage  

E-print Network

The complexity of the certification of properties of Stable Marriage Daniel J. Dougherty bounds on the certificate complexity of some problems concerning stable marriage, answering a question of Gusfield and Irving. Key words: stable marriage, combinatorial problems, computational complexity

Dougherty, Daniel J.

242

High-Order Energy Stable WENO Schemes  

NASA Technical Reports Server (NTRS)

A new third-order Energy Stable Weighted Essentially NonOscillatory (ESWENO) finite difference scheme for scalar and vector linear hyperbolic equations with piecewise continuous initial conditions is developed. The new scheme is proven to be stable in the energy norm for both continuous and discontinuous solutions. In contrast to the existing high-resolution shock-capturing schemes, no assumption that the reconstruction should be total variation bounded (TVB) is explicitly required to prove stability of the new scheme. A rigorous truncation error analysis is presented showing that the accuracy of the 3rd-order ESWENO scheme is drastically improved if the tuning parameters of the weight functions satisfy certain criteria. Numerical results show that the new ESWENO scheme is stable and significantly outperforms the conventional third-order WENO finite difference scheme of Jiang and Shu in terms of accuracy, while providing essentially nonoscillatory solutions near strong discontinuities.

Yamaleev, Nail K.; Carpenter, Mark H.

2008-01-01

243

Concentration of stable elements in food products  

SciTech Connect

Food samples were taken from commercial markets and analyzed for stable element content. The concentrations of most stable elements (Ag, Al, As, Au, Ba, Br, Ca, Ce, Cl, Co, Cr, Cs, Cu, Fe, Hf, I, K, La, Mg, Mn, Mo, Na, Rb, Sb, Sc, Se, Sr, Ta, Th, Ti, V, Zn, Zr) were determined using multiple-element neutron activation analysis, while the concentrations of other elements (Cd, Hg, Ni, Pb) were determined using atomic absorption. The relevance of the concentrations found are noted in relation to other literature values. An earlier study was extended to include the determination of the concentration of stable elements in home-grown products in the vicinity of the Oak Ridge National Laboratory. Comparisons between the commercial and local food-stuff values are discussed.

Montford, M.A.; Shank, K.E.; Hendricks, C.; Oakes, T.W.

1980-01-01

244

Low work function, stable thin films  

DOEpatents

Generation of low work function, stable compound thin films by laser ablation. Compound thin films with low work function can be synthesized by simultaneously laser ablating silicon, for example, and thermal evaporating an alkali metal into an oxygen environment. For example, the compound thin film may be composed of Si/Cs/O. The work functions of the thin films can be varied by changing the silicon/alkali metal/oxygen ratio. Low work functions of the compound thin films deposited on silicon substrates were confirmed by ultraviolet photoelectron spectroscopy (UPS). The compound thin films are stable up to 500.degree. C. as measured by x-ray photoelectron spectroscopy (XPS). Tests have established that for certain chemical compositions and annealing temperatures of the compound thin films, negative electron affinity (NEA) was detected. The low work function, stable compound thin films can be utilized in solar cells, field emission flat panel displays, electron guns, and cold cathode electron guns.

Dinh, Long N. (Concord, CA); McLean, II, William (Oakland, CA); Balooch, Mehdi (Berkeley, CA); Fehring, Jr., Edward J. (Dublin, CA); Schildbach, Marcus A. (Livermore, CA)

2000-01-01

245

Effects of oral supplementation with stable strontium  

PubMed Central

The biologic effects of stable strontium, a naturally occurring trace element in the diet and the body, have been little investigated. This paper discusses the effects of oral supplementation with stable strontium in laboratory studies and clinical investigations. The extent of intestinal absorption of various doses of orally administered strontium was estimated by determining serum and tissue levels with atomic absorption spectrophotometry. The central observation is that increased oral intake produces a direct increase in serum levels and intracellular uptake of strontium. The results of these studies, as well as those of other investigators, demonstrate that a moderate dosage of stable strontium does not adversely affect the level of calcium either in the serum or in soft tissues. In studies of patients receiving 1 to 1.5 g/d of strontium gluconate, a sustained increase in the serum level of strontium produced a 100-fold increase in the strontium:calcium ratio. In rats, studies indicate that an increase in intracellular strontium content following supplementation may exert a protective effect on mitochondrial structure, probably by means of a stabilizing effect of strontium on membranes. The strontium:calcium ratio in animals receiving a standard diet is higher in the cell than in the extracellular fluid; this may be of physiologic significance. An increase in density that corresponded to the deposition of stable strontium was observed in areas of bone lesions due to metastatic cancer in patients receiving stable strontium supplementation. This suggests the possibility of using strontium to mineralize osteophenic areas and to relieve bone pain. Also, because of reports of an inverse relation between the incidence of dental caries and a high strontium content in drinking water, the use of natural water containing relatively high levels of stable strontium should be considered. In each of these instances it is important to maintain a normal dietary intake of calcium. ImagesFIG. 1FIG. 3FIG. 4FIG. 5 PMID:6120036

Skoryna, Stanley C.

1981-01-01

246

Transversely stable soliton trains in photonic lattices  

SciTech Connect

We report the existence of transversely stable soliton trains in optics. These stable soliton trains are found in two-dimensional square photonic lattices when they bifurcate from X-symmetry points with saddle-shaped diffraction inside the first Bloch band and their amplitudes are above a certain threshold. We also show that soliton trains with low amplitudes or bifurcated from edges of the first Bloch band ({Gamma} and M points) still suffer transverse instability. These results are obtained in the continuous lattice model and are further corroborated by the discrete model.

Yang Jianke [Department of Mathematics and Statistics, University of Vermont, Burlington, Vermont 05401 (United States)

2011-09-15

247

The stable fly: prediction of larval temperature  

E-print Network

of these development times clearly indicates that stable flies have the potential to sur- vive the entire winter as larvae or pupae. Several researchers have defined a temperature prefer- endum for insects (Hafez and Gamal-Eddin 1961 and Fraenkel and Gunn 1961...). It is the temperature range over which insects will aggregate if placed on a surface with a thermal gradient. For the stable fly, the temperature preferendum ranges from 15 to 32 C, with a mode temperature of 29 C. Hafez and Gamal-Eddin (1961) did considerable...

Foerster, Kenneth Wayne

1978-01-01

248

Stable isotopic compositions of hydrothermal vent organisms  

Microsoft Academic Search

Stable isotopic analyses were used to study trophic relationships in two communities of deep-sea hydrothermal vent organism in the Pacific Ocean. The community at Hanging Gardens on the East Pacific Rise (21°N), sampled in 1985, is dominated by two species of vestimentiferan tubeworms; communities at Alice Springs and Snail Pits on the Marianas Back Arc Spreading Center (western Pacific), sampled

C. L. Dover; B. Fry

1989-01-01

249

Substitution of stable isotopes in Chlorella  

NASA Technical Reports Server (NTRS)

Replacement of biologically important isotopes in the alga Chlorella by corresponding heavier stable isotopes produces increasingly greater deviations from the normal cell size and changes the quality and distribution of certain cellular components. The usefulness of isotopically altered organisms increases interest in the study of such permuted organisms.

Flaumenhaft, E.; Katz, J. J.; Uphaus, R. A.

1969-01-01

250

TOPOLOGICAL STABLE RANK OF H CIRCULAR DOMAINS  

E-print Network

stable rank of R (denoted by bsr R) is the least n N such that every element a = (a1, . . . , an, an+1 that bsr A tsr A; see [6, Corollary 2.4]. In the case of the classical algebra H(D) of the unit disk D

Mortini, Raymond

251

7, 1158711619, 2007 A compact and stable  

E-print Network

(IPCC, 2007) and currently 20% of the enhanced greenhouse effect is due to methane (IPCC, 2007 a Creative Commons License. Atmospheric Chemistry and Physics Discussions A compact and stable eddy Discussion EGU 1 Introduction Methane is considered to be the third most important greenhouse gas globally

Boyer, Edmond

252

Are two modes of thermohaline circulation stable?  

Microsoft Academic Search

The standard version of the coupled ocean atmosphere model developed at the Geophysical Fluid Dynamics Laboratory (GFDL) of NOAA has at least two stable equilibria. One has a realistic and active thermohaline circulation (THC) with sinking regions in the northern North Atlantic Ocean. The other has a reverse THC with extremely weak upwelling in the North Atlantic and sinking in

Syukuro Manabe; Ronald J. Stouffer

1999-01-01

253

Dynamically stable magnetic suspension/bearing system  

DOEpatents

A magnetic bearing system contains magnetic subsystems which act together to support a rotating element in a state of dynamic equilibrium. However, owing to the limitations imposed by Earnshaw`s Theorem, the magnetic bearing systems to be described do not possess a stable equilibrium at zero rotational speed. Therefore, mechanical stabilizers are provided, in each case, to hold the suspended system in equilibrium until its speed has exceeded a low critical speed where dynamic effects take over, permitting the achievement of a stable equilibrium for the rotating object. A state of stable equilibrium is achieved above a critical speed by use of a collection of passive elements using permanent magnets to provide their magnetomotive excitation. The magnetic forces exerted by these elements, when taken together, levitate the rotating object in equilibrium against external forces, such as the force of gravity or forces arising from accelerations. At the same time, this equilibrium is made stable against displacements of the rotating object from its equilibrium position by using combinations of elements that possess force derivatives of such magnitudes and signs that they can satisfy the conditions required for a rotating body to be stably supported by a magnetic bearing system over a finite range of those displacements. 32 figs.

Post, R.F.

1996-02-27

254

Dynamically stable magnetic suspension/bearing system  

DOEpatents

A magnetic bearing system contains magnetic subsystems which act together to support a rotating element in a state of dynamic equilibrium. However, owing to the limitations imposed by Earnshaw's Theorem, the magnetic bearing systems to be described do not possess a stable equilibrium at zero rotational speed. Therefore, mechanical stabilizers are provided, in each case, to hold the suspended system in equilibrium until its speed has exceeded a low critical speed where dynamic effects take over, permitting the achievement of a stable equilibrium for the rotating object. A state of stable equilibrium is achieved above a critical speed by use of a collection of passive elements using permanent magnets to provide their magnetomotive excitation. The magnetic forces exerted by these elements, when taken together, levitate the rotating object in equilibrium against external forces, such as the force of gravity or forces arising from accelerations. At the same time, this equilibrium is made stable against displacements of the rotating object from its equilibrium position by using combinations of elements that possess force derivatives of such magnitudes and signs that they can satisfy the conditions required for a rotating body to be stably supported by a magnetic bearing system over a finite range of those displacements.

Post, Richard F. (Walnut Creek, CA)

1996-01-01

255

Smart Polymer Coating: Surfaces & Developing Stable Liqui  

E-print Network

Smart Polymer Coating: Surfaces & Developing Stable Liqui University of Wisconsin Nature remains surface energy coating. While this approach is both useful and widely practiced, the practical utility/Coffee at 3: Seminar Hall, TCIS Seminar Smart Polymer Coating: Deigning of Anti-wetting Surfaces & Developing

Shyamasundar, R.K.

256

STABLE SYNCHRONIZATION OF MECHANICAL SYSTEM NETWORKS  

E-print Network

. In this paper we address stabilization of a network of underactuated mechanical systems with unstable dynamics of these and related works, stabilization of coordinated group dynamics is studied in the case of limited, timeSTABLE SYNCHRONIZATION OF MECHANICAL SYSTEM NETWORKS SUJIT NAIR AND NAOMI EHRICH LEONARD Abstract

Nair, Sujit

257

Nanostructured Stable Thin Polymer Films (DMR-0819860)  

E-print Network

Nanostructured Stable Thin Polymer Films (DMR-0819860) SEED: R. D. Priestley and C.B. Arnold. The image (right) illustrates the stability of the nanostructured morphology, against coalescence, at temperatures well above the normal Tg of 350 K. In addition, the nanostructured morphology is formed during

Petta, Jason

258

Stable transformation of papaya via microprojectile bombardment  

Microsoft Academic Search

Stable transformation of papaya (Carica papaya L.) has been achieved following DNA delivery via high velocity microprojectiles. Three types of embryogenic tissues, including immature zygotic embryos, freshly explanted hypocotyl sections, and somatic embryos derived from both, were bombarded with tungsten particles carrying chimeric NPTII and GUS genes. All tissue types were cultured prior to and following bombardment on half-strength MS

Maureen M. M. Fitch; Richard M. Manshardt; Dennis Gonsalves; Jerry L. Slightom; John C. Sanford

1990-01-01

259

UNCERTAINTY IN SOURCE PARTITIONING USING STABLE ISOTOPES  

EPA Science Inventory

Stable isotope analyses are often used to quantify the contribution of multiple sources to a mixture, such as proportions of food sources in an animal's diet, C3 vs. C4 plant inputs to soil organic carbon, etc. Linear mixing models can be used to partition two sources with a sin...

260

Nuclear Structure: From Stable to Unstable Nuclei  

NASA Astrophysics Data System (ADS)

A finite rank separable approximation for Skyrme interactions is applied to study the collective nuclear modes in stable and unstable nuclei. The coupling between one- and two-phonon terms in the wave functions are taken into account. Some possibilities for experimental investigations of the manifestations of the pseudospin symmetry in the spectra of odd nuclei with Z ? 100 are indicated.

Voronov, V. V.

2015-11-01

261

SRC: stable rate control for streaming media  

Microsoft Academic Search

Rate control, in conjunction with congestion control, is important and necessary to maintain both the stability of the overall network and high quality of individual data transfer flows. We study stable rate control algorithms for streaming data, based on control theory. We introduce various control rules to maintain both sending rate and receiver buffer stability. We also propose an adaptive

Cheng Huang; Lihao Xu

2003-01-01

262

Sourcing drugs with stable isotopes James R. Ehleringer  

E-print Network

and trafficking information. These stable isotope ratio measurements are conducted on an isotope ratioing massSourcing drugs with stable isotopes James R. Ehleringer Stable Isotope Ratio Facility@erols.com Michael J. Lott Stable Isotope Ratio Facility for Environmental Research (SIRFER) Department of Biology

Ehleringer, Jim

263

A Search for charged massive stable particles  

SciTech Connect

A search for charged massive (quasi-) stable particles with the D0 detector at the Tevatron collider based on 390 pb{sup -1} of data is presented. The search is performed in the frameworks of gauge-mediated supersymmetry breaking and the minimal supersymmetric extension of the standard model. The hypothetical particles are assumed to be pair-produced in p{bar p} collisions giving a signature of two reconstructed muon-like objects with high invariant mass and time-of-flights indicative of heavy particles. Since no excess over background is observed, cross-section limits for the pair-production of stable staus and charginos are set. Mass limits of 140 GeV for a higgsino-like chargino and 174 GeV for a gaugino-like chargino are set.

Nunnemann, Thomas; /Munich U.

2006-02-01

264

Compact and stable multibeam fiber injector  

NASA Astrophysics Data System (ADS)

A compact and stable 20-beam injector was built for launching laser light into fibers for Fabry Perot velocity measurements of shock-driven surfaces. The fiber injector uses commercial mounts on mini-rails. Dielectric-coated beamsplitters provide accurate amplitude division. Minimal adjustments for stable operation are permitted by the use of a real-time video- viewer. The video system includes a non-linear camera for CW alignment and a linearized camera with a frame grabber for pulsed measurement and analysis. All 20-injection points are displayed on a single monitor. Optical requirements are given for image relay and magnification. Stimulated Brillouin scattering limitations on high-power are quantified.

Collins, Leland F.

1998-10-01

265

Complex symmetric matrices with strongly stable iterates  

NASA Technical Reports Server (NTRS)

Complex-valued symmetric matrices are studied. A simple expression for the spectral norm of such matrices is obtained, by utilizing a unitarily congruent invariant form. A sharp criterion is provided for identifying those symmetric matrices whose spectral norm is not exceeding one: such strongly stable matrices are usually sought in connection with convergent difference approximations to partial differential equations. As an example, the derived criterion is applied to conclude the strong stability of a Lax-Wendroff scheme.

Tadmor, E.

1985-01-01

266

Highly stable six-axis alignment mechanism  

Microsoft Academic Search

One of the major challenges for typical opto-mechanical assemblies is that they require multiple degrees of freedom with large travel (several millimeters) but very small (sub-micron) resolution. After adjustment, assemblies must be stable to a few nanometers to survive environmental and mechanical shock over a lifetime of use. Using parts with engineered mating surfaces, we have developed a low-cost and

Evan Green; Bing Zheng; Alejandro Farinas; Dave Arnone

2005-01-01

267

Stable quasimaps to holomorphic symplectic quotients  

E-print Network

We study the moduli space of twisted quasimaps from a fixed smooth projective curve to a Nakajima's quiver variety and the moduli space of $\\delta$-stable framed twisted quiver bundles with moment map relations. We show that they carry symmetric obstruction theories and when $\\delta$ is large enough, they exactly coincide. These results generalize works of D.E. Diaconescu about the ADHM quiver, in the framework of the quasimap theory of I. Ciocan-Fontanine, D. Maulik and the author.

Bumsig Kim

2014-04-05

268

Uncertainty in source partitioning using stable isotopes  

Microsoft Academic Search

Stable isotope analyses are often used to quan- tify the contribution of multiple sources to a mixture, such as proportions of food sources in an animal's diet, or C3 and C4 plant inputs to soil organic carbon. Linear mixing models can be used to partition two sources with a single isotopic signature (e.g., ?13C) or three sources with a second

Donald L. Phillips; Jillian W. Gregg

2001-01-01

269

Thermally Stable and Flame Retardant Elastomeric Nanocomposites  

Microsoft Academic Search

\\u000a This chapter is dedicated to thermally stable and flame retardant elastomeric composites. Two approaches are considered: the\\u000a synthesis of elastomeric nanocomposites, where the nanoparticles are dispersed at the nanoscale, and the incorporation of\\u000a nanofillers at high loadings where agglomerate of nanoparticles are observed in the elastomeric matrix. The chapter is mainly\\u000a focused on the key parameter influencing the flame retardancy,

O. Cerin; G. Fontaine; S. Duquesne; S. Bourbigot

270

Detonation of Meta-stable Clusters  

SciTech Connect

We consider the energy accumulation in meta-stable clusters. This energy can be much larger than the typical chemical bond energy (~;;1 ev/atom). For example, polymeric nitrogen can accumulate 4 ev/atom in the N8 (fcc) structure, while helium can accumulate 9 ev/atom in the excited triplet state He2* . They release their energy by cluster fission: N8 -> 4N2 and He2* -> 2He. We study the locus of states in thermodynamic state space for the detonation of such meta-stable clusters. In particular, the equilibrium isentrope, starting at the Chapman-Jouguet state, and expanding down to 1 atmosphere was calculated with the Cheetah code. Large detonation pressures (3 and 16 Mbar), temperatures (12 and 34 kilo-K) and velocities (20 and 43 km/s) are a consequence of the large heats of detonation (6.6 and 50 kilo-cal/g) for nitrogen and helium clusters respectively. If such meta-stable clusters could be synthesized, they offer the potential for large increases in the energy density of materials.

Kuhl, Allen; Kuhl, Allen L.; Fried, Laurence E.; Howard, W. Michael; Seizew, Michael R.; Bell, John B.; Beckner, Vincent; Grcar, Joseph F.

2008-05-31

271

A Facile Route to Backbone-Tethered N-Heterocyclic Carbene (NHC) Ligands via NHC to aNHC Rearrangement in NHC Silicon Halide Adducts.  

PubMed

The reaction of 1,3-diisopropylimidazolin-2-ylidene (iPr2 Im) with diphenyldichlorosilane (Ph2 SiCl2 ) leads to the adduct (iPr2 Im)SiCl2 Ph2 1. Prolonged heating of isolated 1 at 66?°C in THF affords the backbone-tethered bis(imidazolium) salt [((a) HiPr2 Im)2 SiPh2 ](2+) ?2?Cl(-) 2 ("(a) " denotes "abnormal" coordination of the NHC), which can be synthesized in high yields in one step starting from two equivalents of iPr2 Im and Ph2 SiCl2 . Imidazolium salt 2 can be deprotonated in THF at room temperature using sodium hydride as a base and catalytic amounts of sodium tert-butoxide to give the stable N-heterocyclic dicarbene ((a) iPr2 Im)2 SiPh2 3, in which two NHCs are backbone-tethered with a SiPh2 group. This easy-to-synthesize dicarbene 3 can be used as a novel ligand type in transition metal chemistry for the preparation of dinuclear NHC complexes, as exemplified by the synthesis of the homodinuclear copper(I) complex [{(a) (ClCu?iPr2 Im)}2 SiPh2 ] 4. PMID:25534013

Schneider, Heidi; Schmidt, David; Radius, Udo

2015-02-01

272

Isotropic turbulence, stable layers: facts or fictions?  

NASA Astrophysics Data System (ADS)

Using state of the art drop sonde data (from 237 sondes over the Pacific) we examine two classical and fundamental idealizations of atmospheric science showing that they are untenable in the light of the vertical structure. The first is the notion of stable atmospheric layers. This is used for understanding atmospheric dynamics and thermodynamics, including the most advanced dynamical meteorological notions such as potential vorticity. Using the drop sonde data, we show that each apparently stable layer is actually composed of a hierarchy of unstable layers themselves with embedded stable sublayers, each with unstable sub-sub layers etc. i.e. in a Russian doll-like fractal hierarchy whose dimension we estimate. We therefore argue that the notion is untenable and must be replaced by modern scaling notions. The second idealization we examine is the turbulence assumption of isotropy. If we include intermittency, Kolmorogov's landmark proposal that fully developed turbulence has an "inertial subrange" with isotropic energy spectrum E(k)=k**-beta with beta=5/3 has apparently been spectacularly confirmed in both the horizontal direction and in the time domain (k is a wavenumber). For gradients over a horizontal distance deltax this implies deltav=deltaz**Hh (Hh=1/3 corresponds to beta=5/3). Remarkably, Hv for gradients over vertical distances deltaz (deltav=deltaz**Hv) has not been seriously investigated. Using drop sonde data of horizontal wind, we find that from scales of 5 m to 10 km from the surface layer through to the top of the troposphere, Hv is close to (or larger) than the Bolgiano-Obukhov value 3/5. Hv greater than Hh implies that a) the atmosphere becomes progressively less stratified at smaller scales although in a scaling way; b) that at most a single (roughly) isotropic "sphero- scale" exists (often in the range 1-100 cm).

Lovejoy, S.; Tuck, A.; Hovde, S.; Schertzer, D.

2007-05-01

273

Stable RNA interference rules for silencing  

PubMed Central

RNA interference has become an indispensable tool for loss-of-function studies across eukaryotes. By enabling stable and reversible gene silencing, shRNAs provide a means to study long-term phenotypes, perform pool-based forward genetic screens and examine the consequences of temporary target inhibition in vivo. However, efficient implementation in vertebrate systems has been hindered by technical difficulties affecting potency and specificity. Focusing on these issues, we analyse current strategies to obtain maximal knockdown with minimal off-target effects. PMID:24366030

Fellmann, Christof; Lowe, Scott W.

