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Sample records for 1h-13c dipolar couplings

  1. Derivatives of pyrazinecarboxylic acid: 1H, 13C and 15N NMR spectroscopic investigations.

    PubMed

    Holzer, Wolfgang; Eller, Gernot A; Datterl, Barbara; Habicht, Daniela

    2009-07-01

    NMR spectroscopic studies are undertaken with derivatives of 2-pyrazinecarboxylic acid. Complete and unambiguous assignment of chemical shifts ((1)H, (13)C, (15)N) and coupling constants ((1)H,(1)H; (13)C,(1)H; (15)N,(1)H) is achieved by combined application of various 1D and 2D NMR spectroscopic techniques. Unequivocal mapping of (13)C,(1)H spin coupling constants is accomplished by 2D (delta,J) long-range INEPT spectra with selective excitation. Phenomena such as the tautomerism of 3-hydroxy-2-pyrazinecarboxylic acid are discussed.

  2. Proton-detected 3D (1)H/(13)C/(1)H correlation experiment for structural analysis in rigid solids under ultrafast-MAS above 60 kHz.

    PubMed

    Zhang, Rongchun; Nishiyama, Yusuke; Ramamoorthy, Ayyalusamy

    2015-10-28

    A proton-detected 3D (1)H/(13)C/(1)H chemical shift correlation experiment is proposed for the assignment of chemical shift resonances, identification of (13)C-(1)H connectivities, and proximities of (13)C-(1)H and (1)H-(1)H nuclei under ultrafast magic-angle-spinning (ultrafast-MAS) conditions. Ultrafast-MAS is used to suppress all anisotropic interactions including (1)H-(1)H dipolar couplings, while the finite-pulse radio frequency driven dipolar recoupling (fp-RFDR) pulse sequence is used to recouple dipolar couplings among protons and the insensitive nuclei enhanced by polarization transfer technique is used to transfer magnetization between heteronuclear spins. The 3D experiment eliminates signals from non-carbon-bonded protons and non-proton-bonded carbons to enhance spectral resolution. The 2D (F1/F3) (1)H/(1)H and 2D (13)C/(1)H (F2/F3) chemical shift correlation spectra extracted from the 3D spectrum enable the identification of (1)H-(1)H proximity and (13)C-(1)H connectivity. In addition, the 2D (F1/F2) (1)H/(13)C chemical shift correlation spectrum, incorporated with proton magnetization exchange via the fp-RFDR recoupling of (1)H-(1)H dipolar couplings, enables the measurement of proximities between (13)C and even the remote non-carbon-bonded protons. The 3D experiment also gives three-spin proximities of (1)H-(1)H-(13)C chains. Experimental results obtained from powder samples of L-alanine and L-histidine ⋅ H2O ⋅ HCl demonstrate the efficiency of the 3D experiment.

  3. Proton-detected 3D 1H/13C/1H correlation experiment for structural analysis in rigid solids under ultrafast-MAS above 60 kHz

    NASA Astrophysics Data System (ADS)

    Zhang, Rongchun; Nishiyama, Yusuke; Ramamoorthy, Ayyalusamy

    2015-10-01

    A proton-detected 3D 1H/13C/1H chemical shift correlation experiment is proposed for the assignment of chemical shift resonances, identification of 13C-1H connectivities, and proximities of 13C-1H and 1H-1H nuclei under ultrafast magic-angle-spinning (ultrafast-MAS) conditions. Ultrafast-MAS is used to suppress all anisotropic interactions including 1H-1H dipolar couplings, while the finite-pulse radio frequency driven dipolar recoupling (fp-RFDR) pulse sequence is used to recouple dipolar couplings among protons and the insensitive nuclei enhanced by polarization transfer technique is used to transfer magnetization between heteronuclear spins. The 3D experiment eliminates signals from non-carbon-bonded protons and non-proton-bonded carbons to enhance spectral resolution. The 2D (F1/F3) 1H/1H and 2D 13C/1H (F2/F3) chemical shift correlation spectra extracted from the 3D spectrum enable the identification of 1H-1H proximity and 13C-1H connectivity. In addition, the 2D (F1/F2) 1H/13C chemical shift correlation spectrum, incorporated with proton magnetization exchange via the fp-RFDR recoupling of 1H-1H dipolar couplings, enables the measurement of proximities between 13C and even the remote non-carbon-bonded protons. The 3D experiment also gives three-spin proximities of 1H-1H-13C chains. Experimental results obtained from powder samples of L-alanine and L-histidine ṡ H2O ṡ HCl demonstrate the efficiency of the 3D experiment.

  4. Determination of glucan phosphorylation using heteronuclear 1H, 13C double and 1H, 13C, 31P triple-resonance NMR spectra.

    PubMed

    Schmieder, Peter; Nitschke, Felix; Steup, Martin; Mallow, Keven; Specker, Edgar

    2013-10-01

    Phosphorylation and dephosphorylation of starch and glycogen are important for their physicochemical properties and also their physiological functions. It is therefore desirable to reliably determine the phosphorylation sites. Heteronuclear multidimensional NMR-spectroscopy is in principle a straightforward analytical approach even for complex carbohydrate molecules. With heterogeneous samples from natural sources, however, the task becomes more difficult because a full assignment of the resonances of the carbohydrates is impossible to obtain. Here, we show that the combination of heteronuclear (1) H,(13) C and (1) H,(13) C,(31) P techniques and information derived from spectra of a set of reference compounds can lead to an unambiguous determination of the phosphorylation sites even in heterogeneous samples.

  5. BEBEtr and BUBI: J-compensated concurrent shaped pulses for 1H-13C experiments

    NASA Astrophysics Data System (ADS)

    Ehni, Sebastian; Luy, Burkhard

    2013-07-01

    Shaped pulses designed for broadband excitation, inversion and refocusing are important tools in modern NMR spectroscopy to achieve robust pulse sequences especially in heteronuclear correlation experiments. A large variety of mostly computer-optimized pulse shapes exist for different desired bandwidths, available rf-field strengths, and tolerance to B1-inhomogeneity. They are usually derived for a single spin 1/2, neglecting evolution due to J-couplings. While pulses with constant resulting phase are selfcompensated for heteronuclear coupling evolution as long as they are applied exclusively on a single nucleus, the situation changes for concurrently applied pulse shapes. Using the example of a 1H,13C two spin system, two J-compensated pulse pairs for the application in INEPT-type transfer elements were optimized: a point-to-point pulse sandwich called BEBEtr, consisting of a broadband excitation and time-reversed excitation pulse, and a combined universal rotation and point-to-point pulse pair called BUBI, which acts as a refocusing pulse on 1H and a corresponding inversion pulse on 13C. After a derivation of quality factors and optimization protocols, a theoretical and experimental comparison with conventionally derived BEBOP, BIBOP, and BURBOP-180° pulses is given. While the overall transfer efficiency of a single pulse pair is only reduced by approximately 0.1%, resulting transfer to undesired coherences is reduced by several percent. In experiments this can lead to undesired phase distortions for pairs of uncompensated pulse shapes and even differences in signal intensities of 5-10% in HSQC and up to 68% in more complex COB-HSQC experiments.

  6. (1)H-(13)C NMR-Based Profiling of Biotechnological Starch Utilization.

    PubMed

    Sundekilde, Ulrik K; Meier, Sebastian

    2016-10-04

    Starch is used in food- and nonfood applications as a renewable and degradable source of carbon and energy. Insight into the chemical detail of starch degradation remains challenging as the starch constituents amylose and amylopectin are homopolymers. We show that considerable molecular detail of starch fragmentation can be obtained from multivariate analysis of spectral features in optimized (1)H-(13)C NMR spectroscopy of starch fragments to identify relevant features that distinguish processes in starch utilization. As a case study, we compare the profiles of starch fragments in commercial beer samples. Spectroscopic profiles of homooligomeric starch fragments can be excellent indicators of process conditions. In addition, differences in the structure and composition of starch fragments have predictive value for downstream process output such as ethanol production from starch. Thus, high-resolution (1)H-(13)C NMR spectroscopic profiles of homooligomeric fragment mixtures in conjunction with chemometric methods provide a useful addition to the analytical chemistry toolbox of biotechnological starch utilization.

  7. Backbone 1H, 13C and 15N assignments of YibK and avariant containing a unique cysteine residue at C-terminus in 8 M urea-denatured states [corrected].

    PubMed

    Hsieh, Shu-Ju Micky; Mallam, Anna L; Jackson, Sophie E; Hsu, Shang-Te Danny

    2014-10-01

    YibK is a tRNA methyltransferase from Haemophilus influenzae, which forms a stable homodimer in solution and contains a deep trefoil 31 knot encompassing the C-terminal helix that threads through a long loop. It has been a model system for investigating knotted protein folding pathways. Recent data have shown that the polypeptide chain of YibK remains loosely knotted under highly denaturing conditions. Here, we report (1)H, (13)C and (15)N chemical shift assignments for YibK and its variant in the presence of 8 M urea. This work forms the basis for further analysis using NMR techniques such as paramagnetic relaxation enhancement, residual dipolar couplings and spin-relaxation dynamics analysis.

  8. Measurement of Large Dipolar Couplings of a Liquid Crystal with Terminal Phenyl Rings and Estimation of the Order Parameters.

    PubMed

    Kumar, R V Sudheer; Ramanathan, Krishna V

    2015-07-20

    NMR spectroscopy is a powerful means of studying liquid-crystalline systems at atomic resolutions. Of the many parameters that can provide information on the dynamics and order of the systems, (1) H-(13) C dipolar couplings are an important means of obtaining such information. Depending on the details of the molecular structure and the magnitude of the order parameters, the dipolar couplings can vary over a wide range of values. Thus the method employed to estimate the dipolar couplings should be capable of estimating both large and small dipolar couplings at the same time. For this purpose, we consider here a two-dimensional NMR experiment that works similar to the insensitive nuclei enhanced by polarization transfer (INEPT) experiment in solution. With the incorporation of a modification proposed earlier for experiments with low radio frequency power, the scheme is observed to enable a wide range of dipolar couplings to be estimated at the same time. We utilized this approach to obtain dipolar couplings in a liquid crystal with phenyl rings attached to either end of the molecule, and estimated its local order parameters.

  9. GFT projection NMR for efficient (1)H/ (13)C sugar spin system identification in nucleic acids.

    PubMed

    Atreya, Hanudatta S; Sathyamoorthy, Bharathwaj; Jaipuria, Garima; Beaumont, Victor; Varani, Gabriele; Szyperski, Thomas

    2012-12-01

    A newly implemented G-matrix Fourier transform (GFT) (4,3)D HC(C)CH experiment is presented in conjunction with (4,3)D HCCH to efficiently identify (1)H/(13)C sugar spin systems in (13)C labeled nucleic acids. This experiment enables rapid collection of highly resolved relay 4D HC(C)CH spectral information, that is, shift correlations of (13)C-(1)H groups separated by two carbon bonds. For RNA, (4,3)D HC(C)CH takes advantage of the comparably favorable 1'- and 3'-CH signal dispersion for complete spin system identification including 5'-CH. The (4,3)D HC(C)CH/HCCH based strategy is exemplified for the 30-nucleotide 3'-untranslated region of the pre-mRNA of human U1A protein.

  10. Experimental and calculated 1H, 13C, 15N NMR spectra of famotidine

    NASA Astrophysics Data System (ADS)

    Barańska, M.; Czarniecki, K.; Proniewicz, L. M.

    2001-05-01

    Famotidine, 3-[[[2-[(aminoiminomethyl)amino]-4-thiazolyl]methyl]thio]- N-(aminosulfonyl), is a histamine H 2-receptor blocker that has been used mainly for the treatment of peptic ulcers and the Zollinger-Ellison syndrome. Its NMR spectra in different solvents were reported earlier; however, detailed interpretation has not been done thus far. In this work, experimental 1H, 13C and 15N NMR spectra of famotidine dissolved in DMSO-d 6 are shown. The assignment of observed chemical shifts is based on quantum chemical calculation at the Hartree-Fock/6-31G ∗ level. The geometry optimization of the famotidine molecule with two internal hydrogen bonds, i.e. [N(3)-H(23)⋯N(9) and N(3)⋯H(34)-N(20)], is done by using the B3LYP method with the 6-31G ∗ basis set.

  11. 1H, 13C and 15N NMR assignments of phenazopyridine derivatives.

    PubMed

    Burgueño-Tapia, Eleuterio; Mora-Pérez, Yolanda; Morales-Ríos, Martha S; Joseph-Nathan, Pedro

    2005-03-01

    Phenazopyridine hydrochloride (1), a drug in clinical use for many decades, and some derivatives were studied by one- and two-dimensional (1)H, (13)C and (15)N NMR methodology. The assignments, combined with DFT calculations, reveal that the preferred protonation site of the drug is the pyridine ring nitrogen atom. The chemoselective acetylation of phenazopyridine (2) and its influence on the polarization of the azo nitrogen atoms were evidenced by the (15)N NMR spectra. Molecular calculations of the phenazopyridines 2-4 show that the pyridine and phenyl groups are oriented in an antiperiplanar conformation with intramolecular hydrogen bonding between the N-b atom and the C-2 amino group preserving the E-azo stereochemistry.

  12. 1H, 13C and 15N NMR assignments of a calcium-binding protein from Entamoeba histolytica.

    PubMed

    Verma, Deepshikha; Bhattacharya, Alok; Chary, Kandala V R

    2016-04-01

    We report almost complete sequence specific (1)H, (13)C and (15)N NMR assignments of a 150-residue long calmodulin-like calcium-binding protein from Entamoeba histolytica (EhCaBP6), as a prelude to its structural and functional characterization.

  13. Detection of intracellular lactate with localized diffusion { 1H- 13C}-spectroscopy in rat glioma in vivo

    NASA Astrophysics Data System (ADS)

    Pfeuffer, Josef; Lin, Joseph C.; DelaBarre, Lance; Ugurbil, Kamil; Garwood, Michael

    2005-11-01

    The aim of this study was to compare the diffusion characteristic of lactate and alanine in a brain tumor model to that of normal brain metabolites known to be mainly intracellular such as N-acetylaspartate or creatine. The diffusion of 13C-labeled metabolites was measured in vivo with localized NMR spectroscopy at 9.4 T (400 MHz) using a previously described localization and editing pulse sequence known as ACED-STEAM ('adiabatic carbon editing and decoupling'). 13C-labeled glucose was administered and the apparent diffusion coefficients of the glycolytic products, { 1H- 13C}-lactate and { 1H- 13C}-alanine, were determined in rat intracerebral 9L glioma. To obtain insights into { 1H- 13C}-lactate compartmentation (intra- versus extracellular), the pulse sequence used very large diffusion weighting (50 ms/μm 2). Multi-exponential diffusion attenuation of the lactate metabolite signals was observed. The persistence of a lactate signal at very large diffusion weighting provided direct experimental evidence of significant intracellular lactate concentration. To investigate the spatial distribution of lactate and other metabolites, 1H spectroscopic images were also acquired. Lactate and choline-containing compounds were consistently elevated in tumor tissue, but not in necrotic regions and surrounding normal-appearing brain. Overall, these findings suggest that lactate is mainly associated with tumor tissue and that within the time-frame of these experiments at least some of the glycolytic product ([ 13C] lactate) originates from an intracellular compartment.

  14. 1H, 13C, and 15N resonance assignments for Escherichia coli ytfP, a member of the broadly conserved UPF0131 protein domain family

    SciTech Connect

    Aramini, James M.; Swapna, G.V.T.; Huang, Yuanpeng; Rajan, Paranji K.; Xiao, Rong; Shastry, Ritu; Acton, Thomas; Cort, John R.; Kennedy, Michael A.; Montelione, Gaetano

    2005-11-01

    Protein ytfP from Escherichia coli (Swiss-Prot ID: YTFP-ECOLI; NESG target ID: ER111; Wunderlich et al., 2004) is a 113-residue member of the UPF0131 protein family (Pfam ID: PF03674) of unknown function. This domain family is found in organisms from all three kingdoms, archaea, eubacteria and eukaryotes. Using triple resonance NMR techniques, we have determined 97% of backbone and 91% of side chain 1H, 13C, and 15N resonance assignments. The chemical shift and 3J(HN?Ha) scalar coupling data reveal a mixed a/b topology,????????. BMRB deposit with Accession No. 6448. Reference: Wunderlich et al. (2004) Proteins, 56, 181?187.

  15. 1H, 13C, and 15N resonance assignments for the protein coded by gene locus BB0938 of Bordetella bronchiseptica

    SciTech Connect

    Rossi, Paolo; Ramelot, Theresa A.; Xiao, Rong; Ho, Chi K.; Ma, LiChung; Acton, Thomas; Kennedy, Michael A.; Montelione, Gaetano

    2005-11-01

    The product of gene locus BB0938 from Bordetella bronchiseptica (Swiss-Prot ID: Q7WNU7-BORBR; NESG target ID: BoR11; Wunderlich et al., 2004; Pfam ID: PF03476) is a 128-residue protein of unknown function. This broadly conserved protein family is found in eubacteria and eukaryotes. Using triple resonance NMR techniques, we have determined 98% of backbone and 94% of side chain 1H, 13C, and 15N resonance assignments. The chemical shift and 3J(HN?Ha) scalar coupling data reveal a b topology with a seven-residue helical insert, ??????????. BMRB deposit with accession number 6693. Reference: Wunderlich et al. (2004) Proteins, 56, 181?187.

  16. Pursuing structure in microcrystalline solids with independent molecules in the unit cell using 1H- 13C correlation data

    NASA Astrophysics Data System (ADS)

    Harper, James K.; Strohmeier, Mark; Grant, David M.

    2007-11-01

    The 1H- 13C solid-state NMR heteronuclear correlation (HETCOR) experiment is demonstrated to provide shift assignments in certain powders that have two or more structurally independent molecules in the unit cell (i.e. multiple molecules per asymmetric unit). Although this class of solids is often difficult to characterize using other methods, HETCOR provides both the conventional assignment of shifts to molecular positions and associates many resonances with specific molecules in the asymmetric unit. Such assignments facilitate conformational characterization of the individual molecules of the asymmetric unit and the first such characterization solely from solid-state NMR data is described. HETCOR offers advantages in sensitivity over prior methods that assign resonances in the asymmetric unit by 13C- 13C correlations and therefore allows shorter average analysis times in natural abundance materials. The 1H- 13C analysis is demonstrated first on materials with known shift assignments from INADEQUATE data (santonin and Ca(OAc) 2 phase I) to verify the technique and subsequently is extended to a pair of unknown solids: (+)-catechin and Ca(OAc) 2 phase II. Sufficient sensitivity and resolution is achieved in the spectra to provide assignments to one of the specific molecules of the asymmetric unit at over 54% of the sites.

  17. 1H, 13C and 15N chemical shift assignments of the thioredoxin from the obligate anaerobe Desulfovibrio vulgaris Hildenborough.

    PubMed

    Garcin, Edwige B; Bornet, Olivier; Pieulle, Laetitia; Guerlesquin, Françoise; Sebban-Kreuzer, Corinne

    2011-10-01

    Thioredoxins are ubiquitous key antioxidant enzymes which play an essential role in cell defense against oxidative stress. They maintain the redox homeostasis owing to the regulation of thiol-disulfide exchange. In the present paper, we report the full resonance assignments of (1)H, (13)C and (15)N atoms for the reduced and oxidized forms of Desulfovibrio vulgaris Hildenborough thioredoxin 1 (Trx1). 2D and 3D heteronuclear NMR experiments were performed using uniformly (15)N-, (13)C-labelled Trx1. Chemical shifts of 97% of the backbone and 90% of the side chain atoms were obtained for the oxidized and reduced form (BMRB deposits with accession number 17299 and 17300, respectively).

  18. (1)H, (13)C, and (15)N resonance assignments for the pro-inflammatory cytokine interleukin-36α.

    PubMed

    Goradia, Nishit; Wißbrock, Amelie; Wiedemann, Christoph; Bordusa, Frank; Ramachandran, Ramadurai; Imhof, Diana; Ohlenschläger, Oliver

    2016-10-01

    Interleukin-36α (IL-36α) is a recently characterised member of the interleukin-1 superfamily. It is involved in the pathogenesis of inflammatory arthritis in one third of psoriasis patients. By binding of IL-36α to its receptor IL-36R via the NF-κB pathway other cytokines involved in inflammatory and apoptotic cascade are activated. The efficacy of complex formation is controlled by N-terminal processing. To obtain a more detailed view on the structure function relationship we performed a heteronuclear multidimensional NMR investigation and here report the (1)H, (13)C, and (15)N resonance assignments for the backbone and side chain nuclei of the pro-inflammatory cytokine interleukin-36α.

  19. Inverse nonionic microemulsion studied by means of 1H, 13C, and PGSTE NMR during silica nanoparticle synthesis.

    PubMed

    Asaro, Fioretta; Benedetti, Alvise; Savko, Nina; Pellizer, Giorgio

    2009-03-03

    The soluble species present in the reaction mixture that leads to silica nanoparticle production through the base catalyzed hydrolysis of tetraethyl orthosilicate (TEOS) and the successive condensation were investigated in situ, under the actual synthesis conditions, by means of 1H, 13C, and 29Si NMR spectroscopy. The two former nuclei, owing to higher sensitivity and their presence both in the reacting species and in the constituents of the W/O microemulsion (cyclohexane-igepal-CA-520-concentrated ammonia solution) afforded insight into the inverse microemulsion and allowed us to assess the kinetic rate of the hydrolysis step. It was verified that the microemulsion microstructure is maintained during the reaction. The characterization of the final nanoparticles was carried out by means of transmission electron microscopy (TEM). Special attention was paid to the reaction medium, and an extended assignment of the 1H and 13C resonances of the surfactant headgroup is reported together with the discussion of the changes they undergo due to the environmental modifications induced by transition from cyclohexane solution to W/O microemulsion and further to NH3 containing W/O microemulsion. The self-diffusion coefficient measurements revealed that NH3 exchanges among the inverse micelles diffusing through cyclohexane and confirmed that the preferred localization for ethanol, a byproduct of the reaction, is the bulk oil.

  20. Model-free estimation of the effective correlation time for C-H bond reorientation in amphiphilic bilayers: 1H-13C solid-state NMR and MD simulations

    NASA Astrophysics Data System (ADS)

    Ferreira, Tiago Mendes; Ollila, O. H. Samuli; Pigliapochi, Roberta; Dabkowska, Aleksandra P.; Topgaard, Daniel

    2015-01-01

    Molecular dynamics (MD) simulations give atomically detailed information on structure and dynamics in amphiphilic bilayer systems on timescales up to about 1 μs. The reorientational dynamics of the C-H bonds is conventionally verified by measurements of 13C or 2H nuclear magnetic resonance (NMR) longitudinal relaxation rates R1, which are more sensitive to motional processes with correlation times close to the inverse Larmor frequency, typically around 1-10 ns on standard NMR instrumentation, and are thus less sensitive to the 10-1000 ns timescale motion that can be observed in the MD simulations. We propose an experimental procedure for atomically resolved model-free estimation of the C-H bond effective reorientational correlation time τe, which includes contributions from the entire range of all-atom MD timescales and that can be calculated directly from the MD trajectories. The approach is based on measurements of 13C R1 and R1ρ relaxation rates, as well as 1H-13C dipolar couplings, and is applicable to anisotropic liquid crystalline lipid or surfactant systems using a conventional solid-state NMR spectrometer and samples with natural isotopic composition. The procedure is demonstrated on a fully hydrated lamellar phase of 1-palmitoyl-2-oleoyl-phosphatidylcholine, yielding values of τe from 0.1 ns for the methyl groups in the choline moiety and at the end of the acyl chains to 3 ns for the g1 methylene group of the glycerol backbone. MD simulations performed with a widely used united-atom force-field reproduce the τe-profile of the major part of the acyl chains but underestimate the dynamics of the glycerol backbone and adjacent molecular segments. The measurement of experimental τe-profiles can be used to study subtle effects on C-H bond reorientational motions in anisotropic liquid crystals, as well as to validate the C-H bond reorientation dynamics predicted in MD simulations of amphiphilic bilayers such as lipid membranes.

  1. Estimation of procyanidin/prodelphinidin and cis/trans flavanol ratios of condensed tannin fractions by 1H-13C HSQC NMR spectroscopy: Correlation with thiolysis

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Integration of cross-peak contours of H/C-2’,6’ signals from prodelphinidin (PD) and of H/C-6’ signals from procyanidin (PC) units in 1H-13C HSQC nuclear magnetic resonance (NMR) spectra of condensed tannins yielded nuclei-adjusted PC/PD estimates that were highly correlated with PC/PD ratios obtain...

  2. 1H-13C HSQC NMR spectroscopy for estimating procyanidin/prodelphinidin and cis/trans flavan-3-ol ratios of condensed tannin samples: correlation with thiolysis

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Studies with a diverse array of 22 condensed tannin (CT) fractions from 9 plant species demonstrated that procyanidin/prodelphinidin (PC/PD) and cis/trans flavan-3-ol ratios can be appraised by 1H-13C HSQC NMR. The method was developed from fractions containing 44 to ~100% CT, PC/PD ratios ranging f...

  3. Resolution-optimized NMR measurement of (1)D(CH), (1)D(CC) and (2)D(CH) residual dipolar couplings in nucleic acid bases.

    PubMed

    Boisbouvier, Jérôme; Bryce, David L; O'neil-Cabello, Erin; Nikonowicz, Edward P; Bax, Ad

    2004-11-01

    New methods are described for accurate measurement of multiple residual dipolar couplings in nucleic acid bases. The methods use TROSY-type pulse sequences for optimizing resolution and sensitivity, and rely on the E.COSY principle to measure the relatively small two-bond (2)D(CH) couplings at high precision. Measurements are demonstrated for a 24-nt stem-loop RNA sequence, uniformly enriched in (13)C, and aligned in Pf1. The recently described pseudo-3D method is used to provide homonuclear (1)H-(1)H decoupling, which minimizes cross-correlation effects and optimizes resolution. Up to seven (1)H-(13)C and (13)C-(13)C couplings are measured for pyrimidines (U and C), including (1)D(C5H5), (1)D(C6H6), (2)D(C5H6), (2)D(C6H5), (1)D(C5C4), (1)D(C5C6), and (2)D(C4H5). For adenine, four base couplings ((1)D(C2H2), (1)D(C8H8), (1)D(C4C5), and (1)D(C5C6)) are readily measured whereas for guanine only three couplings are accessible at high relative accuracy ((1)D(C8H8), (1)D(C4C5), and (1)D(C5C6)). Only three dipolar couplings are linearly independent in planar structures such as nucleic acid bases, permitting cross validation of the data and evaluation of their accuracies. For the vast majority of dipolar couplings, the error is found to be less than +/-3% of their possible range, indicating that the measurement accuracy is not limiting when using these couplings as restraints in structure calculations. Reported isotropic values of the one- and two-bond J couplings cluster very tightly for each type of nucleotide.

  4. Simultaneous quantification and identification of individual chemicals in metabolite mixtures by two-dimensional extrapolated time-zero (1)H-(13)C HSQC (HSQC(0)).

    PubMed

    Hu, Kaifeng; Westler, William M; Markley, John L

    2011-02-16

    Quantitative one-dimensional (1D) (1)H NMR spectroscopy is a useful tool for determining metabolite concentrations because of the direct proportionality of signal intensity to the quantity of analyte. However, severe signal overlap in 1D (1)H NMR spectra of complex metabolite mixtures hinders accurate quantification. Extension of 1D (1)H to 2D (1)H-(13)C HSQC leads to the dispersion of peaks along the (13)C dimension and greatly alleviates peak overlapping. Although peaks are better resolved in 2D (1)H-(13)C HSQC than in 1D (1)H NMR spectra, the simple proportionality of cross peaks to the quantity of individual metabolites is lost by resonance-specific signal attenuation during the coherence transfer periods. As a result, peaks for individual metabolites usually are quantified by reference to calibration data collected from samples of known concentration. We show here that data from a series of HSQC spectra acquired with incremented repetition times (the time between the end of the first (1)H excitation pulse to the beginning of data acquisition) can be extrapolated back to zero time to yield a time-zero 2D (1)H-(13)C HSQC spectrum (HSQC(0)) in which signal intensities are proportional to concentrations of individual metabolites. Relative concentrations determined from cross peak intensities can be converted to absolute concentrations by reference to an internal standard of known concentration. Clustering of the HSQC(0) cross peaks by their normalized intensities identifies those corresponding to metabolites present at a given concentration, and this information can assist in assigning these peaks to specific compounds. The concentration measurement for an individual metabolite can be improved by averaging the intensities of multiple, nonoverlapping cross peaks assigned to that metabolite.

  5. A 1H, 13C and 15N NMR study in solution and in the solid state of six N-substituted pyrazoles and indazoles.

    PubMed

    Claramunt, Rosa M; Santa María, M Dolores; Sanz, Dionisia; Alkorta, Ibon; Elguero, José

    2006-05-01

    Three N-substituted pyrazoles and three N-substituted indazoles [1-(4-nitrophenyl)-3,5-dimethylpyrazole (1), 1-(2,4-dinitrophenyl)-3,5-dimethylpyrazole (2), 1-tosyl-pyrazole (3), 1-p-chlorobenzoylindazole (4), 1-tosylinda-zole (5) and 2-(2-hydroxy-2-phenylethyl)-indazole (6)] have been studied by NMR spectroscopy in solution (1H, 13C, 15N) and in the solid state (13C, 15N). The chemical shifts have been compared with GIAO/DFT calculated absolute shieldings. Some discrepancies have been analyzed.

  6. Phosphatidylcholine and cholesteryl esters identify the infiltrating behaviour of a clear cell renal carcinoma: 1H, 13C and 31P MRS evidence.

    PubMed

    Tugnoli, V; Poerio, A; Tosi, M R

    2004-08-01

    This study presents a multinuclear (1H, 13C and 31P) magnetic resonance spectroscopy characterization of the total lipid fraction extracted from different regions of a human kidney affected by a clear cell renal carcinoma. It was thus possible to demonstrate that cholesteryl esters and phosphatidylcholine are markers of the tumor infiltration, histologically confirmed, in the kidney medulla. The tumor tissue contains twice the amount of phosphatidylcholine compared to normal cortex. The results appear relevant in light of new clinical applications based on the biochemical composition of human tissues.

  7. Measurement of small scalar and dipolar couplings in purine and pyrimidine bases.

    PubMed

    Zídek, L; Wu, H; Feigon, J; Sklenár, V

    2001-10-01

    A suite of spin-state-selective excitation (S3E) NMR experiments for the measurements of small one-bond (13C-13C, 15N-13C) and two-bond (1H-13C, 1H-15N) coupling constants in 13C,15N labeled purine and pyrimidine bases is presented. The incorporation of band-selective shaped pulses, elimination of the cross talk between alpha and beta sub-spectra, and accuracy and precision of the proposed approach are discussed. Merits of using S3E rather than alpha/beta-half-filter are demonstrated using results obtained on isotopically labeled DNA oligonucleotides.

  8. Protonation of carbon single-walled nanotubes studied using 13C and 1H-13C cross polarization nuclear magnetic resonance and Raman spectroscopies.

    PubMed

    Engtrakul, Chaiwat; Davis, Mark F; Gennett, Thomas; Dillon, Anne C; Jones, Kim M; Heben, Michael J

    2005-12-14

    The reversible protonation of carbon single-walled nanotubes (SWNTs) in sulfuric acid and Nafion was investigated using solid-state nuclear magnetic resonance (NMR) and Raman spectroscopies. Magic-angle spinning (MAS) was used to obtain high-resolution 13C and 1H-13C cross polarization (CP) NMR spectra. The 13C NMR chemical shifts are reported for bulk SWNTs, H2SO4-treated SWNTs, SWNT-Nafion polymer composites, SWNT-AQ55 polymer composites, and SWNTs in contact with water. Protonation occurs without irreversible oxidation of the nanotube substrate via a charge-transfer process. This is the first report of a chemically induced change in a SWNT 13C resonance brought about by a reversible interaction with an acidic proton, providing additional evidence that carbon nanotubes behave as weak bases. Cross polarization was found to be a powerful technique for providing an additional contrast mechanism for studying nanotubes in contact with other chemical species. The CP studies confirmed polarization transfer from nearby protons to nanotube carbon atoms. The CP technique was also applied to investigate water adsorbed on carbon nanotube surfaces. Finally, the degree of bundling of the SWNTs in Nafion films was probed with the 1H-13C CP-MAS technique.

  9. Modulated magnetization depth profile in dipolarly coupled magnetic multilayers

    SciTech Connect

    Bedanta, S.; Petracic, O.; Kleemann, W.; Kentzinger, E.; Ruecker, U.; Brueckel, Th.; Paul, A.; Cardoso, S.; Freitas, P. P.

    2006-08-01

    Polarized neutron reflectivity (PNR) and magnetometry studies have been performed on the metal-insulator multilayer [Co{sub 80}Fe{sub 20}(1.6 nm)/Al{sub 2}O{sub 3}(3 nm)]{sub 9} which exhibits dominant dipolar coupling between the ferromagnetic layers. Our PNR measurements at the coercive field reveal a novel and unexpected magnetization state of the sample, exhibiting an oscillating magnetization depth profile from CoFe layer to CoFe layer with a period of five bilayers along the multilayer stack. With the help of micromagnetic simulations we demonstrate that competition between long- and short-ranged dipolar interactions apparently gives rise to this unprecedented phenomenon.

  10. Structure and equilibria of Ca 2+-complexes of glucose and sorbitol from multinuclear ( 1H, 13C and 43Ca) NMR measurements supplemented with molecular modelling calculations

    NASA Astrophysics Data System (ADS)

    Pallagi, A.; Dudás, Cs.; Csendes, Z.; Forgó, P.; Pálinkó, I.; Sipos, P.

    2011-05-01

    Ca 2+-complexation of D-glucose and D-sorbitol have been investigated with the aid of multinuclear ( 1H, 13C and 43Ca) NMR spectroscopy and ab initio quantum chemical calculations. Formation constants of the forming 1:1 complexes have been estimated from one-dimensional 13C NMR spectra obtained at constant ionic strength (1 M NaCl). Binding sites were identified from 2D 1H- 43Ca NMR spectra. 2D NMR measurements and ab initio calculations indicated that Ca 2+ ions were bound in a tridentate manner via the glycosidic OH, the ethereal oxygen in the ring and the OH on the terminal carbon for the α- and β-anomers of glucose and for sorbitol simultaneous binding of four hydroxide moieties (C1, C2, C4 and C6) was suggested.

  11. (1)H, (13)C and (15)N resonance assignments of the RodA hydrophobin from the opportunistic pathogen Aspergillus fumigatus.

    PubMed

    Pille, Ariane; Kwan, Ann H; Cheung, Ivan; Hampsey, Matthew; Aimanianda, Vishukumar; Delepierre, Muriel; Latge, Jean-Paul; Sunde, Margaret; Guijarro, J Iñaki

    2015-04-01

    Hydrophobins are fungal proteins characterised by their amphipathic properties and an idiosyncratic pattern of eight cysteine residues involved in four disulphide bridges. The soluble form of these proteins spontaneously self-assembles at hydrophobic/hydrophilic interfaces to form an amphipathic monolayer. The RodA hydrophobin of the opportunistic pathogen Aspergillus fumigatus forms an amyloid layer with a rodlet morphology that covers the surface of fungal spores. This rodlet layer bestows hydrophobicity to the spores facilitating their dispersal in the air and rendering the conidia inert relative to the human immune system. As a first step in the analysis of the solution structure and self-association of RodA, we report the (1)H, (13)C and (15)N resonance assignments of the soluble monomeric form of RodA.

  12. Analytical polarization and coherence transfer functions for three dipolar coupled spins 12.

    PubMed

    Luy, B; Glaser, S J

    2000-02-01

    Analytical polarization and coherence transfer functions are presented for a spin system consisting of three dipolar coupled homonuclear spins 12 under energy matched conditions. Based on these transfer functions, optimal durations of Hartmann-Hahn mixing periods can be determined for arbitrary dipolar coupling constants D(12), D(13), and D(23). In addition, the dependence of the transfer efficiency on the relative size of the dipolar coupling constants is illustrated.

  13. Syntheses, structures, and 1H, 13C{1H} and 119Sn{1H} NMR chemical shifts of a family of trimethyltin alkoxide, amide, halide and cyclopentadienyl compounds

    DOE PAGES

    Lichtscheidl, Alejandro G.; Janicke, Michael T.; Scott, Brian L.; ...

    2015-08-21

    The synthesis and full characterization, including Nuclear Magnetic Resonance (NMR) data (1H, 13C{1H} and 119Sn{1H}), for a series of Me3SnX (X = O-2,6-tBu2C6H3 (1), (Me3Sn)N(2,6-iPr2C6H3) (3), NH-2,4,6-tBu3C6H2 (4), N(SiMe3)2 (5), NEt2, C5Me5 (6), Cl, Br, I, and SnMe3) compounds in benzene-d6, toluene-d8, dichloromethane-d2, chloroform-d1, acetonitrile-d3, and tetrahydrofuran-d8 are reported. The X-ray crystal structures of Me3Sn(O-2,6-tBu2C6H3) (1), Me3Sn(O-2,6-iPr2C6H3) (2), and (Me3Sn)(NH-2,4,6-tBu3C6H2) (4) are also presented. As a result, these compiled data complement existing literature data and ease the characterization of these compounds by routine NMR experiments.

  14. Near-complete 1H, 13C, 15N resonance assignments of dimethylsulfoxide-denatured TGFBIp FAS1-4 A546T.

    PubMed

    Kulminskaya, Natalia V; Yoshimura, Yuichi; Runager, Kasper; Sørensen, Charlotte S; Bjerring, Morten; Andreasen, Maria; Otzen, Daniel E; Enghild, Jan J; Nielsen, Niels Chr; Mulder, Frans A A

    2016-04-01

    The transforming growth factor beta induced protein (TGFBIp) is a major protein component of the human cornea. Mutations occurring in TGFBIp may cause corneal dystrophies, which ultimately lead to loss of vision. The majority of the disease-causing mutations are located in the C-terminal domain of TGFBIp, referred as the fourth fascilin-1 (FAS1-4) domain. In the present study the FAS1-4 Ala546Thr, a mutation that causes lattice corneal dystrophy, was investigated in dimethylsulfoxide using liquid-state NMR spectroscopy, to enable H/D exchange strategies for identification of the core formed in mature fibrils. Isotope-labeled fibrillated FAS1-4 A546T was dissolved in a ternary mixture 95/4/1 v/v/v% dimethylsulfoxide/water/trifluoroacetic acid, to obtain and assign a reference 2D (1)H-(15)N HSQC spectrum for the H/D exchange analysis. Here, we report the near-complete assignments of backbone and aliphatic side chain (1)H, (13)C and (15)N resonances for unfolded FAS1-4 A546T at 25 °C.

  15. (1)H, (13)C and (15)N resonance assignments and secondary structure analysis of translation initiation factor 1 from Pseudomonas aeruginosa.

    PubMed

    Bernal, Alejandra; Hu, Yanmei; Palmer, Stephanie O; Silva, Aaron; Bullard, James; Zhang, Yonghong

    2016-10-01

    Pseudomonas aeruginosa is a Gram-negative opportunistic pathogen and a primary cause of infection in humans. P. aeruginosa can acquire resistance against multiple groups of antimicrobial agents, including β-lactams, aminoglycosides and fluoroquinolones, and multidrug resistance is increasing in this organism which makes treatment of the infections difficult and expensive. This has led to the unmet need for discovery of new compounds distinctly different from present antimicrobials. Protein synthesis is an essential metabolic process and a validated target for the development of new antibiotics. Translation initiation factor 1 from P. aeruginosa (Pa-IF1) is the smallest of the three initiation factors that acts to establish the 30S initiation complex to initiate translation during protein biosynthesis, and its structure is unknown. Here we report the (1)H, (13)C and (15)N chemical shift assignments of Pa-IF1 as the basis for NMR structure determination and interaction studies. Secondary structure analyses deduced from the NMR chemical shift data have identified five β-strands with an unusually extended β-strand at the C-terminal end of the protein and one short α-helix arranged in the sequential order β1-β2-β3-α1-β4-β5. This is further supported by (15)N-{(1)H} hetero NOEs. These secondary structure elements suggest the Pa-IF1 adopts the typical β-barrel structure and is composed of an oligomer-binding motif.

  16. 1H, 13C and 15N resonance assignments and secondary structure analysis of translation initiation factor 1 from Pseudomonas aeruginosa

    PubMed Central

    Bernal, Alejandra; Hu, Yanmei; Palmer, Stephanie O.; Silva, Aaron; Bullard, James; Zhang, Yonghong

    2016-01-01

    Pseudomonas aeruginosa is a Gram-negative opportunistic pathogen and a primary cause of infection in humans. P. aeruginosa can acquire resistance against multiple groups of antimicrobial agents, including β-lactams, aminoglycosides and fluoroquinolones, and multidrug resistance is increasing in this organism which makes treatment of the infections difficult and expensive. This has led to the unmet need for discovery of new compounds distinctly different from present antimicrobials. Protein synthesis is an essential metabolic process and a validated target for the development of new antibiotics. Translation initiation factor 1 from P. aeruginosa (Pa-IF1) is the smallest of the three initiation factors that acts to establish the 30S initiation complex to initiate translation during protein biosynthesis, and its structure is unknown. Here we report the 1H, 13C and 15N chemical shift assignments of Pa-IF1 as the basis for NMR structure determination and interaction studies. Secondary structure analyses deduced from the NMR chemical shift data have identified five β-strands with an unusually extended β-strand at the C-terminal end of the protein and one short α-helix arranged in the sequential order β1–β2–β3–α1–β4–β5. This is further supported by 15N–{1H} hetero NOEs. These secondary structure elements suggest the Pa-IF1 adopts the typical β-barrel structure and is composed of an oligomer-binding motif. PMID:26983940

  17. Probing crystal packing of uniformly (13)C-enriched powder samples using homonuclear dipolar coupling measurements.

    PubMed

    Mollica, Giulia; Dekhil, Myriam; Ziarelli, Fabio; Thureau, Pierre; Viel, Stéphane

    2015-02-01

    The relationship between the crystal packing of powder samples and long-range (13)C-(13)C homonuclear dipolar couplings is presented and illustrated for the case of uniformly (13)C-enriched L-alanine and L-histidine·HCl·H2O. Dipolar coupling measurement is based on the partial reintroduction of dipolar interactions by spinning the sample slightly off-magic-angle, while the coupling of interest for a given spin pair is isolated with a frequency-selective pulse. A cost function is used to correlate the so-derived dipolar couplings to trial crystal structures of the samples under study. This procedure allowed for the investigation of the l-alanine space group and L-histidine·HCl·H2O space group and unit-cell parameters.

  18. Performance of RINEPT is amplified by dipolar couplings under ultrafast MAS conditions.

    PubMed

    Zhang, Rongchun; Ramamoorthy, Ayyalusamy

    2014-06-01

    The refocused insensitive nuclei enhanced by polarization transfer (RINEPT) technique is commonly used for heteronuclear polarization transfer in solution and solid-state NMR spectroscopy. Suppression of dipolar couplings, either by fast molecular motions in solution or by a combination of MAS and multiple pulse sequences in solids, enables the polarization transfer via scalar couplings. However, the presence of unsuppressed dipolar couplings could alter the functioning of RINEPT, particularly under fast/ultrafast MAS conditions. In this study, we demonstrate, through experiments on rigid solids complemented by numerical simulations, that the polarization transfer efficiency of RINEPT is dependent on the MAS frequency. In addition, we show that heteronuclear dipolar coupling is the dominant factor in the polarization transfer, which is strengthened by the presence of (1)H-(1)H dipolar couplings. In fact, the simultaneous presence of homonuclear and heteronuclear dipolar couplings is the premise for the polarization transfer by RINEPT, whereas the scalar coupling plays an insignificant role under ultrafast MAS conditions on rigid solids. Our results additionally reveal that the polarization transfer efficiency decreases with the increasing duration of RF pulses used in the RINEPT sequence.

  19. Superposition of scalar and residual dipolar couplings: analytical transfer functions for three spins 1/2 under cylindrical mixing conditions.

    PubMed

    Luy, B; Glaser, S J

    2001-01-01

    The superposition of scalar and residual dipolar couplings gives rise to so-called cylindrical mixing Hamiltonians in dipolar coupling spectroscopy. General analytical polarization and coherence transfer functions are presented for three cylindrically coupled spins 12 under energy-matched conditions. In addition, the transfer efficiency is analyzed as a function of the relative coupling constants for characteristic special cases.

  20. Two-component dipolar Bose-Einstein condensate in concentrically coupled annular traps

    PubMed Central

    Zhang, Xiao-Fei; Han, Wei; Wen, Lin; Zhang, Peng; Dong, Rui-Fang; Chang, Hong; Zhang, Shou-Gang

    2015-01-01

    Dipolar Bosonic atoms confined in external potentials open up new avenues for quantum-state manipulation and will contribute to the design and exploration of novel functional materials. Here we investigate the ground-state and rotational properties of a rotating two-component dipolar Bose-Einstein condensate, which consists of both dipolar bosonic atoms with magnetic dipole moments aligned vertically to the condensate and one without dipole moments, confined in concentrically coupled annular traps. For the nonrotational case, it is found that the tunable dipolar interaction can be used to control the location of each component between the inner and outer rings, and to induce the desired ground-state phase. Under finite rotation, it is shown that there exists a critical value of rotational frequency for the nondipolar case, above which vortex state can form at the trap center, and the related vortex structures depend strongly on the rotational frequency. For the dipolar case, it is found that various ground-state phases and the related vortex structures, such as polygonal vortex clusters and vortex necklaces, can be obtained via a proper choice of the dipolar interaction and rotational frequency. Finally, we also study and discuss the formation process of such vortex structures. PMID:25731962

  1. Review: Use of residual dipolar couplings to determine the structure of carbohydrates.

    PubMed

    Canales, A; Jiménez-Barbero, J; Martín-Pastor, M

    2012-12-01

    Solution nuclear magnetic resonance spectroscopy is especially useful in the carbohydrate field. The measurement of residual dipolar couplings provides long-range structural information, a valuable complement for the structural study of carbohydrates either in its free form or in the bound state to proteins. They permit to deduce the geometry and the flexibility of the glycosidic linkages, which have a major influence on the conformation of carbohydrates and their overall shape. This article reviews the current application of the residual dipolar couplings methodology to carbohydrates.

  2. Structural study of (±) ethyl 3-acyloxy-1-azabicyclo[2.2.2]octane-3-carboxylates by 1H, 13C NMR spectroscopy, X-ray crystallography and DFT calculations

    NASA Astrophysics Data System (ADS)

    Arias-Pérez, M. S.; Cosme, A.; Gálvez, E.; Morreale, A.; Sanz-Aparicio, J.; Fonseca, I.

    2006-05-01

    1H, 13C NMR spectroscopy and DFT/B3LYP calculations were applied to investigate the conformational preferences of the ethoxycarbonyl and acyloxy groups of some α-acyloxyesters derived from (±) ethyl 3-hydroxy-1-azabicyclo[2.2.2]octane-3-carboxylate. The crystal structure of (±) ethyl 3-diphenylacetoxy-1-azabicyclo[2.2.2]octane-3-carboxylate was determined by X-ray diffraction. To correlate between calculated conformations and the structure in solution, NMR chemical shifts calculations were also performed using the GIAO approach. It has been found that the lowest energetic conformer computed gives the greatest correspondance with experimental solution and solid state data.

  3. Coupled states of electromagnetic fields with magnetic-dipolar-mode vortices: Magnetic-dipolar-mode vortex polaritons

    SciTech Connect

    Kamenetskii, E. O.; Joffe, R.; Shavit, R.

    2011-08-15

    A coupled state of an electromagnetic field with an electric or magnetic dipole-carrying excitation is well known as a polariton. Such a state is the result of the mixing of a photon with the excitation of a material. The most discussed types of polaritons are phonon polaritons, exciton polaritons, and surface-plasmon polaritons. Recently, it was shown that, in microwaves, strong magnon-photon coupling can be achieved due to magnetic-dipolar-mode (MDM) vortices in small thin-film ferrite disks. These coupled states can be specified as MDM-vortex polaritons. In this paper, we study the properties of MDM-vortex polaritons. We numerically analyze a variety of topological structures of MDM-vortex polaritons. Based on analytical studies of the MDM spectra, we give theoretical insight into a possible origin for the observed topological properties of the fields. We show that the MDM-vortex polaritons are characterized by helical-mode resonances. We demonstrate the PT-invariance properties of MDM oscillations in a quasi-two-dimensional ferrite disk and show that such properties play an essential role in the physics of the observed topologically distinctive states with the localization or cloaking of electromagnetic fields. We may suppose that one of the useful implementations of the MDM-vortex polaritons could be microwave metamaterial structures and microwave near-field sensors.

  4. Coupled states of electromagnetic fields with magnetic-dipolar-mode vortices: Magnetic-dipolar-mode vortex polaritons

    NASA Astrophysics Data System (ADS)

    Kamenetskii, E. O.; Joffe, R.; Shavit, R.

    2011-08-01

    A coupled state of an electromagnetic field with an electric or magnetic dipole-carrying excitation is well known as a polariton. Such a state is the result of the mixing of a photon with the excitation of a material. The most discussed types of polaritons are phonon polaritons, exciton polaritons, and surface-plasmon polaritons. Recently, it was shown that, in microwaves, strong magnon-photon coupling can be achieved due to magnetic-dipolar-mode (MDM) vortices in small thin-film ferrite disks. These coupled states can be specified as MDM-vortex polaritons. In this paper, we study the properties of MDM-vortex polaritons. We numerically analyze a variety of topological structures of MDM-vortex polaritons. Based on analytical studies of the MDM spectra, we give theoretical insight into a possible origin for the observed topological properties of the fields. We show that the MDM-vortex polaritons are characterized by helical-mode resonances. We demonstrate the PT-invariance properties of MDM oscillations in a quasi-two-dimensional ferrite disk and show that such properties play an essential role in the physics of the observed topologically distinctive states with the localization or cloaking of electromagnetic fields. We may suppose that one of the useful implementations of the MDM-vortex polaritons could be microwave metamaterial structures and microwave near-field sensors.

  5. Determination of residual dipolar couplings in homonuclear MOCCA-SIAM experiments.

    PubMed

    Möglich, Andreas; Wenzler, Michael; Kramer, Frank; Glaser, Steffen J; Brunner, Eike

    2002-07-01

    In solutions with partial molecular alignment, anisotropic magnetic interactions such as the chemical shift anisotropy, the electric quadrupole interaction, and the magnetic dipole-dipole interaction are no longer averaged out to zero in contrast to isotropic solutions. The resulting residual anisotropic magnetic interactions are increasingly used in biological NMR studies for the determination of 3D structures of proteins and other biomolecules. In the present paper we propose a new approach allowing the measurement of residual HN-H(alpha) dipolar couplings of non-isotope enriched proteins based on the application of the MOCCA-SIAM experiment. This experiment allows the measurement of homonuclear coupling constants with an accuracy of ca. +/- 0.2 Hz and is therefore particularly well suited to determine residual dipolar couplings at relatively low degrees of molecular orientation. The agreement between experimentally determined residual HN-H(alpha) couplings and calculated values is demonstrated for BPTI.

  6. Coherence Transfer in Dipolar-Coupled Homonuclear Spin Systems in Solids Rotating at the Magic Angle

    NASA Astrophysics Data System (ADS)

    Weintraub, O.; Vega, S.; Hoelger, C.; Limbach, H. H.

    Two routes for the exploitation of the t-SEDRA pulse scheme, which induces coherence transfer in dipolar-coupled homonuclear spin systems in rotating samples, are demonstrated and discussed. This sequence is utilized to deduce intramolecular connectivities by creating an initial coherence of one spin only, applying the t-SEDRA sequence, and monitoring the signal enhancement of the coupled spin. Probing the signal amplitude variations of the two spins and comparing them to simulations can also yield molecular distances. Using 2D spectroscopy, t-SEDRA can also be utilized to establish spin correlations. In this case, the t-SEDRA sequence is applied during the mixing time of a 2D dipolar-correlation experiment. These two approaches are demonstrated by performing 15N CPMAS NMR experiments on a 15N-doubly labeled sample of 3(5)-methyl-5(3)-phenylpyrazole.

  7. Ionic liquid crystals as alignment medium to measure residual dipolar couplings for carbohydrates.

    PubMed

    Dama, Murali; Berger, Stefan

    2013-08-09

    Ionic liquids consisting of N-dodecyl-N-methyl pyrrolidinium bromide [C12MPB] in a mixture with D2O, decanol, and DMSO were for the first time found to give anisotropic molecular alignment in magnetic fields and are useful to measure residual dipolar couplings (RDCs) from polar analytes, for example, glucose. The system shows less quadrupolar splitting of the deuterated solvent signal compared with other liquid crystal systems and hence less undesired line broadening.

  8. Collection of NMR Scalar and Residual Dipolar Couplings Using a Single Experiment.

    PubMed

    Gil-Silva, Leandro F; Santamaría-Fernández, Raquel; Navarro-Vázquez, Armando; Gil, Roberto R

    2016-01-11

    A new DMSO-compatible aligning gel based on cross-linked poly(2-hydroxylethyl methacrylate) (poly-HEMA) has been developed. Due to a significant difference in bulk magnetic susceptibility between the DMSO inside and outside the gel, it is possible to simultaneously collect isotropic and anisotropic NMR data, such as residual dipolar couplings (RDC), in the same NMR tube. RDC-assisted structural analysis of menthol and the alkaloid retrorsine is reported as proof of concept.

  9. Direct Observation of Field and Temperature Induced Domain Replication in Dipolar Coupled Perpendicular Anisotropy Films

    SciTech Connect

    Hauet, T.; Gunther, C.M.; Pfau, B.; Eisebitt, S.; Fischer, P.; Rick, R. L.; Thiele, J.-U.; Hellwig, O.; Schabes, M.E.

    2007-07-01

    Dipolar interactions in a soft/Pd/hard [CoNi/Pd]{sub 30}/Pd/[Co/Pd]{sub 20} multilayer system, where a thick Pd layer between two ferromagnetic units prevents direct exchange coupling, are directly revealed by combining magnetometry and state-of-the-art layer resolving soft x-ray imaging techniques with sub-100-nm spatial resolution. The domains forming in the soft layer during external magnetic field reversal are found to match the domains previously trapped in the hard layer. The low Curie temperature of the soft layer allows varying its intrinsic parameters via temperature and thus studying the competition with dipolar fields due to the domains in the hard layer. Micromagnetic simulations elucidate the role of [CoNi/Pd] magnetization, exchange, and anisotropy in the duplication process. Finally, thermally driven domain replication in remanence during temperature cycling is demonstrated.

  10. Rotating colloids in rotating magnetic fields: Dipolar relaxation and hydrodynamic coupling

    NASA Astrophysics Data System (ADS)

    Coughlan, Anna C. H.; Bevan, Michael A.

    2016-10-01

    Video microscopy (VM) experiments and Brownian dynamics (BD) simulations were used to measure and model superparamagnetic colloidal particles in rotating magnetic fields for interaction energies on the order of the thermal energy, kT . Results from experiments and simulations were compared for isolated particle rotation, particle rotation within doublets, doublet rotation, and separation within doublets vs field rotation frequency. Agreement between VM and BD results was obtained at all frequencies and amplitudes only by including exact two-body hydrodynamic interactions and relevant relaxation times of magnetic dipoles. Frequency-dependent particle forces and torques cause doublets to rotate at low frequencies via dipolar interactions and at high frequencies via hydrodynamic translation-rotation coupling. By matching measurements and simulations for a range of conditions, our findings unambiguously demonstrate the quantitative forms of dipolar and hydrodynamic interactions necessary to capture nonequilibrium, steady-state dynamics of Brownian colloids in magnetic fields.

  11. Conditions for the spin wave nonreciprocity in an array of dipolarly coupled magnetic nanopillars

    NASA Astrophysics Data System (ADS)

    Verba, Roman; Tiberkevich, Vasil; Bankowski, Elena; Meitzler, Thomas; Melkov, Gennadiy; Slavin, Andrei

    2013-08-01

    It is demonstrated that collective spin waves (SWs) propagating in complex periodic arrays of dipolarly coupled magnetic nanopillars existing in a saturated (single-domain) ground state in a zero bias magnetic field could be nonreciprocal. To guarantee the SW nonreciprocity, two conditions should be fulfilled: (i) existence of a nonzero out-of-plane component of the pillars' static magnetization and (ii) a complex periodicity of array's ground state with at least two elements per a primitive cell, if the elements are different, and at least three elements per a primitive cell, if the elements are identical.

  12. Computer-Assisted 3D Structure Elucidation of Natural Products using Residual Dipolar Couplings.

    PubMed

    Troche-Pesqueira, Eduardo; Anklin, Clemens; Gil, Roberto R; Navarro-Vázquez, Armando

    2017-03-20

    An enhanced computer-assisted procedure for the determination of the relative configuration of natural products, which starts from the molecular formula and uses a combination of conventional 1D and 2D NMR spectra, and residual dipolar couplings (RDCs), is reported. Having already the data acquired (1D/2D NMR and RDCs), the procedure begins with the determination of the molecular constitution using standard computer-assisted structure elucidation (CASE) and is followed by fully automated determination of relative configuration through RDC analysis. In the case of moderately flexible molecules the simplest data-explaining conformational model is selected by the use of the Akaike information criterion.

  13. Changes in Lignin and Polysaccharide Components in 13 Cultivars of Rice Straw following Dilute Acid Pretreatment as Studied by Solution-State 2D 1H-13C NMR

    PubMed Central

    Teramura, Hiroshi; Sasaki, Kengo; Oshima, Tomoko; Aikawa, Shimpei; Matsuda, Fumio; Okamoto, Mami; Shirai, Tomokazu; Kawaguchi, Hideo; Ogino, Chiaki; Yamasaki, Masanori; Kikuchi, Jun; Kondo, Akihiko

    2015-01-01

    A renewable raw material, rice straw is pretreated for biorefinery usage. Solution-state two-dimensional (2D) 1H-13 C hetero-nuclear single quantum coherence (HSQC) nuclear magnetic resonance (NMR) spectroscopy, was used to analyze 13 cultivars of rice straw before and after dilute acid pretreatment, to characterize general changes in the lignin and polysaccharide components. Intensities of most (15 of 16) peaks related to lignin aromatic regions, such as p-coumarate, guaiacyl, syringyl, p-hydroxyphenyl, and cinnamyl alcohol, and methoxyl, increased or remained unchanged after pretreatment. In contrast, intensities of most (11 of 13) peaks related to lignin aliphatic linkages or ferulate decreased. Decreased heterogeneity in the intensities of three peaks related to cellulose components in acid-insoluble residues resulted in similar glucose yield (0.45–0.59 g/g-dry biomass). Starch-derived components showed positive correlations (r = 0.71 to 0.96) with glucose, 5-hydroxymethylfurfural (5-HMF), and formate concentrations in the liquid hydrolysates, and negative correlations (r = –0.95 to –0.97) with xylose concentration and acid-insoluble residue yield. These results showed the fate of lignin and polysaccharide components by pretreatment, suggesting that lignin aromatic regions and cellulose components were retained in the acid insoluble residues and starch-derived components were transformed into glucose, 5-HMF, and formate in the liquid hydrolysate. PMID:26083431

  14. 1H, 13C, and 15N resonance assignments of an enzymatically active domain from the catalytic component (CDTa, residues 216-420) of a binary toxin from Clostridium difficile.

    PubMed

    Roth, Braden M; Godoy-Ruiz, Raquel; Varney, Kristen M; Rustandi, Richard R; Weber, David J

    2016-04-01

    Clostridium difficile is a bacterial pathogen and is the most commonly reported source of nosocomial infection in industrialized nations. Symptoms of C. difficile infection (CDI) include antibiotic-associated diarrhea, pseudomembranous colitis, sepsis and death. Over the last decade, rates and severity of hospital infections in North America and Europe have increased dramatically and correlate with the emergence of a hypervirulent strain of C. difficile characterized by the presence of a binary toxin, CDT (C. difficile toxin). The binary toxin consists of an enzymatic component (CDTa) and a cellular binding component (CDTb) that together form the active binary toxin complex. CDTa harbors a pair of structurally similar but functionally distinct domains, an N-terminal domain (residues 1-215; (1-215)CDTa) that interacts with CDTb and a C-terminal domain (residues 216-420; (216-420)CDTa) that harbors the intact ADP-ribosyltransferase (ART) active site. Reported here are the (1)H, (13)C, and (15)N backbone resonance assignments of the 23 kDa, 205 amino acid C-terminal enzymatic domain of CDTa, termed (216-420)CDTa. These NMR resonance assignments for (216-420)CDTa represent the first for a family of ART binary toxins and provide the framework for detailed characterization of the solution-state protein structure determination, dynamic studies of this domain, as well as NMR-based drug discovery efforts.

  15. pH-dependent random coil (1)H, (13)C, and (15)N chemical shifts of the ionizable amino acids: a guide for protein pK a measurements.

    PubMed

    Platzer, Gerald; Okon, Mark; McIntosh, Lawrence P

    2014-11-01

    The pK a values and charge states of ionizable residues in polypeptides and proteins are frequently determined via NMR-monitored pH titrations. To aid the interpretation of the resulting titration data, we have measured the pH-dependent chemical shifts of nearly all the (1)H, (13)C, and (15)N nuclei in the seven common ionizable amino acids (X = Asp, Glu, His, Cys, Tyr, Lys, and Arg) within the context of a blocked tripeptide, acetyl-Gly-X-Gly-amide. Alanine amide and N-acetyl alanine were used as models of the N- and C-termini, respectively. Together, this study provides an essentially complete set of pH-dependent intra-residue and nearest-neighbor reference chemical shifts to help guide protein pK a measurements. These data should also facilitate pH-dependent corrections in algorithms used to predict the chemical shifts of random coil polypeptides. In parallel, deuterium isotope shifts for the side chain (15)N nuclei of His, Lys, and Arg in their positively-charged and neutral states were also measured. Along with previously published results for Asp, Glu, Cys, and Tyr, these deuterium isotope shifts can provide complementary experimental evidence for defining the ionization states of protein residues.

  16. Detection of intermolecular homonuclear dipolar coupling in organic rich shale by transverse relaxation exchange.

    PubMed

    Washburn, Kathryn E; Cheng, Yuesheng

    2017-03-04

    The mechanism behind surface relaxivity within organic porosity in shales has been an unanswered question. Here, we present results that confirm the existence of intermolecular homonuclear dipolar coupling between solid and liquid phases in sedimentary organic matter. Transverse magnetization exchange measurements were performed on an organic-rich shale saturated with liquid hydrocarbon. Liquid and solid constituents were identified through both sample resaturation and through their T1/T2 ratios. Extensive cross peaks are observed in the T2-T2 exchange spectra between the solid and liquid constituents, indicating an exchange of magnetization between the two phases. This result cannot arise from physical molecular diffusion, and the dissolution energies are too high for chemical exchange, such that the magnetization exchange must arise from intermolecular homonuclear dipolar coupling. These results both confirm a possible source of surface relaxivity in organic matter and emphasize caution in the use of standard porous media interpretations of relaxation results in shales because of coupling between different magnetization environments.

  17. Dipolar Coupling Information in Multispin Systems: Application of a Compensated REDOR NMR Approach to Inorganic Phosphates

    NASA Astrophysics Data System (ADS)

    Chan, Jerry C. C.; Eckert, Hellmut

    2000-12-01

    Anexperimental strategy has been developed for measuring multiple dipole-dipole interactions in inorganic compounds using the technique of rotational echo double resonance (REDOR) NMR. Geometry-independent information about the dipole couplings between the observe nuclear species S (arbitrary quantum number) and the heteronuclear species I (spin-{1}/{2}) can be conveniently obtained from the experimental curve of ΔS/S0 versus dipolar evolution time by limiting the analysis to the initial data range 0 < ΔS/S0 < 0.30. Numerical simulations have been carried out on a three-spin system of type SI2 in order to assess the effect of the I-I homonuclear dipole-dipole coupling and the influence of experimental imperfections such as finite pulse length and misadjustments of the 180° pulses applied to the I-spin species. The simulations show further that within the initial data range the effects of such misadjustments can be internally compensated by a modified sequence having an additional 180° pulse on the I channel in the middle of the dipolar evolution periods. Experimental 27Al{31P} REDOR results on the multispin systems Al(PO3)3, AlPO4, [AlPO4]12(C3H7)4NF, and Na3PO4 confirm the general utility of this approach. Thus, for applications to unknown systems the compensation strategy obviates calibration procedures with model compounds.

  18. Measurement of absolute concentrations of individual compounds in metabolite mixtures by gradient-selective time-zero 1H-13C HSQC with two concentration references and fast maximum likelihood reconstruction analysis.

    PubMed

    Hu, Kaifeng; Ellinger, James J; Chylla, Roger A; Markley, John L

    2011-12-15

    Time-zero 2D (13)C HSQC (HSQC(0)) spectroscopy offers advantages over traditional 2D NMR for quantitative analysis of solutions containing a mixture of compounds because the signal intensities are directly proportional to the concentrations of the constituents. The HSQC(0) spectrum is derived from a series of spectra collected with increasing repetition times within the basic HSQC block by extrapolating the repetition time to zero. Here we present an alternative approach to data collection, gradient-selective time-zero (1)H-(13)C HSQC(0) in combination with fast maximum likelihood reconstruction (FMLR) data analysis and the use of two concentration references for absolute concentration determination. Gradient-selective data acquisition results in cleaner spectra, and NMR data can be acquired in both constant-time and non-constant-time mode. Semiautomatic data analysis is supported by the FMLR approach, which is used to deconvolute the spectra and extract peak volumes. The peak volumes obtained from this analysis are converted to absolute concentrations by reference to the peak volumes of two internal reference compounds of known concentration: DSS (4,4-dimethyl-4-silapentane-1-sulfonic acid) at the low concentration limit (which also serves as chemical shift reference) and MES (2-(N-morpholino)ethanesulfonic acid) at the high concentration limit. The linear relationship between peak volumes and concentration is better defined with two references than with one, and the measured absolute concentrations of individual compounds in the mixture are more accurate. We compare results from semiautomated gsHSQC(0) with those obtained by the original manual phase-cycled HSQC(0) approach. The new approach is suitable for automatic metabolite profiling by simultaneous quantification of multiple metabolites in a complex mixture.

  19. Efficient Synchronization of Dipolarly Coupled Vortex-Based Spin Transfer Nano-Oscillators

    PubMed Central

    Locatelli, Nicolas; Hamadeh, Abbass; Abreu Araujo, Flavio; Belanovsky, Anatoly D.; Skirdkov, Petr N.; Lebrun, Romain; Naletov, Vladimir V.; Zvezdin, Konstantin A.; Muñoz, Manuel; Grollier, Julie; Klein, Olivier; Cros, Vincent; de Loubens, Grégoire

    2015-01-01

    Due to their nonlinear properties, spin transfer nano-oscillators can easily adapt their frequency to external stimuli. This makes them interesting model systems to study the effects of synchronization and brings some opportunities to improve their microwave characteristics in view of their applications in information and communication technologies and/or to design innovative computing architectures. So far, mutual synchronization of spin transfer nano-oscillators through propagating spinwaves and exchange coupling in a common magnetic layer has been demonstrated. Here we show that the dipolar interaction is also an efficient mechanism to synchronize neighbouring oscillators. We experimentally study a pair of vortex-based spin transfer nano-oscillators, in which mutual synchronization can be achieved despite a significant frequency mismatch between oscillators. Importantly, the coupling efficiency is controlled by the magnetic configuration of the vortices, as confirmed by an analytical model and micromagnetic simulations highlighting the physics at play in the synchronization process. PMID:26608230

  20. Efficient Synchronization of Dipolarly Coupled Vortex-Based Spin Transfer Nano-Oscillators

    NASA Astrophysics Data System (ADS)

    Locatelli, Nicolas; Hamadeh, Abbass; Abreu Araujo, Flavio; Belanovsky, Anatoly D.; Skirdkov, Petr N.; Lebrun, Romain; Naletov, Vladimir V.; Zvezdin, Konstantin A.; Muñoz, Manuel; Grollier, Julie; Klein, Olivier; Cros, Vincent; de Loubens, Grégoire

    2015-11-01

    Due to their nonlinear properties, spin transfer nano-oscillators can easily adapt their frequency to external stimuli. This makes them interesting model systems to study the effects of synchronization and brings some opportunities to improve their microwave characteristics in view of their applications in information and communication technologies and/or to design innovative computing architectures. So far, mutual synchronization of spin transfer nano-oscillators through propagating spinwaves and exchange coupling in a common magnetic layer has been demonstrated. Here we show that the dipolar interaction is also an efficient mechanism to synchronize neighbouring oscillators. We experimentally study a pair of vortex-based spin transfer nano-oscillators, in which mutual synchronization can be achieved despite a significant frequency mismatch between oscillators. Importantly, the coupling efficiency is controlled by the magnetic configuration of the vortices, as confirmed by an analytical model and micromagnetic simulations highlighting the physics at play in the synchronization process.

  1. Bright solitons in a two-dimensional spin-orbit-coupled dipolar Bose-Einstein condensate

    NASA Astrophysics Data System (ADS)

    Xu, Yong; Zhang, Yongping; Zhang, Chuanwei

    2015-07-01

    We study a two-dimensional spin-orbit-coupled dipolar Bose-Einstein condensate with repulsive contact interactions by both the variational method and the imaginary-time evolution of the Gross-Pitaevskii equation. The dipoles are completely polarized along one direction in the two-dimensional plane to provide an effective attractive dipole-dipole interaction. We find two types of solitons as the ground states arising from such attractive dipole-dipole interactions: a plane-wave soliton with a spatially varying phase and a stripe soliton with a spatially oscillating density for each component. Both types of solitons possess smaller size and higher anisotropy than the soliton without spin-orbit coupling. Finally, we discuss the properties of moving solitons, which are nontrivial because of the violation of Galilean invariance.

  2. A method of determining RNA conformational ensembles using structure-based calculations of residual dipolar couplings

    NASA Astrophysics Data System (ADS)

    Borkar, Aditi N.; De Simone, Alfonso; Montalvao, Rinaldo W.; Vendruscolo, Michele

    2013-06-01

    We describe a method of determining the conformational fluctuations of RNA based on the incorporation of nuclear magnetic resonance (NMR) residual dipolar couplings (RDCs) as replica-averaged structural restraints in molecular dynamics simulations. In this approach, the alignment tensor required to calculate the RDCs corresponding to a given conformation is estimated from its shape, and multiple replicas of the RNA molecule are simulated simultaneously to reproduce in silico the ensemble-averaging procedure performed in the NMR measurements. We provide initial evidence that with this approach it is possible to determine accurately structural ensembles representing the conformational fluctuations of RNA by applying the reference ensemble test to the trans-activation response element of the human immunodeficiency virus type 1.

  3. Spin-wave edge modes in finite arrays of dipolarly coupled magnetic nanopillars

    NASA Astrophysics Data System (ADS)

    Lisenkov, Ivan; Tyberkevych, Vasyl; Slavin, Andrei; Bondarenko, Pavel; Ivanov, Boris A.; Bankowski, Elena; Meitzler, Thomas; Nikitov, Sergey

    2014-09-01

    The frequency spectrum of spin-wave edge modes localized near the boundaries of a finite array of dipolarly coupled magnetic nanopillars is calculated theoretically. Two mechanisms of edge mode formation are revealed: inhomogeneity of the internal static magnetic field existing near the array boundaries and time-reversal symmetry breaking of the dipole-dipole interaction. The latter mechanism is analogous to the formation mechanism of a surface Damon-Eschbach mode in continuous in-plane magnetized magnetic films and is responsible for the nonreciprocity of edge modes in finite-width nanopillar arrays. The number of edge modes in nanopillar arrays depends on the spatial profile of the internal static magnetic field near the array boundaries and several edge modes are formed if a substantial field inhomogeneity extends over several rows of nanopillars.

