CONCEPTS IN MAGNETIC RESONANCE, Issue 1 2003
P.W. Stroman
Abstract A review of functional magnetic resonance imaging (fMRI) signal changes in spin,echo image data is presented. Spin,echo fMRI data from the human brain and spinal cord show a consistent departure from that expected with blood oxygen level dependent (BOLD) contrast. Studies to investigate this finding demonstrate fMRI signal changes of 2.5% in the spinal cord and 0.7% in the brain at 1.5 T, which is extrapolated to an echo time of zero. Consistent evidence of a non-BOLD contrast mechanism arising from a proton-density change at sites of neuronal activation is demonstrated. A mathematical model and physiological explanation for signal enhancement by extravascular protons is also presented. © 2003 Wiley Periodicals, Inc. Concepts Magn Reson 16A: 28,34, 2003 [source]

Spin- and Spray-Deposited Single-Walled Carbon-Nanotube Electrodes for Organic Solar Cells

ADVANCED FUNCTIONAL MATERIALS, Issue 14 2010
Sungsoo Kim
Abstract Organic bulk-heterojunction solar cells using thin-film single-walled carbon-nanotube (SWCNT) anodes deposited on glass are reported. Two types of SWCNT films are investigated: spin-coated films from dichloroethane (DCE), and spray-coated films from deionized water using sodium dodecyl sulphate (SDS) or sodium dodecyl benzene sulphonate (SDBS) as the surfactant. All of the films are found to be mechanically robust, with no tendency to delaminate from the underlying substrate during handling. Acid treatment with HNO3 yields high conductivities >1000,S,cm,1 for all of the films, with values of up to 7694,±,800,S,cm,1 being obtained when using SDS as the surfactant. Sheet resistances of around 100,,,sq,1 are obtained at reasonable transmission, for example, 128,±,2,,,sq,1 at 90% for DCE, 57,±,3,,,sq,1 at 65% for H2O:SDS, and 68,±,5,,,sq,1 at 70% for H2O:SDBS. Solar cells are fabricated by successively coating the SWCNT films with poly(3,4-ethylenedioxythiophene):poly(styrene sulphonate) (PEDOT:PSS), a blend of regioregular poly(3-hexylthiophene) (P3HT) and 1-(3-methoxy-carbonyl)-propyl-1-phenyl-(6,6)C61 (PCBM), and LiF/Al. The resultant devices have respective power conversions of 2.3, 2.2 and 1.2% for DCE, H2O:SDS and H2O:SDBS, with the first two being at a virtual parity with reference devices using ITO-coated glass as the anode (2.3%). [source]

The spinorial method of classifying supersymmetric backgrounds

FORTSCHRITTE DER PHYSIK/PROGRESS OF PHYSICS, Issue 5-6 2006
U. Gran
Abstract We review how the classification of all supersymmetric backgrounds of IIB supergravity can be reduced to the evaluation of the Killing spinor equations and their integrability conditions, which contain the field equations, on five types of spinors. This is an extension of the work [hep-th/0503046] to IIB supergravity. By using the explicit expressions for the Killing spinor equations evaluated on the five types of spinors the Killing spinor equations become a linear system in terms of the fluxes, the geometry and the spacetime derivatives of the functions that determine the Killing spinors. This system can be solved to express the fluxes in terms of the geometry and to determine the conditions on the geometry of any supersymmetric background. Similarly, the integrability conditions of the Killing spinor equations are turned into a linear system. This can be used to determine the field equations that are implied by the Killing spinor equations for any supersymmetric background. These linear systems simplify for generic backgrounds with maximal and half-maximal number of H -invariant Killing spinors, H , Spin(9,1). In the maximal case, the Killing spinor equations factorise, whereas in the half-maximal case they do not. [source]