2014-01-01

274

Multiplier provides stable performance with temperature  

NASA Astrophysics Data System (ADS)

A high-efficiency frequency quadrupler design is presented which is based on a pair of cascaded frequency doublers. The device provides stable conversion gain over a broad temperature range. The multiplier accepts 2-GHz input signals at -14 dBm and delivers 8-GHz output signals with 0-dBm power. The broadband resistive doublers incorporated into the design generate harmonics using the switching characteristics of a diode in a balanced circuit. Amplifier stages between the doubler sections offset conversion loss. The design's operating range can be changed by simply replacing the bandwidth filters. This design approach can be applied to multipliers with outputs up to 40 GHz.

Hey-Shipton, Greg L.; Mortezaie, Mostafa

1989-10-01

275

Stable Oxide Nanoparticle Clusters Obtained by Complexation  

E-print Network

We report on the electrostatic complexation between polyelectrolyte-neutral copolymers and oppositely charged 6 nm-crystalline nanoparticles. For two different dispersions of oxide nanoparticles, the electrostatic complexation gives rise to the formation of stable nanoparticle clusters in the range 20 - 100 nm. It is found that inside the clusters, the particles are pasted together by the polyelectrolyte blocks adsorbed on their surface. Cryo-transmission electronic microscopy allows to visualize the clusters and to determine the probability distributions functions in size and in aggregation number. The comparison between light scattering and cryo-microscopy results suggests the existence of a polymer brush around the clusters.

J. -F. Berret; A. Sehgal; M. Morvan; O. Sandre; A. Vacher; M. Airiau

2006-08-08

276

Stable metallization for diamond and other materials  

NASA Technical Reports Server (NTRS)

An adherent and metallurgically stable metallization system for diamond is presented. The big improvement in metallurgical stability is attributed to the use of a ternary, amorphous Ti--Si--N diffusion barrier. No diffusion between the layers and no delamination of the metallization was observed after annealing the schemes at 400.degree. C. for 100 hours and at 900.degree. C. for 30 minutes. Thermal cycling experiments in air from -65 to 155.degree. C. and adhesion tests were performed. Various embodiments are disclosed.

Bachli, Andreas (Inventor); Kolawa, Elzbieta (Inventor); Nicolet, Marc-Aurele (Inventor); Vandersande, Jan W. (Inventor)

2000-01-01

277

MHD stable high beta spheromak equilibrium  

SciTech Connect

Recent observations of a pressure driven mode in CTX indicate that its performance is being limited by the low beta stability requirements typical of conventional spheromak designs. Improved designs with higher beat limits therefore have the potential to dramatically increase the temperature and lifetime of CTX and other spheromak experiments. This paper describes the results of an optimization study examining radically different geometries, but all with minimum energy current profiles which can easily be created experimentally and should be automatically stable to all ideal and resistive current drive modes. 2 refs., 3 figs.

Marklin, G.J.

1989-01-01

278

Stable quark matter in cosmic rays?  

E-print Network

Stable lumps of quark matter may be present in cosmic rays at a flux level, which can be detected by high precision cosmic ray experiments sensitive to anomalous "nuclei" with high mass-to-charge ratio. The properties of these lumps, called strangelets, are described, and so is the production and propagation of strangelets in cosmic rays. Two experiments underway which are sensitive to a strangelet flux in the predicted range are briefly described. Finally it is summarized how strangelets circumvent the acceleration problem encountered by conventional candidates for ultra-high energy cosmic rays and move the Greisen-Zatsepin-Kuzmin cutoff to energies well above the observed maximum energies.

Jes Madsen

2005-12-20

279

Rapid mixing renders quantum dissipative systems stable  

E-print Network

The physics of many materials is modeled by quantum many-body systems with local interactions. If the model of the system is sensitive to noise from the environment, or small perturbations to the original interactions, it will not model properly the robustness of the real physical system it aims to describe, or be useful when engineering novel systems for quantum information processing. We show that local observables and correlation functions of local Liouvillians are stable to local perturbations if the dynamics is rapidly mixing and has a unique fixed point. No other condition is required.

Angelo Lucia; Toby S. Cubitt; Spyridon Michalakis; David Pérez-García

2014-09-27

280

Shear viscosity of $?$-stable nuclear matter  

E-print Network

Viscosity plays a critical role in determining the stability of rotating neutron stars. We report the results of a calculation of the shear viscosity of $\\beta$~-~stable matter, carried out using an effective interaction based on a state-of-the-art nucleon-nucleon potential and the formalism of correlated basis functions. Within our approach the equation of state, determining the proton fraction, and the nucleon-nucleon scattering probability are consistently obtained from the same dynamical model. The results show that, while the neutron contribution to the viscosity is always dominant, above nuclear saturation density the electron contribution becomes appreciable.

Omar Benhar; Arianna Carbone

2009-12-01

281

Stable, Electroinactive Wetting Agent For Fuel Cells  

NASA Technical Reports Server (NTRS)

Straight-chain perfluorooctanesulfonic acid (C8 acid) identified as innocuous and stable wetting agent for use with polytetrafluoroethylene-containing electrodes in liquid-feed direct-oxidation fuel cells suggested for use in vehicles and portable power supplies. C8 acid in small concentrations in aqueous liquid solutions of methanol, trimethoxymethane, dimethoxymethane, and trioxane enables oxidation of these substances by use of commercially available electrodes of type designed originally for use with gases. This function specific to C8 acid molecule and not achieved by other related perfluorolkanesulfonic acids.

Prakash, Surya G.; Olah, George A.; Narayanan, Sekharipuram R.; Surampudi, Subbarao; Halpert, Gerald

1994-01-01

282

Electrochemical Fractionation of Molybdenum Stable Isotopes  

Microsoft Academic Search

Stable isotope signatures were measured from Molybdenum (Mo) electrodeposited from aqueous solution. As potential varied from -1.35 V to -2.00 V (relative to Ag\\/AgCl), fractionation decreases from Delta97\\/95Mo = -1.3 0\\/00 to -0.9 0\\/00 (Delta97\\/95Mo defined as the difference in the 97Mo\\/95Mo ratio of deposited Mo relative to aqueous Mo). Natural variations of delta97\\/95Mo span a range of ~ 3

J. Crawford; J. Black; L. Wasylenki; G. Gordon; A. Anbar; A. Kavner

2008-01-01

283

[Highly stable regulatory oligopeptides: experience and applications].  

PubMed

The most stable regulatory peptides (RP) including the new family of RP (glyprolines) and derivatives of hybrid peptide MEHFPGP are characterized. High ability of glyprolines to penetrate into the blood-stream through the gastrointestinal tract is demonstrated. Antiulcer, antithrombotic and antidiabetic activities of glyprolines were discovered in experiments on white rats. The activity of oligopeptides PGP, PG and GP is compared. Mechanisms of glycoprolines activities and feasibility of their administration with connective tissue food proteins are discussed. Thus, glyprolines are perspective drugs for treatment of gastric ulcer, correction of hemostasis and thrombosis suppression prepared for preclinical trial. PMID:14682258

Ashmarin, I P; Bakaeva, Z V; Vas'kovski?, B V; Zheliaznik, N Ia; Zhu?kova, S E; Zolotarev, Iu A; Kamenski?, A A; Levitskaia, N G; Liapina, L A; Miasoedov, N F

2003-01-01

284

2. Historic American Buildings Survey 'Stable and Smoke House' Photocopy ...  

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

2. Historic American Buildings Survey 'Stable and Smoke House' Photocopy of Plate XXX From: Brown, Glenn, The Octagon, Washington, N.D. - Octagon House, Stable, 1799 New York Avenue Northwest, Washington, District of Columbia, DC

285

Electrochemical Fractionation of Molybdenum Stable Isotopes  

NASA Astrophysics Data System (ADS)

Stable isotope signatures were measured from Molybdenum (Mo) electrodeposited from aqueous solution. As potential varied from -1.35 V to -2.00 V (relative to Ag/AgCl), fractionation decreases from ?97/95Mo = -1.3 ‰ to -0.9 ‰ (?97/95Mo defined as the difference in the 97Mo/95Mo ratio of deposited Mo relative to aqueous Mo). Natural variations of ?97/95Mo span a range of ~ 3 ‰ [Barling, J. and Anbar, A. D., EPSL. 2004, 217: 315], therefore, charge transfer driven fractionation may be responsible for some of the observed variation in Mo stable isotope geochemistry. Following previous approaches with Fe and Zn [Kavner, A. et al. Geochim. Cosmochim. Acta. 2005, 69: 2971; 2008, 72: 1731], Mo was plated in a three-electrode cell from a neutral to slightly alkaline solution (pH ~ 8.7). Voltage was held constant during electrodeposition using an Autolab Potentiostat. In all experiments, less than 0.5 % of the Mo was deposited, which insures that the plating reservoir remains at an approximately constant isotopic composition. Plated Mo was then recovered in acid, and the isotopic composition of samples and stock solutions were measured using a Thermo Scientific Neptune MC-ICP-MS. These experiments show that the redox process induces an isotopic signature with respect to the starting material, with a trend showing that fractionation decreases as a function of applied voltage.

Crawford, J.; Black, J.; Wasylenki, L.; Gordon, G.; Anbar, A.; Kavner, A.

2008-12-01

286

On feedback and stable price adjustment mechanisms  

NASA Astrophysics Data System (ADS)

Given an excess demand function of an economy, say Z(p), a stable price adjustment mechanism (SPAM) guarantees convergence of solution path p(t,p0) to an equilibrium peq solution of Z(p)=0. Besides, all equilibrium points of Z(p) are asymptotically stable. Some SPAMs have been proposed, including Newton and transpose Jacobian methods. Despite this powerful stability property of SPAMs, their acceptation in the economics community has been limited by a lack of interpretation. This paper focuses on this issue. Specifically, feedback control theory is used to link SPAMs and price dynamics models with control inputs, which match the economically intuitive Walrasian Hypothesis (i.e., prices change with excess demand sign). Under mild conditions, it is shown the existence of a feedback function that transforms the price dynamics into a desired SPAM. Hence, a SPAM is interpreted as a fundamental (e.g., Walrasian) price dynamics under the action of a feedback function aimed to stabilize the equilibrium set of the excess demand function.

Fernandez-Anaya, Guillermo; Alvarez-Ramirez, Jose; Ibarra-Valdez, Carlos

2007-04-01

287

Stable counteralignment of a circumbinary disc  

NASA Astrophysics Data System (ADS)

In general, when gas accretes on to a supermassive black hole (SMBH) binary, it is likely to have no prior knowledge of the binary angular momentum. Therefore, a circumbinary disc forms with a random inclination angle ? to the binary. It is known that for ? < 90° the disc will coalign with respect to the binary. If ? > 90°, the disc wholly counteraligns if it satisfies cos ? < -Jd/2Jb, where Jd and Jb are the magnitudes of the disc and binary angular momentum vectors, respectively. If, however, ? > 90° and this criterion is not satisfied, the same disc may counteralign its inner regions and, on longer time-scales, coalign its outer regions. I show that for typical disc parameters, describing an accretion event on to an SMBH binary, a misaligned circumbinary disc is likely to wholly coalign or counteralign with the binary plane. This is because the binary angular momentum dominates the disc angular momentum. However, with extreme parameters (binary mass ratio M2/M1? 1 or binary eccentricity e˜ 1), the same disc may simultaneously coalign and counteralign. It is known that coplanar prograde circumbinary discs are stable. I show that coplanar retrograde circumbinary discs are also stable. A chaotic accretion event on to an SMBH binary will therefore result in a coplanar circumbinary disc that is either prograde or retrograde with respect to the binary plane.

Nixon, Christopher J.

2012-07-01

288

Pulmonary toxicity of stable and radioactive lanthanides.  

PubMed

The pulmonary toxicity of inhaled lanthanides has been the subject of debate. In question have been the relative contributions of radioactive vs. stable elements in the development of lanthanide-associated progressive pulmonary interstitial fibrosis. The central question of this debate is: Are lanthanide dusts that are devoid of radioactive contaminants capable of producing progressive pulmonary disease, or are lanthanide-induced lesions more appropriately termed "benign pneumoconioses"? This paper examines the epidemiologic and experimental record in order to answer the above question. It is clear from the available data that significant pathogenic potential of inhaled lanthanides exists and is related to the type and physicochemical form of the material inhaled and to the dose and duration of exposure. Contamination of the dust with radioactive materials may accelerate and enhance the pathologic response, depending on the form and dose of radioactivity encountered. Nevertheless, there is little evidence to suggest that the level of radioactive contamination of occupationally encountered lanthanide dusts is sufficient to be included as a risk factor for pulmonary disease. Thus, the pulmonary syndrome induced by stable rare earths includes progressive pulmonary fibrosis and should not be referred to as "benign pneumoconiosis." PMID:1955325

Haley, P J

1991-12-01

289

Stable isotope enrichment using a plasma centrifuge  

NASA Astrophysics Data System (ADS)

A primary goal of the Department of Energy's Isotope Development and Production for Research and Applications Program (Isotope Program) within the Office of Nuclear Physics (NP) is to produce isotopes that are in short supply in the U.S. and of which there exists no or insufficient domestic commercial production capability. A vacuum arc plasma centrifuge is a rigid rotor column of metal plasma in which centrifugal forces re-distribute ions radially according to their mass/charge ratio. Early work demonstrated rotation at 2 million rpm and separation of various stable isotopes. The spinning plasma column had a Gaussian flux profile, peaked on the rigid rotor axis. This work adopts a more efficient approach, with the plasma created as a hollow column, wherein the flux is concentrated at larger radii where the centrifugal action is highest. By tailoring the vacuum arc discharge geometry, the rotation rate can also be increased to ˜10 million rpm. Data from Cu, Al and other metal plasmas will be presented and discussed in light of enriched stable isotopes needed for research and medicine.

Krishnan, Mahadevan; Bures, Brian; Madden, Robert

2012-10-01

290

Gale-Shapley Stable Marriage Problem Revisited: Strategic Issues  

E-print Network

Gale-Shapley Stable Marriage Problem Revisited: Strategic Issues and Applications Chung-Piaw Teo@nus.edu.sg · jay@ieor.columbia.edu We study strategic issues in the Gale-Shapley stable marriage model behavior of the students need not be a major concern. (Stable Marriage; Strategic Issues; Gale

Sethuraman, Jay

291

Weights in stable marriage problems increase manipulation opportunities  

E-print Network

Weights in stable marriage problems increase manipulation opportunities Maria Silvia Pini Walsh NICTA and UNSW Sydney, Australia toby.walsh@nicta.com.au ABSTRACT The stable marriage problem-sided mar- ket. In the classical stable marriage problem, both men and women express a strict preference

Rossi, Francesca

292

Manipulation complexity and gender neutrality in stable marriage procedures  

E-print Network

Manipulation complexity and gender neutrality in stable marriage procedures Maria Silvia Pini1, Australia. Email: Toby.Walsh@nicta.com.au Abstract. The stable marriage problem is a well-known problem-Shapley algorithm, which runs in quadratic time in the number of men/women. It has been proven that stable marriage

Rossi, Francesca

293

Stable Games Josef Hofbauer and William H. Sandholm  

E-print Network

Stable Games Josef Hofbauer and William H. Sandholm Abstract-- We introduce a new class of population games called stable games. These games are characterized by self- defeating externalities: when are aban- doning. Stable games subsume many well-known classes of examples, including zero-sum games, games

Hofbauer, Josef

294

The stable isotope ecology of terrestrial plant succession  

Microsoft Academic Search

We review the relevance and use of stable isotopes for the study of plant community succession. Stable isotope measurements provide information on the origin of resources acquired by plants, the processes governing resource uptake and transformation, and the physiological and environmental conditions of plant growth. When combined with measurements of the stable isotope ratio values of soil microbial biomass, soil

Víctor Resco; Juan P. Ferrio; José A. Carreira; Leonor Calvo; Pere Casals; Ángel Ferrero-Serrano; Elena Marcos; José M. Moreno; David A. Ramírez; M. Teresa Sebastià; Fernando Valladares; David G. Williams

2011-01-01

295

Perceptual Learning Immediately Yields New Stable Motor Coordination  

ERIC Educational Resources Information Center

Coordinated rhythmic movement is specifically structured in humans. Movement at 0[degrees] mean relative phase is maximally stable, 180[degrees] is less stable, and other coordinations can, but must, be learned. Variations in perceptual ability play a key role in determining the observed stabilities so we investigated whether stable movements can…

Wilson, Andrew D.; Snapp-Childs, Winona; Bingham, Geoffrey P.

2010-01-01

296

Synthesis and characterization of thermally stable polymers containing phenazine  

E-print Network

-shaped structures. Doping with 15% iodine resulted in a conductivity of 9 Ã? 10 7 mho/cm. It was thermally stableSynthesis and characterization of thermally stable polymers containing phenazine H.M. Gajiwala*, R and characterization of two thermally stable polymers containing a polybenzimidazole and a ladder polymer structure

Zand, Robert

297

IS SOLAR SYSTEM STABLE? Vladik Kreinovich, Andrew Bernat  

E-print Network

IS SOLAR SYSTEM STABLE? A REMARK Vladik Kreinovich, Andrew Bernat Computer Science Department System is stable or not. Common belief is that the Solar System is stable if and only, a similar inequality is true for randomly chosen frequencies. In this paper, we show that the Solar system

Kreinovich, Vladik

298

IS SOLAR SYSTEM STABLE? Vladik Kreinovich, Andrew Bernat  

E-print Network

IS SOLAR SYSTEM STABLE? A REMARK Vladik Kreinovich, Andrew Bernat Computer Science Department System is stable or not. Common belief is that the Solar System is stable if and only that the Solar system does not have such resonances, and therefore (if the above­mentioned belief is correct), we

Kreinovich, Vladik

299

Population games, stable games, and passivity Michael J. Fox  

E-print Network

Population games, stable games, and passivity Michael J. Fox Jeff S. Shamma March 31, 2013 July 23, 2013 (revised) September 2, 2013 (revised) Abstract The class of "stable games", introduced by Hofbauer evolutionary dynamics. We show that stable games can be identified as a special case of the feedback

Shamma, Jeff S.

300

Gaudin subalgebras and stable rational curves  

E-print Network

Gaudin subalgebras are abelian Lie subalgebras of maximal dimension spanned by generators of the Kohno-Drinfeld Lie algebra t_n. We show that Gaudin subalgebras form a variety isomorphic to the moduli space of stable curves of genus zero with n+1 marked points. In particular, this gives an embedding of the moduli space in a Grassmannian of (n-1)-planes in an n(n-1)/2-dimensional space. We show that the sheaf of Gaudin subalgebras over the moduli space is isomorphic to a sheaf of twisted first order differential operators. For each representation of the Kohno--Drinfeld Lie algebra with fixed central character, we obtain a sheaf of commutative algebras whose spectrum is a coisotropic subscheme of a twisted version of the logarithmic cotangent bundle of the moduli space.

Aguirre, Leonardo; Veselov, Alexander P

2010-01-01

301

Ultra-stable oscillator with complementary transistors  

NASA Technical Reports Server (NTRS)

A high frequency oscillator, having both good short and long term stability, is formed by including a piezoelectric crystal in the base circuit of a first bi-polar transistor circuit, the bi-polar transistor itself operated below its transitional frequency and having its emitter load chosen so that the input impedance, looking into the base thereof, exhibits a negative resistance in parallel with a capacitive reactance. Combined with this basic circuit is an auxiliary, complementary, second bi-polar transistor circuit of the same form with the piezoelectric crystal being common to both circuits. By this configuration small changes in quiescent current are substantially cancelled by opposite variations in the second bi-polar transistor circuit, thereby achieving from the oscillator a signal having its frequency of oscillation stable over long time periods as well as short time periods.

Kleinberg, L. L. (inventor)

1974-01-01

302

A belief-based evolutionarily stable strategy.  

PubMed

As an equilibrium refinement of the Nash equilibrium, evolutionarily stable strategy (ESS) is a key concept in evolutionary game theory and has attracted growing interest. An ESS can be either a pure strategy or a mixed strategy. Even though the randomness is allowed in mixed strategy, the selection probability of pure strategy in a mixed strategy may fluctuate due to the impact of many factors. The fluctuation can lead to more uncertainty. In this paper, such uncertainty involved in mixed strategy has been further taken into consideration: a belief strategy is proposed in terms of Dempster-Shafer evidence theory. Furthermore, based on the proposed belief strategy, a belief-based ESS has been developed. The belief strategy and belief-based ESS can reduce to the mixed strategy and mixed ESS, which provide more realistic and powerful tools to describe interactions among agents. PMID:25036441

Deng, Xinyang; Wang, Zhen; Liu, Qi; Deng, Yong; Mahadevan, Sankaran

2014-11-21

303

Bounded excursion stable gravastars and black holes  

SciTech Connect

Dynamical models of prototype gravastars were constructed in order to study their stability. The models are the Visser-Wiltshire three-layer gravastars, in which an infinitely thin spherical shell of stiff fluid divides the whole spacetime into two regions, where the internal region is de Sitter, and the external one is Schwarzschild. It is found that in some cases the models represent the 'bounded excursion' stable gravastars, where the thin shell is oscillating between two finite radii, while in other cases they collapse until the formation of black holes occurs. In the phase space, the region for the 'bounded excursion' gravastars is very small in comparison to that of black holes, but not empty. Therefore, although the possibility of the existence of gravastars cannot be excluded from such dynamical models, our results indicate that, even if gravastars do indeed exist, that does not exclude the possibility of the existence of black holes.

Rocha, P [Instituto de Fisica, Universidade Federal Fluminense, Avenida Litoranea, s/n, Boa Viagem 24210-340, Niteroi, RJ (Brazil)] [Instituto de Fisica, Universidade Federal Fluminense, Avenida Litoranea, s/n, Boa Viagem 24210-340, Niteroi, RJ (Brazil); Miguelote, A Y; Chan, R [Coordenacao de Astronomia e Astrofisica, Observatorio Nacional, Rua General Jose Cristino, 77, Sao Cristovao 20921-400, Rio de Janeiro, RJ (Brazil)] [Coordenacao de Astronomia e Astrofisica, Observatorio Nacional, Rua General Jose Cristino, 77, Sao Cristovao 20921-400, Rio de Janeiro, RJ (Brazil); Da Silva, M F; Wang, Anzhong [Departamento de Fisica Teorica, Instituto de Fisica, Universidade do Estado do Rio de Janeiro, Rua Sao Francisco Xavier 524, Maracana 20550-900, Rio de Janeiro-RJ (Brazil)] [Departamento de Fisica Teorica, Instituto de Fisica, Universidade do Estado do Rio de Janeiro, Rua Sao Francisco Xavier 524, Maracana 20550-900, Rio de Janeiro-RJ (Brazil); Santos, N O, E-mail: pedrosennarocha@gmail.com, E-mail: yasuda@on.br, E-mail: chan@on.br, E-mail: mfasnic@gmail.com, E-mail: N.O.Santos@qmul.ac.uk, E-mail: anzhong_wang@baylor.edu [LERMA/CNRS-FRE 2460, Universite Pierre et Marie Curie, ERGA, Boite 142, 4 Place Jussieu, 75005 Paris Cedex 05 (France)

2008-06-15

304

Open string instantons and relative stable morphisms  

E-print Network

We show how topological open string theory amplitudes can be computed by using relative stable morphisms in the algebraic category. We achieve our goal by explicitly working through an example which has been previously considered by Ooguri and Vafa from the point of view of physics. By using the method of virtual localization, we successfully reproduce their results for multiple covers of a holomorphic disc, whose boundary lies in a Lagrangian submanifold of a Calabi-Yau 3-fold, by Riemann surfaces with arbitrary genera and number of boundary components. In particular we show that in the case we consider there are no open string instantons with more than one boundary component ending on the Lagrangian submanifold.