  4. Block-restraining of residual dipolar couplings to allow fluctuating relative alignments of molecular subdomains.

    PubMed

    Wirz, Lukas N; Allison, Jane R

    2017-02-20

    Residual dipolar couplings (RDCs), unlike most other types of NMR observables, provide orientational information, reporting on the alignment of inter-spin vectors (ISVs) relative to the magnetic field. A great challenge in using experimental RDCs to restrain molecular dynamics (MD) simulations is how to represent this alignment. An alignment tensor is often used to parameterise the contribution of molecular alignment to the angular dependence of RDCs. All ISVs that share the same tensor have fixed relative alignment, i.e. if just one tensor is used, the molecule is internally rigid. Here we propose and illustrate a method for subdividing molecules into individually aligned blocks during MD simulations restrained to fit RDCs. This allows the relative orientation of each block to vary during the simulation, which in turn ensures that the internal structure of each block is more realistically reproduced.

  5. Compiled data set of exact NOE distance limits, residual dipolar couplings and scalar couplings for the protein GB3.

    PubMed

    Vögeli, Beat; Olsson, Simon; Riek, Roland; Güntert, Peter

    2015-12-01

    We compiled an NMR data set consisting of exact nuclear Overhauser enhancement (eNOE) distance limits, residual dipolar couplings (RDCs) and scalar (J) couplings for GB3, which forms one of the largest and most diverse data set for structural characterization of a protein to date. All data have small experimental errors, which are carefully estimated. We use the data in the research article Vogeli et al., 2015, Complementarity and congruence between exact NOEs and traditional NMR probes for spatial decoding of protein dynamics, J. Struct. Biol., 191, 3, 306-317, doi:10.1016/j.jsb.2015.07.008 [1] for cross-validation in multiple-state structural ensemble calculation. We advocate this set to be an ideal test case for molecular dynamics simulations and structure calculations.

  6. Efficient creation of dipolar coupled nitrogen-vacancy spin qubits in diamond

    NASA Astrophysics Data System (ADS)

    Jakobi, I.; Momenzadeh, S. A.; Fávaro de Oliveira, F.; Michl, J.; Ziem, F.; Schreck, M.; Neumann, P.; Denisenko, A.; Wrachtrup, J.

    2016-09-01

    Coherently coupled pairs or multimers of nitrogen-vacancy defect electron spins in diamond have many promising applications especially in quantum information processing (QIP) but also in nanoscale sensing applications. Scalable registers of spin qubits are essential to the progress of QIP. Ion implantation is the only known technique able to produce defect pairs close enough to allow spin coupling via dipolar interaction. Although several competing methods have been proposed to increase the resulting resolution of ion implantation, the reliable creation of working registers is still to be demonstrated. The current limitation are residual radiation-induced defects, resulting in degraded qubit performance as trade-off for positioning accuracy. Here we present an optimized estimation of nanomask implantation parameters that are most likely to produce interacting qubits under standard conditions. We apply our findings to a well-established technique, namely masks written in electron-beam lithography, to create coupled defect pairs with a reasonable probability. Furthermore, we investigate the scaling behavior and necessary improvements to efficiently engineer interacting spin architectures.

  7. Ordering and thermal excitations in dipolar coupled single domain magnet arrays (Presentation Recording)

    NASA Astrophysics Data System (ADS)

    Östman, Erik; Arnalds, Unnar; Kapaklis, Vassilios; Hjörvarsson, Björgvin

    2015-09-01

    For a small island of a magnetic material the magnetic state of the island is mainly determined by the exchange interaction and the shape anisotropy. Two or more islands placed in close proximity will interact through dipolar interactions. The state of a large system will thus be dictated by interactions at both these length scales. Enabling internal thermal fluctuations, e.g. by the choice of material, of the individual islands allows for the study of thermal ordering in extended nano-patterned magnetic arrays [1,2]. As a result nano-magnetic arrays represent an ideal playground for the study of physical model systems. Here we present three different studies all having used magneto-optical imaging techniques to observe, in real space, the order of the systems. The first study is done on a square lattice of circular islands. The remanent magnetic state of each island is a magnetic vortex structure and we can study the temperature dependence of the vortex nucleation and annihilation fields [3]. The second are long chains of dipolar coupled elongated islands where the magnetization direction in each island only can point in one of two possible directions. This creates a system which in many ways mimics the Ising model [4] and we can relate the correlation length to the temperature. The third one is a spin ice system where elongated islands are placed in a square lattice. Thermal excitations in such systems resemble magnetic monopoles [2] and we can investigate their properties as a function of temperature and lattice parameters. [1] V. Kapaklis et al., New J. Phys. 14, 035009 (2012) [2] V. Kapaklis et al., Nature Nanotech 9, 514(2014) [3] E. Östman et al.,New J. Phys. 16, 053002 (2014) [4] E. Östman et al.,Thermal ordering in mesoscopic Ising chains, In manuscript.

  8. Heteronuclear dipolar couplings, total spin coherence, and bilinear rotations in NMR spectroscopy

    SciTech Connect

    Garbow, J.R.

    1983-07-01

    In Chapter 1 a variety of different introductory topics are presented. The potential complexity of the nuclear magnetic resonsnace (NMR) spectra of molecules dissolved in liquid crystal solvents serves to motivate the development of multiple quantum (MQ) spectroscopy. The basics of MQ NMR are reviewed in Chapter 2. An experimental search procedure for the optimization of MQ pulse sequences is introduced. Chapter 3 discusses the application of MQ NMR techniques to the measurement of dipolar couplings in heteronuclear spin systems. The advantages of MQ methods in such systems are developed and experimental results for partially oriented (1-/sup 13/C) benzene are presented. Several pulse sequences are introduced which employ a two-step excitation of heteronuclear MQ coherence. A new multiple pulse method, involving the simultaneous irradiation of both rare and abundant spin species, is described. The problem of the broadening of MQ transitions due to magnetic field inhomogeneity is considered in Chapter 4. The method of total spin coherence transfer echo spectroscopy (TSCTES) is presented, with experimets on partially oriented acetaldehyde serving to demonstrate this new technique. TSCTES results in MQ spectra which are sensitive to all chemical shifts and spin-spin couplings and which are free of inhomogeneous broadening. In Chapter 5 the spectroscopy of spin systems of several protons and a /sup 13/C nucleus in the isotropic phase is discussed. The usefulness of the heteronuclear bilinear rotation as a calculational tool is illustrated. Compensated bilinear ..pi.. rotations, which are relatively insensitive to timing parameter missets, are presented. A new technique for homonuclear proton decoupling, Bilinear Rotation Decoupling, is described and its success in weakly coupled systems is demonstrated.

  9. Residual dipolar coupling constants and structure determination of large DNA duplexes.

    PubMed

    Mauffret, Olivier; Tevanian, Georges; Fermandjian, Serge

    2002-12-01

    Several NMR works have shown that long-range information provided by residual dipolar couplings (RDCs) significantly improve the global structure definition of RNAs and DNAs. Most of these are based on the use of a large set of RDCs, the collect of which requires samples labeled with (13)C, (15)N, and sometimes, (2)H. Here, we carried out torsion-angle dynamics simulations on a non-self complementary DNA fragment of 17 base-pairs, d(GGAAAATATCTAGCAGT).(ACTGCTAGAGATTTTCC). This reproduces the U5 LTR distal end of the HIV-1 cDNA that contains the enzyme integrase binding site. Simulations aimed at evaluating the impact of RDCs on the structure definition of long oligonucleotides, were performed in incorporating (i) nOe-distances at both < 4.5 A and < 5 A; (ii) a small set of (13)C-(1)H RDCs, easily detectable at the natural abundance, and (iii) a larger set of RDCs only accessible through the (13)C labeling of DNAs. Agreement between a target structure and a simulated structure was measured in terms of precision and accuracy. Results allowed to define conditions in which accurate DNA structures can be determined. We confirmed the strong impact of RDCs on the structure determination, and, above all, we found that a small set of RDC constraints (ca. 50) detectable at the natural abundance is sufficient to accurately derive the global and local DNA duplex structures when used in conjunction with nOe-distances < 5 A.

  10. Measuring membrane protein bond orientations in nanodiscs via residual dipolar couplings

    PubMed Central

    Bibow, Stefan; Carneiro, Marta G; Sabo, T Michael; Schwiegk, Claudia; Becker, Stefan; Riek, Roland; Lee, Donghan

    2014-01-01

    Membrane proteins are involved in numerous vital biological processes. To understand membrane protein functionality, accurate structural information is required. Usually, structure determination and dynamics of membrane proteins are studied in micelles using either solution state NMR or X-ray crystallography. Even though invaluable information has been obtained by this approach, micelles are known to be far from ideal mimics of biological membranes often causing the loss or decrease of membrane protein activity. Recently, nanodiscs, which are composed of a lipid bilayer surrounded by apolipoproteins, have been introduced as a more physiological alternative than micelles for NMR investigations on membrane proteins. Here, we show that membrane protein bond orientations in nanodiscs can be obtained by measuring residual dipolar couplings (RDCs) with the outer membrane protein OmpX embedded in nanodiscs using Pf1 phage as an alignment medium. The presented collection of membrane protein RDCs in nanodiscs represents an important step toward more comprehensive structural and dynamical NMR-based investigations of membrane proteins in a natural bilayer environment. PMID:24752984

  11. Direct prediction of residual dipolar couplings of small molecules in a stretched gel by stochastic molecular dynamics simulations.

    PubMed

    Frank, Andreas O; Freudenberger, J Christoph; Shaytan, Alexey K; Kessler, Horst; Luy, Burkhard

    2015-03-01

    Residual dipolar couplings are highly useful NMR parameters for calculating and refining molecular structures, dynamics, and interactions. For some applications, however, it is inevitable that the preferred orientation of a molecule in an alignment medium is calculated a priori. Several methods have been developed to predict molecular orientations and residual dipolar couplings. Being beneficial for macromolecules and selected small-molecule applications, such approaches lack sufficient accuracy for a large number of organic compounds for which the fine structure and eventually the flexibility of all involved molecules have to be considered or are limited to specific, well-studied liquid crystals. We introduce a simplified model for detailed all-atom molecular dynamics calculations with a polymer strand lined up along the principal axis as a new approach to simulate the preferred orientation of small to medium-sized solutes in polymer-based, gel-type alignment media. As is shown by a first example of strychnine in a polystyrene/CDCl3 gel, the simulations potentially enable the accurate prediction of residual dipolar couplings taking into account structural details and dynamic averaging effects of both the polymer and the solute.

  12. Perspectives in the application of residual dipolar couplings in the structure elucidation of weakly aligned small molecules.

    PubMed

    Schmidts, Volker

    2017-01-01

    This perspective article aims to review the general methodology in the application of residual dipolar couplings (RDCs) in the structure elucidation of small molecules and give the author's view on challenges for future applications. Recent improvements in the availability of alignment media, new pulse sequences for the measurement of couplings and improvements in the analysis software have garnered widespread interest in the technique. However, further generalization is needed in order to make RDC analysis into a truly "routine" method. Copyright © 2016 John Wiley & Sons, Ltd.

  13. Alignment of druglike compounds in lipid bilayers analyzed by solid-state (19)F-NMR and molecular dynamics, based on dipolar couplings of adjacent CF3 groups.

    PubMed

    Dürr, Ulrich H N; Afonin, Sergii; Hoff, Barbara; de Luca, Giuseppina; Emsley, James W; Ulrich, Anne S

    2012-04-26

    Solid-state (19)F-NMR spectroscopy is frequently used to analyze the structure and dynamics of lipophilic drugs and peptides embedded in biomembranes. The homonuclear dipolar couplings of trifluoromethyl (CF3) labels can provide valuable parameters such as orientational constraints and/or distances. To characterize the complex dipolar patterns of multiple (19)F spin interactions, three different model compounds carrying two CF3 groups in meta-position on a phenyl ring were incorporated in macroscopically aligned DMPC bilayers. The dipolar patterns obtained with the CPMG (Carr-Purcell-Meiboom-Gill) multipulse sequence were analyzed to yield simultaneously the intra-CF3 and intergroup dipolar coupling values. The fluorine-fluorine distances were predicted by a density functional calculation, and the alignment of the labeled molecular segment could be determined from these distances and the dipolar coupling values. The different compounds were found to align in the lipid bilayer according to their amphiphilic properties, though with a weak anisotropic preference that is typical of solutes in liquid crystals. The residual dipolar couplings were used to calculate Saupe order parameters. For the least complex molecule, (CF3)2-BA, an orientational probability function for the solute in the lipid matrix could be derived. The overall description of how (CF3)2-BA is embedded in the bilayer was independently assessed by molecular dynamics simulations, and compared in structural and dynamical terms with the results of the NMR experiments.

  14. Accurate measurement of heteronuclear dipolar couplings by phase-alternating R-symmetry (PARS) sequences in magic angle spinning NMR spectroscopy

    SciTech Connect

    Hou, Guangjin E-mail: tpolenov@udel.edu; Lu, Xingyu E-mail: lexvega@comcast.net; Vega, Alexander J. E-mail: lexvega@comcast.net; Polenova, Tatyana E-mail: tpolenov@udel.edu

    2014-09-14

    We report a Phase-Alternating R-Symmetry (PARS) dipolar recoupling scheme for accurate measurement of heteronuclear {sup 1}H-X (X = {sup 13}C, {sup 15}N, {sup 31}P, etc.) dipolar couplings in MAS NMR experiments. It is an improvement of conventional C- and R-symmetry type DIPSHIFT experiments where, in addition to the dipolar interaction, the {sup 1}H CSA interaction persists and thereby introduces considerable errors in the dipolar measurements. In PARS, phase-shifted RN symmetry pulse blocks applied on the {sup 1}H spins combined with π pulses applied on the X spins at the end of each RN block efficiently suppress the effect from {sup 1}H chemical shift anisotropy, while keeping the {sup 1}H-X dipolar couplings intact. Another advantage over conventional DIPSHIFT experiments, which require the signal to be detected in the form of a reduced-intensity Hahn echo, is that the series of π pulses refocuses the X chemical shift and avoids the necessity of echo formation. PARS permits determination of accurate dipolar couplings in a single experiment; it is suitable for a wide range of MAS conditions including both slow and fast MAS frequencies; and it assures dipolar truncation from the remote protons. The performance of PARS is tested on two model systems, [{sup 15}N]-N-acetyl-valine and [U-{sup 13}C,{sup 15}N]-N-formyl-Met-Leu-Phe tripeptide. The application of PARS for site-resolved measurement of accurate {sup 1}H-{sup 15}N dipolar couplings in the context of 3D experiments is presented on U-{sup 13}C,{sup 15}N-enriched dynein light chain protein LC8.

  15. Accurate measurement of heteronuclear dipolar couplings by phase-alternating R-symmetry (PARS) sequences in magic angle spinning NMR spectroscopy.

    PubMed

    Hou, Guangjin; Lu, Xingyu; Vega, Alexander J; Polenova, Tatyana

    2014-09-14

    We report a Phase-Alternating R-Symmetry (PARS) dipolar recoupling scheme for accurate measurement of heteronuclear (1)H-X (X = (13)C, (15)N, (31)P, etc.) dipolar couplings in MAS NMR experiments. It is an improvement of conventional C- and R-symmetry type DIPSHIFT experiments where, in addition to the dipolar interaction, the (1)H CSA interaction persists and thereby introduces considerable errors in the dipolar measurements. In PARS, phase-shifted RN symmetry pulse blocks applied on the (1)H spins combined with π pulses applied on the X spins at the end of each RN block efficiently suppress the effect from (1)H chemical shift anisotropy, while keeping the (1)H-X dipolar couplings intact. Another advantage over conventional DIPSHIFT experiments, which require the signal to be detected in the form of a reduced-intensity Hahn echo, is that the series of π pulses refocuses the X chemical shift and avoids the necessity of echo formation. PARS permits determination of accurate dipolar couplings in a single experiment; it is suitable for a wide range of MAS conditions including both slow and fast MAS frequencies; and it assures dipolar truncation from the remote protons. The performance of PARS is tested on two model systems, [(15)N]-N-acetyl-valine and [U-(13)C,(15)N]-N-formyl-Met-Leu-Phe tripeptide. The application of PARS for site-resolved measurement of accurate (1)H-(15)N dipolar couplings in the context of 3D experiments is presented on U-(13)C,(15)N-enriched dynein light chain protein LC8.

  16. Two dimensional dipolar coupling in monolayers of silver and gold nanoparticles on a dielectric substrate.

    PubMed

    Liu, Yu; Begin-Colin, Sylvie; Pichon, Benoît P; Leuvrey, Cedric; Ihiawakrim, Dris; Rastei, Mircea; Schmerber, Guy; Vomir, Mircea; Bigot, Jean Yves

    2014-10-21

    The dimensionality of assembled nanoparticles plays an important role in their optical and magnetic properties, via dipolar effects and the interaction with their environment. In this work we develop a methodology for distinguishing between two (2D) and three (3D) dimensional collective interactions on the surface plasmon resonance of assembled metal nanoparticles. Towards that goal, we elaborate different sets of Au and Ag nanoparticles as suspensions, random 3D arrangements and well organized 2D arrays. Then we model their scattering cross-section using effective field methods in dimension n, including interparticle as well as particle-substrate dipolar interactions. For this modelling, two effective field medium approaches are employed, taking into account the filling factors of the assemblies. Our results are important for realizing photonic amplifier devices.

  17. Quantum mechanical and spectroscopic (FT-IR, FT-Raman,1H,13C NMR, UV-Vis) studies, NBO, NLO, HOMO, LUMO and Fukui function analysis of 5-Methoxy-1H-benzo[d]imidazole-2(3H)-thione by DFT studies

    NASA Astrophysics Data System (ADS)

    Pandey, Manju; Muthu, S.; Nanje Gowda, N. M.

    2017-02-01

    Theoretical analysis of the molecular structure, spectroscopic (FT-IR, FT-Raman, 1H, 13C NMR, UV-Vis) studies, and thermodynamic characteristics of 5-Methoxy-1H-benzo[d]imidazole-2(3H)-thione (5MBIT) molecule were done by DFT/B3LYP using 6-311++G(d, p) basis set. Theoretical parameters were compared with experimental data. The dipole moment (μ), polarizability (Δα) and first order hyperpolarizability (β) of the molecule were calculated. Thermodynamic properties, HOMO and LUMO energies were determined. Global reactivity parameters and Fukui function of the 5MBIT molecule were predicted.

  18. Application of Residual Dipolar Couplings and Selective Quantitative NOE to Establish the Structures of Tetranortriterpenoids from Xylocarpus rumphii.

    PubMed

    Waratchareeyakul, Watcharee; Hellemann, Erich; Gil, Roberto R; Chantrapromma, Kan; Langat, Moses K; Mulholland, Dulcie A

    2017-02-24

    Nine triterpenoid derivatives were isolated from the heartwood of Xylocarpus rumphii and were identified as xylorumphiins E (1), C (2), L (3), and M-R (4-9). Compounds 4-9 have a hemiacetal group in the triterpenoid side chain, making them impossible to purify. Purification was achieved after acetylation and subsequent separation of the epimeric mixtures of acetates; however differentiaition of the R and S epimers was not possible using standard NMR techniques. In one case, the relative configuration of a remotely located stereocenter with respect to the stereocenters in the main skeleton was unambiguously determined using residual dipolar couplings. Dipolar couplings were collected from the sample oriented in compressed poly(methyl methacrylate) gels swollen in CDCl3. In another case, the relative configuration was determined using 1D selective quantitative NOE experiments. Xylorumphiin K (10), xyloccensin E, taraxer-14-en-3β-ol, (22S)-hydroxytirucalla-7,24-diene-3,23-dione, and 25-hydroxy-(20S,24S)-epoxydammaran-3-one were isolated from the bark of the same plant. Compounds 3-10 are new compounds. Compounds 1-6 and xyloccensin E were tested at one concentration, 1 × 10(-5) M, in the NCI59 cell one-dose screen but did not show significant activity.

  19. Interlayer exchange coupling, dipolar coupling and magnetoresistance in Fe/MgO/Fe trilayers with a subnanometer MgO barrier

    NASA Astrophysics Data System (ADS)

    Kozioł-Rachwał, A.; Skowroński, W.; Frankowski, M.; Chęciński, J.; Ziętek, S.; Rzeszut, P.; Ślęzak, M.; Matlak, K.; Ślęzak, T.; Stobiecki, T.; Korecki, J.

    2017-02-01

    Fe/MgO/Fe trilayers with a subnanometer MgO tunnel barrier were grown by molecular beam epitaxy. Longitudinal magnetooptic Kerr effect measurements confirmed the existence of the antiferromagnetic interlayer exchange coupling (IEC) between the Fe layers for 2 Åcoupling was enhanced for the trilayer grown on a homoepitaxial MgO buffer layer, and its IEC constant was estimated to be -3.3 erg/cm2 at a MgO thickness of 2.7 Å. After magnetic characterization, the sample was patterned into circular-shaped pillars with diameters ranging from 200 nm to 520 nm. We showed that the dipolar coupling that appeared after the nanofabrication process modified the effective coupling between layers, and we determined dependence of the dipolar coupling on the pillar diameter. Finally, magnetoresistance (MR) was measured as a function of MgO thickness (dMgO), and a non-zero MR was found for the MgO as thin as 3.4 Å. Extrapolation of the MR (dMgO) dependence to MR=0 allowed us to determine the length of the pinholes in our sample, which was estimated to be (3.2±0.5) Å.

  20. 1H, 13C NMR spectral and single crystal structural studies of toxaphene congeners. Quantum chemical calculations for preferred conformers of 2,5- endo,6- exo,8,9,9,10,10-octachloro-2-bornene and their DFT/GIAO 13C chemical shifts

    NASA Astrophysics Data System (ADS)

    Laihia, K.; Valkonen, A.; Kolehmainen, E.; Suontamo, R.; Nissinen, M.; Nikiforov, V.; Selivanov, S.

    2005-11-01

    The 1H and 13C NMR chemical shifts for six toxaphene congeners: 2- exo,3- endo,6- exo,8,9,10-hexachloro- ( 1), 2- exo,3- endo,5- exo,9,9,10,10-heptachloro- ( 2), 2- exo,3- endo,6- exo,8,9,10,10-heptachloro- ( 3), 2- exo,3- endo,5- exo,6- endo,8,9,10-heptachloro- ( 4), 2- exo,3- endo,5- exo,6- endo,8,9,9,10-octachlorobornane ( 5) and 2,5- endo,6- exo,8,9,9,10,10-octachloro-2-bornene ( 6) are reported. Their chemical shift assignments have been obtained by means of Pulsed Field Gradient (PFG) Double Quantum Filtered (DQF) 1H, 1H correlation spectroscopy (COSY), PFG 1H, 13C Heteronuclear Multiple Quantum Coherence (HMQC) and PFG 1H, 13C Heteronuclear Multiple Bond Correlation (HMBC) experiments. A single crystal X-ray structural analysis was made for compounds 1, 3, 4 and 6. The prevalences of two octachlorobornene rotamers ( 6 a, 6 b) were elucidated by ab initio MO method and single point DFT/GIAO calculations for 13C chemical shifts. Theoretical calculations proved that the single crystal structure of 6 corresponds its most stable conformer in solution.

  1. An Alignment Medium for Measuring Residual Dipolar Couplings in Pure DMSO: Liquid Crystals from Graphene Oxide Grafted with Polymer Brushes.

    PubMed

    Zong, Wen; Li, Gao-Wei; Cao, Jiang-Ming; Lei, Xinxiang; Hu, Mao-Lin; Sun, Han; Griesinger, Christian; Tan, Ren Xiang

    2016-03-07

    Residual dipolar couplings (RDCs) have attracted attention in light of their great impact on the structural elucidation of organic molecules. However, the effectiveness of RDC measurements is limited by the shortage of alignment media compatible with widely used organic solvents, such as DMSO. Herein, we present the first liquid crystal (LC) based alignment medium that is compatible with pure DMSO, thus enabling RDC measurements of polar and intermediate polarity molecules. The liquid crystals were obtained by grafting polymer brushes onto graphene oxide (GO) using free radical polymerization. The resulting new medium offers several advantages, such as absence of background signals, narrow line shapes, and tunable alignment. Importantly, this medium is compatible with π-conjugated molecules. Moreover, sonication-induced fragmentation can reduce the size of GO sheets. The resulting anisotropic medium has moderate alignment strength, which is a prerequisite for an accurate RDC measurement.

  2. Controllable emission of a dipolar source coupled with a magneto-dielectric resonant subwavelength scatterer

    PubMed Central

    Rolly, Brice; Geffrin, Jean-Michel; Abdeddaim, Redha; Stout, Brian; Bonod, Nicolas

    2013-01-01

    We demonstrate experimentally and theoretically that a local excitation of a single scatterer of relative dielectric permittivity ε = 6 permits to excite broad dipolar and quadrupolar electric and magnetic resonances that shape the emission pattern in an unprecedented way. By suitably positioning the feed with respect to the sphere at a λ/3 distance, this compact antenna is able to spectrally sort the electromagnetic emission either in the forward or in the backward direction, together with a high gain in directivity. Materials with ε = 6 can be found in the whole spectrum of frequencies promising Mie antennas to become an enabling technology in numbers of applications, ranging from quantum single photon sources to telecommunications. PMID:24165924

  3. A graphical method for analyzing distance restraints using residual dipolar couplings for structure determination of symmetric protein homo-oligomers.

    PubMed

    Martin, Jeffrey W; Yan, Anthony K; Bailey-Kellogg, Chris; Zhou, Pei; Donald, Bruce R

    2011-06-01

    High-resolution structure determination of homo-oligomeric protein complexes remains a daunting task for NMR spectroscopists. Although isotope-filtered experiments allow separation of intermolecular NOEs from intramolecular NOEs and determination of the structure of each subunit within the oligomeric state, degenerate chemical shifts of equivalent nuclei from different subunits make it difficult to assign intermolecular NOEs to nuclei from specific pairs of subunits with certainty, hindering structural analysis of the oligomeric state. Here, we introduce a graphical method, DISCO, for the analysis of intermolecular distance restraints and structure determination of symmetric homo-oligomers using residual dipolar couplings. Based on knowledge that the symmetry axis of an oligomeric complex must be parallel to an eigenvector of the alignment tensor of residual dipolar couplings, we can represent distance restraints as annuli in a plane encoding the parameters of the symmetry axis. Oligomeric protein structures with the best restraint satisfaction correspond to regions of this plane with the greatest number of overlapping annuli. This graphical analysis yields a technique to characterize the complete set of oligomeric structures satisfying the distance restraints and to quantitatively evaluate the contribution of each distance restraint. We demonstrate our method for the trimeric E. coli diacylglycerol kinase, addressing the challenges in obtaining subunit assignments for distance restraints. We also demonstrate our method on a dimeric mutant of the immunoglobulin-binding domain B1 of streptococcal protein G to show the resilience of our method to ambiguous atom assignments. In both studies, DISCO computed oligomer structures with high accuracy despite using ambiguously assigned distance restraints.

  4. Relationship between molecular stacking and optical properties of 9,10-bis((4-N,N-dialkylamino)styryl) anthracene crystals: the cooperation of excitonic and dipolar coupling.

    PubMed

    Li, Feng; Gao, Na; Xu, Hai; Liu, Wei; Shang, Hui; Yang, Wenjun; Zhang, Ming

    2014-08-04

    Five 9,10-bis((4-N,N-dialkylamino)styryl) anthracene derivatives (DSA-C1-DSA-C7) with different length alkyl chains were synthesized. They showed the same color in dilute solutions but different colors in crystals. The absorption, photoluminescence, and fluorescence decay indicate that there exist both excitonic and dipolar coupling in crystals of DSA-C1-DSA-C7. X-ray crystallographic analysis revealed that all the crystals belong to the triclinic space group P1 with one molecule per unit cell and that the molecules in every crystal have the identical orientation. This offers ideal samples to investigate the impact of the molecular stacking on the optical properties of the crystals. For the first time, the cooperation of excitonic and dipolar coupling has been comprehensively studied, and the contribution to the spectral shift from the excitonic and dipolar couplings quantitatively obtained. The experiments of amplified spontaneous emission (ASE) together with measurements of the quantum efficiency further confirmed this interpretation. The results suggest that the excitonic and dipolar couplings between the adjacent molecules are both important and jointly induce the spectral shifts of the crystals.

  5. 1H, 13C, and 15N backbone, side-chain, and heme chemical shift assignments for oxidized and reduced forms of the monoheme c-type cytochrome ApcA isolated from the acidophilic metal-reducing bacterium Acidiphilium cryptum.

    SciTech Connect

    Cort, John R.; Swenson, Michael; Magnuson, Timothy S.

    2011-03-04

    We report the 1H, 13C, and 15N chemical shift assignments of both oxidized and reduced forms of an abundant periplasmic c-type cytochrome, designated ApcA, from the acidophilic gram-negative facultatively anaerobic metal-reducing alpha-proteobacterium Acidiphilium cryptum. These resonance assignments prove that ApcA is a monoheme cytochrome c2 and the product of the Acry_2099 gene. An absence of resonance peaks in the NMR spectra for the 21 N-terminal residues suggests that a predicted N-terminal signal sequence is cleaved. We also describe the preparation and purification of the protein in labeled form from laboratory cultures of A. cryptum growing on 13C- and 15N- labeled substrates.

  6. Evidence for a dipolar-coupled AM system in carnosine in human calf muscle from in vivo 1H NMR spectroscopy

    NASA Astrophysics Data System (ADS)

    Schröder, Leif; Bachert, Peter

    2003-10-01

    Spin systems with residual dipolar couplings such as creatine, taurine, and lactate in skeletal muscle tissue exhibit first-order spectra in in vivo 1H NMR spectroscopy at 1.5 T because the coupled protons are represented by (nearly) symmetrized eigenfunctions. The imidazole ring protons (H2, H4) of carnosine are suspected to form also a coupled system. The ring's stiffness could enable a connectivity between these anisochronous protons with the consequence of second-order spectra at low field strength. Our purpose was to study whether this deviation from the Paschen-Back condition can be used to detect the H2-H4 coupling in localized 1D 1H NMR spectra obtained at 1.5 T (64 MHz) from the human calf in a conventional whole-body scanner. As for the hydrogen hyperfine interaction, a Breit-Rabi equation was derived to describe the transition from Zeeman to Paschen-Back regime for two dipolar-coupled protons. The ratio of the measurable coupling strength ( Sk) and the difference in resonance frequencies of the coupled spins (Δ ω) induces quantum-state mixing of various degree upon definition of an appropriate eigenbase of the coupled spin system. The corresponding Clebsch-Gordan coefficients manifest in characteristic energy corrections in the Breit-Rabi formula. These additional terms were used to define an asymmetry parameter of the line positions as a function of Sk and Δ ω. The observed frequency shifts of the resonances were found to be consistent with this parameter within the accuracy achievable in in vivo NMR spectroscopy. Thus it was possible to identify the origin of satellite peaks of H2, H4 and to describe this so far not investigated type of residual dipolar coupling in vivo.

  7. Dipolar Coupling between Nitroxide Spin Labels: The Development and Application of a Tether-in-a-Cone Model

    PubMed Central

    Hustedt, Eric J.; Stein, Richard A.; Sethaphong, Latsavongsakda; Brandon, Suzanne; Zhou, Zheng; DeSensi, Susan C.

    2006-01-01

    A tether-in-a-cone model is developed for the simulation of electron paramagnetic resonance spectra of dipolar coupled nitroxide spin labels attached to tethers statically disordered within cones of variable halfwidth. In this model, the nitroxides adopt a range of interprobe distances and orientations. The aim is to develop tools for determining both the distance distribution and the relative orientation of the labels from experimental spectra. Simulations demonstrate the sensitivity of electron paramagnetic resonance spectra to the orientation of the cones as a function of cone halfwidth and other parameters. For small cone halfwidths (<∼40°), simulated spectra are strongly dependent on the relative orientation of the cones. For larger cone halfwidths, spectra become independent of cone orientation. Tether-in-a-cone model simulations are analyzed using a convolution approach based on Fourier transforms. Spectra obtained by the Fourier convolution method more closely fit the tether-in-a-cone simulations as the halfwidth of the cone increases. The Fourier convolution method gives a reasonable estimate of the correct average distance, though the distance distribution obtained can be significantly distorted. Finally, the tether-in-a-cone model is successfully used to analyze experimental spectra from T4 lysozyme. These results demonstrate the utility of the model and highlight directions for further development. PMID:16214868

  8. Discrete modes of a ferromagnetic stripe dipolarly coupled to a ferromagnetic film: a Brillouin light scattering study.

    PubMed

    Gubbiotti, G; Tacchi, S; Carlotti, G; Ono, T; Roussigné, Y; Tiberkevich, V S; Slavin, A N

    2007-06-20

    Spin wave excitations in a magnetic structure consisting of a series of long permalloy stripes of a rectangular cross section magnetized along the stripe length and situated above a continuous permalloy film are studied both experimentally and theoretically. Stripes and continuous film are coupled by dipole-dipole interaction across 10 nm thick Cu spacers. Experimental measurements made using the Brillouin light scattering technique (with the light wavevector oriented along the stripe width) provide evidence for one dispersive spin wave mode associated with the continuous film and several discrete non-dispersive modes resonating within the finite width of the stripes.To interpret the experimental spectra, an analytic theory based on the spin wave formalism for finite-width magnetic stripes has been developed, achieving a good qualitative and partly quantitative description of the experimentally observed spin wave spectrum of the system. In particular, it is explained why the presence of a continuous magnetic film near the magnetic stripe leads to a substantial decrease of the frequencies of the discrete dipolar spin wave modes localized within the stripes. A more quantitative description of the measured frequencies and of the spatial profiles of the spin wave eigenmodes has been obtained by numerical calculations performed using a finite element method.

  9. Effect of strongly coupled plasma on the magnetic dipolar and quadrupolar transitions of two-electron ions

    SciTech Connect

    Saha, Jayanta K.; Mukherjee, T. K.; Mukherjee, P. K.; Fricke, B.

    2013-04-15

    Effect of strongly coupled plasma on the excitation energies and transition probabilities for the respective transitions 1s{sup 2}:{sup 1}S{sup e}{yields} 1sns:{sup 3}S{sup e} (n = 2, 3, 4) and 1s{sup 2}:{sup 1}S{sup e}{yields} 1snp:{sup 3}P{sup o} (n = 2, 3, 4) allowed by magnetic dipolar and quadrupolar excitations have been analyzed for the first time for the two-electron ions C{sup 4+}, O{sup 6+}, Ne{sup 8+}, Mg{sup 10+}, Si{sup 12+}, and S{sup 14+}. Time dependent Hatree-Fock theory within variational approach has been adopted for such a study. The effect of surrounding plasma has been treated through the standard Ion-Sphere (IS) model of the plasma where the plasma density is varied systematically from a low value to a pretty high value such that the respective excited states go over to continuum due to such a confinement. The effect of external pressure generated due to plasma confinement on the estimated spectral properties has been analyzed systematically.

  10. Paramagnetic-based NMR restraints lift residual dipolar coupling degeneracy in multidomain detergent-solubilized membrane proteins.

    PubMed

    Shi, Lei; Traaseth, Nathaniel J; Verardi, Raffaello; Gustavsson, Martin; Gao, Jiali; Veglia, Gianluigi

    2011-02-23

    Residual dipolar couplings (RDCs) are widely used as orientation-dependent NMR restraints to improve the resolution of the NMR conformational ensemble of biomacromolecules and define the relative orientation of multidomain proteins and protein complexes. However, the interpretation of RDCs is complicated by the intrinsic degeneracy of analytical solutions and protein dynamics that lead to ill-defined orientations of the structural domains (ghost orientations). Here, we illustrate how restraints from paramagnetic relaxation enhancement (PRE) experiments lift the orientational ambiguity of multidomain membrane proteins solubilized in detergent micelles. We tested this approach on monomeric phospholamban (PLN), a 52-residue membrane protein, which is composed of two helical domains connected by a flexible loop. We show that the combination of classical solution NMR restraints (NOEs and dihedral angles) with RDC and PRE constraints resolves topological ambiguities, improving the convergence of the PLN structural ensemble and giving the depth of insertion of the protein within the micelle. The combination of RDCs with PREs will be necessary for improving the accuracy and precision of membrane protein conformational ensembles, where three-dimensional structures are dictated by interactions with the membrane-mimicking environment rather than compact tertiary folds common in globular proteins.

  11. Combined NMR analysis of huge residual dipolar couplings and pseudocontact shifts in terbium(III)-phthalocyaninato single molecule magnets.

    PubMed

    Damjanovic, Marko; Katoh, Keiichi; Yamashita, Masahiro; Enders, Markus

    2013-09-25

    Several small paramagnetic complexes combine large hyperfine NMR shifts with large magnetic anisotropies. The latter are a prerequisite for single molecule magnet (SMM) behavior. We choose the SMM tris(octabutoxyphthalocyaninato) diterbium (1) for a high resolution NMR study where we combined for the first time a comprehensive (1)H and (13)C chemical shift analysis of a SMM with the evaluation of large residual dipolar couplings (RDCs). The latter are a consequence of partial alignment of SMM 1 in the strong magnetic field of the NMR spectrometer. To the best of our knowledge RDCs in SMMs have never been reported before. We measured RDCs between -78 and +99 Hz for the (13)C-(1)H vectors of CH bonds and up to -109 Hz for (1)H-(1)H vectors of geminal hydrogen atoms (magnetic field of 14.09 T, temperature 295 K). Considerable negative Fermi contact shifts (up to -60 ppm) were determined for (13)C atoms at the phthalocyaninato core. Paramagnetic (13)C NMR shifts of the butoxy chains as well as all (1)H NMR chemical shifts are a result of pseudocontact shifts (pcs), and therefore it is easily possible to determine the positions of the respective nuclei in solution. Measurements of CH and HH vectors by RDC analysis are in accordance with the geometry as determined by the pseudocontact shifts, but in addition to that, RDCs give information about internal mobility. The axial component of the magnetic susceptibility tensor has been determined independently by pcs and by RDC.

  12. Strong coupling of gold dipolar nanoantennas by symmetry-breaking in evanescent wave

    NASA Astrophysics Data System (ADS)

    Yang, Jhen-Hong; Chen, Kuo-Ping

    2016-09-01

    Observing the resonance wavelengths of nanoantennas (NAs) with changing incident angles in TM and TE polarization. Extinction cross section shows the dark and bright coupling modes at resonance wavelength of NAs with symmetry breaking oblique incidence. The plasmonic enhancement is stronger under evanescent wave in total internal reflection.

  13. Efficiency of homonuclear Hartmann-Hahn and COSY-type mixing sequences in the presence of scalar and residual dipolar couplings.

    PubMed

    Kramer, Frank; Glaser, Steffen J

    2002-03-01

    In the presence of scalar (J) and residual dipolar (D) couplings, the transfer efficiency of homonuclear Hartmann-Hahn and COSY-type mixing depends on the ratio D/J and on the mixing sequence. This dependence is analyzed theoretically and the results are confirmed experimentally. At least two different mixing sequences are required to yield good transfer efficiencies for all ratios D/J. In contrast to COSY-type experiments, homonuclear Hartmann-Hahn sequences can provide efficient transfer even if the sum of D and J is zero, i.e., if the coupling vanishes in the weak coupling limit.

  14. (15)N CSA tensors and (15)N-(1)H dipolar couplings of protein hydrophobic core residues investigated by static solid-state NMR.

    PubMed

    Vugmeyster, Liliya; Ostrovsky, Dmitry; Fu, Riqiang

    2015-10-01

    In this work, we assess the usefulness of static (15)N NMR techniques for the determination of the (15)N chemical shift anisotropy (CSA) tensor parameters and (15)N-(1)H dipolar splittings in powder protein samples. By using five single labeled samples of the villin headpiece subdomain protein in a hydrated lyophilized powder state, we determine the backbone (15)N CSA tensors at two temperatures, 22 and -35 °C, in order to get a snapshot of the variability across the residues and as a function of temperature. All sites probed belonged to the hydrophobic core and most of them were part of α-helical regions. The values of the anisotropy (which include the effect of the dynamics) varied between 130 and 156 ppm at 22 °C, while the values of the asymmetry were in the 0.32-0.082 range. The Leu-75 and Leu-61 backbone sites exhibited high mobility based on the values of their temperature-dependent anisotropy parameters. Under the assumption that most differences stem from dynamics, we obtained the values of the motional order parameters for the (15)N backbone sites. While a simple one-dimensional line shape experiment was used for the determination of the (15)N CSA parameters, a more advanced approach based on the "magic sandwich" SAMMY pulse sequence (Nevzorov and Opella, 2003) was employed for the determination of the (15)N-(1)H dipolar patterns, which yielded estimates of the dipolar couplings. Accordingly, the motional order parameters for the dipolar interaction were obtained. It was found that the order parameters from the CSA and dipolar measurements are highly correlated, validating that the variability between the residues is governed by the differences in dynamics. The values of the parameters obtained in this work can serve as reference values for developing more advanced magic-angle spinning recoupling techniques for multiple labeled samples.

  15. Wave modes of collective vortex gyration in dipolar-coupled-dot-array magnonic crystals

    PubMed Central

    Han, Dong-Soo; Vogel, Andreas; Jung, Hyunsung; Lee, Ki-Suk; Weigand, Markus; Stoll, Hermann; Schütz, Gisela; Fischer, Peter; Meier, Guido; Kim, Sang-Koog

    2013-01-01

    Lattice vibration modes are collective excitations in periodic arrays of atoms or molecules. These modes determine novel transport properties in solid crystals. Analogously, in periodical arrangements of magnetic vortex-state disks, collective vortex motions have been predicted. Here, we experimentally observe wave modes of collective vortex gyration in one-dimensional (1D) periodic arrays of magnetic disks using time-resolved scanning transmission x-ray microscopy. The observed modes are interpreted based on micromagnetic simulation and numerical calculation of coupled Thiele equations. Dispersion of the modes is found to be strongly affected by both vortex polarization and chirality ordering, as revealed by the explicit analytical form of 1D infinite arrays. A thorough understanding thereof is fundamental both for lattice vibrations and vortex dynamics, which we demonstrate for 1D magnonic crystals. Such magnetic disk arrays with vortex-state ordering, referred to as magnetic metastructure, offer potential implementation into information processing devices. PMID:23877284

  16. Metal-mediated coupling of a coordinated isocyanide and indazoles.

    PubMed

    Kinzhalov, Mikhail A; Boyarskiy, Vadim P; Luzyanin, Konstantin V; Dolgushin, Fedor M; Kukushkin, Vadim Yu

    2013-08-07

    A reaction between equimolar amounts of cis-[PdCl2(CNCy)2] (1) and indazole (HInd, 2) or 5-methylindazole (HInd(Me), 3) proceeded in refluxing CHCl3 for ca. 6 h affording the aminocarbene species cis-[PdCl2{C(Ind)=N(H)Cy}(CNCy)] (4) or cis-[PdCl2{C(Ind(Me))=N(H)Cy}(CNCy)] (5) in good (72-83%) isolated yields. Complexes 4 and 5 were characterized by elemental analyses (C, H, N), HR ESI(+)-MS, IR, and 1D ((1)H, (13)C{(1)H}) and 2D ((1)H,(1)H-COSY, (1)H,(13)C-HMQC/(1)H,(13)C-HSQC, (1)H,(13)C-HMBC) NMR spectroscopies, and complex 4 as well by X-ray diffraction. The observed coupling represents the first example of metal-mediated integration between any isocyanide and any aromatic heterocyclic system having an HN center.

  17. Phase modulation in dipolar-coupled A 2 spin systems: effect of maximum state mixing in 1H NMR in vivo

    NASA Astrophysics Data System (ADS)

    Schröder, Leif; Schmitz, Christian; Bachert, Peter

    2004-12-01

    Coupling constants of nuclear spin systems can be determined from phase modulation of multiplet resonances. Strongly coupled systems such as citrate in prostatic tissue exhibit a more complex modulation than AX connectivities, because of substantial mixing of quantum states. An extreme limit is the coupling of n isochronous spins (A n system). It is observable only for directly connected spins like the methylene protons of creatine and phosphocreatine which experience residual dipolar coupling in intact muscle tissue in vivo. We will demonstrate that phase modulation of this "pseudo-strong" system is quite simple compared to those of AB systems. Theory predicts that the spin-echo experiment yields conditions as in the case of weak interactions, in particular, the phase modulation depends linearly on the line splitting and the echo time.

  18. Graphene oxide liquid crystals as a versatile and tunable alignment medium for the measurement of residual dipolar couplings in organic solvents.

    PubMed

    Lei, Xinxiang; Xu, Zhen; Sun, Han; Wang, Shun; Griesinger, Christian; Peng, Li; Gao, Chao; Tan, Ren X

    2014-08-13

    Residual dipolar couplings (RDCs) have proven to be an invaluable anisotropic NMR parameter for the structural elucidation of complex biopolymers and organic molecules. However, a remaining bottleneck limiting its wider use by organic and natural product chemists is the lack of a range of easily applicable aligning media for diverse organic solvents. In this study, graphene oxide (GO) liquid crystals (LCs) were developed to induce partial orientation of organic molecules to allow RDC measurements. These LCs were determined to be maintainable at very low concentrations (as low as 1 mg/mL, corresponding to quadrupolar (2)H splittings ranging from 2.8 to 30 Hz and maximum (13)C-(1)H dipolar couplings of 20 Hz for camphor in a CH3COCH3/water system) and to be remarkably stable and broadly compatible with aqueous and organic solvents such as dimethyl sulfoxide, CH3COCH3, and CH3CN. Moreover, compared with those for other alignment media, very clean and high-quality NMR spectra were acquired with the GO molecules in solution because of their rigidity and high molecular weight. The developed medium offers a versatile and robust method for RDC measurements that may routinize the RDC-based structure determination of organic molecules.

  19. Molecular dynamics and information on possible sites of interaction of intramyocellular metabolites in vivo from resolved dipolar couplings in localized 1H NMR spectra

    NASA Astrophysics Data System (ADS)

    Schröder, Leif; Schmitz, Christian; Bachert, Peter

    2004-12-01

    Proton NMR resonances of the endogenous metabolites creatine and phosphocreatine ((P)Cr), taurine (Tau), and carnosine (Cs, β-alanyl- L-histidine) were studied with regard to residual dipolar couplings and molecular mobility. We present an analysis of the direct 1H- 1H interaction that provides information on motional reorientation of subgroups in these molecules in vivo. For this purpose, localized 1H NMR experiments were performed on m. gastrocnemius of healthy volunteers using a 1.5-T clinical whole-body MR scanner. We evaluated the observable dipolar coupling strength SD0 ( S = order parameter) of the (P)Cr-methyl triplet and the Tau-methylene doublet by means of the apparent line splitting. These were compared to the dipolar coupling strength of the (P)Cr-methylene doublet. In contrast to the aliphatic protons of (P)Cr and Tau, the aromatic H2 ( δ = 8 ppm) and H4 ( δ = 7 ppm) protons of the imidazole ring of Cs exhibit second-order spectra at 1.5 T. This effect is the consequence of incomplete transition from Zeeman to Paschen-Back regime and allows a determination of SD0 from H2 and H4 of Cs as an alternative to evaluating the multiplet splitting which can be measured directly in high-resolution 1H NMR spectra. Experimental data showed striking differences in the mobility of the metabolites when the dipolar coupling constant D0 (calculated with the internuclear distance known from molecular geometry in the case of complete absence of molecular dynamics and motion) is used for comparison. The aliphatic signals involve very small order parameters S ≈ (1.4 - 3) × 10 -4 indicating rapid reorientation of the corresponding subgroups in these metabolites. In contrast, analysis of the Cs resonances yielded S ≈ (113 - 137) × 10 -4. Thus, the immobilization of the Cs imidazole ring owing to an anisotropic cellular substructure in human m. gastrocnemius is much more effective than for (P)Cr and Tau subgroups. Furthermore, 1H NMR experiments on aqueous model

  20. A device for the measurement of residual chemical shift anisotropy and residual dipolar coupling in soluble and membrane-associated proteins

    PubMed Central

    Liu, Yizhou

    2010-01-01

    Residual dipolar coupling (RDC) and residual chemical shift anisotropy (RCSA) report on orientational properties of a dipolar bond vector and a chemical shift anisotropy principal axis system, respectively. They can be highly complementary in the analysis of backbone structure and dynamics in proteins as RCSAs generally include a report on vectors out of a peptide plane while RDCs usually report on in-plane vectors. Both RDC and RCSA average to zero in isotropic solutions and require partial orientation in a magnetic field to become observable. While the alignment and measurement of RDC has become routine, that of RCSA is less common. This is partly due to difficulties in providing a suitable isotopic reference spectrum for the measurement of the small chemical shift offsets coming from RCSA. Here we introduce a device (modified NMR tube) specifically designed for accurate measurement of reference and aligned spectra for RCSA measurements, but with a capacity for RDC measurements as well. Applications to both soluble and membrane anchored proteins are illustrated. PMID:20506033

  1. An encodable lanthanide binding tag with reduced size and flexibility for measuring residual dipolar couplings and pseudocontact shifts in large proteins

    PubMed Central

    Barb, Adam W.; Subedi, Ganesh P.

    2016-01-01

    Metal ions serve important roles in structural biology applications from long-range perturbations seen in magnetic resonance experiments to electron-dense signatures in x-ray crystallography data; however, the metal ion must be secured in a molecular framework to achieve the maximum benefit. Polypeptide-based lanthanide-binding tags (LBTs) represent one option that can be directly encoded within a recombinant protein expression construct. However, LBTs often exhibit significant mobility relative to the target molecule. Here we report the characterization of improved LBTs sequences for insertion into a protein loop. These LBTs were inserted to connect two parallel alpha helices of an immunoglobulin G (IgG)-binding Z domain platform. Variants A and B bound Tb3+ with high affinity (0.70 and 0.13 µM, respectively) and displayed restricted LBT motion. Compared to the parent construct, the metal-bound A experienced a 2.5-fold reduction in tag motion as measured by magnetic field-induced residual dipolar couplings and was further studied in a 72.2 kDa complex with the human IgG1 fragment crystallizable (IgG1 Fc) glycoprotein. The appearance of both pseudo-contact shifts (-0.221 to 0.081 ppm) and residual dipolar couplings (-7.6 to 14.3 Hz) of IgG1 Fc resonances in the IgG1 Fc:(variant A:Tb3+)2 complex indicated structural restriction of the LBT with respect to the Fc. These studies highlight the applicability of improved LBT sequences with reduced mobility to probe the structure of macromolecular systems. PMID:26728077

  2. An encodable lanthanide binding tag with reduced size and flexibility for measuring residual dipolar couplings and pseudocontact shifts in large proteins.

    PubMed

    Barb, Adam W; Subedi, Ganesh P

    2016-01-01

    Metal ions serve important roles in structural biology applications from long-range perturbations seen in magnetic resonance experiments to electron-dense signatures in X-ray crystallography data; however, the metal ion must be secured in a molecular framework to achieve the maximum benefit. Polypeptide-based lanthanide-binding tags (LBTs) represent one option that can be directly encoded within a recombinant protein expression construct. However, LBTs often exhibit significant mobility relative to the target molecule. Here we report the characterization of improved LBTs sequences for insertion into a protein loop. These LBTs were inserted to connect two parallel alpha helices of an immunoglobulin G (IgG)-binding Z domain platform. Variants A and B bound Tb(3+) with high affinity (0.70 and 0.13 μM, respectively) and displayed restricted LBT motion. Compared to the parent construct, the metal-bound A experienced a 2.5-fold reduction in tag motion as measured by magnetic field-induced residual dipolar couplings and was further studied in a 72.2 kDa complex with the human IgG1 fragment crystallizable (IgG1 Fc) glycoprotein. The appearance of both pseudo-contact shifts (-0.221 to 0.081 ppm) and residual dipolar couplings (-7.6 to 14.3 Hz) of IgG1 Fc resonances in the IgG1 Fc:(variant A:Tb(3+))2 complex indicated structural restriction of the LBT with respect to the Fc. These studies highlight the applicability of improved LBT sequences with reduced mobility to probe the structure of macromolecular systems.

  3. Rotational ratchets with dipolar interactions.

    PubMed

    Jäger, Sebastian; Klapp, Sabine H L

    2012-12-01

    We report results from a computer simulation study on the rotational ratchet effect in systems of magnetic particles interacting via dipolar interactions. The ratchet effect consists of directed rotations of the particles in an oscillating magnetic field, which lacks a net rotating component. Our investigations are based on Brownian dynamics simulations of such many-particle systems. We investigate the influence of both the random and deterministic contributions to the equations of motion on the ratchet effect. As a main result, we show that dipolar interactions can have an enhancing as well as a dampening effect on the ratchet behavior depending on the dipolar coupling strength of the system under consideration. The enhancement is shown to be caused by an increase in the effective field on a particle generated by neighboring magnetic particles, while the dampening is due to restricted rotational motion in the effective field. Moreover, we find a nontrivial influence of the short-range, repulsive interaction between the particles.

  4. Orientation of the antimicrobial peptide PGLa in lipid membranes determined from 19F-NMR dipolar couplings of 4-CF3-phenylglycine labels.

    PubMed

    Glaser, Ralf W; Sachse, Carsten; Dürr, Ulrich H N; Wadhwani, Parvesh; Ulrich, Anne S

    2004-05-01

    A highly sensitive solid state (19)F-NMR strategy is described to determine the orientation and dynamics of membrane-associated peptides from specific fluorine labels. Several analogues of the antimicrobial peptide PGLa were synthesized with the non-natural amino acid 4-trifluoromethyl-phenylglycine (CF(3)-Phg) at different positions throughout the alpha-helical peptide chain. A simple 1-pulse (19)F experiment allows the simultaneous measurement of both the anisotropic chemical shift and the homonuclear dipolar coupling within the rotating CF(3)-group in a macroscopically oriented membrane sample. The value and sign of the dipolar splitting determines the tilt of the CF(3)-rotational axis, which is rigidly attached to the peptide backbone, with respect to the external magnetic field direction. Using four CF(3)-labeled peptide analogues (with L-CF(3)-Phg at Ile9, Ala10, Ile13, and Ala14) we confirmed that PGLa is aligned at the surface of lipid membranes with its helix axis perpendicular to the bilayer normal at a peptide:lipid ratio of 1:200. We also determined the azimuthal rotation angle of the helix, which agrees well with the orientation expected from its amphiphilic character. Peptide analogues with a D-CF(3)-Phg label resulting from racemization of the amino acid during synthesis were separately collected by HPLC. Their spectra provide additional information about the PGLa structure and orientation but allow only to discriminate qualitatively between multiple solutions. The structural and functional characterization of the individual CF(3)-labeled peptides by circular dichroism and antimicrobial assays showed only small effects for our four substitutions on the hydrophobic face of the helix, but a significant disturbance was observed in a fifth analogue where Ala8 on the hydrophilic face had been replaced. Even though the hydrophobic CF(3)-Phg side chain cannot be utilized in all positions, it allows highly sensitive NMR measurements over a wide range of

  5. Side Chain Conformational Distributions of a Small Protein Derived from Model-Free Analysis of a Large Set of Residual Dipolar Couplings.

    PubMed

    Li, Fang; Grishaev, Alexander; Ying, Jinfa; Bax, Ad

    2015-11-25

    Accurate quantitative measurement of structural dispersion in proteins remains a prime challenge to both X-ray crystallography and NMR spectroscopy. Here we use a model-free approach based on measurement of many residual dipolar couplings (RDCs) in differentially orienting aqueous liquid crystalline solutions to obtain the side chain χ1 distribution sampled by each residue in solution. Applied to the small well-ordered model protein GB3, our approach reveals that the RDC data are compatible with a single narrow distribution of side chain χ1 angles for only about 40% of the residues. For more than half of the residues, populations greater than 10% for a second rotamer are observed, and four residues require sampling of three rotameric states to fit the RDC data. In virtually all cases, sampled χ1 values are found to center closely around ideal g(-), g(+) and t rotameric angles, even though no rotamer restraint is used when deriving the sampled angles. The root-mean-square difference between experimental (3)JHαHβ couplings and those predicted by the Haasnoot-parametrized, motion-adjusted Karplus equation reduces from 2.05 to 0.75 Hz when using the new rotamer analysis instead of the 1.1-Å X-ray structure as input for the dihedral angles. A comparison between observed and predicted (3)JHαHβ values suggests that the root-mean-square amplitude of χ1 angle fluctuations within a given rotamer well is ca. 20°. The quantitatively defined side chain rotamer equilibria obtained from our study set new benchmarks for evaluating improved molecular dynamics force fields, and also will enable further development of quantitative relations between side chain chemical shift and structure.

  6. Asymmetric dipolar ring

    DOEpatents

    Prosandeev, Sergey A.; Ponomareva, Inna V.; Kornev, Igor A.; Bellaiche, Laurent M.

    2010-11-16

    A device having a dipolar ring surrounding an interior region that is disposed asymmetrically on the ring. The dipolar ring generates a toroidal moment switchable between at least two stable states by a homogeneous field applied to the dipolar ring in the plane of the ring. The ring may be made of ferroelectric or magnetic material. In the former case, the homogeneous field is an electric field and in the latter case, the homogeneous field is a magnetic field.

  7. Second virial coefficients of dipolar hard spheres.

    PubMed

    Philipse, Albert P; Kuipers, Bonny W M

    2010-08-18

    An asymptotic formula is reported for the second virial coefficient B(2) of a dipolar hard-sphere (DHS) fluid, in zero external field, for strongly coupled dipolar interactions. This simple formula, together with the one for the weak-coupling B(2), provides an accurate prediction of the second virial coefficient for a wide range of dipole moments, including those that are experimentally accessible in magnetite ferrofluids. The weak-coupling B(2) also yields an estimate of the magnetic moment minimally needed for isotropic gas-liquid phase-separation, if any, in the DHS fluid.

  8. High-throughput backbone resonance assignment of small 13C, 15N-labeled proteins by a triple-resonance experiment with four sequential connectivity pathways using chemical shift-dependent, apparent 1J ( 1H, 13C): HNCACB codedHAHB

    NASA Astrophysics Data System (ADS)

    Pegan, Scott; Kwiatkowski, Witek; Choe, Senyon; Riek, Roland

    2003-12-01

    The proposed three-dimensional triple-resonance experiment HNCACB codedHAHB correlates sequential 15N, 1H moieties via the chemical shifts of 13C α, 13C β, 1H α, and 1H β. The four sequential correlation pathways are achieved by the incorporation of the concept of chemical shift-coding [J. Biomol. NMR 25 (2003) 281] to the TROSY-HNCACB experiment. The monitored 1H α and 1H β chemical shifts are then coded in the line shape of the cross-peaks of 13C α, 13C β along the 13C dimension through an apparent residual scalar coupling, the size of which depends on the attached hydrogen chemical shift. The information of four sequential correlation pathways enables a rapid backbone assignment. The HNCACB codedHAHB experiment was applied to ˜85% labeled 13C, 15N-labeled amino-terminal fragment of Vaccinia virus DNA topoisomerase I comprising residues 1-77. After one day of measurement on a Bruker Avance 700 MHz spectrometer and 8 h of manual analysis of the spectrum 93% of the backbone assignment was achieved.

  9. Self-consistent residual dipolar coupling based model-free analysis for the robust determination of nanosecond to microsecond protein dynamics.

    PubMed

    Lakomek, Nils-Alexander; Walter, Korvin F A; Farès, Christophe; Lange, Oliver F; de Groot, Bert L; Grubmüller, Helmut; Brüschweiler, Rafael; Munk, Axel; Becker, Stefan; Meiler, Jens; Griesinger, Christian

    2008-07-01

    Residual dipolar couplings (RDCs) provide information about the dynamic average orientation of inter-nuclear vectors and amplitudes of motion up to milliseconds. They complement relaxation methods, especially on a time-scale window that we have called supra-tau(c) (tau(c) < supra-tau(c) < 50 micros). Here we present a robust approach called Self-Consistent RDC-based Model-free analysis (SCRM) that delivers RDC-based order parameters-independent of the details of the structure used for alignment tensor calculation-as well as the dynamic average orientation of the inter-nuclear vectors in the protein structure in a self-consistent manner. For ubiquitin, the SCRM analysis yields an average RDC-derived order parameter of the NH vectors 0.72 +/- 0.02 compared to = 0.778 +/- 0.003 for the Lipari-Szabo order parameters, indicating that the inclusion of the supra-tau(c) window increases the averaged amplitude of mobility observed in the sub-supra-tau(c) window by about 34%. For the beta-strand spanned by residues Lys48 to Leu50, an alternating pattern of backbone NH RDC order parameter S2(rdc)(NH) = (0.59, 0.72, 0.59) was extracted. The backbone of Lys48, whose side chain is known to be involved in the poly-ubiquitylation process that leads to protein degradation, is very mobile on the supra-tau(c) time scale (S2(rdc)(NH) = 0.59 +/- 0.03), while it is inconspicuous (S2(LS)(NH)= 0.82) on the sub-tau(c) as well as on micros-ms relaxation dispersion time scales. The results of this work differ from previous RDC dynamics studies of ubiquitin in the sense that the results are essentially independent of structural noise providing a much more robust assessment of dynamic effects that underlie the RDC data.

  10. Expression, Functional Characterization, and Solid-State NMR Investigation of the G Protein-Coupled GHS Receptor in Bilayer Membranes

    PubMed Central

    Schrottke, Stefanie; Kaiser, Anette; Vortmeier, Gerrit; Els-Heindl, Sylvia; Worm, Dennis; Bosse, Mathias; Schmidt, Peter; Scheidt, Holger A.; Beck-Sickinger, Annette G.; Huster, Daniel

    2017-01-01

    The expression, functional reconstitution and first NMR characterization of the human growth hormone secretagogue (GHS) receptor reconstituted into either DMPC or POPC membranes is described. The receptor was expressed in E. coli. refolded, and reconstituted into bilayer membranes. The molecule was characterized by 15N and 13C solid-state NMR spectroscopy in the absence and in the presence of its natural agonist ghrelin or an inverse agonist. Static 15N NMR spectra of the uniformly labeled receptor are indicative of axially symmetric rotational diffusion of the G protein-coupled receptor in the membrane. In addition, about 25% of the 15N sites undergo large amplitude motions giving rise to very narrow spectral components. For an initial quantitative assessment of the receptor mobility, 1H-13C dipolar coupling values, which are scaled by molecular motions, were determined quantitatively. From these values, average order parameters, reporting the motional amplitudes of the individual receptor segments can be derived. Average backbone order parameters were determined with values between 0.56 and 0.69, corresponding to average motional amplitudes of 40–50° of these segments. Differences between the receptor dynamics in DMPC or POPC membranes were within experimental error. Furthermore, agonist or inverse agonist binding only insignificantly influenced the average molecular dynamics of the receptor. PMID:28387359

  11. Facile one-pot synthesis of 4,5-disubstituted 1,2,3-(NH)-triazoles through Sonogashira coupling/1,3-dipolar cycloaddition of acid chlorides, terminal acetylenes, and sodium azide.

    PubMed

    Li, Jihui; Wang, Dong; Zhang, Yuanqing; Li, Jiting; Chen, Baohua

    2009-07-16

    A novel and efficient way of synthesizing 4,5-disubstituted-1,2,3-(NH)-triazoles through palladium-catalyzed and ultrasonic promoted Sonogashira coupling/1,3-dipolar cycloaddition of acid chlorides, terminal acetylenes, and sodium azide in one pot is developed. The reaction scope is quite general, and the methodology can produce excellent yields. The regioselective 1,4,5-trisubstituted-1,2,3-(NH)-triazoles can be made easily from 4,5-disubstituted-1,2,3-(NH)-triazoles.

  12. Pulsed electron spin nutation spectroscopy for weakly exchange-coupled multi-spin molecular systems with nuclear hyperfine couplings: a general approach to bi- and triradicals and determination of their spin dipolar and exchange interactions

    NASA Astrophysics Data System (ADS)

    Ayabe, Kazuki; Sato, Kazunobu; Nakazawa, Shigeaki; Nishida, Shinsuke; Sugisaki, Kenji; Ise, Tomoaki; Morita, Yasushi; Toyota, Kazuo; Shiomi, Daisuke; Kitagawa, Masahiro; Suzuki, Shuichi; Okada, Keiji; Takui, Takeji

    2013-10-01

    Weakly exchange-coupled biradicals have attracted much attention in terms of their dynamic nuclear polarisation application in NMR spectroscopy for biological systems or the use of synthetic electron-spin qubits in quantum information processing/quantum-computing technology. Analogues multi-partite molecular systems are important in entering a new phase of the relevant fields. Many stable organic biradicals known so far have nitrogen nuclei at their electron spin sites, where singly occupied molecular orbitals are dominating and large hyperfine couplings occur. A salient feature of such weakly exchange-coupled molecular systems in terms of electronic spin structures is underlain by small zero-field splitting (ZFS) parameters comparable with nuclear hyperfine and/or exchange interactions. Pulse-based electron spin nutation (ESN) spectroscopy of weakly exchange-coupled biradicals, applicable to oriented or non-oriented media, has proven to be a useful and facile approach to the determination of ZFS parameters, which reflect relatively short distances between unpaired electron spins. In the present study, we first treat two-dimensional single-crystal ESN spectroscopy (Q-band) of a 15N-labelled weakly exchange-coupled biradical, showing the nuclear hyperfine effects on the ESN phenomena from both the experimental and theoretical side. ESN spectroscopy is transition moment spectroscopy, in which the nutation frequency as a function of the microwave irradiation strength ω1 (angular frequency) for any cases of weakly exchange-coupled systems can be treated. The results provide a testing ground for the simplified but general approach to the ESN analysis. In this study, we have invoked single-crystal electron-electron double resonance measurements on a typical biradical well incorporated in a diamagnetic host lattice and checked the accuracy of our ESN analysis for the spin dipolar tensor and exchange interaction. Next, we extend the general approach to analogues multi

  13. Self-consistent residual dipolar coupling based model-free analysis for the robust determination of nanosecond to microsecond protein dynamics

    PubMed Central

    Lakomek, Nils-Alexander; Walter, Korvin F. A.; Farès, Christophe; Lange, Oliver F.; de Groot, Bert L.; Grubmüller, Helmut; Brüschweiler, Rafael; Munk, Axel; Becker, Stefan; Meiler, Jens

    2008-01-01

    Residual dipolar couplings (RDCs) provide information about the dynamic average orientation of inter-nuclear vectors and amplitudes of motion up to milliseconds. They complement relaxation methods, especially on a time-scale window that we have called supra-\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\tau _c $$\\end{document} (\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\tau _c $$\\end{document} < supra-\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\tau _c $$\\end{document} < 50 μs). Here we present a robust approach called Self-Consistent RDC-based Model-free analysis (SCRM) that delivers RDC-based order parameters—independent of the details of the structure used for alignment tensor calculation—as well as the dynamic average orientation of the inter-nuclear vectors in the protein structure in a self-consistent manner. For ubiquitin, the SCRM analysis yields an average RDC-derived order parameter of the NH vectors \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\left\\langle {S_{rdc}^2 } \\right\\rangle = 0.72 \\pm 0.02 $$\\end{document} compared to \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage

  14. Propagation of collective modes in non-overlapping dipolar Bose-Einstein Condensates

    NASA Astrophysics Data System (ADS)

    Gallemi, A.; Guilleumas, M.; Mayol, R.; Pi, M.

    2014-04-01

    We investigate long-range effects of the dipolar interaction in Bose-Einstein condensates by solving the time-dependent 3D Gross-Pitaevskii equation. We study the propagation of excitations between non-overlapping condensates when a collective mode is excited in one of the condensates. We obtain the frequency shifts due to the long-range character of the dipolar coupling for the bilayer and also the trilayer system when the dipolar mode is excited in one condensate. The propagation of the monopolar and quadrupolar modes are also investigated. The coupled-pendulum model is proposed to qualitatively explain the long range effects of the dipolar coupling.

  15. Cross-Correlated Relaxation of Dipolar Coupling and Chemical-Shift Anisotropy in Magic-Angle Spinning R1ρ NMR Measurements: Application to Protein Backbone Dynamics Measurements

    PubMed Central

    Kurauskas, Vilius; Weber, Emmanuelle; Hessel, Audrey; Ayala, Isabel; Marion, Dominique; Schanda, Paul

    2016-01-01

    Transverse relaxation rate measurements in MAS solid-state NMR provide information about molecular motions occurring on nanoseconds-to-milliseconds (ns-ms) time scales. The measurement of heteronuclear (13C, 15N) relaxation rate constants in the presence of a spin-lock radio-frequency field (R1ρ relaxation) provides access to such motions, and an increasing number of studies involving R1ρ relaxation in proteins has been reported. However, two factors that influence the observed relaxation rate constants have so far been neglected, namely (i) the role of CSA/dipolar cross-correlated relaxation (CCR), and (ii) the impact of fast proton spin flips (i.e. proton spin diffusion and relaxation). We show that CSA/D CCR in R1ρ experiments is measurable, and that this cross-correlated relaxation rate constant depends on ns-ms motions, and can thus itself provide insight into dynamics. We find that proton spin-diffusion attenuates this cross-correlated relaxation, due to its decoupling effect on the doublet components. For measurements of dynamics, the use of R1ρ rate constants has practical advantages over the use of CCR rates, and the present manuscript reveals factors that have so far been disregarded and which are important for accurate measurements and interpretation. PMID:27500976

  16. Evanescent Wave-Assisted Symmetry Breaking of Gold Dipolar Nanoantennas

    PubMed Central

    Yang, Jhen-Hong; Chen, Kuo-Ping

    2016-01-01

    Symmetry-breaking and scattering cancellation were observed in the dark-mode resonance of dipolar gold nanoantennas (NAs) on glass substrates coupled with oblique incidence and total internal reflection. With the assistance of evanescent waves, the coupling efficiency was twice as strong when the incidence angle was larger than the critical angle. The Hamiltonian equation and absorption spectra were used to analyze the hybridization model of symmetric dipolar gold NAs. The antibonding mode could be coupled successfully by both transverse-magnetic (TM) and transverse-electric (TE) polarizations to NAs when the dimers orientation is parallel to the propagation direction of evanescent waves. PMID:27581766

  17. Evanescent Wave-Assisted Symmetry Breaking of Gold Dipolar Nanoantennas

    NASA Astrophysics Data System (ADS)

    Yang, Jhen-Hong; Chen, Kuo-Ping

    2016-09-01

    Symmetry-breaking and scattering cancellation were observed in the dark-mode resonance of dipolar gold nanoantennas (NAs) on glass substrates coupled with oblique incidence and total internal reflection. With the assistance of evanescent waves, the coupling efficiency was twice as strong when the incidence angle was larger than the critical angle. The Hamiltonian equation and absorption spectra were used to analyze the hybridization model of symmetric dipolar gold NAs. The antibonding mode could be coupled successfully by both transverse-magnetic (TM) and transverse-electric (TE) polarizations to NAs when the dimers orientation is parallel to the propagation direction of evanescent waves.