Flux compactification of M-theory on compact manifolds with Spin(7) holonomy,

FORTSCHRITTE DER PHYSIK/PROGRESS OF PHYSICS, Issue 11-12 2005
D. Constantin
At the leading order, M-theory admits minimal supersymmetric compactifications if the internal manifold has exceptional holonomy. The inclusion of non-vanishing fluxes in M-theory and string theory compactifications induce a superpotential in the lower dimensional theory, which depends on the fluxes. In this work, we check the conjectured form of this superpotential in the case of warped M-theory compactifications on Spin(7) holonomy manifolds. We perform a Kaluza-Klein reduction of the eleven-dimensional supersymmetry transformation for the gravitino and we find by direct comparison the superpotential expression. We check the conjecture for the heterotic string compactified on a Calabi-Yau three-fold as well. The conjecture can be checked indirectly by inspecting the scalar potential obtained after the compactification of M-theory on Spin(7) holonomy manifolds with non-vanishing fluxes. The scalar potential can be written in terms of the superpotential and we show that this potential stabilizes all the moduli fields describing deformations of the metric except for the radial modulus. All the above analyses require the knowledge of the minimal supergravity action in three dimensions. Therefore we calculate the most general causal ,, =1 three-dimensional, gauge invariant action coupled to matter in superspace and derive its component form using Ectoplasmic integration theory. We also show that the three-dimensional theory which results from the compactification is in agreement with the more general supergravity construction. The compactification procedure takes into account higher order quantum correction terms in the low energy effective action. We analyze the properties of these terms on a Spin(7) background. We derive a perturbative set of solutions which emerges from a warped compactification on a Spin(7) holonomy manifold with non-vanishing flux for the M-theory field strength and we show that in general the Ricci flatness of the internal manifold is lost, which means that the supergravity vacua are deformed away from the exceptional holonomy. Using the superpotential form we identify the supersymmetric vacua out of this general set of solutions. [source]

Synthesis and Processing of Monodisperse Oligo(fluorene- co -bithiophene)s into Oriented Films by Thermal and Solvent Annealing

ADVANCED FUNCTIONAL MATERIALS, Issue 12 2009
Lichang Zeng
Abstract A series of oligo(fluorene- co -bithiophene)s, OF2Ts, have been synthesized and characterized to investigate the effects of oligomer length and pendant aliphatic structure on glassy-nematic mesomorphism. The OF2Ts comprising more than one repeat unit and their polymer analogue, PF2T, carrying 52 number-average repeat units, possess the highest occupied molecular orbital energy level at ,5.3,±,0.2,eV, but the anisotropic field-effect mobilities increase with the oligomer length. Spin coating from high-boiling chlorobenzene with and without subsequent exposure to saturated chlorobenzene vapor constitute solvent-vapor annealing and quasi-solvent annealing, respectively. Solvent-vapor annealing yields monodomain glassy-nematic films in which OF2Ts are aligned as well as with thermal annealing across a 2,cm diameter. Quasi-solvent annealing, however, amounts to kinetically trapping a lower orientational order than solvent-vapor or thermal annealing. While amenable to thermal annealing at elevated temperatures, PF2T shows no alignment at all following either strategy of solvent annealing. [source]

Spin-Based Optical Quantum Information Processing

ISRAEL JOURNAL OF CHEMISTRY, Issue 4 2006
Ehoud Pazy
We shall present a review of semiconductor spin-based implementation schemes for the realization of quantum information/computation solid-state devices. After briefly describing the fundamentals of quantum computation theory, we shall introduce and discuss potential implementation schemes based on the spin degrees of freedom in semiconductor nanostructures. More specifically, we shall describe an implementation scheme for quantum information processing in which the spin degrees of freedom of electrons confined to a quantum dot are the computational degrees of freedom, and spins are manipulated/controlled through interaction between trionic states created by interband optical transitions by ultrafast sequences of multicolor laser pulses. We will also review briefly an adiabatic method for operating the two-qubit gate that avoids the main imperfections present in real quantum dots: exciton decay, hole mixing, and phonon decoherence. [source]

Primetime Spin: Media Bias and Belief Confirming Information

JOURNAL OF ECONOMICS & MANAGEMENT STRATEGY, Issue 3 2008
Jeremy Burke
This paper develops a model of media bias in which rational agents acquire all their news from the source that is most likely to confirm their prior beliefs. Despite only wishing to make the correct decision, agents act as if they enjoy receiving news that supports their preconceptions. By exclusively gathering information from a source biased towards his prior, there is little chance an agent will be persuaded to change his mind. Moreover, it is shown that even an unbiased agent prefers to receive biased news as it is unlikely to produce conflicting reports. The media caters to the informational demands of consumers and accordingly slants its reporting. It is shown that competition may not decrease bias, but may actually enhance it. Finally, even when it increases bias, competition may improve welfare by expanding the market for news. [source]