Jun Li; Yun S. Song

2001-03-13

305

Asystole following regadenoson infusion in stable outpatients.  

PubMed

Regadenoson is a selective A2A receptor agonist approved for use as a pharmacologic stress agent for myocardial perfusion imaging after several multicenter trials demonstrated its equivalence in diagnostic accuracy for the detection of coronary artery disease and a decreased incidence of serious side effects as compared to adenosine. Recently, the FDA released a safety announcement advising of the rare but serious risk of heart attack and death associated with regadenoson and adenosine in cardiac stress testing, particularly in patients with unstable angina or cardiovascular instability. We report two cases of asystole with hemodynamic collapse in stable outpatients soon after receiving a standard regadenoson injection. The prevalence of potentially life threatening bradycardia, including asystole, associated with the use of regadenoson may be greater than previously expected. These cases highlight the need for cardiac stress labs to anticipate the potential for serious side effects with all patients during the administration of coronary vasodilators. PMID:24879452

Rosenblatt, Jeffrey; Mooney, Deirdre; Dunn, Timothy; Cohen, Mylan

2014-10-01

306

Towards stable silicon nanoarray hybrid solar cells  

PubMed Central

Silicon nanoarray hybrid solar cells benefit from the ease of fabrication and the cost-effectiveness of the hybrid structure, and represent a new research focus towards the utilization of solar energy. However, hybrid solar cells composed of both inorganic and organic components suffer from the notorious stability issue, which has to be tackled before the hybrid solar cells could become a viable alternative for harvesting solar energy. Here we show that Si nanoarray/PEDOT:PSS hybrid solar cells with improved stability can be fabricated via eliminating the water inclusion in the initial formation of the heterojunction between Si nanoarray and PEDOT:PSS. The Si nanoarray hybrid solar cells are stable against rapid degradation in the atmosphere environment for several months without encapsulation. This finding paves the way towards the real-world applications of Si nanoarray hybrid solar cells. PMID:24430057

He, W. W.; Wu, K. J.; Wang, K.; Shi, T. F.; Wu, L.; Li, S. X.; Teng, D. Y.; Ye, C. H.

2014-01-01

307

Stable homotopical algebra and [Gamma]-spaces  

NASA Astrophysics Data System (ADS)

In this paper we advertise the category of [Gamma]-spaces as a convenient framework for doing ‘algebra’ over ‘rings’ in stable homotopy theory. [Gamma]-spaces were introduced by Segal [Se] who showed that they give rise to a homotopy category equivalent to the usual homotopy category of connective (i.e. ([minus sign]1)-connected) spectra. Bousfield and Friedlander [BF] later provided model category structures for [Gamma]-spaces. The study of ‘rings, modules and algebras’ based on [Gamma]-spaces became possible when Lydakis [Ly] introduced a symmetric monoidal smash product with good homotopical properties. Here we develop model category structures for modules and algebras, set up (derived) smash products and associated spectral sequences and compare simplicial modules and algebras to their Eilenberg-MacLane spectra counterparts.

Schwede, Stefan

1999-03-01

308

Stable quarks of the 4th family?  

E-print Network

Existence of metastable quarks of new generation can be embedded into phenomenology of heterotic string together with new long range interaction, which only this new generation possesses. We discuss primordial quark production in the early Universe, their successive cosmological evolution and astrophysical effects, as well as possible production in present or future accelerators. In case of a charge symmetry of 4th generation quarks in Universe, they can be stored in neutral mesons, doubly positively charged baryons, while all the doubly negatively charged "baryons" are combined with He-4 into neutral nucleus-size atom-like states. The existence of all these anomalous stable particles may escape present experimental limits, being close to present and future experimental test. Due to the nuclear binding with He-4 primordial lightest baryons of the 4th generation with charge +1 can also escape the experimental upper limits on anomalous isotopes of hydrogen, being compatible with upper limits on anomalous lithium. While 4th quark hadrons are rare, their presence may be nearly detectable in cosmic rays, muon and neutrino fluxes and cosmic electromagnetic spectra. In case of charge asymmetry, a nontrivial solution for the problem of dark matter (DM) can be provided by excessive (meta)stable anti-up quarks of 4th generation, bound with He-4 in specific nuclear-interacting form of dark matter. Such candidate to DM is surprisingly close to Warm Dark Matter by its role in large scale structure formation. It catalyzes primordial heavy element production in Big Bang Nucleosynthesis and new types of nuclear transformations around us.

K. Belotsky; M. Khlopov; K. Shibaev

2008-06-05

309

Modeling the dynamics of stable isotope tissue-diet enrichment.  

PubMed

Reconstructions of dietary composition and trophic level from stable isotope measurements of animal tissue rely on predictable offsets of stable isotope ratios from diet to tissue. Physiological processes associated with metabolism shape tissue stable isotope ratios, and as such the spacing between stable isotope ratios of diet and tissue may be influenced by processes such as growth, nutritional stress, and disease. Here, we develop a model of incorporation stable isotopes in diet to tissues by coupling stable isotope dynamics to a model of macronutrient energy metabolism. We use the model to explore the effect of changes in dietary intake, both composition and amount, and in energy expenditure, on body mass and carbon and nitrogen stable isotope ratios of tissue. PMID:25457228

Remien, Christopher H

2015-02-21

310

Color stable manganese-doped phosphors  

DOEpatents

A lighting apparatus capable of emitting white light includes a semiconductor light source; and a phosphor material radiationally coupled to the light source. The phosphor material includes a color-stable Mn.sup.+4 doped phosphor prepared by a process including providing a phosphor of formula I; A.sub.x[MF.sub.y]:Mn.sup.+4 I and contacting the phosphor in particulate form with a saturated solution of a composition of formula II in aqueous hydrofluoric acid; A.sub.x[MF.sub.y]; II wherein A is Li, Na, K, Rb, Cs, NR.sub.4 or a combination thereof; M is Si, Ge, Sn, Ti, Zr, Al, Ga, In, Sc, Y, La, Nb, Ta, Bi, Gd, or a combination thereof; R is H, lower alkyl, or a combination thereof; x is the absolute value of the charge of the [MF.sub.y] ion; and y is 5, 6 or 7. In particular embodiments, M is Si, Ge, Sn, Ti, Zr, or a combination thereof.

Lyons, Robert Joseph; Setlur, Anant Achyut; Deshpande, Anirundha Rajendra; Grigorov, Ljudmil Slavchev

2014-04-29

311

Low energy stable plasma calibration facility  

SciTech Connect

We have designed and fabricated a low energy plasma calibration facility for testing and calibration of rocket-borne charged-particle detectors and for the investigation of plasma sheath formation in an environment with ionospheric plasma energies, densities, and Debye lengths. We describe the vacuum system and associated plasma source, which was modified from a Naval Research Laboratory design [Bowles et al. Rev. Sci. Instrum. 67, 455 (1996)]. Mechanical and electrical modifications to this cylindrical microwave resonant source are outlined together with a different method of operating the magnetron that achieves a stable discharge. This facility produces unmagnetized plasmas with densities from 1x10{sup 3}/cm{sup 3} to 6x10{sup 5}/cm{sup 3}, electron temperatures from 0.1 to 1.7 eV, and plasma potentials from 0.5 to 8 V depending on varying input microwave power and neutral gas flow. For the range of input microwave power explored (350-600 W), the energy density of the plasma remains constant because of an inverse relationship between density and temperature. This relationship allows a wide range of Debye lengths (0.3-8.4 cm) to be investigated, which is ideal for simulating the ionospheric plasma sheaths we explore.

Frederick-Frost, K. M.; Lynch, K. A. [Physics and Astronomy Department, Wilder Laboratory, Dartmouth College, Hanover, New Hampshire 03755 (United States)

2007-07-15

312

The Stable K0 Giant Star ? Gem  

NASA Astrophysics Data System (ADS)

A nine-season spectroscopic study of the photosphere of ? Gem (K0 III) shows this low-luminosity giant to be stable, with no effective temperature variations above ~2 K, and no secular temperature variations over the 2002-2010 time span above 0.2 K per year. The radial-velocity variations are consistent with an orbital variation of ~40 m s-1. The projected rotation rate is found to be 1.70 ± 0.20 km s-1 with a macroturbulence dispersion of 4.53 ± 0.10 km s-1. The third-signature plot is also invariant and shows a granulation velocity gradient 20% smaller than the solar gradient. The absolute shift of the third-signature plot gives a blueshift-corrected radial velocity of 3385 ± 70 m s-1. Bisector mapping of the Fe I ?6253 line yields a flux deficit of 12% ± 1% in area, somewhat smaller than for other giants, but the shape and the position of the peak at 4.8 km s-1 is consistent with other giants. All of the investigated photospheric parameters are consistent with ? Gem being a low-luminosity giant in agreement with its absolute magnitude.

Gray, David F.

2014-12-01

313

Stable Isotope Spectroscopy for Diagnostic Medicine  

NASA Astrophysics Data System (ADS)

Isotopic tracers have been used in medical research for more than fifty years. Radioactive isotopes have been most used because of the high detection efficiencies possible. With increased awareness of the effects of low level radiation and radioactive waste management problems, the need for safe non radioactive tracers has become apparent. Rare stable isotopes of biologically active elements can be used for metabolic and pharmacokinetic studies provided that both sufficient detection sensitivity can be achieved and reliable cost effective instruments can be developed. High resolution optical spectroscopic methods which can determine isotopic ratios with high precision and accuracy are viable for research and clinical use. The study of 13C/12C ratios in CO2 for breath test diagnostics will be described in detail. Using the laser optogalvonic effect with isotopic lasers a specific medical diagnostic for h-pylori infection, has recently received FDA approval. Opportunities exist to study D/H ratios in water and 18O/16O ratios in CO2 and water for basic metabolism diagnostics and 15N/14N ratios in urine for liver function and related studies.

Murnick, D. E.

2000-06-01

314

Stable ultracompact objects and submillisecond pulsars.  

NASA Astrophysics Data System (ADS)

Relativistic objects with the compaction parameter u ? (M/R) (mass to size ratio in geometrized units) ? (1/3) are important in studying ultra-compact objects (UCOs) and the sub-millisecond pulsars (SMPs). The authors have proposed a model with the stiffest equation of state, dP/dE = 1 (in geometrized units) in the core and a polytropic equation with constant adiabatic index ? = dln?/dln? (where ? is the rest-mass density) in the envelope, acid obtained a stable configuration with a maximum value of u ? 0.3574, when the ratio of pressure (P) to energy density (E) on the core-envelope boundary reaches about 0.014. The minimum uniform rotation period (Tmin) of the 1.442 Msun neutron star (the maximum mass of neutron star accurately known to date) based upon this model turns out to be 0.2828 ms and the corresponding average energy density of the configuration is 3.25×1015g cm-3. The M(envelope)/M(star) ratio is found to be about 10-2, which may be relevant in explaining the rotational irregularities in some pulsars known as the timing noise and glitches.

Negi, P. S.; Durgapal, M. C.

1999-09-01

315

Stable Isotope Database: present and past archives  

NASA Astrophysics Data System (ADS)

Paleoclimate data provide benchmarks against which the realism of the processes simulated by climate models can be assessed. Within this framework, it is essential to avoid introducing uncertainties associated with transfer functions and therefore to operate with robust proxies. The implementation of stable isotopes of water or carbon inside climate models motivates a synthesis of available data. Supported by the LABEX L-IPSL and involving a team of climate modelers and paleoclimatologists, this project aims to establish a worldwide database of ?18O, ?D ?17O and ?13C from oceanic microfossils, corals, ice cores, cave speleothems, lakes, tree rings, and vegetation leaves wax. The aim is to provide a global vision of the hydrological cycle during the LGM and other selected key periods (last 2000 years, Mid-Holocene, Dansgaard-Oeschger events, and the Eemian). It requires screening through hundreds of published oceanic and continental records, validating the selection of the data based on resolution and chronological information. We extracted ~900 dated ?18O records from 650 marine sediment cores, 65 ?18O records from 50 ice cores, ~200 ?18O speleothems records from 60 caves, and 540 ?13C records from 290 marine sediment cores. An additional aspect of this project consists in the construction of an online portal providing an intuitive and interactive platform allowing selecting, visualizing, and downloading of the records included in this database, thus improving the distribution and comparison of paleoclimatic records from various sites.

Bolliet, Timothé

2014-05-01

316

Long solitary internal waves in stable stratifications  

NASA Astrophysics Data System (ADS)

Observations of internal solitary waves over an antarctic ice shelf (Rees and Rottman, 1994) demonstrate that even large amplitude disturbances have wavelengths that are bounded by simple heuristic arguments following from the Scorer parameter based on linear theory for wave trapping. Classical weak nonlinear theories that have been applied to stable stratifications all begin with perturbations of simple long waves, with corrections for weak nonlinearity and dispersion resulting in nonlinear wave equations (Korteweg-deVries (KdV) or Benjamin-Davis-Ono) that admit localized propagating solutions. It is shown that these theories are apparently inappropriate when the Scorer parameter, which gives the lowest wavenumber that does not radiate vertically, is positive. In this paper, a new nonlinear evolution equation is derived for an arbitrary wave packet thus including one bounded below by the Scorer parameter. The new theory shows that solitary internal waves excited in high Richardson number waveguides are predicted to have a halfwidth inversely proportional to the Scorer parameter, in agreement with atmospheric observations. A localized analytic solution for the new wave equation is demonstrated, and its soliton-like properties are demonstrated by numerical simulation.

Zimmerman, W. B.; Rees, J. M.

2004-04-01

317

Organized polysaccharide fibers as stable drug carriers  

PubMed Central

Many challenges arise during the development of new drug carrier systems, and paramount among them are safety, solubility and controlled release requirements. Although synthetic polymers are effective, the possibility of side effects imposes restrictions on their acceptable use and dose limits. Thus, a new drug carrier system that is safe to handle and free from side effects is very much in need and food grade polysaccharides stand tall as worthy alternatives. Herein, we demonstrate for the first time the feasibility of sodium iota-carrageenan fibers and their distinctive water pockets to embed and release a wide variety of drug molecules. Structural analysis has revealed the existence of crystalline network in the fibers even after encapsulating the drug molecules, and iota-carrageenan maintains its characteristic and reproducible double helical structure suggesting that the composites thus produced are reminiscent of cocrystals. The melting properties of iota-carrageenan:drug complexes are distinctly different from those of either drug or iota-carrageenan fiber. The encapsulated drugs are released in a sustained manner from the fiber matrix. Overall, our research provides an elegant opportunity for developing effective drug carriers with stable network toward enhancing and/or controlling bioavailability and extending shelf-life of drug molecules using GRAS excipients, food polysaccharides, that are inexpensive and non–toxic. PMID:23544530

Janaswamy, Srinivas; Gill, Kristin L.; Campanella, Osvaldo H.; Pinal, Rodolfo

2013-01-01

318

HUNT STABLE COMPLEX LOOKING NORTHWEST TOWARD DOG KENNEL RUINS ACROSS ...  

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

HUNT STABLE COMPLEX LOOKING NORTHWEST TOWARD DOG KENNEL RUINS ACROSS THE GREAT CIRCUS - Overhills, Fort Bragg Military Reservation, Approximately 15 miles NW of Fayetteville, Overhills, Harnett County, NC

319

Modelling fractionation of stable isotopes in stalagmites  

NASA Astrophysics Data System (ADS)

High resolution ?13C and ?18O profiles recorded in precisely dated speleothems are widely used proxies for the climate of the past. Both ?13C and ?18O depend on several climate related effects including meteorological processes, processes occurring in the soil zone above the cave and isotope fractionation processes occurring in the solution layer on the stalagmite surface. Here we model the latter using a stalagmite isotope and growth model and determine the relationship between the stable isotope values in speleothem calcite and cave parameters, such as temperature, drip interval, water p and a mixing coefficient describing mixing processes between the solution layer and the impinging drop. The evolution of ?13C values is modelled as a Rayleigh distillation process and shows a pronounced dependence on the residence time of the solution on the stalagmite surface and the drip interval, respectively. The evolution of ?18O values, in contrast, is also influenced by buffering reactions between the bicarbonate in the solution and the drip water driving the ?18O value of the bicarbonate towards the value expected for equilibrium isotope fractionation between drip water and calcite. This attenuates the dependence of the ?18O values on drip interval. The temperature dependence of ?18O, however, is more pronounced than for ?13C and in a similar range as expected for fractionation under equilibrium conditions. We also investigate the isotopic enrichment of the ?13C and ?18O values along individual growth layers and, thus, the slopes expected for Hendy tests. The results show that a positive Hendy test is only possible if isotope fractionation occurred under disequilibrium conditions. However, a negative Hendy test does not exclude that isotope fractionation occurred under disequilibrium conditions. A more reliable indicator for disequilibrium fractionation is the enrichment of the ?13C values along an individual growth layer.

Mühlinghaus, Christian; Scholz, Denis; Mangini, Augusto

2009-12-01

320

Stable representation homology and Koszul duality.  

E-print Network

This paper is a sequel to [BKR], where we studied the derived affine scheme DRep_n(A) of the classical representation scheme Rep_n(A) for an associative k-algebra A. In [BKR], we have constructed canonical trace maps Tr_n(A): HC(A) -> H[DRep_n(A)]^GL extending the usual characters of representations to higher cyclic homology. This raises a question whether a well known theorem of Procesi [P] holds in the derived setting: namely, is the algebra homomorphism Sym[Tr_n(A)]: Sym[HC(A)] -> H[DRep_n(A)]^GL defined by Tr_n(A) surjective ? In the present paper, we answer this question for augmented algebras. Given such an algebra, we construct a canonical dense DG subalgebra DRep_\\infty(A)^Tr of the topological DG algebra DRep_\\infty(A)^{GL_\\infty}. It turns out that on passing to the inverse limit (as n -> \\infty), the family of maps Sym[Tr_n(A)] "stabilizes" to an isomorphism Sym[\\bar{HC}(A)] = H[DRep_\\infty(A)^Tr]. The derived version of Procesi's theorem does therefore hold in the limit. However, for a fixed (finite) n, there exist homological obstructions to the surjectivity of Sym[Tr_n(A)], and we show on simple examples that these obstructions do not vanish in general. We compare our result with the classical theorem of Loday-Quillen and Tsygan on stable homology of matrix Lie algebras. We show that the relative Chevalley-Eilenberg complex C(gl_\\infty(A), gl_\\infty(k); k) equipped with the natural coalgebra structure is Koszul dual to the DG algebra DRep_\\infty(A)^Tr. We also extend our main results to bigraded DG algebras, in which case we show that DRep_{\\infty}(A)^Tr = DRep_{\\infty}(A)^GL_{\\infty}. As an application, we compute the (bigraded) Euler characteristics of DRep_\\infty(A)^GL_{\\infty} and \\bar{HC}(A) and derive some interesting combinatorial identities.

Yuri Berest; Ajay Ramadoss

321

Uncertainty in source partitioning using stable isotopes.  

PubMed

Stable isotope analyses are often used to quantify the contribution of multiple sources to a mixture, such as proportions of food sources in an animal's diet, or C3 and C4 plant inputs to soil organic carbon. Linear mixing models can be used to partition two sources with a single isotopic signature (e.g., ?(13)C) or three sources with a second isotopic signature (e.g., ?(15)N). Although variability of source and mixture signatures is often reported, confidence interval calculations for source proportions typically use only the mixture variability. We provide examples showing that omission of source variability can lead to underestimation of the variability of source proportion estimates. For both two- and three-source mixing models, we present formulas for calculating variances, standard errors (SE), and confidence intervals for source proportion estimates that account for the observed variability in the isotopic signatures for the sources as well as the mixture. We then performed sensitivity analyses to assess the relative importance of: (1) the isotopic signature difference between the sources, (2) isotopic signature standard deviations (SD) in the source and mixture populations, (3) sample size, (4) analytical SD, and (5) the evenness of the source proportions, for determining the variability (SE) of source proportion estimates. The proportion SEs varied inversely with the signature difference between sources, so doubling the source difference from 2‰ to 4‰ reduced the SEs by half. Source and mixture signature SDs had a substantial linear effect on source proportion SEs. However, the population variability of the sources and the mixture are fixed and the sampling error component can be changed only by increasing sample size. Source proportion SEs varied inversely with the square root of sample size, so an increase from 1 to 4 samples per population cut the SE in half. Analytical SD had little effect over the range examined since it was generally substantially smaller than the population SDs. Proportion SEs were minimized when sources were evenly divided, but increased only slightly as the proportions varied. The variance formulas provided will enable quantification of the precision of source proportion estimates. Graphs are provided to allow rapid assessment of possible combinations of source differences and source and mixture population SDs that will allow source proportion estimates with desired precision. In addition, an Excel spreadsheet to perform the calculations for the source proportions and their variances, SEs, and 95% confidence intervals for the two-source and three-source mixing models can be accessed at http://www.epa.gov/wed/pages/models.htm. PMID:24577646

Phillips, D L; Gregg, J W

2001-04-01

322

Stable isotope probing — linking microbial identity to function  

Microsoft Academic Search

Stable isotope probing (SIP) is a technique that is used to identify the microorganisms in environmental samples that use a particular growth substrate. The method relies on the incorporation of a substrate that is highly enriched in a stable isotope, such as 13C, and the identification of active microorganisms by the selective recovery and analysis of isotope-enriched cellular components. DNA

Marc G. Dumont; J. Colin Murrell

2005-01-01

323

STABLE STATE OF INTERCONNECT UNDER TEMPERATURE CHANGE AND ELECTRIC CURRENT  

E-print Network

STABLE STATE OF INTERCONNECT UNDER TEMPERATURE CHANGE AND ELECTRIC CURRENT Z. SUO Mechanical electric current, such an interconnect evolvesÐafter a compli- cated sequence of eventsÐinto a stable state, and no further mass diusion. The electric current continues in the shunt layers where aluminum is depleted

Suo, Zhigang

324

APPROACHES FOR MEASURING STABLE CARBON AND NITROGEN ISOTOPES IN BACTERIA  

EPA Science Inventory

Stable isotopes have been used successfully over the past three decades to trace through aquatic food chairs. his technique, however, has only recently been used to examine aquatic microbial roles in elemental cycling. he major obstacle to measuring stable isotope compositions in...

325

Stable Isotopes and Mineral Resource Investigations in the United States  

NSDL National Science Digital Library

This USGS handout is a page providing a good, brief summary of stable isotope techniques and applications in the geosciences. A map indicating the locations of current USGS stable isotopic studies accompanies the text. A discussion of mineral weathering effects and case studies from ore deposits in Maine and North Carolina complement the general overview.