  18. Toroidal dipolar responses in a planar metamaterial

    NASA Astrophysics Data System (ADS)

    Guo, Linyan; Li, Minhua; Yang, Helin; Huang, Xiaojun; Wu, Song

    2014-10-01

    Both the magnetic toroidal dipolar (MTD) response and electric toroidal dipolar (ETD) response have been achieved and studied in the microwave region by designing a feasible planar metamaterial. By changing the polarized direction of a normally incident wave, two different coupling modes are observed, and therefore MTD and ETD responses can be achieved accordingly. It is also confirmed by scattered powers for various multipole moments and field distributions that they dominate over other traditional multipole responses at 5.69 GHz and 11.69 GHz, respectively. In view of the design feasibility of planar metamaterial, these resonance-enhanced MTD and ETD responses could provide an avenue for various interesting phenomena associated with the elusive toroidal moments.

  19. Characterization of slow conformational dynamics in solids: dipolar CODEX.

    PubMed

    Li, Wenbo; McDermott, Ann E

    2009-09-01

    A solid state NMR experiment is introduced for probing relatively slow conformational exchange, based on dephasing and refocusing dipolar couplings. The method is closely related to the previously described Centerband-Only Detection of Exchange or CODEX experiment. The use of dipolar couplings for this application is advantageous because their values are known a priori from molecular structures, and their orientations and reorientations relate in a simple way to molecular geometry and motion. Furthermore the use of dipolar couplings in conjunction with selective isotopic enrichment schemes is consistent with selection for unique sites in complex biopolymers. We used this experiment to probe the correlation time for the motion of (13)C, (15)N enriched urea molecules within their crystalline lattice.

  20. Integrated Paramagnetic Resonance of High-Spin Co(II) in Axial Symmetry: Chemical Separation of Dipolar and Contact Electron-Nuclear Couplings

    PubMed Central

    Myers, William K.; Duesler, Eileen N.; Tierney, David L.

    2015-01-01

    Integrated paramagnetic resonance, utilizing EPR, NMR and ENDOR, of a series of cobalt bis-trispyrazolylborates, Co(Tpx)2, are reported. Systematic substitutions at the ring carbons and on the apical boron provide a unique opportunity to separate through-bond and through-space contributions to the NMR hyperfine shifts for the parent, unsubstituted Tp complex. A simple relationship between the chemical shift difference (δH − δMe) and the contact shift of the proton in that position is developed. This approach allows independent extraction of the isotropic hyperfine coupling, Aiso, for each proton in the molecule. The Co··H contact coupling energies derived from the NMR, together with the known metrics of the compounds, were used to predict the ENDOR couplings at gζ. Proton ENDOR data is presented that shows good agreement with the NMR-derived model. ENDOR signals from all other magnetic nuclei in the complex (14N, coordinating and non-coordinating, 11B and 13C) are also reported. PMID:18605690

  1. Fermionized Dipolar Bosons Trapped in a Harmonic Trap

    NASA Astrophysics Data System (ADS)

    Kościk, Przemysław

    2017-03-01

    We explore entanglement properties of systems of identical dipolar bosons confined in a 1D harmonic trap by using explicitly correlated Jastrow-type wavefunctions. Results for the linear entropy in dependence on the dimensionless coupling and the number of particles are provided and discussed.

  2. Solution NMR structure of putidaredoxin-cytochrome P450cam complex via a combined residual dipolar coupling-spin labeling approach suggests a role for Trp106 of putidaredoxin in complex formation

    PubMed Central

    Zhang, Wei; Pochapsky, Susan S.; Pochapsky, Thomas C.; Jain, Nitin U.

    2017-01-01

    The 58 kDa complex formed between the [2Fe-2S] ferredoxin, putidaredoxin (Pdx), and cytochrome P450cam (CYP101) from the bacterium Pseudomonas putida has been investigated by high-resolution solution NMR spectroscopy. Pdx serves as both the physiological reductant and effector for CYP101 in the enzymatic reaction involving conversion of substrate camphor to 5-exo-hydroxy-camphor. In order to obtain an experimental structure for the oxidized Pdx-CYP101 complex, a combined approach using orientational data on the two proteins derived from residual dipolar couplings and distance restraints from site-specific spin labeling of Pdx has been applied. Spectral changes for residues in and near the paramagnetic metal cluster region of Pdx in complex with CYP101 have also been mapped for the first time using 15N and 13C NMR spectroscopy, leading to direct identification of the residues strongly affected by CYP101 binding. The new NMR structure of the Pdx-CYP101 complex agrees well with results from previous mutagenesis and biophysical studies involving residues at the binding interface such as formation of salt bridge between Asp38 of Pdx and Arg112 of CYP101, while at the same time identifying key features different from earlier modeling studies. Analysis of the binding interface of the complex reveals that the side-chain of Trp106, the C-terminal residue of Pdx and critical for binding to CYP101, is located across from the heme-binding loop of CYP101 and forms non-polar contacts with several residues in the vicinity of heme group on CYP101, pointing to a potentially important role in complex formation. PMID:18835276

  3. Increased tricarboxylic acid cycle flux in rat brain during forepaw stimulation detected with 1H[13C]NMR.

    PubMed Central

    Hyder, F; Chase, J R; Behar, K L; Mason, G F; Siddeek, M; Rothman, D L; Shulman, R G

    1996-01-01

    NMR spectroscopy was used to test recent proposals that the additional energy required for brain activation is provided through nonoxidative glycolysis. Using localized NMR spectroscopic methods, the rate of C4-glutamate isotopic turnover from infused [1-(13)C]glucose was measured in the somatosensory cortex of rat brain both at rest and during forepaw stimulation. Analysis of the glutamate turnover data using a mathematical model of cerebral glucose metabolism showed that the tricarboxylic acid cycle flux [(V(TCA)] increased from 0.49 +/- 0.03 at rest to 1.48 +/- 0.82 micromol/g/min during stimulation (P < 0.01). The minimum fraction of C4-glutamate derived from C1-glucose was approximately 75%, and this fraction was found in both the resting and stimulated rats. Hence, the percentage increase in oxidative cerebral metabolic rate of glucose use (CMRglc) equals the percentage increases in V(TCA) and cerebral metabolic rate of oxygen consumption (CMRO2). Comparison with previous work for the same rat model, which measured total CMRglc [Ueki, M., Linn, F. & Hossman, K. A. (1988) J. Cereb. Blood Flow Metab. 8, 486-4941, indicates that oxidative CMRglc supplies the majority of energy during sustained brain activation. Images Fig. 2 PMID:8755523

  4. Quantitative and qualitative 1H, 13C, and 15N NMR spectroscopic investigation of the urea-formaldehyde resin synthesis.

    PubMed

    Steinhof, Oliver; Kibrik, Éléonore J; Scherr, Günter; Hasse, Hans

    2014-04-01

    Urea-formaldehyde resins are bulk products of the chemical industry. Their synthesis involves a complex reaction network. The present work contributes to its elucidation by presenting results from detailed NMR spectroscopic studies with different methods. Besides (1)H NMR and (13)C NMR, (15)N NMR spectroscopy is also applied. (15)N-enriched urea was used for the investigations. A detailed NMR signal assignment and a model of the reaction network of the hydroxymethylation step of the synthesis are presented. Because of its higher spectral dispersion and the fact that all key reactions directly involve the nitrogen centers, (15)N NMR provides a much larger amount of detail than do (1)H and (13)C NMR spectroscopy. Symmetric and asymmetric dimethylol urea can be clearly distinguished and separated from monomethylol urea, trimethylol urea, and methylene-bridged urea. The existence of hemiformals of methylol urea is confirmed. 1,3,5-Oxadiazinan-4-on (uron) and its derivatives were not found in the reaction mixtures investigated here but were prepared via alternative routes. The molar ratios of formaldehyde to urea were 1, 2, and 4, the pH values 7.5 and 8.5, and the reaction temperature 60 °C.

  5. 1H, 13C, and 15N backbone and side chain resonance assignments of thermophilic Geobacillus kaustophilus cyclophilin-A

    SciTech Connect

    Holliday, Michael; Zhang, Fengli; Isern, Nancy G.; Armstrong, Geoffrey S.; Eisenmesser, Elan Z.

    2014-04-01

    Cyclophilins catalyze the reversible peptidyl-prolyl isomerization of their substrates and are present across all kingdoms of life from humans to bacteria. Although numerous biological roles have now been discovered for cyclophilins, their function was initially ascribed to their chaperone-like activity in protein folding where they catalyze the often rate-limiting step of proline isomerization. This chaperone-like activity may be especially important under extreme conditions where cyclophilins are often over expressed, such as in tumors for human cyclophilins {Lee, 2010 #1167}, but also in organisms that thrive under extreme conditions, such as theromophilic bacteria. Moreover, the reversible nature of the peptidyl-prolyl isomerization reaction catalyzed by cyclophilins has allowed these enzymes to serve as model systems for probing the role of conformational changes during catalytic turnover {Eisenmesser, 2002 #20;Eisenmesser, 2005 #203}. Thus, we present here the resonance assignments of a thermophilic cyclophilin from Geobacillus kaustophilus derived from deep-sea sediment {Takami, 2004 #1384}. This thermophilic cyclophilin may now be studied at a variety of temperatures to provide insight into the comparative structure, dynamics, and catalytic mechanism of cyclophilins.

  6. 1H, 13C and 15N resonance assignment of the cytosolic dithiol glutaredoxin 1 from the pathogen Trypanosoma brucei.

    PubMed

    Stefani, Monica; Sturlese, Mattia; Manta, Bruno; Löhr, Frank; Mammi, Stefano; Comini, Marcelo; Bellanda, Massimo

    2016-04-01

    Trypanosomatids are parasites responsible for several tropical and subtropical diseases, such as Chaga's disease, sleeping sickness and Leishmaniasis. In contrast to the mammalian host, the thiol-redox metabolism of these pathogens depends on trypanothione [bis-glutathionylspermidine, T(SH)2] instead of glutathione (GSH) providing a set of lineage-specific proteins as drug target candidates. Glutaredoxins (Grx) are ubiquitous small thiol-disulfide oxidoreductases that belong to the thioredoxin-fold family. They play a central role in redox homeostasis and iron sulfur-cluster biogenesis. Each species, including trypanosomes, possesses its own set of isoforms distributed in different subcellular compartments. The genome of trypanosomatids encodes for two class I (dithiolic) Grxs named 2-C-Grx1 and 2-C-Grx2. Both proteins were shown to efficiently reduce different disulfides at the expenses of T(SH)2 using a mechanism that involves the two cysteines in the active site. Moreover, the cytosolic Trypanosoma brucei 2-C-Grx1 but not the mitochondrial 2-C-Grx2 was able to coordinate an iron-sulfur cluster with T(SH)2 or GSH as ligand. As a first step to unravel the structural basis for the specificity observed in the trypanosomal glutaredoxins, we present here the NMR resonance assignment of 2-C-Grx1 from the parasite T. brucei brucei.

  7. 1H, 13C NMR and DFT Study of Hydrogen Bonding in Imidazolium-based Ionic Liquids.

    PubMed

    Balevičius, Vytautas; Gdaniec, Zofia; Džiaugys, Lukas; Kuliešius, Feliksas; Maršalka, Arūnas

    2011-09-01

    The ionic liquid 1-decyl-3-methyl-imidazolium bromide [C10mim][Br], the neat material, and also dissolved (~0.01 mole fraction) in various dielectric media (acetonitrile, benzene, chloroform, dichloromethane, methanol, 2-butanol and H2O) was studied using 1H and 13C NMR spectroscopy. The most important interaction in this compound is considered to be the Br-...H-C2+ hydrogen bond, which is formed between the anions and cations. The obtained results show that dielectric medium influence mostly the behavior of the Br-...H-C2+ bridge proton. The changes observed in 1H and 13C NMR spectra of [C10mim][Br] with increasing solvents polarity and temperature can be explained applying the model of the lengthening of the H2...Br- bond with the accompanying thickening of the solvation shell of bromine anion and C2-H bond contraction. The short-range order effects related to the configuration of neighboring dipoles of solvent molecules are more important for the solvation ability of small anions than the bulk solvent field effect. However, the solvents, molecules of which tend to associate via hydrogen bonding, can significantly affect the dynamics of anions.

  8. Experimental (FT-IR, FT-Raman, 1H, 13C NMR) and theoretical study of alkali metal syringates

    NASA Astrophysics Data System (ADS)

    Świsłocka, Renata

    2013-07-01

    In this work the influence of lithium, sodium, potassium, rubidium and cesium on the electronic system of the syringic acid (4-hydroxy-3,5-dimethoxybenzoic acid) was studied. This paper presents spectroscopic vibrations (FT-IR, FT-Raman) and NMR (1H and 13C) study of the series of alkali metal syringates from lithium to cesium syringates. Characteristic shifts of band wavenumbers and changes in band intensities along the metal series were observed. Optimized geometrical structures of the studied compounds were calculated by the B3LYP method using the 6-311++G∗∗ basis set. Aromaticity indices, atomic charges, dipole moments and energies were also calculated. The theoretical wavenumbers and intensities of IR and NMR spectra were obtained. The calculated parameters were compared to experimental characteristics of studied compounds.

  9. (1)H, (13)C NMR and X-ray crystallographic studies of highly polyhalogenated derivatives of costunolide lactone.

    PubMed

    Corona, D; Díaz, E; Nava, J L; Guzmán, A; Barrios, H; Fuentes, A; Hernandez-Plata, S A; Allard, J; Jankowski, C K

    2005-11-01

    The costunolide lactone, a sesquiterpene compound isolated from Zaluzania triiloba species, reacted with several dihalocarbene sources produced by trihaloform-NaOH under successive phase transfer reactions yielding mono-, bis- and tris-dihalocyclopropane adducts. The structures, as well as the configurational assignments of the different derivatives, were established by (1)H and (13)C NMR spectroscopy and assisted by X-ray crystallographic and molecular modelling studies. The specific shielding of protons in the neighbourhood of different halogens on the cyclopropane moieties was correlated to the pseudocontact interactions.

  10. Ion acceleration in dipolarization fronts

    NASA Astrophysics Data System (ADS)

    Birn, J.; Hesse, M.

    2014-12-01

    The electric field associated with flow bursts and dipolarization fronts has been shown to be an efficient mechanism for producing energetic ions and electrons. Using an MHD simulation of magnetotail reconnection, flow bursts and dipolarization, we investigate the acceleration of test particles to suprathermal energies. Particular emphasis of this presentation is on spatial, temporal, and angular variations of the modeled energetic ion fluxes. The test particle simulations reproduce characteristic features of observed injection events, such as a fast rise of energetic particle fluxes, limitations in energy, and demonstrate the large variability of energetic ion features.

  11. Modification of roton instability due to the presence of a second dipolar Bose-Einstein condensate

    SciTech Connect

    Asad-uz-Zaman, M.; Blume, D.

    2011-03-15

    We study the behavior of two coupled purely dipolar Bose-Einstein condensates (BECs), each located in a cylindrically symmetric pancake-shaped external confining potential, as the separation b between the traps along the tight confining direction is varied. The solutions of the coupled Gross-Pitaevskii and Bogoliubov-de Gennes equations, which account for the full dynamics, show that the system behavior is modified by the presence of the second dipolar BEC. For sufficiently small b, the presence of the second dipolar BEC destabilizes the system dramatically. In this regime, the coupled system collapses through a mode that is notably different from the radial roton mode that induces the collapse of the uncoupled system. Finally, we comment on the shortcomings of an approach that employs a separable wavefunction, which is assumed to be a good approximation for highly pancake-shaped dipolar BECs in the literature.

  12. Dielectric Metamaterials with Toroidal Dipolar Response

    NASA Astrophysics Data System (ADS)

    Basharin, Alexey A.; Kafesaki, Maria; Economou, Eleftherios N.; Soukoulis, Costas M.; Fedotov, Vassili A.; Savinov, Vassili; Zheludev, Nikolay I.

    2015-01-01

    Toroidal multipoles are the terms missing in the standard multipole expansion; they are usually overlooked due to their relatively weak coupling to the electromagnetic fields. Here, we propose and theoretically study all-dielectric metamaterials of a special class that represent a simple electromagnetic system supporting toroidal dipolar excitations in the THz part of the spectrum. We show that resonant transmission and reflection of such metamaterials is dominated by toroidal dipole scattering, the neglect of which would result in a misunderstanding interpretation of the metamaterials' macroscopic response. Because of the unique field configuration of the toroidal mode, the proposed metamaterials could serve as a platform for sensing or enhancement of light absorption and optical nonlinearities.

  13. Angular momentum conservation in dipolar energy transfer.

    PubMed

    Guo, Dong; Knight, Troy E; McCusker, James K

    2011-12-23

    Conservation of angular momentum is a familiar tenet in science but has seldom been invoked to understand (or predict) chemical processes. We have developed a general formalism based on Wigner's original ideas concerning angular momentum conservation to interpret the photo-induced reactivity of two molecular donor-acceptor assemblies with physical properties synthetically tailored to facilitate intramolecular energy transfer. Steady-state and time-resolved spectroscopic data establishing excited-state energy transfer from a rhenium(I)-based charge-transfer state to a chromium(III) acceptor can be fully accounted for by Förster theory, whereas the corresponding cobalt(III) adduct does not undergo an analogous reaction despite having a larger cross-section for dipolar coupling. Because this pronounced difference in reactivity is easily explained within the context of the angular momentum conservation model, this relatively simple construct may provide a means for systematizing a broad range of chemical reactions.

  14. Dipolar dark matter with massive bigravity

    SciTech Connect

    Blanchet, Luc; Heisenberg, Lavinia E-mail: laviniah@kth.se

    2015-12-01

    Massive gravity theories have been developed as viable IR modifications of gravity motivated by dark energy and the problem of the cosmological constant. On the other hand, modified gravity and modified dark matter theories were developed with the aim of solving the problems of standard cold dark matter at galactic scales. Here we propose to adapt the framework of ghost-free massive bigravity theories to reformulate the problem of dark matter at galactic scales. We investigate a promising alternative to dark matter called dipolar dark matter (DDM) in which two different species of dark matter are separately coupled to the two metrics of bigravity and are linked together by an internal vector field. We show that this model successfully reproduces the phenomenology of dark matter at galactic scales (i.e. MOND) as a result of a mechanism of gravitational polarisation. The model is safe in the gravitational sector, but because of the particular couplings of the matter fields and vector field to the metrics, a ghost in the decoupling limit is present in the dark matter sector. However, it might be possible to push the mass of the ghost beyond the strong coupling scale by an appropriate choice of the parameters of the model. Crucial questions to address in future work are the exact mass of the ghost, and the cosmological implications of the model.

  15. Dipolar dark matter with massive bigravity

    SciTech Connect

    Blanchet, Luc; Heisenberg, Lavinia

    2015-12-14

    Massive gravity theories have been developed as viable IR modifications of gravity motivated by dark energy and the problem of the cosmological constant. On the other hand, modified gravity and modified dark matter theories were developed with the aim of solving the problems of standard cold dark matter at galactic scales. Here we propose to adapt the framework of ghost-free massive bigravity theories to reformulate the problem of dark matter at galactic scales. We investigate a promising alternative to dark matter called dipolar dark matter (DDM) in which two different species of dark matter are separately coupled to the two metrics of bigravity and are linked together by an internal vector field. We show that this model successfully reproduces the phenomenology of dark matter at galactic scales (i.e. MOND) as a result of a mechanism of gravitational polarisation. The model is safe in the gravitational sector, but because of the particular couplings of the matter fields and vector field to the metrics, a ghost in the decoupling limit is present in the dark matter sector. However, it might be possible to push the mass of the ghost beyond the strong coupling scale by an appropriate choice of the parameters of the model. Crucial questions to address in future work are the exact mass of the ghost, and the cosmological implications of the model.

  16. Monte Carlo simulations of kagome lattices with magnetic dipolar interactions

    NASA Astrophysics Data System (ADS)

    Plumer, Martin; Holden, Mark; Way, Andrew; Saika-Voivod, Ivan; Southern, Byron

    Monte Carlo simulations of classical spins on the two-dimensional kagome lattice with only dipolar interactions are presented. In addition to revealing the sixfold-degenerate ground state, the nature of the finite-temperature phase transition to long-range magnetic order is discussed. Low-temperature states consisting of mixtures of degenerate ground-state configurations separated by domain walls can be explained as a result of competing exchange-like and shape-anisotropy-like terms in the dipolar coupling. Fluctuations between pairs of degenerate spin configurations are found to persist well into the ordered state as the temperature is lowered until locking in to a low-energy state. Results suggest that the system undergoes a continuous phase transition at T ~ 0 . 43 in agreement with previous MC simulations but the nature of the ordering process differs. Preliminary results which extend this analysis to the 3D fcc ABC-stacked kagome systems will be presented.

  17. Stochastic dipolar recoupling in nuclear magnetic resonance of solids

    PubMed Central

    Tycko, Robert

    2008-01-01

    I describe a nuclear magnetic resonance (NMR) technique, called stochastic dipolar recoupling (SDR), that permits continuous experimental control of the character of spin dynamics between coherent and incoherent limits in a system of magnetic dipole-coupled nuclei. In the fully incoherent limit of SDR, spin polarization transfers occur at distance-dependent rates without the quantum mechanical interferences among pairwise dipole-dipole couplings that often limit the feasibility or precision of structural studies of solids by NMR. In addition to facilitating structural studies, SDR represents a possible route to experimental studies of effects of decoherence on the dynamics of quantum many-body systems. PMID:17995438

  18. Stochastic dipolar recoupling in nuclear magnetic resonance of solids.

    PubMed

    Tycko, Robert

    2007-11-02

    I describe a nuclear magnetic resonance (NMR) technique, called stochastic dipolar recoupling (SDR), that permits continuous experimental control of the character of spin dynamics between coherent and incoherent limits in a system of magnetic dipole-coupled nuclei. In the fully incoherent limit of SDR, spin polarization transfers occur at distance-dependent rates without the quantum mechanical interferences among pairwise dipole-dipole couplings that often limit the feasibility or precision of structural studies of solids by NMR. In addition to facilitating structural studies, SDR represents a possible route to experimental studies of effects of decoherence on the dynamics of quantum many-body systems.

  19. Stochastic Dipolar Recoupling in Nuclear Magnetic Resonance of Solids

    SciTech Connect

    Tycko, Robert

    2007-11-02

    I describe a nuclear magnetic resonance (NMR) technique, called stochastic dipolar recoupling (SDR), that permits continuous experimental control of the character of spin dynamics between coherent and incoherent limits in a system of magnetic dipole-coupled nuclei. In the fully incoherent limit of SDR, spin polarization transfers occur at distance-dependent rates without the quantum mechanical interferences among pairwise dipole-dipole couplings that often limit the feasibility or precision of structural studies of solids by NMR. In addition to facilitating structural studies, SDR represents a possible route to experimental studies of effects of decoherence on the dynamics of quantum many-body system000.

  20. Energetic ions in dipolarization events

    NASA Astrophysics Data System (ADS)

    Birn, J.; Runov, A.; Hesse, M.

    2015-09-01

    We investigate ion acceleration in dipolarization events in the magnetotail, using the electromagnetic fields of an MHD simulation of magnetotail reconnection and flow bursts as basis for test particle tracing. The simulation results are compared with "Time History of Events and Macroscale Interactions during Substorms" observations. We provide quantitative answers to the relative importance of source regions and source energies. Flux decreases at proton energies up to 10-20 keV are found to be due to sources of lobe or plasma sheet boundary layer particles that enter the near tail via reconnection. Flux increases result from both thermal and suprathermal ion sources. Comparable numbers of accelerated protons enter the acceleration region via cross-tail drift from the dawn flanks of the near-tail plasma sheet and via reconnection of field lines extending into the more distant tail. We also demonstrate the presence of earthward plasma flow and accelerated suprathermal ions ahead of a dipolarization front. The flow acceleration stems from a net Lorentz force, resulting from reduced pressure gradients within a pressure pile-up region ahead of the front. Suprathermal precursor ions result from, typically multiple reflections at the front. Low-energy ions also become accelerated due to inertial drift in the direction of the small precursor electric field.

  1. Studying electric fields in dipolarization fronts

    NASA Astrophysics Data System (ADS)

    Balcerak, Ernie

    2014-11-01

    In Earth's magnetotail, sharp increases in the magnetic field known as dipolarization fronts are associated with high-speed plasma flows that connect Earth's ionosphere via electric currents. Some aspects of these dipolarization fronts have puzzled scientists; in particular, the dip in magnetic field that occurs just ahead of the dipolarization front layer is not well understood. Sun et al. analyze observations made using the Cluster satellites to elucidate the details of electric fields associated with dipolarization fronts. The study shows that a type of electric current known as a Hall current dominates in the dipolarization front region and in the region where the magnetic field dips, but this current flows in opposite directions in these two regions.

  2. Control of dipolar relaxation in external fields

    NASA Astrophysics Data System (ADS)

    Pasquiou, B.; Bismut, G.; Beaufils, Q.; Crubellier, A.; Maréchal, E.; Pedri, P.; Vernac, L.; Gorceix, O.; Laburthe-Tolra, B.

    2010-04-01

    We study dipolar relaxation in both ultracold thermal and Bose-condensed Cr atom gases. We show three different ways to control dipolar relaxation, making use of either a static magnetic field, an oscillatory magnetic field, or an optical lattice to reduce the dimensionality of the gas from three-dimensional (3D) to two-dimensional (2D). Although dipolar relaxation generally increases as a function of a static magnetic-field intensity, we find a range of nonzero magnetic-field intensities where dipolar relaxation is strongly reduced. We use this resonant reduction to accurately determine the S=6 scattering length of Cr atoms: a6=103±4a0. We compare this new measurement to another new determination of a6, which we perform by analyzing the precise spectroscopy of a Feshbach resonance in d-wave collisions, yielding a6=102.5±0.4a0. These two measurements provide, by far, the most precise determination of a6 to date. We then show that, although dipolar interactions are long-range interactions, dipolar relaxation only involves the incoming partial wave l=0 for large enough magnetic-field intensities, which has interesting consequences on the stability of dipolar Fermi gases. We then study ultracold Cr gases in a one-dimensional (1D) optical lattice resulting in a collection of independent 2D gases. We show that dipolar relaxation is modified when the atoms collide in reduced dimensionality at low magnetic-field intensities, and that the corresponding dipolar relaxation rate parameter is reduced by a factor up to 7 compared to the 3D case. Finally, we study dipolar relaxation in the presence of rf oscillating magnetic fields, and we show that both the output channel energy and the transition amplitude can be controlled by means of the rf frequency and Rabi frequency.

  3. Reorientation of a dipolar monolayer and dipolar solvent.

    PubMed

    Yi, Taeil; Lichter, Seth

    2014-06-01

    The reliable persistence of an adhered monolayer film on a substrate is critical for film function. The process by which monolayers degrade or disperse remains unclear. Our study investigates the properties and dynamics of a solute of dipolar molecules initially adhered as a monolayer on a substrate in a water-like Stockmayer solvent. We find that for a rigid solute, both the solute and solvent show qualitatively different dynamics than for a flexible solute and its solvent. For the rigid solute, spreading is hindered and solvent orientation is more pronounced. We formulate a simple kinetic model that shows qualitatively similar results to the molecular dynamics simulations of the time evolution of the monolayer. Simple kinetics of molecules on substrates is a starting point for understanding important industrial monolayer applications and complex interactions on membranes.

  4. Crossover from normal to anomalous diffusion in systems of field-aligned dipolar particles.

    PubMed

    Jordanovic, Jelena; Jäger, Sebastian; Klapp, Sabine H L

    2011-01-21

    Using molecular dynamics simulations we investigate the translational dynamics of particles with dipolar interactions in homogenous external fields. For a broad range of concentrations, we find that the anisotropic, yet normal diffusive behavior characterizing weakly coupled systems becomes anomalous both parallel and perpendicular to the field at sufficiently high dipolar coupling and field strength. After the ballistic regime, chain formation first yields cagelike motion in all directions, followed by transient, mixed diffusive-superdiffusive behavior resulting from cooperative motion of the chains. The enhanced dynamics disappears only at higher densities close to crystallization.

  5. Synchronization of spin torque nano-oscillators through dipolar interactions

    SciTech Connect

    Chen, Hao-Hsuan Wu, Jong-Ching Horng, Lance; Lee, Ching-Ming; Chang, Ching-Ray Chang, Jui-Hang

    2014-04-07

    In an array of spin-torque nano-oscillators (STNOs) that combine a perpendicular polarized fixed layer with strong in-plane anisotropy in the free layers, magnetic dipolar interactions can effectively phase-lock the array, thus further enhancing the power of the output microwave signals. We perform a qualitative analysis of the synchronization of an array based on the Landau-Lifshitz-Gilbert equation, with a spin-transfer torque that assumes strong in-plane anisotropy. Finally, we present the numerical results for four coupled STNOs to provide further evidence for the proposed theory.

  6. Model independence in two dimensions and polarized cold dipolar molecules.

    PubMed

    Volosniev, A G; Fedorov, D V; Jensen, A S; Zinner, N T

    2011-06-24

    We calculate the energy and wave functions of two particles confined to two spatial dimensions interacting via arbitrary anisotropic potentials with negative or zero net volume. The general rigorous analytic expressions are given in the weak coupling limit where universality or model independence are approached. The monopole part of anisotropic potentials is crucial in the universal limit. We illustrate the universality with a system of two arbitrarily polarized cold dipolar molecules in a bilayer. We discuss the transition to universality as a function of polarization and binding energy and compare analytic and numerical results obtained by the stochastic variational method. The universal limit is essentially reached for experimentally accessible strengths.

  7. Dipolar excitation in the third stability region.

    PubMed

    Konenkov, Nikolai V; Chernyak, Eugenii Ya; Stepanov, Vladimir A

    2016-01-01

    Dipole resonant excitation of ions creates instability bands which follow iso-β lines where β is the characteristic exponent (stability parameter). Instability bands are exited most effectively on the fundamental frequency π= βΩ/2. Here π is the angle resonance frequency of the dipolar voltage applied to x or y pair rods of the analyzer, and Ω is the angle frequency of the main drive voltage. Our goal is to study the mass peak shape in the third stability region with dipolar resonance excitation of the instability band with respect to the resonance frequency π and the dipolar potential amplitude. Numerical integration of the ion motion equations with a given ion source emittance is used to investigate peak shapes and ion transmission. We show that it is possible to vary the resolution power at any part of the third stability region. A change of the dipolar potential phase leads to a periodical variation of the resolution with period π.The most effective dipolar excitation in the y direction is along βy near the stability boundary. The mass peak shape is calculated also for a quadrupole with round rods. The best peak shape (small tails and high resolution) takes place for the rod set with r/r0=1.130. Dipolar excitation increases the transmission by approximately 5-10% at a given resolution.

  8. Investigation of slow molecular dynamics using R-CODEX

    NASA Astrophysics Data System (ADS)

    Li, Wenbo; McDermott, Ann

    2012-09-01

    A solid state NMR experiment is introduced for probing motions on the millisecond time scale, based on dephasing and refocusing 1H-13C or 1H-15N dipolar couplings. The method is related to the previously described Centerband-Only Detection of Exchange or CODEX experiment. The use of an R-type dipolar recoupling sequence takes advantage of the strong 1H-13C or 1H-15N dipolar coupling, while suppressing the effect of 1H-1H homonuclear coupling. This approach paves the way to detect both the correlation time and reorientational angle of the dynamics in fully protonated samples. The performance of this pulse sequence is demonstrated using imidazole methyl sulfonate.

  9. Investigation of slow molecular dynamics using R-CODEX.

    PubMed

    Li, Wenbo; McDermott, Ann

    2012-09-01

    A solid state NMR experiment is introduced for probing motions on the millisecond time scale, based on dephasing and refocusing (1)H-(13)C or (1)H-(15)N dipolar couplings. The method is related to the previously described Centerband-Only Detection of Exchange or CODEX experiment. The use of an R-type dipolar recoupling sequence takes advantage of the strong (1)H-(13)C or (1)H-(15)N dipolar coupling, while suppressing the effect of (1)H-(1)H homonuclear coupling. This approach paves the way to detect both the correlation time and reorientational angle of the dynamics in fully protonated samples. The performance of this pulse sequence is demonstrated using imidazole methyl sulfonate.

  10. Dipolar correlations in liquid water

    SciTech Connect

    Zhang, Cui; Galli, Giulia

    2014-08-28

    We present an analysis of the dipolar correlations in water as a function of temperature and density and in the presence of simple ionic solutes, carried out using molecular dynamics simulations and empirical potentials. We show that the dipole-dipole correlation function of the liquid exhibits sizable oscillations over nanodomains of about 1.5 nm radius, with several isosbestic points as a function of temperature; the size of the nanodomains is nearly independent on temperature and density, between 240 and 400 K and 0.9 and 1.3 g/cm{sup 3}, but it is substantially affected by the presence of solvated ions. In the same range of thermodynamic conditions, the decay time (τ) of the system dipole moment varies by a factor of about 30 and 1.5, as a function of temperature and density, respectively. At 300 K, we observed a maximum in τ as a function of density, and a corresponding shallow maximum in the tetrahedral order parameter, in a range where the diffusion coefficient, the pressure and the dielectric constant increase monotonically.

  11. Improved narrowband dipolar recoupling for homonuclear distance measurements in rotating solids.

    PubMed

    Goobes, G; Vega, S

    2002-02-01

    Recovery of the magnetic dipolar interaction between nuclei bearing the same gyromagnetic ratio in rotating solids can be promoted by synchronous rf irradiation. Determination of the dipolar interaction strength can serve as a tool for structural elucidation in polycrystalline powders. Spinning frequency dependent narrow-band (nb) RFDR and SEDRA experiments are utilized as simple techniques for the determination of dipolar interactions between the nuclei in coupled homonuclear spin pairs. The magnetization exchange and coherence dephasing due to a fixed number of rotor-synchronously applied pi-pulses is monitored at spinning frequencies in the vicinity of the rotational resonance (R(2)) conditions. The powder nbRFDR and nbSEDRA decay curves of spin magnetizations and coherences, respectively, as a function of the spinning frequency can be measured and analyzed using simple rate equations providing a quantitative measure of the dipolar coupling. The effects of the phenomenological relaxation parameters in these rate equations are discussed and an improved methodology is suggested for analyzing nbRFDR data for small dipolar couplings. The distance between the labeled nuclei in the 1,3-(13)C(2)-hydroxybutyric acid molecule is rederived using existing nbRFDR results and the new simulation procedure. A nbSEDRA experiment has been performed successfully on a powder sample of singly labeled 1-(13)C-L-leucine measuring the dipolar interaction between the labeled carboxyl carbon and the natural abundant beta-carbon. Both narrowband techniques are employed for the determination of the nuclear distances between the side-chain carbons of leucine and its carbonyl carbon in a tripeptide Leu-Gly-Phe that is singly (13)C-labeled at the leucine carbonyl carbon position.

  12. Improved Narrowband Dipolar Recoupling for Homonuclear Distance Measurements in Rotating Solids

    NASA Astrophysics Data System (ADS)

    Goobes, G.; Vega, S.

    2002-02-01

    Recovery of the magnetic dipolar interaction between nuclei bearing the same gyromagnetic ratio in rotating solids can be promoted by synchronous rf irradiation. Determination of the dipolar interaction strength can serve as a tool for structural elucidation in polycrystalline powders. Spinning frequency dependent narrow-band (nb) RFDR and SEDRA experiments are utilized as simple techniques for the determination of dipolar interactions between the nuclei in coupled homonuclear spin pairs. The magnetization exchange and coherence dephasing due to a fixed number of rotor-synchronously applied π-pulses is monitored at spinning frequencies in the vicinity of the rotational resonance (R2) conditions. The powder nbRFDR and nbSEDRA decay curves of spin magnetizations and coherences, respectively, as a function of the spinning frequency can be measured and analyzed using simple rate equations providing a quantitative measure of the dipolar coupling. The effects of the phenomenological relaxation parameters in these rate equations are discussed and an improved methodology is suggested for analyzing nbRFDR data for small dipolar couplings. The distance between the labeled nuclei in the 1,3-13C2-hydroxybutyric acid molecule is rederived using existing nbRFDR results and the new simulation procedure. A nbSEDRA experiment has been performed successfully on a powder sample of singly labeled 1-13C-L-leucine measuring the dipolar interaction between the labeled carboxyl carbon and the natural abundant β-carbon. Both narrowband techniques are employed for the determination of the nuclear distances between the side-chain carbons of leucine and its carbonyl carbon in a tripeptide Leu-Gly-Phe that is singly 13C-labeled at the leucine carbonyl carbon position.

  13. Theory of Stochastic Dipolar Recoupling in Solid State Nuclear Magnetic Resonance

    PubMed Central

    Tycko, Robert

    2008-01-01

    Dipolar recoupling techniques in solid state nuclear magnetic resonance (NMR) consist of radio-frequency (rf) pulse sequences applied in synchrony with magic-angle spinning (MAS) that create non-zero average magnetic dipole-dipole couplings under MAS. Stochastic dipolar recoupling (SDR) is a variant in which randomly chosen rf carrier frequency offsets are introduced to cause random phase modulations of individual pairwise couplings in the dipolar spin Hamiltonian. Several aspects of SDR are investigated through analytical theory and numerical simulations: (1) An analytical expression for the evolution of nuclear spin polarization under SDR in a two-spin system is derived and verified through simulations, which show a continuous evolution from coherent, oscillatory polarization exchange to incoherent, exponential approach to equilibrium as the range of random carrier offsets (controlled by a parameter fmax) increases; (2) In a many-spin system, polarization transfers under SDR are shown to be described accurately by a rate matrix in the limit of large fmax, with pairwise transfer rates that are proportional to the inverse sixth power of pairwise internuclear distances; (3) Quantum mechanical interferences among non-commuting pairwise dipole-dipole couplings, which are a complicating factor in solid state NMR studies of molecular structures by traditional dipolar recoupling methods, are shown to be absent from SDR data in the limit of large fmax, provided that coupled nuclei have distinct NMR chemical shifts. PMID:18085769

  14. Synthesis of 2H-indazoles by the [3 + 2] dipolar cycloaddition of sydnones with arynes.

    PubMed

    Fang, Yuesi; Wu, Chunrui; Larock, Richard C; Shi, Feng

    2011-11-04

    A rapid and efficient synthesis of 2H-indazoles has been developed using a [3 + 2] dipolar cycloaddition of sydnones and arynes. A series of 2H-indazoles have been prepared in good to excellent yields using this protocol, and subsequent Pd-catalyzed coupling reactions can be applied to the halogenated products to generate a structurally diverse library of indazoles.

  15. Dipolarization front and current disruption

    NASA Astrophysics Data System (ADS)

    Lui, A. T. Y.

    2016-10-01

    The modification of current density on the dawn-dusk cross section of the magnetotail with the earthward approach of a dipolarization front (DF) is examined through the recently published results of a three-dimensional (3-D) particle-in-cell (PIC) simulation. It is found that the current density intensifies by 37% abruptly within 1.5 ion gyrotime as the DF approaches and shows localized regions with north-south extrusions. After reaching its peak value, it undergoes a drastic current reduction (DCR) by 65% within 2 ion gyrotime. Breakdown of the frozen-in condition occurs in the neutral sheet region in association with DCR, demonstrating the non-MHD behavior of the phenomenon. The evolution of current density from this 3-D PIC simulation bears several similarities to those observed for the current disruption (CD) phenomenon, such as explosive growth and disruption of the current density leading to a breakdown of the frozen-in condition. The evolution is also similar to those from a previous two-dimensional (2-D) PIC simulation specially designed to investigate the nonlinear evolution of the cross-field current instability for CD. One interpretation of these findings is that CD and substorm triggering can be associated with earthward intrusion of a DF into the near-Earth plasma sheet as indicated by previous Cluster and Time History of Events and Macroscale Interactions during Substorms observations. An alternative interpretation is that both DF and CD are consequences of a global evolution from an ion-tearing-like instability of the magnetotail.

  16. X-filtering for a range of coupling constants: application to the detection of intermolecular NOEs

    NASA Astrophysics Data System (ADS)

    Zangger, Klaus; Oberer, Monika; Keller, Walter; Sterk, Heinz

    2003-02-01

    A new method for heteronuclear X-filtering is presented, which relies on repetitive applications of 90°( 1H)-τ(1/4 1J HC)-180°( 1H, 13C)-τ(1/4 1J HC)-90°( 1H, 13C)- PFG building blocks employing gradient-mediated suppression of magnetization built up for directly heteronuclear coupled protons. Thereby, a range of heteronuclear coupling constants can be suppressed by varying the delays of scalar coupling evolution both within and between individual transients. To achieve efficient destruction of 13C-coupled protons in macromolecular systems, the scalar coupling evolution delays were optimized using simulated annealing by including transverse relaxation effects. With a combination of regular hard pulses, delays and pulsed field gradients only, this method yields sufficient X-filtering to allow the observation of intermolecular nuclear overhauser effects in a molecular complex consisting of a 13C, 15N double-labeled, and an unlabeled protein. This is achieved by exciting magnetization of 12C- and 14N-bound protons and detecting 13C-bound 1H magnetization in a 3D 13C-filtered, 13C-edited NOESY-HSQC experiment. The method is tested on the 18 kDa homodimeric bacterial antidote ParD.

  17. Vertical shift register using dipolar interaction in magnetic multilayers

    NASA Astrophysics Data System (ADS)

    Chin, Shin-Liang; Fernández-Pacheco, Amalio; Petit, Dorothée C. M. C.; Cowburn, Russell P.

    2015-12-01

    A vertical shift register consisting of multi-layered ferromagnetic bars with in-plane magnetization is investigated numerically using macrospin simulations. These layers are anti-ferromagnetically coupled via dipolar interactions and their in-plane aspect ratio determines their anisotropy. A single data bit is represented by a magnetic kink soliton, which forms at the boundary of two anti-parallel domains with opposite phases. It can be propagated bi-directionally using an externally applied rotating magnetic field. The soliton propagation is dependent on the applied field strength, the magnetic anisotropy of the ferromagnetic layers, and the dipolar coupling energies. For the device investigated here, the largest field range for soliton propagation is found to be from 35 Oe to 235 Oe at a lateral aspect ratio of 1.33. The soliton is also subjected to edge effects where it can be either pinned or reflected rather than being expelled from the stack. It is found that by reducing the thickness of the edge layer, these effects can be reduced substantially. By reducing the thickness of the edge layer by 20%, the field range in which the soliton is expelled increases by more than a factor of two.

  18. Dissipative effects in dipolar, quantum many-body systems

    NASA Astrophysics Data System (ADS)

    Safavi-Naini, Arghavan; Capogrosso-Sansone, Barbara; Rey, Ana Maria

    2015-03-01

    We use Quantum Monte Carlo simulations, by the Worm algorithm, to study the ground state phase diagram of two-dimensional, dipolar lattice bosons where each site is coupled, via density operators, to an external reservoir. A recent related study of the XXZ model with ohmic coupling to an external reservoir reported the existence of a bath-induced Bose metal phase in the ground state phase diagram away from half filling, and a Luttinger liquid and a charge density wave at half-filling. Our work extends this methodology to higher dimensional systems with long-range interactions. In the case of hard-core bosons, our method can be applied to experimental systems featuring dipolar fermionic molecules in the presence of losses. This work utilized the Janus supercomputer, which is supported by the NSF (award number CNS-0821794) and the University of Colorado Boulder, and is a joint effort with the University of Colorado Denver and the National Center for Atmospheric Research, as well as OU Supercomputing Center for Education and Research (OSCER) at the University of Oklahoma. NIST, JILA-NSF-PFC-1125844, NSF-PIF-1211914, NSF-PHY11-25915, ARO, ARO-DARPA-OLE, AFOSR, AFOSR-MURI.

  19. Quantum Monte Carlo study of entanglement entropy for dipolar hardcore bosons in optical lattices

    NASA Astrophysics Data System (ADS)

    Wang, Wei; Safavi-Naini, Arghavan; Capogrosso-Sansone, Barbara

    2016-05-01

    Entanglement entropy and its scaling with system size provide an alternative way to characterize quantum phases and phase transitions, and can be used to probe topological order. Motivated by the recent theoretical investigation of entanglement properties of the ground-states of hard-core lattice bosons, we use Quantum Monte Carlo simulations, well suited to studying equilibrium properties, to calculate the Renyi entropy and topological entanglement entropy of the ground state of dipolar lattice bosons. In contrast to the traditional observables, these probes allow us to study the emergence of long-range entanglement in the ground state, as well as its dependence on the dipolar coupling. Additionally, in light of recent experimental success in creating low entropy dipolar lattice gases we discuss the possibility of observing these phases experimentally.

  20. Multi-dipolar microwave plasmas and their application to negative ion production

    SciTech Connect

    Béchu, S.; Bès, A.; Lacoste, A.; Aleiferis, S.; Ivanov, A. A. Jr.; Bacal, M.

    2013-10-15

    During the past decade multi-dipolar plasmas have been employed for various purposes such as surface treatments in biomedicine, physical and chemical vapour deposition for hydrogen storage, and applications in mechanical engineering. On the other hand, due to the design and operational mode of these plasma sources (i.e., strong permanent magnets for the electron cyclotron resonance coupling, low working pressure, and high electron density achieved) they are suitable for studying fundamental mechanisms involved in negative ion sources used in magnetically confined fusion and particle accelerators. Thus, this study presents an overview of fundamental results obtained with: (i) a single dipolar source, (ii) a network of seven dipolar plasma sources inserted into a magnetic multipolar chamber (Camembert III), and (iii) four dipolar sources housed in a smaller metallic cylinder (ROSAE III). Investigations with Langmuir probes of electron energy probability functions revealed the variation of the plasma properties versus the radial distance from the axis of a dipolar source in its mid plane and allowed the determination of the proportion between hot and cold electron populations in both chambers. These results are compared with the density of hydrogen negative ions, measured using the photodetachment technique. Electron energy probability functions obtained in these different configurations show the possibility of both hot and cold electron production. The former is a prerequisite for increasing the vibrational level of molecules and the dissociation degree and the latter for producing negative ions via dissociative attachment of the cold electrons or via surface production induced by H atoms.

  1. Planar dipolar polymer brush: field theoretical investigations

    NASA Astrophysics Data System (ADS)

    Mahalik, Jyoti; Kumar, Rajeev; Sumpter, Bobby

    2015-03-01

    Physical properties of polymer brushes bearing monomers with permanent dipole moments and immersed in a polar solvent are investigated using self-consistent field theory (SCFT). It is found that mismatch between the permanent dipole moments of the monomer and the solvent plays a significant role in determining the height of the polymer brush. Sign as well as magnitude of the mismatch determines the extent of collapse of the polymer brush. The mismatch in the dipole moments also affects the force-distance relations and interpenetration of polymers in opposing planar brushes. In particular, an attractive force between the opposing dipolar brushes is predicted for stronger mismatch parameter. Furthermore, effects of added monovalent salt on the structure of dipolar brushes will also be presented. This investigation highlights the significance of dipolar interactions in affecting the physical properties of polymer brushes. Csmd division, Oak Ridge National Laboratory, 1 Bethel Valley Rd, Oak Ridge, TN 37831, USA.

  2. Improving resolution in proton solid-state NMR by removing nitrogen-14 residual dipolar broadening

    NASA Astrophysics Data System (ADS)

    Stein, Robin S.; Elena, Bénédicte; Emsley, Lyndon

    2008-06-01

    Residual dipolar coupling between quadrupolar and other nuclei under MAS has not usually been thought to be important in high field NMR spectroscopy. We show that coupling to 14N broadens 1H lineshapes significantly even at 11.7 T, and that we can decouple 14N from 1H during 1H homonuclear decoupling to successfully improve 1H resolution. The method used for decoupling is the application of evenly spaced pulses to the quadrupolar nucleus.

  3. Nonlinear dielectric effect of dipolar fluids.

    PubMed

    Szalai, I; Nagy, S; Dietrich, S

    2009-10-21

    The nonlinear dielectric effect for dipolar fluids is studied within the framework of the mean spherical approximation (MSA) of hard core dipolar Yukawa fluids. Based on earlier results for the electric field dependence of the polarization our analytical results show so-called normal saturation effects, which are in good agreement with corresponding NVT ensemble Monte Carlo (MC) simulation data. The linear and the nonlinear dielectric permittivities obtained from MC simulations are determined from the fluctuations of the total dipole moment of the system in the absence of an applied electric field. We compare the MSA based theoretical results with the corresponding Langevin and Debye-Weiss behaviors and with actual experimental data.

  4. Temperature dependence of contact and dipolar NMR chemical shifts in paramagnetic molecules

    SciTech Connect

    Martin, Bob; Autschbach, Jochen

    2015-02-07

    Using a recently proposed equation for NMR nuclear magnetic shielding for molecules with unpaired electrons [A. Soncini and W. Van den Heuvel, J. Chem. Phys. 138, 021103 (2013)], equations for the temperature (T) dependent isotropic shielding for multiplets with an effective spin S equal to 1/2, 1, 3/2, 2, and 5/2 in terms of electron paramagnetic resonance spin Hamiltonian parameters are derived and then expanded in powers of 1/T. One simplifying assumption used is that a matrix derived from the zero-field splitting (ZFS) tensor and the Zeeman coupling matrix (g-tensor) share the same principal axis system. The influence of the rhombic ZFS parameter E is only investigated for S = 1. Expressions for paramagnetic contact shielding (from the isotropic part of the hyperfine coupling matrix) and pseudo-contact or dipolar shielding (from the anisotropic part of the hyperfine coupling matrix) are considered separately. The leading order is always 1/T. A temperature dependence of the contact shielding as 1/T and of the dipolar shielding as 1/T{sup 2}, which is sometimes assumed in the assignment of paramagnetic chemical shifts, is shown to arise only if S ≥ 1 and zero-field splitting is appreciable, and only if the Zeeman coupling matrix is nearly isotropic (Δg = 0). In such situations, an assignment of contact versus dipolar shifts may be possible based only on linear and quadratic fits of measured variable-temperature chemical shifts versus 1/T. Numerical data are provided for nickelocene (S = 1). Even under the assumption of Δg = 0, a different leading order of contact and dipolar shifts in powers of 1/T is not obtained for S = 3/2. When Δg is not very small, dipolar and contact shifts both depend in leading order in 1/T in all cases, with sizable contributions in order 1/T{sup n} with n = 2 and higher.

  5. Temperature dependence of contact and dipolar NMR chemical shifts in paramagnetic molecules.

    PubMed

    Martin, Bob; Autschbach, Jochen

    2015-02-07

    Using a recently proposed equation for NMR nuclear magnetic shielding for molecules with unpaired electrons [A. Soncini and W. Van den Heuvel, J. Chem. Phys. 138, 021103 (2013)], equations for the temperature (T) dependent isotropic shielding for multiplets with an effective spin S equal to 1/2, 1, 3/2, 2, and 5/2 in terms of electron paramagnetic resonance spin Hamiltonian parameters are derived and then expanded in powers of 1/T. One simplifying assumption used is that a matrix derived from the zero-field splitting (ZFS) tensor and the Zeeman coupling matrix (g-tensor) share the same principal axis system. The influence of the rhombic ZFS parameter E is only investigated for S = 1. Expressions for paramagnetic contact shielding (from the isotropic part of the hyperfine coupling matrix) and pseudo-contact or dipolar shielding (from the anisotropic part of the hyperfine coupling matrix) are considered separately. The leading order is always 1/T. A temperature dependence of the contact shielding as 1/T and of the dipolar shielding as 1/T(2), which is sometimes assumed in the assignment of paramagnetic chemical shifts, is shown to arise only if S ≥ 1 and zero-field splitting is appreciable, and only if the Zeeman coupling matrix is nearly isotropic (Δg = 0). In such situations, an assignment of contact versus dipolar shifts may be possible based only on linear and quadratic fits of measured variable-temperature chemical shifts versus 1/T. Numerical data are provided for nickelocene (S = 1). Even under the assumption of Δg = 0, a different leading order of contact and dipolar shifts in powers of 1/T is not obtained for S = 3/2. When Δg is not very small, dipolar and contact shifts both depend in leading order in 1/T in all cases, with sizable contributions in order 1/T(n) with n = 2 and higher.

  6. Transfer of dipolar gas through the discrete localized mode

    NASA Astrophysics Data System (ADS)

    Bai, Xiao-Dong; Zhang, Ai-Xia; Xue, Ju-Kui

    2013-12-01

    By considering the discrete nonlinear Schrödinger model with dipole-dipole interactions for dipolar condensate, the existence, the types, the stability, and the dynamics of the localized modes in a nonlinear lattice are discussed. It is found that the contact interaction and the dipole-dipole interactions play important roles in determining the existence, the type, and the stability of the localized modes. Because of the coupled effects of the contact interaction and the dipole-dipole interactions, rich localized modes and their stability nature can exist: when the contact interaction is larger and the dipole-dipole interactions is smaller, a discrete bright breather occurs. In this case, while the on-site interaction can stabilize the discrete breather, the dipole-dipole interactions will destabilize the discrete breather; when both the contact interaction and the dipole-dipole interactions are larger, a discrete kink appears. In this case, both the on-site interaction and the dipole-dipole interactions can stabilize the discrete kink, but the discrete kink is more unstable than the ordinary discrete breather. The predicted results provide a deep insight into the dynamics of blocking, filtering, and transfer of the norm in nonlinear lattices for dipolar condensates.

  7. Concertedness of 1,3-Dipolar Cycloadditions.

    ERIC Educational Resources Information Center

    Haque, M. Serajul

    1984-01-01

    There are two conflicting views about the mechanism of 1,3-dipolar cycloadditions to multibonds. To reconcile these viewpoints a concerted, spin-paired, diradical mechanism, based on valence bond theory, is proposed. Each of these three mechanisms is discussed. (JN)

  8. Backbone (1)H, (13)C, and (15)N NMR resonance assignments of the Krüppel-like factor 4 activation domain.

    PubMed

    Conroy, Brigid S; Weiss, Emma R; Smith, Steven P; Langelaan, David N

    2017-04-01

    Krüppel-like factor 4 (KLF4) is a transcription factor involved in diverse biological processes, including development, cellular differentiation and proliferation, and maintenance of tissue homeostasis. KLF4 has also been associated with disease states, such as cardiovascular disease and several cancers. KLF4 contains an activation domain, repression domain, and a structurally characterized C-terminal zinc finger domain that mediates its binding to DNA. The structurally uncharacterized KLF4 activation domain is critical for transactivation by KLF4 and mediates its binding to the transcriptional coactivator CBP/p300. Here, we report the (1)H, (15)N, (13)CO, (13)Cα and (13)Cβ NMR chemical shift assignments of KLF41-130, which contains the KLF4 activation domain. Narrow chemical shift dispersion in the (1)H dimension of the (1)H-(15)N HSQC spectrum suggests that the KLF41-130 fragment is intrinsically disordered.

  9. Comprehensive quantum chemical and spectroscopic (FTIR, FT-Raman, 1H, 13C NMR) investigations of O-desmethyltramadol hydrochloride an active metabolite in tramadol - An analgesic drug

    NASA Astrophysics Data System (ADS)

    Arjunan, V.; Santhanam, R.; Marchewka, M. K.; Mohan, S.

    2014-03-01

    O-desmethyltramadol is one of the main metabolites of tramadol widely used clinically and has analgesic activity. The FTIR and FT-Raman spectra of O-desmethyl tramadol hydrochloride are recorded in the solid phase in the regions 4000-400 cm-1 and 4000-100 cm-1, respectively. The observed fundamentals are assigned to different normal modes of vibration. Theoretical studies have been performed as its hydrochloride salt. The structure of the compound has been optimised with B3LYP method using 6-31G** and cc-pVDZ basis sets. The optimised bond length and bond angles are correlated with the X-ray data. The experimental wavenumbers were compared with the scaled vibrational frequencies determined by DFT methods. The IR and Raman intensities are determined with B3LYP method using cc-pVDZ and 6-31G(d,p) basic sets. The total electron density and molecular electrostatic potential surfaces of the molecule are constructed by using B3LYP/cc-pVDZ method to display electrostatic potential (electron + nuclei) distribution. The electronic properties HOMO and LUMO energies were measured. Natural bond orbital analysis of O-desmethyltramadol hydrochloride has been performed to indicate the presence of intramolecular charge transfer. The 1H and 13C NMR chemical shifts of the molecule have been anlysed.

  10. 1H, 13C and 15N resonance assignments and secondary structure analysis of CmPI-II, a serine protease inhibitor isolated from marine snail Cenchritis muricatus.

    PubMed

    Cabrera-Muñoz, Aymara; Rojas, Laritza; Alonso-del-Rivero Antigua, Maday; Pires, José Ricardo

    2016-04-01

    A protease inhibitor (CmPI-II) (UNIPROT: IPK2_CENMR) from the marine mollusc Cenchritis muricatus, has been isolated and characterized. It is the first member of a new group (group 3) of non-classical Kazal-type inhibitors. CmPI-II is a tight-binding inhibitor of serine proteases: trypsin, human neutrophil elastase (HNE), subtilisin A and pancreatic elastase. This specificity is exceptional in the members of Kazal-type inhibitor family. Several models of three-dimensional structure of CmPI-II have been constructed by homology with other inhibitors of the family but its structure has not yet been solved experimentally. Here we report the (1)H, (15)N and (13)C chemical shift assignments of CmPI-II as basis for NMR structure determination and interaction studies. Secondary structure analyses deduced from the NMR chemical shift data have identified three β-strands β1: residues 14-19, β2: 23-35 and β3: 43-45 and one helix α1: 28-37 arranged in the sequential order β1-β2-α1-β3. These secondary structure elements suggest that CmPI-II adopts the typical scaffold of a Kazal-type inhibitor.

  11. 1H, 13C and 15N resonance assignments and second structure information of Fag s 1: Fagales allergen from Fagus sylvatica.

    PubMed

    Moraes, A H; Asam, C; Batista, A; Almeida, F C L; Wallner, M; Ferreira, F; Valente, A P

    2016-04-01

    Fagales allergens belonging to the Bet v 1 family account responsible for the majority of spring pollinosis in the temperate climate zones in the Northern hemisphere. Among them, Fag s 1 from beech pollen is an important trigger of Fagales pollen associated allergic reactions. The protein shares high similarity with birch pollen Bet v 1, the best-characterized member of this allergen family. Of note, recent work on Bet v 1 and its homologues found in Fagales pollen demonstrated that not all allergenic members of this family have the capacity to induce allergic sensitization. Fag s 1 was shown to bind pre-existing IgE antibodies most likely primarily directed against other members of this multi-allergen family. Therefore, it is especially interesting to compare the structures of Bet v 1-like pollen allergens, which have the potential to induce allergic sensitization with allergens that are mainly cross-reactive. This in the end will help to identify allergy eliciting molecular pattern on Bet v 1-like allergens. In this work, we report the (1)H, (15)N and (13)C NMR assignment of beech pollen Fag s 1 as well as the secondary structure information based on backbone chemical shifts.

  12. Shielding 2Σ ultracold dipolar molecular collisions with electric fields

    NASA Astrophysics Data System (ADS)

    Quéméner, Goulven; Bohn, John L.

    2016-01-01

    The prospects for shielding ultracold, paramagnetic, dipolar molecules from inelastic and chemical collisions are investigated. Molecules placed in their first rotationally excited states are found to exhibit effective long-range repulsion for applied electric fields above a certain critical value, as previously shown for nonparamagnetic molecules. This repulsion can safely allow the molecules to scatter while reducing the risk of inelastic or chemically reactive collisions. Several molecular species of 2Σ molecules of experimental interest—RbSr, SrF, BaF, and YO—are considered, and all are shown to exhibit orders of magnitude suppression in quenching rates in a sufficiently strong laboratory electric field. It is further shown that, for these molecules described by Hund's coupling case (b), electronic and nuclear spins play the role of spectator with respect to the shielding.

  13. Charge transport and exciton dissociation in organic solar cells consisting of dipolar donors mixed with C70

    NASA Astrophysics Data System (ADS)

    Griffith, Olga L.; Liu, Xiao; Amonoo, Jojo A.; Djurovich, Peter I.; Thompson, Mark E.; Green, Peter F.; Forrest, Stephen R.

    2015-08-01

    We investigate dipolar donor materials mixed with a C70 acceptor in an organic photovoltaic (OPV) cell. Dipolar donors that have donor-acceptor-acceptor (d-a-a') structure result in high conductivity pathways due to close coupling between neighboring molecules in the mixed films. We analyze the charge transfer properties of the dipolar donor:C70 mixtures and corresponding neat donors using a combination of time-resolved electroluminescence from intermolecular polaron pair states and conductive tip atomic force microscopy, from which we infer that dimers of the d-a-a' donors tend to form a continuous network of nanocrystalline clusters within the blends. Additional insights are provided by quantum-mechanical calculations of hole transfer coupling and hopping rates between donor molecules using nearest-neighbor donor packing motifs taken from crystal structural data. The approximation using only nearest-neighbor interactions leads to good agreement between donor hole hopping rates and the conductive properties of the donor:C70 blends. This represents a significant simplification from requiring details of the nano- and mesoscale morphologies of thin films to estimate their electronic characteristics. Using these dipolar donors, we obtain a maximum power conversion efficiency of 9.6 ±0.5 % under 1 sun, AM1.5G simulated illumination for an OPV comprised of an active layer containing a dipolar donor mixed with C70.

  14. Dimensional crossover in dipolar magnetic layers

    NASA Astrophysics Data System (ADS)

    Bulenda, M.; Täuber, U. C.; Schwabl, F.

    2000-01-01

    We investigate the static critical behaviour of a uniaxial magnetic layer, with finite thickness L in one direction, yet infinitely extended in the remaining d dimensions. The magnetic dipole-dipole interaction is taken into account. We apply a variant of Wilson's momentum shell renormalization group approach to describe the crossover between the critical behaviour of the 3D Ising, 2D Ising, 3D uniaxial dipolar, and the 2D uniaxial dipolar universality classes. The corresponding renormalization group fixed points are in addition to different effective dimensionalities characterized by distinct analytic structures of the propagator, and are consequently associated with varying upper critical dimensions. While the limiting cases can be discussed by means of dimensional icons/Journals/Common/epsilon" ALT="epsilon" ALIGN="TOP"/> expansions with respect to the appropriate upper critical dimensions, respectively, the crossover features must be addressed in terms of the renormalization group flow trajectories at fixed dimensionality d .

  15. Zero sound in dipolar Fermi gases

    SciTech Connect

    Ronen, Shai; Bohn, John L.

    2010-03-15

    We study the propagation of sound in a homogeneous dipolar gas at zero temperature, which is known as zero sound. We find that undamped zero sound propagation is possible only in a range of solid angles around the direction of polarization of the dipoles. Above a critical dipole moment, we find an unstable mode, by which the gas collapses locally perpendicular to the dipoles' direction.

  16. Theory of substorm onset and dipolarization

    NASA Astrophysics Data System (ADS)

    Cheng, C. Z.; Zaharia, S.

    2003-04-01

    We present a theory of substorm onset and dipolarization. At the end of the substorm growth phase, the plasma pressure profile steepens and a thin current sheet is formed in the near-Earth plasma sheet around the local midnight with a finite radial and azimuthal domain. In the current sheet the plasma beta becomes about 50 or larger and magnetic field curvature is enhanced, and the kinetic ballooning instability (KBI) is excited with amplitude localized at the maximum plasma beta region. The KBI explains the low frequency (about 1 min period) instability observed by AMPTE/CCE with period on the order of 1 min is observed about 2-3 minutes before the substorm onset [Cheng and Lui, GRL, 1998]. The KBI is responsible for substorm onset because as it grows to a large amplitude with Δ B/B > 01, it causes an enhanced westward ion drift during the explosive growth phase that lasts about 30 sec. The KBI then excites higher frequency instabilities, and the plasma and magnetic field become strongly turbulent. The plasma transport in both radial and azimuthal direction caused by the turbulence relaxes the steep plasma pressure profile during the expansion phase. As the plasma pressure profile relaxes, the magnetic field configuration dipolarizes and returns to the pre-substorm more dipole-like geometry. Theories of current sheet formation, KBI mechanism and dipolarization will be presented along with numerical solutions of 3D magnetospheric structure.

  17. Synthesis of 2H-Indazoles by the [3 + 2] Dipolar Cycloaddition of Sydnones with Arynes

    PubMed Central

    Fang, Yuesi; Wu, Chunrui; Larock, Richard C.; Shi, Feng

    2011-01-01

    A rapid and efficient synthesis of 2H-indazoles has been developed using a [3 + 2] dipolar cycloaddition of sydnones and arynes. A series of 2H-indazoles have been prepared in good to excellent yields using this protocol, and subsequent Pd-catalyzed coupling reactions can be applied to the halogenated products to generate a structurally diverse library of indazoles. PMID:21970468

  18. Substituent effect in 2-benzoylmethylenequinoline difluoroborates exhibiting through-space couplings. Multinuclear magnetic resonance, X-ray diffraction, and computational study.

    PubMed

    Zakrzewska, Anna; Kolehmainen, Erkki; Valkonen, Arto; Haapaniemi, Esa; Rissanen, Kari; Chęcińska, Lilianna; Ośmiałowski, Borys

    2013-01-10

    The series of nine 2-benzoylmethylenequinoline difluoroborates have been synthesized and characterized by multinuclear magnetic resonance, X-ray diffraction (XRD), and computational methods. The through-space spin-spin couplings between (19)F and (1)H/(13)C nuclei have been observed in solution. The NMR chemical shifts have been correlated to the Hammett substituent constants. The crystal structures of six compounds have been solved by XRD. For two derivatives the X-ray wave function refinement was performed to evaluate the character of bonds in the NBF(2)O moiety by topological and integrated bond descriptors.

  19. Suppression of quantum phase interference in the molecular magnet Fe8 with dipolar-dipolar interaction

    NASA Astrophysics Data System (ADS)

    Chen, Zhi-De; Liang, J.-Q.; Shen, Shun-Qing

    2002-09-01

    Renormalized tunnel splitting with a finite distribution in the biaxial spin model for molecular magnets is obtained by taking into account the dipolar interaction of enviromental spins. Oscillation of the resonant tunnel splitting with a transverse magnetic field along the hard axis is smeared by the finite distribution, which subsequently affects the quantum steps of the hysteresis curve evaluated in terms of the modified Landau-Zener model of spin flipping induced by the sweeping field. We conclude that the dipolar-dipolar interaction drives decoherence of quantum tunneling in the molecular magnet Fe8, which explains why the quenching points of tunnel splitting between odd and even resonant tunneling predicted theoretically were not observed experimentally.

  20. Robust and efficient 19F heteronuclear dipolar decoupling using refocused continuous-wave rf irradiation

    NASA Astrophysics Data System (ADS)

    Vinther, Joachim M.; Khaneja, Navin; Nielsen, Niels Chr.

    2013-01-01

    Refocused continuous wave (rCW) decoupling is presented as an efficient and robust means to obtain well-resolved magic-angle-spinning solid-state NMR spectra of low-γ spins, such as 13C dipolar coupled to fluorine. The rCW decoupling sequences, recently introduced for 1H decoupling, are very robust towards large isotropic and anisotropic shift ranges as often encountered for 19F spins. In rCW decoupling, the so-called refocusing pulses inserted into the CW irradiation eliminate critical residual second- and third-order dipolar coupling and dipolar-coupling against chemical shielding anisotropy cross-terms in the effective Hamiltonian through time-reversal (i.e. refocusing). As important additional assets, the rCW decoupling sequences are robust towards variations in rf amplitudes, operational at low to high spinning speeds, and easy to set-up for optimal performance experimentally. These aspects are demonstrated analytically/numerically and experimentally in comparison to state-of-the-art decoupling sequences such as TPPM, SPINAL-64, and frequency-swept variants of these.

  1. Ultracold Dipolar Molecules Composed of Strongly Magnetic Atoms

    NASA Astrophysics Data System (ADS)

    Frisch, A.; Mark, M.; Aikawa, K.; Baier, S.; Grimm, R.; Petrov, A.; Kotochigova, S.; Quéméner, G.; Lepers, M.; Dulieu, O.; Ferlaino, F.

    2015-11-01

    In a combined experimental and theoretical effort, we demonstrate a novel type of dipolar system made of ultracold bosonic dipolar molecules with large magnetic dipole moments. Our dipolar molecules are formed in weakly bound Feshbach molecular states from a sample of strongly magnetic bosonic erbium atoms. We show that the ultracold magnetic molecules can carry very large dipole moments and we demonstrate how to create and characterize them, and how to change their orientation. Finally, we confirm that the relaxation rates of molecules in a quasi-two-dimensional geometry can be reduced by using the anisotropy of the dipole-dipole interaction and that this reduction follows a universal dipolar behavior.

  2. Dipolar effects on the critical fluctuations in Fe: Investigation by the neutron spin-echo technique MIEZE

    NASA Astrophysics Data System (ADS)

    Kindervater, J.; Säubert, S.; Böni, P.

    2017-01-01

    Iron is one of the archetypical ferromagnets to study the critical fluctuations at a continuous phase transition thus serving as a model system for the application of scaling theory. We report a comprehensive study of the critical dynamics at the transition from the ferro- to the paramagnetic phase in Fe, employing the high-resolution neutron spin-echo technique, modulated intensity of zero effort (MIEZE). The results show that the dipolar interactions lead to an additional damping of the critical spin fluctuations at small momentum transfers q . The results agree essentially with scaling theory if the dipolar interactions are taken into account by means of the mode-coupling equations. However, in contrast to expectations, the dipolar wave number qD that plays a central role in the scaling function f (κ /q ,qD/κ ) becomes temperature dependent. In the limit of small q the critical exponent z crosses over from 2.5 to 2.0.

  3. The dipolar interaction in CoFeB/MgO/CoFeB perpendicular magnetic tunnel junction

    NASA Astrophysics Data System (ADS)

    Tsai, C. C.; Cheng, Chih-Wei; Weng, Yi-Chien; Chern, G.

    2014-05-01

    Ultrathin CoFeB/MgO/CoFeB system with perpendicular magnetic anisotropy is a promising candidate for the high density magnetic random access memory. However, a dipolar interaction between the CoFeB layers may introduce a minor loop shift (Hs) and causes uncertainty during the operation. In this report, we systematically studied the dipolar effect in these structures and found that the coupling may be either ferromagnetic or antiferromagnetic (15 Oe > Hs > -15 Oe) depending upon the CoFeB thickness (0.9-1.4 nm). A modified Fabry-Perot model, which accounts the Bloch wave interference, may explain the present observations of the dipolar effect in the perpendicular junctions of CoFeB/MgO/CoFeB.

  4. Nuclear magnetic relaxation by the dipolar EMOR mechanism: Three-spin systems

    NASA Astrophysics Data System (ADS)

    Chang, Zhiwei; Halle, Bertil

    2016-07-01

    In aqueous systems with immobilized macromolecules, including biological tissue, the longitudinal spin relaxation of water protons is primarily induced by exchange-mediated orientational randomization (EMOR) of intra- and intermolecular magnetic dipole-dipole couplings. Starting from the stochastic Liouville equation, we have developed a non-perturbative theory that can describe relaxation by the dipolar EMOR mechanism over the full range of exchange rates, dipole couplings, and Larmor frequencies. Here, we implement the general dipolar EMOR theory for a macromolecule-bound three-spin system, where one, two, or all three spins exchange with the bulk solution phase. In contrast to the previously studied two-spin system with a single dipole coupling, there are now three dipole couplings, so relaxation is affected by distinct correlations as well as by self-correlations. Moreover, relaxation can now couple the magnetizations with three-spin modes and, in the presence of a static dipole coupling, with two-spin modes. As a result of this complexity, three secondary dispersion steps with different physical origins can appear in the longitudinal relaxation dispersion profile, in addition to the primary dispersion step at the Larmor frequency matching the exchange rate. Furthermore, and in contrast to the two-spin system, longitudinal relaxation can be significantly affected by chemical shifts and by the odd-valued ("imaginary") part of the spectral density function. We anticipate that the detailed studies of two-spin and three-spin systems that have now been completed will provide the foundation for developing an approximate multi-spin dipolar EMOR theory sufficiently accurate and computationally efficient to allow quantitative molecular-level interpretation of frequency-dependent water-proton longitudinal relaxation data from biophysical model systems and soft biological tissue.