Susceptibility Contrast and Arterial Spin Labeled Perfusion MRI in Cerebrovascular Disease

JOURNAL OF NEUROIMAGING, Issue 1 2003
Ronald L. Wolf MD
ABSTRACT Purpose. To directly compare dynamic susceptibility contrast (DSC) and continuous arterial spin labeled (CASL) magnetic resonance (MR) perfusion techniques in patients with known cerebrovascular disease, with the goals of identifying possible pitfalls in interpretation and determining potential for a complementary role in this setting. Methods. DSC and CASL MR perfusion studies were performed and compared in 11 patients with acute and/or chronic cerebrovascular disease. Using an automated segmentation technique, Pearson correlation coefficients were generated for CASL perfusion measurements compared to DSC perfusion maps (time-to-peak [TTP], relative cerebral blood volume [rCBV], cerebral blood flow [rCBF], and mean transit time [MTT]) by hemisphere and vascular territory. Results. TTP maps obtained using DSC perfusion MR correlated best both subjectively and objectively with CASL perfusion MRmeasurements when all patients studied were considered. If patients with a major transit delay were excluded, DSC rCBF correlated best with CASL CBF measurements. Conclusion. There may be a complementary role for CASL and DSC perfusion MR methods in cerebrovascular disease, especially in the setting of a marked transit delay. [source]

Spin: from tactic to tabloid

JOURNAL OF PUBLIC AFFAIRS, Issue 1 2006
Leighton Andrews
Over the last fifteen years, the word Spin has come to define both the process of political communication, and the practice of public relations itself. The history of the term requires some examination. Arguably, until around 1992, Spin did not have such a widespread meaning,it was simply one tactic in an election campaigner's armoury. Now it seems to embrace the whole process of communication, not only between election campaigners and the media, but also between a Government and its people, or between a public relations professional in any field, and his or her target publics. The development of Spin as a word has gone through a number of stages which will be addressed in the course of this paper. It now has widespread popular usage, which has arisen through two principal processes: The increasing celebrity status of the spin-doctor role: and the usefulness of the word to tabloid sub-editors. By 1997, when New Labour came into Government, the discourse of spin was firmly established. Copyright © 2006 John Wiley & Sons, Ltd. [source]

Structural studies on aryl-substituted enaminoketones and their thio analogues.

MAGNETIC RESONANCE IN CHEMISTRY, Issue 10 2009
Part II.
Abstract Spin,spin carbon,carbon coupling constants across one, two and three bonds, J(CC), have been measured for a series of aryl-substituted Z-s-Z-s-E enaminoketones and their thio analogues. As a result, a large set, altogether 178, of J(CC)s has been obtained. It consists of 82 couplings across one bond, 31 couplings across two bonds and 65 couplings across three bonds. Independently, the DFT calculations at the B3PW91/6-311++G(d,p)//B3PW91/6-311++G(d,p) level yielded a set of theoretical J(CC) values. A comparison of these two sets of data gave an excellent linear correlation with parameters a and b close to ideal; a = 0.9978 which is not far from unity and b = 0.22 Hz which is close to zero. The 1J(CC) couplings determined for the crucial fragment of the molecules, i.e. CCCO (or CCCS), are: 1J(CC) , 68 Hz (67 Hz) and 1J(CC) = 60.5 Hz (60.0 Hz). The corresponding couplings found for the Z-s-Z-s-E isomer of the parent enaminoketone, 4-methylamino-but-3-en-2-one are 64.1 and 59.3 Hz, respectively. The most sensitive towards substitution of the oxygen atom by sulfur are two-bond couplings between the ,-vinylic and aromatic Cipso carbon atoms, which attain 12 Hz in the enaminoketone derivatives and decrease to 5 Hz in their thio analogues. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Spin,spin coupling and substituent and halogen isotope shift effects in the fluorine NMR spectra of fluorinated cyclopropanes and cyclopropyl ethers