326

Compact preference representation in stable marriage E. Pilotto1  

E-print Network

Compact preference representation in stable marriage problems E. Pilotto1 , F. Rossi1 , K. B.Walsh@nicta.com.au Abstract. The stable marriage problem has many practical applications in two- sided markets like those marriages assume that the par- ticipants explicitly expresses a preference ordering. This can be problematic

Rossi, Francesca

327

Treatment of stable vitiligo with autologous epidermal grafting and PUVA  

Microsoft Academic Search

Background: Previous reports have shown the benefits of epidermal grafting for vitiligo.Objective: Our purpose was to evaluate the effectiveness and complications of epidermal grafting in combination with PUVA on stable vitiligo refractory to conventional treatments.Methods: In 100 patients with stable refractory vitiligo we performed epidermal grafting with suction blisters followed by PUVA treatment. The grafted sites were examined for repigmentation

Seung Kyung Hann; Sungbin Im; Ha Wook Bong; Yoon-Kee Park

1995-01-01

328

11. INTERIOR VIEW OF STABLES, ROOM 110, LOOKING NORTHEAST TOWARD ...  

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

11. INTERIOR VIEW OF STABLES, ROOM 110, LOOKING NORTHEAST TOWARD EXIT DOORS. PAINTED WOOD PANELS ON MASONRY WALLS SERVE AS POCKETS FOR SLIDING DOORS. CONCRETE SLAB FLOOR SLOPES AWAY FROM DOORS INTO ROOM. - Presidio of San Francisco, Cavalry Stables, Cowles Street, between Lincoln Boulevard & McDowell Street, San Francisco, San Francisco County, CA

329

A VIEW OF THE STABLES LOOKING TO THE SOUTH, TOWARD ...  

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

A VIEW OF THE STABLES LOOKING TO THE SOUTH, TOWARD THE HUACHUCA MOUNTAINS, CIRCA 1910. HORSES ARE TIED TO THE EXTERIOR OF ONE OF THE PADDOCK CORRALS (FORT HUACHUCA HISTORICAL MUSEUM, PHOTOGRAPH 1918.00.00.126, PHOTOGRAPHER UNIDENTIFIED, CREATED BY AND PROPERTY OF THE UNITED STATES ARMY) - Fort Huachuca, Cavalry Stables, Clarkson Road, Sierra Vista, Cochise County, AZ

330

Locally Stable Marriage with Strict Preferences Martin Hoefer1  

E-print Network

Locally Stable Marriage with Strict Preferences Martin Hoefer1 and Lisa Wagner2 1 Max to workers [2,5], organs to patients [18], or general buyers to sellers. In ad- dition, stable marriage relationship or activity, Supported by DFG Cluster of Excellence MMCI and grant Ho 3831/3-1. An extended full

331

Are Risk Preferences Stable across Contexts? Evidence from Insurance Data  

Microsoft Academic Search

Using a unique dataset, we test whether households' deductible choices in auto and home insurance reflect stable risk preferences. Our test relies on a structural model that assumes households are objective expected utility maximizers and claims are generated by household-coverage specific Poisson processes. We find that the hypothesis of stable risk preferences is rejected by the data. Our analysis suggests

Levon Barseghyan; Jeffrey Prince; Joshua C. Teitelbaum

2011-01-01

332

Design and Implementation of WSN Based Stable Management System  

Microsoft Academic Search

WSN (Wireless sensor networks) based on low-power technologies is one of the important technologies currently available in constructing ubiquitous society and is applied in various fields, including, environmental monitoring, disaster management, logistics management, and home network. In this paper, we proposed a WSN-based stable management system as one of the WSN applications. This stable management system consists of sensor manager

Jeong-Hwan Hwang; Hyun-joong Kang; Hyun Yoe

2010-01-01

333

Use of stable isotope analysis in determining aquatic food webs  

EPA Science Inventory

Stable isotope analysis is a useful tool for describing resource-consumer dynamics in ecosystems. In general, organisms of a given trophic level or functional feeding group will have a stable isotope ratio identifiable different than their prey because of preferential use of one ...

334

Three-dimensional stable matching with cyclic preferences  

E-print Network

[Alkan, A., 1988. Non- existence of stable threesome matchings. Mathematical Social Sciences 16, 207 Mathematics 286, 1­10] showed that if preferences are cyclic, and the number of agents is limited to three of each gender, then a stable matching always exists. Here we extend this result to four agents of each

335

Formation of thermodynamically stable dications in the gas phase by thermal ion-molecule reactions: Ta sup 2+ and Zr sup 2+ with small alkanes  

SciTech Connect

The reactions of doubly charged tantalum and singly and doubly charged zirconium with small linear alkanes are reported. The rate constants for the reactions of singly and doubly charged Zr and Ta with methane are also reported. Ta{sup 2+} reacts with methane formally by carbene and hydride abstraction along with some charge transfer. Reactions of Ta{sup 2+} with longer chain alkanes result in complete charge transfer. Zr{sup 2+} also reacts with methane formally be carbene and hydride abstraction and undergoes dehydrogenation and demethanation reactions and hydride and methide abstraction in addition to charge transfer with propane and butane. With alkanes larger than butane only charge transfer is observed. Zr{sup +} reacts similarly to other early transition metals to multiply dehydrogenate alkanes and, to a lesser extent, yield C-C cleavage fragments.

Ranasinghe, Y.A.; MacMahon, T.J.; Freiser, B.S. (Purdue Univ., West Lafayette, IN (United States))

1991-10-03

336

Negative tension branes as stable thin shell wormholes  

E-print Network

We investigate negative tension branes as stable thin shell wormholes in Reissner-Nordstrom-(anti) de Sitter spacetimes in $d$ dimensional Einstein gravity. Imposing Z2 symmetry, we construct and classify traversable static thin shell wormholes in spherical, planar (or cylindrical) and hyperbolic symmetries. In spherical geometry, we find the higher dimensional counterpart of Barcelo and Visser's wormholes, which are stable against spherically symmetric perturbations. We also find the classes of thin shell wormholes in planar and hyperbolic symmetries with a negative cosmological constant, which are stable against perturbations preserving symmetries. In most cases, stable wormholes are found with the combination of an electric charge and a negative cosmological constant. However, as special cases, we find stable wormholes even with vanishing cosmological constant in spherical symmetry and with vanishing electric charge in hyperbolic symmetry.

Kokubu, Takafumi

2014-01-01

337

Carbene reactions produced by recoil excitation methods  

E-print Network

which can not be accounted for in comparison with the CH2F2-02 system and the 1, 3- butadiene-02 system are two radioactivity peaks, one appearing at 200 min and the other appearing at 605 min. Presumably these two addi. tional products correspond...(-t) F DMS Column 11 min 19 30 30 51 78 Product Observed C~HF2 Sy Product Observed in ~H C=CH-CH=CH2 System Relative 7, 370 3, 409 336 196 1, 000 15, 353 859 Yields 5, 990 3, 910 461 179 1, 000 13, 521 869 HC=CH7 200 243 320...

Lowery, Kirby

2012-06-07

338

Use of stable isotopes in mineral nutrition research  

SciTech Connect

Stable isotopes are valuable tools for research on mineral bioavailability and metabolism. They can be used as tracers with no exposure to radiation and they do not decay over time. Attempts to use stable isotopes of minerals as metabolic tracers were first described only 25 years ago. There were relatively few reports of their use over the next 15 years, but interest in stable isotopes has expanded markedly in the last 10 years. The advantages of stable isotope tracers are so great that scientists have been willing to accept the laborious and costly nature of mineral isotope analysis, and substantial progress has been made in the field. New applications for stable isotopes and new analytical methods have been introduced recently. However, limitations to the approach and methodological problems remain to be resolved. This review describes early work in the field and discusses the advantages and disadvantages of stable isotope tracers and of the various methods of analysis. Information discovered with stable isotopes is reviewed, and probable future applications are discussed.69 references.

Turnlund, J.R.

1989-01-01

339

Stable non-uniform black strings below the critical dimension  

NASA Astrophysics Data System (ADS)

The higher-dimensional vacuum Einstein equation admits translationally non- uniform black string solutions. It has been argued that infinitesimally non-uniform black strings should be unstable in 13 or fewer dimensions and otherwise stable. We construct numerically non-uniform black string solutions in 11, 12, 13, 14 and 15 dimensions. Their stability is investigated using local Penrose inequalities. Weakly non-uniform solutions behave as expected. However, in 12 and 13 dimensions, strongly non-uniform solutions appear to be stable and can have greater horizon area than a uniform string of the same mass. In 14 and 15 dimensions all non-uniform black strings appear to be stable.

Figueras, Pau; Murata, Keiju; Reall, Harvey S.

2012-11-01

340

High-Order Entropy Stable Formulations for Computational Fluid Dynamics  

NASA Technical Reports Server (NTRS)

A systematic approach is presented for developing entropy stable (SS) formulations of any order for the Navier-Stokes equations. These SS formulations discretely conserve mass, momentum, energy and satisfy a mathematical entropy inequality. They are valid for smooth as well as discontinuous flows provided sufficient dissipation is added at shocks and discontinuities. Entropy stable formulations exist for all diagonal norm, summation-by-parts (SBP) operators, including all centered finite-difference operators, Legendre collocation finite-element operators, and certain finite-volume operators. Examples are presented using various entropy stable formulations that demonstrate the current state-of-the-art of these schemes.

Carpenter, Mark H.; Fisher, Travis C.

2013-01-01

341

Environmental and biomedical applications of natural metal stable isotope variations  

USGS Publications Warehouse

etal stable isotopes are now being used to trace metal contaminants in the environment and as indicators of human systemic function where metals play a role. Stable isotope abundance variations provide information about metal sources and the processes affecting metals in complex natural systems, complementing information gained from surrogate tracers, such as metal abundance ratios or biochemical markers of metal metabolism. The science is still in its infancy, but the results of initial studies confirm that metal stable isotopes can provide a powerful tool for forensic and biomedical investigations.

Bullen, T.D.; Walczyk, T.

2009-01-01

342

New steroid-fused P-heterocycles. Part I. Synthesis and conformational study of dioxaphosphorino[16,17-d]estrone derivatives.  

PubMed

D-ring-fused dioxaphosphorinanes (4-6) in the estrone series were synthetized as epimeric pairs and investigated by NMR and computational methods in order to determine their stereostructures and predominant conformations. The study was performed to evaluate the influence of the rigid sterane framework on the geometry of the condensed hetero ring, with regard to the possible steric effect of the angular methyl group at position 13. Additionally, the steric and electronic effects of the P-substituents on the conformational equilibrium were examined. The distorted-boat conformation of the hetero ring of dioxaphosphorinoestrone 3-methyl ether 4a was confirmed by single-crystal X-ray analysis. This is in good agreement with the observation in solution that, in the case of the boat conformation, the anisotropic shielding effect of the phenyl group of cyclic phosphonate 4a generates an upfield shift for 17-H, as compared with the corresponding chemical shift for epimer 4b. A similar boat conformation was substantiated for derivatives 4b, 5a, 5b and 6b on the basis of the J(H, H) and J(H, P) coupling constants and also ab initio calculations, regardless of the P-configuration. At the same time, the hetero ring of 6a seems to tilt towards a chair-like conformation due to the strong equatorial preference of the N-bis(2-chloroethyl) group. PMID:17383699

Frank, Eva; Körtvélyesi, Tamás; Czugler, Mátyás; Mucsi, Zoltán; Keglevich, György

2007-05-01

343

Massive stable charged particle signatures in simulations at the LHC  

E-print Network

The importance of heavy stable charged (HSCP) particles lies in the exploration of extensions to the standard model. Extensions of the standard model attempt to solve current problems in the standard model such as the ...

Silva, James B. (James Brian)

2008-01-01

344

A Search for Charged Massive Stable Particles at D0  

SciTech Connect

A search for charged massive stable particles has been performed with the D0 detector at the Fermilab Tevatron. The signature is two particles reconstructed as muons, but with speed and invariant mass inconsistent with beam-produced muons. No excess of events is observed and limits are set on the production cross-section for pair-produced stable stau sleptons based on 390 pb{sup -1} of data. Limits vary from 0.06 pb to 0.62 pb, depending on the stau mass, and are the strictest Tevatron limits to date. Mass limits are also set for stable charginos. The limits are 140 GeV/c{sup 2} for a higgsino-like chargino and 174 GeV/c{sup 2} for a gaugino-like chargino. These are currently the best limits to date for stable charginos.

Eads, Michael T.; /Northern Illinois U.; ,

2005-08-01

345

Dark Atoms of Dark Matter and their Stable Charged Constituents  

E-print Network

Direct searches for dark matter lead to serious problems for simple models with stable neutral Weakly Interacting Massive Particles (WIMPs) as candidates for dark matter. A possibility is discussed that new stable quarks and charged leptons exist and are hidden from detection, being bound in neutral dark atoms of composite dark matter. Stable -2 charged particles $O^{--}$ are bound with primordial helium in O-helium (OHe) atoms, being specific nuclear interacting form of composite dark matter. The positive results of DAMA experiments can be explained as annual modulation of radiative capture of O-helium by nuclei. In the framework of this approach test of DAMA results in detectors with other chemical content becomes a nontrivial task, while the experimental search of stable charged particles at LHC or in cosmic rays acquires a meaning of direct test for composite dark matter scenario.

Maxim Yu. Khlopov

2011-11-11

346

STABLE ISOTOPIC RESPONSE TO THE LATE EOCENE EXTRATERRESTRIAL IMPACT EVENTS  

E-print Network

STABLE ISOTOPIC RESPONSE TO THE LATE EOCENE EXTRATERRESTRIAL IMPACT EVENTS by AIMEE E PUSZ A thesis to the Late Eocene Extraterrestrial Impact Events by AIMEE ELIZABETH PUSZ Thesis Director: Dr. Kenneth G

347

THE STABLE MANIFOLD THEOREM FOR SEMILINEAR STOCHASTIC EVOLUTION EQUATIONS AND  

E-print Network

THE STABLE MANIFOLD THEOREM FOR SEMILINEAR STOCHASTIC EVOLUTION EQUATIONS AND STOCHASTIC PARTIAL of this paper is to characterize the pathwise local structure of solutions of semilinear stochastic evolution finite dimension. The proof uses infinite-dimensional multiplicative ergodic theory techniques

348

Highly stable high-rate discriminator for nuclear counting  

NASA Technical Reports Server (NTRS)

Pulse amplitude discriminator is specially designed for nuclear counting applications. At very high rates, the threshold is stable. The output-pulse width and the dead time change negligibly. The unit incorporates a provision for automatic dead-time correction.

English, J. J.; Howard, R. H.; Rudnick, S. J.

1969-01-01

349

Stable isotope views on ecosystem function: challenging or challenged?  

PubMed Central

Stable isotopes and their potential for detecting various and complex ecosystem processes are attracting an increasing number of scientists. Progress is challenging, particularly under global change scenarios, but some established views have been challenged. The IX meeting of the Spanish Association of Terrestrial Ecology (AAET, Úbeda, 18–22 October 2009) hosted a symposium on the ecology of stable isotopes where the linear mixing model approach of partitioning sinks and sources of carbon and water fluxes within an ecosystem was challenged, and new applications of stable isotopes for the study of plant interactions were evaluated. Discussion was also centred on the need for networks that monitor ecological processes using stable isotopes and key ideas for fostering future research with isotopes. PMID:20015858

Resco, Víctor; Querejeta, José I.; Ogle, Kiona; Voltas, Jordi; Sebastià, Maria-Teresa; Serrano-Ortiz, Penélope; Linares, Juan C.; Moreno-Gutiérrez, Cristina; Herrero, Asier; Carreira, José A.; Torres-Cañabate, Patricia; Valladares, Fernando

2010-01-01

350

9 CFR 108.10 - Outer premises and stables.  

Code of Federal Regulations, 2010 CFR

...108.10 Section 108.10 Animals and Animal Products ANIMAL AND PLANT HEALTH INSPECTION SERVICE, DEPARTMENT...premises. (b) Stables or other premises for animals used in the production or testing of biological products at licensed...

2010-01-01

351

Temperature transducer has high output, is time stable  

NASA Technical Reports Server (NTRS)

Compact, lightweight temperature transducer requires no amplification of its output signal and is time stable. It uses the temperature-dependent characteristics of a silicon transistor to provide a zero-to-five-volt signal proportional to temperature.

Follett, W. H.

1965-01-01

352

Stable commutator length is rational in free groups  

NASA Astrophysics Data System (ADS)

For any group, there is a natural (pseudo-)norm on the vector space B_1^H of real homogenized (group) 1 -boundaries, called the stable commutator length norm. This norm is closely related to, and can be thought of as a relative version of, the Gromov (pseudo)-norm on (ordinary) homology. We show that for a free group, the unit ball of this pseudo-norm is a rational polyhedron. It follows that the stable commutator length in free groups takes on only rational values. Moreover every element of the commutator subgroup of a free group rationally bounds an injective map of a surface group. The proof of these facts yields an algorithm to compute the stable commutator length in free groups. Using this algorithm, we answer a well-known question of Bavard in the negative, constructing explicit examples of elements in free groups whose stable commutator length is not a half-integer.

Calegari, Danny

2009-10-01

353

9 CFR 108.10 - Outer premises and stables.  

...108.10 Section 108.10 Animals and Animal Products ANIMAL AND PLANT HEALTH INSPECTION SERVICE, DEPARTMENT...premises. (b) Stables or other premises for animals used in the production or testing of biological products at licensed...

2014-01-01

354

9 CFR 108.10 - Outer premises and stables.  

Code of Federal Regulations, 2012 CFR

...108.10 Section 108.10 Animals and Animal Products ANIMAL AND PLANT HEALTH INSPECTION SERVICE, DEPARTMENT...premises. (b) Stables or other premises for animals used in the production or testing of biological products at licensed...

2012-01-01

355

9 CFR 108.10 - Outer premises and stables.  

Code of Federal Regulations, 2013 CFR

...108.10 Section 108.10 Animals and Animal Products ANIMAL AND PLANT HEALTH INSPECTION SERVICE, DEPARTMENT...premises. (b) Stables or other premises for animals used in the production or testing of biological products at licensed...

2013-01-01

356

Constraints on stable equilibria with fluctuation-induced (Casimir)  

E-print Network

We examine whether fluctuation-induced forces can lead to stable levitation. First, we analyze a collection of classical objects at finite temperature that contain fixed and mobile charges and show that any arrangement in ...

Rahi, Sahand Jamal

357

Controlled Stable Oscillation of Nanomechanical Systems Based on Carbon Nanotubes  

NASA Astrophysics Data System (ADS)

Numerical simulations are used to study the conditions controlling the stable oscillation of nanomechanical systems based on carbon nanotubes under periodic harmonic driving force. It is shown that the conditions to sustain the stable oscillation are not only dependent on the driving frequency, but also dependent on the amplitude and the initial phase of the driving force. Once the oscillatory frequency is given, the driving frequency must be equal to the integral multiple of the oscillatory frequency in order to sustain the stable oscillation. We determine the conditions by a combination of equations containing the parameters of the oscillator and the driving force, and solve it numerically. Sustained stable oscillation for the systems with a nonlinear dependence of the friction force on the relative velocity of the tubes can be obtained by properly choosing the amplitude and the initial phase of the periodic harmonic driving force. Both regular and irregular oscillatory modes are observed.

Li, Jian-Wen; Liu, Nian-Hua

2015-02-01

358

Understanding stable levitation of superconductors from intermediate electromagnetics  

E-print Network

Understanding stable levitation of superconductors from intermediate electromagnetics A. Bad for electromagnetic energy related quantities. Comprehensible illustrations, based on the calculated lines of magnetic at students who have followed an intermediate course on Electromagnetics and have some background in Classical

Majós, Antonio Badía

359

1. GENERAL VIEW. TRIM, ROOF AND STABLE DOORS ALL ARE ...  

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

1. GENERAL VIEW. TRIM, ROOF AND STABLE DOORS ALL ARE PAINTED RED. HEX SIGNS ARE PAINTED OCHRE, BLACK, RED, WHITE AND BLUE. NOTE PAINTED FLAGS ON SHED - Decorated White Barn, (Maiden Creek Township), Maiden Creek, Berks County, PA

360

New York City Ebola Patient in Stable Condition  

MedlinePLUS

... sharing features on this page, please enable JavaScript. New York City Ebola Patient in Stable Condition Three ... Ebola FRIDAY, Oct. 24, 2014 (HealthDay News) -- A New York City doctor who recently returned from West ...

361

A new intermediate for the production of flexible stable polymers  

NASA Technical Reports Server (NTRS)

Method of incorporating ether linkages into perfluoroalkylene segment of a dianydride intermediate yields intermediate that may be used in synthesis of flexible, stable polyimides for use as high-temperature, solvent-resistant sealants.

Webster, J. A.

1973-01-01

362

15 CFR 971.605 - Stable Reference Areas. [Reserved  

Code of Federal Regulations, 2011 CFR

...OCEANIC AND ATMOSPHERIC ADMINISTRATION, DEPARTMENT OF COMMERCE GENERAL REGULATIONS OF THE ENVIRONMENTAL DATA SERVICE DEEP SEABED MINING REGULATIONS FOR COMMERCIAL RECOVERY PERMITS Environmental Effects § 971.605 Stable Reference...

2011-01-01

363

Stable nonlinear identification from noisy repeated experiments via convex optimization  

E-print Network

This paper introduces new techniques for using convex optimization to fit input-output data to a class of stable nonlinear dynamical models. We present an algorithm that guarantees consistent estimates of models in this ...

Tobenkin, Mark M.

364

Chlorine stable isotopes in sedimentary systems: does size matter?  

NASA Technical Reports Server (NTRS)

Stable isotope abundances vary because of size differences. The chlorine stable isotope system was one of the first described theoretically, but had a slow, disappointment strewn development, relative to other elements. Method improvement gave only small, but significant, differences in compositions of geological materials. Eventually, brines and groundwater chlorides gave larger differences. Physical processes like diffusion and adsorption, probably are the main controls of groundwater compositions. Recent work on anthropogenic groundwater contaminants shows variations resulting from manufacturing processes; implying possibilities of tracing sources.

Coleman, Max

2004-01-01

365

Gelled mechanically stable high energy fuel composition containing metal platelets  

SciTech Connect

A gelled mechanically stable high energy fuel composition is disclosed comprising a hydrazine selected from the group consisting of hydrazine, unsymmetrical dimethyl hydrazine and mixtures thereof and an amount of metal platelets effective to produce a mechanically stable gel. Said platelets have a diameter of less than about 44 microns and an average diameter of about 1 micron, and said metal platelets are composed of a metal selected from the group consisting of aluminum, beryllium and aluminumberyllium alloy.

Bost, J.J.; Cabeal, J.A.; Rosenberg, S.D.

1980-02-05

366

Does avian malaria infection affect feather stable isotope signatures?  