  5. Nonequilibrium nuclear polarization and induced hyperfine and dipolar magnetic fields in semiconductor nanostructures

    NASA Astrophysics Data System (ADS)

    Ţifrea, Ionel; Flatté, Michael E.

    2011-10-01

    We investigate the dynamic nuclear polarization (DNP) caused by hyperfine coupling between nonequilibrium electronic spins and nuclear spins in semiconductor nanostructures. We derive the time and position dependence of the resulting hyperfine and dipolar magnetic fields. In GaAs quantum wells the induced nuclear spin polarization greatly exceeds the polarization of the electronic system that causes the DNP. The induced magnetic fields vary between tens of tesla for the electronic hyperfine field acting on nuclei, to hundreds of gauss for the nuclear hyperfine field acting on electrons, to a few gauss for the induced nuclear dipolar fields that act on both nuclei and electrons. The field strengths should be measurable via optically induced nuclear magnetic resonance or time-resolved Faraday rotation experiments. We discuss the implications of our calculations for low-dimensional semiconductor nanostructures.

  6. Superfluid, solid, and supersolid phases of dipolar bosons in a quasi-one-dimensional optical lattice

    SciTech Connect

    Fellows, Jonathan M.; Carr, Sam T.

    2011-11-15

    We discuss a model of dipolar bosons trapped in a weakly coupled planar array of one-dimensional tubes. We consider the situation where the dipolar moments are aligned by an external field, and we find a rich phase diagram as a function of the angle of this field exhibiting quantum phase transitions between solid, superfluid, and supersolid phases. In the low energy limit, the model turns out to be identical to one describing quasi-one-dimensional superconductivity in condensed matter systems. This opens the possibility of using bosons as a quantum analog simulator of electronic systems, a scenario arising from the intricate relation between statistics and interactions in quasi-one-dimensional systems.

  7. Dielectric antennas--a suitable platform for controlling magnetic dipolar emission.

    PubMed

    Schmidt, M K; Esteban, R; Sáenz, J J; Suárez-Lacalle, I; Mackowski, S; Aizpurua, J

    2012-06-18

    Plasmonic nanoparticles are commonly used to tune and direct the radiation from electric dipolar emitters. Less progress has been made towards understanding complementary systems of magnetic nature. However, it has been recently shown that high-index dielectric spheres can act as effective magnetic antennas. Here we explore the concept of coupling dielectric magnetic antennas with either an electric or magnetic dipolar emitter in a similar fashion to the purely electric systems reported previously. We investigate the enhancement of radiation from systems comprising admixtures of these electric and magnetic elements and perform a full study of its dependence on the distance and polarization of the emitter with respect to the antenna. A comparison to the plasmon antennas reveals remarkable symmetries between electric and magnetic systems, which might lead to novel paradigms in the design of nanophotonic devices that involve magnetic activity.

  8. Monte Carlo simulations of a kagome lattice with magnetic dipolar interactions

    NASA Astrophysics Data System (ADS)

    Holden, M. S.; Plumer, M. L.; Saika-Voivod, I.; Southern, B. W.

    2015-06-01

    The results of extensive Monte Carlo simulations of classical spins on the two-dimensional kagome lattice with only dipolar interactions are presented. In addition to revealing the sixfold-degenerate ground state, the nature of the finite-temperature phase transition to long-range magnetic order is discussed. Low-temperature states consisting of mixtures of degenerate ground-state configurations separated by domain walls can be explained as a result of competing exchange-like and shape-anisotropy-like terms in the dipolar coupling. Fluctuations between pairs of degenerate spin configurations are found to persist well into the ordered state as the temperature is lowered until locking in to a low-energy state.

  9. A combined discontinuous Galerkin method for the dipolar Bose-Einstein condensation

    NASA Astrophysics Data System (ADS)

    Li, Xiang-Gui; Zhu, Jiang; Zhang, Rong-Pei; Cao, Shengshan

    2014-10-01

    In this work, a combined discontinuous Galerkin (DG) method, which is a hybridized mixed discontinuous Galerkin (HMDG) method combined with the direct discontinuous Galerkin (DDG) method, is proposed to compute ground states and dynamics of dipolar Bose-Einstein condensates (BECs) described by a multi-dimensional Gross-Pitaevskii equation (GPE) coupled with a first-order velocity system. Due to the adaption of the first-order velocity system instead of dipolar interactions, the proposed combined DG method avoids to evaluate integrals with high singularity. Additionally, this method keeps the conservation of the particle number. The Krylov semi-implicit method is applied to the time discretization. Finally, numerical examples are presented to demonstrate the accuracy and capability of the proposed method.

  10. Quantum non-Markovian reservoirs of atomic condensates engineered via dipolar interactions

    NASA Astrophysics Data System (ADS)

    Yuan, Ji-Bing; Xing, Hai-Jun; Kuang, Le-Man; Yi, Su

    2017-03-01

    We investigate the quantum dephasing dynamics of an impurity qubit immersed in a quasi-two-dimensional dipolar Bose-Einstein condensate whose collective excitations act as a reservoir for the qubit. We show that the properties of the environment are highly engineerable through the relative strength of the dipolar and contact interactions such that qubit's dephasing dynamics could be Markovian, weak non-Markovian, or even highly non-Markovian. It is also revealed that the appearance of the roton excitation is responsible for the highly non-Markovian dephasing dynamics. Since rotonlike dispersions also appear in condensates placed in cavities or with spin-orbit couplings, our results pave the way for searching for systems that are suitable environment engineering.

  11. Influence of dipolar interactions on hyperthermia properties of ferromagnetic particles

    NASA Astrophysics Data System (ADS)

    Serantes, D.; Baldomir, D.; Martinez-Boubeta, C.; Simeonidis, K.; Angelakeris, M.; Natividad, E.; Castro, M.; Mediano, A.; Chen, D.-X.; Sanchez, A.; Balcells, LI.; Martínez, B.

    2010-10-01

    We show both experimental evidences and Monte Carlo modeling of the effects of interparticle dipolar interactions on the hysteresis losses. Results indicate that an increase in the intensity of dipolar interactions produce a decrease in the magnetic susceptibility and hysteresis losses, thus diminishing the hyperthermia output. These findings may have important clinical implications for cancer treatment.

  12. Current system associated with small dipolarization fronts

    NASA Astrophysics Data System (ADS)

    Palin, Laurianne; Jacquey, Christian; Opgenoorth, Hermann; Connors, Martin; Sergeev, Victor; Sauvaud, Jean-André; Nakamura, Rumi; Reeves, Geoffrey D.; Singer, Howard; Angelopoulos, Vassilis; Turc, Lucile

    2015-04-01

    We present a case study of eight successive Plasma Sheet (PS) activations (usually referred to as « Bursty Bulk Flows » or « Dipolarisation Fronts ») associated with small individual BZGSM increases on 31 March 2009 (0200 - 0900 UT). This series of events happens during generally very quiet SW conditions, over a period of 7 hours preceding a substorm onset at 1230 UT. The amplitude of the dipolarizations increases with time. The low amplitude dipolarization fronts are associated with few (1 or 2) Rapid Flux Transfer events (Eh > 2mV/m), whereas the large amplitude ones engulf many more RFT events. All PS activations are associated with a small and localised current wedge(« wedgelet ») which seems to be the consequence of RFT arrival in the near tail. Ground magnetic perturbations affect a larger part of the contracted auroral oval for the events with more RTF event embedded (> 5). Dipolarisation Fronts with very low amplitude, a type usually not included in statistical studies, are of particular interest because we found them associated with clear wedgelets and particle injections at geosynchronous orbit. This exceptional dataset highlights the role of flow bursts in the magnetotail and brings up the question: are we in this case observing the smallest form of a substorm ?

  13. Particle energization by a substorm dipolarization

    NASA Astrophysics Data System (ADS)

    Kabin, K.; Kalugin, G.; Donovan, E.; Spanswick, E.

    2017-01-01

    Magnetotail dipolarizations, often associated with substorms, produce significant energetic particle enhancements in the nighttime magnetosphere. In this paper, we apply our recently developed magnetotail dipolarization model to the problem of energizing electrons and ions. Our model is two-dimensional in the meridional plane and is characterized by the ability to precisely control the location of the transition from the dipole-like to tail-like magnetic fields. Both magnetic and electric fields are calculated, self-consistently, as the transition zone retreats farther into the tail and the area around the Earth occupied by dipole-like lines increases in size. These fields are used to calculate the motion of electrons and ions and changes in their energies. We consider the energizing effects of the fields restricted to ±15° and ±30° sectors around the midnight meridian, as well the axisymmetric case. Energies of some electrons increase by a factor of 25, which is more than enough to produce observable ionospheric signatures. Electrons are treated using the Guiding Center approximation, while protons and heavier particles generally require description based on the Lorentz equations.

  14. COUPLING

    DOEpatents

    Frisch, E.; Johnson, C.G.

    1962-05-15

    A detachable coupling arrangement is described which provides for varying the length of the handle of a tool used in relatively narrow channels. The arrangement consists of mating the key and keyhole formations in the cooperating handle sections. (AEC)

  15. Specific heat anomaly in relaxor ferroelectrics and dipolar glasses

    NASA Astrophysics Data System (ADS)

    Kutnjak, Z.; Pirc, R.

    2017-03-01

    The temperature and electric field dependence of the specific heat of relaxor ferroelectrics and dipolar glasses is investigated by means of a Landau-type theoretical model. It is shown that the dipolar specific heat, which is due to the randomly interacting polar nanoregions in relaxors and electric dipoles in dipolar glasses, is negative in a temperature region below the permittivity maximum. Also, it follows that for sufficiently low values of the field, where the induced polarization shows a quasi linear field dependence, the dipolar specific heat is proportional to the second temperature derivative of the dielectric polarization. This quantity can be extracted from the experimental temperature profile of the polarization, thus enabling an indirect experimental estimate of the negative specific heat, which is demonstrated for a set of representative relaxor and dipolar glass systems.

  16. Orientational structure of dipolar hard-spherical colloids.

    PubMed

    Alarcón-Waess, O; Diaz-Herrera, E; Gil-Villegas, A

    2002-03-01

    We have studied the orientational structure of a dipolar hard-spherical colloid on a homogeneous isotropic phase. The results are expressed as a function of the dipolar strength mu and volume fraction phi of dipolar colloids, and the refractive index of the scattering medium, n(s). The study is based on the self-correlation of the orientation density of the dipolar colloids, which is the static orientational structure factor [F(q)], where q is the wave vector. The importance of this quantity is that for very low phi values, it can be probed in a depolarized light scattering experiment. We have found that the structure of the suspension is better observed for high n(s). F(q) presents a different behavior for dilute and dense concentrations, it is also observed that the position of its minimum depends on phi. The response of a dipolar colloid due to its collective orientational behavior is also studied, using as an "ordering parameter" the static orientational structure factor at q=0[F(q=0)]. The study is performed for isochores as a function of mu. We have divided the analysis into five regimes, from very low to very high phi; values, i.e., phi=0.005 24, 0.1, 0.2, 0.35, and 0.45. Our analysis suggests that the dipolar colloid evolves to an orientationally ordered phase when the dipolar strength is increased, for all concentrations except for the lowest value case, phi=0.005 24. When phi=0.1 the dipolar colloid reaches the transition suddenly, whereas for the very low regime, the slope of F(q=0) first increases as if the dipolar colloid would evolve to an orientationally ordered phase; but near the transition the slope is inverted, resulting in a no global orientational order. Thus, our results suggest that in the very low regime a dipolar colloid may have a reentrant transition.

  17. Refocused continuous-wave decoupling: A new approach to heteronuclear dipolar decoupling in solid-state NMR spectroscopy

    NASA Astrophysics Data System (ADS)

    Vinther, Joachim M.; Nielsen, Anders B.; Bjerring, Morten; van Eck, Ernst R. H.; Kentgens, Arno P. M.; Khaneja, Navin; Nielsen, Niels Chr.

    2012-12-01

    A novel strategy for heteronuclear dipolar decoupling in magic-angle spinning solid-state nuclear magnetic resonance (NMR) spectroscopy is presented, which eliminates residual static high-order terms in the effective Hamiltonian originating from interactions between oscillating dipolar and anisotropic shielding tensors. The method, called refocused continuous-wave (rCW) decoupling, is systematically established by interleaving continuous wave decoupling with appropriately inserted rotor-synchronized high-power π refocusing pulses of alternating phases. The effect of the refocusing pulses in eliminating residual effects from dipolar coupling in heteronuclear spin systems is rationalized by effective Hamiltonian calculations to third order. In some variants the π pulse refocusing is supplemented by insertion of rotor-synchronized π/2 purging pulses to further reduce the residual dipolar coupling effects. Five different rCW decoupling sequences are presented and their performance is compared to state-of-the-art decoupling methods. The rCW decoupling sequences benefit from extreme broadbandedness, tolerance towards rf inhomogeneity, and improved potential for decoupling at relatively low average rf field strengths. In numerical simulations, the rCW schemes clearly reveal superior characteristics relative to the best decoupling schemes presented so far, which we to some extent also are capable of demonstrating experimentally. A major advantage of the rCW decoupling methods is that they are easy to set up and optimize experimentally.

  18. Dielectric relaxation in ionic liquid/dipolar solvent binary mixtures: A semi-molecular theory

    NASA Astrophysics Data System (ADS)

    Daschakraborty, Snehasis; Biswas, Ranjit

    2016-03-01

    estimates for the effective rotational volume ( Veff dip ) are used as inputs. The fraction, Veff dip / Vmol dip , sharply decreases from ˜1 at pure dipolar solvent to ˜0.01 at neat IL, reflecting a dramatic crossover from viscosity-coupled hydrodynamic angular diffusion at low IL mole fractions to orientational relaxation predominantly via large angle jumps at high xIL. Similar results are obtained on applying the present theory to the aqueous solution of an electrolyte guanidinium chloride (GdmCl) having a permanent dipole moment associated with the cation, Gdm+.

  19. Dielectric relaxation in ionic liquid/dipolar solvent binary mixtures: A semi-molecular theory.

    PubMed

    Daschakraborty, Snehasis; Biswas, Ranjit

    2016-03-14

    experimental estimates for the effective rotational volume (V(eff)(dip)) are used as inputs. The fraction, V(eff)(dip)/V(mol)(dip), sharply decreases from ∼1 at pure dipolar solvent to ∼0.01 at neat IL, reflecting a dramatic crossover from viscosity-coupled hydrodynamic angular diffusion at low IL mole fractions to orientational relaxation predominantly via large angle jumps at high x(IL). Similar results are obtained on applying the present theory to the aqueous solution of an electrolyte guanidinium chloride (GdmCl) having a permanent dipole moment associated with the cation, Gdm(+).

  20. Self-replicating devices with dipolar colloids

    NASA Astrophysics Data System (ADS)

    Dempster, Joshua; Zhang, Rui; Olvera de La Cruz, Monica

    2014-03-01

    Ubiquitous in nature, self-replication on the nano-scale has been challenging to produce in the laboratory. Recent efforts with DNA tiles have shown great success in correctly replicating tile-sequence templates but require frequent manipulation by the experimenter. We propose a scheme for achieving self-replication with dipolar colloids. Dimers in these systems replicate exponentially over millisecond time scales with no intervention other than periodic energy pulses supplied by external fields. We develop a general formalism governing the rate of self-replication as a function of the interval between pulses. Results from kinetic Monte Carlo simulations show good agreement with the growth rates predicted by simple models of the replication process. We thank the Office of the Director of Defense Research and Engineering (DDR&E) and Air Force Office of Scientific Research (AFOSR) for their support under Award FA9550-10-1-0167.

  1. Electric fields associated with dipolarization fronts

    NASA Astrophysics Data System (ADS)

    Sun, Wei-Jie; Fu, Suiyan; Parks, George K.; Pu, Zuyin; Zong, Qiu-Gang; Liu, Jiang; Yao, Zhonghua; Fu, Huishan; Shi, Quanqi

    2014-07-01

    Electric fields associated with dipolarization fronts (DFs) have been investigated in the magnetotail plasma sheet using Cluster observations. We have studied each term in the generalized Ohm's law using data obtained from the multispacecraft Cluster. Our results show that in the plasma flow frame, electric fields are directed normal to the DF in the magnetic dip region ahead of the DF as well as in the DF layer but in opposite directions. Case and statistical studies show that the Hall electric field is important while the electron pressure gradient term is much smaller. The ions decouple from the magnetic field in the DF layer and dip region (E + Vi×B ≠ 0), whereas electrons remain frozen-in (E + Ve×B=∇pe/nee).

  2. Droplets of Trapped Quantum Dipolar Bosons

    NASA Astrophysics Data System (ADS)

    Macia, A.; Sánchez-Baena, J.; Boronat, J.; Mazzanti, F.

    2016-11-01

    Strongly interacting systems of dipolar bosons in three dimensions confined by harmonic traps are analyzed using the exact path integral ground-state Monte Carlo method. By adding a repulsive two-body potential, we find a narrow window of interaction parameters leading to stable ground-state configurations of droplets in a crystalline arrangement. We find that this effect is entirely due to the interaction present in the Hamiltonian without resorting to additional stabilizing mechanisms or specific three-body forces. We analyze the number of droplets formed in terms of the Hamiltonian parameters, relate them to the corresponding s -wave scattering length, and discuss a simple scaling model for the density profiles. Our results are in qualitative agreement with recent experiments showing a quantum Rosensweig instability in trapped Dy atoms.

  3. Mixed parity pairing in a dipolar gas

    NASA Astrophysics Data System (ADS)

    Bruun, G. M.; Hainzl, C.; Laux, M.

    2016-10-01

    We show that fermionic dipoles in a two-layer geometry form Cooper pairs with both singlet and triplet components when they are tilted with respect to the normal of the planes. The mixed parity pairing arises because the interaction between dipoles in the two different layers is not inversion symmetric. We use an efficient eigenvalue approach to calculate the zero-temperature phase diagram of the system as a function of the dipole orientation and the layer distance. The phase diagram contains purely triplet as well as mixed singlet and triplet superfluid phases. We show in detail how the pair wave function for dipoles residing in different layers smoothly changes from singlet to triplet symmetry as the orientation of the dipoles is changed. Our results indicate that dipolar quantum gases can be used to unambiguously observe mixed parity pairing.

  4. Slow spin relaxation in dipolar spin ice.

    NASA Astrophysics Data System (ADS)

    Orendac, Martin; Sedlakova, Lucia; Orendacova, Alzbeta; Vrabel, Peter; Feher, Alexander; Pajerowski, Daniel M.; Cohen, Justin D.; Meisel, Mark W.; Shirai, Masae; Bramwell, Steven T.

    2009-03-01

    Spin relaxation in dipolar spin ice Dy2Ti2O7 and Ho2Ti2O7 was investigated using the magnetocaloric effect and susceptibility. The magnetocaloric behavior of Dy2Ti2O7 at temperatures where the orientation of spins is governed by ``ice rules`` (T < Tice) revealed thermally activated relaxation; however, the resulting temperature dependence of the relaxation time is more complicated than anticipated by a mere extrapolation of the corresponding high temperature data [1]. A susceptibility study of Ho2Ti2O7 was performed at T > Tice and in high magnetic fields, and the results suggest a slow relaxation of spins analogous to the behavior reported in a highly polarized cooperative paramagnet [2]. [1] J. Snyder et al., Phys. Rev. Lett. 91 (2003) 107201. [2] B. G. Ueland et al., Phys. Rev. Lett. 96 (2006) 027216.

  5. Heating and acceleration of charged particles during magnetic dipolarizations

    NASA Astrophysics Data System (ADS)

    Grigorenko, E. E.; Kronberg, E. A.; Daly, P. W.

    2017-01-01

    In this paper, we analyzed the thermal and energy characteristics of the plasma components observed during the magnetic dipolarizations in the near tail by the Cluster satellites. It was previously found that the first dipolarization the ratio of proton and electron temperatures ( T p/ T e) was 6-7. At the time of the observation of the first dipolarization front T p/ T e decreases by up to 3-4. The minimum value T p/ T e ( 2.0) is observed behind the front during the turbulent dipolarization phase. Decreases in T p/ T e observed at this time are associated with an increase in T e, whereas the proton temperature either decreases or remains unchanged. Decreases of the value T p/ T e during the magnetic dipolarizations coincide with increase in wave activity in the wide frequency band up to electron gyrofrequency f ce. High-frequency modes can resonantly interact with electrons causing their heating. The acceleration of ions with different masses up to energies of several hundred kiloelectron-volts is also observed during dipolarizations. In this case, the index of the energy spectrum decreases (a fraction of energetic ions increases) during the enhancement of low-frequency electromagnetic fluctuations at frequencies that correspond to the gyrofrequency of this ion component. Thus, we can conclude that the processes of the interaction between waves and particles play an important role in increasing the energy of plasma particles during magnetic dipolarizations.

  6. Decoherence of multiple quantum coherences generated from a dipolar ordered state

    NASA Astrophysics Data System (ADS)

    González, C. E.; Segnorile, H. H.; Zamar, R. C.

    2011-01-01

    Starting from the hypothesis that the decay of coherent signals observed in H1 NMR experiments is driven by quantum interference, irreversible decoherence, and nonidealities in the experiment, we design an experiment to isolate and identify the irreversible attenuation of multiple-quantum coherences toward quasiequilibrium states of dipolar order in nematic liquid crystals (LCs). The experiment combines the well-known “magic sandwich” pulse sequence with preparation of dipolar ordered states and encoding of multiple-quantum coherences. The spin system composed of the dipole-coupled protons of a LC molecule provides an example of a small cluster of strongly interacting spins. We study decoherence rates under a sequence that reverses time evolution with the secular dipolar Hamiltonian to compensate coherent evolution of a closed quantum system. In this way, the time scale is made evident where irreversible decoherence takes place, providing insight into the nature of the processes responsible for the attainment of quasiequilibrium. The behavior of single- and double-quantum-coherence amplitudes with reversal time is interpreted as evidence of the quantum character (as opposed to stochastic character) of the processes that drive irreversible decoherence. The experimental method proposed is useful for probing the action of the environment on materials with quantum information processing potential.

  7. EPR-correlated dipolar spectroscopy by Q-band chirp SIFTER.

    PubMed

    Doll, Andrin; Jeschke, Gunnar

    2016-08-17

    While two-dimensional correlation spectra contain more information as compared to one-dimensional spectra, typical spectral widths encountered in electron paramagnetic resonance (EPR) spectroscopy largely restrict the applicability of correlation techniques. In essence, the monochromatic excitation pulses established in pulsed EPR often cannot uniformly excite the entire spectrum. Here, this restriction is alleviated for nitroxide spin labels at Q-band microwave frequencies around 35 GHz. This is achieved by substitution of monochromatic pulses by frequency-swept chirp pulses tailored for uniform excitation. Unwanted interference effects brought by this substitution are analyzed for a pair of electron spins with secular dipolar coupling. Experimentally, the dipole-dipole interaction can be separated from other interactions by a constant-time Zeeman-compensated solid echo sequence called SIFTER. Such SIFTER experiments usually yield a one-dimensional dipolar spectrum. EPR-correlated dipolar spectra can be obtained when the four pulses are replaced by chirp pulses. These two-dimensional spectra encode additional information on the geometrical arrangement of the two spin labels. With the excitation parameters achieved by a home-built Q-band spectrometer capable of frequency-swept excitation, unwanted interference effects can be largely neglected for the examined model compound with a spin-spin distance of 4 nm. The experimentally obtained correlation pattern conforms to the expectation based on the inter-spin geometry of the investigated rigid model compound.

  8. Bose-Einstein condensation of dipolar excitons in quantum wells

    NASA Astrophysics Data System (ADS)

    Timofeev, V. B.; Gorbunov, A. V.

    2009-02-01

    The experiments on Bose-Einstein condensation (BEC) of dipolar (spatially-indirect) excitons in the lateral traps in GaAs/AlGaAs Schottky-diode heterostructures with double and single quantum wells are presented. The condensed part of dipolar excitons under detection in the far zone is placed in k-space in the range which is almost two orders of magnitude less than thermal exciton wave vector. BEC occurs spontaneously in a reservoir of thermalized excitons. Luminescence images of Bose-condensate of dipolar excitons exhibit along perimeter of circular trap axially symmetrical spatial structures of equidistant bright spots which strongly depend on excitation power and temperature. By means of two-beam interference experiments with the use of cw and pulsed photoexcitation it was found that the state of dipolar exciton Bose-condensate is spatially coherent and the whole patterned luminescence configuration in real space is described by a common wave function.

  9. Artificial kagome arrays of nanomagnets: a frozen dipolar spin ice.

    PubMed

    Rougemaille, N; Montaigne, F; Canals, B; Duluard, A; Lacour, D; Hehn, M; Belkhou, R; Fruchart, O; El Moussaoui, S; Bendounan, A; Maccherozzi, F

    2011-02-04

    Magnetic frustration effects in artificial kagome arrays of nanomagnets are investigated using x-ray photoemission electron microscopy and Monte Carlo simulations. Spin configurations of demagnetized networks reveal unambiguous signatures of long range, dipolar interaction between the nanomagnets. As soon as the system enters the spin ice manifold, the kagome dipolar spin ice model captures the observed physics, while the short range kagome spin ice model fails.

  10. Effective Hamiltonians by optimal control: solid-state NMR double-quantum planar and isotropic dipolar recoupling.

    PubMed

    Tosner, Zdenek; Glaser, Steffen J; Khaneja, Navin; Nielsen, Niels Chr

    2006-11-14

    We report the use of optimal control algorithms for tailoring the effective Hamiltonians in nuclear magnetic resonance (NMR) spectroscopy through sophisticated radio-frequency (rf) pulse irradiation. Specifically, we address dipolar recoupling in solid-state NMR of powder samples for which case pulse sequences offering evolution under planar double-quantum and isotropic mixing dipolar coupling Hamiltonians are designed. The pulse sequences are constructed numerically to cope with a range of experimental conditions such as inhomogeneous rf fields, spread of chemical shifts, the intrinsic orientation dependencies of powder samples, and sample spinning. While the vast majority of previous dipolar recoupling sequences are operating through planar double-or zero-quantum effective Hamiltonians, we present here not only improved variants of such experiments but also for the first time homonuclear isotropic mixing sequences which transfers all I(x), I(y), and I(z) polarizations from one spin to the same operators on another spin simultaneously and with equal efficiency. This property may be exploited to increase the signal-to-noise ratio of two-dimensional experiments by a factor of square root 2 compared to conventional solid-state methods otherwise showing the same efficiency. The sequences are tested numerically and experimentally for a powder of (13)C(alpha),(13)C(beta)-L-alanine and demonstrate substantial sensitivity gains over previous dipolar recoupling experiments.

  11. Ground-state and dynamical properties of two-dimensional dipolar Fermi liquids

    SciTech Connect

    Abedinpour, Saeed H.; Asgari, Reza; Tanatar, B.; Polini, Marco

    2014-01-15

    We study the ground-state properties of a two-dimensional spin-polarized fluid of dipolar fermions within the Euler–Lagrange Fermi-hypernetted-chain approximation. Our method is based on the solution of a scattering Schrödinger equation for the “pair amplitude” √(g(r)), where g(r) is the pair distribution function. A key ingredient in our theory is the effective pair potential, which includes a bosonic term from Jastrow–Feenberg correlations and a fermionic contribution from kinetic energy and exchange, which is tailored to reproduce the Hartree–Fock limit at weak coupling. Very good agreement with recent results based on quantum Monte Carlo simulations is achieved over a wide range of coupling constants up to the liquid-to-crystal quantum phase transition. Using the fluctuation–dissipation theorem and a static approximation for the effective inter-particle interactions, we calculate the dynamical density–density response function, and furthermore demonstrate that an undamped zero-sound mode exists for any value of the interaction strength, down to infinitesimally weak couplings. -- Highlights: •We have studied the ground state properties of a strongly correlated two-dimensional fluid of dipolar fermions. •We have calculated the effective inter-particle interaction and the dynamical density–density response function. •We have shown that an undamped zero sound mode exists at any value of the interaction strength.

  12. Open-chain unsaturated selanyl sulfides: stereochemical structure and stereochemical behavior of their 77Se-1H spin-spin coupling constants.

    PubMed

    Rusakov, Yury Yu; Krivdin, Leonid B; Penzik, Maxim V; Potapov, Vladimir A; Amosova, Svetlana V

    2012-10-01

    Stereochemical structure of nine Z-2-(vinylsulfanyl)ethenylselanyl organyl sulfides has been investigated by means of experimental measurements and second-order polarization propagator approach calculations of their (1)H-(1)H, (13)C-(1)H, and (77)Se-(1)H spin-spin coupling constants together with a theoretical conformational analysis performed at the MP2/6-311G** level. All nine compounds were shown to adopt the preferable skewed s-cis conformation of their terminal vinylsulfanyl group, whereas the favorable rotational conformations with respect to the internal rotations around the C-S and C-Se bonds of the internal ethenyl group are both skewed s-trans. Stereochemical trends of (77)Se-(1)H spin-spin coupling constants originating in the geometry of their coupling pathways and the selenium lone pair effect were rationalized in terms of the natural J-coupling analysis within the framework of the natural bond orbital approach.

  13. Self-replication with magnetic dipolar colloids.

    PubMed

    Dempster, Joshua M; Zhang, Rui; Olvera de la Cruz, Monica

    2015-10-01

    Colloidal self-replication represents an exciting research frontier in soft matter physics. Currently, all reported self-replication schemes involve coating colloidal particles with stimuli-responsive molecules to allow switchable interactions. In this paper, we introduce a scheme using ferromagnetic dipolar colloids and preprogrammed external magnetic fields to create an autonomous self-replication system. Interparticle dipole-dipole forces and periodically varying weak-strong magnetic fields cooperate to drive colloid monomers from the solute onto templates, bind them into replicas, and dissolve template complexes. We present three general design principles for autonomous linear replicators, derived from a focused study of a minimalist sphere-dimer magnetic system in which single binding sites allow formation of dimeric templates. We show via statistical models and computer simulations that our system exhibits nonlinear growth of templates and produces nearly exponential growth (low error rate) upon adding an optimized competing electrostatic potential. We devise experimental strategies for constructing the required magnetic colloids based on documented laboratory techniques. We also present qualitative ideas about building more complex self-replicating structures utilizing magnetic colloids.

  14. Tailored real-time scaling of heteronuclear couplings.

    PubMed

    Schilling, Franz; Glaser, Steffen J

    2012-10-01

    Heteronuclear couplings are a valuable source of molecular information, which is measured from the multiplet splittings of an NMR spectrum. Radiofrequency irradiation on one coupled nuclear spin allows to modify the effective coupling constant, scaling down the multiplet splittings in the spectrum observed at the resonance frequency of the other nuclear spin. Such decoupling sequences are often used to collapse a multiplet into a singlet and can therefore simplify NMR spectra significantly. Continuous-wave (cw) decoupling has an intrinsic non-linear offset dependence of the scaling of the effective J-coupling constant. Using optimal control pulse optimization, we show that virtually arbitrary off-resonance scaling of the J-coupling constant can be achieved. The new class of tailored decoupling pulses is named SHOT (Scaling of Heteronuclear couplings by Optimal Tracking). Complementing cw irradiation, SHOT pulses offer an alternative approach of encoding chemical shift information indirectly through off-resonance decoupling, which however makes it possible for the first time to achieve linear J scaling as a function of offset frequency. For a simple mixture of eight aromatic compounds, it is demonstrated experimentally that a 1D-SHOT {(1)H}-(13)C experiment yields comparable information to a 2D-HSQC and can give full assignment of all coupled spins.

  15. Stokes shift dynamics in (non-dipolar ionic liquid + dipolar solvent) binary mixtures: a semi-molecular theory.

    PubMed

    Pal, Tamisra; Biswas, Ranjit

    2014-10-28

    A semi-molecular theory for studying composition dependent Stokes shift dynamics of a dipolar solute in binary mixtures of (non-dipolar ionic liquid + common dipolar solvent) is developed here. The theory provides microscopic expressions for solvation response functions in terms of static and dynamic structure factors of the mixture components and solute-solvent static correlations. In addition, the theory provides a framework for examining the interrelationship between the time dependent solvation response in and frequency dependent dielectric relaxation of a binary mixture containing electrolyte. Subsequently, the theory has been applied to predict ionic liquid (IL) mole fraction dependent dynamic Stokes shift magnitude and solvation energy relaxation for a dipolar solute, C153, in binary mixtures of an ionic liquid, trihexyltetradecylphosphonium chloride ([P(14,666)][Cl]) with a common dipolar solvent, methanol (MeOH). In the absence of suitable experimental data, necessary input parameters have been obtained from approximate methods. Dynamic shifts calculated for these mixtures exhibit a linear increase with IL mole fraction for the most part of the mixture composition, stressing the importance of solute-IL dipole-ion interaction. Average solvation rates, on the other hand, show a nonlinear IL mole fraction dependence which is qualitatively similar to what has been observed for such binary mixtures with imidazolium (dipolar) ILs. These predictions should be re-examined in suitable experiments.

  16. Observations and Effects of Dipolarization Fronts Observed in Earth's Magnetotail

    NASA Technical Reports Server (NTRS)

    Goldstein, Melvyn L.

    2011-01-01

    Dipolarization fronts in Earth's magnetotail are characterized by sharp jumps in magnetic field, a drop in density, and often follow earthward fast plasma flow. They are commonly detected near the equatorial plane of Earth s tail plasma sheet. Sometimes, but not always, dipolarization fronts are associated with global substorms and auroral brightenings. Both Cluster, THEMIS, and other spacecraft have detected dipolarization fronts in a variety of locations in the magnetotail. Using multi-spacecraft analyses together with simulations, we have investigated the propagation and evolution of some dipolarization events. We have also investigated the acceleration of electrons and ions that results from such magnetic-field changes. In some situations, the velocities of fast earthward flows are comparable to the Alfven speed, indicating that the flow bursts might have been generated by bursty reconnection that occurred tailward of the spacecraft. Based on multi-spacecraft timing analysis, dipolarization fronts are found to propagate mainly earthward at 160-335 km/s and have thicknesses of 900-1500 km, which corresponds to the ion inertial length or gyroradius scale. Following the passage of dipolarization fronts, significant fluctuations are observed in the x and y components of the magnetic field. These peaks in the magnetic field come approximately 1-2 minutes after passage of the dipolarization front. These Bx and By fluctuations propagate primarily dawnward and earthward. Field-aligned electron beams are observed coincident with those magnetic field fluctuations. Non-Maxwellian electron and ion distributions are observed that are associated with the dipolarization that may be unstable to a range of electrostatic and/or whistler instabilities. Enhanced electrostatic broadband noise at frequencies below and near the lower-hybrid frequency is also observed at or very close to these fronts. This broadband noise is thought to play a role in further energizing the particles

  17. OBSERVATION OF DIPOLAR FERROMAGNETISM BY TEM TECHNIQUES.

    SciTech Connect

    BELEGGIA, M.ZHU,Y.TANDON,S.ET AL.

    2004-08-01

    Magnetostatic interactions play a central role in determining the magnetic response of an array of patterned magnetic elements or magnetized nanoparticles of given shape. The Fourier space approach recently introduced for the analytical computation of the demagnetizing tensor, field and energy for particles of arbitrary shape [1], has been recently extended to cover interactions between elements [2]. The main achievement has been the definition of a generalized dipole-dipole interaction for cylindrical objects, which takes into account the influence of shape anisotropy without resorting to,any kind of approximations [3]. Once the interaction energy is available, it becomes possible to evaluate the minimum energy state of the system for a given set of external parameters (such as applied field, aspect ratio, distance between elements). It turns out that, below a critical combination of aspect ratios and distances, the system undergoes a phase transition, changing abruptly from a closure domain state, with zero net magnetization, to a dipolar ferromagnetic state with a net magnetization which depends on the interaction strength between the elements. In order to observe this phenomenon by TEM, it is necessary to estimate the feasibility of the experiment by a series of simulations. Figure 1 shows the electron optical phase shifts for the system of three weakly (a-c) and strongly (d) interacting disks. The elements have a radius of 50 nm, a thickness of 5 nm (aspect ratio 1/20), and are uniformly magnetized at 2 T. By comparing Fig.1 (c) and (d), it can be seen that the fingerprint of the transition is the presence of fringing fields around the elements, revealed by the cosine fringes which resemble a dipole-like field in (d). When the system is in the closure-domain state, as in (a-c), no fringing field can be observed on a large scale. Figure 2 shows a set of Fresnel images, calculated for the same configurations as in Fig.1. As the Fresnel technique is scarcely

  18. Cluster Observations of Multiple Dipolarization Fronts

    NASA Technical Reports Server (NTRS)

    Hwang, Kyoung-Joo; Goldstein, Melvyn L.; Lee, Ensang; Pickett, Jolene S.

    2011-01-01

    We present Cluster observations of a series of dipolarization fronts (DF 1 to 6) at the central current sheet in Earth's magnetotail. The velocities of fast earthward flow following behind each DF 1-3, are comparable to the Alfven velocity, indicating that the flow bursts might have been generated by bursty reconnection that occurred tailward of the spacecraft. Based on multi-spacecraft timing analysis, DF normals are found to propagate mainly earthward at $160-335$ km/s with a thickness of 900-1500 km, which corresponds to the ion inertial length or gyroradius scale. Each DF is followed by significant fluctuations in the $x$ and $y$ components of the magnetic field whose peaks are found 1-2 minutes after the DF passage. These $(B_{x},B_{y} )$-fluctuations propagate dawnward (mainly) and earthward. Strongly enhanced field-aligned beams are observed coincidently with $(B_{x},B_{y})$ fluctuations, while an enhancement of cross-tail currents is associated with the DFs. From the observed pressure imbalance and flux-tube entropy changes between the two regions separated by the DF, we speculate that interchange instability destabilizes the DFs and causes the deformation of the mid-tail magnetic topology. This process generates significant field-aligned currents, and might power the auroral brightening in the ionosphere. However, this event is neither associated with the main substorm auroral breakup nor the poleward expansion, which might indicate that the observed multiple DFs have been dissipated before they reach the inner plasma sheet boundary.

  19. Cluster Observations of Multiple Dipolarization Fronts

    NASA Technical Reports Server (NTRS)

    Hwang, K.-J.; Goldstein, M. L.; Lee, E.; Pickett, J. S.

    2011-01-01

    We present Cluster observations of a series of dipolarization fronts (DF 1 to 6) at the central current sheet in Earth's magnetotail. The velocities of fast earthward flow following behind each DF 1.3 are comparable to the Alfven velocity, indicating that the flow bursts might have been generated by bursty reconnection that occurred tailward of the spacecraft. Based on multispacecraft timing analysis, DF normals are found to propagate mainly earthward at 160.335 km/s with a thickness of 900-1500 km, which corresponds to the ion inertial length or gyroradius scale. Each DF is followed by significant fluctuations in the x and y components of the magnetic field whose peaks are found 1.2 min after the DF passage. These (B(sub x), B(sub y)) fluctuations propagate dawnward (mainly) and earthward. Strongly enhanced field-aligned beams are observed coincidently with (B(sub x), B(sub y)) fluctuations, while an enhancement of cross-tail currents is associated with the DFs. From the observed pressure imbalance and flux tube entropy changes between the two regions separated by the DF, we speculate that interchange instability destabilizes the DFs and causes the deformation of the midtail magnetic topology. This process generates significant field-aligned currents and might power the auroral brightening in the ionosphere. However, this event is associated with neither the main substorm auroral breakup nor the poleward expansion, which might indicate that the observed multiple DFs have been dissipated before they reach the inner plasma sheet boundary.

  20. Jet Dipolarity: Top Tagging with Color Flow

    SciTech Connect

    Hook, Anson; Jankowiak, Martin; Wacker, Jay G.; /SLAC

    2011-08-12

    A new jet observable, dipolarity, is introduced that can distinguish whether a pair of subjets arises from a color singlet source. This observable is incorporated into the HEPTopTagger and is shown to improve discrimination between top jets and QCD jets for moderate to high p{sub T}. The impressive resolution of the ATLAS and CMS detectors means that a typical QCD jet at the LHC deposits energy in {Omicron}(10-100) calorimeter cells. Such fine-grained calorimetry allows for jets to be studied in much greater detail than previously, with sophisticated versions of current techniques making it possible to measure more than just the bulk properties of jets (e.g. event jet multiplicities or jet masses). One goal of the LHC is to employ these techniques to extend the amount of information available from each jet, allowing for a broader probe of the properties of QCD. The past several years have seen significant progress in developing such jet substructure techniques. A number of general purpose tools have been developed, including: (i) top-tagging algorithms designed for use at both lower and higher p{sub T} as well as (ii) jet grooming techniques such as filtering, pruning, and trimming, which are designed to improve jet mass resolution. Jet substructure techniques have also been studied in the context of specific particle searches, where they have been shown to substantially extend the reach of traditional search techniques in a wide variety of scenarios, including for example boosted Higgses, neutral spin-one resonances, searches for supersymmetry, and many others. Despite these many successes, however, there is every reason to expect that there remains room for refinement of jet substructure techniques.

  1. Composite dipolar recoupling: anisotropy compensated coherence transfer in solid-state nuclear magnetic resonance.

    PubMed

    Khaneja, Navin; Kehlet, Cindie; Glaser, Steffen J; Nielsen, Niels Chr

    2006-03-21

    The efficiency of dipole-dipole coupling driven coherence transfer experiments in solid-state nuclear magnetic resonance (NMR) spectroscopy of powder samples is limited by dispersion of the orientation of the internuclear vectors relative to the external magnetic field. Here we introduce general design principles and resulting pulse sequences that approach full polarization transfer efficiency for all crystallite orientations in a powder in magic-angle-spinning experiments. The methods compensate for the defocusing of coherence due to orientation dependent dipolar coupling interactions and inhomogeneous radio-frequency fields. The compensation scheme is very simple to implement as a scaffold (comb) of compensating pulses in which the pulse sequence to be improved may be inserted. The degree of compensation can be adjusted and should be balanced as a compromise between efficiency and length of the overall pulse sequence. We show by numerical and experimental data that the presented compensation protocol significantly improves the efficiency of known dipolar recoupling solid-state NMR experiments.

  2. Second virial coefficient for the dipolar hard sphere fluid.

    PubMed

    Henderson, Douglas

    2011-07-28

    The dipolar hard sphere fluid is a useful model for a polar fluid. Some years ago, the second virial coefficient, B(2), of this fluid was obtained as a series expansion in the inverse temperature or (dipole strength) by Keesom. Little work on this problem seems to have been done since that time. Using a result of Chan and Henderson for the spherical average of the Boltzmann factor of this fluid, more complete results are obtained for B(2). The more complete results are more negative than the Keesom series, as one would expect, but his expansion is remarkably accurate. This method can be used to obtain the second virial coefficient of the dipolar Lennard-Jones (Stockmayer) or dipolar Yukawa fluids.

  3. Landau damping in a dipolar Bose-Fermi mixture in the Bose-Einstein condensation (BEC) limit

    NASA Astrophysics Data System (ADS)

    Moniri, S. M.; Yavari, H.; Darsheshdar, E.

    2016-12-01

    By using a mean-field approximation which describes the coupled oscillations of condensate and noncondensate atoms in the collisionless regime, Landau damping in a dilute dipolar Bose-Fermi mixture in the BEC limit where Fermi superfluid is treated as tightly bounded molecules, is investigated. In the case of a uniform quasi-two-dimensional (2D) case, the results for the Landau damping due to the Bose-Fermi interaction are obtained at low and high temperatures. It is shown that at low temperatures, the Landau damping rate is exponentially suppressed. By increasing the strength of dipolar interaction, and the energy of boson quasiparticles, Landau damping is suppressed over a broader temperature range.

  4. Anisotropic Expansion of a Thermal Dipolar Bose Gas

    NASA Astrophysics Data System (ADS)

    Tang, Y.; Sykes, A. G.; Burdick, N. Q.; DiSciacca, J. M.; Petrov, D. S.; Lev, B. L.

    2016-10-01

    We report on the anisotropic expansion of ultracold bosonic dysprosium gases at temperatures above quantum degeneracy and develop a quantitative theory to describe this behavior. The theory expresses the postexpansion aspect ratio in terms of temperature and microscopic collisional properties by incorporating Hartree-Fock mean-field interactions, hydrodynamic effects, and Bose-enhancement factors. Our results extend the utility of expansion imaging by providing accurate thermometry for dipolar thermal Bose gases. Furthermore, we present a simple method to determine scattering lengths in dipolar gases, including near a Feshbach resonance, through observation of thermal gas expansion.

  5. Nonlocal and nonlinear electrostatics of a dipolar Coulomb fluid.

    PubMed

    Sahin, Buyukdagli; Ralf, Blossey

    2014-07-16

    We study a model Coulomb fluid consisting of dipolar solvent molecules of finite extent which generalizes the point-like dipolar Poisson-Boltzmann model (DPB) previously introduced by Coalson and Duncan (1996 J. Phys. Chem. 100 2612) and Abrashkin et al (2007 Phys. Rev. Lett. 99 077801). We formulate a nonlocal Poisson-Boltzmann equation (NLPB) and study both linear and nonlinear dielectric response in this model for the case of a single plane geometry. Our results shed light on the relevance of nonlocal versus nonlinear effects in continuum models of material electrostatics.

  6. Engineering bright matter-wave solitons of dipolar condensates

    NASA Astrophysics Data System (ADS)

    Edmonds, M. J.; Bland, T.; Doran, R.; Parker, N. G.

    2017-02-01

    We present a comprehensive analysis of the form and interaction of dipolar bright solitons across the full parameter space afforded by dipolar Bose–Einstein condensates, revealing the rich behavior introduced by the non-local nonlinearity. Working within an effective one-dimensional description, we map out the existence of the soliton solutions and show three collisional regimes: free collisions, bound state formation and soliton fusion. Finally, we examine the solitons in their full three-dimensional form through a variational approach; along with regimes of instability to collapse and runaway expansion, we identify regimes of stability which are accessible to current experiments.

  7. Anisotropic Expansion of a Thermal Dipolar Bose Gas.

    PubMed

    Tang, Y; Sykes, A G; Burdick, N Q; DiSciacca, J M; Petrov, D S; Lev, B L

    2016-10-07

    We report on the anisotropic expansion of ultracold bosonic dysprosium gases at temperatures above quantum degeneracy and develop a quantitative theory to describe this behavior. The theory expresses the postexpansion aspect ratio in terms of temperature and microscopic collisional properties by incorporating Hartree-Fock mean-field interactions, hydrodynamic effects, and Bose-enhancement factors. Our results extend the utility of expansion imaging by providing accurate thermometry for dipolar thermal Bose gases. Furthermore, we present a simple method to determine scattering lengths in dipolar gases, including near a Feshbach resonance, through observation of thermal gas expansion.

  8. Infrared Behavior of Dipolar Bose Systems at Low Temperatures

    NASA Astrophysics Data System (ADS)

    Pastukhov, Volodymyr

    2017-01-01

    We rigorously discuss the infrared behavior of the uniform three-dimensional dipolar Bose systems. In particular, it is shown that low-temperature physics of the system is controlled by two parameters, namely isothermal compressibility and intensity of the dipole-dipole interaction. By using a hydrodynamic approach, we calculate the spectrum and damping of low-lying excitations and analyze the infrared behavior of the one-particle Green's function. The low-temperature corrections to the anisotropic superfluid density as well as condensate depletion are found. Additionally, we derive equations of the two-fluid hydrodynamics for dipolar Bose systems and calculate velocities of first and second sound.

  9. Strongly correlated quasi-two-dimensional dipolar fermions

    NASA Astrophysics Data System (ADS)

    Babadi, Mehrtash; Skinner, Brian; Fogler, Michael; Demler, Eugene

    2013-03-01

    We study the collective oscillations of strongly correlated quasi-two-dimensional dipolar fermions at zero temperature. The correlation energy of the quasi-two-dimensional gas is obtained using a novel variational method based on the fixed-node diffusion Monte-Carlo analysis of strictly two-dimensional dipolar Fermi gas. As an application, we predict the dependence of the Wigner crystal transition point on the thickness of the layer, as well as the shift of the monopole oscillation frequency in harmonic traps.

  10. Anisotropic superfluidity in a dipolar Bose gas

    SciTech Connect

    Ticknor, Christopher; Wilson, Ryan M; Bohn, John L

    2010-11-04

    A quintessential feature of superfluidity is the ability to support dissipationless flow, for example, when an object moves through a superfluid and experiences no drag. This, however, only occurs when the object is moving below a certain critical velocity; when it exceeds this critical velocity it dissipates energy into excitations of the superfluid, resulting in a net drag force on the object and the breakdown of superfluid flow. In many superfluids, such as dilute Bose-Einstein condensates (BECs) of atoms with contact interactions, this critical velocity is simply the speed of sound in the system, where the speed of sound is set by the density and the s-wave scattering length of the atoms. However, for other superfluids, such as liquid {sup 4}He, this is not the case. In {sup 4}He, the critical velocity is set by a roton mode, corresponding to a peak in the static structure factor of the system at some finite, non-zero momentum, with a characteristic velocity that is considerably less than the speed of sound in the liquid. This feature has been verified experimentally via measurements of ion-drift velocity in the fluid, thereby providing insight into the detailed structure of the system. Interestingly, a roton-like feature was predicted to exist in the dispersion relation of a quasi-two-dimensional (q2D) dipolar BEC (DBEC) [16], or a BEC with dipole-dipole interactions. However, unlike the dispersion of {sup 4}He, the disperSion of a DBEC is highly tunable as a function of the condensate density or dipole-dipole interaction (ddi) strength. Additionally, the DBEC is set apart from liquid {sup 4}He in that its interactions depend on how the dipoles are oriented in space. Thus, the DBEC provides an ideal system to study the effects that anisotropies have on the bulk properties of a superfluid, such as the critical velocity. Here we consider a DBEC in a quasi-two-dimensional (q2D) geometry and allow for the dipoles to be polarized at a nonzero angle into the plane

  11. Effect of simple solutes on the long range dipolar correlations in liquid water

    NASA Astrophysics Data System (ADS)

    Baul, Upayan; Kanth, J. Maruthi Pradeep; Anishetty, Ramesh; Vemparala, Satyavani

    2016-03-01

    Intermolecular correlations in liquid water at ambient conditions have generally been characterized through short range density fluctuations described through the atomic pair distribution functions. Recent numerical and experimental results have suggested that such a description of order or structure in liquid water is incomplete and there exist considerably longer ranged orientational correlations in water that can be studied through dipolar correlations. In this study, using large scale classical, atomistic molecular dynamics simulations using TIP4P-Ew and TIP3P models of water, we show that salts such as sodium chloride (NaCl), potassium chloride (KCl), caesium chloride (CsCl), and magnesium chloride (MgCl2) have a long range effect on the dipolar correlations, which cannot be explained by the notion of structure making and breaking by dissolved ions. Observed effects are explained through orientational stratification of water molecules around ions and their long range coupling to the global hydrogen bond network by virtue of the sum rule for water. The observations for single hydrophilic solutes are contrasted with the same for a single methane (CH4) molecule. We observe that even a single small hydrophobe can result in enhancement of long range orientational correlations in liquid water, contrary to the case of dissolved ions, which have been observed to have a reducing effect. The observations from this study are discussed in the context of hydrophobic effect.

  12. Two-dimensional dipolar scattering with a tilt

    SciTech Connect

    Ticknor, Christopher

    2011-09-15

    We study two-body dipolar scattering in two dimensions with a tilted polarization axis. This tilt reintroduces the anisotropic interaction in a controllable manner. As a function of this polarization angle, we present the scattering rates in both the threshold and semiclassical regimes. Additionally, we study the properties of the molecular bound states as a function of the polarization angle.

  13. Non-dipolar Wilson Links for Parton Densities

    NASA Astrophysics Data System (ADS)

    Li, Hsiang-nan

    We propose a new definition of a transverse-momentum-dependent wave function with simpler soft subtraction. The unsubtracted wave function involves two pieces of non-light-like Wilson links oriented in different directions, so that the rapidity singularity appearing in usual kT factorization is regularized, and the pinched singularity from Wilson-link self-energy corrections is alleviated to a logarithmic one. We show explicitly at one-loop level that the simpler definition with the non-dipolar Wilson links exhibits the same infrared behavior as the one with the dipolar Wilson links. The non-dipolar Wilson links are also introduced to the quasi-parton distribution function (QPDF) with an equal-time correlator in the large momentum limit, which can remove the involved linear divergence, and allow perturbative matching to the standard light-cone parton distribution function. The latter can then be extracted reliably from Euclidean lattice data for the QPDF with the non-dipolar Wilson links.

  14. Stability of solid phases in the dipolar hard sphere system

    NASA Astrophysics Data System (ADS)

    Levesque, D.; Weis, J.-J.

    2011-12-01

    Free energy differences between solid phases of dipolar hard spheres are estimated by Monte Carlo simulation using a nonequilibrium work method. These calculations allow one to determine which of the considered phases has the minimum free energy. The phase diagram which we obtain is confirmed by simulations in the isothermal-isobaric ensemble over a wide region of the density and temperature domain.

  15. Dipolar Vortices and Dark Solitons in Quantum Ferrofluids

    NASA Astrophysics Data System (ADS)

    Parker, Nick; Bland, Thomas; Edmonds, Matthew; Proukakis, Nick; Martin, Andrew; O'Dell, Duncan

    2016-05-01

    The experimental achievement of Bose-condensed gases of atoms with large magnetic dipole moments has realized a quantum ferrofluid, which combines both superfluid and ferrofluid properties. Here the conventional isotropic and short-range atom-atom interactions become supplemented by long-range and anisotropic dipolar interactions, enriching the physical properties of the system. Here we discuss how the dipolar interactions modify quantized vortices, the fundamental nonlinear excitations of superfluids in two and three dimensions. As well as distorting the vortex profile, the dipolar interactions cause each vortex to approximate a macroscopic dipole; the vortex-vortex interaction then develops a novel anisotropic and long-range contribution. This is shown to significantly modify the two-vortex dynamics, and has implications for multi-vortex states. We also extend our analysis to dark solitons, the one-dimensional analogs of vortices, where dipolar interactions support unconventional dark soliton bound states. This work was supported by the Engineering and Physical Sciences Research Council of the UK (Grant No. EP/M005127/1).

  16. Asymptotic behavior of local dipolar fields in thin films

    NASA Astrophysics Data System (ADS)

    Bowden, G. J.; Stenning, G. B. G.; van der Laan, G.

    2016-10-01

    A simple method, based on layer by layer direct summation, is used to determine the local dipolar fields in uniformly magnetized thin films. The results show that the dipolar constants converge ~1/m where the number of spins in a square film is given by (2m+1)2. Dipolar field results for sc, bcc, fcc, and hexagonal lattices are presented and discussed. The results can be used to calculate local dipolar fields in films with either ferromagnetic, antiferromagnetic, spiral, exponential decay behavior, provided the magnetic order only changes normal to the film. Differences between the atomistic (local fields) and macroscopic fields (Maxwellian) are also examined. For the latter, the macro B-field inside the film is uniform and falls to zero sharply outside, in accord with Maxwell boundary conditions. In contrast, the local field for the atomistic point dipole model is highly non-linear inside and falls to zero at about three lattice spacing outside the film. Finally, it is argued that the continuum field B (used by the micromagnetic community) and the local field Bloc(r) (used by the FMR community) will lead to differing values for the overall demagnetization energy.

  17. Tuning ultracold collisions of excited rotational dipolar molecules

    NASA Astrophysics Data System (ADS)

    Quéméner, Goulven

    2015-05-01

    Ultracold molecular dipolar gases often suffer from losses due to chemical reactions (or eventual sticky collisions for non-reactive molecules). Loss suppression for both bosonic and fermionic dipolar species can be obtained in a one-dimensional optical lattice but this requires usually strong confinements to get into a pure two-dimensional collision regime. An alternative way can be found without confinement using rotationally excited molecules. In this talk I will explore the ultracold collisions of rotationally excited dipolar molecules in free space. I will focus on electric dipolar molecules of KRb and electric and magnetic dipolar molecules of RbSr. I will show that we can sharply tune the elastic, inelastic and reactive rate coefficients of lossy molecular collisions when a second rotationally excited colliding channel crosses the threshold of the initial colliding channel, with the help of an applied electric field. We can increase or decrease the loss processes whether the second channel is above or below the initial channel. This could lead to favorable conditions for evaporative cooling. Additionally, we include the electric quadrupole and octopole moment to the dipole moment in the expression of the long-range multipole-multipole interaction. For processes mediated by the incident channel like elastic and loss collisions, the inclusion of quadrupole and octopole moments are not important at ultralow energies. They are important for processes mediated by state-to-state transitions like inelastic collisions. I acknowledge the financial support of the COPOMOL project (ANR-13-IS04-0004) from Agence Nationale de la Recherche.

  18. Highly enantioselective intramolecular 1,3-dipolar cycloaddition: a route to piperidino-pyrrolizidines.

    PubMed

    Vidadala, Srinivasa Rao; Golz, Christopher; Strohmann, Carsten; Daniliuc, Constantin-G; Waldmann, Herbert

    2015-01-07

    Enantioselective catalytic intermolecular 1,3-dipolar cycloadditions are powerful methods for the synthesis of heterocycles. In contrast, intramolecular enantioselective 1,3-dipolar cycloadditions are virtually unexplored. A highly enantioselective synthesis of natural-product-inspired pyrrolidino-piperidines by means of an intramolecular 1,3-dipolar cycloaddition with azomethine ylides is now reported. The method has a wide scope and yields the desired cycloadducts with four tertiary stereogenic centers with up to 99% ee. Combining the enantioselective catalytic intramolecular 1,3-dipolar cycloaddition with a subsequent diastereoselective intermolecular 1,3-dipolar cycloaddition yielded complex piperidino-pyrrolizidines with very high stereoselectivity in a one-pot tandem reaction.

  19. Pulse Dipolar ESR and Protein Superstructures and Function

    NASA Astrophysics Data System (ADS)

    Freed, Jack

    2014-03-01

    Pulse dipolar electron-spin resonance (PDS-ESR) has emerged as a powerful methodology for the study of protein structure and function. This technology, in the form of double quantum coherence (DQC) - ESR and double-electron-electron resonance (DEER) in conjunction with site-directed spin-labeling will be described. It enables the measurement of distances and their distributions in the range of 1-9 nm between pairs of spins labeled at two sites in the protein. Many biological objects can be studied: soluble and membrane proteins, protein complexes, etc. Many sample morphologies are possible: uniform, heterogeneous, etc. thereby permitting a variety of sample types: solutions, liposomes, micelles, bicelles. Concentrations from micromolar to tens of millimolar are amenable, requiring only small amounts of biomolecules. The distances are quite accurate, so a relatively small number of them are sufficient to reveal structures and functional details. Several examples will be shown. The first is defining the protein complexes that mediate bacterial chemotaxis, which is the process whereby cells modulate their flagella-driven motility in response to environmental cues. It relies on a complex sensory apparatus composed of transmembrane receptors, histidine kinases, and coupling proteins. PDS-based models have captured key architectural features of the receptor kinase arrays and the flagellar motor, and their changes in conformation and dynamics that accompany kinase activation and motor switching. Another example will be determining the conformational states and cycling of a membrane transporter, GltPh, which is a homotrimer, in its apo, substrate-bound, and inhibitor-bound, states in membrane vesicles providing insight into its energetics. In a third example the structureless (in solution) proteins alpha-synuclein and tau, which are important in Parkinson's disease and in neurodegeneration will be described and the structures they take on in contact with membranes will be

  20. Spin configuration of magnetic multi-layers: effect of exchange, dipolar and Dzyalozhinski-Moriya interactions.

    PubMed

    Franco, A F; Kachkachi, H

    2013-08-07

    We investigate the effect of coupling (intensity and nature), applied field, and anisotropy on the spin dynamics of a multi-layer system composed of a hard magnetic layer coupled to a soft magnetic layer through a nonmagnetic spacer. The soft layer is modeled as a stack of several atomic planes while the hard layer, of a different material, is either considered as a pinned macroscopic magnetic moment or again as a stack of atomic planes. We compute the magnetization profile and hysteresis loop of the whole multi-layer system by solving the Landau-Lifshitz equations for the net magnetic moment of each (atomic) plane. We study the competition between the intra-layer anisotropy and exchange interaction, applied magnetic field, and the interface exchange, dipolar or Dzyalozhinski-Moriya interaction. Compared with the exchange coupling, the latter two couplings present peculiar features in the magnetization profile and hysteresis loop that may help identify the nature of the interface coupling in multi-layer magnetic systems.

  1. Asynchronous symmetry-based sequences for homonuclear dipolar recoupling in solid-state nuclear magnetic resonance

    NASA Astrophysics Data System (ADS)

    Tan, Kong Ooi; Rajeswari, M.; Madhu, P. K.; Ernst, Matthias

    2015-02-01

    We show a theoretical framework, based on triple-mode Floquet theory, to analyze recoupling sequences derived from symmetry-based pulse sequences, which have a non-vanishing effective field and are not rotor synchronized. We analyze the properties of one such sequence, a homonuclear double-quantum recoupling sequence derived from the C72 1 sequence. The new asynchronous sequence outperforms the rotor-synchronized version for spin pairs with small dipolar couplings in the presence of large chemical-shift anisotropy. The resonance condition of the new sequence is analyzed using triple-mode Floquet theory. Analytical calculations of second-order effective Hamiltonian are performed to compare the efficiency in suppressing second-order cross terms. Experiments and numerical simulations are shown to corroborate the results of the theoretical analysis.

  2. Lifshitz transitions and crystallization of fully polarized dipolar fermions in an anisotropic two-dimensional lattice

    SciTech Connect

    Carr, Sam T.; Quintanilla, Jorge; Betouras, Joseph J.

    2010-07-15

    We consider a two-dimensional model of noninteracting chains of spinless fermions weakly coupled via a small interchain hopping and a repulsive interchain interaction. The phase diagram of this model has a surprising feature: an abrupt change in the Fermi surface as the interaction is increased. We study in detail this metanematic transition and show that the well-known 2(1/2)-order Lifshitz transition is the critical end point of this first-order quantum phase transition. Furthermore, in the vicinity of the end point, the order parameter has a nonperturbative BCS-type form. We also study a competing crystallization transition in this model and derive the full phase diagram. This physics can be demonstrated experimentally in dipolar ultracold atomic or molecular gases. In the presence of a harmonic trap, it manifests itself as a sharp jump in the density profile.

  3. Beyond mean-field properties of binary dipolar Bose mixtures at low temperatures

    NASA Astrophysics Data System (ADS)

    Pastukhov, Volodymyr

    2017-02-01

    We rigorously analyze the low-temperature properties of homogeneous three-dimensional two-component Bose mixture with dipole-dipole interaction. For such a system the effective hydrodynamic action that governs the behavior of low-energy excitations is derived. The infrared structure of the exact single-particle Green's functions is obtained in terms of macroscopic parameters, namely the inverse compressibility and the superfluid density matrices. Within the one-loop approximation we calculate some of the most relevant observable quantities and give the beyond mean-field stability condition for the binary dipolar Bose gas in the dilute limit. A brief variational derivation of the coupled equations that describe macroscopic hydrodynamics of the system in the external nonuniform potential at zero temperature is presented.

  4. Pitchfork bifurcations in blood-cell-shaped dipolar Bose-Einstein condensates

    SciTech Connect

    Rau, Stefan; Main, Joerg; Koeberle, Patrick; Wunner, Guenter

    2010-03-15

    We demonstrate that the method of coupled Gaussian wave packets is a full-fledged alternative to direct numerical solutions of the Gross-Pitaevskii equation of condensates with electromagnetically induced attractive 1/r interaction or with dipole-dipole interaction. Moreover, Gaussian wave packets are superior in that they are capable of producing both stable and unstable stationary solutions and thus of giving access to yet unexplored regions of the space of solutions of the Gross-Pitaevskii equation. We apply the method to clarify the theoretical nature of the collapse mechanism of blood-cell-shaped dipolar condensates: On the route to collapse the condensate passes through a pitchfork bifurcation, where the ground state itself turns unstable, before it finally vanishes in a tangent bifurcation.

  5. Variational calculations for anisotropic solitons in dipolar Bose-Einstein condensates

    SciTech Connect

    Eichler, Ruediger; Main, Joerg; Wunner, Guenter

    2011-05-15

    We present variational calculations using a Gaussian trial function to calculate the ground state of the Gross-Pitaevskii equation (GPE) and to describe the dynamics of the quasi-two-dimensional solitons in dipolar Bose-Einstein condensates (BECs). Furthermore, we extend the ansatz to a linear superposition of Gaussians, improving the results for the ground state to exact agreement with numerical grid calculations using imaginary time and the split-operator method. We are able to give boundaries for the scattering length at which stable solitons may be observed in an experiment. By dynamic calculations with coupled Gaussians, we are able to describe the rather complex behavior of the thermally excited solitons. The discovery of dynamically stabilized solitons indicates the existence of such BECs at experimentally accessible temperatures.

  6. Nuclear magnetic relaxation by the dipolar EMOR mechanism: General theory with applications to two-spin systems

    NASA Astrophysics Data System (ADS)

    Chang, Zhiwei; Halle, Bertil

    2016-02-01

    In aqueous systems with immobilized macromolecules, including biological tissue, the longitudinal spin relaxation of water protons is primarily induced by exchange-mediated orientational randomization (EMOR) of intra- and intermolecular magnetic dipole-dipole couplings. We have embarked on a systematic program to develop, from the stochastic Liouville equation, a general and rigorous theory that can describe relaxation by the dipolar EMOR mechanism over the full range of exchange rates, dipole coupling strengths, and Larmor frequencies. Here, we present a general theoretical framework applicable to spin systems of arbitrary size with symmetric or asymmetric exchange. So far, the dipolar EMOR theory is only available for a two-spin system with symmetric exchange. Asymmetric exchange, when the spin system is fragmented by the exchange, introduces new and unexpected phenomena. Notably, the anisotropic dipole couplings of non-exchanging spins break the axial symmetry in spin Liouville space, thereby opening up new relaxation channels in the locally anisotropic sites, including longitudinal-transverse cross relaxation. Such cross-mode relaxation operates only at low fields; at higher fields it becomes nonsecular, leading to an unusual inverted relaxation dispersion that splits the extreme-narrowing regime into two sub-regimes. The general dipolar EMOR theory is illustrated here by a detailed analysis of the asymmetric two-spin case, for which we present relaxation dispersion profiles over a wide range of conditions as well as analytical results for integral relaxation rates and time-dependent spin modes in the zero-field and motional-narrowing regimes. The general theoretical framework presented here will enable a quantitative analysis of frequency-dependent water-proton longitudinal relaxation in model systems with immobilized macromolecules and, ultimately, will provide a rigorous link between relaxation-based magnetic resonance image contrast and molecular parameters.

  7. The dipolar endofullerene HF@C60

    NASA Astrophysics Data System (ADS)

    Krachmalnicoff, Andrea; Bounds, Richard; Mamone, Salvatore; Alom, Shamim; Concistrè, Maria; Meier, Benno; Kouřil, Karel; Light, Mark E.; Johnson, Mark R.; Rols, Stéphane; Horsewill, Anthony J.; Shugai, Anna; Nagel, Urmas; Rõõm, Toomas; Carravetta, Marina; Levitt, Malcolm H.; Whitby, Richard J.

    2016-10-01

    The cavity inside fullerenes provides a unique environment for the study of isolated atoms and molecules. We report the encapsulation of hydrogen fluoride inside C60 using molecular surgery to give the endohedral fullerene HF@C60. The key synthetic step is the closure of the open fullerene cage with the escape of HF minimized. The encapsulated HF molecule moves freely inside the cage and exhibits quantization of its translational and rotational degrees of freedom, as revealed by inelastic neutron scattering and infrared spectroscopy. The rotational and vibrational constants of the encapsulated HF molecules were found to be redshifted relative to free HF. The NMR spectra display a large 1H-19F J coupling typical of an isolated species. The dipole moment of HF@C60 was estimated from the temperature dependence of the dielectric constant at cryogenic temperatures and showed that the cage shields around 75% of the HF dipole.

  8. The dipolar endofullerene HF@C60.

    PubMed

    Krachmalnicoff, Andrea; Bounds, Richard; Mamone, Salvatore; Alom, Shamim; Concistrè, Maria; Meier, Benno; Kouřil, Karel; Light, Mark E; Johnson, Mark R; Rols, Stéphane; Horsewill, Anthony J; Shugai, Anna; Nagel, Urmas; Rõõm, Toomas; Carravetta, Marina; Levitt, Malcolm H; Whitby, Richard J

    2016-10-01

    The cavity inside fullerenes provides a unique environment for the study of isolated atoms and molecules. We report the encapsulation of hydrogen fluoride inside C60 using molecular surgery to give the endohedral fullerene HF@C60. The key synthetic step is the closure of the open fullerene cage with the escape of HF minimized. The encapsulated HF molecule moves freely inside the cage and exhibits quantization of its translational and rotational degrees of freedom, as revealed by inelastic neutron scattering and infrared spectroscopy. The rotational and vibrational constants of the encapsulated HF molecules were found to be redshifted relative to free HF. The NMR spectra display a large (1)H-(19)F J coupling typical of an isolated species. The dipole moment of HF@C60 was estimated from the temperature dependence of the dielectric constant at cryogenic temperatures and showed that the cage shields around 75% of the HF dipole.

  9. Manipulating microwaves with magnetic-dipolar-mode vortices

    SciTech Connect

    Kamenetskii, E. O.; Sigalov, M.; Shavit, R.

    2010-05-15

    There has been a surge of interest in the subwavelength confinement of electromagnetic fields. It is well known that, in optics, subwavelength confinement can be obtained from surface plasmon (quasielectrostatic) oscillations. In this article, we propose to realize subwavelength confinement in microwaves by using dipolar-mode (quasimagnetostatic) magnon oscillations in ferrite particles. Our studies of interactions between microwave electromagnetic fields and small ferrite particles with magnetic-dipolar-mode (MDM) oscillations show strong localization of electromagnetic energy. MDM oscillations in a ferrite disk are at the origin of topological singularities resulting in Poynting vector vortices and symmetry breakings of the microwave near fields. We show that new subwavelength microwave structures can be realized based on a system of interacting MDM ferrite disks. Wave propagation of electromagnetic signals in such structures is characterized by topological phase variations. Interactions of microwave fields with an MDM ferrite disk and MDM-disk arrays open a perspective for creating engineered electromagnetic fields with unique symmetry properties.

  10. Triplet superfluidity on a triangular ladder with dipolar fermions

    NASA Astrophysics Data System (ADS)

    Pandey, Bradraj; Pati, Swapan K.

    2017-02-01

    Motivated by recent experimental progress in the field of dipolar-Fermi gases, we investigate the quantum phases of dipolar fermions on a triangular ladder at half filling. Using density matrix renormalization group method, in the presence of onsite repulsion and intersite attractive interaction, we find an exotic spin-triplet superfluid phase in addition to the usual spin-density and charge-density waves. We examine the stability of the spin-triplet superfluid phase by varying hopping along the rungs of the triangle. The possibility of fermionic supersolidity has also been discussed, by considering three-body interaction in the Hamiltonian. We also study the effect of spin-dependent hopping on the stability of the spin-triplet superfluid phase.