MAGNETIC RESONANCE IN CHEMISTRY, Issue 3 2007
Wallace S. Brey
Abstract The 19F NMR spectra of a series of fluorinated cyclopropanes, most of which contain chlorine or bromine on the ring, have been observed and analyzed. A scheme has been developed to assign the resonances and the molecular stereochemistry, based on substituent effects, comparison of related molecules, and isotope shifts induced by the halogens. Replacement of fluorine by chlorine shifts cis fluorine resonances to lower field, and bromine has an even greater downfield influence. However, the shift effect of bromine compared to chlorine on gem or trans fluorines is variable. The magnitude of the isotope shifts is found to be regularly related to the geometrical relationship of the halogen to the observed fluorine and thus makes a significant contribution to the fluorine assignments. The three-bond spin,spin coupling constants between fluorine atoms in cyclopropanes display unusual behavior and are not helpful for assignment of the fluorine resonances. The signs of the coupling constants have been investigated by spin-tickling experiments, and the previously developed relation of the coupling constant sign to its temperature dependence has been found to be violated for some molecules. Copyright © 2007 John Wiley & Sons, Ltd. [source]

Conformational and substituent effects in the 19F spectra of C7,C10 straight-chain chlorofluoroalkanes

MAGNETIC RESONANCE IN CHEMISTRY, Issue 11 2004
Wallace S. Brey
Abstract One- and two-dimensional fluorine NMR spectra of straight-chain chlorofluoroalkanes having 7,10 carbons were obtained and interpreted. Spectral assignments were based primarily on indirect spin,spin correlations. A scale of chlorine substituent effects was developed. The effects of asymmetric CFCl centers on chemical-shift differences in nearby CF2 groups were analyzed in terms of molecular conformational effects. Spin,spin coupling patterns of CF3 groups were elucidated. Copyright © 2004 John Wiley & Sons, Ltd. [source]

Latino Spin: Public Image and the Whitewashing of Race by Arlene Dávila

AMERICAN ETHNOLOGIST, Issue 2 2010
GILBERTO ROSAS
No abstract is available for this article. [source]

Dynamics of spin interactions in diluted magnetic semiconductor heterostructures

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 1 2007
*Article first published online: 19 DEC 200, D. R. Yakovlev
Abstract This paper gives an overview of the recent studies of spin dynamics in diluted magnetic semiconductor heterostructures based on (Zn,Mn)Se and (Cd,Mn)Te. The spin dynamics is controlled by energy and spin transfer between systems of magnetic ions, lattice (phonon system) and free carriers. Spin,lattice relaxation time of the Mn spin system is a very strong function of the Mn content, it decreases by five orders of magnitude when the Mn content changes from 0.4 to 11%. Additionally this time can be tuned by the varying free carrier concentration and by the growth of heteromagnetic structures with inhomogeneous profile of Mn ions. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Spin and energy transfer between magnetic ions and freecarriers in diluted-magnetic semiconductor heterostructures

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 4 2004
D.R. Yakovlev
Abstract In this paper we give a brief overview of our studies on dynamical processes in diluted-magnetic-semiconductor heterostructures based on (Zn,Mn)Se and (Cd,Mn)Te. Presence of free carriers is an important factor which determines the energy- and spin transfer in a coupled systems of magnetic ions, lattice (the phonon system) and carriers. We report also new data on dynamical response of magnetic ions interacting with photogenerated electron-hole plasma. (Zn,Mn)Se/(Zn,Be)Se structures with relatively high Mn content of 11% provide spin-lattice relaxation time of about 20 ns, which is considerably shorter then the characterictic times of nonequilibrium phonons ranging to 1 ,s. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Spin(n)t die Elektronik des 21.