Microsoft Academic Search

It is widely accepted that stable isotope ratios in inert tissues such as feather keratin reflect the dietary isotopic signature\\u000a at the time of the tissue synthesis. However, some elements such as stable nitrogen isotopes can be affected by individual\\u000a physiological state and nutritional stress. Using malaria infection experiment protocols, we estimated the possible effect\\u000a of malaria parasite infections on

Elizabeth Yohannes; Vaidas Palinauskas; Gediminas Valki?nas; Raymond W. Lee; Casimir V. Bolshakov; Staffan Bensch

367

Stable Storage of Helium in Nanoscale Platelets at Semicoherent Interfaces  

NASA Astrophysics Data System (ADS)

He implanted into metals precipitates into nanoscale bubbles that may later grow into voids, degrading the properties of engineering alloys. Using multiscale modeling, we show that a different class of He precipitates may form at semicoherent interfaces: nanoscale platelets. These platelets grow by wetting high-energy interface regions, remain stable under irradiation, and reduce He-induced swelling. Stable storage of He at interfaces may impart unprecedented He resistance to future structural materials.

Kashinath, A.; Misra, A.; Demkowicz, M. J.

2013-02-01

368

Ultra-Stable Oscillators for Probe Radio Science Investigations  

NASA Technical Reports Server (NTRS)

An Ultra-Stable Oscillator (USO) is: A frequency reference, and A clock It is stable, small, and sensitive. It is a science and an art form. It is flown on spacecraft/probes. It]is utilized at ground stations alone or as a cleanup loop. It eliminates lock-up time on uplink for occultation egress & effect of media on uplink signal. It has enabled significant planetary science investigations.

Asmar, Sami

2012-01-01

369

Observation of a stable high-beta axisymmetric plasma equilibrium  

Microsoft Academic Search

Stable, steady-state plasma equilibrium is generated in an axisymmetric configuration. The diamagnetic current is maintained by electromagnetic fields rotating in the electron diamagnetic sense. The stable, free-standing equilibrium exists for all values of beta up to 0.98, limited only by the available rf power. The plasma is centered on the axis well removed from the metal chamber walls, the limiters,

A. Kuthi; H. Zwi; L. Schmitz; A. Y. Wong

1989-01-01

370

COMPARING FRECHET AND POSITIVE STABLE LAWS THOMAS SIMON  

E-print Network

to Chapter 8.3 resp. 8.13 in [3] for more on this topic. Both positive stable and Fr´echet distributions, 60E15, 60G52, 62E15. Key words and phrases. Convex order - Fr´echet distribution - Median - MittagCOMPARING FR´ECHET AND POSITIVE STABLE LAWS THOMAS SIMON Abstract. Let L be the unit exponential

Recanati, Catherine

371

COMPARING FRECHET AND POSITIVE STABLE LAWS THOMAS SIMON  

E-print Network

to Chapter 8.3 resp. 8.13 in [5] for more on this topic. Both positive stable and Fr´echet distributions, 60E15, 60G52, 62E15. Key words and phrases. Convex order - Fr´echet distribution - Median - MittagCOMPARING FR´ECHET AND POSITIVE STABLE LAWS THOMAS SIMON Abstract. Let L be the unit exponential

Paris-Sud XI, Université de

372

Stable isotopes in precipitation in the Asian monsoon region  

Microsoft Academic Search

The influence of the Asian monsoon on the delta18O composition of precipitation is investigated on the basis of the ECHAM-4 Atmospheric General Circulation Model (AGCM), fitted with stable isotopic tracers. The model is forced with prescribed sea surface temperatures (SST) over the last few decades of the 20th century. The simulated climate and climate-stable isotope relationships are validated with observational

M. Vuille; M. Werner; R. S. Bradley; F. Keimig

2005-01-01

373

Error Analysis of Space-Stable Inertial Navigation Systems  

Microsoft Academic Search

The error equations for a space-stable inertial navigation system are derived. This is done by directly perturbing the mechanization equations in the inertial frame and then transforming in open-loop fashion to the local-level frame. A rotating inertial platform and velocity and altitude damping are considered. The relations between errors in space-stable and local-level systems are noted. Numerical results are presented

Stephen Levine; Kenneth Roy

1971-01-01

374

Generalization of symmetric ?-stable Lévy distributions for q >1  

NASA Astrophysics Data System (ADS)

The ?-stable distributions introduced by Lévy play an important role in probabilistic theoretical studies and their various applications, e.g., in statistical physics, life sciences, and economics. In the present paper we study sequences of long-range dependent random variables whose distributions have asymptotic power-law decay, and which are called (q,?)-stable distributions. These sequences are generalizations of independent and identically distributed ?-stable distributions and have not been previously studied. Long-range dependent (q,?)-stable distributions might arise in the description of anomalous processes in nonextensive statistical mechanics, cell biology, finance. The parameter q controls dependence. If q =1 then they are classical independent and identically distributed with ?-stable Lévy distributions. In the present paper we establish basic properties of (q,?)-stable distributions and generalize the result of Umarov et al. [Milan J. Math. 76, 307 (2008)], where the particular case ? =2,q?[1,3) was considered, to the whole range of stability and nonextensivity parameters ? ?(0,2] and q ?[1,3), respectively. We also discuss possible further extensions of the results that we obtain and formulate some conjectures.

Umarov, Sabir; Tsallis, Constantino; Gell-Mann, Murray; Steinberg, Stanly

2010-03-01

375

Generalization of symmetric ?-stable Lévy distributions for q>1  

PubMed Central

The ?-stable distributions introduced by Lévy play an important role in probabilistic theoretical studies and their various applications, e.g., in statistical physics, life sciences, and economics. In the present paper we study sequences of long-range dependent random variables whose distributions have asymptotic power-law decay, and which are called (q,?)-stable distributions. These sequences are generalizations of independent and identically distributed ?-stable distributions and have not been previously studied. Long-range dependent (q,?)-stable distributions might arise in the description of anomalous processes in nonextensive statistical mechanics, cell biology, finance. The parameter q controls dependence. If q=1 then they are classical independent and identically distributed with ?-stable Lévy distributions. In the present paper we establish basic properties of (q,?)-stable distributions and generalize the result of Umarov et al. [Milan J. Math. 76, 307 (2008)], where the particular case ?=2,q?[1,3) was considered, to the whole range of stability and nonextensivity parameters ??(0,2] and q?[1,3), respectively. We also discuss possible further extensions of the results that we obtain and formulate some conjectures. PMID:20596232

Umarov, Sabir; Tsallis, Constantino; Gell-Mann, Murray; Steinberg, Stanly

2010-01-01

376

Medieval horse stable; the results of multi proxy interdisciplinary research.  

PubMed

A multi proxy approach was applied in the reconstruction of the architecture of Medieval horse stable architecture, the maintenance practices associated with that structure as well as horse alimentation at the beginning of 13th century in Central Europe. Finally, an interpretation of the local vegetation structure along Morava River, Czech Republic is presented. The investigated stable experienced two construction phases. The infill was well preserved and its composition reflects maintenance practices. The uppermost part of the infill was composed of fresh stabling, which accumulated within a few months at the end of summer. Horses from different backgrounds were kept in the stable and this is reflected in the results of isotope analyses. Horses were fed meadow grasses as well as woody vegetation, millet, oat, and less commonly hemp, wheat and rye. Three possible explanations of stable usage are suggested. The stable was probably used on a temporary basis for horses of workers employed at the castle, courier horses and horses used in battle. PMID:24670874

Dejmal, Miroslav; Lisá, Lenka; Fišáková Nývltová, Miriam; Bajer, Aleš; Petr, Libor; Ko?ár, Petr; Ko?árová, Romana; Nejman, Ladislav; Rybní?ek, Michal; S?vová, Zdenka; Culp, Randy; Vavr?ík, Hanuš

2014-01-01

377

Medieval Horse Stable; The Results of Multi Proxy Interdisciplinary Research  

PubMed Central

A multi proxy approach was applied in the reconstruction of the architecture of Medieval horse stable architecture, the maintenance practices associated with that structure as well as horse alimentation at the beginning of 13th century in Central Europe. Finally, an interpretation of the local vegetation structure along Morava River, Czech Republic is presented. The investigated stable experienced two construction phases. The infill was well preserved and its composition reflects maintenance practices. The uppermost part of the infill was composed of fresh stabling, which accumulated within a few months at the end of summer. Horses from different backgrounds were kept in the stable and this is reflected in the results of isotope analyses. Horses were fed meadow grasses as well as woody vegetation, millet, oat, and less commonly hemp, wheat and rye. Three possible explanations of stable usage are suggested. The stable was probably used on a temporary basis for horses of workers employed at the castle, courier horses and horses used in battle. PMID:24670874

Dejmal, Miroslav; Lisá, Lenka; Fišáková Nývltová, Miriam; Bajer, Aleš; Petr, Libor; Ko?ár, Petr; Ko?árová, Romana; Nejman, Ladislav; Rybní?ek, Michal; S?vová, Zdenka; Culp, Randy; Vavr?ík, Hanuš

2014-01-01

378

Concurrent stable and unstable cortical correlates of human wrist movements.  

PubMed

Cortical activity has been shown to correlate with different parameters of movement. However, the dynamic properties of cortico-motor mappings still remain unexplored in humans. Here, we show that during the repetition of simple stereotyped wrist movements both stable and unstable correlates simultaneously emerge in human sensorimotor cortex. Using visual feedback of wrist movement target inferred online from MEG, we assessed the dynamics of the tuning properties of two neuronal signals: the MEG signal below 1.6 Hz and within the 4 to 6 Hz range. We found that both components are modulated by wrist movement allowing for closed-loop inference of movement targets. Interestingly, while tuning of 4 to 6 Hz signals remained stable over time leading to stable inference of movement target using a static classifier, the tuning of cortical signals below 1.6 Hz significantly changed resulting in steadily decreasing inference accuracy. Our findings demonstrate that non-invasive neuronal population signals in human sensorimotor cortex can reflect a stable correlate of voluntary movements. Hence, we provide first evidence for a stable control signal in non-invasive human brain-machine interface research. However, as not all neuronal signals initially tuned to movement were stable across days, a careful selection of features for real-life applications seems to be mandatory. PMID:24453113

Witte, Matthias; Galán, Ferran; Waldert, Stephan; Braun, Christoph; Mehring, Carsten

2014-08-01

379

Development of Stable Influenza Vaccine Powder Formulations: Challenges and Possibilities  

PubMed Central

Influenza vaccination represents the cornerstone of influenza prevention. However, today all influenza vaccines are formulated as liquids that are unstable at ambient temperatures and have to be stored and distributed under refrigeration. In order to stabilize influenza vaccines, they can be brought into the dry state using suitable excipients, stabilizers and drying processes. The resulting stable influenza vaccine powder is independent of cold-chain facilities. This can be attractive for the integration of the vaccine logistics with general drug distribution in Western as well as developing countries. In addition, a stockpile of stable vaccine formulations of potential vaccines against pandemic viruses can provide an immediate availability and simple distribution of vaccine in a pandemic outbreak. Finally, in the development of new needle-free dosage forms, dry and stable influenza vaccine powder formulations can facilitate new or improved targeting strategies for the vaccine compound. This review represents the current status of dry stable inactivated influenza vaccine development. Attention is given to the different influenza vaccine types (i.e. whole inactivated virus, split, subunit or virosomal vaccine), the rationale and need for stabilized influenza vaccines, drying methods by which influenza vaccines can be stabilized (i.e. lyophilization, spray drying, spray-freeze drying, vacuum drying or supercritical fluid drying), the current status of dry influenza vaccine development and the challenges for ultimate market introduction of a stable and effective dry-powder influenza vaccine. PMID:18338241

Amorij, J-P.; Huckriede, A.; Wilschut, J.; Frijlink, H. W.

2008-01-01

380

Development of stable influenza vaccine powder formulations: challenges and possibilities.  

PubMed

Influenza vaccination represents the cornerstone of influenza prevention. However, today all influenza vaccines are formulated as liquids that are unstable at ambient temperatures and have to be stored and distributed under refrigeration. In order to stabilize influenza vaccines, they can be brought into the dry state using suitable excipients, stabilizers and drying processes. The resulting stable influenza vaccine powder is independent of cold-chain facilities. This can be attractive for the integration of the vaccine logistics with general drug distribution in Western as well as developing countries. In addition, a stockpile of stable vaccine formulations of potential vaccines against pandemic viruses can provide an immediate availability and simple distribution of vaccine in a pandemic outbreak. Finally, in the development of new needle-free dosage forms, dry and stable influenza vaccine powder formulations can facilitate new or improved targeting strategies for the vaccine compound. This review represents the current status of dry stable inactivated influenza vaccine development. Attention is given to the different influenza vaccine types (i.e. whole inactivated virus, split, subunit or virosomal vaccine), the rationale and need for stabilized influenza vaccines, drying methods by which influenza vaccines can be stabilized (i.e. lyophilization, spray drying, spray-freeze drying, vacuum drying or supercritical fluid drying), the current status of dry influenza vaccine development and the challenges for ultimate market introduction of a stable and effective dry-powder influenza vaccine. PMID:18338241

Amorij, J-P; Huckriede, A; Wilschut, J; Frijlink, H W; Hinrichs, W L J

2008-06-01

381

Results of the Stable Microgravity Vibration Isolation Flight Experiment  

NASA Technical Reports Server (NTRS)

This paper presents an overview of the STABLE microgravity isolation system developed and successfully flight tested in October 1995. A description of the hardware design and operational principles is given. A sample of the measured flight data is presented, including an evaluation of attenuation performance provided by the actively controlled electromagnetic isolation system. Preliminary analyses of flight data show that the acceleration environment aboard STABLE's isolated platform was attenuated by a factor of more than 25 between 0.1 and 100 Hz. STABLE was developed under a cooperative agreement between National Aeronautics and Space Administration, Marshall Space Flight Center, and McDonnell Douglas Aerospace. The flight hardware was designed, fabricated, integrated, tested, and delivered to the Cape during a five month period.

Edberg, Donald; Boucher, Robert; Schenck, David; Nurre, Gerald; Whorton, Mark; Kim, Young; Alhorn, Dean

1996-01-01

382

Stable marriage and roommate problems with individual-based stability  

E-print Network

Research regarding the stable marriage and roommate problem has a long and distinguished history in mathematics, computer science and economics. Stability in this context is predominantly core stability or one of its variants in which each deviation is by a group of players. There has been little focus in matching theory on stability concepts such as Nash stability and individual stability in which the deviation is by a single player. Such stability concepts are suitable especially when trust for the other party is limited, complex coordination is not feasible, or when only unmatched agents can be approached. Furthermore, weaker stability notions such as individual stability may in principle circumvent the negative existence and computational complexity results in matching theory. We characterize the computational complexity of checking the existence and computing individual-based stable matchings for the marriage and roommate settings. One of our key computational results for the stable marriage setting also...

Aziz, Haris

2012-01-01

383

Development and characterization of stable nanovesicular carrier for drug delivery.  

PubMed

Lipid vesicles are an important drug carrier which can serve for controlled delivery of drugs; however, these vesicles are quite unstable at ambient temperature and require stringent storage condition. Present work was done to develop a stable vesicular system for drug delivery. Vesicles of ceramide-2, cholesterol, cholesterol sulfate, and palmitic acid were prepared and compared with phosphatidylcholine vesicles for physicochemical parameters and accelerated stability. Diclofenac sodium was used as a model drug. Based on physicochemical parameter and in vitro release PCV-3 and CV-3 were selected for further studies in three different accelerated stability conditions. PCV-3 showed moderate changes at 4°C but was severely affected at 25°C and 40°C. CV-3 showed stable characteristics at 4°C and 25°C whereas at 40°C, CV-3 showed signs of slight modification owing to moisture absorption. Based on the study, CV-3 containing highest content of palmitic acid was found to be most stable. PMID:23865793

Gaur, Praveen Kumar; Purohit, Suresh; Kumar, Yatendra; Mishra, Shikha; Bhandari, Anil

2014-10-01

384

Dynamical SUSY Breaking in Meta-Stable Vacua  

E-print Network

Dynamical supersymmetry breaking in a long-lived meta-stable vacuum is a phenomenologically viable possibility. This relatively unexplored avenue leads to many new models of dynamical supersymmetry breaking. Here, we present a surprisingly simple class of models with meta-stable dynamical supersymmetry breaking: N=1 supersymmetric QCD, with massive flavors. Though these theories are strongly coupled, we definitively demonstrate the existence of meta-stable vacua by using the free-magnetic dual. Model building challenges, such as large flavor symmetries and the absence of an R-symmetry, are easily accommodated in these theories. Their simplicity also suggests that broken supersymmetry is generic in supersymmetric field theory and in the landscape of string vacua.

Kenneth Intriligator; Nathan Seiberg; David Shih

2006-04-01

385

A Note on (Meta)stable Brane Configurations in MQCD  

E-print Network

We examine the M-theory version of SQCD which is known as MQCD. In the IIA limit, this theory appears to have a supersymmetry-breaking brane configuration which corresponds to the meta-stable state of N=1 SU(Nc) SQCD. However, the behavior at infinity of this non-supersymmetric brane construction differs from that of the supersymmetric ground state of MQCD. We interpret this to mean that it is not a meta-stable state in MQCD, but rather a state in another theory. This provides a concrete example of the fact that, while MQCD accurately describes the supersymmetric features of SCQD, it fails to reproduce its non-supersymmetric features (such as meta-stable states) not only quantitatively but also qualitatively.

I. Bena; E. Gorbatov; S. Hellerman; N. Seiberg; D. Shih

2006-09-07

386

Anomaly detection in hyperspectral imagery using stable distribution  

NASA Astrophysics Data System (ADS)

In hyperspectral imaging applications, the background generally exhibits a clearly non-Gaussian impulsive behavior, where valuable information stays in the tail. In this paper, we propose a new technique, where the background is modeled using the stable distribution for robust detection of outliers. The outliers of the distribution can be considered as potential anomalies or regions of interests (ROIs). We effectively utilize the stable model for detecting targets in impulsive hyperspectral data. To decrease the false alarm rate, it is necessary to compare the ROI with the known reference using a suitable technique, such as the Euclidian distance. Modeling data with stable distribution compensates a drawback of the Gaussian model, which is not well suited for describing signals with impulsive behavior. In addition, thresholding is considered to avoid misclassification of targets. Test results using real life hyperspectral image datasets are presented to verify the effectiveness of the proposed technique.

Mercan, S.; Alam, Mohammad S.

2011-06-01

387

Stable and generalized-t distributions and applications  

NASA Astrophysics Data System (ADS)

In this paper a generalized-t distribution is introduced and used as an alternative to the symmetric stable distribution. To do so, the ?2-divergence is presented and minimized to approximate the symmetric stable distribution, as accurately as possible, by the generalized-t distribution. Kth moments for the generalized-t distribution function are given. The stable distribution is defined in terms of generalized hypergeometric functions. Five applications with natural data (sunspots activity), and financial data (stock exchange in Brazil, South Africa and Venezuela, and daily variation of Petrobras stock market) are analyzed. A time series analysis is used to eliminate data correlation in each data set, and then the distributions are used to fit the residuals of these models.

Rathie, P. N.; Coutinho, M.; Sousa, T. R.; Rodrigues, G. S.; Carrijo, T. B.

2012-12-01

388

Source Partitioning Using Stable Isotopes: Coping with Too Much Variation  

PubMed Central

Background Stable isotope analysis is increasingly being utilised across broad areas of ecology and biology. Key to much of this work is the use of mixing models to estimate the proportion of sources contributing to a mixture such as in diet estimation. Methodology By accurately reflecting natural variation and uncertainty to generate robust probability estimates of source proportions, the application of Bayesian methods to stable isotope mixing models promises to enable researchers to address an array of new questions, and approach current questions with greater insight and honesty. Conclusions We outline a framework that builds on recently published Bayesian isotopic mixing models and present a new open source R package, SIAR. The formulation in R will allow for continued and rapid development of this core model into an all-encompassing single analysis suite for stable isotope research. PMID:20300637

Parnell, Andrew C.; Inger, Richard; Bearhop, Stuart; Jackson, Andrew L.

2010-01-01

389

STABLE ISOTOPE DYNAMICS IN SUMMER FLOUNDER TISSUES, WITH APPLICATION TO DIETARY ASSESSMENTS IN CHESAPEAKE BAY  

E-print Network

STABLE ISOTOPE DYNAMICS IN SUMMER FLOUNDER TISSUES, WITH APPLICATION TO DIETARY ASSESSMENTS Growth rates........................................................................18 Isotopic turnover 2: STABLE ISOTOPE ANALYSIS OF SUMMER FLOUNDER DIETS IN CHESAPEAKE BAY

Newman, Michael C.

390

Stable subspaces of positive maps of matrix algebras  

E-print Network

We study stable subspaces of positive extremal maps of finite dimensional matrix algebras that preserve trace and matrix identity (so-called bistochastic maps). We have established the existence of the isometric-sweeping decomposition for such maps. As the main result of the paper, we have shown that all extremal bistochastic maps acting on the algebra of matrices of size 3x3 fall into one of the three possible categories, depending on the form of the stable subspace of the isometric-sweeping decomposition. Our example of an extremal atomic positive map seems to be the first one that handles the case of that subspace being non-trivial.

Marek Miller; Robert Olkiewicz

2014-12-23

391

Stable polarization-encoded quantum key distribution in fiber  

E-print Network

Polarizations of single-photon pulses have been controlled with long-term stability of more than 10 hours by using an active feedback technique for auto-compensation of unpredictable polarization scrambling in long-distance fiber. Experimental tests of long-term operations in 50, 75 and 100 km fibers demonstrated that such a single-photon polarization control supported stable polarization encoding in long-distance fibers to facilitate stable one-way fiber system for polarization-encoded quantum key distribution, providing quantum bit error rates below the absolute security threshold.

Guang Wu; Jie Chen; Yao Li; Heping Zeng

2006-06-13

392

Stable three-dimensional metallic carbon with interlocking hexagons  

PubMed Central

Design and synthesis of 3D metallic carbon that is stable under ambient conditions has been a long-standing dream. We predict the existence of such phases, T6- and T14-carbon, consisting of interlocking hexagons. Their dynamic, mechanical, and thermal stabilities are confirmed by carrying out a variety of state-of-the-art theoretical calculations. Unlike the previously studied K4 and the simple cubic high pressure metallic phases, the structures predicted in this work are stable under ambient conditions. Equally important, they may be synthesized chemically by using benzene or polyacenes molecules. PMID:24191020

Zhang, Shunhong; Wang, Qian; Chen, Xiaoshuang; Jena, Puru

2013-01-01

393

Target-like Pigmentation After Minipunch Grafting in Stable Vitiligo  

PubMed Central

Surgical treatment for vitiligo has been ever evolving. Each surgical modality has its own benefits and limitations. Miniature punch grafting is the most extensively performed surgery, which gives good results in stable vitiligo. Herein we report an unusual type of repigmentation observed after minipunch grafting in a patient of stable vitiligo, which resembled target-like lesions with a “perigraft halo” surrounding individual grafts. Such pigment spread occurred despite the use of 0.5 mm larger graft from the donor site. PMID:25071253

Bisen, Nelee; Bhat, Ramesh M; Lahiri, Koushik; Kambil, Srinath M

2014-01-01

394

Synthesis and investigation of stable copper nanoparticle colloids  

NASA Astrophysics Data System (ADS)

The synthesis of stable nanoparticle colloids by laser ablation of the copper target in water and fragmentation of Cu + CuO nanopowder with pulsed fiber laser irradiation with a wavelength of 1064 nm and pulse duration of 100 ns has been investigated experimentally. The influence of the technological parameters on the nanoparticle size and stability of the colloid has been studied. It has been shown that the laser ablation creates the CuO spherical nanoparticles. Subsequent fragmentation makes it possible to reduce the nanoparticle size in a colloid and to produce a stable colloidal solution from an aqueous suspension of Cu + CuO nanopowder.