  11. Magnetization plateaus of dipolar spin ice on kagome lattice

    SciTech Connect

    Xie, Y. L.; Wang, Y. L.; Yan, Z. B.; Liu, J.-M.

    2014-05-07

    Unlike spin ice on pyrochlore lattice, the spin ice structure on kagome lattice retains net magnetic charge, indicating non-negligible dipolar interaction in modulating the spin ice states. While it is predicted that the dipolar spin ice on kagome lattice exhibits a ground state with magnetic charge order and √3 × √3 spin order, our work focuses on the magnetization plateau of this system. By employing the Wang-Landau algorithm, it is revealed that the lattice exhibits the fantastic three-step magnetization in response to magnetic field h along the [10] and [01] directions, respectively. For the h//[1 0] case, an additional √3/6M{sub s} step, where M{sub s} is the saturated magnetization, is observed in a specific temperature range, corresponding to a new state with charge order and short-range spin order.

  12. Noncommutative geometry and the primordial dipolar imaginary power spectrum

    NASA Astrophysics Data System (ADS)

    Jain, Pankaj; Rath, Pranati K.

    2015-03-01

    We argue that noncommutative space-times lead to an anisotropic dipolar imaginary primordial power spectrum. We define a new product rule, which allows us to consistently extract the power spectrum in such space-times. The precise nature of the power spectrum depends on the model of noncommutative geometry. We assume a simple dipolar model which has a power dependence on the wave number, , with a spectral index, . We show that such a spectrum provides a good description of the observed dipole modulation in the cosmic microwave background radiation (CMBR) data with . We extract the parameters of this model from the data. The dipole modulation is related to the observed hemispherical anisotropy in the CMBR data, which might represent the first signature of quantum gravity.

  13. Spinor condensate of {sup 87}Rb as a dipolar gas

    SciTech Connect

    Swislocki, Tomasz; Gajda, Mariusz; RzaPzewski, Kazimierz

    2010-03-15

    We consider a spinor condensate of {sup 87}Rb atoms in the F=1 hyperfine state confined in an optical dipole trap. Putting initially all atoms in the m{sub F}=0 component, we find that the system evolves toward a state of thermal equilibrium with kinetic energy equally distributed among all magnetic components. We show that this process is dominated by the dipolar interaction of magnetic spins rather than spin-mixing contact potential. Our results show that because of a dynamical separation of magnetic components, the spin-mixing dynamics in the {sup 87}Rb condensate is governed by the dipolar interaction which plays no role in a single-component rubidium system in a magnetic trap.

  14. Properties of strongly dipolar Bose gases beyond the Born approximation

    NASA Astrophysics Data System (ADS)

    Ołdziejewski, Rafał; Jachymski, Krzysztof

    2016-12-01

    Strongly dipolar Bose gases can form liquid droplets stabilized by quantum fluctuations. In a theoretical description of this phenomenon, the low-energy scattering amplitude is utilized as an effective potential. We show that for magnetic atoms, corrections with respect to the Born approximation arise, and we derive a modified pseudopotential using a realistic interaction model. We discuss the resulting changes in collective mode frequencies and droplet stability diagrams. Our results are relevant to recent experiments with erbium and dysprosium atoms.

  15. Random acoustic metamaterial with a subwavelength dipolar resonance.

    PubMed

    Duranteau, Mickaël; Valier-Brasier, Tony; Conoir, Jean-Marc; Wunenburger, Régis

    2016-06-01

    The effective velocity and attenuation of longitudinal waves through random dispersions of rigid, tungsten-carbide beads in an elastic matrix made of epoxy resin in the range of beads volume fraction 2%-10% are determined experimentally. The multiple scattering model proposed by Luppé, Conoir, and Norris [J. Acoust. Soc. Am. 131(2), 1113-1120 (2012)], which fully takes into account the elastic nature of the matrix and the associated mode conversions, accurately describes the measurements. Theoretical calculations show that the rigid particles display a local, dipolar resonance which shares several features with Minnaert resonance of bubbly liquids and with the dipolar resonance of core-shell particles. Moreover, for the samples under study, the main cause of smoothing of the dipolar resonance of the scatterers and the associated variations of the effective mass density of the dispersions is elastic relaxation, i.e., the finite time required for the shear stresses associated to the translational motion of the scatterers to propagate through the matrix. It is shown that its influence is governed solely by the value of the particle to matrix mass density contrast.

  16. Anisotropic dynamics of dipolar liquids in narrow slit pores.

    PubMed

    Froltsov, Vladimir A; Klapp, Sabine H L

    2006-04-07

    We report molecular dynamics simulation results for Stockmayer fluids confined to narrow slitlike pores with structureless, nonconducting walls. The translational and rotational dynamics of the dipolar particles have been investigated by calculating autocorrelation functions, diffusion coefficients, and relaxation times for various pore widths (five or less particle diameters) and directions parallel and perpendicular to the walls. The dynamic properties of the confined systems are compared to bulk properties, where corresponding bulk and pore states at the same temperature and chemical potential are determined in parallel grand canonical Monte Carlo simulations. We find that the dynamic behavior inside the pore depends on the distance from the walls and can be strongly anisotropic even in globally isotropic systems. This concerns especially the particles in the surface layers close to the walls, where the single particle and collective dipolar relaxation resemble that of true two-dimensional dipolar fluids with different in-plane and out-of-plane relaxations. On the other hand, bulklike relaxation is observed in the pore center of sufficiently wide pores.

  17. Phase diagram of split 2D dipolar spin ice

    NASA Astrophysics Data System (ADS)

    Roscilde, Tommaso; Henry, Louis-Paul

    2013-03-01

    Long-ranged dipolar interactions, which are very natural in artificial square-lattice spin ice, can mask some of the most relevant aspects of spin-ice physics, as they remove the extensive degeneracy of the ground state manifold to give a unique ground state, and they bind monopole pairs into localized spin flips. Following an earlier idea of G. Möller and R. Moessner [Phys. Rev. Lett. 96, 237202 (2006)] we investigate how adding a third direction to square ice allows to recover fundamental traits of spin-ice physics even in the presence of dipolar interactions. Using Monte Carlo simulations based on a generalized loop algorithm, we explore the phase diagram of square dipolar spin ice in which horizontal and vertical dipoles are spatially separated in a third direction (split 2D spin ice). As a function of the splitting we recover a two-fold degenerate staggered state for coplanar dipoles, and a four-fold degenerate ``Manhattan'' state for strongly split dipoles, separated by a first order transition. The competition between the two states at intermediate splitting leads to a strong suppression of the ordering transition temperatures, and makes space for the observation of a hallmark of spin-ice physics in the paramagnetic phase: pinch points in the static structure factor.

  18. Magnetic Reversal of an Artificial Square Ice: Dipolar Correlation and Charge Ordering

    SciTech Connect

    Stein A.; Morgan J.P.; Langridge S.; Marrows C.H.

    2011-10-13

    Magnetic reversal of an artificial square ice pattern subject to a sequence of magnetic fields applied slightly off the diagonal axis is investigated via magnetic force microscopy of the remanent states that result. Sublattice independent reversal is observed via correlated incrementally pinned flip cascades along parallel dipolar chains, as evident from analysis of vertex populations and dipolar correlation functions. Weak dipolar interactions between adjacent chains favour antialignment and give rise to weak charge ordering of 'monopole' vertices during the reversal process.

  19. Low-power broadband homonuclear dipolar recoupling in MAS NMR by two-fold symmetry pulse schemes for magnetization transfers and double-quantum excitation

    NASA Astrophysics Data System (ADS)

    Teymoori, Gholamhasan; Pahari, Bholanath; Edén, Mattias

    2015-12-01

    We provide an experimental, numerical, and high-order average Hamiltonian evaluation of an open-ended series of homonuclear dipolar recoupling sequences, SR2 2p 1 with p = 1, 2, 3, … . While operating at a very low radio-frequency (rf) power, corresponding to a nutation frequency of 1/2 of the magic-angle spinning (MAS) rate (ωnut =ωr / 2), these recursively generated double-quantum (2Q) dipolar recoupling schemes offer a progressively improved compensation to resonance offsets and rf inhomogeneity for increasing pulse-sequence order p. The excellent recoupling robustness to these experimental obstacles, as well as to CSA, is demonstrated for 2Q filtering (2QF) experiments and for driving magnetization transfers in 2D NMR correlation spectroscopy, where the sequences may provide either double or zero quantum dipolar Hamiltonians during mixing. Experimental and numerical demonstrations, which mostly target conditions of "ultra-fast" MAS (≳50 kHz) and high magnetic fields, are provided for recoupling of 13C across a wide range of isotropic and anisotropic chemical shifts, as well as dipolar coupling constants, encompassing [2,3-13C2 ]alanine, [1,3-13C2 ]alanine, diammonium [1,4-13C2 ]fumarate, and [U-13 C]tyrosine. When compared at equal power levels, a superior performance is observed for the SR2p 1 sequences with p ⩾ 3 relative to existing and well-established 2Q recoupling techniques. At ultra-fast MAS, proton decoupling is redundant during the homonuclear dipolar recoupling of dilute spins in organic solids, which renders the family of SR2p 1 schemes the first efficient 2Q recoupling option for general applications, such as 2Q-1Q correlation NMR and high-order multiple-quantum excitation, under truly low-power rf conditions.

  20. Low-power broadband homonuclear dipolar recoupling in MAS NMR by two-fold symmetry pulse schemes for magnetization transfers and double-quantum excitation.

    PubMed

    Teymoori, Gholamhasan; Pahari, Bholanath; Edén, Mattias

    2015-12-01

    We provide an experimental, numerical, and high-order average Hamiltonian evaluation of an open-ended series of homonuclear dipolar recoupling sequences, SR [Formula: see text] with p=1,2,3,…. While operating at a very low radio-frequency (rf) power, corresponding to a nutation frequency of 1/2 of the magic-angle spinning (MAS) rate (ωnut=ωr/2), these recursively generated double-quantum (2Q) dipolar recoupling schemes offer a progressively improved compensation to resonance offsets and rf inhomogeneity for increasing pulse-sequence order p. The excellent recoupling robustness to these experimental obstacles, as well as to CSA, is demonstrated for 2Q filtering (2QF) experiments and for driving magnetization transfers in 2D NMR correlation spectroscopy, where the sequences may provide either double or zero quantum dipolar Hamiltonians during mixing. Experimental and numerical demonstrations, which mostly target conditions of "ultra-fast" MAS (≳50kHz) and high magnetic fields, are provided for recoupling of (13)C across a wide range of isotropic and anisotropic chemical shifts, as well as dipolar coupling constants, encompassing [2,3-(13)C2]alanine, [1,3-(13)C2]alanine, diammonium [1,4-(13)C2]fumarate, and [U-(13)C]tyrosine. When compared at equal power levels, a superior performance is observed for the SR [Formula: see text] sequences with p⩾3 relative to existing and well-established 2Q recoupling techniques. At ultra-fast MAS, proton decoupling is redundant during the homonuclear dipolar recoupling of dilute spins in organic solids, which renders the family of SR [Formula: see text] schemes the first efficient 2Q recoupling option for general applications, such as 2Q-1Q correlation NMR and high-order multiple-quantum excitation, under truly low-power rf conditions.

  1. Ground-state and dynamical properties of two-dimensional dipolar Fermi liquids

    NASA Astrophysics Data System (ADS)

    Abedinpour, Saeed H.; Asgari, Reza; Tanatar, B.; Polini, Marco

    2014-01-01

    We study the ground-state properties of a two-dimensional spin-polarized fluid of dipolar fermions within the Euler-Lagrange Fermi-hypernetted-chain approximation. Our method is based on the solution of a scattering Schrödinger equation for the "pair amplitude" g(r), where g(r) is the pair distribution function. A key ingredient in our theory is the effective pair potential, which includes a bosonic term from Jastrow-Feenberg correlations and a fermionic contribution from kinetic energy and exchange, which is tailored to reproduce the Hartree-Fock limit at weak coupling. Very good agreement with recent results based on quantum Monte Carlo simulations is achieved over a wide range of coupling constants up to the liquid-to-crystal quantum phase transition. Using the fluctuation-dissipation theorem and a static approximation for the effective inter-particle interactions, we calculate the dynamical density-density response function, and furthermore demonstrate that an undamped zero-sound mode exists for any value of the interaction strength, down to infinitesimally weak couplings.

  2. Synthesis, X-ray crystallography, spectroscopic (FT-IR, 1H &13C NMR and UV), computational (DFT/B3LYP) and enzymes inhibitory studies of 7-hydroximinocholest-5-en-3-ol acetate

    NASA Astrophysics Data System (ADS)

    Ahmad, Faheem; Parveen, Mehtab; Alam, Mahboob; Azaz, Shaista; Malla, Ali Mohammed; Alam, Mohammad Jane; Lee, Dong-Ung; Ahmad, Shabbir

    2016-07-01

    The present study reports the synthesis of 7-Hydroximinocholest-5-en-3-ol acetate (syn. 3β-acetoxycholest-5-en-7-one oxime; in general, steroidal oxime). The identity of steroidal molecule was confirmed by NMR, FT-IR, MS, CHN microanalysis and X-ray crystallography. DFT calculations on the titled molecule have been performed. The molecular structure and spectra interpreted by Gaussian hybrid computational analysis theory (B3LYP) are found to be in good correlation with the experimental data obtained from the various spectrophotometric techniques. The vibrational bands appearing in the FTIR are assigned with great accuracy using harmonic frequencies along with intensities and animated modes. Molecular properties like HOMO-LUMO analysis, chemical reactivity descriptors, MEP mapping, dipole moment and natural atomic charges have been presented at the same level of theory. Moreover, the Hirshfeld analysis was carried out to ascertain the secondary interactions and associated 2D fingerprint plots. The percentages of various interactions are pictorialized by fingerprint plots of Hirshfeld surface. Steroidal oxime exhibited promising inhibitory activity against acetylcholinesterase (AChE) as compared to the reference drug, tacrine. Molecular docking was performed to introduce steroidal molecules into the X-ray crystal structures of acetylcholinesterase at the active site to find out the probable binding mode. The results of molecular docking admitted that steroidal oxime may exhibit enzyme inhibitor activity.

  3. MetaboQuant: a tool combining individual peak calibration and outlier detection for accurate metabolite quantification in 1D (1)H and (1)H-(13)C HSQC NMR spectra.

    PubMed

    Klein, Matthias S; Oefner, Peter J; Gronwald, Wolfram

    2013-05-01

    Solution nuclear magnetic resonance (NMR) spectroscopy is widely used to analyze complex mixtures of organic compounds such as biological fluids and tissue extracts. Targeted profiling approaches with reliable compound quantitifcation are hampered, however, by signal overlap and other interferences. Here, we present a tool named MetaboQuant for automated compound quantification from pre-processed 1D and 2D heteronuclear single quantum coherence (HSQC) NMR spectral data and concomitant validation of results. Performance of MetaboQuant was tested on a urinary spike-in data set and compared with other quantification strategies. The use of individual calibration factors in combination with the validation algorithms of MetaboQuant raises the reliability of the quantification results. MetaboQuant can be downloaded at http://genomics.uni-regensburg.de/site/institute/software/metaboquant/ as stand-alone software for Windows or run on other operating systems from within Matlab. Separate software for peak fitting and integration is necessary in order to use MetaboQuant.

  4. Di-n-butyltin(IV) Complexes Derived from Heterocyclic β-diketones and N-Phthaloyl Amino Acids: Preparation, Biological Evaluation, Structural Elucidation Based upon Spectral [IR, NMR (1H, 13C, 19F and 119Sn)] Studies

    PubMed Central

    Verma, Shashi; Gaurb, R. B.; Sharma, R. R.

    2005-01-01

    Stable, six coordinated Bu2SnLA type complexes have been prepared [where LH = RCOC:C(OH)N(C6 H5)N:CCH3; R = -4-F-C6H4-(L1H), R = -4-Cl-C6H4-(L2H), R= -4-Br-C6H4-(L3H), R=-CF3(L4H) and AH = C(O)C6 H4 C(O)NCHR'COOH; R'= -H(A1H), -CH3(A2H), -CH(CH3)2(A3H)] by the interaction of 1:1:1 molar ratios of di-n-butyltin(IV) dichloride with corresponding organic moieties in refluxing benzene using two moles of Et3N as a base. In these complexes LH and AH behave as bidentate and coordination is taking place through oxygen, this is inferred from IR and 13C NMR studies. These complexes possess tin atoms in skew trapezoidal bipyramidal geometry with the C-Sn-C angles ranging from 149.88° to 156.84°. Some of these complexes with their corresponding organic moieties (LH, AH) were tested for their antimicrobial activities. PMID:18365100

  5. Comprehensive quantum chemical and spectroscopic (FTIR, FT-Raman, (1)H, (13)C NMR) investigations of (1,2-epoxyethyl)benzene and (1,2-epoxy-2-phenyl)propane.

    PubMed

    Arjunan, V; Anitha, R; Devi, L; Mohan, S; Yang, Haifeng

    2015-01-25

    Aromatic epoxides are causative factors for mutagenic and carcinogenic activity of polycyclic arenes. The 1,2- or 2,3-epoxy compounds are widely used to a considerable extent in the textile, plastics, pharmaceutical, cosmetics, detergent and photochemical industries. The FTIR and FT-Raman spectra of (1,2-epoxyethyl)benzene and (1,2-epoxy-2-phenyl)propane are recorded in the regions 4000-400 cm(-1) and 4000-100 cm(-1), respectively. The observed fundamentals are assigned to different normal modes of vibration. The structure of the compound has been optimised with B3LYP method using 6-311++G(**) and cc-pVTZ basis sets. The IR and Raman intensities are determined. The total electron density and molecular electrostatic potential surfaces of the molecule are constructed by using B3LYP/6-311++G(d,p) method to display electrostatic potential (electron+nuclei) distribution. The electronic properties HOMO and LUMO energies were measured. Natural bond orbital analysis of the compounds has been performed to indicate the presence of intramolecular charge transfer. The (1)H and (13)C NMR chemical shifts of the molecules have been analysed.

  6. Di-n-butyltin(IV) complexes derived from heterocyclic beta-diketones and N-phthaloyl amino acids: preparation, biological evaluation, structural elucidation based upon spectral [IR, NMR (1H, 13C, 19F and 119Sn)] studies.

    PubMed

    Joshi, Anurag; Verma, Shashi; Gaurb, R B; Sharma, R R

    2005-01-01

    Stable, six coordinated Bu(2)SnLA type complexes have been prepared [where LH = RCOC:C(OH)N(C(6) H(5))N:CCH(3); R = -4-F-C(6)H(4)-(L(1)H), R = -4-Cl-C(6)H(4)-(L(2)H), R= -4-Br-C(6)H(4)-(L(3)H), R=-CF(3)(L(4)H) and AH = C(O)C(6) H(4) C(O)NCHR'COOH; R'= -H(A(1)H), -CH(3)(A(2)H), -CH(CH(3))(2)(A(3)H)] by the interaction of 1:1:1 molar ratios of di-n-butyltin(IV) dichloride with corresponding organic moieties in refluxing benzene using two moles of Et(3)N as a base. In these complexes LH and AH behave as bidentate and coordination is taking place through oxygen, this is inferred from IR and (13)C NMR studies. These complexes possess tin atoms in skew trapezoidal bipyramidal geometry with the C-Sn-C angles ranging from 149.88( degrees ) to 156.84( degrees ). Some of these complexes with their corresponding organic moieties (LH, AH) were tested for their antimicrobial activities.

  7. (1)H, (13)C, (15)N backbone and side chain NMR resonance assignments for E73 from Sulfolobus spindle-shaped virus ragged hills, a hyperthermophilic crenarchaeal virus from Yellowstone National Park.

    PubMed

    Schlenker, Casey; Menon, Smita; Lawrence, C Martin; Copié, Valérie

    2009-12-01

    Crenarchaeal viruses are commonly found in hyperthermal acidic environments such as those of Yellowstone National Park. These remarkable viruses not only exhibit unusual morphologies, but also display extreme genetic diversity. However, little is known about crenarchaeal viral life cycles, virus-host interactions, and their adaptation to hyperthermophilic environments. In an effort to better understand the functions of crenarchaeal viruses and the proteins encoded by their genomes, we have undertaken detailed structural and functional studies of gene products encoded in the open reading frames of Sulfolobus spindle-shaped virus ragged hills. Herein, we report ((15)N, (13)C, (1)H) resonance assignments of backbone and side chain atoms of a 19.1 kDa homodimeric E73 protein of SSVRH.

  8. NMR study of non-structural proteins--part II: (1)H, (13)C, (15)N backbone and side-chain resonance assignment of macro domain from Venezuelan equine encephalitis virus (VEEV).

    PubMed

    Makrynitsa, Garyfallia I; Ntonti, Dioni; Marousis, Konstantinos D; Tsika, Aikaterini C; Lichière, Julie; Papageorgiou, Nicolas; Coutard, Bruno; Bentrop, Detlef; Spyroulias, Georgios A

    2015-10-01

    Macro domains consist of 130-190 amino acid residues and appear to be highly conserved in all kingdoms of life. Intense research on this field has shown that macro domains bind ADP-ribose and other similar molecules, but their exact function still remains intangible. Macro domains are highly conserved in the Alphavirus genus and the Venezuelan equine encephalitis virus (VEEV) is a member of this genus that causes fatal encephalitis to equines and humans. In this study we report the high yield recombinant expression and preliminary solution NMR study of the macro domain of VEEV. An almost complete sequence-specific assignment of its (1)H, (15)N and (13)C resonances was obtained and its secondary structure predicted by TALOS+. The protein shows a unique mixed α/β-fold.

  9. Spectroscopic (FT-IR, FT-Raman, 1H, 13C NMR, UV/VIS), thermogravimetric and antimicrobial studies of Ca(II), Mn(II), Cu(II), Zn(II) and Cd(II) complexes of ferulic acid

    NASA Astrophysics Data System (ADS)

    Kalinowska, M.; Piekut, J.; Bruss, A.; Follet, C.; Sienkiewicz-Gromiuk, J.; Świsłocka, R.; Rzączyńska, Z.; Lewandowski, W.

    2014-03-01

    The molecular structure of Mn(II), Cu(II), Zn(II), Cd(II) and Ca(II) ferulates (4-hydroxy-3-methoxycinnamates) was studied. The selected metal ferulates were synthesized. Their composition was established by means of elementary and thermogravimetric analysis. The following spectroscopic methods were used: infrared (FT-IR), Raman (FT-Raman), nuclear magnetic resonance (13C, 1H NMR) and ultraviolet-visible (UV/VIS). On the basis of obtained results the electronic charge distribution in studied metal complexes in comparison with ferulic acid molecule was discussed. The microbiological study of ferulic acid and ferulates toward Escherichia coli, Bacillus subtilis, Candida albicans, Pseudomonas aeruginosa, Staphylococcus aureus and Proteus vulgaris was done.

  10. 1H, 13C, 15N resonance assignments of the extracellular loop 1 domain (ECL1) of Streptococcus pneumoniae D39 FtsX, an essential cell division protein

    PubMed Central

    Fu, Yue; Bruce, Kevin E.; Rued, Britta; Winkler, Malcolm E.; Giedroc, David P.

    2015-01-01

    FtsX is an integral membrane protein from Streptococcus pneumoniae (pneumococcus) that harbors an extracellular loop 1 domain (FtsXECL1Spn) that interacts with PcsB, an peptidoglycan hydrolase that is essential for cell growth and division. Here, we report nearly complete backbone and side chain resonance assignments and a secondary structural analysis of FtsXECL1Spn (residues 47–168 of FtsX) as first steps toward structure determination of FtsXECL1Spn. PMID:26370567

  11. Comprehensive quantum chemical and spectroscopic (FTIR, FT-Raman, 1H, 13C NMR) investigations of (1,2-epoxyethyl)benzene and (1,2-epoxy-2-phenyl)propane

    NASA Astrophysics Data System (ADS)

    Arjunan, V.; Anitha, R.; Devi, L.; Mohan, S.; Yang, Haifeng

    2015-01-01

    Aromatic epoxides are causative factors for mutagenic and carcinogenic activity of polycyclic arenes. The 1,2- or 2,3-epoxy compounds are widely used to a considerable extent in the textile, plastics, pharmaceutical, cosmetics, detergent and photochemical industries. The FTIR and FT-Raman spectra of (1,2-epoxyethyl)benzene and (1,2-epoxy-2-phenyl)propane are recorded in the regions 4000-400 cm-1 and 4000-100 cm-1, respectively. The observed fundamentals are assigned to different normal modes of vibration. The structure of the compound has been optimised with B3LYP method using 6-311++G** and cc-pVTZ basis sets. The IR and Raman intensities are determined. The total electron density and molecular electrostatic potential surfaces of the molecule are constructed by using B3LYP/6-311++G(d,p) method to display electrostatic potential (electron + nuclei) distribution. The electronic properties HOMO and LUMO energies were measured. Natural bond orbital analysis of the compounds has been performed to indicate the presence of intramolecular charge transfer. The 1H and 13C NMR chemical shifts of the molecules have been analysed.

  12. Isolation and structural characterization of unusual pyranoanthocyanins and related anthocyanins from Staghorn sumac (Rhus typhina L.) via UPLC-ESI-MS, (1)H, (13)C, and 2D NMR spectroscopy.

    PubMed

    Kirby, Christopher W; Wu, Tao; Tsao, Rong; McCallum, Jason L

    2013-10-01

    The six major anthocyanins found in the burgundy coloured fruits of Staghorn sumac (Rhus typhina L.) were isolated and the structures of four compounds were determined by NMR spectroscopic methods as being: 7-O-methyl-delphinidin-3-O-(2″galloyl)-β-d-galactopyranoside; 7-O-methyl-cyanidin-3-O-(2″galloyl)-β-d-galactopyranoside; 7-O-methyl-delphinidin-3-O-(2″'galloyl)-β-d-galactopyranoside-4-vinyl-catechol-3″-O-β-d-glucopyranoside; and 7-O-methyl-cyanidin-3-O-(2″'galloyl)-β-d-galactopyranoside-4-vinyl-catechol-3″-O-β-d-glucopyranoside, respectively. Additionally, two related anthocyanin compounds, cyanidin-3-O-(2″galloyl)-β-d-galactopyranoside and 7-O-methyl-cyanidin-3-O-β-d-galactopyranoside were also recovered, with NMR spectroscopic values closely matching previous reports from other plant species. The prevalence of 7-O-methyl anthocyanins and their galloylated derivatives in sumac is highly unusual, and warrants special attention. Additionally, the in planta occurrence of two 7-O-methyl-pyranoanothocyanin-vinyl-catechol aglycones, Sumadin A and Sumadin B, and their derivatives is noted. To our knowledge, E-ring glycosylated vinyl-catechol pyranoanthocyanins were previously unknown.

  13. (1)H, (13)C, and (15)N backbone resonance assignments of the full-length 40 kDa S. acidocaldarius Y-family DNA polymerase, dinB homolog.

    PubMed

    Moro, Sean L; Cocco, Melanie J

    2015-10-01

    The dinB homolog (Dbh) is a member of the Y-family of translesion DNA polymerases, which are specialized to accurately replicate DNA across from a wide variety of lesions in living cells. Lesioned bases block the progression of high-fidelity polymerases and cause detrimental replication fork stalling; Y-family polymerases can bypass these lesions. The active site of the translesion synthesis polymerase is more open than that of a replicative polymerase; consequently Dbh polymerizes with low fidelity. Bypass polymerases also have low processivity. Short extension past the lesion allows the high-fidelity polymerase to switch back onto the site of replication. Dbh and the other Y-family polymerases have been used as structural models to investigate the mechanisms of DNA polymerization and lesion bypass. Many high-resolution crystal structures of Y-family polymerases have been reported. NMR dynamics studies can complement these structures by providing a measure of protein motions. Here we report the (15)N, (1)H, and (13)C backbone resonance assignments at two temperatures (35 and 50 °C) for Sulfolobus acidocaldarius Dbh polymerase. Backbone resonance assignments have been obtained for 86 % of the residues. The polymerase active site is assigned as well as the majority of residues in each of the four domains.

  14. NMR study of non-structural proteins--part I: (1)H, (13)C, (15)N backbone and side-chain resonance assignment of macro domain from Mayaro virus (MAYV).

    PubMed

    Melekis, Efstathios; Tsika, Aikaterini C; Lichière, Julie; Chasapis, Christos T; Margiolaki, Irene; Papageorgiou, Nicolas; Coutard, Bruno; Bentrop, Detlef; Spyroulias, Georgios A

    2015-04-01

    Macro domains are ADP-ribose-binding modules present in all eukaryotic organisms, bacteria and archaea. They are also found in non-structural proteins of several positive strand RNA viruses such as alphaviruses. Here, we report the high yield expression and preliminary structural analysis through solution NMR spectroscopy of the macro domain from New World Mayaro Alphavirus. The recombinant protein was well-folded and in a monomeric state. An almost complete sequence-specific assignment of its (1)H, (15)N and (13)C resonances was obtained and its secondary structure determined by TALOS+.

  15. Broadband cross-polarization-based heteronuclear dipolar recoupling for structural and dynamic NMR studies of rigid and soft solids

    SciTech Connect

    Kharkov, B. B.; Chizhik, V. I.; Dvinskikh, S. V.

    2016-01-21

    Dipolar recoupling is an essential part of current solid-state NMR methodology for probing atomic-resolution structure and dynamics in solids and soft matter. Recently described magic-echo amplitude- and phase-modulated cross-polarization heteronuclear recoupling strategy aims at efficient and robust recoupling in the entire range of coupling constants both in rigid and highly dynamic molecules. In the present study, the properties of this recoupling technique are investigated by theoretical analysis, spin-dynamics simulation, and experimentally. The resonance conditions and the efficiency of suppressing the rf field errors are examined and compared to those for other recoupling sequences based on similar principles. The experimental data obtained in a variety of rigid and soft solids illustrate the scope of the method and corroborate the results of analytical and numerical calculations. The technique benefits from the dipolar resolution over a wider range of coupling constants compared to that in other state-of-the-art methods and thus is advantageous in studies of complex solids with a broad range of dynamic processes and molecular mobility degrees.

  16. Broadband cross-polarization-based heteronuclear dipolar recoupling for structural and dynamic NMR studies of rigid and soft solids

    NASA Astrophysics Data System (ADS)

    Kharkov, B. B.; Chizhik, V. I.; Dvinskikh, S. V.

    2016-01-01

    Dipolar recoupling is an essential part of current solid-state NMR methodology for probing atomic-resolution structure and dynamics in solids and soft matter. Recently described magic-echo amplitude- and phase-modulated cross-polarization heteronuclear recoupling strategy aims at efficient and robust recoupling in the entire range of coupling constants both in rigid and highly dynamic molecules. In the present study, the properties of this recoupling technique are investigated by theoretical analysis, spin-dynamics simulation, and experimentally. The resonance conditions and the efficiency of suppressing the rf field errors are examined and compared to those for other recoupling sequences based on similar principles. The experimental data obtained in a variety of rigid and soft solids illustrate the scope of the method and corroborate the results of analytical and numerical calculations. The technique benefits from the dipolar resolution over a wider range of coupling constants compared to that in other state-of-the-art methods and thus is advantageous in studies of complex solids with a broad range of dynamic processes and molecular mobility degrees.

  17. Broadband cross-polarization-based heteronuclear dipolar recoupling for structural and dynamic NMR studies of rigid and soft solids.

    PubMed

    Kharkov, B B; Chizhik, V I; Dvinskikh, S V

    2016-01-21

    Dipolar recoupling is an essential part of current solid-state NMR methodology for probing atomic-resolution structure and dynamics in solids and soft matter. Recently described magic-echo amplitude- and phase-modulated cross-polarization heteronuclear recoupling strategy aims at efficient and robust recoupling in the entire range of coupling constants both in rigid and highly dynamic molecules. In the present study, the properties of this recoupling technique are investigated by theoretical analysis, spin-dynamics simulation, and experimentally. The resonance conditions and the efficiency of suppressing the rf field errors are examined and compared to those for other recoupling sequences based on similar principles. The experimental data obtained in a variety of rigid and soft solids illustrate the scope of the method and corroborate the results of analytical and numerical calculations. The technique benefits from the dipolar resolution over a wider range of coupling constants compared to that in other state-of-the-art methods and thus is advantageous in studies of complex solids with a broad range of dynamic processes and molecular mobility degrees.

  18. Magnetic hysteresis based on dipolar interactions in granular magnetic systems

    NASA Astrophysics Data System (ADS)

    Allia, Paolo; Coisson, Marco; Knobel, Marcelo; Tiberto, Paola; Vinai, Franco

    1999-11-01

    The magnetic hysteresis of granular magnetic systems is investigated in the high-temperature limit (T>> blocking temperature of magnetic nanoparticles). Measurements of magnetization curves have been performed at room temperature on various samples of granular bimetallic alloys of the family Cu100-xCox (x=5-20 at. %) obtained in ribbon form by planar flow casting in a controlled atmosphere, and submitted to different thermal treatments. The loop amplitude and shape, which are functions of sample composition and thermal history, are studied taking advantage of a novel method of graphical representation, particularly apt to emphasize the features of thin, elongated loops. The hysteresis is explained in terms of the effect of magnetic interactions of the dipolar type among magnetic-metal particles, acting to hinder the response of the system of moments to isothermal changes of the applied field. Such a property is accounted for in a mean-field scheme, by introducing a memory term in the argument of the Langevin function which describes the anhysteretic behavior of an assembly of noninteracting superparamagnetic particles. The rms field arising from the cumulative effect of dipolar interactions is linked by the theory to a measurable quantity, the reduced remanence of a major symmetric hysteresis loop. The theory's self-consistence and adequacy have been properly tested at room temperature on all examined systems. The agreement with experimental results is always striking, indicating that at high temperatures the magnetic hysteresis of granular systems is dominated by interparticle, rather than single-particle, effects. Dipolar interactions seem to fully determine the magnetic hysteresis in the high-temperature limit for low Co content (x<=10). For higher concentrations of magnetic metal, the experimental results indicate that additional hysteretic mechanisms have to be introduced.

  19. Phases of dipolar bosons in a bilayer geometry

    NASA Astrophysics Data System (ADS)

    Cinti, Fabio; Wang, Daw-Wei; Boninsegni, Massimo

    2017-02-01

    We study, by first-principles computer simulations, the low-temperature phase diagram of bosonic dipolar gases in a bilayer geometry as a function of the two control parameters, i.e., the in-plane density and the interlayer distance. We observe four distinct phases, namely, paired and decoupled superfluids, as well as a crystal of dimers and one consisting of two aligned crystalline layers. A direct quantum phase transition from a dimer crystal to two independent superfluids is observed in a relatively wide range of parameters. No supersolid phase is predicted for this system.

  20. Field-induced layer formation in dipolar nanofilms.

    PubMed

    Jordanovic, Jelena; Klapp, Sabine H L

    2008-07-18

    Using molecular dynamics simulations, we demonstrate that the layering of confined colloidal particles with dipolar interactions, such as ferrofluids, in slablike geometries can be controlled by homogeneous external fields. For suitable surface separations, strong fields directed perpendicular to the film plane do not only align the particles but create additional layers in the system. The reverse effect occurs with an in-plane field which can induce a collapse of layers. Both effects are accompanied by pronounced particle rearrangements in lateral directions. Our simulation results are consistent with recent experiments of ferrofluids at surfaces.

  1. Compensation of dipolar-exciton spin splitting in magnetic field

    NASA Astrophysics Data System (ADS)

    Gorbunov, A. V.; Timofeev, V. B.

    2013-03-01

    Magnetoluminescence of spatially indirect dipolar excitons in 25 nm GaAs/AlGaAs single quantum well collected within a lateral potential trap has been studied in Faraday geometry. The paramagnetic spin splitting of the luminescence line of the heavy-hole excitons in the trap centre is completely compensated at magnetic field below critical value ≈2 Т. The effect of spin splitting compensation is caused by the exchange interaction in dense exciton Bose gas which is in qualitative agreement with the existing theoretical concepts.

  2. Exact second virial coefficient for dipolar hard spheres.

    PubMed

    Virga, Epifanio G

    2013-11-20

    The second virial coefficient B2 for a fluid of dipolar hard spheres has been given several approximate forms valid in the limits of weak and strong interactions. They have been formulated as asymptotic expressions in a dimensionless interaction parameter λ. In this paper, B2 is determined exactly for all values of λ in both the three-dimensional case, where spheres may access the whole space and their dipole moments may be oriented in all directions, and in the quasi-two-dimensional case, where spheres have their centres bound to glide on a plane, while their dipole moments are still freely orientable in space.

  3. Dipolar Rings of Microscopic Ellipsoids: Magnetic Manipulation and Cell Entrapment

    NASA Astrophysics Data System (ADS)

    Martinez-Pedrero, Fernando; Cebers, Andrejs; Tierno, Pietro

    2016-09-01

    We study the formation and the dynamics of dipolar rings composed by microscopic ferromagnetic ellipsoids, which self-assemble in water by switching the direction of the applied field. We show how to manipulate these fragile structures and control their shape via the application of external static and oscillating magnetic fields. We introduce a theoretical framework which describes the ring deformation under an applied field, allowing us to understand the underlying physical mechanism. Our microscopic rings are finally used to capture, entrap, and later release a biological cell via a magnetic command, i.e., performing a simple operation which can be implemented in other microfluidic devices which make use of ferromagnetic particles.

  4. Characterization of ionic, dipolar and molecular mobility in polymer systems

    NASA Astrophysics Data System (ADS)

    Guo, Zhenrong

    Changes in the ionic and dipolar molecular mobility in a polymer system are the basis for the changes in the dielectric mechanical properties of polymer materials. Frequency Dependent Dielectric Measurements (FDEMS) and Ion Time-of-Flight (ITOF) are two important techniques to investigate ionic and dipolar molecular mobility in polymer systems. The results can be related to the macro- and molecular dielectric, electrical and dynamic properties of polymeric materials. The combination of these two methods provides a full view of electric, dielectric and dynamic behavior for the systems as they undergo chemical and/or physical changes during polymerization crystallization, vitrification, and/or phase separation. The research on microscopic mass mobility in polymer systems was done on three aspects: (1) ion mobility in an epoxy-amine reaction system; (2) dipolar mobility and relaxation during dimethacrylate resin cure and (3) dye molecule migration and diffusion in polymer films. In the ion mobility study, we separately monitor the changes in the ion mobility and the number of charge carriers during the epoxy-amine polymerization with FDEMS and ITOF measurements. The isolation of the number of carriers and their mobility allows significant improvement in monitoring changes in the state and structure of a material as it cures. For the dipolar mobility and relaxation study, FDEMS measurements were used to detect structural evolution and spatial heterogeneity formation during the polymerization process of dimethacrylate resins. The dielectric spectra, glass transition (Tg) profiles and dynamic mechanical measurements were used to investigate the existence of two cooperative regions of sufficient size to create two alpha-relaxation processes representing oligomer rich and polymer microgel regions during the polymerization. For the dye migration research, we tried to develop a visually color changing paper (VCP) due to dye molecule migration in polymer films. The mobility

  5. Stability spectroscopy of rotons in a dipolar Bose gas

    NASA Astrophysics Data System (ADS)

    Corson, John P.; Wilson, Ryan M.; Bohn, John L.

    2013-05-01

    We study the stability of a quasi-one-dimensional dipolar Bose-Einstein condensate that is perturbed by a weak lattice potential along its axis. Our numerical simulations demonstrate that systems exhibiting a roton-maxon structure destabilize readily when the lattice wavelength equals either half the roton wavelength or a low roton subharmonic. We apply perturbation theory to the Gross-Pitaevskii and Bogoliubov-de Gennes equations to illustrate the mechanisms behind the instability threshold. The features of our stability diagram may be used as a direct measurement of the roton wavelength for quasi-one-dimensional geometries.

  6. Stability Spectroscopy of Rotons in a Dipolar Bose Gas

    NASA Astrophysics Data System (ADS)

    Corson, John; Wilson, Ryan; Bohn, John

    2013-05-01

    We study the stability of a quasi-one-dimensional dipolar Bose-Einstein condensate that is perturbed by a weak lattice potential along its axis. Our numerical simulations demonstrate that systems exhibiting a roton-maxon structure destabilize readily when the lattice wavelength equals either half the roton wavelength or a low roton subharmonic. We apply perturbation theory to the Gross-Pitaevskii and Bogoliubov de Gennes equations to illustrate the mechanisms behind the instability threshold. The features of our stability diagram are a novel signature of roton physics, and their experimental observation would constitute a direct measurement of the roton wavelength for quasi-one-dimensional geometries.

  7. Emergent structure in a dipolar Bose gas in a one-dimensional lattice

    SciTech Connect

    Wilson, Ryan M.; Bohn, John L.

    2011-02-15

    We consider an ultracold dipolar Bose gas in a one-dimensional lattice. For a sufficiently large lattice recoil energy, such a system becomes a series of nonoverlapping Bose-Einstein condensates that interact via the long-range dipole-dipole interaction (ddi). We model this system via a coupled set of nonlocal Gross-Pitaevskii equations (GPEs) for lattices of both infinite and finite extent. We find significantly modified stability properties in the lattice due to the softening of a discrete roton-like mode, as well as ''islands'' in parameter space where biconcave densities are predicted to exist and that only exist in the presence of the other condensates on the lattice. We solve for the elementary excitations of the system to check the dynamical stability of these solutions and to uncover the nature of their collapse. By solving a coupled set of GPEs exactly on a full numeric grid, we show that this emergent biconcave structure can be realized in a finite lattice with atomic {sup 52}Cr.

  8. A comparative study of dipolarization fronts at MMS and Cluster

    NASA Astrophysics Data System (ADS)

    Schmid, D.; Nakamura, R.; Volwerk, M.; Plaschke, F.; Narita, Y.; Baumjohann, W.; Magnes, W.; Fischer, D.; Eichelberger, H. U.; Torbert, R. B.; Russell, C. T.; Strangeway, R. J.; Leinweber, H. K.; Le, G.; Bromund, K. R.; Anderson, B. J.; Slavin, J. A.; Kepko, E. L.

    2016-06-01

    We present a statistical study of dipolarization fronts (DFs), using magnetic field data from MMS and Cluster, at radial distances below 12 RE and 20 RE, respectively. Assuming that the DFs have a semicircular cross section and are propelled by the magnetic tension force, we used multispacecraft observations to determine the DF velocities. About three quarters of the DFs propagate earthward and about one quarter tailward. Generally, MMS is in a more dipolar magnetic field region and observes larger-amplitude DFs than Cluster. The major findings obtained in this study are as follows: (1) At MMS ˜57 % of the DFs move faster than 150 km/s, while at Cluster only ˜35 %, indicating a variable flux transport rate inside the flow-braking region. (2) Larger DF velocities correspond to higher Bz values directly ahead of the DFs. We interpret this as a snow plow-like phenomenon, resulting from a higher magnetic flux pileup ahead of DFs with higher velocities.

  9. Field-induced ordering in dipolar spin ice

    NASA Astrophysics Data System (ADS)

    Kao, Wen-Han; Holdsworth, Peter C. W.; Kao, Ying-Jer

    2016-05-01

    We present numerical studies of dipolar spin ice in the presence of a magnetic field slightly tilted away from the [111] axis. We find a first-order transition from a kagome ice to a q =X state when the external field is tilted toward the [11 2 ¯] direction. This is consistent with the anomalous critical scattering previously observed in the neutron scattering experiment on the spin ice material Ho2Ti2O7 in a tilted field [T. Fennell et al., Nat. Phys. 3, 566 (2007), 10.1038/nphys632]. We show that this ordering originates from the antiferromagnetic alignment of spin chains on the kagome planes. The residual entropy of the kagome ice is fully recovered. Our result captures the features observed in the experiments and points to the importance of the dipolar interaction in determining ordered states in the spin ice materials. We place our results in the context of recent susceptibility measurements on Dy2Ti2O7 , showing two features for a [111] field.

  10. Dipolar clusters and ferroelectricity in high Tc superconductors

    NASA Astrophysics Data System (ADS)

    Kusmartsev, F. V.; Saarela, M.

    2015-08-01

    In this paper, we show that doping of hole charge carriers induces formation of resonance plaquettes (RPs) having electric dipolar moments and fluctuating stripes in cuprates. A single RP is created by many-body interactions between the dopant ion or a charge fluctuation outside and holes inside the CuO plane. In such a process, Coulomb interacting holes in the CuO plane are self-organized into four-particles resonance valence bond plaquettes bound with dopants or polarons located in the spacer layer between CuO planes. Such RPs have ordered and disordered phases. They are ordered into charge density waves (CDW) or stripes only at certain conditions. The lowest energy of the ordered phase corresponds to a local antiferroelectric ordering. The RPs mobility is very low at low temperatures and they are bound into dipole-dipole pairs. Electromagnetic radiation interacts strongly with RPs electric dipoles and when the sample is subjected to it, the mobility changes significantly. This leads to a fractal growth of dipolar RP clusters. The existence of electric dipoles and CDW reveal a series of new phenomena such as ferroelectricity, strong light and microwave absorption and the field induced superconductivity.

  11. Rotational friction of dipolar colloids measured by driven torsional oscillations

    PubMed Central

    Steinbach, Gabi; Gemming, Sibylle; Erbe, Artur

    2016-01-01

    Despite its prominent role in the dynamics of soft materials, rotational friction remains a quantity that is difficult to determine for many micron-sized objects. Here, we demonstrate how the Stokes coefficient of rotational friction can be obtained from the driven torsional oscillations of single particles in a highly viscous environment. The idea is that the oscillation amplitude of a dipolar particle under combined static and oscillating fields provides a measure for the Stokes friction. From numerical studies we derive a semi-empirical analytic expression for the amplitude of the oscillation, which cannot be calculated analytically from the equation of motion. We additionally demonstrate that this expression can be used to experimentally determine the rotational friction coefficient of single particles. Here, we record the amplitudes of a field-driven dipolar Janus microsphere with optical microscopy. The presented method distinguishes itself in its experimental and conceptual simplicity. The magnetic torque leaves the local environment unchanged, which contrasts with other approaches where, for example, additional mechanical (frictional) or thermal contributions have to be regarded. PMID:27680399

  12. Dynamical simulation of dipolar Janus colloids: Dynamical properties

    NASA Astrophysics Data System (ADS)

    Hagy, Matthew C.; Hernandez, Rigoberto

    2013-05-01

    The dynamical properties of dipolar Janus particles are studied through simulation using our previously-developed detailed pointwise (PW) model and an isotropically coarse-grained (CG) model [M. C. Hagy and R. Hernandez, J. Chem. Phys. 137, 044505 (2012), 10.1063/1.4737432]. The CG model is found to have accelerated dynamics relative to the PW model over a range of conditions for which both models have near identical static equilibrium properties. Physically, this suggests dipolar Janus particles have slower transport properties (such as diffusion) in comparison to isotropically attractive particles. Time rescaling and damping with Langevin friction are explored to map the dynamics of the CG model to that of the PW model. Both methods map the diffusion constant successfully and improve the velocity autocorrelation function and the mean squared displacement of the CG model. Neither method improves the distribution of reversible bond durations f(tb) observed in the CG model, which is found to lack the longer duration reversible bonds observed in the PW model. We attribute these differences in f(tb) to changes in the energetics of multiple rearrangement mechanisms. This suggests a need for new methods that map the coarse-grained dynamics of such systems to the true time scale.

  13. Optical switching of nuclear spin-spin couplings in semiconductors.

    PubMed

    Goto, Atsushi; Ohki, Shinobu; Hashi, Kenjiro; Shimizu, Tadashi

    2011-07-05

    Two-qubit operation is an essential part of quantum computation. However, solid-state nuclear magnetic resonance quantum computing has not been able to fully implement this functionality, because it requires a switchable inter-qubit coupling that controls the time evolutions of entanglements. Nuclear dipolar coupling is beneficial in that it is present whenever nuclear-spin qubits are close to each other, while it complicates two-qubit operation because the qubits must remain decoupled to prevent unwanted couplings. Here we introduce optically controllable internuclear coupling in semiconductors. The coupling strength can be adjusted externally through light power and even allows on/off switching. This feature provides a simple way of switching inter-qubit couplings in semiconductor-based quantum computers. In addition, its long reach compared with nuclear dipolar couplings allows a variety of options for arranging qubits, as they need not be next to each other to secure couplings.

  14. Intermediate couplings: NMR at the solids-liquids interface

    NASA Astrophysics Data System (ADS)

    Spence, Megan

    2006-03-01

    Anisotropic interactions like dipolar couplings and chemical shift anisotropy have long offered solid-state NMR spectroscopists valuable structural information. Recently, solution-state NMR structural studies have begun to exploit residual dipolar couplings of biological molecules in weakly anisotropic solutions. These residual couplings are about 0.1% of the coupling magnitudes observed in the solid state, allowing simple, high-resolution NMR spectra to be retained. In this work, we examine the membrane-associated opioid, leucine enkephalin (lenk), in which the ordering is ten times larger than that for residual dipolar coupling experiments, requiring a combination of solution-state and solid-state NMR techniques. We adapted conventional solid-state NMR techniques like adiabatic cross- polarization and REDOR for use with such a system, and measured small amide bond dipolar couplings in order to determine the orientation of the amide bonds (and therefore the peptide) with respect to the membrane surface. However, the couplings measured indicate large structural rearrangements on the surface and contradict the published structures obtained by NOESY constraints, a reminder that such methods are of limited use in the presence of large-scale dynamics.

  15. Free energy of dipolar hard spheres: The virial expansion under the presence of an external magnetic field

    NASA Astrophysics Data System (ADS)

    Elfimova, Ekaterina A.; Karavaeva, Tatyana E.; Ivanov, Alexey O.

    2014-12-01

    A method for calculation of the free energy of dipolar hard spheres under the presence of an applied magnetic field is presented. The method is based on the virial expansion in terms of density as well as the dipolar coupling constant λ, and it uses diagram technique. The formulas and the diagrams, needed to calculate the second B2 and third B3 virial coefficients, are derived up to the order of ˜λ3, and compared to the zero-field case. The formula for B2 is the same as in the zero-field case; the formula for B3, however, is different in an applied field, and a derivation is presented. This is a surprising result which is not emphasized in standard texts, but which has been noticed before in the virial expansion for flexible molecules (Caracciolo et al., 2006; Caracciolo et al., 2008). To verify the correctness of the obtained formulas, B2 and B3 were calculated within the accuracy of λ2, which were applied to initial magnetic susceptibility. The obtained expression fully coincides with the well-known theories (Morozov and Lebedev, 1990; Huke and Lücke, 2000; Ivanov and Kuznetsova, 2001), which used different methods to calculate the initial magnetic susceptibility.

  16. Tight Coupling of Metabolic Oscillations and Intracellular Water Dynamics in Saccharomyces cerevisiae

    PubMed Central

    Thoke, Henrik Seir; Tobiesen, Asger; Brewer, Jonathan; Hansen, Per Lyngs; Stock, Roberto P.; Olsen, Lars F.; Bagatolli, Luis A.

    2015-01-01

    We detected very strong coupling between the oscillating concentration of ATP and the dynamics of intracellular water during glycolysis in Saccharomyces cerevisiae. Our results indicate that: i) dipolar relaxation of intracellular water is heterogeneous within the cell and different from dilute conditions, ii) water dipolar relaxation oscillates with glycolysis and in phase with ATP concentration, iii) this phenomenon is scale-invariant from the subcellular to the ensemble of synchronized cells and, iv) the periodicity of both glycolytic oscillations and dipolar relaxation are equally affected by D2O in a dose-dependent manner. These results offer a new insight into the coupling of an emergent intensive physicochemical property of the cell, i.e. cell-wide water dipolar relaxation, and a central metabolite (ATP) produced by a robustly oscillating metabolic process. PMID:25705902

  17. Collisional effects in the dynamics of a dipolar gas

    NASA Astrophysics Data System (ADS)

    Sykes, Andrew

    2016-05-01

    In this talk, we discuss the role of collisions in dipolar gases which are far from equilibrium. We compare and contrast collisional mechanisms with mean-field effects. We consider several cases of dynamical behaviour. We begin with cross-dimensional relaxation, where the time-scale of equilibration is studied following a quench in the trap parameters. We also discuss the damping of monopole and quadrupole excitations. Finally we discuss time-of-flight expansion dynamics. Our results demonstrate that collisions can play a significant role. We use these results to extract an estimate of the deca-heptuplet s-partial-wave scattering length of bosonic dysprosium, and to improve the accuracy of experimental time-of-flight expansion imaging. Financial support from the Marie Sklodowska-Curie H2020 framework program.

  18. CHARGED TORI IN SPHERICAL GRAVITATIONAL AND DIPOLAR MAGNETIC FIELDS

    SciTech Connect

    Slany, P.; Kovar, J.; Stuchlik, Z.; Karas, V.

    2013-03-01

    A Newtonian model of non-conductive, charged, perfect fluid tori orbiting in combined spherical gravitational and dipolar magnetic fields is presented and stationary, axisymmetric toroidal structures are analyzed. Matter in such tori exhibits a purely circulatory motion and the resulting convection carries charges into permanent rotation around the symmetry axis. As a main result, we demonstrate the possible existence of off-equatorial charged tori and equatorial tori with cusps that also enable outflows of matter from the torus in the Newtonian regime. These phenomena qualitatively represent a new consequence of the interplay between gravity and electromagnetism. From an astrophysical point of view, our investigation can provide insight into processes that determine the vertical structure of dusty tori surrounding accretion disks.

  19. Nonequilibrium condensation and coarsening of field-driven dipolar colloids

    NASA Astrophysics Data System (ADS)

    Jäger, Sebastian; Schmidle, Heiko; Klapp, Sabine H. L.

    2012-07-01

    In colloidal suspensions, self-organization processes can be easily fueled by external fields. Here we consider monolayers of particles with permanent dipole moments that are driven by rotating external fields. In recent experiments, it has been shown that the particles in such systems self-organize into two-dimensional clusters. Here we report results from a computer simulation study of these pattern forming systems. Specifically, we employ Langevin dynamics simulations, Brownian dynamics simulations that include hydrodynamic interactions, and Wang-Landau Monte Carlo simulations of soft spheres interacting via dipolar potentials. We investigate at which field strengths and frequencies clusters form and explore the influence of hydrodynamic interactions. We also examine the phase behavior of the equilibrium system resulting from a time average of the colloidal interactions in the rotating field. In this way we demonstrate that the clustering described in the driven system arises from a first-order phase transition between a vapor and a condensed phase.

  20. Fibonacci anyon excitations of one-dimensional dipolar lattice bosons

    NASA Astrophysics Data System (ADS)

    Äńurić, Tanja; Biedroń, Krzysztof; Zakrzewski, Jakub

    2017-02-01

    We study a system of dipolar bosons in a one-dimensional optical lattice using exact diagonalization and density matrix renormalization group methods. In particular, we analyze low energy properties of the system at an average filling of 3/2 atoms per lattice site. We identify the region of the parameter space where the system has non-Abelian Fibonacci anyon excitations that correspond to fractional domain walls between different charge-density waves. When such one-dimensional systems are combined into a two-dimensional network, braiding of Fibonacci anyon excitations has potential application for fault tolerant, universal, topological quantum computation. Contrary to previous calculations, our results also demonstrate that super-solid phases are not present in the phase diagram for the discussed 3/2 average filling. Instead, decreasing the value of the nearest-neighbor tunneling strength leads to a direct, Berezinskii-Kosterlitz-Thouless, superfluid to charge-density-wave quantum phase transition.

  1. Shielding ultracold dipolar molecular collisions with electric fields

    NASA Astrophysics Data System (ADS)

    Quéméner, Goulven; Bohn, John

    2016-05-01

    The prospect for shielding ultracold dipolar molecules from inelastic and reactive collisions is investigated. Molecules placed in their first rotationally excited states are found to exhibit effective long-range repulsion for applied electric fields above a certain critical value. This repulsion can safely allow the molecules to scatter while reducing the risk of inelastic or chemically reactive collisions. Several molecular species of molecules of experimental interest such as NaRb, NaK, RbSr, SrF, BaF, and YO, are considered and all are shown to exhibit orders of magnitude suppression in quenching rates in a sufficiently strong laboratory electric field. We acknowledge the financial support of the COPOMOL project (ANR-13-IS04-0004) from Agence Nationale de la Recherche and the ARO MURI Grant No. W911NF-12-1-0476.

  2. Optical force and torque on dipolar dual chiral particles

    NASA Astrophysics Data System (ADS)

    Rahimzadegan, A.; Fruhnert, M.; Alaee, R.; Fernandez-Corbaton, I.; Rockstuhl, C.

    2016-09-01

    On the one hand, electromagnetic dual particles preserve the helicity of light upon interaction. On the other hand, chiral particles respond differently to light of opposite helicity. These two properties on their own constitute a source of fascination. Their combined action, however, is less explored. Here, we study on analytical grounds the force and torque as well as the optical cross sections of dual chiral particles in the dipolar approximation exerted by a particular wave of well-defined helicity: A circularly polarized plane wave. We put emphasis on particles that possess a maximally electromagnetic chiral and hence dual response. Besides the analytical insights, we also investigate the exerted optical force and torque on a real particle using the example of a metallic helix that is designed to approach the maximal electromagnetic chirality condition. Various applications in the context of optical sorting but also nanorobotics can be foreseen considering the particles studied in this contribution.

  3. Nonequilibrium condensation and coarsening of field-driven dipolar colloids.

    PubMed

    Jäger, Sebastian; Schmidle, Heiko; Klapp, Sabine H L

    2012-07-01

    In colloidal suspensions, self-organization processes can be easily fueled by external fields. Here we consider monolayers of particles with permanent dipole moments that are driven by rotating external fields. In recent experiments, it has been shown that the particles in such systems self-organize into two-dimensional clusters. Here we report results from a computer simulation study of these pattern forming systems. Specifically, we employ Langevin dynamics simulations, Brownian dynamics simulations that include hydrodynamic interactions, and Wang-Landau Monte Carlo simulations of soft spheres interacting via dipolar potentials. We investigate at which field strengths and frequencies clusters form and explore the influence of hydrodynamic interactions. We also examine the phase behavior of the equilibrium system resulting from a time average of the colloidal interactions in the rotating field. In this way we demonstrate that the clustering described in the driven system arises from a first-order phase transition between a vapor and a condensed phase.

  4. Dipolar bilayer with antiparallel polarization: A self-bound liquid

    NASA Astrophysics Data System (ADS)

    Hebenstreit, Martin; Rader, Michael; Zillich, Robert E.

    2016-01-01

    Dipolar bilayers with antiparallel polarization, i.e., opposite polarization in the two layers, exhibit liquidlike rather than gaslike behavior. In particular, even without external pressure, a self-bound liquid droplet of constant density will form. We investigate the symmetric case of two identical layers, corresponding to a two-component Bose system with equal partial densities. The zero-temperature equation of state E (ρ )/N , where ρ is the total density, has a minimum, with an equilibrium density that can be adjusted by the distance d between the layers (decreasing with increasing d ). The attraction necessary for a self-bound liquid comes from the interlayer dipole-dipole interaction that leads to a mediated intralayer attraction. We investigate the regime of negative pressure towards the spinodal instability, where the bilayer is unstable against infinitesimal fluctuations of the total density, confirmed by calculations of the speed of sound of total density fluctuations.

  5. Strongly dipolar fluids at low densities compared to living polymers

    NASA Astrophysics Data System (ADS)

    Tavares, J. M.; Weis, J. J.; Telo da Gama, M. M.

    1999-04-01

    We carried out extensive canonical Monte Carlo (MC) simulations of the dipolar hard-sphere (DHS) fluid, with N=1024 particles at fixed reduced density ρ*=0.05, in order to investigate the chainlike structure that occurs at low densities, for sufficiently large reduced dipole moments μ*. The dissociation and recombination of chains during equilibrium runs suggest an analogy between the DHS's and a system of living polymers. This was checked quantitatively by comparing the results of the simulations with those of a theory for living polymers taking into account the indistinguishability of the particles in self-assembled chains. Quantitative agreement between theoretical and simulated mean chain lengths and number of monomers, was found for particular choices of the parameters used in the working definition of the MC chains.

  6. Plasmonic Toroidal Dipolar Response under Radially Polarized Excitation

    PubMed Central

    Bao, Yanjun; Zhu, Xing; Fang, Zheyu

    2015-01-01

    Plasmonic toroidal resonance has attracted growing interests because of its low loss electromagnetic properties and potential high sensitive nanophotonic applications. However, the realization in a metamaterial requires three-dimensional complicated structural design so far. In this paper, we design a simple metal-dielectric-metal (MIM) sandwich nanostructure, which exhibits a strong toroidal dipolar resonance under radially polarized excitation. The toroidal dipole moment as the dominant contribution for the scattering is demonstrated by the mirror-image method and further analyzed by Lagrangian hybridization model. The proposed toroidal configuration also shows a highly tolerant for misalignment between the structure center and the incident light focus. Our study proves the way for the toroidal plasmonic application with the cylindrical vector beams. PMID:26114966

  7. Tunnel Splitting Distributions and Dipolar Shuffling in Mn12-acetate

    NASA Astrophysics Data System (ADS)

    Mertes, K. M.; Suzuki, Yoko; Sarachik, M. P.; Rumberger, E. M.; Hendrickson, D. N.; Christou, G.; Myasoedov, Y.; Shtrikman, H.; Zeldov, E.

    2003-03-01

    In magnetic fields applied parallel to the anisotropy axis, the magnetization of Mn12 has been measured in response to a field that is swept back and forth across each of the ground state energy resonances corresponding to steps N=4...9, which provides a means of more directly [1] determining the distribution of tunnel splittings. The analysis of the data in terms of a distribution of tunnel splittings will be presented. Deviations from the expected curves at slow sweep rates are attributed to dipolar shuffling [2] which results in a redistribution of internal magnetic fields whenever a molecule tunnels. [1] K. M. Mertes, Yoko Suzuki, M. P. Sarachik, Y. Paltiel, H. Shtrikman, E. Zeldov, E. M. Rumberger, D. N. Hendrickson and G. Christou, Phys. Rev. Lett. 87, 227205 (2001) [2] Jie Liu, Biao Wu, Libin Fu, R. B. Diener and Qian Niu, Phys. Rev. B, 65 224401 (2002)

  8. Fragmentation of magnetism in artificial kagome dipolar spin ice

    PubMed Central

    Canals, Benjamin; Chioar, Ioan-Augustin; Nguyen, Van-Dai; Hehn, Michel; Lacour, Daniel; Montaigne, François; Locatelli, Andrea; Menteş, Tevfik Onur; Burgos, Benito Santos; Rougemaille, Nicolas

    2016-01-01

    Geometrical frustration in magnetic materials often gives rise to exotic, low-temperature states of matter, such as the ones observed in spin ices. Here we report the imaging of the magnetic states of a thermally active artificial magnetic ice that reveal the fingerprints of a spin fragmentation process. This fragmentation corresponds to a splitting of the magnetic degree of freedom into two channels and is evidenced in both real and reciprocal space. Furthermore, the internal organization of both channels is interpreted within the framework of a hybrid spin–charge model that directly emerges from the parent spin model of the kagome dipolar spin ice. Our experimental and theoretical results provide insights into the physics of frustrated magnets and deepen our understanding of emergent fields through the use of tailor-made magnetism. PMID:27173154

  9. Strongly Correlated States of Ultracold Rotating Dipolar Fermi Gases

    SciTech Connect

    Osterloh, Klaus; Barberan, Nuria; Lewenstein, Maciej

    2007-10-19

    We study strongly correlated ground and excited states of rotating quasi-2D Fermi gases constituted of a small number of dipole-dipole interacting particles with dipole moments polarized perpendicular to the plane of motion. As the number of atoms grows, the system enters an intermediate regime, where ground states are subject to a competition between distinct bulk-edge configurations. This effect obscures their description in terms of composite fermions and leads to the appearance of novel quasihole ground states. In the presence of dipolar interactions, the principal Laughlin state at filling {nu}=1/3 exhibits a substantial energy gap for neutral (total angular momentum conserving) excitations and is well-described as an incompressible Fermi liquid. Instead, at lower fillings, the ground state structure favors crystalline order.

  10. Fragmentation of magnetism in artificial kagome dipolar spin ice.

    PubMed

    Canals, Benjamin; Chioar, Ioan-Augustin; Nguyen, Van-Dai; Hehn, Michel; Lacour, Daniel; Montaigne, François; Locatelli, Andrea; Menteş, Tevfik Onur; Burgos, Benito Santos; Rougemaille, Nicolas

    2016-05-13

    Geometrical frustration in magnetic materials often gives rise to exotic, low-temperature states of matter, such as the ones observed in spin ices. Here we report the imaging of the magnetic states of a thermally active artificial magnetic ice that reveal the fingerprints of a spin fragmentation process. This fragmentation corresponds to a splitting of the magnetic degree of freedom into two channels and is evidenced in both real and reciprocal space. Furthermore, the internal organization of both channels is interpreted within the framework of a hybrid spin-charge model that directly emerges from the parent spin model of the kagome dipolar spin ice. Our experimental and theoretical results provide insights into the physics of frustrated magnets and deepen our understanding of emergent fields through the use of tailor-made magnetism.

  11. Properties of a dipolar condensate with three-body interactions

    NASA Astrophysics Data System (ADS)

    Blakie, Peter

    2016-05-01

    We discuss the properties of a harmonically trapped dilute dipolar condensate with a short ranged conservative three-body interaction. We show that this system supports two distinct fluid states: a usual condensate state and a self-cohering droplet state. We develop a simple model to quantify the energetics of these states, which we verify with full numerical calculations. Based on our simple model we develop a phase diagram showing that there is a first order phase transition between the states. Using dynamical simulations we explore the phase transition dynamics, revealing that the droplet crystal observed in previous work is an excited state that arises from heating as the system crosses the phase transition. Utilising our phase diagram we show it is feasible to produce a single droplet by dynamically adjusting the confining potential. We acknowledge support from the Marsden Fund of New Zealand.

  12. Toroidal dipolar excitation and macroscopic electromagnetic properties of metamaterials

    NASA Astrophysics Data System (ADS)

    Savinov, V.; Fedotov, V. A.; Zheludev, N. I.

    2014-05-01

    The toroidal dipole is a peculiar electromagnetic excitation that can not be presented in terms of standard electric and magnetic multipoles. A static toroidal dipole has been shown to lead to violation of parity in atomic spectra and many other unusual electromagnetic phenomena. The existence of electromagnetic resonances of toroidal nature was experimentally demonstrated only recently, first in the microwave metamaterials, and then at optical frequencies, where they could be important in spectroscopy analysis of a wide class of media with constituents of toroidal symmetry, such as complex organic molecules, fullerenes, bacteriophages, etc. Despite the experimental progress in studying toroidal resonances, no direct link has yet been established between microscopic toroidal excitations and macroscopic scattering characteristics of the medium. To address this essential gap in the electromagnetic theory, we have developed an analytical approach for calculating the transmissivity and reflectivity of thin slabs of materials that exhibit toroidal dipolar excitations.

  13. Evolution of dipolarization fronts observed by Cluster and MMS

    NASA Astrophysics Data System (ADS)

    Schmid, Daniel; Nakamura, Rumi; Plaschke, Ferdinand; Volwerk, Martin; Narita, Yasuhito; Baumjohann, Wolfgang; Magnes, Werner; Fischer, David; Tobert, Roy; Russel, Christopher T.; Strangeway, Robert J.; Leinweber, Hannes; Bormund, Kenneth; Anderson, Brian J.; Le, Guan; Chutter, Mark; Slavin, James A.; Kepko, Larry; Moldwin, Mark; LeContel, Oliver

    2016-04-01

    Dipolarization fronts (DFs) are characterized by a rapid increase in the northward magnetic field component (B_z) and play a crucial role in the energy and magnetic flux transport in the magnetotail. Multispacecraft observations of DFs in a large portion of the magnetotail by e.g. Geotail, Cluster and THEMIS have been reported for over three decades. During the commissioning phase of MMS the spacecraft observed DFs in a string of pearl configuration at radial distances within 12 Re, and hence events within the flow braking region are also included. We present a statistical study of DFs, using magnetic field data from both MMS and Cluster at radial distances between 12-20 Re and interspacecraft distances less than 200 km.The amplitude of the DFs observed by MMS is larger compared to similar events observed by Cluster further down the tail as expected from flow braking. Both spacecraft flotillas found that DFs with velocities greater than 100 km/s are observed when the field is in a more dipolar field configuration (higher average B_z), are temporally shorter and spatially larger, compared to slow propagating DFs (velocities smaller than 100 km/s). This relationship between velocity and Bz indicates a higher flux transport rate when the ambient Bz is larger and is not expected when the flow is simply stopping in a near-Earth dipole region. It suggest rather that the flow with high flux transport rate causes an enhanced magnetic flux pileup ahead of the front or importance of additional processes such as rebound (bouncing) of the DF at the magnetic dipole-dominated near-Earth plasma sheet.

  14. Two states of magnetotail dipolarization fronts: A statistical study

    PubMed Central

    Schmid, D; Nakamura, R; Plaschke, F; Volwerk, M; Baumjohann, W

    2015-01-01

    We study the ion density and temperature in the predipolarization and postdipolarization plasma sheets in the Earth's magnetotail using 9 years (2001–2009) of Cluster data. For our study we selected cases when Cluster observed dipolarization fronts (DFs) with an earthward plasma flow greater than 150km/s. We perform a statistical study of the temperature and density variations during the DF crossings. Earlier studies concluded that on average, the temperature increases while the density decreases across the DF. Our statistical results show a more diverse picture: While ∼54% of the DFs follow this pattern (category A), for ∼28% the temperature decreases while the density increases across the DF (category B). We found an overall decrease in thermal pressure for category A DFs with a more pronounced decrease at the DF duskside, while DFs of category B showed no clear pattern in the pressure change. Both categories are associated with earthward plasma flows but with some difference: (1) category A flows are faster than category B flows, (2) the observations indicate that category B flows are directed perpendicular to the current in the near-Earth current sheet while category A flows are tilted slightly duskward from this direction, and (3) the background Bz of category B is higher than that of category A. Based on these results, we hypothesize that after reconnection takes place, a bursty bulk flow emerges with category A characteristics, and as it travels earthward, it further evolves into category B characteristics, which is in a more dipolarized region with slower plasma flow (closer to the flow-braking region). PMID:26167443

  15. Ordering and short-time orientational diffusion in dipolar hard-spherical colloids.

    PubMed

    Alarcón-Waess, O; Diaz-Herrera, E

    2002-03-01

    Orientational hydrodynamic functions and short-time, self-orientational and collective orientational diffusion coefficients of dipolar hard-spherical colloids are performed on a homogeneous isotropic phase, as functions of the wave vector q, for various values of the volume fraction and the dipolar strength of the macroparticles. The calculation is based on the dynamic orientational structure factor, which is the time-dependent self-correlation of the orientation density. We assume that the time evolution of the orientation density is given by the Smoluchoswki's equation, taking into account the hydrodynamic interactions as well as the dipolar interaction. The former are considered assuming pairwise additivity. The importance of the dynamic orientational structure factor is that its initial slope can be measured in a depolarized light scattering experiment. The results predict a different behavior for dilute and for dense dipolar colloids. The ordering phenomena are studied via the ordering coefficients, which are the orientational hydrodynamic functions at q=0. The results show that as the dipolar colloid evolves to the instability line, the translational ordering velocity increases while the rotational one reduces. The short-time orientational diffusion coefficients at q=0 are also performed. They predict that near to the instability line, the dipolar colloid diffuses translationally more than rotationally. At very dilute concentration the dipolar colloid presents an unexpected dynamical behavior, which seems to indicate that the colloid could be evolving to a reentrant phase.