PHYSIK IN UNSERER ZEIT (PHIUZ), Issue 6 2008
Jahrhunderts?
No abstract is available for this article. [source]

Hochtemperatur-Supraflüssigkeit in ultrakaltem Fermi-Gas

PHYSIK IN UNSERER ZEIT (PHIUZ), Issue 5 2005
Martin Zwierlein
Ultrakalte atomare Gase, eine Million mal dünner als Luft, bieten die faszinierende Möglichkeit, das Phänomen der Supraflüssigkeit in seiner Reinstform zu beobachten. Bisher ist dies nur für Gase aus Bosonen, Teilchen mit ganzzahligem Spin, gelungen. Nun wurde auch in einem rotierenden Gas aus Fermionen, Teilchen mit halbzahligem Spin, der Nachweis für Supraflüssigkeit erbracht: Es gelang die Beobachtung regelmäßig angeordneter Vortices [1]. Diese neue Form der Supraflüssigkeit würde, skaliert auf die Dichte von Elektronen im Festkörper, bereits oberhalb der Zimmertemperatur eintreten. [source]

Radio bimodality: Spin, accretion mode, or both?

ASTRONOMISCHE NACHRICHTEN, Issue 2-3 2009
M. Sikora
Abstract A new scenario is suggested to explain a large diversity of the AGN radio properties and their dependence on the galaxy morphology. The scenario is based on the assumption that the growth of supermassive BHs is dominated by the accretion only during the quasar (high accretion rate) phase, otherwise , by mergers with less massive black holes. Following that, BHs are expected to spin much faster in giant ellipticals than in disk galaxies. Within the frame of the spin paradigm this explains the observed relation of the radio-dichotomy with the galaxy morphology. Various theoretical and observational aspects of such a dichotomy are discussed. In particular, the issue of the intermittency and suppression of a jet production at high accretion rates is addressed and a scenario for production of powerful, extended radio sources is drafted (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

ChemInform Abstract: Density Functional Theory Studies of Spin, Charge, and Orbital Ordering in YBaT2O5 (T: Mn, Fe, Co).

CHEMINFORM, Issue 40 2008
R. Vidya
Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source]

A Theoretical Study of the NMR Spin,Spin Coupling Constants of the Complexes [(NC)5Pt,Tl(CN)n]n- (n = 0,3) and [(NC)5Pt,Tl,Pt(CN)5]3- : A Lesson on Environmental Effects.

CHEMINFORM, Issue 2 2004
Jochen Autschbach
No abstract is available for this article. [source]

ChemInform Abstract: Spin, Charge, and Orbital Ordering in the B-Site Diluted Manganates La2-xSrxGaMnO6.

CHEMINFORM, Issue 14 2002
P. D. Battle
Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source]

Antiferromagnetism or Delocalized Spin in a Cu3S2 Core?

CHEMISTRY - A EUROPEAN JOURNAL, Issue 9 2010
Santiago Alvarez
Is there a bond or isn,t there? In a further effort to bring light to the debate on the existence of an SS bond in Tolman,s cluster compound (shown here), this correspondence is a reply to the preceeding communication. [source]

BINOL-3,3,-Triflone N,N -Dimethyl Phosphoramidites: Through-Space 19F,31P Spin,Spin Coupling with a Remarkable Dependency on Temperature and Solvent Internal Pressure

CHEMISTRY - A EUROPEAN JOURNAL, Issue 26 2008
Matthias Kruck
Abstract A combined computational and experimental study of the effects of solvent, temperature and stereochemistry on the magnitude of the through-space spin,spin coupling between 31P and 19F nuclei which are six-bonds apart is described. The reaction of 3-trifluoromethylsulfonyl-2,,2-dihydroxy-1,1,-binaphthalene (3-SO2CF3 -BINOL) with hexamethylphosphorous triamide (P(NMe2)3) generates a pair of N,N -dimethylphosphoramidites which are diastereomeric due to their differing relative configurations at the stereogenic phosphorous centre and the axially chiral (atropisomeric) BINOL unit. Through-space NMR coupling of the 31P and 19F nuclei of the phosphoramidite and sulfone is detected in one diastereomer only. In the analogous N,N -dimethylphosphoramidite generated from 3,3,-(SO2CF3)2 -BINOL only one of the diastereotopic trifluoromethylsulfone moieties couples with the 31P of the phosphoramidite. In both cases, the magnitude of the coupling is strongly modulated (up to 400,%) by solvent and temperature. A detailed DFT analysis of the response of the coupling to the orientation of the CF3 moiety with respect to the P-lone pair facilitates a confident assignment of the stereochemical identity of the pair of diastereomers. The analysis shows that the intriguing effects of environment on the magnitude of the coupling can be rationalised by a complex interplay of solvent internal pressure, molecular volume and thermal access to a wider conformational space. These phenomena suggest the possibility for the design of sensitive molecular probes for local environment that can be addressed via through-space NMR coupling. [source]