Tyurnina, A. E.; Shur, V. Ya.; Kozin, R. V.; Kuznetsov, D. K.; Pryakhina, V. I.; Burban, G. V.

2014-07-01

395

Stable Isotopic Tracing—A Way Forward for Nanotechnology  

PubMed Central

Numerous publications and reports have expressed health and safety concerns about the production and use of nanoparticles, especially in areas of exposure monitoring, personal use, and environmental fate and transport. We suggest that stable isotopic tracers, which have been used widely in the earth sciences and in metabolic and other health-related studies for several decades, could be used to address many of these issues. One such example we are pursuing is the use of stable isotopes to monitor dermal absorption of zinc and titanium oxides in sunscreen preparations and other personal care products. Other potential applications of this tracing approach are discussed. PMID:17035130

Gulson, Brian; Wong, Herbert

2006-01-01

396

Thermally stable surfactants and compositions and methods of use thereof  

DOEpatents

There are provided novel thermally stable surfactants for use with fillers in the preparation of polymer composites and nanocomposites. Typically, surfactants of the invention are urethanes, ureas or esters of thiocarbamic acid having a hydrocarbyl group of from 10 to 50 carbons and optionally including an ionizable or charged group (e.g., carboxyl group or quaternary amine). Thus, there are provided surfactants having Formula I: ##STR00001## wherein the variables are as defined herein. Further provided are methods of making thermally stable surfactants and compositions, including composites and nanocomposites, using fillers coated with the surfactants.

Chaiko, David J. (Woodridge, IL)

2008-09-02

397

Fiber Optic Cable Thermal Preparation to Ensure Stable Operation  

NASA Technical Reports Server (NTRS)

Fiber optic cables are widely used in modern systems that must provide stable operation during exposure to changing environmental conditions. For example, a fiber optic cable on a satellite may have to reliably function over a temperature range of -50 C up to 125 C. While the system requirements for a particular application will dictate the exact method by which the fibers should be prepared, this work will examine multiple ruggedized fibers prepared in different fashions and subjected to thermal qualification testing. The data show that if properly conditioned the fiber cables can provide stable operation, but if done incorrectly, they will have large fluctuations in transmission.

Thoames Jr, William J.; Chuska, Rick F.; LaRocca, Frank V.; Switzer, Robert C.; Macmurphy, Shawn L.; Ott, Melanie N.

2008-01-01

398

Remarks on search methods for stable, massive, elementary particles  

NASA Astrophysics Data System (ADS)

This paper was presented at the 69th birthday celebration of Professor Eugene Commins, honoring his research achievements. These remarks are about the experimental techniques used in the search for new stable, massive particles, particles at least as massive as the electron. A variety of experimental methods such as accelerator experiments, cosmic ray studies, searches for halo particles in the galaxy and searches for exotic particles in bulk matter are described. A summary is presented of the measured limits on the existence of new stable, massive particle. .

Perl, Martin L.

2001-11-01

399

Hecke correspondence, stable maps, and the Kirwan desingularization  

Microsoft Academic Search

We prove that the moduli space $\\\\overline{\\\\mathbf{M}}_{0,0}(\\\\mathcal{N},2)$ of stable maps of degree $2$ to the moduli space $\\\\mathcal{N}$ of rank $2$ stable bundles of fixed odd determinant $\\\\mathcal{O}_X(-x)$ over a smooth projective curve $X$ of genus $g\\\\ge 3$ has two irreducible components that intersect transversely. One of them is Kirwan's partial desingularization $\\\\widetilde{\\\\mathcal{M}}_X$ of the moduli space $\\\\mathcal{M}_X$ of rank

Young-Hoon Kiem

2007-01-01

400

Maximum mass of stable magnetized highly super-Chandrasekhar white dwarfs: stable solutions with varying magnetic fields  

E-print Network

We address the issue of stability of recently proposed significantly super-Chandrasekhar white dwarfs. We present stable solutions of magnetostatic equilibrium models for super-Chandrasekhar white dwarfs pertaining to various magnetic field profiles. This has been obtained by self-consistently including the effects of the magnetic pressure gradient and total magnetic density in a general relativistic framework. We estimate that the maximum stable mass of magnetized white dwarfs could be more than 3 solar mass. This is very useful to explain peculiar, overluminous type Ia supernovae which do not conform to the traditional Chandrasekhar mass-limit.

Upasana Das; Banibrata Mukhopadhyay

2014-05-20

401

Reducing the spin-spin interaction of stable carbon radicals.  

PubMed

We report the discovery that a flow of CO2, N2 or He can sufficiently reduce the spin-spin interactions of specific stable carbon centered radicals by displacing the molecular oxygen in the atmosphere enabling their detection via electron paramagnetic resonance (EPR). This finding unlike other reported effects on carbon radicals occurs under STP conditions and is reversible. PMID:23518921

Green, Uri; Aizenshtat, Zeev; Ruthstein, Sharon; Cohen, Haim

2013-05-01

402

Stable Isotope Tracers in Large Scale Hydrological Models  

Microsoft Academic Search

Stable isotopes of oxygen and hydrogen (deuterium and oxygen-18) have been shown to be effective tracers for characterizing hydrological processes in small river basins. Their application in large river basins has lagged behind due to the lack of sufficient isotope data. Recent availability of isotope data from most US rivers and subsequent efforts by the International Atomic Energy Agency (IAEA)

B. M. Fekete; P. Aggarwal

2004-01-01

403

Scaling in Stock Market Data: Stable Laws and Beyond  

Microsoft Academic Search

The concepts of scale invariance, self-similarity and scaling have been fruitfully applied to the study of price fluctuations in financial markets. After a brief review of the properties of stable Levy distributions and their applications to market data we indicate the shortcomings of such models and describe the truncated Levy flight as an alternative model for price movements. Furthermore, studying

Rama Cont; Marc Potters; Jean-Philippe Bouchaud

1997-01-01

404

PERTURBATIONS OF HELIOSYNCHRONOUS ORBITS IN STABLE KALUZA--KLEIN THEORY  

E-print Network

PERTURBATIONS OF HELIOSYNCHRONOUS ORBITS IN STABLE KALUZA--KLEIN THEORY M. Kuassivi 170374 Cotonou of the latter theory by computing the expected on-- orbit GE perturbation for heliosynchronous satellites perturbation. In section 4, I discuss the consistency of the theory with respect to the orbital motion

Paris-Sud XI, Université de

405

Carbon Stable Isotopes as Indicators of Coastal Eutrophication  

EPA Science Inventory

Coastal ecologists and managers have frequently used nitrogen stable isotopes (?15N) to trace and monitor anthropogenic nitrogen (N) in coastal ecosystems. However, the interpretation of ?15N data can often be challenging, if not confounding, as the isotope values fr...

406

MixSIAR: advanced stable isotope mixing models in R  

EPA Science Inventory

Background/Question/Methods The development of stable isotope mixing models has coincided with modeling products (e.g. IsoSource, MixSIR, SIAR), where methodological advances are published in parity with software packages. However, while mixing model theory has recently been ext...

407

Stable Isotopic Constraints of the Turpan Basin in Northwestern China  

Microsoft Academic Search

Stable isotopic analysis of sedimentary rocks can be used to reconstruct past geologic changes in the elevation and climate of topographic features such as mountain ranges and plateaus. The Tibetan Plateau is an ideal field laboratory for conducting this type of study because of the Plateau's extreme topographic relief and relatively recent geologic growth. Here we present oxygen and carbon

A. J. Schaen

2010-01-01

408

Standards for stable isotope measurements in natural compounds  

Microsoft Academic Search

RESEARCH based on stable isotope variations in natural compounds is expanding in scientific fields such as geochemistry, hydrology, environmental studies and biochemistry. However, intercomparison of results obtained in different laboratories is often not fully reliable and therefore to improve the intercalibration of deuterium and 18O measurements in natural waters, two water standards have been distributed by the International Atomic Energy

R. Gonfiantini

1978-01-01

409

Resources on Isotopes: Fundamentals of Stable Isotope Geochemistry  

NSDL National Science Digital Library

This is a brief review of some of the fundamentals of stable isotope geochemistry, including definitions, terminology, basic principles, standards, and guidelines on reporting data. Users can follow the link on the top right for the periodic table and read about the isotopic systems of several dozen elements.

410

STABLE ISOTOPES AS INDICATORS OF SOIL WATER DYNAMICS IN WATERSHEDS  

EPA Science Inventory

Stream water quality and quantity depend on discharge rates of water and nutrients from soils. However, soil-water storage is very dynamic and strongly influenced by plants. We analyzed stable isotopes of oxygen and hydrogen to quantify spatial and temporal changes in evaporati...

411

Stable Isotopic Analysis of Porcine, Bovine, and Ovine Heparins.  

PubMed

The assessment of provenance of heparin is becoming a major concern for the pharmaceutical industry and its regulatory bodies. Batch-specific [carbon (?(13) C), nitrogen (?(15) N), oxygen (?(18) O), sulfur (?(34) S), and hydrogen (?D)] stable isotopic compositions of five different animal-derived heparins were performed. Measurements readily allowed their differentiation into groups and/or subgroups based on their isotopic provenance. Principle component analysis showed that a bivariate plot of ?(13) C and ?(18) O is the best single, bivariate plot that results in the maximum discrimination ability when only two stable isotopes are used to describe the variation in the data set. Stable isotopic analyses revealed that (1) stable isotope measurements on these highly sulfated polysaccharide (molecular weight ?15 kDa) natural products ("biologics") were feasible; (2) in bivariate plots, the ?(13) C versus ?(18) O plot reveals a well-defined relationship for source differentiation of hogs raised in the United States from hogs raised in Europe and China; (3) the ?D versus ?(18) O plot revealed the most well-defined relationship for source differentiation based on the hydrologic environmental isotopes of water (D/H and (18) O/(16) O); and (4) the ?(15) N versus ?(18) O and ?(34) S versus ?(18) O relationships are both very similar, possibly reflecting the food sources used by the different heparin producers. © 2014 Wiley Periodicals, Inc. and the American Pharmacists Association J Pharm Sci. PMID:25186630

Jasper, John P; Zhang, Fuming; Poe, Russell B; Linhardt, Robert J

2014-09-01

412

Stable isotopes as one of nature's ecological recorders  

E-print Network

and spatial analysis with those in isotope analyses and modeling sophistication opens the door to an exciting], to reconstructing climate from tree rings [3], stable isotope analyses are an important part of the ecologist]; and hydrogen (d2 H) and oxygen isotope ratios (d18 O) record water-related dynamics in plants and animals [9

Ehleringer, Jim

413

Intraseasonal variability in South America recorded in stable water isotopes  

Microsoft Academic Search

The recent number isotopic records extracted from Andean ice cores (South America) has illustrated the key role such archives can play in past climate reconstructions. Nevertheless, interpreting isotopic archives as quantified climate proxies requires an understanding of which climate parameters control the stable isotopic composition of water. Mesoscale modeling sheds new light on the meteorological mechanisms dominant during austral summer.

Christophe Sturm; Françoise Vimeux; Gerhard Krinner

2007-01-01

414

A stable tracking control method for an autonomous mobile robot  

Microsoft Academic Search

A stable tracking control rule is proposed for nonholonomic vehicles. The stability of the rule is proved through the use of a Liapunov function. Inputs to the vehicle are a reference posture (x r, yr, ?r)t and reference velocities (?r, ?r) t. The major objective of this study is to propose a control rule to find reasonable target linear and

Yutaka Kanayama; Yoshihiko Kimura; Fumio Miyazaki; Tetsuo Noguchi

1990-01-01

415

Stable colloidal solutions of strontium hexaferrite hard magnetic nanoparticles.  

PubMed

Herein we demonstrate an approach to prepare a colloidal solution of strontium hexaferrite via a glass-ceramic route. The as obtained colloids are stable and resistive to aggregation or sedimentation. They reveal outstanding magnetic and magneto-optical properties because of their platelet-like anisotropic shape and high permanent magnetic moment. PMID:25307164

Trusov, Lev A; Vasiliev, Alexander V; Lukatskaya, Maria R; Zaytsev, Dmitry D; Jansen, Martin; Kazin, Pavel E

2014-10-28

416

Two Stable Equilibria of a Coupled Ocean-Atmosphere Model  

Microsoft Academic Search

Two stable equilibria have been obtained from a global model of the coupled ocean-atmosphere system developed at the Geophysical Fluid Dynamics Laboratory of NOAA. The model used for this study consists of general circulation models of the atmosphere and the world oceans and a simple model of land surface. Starting from two different initial conditions, `asynchronous' time integrations of the

S. Manabe; R. J. Stouffer

1988-01-01

417

Design of Hard Water Stable Emulsifier Systems for Petroleum-  

E-print Network

Design of Hard Water Stable Emulsifier Systems for Petroleum- and Bio-based Semi for petroleum and bio-based MWFs that improve fluid lifetime by providing emulsion stability under hard water. The newly developed petroleum and bio-based formulations with improved hard water stability are competitive

Clarens, Andres

418

Possible Potentials Responsible for Stable Circular Relativistic Orbits  

ERIC Educational Resources Information Center

Bertrand's theorem in classical mechanics of the central force fields attracts us because of its predictive power. It categorically proves that there can only be two types of forces which can produce stable, circular orbits. In this paper an attempt has been made to generalize Bertrand's theorem to the central force problem of relativistic…

Kumar, Prashant; Bhattacharya, Kaushik

2011-01-01

419

Stable Isotope Tracers of Process in Great Lakes Food Webs  

EPA Science Inventory

Stable isotope analyses of biota are now commonly used to discern trophic pathways between consumers and their foods. However, those same isotope data also hold information about processes that influence the physicochemical setting of food webs as well as biological processes ope...

420

LATERAL TURBULENCE INTENSITY AND PLUME MEANDERING DURING STABLE CONDITIONS  

EPA Science Inventory

There is much evidence in the literature for the presence of mesoscale lateral meanders in the stable nighttime boundary layer. These meanders result in relatively high lateral turbulence intensities and diffusion rates when averaged over an hour. Anemometer data from 17 overnigh...

421

Stable isotope composition of human fingernails from Slovakia.  

PubMed

Stable isotope composition of human fingernails has proven to be useful for documenting human dietary information and geographical patterns in archeological, forensic, anthropological and biological studies. Therefore, it is of interest to detect all factors influencing the stable isotopic composition in the certain regions in the world. Carbon and nitrogen isotope data of human fingernail keratin from 52 individuals from Slovakia were reported in this study. The online combustion and continuous flow isotope-ratio mass spectrometer Delta V Advantage was used for ?(13)C and ?(15)N analysis of fingernail keratin samples from 24 vegetarian and 28 omnivorous individuals. A group of people with frequent meat consumption showed enrichment in (13)C and (15)N isotopes in fingernails. A similar trend was observed with increasing seafood in an individual's diet. Moreover a significant difference was revealed between smokers and nonsmokers for both ?(13)C and ?(15)N values. These data were compared to previously published ?(13)C and ?(15)N fingernail values from across the globe. This study brings new information on the stable isotope signature of individuals from Slovakia and characterizes the Central European region for the first time. The stable isotope composition of fingernails is influenced by the frequency of meat and seafood consumption as well as smoking. PMID:25086300

Grolmusová, Zuzana; Rap?anová, Anna; Michalko, Juraj; ?ech, Peter; Veis, Pavel

2014-10-15

422

Historical Variations in the Stable Isotope Composition of Mercury in  

E-print Network

Historical Variations in the Stable Isotope Composition of Mercury in Arctic Lake Sediments T O G W, and biological data, could yield important new information about the biogeochemical cycle of Hg. Introduction could provide valuable information on the sources and biogeochemical cycling of the Hg, but until

Vincent, Warwick F.

423

Stable Gene Selection from Microarray Data via Sample Weighting  

E-print Network

Stable Gene Selection from Microarray Data via Sample Weighting Lei Yu, Yue Han, and Michael E. Berens Abstract--Feature selection from gene expression microarray data is a widely used technique for selecting candidate genes in various cancer studies. Besides predictive ability of the selected genes

Yu, Lei

424

Constant density and stable territoriality in some tropical insectivorous birds  

Microsoft Academic Search

Four species of understory antbirds (Formicariidae: Myrmotherula fulviventris, M. axillaris, Microrhopias quixensis, and Thamnophilus punctatus) had stable populations over eight rainy seasons on Barro Colorado Island, Panama. The co-defended territories of M. fulviventris and Microrhopias quixensis, were essentially identical from year to year on our intensive study site, despite a moderate turnover of territory owners. The location of the territories

Russell Greenberg; Judith Gradwohl

1986-01-01

425

From birds to butterflies: animal movement patterns and stable isotopes  

Microsoft Academic Search

Establishing patterns of movement of wild animals is crucial for our understanding of their ecology, life history and behavior, and is a prerequisite for their effective conservation. Advances in the use of stable isotope markers make it possible to track a diversity of animal species in a variety of habitats. This approach is revolutionizing the way in which we make

Dustin R. Rubenstein; Keith A. Hobson

2004-01-01

426

Eye development: stable cell fate decisions in insect colour vision.  

PubMed

The retina provides an example of a fundamental property of developing cells: cell fate decisions are stable. A recent paper reports a double negative feedback loop that leads to bistable fate decisions in the colour-detecting photoreceptors of Drosophila. PMID:16303550

Freeman, Matthew

2005-11-22

427

Stable periodic billiard paths in obtuse isosceles triangles  

E-print Network

Stable periodic billiard paths in obtuse isosceles triangles W. Patrick Hooper March 27, 2006 Can you place a small billiard ball on a frictionless triangular pool table and hit it so that it comes dynamics s of a periodic billiard path is the bi-infinite sequence of edges the billiard path hits, which

Hooper, Patrick

428

Stable periodic billiard paths in obtuse isosceles triangles  

E-print Network

Stable periodic billiard paths in obtuse isosceles triangles W. Patrick Hooper March 27, 2006 Can you place a small billiard ball on a frictionless triangular pool table and hit it so that it comes dynamics s # of a periodic billiard path # is the bi­infinite sequence of edges the billiard path hits

Hooper, Patrick

429

BaC: a thermodynamically stable layered superconductor.  

PubMed

To predict all stable compounds in the Ba-C system, we perform a comprehensive study using first-principles variable-composition evolutionary algorithm USPEX. We find that at 0 K the well-known compound BaC2 is metastable in the whole pressure range 0-40 GPa, while intercalated graphite phase BaC6 is stable at 0-19 GPa. A hitherto unknown layered orthorhombic Pbam phase of BaC has structure consisting of alternating layers of Ba atoms and layers of stoichiometry Ba2C3 containing linear C3 groups and is predicted to be stable in the pressure range 3-32 GPa. From our electron-phonon coupling calculations, the newly found BaC compound is a phonon-mediated superconductor and has a critical superconductivity temperature Tc of 4.32 K at 5 GPa. This compound is dynamically stable at 0 GPa and therefore may be quenchable under normal conditions. PMID:25163859

Wang, Dian-Hui; Zhou, Huai-Ying; Hu, Chao-Hao; Oganov, Artem R; Zhong, Yan; Rao, Guang-Hui

2014-10-14

430

Apparatus and method for monitoring of gas having stable isotopes  

DOEpatents

Gas having stable isotopes is monitored continuously by using a system that sends a modulated laser beam to the gas and collects and transmits the light not absorbed by the gas to a detector. Gas from geological storage, or from the atmosphere can be monitored continuously without collecting samples and transporting them to a lab.

Clegg, Samuel M; Fessenden-Rahn, Julianna E

2013-03-05

431

Fire Feedbacks with Vegetation and Alternative Stable States  

E-print Network

Fire Feedbacks with Vegetation and Alternative Stable States Brian Beckage* Chris Ellingwood.Beckage@uvm.edu Positive feedbacks between vegetation and fire disturbance may lead to nonlinear ecosystem responses to variation in fire regime. We used a cellular automaton model of fire|vegetation dynamics based on pine

Beckage, Brian

432

Do stable atmospheric layers exist? S. Lovejoy,1,2  

E-print Network

Do stable atmospheric layers exist? S. Lovejoy,1,2 A. F. Tuck,3 S. J. Hovde,3 and D. Schertzer4 layers is untenable and must be replaced by modern scaling notions. Citation: Lovejoy, S., A. F. Tuck, S with scale) is the best available - we develop this elsewhere [Schertzer and Lovejoy, 1985; Tuck et al., 2004

Long, Bernard

433

Highly Stable Silver Nanoplates for Surface Plasmon Resonance Biosensing  

SciTech Connect

An SPR biosensor was developed by employing highly stable Au-protected Ag nanoplates (NP) as enhancers (see picture). Superior performance was achieved by depositing a thin and uniform coating of Au on the Ag surface while minimizing disruptive galvanic replacement and retaining the strong surface plasmon resonance (SPR) of the silver nanoplates.

Gao, Chuanbo [University of California, Riverside; Lu, Zhenda [University of California, Riverside; Chi, Miaofang [ORNL; Liu, ying [University of California, Riverside; Cheng, Quan [University of California, Riverside; Yin, Yadong [University of California, Riverside

2012-01-01

434

Development of stable isotope mixing models in ecology - Perth  

EPA Science Inventory

More than 40 years ago, stable isotope analysis methods used in geochemistry began to be applied to ecological studies. One common application is using mathematical mixing models to sort out the proportional contributions of various sources to a mixture. Examples include contri...

435

Stable fan filter design using two-variable reactance functions  

Microsoft Academic Search

Two-variable reactance transformation (as proposed by King et al., 1982) for the design of stable two-dimensional recursive fan filters with narrow stopbands is compared with the design method proposed by Bruton et al. (1981) using numerical optimization of a resistively terminated (2 + n sub 1 + n sub 2)-port network. The method of King et al. is found to

L. T. Bruton; N. R. Bartley

1982-01-01

436

AIAA 2002--0227 On Constructing Stable Perfectly  

E-print Network

AIAA 2002--0227 On Constructing Stable Perfectly Matched Layers as an Absorbing Boundary Condition, Virginia 23529 40th AIAA Aerospace Sciences Meeting and Exhibit 14­17 January 2002/Reno, NV For permission AIAA Copyright c 2002 by F. Q. Hu. Published by the American Institute of Aeronautics

Hu, Fang Q.

437

Development of stable isotope mixing models in ecology - Dublin  

EPA Science Inventory

More than 40 years ago, stable isotope analysis methods used in geochemistry began to be applied to ecological studies. One common application is using mathematical mixing models to sort out the proportional contributions of various sources to a mixture. Examples include contri...