  16. Optical Switching Using Transition from Dipolar to Charge Transfer Plasmon Modes in Ge2Sb2Te5 Bridged Metallodielectric Dimers

    PubMed Central

    Ahmadivand, Arash; Gerislioglu, Burak; Sinha, Raju; Karabiyik, Mustafa; Pala, Nezih

    2017-01-01

    Capacitive coupling and direct shuttling of charges in nanoscale plasmonic components across a dielectric spacer and through a conductive junction lead to excitation of significantly different dipolar and charge transfer plasmon (CTP) resonances, respectively. Here, we demonstrate the excitation of dipolar and CTP resonant modes in metallic nanodimers bridged by phase-change material (PCM) sections, material and electrical characteristics of which can be controlled by external stimuli. Ultrafast switching (in the range of a few nanoseconds) between amorphous and crystalline phases of the PCM section (here Ge2Sb2Te5 (GST)) allows for designing a tunable plasmonic switch for optical communication applications with significant modulation depth (up to 88%). Judiciously selecting the geometrical parameters and taking advantage of the electrical properties of the amorphous phase of the GST section we adjusted the extinction peak of the dipolar mode at the telecommunication band (λ~1.55 μm), which is considered as the OFF state. Changing the GST phase to crystalline via optical heating allows for direct transfer of charges through the junction between nanodisks and formation of a distinct CTP peak at longer wavelengths (λ~1.85 μm) far from the telecommunication wavelength, which constitutes the ON state. PMID:28205643

  17. Optical Switching Using Transition from Dipolar to Charge Transfer Plasmon Modes in Ge2Sb2Te5 Bridged Metallodielectric Dimers.

    PubMed

    Ahmadivand, Arash; Gerislioglu, Burak; Sinha, Raju; Karabiyik, Mustafa; Pala, Nezih

    2017-02-16

    Capacitive coupling and direct shuttling of charges in nanoscale plasmonic components across a dielectric spacer and through a conductive junction lead to excitation of significantly different dipolar and charge transfer plasmon (CTP) resonances, respectively. Here, we demonstrate the excitation of dipolar and CTP resonant modes in metallic nanodimers bridged by phase-change material (PCM) sections, material and electrical characteristics of which can be controlled by external stimuli. Ultrafast switching (in the range of a few nanoseconds) between amorphous and crystalline phases of the PCM section (here Ge2Sb2Te5 (GST)) allows for designing a tunable plasmonic switch for optical communication applications with significant modulation depth (up to 88%). Judiciously selecting the geometrical parameters and taking advantage of the electrical properties of the amorphous phase of the GST section we adjusted the extinction peak of the dipolar mode at the telecommunication band (λ~1.55 μm), which is considered as the OFF state. Changing the GST phase to crystalline via optical heating allows for direct transfer of charges through the junction between nanodisks and formation of a distinct CTP peak at longer wavelengths (λ~1.85 μm) far from the telecommunication wavelength, which constitutes the ON state.

  18. Optical Switching Using Transition from Dipolar to Charge Transfer Plasmon Modes in Ge2Sb2Te5 Bridged Metallodielectric Dimers

    NASA Astrophysics Data System (ADS)

    Ahmadivand, Arash; Gerislioglu, Burak; Sinha, Raju; Karabiyik, Mustafa; Pala, Nezih

    2017-02-01

    Capacitive coupling and direct shuttling of charges in nanoscale plasmonic components across a dielectric spacer and through a conductive junction lead to excitation of significantly different dipolar and charge transfer plasmon (CTP) resonances, respectively. Here, we demonstrate the excitation of dipolar and CTP resonant modes in metallic nanodimers bridged by phase-change material (PCM) sections, material and electrical characteristics of which can be controlled by external stimuli. Ultrafast switching (in the range of a few nanoseconds) between amorphous and crystalline phases of the PCM section (here Ge2Sb2Te5 (GST)) allows for designing a tunable plasmonic switch for optical communication applications with significant modulation depth (up to 88%). Judiciously selecting the geometrical parameters and taking advantage of the electrical properties of the amorphous phase of the GST section we adjusted the extinction peak of the dipolar mode at the telecommunication band (λ~1.55 μm), which is considered as the OFF state. Changing the GST phase to crystalline via optical heating allows for direct transfer of charges through the junction between nanodisks and formation of a distinct CTP peak at longer wavelengths (λ~1.85 μm) far from the telecommunication wavelength, which constitutes the ON state.

  19. Finite-length Fe nanowire arrays: the effects of magnetic anisotropy energy, dipolar interaction and system size on their magnetic properties

    NASA Astrophysics Data System (ADS)

    Ochoa, Andrés; Mejía-López, J.; Velásquez, E. A.; Mazo-Zuluaga, J.

    2017-03-01

    In this study we report on the magnetic properties of finite-length Fe nanowire arrays. The samples are built from nanowires that exhibit different anisotropy directions. There are L h-long wires per side, which are separated from each other by a distance d. h and d vary in the ranges 0.7–40.0 nm and 2.0–20.0 nm, respectively. These features allow us to discuss the dependence of the magnetic properties on the direction of the anisotropy, and the length of the wires and the separation between them. The system’s Hamiltonian is composed of (i) the magnetocrystalline anisotropy energy, which depends on the spin–orbit coupling; (ii) the dipolar interactions between the atomic magnetic moments comprising the wires (which give place to the shape anisotropy); (iii) the Zeeman interaction with an external magnetic field; and (iv) the dipolar interactions between the individual wires. We present and discuss the interesting non-monotonic dependences of the coercivity and remanence on the related parameters. We also discuss the interplay between size and the effects of dipolar and magnetic anisotropy energies. Our results indicate that the magnetic configurations and anisotropy properties can be tailored by tuning the length of the wires, their separation distances and the size of the arrays, which might be of interest for experiments in the field of technical applications.

  20. Fermion production in dipolar electric field on de Sitter expanding universe

    SciTech Connect

    Băloi, Mihaela-Andreea Crucean, Cosmin

    2015-12-07

    The production of fermions in dipolar electric fields on de Sitter universe is studied. The amplitude and probability of pair production are computed using the exact solution of the Dirac equation in de Sitter spacetime. The form of the dipolar fields is established using the conformal invariance of the Maxwell equations. We obtain that the momentum conservation law is broken in the process of pair production in dipolar electric fields. Also we establish that there are nonvanishing probabilities for processes in which the helicity is conserved/nonconserved. The Minkowski limit is recovered when the expansion factor becomes zero.

  1. Van Allen Probes observations of dipolarization and its associated O+ flux variations in the inner magnetosphere

    NASA Astrophysics Data System (ADS)

    Nose, M.; Keika, K.; Kletzing, C.; Smith, C. W.; MacDowall, R. J.; Reeves, G. D.; Spence, H. E.

    2015-12-01

    Recent study employing the MDS-1 satellite reveals that magnetic field dipolarization in the deep inner magnetosphere is not unusual. When the MDS-1 satellite was located at L=3.5-5.0 near the auroral onset longitude (MLT difference of ≤2.5 h), the occurrence probability of local dipolarization was about 16%. Surprisingly, an event was found at L~3.6, far inside the geosynchronous altitude. It was also shown that after the dipolarization, the oxygen ENA flux in the nightside ring current region measured by the IMAGE satellite was predominantly enhanced by a factor of 2-5 and stayed at an enhanced level for more than 1 h, while clear enhancement was scarcely seen in the hydrogen ENA flux. To better understand mechanisms of the selective acceleration of O+ ions during dipolarization, an in-situ measurement of ion fluxes is needed. However, there are few studies investigating H+ and O+ flux variations during dipolarization in the deep inner magnetosphere. In this study we investigate magnetic field dipolarization and its associated ion flux variations in the deep inner magnetosphere, using magnetic field and ion flux data obtained by the Van Allen Probes. From the magnetic field data recorded on the nightside (1800-0600 MLT) in the inner magnetosphere (L=3.0-6.6) in VDH coordinates, we select substorm-related dipolarization events in which the H component increases by more than 20 nT and the absolute value of the V component decreases by more than 8 nT in 5 minutes. About 150 dipolarization events are identified from 1 October 2012 to 30 June 2015. We find that the dipolarization mostly occurs at L=4.5-6.5 in the premidnight sector (2100-0000 MLT). No events are found at L<4.0. Some dipolarization events are accompanied by O+ flux enhancements in the energy range higher than a few keV, which have the pitch angle distribution peaked around 45 or 135 degrees. We also find that low energy O+ ions often appear after dipolarization with an energy dispersion starting from

  2. Phase transitions of two-dimensional dipolar fluids in external fields.

    PubMed

    Schmidle, Heiko; Klapp, Sabine H L

    2011-03-21

    In this work, we study condensation phase transitions of two-dimensional Stockmayer fluids under additional external fields using Monte-Carlo (MC) simulations in the grand-canonical ensemble. We employ two recently developed methods to determine phase transitions in fluids, namely Wang-Landau (WL) MC simulations and successive-umbrella (SU) sampling. Considering first systems in zero field (and dipolar coupling strengths μ(2)∕εσ(3) ≤ 6), we demonstrate that the two techniques yield essentially consistent results but display pronounced differences in terms of efficiency. Indeed, comparing the computation times for these systems on a qualitative level, the SU sampling turns out to be significantly faster. In the presence of homogeneous external fields, however, the SU method becomes plagued by pronounced sampling difficulties, yielding the calculation of coexistence lines essentially impossible. Employing the WL scheme, on the other hand, we find phase coexistence even for strongly field-aligned systems. The corresponding critical temperatures are significantly shifted relative to the zero-field case.

  3. Atomic-scale sensing of the magnetic dipolar field from single atoms.

    PubMed

    Choi, Taeyoung; Paul, William; Rolf-Pissarczyk, Steffen; Macdonald, Andrew J; Natterer, Fabian D; Yang, Kai; Willke, Philip; Lutz, Christopher P; Heinrich, Andreas J

    2017-03-06

    Spin resonance provides the high-energy resolution needed to determine biological and material structures by sensing weak magnetic interactions. In recent years, there have been notable achievements in detecting and coherently controlling individual atomic-scale spin centres for sensitive local magnetometry. However, positioning the spin sensor and characterizing spin-spin interactions with sub-nanometre precision have remained outstanding challenges. Here, we use individual Fe atoms as an electron spin resonance (ESR) sensor in a scanning tunnelling microscope to measure the magnetic field emanating from nearby spins with atomic-scale precision. On artificially built assemblies of magnetic atoms (Fe and Co) on a magnesium oxide surface, we measure that the interaction energy between the ESR sensor and an adatom shows an inverse-cube distance dependence (r(-3.01±0.04)). This demonstrates that the atoms are predominantly coupled by the magnetic dipole-dipole interaction, which, according to our observations, dominates for atom separations greater than 1 nm. This dipolar sensor can determine the magnetic moments of individual adatoms with high accuracy. The achieved atomic-scale spatial resolution in remote sensing of spins may ultimately allow the structural imaging of individual magnetic molecules, nanostructures and spin-labelled biomolecules.

  4. Chiral spin-wave edge modes in dipolar magnetic thin films

    NASA Astrophysics Data System (ADS)

    Shindou, Ryuichi; Ohe, Jun-ichiro; Matsumoto, Ryo; Murakami, Shuichi; Saitoh, Eiji

    2013-05-01

    Based on a linearized Landau-Lifshitz equation, we show that two-dimensional periodic allay of ferromagnetic particles coupled with magnetic dipole-dipole interactions supports chiral spin-wave edge modes, when subjected under the magnetic field applied perpendicular to the plane. The mode propagates along a one-dimensional boundary of the system in a unidirectional way and it always has a chiral dispersion within a band gap for spin-wave volume modes. Contrary to the well-known Damon-Eshbach surface mode, the sense of the rotation depends not only on the direction of the field but also on the strength of the field; its chiral direction is generally determined by the sum of the so-called Chern integers defined for spin-wave volume modes below the band gap. Using simple tight-binding descriptions, we explain how the magnetic dipolar interaction endows spin-wave volume modes with nonzero Chern integers and how their values will be changed by the field.

  5. Phase transitions of two-dimensional dipolar fluids in external fields

    NASA Astrophysics Data System (ADS)

    Schmidle, Heiko; Klapp, Sabine H. L.

    2011-03-01

    In this work, we study condensation phase transitions of two-dimensional Stockmayer fluids under additional external fields using Monte-Carlo (MC) simulations in the grand-canonical ensemble. We employ two recently developed methods to determine phase transitions in fluids, namely Wang-Landau (WL) MC simulations and successive-umbrella (SU) sampling. Considering first systems in zero field (and dipolar coupling strengths μ2/ɛσ3 ⩽ 6), we demonstrate that the two techniques yield essentially consistent results but display pronounced differences in terms of efficiency. Indeed, comparing the computation times for these systems on a qualitative level, the SU sampling turns out to be significantly faster. In the presence of homogeneous external fields, however, the SU method becomes plagued by pronounced sampling difficulties, yielding the calculation of coexistence lines essentially impossible. Employing the WL scheme, on the other hand, we find phase coexistence even for strongly field-aligned systems. The corresponding critical temperatures are significantly shifted relative to the zero-field case.

  6. Effects of a perpendicular magnetic field in the dipolar Heisenberg model with dominant exchange interaction.

    PubMed

    Abu-Labdeh, A M; MacIsaac, A B; De'Bell, K

    2011-07-27

    The effects of a uniform magnetic field on the phase diagram of the dipolar Heisenberg model with a dominant antiferromagnetic exchange interaction have been investigated. The model consists of a square lattice of classical spin vectors, where the spins interact through an antiferromagnetic exchange interaction of strength J and a dipole-dipole interaction of strength g. The spins couple to a magnetic surface anisotropy of strength κ and to an applied external magnetic field of strength H. The external field is applied perpendicular to the plane of the lattice. From extensive Monte Carlo simulations, representative magnetic phase diagrams have been determined as a function of the ratios κ/g and T/g, where T is temperature, and at three different ratios of H/g (H/g = 10, 20, 27). These results are compared to the previously investigated case of H/g = 0 and to analytic calculations for the ground state energies. The nature of the equilibrium phases and order of the phase boundaries separating them are considered and changes due to the strength of the applied field are highlighted.

  7. Ground states of dipolar gases in quasi-one-dimensional ring traps

    SciTech Connect

    Zoellner, Sascha

    2011-12-15

    We compute the ground state of dipoles in a quasi-one-dimensional ring trap using few-body techniques combined with analytical arguments. The effective interaction between two dipoles depends on their center-of-mass coordinate and can be tuned by varying the angle between dipoles and the plane of the ring. For sufficiently weak interactions, the state resembles a weakly interacting Fermi gas or a (inhomogeneous) Lieb-Liniger gas. A mapping between the Lieb-Liniger-gas parameters and the dipolar-gas parameters in and beyond the Born approximation is established, and we discuss the effect of inhomogeneities based on a local-density approximation. For strongly repulsive interactions, the system exhibits a crystal-like localization of the particles. Their inhomogeneous distribution may be understood in terms of a simple few-body model as well as a local-density approximation. In the case of partially attractive interactions, clustered states form for sufficiently strong coupling, and the dependence of the state on particle number and orientation angle of the dipoles is discussed analytically.

  8. Water Alignment, Dipolar Interactions, and Multiple Proton Occupancy during Water-Wire Proton Transport

    PubMed Central

    Chou, Tom

    2004-01-01

    A discrete multistate kinetic model for water-wire proton transport is constructed and analyzed using Monte Carlo simulations. In the model, each water molecule can be in one of three states: oxygen lone-pairs pointing leftward, pointing rightward, or protonated (H3O+). Specific rules for transitions among these states are defined as protons hop across successive water oxygens. Our model also includes water-channel interactions that preferentially align the water dipoles, nearest-neighbor dipolar coupling interactions, and Coulombic repulsion. Extensive Monte Carlo simulations were performed and the observed qualitative physical behaviors discussed. We find the parameters that allow the model to exhibit superlinear and sublinear current-voltage relationships, and show why alignment fields, whether generated by interactions with the pore interior or by membrane potentials, always decrease the proton current. The simulations also reveal a “lubrication” mechanism that suppresses water dipole interactions when the channel is multiply occupied by protons. This effect can account for an observed sublinear-to-superlinear transition in the current-voltage relationship. PMID:15111400

  9. Pulse-assisted homonuclear dipolar recoupling of half-integer quadrupolar spins in magic-angle spinning NMR

    NASA Astrophysics Data System (ADS)

    Edén, Mattias; Annersten, Hans; Zazzi, Åsa

    2005-07-01

    We demonstrate numerically and experimentally that zero-quantum homonuclear dipolar recoupling techniques employing rotor-synchronized 180° pulses, previously introduced for spin-1/2 applications, are useful also for magnetization transfers between half-integer quadrupolar nuclei in rotating solids. The recoupling sequences are incorporated as mixing periods in two-dimensional experimental protocols, that correlate either single-quantum coherences of coupled spins, or triple-quantum with single-quantum coherences for improving spectral resolution. We present 23Na and 27Al NMR experiments on powders of sodium sulphite [Na 2SO 3], YAG [Y 3Al 5O 12] and a synthetic chlorite mineral [Mg 4.5Al 3Si 2.5O 10(OH) 8].

  10. Thermal 1,3-dipolar cycloaddition reaction of azomethine imines with active esters.

    PubMed

    He, Liwenze; Liu, Lin; Han, Runfeng; Zhang, Weiwei; Xie, Xingang; She, Xuegong

    2016-07-12

    An efficient method for the 1,3-dipolar cycloaddition of azomethine imines with active esters under thermal conditions has been described in good to high yields. This method offers a straightforward pathway to synthesize bioactive pyrazolidinones.

  11. Exploring the stability and dynamics of dipolar matter-wave dark solitons

    NASA Astrophysics Data System (ADS)

    Edmonds, M. J.; Bland, T.; O'Dell, D. H. J.; Parker, N. G.

    2016-06-01

    We study the stability, form, and interaction of single and multiple dark solitons in quasi-one-dimensional dipolar Bose-Einstein condensates. The solitons are found numerically as stationary solutions in the moving frame of a nonlocal Gross Pitaevskii equation and characterized as a function of the key experimental parameters, namely the ratio of the dipolar atomic interactions to the van der Waals interactions, the polarization angle, and the condensate width. The solutions and their integrals of motion are strongly affected by the phonon and roton instabilities of the system. Dipolar matter-wave dark solitons propagate without dispersion and collide elastically away from these instabilities, with the dipolar interactions contributing an additional repulsion or attraction to the soliton-soliton interaction. However, close to the instabilities, the collisions are weakly dissipative.

  12. Spectral collocation and a two-level continuation scheme for dipolar Bose-Einstein condensates

    NASA Astrophysics Data System (ADS)

    Jeng, B.-W.; Chien, C.-S.; Chern, I.-L.

    2014-01-01

    We exploit the high accuracy of spectral collocation methods in the context of a two-level continuation scheme for computing ground state solutions of dipolar Bose-Einstein condensates (BEC), where the first kind Chebyshev polynomials and Fourier sine functions are used as the basis functions for the trial function space. The governing Gross-Pitaevskii equation (or Schrödinger equation) can be reformulated as a Schrödinger-Poisson (SP) type system [13]. The two-level continuation scheme is developed for tracing the first solution curves of the SP system, which in turn provide an appropriate initial guess for the Newton method to compute ground state solutions for 3D dipolar BEC. Extensive numerical experiments on 3D dipolar BEC and dipolar BEC in optical lattices are reported.

  13. Many-Body Dynamics of Dipolar Molecules in an Optical Lattice

    NASA Astrophysics Data System (ADS)

    Hazzard, Kaden R. A.; Gadway, Bryce; Foss-Feig, Michael; Yan, Bo; Moses, Steven A.; Covey, Jacob P.; Yao, Norman Y.; Lukin, Mikhail D.; Ye, Jun; Jin, Deborah S.; Rey, Ana Maria

    2014-11-01

    We use Ramsey spectroscopy to experimentally probe the quantum dynamics of disordered dipolar-interacting ultracold molecules in a partially filled optical lattice, and we compare the results to theory. We report the capability to control the dipolar interaction strength. We find excellent agreement between our measurements of the spin dynamics and theoretical calculations with no fitting parameters, including the dynamics' dependence on molecule number and on the dipolar interaction strength. This agreement verifies the microscopic model expected to govern the dynamics of dipolar molecules, even in this strongly correlated beyond-mean-field regime, and represents the first step towards using this system to explore many-body dynamics in regimes that are inaccessible to current theoretical techniques.

  14. Many-body dynamics of dipolar molecules in an optical lattice.

    PubMed

    Hazzard, Kaden R A; Gadway, Bryce; Foss-Feig, Michael; Yan, Bo; Moses, Steven A; Covey, Jacob P; Yao, Norman Y; Lukin, Mikhail D; Ye, Jun; Jin, Deborah S; Rey, Ana Maria

    2014-11-07

    We use Ramsey spectroscopy to experimentally probe the quantum dynamics of disordered dipolar-interacting ultracold molecules in a partially filled optical lattice, and we compare the results to theory. We report the capability to control the dipolar interaction strength. We find excellent agreement between our measurements of the spin dynamics and theoretical calculations with no fitting parameters, including the dynamics' dependence on molecule number and on the dipolar interaction strength. This agreement verifies the microscopic model expected to govern the dynamics of dipolar molecules, even in this strongly correlated beyond-mean-field regime, and represents the first step towards using this system to explore many-body dynamics in regimes that are inaccessible to current theoretical techniques.

  15. How to Observe Dipolar Effects in Spinor Bose-Einstein Condensates

    SciTech Connect

    Gawryluk, Krzysztof; Brewczyk, Miroslaw; Bongs, Kai

    2011-04-08

    We propose an experiment which proves the possibility of spinning gaseous media via dipolar interactions in the spirit of the famous Einstein-de Haas effect for ferromagnets. The main idea is to utilize resonances that we find in spinor condensates of alkali atoms while these systems are placed in an oscillating magnetic field. A significant transfer of angular momentum from spin to motional degrees of freedom observed on resonance is a spectacular manifestation of dipolar effects in spinor condensates.

  16. Dipolar nuclear spin relaxation in liquids and plane fluids undergoing chemical reactions

    NASA Astrophysics Data System (ADS)

    Fries, P. H.

    We describe the correlated translational and rotational relative brownian motions of two reacting groups of atoms, alternatively bound and free, by the normalized solutions of a set of coupled diffusion equations. Under equilibrium conditions we calculate the spectral densities j(ω) characteristic of the fluctuations of the intermolecular dipolar coupling between spins of these diffusing groups of atoms. When ωτ << 1, where τ is the translational correlation time, the form of the spectral density j2(ω) in three-dimensional liquids is j2(0) - α3ω1/2. The coefficient α3 is independent of the molecular local order, of the diffusional rotation speed of the spin-carrying groups of atoms and of their association and dissociation rates. In plane fluids, when ωτ << 1, the spectral density j(0)(ω) may be written as -a2 ln (ωτ) where the dependence of a2 on the average relative distribution of the interacting spins varies with the rate of the chemical reactions. In both three- and two-dimensional fluids spectral densities show an ω-3/2 or ω-2 behaviour for ωτ >> 1 according to the magnitude of the association rate of the reacting groups of atoms. In liquid glycerol we analyse the low- and high-frequency limits of the experimental proton relaxation rate 1/T1 and 1/T1ρ measured by Harmon, Harmon and Burnett, and Lenk. We also discuss the proton spin-lattice relaxation times measured by Kleinberg and Silbernagel in layered intercalation compounds TiS2-NH3 and TaS2-NH3.

  17. Vertical Phase Segregation Induced by Dipolar Interactions in Planar Polymer Brushes

    DOE PAGES

    Mahalik, Jyoti P.; Sumpter, Bobby G.; Kumar, Rajeev

    2016-09-13

    In this paper, we present a generalized theory for studying structural properties of a planar dipolar polymer brush immersed in a polar solvent. We show that an explicit treatment of the dipolar interactions yields a macroscopic concentration dependent effective “chi” (the Flory–Huggins-like interaction) parameter. Furthermore, it is shown that the concentration dependent chi parameter promotes phase segregation in polymer solutions and brushes so that the polymer-poor phase consists of a finite/nonzero polymer concentration. Such a destabilization of the homogeneous phase by the dipolar interactions appears as vertical phase segregation in a planar polymer brush. In a vertically phase segregated polymermore » brush, the polymer-rich phase near the grafting surface coexists with the polymer-poor phase at the other end. Predictions of the theory are directly compared with prior reported experimental results for dipolar polymers in polar solvents. Excellent agreements with the experimental results are found, hinting that the dipolar interactions play a significant role in vertical phase segregation of planar polymer brushes. We also compare our field theoretical approach with the two-state and other models invoking ad hoc concentration dependence of the chi parameter. Interplay between the short-ranged excluded volume interactions and long-ranged dipolar interactions is shown to play an important role in affecting the vertical phase separation. Finally, effects of mismatch between the dipole moments of the polymer segments and the solvent molecules are investigated in detail.« less

  18. Vertical Phase Segregation Induced by Dipolar Interactions in Planar Polymer Brushes

    SciTech Connect

    Mahalik, Jyoti P.; Sumpter, Bobby G.; Kumar, Rajeev

    2016-09-13

    In this paper, we present a generalized theory for studying structural properties of a planar dipolar polymer brush immersed in a polar solvent. We show that an explicit treatment of the dipolar interactions yields a macroscopic concentration dependent effective “chi” (the Flory–Huggins-like interaction) parameter. Furthermore, it is shown that the concentration dependent chi parameter promotes phase segregation in polymer solutions and brushes so that the polymer-poor phase consists of a finite/nonzero polymer concentration. Such a destabilization of the homogeneous phase by the dipolar interactions appears as vertical phase segregation in a planar polymer brush. In a vertically phase segregated polymer brush, the polymer-rich phase near the grafting surface coexists with the polymer-poor phase at the other end. Predictions of the theory are directly compared with prior reported experimental results for dipolar polymers in polar solvents. Excellent agreements with the experimental results are found, hinting that the dipolar interactions play a significant role in vertical phase segregation of planar polymer brushes. We also compare our field theoretical approach with the two-state and other models invoking ad hoc concentration dependence of the chi parameter. Interplay between the short-ranged excluded volume interactions and long-ranged dipolar interactions is shown to play an important role in affecting the vertical phase separation. Finally, effects of mismatch between the dipole moments of the polymer segments and the solvent molecules are investigated in detail.

  19. Decay of dipolar vortex structures in a stratified fluid

    NASA Astrophysics Data System (ADS)

    Flór, J. B.; van Heijst, G. J. F.; Delfos, R.

    1995-02-01

    In this paper the viscous decay of dipolar vortex structures in a linearly stratified fluid is investigated experimentally, and a comparison of the experimental results with simple theoretical models is made. The dipoles are generated by a pulsed horizontal injection of fluid. In a related experimental study by Flór and van Heijst [J. Fluid Mech. 279, 101 (1994)], it was shown that, after the emergence of the pancake-shaped vortex structure, the flow is quasi-two-dimensional and decays due to the vertical diffusion of vorticity and entrainment of ambient irrotational fluid. This results in an expansion of the vortex structure. Two decay models with the horizontal flow based on the viscously decaying Lamb-Chaplygin dipole, are presented. In a first model, the thickness and radius of the dipole are assumed constant, and in a second model also the increasing thickness of the vortex structure is taken into account. The models are compared with experimental data obtained from flow visualizations and from digital analysis of particle-streak photographs. Although both models neglect entrainment and the decay is modeled by diffusion only, a reasonable agreement with the experiments is obtained.

  20. Plasma Entry from Tail into the Dipolar Magnetosphere During Substorms

    NASA Astrophysics Data System (ADS)

    Haerendel, Gerhard

    Plasma entering the dipolar magnetosphere from the tail has to overcome the obstacle presented by the conductivity enhancements caused by the poleward arc(s). While the arcs move poleward, the plasma proceeds equatorward as testified by the existence of a westward electric field. The arcs break into smaller-scale structures and loops with a tendency of eastward growth and expansion, although the basic driving force is directed earthward/equatorward. The likely reason is that the arc-related conductivity enhancements act as flow barriers and convert normal into shear stresses. The energy derived from the release of the shear stresses and dissipated in the arcs lowers the entropy content of the flux tubes and enables their earthward progression. In addition, poleward jumps of the breakup arcs are quite common. They result from refreshments of the generator plasma by the sequential arrival of flow bursts from the near-Earth neutral line. Once inside the oval, the plasma continues to move equatorward as manifested through north-south aligned auroral forms. Owing to the existence of an inner border of the oval, marked by the Region 2 currents, all flows are eventually diverted sunward.

  1. Dynamical Properties of Surface-mounted Dipolar Molecular Rotators

    NASA Astrophysics Data System (ADS)

    Underwood, Jason; Price, John; Caskey, Douglas; Michl, Josef

    2007-03-01

    We use dielectric relaxation spectroscopy (DRS) to study the rotational dynamics of dipolar molecules mounted on fused SiO2 surfaces. Each ``molecular rotor'' consists of three parts: 1) a mounting group for attachment to the substrate, 2) a rotating group having a permanent dipole moment, and 3) an axis connecting the rotor to the attachment group. Attachment is facilitated either by covalent bonding through reaction of silane groups with surface hydroxyls or by van der Waals interactions. Fused SiO2 substrates are patterned with interdigitated electrode Au capacitors (C ˜ 1 pF), and rotor molecule dynamics are characterized by measurement of the capacitance C and loss tangent δ≡ReZ/ImZ. We employ a ratio-transformer bridge technique to measure these quantities, with sensitivities in C and δ of 1 aF and 1 ppm, respectively. A unique aspect of this work is the experimental apparatus, which allows us to prepare sub-monolayer films, determine coverage via two independent methods (DRS and XPS), and study molecule rotational motion, in-situ in ultra-high vacuum. Results will be presented on the kinetics of rotor adsorption/desorption, barrier height and asymmetry of the rotational potential of the molecules, and the effects of varying rotor coverages and adventitious H2O.

  2. Pollux: a stable weak dipolar magnetic field but no planet?

    NASA Astrophysics Data System (ADS)

    Aurière, Michel; Konstantinova-Antova, Renada; Espagnet, Olivier; Petit, Pascal; Roudier, Thierry; Charbonnel, Corinne; Donati, Jean-François; Wade, Gregg A.

    2014-08-01

    Pollux is considered as an archetype of a giant star hosting a planet: its radial velocity (RV) presents sinusoidal variations with a period of about 590 d, which have been stable for more than 25 years. Using ESPaDOnS and Narval we have detected a weak (sub-gauss) magnetic field at the surface of Pollux and followed up its variations with Narval during 4.25 years, i.e. more than for two periods of the RV variations. The longitudinal magnetic field is found to vary with a sinusoidal behaviour with a period close to that of the RV variations and with a small shift in phase. We then performed a Zeeman Doppler imaging (ZDI) investigation from the Stokes V and Stokes I least-squares deconvolution (LSD) profiles. A rotational period is determined, which is consistent with the period of variations of the RV. The magnetic topology is found to be mainly poloidal and this component almost purely dipolar. The mean strength of the surface magnetic field is about 0.7 G. As an alternative to the scenario in which Pollux hosts a close-in exoplanet, we suggest that the magnetic dipole of Pollux can be associated with two temperature and macroturbulent velocity spots which could be sufficient to produce the RV variations. We finally investigate the scenarii of the origin of the magnetic field which could explain the observed properties of Pollux.

  3. Energetic Electrons in Dipolarization Events: Spatial Properties and Anisotropy

    NASA Technical Reports Server (NTRS)

    Birn, J.; Runov, A.; Hesse, M.

    2014-01-01

    Using the electromagnetic fields of an MHD simulation of magnetotail reconnection, flow bursts, and dipolarization, we further investigate the acceleration of electrons to suprathermal energies. Particular emphasis is on spatial properties and anisotropies as functions of energy and time. The simulation results are compared with Time History of Events and Macroscale Interactions during Substorms observations. The test particle approach successfully reproduces several observed injection features and puts them into a context of spatial maps of the injection region(s): a dominance of perpendicular anisotropies farther down the tail and closer to the equatorial plane, an increasing importance of parallel anisotropy closer to Earth and at higher latitudes, a drop in energy fluxes at energies below approximately 10 keV, coinciding with the plasma density drop, together with increases at higher energy, a triple peak structure of flux increases near 0 deg, 90 deg, and 180 deg, and a tendency of flux increases to extend to higher energy closer to Earth and at lower latitudes. We identified the plasma sheet boundary layers and adjacent lobes as a main source region for both increased and decreased energetic electron fluxes, related to the different effects of adiabatic acceleration at high and low energies. The simulated anisotropies tend to exceed the observed ones, particularly for perpendicular fluxes at high energies. The most plausible reason is that the MHD simulation lacks the effects of anisotropy-driven microinstabilities and waves, which would reduce anisotropies.

  4. Conformations of a dipolar solute in a Stockmayer solvent channel.

    PubMed

    Yi, Taeil; Wang, Qian; Lichter, Seth

    2012-10-30

    A wide range of molecules, from inorganic to biological, self-assemble on surfaces. Previous studies have elucidated many features of solute reorganization on surfaces using coarse-grained modeling, implicit solvents, and constraints such as chemically bonding the solute to the surface. Using molecular dynamics simulations under various combinations of interaction parameters, solute fractions, and solute dipole moment, we study the redistribution of freely-rotating dipolar solute molecules solvated by a water-like Stockmayer solvent initially adhered to a face-centered cubic substrate. The balance of attractive and repulsive forces is essential for acquiring a particular stable conformation. Here we show that the adsorbed molecules redistribute into different conformations--wetting film, nonwetting, partial wetting, and pseudopartial wetting drops--depending on the parameter values. We observe that the pseudopartial wetting drop is transient and its rate of spreading fluctuates, slowing to nearly zero as it passes through particular conformations before reaching an equilibrium thin film. Strong attraction between solute molecules yields a droplet with a net dipole moment. A high solute fraction leads to a pancake-like conformation arising from a balance of surface tension and van der Waals forces. This study augments our understanding of the evolution of aggregates in biological systems and also the design of polymers for self-assembled monolayers for industrial applications.

  5. Rapid acceleration of protons upstream of earthward propagating dipolarization fronts

    PubMed Central

    Ukhorskiy, AY; Sitnov, MI; Merkin, VG; Artemyev, AV

    2013-01-01

    [1] Transport and acceleration of ions in the magnetotail largely occurs in the form of discrete impulsive events associated with a steep increase of the tail magnetic field normal to the neutral plane (Bz), which are referred to as dipolarization fronts. The goal of this paper is to investigate how protons initially located upstream of earthward moving fronts are accelerated at their encounter. According to our analytical analysis and simplified two-dimensional test-particle simulations of equatorially mirroring particles, there are two regimes of proton acceleration: trapping and quasi-trapping, which are realized depending on whether the front is preceded by a negative depletion in Bz. We then use three-dimensional test-particle simulations to investigate how these acceleration processes operate in a realistic magnetotail geometry. For this purpose we construct an analytical model of the front which is superimposed onto the ambient field of the magnetotail. According to our numerical simulations, both trapping and quasi-trapping can produce rapid acceleration of protons by more than an order of magnitude. In the case of trapping, the acceleration levels depend on the amount of time particles stay in phase with the front which is controlled by the magnetic field curvature ahead of the front and the front width. Quasi-trapping does not cause particle scattering out of the equatorial plane. Energization levels in this case are limited by the number of encounters particles have with the front before they get magnetized behind it. PMID:26167430

  6. Transient Magnetic Reconnection and Dipolarization Fronts in the Terrestrial Magnetotail

    NASA Astrophysics Data System (ADS)

    Zhou, Meng; Deng, Xiaohua; Pang, Ye; Xu, Xiaojun; Huang, Shiyong; Tang, Rongxin; Yuan, Zhigang

    2015-04-01

    We report a Cluster observation of transient magnetic reconnection in the Earth's magnetotail at the location of [Xgsm~ -17.2 RE, Ygsm~ -4.5 RE and Zgsm~ 0]. The reconnection X-line retreated tailward with a speed of 34 km/s based on multi-spacecraft analysis. An ion diffusion region with a weak guide field (~10% of lobe field) was encountered during the flow reversal. A flux rope was embedded in the tailward flow. Transient suprathermal electron beams, which directed away from the X-line, were detected repeatedly around the separatrix region with periods of about 60s during the tailward flow bursts. On the earthward side of X-line, multiple earthward-propagating dipolarization fronts were observed quasi-periodically at the edge of the ion diffusion region with time period of 60s-90s. Particle and wave characteristics also show distinct signatures at different stages of the transient reconnection. The implications of this observation will be discussed.

  7. Statistical and superposed epoch study of dipolarization events using data from Wind perigee passes

    NASA Astrophysics Data System (ADS)

    Sigsbee, K.; Slavin, J. A.; Lepping, R. P.; Szabo, A.; Øieroset, M.; Kaiser, M. L.; Reiner, M. J.; Singer, H. J.

    2005-03-01

    From 1995 to 2000, the Wind spacecraft spent over 500h in the magnetotail, much of it within ~2x104km of the predicted location of the neutral sheet. Wind passed through the near magnetotail at distances of -15 REdipolarization events in the Wind magnetic field data set between Y GSM~-16 and +16 RE based upon our requirements that the magnetic field inclination had to change by more than 15°, the maximum inclination angle had to be greater than 20°, and the inclination angle had to increase by a factor of at least 1.5. Most of the dipolarization events occurred in the pre-midnight region of the magnetotail and were accompanied by earthward flows with speeds greater than 100km/s. The properties of the dipolarization events did not depend upon the Y GSM position. However, they did vary with the distance to the neutral sheet. Isolated dipolarization events, defined as occurring more than 20min apart, were characterized by a decrease in Bx GSM and BTOTAL, and an increase in Bz GSM and the magnetic field inclination. Dipolarizations that occurred as part of a series of small dipolarizations spaced less than 20min apart were characterized by a transient increase in Bz GSM and the magnetic field inclination, but no significant change in Bx GSM and BTOTAL. The events consisting of a series of small dipolarizations occurred predominantly near midnight. We interpret these results in terms of two different modes of magnetotail convection: 1) a classical substorm pattern featuring storage of magnetic energy in the tail lobes which is explosively released at onset, and 2) a directly driven process.

  8. Studies of heteronuclear dipolar interactions between spin-1/2 and quadrupolar nuclei by using REDOR during multiple quantum evolution

    NASA Astrophysics Data System (ADS)

    Pruski, M.; Bailly, A.; Lang, D. P.; Amoureux, J.-P.; Fernandez, C.

    1999-06-01

    A new technique for measurements of dipolar interactions in rotating solids is presented that combines the capabilities of multiple quantum magic angle spinning (MQMAS) with the rotational echo double resonance (REDOR). It employs the dipolar recoupling between spin-1/2 ( I) and quadrupolar ( S) nuclei by applying a series of π pulses to the I spins. In contrast to the previously reported MQ-REDOR method, the recoupling sequence is applied during the triple quantum, rather than single quantum evolution. As the dipolar effect is enhanced by the MQ coherence order, this new technique exhibits improved sensitivity toward weak dipolar interactions.

  9. Oxygen impacts on dipolarization fronts and reconnection rate

    NASA Astrophysics Data System (ADS)

    Liang, Haoming; Ashour-Abdalla, Maha; Lapenta, Giovanni; Walker, Raymond J.

    2016-02-01

    Spacecraft observations near a magnetotail X line show that oxygen (O+) ions are minor species during nonstorm substorms, but they can become major species during some of the storm time substorms. Dipolarization fronts (DFs), which are characterized by a sharp increase northward magnetic field in the magnetotail, are commonly observed during magnetospheric substorms. In this study, we investigated the O+ effects on DFs and the reconnection rate during magnetotail reconnection. We used a 2.5-D implicit particle-in-cell simulation in a 2-D Harris current sheet in the presence of H+ and O+ ions. Simulation runs with equal number densities of O+ and H+ (O+ run) and with pure H+ ion species (H+ run) were performed. Comparing the two different runs, we found that both the reconnection rate and the DF speed in the O+ run were much less than those in the H+ run. By studying the force balance and plasma composition at the DF, we found that the outflow magnetic flux and DF propagation were encumbered by the current sheet O+ inertia, which reduced the DF speed and delayed the reconnection rate in the O+ run. We also found an ambipolar electric field in the O+ run due to the different inflow and outflow speeds of O+ and electrons in the O+ diffusion region. As a result, this ambipolar electric field induced O+ drag on the convective magnetic field in the O+ diffusion region. The small reconnection rate determined in the O+ run can be attributed to the current sheet inertia and the O+ drag on the convective magnetic flux.

  10. Physics of Substorm Growth Phase, Onset, and Dipolarization

    SciTech Connect

    C.Z. Cheng

    2003-10-22

    A new scenario of substorm growth phase, onset, and depolarization during expansion phase and the corresponding physical processes are presented. During the growth phase, as a result of enhanced plasma convection, the plasma pressure and its gradient are continued to be enhanced over the quiet-time values in the plasma sheet. Toward the late growth phase, a strong cross-tail current sheet is formed in the near-Earth plasma sheet region, where a local magnetic well is formed, the plasma beta can reach a local maximum with value larger than 50 and the cross-tail current density can be enhanced to over 10nA/m{sup 2} as obtained from 3D quasi-static magnetospheric equilibrium solutions for the growth phase. The most unstable kinetic ballooning instabilities (KBI) are expected to be located in the tailward side of the strong cross-tail current sheet region. The field lines in the most unstable KBI region map to the transition region between the region-1 and region-2 currents in the ionosphere, which is consistent with the observed initial brightening location of the breakup arc in the intense proton precipitation region. The KBI explains the AMPTE/CCE observations that a low-frequency instability with a wave period of 50-75 seconds is excited about 2-3 minutes prior to substorm onset and grows exponentially to a large amplitude at the onset of current disruption (or current reduction). At the current disruption onset higher frequency instabilities are excited so that the plasma and electromagnetic field fluctuations form a strong turbulent state. Plasma transport takes place due to the strong turbulence to relax the ambient plasma pressure profile so that the plasma pressure and current density are reduced and the ambient magnetic field intensity increases by more than a factor of 2 in the high-beta(sub)eq region and the field line geometry recovers from tail-like to dipole-like dipolarization.

  11. Re-creation of Dipolarization fronts observed by Cluster

    NASA Astrophysics Data System (ADS)

    Wang, Guoqiang; Zhang, Tielong; Volwerk, Martin; Schmid, Daniel

    2016-04-01

    Dipolarization fronts (DFs) are an important structure ahead of busty bulk flows (BBFs) and can accelerate electrons and ions in the plasma sheet, is. The evolution of two DFs, observed by four Cluster satellites, are studied. One DF is observed on 9 July 2002 at ~0417 UT when Cluster is located near [-9.0, -15.0, 4.6] RE in GSM. The inter-satellite separation is ~4000 km, while the ion initial length is ~447 km. C1 and C2 are mainly separated along the X direction, observe similar profiles of BZ. The DF is first observed by C2, and then observed by C1. Interestingly, the front observed by C1 displays wave profiles on the ion initial length scale, which are observed by C2 just ahead of the front. Another DF is observed on 14 September 2004 at ~2042 UT when Cluster is located near [-17.4, 1.8, 0.9] RE. The ion initial length is ~646 km, and the inter-spacecraft separation distance is ~1000 km. The distance between C1, C3 and C4 is less than 500 km along Y direction, and we find that these three satellites observe similar magnetic profiles behind the DF, and a waves with period ~2.5 s ahead of DF. The amplitude of the waves ahead of the DF becomes larger as time increases. This suggests that waves of ion initial length scale ahead of a DF can become larger in amplitude and may re-create the DF, while the previous DF can be found as large magnetic oscillations behind the new DF.

  12. Conditions for the Spin Wave Nonreciprocity in an Array of Dipolarly Coupled Magnetic Nanopillars

    DTIC Science & Technology

    2013-06-07

    development of miniature unbiased microwave isolators and circulators. PACS numbers: 75.30.Ds, 75.75.-c, 75.40.Gb The wave nonreciprocity can be...propagation is reversed. The wave nonreciprocity is widely used in signal transmission and information processing to design microwave isolators and...with asymmetrically placed ferro- or ferrimagnetic materials (usually ferrites ), in which the electromagnetic waves propagating in opposite directions

  13. Ordering, thermal excitations and phase transitions in dipolar coupled mono-domain magnet arrays

    NASA Astrophysics Data System (ADS)

    Kapaklis, Vassilios

    2015-03-01

    Magnetism has provided a fertile test bed for physical models, such as the Heisenberg and Ising models. Most of these investigations have focused on solid materials and relate to their atomic properties such as the atomic magnetic moments and their interactions. Recently, advances in nanotechnology have enabled the controlled patterning of nano-sized magnetic particles, which can be arranged in extended lattices. Tailoring the geometry and the magnetic material of these lattices, the magnetic interactions and magnetization reversal energy barriers can be tuned. This enables interesting interaction schemes to be examined on adjustable length and energy scales. As a result such nano-magnetic systems represent an ideal playground for the study of physical model systems, being facilitated by direct magnetic imaging techniques. One particularly interesting case is that of systems exhibiting frustration, where competing interactions cannot be simultaneously satisfied. This results in a degeneracy of the ground state and intricate thermodynamic properties. An archetypical frustrated physical system is water ice. Similar physics can be mirrored in nano-magnetic arrays, by tuning the arrangement of neighboring magnetic islands, referred to as artificial spin ice. Thermal excitations in such systems resemble magnetic monopoles. In this presentation key concepts related to nano-magnetism and artificial spin ice will be introduced and discussed, along with recent experimental and theoretical developments.

  14. Phenylenevinylene oligomers by Mizoroki-Heck cross coupling reaction. Structural and optoelectronic characterization

    NASA Astrophysics Data System (ADS)

    Estrada, Sandra E.; Ochoa-Puentes, Cristian; Sierra, Cesar A.

    2017-04-01

    In order to study the effect of the molecular structure on the optical properties of totally trans-trans phenylenevinylene oligomers (OPVs), sixteen 1,4-distyrylbenzene derivatives (1a-i and 2a-g) functionalized with different electron-donating (ED) and electron-withdrawing (EW) groups were synthesized by the Mizoroki-Heck cross coupling reaction in moderate to good yields (40-95%). The implemented methodology, with a small modification previously reported by our group, allows obtaining the desired vinyl configuration as well as one novel OPV compound (1h). After structural characterization by several techniques (e.g. FTIR, 1H, 13C and Solid-State NMR), particular emphasis was placed upon the investigation of their optical properties by UV-vis and fluorescence spectroscopies. The results showed that, with only one exception, the ED and EW groups at the ends of OPV systems lead to a bathochromic shift. This effect is intensified with the introduction of methoxy groups on the central ring. Consistent with these, the HOMO-LUMO gaps (ΔE) decreases as the strength of ED and EW substituents increases. The ED and EW substituents also lead to a decrease in the Φf values. This contribution in the area of organic electronics can be used as a reference to better select the most appropriate technological application for each OPV and this can be extrapolated to their respective structurally analogous segmented polymer.

  15. Estimation of interdomain flexibility of N-terminus of factor H using residual dipolar couplings†

    PubMed Central

    Maciejewski, Mateusz; Tjandra, Nico; Barlow, Paul N.

    2011-01-01

    Characterization of segmental flexibility is needed to understand the biological mechanisms of the very large category of functionally diverse proteins, exemplified by the regulators of complement activation, that consist of numerous compact modules or domains linked by short, potentially flexible, sequences of amino acid residues. The use of NMR-derived residual dipolar couplings (RDCs), in magnetically aligned media, to evaluate interdomain motion is established but only for two-domain proteins. We focused on the three N-terminal domains (called CCPs or SCRs) of the important complement regulator, human factor H (i.e. FH1-3). These domains cooperate to facilitate cleavage of the key complement activation-specific protein fragment, C3b, forming iC3b that no longer participates in the complement cascade. We refined a three-dimensional solution structure of recombinant FH1-3 based on nuclear Overhauser effects and RDCs. We then employed a rudimentary series of RDC datasets, collected in media containing magnetically aligned bicelles (disk-like particles formed from phospholipids) under three different conditions, to estimate interdomain motions. This circumvents a requirement of previous approaches for technically difficult collection of five independent RDC datasets. More than 80% of conformers of this predominantly extended three-domain molecule exhibit flexions of < 40 °. Such segmental flexibility (together with the local dynamics of the hypervariable loop within domain 3), could facilitate recognition of C3b via initial anchoring and eventual reorganization of modules to the conformation captured in the previously solved crystal structure of a C3b:FH1-4 complex. PMID:21793561

  16. Influence of dipolar interactions on the magnetic susceptibility spectra of ferrofluids

    NASA Astrophysics Data System (ADS)

    Sindt, Julien O.; Camp, Philip J.; Kantorovich, Sofia S.; Elfimova, Ekaterina A.; Ivanov, Alexey O.

    2016-06-01

    The frequency-dependent magnetic susceptibility of a ferrofluid is calculated under the assumption that the constituent particles undergo Brownian relaxation only. Brownian-dynamics simulations are carried out in order to test the predictions of a recent theory [A. O. Ivanov, V. S. Zverev, and S. S. Kantorovich, Soft Matter 12, 3507 (2016), 10.1039/C5SM02679B] that includes the effects of interparticle dipole-dipole interactions. The theory is based on the so-called modified mean-field approach and possesses the following important characteristics: in the low-concentration, noninteracting regime, it gives the correct single-particle Debye-theory results; it yields the exact leading-order results in the zero-frequency limit; it includes particle polydispersity correctly from the outset; and it is based on firm theoretical foundations allowing, in principle, systematic extensions to treat stronger interactions and/or higher concentrations. The theory and simulations are compared in the case of a model monodisperse ferrofluid, where the effects of interactions are predicted to be more pronounced than in a polydisperse ferrofluid. The susceptibility spectra are analyzed in detail in terms of the low-frequency behavior, the position of the peak in the imaginary (out-of-phase) part, and the characteristic decay time of the magnetization autocorrelation function. It is demonstrated that the theory correctly predicts the trends in all of these properties with increasing concentration and dipolar coupling constant, the product of which is proportional to the Langevin susceptibility χL. The theory is in quantitative agreement with the simulation results as long as χL≲1 .

  17. Numerical and experimental studies of long-range magnetic dipolar interactions

    NASA Astrophysics Data System (ADS)

    Ledbetter, M. P.; Savukov, I. M.; Bouchard, L.-S.; Romalis, M. V.

    2004-07-01

    We describe several numerical methods developed to analyze the behavior of spin polarized liquids in the presence of long-range magnetic dipolar interactions and external field gradients. Two of the methods use a discrete lattice of spins. In the first we calculate the magnetic field from the lattice of spins directly, either in the rotating frame, or in the lab frame. In the second method we include the dipolar fields from linear magnetization gradients analytically and calculate the dipolar fields from higher order gradients in Fourier space, where they are a local function of the magnetization. In the third method the magnetization is expanded in a Taylor series and the dipolar fields are calculated analytically for each term. The results of these calculations are compared to experimental data, in which we use two superconducting quantum interference device magnetometers adjacent to a spherical sample of hyperpolarized liquid 129Xe to detect the evolution of magnetization gradients. In particular, we observe an increase by a factor of 100 of the spin dephasing time in a longitudinal magnetic field gradient due to dipolar interactions of the spins. While each of the numerical techniques has certain limitations, they are generally in agreement with each other and with experimental data.

  18. Exotic vortex lattices in a rotating binary dipolar Bose-Einstein condensate

    PubMed Central

    Zhang, Xiao-Fei; Wen, Lin; Dai, Cai-Qing; Dong, Rui-Fang; Jiang, Hai-Feng; Chang, Hong; Zhang, Shou-Gang

    2016-01-01

    In the last decade, considerable advances have been made in the investigation of dipolar quantum gases. Previous theoretical investigations of a rotating binary dipolar Bose-Einstein condensate, where only one component possesses dipole moment, were mainly focused on two special orientations of the dipoles: perpendicular or parallel to the plane of motion. Here we study the ground-state and rotational properties of such a system for an arbitrary orientation of the dipoles. We demonstrate the ground-state vortex structures depend strongly on the relative strength between dipolar and contact interactions and the rotation frequency, as well as on the orientation of the dipoles. In the absence of rotation, the tunable dipolar interaction can be used to induce the squeezing or expansion of the cloud, and to derive the phase transition between phase coexistence and separation. Under finite rotation, the system is found to exhibit exotic ground-state vortex configurations, such as kernel-shell, vortex necklace, and compensating stripe vortex structures. We also check the validity of the Feynman relation, and find no significant deviations from it. The obtained results open up alternate ways for the quantum control of dipolar quantum gases. PMID:26778736

  19. Pitch-Angle Distribution for Electrons at Dipolarization Sites: Field Aligned Anisotropy and Isotropization

    NASA Astrophysics Data System (ADS)

    Wang, K.; Lin, C. H.; Hada, T.; Nishimura, T.; Angelopoulos, V.; Lee, W. J.; Lang, Z. R.

    2015-12-01

    Investigation of Earth's radiation environment is important not only because of its geophysical significance but also because it can inform the design of future satellites. The observed dipolarization effects on pitch-angle distributions (PAD) of electrons at the tailside in the inner plasmasheet during geomagnetic activity identified by AL index has been studied via analyzing data from THEMIS mission. We have shown that cigar distributions below about 1keV tend to become isotropized at the fronts at the dipolarization sites whereas isotropic distributions above 1keV tend to become more cigar-shaped (i.e., fluxes peak at pitch-angle of 0o and 180o). We have previously suggested that the ineffectiveness of Fermi acceleration below 1keV could be the factor causing this difference. We examine the dependence of this effect on radial distance from Earth taking place at or near dipolarization sites during times of geomagnetic activity. Because both the field line length and the properties of dipolarizations vary with radial distance. We anticipate significant dependence of this effect on radial distance. Our study contributes to our understanding of the electron environment during dipolarizations in Earth's magnetosphere.

  20. Breakdown of long-wavelength magnons in cubic antiferromagnets with dipolar forces at small temperature

    NASA Astrophysics Data System (ADS)

    Batalov, L. A.; Syromyatnikov, A. V.

    2015-06-01

    Using 1 /S expansion, we discuss the magnon spectrum of Heisenberg antiferromagnet (AF) on a simple cubic lattice with small dipolar interaction at small temperature T ≪TN , where TN is the Néel temperature. Similar to three-dimensional and two-dimensional ferromagnets, quantum and thermal fluctuations renormalize greatly the bare gapless spectrum leading to a gap Δ ˜ω0 , where ω0 is the characteristic dipolar energy. This gap is accompanied by anisotropic corrections to the free energy which make the cube edges easy directions for the staggered magnetization (dipolar anisotropy). In accordance with previous results, we find that dipolar forces split the magnon spectrum into two branches. This splitting makes possible two types of processes which lead to a considerable enhancement of the damping compared to the Heisenberg AF: a magnon decay into two other magnons and a confluence of two magnons. It is found that magnons are well defined quasiparticles in quantum AF. We demonstrate however that a small fraction of long-wavelength magnons can be overdamped in AFs with S ≫1 and in quantum AFs with a single-ion anisotropy competing with the dipolar anisotropy. Particular materials are pointed out which can be suitable for experimental observation of this long-wavelength magnons breakdown that contradicts expectation of the quasiparticle concept.

  1. Exotic vortex lattices in a rotating binary dipolar Bose-Einstein condensate.

    PubMed

    Zhang, Xiao-Fei; Wen, Lin; Dai, Cai-Qing; Dong, Rui-Fang; Jiang, Hai-Feng; Chang, Hong; Zhang, Shou-Gang

    2016-01-18

    In the last decade, considerable advances have been made in the investigation of dipolar quantum gases. Previous theoretical investigations of a rotating binary dipolar Bose-Einstein condensate, where only one component possesses dipole moment, were mainly focused on two special orientations of the dipoles: perpendicular or parallel to the plane of motion. Here we study the ground-state and rotational properties of such a system for an arbitrary orientation of the dipoles. We demonstrate the ground-state vortex structures depend strongly on the relative strength between dipolar and contact interactions and the rotation frequency, as well as on the orientation of the dipoles. In the absence of rotation, the tunable dipolar interaction can be used to induce the squeezing or expansion of the cloud, and to derive the phase transition between phase coexistence and separation. Under finite rotation, the system is found to exhibit exotic ground-state vortex configurations, such as kernel-shell, vortex necklace, and compensating stripe vortex structures. We also check the validity of the Feynman relation, and find no significant deviations from it. The obtained results open up alternate ways for the quantum control of dipolar quantum gases.

  2. AC susceptibility as a tool to probe the dipolar interaction in magnetic nanoparticles

    NASA Astrophysics Data System (ADS)

    Landi, Gabriel T.; Arantes, Fabiana R.; Cornejo, Daniel R.; Bakuzis, Andris F.; Andreu, Irene; Natividad, Eva

    2017-01-01

    The dipolar interaction is known to substantially affect the properties of magnetic nanoparticles. This is particularly important when the particles are kept in a fluid suspension or packed within nano-carriers. In addition to its usual long-range nature, in these cases the dipolar interaction may also induce the formation of clusters of particles, thereby strongly modifying their magnetic anisotropies. In this paper we show how AC susceptibility may be used to obtain information regarding the influence of the dipolar interaction in a sample. We develop a model which includes both aspects of the dipolar interaction and may be fitted directly to the susceptibility data. The usual long-range nature of the interaction is implemented using a mean-field approximation, whereas the particle-particle aggregation is modeled using a distribution of anisotropy constants. The model is then applied to two samples studied at different concentrations. One consists of spherical magnetite nanoparticles dispersed in oil and the other of cubic magnetite nanoparticles embedded on polymeric nanospheres. We also introduce a simple technique to address the presence of the dipolar interaction in a given sample, based on the height of the AC susceptibility peaks for different driving frequencies.

  3. Forces driving fast flow channels, dipolarizations, and turbulence in the magnetotail

    NASA Astrophysics Data System (ADS)

    El-Alaoui, Mostafa; Richard, Robert L.; Nishimura, Yukitoshi; Walker, Raymond J.

    2016-11-01

    Fast flow channels are a major contributor to earthward transport in the magnetotail. Fast flow channels originate at reconnection sites in the magnetotail and terminate with dipolarizations, earthward moving regions of enhanced magnetic field. We have used a global magnetohydrodynamic simulation of magnetotail dynamics during a substorm on 7 February 2009 to investigate the stresses in the plasma sheet. In particular, we present an analysis of forces in and around flow channels and dipolarizations. Earthward of the dipolarization magnetic and thermal pressure forces are nearly in equilibrium. Tailward of the dipolarization the pattern of stresses is complex, but several general features are evident. In the earthward flow channel the magnetic tension force dominates. In the dipolarization a tailward magnetic force is partially balanced by the earthward pressure force. The stresses in azimuth (y) are variable. In some places they cause the flow stream to meander, while in others they cause the stream to become wider or narrower. A major consequence of fast earthward flow channels is that they drive large-scale vortices that initiate turbulence.

  4. Mixing, demixing, and structure formation in a binary dipolar Bose-Einstein condensate

    NASA Astrophysics Data System (ADS)

    Young-S., Luis E.; Adhikari, S. K.

    2012-12-01

    We study the static properties of disk-shaped binary dipolar Bose-Einstein condensates of 168Er-164Dy and 52Cr-164Dy mixtures under the action of interspecies and intraspecies contact and dipolar interactions and demonstrate the effect of dipolar interaction using the mean-field approach. Throughout this study we use realistic values of interspecis and intraspecies dipolar interactions and the intraspecies scattering lengths and consider the interspecies scattering length as a parameter. The stability of the binary mixture is illustrated through phase plots involving a number of atoms of the species. The binary system always becomes unstable as the number of atoms increases beyond a certain limit. As the interspecies scattering length increases corresponding to more repulsion, an overlapping mixed state of the two species changes to a separated demixed configuration. During the transition from a mixed to a demixed configuration as the interspecies scattering length is increased for parameters near the stability line, the binary condensate shows special transient structures in density in the form of red-blood-cell-like biconcave and Saturn-ring-like shapes, which are direct manifestations of the dipolar interaction.

  5. Low-frequency wave activity related to dipolarization fronts detected by MMS in the magnetotail

    NASA Astrophysics Data System (ADS)

    Le Contel, O.; Retino, A.; Breuillard, H.; Mirioni, L.; Roux, A.; Chust, T.; Chasapis, A.; Lavraud, B.; Lindqvist, P. A.; Khotyaintsev, Y. V.; Vaivads, A.; Fu, H.; Marklund, G. T.; Nakamura, R.; Burch, J. L.; Torbert, R. B.; Moore, T. E.; Ergun, R.; Goodrich, K.; Needell, J.; Chutter, M.; Rau, D.; Dors, I.; Russell, C. T.; Magnes, W.; Strangeway, R. J.; Le, G.; Bromund, K. R.; Plaschke, F.; Fischer, D.; Leinweber, H. K.; Anderson, B. J.; Argall, M. R.; Slavin, J. A.; Kepko, L.; Baumjohann, W.; Pollock, C. J.; Mauk, B.; Fuselier, S. A.

    2015-12-01

    Dipolarization fronts are often associated to reconnection jets in the magnetotail current sheet and are sites of important energy dissipation and particle energization. Since the launch on March 12th and until the 9th of July 2015, the MMS constellation has been moving from dawn to dusk in a string of pearls formation. Although particle instruments were rarely operating and only FIELDS instrument suite was often gathering data, the MMS spacecraft have detected numerous dipolarization fronts, in particular on May 15th. Since 9th of July, the MMS evolved into a tetrahedral configuration with an average inter-satellite distance of 160 km and was still able to detect dipolarization fronts in the dusk magnetotail. As the Larmor radius of thermal protons is about 500 km in this region and dipolarization fronts have a typical thickness of the order of the Larmor radius, such a separation allows us to investigate in detail the microphysics of dipolarization fronts. In this study, we focus in particular on low-frequency electromagnetic wave activity related to the fronts and discuss possible mechanisms of particle heating and acceleration both at large scales (string of pearls configuration) and at kinetic scales (tetrahedral configuration).

  6. Model energy landscapes of low-temperature fluids: Dipolar hard spheres.

    PubMed

    Matyushov, Dmitry V

    2007-07-01

    An analytical model of non-Gaussian energy landscape of low-temperature fluids is developed based on the thermodynamics of the fluid of dipolar hard spheres. The entire excitation profile of the liquid, from the high-temperature liquid to the point of ideal-glass transition, has been obtained from Monte Carlo simulations. The fluid of dipolar hard spheres loses stability close to the point of ideal-glass transition transforming via a first-order transition into a columnar liquid phase of dipolar chains locally arranged in a body-centered-tetragonal order. Significant non-Gaussianity of the energy landscape is responsible for narrowing of the distribution of potential energies and energies of inherent structures with decreasing temperature. We suggest that the proposed functionality of the enumeration function is widely applicable to both polar and nonpolar low-temperature liquids.

  7. Effect of Dipolar Orientational Polarization on Electronic Conductivity in Ferroelectric Polymer Electrets

    NASA Astrophysics Data System (ADS)

    Yang, Lianyun; Zhu, Lei

    2014-03-01

    The leakage current, ion migration, and dipolar orientational polarization are major losses in ferroelectric polymers. The loss from the leakage current originates from electronic conduction and its behavior could be significantly affected by the internal electric field, which is induced by the dipolar orientational polarization. In this work, the leakage current in the corona charged PVDF electrets is studied under different external electric fields. Under low applied electric field, when no or very few dipoles could flip, the conductivity from the leakage direct current increases upon increasing the electric field. Under higher electric field, the aligned dipole-induced internal field would prevent the electrons from going through so that the conductivity decreases. After all the dipoles are aligned with the external electric field, the conductivity can increase again. This study will help us better understand the interplay between electronic conduction and dipolar orientation in ferroelectric materials.

  8. Topological defect formation in rotating binary dipolar Bose-Einstein condensate

    NASA Astrophysics Data System (ADS)

    Zhang, Xiao-Fei; Han, Wei; Jiang, Hai-Feng; Liu, Wu-Ming; Saito, Hiroki; Zhang, Shou-Gang

    2016-12-01

    We investigate the topological defects and spin structures of a rotating binary Bose-Einstein condensate, which consists of both dipolar and scalar bosonic atoms confined in spin-dependent optical lattices, for an arbitrary orientation of the dipoles with respect to their plane of motion. Our results show that the tunable dipolar interaction, especially the orientation of the dipoles, can be used to control the direction of stripe phase and its related half-vortex sheets. In addition, it can also be used to obtain a regular arrangement of various topological spin textures, such as meron, circular and cross disgyration spin structures. We point out that such topological defects and regular arrangement of spin structures arise primarily from the long-range and anisotropic nature of dipolar interaction and its competition with the spin-dependent optical lattices and rotation.

  9. Exploring Few- and Many-Body Dipolar Quantum Phenomena with Ultracold Erbium Atoms

    NASA Astrophysics Data System (ADS)

    Ferlaino, Francesca

    2016-05-01

    Given their strong magnetic moment and exotic electronic configuration, rare-earth atoms disclose a plethora of intriguing phenomena in ultracold quantum physics with dipole-dipole interaction. Here, we report on the first degenerate Fermi gas of erbium atoms, based on direct cooling of identical fermions via dipolar collisions. We reveal universal scattering laws between identical dipolar fermions close to zero temperature, and we demonstrate the long-standing prediction of a deformed Fermi surface in dipolar gas. Finally, we present the first experimental study of an extended Bose-Hubbard model using bosonic Er atoms in a three-dimensional optical lattice and we report on the first observation of nearest-neighbor interactions.

  10. Numerical method for evolving the dipolar projected Gross-Pitaevskii equation.

    PubMed

    Blakie, P B; Ticknor, C; Bradley, A S; Martin, A M; Davis, M J; Kawaguchi, Y

    2009-07-01

    We describe a method for evolving the projected Gross-Pitaevskii equation (PGPE) for an interacting Bose gas in a harmonic-oscillator potential, with the inclusion of a long-range dipolar interaction. The central difficulty in solving this equation is the requirement that the field is restricted to a small set of prescribed modes that constitute the low-energy c -field region of the system. We present a scheme, using a Hermite-polynomial-based spectral representation, which precisely implements this mode restriction and allows an efficient and accurate solution of the dipolar PGPE. We introduce a set of auxiliary oscillator states to perform a Fourier transform necessary to evaluate the dipolar interaction in reciprocal space. We extensively characterize the accuracy of our approach and derive Ehrenfest equations for the evolution of the angular momentum.

  11. Numerical method for evolving the dipolar projected Gross-Pitaevskii equation

    SciTech Connect

    Blakie, P. B.; Bradley, A. S.; Ticknor, C.; Martin, A. M.; Davis, M. J.; Kawaguchi, Y.

    2009-07-15

    We describe a method for evolving the projected Gross-Pitaevskii equation (PGPE) for an interacting Bose gas in a harmonic-oscillator potential, with the inclusion of a long-range dipolar interaction. The central difficulty in solving this equation is the requirement that the field is restricted to a small set of prescribed modes that constitute the low-energy c-field region of the system. We present a scheme, using a Hermite-polynomial-based spectral representation, which precisely implements this mode restriction and allows an efficient and accurate solution of the dipolar PGPE. We introduce a set of auxiliary oscillator states to perform a Fourier transform necessary to evaluate the dipolar interaction in reciprocal space. We extensively characterize the accuracy of our approach and derive Ehrenfest equations for the evolution of the angular momentum.

  12. Stability spectroscopy: recurring roton signatures in a dipolar-BEC phase diagram

    NASA Astrophysics Data System (ADS)

    Corson, John; Wilson, Ryan; Bohn, John

    2015-05-01

    When a strongly-dipolar Bose-Einstein condensate (BEC) is tightly confined in either one or two dimensions, the excitation spectrum is predicted to exhibit a nontrivial local minimum, termed ``roton.'' Rotons have proven to be elusive in dipolar-BEC experiments, and it is therefore of interest to devise a straightforward scheme whereby rotons may be measured. We propose observing the stability of a dipolar BEC that is perturbed by a tunable optical lattice. When the stability is mapped in terms of lattice depth s and spacing λ, we find regularly-spaced features whose positions and periodicity are determined by the roton wavelength. In this sense, a measurement of the phase diagram represents a spectroscopic measurement of the roton itself. In quasi-two-dimensional geometry, the polarization tilt plays an important role in determining which features appear in the stability diagram.

  13. Magnetic dipolar and quadrupolar transitions in two-electron atoms under exponential-cosine-screened Coulomb potential

    SciTech Connect

    Modesto-Costa, Lucas; Canuto, Sylvio; Mukherjee, Prasanta K.

    2015-03-15

    A detailed investigation of the magnetic dipolar and quadrupolar excitation energies and transition probabilities of helium isoelectronic He, Be{sup 2+}, C{sup 4+}, and O{sup 6+} have been performed under exponential cosine screened Coulomb potential generated in a plasma environment. The low-lying excited states 1s{sup 2}:{sup 1}S{sup e} → 1sns:{sup 3}S{sup e}{sub 0}, and 1snp:{sup 3}P{sup o}{sub 2} (n = 2, 3, 4, and 5) are considered. The variational time-dependent coupled Hartree-Fock scheme has been used. The effect of the confinement produced by the potential on the structural properties is investigated for increasing coupling strength of the plasma. It is noted that there is a gradual destabilization of the energy of the system with the reduction of the ionization potential and the number of excited states. The effect of the screening enhancement on the excitation energies and transition probabilities has also been investigated and the results compared with those available for the free systems and under the simple screened Coulomb potential.

  14. Temperature effect on dipolar and exchange interactions for SmCo5 + Fe65Co35 nanocomposite powders

    NASA Astrophysics Data System (ADS)

    Muñoz Ortega, L. P.; Elizalde Galindo, J. T.; Farias Mancilla, J. R.; Santillan, C. R.; Matutes Aquino, J. A.

    2012-04-01

    DC magnetization measurements were used to determine the temperature dependencies of the magnetic properties for (90%wt)SmCo5 + (10%wt)Fe65Co35 nanocomposite powders synthesized by mechanical milling and subsequent annealing. The annealing conditions were T equal to 1073 K and time, t, equal to 1.5, 3.0, 4.5, 6.0 min. Maximum magnetization decreased upon cooling in temperature range from 290 to 10 K. Coercivity increased its value to a maximum at the lowest temperature. On the other hand, hysteresis loops collected at low temperatures showed a "knee" in the second quadrant of the demagnetization curve, which suggests that dipolar interactions are becoming stronger than intergrain exchange coupling as temperature is lowered. This low temperature reduction of exchange interactions is confirmed by the temperature dependence of the exchange coupled volume ratio, R. Finally, the temperature effect on magnetic properties is explained on the basis of anisotropy enhancement and reduction of thermal fluctuations as temperature decreases.

  15. Consequences of rotating off-centred dipolar electromagnetic field in vacuum around Pulsars

    NASA Astrophysics Data System (ADS)

    Kundu, A.; Pétri, J.