Spins as probes of different electronic states

CONCEPTS IN MAGNETIC RESONANCE, Issue 2 2007
Dieter Suter
Abstract Nuclear spins are efficient probes of electronic states. Because most NMR experiments are performed in thermal equilibrium, they probe the electronic ground state,the only state that is significantly populated under ambient conditions. Probing electronically excited states becomes possible, if magnetic resonance techniques are combined with optical (laser) excitation. Depending on the nature of the electronic state, drastic changes of the magnetic resonance parameters may be observed. We discuss the basic principles of this type of investigation. Depending on the lifetime of the electronically excited state, it is possible to measure separate spectra of ground and excited state if the lifetime is long on the NMR timescale, or an averaged spectrum if the lifetime is short. We present examples for both limiting cases using rare earth ions and semiconductor heterostructures. © 2007 Wiley Periodicals, Inc. Concepts Magn Reson Part A 30A: 116,126, 2007. [source]

Herzdiagnose mit Spins: Magnetokardiographie mit optisch gepumpten Magnetometern

PHYSIK IN UNSERER ZEIT (PHIUZ), Issue 1 2007
Georg Bison
Abstract Die Magnetokardiographie (MKG) misst das extrem schwache Magnetfeld der Herzmuskeln mit hoch empfindlichen Sensoren. Es kann verschiedene Herzkrankheiten wesentlich zuverlässiger diagnostizieren als etablierte Verfahren. Ihr heutiger Nachteil liegt in der Verwendung von SQUID-Sensoren. Diese müssen auf Temperaturen von 4 K gekühlt werden, was hohe Anschaffungs- und Betriebskosten verursacht. Optisch gepumpte Magnetometer könnten der MKG zum Durchbruch in der Praxis verhelfen. Diese Sensoren arbeiten bei Raumtemperatur, was den technischen Aufwand und die Kosten erheblich reduziert. Ein Demonstrationsaufbau an der Universität Fribourg zeigt, dass die Methode zuverlässig funktioniert. [source]

Lithium-Ammoniak-Lösungen: eine molekulare Betrachtung

ANGEWANDTE CHEMIE, Issue 44 2009
Eva Zurek Dr.
Abstract Dieser Aufsatz gibt eine detaillierte Molekülorbitalanalyse der Strukturen und elektronischen Eigenschaften der vielfältigen Spezies, die in Lithium-Ammoniak-Lösungen auftreten. Als Spezies mit ungerader Elektronenzahl (Dublett-Zustände) betrachten wir: e,@(NH3)n (das solvatisierte Elektron, wahrscheinlich ein dynamisches Ensemble von Molekülen), das Li(NH3)4 -Monomer und die [Li(NH3)4+,,,e,@(NH3)n]-Ionenpaare. Das 2s-Elektron des Li besetzt ein diffuses Orbital, das hauptsächlich von den niedrigsten unbesetzten Molekülorbitalen (MOs) der Ammoniakmoleküle gebildet wird. Die einfach besetzten MOs sind zwischen den Wasserstoffatomen bindend; wir bezeichnen diese stabilisierende Wechselwirkung als H H-Brücke. Im e,@(NH3)n befindet sich das Überschusselektron nicht im Zentrum des von den Ammoniakmolekülen gebildeten Käfigs. Denkbare Spezies mit zwei oder mehr schwach wechselwirkenden Elektronen bilden ebenfalls H H-Brücken. Für diese Spezies finden wir, dass die Singulett-Zustände (S=0) bei etwas tieferer Energie liegen als die Zustände mit ungepaarten Spins (S=1, 2,). TD-DFT-Rechnungen an verschiedenen Ionenpaaren zeigen, dass die drei intensivsten elektronischen Anregungen von den Übergängen aus dem SOMO (mit s-Pseudosymmetrie) in die niedrigsten p-artigen Niveaus stammen. Die optischen Absorptionsspektren sind weitgehend unabhängig vom Metall, und wir können die in das Sichtbare reichende Absorptionsflanke gut erklären. Letztere verursacht die "schöne blaue Farbe", die Sir Humphry Davy vor 200 Jahren erstmals beobachtete. [source]