438

Development of stable isotope mixing models in ecology - Fremantle  

EPA Science Inventory

More than 40 years ago, stable isotope analysis methods used in geochemistry began to be applied to ecological studies. One common application is using mathematical mixing models to sort out the proportional contributions of various sources to a mixture. Examples include contri...

439

Historical development of stable isotope mixing models in ecology  

EPA Science Inventory

More than 40 years ago, stable isotope analysis methods used in geochemistry began to be applied to ecological studies. One common application is using mathematical mixing models to sort out the proportional contributions of various sources to a mixture. Examples include contri...

440

Development of stable isotope mixing models in ecology - Sydney  

EPA Science Inventory

More than 40 years ago, stable isotope analysis methods used in geochemistry began to be applied to ecological studies. One common application is using mathematical mixing models to sort out the proportional contributions of various sources to a mixture. Examples include contri...

441

Highly Sensitive, Mechanically Stable Nanopore Sensors for DNA Analysis  

E-print Network

Highly Sensitive, Mechanically Stable Nanopore Sensors for DNA Analysis By Bala Murali Venkatesan the biophysics governing single-molecule trans- port through solid-state nanopores is of fundamental importance in working toward the goal of DNA detection and genome sequencing using nanopore-based sensors. Even

Bashir, Rashid

442

Seismic Hazard Assessment in Stable Continental Regions of Northen Eurasia  

Microsoft Academic Search

Assessment of the seismic potential and related risk level of stable continental regions (SCR) is a highly complex problem, as the applicability of techniques developed for seismically active areas to the areas that have no or limited seismic records is still under discussion. The seismotectonic data of the SCR are very poor because of low seismic activity and an insufficient

V. Levshenko; S. Yunga

2009-01-01

443

Storage-stable foamable polyurethane is activated by heat  

NASA Technical Reports Server (NTRS)

Polyurethane foamable mixture remains inert in storage unit activated to produce a rapid foaming reaction. The storage-stable foamable composition is spread as a paste on the surface of an expandable structure and, when heated, yields a rigid open-cell polyurethane foam that is self-bondable to the substrate.

1966-01-01

444

SOURCE PARTITIONING USING STABLE ISOTOPES: COPING WITH TOO MANY SOURCES  

EPA Science Inventory

Stable isotopes are increasingly being used as tracers in environmental studies. One application is to use isotopic ratios to quantitatively determine the proportional contribution of several sources to a mixture, such as the proportion of various pollution sources in a waste st...

445

A Logical Approach to Stable Domains Yi-Xiang Chen  

E-print Network

-domain, domain theory in logical form. 1 Introduction This paper takes up a number of research strands that have the logical apparatus is that of information systems. Scott showed that domain theory can be based relevant for us are G.-Q. Zhang's papers on information systems for stable domain theory [28, 29, 30

Jung, Achim

446

APPLICATION OF STABLE ISOTOPE TECHNIQUES TO AIR POLLUTION RESEARCH  

EPA Science Inventory

Stable isotope techniques provide a robust, yet under-utilized tool for examining pollutant effects on plant growth and ecosystem function. Here, we survey a range of mixing model, physiological and system level applications for documenting pollutant effects. Mixing model examp...

447

Generating thermal stable variants of protein domains through phage display.  

PubMed

Often in protein design research, one desires to generate thermally stable variants of a protein or domain. One route to identifying mutations that yield domains that remain folded and active at a higher temperature is through the use of directed evolution. A library of protein domain variants can be generated by mutagenic PCR, expressed on the surface of bacteriophage M13, and subjected to heat, such that the unfolded forms of the domain, showing reduced or no binding activity, are lost during subsequent affinity selection, whereas variants that still retain binding to their target are selected and enriched with each subsequent round of affinity selection. This approach takes advantage of the fact that bacteriophage M13 particles are heat stable and resistant to many proteases and protein denaturants. We present the application of this general approach to generating thermally stable variants of a eukaryotic peptide-binding domain. The benefits of producing such variants are that they typically express at high levels in Escherichia coli (30-60 mg/L shake flask) and remain soluble in solution at higher concentrations for longer periods of time than the wild-type form of the domain. The process of library generation and screening generally requires about one month of effort, and yields variants with >10 °C increase in thermal stability, as measured in a simple fluorescence-based thermal shift assay. It is anticipated that thermally stable variants will serve as excellent scaffolds for generating affinity reagents to a variety of targets of interest. PMID:23276752

Pershad, Kritika; Kay, Brian K

2013-03-15

448

Copper stable isotopes to trace copper behavior in wetland systems.  

PubMed

Wetlands are reactive zones of the landscape that can sequester metals released by industrial and agricultural activities. Copper (Cu) stable isotope ratios (?(65)Cu) have recently been used as tracers of transport and transformation processes in polluted environments. Here, we used Cu stable isotopes to trace the behavior of Cu in a stormwater wetland receiving runoff from a vineyard catchment (Alsace, France). The Cu loads and stable isotope ratios were determined in the dissolved phase, suspended particulate matter (SPM), wetland sediments, and vegetation. The wetland retained >68% of the dissolved Cu and >92% of the SPM-bound Cu, which represented 84.4% of the total Cu in the runoff. The dissolved Cu became depleted in (65)Cu when passing through the wetland (?(65)Cuinlet-outlet from 0.03‰ to 0.77‰), which reflects Cu adsorption to aluminum minerals and organic matter. The ?(65)Cu values varied little in the wetland sediments (0.04 ± 0.10‰), which stored >96% of the total Cu mass within the wetland. During high-flow conditions, the Cu flowing out of the wetland became isotopically lighter, indicating the mobilization of reduced Cu(I) species from the sediments and Cu reduction within the sediments. Our results demonstrate that the Cu stable isotope ratios may help trace Cu behavior in redox-dynamic environments such as wetlands. PMID:24787375

Babcsányi, Izabella; Imfeld, Gwenaël; Granet, Mathieu; Chabaux, François

2014-05-20

449

Investigation of effectiveness of microbubble stable cavitation in thrombolysis  

Microsoft Academic Search

Ultrasound and intravenous microbubbles have been used in recanalizing intravascular thrombi which cause ischemic stroke, myocardial infarction, and other vascular thrombo- embolic events. In previous studies, inertial cavitation (IC) produced by high mechanical index (MI) ultrasound has been shown to be effective in dissolving acute thrombi. However, IC is more likely to cause adverse bioeffects than stable cavitation (SC). This

William T. Shi; Shunji Gao; Vignon Francois; Jeff E. Powers; Lucas Drvol; Ki Won Jung; Feng Xie; John Lof; E. Carr Everbach; Thomas R. Porter

2010-01-01

450

Stable isotope ecology in the Omo-Turkana Basin.  

PubMed

Stable isotopes provide an independent assessment of paleoenvironments in the Omo-Turkana Basin. Stable isotopes track the flow of oxygen and carbon through ecosystems and accordingly are not directly related to changes in mammalian faunal composition or sedimentology. Therefore, isotope studies give insight into the paleoenvironmental conditions in which human evolutionary trends have been recorded. The development of stable isotopes as indicators of continental environmental conditions has proceeded in parallel with questions about the conditions of human environment. What was the vegetation? How hot was it? How dry? What were the diets of animals living among early humans? And most persistently, how important were "savannas" to early hominids? In this review, we take the opportunity to provide extensive background on the use of isotopes in anthropological sites. The application of stable isotope ecology to anthropological sites in the Turkana Basin has a long history, but in many ways the Omo-Turkana Basin has been a proving ground for the development of new proxy methods for understanding tropical terrestrial environments in the Neogene and Quaternary. For that reason, we also describe some of the fundamental aspects of isotope ecology that developed outside the field of paleoanthropology. PMID:22170692

Cerling, Thure E; Levin, Naomi E; Passey, Benjamin H

2011-01-01

451

Stable thermal oscillations in columns of partially supercool water  

E-print Network

. Here we cool from below and used either heavy water (D2O) and or sugar as the solute. We show several in diameter and ~10 cm in length. Fig. 2. Sugar (120mg) as sugar water was added to 12 ml DD water just priorStable thermal oscillations in columns of partially supercool water A poster presentation by James

Suzuki, Masatsugu

452

Incorporating concentration dependence in stable isotope mixing models  

Microsoft Academic Search

Stable isotopes are often used as natural labels to quantify the contributions of multiple sources to a mixture. For example, C and N isotopic signatures can be used to determine the fraction of three food sources in a consumer's diet. The standard dual isotope, three source linear mixing model assumes that the proportional contribution of a source to a mixture

Donald L. Phillips; Paul L. Koch

2002-01-01

453

UNCONDITIONALLY STABLE SPLITTING METHODS FOR THE SHALLOW WATER EQUATIONS  

E-print Network

. Introduction The shallow water equations model free surface flow for a fluid under the influence of gravityUNCONDITIONALLY STABLE SPLITTING METHODS FOR THE SHALLOW WATER EQUATIONS RUNAR HOLDAHL, HELGE is combined with operator splitting in order to study the shallow water equations. Furthermore, the method

454

Stable isotopes sales: Mound customer and shipment summaries, FY 1985  

SciTech Connect

A listing is given of Mound's sales of stable isotopes of noble gases, deuterium, carbon, oxygen, nitrogen, chlorine, bromine, and sulfur for fiscal year 1985. Purchasers are listed alphabetically and are divided into domestic and foreign groups. A cross-reference index by location is included for domestic and foreign customers. Cross-reference listings by isotope purchased are included for all customers.

Flayler, K.A. (comp.)

1987-12-15

455

Stable isotope sales: Mound customer and shipment summaries, FY 1986  

SciTech Connect

A listing is given of Mound's sales of stable isotopes of noble gases, carbon, oxygen, nitrogen, chlorine, and sulfur for fiscal year 1986. Purchasers are listed alphabetically and are divided into domestic and foreign groups. Cross-reference indexes by location and by isotope are included for all customers. 3 tabs.

Kramer, L.R. (ed.); Flayler, K.A. (comp.)

1988-05-20

456

Compressive Sensing for Ultrasound RF Echoes Using -Stable Distributions  

E-print Network

is arguably the most widely used cross-sectional medical imaging modality worldwide. In- deed, ultrasound hasCompressive Sensing for Ultrasound RF Echoes Using -Stable Distributions Alin Achim, Benjamin or orthogonal matching pursuit, both visually and in terms of PSNR. I. INTRODUCTION Ultrasound imaging

Tsakalides, Panagiotis

457

Supporting Information Abundant and Stable Char Residues in Soils  

E-print Network

S 1 Supporting Information for Abundant and Stable Char Residues in Soils: Implications for Soil, Ames IA 50011, USA. 3 Department of Crop and Soil Sciences, Cornell University, Ithaca, New York 14853: 7 (including this cover page) Number of figures: 3 Number of tables: 1 #12;S 2 Proof of COO bonding

Lehmann, Johannes

458

Stable and accurate wave-propagation in discontinuous media  

Microsoft Academic Search

A time stable discretization is derived for the second-order wave equation with discontinuous coefficients. The discontinuity corresponds to inhomogeneity in the underlying medium and is treated by splitting the domain. Each (homogeneous) sub domain is discretized using narrow-diagonal summation by parts operators and, then, patched to its neighbors by using a penalty method, leading to fully explicit time integration. This

Ken Mattsson; Frank Ham; Gianluca Iaccarino

2008-01-01

459

Development of a Stable Laser Lock System Pavel Zhuravlev  

E-print Network

that will stabilize the frequency of light being output by a laser. This is accomplished using a process called dither was shown to stably lock the laser light's frequency for over an hour and be able to achieve the lock within on the frequency of the input laser light. The purpose of the experiment is to create a stable second harmonic

Novikova, Irina

460

Geometric properties of forking in stable theories David Evans  

E-print Network

Geometric properties of forking in stable theories David Evans School of Mathematics, UEA, Norwich. David Evans (UEA) 1 / 16 #12;Stability and independence NOTATION: L countable language; T complete first is independent from B over A. REMARK: This is really non-dividing... . David Evans (UEA) 2 / 16 #12;Stability

Evans, David M

461

Stable closed equilibria for anisotropic surface energies: Surfaces with edges  

E-print Network

Hoffman field can be extended continuously to the whole surface and if the surface is stable and Hoffman [3] is satisfied. The main result states that if the the Cahn-Hoffman field extends the volume enclosed by . The condition of extendability of the Cahn-Hoffman map is a natural one since

Palmer, Bennett

462

STUDY OF THE FORMATION OF STABLE HIGH CONCENTRATED MONOCHLORAMINE SOLUTIONS  

Microsoft Academic Search

Disinfection is a very important step in the water treatment independent on the water application. Chlorination is the practice adopted in many industries, but chlorine can cause environmental damage and health hazards in the industry. A less aggressive agent to the environment is desirable to be found. The objective of this work is to prepare stable monochloramine solutions without any

M. K. Silva; I. C. Tessaro; K. Wada

463

Reversibly stable thiopolyplexes for intracellular delivery of genes  

Microsoft Academic Search

Novel polyaspartamide non-viral carriers for gene therapy were synthesized by introducing, on the same polymer backbone, positively charged groups, for electrostatic interactions with DNA, and thiol groups for the formation of disulfide bridges between polymer chains. The introduction of thiols was aimed to have a vector with low redox potential sensitivity: disulfide crosslinking in fact, being stable in extracellular environment,

Gennara Cavallaro; Monica Campisi; Mariano Licciardi; Manfred Ogris; Gaetano Giammona

2006-01-01

464

Effects of Finite Populations on Evolutionary Stable Strategies  

Microsoft Academic Search

A strong assumption made in evolutionarygame theory (EGT) [7] is that the evolvingpopulation is infinitely large. Recent simulationsby Fogel, et al, [3, 4, 5] show that finitepopulations produce behavior that, at best,deviate with statistical significance from theevolutionary stable strategy (ESS) predictedby EGT. They conclude that evolutionarygame theory loses its predictive power withfinite populations. In this paper, we revisitthe question of

Sevan G. Ficici; Jordan B. Pollack

2000-01-01

465

De novoDe novo biosyntheses versus sequestration in leaf beetlesbiosyntheses versus sequestration in leaf beetles a mechanistic approach by stable isotopesa mechanistic approach by stable isotopes  

E-print Network

in leaf beetles ­­ a mechanistic approach by stable isotopesa mechanistic approach by stable isotopes biosynthesis OGlc OH #12;The picture is different in another leaf beetle larvae O O O O JA treatm ent H 2O

466

Construction of energy-stable Galerkin reduced order models.  

SciTech Connect

This report aims to unify several approaches for building stable projection-based reduced order models (ROMs). Attention is focused on linear time-invariant (LTI) systems. The model reduction procedure consists of two steps: the computation of a reduced basis, and the projection of the governing partial differential equations (PDEs) onto this reduced basis. Two kinds of reduced bases are considered: the proper orthogonal decomposition (POD) basis and the balanced truncation basis. The projection step of the model reduction can be done in two ways: via continuous projection or via discrete projection. First, an approach for building energy-stable Galerkin ROMs for linear hyperbolic or incompletely parabolic systems of PDEs using continuous projection is proposed. The idea is to apply to the set of PDEs a transformation induced by the Lyapunov function for the system, and to build the ROM in the transformed variables. The resulting ROM will be energy-stable for any choice of reduced basis. It is shown that, for many PDE systems, the desired transformation is induced by a special weighted L2 inner product, termed the %E2%80%9Csymmetry inner product%E2%80%9D. Attention is then turned to building energy-stable ROMs via discrete projection. A discrete counterpart of the continuous symmetry inner product, a weighted L2 inner product termed the %E2%80%9CLyapunov inner product%E2%80%9D, is derived. The weighting matrix that defines the Lyapunov inner product can be computed in a black-box fashion for a stable LTI system arising from the discretization of a system of PDEs in space. It is shown that a ROM constructed via discrete projection using the Lyapunov inner product will be energy-stable for any choice of reduced basis. Connections between the Lyapunov inner product and the inner product induced by the balanced truncation algorithm are made. Comparisons are also made between the symmetry inner product and the Lyapunov inner product. The performance of ROMs constructed using these inner products is evaluated on several benchmark test cases.

Kalashnikova, Irina; Barone, Matthew Franklin; Arunajatesan, Srinivasan; van Bloemen Waanders, Bart Gustaaf

2013-05-01

467

An enzymatically stable kyotorphin analog induces pain in subattomol doses.  

PubMed

Intraplantar injection of the enzymatically stable, N-methylated kyotorphin analog Tyr(NMe)-Arg-OH produced marked and sharp nociceptive flexor responses in a dose-dependent manner. A significant response was observed with this compound at a dose of 0. 01 amol (6000 molecules). Tyr(NMe)-Arg-OH-nociception was completely blocked by the kyotorphin antagonist leucyl-arginine and its enzymatically stable, N-methylated analog, as well as by CP-99994, a specific neurokinin 1 antagonist. These findings suggest that the nociceptive effect produced by Tyr(NMe)-Arg-OH in subattomol doses occurs via specific interaction with the kyotorphin receptor and that the extraordinary potency observed may result from amplification through local substance P release. PMID:10876055

Ueda, H; Inoue, M; Weltrowska, G; Schiller, P W

2000-05-01

468

Stable platinum isotope measurements in presolar nanodiamonds by TEAMS.  

PubMed

Nanodiamonds are stardust grains commonly found in primitive meteorites. They survived the formation of the solar system and kept their own individuality. Measurements of trace-element isotopic signatures in these grains will help understanding heavy element nucleosynthesis in massive stars and dust formation from their ejecta. We have continued previous attempts to search for stable Pt isotope anomalies in nanodiamonds via trace element accelerator mass spectrometry (TEAMS). The installation of a new injector beam line at the VERA facility allowed studying low traces of stable elements in different materials. Moreover, recent experiments showed that VERA provides the required measurement precision together with a low Pt machine background. Here, we observed for the first time an indication for enhancements of (198)Pt/(195)Pt isotope ratios in two diamond residues prepared by different chemical separation techniques from the Allende meteorite. Variations in other isotopic ratios were within analytical uncertainty, and no anomaly was identified in a third diamond fraction. PMID:23565017

Wallner, A; Melber, K; Merchel, S; Ott, U; Forstner, O; Golser, R; Kutschera, W; Priller, A; Steier, P

2013-01-01

469

Stable platinum isotope measurements in presolar nanodiamonds by TEAMS  

PubMed Central

Nanodiamonds are stardust grains commonly found in primitive meteorites. They survived the formation of the solar system and kept their own individuality. Measurements of trace-element isotopic signatures in these grains will help understanding heavy element nucleosynthesis in massive stars and dust formation from their ejecta. We have continued previous attempts to search for stable Pt isotope anomalies in nanodiamonds via trace element accelerator mass spectrometry (TEAMS). The installation of a new injector beam line at the VERA facility allowed studying low traces of stable elements in different materials. Moreover, recent experiments showed that VERA provides the required measurement precision together with a low Pt machine background. Here, we observed for the first time an indication for enhancements of 198Pt/195Pt isotope ratios in two diamond residues prepared by different chemical separation techniques from the Allende meteorite. Variations in other isotopic ratios were within analytical uncertainty, and no anomaly was identified in a third diamond fraction. PMID:23565017

Wallner, A.; Melber, K.; Merchel, S.; Ott, U.; Forstner, O.; Golser, R.; Kutschera, W.; Priller, A.; Steier, P.

2013-01-01

470

Stable Isotope Characterization of TICs/TIMs: Analytical Progress Report  

SciTech Connect

We measured twelve alkali cyanide samples that were also sent to ORNL and PNNL collaborators. While results indicate distinct {delta}{sup 13}C and {delta}{sup 15}N values that would be useful to signature studies, the alkali cyanides, especially NaCN, show chemical breakdown during storage that will influence forensic analysis. Carbon and nitrogen stable isotopic compositions of raw materials used to synthesis TETS were measured. Results indicate wide ranges in {delta}{sup 13}C and {delta}{sup 15}N values. Using these raw materials, LLNL scientists synthesized three batches of TETS following published procedures. Stable isotopic measurements of TETS synthesis products indicates nitrogen ({var_epsilon} {sup 15}N = -1.7 to -0.8) and carbon ({var_epsilon} {sup 13}C = -1.0 to -0.1) fractionation during production.

Volpe, A M; Singleton, M J

2009-06-05

471

Stable Divergence Angles of a Magnetic Dipole Spiral Array  

NASA Astrophysics Data System (ADS)

An analytical model is introduced for the experiment of Douady and Couder [Phys. Rev. Lett. 68, 2098 (1992), where phyllotactic patterns appear as a dynamical result of the interaction between magnetic dipoles. The difference equation for the divergence angle (i.e. the angle between successive radial vectors) is obtained by solving the equations of motion with a second nearest neighbor (SNN) approximation. A one-dimensional map analysis as well as a comprehensive analytical proof shows that the divergence angle always converges to a single attractor regardless of the initial conditions. This attractor is approximately the Fibonacci angle(~ 138°) within variations due to a growth factor ? of the pattern. The system is proved to be stable with the SNN approximation. Further analysis with a third nearest neighbor approximation (TNN) shows extra linearly stable attractors may appear around the Lucas angle (~ 99.5°).

Fan, X. D.; Bursill, L. A.

472

Stable Higgs Bosons - new candidate for cold dark matter -  

E-print Network

The Higgs boson is in the backbone of the standard model of electroweak interactions. It must exist in some form for achieving unification of interactions. In the gauge-Higgs unification scenario the Higgs boson becomes a part of the extra-dimensional component of gauge fields. The Higgs boson becomes absolutely stable in a class of the gauge-Higgs unification models, serving as a promising candidate for cold dark matter in the universe. The observed relic abundance of cold dark matter is obtained with the Higgs mass around 70 GeV. The Higgs-nucleon scattering cross section is found to be close to the recent CDMS II and XENON10 bounds in the direct detection of dark matter. In collider experiments stable Higgs bosons are produced in a pair, appearing as missing energies and momenta so that the way of detecting Higgs bosons must be altered.

Yutaka Hosotani

2010-03-31

473

Stable isotope analysis of breath using the optogalvanic effect  

NASA Astrophysics Data System (ADS)

A new technique based on the optogalvanic effect has been developed for the measurement of stable isotope ratios in the carbon dioxide of exhaled breath. Data obtained before and after ingestion of harmless stable isotope labeled compounds, metabolized to carbon dioxide, can be used for sensitive noninvasive diagnostics of various disease conditions. The technique uses the specificity of laser resonance spectroscopy and achieves sensitivity and accuracy typical of sophisticated isotope ratio mass spectrometers. Using fixed frequency carbon dioxide lasers, 13C/12C ratios can be determined with a precision of 2 ppm with 100 second averaging times. Multiple samples can be analyzed simultaneously providing real time continuous calibration. In a first application, analysis of 13C/12C ratios in exhaled human breath after ingestion of 13C labeled urea is being developed as a diagnostic for the bacterium H-pylori, known to be the causative agent for most peptic and duodenal ulcers.

Murnick, Daniel E.; Colgan, M. J.; Lie, H. P.; Stoneback, D.