    2016-12-01

    Studying the electromagnetic field of pulsars is one of the key themes in neutron star physics. While most of the works assume a standard central dipolar electromagnetic field model, recently some efforts had been made in explaining how inclusion of higher field components produces drastic consequences in our understanding of these objects. We put forward the effects of a unique recently presented approach in which the magnetic axis is shifted off from the centre. It is found that the rotating off-centred dipolar electromagnetic field itself reveals the presence of the higher components within. The consequences of this approach on the shape of the polar caps and the emission diagrams are discussed.

  16. Acoustic-excitonic effects in a two-dimensional gas of dipolar excitons

    NASA Astrophysics Data System (ADS)

    Boev, M. V.; Kovalev, V. M.; Chaplik, A. V.

    2016-08-01

    The theory of the interaction of a two-dimensional gas of indirect dipolar excitons with Rayleigh surface elastic waves has been developed. The absorption and renormalization of the phase velocity of a surface wave, as well as the drag of excitons by the surface acoustic wave and the generation of bulk acoustic waves by a twodimensional gas of dipolar excitons irradiated by external electromagnetic radiation, have been considered. These effects have been studied both in a normal phase at high temperatures and in a condensed phase of the exciton gas. The calculations have been performed in the ballistic and diffusion limits for both phases.

  17. Achieving high dielectric constant and low loss property in a dipolar glass polymer containing strongly dipolar and small-sized sulfone groups.

    PubMed

    Wei, Junji; Zhang, Zhongbo; Tseng, Jung-Kai; Treufeld, Imre; Liu, Xiaobo; Litt, Morton H; Zhu, Lei

    2015-03-11

    In this report, a dipolar glass polymer, poly(2-(methylsulfonyl)ethyl methacrylate) (PMSEMA), was synthesized by free radical polymerization of the corresponding methacrylate monomer. Due to the large dipole moment (4.25 D) and small size of the side-chain sulfone groups, PMSEMA exhibited a strong γ transition at a temperature as low as -110 °C at 1 Hz, about 220 °C below its glass transition temperature around 109 °C. Because of this strong γ dipole relaxation, the glassy PMSEMA sample exhibited a high dielectric constant of 11.4 and a low dissipation factor (tan δ) of 0.02 at 25 °C and 1 Hz. From an electric displacement-electric field (D-E) loop study, PMSEMA demonstrated a high discharge energy density of 4.54 J/cm(3) at 283 MV/m, nearly 3 times that of an analogue polymer, poly(methyl methacrylate) (PMMA). However, the hysteresis loss was only 1/3-1/2 of that for PMMA. This study suggests that dipolar glass polymers with large dipole moments and small-sized dipolar side groups are promising candidates for high energy density and low loss dielectric applications.

  18. Antenna-coupled microcavities for terahertz emission

    SciTech Connect

    Madéo, J. Todorov, Y.; Sirtori, C.

    2014-01-20

    We have investigated the capacitive coupling between dipolar antennas and metal-dielectric-metal wire microcavities with strong sub-wavelength confinement in the terahertz region. The coupling appears in reflectivity measurements performed on arrays of antenna-coupled elements, which display asymmetric Fano lineshapes. The experimental data are compared to a temporal coupled-mode theory and finite elements electromagnetic simulations. We show that the Fano interferences correspond to coupling between a subradiant mode (microcavity) and a superradiant mode (antennas). This phenomenon allows one to enhance and control the radiative coupling of the strongly confined mode with the vacuum. These concepts are very useful for terahertz optoelectronic devices based on deep-sub-wavelength active regions.

  19. Domain walls in antiferromagnetically coupled multilayer films.

    PubMed

    Hellwig, Olav; Berger, Andreas; Fullerton, Eric E

    2003-11-07

    We report experimentally observed magnetic domain-wall structures in antiferromagnetically coupled multilayer films with perpendicular anisotropy. Our studies reveal a first-order phase transition from domain walls with no net moment to domain walls with ferromagnetic cores. The transition originates from the competition between dipolar and exchange energies, which we tune by means of layer thickness. Although observed in a synthetic antiferromagnetic system, such domain-wall structures may be expected to occur in A-type antiferromagnets with anisotropic exchange coupling.

  20. Dipolar-Distribution Cavity γ-Fe2 O3 @C@α-MnO2 Nanospindle with Broadened Microwave Absorption Bandwidth by Chemically Etching.

    PubMed

    You, Wenbin; Bi, Han; She, Wen; Zhang, Yu; Che, Renchao

    2017-02-01

    Developing microwave absorption materials with ultrawide bandwidth and low density still remains a challenge, which restricts their actual application in electromagnetic signal anticontamination and defense stealth technology. Here a series of olive-like γ-Fe2 O3 @C core-shell spindles with different shell thickness and γ-Fe2 O3 @C@α-MnO2 spindles with different volumes of dipolar-distribution cavities were successfully prepared. Both series of absorbers exhibit excellent absorption properties. The γ-Fe2 O3 @C@α-MnO2 spindle with controllable cavity volume exhibits an effective absorption (<-10 dB) bandwidth as wide as 9.2 GHz due to the chemically dipolar etching of the core. Reflection loss of the γ-Fe2 O3 @C spindle reaches as high as -45 dB because of the optimized electromagnetic impedance balance between polymer shell and γ-Fe2 O3 core. Intrinsic ferromagnetism of the anisotropy spindle is confirmed by electron holography. Strong coupling of magnetic flux stray lines between spindles is directly imaged. This unique morphology and facile etching technique might facilitate the study of core-shell type microwave absorbers.

  1. Modulation of Magnetic Heating via Dipolar Magnetic Interactions in Monodisperse and Crystalline Iron Oxide Nanoparticles

    DOE PAGES

    Salas, Gorka; Camarero, Julio; Cabrera, David; ...

    2014-07-23

    Here, we report on the study of heat dissipation power in monodisperse and crystalline magnetite nanoparticles as function of particle and aggregate sizes, magnetic field frequencies (up to 435 kHz) and amplitudes (up to 50 mT), media viscosity and particle concentration. These nanoparticles display specific absorption rate values of few hundreds of WgFe-1 at moderate frequencies (~100 kHz), increasing up to 3632 WgFe-1 at more extreme field conditions (430 kHz and 40 mT) for the largest size. We have found that Néelian relaxation processes are dominant for all nanoparticle sizes, whereas Brownian contribution dominates only for the largest size (22more » nm) at high particle concentrations when dipolar interactions enhance the effective magnetic anisotropy. Besides, the particle concentration dependence of the specific absorption rate reflects the importance of magnetic dipolar interactions which strongly depend on aggregate and particle size. Our results show that dipolar interactions tune the effective magnetic anisotropy determining the Néelian and Brownian contributions into SAR values. The possibility of switching between heating mechanisms via dipolar interactions is of great importance towards controlling the heat exposure supplied by IONP as intracellular heating mediators.« less

  2. Modulation of Magnetic Heating via Dipolar Magnetic Interactions in Monodisperse and Crystalline Iron Oxide Nanoparticles

    SciTech Connect

    Salas, Gorka; Camarero, Julio; Cabrera, David; Takacs, Hélène; Varela, María; Ludwig, Robert; Dähring, Heidi; Hilger, Ingrid; Miranda, Rodolfo; Morales, María del Puerto; Teran, Francisco Jose

    2014-07-23

    Here, we report on the study of heat dissipation power in monodisperse and crystalline magnetite nanoparticles as function of particle and aggregate sizes, magnetic field frequencies (up to 435 kHz) and amplitudes (up to 50 mT), media viscosity and particle concentration. These nanoparticles display specific absorption rate values of few hundreds of WgFe-1 at moderate frequencies (~100 kHz), increasing up to 3632 WgFe-1 at more extreme field conditions (430 kHz and 40 mT) for the largest size. We have found that Néelian relaxation processes are dominant for all nanoparticle sizes, whereas Brownian contribution dominates only for the largest size (22 nm) at high particle concentrations when dipolar interactions enhance the effective magnetic anisotropy. Besides, the particle concentration dependence of the specific absorption rate reflects the importance of magnetic dipolar interactions which strongly depend on aggregate and particle size. Our results show that dipolar interactions tune the effective magnetic anisotropy determining the Néelian and Brownian contributions into SAR values. The possibility of switching between heating mechanisms via dipolar interactions is of great importance towards controlling the heat exposure supplied by IONP as intracellular heating mediators.

  3. 3+2-Dipolar cycloaddition of dianhydrohexitol azidoderivatives with N-arylmaleimides

    NASA Astrophysics Data System (ADS)

    Gella, I. M.; Babak, N. L.; Drushlyak, T. G.; Shishkina, S. V.; Musatov, V. I.; Lipson, V. V.

    2015-11-01

    Dianhydrohexitol azides dipolar 3+2 cycloaddition with N-arylmaleimides has been studied with NMR (1H and 13C, COSY, NOESY and HSQC) and X-ray analysis. In spite of low asymmetrical induction in this reaction, diastereomerically pure products have been obtained. These products are interesting over their structural similarity to griseolic acid derivatives and dihydropyrrolotriazoles, significant for pharmaceutics.

  4. Asymmetric Synthesis of α-Trifluoromethyl Pyrrolidines through Organocatalyzed 1,3-Dipolar Cycloaddition Reaction.

    PubMed

    Dong, Zhenghao; Zhu, Yuanyuan; Li, Boyu; Wang, Cui; Yan, Wenjin; Wang, Kairong; Wang, Rui

    2017-02-28

    The optically active α-trifluoromethyl pyrrolidines have been achieved through organocatalyzed 1, 3-dipolar cycloaddition reaction firstly. With diphenyl- prolinol trimethylsilyl ether as catalyst and in the presence of 3, 5-dinitrobenzoic acid, the reaction of trifluoroethylamine-derived ketimine with 2-enals gave α-trifluoro-methyl pyrrolidines bearing three contiguous stereogenic centers in excellent diastereoselectivies, stereoselectivities and yields.

  5. Effect of Nanoclustering and Dipolar Interactions in Heat Generation for Magnetic Hyperthermia.

    PubMed

    Coral, Diego F; Zélis, Pedro Mendoza; Marciello, Marzia; Morales, María del Puerto; Craievich, Aldo; Sánchez, Francisco H; van Raap, Marcela B Fernández

    2016-02-09

    Biomedical magnetic colloids commonly used in magnetic hyperthermia experiments often display a bidisperse structure, i.e., are composed of stable nanoclusters coexisting with well-dispersed nanoparticles. However, the influence of nanoclusters in the optimization of colloids for heat dissipation is usually excluded. In this work, bidisperse colloids are used to analyze the effect of nanoclustering and long-range magnetic dipolar interaction on the magnetic hyperthermia efficiency. Two kinds of colloids, composed of magnetite cores with mean sizes of around 10 and 18 nm, coated with oleic acid and dispersed in hexane, and coated with meso-2,3-dimercaptosuccinic acid and dispersed in water, were analyzed. Small-angle X-ray scattering was applied to thoroughly characterize nanoparticle structuring. We proved that the magnetic hyperthermia performances of nanoclusters and single nanoparticles are distinctive. Nanoclustering acts to reduce the specific heating efficiency whereas a peak against concentration appears for the well-dispersed component. Our experiments show that the heating efficiency of a magnetic colloid can increase or decrease when dipolar interactions increase and that the colloid concentration, i.e., dipolar interaction, can be used to improve magnetic hyperthermia. We have proven that the power dissipated by an ensemble of dispersed magnetic nanoparticles becomes a nonextensive property as a direct consequence of the long-range nature of dipolar interactions. This knowledge is a key point in selecting the correct dose that has to be injected to achieve the desired outcome in intracellular magnetic hyperthermia therapy.

  6. Lorentz microscopy sheds light on the role of dipolar interactions in magnetic hyperthermia.

    PubMed

    Campanini, M; Ciprian, R; Bedogni, E; Mega, A; Chiesi, V; Casoli, F; de Julián Fernández, C; Rotunno, E; Rossi, F; Secchi, A; Bigi, F; Salviati, G; Magén, C; Grillo, V; Albertini, F

    2015-05-07

    Monodispersed Fe3O4 nanoparticles with comparable size distributions have been synthesized by two different synthesis routes, co-precipitation and thermal decomposition. Thanks to the different steric stabilizations, the described samples can be considered as a model system to investigate the effects of magnetic dipolar interactions on the aggregation states of the nanoparticles. Moreover, the presence of magnetic dipolar interactions can strongly affect the nanoparticle efficiency as a hyperthermic mediator. In this paper, we present a novel way to visualize and map the magnetic dipolar interactions in different kinds of nanoparticle aggregates by the use of Lorentz microscopy, an easy and reliable in-line electron holographic technique. By exploiting Lorentz microscopy, which is complementary to the magnetic measurements, it is possible to correlate the interaction degrees of magnetic nanoparticles with their magnetic behaviors. In particular, we demonstrate that Lorentz microscopy is successful in visualizing the magnetic configurations stabilized by dipolar interactions, thus paving the way to the comprehension of the power loss mechanisms for different nanoparticle aggregates.

  7. Dipolarization Front: A Distinctive Feature of the Reconnection Onset in the Magnetotail

    NASA Astrophysics Data System (ADS)

    Sitnov, M. I.; Swisdak, M.; Divin, A. V.

    2008-12-01

    Recent particle simulations with open boundaries revealed interesting new effects in collisionless magnetic reconnection, including its intermittent regimes with the formation of the secondary plasmoids in the outflow regions. In this presentation we show that, apart from rather conventional plasmoids forming near the electron diffusion region of the central X-line, there is another group of the secondary reconnection structures that strongly resemble the dipolarization fronts, reported in Geotail, Cluster, and Themis observations of bursty bulk flows and substorm activations in the terrestrial magnetotail. These structures are characterized by a strong and quick increase of the original tail field Bz, normal to the neutral plane, up a half of the lobe field, in contrast to a relatively small and shallow negative dip of Bz in the front precursor, comparable in amplitude to the field Bz prior to the dipolarization onset. Both electrons and ions are magnetized at the front of the dipolarization wave. In contrast, in its trail, ions are unmagnetized and move slower compared to the ExB drift, whereas the magnetized electrons either follow that drift or move even faster, forming super-Alfvenic jets. In spite of drastically different motions of electrons and ions, the formation and growth of the dipolarization front is not accompanied by the corresponding growth of the electrostatic field. This suggests that the electron compressibility effect, stabilizing the ion tearing mode in the tail-like systems with trapped magnetized electrons [Lembege and Pellat, 1982], is strongly attenuated in open systems.

  8. Dipolar interactions between domains in lipid monolayers at the air-water interface.

    PubMed

    Rufeil-Fiori, Elena; Wilke, Natalia; Banchio, Adolfo J

    2016-05-25

    A great variety of biologically relevant monolayers present phase coexistence characterized by domains formed by lipids in an ordered phase state dispersed in a continuous, disordered phase. From the difference in surface densities between these phases, inter-domain dipolar interactions arise. These interactions are relevant for the determination of the spacial distribution of domains as well as their dynamics. In this work, we propose a novel way of estimating the dipolar repulsion using a passive method that involves the analysis of images of the monolayer with phase coexistence. This method is based on the comparison of the pair correlation function obtained from experiments with that obtained from Brownian dynamics simulations of a model system. As an example, we determined the difference in dipolar density of a binary monolayer of DSPC/DMPC at the air-water interface from the analysis of the radial distribution of domains, and the results are compared with those obtained by surface potential determinations. A systematic analysis for the experimentally relevant parameter range is given, which may be used as a working curve for obtaining the dipolar repulsion in different systems.

  9. Observational test of the interchange stability associated with near-tail dipolarizations

    NASA Astrophysics Data System (ADS)

    Lee, D.; Kim, K.; Ohtani, S.; Park, M.

    2010-12-01

    The interchange instability is a pressure gradient-driven instability. Formally speaking, the interchange mode can be considered to be a special case of the more general ballooning mode in the sense that the perpendicular displacement (as multiplied by the magnetic field strength) of the interchange mode is defined to be constant along the magnetic field line while that of a ballooning mode can be localized to the “bad curvature” region (i.e. the equatorial plane). Since the radial pressure profile in the near-earth tail is expected to become steeper prior to the substorm onset, instability of either interchange or ballooning type mode may be expected to occur. An observational test is generally non-trivial and difficult for the ballooning mode. For the interchange mode, however, the classic analytic criterion has long been known and thus using this criterion an observational test of the instability can be more feasible. The only difficulty has been how to evaluate the flux tube volume, for which Wolf et al. [2006] have suggested a useful formula. Using the formula, we have evaluated the interchange criterion for a set of pair-dipolarization events that are radially aligned. We found that the near-tail configuration before and during a dipolarization is likely stable against the interchange mode. Using a number of more dipolarizations, we have performed an analysis on evaluating the interchange criterion in a statistical manner and reached the results that support the conclusion of the interchange stability. This seems to suggest to us that the interchange instability is unlikely a candidate to trigger dipolarizations in association with substorms. But, the ballooning instability, the mode structure of which can be localized near the equatorial plane, remains a possibility responsible for dipolarizations.

  10. Vibrational Spectroscopy of Transient Dipolar Radicals via Autodetachment of Dipole-Bound States of Cold Anions

    NASA Astrophysics Data System (ADS)

    Huang, Dao-Ling; Liu, Hong-Tao; Dau, Phuong Diem; Wang, Lai-Sheng

    2014-06-01

    High-resolution vibrational spectroscopy of transient species is important for determining their molecular structures and understanding their chemical reactivity. However, the low abundance and high reactivity of molecular radicals pose major challenges to conventional absorption spectroscopic methods. The observation of dipole-bound states (DBS) in anions extend autodetachment spectroscopy to molecular anions whose corresponding neutral radicals possess a large enough dipole moment (>2.5 D).1,2 However, due to the difficulty of assigning the congested spectra at room temperature, there have been only a limited number of autodetachment spectra via DBS reported. Recently, we have built an improved version of a cold trap3 coupled with high-resolution photoelectron imaging.4 The first observation of mode-specific auotodetachment of DBS of cold phenoxide have shown that not only vibrational hot bands were completely suppressed, but also rotational profile was observed.5 The vibrational frequencies of the DBS were found to be the same as those of the neutral radical, suggesting that vibrational structures of dipolar radicals can be probed via DBS.5 More significantly, the DBS resonances allowed a number of vibrational modes with very weak Frank-Condon factors to be "lightened" up via vibrational autodetachment.5 Recently, our first high-resolution vibrational spectroscopy of the dehydrogenated uracil radical, with partial rotational resolution, via autodetachment from DBS of cold deprotonated uracil anions have been reported.6 Rich vibrational information is obtained for this important radical species. The resolved rotational profiles also allow us to characterize the rotational temperature of the trapped anions for the first time.6 1 K. R. Lykke, D. M. Neumark, T. Andersen, V. J. Trapa, and W. C. Lineberger, J. Chem. Phys. 87, 6842 (1987). 2 D. M. Wetzel, and J. I. Brauman, J. Chem. Phys. 90, 68 (1989). 3 P. D. Dau, H. T. Liu, D. L. Huang, and L. S. Wang, J. Chem. Phys

  11. Spinor dipolar bose-einstein condensates: classical spin approach.

    PubMed

    Takahashi, M; Ghosh, Sankalpa; Mizushima, T; Machida, K

    2007-06-29

    Bose-Einstein condensates which are dominated by magnetic dipole-dipole interaction are discussed under spinful situations. We treat the spin degrees of freedom as a classical spin vector, approaching from the large spin limit to obtain an effective minimal Hamiltonian. This is a version extended from a nonlinear sigma model. By solving the Gross-Pitaevskii equation, we find several novel spin textures where the mass density and spin density are strongly coupled, depending upon trap geometries due to the long-range and anisotropic natures of the dipole-dipole interaction.

  12. Spinor Dipolar Bose-Einstein Condensates: Classical Spin Approach

    SciTech Connect

    Takahashi, M.; Mizushima, T.; Machida, K.; Ghosh, Sankalpa

    2007-06-29

    Bose-Einstein condensates which are dominated by magnetic dipole-dipole interaction are discussed under spinful situations. We treat the spin degrees of freedom as a classical spin vector, approaching from the large spin limit to obtain an effective minimal Hamiltonian. This is a version extended from a nonlinear sigma model. By solving the Gross-Pitaevskii equation, we find several novel spin textures where the mass density and spin density are strongly coupled, depending upon trap geometries due to the long-range and anisotropic natures of the dipole-dipole interaction.

  13. Significance of symmetry in the nuclear spin Hamiltonian for efficient heteronuclear dipolar decoupling in solid-state NMR: A Floquet description of supercycled rCW schemes

    NASA Astrophysics Data System (ADS)

    Equbal, Asif; Shankar, Ravi; Leskes, Michal; Vega, Shimon; Nielsen, Niels Chr.; Madhu, P. K.

    2017-03-01

    Symmetry plays an important role in the retention or annihilation of a desired interaction Hamiltonian in NMR experiments. Here, we explore the role of symmetry in the radio-frequency interaction frame Hamiltonian of the refocused-continuous-wave (rCW) pulse scheme that leads to efficient 1H heteronuclear decoupling in solid-state NMR. It is demonstrated that anti-periodic symmetry of single-spin operators (Ix, Iy, Iz) in the interaction frame can lead to complete annihilation of the 1H-1H homonuclear dipolar coupling effects that induce line broadening in solid-state NMR experiments. This symmetry also plays a critical role in cancelling or minimizing the effect of 1H chemical-shift anisotropy in the effective Hamiltonian. An analytical description based on Floquet theory is presented here along with experimental evidences to understand the decoupling efficiency of supercycled (concatenated) rCW scheme.

  14. Significance of symmetry in the nuclear spin Hamiltonian for efficient heteronuclear dipolar decoupling in solid-state NMR: A Floquet description of supercycled rCW schemes.

    PubMed

    Equbal, Asif; Shankar, Ravi; Leskes, Michal; Vega, Shimon; Nielsen, Niels Chr; Madhu, P K

    2017-03-14

    Symmetry plays an important role in the retention or annihilation of a desired interaction Hamiltonian in NMR experiments. Here, we explore the role of symmetry in the radio-frequency interaction frame Hamiltonian of the refocused-continuous-wave (rCW) pulse scheme that leads to efficient (1)H heteronuclear decoupling in solid-state NMR. It is demonstrated that anti-periodic symmetry of single-spin operators (Ix, Iy, Iz) in the interaction frame can lead to complete annihilation of the (1)H-(1)H homonuclear dipolar coupling effects that induce line broadening in solid-state NMR experiments. This symmetry also plays a critical role in cancelling or minimizing the effect of (1)H chemical-shift anisotropy in the effective Hamiltonian. An analytical description based on Floquet theory is presented here along with experimental evidences to understand the decoupling efficiency of supercycled (concatenated) rCW scheme.

  15. N-heterocyclic carbene-catalyzed 1,3-dipolar cycloaddition reactions: a facile synthesis of 3,5-di- and 3,4,5-trisubstituted isoxazoles.

    PubMed

    Kankala, Shravankumar; Vadde, Ravinder; Vasam, Chandra Sekhar

    2011-10-26

    A first example of organo-N-heterocyclic carbene (NHC) catalyzed click-type fast 1,3-dipolar cycloaddition of nitrile oxides with alkynes was developed for the regioselective synthesis of 3,5-di- and 3,4,5-trisubstituted isoxazoles. Triethylamine (Et(3)N) was employed as an effective base to generate both nitrile oxide and the organo-NHC catalyst in situ. This catalytic approach was used to attach a variety of substituents, including other biologically active fragments, onto the isoxazole ring to selectively design multinucleus structures. Further, we have also optimized the conditions for Cu(I)-free Sonogashira cross-coupling to obtain internal alkynes in high yields, which were subsequently used in cycloaddition. A catalytic cycle is proposed and the remarkable regiocontrol in the formation of isoxazoles was ascribed to a beneficial zwitterion intermediate developed by the interaction of the strongly nucleophilic organo-NHC catalyst with alkyne followed by nitrile oxide.

  16. Multicomponent synthesis of spiropyrrolidine analogues derived from vinylindole/indazole by a 1,3-dipolar cycloaddition reaction

    PubMed Central

    Narayanarao, Manjunatha; Koodlur, Lokesh; Revanasiddappa, Vijayakumar G; Gopal, Subramanya

    2016-01-01

    A new series of spiropyrrolidine compounds containing indole/indazole moieties as side chains have been accomplished via a one-pot multicomponent synthesis. The method uses the 1,3-dipolar cycloaddition reaction between N-alkylvinylindole/indazole and azomethine ylides, prepared in situ from cyclic/acyclic amino acids. The 1,3-dipolar cycloaddition proceeds efficiently under thermal conditions to afford the regio- and stereospecific cyclic adducts. PMID:28144362

  17. Chemical structural studies of natural lignin by dipolar dephasing solid-state 13C nuclear magnetic resonance

    USGS Publications Warehouse

    Hatcher, P.G.

    1987-01-01

    Two natural lignins, one from a gymnosperm wood the other from angiosperm wood, were examined by conventional solid-state and dipolar dephasing 13C nuclear magnetic resonance (NMR) techniques. The results obtained from both techniques show that the structure of natural lignins is consistent with models of softwood and hardwood lignin. The dipolar dephasing NMR data provide a measure of the degree of substitution on aromatic rings which is consistent with the models. ?? 1987.

  18. Multicomponent synthesis of spiropyrrolidine analogues derived from vinylindole/indazole by a 1,3-dipolar cycloaddition reaction.

    PubMed

    Narayanarao, Manjunatha; Koodlur, Lokesh; Revanasiddappa, Vijayakumar G; Gopal, Subramanya; Kamila, Susmita

    2016-01-01

    A new series of spiropyrrolidine compounds containing indole/indazole moieties as side chains have been accomplished via a one-pot multicomponent synthesis. The method uses the 1,3-dipolar cycloaddition reaction between N-alkylvinylindole/indazole and azomethine ylides, prepared in situ from cyclic/acyclic amino acids. The 1,3-dipolar cycloaddition proceeds efficiently under thermal conditions to afford the regio- and stereospecific cyclic adducts.

  19. Collective excitations of dipolar gases based on local tunneling in superlattices

    NASA Astrophysics Data System (ADS)

    Cao, Lushuai; Mistakidis, Simeon I.; Deng, Xing; Schmelcher, Peter

    2017-01-01

    The collective dynamics of a dipolar fermionic quantum gas confined in a one-dimensional double-well superlattice is explored. The fermionic gas resides in a paramagnetic-like ground state in the weak interaction regime, upon which a new type of collective dynamics is found when applying a local perturbation. This dynamics is composed of the local tunneling of fermions in separate supercells, and is a pure quantum effect, with no classical counterpart. Due to the presence of the dipolar interactions the local tunneling transports through the entire superlattice, giving rise to a collective dynamics. A well-defined momentum-energy dispersion relation is identified in the ab-initio simulations demonstrating the phonon-like behavior. The phonon-like characteristic is also confirmed by an analytical description of the dynamics within a semiclassical picture.

  20. Low-loss metamaterial electromagnetically induced transparency based on electric toroidal dipolar response

    SciTech Connect

    Li, Hai-ming; Liu, Shao-bin Liu, Si-yuan; Ding, Guo-wen; Yang, Hua; Yu, Zhi-yang; Zhang, Hai-feng; Wang, Shen-yun

    2015-02-23

    In this paper, a low-loss and high transmission analogy of electromagnetically induced transparency based on electric toroidal dipolar response is numerically and experimentally demonstrated. It is obtained by the excitation of the low-loss electric toroidal dipolar response, which confines the magnetic field inside a dielectric substrate with toroidal geometry. The metamaterial electromagnetically induced transparency (EIT) structure is composed of the cut wire and asymmetric split-ring resonators. The transmission level is as high as 0.88, and the radiation loss is greatly suppressed, which can be proved by the surface currents distributions, the magnetic field distributions, and the imaginary parts of the effective permeability and permittivity. It offers an effective way to produce low-loss and high transmission metamaterial EIT.

  1. Arrays of dipolar molecular rotors in Tris(o-phenylenedioxy) cyclotriphosphazene.

    PubMed

    Zhao, Ke; Dron, Paul I; Kaleta, Jiří; Rogers, Charles T; Michl, Josef

    2014-01-01

    Regular two-dimensional or three-dimensional arrays of mutually interacting dipolar molecular rotors represent a worthy synthetic objective. Their dielectric properties, including possible collective behavior, will be a sensitive function of the location of the rotors, the orientation of their axes, and the size of their dipoles. Host-guest chemistry is one possible approach to gaining fine control over these factors. We describe the progress that has been achieved in recent years using tris (o-phenylenedioxy)cyclotriphosphazene as a host and a series of rod-shaped dipolar molecular rotors as guests. Structures of both surface and bulk inclusion compounds have been established primarily by solid-state nuclear magnetic resonance (NMR) and powder X-ray diffraction (XRD) techniques. Low-temperature dielectric spectroscopy revealed rotational barriers as low as 1.5 kcal/mol, but no definitive evidence for collective behavior has been obtained so far.

  2. Resonant dipolar relaxation in poly ( ɛ -caprolactone)—A thermally stimulated depolarization current study

    NASA Astrophysics Data System (ADS)

    Patidar, M. M.; Jain, D.; Nath, R.; Ganesan, V.

    2016-07-01

    Resonant dipolar relaxation in poly( ɛ-caprolactone) (PCL) is reported using thermally stimulated discharge current spectroscopy. PCL is a bio-medically known shape memory polymer having a well defined γ, β, α, and α ' relaxations, respectively, centered around 125 K, 170 K, 220 K, and 270 K as seen by the measurements. By employing a new protocol variable poling temperature at constant freezing temperature, resonant dipolar relaxation in PCL could be induced, especially in the vicinity of α relaxation. Such a protocol is useful in de-convoluting the features in a more meaningful fashion. By an analysis of activation process, we could show a clear contrast enhancement of the dynamics of the participating dipoles by means of a minimum in the activation energies situated around the glass transition region. The relevant parameters of interest such as activation energies and relaxation times are estimated and discussed.

  3. Mean-field regime of trapped dipolar Bose-Einstein condensates in one and two dimensions

    SciTech Connect

    Cai Yongyong; Rosenkranz, Matthias; Lei Zhen; Bao Weizhu

    2010-10-15

    We derive rigorous one- and two-dimensional mean-field equations for cigar- and pancake-shaped dipolar Bose-Einstein condensates with arbitrary polarization angle. We show how the dipolar interaction modifies the contact interaction of the strongly confined atoms. In addition, our equations introduce a nonlocal potential, which is anisotropic for pancake-shaped condensates. We propose to observe this anisotropy via measurement of the condensate aspect ratio. We also derive analytically approximate density profiles from our equations. Both the numerical solutions of our reduced mean-field equations and the analytical density profiles agree well with numerical solutions of the full Gross-Pitaevskii equation while being more efficient to compute.

  4. Clusters in sedimentation equilibrium for an experimental hard-sphere-plus-dipolar Brownian colloidal system

    PubMed Central

    Newman, Hugh D.; Yethiraj, Anand

    2015-01-01

    In this work, we use structure and dynamics in sedimentation equilibrium, in the presence of gravity, to examine, via confocal microscopy, a Brownian colloidal system in the presence of an external electric field. The zero field equation of state (EOS) is hard sphere without any re-scaling of particle size, and the hydrodynamic corrections to the long-time self-diffusion coefficient are quantitatively consistent with the expected value for hard spheres. Care is taken to ensure that both the dimensionless gravitational energy, which is equivalent to a Peclet number Peg, and dipolar strength Λ are of order unity. In the presence of an external electric field, anisotropic chain-chain clusters form; this cluster formation manifests itself with the appearance of a plateau in the diffusion coefficient when the dimensionless dipolar strength Λ ~ 1. The structure and dynamics of this chain-chain cluster state is examined for a monodisperse system for two particle sizes. PMID:26323363

  5. Stability and structure of an anisotropically trapped dipolar Bose-Einstein condensate: Angular and linear rotons

    NASA Astrophysics Data System (ADS)

    Martin, A. D.; Blakie, P. B.

    2012-11-01

    We study theoretically Bose-Einstein condensates with polarized dipolar interactions in anisotropic traps. We map the parameter space by varying the trap frequencies and dipolar interaction strengths and find an irregular-shaped region of parameter space in which density-oscillating condensate states occur, with maximum density away from the trap center. These density-oscillating states may be biconcave (red-blood-cell-shaped), or have two or four peaks. For all trap frequencies, the condensate becomes unstable to collapse for sufficiently large dipole interaction strength. The collapse coincides with the softening of an elementary excitation. When the condensate mode is density oscillating, the character of the softening excitation is related to the structure of the condensate. We classify these excitations by linear and angular characteristics. We also find excited solutions to the Gross-Pitaevskii equation, which are always unstable.

  6. Geometric stability spectra of dipolar Bose gases in tunable optical lattices

    NASA Astrophysics Data System (ADS)

    Corson, John P.; Wilson, Ryan M.; Bohn, John L.

    2013-07-01

    We examine the stability of quasi-two-dimensional dipolar Bose-Einstein condensates in the presence of weak optical lattices of various geometries. We find that when the condensate possesses a roton-maxon quasiparticle dispersion, the conditions for stability exhibit a strong dependence both on the lattice geometry and the polarization tilt. This results in rich structures in the system's stability diagram akin to spectroscopic signatures. We show how these structures originate from the mode matching of rotons to the perturbing lattice. In the case of a one-dimensional lattice, some of the features emerge only when the polarization axis is tilted into the plane of the condensate. Our results suggest that the stability diagram may be used as a novel means to spectroscopically measure rotons in dipolar condensates.

  7. Spin squeezing of a dipolar Bose gas in a double-well potential

    NASA Astrophysics Data System (ADS)

    Tan, Qing-Shou; Lu, Hai-Yan; Yi, Su

    2016-01-01

    The spin-squeezing dynamics of a quasi-one-dimensional dipolar Bose gas trapped in a double-well potential is studied by employing the method of the multiconfigurational time-dependent Hartree for bosons. We find that optimal squeezing generated by the dipolar interaction can be improved over the one-axis twisting limit, and this squeezing is much stronger than that obtained by the contact interaction. Moreover, natural orbital-related squeezing can be controlled by the direction of the dipole moment, which provides control for storing the optimal spin squeezing. The origin of the squeezing as well as the relationship between spin squeezing and the two-order correlation function are also discussed.

  8. Three-dimensional current systems and ionospheric effects associated with small dipolarization fronts

    NASA Astrophysics Data System (ADS)

    Palin, L.; Jacquey, C.; Opgenoorth, H.; Connors, M.; Sergeev, V.; Sauvaud, J.-A.; Nakamura, R.; Reeves, G. D.; Singer, H. J.; Angelopoulos, V.; Turc, L.

    2015-05-01

    We present a case study of eight successive plasma sheet (PS) activations (usually referred to as bursty bulk flows or dipolarization fronts), associated with small individual BZGSM increases on 31 March 2009 (0200-0900 UT), observed by the Time History of Events and Macroscale Interactions During Substorms mission. This series of events happens during very quiet solar wind conditions, over a period of 7 h preceding a substorm onset at 1230 UT. The amplitude of the dipolarizations increases with time. The low-amplitude dipolarization fronts are associated with few (1 or 2) rapid flux transport events (RFT, Eh>2 mV/m), whereas the large-amplitude ones encompass many more RFT events. All PS activations are associated with small and localized substorm current wedge (SCW)-like current system signatures, which seems to be the consequence of RFT arrival in the near tail. The associated ground magnetic perturbations affect a larger part of the contracted auroral oval when, in the magnetotail, more RFT are embedded in PS activations (>5). Dipolarization fronts with very low amplitude, a type usually not included in statistical studies, are of particular interest because we found even those to be associated with clear small SCW-like current system and particle injections at geosynchronous orbit. This exceptional data set highlights the role of flow bursts in the magnetotail and leads to the conclusion that we may be observing the smallest form of a substorm or rather its smallest element. This study also highlights the gradual evolution of the ionospheric current disturbance as the plasma sheet is observed to heat up.

  9. 1,3-Dipolar cycloaddition of diazomethane to element-substituted (Si, Ge, Sn)-alkoxyacetylenes

    SciTech Connect

    Kostyuk, A.S.; Knyaz'kov, K.A.; Ponomarev, S.V.; Lutsenko, I.F.

    1986-03-10

    1,3-Dipolar cycloaddition of diazomethane to the triple bond of trialkylsilyl-, trialkylgermyl-, and trialkylstannylalkoxyacetylenes proceeds regioselectivity and is a convenient method for synthesis of the previously not described 3(5)-element-substituted 4-alkoxypyrazoles. When heated in methanol in the presence of an acid, 3(5)-silyl(germyl)-4-alkoxypyrazoles are slowly hydrolyzed with cleavage of the element-carbon bond.

  10. Chiral phosphoric acid catalyzed enantioselective 1,3-dipolar cycloaddition reaction of azlactones.

    PubMed

    Zhang, Zhenhua; Sun, Wangsheng; Zhu, Gongming; Yang, Junxian; Zhang, Ming; Hong, Liang; Wang, Rui

    2016-01-25

    The first chiral phosphoric acid catalyzed highly diastereo- and enantioselective 1,3-dipolar cycloaddition reaction of azlactones and methyleneindolinones was disclosed. By using a BINOL-derived chiral phosphoric acid as the catalyst, azlactones were activated as chiral anti N-protonated 1,3-dipoles to react with methyleneindolinones to yield biologically important 3,3'-pyrrolidonyl spirooxindole scaffolds in high yields, with good-to-excellent diastereo- and enantioselectivity.

  11. Coexistence, Interfacial Energy, and the Fate of Microemulsions of 2D Dipolar Bosons

    NASA Astrophysics Data System (ADS)

    Moroni, Saverio; Boninsegni, Massimo

    2014-12-01

    The superfluid-crystal quantum phase transition of a system of purely repulsive dipolar bosons in two dimensions is studied by quantum Monte Carlo simulations at zero temperature. We determine freezing and melting densities and estimate the energy per unit length of a macroscopic interface separating the two phases. The results rule out the microemulsion scenario for any physical realization of this system, given the exceedingly large predicted size of the bubbles.

  12. Direct observation of dipolar chains in ferrofluids in zero field using cryogenic electron microscopy

    NASA Astrophysics Data System (ADS)

    Butter, K.; Bomans, P. H.; Frederik, P. M.; Vroege, G. J.; Philipse, A. P.

    2003-04-01

    The particle structure of ferrofluids is studied in situ, by cryogenic electron microscopy, on vitrified films of iron and magnetite dispersions. By means of synthesis of iron colloids with controlled particle size and different types of surfactant, dipolar particle interactions can be varied over a broad range, which significantly influences the ferrofluid particle structure. Our experiments on iron dispersions (in contrast to magnetite dispersions) for the first time demonstrate, in ferrofluids in zero field, a transition with increasing particle size from separate particles to linear chains of particles (Butter K, Bomans P H, Frederik P M, Vroege G J and Philipse A P 2003 Nature Mater. 2 88). These chains, already predicted theoretically by de Gennes and Pincus (de Gennes P G and Pincus P A 1970 Phys. Kondens. Mater. 11 189), very much resemble the fluctuating chains found in simulations of dipolar fluids (Weis J J 1998 Mol. Phys. 93 361, Chantrell R W, Bradbury A, Popplewell J and Charles S W 1982 J. Appl. Phys. 53 2742). Decreasing the range of steric repulsion between particles by employing a thinner surfactant layer is found to change particle structures as well. The dipolar nature of the aggregation is confirmed by the alignment of existing chains and individual particles in the field direction upon vitrification of dispersions in a saturating magnetic field. Frequency-dependent susceptibility measurements indicate that particle structures in truly three-dimensional ferrofluids are qualitatively similar to those in liquid films.

  13. Quantum spin ices and magnetic states from dipolar-octupolar doublets on the pyrochlore lattice

    NASA Astrophysics Data System (ADS)

    Chen, Gang

    We consider a class of electron systems in which dipolar-octupolar Kramers doublets arise on the pyrochlore lattice. In the localized limit, the Kramers doublets are described by the effective spin 1/2 pseudospins. The most general nearest-neighbor exchange model between these pseudospins is the XYZ model. In additional to dipolar ordered and octupolar ordered magnetic states, we show that this XYZ model exhibits two distinct quantum spin ice (QSI) phases, that we dub dipolar QSI and octupolar QSI. These two QSIs are distinct symmetry enriched U(1) quantum spin liquids, enriched by the lattice symmetry. Moreover, the XYZ model is absent from the notorious sign problem for a quantum Monte Carlo simulation in a large parameter space. We discuss the potential relevance to real material systems such as Dy2Ti2O7, Nd2Zr2O7, Nd2Hf2O7, Nd2Ir2O7, Nd2Sn2O7 and Ce2Sn2O7. chggst@gmail.com, Refs: Y-P Huang, G Chen, M Hermele, Phys. Rev. Lett. 112, 167203 (2014).

  14. Sulfone-Containing Dipolar Glass Polymers with High Dielectric Constant and Low Loss Property

    NASA Astrophysics Data System (ADS)

    Zhu, Yufeng; Zhang, Zhongbo; Litt, Morton; Zhu, Lei

    Sulfone-containing polyoxetanes are designed and synthesized for high dielectric constant and low loss dipolar glasses. The precursor polymer, poly(3,3-bis(chloromethyl)oxetane) (PBCMO) is synthesized by bulk cationic polymerization with boron trifluoride diethyl etherate as initiator. The number-average molecular weight of PBCMO is 73 kDa, with a polydispersity of 1.53 as obtained from size-exclusion chromatography results. Post-modification of PBCMO yields the dipolar glass polymer, poly(3,3-bis(methylsulfonylmethyl)oxetane) (MST). Nuclear magnetic resonance result shows 100% conversion. Differential scanning calorimetry result indicates that MST has a glass transition temperature of ca. 120 °C. Due to the large dipole moment (4.25 D) and small size of the side-chain sulfone groups, MST exhibits a high dielectric constant of 8.7 and a low dissipation factor of 0.01 at 25 °C and 1 Hz. This study suggests that dipolar glass polymers with large dipole moments and small-sized dipoles in the side chains are promising candidates for high energy density and low loss dielectric applications. This work is supported by NSF Polymers Program (DMR-1402733).

  15. Dipolar Magnetism in Ordered and Disordered Low-Dimensional Nanoparticle Assemblies

    PubMed Central

    Varón, M.; Beleggia, M.; Kasama, T.; Harrison, R. J.; Dunin-Borkowski, R. E.; Puntes, V. F.; Frandsen, C.

    2013-01-01

    Magnetostatic (dipolar) interactions between nanoparticles promise to open new ways to design nanocrystalline magnetic materials and devices if the collective magnetic properties can be controlled at the nanoparticle level. Magnetic dipolar interactions are sufficiently strong to sustain magnetic order at ambient temperature in assemblies of closely-spaced nanoparticles with magnetic moments of ≥ 100 μB. Here we use electron holography with sub-particle resolution to reveal the correlation between particle arrangement and magnetic order in self-assembled 1D and quasi-2D arrangements of 15 nm cobalt nanoparticles. In the initial states, we observe dipolar ferromagnetism, antiferromagnetism and local flux closure, depending on the particle arrangement. Surprisingly, after magnetic saturation, measurements and numerical simulations show that overall ferromagnetic order exists in the present nanoparticle assemblies even when their arrangement is completely disordered. Such direct quantification of the correlation between topological and magnetic order is essential for the technological exploitation of magnetic quasi-2D nanoparticle assemblies. PMID:23390584

  16. Nuclear magnetic resonance signal dynamics of liquids in the presence of distant dipolar fields, revisited.

    PubMed

    Barros, Wilson; Gochberg, Daniel F; Gore, John C

    2009-05-07

    The description of the nuclear magnetic resonance magnetization dynamics in the presence of long-range dipolar interactions, which is based upon approximate solutions of Bloch-Torrey equations including the effect of a distant dipolar field, has been revisited. New experiments show that approximate analytic solutions have a broader regime of validity as well as dependencies on pulse-sequence parameters that seem to have been overlooked. In order to explain these experimental results, we developed a new method consisting of calculating the magnetization via an iterative formalism where both diffusion and distant dipolar field contributions are treated as integral operators incorporated into the Bloch-Torrey equations. The solution can be organized as a perturbative series, whereby access to higher order terms allows one to set better boundaries on validity regimes for analytic first-order approximations. Finally, the method legitimizes the use of simple analytic first-order approximations under less demanding experimental conditions, it predicts new pulse-sequence parameter dependencies for the range of validity, and clarifies weak points in previous calculations.

  17. New cofactor supports α,β-unsaturated acid decarboxylation via 1,3-dipolar cycloaddition.

    PubMed

    Payne, Karl A P; White, Mark D; Fisher, Karl; Khara, Basile; Bailey, Samuel S; Parker, David; Rattray, Nicholas J W; Trivedi, Drupad K; Goodacre, Royston; Beveridge, Rebecca; Barran, Perdita; Rigby, Stephen E J; Scrutton, Nigel S; Hay, Sam; Leys, David

    2015-06-25

    The bacterial ubiD and ubiX or the homologous fungal fdc1 and pad1 genes have been implicated in the non-oxidative reversible decarboxylation of aromatic substrates, and play a pivotal role in bacterial ubiquinone (also known as coenzyme Q) biosynthesis or microbial biodegradation of aromatic compounds, respectively. Despite biochemical studies on individual gene products, the composition and cofactor requirement of the enzyme responsible for in vivo decarboxylase activity remained unclear. Here we show that Fdc1 is solely responsible for the reversible decarboxylase activity, and that it requires a new type of cofactor: a prenylated flavin synthesized by the associated UbiX/Pad1. Atomic resolution crystal structures reveal that two distinct isomers of the oxidized cofactor can be observed, an isoalloxazine N5-iminium adduct and a N5 secondary ketimine species with markedly altered ring structure, both having azomethine ylide character. Substrate binding positions the dipolarophile enoic acid group directly above the azomethine ylide group. The structure of a covalent inhibitor-cofactor adduct suggests that 1,3-dipolar cycloaddition chemistry supports reversible decarboxylation in these enzymes. Although 1,3-dipolar cycloaddition is commonly used in organic chemistry, we propose that this presents the first example, to our knowledge, of an enzymatic 1,3-dipolar cycloaddition reaction. Our model for Fdc1/UbiD catalysis offers new routes in alkene hydrocarbon production or aryl (de)carboxylation.

  18. Dipolar interaction effects in the magnetic and magnetotransport properties of ordered nanoparticle arrays.

    PubMed

    Kechrakos, D; Trohidou, K N

    2008-06-01

    Assemblies of magnetic nanoparticles exhibit interesting physical properties arising from the competition of intraparticle dynamics and interparticle interactions. In ordered arrays of magnetic nanoparticles magnetostatic interparticle interactions introduce collective dynamics acting competitively to random anisotropy. Basic understanding, characterization and control of dipolar interaction effects in arrays of magnetic nanoparticles is an issue of central importance. To this end, numerical simulation techniques offer an indispensable tool. We report on Monte Carlo studies of the magnetic hysteresis and spin-dependent transport in thin films formed by ordered arrays of magnetic nanoparticles. Emphasis is given to the modifications of the single-particle behavior due to interparticle dipolar interactions as these arise in quantities of experimental interest, such as, the magnetization, the susceptibility and the magnetoresistance. We investigate the role of the structural parameters of an array (interparticle separation, number of stacked monolayers) and the role of the internal structure of the nanoparticles (single phase, core-shell). Dipolar interactions are responsible for anisotropic magnetic behavior between the in-plane and out-of-plane directions of the sample, which is reflected on the investigated magnetic properties (magnetization, transverse susceptibility and magnetoresistance) and the parameters of the array (remanent magnetization, coercive field, and blocking temperature). Our numerical results are compared to existing measurements on self-assembled arrays of Fe-based and Co nanoparticles is made.

  19. Magnetotail dipolarization and associated current systems observed by Cluster and Double Star

    NASA Astrophysics Data System (ADS)

    Volwerk, M.; Lui, A. T. Y.; Lester, M.; Walsh, A. P.; Alexeev, I.; Cao, X.; Dunlop, M. W.; Fazakerley, A. N.; Grocott, A.; Kistler, L.; Lun, X.; Mouikis, C.; Pu, Z.; Shen, C.; Shi, J. K.; Taylor, M. G. G. T.; Baumjohann, W.; Nakamura, R.; Runov, A.; VöRöS, Z.; Zhang, T. L.; Takada, T.; RèMe, H.; Klecker, B.; Carr, C. M.

    2008-08-01

    A dipolarization and its associated current systems are studied using Cluster, Double Star TC1, and ground-based observations. The Cluster spacecraft are located approximately 16 RE downtail near 0030 LT. The Double Star TC1 spacecraft is located more earthward at approximately 7 RE just before local midnight. Auroral observations by the Wideband Imaging Camera on the Imager for Magnetopause-to-Aurora Global Exploration spacecraft are used to determine the onset times of substorms. It is shown that the magnetic phenomena at the earthward site of a magnetic reconfiguration region are governed by field-aligned currents, which in their turn generate auroral brightenings near the foot points of the spacecraft. It is also shown that the inward and outward motion of the dipolarization front near Cluster has a direct influence on the parallel plasma flow at TC1, indicating a piston mechanism. Just like a piston, the inward moving dipolarization at Cluster pushes in plasma along with the flux transport, which turns to parallel plasma flow at TC1. When the flow reverses at Cluster, i.e., outgoing flux transport, the plasma gets "sucked out" again, which is directly reflected in the plasma data from TC1.

  20. Dipolar condensates with tilted dipoles in a pancake-shaped confinement

    NASA Astrophysics Data System (ADS)

    Mishra, Chinmayee; Nath, Rejish

    2016-09-01

    The effect of dipolar orientation with respect to the condensate plane on the mean-field dynamics of dipolar Bose-Einstein condensates in a pancake-shaped confinement is discussed. The stability of a quasi-two-dimensional condensate, with respect to the tilting angle, is found to be different from a two-dimensional layer of dipoles, indicating the relevance of the transverse extension while characterizing two-dimensional dipolar systems. An anisotropic excitation spectrum exhibiting a highly tunable, rotonlike minimum can arise entirely from the dipole-dipole interactions, by tilting the dipoles. At the magic angle and in the absence of contact interactions, the long-wavelength excitations are not phononlike and always unstable. The post-roton-instability dynamics, in contrast to phonon instability, in a uniform condensate, is featured by a transient, defect-free, stripe pattern, which eventually undergoes local collapses, and driving the condensate back into the stable regime can make them sustained for longer. Hopping between stripes has been observed before it melts into a uniform state in the presence of dissipation. Finally, we discuss a class of solutions, in which a quasi-two-dimensional condensate is self-trapped in one direction, as well as a regime of interaction parameters, including attractive short-range interactions, at which a two-dimensional anisotropic soliton can be stabilized, and we show that a chromium condensate with a relatively small number of atoms is well suited for this.

  1. Constraining the dipolar magnetic field of M82 X-2 by the accretion model

    NASA Astrophysics Data System (ADS)

    Chen, Wen-Cong

    2017-02-01

    Recently, ultraluminous X-ray source (ULX) M82 X-2 has been identified to be an accreting neutron star, which has a P = 1.37 s spin period, and is spinning up at a rate dot{P}=-2.0× 10^{-10} s s^{-1}. Interestingly, its isotropic X-ray luminosity Liso = 1.8 × 1040 erg s- 1 during outbursts is 100 times the Eddington limit for a 1.4 M⊙ neutron star. In this Letter, based on the standard accretion model we attempt to constrain the dipolar magnetic field of the pulsar in ULX M82 X-2. Our calculations indicate that the accretion rate at the magnetospheric radius must be super-Eddington during outbursts. To support such a super-Eddington accretion, a relatively high multipole field ( ≳ 1013 G) near the surface of the accretor is invoked to produce an accreting gas column. However, our constraint shows that the surface dipolar magnetic field of the pulsar should be in the range of 1.0-3.5 × 1012 G. Therefore, our model supports that the neutron star in ULX M82 X-2 could be a low-magnetic-field magnetar (proposed by Tong) with a normal dipolar field (˜1012 G) and relatively strong multipole field. For the large luminosity variations of this source, our scenario can also present a self-consistency interpretation.

  2. Theoretical Study of Dual-Direction Dipolar Excitation of Ions in Linear Ion Traps.

    PubMed

    Dang, Qiankun; Xu, Fuxing; Wang, Liang; Huang, Xiaohua; Dai, Xinhua; Fang, Xiang; Wang, Rizhi; Ding, Chuan-Fan

    2016-04-01

    The ion enhanced activation and collision-induced dissociation (CID) by simultaneous dipolar excitation of ions in the two radial directions of linear ion trap (LIT) have been recently developed and tested by experiment. In this work, its detailed properties were further studied by theoretical simulation. The effects of some experimental parameters such as the buffer gas pressure, the dipolar excitation signal phases, power amplitudes, and frequencies on the ion trajectory and energy were carefully investigated. The results show that the ion activation energy can be significantly increased by dual-direction excitation using two identical dipolar excitation signals because of the addition of an excitation dimension and the fact that the ion motion radius related to ion kinetic energy can be greater than the field radius. The effects of higher-order field components, such as dodecapole field on the performance of this method are also revealed. They mainly cause ion motion frequency shift as ion motion amplitude increases. Because of the frequency shift, there are different optimized excitation frequencies in different LITs. At the optimized frequency, ion average energy is improved significantly with relatively few ions lost. The results show that this method can be used in different kinds of LITs such as LIT with 4-fold symmetric stretch, linear quadrupole ion trap, and standard hyperbolic LIT, which can significantly increase the ion activation energy and CID efficiency, compared with the conventional method.

  3. Nonlinear localized modes in dipolar Bose-Einstein condensates in optical lattices

    SciTech Connect

    Rojas-Rojas, S.; Vicencio, R. A.; Molina, M. I.; Abdullaev, F. Kh.

    2011-09-15

    Modulational instability and discrete matter wave solitons in dipolar BECs, loaded into a deep optical lattice, are investigated analytically and numerically. The process of modulational instability of nonlinear plane matter waves in a dipolar nonlinear lattice is studied and the regions of instability are established. The existence and stability of bulk discrete solitons are analyzed analytically and confirmed by numerical simulations. In marked contrast with the usual discrete nonlinear Schroedinger behavior (no dipolar interactions), we found a region where the two fundamental modes are simultaneously unstable, allowing enhanced mobility across the lattice for large norm values. To study the existence and properties of surface discrete solitons, an analysis of the dimer configuration is performed. The properties of symmetric and antisymmetric modes including stability diagrams and bifurcations are investigated in closed form. For the case of a bulk medium, properties of fundamental on-site and intersite localized modes are analyzed. On-site and intersite surface localized modes are studied, and we find that they do not exist when nonlocal interactions predominate with respect to local ones.

  4. Impurity modes in Frenkel exciton systems with dipolar interactions and cubic symmetry.

    PubMed

    Avgin, I; Huber, D L

    2013-04-28

    We introduce a continuum model for impurity modes of Frenkel excitons in fully occupied face-centered and body-centered cubic lattices with dipole-dipole interactions and parallel moments. In the absence of impurities, the model reproduces the small-k behavior found in numerical calculations of dipolar lattice sums. The exciton densities of states near the upper and lower band edges are calculated and compared with the corresponding results for a random array of dipoles. The Green function obtained with the continuum model, together with a spherical approximation to the Brillouin zone, is used to determine the conditions for the formation of a localized exciton mode associated with a shift in the transition energy of a single chromophore. The dependence of the local mode energy on the magnitude of the shift is ascertained. The formation of impurity bands at high concentrations of perturbed sites is investigated using the coherent potential approximation. The contribution of the impurity bands to the optical absorption is calculated in the coherent potential approximation. The locations of the optical absorption peaks of the dipolar system are shown to depend on the direction of propagation of the light relative to the dipolar axis, a property that is maintained in the presence of short-range interactions.

  5. The effect of bottom friction on tidal dipolar vortices and the associated transport

    NASA Astrophysics Data System (ADS)

    Duran-Matute, Matias; Kamp, Leon; van Heijst, Gertjan

    2016-11-01

    Tidal dipolar vortices can be formed in a semi-enclosed basin as the tides flow in and out through an inlet. If they are strong enough to overcome the opposing tidal currents, these vortices can travel away from the inlet due to their self-propelling mechanism, and hence, act as an efficient transport agent for suspended material. We present results of two-dimensional numerical simulations of the flow through an idealized tidal inlet, with either a linear or a nonlinear parameterization of the bottom friction. We then quantify the effect of the bottom friction on the propagation of the dipolar vortex and on its ability as a transport agent by computing the flushing and residence times of passive particles. Bottom friction is detrimental to the ability of tidal dipolar vortices to propagate and hinders transport away from the inlet. The magnitude of this effect is related to the relative duration of the tidal period as compared to the typical decay time scale of the vortex dipole. This research is funded by NWO (the Netherlands) through the VENI Grant 863.13.022.

  6. Chain-based order and quantum spin liquids in dipolar spin ice

    NASA Astrophysics Data System (ADS)

    McClarty, P. A.; Sikora, O.; Moessner, R.; Penc, K.; Pollmann, F.; Shannon, N.

    2015-09-01

    Recent experiments on the spin-ice material Dy2Ti2O7 suggest that the Pauling "ice entropy," characteristic of its classical Coulombic spin-liquid state, may be lost at low temperatures [Pomaranski et al., Nat. Phys. 9, 353 (2013), 10.1038/nphys2591]. However, despite nearly two decades of intensive study, the nature of the equilibrium ground state of spin ice remains uncertain. Here we explore how long-range dipolar interactions D , short-range exchange interactions, and quantum fluctuations combine to determine the ground state of dipolar spin ice. We identify the organizational principle that ordered ground states are selected from a set of "chain states" in which dipolar interactions are exponentially screened. Using both quantum and classical Monte Carlo simulation, we establish phase diagrams as a function of quantum tunneling g and temperature T , and find that only a very small gc≪D is needed to stabilize a quantum spin liquid ground state. We discuss the implications of these results for Dy2Ti2O7 .

  7. New cofactor supports α,β-unsaturated acid decarboxylation via 1,3-dipolar cycloaddition

    PubMed Central

    Payne, Karl A.P.; White, Mark D.; Fisher, Karl; Khara, Basile; Bailey, Samuel S.; Parker, David; Rattray, Nicholas J.W.; Trivedi, Drupad K.; Goodacre, Royston; Beveridge, Rebecca; Barran, Perdita; Rigby, Stephen E.J.; Scrutton, Nigel S.; Hay, Sam; Leys, David

    2016-01-01

    The ubiD/ubiX or the homologous fdc/pad genes have been implicated in the non-oxidative reversible decarboxylation of aromatic substrates, and play a pivotal role in bacterial ubiquinone biosynthesis1–3 or microbial biodegradation of aromatic compounds4–6 respectively. Despite biochemical studies on individual gene products, the composition and co-factor requirement of the enzyme responsible for in vivo decarboxylase activity remained unclear7–9. We show Fdc is solely responsible for (de)carboxylase activity, and that it requires a new type of cofactor: a prenylated flavin synthesised by the associated UbiX/Pad10. Atomic resolution crystal structures reveal two distinct isomers of the oxidized cofactor can be observed: an isoalloxazine N5-iminium adduct and a N5 secondary ketimine species with drastically altered ring structure, both having azomethine ylide character. Substrate binding positions the dipolarophile enoic acid group directly above the azomethine ylide group. The structure of a covalent inhibitor-cofactor adduct suggests 1,3-dipolar cycloaddition chemistry supports reversible decarboxylation in these enzymes. While 1,3-dipolar cycloaddition is commonly used in organic chemistry11–12, we propose this presents the first example of an enzymatic 1,3-dipolar cycloaddition reaction. Our model for Fdc/UbiD catalysis offers new routes in alkene hydrocarbon production or aryl (de)carboxylation. PMID:26083754

  8. Phase transitions to dipolar clusters and charge density waves in high Tc superconductors

    NASA Astrophysics Data System (ADS)

    Saarela, M.; Kusmartsev, F. V.

    2017-02-01

    We show that doping of hole charge carriers leads to formation of electric dipolar clusters in cuprates. They are created by many-body interactions between the dopant ion outside and holes inside the CuO planes. Because of the two-fold degeneracy holes in the CuO plane cluster into four-particles resonance valence bond plaquettes bound with dopant ions. Such dipoles may order into charge-density waves (CDW) or stripes or form a disordered state depending on doping and temperature. The lowest energy of the ordered system corresponds to a local anti-ferroelectric ordering. The mobility of individual disordered dipoles is very low at low temperatures and they prefer first to bind into dipole-dipole pairs. Electromagnetic radiation interacts strongly with electric dipoles and when the sample is subjected to it the mobility changes significantly. This leads to a fractal growth of dipolar clusters. The existence of electric dipoles and CDW induce two phase transitions with increasing temperature, melting of the ordered state and disappearance of the dipolar state. Ferroelectricity at low doping is a natural consequence of such dipole moments. We develop a theory based on two-level systems and dipole-dipole interaction to explain the behavior of the polarization as a function of temperature and electric field.

  9. Theoretical Study of Dual-Direction Dipolar Excitation of Ions in Linear Ion Traps

    NASA Astrophysics Data System (ADS)

    Dang, Qiankun; Xu, Fuxing; Wang, Liang; Huang, Xiaohua; Dai, Xinhua; Fang, Xiang; Wang, Rizhi; Ding, Chuan-Fan

    2016-04-01

    The ion enhanced activation and collision-induced dissociation (CID) by simultaneous dipolar excitation of ions in the two radial directions of linear ion trap (LIT) have been recently developed and tested by experiment. In this work, its detailed properties were further studied by theoretical simulation. The effects of some experimental parameters such as the buffer gas pressure, the dipolar excitation signal phases, power amplitudes, and frequencies on the ion trajectory and energy were carefully investigated. The results show that the ion activation energy can be significantly increased by dual-direction excitation using two identical dipolar excitation signals because of the addition of an excitation dimension and the fact that the ion motion radius related to ion kinetic energy can be greater than the field radius. The effects of higher-order field components, such as dodecapole field on the performance of this method are also revealed. They mainly cause ion motion frequency shift as ion motion amplitude increases. Because of the frequency shift, there are different optimized excitation frequencies in different LITs. At the optimized frequency, ion average energy is improved significantly with relatively few ions lost. The results show that this method can be used in different kinds of LITs such as LIT with 4-fold symmetric stretch, linear quadrupole ion trap, and standard hyperbolic LIT, which can significantly increase the ion activation energy and CID efficiency, compared with the conventional method.

  10. Statics and dynamics of a self-bound dipolar matter-wave droplet

    NASA Astrophysics Data System (ADS)

    Adhikari, S. K.

    2017-02-01

    We study the statics and dynamics of a stable, mobile, self-bound three-dimensional dipolar matter-wave droplet created in the presence of a tiny repulsive three-body interaction. In frontal collision with an impact parameter and in angular collision at large velocities along all directions two droplets behave like quantum solitons. Such a collision is found to be quasi elastic and the droplets emerge undeformed after collision without any change of velocity. However, in a collision at small velocities the axisymmeric dipolar interaction plays a significant role and the collision dynamics is sensitive to the direction of motion. For an encounter along the z direction at small velocities, two droplets, polarized along the z direction, coalesce to form a larger droplet—a droplet molecule. For an encounter along the x direction at small velocities, the same droplets stay apart and never meet each other due to the dipolar repulsion. The present study is based on an analytic variational approximation and a numerical solution of the mean-field Gross-Pitaevskii equation using the parameters of 52Cr atoms.

  11. Parametric pumping and kinetics of magnons in dipolar ferromagnets

    SciTech Connect

    Kloss, Thomas; Kreisel, Andreas; Kopietz, Peter

    2010-03-01

    The time evolution of magnons subject to a time-dependent microwave field is usually described within the so-called 'S-theory', where kinetic equations for the distribution function are obtained within the time-dependent Hartree-Fock approximation. To explain the recent observation of 'Bose-Einstein condensation of magnons' in an external microwave field [Demokritov et al., Nature (London) 443, 430 (2006)], we extend the S-theory to include the Gross-Pitaevskii equation for the time-dependent expectation values of the magnon creation and annihilation operators. We explicitly solve the resulting coupled equations within a simple approximation where only a single condensed mode is retained. We also re-examine the usual derivation of an effective boson model from a realistic spin model for yttrium-iron garnet films and argue that in the parallel pumping geometry (where both the static and the time-dependent magnetic field are parallel to the macroscopic magnetization) the time-dependent Zeemann energy cannot give rise to magnon condensation.

  12. Dynamic mesoscale model of dipolar fluids via fluctuating hydrodynamics

    SciTech Connect

    Persson, Rasmus A. X.; Chu, Jhih-Wei; Voulgarakis, Nikolaos K.

    2014-11-07

    Fluctuating hydrodynamics (FHD) is a general framework of mesoscopic modeling and simulation based on conservational laws and constitutive equations of linear and nonlinear responses. However, explicit representation of electrical forces in FHD has yet to appear. In this work, we devised an Ansatz for the dynamics of dipole moment densities that is linked with the Poisson equation of the electrical potential ϕ in coupling to the other equations of FHD. The resulting ϕ-FHD equations then serve as a platform for integrating the essential forces, including electrostatics in addition to hydrodynamics, pressure-volume equation of state, surface tension, and solvent-particle interactions that govern the emergent behaviors of molecular systems at an intermediate scale. This unique merit of ϕ-FHD is illustrated by showing that the water dielectric function and ion hydration free energies in homogeneous and heterogenous systems can be captured accurately via the mesoscopic simulation. Furthermore, we show that the field variables of ϕ-FHD can be mapped from the trajectory of an all-atom molecular dynamics simulation such that model development and parametrization can be based on the information obtained at a finer-grained scale. With the aforementioned multiscale capabilities and a spatial resolution as high as 5 Å, the ϕ-FHD equations represent a useful semi-explicit solvent model for the modeling and simulation of complex systems, such as biomolecular machines and nanofluidics.

  13. Dynamic mesoscale model of dipolar fluids via fluctuating hydrodynamics.

    PubMed

    Persson, Rasmus A X; Voulgarakis, Nikolaos K; Chu, Jhih-Wei

    2014-11-07

    Fluctuating hydrodynamics (FHD) is a general framework of mesoscopic modeling and simulation based on conservational laws and constitutive equations of linear and nonlinear responses. However, explicit representation of electrical forces in FHD has yet to appear. In this work, we devised an Ansatz for the dynamics of dipole moment densities that is linked with the Poisson equation of the electrical potential ϕ in coupling to the other equations of FHD. The resulting ϕ-FHD equations then serve as a platform for integrating the essential forces, including electrostatics in addition to hydrodynamics, pressure-volume equation of state, surface tension, and solvent-particle interactions that govern the emergent behaviors of molecular systems at an intermediate scale. This unique merit of ϕ-FHD is illustrated by showing that the water dielectric function and ion hydration free energies in homogeneous and heterogenous systems can be captured accurately via the mesoscopic simulation. Furthermore, we show that the field variables of ϕ-FHD can be mapped from the trajectory of an all-atom molecular dynamics simulation such that model development and parametrization can be based on the information obtained at a finer-grained scale. With the aforementioned multiscale capabilities and a spatial resolution as high as 5 Å, the ϕ-FHD equations represent a useful semi-explicit solvent model for the modeling and simulation of complex systems, such as biomolecular machines and nanofluidics.

  14. Magneto-thermally activated spin-state transition in La0.95Ca0.05CoO3: magnetically-tunable dipolar glass and giant magneto-electricity.

    PubMed

    Pandey, Suchita; Kumar, Jitender; Awasthi, A M

    2016-03-07

    The magneto-dielectric spectroscopy of La0.95Ca0.05CoO3 covering the crossover of spin states reveals the strong coupling of its spin and dipolar degrees of freedom. The signature of the spin-state transition at 30 K clearly manifests in the magnetization data at a 1 Tesla optimal field. Our Co L3,2-edge X-ray absorption spectrum on the doped specimen is consistent with its suppressed low-to-intermediate spin-state transition temperature at ∼30 K compared to ∼150 K, documented for pure LaCoO3. The dispersive activation step in the dielectric constant with the associated relaxation peak in imaginary permittivity characterize the allied influence of coexistent spin-states on the dielectric character. Dipolar relaxation in the low-spin regime below the transition temperature is partly segmental (Vogel-Fulcher-Tamman (VFT) kinetics) and features magnetic-field tunability, whereas in the low/intermediate-spin disordered state above ∼30 K, it is uncorrelated (Arrhenic kinetics) and almost impervious to the magnetic field H. Kinetics-switchover defines the dipolar-glass transition temperature Tg(H) (=27 K|0T), below which their magneto-thermally-activated cooperative relaxations freeze out by the VFT temperature T0(H) (=15 K|0T). An applied magnetic field facilitates thermal activation in toggling the low spins up into the intermediate states. Consequently, the downsized dipolar-glass segments in the low-spin state and the independent dipoles in the intermediate state exhibit accelerated dynamics. A critical 5 Tesla field collapses the entire relaxation kinetics into a single Arrhenic behaviour, signaling that the dipolar glass is completely devitrified under all higher fields. The magneto-electricity (ME) spanning sizeable thermo-spectral range registers diverse signatures here in kinetic, spectral, and field behaviors, in contrast to the static/perturbative ME observed close to the spin-ordering in typical multiferroics. Intrinsic magneto-dielectricity (50%) along

  15. The [3 + 3]-Cycloaddition Alternative for Heterocycle Syntheses: Catalytically Generated Metalloenolcarbenes as Dipolar Adducts

    PubMed Central

    2015-01-01

    Conspectus The combination of two or more unsaturated structural units to form cyclic organic compounds is commonly referred to as cycloaddition, and the combination of two unsaturated structural units that forms a six-membered ring is formally either a [5 + 1]-, [4 + 2]-, [2 + 2 + 2]-, or [3 + 3]-cycloaddition. Occurring as concerted or stepwise processes, cycloaddition reactions are among the most useful synthetic constructions in organic chemistry. Of these transformations, the concerted [4 + 2]-cycloaddition, the Diels–Alder reaction, is by far the best known and most widely applied. However, although symmetry disallowed as a concerted process and lacking certifiable examples until recently, stepwise [3 + 3]-cycloadditions offer advantages for the synthesis of a substantial variety of heterocyclic compounds, and they are receiving considerable attention. In this Account, we present the development of stepwise [3 + 3]-cycloaddition reactions from virtual invisibility in the 1990s to a rapidly growing synthetic methodology today, involving organocatalysis or transition metal catalysis. With origins in organometallic or vinyliminium ion chemistry, this area has blossomed into a viable synthetic transformation for the construction of six-membered heterocyclic compounds containing one or more heteroatoms. The development of [3 + 3]-cycloaddition transformations has been achieved through identification of suitable and compatible reactive dipolar adducts and stable dipoles. The reactive dipolar species is an energetic dipolar intermediate that is optimally formed catalytically in the reaction. The stepwise process occurs with the reactive dipolar adduct reacting as an electrophile or as a nucleophile to form the first covalent bond, and this association provides entropic assistance for the construction of the second covalent bond and the overall formal [3 + 3]-cycloaddition. Organocatalysis is well developed for both inter- and intramolecular synthetic

  16. The [3 + 3]-cycloaddition alternative for heterocycle syntheses: catalytically generated metalloenolcarbenes as dipolar adducts.