The hydrogen atom, revisited: Parallel-field magnetic resonance,

CONCEPTS IN MAGNETIC RESONANCE, Issue 5 2006
John A. Weil
Abstract Consideration of the magnetic resonance spectroscopy of the free hydrogen atom (1H0) reveals that, in addition to the well-known transitions (EPR and NMR) occurring between the four spin states when the excitation magnetic field B1 is perpendicular to the static external field B, there exists a combination line (simultaneous electronic and nuclear spin flips) when B1 , B, which becomes strong under some circumstances. The latter phenomenon is focused on and discussed herein, in some detail. © 2006 Wiley Periodicals, Inc. Concepts Magn Reson Part A 28A: 331,336, 2006 [source]

Thermal relaxation and coherence dynamics of spin 3/2.

CONCEPTS IN MAGNETIC RESONANCE, Issue 2 2003

Abstract The relaxation dynamics of the spin 3/2 density operator in the presence of fluctuating and static quadrupolar interactions is reviewed. The nuclear magnetic resonance (NMR) line shapes are analyzed for any value of the static quadrupolar interaction, ranging from isotropic systems to systems exhibiting large splitting far exceeding the line widths. Pulse sequences optimized for the elimination of line broadening due to an inhomogeneous static quadrupolar interaction and for the detection of nuclei involved in slow molecular motion and/or in anisotropic, liquid crystalline environment are discussed. In Part II, the dynamics of spin 3/2 in the presence of a (pulsed) radio frequency (RF) field is reviewed. © 2003 Wiley Periodicals, Inc. Concepts Magn Reson Part A 19A: 97,116, 2003. [source]

Spin-lattice relaxation of spin-½ nuclei in solids containing diluted paramagnetic impurity centers.

CONCEPTS IN MAGNETIC RESONANCE, Issue 1 2003

Abstract Dynamic nuclear polarization of nuclear spins via the solid-state and thermal mixing effects is discussed. Continuous-wave S- and X-band microwave radiation have been employed to measure 13C signal enhancements and polarization times for 13C nuclei in a natural type Ib diamond as a function of magnetic field. It was found that thermal mixing plays an important role in the 13C signal enhancement because the central electron spin resonance (ESR) line width HL , H0,C/,e, resulting in flip-flip and flip-flop forbidden transitions taking place simultaneously. On the other hand, the 13C spin-lattice relaxation rate is determined to a large extent by the solid-state effect (forbidden transitions). 13C polarization rates have also been measured for a suite of natural diamonds. It is shown that the polarization rate is proportional to the paramagnetic impurity concentration, in agreement with the theory. © 2003 Wiley Periodicals, Inc. Concepts Magn Reson 19A: 36,43, 2003. [source]

Spin-lattice relaxation of spin-½ nuclei in solids containing diluted paramagnetic impurity centers.

CONCEPTS IN MAGNETIC RESONANCE, Issue 1 2003

Abstract Dynamic nuclear polarization of nuclei by means of paramagnetic electron spin locking (Hartmann-Hahn cross-polarization between paramagnetic electrons and nuclei, or NOVEL) is discussed. The theory is demonstrated by experiments executed at 2.4 and 9.6 GHz on a natural type Ib diamond. It is shown that the 13C polarization rate is independent of the microwave frequency, in agreement with theory. NOVEL polarization takes place only while the spin-locking pulse is on. The rate at which the nuclei are polarized is proportional to the electron polarization in the rotating frame. Therefore, the length of the spin-locking pulse is limited by the value of T1,(e), and because T1,(e) , T1(e) for diamond the effective NOVEL polarization rate of 13C nuclei is usually relatively low. A comparison between the relative effectiveness of 13C polarization rates between NOVEL and the solid-state effect is made for high and low paramagnetic impurity concentrations. The dependence of the 13C polarization rate on the paramagnetic impurity concentration has been determined for a suite of natural diamonds. © 2003 Wiley Periodicals, Inc. Concepts Magn Reson 19A: 44,49, 2003. [source]