1996-05-01

474

Searching Stable CuxS Structures for Photovoltaic Application (Presentation)  

SciTech Connect

The crystal and electronic band structures of CuxS (1.25 < x ? 2) are systematically studied using the density-functional theory method. For Cu2S, all the three chalcocite phases, i.e., the low-chalcocite, the high-chalcocite, and the cubic-chalcocite phases have direct band gaps around 1.3-1.5 eV, with the low-chalcocite being the most stable one. However, Cu vacancies can form spontaneously in these compounds, causing instability of Cu2S. We find that under Cu-rich condition, the anilite Cu1.75S is the most stable structure. It has a predicted band gap of 1.4 eV and is a promising solar cell absorber.

Zhao, Y.; Xu, O.; Huang, B.; Yan, Y.; Noufi, R,; Wei, S-H

2014-03-01

475

Direct Mediation of Meta-Stable Supersymmetry Breaking  

SciTech Connect

The supersymmetric SU(N{sub c}) Yang-Mills theory coupled to NF matter fields in the fundamental representation has meta-stable vacua with broken supersymmetry when N{sub C} < N{sub F} < 3/2 N{sub C}. By gauging the flavor symmetry, this model can be coupled directly to the standard model. We show that it is possible to make a slight deformation to the model so that gaugino masses are generated and the Landau pole problem can be avoided. The deformed model has simple realizations on intersecting branes in string theory, where various features of the meta-stable vacua are encoded geometrically as brane configurations.

Kitano, Ryuichiro; Ooguri, Hirosi; Ookouchi, Yutaka

2006-12-13

476

System and circuitry to provide stable transconductance for biasing  

NASA Technical Reports Server (NTRS)

An amplifier system can include an input amplifier configured to receive an analog input signal and provide an amplified signal corresponding to the analog input signal. A tracking loop is configured to employ delta modulation for tracking the amplified signal, the tracking loop providing a corresponding output signal. A biasing circuit is configured to adjust a bias current to maintain stable transconductance over temperature variations, the biasing circuit providing at least one bias signal for biasing at least one of the input amplifier and the tracking loop, whereby the circuitry receiving the at least one bias signal exhibits stable performance over the temperature variations. In another embodiment the biasing circuit can be utilized in other applications.

Garverick, Steven L. (Inventor); Yu, Xinyu (Inventor)

2012-01-01

477

Geometric Brownian Motion with Tempered Stable Waiting Times  

NASA Astrophysics Data System (ADS)

One of the earliest system that was used to asset prices description is Black-Scholes model. It is based on geometric Brownian motion and was used as a tool for pricing various financial instruments. However, when it comes to data description, geometric Brownian motion is not capable to capture many properties of present financial markets. One can name here for instance periods of constant values. Therefore we propose an alternative approach based on subordinated tempered stable geometric Brownian motion which is a combination of the popular geometric Brownian motion and inverse tempered stable subordinator. In this paper we introduce the mentioned process and present its main properties. We propose also the estimation procedure and calibrate the analyzed system to real data.

Gajda, Janusz; Wy?oma?ska, Agnieszka

2012-08-01

478

Calculations predict a stable molecular crystal of N8  

NASA Astrophysics Data System (ADS)

Nitrogen, one of the most abundant elements in nature, forms the highly stable N2 molecule in its elemental state. In contrast, polynitrogen compounds comprising only nitrogen atoms are rare, and no molecular crystal made of these compounds has been prepared. Here, we predict the existence of such a molecular solid, consisting of N8 molecules, that is metastable even at ambient pressure. In the solid state, the N8 monomers retain the same structure and bonding pattern as those they adopt in the gas phase. The interactions that bind N8 molecules together are weak van der Waals and electrostatic forces. The solid is, according to calculations, more stable than a previously reported polymeric nitrogen solid, including at low pressure (below 20 GPa). The structure and properties of the N8 molecular crystal are discussed and a possible preparation strategy is suggested.

Hirshberg, Barak; Gerber, R. Benny; Krylov, Anna I.

2014-01-01

479

Stable doping of carbon nanotubes via molecular self assembly  

SciTech Connect

We report a novel method for stable doping of carbon nanotubes (CNT) based on methods of molecular self assembly. A conformal growth of a self-assembled monolayer of fluoroalkyl trichloro-silane (FTS) at CNT surfaces results in a strong increase of the sheet conductivity of CNT electrodes by 60–300%, depending on the CNT chirality and composition. The charge carrier mobility of undoped partially aligned CNT films was independently estimated in a field-effect transistor geometry (?100?cm{sup 2}V{sup ?1}s{sup ?1}). The hole density induced by the FTS monolayer in CNT sheets is estimated to be ?1.8?×?10{sup 14?}cm{sup ?2}. We also show that FTS doping of CNT anodes greatly improves the performance of organic solar cells. This large and stable doping effect, easily achieved in large-area samples, makes this approach very attractive for applications of CNTs in transparent and flexible electronics.

Lee, B.; Chen, Y.; Podzorov, V., E-mail: podzorov@physics.rutgers.edu [Department of Physics and Institute for Advanced Materials and Devices for Nanotechnology, Rutgers University, New Jersey 08854 (United States); Cook, A.; Zakhidov, A. [Department of Physics and NanoTech Institute, University of Texas at Dallas, Richardson, Texas 75083 (United States)

2014-10-14

480

Closed-Cycle, Frequency-Stable CO2 Laser Technology  

NASA Technical Reports Server (NTRS)

These proceedings contain a collection of papers and comments presented at a workshop on technology associated with long-duration closed-cycle operation of frequency-stable, pulsed carbon dioxide lasers. This workshop was held at the NASA Langley Research Center June 10 to 12, 1986. The workshop, jointly sponsored by the National Aeronautics and Space Administration (NASA) and the Royal Signals and Radar Establishment (RSRE), was attended by 63 engineers and scientists from the United States and the United Kingdom. During the 2 1/2 days of the workshop, a number of issues relating to obtaining frequency-stable operation and to the catalytic control of laser gas chemistry were discussed, and specific recommendations concerning future activities were drafted.

Batten, Carmen E. (editor); Miller, Irvin M. (editor); Wood, George M., Jr. (editor); Willetts, David V. (editor)

1987-01-01

481

Low work function, stable compound clusters and generation process  

DOEpatents

Low work function, stable compound clusters are generated by co-evaporation of a solid semiconductor (i.e., Si) and alkali metal (i.e., Cs) elements in an oxygen environment. The compound clusters are easily patterned during deposition on substrate surfaces using a conventional photo-resist technique. The cluster size distribution is narrow, with a peak range of angstroms to nanometers depending on the oxygen pressure and the Si source temperature. Tests have shown that compound clusters when deposited on a carbon substrate contain the desired low work function property and are stable up to 600.degree. C. Using the patterned cluster containing plate as a cathode baseplate and a faceplate covered with phosphor as an anode, one can apply a positive bias to the faceplate to easily extract electrons and obtain illumination.

Dinh, Long N. (Concord, CA); Balooch, Mehdi (Berkeley, CA); Schildbach, Marcus A. (Livermore, CA); Hamza, Alex V. (Livermore, CA); McLean, II, William (Oakland, CA)

2000-01-01

482

Selection-Migration Regimes Characterized by a Globally Stable Equilibrium  

PubMed Central

The principle that a subdivided population subject to overdominance viability selection in each habitat will manifest a unique, globally attractng polymorphic equilibrium is posited. This follows as a corollary to the stronger principle that, if haploid selection or submultiplicative diploid selection (definition: the geometric mean of the homozygote viabilities is less than or equal to the heterozygote viability) is operating in each habitat,there is a unique, globally attracting stable equilibrium that may be monomorphic or polymorphic. These principles are proven for a broad spectrum of migration patterns. In all such migration selection systems, multiple fixation states cannot be simultaneously stable under submultiplicative viability regimes. Contrasting examples where submultiplicative viabilities are not in force are given. PMID:17249019

Karlin, Samuel; Campbell, R. B.

1980-01-01

483

Fixed points, stable manifolds, weather regimes, and their predictability  

In a simple, one-layer atmospheric model, we study the links between low-frequency variability and the model’s fixed points in phase space. The model dynamics is characterized by the coexistence of multiple “weather regimes.” To investigate the transitions from one regime to another, we focus on the identification of stable manifolds associated with fixed points. We show that these manifolds act as separatrices between regimes. We track each manifold by making use of two local predictability measures arising from the meteorological applications of nonlinear dynamics, namely, “bred vectors” and singular vectors. These results are then verified in the framework of ensemble forecasts issued from “clouds” (ensembles) of initial states. The divergence of the trajectories allows us to establish the connections between zones of low predictability, the geometry of the stable manifolds, and transitions between regimes.

Deremble, Bruno; D'Andrea, Fabio; Ghil, Michael [Univ. of California, Los Angeles, CA (United Staes). Atmospheric and Oceanic Sciences and Institute of Geophysics and Planetary Physics

2009-10-27

484

Stable Carbon Isotope Fractionation by Methylotrophic Methanogenic Archaea  

PubMed Central

In natural environments methane is usually produced by aceticlastic and hydrogenotrophic methanogenic archaea. However, some methanogens can use C1 compounds such as methanol as the substrate. To determine the contributions of individual substrates to methane production, the stable-isotope values of the substrates and the released methane are often used. Additional information can be obtained by using selective inhibitors (e.g., methyl fluoride, a selective inhibitor of acetoclastic methanogenesis). We studied stable carbon isotope fractionation during the conversion of methanol to methane in Methanosarcina acetivorans, Methanosarcina barkeri, and Methanolobus zinderi and generally found large fractionation factors (?83‰ to ?72‰). We further tested whether methyl fluoride impairs methylotrophic methanogenesis. Our experiments showed that even though a slight inhibition occurred, the carbon isotope fractionation was not affected. Therefore, the production of isotopically light methane observed in the presence of methyl fluoride may be due to the strong fractionation by methylotrophic methanogens and not only by hydrogenotrophic methanogens as previously assumed. PMID:22904062

Penger, Jörn; Conrad, Ralf

2012-01-01

485

Etching Technology Using Ozone for Chemically Stable Polymer in MEMS  

NASA Astrophysics Data System (ADS)

We have developed the etching technology using an ozone solution for chemically stable polymers such as polyimide, SU-8 and BCB, which are often used for MEMS, and a carbonized resist. Conventionally, these polymers are difficult to remove by O2 plasma and organic solutions. In this study, the etching experiments of these chemically stable polymers were carried out using an acetic solution of ozone. The residues after the etching of the polymers were evaluated with surface profiler, scanning electron microscope and X-ray photoelectron spectroscopy. It was demonstrated that the acetic solution of ozone can etch and remove these polymers without residue. The developed method can remove not only organic polymers but also polymers containing inorganic materials, and is safe and easy.

Yanagida, Hideaki; Yoshida, Shinya; Esashi, Masayoshi; Tanaka, Shuji

486

Black chromium-molybdenum - A new stable solar absorber  

NASA Astrophysics Data System (ADS)

A new solar selective black which is more stable at high temperatures in air than standard black chrome has been electrodeposited. It is based on two refractory metals and their oxides, chromium and molybdenum. Their micromorphology is the same as found in black chrome and the solar absorption mechanisms are similar. Plating mechanisms are discussed and related to film structure. Chemical structure via X-ray photoelectron spectroscopy and Auger electron spectroscopy as a function of depth reveal important differences to the structure of standard black chrome which affect stability but not optical response before heating. Absorptance is stable at a value of 0.95 to at least 425 C in air in the best composites which have Mo/Cr ratios of about 0.05. The molybdenum is not present as metal and the total metallic Cr content decreases as the Mo content increases. The Mo percentage is very high near the surface of the film.

Smith, G. B.; Ignatiev, A.

1981-02-01

487

Biomedical research applications of electromagnetically separated enriched stable isotopes  

NASA Astrophysics Data System (ADS)

The current and projected annual requirements through 1985 for stable isotopes enriched by electromagnetic separation methods were reviewed for applications in various types of biomedical research: (1) medical radiosiotope production, labeled compounds, and potential radio-pharmaceuticals; (2) nutrition, food science, and pharmacology: (3) metallobiochemistry and environmental toxicology; (4) nuclear magnetic resonance, electron paramagnetic resonance, and moessbauer spectroscopy in biochemical, biophysical, and biomedical research; and (5) miscellaneous advances in radioactive and nonradioactive tracer technology. Radioisotopes available from commercial sources or routinely used in clinical nuclear medicine were excluded. Current requirements for enriched stable isotopes in biomedical research are not being satisfied. Severe shortages exist for Mg 26, Ca 43, Zn 70, Se 76, Se 77, Se 78, Pd 102, Cd 111, Cd 113, and Os 190. Many interesting and potentially important investigations in biomedical research require small quantities of specific elements at high isotopic enrichments.

Lambrecht, R. M.

488

Stable isotope geochemistry of East African waters. [Abstract only  

SciTech Connect

Lakes and Rivers in East Africa have varied stable isotopic compositions. Lakes exhibit enriched delta13-C values (-2 to +5%), while their inflowing rivers show depleted values (-15 to -8%). Hot springs and standing pools of water have intermediate values. Some small lakes are extremely variable in delta18-0 or deltaD (+2 to +8% and +20 to +40%, respectively for Lake Naivasha), whereas larger lakes are relatively constant for long periods of time (+5.6 to 6.1 and +36 to 40, respectively for Lake Turkana). Isotopic values are unrelated to salinity for comparison between lakes. Stable isotopes also reveal the sources of hot spring discharges: the Kapedo hot springs probably originate from Maralel and not from Lake Baringo as local legend has it; the hot springs north of Lake Naivasha are of meteoric origin while those to the south of Lake Naivasha have similar isotopic compositions to Lake Naivasha.

Sayer, M.D.; Cerling, T.E.; Bowman, J.R.

1983-03-01

489

Stable carbon isotope fractionation during aerobic biodegradation of chlorinated ethenes  

Microsoft Academic Search

Stable isotope analysis is recognized as a powerful tool for monitoring, assessing, and validating in-situ bioremediation processes. In this study, kinetic carbon isotope fractionation factors () associated with the aerobic biodegradation of vinyl chloride (VC), cis-1,2-dichloroethylene (cDCE), and trichloroethylene (TCE) were examined. Of the three solvents, the largest fractionation effects were observed for biodegradation of VC. Both metabolic and cometabolic

Kung-Hui Chu; Shaily Mahendra; Donald L. Song; Mark E. Conrad; Lisa Alvarez-Cohen

2003-01-01

490

Stable isotope deltas: Tiny, yet robust signatures in nature  

USGS Publications Warehouse

Although most of them are relatively small, stable isotope deltas of naturally occurring substances are robust and enable workers in anthropology, atmospheric sciences, biology, chemistry, environmental sciences, food and drug authentication, forensic science, geochemistry, geology, oceanography, and paleoclimatology to study a variety of topics. Two fundamental processes explain the stable isotope deltas measured in most terrestrial systems: isotopic fractionation and isotope mixing. Isotopic fractionation is the result of equilibrium or kinetic physicochemical processes that fractionate isotopes because of small differences in physical or chemical properties of molecular species having different isotopes. It is shown that the mixing of radioactive and stable isotope end members can be modelled to provide information on many natural processes, including 14C abundances in the modern atmosphere and the stable hydrogen and oxygen isotopic compositions of the oceans during glacial and interglacial times. The calculation of mixing fractions using isotope balance equations with isotope deltas can be substantially in error when substances with high concentrations of heavy isotopes (e.g. 13C, 2H, and 18O ) are mixed. In such cases, calculations using mole fractions are preferred as they produce accurate mixing fractions. Isotope deltas are dimensionless quantities. In the International System of Units (SI), these quantities have the unit 1 and the usual list of prefixes is not applicable. To overcome traditional limitations with expressing orders of magnitude differences in isotope deltas, we propose the term urey (symbol Ur), after Harold C. Urey, for the unit 1. In such a manner, an isotope delta value expressed traditionally as?25 per mil can be written as?25 mUr (or?2.5 cUr or?0.25 dUr; the use of any SI prefix is possible). Likewise, very small isotopic differences often expressed in per meg ‘units’ are easily included (e.g. either+0.015 ‰ or+15 per meg can be written as+15 ?Ur.

Brand, Willi A.; Coplen, Tyler B.

2012-01-01

491

The use of stable carbon isotope analysis in rooting studies  

Microsoft Academic Search

Stable carbon isotope analysis was evaluated as a means of predicting the relative proportions of C3 and C4 root phytomass in species mixtures. The following mixtures of C3 and C4 species were used: 1) big bluestem (Andropogon gerardii)\\/cheatgrass (Bromus tectorum), 2) little bluestem (Schizachyrium scoparium)\\/cheatgrass, and 3) sorghum (Sorghum bicolor)\\/sunflower (Helianthus annuus). There was a significant correlation (P4 phytomass and

Tony J. Svejcar; Thomas W. Boutton

1985-01-01

492

Hermitian-einstein metrics on parabolic stable bundles  

Microsoft Academic Search

Let \\u000a $$\\\\overline M $$\\u000a be a compact complex manifold of complex dimension two with a smooth Kähler metric and D a smooth divisor on \\u000a $$\\\\overline M $$\\u000a . If E is a rank 2 holomorphic vector bundle on \\u000a $$\\\\overline M $$\\u000a with a stable parabolic structure along D, we prove the existence of a metric on \\u000a $$E'{\\\\text{ = }}E|_{\\\\overline M

Jiayu Li; M. S. Narasimhan

1999-01-01

493

Nitroxide stable radical suppresses autoimmune uveitis in rats  

Microsoft Academic Search

Free radicals have been implicated in the pathogenesis of experimental autoimmune uveoretinitis (EAU). Nitroxides are stable radicals with a superoxide-dismutase-mimicking activity, which exert an anti-inflammatory effect in various animal models of oxidative damage and inflammation, such as experimental colitis and head trauma. We examined the use of the SOD mimic nitroxide 4-hydroxy-2,2,6,6,-tetramethylpiperidine-1-N-oxyl (TPL) to suppress EAU. Adult male Lewis rats

Ehud Zamir; RenLiang Zhang; Amram Samuni; Michael Kogan; Jacob Pe’er

1999-01-01

494

A Spectral Lyapunov Function for Exponentially Stable LTV Systems  

NASA Technical Reports Server (NTRS)

This paper presents the formulation of a Lyapunov function for an exponentially stable linear timevarying (LTV) system using a well-defined PD-spectrum and the associated PD-eigenvectors. It provides a bridge between the first and second methods of Lyapunov for stability assessment, and will find significant applications in the analysis and control law design for LTV systems and linearizable nonlinear time-varying systems.

Zhu, J. Jim; Liu, Yong; Hang, Rui

2010-01-01

495

Stable adaptive fuzzy controllers with application to inverted pendulum tracking  

Microsoft Academic Search

An adaptive fuzzy controller is constructed from a set of fuzzy IF-THEN rules whose parameters are adjusted on-line according to some adaptation law for the purpose of controlling the plant to track a given-trajectory. In this paper, two adaptive fuzzy controllers are designed based on the Lyapunov synthesis approach. We require that the final closed-loop system must be globally stable

Li-Xin Wang

1996-01-01

496

STABLE RANKS FOR THE REAL FUNCTION ALGEBRA C(X, )  

E-print Network

, denoted by bsr A, is the smallest integer n such that every element in Un+1(A) is reducible. If no such n exists, then bsr A = . The topological stable rank, tsr A, of A is the least integer n for which Un(A) is dense in An, or infinite if no such n exists. Note that if bsr A = n, then any m + 1-tuple (f1

Mortini, Raymond

497

Atomically precise metal nanoclusters: stable sizes and optical properties.  

PubMed

Controlling nanoparticles with atomic precision has long been a major dream of nanochemists. Breakthroughs have been made in the case of gold nanoparticles, at least for nanoparticles smaller than ?3 nm in diameter. Such ultrasmall gold nanoparticles indeed exhibit fundamentally different properties from those of the plasmonic counterparts owing to the quantum size effects as well as the extremely high surface-to-volume ratio. These unique nanoparticles are often called nanoclusters to distinguish them from conventional plasmonic nanoparticles. Intense work carried out in the last few years has generated a library of stable sizes (or stable stoichiometries) of atomically precise gold nanoclusters, which are opening up new exciting opportunities for both fundamental research and technological applications. In this review, we have summarized the recent progress in the research of thiolate (SR)-protected gold nanoclusters with a focus on the reported stable sizes and their optical absorption spectra. The crystallization of nanoclusters still remains challenging; nevertheless, a few more structures have been achieved since the earlier successes in Au102(SR)44, Au25(SR)18 and Au38(SR)24 nanoclusters, and the newly reported structures include Au20(SR)16, Au24(SR)20, Au28(SR)20, Au30S(SR)18, and Au36(SR)24. Phosphine-protected gold and thiolate-protected silver nanoclusters are also briefly discussed in this review. The reported gold nanocluster sizes serve as the basis for investigating their size dependent properties as well as the development of applications in catalysis, sensing, biological labelling, optics, etc. Future efforts will continue to address what stable sizes are existent, and more importantly, what factors determine their stability. Structural determination and theoretical simulations will help to gain deep insight into the structure-property relationships. PMID:25532730

Jin, Rongchao

2015-01-22

498

Boron clusters as highly stable magnesium-battery electrolytes.  

PubMed

Boron clusters are proposed as a new concept for the design of magnesium-battery electrolytes that are magnesium-battery-compatible, highly stable, and noncorrosive. A novel carborane-based electrolyte incorporating an unprecedented magnesium-centered complex anion is reported and shown to perform well as a magnesium-battery electrolyte. This finding opens a new approach towards the design of electrolytes whose likelihood of meeting the challenging design targets for magnesium-battery electrolytes is very high. PMID:24519845

Carter, Tyler J; Mohtadi, Rana; Arthur, Timothy S; Mizuno, Fuminori; Zhang, Ruigang; Shirai, Soichi; Kampf, Jeff W

2014-03-17

499

Boron Clusters as Highly Stable Magnesium-Battery Electrolytes**  

PubMed Central

Boron clusters are proposed as a new concept for the design of magnesium-battery electrolytes that are magnesium-battery-compatible, highly stable, and noncorrosive. A novel carborane-based electrolyte incorporating an unprecedented magnesium-centered complex anion is reported and shown to perform well as a magnesium-battery electrolyte. This finding opens a new approach towards the design of electrolytes whose likelihood of meeting the challenging design targets for magnesium-battery electrolytes is very high. PMID:24519845

Carter, Tyler J; Mohtadi, Rana; Arthur, Timothy S; Mizuno, Fuminori; Zhang, Ruigang; Shirai, Soichi; Kampf, Jeff W

2014-01-01

500

Highly Potent, Chemically Stable Quorum Sensing Agonists for Vibrio Cholerae.  

PubMed

In the Vibrio cholerae pathogen, initiation of bacterial quorum sensing pathways serves to suppress virulence. We describe herein a potent and chemically stable small molecule agonist of V. cholerae quorum sensing, which was identified through rational drug design based on the native quorum sensing signal. This novel agonist may serve as a useful lead compound for the control of virulence in V. cholerae. PMID:24436778

Perez, Lark J; Karagounis, Theodora K; Hurley, Amanda; Bassler, Bonnie L; Semmelhack, Martin F

2014-01-01