    PubMed

    Xu, Xinfang; Doyle, Michael P

    2014-04-15

    The combination of two or more unsaturated structural units to form cyclic organic compounds is commonly referred to as cycloaddition, and the combination of two unsaturated structural units that forms a six-membered ring is formally either a [5 + 1]-, [4 + 2]-, [2 + 2 + 2]-, or [3 + 3]-cycloaddition. Occurring as concerted or stepwise processes, cycloaddition reactions are among the most useful synthetic constructions in organic chemistry. Of these transformations, the concerted [4 + 2]-cycloaddition, the Diels-Alder reaction, is by far the best known and most widely applied. However, although symmetry disallowed as a concerted process and lacking certifiable examples until recently, stepwise [3 + 3]-cycloadditions offer advantages for the synthesis of a substantial variety of heterocyclic compounds, and they are receiving considerable attention. In this Account, we present the development of stepwise [3 + 3]-cycloaddition reactions from virtual invisibility in the 1990s to a rapidly growing synthetic methodology today, involving organocatalysis or transition metal catalysis. With origins in organometallic or vinyliminium ion chemistry, this area has blossomed into a viable synthetic transformation for the construction of six-membered heterocyclic compounds containing one or more heteroatoms. The development of [3 + 3]-cycloaddition transformations has been achieved through identification of suitable and compatible reactive dipolar adducts and stable dipoles. The reactive dipolar species is an energetic dipolar intermediate that is optimally formed catalytically in the reaction. The stepwise process occurs with the reactive dipolar adduct reacting as an electrophile or as a nucleophile to form the first covalent bond, and this association provides entropic assistance for the construction of the second covalent bond and the overall formal [3 + 3]-cycloaddition. Organocatalysis is well developed for both inter- and intramolecular synthetic transformations, but the

  17. Fortran and C programs for the time-dependent dipolar Gross-Pitaevskii equation in an anisotropic trap

    NASA Astrophysics Data System (ADS)

    Kumar, R. Kishor; Young-S., Luis E.; Vudragović, Dušan; Balaž, Antun; Muruganandam, Paulsamy; Adhikari, S. K.

    2015-10-01

    Many of the static and dynamic properties of an atomic Bose-Einstein condensate (BEC) are usually studied by solving the mean-field Gross-Pitaevskii (GP) equation, which is a nonlinear partial differential equation for short-range atomic interaction. More recently, BEC of atoms with long-range dipolar atomic interaction are used in theoretical and experimental studies. For dipolar atomic interaction, the GP equation is a partial integro-differential equation, requiring complex algorithm for its numerical solution. Here we present numerical algorithms for both stationary and non-stationary solutions of the full three-dimensional (3D) GP equation for a dipolar BEC, including the contact interaction. We also consider the simplified one- (1D) and two-dimensional (2D) GP equations satisfied by cigar- and disk-shaped dipolar BECs. We employ the split-step Crank-Nicolson method with real- and imaginary-time propagations, respectively, for the numerical solution of the GP equation for dynamic and static properties of a dipolar BEC. The atoms are considered to be polarized along the z axis and we consider ten different cases, e.g., stationary and non-stationary solutions of the GP equation for a dipolar BEC in 1D (along x and z axes), 2D (in x- y and x- z planes), and 3D, and we provide working codes in Fortran 90/95 and C for these ten cases (twenty programs in all). We present numerical results for energy, chemical potential, root-mean-square sizes and density of the dipolar BECs and, where available, compare them with results of other authors and of variational and Thomas-Fermi approximations.

  18. Observation of coupled vortex gyrations by 70-ps-time and 20-nm-space- resolved full-field magnetic transmission soft x-ray microscopy

    SciTech Connect

    Jung, Hyunsung; Yu, Young-Sang; Lee, Ki-Suk; Im, Mi-Young; Fischer, Peter; Bocklage, Lars; Vogel, Andreas; Bolte, Markus; Meier, Guido; Kim, Sang-Koog

    2010-09-01

    We employed time-and space-resolved full-field magnetic transmission soft x-ray microscopy to observe vortex-core gyrations in a pair of dipolar-coupled vortex-state Permalloy (Ni{sub 80}Fe{sub 20}) disks. The 70 ps temporal and 20 nm spatial resolution of the microscope enabled us to simultaneously measure vortex gyrations in both disks and to resolve the phases and amplitudes of both vortex-core positions. We observed their correlation for a specific vortex-state configuration. This work provides a robust and direct method of studying vortex gyrations in dipolar-coupled vortex oscillators.

  19. Dipolar colloids in nematostatics: Tensorial structure, symmetry, different types, and their interaction

    NASA Astrophysics Data System (ADS)

    Pergamenshchik, V. M.; Uzunova, V. A.

    2011-02-01

    In spite of the analogy to the electrostatics, the three-dimensional colloidal nematostatics is substantially different in both its mathematical structure and its physical implications. The general tensorial structure of elastic multipoles derived in V. M. Pergamenshchik and V. O. Uzunova [Eur. Phys. J. EEPJSFH1292-894110.1140/epje/i2006-10169-x 23, 161 (2007); Phys. Rev. EEPJSFH1539-375510.1103/PhysRevE.76.011707 76, 011707 (2007)] allows for a classification of different types of colloids in the nematostatics. In comparison to their electrostatic counterparts, the elastic multipoles have one extra tensorial index. Based on this structure, we identify possible types of elastic dipoles. An elastic dipole is characterized by three coefficients—isotropic strength, anisotropy, and chirality—and a two-component vector along the unperturbed director. The relationship between the dipole type and symmetry groups is established and sketches of various representative types of dipolar colloids are given. Instead of a single electric dipole, in the nematostatics there are four different pure types (dipolar singlets) and eight mixed types of elastic dipoles (one quintet, one quartet, two triplets, and four doublets). It is shown that the full symmetry of the colloid-induced director field and the colloid’s shape (body) symmetry determine different dipole components. For instance, a helicoidal component of the anchoring easy axes can make a chiral elastic dipole of a colloid with the quadrupolar shape symmetry. The interaction potentials for different singlet and doublet dipoles are derived and illustrated in terms of the dipolar dyads and elastic Coulomb law. We argue that multipole parameters must be found by pure numerical means, as from ansatz director distributions one can find only orders of their magnitudes.

  20. Different approaches to analyze the dipolar interaction effects on diluted and concentrated granular superparamagnetic systems

    NASA Astrophysics Data System (ADS)

    Moscoso-Londoño, O.; Tancredi, P.; Muraca, D.; Mendoza Zélis, P.; Coral, D.; Fernández van Raap, M. B.; Wolff, U.; Neu, V.; Damm, C.; de Oliveira, C. L. P.; Pirota, K. R.; Knobel, M.; Socolovsky, L. M.

    2017-04-01

    Controlled magnetic granular materials with different concentrations of magnetite nanoparticles immersed in a non-conducting polymer matrix were synthesized and, their macroscopic magnetic observables analyzed in order to advance towards a better understanding of the magnetic dipolar interactions and its effects on the obtained magnetic parameters. First, by means of X-ray diffraction, transmission electron microscopy, small angle X-ray scattering and X-ray absorption fine structure an accurate study of the structural properties was carried out. Then, the magnetic properties were analyzed by means of different models, including those that consider the magnetic interactions through long-range dipolar forces as: the Interacting Superparamagnetic Model (ISP) and the Vogel-Fulcher law (V-F). In systems with larger nanoparticle concentrations, magnetic results clearly indicate that the role played by the dipolar interactions affects the magnetic properties, giving rise to obtaining magnetic and structural parameters without physical meaning. Magnetic parameters as the effective anisotropic constant, magnetic moment relaxation time and mean blocking temperature, extracted from the application of the ISP model and V-F Law, were used to simulate the zero-field-cooling (ZFC) and field-cooling curves (FC). A comparative analysis of the simulated, fitted and experimental ZFC/FC curves suggests that the current models depict indeed our dilute granular systems. Notwithstanding, for concentrated samples, the ISP model infers that clustered nanoparticles are being interpreted as single entities of larger magnetic moment and volume, effect that is apparently related to a collective and complex magnetic moment dynamics within the cluster.

  1. Persistent Superfluid Flow Arising from the He-McKellar-Wilkens Effect in Molecular Dipolar Condensates

    NASA Astrophysics Data System (ADS)

    Wood, A. A.; McKellar, B. H. J.; Martin, A. M.

    2016-06-01

    We show that the He-McKellar-Wilkens effect can induce a persistent flow in a Bose-Einstein condensate of polar molecules confined in a toroidal trap, with the dipolar interaction mediated via an electric dipole moment. For Bose-Einstein condensates of atoms with a magnetic dipole moment, we show that although it is theoretically possible to induce persistent flow via the Aharonov-Casher effect, the strength of the electric field required is prohibitive. We also outline an experimental geometry tailored specifically for observing the He-McKellar-Wilkens effect in toroidally trapped condensates.

  2. Persistent Superfluid Flow Arising from the He-McKellar-Wilkens Effect in Molecular Dipolar Condensates.

    PubMed

    Wood, A A; McKellar, B H J; Martin, A M

    2016-06-24

    We show that the He-McKellar-Wilkens effect can induce a persistent flow in a Bose-Einstein condensate of polar molecules confined in a toroidal trap, with the dipolar interaction mediated via an electric dipole moment. For Bose-Einstein condensates of atoms with a magnetic dipole moment, we show that although it is theoretically possible to induce persistent flow via the Aharonov-Casher effect, the strength of the electric field required is prohibitive. We also outline an experimental geometry tailored specifically for observing the He-McKellar-Wilkens effect in toroidally trapped condensates.

  3. Influence of the black hole spin on the chaotic particle dynamics within a dipolar halo

    NASA Astrophysics Data System (ADS)

    Nag, Sankhasubhra; Sinha, Siddhartha; Ananda, Deepika B.; Das, Tapas K.

    2017-04-01

    We investigate the role of the spin angular momentum of astrophysical black holes in controlling the special relativistic chaotic dynamics of test particles moving under the influence of a post-Newtonian pseudo-Kerr black hole potential, along with a perturbative potential created by an asymmetrically placed (dipolar) halo. Proposing a Lyapunov-like exponent to be the effective measure of the degree of chaos observed in the system under consideration, it has been found that black hole spin anti-correlates with the degree of chaos for the aforementioned dynamics. Our findings have been explained applying the general principles of dynamical systems analysis.

  4. Single molecule tunneling spectroscopy investigation of reversibly switched dipolar vanadyl phthalocyanine on graphite

    SciTech Connect

    Zhang, Jialin; Wang, Zhunzhun; Li, Zhenyu E-mail: phycw@nus.edu.sg; Niu, Tianchao; Chen, Wei E-mail: phycw@nus.edu.sg

    2014-03-17

    We report a spatially resolved scanning tunneling spectroscopy (STS) investigation of reversibly switchable dipolar vanadyl phthalocyanine (VOPc) on graphite by using low temperature scanning tunneling microscopy. VOPc molecule can be switched between O-up and O-down configurations by changing the polarity of the pulse voltage applied to the tip, actuated by the inelastic tunneling electrons. The spatially resolved STS measurements allow the identification of the electronic structures of VOPc with different dipole orientation. The present approach provides geometry images and electronic characterization of a molecular switch on surface spontaneously.

  5. Dipolar field-induced spin-wave waveguides for spin-torque magnonics

    SciTech Connect

    Demidov, V. E.; Urazhdin, S.; Zholud, A.; Sadovnikov, A. V.; Demokritov, S. O.

    2015-01-12

    We use high-resolution imaging to study the propagation of spin waves in magnonic waveguides created by the dipolar magnetic fields of microscopic patterns. We show that the characteristics of spin-wave modes in such waveguides depend strongly on their geometry. In particular, by tuning the geometrical parameters, field-induced confinement for both the edge and the center waveguide modes can be achieved, enabling control over the spin-wave transmission characteristics. The studied waveguiding structures are particularly promising for the implementation of magnonic devices utilizing spin-torque phenomena.

  6. s -wave scattering lengths of the strongly dipolar bosons 162Dy and 164Dy

    NASA Astrophysics Data System (ADS)

    Tang, Yijun; Sykes, Andrew; Burdick, Nathaniel Q.; Bohn, John L.; Lev, Benjamin L.

    2015-08-01

    We report the measurement of the deca-heptuplet s -partial-wave scattering length a of two bosonic isotopes of the highly magnetic element dysprosium: a =112 (10 ) a0 for 162Dy and a =92 (8 ) a0 for 164Dy, where a0 is the Bohr radius. The scattering lengths are determined by the cross-dimensional relaxation of ultracold gases of these Dy isotopes at temperatures above quantum degeneracy. In this temperature regime, the measured rethermalization dynamics can be compared to simulations of the Boltzmann equation using a direct-simulation Monte Carlo method employing the anisotropic differential scattering cross section of dipolar particles.

  7. Triazol-substituted titanocenes by strain-driven 1,3-dipolar cycloadditions

    PubMed Central

    Okkel, Andreas; Schwach, Lukas; Wagner, Laura; Selig, Anja; Prokop, Aram

    2014-01-01

    Summary An operationally simple, convenient, and mild strategy for the synthesis of triazole-substituted titanocenes via strain-driven 1,3-dipolar cycloadditions between azide-functionalized titanocenes and cyclooctyne has been developed. It features the first synthesis of titanocenes containing azide groups. These compounds constitute ‘second-generation’ functionalized titanocene building blocks for further synthetic elaboration. Our synthesis is modular and large numbers of the complexes can in principle be prepared in short periods of time. Some of the triazole-substituted titanocenes display high cyctotoxic activity against BJAB cells. Comparison of the most active complexes allows the identification of structural features essential for biological activity. PMID:25161720

  8. Vortex dipolar structures in a rigid model of the larynx at flow onset

    NASA Astrophysics Data System (ADS)

    Chisari, N. E.; Artana, G.; Sciamarella, D.

    2011-02-01

    Starting jet airflow is investigated in a channel with a pair of consecutive slitted constrictions approximating the true and false vocal folds in the human larynx. The flow is visualized using the Schlieren optical technique and simulated by solving the Navier-Stokes equations for an incompressible two-dimensional viscous flow. Laboratory and numerical experiments show the spontaneous formation of three different classes of vortex dipolar structures in several regions of the laryngeal profile under conditions that may be assimilated to those of voice onset.

  9. Biological colloid engineering: Self-assembly of dipolar ferromagnetic chains in a functionalized biogenic ferrofluid.

    PubMed

    Ruder, Warren C; Hsu, Chia-Pei D; Edelman, Brent D; Schwartz, Russell; Leduc, Philip R

    2012-08-06

    We have studied the dynamic behavior of nanoparticles in ferrofluids consisting of single-domain, biogenic magnetite (Fe(3)O(4)) isolated from Magnetospirillum magnetotacticum (MS-1). Although dipolar chains form in magnetic colloids in zero applied field, when dried upon substrates, the solvent front disorders nanoparticle aggregation. Using avidin-biotin functionalization of the particles and substrate, we generated self-assembled, linear chain motifs that resist solvent front disruption in zero-field. The engineered self-assembly process we describe here provides an approach for the creation of ordered magnetic structures that could impact fields ranging from micro-electro-mechanical systems development to magnetic imaging of biological structures.

  10. 1,3-Dipolar Cycloaddition Reactions of Azomethine Ylides with Carbonyl Dipolarophiles Yielding Oxazolidine Derivatives.

    PubMed

    Meyer, Adam G; Ryan, John H

    2016-07-23

    We provide a comprehensive account of the 1,3-dipolar cycloaddition reactions of azomethine ylides with carbonyl dipolarophiles. Many different azomethine ylides have been studied, including stabilized and non-stabilized ylides. Of the carbonyl dipolarophiles, aldehydes including formaldehyde are the most studied, although there are now examples of cycloadditions with ketones, ketenes and carboxyl systems, in particular isatoic anhydrides and phthalic anhydrides. Intramolecular cycloadditions with esters can also occur under certain circumstances. The oxazolidine cycloadducts undergo a range of reactions triggered by the ring-opening of the oxazolidine ring system.

  11. Three-body interacting dipolar bosons and the fate of lattice supersolidity

    NASA Astrophysics Data System (ADS)

    Singh, Manpreet; Mishra, Tapan

    2016-12-01

    We investigate a system of dipolar bosons in an optical lattice with local two- and three-body interactions. Using the mean-field-theory approach, we obtain the ground-state phase diagram of the extended Bose-Hubbard model with both repulsive and attractive three-body interactions. We show that the additional three-body on-site interaction has strong effects on the phase diagram, especially on the supersolid phase. Positive values of the three-body interaction lead to the enhancement of the gapped phases at densities larger than unity by reducing the supersolid region. However, a small attractive three-body interaction enhances the supersolid phase.

  12. Theoretical Study of 1,3-Dipolar Cycloaddition of Hydrazoic Acid to Substituted Ynamines

    NASA Astrophysics Data System (ADS)

    Chen, Xiao-fang; Yang, Kun; Han, Ke-li

    2009-04-01

    The 1,3-dipolar cycloaddition reactions of various substituted ynamines with hydrazoic acid were theoretically investigated with the high-accuracy CBS-QB3 method. Two regioisomers, 4-amine, and 5-amine substituted adducts, were obtained, with the former as the preferred yield. This regioselectivity is rationalized by the frontier molecular orbital theory. The reactivity and synchronicity are enhanced with the increase of the electron-withdrawing character of the substitute on ynamine fragment. The calculations also show that the effect of solvent increases the activation energy, and the reaction becomes even harder in polar solvent.

  13. Multiple Field Induced Transitions in the Dipolar Pyrochlore Gd2 Ti2 O_7

    NASA Astrophysics Data System (ADS)

    Shastry, B. Sriram

    2003-03-01

    Pyrochlore frustrated magnetic systems have received considerable attention after the experiment by Ramirez and coworkers on the ``Spin Ice'' compound DTO or Dy2 Ti2 O_7, a magnetic realization of entropic Ice originally studied by Pauling, Bernal and Fowler. DTO consists of effective spin half moments residing on the Pyrochlore lattice, but by changing the rare earth, one has realizations of the XY and also Heisenberg models. GTO, or Gd2 Ti2 O7 is a Heisenberg system, where the interactions are predominantly dipolar with a weak isotropic superexchange. This enables one to study almost for the first time, the rich and novel behavior of spins living on undistorted cubic systems with dipolar interactions, in contrast to the well understood spin flop transition in uniaxial magnets. The thermodynamics in the presence of a magnetic field of (powder) GTO shows a remarkably rich phase diagram[1], with several phase transitions occurring at a given temperature as the field is varied. In an effort to understand this, we have studied a 4- sublattice mean field theory[1] wherein the spins interact via a dipolar interaction plus superexchange. This mean field theory is intriguingly non trivial and reproduces the observed transitions with only one free parameter (J). The magnetic field partially lifts the degeneracy of the six zero field states in a specific ways depending on the direction of the field, signaling the transitions. The nature of some of the transitions is best described in terms of a nematic type order parameter T^α, β=1/4 sum_i=1^4 m^αi m^βi where mi is the sublattice magnetization vector. This talk describes the above experiment and theory, its recent extensions, and also some more recent experiments on GTO. [1] "Multiple Phase Transitions in a Geometrically-Frustrated Dipolar Spin System Gd_2Ti_2O_7, (A P Ramirez, B S Shastry , A Hayashi, J J Krajewski, D A Huse, and R J Cava), Phys. Rev. Letts. 89, 067202 (2002).

  14. Charged, dipolar soft matter systems from a combined microscopic-mesoscopic viewpoint

    NASA Astrophysics Data System (ADS)

    Schröder, Christian; Steinhauser, Othmar

    2016-09-01

    As an example of charged, dipolar soft matter, the ionic liquid 1-ethyl-3-methyl-imidazolium dicyanamide is studied by coarse-grained molecular dynamics simulations. We focus on the link between microscopic and mesoscopic properties for both structure and dynamics. Thereby, the generalized Kirkwood g K-factor plays a central role in establishing this link which is not possible on the basis of molecular hydrodynamics. The decoupling between translational and rotational motion is indicative of the dynamical heterogeneity in ionic liquids.

  15. Comprehensive analysis of lipid dynamics variation with lipid composition and hydration of bicelles using nuclear magnetic resonance (NMR) spectroscopy.

    PubMed

    Yamamoto, Kazutoshi; Soong, Ronald; Ramamoorthy, Ayyalusamy

    2009-06-16

    Bicelles of various lipid/detergent ratios are commonly used in nuclear magnetic resonance (NMR) studies of membrane-associated molecules without the need to freeze the sample. While a decrease in the size (defined at a low temperature or by the q value) of a bicelle decreases its overall order parameter, the variation of lipid dynamics with a change in the lipid/detergent ratio is unknown. In this study, we report a thorough atomistic level analysis on the variation of lipid dynamics with the size and hydration level of bicelles composed of a phospholipid, 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC), and a detergent, 1,2-dihexanoyl-sn-glycero-3-phosphocholine (DHPC). Two-dimensional (2D) separated-local-field NMR experiments were performed on magnetically aligned bicelles to measure (1)H-(13)C dipolar couplings, which were used to determine order parameters at various (head-group, glycerol, and acyl chain) regions of lipids in the bilayer. From our analysis, we uncover the extreme sensitivity of the glycerol region to the motion of the bicelle, which can be attributed to the effect of viscosity because of an extensive network of hydrogen bonds. As such, the water-membrane interface region exhibits the highest order parameter values among all three regions of a lipid molecule. Our experimental results demonstrate that the laboratory-frame 2D proton-detected-local-field pulse sequence is well-suited for the accurate measurement of motionally averaged (or long-range) weak and multiple (1)H-(13)C dipolar couplings associated with a single carbon site at the natural abundance of (13)C nuclei.

  16. Massively parallel implementations of coupled-cluster methods for electron spin resonance spectra. I. Isotropic hyperfine coupling tensors in large radicals

    NASA Astrophysics Data System (ADS)

    Verma, Prakash; Perera, Ajith; Morales, Jorge A.

    2013-11-01

    Coupled cluster (CC) methods provide highly accurate predictions of molecular properties, but their high computational cost has precluded their routine application to large systems. Fortunately, recent computational developments in the ACES III program by the Bartlett group [the OED/ERD atomic integral package, the super instruction processor, and the super instruction architecture language] permit overcoming that limitation by providing a framework for massively parallel CC implementations. In that scheme, we are further extending those parallel CC efforts to systematically predict the three main electron spin resonance (ESR) tensors (A-, g-, and D-tensors) to be reported in a series of papers. In this paper inaugurating that series, we report our new ACES III parallel capabilities that calculate isotropic hyperfine coupling constants in 38 neutral, cationic, and anionic radicals that include the 11B, 17O, 9Be, 19F, 1H, 13C, 35Cl, 33S,14N, 31P, and 67Zn nuclei. Present parallel calculations are conducted at the Hartree-Fock (HF), second-order many-body perturbation theory [MBPT(2)], CC singles and doubles (CCSD), and CCSD with perturbative triples [CCSD(T)] levels using Roos augmented double- and triple-zeta atomic natural orbitals basis sets. HF results consistently overestimate isotropic hyperfine coupling constants. However, inclusion of electron correlation effects in the simplest way via MBPT(2) provides significant improvements in the predictions, but not without occasional failures. In contrast, CCSD results are consistently in very good agreement with experimental results. Inclusion of perturbative triples to CCSD via CCSD(T) leads to small improvements in the predictions, which might not compensate for the extra computational effort at a non-iterative N7-scaling in CCSD(T). The importance of these accurate computations of isotropic hyperfine coupling constants to elucidate experimental ESR spectra, to interpret spin-density distributions, and to

  17. Ground-state properties of few dipolar bosons in a quasi-one-dimensional harmonic trap

    SciTech Connect

    Deuretzbacher, F.; Cremon, J. C.; Reimann, S. M.

    2010-06-15

    We study the ground state of few bosons with repulsive dipole-dipole interaction in a quasi-one-dimensional harmonic trap by means of the exact diagonalization method. Up to three interaction regimes are found, depending on the strength of the dipolar interaction and the ratio of transverse to axial oscillator lengths: a regime where the dipolar Bose gas resembles a system of weakly {delta}-interacting bosons, a second regime where the bosons are fermionized, and a third regime where the bosons form a Wigner crystal. In the first two regimes, the dipole-dipole potential can be replaced by a {delta} potential. In the crystalline state, the overlap between the localized wave packets is strongly reduced and all the properties of the boson system equal those of its fermionic counterpart. The transition from the Tonks-Girardeau gas to the solidlike state is accompanied by a rapid increase of the interaction energy and a considerable change of the momentum distribution, which we trace back to the different short-range correlations in the two interaction regimes.

  18. Creation of a strongly dipolar gas of ultracold ground-state 23 Na87 Rb molecules

    NASA Astrophysics Data System (ADS)

    Guo, Mingyang; Zhu, Bing; Lu, Bo; Ye, Xin; Wang, Fudong; Wang, Dajun; Vexiau, Romain; Bouloufa-Maafa, Nadia; Quéméner, Goulven; Dulieu, Olivier

    2016-05-01

    We report on successful creation of an ultracold sample of ground-state 23 Na87 Rb molecules with a large effective electric dipole moment. Through a carefully designed two-photon Raman process, we have successfully transferred the magneto-associated Feshbach molecules to the singlet ground state with high efficiency, obtaining up to 8000 23 Na87 Rb molecules with peak number density over 1011 cm-3 in their absolute ground-state level. With an external electric field, we have induced an effective dipole moment over 1 Debye, making 23 Na87 Rb the most dipolar ultracold particle ever achieved. Contrary to the expectation, we observed a rather fast population loss even for 23 Na87 Rb in the absolute ground state with the bi-molecular exchange reaction energetically forbidden. The origin for the short lifetime and possible ways of mitigating it are currently under investigation. Our achievements pave the way toward investigation of ultracold bosonic molecules with strong dipolar interactions. This work is supported by the Hong Kong RGC CUHK404712 and the ANR/RGC Joint Research Scheme ACUHK403/13.

  19. Low density mesostructures of confined dipolar particles in an external field.

    PubMed

    Richardi, J; Weis, J-J

    2011-09-28

    Mesostructures formed by dipolar particles confined between two parallel walls and subjected to an external field are studied by Monte Carlo simulations. The main focus of the work is the structural behavior of the Stockmayer fluid in the low density regime. The dependence of cluster thickness and ordering is estimated as a function of density and wall separation, the two most influential parameters, for large dipole moments and high field strengths. The great sensitivity of the structure to details of the short-range part of the interactions is pointed out. In particular, the attractive part of the Lennard-Jones potential is shown to play a major role in driving chain aggregation. The effect of confinement, evaluated by comparison with results for a bulk system, is most pronounced for a short range hard sphere potential. No evidence is found for a novel "gel-like" phase recently uncovered in low density dipolar colloidal suspensions [A. K. Agarwal and A. Yethiraj, Phys. Rev. Lett. 102, 198301 (2009)].

  20. Dipolar Effects in an Ultracold Gas of LiCs Molecules

    NASA Astrophysics Data System (ADS)

    Weidemueller, Matthias

    2011-05-01

    Recently, there has been important progress in the investigation of ultracold polar molecules in the absolute ground state, thus opening intriguing perspectives for strongly correlated quantum systems under the influence of long-range dipolar forces. We have studied the formation of LiCs molecules via photoassociation (PA) in a double-species magneto-optical trap. The LiCs dimer is a particularly promising candidate for observing dipolar effects, as it possesses the largest dipole moment of all alkali dimers (5.5 Debye in the ground state). Ultracold LiCs molecules in the absolute rovibrational ground state are formed by a single photo-association step. The dipole moment of ground state levels is determined by Stark spectroscopy and was found to be in excellent agreement with the theoretical predictions. Vibrational redistribution due to spontaneous emission and blackbody radiation is observed and compared a rate-equation model.In collaboration with Johannes Deiglmayr, Marc Repp, University of Heidelberg; Roland Wester, University of Innsbruck; and Olivier Dulieu, Laboratoire Aime Cotton. Work was supported by DFG and ESF in the framework of the Eurocores EuroQUAM as well as the Heidelberg Center for Quantum Dynamics.

  1. 1,3-Dipolar cycloaddition of organic azides to alkynes by a dicopper-substituted silicotungstate.

    PubMed

    Kamata, Keigo; Nakagawa, Yoshinao; Yamaguchi, Kazuya; Mizuno, Noritaka

    2008-11-19

    The dicopper-substituted gamma-Keggin silicotungstate TBA 4[gamma-H2SiW10O36Cu2(mu-1,1-N3)2] (I, TBA = tetra- n-butylammonium) could act as an efficient precatalyst for the regioselective 1,3-dipolar cycloaddition of organic azides to alkynes. Various combinations of substrates (four azides and eight alkynes) were efficiently converted to the corresponding 1,2,3-triazole derivatives in excellent yields without any additives. The present system was applicable to a larger-scale cycloaddition of benzyl azide to phenylacetylene under solvent-free conditions (100 mmol scale) in which 21.5 g of the analytically pure corresponding triazole could be isolated. In this case, the turnover frequency and the turnover number reached up to 14,800 h(-1) and 91,500, respectively, and these values were the highest among those reported for the copper-mediated systems so far. In addition, I could be applied to the one-pot synthesis of 1-benzyl-4-phenyl-1H-1,2,3-triazole from benzyl chloride, sodium azide, and phenylacetylene. The catalyst effect, kinetic, mechanistic, and computational studies show that the reduced dicopper core plays an important role in the present 1,3-dipolar cycloaddition.

  2. Asymmetric 1,3-Dipolar Cycloaddition Reactions Catalyzed by Heterocycle-Based Metal Complexes

    NASA Astrophysics Data System (ADS)

    Suga, Hiroyuki

    Highly enantioselective 1,3-dipolar cycloaddition reactions of several 1,3-dipoles, such as nitrones, nitrile oxides, nitrile imines, diazoalkanes, azomethine imines and carbonyl ylides, catalyzed by heterocyclic supramolecular type of metal complexes consisting of chiral heterocyclic compounds and metal salts were described in terms of their ability of asymmetric induction and enantioface differentiation. The scope and limitations of each cycloaddition reactions were also briefly described. Of the chiral hererocycle-based ligands, chiral bisoxazoline, 2,6-bis(oxazolinyl)pyridine, and related oxazoline ligands are shown to be quite effective in obtaining high levels of asymmtric induction. The combination of the bisoxazoline ligand derived from (1S,2R)-cis-1-amino-2-indanol and metal salts was especially efficient for asymmetric cycloaddition reactions of a number of 1,3-dipoles, such as nitrones, nitrile oxide, nitrile imines, diazoacetates and azomethine imines. The metals utilized for the heterocycle-based complexes show a crucial role for degree of asymmetric induction depending upon the 1,3-dipole used. High levels of enantioselectivity were achieved in 1,3-dipolar cycloaddition reactions of unstable carbonyl ylides with benzyloxyacetaldehyde derivatives, α-keto esters, 3-(2-alkenoyl)-2-oxazolidinones, and even vinyl ethers, which were catalyzed by Pybox-lanthanoid metal complexes.

  3. Spectroscopy of dipolar fermions in layered two-dimensional and three-dimensional lattices

    SciTech Connect

    Hazzard, Kaden R. A.; Rey, Ana Maria; Gorshkov, Alexey V.

    2011-09-15

    Motivated by ongoing measurements at JILA, we calculate the recoil-free spectra of dipolar interacting fermions, for example ultracold heteronuclear molecules, in a one-dimensional lattice of two-dimensional layers or ''pancakes'', spectroscopically probing transitions between different internal (e.g., rotational) states. We additionally incorporate p-wave interactions and losses, which are important for reactive molecules such as KRb. Moreover, we consider other sources of spectral broadening: interaction-induced quasiparticle lifetimes and the different polarizabilities of the rotational states used for the spectroscopy. Although our main focus is molecules, some of the calculations are also useful for optical lattice atomic clocks. For example, understanding the p-wave shifts between identical fermions and small dipolar interactions coming from the excited clock state is necessary to reach future precision goals. Finally, we consider the spectra in a deep three-dimensional lattice and show how they give a great deal of information about static correlation functions, including all the moments of the density correlations between nearby sites. The range of correlations measurable depends on spectroscopic resolution and the dipole moment.

  4. Reversible switching of liquid crystalline order permits synthesis of homogeneous populations of dipolar patchy microparticles

    SciTech Connect

    Wang, Xiaoguang; Miller, Daniel S.; de Pablo, Juan J.; Abbott, Nicholas L.

    2014-08-15

    The spontaneous positioning of colloids on the surfaces of micrometer-sized liquid crystal (LC) droplets and their subsequent polymerization offers the basis of a general and facile method for the synthesis of patchy microparticles. The existence of multiple local energetic minima, however, can generate kinetic traps for colloids on the surfaces of the LC droplets and result in heterogeneous populations of patchy microparticles. To address this issue, in this paper it is demonstrated that adsorbate-driven switching of the internal configurations of LC droplets can be used to sweep colloids to a single location on the LC droplet surfaces, thus resulting in the synthesis of homogeneous populations of patchy microparticles. The surface-driven switching of the LC can be triggered by addition of surfactant or salts, and permits the synthesis of dipolar microparticles as well as “Janus-like” microparticles. Finally, by using magnetic colloids, the utility of the approach is illustrated by synthesizing magnetically responsive patchy microdroplets of LC with either dipolar or quadrupolar symmetry that exhibit distinct optical responses upon application of an external magnetic field.

  5. Reversible switching of liquid crystalline order permits synthesis of homogeneous populations of dipolar patchy microparticles

    DOE PAGES

    Wang, Xiaoguang; Miller, Daniel S.; de Pablo, Juan J.; ...

    2014-08-15

    The spontaneous positioning of colloids on the surfaces of micrometer-sized liquid crystal (LC) droplets and their subsequent polymerization offers the basis of a general and facile method for the synthesis of patchy microparticles. The existence of multiple local energetic minima, however, can generate kinetic traps for colloids on the surfaces of the LC droplets and result in heterogeneous populations of patchy microparticles. To address this issue, in this paper it is demonstrated that adsorbate-driven switching of the internal configurations of LC droplets can be used to sweep colloids to a single location on the LC droplet surfaces, thus resulting inmore » the synthesis of homogeneous populations of patchy microparticles. The surface-driven switching of the LC can be triggered by addition of surfactant or salts, and permits the synthesis of dipolar microparticles as well as “Janus-like” microparticles. Finally, by using magnetic colloids, the utility of the approach is illustrated by synthesizing magnetically responsive patchy microdroplets of LC with either dipolar or quadrupolar symmetry that exhibit distinct optical responses upon application of an external magnetic field.« less

  6. Transport of dipolar excitons in (Al,Ga)N/GaN quantum wells

    NASA Astrophysics Data System (ADS)

    Fedichkin, F.; Andreakou, P.; Jouault, B.; Vladimirova, M.; Guillet, T.; Brimont, C.; Valvin, P.; Bretagnon, T.; Dussaigne, A.; Grandjean, N.; Lefebvre, P.

    2015-05-01

    We investigate the transport of dipolar indirect excitons along the growth plane of polar (Al,Ga)N/GaN quantum well structures by means of spatially and time-resolved photoluminescence spectroscopy. The transport in these strongly disordered quantum wells is activated by dipole-dipole repulsion. The latter induces an emission blue shift that increases linearly with exciton density, whereas the radiative recombination rate increases exponentially. Under continuous, localized excitation, we observe continuously decreasing emission energy, as excitons propagate away from the excitation spot. This corresponds to a steady-state gradient of exciton density, measured over several tens of micrometers. Time-resolved microphotoluminescence experiments provide information on the dynamics of recombination and transport of dipolar excitons. We account for the ensemble of experimental results by solving the nonlinear drift-diffusion equation. Quantitative analysis suggests that in such structures, exciton propagation on the scale of 10 to 20 μ m is mainly driven by diffusion, rather than by drift, due to the strong disorder and the presence of nonradiative defects. Secondary exciton creation, most probably by the intense higher-energy luminescence, guided along the sample plane, is shown to contribute to the exciton emission pattern on the scale up to 100 μ m . The exciton propagation length is strongly temperature dependent, the emission being quenched beyond a critical distance governed by nonradiative recombination.

  7. Solar Micro-Type III Burst Storms and Long Dipolar Magnetic Field in the Outer Corona

    NASA Astrophysics Data System (ADS)

    Morioka, A.; Miyoshi, Y.; Iwai, K.; Kasaba, Y.; Masuda, S.; Misawa, H.; Obara, T.

    2015-08-01

    Solar micro-type III radio bursts are elements of the so-called type III storms and are characterized by short-lived, continuous, and weak emissions. Their frequency of occurrence with respect to radiation power is quite different from that of ordinary type III bursts, suggesting that the generation process is not flare-related, but due to some recurrent acceleration processes around the active region. We examine the relationship of micro-type III radio bursts with coronal streamers. We also explore the propagation channel of bursts in the outer corona, the acceleration process, and the escape route of electron beams. It is observationally confirmed that micro-type III bursts occur near the edge of coronal streamers. The magnetic field line of the escaping electron beams is tracked on the basis of the frequency drift rate of micro-type III bursts and the electron density distribution model. The results demonstrate that electron beams are trapped along closed dipolar field lines in the outer coronal region, which arise from the interface region between the active region and the coronal hole. A 22 year statistical study reveals that the apex altitude of the magnetic loop ranges from 15 to 50 RS. The distribution of the apex altitude has a sharp upper limit around 50 RS suggesting that an unknown but universal condition regulates the upper boundary of the streamer dipolar field.

  8. Supra Arcade Downflows with XRT Informed by Dipolarization Fronts with THEMIS

    NASA Technical Reports Server (NTRS)

    Kobelski, Adam; Savage, Sabrina L.; Malaspina, David M.

    2016-01-01

    Magnetic reconnection can rapidly reconfigure the magnetic field of the corona, accelerating plasma through the site of reconnection. Ambiguities due to the nature of remote sensing have complicated the interpretation of observations of the inflowing and outflowing plasma in reconnecting regions. In particular, the interpretation of sunward moving density depletions above flare arcades (known as Supra Arcade Downflows - SADs) is still debated. Hinode/XRT has provided a wealth of observations for SADs and helped inform our current understanding of these structures. SADs have been interpreted as wakes behind newly reconnected and outflowing loops (Supra Arcade Downflowing Loops - SADLs). Models have shown the plausibility of this interpretation, though this interpretation has not yet been fully accepted. We present here observations of newly reconnected outflowing loops observed via in situ instruments in the magnetosphere. These observations, provided by five THEMIS spacecraft, show that around retracting loops (dipolarization fronts in this context) similar dynamic temperature and density structures are found as seen in SADs. We compare data from multiple SADs and dipolarization fronts to show that the observational signatures implied in the corona can be directly observed in similar plasma regimes in the magnetosphere, strongly favoring the interpretation of SADs as wakes behind retracting loops.

  9. Supramolecular Magnetic Brushes: The Impact of Dipolar Interactions on the Equilibrium Structure

    PubMed Central

    2015-01-01

    The equilibrium structure of supramolecular magnetic filament brushes is analyzed at two different scales. First, we study the density and height distributions for brushes with various grafting densities and chain lengths. We use Langevin dynamics simulations with a bead–spring model that takes into account the cross-links between the surface of the ferromagnetic particles, whose magnetization is characterized by a point dipole. Magnetic filament brushes are shown to be more compact near the substrate than nonmagnetic ones, with a bimodal height distribution for large grafting densities. This latter feature makes them also different from brushes with electric dipoles. Next, in order to explain the observed behavior at the filament scale, we introduce a graph theory analysis to elucidate for the first time the structure of the brush at the scale of individual beads. It turns out that, in contrast to nonmagnetic brushes, in which the internal structure is determined by random density fluctuations, magnetic forces introduce a certain order in the system. Because of their highly directional nature, magnetic dipolar interactions prevent some of the random connections to be formed. On the other hand, they favor a higher connectivity of the chains’ free and grafted ends. We show that this complex dipolar brush microstructure has a strong impact on the magnetic response of the brush, as any weak applied field has to compete with the dipole–dipole interactions within the crowded environment. PMID:26538768

  10. SOLAR MICRO-TYPE III BURST STORMS AND LONG DIPOLAR MAGNETIC FIELD IN THE OUTER CORONA

    SciTech Connect

    Morioka, A.; Misawa, H.; Obara, T.; Miyoshi, Y.; Masuda, S.; Iwai, K.; Kasaba, Y.

    2015-08-01

    Solar micro-type III radio bursts are elements of the so-called type III storms and are characterized by short-lived, continuous, and weak emissions. Their frequency of occurrence with respect to radiation power is quite different from that of ordinary type III bursts, suggesting that the generation process is not flare-related, but due to some recurrent acceleration processes around the active region. We examine the relationship of micro-type III radio bursts with coronal streamers. We also explore the propagation channel of bursts in the outer corona, the acceleration process, and the escape route of electron beams. It is observationally confirmed that micro-type III bursts occur near the edge of coronal streamers. The magnetic field line of the escaping electron beams is tracked on the basis of the frequency drift rate of micro-type III bursts and the electron density distribution model. The results demonstrate that electron beams are trapped along closed dipolar field lines in the outer coronal region, which arise from the interface region between the active region and the coronal hole. A 22 year statistical study reveals that the apex altitude of the magnetic loop ranges from 15 to 50 R{sub S}. The distribution of the apex altitude has a sharp upper limit around 50 R{sub S} suggesting that an unknown but universal condition regulates the upper boundary of the streamer dipolar field.

  11. Three-dimensional Transient Magnetic Reconnection and Dipolarization Fronts in the Terrestrial Magnetotail

    NASA Astrophysics Data System (ADS)

    Zhou, M.; Deng, X.; Ashour-Abdalla, M.; Pang, Y.; Lapenta, G.; Fu, H.; Walker, R. J.; Huang, S.; Tang, R.

    2015-12-01

    We report a Cluster observation of transient magnetic reconnection in the Earth's magnetotail at the location of [Xgsm ~ -17.2 RE, Ygsm ~ -4.5 RE and Zgsm ~ 0]. The reconnection X-line retreated tailward with a speed of 34 km/s. An ion diffusion region with a weak guide field (~10% of the lobe field) was encountered during the flow reversal. Transient energetic electron beams, which directed away from the X-line, were detected repeatedly around the current sheet boundary layer with periods of about 60s during the tailward flow burst. On the earthward side of X-line, multiple earthward-propagating dipolarization fronts were observed quasi-periodically with time period of 60s-90s. Surprisingly the cross-tail sizes of some observed dipolarization fronts are only 1-2 ion inertial lengths. The X-line expanded across the tail in the electron flow direction with a speed about 0.03VA, here VA is the Alfven speed. Two spacecraft, which were separated in the cross-tail direction by 1 RE, observed distinct structures and different tones of reconnection, which implies that reconnection proceeds drastically different in different segments of X-line.

  12. Theoretical study of homonuclear J coupling between quadrupolar spins: single-crystal, DOR, and J-resolved NMR.

    PubMed

    Perras, Frédéric A; Bryce, David L

    2014-05-01

    The theory describing homonuclear indirect nuclear spin-spin coupling (J) interactions between pairs of quadrupolar nuclei is outlined and supported by numerical calculations. The expected first-order multiplets for pairs of magnetically equivalent (A2), chemically equivalent (AA'), and non-equivalent (AX) quadrupolar nuclei are given. The various spectral changeovers from one first-order multiplet to another are investigated with numerical simulations using the SIMPSON program and the various thresholds defining each situation are given. The effects of chemical equivalence, as well as quadrupolar coupling, chemical shift differences, and dipolar coupling on double-rotation (DOR) and J-resolved NMR experiments for measuring homonuclear J coupling constants are investigated. The simulated J coupling multiplets under DOR conditions largely resemble the ideal multiplets predicted for single crystals, and a characteristic multiplet is expected for each of the A2, AA', and AX cases. The simulations demonstrate that it should be straightforward to distinguish between magnetic inequivalence and equivalence using J-resolved NMR, as was speculated previously. Additionally, it is shown that the second-order quadrupolar-dipolar cross-term does not affect the splittings in J-resolved experiments. Overall, the homonuclear J-resolved experiment for half-integer quadrupolar nuclei is demonstrated to be robust with respect to the effects of first- and second-order quadrupolar coupling, dipolar coupling, and chemical shift differences.

  13. Coherence and modality of driven interlayer-coupled magnetic vortices.

    PubMed

    Pulecio, J F; Warnicke, P; Pollard, S D; Arena, D A; Zhu, Y

    2014-04-30

    The high-frequency dynamics of mode-coupled magnetic vortices have generated great interest for spintronic technologies, such as spin-torque nano-oscillators. While the spectroscopic characteristics of vortex oscillators have been reported, direct imaging of driven coupled magnetic quasi-particles is essential to the fundamental understanding of the dynamics involved. Here, we present the first direct imaging study of driven interlayer coaxial vortices in the dipolar- and indirect exchange-coupled regimes. Employing in situ high-frequency excitation with Lorentz microscopy, we directly observe the steady-state orbital amplitudes in real space with sub-5 nm spatial resolution. We discuss the unique frequency response of dipolar- and exchange-coupled vortex motion, wherein mode splitting and locking demonstrates large variations in coherent motion, as well as detail the resultant orbital amplitudes. This provides critical insights of the fundamental features of collective vortex-based microwave generators, such as their steady-state amplitudes, tunability and mode-coupled motion.

  14. Ion trajectory simulations of axial ac dipolar excitation in the Orbitrap

    NASA Astrophysics Data System (ADS)

    Wu, Guangxiang; Noll, Robert J.; Plass, Wolfgang R.; Hu, Qizhi; Perry, Richard H.; Cooks, R. Graham

    2006-07-01

    The newly developed version of the multi-particle ion trajectory simulation program, ITSIM 6.0, was applied to simulate ac dipolar excitation of ion axial motion in the Orbitrap. The Orbitrap inner and outer electrodes were generated in AutoCAD, a 3D drawing program. The electrode geometry was imported into the 3D field solver COMSOL; the field array was then imported into ITSIM 6.0. Ion trajectories were calculated by solving Newton's equations using Runge-Kutta integration methods. Compared to the analytical solution, calculated radial components of the field at the device's "equator" (z = 0) were within 0.5% and calculated axial components midway between the inner and outer electrodes were within 0.2%. The experiments simulated here involved the control of axial motion of ions in the Orbitrap by the application of dipolar ac signals to the split outer electrodes, as described in a recently published paper from this laboratory [Hu et al., J. Phys. Chem. A 110 (2006) 2682]. In these experiments, ac signal was applied at the axial resonant frequency of a selected ion. Axial excitation and eventual ion ejection resulted when the ac was in phase with, i.e., had 0° phase relative to ion axial motion. De-excitation of ion axial motion until the ions were at z = 0 and at rest with respect to the z-axis resulted if the applied ac was out of phase with ion motion, with re-excitation of ion axial motion occurring if the dipolar ac was continued beyond this point. Both de-excitation and re-excitation could be achieved mass-selectively and depended on the amplitude and duration (number of cycles) of the applied ac. The effects of ac amplitude, frequency, phase relative to ion motion, and bandwidth of applied waveform were simulated. All simulation results were compared directly with the experimental data and good agreement was observed. Such ion motion control experiments and their simulation provide the possibility to improve Orbitrap performance and to develop tandem mass

  15. Application of an intramolecular dipolar cycloaddition to an asymmetric synthesis of the fully oxygenated tricyclic core of the stemofoline alkaloids

    PubMed Central

    Carra, Ryan J.; Epperson, Matthew T.; Gin, David Y.

    2008-01-01

    An intramolecular non-stabilized azomethine ylide dipolar cycloaddition was applied toward the first non-racemic synthesis of the fully-oxygenated bridged pyrrolizidine core (45) of (+)-stemofoline (1) in eleven steps from a commercially available starting material. PMID:18443655

  16. Vapor-liquid transitions of dipolar fluids in disordered porous media: Performance of angle-averaged potentials

    NASA Astrophysics Data System (ADS)

    Spöler, C.; Klapp, S. H. L.

    2004-11-01

    Using replica integral equations in the reference hypernetted-chain (RHNC) approximation we calculate vapor-liquid spinodals, chemical potentials, and compressibilities of fluids with angle-averaged dipolar interactions adsorbed to various disordered porous media. Comparison with previous RHNC results for systems with true angle-dependent Stockmayer (dipolar plus Lennard-Jones) interactions [C. Spöler and S. H. L. Klapp, J. Chem. Phys. 118, 3628 (2003); ibid.120, 6734 (2004)] indicate that, for a dilute hard sphere matrix, the angle-averaged fluid-fluid (ff) potential is a reasonable alternative for reduced fluid dipole moments m*2=μ2/(ɛ0σ3)⩽2.0. This range is comparable to that estimated in bulk fluids, for which RHNC results are presented as well. Finally, results for weakly polar matrices suggest that angle-averaged fluid-matrix (fm) interactions can reproduce main features observed for true dipolar (fm) interactions such as the shift of the vapor-liquid spinodals towards lower temperatures and higher densities. However, the effective attraction induced by dipolar (fm) interaction is underestimated rather than overestimated as in the case of angle-averaged ff interactions.

  17. P-wave superfluid in a quasi-two-dimensional dipolar Bose-Fermi quantum gas mixture

    NASA Astrophysics Data System (ADS)

    Kain, Ben; Ling, Hong

    2013-03-01

    The p-wave (px + ipy) superfluid has attracted significant attention in recent years mainly because its vortex core supports a Majorana fermion which, due to its non-Abelian statistics, can be explored for implementing topological quantum computation (TQC). Mixing in bosons may lead to p-wave pairing in a Fermi gas. In a dipolar condensate, the dipole-dipole interaction represents a control knob inaccessible to nondipolar Bosons. Thus, mixing dipolar bosons with fermions opens up new possibilities. We consider a mixture of a spin-polarized Fermi gas and a dipolar Bose-Einstein condensate in a quasi-two-dimensional trap setting. We take the Hartree-Fock-Bogoliubov mean-field approach and develop a theory for studying the stability of the mixture and estimating the critical temperature of the p-wave superfluid. We use this theory to identify the experimentally accessible parameter space in which the mixture is stable against phase separation and the p-wave superfluid pairing can be resonantly enhanced. An enhanced p-wave superfluid order parameter can make the fault tolerant TQC less susceptible to thermal fluctuations. This work aims to stimulate experimental activity in creating dipolar Bose-Fermi mixtures. This work is supported by the US National Science Foundation and the US Army Research Office

  18. Synthesis of 2-aminoindolizines by 1,3-dipolar cycloaddition of pyridinium ylides with electron-deficient ynamides.

    PubMed

    Brioche, Julien; Meyer, Christophe; Cossy, Janine

    2015-06-05

    Electron-deficient ynamides, possessing an ynoate or an ynone moiety, have been successfully involved for the first time in a 1,3-dipolar cycloaddition with stabilized pyridinium ylides. These reactions afford an efficient and general access toward a variety of substituted 2-aminoindolizines which can serve as useful precursors for the synthesis of other more complex nitrogen heterocycles.

  19. Facile Synthesis of Stapled, Structurally Reinforced Peptide Helices via A Photoinduced Intramolecular 1,3-Dipolar Cycloaddition Reaction†

    PubMed Central

    Madden, Michael M.; Vera, Claudia I. Rivera; Song, Wenjiao; Lin, Qing

    2009-01-01

    We report the first use of a photoinduced 1,3-dipolar cycloaddition reaction in “stapling” peptide side chains to reinforce a model peptide helical structure with moderate to excellent yields. The resulting pyrazoline “staplers” exhibit unique fluorescence useful in a cell permeability study. PMID:19753366

  20. Highly Efficient and Stereoselective Construction of Bispirooxindole Derivatives via a Three-Component 1,3-Dipolar Cycloaddition Reaction.

    PubMed

    Xu, Qin; Wang, De; Wei, Yin; Shi, Min

    2014-06-01

    A highly regio- and stereoselective synthesis of bispirooxindoles by 1,3-dipolar cycloaddition of in situ generated azomethine ylides from isatin and proline to different electron-deficient alkenes has been developed. The synthesis affords the desired bispiro scaffold compounds in excellent yields with high regioselectivity under mild conditions. The stereochemistry was determined by single-crystal X-ray analysis.

  1. Dimerization of propargyl and homopropargyl 6-azido-6-deoxy-glycosides upon 1,3-dipolar cycloaddition

    PubMed Central

    Pietrzik, Nikolas; Schmollinger, Daniel

    2008-01-01

    Summary Copper-catalyzed, thermal or microwave promoted 1,3-dipolar cycloaddition (Click Reaction) of 2-propynyl and 3-butynyl 2,3,4-tri-O-acetyl-6-azido-6-deoxy-glycopyranosides in the D-gluco, D-galacto and D-manno series afford the corresponding dimeric cycloaddition products. PMID:18941499

  2. The 3D Kasteleyn transition in dipolar spin ice: a numerical study with the conserved monopoles algorithm.

    PubMed

    Baez, M L; Borzi, R A

    2017-02-08

    We study the three-dimensional Kasteleyn transition in both nearest neighbours and dipolar spin ice models using an algorithm that conserves the number of excitations. We first limit the interactions range to nearest neighbours to test the method in the presence of a field applied along [Formula: see text], and then focus on the dipolar spin ice model. The effect of dipolar interactions, which is known to be greatly self screened at zero field, is particularly strong near full polarization. It shifts the Kasteleyn transition to lower temperatures, which decreases  ≈0.4 K for the parameters corresponding to the best known spin ice materials, [Formula: see text] and [Formula: see text]. This shift implies effective dipolar fields as big as 0.05 T opposing the applied field, and thus favouring the creation of 'strings' of reversed spins. We compare the reduction in the transition temperature with results in previous experiments, and study the phenomenon quantitatively using a simple molecular field approach. Finally, we relate the presence of the effective residual field to the appearance of string-ordered phases at low fields and temperatures, and we check numerically that for fields applied along [Formula: see text] there are only three different stable phases at zero temperature.

  3. The 3D Kasteleyn transition in dipolar spin ice: a numerical study with the conserved monopoles algorithm

    NASA Astrophysics Data System (ADS)

    Baez, M. L.; Borzi, R. A.

    2017-02-01

    We study the three-dimensional Kasteleyn transition in both nearest neighbours and dipolar spin ice models using an algorithm that conserves the number of excitations. We first limit the interactions range to nearest neighbours to test the method in the presence of a field applied along ≤ft[1 0 0\\right] , and then focus on the dipolar spin ice model. The effect of dipolar interactions, which is known to be greatly self screened at zero field, is particularly strong near full polarization. It shifts the Kasteleyn transition to lower temperatures, which decreases  ≈0.4 K for the parameters corresponding to the best known spin ice materials, \\text{D}{{\\text{y}}2}\\text{T}{{\\text{i}}2}{{\\text{O}}7} and \\text{H}{{\\text{o}}2}\\text{T}{{\\text{i}}2}{{\\text{O}}7} . This shift implies effective dipolar fields as big as 0.05 T opposing the applied field, and thus favouring the creation of ‘strings’ of reversed spins. We compare the reduction in the transition temperature with results in previous experiments, and study the phenomenon quantitatively using a simple molecular field approach. Finally, we relate the presence of the effective residual field to the appearance of string-ordered phases at low fields and temperatures, and we check numerically that for fields applied along ≤ft[1 0 0\\right] there are only three different stable phases at zero temperature.

  4. Characterization of Stable Kinetic Equilibria of Rigid, Dipolar Rod Ensembles for Coupled Dipole-Dipole and Maier-Saupe Potentials

    DTIC Science & Technology

    2007-01-18

    concentration, which is the second virial coefficient of the chemical potential. In (2), for simplicity, we have normalized the potential by kBT . In this...of the uniaxial second moment tensor. The stability is essential in establishing the axisymmetry. To demonstrate that the 5 Also at: School of...symmetry: the peak axis of orientation is aligned with both the polarity vector (first moment) and the distinguished director of the uniaxial second

  5. Anomalous negative electrocaloric effect in a relaxor/normal ferroelectric polymer blend with controlled nano- and meso-dipolar couplings

    NASA Astrophysics Data System (ADS)

    Qian, Xiaoshi; Yang, Tiannan; Zhang, Tian; Chen, Long-Qing; Zhang, Q. M.

    2016-04-01

    In general, a dielectric material will eject (or absorb) heat when an electric field is applied and absorb (or eject) heat when the field is removed, under isothermal condition, which is known as the normal (or negative) electrocaloric (EC) effect. For some applications, it is highly desired that an EC material will absorb heat (cooling the surrounding) without subsequent heating under an electric pulse. Here, we show that such an EC material can be realized in a properly designed hybrid normal ferroelectric/relaxor ferroelectric polymer blend in which the normal ferroelectric component induces dipole ordering in the relaxor polymer in the poled state, which can be switched to a de-poled state by an external field. More importantly, the de-poled state can be maintained by the relaxor component when the de-poling field is removed. Consequently, the hybrid blend exhibits a large cooling (an isothermal entropy change ΔS = 11.5 J kg-1 K-1) without the subsequent heating upon the application of an electric pulse.

  6. Existence of a Thermodynamic Spin-Glass Phase in the Zero-Concentration Limit of Anisotropic Dipolar Systems

    NASA Astrophysics Data System (ADS)

    Andresen, Juan Carlos; Katzgraber, Helmut G.; Oganesyan, Vadim; Schechter, Moshe

    2014-10-01

    The nature of ordering in dilute dipolar interacting systems dates back to the work of Debye and is one of the most basic, oldest and as-of-yet unsettled problems in magnetism. While spin-glass order is readily observed in several RKKY-interacting systems, dipolar spin glasses are the subject of controversy and ongoing scrutiny, e.g., in LiHoxY1 -xF4, a rare-earth randomly diluted uniaxial (Ising) dipolar system. In particular, it is unclear if the spin-glass phase in these paradigmatic materials persists in the limit of zero concentration or not. We study an effective model of LiHoxY1 -xF4 using large-scale Monte Carlo simulations that combine parallel tempering with a special cluster algorithm tailored to overcome the numerical difficulties that occur at extreme dilutions. We find a paramagnetic to spin-glass phase transition for all Ho+ ion concentrations down to the smallest concentration numerically accessible, 0.1%, and including Ho+ ion concentrations that coincide with those studied experimentally up to 16.7%. Our results suggest that randomly diluted dipolar Ising systems have a spin-glass phase in the limit of vanishing dipole concentration, with a critical temperature vanishing linearly with concentration. The agreement of our results with mean-field theory testifies to the irrelevance of fluctuations in interactions strengths, albeit being strong at small concentrations, to the nature of the low-temperature phase and the functional form of the critical temperature of dilute anisotropic dipolar systems. Deviations from linearity in experimental results at the lowest concentrations are discussed.

  7. Nanostructure and free volume effects in enhancing the dielectric response of strongly dipolar polymers

    NASA Astrophysics Data System (ADS)

    Dong, Rui; Thakur, Yash; Ranjan, Vivek; Buongiorno Nardelli, Marco; Zhang, Qiming; Bernholc, Jerry

    Materials for capacitive energy storage with high energy density and low loss are desired in many fields. We perform multiscale simulations to investigate several members of the aromatic polyurea family. We find that the disordered structures with misaligned chains have considerably larger dielectric constants, due to significant increase in the free volume, which leads to easier reorientation of dipolar groups in the presence of an electric field. Large segment motion is still not allowed below the glass transition temperature, upholding the very low loss at high field and elevated temperature that we observe experimentally. Optimization of the nanostructure and free volume effects thus provides a new, very promising pathway for the design of high-performance dielectrics for capacitive energy storage.

  8. Proterozoic low orbital obliquity and axial-dipolar geomagnetic field from evaporite palaeolatitudes

    NASA Astrophysics Data System (ADS)

    Evans, David A. D.

    2006-11-01

    Palaeomagnetism of climatically sensitive sedimentary rock types, such as glacial deposits and evaporites, can test the uniformitarianism of ancient geomagnetic fields and palaeoclimate zones. Proterozoic glacial deposits laid down in near-equatorial palaeomagnetic latitudes can be explained by `snowball Earth' episodes, high orbital obliquity or markedly non-uniformitarian geomagnetic fields. Here I present a global palaeomagnetic compilation of the Earth's entire basin-scale evaporite record. Magnetic inclinations are consistent with low orbital obliquity and a geocentric-axial-dipole magnetic field for most of the past two billion years, and the snowball Earth hypothesis accordingly remains the most viable model for low-latitude Proterozoic ice ages. Efforts to reconstruct Proterozoic supercontinents are strengthened by this demonstration of a consistently axial and dipolar geomagnetic reference frame, which itself implies stability of geodynamo processes on billion-year timescales.

  9. Proterozoic low orbital obliquity and axial-dipolar geomagnetic field from evaporite palaeolatitudes.

    PubMed

    Evans, David A D

    2006-11-02

    Palaeomagnetism of climatically sensitive sedimentary rock types, such as glacial deposits and evaporites, can test the uniformitarianism of ancient geomagnetic fields and palaeoclimate zones. Proterozoic glacial deposits laid down in near-equatorial palaeomagnetic latitudes can be explained by 'snowball Earth' episodes, high orbital obliquity or markedly non-uniformitarian geomagnetic fields. Here I present a global palaeomagnetic compilation of the Earth's entire basin-scale evaporite record. Magnetic inclinations are consistent with low orbital obliquity and a geocentric-axial-dipole magnetic field for most of the past two billion years, and the snowball Earth hypothesis accordingly remains the most viable model for low-latitude Proterozoic ice ages. Efforts to reconstruct Proterozoic supercontinents are strengthened by this demonstration of a consistently axial and dipolar geomagnetic reference frame, which itself implies stability of geodynamo processes on billion-year timescales.

  10. Fractional quantum Hall states of dipolar fermions in a strained optical lattice

    NASA Astrophysics Data System (ADS)

    Fujita, Hiroyuki; Nakagawa, Yuya O.; Ashida, Yuto; Furukawa, Shunsuke

    2016-10-01

    We study strongly correlated ground states of dipolar fermions in a honeycomb optical lattice with spatial variations in hopping amplitudes. Similar to strained graphene, such nonuniform hopping amplitudes produce valley-dependent pseudomagnetic fields for fermions near the two Dirac points, resulting in the formation of Landau levels. The dipole moments aligned perpendicular to the honeycomb plane yield a long-range repulsive interaction. By exact diagonalization in the zeroth-Landau-level basis, we show that this repulsive interaction stabilizes a variety of valley-polarized fractional quantum Hall states such as Laughlin and composite-fermion states. The present system thus offers an intriguing platform for emulating fractional quantum Hall physics in a static optical lattice. We calculate the energy gaps above these incompressible states and discuss the temperature scales required for their experimental realization.

  11. Robustness of fractional quantum Hall states with dipolar atoms in artificial gauge fields

    SciTech Connect

    Grass, T.; Baranov, M. A.; Lewenstein, M.

    2011-10-15

    The robustness of fractional quantum Hall states is measured as the energy gap separating the Laughlin ground state from excitations. Using thermodynamic approximations for the correlation functions of the Laughlin state and the quasihole state, we evaluate the gap in a two-dimensional system of dipolar atoms exposed to an artificial gauge field. For Abelian fields, our results agree well with the results of exact diagonalization for small systems but indicate that the large value of the gap predicted [Phys. Rev. Lett. 94, 070404 (2005)] was overestimated. However, we are able to show that the small gap found in the Abelian scenario dramatically increases if we turn to non-Abelian fields squeezing the Landau levels.

  12. Suprathermal particle energization in dipolarization fronts: Particle-in-cell simulations

    NASA Astrophysics Data System (ADS)

    Lu, San; Angelopoulos, V.; Fu, Huishan

    2016-10-01

    Within dipolarization fronts (DFs) in the Earth's magnetotail, significant magnetic energy is converted to plasma energy, and a significant portion of the electrons and ions therein are accelerated to suprathermal energies. The mechanism that produces these suprathermal particles while simultaneously reducing magnetic field energy is poorly understood, however. We use two-dimensional particle-in-cell simulations to explore this process in conventional flux bundle-type DFs, which are formed by single X line reconnection and connected to the Earth, and in newly proposed flux rope-type DFs, which are formed and bracketed by two X lines. In flux bundle-type DFs, electrons are betatron accelerated near the Bz peak, and ions are energized through reflection at the front. In flux rope-type DFs, most suprathermal electrons and ions are confined to the flux rope's magnetic structure and are accelerated through repeated reflections at the structure's two ends.

  13. Testing physical models for dipolar asymmetry: From temperature to k space to lensing

    NASA Astrophysics Data System (ADS)

    Zibin, J. P.; Contreras, D.

    2017-03-01

    One of the most intriguing hints of a departure from the standard cosmological model is a large-scale dipolar power asymmetry in the cosmic microwave background (CMB). If not a statistical fluke, its origins must lie in the modulation of the position-space fluctuations via a physical mechanism, which requires the observation of new modes to confirm or refute. We introduce an approach to describe such a modulation in k space and calculate its effects on the CMB temperature and lensing. We fit the k -space modulation parameters to Planck 2015 temperature data and show that CMB lensing will not provide us with enough independent information to confirm or refute such a mechanism. However, our approach elucidates some poorly understood aspects of the asymmetry, in particular that it is weakly constrained. Also, it will be particularly useful in predicting the effectiveness of polarization in testing a physical modulation.

  14. Long-range transverse Ising model built with dipolar condensates in two-well arrays

    NASA Astrophysics Data System (ADS)

    Li, Yongyao; Pang, Wei; Xu, Jun; Lee, Chaohong; Malomed, Boris A.; Santos, Luis

    2017-01-01

    Dipolar Bose–Einstein condensates in an array of double-well potentials realize an effective transverse Ising model with peculiar inter-layer interactions, that may result under proper conditions in an anomalous first-order ferromagnetic–antiferromagnetic phase transition, and non-trivial phases due to frustration. The considered setup allows as well for the study of Kibble–Zurek defect formation, whose kink statistics follows that expected from the universality class of the mean-field one-dimensional transverse Ising model. Furthermore, random occupation of each layer of the stack leads to random effective Ising interactions and local transverse fields, that may lead to the Anderson-like localization of imbalance perturbations.

  15. Quantum control of spin-nematic squeezing in a dipolar spin-1 condensate.

    PubMed

    Huang, Yixiao; Xiong, Heng-Na; Yang, Yang; Hu, Zheng-Da; Xi, Zhengjun

    2017-02-24

    Versatile controllability of interactions and magnetic field in ultracold atomic gases ha now reached an era where spin mixing dynamics and spin-nematic squeezing can be studied. Recent experiments have realized spin-nematic squeezed vacuum and dynamic stabilization following a quench through a quantum phase transition. Here we propose a scheme for storage of maximal spin-nematic squeezing, with its squeezing angle maintained in a fixed direction, in a dipolar spin-1 condensate by applying a microwave pulse at a time that maximal squeezing occurs. The dynamic stabilization of the system is achieved by manipulating the external periodic microwave pulses. The stability diagram for the range of pulse periods and phase shifts that stabilize the dynamics is numerical simulated and agrees with a stability analysis. Moreover, the stability range coincides well with the spin-nematic vacuum squeezed region which indicates that the spin-nematic squeezed vacuum will never disappear as long as the spin dynamics are stabilized.

  16. Mirror mode structures ahead of dipolarization front near the neutral sheet observed by Cluster

    NASA Astrophysics Data System (ADS)

    Wang, G. Q.; Zhang, T. L.; Volwerk, M.; Schmid, D.; Baumjohann, W.; Nakamura, R.; Pan, Z. H.

    2016-09-01

    Magnetic compressional structures ahead of a dipolarization front (DF) on 30 August 2002 are investigated by using Cluster data. Our findings are as follows: (1) the structures, observed near the neutral sheet, are mainly compressional and dominant in BZ; (2) they are almost nonpropagating relative to the local ion bulk flow and their lengths are several local proton gyroradius; (3) the ion density increases when BT decreases; (4) ions are partially trapped by the structures with parallel and perpendicular velocities varying in antiphase; and (5) local conditions are favorable for excitation of the mirror instability, and we suggest that these structures are mirror mode-like. Our findings also suggest that local conditions ahead of the DF are viable for exciting the mirror instability to generate mirror mode waves or structures.

  17. Uranyl triazolate formation via an in situ Huisgen 1,3-dipolar cycloaddition reaction

    SciTech Connect

    Knope, Karah E.; Cahill, Christopher L.

    2010-08-27

    A two dimensional UO22+ coordination polymer, (UO2)3(C10H5N3O4)2(OH)2(H2O)2, has been synthesized under solvothermal conditions. The triazolate ligand, 1-(4-carboxyphenyl)-1H-1,2,3-triazole-4-carboxylic acid (CPTAZ) has been generated via a 1,3-dipolar cycloaddition of 4-azidobenzoic acid and propiolic acid. Reactions of the UO22+ cation with both the in situ generated triazolate ligand and the presynthesized ligand have been explored. The structure, fluorescent and thermal behaviour of this material are presented, as is a discussion of the utility of in situ ligand formation versus direct assembly.

  18. Phase diagram of dipolar hard-core bosons on a honeycomb lattice

    NASA Astrophysics Data System (ADS)

    Nakafuji, Takashi; Ito, Takeshi; Nagamori, Yuya; Ichinose, Ikuo

    2016-08-01

    In this paper, we study phase diagrams of dipolar hard-core boson gases on a honeycomb lattice. The system is described by the Haldane-Bose-Hubbard model with complex hopping amplitudes and nearest-neighbor repulsion. By using the slave-particle representation of the hard-core bosons and also the path-integral quantum Monte Carlo simulations, we investigate the system and show that the systems have a rich phase diagram. There are Mott, superfluid, chiral superfluid, and sublattice chiral superfluid phases as well as the density-wave phase. We also found a coexisting phase of superfluid and chiral superfluid. Critical behaviors of the phase transitions are also clarified.

  19. Dipolar colloids in apolar media: direct microscopy of two-dimensional suspensions

    PubMed Central

    Janai, Erez; Cohen, Avner P.; Butenko, Alexander V.; Schofield, Andrew B.; Schultz, Moty; Sloutskin, Eli

    2016-01-01

    Spherical colloids, in an absence of external fields, are commonly assumed to interact solely through rotationally-invariant potentials, u(r). While the presence of permanent dipoles in aqueous suspensions has been previously suggested by some experiments, the rotational degrees of freedom of spherical colloids are typically neglected. We prove, by direct experiments, the presence of permanent dipoles in commonly used spherical poly(methyl methacrylate) (PMMA) colloids, suspended in an apolar organic medium. We study, by a combination of direct confocal microscopy, computer simulations, and theory, the structure and other thermodynamical properties of organic suspensions of colloidal spheres, confined to a two-dimensional (2D) monolayer. Our studies reveal the effects of the dipolar interactions on the structure and the osmotic pressure of these fluids. These observations have far-reaching consequences for the fundamental colloidal science, opening new directions in self-assembly of complex colloidal clusters. PMID:27346611

  20. Dipolar colloids in apolar media: direct microscopy of two-dimensional suspensions

    NASA Astrophysics Data System (ADS)

    Janai, Erez; Cohen, Avner P.; Butenko, Alexander V.; Schofield, Andrew B.; Schultz, Moty; Sloutskin, Eli

    2016-06-01

    Spherical colloids, in an absence of external fields, are commonly assumed to interact solely through rotationally-invariant potentials, u(r). While the presence of permanent dipoles in aqueous suspensions has been previously suggested by some experiments, the rotational degrees of freedom of spherical colloids are typically neglected. We prove, by direct experiments, the presence of permanent dipoles in commonly used spherical poly(methyl methacrylate) (PMMA) colloids, suspended in an apolar organic medium. We study, by a combination of direct confocal microscopy, computer simulations, and theory, the structure and other thermodynamical properties of organic suspensions of colloidal spheres, confined to a two-dimensional (2D) monolayer. Our studies reveal the effects of the dipolar interactions on the structure and the osmotic pressure of these fluids. These observations have far-reaching consequences for the fundamental colloidal science, opening new directions in self-assembly of complex colloidal clusters.